# Little Dot MK8SE / MK6 Super Mods (All verified mods are on first page)



## Redge78

*If you're a beginner in electronics or, better yet, don't know crap about it, stay at the first page where all verified mods are explained in a newbie friendly fashion. *
_*If you read the thread backwards things can get very confusing.*_
  
  
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*PREAMBLE - SAFETY PRECAUTIONS*
  
 Before opening your amp and start modding it, you are supposed to be aware of all the safety rules that go with this activity. Voltages and currents may be harmful, and even life-threatening...even when switched off, even when unplugged.
  
 - Always unplug your amp before opening it.
 - Wait for some minutes after switching-off before moving the amp and opening it _(discharge of the remaining energy in the "discharge resistors")_ 
 - Always check the voltage of your power rails.
  
  
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 We've been talking about this mods thread since too long, so here it is.
  
*Maxx134 and I will be feeding it in the next few weeks, filling the "reserved" posts and editing them as we progress in our writing. *
  
 Some pictures for appetizers, we will do better ones if needed. They were taken from my amp, but we will had Maxx/Coin/others as their layouts/components may differ from mine.
  
  
  
*Introduction / Context*
  
_Little Dot has done a fine job with those amps and we fully understand that the "price tag" leads to some compromises ..._
  
_Since I was little, I always dreamed that one day I would mod an MK8 ... bla bla bla_
  
  
*What we want to do in this thread*
  
_It was (and still is) an adventure and we wanted to share what we have found and done._
_We don't claim we have found any "final truth" or our mods are the best. But everything has been tested and is operational in our amps._
  
  
*What we DO NOT want to do in this thread*
  
_We will not feed the trolls, obviously._
_We will not answer to rude/impolite comments. _
  
  
*Table of Contents:*

 1 - Coupling Caps
 2 - Decoupling Caps
 3 - Around the Power Cathode
      3.1 - Cathode Bypass Caps
      3.2 - 5998 / WE421A Bias switch mod for the MK6 _(by SonicTrance)_
 4 - PSU "Last stage" Caps
 5 - Resistances
      5.1 - Power resistors
      5.2 - Grid resistors
 6 - Internal Cabling/Fuses/Pwr Cord/Heat/Rectfier Diode
 7 - Tubes
 8 - Background stuff / Documentation
 9 - Around the Amps (Headphones, DACs, Power Supply, cables, ... )
 10 - The next mods
      10.1 The "WCF" Coupling cap _(Tested/Verified on Maxx/Redge)_
  
  
*Overview of the "cap mods" done in the Power Stage (ie "The Quadfecta")*


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## Redge78

*1 - Coupling Caps*
  
 The Coupling caps (or Interstage caps) mod is one of the most important mod we will present.

 The Coupling cap is in the main signal path, between the Driver stage and the Power Stage. Its main role is to remove any DC voltage from the signal. 
  
 Basically, the impact of this cap on the sound will always be negative. All this mod is about, is to make it the least negative as possible. This cap will have the greatest impact on the sonic signature of the amp.

_Ideally, the best coupling cap would be NO coupling cap (a straight wire),
 Second best would be a interstage transformer. But we would need four of them, and good quality ones are even more expensive than the caps. (And the circuit needs to be finely tuned ... too complex/risky in a mod perspective.)_

*Values : *
  
*Capacity :*
 (MK8se) we have increased two steps (0,22µF > 0,33µF > 0,47µF) the capacity of the replacement caps, in order to lower the cut frequency of the "high pass" filter.
 As there is many "high pass" filters in the amp, the addition of them may have an impact on the lowest usable frequencies.
 The "original" capacity should be fine nevertheless, but we are going for improvements.
 (MK6) From "original" value up to 1µF _(CoinM will confirm)_
*Voltage :*
 The lowest limit should always be the Voltage of the cap you're replacing,_ unless you really understand what you are doing. _
 The SCR cap is interesting because the rated Voltage ("630V") is way higher than what's the PSU is providing (around 200V for the MK8). A "derating" _(ratio between "Cap Rated" and "Max Real" voltages)_ of 3x has been applied when choosing these caps and actually this derating of "3x" on caps is good practice.
 Can we go higher than "630Vdc" ? Yes indeed. The "Mundorf S/G/O" that are part of an official LD upgrade are 1000Vdc.
 Can we go lower than "630Vdc" ? Yes. I have been using "500V" coupling caps on my amp for months. But the more you will want to lower the rated voltage, the more you'll have to be sure of what is the "Max Real" DC voltage.
*Temperature :*
 Temp is THE cap-killer. If you have to choose between two caps of same quality, always choose the one with the highest Max Temp. I wouldn't buy a cap with a Max Operating Temp of 70° ... 80/85° seems the reasonnable minimum.
  
  
*The "Original" part :*
 A small black "SCR PB" cap. Funnily, it was a 0,22µF/630V in the early MK8se (Redge's), and was upped to 0,33µF/630V latter on (Maxx's)
 Those "SCR PA/PB" caps are really the very bottom of the entry-level of the MKP caps, but they will do a better job than any Lytics cap anyway. They are cheap, easily available and used in a very large number of amps (including some pretty expensive ones). Virtually any other MKP/PIO/Teflon cap will do better than those SCR PB, inclusing some beauties up in the SCR line.
  
  
*The "boutique" caps* _(High quality / high price)_
  
*Jupiter "Copper Foil in Wax"* : Clear upgrade from the Mundorf S/G/O - Wonderfull overall organic sound & holography - Quite expensive
*Duelund Cast Cu :** *Best only if you can afford them
*Mundorf Silver/Gold/Oil* : Little Dot is offering them as an official upgrade - Best value for overall performance, with a brighter sweet tonality
_Other options exist : V-cap, Audio-Note, Jensen that can offer a very high quality with different flavors._
  
  
*The "russian" caps* _(Good quality / very low price)_
  
*K75-10* : _(Hybrid tech)_ They are big, green things. Wonderful mid-range, quite enough bass, slightly recessed treble. A good companion of the HD800. Cost virtually nothing
*K73-16* : _(__polyethylene-terephthalate PEPT)_ Dynamic, lots of details, less bass than the K75-10 but more treble. A good companion of the HD650. Cost virtually nothing too.
*The "Teflon" family* : can be used as "bypass" of the caps above or as main caps. FT-1/2/3, K72N-6 depending on the value you want. As bypasses, they are said to help the treble/detail area. Bypass value between 1/10 and 1/100 of the main cap, depending on the effects you want.
_We were going to test those, but as we have now Jupiters and Duelung in our amps, there is not much point trying to bypass those beauties with "Teflon caps"._
*K40Y-9 *: _("Paper In Oil" (PIO))_ Not tested but highly regarded as main caps
*The "Silver/Mica" family* : Can be used as Bypass too. Or bypass of bypass ...
  
  
  
*Some Pics*
  
 Before (_SCR PB 0,22µF/630V_) :
  

  
  
 After (the replacement pack - tested or to be tested)) :


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## Redge78

*2 - Decoupling Caps*
  
  
 This addition to the original design is used for creating a reservoir of "fast delivery" power for the tubes to use, the supply of the power will be more independant of the PSU, hence the name "DE-coupling"...
  
  
  
 The PSU has "large output caps" and is working on "constant load" mode. This is one design that is very musical and  effective. It brings/improves silences, air, dynamic, clarity ...
  
 To improve this PSU, we have decided to add to the original design a "decoupling" cap near each power tube. The current feeding the headphones will be provided by the PSU and/or the decoupling cap, depending on the respective impedence at this time.
  
 The impedence will be both resistive (ESR) and inductive (ESL) and will depend on the technology of the cap, its value and the frequency of the signal. And the higher the impedance, the more difficulty the PSU will have to provide the current, resulting in ... well ... less air, less dynamic, less clarity ...
  
 Electrolytics caps can have huge values in a compact package, the average ones have high (bad) ESR and ESL. Their impedance rise significantly from the 10Khz onwards, even for the rather small value ones used in Tube amps. 
_Of course, there are better Lytics ... FRS type (Philips BC 56-57 series), TFRS type (Philips BC 154-155 series) or low impedance ones (Philips BC 135-136 series) but they are hard to find and mostly offered in packs of 1000, which makes the few we need a bit costly._
  
 Good film caps (MKP or PIO) on the contrary have virtually no ESR ( +/- 1milliOhm) and can have a significantly lower impedance on a large frequency band (few thousands Hz and above). Therefore, they will provide most of the "fast" energy/current in this FB. And this will improve significantly the sound.
  
*Good Decoupling caps :*
 - (stellar) Foiled/Metalized polypropylene (FKP/MKP) for pulse circuit or with huge current capacity ( +/- 100 Irms). _See what Coinmaster has stuffed his extrabox with ..._
 - All other FKP/MKP caps
 - The "Paper In Oil" (PIO) will do well 
 The value/capacity will be the prime factor here, no need to go "boutique" here, WIMA DC-LINK, Mundorf EVO or SCR/Solen will do fine.
_For those "on a budget", the motor-run MKP caps used in DC electrical motor are cheap and can be found in high values. And they are very good (and very large) _
  
*Where to put those Decoupling caps ?*
 Each centimeter/inch of wire will bring an extra impedance that will have an impact on the speed of the current needed.
 So those caps need to be put as close to their associated tube as possible.
 Ideally, they will be soldered directly on the leads of the Anode resistor (+200V side)  and the Cathode resistor (Ground side). 
_Don't underestimate the difficulties that this constraint will bring, having to stick large caps in a small space is not that easy. The extra-box option will seem more appealing then. If you really don't want the extraBox, talk to Maxx, he's been through this and survived ... mostly._
  
From the top :
  

  
 A closer view, look for the red vertical wires soldered to the blue ("original" cathode) cap and to the black ("original" anode) resistors.
_The resistors may not be black in yours tho. _
  

  
  
*Values :*
  
*Capacity :*
 It's not worth putting anything lower than 10µF, the impedence at high freq. will be too high.
 The higher the value, the better. Between 47µF and 100µF should be fine.
 From what I remember from Maxx experience, 47µF is the largest he was able to put in an amp without extra-box. 
*Voltage (*) :*
 Basically, we have the same requirements than for the Coupling caps.
 Min : 250Vdc 
 Good : 600Vdc
 Stellar : The sky's the limit
*Temperature :*
 Same as above. MKP caps should be given for Max T° : 85°, it may be less for PIOs. So you have to be careful and adapt the choices you make with the Max Temp° in your amp. 
  
_(*) we have been said that choosing a cap with a higher "rated voltage" could be beneficial to the "max. pulse rise time" (V/msec), giving faster current to the system. WIMA is documenting this in its datasheets, but only for pulses equal to the rated voltage. _
_As there is no negative impact in increasing this "Rated Voltage", we tend to always choose the highest ones, if size, price, avaibility ... are similar.   _
  
  
  
Before (none, this is an addition to the design) :
  
  
After :
  
 A quad of "Clarity Caps SA 33µF/630V" ... _and a secret ingredient_
  

  

  
 Or the compact version (white Mundorf Mcap 47µF) :
  

  
 Or some industrial _"over the top / because I'm worth it"_ AVX FFVI 100µF/1100V monsters ! The 4 in a row.
 More to come in the "how to connect those beauties" chapter...
  

  
 Or the very inspiring Decoupling caps of a Belgium MK2 ... a pair of white Mundorf Evo 82µF
  

  
  
  
*About soldering points for the Driver Stage decoupling caps :*
  
You can take the board out : the easiest is to remove the small round cap and the red rectangular WIMA near it (both are connected together in parallel) and put/solder the decoupling one there
  
 The 'round cap', one at each side of the amp.

  

  
 Same location, from the other side of the board :
  

  
  
  
You can't take the board out : it's more tricky, you'll have to solder at the Driver's Anode/Cathode ends (you leave the round caps alone). This is what I did, I'll put some pics in the 1st page post.
  
*Anode* : From Maxx's pic, it's the (+) at the top, from the other side of the board, it's the leads of the 215K/220K 2W resistors (the side the 2 leads have "0" Ohm resistance). Easy to find, easy to solder. The "decoupling" wire is the yellow twisted one, obviously !
  

  
  
*Cathode* : the tricky part ! From the group of 3 resistors you have both ways near the pot, the CathoDe are the caps nearer the pot (the 2 other ones are Grid resistors for each triode of one tube).
 In the pic below, they are the soldering points (on the left) just above the "Dot" writing and (on the right) just above the " sword_yang"


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## Redge78

*3.1 - Cathode Bypass Caps*
  
  
 We are here in the Power stage. Each 6H30 tube is made of 2 triodes, those 2 triodes are used together in a "White Cathode Follower" (WCF) design.
 So, one cathode for a 6H30 tube, composed of a resistor setiing the polarisation voltage and a bypass cap.
  
 This bypass cap is important as a significant part(*) of the modulated (AC) current that will feed the headphones will go through the cathode (and the "Regulating Triode"). This AC Current will preferably go through the caps (rather than through the resistor).
_(*) half the current around the "Push-Pull" functionning point._
  
 In a WCF, the "cathode bypass cap" also plays a role in increasing the gain and lowering the output impedance, all of which are pretty good for us.
  
 The difficulty here is to find a upgrade of at least the same "rather high" value than the "original" cap (220µF).
 This 220µF value starts to be a significant value if you want to switch technology to some MKP or PIO caps. It's even worse if when you want to push the values two steps up (470µF). Those huge MKP/PIO caps would weight pounds (or even kilogrammes) each. It's feasable, it would be expensive, hard to manage ... but it could be better than even the best Lytics.
  
  
*"Main" Lytics caps : *
 The reasonnable alternative is to find the best Lytic caps possible.
 There are several Lytic caps that have been developped with audio in mind and we'll stick with those, we can't try every single brand/product ...
 BlackGate, Elna Silmic, Nichicon Muse, Mundorf, Panasonic FC ... 
 - BlackGate : probably the best, but they are out of production and hard to find (and bloody expensive). Also, burning-time is in hundreds of hours before they stabilise.
 - Elna Silmic 2 : our second best, cheap and available everywhere. Probably as good as the BlackGate above when properly bypassed. 
 - Mundorf : our other second best, if you want to spend more
*CAREFUL *: The Lytics are polarized caps, they have a (+) and a (-) and you need to solder them the correct way.
  
  
*Bypass :* in order to help the Lytic cap in the areas it is weakest (treble, microdynamics, ...), we add in parallel an another cap of a different techno, smaller and faster.
 After having tested various caps (Teflon, Polypro, PIO, Styroflex, ...) the best "musical" match was with some (multilayer metallized paper) PME271 used as "electromagnetic interference suppressor". 
  
  
*Values :*
  
*Capacity :* 
 From 220µF up to 470µF (that would set the cut-off frequency from 5Hz to 2,5Hz). Around 0,1µF for the PME271 bypass.
*Voltage :* 
 Not much voltage here, the "original" 50V is more than enough. The PME271 is given for 275V
*Temp :* 
 Same as always, higher is better. But we should not have much problem here : the Elna are given for 85°, the PME271 for 110°
  
  
Before ("Blue" Philips BC 220µF/50V) 
  

  
  
  
  
  
After (Elna Silmic 2 470µF/50v // RIFA PME 0,1µF/250V)
  

  
 And installed (_with the huge green K75-10 Coupling Caps behind_) :
  

  
  
  
  
*3.2 - 5998 / WE421A Bias switch mod for the MK6 (by SonicTrance)*
  
 This mod is only for MK6 users and is a mod that optimizes the MK6 to use the 5998's and WE421A's power tubes. Sure, you can use those tubes without doing this mod and it'll sound good. But when your done and the mod is complete you wont regret doing it. That's a promise! 
  
 The sonic gain is incredible. Especially the low end gets improved with much more weight and slam. Also overall dynamics and clarity improves. I rate this mod as one of the big ones for the MK6, if you’re using these tubes that is. 
  
 You may have noticed, if you’re using 5998’s or 421A’s as power tubes in your MK6, that the amp runs much cooler and bias meters only reads about 30mA, while the 6080/6AS7G’s gives you 60mA on the meters and amp runs hot? That’s because the 5998/421A’s bias differently and doesn't get enough current in a 6080/6AS7G circuit.
  
  
*What are we doing here?*
  
 The goal with this mod is to cut the stock cathode resistor value in half, which in turn will double the amount of current to the tubes. The MK6 has 330 ohm cathode resistors, so 165 ohms is what we're looking for here.
  
 To do this you could either just swap the stock cathode resistors for some 165 ohm ones. But then you can’t use any 6080/6AS7G’s. So we implement a bias switch. That way we can use all our favorite power tubes.
  
 Basically what we do is get a 4 pole switch (one pole/tube) and 4 additional 330 ohm cathode resistors. Then connect the new resistors in parallel to existing resistors through the switch.
 As the stock cathode resistors are on top side of the board it’s easier to connect the new ones on component side in parallel to the cathode bypass caps. When the switch is on the cathode resistor value will be 165 ohms which is the new 5998/421A setting. And when switch is off the cathode resistor value will be stock 330 ohms for the 6080/6AS7G’s.
  
*These are the cathode bypass caps*
  

  
*Here's pics of the finished mod*
  

  

  

  

  

  
*How do we do this?*
 You can see from above pics that I've soldered the resistors on one end of the cathode bypass caps, and a wire from the other end. Then run the wires to the switch which makes them parallel to the stock cathode resistors. It is that simple. 
  
 I chose to have my bias switch through the bottom cover as the case is 10mm thick and it was hard to find a switch that would fit. Plus it was handy to be able to take the bottom cover off and drill the hole for the switch and not worry about getting metal residues inside the amp.
  
  
*What parts do we need?*
  
 - 4 x 330 ohm resistors, Mills MRA5
  
 - A 4 pole switch, the higher the voltage rating the better. Be sure to measure size first as well. A lot of switches are huge and wont fit depending on where you're planning to put it. 
  
 - Wire. I used 22awg silver plated copper with PTFE insulation. Decent size and easy to work with.
  
  
*It’s only recommended to switch while amp is off. If you have to switch while amp is on then be sure to unplug your headphones first!*
  
  
 Big thanks to user and amp builder @2359glenn for help and information about this mod!


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## Redge78

*4 - Power Supply Units (PSU)*


We didn't feel the need to change much on that part, the PSU is already quite "beasty" with a C-R-C Pi filter with 1000µF before the "regulators".
It's excessive, unusual but effective. The 330µF output caps that are providing the modulated currents are constantly feeded by the regulators (MJ15020/MJ15021) and that's a very "musical" design.

The only main change done here are those Electrolytic (AKA "Lytics") 330µF output caps, replaced by much faster ones ("MKP" Film caps) that will better feed the Decoupling caps down the line. 
Maxx wanted to keep everything into the "original" box, so the "MKP caps" solution was not possible (those caps are too big), we chose the best Lytics caps that fitted (Mundorf M-Lytics 1500µF).




Installed:







Schematics of the PSU feeding the Power stage :


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## Redge78

*5 - Resistances*
  
*5.1 - Power Stage resistors*
  
MK8 - 150ohm (Mills MR5)
MK6 - 330ohm (Mills MR5)

Mills MR5 are best choice in this location, being a compact non-inductive wirewound of superior performance.
_The anode resistors are the most important ones here, they are the "sense resistors" : their voltage will trigger the "WCF" regulating triodes (the bottom ones in the schematics). So the less distortion there is in the resistor the less it is amplified._ 

The Mills MRA resistors exceed MIL-R-26E specs and are 1% tolerance.
The MRA-5 is a 5 watt resistor which will handle overloads 5X its power rating (25 watts) for 5 seconds with operating voltages up to 500V.
TCR:
10+Ω: ±20ppm/°C;
1-10Ω: ±50ppm/°C;
<1Ω: ±90ppm/°C
  
*5.2 - Grid/"Driver stage" resistors*
  
*VALUES*:

*Driver Stage:*
4X 220K Ohm (Anode resistors) - _TKD CM2 Series 2 Watt - __1% Metal Film Resistors - High quality (Japanese) Audio grade resistor._
4 X 10k ohm ("Grid stopper" resistors)
2 X 1.5k ohm ("Common" Cathode esistors)

*Power Tube Grids:*
MK8: 8 X 300ohm
MK6: 4 X 300ohm
  
*"Power rating" recommendation* : always take the highest power handling you can (reasonnably) find, it generates less noise and the cooling is better.  

*Resistor Brand choice*:
1 - Vishay zfoils (tested)
2 - Shinkoh "Tantalum" (tested)
3 - Takman "REY" (not verified)

The choice of resistor here is based on sound quality. So only resistors with history of audiofile preference is recommended.
  
  
*MK8 overview*
  

  
 Red = grid resistors
 Yellow = WCF grid resistors
 Purple = driver stage resistors
 Purple = WCF Coupling caps..
  
  
*MK6 Overview :*
  

  
  
 Red = grid resistors
 Yellow = WCF grid resistors
 Purple = driver stage resistors (anode/Cathode)
 Pink = WCF Coupling Caps


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## Redge78

*6 - Internal Cabling / Fuses / Power Cord / "Heat management" / Diode Bridge*


*Internal Cabling :*

 This is a *noticable upgrade* potential area. You will hear a difference.
 For some reason, the stock wiring is not really up to par, and was initially an optional upgrade, for a time at LD.

 The LD designer himself recomended the upgrade be a silver plated teflon coated wire.
 Maxx134 also chose supplement silverplated with "OCC copper" for the outputs of board to jacks.

 The internal chasis of this amp uses four runs of 2-foot long cables, that are 3-conductor each.

 Regarding the recabling, advice :
 Cooper with silver platting, section 0,3 à 0,5 mm² (you'll work out the awg equiv. [22 to 20...]), light teflon coating, twisted pairs
 normalised : UL1213 (industrialà and/or MIL-DTL-16878/4 (Type E) (mil) for high temp.

 Links :
http://fr.rs-online.com/web/p/fil-de-cablage-electrique/1771113/​
http://www.mouser.com/Alpha-Wire/Wire-Cable/Hook-up-Wire/_/N-5ggs?P=1z0zo8oZ1yzs67rZ1yzoop6

 Also can find similar teflon coated, silver plated, 3conductors (twisted & shielded).
 You can find also on ebay:


*BUT:*
 If you are like Redge78 & coinmaster, who are not confined to internal dimensions of the amp or stock heat issues, then you can choose many many more cable options.


*Fuses*
  
 Why not ... won't break the bank, anyway and you'll have a new way to sound crazy at the office.
  
 There is 3 fuses in the amp.
 One on the power plug at the back and two inside the amp, each side of the middle relay (one inch above the pot).
 Obviously, you need to replace the old fuses by an audiophile ones of same values.
  
 You can go for some "inexpensive" PADIS (_kind of rebranded "Furutech" fuses_), some "HiFi-Tuning", or for the rich kids some "Synergistic Research RED Quantum"
  

*Power Cord :*
  
 Same as above.
 Redge is using a massive *Zavfino "THE MAJESTIC"*  (_PC-OCC Single Crystal 6N Copper Conductor - 12AWG/Core )_
  
  

*"Heat management" :*


*Diode Bridge :* _(Optional)_

 IXYS FRED Rectifier Bridge FBE22-06N1 ( High performance 600v/22amp rectifier bridge with fast recovery diodes). Sonic improvements were not verified at time of installation.
http://www.mouser.com/ds/2/205/FBE22-06N1-6885.pdf


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## Redge78

*7 - The Tubes*
  
  
*7.1 The Power Tubes*
  
MK6
  
MK8se (6H30PI - Electro Harmonic "Gold pins")
  
  
  
*7.2 The Driver Tubes*
  
MK6
  
MK8se (12AT7)


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## Redge78

reserved


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## Redge78

*8 - Background stuff / Documentation*
  
  
*Balanced vs Unbalanced*
  
 - Wikipedia : "Balanced audio"
https://en.wikipedia.org/wiki/Balanced_audio
  
  
*"White Cathode Follower"*_ (the "Power Stage" circuit design)_
  
 - John Broskie's Guide to Tube Circuit Analysis & Design :  A good introduction to the WCF 
http://www.tubecad.com/2014/05/blog0292.htm
  

  
  
_"... Mr. Eric White, the British inventor who worked for EMI, patented his famous White cathode follower in 1940 in England (GB564250), which was also patented in the USA in 1944 (US 2,358,428). His circuit is a unity-gain, push-pull buffer that accepts an unbalanced input signal and presents an unbalanced output. _
_This feat of magic is performed by the top triode's plate resistor that functions current-sense resistor that experiences a variation in voltage drop corresponding to the variation in current conduction by the top triode. This variation in voltage drop becomes the input signal for the bottom triode, which responds in an anti-current phase fashion, creating a complementary, balanced push-pull operation by the two triodes. As the top triode conducts more, the bottom triode conducts equally less; as the top triode conducts less, the bottom triode conducts equally more._
 
_*The result is class-A, push-pull operation that yields an output impedance half of what it would be with the same tube in a cathode follower and lower distortion. *Moreover, the White cathode follower can deliver a peak output current swing into the load twice that of its idle current. The load is all important and its impedance must be factored into the calculation of the sense resistor’s value. Without the external load, the two triodes could not differ in current conduction, so no push-pull operation would be possible. Without the load, the sense resistor would not create the needed drive signal for the bottom triode..."_
 
_(See in "New mods" : White Cathode Follower - Balanced Push-pull)_
  
  
 - A paper from Alex Cavalli from Cavalliaudio : "...The White Cathode Follower as An OTL Power Stage for Headphones..."
_A good introduction and a lot of number crunching. You'll learn here how to calculate the Zout of your amp !_
https://www.cavalliaudio.com/diy/docs/WCFOptimization.pdf *[EDIT : dead link, have to find an another one]*
  
  
*Capacitor reviews*
  
 - Humble Homemade Hifi - Capacitor Test
_Large selection of boutique caps, can be useful for our "Coupling caps" _
http://www.humblehomemadehifi.com/Cap.html
 - Capacitor Musing
_Large selection of various caps, including Russian ones. Bypasses are discussed as well._
http://www.enjoythemusic.com/diy/0708/capacitor1.htm
  
  
*Film capacitors Vs. Electrolytic capacitors*_ (From "ClarityCap" documentation)_
  
_"... The ESR (Equivalent Series Resistance) of a film cap is up to several orders of magnitude lower than an electrolytic capacitor. This enables the capacitor to remain charged at all times and to *quickly deliver higher peak power when required*. ESL (Equivalent Series Inductance) is also many times lower than an electrolytic. This *reduces distortion and phase shift* and ensures that there are *no delays or ringing in response to step changes in demand* on the capacitor. The dry construction of a film capacitor *extends lifetime* relative to an electrolytic cap. In an electrolytic capacitor, the gradual evaporation of electrolyte reduces capacitance and increases ESR, leading to degraded performance and eventual failure. Film cap is non-polarized, ensuring *simplified assembly* [...] The higher voltage ratings eliminate any need in circuit design for complex series/parallel connections and balancing resistor networks._
  
_When selecting a film capacitor to replace an electrolytic, consider that due to the *minimal heat loss and faster transient response* of the film cap, *a relatively low-capacitance film cap may typically be provisioned*. OEMs that have implemented the technology have successfully used TC to replace electrolytics in ratios of capacitance from 1:2 to 1:10..."_
  
  
 ... much more...


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## Redge78

*Around the Amps (Headphones, DACs, Power Supply, cables, ... )*
  
  
Design (because uglyness is not a fatality)
_This is where Maxx will demonstrate that the more the amp shines, the better the sound is ! Voodoo magic !_


----------



## Redge78

*The new mods*
  
 because we always think of new ways to torture the amp
 because you guys help us
 ...
  
*White Cathode Follower - Balanced Push-pull*
  
_" ...The load is all important and its impedance must be factored into the calculation of the sense (Anode) resistor’s value. Without the external load, the two triodes could not differ in current conduction, so no push-pull operation would be possible. Without the load, the sense resistor would not create the needed drive signal for the bottom triode..."_
 
=> if the "load resistance calculation" seems not very important for the MK8 - the load will always be high between 300/600 Ohms - what about the MK6 with its alleged 32Ohms to 300Ohms allowed Loads? What about the push-pull operation when a 32 Ohms load is plugged ? Is it still balanced or do we have one triode working more than the other one ? And therefore is it possible to adjust the "sense (anode) resistor" to bring back balance between the 2 triodes and maximise the power output ?
  
 Cavalli formula : Ra = 1/Gm*[1+2*"Load resistance"/"Plate resistance")   Gm = Transconductance of the triode
  
  
  
  
*10.1 The "WCF" Coupling cap (Tested/Verified on Maxx/Redge) **[EDIT Oct. 08th, 2015]*
  
 The functionning of the "White Cathode Follower" has been explained above (chapt 8).
 When analysing it, what struck us is the regulating triode (T2) is driven by a capacitor and resistor in series to the T2 grid. We can consider this cap as a coupling cap for the T2.
 So, even if this cap is less important that the "Coupling cap" fed by the Driver Stage that impact the whole Power Stage, it will have a direct sonic impact on half the power triodes. Which is more than enough to have a closer look at them in our books.
  

  
  
 The bad news are that the caps put originally by LD are pretty lame (for the MK8se at least), some WIMA MKS4 0,22µF/250V that they also use on other areas for antiparasitic purposes. 
 We were not very happy with the original "SCR PB" coupling caps put by LD, but at least those were "Polypropylene" MKP with half-decent dissipation factors. Those "polyester" WIMA MKS4 are bloody garbage and need to be replaced *ASAP*.
  
  
*Values :*
  
Capacitance :
 No need to push it here, the associated Cut-off frequency is already low enough. So 0,22µF should be quite sufficient. But we tested 0,33µF and 0,47µF (because those were the best "audio" caps we had available) without any problem.
  
Voltage :
 Same as "original" 250V or higher
  
Temperature :
 As always, higher max temp is better. 
  
Recommended caps :
 - Same as for "Coupling caps", they will perform the same task
 - As we don't want to be sued, we also recommend to try some WIMA FKP1 _(Foiled "polypropylene" caps, the best line of product WIMA do in that kind of capacitance)_. They should be way much better than the original crap and are very affordable. And they are square ... and red ... and large ...
 - As the capacitance is quite low, why not trying some FT3 russian teflon ? 
  
  
*Appreciation / subjectives results*
  
 The impact on sound was not minimal or trivial.

 Basically, there is an increase in sonic quality overall which is like the missing third piece to the trifecta of coupling, cathode, & now this "WCF" C.cap
 All three play an intimate role of the sonic signature...
 But...
 Since this cap was the *weakest* link of the three,
 It will make a MORE NOTICABLE sonic improvement than the Cathode cap (maxx134 observation)

 The main sonic aspects of this cap are:

 Increased Clarity
 Increased depth
 Increased holography
 Increased dynamics
 In that order..

 As a result, PowerTube swapping is easily noticable, even in MK8.

 The sound turns much more intense and real.
 And remember, the sonic qualities of this cap will pervade into the signature of the amp,
 So get a cap of your sonic preference..
  
  
*"How to .."*
  
 The caps can be nicely unsoldered if you move the board. That's the elegant way.
 Or ... you can crush /cut the garbage caps _("medieval style")_ and only keep the leads intact on the board. 
  
 The caps don't have to be positionned near the board, you can use some inches of wires for easier fit.
  
  
*Pictures :*
  
 Precise locations (MK8se)
  

  
 Precise locations (MK6)
  

  
  
  
  
 The Garbage cap was just below the circle of pins, where it is written "0.22µ/250V".
 Two "Silver coated ultra high purity cooper teflon insulated" wires are soldered to the remaining leads ...
  

  
  
 The new "WCF" caps have been artistically positionned above the Jup'
  

  
  
 And finally in the box, with all the other caps ...


----------



## Maxx134 (Mar 11, 2022)

UPDATE ~ UPDATE ~ UPDATE!

The following post by member @baronbeehive   lists the recent latest updates to this old thread.
Use it before reading on the next posts of mods... Also keep in mind he has the MK6, which is the more popular version:
https://www.head-fi.org/threads/lit...d-mods-are-on-first-page.782183/post-16858811

So check that link for the updates besides all posts this page.


Ok below is co tinued mods:
***************

*COMPACT VERSION*

This is a current picture of the *Compact version *internals...


Udated with new WCF Coupling caps:



Still a "work in progress",
As it will be implementing a few last Ridge78 (secret) mods that will be tested...



*Coupling caps:*
As you can see, .47uf jupter caps are implemented.
They are a bit thinner and a bit longer than the Mundorf .47uf..
The Jupiter cap is rather new to gaining top status,
 and I feel is tuley at the very top with few others.

Since we are aiming for "supermod" level, I can only recommend this cap.
Although, my second place choice for now, would still be Mundorf.

For MK6, a .67uf size is recommended, while coinmaster went a bit far to the suggested limit of 1uf..


*Decoupling caps*:
The red and white "Decoupling" caps were chosen as largest possible within original confines of the amp.

The 25uf red WIMA Decoupling caps feed the driver tubes,
While the white 47uf Mundorf decoupling caps feed the power tubes..

Although these caps are not as large as Redge78 or Coinmaster caps,
 they are within values to be an effective solution,
As well as having advantage of both proximity,
And being directly soldered onto board..

The method used, to secure the large .47uf mundorf caps on board,
Was to Insert one end into the hole designated for the resistor...
Then just wrap the resistor lead on the newly inserted cap lead..


The gold .33uf RIFA "bypass" caps are also connected in inparallel to them..

I was going to place these .33uf Rifa,
 on other side of board, like member "coinmaster":

This is good for an MK6,
As most the heater feed runs in between tubes(red wires)...

But take note, the blue "Output wire" is too thin(!)
As are *ALL* the output wires,
Leading from the board to the XLR jacks..
 And so they all need upgrading...(!)

For the MK8, there was some space restrictions for placing the .33uf RIFAs on top like the pic above,
 because the wiring is on the side those caps would be..


The smart move is to do this bypass cap installation at same time as replacing the super thin output wires, (from board to sockets).
That way, you only pull out the board ONCE...

My wire upgrade (from board to sockets), was done with OCC copper there(doubled,twisted& taped),
Which is extremely difficult to keep in place without hotglue..




*Cathode Bypass caps*:
**Edit: higher recommend values determined late in thread, up to 660uf, by member @CopperFox , _*here*_.
Pictured are Mundorf 220uf 63V Bipolar caps..
Why bipolar?
The layout.
Also,if you look at data sheet you will read it's advantages for music signals:

http://www.soniccraft.com/datasheets/Mundorf_ECap_RAW-data.jpg

http://www.hificollective.co.uk/catalog/ecap63030-220uf-63vdc-mundorf-ecap-electrolytic-p-4010.html

 They are preferred for this Compact version,
as they can be "stacked" one on top of the other to conserve space:



...with the accompanying RIFA .1uf "bypass" caps on other side of board:

With Mills MR5 wirewound power resistors moved over the vent holes..


There are also "Optional" mods in place which are currently unverified for sonic gains:

1- Larger (black gate) caps for PSU control circuit stage.

2- Implementation of "IXYS FRED Rectifier Bridge" in place of original bridge..

3-Black damping material on all the elecrrolytics...

OPTIONAL MODS remain only as an option.
They are separate from the main posted mods above.

WE will focus first on the mods which were sonically verified to give performance gains.


*Heat/ventilation*
This is important modification for this compact veraion..
The wiring (stock or replaced) suggestion is to raised up,
for better air circulation around to top of board..(done in picture)
The existing stock wire placement prevents air flow on sides to top.

This is where a hotglue gun comes handy to hold all in place,
and yes I like to use alot wherever needed.


So, the combination of all these upgrades,
 provides for an *extremely* fast, responsive, detailed, dynamic and musical design(!).

It is now one of best amp for the HD800, presenting a powerfull experience rarely heard anywhere else.(!)

More is being added daily so keep checking first page!

*HEAT MANAGEMENT :*

For the compact version,
We most definitely need to upgrade fans..

Go with this post by:
Sound Engineer:
http://www.head-fi.org/t/522099/lit...mk-viii-se-owners-unite/1860_20#post_11586342

There you will see to open larger hole and place largest fan possible,

Instead of smaller noisy fans. .

And also a fan speed controller which I use and highly recommend.


----------



## Maxx134

*CAN ANYONE DO THIS?..*

Quote, MisterX:
"*...No shame in letting someone else do the job though...*"

I have been asked this question from members not feeling confident to do the mods...

I have proposed one possible solution..

Post a "electronics or amplifier job" in your local college..
There are many "starving students" in electronics field who would take on this job, quite enthusiastically, for a nominal fee, and can also use it for their own benifits for project requirements in college.

This way, you wont get ripped off going to some "Joe Shmo" tube repair shop where the guy will take forever and complain it goes against his training..

College Students are a ripe source for young, sharp, enthusiastic minds open to new things...

Just make sure you can trust the person to be responsible to carry it out...






*COSMETIC MODS:*

SonicTrance MK6 transformer mod:
http://www.head-fi.org/t/782183/little-dot-mk8se-mk6-super-mods/80_20#post_11966905



Visual mods are separate from sound quality of super mods,
But can inquire in thread.


SonicTrance 
Mk6 visuals:

























Extra pics for visuals to compliment mods:

MK8:


----------



## SonicTrance

Nice guys! Been looking forward to this. I still can't believe the huge improvement I got from only changing coupling caps and power resistors
	

	
	
		
		

		
			




  
@Maxx134 Dude, your amp looks crazy now! In a good way


----------



## Maxx134

The major sonic improvements are what motivated that.


----------



## coinmaster

Yay, now I can finally blabber my mouth about the mods! Although there is a enormous amount of information missing from here so I think I'll wait, no point yet.


----------



## coinmaster

Reserved.


----------



## Mogos

Patrs list will be welcomed with spec and palce to be used.


----------



## Redge78

coinmaster said:


> Ah, screw it who cares.
> 
> BOOMshakalaka


 
 I care, actually !


----------



## coinmaster

mogos said:


> Patrs list will be welcomed with spec and palce to be used.


 
 That's getting too deep into a full blown guide. I don't wana take Maxx's job away from him.
 Wait until they finish writing it.
  


> I care, actually !


 
 Oh, sorry 
	

	
	
		
		

		
			




  
 It's on the second page anyway, so no big deal 
	

	
	
		
		

		
		
	


	




 I didn't take anything away from your guide. Just generating hype!
 I can always delete it later.


----------



## Mogos

OK


----------



## Redge78

mogos said:


> Patrs list will be welcomed with spec and palce to be used.


 
 We will be experimenting with the "Coupling caps" chapter how much information we can/have to put.
 Maxx and I have been so much into it that we may forget something.
  
 So your feedback is more than welcome, really.


----------



## Maxx134

As your pics may create confusion or intimidation,
So a reminder that we will be updating reserved posts with explanations..


----------



## coinmaster

Yeah, be patient for the guide, my pics are just for hype 
	

	
	
		
		

		
		
	


	




, yours may not be anywhere near the same as mine. There's lots of ways to do it. I went over the top with my build.
  
 Edt: I got in trouble, pics are gone


----------



## Maxx134

Correct, mine is very different actually, 
Yet same methodology is applied.
We will first focus modification that have been known and tested to "hear" improvements.
That is why we starting reserved post of the coupling cap.

We like to be as informative as possible, so all will have a better understanding of these amps,
And it also helps others to grow and contribute to future improvements..


----------



## Maxx134

coinmaster said:


> Yeah, be patient for the guide, my pics are just for hype  , yours may not be anywhere near the same as mine. There's lots of ways to do it. I went over the top with my build.
> 
> Edt: I got in trouble, pics are gone



Sorry didnt want you to remove *all* of them.

Lets see your choice of parts and why.

For clarification,
Both Redge78 and coinmaster chose to expand the bottom of the amp,
In order to place the Larger capacitors..

It was an necessary evil,
As "MKP" caps are inherently larger than electrolytics...
That does not mean you would want "MKP" everywhere, as they are not suitable for every purpose.

For instance, you would not want them right after a rectifier in a power supply stage, for example.

We used the optimal types for the intended usage.


----------



## coinmaster

Eh, my pics were more of a time lapse progression than a guide. If I was going to post explanations I would have gone in depth. We don't need 2 guides here.


----------



## colliedoggy

Thanks for this thread!
  
 I would like to re-echo Mogos' request for more particulars about each mod. E.g. in the coupling capacitor section, how are these labelled on the pcbs, where do we find them (arrows on photos would help)? What voltage specifications should replacements be, etc.


----------



## coinmaster

The guide isn't complete yet. Patience. *READ*! They will be updating it over the next two weeks. It's not even remotely finished yet.


----------



## Redge78

colliedoggy said:


> I would like to re-echo Mogos' request for more particulars about each mod. E.g. in the coupling capacitor section, how are these labelled on the pcbs, where do we find them (arrows on photos would help)? What voltage specifications should replacements be, etc.


 
  
 OK, no problem. I'll add the Voltage specs. And caps orientation _(the Fen-shui of the amp ...) _as we discussed that in the MK6/MK8 main thread
 We may also add an "How to ..." chapter with all the "less formal" data we gathered and that can make one's life easier.


----------



## Maxx134

Cathode bypass cap section updated...

I consider this a huge beneficial upgrade from the cheapo blue electrolytics,
Which seem as two tiny caps encased in an imitation bipolar configuration,
Inside a blue "see thru" housing...
Edit:
But actually is just one dual cap with 3 pins converted to two.. 

It is an Extremely *smart* cost effective solution for a manufacturer,
But far from optimal sonic performance,
So a clear upgrade potential.

Take note I am not bashing in any way LittleDot, 
But commending how smart their solutions were to maximize cost effective solutions.

Yet remember, this thread is about maximizing the true sonic potential,
*hidden* in the Little Dot amps...


----------



## coinmaster

Quote: 





> *Where to put those Decoupling caps ?*
> Each centimeter/inch of wire will bring an extra impedance that will have an impact on the speed of the current needed.
> So those caps need to be put as close to their associated tube as possible.
> Ideally, they will be soldered directly on the leads of the Anode resistor (+200V side)  and the Cathode resistor (Ground side).
> _*Don't underestimate the difficulties that this constraint will bring, having to stick large caps in a small space is not that easy*._


 
 True statement!!!!!!! 
 I'm in the middle of ripping everything out of the aluminum chassis. It was simply too hard to put back together once taken apart with those giant capacitors I'm using for the decoupling. 
  
 I'm going to make the entire structure out of wood and I'm taking this opportunity to upgrade the Enla Silmic electrolytic capacitors I'm using for the cathode bypass capacitors with 8 of the giant MKP capacitor types I have littering my wood box, like the ones below.


 Why 8 of them? Because they don't come in 470uf so I'm doubling up.
 The only reason this is going to work is because I no longer have the aluminum chassis getting in my way.
 Now I just gotta blow 700 bucks on some more caps.


----------



## Maxx134

What you *really* need is to be very carfull you dont get shocked(!) By those caps!

You wont know if there is any charge on them if they have been tested before shipped...

Wear surgical gloves,
As this *IS* surgery when you go down the "rabbit hole" of supermods which will truley bring you to another world...
Another level where very few other amps reach(!)


----------



## Mogos

maxx134 said:


> *COMPACT VERSION*
> 
> Ok this is a current picture of my amp internals...
> 
> ...





> Maxx134 all the bypass caps are as these ones:
> PME-040: 0.033uF 275Vdc Evox Rifa PME271M





>


----------



## Mogos

One more thing. Could you guys point out the soldering points of the added decoupling caps on the PCB (Anode resistor (+200V side)  and the Cathode resistor (Ground side)).


----------



## colliedoggy

And I'd like to add further to Mogos' request for the same information please about the 'bypass' and 'cathode' caps.
  
 Thanks


----------



## coinmaster

I'm sure he will update the guide with that information but for now

 See the large brown capacitors in the middle? Those are what replaced the blue caps (cathode bypass), and the black resistors to the right and left of them? Those are the power resistors we replaced.
 You want the decoupling caps to go between those two points from the south side lead, you will also be putting another bypass cap (those rifa caps) in .33uf between those points as welll. You see how this area will end up having a lot of components..
  
 This is what I did for the bypass caps


----------



## Maxx134

That was a very good idea to put on other side of board, but I didnt want to go thru the hassle..

Only the bypass caps on my component side are .33uf, NOT .033uf

This side is not critical, and can be .22 as well.. but I would not go higher than .33uf, and use types (RIFA)suggested in fisrt page for optimal sonics.

What IS ALSO very important, are the *Cathode bypass* caps...
They were selected specifically for their sonic traits and need be the same *.1uf RIFA*, as stated in first page, exact type.
 Size was determined so as to not interfere with the electrolytic sonics of the electrolytic choices of cathode bypass caps..


----------



## Maxx134

Here is a pic of the decoupling cap locations, 
I May include it later in first page..

Once you see, it is very straightforward and easy..


----------



## Maxx134

There will be more info updated in first page, as we find time.

For example the resistors..
The MK8 has a more linear "enhanced" version of the "white Cathode Follower", which includes grid resistors to upgrade,
Which are not in the mk6..
Yet the mk6 still needs upgrade of grid resistors in driver tube stage, by volume control,
IF they are the blue resistors..
If they are the brown type, you are good.


----------



## Mogos

maxx134 said:


> ............
> 
> What IS very important, are the Cathode bypass caps...
> They were selected specifically for their sonic traits and need be .1uf wimas, as stated in first page, and exact type,
> so as to not interfere with the electrolytic sonics of the 220uf cathode bypass cap..


 
 Maxx134 I am a little confused. On the first page as an example solution are shown (Elna Silmic 2 470µF/50v // RIFA PME 0,1µF/250V). So no wimas. My question was about bypass caps for decoupling (by the way thank you very mutch for the photo. I need to know the points of soldering to plann maximum "volume" capcitors).
So for the bypassing of the decoupling caps you have used 0.33uF 275Vdc Evox Rifa PME271M.


----------



## coinmaster

.33uf Rifa caps for bypassing the decoupling caps. 
 Elna Simic caps for replacing the cathode bypass caps (blue caps)
 .1uf Rifa caps for bypassing the cathode bypass cap replacements (Elna Simic)
  
 He meant Rifa not Wima, that was a typo.


----------



## Mogos

Now everything is as plain as a day.


----------



## Maxx134

coinmaster said:


> ...He meant Rifa not Wima, that was a typo.



Yes thank you


----------



## coinmaster

I'm using industrial MKP caps for my cathode bypass, now that I have ripped everything out of it's case.
 I'm wondering, do I even need the .1uf bypass caps if I'm using mkp?


----------



## Maxx134

I believe so, as I asked same question to Redge78.

Their very small capacitance and proximity is an advantage.


----------



## Mogos

I hope you are preapred for many somtimes so obvious questions.What about the connection points for the driver tubes decoupling caps.
 Is the one

 replaced with Wima one

 or tere is another situation hidden behind ? 
	

	
	
		
		

		
			




 And wat is the rule to connect the cap with 4 legs in to two connection points.
  
 I am planning to use as a decoupling caps 
 MKP 50 µF Wima
 DC-LINK 900 V/DC 20 % 
 But they have four legs.
 The Mundorf Lytics AG+ also.


----------



## Maxx134

Those are very nice caps...
 The legs on the same side can be combined..
For instance look at the pic first page of my mundorf..
 legs on same side are pointed to each other..


----------



## Maxx134

I will take a closer pic once I am home in about 8hours


----------



## coinmaster

You are replacing the capacitor at the top yes, from this trace on the right (the two prong one for the capacitor) to the one at the top (one of the resistors we replaced).
  
 You can either just replace the capacitor from the soldering points or solder to the capacitor ground (the soldering point on the left that has no trace) and the resistor up top which would leave a shorter signal path.
  
 One thing I will say is *don't start buying anything until you have a complete understanding of what you are buying and why*. You should see how many questions I have asked Maxx and Redge!, gazillions of pages worth, we just opened our third private thread because the other 2 took too long to load and scroll down from being so gigantically big.
  
 Props to Maxx and Redge for putting up with me


----------



## Maxx134

Took Ur pic 2 draw:


----------



## Mogos

Thank you this is it. From your photo and what have Coinmaster written it looks like the capacitor on the top is taken away. But from the connection photo (and what it was said about adding a new decoupling elements) I conclude that the top capacitor shall be there where it was. I have a question can I use the same type of capacitor MKP 50 µF Wima DC-LINK 900 V/DC 20 % for the drive stage? Can you also pint out the position of the resistors you have written before:_ Yet the mk6 still needs upgrade of grid resistors in driver tube stage, by volume control,_
_IF they are the blue resistors..
 If they are the brown type, you are good. _
  
 Slowly we will understand what you are guys talking with ech other about .


----------



## Redge78

mogos said:


> Thank you this is it. From your photo and what have Coinmaster written it looks like the capacitor on the top is taken away. But from the connection photo (and what it was said about adding a new decoupling elements) I conclude that the top capacitor shall be there where it was. I have a question can I use the same type of capacitor MKP 50 µF Wima DC-LINK 900 V/DC 20 % for the drive stage? Can you also pint out the position of the resistors you have written before:_ Yet the mk6 still needs upgrade of grid resistors in driver tube stage, by volume control,_
> _IF they are the blue resistors..
> If they are the brown type, you are good. _
> 
> Slowly we will understand what you are guys talking with ech other about .


 
 Hi Mogos,
  
*"capacitor MKP 50 µF Wima DC-LINK 900 V/DC" :*
 - Which one ? There are 5 or 6 different types of "WIMA DC-link". Better to put a link to a datasheet or a site, that limits misunderstandings.
 - 50µF is probably too much. Decoupling capacity is linked to the modulated current/power you have in the stage you feed. And there is not much power in the Driver stage. Maxx's 25µF should be just fine, and they fit. But 50µF (or more) won't hurt. The "min 50µF" was more for the Power Stage decoupling.
 - About the "4 leads" ... it's always good to read the datasheet of the component you study/buy, you have plenty of useful informations in them, and among them "how to deal with the leads ...". And my "WIMA DC-LINK MKP5" have 5 leads, so don't complain !
  
  
  
*About soldering points :*
 You can take the board out : the easiest is to remove the small round cap and put/solder the decoupling one there
 You can't take the board out : it's more tricky, you'll have to solder at the Driver's Anode/Cathode ends (you leave the round caps alone). This is what I did, I'll put some pics in the 1st page post.
  
*Anode* : From Maxx's pic, it's the (+) at the top, from the other side of the board, it's the leads of the 215K/220K 2W resistors (the side the 2 leads have "0" Ohm resistance). Easy to find, easy to solder. The "decoupling" wire is the yellow twisted one, obviously !
  

  
  
*Cathode *: the tricky part ! From the group of 3 resistors you have both ways near the pot, the CathoDe are the caps nearer the pot (the 2 other ones are Grid resistors for each triode of one tube).
 In the pic below, they are the soldering points (on the left) just above the "Dot" writing and (on the right) just above the " sword_yang"


----------



## Mogos

Data sheet for Wimas. Suitable or not this is the question.


----------



## Mogos

I have found another one with better tolerance MKP 60 µF Wima DCP4L056007KD4KYSD 800 V 10 %
 But costs two times more.


----------



## SonicTrance

If anyone is looking for cathode caps, hificollective sells 220uF 63V Mundorf ECap AC RAW electrolytic capacitor for £1,79 a piece!
  
 http://www.hificollective.co.uk/catalog/ecap63030-220uf-63vdc-mundorf-ecap-electrolytic-p-4010.html


----------



## coinmaster

This is what I'm using for the driver tube decoupling. http://www.mouser.com/Search/ProductDetail.aspx?R=DCP4I061508CD4KSSDvirtualkey50520000virtualkey505-DCP4-150%2f600%2f10
 I was surprised how big a difference simply upgrading the power caps and these made. It was huge.
  
 You haven't stated whether you are planning on keeping everything inside the case or what your budget is.
 Personally, for me this amp is a long term investment, I'd be hesitant if there was a potential to buy a better amp but nothing I've heard at any price comes close. So I'm putting as much as I can into the amp.


----------



## Maxx134

sonictrance said:


> If anyone is looking for cathode caps, hificollective sells 220uF 63V Mundorf ECap AC RAW electrolytic capacitor for £1,79 a piece!
> 
> http://www.hificollective.co.uk/catalog/ecap63030-220uf-63vdc-mundorf-ecap-electrolytic-p-4010.html



This is MY recomended cap.
Check the datasheet to see what they say about its signal passing quality.
It has the advantage of laying flat like original.
In my amp, I stacked them one on top of another, for even more space.

I cannot recommend these highly enough and it seems mundorf os making some lower voltage types that look same.
So dont get confused..

Also , at that price they are a steal.
So IF you choose an electrolytic for the Cathode bypass(which is more practtical) 
Use this one!

Also, Using the bypass .1uf Rifas with them (to me) negates the reasoning to go full "mkp" type on the Cathode caps, 
Unless your coinmaster 
Hey Coin, I wanna hear your beauty in future once all setup.


----------



## Redge78

maxx134 said:


> Hey Coin, I wanna hear your beauty in future once all setup.


 
 He'll have to rent a truck to carry his stuff ...


----------



## Maxx134

redge78 said:


> maxx134 said:
> 
> 
> > Hey Coin, I wanna hear your beauty in future once all setup.
> ...



Yes I realized I may have 2 go2 him, 
as it will be too much to move...


I also have issue of losing a diamond or two if I transport my jeweled coverd unit ..


----------



## coinmaster

Lol, tell me about it


----------



## Maxx134

There comes a time in everyones life when they realize they went overboard....

Lol time to tone it down & focus on the mods..

I have a short list of tubes will post soon..

 and for coupling caps(those that can afford it),
 get the Jupiters even if you have to save up,
as they are worth it over the mundorf silver/gold/ oil..
Which in comparison (Mundorf)have a sweet tonal balance, but not as natural and realistic timbre of the jupiters...


----------



## coinmaster

No such thing as overboard, although I agree you should focus on practical upgrades first


----------



## SonicTrance

Are there any sonic benefits to solder the driver stage decoupling caps directly on the resistors vs solder them on the same spot as the 33uf stock cap?


----------



## Redge78

sonictrance said:


> Are there any sonic benefits to solder the driver stage decoupling caps directly on the resistors vs solder them on the same spot as the 33uf stock cap?


 
 Theorically, yes. The less added impedence you add from the wires/board trace, the better.
 Now ... how much better ? It will depends on how close you can put them.
  
 And you'll have to remember that this area is going to be pretty crowded fast and you'll have to work a lot around there.
  
 So, my "no nonsense" recommendation would be to have your main Driver Decoupling cap (red Wima, for instance) at each corner, where Maxx put them, soldered to the round cap pastilles (cap that you'll have removed).
 The associated bypass cap (smaller) can be soldered on the resistors leads, if you have some space left. 
  
  
 And I can't emphasise enough the importance of careful planning of your layout. You'll have to think 3D !
  
 From the pic of my amp (upside down), I have 4 layers of caps
 - On the left (bottom to top) : *"PME271 Driver Decoupling Bypass" *> "Jupiter Coupling" > "K75-10 experiment" >* "TCP Industrial Driver Decoupling" *... and some space left for more experiments
 - On the right ; "PME271 Cathode Bypass" > "Elna Silmic "Cathode cap" > "ClarityCaps Power Decoupling" > "TCP Industrial Power Decoupling" = "WIMA DC-LINK MK5 Last PSU" (*Green *: not in picture)


----------



## SonicTrance

@Redge78
 Thanks for the very detailed answer! I'm going to fit everything in the stock case, so my caps are (a lot) smaller than yours. I plan to put all PME271 bypass caps on top side of the board to save space.


----------



## Maxx134

If more space is needed, both caps feeding the driver tube stage pictured, can be removed.
They are connected "together", and as such, unnecessary, when you are replacing with the much greater mod solution..


----------



## SonicTrance

Aah, ok. Thanks Maxx! Thats good to know


----------



## Maxx134

First page updated again


----------



## Bazile

Folks;
  
 I have to ask, although I'm afraid I know the answer. What level of DIY ability do these mods take? I have the money to do them. Heck, I even thought about having parts milled (made) to make my MK6 bottom (not a plus) 4 inches tall instead of 2..., but I think I'd screw up the mods if I try. Are there folks doing this for pay yet? thanks.


----------



## SonicTrance

bazile said:


> Folks;
> 
> I have to ask, although I'm afraid I know the answer. What level of DIY ability do these mods take? I have the money to do them. Heck, I even thought about having parts milled (made) to make my MK6 bottom (not a plus) 4 inches tall instead of 2..., but I think I'd screw up the mods if I try. Are there folks doing this for pay yet? thanks.


 
 As Redge and Maxx are kind enough to post this guide, all you really need to know is how to solder and follow instructions. I myself don't know much about electronics, but I've learned quite a bit about my amp thanks to this guide (and a bunch of PM's with Maxx)


----------



## coinmaster

Um, I have never done a diy electronic project before and i reconfigured the entire amp. Even if you break something it's a simple replacement. Just get a soldering iron, solder sucker, and some solder and your good. Try to practice with it for a few minutes on something before desoldering your amp.
 Just make sure you don't rush anything, always keep yourself in check because that's how things get broken/melted.
  
 Here's my current progress.

  
 I don't recommend anyone do it this way. Even though I tried my hardest to document everything so I could reassemble it I still managed to put it together incorrectly.
 (so many wires!)
 This caused a few components to break, easy enough to replace, hard to diagnose, except for the crappy resistor that went up in smoke.
 It's also incredibly dangerous to have your amplifier set up in this manner, those large capacitors I have in the box will kill you instantly if you touch them and they aren't discharged.
*Everyone needs to be aware of the danger of touching undischarged capacitors*, always let them sit for a few minutes after unplugging the amp with your headphones plugged in and the power switch on.


----------



## Maxx134

Yes guys no much need for PMs anymore as you can ask away here...
I have thought about if someone asked me to making one, and although it woulf be alot easier second time around, 
I wont have the time to do one quicly, and I wont be retired to do them in another 5years lol.

What I can say, is that yes this model is not hard at all, 
But at same time, easy to break wires off board, and it needs a gentle determined hand to work..
No rushing, no bruteness, 
And alot of double checking.
Because if you mess up and you dont know what your doing,
Then you wont be able to "read" the syptoms...

That is why the "RECOMMENDED" installation be done IN STAGES, NOT ALL AT ONCE...

It makes things ALOT EASIER to point out an oversight or flaw...

So average comeptence required...

Also take note, 
It you want this super mod,
And you do not have ability or patience,
Just get the parts and bring it to a competant electronics person or repair place for installation...


----------



## Mogos

Coinmaster you made me speech less again. I thought it is not possible to suprise after I have already seen what you have done. But they say you never know. Congrats creativity.
 Guys nobody touches the pot . Do I will be only one who will do it?


----------



## coinmaster

> Coinmaster you made me speech less again. I thought it is not possible to suprise after I have already seen what you have done. But they say you never know. Congrats creativity.


 
  Yeah except I bricked it. Not sure what to to test with my multimeter to find what I broke. Sucks not knowing what you're doing.
  
 Quote:


> Guys nobody touches the pot . Do I will be only one who will do it?


 
  
 Is there some advantage to upgrading the pot?


----------



## Mogos

I will find out. One thing is strange. I did not find any where an information datashet whatever about Alps? pot we have. I have asked you guys about and nothing. What the heck.


----------



## Mogos

One more thing about getting the advantage. The existing pot is a carbon path, if I am correct, with slider over it. The pot I will use is a grid of Vishai precision resistors in shunt topology. It means that on every position (level of attenuation) I will have only two resistors (metal film SMD) in the signal path.


----------



## SonicTrance

coinmaster said:


> Yeah except I bricked it. Not sure what to to test with my multimeter to find what I broke. Sucks not knowing what you're doing.


 
 So, you decided to ditch the case, took it apart, and then assembly went wrong? Man, that sucks I hope you figure it out soon.


----------



## Redge78

mogos said:


> I will find out. One thing is strange. I did not find any where an information datashet whatever about Alps? pot we have.


 
 No kidding !
  
 Alps site  > Potentiometers > Rotary potentiometers > list of 16 pots with only two that have "quad units" and it's pretty straighforward to recognise which one is ours ... "RK168" ... and there the Datasheet.
http://www.alps.com/prod/info/E/HTML/Potentiometer/RotaryPotentiometers/RMP_RK16/RK16814MGA0K.html
  
_Just in case you ask, the ALPS RK501 (the "Audiophile" beauty) is 50K in Quad-units, we can't use it._
  


> Guys nobody touches the pot .


 
 Yet ... but just an hint ... 
  

  
  
  
 But we will be happy to hear from you once you have done the mod !


----------



## Maxx134

redge78 said:


> Just in case you ask, the ALPS RK501 (the "Audiophile" beauty) is 50K in Quad-units, we can't use it.




Actually I have an idea willl PM.


----------



## Mogos

Ok Ok. I thought it is RK168 but I don't understand whay the marking on ours says something else. The one on the photo is Kozmo akustic. Very nice and with remote control. It will take me some time to do the mod. Recently I am collecting parts. As I will be ready I will share with you the details, especially in the topic how I have fitted the pot in place of the original one and in the same place on the front panel. It will be very tricky but I hope it will work. It will be difficult to judge the influence of the pot itself on the amp sonics as I want to limit the nessecity for dissmantling the pcb to minimum. So I will change a lot of compnents:tube sockets,wires,xlr sockets, caps, resistors etc.


----------



## Redge78

mogos said:


> It will be difficult to judge the influence of the pot itself on the amp sonics as I want to limit the nessecity for dissmantling the pcb to minimum.


 
 Yes, we all have had this problem 
  
  
  
 And yes, a Khosmo ! And I have been soft, I didn't show the 8-channel Z-foil version !
 And if I had one of those, I wouldn't put it in the box, I'll make sure that everybody can see it !


----------



## Maxx134

Lots can be done always, to anything...

But me and Redge78 have focused on explaining the important mods that make the most improvements.

I never thought about replacing things like sockets & xlr jacks.

The more you intend to change, should be on par to level of expertise you have. 

If you over reach, you may end up having to learn how to fix.


----------



## coinmaster

> If you over reach, you may end up having to learn how to fix


 
 Like me! 
	

	
	
		
		

		
		
	


	




.
  
 And yeah, personally I have minimal interest in changing menial things like sockets and xlr jacks and whatnot. It's gotta be worth my time


----------



## coinmaster

Looks like I fried my white rectangular caps

 At  least now I know. Hopefully that's the only thing that's fried.
  
 At least it gives me an excuse to get some over the top replacements 
 Also ordered 4 more of those giant industrial caps in 220uf 700v for the cathode bypass to replace my elna silmic electrolytics.
 I was gunna get 8 caps and use 2 in parallel for each one but it's not important enough for now to spend another 400 bucks on 4 more.
 Mogos, prepare to be amazed yet again 
	

	
	
		
		

		
		
	


	




 assuming I can get my amp to work again first


----------



## Mogos

One more thing about the shunt type resistors. I have found such a note about them: _SERIES-SHUNT type, a good approximation to ture ladder, since it only has 2 resistors in the signal path. However, the input resistance is not constant, so the source must be current-capable. _I have read that the minimum resistance of the pot (loudest signal, correct me if I am wrong) shall be four times the impedance of the source. I am lucky as my DAC on XRL cables has less then 3 ohm impedance. 
 Redge it will be a waste to install such a "jewerly" and hide it from the eyes 
	

	
	
		
		

		
		
	


	




.


----------



## Mogos

coinmaster said:


> Like me!
> 
> 
> 
> ...


 
 Coinmaster did you change your internal wiring? If yes then changing the sockets shall have tha same importance. Without changing them you have reach only half of the potential improvment effect unless they are of good quality, at least that is my experience. So I wouldn't call menial. The original tube sockets are bad quality and gives poor contact.


----------



## Maxx134

mogos said:


> ...  The original tube sockets are bad quality and gives poor contact.




This "could" be why some experience slight hum and swapping tubes around helps for better fit,
But ever since I purchased some gold pin tube socket extenders, 
I have essentially solved both that issue of any possible poor contact, 
AND Also reduced heat issues,
 by having tubes elevated away from original sockets..


----------



## Mogos

Maxx those extenders is a very good idea from the point of heat issue . I didn't know that such a solution exists. I have seen adapters but not extenders.
 Ok may have seen them but did not figure out they ncould br usefull .


----------



## SonicTrance

I use socket savers too. Works great, amp runs cooler and "saves" the sockets.



I've changed the transformer covers to 130x100x116mm silver ones. Makes the amp look much better IMO
Also, if you wanna use these covers and still fit the little black cover for the regulators, you need to file/cut the little black cover a bit to make it fit


----------



## coinmaster

I dunno, I have a hard time believing that replacing the sockets with unobtainium is going to make any noticeable increase in sound. Afterall, at the points of non-contact like the wires that are soldered into the sockets we speak of the signal is passing through sometimes a couple centimeters of tin which has a resistance 5 times that of copper.
  
 I'm not a cable "naysayer" but I feel like if there is truth to it, a crimped connection might be a priority, rather than a soldered one, compared to simply replacing the sockets with .005% more conductive material.
  
 I suspect most of the "snake oil" naysayers simply don't have a set-up that is good enough to hear said differences anyway. Not to say there isn't a lot of balogna snake oil out there.
 But I don't think the current sockets are that low quality, the xlr sockets come from a reputable vendor, not sure about the tube sockets.
  
 Also I'd like to hear your theory of why upgrading the potentiometer will improve the sound.


----------



## Maxx134

sonictrance said:


> I use socket savers too. Works great, amp runs cooler and "saves" the sockets.



This MK6 amp looks absolutley wonderfull,
 so would be great to post details like your tranformer covers which are different size than mine...

Truly, this is how all MK6&8 should have come...


----------



## coinmaster

Oh Maxx, you are such a fashion victim. I bet your house is spotless


----------



## SonicTrance

maxx134 said:


> This MK6 amp looks absolutley wonderfull,
> so would be great to post details like your tranformer covers which are different size than mine...
> 
> Truly, this is how all MK6&8 should have come...




Thanks Maxx! Much appreciated!
I've edited the post above with details about the covers


----------



## Maxx134

coinmaster said:


> Oh Maxx, you are such a fashion victim. I bet your house is spotless



Its about as clean as my twin brothers house...



We have no time for petty cleanups when we experimentinnn...


Oh, woops I just let you "see" what may be next...


----------



## coinmaster

So I just read that the potentiometer is in the signal path. I didn't know that. That should be a priority upgrade shouldn't it? At least on the same level as the grid resistors.
 If so a z-foil pot would probably be best http://www.khozmo.com/products_dale_shunt.html


----------



## SonicTrance

maxx134 said:


> Its about as clean as my twin brothers house...
> 
> 
> 
> ...




You're throwing in your "old" Mundorfs to bypass the Jupiters?


----------



## Maxx134

sonictrance said:


> maxx134 said:
> 
> 
> > Its about as clean as my twin brothers house...
> ...



oh no,
They are for something else...

 Mmuuaahahahahaaaaahhh..!


----------



## coinmaster

Historically the Mmuuahahaha laugh means something good, and less money in my pockets.


----------



## Maxx134

Yes very different, very good, all thanks to Redge78 brain calculating powers...
But For you, I dont know lol!


----------



## coinmaster

Didn't know Redge78 calculated brains..


----------



## Maxx134

coinmaster said:


> Didn't know Redge78 calculated brains..


. He 
 Calculates everthing..


----------



## coinmaster

The wire length on my driver decoupling caps and power supply caps are about 8 inches. I know Redge said they aren't "as" important as the power tube decoupling caps when it comes to getting them close to the board but I should still gain a benefit right? Might as well do something while I wait for my replacement components to get here.
  
 Also have a question about those black gates you have in your power control circuit. Was there some theoretical benefit to upgrading those or were you doing it "just because"?


----------



## Maxx134

coinmaster said:


> ...or were you doing it "just because"?



Yes "coin"...
It was a "just because, I can" thing...

Those stock caps just looked rediculously small for the opamp circuit it feeds...
But its only 4 opamps...

This is where we are at a disadvantage because we do not have the schematics..


Also, first page has been updated again while site crashed...


----------



## coinmaster

Well, if duty calls I can make a schematic. If I draw a layout of all the components it wouldn't be too hard to "connect the dots" from there.
 The main thing that concerns me about that is I don't wana stress the wires on my board with all that board flipping. Wouldn't want another "accident" from a loose wire.
 Plus I'm critically low on solder and money to buy it with 
	

	
	
		
		

		
			





 
 Buuut, if having a schematic is really needed to get the information you need to figure out optimal upgrades then I can figure something out.
 Or you could just google translate yourself to that chinese forum you spoke of and ask the creator himself for a schematic. I've had full on conversations with koreans that way.


----------



## Redge78

maxx134 said:


> . He
> Calculates everthing..


 
 Yeah, easy. And the answer is 42 !


----------



## baronbeehive

coinmaster said:


> ....
> Also I'd like to hear your theory of why upgrading the potentiometer will improve the sound.


 
  
 The pots conduct the signal through them in stereo which means 2 signals. Not only must they be closely matched but the shape of the signal curve is important as well so plenty of chance for something untoward to happen. That's also why people like stepped attenuators in place of pots because of precision control.
  
 Interesting thread guys, much of it above my head unfortunately


----------



## Redge78

Quote:


coinmaster said:


> Plus I'm critically low on solder and money to buy it with


 
 This is why you bought those 8 (?) AVX 220µF ... Caps are always better, who cares about solder anyway ! 
  
  
  
  


baronbeehive said:


> The pots conduct the signal through them in stereo which means 2 signals.


 
  
 We are running Symetrical/balanced, so it's 4 channels for us
 ... or 8 channels paralleled 2by2 if you want to show off
 ... or one "2 channels"pot for Left and one for Right (motorised, so they could be synchronised !) That you be something pretty cool actually !


----------



## Mogos

The decoupling caps are on the way . All other parts also. Cause of them I have been forced to do one more modification to the chasis. I have to move the ventilators out side. Idea was simple to do the frame and just put them on the other side. But to do all cutting, sand papering, painting, threading took a lot of time. But I am quite satisfied with the effect. The proportions with the cage on the top has been improved. Moving of the ventilators I have to move the yellow led lights. Doing it I had an idea to use the led lights to light up the interior of the chasis so you can see from the close distance the "jewelery" installed inside.


----------



## SonicTrance

Nice work, very nice! I don't really care for the cage, but that's personal preference. Amazing job nonetheless!
  
 Btw, have gotten rid of the noise/hum you had? (I think it was you anyway, lol)


----------



## Mogos

redge78 said:


> This is why you bought those 8 (?) AVX 220µF ... Caps are always better, who cares about solder anyway !
> 
> 
> 
> ...


 
 Two pots with resistor ladder will be perfect solution. I thought about it also. To synchronise their turning and maintain equal switching for left and right channel shall not be a problem as they "jump" from a contact point to a contact point ( it is so on the type I have bought). I think I will do it in the stage four . There is only one problem at least with the type of switch I have. It requires some force to turn and two of them will double the problem. Kozmo or Goldpoint (goldpoint is serial resistor topology) it seams they are behaving mechanically like a normal pots.The contact arm is rather sliding and not jumping/clicking.


----------



## Mogos

The swirly-dirly is still there but not all the time. I suspect the one of the tubes is a problem. But in front of me operation on the open heart  and I will change this and that. If it will not help tube rolling will start


----------



## coinmaster

> The decoupling caps are on the way . All other parts also


 
 Just keep in mind the guide hasn't started on the resistor section yet so if you are going off of the guide just know it is not complete yet. You don't really wana implement the decoupling caps without also doing the resistors as well or else it will get really annoying later when you have to put them in.


----------



## Mogos

I know. I have decided do not change everything at once. Doing it all now will not let me judge the influence of the changes on the sonics of the amp. I have already planned to do much this time. So the stage four is almost certain and I am starting to think about stage five. I would like to minimise the times for dissasembly of the amp but on the other hand not doing it in stages I will loose the invaluable experience to hear the character of the changes. And to hear them it is needed some time for burning in of the new components and houers of different music to be listend.


----------



## Maxx134

mogos said:


> ...
> 
> 
> 
> ...



Very very nice, excellent work!

Although it seems you may need plexiglass on the see thru front grills,
So that the air does not escape out the sides,
So it can be pushed up to top of board and out holes by tube sockets...


Also, Can you post pic & link for your pot solution.


----------



## Mogos

Or maybe I shall name it hallowen .

 I would to add that the light is up when the temperature inside reach 55 C and off when cool down to 36 C.


----------



## Mogos

maxx134 said:


> Very very nice, excellent work!
> 
> Although it seems you may need plexiglass on the see thru front grills,
> So that the air does not escape out the sides,
> ...


 
 I thought that the mesh may have negative impact on the air stream up. But the idea was to have ventilators not working in winter time ambient temperatures (18 degrees for me is comfortable).During the cooler days the circulation of the air (in conjunction with the temperature gradient) is faster and gravitational. When there are cooler days (temperate at home is oscilating above 20 C) the ventilators turn on after more then one hour and in this case the open sides of the base is a must.  Also using it now I didn't noticed any problem with coolong the gear down. I havent mesure the time to reach the cool down temperature (36 C) but it seams that moving the vents out even helped to improve the efficiency. The bigger size of the vents (twice as much of the air pumped inside with lower rotation speed compared to the originals) also helps. Before the installation of the new vents and changing the chasis I have been using the temperature measuring. The temperature was oscilating around 53 C with the vents turned all the time on.


----------



## Mogos

maxx134 said:


> Also, Can you post pic & link for your pot solution.


 
 I was hesitating to post it now. It is still just and idea and I don't know if it will work at all. From the photo you should figure out what is my plan.
 Here it is

 The donor of the parts was a HP InkJet printer.


----------



## Mogos

I bought the attenuattor  here: http://www.ebay.com/itm/Balance-XLR-23-Stepped-Attenuator-Potentiometer-10K-Log-/252108559541?hash=item3ab2d754b5


----------



## Redge78

A 10K Log ? not a 100K Log like the ALPS RK168 we have ?
  
 How are you going to adapt the impedance change ?


----------



## Maxx134

The way I see it is if total impedance input to driver tube is 110K,
then controlling only 10k would need to adjust grid resistor to compensate for input resistance and so the resulting volume control would be only a small portion of the total volume...

if you do not compensate to have 110k total, and just put a 10k pot in, 
Then you would have loud blasting volume with little control and probable overload..


----------



## Mogos

Guys everything is ok. This was a link to the site with the first type of the pot I found. I do have 100 k . There are also another impedances 50, 20 250 k.


----------



## Maxx134

mogos said:


> Guys everything is ok. This was a link to the site with the first type of the pot I found. I do have 100 k . There are also another impedances 50, 20 250 k.



Can I ask for reference before I go down that upgrade path, 
Since I have not begun to look yet...
What was your desicion making process, 
On settling for this one?
Just curious as there are a whole new set of parameters we need to know/look for in terms of a volume pot...


----------



## Mogos

baronbeehive said:


> The pots conduct the signal through them in stereo which means 2 signals. Not only must they be closely matched but the shape of the signal curve is important as well so plenty of chance for something untoward to happen. That's also why people like stepped attenuators in place of pots because of precision control.


 
 Above is an explanation why I have decided to change the pot. There was a limited choice if you are looking for balanced shunt configuration ( in the price range up to 100$). I could not find anything else. Important factor was that the resistors are Vishai precision (0,1% tolerance). And thats all.


----------



## Maxx134

mogos said:


> Important factor was that the resistors are Vishai presision (0,1% tolerance). And thats all.



So how much did yours hit the wallet?

I am interested to know the size & layout of it as well..


----------



## Mogos

It costed 50$. Diameter (with resistor ring) 37 mm, length of the body 45 mm. Comparing to Goldpoint, Kozmo or DACT it was good price. 
 Guys I have a question. Are the yellow lines showing correct connection of the cap pins. There is no indication of polarity or any other graphical sign indicating it. I gues that in case of MKP or this caps there is no polarity issue.


----------



## coinmaster

So I'm going to be using an LDR (light dependant resistor) pot. It uses photoresistors which aren't really resistors but semiconductors, meaning they don't have an effect on the signal like resistors do. Pretty much like having no resistor in the signal path.
 It's expensive ($580) and complex, needing it's own transformer power supply and microchips and such for onboard software auto-calibration so the resistors are all matched and don't go out of spec over time.
 http://www.tortugaaudio.com/products/ldr3x-v2-1/
 http://www.tortugaaudio.com/whats-wrong-with-audio-volume-control/
  
 I've also 99.9% decided to strip down my amp and rebuild it from scratch using point to point construction. The increasing amount of massive industrial capacitors that are going into my amp has made it a  flimsy mess and ridiculously hard to put and keep together. Add LDR control circuits and another transformer onto that and it's getting way out of hand. The original design was just not meant for all of these add ons.
 If I rebuild I can put it all in a nice custom chassis.


----------



## Mogos

I think I have found an answer to my question 
	

	
	
		
		

		
			





. But could you guys just confirmed if the connection way of the pins is correct. Please.


----------



## coinmaster

You have it right.


----------



## Redge78

mogos said:


> I think I have found an answer to my question
> 
> 
> 
> ...


 
  
 The best way to be sure would be to use an Ohmeter and find which pairs of leads have a zero ohm impedance.
 And no polarity issue, you're correct.


----------



## Mogos

Thank you Coinmaster. For volume control I shall expect from you that you will seek for an uncompromising solution. I thought it might be one of the DACT resistors. But you suprised again. Very interesting approach to the means of controling the volume.


----------



## Mogos

Ok I can measure it. And if the pair will have a zero ohm impedance what that will mean?


----------



## coinmaster

It means there is no connection to the other end of the capacitor making it the right side to tie up. Kind of like a continuity test.


----------



## Mogos

I think I have got it. Zero or very close to will mean that they are connected.


----------



## coinmaster

Zero should mean they *aren't* connected. As in there is no connection to give a resistance reading.


----------



## Maxx134

mogos said:


> Ok I can measure it. And if the pair will have a zero ohm impedance what that will mean?



Zero ohm equals same side and can connect together...

Same as on mine, they are on same side..

From internal construcruon, this should be true if all of them...




coinmaster said:


> ... mean they *aren't* connected.


 you are talkn about infinity ohm which is opposite of zero ohm..
Or you are talking in reference to the other side...
But we refering to the "measured" pins..


----------



## Mogos

Thank you for all hints. I find out that the continuity test is the best 
	

	
	
		
		

		
			





. I have also measured the capacity. Between oposite ends is the one the capacitor should have.


----------



## Maxx134

OMG guys,..


 Redge78 experimantal mod WORKED!!!

OMG guys your not gona believe the improvement!!!...
Imagine your HD800 shaking from impact power,
 with ability to cause eardrum injury level without distortion!!!

My unit has been the recipient of much abuse,
in form of testing & repair, in past...

I have worked all sunday & straight into night till 3:30am going over it and testing, with what I *thought* was a preliminary failure...


But NO!
 I have to say, 
This time it was definitely worth it!

We have noticable sonic gains!



So now...

I must colaborate more with Redge78, on specific values for added components...

So ...
Please be patient....

Info will be compiled and presented soon


----------



## coinmaster

Yaaaaaaay!!!!!! More money for me to spend.
  
 Must be a pretty significant sonic gain it if includes


----------



## Maxx134

Lol!

I forgot this!

IT'S.......

AAALLLLIIIEEEEEEVVHH


Muuuuuuuaaaaaaahahahahahahahahahaaaaaaaaaaaawwwwww

(Suck air)
Wew!
Ahh the smell of melting solder smoke all over your face for hours, has that effect!


----------



## coinmaster

I bet this is going to involve me buying more industrial caps. Like I don't have enough already.


----------



## Maxx134

Ummmm....
No...


----------



## Maxx134

Because of installation location, it would be wise to note now that latest mod will be along, and under the decouling cap area, or by the power tubes, 
So my recomendation is to wait for that info before continuing, 
Or else be like me, and end up having to face the job of tearing down or moving the decoupling caps out of the way...


----------



## SonicTrance

This is good news. I'll wait for the info of this mod for sure


----------



## Maxx134

Update:
New mod values/types specifics should be realized over weekend if not sooner.
This was Redge78 idea and currently gathering info on both theory and optimal solution for implementation..

Second update:
Updated first page to note to do BOTh the bypass caps AnD the thin wire replacment at same time, 
So you only have to pull out the board ONCE..


----------



## Maxx134

Third update:
I am currently in PMs to gather more data for implementation to the MK6...

As you know, both me and Redge78 have an MK8,
So modifications of the new mod are necessary,
 to implement for the MK6 and so have it for both models..


----------



## coinmaster

Look guys it's my MKVI+!! 
	

	
	
		
		

		
		
	


	




 
  

 New and improved.


----------



## Maxx134

Hmmm you are too ambitious...
The actual mods balance a safe approach...
Cardboard box upgrade?
Save those parts!


----------



## Maxx134

Ok more news,
From my listening trials,
This "new" cap to upgrade is more important in quality over size, 
Which Redge78 is currently finalizing..

So we are talking about, and very similar to coupling cap quality...

What I can also say,
For those that have an MK8, the clarity increase actually allows you to easily differentiate between the power tubes..

In case no one realizes, there IS NO tube swap available for MK8 power tubes, 
Except for only three made types,
In which only the DR supertube was said to be best....

I have two, the EH gold pin, and the elusive Russian "DR" Supertubes...

Now with the mod in place, 
there is NO LONGER any clear superiority of the DR tubes...
Instead a more clear differentiation of their positive traits...
They are more like just a tube swap, with preference being the *choice*, not superiority..

*So it is now clear that the DR superiority was its ability to perform superior, under "non" optimal conditions...
Now that this new cap upgrade is in place, the performance of the powertube circuity is elevated to let the tubes perform more optimally, removing the DR's advantage....*
Edit: this observation is specific to parameters of this amp's circuit.




The MK6, having a larger tube with 8pins, does have different WCF grid resistor locations,
 that may or may not need upgrading(depends if you have blue resistors)...
But the cap upgrade is the same.
You WILL hear 
BOTH :
a more holographic clear performance

and a more tube characteristic performance

Edit:
Also, as mentioned in beginning,
 the cap upgrade itself will also introduce its sonic trait/influence on the performance as well, 
So my suggestion of sound quality over size is in order.


----------



## coinmaster

Time to order more Duelunds LOL. No actually I'm not that patient, with the mods I'm planning to do for my amp I'll be out of money until next year already lol. Don't wana spend another $900 on another quad of duelunds.
 Jensens perhaps.
 Wish there was an easy way to test the sonic qualities of my industrial caps, since their "technical" specs like esr/esl/irms seem to surpass every other cap in existence that I have ever seen. Not sure what makes a "good" sounding cap.


----------



## Mogos

maxx134 said:


> *.........................*.
> 
> I was going to place these .33uf Rifa,
> on other side of board, like member "coinmaster":
> ...


 
 Maxx what was the gauge of the thin wire. If I have undersood you correctly you have replaced it with two wires (twisted). Will it not borne any side effects - raise in wire capacitance or something else.


----------



## SonicTrance

maxx134 said:


> Ok more news,
> From my listening trials,
> This "new" cap to upgrade is more important in quality over size,
> Which Redge78 is currently finalizing..
> ...




You can use 6SN7's as powers with a 6CG7 to 6SN7 adapter. So there are other options


----------



## Maxx134

mogos said:


> maxx134 said:
> 
> 
> > *.........................*.
> ...



The stock wire was shockingly thin..
Thinner than the wires used evrerywhere else..
They were the thinnest wire!

I recommend some good quality OCCcopper, 20-22ga min.
In the begining Ridge posts covers wire guage, althoughbit deals with the wire type that goes along side the amp, not the board wires ,
Which are short and thin..

I was quite shocked just how thin are these wire,
But the length isnshor anyways, maybe 8in...

So you need four runs of wire to come off each tube, 
To the rear sockets...

I doubles my wiring because I am a bit onbessive, 
And twisting them is the common procedure for running wires with least interference...

But a good single 20guage run is what would work perfect...


----------



## Maxx134

sonictrance said:


> maxx134 said:
> 
> 
> > Ok more news,
> ...



Really?!
Are you sure?
I have the MK8 not 6.
Hmm interesting...
I will look into it..


----------



## SonicTrance

maxx134 said:


> Really?!
> Are you sure?
> I have the MK8 not 6.
> Hmm interesting...
> I will look into it..




I know you have mk8, lol
I had a mkivse that also uses 6H30Pi power tubes. I used 6sn7's in my mk4 with very good results. But in the end I used 6AS7G's with external heater psu. That took the little amp to another level


----------



## Maxx134

Dam just when I was over the hill with upgrading.


----------



## SonicTrance

Haha. And there's a LOT of different sounding 6sn7's out there. You could even use the Mullard ECC32 as powers with same adapter. They draw same amount of heater current as 6h30pi, 0,9A.


----------



## Redge78

sonictrance said:


> I know you have mk8, lol
> I had a mkivse that also uses 6H30Pi power tubes. I used 6sn7's in my mk4 with very good results. But in the end I used 6AS7G's with external heater psu. That took the little amp to another level


 
  
 You know you just created a monster !
  
 Now you'll have to tell us everything about that !
  
 How you moved from noval to octal tubes ?
 How did you adjust the electrical constants, if so ? If not, why not ?
  
 Welcome !


----------



## SonicTrance

redge78 said:


> You know you just created a monster !
> 
> Now you'll have to tell us everything about that !
> 
> ...




No electrical adjustments. Just a simple pin adapter and the tubes are plug n play. Before a did anything though, I read about 600 pages of the LD tube rolling thread


----------



## Redge78

sonictrance said:


> No electrical adjustments. Just a simple pin adapter and the tubes are plug n play. Before a did anything though, I read about 600 pages of the LD tube rolling thread


 
 How detumefying !  I have had a brief look at the datasheets and I was wondering how you managed the tenfold rise of the plate resistance ... 
  
  
  
 There is not one tube in the world _(that I know of)_ that is "plug'n'play" with the 6H30 ! Not one. Nada. Que dalle.
  
 ... which doesn't mean that your swap didn't work wonders. But most probably you were pushing your tubes outside their nominal specs, with an undefined impact on their life expectancy.
 Which may or may not be trivial, depending on how much you paid them, I suppose.


----------



## coinmaster

Hey look! More of these!
  
  

  
 That makes SIXTEEN giant capacitors 
	

	
	
		
		

		
		
	


	




 Now you are beginning to see why I'm rebuilding my amp from scratch with point to point construction. Even with my giant wooden box it still wasn't enough.
 Take that along with the LDR control system I'm replacing my pot with and the capacitors I will be using for his "new" mod it's going to be big. Very big.
 So big in fact that I decided I'm going to see if I can make MKVI+ monoblocks instead of 1 giant amp.


----------



## Maxx134

Well then Coin,
Get ready to *BUY MORE*!
LOL

Because...

*NEW UPDATE MOD HAS BEEN POSTED!!!

Will also be refined soon..*


----------



## coinmaster

Gunna get some Jupiter copper foil pio caps for that. I'd rather have Duelunds but money is an issue right now. 
 The overall cost of my particular modifications are going to be about $4,000-$5000.


----------



## Maxx134

I have noticed a more noticable sonic change in tube swapping of the driver tubes...

The means that the clarity has increased due to the latest mod.

Before this new mod,
The amp was more sweeter and forgiving before the change of coupling cap,
from the Mundorf to the jupiters.

The jupiters made sound very natural and not sweet, but more neutral and deep..

As I have noted to Redge78, the sonic traits of sweetness came back when I put the Mundorf in the new WCF Coupln Cap locations...

SO the sweetness of trebles came back, 
But not the forgiveness..
This tells me it was the garbage red cap holding it back..

The increase in clarity makes it much more realistic and spooky, depending on your tubes..
Changing tubes have greater influence, so time for tube re-evaluation...



The next test I will perform, will be swapping out my Mundorf caps with a different type to verify further the sonic infuences, specifically in treble area...


----------



## Bazile

A couple of questions, although I'm afraid I know the answer to the first one.
 Are these mods a rank amateur could do? I have a soldering iron, and built a Heathkit TV with my dad as a kid, but expert, I am not. (note...almost 50 yrs ago...sigh)
 Secondly, are the mods basically listed in the order they should be done, or in order of importance?
 I have a Little Dot MK6, not a plus. It sounds wonderful with a Schitt GMB Dac and stock tubes though a pre fazor LCD 2.2, but you always want more.
 With no modding skills what so ever should I just move to tube swapping, or a MJ2 and tube swapping?  A great thread, and thank you in advance for the help.


----------



## coinmaster

You don't need to be an expert, just need patience.
 Order of important = coupling cap, cathode bypass, new cathode follower mod, decoupling, resistors.


----------



## Bazile

Thank you.
 So there is no order they have to be done in?


----------



## Maxx134

bazile said:


> A couple of questions, although I'm afraid I know the answer to the first one.
> Are these mods a rank amateur could do? I have a soldering iron, and built a Heathkit TV with my dad as a kid, but expert, I am not. (note...almost 50 yrs ago...sigh)
> Secondly, are the mods basically listed in the order they should be done, or in order of importance?
> I have a Little Dot MK6, not a plus. It sounds wonderful with a Schitt GMB Dac and stock tubes though a pre fazor LCD 2.2, but you always want more.
> With no modding skills what so ever should I just move to tube swapping, or a MJ2 and tube swapping?  A great thread, and thank you in advance for the help.



It WAS in order of importance untill today with latest mod...

I would consider the three caps as the "trifecta" for sonic signature:
1-Coupling
2-Cathode bypass
3-What coupling


And the large Decoupling caps for:
impact/definition/dynamics and speed...

Bypass caps for sparkle/air/edge/+speed

PSU last stage caps for weight/authority/power in low end.

The wiring and grid resistors are for clarity as well.


There is even another grid resistor mod we havent mentioned, but already implemented,
 involving the grid resitor right after the WCF "new cap" mods..

We felt we need to only mention and emphasize the most important mods first,
Which are the caps...


I would say the mods are at least an intermediate level, 
Not a beginner level.
Each change are recommended to be done in stages, 
in order to solve problems along the way... Like mistakes or brittle wires breaking off with board removal...

For you, I would see great accomplishment by TAKING IT SLOW, 

And also studying the board and clicking every link, schematic Refge78 offers...

It's there FOR A REASON.
We want people to have an UNDERSTANDING of the project involved..

Yes, this must be considered a DIY project amp in this thread..

So beginners not recommended, 
BUT LEARN in first page posta, and you will succeed!

You can always find someone competent to do the job if you are not inclined...

For me I had to be both a surgeon and a jewler 

So only you can answer that question of, "can I do it"..


----------



## Maxx134

coinmaster said:


> You don't need to be an expert, just need patience.
> Order of important = coupling cap, cathode bypass, new cathode follower mod, decoupling, resistors.



Correct! 
Now I can goto sleep & you can take over!


----------



## SonicTrance

redge78 said:


> How detumefying !  I have had a brief look at the datasheets and I was wondering how you managed the tenfold rise of the plate resistance ...
> 
> 
> 
> ...



Most tube rollers run tubes out of spec all the time. I have not once run my mk6 with driver tubes It's designed for. I even bought my amp without tubes. 

Dont overthink this now, just try it and listen. You might like what you hear


----------



## Maxx134

sonictrance said:


> Most tube rollers run tubes out of spec all the time. I have not once run my mk6 with driver tubes It's designed for. I even bought my amp without tubes...



I understand this,
as operating outside the linear parmeters of a given tube, to get another result, 
which is a heavier signature of the tube, that some people prefer.
Edit: Yes some can be very sweet.

Rather than go for a certain tube sound, higher end tube amps go for transparency,
 which is what we now have in spades..


----------



## Redge78

sonictrance said:


> Most tube rollers run tubes out of spec all the time. I have not once run my mk6 with driver tubes It's designed for. I even bought my amp without tubes.
> 
> Dont overthink this now, just try it and listen. You might like what you hear


 
 Understanding the mods is 50% of the fun _(and 90% of my time ...)_, with a 25% when the experiments are successful, and a 25% in sharing things with nice people.
 Overthinking things is kind of a second nature, I guess.
  
 It's not the first time I hear this "6H30 vs 6SN7" comparaison, with 6SN7 being more appreciated. That's real, no doubts in that. But in what context ?
 There is so much difference between an "original" amp and a "fully modded" amp that the results of tube rolling done with an "original" may very much be different with a "fully modded".
  
 Maxx has experimented that with his (plain)" 6H30-EH" vs (precious)"6H30-DR". The differences between those 2 varie a lot depending on how "refined" your amp is.
  
  
_And I always keep in mind that Audio Research and Ayon put 6H30 in their (top of the line) output stages. That's for a reason, for sure. Those guys aren't slouch. _


----------



## SonicTrance

redge78 said:


> Understanding the mods is 50% of the fun _(and 90% of my time ...)_, with a 25% when the experiments are successful, and a 25% in sharing things with nice people.
> Overthinking things is kind of a second nature, I guess.
> 
> It's not the first time I hear this "6H30 vs 6SN7" comparaison, with 6SN7 being more appreciated. That's real, no doubts in that. But in what context ?
> ...




I'm sure you are right that a modded amp reacts differently to tube rolling. I have only made the coupling cap and power resistor mod as of yet, and tube rolling is still very noticeable. I hope the coming mods doesn't take away the magic sound of my present tubes 

Btw, that ECC32/33/35 comparison I made in the other thread, the ECC32 came out on top. And thats the tube furthest away from original spec


----------



## Redge78

bazile said:


> Thank you.
> So there is no order they have to be done in?


 
 Hi Bazile,
  
 Assuming you want to do all four main mods, there are several orders you can consider.
 Below are general guidelines, they may vary if you choose to remove the board or not, if you build an extra-case or not, ... 
  
 Practicality / Ease/order of modding :  Cathode bypass > "WCF" Coupling > Decoupling = "Main" Coupling
 Cost :                                               Cathode bypass >>>  "WCF" Coupling = Decoupling = "Main" Coupling
 Sonic gain :                                      "Main" Coupling > Decoupling > "WCF" Coupling = Cathode bypass  _(but not really sure here)_
  
_Anyway, whatever choice you make, you can come here and we will guide you the best we can._


----------



## Maxx134

sonictrance said:


> I hope the coming mods doesn't take away the magic sound of my present tubes



Magic??...

Don't remember any magic???...

I only observed the amp being possessed...
*Alive*!


----------



## Redge78

sonictrance said:


> I hope the coming mods doesn't take away the magic sound of my present tubes


 
 If I believe the testimonies of mister M****23, you're in for re-assessing what "magic" is ... several times.


----------



## SonicTrance

redge78 said:


> If I believe the testimonies of mister M****23, you're in for re-assessing what "magic" is ... several times.




Don't know who that is but I'm sure you are right. I wouldn't plan mods and buy parts like I do if I didn't believe that


----------



## coinmaster

Mister-X, There are no words for how much of a piece of crap the stock amp is compared to after the upgrades, It's not even in the same ballpark. The changes in sound quality aren't going to be subtle.
 If magic is what you want, then the stock mk6/8 is like getting a high quality magic set from the toy store 
	

	
	
		
		

		
		
	


	




.
 The mods turn it into Houdini. 
 Unfortunately I won't be able to listen to mine again for months due to my ......advanced upgrade plans.
  
 I can't imagine what it can possibly sound like if I improve on the sound even more. But I'm getting rid of the resistors in the pot, replacing cathode bypass cap with mkp, and now there's this new WCF mod that is supposed to be nearly on par with coupling upgrade???
	

	
	
		
		

		
		
	


	




 I can't even imagine how there is enough ROOM for another coupling cap level improvement in the sound.


----------



## Maxx134

sonictrance said:


> redge78 said:
> 
> 
> > If I believe the testimonies of mister M****23, you're in for re-assessing what "magic" is ... several times.
> ...





That's probably me as I have made sure to verify sonic observations, 
In case any trolls come in from "DIY" comunities, or "Sound science" thread guys to try question these upgrade...

*ALL MAIN MODS HAVE BEEN SONICALLY VERIFIED...*
And of course *EXPLAINED IN FIRST POST!* ..

I should have my amp available for listening at the next NY headfi meet..(!)

So the "proof is in the pudding" for any future "doubters" that want to hear! Lol

They would have to supply 
a stock MK8 for comparison...


----------



## SonicTrance

coinmaster said:


> Mister-X, There are no words for how much of a piece of crap the stock amp is compared to after the upgrades, It's not even in the same ballpark. The changes in sound quality aren't going to be subtle.
> If magic is what you want, then the stock mk6/8 is like getting a high quality magic set from the toy store  .
> The mods turn it into Houdini...




Lol, yes I understand that. I was talking about the tubes. Rolling tubes to get ultimate/different sound signature is a huge part of having a tube amp for me. It would be boring without tuberolling. That's one of the reasons I chose the mk6, as it can handle lots of different tubes


----------



## Maxx134

Actually, tube rolling experience will be "*edit*"(made more noticable), 
As I made note (in a past PM) on a sonic occurance (more holography on piano keys), that I was able to pinpoint source being my driver tubes...

This was result of lastest mod implemented...


----------



## SonicTrance

maxx134 said:


> Actually, tube rolling experience will be "*edit*"(made more noticable),
> As I made note (in a past PM) on a sonic occurance (more holography on piano keys), that I was able to pinpoint source being my driver tubes...
> 
> This was result of lastest mod implemented...


 
 Now that's more like it


----------



## Redge78

sonictrance said:


> Lol, yes I understand that. I was talking about the tubes. Rolling tubes to get ultimate/different sound signature is a huge part of having a tube amp for me. It would be boring without tuberolling. That's one of the reasons I chose the mk6, as it can handle lots of different tubes


 
 You'll see that "Cap rolling" can be lots of fun too.
  
 And there is MUCH more caps than there is tubes in our amps ... and you can bypass all those caps with other caps .... several times !


----------



## SonicTrance

redge78 said:


> You'll see that "Cap rolling" can be lots of fun too.
> 
> And there is MUCH more caps than there is tubes in our amps ... and you can bypass all those caps with other caps .... several times !


 
 I have no doubts about that. But my plan is to finish building the "compact" mod and be done with it. There's no room for several bypass caps


----------



## baronbeehive

sonictrance said:


> I have no doubts about that. But my plan is to finish building the "compact" mod and be done with it. There's no room for several bypass caps


 
  
 Spoilsport.... I'm building a house extension to accomadate my mods........seriously I agree with you, I don't want anything too unwieldy. This thread has come at just the right time. I've already bought the Mundorf silver in oil caps so the sound should be slightly different to the guys on the LD thread that have the SG in oil. But I can now look into the other 2 caps mods talked about by Maxx123 at the same time. I doubt if I can do it myself though, I just don't trust myself not to touch undischarged caps, ideally I would like to be here to hear the results.
  
 The only problem is my Miniwatt speaker amp which ATM is slightly better than the standard LD. I've looked into the possibility of modding this but its too small for mods so it looks like it could get left behind when my MKVI comes back.


----------



## SonicTrance

baronbeehive said:


> Spoilsport.... I'm building a house extension to accomadate my mods........seriously I agree with you, I don't want anything too unwieldy. This thread has come at just the right time. I've already bought the Mundorf silver in oil caps so the sound should be slightly different to the guys on the LD thread that have the SG in oil. But I can now look into the other 2 caps mods talked about by Maxx123 at the same time. I doubt if I can do it myself though, I just don't trust myself not to touch undischarged caps, ideally I would like to be here to hear the results.
> 
> The only problem is my Miniwatt speaker amp which ATM is slightly better than the standard LD. I've looked into the possibility of modding this but its too small for mods so it looks like it could get left behind when my MKVI comes back.


 
 I wonder how big a difference it is between the Mundorf S/O and S/G/O. I have the S/G/O's and like them very much, don't have anything to compare to though except the stock garbage caps... 
  
 Just take the precautions stated on first page and use a multimeter. No shame in letting someone else do the job though. It'll sound the same nonetheless


----------



## Maxx134

Quote:
*I wonder how big a difference it is between the Mundorf S/O and S/G/O. *

Check the cap review links first page.


----------



## Redge78

sonictrance said:


> I wonder how big a difference it is between the Mundorf S/O and S/G/O. I have the S/G/O's and like them very much, don't have anything to compare to though except the stock garbage caps...
> 
> Just take the precautions stated on first page and use a multimeter. No shame in letting someone else do the job though. It'll sound the same nonetheless


 
 For Mundorf S/O vs S/G/O, you can see there :
http://www.humblehomemadehifi.com/Cap2.html
  
 Reading between the lines, both are really good caps, with S/G/O having a accentuated treble, giving more (real?) air and detail.
 Maxx loved that (until he heard the Jup's), I'm not that fond of treble so I recon I should be more a S/O kind of guy.


----------



## Maxx134

Quote, MisterX:
*...No shame in letting someone else do the job though...*

I have been asked about this question of a member not feeling confident to do the mods...

I have proposed one possible solution..

Post a "electronics or amplifier job" in your local college..
There are many "starving students" in electronics field who would take on this job, quite enthusiastically, for a nominal fee, and can also use it for their own benifits for project requirements in college.

You wont get ripped off going to some "Joe Shmo" tube repair shop where the guy will take forever and complain it goes against his training..

College Students are a ripe source for young, sharp, enthusiastic minds open to new things...

Just make sure you can trust the person to be responsible to carry it out...


----------



## SonicTrance

maxx134 said:


> Quote:
> *...No shame in letting someone else do the job though...*
> 
> I have been asked about this question of a member not feeling confident to do the mods...
> ...


 
 That's some good advice! I'm doing it myself though, as I enjoy tinkering and learning new things


----------



## Maxx134

redge78 said:


> sonictrance said:
> 
> 
> > I wonder how big a difference it is between the Mundorf S/O and S/G/O. I have the S/G/O's and like them very much, don't have anything to compare to though except the stock garbage caps...
> ...




Exactly...
I have found that the MK8 is so revieling that the treble needs to be in high order, so my recommended choice are the more neutral natural Jupiters for the MK8...

Yet I believe the MK6 should be great with many caps...
 The mundorf I found to be sweet in trebles...

Actually I am thinking that it is VERY important the *everyone* NEEDs to check out the cap link that Redge78 posted to "match" the signature of thier amp, to their own liking...


----------



## baronbeehive

maxx134 said:


> Quote, MisterX:
> *...No shame in letting someone else do the job though...*
> 
> I have been asked about this question of a member not feeling confident to do the mods...
> ...


 
 Thanks for all the encouraging comments guys. Maxx134 that's a great idea, in fact the electronics person I use has had close links with the local technical college so he might be a source of information.
  
 Regarding the S/Oil caps I hate any harshness in amplification, and ATM I don't have any so wouldn't want to introduce it with the SG/Oil caps whereas I believe the silver caps are completely forgiving and fluid, and many regard them as superior, certainly taking account of price. As I do most of my listening through speakers I'm only interested in getting maximum value for money with the LD, but I'll be following this thread with interest. I'm fortunate in that I can play music as loud as I like in the middle of the night and nobody would hear a thing, but that may change with an impending house move.


----------



## coinmaster

> As I do most of my listening through speakers I'm only interested in getting maximum value for money with the LD


 
 This baby is going to make one helluva preamp for my future speaker system 
	

	
	
		
		

		
		
	


	



  
 I've destroyed my amp for the cause mapping out a schematic.
 I'm still correcting errors here and there but it is mostly complete.
  
 Even though my technical understanding of electronics is limited I still learned many things about how the amp functions.
 I also isolated some more potential areas of upgrading that I will have to refer to Maxx and Redge about.
  
  
 After what must be 4-5 days of non stop analysis I almost have my plans figured out for my monoblock MK6 design. Little Dot monoblocks baby!


----------



## Maxx134

Just a note,
we never told/condoned/suggested in any way what "coinmaster" is doing...
He has his own vision of what he wants to do, and how he sees his amp.
That is fine, but not necessary for these mods...


----------



## baronbeehive

coinmaster said:


> ......
> After what must be 4-5 days of non stop analysis I almost have my plans figured out for my monoblock MK6 design. Little Dot monoblocks baby!


 
  
 What is the advantage in monoblocks compared to existing LD design?


----------



## coinmaster

baronbeehive said:


> What is the advantage in monoblocks compared to existing LD design?


 
 Each channel has a separated power supply and circuits.
 Meaning complete channel separation and no crosstalk.


----------



## Maxx134

All possible parasitics, are eliminated with this set of caps per tube circled in red:

The green, circled for the opamp stage,
 will be a future point of interest to look into, but the chip & circuit itself is perfectly fine and impressive for what is does(DC offset control).


Also of note, is that I intentionally sat on practically every table on last headfi meet a few months ago, 
To guage the level of performance achieved...

There were quite a few excellent tables, actually practically all end game quality,
 and with a few of exceptional wow factor..

So what I want to make note, 
Is that I can now say,
that I am finally satisfied with the level of performance achieved here, 
in comparison to what I heard in past...

Except for Stax..


Which is "maybe" the only point of interest,
 I could look at to be interested past this position, with exception of more headphones!

As for now, I am able to tune this amp to my liking, with the "Quaffecta of caps"
To change...

First page updated today, but will be updated again tomorrow!
It never ends..


----------



## coinmaster

> All parasitics such as the type you speak of, are eliminated with this set of caps per tube circled in red


 
 Are you implying those caps negate the benefits of going monoblock?


----------



## Maxx134

I adjusted my comment due to the complexity of the answer necessitated by the broad question you asked ..

Edit: 
Google parasitics in audio...
They can come from components themselves, not just board design layout..


----------



## coinmaster

> Just a note,
> we never told/condoned/suggested in any way what "coinmaster" is doing...
> He has his own vision of what he wants to do, and how he sees his amp.
> That is fine, but not necessary for these mods...


 
 I don't condone it either 
	

	
	
		
		

		
		
	


	



 This is end game, never have to worry about it again, perfectionist stuff I'm doing.


----------



## Maxx134

I edited my previous post, and first page updated again..


----------



## Mogos

redge78 said:


>


 
 Mundorf Lytics have very confusing marking of the poles. In - In+ Out - Out +.
  
 Is this photo showing correct way of the caps preparation before installation?


----------



## Redge78

mogos said:


> Mundorf Lytics have very confusing marking of the poles. In - In+ Out - Out +.
> 
> Is this photo showing correct way of the caps preparation before installation?


 
 Yes, that's the correct way, you solder the 2 (+) together and the 2 (-) together.


----------



## Maxx134

As you can see in this pic:

The positives are joined together, for one pos...
 and then the two negatives are joined together for one neg..

Circuit is performing as intended with no problems.(actually, rather spectacular & impressive). 
The "input-output" designations, are for optional usage in other type circuits which have differently designed power supplys.
Check datasheet for more info.


----------



## Maxx134

From my current observations so far,
THESE TWO caps pictured:

These two caps(coupling &WCF coupling) are *MOST* responsible for sonic signature of amp...
Other two caps, not pictured(Cathode & DeCoup) actually help on noticable gains of sonics, 
BUT 
These two most intimately carve out the signature of this amp, whether it be:
1- sweet(mundorf)
2- natural (jupiter) 
3- dark (Cardas, unverfied) 
4- soft (stock cap, vitamin Q, unverified) 
...or varying degrees...

Also remember caps not just affect tonality,
But depth and staging as well..
So *very* important is your choice of capacitors in these locations...
I suggest google links on cap sound, like posted first page...
Another good tip from Redge78,
Is that you can "shape" the sound by adding a "bypass" (in parallel) to these two caps...
Thus adjusting sound...


----------



## Maxx134

Resistor & driver tubes to be covered soon..

The resistors are less of an improvement in overall picture..

Yet, they are still an important choice for finding the best ones,
 because we need different types in key areas for optimal use, 
Or else the potential of increased refinement & reliability are wasted...

Also,
Tube roll has been generally covered in various other threads for LittleDot...

Too many choices for MK6, and too few for MK8...
But since we are gunning for "super mod" status,
I personally will only be suggesting the best tubes I have heard...
There is a sea of mediocre tubes out there.
And also many expensive and famous named tubes, which are continually climbing in price, that are truley overrated in my book.

Unfortunately there are so many factors involved I dont want to open that "pandoras box" , 
But the good news is that once moded, the amp's transparency makes tube rolling a bigger experience..


----------



## Maxx134

Resistor & fuse section updated on first page.
Pics to follow..


----------



## SonicTrance

That resistor does not look to be in good shape. And it looks like someone has taken a bite out of that cap on the left, lol.


----------



## john57

sonictrance said:


> That resistor does not look to be in good shape. And it looks like someone has taken a bite out of that cap on the left, lol.


 
 That cap on the left look like it was a solder iron hit but otherwise it looks okay.


----------



## SonicTrance

john57 said:


> That cap on the left look like it was a solder iron hit but otherwise it looks okay.




Are you going to mod your mk6 John?


----------



## Maxx134

This is what I would like to do with all the stock caps...



As you can see, the soldering iron cannot hurt the cap's thick hard exterior, 
But my side cutters can..


----------



## Maxx134

sonictrance said:


> That resistor does not look to be in good shape...



That was an MK6 pic from the old thread...
The later Stock blue resistors are probably not their rated value in watts.


*This is what happens when you do not want to do our "Super-Mods*"...

Pics of either blue type Resistors,
Or power supply resistors,
 in various early stages of failure or premature wear,
In both MK6 & MK8:



and:



And :


And:


----------



## Maxx134

First page is updated yet again with pic locations for grid resistors,
Except for these burning power resistors,
Which is easy to find.

Anyways we will have that pic up later..


----------



## Bazile

Maxx;
  
 Could you confirm that the MK-VI pictures in post #6 and #12 are showing the botton of the circuit board?  I've had preliminary talks with my local machine shop to make my MK-6 about 2 inches taller to make placing the parts easier. Thank You.


----------



## Maxx134

If you are going with caps the size of Redge78, I would go for at about 3 inches..
The pics are of center of board where his large caps are...

I too am considering extending bottom in future, if needed..

Edit ,
To answer your question differently,
Yes they showing the unit upside down so it is the "bottom" , which needs to be extendid..


----------



## Redge78

maxx134 said:


> If you are going with caps the size of Redge78, I would go for at about 3 inches..
> The pics are of center of board where his large caps are...
> 
> I too am considering extending bottom in future, if needed..


 
 Hi there,
  
 actually, I have a 6 inches (15cm) extra-box and it's starting to be crowded.
 This is not just how much more you can put in the extra-box, but also how you screw/unscrew or plug/unplug things when you need to work on the amp.
  
 And ventilation needs to be taken into account too, more space needed.


----------



## Mogos

redge78 said:


> ......
> 
> *5.2 - Grid/"Driver stage" resistors*
> 
> ...


 
 I want to make my self sure if I had understood the description correctly (for MK 6):
  
 Red = grid resistors
  
4 X 10k ohm ("Grid stopper" resistors)
2 X 1.5k ohm ("Common" Cathode esistors)

 Yellow = WCF grid resistors
  
4 X 300 ohm

 Purple = driver stage resistors (anode/Cathode)
  
4X 220K Ohm


----------



## SonicTrance

mogos said:


> I want to make my self sure if I had understood the description correctly (for MK 6):
> 
> Red = grid resistors
> 
> ...


 
 Those are correct values!


----------



## Mogos

Thank you for prompt answer


----------



## Maxx134

Tip:

I like to work in stages ,
So I know which area to focus on for any issue.

Once you know your amp more intimately, you will be able to diagnose more symptoms, and have a greater appreciation of the design,
Which is what this thread is all about..

You will end up with an amplifier more greatly tuned and personalized for "big league" performance.

There is no amp out there you can buy stock, 
That will have this much attention on the inside, once moded.

No manufacturer could possibly sell such a "hot-rodded" system without charging in the thousands easily...


----------



## SonicTrance

mogos said:


> Thank you for prompt answer




Also, don't forget the eight 5w 330ohm power resistors. There's four on each side of the board.


----------



## Mogos

I remember. I have already 10 pcs. Mills MRA12


----------



## SonicTrance

Nice


----------



## Maxx134

sonictrance said:


> mogos said:
> 
> 
> > Thank you for prompt answer
> ...





Yes sorry to overlook that early mod.

I must recommend a "wirewound" over ANY other type for that specific position in 
powertube section.

Even the designer Sword-yang initially used them before the cost cutting.

I also used to have the "Vishay" brand version in black.
They were slightly larger, and of older materials such as steatite instead of alumina, and didnt have the "Aryton-Perry" type winding which would have made them non-inductive.

So I replaced them with the Mills wirewounds which are more modern, compact and non-inductive type.

They are the only ones I would currently recommend in that position.

Remember that other type resistors such as carbon or film types in this position are subject to to effects of heat from power applied to that location.
Effects vary with resistor.
Power handling derating effects of heat and on sound....


Notice how the driver stage we choose another type, audio grade resistor.
Less power here, yet even more important.

In engineering world (pen&paper), a resistor is the simplist passive component.
In the real world, actual material, type & placement matter, as theres no such thing as "resistance alone" without other factors involved.

This is where you begin to "appreciate" the issues a designer faces over an engineer...
Making a reality out of paper design is not easy.


----------



## SonicTrance

Just an FYI for anyone thats doing the compact version of this mod and wants to put all Rifa bypass caps on top side of board. 
The .33uf rifas are slightly taller than the PCB-standoffs, so you need to use washers under each standoff for them to fit. Also, there cant be anything between the rifas, pcb and case. They need to sit flush. 
The pot goes in without issues even with washers in place.


----------



## coinmaster

> The .33uf rifas are slightly taller than the PCB-standoffs


 
 True but this wasn't an issue for me, as long as you avoid the soldering points sticking up from the board, the tiny amount of extra space they have won't be noticeable when you put the amp back together.


----------



## SonicTrance

coinmaster said:


> True but this wasn't an issue for me, as long as you avoid the soldering points sticking up from the board, the tiny amount of extra space they have won't be noticeable when you put the amp back together.


 
 Well, if you overtighten the screws without washers in place you'd most likely bend the pcb, which isn't good.


----------



## coinmaster

Hmm, making the screws dead tight isn't that important, I just screw it in until it meets resistance and I stop. As long as it is attached to the chassis it's fine.


----------



## SonicTrance

Yes, I was just writing an FYI so people don't warp their boards without noticing.


----------



## Mogos

redge78 said:


> *The new mods*
> 
> because we always think of new ways to torture the amp
> because you guys help us
> ...


 
*0,68 µF will also be ok. I am planing to switch the positions of the WCF coupling cap (not yet selected) and Coupling Cap (Jupiter). *


----------



## Maxx134

sonictrance said:


> Just an FYI for anyone thats doing the compact version of this mod and wants to put all Rifa bypass caps on top side of board.
> The .33uf rifas are *slightly taller* than the PCB-standoffs, so you need to use washers under each standoff for them to fit. Also, there cant be anything between the rifas, pcb and case. They need to sit flush.
> The pot goes in without issues even with washers in place.




*This is correct..*
I would take MisterX recommendation.
I did not have this issue, 
Because I did not install my .33Rifa there..
As the MK8 board wiring is in that area, 
Which I considered optimal for keeping the signal wires away from the heater wiring...

Also of note is that since purpose of these caps are for fast performance(V/µs) and not sound,
I am currently testing using a FKP WIMA in its place,
And they are huge caps:

 so I have them squeezed on the component side..




mogos said:


> *0,68 µF will also be ok. I am planing to switch the positions of the WCF coupling cap (not yet selected) and Coupling Cap (Jupiter). *




Selecting 0.68uf is totally unnecessary and I would not recommend..
Increasing capacitance in this position, only serves in lowering the frequency, not improving sound.
Higher capacitance is not always the solution and this is an example.
In this position with a .47uf we are already near 7 hertz "operational", noticably lower than the stock .22uf,
 and .68uf would only drop you a meager 2hertz more lower than .47uf.
Another issue is that we do not have a full schematic to learn of possible effects and so can only recommend what was tested.

Your money and size space can be better used with a cap of faster "Max pulse rise time" (V/µs), 
and also of greater sonic quality. 
This usually translates to a cap of higher voltage capacity (even though it is handling same circuit voltage parameters).
Therefore I would only suggest the best sonically rated caps you can afford at .33-47uf 

For an amp that we do not have a schematic for, much has been accomplished.


----------



## coinmaster

> Another issue is that we do not have a full schematic


 
 Oh yeah? 
  
 BAM!
  

  

  
  


  
  
  
  
  
  
 Eat it suckers! Over a thousand hours of effort and research and the complete destruction of my MK6 and I'm finally finished.
 I've literally spent the entire day, every day, since early-mid september reverse engineering the amp and researching upgrades.
  
  
 Voltage labels on the rails to come when it's back together again.
  
 I'm going to make this baby into an amp that will be one for the records on head-fi.org.
  
 I'm changing the power supply from a bipolar RC filter to a bipolar cascaded LC filter, adding shunt regulators to the driver power supply since stock is unregulated, adding a constant current source for plate loads instead of resistors, upgrading to top end EI transformers, replacing the potentiometer with an LDR circuit to remove the pot from the signal path, possibly use ferrite beads for grid stoppers instead of resistors,  possibly changing bias method from cathode bypass to fixed, LED, or battery bias, using single/multi-chip Z-foil resistors everywhere not in the power supply, Duelund cast PIO coupling caps, Jupiter PIO WCF caps, world class specced industrial film caps from AVX for cathode bypass, PS upgrade caps, decoupling caps, and more!
  
 The end result will be ginormous monoblocks with 3-5 transformers and 4 10lb inductors on each block. Each block will literally probably weigh 80+ lbs and that's not counting the mu-metal shielding I'll need for all the transformers/inductors, so make that 100-120 lbs per block.
  
 I'm going to make this beautiful baby to test all the potential mods and their effects on the sound before I officially build.
 It's a drag and drop, cold-swap modding center for tube amps(or anything else).

 info here for those interested in making this http://tubelab.com/articles/tubelab-prototyping-system/


----------



## coinmaster

.


----------



## Mogos

maxx134 said:


> Selecting 0.68uf is totally unnecessary and I would not recommend..
> Increasing capacitance in this position, only serves in lowering the frequency, not improving sound.
> Higher capacitance is not always the solution and this is an example.
> In this position with a .47uf we are already near 7 hertz "operational", noticably lower than the stock .22uf,
> ...


 
 Thank you once again for guidance and detail explanation helping to understand how the components parameters influence the sound. It is very valuable for me and I think not only for me.


----------



## Maxx134

coinmaster said:


> > Another issue is that we do not have a full schematic
> 
> 
> 
> ...



Somehow I knew this was going to egg you to post your info..

Unfortunately I have not looked it over and verified it's correctness.

Once it has been verified to not have *errors* is when you* should have * posted this...


And I fully expect your monoblocks to look something like this:

So next time you boast I like to see it materialized.
Unfortunately since you changed its design it can no longer be called an MK6 supermod...
Instead more MK6 based derivative...
You will have to start a new thread on it.
An "MK6 Zombie resurrection"...


----------



## coinmaster

> Once it has been verified to not have errors is when you *should have* posted this...


 
 That's the glory of head-fi.org. You can edit your posts anytime. It sucks over there at DIY forums where you can't edit after 30min. I like to say things as they come to mind 
	

	
	
		
		

		
			





 
 Besides, I'm like super-duper sure it's error free. Probably. 
  


> You will have to start a new thread on it.
> An "MK6 Zombie resurrection"...


 
 Indeed, first I have to wait a few weeks for my "tube prototype lab" and my stock replacement parts to get here. I'm going to go ahead and order those jupiters too for the WCF, since you claimed you got the best of both worlds when using those mundorfs maybe I'll get the best of both worlds using duelund/jupiter.
 Differences reviewed here http://www.enjoythemusic.com/diy/0514/jupiter_copper_foil_paper_wax_capacitor.htm


----------



## Maxx134

For those who would like a little insight on this area of WCF cap replacement,
I would suggest replacing with a cap of equal or lesser brightness, 
unless you seek to alter the signature of your coupling cap..
Any quality cap will beat the stock soft smaller sounding lame red caps,
And will give better sound, 
But we dont want any plastic trebles from cheaper caps to affect the signature..


----------



## Maxx134

Coinmaster, I have to give you credit for your perserverance so hats off to you.
I will look it over soon.

I have been busy and accomplished upgrades of all jupiters and also upgrade of the two driver stage RIFAs with WIMA "FKP"..

So time for some listening..

I will also compile a short list with some of the best driver tubes for MK8..


----------



## Benny-x

You guys are crazy. I've been wanting a MkVI+ for years, but one thing has lead to another which has lead to me still being sans MkVI+. I'm so happy that I didn't now or I'd have spent all my money trying to be a part of this insanity. 
  
 Though the options are nice to have, I've got a lot of things taking my time and I'll be happy once the modding is almost fully fleshed out and I can make my own list of what I'll need to do to my future MkIV+ to make it a real monster. Not as much a monster as Coinmater, who must really be a master of coin for all the ones he's spent on the $600 amp...


----------



## coinmaster

> You guys are crazy. I've been wanting a MkVI+ for years


 

 Quote: 





> I'm so happy that I didn't now or I'd have spent all my money trying to be a part of this insanity.


 
 There's good news. A stock MK6 can be built for a fraction of the retail price. So my sacrifices may *save* you money.
 You can build my completely modded finished model  for less than a stock MK6 provided you don't buy super duelund caps (With jupiter pio caps you might spent slightly more than stock price)
  
 Also, there is some very interesting things I have discovered.
 For example, our driver tubes are running on fumes with the input voltage they are getting with those 220k power resistors. There's also some other majors flaws in the driver stage but I won't get into it here until I understand it better.
  
 Also, if I use a constant current source (a circuit that keeps the current constant no matter what the voltage is) on the cathodes, the power supply should make no difference in the sound and the tubes will perform much better. Meaning I can keep the stock power supply and still get better sound than I would have even with an upgraded supply.
  
 Don't take anything I say for granted yet, it's probably accurate since this was information I got from people that have been building amps for decades after they reviewed my schematic but I always like to get second opinions just in case.


----------



## Maxx134

Well its either spend the thousands right away on an uber amp...
 Or buy one of these and spend as you go along,
 while being able to have things "your way" inside...
Plus learn a lot along the way.


.


----------



## coinmaster

Not thousands, my point is, the stock MK6 can be built for around $150-$250. (I'm guesstimating the top end as I don't know the price of the transformers)
 Leaving you with around $600 in upgrade cash.
 You can easily squeeze in sub-duelund upgrades with that money.
 Of course once you add in some PTP terminal strips/chassis/connectors/meters that probably throws it off by $100.
  
 Assuming the CCS idea works out, the upgraded power supply may theoretically be unnecessary and so will the cathode bypass cap and cathode resistor (and maybe the decoupling cap?) saving even more money, and with no cathode bypass cap/resistor, there's obviously going to be a sound quality increase in that area better than if one were to throw in even a duelund cap since the best cap/resistor is no cap/resistor, and it's self biasing!
  
 There is one downside (which is technically an upside) to using CCS biasing. Since it converts the output stage into a long tailed pair topology (connecting the biasing cathodes to each other) to keep the tubes balanced with each other it relies on the the fact their bias point is the same.
 Meaning I won't be able to mix tube types anymore 
	

	
	
		
		

		
			




  
  
 Currently the tubes are unbalanced because they operate at different ground references so each tube is pretty much doing what it wants. Similar to using "unmatched" tubes.
  
 Will a CCS bias on a long tail pair topology outdo the sonic advantages of my tube mixing? More than likely since the signal will no longer be passing through the cathode cap and the tube operations will be balanced but I'll have to test it anyway before deciding in the unlikely even it somehow doesn't.
  
  
 Unlike what the circuit board makes it look like, the amp is really not that complicated to build as you can see from the schematic. A simple guide can do the trick for beginners.


----------



## Redge78

@ Coin
  
 Just to remind you what the objectives of this thread are ...
  


> *What we want to do in this thread*
> 
> _It was (and still is) an adventure and we wanted to share what we have found and done._
> _We don't claim we have found any "final truth" or our mods are the best. *But everything has been tested and is operational in our amps.*_


----------



## coinmaster

I'm not claiming any "final truths". Just telling people what I am planning to test in the future and giving them something to look forward to, kind of why I said


> I'll have to test it anyway before deciding


 
 Also mentioning that if people wanted they could* build* an mk6/8 and have a boat load of money left for all the mods they want.
  
 Poor Benny-X said he's been wanting an MK6 for years and has been scared off by the temptation of all the crazy mods 
	

	
	
		
		

		
		
	


	




.
 I was giving him a solution.
  
 If you build an mk6/8, you could mod it with *all* of the mods and still spend less than the retail price.


----------



## Maxx134

*This thread will remain as Redge78 stated.
So I will respond only once to this...*

Unloading these ideas,
 of alternate design possibilities here,
will only serve to confuse/put off/scare away those who are interested in getting the most out of the MK6/MK8 amps.

Thus we have results like what member "Benny-X" posted, who think we are crazy & mods not finalized..

Everything disclosed in first posts are pretty much finalized.
As noted, we may add more as we go along.

So our mods are already figured out, materialized, explained, and tested before posting in first page,
 to have positive results, 
In order to *encourage* others...

Do you remember we did not want to confuse the original MK6,8 thread with our mods?..
Similarly, "coinmaster" recent posts with other ideas is also confusing this thread.

*Coinmaster*,
I am not discounting your enthusiasm and motivation, 
So please do not be discouraged or insulted.
In fact I admire your incredible efforts to learn from ground zero,
And I find that very positive and refreshing.

What you should have done is choose electronics as your carrer or as classes to boost your credits if possible if your going to college, or take a trade school on the side which is alot faster than college.

So you should continue your ideas apart from this thread because it truley confuses our objective to encourage members to do these mods, not to rebuild an amp...

I am sure you can have much input pertaining to our actual mods instead...
Your schematic, for instance is very good thing and we can straighten out any details missed.



*AS FOR YOUR IDEAS:*
In electronics there are a multitude of choices to make.
As a designer, you are faced with many ideas and methods, plus experience an even secrets that dont all blend nicely easily...

Think of it like being a cook.
You need to come up with a recipe that will work with what you have, in both intelect and resource.

If you look around, 
You will find MANY designs with tubes running low or very low, especially for preamp/small signal stages. This is normal, popular and desireable. 
Look at both datasheet linearity curves and signal input parameters not just voltages for the tube choices in question.
So you see these "ideas" are what comes to you as you learn, which is very good "for you".
Not for everyone.

Nothing in reality which is actually materialized, is as pretty as it seems..
For instance, the suggestions that were given to you, seem to me, more toward being a gunea pig, than actual projects done..
Be wise.
If it worked it would have been done already.
So thats your choice.
Just stay on topic and contribute instead of "unloading" here...


----------



## coinmaster

Quote:


> Everything disclosed in first posts are pretty much finalized.
> As noted, we may add more as we go along.


 


> So our mods are already figured out, materialized, explained, and tested before posting in first page,
> to have positive results


 
 You keep treating every page after the first one as the first page. Everything after the first page is part of the *discussion*. I'm pretty sure my ideas fall well into the category of modding the mk6/8 and all that implies, which is kind of what forums are about to begin with, not to be a magazine cover, but a discussion area.
  


> Unloading these ideas,
> of alternate design possibilities here,
> will only serve to confuse/put off/scare away those who are interested in getting the most out of the MK6/MK8 amps.


 
 No need to sugar coat things for people. Complete and accurate information is better than sugar coating which may as well be the same as lying to people.
 What they do with that information is up to them, it is our job to make sure that information is clearly conveyed and fully understood.
 If you want to avoid scaring people away you should emphasize the fact that these mods aren't difficult and don't have to be expensive and can even *save *you money as I've shown.
  
 I gave some pretty valuable information to the table, maybe not in terms of your "ideal" version of this thread but in terms of the interests of the individual people reading it. 
 It would have been a crime *not* to give people a schematic and the knowledge that they can build from scratch if they wanted to and save lots of money.
  
 Giving them some more potential mods to look forward to wasn't a bad thing either. I know you said my mods don't "quality" as mods *to you *but this is a public forum comprised of many people with different interests and the term mod means modification which from the dictionary means "a change made". In a thread about modding an mk6/8 even doing something like changing bias methods is fair game to people interested. It's not like I'm changing an OTL amp into a SET amp or something, just simple changes which can be implemented just as easily as the mods you have posted.
  
 For example, the last paragraph you posted above me is discussion about the MK6/8 mods I'm going to do furthering peoples understanding on the subject.
 I learned something I didn't know which was that small signal stages are often run on low voltage as ours is.
  
 Will it sound better running it at a higher voltage though? I don't know, we'll have to find out won't we.
 I suspect many of the current design decisions were made to cut cost/space/weight as the alternatives would be larger, (usually much) heavier, and/or more expensive.
 As is, the mk6/8 is probably the best bang for buck balanced tube amp you can buy. Making it larger, heavier and more expensive would just serve to increase retail price and shipping costs and make the targeted market audience smaller.
  
  
 Just to be clear to all the people that may possibly be thrown off by our modding. It doesn't have to be expensive (as I said you can even save money), and you don't need any prior experience, it's really not that hard, tedious maybe but not hard.
 The only thing you do need is patience, and the ability to follow instructions and ask questions when needed. Slow and steady wins the race when modding and remember, anything you might accidentally "break" (unlikely) can be easily fixed since we are dealing with the circuitry itself here, and usually if you do something *really* bad one of the components will sacrifice itself to save the rest of it (as long as you cut the power after that happens). That is worst case scenario and shouldn't ever happen when doing our simple mods.
 That being said (and I would know, I "broke" it numerous times in my experiments) this amp is very hard to break, even when you do something you _really_ shouldn't to it..like wire the transformer connections the wrong way "cough" "cough" 
	

	
	
		
		

		
		
	


	




.
 As long as you follow the instructions none of that will happen anyway, it's pretty clearly laid out, and again *ask questions*.


----------



## Maxx134

coinmaster said:


> You keep treating every page after the first one as the first page. Everything after the first page is part of the *discussion*.




Exactly!
Stay on topic to accomplish the mods, as it can easily get confusing and turn into a mess with your off topic posts..

For new ideas we do in PMs, then we do all the work in making it a *reality*
And *THEN* we post about it *after*,
 IF,IF

*IF*
 it actually gives us *sonic benifits*..

We dont just spout off ideas.
There are millions of ideas when you are not being specific to this amp parameters.

You are posting ideas like starting from scratch that may be discarded tomorrow...

This thread is an *instructional* thread to "SuperMod" the MK6&MK8 with real verified improvements.


You are confusing it..
We did not title it "SuperMod *Ideas*.

 Posibilities that are not impemented yet,
 or actually modded is just "hot air"...

Even when worked out on paper many ideas will not yeild enough sonic benifit to waste the effort...

There are SO many design ideas people can boast about and try convince to you in other threads,
 yet is an unknown if it is even applicable here.[/B]
Has anyone outside of this thread admitted to ANY of these mods, and if not why?
You need to show what you are starting with, before accepting ideas.

Anyways I am all ears for realistic improvements on the actual mods at hand.
Im not here "reinvent the wheel", just enjoy the amp which has top end potential while being a great learning project.


Ridge78 already posted in BoLD what the objectives were..
It is not to be reinterpreted as a place to throw out ideas for us to explain why they are not chosen.




coinmaster said:


> I gave some pretty valuable information to the table, maybe not in terms of your "ideal" version of this thread but in terms of the interests of the individual people reading it.
> It would have been a crime *not* to give people a schematic and the knowledge that they can build from scratch if they wanted to and save lots of money.



I already agreed on this info. 
It is obvious the schematic pertains to this thread topic.
I dont see how they will save money by knowing a schematic..
You can get a Cavali schematic and make that too and be done also.
I consider him at the top with current line of amps.

My point is your post show good info like schematic,
But then you throw in *unsolved/unresolved* ideas, not actual mods..
They are not worked out to see if it is even viable to be made into reality..
So this type of fluff ideas are best left to PMs, or DIY threads to munch over..


----------



## Maxx134

One of the reasons I have not attempted to look at bolder ideas was lack of a schematic,
Which Coinmaster has worked on..
This will be greatly benificial to looked further to see what else can be done, so yes more will be thought about.

Right now I am very satisfied with my results so will be testing tubes,
But like to thank Coinmaster again for the schematic work,
And finnally everyone will have a greater insight to the design.

Also of note, is that it is Coinmaster's interpretation schematic of the amp, 
Not the actual schematic, which we have never recieved or used.

This is important, as we dont want any problems with asking for, or using an original schematic for different intentions.


----------



## coinmaster

> here are millions of ideas when you are not being specific to this amp parameters.
> 
> You are posting ideas like starting from scratch that may be discarded tomorrow...


 


> They are not worked out to see if it is even viable to be made into reality..


 
 The mods I was talking about were specifically deduced and fall in line with the potential short comings of our particular amp design. They aren't randomly thrown out there. Will they turn out to be better sounding than our current design? I suspect at the very least it will sound different but probably better if for no other reason than getting rid of the cathode bypass cap while still maintaining autobias, and different alone isn't always a bad thing. Which is why we roll tubes.
  


> You are confusing it..
> We did not title it "SuperMod *Ideas*.


 
 That kind of falls in line with the whole "discussion" thing I talked about. If people want instructions, they can go to the first page. I agree that it shouldn't turn into a "what if I" thread. But I spent countless hours getting that done elsewhere, what I have now is a narrowly deduced set of clearly defined technical upgrades to fill in the (from an engineering perspective at least) downfalls of our current design given to me by multiple people with years/decades of experience and extensive experience with the driver tubes the mk6 uses. Being as meticulous as I am when it comes to reliable info on the potential amp upgrades, I wouldn't have posted it here if I didn't get all the details worked out and wasn't sure it was the right path for me to take and if it didn't make sense to me itself. (as you noticed, I've spent months getting it right)
  
*But* I don't want to turn this into an argument, so I'll keep my nose out of this.
  


> Also of note, is that it is Coinmaster's interpretation schematic of the amp,
> Not the actual schematic, which we have never recieved or used.


 
 Yeah, I asked David like 4 times for a schematic over the last 2 months, even told him I was going to resort to taking my amp apart if I had to to get a schematic, no response. He responded to a number of other emails I sent him at the same time though. He truly does only respond to what he wants 
	

	
	
		
		

		
		
	


	



  
 I almost want to send him an email with my schematic just to rub it in


----------



## Maxx134

coinmaster said:


> > Also of note, is that it is Coinmaster's interpretation schematic of the amp,
> >
> > Not the actual schematic, which we have never recieved or used.
> 
> ...




Noooooowwaahh


Trouble maker!


Edit:
This is a good pic for me to answer your posts!
Ha!


----------



## coinmaster

I'd hate for you to be my dad


----------



## Benny-x

Thanks for being concerned for me guys, but don't worry or get the wrong idea.
  
 I've actually had a love affair with the LD MkVI+ for like 4-5 years. When the time came for me to buy one a few years back I didn't get it because my company's accounting department missed a paycheque and I didn't have the cash. Then after I had the money I had to pay for a vacation, and then so on and so on. By the time I had the money again there weren't any used MkIV+'s up for sale, so I bought a used Audio-gd Phoenix locally. I don't regret that at all, that's one hell of an amp and an AMAZING pre-amp. It's probably a better pre-amp than headphone amp. And it's got a remote.
  
 The Phoenix had also been on my love affair list for a while, and also because in the long Audio-gd Phoenix thread an old super-modder named Pricklely Pete started detailing his mods over a few pages which he dubbed the "Phoenix Max Mod". His results were great, well documented, and I got the BOM and instructions in the end. I almost have all the components for this now, minus some Russian caps he put in later.
  
 What drew me to this mod were both his feedback on the effects of the component changes and how he presented it in a step-by-step "build thread" kind of way, and not in an "ideas and discussion" kind of way.
  
 There is a time and place for discussion, but when you're trying to mod something and it's NOT your pride and joy, it's NOT a pass time for you, and you DO want to get better results, then following someone's steps vs. someone's discussion is what's going to work.
  
 What we have here, at least in my understanding, is a "build thread". The "ideas and discussions" are going on behind the scenes and we're getting the fruits of that labour. If you want to ask for help on a step, that's good. If you want to ask component vs. component, that's good. But this isn't a discussion for other potential mods on a MONSTER of a project. That needs it's own thread. And all of that, it's for our benefit 
  
 As for posting "The Schematics", I agree and actually think they should be taken down. They need to be verified by someone who isn't coinmaster and who has a MK6+ to actually take a part and check piece by piece. That's really dangerous and no matter how precise you are, you're emotionally invested in it and no longer have a functioning amp for someone else to compare them against. Think about someone looking to mod that doesn't read the post right after "HERE IT IS" to find out that those aren't in fact official schematics from David at LD? That guy is playing with tube level voltages and loaded caps, he could kill himself if you made an error. I'm not doubting you, I'm saying you should doubt yourself until someone else has confirmed it.
  
 So, in the end, I'll stand by, let the mods and detailed effects settle, then take note of what I want to do come the time I get finally get my own Mk6+. And I'll also make sure to poke my nose into coinmaster's new Monster Mk6+ "gut and overhaul" thread because there will be valuable stuff to learn there too. Things that certainly aren't going to be learned in this thread due to what it is and what it isn't


----------



## coinmaster

> I'm not doubting you, I'm saying you should doubt yourself until someone else has confirmed it.


 
 I've been doubting myself for months, the fact I posted anything is a testament to my confidence in the reliability of the information. Don't underestimate the vast tediousness I went through to make sure I have worked out all the details with a well rounded understanding. I always check things from all angles to be sure, and then check it again.
  
  
 Does the schematic have errors? I literally sleep next to my mk6 circuit board if that says anything (no joke) so I doubt it.  I'll be running it in spice and doing 1 last check for potential missed grounding points but the probability almost null. Not to mention it's been picked over by people with years of experience designing amps. So I'd say it's pretty sound,
  
 As for the ideas and discussions, all I did was give an update on what I'm going to do and why, no theory crafting involved. I mean jeez I feel like I'm in a communistic society.


----------



## Redge78

> Does the schematic have errors? I literally sleep next to my mk6 circuit board if that says anything (no joke) so I doubt it.  I'll be running it in spice and doing 1 last check for potential missed grounding points but the probability almost null. Not to mention it's been picked over by people with years of experience designing amps. So I'd say it's pretty sound,


 
  
 So I suppose you can ask your "people with years of experience designing amps" where are gone the "330R" Anode/plate resistors of your 6080 tubes in your "_BAM !_" schematics.
  
 Because as it is, regardless of how many CCS you put in there (more on that latter), it's gonna be working funny, with sparkles and fumes eventually ...
  
  

 You could have noticed that we wrote about those resistors as they are utterly important (yes, I know ... in page 1 ... again) : _This feat of magic is performed by the *top triode's plate resistor *that functions current-sense resistor that experiences a variation in voltage drop corresponding to the variation in current conduction by the top triode. This variation in voltage drop becomes the input signal for the bottom triode, which responds in an anti-current phase fashion, creating a complementary, balanced push-pull operation by the two triodes. _
  
 You can also go to the Cavali paper and see how this resistor is impacting the "Balanced Push-pull" operation, how it must be calculated for each headphone type. We could even discuss about the way to optimise it when dealing with "high res" or "low res" headphones ( to maintain best Push/pull operation and therefore to extract as much power as possible, I mean).


----------



## coinmaster

> where are gone the "330R" Anode/plate resistors of your 6080 tubes in your "_BAM !_" schematics.
> 
> Because as it is, regardless of how many CCS you put in there (more on that latter), it's gonna be working funny, with sparkles and fumes eventually ...


 
  

 You're right. It seems some things got mixed up during conversion from proteus software (never use that software btw, it's a dissapointment 
	

	
	
		
		

		
			





).
  
 It should look like this.
  

  
  
 Meaning it *was* a long tailed pair topology all along, giving even more validity to my plans to use CCS instead of cathode bias since I was going to have to make it LTP for that to work, _but_ you get to watch me eat my own words. So win win 
	

	
	
		
		

		
		
	


	




 
  
 At least it makes sense now, I was wondering why they would opt out of LTP since that would unbalance everything.


----------



## Maxx134

It is still going to make very nice sparks & smoke because it is still not correct.
You can PM me as I am not going to litter this thread on schematics.

What I would like to bring to everyones attention, is an important issue that I feel our amps can benifit from..
In terms of heat management, stability, and reliability.
It can also be considered a sonic improvent if your amp's values are off, which is VERY possible..

So here it is:
Due to cost cutting, 
We have areas where power resistors are not only turning brown, but changing value, which is "not good" 

Here is a pic of the locations, board values, and updates not printed to the board..



Values are total resistance values.
The MK6 info was courtesy of MisterX who noted changes and informed me.

My MK8 changes were implemented and verified as an update,(not printed on board),
 thru email with David a few months ago.

So it is important we update these resistors with higher wattage..
Stock is pure garbage.
I can only recommend same type as the used for power tube anode/cathode resistors: Mills MR5 wirewound..
You will still need to double up on the center resistors(4k1&2k5), as they run the hottest in the amp.

I will update first post when able..


----------



## Mogos

No good no good. I have got the resistors with board values. You say they are wrong and should not be used.


----------



## SonicTrance

Yes,
  
 For the board value 8K2 you can use 2 x 8K2 MRA5's in parallel = 4K1 
 For the board value 5K1 you can use 2 x 5K1 MRA5's in parallel = 2K55
  
 These were the values installed by LD in my unit. Did you check your original values?


----------



## Maxx134

Yes for some reason the LD MK6 board printed the value of a doubled/paralleled resistor, not the total,
and never updated it so it should be ok in value.
This is what Mr-X pointed out.

The real issue is that these resistors need to be higher wattage as they turn in color and value:


Look:


This goes for all your power tube anode/cathode(the 8 power resistors) resistors as well.
Take care of these resistors and you should be good.


----------



## Mogos

I have to check the original values. Maybe they are as the one indicated on the board and then I will follow it. Thank you for the eventual solution.
 Below is the list of the parts I will install:
  
 Capacitors:
  
 MKP 60 µF Wima  DCP4L056007KD4KYSD 800 V 10 %         4 pcs.
 MKP 40 µF Wima  DCP4L054007ID4KYSD 800 V 10 %         2 pcs.
 PME-140: 0.33uF 275 Vdc Evox Rifa PME271M        6 pcs.
 PME-080: 0.1uF 275Vdc Evox Rifa PME271M            4 pcs.
 Elna Silmic 2 470µF/50v                    4 pcs.
 Mundorf M-Lytics AG 1500µF 160V                2 pcs.
 Jupiter Round COPPER, WAX & PAPER, 0.47uF 600VDC    4 pcs.
 Audyn MKP Gold Silver 0.33 UF 1200V 2%            4 pcs.
  
 Resistors:
  
 330 Ohm Mills MRA-12
 100 Ohm Mills MRA-5
 8.2K Ohm Mills MRA-5
 2.2K Ohm Mills MRA-5
 5.1K Ohm Mills MRA-5
 3.3K Ohm Mills MRA-5
 56K Ohm Mills MRA-12
 10K 1Watt Shinkoh Tantalum 
 1K5 1Watt Shinkoh Tantalum 
 300R 2Watt Shinkoh Tantalum
 0.68 Ohm Vishay Mills MRA-5
 CM2610 220K 2W TKD Correctohm Metal Film Resistor
  
 Wires:
  
 Neotech Solid UPOCC Silver in Teflon 22 AWG Blue
 Neotech 20 AWG, UP-OCC copper wire, RED teflon
 Wire (silver/gold) Mundorf MConnect SGW110W 20AWG
 22 AWG Shielded Silver Kapton Teflon Wire 3 Twisted
 22 AWG Shielded Silver Kapton Teflon Wire 2 Twisted red black
 20 AWG Shielded Silver Kapton Teflon Wire 2 Twisted
 20 AWG 1000 Volt Silver Teflon Wire
  
 Other:
  
 Aucharm Audio 99% Silver Alloy Fuse Tube 5x20mm 3A
 Balance XLR 23 Step Attenuator Potentiometer 100K Log
 AMR Audio 90% Silver Alloy Fuse Tube 5x20mm 0.5A
 Cardas CM F XLR Chassis XLR
  
  
  

  
 It started so innocently with just few capacitors and resistors and got so seriuous


----------



## Benny-x

coinmaster said:


> I've been doubting myself for months, the fact I posted anything is a testament to my confidence in the reliability of the information. Don't underestimate the vast tediousness I went through to make sure I have worked out all the details with a well rounded understanding. I always check things from all angles to be sure, and then check it again.
> 
> 
> Does the schematic have errors? I literally sleep next to my mk6 circuit board if that says anything (no joke) so I doubt it.  I'll be running it in spice and doing 1 last check for potential missed grounding points but the probability almost null. Not to mention it's been picked over by people with years of experience designing amps. So I'd say it's pretty sound,
> ...


 
 15mins after my comment you post again about your assuredness that the schematic is 100%
  


redge78 said:


> So I suppose you can ask your "people with years of experience designing amps" where are gone the "330R" Anode/plate resistors of your 6080 tubes in your "_BAM !_" schematics.
> 
> Because as it is, regardless of how many CCS you put in there (more on that latter), it's gonna be working funny, with sparkles and fumes eventually ...


 
 And then 8hours later this error is found in your schematic.
  
 I hope you're seeing that as a wake up call about what the 3 of us have said being true. I also hope that you're not discounting it and telling yourself it was "only" a programme error and that there "shouldn't" be any other mistakes.
  
 This isn't a slight at you, what you've grinded and toiled to make is the closest thing anyone has had to a working schematic for the amp in like 6 years. Unfortunately it's not vetted and already has an error. Wait until your magic is confirmed, until then just post that you potentially have a schematic and people can PM you for a Dropbox link if they're feeling adventurous. It's the safe play. What's the harm in doing it that way?
  
 I'm not going to badger you about it any further, I just hope you see where we're coming from.
 (congrats on the work, though, it's impressive. I've always wanted to learn more about "writing" out circuits, but I've never moved beyond the want. Props)


----------



## Benny-x

mogos said:


> I have to check the original values. Maybe they are as the one indicated on the board and then I will follow it. Thank you for the eventual solution.
> Below is the list of the parts I will install:
> 
> Capacitors:
> ...


 
 Nice new pot, when are you going to try it?
  
 And that looks awesome, man. Down the road that's like the outline I hope to find/make for what I'll get to trick out my Mk6+. Congrats on getting all your stuff. Make sure to photo-document your build and post it up in here.
  
 The more work you guys do and the more people that get in on this, the more I'd love to try it too. Haha, that's sad because I really don't see this happening for like a year...


----------



## coinmaster

> 15mins after my comment you post again about your assuredness that the schematic is 100%


 


> And then 8hours later this error is found in your schematic.


 
 If you want to get petty about it I can go find a time stamped screenshot of one of my old p.m.s showing the schematic in proteus with those connections in tact.
  
 My reverse engineering is correct, I just didn't copy it from the mess that is my proteus schematic to multisim correctly.
  
 Honestly, you people care too much about what is posted on an_ internet_ (as in not real life) forum. You guys are as stiff as nails, loosen up.


----------



## Mogos

New pot will be installed. It will be tricky but I hope I know the way. I plan to start the job mid of November. Photo photo will be done for every detail and I will share it with you guys.
 I have checked my amp and the resistors.
 For me my situation dosen't correspond to what you have written about the resistors values. Maybe I not getting something correctly. Look what is installed in my LD mk6
 I could not measure the value of the resistors 56k 2W. The ohmometer was runing up and down from kilo to mega and so on. What the heck??
 The 3,3K are Dale resistors and they show correct value.
 Other resistors show approximately the same value as printed on the board.


----------



## coinmaster

> The ohmometer was runing up and down from kilo to mega and so on. What the heck??


 
 You may have to desolder one end of the resistor to get a correct value, that can sometimes happen depending on what the surrounding circuitry is, which in this case for the 56k is a resistor and a large capacitor on both sides.
 This is assuming you haven't desoldered them already.
 Also sometimes that can happen if you don't have enough stable pressure on the connection while measuring.


----------



## SonicTrance

mogos said:


> New pot will be installed. It will be tricky but I hope I know the way. I plan to start the job mid of November. Photo photo will be done for every detail and I will share it with you guys.
> I have checked my amp and the resistors.
> For me my situation dosen't correspond to what you have written about the resistors values. Maybe I not getting something correctly. Look what is installed in my LD mk6
> I could not measure the value of the resistors 56k 2W. The ohmometer was runing up and down from kilo to mega and so on. What the heck??
> ...




The 8K2 and 5K1's are double resistors in parallel on my unit, making total resistance 4K1 and 2K55. But as they're single resistors on your unit maybe you should stick with the written board values as it has worked for you? I don't know...

You don't need to change those brown Dale resistors...


----------



## Maxx134

mogos said:


> New pot will be installed. It will be tricky but I hope I know the way. I plan to start the job mid of November. Photo photo will be done for every detail and I will share it with you guys.
> I have checked my amp and the resistors.
> For me my situation dosen't correspond to what you have written about the resistors values. Maybe I not getting something correctly. Look what is installed in my LD mk6
> I could not measure the value of the resistors 56k 2W. The ohmometer was runing up and down from kilo to mega and so on. What the heck??
> ...




You have an older board where they used BETTER parts...
The zener diode is probably different so as to use that different value resistor, but still needs upgrade..

KEEP the resistors SAME AS MEASURED.

Only need to change one resistor...
Look:

Also,
Your parts choices are all excellent!


----------



## Mogos

Thank you Maxx. After analysis of the all informations I was going to do what you have advised me. Only one thing I have the 8.2K Ohm Mills MRA-5 resistor (the same value as on the borad) and I will use it. The value 8k1 was measured by me and is error-burdened or showing preliminary destruction of the resistor.


----------



## Redge78

@ Mogos
  
 I have been through your shopping list and I have understood everything ! Seems all good to me.
  
 Just one question : _why this particular Audyn ? why not the "AUDYN TRUE COPPER MAX" or the Mundorf equivalency ? _
 Just interested, I never came across those.
  
  
 Obviously, we will be interested to know how this stepped attenuator is fitting in (and how it sounds).
  
  
 Good luck for the mods anyway, don't hesitate to bother Maxx for advices on planning all those mods, and asks for his secret tricks ...
 You just have to be aware that he'll try to sell you his "glue everything" way of life. Be strong, resist !  
  
  
_And don't listen to Maxx about those PSU resistors. Change everything, this is a problem you will not have to worry about anymore. _


----------



## Mogos

sonictrance said:


> You don't need to change those brown Dale resistors...


 
 I will for sure change the Dale resistors in Power Tube grids as there are on the way Shinkoh Tantalum 2W ones. With the other ones there could be an advatage as the ones I have are higher wattage 3.3K Ohm Mills MRA-5.


----------



## SonicTrance

mogos said:


> I will for sure change the Dale resistors in Power Tube grids as there are on the way Shinkoh Tantalum 2W[COLOR=454434] ones. With the other ones there could be an advatage as the ones I have are higher wattage [/COLOR]3.3K Ohm Mills MRA-5.




Are you talking about the four 300R grid resistors for power tubes? If so, there's no need for 2w resistors and will probably not fit through the holes on the board + being huge...

I used Takman 0,25w 300R resistors for that area.


----------



## Redge78

sonictrance said:


> Are you talking about the four 300R grid resistors for power tubes? If so, there's no need for 2w resistors and will probably not fit through the holes on the board + being huge...
> 
> I used Takman 0,25w 300R resistors for that area.


 
 Well, I have changed my (already nice) 300R Dale for some Shinkoh Tantalum 300R 0,5W.
  
 If I have had the posibility to flip my board and to properly unsolder the Dales, I may have chosen the Shinkoh 2W version as well.
  
 Electricaly, it makes sense to go "high power resistor". Better heat dissipation, less noise, ...


----------



## Mogos

redge78 said:


> @ Mogos
> 
> I have been through your shopping list and I have understood everything ! Seems all good to me.
> 
> ...


 
  
 I am expecting that the Audyn will master the transients and make the sound of the amplifier even more live like. As I am not a specialist I have based my choice on what Maxx has written, description of sound signature of similar Mundorf Cap and my imagination 
	

	
	
		
		

		
			





. So I have found 1200V cap. And I think out that silver shall provide the speed slightly warmed by gold (this is my theory)
	

	
	
		
		

		
		
	


	




.
  
_Your money and size space can be better used with a cap of faster "Max pulse rise time" (V/µs),
 and also of greater sonic quality.
 This usually translates to a cap of higher voltage capacity (even though it is handling same circuit voltage parameters).
 Therefore I would only suggest the best sonically rated caps you can afford at .33-47uf_
  
 This is  just my imagination that I will connect rich timbred sound of jupiters with lightning speed of Audyns. We will see or rather I will hear and you will read.


----------



## SonicTrance

redge78 said:


> Well, I have changed my (already nice) 300R Dale for some Shinkoh Tantalum 300R 0,5W.
> 
> If I have had the posibility to flip my board and to properly unsolder the Dales, I may have chosen the Shinkoh 2W version as well.
> 
> Electricaly, it makes sense to go "high power resistor". Better heat dissipation, less noise, ...




Ok, not an option for me though as I'm doing the "compact version". No room for large resistors in that area


----------



## Mogos

sonictrance said:


> Are you talking about the four 300R grid resistors for power tubes? If so, there's no need for 2w resistors and will probably not fit through the holes on the board + being huge...
> 
> I used Takman 0,25w 300R resistors for that area.


 
 I meant, Yellow marked  = WCF grid resistors. I know that there is no need for 2W. I could get only the 2W ones. I know also that I may have some problems with installation of them. I am expecting that it will be not the only one problem I will encounter. Before the start of modification I plan to meditate for one day 
	

	
	
		
		

		
		
	


	




. I think more wattage will not influence the sound.


----------



## SonicTrance

mogos said:


> I meant, Yellow marked  = WCF grid resistors. I know that there is no need for 2W. I could get only the 2W ones. I know also that I may have some problems with installation of them. I am expecting that it will be not the only one problem I will encounter. Before the start of modification I plan to meditate for one day  . I think more wattage will not influence the sound.




I'm sure you'll be fine. I forgot you're not fitting everything in stock case. Meditation might help, lol. Just take your time and don't rush things. That's what I'm currently doing...


----------



## Redge78

mogos said:


> Before the start of modification I plan to meditate for one day
> 
> 
> 
> ...


 
  
 That's the smartest thing I've heard for a long time ... 
	

	
	
		
		

		
		
	


	



  
 I don't want to put too much pressure on you but you realise that yo_ur_ _only f__ocus is perfection of execution__._
  
 So ... no rage, no hurry, no "that should be good".
 Always calm, always thinking twice, never more than 4/5 hours straight. Breathe and rest every hour.
 Test each solder, each mod, each block of mods ... and test everything again.


----------



## baronbeehive

mogos said:


> .........
> 
> Capacitors:
> 
> ...


 
  
 Just so I understand in your list of caps:
  
 Capacitors:
  
 1) MKP 60 µF Wima DCP4L056007KD4KYSD 800 V 10 % 4 pcs.
 2) Decoupling - MKP 40 µF Wima DCP4L054007ID4KYSD 800 V 10 % 2 pcs.
 3) PME-140: 0.33uF 275 Vdc Evox Rifa PME271M 6 pcs.
 4) Cathode By Pass By Pass - PME-080: 0.1uF 275Vdc Evox Rifa PME271M 4 pcs.
 5) Cathode By Pass - Elna Silmic 2 470µF/50v 4 pcs.
 6) PSU - Mundorf M-Lytics AG 1500µF 160V 2 pcs.
 7) Coupling - Jupiter Round COPPER, WAX & PAPER, 0.47uF 600VDC 4 pcs.
 8) Decoupling - Audyn MKP Gold Silver 0.33 UF 1200V 2% 4 pcs.
  
 Assuming that's right what are nos. 1 and 3 in the list, maybe they are decoupling and no. 8 is the WCF caps? And the PSU caps are untested for sonic gains, correct?
  
 You guys are racing ahead and I'm hoping to tag along...... I'm, trying a little zen in the meantime.


----------



## coinmaster

> Before the start of modification I plan to meditate for one day
> 
> 
> 
> ...


 
  


> I'm, trying a little zen in the meantime


 
 Zen is what I need. I've spent nearly 100% of my waking hours for the last month and a half picking apart my amp and researching upgrades.
 I feel like I'm staring at a bowl of candy after I just threw up from eating too much of it.
 Words can't express how sick of it I am, but I need to get it done since it's too late to turn back now.
  
 The physical modding is easy and straightforward enough, once you know what to do. It's the constant problem solving and theory crafting with difficult to understand information that makes me wana jump off a bridge. 
	

	
	
		
		

		
		
	


	




 
  
 I'm on the last step, so close to finishing yet still so far since I refuse to build my "zombie" mk6 until I get it working in a spice simulator to be absolutely sure.
 It can't end soon enough.


----------



## Maxx134

mogos said:


> I have to check the original values. Maybe they are as the one indicated on the board and then I will follow it. Thank you for the eventual solution.
> Below is the list of the parts I will install:
> 
> Capacitors:
> ...



Lol , me too. 
Started out small and then exploded into a Project.

You have a truley excellent parts list.
All most optimal that I would choose,
IF I were to extend the bottom a few inches...


That volume IS exactly same one I was thinking to use and the last issue that bothers me.
As I often hear some dust in my volume at times and it annoys the hell out of me...

Same exact issue with the OPPO HA-1 that use same brand pot.
The pot is actually a really nice volume but of course it not good enough "for us" lol.
The shaft and replacement will be the issue though..

Anyways, I like to know about your:
 0.68 Ohm 
100 Ohm 
Where will these be placed?

I myself ended up changing almost all the power supply section resistors due to them being stock blue garbage resistors..
I only left them in the opamp circuit stage as that is low wattage..



baronbeehive said:


> Assuming that's right what are nos. 1 and 3 in the list, maybe they are decoupling and no. 8 is the WCF caps? And the PSU caps are untested for sonic gains, correct?
> 
> You guys are racing ahead and I'm hoping to tag along...... I'm, trying a little zen in the meantime.



You are correct except the PSU caps ARE tested and ARE necessary for sonic gains.
They feed the Decoupling caps to give suatained weight with their impact.
I have HUGE dynamic range and impact on my amp... ]




coinmaster said:


> > The ohmometer was runing up and down from kilo to mega and so on. What the heck??
> 
> 
> 
> ...



Actually this is because of the last stage PSU 330uf caps getting charged by the tester and is not necessary to pull out to test,
Because we all know it is a 56k resistor in these amps.
But you are correct that the only way would be to pull out but risk damaging it.
Anyways they are not the hottest resistors.
The other two next to them (5k1 & 8k2) are..
We should at least update those two.




redge78 said:


> @ Mogos
> 
> I have been through your shopping list and I have understood everything ! Seems all good to me.
> 
> ...




Haha I see he has somthing to hold those jupiters already...
Still, hotglue works well to hold wires in place..

Redge78 is right though.
Change all those blue resistors, and you wont have to worry..
Thats what I did for most of it..


These are hottest resistors on the board, crying to be replaced...



mogos said:


> redge78 said:
> 
> 
> > @ Mogos
> ...



I never heard the "Audyns" , but you are correct in that the WCF cap will be noticable in the top end.
Similar to what I had with the mundorf.
They imparted a change to my super smooth natural jupiters sound.
At first I was not that impressed as the energy seemed disjointed, 
But then they actually integrated together and seemed as one seemless cohesive pair...
I was beginning to desire this energetic combo, but I had the second set jupiters come in so I changed them.
Now my current combo is extremely natural sounding, which is what I was aiming for as I am using with an HD800..

So the point is yes, a combo is good but will take a few hours burn in for them to "blend as one"...
AND I commend you on using your "imagination"...


Also a "combo" is what everyone has already, as most MK6 & MK8 have a coupling cap different from the stock red, unless they didnt upgrade.


----------



## Mogos

baronbeehive said:


> Just so I understand in your list of caps:
> 
> Capacitors:
> 
> ...


 
 1) MKP 60 µF Wima DCP4L056007KD4KYSD 800 V 10 % 4 pcs.                                 DECOUPLING POWER STAGE
 2) MKP 40 µF Wima DCP4L054007ID4KYSD 800 V 10 % 2 pcs.                                  DECOUPLING DRIVER STAGE
 3) PME-140: 0.33uF 275 Vdc Evox Rifa PME271M 6 pcs.                                           DECOUPLING POWER AND DRIVER STAGE 
 4) PME-080: 0.1uF 275Vdc Evox Rifa PME271M 4 pcs.                                              CATHODE BY PASS
 5) Elna Silmic 2 470µF/50v 4 pcs.                                                                              CATHODE BY PASS
 6) Mundorf M-Lytics AG 1500µF 160V 2 pcs.                                                              PSU
 7) Jupiter Round COPPER, WAX & PAPER, 0.47uF 600VDC 4 pcs.                             COUPLING
 8) Audyn MKP Gold Silver 0.33 UF 1200V 2% 4 pcs.                                                  WCF COUPLING


----------



## Mogos

maxx134 said:


> ..................
> 
> I never heard the "Audyns" , but you are correct in that the WCF cap will be noticable in the top end.
> Similar to what I had with the mundorf.
> ...


 
 I had the HD800 for more then 3 years. I understand what you are aiming for. The HD800 has been replaced by Sony MDR-Z7 (slightly moded). 
 And if I can still afford it I am thinking about HiManns 1000
	

	
	
		
		

		
		
	


	




. So a little edginess and speed may be very welcomed. The WCF caps will be soldered in the way for letting easy replacment without the need to move the board (just in case). I have seen how guys are testing the caps. They are changing the caps in the circut using the switch. Can you imagine to have such an additional box with three different sound signatures (read capacitors). My imagination is going wild no good no good. I think Coinmaster shall not read this post 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

mogos said:


> 1) MKP 60 µF Wima DCP4L056007KD4KYSD 800 V 10 % 4 pcs.                                 DECOUPLING POWER STAGE
> 2) MKP 40 µF Wima DCP4L054007ID4KYSD 800 V 10 % 2 pcs.                                  DECOUPLING DRIVER STAGE
> 3) PME-140: 0.33uF 275 Vdc Evox Rifa PME271M 6 pcs.                                           DECOUPLING POWER AND DRIVER STAGE
> 4) PME-080: 0.1uF 275Vdc Evox Rifa PME271M 4 pcs.                                              CATHODE BY PASS
> ...


 
  
 Thanks, I might have to modify some of that though for the "compact" version as I don't have the apartment constructions skills for the "over the top" version, I should think the floor joists would need doubling up at the very least.
  


coinmaster said:


> .......
> I'm on the last step, so close to finishing yet still so far since I refuse to build my "zombie" mk6 until I get it working in a spice simulator to be absolutely sure.
> It can't end soon enough.


 
  
 I think zombie might refer to you after all this  
	

	
	
		
		

		
		
	


	




........ and your hideous Frankenstein monster that you have created out of spare parts waiting for the spark of life.........


----------



## Maxx134

Remember what Redge78 says,
Its all about the EXECUTION, of the installation...
HOW will you solder the parts...
The positions..
The wiring used..
The insulation...
The bends..
The ORDER of which components you will install first...
I would start with power supply,
Then top side(socket side) output wiring and decoupling caps..
Then rest of power resistors and grid resistors..
Then bigger components like the caps...

Remember we need wiring on the WCF caps as they will be placed further away...(pictured)

Remember to NOT solder the Power anode/cathode resistor close to board,
As they need to be away from board to dissipate heat...

The object is not to just install,
But to install as "beautifull" as possible, 
NO SLOP JOBS...
Thats the only way to not encounter problems...
Install gently and carefully..
No rushing allowed..

Take breaks from the "operating table", 
To keep your mind fresh and alert,
 with also a steady hand on that soldering iron..

It is all too easy to melt caps and wires with your soldering iron..

Do not work into the night unless you are wired with drinks, as nightime is our enemy to getting things right..

I made "4X" too many mistakes and had to learn how to troubleshoot/repair this amp without a schematic..

So we want to focus on what works and what is recommended only.

It may be just an amp, but you will be rewarded with an amp that can reach the full potential of the design, 
Which was meant to be an "end-game" level amp...


Edit: yes, I use the schiit yggy for an "operating table"!


----------



## SonicTrance

maxx134 said:


> Remember to NOT solder the Power anode/cathode resistor close to board,
> As they need to be away from board to dissipate heat...


 
 My power resistors for power tubes are fairly close to board as I installed them a long time ago. But they do have direct airflow so should still be OK.
  

  
 The coupling/WCF caps (not pictured) are however positioned over the power resistors for driver stage. Do you recommend extending the leads on those resistors to move them out the way?
  
 Edit: Btw, I bought that same Cardas solder and it's by far the easiest solder I've worked with!


----------



## baronbeehive

Mogos, I've just looked up your parts list and they would appear to fit OK in the space at the bottom of the PCB, with the fans moved, so presumably any problems could only come with the siting of the parts in situ?


----------



## Maxx134

sonictrance said:


> maxx134 said:
> 
> 
> > Remember to NOT solder the Power anode/cathode resistor close to board,
> ...




Yes Cardas is the best solder I ever worked with.

No dont worry about the driver tube anode/cathode power resistors as they wont get as hot.

Also dont worry about caps covering that area.

You might need to bend those zfoils grid resistors to the side a bit, to fit the caps...

Also, I hope you installed the WCF grid resistors in or you will have to pull those big white caps out...

Dam your board looks so cleanly done, beautiful job!


----------



## Maxx134

baronbeehive said:


> Mogos, I've just looked up your parts list and they would appear to fit OK in the space at the bottom of the PCB, with the fans moved, so presumably any problems could only come with the siting of the parts in situ?




Mogos will be using 60uf Wima MKP caps in place of my white caps...

I didnt look at the dimensions to see how these would fit, but these would be the only ones to worry about fitting in a stock slim version..(DCP4L056007KD4KYSD 800V 10 %) 4 pcs.
Edit: 
In his pic they look very nice and compact.


----------



## Maxx134

Aha! 
*snip* never mind I need my glasses looking at these pics..
I see your WCF grid resistors


----------



## SonicTrance

maxx134 said:


> Aha!
> *snip* never mind I need my glasses looking at these pics..
> I see your WCF grid resistors




Yes, don't worry. They're in here. They were one of the first things i did 



Edit: pic


----------



## SonicTrance

Here's how she looks right now:
  

  
 I'm basically done. Only waiting for the resistors for psu stage to arrive and then I can finally test her. I've been extremely careful with each step so I doubt that there's any problems, but you never know.
  
 I also have pics of each step that I'll post once I'm finished and I've verified that everything's working 
	

	
	
		
		

		
			





 
  
 Edit: Look Maxx: No glue!


----------



## Mogos

baronbeehive said:


> Mogos, I've just looked up your parts list and they would appear to fit OK in the space at the bottom of the PCB, with the fans moved, so presumably any problems could only come with the siting of the parts in situ?


 
 Fans have to be moved definetly. But I have some doubts if it is possible to fit the big Wimas inside the original housing. I have moved the fans in the expanded one because of the caps. Well maybe in horizontal position.


----------



## baronbeehive

Just trying to work out from your diagram in the resistances section which are the various resistors and how many of each? There appear to be 4 driver stage resistors (anode/Cathode), 6 grid resistors and 4 WCF grid resistors. You also mention power stage resistors in section 5.1, and in section 5.2 you mention anode resistors, grid stopper resistors, common cathode resistors and then power tube grids, that's where you've totally lost me so could you explain in language suitable for 2 year olds please.
   
 Quote:


mogos said:


> Fans have to be moved definetly. But I have some doubts if it is possible to fit the big Wimas inside the original housing. I have moved the fans in the expanded one because of the caps. Well maybe in horizontal position.


 
  
 Yes thanks I was wondering about those.


----------



## Maxx134

baronbeehive said:


> you mention anode resistors, grid stopper resistors, common cathode resistors and then power tube grids, that's where you've totally lost me so could you explain in language suitable for 2 year olds please.



Everything you said before this was good.....

The only thing left for you to be clear on:

1-the anode cathode resistors for the power tubes 

2-resistors for PSU stage..


 your choice of how many on PSU to replace,

 but I would at least replace the 5k1 and 8K2 resistors as they are the hottest resistors in the amp.
Replace these and the anode/cathode resistors with MILLs wirewounds.

The driver tube anode/cathode is acutally better suited with an "audio grade" resistor..
In other words, it assured to have a good sound.
We can all agree that on paper a resistor should not impart any sound,
But this is real life where materials, types, and everything matters, 
So like I always say,
 this thread pertains to "what works", and what's recommended works nicely.



 Depending on your amp age,
 you may have old, or newer version which doubles the resistors,

 So you need to measure those two power supply stage resistor sections.
(5k1 & 8k2)
Anything else extra, is your call..


----------



## Maxx134

sonictrance said:


> Here's how she looks right now:
> 
> 
> 
> ...



Hey!
No fair!
My amp was the "gunia pig:!
Lol
How you get those PSU caps to hold?
Double sided foam tape?
If so, I would recommend some extra glue! Ha!


----------



## baronbeehive

So would the white Mundorf Mcap 47µF's mentioned on page 1 substitute in place of the big WIMA's and keeping the 6 PME-140 Evox Rifa's as mentioned previously?
  
 Also would the 220µF 63V Mundorf ECap AC RAW caps you mentioned for the cathode by pass work well with the PME-080 0.1uF Evox Rifa's, not sure what you recommended on this.


----------



## coinmaster

My "MK6 Zombie Ressurection" preliminary thread is up.
 The time is nigh, just waiting on the parts to get delivered.
 http://www.head-fi.org/t/786458/little-dot-mk6-zombie-resurrection-ultra-mods#post_12044764


----------



## Maxx134

Yes on both counts..and :

I am using the RiFA .1uf on other side of board but same solder points..

Also you can try Redge78 suggestion of using the Elna Silmic 2 470µF/50v with RIFA combo in first page :
 
But it wont fit compact version unless you lay them flat and put the RIFA on other side of board like what me & Mister-X did..


----------



## baronbeehive

That's a great help Maxx, the board will have to come out anyway, my electronics man is already taking the valium. Lets see what this lump of tin will do. Should be interesting.........
  


sonictrance said:


> Here's how she looks right now:
> 
> 
> 
> ......


 
  
 Now that is QUALITY !!! And you've got it all to fit...... BRILLIANT. Could you say what you parts you've used I would be interested because I want mine to fit as well. I can't remember if you have the MKVI.


----------



## baronbeehive

coinmaster said:


> My "MK6 Zombie Ressurection" preliminary thread is up.
> The time is nigh, just waiting on the parts to get delivered.
> http://www.head-fi.org/t/786458/little-dot-mk6-zombie-resurrection-ultra-mods#post_12044764


 
 Congratulations on getting  your own thread up and running, that's great after all that hard work.


----------



## Maxx134

baronbeehive said:


> That's a great help Maxx, the board will have to come out anyway, my electronics man is already taking the valium. Lets see what this lump of tin will do. Should be interesting.........
> 
> 
> 
> ...



I just PMed him that pic is making me drool! 
Lol
Here is info I PMed him but feel a good REMINDER for everyone:


Quote:
The ONLY thing that can go wrong, is the brittle stock wire that comes from the regulators to the power supply(circled):

they broke on me twice,
So check before closing..

Also, I know that the wire from the rear jacks that run alongside the body to the front jacks are a pain in ass to replace:


BUT ...

IF you want to hear FULL POTENTIAL of this amp,

You will NEED to replace these stock wires!

Stock cable is "poor" wire!

I replaced mine with 3-conductor silver plated cable, noted on first page...
Actually any good quality 3-conductor will do!

I can only recommmend 3-conductor, because it reduces the MESS of wires you would have if not using 3-conductor like I used...
And yes I tried using 3 single conductors, twisted..
It was a huge ugly mess!
Lol


Goodluck!


----------



## SonicTrance

maxx134 said:


> Hey!
> No fair!
> My amp was the "gunia pig:!
> Lol
> ...



Haha
Yes, I'll use some double sided tape on them once I've installed the resistors. Right now they're just laying there, being pretty 



baronbeehive said:


> That's a great help Maxx, the board will have to come out anyway, my electronics man is already taking the valium. Lets see what this lump of tin will do. Should be interesting.........
> 
> 
> Now that is QUALITY !!! And you've got it all to fit...... BRILLIANT. Could you say what you parts you've used I would be interested because I want mine to fit as well. I can't remember if you have the MKVI.



Thanks!
Yes, I have mk6. I can post a partslist tomorrow as it's late over here and I have to sleep


----------



## Maxx134

coinmaster said:


> My "MK6 Zombie Ressurection" preliminary thread is up.
> The time is nigh, just waiting on the parts to get delivered.
> http://www.head-fi.org/t/786458/little-dot-mk6-zombie-resurrection-ultra-mods#post_12044764



Congradulations I just checked it.
Seems written like the antithesis/dark side of this this thread...
Therefore I must post:

Lol!

Resist the darkside...

I know Coin you have chosen your path.. 
It is too late for Coin,
A dangerous and powerfull road he has chosen...
Full of trials till its fully realized.


I too wanted to exclaim how good the MK8 can be,
But any form of arrogance repulses me. 
I rather say it reaches that level of end-game toys to have,
And fully realize there is never an "absolute" end game amp..

Something you will not believe if going over to the "darkside"..


----------



## coinmaster

> But any form of arrogance repulses me.


 
 Only if it's serious 
	

	
	
		
		

		
			





 
 I'm never serious.
 Oh wait you said any form, I guess I'm repulsive then


----------



## SonicTrance

baronbeehive said:


> Now that is QUALITY !!! And you've got it all to fit...... BRILLIANT. Could you say what you parts you've used I would be interested because I want mine to fit as well. I can't remember if you have the MKVI.


 
 I promised a parts list, so here you go:
  
*Coupling caps*:
 Mundorf Supreme S/G/O 0,68uf
  
*WCF coupling:*
 Mundorf Supreme S/G/O 0,47uf
  
*Decoupling caps:*
  
 Output stage:
 Mundorf Mcap 33uf, Rifa PME271 0,33uf
  
 Preamp stage:
 Mundorf Mcap 15uf, Rifa PME271 0,33uf
  
*Chathode bypass caps:*
 Mundorf E-cap 220uf, Rifa PME271 0,1uf
  
*PSU caps:*
 Mundorf M-Lytic 1500uf 160vdc
  
*Resistors:*
 Power tube power resistors:
 Mills MRA5 330R x 8
  
 Driver tube power resistors:
 TKD 2w 220K metal film x 4
  
 Grid resistors:
 Charcroft Z-foils 10K x 4, 1K5 x 2
  
 WCF grid resistors:
 Takman 0,25w 300R x 4
  
 PSU stage resistors: (yet to be installed)
 Mills MRA5 8K2 (parallel)
 Mills MRA5 5K1 (parallel)
 Mills MRA5 3K3 x 2
 Mills MRA12 56K x 2 
  
*Output cables:*
 20awg silver plated PTFE 19 strand wire, doubled and twisted. From board to jacks.
  
*Note!*
 You can fit the slightly larger 47uf mcaps for the output stage decoupling. I only chose 33uf for ease of installation, I might change these in the future.
 This is NOT a finished mod as I still haven't got my psu stage resistors, so I can't tell you how it sounds, but everything fits like a glove in the chassis


----------



## Maxx134

sonictrance said:


> *PSU stage resistors: (yet to be installed)
> Mills MRA5 8K2 (parallel)
> Mills MRA5 5K1 (parallel)
> Mills MRA5 3K3 x 2
> ...


*

Excellent...
The resistors locations you have chosen,
Cover all the most important points to replace, 
Which are exactly what I would suggest:

Color Code:
Green = recommended
Yellow = suggested
Red = Highly suggested

Purple = optional


You have chosen well.
Although I would like to see a bit more than 15uf for preamp/driver tubes, you can always add more.*


----------



## SonicTrance

maxx134 said:


> Excellent...
> The resistors locations you have chosen,
> Cover all the most important points to replace,
> Which are exactly what I would suggest:
> ...


 
 It's mostly thanks to you and this thread. I only go by recommendation and try to learn in the process.
 Yes, the 15uf was chosen because of its size. The bigger 22uf wont fit nicely. But we discussed that cap a little in PMs before I ordered, so I'm confident that it'll do.


----------



## Maxx134

This is latest pic of my unit to compare:

Nowhere as clean as Mister-X

Notice the size of the .22uf red WIMA FKP at the front of unit I am using for driver tube decoupling..

Also:
I using modeling clay on all electrolytics to dampen them...
It was a "vodoo audio" mod to try.
Hasn't been verified to make any difference, so I just left it..


----------



## baronbeehive

......yours isn't that bad Maxx......
  
 Quote:


sonictrance said:


> I promised a parts list, so here you go:
> 
> *Coupling caps*:
> Mundorf Supreme S/G/O 0,68uf
> ...


 
  
 Yes thanks. My preliminary list will be much like yours except that the coupling caps will be Mundorf S/O .33uF, WCF caps will be Audyn True Copper .22uF which I had but sold on so will have to repurchase. I also will do the main position resistors and the minumum necessary output wiring including possibly the regulators to the power supply and rear to front jacks and leave it at that I think. How long would it take for a competent professional, (not me!), to replace all the wiring recommended in page 1 just in case I do decide?
  
 Thats it subject to revisions......... oh, and then there's the tricky question of the bling........


----------



## Mogos

Shinkoh Tantalum resistors have landed.

 So no more excuses for not starting the mod. Time is required but I will manage to have some.
 Special tools for desoldering tested and ready.

 For the pot even more specialized


----------



## Maxx134

mogos said:


> ...
> Special tools for desoldering tested and ready.
> 
> 
> For the pot even more specialized



Interesting, I have not seen these before..


----------



## coinmaster

Wow that bottom one would be really nice for me to have. I can't get the pot out because it's impossible to get rid of all of the solder between all of the pins.


----------



## Mogos

I plan to do it in two stages (about pot). First to remove solder as mutch as possible with the desoldering pump and then heat up the pins with the special tip. It is done/shaped by me. Just old transformer soldering iron and copper wire shaped as you can see on the photo.


----------



## Mogos

I have just find out that they have send me 330R instead of 300R.


----------



## baronbeehive

Going back to resistors for a moment, I think I have the old board so the 8k2 and 5k1 readings may be accurate but are you saying that you should put in new resistors equal to the readings of the old ones or to the board readings, and were the right resistors put in in the first place? I was wondering because of the need to double up these 2 resistors.


----------



## SonicTrance

baronbeehive said:


> Going back to resistors for a moment, I think I have the old board so the 8k2 and 5k1 readings may be accurate but are you saying that you should put in new resistors equal to the readings of the old ones or to the board readings, and were the right resistors put in in the first place? I was wondering because of the need to double up these 2 resistors.




Use same value resistors to replace the old ones. I don't think the old board had paralleled resistors? Do you have the brown Dale grid resistors? Pics please


----------



## Maxx134

mogos said:


> I have just find out that they have send me 330R instead of 300R. :mad:



Which resistors grid?
Or an anode/cathode of power tubes?




baronbeehive said:


> Going back to resistors for a moment, I think I have the old board so the 8k2 and 5k1 readings may be accurate but are you saying that you should put in new resistors equal to the readings of the old ones or to the board readings, and were the right resistors put in in the first place? I was wondering because of the need to double up these 2 resistors.



Show me a pic of your *amp* to see what they used you must go by what is inserted.

Check color code amount, not measured,
 because measured will not be accurate if it's an old or blue resistor


----------



## SonicTrance

Who wants to buy these high quality parts from me? Starting bid @ $100


----------



## baronbeehive

NICE...... not a burnt one anywhere


----------



## coinmaster

Hello peoples.
 With my efforts at reverse engineering the amp and the help of many others I have effectively deduced and just finished writing pretty much all of the "downfalls" of this amp and have come up with ways to "fix" it.
 Keep in mind this is from an engineering perspective, not all imperfection is a bad thing sonically however the upgrades have great promise to improve on overall general sonics, and ironically it's dirt cheap. I'm almost hoping they all suck because of all the money I spent on capacitors recently 
	

	
	
		
		

		
		
	


	




 I just spent 400 bucks on those .22uf jupiter WCF caps too.
  
 Keep in mind it's beyond the scope just "changing components". It's just as easy to apply but it does involve alterations to the design rather than simply changing the quality of parts.
  
 The full details here
  
  
 http://www.head-fi.org/t/786458/little-dot-mk6-zombie-resurrection-ultra-mods
  
  
 First trials should begin on monday.


----------



## Maxx134

sonictrance said:


> Who wants to buy these high quality parts from me? Starting bid @ $100




HAHA!
You forgot to label the parts:


----------



## baronbeehive

........ I see they are still for sale.....
  

  


sonictrance said:


> Use same value resistors to replace the old ones. I don't think the old board had paralleled resistors? Do you have the brown Dale grid resistors? Pics please


 
  
 The WCF ones appear to be Dale resistors but not the others.


----------



## Maxx134

baronbeehive said:


> ........ I see they are still for sale.....
> 
> 
> 
> ...



You have THE BEST stock board I have seen!
This must be an old version!

Also:
This board PROVES that we were right ALL ALONG in changing those WCF grid resistors...!!

You do not have to replace any of the small resistors on your whole board..
Although, the Shinkoh should still be a preferred option, 
But the MAIN THING,
IS NO CHEAPO BLUE RESISTORS on your board!!


Now, onto this pic:


Notice that you have either some old wirewound, or most likely carbon film resistors for the powertube "Anode/Cathode"....
These need to come out either way as neither is sonically optimal.
Replace with MILLs non-inductive MR5 Wirewould.
Any wirewould older is surely inductive..

Also, the Driver tube Anode/Cathode is certainly using a Carbon film.
Carbon film is widely known to have a themal noise curve according to temp.

Replace with an audio quality resistor ad suggested,
Because this is the driver stage so small signal changes matter here...

Now onto last but not least, your ONLY BLUE CAP!!!
In PSU stage!
Replace with Mills MR5 and you are done there!.
The others are most likely high watt Carbon films, but that doesn mayter as they are in PSU stage and there is filtering there..

Edit: really up to you if you want to do more.
Measure&read the resistor value.


----------



## Mogos

maxx134 said:


> Which resistors grid?
> Or an anode/cathode of power tubes?


 
 WCF grid resistors 300R. Correct ones  are on the way


----------



## baronbeehive

maxx134 said:


> You have THE BEST stock board I have seen!
> This must be an old version!
> 
> .........


 
   
 yes, circa 2008, its got a lot Dales in which I assume are no longer put in now!
  
 Quote:


maxx134 said:


> ........
> You do not have to replace any of the small resistors on your whole board..
> Although, the Shinkoh should still be a preferred option,
> But the MAIN THING,
> IS NO CHEAPO BLUE RESISTORS on your board!!


 
  
 ............ that's fantastic!
  


maxx134 said:


> Now, onto this pic:
> 
> 
> Notice that you have either some old wirewound, or most likely carbon film resistors for the powertube "Anode/Cathode"....
> ...


 
  
 OK, many thanks! To sum up I'll need 4 x 220k Ohm driver stage (you've marked "OK carbon" in yellow), 4 x 330 Ohm power stage (crossed out in yellow), and 1 (marked "bad" in purple) which is the 4k1 resistor, I think I only need one of these not the 2 8k2? In actual fact those power stage resistors are new Kiwame's but I put in the carbon film ones which are obviously not optimal unfortunately 
	

	
	
		
		

		
		
	


	



  
 MisterX I think you ordered 4 too many power stage resistors....... any going cheap???


----------



## SonicTrance

You got 4 more power resistors on top side of the board. So you'll need 8 of them.


----------



## Maxx134

*which is the 4k1 resistor, I think I only need one of these not the 2 8k2? *

Using two 8k2, is equal to one 4k1 ,
And can take double the watt rating..
We ALWAYS want more watt capability here,
As they are hottest resistors on the board.

The board will get hot anyway because of the tubes, 
But my concern has always been that the capacitors in this area are getting heat from the resistors thru the board traces,
So we need good power resistors here, not blue ones...

Blue resistors are supposed to be metal film, but cheap sources like taiwan produces resistors which are only ok for low watt circuit conditions...
NONE of the higher wattage blue resistors hold their value, mainly because our amp really does get hot.
Most electronics dont get as hot as a tube amp can.
So you may never have an issue with these blue resistors in other gear.
But, my position is, they are not good for this amp..
This is NOT LittleDot fault at all, if a manufacturer doesnt produce as claimed.
So I dont blame LittleDot at all and they may be aware of this, which is why they started to use double resistor solution..


----------



## Maxx134

sonictrance said:


> You got 4 more power resistors on top side of the board. So you'll need 8 of them.



YES! 
THEY are hiding behind the Cathode bypass caps on socket side of board!


----------



## coinmaster

Those sneaky little bastards. How dare they.


----------



## baronbeehive

sonictrance said:


> You got 4 more power resistors on top side of the board. So you'll need 8 of them.


 
  
 Dammit, I was hoping to save some dosh!
  
 Quote:


maxx134 said:


> *which is the 4k1 resistor, I think I only need one of these not the 2 8k2? *
> 
> Using two 8k2, is equal to one 4k1 ,
> And can take double the watt rating..
> ...


 
  
 Oh I see, I'm learning!
  


maxx134 said:


> This is NOT LittleDot fault at all, if a manufacturer doesnt produce as claimed.
> So I dont blame LittleDot at all and they may be aware of this, which is why they started to use double resistor solution..


 
  
 No, absolutely, how can we blame them when they've produced this fantastic amp what we are all getting so much enjoyement from. Whenever I email David I always say hey I'm still enjoying your Little Dot!!
  
 Thanks guys for all your encouragement, I feel that I could begin to tackle something like this now myself but I think I would be well advised to get the main mods done by a professional, then maybe if I want to say upgrade to Jupiters or some such then that is something I could tackle.


----------



## SonicTrance

baronbeehive said:


> Oh I see, I'm learning!
> 
> 
> No, absolutely, how can we blame them when they've produced this fantastic amp what we are all getting so much enjoyement from. Whenever I email David I always say hey I'm still enjoying your Little Dot!!
> ...




But you're already saving as you dont "need" to change that many resistors on your board. Lucky person


----------



## baronbeehive

sonictrance said:


> But you're already saving as you dont "need" to change that many resistors on your board. Lucky person


 
  
 Can I help it if I was the first here to spot this beautiful beast way back in 2008, he he.......


----------



## coinmaster

> Oh I see, I'm learning!


 
 Can you tell me what a long tail pair phase inversion is?
 Calculate the square root of cheese divided by the body fat % of rosie o'donnell plus the amount of dollars you've spent so far on your upgrades and get back to me.


----------



## baronbeehive

coinmaster said:


> Can you tell me what a long tail pair phase inversion is?
> Calculate the square root of cheese divided by the body fat % of rosie o'donnell plus the amount of dollars you've spent so far on your upgrades and get back to me.


 
  
 Now you're just showing off!! But I haven't spent any dollars at all.......(£'s actually)..... we do have a long tailed tit here, I've seen them in the garden


----------



## Maxx134

Its good to learn the generalities.
Not many would deal with the more tedious number crunching procedures..

Of course coinmaster is just talkn outa his tail..


In contrast to that, here is some real info:

Question,
What do these pics have in common?:



And 



And:



Answer:
They have a common condition of an "old" & "failing" Anode resistor..
Yet, In our amps, it is more like premature wear if you have the new blue "metal films"(?)..

So how do you know without opening up amp?

The sonic trait is a slight noise/hissing/crackle sound,
Similar to a tube dying.
So it may not be your tubes if you experience that..

I personally had a NOS tube brand new die in front of me, portraying just that.
Amplitude loss, hiss crakle and slight pop..
Then dead!!..
And it looked so new!
No sign of damage either!
The seller is currently replacing them so no loss..


----------



## baronbeehive

So the cost of parts comes to the grand total of £175, absolute bargain in anyones language...... Coinmaster was right when he said he said that it was dirt cheap to build/modify this amp. I can't wait and it's interesting everyone has chosen slightly different combinations. Should be good when the reports of the sound come in.


----------



## coinmaster

If my upcoming mods work as well as the people and data suggest, especially mod #7, the price will go down even more, a lot more.


----------



## SonicTrance

I'm finally done! And it WORKS! What a relief, lol 
	

	
	
		
		

		
		
	


	



  
 Here's some time lapse pictures. All pics are high res. Click "original image" for mega size! I'll post sonic impressions after I got some serious listening time. Any questions, don't hesitate to ask
	

	
	
		
		

		
		
	


	



  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  
 I'm so happy right now!


----------



## baronbeehive

sonictrance said:


> I'm finally done! And it WORKS! What a relief, lol
> 
> 
> 
> ...


 
  
 How long would you say it took?
  
 Really great job! You can go and get some sleep now.


----------



## SonicTrance

baronbeehive said:


> How long would you say it took?
> 
> Really great job! You can go and get some sleep now.


 
 I've worked on it a few hours a day for 2 weeks. I'm sure it can be done a lot faster, but since this was my first time doing something like this I was very careful with each step.
  
 Thank you!


----------



## Redge78

This is electronic pornography ! Well done.
  
 We will be eagerly waiting for your listening feedbacks


----------



## SonicTrance

redge78 said:


> This is electronic pornography ! Well done.
> 
> We will be eagerly waiting for your listening feedbacks




Thanks!
Working night shift this week so I'm free tomorrow  I will be listening then. That I can promise you


----------



## Maxx134

sonictrance said:


> baronbeehive said:
> 
> 
> > How long would you say it took?
> ...



I never seen a neater job!
You have excellent modding skills!
We will need to use them for first page!


----------



## Maxx134

Also, once you have some impressions, 
Please also let us know whether you have the amp on high or low gain setting..


----------



## SonicTrance

maxx134 said:


> I never seen a neater job!
> You have excellent modding skills!
> We will need to use them for first page!




Thanks Maxx! Really appreciate it


----------



## SonicTrance

Time for some sonic impressions.
  
 First off I just like to thank Redge and Maxx for making this thread and all the extensive testing they have done, amazing work guys!
  
 So, how does it sound? Basic sound signature is the same as before as I already had the Mundorf S/G/O ,68uf coupling caps and power resistor mod done a few months back. BUT the improvement in SQ is still as dramatic with these extra mods in place as it was when first upgrading coupling caps! Yet another layer of "dirt" has come off and lets the music shine.
 The first thing I noticed was the SPEED! It's fast and accurate, which is very nice. Huge improvement there. Details were great before but are even greater now. Very nice and sweet mid range.
  
 At first I thought the bass was lacking, BUT after a while of listening I realized the bass were actually better than before, much more accurate and detailed with huge impact and slam! I guess the bass must have been a little "muddy" before, that's why I thought it was lacking now, but I just had to get used to the new IMPROVED sound! 
  
 There're also other things that has improved...
 Background is a lot darker. It's not pitch black (we are still using tubes after all), but very quiet. I also had this annoying noise when changing volume before. It could only be heard when no music was playing, but still quite annoying. That is now completely gone! I thought the noise had to do with the pot. As I haven't touched the pot, I was clearly wrong. I'm using the same sets of tubes I used before doing these mods, Mullard ECC35's and GEC A1834's.
  
 It's still early impressions though, I've only listened a few hours. So things might change with more burnin 
	

	
	
		
		

		
			




  
 One more thing:
 I don't have a new pic of this but, if you're doing the compact mod and are using external fans it's a good idea to use grills between the fan and case, to prevent any cap vs fanblade action.
  
 Here's how I had my fans before. I have now installed fan filters with grills in between case panel and fans.


----------



## baronbeehive

Very interesting! That's a little surprising that the bass impact was not immediately apparent with your .68uF Mundorfs and PSU mods however the fact that it sounds cleaner would be in accord with a better signal reproduction getting rid of bass boom which I'm all in favour of. Bass is the only area I find that needs slight improvement with the stock LD. I have a feeling if I remember right that every Mullard I have heard is slightly lacking on bass but where they are good is mid range so you might find different tubes are in order possibly.
  
 Also the speed...... well the LD was already good on that!
  
 It would be interesting with a mix of caps such as I'm thinking of to see how that affects sound, you've obviously got Mundorf ++ sound now.
  
 Re: the fans were you getting some sort of interference then?


----------



## SonicTrance

baronbeehive said:


> Very interesting! That's a little surprising that the bass impact was not immediately apparent with your .68uF Mundorfs and PSU mods however the fact that it sounds cleaner would be in accord with a better signal reproduction getting rid of bass boom which I'm all in favour of. Bass is the only area I find that needs slight improvement with the stock LD. I have a feeling if I remember right that every Mullard I have heard is slightly lacking on bass but where they are good is mid range so you might find different tubes are in order possibly.
> 
> Also the speed...... well the LD was already good on that!
> 
> ...


 
 Then you and I have completely different opinions on the Mullard ECC32/33/35's. Granted I'm using 35's at the moment and the 32's and 33's do have more sub-bass, but the 35's are not lacking in bass IMO. And like I said, I had to get used to the better bass sound! 
	

	
	
		
		

		
		
	


	



 I've not heard a better tube than the Mullards. But it's personal preference of course.
  


> Also the speed...... well the LD was already good on that!


 
 Not if you compare it to my unit...
	

	
	
		
		

		
		
	


	



  


> Re: the fans were you getting some sort of interference then?


 
 No, the grills are to prevent any caps from touching the fan blades. Don't get me wrong, my caps are secure, this is just for peace of mind. I realize that the fan frame acts like a grill but it doesn't cover the blades completely.


----------



## baronbeehive

sonictrance said:


> Then you and I have completely different opinions on the Mullard ECC32/33/35's. Granted I'm using 35's at the moment and the 32's and 33's do have more sub-bass, but the 35's are not lacking in bass IMO. And like I said, I had to get used to the better bass sound!
> 
> 
> 
> ...


 
  
 OK, the mullards I've heard were admittedly on my other amp but I did love the mid range aspect and the tubeyness.


----------



## SonicTrance

baronbeehive said:


> OK, the mullards I've heard were admittedly on my other amp but I did love the mid range aspect and the tubeyness.




Ok, but what tubes are you talking about then? I'm sure that not all tube types made by Mullard sounds the same...


----------



## coinmaster

I'm also surprised you didn't notice a *huge* upgrade in bass quality from the psu mods. My bass quality jumped literally 5-10 fold, it was like a different beast.
 Then again, I also added a 150uf mkp cap to the driver decoupling at the same time, maybe that had something to do with it. Or it could have something to do with the fact my psu mod consists of those industrial AVX caps, you can't really buy caps with better specs than those that I've seen unless you're nasa.
  
 Did anyone else notice a similar bass quality increase when upgrading the PSU or driver decoupling?


----------



## SonicTrance

coinmaster said:


> I'm also surprised you didn't notice a *huge* upgrade in bass quality from the psu mods. My bass quality jumped literally 5-10 fold, it was like a different beast.
> Then again, I also added a 150uf mkp cap to the driver decoupling at the same time, maybe that had something to do with it. Or it could have something to do with the fact my psu mod consists of those industrial AVX caps, you can't really buy caps with better specs than those that I've seen unless you're nasa.
> 
> Did anyone else notice a similar bass quality increase when upgrading the PSU or driver decoupling?


 
  
 To quote myself...
  


> BUT after a while of listening I realized the bass were actually better than before, much more accurate and detailed with huge impact and slam!


----------



## coinmaster

Well my point being that when I upgraded, it was immediately noticeable, I wasn't exaggerating about the 5-10 fold increase in bass.
 You mentioned at first you thought the bass was lacking, there's no way you could have made that mistake if the bass increase was to the same level as mine.
 Sure the overall sound was better, but the bass change completely.


----------



## baronbeehive

sonictrance said:


> Ok, but what tubes are you talking about then? I'm sure that not all tube types made by Mullard sounds the same...


 
  
 EL84 and ECC83. I've tried them on my Miniwatt. I'm sure they don't sound the same but they do have a characteristic sound though which distinguishes them from other makes. I haven't tried them on the LD because in the tube rolling thread the ones I saw were not particularly rated but those may not have been the ECC32/33/35's which I'm quite interested in now because of what you say.
  
 Edit: I remember now the mullards I saw in the tube rolling thread not rated were the power tubes
  
 But the improvemenet in speed you mention, that is fantastic and that's what I already love on the stock amp, the LD's are not slow, sloppy wet old style tube amps at all!
  
 And the improvement over and above the original caps upgrade makes this upgrade really seem worthwhile......... how much better can it get


----------



## SonicTrance

baronbeehive said:


> EL84 and ECC83. I've tried them on my Miniwatt. I'm sure they don't sound the same but they do have a characteristic sound though which distinguishes them from other makes. I haven't tried them on the LD because in the tube rolling thread the ones I saw were not particularly rated but those may not have been the ECC32/33/35's which I'm quite interested in now because of what you say.


 
 Yes, the sound characteristics can very well be the same. I have not heard the EL84's or ECC83's though. 
  
 I can recommend the ECC32/33/35's. I did a comparison in the other MK6/8 thread. Bare in mind the ECC32's draws almost 1A of heater current...


----------



## baronbeehive

sonictrance said:


> Yes, the sound characteristics can very well be the same. I have not heard the EL84's or ECC83's though.
> 
> I can recommend the ECC32/33/35's. I did a comparison in the other MK6/8 thread. Bare in mind the ECC32's draws almost 1A of heater current...


 
  
 Yes I remember your review and your good rating of them.
  
 BTW what are you doing on this thread........... you should be listening to the results of your hard labour


----------



## SonicTrance

baronbeehive said:


> Yes I remember your review and your good rating of them.
> 
> BTW what are you doing on this thread........... you should be listening to the results of your hard labour


 
 I'm multitasking baby, listening as I type
	

	
	
		
		

		
		
	


	



  
 Just so there's no more confusion...
 I'm very happy with the sound, including the bass, lol. It's really mind blowing!


----------



## baronbeehive

sonictrance said:


> I'm multitasking baby, listening as I type
> 
> 
> 
> ...


 
  
 Thanks.......that's what we wanted!!!


----------



## coinmaster

It's been months since I've been able to listen


----------



## Mogos

Guys look what I have found out. There is no metal in metal? I have bought them here: http://www.goodcomponent.com/. Was I cheated. Whether all Chinese Companies are one big scam?
  

 This type of tube sockets are not fitting the hole arrangment.


----------



## coinmaster

Not all chinese stuff is a scam. But you should assume they are.
 Buy from http://www.partsconnexion.com/index.html


----------



## SonicTrance

Guys, the more I listen, the more the sound is opening up. I can't explain what's happening. Good stuff, good stuff indeed. I'm speechless! If you're thinking about doing these mods but aren't sure? Think no more, just do it, NOW!


----------



## Maxx134

That is normal in electronics for parts to "settle in"..
Not just caps, but remember whole circuitry is operating at a highly precise level now, especially with the zfoils and others which are all higher tolerance..
Dont forget you have both your PSU electrolytics and your Decoupling caps all new...

As dynamic and focused as you think it is now, expect further improvements as it burns in...

I myself have been experiencing this almost every time I turn it on it changes, always giving me MOre!
Its quite a shocking process and just beyond description..

I am at a point where every good tube I put in is just highly musical, 
And I can choose different signatures at will..
Highly addicting to swap tubes now!


----------



## SonicTrance

maxx134 said:


> That is normal in electronics for parts to "settle in"..
> Not just caps, but remember whole circuitry is operating at a highly precise level now, especially with the zfoils and others which are all higher tolerance..
> Dont forget you have both your PSU electrolytics and your Decoupling caps all new...
> 
> ...


 
 No kidding! I can't believe what I'm hearing to be honest, the quality is astounding!
  
 Just rolled in a pair of Mullard ECC33's now, and yes, tuberolling is still very noticeable! I'm blown away once again.


----------



## SonicTrance

> Background is a lot darker. It's not pitch black (we are still using tubes after all), but very quiet. I also had this annoying noise when changing volume before. It could only be heard when no music was playing, but still quite annoying. That is now completely gone! I thought the noise had to do with the pot. As I haven't touched the pot, I was clearly wrong.


 
 Maxx, 
 The above "side effects" of the upgrades are very nice. It has to be the z-foils, correct? As they're just by the pot?


----------



## Maxx134

sonictrance said:


> > Background is a lot darker. It's not pitch black (we are still using tubes after all), but very quiet. I also had this annoying noise when changing volume before. It could only be heard when no music was playing, but still quite annoying. That is now completely gone! I thought the noise had to do with the pot. As I haven't touched the pot, I was clearly wrong.
> 
> 
> 
> ...



No, although the zfoils are doing alot more than being in signal path, you have alot of parts contributing to your sound.
Remember my "Quadfecta" pic.
You essentially changed all at once, 
not in stages like me..
You have your Rifas and just everything we suggested is playing a part, or we would not have included it into first page..
So you essentially went into this with just a coupling cap upgraded.
The changes for you will be monumental bordering dumbfounding..
Sorry for you to have to take in so much all at once..


----------



## Maxx134

Woops I didnt see you were talkn about the pot..

The pot is actually a picky thing..
Having the unit upside down & sideways also removed the dust noise,
But that comes as goes,
Probably due to fan blowing air into the unit.
I have not looked too much into this pot, but I believe it is prone to this issue..

Just a couple of swipes up and down while unit is off will keep that noise away...


----------



## SonicTrance

maxx134 said:


> No, although the zfoils are doing alot more than being in signal path, you have alot of parts contributing to your sound.
> Remember my "Quadfecta" pic.
> You essentially changed all at once,
> not in stages like me..
> ...


 
 This is very true, lol. I would also recommend doing it in stages in case something goes wrong, you'd know exactly what it is. It's so much more work though (if you manage to get it right first time that is)


----------



## baronbeehive

sonictrance said:


> Guys, the more I listen, the more the sound is opening up. I can't explain what's happening. Good stuff, good stuff indeed. I'm speechless! If you're thinking about doing these mods but aren't sure? Think no more, just do it, NOW!


 
  I certainly will!!!
  
 Would you have been able to fit any larger MCaps in, the space look pretty tight especially up against the headphone socket?
  
 As a side issue what is the construction of your Mullard ECC35's, there appear to be 2 types, one cylindrical plates the other I can't quite see what they are.


----------



## SonicTrance

baronbeehive said:


> I certainly will!!!
> 
> Would you have been able to fit any larger MCaps in, the space look pretty tight especially up against the headphone socket?
> 
> As a side issue what is the construction of your Mullard ECC35's, there appear to be 2 types, one cylindrical plates the other I can't quite see what they are.


 
 The only caps that I installed that could easily increase in size are the power stage decoupling. It is possible to fit the one size larger mcaps 47uf. If I rearranged the 10 caps in the bottom of pic, I could possibly fit the one size larger mcap 22uf driver stage decoupling as well. The 22uf are 29x44mm in size vs. 26x39mm for 15uf (the S/G/O's are 26x41mm)
 It would NOT be possible to increase size of all those ten caps though.
  

  
  
 The Mullard ECC35's only have ONE style plates. All others are NOT true Mullards. There're however both black and grey plate versions. Click "original image" for large size to study the plates. 
	

	
	
		
		

		
		
	


	



  

  
 Also the ECC33's have the same style plates as ECC35's. The ECC32's also have same style plates but both long and short version, but they have ST shape glass so very hard not to recognize


----------



## baronbeehive

sonictrance said:


> The only caps that I installed that could easily increase in size are the power stage decoupling. It is possible to fit the one size larger mcaps 47uf. If I rearranged the 10 caps in the bottom of pic, I could possibly fit the one size larger mcap 22uf driver stage decoupling as well. The 22uf are 29x44mm in size vs. 26x39mm for 15uf (the S/G/O's are 26x41mm)
> It would NOT be possible to increase size of all those ten caps though.
> 
> .....


 
  
 Looking at your pic the .47uF's are 4mm wider and 5mm longer so thats a total of 20mm longer and it doesn't look like you have the room? Also the extra width looks like it would push your .15uF's up against the headphone socket?


----------



## SonicTrance

baronbeehive said:


> Looking at your pic the .47uF's are 4mm wider and 5mm longer so thats a total of 20mm longer and it doesn't look like you have the room? Also the extra width looks like it would push your .15uF's up against the headphone socket?




I guess you mean 47uf not .47uf? And no, the larger size power stage decoupling wont be a problem, just a little harder to install as space would be tight. Just have to do everything in "correct" order, so you wont hit other caps with solder iron.


----------



## baronbeehive

sonictrance said:


> I guess you mean 47uf not .47uf? And no, the larger size power stage decoupling wont be a problem, just a little harder to install as space would be tight. Just have to do everything in "correct" order, so you wont hit other caps with solder iron.


 
  
 Yes 47uF 
	

	
	
		
		

		
		
	


	




 Thanks for the info...... difficult to see without having it infront of you. If I do go for the Audyn True Copper's I will save 24mm total width, or 28mm if I go with the Mundort SO for coupling, over your Mundorf SGO's which would leave extra space for the 2 MCaps (15uF) which could help as well. And I've hear good things about the mullards on tubeworld.com. Some of the ones I've seen don't look like yours but I can't really tell on some pics.


----------



## Maxx134

The 47 uf width is not a problem,
 as the shape is cylyndrical.
So you actually have more space where the small red caps are closer to the board.


----------



## baronbeehive

maxx134 said:


> The 47 uf width is not a problem,
> as the shape is cylyndrical.
> So you actually have more space where the small red caps are closer to the board.


 
  
 Good point, I didn't think of that.


----------



## Mogos

Ok it started.


 Despite of questionable sockets quality I have decided to adopt them. It was hole day of tedious work but finally I have succeded to install them.


 I could not stand the thought that my High-End amp will have sockets like this

 So I have done that


 Removing the pot was difficult. It almoust finished with success. Unfortunately pot was damaged.

 Look at this resistors. They are under the PSU section. I have measured 9 ohm (two parrarel).


----------



## SonicTrance

Wow, you are brave! You unsoldered all wires from board! Granted it will be a lot easier to work on now. I hope you have marked every wire and taken pictures so you know exactly where to solder them later.
  
 Those sockets looks great btw! 
	

	
	
		
		

		
			





 But those resistors in last pic...does not, lol. Yet another example of older board (yours) vs. newer board (mine). I only have two single resistors in that position.
  
 You see them up in the left corner.


----------



## baronbeehive

Maxx did you try swopping your WCF caps with the Coupling Caps ie. the Mundorfs with the Jupiters, to see  how it affect sound?


----------



## coinmaster

> I hope you have marked every wire and taken pictures so you know exactly where to solder them later.


 
 What he said.
 I spent tedious hours marking all my wires and I still managed to screw up somehow. Although technically I went a little farther than you did but be very careful. If you do it wrong horrible things can happen to your new components.


----------



## Maxx134

mogos said:


> Ok it started.
> ....*snip*.....
> 
> 
> ...




I am very concerned here...
DO NOT go by the resistance measured..
You need to find out the intendid resistance...

The resistors looked missing from top board,

 but where there all along under while the updated the MK8 board to have on top..

They feed the PSU fron the transformer so they need to be high wattage.

The problem is my MK8 value is most likely different from yours..

Those four on the MK6 look really bad from the heat.
They should be two high wattage wirewounds here.
.
The problem is knowing the proper value..




sonictrance said:


> ....
> But those resistors in last pic...does not, lol. Yet another example of older board (yours) vs. newer board (mine). I only have two single resistors in that position.
> 
> You see them up in the left corner.



The problem on yours,
Is that I never realized you had them since they were "hidden",

And the problem is that yours is using the blue resistors which are somewhat known to age prematurely, 
But looks like they are fine from your pic.


----------



## SonicTrance

maxx134 said:


> The problem on yours,
> Is that I never realized you had them since they were "hidden",
> 
> And the problem is that yours is using the blue resistors which are somewhat known to age prematurely,
> But looks like they are fine from your pic.


 
 Yes, they are the blue ones but do look OK. Actually, only one of all the blue resistors I've taken out (I measured all of them) measured bad. But as they are low quality, I feel a lot better after replacing most of them.


----------



## coinmaster

> but where there all along under while the updated the MK8 board to have on top..


 
 Oh I didn't know you had them.
 Based on my schematic they are some sort of bypass for when the relay isn't engaged. What is the purpose of this? To stabilize the PS while it waits for the relay to kick in?


----------



## Maxx134

sonictrance said:


> maxx134 said:
> 
> 
> > The problem on yours,
> ...



Maybe you can help MOGOS verify the value for him.

You are lucky with your resistors as I had about 5 that were off..
What I found was the lower watt areas were much better ,
While the higher wattage ones did not handle the circuit well..


----------



## SonicTrance

Just for the hell of it, I tried listening through the SE jack.... and it still hums like crazy and the sound is inferior to the balanced output. When I upgrade the input/output cables that runs a long side of the amp, I'll remove and blank off the SE jack. I see no point in keeping it as I never use it.


----------



## Maxx134

coinmaster said:


> > but where there all along under while the updated the MK8 board to have on top..
> 
> 
> 
> ...


 
Good guess.
What are your values..


----------



## Maxx134

sonictrance said:


> Just for the hell of it, I tried listening through the SE jack.... and it still hums like crazy and the sound is inferior to the balanced output. When I upgrade the input/output cables that runs a long side of the amp, I'll remove and blank off the SE jack. I see no point in keeping it as I never use it.



I believe your hum is same like mine.
I have a tiny hum from left side on single ended jack.
I believe it is one of my small red caps..
Once I open to find out,
 I will let you know.


----------



## SonicTrance

maxx134 said:


> Maybe you can help MOGOS verify the value for him.
> 
> You are lucky with your resistors as I had about 5 that were off..
> What I found was the lower watt areas were much better ,
> While the higher wattage ones did not handle the circuit well..


 
 From looking at one of my pictures, the band codes suggests 15K


----------



## SonicTrance

maxx134 said:


> I believe your hum is same like mine.
> I have a tiny hum from left side on single ended jack.
> I believe it is one of my small red caps..
> Once I open to find out,
> I will let you know.


 
 My hum is not tiny, lol. And it's in both channels. It has been like that from the start.


----------



## coinmaster

Yeah, 15k 1% on the MK6.


----------



## Maxx134

coinmaster said:


> > but where there all along under while the updated the MK8 board to have on top..
> 
> 
> 
> ...



Last time I checked, the resistors were from transformer feeding the relay.

I have not seen you show it in your schematic.
And since not verified I rather you not post another one here.

As it stands, 
there is no bypass.


----------



## Maxx134

coinmaster said:


> Yeah, 15k 1% on the MK6.


same on my MK8.
Mogos different measurement is probably because while still on board.


----------



## Mogos

sonictrance said:


> From looking at one of my pictures, the band codes suggests 15K


 
 Thank you Mister X. Do you have the same type of component above.


----------



## Mogos

maxx134 said:


> same on my MK8.
> Mogos different measurement is probably because while still on board.


 
 After desoldering also 9 ohm parrarel. Seperately 18,3 ohm


----------



## Mogos

The board striped down.


 I have damaged the protecting lacquer aroud the pot connections slots. I will use glu after soldering the new pot to renew the protection.


----------



## SonicTrance

mogos said:


> Thank you Mister X. Do you have the same type of component above.


 
 Yes, looks same as mine.


----------



## SonicTrance

mogos said:


> The board striped down.


 
 So, you're keeping those green coupling caps


----------



## Mogos

sonictrance said:


> From looking at one of my pictures, the band codes suggests 15K


 
 My board looks different in this area


----------



## Mogos

sonictrance said:


> So, you're keeping those green coupling caps


 
 Ha ha. You got me. This place is for jupiters. I am going back to finish desoldering


----------



## SonicTrance

mogos said:


> sonictrance said:
> 
> 
> > From looking at one of my pictures, the band codes suggests 15K
> ...


 
 It seems so. Your resistors are higher up on board for some reason. They have soldered the cables directly on the resistors on my unit.


----------



## SonicTrance

mogos said:


> maxx134 said:
> 
> 
> > same on my MK8.
> ...


 
 This feels strange? Ok, they do look beat up but 18,3 ohms seems very low when they're suppose to be 30K if in parallel. But then again, they're not soldered on exact same position... Makes you wonder if your amp really should have 15K there?


----------



## Mogos

Yes it is strange. Another question if they suppose to be 15k and are 9R then the difference is big and somthing shall stop working. They have lost paint but measurements of every one shows 18 ohms or in parallel 9 ohms. I think I will put the same values. Any other conspiracy theories before I will order them?


----------



## SonicTrance

mogos said:


> Yes it is strange. Another question if they suppose to be 15k and are 9R then the difference is big and somthing shall stop working. They have lost paint but measurements of every one shows 18 ohms or in parallel 9 ohms. I think I will put the same values. Any other conspiracy theories before I will order them?




Yes, I believe you should stick with same values. Maybe Maxx or Redge will shime in...


----------



## SONYES

I have an opportunity tomorrow to buy LD MK8
 my MARANTZ SA11 + CDA94 -
 HOW ? 
it integrates with HD800 transparency in terms of the depth of sound across the stage tonality separation of instruments -
 I have the Laxman P-1U and BCL original - as amps
Thanks


----------



## coinmaster

Experimental test subject B-12.
 Round 1 of test trials are about to begin.
  
 We have the technology.
 We can make him stronger, faster, smarter, better.
 It will live again!!!


----------



## Maxx134

mogos said:


> Yes it is strange. Another question if they suppose to be 15k and are 9R then the difference is big and somthing shall stop working. They have lost paint but measurements of every one shows 18 ohms or in parallel 9 ohms. I think I will put the same values. Any other conspiracy theories before I will order them?



Yes order same as measured.

It makes perfect sense that they are lower value,
As they are connected to a different location...

DoNOT FORGET THE EXACT POSITION of these resistors!!

Edit:

I see they go straight into the brige but I cannot see where the other ends go.

Anyways, put them in same way and you are fine.
Get two 9ohm Mills mr5.
If you cant find two 9ohm, 
Then you will nees four 18ohm..


----------



## Maxx134

mogos said:


> Guys look what I have found out. There is no metal in metal? I have bought them here: http://www.goodcomponent.com/. Was I cheated. Whether all Chinese Companies are one big scam?
> 
> 
> 
> This type of tube sockets are not fitting the hole arrangment.



I believe there is cement in center because design for high heat.
You cant expect it so be solid pin of gold.

Also I see you soldered pins to the new sockets...
This is fine, but I believe you should get some extension sockets, 
To relieve any stress from pulling & swapping tubes...


----------



## Mogos

Another suprise my pot is 20K not like every others 100K. I did not check it as it was for me so obvious that it should be 100K. The resistros behind it are the same 10K and 1K5. I hope the 100K I have will work somehow.


----------



## Mogos

maxx134 said:


> I believe there is cement in center because design for high heat.
> You cant expect it so be solid pin of gold.
> 
> Also I see you soldered pins to the new sockets...
> ...


 

 I have tested the push pull operation with tube (on the board out side of the case). The sockets are more tight (and and that's fine) and you have to be carfull insterting or pulling out the tube. For pulling out there is sttoper in the body of the socket against the top plate. Pushing down worked also ok. It should not be a problem. Now in place of uknown material for the pins I have 1 mm dia solid sliver/gold Mundorf wire .


----------



## Redge78

maxx134 said:


> Yes order same as measured.
> 
> It makes perfect sense that they are lower value,
> As they are connected to a different location...
> ...


 
 I have read your posts about those resistors but I still don't understand where they are in the schematics ...
  
 So, same as Maxx, if you don't understand what it is, don't change the R value, you can go as high as possible with Power rating tho ...


----------



## Redge78

mogos said:


> Another suprise my pot is 20K not like every others 100K. I did not check it as it was for me so obvious that it should be 100K. The resistros behind it are the same 10K and 1K5. I hope the 100K I have will work somehow.


 
 This is strange, the only Alps "quad unit" of this series "RK168" is a 100K (from the current documentation tho).
  
 How do you measure it ?


----------



## Mogos

redge78 said:


> This is strange, the only Alps "quad unit" of this series "RK168" is a 100K (from the current documentation tho).
> 
> How do you measure it ?


 

 I try to mesure it. Look at the description on the board 4x20k. Later on I will post photo.


----------



## Redge78

mogos said:


> I try to mesure it. Look at the description on the board 4x20k. Later on I will post photo.


 
 My pot is labelled "alps 017M-100KAX4"


----------



## baronbeehive

sonictrance said:


> Here's how she looks right now:
> 
> 
> 
> ...


 
  
 I'm wondering about ordering 6 47uF Mundorf MCaps for the decoupling caps. I'm thinking of switching the 2 on their own in the pic to where MisterX has got 2 of his WCF Mundorfs either side of the pot where it looks like there may be room. It looks like they may be as close to the driver tubes from here as where you have got them now?


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Here's how she looks right now:
> ...


 
 I don't think you can fit 47uf mcaps on either side of the pot. I haven't measured but I'm pretty sure they wont fit between the pot and the meters. And if they do, the wiring for the meters would be in the way. It's not possible to re-route those wires without extending them..
  
 I have soldered my driver stage decoupling in the holes for the stock 33uf lytics. So would need long wires to solder in that position. You could also solder on the resistors of course, then the wires would be a little shorter. If you're going for mcaps for driver stage decoupling, I wouldn't recommend any larger than 22uf.


----------



## SonicTrance

You might also wanna think about airflow. You don't want to block every vent in the board. My amp gets much warmer now after the upgrades. Still not hot to the touch though, only warm.


----------



## Mogos

redge78 said:


> My pot is labelled "alps 017M-100KAX4"


 
 And my is 843M-20KAX4.

 I have measured between pin IN and pin GND and the value was 18,6 k.
 The resistors after the pot are the same as you have. So I think all parts after the pot are like yours and the 100K pot shall work. Am I not wrong?


----------



## baronbeehive

sonictrance said:


> You might also wanna think about airflow. You don't want to block every vent in the board. My amp gets much warmer now after the upgrades. Still not hot to the touch though, only warm.


 
  
 Yes that occurred to me, there's not nearly as much free space for air circulation after the mods. Thanks for letting me know about the mcaps size, I will be able to go ahead now with the parts.


----------



## Maxx134

mogos said:


> redge78 said:
> 
> 
> > My pot is labelled "alps 017M-100KAX4"
> ...



Looks like your pot is 5X greater value..
Verify with others with mk6...


----------



## Redge78

maxx134 said:


> Looks like your pot is 5X greater value..
> Verify with others with mk6...


 
 Yes, would have been better to know for sure what is used in other MK6s
  
  
 What I think is that your 100K pot will still act as a Voltage divider and basically can be used as a replacement.
 You may notice that your "listening position" will differ from what you were accustomed with the 20K pot, but those pots being on log scale, that should not be too bad.
 If it's too inconfortable, we may dig into the subject and rework the values of the surrounding resistors (that should part of the overall Voltage divider) to find a better listening position.
  
 From Wiki :
  

 The question will be to know how R2 is compared to RL ... and so to know what is the value of RL => increase it to make it non-significant in the Voltage divider.
 But RL seems to be also part of the Negative Feedback loop, so we may be limited here ...


----------



## baronbeehive

sonictrance said:


> But you're already saving as you dont "need" to change that many resistors on your board. Lucky person


 
  
 Caps on the way, and just the 220k, 330 and 8k2 resistors


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > But you're already saving as you dont "need" to change that many resistors on your board. Lucky person
> ...




Nice! Looking forward to see your build!


----------



## baronbeehive

sonyes said:


> I have an opportunity tomorrow to buy LD MK8
> my MARANTZ SA11 + CDA94 -
> HOW ?
> it integrates with HD800 transparency in terms of the depth of sound across the stage tonality separation of instruments -
> ...


 
  
 Sorry I can't tell you but I know the HD800 goes well with the Mk8, there are people here with the HD800 though who will tell you I'm sure


----------



## Maxx134

redge78 said:


> maxx134 said:
> 
> 
> > Looks like your pot is 5X greater value..
> ...



A better solution for him, is to buy a 20k pot and sell me his 100k..





baronbeehive said:


> sonyes said:
> 
> 
> > I have an opportunity tomorrow to buy LD MK8
> ...



Well, when you think about it, was the name MK"8" a hint?
If thats not enough hint,
 how about the prototype, called *MK800*?..(!)

So the answer is yes, the MK8 *is* one of the best suited amps for the HD800 ever designed..
Notice I did not say "made", because as is, it sounds handicapped by the cost cutting choices made..

If I was not wanting to mod, I would go for a Cavali amp.
If I wanted to save money and learn about tube amps,
Then this DIY SuperMod thread is ideal, 
As you are basically pushing the sound quality to true "end-game-toys" status.


----------



## Mogos

So MisterX,s LD has 100ka pot.

 baronbeehive
 can you make photo of yours or write down what is on your pot.
  
 The listening position for me is not so important. With the one I had  I have been listening on 10 o'clock and it was quite aloud. I am controling volume digitaly (mostly going down max 10 db) If MisterX have 100K with the same resistors behind it so my shall work as well. And maybe it will be installing a correct one finaly .


----------



## baronbeehive

Looks like 100k.


----------



## Mogos

Thank you *baronbeehive. *The photograph answers to all my questions. Yours is 100k. Look at the description on the board along side of the pot. It is written 4x20KA. It looks that my amp is the oldest one with all yours and the pot was installed according to original design.


----------



## Maxx134

Mogos, you can also keep your upgraded pot value by changing the resistors that I PMed you and we are currently looking into.
 Coinmaster schematic seems to show a variable in the gain switch area which "could" be a feedback resistor which we have to verify.

If so, this is another area to optimize,
But for now, it is still being looked into..
The real problem is I tired of opening my unit..


----------



## baronbeehive

maxx134 said:


> Mogos, you can also keep your upgraded pot value by changing the resistors that I PMed you and we are currently looking into.
> Coinmaster schematic seems to show a variable in the gain switch area which "could" be a feedback resistor which we have to verify.
> 
> If so, this is another area to optimize,
> ...


 
 Maybe some sort of quick release mechanism is called for.
  
 I confirmed what MisterX said about the measurement of the 47uFMcaps decoupling caps for the driver tubes while I had the bottom off, there doesn't seem to be any way that they would fit. Now I've just go to wait and see when I get the parts.


----------



## Maxx134

You don't need those type caps there...
you should use more compact form like wima for that, like what I used


----------



## SonicTrance

baronbeehive said:


> maxx134 said:
> 
> 
> > Mogos, you can also keep your upgraded pot value by changing the resistors that I PMed you and we are currently looking into.
> ...




What size caps did you get?


----------



## Maxx134

The purpose of these caps is not for PSU regulation or for sound,
 but for fast response time..
Edit:
Which in turn affects sound..
Edit:
The original design had both a "reservoir" electrolytic, and an antiparasitic wima...
Neither we are using here..
Yet it will do both better


----------



## baronbeehive

sonictrance said:


> What size caps did you get?


 
  
 I got 4x47uF and 2x15 like you got, I didn't want to take any chances.
  
 I did look into getting the wimas for the reason you suggest Maxx but they are very large, even the 25uF's, and I didn't think they would fit either. I'll just check while I've got the back off.
  
 Incidently, MisterX, your pics of the different stages are so clear they should be a massive help to anyone doing the mods.


----------



## SONYES

baronbeehive said:


> Sorry I can't tell you but I know the HD800 goes well with the Mk8, there are people here with the HD800 though who will tell you I'm sure



 


thank you


----------



## baronbeehive

sonyes said:


> baronbeehive said:
> 
> 
> > Sorry I can't tell you but I know the HD800 goes well with the Mk8, there are people here with the HD800 though who will tell you I'm sure" src="http://files.head-fi.org/images/smilies/jecklinsmile.gif">
> ...


 
  
 That's OK, hope you read the post by Maxx134!
  
 I've just measured the space and depending if it doesn't matter which way round they go it could lie flat but the limiting factor would be the height from the board and it looks like the 25uF would fit but the 40uF would probably be  4 or 5mm too high. It's difficult to say without the part though. I have extra width than MisterX because my coupling/WCF caps are thinner.


----------



## SonicTrance

maxx134 said:


> The purpose of these caps is not for PSU regulation or for sound,
> but for fast response time..
> Edit:
> Which in turn affects sound..
> ...


 
 Yes, and the speed was one of the things I noticed a huge improvement on right away. So those 15uf mcaps together with .33uf rifas are doing a great job! Would 22uf do a even better job? I don't know.
  


baronbeehive said:


> sonictrance said:
> 
> 
> > What size caps did you get?
> ...


 
 I actually got 4x33uf and 2x15uf, but yes, those will be great!
 I'm glad you like the pics! They are meant to help others.


----------



## Mogos

The resistors around the switches in my mk6
 m-> means measured, b-> means read from board.
 I was not able to read the values under all resistors but I think they are somehow corresponding to the measured values.
 I am curious what have in this place MisterX and baronbeehive installed.


----------



## Maxx134

sonictrance said:


> Would 22uf do a even better job? I don't know..



It depends, for some things & not for others.

You still need the benifit from a small capacitance (speed), which are what the Rifa bypass on top of those caps are for.
 I replaced them with an even superior Wima FKP thanks to Redge78 letting me know. Yet the larger size for less capacitance can be a factor on installation.

Larger capacitance of the decoupling caps mostly translates to other factors, like dynamics.


----------



## SonicTrance

mogos said:


> The resistors around the switches in my mk6
> m-> means measured, b-> means read from board.
> I was not able to read the values under all resistors but I think they are somehow corresponding to the measured values.
> I am curious what have in this place MisterX and baronbeehive installed.


 
 As I don't want to open the amp ATM, I'm trying to look at pictures and read band codes. But I'm not sure about the colors.


----------



## Maxx134

I am comparing my pics as well..


----------



## Maxx134

What Bogos has are basically ??k & 2k..
Forget the exact numbers due to tolerance percentage in the reaistors.


----------



## Mogos

I think they shall be 2 k and 100k as it is written on my board. I have decoded  2k and the other one looks like 680 x 10 -> 6,8k at MisterX board. The brown one is ????
 Coinmaster you do have mk6? Can you tell us the values written on the board or mesure.


----------



## SonicTrance

mogos said:


> I think they shall be 2 k and 100k as it is written on my board. I have decoded  2k and the other one looks like 680 x 10 -> 6,8k at MisterX board. The brown one is ????
> Coinmaster you do have mk6? Can you tell us the values written on the board or mesure.


 
 How did you get 6K8? I see it as 68K, blue, gray(?), black, red, brown


----------



## baronbeehive

mogos said:


> The resistors around the switches in my mk6
> m-> means measured, b-> means read from board.
> I was not able to read the values under all resistors but I think they are somehow corresponding to the measured values.
> I am curious what have in this place MisterX and baronbeehive installed.


 
  
 The only ones I can see under are from left to right on your pic x,100k,x,2k,100k. So what I can see agrees with your, I can't take readings atm because I haven't got a multimeter yet. My resistors are all brown so I assume they are mills?
 Edit: I meant dale not mills.


----------



## Mogos

Thank you baronbeehive. It will somehow indicate that you have the same set of resistors as I. And you do have the 100k pot


----------



## baronbeehive

sonictrance said:


> How did you get 6K8? I see it as 68K, blue, gray(?), black, red, brown


 
 I agree with you, its multiplied by 100 not 10.


----------



## Maxx134

You measured with the switch on and with resistors in the circuit board so that is why you getting those measurements...
The measurements are fine and correct...

Regardless, I can only account for 30k resistance difference in feedback ,
so I assume the rest is done throughout the board to reduce your gain a bit.

I will discuss with coin and ridge but my guess is that increasing your blue 360k resistors to the 390 K that the others have, in combination with putting on high gain,
 will not only solve your issue but reduce feedback to the level that we have.

In other words you should have a better sounding unit than before, as you will have the revised values when switch is on high gain...
Of course you can just leave all as is and switch to high gain , and try it that way for now which is my recommendation.


----------



## Maxx134

The fact that the resistors I'm talking about are the blue ones in the old boards,
and brown , in later boards,
certainly means & translates to the fact that I have to upgrade that resistor on my board,
 which is totally different anyway as I have a lot more circuitry around the switch on the MK 8..


----------



## Maxx134

What needs to be verified in a pic for me,
is the actual resistor value of the latter MK6 amps..

Although the board value may say 390k,
That is irrelevant to what is actually used..

Looking over pics,
I did see a unit with 333k instead of 360k or 390k(board value),
 which translates to a lower gain, when setting on "high gain"..


The only *other* thing I can tell for sure,
 is that the "low gain" setting on later MK6 amps have the 68k resistors paarallel connected,
instead of board values of 100k or Mogos 107k..

Which translates to a lower gain on that "low" setting than earlier models...


----------



## Mogos

maxx134 said:


> What needs to be verified in a pic for me,
> is the actual resistor value of the latter MK6 amps..
> 
> Although the board value may say 390k,
> ...


 
 I get lost. Which one is 360k. You are refering to MisterX board and the brown resistor close to the switch? I do not have in this area any 360k. There are according to the board descriptions 2K and 100K (measured 1,96k and 82,2k). Could you point out on the photo of my switches which one I can change (cause I donn't have any 360k around). It looks like Baronbeehive has the same setup of resistors and the 100k pot. I will go with what is installed and check if I can use it that way. But I need to be prepared for a change of resistors just in case if it will not work somehow for me. I will order today the resistors for PSU section so it would be a good to order also a set for gain changing. Which ones I shall change the 100K for ?? Get 68k as MisterX has? What about the brown resistors on MisterX board? It looks like it is not 68k,2k,100k. And the setup of values for left and right is not the same 
	

	
	
		
		

		
		
	


	




(look at my photos). I understand they are in signal path so it will be nice to have a nice ones .


----------



## Redge78

mogos said:


> The resistors around the switches in my mk6
> m-> means measured, b-> means read from board.
> I was not able to read the values under all resistors but I think they are somehow corresponding to the measured values.
> I am curious what have in this place MisterX and baronbeehive installed.


 
 It would have been interesting to do the same measurements with the switch in the High Gain position.
 According to the Coin schematics (...), the 2 resistors in parallel should be easier to read, as one will be in an open circuit.


----------



## Mogos

Ok I think now everything will be clear. I have desoldered the blue resistor.

 I have measured the blue resistor and it is 360k 
	

	
	
		
		

		
			





.
 Any proposals for change in conjuction with 100k pot?


----------



## Maxx134

Like I said, you can try 390k with best resistor you can find.

The fact that these are blue, indicates that they are already better than the others...

You will not need to touch others, as your 107k or other members 68k only enabled in low gain setting, which you will no longer be using because of your new pot.

I is probably important that this resistor is whithin tight tolerance.


----------



## Maxx134

mogos said:


> Ok I think now everything will be clear. I have desoldered the blue resistor.
> 
> 
> I have measured the blue resistor and it is 360k :rolleyes: .



I knew this by reading the numbers on your resistors..


----------



## Maxx134

What needs to be verify is member MisterX or baronbeehive resistor if his is 390k or 360k.
I will ask coinmaster what his 390k resistor measured.
A measurement should be possible without taking it out of board


----------



## Mogos

maxx134 said:


> What needs to be verify is member MisterX or baronbeehive resistor if his is 390k or 360k.
> I will ask coinmaster what his 390k resistor measured.
> A measurement should be possible without taking it out of board


 
 In my case it always showed the value of two parallel resistors 82,2. Maxx134 if I would like to keep the low and high gain options what are your recomendations for the resistors values. 
 I have installed (mechanicaly) the pot.



 It is working but the time will show how reliable is the solution. I have used some parts from scrap printer and hard drive 
	

	
	
		
		

		
		
	


	




.
 The values of the pot steps are:
 99,7k
 99,6k
 99,5k
 99,4k
 99,2k
 98,8k
 98,5k
 98,2k
 97,8k
 97,3k
 96,7k
 96,0k
 95,2k
 94,0k
 92,5k
 90,7k
 87,1k
 81,9k
 74,6k
 64,3k
 49,7k
 29,26k
 0,0k


----------



## baronbeehive

mogos said:


> The resistors around the switches in my mk6
> m-> means measured, b-> means read from board.
> I was not able to read the values under all resistors but I think they are somehow corresponding to the measured values.
> I am curious what have in this place MisterX and baronbeehive installed.


 
  
 It looks like you were wrong about the values. Going from my resistor, not board this time, markings, they are: 2001F, 68K1, 332K, 2001F, 68K1.
  

  
 and: 68K1, 332K, 332K, 68K1, 2001F.
  
 So the one you desoldered would be the 332K and then there are 2x332K on the other side for some reason. I don't know if this helps.


----------



## Mogos

baronbeehive said:


> It looks like you were wrong about the values. Going from my resistor, not board this time, markings, they are: 2001F, 68K1, 332K, 2001F, 68K1.
> 
> 
> 
> ...


 
 Thank you baronbeehive. It looks like the higher the value of the pot (you have 100k) the lower the values of the resistors.
  
  
 Maxx134 maybe I should install the values given by baronbeehive to keep both options low and high gain?


----------



## Mogos

redge78 said:


> It would have been interesting to do the same measurements with the switch in the High Gain position.
> According to the Coin schematics (...), the 2 resistors in parallel should be easier to read, as one will be in an open circuit.


 
 In the High Gain position the measured values are as for single resistors in my case 2k, 107k, 360k. The 2k stays 2k but all the previously measured 82,2k are now 2x107k and 360k. It is interesting cause the value 82,2 is for two resistors 107 and 360. But in Low Gain all three are 82,2k.


----------



## baronbeehive

sonictrance said:


> ............
> 
> 
> 
> I'm so happy right now!


 
  
 I've got most of the parts back already so I checked them inside the chassis and you are quite right about the 4 power Mcaps fitting very well. However It looks very much like the 2 driver 47uF Mcaps will fit in the space I suggested - I tried them here - on either side of the pot just to the side of the wiring where you have got the WCF caps, so I may go ahead and reorder. Also the space may be big enough to fit the 40uF wimas that Maxx suggested but the cylindrical shape of the Mcaps would be better I think.
  
 I know they would be positioned over the ventilation holes but as there is a large gap around the edge of the PCB I would have thought that sufficient.
  
 So my question is the solder points to the drivers anode and cathode look to be nearer to the Mcap in this position than at either end where you have yours. So this would be better from the point of view of reduced impedance wouldn't it?


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > ............
> ...




If they do fit then I'd say go for it. I can't see how they could fit though, must be extremely tight. 
Re solder points...
If you solder them directly on the resistors it would be good to place the caps by the pot (short wires). But if you, like me, solder them in the board holes for the 33uf lytic cap, placing the caps on either side would be best.


----------



## SonicTrance

mogos said:


> maxx134 said:
> 
> 
> > What needs to be verify is member MisterX or baronbeehive resistor if his is 390k or 360k.
> ...




That pot looks impressive Mogos. Well done!


----------



## Maxx134

mogos said:


> Thank you baronbeehive. It looks like the higher the value of the pot (you have 100k) the lower the values of the resistors.
> 
> Maxx134 maybe I should install the values given by baronbeehive to keep both options low and high gain?



Quick answer:
YES
Change out your 107k to 68k,
And your 360k to 332k,
as stated by baronbeehive.

Do this and I believe you will be fine.
The reason is that I believe there is a mix up.

Upon further investigation,
It seems the larger 332k, 360k, 390k type resistors are the ones being switched in and out with the gain setting switch...

While the 107k,68k type resistors are the ones in the circuit!

I have noticed the switch operation with the MK8 by looking at the tube side board traces:



Since these resistors deal with the gain,
I would now recommend higher quality regardless however we find they are implemented.

At this point I would also disregard any talk of feedback untill it is verified, as I beleive there is still some error or variance in coinmaster's schematic.






baronbeehive said:


> So my question is the solder points to the drivers anode and cathode look to be nearer to the Mcap in this position than at either end where you have yours. So this would be better from the point of view of reduced impedance wouldn't it?



Its ok to leave at corners, and place the smaller Decoupling "bypass" closer to the driver tube cathode resistor ground point.


----------



## baronbeehive

It is tight! I will get 2 more 47uF Mcaps and put them here instead of the smaller .15uF's that MisterX has at the corners, Maxx if thats fine.
  
 Edit: 15uF NOT .15uF of course!


----------



## Maxx134

baronbeehive said:


> It is tight! I will get 2 more 47uF Mcaps and put them here instead of the smaller .15uF's that MisterX has at the corners, Maxx if thats fine.
> 
> Edit: 15uF NOT .15uF of course!



What will you be using this for?
You need this area for the WCF caps, 
NOT the Decoupling caps...
The smaller Rifa should be there by the Cathode resistors...

Smaller caps are faster than larger caps.

Actually, you are proposing an interesting alternative,
As the other caps(coupling& WCF) can be pushed further out to sides,
 because the lead length not matter as much.

Hmmm would be interesting to see..
Edit:
You do not need 2 more here..
You need 4 other caps here..
Per side!
Plus two rifas!

Look mine:

Notice on left side I stacked 2 ?


----------



## baronbeehive

Yes I was just placing the 47uF Mcaps for driver decoupling to show that they would fit here but everything else would be as in your pic, ie the other 4 power decoupling Mcaps end to end on the other side of the coupling caps with cathode bypass in between and then the coupling and WCF caps more or less where you have yours but moving what would be your wimas, but are my Mcaps from the corner to either side of the pot as I think they would be just as near to the solder points as they would be if they were in each corner.
  
 ATM I have 2 15uF driver mcaps which I was going to place in the corners where you have your wimas but now that I know that I can get the bigger size where I have shown in the pic I'm thinking of ordering the 47uF's instead for better speed PSU unit, if that makes sense. (The rifa's would most likely go on the other side of the PCB)
  
 I believe the larger Mcaps would be a better fit by the pot, than the wimas in the corners according to my measurements Maxx.


----------



## Maxx134

baronbeehive said:


> I'm thinking of ordering the 47uF's instead for better speed PSU unit, if that makes sense. (The rifa's would most likely go on the other side of the PCB)
> 
> I believe the larger Mcaps would be a better fit by the pot, than the wimas in the corners according to my measurements Maxx.



Yes this sounds good,
What the main benifit here would be more reserves for impact and so the driver tubes wont distort/drain caps at max volumes.
My amp has smaller driver tubes so I am still good with my configuration.


----------



## baronbeehive

Thanks for your confirmation, it looks good so far............ of course that may change when it comes to wiring it in place 
	

	
	
		
		

		
			





 ........ better to be prepared for disappointment!
  
 Be prepared for some annoying questions Maxx.
  
 Incidently I notice in the stock LD nothing inside is touching anything else, is that important because with the mods there's bound to be some contact.


----------



## Maxx134

baronbeehive said:


> Thanks for your confirmation, it looks good so far............ of course that may change when it comes to wiring it in place :eek:  ........ better to be prepared for disappointment!
> 
> Be prepared for some annoying questions Maxx.
> 
> Incidently I notice in the stock LD nothing inside is touching anything else, is that important because with the mods there's bound to be some contact.



I never have a problem with questions or PMs, its not a bother for me, as it is a hobby..

The issue on this page I would rather have avoided, was give any premature suggestions like those resistors..
The best thing would have just test the pot travel as is, then adust after.

Plus the issue is I have not had the chance to open and verify anything yet,
So all I could verify was what the switch actually connecting,
But any values cannot be tabulated without verifying for sure the circuit path.
Coinmaster schematic is a great help but still needs to be verified.


----------



## Redge78

mogos said:


> It is working but the time will show how reliable is the solution. I have used some parts from scrap printer and hard drive
> 
> 
> 
> ...


 
  
 Mogos, I don't understand those values ...
  
 Is it a *series *stepped attenuator or is it a "only 2 resistors in the circuit" kind of thing ? and then what is the shunt resistor value ?
  
 The kind of values I came across was more like the ones found here (for series pot tho):
http://www.goldpt.com/r_series.html


----------



## Mogos

redge78 said:


> Mogos, I don't understand those values ...
> 
> Is it a *series *stepped attenuator or is it a "only 2 resistors in the circuit" kind of thing ? and then what is the shunt resistor value ?
> 
> ...


 
 It is shunt type with two resistors in the path. I don't know the value of the shunt resistor. There was no contact with the seller. He never answered to my questions.


----------



## SonicTrance

maxx134 said:


> baronbeehive said:
> 
> 
> > I'm thinking of ordering the 47uF's instead for better speed PSU unit, if that makes sense. (The rifa's would most likely go on the other side of the PCB)
> ...


 
 Damnit, lol! Now I already wanna change my decoupling caps
	

	
	
		
		

		
		
	


	



 I've noticed that the 33uf 400v mcap is about the same size as the 47uf 250v mcap... Which one would be better for decoupling?


----------



## baronbeehive

maxx134 said:


> I never have a problem with questions or PMs, its not a bother for me, as it is a hobby..
> 
> The issue on this page I would rather have avoided, was give any premature suggestions like those resistors..
> The best thing would have just test the pot travel as is, then adust after.
> ...


 
  
 I don't think you can help that. There will always be things you have to do on the fly! So log as you make it clear.
  


sonictrance said:


> Damnit, lol! Now I already wanna change my decoupling caps
> 
> 
> 
> ...


 
  
 Woaaaah, I never noticed those either. I don't know but looks like what you lose from higher impedance you gain again from faster current speed with the 33uF/400v? If as I assume the main benefit comes at max volume then it's not going to affect me much. There's not a massive difference anyway, but the wimas look better in this respect but they're such an awkward shape.


----------



## Mogos

I have manage to install the WCF grid 300k resistors. In normal conditions it will be a piece of cake. But installing giant 2W in place of tiny 0,5W was difficult. Ok there are some electrical advantages but I do not recomend to do it.




 Are RIFA capacitors non polarised? Will it be irrelevant which way I will solder them?


----------



## SonicTrance

Nice job on those resistors Mogos. They look a little "out of place" though, lol


----------



## Mogos

Yeah. A little 
	

	
	
		
		

		
		
	


	




. But I will not be able to beat coinmaster.


----------



## coinmaster

No one's beating me since my power supply refuses to work.
 Even the stock power supply refuses to work for some magical reason that I can't seem to deduce even after replacing the stock parts for good measure.
 In other words, game over, I bricked my amp and my wallet for nothing. It was a valiant and annoying effort but all I did was end up with a lot of scraps and wasted time/money. I simply don't have the knowledge to troubleshoot this on my own and it's not something I can do with internet help since all logical reasons for why it isn't working seems to have failed.
 I see no reliable way out of this without buying another mk6.


----------



## Redge78

> Are RIFA capacitors non polarised? Will it be irrelevant which way I will solder them?


 
 Yes, the RIFA caps are non-polarised, you can solder them any way you want.
  
 As a general rule, all lytics/chemicals are polarised, all "film/metalised" caps are not.
  
 On some "Top quality" film caps (the "Jupiter" for instance), even if they are "non polarised" you may have a "preferred" way of soldering them, that may have a slight impact on the sound (due to the internal construction of the cap being not perfectly symetrical on both sides).
  
  
  
 ANd yes, those "WCF grid 300*R* resistors" seem huge ! That's fun.
  
  


> Damnit, lol! Now I already wanna change my decoupling caps
> 
> 
> 
> ...


 
 Don't expect much differences between those two.


----------



## SonicTrance

> Damnit, lol! Now I already wanna change my decoupling caps
> I've noticed that the 33uf 400v mcap is about the same size as the 47uf 250v mcap... Which one would be better for decoupling?





> Don't expect much differences between those two.




Ok, thanks.


----------



## baronbeehive

Quote:


coinmaster said:


> No one's beating me since my power supply refuses to work.
> Even the stock power supply refuses to work for some magical reason that I can't seem to deduce even after replacing the stock parts for good measure.
> In other words, game over, I bricked my amp and my wallet for nothing. It was a valiant and annoying effort but all I did was end up with a lot of scraps and wasted time/money. I simply don't have the knowledge to troubleshoot this on my own and it's not something I can do with internet help since all logical reasons for why it isn't working seems to have failed.
> I see no reliable way out of this without buying another mk6.


 

  
 Well that's really bad luck. I've had experience of this type of thing happening when I've programmed computers. When you've done a whole lot of work and then something goes wrong you can't pin it down to a single cause, so then you have to go back to the start and remember what you did all over again. I don't know if that's what happened to you. Can you remember the last time it was working and what have you done since then to break it? There's no substitute for modify>test in small steps repeatedly, its boring but a necessary evil. Hope you can pick up the pieces!


----------



## coinmaster

Well it initially broke about 1.5 months ago when I first took it out of the case. I left it alone because I was going to map a schematic and get new parts anyway.
 Now that I have said parts and schematic I decided to use the power supply on the board for now instead of creating a new one from scratch since there was really no need.
 However it's been one problem after another. Every time I fix something I seem to break something else. I finally decided to just replace all the stock components with the new ones and it still doesn't work right.
 The power supply really isn't that complicated to understand. I've checked continuity on every connection and I've tested the individual components to see if they are still working.
 It seems like magic is the only reason it isn't working because the connections are good and the components are good.
 I don't know what else I can do at this point.


----------



## Mogos

The resistors has been orderd. I shall have all of them next week. I have orderd the Audio Note tantalum 330k and 68k. The board is ready to have them.


 Work is slowly progressing.


----------



## SonicTrance

How are you connecting the coupling caps when those clamps are there?


----------



## Maxx134

sonictrance said:


> maxx134 said:
> 
> 
> > baronbeehive said:
> ...



I do not like the 47uf because it has a lower voltage rating. 
Therefore I do not recommend.


Also,
@Mogos:
I think your resistors are excellent,
But I do not choose the size as they may be a bit too large for when you put the large Decoupling caps there...

Also, how in the world did you fit such a huge resistor in the super tiny hole size of the board?!?!

I must recommend that you test every connection for continuity with the board traces, 
Because I *assume* some redrilling of the hole was required to fit those monsters...


----------



## SonicTrance

maxx134 said:


> sonictrance said:
> 
> 
> > maxx134 said:
> ...



But they are the same as your power tube decoupling. You're using 47uf 250v correct? Currently, all my decoupling caps have 250v spec and it sounds great. Question is if it would sound better to choose caps with higher vdc and lower uf rating.


----------



## Maxx134

The driver stage is running at higher voltage than the power tube stage,
Thats why.
The driver stage is a low level signal which benifit more from a faster cap, with almost doubled voltage, over a bit more capacitance.
remember the max pulse rise time.


----------



## SonicTrance

maxx134 said:


> The driver stage is running at higher voltage than the power tube stage,
> Thats why.
> The driver stage is a low level signal which benifit more from a faster cap, with almost doubled voltage, over a bit more capacitance.
> remember the max pulse rise time.



Then maybe the 630v 15uf mcap would be best for driver stage. It would also fit.


----------



## baronbeehive

coinmaster said:


> Well it initially broke about 1.5 months ago when I first took it out of the case. I left it alone because I was going to map a schematic and get new parts anyway.
> Now that I have said parts and schematic I decided to use the power supply on the board for now instead of creating a new one from scratch since there was really no need.
> However it's been one problem after another. Every time I fix something I seem to break something else. I finally decided to just replace all the stock components with the new ones and it still doesn't work right.
> The power supply really isn't that complicated to understand. I've checked continuity on every connection and I've tested the individual components to see if they are still working.
> ...


 
  
 This is really beyond me but have you ever had it working properly because if not you have no base to go back to. Normally you start from when everythings good and trace forward to every change you have made by a process of elimination. But if everythings reading good it could be the board or something that happened to it before you had it. What about getting some sort of diagnostic check from, a qualified engineer and going from there, there's no harm in admitting you may have missed something. At least all your parts are still good. I found with computer programming it usually came down to something simple that was overlooked and practically impossible to see.
  
 There's also the possiilty that the parts may be individually OK but do not work together because of incompatability perhaps because the values are beyond the specified margins. They may be having unforseen effects.
  
 Remember, small steps and check everything because if you don't it's impossible to figure it out.


----------



## baronbeehive

sonictrance said:


> Then maybe the 630v 15uf mcap would be best for driver stage. It would also fit.


 
  
 So you're going for the upgrade of the upgrade? I want to be convinced about this. Maxx mentioned the 3x rule for voltage but surely that's only for a safety margin not for enhanced sound? The thing that matters is that there is an adequate margin over and above the board voltage. For example coupling caps of 500v, -  or 630v for the Audyns, are the norm, there's not need to go for the 1000v of the Mundorfs. What about the Elna Silmics for cathode bypass? The trouble is were talking £50 instead of £6 in that case 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Then maybe the 630v 15uf mcap would be best for driver stage. It would also fit.
> ...




I've not decided yet. I think I'll leave my power stage decoupling caps alone, as I dont think I'll notice any difference going from 33uf to 47uf. 
Driver stage decoupling on the other hand I'll be upgrading. Not sure to what cap just yet. I chose the 15uf mcap as I knew it would fit but now that I know that larger caps fit, I have more options. 

But I'm in no hurry as the amp is sounding so damn good as is!


----------



## baronbeehive

Well maybe you should consider the 40uF, 800v wimas then, I think they will fit either side of the pot, they would clear the wires in mine away. I don't know whether to try that myself.


----------



## SonicTrance

Where can you get those wimas from?


----------



## baronbeehive

sonictrance said:


> Where can you get those wimas from?


 
  
 Looks like here for Sweden:
  
http://www.conrad.se/websale8/?Ctx=%7bver%2f8%2fver%7d%7bst%2f3ec%2fst%7d%7bcmd%2f0%2fcmd%7d%7bm%2fwebsale%2fm%7d%7bs%2fconrad%2dswe%2fs%7d%7bl%2f01%2daa%2fl%7d%7bmd5%2fc1df017ca847b76cc081ea600f2f0605%2fmd5%7d&act=search&dp2=ff_search&search_input=Wima&wsps_filter_brand=Wima&tpl=ws_search.htm&channel=conrad-se&queryFromSuggest=1&refKey=lkoMWEoe6
  
 If I do get some I'll let you know


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Where can you get those wimas from?
> ...


 
 That place is no good. I usually order from the UK hificollective, but they don't sell Wima.
  
 Edit: Never mind. I found a good seller from Sweden.


----------



## SonicTrance

Those Wima caps do come in A LOT of different sizes, lol.
 I've looked around now, and the biggest ones that can fit on either side of the pot seems to be the 60uf 600v or 50uf 800v.
  
 They both have these dimensions:
 Length: 41,5mm
 Height: 50mm
 Width: 35mm 
  
 I'm very tempted 
	

	
	
		
		

		
		
	


	




 
  
 Edit: I've opened my unit and measured the space between the pot and meters, and it's 42mm, so these caps JUST fit. Only downside about getting these is it would feel stupid to have larger decoupling caps for driver tubes than power tubes.


----------



## Mogos

maxx134 said:


> Also,
> @Mogos:
> I think your resistors are excellent,
> But I do not choose the size as they may be a bit too large for when you put the large Decoupling caps there...
> ...


 
 Decoupling caps will fit, photos soon 
	

	
	
		
		

		
			





. Redriling of the hole is very dangerous !! I had aleardy bad experience with it. So I didn't drill the hole. I have thinned the legs 
	

	
	
		
		

		
		
	


	




.


----------



## Mogos

sonictrance said:


> How are you connecting the coupling caps when those clamps are there?


 
 It will be done like that. I have to stop working in this area as I have to install the resistors and I have used all the wire I had for caps installation doing legs for the tube sockets. So the photographs shows the preassembly stage. I have a big advantage that I can Grow Up 
	

	
	
		
		

		
		
	


	




.


----------



## Mogos

Work in progress.


----------



## SonicTrance

Man, you're not skimping on resistor size, HUGE resistors everywhere, love it lol


----------



## Mogos

One more inside the casing.


----------



## Mogos

sonictrance said:


> Man, you're not skimping on resistor size, HUGE resistors everywhere, love it lol


 
 As we all know the bigger wattage (read size) is better. I didn't intend to go with higher wattage but I have decided to go with tantalum resistors and the ones suitable for me were not available in 0,5 W.


----------



## SonicTrance

mogos said:


> sonictrance said:
> 
> 
> > Man, you're not skimping on resistor size, HUGE resistors everywhere, love it lol
> ...


 
 Yes, I see you only chose tantalum resistors. I also like matching things, why do you think I only went with Mundorf caps 
	

	
	
		
		

		
		
	


	




 Great job so far!


----------



## Redge78

mogos said:


> As we all know the bigger wattage (read size) is better. I didn't intend to go with higher wattage but I have decided to go with tantalum resistors and the ones suitable for me were not available in 0,5 W.


 
 One quick question :
  
 You've changed the WCF Grid 300R (for your large tant), fine.
  
 But I didn't see a change of the MAIN "coupling Grid" 300R (the one behind the Jupiter and that is feeding the whole WCF).


----------



## SonicTrance

redge78 said:


> mogos said:
> 
> 
> > As we all know the bigger wattage (read size) is better. I didn't intend to go with higher wattage but I have decided to go with tantalum resistors and the ones suitable for me were not available in 0,5 W.
> ...




According to first page, those resistors are not in need of change in the mk6, only mk8


----------



## Mogos

sonictrance said:


> According to first page, those resistors are not in need of change in the mk6, only mk8


 
 Yes. Exactly. Please update us if it was omitted as soon as possible. I hope I can stil update my order tomorrow.
	

	
	
		
		

		
		
	


	




. Please mark this resistors.


----------



## Redge78

mogos said:


> Yes. Exactly. Please update us if it was omitted as soon as possible. I hope I can stil update my order tomorrow.
> 
> 
> 
> ...


 
 Well, that's the "Resistor Chief of Operation" that will have the final word on this, I didn't work on the MK6 at all.
  
 Finding them should be easy tho, logically they should be at the same spots as in the MK8, and an Ohmeter will confirm this :
 How many Ohms between your coupling cap and the Grid pin of the amplifying Triode of the 6080 (pin1 or pin4, I don't remember) ?


----------



## SonicTrance

mogos said:


> sonictrance said:
> 
> 
> > According to first page, those resistors are not in need of change in the mk6, only mk8
> ...


 
 Look at the board traces on top side (tube side) and see if those resistors actually leads to the grid pin of the power tube.


----------



## SonicTrance

redge78 said:


> mogos said:
> 
> 
> > Yes. Exactly. Please update us if it was omitted as soon as possible. I hope I can stil update my order tomorrow.
> ...


 
 Both pin 1 and pin 4 are for the grid, different sections.


----------



## Mogos

sonictrance said:


> Both pin 1 and pin 4 are for the grid, different sections.


 
 They go to the pins of power tubes. So they are as Redge has written - important.


----------



## baronbeehive

sonictrance said:


> Those Wima caps do come in A LOT of different sizes, lol.
> I've looked around now, and the biggest ones that can fit on either side of the pot seems to be the 60uf 600v or 50uf 800v.
> 
> They both have these dimensions:
> ...


 
  
 Yes, as you said they would have to clear the wires to the pot so if you were unsure the 30uF at 24mm width should be a dead certainty. I've gone ahead and ordered the 40uF at 31 which should fit in mine as the wires don't seem to be in the way. But you could possibly go up to the 50uF at the higher voltage. If you want to wait until I get mine I will post a pic of the fit. If they are OK I will have two spare 47uF MCaps which I already got going cheap if you want to update your power caps, let me know.


----------



## Mogos

Redge78. It is tragic what happend in Paris. I hope you have not been touched personally. I am gather in sorrow with all who lost their loved ones.


----------



## Mogos

Guys I need your help. Is the marking on the photo correct?
 To find the right and left plus minus inn is simple. But the plus minus out is already not so obvious at least for me.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Those Wima caps do come in A LOT of different sizes, lol.
> ...


 
 As we are laying the cap down flat, you should be looking at the length of the cap to clear the meters. The 30uf has same length as the bigger ones @ 41,5mm. There's 42mm between the pot and meters. You can bend the meter-wires to go over the wima cap.


----------



## SonicTrance

mogos said:


> sonictrance said:
> 
> 
> > Both pin 1 and pin 4 are for the grid, different sections.
> ...


 
 Which pin do they lead to?


----------



## Mogos

To pin 1 (first clockwise from the guiding nose).


----------



## SonicTrance

mogos said:


> To pin 1 (first clockwise from the guiding nose).


 
 On all four power tubes? Notice how those resistors are positioned differently. On power tube 2 and 4 they are positioned right next to a grid pin, but on tube 1 and 3 they are next to the heater pins. However, this all depends on the board traces of course.
  
 This actually applies to the WCF resistors as well. Were the resistors for power tube 1 and 3 connects straight to pin4 (grid section 1) and the resistors for tube 2 and 4 connects to pin6 (cathode section 1), although it seems they are connected to pin4 also on the other end, which connects to the 470K resistor.
  
  
 Edit: If you zoom in on this pic you can clearly see a trace from that 300R coupling resistor on tube3, leading straight to pin4 (grid). No traces available on the other 3 tubes though.
  

  
 Looks like I'm in need of some more resistors...


----------



## Maxx134

Stop making things so complex.
If you know the pin layout of the tube, 
You know there are two grids.
On the MK6 One is the 300ohm for the WCF grid.

So the second grid is what we want to look for any resistor ONLY in the path from the coupling cap.

That is easy to do.
Just put your ohm meter to test for continuity (low ohm setting) between the coupling cap and the grid.
Test these two points and if you get zero resistance,
There IS NO resistor in the signal path.
There may be other resistors leading to the op amps, be we are not concerned with those..

I have not found a resistor in between myself from looking at pics.
Thay is why I never mentioned any grid resistor for the MK6,
Also this coincides with my assumption that the MK8 has a slightly different version of the WCF, shown in cavali diagrams using extra resistors in his second diagram, if you bother to look at the links Redge78 posted.

Anyways just test those two points to make sure:
the coupling cap to the main grid, not the WCF grid.


----------



## Maxx134

Quote:
*Looks like I'm in need of some more resistors...*

Repeat,
We are not concernd with any resistors leading to the opamp circuitry,

We are only concerned with coupling cap to grid..


----------



## SonicTrance

maxx134 said:


> Quote:
> *Looks like I'm in need of some more resistors...*
> 
> Repeat,
> ...


 
 Fair enough, I'll measure.


----------



## Mogos

sonictrance said:


> On all four power tubes? Notice how those resistors are positioned differently. On power tube 2 and 4 they are positioned right next to a grid pin, but on tube 1 and 3 they are next to the heater pins. However, this all depends on the board traces of course.
> 
> This actually applies to the WCF resistors as well. Were the resistors for power tube 1 and 3 connects straight to pin4 (grid section 1) and the resistors for tube 2 and 4 connects to pin6 (cathode section 1), although it seems they are connected to pin4 also on the other end, which connects to the 470K resistor.
> 
> ...


 
 I have found 4 traces (some up some down the board) to the pin 1


----------



## SonicTrance

That's a great help, thanks!


----------



## Maxx134

Edit:
 Sorry my mistake Ur mk6 is 8pin tubes


Measure the points I stated from the coupling cap to grid...


----------



## Maxx134

sonictrance said:


> ...
> Then maybe the 630v 15uf mcap would be best for driver stage. It would also fit.




Look at datasheet for the tube.

Remember the original function of the stock33uf cap was for low level ripple.

Now we are using for a bit different purpose here.
My amp using small 12at7 while your amp using larger tube.
Therefore I would prefer largest capacitance and then a bypass cap along with it( Rifa ).

I do not like less than what I put in mine.
It is true a film cap will outperform an electrolytic double its size or more actually.
I forget the exact figures shown to me by Redge78.
Therefore any of the ones talked about so far, are all superior to the stock 33uf electrolytic. 

The trick here is to find the optimal value of film cap replacement, which would not need to go any larger.

Redge78 should be able to tell you, but I am settled on what I have for me, so I assume you should be fine with anything 25uf minimum for driver stage...

 and it was already stated 47uf minumum for powertube stage..

MisterX you may not notice a difference with slightly less 33uf on your power stage, specifically because of your power suppy upgrade with the large mundorfs.





sonictrance said:


> Those Wima caps do come in A LOT of different sizes, lol.
> ...
> Only downside about getting these is it would feel stupid to have larger decoupling caps for driver tubes than power tubes.



It is not stupid, on contrary it is very *SMART*, 
as the driver stage power supply is very minimal(!), 
and not beefed up like the powertube stage..!





mogos said:


> ...Redriling of the hole is very dangerous !! I had aleardy bad experience with it. So I didn't drill the hole. I have thinned the legs h34r: .



You are absolutely correct!!
I thought I was the only one who had to file all my tips down!
I would need to file all my tips ao that they go in hole easier,
Even the tinned leads of wires I used to extend the coupling & WCF caps..





mogos said:


> One more inside the casing.



The only problem I see with pic is no internal space for your power button.
I assume you will replace your power button for a shorter one?





redge78 said:


> ...
> 
> But I didn't see a change of the MAIN "coupling Grid" 300R (the one behind the Jupiter and that is feeding the whole WCF).



I dont believe the MK6 has a resistor going into the main grid.
Need Mogos & MisterX to verify..


----------



## Mogos

maxx134 said:


> .......
> The only problem I see with pic is no internal space for your power button.
> I assume you will replace your power button for a shorter one?
> I dont believe the MK6 has a resistor going into the main grid.
> Need Mogos & MisterX to verify..


 
 It will be very tight fitting but should work. I can push the capacitors a little back. The switch is longer on the bottom. On the hight when the capacitors hang it is 2-3 mm less 
	

	
	
		
		

		
		
	


	




. If problem then I will change the switch.


 You have asked me about the 0.68R and 100R. I don't know what they are for but I have change them for higher wattage.


----------



## Mogos

Resistors connected to the pin 1.




  
  
 Can somebody help me with +- for the pot out connections?


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## SonicTrance

Thanks for those pics Mogos. And I can confirm. I just opened my amp and measured 300ohms between each coupling cap and pin1, grid.
  
 I have some three conductor wire on order for the input/output wires that runs along side of the amp, and will probably do those grid resistors and driver decoupling upgrade at the same time. But I just have a hard time believing that the sound can improve much more, lol. It truly sounds amazing as it is now 
	

	
	
		
		

		
			




  
 Sorry Mogos, I can't help you regarding the pot.


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## Maxx134

Ok thanks guys I will update the pic for first page post to include the grid resistors which had the traces covered up in past pics by the stock WCF caps..

The issue with the pot I will look into


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## Maxx134

Mogos, test for continuity (ohm meter) between the coupling cap and the driver tube output (anode/plate).
Then you will know which coupling cap is for which set of triode within tube.
Then you will know which pins correspond to the grid resistor by the volume..
Here you go:

Since I do not have MK6 I cannot trace other side.
Also my amp is not opened yet.


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## Mogos

Shall not these legs to be very weel insulated from the casing? The shrinking tube was installed over the connection and touch only the top surfase not going inside the hole.


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## SonicTrance

Mine has heat shrink that goes through the holes.


----------



## baronbeehive

So the 40uF 800V wimas fit here. You could probably go up to the 50uF but it would be tight. I'm not replacing the driver stage 10k ohm and 1.5k ohm grid resistors though, they're pretty small on mine.


----------



## SonicTrance

Nice! Thanks for the pics 
Yeah, I'd have to lay my Z-foils almost flat for them to fit, lol.


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## SonicTrance

baronbeehive said:


> So the 40uF 800V wimas fit here. You could probably go up to the 50uF but it would be tight. I'm not replacing the driver stage 10k ohm and 1.5k ohm grid resistors though, they're pretty small on mine.




I just realized that your meters are spaced further apart than mine as you don't have the SE jack on the front. So these caps will just fit in my unit. They're 41,5mm, correct?


----------



## baronbeehive

Yes, that's right. The space between the edge of the pot and the meters is 50mm on mine.


----------



## baronbeehive

How does one solder these into the PCB holes, they're multistranded so you can't just file them down?


----------



## SonicTrance

baronbeehive said:


> How does one solder these into the PCB holes, they're multistranded so you can't just file them down?




Tin the wire, push through the holes and solder, done 
Or do you mean that the wires are too thick for the holes? If so, just cut off strands until they fit.


----------



## Mogos

Finaly I have received the missing resistors. Now I can start making progress again 
	

	
	
		
		

		
		
	


	




.
  






  
 One of the biggest chalanges in this SuperMod is fitting in what does not fit in.


----------



## Maxx134

mogos said:


> Finaly I have received the missing resistors. Now I can start making progress again  .
> 
> 
> 
> ...




You guys are making fantastic progress,
 but here I'm wondering why was the design choice not putting those RIFAs on other side of board?
that would have been optimal for less length of leads..

Placing a washer/spacer so that the boards caps will fit on other side actually also ,

I was thinking you can go down one size, to .22uf so that they will fit


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## Mogos

Is getting bigger and bigger. Heavy also.


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## SonicTrance

mogos said:


> Is getting bigger and bigger. Heavy also.


 
 OMG
	

	
	
		
		

		
		
	


	




! What are those huge green things? Wasn't that the place were you had those 18ohm resistors?
  
 Edit: I just looked at original image and saw that those are 18ohm resistors as well. HUGE though!


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## Mogos

I have gone with their size to far. I did not look at the dimensions.


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## SonicTrance

mogos said:


> I have gone with their size to far. I did not look at the dimensions.


 
 Hehe, ok. As long as they fit it's all good!


----------



## Mogos

Now I can see it was crazy idea to strat the mod (especially the way I have decided to go). I have tried to be very careful doing the unsoldering and soldering but there are some difficult (crowdy areas) I am not sure about to be 100% correct. Today I know I will be afraid to turn it on 
	

	
	
		
		

		
		
	


	




. The board is ready to go inside the casing and I know  it won't be easy to do it.


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## SonicTrance

Looks good Mogos! What are those blue cables for that's coming from the grid resistors?


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## Mogos

As I am changing the pot I decided to make connection with wires (pure silver) directly from the resistors to the pot skipping out the circut paths on the board.


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## SonicTrance

I see. I hope those Shinkohs are as good as the zfoils. My amp is now noise free with very dark background. Previously, I had this noise when changing volume and also not as dark background. I believe it's because of the zfoil grid resistors.


----------



## Mogos

Will see. They say that the tantalum resistors are good for music applications. Bigger wattage also less noise
	

	
	
		
		

		
		
	


	




.


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## SonicTrance

I'm sure they will be!
Btw, your build looks massive and impressive! I'm looking forward to your impressions once finished


----------



## baronbeehive

sonictrance said:


> I'm sure they will be!
> Btw, your build looks massive and impressive! I'm looking forward to your impressions once finished


 
  
 Me too....... looks very complicated build compared to the compact version. I was on the verge of giving up doing it myself when I realised what could go wrong but seeing yours gave me fresh hope, if you can get that thing going mine should be a breeze. Those Audyns are massive for .33uF, I have had a problem with the size of the true copper ones.


----------



## coinmaster

> Now I can see it was crazy idea to strat the mod (especially the way I have decided to go)


 
 You should have learned from me. This was a bad idea from the start.
  


> I will be afraid to turn it on


 
 You should be, if you got the slightest thing incorrect you could and probably will fry your expensive components and fry a few others as well, leading to complicated troubleshooting and repairs.
 It's very difficult to figure out what you broke and if you turn it on before fixing everything you broke, it will just be a never ending chain of you breaking more and more things in a repeating cycle.
 I learned this the hard way.


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## baronbeehive

coinmaster said:


> ..............
> 
> I learned this the hard way.


 
  
 Yeah, little things like getting the soldering/desoldering right worry me, very easy to mess things up if you don't watch what you're doing.
  
 So is your's beyond hope now? You said that all the readings were OK, so perhaps the way it was put together was not right. What are your plans now?


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## coinmaster

No actually I'm doing pretty well on mine. I once again fried a bunch of things because of the smallest minute detail that I missed so I'm waiting on new parts.
 I should have it down this time.


----------



## Mogos

Difficult, difficult. This casing is just not suitable for the mod. With a lot of problems finaly inside. I don't know if everything stayed in place under the board. Tomorrow moment of truth. Either way I will get drunk after all.
 Maxx134 I have moved the Riffa cap in front of the power switch to the other side. Thank you that you pointed out that one. You spare me at least two hours of fight.


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## SonicTrance

Good luck tomorrow Mogos! Lets hope it turns on


----------



## Redge78

sonictrance said:


> Good luck tomorrow Mogos! Lets hope it turns on


 
 Yeah, fingers crossed !
  
 But your work is impressivelly neat, so you should not expect much problems. It's all about replacing one component by one another one.
 Apart from the polarity of the Lytics caps and obviously everything around your new pot and the isulation of the new component leads, it's pretty straightforward, I think.
  
 You may notice that your meters will hit hard on the right when the relay switch on. That's the surge of current from the larger caps you have now.
 My meters are hitting so hard that the needles get stuck sometimes ...
  
 Anyway, it better be good, because with all the layers of caps you have now above your board, it is going to be funny if you have a bad solder ...


----------



## Mogos

Hurrrrrrrrrrrrrrrrrrrray it did not blow up. It started longer then usual and make me almost hart attack. Sitting in the armchair I am still not beleving that I can hear music from the headphones.






 
	

	
	
		
		

		
		
	


	




 
	

	
	
		
		

		
		
	


	




 
	

	
	
		
		

		
		
	


	




 
	

	
	
		
		

		
		
	


	




 
	

	
	
		
		

		
		
	


	



 First time I have read about LD modifications two years ago. Then it was just a wish to change something inside. But without any knowlege it was just a dream. And aroud one year ago two pioneers Maxx134 and Redge78 have started the LD SuperMod modification/experimenting. In the meantime I had an idea to change the amp for "somthing" better. I had an opportunity to test Auralic Taurus for one week. And even if I had some problems with random noises LD had I preferd LD  presentation (Taurus was a little better in the lower frequencies). Taurus lacked the live factor and few other things  I value the most. 
 Now testing heating up and observing.


----------



## Mogos

redge78 said:


> ........................
> It's all about replacing one component by one another one.
> .....................


 
 If it will be like that that then I will be more sure about the final result. But it was not in my case. I could not check many points. New different pot and matching with new resistors was an uknown. From what I hear now I have to go behind 12 o'clock to achive similar level of amplification ( before 10, another story that for testing I have hook up my secondary tube, wire,dac, headphones set
	

	
	
		
		

		
		
	


	




) I have done few small mistakes with selection of materials. The 1,5 mm solid wire for the decoupling caps was not a good idea. Putting them as close as possible to the connection points because of the electrical reasons and space confindments did make things even more complicated, tidious and without any chanse for checking for errors. Now testing testing. But at least no critical errors 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

mogos said:


> redge78 said:
> 
> 
> > ........................
> ...


 
 Glad to hear it works! But volume past 12 o'clock doesn't seem right? What headphones and output tubes are you using? I can't listen past 10,30 on the volume without going deaf. And that's on low gain.


----------



## Mogos

The output tubes are 6080. I think it is the 100k pot. Changing the resistors for the values of yours have helped but not to the end. I think without changing them it will be even worser. Before I have had the same findings on the amplification levels like you. Past 10:30 was to much. The pot design is also different so it will totaly not correspod to the original one in  position-volume amplification.  I will check how it works on the Hi gain later on. First obvoius sonic imperssions are low frequencies. They are more prominent and articulated. I do have a problem with ground hum in the left channel. I do suspect one connection. But for now testing the "stability". I hope I will find easly the hum source. It is dimishing or going up with turning the pot.


----------



## SonicTrance

Ok, 6080 do have low gain, but it's probably the new pot that's causing it, of course.
  
 I'm currently burning in newly acquired WE421A's. And with their gain being triple that of the 6080/6AS7G, any volume past 9 o'clock is too loud. Especially with a 6SL7/ECC35 in the driver seat. With a 6SN7 or even a ECC33, I get a little more play on the volume dial.


----------



## Maxx134

mogos said:


> Difficult, difficult. This casing is just not suitable for the mod. With a lot of problems finaly inside. I don't know if everything stayed in place under the board. Tomorrow moment of truth. Either way I will get drunk after all.
> Maxx134 I have moved the Riffa cap in front of the power switch to the other side. Thank you that you pointed out that one. You spare me at least two hours of fight.



This is truly excellent work!

 I was waiting to see how your volume knob would fit,
 and now that I see it, I feel more confident to try that next.

Also,
 I am wondering what headphones you are using?


----------



## Mogos

I had the HD800 for three years. Now I have Sony Z7. Somehow in my setup they have almost all HD800 qualities and some more making me to sell the HD800. I was looking for very long time for the headphones with similar sound stage to the HD800 and Sony with small modification do have it.


----------



## SonicTrance

I see that you extended the standoffs under the board quite a lot. Was it a tight fit? I only used washers under the standoffs. It was enough to make the rifas fit.


----------



## Redge78

mogos said:


> I do have a problem with ground hum in the left channel. I do suspect one connection. But for now testing the "stability". I hope I will find easly the hum source. It is dimishing or going up with turning the pot.


 
 If the sound changes with the pot, it most probably is a fault on the "music line" (Input > pot > Grid).
 Check if you still have the noise when you remove your input cable.
 Then check the insulation between the three lines of the left XLR connector.


----------



## Mogos

Thank you Redge for the suggestions. I have checked already all wires with continuity test between all minus and plus wires to the ground. And nothing dead silent.
 I have disconnected the interconnects. No change. I think I will have to dig deeper. For now it is not so annoying and I want finally to listen to the music buring in  the parts.
 I hope I can find finally the hum source.
 Few pics just before  and after launching the amp.
  
  
 Big Wimas just milimiters from the bottom


----------



## Mogos

MisterX
  
 I have to extend the snadoffs not because of the capacitors. The new modified tube sockets needed more space (exactly 4 mm).


----------



## coinmaster

Make sure the mounting hole next to the driver stage power supply is connected to the chassis. It is the only ground exit for the board and should be the only direct connection between ground on the board and ground on the transformers/wall.


----------



## Mogos

Thank you Coinmaster. It is very valuable information. I think that one I have screw down. Cause of the way the capacitors are installed I could not srew down the connecting points around the driver tubes the ones closer to the capacitors. 
 I could not stand the thought that somthing is wrong and I don't know what. My biggest concern was if the problem is connected with the board installations/soldering. I have decided to swap the wires on the pot. Just to check if swapping the connection points to the rings of the pot for right and left channel will cause the movment of the hum to the right chanell. I have found one thing for sure. If the pot is opened full (the in wires from sockets are connected directly to the in wires of the board) then there is silence like in the black hole. Can I assume that there is no problem with the board?
 Second thing. The hum did not skip to the rigth channel as I expected 
	

	
	
		
		

		
		
	


	




. The hum almost dissapeared. I can hear something with almost (in full open position is dead silent) full open position of the pot. Desoldering the wires I have desolder all of them. The position of the  + - in out wires was changed on the rings (but of course still corresponding to each other plus to plus minus to minus of the appropriatte channels 
	

	
	
		
		

		
		
	


	




). I did desolder the ground wires not paying any attention which way they have been connected. Soldering them back most probably I have done it different way. In the original design the ground wires of the sockets were connected accordingly to the two pin grounds of the left and two of the right channel positioned on the board side by side (connected with each other on the board for each channel). I don't know if it could have any importance as the ground for me is global. Any way doing the above significantly improved the situation. Later on I will solder the ground wires exactly as in the original design separating left and right channel and going with two wires to one point on the pot and then make a connection the other one of the same channel. Could I have created local ground loop. Is somthing like that possible?  Maybe the pot itself has some kind of defective design?
  
 So guys can I assume that the board has no problem??


----------



## Redge78

The board is not the prime suspect here, it must be around the pot (bad wiring, bad soldering or inside the pot itself).
  
 To be sure about the board, it should be pretty easy. You connect "in wires from sockets to the in wires of the board" (you'll be full volume here) and you "digitally"control the volume from a PC player, starting at 0 of course.
  
  
 Did you try to solder back the old ALPS pot, just for a test ? 
 Did you test the pot itself, at some positions you know there is problems ? Resistance values for each channel, insulation between channels two by two ?


----------



## baronbeehive

I hesitate to suggest anything with my very limited knowledge but sometimes the obvious can be the culprit. To me it doesn't seem like the pot is bad with the hum changing with a wiring change and lessening. And it doesn't appear any problem with specific positions of the pot. Assuming the grounding is OK and that the hum varies with a wiring change have you tried discarding the old wires and resoldering new ones in place, instead of just changing the positions. Just a thought but they may not be optimal length for the that component function.


----------



## Mogos

redge78 said:


> The board is not the prime suspect here, it must be around the pot (bad wiring, bad soldering or inside the pot itself).
> 
> To be sure about the board, it should be pretty easy. You connect "in wires from sockets to the in wires of the board" (you'll be full volume here) and you "digitally"control the volume from a PC player, starting at 0 of course.
> 
> ...


 
 I thought so. So the good news is the board is ok. I did not use Alps pot  as it has one leg broken and it will be difficult to solder it to the wires. But I do have few 47 kOhm 2W resistors and I can put them in the circut. It will be the same situation as you have describded with the connection of the wires directly but I will be more or less on the desired level of analog amplification.The new pot worked normaly except that going up with volume the loudness of the hum was going up. Now I have dead silent background with the pot in the position halfway to max. It is usaul position for listening for me. The volume control making signal louder or quieter I am doing digitaly. So somehow I have succeded. I will polish some things later on 
	

	
	
		
		

		
			





.


----------



## Maxx134

mogos said:


> I had the HD800 for three years. Now I have Sony Z7.



Are you using these headphones with a balanced plug connector? Or single ended?


----------



## Makiah S

I've had my eye on the MK 6 for years now, an I'm farmillar with the mods. Though is any one offering an upgrade service to those of us with no soddering iron experince?


----------



## Mogos

I have never used unbalanced connections. I am using A Pure Sound v. 3 (silver-copper) cable for headphones and of course ballanced one. After seling HD800 I have just changed the plugs for headphones soldering the mini jacks. The balanced cable included with Sony headphones is quite good. But to check it I have to do adapters. I have not been able to dismantle the original plugs (glued or somthing else??). APS is clearly better giving much more let say organic presentation. Starting from the DAC (dcs Elgar plus) and ending on the headphones everything is balanced . Modding the amp I have disconnected the unbalanced headphone socket 
	

	
	
		
		

		
		
	


	




.
 On the photo you can see the mod to the headphones. For me they had to big clamping force making the presentation not so open as it is now and shifting the frequecy balance to much to bass frequencies.


----------



## Redge78

> Starting from the DAC (dcs Elgar plus) ...


 
 That's serious **** ! I dreamt of this one for a looooonnnnng time !


----------



## Mogos

redge78 said:


> That's serious **** ! I dreamt of this one for a looooonnnnng time !


 

 As the Super Moded LD is. The new DACs with femto clocks and good analog out stage could be better 
	

	
	
		
		

		
		
	


	




. But I am far from saying that I am not happy with what I have 
	

	
	
		
		

		
		
	


	




.


----------



## Mogos

mshenay said:


> I've had my eye on the MK 6 for years now, an I'm farmillar with the mods. Though is any one offering an upgrade service to those of us with no soddering iron experince?


 
 I think the one way is to find near you a repair workshop for electronic gears and ask if there is somebody who will be willing to do the changing of the parts. Collect all the information about parts from this thread and buy them. Then just show the guy this thread to look for instructions. Sending the 12 kg amp will generate some costs. I recommend to enlarge the casing first 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

mogos said:


> I think the one way is to find near you a repair workshop for electronic gears and ask if there is somebody who will be willing to do the changing of the parts. Collect all the information about parts from this thread and buy them. Then just show the guy this thread to look for instructions. Sending the 12 kg amp will generate some costs. I recommend to enlarge the casing first
> 
> 
> 
> ...


 
  
 Are you sticking with the existing internal power supply for the fans then, and did you go for larger fans?


----------



## Mogos

baronbeehive said:


> Are you sticking with the existing internal power supply for the fans then, and did you go for larger fans?


 
 Definetly larger fans. There are two advantages. They are silent, very silent and in the same time will give you more air stream flow. In case of modification in "standard" casing the air flow is definetly disturbded and shall be aided.  Higher temperature equals faster aging of the precious parts 
	

	
	
		
		

		
		
	


	




. I am using external power supply for the fans with advanced control.
  
 You have to cut bigger holes in the bottom plate and that could be a little difficult. I ask local workshop to do that for me.

  
 I can recommend the Nouctua Noctua NF-S12B redux-700 (they are budget versions of Noctuas and are sold without any rubber installation pins 
	

	
	
		
		

		
		
	


	




) with only 6.8 db and even bigger air flow then original ones 
	

	
	
		
		

		
		
	


	




. Put them out side even if you have nothing to cover them. To do that you need only to change legs for higher ones or do a frame like me. 
  

 Photograph above shows the fans inside the expanded casing. At this time I didn't know that I will install much more then I can imagine. Big Wimas forced me to move the fans outside.
  

  
  
 And below something may not be very necessary but I had such an idea to have from time to time fan less solution 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

So the bottom comes off in cold weather? Is that socket on the bottom for headphones or for powering your fans? It will be getting pretty crowded by the wall socket for me, 2 amps, DAC, PC....... and now power for fans!!
  
 Thanks for your detailed answer.


----------



## baronbeehive

So the bottom comes off in cold weather? Is that socket on the bottom for headphones or for powering your fans? It will be getting pretty crowded by the wall socket for me, 2 amps, DAC, PC....... and now power for fans!!
  
 Thanks for your detailed answer.


----------



## baronbeehive

So the bottom comes off in cold weather? Is that socket on the bottom for headphones or for powering your fans? It will be getting pretty crowded by the wall socket for me, 2 amps, DAC, PC....... and now power for fans!!
  
 Thanks for your detailed answer.
  
 Sorry about that multiple post, embarrassing.......... I submitted and nothing happened - and again....... I think you were submitting at the same time.
  
 Are you any closer to isolating that hum?


----------



## Mogos

baronbeehive said:


> So the bottom comes off in cold weather? Is that socket on the bottom for headphones or for powering your fans? It will be getting pretty crowded by the wall socket for me, 2 amps, DAC, PC....... and now power for fans!!
> 
> Thanks for your detailed answer.


 
 The socket is for powering fans through the temperature regulator. I have used the mini XLR plug. It has locking mechanism and looks good.


----------



## Mogos

baronbeehive said:


> So the bottom comes off in cold weather?


 
  
	

	
	
		
		

		
		
	


	




 No it will be very cumbersome solution. Inside the casing are two temperature sensors responsible for turing on the fans if the max set temperature occures. So during cold days I can seat in my room wearing the coat and the fans will never turn on. The amp will work like a heater 
	

	
	
		
		

		
		
	


	




 keeping me not frozen to death.
 Of course with this coat I was joking. But with big love to the music and the pursuit of perfection in its reproduction everything can be possible. Isn't it?


----------



## baronbeehive

mogos said:


> No it will be very cumbersome solution. Inside the casing are two temperature sensors responsible for turing on the fans if the max set temperature occures. So during cold days I can seat in my room wearing the coat and the fans will never turn on. The amp will work like a heater
> 
> 
> 
> ...


 
  
 Oh.... excellent work, I hadn't thought to turn the amp into a heater!!
  
 Edit: on second thoughts by the time I've finished soldering there will be enough shorts in it to provide enough heat for the coming winter 
	

	
	
		
		

		
		
	


	




.


----------



## Mogos

baronbeehive said:


> Oh.... excellent work, I hadn't thought to turn the amp into a heater!!
> 
> Edit: on second thoughts by the time I've finished soldering there will be enough shorts in it to provide enough heat for the coming winter
> 
> ...


 
  
 If it will not play music then at least will be very stylish and interesting heater 
	

	
	
		
		

		
		
	


	




. I have no problem with the hum any more. I am not shure what I have done but now evrything is ok 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

mogos said:


> baronbeehive said:
> 
> 
> > Oh.... excellent work, I hadn't thought to turn the amp into a heater!!
> ...




Thats great news Mogos! Any first impressions yet?


----------



## Mogos

I plan to wirte about my impersions tomorrow. I am still a little dizzy and I want to cool down a little not beeing prone to exaggerate


----------



## baronbeehive

MisterX are your fans powered externally as well?


----------



## Maxx134

mogos said:


> I plan to wirte about my impersions tomorrow. I am still a little dizzy and I want to cool down a little not beeing prone to exaggerate :basshead:



This will be hard to do to find words that can describe what you "should" be hearing.


----------



## SonicTrance

baronbeehive said:


> MisterX are your fans powered externally as well?


 
 Yes, I use a psu like this, with a 4-pin molex plug:

  
 And then I connect it to this:

  
 Remote controlled fans is the only way to go


----------



## SonicTrance

A couple of weeks ago I received a quad set of NOS WE421A's.
 I never thought I'd find a matched quad set of these tubes, let alone buy them, lol. But when I saw these for sale I just had to get them.
  
 They are all made in 1967 week 52, and are new and unused. I was very curious how they would test in my Heathkit TT1A tester. As you may know, the WE421A datasheet suggests a GM of 20000, compared to the 14000 of a "normal" 5998. These all tested around 16500-17000 on my tester, which is quite far from the 20000 spec, but still way higher than any 5998 I've tested before. Now that I think about it, I've never actually seen a listing for a WE421A were the seller states a transconductance of 20000 umhos.
  
 In the past I've compared the 5998's to the GEC A1834/CV2523/6AS7G's. And found the GEC's to be the superior tube IMO. I've actually recently sold all my 5998's thinking that the GEC's were the only powertube I'd ever need.
 The 5998 has huge soundstage, clarity, detail and impact. But I found the GEC's to have just that plus more of everything and a warmer smoother sound than the 5998's.
  
 Now, comparing the GEC's to the WE421A's I've found the new (IMO) king of powertubes for my setup. I fell in love with their sound almost immediately. Bass slam is incredible, hits hard, fast and accurate. Amazing clarity and detail. Basically a 5998 on steroids! One thing I noticed though is with the GEC's I preferred using the Mullard ECC32/33/35 as drivers. With the WE421A's, the slightly warmer TS BGRP really lets these output tubes shine.
  
 So I think anyone that's stating that there's no difference between the 5998's and the 421A's just have not heard the 421A. Granted, none of my previous 5998's were manufactured in 1967, like these 421A's, nor were they NOS. But still, the difference is clearly noticeable. At least in my setup!
  
 YMMV, and all that good stuff.


----------



## Redge78

> I have no problem with the hum any more. I am not shure what I have done but now evrything is ok
> 
> 
> 
> ...


 
 I don't like that, problems just don't vanish in thin air !
 You have to go back to your "hum" situation and find what happened then.
 This is not decent for a Mod thread when luck is more efficient than knowledge (or lack of ...)
 ...
 ...
 ...
 Kidding ... 
	

	
	
		
		

		
		
	


	



  
 Good you get rid of the bugger. 
  
  
 Noctua : yes, I have used those fans for years and they always performed without problem.
 My MK8 is cooled by a 140mm *NOCTUA NF-A14 PWM.*
 It is powered directly by my PC PSU through a Molex extension, and I can manage the air flow with the little resistance extensions Noctua provides with the fan.
 In winter I use them all, the fan is running at lowest speed, and that's more than enough. I tend to think now that the *"extra low noise version **NOCTUA NF-A14 ULN**" *could have been even more appropriate.* *
 The fan is 3 feet away from my ears and it's making less moise than the PC fans, even in summer when it blows more air. 
 Personnaly, I don't like the idea of having no cooling at all in the amp, so being driven by the PC is just perfect for me. I don't have to think about it.
 What I have add is a filter grill in front of the fan, I want as few dust to come in the amp as possible. Vaccum cleaned every week and that's perfect.


----------



## Mogos

Hum may come back and I suspect the pot. Now I have a bigger problem. I have change the tubes for another set and after 10 min of operation suddenly there was a short sound the the DC meters went to zero. Where to look for a problem?


----------



## Maxx134

Sometimes the protection relay kick in if there's a problem I would replace the original tubes and try again..


----------



## Mogos

I have tried with different set of tubes and nothing. But look it coud be this place responsible for lack of DC?

 During the change of the tubes I have been pushing a little the board and the after 10 minutes ther was sudden sounf and the DC went down.
 I have touched the wires and I thing there was no connection.


----------



## baronbeehive

sonictrance said:


> ........
> 
> Remote controlled fans is the only way to go


 
  
 Thanks, I may go that way, don't know yet, it doesn't bother me that the fans are powered internally though 
	

	
	
		
		

		
		
	


	




,
   
 Quote:


sonictrance said:


> A couple of weeks ago I received a quad set of NOS WE421A's.
> 
> .........


 
  
 Lucky person, your wallet must be suffering 
	

	
	
		
		

		
		
	


	




.....
   
  Quote:


sonictrance said:


> .........
> 
> Now, comparing the GEC's to the WE421A's I've found the new (IMO) king of powertubes for my setup. I fell in love with their sound almost immediately. Bass slam is incredible, hits hard, fast and accurate. Amazing clarity and detail. Basically a 5998 on steroids! One thing I noticed though is with the GEC's I preferred using the Mullard ECC32/33/35 as drivers. With the WE421A's, the slightly warmer TS BGRP really lets these output tubes shine.
> 
> ........


 
  
 That's very interesting. I'm really surprised about that. The 5998 is the one tube I'm curious about. I haven't bothered with them because with having the TS RP drivers I thought that I would be getting a similar sound to the 5998 power tubes, and also having both power and driver tubes by TS might be too much of a good thing. I am really surprised because I did think that the 5998 and WE421A were one and the same tube, except that some people that have tried them say that there is a difference in sound. So would you say that the combo of 421A and TS RP is especially magical sounding as I would imagine? And would you say that the 5998 is warm and tubey as some people have said or more clear and detailed as you have said. I ask this because I have heard different opinions about that.
  
 Your amp looks fantastic btw, almost pornographic 
	

	
	
		
		

		
		
	


	




 !!
  
 Quote:



> Originally Posted by *Redge78* /img/forum/go_quote.gif
> 
> I don't like that, problems just don't vanish in thin air !
> You have to go back to your "hum" situation and find what happened then.
> ...


 
  
 He, he...... you had Mogos going there 
	

	
	
		
		

		
		
	


	




. I agree I would not be happy with no cooling, Regarding dust, the surprising thing is that when we take the bottom plate off, how little there is inside. I vacuum mine poking a nozzle on the air holes on top!
  


mogos said:


> Hum may come back and I suspect the pot. Now I have a bigger problem. I have change the tubes for another set and after 10 min of operation suddenly there was a short sound the the DC meters went to zero. Where to look for a problem?


 
  
 As I said before, the one major thing I learned the hard way when computer programming is don't do more than one thing before testing it. The trouble is obviously you want to do everything while you have the back off, and that is understandable, but it is a nightmare when fault finding. Good luck, I hope you can trace the problem soon though.
  
 I might add, I won't be following my own advice!


----------



## Maxx134

I cant tell but it could be the wiring from the regulators to the board.


----------



## Maxx134

No that looks good.
Check the last stage psu caps didnt get loose..


----------



## SonicTrance

> Originally Posted by *baronbeehive* /img/forum/go_quote.gif
> 
> That's very interesting. I'm really surprised about that. The 5998 is the one tube I'm curious about. I haven't bothered with them because with having the TS RP drivers I thought that I would be getting a similar sound to the 5998 power tubes, and also having both power and driver tubes by TS might be too much of a good thing. I am really surprised because I did think that the 5998 and WE421A were one and the same tube, except that some people that have tried them say that there is a difference in sound. So would you say that the combo of 421A and TS RP is especially magical sounding as I would imagine? And would you say that the 5998 is warm and tubey as some people have said or more clear and detailed as you have said. I ask this because I have heard different opinions about that.
> Your amp looks fantastic btw, almost pornographic
> ...


 
 Yes, 421A and TS BGRP sounds really good to my ears. And to me the 5998 is NOT warm, at all. Neither is the WE421A, but you compensate that with slightly warm drivers  Like I said above, I think the WE421A is a 5998 on steroids and the sound I'm getting is unreal, lol.
  
 Yes, they did brake the bank but they're worth it.


----------



## baronbeehive

sonictrance said:


> Yes, 421A and TS BGRP sounds really good to my ears. And to me the 5998 is NOT warm, at all. Neither is the WE421A, but you compensate that with slightly warm drivers  Like I said above, I think the WE421A is a 5998 on steroids and the sound I'm getting is unreal, lol.
> 
> Yes, they did brake the bank but they're worth it.


 
  
 I was just thinking, did you try the 5998's after the mods because if you haven't heard them after doing the modding maybe it was the amp that was on steroids.......


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Yes, 421A and TS BGRP sounds really good to my ears. And to me the 5998 is NOT warm, at all. Neither is the WE421A, but you compensate that with slightly warm drivers  Like I said above, I think the WE421A is a 5998 on steroids and the sound I'm getting is unreal, lol.
> ...




Yes, I did try the 5998's after the mods but have since then sold them off. And I don't regret selling them as I think the GEC's and the WE421A's are superior, with the 421A's being my personal favorite.


----------



## baronbeehive

sonictrance said:


> Yes, I did try the 5998's after the mods but have since then sold them off. And I don't regret selling them as I think the GEC's and the WE421A's are superior, with the 421A's being my personal favorite.


 
  
 Neverthless......the amp IS on steroids! Where did you get your GEC's from, I've never been able to find any.


----------



## Maxx134

What headphones are you guys using? ..

I am asking just for reference...


----------



## SonicTrance

maxx134 said:


> What headphones are you guys using? ..
> 
> I am asking just for reference...




LCD-XC 95% of time. HE-400i the other 5%


----------



## baronbeehive

Quote:


maxx134 said:


> What headphones are you guys using? ..
> 
> I am asking just for reference...


 
  
 HE-500's.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Yes, I did try the 5998's after the mods but have since then sold them off. And I don't regret selling them as I think the GEC's and the WE421A's are superior, with the 421A's being my personal favorite.
> ...




Yes it is! 
Mostly of eBay. You need to have patients with these kinds of tubes as they rarely show up in good condition. I've managed to get several sets of GEC's so you need to watch eBay closely.


----------



## baronbeehive

sonictrance said:


> Yes it is!
> 
> 
> 
> ...


 
  
 ......."patience", not patients....... sorry to catch you out there, that's the only time you've ever slipped up.
	

	
	
		
		

		
		
	


	



  
 I find Ebay UK items expensive. The UK has rip off prices unfortunately, so I never start a search on ebay.co.uk, I always go to ebay.com for tubes because I know that UK tubes cost too much and I'm going to have to import them from elsewhere, usually USA.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Yes it is!
> ...




If you want the GEC's, you're more than likely gonna have to buy from the UK. Almost all of them are sold there, IME. 
I also use eBay.com as that page searches all the big eBay sites.


----------



## baronbeehive

maxx134 said:


> What headphones are you guys using? ..
> 
> I am asking just for reference...


 
  
 The only others I'm interested in trying sometime are the Alpha Prime's, as cans that possibly combine the best of the HiFiMan type and the LCD's. Incidently, a bit off topic but what headphone cables do you guys use, the silver one that came with the HE-500's was crap but I think good quality silver might improve sound. But what I can't get my head around is that why use silver when most of the cabling in most systems in components upstream from the actual cans, for example inside the LD, is most likely copper in which case I can't see the point of putting silver right at the end of the line, unless everything is silver. And some say silver plated copper is neither one thing nor the other.
  
 Edit: just trying to pass the time before Mogos gets his amp going 
	

	
	
		
		

		
		
	


	




.


----------



## Maxx134

The internals of the amp is totally separate from the cable that is coupling the headphone to the amp,

So yes the cable matters no matter what anyone says.

The problem lies in the fact that the differences are so minute that they require both ear and brain work together to notice the changes in perception, soundstaging and overal tonality.

These aspects are where standard simplistic blind A/B testing does not begin to cover or aknowledge. 
You have to be familiar with the gear you listening to,
 to notice the change, real differences in cables.

 Anyways I don't want to go off topic, but everyone looks for both coponent matching, cables, and even here with tubes, so bottom line, we're all looking for sonic bliss.


----------



## Mogos

Working,working. Scratching head. Working, working. Looking for errors 
	

	
	
		
		

		
		
	


	




. Working, working. Scratching head.


----------



## baronbeehive

Mogos, sorry to hear of your problem, I assume it is the same hum thing, or the short circuit. I don't know what you are doing but I can only suggest you work through every component or group of components eg coupling caps, WCF caps etc., and desolder and resolder - and test after every stage. I know it sounds a pain but assuming the readings are ok, I don't know how else you will find what it is and you might get lucky and find it straight away. It wouldn't take so long anyway. Could be a simple cold solder or oxidation that you missed of faulty connection or whatever. Your components are top quality so no problem there. The only thing that you've done that MisterX didn't was the pot so perhaps you could start there, although it didn't seem to be faulty when you were trying it out I believe. Do you think the fact that your replaced it with a different value pot to the original together with different resistor made any difference?
  
 Maybe I will follow my own advice after all when I do mine !! Good luck


----------



## Maxx134

We are helping him.
Just a Matter of time.


----------



## Mogos

baronbeehive said:


> Mogos, sorry to hear of your problem, I assume it is the same hum thing, or the short circuit. I don't know what you are doing but I can only suggest you work through every component or group of components eg coupling caps, WCF caps etc., and desolder and resolder - and test after every stage. I know it sounds a pain but assuming the readings are ok, I don't know how else you will find what it is and you might get lucky and find it straight away. It wouldn't take so long anyway. Could be a simple cold solder or oxidation that you missed of faulty connection or whatever. Your components are top quality so no problem there. The only thing that you've done that MisterX didn't was the pot so perhaps you could start there, although it didn't seem to be faulty when you were trying it out I believe. Do you think the fact that your replaced it with a different value pot to the original together with different resistor made any difference?
> 
> Maybe I will follow my own advice after all when I do mine !! Good luck


 

 It looks like it is hidden shortcut or some broken part. Maxx and Redge are taking care about me
	

	
	
		
		

		
		
	


	




. The hum thing in headphone is not a problem. The pot mechanics-contacts can be a little problematic but works (good reason for next upgrade 
	

	
	
		
		

		
		
	


	




). The different value of the pot and different resistors are not a problem for sure. One good thing in all this situation is that I have been listening to the moded amp for three days. And except some hum problems it was operating marvelously. The problem is connected with powering the amp. Maxx has prepared for me a plan of action. Step by step I will folow it. I beleve I can fix the problem with such a help.


----------



## SonicTrance

I hope you get it sorted soon, Mogos!
  
 In the meantime, here's some LD porn for you guys
	

	
	
		
		

		
			





 
  

  

  
 WE421A's together with Tung-Sol 6SU7GTY's. Wonderful combination of tubes!


----------



## baronbeehive

How brazen can you get 
	

	
	
		
		

		
		
	


	




.


----------



## Maxx134

sonictrance said:


> I hope you get it sorted soon, Mogos!
> 
> In the meantime, here's some LD porn for you guys
> 
> ...



What is the unit right under the amp?

I have LD-P*rn as well:

I bought a replacement laptop from Newegg but it died in days so I have to wait to replace my toy laptop there.


I wish Little Dot made the power conditioner for 110v so I could match ad it look nice.
Does anyone have it?

Edit wait :
I like that dam fan! Lol
And I see that is the LD dac! Nice.


----------



## SonicTrance

@Maxx134
 Yes, it's the DAC_III
 It doesn't matter if LD would make their power conditioner for 110v cause they refuse to ship it outside of China! As you know, I managed to get a LDP_500 from ebay that arrived in wrong color. After sending that unit back It's impossible to get a replacement. As the LDP series is quite new, they need to have it on the market for a while before shipping abroad.
  
 How do you like those Edition X's? Does the mk8 drive them well?


----------



## Maxx134

As you know the LDMK8SE was designed for high impedance headphones so whith help of Redge78 I made internal changes in amp to handle the HEX & Ether, still under testing..


----------



## SonicTrance

maxx134 said:


> As you know the LDMK8SE was designed for high impedance headphones so whith help of Redge78 I made internal changes in amp to handle the HEX & Ether, still under testing..


 
 I knew it! You're modding again to make your amp more like the mk6............KIDDING!
	

	
	
		
		

		
		
	


	



  
 Isn't it the tubes that sets the output impedance in our OCL amps? I'm very interested in what changes you made.


----------



## Maxx134

sonictrance said:


> maxx134 said:
> 
> 
> > As you know the LDMK8SE was designed for high impedance headphones so whith help of Redge78 I made internal changes in amp to handle the HEX
> ...



 Dam... 
Found out!







sonictrance said:


> Isn't it the tubes that sets the output impedance in our OCL amps? I'm very interested in what changes you made.




Too early to disclose untill refined.


----------



## SonicTrance

Fair enough. You'll tell us when you're good and ready.


----------



## Maxx134

baronbeehive said:


> maxx134 said:
> 
> 
> > What headphones are you guys using? ..
> ...



To me, the Oppo PM2(velour pads) and the ZMF Omni are superior to the HE560, which in turn are superior to the Alpha prime...
Have you noticed the trend in popularity to planars?
This is more ideal type headphone because of the steady impedance it has,
Compared to dynamic drivers which vary a certain range according to frequency response.
I have sold all my headphones that aren't planars types, except HD800..
So far..


----------



## SonicTrance

I'm thinking about getting a pair of LCD-3's. They should be a perfect match for the mk6 @ 110 ohms. But with all the driver failures I don't know...


----------



## baronbeehive

sonictrance said:


> I'm thinking about getting a pair of LCD-3's. They should be a perfect match for the mk6 @ 110 ohms. But with all the driver failures I don't know...


 
  
 .....really, I hadn't heard that. If I was to go for an LCD it would probably be the LCD3, with better treble possibly in better balance to the bass.
  


maxx134 said:


> To me, the Oppo PM2(velour pads) and the ZMF Omni are superior to the HE560, which in turn are superior to the Alpha prime...
> Have you noticed the trend in popularity to planars?
> This is more ideal type headphone because of the steady impedance it has,
> Compared to dynamic drivers which vary a certain range according to frequency response.
> ...


 
  
 Have you heard these at meets then? That's interesting feedback. I have dismissed the HE560's already because I like the slightly warm quality of the HE500's and don't want to lose that, so I see no reason to change. If I wanted out and out detail I would go for the HE6. But from the Alpha Prime thread it does seem to combine the best of the HiFiMan and LCD types. I like the immediate sound of the HiFiMan and that's basically why I don't like the Senns, they are too much at a distance. If you could get the immediacy of the HiFiMan and the sounstage of the Senns that would be ideal but of course that's impossible.
  
 I  have noticed the trend to planars, yes. However they don't seem to get the more in your face type of sound you get with the HD800 - by in your face I don't mean near the head I mean big unsubtle sound - though so I don't see the dynamics disappearing yet. What I do know about the planars it does seem that they provide a more sensitive and balanced response over the whole frequency spectrum due to the way the magnetic diaphragm responds over the entire surface of the membrane, as compared to the dynamic drivers. I find the frequency response of the HE-500 to be effortless.


----------



## SonicTrance

Any progress so far? @Mogos @baronbeehive
  
 I'm finally going to replace the wiring, second set of grid resistors and driver stage decoupling caps during the holidays. Will report back!


----------



## baronbeehive

Just working on my fitness atm prior to PCB removal. Only joking, I'll be ready to start around the same time that you're doing your next mods, beginning with replacing the output wires. Maybe I will do the same and replace the lot later, not now, I'll see how that goes first. I'll let you know when I'm ready to go.
  
 Are you going for solid silver or silver plated wires?
  
 Let us know your progress.


----------



## SonicTrance

baronbeehive said:


> Just working on my fitness atm prior to PCB removal. Only joking, I'll be ready to start around the same time that you're doing your next mods, beginning with replacing the output wires. Maybe I will do the same and replace the lot later, not now, I'll see how that goes first. I'll let you know when I'm ready to go.
> 
> Are you going for solid silver or silver plated wires?
> 
> Let us know your progress.


 
 Sound good! Keep us updated
	

	
	
		
		

		
		
	


	



  
 I'm gonna use silver plated copper wire, same as I used for the output from board to jacks, only one size smaller (22awg) and obviously three conductor.
 This is the wire I'm gonna use: http://www.ebay.com/itm/381386809718?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
  
 Edit: I'll also remove and blank off the SE output as I'm never gonna use it. Plus it means more room for caps


----------



## Mogos

I am also in progress for finding the fault. I had some health problems that slowed me down. It looks like I will have to order few more replacement parts. Probably the transistors are behaving not as it shall be. Without scheme and measuring reference points it is difficult to find out what is going wrong. PSU is very sensitive system.


----------



## SonicTrance

mogos said:


> I am also in progress for finding the fault. I had some health problems that slowed me down. It looks like I will have to order few more replacement parts. Probably the transistors are behaving not as it shall be. Without scheme and measuring reference points it is difficult to find out what is going wrong. PSU is very sensitive system.


 
 Sorry to hear about your health, Mogos. I do hope you get your amp sorted out soon! I'll open my amp up over the weekend for some surgery, let me know if you need me to make any measurements.


----------



## coinmaster

I have successfully created all of the stages of the MK6 from scratch components!

  
 I now have an understanding of how each section of the amp functions, except for the WCF which I don't 100% understand the fine details of yet.
 Also ironically, it turns out the reason that my PCB version of the amp did not work was because I had a faulty transistor in the power supply all this time.
  
 In any case, I have beefed up the input stage to make the old one look like an insect. The input tube cathode was referenced to ground with only a plate resistor to adjust current which isn't good because 6SN7s like to be run on high current and the current was rather low. also the plates voltages were not regulated nor were they running at optimal voltages based on the load lines of the tube.
 I have fixed all of this and added a gyrator (synthetic inductor) to replace the plate resistor which serves the same function except it also maintains a stable current for the tube.
 The result is the amplifier has twice as many components (maybe more?) and I cannot plug n play any tube I want, but at the same time I can technically use more tube types than I could before. I have to manually adjust the voltage and current via potentiometers to match the "happy spot" from the load line curves in the datasheets for each different tube I use but that means that each tube will be fine tuned for optimal performance. It's pretty obvious based on design and component values that the designer intended this amp to be a jack of all trades rather than refine it toward something specific.
  
 As for the output stage,  I may adjust the voltages because the the voltage that the output tubes are running at are an act against god if you look at the load lines for a 6080 tube, the only reason the amp doesn't sound like a potato is because the amp employs negative feedback to flatten out the huge distortion this would cause (the gain switch, lower = less distortion) which more or less isn't a good thing in itself. First I need to try and figure out if this was lazy design or if this was some sort of compromise for the direct drive output.
  
 For the cathode bypass cap I'm going to experiment with using an LED (light emiting diode) bias instead of a cathode resistor and a cathode bypass cap, LEDs have a good reputation for sounding better but I think that generally assumes the alternative is a lytic cap and not a high value high quality MKP cap which is what I have.
  
  
 Sadly I need another set of transformers and quite a few more parts in order to completely rebuild both channels with my upgrades so it might be another month or so before I can really listen and experiment.
  
 Also mogos I notice you are still having issues, I have done troubleshooting up the wazuu with this amp and ended up building it from scratch in the end so maybe I can help. Hit me up in a P.M.


----------



## Mogos

Coinmaster congratulations 
	

	
	
		
		

		
			





.  You should have a nick name: NocompromiseMan. Somehow your persistence in action is a motivation for me to fix my problem. Maxx and Regde are helpng me. It may be also a problem with transistors in my case.


----------



## baronbeehive

mogos said:


> I am also in progress for finding the fault. I had some health problems that slowed me down. It looks like I will have to order few more replacement parts. Probably the transistors are behaving not as it shall be. Without scheme and measuring reference points it is difficult to find out what is going wrong. PSU is very sensitive system.


 
  
 Hope you......... and your amp are better soon, you're keeping us in suspense 
	

	
	
		
		

		
		
	


	




.
  


coinmaster said:


> I have successfully created all of the stages of the MK6 from scratch components!
> 
> ...........


 
  
 I thought you were quiet recently,  now I know why, glad you didn't give up when you sounded like you were on that downer!!
  
 You've picked up a staggering amount of knowledge, let me know when you are marketting your monoblocks 
	

	
	
		
		

		
		
	


	




.
  
 MisterX, I hope you don't get affected by this dreaded transistor problem 
	

	
	
		
		

		
		
	


	




. I'll be interested in how much of a problem the rewiring is.


----------



## SonicTrance

coinmaster said:


> I have successfully created all of the stages of the MK6 from scratch components!
> 
> 
> 
> ...



Congrats on getting things working again! 
I'm sure you know that the mk6 is designed around the 6SL7 and not 6SN7. How were the voltages if you compare them to 6SL7 spec?



baronbeehive said:


> mogos said:
> 
> 
> > MisterX, I hope you don't get affected by this dreaded transistor problem :mad: . I'll be interested in how much of a problem the rewiring is.
> ...


----------



## coinmaster

> I'm sure you know that the mk6 is designed around the 6SL7 and not 6SN7. How were the voltages if you compare them to 6SL7 spec?


 
 The initial voltages and current does fit the 6SL7 better but 6SN7 seems to sound better even if it's not being run optimally.
 6SL7 seems to be happy around 220v at 2ma which was pretty much what the original input stage was, although the triodes did not seem to have matching voltages across them last time I checked, actually if I recall the plates were 130v and 115v even though the B+ was 220v which is a serious imbalance and kind of a strange voltage drop.
 The 6SN7 likes to hang around 150v at 10ma, and with my new design, the current and voltage is stable at 150v 10ma.
  


baronbeehive said:


> mogos said:
> 
> 
> > MisterX, I hope you don't get affected by this dreaded transistor problem
> ...


 
 I've been gone awhile, didn't realize this problem became so prevalent. I've dealt with the transistor problem a bunch of times, I got a bunch of dead ones sitting in a pile 
	

	
	
		
		

		
		
	


	




. It's really not that hard to fix, the transistor itself is obviously a cakewalk to replace other than getting it out of the case first. The problems that caused it may be another story but it's not that hard to determine the source of the issues once you know how the amp works. I gave mogos a set of instructions that will solve his issue in one way or another, although he has been struggling this whole time without replacing his transistor once! I've found that a rule of thumb in my experience for this power supply is that if you break the 100v zener diode before the transistor then the transistor is probably fried too. Also if you're 2k2 resistor starts smoking right as you turn it on, your transistor is probably fried.


----------



## SonicTrance

coinmaster said:


> > I'm sure you know that the mk6 is designed around the 6SL7 and not 6SN7. How were the voltages if you compare them to 6SL7 spec?
> 
> 
> 
> ...


 
 I don't agree, nor do I disagree. There are so many different 6SL7's and 6SN7's to choose from and, IMO, both tube familys sounds great in the MK6. I also enjoy the 6C8G's and 6F8G's and not to forget the Mullard ECC32/33/35's.
 All tubes with quite different specs but they all sound great in the MK6. I don't really care if I run tubes out of spec, the important thing is how they sound!


----------



## coinmaster

> I don't really care if I run tubes out of spec, the important thing is how they sound!


 
 Yeah but there are reasons they sound the way they do when they are in or out of spec, it is not a mystery it is based on the load line curves.
 If they are out of spec they can run into clipping, unlinearities, and who knows what other distortion. Plus like I said, even though the amp was more biased toward the 6SL7 there was still an imbalance on the amplification and the voltage/current was not regulated or even filtered(much) so even when it was biased correctly it was still not biased correctly. All kinds of unoptimal things happening in the input stage.


----------



## SonicTrance

coinmaster said:


> > I don't really care if I run tubes out of spec, the important thing is how they sound!
> 
> 
> 
> ...


 
 Yes, of course it'd be optimal to run tubes according to spec. I'm just saying, since I'm not building my amp from scratch, I'm happy to run any tube that works and sounds good out of spec.


----------



## Maxx134

Hey from my only few year experience with tube,
I don't believe they "clip" .
They perform differently from transistor and the distortion is a much different type than that from transistors, 
It is totally listenable and desirable in guitar amps, 
So it is my opinion the designer intended the amp to run the tube's in his desired preference of tube linearity..
There are alot of tube amps that sound heavily tubey because of same thing about running the tube's a certain way.

Anyways if you want that tube majic then I would keep the power output stage similar,
Yet I also agree to make the driver stage as linear as possible as that is a low level stage.

In the MK8, the opposite is done, as the output stage has the most linear tubes, famously labeled the "Supertubes" because of superior tube characteristics..
Makes me think the MK8 would have less tube sound...


----------



## baronbeehive

maxx134 said:


> Hey from my only few year experience with tube,
> I don't believe they "clip" .
> They perform differently from transistor and the distortion is a much different type than that from transistors,
> It is totally listenable and desirable in guitar amps,
> ...


 
  
 Absolutely, I think the designer knows a lot more than we do re tube characteristics and how they perform in a given amp.
  
 Yes, distortion is desirable indeed in guitar amps. Talk to Jim Marshall about the distortion deliberately built in to his guitar amps without which we would not have rock and roll as we know it today! Just think of Hendrix for example. Whereas in hifi amplification the aim is to minimize distortion not exaggerate it.


----------



## coinmaster

> Anyways if you want that tube majic then I would keep the power output stage similar


 
 I am building myself a monster bench variable power supply so I can test the output stage at different voltages and do some other experiments. We'll see what happens.


----------



## SonicTrance

Rewiring is complete. I also changed the second set of 300 ohm grid resistors for the power tubes with z-foils! 
	

	
	
		
		

		
		
	


	



 I was going to install the Wima MKP4 50uf's as driver stage decoupling, but decided not to. They do fit between the pot and meters but I'd have to extend the meter wires to make them fit. I knew this before ordering thinking it'd be a "piece of cake", but it'd be a pain to do without removing the board and I'm just not doing that ever again, unless I have to. I have 33uf mcaps on the way with express delivery instead. Should be here on Tuesday.
  
 The wiring was pretty straight forward. The tricky bit was the inputs on the board as the solder points are so close together. I also removed the SE jack on the front and disconnected the RCA's on the back.


----------



## baronbeehive

sonictrance said:


> Rewiring is complete. I also changed the second set of 300 ohm grid resistors for the power tubes with z-foils!
> 
> 
> 
> ...


 
  
 Another very nice job 
	

	
	
		
		

		
		
	


	




. You've answered my question, the wiring is not the massive problem that I thought it might be. It looks like just the 4 runs on the left from board to phone socket to input and output jacks. You don't need to touch the wiring from the power socket to on/off switch. I assume you changed the wiring on top of the board when you last had it out?
  
 Your wiring is a lot lower down towards the bottom than mine which is up near the top side.
  
 You had the stock 300ohm power grid resistors before didn't you?
  
 Shame about the wimas though.
  I'm going to have to think about that now and maybe be more ambitious while the PCB is out....... if I can get it out that is 
	

	
	
		
		

		
		
	


	




.
  
 Edit: And not a sign of hot glue anywhere 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Rewiring is complete. I also changed the second set of 300 ohm grid resistors for the power tubes with z-foils!
> ...




Thanks
Yes, no need to change the wiring from the power switch. 
I did change the output wires from board to jacks when I first did the mods. 
Which wires are lower?
Yes, I only changed four grid resistors before because we missed the second set of grid resistors for the power tubes. You need to change eight 300 ohms grid resistors in total, same as the MK8 if you look at first page. 
Yours should be fine as you have more room between the pot and meters than I do. I also re-routed my meter wires when I first did the mods so they are very tight. No wiggle room.


----------



## baronbeehive

sonictrance said:


> Thanks
> Yes, no need to change the wiring from the power switch.
> I did change the output wires from board to jacks when I first did the mods.
> Which wires are lower?
> ...


 
  
 Yes there is wiggle room on mine. The 4 wire runs and the power wires ie all the wires are toward the top of the unit ie. above the PCB whereas yours are below.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Thanks
> ...




My wires were also routed like yours, toward the top. I rerouted them like this for better airflow to the top side of board.


----------



## baronbeehive

sonictrance said:


> My wires were also routed like yours, toward the top. I rerouted them like this for better airflow to the top side of board.


 
  
 Oh I see, I didn't know you rerouted the old wiring. I misunderstood Maxx's advice on this when he said it is advisable to raise up the wiring, I think he means lower the wiring toward the bottom so that air can flow around the sides of the board to the top.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > My wires were also routed like yours, toward the top. I rerouted them like this for better airflow to the top side of board.
> ...




Yes. While you're working on the amp and it's upside down, you're in fact raising the wires.


----------



## baronbeehive

sonictrance said:


> Yes. While you're working on the amp and it's upside down, you're in fact raising the wires.


 
  
 Correct, up is down and vica versa 
	

	
	
		
		

		
		
	


	




.
  
 I hope to try removing the board any day now, but I may be a while working on it because I might change plans as I go along.


----------



## baronbeehive

.......no soldering experience, no knowledge........ what can go wrong??


----------



## SonicTrance

I would not recommend removing the board completely. Just tilt it so you can get to the top side, leaving all those brittle wires attached. Take lots of photos so you know where all the wires go if/when they brake. 
If you unscrew the meters, you can tilt the board pretty far. Remember to support the board so it doesn't strain the wires. 
Good luck!


----------



## baronbeehive

OK, thanks, I appreciate any advice, should be ..... fun?
  
 At least I have my speaker amp, should anything untoward happen, which of course it won't!


----------



## Maxx134

sonictrance said:


> Rewiring is complete. I also changed the second set of 300 ohm grid resistors for the power tubes with z-foils!
> I was going to install the Wima MKP4 50uf's as driver stage decoupling, but decided not to. They do fit between the pot and meters but I'd have to extend the meter wires to make them fit. I knew this before ordering thinking it'd be a "piece of cake", but it'd be a pain to do without removing the board and I'm just not doing that ever again, unless I have to. I have 33uf mcaps on the way with express delivery instead. Should be here on Tuesday.
> 
> The wiring was pretty straight forward. The tricky bit was the inputs on the board as the solder points are so close together. I also removed the SE jack on the front and disconnected the RCA's on the back.



Ver nicely done.

Aldo remember that the fan blowing air into unit may escape out that removed socket in front.


----------



## Maxx134

baronbeehive said:


> .......no soldering experience, no knowledge........ what can go wrong??



Nothing as long as you remember there is a nut holding the volume in place when trying to pull out the board!


----------



## SonicTrance

maxx134 said:


> sonictrance said:
> 
> 
> > Rewiring is complete. I also changed the second set of 300 ohm grid resistors for the power tubes with z-foils!
> ...




Thanks!
You didn't think I was gonna leave that empty did you?  I got one of these: http://www.ebay.com/itm/361388769935?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Silver painted of course.


----------



## baronbeehive

sonictrance said:


> Thanks!
> You didn't think I was gonna leave that empty did you?
> 
> 
> ...


 
  
 Mogos has turned his amp into a heater, you could go for the air conditioning option by leaving the chassis plate off, or maybe have lights flashing through the hole in sync to the music 
	

	
	
		
		

		
		
	


	




.
  
 I received my 2 western electric 421a's the other day, a bit loose at the base but not a problem, otherwise look new apart from the branding. Just got to wait for another 2 sometime so I can hear that fabulous sound 
	

	
	
		
		

		
		
	


	




. At least I can justify the expense by telling myself that I only use TS 6SL7's not 6SU7's, one set cheap, the other pretty dam pricey!


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Thanks!
> ...


 
 Haha, yeah! I believe @Maxx134 has some kind of tube that flashes to the music on his regulator cover, between the transformers. 
  
 Nice! You've got a pair of WE421A's. Where did you get them? I've seen more and more on ebay lately but they usually don't test that great.


----------



## SonicTrance

I got my new driver stage decoupling caps today, Mundorf mcap 33uf. So I quickly threw myself over the soldering iron to get them installed. I've been without my amp for several days and need to get my fix, lol 
	

	
	
		
		

		
		
	


	



  
 I've changed three things since I last listened to the amp. Input/output wiring, grid resistors that are between the coupling caps and power tube grid and the driver stage decoupling (had 15uf, now 33uf) Since I placed the new decoupling caps by the pot, I soldered them directly on the anode/cathode resistors for shorter wire runs.

  

  

  
 You can barely see it, but the decoupling cap lead is soldered on the z-foil cathode resistor.

  

  
 I'm happy to say light up and plays (I get nervous every time I've had my soldering iron in the amp)
 First impressions is that the bass is fuller and overall sound quality clearer. In short, it sounded beautiful before and now it's even better. It's amazing what this amp can do with these mods in place!


----------



## baronbeehive

sonictrance said:


> Haha, yeah! I believe @Maxx134 has some kind of tube that flashes to the music on his regulator cover, between the transformers.
> 
> Nice! You've got a pair of WE421A's. Where did you get them? I've seen more and more on ebay lately but they usually don't test that great.


 
  
 Yeah, Maxx probably has the all singing, all dancing model 
	

	
	
		
		

		
		
	


	




. Only joking! I got the tubes from an ebayer in the US for about TS5998 prices. ATM there are some sellers selling pretty weak WE's for astronomical money. I tend to ignore tubes with only percentage ratings without a reference to an absolute value. And very few professional seller have these tube types these days.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Haha, yeah! I believe @Maxx134 has some kind of tube that flashes to the music on his regulator cover, between the transformers.
> ...


 
 Ok, nice! You got a good deal then. Hope you manage to get another pair soon!


----------



## baronbeehive

sonictrance said:


> I got my new driver stage decoupling caps today, Mundorf mcap 33uf. So I quickly threw myself over the soldering iron to get them installed. I've been without my amp for several days and need to get my fix, lol
> 
> 
> 
> ...


 
 You don't say if it's you that lit up or the amp 
	

	
	
		
		

		
		
	


	




. Good that everything still works, no transistor problems. It looks good inside, like you've been round with some polish, very clean! Those new z-foils fit neatly, do they have to stand upright? Do you use heatshrink, and do you heat the heatshrink?
  
 I reckon the wiring has made a difference, it would be a shame to skimp on this when everything else is done I think.
  
 Those pictures are very helpful again.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > I got my new driver stage decoupling caps today, Mundorf mcap 33uf. So I quickly threw myself over the soldering iron to get them installed. I've been without my amp for several days and need to get my fix, lol
> ...


 
 Haha, true! I too lit up out of happiness. I'm telling you, those four minutes that it takes for the amp to start feels like an hour when you're just sitting there staring at it, lol.
  
 The z-foils look like this:

 So it's easiest to have them standing. I've lots of 18awg PC wire that I strip and use as insulation on the leads. On most solder joints were I've extended the leads, I use heatshrink which I heat. I've also used stripped wire insulation on some solder joints.
  
 I'm glad you find the pictures helpful, that's the whole point!


----------



## baronbeehive

I mentioned about cables in a recent post and am having a rethink now that I've decided to do the 4 internal cable runs with the rest of the work. Although I'm not a big fan of exotic cables I do want to get this right while I'm doing the other work. The choices boil down to OFC copper without silver plating, OCC copper without silver plating and finally either of these with silver plating. I've just seen a quote from Atlas cables where they mention that they refuse to use two materials of differing resistance ie copper and silver plating, they say its best to go for one or the other provided they are of high quality materials, ie OCC copper for example. That comes back to what I said in my other post about silver plated copper being neither one thing nor the other.
  
 I notice Mogos is using solid silver mainly and I myself like copper so I wondered what your thoughts were on this? Maxx you said you went for OCC copper was this silver plated as well, as Sword Yang recommended?


----------



## SonicTrance

baronbeehive said:


> I mentioned about cables in a recent post and am having a rethink now that I've decided to do the 4 internal cable runs with the rest of the work. Although I'm not a big fan of exotic cables I do want to get this right while I'm doing the other work. The choices boil down to OFC copper without silver plating, OCC copper without silver plating and finally either of these with silver plating. I've just seen a quote from Atlas cables where they mention that they refuse to use two materials of differing resistance ie copper and silver plating, they say its best to go for one or the other provided they are of high quality materials, ie OCC copper for example. That comes back to what I said in my other post about silver plated copper being neither one thing nor the other.
> 
> I notice Mogos is using solid silver mainly and I myself like copper so I wondered what your thoughts were on this? Maxx you said you went for OCC copper was this silver plated as well, as Sword Yang recommended?


 
 I'm not a fancy cable guy myself, but chose to go with silver plated copper because that's what the designer recommends.


----------



## baronbeehive

sonictrance said:


> I'm not a fancy cable guy myself, but chose to go with silver plated copper because that's what the designer recommends.


 
  
 Yes! I'm tempted by OCC copper myself. I've seen many silver plated copper cables but do you know of any silver plated OCC copper cables offhand?


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > I'm not a fancy cable guy myself, but chose to go with silver plated copper because that's what the designer recommends.
> ...


 
 Sorry, I don't. I just went with OF copper.


----------



## baronbeehive

sonictrance said:


> ...............
> 
> I'm happy to say light up and plays (I get nervous every time I've had my soldering iron in the amp)
> First impressions is that the bass is fuller and overall sound quality clearer. In short, it sounded beautiful before and now it's even better. It's amazing what this amp can do with these mods in place!


 
  
 Would you say that the treble is any brighter with the new wiring in place? Still trying to decide 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > ...............
> ...




To my ears, it sounds more detailed, not only in treble, after the wiring upgrade. Not brighter. Hope that helps.


----------



## baronbeehive

sonictrance said:


> To my ears, it sounds more detailed, not only in treble, after the wiring upgrade. Not brighter. Hope that helps.


 
  
 Thanks, that helps, I don't want bright treble. I think I've decided, I may go for the high purity OCC copper on the grounds that high purity will give better all round sound and then that warm copper sound on top.............. on the other hand .............if the silver doesn't increase brightness..........OMG 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > To my ears, it sounds more detailed, not only in treble, after the wiring upgrade. Not brighter. Hope that helps.
> ...




I don't think the difference will be night and day anyway. You wont change the sound signature of the amp with the wiring, just enhance it. You get sound signature from coupling caps/WCF caps and tubes.


----------



## Mogos

My amp came back to live!!. I would like to thank Maxx and Redge for help and Coinmaster for very valuable instructions in the final stage of reanimation. The main problem was connected with the transistors MJ15020 and MJ15021. On the way to fix it I have found out a broken circut and I have changed few parts which do not necessarily have to be changed 
	

	
	
		
		

		
		
	


	




. I have also improved few other things. The transistors MJ15020 and MJ15021 are not produced any more. I have used replacements recomended by the producer MJ15024G and MJ15025G. The new transistors do have different parameters then the originals. There was a concern if they will have impact on the sonics of the amp. I can report back that there is none. The amp sounds as great as with originals. To bring back the amp to live  was not easy. Especialy the final stage was difficult for me. On Tuesday I have recieved the transistors (they have been on the last positions of the potential problem makers for change) and have had installed them. I was very carefull with soldering and all other things. After all I have putted back the board in place and turned on the amp with big hope the meters will show the values as before. And it did not happend 
	

	
	
		
		

		
		
	


	




. My hands went down. I have done voltage measurements. The values were not as supposed to be for the circut of one of the transistors. I thought how bad lack. A new and already faulty transistor 
	

	
	
		
		

		
		
	


	




. So after some time I have started again to dismantle the board and find out that the wire from the transistor Base was broken. How it could happend!!! I don't know . I have soldered everything realy very carefully. But doesn't matter. The hope came back. I have soldered the wire and powered the amp. The meters showed that with the PSU evrything is ok this time. The measurement of the voltages in all points have showed correct values. I get excited and had started thinking there will be music flowing from my headphones soon. I have soldered all socket wires and the pot. I have done everything and closed the casing. Connected the amp with the rest of my gear powerd on and ............. no sound 
	

	
	
		
		

		
		
	


	
















What? Why? How come? Meters ok and no sound? The pot was on the half way to full. I have turned the pot almost full and I have started to hear very weak and distorded signal. Again hands down. The next steps plan has been consulted with coinmaster. I did not have any more power to fight with the amp especially that it looked like I will have to dismantle so tidiously installed new parts. I decided to leave it for some time later. Thinking how to survive without the music (real and live, for just listening or if I have to travel in business I have Graham Slee Solo) I have decided to do last thing before I will put it a side for some time. I did have some suspicion about the pot. I decided to desolder the pot and put just resistors (56k). And that was it!!! Pot proved to be problematic. For now I have decided to stay with the resistors in place of the pot. I did not use the pot before. It stayed always on 10 o'clock all the time as I am controling the volume digitaly. I am thinking to install in the future a Kozmo pot. For now 4 tantalum resistors will be good enough.
 After few months of fight I have herd music from my amp 
	

	
	
		
		

		
		
	


	




. Now testing and observing. I hope this time it will work for good not just few days 
	

	
	
		
		

		
		
	


	




.
  
 My pot now looks like this 
	

	
	
		
		

		
		
	


	




. (temporay metal film 56k resistors, I think I will have to install the value around 80k to be in a desired range of volume control)


----------



## SonicTrance

Wow Mogos! You've been on a emotional roller coaster! I'm glad to hear your amp's working again


----------



## Mogos

I am still feeling dizzy 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

mogos said:


> ...........
> After few months of fight I have herd music from my amp
> 
> 
> ...


 
  
 So it was a faulty pot! And the other problems ........ you must have been having kittens over it!! When the problem is unrelated to the alterations you have done that is something that is practically impossible to find the cause of. Glad you've finally solved it!
  
 Now have a rest and let the music flow!! And when you're ready maybe give us your impressions
	

	
	
		
		

		
		
	


	



  
 Edit: I also had a Graham Slee amp!


----------



## SonicTrance

Some pics on how the amp looks now. I've painted the Neutrik cover and the regulator cover in silver to match the case. 
 Running a pair of TS BGRP 6C8G's with the WE421A's now. I'm extremely happy with the sound. Wouldn't want to add anything nor take anything away, simply perfect!


----------



## Mogos

Beautifull. I envy you the tube set. Great looking and I believe very good sounding. I am trying to imagine the sound of the moded LD with the set of Mister X tubes. The moded LD is like LD on steroids. If you add the tube set on steroids than my imagination do not reach so far. I did have some expectations about the mods suppose to bring to the amp. I have got everything plus more. So adding to that more even more is really out of my imagination. Congratulations Mister X. I truly belive that you have your nirvana every time the music flows.


----------



## SonicTrance

mogos said:


> Beautifull. I envy you the tube set. Great looking and I believe very good sounding. I am trying to imagine the sound of the moded LD with the set of Mister X tubes. The moded LD is like LD on steroids. If you add the tube set on steroids than my imagination do not reach so far. I did have some expectations about the mods suppose to bring to the amp. I have got everything plus more. So adding to that more even more is really out of my imagination. Congratulations Mister X. I truly belive that you have your nirvana every time the music flows.


 
 Thanks Mogos!
 Yes, I can't imagine a better sound than what I'm hearing. I'm very happy.
	

	
	
		
		

		
		
	


	



  
 Now I'm searching for a used pair of LCD-3's. They should match this amp perfect with its 110ohm impedance.


----------



## baronbeehive

sonictrance said:


> I don't think the difference will be night and day anyway. You wont change the sound signature of the amp with the wiring, just enhance it. You get sound signature from coupling caps/WCF caps and tubes.


 
 No, you're right. I've just had a look at the thread discussing the supposed benefits, or otherwise of silver plating on cables and to be quite honest there is a whole lot of prejudice being thrown about there and a lot of opinions but very little facts. Also OCC copper is incredibly expensive! So I've just got to decide on OFC or OFC with silver now and I doubt if there will be much difference. Whatever, I think the main differences in components such as cables is in their quality of manufacture not in the materials themselves, ie there are good and bad silver cables and good and bad copper ones and so on.
  
 Mogos, I see most of your wiring is solid silver, can I ask would you say that your treble is bright and your bass light or is it as I suspect very full and rich sounding. Are you using any copper wiring?
  
 Talking of predudice what I like about this thread is that everything is experimentally verified where possible and Maxx and Redge have not made false claims for their mods and have not said anything about the mods until they were satisfied that what they were saying was correct. Well done to them


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > I don't think the difference will be night and day anyway. You wont change the sound signature of the amp with the wiring, just enhance it. You get sound signature from coupling caps/WCF caps and tubes.
> ...




The wire I use is 19 strands and very stiff, good for bending and staying in place. I use the same wire to extend the cap leads where needed.


----------



## Mogos

I did use some slilver/gold (Mundorf), silver (Neotech) and OCC copper (Neotech) solid wires for making extensions of the capacitors legs or other connections on the board (eg. for pot installation). For wiring the audio inputs I have used a silver plated OFC in teflon insulation (19 strands) wires. I think the most universal and with high probability of satisfaction garantee should be a silver plated OFC wires (with high purity of copper). I am always using wires with addition of silver or pure silver. In my opinion silver has a big role in creation of live like sound giving overal speed to the sound and high frequencies easy flow.
 I forgot to wright about the sound signature I have. But now just in few words: bass is deep, fast, there is no brighness in high frequencies. They are as suppose to be. I will share more about the sound signature of SMLD (Super Moded Little Dot) later.


----------



## baronbeehive

mogos said:


> I did use some slilver/gold (Mundorf), silver (Neotech) and OCC copper (Neotech) solid wires for making extensions of the capacitors legs or other connections on the board (eg. for pot installation). For wiring the audio inputs I have used a silver plated OFC in teflon insulation (19 strands) wires. I think the most universal and with high probability of satisfaction garantee should be a silver plated OFC wires (with high purity of copper). I am always using wires with addition of silver or pure silver. In my opinion silver has a big role in creation of live like sound giving overal speed to the sound and high frequencies easy flow.
> I forgot to wright about the sound signature I have. But now just in few words: bass is deep, fast, there is no brighness in high frequencies. They are as suppose to be. I will share more about the sound signature of SMLD (Super Moded Little Dot) later.


 
  
 Thanks! In the thread on silver plated copper wires the general conscensus was that either silver or copper but not silver plated copper was best, but frankly I am rather skeptical about these opinions.
  
 Look forward to hearing your impressions, and perhaps more pics of that amazing amp, hope it keeps working nicely 
	

	
	
		
		

		
		
	


	




 !!!


----------



## Mogos

Yes working very nicely 
	

	
	
		
		

		
		
	


	




. I know alredy that I will have a big problem to describe some of the new qualities of the amp sound signature. One thing is simple and obvoius: It is very difficult to stop listening the music on it. You want more and more.
 One more thing about wires. In the cross section of the wire the high frequencies flow in out side layers and the low and mid frequencies occupy the inside area of the wire. So the solution with sliver plated copper shall suit very well the frequency transmission (high - fast, low and mid full, colorfull and power).


----------



## baronbeehive

mogos said:


> Yes working very nicely
> 
> 
> 
> ...


 
  
 Yes but the interpretation on that thread I mentioned was that there would be interference between the outside and inside layers resulting in incoherence, and that view is echoed in the quote by Atlas cables that I mentioned where they said that a metal plated by another metal of different resistance would react badly for audiophile purposes. I only mention it because it is an example of how one can interpret differently the same finding. As I said I view these findings with the utmost skepticism!


----------



## Maxx134

Happy New Year everyone! 
Been busy modding headphones. ..





baronbeehive said:


> I mentioned about cables in a recent post and am having a rethink now that I've decided to do the 4 internal cable runs with the rest of the work. Although I'm not a big fan of exotic cables I do want to get this right while I'm doing the other work. The choices boil down to OFC copper without silver plating, OCC copper without silver plating and finally either of these with silver plating. I've just seen a quote from Atlas cables where they mention that they refuse to use two materials of differing resistance ie copper and silver plating, they say its best to go for one or the other provided they are of high quality materials, ie OCC copper for example. That comes back to what I said in my other post about silver plated copper being neither one thing nor the other.
> 
> I notice Mogos is using solid silver mainly and I myself like copper so I wondered what your thoughts were on this? Maxx you said you went for OCC copper was this silver plated as well, as Sword Yang recommended?



I using both..




sonictrance said:


> baronbeehive said:
> 
> 
> > I mentioned about cables in a recent post and am having a rethink now that I've decided to do the 4 internal cable runs with the rest of the work. Although I'm not a big fan of exotic cables I do want to get this right while I'm doing the other work. The choices boil down to OFC copper without silver plating, OCC copper without silver plating and finally either of these with silver plating. I've just seen a quote from Atlas cables where they mention that they refuse to use two materials of differing resistance ie copper and silver plating, they say its best to go for one or the other provided they are of high quality materials, ie OCC copper for example. That comes back to what I said in my other post about silver plated copper being neither one thing nor the other.
> ...




The wiring I initially bought was a 3conductor silver plated which is excellent for INPUT wiring from jacks to board by the volume,
But for output, I found that it can add a bit of edge to transients, making an almost exaggerated dynamic sound to me.
Since my pursuit is for most natural sound, 
 I ADDED some OCC copper after,
 to supplement the output wiring to headphone jack.
That solved my issue.






sonictrance said:


> Some pics on how the amp looks now. I've painted the Neutrik cover and the regulator cover in silver to match the case.
> Running a pair of TS BGRP 6C8G's with the WE421A's now. I'm extremely happy with the sound. Wouldn't want to add anything nor take anything away, simply perfect!



Wanna trade?

Lol just kidding, but I whish we could do a comparison. 



On another note, 
It is MY belief that the transistor failure may have been due to swapping the power tubes prematurely before the new extra capacitance fully discharge...


Also, 
I may look into the long wait time for this amp to turn on.
It was meant to do so for the heaters to properly warm up.


----------



## SonicTrance

maxx134 said:


> Wanna trade?
> 
> Lol just kidding, but I whish we could do a comparison.
> 
> ...




It would be an interesting comparison indeed! What I really would like to compare is a stock mk6 vs my modded one. I can't really remember how my amp sounded before I started modding it, lol


----------



## baronbeehive

maxx134 said:


> Happy New Year everyone!
> Been busy modding headphones. ..
> I using both..
> 
> ...


 
  
 I was thinking about this recently and I agree with you about this. I've noticed some bad practises coming in for a while with members switching on and off without leaving adequate cool down and warm up time for tubes, swapping in and out tubes and back again too quickly, also mixing tube types which may or may not be OK. Also regarding the transistors the fact that we will have added components with different parameters must be taken into account which means that good practise for tube amps is that much more important. I think part of the problem is because we want to do comparisons but we are too impatient to compare tubes instead of waiting and allowing the amp to function naturally.  Tube amps are not SS amps after all.
  
 What you say about the edge to transients, others have mentioned elsewhere which is why I wanted to know what others thought about the silver plating.
  
 Where did you get the OCC copper wiring Maxx?
  
 Edit: Happy New Year, and HAPPY LISTENING ...... AND MODDING everyone!!


----------



## baronbeehive

maxx134 said:


> ........


 
  
 Maxx, are those wind speed indicators on top of your transformers lol 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

Silver plated OFC 3 core wire on its way for inputs and OCC single core for outputs, no more messing........
  
 I've decided to go for OCC copper only for outputs not a mix as Maxx has done. I think I'll use the time it takes for the wires to arrive from the US to try to lever out the board, I should have a week or so......... and I might need it 
	

	
	
		
		

		
		
	


	




.
  
 Oh and some cheapo silver alloy fuses like Mogos, well you never know!


----------



## baronbeehive

maxx134 said:


> Happy New Year everyone!
> Been busy modding headphones. ..


 
  
 In what way?
   
 Quote:


sonictrance said:


> Some pics on how the amp looks now. I've painted the Neutrik cover and the regulator cover in silver to match the case.
> Running a pair of TS BGRP 6C8G's with the WE421A's now. I'm extremely happy with the sound. Wouldn't want to add anything nor take anything away, simply perfect!
> 
> 
> ...


 
  
 I'm after a bit of that perfection any day now 
	

	
	
		
		

		
		
	


	




.
  
 Sorry I had to delete your pics...... your LD looks too good lol!
   
 Quote:


mogos said:


> .......
> 
> I forgot to wright about the sound signature I have. But now just in few words: bass is deep, fast, there is no brighness in high frequencies. They are as suppose to be. I will share more about the sound signature of SMLD (Super Moded Little Dot) later.


 
  
 I think Mogos is too busy listening to his SMLD to write about it


----------



## SonicTrance

baronbeehive said:


> Silver plated OFC 3 core wire on its way for inputs and OCC single core for outputs, no more messing........
> 
> I've decided to go for OCC copper only for outputs not a mix as Maxx has done. I think I'll use the time it takes for the wires to arrive from the US to try to lever out the board, I should have a week or so......... and I might need it  .
> 
> Oh and some cheapo silver alloy fuses like Mogos, well you never know!




That's good news! Good luck! And post pictures


----------



## baronbeehive

sonictrance said:


> That's good news! Good luck! And post pictures


 
  
 Will do! If I get it to look and sound anywhere near as good as the other SMLD's I will be very happy 
	

	
	
		
		

		
			





. If I even get it to work it will be something 
	

	
	
		
		

		
		
	


	




.


----------



## Maxx134

The good thing around here is that most of what could go wrong, has already gone wrong and been repaired, 
So whoever has an issue it can most likely be resolved here. 
I myself have had some mishaps along the way, so no one is perfect.

Oh and another thing...
the *sonic* mods have not ended..

In fact the fun has yet to begin.


Waiting on parts, suks though. .


----------



## coinmaster

> the *sonic* mods have not ended..
> 
> In fact the fun has yet to begin.


 
 Yeah, I've got a substantial list of tests I'm going to conduct in the coming months, I spent a lot of money lab equipment so I can tweak, alter, and perfect. However I don't find it fun at all, I'll be glad when it's over and I never have to touch it again.
 I still haven't rebuilt my mk6 yet, almost 6 months with no music so far 
	

	
	
		
		

		
		
	


	




. 
 Just waiting on some prototype PCB boards so I have something to put the components on. Point to point has turned out to be more of a flimsy hassle than it's worth.
 Quote:


> Waiting on parts, suks though. .


 
 Ugh, tell me about it. I've done nothing but wait and wait and wait.


----------



## Maxx134

* Point to point has turned out to be more of a flimsy hassle than it's worth.*

Point to point with high voltages is pretty dangerous. .


----------



## coinmaster

> Point to point with high voltages is pretty dangerous. .


 
 Yeah, I've already had a couple small explosions from accidental shorts.
 Point to point makes it easy to build and test but it's so flimsy, move something a little bit and you can accidentally short something, especially those opamps.
 It would only be viable and safe if there was a predetermined structure for the components to rest on.
  
 I think I may just rebuild my mk6 as it was and then rebuild another one for testing because I can't keep living without my tunes


----------



## Maxx134

baronbeehive said:


> maxx134 said:
> 
> 
> > Happy New Year everyone!
> ...



In a good way.
I have successfully done two in my profile and have three others to go..


But the next amp mod must be done soon.


----------



## Mogos

So it’s time to write something about sonics of the Supper Moded LD. I am using rather standard setup of tubes compared to Mister X best you can get set. Those are Telefunken 6080WB and Tung Sol 6SN7 (new production). First of all the standard version of LD mk VI is very good sounding amp.
 Without any comparison of the LD mkVI to other amps and moded version I will say that there is only deficiency in articulation of short and energetic sounds (eg. percussion ones). So called pratt is a weak point and that could also be concluded that the amp is slow. All percussive sounds and similar ones where a little blurred and energy less. All other qualities were for me satisfactory as I have enjoyed to listen to music with this amp for more than three years. In this time I have been using Sennheiser HD 800.
 The mod has showed that in few regards you can get more than you can expect.  There are four qualities which gained a lot with the modification. Bass, transients articulation-speed,pratt, ease of swallowing wall of sound, and difficult to describe silkiness in high frequency registers similar to what I have heard in the Stax setup 009 with one of their top SS amps( I don’t remember exactly the numbering of the amp). By the way the silky sound of Stax setup did not impressed me at all. For me it was going aside from the live like music. The moded amp has only some similarities to the Stax setup and that’s good for me in this regard. Gain in the low frequencies registers is obvious and in very good direction. Bass is deeper and very well controlled. The improved responsiveness-speed is now making the percussive sounds more energetic and live like. What I have meant writing ease of swallowing wall of sound? I will described it like that . Sometimes in the song there is a moment that all instruments starts to play their part "screaming and shouting" at each other. I am calling it as the wall of sound. The music is getting loud and if your setup is not capable to handle it you will get noise instead of loud music. If the amp cannot cope correctly with such a moments in the recording than the instruments get glued to each other and a noise is produced instead of music. The moded amp copes with the wall of sound very well. You don’t feel any discomfort despite the loud and screaming at each other instruments and you hear every one separately and clearly. Overal separation of the instruments is very good. So those are the obvious improvements. There are other ones more subtle but making the whole presentation very enjoyable and addictive. You just don’t want to stop to listen to the music.
  
 Below healthy and happy playing music SMLD.


----------



## SonicTrance

Nice Mogos! 
I'm glad you finally get to enjoy and listen to your amp!

Ps. One thing I've noticed after modding is that the amp really "scales" well with nice tubes!


----------



## baronbeehive

mogos said:


> So it’s time to write something about sonics of the Supper Moded LD. I am using rather standard setup of tubes compared to Mister X best you can get set. Those are Telefunken 6080WB and Tung Sol 6SN7 (new production). First of all the standard version of LD mk VI is very good sounding amp.
> Without any comparison of the LD mkVI to other amps and moded version I will say that there is only deficiency in articulation of short and energetic sounds (eg. percussion ones). So called pratt is a weak point and that could also be concluded that the amp is slow. All percussive sounds and similar ones where a little blurred and energy less. All other qualities were for me satisfactory as I have enjoyed to listen to music with this amp for more than three years. In this time I have been using Sennheiser HD 800.
> The mod has showed that in few regards you can get more than you can expect.  There are four qualities which gained a lot with the modification. Bass, transients articulation-speed,pratt, ease of swallowing wall of sound, and difficult to describe silkiness in high frequency registers similar to what I have heard in the Stax setup 009 with one of their top SS amps( I don’t remember exactly the numbering of the amp). By the way the silky sound of Stax setup did not impressed me at all. For me it was going aside from the live like music. The moded amp has only some similarities to the Stax setup and that’s good for me in this regard. Gain in the low frequencies registers is obvious and in very good direction. Bass is deeper and very well controlled. The improved responsiveness-speed is now making the percussive sounds more energetic and live like. What I have meant writing ease of swallowing wall of sound? I will described it like that . Sometimes in the song there is a moment that all instruments starts to play their part "screaming and shouting" at each other. I am calling it as the wall of sound. The music is getting loud and if your setup is not capable to handle it you will get noise instead of loud music. If the amp cannot cope correctly with such a moments in the recording than the instruments get glued to each other and a noise is produced instead of music. The moded amp copes with the wall of sound very well. You don’t feel any discomfort despite the loud and screaming at each other instruments and you hear every one separately and clearly. Overal separation of the instruments is very good. So those are the obvious improvements. There are other ones more subtle but making the whole presentation very enjoyable and addictive. You just don’t want to stop to listen to the music.
> 
> Below healthy and happy playing music SMLD.


 
  
 That's good that you've managed to get some listening time in without having to bother about faulty parts for once! I too think the bass leading edge and transients speed are the main deficiencies in the bog standard LD. So the improvement from the mods is interesting, and very welcome. Also the improved instrumental separation and treble quality shows IMO that the mods are really taking the amps performance to another level, because you would expect improvements in these areas.
  


sonictrance said:


> Nice Mogos!
> I'm glad you finally get to enjoy and listen to your amp!
> 
> Ps. One thing I've noticed after modding is that the amp really "scales" well with nice tubes!


 
  
 Yes, I wonder, Mogos, if you've thought about NOS tubes, rather than new issue. I really think you would be amazed at, for example, NOS 6SL7 round plate Tungsols rather than new issue TS's. I have my opinions about new issue tubes. I've had them on my miniwatt amp, both Tungsols and TJ Full Music tubes. Also, I don't know what 6080 Telefunkens are suppposed to be like but I've tried Telefunkens on my other amp and didn't like them at all. I found them to be rather flat, both in frequency response and musical qualities. Some people like that because it gives quite a true sound but I much prefer something with good tonal colour. I don't know what you think about this?
  
 Keep enjoying your SMLD, and no more breakdowns please 
	

	
	
		
		

		
		
	


	




.


----------



## Mogos

I did not want to invest in tubes to much money as I was thinking from time to time to change the amp for something better 
	

	
	
		
		

		
		
	


	




. So I have never done some serious tube rolling. I have the original set of 6080WB and new production Tung Sols 6SN7 and 6SL7. The telefunkens are very similar or the same as the originals 6080. I am also reluctant to buy the so called NOS tubes as I am afraid to be cheated not beeing able to really verify what I have bought. I will serch for some NOS tube with good recomendations. What do you think about the Psvane tubes? I have heard that they are good and they are new production ones.


----------



## SonicTrance

mogos said:


> I did not want to invest in tubes to much money as I was thinking from time to time to change the amp for something better :rolleyes: . So I have never done some serious tube rolling. I have the original set of 6080WB and new production Tung Sols 6SN7 and 6SL7. The telefunkens are very similar or the same as the originals 6080. I am also reluctant to buy the so called NOS tubes as I am afraid to be cheated not beeing able to really verify what I have bought. I will serch for some NOS tube with good recomendations. What do you think about the Psvane tubes? I have heard that they are good and they are new production ones.




Now that you've invested time and money into your mk6 I strongly recommend investing in some nice tubes!

If you want to spend as little money as possible I'd recommend the Tung Sol BGRP 6SL7's for driver and Chatham 6AS7G/6520 (with copper grid posts) as powers. The psvanes does sound OK, but they can't compete with NOS tubes IMO. I've tried both the uk-6sn7 and "treasure cv-181". 

My favorite tubes are the following:

Power tubes:
WE421A
GEC 6AS7G
Tung Sol 5998
Chatham 6AS7G/6520

Driver tubes:
Mullard ECC32/33/35
Tung Sol BGRP 6SL7, 6F8G, 6C8G, 6SU7GTY
Ken Rad 6SN7


----------



## baronbeehive

sonictrance said:


> Now that you've invested time and money into your mk6 I strongly recommend investing in some nice tubes!
> 
> If you want to spend as little money as possible I'd recommend the Tung Sol BGRP 6SL7's for driver and Chatham 6AS7G/6520 (with copper grid posts) as powers. The psvanes does sound OK, but they can't compete with NOS tubes IMO. I've tried both the uk-6sn7 and "treasure cv-181".
> 
> ...


 
  
 Good tubes will lift your amp to yet another level as MisterX says, such that you may not need to change amps even! The Psvanes are probably the best of the new issues from what I've heard but are incredibly expensive. I think you will hear a difference even with the cheap and plentiful RCA 6AS7G's, they are more musical, but power tubes will not make as much difference as drivers. You can't really go wrong with tubes such as these and are not likely to be fooled by fakes. The 6SL7 TS's are still quite cheap and I believe are still less than £40 each, they were about half that when I bought mine. If you are not sure about what you are getting there are some reputable seller out there who will also advise you by email such as here: http://www.audiotubes.com/6sl7.htm They will not sell you fakes.
  
 I find new issue tubes are quite brittle sounding, OK, but there are no harmonic overtones or depth of sound, it is all superficial. NOS tubes transformed my cheap Miniwatt amp into a true audiophile amp.
  
 As you get more familiar with different tube varieties you will learn the identifying features, and learn to avoid some Russian fakes for example which have cheap plastic looking bases and usually very new looking branding, whereas most branding of NOS tubes fade and do not look new.
  
 Hope that helps!


----------



## Maxx134

Would like to see some nite time pics...


Most of time I get to listen is at night, so was wondering how others looked. .
Love tube glow..


----------



## Maxx134

baronbeehive said:


> mogos said:
> 
> 
> > Yes working very nicely :atsmile: . I know alredy that I will have a big problem to describe some of the new qualities of the amp sound signature. One thing is simple and obvoius: It is very difficult to stop listening the music on it. You want more and more.
> ...



The noted issues with silver plated wire are primarily involved in lengths for headphone cable.
Inside an amp silver would aid in contact transfer.
Most all solder has silver in it.
Silver contacts in XLR plugs are better than gold plated..
So the application matters..


----------



## Mogos

Thank you guys for info about tubes. I belive you that the tubes matters. I am just not aware yet how much. It is a greater improvement than eg. a high quality headphone cable or equal or less? With the cables I do have experience and they can do an improvement. I know there is no way back I will have to check it 
	

	
	
		
		

		
			





. When there was posted an idea about changing the inside components of the amp I have had a strong belive that it will be worth the effort and money. With tubes rolling I do have less belive or may say less expectations.  And you say it could be even better than it is now 
	

	
	
		
		

		
		
	


	




. It is getting hard to imagine even more improved sound of the amp. And if you tray to add what Maxx and Redge are "cooking" for additional sound "boosting" then it is definetly beyond my imagination 
	

	
	
		
		

		
		
	


	




.
  
 I don't know if you would like to see my amp at night.
 But what the hell here you have.


----------



## SonicTrance

Different tubes makes a HUGE difference! Much more than cables. You change the overall sound signature with different tubes. You have a lot to look forward to!


----------



## baronbeehive

The fun is just beginning 
	

	
	
		
		

		
		
	


	




.
  
 Quote:


maxx134 said:


> The noted issues with silver plated wire are primarily involved in lengths for headphone cable.
> Inside an amp silver would aid in contact transfer.
> Most all solder has silver in it.
> Silver contacts in XLR plugs are better than gold plated..
> So the application matters..


 
  
 Thanks, that's clarified the position. I have silver plated DAC>AMP cables which I may compare sometime with OCC copper, but looking forward to trying OCC copper outputs for the SMLD. Just waiting for the rest of the cabling to arrive.


----------



## SonicTrance

maxx134 said:


> Would like to see some nite time pics...
> 
> 
> 
> ...


 
 I rolled in a set of GEC A1834's today. They have a nice glow.


----------



## Mogos

I have never seen such strong illuminating tubes. Wow very nice. How has changed the sound signature compared to WE 421A?


----------



## SonicTrance

mogos said:


> I have never seen such strong illuminating tubes. Wow very nice. How has changed the sound signature compared to WE 421A?


 
 Long exposure "adds" a bit of light as well
	

	
	
		
		

		
		
	


	



  
 The GEC's sound warmer, smoother, more tubey than the WE421A. Bass isn't hitting as hard as the WE421A. Still lots of detail big soundstage and all that goodness. These are, IMHO, without a doubt the best sounding 6AS7G you can get.
  
 To me the WE421A (and the 5998's) sound completely different than any 6AS7G. They're both TOTL tubes, only different. 
  
  
 What I don't understand though is why does the amp run SO much hotter with 6AS7G than with WE421A/5998? The amp barely gets warm when using WE421A/5998. I've seen many others saying this also but I don't understand why?


----------



## baronbeehive

sonictrance said:


> I rolled in a set of GEC A1834's today. They have a nice glow.


 
  
 Now I see why you had the reflective transformer covers installed 
	

	
	
		
		

		
		
	


	




.
  


sonictrance said:


> ........
> 
> The GEC's sound warmer, smoother, more tubey than the WE421A. Bass isn't hitting as hard as the WE421A. Still lots of detail big soundstage and all that goodness. These are, IMHO, without a doubt the best sounding 6AS7G you can get.
> 
> ...


 
  
 So are the GEC's close to RCA 6AS7G's? They have a warm smooth sound also.
  
 I can't wait to try my WE's!
  
 The very first time I read about TS5998's someone said that they have a warm tubey sound, and that is why I asked you because every time I've heard about them since everyone has said they have a very detailed, not tubey sound at all! Also a review on tubemaze.info said the 421A's and the TS5998's were definately different tubes, they do have bottom getters rather than top getters for a start.
  
 I love Tungsols, I've got them on my Miniwatt as well


----------



## SonicTrance

baronbeehive said:


> So are the GEC's close to RCA 6AS7G's? They have a warm smooth sound also.
> 
> I can't wait to try my WE's!
> 
> ...




No no, the RCA's don't have the same amount of detail, clarity, separation etc. Totally different sound IMO. 

There's also 5998's with bottom mounted getters, though I've never heard one. The 421A has higher transconductance (20000 vs 14000 umhos)


----------



## baronbeehive

sonictrance said:


> No no, the RCA's don't have the same amount of detail, clarity, separation etc. Totally different sound IMO.
> 
> There's also 5998's with bottom mounted getters, though I've never heard one. The 421A has higher transconductance (20000 vs 14000 umhos)


 
  
 Yes of course, you're right TS make bottom getters as well, but they are much rarer. I wonder if this fact confuses people about the sound. If they had compared like with like, bottom getter TS with bottom getter WE maybe there would not have been the difference. I'm just speculating without going through the thread again. It was skylab I think that said that they were one and the same tube. There is another difference, apparently the plate colour is dull black on the WE whereas it is shiny black on the TS and we know that plate colour influences sound as well. That's as well as the transconductance being different which probably accounts for the sound difference, although you say you haven't heard of any with the higher transconductance of 20000umhos.


----------



## Maxx134

sonictrance said:


> Different tubes makes a HUGE difference! Much more than cables. You change the overall sound signature with different tubes. You have a lot to look forward to!



I have to agree here...
The tubes are the HEART of the amp..
So you need quality tubes.

In tube history,
The "ART" of making tubes was at its prime in the 50s-60s.
Once the popularity and mass production demands set in, the tubes were generaly cheaper made.

Once the transistor came in, the tube factories where scrapped and sold off.

Company secrets and techniques, such as "frame grids" became a lost art.
Also, certain factories (like blackburn) were renowned for their tubes.

No new production tube today can "hold a candle" next to original old stock tubes.




sonictrance said:


> mogos said:
> 
> 
> > I have never seen such strong illuminating tubes. Wow very nice. How has changed the sound signature compared to WE 421A?
> ...



Haha so nice looking tubes!
The answer of the heat is simple. 
Different tube heater element current draw..


----------



## SonicTrance

@Maxx134
But the difference is only 0.1A. 2.5A for 6AS7 and 2.4A for 5998/421A. The difference in heat is quite big.


----------



## Benny-x

sonictrance said:


> Long exposure "adds" a bit of light as well
> 
> 
> 
> ...


 
 What I don't understand though is why doesn't anyone mix them together since the amp takes 4 total, so 2 and 2, 1 each per side, and then get the best of all of it?? We've already read a few reports in here of people mixing and loving


----------



## SonicTrance

benny-x said:


> sonictrance said:
> 
> 
> > Long exposure "adds" a bit of light as well
> ...


 
 I'm not sure what that would do to the bias of power tubes? When using 421A/5998 the meters read about 30mA, while 6AS7G/6080 gives you a 60mA reading. Which tube will be biased correctly? If any?
  
 I'm sure you could mix your favorite 6AS7G's and 6080's though as the specs are identical.


----------



## baronbeehive

sonictrance said:


> I'm not sure what that would do to the bias of power tubes? When using 421A/5998 the meters read about 30mA, while 6AS7G/6080 gives you a 60mA reading. Which tube will be biased correctly? If any?
> 
> I'm sure you could mix your favorite 6AS7G's and 6080's though as the specs are identical.


 
 That's right, it would not necessarily be harmful but matching the power tubes is more important than the drivers because of the balanced signal so I wonder if what people are hearing when they mix power tubes is really an improvement, after all the amp is balanced and that is a crucial element of its performance, mess with this and the sound could go awry possibly.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > I'm not sure what that would do to the bias of power tubes? When using 421A/5998 the meters read about 30mA, while 6AS7G/6080 gives you a 60mA reading. Which tube will be biased correctly? If any?
> ...


 
 Plus, the 421A has an amplification factor of 6, and the 6AS7G/6080 has 2. So the 421A/5998 plays a lot louder than the 6AS7G/6080.


----------



## baronbeehive

Quote:



maxx134 said:


> .......
> 
> The answer of the heat is simple.
> Different tube heater element current draw..


 
  
 Quote:


sonictrance said:


> @Maxx134
> But the difference is only 0.1A. 2.5A for 6AS7 and 2.4A for 5998/421A. The difference in heat is quite big.


 
  
 I know that the 6SL7 specs state that the plates have lower wattage dissipation to the power tubes and higher plate resistance than the 6SN7's. I don't know the comparative figures for the 421a's as compared to the 6AS7G's for example, perhaps this would explain it?


----------



## SonicTrance

Plate dissipation is the same @ 13w. Plate resistance also very similar, 280 ohms for 6AS7 and 305-330 ohms for 421A
  
 http://www.westernelectric.com/spec_sheets/421A.pdf
  
 http://www.r-type.org/pdfs/6as7g-1.pdf


----------



## baronbeehive

I haven't noticed a heat difference between 6SN7's and 6SL7's anyway!


----------



## SonicTrance

baronbeehive said:


> I haven't noticed a heat difference between 6SN7's and 6SL7's anyway!


 
 Neither have I, but it is apparent in the case of 6AS7 vs 5998/421A. Also 6080's turns the amp even hotter than the 6AS7G's.


----------



## Maxx134

Has anyone looked into how the WCF design reacts?

Specifically, how the dual triodes behave with impedance values above and below it's specified setting?

This is food for thought on next mods..


----------



## Mogos

Yes next mods. I have already forgotten about the bad time of fixing problems with my amp. Now is time for next mods 
	

	
	
		
		

		
		
	


	




. Could you tell us guys how far you are with testing/experimenting with the resistance matching one.


----------



## Redge78

mogos said:


> Yes next mods. I have already forgotten about the bad time of fixing problems with my amp. Now is time for next mods
> 
> 
> 
> ...


 
 On its way ...
  
 Theory is OK.
 The first experiments done by Maxx sound promicing.
 We're working on the final typology, number and values of resistance (and Maxx will have to work on how to put all this in his already stuffed amp...).
_May be simplier for MK8 (with only one possible Power tube) than for MK6 with all those various power tubes with their electrical differences._
  
  
  
_Maxx will be the guinea pig on this one _


----------



## baronbeehive

maxx134 said:


> Has anyone looked into how the WCF design reacts?
> 
> Specifically, how the dual triodes behave with impedance values above and below it's specified setting?
> 
> This is food for thought on next mods..


 
  
 OK, since nobody else has answered I'll have a go 
	

	
	
		
		

		
		
	


	




.
  
 The triodes can no longer function in balanced push pull mode so some sort of optimisation has to be provided for extreme resistances? I don't know how this would affect the sound coming out when the optimisation is in place, nor do I know what components have to be provided for this mod 
	

	
	
		
		

		
		
	


	




.
  
 Do we have to take out the board for this again
	

	
	
		
		

		
		
	


	



  
 So come on guys, a little hint perhaps 
	

	
	
		
		

		
		
	


	




.


----------



## Maxx134

The first page of this thread is the clue.
The Cavalli article on Cathode followers.. Specifically our White Cathode Follower.
Carefully analysis lead not only to having impedance matching as optimal for the design,
 but it dawned on me, once Ridge commented about the triode balance,
 that it also eludes to the fact that the WCF cap can plays more of a role in the overall signature, depending on your headphone impedance(!) in relation to, not to the amp impedance, but to the power tubes, based on the wonderful formula:


...
In other words, impedance matching to the WCF circuit design will give even better performance once achieved...

There is the hard pill to swallow, as we have many headphones, and why traditionally, equipment matching was always key .

Yet no amp was made to match a headphone...

They all have a range and limit...

We have a limit. ..

Yet, why should we?
Why can't we have it all?
Why can't we have our amp MATCHED to our headphones? 
Why do we have to buy a different amp, just to match, say an HD800, or settle for a dam transistor amp for a low impedance Ether?

Actually we don't need to be limited by what's available..

No, we don't have to have no limit...
Why?
Because we are in the "SuperMod" thread!

Yes we have no limits! 

I have been running my newly tuned MK8, for some time now, tuned for the low impedance Ether! 

The MK8 is traditionally for high impedance Sennheiser cans only. 
No more..

Yes, the impossible is possible here.

 Think of this next mod to make YOUR AMP,
THE ONLY amp ever made(!),
 to be specifically matched to YOUR HEADPHONES, 
OR ANY HEADPHONE you desire ever CREATED..!!**

(**within limits, lol).

There you have it..
Pandora box opened...
I am currently getting the number crunching done for mk6 and all possible headphones..

Mk8 done but probably will alter stock value as Ridge78 suggested, which will throw off all Calculations to do again.
Never used a calculator memory so much. lol

I guess it was time for me to spill the beans..

 But there is yet another "refinement" coming from Redge78, I won't never spill...
muuaahaha.


----------



## Maxx134

These are the most popular headphones I made a list as a guide to the values I will set the amp for...
LCD X = 20ohm
LCD XC = 20ohm
Ether = 22 ohm
HEX = 25ohm
Fostex th600 = 25ohm 
Oppo PM3 = 26ohm

LCD EL8 = 30ohm
Beyer t51i = 32ohm
Oppo PM1 = 32ohm
Oppo PM2 = 33ohm
HE1K = 35ohm
He400i =35ohm

HE560 = 45ohm
T50rp = 50ohm
HE6 = 50ohm

Sony Z7=70 Ohm 
LCD4 = 100ohm
LCD3 = 110ohm

HD650 = 300ohm 
HD800 = 300ohm
DT880 =250ohm
DT990 = 250ohm
T770 = 250ohm
T90 = 250ohm

T1 = 600 ohm

If any other left out that should make this list let me know. 

Too many calculations to be made..


----------



## Maxx134

baronbeehive said:


> Do we have to take out the board for this again:mad:



No!


----------



## coinmaster

Didn't I suggest this before and you mentioned it was pointless because of the uneven curves of the headphones at different frequencies? Or were you just referring to the HD800s?
 For the HD800s using a 6080 tube I came up with 440ohms using    Ra = (rp + 2RL)/mu


----------



## Maxx134

Here we go again with your *edit* misinformation..

 I never communicated to you about any of this topic.

You never suggested anything, you asked questions.

The PMs were between Ridge78 and you .

You asking him to explain to you what is going on.

Meanwhile I had already installed the this new mod long before while you was still fixing your amp.

I PMed MrSpeakers about my success on his headphones long ago..

We could pull up the PM's and post it here,
Edit*
 But that would be off topic and petty and clutter the thread.


----------



## Maxx134

Well it's true that the Sennheisers impediance will vary with frequency,
the amp is tuned to have maximum power in the bass region,
Which means in general it is tuned for the headphone..


----------



## Maxx134

The Sennheiser headphones change in impedance is also a good example of how the second triode will take amplification precedence, when the headphones impedance falls below the circuit impedance setting.
 And so the WCF capacitor will be more involved in the signature of the amp.

This is another reason of the importance of WCF cap upgrading.


----------



## baronbeehive

maxx134 said:


> The first page of this thread is the clue.
> The Cavalli article on Cathode followers.. Specifically our White Cathode Follower.
> Carefully analysis lead not only to having impedance matching as optimal for the design,
> 
> ...


 
  
 .........is that SuperMod a bird of a plane 
	

	
	
		
		

		
			





, sorry, getting carried away there!
  
 Perhaps I would have had a better idea if I had read past section 8 to the new mods section 
	

	
	
		
		

		
		
	


	




. So the headphone impedance could influence the functioning of the triodes, and in theory could push them out of sync with each other? So the WCF caps act like a reservoir when the circuit impedance goes off limits. It is sinking in slowly.....


----------



## Redge78

baronbeehive said:


> Perhaps I would have had a better idea if I had read past section 8 to the new mods section
> 
> 
> 
> ...


 
 Yes, the headphone impedance influence the functionning of the triodes WCF, and not just in theory.
  
 Basically, the WCF is a special typology where the 2 triodes will add their power, will lower the overall output impedance and will cancel some distortion.
 The optimum is when the WCF is working at "perfect push-pull", meaning that both triodes are producing the same amount of power.
 In order to do that, the grid of triode two has to receive the proper voltage, voltage that will be dependent of the values of the anode/plate resistance and the headphone impedance.
 Therefore, when the headphone impedance changes, the  anode/plate resistance has to be modified if the "perfect push-pull" is to be kept.
  
 But is it important to have a "perfect push-pull" ?
 I'd say ... yes and no, depends ... (but this answer could change in the future)
  
 For the planar, having max power available and less distortion is a must. On top of that, as the planar have a fixed impedance over the BF, it is "easy" to be spot on on the perfect Ranode value (what we did with Maxx' MrSpeaker Ether). The lower output resistance is supposed to be of no use as the Planars don't care about "Impedance matching", they are not generators. 
  
 The case of the HD800 is more complex ...
 1 - There will be no perfect Ranode value, as the headphone impedance varies with the freq. band, roughly from 300R to 450/500R
 2 - The change of WCF output resistance will impact the overall sound presentation, especially in the bass region (there is a good paper of the subject on Innerfidelity). Basically, more resistance will give more bass but an overall "slower" sound, which may suit some people (me included) or work better with different headphones (of same impedance).
 So, before having experimented it, it's difficult to say which Ranode will work best for the HD800. So we can assume that the value chosen by LD is good enough, as it is is one of the "possible best" (for the MK8 at least).
  
 You can add to the equation that the two triodes are not exactly the same in real life, "triode two" has an extra cap in its circuit (the "WCF" cap) that will impact its sound negativally (as all caps do).
  
 So, having more or less of the Triode 2 may impact the final sound in two opposite ways ... at the same time ... but differently... depending of the headphone ... and depending of the listener's tastes. Bugger me ! 
  
 Obviously, as we can expect you to unsolder/solder some extra resistances each time you change headphone, some kind of "resistance selector" makes sense.
  
 And as I have already written above, this selector/pot will even make more sense for the MK6 if you're doing some tube rolling (I kind of understood you all do it).  
  
  
  
@Coin and others.
 Frankly, you telling us that or not is not the point.
 There are hundreds of mods that could be done on that amp, and we have to choose in our limited time allowed for this hobby which mods we will be working on.
 Everything starts with feedbacks from reliable and educated sources, with actual work to prove their sayings. That means "not just some computerised simulation" but testimony from guys that have sound quality as their prime objective. We take into account how easy it is supposed to be and how large the sound improvement can be. ... And the cost, obviously.
 And I am sorry to remind you that in term of "electrical engineering", you're close to nill, you yourself keep telling us that.
 So, at best, what you were saying _(amongst tens of other things) _were taken from other sources without the necessary tech background (the WHY, the HOW, the HOW MUCH, the WHAT ELSE ...) we need to consider it.
 And we already explained to you how Maxx and I are working : understanding how stuff works is half the pleasure, with an another half in having the mods to perform as expected; and an new another half in sharing what we've done with people.
  
 That being said, you're more that welcome to try new ways of thinking, I have heard a lot of good stuff about voodoo.
 And that post-modern "Deconstruction" philosophy that Coin has embrassed is interesting. Derrida would be so proud  
	

	
	
		
		

		
		
	


	



  
  
 How this mod did appear ? That's pretty simple. We knew the Cavalli paper for quite a long time, long before this SuperMod thread was created. But we didn't bother to test this mod previously as we were listening to the HD800.
 But when Maxx tested his Ether on the MK8, it was performing below expectations, so we gave the mod a go ... without really knowing what to expect apart from the optimised power output we were pretty sure of.
 It happened that the power output is not a real issue in that particular case (but you will have the satisfaction to know that both triodes of a tube will wear out at the same rate) but the impact on sound was significant. Maxx will be able to give more precision on that.
  
  
 That's all, Folks !
  
  
_Sorry for this much too long post, sometimes it's a pain for me to write in english, sometimes the words flow (awkwardly ... I know) _
_To make proper amends, I'll tell you that this is not the last mod, the best is yet to come ... and you can count on me to tell you nothing until it's done and validated  _


----------



## baronbeehive

Very interesting, I wondered when Post Modernism would appear in this thread 
	

	
	
		
		

		
		
	


	




. Thanks for the explanation, I'm not worried about the length so long as it makes sense!
  
 Yes the subject is contradictory which makes one appreciate the designers all the more, but the experimental rigour is to be commended.
  
 I look forward to hearing more of Maxx's, and your, mods.


----------



## Redge78

baronbeehive said:


> Very interesting, I wondered when Post Modernism would appear in this thread
> 
> 
> 
> ...


 
 Ah !!! a connoisseur of the fine music, I presume !
 I had planned to speak of the contemporary classical music, but as I'm still crying after the death of Pierre Boulez two weeks ago ... that was too hard for me.
  
  
  
  
 ... kidding ! apart from the death of Pierre Boulez two weeks ago which is true ... the 27 grammy awards director and the "enfant terrible" of the 20th century classical music ...
_The funny stuff is that I met two months ago a belgium music editor at a Nagra show where they were exposing their new production. The guy (a funny little precious dandy) was in the process of editing/rearanging/recording all the Boulez compositions that had never been recorded previously, with the help of Boulez himself (or what was left of him, as he was already very sick). The guy was so enthousiast about the all thing that I didn't find the courage to tell him that I couldn't stand comtemporary music ... Nobody on the show did tell him, we're polite. But we should have, as we lost one full hour listening to this chap ! _


----------



## baronbeehive

Here goes............. I'm starting the process 
	

	
	
		
		

		
		
	


	




. I'm just at the beginning and I'm going to try to follow my own advice and test as I go along as far as possible. I hope to put the tubes in the board outside of the chassis and test it works after every stage, if anyone doesn't think this is a good idea please let me know first before I disappear in a puff of smoke!
  
 I thought I might start every post to do with the mods with *SMLD MODS:* so if anyone wants to follow it will be easy.
  
 Thanks to everyone for their help.


----------



## SonicTrance

baronbeehive said:


> Here goes............. I'm starting the process
> 
> 
> 
> ...


 
 Just be careful and don't touch anything while it's powered ON outside the case. And remember to wait 5-10 minutes after power down before you take out the tubes, so the caps have time to discharge.
  
 Good luck!


----------



## baronbeehive

*SMLD MODS:*
  
*Stage 1.*
 Pics of the wiring connections taken and diagrams drawn as well as a back up. Connections checked and double checked 
	

	
	
		
		

		
		
	


	




. Next stage remove the board, I've begun and I'll update when completed.
  
 Still haven't received the silver plated wire yet.


----------



## baronbeehive

sonictrance said:


> Just be careful and don't touch anything while it's powered ON outside the case. And remember to wait 5-10 minutes after power down before you take out the tubes, so the caps have time to discharge.
> 
> Good luck!


 
  
 Thanks! Please remember anyone doing this to follow this advice.


----------



## Redge78

baronbeehive said:


> Thanks! Please remember anyone doing this to follow this advice.


 
 While we are at it ...
  
 Always check the large PSU caps voltage before working on the amp.
 Wait until they are fully discharged or make yourself a discharge apparatus (a 50Kohms/5W resistor with insulated leads at each end).
 Wearing protective gloves (surgerical stuff) is a must.
  
 And good luck, and remember the 3 rules :
 - Think first
 - Work slow
 - Check twice
_I just made them up, but hey ! they sound pretty good !_


----------



## SonicTrance

redge78 said:


> baronbeehive said:
> 
> 
> > Thanks! Please remember anyone doing this to follow this advice.
> ...


 
 Haha! They sure did!


----------



## baronbeehive

redge78 said:


> While we are at it ...
> 
> Always check the large PSU caps voltage before working on the amp.
> Wait until they are fully discharged or make yourself a discharge apparatus (a 50Kohms/5W resistor with insulated leads at each end).
> ...


 
  
 Are surgical gloves a protection or just a fetish of yours 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

redge78 said:


> Ah !!! a connoisseur of the fine music, I presume !
> I had planned to speak of the contemporary classical music, but as I'm still crying after the death of Pierre Boulez two weeks ago ... that was too hard for me.
> 
> 
> ...


 
  
 I hope he wasn't going on about post modernism as well! I don't really go in for all this deconstructionism nowadays, I suppose it has its place. I must own up, I don't know a lot about Pierre Boulez but he sounds interesting, I'm all for new ideas but not a big fan of electronic music, my favourite genre is modern jazz in the style of Larry Carlton for example.
  
 Oh and I hate deconstructionist chefs 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

@baronbeehive , @Mogos
  
 Someone should get these if you don't own a pair. Wonderful tubes 
	

	
	
		
		

		
		
	


	



  
 http://www.ebay.com/itm/TUNG-SOL-MATCHED-PAIR-6SU7GTY-ROUND-PLATE-TUBES-TEST-NEW-TV-7D-U-/371528207915?hash=item5680ce8e2b:g:Ax0AAOSwFqJWkSLh


----------



## baronbeehive

sonictrance said:


> @baronbeehive , @Mogos
> 
> Someone should get these if you don't own a pair. Wonderful tubes
> 
> ...


 
 Go on Mogos, I've had these but have to say I'm happy with the bog standard TS 6SL7 round plates.
  
 They are beautifully sweet sounding aren't they, but I just wonder if Mogos will like them if he likes the live sound, worth a try I would have thought!


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > @baronbeehive , @Mogos
> ...


 
 Definitely worth a try at that price. Granted, it's 8h left on the auction but you never know. They usually go for 2-3 times more than current bid.


----------



## baronbeehive

sonictrance said:


> Definitely worth a try at that price. Granted, it's 8h left on the auction but you never know. They usually go for 2-3 times more than current bid.


 
  
 Or he could go for these TS 6SL7's for a fixed price, more than I would have paid but they are military VT229's so will last longer. There don't appear to be any ordinary NOS 6SL7 matched pairs ATM.
  
http://www.ebay.com/itm/Vintage-Tube-Pair-Tung-Sol-JAN-6SL7GT-Black-Glass-Round-Plate-VT-229-/311524656716?hash=item488851064c:g:aOUAAOSwL7VWlW-m&rmvSB=true
  
 or these TS 6SUGTY's, one branded GE, at a fixed price, $40 cheaper than another pair testing the same!
  
http://www.ebay.com/itm/2-matched-Tung-Sol-GE-6SU7GTY-tubes-Black-Round-Plates-Bottom-Getter-/360992754210?hash=item540cd84a22:g:HgAAAOSwI~VTxpN8&rmvSB=true
  
 What about it Mogos?


----------



## baronbeehive

redge78 said:


> While we are at it ...
> 
> Always check the large PSU caps voltage before working on the amp.
> Wait until they are fully discharged or make yourself a discharge apparatus (a 50Kohms/5W resistor with insulated leads at each end).
> ...


 
  I've spotted and error............check twice..........then check twice again!!!


----------



## Mogos

I will tray to bid the first proposal. Thank you guys for prompts. For sure I will buy that ones.
 http://psvanetube.com/wordpress/store/products/1-6sl7-z-select-pair-equivalent-to-6n9p/
  
 But first I have to collect some money as my walet had been broken lately 
	

	
	
		
		

		
			





.


----------



## baronbeehive

mogos said:


> I will tray to bid the first proposal. Thank you guys for prompts. For sure I will buy that ones.
> http://psvanetube.com/wordpress/store/products/1-6sl7-z-select-pair-equivalent-to-6n9p/
> 
> But first I have to collect some money as my walet had been broken lately
> ...


 
  
 Are you going for Psvanes then?
  
 My sympathies to your wallet 
	

	
	
		
		

		
		
	


	




 .


----------



## Mogos

baronbehive good luck. Just take your time. I know it is hard after so many days of wating and the imagination running wild but that's the only way to succeed. 
 Be carful putting the board back. Most of my problems happend putting the board back. Just slowly. Removing one of the posts around the drive tubes will make the installation of the board much easier but then you have to be carefull insttaling the tubes (pushing). I have only one support in this are as my caps did not allow me to screw the board in this place.


----------



## SonicTrance

mogos said:


> I will tray to bid the first proposal. Thank you guys for prompts. For sure I will buy that ones.
> http://psvanetube.com/wordpress/store/products/1-6sl7-z-select-pair-equivalent-to-6n9p/
> 
> But first I have to collect some money as my walet had been broken lately
> ...


 
 Great, I hope you win the Tung-Sols!
  
 Regarding the Shuggies;
 I've not heard the 6SL7 variant but I've heard the 6SN7 one and they're not worth the money IMHO. If you're looking to spend that kind of money I suggest you look at Mullard ECC35's.
  
 Here's a nice pair:
 http://www.ebay.com/itm/262234477467?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
 I'm sure price will ramp up towards the end of the auction though.


----------



## Mogos

Compering to tungsols the difference is not so drastic. Tungsols are offered as they are (no NOS/NIB, I know it is written tested 
	

	
	
		
		

		
		
	


	




 ). I thing Tungsols in NOS/NIB condition will cost the same money as Psvane. But I will tray to bid the Tungsol for reasonable price.


----------



## baronbeehive

mogos said:


> Compering to tungsols the difference is not so drastic. Tungsols are offered as they are (no NOS/NIB, I know it is written tested
> 
> 
> 
> ...


 
 Don't go above $125 for 6SL7's or $140 for 6SU7GTY's as you could get these for fixed price, they both look NOS values, don't forget it's difficult to prove NOS you can only go by testing values. If you want to get the Shugangs you could hold off and wait for some cheaper ordinary TS6SL7's later.
  
 Quote:


mogos said:


> baronbehive good luck. Just take your time. I know it is hard after so many days of wating and the imagination running wild but that's the only way to succeed.
> Be carful putting the board back. Most of my problems happend putting the board back. Just slowly. Removing one of the posts around the drive tubes will make the installation of the board much easier but then you have to be carefull insttaling the tubes (pushing). I have only one support in this are as my caps did not allow me to screw the board in this place.


 
  
 Thanks, I'm a way away from putting the board back yet though!


----------



## Mogos

I have at home this lamp.

  

  

  I think they are Russian.
 I have to tray them.


----------



## baronbeehive

I've no idea, don't know if MisterX has?


----------



## baronbeehive

sonictrance said:


> Great, I hope you win the Tung-Sols!
> 
> Regarding the Shuggies;
> I've not heard the 6SL7 variant but I've heard the 6SN7 one and they're not worth the money IMHO. If you're looking to spend that kind of money I suggest you look at Mullard ECC35's.
> ...


 
  
 I don't want to influence you but I agree with MisterX, I've picked up some Mullards recently and am sure that he's right about them being excellent.
  
 You can always sell them back on ebay if you don't like the sound.


----------



## SonicTrance

mogos said:


> I have at home this lamp.
> 
> 
> 
> ...


 
 They do look like Russian 6N9S's. I've never heard one. You should definitely try them if you already have them at home. Tell us what they sound like.


----------



## coinmaster

> Here we go again with your *edit* misinformation..
> 
> I never communicated to you about any of this topic.
> 
> You never suggested anything, you asked questions.


 
  
	

	
	
		
		

		
		
	


	



 Me


> > The load is all important and its impedance must be factored into the calculation of the sense resistor’s value
> 
> 
> 
> ...


 
  Redge
 Quote:


> If the balance is not achieved, one triode will have an output power lower than the other one, the overall power will be dercreased by an amount that can be calculated.
> Keeping in mind that for the HD800 (with its fluctuating impedance vs Freq. band) there is not one good value, but a range of acceptable solutions.
> And the resistors values of the MK8 are already spot on for the HD800.


 





 
  
 Doesn't matter anyway, I'm becoming more and more irrelevant on this forum, my amp no longer resembles anything like an mk6 other than the fact it still uses a WCF output stage, sort of.


----------



## Redge78

Coin ... sorry but you'll play alone your little game of "partial" posts. Not interested.
  


			
				coinmaster said:
			
		

>





> my amp no longer resembles anything like an mk6 other than the fact it still uses a WCF output stage, sort of.


 
 I hope that when you'll have it up and running you'll come back to tell us everything about it.
 Good luck anyway.
  
  
@Mogos
 Reflector 1579 (6SN7 equivalent, they say), so yes, russian ...but not much info about them on the Internet ... They're damn cheap on ebay anyway.


----------



## SonicTrance

@Redge78
 I'd love to see a pic of your amp with the extended wood box.


----------



## Redge78

sonictrance said:


> @Redge78
> I'd love to see a pic of your amp with the extended wood box.


 
  
 OK ... don't judge me on how it looks, you have to remember that I have two left hands.
  
 The case is 15cm (6") high, 1cm thick, made of basic pine wood.
 On top and bottom, I have put a large sticky rubber band that may help in cancelling some vibration, and will help close hermetically the case for the forced air that will blow from below.
  

  
  
 The holes are where the forced air is supposed to came out of the box. This is near the PSU area on the PCB which should be the hottest area around.
  

  
 This is how it is when I have to work on the amp.
 The 4 large black caps are screwed on the case, the 2 white WIMA are fixed with a plastic "ring" (don't know the english name of it).
 The pic was taken quite a long time ago.
  

  
 The same when put back.
 I am using some "good quality" forks for the 4 black caps, and some RC modeling plugs (surprisingly handy and high quality) for the white caps.

  
 A more recent pic, with the Jupiter "coupling cap" underneath the green K75-10 "WCF caps".
 Currently, there is an added layer of cap above the green ones (Teflon bypass).
  
 And OK, those yellow wires look like some spagetti leftovers ..

  
 When put together.
  

  
 The overall layout is not ideal but it has been working flawlessly for one year now.
 The air flow is OK but will need to be optimised when the final layout is validated. 
  
 Thinking of it, a 20cm (8") would have given me more flexibility. This is something I'll have to think over as some future mods ...
  
  
*[Spoil alert !!! ]*
  
*[Spoil alert !!! ]*
  
*[Spoil alert !!! ]*
  
*[Spoil alert !!! ]*
  
*[Spoil alert !!! ]*
  
*[Spoil alert !!! ]*


----------



## SonicTrance

Thanks for the pics Redge! It doesn't look too bad and I can only imagine how it sounds! Though, a slap of black paint wouldn't hurt the aesthetics I think
	

	
	
		
		

		
		
	


	



 You could also dress the wood from the outside with some thin black anodized aluminium sheets. That could look sweet!
  
  
PS. the "white rings" are cable ties.


----------



## coinmaster

Looks much better than the crude box I made.
  
 I am working on a solution to the plate resistor problem with the HD800s changing impedance based on frequency.
 There's a few issues here, the first is using a current sensor or rms to dc converter won't work to measure load impedance because a music signal has dynamic amplitudes.
 The second issue is music has many frequencies simultaneously.
 What I propose is to use a digital solution that samples the frequencies and their amplitude at any one moment and calculates an average of the frequencies and their amplitudes based on the impedance curves of the HD800s which will then produce a reference voltage for a SIC JFET to act as a variable plate resistor.
  
 This should in theory maintain a perfect WCF balance no matter what the changing impedances are.
 What is your input on this? I asked about the idea on an electronics forum and they seem to think it will undo the design of the headphones because I would be changing the output impedance constantly. Either they or myself have something confused because the way I see it, I would actually be stabilizing the output impedance. 
 What do you think?
  
 Also looking at this chart http://www.innerfidelity.com/images/SennheiserHD800.pdf wouldn't the average impedance be more like 400 ohms?


----------



## Redge78

coinmaster said:


> Looks much better than the crude box I made.
> 
> I am working on a solution to the plate resistor problem with the HD800s changing impedance based on frequency.
> There's a few issues here, the first is using a current sensor or rms to dc converter won't work to measure load impedance because a music signal has dynamic amplitudes.
> ...


 
  
 Sorry but a lot of things to say against it ...
  
*1 - There is no proven relationship between the overall sound quality and a "finely tuned" WCF push-pull.*
 Yes, it seems important when there is a great inbalance between the WCF setting and impedance of the headphone, but nothing proven when you are at +/- 10% of the optimum. Before doing all this, it could be interesting to make some listening tests with the WCF set for 300/350/400/450 ohms to validate that there is a audible difference here.
  
*2 - More of what the "HD800 push-pull" WCF will do may not be very useful*
 The increase of power output is worthless, we already have too much
 The lower Output resistance may be counter-productive, as the HD800 works pretty well with 50+ ohms amp, that allow a bit more of bass
 The lower distortion is always good but I can't quantify it, so tests are requered.
  
*3 - Some of what the "HD800 push-pull" WCF will do may downgrade the sound*
 The Triode 2 (the regulating one) will have 2 "grid" caps in series (instead of one for Triode1), Triode 2 will also have the current going through the Cathode caps.
 You can expect to have the T2 sound to be a bit below what T1 produces.
  
*4 - Rplate quality*
 Rplate quality is as important as Rgrid. I am not sure (at all) that your SIC JFET will have the quality of a Zfoil or a Tantalum Shinko. Actually, I'm pretty sure it will not as nothing is. And that will have a direct and proven impact on sound. 
  
*5 - Theory*
 The average of Freq/Amplitude may be tricky to do, and for most music (with bass/voice/highs) will finish to be in a narrow "middle freq" band setting, where the headphone impedance is highest. That will have an impact.
  
 The double conversion Analogic=>Digital and Digital=>Analogic will have a possible double impact on sound (given that the all thing can have an impact on sound in the first place).
 - the double quantification will degrade the sound more or less depending on how much tech you put in it, but having something efficient will cost you.
 - the "double quantification + processing" may have an impact on "time delay"
  
 You didn't factor the tubes transconductance (Gm)  in your process. It's OK for the MK8 as we only have one sort of tube available (6H30) but for MK6 the choices are vast, with very different Gm.
  
 You could also factor the non-linearity of your amplification around your "static point of functionning" (the Kr/Ka in the Cavalli formula) which may be significant (very different from tube to tube) for the 6SN7 tubes type.
  
  
_... And what's the point of having a Tube amp if it's to put an extra "transistor" stage in it ?_
  
  
 All that to say that I very much prefer the 5 positions "high quality resistors" pot solution that is much easier to understand, to implement and to fix. At least for a "I'm not destroying my amp and my bank account" kind of mod.
  
 If you really want to improve the sound of your HD800 with something "complicated", you may have a look at some digital equalisation, either by software that you can plug to your player (a lot on that on Innerfidelity) or as an extra-box ... a "Smyth Realiser A8" maybe.
  
  
 Just IMHO, I may be proven totally wrong... that would be quite exciting actually.
 Coin, did you cross any concrete mod like this one, I mean .. things that really exist ?


----------



## coinmaster

> Before doing all this, it could be interesting to make some listening tests with the WCF set for 300/350/400/450 ohms to validate that there is a audible difference here.


 
 This is a good point. I'll have to add it to my list of things to do.


> Rplate quality is as important as Rgrid. I am not sure (at all) that your SIC JFET will have the quality of a Zfoil or a Tantalum Shinko. Actually, I'm pretty sure it will not as nothing is. And that will have a direct and proven impact on sound.


 
 SIC JFETs are supposed to be the most linear solid state device in existence and they also have only a few PF of capacitance. JFETs by themselves are supposed to be super linear compared to everything else and have the lowest noise of any transistor but they normally are limited to low voltages. SIC JFETS are a relatively new technology due to the growing demand of electric cars and solar technology. Silicon carbide is like the new miracle material that allows high voltages and better performance. 
 So if they are truly as ideally linear as they are claimed to be then I say it's promising. I took a glance at at the curves of one of them and the load lines were perfectly flat within the linear range.
  
  
 As for the theory, this is what was suggested to me. I don't know much about digital tech yet so I only partially understand it.


> That can be done by using a VCO in a PLL (all analog). Then we have to use that information through some sort of strange function generator that matches headphone impedance. Then that runs through a control circuit to manage the plate resistance.
> Personally, I prefer the idea of the multiple band analyzer. It's a lot like an equalizer, and you only need about six bands to make it work. They don't have to be equally spaced. And it's also all analog. By the way, all of these suggestions are things outside of the primary signal path.


 
 My theory is that, since the tube can only have 1 operating point at a time, then it will change it's operating point based on an average of impedance from simultaneous frequencies based on the impedance curves of the headphone. So my idea is to sample the frequencies and create a changing reference voltage based on their average.
  
  


> Coin, did you cross any concrete mod like this one, I mean .. things that really exist ?


 
 No, nothing exists that I know of. I'm just looking at problems and finding solutions.
 I've already figured out how to remove all of the capacitors with only downside of loss of gain, a pretty huge loss of gain but that can be compensated for with a higher mu input stage.
 I've also figured out an improved version of the WCF that has dreamlike frequency response and distortion numbers compared to a normal WCF based upon my simulations. It is also powerful enough to drive speakers. I have no idea if it has ever been thought of before but I haven't seen or heard of any output stage that resembles it yet. I haven't finished tweaking it yet and I'll probably need help doing so before all is said and done but the idea behind the topology makes sense and is interesting.
  
 So far my plan of creating my own monster is coming along nicely.


----------



## SonicTrance

@Redge78
If the GM is of that much importance, matched tubes seems to be very important in our case?

Also, there's only three different GM values for the mk6 output:
6080/6AS7G: 7000umhos
5998: 14000umhos
421A: 20000umhos
Note that the above is according to spec sheet. Actuall transconductance will of course be different.


----------



## baronbeehive

coinmaster said:


> Looks much better than the crude box I made.
> 
> I am working on a solution to the plate resistor problem with the HD800s changing impedance based on frequency.
> There's a few issues here, the first is using a current sensor or rms to dc converter won't work to measure load impedance because a music signal has dynamic amplitudes.
> ...


 
  
 Very interesting ideas there. I agree with Redge though, while you may be able to track impedance changes, that doesn't necessarily mean better sound. For a start it looks like the musical harmonics coming from the peaks and troughs of the different frequencies going on at any given moment will be lost from the averaging out, resulting in degraded musical sound. Then it looks like you are addiing in too much additional processing from the ADC and DAC processing in addition to the DAC upstream from the amp.
  
 Also the character of the HD800 comes partly from the dynamic impedances so I don't know what the HD800 would sound like after all this processing. Maybe some sort of equalizer would be better although it would not work in the way you are interested in.


----------



## coinmaster

> For a start it looks like the musical harmonics coming from the peaks and troughs of the different frequencies going on at any given moment will be lost from the averaging out, resulting in degraded musical sound.


 
 I don't see how it would affect harmonics, what I want to do is maintain balanced operation between the two triodes. When they aren't balanced distortion increases and power levels vary all over the place along with the output impedance. Not every output stage topolgy has this issue so if a stable output impedance was going to degrade musical sound I would imagine there would be issues with certain amps.


> Then it looks like you are addiing in too much additional processing from the ADC and DAC processing in addition to the DAC upstream from the amp.


 
 It shouldn't matter because it will not be in the signal path, it's just to determine the variable resistance value of the plate resistor.
  
 A quote from the cavalli paper 



> _ The goal in selecting the operating point and component values for the WCF OTL stage is to achieve push-pull balance in the amplifying and regulating triodes. Balanced pushpull operation will maximize the power and minimize the distortion
> 
> _


 




> _ The calculations in the current balance section above together with Eq. 28 make it clear that there is no *single* value of Ra that will balance the WCF for a range of loads and for both small and large signal regimes. Any choice of Ra is, therefore, a compromise to get the best possible behavior for these two separate constraints
> 
> _


----------



## baronbeehive

Quote:


coinmaster said:


> I don't see how it would affect harmonics, what I want to do is maintain balanced operation between the two triodes. When they aren't balanced distortion increases and power levels vary all over the place along with the output impedance. Not every output stage topolgy has this issue so if a stable output impedance was going to degrade musical sound I would imagine there would be issues with certain amps.
> It shouldn't matter because it will not be in the signal path, it's just to determine the variable resistance value of the plate resistor.
> 
> ......


 
 Ah, yes so the processing is going on off stream, yes that should work, but is this the only solution to impedance tracking that you propose?


----------



## coinmaster

baronbeehive said:


> Ah, yes so the processing is going on off stream, yes that should work, but is this the only solution to impedance tracking that you propose?


 
 This was suggested to me 


> That can be done by using a VCO in a PLL (all analog). Then we have to use that information through some sort of strange function generator that matches headphone impedance. Then that runs through a control circuit to manage the plate resistance.
> Personally, I prefer the idea of the multiple band analyzer. It's a lot like an equalizer, and you only need about six bands to make it work. They don't have to be equally spaced. And it's also all analog. By the way, all of these suggestions are things outside of the primary signal path. We tap the signal as it comes in, without distortion, process it on the side, but we don't insert anything into the signal path. I assume that meets your expectations.


 
 I'm still trying to figure out what he said 
 I think there are numerous ways to do it, the main issue is how to do the calibration. Cross referencing the sampled frequencies with the impedance curve seems the most obvious solution.
 I could use a voltage/current sensor and divide them to get impedance but I'm not sure how multiple frequency impedances affect the current flow. If I have 1 frequency at 600 ohms and I have another frequency at 300 ohms does the current average somewhere in the middle?


----------



## baronbeehive

coinmaster said:


> This was suggested to me
> I'm still trying to figure out what he said
> I think there are numerous ways to do it, the main issue is how to do the calibration. Cross referencing the sampled frequencies with the impedance curve seems the most obvious solution.
> I could use a voltage/current sensor and divide them to get impedance but I'm not sure how multiple frequency impedances affect the current flow. If I have 1 frequency at 600 ohms and I have another frequency at 300 ohms does the current average somewhere in the middle?


 
 Sorry I can't help there, but in principle I see no problem. How it affects plate function and headphone function is another thing 
	

	
	
		
		

		
		
	


	




. (In other words I don't know). From what I can gather the impedance on the plates is normally a fixed not a moving point, if so why hasn't this been thought of before? I'm struggling to understand it.


----------



## coinmaster

> From what I can gather the impedance on the plates is normally a fixed not a moving point, if so why hasn't this been thought of before? I'm struggling to understand it.


 
 Don't underestimate the lack of innovation in the tube field. Tube tech innovation is mostly restricted to hobbyists that were alive in the 60s. It is not a mainstream field of science anymore. Tubes are obsolete and have been for ages. Most people don't even know they exist.
 John Broskie is the only person that I've seen that has strived for innovation. He has created countless new tube and hybrid designs and one of his designs is my inspiration for my improved WCF topology that I came up with and seems promising according to the simulations I've done.
 But I don't think anyone has mixed digital tech and tubes yet and the solution to the problem I've trying to solve is beyond what a hobbyist from the 60s is likely to try.
 Also, there's the fact that a linear variable resistor has only just become possible. Jfets are known to be by far the most linear and least noisy solid state device but they have not been available in high voltages until very recently.


> How it affects plate function and headphone function is another thing


 
 Well, the idea is to stabilize the voltage and current running through it to match that of the bottom triode. When the load impedance changes so does the operating points of the top triode which interferes with a perfect push pull operation. I expect the result will be reduced distortion and a stable output impedance.


----------



## Redge78

sonictrance said:


> @Redge78
> If the GM is of that much importance, matched tubes seems to be very important in our case?
> 
> Also, there's only three different GM values for the mk6 output:
> ...


 
  
 You want to know the funny thing ? 
 Gm is not even a constant value for a tube/triode, it will vary significantly with the Plate Current. 
 In the link below, the 12AX7 has a Gm from 400 up to 1900.
 Age/wear may also have an impact on Gm. 
 Good luck with that !
  
http://www.mif.pg.gda.pl/homepages/frank/sheets/093/1/12AX7.pdf
  
  
 The Cavalli formula assumes that both triodes of the WCF will have the same Gm, and that's normally the case for the triodes of a same tube, unless you have been running unbalanced for a long time.
  
  
 So, matched tubes ?
 - Matched triodes within a tube, most certainly. I can see any simple way to compensate a Gm unbalance between those 2 triodes. And as you can expect to have triode 1 (the most important "amplifying" one) to be worn out, that will be bad.
 - Matched tubes within a channel ... I'd say yes instinctively, but I don't know really.


----------



## SonicTrance

redge78 said:


> sonictrance said:
> 
> 
> > @Redge78
> ...


 
 Yes, I know this. I've looked at many datasheets before and I also have a tube tester. So I obviously test all my tubes. And sure, NOS tubes are usually quite balanced between the triodes, used tubes not so much. It's a bit of a lottery when buying untested tubes. I have a pair of Chatham 6AS7G for example that tests like new on one triode and is almost dead on the the other triode, lol.


----------



## Maxx134

*Just wanted to clarify so no hard feelings...*

Posted on 9/4/15:


maxx134 said:


> ...
> It is coincidental that Ridge78 proposed to me solution for harder to drive planars that we might look into, yet the mk6 should not have any problem with newer planars like, say an Ether or he560.



*
************

Experiments completed before,
then tested and posted in PM on 12/6/15

*pic*


*************

Coinmaster post was on 12/24/15 which also using a formula I did not use:



coinmaster said:


> Value for that is
> 
> Ra= (rp + 2RL)/mu
> where RL equals the load impedance
> ...



Beginning of that post shows date"
*pic*



****************

*OK
Now that that is settled:*


So anyways, Thanks to MisterX, 
I have found a great way to add my switch to the front, 
Using an neutrik rca plate (!).
I will be fitting in this switch soon after I decide on my resistor values. 

*pic*

just need to change that knob.






redge78 said:


> ....
> You can expect to have the T2 sound to be a bit below what T1 produces.




It is my belief, based on the Ether performance, that the T2 triode amplifies a more mid focused and less airy sound.(!)
Almost like a more "tuby" signature. 
This is based off what I hear from the Ether which is a planar and so not change impedance.
As the top triode amplifies more when I lowered the circuit impedance,
I heard more "air" and detailing in the higher registers. 
I will now have to upgrade the WCF capacitor to a brighter,sharper,faster capacitor, in order for the T2 triode to "match" the top triode (T1) clarity, as it has main coupling cap as its source. 

For the WCF cap, 
I am currently using the Jupiter HT cap which proved be a "smooth" solution but when the headphone impedance falls below the WCF circuit impedance setting, the dependance on this cap is increased...


----------



## Redge78

maxx134 said:


> I will now have to upgrade the WCF capacitor to a brighter,sharper,faster capacitor, in order for the T2 triode to "match" the top triode (T1) clarity, as it has main coupling cap as its source.
> 
> For the WCF cap,
> I am currently using the Jupiter HT cap which proved be a "smooth" solution but when the headphone impedance falls below the WCF circuit impedance setting, the dependance on this cap is increased...


 
  
 If I remember well, before the WCF with Jups' you had the Mundorf S/G/O, isn't it ?
 Those S/G/O should fit the bill in term of brightness/sharpness/... or not ? Even if I think I remember you telling the the Jup HT was better ...
 Maybe with the help of a ultra-fast teflon or polystyrene by-pass cap (russian FT-1 or K71-7 ?)
  
 I have some russian K73-16 that are lovely and lively little beasts, a lot of punch and nice and dynamic highs. They may be worth a try, they are dead cheap.
  
 Or if you really want to "upgrade" ... Teflon seems an obvious choice.
 Cheap: some russian 0.22µF/600V 5% FT-3  (I have a quad of those I'll try as WCF too, alongside the WIMA FKP1)
 Expensive: V-cap TFTF/CuTF ...


----------



## Maxx134

redge78 said:


> maxx134 said:
> 
> 
> > I will now have to upgrade the WCF capacitor to a brighter,sharper,faster capacitor, in order for the T2 triode to "match" the top triode (T1) clarity, as it has main coupling cap as its source.
> ...



You are exactly on point again!!

 I remember specifically noting to you that I like the combination of having the Mundorf in that WCF position!!

 And it was extremely musical...

Then I use the Jupiter HT and that musicality was diminished somewhat,
But I dismissed it as the cap burning in...

But now it all makes sense!

 I am thus calculating values to go with an "RL" slightly below the projected targeted value of headphone,
 so that we can have the "T1" triode to dominate in the the impedance resistor settings...


----------



## Maxx134

Dammit now I have to look for new WCF caps...


----------



## baronbeehive

maxx134 said:


> You are exactly on point again!!
> 
> I remember specifically noting to you that I like the combination of having the Mundorf in that WCF position!!
> 
> ...


 
  
 That's just come at the right time for me, I've been wondering which positions to have my caps in, the Audyn True Copper and the Mundorf Silver! I was always leaning towards having the Audyns as coupling caps.


----------



## Maxx134

These are the impedance values I have been gathering for headphones settings...
I picked alot of planar headphones as they are same impedance with respect to frequency.
I need to round out to only FIVE settings for my switch...


*Headphones*:

LCD X = 20ohm
LCD XC = 20ohm
Ether = 22 ohm
HEX = 25ohm
Oppo PM3 = 26ohm

LCD EL8 = 30ohm
HE-5 =31ohm
Code-X = 31ohm
Beyer t51i = 32ohm
Grado (most) = 32ohm
Oppo PM1 = 32ohm
Oppo PM2 = 33ohm
HE1K = 35ohm
He400i =35ohm
HE560 =38ohm
HE5LE = 38, 41ohm


Pioneer SE Master1 @ 45ohms
HE560 = 45ohm
T50rp = 50ohm
HE6 = 50ohm
LCD2 = 47,50,60,70 ohm (!)
AKG k701= 62ohm
JVC HP-DX1000 @ 64 ohms


LCD4 = 100ohm
LCD3 = 110ohm
AKG K1000 = 120ohm

DT880 =250ohm
DT990 = 250ohm
T770 = 250ohm
T90 = 250ohm

HD600 = 300ohm
HD650 = 300ohm 
HD800 = 300ohm


T1 = 600 ohm


----------



## Maxx134

baronbeehive said:


> maxx134 said:
> 
> 
> > You are exactly on point again!!
> ...



You were correct on your assumptions. .
Looks like we have new guidlines:

Place the smoother better copper cap as coupling, and a teflon or brighter cap as WCF..


----------



## SonicTrance

@baronbeehive
We need progress pics!


----------



## baronbeehive

sonictrance said:


> @baronbeehive
> We need progress pics!


 
  
 Sorry MisterX, the reason is there aren't any due to lack of progress 
	

	
	
		
		

		
		
	


	




. I promise there will be when there are though 
	

	
	
		
		

		
		
	


	




. I am not going to be very quick doing this, mainly due to the fact that i've got to fit it in with a house move ATM, annoying but that's the problem I have!
  
 I have everything I need, I may get the odd thing like zfoils as I go along, which I wasn't going to bother with. Then there's new tips for the solder iron surgical gloves etc. which I may need but I can get as I go along but shouldn't hold me up, time is the main problem 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > @baronbeehive
> ...




I see. No rush! Good luck with your new house!


----------



## baronbeehive

*SMLD MODS*:
  
*Stage 1*  - Pics
  
 Maybe this is a bit over the top but these are the pics I took for the wiring, together with some more close ups, (I didn't want to strip out all the wiring and forget how to put it together again..... or have 1 nut left over 
	

	
	
		
		

		
		
	


	




).
  
 It may be helpful for anyone following me.


----------



## SonicTrance

What are those coupling caps? Did they come stock with your amp?


----------



## baronbeehive

sonictrance said:


> What are those coupling caps? Did they come stock with your amp?


 
 Probably didn't need all those pics but better safe than sorry!
  
 No they're Ansars recommended to me by my tech man when I couldn't fit the Audyns I bought because of their size. The idea was to see if I could tell the difference with a cap of a higher capacitance. I since bought the S/O Mundorfs to put in in their place before the mods thread started. He actually put in some posts to the PCB so that there would be no need to remove it again for changing the caps, some hope now that the main mods are about to be done!!!!
  
 BTW Maxx don't forget the HE-500's at 38 ohms, I see you have several cans at around that figure anyway.
  
 And would you say that low impedance cans respond less well to amplification than high impedance ones?


----------



## baronbeehive

*SMLD: Parts List*
  
 This is my parts list so that if you think there is anything missing you can let me know now, perhaps you could tell me before I start. I'm only going for the minimum necessary resistors as recommended by Maxx and what I think I need, for example I wasn't going to get any new driver stage resistors - the 2 groups of 3 on the other side of the driver tubes from the 220k ohm ones. These could be the zfoils. If you think I ought to have them let me know because I only want to do this once 
	

	
	
		
		

		
		
	


	




.
  
*Capacitors:*
  
  - Output stage decoupling     - Mundorf Mcap 47uf, 250V x 4
  - Driver stage decoupling      - MKP 40 µF Wima  800V 10 % x 2
  - Decoupling                          - PME-140: 0.33uF 275Vdc Evox Rifa PME271M x 6
  - Cathode bypass                  - PME-080: 0.1uF 275Vdc Evox Rifa PME271M x 4
  - Cathode bypass                  - Mundorf E-cap 220uf, 63V x 4
  - PSU caps                            - Mundorf M-Lytics AG 1500µF 160V x 2
  - Coupling, or WCF coupling - Audyn True Copper 0.22uF 630VDC x 4
  - WCF coupling, or coupling  - Mundorf Silver in Oil 0.33 UF 1200V 2% x 4
  
*Resistors:*
  
  - PSU stage    - Mills MRA5 8K2 x 2
   - Power stage - Mills MRA5 330R x 8

   - Driver stage  -TKD 2w 220K metal film x 4
  

*Wires:*
  
 - Chassis cable runs - 4 x 2-foot long cables, 3 core 22 AWG silver plated PTFE 19 strand wire
 - Output cables - Neotech 20 AWG, UP-OCC copper single core wire, RED teflon
  
*Misc:*
  
  - AMR Audio 90% Silver Alloy Fuse Tube 5x20mm 3.15A (Slow Blow) x 1
 - AMR Audio 90% Silver Alloy Fuse Tube 5x20mm 0.5A  (Slow Blow) x 2
  
 ......Oh, and there's the soldering video.............or soddering as you call it in the US .........most essential part of all!!


----------



## SonicTrance

@baronbeehive
 Looks good!
  
 Regarding the cables;
 20 awg cable is going to be tricky to solder at the inputs by the pot, you're more than likely gonna have to cut some strands off as the solder points are so close together. 22 awg was perfect btw.
 The single core 20 awg wire will probably make it very difficult to get the board back in the case as it's going to be very stiff. At least if you do like me and solder the wires while having the board out. You could of course just solder the board ends, then install the board and finally solder the XLR ends, that would work too.
  
 Btw, I'm interested why you chose the rather low values for the coupling and WCF caps?


----------



## baronbeehive

sonictrance said:


> @baronbeehive
> Looks good!
> 
> Regarding the cables;
> ...


 
 My mistake in copying over - should read 22 AWG silver plated, and 20 AWG OCC copper. (I will correct that).
  
 Thanks for that advice, I hope it will be the least of my problems!!!
  
 The caps values were purely in price terms for the Mundorfs if I remember correctly, and the .33uF was a compromise, I thought it would do. I would however have got .47uF for the Audyns later on with an eye on the mods, but as you know I mentioned that the site I bought them from got the sizes all wrong and in the end I found out that the .22uF was the only one that would fit the compact version unfortunately. That was what made it confusing choosing which was which for the coupling and WCF's. If I had gone for the Audyns for WCF, and the Mundorfs for coupling that would have been nearer to the ideal values. Maybe I will get the Jupiters eventually, but ATM I listen mostly to speakers so it wasn't such an issue 
	

	
	
		
		

		
		
	


	



  
 Edit:
 Also as the LD factory mod use .22uF I wasn't going to quibble about it


----------



## SonicTrance

@baronbeehive
  
 That's right, I forgot the Audyns were huge!
  
 Parts list look excellent and will most definitely sound excellent as well!


----------



## baronbeehive

I might have had to employ my carpentry skills and make a big box like Redge 
	

	
	
		
		

		
		
	


	




. I'm quite keen to hear the Audyns anyway, shame they can't make a compact version of them as well to suit our mods!


----------



## Mogos

Few questions regarding the coming mod. *Does the modifictaion to be somehow connected with the Lo-Hi gain switch?* Will it be still possible to switch between the two modes?
 If I will match the amp with my primary headphones 35 ohm (no switch) how it will influence the sound of my secondary once with 70 ohm resistance. They are quite close.
*I am wondering for which range of resistance the MKVI was better optimised.* Now it can work with 25 ohm and 600 ohm as well doing good job. But there should be a range in which it works more or less optimal. Do you now what is the range value? Just curious as I hope very soon I will optimise the amp for not only the range but for accurate value 
	

	
	
		
		

		
		
	


	




, thanks to you guys. I know that I will use the secondary headphones very rarely and for now I don't see any competiton for my primary headphones (including the hd800 new and old). Somehow I don't want to have choices 
	

	
	
		
		

		
		
	


	




. I just want to listen to my music. Having many options with tube rolling is more than I wish for as the MK VI with some adapters has endless combination of them. From my point of view the resistor switch will be more suitable for the tube rolling capability of MK VI than for changing the headphones. Having the matching for the different types of tubes eg. 6080, 421A and 5998 families will be a good thing. If you will post an instructions for the mod can you also show us one example of equation with values in it corresponding to the data sheet of the tube eg. 6080 ? I think I can figure it out by my self but good example is always a help. 
 One more thing. I am testing the russian tubes. They are a 6SL7 family and seems to better the new production Tung Sols. There is not a big difference. In general they are giving more expressive sound.
 In my opinion the 6SL7 tube family is more suitable for headphones with low sensitivity (less then 98 db).


----------



## baronbeehive

mogos said:


> Few questions regarding the coming mod. *Does the modifictaion to be somehow connected with the Lo-Hi gain switch?* Will it be still possible to switch between the two modes?
> If I will match the amp with my primary headphones 35 ohm (no switch) how it will influence the sound of my secondary once with 70 ohm resistance. They are quite close.
> *I am wondering for which range of resistance the MKVI was better optimised.* Now it can work with 25 ohm and 600 ohm as well doing good job. But there should be a range in which it works more or less optimal. Do you now what is the range value? Just curious as I hope very soon I will optimise the amp for not only the range but for accurate value
> 
> ...


 
  
 I agree about just enjoying the music, that's my aim, I've more or less finished with tube rolling anway, I have my preferred set.
  
 So your secondary headphones are the HD800's now? Wow! I am intrigued about this new mod as well.
  
 Did you manage to get any NOS tubes! Some say the 6SL7 tubes sound slightly different to the equivalent make of 6SN7's, and this may be due to the different wattage and resistance figures, I don't know.


----------



## Mogos

I did not get the NOS tubes 
	

	
	
		
		

		
		
	


	




. But if not this time then next. Any way I feel that the Psvane 6SL7-Z's may be be good enough to stop rolling the driver stage tubes. But I would like to have some good NOSes to experience the difference and understand what you guys are writing about 
	

	
	
		
		

		
		
	


	




. The power tubes are a challange to my wallet. I am aming to get the WE 421A and good 6080. Then do a change just when I will have urge for a change (this sickness calls audiofillionervosa and happends from time to time 
	

	
	
		
		

		
		
	


	




). I have to pospone the hunting in time for the power tubes as my wallet right now is totaly broken. 
 My secondary headphones are Sony Z-7. I have sold my HD800 half a year ago after more then three years of very happy listening.


----------



## baronbeehive

mogos said:


> I did not get the NOS tubes
> 
> 
> 
> ...


 
  
 We have a similar disease, its called upgraditis over here!
  


> ................
> 
> My secondary headphones are Sony Z-7. I have sold my HD800 half a year ago after more then three years of very happy listening.


 
  
 Oh I misunderstood, so the Sony's are your secondaries, and your HD800's the primaries. What are you using now if you have sold your HD800's?
  
 Let us know if you want any advice on the NOS tubes, you needn't spend a fortune!


----------



## Mogos

baronbeehive said:


> We have a similar disease, its called upgraditis over here!
> 
> 
> Oh I misunderstood, so the Sony's are your secondaries, and your HD800's the primaries. What are you using now if you have sold your HD800's?
> ...


 
 I am using HE1000 as primaries. And I realy don't have any desire to plug in other ones even for comparison. It will be just a waste of time 
	

	
	
		
		

		
		
	


	




.


----------



## Mogos

baronbeehive said:


> .....................
> 
> Let us know if you want any advice on the NOS tubes, you needn't spend a fortune!


 
 Till now I havent seen NOS (or even used) WE421A in the internet costing less then fortune (speaking about tubes, I am not used to buy such expensive tubes). I have to get used to the idea that it is worth to have them and then enjoy the best sounding headphone amp in the world. Difficult to imagine how it could be better sounding but I will have to check it. Now there is no way back. This is getting crazy 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

mogos said:


> baronbeehive said:
> 
> 
> > .....................
> ...




What sound signature do you like? Warm and smooth or clear and detailed?


----------



## baronbeehive

mogos said:


> Till now I havent seen NOS (or even used) WE421A in the internet costing less then fortune (speaking about tubes, I am not used to buy such expensive tubes). I have to get used to the idea that it is worth to have them and then enjoy the best sounding headphone amp in the world. Difficult to imagine how it could be better sounding but I will have to check it. Now there is no way back. This is getting crazy
> 
> 
> 
> ...


 
 Ha ha, welcome to the crazy world of the audiophiles..... 
	

	
	
		
		

		
		
	


	




. I was watching 3 western electric 421A's just now, put in a hopeful bid but they went too high for me also. I have 2 but need 2 more obviously but I won't pay too much like you! You have chosen to get the most expensive tubes out there, and having to get 4 of them for power tubes doesn't help! If I were you I would get some cheap and good RCA 6AS7G's for $20 each and then try some really interesting driver tubes so that you can get an idea what NOS sound like. Don't forget you have to go by the testing figures to see if you think they are NOS or not, you cannot tell just by the seller saying they are NOS. In any case a set of strong testing could be OK so long as they are closely matched, and they will be cheaper!


----------



## Mogos

sonictrance said:


> What sound signature do you like? Warm and smooth or clear and detailed?


 
 Clear and detailed. I have auditioned few times the Stax 009 with solid and tube amps and they did not impresed me. I like the sound reproduction getting close to live performance without coloration. So besides the nice timbre of instruments there is also important good reproduction of transients giving vivid feeling of short and energetic sounds (eg percussion but not only).


----------



## baronbeehive

What DAC do you use?


----------



## SonicTrance

mogos said:


> sonictrance said:
> 
> 
> > What sound signature do you like? Warm and smooth or clear and detailed?
> ...




Then the we421a's will suit you perfectly. Make sure, as baron suggested, to get NOS or strong testing ones. They won't come cheap though. You could also try the 5998's which has similar sound signature as the we421a's. They're usually about half price of the 421a's.


----------



## Mogos

baronbeehive said:


> Ha ha, welcome to the crazy world of the audiophiles.....
> 
> 
> 
> ...


 
 Yes this hunting can be long and exhausting. But with what I have achived alredy I don't feel any need to get them now or even at all. Especialy for the prices they are proposed for. There are other alternatives which may sound very close. As I said it is difficult for me to imagine right now what way the sound could be improved but I belive it can. If I will not get them then I will ran my imagination from time to time how they can sound and still have  a banana smile on my face.


----------



## baronbeehive

Mogos, if you want clear and detailed then TS998 as MisterX suggested for about $150 each, expensive! Then there's Bendix 6080WB superbly clear, detailed and musical but not harsh. I had these for many years and only changed because I prefer a warmer sound hence the RCA 6AS7G's. Bendixes are now approaching 5998 prices, they were just starting to get expensive when I got mine. Some on the other LD Mkvi/mk8 thread mentioned the Svetlana Winged C as being a very detailed power tube which I haven't tried.
  
 Pretty much all power tubes are getting expensive!
  
 I can't really think of any live sounding driver tubes, I prefer warm sound. The only ones that spring to mind are Raytheon 6SN7's which are good, and not expensive last time I looked. Failing that you could try mixing some RCA 6AS7G's with Psvane driver tubes which should give a very detailed dynamic sound, but of course are not NOS tubes.
  
 Only other thing I can think of change your DAC for a live sounding one, such as the Chord Hugo, or M-DAC, yet more expense and audiophillionervosa I'm afraid


----------



## Maxx134

baronbeehive said:


> sonictrance said:
> 
> 
> > What are those coupling caps? Did they come stock with your amp?
> ...



Hello, I didn't know that your copper caps were only 22uf, so although you input may not gp down to 5hz (lol) .22 should stilll get you in the 20hz region.
Main thing is that you will have a great signature, as I verified when I had the copper type cap as main coupling, and the Mundorf as WCF.

Now don't get carried away, as your board is one of the better made boards before they cut costs,
 because your small installed resistors are great quality Dale types.

So all your parts are excellent. 
I would also almost insist on Cardas Solder.
It will save you headaches. 

Also listen to MisterX suggestion with the solid wire, by installing on board first, and soldering onto plugs last.

I WROTE inside my amp with a black marker, where every wire goes.

As for your question, impedance of headphone will be closely matched with the amps output circuit,
So the common story of headphones impedance matching issues with amplifiers,
Will be irrelevant here. 


This next mod will be an addition of resistors to the Anode/Plate resistors.

Yet you will not have to pull board out,
As the design of this board places the Anode/Plate resistors on the component side.


----------



## Mogos

baronbeehive said:


> Mogos, if you want clear and detailed then TS998 as MisterX suggested for about $150 each, expensive! Then there's Bendix 6080WB superbly clear, detailed and musical but not harsh. I had these for many years and only changed because I prefer a warmer sound hence the RCA 6AS7G's. Bendixes are now approaching 5998 prices, they were just starting to get expensive when I got mine. Some on the other LD Mkvi/mk8 thread mentioned the Svetlana Winged C as being a very detailed power tube which I haven't tried.
> 
> Pretty much all power tubes are getting expensive!
> 
> ...


 

 Thank you baron for info. What I have been writing about my sound preferences may sugest that I am not having the sound signature I am seeking for. But that is far from reality. I do have rigth now live like sound signature (Telefunken 6080 Diamond series mached, balaced halves + russian 1596). All what I am doing right now is just the last polish up going beyond my imagination, perfecting alredy perfect e.t.c.
 I will seek for available tubes in resonable price. There is no presure. Now lets wait for the next mod and do an application of it afterwards.
 Regarding the capacitors. There is in earlier posts info/ tip from Maxx about the capacitors speed saying that higher the nominal voltage the faster capacitor responce. Beeing made of silver also should give the speed to the capacitor.


----------



## baronbeehive

b


maxx134 said:


> Hello, I didn't know that your copper caps were only 22uf, so although you input may not gp down to 5hz (lol) .22 should stilll get you in the 20hz region.
> Main thing is that you will have a great signature, as I verified when I had the copper type cap as main coupling, and the Mundorf as WCF.
> 
> Now don't get carried away, as your board is one of the better made boards before they cut costs,
> ...


 
  
 Thanks for the suggestions guys. Re: the caps I may yet put the .33 Mundorf SO cap as coupling ......but then I've lost the speed of silver in the WCF position. Anyway after a lifetime of headphone use I would think that hearing 20hz would be pretty good.
	

	
	
		
		

		
		
	


	




.
  
 I will be using Cardas solder thanks Maxx, anything that makes it that much easier!
  
 Quote:


mogos said:


> Thank you baron for info. What I have been writing about my sound preferences may sugest that I am not having the sound signature I am seeking for. But that is far from reality. I do have rigth now live like sound signature (Telefunken 6080 Diamond series mached, balaced halves + russian 1596). All what I am doing right now is just the last polish up going beyond my imagination, perfecting alredy perfect e.t.c.
> I will seek for available tubes in resonable price. There is no presure. Now lets wait for the next mod and do an application of it afterwards.
> Regarding the capacitors. There is in earlier posts info/ tip from Maxx about the capacitors speed saying that higher the nominal voltage the faster capacitor responce. Beeing made of silver also should give the speed to the capacitor.


 
  
 When I said previously that I didn't like Telefunken, that doesn't mean they aren't any good. For you they are probably right because they give that very true sound without any colouration, which I think you prefer. So regarding the NOS tubes what I suggest you could do now is that you keep the Telefunkens which I assume are NOS, or at least not new issue, and you could pick up a pair of Raytheon 6SN7GT's such as these:
http://www.ebay.com/itm/RAYTHEON-6SN7GTB-TIGHT-MATCH-PAIR-BLACK-PLATE-SIDE-GETR-TEST-NOS-VINTAGE-1956-/331762388448?hash=item4d3e944de0:g:an8AAOSwiLdWBvL8&rmvSB=true
 only $19.95, fixed price, just to get a feel of NOS tube and if you like them you can go into it more later I leave it entirely up to you.


----------



## baronbeehive

*SMLD MODS:*
  
*Stage 2 - *Remove PCB
  
 Woooooo............the board's out. Just half an hours heaving did it 
	

	
	
		
		

		
		
	


	




.I was expecting much worse!


----------



## Redge78

baronbeehive said:


> *SMLD MODS:*
> 
> *Stage 2 - *Remove PCB
> 
> ...


 
 As I have understood things, the challenge is not to take it out, but to put it back without breaking anything ... no pressure ... at all  
	

	
	
		
		

		
		
	


	



  
  


baronbeehive said:


> Anyway after a lifetime of headphone use I would think that hearing 20hz would be pretty good.
> 
> 
> 
> ...


 
 Jez, I'd like to hear that 20Hz as well, but at the present time, this is way out of reach of my MK8/HD800.
 I have some few dedicated tracks just to test that, if someone is interested.


----------



## baronbeehive

redge78 said:


> As I have understood things, the challenge is not to take it out, but to put it back without breaking anything ... no pressure ... at all
> 
> 
> 
> ...


 
  Damn and blast..... thanks very much 
	

	
	
		
		

		
		
	


	




.
  


> .............
> 
> Jez, I'd like to hear that 20Hz as well, but at the present time, this is way out of reach of my MK8/HD800.
> I have some few dedicated tracks just to test that, if someone is interested.


 
  
 I would be very interested in that! That's one of the reasons to not exceed the 1uF value for coupling caps because it wouldn't be possible to hear below 20hz.........apart from the fact that you could introduce rather unpleasant instability into the amp at those levels. I have heard that it's possible to hear below 20hz which I doubt very much, I suspect its rather like people saying they can hear compression effects in mp3's compared to say flac files. You may be aware of the absence of something but could probably not tell what it was exactly! I've tried comparing high res, (24 bit, 2116kbps), and standard res, (16 bit, 1411kbps), apple lossless files and got a majority right in a blind test but when I repeated this I got them practically all wrong. I still think I could tell but I haven't repeated it since!
  
 I suspect I'm going to have to watch where I put those rifa's now and I don't expect any of you guys is going to tell me where to put them, you want to see me suffer 
	

	
	
		
		

		
		
	


	




.


----------



## Mogos

baronbeehive said:


> Damn and blast..... thanks very much
> 
> 
> 
> ...


 

 Do you need some photos? I can send you what I have done.


----------



## Redge78

baronbeehive said:


> I would be very interested in that! That's one of the reasons to not exceed the 1uF value for coupling caps because it wouldn't be possible to hear below 20hz.........apart from the fact that you could introduce rather unpleasant instability into the amp at those levels. I have heard that it's possible to hear below 20hz which I doubt very much, I suspect its rather like people saying they can hear compression effects in mp3's compared to say flac files. You may be aware of the absence of something but could probably not tell what it was exactly! I've tried comparing high res, (24 bit, 2116kbps), and standard res, (16 bit, 1411kbps), apple lossless files and got a majority right in a blind test but when I repeated this I got them practically all wrong. I still think I could tell but I haven't repeated it since!
> 
> I suspect I'm going to have to watch where I put those rifa's now and I don't expect any of you guys is going to tell me where to put them, you want to see me suffer
> 
> ...


 
 1 - Enduring pain and suffering with a steady composure will make you a better man ... so they say.
  
 2 - It's possible to ear below 20Hz, even if "naturally" there is very few occasion to have these produced. 32" Great organs can produce 16.5Hz, and the 64" ones can produce 8.25Hz but that's about all I know.
 And "electronic music" can produce whatever they want (but the "more commercial" ones will be listened through Apple earbuds, which will severelly limit the utility to introduce that kind of ultra-low frequencies in their tracks). 
  
  
 3 - The tracks (both "electronica")
  
*Covenant > In transit > Intro* (from start to 2:00). https://www.youtube.com/watch?v=nruLq9h-fOg
 In this track, the 20Hz is "certified present" even if you can't hear it. When you'll ear the track, you'll find it "self-explainatory"
  
*Isan > Salle d'Isan > Day & Later* (didn't find it on YT - _PM me if you can't find it_)
 This one is a bitch, with a bass line you should be able to follow all the time, and some octaves below the same line (that is the real challenge to hear), with inter-modulations to boot.


----------



## SonicTrance

baronbeehive said:


> redge78 said:
> 
> 
> > As I have understood things, the challenge is not to take it out, but to put it back without breaking anything ... no pressure ... at all
> ...


 
 Just look at my pics and you'll see where I put mine. Remember that they need to sit flush against the board (no solder points in between). They are a little taller than the PCB standoffs so you can use washers if you want, otherwise you need to be careful not to over tighten the screws when you put it back together.


----------



## baronbeehive

mogos said:


> Do you need some photos? I can send you what I have done.


 
  
 Thanks, I will PM you when I'm at that stage. I was wondering whether to put those rifa's on top like Maxx after what you guys said about the difficulty with the board. Failing that I will look very carefully at their position with regard to the posts.
  
 I just checked out those HE1000's, wow 
	

	
	
		
		

		
		
	


	




.
  


redge78 said:


> 1 - Enduring pain and suffering with a steady composure will make you a better man ... so they say.
> 
> 2 - It's possible to ear below 20Hz, even if "naturally" there is very few occasion to have these produced. 32" Great organs can produce 16.5Hz, and the 64" ones can produce 8.25Hz but that's about all I know.
> And "electronic music" can produce whatever they want (but the "more commercial" ones will be listened through Apple earbuds, which will severelly limit the utility to introduce that kind of ultra-low frequencies in their tracks).
> ...


 
  
 Thanks Redge I will try those out. That organ music is one of the best types to try out hifi gear with too! I can try it with my HE-500's and my speakers so it will be interesting. My speakers are stand mounts so do not go down very low anyway but I have heard the occasional low rumble with them. I'll check out the freq response of the HE-500's I don't know what the figures are off hand. Up till recently the HE-500's were one of the best for bass............. except for the LCD's of course, alright and the HD800's aren't bad!! Alright, alright..........


----------



## baronbeehive

sonictrance said:


> Just look at my pics and you'll see where I put mine. Remember that they need to sit flush against the board (no solder points in between). They are a little taller than the PCB standoffs so you can use washers if you want, otherwise you need to be careful not to over tighten the screws when you put it back together.


 
 Thanks, I'll check it out 
	

	
	
		
		

		
		
	


	




. Did you have trouble avoiding the posts? I know you said you never wanted to remove the PCB ever again 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Just look at my pics and you'll see where I put mine. Remember that they need to sit flush against the board (no solder points in between). They are a little taller than the PCB standoffs so you can use washers if you want, otherwise you need to be careful not to over tighten the screws when you put it back together.
> ...



Yes, if I can avoid removing it again I will. It's just a pain to remove it, especially now with all the extra caps on. I have removed two standoffs, one on each side by the driver tubes for easier installation.


----------



## baronbeehive

redge78 said:


> .........
> 
> 3 - The tracks (both "electronica")
> 
> ...


 
  
 I tried them both over my speakers which have a lower frequency limit of 45hz and despite that I picked it up on the Covenant track as a very low frequency hum, more felt than heard! The other track is here if anyone didn't find it:
  
http://isan.bandcamp.com/track/days-later
  
 Its much more difficult to hear, I can't tell if the bass line I'm hearing is the 20hz or one a bit higher! It's much like a low frequency hum that people around here report hearing at night and nobody knows what is causing it! I think the higher frequencies would be more of a problem for me.
  
 I haven't tried it over headphones.
  
 Don't know if anyone else tried it??


----------



## Redge78

baronbeehive said:


> I tried them both over my speakers which have a lower frequency limit of 45hz and despite that I picked it up on the Covenant track as a very low frequency hum, more felt than heard! The other track is here if anyone didn't find it:
> 
> http://isan.bandcamp.com/track/days-later
> 
> ...


 
 On Covenant, with the MK8/HD800 I can clearly ear the 31Hz, I have a significant decrease of volume at 25Hz and I can only vaguely/faintly distinguish the 20Hz. I guess my system cut-off frequency should be between 25 and 30Hz, which is not so bad actually.
 On Isan, on the highest notes of the bass line, I can clearly hear both the bass and the sub-bass. When the notes get lower, the sub-bass vanishes.
  
 I have heard those two tracks on a "bloody good" speaker system (Accuphase > Audio Research > Tube amp 845/845 > Wilson Sacha) and I can guaranty you that the lowest notes (20Hz and below) are not just felt or like some hummings, they are real/clear/separate notes you can ear/follow at full volume, with an impressive feeling of power delivered. 
  
 But to be honest, most systems feel on Isan, no matter the price tag.


----------



## baronbeehive

redge78 said:


> On Covenant, with the MK8/HD800 I can clearly ear the 31Hz, I have a significant decrease of volume at 25Hz and I can only vaguely/faintly distinguish the 20Hz. I guess my system cut-off frequency should be between 25 and 30Hz, which is not so bad actually.
> On Isan, on the highest notes of the bass line, I can clearly hear both the bass and the sub-bass. When the notes get lower, the sub-bass vanishes.
> 
> I have heard those two tracks on a "bloody good" speaker system (Accuphase > Audio Research > Tube amp 845/845 > Wilson Sacha) and I can guaranty you that the lowest notes (20Hz and below) are not just felt or like some hummings, they are real/clear/separate notes you can ear/follow at full volume, with an impressive feeling of power delivered.
> ...


 
  
 Yes that's exactly how I would describe hearing it, as I said it was difficult to tell which was the 20hz bass line in the Isan and it did begin to disappear the lower it got, so that speaker system must be impressive!


----------



## Benny-x

maxx134 said:


> These are the impedance values I have been gathering for headphones settings...
> I picked alot of planar headphones as they are same impedance with respect to frequency.
> I need to round out to only FIVE settings for my switch...
> 
> ...


 
  
 + Pioneer SE Master1 @ 45ohms
 + JVC HP-DX1000 @ 64 ohms
  
 I also see that the thread is coming right along. Hopefully in a year's time when I've got the means and time to handle this you guys will have a pretty sound "formula" for upgrades. 
  
@Redge78
 Your mods are looking amazing. I'm sure once you've more or less finalized what's happening to your amp you'll work on the case and make it den worthy. I love the gigantic caps you've got in there. The only other place I've seen ones physically that big were in '70s - mid-'80s giant amps and receivers from Japan. I'm a fan of them too, haha.
 As for those white place "rings", they're called "zip ties" or sometimes "cable fasteners", but I think the second one is too limiting since those things are perfect for pretty much anything!
  
 You guys keep up the good work, and @baronbeehive good job with getting your mods started. Titling your posts will help me follow them later on when I get this project started myself. In retrospect, minus the first post that Maxx and Redge keep updating, it'd have been good if they followed the same approach. It makes finding the posts and following the immediate ensuing discussion around the mods really easy. All of you guys should number the posts as well, so they come up in "steps" that can be followed.


----------



## Redge78

maxx134 said:


> These are the impedance values I have been gathering for headphones settings...
> I picked alot of planar headphones as they are same impedance with respect to frequency.
> I need to round out to only FIVE settings for my switch...
> 
> ...


 
  
 Great list ! Exactly the kind of thing we need.
  
 If I remember well, the original LCD3 is 22ohm, the LCD3-Fazor is 110ohms.
 When I wanted to upgrade from my HD650, I had a close look at the HD800 and the LCD3f, both being "impedance adaptation compatible" with the MK8.


----------



## baronbeehive

benny-x said:


> ..........
> 
> You guys keep up the good work, and @baronbeehive good job with getting your mods started. Titling your posts will help me follow them later on when I get this project started myself. In retrospect, minus the first post that Maxx and Redge keep updating, it'd have been good if they followed the same approach. It makes finding the posts and following the immediate ensuing discussion around the mods really easy. All of you guys should number the posts as well, so they come up in "steps" that can be followed.


 
  
 We will. Nice to have another convert along for the ride! By the time you get yours started we ........may......... have ironed out the problems, and I may have finished mine
	

	
	
		
		

		
		
	


	




.
  
 I'm hoping to follow the tradition started by the others in providing some helpful info, as you probably know from the other LD thread I'm a complete beginner at this so it should give hope to others! If you want to see what the others have done look at page 23 & 43 for MisterX and page 33-38 for Mogos' main work, most of the pics are there before and after.


----------



## Maxx134

sonictrance said:


> baronbeehive said:
> 
> 
> > sonictrance said:
> ...




The problem I see with removing those tiny metal "standoffs" is that they keep the board steady when you are pulling and pushing in tubes..

So be careful about the board flex without the "standoff" in place.

Since I use tube socket savers, I hold them down in place while I pry up the tubes.

But pushing in, you can't avoid, so be careful pushing tubes in..


----------



## Maxx134

The status on the next mod is:
1- Most data is complete.
2- Two members on board to help in test phase (MisterX & Mogos)
3-ordered parts wait time

Thanks aging to MisterX for the front plate idea on the switch.

Basically, we will be swapping out the single ended pug for a switch,
For the impedance selector.

For those that want to keep the single ended jack, 
They make plugs that are combination single ended and XLR.
Yet I don't like plastic looking items..
Now if they made crystal. .


----------



## baronbeehive

maxx134 said:


> The problem I see with removing those tiny metal "standoffs" is that they keep the board steady when you are pulling and pushing in tubes..
> 
> So be careful about the board flex without the "standoff" in place.
> 
> ...


 
  
 I  haven't got as far as investigating that yet but would it be possible to stick a post on to the back of the board so that when it was back in it made contact with the top of the chassis to provide some stability? It may be a cause of vibration though.
  


maxx134 said:


> The status on the next mod is:
> 1- Most data is complete.
> 2- Two members on board to help in test phase (MisterX & Mogos)
> 3-ordered parts wait time
> ...


 
  
 ............he he........ 
	

	
	
		
		

		
		
	


	




. Looking forward to your results.


----------



## Mogos

baronbeehive said:


> I  haven't got as far as investigating that yet but would it be possible to stick a post on to the back of the board so that when it was back in it made contact with the top of the chassis to provide some stability? It may be a cause of vibration though.
> 
> 
> ............he he........
> ...


 
 Putting the post on the other side of the board could be a good idea. You need it only to withstanding pushing forces. Pulling is secured by the socket stopper against the top plate. To make it stable you can screw it to the borad and on the other side just stick a little rubber bumper (I don't know how it shall be called in Englih). You can buy them in harware stores and they are comming in different sizes. The olny thing you have to calculate the exact distance taging in to account the rubber cussion. And It may be that in place of the contact point there is a hole for ventilator. But in this case you can install a bar for support of the post. Even if it will be on the way of flowing air it will have no significant effect for cooling. I don't have installed the posts in this places and my sockets are different type with very tight pin holders. Till noe puching the tubes cafully did not result in any problems.


----------



## SonicTrance

maxx134 said:


> sonictrance said:
> 
> 
> > baronbeehive said:
> ...


 
 I do the same thing, using socket savers. The board is plenty stable though even without the two removed standoffs. It's such a tight fit to get the sockets through the holes on top of the case, so when they "snap in" it's very stable.


----------



## SonicTrance

So, are you guys ready for some viking rock? Swedish Sabaton!
 Don't expect any of you to like it but I do,haha!


----------



## Maxx134

@mogos,
Rubber bumper , maybe "hotglue" onto board is a dam excellent idea!
In fact, it would even be optimal to have more around board as long as not inhibit air flow..


----------



## baronbeehive

sonictrance said:


> So, are you guys ready for some viking rock? Swedish Sabaton!
> Don't expect any of you to like it but I do,haha!
> 
> 
> ...


 
  
 Is that the Swedish entry for Eurovision then 
	

	
	
		
		

		
		
	


	




. Reminds me a bit of Epica or Rammstein. Perhaps we should include a music spot on this thread!!


----------



## Mogos

maxx134 said:


> @mogos,
> Rubber bumper , maybe "hotglue" onto board is a dam excellent idea!
> In fact, it would even be optimal to have more around board as long as not inhibit air flow..


 
 But we have to remeber that the hot glue gets stiff as it cools down. Or maybe there are some kind which maintain elasticity. Ok now I get it you want to put some extra ones with hot glue. It wil be for certain good for the board stability. But any way to obtain good support and contact of the post to the plate it will be good to put some rubber material on one end.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > So, are you guys ready for some viking rock? Swedish Sabaton!
> ...


 
 Haha! No Eurovision for Sabaton I think


----------



## baronbeehive

sonictrance said:


> Haha! No Eurovision for Sabaton I think


 
  
 Why not? I seem to remember Norway had a very heavy metal band one year. Seriously I still love Abba, to me on a par with the Beatles.


----------



## Maxx134

I will soon be testing my third set of WCF caps,
 on my quest on fine tunning the amp...

Based on these results, they will either verify or not,
 my conclusions based on the two previous caps.

Third set will rule out chance in my observations.
Then I will have new cap recommendations for this position.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Haha! No Eurovision for Sabaton I think
> ...


 
 Yes, Abba is by far Swedens biggest music export of all time. They were (and still is) huge worldwide!


----------



## Maxx134

It turns out that the first mod tried in the other thread is much more important than ever contemplated. ..

I am talking about the power resistors (330ohm in MK6) for the plate/anode. 

Even so much as a slight variance in resistance will affect sound, depending what headphone you ate using! 

Why? 

Because this resistor directly affects the output impedance operational points. ..
And the resistance change is an exponential one, not a linear progression at all..
A few ohm difference can make a tenfold difference in the circuit/tube operation for headphone impedance setting..

So I was correct all along to insist on using tight tolerance, non-inductive wirewound MILLS resistors. ..

I have to credit to :
http://www.soniccraft.com/index.php

As they went above and beyond the already tight tolerance of these resistors, 
And offered an amazing "precision matching",
Down to level "L3":
*L3 = 1/4 factory tolerance 1/4% matching.
*

So all my resistors for the next mod (headphone impedance matching mod), 
are down to tolerance levels beyond what test equipment use!


----------



## Maxx134

Also, my next set of WCF caps came in, for testing..

Of course they will be doubled to achieve the .22uf ,
But the the interesting point is in using two caps instead of one..
As the actually measure .115uf each:


Using two smaller caps should make for a more responsive performance.


----------



## coinmaster

Maxx, I cannot grasp how the plate resistor in a servo design can affect the output impedance. The only way there will be 0 volts DC at the output is if both tubes have matching impedances, the servo adjusts the top triode impedance so there is 0 volts on the output at all times therefore maintaining a constant output impedance correct? The only thing I see the plate resistor doing is setting the voltage/current to fit the linear range on the load lines.
 Have you personally tested that the plate resistor has any affect on a servoed WCF?


----------



## Redge78

coinmaster said:


> Maxx, I cannot grasp how the plate resistor in a servo design can affect the output impedance. The only way there will be 0 volts DC at the output is if both tubes have matching impedances, the servo adjusts the top triode impedance so there is 0 volts on the output at all times therefore maintaining a constant output impedance correct? The only thing I see the plate resistor doing is setting the voltage/current to fit the linear range on the load lines.
> Have you personally tested that the plate resistor has any affect on a servoed WCF?


 
  
 I don't know what is a "servo design", but the Zo of a WCF is calculated like that :
  

 and the plate resistor ("Ra" here) is part of it.
  
 I had run some simulations from this formula some months ago and the variation of Ra had a significant impact on the overall Zo.
  
 The funny thing with this formula is to play with the Rk, when considering the Rk as an high-pass RC filter, and see how the Zo drops with the increase of frequency.
 From that, you have a better idea of what's the "best" value for the Cathode bypass caps.
  
  
 [EDIT]
 and obviously, the second reason for choosing the best possible Plate resistors is that the "signal" current will run through them.
 Any "resistor coloration" will be heard straightaway, which is not the case for the Cathode resistors for instance.


----------



## baronbeehive

*SMLD MODS:*
  
*Stage 3 -* Identify changes on PCB.
  
 Wiring: The 2 brown, 2 blue and 2 yellow output wires in the centre of the board tied together. Replace these with 20AWG OCC copper which should not need to be doubled or twisted. Also the 4 runs of wiring around the chassis from board to output jacks to be replaced with 22AWG silver plated copper wires, easy to see.
  

  
 Resistors:
 1. The 8 x 330 ohm power stage green resistors. 4 on either side of the board, (2 of which in pic above, reverse of board). Replace with 8 x Mills MRA5 330R.
 2. 4 x 220k ohm driver stage blue resistors, 2 together in the top right of pic next to driver tube. Replace with 4 x TKD 2w 220K metal film.
  

  
 3. 1 x 4k1 resistor on the right of the 3 resistors on the bottom edge next to the small brown vertical cap. Replace with 2 x Mills MRA5 8K2.
  

  
 Capacitors:
 1. Coupling caps, the 2 large black caps in centre pic in the middle. Replace these with 4 x Audyn True Copper 0.22uF 630VDC.
 2. WCF caps, the 2 horizontal red oblong caps in the centre of the centre pic above the power tubes. Replace these with 4 x Mundorf Silver in Oil 0.33 uF 1200V.
 3. Decoupling cap. Add 4 x Mundorf Mcap 47uf, 250V for power stage, and 2 x MKP 40 µF Wima 800V for driver stage. Also 6 x 0.33uF 275Vdc Evox Rifa bypass caps. Pics to follow.
 4. Cathode Bypass caps, The 2 large blue 220uF caps in bottom centre of the pic in the centre in between the 2 power tubes. Replace with 4 x Mundorf E-cap 220uf, 63V. Also 4 x 0.1uF 275Vdc Evox Rifa bypass caps.
 5. PSU caps, the 2 black vertical caps on left of pic above. Replace with 2 x Mundorf M-Lytics AG 1500µF 160V.
  
 Next section should be the mods themselves with locations etc. 
	

	
	
		
		

		
		
	


	




. I've found out that it's possible to put the tubes in to test the mods with the board as it is half in and half out providing you are careful. I haven't tried it switched on.


----------



## SonicTrance

Looking good there baron! You've everything under control. Looking forward to see more progress pics!


----------



## baronbeehive

sonictrance said:


> Looking good there baron! You've everything under control. Looking forward to see more progress pics!


 
  Thanks 
	

	
	
		
		

		
		
	


	




. Still one or two things on order which I couldn't get locally but it's getting critical now with the soldering/desoldering stage coming up. Should be interesting......... I don't know one end of a soldering iron from the other!


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Looking good there baron! You've everything under control. Looking forward to see more progress pics!
> ...


 
 Soldering is easy, especially with the Cardas solder! Do some practise on the side first and you'll be OK.


----------



## Maxx134

baronbeehive said:


> ...
> I don't know one end of a soldering iron from the other!



Sure you do.
Make sure you have smallest tip possible.
You can get a file to clean the tip too. 

Keep an eye on the angle of the iron, so you don't end up touching other parts and making melted marks on them.
It's not easy but if you melt a bit off your caps don't worry.


----------



## baronbeehive

maxx134 said:


> It turns out that the first mod tried in the other thread is much more important than ever contemplated. ..
> 
> I am talking about the power resistors (330ohm in MK6) for the plate/anode.
> 
> ...


 
  
 This is very exciting, getting down to experimental territory, this could be very interesting, well done Maxx and co. Maths isn't my strong point but I just about get where you're coming from.


----------



## coinmaster

> I don't know what is a "servo design", but the Zo of a WCF is calculated like that


 
 Our WCF uses a DC servo to null the DC at the output. The only time the DC is zero at the output is when both tubes have a matching impedance, therefore the servo maintains an equal impedance between them. Changing the plate resistor value will screw up the impedance divider of the tubes and will probably cause a required uneven impedance between the tubes to maintain a 0v output and it will alter the intended load line operating point of 75ma/75v on the MK6 which is what the amp was designed for given its voltage swing (which is close to cutoff to begin with which is why the NFB is needed).
  
 So I question whether the cavalli paper refers to an OCL WCF at all.


----------



## Maxx134

coinmaster said:


> Maxx, I cannot grasp how ...



If you were thinking about the opamp control in relation to the plate resistor, 
Remember that opamp control is between two tube circuits, not between two triodes within a tube.

My testing has been verified long ago.
The currently "in progress" mod is the selector switch with setrings for various headphone impedances. 


Oh yeah, I just read your last post..

All plate resistors are changed to be even more precisely & exactly matched the same..

 And with new ability for all plate resistors to be "switched" to new values, *all evenly at the same time.* 

The new design is also "fool proof" against switch failure, so it is impossible to cause damage.

So your point is "moot", or does not apply.

But your points were interesting of how you are understanding things.

I edited the end of this post for clarity.

Edit:
Another point you forgot is the amp protection circuit which will trigger the output relay instantly against this type of "DC offset" fault.

I know because in my tests I have triggered it this way, by simulating this condition by turning to maximum, one of the four tiny trimpots for the opamp.

Anyways there is your answer.


----------



## Redge78

Coin, this is how I see this thing working.
  
  


> Our WCF uses a DC servo to null the DC at the output.


 
  
 A "DC servo" does not "nullify the DC at the output", only output transformers or ouput capacitors can do that, in my book. And we don't have any of those in either the MK6 or MK8. More of that below.
 My understanding is that this "DC servo" is only monitoring the output. I confess I didn't pay much attention to it as it is not supposed to be in the signal path.
 Whatever, when the "what it is monitoting" (voltage or current) exceeds the programmed value, it triggers the relay and cut the output.
 Plain and simple.
  
   


> The only time the DC is zero at the output is when both tubes have a matching impedance, therefore the servo maintains an equal impedance between them.


 


  
 You should be more precise about what is your reference voltage. Here it really matters as it differs between "SE operation" and "symetrical".
  
 The output voltage of an OCL WCF is roughly half the rail voltage, minus the voltage drops due to the Ra and Rk. Basically,
 100V for a 200V power rail. The voltage reference is taken at the bottom rail, below the cathode.
 And basically the only thing that can change this 100V voltage would be to have a significant unbalance between the internal resistance of the two triode of the tube.
 Whatever tube you put, intil they have the same internal resistance, they will output the same 100V. 
  
 So what ?
  
 When running symetrical, both tubes of a channel are running at 100V. The "difference in potential" (_not sure of the trad. here_) which is the true definition of a voltage by the way is 100V - 100V => 0V.
 So, we don't get electrocuted ! Nice !
  
 When running SE, it's a bit more tricky ! Only one tube is being used and its WCF is still outputing 100V. But we need to have a "difference in potential" of 0V at the headphone if we want to not fry everything ...
 That's why the "ground" of the SE plug is not linked to the rail ground but to the "mid-point" of the power PSU where the potential is also at 100V above the one of the "rail ground".
 And then TA DA !!! we have our equilibrium/balance between potential as they are seen by the headphone : 100V - 100V = 0V.
  
  
   


> Changing the plate resistor value [...] will probably cause a required uneven impedance between the tubes to maintain a 0v output


 



  
 I don't see why we would end up with an "uneven impedance between the tubes" when we have applied the same Ra for both tubes of a channel.
  
  


> ... and it will alter the intended load line operating point of 75ma/75v on the MK6 which is what the amp was designed for given its voltage swing (which is close to cutoff to begin with which is why the NFB is needed).


 

  
  
 You're right in saying that it will change the "operating point". That's a good point. 
  
*And it would be bothering that by lowering the Rplate we increase the plate current above the "max Ia specs". We'll have a look into that.*


----------



## coinmaster

> My understanding is that this "DC servo" is only monitoring the output. I confess I didn't pay much attention to it as it is not supposed to be in the signal path.
> Whatever, when the "what it is monitoting" (voltage or current) exceeds the programmed value, it triggers the relay and cut the output.
> Plain and simple.


 
 Not at all, the WCF is like a resistor divider, If you have equal and opposite voltages feeding two equal value resistors you are going to have 0v between them and tubes are not perfect resistors. Each tube of the same type is going to vary from one another and shift with time. The DC servo (opamps) vary their output voltage (the grid bias voltage of the top tube) based on their input (the output voltage of the amplifier), an opamp will keep changing it's output until its input is 0v. Without the opamp you cannot have an OCL WCF.
  
 The "flat" IC in the center of the amp is the thing that cuts the output when the DC offset is higher than the threshhold value. Otherwise if something fails it's your headphones that will go up in smoke since they are not designed for any amount of dissipation.


----------



## Maxx134

Ok, enough speculations of "DC offset" class 101 .
Take enineering questions /concerns to PMs so as not to confuse the masses..

Nice read, but the opamp don't care about the resistors or the tubes.
They only monitoring/regulating the plus and minus output levels of tubes...

That's why *YOU* had two different power tubes and didn't blow your amp.

Now suddenly your all worried about their parameters.

Oh well, semantics here, 
You can't please everyone.

The main point is that all will be fine on next mod.


----------



## coinmaster

You're missing the point. The opamps provide the bias voltage to the top triode always keeping it's impedance in line with the bottom triode.
 Therefore the current's through both tubes should always be equal no matter what, assuming ra and rk are the same value. The only thing I see changing resistor values would do in a servoed design is change the load line operating point.
  
 I could understand the resistor optimization if this was a capacitor or transformer output WCF because there would be no dynamic bias adjustment but in our case the currents are always kept in line.


----------



## Maxx134

coinmaster said:


> The "flat" IC in the center of the amp is the thing that cuts the output ...




We went over this in PMs long ago about that skinny chip...
You later confirmed it's function in PMs, 
So you know Ridge78 knows all this.
What you don't know, is our testing on the timing cap that is next to it.

And of course the designer Sword-Yang once again made the best choice. .

In fact, the circuit board is a thing of beauty. ..
All plate resistors on component side, 
All Cathode resistors on other side...
Grid caps, 
WCF caps, 
All is extremely well laid out.
The board design is a thing of beauty, 
Once you can see it...


----------



## Maxx134

I don't see what you see.
I saw the opamp only recieving from output, and sending back a control to the * grid.


You will have to take up your conclusions with the designer.

In any case, I will have to label your theories incorrect.
Why?
Because the DC offset part of this design has nothing to do with what we are doing. 

The DC offset keeps on doing what it always does.
You are mixing two different topics.

Edit:
Side note:
I been running my amp daily for months at a calculated setting of 31.5ohm,
 and verified predicted sonic changes of both low impedance Ether, and high impedance HD800.

They behaved predicably according to an impedance change. 

If you can't wrap your head around that, sorry.

But don't come in hear speculating and confusing others.

As stated from beginning of this thread,
All mods are done, tested and confirmed before being suggested here.

It is not a design thread.

You can make a design thread and we can go back and forth all day there.


----------



## coinmaster

> All is extremely well laid out.
> The board design is a thing of beauty.


 
 Tell that to someone who reverse engineered it. The thing is an incoherent mess when you follow the traces 
	

	
	
		
		

		
			





, both channels are totally different in their trace layout as well.
  


> Because the DC offset part of this design has nothing to do with what we are doing.


 
 The DC servo has everything to do with the triodes operating point and current matching, without the dynamic grid voltage the tube would not remain at 75v/75ma when the load impedance changes or when the tube ages. This isn't speculation, this is fact. I've tested and confirmed it in simulations and on the bench.
  


> I been running my amp daily for months at a calculated setting of 31.5ohm,
> and verified predicted sonic changes of both low impedance Ether, and high impedance HD800.


 
 You should have said that a long time ago, I've asked you at least 4 times if you've actually verified any sonic differences so we are not chasing our tails here and you kept ignoring me.


----------



## Maxx134

Yes, yes I know each opamp directly control each tube output levels,
But the parameters of the tubes are independent of the opamp control, as you already shown with using two different tubes. .
Although the Plate/Anodes where the same, yet even if they were off a bit,(affecting plate current AND circuit impedance) as in stock cheapo units,

I believe that is what the trim pot is for...

Side note:
I have had loose pin connection on one of the opamps, and the result is a dip or loss in volume on whichever tube it corresponds to..

So anyone having that symptom would know its most likely the board pin socket problem..

Edit:
Sorry my phone went crazy in my pocket! Lol


----------



## coinmaster

> But the parameters of the tubes are independent of the opamp control, as you already shown with using two different tubes. .
> Although the Plate/Anodes where the same, yet even if they were off a bit,(affecting plate current AND circuit impedance) as in stock cheapo units,
> 
> I believe that is what the trim pot is for...


 
 Well the opamp provides the bias for the top triode, so the operating point of the top triode is directly based upon ra and the bias voltage provided by the opamp.
 The bottom triode is always at a fixed operating point because the bias and rk do not change. Hence the opamp is always struggling to keep the top triode in line with the bottom triode in order to maintain the 0v output because the non inverting input of the opamp is attached to ground so the opamp will do everything it can so that the inverting input is also at ground potential.
 The trim pot shunts the supply voltage to the opamp allowing different output voltages based upon the input voltage to the opamp. You want to make sure there's less than 100mv on the output of the amp, preferable below 50mv using the trimpot to adjust.


----------



## Maxx134

I bought 4 opamps to replace and will be looking into trimpot adjusting once I get my oscilloscope in.
Do you have oscilloscope?
I just got a kit it was cheaper than buying one.

Edit: 
The reason for opamp purchase was a mistake as I didn't realize the chip contacts into the socket was loose.

The issue remains even though I cleaned and slightly bent the pins for optimal contact,
Because with the heat of the amp, the one chip in question, somehow still manages to get loose.


So I will be replacing it.

And since I get carried away, I bought 4 opamps chips.


----------



## coinmaster

I bought a https://www.picotech.com/oscilloscope/2200/picoscope-2200-specifications since picoscope is well renowned and it beats paying 600 bucks. Has worked well so far.


----------



## Maxx134

Yes that is an excellent idea as it has software for computer interface and can do more things easily. 

I purchased a much simpler unit.
A small kit with 4 inch led screen.
Once it arrives I will see how good it is.


----------



## baronbeehive

coinmaster said:


> Make sure the mounting hole next to the driver stage power supply is connected to the chassis. It is the only ground exit for the board and should be the only direct connection between ground on the board and ground on the transformers/wall.


 
  
 So I can't test it with the board out after all, this was what I was worried about. Lucky I haven't switched it on yet.


----------



## coinmaster

Just use a clip and a wire to connect it to ground.


----------



## baronbeehive

coinmaster said:


> Just use a clip and a wire to connect it to ground.


 
  
 Oh you idiot....... me, not you 
	

	
	
		
		

		
		
	


	




. I had a feeling there might be a ground in there somewhere, luckily I was going over some past posts looking for solder locations and came across your post.


----------



## coinmaster

It's entirely possible that nothing bad will happen if you don't connect that part to ground. The black wire that leads from the transformers to the capacitors in the power supply is also connected to ground through some sort of tap in the transformer, but this tap is a mystery to me. It's certainly not a normal ground point as I've blown a few fuses while using it as one.
 The grounding hole that I spoke of near the input stage put supply is required for the rectifier operation and bad things can happen if it isn't grounded. I wouldn't risk it.


----------



## SonicTrance

This should not be an issue for you @baronbeehive as you're not removing the board completely, only tilting it down leaving all wires attached, correct?


----------



## baronbeehive

sonictrance said:


> This should not be an issue for you @baronbeehive as you're not removing the board completely, only tilting it down leaving all wires attached, correct?


 
  
 Yes that's right. But I assumed that this connection between board and chassis was the only grounding.
  
 Also I will be rewiring it as well!


----------



## SonicTrance

Yes, just make sure that connection stays intact and you're all good. And all other connections obviously.


----------



## Maxx134

When board is out, I only test connections with continuity testing...

 I never test it live until the board is in place .

I never tested my amp with the board out.

 I do not advise that.
 I like everything to be in place and ready to close up before I test.

That way I know everything is positioned in place, with tubes inserted properly,
and nothing is touching the wrong things.


----------



## SonicTrance

maxx134 said:


> When board is out, I only test connections with continuity testing...
> 
> I never test it live until the board is in place .
> 
> ...


 
 This is good advise! 
 I too have never power ON with the board out. It is possible though if you're really careful.


----------



## baronbeehive

coinmaster said:


> It's entirely possible that nothing bad will happen if you don't connect that part to ground. The black wire that leads from the transformers to the capacitors in the power supply is also connected to ground through some sort of tap in the transformer, but this tap is a mystery to me. It's certainly not a normal ground point as I've blown a few fuses while using it as one.
> The grounding hole that I spoke of near the input stage put supply is required for the rectifier operation and bad things can happen if it isn't grounded. I wouldn't risk it.


 
  
 Do you mean the hole on top right next to the power socket? That one and the other one on the top left are the only ones disappearing into the transformers which I haven't looked in. The others do not appear to have any associated circuitry or connections on the board or chassis to ground so using any of those as ground would not appear to make any difference.
  
 Quote:


maxx134 said:


> When board is out, I only test connections with continuity testing...
> 
> I never test it live until the board is in place .
> 
> ...


 
  
 I see your point but providing I can be sure of the ground connection I will probably try it because I can't see any problem apart from the ground connection. The board in appears to be exactly the same as the board out regarding touching things, so long as it is resting on something non conductive and not touching any bare connections.


----------



## Maxx134

When you grab the board you tend to touch things,
 and things get bent out of position.

Also this amp does not have a normal power supply. 
If using the "ground" or center, you will be able to measure both positive and negative power supply to the tubes.

The driver stage is a different, "normal" power supply though. 

The issue is that they are totally separate power supplies.

Also coin, you asked what where the differences between the MK6&MK8.

The tube pin sockets make the board traces different, but so far,
Other than the tubes,
 I see the power resistors the and transformers as the obvious things. 
Most of the design is similar.


----------



## coinmaster

The hole next to the input stage power supply rectifier is connected to the ground plane of the pcb. The ground lug on the transformers that is connected to chassis and the chassis is connected to that hole, therefore that hole is the link to ground for the amplifier.
 The black wire that leads into the large capacitor section is kind of a mystery, it's sort of ground but it sort of isn't. Moral of the story is keep the hole next to the input stage power supply connected to chassis.
 If you are unsure where it is use a continuity test on the screw holes until you find one that links to the ground plane on the PCB.


----------



## SonicTrance

Guys, finally got my LCD-3's today! Man, these are great headphones! Just start listening now.


----------



## baronbeehive

sonictrance said:


> Guys, finally got my LCD-3's today! Man, these are great headphones! Just start listening now.


 
  
 Fantastic! I believe they're a bit better balanced between bass and treble than the LCD-2's. Every LCD is a bit different from the last one too. Are you keeping the LCD-X's now? I really don't know what I would get to replace the HE-500's I've got, the LCD's have a totally different sound. I don't think the Ether's are the ones yet!
  
 I'm OK I'm listening to the speaker amp ATM!
  
 Happy listening 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Guys, finally got my LCD-3's today! Man, these are great headphones! Just start listening now.
> ...


 
 Yes, I'm keeping the XC's as I need closed cans too. And from what I've heard so far they complement each other nicely. The LCD-3's being slightly warmer/darker sounding but with amazing soundstage and detail. I think I'll buy a Silver Dragon cable for the 3's though. I'm using Custom Cans Litz copper cable for the XC's which is nice but the 3's would benefit from a silver cable I think.


----------



## baronbeehive

I see you had Audio Technicas btw, what did you think of them, I loved the ones I had.
  
 People seem to fall into the LCD camp or the HiFiMan camp in terms of the type of sound you get......... then there's the Sennheiser sound!!!!


----------



## Mogos

I did have Sennheisers HD800 for long time. They was from early production. The serial number was something around 1340. In this time I have been auditioning many different headphones including Stax 009 plus their solid state amp. But I have had  never been impressed to the extent that I would like to change my beloved Sennheisers. Mostly the sound stage of the competitors was inferior and other qualities like speed and impact could not match Senk's performance.
 I was pleased with them but I knew from the sound signature of the other headphones that some things can be done better. For example they could be a little warmer and giving more engaging timbre of the instruments.
 But I have used them with the standard LD and I know now for sure they will sound different with SMLD. Maybe I will have to tray them again. I have never herd the LCD-3's. Maybe beacause I am totaly not interested in headphones  tend to the warmer/darker side. The Stax Omega II had such a characteristic with some details jumping out of the heavy dark abyss . Quite pleasant but far from a live sound you can experience going for concert or chamber live performance.
 With HEK and SMLD I have no space for any complaints like above. Could that be the end of the road? No more imagination running wild 
	

	
	
		
		

		
		
	


	




 ?. I will miss it. And you are saying that the tube can make huge difference to what I am already hearing. Hard to believe. But the last mod (still in testing stage) shows that you shall never say never or that some things are not possible. Can I be suprised again? Do I?


----------



## SonicTrance

baronbeehive said:


> I see you had Audio Technicas btw, what did you think of them, I loved the ones I had.
> 
> People seem to fall into the LCD camp or the HiFiMan camp in terms of the type of sound you get......... then there's the Sennheiser sound!!!!


 
 I loved the sound but the fit was awkward with those 3D wings. I also didn't like that they were so damn sensitive, picking up every little noise from tubes etc. And once I got the XC's, there was no point in keeping the AT's.
  
 I've only had the 400i's from Hifiman, and to me they are way to warm sounding. These LCD-3's are bright in comparison IMO. I guess it's fair to say I'm in the LCD camp now, lol.


----------



## SonicTrance

mogos said:


> I did have Sennheisers HD800 for long time. They was from early production. The serial number was something around 1340. In this time I have been auditioning many different headphones including Stax 009 plus their solid state amp. But I have had  never been impressed to the extent that I would like to change my beloved Sennheisers. Mostly the sound stage of the competitors was inferior and other qualities like speed and impact could not match Senk's performance.
> I was pleased with them but I knew from the sound signature of the other headphones that some things can be done better. For example they could be a little warmer and giving more engaging timbre of the instruments.
> But I have used them with the standard LD and I know now for sure they will sound different with SMLD. Maybe I will have to tray them again. I have never herd the LCD-3's. Maybe beacause I am totaly not interested in headphones  tend to the warmer/darker side. The Stax Omega II had such a characteristic with some details jumping out of the heavy dark abyss . Quite pleasant but far from a live sound you can experience going for concert or chamber live performance.
> With HEK and SMLD I have no space for any complaints like above. Could that be the end of the road? No more imagination running wild
> ...


 
 I might have said this before but...
 To me, the biggest difference in sound signature you can make if you want clarity and detail, is to put in some 5998's or WE421A's as power tubes. I promise you Mogos, you will not be disappointed. Just make sure you get NOS tubes or tubes that tests good.


----------



## baronbeehive

mogos said:


> I did have Sennheisers HD800 for long time. They was from early production. The serial number was something around 1340. In this time I have been auditioning many different headphones including Stax 009 plus their solid state amp. But I have had  never been impressed to the extent that I would like to change my beloved Sennheisers. Mostly the sound stage of the competitors was inferior and other qualities like speed and impact could not match Senk's performance.
> I was pleased with them but I knew from the sound signature of the other headphones that some things can be done better. For example they could be a little warmer and giving more engaging timbre of the instruments.
> 
> ............


 
  
 Interesting comments guys. Yes the soundstage is the key to the Senns popularity. I found that with my HD600's you could be very impressed with the way they produced the music, technically but  it was totally lacking in emotional engagement and warmth as you say. Exactly!
  


> ............
> 
> But I have used them with the standard LD and I know now for sure they will sound different with SMLD. Maybe I will have to tray them again. I have never herd the LCD-3's. Maybe beacause I am totaly not interested in headphones tend to the warmer/darker side. The Stax Omega II had such a characteristic with some details jumping out of the heavy dark abyss . Quite pleasant but far from a live sound you can experience going for concert or chamber live performance.
> .............


 
  
 Yes, I agree with you again out darker sounding cans, although I don't like bright sounds either.
  
 Quote:


> Originally Posted by *Mogos* /img/forum/go_quote.gif
> 
> ............
> With HEK and SMLD I have no space for any complaints like above. Could that be the end of the road? No more imagination running wild
> ...


 
  
 The end of the road........ Nirvana is at hand, lucky person 
	

	
	
		
		

		
		
	


	




.
  


sonictrance said:


> I loved the sound but the fit was awkward with those 3D wings. I also didn't like that they were so damn sensitive, picking up every little noise from tubes etc. And once I got the XC's, there was no point in keeping the AT's.
> 
> I've only had the 400i's from Hifiman, and to me they are way to warm sounding. These LCD-3's are bright in comparison IMO. I guess it's fair to say I'm in the LCD camp now, lol.


 
  
 Yes, they were sensitive, but the very forward mid range was superb and involving for me, but the HE-500's with the copper cable, not the silver one, improved in every way, and were also very musical sounding and easy to listen to.
  


sonictrance said:


> I might have said this before but...
> To me, the biggest difference in sound signature you can make if you want clarity and detail, is to put in some 5998's or WE421A's as power tubes. I promise you Mogos, you will not be disappointed. Just make sure you get NOS tubes or tubes that tests good.


 
  
 Yes, I agree the tubes make a massive difference............ maybe Nirvana is not here yet Mogos 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

Just messin' around!
  

  
 I'm thinking of putting the Rifa's on this side to get over the problem Redge mentioned about putting back the PCB!! Everything could go like this, the Wima and its bypass could be rotated anticlockwise a quarter turn and the other 4 Rifa's could all line up horizontally on this side of the white Mcaps, similar to how Maxx has got his.


----------



## Maxx134

baronbeehive said:


> ...I really don't know what I would get to replace the HE-500's I've got...



Did you mod them?





sonictrance said:


> I think I'll buy a Silver Dragon cable for the 3's though. I'm using Custom Cans Litz copper cable for the XC's which is nice but the 3's would benefit from a silver cable I think.



I too have a little cable (cardas),
And instead of ordering a silver dragon, 
I just ordered a pure silver cable from ela-audio for less than $200, was a steal at 7ft and having 8 cores of 24awg pure silver wire and teflon sleeving.

In comparison, the silver dragon has a huge thick rubber coating, and a SUPER TINY TINY THIN GUAGE OF WIRE...

When I cut this cable to reterminate it, I was truley shocked at the super thin size...


----------



## baronbeehive

maxx134 said:


> Did you mod them?
> 
> 
> 
> ...


 
  
 No, apart from inserting a length of tube into the pads to increase the distance to the ear, which didn't have much effect.
  


> ......I too have a little cable (cardas),
> And instead of ordering a silver dragon,
> I just ordered a pure silver cable from ela-audio for less than $200, was a steal at 7ft and having 8 cores of 24awg pure silver wire and teflon sleeving.
> 
> ...


 
  
 Brilliant idea! Quite cheap too. What did it sound like?


----------



## Maxx134

I didn't get it yet.
Just ordered yesterday. 

Also, your placement of caps is fine as long as the bypass .1uf Rifa's are close to the cathode caps..


----------



## Mogos

baronbeehive said:


> Just messin' around!
> 
> 
> 
> I'm thinking of putting the Rifa's on this side to get over the problem Redge mentioned about putting back the PCB!! Everything could go like this, the Wima and its bypass could be rotated anticlockwise a quarter turn and the other 4 Rifa's could all line up horizontally on this side of the white Mcaps, similar to how Maxx has got his.


 

 Thats very innovative way of components installation - wire-solderless 
	

	
	
		
		

		
		
	


	




. I could not spot the nanotransmitters 
	

	
	
		
		

		
		
	


	




. Oh me stupid cause they are nano.
  
 But speaking seriously the stock casing is to small for the mods we are doing. I realy don't envy you guys to put all this parts in such a small space. Even with my enlargement I still consider it to be to small. If I will do again the mod I will extend the casing even more to make more space between the top plate and the board.


----------



## SonicTrance

maxx134 said:


> baronbeehive said:
> 
> 
> > ...I really don't know what I would get to replace the HE-500's I've got...
> ...


 
 Interesting! I'll have a look at that. It seems the gauge is the same though @ 24awg, but the ela-audio has 8 conductors vs. 4 conductors for the silver dragon. Definitely less money also, which is a big plus!


----------



## baronbeehive

mogos said:


> Thats very innovative way of components installation - wire-solderless
> 
> 
> 
> ...


 
  
 You have to stay ahead of the game nowadays 
	

	
	
		
		

		
		
	


	




.
  
 Sound quality is superb with only a slight rattle!


----------



## SonicTrance

sonictrance said:


> maxx134 said:
> 
> 
> > baronbeehive said:
> ...


 
 Found another one which is a lot less money for me as it's within EU.
  
 http://www.ebay.com/itm/Ultimate-Pure-Solid-Silver-Audeze-LCD2-LCD3-LCD-X-upgrade-cable-by-Lavricables-/181385832451?hash=item2a3b702803:g:l8UAAMXQrhdTUSmJ
  
 8 x 28awg though, so pretty thin. What do you think?


----------



## baronbeehive

sonictrance said:


> Found another one which is a lot less money for me as it's within EU.
> 
> http://www.ebay.com/itm/Ultimate-Pure-Solid-Silver-Audeze-LCD2-LCD3-LCD-X-upgrade-cable-by-Lavricables-/181385832451?hash=item2a3b702803:g:l8UAAMXQrhdTUSmJ
> 
> 8 x 28awg though, so pretty thin. What do you think?


 
  
 I didn't read the Swedish review!
  
 It does look good quality from what you can tell from his information, I think I would go for one of these though for £160, £10 more, they are OCC silver and have good recommendations. They are 26awg:
  
http://www.toxic-cables.co.uk/index.php?route=product/product&path=59_61&product_id=59
  
 Not really bothered for my HE-500 which sounds good with copper but for the LCD-3 I think silver would be great!
  
 Edit: the UK cost of the Ebay silver cable you posted the link to is £149, I expect it woud be considerably cheaper in Sweden! So the Toxic cables silver cable would probably be quite expensive in comparison but it was only £10 more in UK money, (£160).


----------



## Maxx134

MisterX, 
That link shows a thinner guage wire with no nylon sleeve protection, 
Plus it's only about 6 feet (2 meters), so it is shorter. 

Add shipping to US and it's more money..

Yes it is Less money by you like you say,
 but I wouldn't buy it, 
 only because it is shorter and has no sleeving protection..

It probably looks like IEM cable..


----------



## baronbeehive

As far as I can see from previous pics you connect the 2 legs on the top left and top right together and the same for the bottom legs in the pic for the WIMA, and the same for the PSU cap - (+ to +. and - to -).
  
 As far as I can make out the cathode bypass caps,  PSU caps, and the 8k2 resistors have polarity ie. they are marked positive or negative either on the PCB or on the parts themselves. So do I have to put any of the parts in in a particular position in their respective locations and do I have to connect them up to their bypass caps in a particular position. I know I have to connect caps and their bypass caps head to head and tail to tail, and I know their solder points, I'm talking about orientation.
  
 Also can I use heat shrink in place of sheathing. It just looks a lot thinner than proper sheathing and I wondered if it was as good an insulator?


----------



## SonicTrance

maxx134 said:


> MisterX,
> That link shows a thinner guage wire with no nylon sleeve protection,
> Plus it's only about 6 feet (2 meters), so it is shorter.
> 
> ...




I agree, too thin. The length is no problem for me though. To me 5 feet is perfect as I don't move around when I listen, and I sit right next to the amp. 

The toxic cable that baron linked looks interesting though!


----------



## SonicTrance

You're right about the caps baron. But resistors do not have polarity. Only the psu caps have polarity as you're using the mundorf bipolar for cathode bypass. 

Don't know what sheathing is but you can use heat shrink for insulation, no problem, I also used heat shrink on a few places.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Found another one which is a lot less money for me as it's within EU.
> ...


----------



## baronbeehive

sonictrance said:


> I agree, too thin. The length is no problem for me though. To me 5 feet is perfect as I don't move around when I listen, and I sit right next to the amp.
> 
> The toxic cable that baron linked looks interesting though!


 
  
 That Toxic cable has been used by several members who have given it great recommendation, it's from a relatively new UK company who started up quite small a few years ago as far as I know.
  
 I believe the review of the cable you mention in your link was reviewed in Finnish not Swedish sorry!
  
 Don't know your rates of VAT or Customs but the $200 cable Maxx mentions would work out at $245 even assuming it was the same price for the UK, they usually add on about half as much again for goods to the UK! That works out at about £170 compared to the Toxic cable at £160 + p&p.


----------



## SonicTrance

Yes, import charges are a pain! The ela-audio cable would cost me $63 in shipping + import charge. That's just the way it is. I will look into that toxic cable some more! Thanks for the tip baron.


----------



## baronbeehive

Check out some old English rock guys, I like it, you probably won't. If not blame MisterX for starting this trend 
	

	
	
		
		

		
			





.
  
https://www.youtube.com/watch?v=sdfFAqzrwok&list=PLWfGw2maX1M7tHG1zp-gyRiws9Bxmcx4s&index=7


----------



## SonicTrance

@baronbeehive
 I just ordered the toxic cable! It seems very hard to beat for the price!
  
 And as you expected, I did not enjoy the English rock, lol


----------



## baronbeehive

sonictrance said:


> @baronbeehive
> I just ordered the toxic cable! It seems very hard to beat for the price!
> 
> And as you expected, I did not enjoy the English rock, lol


 
  
 Excellent. I'm sure you will not regret it. I will get one from there when I need one. I was interested to see they incorporate gold into the cable as well!
  
 BTW you have no taste lol 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

Yes it's quiztime folks!!!
  
 Can you tell me the answers to the following questions:
  
 1. Which of the driver stage decoupling and bypass caps is correct if any?
  

  
 2. Which of the power stage decoupling and bypass caps is correct if any?
  

  
  
  
  
  
 3. And finally which of the cathode bypass caps and bypass is correct if any?
  
 Clue - I'm looking for the orientation of the caps with respect to the bypass caps, not the overall position on the board!
  
 Answers please.


----------



## baronbeehive

Sorry can't get the second pic to come out, back again later 
	

	
	
		
		

		
		
	


	




.
  
 Ok it's there now


----------



## baronbeehive

It's not a trick question, I just want to know so that I can make a start!!! Does it matter which way round the caps and bypass caps go?


----------



## SonicTrance

Caps dont have polarity so it doesn't matter. Jupiter marks the outer foil, but since you're using Mundorf it doesn't matter. 
Just place them how you want, in the same direction.


----------



## baronbeehive

sonictrance said:


> Caps dont have polarity so it doesn't matter. Jupiter marks the outer foil, but since you're using Mundorf it doesn't matter.
> Just place them how you want, in the same direction.


 
  
 Correct answer! They're all right. You win the star prize. Thanks for bothering 
	

	
	
		
		

		
		
	


	




.


----------



## Maxx134

baronbeehive said:


> sonictrance said:
> 
> 
> > Found another one which is a lot less money for me as it's within EU.
> ...


----------



## Maxx134

Yes none of the *film* caps we are using have any polarity. 
Only the PSU electrolytic. .

Oh, and Mister X, 
 I didn't read that you bought the cable.
Lets hope my opinion is wrong on that cable and I hope you like it.


----------



## Mogos

maxx134 said:


> Yet even NOW...
> *The utter lack of any veil, extreme clarity and palpable holographic soundstage is what you get with these mods in place. *
> I keep having the dilemma that what I hear cannot be described properly without sounding exaggerated...


 
 I agree with your last sentence in 120% 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

maxx134 said:


> The problems with the toxic cable are:
> 
> 1- "The *total* wire diameter is 26awg(thin!)
> 
> ...


 
  
 I agree with that, that's why I opted for the OCC copper. But I think that the reason for the gold is not for plating but apparently to fill in the gaps between the OCC silver crystals to ensure a smooth transition for the signal, whatever that means. Why one needs this with OCC silver is anybody's guess. I believe it is very minute amounts of gold and if it is anything like the Mundorf SGO caps it should impart a realism to the sound, which the pure silver sound may not quite get. I know that the manufacturer who is an enthusiast has worked at getting this right. If MisterX is in any doubt he could check out the toxic cable thread where there are overwhelming positive comments, for example this one with reviews: http://www.head-fi.org/products/toxic-cables-silver-poison
 I would still go for this cable myself unless I could get a cheaper all silver one.
  


> ............
> 
> Herr is my amp getting last listening done before I open and install new caps and new impedance mod...
> 
> ...


 
  
 What a work of art! The fan looks great...... pity its hidden underneath. Can't wait to experience some of that sound myself 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

maxx134 said:


> Yes none of the *film* caps we are using have any polarity.
> Only the PSU electrolytic. .
> 
> Oh, and Mister X,
> ...


 
 I hope so too!
 Main thing though is that I feel it's a worthy upgrade to my existing cables. Otherwise it's money down the drain, lol. We'll see once I get it.


----------



## Maxx134

Personally I feel any metal with silver won't do anything,
as eletrons will choose the higher conductance silver.

Also if the silver is OCC, then there would be no such gaps in crystals.

 Because by definition, "OCC" is a continuous cast of crystal,
Which leads me to believe it is normal silver.

Normal silver is still very superior to copper or any other metal anyways,
So the claim of gold does not make sense.

The only thing I can see is that the gold platong would keep the silver from getting oxidized, 
Which is a good thing.

Most silver cables are thin but have conductance equivalent to a larger copper wire many times it's size.

Anyways whatever difference the wire does,
It will not be as significant as the impedance mod(!)

The impedance mod brings more precise control of bass, and in my case, a stronger bass for my "Ether" headphones.

That, plus a shift in the headphones signature,
 from a bit mid centric to neutral with more clarity..

That last observation I attribute 50% to the fact that I need to upgrade my WCF caps, which I will be doing today.

They were limiting my clarity with lower impedance phones,
As the second "WCF" triodes took presidence in that situation. 

I will place 2 smaller, faster, more lively caps in parallel, in place of the one original cap, which was a "soft" cap.
It was a Jupiter HT, 
Not their best "copper" foil cap..


----------



## baronbeehive

maxx134 said:


> ...............
> Anyways whatever difference the wire does,
> It will not be as significant as the impedance mod(!)
> 
> ...


 
  
 Right so I'll use the Mundorf S0 caps for WCF as you suggested.
  
 So the impedance mod involves a resistor connected to the power anode resistor, 330ohm? If so should be plenty of room to do that.


----------



## baronbeehive

*SMLD MODS:*
  
*Stage 4 - *Desoldering
  
 I've decided to do all that at once like the others, or maybe half at a time if I think I'm going to forget where everything is! So the idea of testing as I go along has gone out the window. Just have to hope that it works when it's all back together.
  
 Pretty confident now, this is in advance of the actual work which I'm hoping to start next week time permitting. Just one more thing to get and that is possibly to get a continuus vacuum electric desolderer, the reason being that without that I would need 3 hands: one for the soldering iron, one for the solder sucker and the other to pull the part out from the other side. As not many people have that many hands I figure it would be much easier and quicker to use that. It would mean only one process instead of 3 or more to remove a component, so there's less risk to the PCB.
  
 Pics to follow.


----------



## Maxx134

baronbeehive said:


> maxx134 said:
> 
> 
> > ...............
> ...



Yes, mist mods are chosen for sonic impact and simplicity...
We will not redesign special stages...

*Quote : 
The fan looks great...... pity its hidden underneath*

Actually, MisterX has the best implementation of the fan..
I do have a speed control, but his fan just looks better.


----------



## SonicTrance

You only need two hands baron. Just heat up the leads and pull the part out. Then clean with solder sucker. That vacuum desolderer sounds interesting though.


----------



## Maxx134

baronbeehive said:


> *SMLD MODS:*
> 
> ...
> As not many people have that many hands I figure it would be much easier and quicker to use that. It would mean only one process instead of 3 or more to remove a component, so there's less risk to the PCB.
> ...



Haha three hands.
I had to learn how to be quick with a solder sucker..

Edit:
I would heat up and remove component first, 
Then heat again with sucker to have clean hole,
But clean hole is not important as the can be a bit left behind no problem.
The only worry is to not have alot excess solder .
Stock board has very little cheap solder.

Important thing is after soldering, to look for any splashed or fragmented solder left around board or components. .
Have an air gun to blow out stuff and also Q-tips to carefully wipe any particles out .


If you run into problem don't worry it happens to the best of us.


----------



## baronbeehive

maxx134 said:


> Haha three hands.
> I had to learn how to be quick with a solder sucker..
> 
> Edit:
> ...


 
  
 Thanks with the information. I will decide this evening whether to order the electric desolderer, it would certainly save a lot of hassle.
  
 That impedance mod is very similar to something I have  on my Miniwatt N3 amp which has 3 sets of speaker outputs: 40, 60 and 80 Ohm. I hadn't paid much attention to them before but I will experiment with them too see if I can hear any difference. It is only 3.5 watts output so would be important to match up properly. For a cheap amp it is quite remarkable I think!


----------



## SonicTrance

maxx134 said:


> baronbeehive said:
> 
> 
> > maxx134 said:
> ...


 
 Thanks Maxx! 
	

	
	
		
		

		
		
	


	



 If you're interested in buying here's a US link for you.
 http://www.newegg.com/Product/Product.aspx?Item=N82E16835214003


----------



## baronbeehive

OK just one more, Larry Carlton live version of Springville, it doesn't get any better than this! Maxx he's one of your fellow countrymen 
	

	
	
		
		

		
		
	


	




.
  
https://www.youtube.com/watch?v=9som2VsSskU


----------



## SonicTrance

New username guys! Someone else had MisterX so I had to change mine!
 I listened to Trance while I got the message, so yeah - SonicTrance


----------



## baronbeehive

sonictrance said:


> New username guys! Someone else had MisterX so I had to change mine!
> I listened to Trance while I got the message, so yeah - SonicTrance


 
  
 Hello SonicTrance 
	

	
	
		
		

		
		
	


	




. Think I'll change mine to SMLD!


----------



## baronbeehive

*SMLD MODS:*
  
*Stage 4 - *Pics. This is all the gear!


----------



## Mogos

Those are resistors for my impedance matching mod.

 I have written: my impedance matching mod, as there are possible a few setups to be done especially for the MK VI.
 In case of mk VI there are combinations between at least 3 main types of power tubes and headphones you would like to switch between.
 So having three pairs of headphones and three tube sets you will have 9 configurations if I am not mistaken.
 I decided to go the very simple way. For now I have 6080 tubes and HEK headphones. It is more possible that I will change the power tubes than switch the headphones. The resistors I have got are for 6080, 5998 and 421A power tubes in combination with 35 ohm headphones.
 So my mod is just soldering the resistors in the correct position. For 6080 tubes and 35 ohm headphone impedance I have to use two resistors in series to come as close as possible to the requred value of added resistance. The solution is still under the tests by Redge and Maxx. After checking if there is evrything ok and there is no negative influence of the mod over the amp they will post the instructions.
 In the case of my simple configuration I don't see for now any negative impact on the amp electronics. The only one thing I see-hear is that this mod is one of the significant.
 One obvoius change is in lower frequencies registers. I have written that after the mods I had done before the low frequencies get realy good. With the new mod they are even better. The change is not in the amount but in the qualities. Bass is more energetic, better articulated and with even more natural decay. The whole presentations gained in overal add of liveliness.


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## baronbeehive

mogos said:


> ......
> 
> I have written: my impedance matching mod, as there are possible a few setups to be done especially for the MK VI.
> In case of mk VI there are combinations between at least 3 main types of power tubes and headphones you would like to switch between.
> ...


 
  
 So for you there will be 3 new connections to each power resistor leg, with a possible 9 for the others. Would there be any need to lift up the 330 ohm resistor to make more room?
  
 So the other 4 power resistors are left alone?
  
 Very interesting Mogos, when are you doing the other 2 sets of resistors? I see you may be thinking of those Western Electrics 
	

	
	
		
		

		
		
	


	




.


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## Mogos

The details about connections will be posted as the tests will end. But there will be only one conection point to the legs of 330 ohm resistors. It will come from the switch. Maxx correct me if I am wrong. In my solution there will be no more resistors. If I will change the tubes I will have to solder new set of resistors in place of the used ones. So the solution is far from beeing elegant as other guys are doing. But if I can get the WE421A will there be any more reason do change anything? 
	

	
	
		
		

		
		
	


	




. I may have on the way 5998. From your reports they will suite me better then 6080 so again will there be a reason to go back? And about the headphones. HEK's are the best to all music generes I am listening to (fusion jazz, progressive rock, some electronics-berliner school). Any other headphone I had (including the new hd800) are significantly inferior to them so again there is no sense to waste precious time and hearing for just finding that there is something better. At least for now I will go without the switch but it is always an option.


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## baronbeehive

mogos said:


> The details about connections will be posted as the tests will end. But there will be only one conection point to the legs of 330 ohm resistors. .........


 
  
 Yes of course, I forgot about the switch......... how stupid!
  


> ..........
> But if I can get the WE421A will there be any more reason do change anything?
> 
> 
> ...


 
  
 I'm sure Maxx will agree, but the answer to your questions is NO, and NO! Either the 5998 or the 421A would be the best,  most musical you could possibly get. However the drivers are different. You are talking here of Mullard ECC35 which are great I believe, Brimar 6SN7 Black Glass, which are near impossible to get now and I wouldn't get the other Brimars, RCA 5692 which I wouldn't bother with , Sylvania 6SN7GT 1952, impossible to get, and Tungsol 6SN7/6SL7BGRP. The only others worth considering would be the Psvanes that you like but they are new issue so I wouldn't get them.
  
 So will there be a reason to go back...... definately no............ on the other hand..........
  
 BTW your musical tastes look more interesting than either SonicTrance's or mine so how about posting a link to one or 2?


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## Mogos

In reference to your disscusion about headphone cables. I decided to experiment with the same wire I have used for internal connections. It is according the the description from the seller:
  
_This is a very high quality and sharp looking wire. This is a twisted pair with 2 inside conductors that are 20 AWG silver plated oxygen free copper wires. The inside wires are stranded each with 19 strands. They have polyimide film insulation with PTFE covering. The colors of the inside wires are red and red. This is then shielded with a silver plated oxygen free copper shield. This cable then has a polyimide film outside insulation. This is a very high temp. wire.  This would be good for audio and other applications. This wire is rated at 600 volts 200 C. This is lighter and has a much smaller outside diameter than the same size with just PTFE  insulation. The OD of this wire is aprox. 0.1160 inch (2.94mm)._
  

 With my HD800 I have used A Pure Sound V3 wire and I was very pleased with it. It is realy good sounding wire. 
 So I am totaly suprised with the performance od the DIYed wire. There is slightly less bass but separation of the channels the scene imaging and foucusing of the sounds is very good. I think even better then in APS wire. I need more time for testing but every time I am doing the tests I do hear the same differences. And after switching to APS I feel like somthing is missing. I am not so engaged in listening. The DIYed wire dosen't let me to be not engaged. But lets give it a time. It is somthing new interesting let the time to verify 
	

	
	
		
		

		
			





. There is one obvoius disatvantage the DIY cable is quite stiff.


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## Mogos

Here you have one of the tousands others equaly interesting.
 https://www.youtube.com/watch?v=GWXvp0ywSss


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## baronbeehive

mogos said:


> I reference to your disscusion about headphone cables. I decided to experiment with the same wire I have used for internal connections. It is according the the description from the seller:
> 
> _This is a very high quality and sharp looking wire. ..........._
> 
> ...


 
  
 Didn't you get some pure silver and pure copper wire and also silver/gold wire? It would be interesting to experiment with that.


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## Mogos

No. Till now I did have only the stock wires (the HEKs is suprsingly good) and APS and the DIYed. The OCC in litz configuration maybe interesting. Or splice of pure OCC and silver. There are so many options in final creation of the way your setup sounds (tubes, wires, digital interfaces -usb, spdif, computer software, computer optimisations e.t.c) that it will be very tiresome to find out all of them and will require a lot of money. Before the LD mod I had such evaluation of my setup invidual elements: Computer (optimised to the bare bones) with dedicated USB output + USB to SPDIF (HiFace EVO plus EVO Clock) - 30%, DAC - 30%, Headphones-15%, Connection wires 10% and Amplifier 15%. Now it will be 30%, 15%, 20%,10%, 25%.


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## baronbeehive

mogos said:


> No. Till now I did have only the stock wires (the HEKs is suprsingly good) and APS and the DIYed. The OCC in litz configuration maybe interesting. ......


 
  
 Yes would be interesting.......
  


> ............ There are so many options in final creation of the way your setup sounds (tubes, wires, digital interfaces -usb, spdif, computer software, computer optimisations e.t.c) that it will be very tiresome to find out all of them and will require a lot of money. Before the LD mod I had such evaluation of my setup invidual elements: Computer (optimised to the bare bones) with dedicated USB output + USB to SPDIF (HiFace EVO plus EVO Clock) - 30%, DAC - 30%, Headphones-15%, Connection wires 10% and Amplifier 15%. Now it will be 30%, 15%, 20%,10%, 25%.


 
 Yes, many options. My most expensive was the Audiophilleo USB converter which has not made a massive difference but I keep it because some older DAC's don't have the necessary jitter reduction, at least as big a difference was made with the USB cable that came with it, I have a standard copper HiFiMan cable which as you say is good, TS 6SL7 tubes which are as good but much cheaper than the 6SN7's, PC which cost nothing extra, foobar music player which optimises the output for audio which cost nothing.
  
 I agree that computer optimisations and software is probably the way to go now for computer audio and speakers etc., I've seen some interesting examples recently but I don't really like messing with the sound digitally with equalizers and other signal processing.
  
 So I haven't spent a fortune as readers of the forum will probably know, that's why I got the LD in the first place and its why I can't really justify spending a fortune because we've got such a great piece of equipment for so little in the first place 
	

	
	
		
		

		
		
	


	




.


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## SonicTrance

mogos said:


> Those are resistors for my impedance matching mod.
> 
> I have written: my impedance matching mod, as there are possible a few setups to be done especially for the MK VI.
> In case of mk VI there are combinations between at least 3 main types of power tubes and headphones you would like to switch between.
> ...


 
 Looking good Mogos! I will be able to test this mod tomorrow (hopefully). To tired to finish the mod now. All that wiring for the switch got me exhausted, lol.


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## baronbeehive

OMG....... I've been reading reviews of the HE1k again, and I wish I hadn't! I've got to have them........... somehow, I don't know how 
	

	
	
		
		

		
		
	


	




. They would go sooooo well with the SMLD!


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## coinmaster

Don't buy headphones based on reviews, I learned that the hard way, especially ones that cost $3k. I was disappointed with the HE1k http://www.head-fi.org/t/759662/hd800-vs-he1000-mhp1000-impressions-suprises-all-around.
 Always try before you buy, or at least make sure you can return.


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## baronbeehive

coinmaster said:


> Don't buy headphones based on reviews, I learned that the hard way.


 
  
 I take your point but I usuallly read everything I can and go somewhere down the middle.


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## SonicTrance

Not everybody has a chance to audition headphones before buying...


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## coinmaster

sonictrance said:


> Not everybody has a chance to audition headphones before buying...


 
 As a person who has bought and sold HD800s twice and TH900s once, I suggest you do a lot of research and buy something with a reasonable balance between cost and performance or else you'll probably end up losing money. If you buy something you can't audition make sure you can return it.
 For our modded amps I think the HD800s are the perfect price/performance to start with, maybe even the best. As is they absolutely blow away anything else I've ever heard with the perfect balance of both realism and euphony, something I only achieved after the modding, the difference was mind blowing.
 That being said the HD800s are notoriously hard to pair with an amp and will probably sound disappointing on 99.9% of amps out there which is why there are so many used ones floating around on the market.


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## baronbeehive

coinmaster said:


> Don't buy headphones based on reviews, I learned that the hard way, especially ones that cost $3k. I was disappointed with the HE1k http://www.head-fi.org/t/759662/hd800-vs-he1000-mhp1000-impressions-suprises-all-around.
> Always try before you buy, or at least make sure you can return.


 
  
 Very interesting review. I get what you say about the difference between them with the HE1k's sounding hazy and the HD800's sounding clean. This is what I meant when I said a while back that the HD800s are more in your face type sound, like the difference between being caught in a hail storm and a light shower, the HD800's being the hail storm! That being said I much prefer the softer sound so long as it still has good detail.


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## Mogos

sonictrance said:


> Not everybody has a chance to audition headphones before buying...


 
 I was lucky to have the chance to audition HEKs before I had bought them second hand on quite good headphone system. For me HEKs are very good. I do have all what the hd800 had and a lot more. With SMLD they realy rocks and shine.


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## SonicTrance

mogos said:


> sonictrance said:
> 
> 
> > Not everybody has a chance to audition headphones before buying...
> ...




I bet they do! Would love to hear a pair of HEK's some day!


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## coinmaster

I like birds.


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## Maxx134

coinmaster said:


> I like birds.



I like Canarys..
My uncle bred champion singers which sang in teams of 4 harmoniously and won many awards..

But that's besides the point. 
I like your headphone review you mentioned. 
I personally heard them quite well.

My points on each:

1-The HE6 will always be hard to power to get the best out of it.

2-the HE1K is the planar with the largest soundstage and probably a great choice if it weren't so rediculously expensive. 

3- the Mcintosh MHP1000 will always sound more reserved and less lively in the midrange compared to what it copies so well, the HD800.
Regardless, It is probably the best closed headphones I have heard.

4- Nothing made yet will ever be able to superceed the hd800 in soundstage and liveliness.
I have heard the stax 900 in my home and while I truly love their sound, 
The HD800 remain sweeter and more musical to me.
It could have been much due to the setups involved, but the Stax precision was not enough to pull me away from my setup.
In my opinion, and from what I was told,
 only the best electrostatic amps will make the stax009 pull ahead of the hd800.

The HD800s have a superior match with the LDMK8SE, and now with the impedance matching mod, the MK6 will be another extremely great match (using WE421A tube should already make MK6 a good match with hd800s).

Then we have more variables with the new HD800 mods, and with other headphones which can reach TOTL status like the Ether..
In fact there are no other headphones I can recommend more than the HD800/S and the Ether.

There will be big surprises coming on the Ether I cannot say..


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## Maxx134

There are a few points of next mod I have noted:

The matching of the circuit to the headphones creates more prominent effect of the second triode, which is dependent on the WCF cap sound. 

This means the WCF cap will take on much greater importance. .

My observations on testing 3 different sets of WCF caps and 2 sets coupling caps:


The main coupling cap was responsible for 80% of the trebles nuances and clarity of mids...

While the WCF cap affected at least 70% of the bass, and only about 15-20% of the trebles..


In order to have the potential of extremely well defined bass that the impedance mod WILL achieve, 
You need to make sure the WCF cap will not add boomy blurry or excessive bass traits. 

Sadly, I found this to be the case with the lower line of Jupiter, the Jupiter HT caps...
They added to the bass.
So they are not recommended.
We need a very clear neutral cap here, not a natural smooth cap that brings on bass.

Also,
For the main coupling cap,
Nothing, repeat nothing beats copper foil for main coupling cap.
The absolute best caps out there are all copper foils:
Duelund copper
Jupiter copper
V-cap copper
Jensen copper

They present the MOST natural sound you can achieve. 

So for the best match for the money, I would recommend Jupiter copper for the main coupling, and mundorf silver for the WCF.
Of course you can go with many others for the WCF,
But be careful you don't get a bassy cap.
The must be very clear balanced caps.

So far we have three (including me) testers with very prominent results for the impedance mod..
This is a major sonic improvement mod.


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## Mogos

coinmaster said:


> I like birds.


 

 I am dissapointed. I thought you will say: I like chainsaws.
 Speaking about headphones there are many factors making the given headphone to be the one to suite somebody tastes.
 The genere of music, the rest of the setup and your personal prefrences can position such a Stax's 009 as akwardly overpriced and boring. For somebody else it will be everyday nirvana at your hand.
 I think if I will listen to a hard,metal,trash ..... rock then I will not be so pleased with HEK's. They will have some qualiteies totaly unnecessary and lack some others to make the desired spectacle.
 For those who have very wide musical interests the only solution is to have two or more headphones suitable for different music generes.


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## baronbeehive

Quote:


maxx134 said:


> I like Canarys..
> My uncle bred champion singers which sang in teams of 4 harmoniously and won many awards..
> ..........


 
  
 He he, I haven't laughed so much in ages. Only on this thread......
  
 Quote:


mogos said:


> I am dissapointed. I thought you will say: I like chainsaws.
> Speaking about headphones there are many factors making the given headphone to be the one to suite somebody tastes.
> The genere of music, the rest of the setup and your personal prefrences can position such a Stax's 009 as akwardly overpriced and boring. For somebody else it will be everyday nirvana at your hand.
> I think if I will listen to a hard,metal,trash ..... rock then I will not be so pleased with HEK's. They will have some qualiteies totaly unnecessary and lack some others to make the desired spectacle.
> For those who have very wide musical interests the only solution is to have two or more headphones suitable for different music generes.


 
  
 I like birds...... and chainsaws, I can hear the plaintive call of both of them coming from the direction of the garden. The birds forum is thataway, and....... I can't find any chainsaw forum sadly, there must be one for closet chainsaw freaks 
	

	
	
		
		

		
			





.
  
 I'm willing to give up any interest in thrash that I may have had to only have one set of phones........ the HEK's! Looks like they are a more musical version of the electrostatics, apart from Coinmaster I couldn't find any negative comments at all, maybe they were still in shock at the price. Speaking of that when you have a 7 year development cycle in nanotechnologies I can almost forgive Dr Fang Bian for that. Must go now and start saving up.........
  
 BTW, when Coinmaster mentioned euphony with the HD800's it occurred to me that anyone wanting to improve the sound of the HD800's and make it more euphonic should try the Brimar 6SN7's with it. When I said I didn't like the Brimars, I think that they would go very well with the Senns however, because these tubes are very euphonic and therefore would fill out the sound nicely and be a very good match.


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## coinmaster

I think we can all agree we like chainsaws but flamethrowers are the clear winner.
  


> BTW, when Coinmaster mentioned euphony with the HD800's it occurred to me that anyone wanting to improve the sound of the HD800's and make it more euphonic should try the Brimar 6SN7's with it. When I said I didn't like the Brimars, I think that they would go very well with the Senns however, because these tubes are very euphonic and therefore would fill out the sound nicely and be a very good match.


 
 I found the best overall musical yet realistic performance with excellent bass was with 6SN7 tung sol RP drivers and mixing Tungsol 5598s with Mullard 6080s. Keep in mind when you mix tubes there's almost always a "wrong" (as in bad sounding) way to put them in, make sure to switch places so you can find the sweet spot.


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## SonicTrance

coinmaster said:


> I think we can all agree we like chainsaws but flamethrowers are the clear winner.
> 
> 
> 
> ...


 
 Mixing tubes will defeat the purpose with the impedance matching mod we just did, which is based on the tube parameters.


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## SonicTrance

The impedance mod did wonders for my LCD-XC's. They could be a little harsh in the treble before but that's gone now! Good thing about having a switch is that you can A/B the difference with stock setting. 
 Tonal balance is much better with higher quality bass!
 I've not had the chance to listen to the LCD-3's yet after this mod (need to be home alone, lol)


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## coinmaster

sonictrance said:


> Mixing tubes will defeat the purpose with the impedance matching mod we just did, which is based on the tube parameters.


 
 Mixing tubes is effectively the same thing as the impedance mod, more or less. Except with the altered distortion of having 2 different tubes.


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## baronbeehive

sonictrance said:


> The impedance mod did wonders for my LCD-XC's. They could be a little harsh in the treble before but that's gone now! Good thing about having a switch is that you can A/B the difference with stock setting.
> Tonal balance is much better with higher quality bass!
> I've not had the chance to listen to the LCD-3's yet after this mod (need to be home alone, lol)


 
  
 That's amazing, things just seem to get better! It was obviously a noticable difference, and as you say you can do direct comparisons. So how many options do you have with the switch?
  
 Could you post pics of the mod?
  
 Look forward to hearing your impressions with the LCD-3 
	

	
	
		
		

		
		
	


	




.


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## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > The impedance mod did wonders for my LCD-XC's. They could be a little harsh in the treble before but that's gone now! Good thing about having a switch is that you can A/B the difference with stock setting.
> ...


 
 Yes baron! I got lots of pics, just waiting on the OK to post them, lol.
  
 Listening to LCD-3's now and they also improved massively!
 I got a 5 position switch and chose these settings:
  
 1 - Open (stock) - 6AS7G, 110 ohm
 2 - 6AS7G, 20 ohm
 3 - 421A, 20 ohm
 4 - 421A, 110 ohm
 5 - 421A, 300 ohm
  
 I've only listened with 421A's so far, but tried all different settings with both my cans (LCD-XC, LCD-3) and they do sound best at their appropriate setting. Like I said, most difference is in the lower region but everything sounds better! I actually think that the PSU cap mod really shines now with this impedance mod in place.
  
 Here's how my amp looks with the switch installed.


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## SonicTrance

maxx134 said:


> There are a few points of next mod I have noted:
> 
> The matching of the circuit to the headphones creates more prominent effect of the second triode, which is dependent on the WCF cap sound.
> 
> ...


 
 I could not agree more!
 As much as I loved the Mundorf S/G/O as coupling caps, the Jupiters wins. The combination of Jupiter as coupling and Mundorf S/G/O as WCF is wonderfully natural. Nothing is missing!


----------



## baronbeehive

sonictrance said:


> Yes baron! I got lots of pics, just waiting on the OK to post them, lol.
> 
> Listening to LCD-3's now and they also improved massively!
> I got a 5 position switch and chose these settings:
> ...


 
  
 Looks like all the mods are working together.
  
 That really looks so cool in gold 
	

	
	
		
		

		
		
	


	




. My SE jack is on the back unfortunately!
  
 So are you going to try the HD800s then?
  


sonictrance said:


> I could not agree more!
> As much as I loved the Mundorf S/G/O as coupling caps, the Jupiters wins. The combination of Jupiter as coupling and Mundorf S/G/O as WCF is wonderfully natural. Nothing is missing!


 
  
 You must have cut the leads of your old Mundorf coupling caps? Have you got the .47uF's?
  
 Whats next I wonder 
	

	
	
		
		

		
		
	


	




.


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## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Yes baron! I got lots of pics, just waiting on the OK to post them, lol.
> ...




Thanks! Yes, it's all working together!

I chose a 300 ohm setting as a future choise. No plans on buying more cans for a while. 

Yes, I cut the leads when I first installed the Mundorf .68uf coupling caps. Now I just desoldered them. I now use Jupiter .47uf for coupling and Mundorf S/G/O .47uf for WCF.


----------



## Maxx134

It should be noted that the mk6 and produces more current at the output,
Compared to the MK8.

So the gains (in terms of bass control) on this new mod could be more substantial...


----------



## SonicTrance

Today I have rolled tubes and played with the impedance switch. My previous impressions were with WE421A's and Mullard ECC35's.
  
 I now run the GEC 6AS7G with Mullard ECC33's. 
  
 Switch settings (again)
  
 1 - Open (stock) - 6AS7G, 110 ohm
 2 - 6AS7G, 20 ohm
 3 - 421A, 20 ohm
 4 - 421A, 110 ohm
 5 - 421A, 300 ohm
  
 As expected, the LCD-3 sounds best at position 1, which is stock. Actually love these headphones!
  
 The LCD-XC's is most affected with this impedance mod. With both 421A's and the 6AS7's there's a big improvement in bass and tonal balance when running them on their appropriate setting. They truly sound amazing now. Don't really know how to describe it, lol.
  
 All I can say is that if you're using low impedance cans (or maybe high impedance) this mod is a must!
  
 Btw, if someone is looking for a quad set of Mundorf 0,68uf S/G/O's let me know. The Jupiters I got now are never leaving this amp!


----------



## baronbeehive

sonictrance said:


> Today I have rolled tubes and played with the impedance switch. My previous impressions were with WE421A's and Mullard ECC35's.
> 
> I now run the GEC 6AS7G with Mullard ECC33's.
> 
> ...


 
  
 Absolutely amazing! I just can't believe what you seem to be experiencing.
  
 If I remember right those GEC's are even more expensive than the 421a's so I won't be after them but, did you say you were selling those Jupiters, if so I'll have 'em lol.
  
 Can't wait to see what Maxx says about the impedance mod with his HD800's, I don't know what to expect given that the HD's impedance varies with frequency unlike the planars. It could completely change the character of the cans.


----------



## Maxx134

I already know...
The HD800s with lower impedance setting is a bit more recessed in the mids, 
Leaving the trebles more pronounced, and a certain spot in lower trebles where you can hear the "face tweeter" effect that these headphones are complained about. 

The higher impedance balance this out by having the midrange more forward and spacious.

The bass is funny.
It is more tight and powerful on higher impedance setting,
While lower impedance actually gives a soft bassy bump or boost. 

So what happens is you feel like almost a type of "U" shape signature with lower impedance. 

The HD800 sounds very sweet on upper mids to trebles, on the mismatched lower impedance,

While on the closer matching higher impedance, 
The sweetness shifts to a liquid musicality of the midrange. .


----------



## Maxx134

I just realized that the sweetness is the signature of my amp/yggy combo. 

On another setup like my past Oppo HA1, the hd800 was a bit sharper and distant.

So,
 The point is...
 The overall brightness of the hd800 is dependant to the impedance match.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Today I have rolled tubes and played with the impedance switch. My previous impressions were with WE421A's and Mullard ECC35's.
> ...


 
 Actually no. The GEC's can be had cheaper. There's a seller on ebay currently who's selling NOS ones for $199
 http://www.ebay.com/itm/121881779444?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
  
 Though they seem to be untested, which is not good in my book. Even if NOS, the tubes can test very differently.


----------



## baronbeehive

Has anyone noticed the picture of the LDmk2 in the decoupling section on page 1 looks just like a train with its decoupling caps as wheels?


----------



## Maxx134

That was the intention


----------



## baronbeehive

*SMLD MODS:*
  
*Stage 4 - *Desoldering (cont)
  
 I've managed to remove all the (relevant) parts but still have to get rid of surplus solder. God knows what the damage is so far, trouble is you start to get the hang of it, too late when you've burnt up the board, wires etc.!
  
 Soldering iron the wrong shape, fresh air fan packed up half way through etc etc. Par for the course I suppose 
	

	
	
		
		

		
		
	


	




.
  
 Maxx, you said you had several boo boos, that's all that's keeping me going lol.


----------



## Mogos

For surplus solder use desoldering wire. Be brave the prise will be yours. Remember frear is mind killer. We are with you watching how you progress and keep an eye on you. So don't worry 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

mogos said:


> For surplus solder use desoldering wire. Be brave the prise will be yours. Remember frear is mind killer. We are with you watching how you progress and keep an eye on you. So don't worry
> 
> 
> 
> ...


 
  
 Thanks Mogos 
	

	
	
		
		

		
		
	


	




.
  
 The main problem is the soldering iron which was a mistake, there are no flat tips with it like SonicTrance recommended which I was looking for. The tips on this one have a rounded base which means that the iron keeps slipping off whatever you are doing. It makes things more difficult, but I don't think I've made any major mistakes., and its getting easier.
  
 I don't know about 3 hands, you need 4 eyes as well to see what you are doing and make sure you don't touch anything else at the same time, nighmaresville 
	

	
	
		
		

		
		
	


	




.
  
 Pics to follow when desoldering is complete.
  
 Alright, here's one to wet your appetite!
  

  
  
  
 They're better than Mogos' used ones 
	

	
	
		
		

		
		
	


	




. There are a few more somewhere if anyone's interested. Maybe Maxx could find a use for his hotglue.


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## SonicTrance

baronbeehive said:


> mogos said:
> 
> 
> > For surplus solder use desoldering wire. Be brave the prise will be yours. Remember frear is mind killer. We are with you watching how you progress and keep an eye on you. So don't worry
> ...


 
 So, you're snapping all Wima caps in half? Why? lol


----------



## baronbeehive

sonictrance said:


> So, you're snapping all Wima caps in half? Why? lol


 
 I've thought everything through beforehand and I figured it would make it easier removing parts one leg at a time and not forcing them out of the board. The other parts I cut at the leg on one side. The PSU caps were the exception and were really difficult. The idea is to avoid sweat joints where some solder is left between the  leg and the side of the hole.
  
 It's all down to minimizing the number of times I have to heat up the pad. As it turns out I've had to have several goes at everything so I haven't really managed to keep the number of repeat heatings down lol.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > So, you're snapping all Wima caps in half? Why? lol
> ...


 
 But you can remove one leg at a time without cutting them in half. Just hold the cap with one hand and heat the lead from other side of board with the other. But i guess your way works too. I kept all my stock parts, but doubt that I'll have any use for them, lol.


----------



## Maxx134

sonictrance said:


> So, you're snapping all Wima caps in half? Why? lol




Because it is fun..
 to destroy. .lol

All those parts belong in garbage,
 with exception of the electrolytics you may find useful in another project..


No update yet on my end,
 about the switch.
That is currently underway as I recieved my wire.


I do have update on optimal WCF values...

The Stock WCF is an anemic .22uf

Optimal smallest value is .33uf

I am currently at .34uf.

I have tester incrementally with same caps in parallel, and verified improvement.

I have not evaluated a maximun value,
Although I have used .47uf without issue.

I do believe the greater .47uf value runs the risk of altering the bass performance in not good way, as experienced with my Jupiter HT caps..

The.47uf mundorf had no such issues, but those are higher quality.

Anyways, the refinement of .33uf over .22uf is as follows:

Preliminary testing shows that the increase of capacitance, (in the WCF position):

It makes the midrange sound a bit more lush, effortless and expresive.

The bass has more weight, depth, solid slam...
There is more acticulation of bass depth.

Yet the bass improvements may not be realized without the impedance match which I have.


----------



## baronbeehive

*SMLD MODS:*

*Stage 4 -* desoldering, finished, (more or less).
  
 Make no mistake this was very difficult because it's very tricky. I started off trying not to make any booboos such as too much pressure, too much heating, touching other components, and I quicky found that this was impossible and I just had to do it as best as I could. The problem is you are trying to do something and learning about it at the same time. I think it would be good to find an old PCB to practise on first. The other big problem is you have to have the right tools at the start, my soldering iron is not ideal. I would advise a 30 watt iron with a flat tip for easier working.
  
 Having said that I would not have a problem with doing it again now.
  

  
 Some battle scars......
  

  
 ..... more battle scars, and the red wire has broken off.
  

  
  

  
 Driver stage resistors out, 220K ohm and 1.5K ohm:
  

  
 8K2 resistor out:
  

  
 Power stage resistors out, 330 ohm.
 Cathode caps out, WCF caps out:
  

  
 PSU Caps coming out left some damage behind.
  

  
 2 pads left on the legs of the PSU caps during removal due to solder not melting.
  

  
 The next stage, soldering should be a piece of cake after that 
	

	
	
		
		

		
		
	


	




.


----------



## Mogos

Well, well it is going on very nicely. I will drink a beer for you.
	

	
	
		
		

		
		
	


	




 You can not! You have to be sober.


----------



## baronbeehive

mogos said:


> Well, well it is going on very nicely. I will drink a beer for you.
> 
> 
> 
> ...


 
  
 Ha ha. I would probably have made a better job of it if I was drunk 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

Great to see you're making progress Baron! 
	

	
	
		
		

		
		
	


	



  
  
 More tube rolling for me. Today I went with the 421A's and ECC32's, and holy sub-bass batman! Incredible low end with these tubes!


----------



## baronbeehive

sonictrance said:


> Great to see you're making progress Baron!
> 
> 
> 
> ...


 
  
 Yeah, thanks. Hoping to start on the resistors today!
  
 BTW your amp looks good as ever! I really like that impedance switch on the front, sadly mine will have to go on the back.
  
 Are there any more tubes out there you're thinking of trying?


----------



## SonicTrance

baronbeehive said:


> Yeah, thanks. Hoping to start on the resistors today!
> 
> BTW your amp looks good as ever! I really like that impedance switch on the front, sadly mine will have to go on the back.
> 
> Are there any more tubes out there you're thinking of trying?


 
 I'm very happy with my present collection of tubes, but would like to try the Sylvania metal base 6SN7W. I have a pair of both the two hole plate and three hole plate versions of the Sylvania 6SN7GT's. They're nice tubes but not as sweet as the Mullards ECC32/33/35's and Tung-Sol RP's.


----------



## baronbeehive

sonictrance said:


> I'm very happy with my present collection of tubes, but would like to try the Sylvania metal base 6SN7W. I have a pair of both the two hole plate and three hole plate versions of the Sylvania 6SN7GT's. They're nice tubes but not as sweet as the Mullards ECC32/33/35's and Tung-Sol RP's.


 
  
 So am I! Yes the 1952 Sylvania especially is supposed to be something special but the ones I've tried I don't like and they're anything but sweet!
  
 I did try a gold brand Sylvania for my other amp which was supposed to be very special as well but it sounded pretty much like any other Sylvania to me. It was very detailed sounding, very good, but I didn't really hear that lush mid range that people were talking about.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > I'm very happy with my present collection of tubes, but would like to try the Sylvania metal base 6SN7W. I have a pair of both the two hole plate and three hole plate versions of the Sylvania 6SN7GT's. They're nice tubes but not as sweet as the Mullards ECC32/33/35's and Tung-Sol RP's.
> ...


 
 I'd also like to try a pair of B65's. If I could find a pair at a resonable cost, highly unlikely though..


----------



## baronbeehive

sonictrance said:


> I'd also like to try a pair of B65's. If I could find a pair at a resonable cost, highly unlikely though..


 
  
 I don't even know what that is, I believe they are extremely rare, whatever they are!!


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > I'd also like to try a pair of B65's. If I could find a pair at a resonable cost, highly unlikely though..
> ...



It's GEC's version of the 6SN7. And yes, they're rare and expensive.


----------



## baronbeehive

*SMLD MODS:*
  
*Stage 5 - *Soldering: Resistors. (Time spent so far, about 12 hours).
  
 Another very tricky job mainly due to the stupid soldering iron! This cardas solder is a blast though. I would say the soldering joints are not brilliant but acceptable according to industry standards 
	

	
	
		
		

		
		
	


	




. I'm getting more confident and my skills are improving, by the time I've finished I should be capable of doing it 
	

	
	
		
		

		
		
	


	




.
  
 Power stage resistors in, 330 ohm.
  

  

  
 Driver stage resistors in, 220K ohm.
  

  
 8K2 resistors in.
  

  
 More battle damage: another pad lifted on the far left by the red wire. I think it came out when I was pushing in the power resistor from the other side.
  

  
  
 Caps next. I've started imagining what it will sound like when its done lol.


----------



## SonicTrance

Looks good Baron! Keep it up!


----------



## Bruch

Hi Baron, I'm watching your progress with interest. Depending how you get on and your satisfaction level when you're done I'll have a go myself. I admire your courage to give it a go.


----------



## baronbeehive

sonictrance said:


> Looks good Baron! Keep it up!


 
  
 Thanks! I'm reasonably satisfied with the qualitiy of the solder joints and the PCB looks quite robust. Any damage done so far is not a problem I don't believe.
  


bruch said:


> Hi Baron, I'm watching your progress with interest. Depending how you get on and your satisfaction level when you're done I'll have a go myself. I admire your courage to give it a go.


 
  
 Thanks for that! I really want it to succeed because I'm sure there are people llike you that are looking into this and would like to do the same. There are guys who have given it a go and I wanted to give it a go myself 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

bruch said:


> Hi Baron, I'm watching your progress with interest. Depending how you get on and your satisfaction level when you're done I'll have a go myself. I admire your courage to give it a go.


 
 Welcome to Head-Fi Brush!
  
 Do you also have mk6 or maybe mk8se?


----------



## Bruch

I'm on the point of buying a Mk8se with a view to modding, but maybe not all in one go as Baron is doing. I have HD800's, balanced.
  
 Does anyone have any idea how the SQ of this modded amp might compare with (say) the Bottlehead Mainline?


----------



## baronbeehive

bruch said:


> I'm on the point of buying a Mk8se with a view to modding, but maybe not all in one go as Baron is doing. I have HD800's, balanced.
> 
> Does anyone have any idea how the SQ of this modded amp might compare with (say) the Bottlehead Mainline?


 
  
 Before you go ahead with the MK8 it may be worth waiting for the verdict on the new mod we are testing now which allows for the different impedances of different phones. For example with the MK6 + new mod it will handle the HD800 well. Then it's just a matter of which tubes you prefer, the MK8 tubes or the MK6, the MK6 has more tube rolling options.
  
 Also you say you don't want to mod it all in one go. Trouble is......... once you've got the board out it makes sense to do it all there and then 
	

	
	
		
		

		
		
	


	




.
  
 Maxx134 says the modded LD beats off everything in sight!!
  
 My next stage may be the wiring instead of the caps. I've ordered some thicker solid core wire for them to help hold everything in place hopefully 
	

	
	
		
		

		
		
	


	




.


----------



## Bruch

But I would be worried about fault-finding, not having my amp for weeks, rushing to get it finished and then 'poooof'! Better to do one stage at a time when I'm ready for it and make sure that everything still works, rather than do everything at once? Or are you firing it up with the board out, just to make sure?
  
 Good luck with the wiring.


----------



## SonicTrance

It is definitely recommended to do the mods in stages! It's just that some of us here (me included) are to impatient for that, lol


----------



## baronbeehive

bruch said:


> But I would be worried about fault-finding, not having my amp for weeks, rushing to get it finished and then 'poooof'! Better to do one stage at a time when I'm ready for it and make sure that everything still works, rather than do everything at once? Or are you firing it up with the board out, just to make sure?
> 
> Good luck with the wiring.


 
  
 No I'm not testing it with the board out after all. I'm sure you could do that provided you are sure it is grounded properly, but I didn't want to risk that myself, its swings and roundabouts! I agree though, far better to test it stage by stage.


----------



## Maxx134

bruch said:


> I'm on the point of buying a Mk8se with a view to modding, but maybe not all in one go as Baron is doing. I have HD800's, balanced.
> 
> Does anyone have any idea how the SQ of this modded amp might compare with (say) the Bottlehead Mainline?



Yes,
The bottle head is about as good as a woo wa7 without the wa7tp.

It is actually very nice.
Like the schiit tube amps.

None of these are end game level amps...

Neither is mk6/8 stock.

Modding them with the mods in this thread certainly pushed these amps to scary end game levels.

Add a yggy and you are done.


Edit: 
Oh wait, 
You need the 800"S" mod..


----------



## Maxx134

baronbeehive said:


> ...
> 
> Maxx134 says the modded LD beats off everything in sight!!.




No, that could not be further from the truth.

I purposely strayed away from ever saying that the LD beats anything. 
That will always be my public stance. 

I will only state it reached end game territory.
There are simply *edit* many other beautiful end game *TUBE* amps which, when you get there is really a matter of choice. 

The MK8 is my choice for many reasons.
Because it was a super learning experience for me as a first time tube amp modder.

It was a fun hobby for me to make things better. 
When I first saw the LD design, 
I saw a "Balanced Tube Amp" for under $1k,
Which was a huge lure.

I saw both huge potential, and also easier learning because of these amps specifically having a "circuit board".
No mess of spaghetti "point-to-point" wiring that you would see in other tube amps. 

One discovery lead to another and the supermod thread became a reality.
I never envisioned this to happen or to have so much to do in a tube amp project. 

Other members have exclaimed how good their amp can be.

The only thing I would say for sure is that I am currently satisfied with the level so far, yet it is still a work in progress as more mods on way, because this is my hobby. lol.

 The point is that there are many variables to having tube amps, 
and then we have tube rolling, so saying one amp is best or better than all is fairly naive.
It much better to say at what level an amp is at.

With these amps you get the immense satisfaction of accomplishment,
While experiencing how the circuit can be optimized and how it behaves with variables changed.


----------



## baronbeehive

maxx134 said:


> No, that could not be further from the truth.
> 
> I purposely strayed away from ever saying that the LD beats anything.
> That will always be my public stance.
> ...


 
  
 Sorry Maxx I never intended to speak on your behalf about what you thought about the LD, and I wouldn't not do that, but I thought you had gone on record and said that the LD was as good if not better than everything you had heard at meets with the possible exception of the Stax setup, if that was in a private conversation I apologize!  That is my position. Also I never say anything about anything unless it is factual, or if not I make that quite clear, for example I say "others have said", or something like that.
  
 Regarding what I think about the LD or the mods, I haven't said anything about their sound yet, and when I do I will not exaggerate what I think, or cast doubt on what others think. I hate all the hype and mudslinging that goes on on the majority of audio forums.
  
 So, just looking forward to hearing the mods and until then I will remain skeptical as always 
	

	
	
		
		

		
		
	


	




.


----------



## coinmaster

> I purposely strayed away from ever saying that the LD beats anything.
> That will always be my public stance.


 
 Don't worry I'll say it for you. 
  
 A properly modded MK6/8 beats anything 
	

	
	
		
		

		
		
	


	




, except what I have cooking up...
  
 Oh yeah and just because I like to brag, John Broskie (a tube legend) liked one of my ideas 
	

	
	
		
		

		
		
	


	




.
  
 http://tubecad.com/2016/02/blog0339.htm
  
 It was born from my effort to improve the WCF and solve the issue that the "impedance mod" tries to solve, Broskie filled in the gaps like the feedback to the top anode.
  
 From my understanding it's the first new tube output stage topology since sliced bread was invented other than the "broskie follower" which is a slight variation of the WCF.
  
 It completely solves the problem the "impedance mod" attempts to solve but the "impedance mod" only works for certain frequencies.


----------



## baronbeehive

.........right lets see.... switch on soldering iron...........find part from mountain of junk on worktop..........feeling good..........attempt to fit part............. something happens I hadn't anticipated.......... starting to feel bad........  soldering iron goes out the window......... retrieve soldering iron........... where was I.........oh yes.......... pick up soldering iron......... etc etc.
  
 Everyone should have a working method which suits them lol 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

coinmaster said:


> > I purposely strayed away from ever saying that the LD beats anything.
> > That will always be my public stance.
> 
> 
> ...


 
 So you got to impress Broskie! Good for you
	

	
	
		
		

		
		
	


	



  
 Whats the time-frame on your amp build? Have you started yet?


----------



## SonicTrance

baronbeehive said:


> .........right lets see.... switch on soldering iron...........find part from mountain of junk on worktop..........feeling good..........attempt to fit part............. something happens I hadn't anticipated.......... starting to feel bad........  soldering iron goes out the window......... retrieve soldering iron........... where was I.........oh yes.......... pick up soldering iron......... etc etc.
> 
> Everyone should have a working method which suits them lol
> 
> ...


 
 Hahaha!
 Thanks Baron, I needed a good laugh after a long day.


----------



## coinmaster

sonictrance said:


> So you got to impress Broskie! Good for you
> 
> 
> 
> ...


 
 Time frame is probably realistically the summer maybe, I'm trying to bring it way before that though. The problem I've found with prototyping is not that it's hard to build, on the contrary I could build a stock MK6 in a few hours tops. The problem is putting it together in a way that isn't a fragile flimsy mess. I've fried so many components due to accidental shorts. I tried using those perfboards but they are really annoying to use and they short out a lot. One of the big problems is a lot of the components I use have very short leads so It's difficult to use them on anything other than a PCB.
 I've come to the conclusion today that I need to order custom PCBs for a prototyping power supply for both the input and output stage as well as PCBs for the gyrator/CCS so I can easily load up the tubes, this will make it endlessly easier to prototype.
  
 My amp is going to remove the need for coupling caps while still remaining OTL/OCL and it will accept any tube type for both the input stage and the output stage, even DHTs like the 300b. I'm going to make custom interchangeable sockets for this. It will allow both SE and push pull output options in case you want to throw a single 300b on there or something, with the SE being OTL/OCL as well (good luck finding an OTL/OCL SE output stage on the market, especially one that doesn't need coupling capacitors).
 The input stage will be a common-cathode topology which cancels out any and all distortion but I will allow it to use single tubes as well in case I like whatever distortion a tube might create.
 There will be an option to switch from CCS to l.e.d. to gyrator bias on both the cathodes and plates. (which will require hundreds of l.e.d.s to pull off in order to have enough of a selection to  make room for all the possible tube types, it will be very shiny 
	

	
	
		
		

		
		
	


	




)
  
 The load lines for all tubes will be adjustable via software, I'll have a library of load lines so you can visually adjust the load lines and see what your voltage swing is on the load line, it will have an adjustable negative feedback dial so you can do what yang did for the MK6/8 and "cheat" your way into unlinear ranges of the load lines in case your swing is too big and wants to go into cutoff.
 The manual load line adjustment will let you fine-tune your sound in a way no other amp can aside from the fact that it will also allow you to use any tube type you want. Imagine the tube rolling... 
	

	
	
		
		

		
		
	


	



 I'll have a built in curve tracer which scans the load lines of your tubes and is far more accurate than any tube tester, then you can reference the individual load lines of your specific tubes for adjustment and also to see if they are "really" matched because tube testers have a large error margin.
  
 It will have easy access user changeable caps and resistors, assuming I end up having any, as it stands there's no resistors in the signal path other than the grid stoppers and only 2 capacitors per channel. I'm working on a way to remove those as well.
 There are various huge improvements to the implementation of the stages other than the basic topologies like the use of high end gyrators on the plates which act as super high value inductors
 and constant current sources on the cathodes which will always maintain a stable current even as the tube ages and you don't need to use a cathode bypass cap with it.
  
 The power supply will be a shunt regulator because the more current you shunt with a shunt regulator the lower the output impedance is, which is why many people claim it has the best sound.
 The maximum current I currently intend to allow for the tubes is 100ma since there aren't many that need more than that but I'll have the shunt regulator be shunting 1-2 amps which will make the output impedance a practically non-existant number (way below 1 miliohm).
  
 The preliminary schematic so far is very complex and requires a lot of microcontrollers and digital circuitry as well as a 1200v power supply. (not looking forward to paying for that)


----------



## SonicTrance

Sounds interesting. You're basically trying to build the "ultimate" tube amp. And to think you started of by modding an mk6, lol.
  
 Maybe you could build point to point in a nice (and I guess rather large) case? That way no flimsy mess! You can always extend short leads.


----------



## coinmaster

sonictrance said:


> Sounds interesting. You're basically trying to build the "ultimate" tube amp. And to think you started of by modding an mk6, lol.


 
 Indeed, I spent a large amount of time annoying the people on the diy-audio forum so I could learn enough about electronics and possible designs to stand on my own 2 feet. One of the mods eventually banned me for asking too many questions lol, but not before I learned what I needed to learn.
 I've spend the last several months and playing in LTSpice finding possible solutions to current problems and researching ways to implements those solutions and then testing those solutions on the bench. Which is one of the things that spawned my idea that lead to the newest broskie post. I kinda regret letting him post it publicly, he asked me if I wanted to keep it secret since I was using it for a personal design but he did technically put the finishing touches on it that I hadn't gotten around to solving yet because I was busy perfecting other parts of my amp so I told him I didn't feel right to stop him.
  
 One of the things that broskie told me is that no one innovates tube tech anymore, which is basically the same thing I stated on here a while back. It's true, all you have to do is take a standard design, make it look really nice and throw a big price tag on it and you're in business (WA22 "cough" "cough"). Anyone that deals in tube design is basically really old at this point so there's no fresh perspective. I'm the only person that is not that I know of 
	

	
	
		
		

		
		
	


	




 There's a lot of room for improvement, if this was any other field the possible options would probably be exhausted by now but tubes "officially" became dead technology ages ago.
  


sonictrance said:


> Maybe you could build point to point in a nice (and I guess rather large) case? That way no flimsy mess! You can always extend short leads.


 
 Point to point isn't really practical. Most of the amp is digital circuitry and solid state for the control mechanisms, The analog portion is basically limited to the tubes and the grid stoppers. Basically an all tube signal path depending on how you look at it, other than the two "WCF" caps I have't figured out how to get rid of yet without extreme measures like a resistor divider which would require a 4KV+ power supply and 100w resistors.
  
 Technically speaking the power supply and constant current sources and such will have an affect on the audio since the signal spawns from them but only to the extent that any power supply will have an effect on sound mostly due to the output impedance and small capacitances and such but I've basically eliminated the output impedance of the power supply and I'll be designing it handle huge transients so that leaves the constant current sources and their tiny gate capacitances and impedances which shouldn't really do too much of anything when loaded onto the cathode, I don't recall anyone ever saying anything about a CCS on a cathode affecting the sound in anyway, usually it's plate loaded CCS that do.
 I could even ditch the constant current sources and just feed the cathodes direct from the shunt regulator if I wanted to ...hey there's an idea... a shunt regulated constant current source. I just blew my mind 
	

	
	
		
		

		
		
	


	




 The infinitesimal output impedance and supreme transient capabilities would make it a nearly perfect voltage source for a cathode! I could use a digital feedback loop to achieve this, digital technology allows me to cheat the impossible yet again


----------



## MrCurwen

coinmaster said:


> Anyone that deals in tube design is basically really old at this point so there's no fresh perspective. I'm the only person that is not that I know of




Oh?



> There's a lot of room for improvement, if this was any other field the possible options would probably be exhausted by now but tubes "officially" became dead technology ages ago.




Hmmm.


----------



## coinmaster

Oh hello MrCurwen, I did not know you had an account here. I should probably thank you for teaching 
	

	
	
		
		

		
		
	


	




 You are 95% the reason I've been able to get this far. Those mini-lessons you gave me were invaluable.


mrcurwen said:


> Oh?


 
 To quote broskie 


> since the audio market has shriveled down to old, crazy, affluent men, you can make and sell anything you want—for nothing is too outlandish or too silly, as long as it costs a fortune.


 
 I tend to agree given the evidence.
  
 My ultimate goal is to bring high end audio into the affordable market, most people think an ipod and a pair of beats headphones are the best thing there is. This must be stopped 
	

	
	
		
		

		
		
	


	




.


----------



## Redge78

@Coin
 I'm happy to see that your self-esteem is still sky-high... 
 But I'd like to remind you what we're trying to do here ... We're a bunch of guys trying to improve our MK6/MK8 in simple and practical ways, we share our experiences and we help each other. That's about it. And have fun in the process.
 No bragging, no spaceship building, no assumptions, no LTspice modelling. 
  
 So you should ask yourself two questions :
 - Does your spaceship (even if it may be wonderfull one day, who knows ?) has something to do with the MK6/8 anymore, apart from the vague WCF topology ?
 - Are you going to share your "findings" with us ?
 If not, what are you doing here ? I mean ... what's the point ? Why don't you create your onw thread where more skilled people than us will be able to help you ?
  
_And we have already warned you many times, don't play with the 1200V, a guy who's burning half its components is not intellectually prepared for that !_
  
  
 @McCurwen
 I understand your ... *circumscription* (?). Coin has an appaling writing style. 
 Feel free to have a look at what we've already done, and if you have any suggestion, correction or any other advise, we will gladly discuss them.
  
  
  @baronbeehive
 Please, don't forget to open the window, otherwise it will be a little bit embarrasing ... Apart from that, it makes great sense to me. 
 Being french, my education allows me to swear like a pig without prejudice. That's very convenient.
  
  
@Bruch
 You can trust Maxx, he has a extensive knowledge of the headphone market (and a good ear).
 What I can add (to keep it practical) is that the "stock MK8se" is already an amp that was renowned to work well with the HD800. With some simple, not-that-expensive mods, you will very significantly improve the sound of this amp-headphone couple.
 Products from Bottlehead are well-knowned, sound well and can also be widely modded. A good-quality parafeed can be a very decent option for the HD800, taming it in the high and boosting it in the low-medium.


----------



## coinmaster

redge78 said:


> @Coin
> I'm happy to see that your self-esteem is still sky-high...
> But I'd like to remind you what we're trying to do here ... We're a bunch of guys trying to improve our MK6/MK8 in simple and practical ways, we share our experiences and we help each other. That's about it. And have fun in the process.
> No bragging, no spaceship building, no assumptions, no LTspice modelling.


 
 I've already confirmed the key aspects of my new amp on the bench, it is not theory. As ever you need to relax instead of being so uptight all the time. I mean seriously, life is short. The only buzz kill here is you.


> And we have already warned you many times, don't play with the 1200V, a guy who's burning half its components is not intellectually prepared for that !


 
 I've been playing with 400v for months now. I'm pretty well aquainted with the consequences of high voltages. For starters I'm always protected behind plexiglass with the off switch in my hand whenever I on the supply and I wouldn't be touching 600v lines (1200v bipolar) without completely redoing my set-up so I don't have any more incidents with shorts. The 99% of the incidents happen due to my make-shift supply and the mess of wires anyway so the dedicated prototyping supply I'm building will pretty much solve the issue.


> So you should ask yourself two questions :
> - Does your spaceship (even if it may be wonderfull one day, who knows ?) has something to do with the MK6/8 anymore, apart from the vague WCF topology ?
> - Are you going to share your "findings" with us ?
> If not, what are you doing here ? I mean ... what's the point ? Why don't you create your onw thread where more skilled people than us will be able to help you ?


 

  
  
 I used to be a part of this modding project and my amp design spawned from it, I'm not bringing down the apocolypse by reporting my progress every once in a while.
 I know you and Maxx like to think you are the god of this forum but it is a public forum like any other.
  


> Coin has an appaling writing style.


 
 Am I too blunt? Sorry I'm not one to waste time on subtlety. If you get offended by people over the internet I think you are lagging behind on the culture of internet communication.
 Never take anything I say offensively because I never mean it so.


----------



## Maxx134

baronbeehive said:


> maxx134 said:
> 
> 
> > No, that could not be further from the truth.
> ...



Hey! 
No I'm sorry I used your post to clarify my stance as I didn't mean to specifically point you out.
I have a good friend with a stax setup, and a good friend with an end game Eddie Current setup.
I luv the sound of both.
It is naive to think at that end game level, that only one is best, as it becomes a matter of taste.
When I said naive, I didn't mean you, only the person who says it is the best (coin)...
When that is his own personal experience and preference. 
Of course our amp it up there at similar level,
But no need boast as it will always be a preference. 

The main benefit here with the mk6/8 for now is that the amp can be tuned to your liking.

Other than that there are so many beautiful tube amps.







coinmaster said:


> > I purposely strayed away from ever saying that the LD beats anything.
> >
> > That will always be my public stance.
> 
> ...



Contrary to you thinking I am uptight, I actually always wanted to see hopefully have success.
That's why I still answer your PMS. 

 I also agree on the need for circuit board..

 Also I agree that you need to try stay on topic as yuu can divulge in a way to clarify instead of boast, as your ideas are interesting. 

So I'll volunteer to be the first one to test your amp.


Plus I still have an unused fire extinguisher handy from my own testing.


----------



## Maxx134

@coinmaster,
Did you quote "broskie" from a personal PM..?

I do not agree with the tube old-timer stance.

I feel the stax amps are modern, and the hybrid amps out there are a step in the right direction. 
If you think about it, 
These MK6/8 amps also are a step forward in technology by using the circuit boards and the DC servo that traditional tube amps don't have..


----------



## coinmaster

> Contrary to you thinking I am uptight, I actually always wanted to see hopefully have success.
> That's why I still answer your PMS.


 

 Nah, you've had your moments but you're pretty chill overall, I was mostly referring to Redge. He just needs to see things with a bit of perspective. I'm pretty much incapable of sweating the small things, it's not my way.
 I don't see the issue with reporting on my progress every once in a few months...
 Quote:


> So I'll volunteer to be the first one to test your amp.


 

 I'll take you up on that  I was wondering what I was going to do about preliminary feedback. It helps that you are extremely close by.


> Plus I still have an unused fire extinguisher handy from my own testing.


 

 Me too, I'm starting to wonder what it will take to cause a fire though. I think you would have to like, leave the amp on for after majorly screwing up. I always have the power switch ready for instant use.


> @coinmaster,
> Did you quote "broskie" from a personal PM..?


 
  Yeah but he was quoting himself and linked this http://tubecad.com/2014/01/blog0278.htm
  
 Quote:


> I feel the stax amps are modern, and the hybrid amps out there are a step in the right direction.
> If you think about it,
> These MK6/8 amps also are a step forward in technology by using the circuit boards and the DC servo that traditional tube amps don't have..


 

 I think it depends on how much "old timer" we're talking here. Stax amps are pretty ancient tech. Hybrid amps are the right step but I don't think we are there yet.
 The hybrids I've seen or heard so far (like the $8,000 hybrid meant to go with the HE1000) have lazy designs or they sound too solid state. If were' talking about the 21st century there is so much not being done. Broskie has a few blog posts about it.
 I myself have been noticing the possibilities of mixing digital and analog among other things.
  
  
 Servos aren't exactly advanced technology, it uses an opamp "integrator" which is one of the most basic opamp configurations, to offset DC at the output.
  
 The rest of the MK6 is a white cathode follower which was invented in like 1930 and it has the most basic form of input stage.

 There is protection circuitry in there too but that's mainly because you don't want to be using servos without it, it's too risky. The delay circuitry is there to stabilize the servo and because it's bad for the tube to turn on a power tube before it's heated.
  
 When you really look around there really doesn't seem to be much desire to move the industry forward but it's not really exclusive to tubes, the audio industry in general has kind of slowed down in the last decade, tubes aren't helped by being a niche portion of it, also probably in part due to how easy it is to just use a medeocre design and slap a big price on it coupled with the fact most people nowadays haven't been introduced to tube technology and/or don't even know what a tube is, or can't afford the available tube amps to even get aquainted with it to begin with.
 I think if high end audio was brought to the affordable market then there would be more of a drive to move it forward, like I said earlier most people are perplexed when you mention using anything other than an ipod for music and I can't tell you how many times people tell me beats are the best headphones you can buy.


----------



## baronbeehive

*SMLD MODS:*
  
*Stage 5 - *Soldering: Wiring. (Time spent so far, 30 hours approx)
  
 Another tricky job, but not so difficult as PCB work due to the fact that the terminals are less of a worry from over heating. Its so easy to get confused by the wires but thank goodness I had a wiring diagram beforehand which was more or less accurate I think! I've checked and rechecked everything several times lol.
  

  
 Next are the caps.


----------



## Bruch

30Hrs! What have you been doing all that time?
  
 Talking of fires I'm not so sure about wooden enclosures to extend the case. Half considered moulded mdf would look nice before I thought about the fire risk. I will probably opt for some kind of diy metal grill to provide ventilation.


----------



## baronbeehive

bruch said:


> 30Hrs! What have you been doing all that time?
> 
> Talking of fires I'm not so sure about wooden enclosures to extend the case. Half considered moulded mdf would look nice before I thought about the fire risk. I will probably opt for some kind of diy metal grill to provide ventilation.


 
  
 I've been tearing my hair out for most of that time 
	

	
	
		
		

		
			





.
  
 Hey, only the older members can insult me lol.
  
 You could ask Mogos, this is his case.
  
 Quote:


mogos said:


> ............
> Few pics just before  and after launching the amp.
> 
> 
> Big Wimas just milimiters from the bottom


----------



## SonicTrance

It's great to see progress Baron!


----------



## baronbeehive

sonictrance said:


> It's great to see progress Baron!


 
  
 Yeah thanks! Glad to get the wiring out of the way. I'm just hoping the soldering is good enough, I think it is but of course you don't know until you switch it back on 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

Need better pics to be able to tell but looks like a possible short here, between ground and R_-?


----------



## baronbeehive

Quote:


sonictrance said:


> Need better pics to be able to tell but looks like a possible short here, between ground and R_-?


  
 Yes I noticed that on the pic but its not on the board, I think it's the light playing tricks! I'm going to clean the board when I've finished and that will show up more clearly then! I haven't taken any clear close ups yet, I'll try to get a clearer pic when I post the pics of the finished job.


----------



## Mogos

bruch said:


> .........
> Talking of fires I'm not so sure about wooden enclosures to extend the case. Half considered moulded mdf would look nice before I thought about the fire risk. I will probably opt for some kind of diy metal grill to provide ventilation


 
 In previous posts you can see the idea how it was done. I can recommend to do the extension at least with the hight of the original chassis. I have done 10 mm less.


----------



## Mogos

sonictrance said:


> Need better pics to be able to tell but looks like a possible short here, between ground and R_-?


 
 Baron it could be good to have even very cheap meter with continuity check. Sometimes you can not see if there is a short connection.


----------



## baronbeehive

mogos said:


> Baron it could be good to have even very cheap meter with continuity check. Sometimes you can not see if there is a short connection.


 
  
 No, right, thanks Mogos. I have a meter and I will take your advice to check everything out before the big switch on!


----------



## Maxx134

baronbeehive said:


> *SMLD MODS:*
> 
> *Stage 5 -* Soldering: Wiring. (Time spent so far, 30 hours approx)
> 
> ...



This is quite beautifully clean wiring job done here.
30hrs is understandable when doing something this neat and first time.
I actually encourage this type of slow methodic procedure,
As the installation of caps will be different and much foresight is needed.

Also, I see you have wires soldered to the coupling cap holes. 
I probably would do the same for the WCF caps, so you can be able to move them out of way in future,
If you needed to get at the switches or trimpots.

But it looks like it will be hard to strip the wire.

Also, I use alot of Q-tips to clean the area after I solder, 
Because the solder may tend to pop fragments and impurities. 
I always constantly clean board of dust and any particles. . 
Even though my unit looks like a crowded mess!



Wait till my Anode resistors and switch go in!


----------



## baronbeehive

maxx134 said:


> This is quite beautifully clean wiring job done here.
> 30hrs is understandable when doing something this neat and first time.
> I actually encourage this type of slow methodic procedure,
> As the installation of caps will be different and much foresight is needed.
> ...


 
 Look forward to seeing how you manage to fit them in!
  
 30 hours is only approximate and includes the preparation and desoldring, but I spend a lot of time thinking about it lol.
  
 Yes the engineer who did my first lot of coupling caps put the wire posts in because he couldn't face getting the board out again for a second time. I will desolder the wires and put some more in because I'm going to put in the Jupiters at some point.
  
 I intend to go over the board with a toothbrush and Qtips when I've finished 
	

	
	
		
		

		
		
	


	




.
  
 Thanks for the compliments and thanks for overlooking the fact that I nearly wrecked the board!!


----------



## baronbeehive

*SMLD MODS:*
  
*Stage 5 - *Soldering: Caps.
  
 Making good progress now. I think that's the difficult bit over!
  
 Cathode Bypass caps
  

  
 Decoupling caps
  

  
 Whatever works!
  

  
 Mundorf E caps and M caps in.
  

  
 That was tricky due to the lack of space. Getting nearer to my goal now 
	

	
	
		
		

		
		
	


	




.


----------



## Maxx134

Hey, you forgot to line up all the lettering on those white caps, and have one opossite direction of other for voltage readings...
You have to take all out and do over. .

..
sorry..
..



JUST KIDDING! 
HA GREAT WORK!


----------



## Maxx134

You still have the bypass to do..
Will be tricky to squeeze in, but I'm sure you can do it..
Edit:
Get then in before the PSU electrolytics,
And make sure you position to have space for all of them.

For the driver stage, 
I would make sure all fits in place before installation.


----------



## baronbeehive

maxx134 said:


> Hey, you forgot to line up all the lettering on those white caps, and have one opossite direction of other for voltage readings...
> You have to take all out and do over. .
> 
> ..
> ...


 
  
 Ha ha, you had me worried for a second there!
  


maxx134 said:


> You still have the bypass to do..
> Will be tricky to squeeze in, but I'm sure you can do it..
> Edit:
> Get then in before the PSU electrolytics,
> ...


 
  
 I've done 3 of the 4 power stage bypasses but now I want my tea! That was forensic, microscopic work lol.
  
 The driver stage should be OK, it fitted when the board was in, now I have no way of knowing until the board goes back. Also I have 2 new driver stage resistors to go in and they're bigger than stock so all I can do is cross my fingers and hope.......


----------



## SonicTrance

Looks nice and tidy Baron! I'd recommend installing board before installing more caps. So that you have access to all screws.


----------



## Redge78

And one other Mundorf fan boy ... jeez, you really want to help the german economy !
  
 That being said, it's a impressive job for somebody who's not used to solder.


----------



## baronbeehive

sonictrance said:


> Looks nice and tidy Baron! I'd recommend installing board before installing more caps. So that you have access to all screws.


 
  
 I hadn't thought of that, I will certainly get it it when I've finished all the soldering on the reverse. I still have to put the 3 pairs of output wires in, I forgot that when I did the wiring from the front 
	

	
	
		
		

		
		
	


	




.
  


redge78 said:


> And one other Mundorf fan boy ... jeez, you really want to help the german economy !
> 
> That being said, it's a impressive job for somebody who's not used to solder.


 
  
 Encouraging words thanks guys. I really wanted to get the Elna Silmics but you can't argue with the ECaps price.
  
 I learnt from the masters that's how I managed it lol, but that cardas solder - you can't really go wrong, unless you have the wrong soldering iron of course!


----------



## Maxx134

redge78 said:


> And one other Mundorf fan boy ... jeez, you really want to help the german economy !
> 
> That being said, it's a impressive job for somebody who's not used to solder.



If I do it again, I would try something different, like what your planning. 


I will eventually need to extend the bottom a bit..


----------



## Maxx134

Another point I like to make.

From my testing, a .22uf WCF cap is anemic.

Approaching the .33uf mark, a fullness or lushness appears to the mids,
And the bass becomes more alive..

The point to realize is this:
Once you're going higher than .22uf, the sound of the cap becomes more relevant, prevalent, and more important. 

You don't want a boomy dry sound.

Also, the majority of caps today will have artificial treble nuances,
So I can only recommend a PIO or a Copper film cap when used in signal path.

That is my own personal view that I will not deviate from.
Edit :
Those are my "safe" choices, 
But the mundorf oil versions also did well in WCF position.
Mist likely due to their "sweetness" which also is an abbreviation from neutrality.
So we see this cap also inject it's flavor..


----------



## baronbeehive

*SMLD MODS:*
  
*Stage 5 - *Soldering: Caps
  
 Made some more progress, slowing a bit due to the difficulty in squeezing everything in in the right positions.
  
 Put decoupling RIFA's here....
  

  
 ......... and here.
  

  
 The 4 power decoupling bypasses.


----------



## Maxx134

Excellent progress posts.
This really is helpful to the thread.


----------



## baronbeehive

maxx134 said:


> Excellent progress posts.
> This really is helpful to the thread.


 
  
 It helps me as well if you guys spot any mistakes if I have my wires crossed 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

*SMLD MODS:*
  
*Stage 5 - *Soldering: Caps
  
 More battle scars, are these OK? I could cover it over with elastoplast!
  

  
 I hope this is correct? If so the RIFA legs are just long enough lol.


----------



## coinmaster

Those caps are wired wrong. 
 This is what will happen if you put them in like that

  
 The mundorf ones I'm not sure about, you're going to have to refer to the datasheet but the red ones go the other way.


----------



## Maxx134

baronbeehive said:


> *SMLD MODS:*
> 
> *Stage 5 -* Soldering: Caps
> 
> ...




Cover the melt scars on caps with tape like what I did.

The red caps don't wire in the long way.
Turn around and connect the closer pins together:


----------



## Maxx134

coinmaster said:


> Those caps are wired wrong.
> This is what will happen if you put them in like that
> 
> 
> ...



Coin is right. 
Although the caps won't get damaged at all. 

The problem is You just created a short with the wiring.

But if those caps did explode, it would be a mess like that pic lol.

To get a cap to explode would require it to have voltage exceeding it's value..
So no worries there as the caps are all above 250v rating


----------



## Maxx134

Where is your missing resistor?
If it too big no problem, just file the leads thinner to fit the hole...


----------



## coinmaster

maxx134 said:


> Coin is right.
> Although the caps won't get damaged at all.
> 
> The problem is You just created a short with the wiring.
> ...


 
 Yeah but with a 4 pole cap like that I suspect he will be creating a complete short to ground. That's asking for a disaster if the fuse doesn't blow in time.


----------



## baronbeehive

Thanks guys I'll change round the wima/rifa combo, I liked it the way I did it though lol.
  
 Quote:


maxx134 said:


> Where is your missing resistor?
> If it too big no problem, just file the leads thinner to fit the hole...


 
  
 I've got new ones for there. The originals had slight corrosion on the legs and I didn't think I could solder wire to it so I got new ones.


----------



## Maxx134

I like to give some thoughts on the MK8..

Actually, There is a quality to both amps that I like to point out.
The "overdone", "musical" , and even "simple" PSU stage. 

The MK8 has an ability to try a wider range of driver tubes than ANY amp I am aware of...

Every single 12at7,12ax7, 12au7,e180cc, and even the hard to drive largest 9pin like the e80cc with huge heater demands at double the current loads...

There is simply no other amp I know that does this.

I believe it is the fact that this unit runs the heaters off large transformer AC feeds.

There is a stigma about "A/C" fed heaters...


In these amps, it is a plus...


----------



## Mogos

I think it is important to know how it all started.
  
 http://www.head-fi.org/t/522099/little-dot-mk-vi-little-dot-mk-viii-se-owners-unite


----------



## baronbeehive

mogos said:


> I think it is important to know how it all started.
> 
> http://www.head-fi.org/t/522099/little-dot-mk-vi-little-dot-mk-viii-se-owners-unite


 
  
 Where will it all end though 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

maxx134 said:


> I like to give some thoughts on the MK8..
> 
> Actually, There is a quality to both amps that I like to point out.
> The "overdone", "musical" , and even "simple" PSU stage.
> ...


 
  
 My favourite 12ax7's are Amperex Bugle Boy or equivalent, or even better Sylvania JHS 5751 but I prefer above all the TS JTL 5751. The 5751's are preferable to the 12ax7's, the sound goes up a  notch with these. I know this because I use them on my Miniwatt. I didn't think the 12ax7's were compatable with the 12at7's for example though.


----------



## Maxx134

baronbeehive said:


> maxx134 said:
> 
> 
> > I like to give some thoughts on the MK8..
> ...




Compatability depends mainly on amp...

In the driver stage,
The MK8SE can take any and all 9pin "dual" or "twin" triode tubes. .

All that I have tried, regardless of number, or type or heater current... (!)
Here is one of three boxes of tubes I gathered.
All compatible.. 

Every single one compatable, which is very unique.


----------



## Maxx134

Redge78 has suggested in the past,
that we should compile a list of best tube choices for both amps. ..

I have hesitated,
 because a "best tube" can be misinterpreted as a personal choice..

So first we will develop some guidelines.

Like brief descriptions of each tube as it performs in the amp.
Not anywhere else.

My basis for a good tube depends mainly on clarity and soundstage.

The inevitability of other factors will also come into play, 
but to a lesser degree. .


----------



## baronbeehive

maxx134 said:


> Compatability depends mainly on amp...
> 
> In the driver stage,
> The MK8SE can take any and all 9pin "dual" or "twin" triode tubes. .
> ...


 
  
 Great choice  of tubes there. http://www.watfordvalves.com/ do cryoed GE's which are TOTL as well. I haven't tried them because I have my own favourites which I'm happy with.
  
 A tube list would be a good idea, I've tried all the ones I'm interested in including the Amperex, Sylvania and TS which are TOTL. Others I was interested in are the Raytheon, and GE's but I doubt if I will try them now.


----------



## baronbeehive

*SMLD MODS:*
  
*Stage 5 - *Soldering: Wiring, Caps. (Total time spent so far, about 45 hours).
  
 Output wiring on reverse of board finished. Need to reattach some old red and white wires which have come off before putting back PCB. Need to refer to my wiring diagram again.
  

  
 Cathode bypass rifa's on reverse of board, could have done a better job but that should do.
 That red twisted wire needs surgery, it's been burnt, pierced and god knows what.
  

  
 The MCap has seen a surgeon lol.
  

  
 Spent nearly all yesterday trying to tin the leads of the Audyns and gave up. They have an odd coating which makes it impossible to solder. I tried to remove it but couldn't.
  
 Coming to the end now, starting to think of what it will sound like, if it works at all 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

Great to see progress Baron! What I don't get is why you didn't put the cathode resistors by the board vents, like this?
  

  
 I'm having trouble with my amp ATM. Something broke and I don't know what. Redge and Maxx are helping me so hopefully I'll get it fixed.


----------



## baronbeehive

sonictrance said:


> Great to see progress Baron! What I don't get is why you didn't put the cathode resistors by the board vents, like this?
> 
> 
> 
> I'm having trouble with my amp ATM. Something broke and I don't know what. Redge and Maxx are helping me so hopefully I'll get it fixed.


 
  
 Yeah, I wasn't too happy with the RIFA's. The reason I didn't put them where you suggest is because I was going to put all the RIFA's on the other side, but when I tried to do that I couldn't find a suitable position for the cathode bypass bypasses. So I had to put them there because I didn't want to bother desoldering the resistors again and I don't think the legs were long enough anyway. At least the cathode bypasses are above a vent on the other side anyway lol.
  
 Sorry to hear about your amp, what happened, did it short out?
  
 Your blue twisted wire looks new btw, did you replace it?


----------



## SonicTrance

The cathode resistor legs on mine are very short. I've just soldered them to the Rifas which then goes to board. But never mind, your way works too.
  
 No, that's the stock blue heater wire...
  
 Yes, there was a short. It started with a burnt anode resistor, then a short, not sure if the two are related yet...


----------



## Redge78

I may have already posted those, but this is how I managed to have my Cathode bypasses caps all in the side of the board.


----------



## baronbeehive

redge78 said:


> I may have already posted those, but this is how I managed to have my Cathode bypasses caps all in the side of the board.


 
  
 That's alright if you've got a wooden crate to put everything in 
	

	
	
		
		

		
			





.


----------



## Maxx134

baronbeehive said:


> baronbeehive said:
> 
> 
> > *SMLD MODS:*
> ...



My apologies, BUT..

I DO NOT like how your Cathode resistors are next to the caps...
They are power resistors that will handle 2 watts on board,
 and capable of over 5 watts upon any type of stress or problems. 


They will give off much heat,
 and cause premature wear of the caps.

They *should* be over the vent holes for heat circulation. 

I cannot see your perfect work to be marred by this type of mistake.

I Do not recommend you leave those resistors like that without ventilation. 

I know it's a pain, but you MUST redo them in a safe position, *over the vent holes. *

I do not want anything to happen later my friend..

Oh, and keep that twisted wire away from everything,
as it is the heater wires and need to be twisted and away from the output wires.


----------



## baronbeehive

OK. thanks I'll have a look at that. Not much to do now anyway.


----------



## baronbeehive

*SMLD MODS:*
  
*Stage 5 - *Soldering: Caps, Resistors. (Time so far, about 50 hours).
  
 Wired up ready for driver stage decoupling WIMA's.
  

  
 WCF caps.
  

  
 WCF caps going in, and wired up ready for driver stage decoupling WIMA's. New driver stage resistors in.
  

  
 Revised position for cathode bypass bypasses and power stage resistors. Not very clear so as not to highlight my worst soldering so far. The RIFA legs were rather short so it was a bit of a squeeze. Also I was worried about the decoupling caps on the other side of the board coming out inadvertantly with soldering again on this side of the board.


----------



## SonicTrance

Hi Baron!
  
 Cathode resistors looks much better now! 
	

	
	
		
		

		
		
	


	



  
 But you're supposed to connect your driver stage de-coupling caps on the other side of the anode resistors. Look at first page.


----------



## baronbeehive

sonictrance said:


> Hi Baron!
> 
> Cathode resistors looks much better now!
> 
> ...


 
  
 Damn and blast etc. I thought because there was no polarity it wouldn't make any difference. OK, thanks, I will move the wires.
  
 I'm not really happy with the resistors, I'm going to do them again, I'm doubtful about the soldering, and one is too close to the twisted wire.


----------



## Maxx134

Yep, 
It's good to know what's going on.
These are two Anode resistors for the driver tubes..


Side by side, fed together, but going two different places, to the two triodes withing driver tube.

If you look at the trace on the other side, you will see that the top or outer edge of resistors has both of them together being fed from source power.

Then after resistors the trace is going different places (triodes), 
So good to know the details so no mistakes.

Here is your pic I scribbled on:


----------



## baronbeehive

*SMLD MODS:*
  
*Stage 5 - *Soldering: Resistors, Caps. (Time so far, about 55 hours).
  
 Driver stage resistor wiring changed. Coupling caps in.
  

  
 Getting very crowded. Very difficult working in confined spaces.
  



  
 I'm reasonably happy with the soldering but it's getting increasingly tricky due to lack of space. Just hoping that everything's OK. Don't know if everything will fit when the board's back in, especially the driver stage WIMA's and bypass. I can probably use a bit of jiggery pokery.


----------



## SonicTrance

Looks pretty neat Baron. Unusual placement of coupling and WCF caps, refreshing. 

Make sure you insulate those Jupiter caps so they don't short. Those leads looks to be right next to each other.


----------



## baronbeehive

sonictrance said:


> Looks pretty neat Baron. Unusual placement of coupling and WCF caps, refreshing.
> 
> 
> 
> ...


 
  
 Thanks! I actually think the caps are better like that, the leads are slightly shorter and I found putting them the other way round difficult, one of each of the leads would have been a lot longer because of the MCaps being in the way.
  
 The leads are right next to each other, touching, but I've put heatshrink on so there's no exposed wires touching anything. Do you think that's OK?
  
 Also I'm getting some teflon sheets to put between the power resistors and the MCaps because they are touching and the heat might cause problems otherwise.
  
 Do you like the Jupiters!!


----------



## Bruch

It's looking amazing. Fingers crossed for the big switch-on.


----------



## Mogos

The lack of space is major factor making the mod difficult. I have done enlargement of the chassis and I have been suffering badly trying to put all together in place.
 Baron I have some concern about the installation of the caps.


----------



## Mogos

As Maxx has written the leads are close to each other and not insulated. You have to secure the caps against any movement against each other. Maybe with hot glue. It can happend at any time that by accident they will be pushed and shorted and you will not noticed it.


----------



## baronbeehive

mogos said:


> The lack of space is major factor making the mod difficult. I have done enlargement of the chassis and I have been suffering badly trying to put all together in place.
> Baron I have some concern about the installation of the caps.


 
  
 I agree, I'm going to have another go at that tomorrow, but so long as there's no touching bare wires and heatshrink everywhere it should be OK? I'm going to check everything before I put it back together and if I see bare wires likely to touch I will stick on some extra heatshrink and hope that will do the trick.
  
 Do you think the 2 jupiters on the left hand side look alright?
  
 I'm going to secure the caps with cable ties.


----------



## baronbeehive

bruch said:


> It's looking amazing. Fingers crossed for the big switch-on.


 
  
 Yes, not quite there yet, plenty of time for something to happen 
	

	
	
		
		

		
			





.


----------



## Maxx134

mogos said:


> You have to secure the caps against any movement against each other.



THIS ^^

You can secure like others in past did with straps,
Or you can go sloppy hot glue crazy,

But bottom line the caps will move if left unsecured. 
Either from moving amp, or gravity, or heat.

All caps should be secured.


----------



## Maxx134

Although the driver stage Anode resistors have higher voltage, the watt dissipation is much less than the power tube stage resistors.

Therfore is is not such a big deal in the pic below:

Circled in green..

Yet the power resistors I marked in red are under your white caps..

This is a cause for concern. 

Contrary to popular belief, both the power resistors and the coupling and WCF caps can have long leads.
They do not have to be so close to board...

Only the "Decoupling caps"
Need to be close..


----------



## Maxx134

baronbeehive said:


> *I'm going to secure the caps with cable ties.*



Excellent choice.

Also I actalually very much like the unique approach to the layout of the driver stage...
Here :

Remove the two caps circled in orange,
As you won't be needing them once you put in your driver stage decoupling caps ..
Then you will have plenty space to move the jupiters apart. .


----------



## baronbeehive

maxx134 said:


> Excellent choice.
> 
> Also I actalually very much like the unique approach to the layout of the driver stage...
> Here :
> ...


 
  
 Re: the layout, if you look at the coupling caps, underneath the solder points are pretty much in the middle of each cap so the 2 leads are as short as possible and of equal lenght, whereas with the caps at right angles like you did I found that one of the leads was much longer than the other due to the proximity of the MCaps so it was not so satisfactory I think.
  
 Thanks for the advice. I will remove those caps you circled together with the accompanying WIMA's which you recommended to do, which you said are connected in parallel.
  
 I wish I had done that sooner, I could have kept longer leads on everthing. However I will be able to move the jupiters apart slightly and cover the leads with heatshrink and make sure they don't touch.
  
 I don't believe the power resistors will be a problem, the MCaps are slightly above them not quite touching and I'm going to put teflon sheeting between to insulate and keep out the heat from reaching the MCaps. Also I can put the teflon between anything that is close like the leads of the jupiters just to be sure.
  
 Mogos, you must have had a nightmare with your layout?


----------



## baronbeehive

*SMLD MODS:*
  
*Stage 5 - *Soldering: Caps
  
 You can just see that the MCaps aren't touching the power resistors, I intend to keep them like that.
  

  
 I've desoldered the round caps in the corners together with their associated wima's, and then I've moved the coupling caps apart so that the leads aren't touching. The caps will be tied in.
  

  
 The gaps between the coupling caps. Also neither the coupling caps nor the WCF caps are resting on anything, (although I don't think that matters).
  

  
 These coupling caps are a bit closer due to the lead length but not touching.
  


  
 Waiting now for new rifa cathode bypass caps on order, not much more to do! Just:
  
 1. Fit PSU caps.
 2. Re-attach 4 wires at the back just before putting back PCB, also replace heater wires which I totally wrecked!
 3. Fit new Rifas.
 4. Fit Wimas after putting back PCB.
  
 Then it's just check everything!


----------



## SonicTrance

Looks very neat Baron!

I also have a couple of anode resistors close to the de-coupling caps. It's not an issue as long as nothing goes wrong and the resistors overheat. How's your cooling? Are you planning to use some bigger fans than the stock 80mm?
I advice that you drill holes for 120mm fans. They push a lot more air and are quieter than 80mm ones. 

I used a hole saw to cut my holes:


----------



## SonicTrance

Maybe I missed something, but why are you ordering new Rifas for cathode bypass?


----------



## baronbeehive

sonictrance said:


> Looks very neat Baron!
> 
> I also have a couple of anode resistors close to the de-coupling caps. It's not an issue as long as nothing goes wrong and the resistors overheat. How's your cooling? Are you planning to use some bigger fans than the stock 80mm?
> I advice that you drill holes for 120mm fans. They push a lot more air and are quieter than 80mm ones.
> ...


 
  
 Thanks, I have to follow the Masters!! So I can't let the side down.
  
 Yes I am planning to fit bigger fans, thanks for the tip!
  
 I'm ordering new rifas because I cut the legs too short before I moved them to the reverse of the board.


----------



## SonicTrance

Don't worry about the leads. Just extend the leads with wire. No problem!


----------



## baronbeehive

sonictrance said:


> Don't worry about the leads. Just extend the leads with wire. No problem!


 
  
 I have tried that with limited success, it is so fiddly to do, but the rifas are cheap lol!


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Don't worry about the leads. Just extend the leads with wire. No problem!
> ...




You need a "helping hand" if you don't have one. Priceless little item


----------



## baronbeehive

sonictrance said:


> You need a "helping hand" if you don't have one. Priceless little item


 
  
 That's exactly what I need lol. I haven't got all the tools and it's pretty impossible withouth them!


----------



## SonicTrance

Get one ASAP Baron! Helping hand while soldering is a must.


----------



## baronbeehive

sonictrance said:


> Get one ASAP Baron! Helping hand while soldering is a must.


 
  
 For one thing they don't shake do they 
	

	
	
		
		

		
		
	


	




.
  
 Not like my hands!


----------



## baronbeehive

sonictrance said:


> Looks very neat Baron!
> 
> I also have a couple of anode resistors close to the de-coupling caps. It's not an issue as long as nothing goes wrong and the resistors overheat. How's your cooling? Are you planning to use some bigger fans than the stock 80mm?
> I advice that you drill holes for 120mm fans. They push a lot more air and are quieter than 80mm ones.
> ...


 
  
 BTW, how did you get yours to light up at night? I would like to do that!


----------



## SonicTrance

I got white LED Enermax cluster fans.


----------



## Maxx134

sonictrance said:


> baronbeehive said:
> 
> 
> > sonictrance said:
> ...




You cheater!
Now you tell me..





baronbeehive said:


> sonictrance said:
> 
> 
> > Get one ASAP Baron! Helping hand while soldering is a must.
> ...




Just inhale some solder smoke and the shaky hands slow down..


----------



## Maxx134

baronbeehive said:


> sonictrance said:
> 
> 
> > Looks very neat Baron!
> ...




The old mk6&8 thread had :
Edit**
Sound Engineer:
http://www.head-fi.org/t/522099/little-dot-mk-vi-little-dot-mk-viii-se-owners-unite/1860_20#post_11586342

It shows how he used a nice massive hole punch and the Fan was lighted already. 

You can also order a fan speed controller, also linked there .

I should sugggest to have that on first page this thread. .
Edit :
A hole punch is good when you want to go over pre-existing holes. .


----------



## Maxx134

Massive Hole punch:


Insulating bottom with plastic paint:


Fan speed controller :

I placed a temp link on my post untill ridge updates into his "Heat Management" spot that is empty on first page. 
Also his recommend tubes spot is empty so we will eventually fill those in.


----------



## baronbeehive

maxx134 said:


> ........
> Just inhale some solder smoke and the shaky hands slow down..


 
  
 Maxx is so high on hot glue, that's why his hands don't shake lol.
  


sonictrance said:


> You need a "helping hand" if you don't have one. Priceless little item


 
  
 That's not a helping hand, that's R2D2 
	

	
	
		
		

		
		
	


	




.


----------



## Maxx134

baronbeehive said:


> maxx134 said:
> 
> 
> > ........
> ...



Haha,
No,
Hotglue is like a candle stick before it melts in the gun.
No fumes at all..


But solder smoke great!
Plus you get this nice feeling of constructing something when the smoke rises..


----------



## baronbeehive

..............unless the smoke is from a short!
  
 Just ordered this:
http://www.hificollective.co.uk/wire/multistand-copper-wire.html
 to replace the twisted heater wire. It's 20awg, 600v, 105c, 14amp, whereas the stock is 22awg, 300v, 105c, so should be OK.


----------



## Maxx134

Just make sure you twist the wires and run them away from other wires, to avoid hum.
If you look a old pics you will see they are on it front side of tubes, While mk8 they are on backside.
Not sure why they are different sides except maybe for different pins on tube.


----------



## baronbeehive

Can't wait to get this mess cleared up lol.


----------



## Maxx134

baronbeehive said:


> Can't wait to get this mess cleared up lol.



Looks pretty neat to me...

Edit:
Actually, the only "mess" you should worry about are the tiny pieces of solder, dirt, and other particles that end up on & under the board.

They are super tiny and need wet Q-tips and air blasting to cleanup..

Check with magnifying glass..


----------



## Maxx134

baronbeehive said:


> ..............unless the smoke is from a short!
> 
> Just ordered this:
> http://www.hificollective.co.uk/wire/multistand-copper-wire.html
> to replace the twisted heater wire. It's 20awg, 600v, 105c, 14amp, whereas the stock is 22awg, 300v, 105c, so should be OK.



Woops, forgot to mention, 
For heater wires,
The most important thing is to get high temp insulation wires. ..

105C is not the most ideal, but 
Edit*
Looks like it should do..

I have not looked at the value of existing wires.
So good you did.


----------



## baronbeehive

*SMLD MODS:* *Fi*n*ished!* (as good as). Total time spent, about 3 weeks or 60 hours 
	

	
	
		
		

		
		
	


	




.
  
*Stage 5 - *Soldering: Caps, Wiring.
  
 4 wires reattached. (waiting for heater wires on order).
 Cathode bypass rifas resoldered.
  

  
 Just PSU caps to fit and wimas to fit when board goes back.
  

  
 It's all done except for the testing. I've decided to get my electronics guru to do the necessary because I'm a bit concerned about the 5 or 6 pads that have come off during soldering/desoldering. I don't think that will be a major problem but I'm not sure about fixing these. Also I noticed the traces are different on each side of the PCB so it's obviously a double sided board. I don't know if it's plated through but if the traces are different then both sides are doing different things so I think I need the pads on both sides.
  
 On the whole I'm reasonably happy with the way it went, and in answer to the question "can anyone do this?", I would say, yes, have a go. I knew nothing about it when I decided to give it a try. When I started I was determined to avoid booboos but as I've learned you cannot avoid having these, especially if you are new to soldering. Even if you are fairly expert I would still expect occasional blunders.
  
 The main thing is to think it through thoroughly and have the right tools. My booboos can be put down to poor tools mainly. My soldering iron made it more difficult than it should have been, and so I would say make sure about getting the right one for the job. Also I would advise getting the best desolderer you can, and if your finances stretch to an electric one, then get that. Poor desoldering will cause problems in future with poor joints and damage. And desoldering is quite difficult to do well, neither wire nor suckers are perfect. The really annoying part was trying to do something with gloves on and an antistatic wristband on, both of these always got in the way. I might as well have had one hand tied behind my back.
  
 Finally make sure you are familiar with page 1. Also you can follow my mods pages: 50, 53, 55, 57, 62, 65, 66, 68, 69, 70, 71, 72, which include pics. Also Mogos mods are here; 33-38, and SonicTrance here: 23, 43, including some great pics. And if you need any help just ask, we've all been through it here!


----------



## baronbeehive

I'm goint to spend the time now cleaning it up..... and gazing at it........ if I can't switch it on at least I can do that!
  
 No more wristbands, no more surgeons gloves, no more getting high on solder fumes.........yaaaaaayyyyyyyyyyyy!!!


----------



## baronbeehive

Stop Press:
  
 Heater wires in. I don't know what to do when I'm not soldering lol.


----------



## SonicTrance

baronbeehive said:


> *SMLD MODS:* *Fi*n*ished!* (as good as). Total time spent, about 3 weeks or 60 hours
> 
> 
> 
> ...


 
 Use your multimeter and measure a few things. You'll see that you'll get the same results if you measure from top side or component side of the board.
  
 Anyways, hope you'll get it done soon so you get to listen to it!


----------



## baronbeehive

sonictrance said:


> Use your multimeter and measure a few things. You'll see that you'll get the same results if you measure from top side or component side of the board.
> 
> Anyways, hope you'll get it done soon so you get to listen to it!


 
  
 Really, so why do the traces look different?
  
 So what am I testing for exactly? I get testing for continuity for the wiring, but what about the resistors and caps?


----------



## SonicTrance

Test between coupling cap and pin 1 (grid) on power tubes for example. Should be 300 ohms.


----------



## coinmaster

> Really, so why do the traces look different?


 
 Because the symmetry of the components on the PCB doesn't extend to the tracing. Either the designer designed the tracing manually or the software did some unsymmetrical routing when it was routing the output rails since they are on opposite sides of the same design for each channel.
  
 I was confused at first too but they are both the same.


----------



## baronbeehive

coinmaster said:


> Because the symmetry of the components on the PCB doesn't extend to the tracing. Either the designer designed the tracing manually or the software did some unsymmetrical routing when it was routing the output rails since they are on opposite sides of the same design for each channel.
> 
> I was confused at first too but they are both the same.


 
 Thanks. I know that boards can be designed with different traces top and bottom, and even sandwiched in the middle, so I wasn't sure. So I'll see what I can do re: testing, even if I get it done professionally. I'm a bit concerned about switching it on lol, but, hey at least I've got my other amp unlike you 
	

	
	
		
		

		
		
	


	




.


----------



## Maxx134

coinmaster said:


> ...or the software did some unsymmetrical routing



I am fairly certain that everything done was intentionally done and nothing was allowed by some "software".
You talking "Old school" Chinese designer.
Pretty sure today's software was unavailable when MK6 first came out.

I actually like how it is designed. 
Notice how the Anode resistors are on top,
And the Cathode resistors are on bottom?
Lots of little things that look very well placed for modding,
(to me.)

Edit:
Also, like the WCF caps on other front side of tube, apart from the other caps. 
All the stuff we need to update seems very logically placed. .


----------



## SonicTrance

Have any of you cleaned your board with Isopropyl alcohol? I went out and bought some yesterday and cleaned a little on the board using a q-tip. It was very effective at cleaning but dried sticky, so I didn't proceed. But after a few hours it wasn't sticky anymore.
  
 Just wondering if any of you have any experience with this stuff?


----------



## baronbeehive

sonictrance said:


> Have any of you cleaned your board with Isopropyl alcohol? I went out and bought some yesterday and cleaned a little on the board using a q-tip. It was very effective at cleaning but dried sticky, so I didn't proceed. But after a few hours it wasn't sticky anymore.
> 
> Just wondering if any of you have any experience with this stuff?


 
  
 I've been doing little else recently lol. It was recommended to me to do before you do any soldering to get grease etc off then again when you've done the soldering. It's good at removing flux residue as well which is probably why there is still grease on the board. Another go with isopropyl will probably get rid of that. The problem is the difficulty of cleaning between components, that's why I used a toothbrush and then ideally a cloth or sponge buds to polish it up, but as you say it should dry clean.
  
 I've also used it to remove solder residue etc from the chassis with a paint brush.
  
 I thought you had used it, your board and chassis looks so clean!
  
 See...... pretty clean 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

Haha, thanks Baron!
  
 I haven't used any cleaners in the past actually. I just removed small particles by hand or with q-tip. But thought I'd give this isopropyl a try. I'll have another go at it today and see what happens!
 It does clean extremely well though, the board looks brand new after one wipe with q-tip.


----------



## Maxx134

Haha I don't like to take risk to move anything so I only use Qtip, and if it doesn't come off, it stays! Lol.
I only bother looking for soldering particles which are conductive.
Don't move/bend things too much.
Retest after doing so to make sure you didn't break any soldering connections of create shorts by bending things together. .

If you don't have nothing to do like I did, 
You can focus on the visuals...
As you know, I have done excessive visuals, 
And some even more crazy crap not shown yet...


----------



## SonicTrance

I'm happy/done with my aesthetic modding. The only thing I'd like to do is to goldplate the rings around the tubes so they match my knobs and spikes, but it's a hassle since they are aluminium and not brass.
  
 Anyways, I had another go with the isopropyl and it did dry clean this time. I cleaned the entire top side of the board. It was mostly dust but the canned air did not remove it so this stuff is great.


----------



## Maxx134

baronbeehive said:


> See...... pretty clean  .



I am very impressed at this work..
Looking at your yellow output wiring, how nicley you twisted it, and applied a heatshrink to hold in place. ..
Very nice!


----------



## baronbeehive

maxx134 said:


> Haha I don't like to take risk to move anything so I only use Qtip, and if it doesn't come off, it stays! Lol.
> I only bother looking for soldering particles which are conductive.
> Don't move/bend things too much.
> Retest after doing so to make sure you didn't break any soldering connections of create shorts by bending things together. .
> ...


 
  
 Actually I don't mind bending my components, it's a good test of your soldering lol. Only 2 of my joints have come off and if that happens it's a bad joint anyway so it's as well to know. A good joint should not come unstuck because it's welded together effectively.
   
 Quote:


sonictrance said:


> I'm happy/done with my aesthetic modding. The only thing I'd like to do is to goldplate the rings around the tubes so they match my knobs and spikes, but it's a hassle since they are aluminium and not brass.
> 
> Anyways, I had another go with the isopropyl and it did dry clean this time. I cleaned the entire top side of the board. It was mostly dust but the canned air did not remove it so this stuff is great.


 
  
 That's the trouble, you can't remove the dust unless you clean it first because the dust gets attracted to all the grease and flux that's left. I quite enjoy cleaning it!
  
 Maxx, you're lucky you don't have any visible board left to clean 
	

	
	
		
		

		
		
	


	




.
  


maxx134 said:


> I am very impressed at this work..
> Looking at your yellow output wiring, how nicley you twisted it, and applied a heatshrink to hold in place. ..
> Very nice!


 
  
 I have to own up, the output wiring is the red. The yellow is the 4 runs of wire and they came already twisted, but thanks anyway 
	

	
	
		
		

		
		
	


	




. I've glued some of the heatshrink with silicon rubber glue to hold it in place where it's likely to touch bare wires. Also I'm going to tape the underside of the MCaps with teflon tape to reflect any heat back.


----------



## Maxx134

I would like to ask if anyone has had any amount of hum issue,
Even the smallest amount, even on the single ended output only, 
As I am now looking into this, 
And I have a strong suspicion of what is the cause...

Edit:
If anybody want to take a guess where I'm going to be testing it is encouraged to get U thinking. .


----------



## Mogos

I did have some problems with a hum. In first place it was connected with the new pot. In place of the pot I have installed the tantalum 1W resistors. After the recovery from the problems with transistors I had still small hum. One source of the problem was connected with the electrical powering of the system. I am using batteries as a source of the AC power (ON Line UPS). But not all my equipment was connected to one point. And also the PSU of the computer was somehow introducing hum to the system. I think all this was connected with incorrect grounding. I have changed the AC connections and moved some wires powering the transistors (by the way I have changed them for teflon insulated ones) away from the audio signal ground ones. All this chnages gave the total silence in the background (at least for the 35 ohm HEK headphones).


----------



## SonicTrance

mogos said:


> I did have some problems with a hum. In first place it was connected with the new pot. In place of the pot I have installed the tantalum 1W resistors. After the recovery from the problems with transistors I had still small hum. One source of the problem was connected with the electrical powering of the system. I am using batteries as a source of the AC power (ON Line UPS). But not all my equipment was connected to one point. And also the PSU of the computer was somehow introducing hum to the system. I think all this was connected with incorrect grounding. I have changed the AC connections and *moved some wires powering the transistors (by the way I have changed them for teflon insulated ones) away from the audio signal ground ones.* All this chnages gave the total silence in the background (at least for the 35 ohm HEK headphones).


 
 Did this actually make an audible difference? How did you route the transistor wires away from audio signal wires? The connections are very close.
  
  
 I only had hum on the SE output, which I've removed in favor for the Ra switch.


----------



## Mogos

Yes the conections are short but somehow the wires had runned very close to the ground ones. I just push them a side. I am not shure if it was connected directly with hum. I have done few things in one time. I have written about it as it could have connection witht he hum. After all I don't hear any kind of hum as I did before.


----------



## baronbeehive

I agree with Mogos, the only thing that could cause it would be PSU issues, assuming your other components are isolated and grounded and no feedback loops. My other amp has a SMPS power supply and I know that type is not prone to noise issues because any noise it produces is out of the range of human hearing. I have a lot of cables near to each other with having speakers and headphones and I have shielded speaker cables too just in case. But I haven't had any problems since I stopped using the SE output and like Mogos, and I believe SonicTrance, my headphones are sensitive.
  
 Obviously I haven't tried it out post mods...... I'm still trying to book it in for testing, so it could be a while 
	

	
	
		
		

		
		
	


	




.


----------



## Maxx134

mogos said:


> ...(at least for the 35 ohm HEK headphones).




I have same condition where the low impedance planar is not producing any hum, 
Where my HD800 reviels a tiny hum on left side, only audible at lowest and highest volume settings, 
And that is without any signal..
In the center of volume there is no hum or noise.
This I attribute to the balanced design.




sonictrance said:


> ...
> I only had hum on the SE output, which I've removed in favor for the Ra switch.



This is a condition that I read members had on the old "non-super" thread..

The thing is that it is not the PSU causing it.

It is the design reality issues.
The "ground" is actually a "center point" of the PSU, not a normal ground. 

There are 8 red caps which connect the power tubes to this "floating ground" & PSU.
Plus another by the PSU.

If any of these cheap *ss cap connections become bad, 
Guess what happens..


----------



## SonicTrance

maxx134 said:


> mogos said:
> 
> 
> > ...(at least for the 35 ohm HEK headphones).
> ...


 
 Would love to replace them with something more rugged. But there's no room for any more large caps, lol.


----------



## baronbeehive

sonictrance said:


> Would love to replace them with something more rugged. But there's no room for any more large caps, lol.


 
  
 You may have to brush up on your carpentry skills then lol.


----------



## Maxx134

sonictrance said:


> ...
> Would love to replace them with something more rugged. But there's no room for any more large caps, lol.




Hmm..


The tiny white mundorf mcap caps are actually quite optimally sized for the location,
And they are about triple the voltage rating..

So I now have an excuse to destroy a perfectly good, tiny red stock cap...
Oh, Did I mention I hate tiny red caps?


----------



## SonicTrance

You mean the 630v ,22uf mcaps? They might actually fit. They're 10mm in diameter and 23mm long. The wimas are 18mm long and about 7mm wide.


----------



## Maxx134

Well actually this is just an aesthetic change,
 because the objective for that capacitor is accomplish regardless.

 basically what I'm doing is for aesthetic & visual purposes for now,
 because I believe I have a poor solder connection in my existing red caps, which are fine otherwise.

 plus ypu kmow I don't like tiny little red caps! haha

On another topic I have noticed that many manufacturers in order to have a decent profit margin and understandably so...
So I have seen many expensive amps, 
which actually have incredibly cheap caps..

Although the caps they use are actually decent performers,
the bottom line is that they are incredibly poor, compared to what we are doing..


----------



## Maxx134

Edti


----------



## SonicTrance

Size difference:

  
 Installed:


----------



## coinmaster

maxx134 said:


> The "ground" is actually a "center point" of the PSU, not a normal ground.


 
 On the MK6 ground is earth ground.


----------



## Redge78

sonictrance said:


> Size difference:


 
  
 Not sure to understand, SonicT ... did you exchange the WIMA MKP10 for those Mundorf ?
  
 If yes, you should have considered yourself rather lucky in the first place, the MKP10 are the (almost) top of the line of the WIMA products, part of the "Pulse" line, far far above the nasty/cheap  polyester MKS4 that Maxx and I have on our MK8 boards ...


----------



## SonicTrance

redge78 said:


> sonictrance said:
> 
> 
> > Size difference:
> ...




Correct, I replaced them. All wima caps on my board has been MKP10 with varying tolerances 10% and 5%. But now there's none left! Maybe the MKS4 are nasty but the MKP10 are still cheap. They cost pennies. But I did not replace them to get better performance, only for fun.


----------



## Redge78

sonictrance said:


> Correct, I replaced them. All wima caps on my board has been MKP10 with varying tolerances 10% and 5%. But now there's none left! Maybe the MKS4 are nasty but the MKP10 are still cheap. They cost pennies. But I did not replace them to get better performance, only for fun.


 
 Yeah, we all know that .... Mundorf fanboy inside !


----------



## SonicTrance

redge78 said:


> sonictrance said:
> 
> 
> > Correct, I replaced them. All wima caps on my board has been MKP10 with varying tolerances 10% and 5%. But now there's none left! Maybe the MKS4 are nasty but the MKP10 are still cheap. They cost pennies. But I did not replace them to get better performance, only for fun.
> ...




Haha!

At least I changed my coupling caps from Mundorf to Jupiter. But it did hurt my soul a little.


----------



## coinmaster

How did you like the change from Mundorf to Jupiter?


----------



## SonicTrance

coinmaster said:


> How did you like the change from Mundorf to Jupiter?


 
 I feel the Jupiters are a cut above the Mundorf S/G/O's with more natural sound. As predicted, I lost some of the treble sparkle (which sometimes can sound artificial with the Mundorfs). I do still use Mundorf S/G/O's as WCF caps together with Jupiter as coupling. A very nice combo.
  
 Hopefully I'll get the amp up and running again soon. I'm still troubleshooting the damn thing. I've already replaced most psu parts, like filter caps, resistors and transistors....


----------



## coinmaster

What are you troubleshooting?


----------



## SonicTrance

I had a short before that caused one transistor (15020), zener diode and 2k7 resistor to burn. I've replaced transistors with new 15024G and 15025G, zeners with 100V 3w and 2k2 and 2k7 resistors with Mills 5w. Also replaced filter caps and white ceramic resistors. 

But amp's still not working. Symptoms are different now than before though. I get hum from transformer (short?) and meters show 20-30mA after second relay kicks in. They slowly climbed up to that value, instead of the normal overshoot. Before the meters were at zero and there was smoke coming from 2k7 and white ceramic resistors.


----------



## coinmaster

Do you have a multimeter? It's pretty easy to troubleshoot if u have it.
  
  
 Disconnect the power supply from the amp by disconnecting the .68ohm resistors.
 Then tell me the voltage measurements before and after Q1/Q2 and after R8/R11.


----------



## coinmaster

Hah, I just figured out the purpose of those .68ohm resistors after looking at one of my old diagrams. They are current sense resistors for the meters. Also figured out how the delay circuit works, it's just an RC filter with a huge time constant feeding a mosfet switch. 
 It's funny how all these things that were alien to me a few months ago make instant sense now.
 Now I just need to figure out the point of those 2k resistors. Grid leak resistors perhaps?


----------



## Maxx134

Yep,
We can shorten the delay if we wanted..

Hey coin, did you know your amp has .68 ohm resistors and my amp has capacitors?


----------



## coinmaster

> Hey coin, did you know your amp has .68 ohm resistors and my amp has capacitors?


 





 What do you mean? You can't measure current or pass DC with caps. Where are they located?


----------



## SonicTrance

Hey coin. Why the need to remove the .68 ohm resistors to take those measurements?


----------



## coinmaster

Because it's the easiest way to break the connection to the rest of the amp and you don't want the current draw from the amp contaminating the results. You don't have to completely remove them, just unsolder 1 leg.


----------



## coinmaster

I just realized the 2k resistor is actually to create a current through the NFB switch so there is a voltage drop. Looks like I put them in the wrong spot on my current schematic of the stage.
 Oh and by the way, you guys should probably upgrade those NFB resistors too (the 100k and 390k) since they are in the signal path and are directly linked to the amplifier linearity as a whole. 
 They are used for global negative feedback to cheat the amplifier into linearity since the output tubes are under-biased, probably to save money on the power supply since proper biasing would require a much more expensive one.
  
 The 100k and 390k resistors are configured in parallel to switch between 80k and 390k for high-low gain and high-low negative feedback.
 If you believe that resistors can affect the sound then these would possibly be the most important to upgrade since the effect of the feedback signal they carry is amplified through the entire amp.
 Also the 2k resistors should be upgraded too since any theoretical non-linearities would affect the degree that different frequencies are being shunted.
  
 Also I take back what I said about the .68ohm resistors being current sense resistors.
 The meters require current to run through them in order to get a reading, meaning the current sense "resistor" is integrated into the meter already.
  
 However if the current meters were the only path between the power supply and the amplifier then the .68ohm resistor would not be needed anyway.
 The resistor probably has a greater resistance than the meters themselves so the current would not flow through the resistor with the meter in path, so the only reason I can think of for the resistors presence is as a backup in case a meter breaks your amp can still function, which would make sense considering all the other redundancies the creator implemented into the amp.
  
 In this case removing the .68ohm resistor will not actually disconnect your amp SonicTrance. This would be a good time to find out, let me know if your meters still function after disconnecting the .68ohm resistors.


----------



## SonicTrance

Something is very wrong with my negative rail. I just fired the amp up, without changing anything, and took measurements from the transistors:
  
 15024:
 Collector: 134V
 Emitter: 107V
 Base: 106,7V
  
 15025:
 Collector: 1,5V
 Emitter: 1,5V
 Base: 0,0V
  
 Resistors and diodes measures good. Also tested the 15025 transistor before I fired up the amp and it also tested good. Although I don't have a transistor tester I tested the transistors using this guide:
 http://www.vetco.net/blog/?p=184
  
 I did buy extra transistors so I might as well try my spare MJ15025.


----------



## coinmaster

Not the best idea to fire up the amp with the power supply connected when you know it isn't working correctly, that is a recipe for more broken things.
  
 You probably fried the other transistor too. The transistors are the most fragile thing in the amplifier.
 Also if you are getting 1.5v on the collector and 0v on the base it means you either have a short near the diode or the diode is fried.
  
 Replace the transistor and the diode on the negative side.


----------



## SonicTrance

Well, we don't even know if we disconnect the psu by removing the ,68 ohm resistors. You said so yourself.
  
 The funny thing about this is that I initially only had problems with the positive rail. That's where stuff got burnt in the first place. But I changed parts on both rails anyway and now the negative rail is faulty with brand new parts...


----------



## coinmaster

> Well, we don't even know if we disconnect the psu by removing the ,68 ohm resistors. You said so yourself.


 
 I also said the meters carry the current. The meter wires are right next to the .68 resistors.
  


> The funny thing about this is that I initially only had problems with the positive rail. That's where stuff got burnt in the first place. But I changed parts on both rails anyway and now the negative rail is faulty with brand new parts...


 
 Current flows from negative to positive so anything you did to the positive side came through the negative side first, depending on what you did exactly.
  
  I didn't realize you replaced both sides already.
 The only way you are going to fix this is if you disconnect the amp otherwise you'll end up playing whack-a-mole with breaking components.
  
 Disconnect both .68 ohm resistors and both meters.
  
 Then measure the points I told you to measure earlier from the diagram but include the diodes as well.


----------



## SonicTrance

coinmaster said:


> > Well, we don't even know if we disconnect the psu by removing the ,68 ohm resistors. You said so yourself.
> 
> 
> 
> ...


 
 Yes, the meters are actually connected to the .68 ohm resistors from underneath.
  
 I can disconnect resistors and meters and take measurements. What exactly do you mean by "Then tell me the voltage measurements before and after Q1/Q2 and after R8/R11."
  
 Where do I take the measurements?


----------



## coinmaster

> Where do I take the measurements?


 
 Basically on the base/collector/emitters and the other side of the 5k1/8k2 resistors. But only after you disconnect the amp from the power supply.


----------



## SonicTrance

coinmaster said:


> > Where do I take the measurements?
> 
> 
> 
> Basically on the base/collector/emitters and the other side of the 5k1/8k2 resistors. But only after you disconnect the amp from the power supply.


 
 I took the .68 ohm resistors out and disconnected the meters, but only from those two points, I left the meters connected to the other two points.
  
 These are the measurements:
  
 MJ15024:
  
 Collector: 144,7V
 Emitter: 109,4V
 Base: 110,2V
 Diode: 110V
  
 MJ15025:
  
 Collector: 0,4V
 Emitter: 0,7V
 Base: 0,4V
 Diode: 0,39V
  
 I've circled the different points below.
  
 Yellow, +15V: 3,5V
 Red, other side of same resistors: 110V
  
 Green, -36V: 0,75V 
  
 Also measured the AC points on the board:
  
 Black, 15Vac: 14,45Vac
  
 Orange, 230Vac: 108Vac
  
 Brown, 170Vac: 80Vac

  
 You could hear the second relay kick in and both meters lit up, but stayed at zero obviously since disconnected. No hum from transformers, dead quiet.
  
 A little strange that I got 10 more volts on the 15024 collector after disconnecting the resistors and meters? Anyway, that seems to be the least of my troubles...


----------



## Maxx134

You need to make sure the transformer wiring to board is correct and the bridge rectifier on left side is not damaged.

The new heavier diode and transistors should not have instantly died/fried.

Something else is dead now because the previous transformer hum you had is gone.

At least the transformer is not being drained.

Disconnecting the .68ohm resistors was a waste of time,
 compared to what I suggested yesterday,
 about your bridge rectifier being possible damaged.
And swapping would have determined what next to check.

Also disconnecting the 4 PSU power resistors after the first Lyctics,
like I said would have determined similarly, 
if the cause is the bridge,
Or further down where your transistor/diodes are.

Coinmaster had a point to disconnect the PSU stage from the amp, 
As we don't know if the cause was one of your 4 power tube sections having a short in it,
But that is extremely unlikely. 

Edit:
I would also make sure the heater wiring to the power tubes is not accidentally touching other pins. .


----------



## SonicTrance

maxx134 said:


> You need to make sure the transformer wiring to board is correct and the bridge rectifier on left side is not damaged.
> 
> The new heavier diode and transistors should not have instantly died/fried.
> 
> ...


 
 I've not changed the wiring from transformers to board since I got the amp, so shouldn't be any problems there. I'll swap the bridges tomorrow and see if it makes a difference.
  
 The hum only disappeared after removing the .68 ohm resistors and disconnecting meters. I'm sure it'll come back when I connect them again. To be honest, I'm not sure if I'm confusing hum with normal operation though. It wasn't loud, but after taking the resistors out it's dead quiet. So I don't know...
  
 I've checked heater wires but will check again, tomorrow.


----------



## Maxx134

Are you talking about Transformer buzz hum?
Or output sound hum?


----------



## SonicTrance

Definitely not a buzzing sound. More like a low tone hum, and you had to have your ear pretty close to the transformer to hear it. The more I think about it, the more I think it was just normal operation. But why would it be dead quiet after disconnecting psu from amp?


----------



## Maxx134

My amp does not have same type coupling, as there are caps in the places you have your .68ohm resistors ..

Also,

I just checked my amp and yes it has a very very low level hum in operation. 
I had to actually put my ear right on the transformer cover,
And switch on and off,
 to actually hear it..


----------



## coinmaster

> A little strange that I got 10 more volts on the 15024 collector after disconnecting the resistors and meters?


 
 That's one of the reasons I told you to disconnect the power supply because current draw contaminates the results, and because if you don't troubleshoot in sections you risk breaking things as you fix other things.
 Keep the power supply disconnected until you fix the issue.
  


> The hum only disappeared after removing the .68 ohm resistors and disconnecting meters


 
 Unusual hum means you are stressing the transformer, if it is not the normal humming sound it will go away when you fix it.
  
 The first problem you have is that you are not getting any voltage on the collector which is fed directly by the rectifier.
  
 You either have something shorted, something open, or a damaged rectifier on the negative side.
  
 Follow the line from the rectifier to the collector and find out where the voltage stops because you should have -144v or something on the collector.


----------



## SonicTrance

What about the messed up VAC readings?


----------



## coinmaster

Oh right, I misread what you said.
  
 Yeah, those are concerning, plus the 15v zener should be showing 15v since your positive side is working.
  
 The input stage supply is messed up as well which means you messed up something big somewhere.
  
 I'd be surprised if you broke the transformer since I've abused the crap out of mine and it's still fine.
  
 For now you should start by doing what I said to do earlier and find out where the voltage stops on the negative rail.


----------



## SonicTrance

I'll take the bridge rectifier from driver stage and try it in the power stage tomorrow, as Maxx suggested. All parts between rectifier and collector are brand new and not shorted. Has to be the bridge.


----------



## coinmaster

No sense in doing all of that before you test it first. It's a simple matter to find out if the rectifier is the issue by using a multimeter on the rectifier output.


----------



## SonicTrance

coinmaster said:


> Oh right, I misread what you said.
> 
> Yeah, those are concerning, plus the 15v zener should be showing 15v since your positive side is working.
> 
> ...


 
 I did not measure at the 15V diode, I measured at the resistor legs, but should read the same?


----------



## coinmaster

Yeah, the resistor leg should be +15v via the zener voltage. One of the many weird things about your situation, unless the diode is simply broken, but that's not important yet and is another reason I told you to disconnect the amp from the power supply, you don't want the opamps to be non-functional. In fact, you should take the opamps out of their sockets for now since the zeners may not be functioning properly and the opamps are expensive to replace.
 Trust me on this, I've troubleshooted my MK6 endless times and I've build several MK6s from scratch. The only thing I've replaced more than transistors is opamps.
  
 In situations like this you just need to start with the problem closest to the source voltage, which is that there is no voltage on the collector. 
 A broken rectifier would not give you the voltage readins you have, so before you go changing out rectifiers make sure your rectifier is actually not showing any voltage on the output first. But I suspect you have some sort of short somewhere.


----------



## SonicTrance

Ok, I'll measure the negative pin on the rectifier first.


----------



## SonicTrance

I fired it up once more and took measurements from the bridge rectifier.
  
 Positive pin: 150V
 Negative pin: -104V
  
 Then straight after the first filter caps on the resistor legs I've circled in red below, ALL voltage is gone. I get 0,4V reading there.
 Positive rail circled in yellow is staying at 150V.


----------



## coinmaster

Did you measure the resistor leg itself or the solder point?
 If the leg itself is not showing voltage then it's just a cold joint.
  
 Resolder it and make sure the solder flows before letting it cool.


----------



## SonicTrance

Hard to say if I managed to center the probe on the leg or solder, but I've soldered those resistors from both sides. Highly doubt it's a cold joint.
  
 This joint don't look to happy but it's fine on the other side and the rest looks good.


----------



## coinmaster

You need to make sure you measure on the leg and not the solder joint.


----------



## SonicTrance

To do that I'd need to test with board out. Not sure I wanna do that. I always test with board in place.


----------



## coinmaster

It's not like you have a choice since it's the source area of your problem and even when not cold, solder joints don't always respond well to multimeter probes, you need to measure the leg.


----------



## SonicTrance

I can measure resistance from those solder joints very easily. Why would measuring volts be any different?
  
 Here's another fun fact:
  
 The bridge rectifier for driver stage is measuring 224V on positive pin and 0,00V on negative pin.


----------



## coinmaster

> I can measure resistance from those solder joints very easily. Why would measuring volts be any different?


 
 If you're measuring 100ohm resistance then the joint is probably fine but it doesn't change the fact that you still have to take the board out and check the other side.

  


> The bridge rectifier for driver stage is measuring 224V on positive pin and 0,00V on negative pin.


 
 That's normal. The negative pin is grounded.


----------



## SonicTrance

Actually, I measure 50 ohms since those resistors are pairs in parallel.
  
 Good to know about the bridge!


----------



## Maxx134

coinmaster said:


> No sense in doing all of that before you test it first. It's a simple matter to find out if the rectifier is the issue by using a multimeter on the rectifier output.




Hey coin,
like to know if you have a schematic of the relay before the bridge.
Since Sonic is reading voltage before the relay kicks in,
 my suspicions leading me there.


----------



## coinmaster

If he was reading the voltage before the relay kicked in there wouldn't be much voltage on the rectifier on either side because the relay feeds the rectifier. He is getting full voltage on both sides after the rectifier.
 He says the the voltage stops after the first filter cap on the negative side so there's probably something going on with his soldering or something is touching something underneath that shouldn't be.
 Although voltage doesn't just stop halfway through a conductor so it's probably a soldering issue, possibly on the capacitor joint.


----------



## Maxx134

Judging from his past work,
He is too meticulous to have connection errors..

Also,
He also read too much voltage before the relay kicked in :

-104v on the negative rectifier pin 

Which disappears after the relay kicks in.

Nothing should not be leaking thru before relay kicks in.

This leads me to believe the error lies around the relay and the rectifier.


----------



## Maxx134

coinmaster said:


> ...probably a soldering issue, possibly on the capacitor joint.



But the cap joint is not an issue if was no solder,
as the board trace doesn't rely on it.

If the cap was bad and shorting, the transformer would still buzz and the cap would be hot.


----------



## coinmaster

> -104v on the negative rectifier pin
> 
> Which disappears after the relay kicks in.


 
 Where did he say this?
  


> Nothing should not be leaking thru before relay kicks in.


 
 The 15k resistors on the relay are bypass resistors. There will be voltage leaking through when the relay is not open, just not 254v worth.
 He said he is getting 150v on the + and 104 on the -, which is 254v rectified voltage which sounds about right.
  
 The simple fact is that except for the opamp zener supply, the entire positive rail is fine, but the negative rail voltage stops just after the first filter cap, which is half way through a copper conductor.
  
 Logic says there's something cutting off the conduction there.
 A problem in the relay isn't going to magically halt the voltage halfway through a conductor in a later part of the circuit.
 It's possible he ripped the copper lead off the board when pulling out the old capacitors.


----------



## Maxx134

Unfortunately we won't know the answer untill later when he checks.

For all I know he could be getting AC instead of rectified DC..
This is where an Oscilloscope is priceless.


----------



## coinmaster

If it was AC he wouldn't be getting 254v since the AC is 230v before rectification. The multimeter would only show filtered AC if set to AC measurement.


----------



## Maxx134

Herr is a Sonic post that makes me curious :

*Quote :
The -104v on the negative rectifier pin is there instantly when amp power on and stays same after second relay kicks in. The positive 150v only shows after second relay. I get about 22v on positive pin before the relay kicks in.*

Although my amp is not MK6 so I wondering if yours does the same.

Edit :
If this is how yours also functioned, then I would have to agree on your previous assumption of the pad on the cap is broken from the board trace to the rest of PSU.


----------



## coinmaster

That is weird. The positive rail is functioning as it should but it sounds like the negative rail relay is welded to the on position from overcurrent.
  
 If this is true then it's not the cause but an addition to the problem of no voltage on the negative rail since you can't cut off voltage in a conductor.
  
 He must have done something really nasty if he welded the relay, I'm surprised the fuse didn't blow first.


----------



## Maxx134

Coin,

I am not clear on the trace from your 0.68ohm resistors as my amp doesn't have this..
Do you have them in your schematic?


----------



## coinmaster

Only in my old unreadable ones.
  
 They are big black resistors, one in the center of the amp, one at the bottom.
  
 They extend from the positive power supply, 1 for each channel bypassed by the meters.
 Given that the power supply current must flow through the meters in order for the meters to get a reading and that the resistors resistance is probably a higher than the meter I can only assume the resistor is there in case a meter breaks the current can still flow.
  
 Do you know where your "extra capacitors" lead to?


----------



## Maxx134

They are in the exact same locations of your r
.68ohm resistors. .


And 



I will check the trace again next time I open for next mod.


----------



## SonicTrance

_*GOOD NEWS!!!*_
  
 My amp is up and running again!
 There was a bad connection between rectifier bridge and filter cap. I tried to re-solder the cap but no difference. So I connected a wire underneath instead:

  
 Without the .68 ohm resistors and meters connected I fired the amp up and after second relay kicked the four 2K resistors by the gain switches started to smoke!

  
 I connected the .68 ohm resistors (I used new Mills resistors) and connected meters. NO frickin SMOKE!! 
  
 Meters show about 60mA,as they should with 6AS7's and had the normal overshoot after second relay kicked.
  
 Totally different volt measurements as well with everything in place!!
  
 Bridge rectifier.
  
 Before relay kicked:
 +4V
 -4V
  
 After relay kicked:
 +132V
 -132V
  
 MJ15024
  
 Collector: 118,5V
 Emitter: 102,1V
 Base: 102,8
  
 MJ15025
  
 Collector: -116,4
 Emitter: -103,3
 Base: -103,9
  
 +15V diode: 15,7V
  
 -36V diode: -39,5V (a little high, I'm replacing this diode)
  
*I'd definitely not recommend anyone to remove those .68 ohm resistors and power on amp, unless they want burnt resistors!!*
  
 I tested for music today and it's all good! No hum or anything nasty! I have to replace those 2K resistors though, no more listening until I do.


----------



## baronbeehive

sonictrance said:


> _*GOOD NEWS!!!*_
> 
> My amp is up and running again!
> There was a bad connection between rectifier bridge and filter cap. I tried to re-solder the cap but no difference. So I connected a wire underneath instead:
> ...


 
  
 Great news Sonic! Just returned from my house move and didn't realize what was going on.
  
 So was the poor connection you mentioned something that you did previously in the mods or what? How did that problem happen?


----------



## Maxx134

There is a board trace on top board, which runs under the cap so the breaks not visible.

I am assuming as Coinmaster says, that circular pad broke when pulling out the cap.

Soldering from the bottom board does nothing because the trace is in the top..

Every part I ever took out,
I soldered on both sides to be sure.

The replaced components are much more rugged because they don't make those power transistors anymore. 
It has been updated by same company with much more powerful ones.

SonicTrance zener diodes are also much higher wattage rating as well.


----------



## baronbeehive

maxx134 said:


> There is a board trace on top board, which runs under the cap so the breaks not visible.
> 
> I am assuming as Coinmaster says, that circular pad broke when pulling out the cap.
> 
> ................


 
  
 Which cap, why would SonicTrance have pulled it out if it wasn't part of the mods?


----------



## SonicTrance

baronbeehive said:


> maxx134 said:
> 
> 
> > There is a board trace on top board, which runs under the cap so the breaks not visible.
> ...


 
 Hi Baron!
  
 As you know, I had a short in my amp. It started with a burnt anode resistor leading to the switch, then a short while switching.
  
 It turns out that the positive rail took the hit. With a broken transistor, zener diode and resistor. Even though only the positive rail was faulty I changed most psu parts on both rails, including the filter caps. When I pulled out one of the old filter caps I must have broken the internal connection on the board somehow. The solder pads were fine and after removing the cap I tested the trace (which goes under the cap) and it worked fine, but it didn't work from the other side of board (where you solder), hence the wire connection.
  
 Here it is, right after the bridge rectifier:


----------



## baronbeehive

sonictrance said:


> Hi Baron!
> 
> As you know, I had a short in my amp. It started with a burnt anode resistor leading to the switch, then a short while switching.
> 
> ...


 
 That's pretty weird, my problem pads all came from pulling out from the other side to the solder joint, except for one new component which I put in with the leg at a slight angle which caught the edge of the pad. But maybe the you damaged it without any obvious problem, could be a small tear in the covering. That goes to show how careful we should be given that the amps have gone well for years from the factory so the quality is there in the components.
  
 Good to know everythings fine with the help of the other guys.
  
 I think I'm right to put off the big switch on until I've had mine tested properly, still trying to book it in though 
	

	
	
		
		

		
			





.


----------



## Mogos

Sonic I knew you could do it 
	

	
	
		
		

		
		
	


	




.
 Guys it is time to add to the official instruction a recomendation to change the transistors in the mkvi. I am not a specialist but it looks like there is a demand for more current from the super moding parts.


----------



## baronbeehive

mogos said:


> Sonic I knew you could do it
> 
> 
> 
> ...


 
  
 I was wondering about this too, but Maxx and Redge haven't had problems as far as I know?
  
 It will be interesting to see what happens to mine when it's up and running!


----------



## SonicTrance

mogos said:


> Sonic I knew you could do it
> 
> 
> 
> ...


 
 Thanks Mogos!
  
 I was almost ready to give up a few times, but like Maxx and Redge told me, it's been a fast learning period! I have a much greater understanding of how the psu works now.
  
 In hindsight there was only three components that I HAD to change. One transistor and the zener and resistor below it. But I ended up changing, well, a lot more, lol. I don't regret that though, as my amp now have much tougher components in psu area.
  
 It feels so good to listen to my amp again, lol 
	

	
	
		
		

		
		
	


	



 Though, I've not installed the switch again. I just don't trust it. I've measured it countless times for shorts and there's nothing, but still don't trust it, lol.
 I think I'm going to rewire the switch from scratch and then install it again.


----------



## baronbeehive

Sounds like you're just a little bit paranoid about that switch lol.
  
 I wish I was confident enough to test mine myself but I feel better having it done by a professional, I would be starting from a knowledge base of zero! I will try to find out from him what he thinks about those transistors etc., he is a well qualified expert/teacher and has built his own valve amp. I would like to involve him but I think he is too busy for that. That's why I'm having to wait to book it in.


----------



## SonicTrance

baronbeehive said:


> Sounds like you're just a little bit paranoid about that switch lol.
> 
> I wish I was confident enough to test mine myself but I feel better having it done by a professional, I would be starting from a knowledge base of zero! I will try to find out from him what he thinks about those transistors etc., he is a well qualified expert/teacher and has built his own valve amp. I would like to involve him but I think he is too busy for that. That's why I'm having to wait to book it in.


 
 Probably a little paranoid, yes! 
	

	
	
		
		

		
		
	


	




 But I'm still re-wiring it. It took me one month to troubleshoot and fix the amp and I'm not letting the switch ruin it, lol.
  
 That sounds like the perfect guy to go over your amp!


----------



## Maxx134

The pad on either side of the cap most likely* WAS NOT DAMAGED * in any way...!!!

Sonic did nothing wrong except being too ambitious. .

In taking the cap out,.there is simply* NO WAY* to solder that cap from the top component side,
Which is where the board trace is(!),
which leads to the rest of the PSU...

Soldering from the bottom side only *edit*
Is not enough.


----------



## Maxx134

baronbeehive said:


> Sounds like you're just a little bit paranoid about that switch lol.
> 
> I wish I was confident enough to test mine myself but I feel better having it done by a professional, I would be starting from a knowledge base of zero! I will try to find out from him what he thinks about those transistors etc., he is a well qualified expert/teacher and has built his own valve amp. I would like to involve him but I think he is too busy for that. That's why I'm having to wait to book it in.



Simply put, the transistors are outdated, 
Yet fully capable under normal conditions. 

But yes, a short problem will likely cause this area to go first.

Yet the PSU design was already stated by a top tube designer, to be a "highly musical" design.

Probably due to how it uses the caps and transistors.


----------



## SonicTrance

maxx134 said:


> The pad on either side of the cap most likely* WAS NOT DAMAGED * in any way...!!!
> 
> Sonic did nothing wrong except being too ambitious. .
> 
> ...


 
 Yes, no damage to pads!
  
 I guess the connection "pad" on the cap has to make contact with pad on the board:
  

 Mine clearly didn't, even after two attempts. Works just as well with the direct wire connection underneath anyway.


----------



## Bruch

Stupid question alert!
  
 I'm paranoid about damaging the board.
  
 Therefore what would be the effect of piggy-backing the new caps onto the existing caps - soldering new legs onto existing legs? I figure that there is much less chance of causing any irreparable damage or shorts this way.
  
 Also ... could I crush the WIMA driver-stage decoupling caps in the way that Baron did and use those legs as the termination points for new caps?


----------



## coinmaster

Sorry I've been busy and my email hasn't been updating me on new posts.
  


> Without the .68 ohm resistors and meters connected I fired the amp up and after second relay kicked the four 2K resistors by the gain switches started to smoke!


 
 This is because the opamps were driving your grids positive which is why I told you to take the opamps out while doing this. You could have destroyed your tube or a few other things. The 2k resistors were acting as plate resistors with the grid being a pseudo anode.
 Check the 2k resistors and make sure they still measure 2k. They will have an effect on how your amp sounds.
  


> -36V diode: -39,5V (a little high, I'm replacing this diode)


 
 Don't expect it to help much, I've tried 1% vishay diodes and a few others and it still goes that high. I'm not quite sure why.
 In either case you're still within the operating range of the opamp and the trimmer takes some of it off anyway.
  


> They are in the exact same locations of your r
> .68ohm resistors. .


 


 Are you sure those aren't really weird resistors or ferrite beads?
  


> Stupid question alert!
> 
> I'm paranoid about damaging the board.
> 
> ...


 
 What caps are we talking about?
 If you aren't careful you can cause oscillation from the wire inductance by stacking caps. It's pretty difficult to damage the board unless you are rough with it, personally I would just solder them out, as long as you aren't taking things out like the PSU caps there's not a lot of risk of board damage. If yo want to take the lazy approach you can stack the caps but don't blame me if they ring


----------



## baronbeehive

bruch said:


> Stupid question alert!
> 
> I'm paranoid about damaging the board.
> 
> ...


 
  
 Yes, this was my worry, but you won't get anwhere if you worry about it too much. If your soldering iron is good you should be able to get a good solder melt with a max dwell time of 2-3 seconds and providing the solder melts the component should come out no problem. My iron wasn't really up to the job and so I probably overheated some components which caused my problem.
  
 Next time I really mean to get a continuous vacuum desolderer. If you watch a video of this it really makes light work of desoldering, and you don't need that 3rd hand I mentioned lol. This video is definately recommended: https://www.youtube.com/watch?v=h_RiRL-flgs
  
 You can reuse the legs, or new wire but it's tricky and much better to put the new component in the proper place by itself.


----------



## SonicTrance

coinmaster said:


> Sorry I've been busy and my email hasn't been updating me on new posts.
> 
> 
> 
> ...


 
 If you knew that was going to happen you should have said so from the beginning. This is what you wrote: *"In fact, you should take the opamps out of their sockets for now since the zeners may not be functioning properly and the opamps are expensive to replace"* I took that as a recommendation, not a necessity. 
  
 I think when you give advice in a thread like this you need to be very clear and write all facts. If not, then clearly state that you're not sure what's going to happen. I get that it's mostly trial and error for all of us, but when advice are given it should be clear. My 2 cent.
  
 Anyway, I've already replaced the 2K's and the amp is working fine. And yes, you're right about the 36v zener. I've replaced it but that didn't change much. It now reads about 38,5v. Still close enough I think.


----------



## coinmaster

> Quote: If you knew that was going to happen you should have said so from the beginning. This is what you wrote: *"In fact, you should take the opamps out of their sockets for now since the zeners may not be functioning properly and the opamps are expensive to replace"* I took that as a recommendation, not a necessity.


 
  

 I then spent a paragraph explaining to you how you should really listen to me and take them out.
 Sure I didn't go into all the possible reasons of why but I didn't think I really had to since I told you the opamps themselves could be destroyed. At the very least you were willing to risk destroying $60 in opamps so don't look at me if you decided not to listen.
 I'll admit that I forgot to tell you sooner, It slipped my mind, I haven't dealt with troubleshooting a stock MK6 since mogos was having his issues.


----------



## SonicTrance

Destroyed caused of malfunctioning zeners you said, and as I tested the diodes and they were fine I didn't take the opamps out. But hey, no real harm done anyway as opamps are good! Only had to replace the 2K's.
  
  
 So, let me ask you this coin;
  
 What do you think about biasing the 5998/421A's with half of stock cathode resistor value? 165 ohms.
  
 I've measured the cathode voltage using 6AS7's and 421A's and the voltage is about half using 421A's. I get about 21v over the cathode resistor using 6AS7 and 11v using 421A's. Meters show 60mA with 6AS7 and 30-32mA with 421A.
  
 So, would the lower 165 ohms double the current on the 421A? Which would make for much better sound and power as the tubes are more properly biased? Would the opamps take damage? Or maybe compensate the loss of cathode resistance? Would the cathode voltage possibly half as well?
  
 Tell me your thoughts please.


----------



## baronbeehive

sonictrance said:


> If you knew that was going to happen you should have said so from the beginning. This is what you wrote: *"In fact, you should take the opamps out of their sockets for now since the zeners may not be functioning properly and the opamps are expensive to replace"* I took that as a recommendation, not a necessity.
> 
> I think when you give advice in a thread like this you need to be very clear and write all facts. If not, then clearly state that you're not sure what's going to happen. I get that it's mostly trial and error for all of us, but when advice are given it should be clear. My 2 cent.
> 
> Anyway, I've already replaced the 2K's and the amp is working fine. And yes, you're right about the 36v zener. I've replaced it but that didn't change much. It now reads about 38,5v. Still close enough I think.


 
  
 My 2 penny worth, I agree that the advice must be clear and unambiguous. That's why I'm holding fire with my amp and waiting to get it tested properly. It's too risky to go ahead and switch on when I know there are one or two problems. I may be overly cautious but there is so much we don't know here.
  
 That's not to say I'm not grateful for the advice, thanks guys!
  
 BTW Bruch keep us posted on your progress, and good luck!


----------



## coinmaster

> What do you think about biasing the 5998/421A's with half of stock cathode resistor value? 165 ohms.
> 
> I've measured the cathode voltage using 6AS7's and 421A's and the voltage is about half using 421A's. I get about 21v over the cathode resistor using 6AS7 and 11v using 421A's. Meters show 60mA with 6AS7 and 30-32mA with 421A.
> 
> So, would the lower 165 ohms double the current on the 421A? Which would make for much better sound and power as the tubes are more properly biased? Would the opamps take damage? Or maybe compensate the loss of cathode resistance? Would the cathode voltage possibly half as well?


 
 I'm not sure what you mean by "21v over" What are the exact voltages?
  


> My 2 penny worth, I agree that the advice must be clear and unambiguous.


 
 Yeah I'll take the hit for that, I should have been more clear. It's been awhile since I've had to deal with MK6 troubleshooting from the PCB.
 Disconnecting the opamps should always be a priority on the mk6 since they break easily and can cause all sorts of trouble when the amp isn't functioning properly.
  


> That's why I'm holding fire with my amp and waiting to get it tested properly. It's too risky to go ahead and switch on when I know there are one or two problems. I may be overly cautious but there is so much we don't know here.


 
  
 It's really not as bad as all that. Disconnect the .68ohm resistor, the meters and take the opamps out and there's no way you can break anything. Once you know the power supply is working then you connect it again and measure the power supply voltages at all of the key points.
 If it measures wrong after you reconnected it disconnect the power supply again and measure the key points again.
  
 After that, if it measures wrong then it's probably opamp or wiring related.
 If it measures good it's probably still opamp or wiring related but at least you know it's not that bad.
  
 Use a continuity test on pin 3 and 4 of the opamp and make sure they aren't shorted.
 Check wiring, if nothing burned up it probably wasn't a short.
  
 The good news is once you have the power supply working properly there isn't really much that can go wrong other than wiring or a broken opamp unless you have the wrong wiring with the transformer cables but that's an easy fix.
  
 If you are really paranoid you can connect a 100ma fuse somewhere along the line in the negative supply, between the emitter and 300uf cap is probably a good place. This will prevent things from burning up.
  
 Tell me what you did to the amp and what the symptoms are.


----------



## SonicTrance

coinmaster said:


> > What do you think about biasing the 5998/421A's with half of stock cathode resistor value? 165 ohms.
> >
> > I've measured the cathode voltage using 6AS7's and 421A's and the voltage is about half using 421A's. I get about 21v over the cathode resistor using 6AS7 and 11v using 421A's. Meters show 60mA with 6AS7 and 30-32mA with 421A.
> >
> ...


 
 Ok, maybe it's me who's not clear this time.
  
 I've measured the voltage across or "over" the cathode resistors.
  
 I took the measurements from component side ie across the cathode bypass caps:
  

  
 6AS7G - 21,2V
  
 421A: 11,2V


----------



## Bruch

"_If you aren't careful you can cause oscillation from the wire inductance by stacking caps. It's pretty difficult to damage the board unless you are rough with it, personally I would just solder them out, as long as you aren't taking things out like the PSU caps there's not a lot of risk of board damage. If yo want to take the lazy approach you can stack the caps but don't blame me if they ring _"
  
  
 I presume that any oscillation ringing would be apparent when the amp is switched on but without any music? So if I try and there is no ringing then it's good to go, right? If there is ringing then I can try again.
  
 It's not so much an issue of being lazy as a fear of destroying a perfectly good amp through cack-handed use of a soldering iron.


----------



## coinmaster

> 6AS7G - 21,2V
> 
> 421A: 11,2V


 
  
  
 Oh so you're measuring voltage drop then. 11vdrop @ 30ma would probably put the cathode in the high 80s for the 421a and 21v@60ma puts the 6as7 in the high 70s.
 Measure with the black lead on ground this time and let me know if that's right.
 Just stick it in one of the big metal holes between the PS caps.
 The 421a can benefit from hanging out at a higher bias than 30ma.
 80v @ 60ma is where you want to be on the load line.
 Check the plate and cathode voltages with the black multimeter lead on ground this time and tell me what the voltages are.
  
  
  


> I presume that any oscillation ringing would be apparent when the amp is switched on but without any music? So if I try and there is no ringing then it's good to go, right? If there is ringing then I can try again.
> 
> It's not so much an issue of being lazy as a fear of destroying a perfectly good amp through cack-handed use of a soldering iron.


 
 You could hear it, or it could just be silently killing your amp and you'd need an oscilloscope to know.
 I don't have any experience with oscillating parts so I don't know too much about it.
 As for ruining the board, it's pretty tough, I ripped it out with a screwdriver in the socket holes when I wanted to get it out or put it back in.
 Getting it out and in is by far the most annoying and tedious part.
 Don't worry about the soldering iron you can't really ruining anything with it.


----------



## SonicTrance

coinmaster said:


> > 6AS7G - 21,2V
> >
> > 421A: 11,2V
> 
> ...


 
 Yes, voltage drop. Correct.
 I'll try to take those measurements next time I open the amp. Thing is my de-coupling caps are right above the powertube sockets, so not easy to get to without removing the caps. Though I guess I can just measure from the cathode and plate resistors instead.
  
 The plan is to add 330 ohm resistors in parallel to existing cathode resistors. Then to a switch so I can still use 6AS7G's.


----------



## coinmaster

Actually as I look closer at the load line it seems 90v@60ma is where you want to be, which is 166 ohms, so yeah 165 ohms should be fine.
 Let me know how it sounds, my upcoming amp will have complete real-time load line adjustment for tone shaping so I'm curious to know if my efforts are worth it.


----------



## SonicTrance

Yeah, 1 ohm in either direction is definitely within tolerance anyway.
  
 So, you think it should be straight forward and the only thing that would change is the cathode/plate current? No opamp trouble you think?


----------



## coinmaster

You would want to have the same value resistor on the plate as well. Other than that the -10 bias voltage is well within the opamps capability so you should be fine.


----------



## SonicTrance

coinmaster said:


> *You would want to have the same value resistor on the plate as well.* Other than that the -10 bias voltage is well within the opamps capability so you should be fine.


 
 Hm, that is going to be a problem. Since there's also a anode switch in place (not at the moment, but it will be again) to balance the WCF to different loads, and that mod was substantial.
  
 Why would I need same value plate resistor for this to work? 
 I mean, the tubes are cathode biased, correct?


----------



## SonicTrance

I can also add that the tube current, ie the meters, did not change in value with different anode resistor values. 
  
 I used a 5 position switch which gives you these anode resistor values:
  
 -330 ohm (stock)
 -220 ohm
 -77 ohm
 -111 ohm
 -187 ohm


----------



## coinmaster

> Hm, that is going to be a problem. Since there's also a anode switch in place (not at the moment, but it will be again) to balance the WCF to different loads, and that mod was substantial.


 
 The impedance mod essentially just alters the load line of the top triode which is sort of the same thing. I'd try it both ways and see how it sounds. Either way you would have to use an "impedance mod" resistor based on the specs of the 421a and not the 6as7.


> Why would I need same value plate resistor for this to work?
> I mean, the tubes are cathode biased, correct?


 
 The white cathode follower is basically two triodes handling two halves of the signal.
 They both need to be biased the same for the most linear result. This is what the impedance mod attempts to do at certain frequencies although have my suspicions about it. I don't think the equations for the impedance mod take into account the opamp biasing we use. I suspect the change in sound simply due to a change in load line, similar to mixing tubes which can also make a huge improvement with the right combo even though they have different load line linearities..
  
 The point between both tubes is 0v but they are both run at the same potentials. For example if you used 165 ohm resistors on the cathode and the anode they would both be running at 90v because their cathodes/anodes would be 90v apart from eachother.
 But if you left the 330ohm resistor on the plate it would throw off the balance and they would both handle the signal differently creating distortion, which could be a good thing or a bad thing.
  
   


> can also add that the tube current, ie the meters, did not change in value with different anode resistor values.
> 
> I used a 5 position switch which gives you these anode resistor values:
> 
> ...


 
  
 The opamp tries to keep the bias of both triodes the same so it might be that it actually isn't changing current. A drop from 330 ohms to 220 ohms would result in an increase in current which the opamp would then apply a more negative bias to counteract it. The only way you end up with 0v on the output of the amp is when there is an equal impedance between B+ and B-, which usually involves an equal share of current between the tubes, assuming the B+ and B- are equal and opposite.


----------



## SonicTrance

> The impedance mod essentially just alters the load line of the top triode which is sort of the same thing. I'd try it both ways and see how it sounds. Either way you would have to use an "impedance mod" resistor based on the specs of the 421a and not the 6as7.


 
  I have settings for both 421A and 6AS7's for both my headphones, no worries there.
  
 Quote:


> The point between both tubes is 0v but they are both run at the same potentials. For example if you used 165 ohm resistors on the cathode and the anode they would both be running at 90v because their cathodes/anodes would be 90v apart from eachother.
> *But if you left the 330ohm resistor on the plate it would throw off the balance and they would both handle the signal differently creating distortion, which could be a good thing or a bad thing.*


 
 This would essentially mean that every setting on the anode switch would cause that same distortion as the cathode resistor remains stock @ 330 ohms. But from the articles I've read about it that mod is about balancing the WCF, ie the opposite of what you're saying. And I could only hear improvements.
  
  
 I'll still try this though and we'll see if the current changes or not.


----------



## coinmaster

> This would essentially mean that every setting on the anode switch would cause that same distortion as the cathode resistor remains stock @ 330 ohms. But from the articles I've read about it that mod is about balancing the WCF, ie the opposite of what you're saying. And I could only hear improvements.


 
 Yes, it tries to balance them, *but *most tube amps aren't OCL/OTL. It's not often you find one running a servo. Offset servos seem to be an alien concept to most tube designers I've noticed.
 The servo itself balances them otherwise your headphones would be destroyed from DC on the output.
 This is why the current doesn't change when you use different plate resistors. The servo increases the bias as the current tries to increase and vise versa because it tries to maintain the 0v output. It just so happens that the only time there is 0v on the output is when both tube have an equal impedance, assuming equal and opposite supply voltages.
 Normally there would be a capacitor or transformer protecting the output and the voltage on the grid of the top triode would be locked which would cause the WCF to favor different loads.
 This is where the impedance mod was intended to help.
  
 So basically all you're really doing adding distortion, or at least changing the distortion by shifting the load line. The signal criss-crosses between the cathode and plates of either tube in the channel when in operation, so the impedance mod i's effectively the exact same thing as mixing tubes since the signal travels through the different load lines of both tubes when you do that, and mixing tubes can make a gigantic difference in sound as well, especially in the bass region. I've mixed a bunch of popular tubes and I found that mullard 6080 and tunsgol 5998 were the winners.
 When you use a 330 ohm resistor on the cathodes and something different on the anode, the signal travels from 1 cathode into the other anode which is on a different spot on the load line, same as the signal traveling through a 6080 tube into the other 5998 tube by mixing.
  
 Honestly I think you would be better off by getting a quality 5w wirewound pot instead of using fixed resistors. Wirewound pots are basically the same as the mills except there is a tiny amount of inductance however it is so small it would only matter at radio frequencies.
 You would have to put a minimum resistance in series with the pot in order to avoid the possibility of having no bias when someone turns the knob or the contacts disconnect when turning the knob.
  
 Oh yeah and I spaced out on a major factor. You can't use the 165 ohm resistor because the B+/- is 100v. This means you will only have 10v of voltage swing headroom. You would need a higher voltage power supply. 
 It will be cutting it close, but if you use a 15 volt zener in series with the 100v zeners in the power supply you should have enough voltage headroom, but this is cutting it down to the last volt so I can't promise absolute stability. It assumes the collector voltage stays at 115v+ on both sides. In fact you might want to go with a 10v zener to account for error.
  
 This would also change the operating point of your 6as7 but it looks like it would be putting it in a slightly more linear part of the load line though.
  
  
 I think you would be interested in the amp I'm working on 
	

	
	
		
		

		
			





 it overcomes all the limitations of the mk6 and has completely and easily adjustable load lines and NFB ratio for both sections of each channel. The circuity is complex and pretty expensive so it's taking me a while to tweak it and pay for it but hopefully I'll have it finished by june. It will be the ultimate version of these mods.


----------



## SonicTrance

> Oh yeah and I spaced out on a major factor. You can't use the 165 ohm resistor because the B+/- is 100v. This means you will only have 10v of voltage swing headroom. You would need a higher voltage power supply.  It will be cutting it close, but if you use a 15 volt zener in series with the 100v zeners in the power supply you should have enough voltage headroom, but this is cutting it down to the last volt so I can't promise absolute stability. It assumes the collector voltage stays at 115v+ on both sides. In fact you might want to go with a 10v zener to account for error.


 
 But the 421A's is already running @ 90V with stock 330 ohm cathode resistor (still haven't measured, but there's 100V going in and voltage drop is 11V across cathode resistor). I don't understand why I would need to alter the zeners just to get up to 90V/60mA instead of 90V/30mA. And if it's like you think, that the opamps are going to counteract the lower cathode resistance, I should see no change what so ever?
  
 But I'm having a hard time believing that as that would also mean that the opamps would counteract the different plate resistor values. And while the current did not go up with lower plate resistance the sound did definitely change for the better.


----------



## baronbeehive

coinmaster said:


> ...............
> 
> I think you would be interested in the amp I'm working on
> 
> ...


 
  
 Sounds brilliant, I think you might even beat me in having your amp up and running first!!
  
 Re: Bruch's idea of piggybacking his caps, correct me if I'm wrong guys but I think this would reduce signal output quality to that of the existing components and therefore there would be no point in putting in better quality ones.


----------



## SonicTrance

baronbeehive said:


> coinmaster said:
> 
> 
> > ...............
> ...


 
 Yeah, I'd definitely remove the old caps. Don't know which caps he's referring to though. No point in modding if you keep old caps I think. Most caps we replace are wimas and those have to be removed anyway.


----------



## coinmaster

> I don't understand why I would need to alter the zeners just to get up to 90V/60mA instead of 90V/30mA.


 
 You don't. There should be a an amplification factor of 20 on the input stage, this means a signal swing of about around 15-20 volts at full volume.
 This means you would need 15-20 volts of headroom in order to not get clipping at high volumes. If you run at a higher volume I suspect it would sound pretty bad unless the NFB is really big. It's possible some of the signal is clipping and you don't even notice it.
  
 If I were you I would throw in a 10v zener in series to add more headroom to be sure but It's up to you.
  
  


> But I'm having a hard time believing that as that would also mean that the opamps would counteract the different plate resistor values. And while the current did not go up with lower plate resistance the sound did definitely change for the better.


 
 The opamps counteract the change in current, it's not counteracting a change in voltage. The only thing the opamps care about is keeping 0v on the output. A 77 ohm resistor on the anode and a 330 ohm resistor on the cathode with a 60ma current would put it at 80v on the cathode of one triode and 95.6v (talk about lack of headroom) on the anode of the other. In order to get 0v on the output the bias of the top triode would need to be increased, which means a decrease in current which explains your meters not showing any change in current when you change resistors.
  
 You are still shifting the load line though and therefore the linearity of the tube.
  
 If this was a normal WCF then changing the plate resistor would not be compensated by an opamp and there would be an increase or decrease in current which would alter how much current the tubes would sink among other things. This is when the impedance mod would balance the tubes at different loads.
 A higher load impedance would inhibit current flow into the opposing anodes which is why changing the current of the tube though the impedance mod would balance out the triodes. But the opamp already maintains an equal impedance between the triodes on its own.
  
*Unless *you use the impedance mod to make the resistor values of the anodes/cathodes different.
 Remember, the opamp does what it has to to keep 0v on the output and the tubes are basically variable resistors in a resistor divider.
  
  

 Think of the resistors as tubes and the batteries as the voltage you get after the voltage drop on the plate resistors.
 Notice how in order to get 0v on the output the top "triode" on the right needs a change in impedance after a change in plate voltage.
  
 The current flow through both of these dividers is exactly the same.
  
 This is what happens when there is no opamp and you change the plate resistor value
  

  
 That would destroy your headphones which is why there is normally a capacitor or transformer on the output.
 It also reduces the current flow of the divider.
  
 So when you use the impedance mod with opamp servos you are really *unbalancing* the WCF.


----------



## SonicTrance

I hear what you're saying coin. Though the amplification factor on input stage is only 20 if you use 6SN7's, which I rarely use. I tend to use ECC33/35's which has amplification factor of 35/70.


----------



## coinmaster

sonictrance said:


> I hear what you're saying coin. Though the amplification factor on input stage is only 20 if you use 6SN7's, which I rarely use. I tend to use ECC33/35's which has amplification factor of 35/70.


 
 That's way worse lol. That's from almost double to more than triple the voltage swing of the 6SN7. Either the NFB of the amp is saving you or your amp is clipping. I would definitely add that 10v zener in there.


----------



## SonicTrance

Nothing is clipping and you seem to forget that the mk6 is designed to use the 6SL7 with amplification factor of 70.


----------



## coinmaster

Yeah but the MK6 wasn't designed to change plate resistors and have your average power tube run at 5v below supply voltage.
 Normal operating voltage is 70-80v which is a 20-25v headroom.
  
 I just checked and the ratio of the NFB in the MK6 is gigantic. This is indeed the only thing that is preventing your amp from blowing up your headphones


----------



## SonicTrance

No, if I understand correctly it was designed to run the power tubes at about 80v, which is 20v under supply voltage. And with the 6SL7 in driver stage headphones would blow anyways.


----------



## SonicTrance

I can't understand though why you recommend an additional 10v zener in series instead of going with single 110v zeners?


----------



## coinmaster

> No, if I understand correctly it was designed to run the power tubes at about 80v which is 20v under supply voltage


 
 This is what I said. It is 70-80v depending on which tube you use, assuming stock resistor values.
  


> And with the 6SL7 in driver stage headphones would blow anyways.


 
 I don't think you understand what NFB is. 
 NFB is the 390k and 100k resistors that are connected to the gain switch. They form a negative feedback loop which feeds the output signal back to the input signal. The more negative feedback you apply the more any amplified non-linearities will be attenuated. This also reduces the amplitude of the signal. It's also why you should use good quality resistors in this area if you believe resistors change the sound.
  
 The NFB on the MK6 is huge so even with a even if you were to have a 70v signal with the amplification of the input tube it would be less than a volt with low gain switched.
  


> I can't understand though why you recommend an additional 10v zener in series instead of going with single 110v zeners?


 
 You could do either. Adding them in series allows you to fine tune easier since you can add small value resistors until you reach the sweet spot. This only matters if you care enough. A 110v would be fine. But It seems the crazy amount of NFB on this amp makes it irrelevant.


----------



## SonicTrance

70-80v if you use 6080/6AS7. It's still 90v when using 5998/421A even with stock plate/cathode resistors. Though the amp was not designed for those tubes of course.


----------



## coinmaster

Yeah that's what I meant by "normal" operating voltage. 5998 and 421a aren't a part of the normal design intention.
 Especially if you decide to change the plate resistor to 77 ohms.
  
 However I just did a simulation of the MK6 with "low gain" switched and a 6SL7 and the output swing into a 300 ohm headphone is about 3 volts. So you should be fine either way.


----------



## SonicTrance

What about 20 ohm and 110 ohm headphones? Much difference?


----------



## coinmaster

The lower the load impedance the lower the voltage. However I just double checked the placement of the 2k shunt resistor in the NFB loop on the PCB 
 and my original conclusion was correct that is it placed at the output. Meaning the NFB is series type, not shunt type.
  
 This means that low gain with a 300 ohm headphone will actually give you 13v of swing. Meaning that 77 ohm resistor will make it clip if only barely, with your 105v supply. In this case I would actually once again suggest throwing in that 110v zener. A 105v zener would be fine too assuming it has as much error as your current ones.
  
 Although keep in mind it would only clip at high volume.
  
 However the impedance rating of a headphone is only an average and actually most of the frequencies on the HD800 for example are 400-650 ohms. This would put it at 15v swing maximum and would cause distortion on certain frequencies if you didn't have the headroom.
  
 However since the 2k resistor is not part of a shunt NFB loop I wonder what the heck is it there for? It does nothing for the current or voltage at the load.


----------



## SonicTrance

> The point between both tubes is 0v but they are both run at the same potentials. For example if you used 165 ohm resistors on the cathode and the anode they would both be running at 90v because their cathodes/anodes would be 90v apart from eachother. But if you left the 330ohm resistor on the plate it would throw off the balance and they would both handle the signal differently creating distortion, which could be a good thing or a bad thing.


 


> The opamp tries to keep the bias of both triodes the same so it might be that it actually isn't changing current. A drop from 330 ohms to 220 ohms would result in an increase in current which the opamp would then apply a more negative bias to counteract it. The only way you end up with 0v on the output of the amp is when there is an equal impedance between B+ and B-, which usually involves an equal share of current between the tubes, assuming the B+ and B- are equal and opposite.


 
 So, maybe the only way to get the 5998/421A's to run at 60mA would be to use 165 ohm resistors on both cathode and plate. That way the opamps would not counteract the new bias and we'd get the full 60mA?
  
 I guess we wont know for sure until we test. And I would need a 8 pole switch for that...
  


> However the impedance rating of a headphone is only an average and actually most of the frequencies on the HD800 for example are 400-650 ohms. This would put it at 15v swing maximum and would cause distortion on certain frequencies if you didn't have the headroom.


 
 This is not true for planars, which I use. Their impedance is constant as far as I know.
  
 I think I mentioned this before when I had just installed the Ra switch, but I noticed most improvements when listening through my LCD-XC's which are only 20 ohms. That lowest setting of 77 ohm plate resistor is for use with LCD-XC's and 421A tubes. It really did wonders for the XC's. I also heard improvements with the LCD-3 (110 ohms), but not as much as with the XC's.


----------



## coinmaster

> I think I mentioned this before when I had just installed the Ra switch, but I noticed most improvements when listening through my LCD-XC's which are only 20 ohms. That lowest setting of 77 ohm plate resistor is for use with LCD-XC's and 421A tubes. It really did wonders for the XC's. I also heard improvements with the LCD-3 (110 ohms), but not as much as with the XC's.


 
 You could say the same about tube mixing though.


----------



## Maxx134

I been away a few days researching other projects, 
And I see Coinmaster has turned this thread to hell.

Too many wrong assumptions and suggestions I don't know where to begin..
Better to scrap the last two pages of this thread than try to fix it..

Edit not to take away from the motivation,
But design, theories and speculation is not part of the supermod thread.
Mostly this is done in PM, but a thread for this is better than to confuse/clutter the Mod thread.


----------



## coinmaster

> I been away a few days researching other projects,
> And I see Coinmaster has turned this thread to hell.


 
 Sorry, it's easy to forget that this is a dictatorist thread where your vision and opinion is the only one that matters and everything must be run by you first.
  


> Too many wrong assumptions and suggestions I don't know where to begin..


 
 If you think I was wrong about that many things then you are the one who is wrong.
  
 Not much of what I said was based in theory except for the v-swing of the amp and my musings behind the impedance mod.
 I see where I could be wrong about my thoughts on the impedance mod though, since the top triodes should sink the combined current of the bottom triode and the incoming current through the load, requiring an unequal impedance between the two triodes to get a balance of AC level current, even if the DC currents are already balanced.
 In this case the impedance mod makes sense, it would be unbalancing the load lines but balancing the AC currents.
  
 In either case you should stop caring so much about what's discussed here. You are way too obsessed with your vision of the way this thread is supposed to go regardless of other peoples interests. This is a public forum, get used to people discussing what they want on it. If people want to see the mods they can go to the front page.
  
 Sorry if discussing mods on a mod thread is against the dictatorship rules of the thread. Which by the way, you should put those rules on the front page if you don't want people talking about mods on a public mod thread.


----------



## Bruch

I love you all. I think that this thread is amazing and you have all done such a terrific job in deconstructing and reconstructing this amp.
  
 However, for what it's worth, I do get a little lost inside Coinmaster's head. There's a lot going on in there that I have no idea about at all. It's quite fun to read his posts and I don't object to latest little flurry of incomprehensible (to me) musings but it would be a shame if that became the norm and this amazing thread lost its way in a jungle of techni-speak.
  
 Don't you just love free sharing of ideas?


----------



## coinmaster

> However, for what it's worth, I do get a little lost inside Coinmaster's head. There's a lot going on in there that I have no idea about at all


 




  


> but it would be a shame if that became the norm and this amazing thread lost its way in a jungle of techni-speak.


 
 I agree which is why I don't do it much, but when something about the mods needs or wants to be discussed it shouldn't be inhibited.


----------



## Maxx134

Coin. Look at the Cavali papers. 
Think not individual triodes or tubes.
Think the circuit design behavior.
Then think about this is balanced design.

Also, about the power. 
I do not condone:

 1-adding another 15vdiode
Remember this section feeds the opamp & protection PSU sections which will take the hit of voltage change and so have to also be adjusted accordingly. 

2-disconnection of resistors and meters.
You essentially created a worse condition. 
No matter what the PSU could possibly do, it would never be able to create that type os damage potential. 

You cannot easily disconnect the PSU from the amp as the other two sections still connected. 

That's just off the top of my head but basically your assumptions are incomplete.


----------



## coinmaster

> 1-adding another 15vdiode
> Remember this section feeds the opamp & protection PSU sections which will take the hit of voltage change and so have to also be adjusted accordingly.


 
 The opamps are fed by separate zener shunts and the increase in voltage would not put them over their rated wattage.
 The protection circuitry is fed by another supply all together. The only thing the 15v diode would affect is the tubes.
  


> 2-disconnection of resistors and meters.
> You essentially created a worse condition.


 
 Completely wrong. You only create a worse condition when you leave the power supply connected when you know there is something wrong. Unless you like smoke.
  


> No matter what the PSU could possibly do, it would never be able to create that type os damage potential.


 
 Lol, do you have any idea how much money I've wasted on fried components because I left the power supply connected during troubleshooting? No connection = no current. No current = no smoke. If you have a problem with the amplifier it will either be caused _by_ the power supply or it could cause problems _for_ the power supply. 
 Disconnecting the power supply before troubleshooting is *the *most fundamental thing to do, troubleshooting 101. You don't troubleshoot an entire system at once. You do it section by section. Not only for the safety of the components but because leaving the power supply connected with a malfunctioning system can give you unusable results during diagnosis with the meter.
  
 Once you have made sure that the power supply itself is in working condition, then you move on to the remaining sections.
  
  
 I've been troubleshooting the mk6 for 8 months and I've built several from scratch. Don't challenge me on this.
  
  


> Coin. Look at the Cavali papers.
> Think not individual triodes or tubes.
> Think the circuit design behavior.
> Then think about this is balanced design.


 
  
 If you think I was talking about individual triode behavior then you didn't read what I said.
 I looked at the Cavali papers. It gave a lot of mathematical equations without too much logic 
 behind it, which is why I became skeptical whether it applied to our situation given the way our servoed design affects tube impedances.
  
 However, like I said before I realized that the top triodes have to sink both the bottom triodes current as well as the incoming current from the load. In this situation the impedance imbalance the impedance mod creates does make sense as it would reduce the AC current into the top triode which would balance it out with the bottom one.
  


> You cannot easily disconnect the PSU from the amp as the other two sections still connected.


 
 Disconnecting the meters and the .68 ohm resistor will completely disconnect the amp from the power supply. The negative supply has nowhere to go so it will only charge the cathodes. As long as you take the opamps out there will be no issue.
 The protection circuity is the only other supply and it can care less whether the main power supply is connected or not, it's completely isolated from the rest of the amp and the main power supply except for the offset detector pin on the protection IC at the output.


----------



## Maxx134

Coinmaster, remember vanity is the cause of failure. 

You need admit SonicTrance 2k resistors burned because of your suggestion on disconnecting the 0.68 resistors, which as you know realize did not fully remove the PSU. 

I know you think disconnecting the PSU is "troubleshooting 101",
But in this case, with this amp we don't need "textbook".
The sections are not designed to be easily separated, and there was no need to disconnect.

As you noted the opamp had its own resistor/zener regulation.
The danger was in altering the circuit the way you have done.
This is reason why your burned components. 

Not gona argue about "troubleshooting101".
Be open to possibly of "troubleshooting 202" & reasons why circuits have "test points". 

I don't appreciate being labeled as inhibiting discussion,
ONLY MISINFORMATION AND SPECULATION.

As stated from beginning, 
We always test and verify before we push out a new mod.

The impedance/headphone matching mod is already tested and verified regardless what you believe.

The only thing is that it has been slow to push out because we have a life apart from this hobby.


----------



## Maxx134

The PSU voltage change idea can be a decent, or even a good idea,
 so I will look into it.

Let us know if you have success, which is different than telling Sonic to do it.


Edit:
Still have 5o adjust the other sections of the PSU for the change. 
Can't rely on the tiny zener to handle that.

The approach is having a component that can handle a safety margin higher than what is actually needed.
This is the norm especially for higher temperature ranges which this amp will produce. 

Also has to be decided is a choice of the accompanying resistor change as well.

So just saying to pop in another 15v zener diode is not looking at whole picture


----------



## coinmaster

> You need admit SonicTrance 2k resistors burned because of your suggestion on disconnecting the 0.68 resistors, which as you know realize did not fully remove the PSU.


 
 I already did.
 In case you forgot the same thing happened to me with my 300 ohm resistors a while back. I always remove the opamps while troubleshooting but the last time I've done any mk6 troubleshooting on the original PCB was when I helped mogos so it slipped my mind.
  


> I know you think disconnecting the PSU is "troubleshooting 101",
> But in this case, with this amp we don't need "textbook".


 
 That is about as far away from truth as it can get. This amp has so many potential issues when you break it and then leave the power supply connected. It's not "textbook" it's fact.
  
  


> The sections are not designed to be easily separated, and there was no need to disconnect.


 
 Yeah well you can take the easy way or you can take the safe way. I used to be lazy and take the easy way and I ended up blowing hundreds of dollars on components because the easy way turns out to be too risky on average. Besides, desoldering a couple of components legs isn't that hard.
  


> As you noted the opamp had its own resistor/zener regulation.
> The danger was in altering the circuit the way you have done.


 
 Lol, there's no danger of "altering the circuit" did you even read why I mentioned changing the regulator voltage?
 The only thing adding a 15v zener would do is increase the output voltage to the tubes to 115v assuming the collector voltage was always 115v+.
 If you adjust the resistors to compensate the only difference is the voltage headroom for the signal.
  


> This is reason why your burned components.


 
 Lots of assumptions coming from someone claiming that I assume everything.
 I never burned any components in the MK6 from altering a circuit, it has always been from troubleshooting and leaving the power supply connected.
 I have never altered the stock MK6 other than the mods from this thread.
 The only other time I burn components is when I do breadboard testing for my other project.
  


> Be open to possibly of "troubleshooting 202" & reasons why circuits have "test points".


 
 Do *you* even know? Circuits have "test points" because when they are working properly they have a predictable operating point relative to their function. Which is one of the reasons why you don't leave the power supply connected to the amplifier so the current draw from whatever is broken does not interfere with the voltages you are testing. One of the many things I learned from 8 months of actual experience troubleshooting just about every problem the MK6 can have.
  


> I don't appreciate being labeled as inhibiting discussion


 
 Then stop complaining all the time.
  


> ONLY MISINFORMATION AND SPECULATION.


 
dis·cus·sion dəˈskəSH(ə)n/
_noun_
 

    the action or process of talking about something, typically in order to reach a decision or to exchange ideas.
  
  
  



 



> We always test and verify before we push out a new mod.


 
 So what happens when somebody that's not you decides they want to contribute. They have to run everything by you? Why isn't that listed as a rule on the front page?
  


> The impedance/headphone matching mod is already tested and verified regardless what you believe.
> 
> The only thing is that is has been slow to push out because we have a life apart from this hobby.


 
 I never said I didn't believe in it. I said I was skeptical about it due to my current understanding of the cavalli paper and the way the servo interacts with the tubes as well as the sonic similarities between the impedance mod and tube mixing. All of the reasons behind my skepticism were facts, not assumptions. 
  


> Let us know if you have success, which is different than telling Sonic to do it.


 
 I wasn't telling him to do anything, I was making a suggestion that I specifically said was his decision.


----------



## baronbeehive

n


maxx134 said:


> ........
> The only thing is that it has been slow to push out because we have a life apart from this hobby.


 
  Oh, lucky you 
	

	
	
		
		

		
		
	


	




. Wish I did, most of my year so far has been involved in the house move!
  
 I also enjoy Coin's contributions, so maybe if they were preceeded by a health warning..........

 I certainly am not qualified to question them and any contributions in theory should  be welcome, also now given that Coin is building real world systems. However I do value the way that the mods in this thread are subject to rigorous testing before approval.


----------



## coinmaster

> I also enjoy Coin's contributions, so maybe if they were preceeded by a health warning..........


 
 I really shouldn't say this, but I don't think you can do anything to this amplifier to make it dangerous, at least not in the "blowing up" kind of way. There's not enough power and the fuse would trip before there was. 
 The health hazard lies in creating a short through your body for the current to flow, especially through your heart. Just make sure your body doesn't have a connection to ground through your other hand. A grounding bracelet would make it easy.
 Even if you do get shocked it's likely to be uneventful, but obviously don't take the risk and it's easy to avoid anyway.
  
 You shouldn't be scared but don't be stupid either.
  


> The only thing is that it has been slow to push out because we have a life apart from this hobby


 
 My landscaping duties have been slow lately so I have the opposite problem.


----------



## Maxx134

coinmaster said:


> I used to be lazy and take the easy way and I ended up blowing hundreds of dollars on components because the easy way turns out to be too risky on average..




OK I'll bite. .
What are the components that costs hundreds and why they broke. 




coinmaster said:


> So what happens when somebody that's not you decides they want to contribute. They have to run everything by you? Why isn't that listed as a rule on the front page?


 


This is not a sound science thread to post massive speculations without stating they are your speculations and not fact.
Read first page again. 

Where is your actual contribution besides speculations.

To me, So far you have littered about 3 pages of disinformation/speculations ..

Here are but a few examples :

"So when you use the impedance mod with opamp servos you are really unbalancing the WCF."

Nonsense.

 "Either the NFB of the amp is saving you or your amp is clipping. I would definitely add that 10v zener in. there."

Nonsense 


I just checked and the ratio of the NFB in the MK6 is gigantic. This is indeed the only thing that is preventing your amp from blowing up your headphones  

More nonsense.

You think those resistors are applying feedback in a traditional sense.
They are not.




coinmaster said:


> I wasn't telling him to do anything, I was making a suggestion that I specifically said was his decision.




Why did you tell him to add diode?
Do you know why the PSU is set that way to begin with?
Your not giving tube headroom. 
Only changing the parameters while diminishing the PSU headroom.


----------



## Maxx134

To be fair, I am always impressed with Coinmaster determination and injenuity and growth.
I do expect nice DIY future from him. 
We just but heads from time to time.
Maybe we should open a different thread on "analysis of MK6&8 design".


----------



## baronbeehive

The bickering on this thread has a way to go before it reaches the lofty heights of other audio forums! Thank god for that.


----------



## coinmaster

> Still have 5o adjust the other sections of the PSU for the change. Can't rely on the tiny zener to handle that. The approach is having a component that can handle a safety margin higher than what is actually needed. This is the norm especially for higher temperature ranges which this amp will produce. Also has to be decided is a choice of the accompanying resistor change as well. So just saying to pop in another 15v zener diode is not looking at whole picture


 
 Ohms law says the zeners will be fine. The negative zener is cutting it close a little bit but it's not like the power supply is capable of bringing it any higher.
  


> OK I'll bite. .
> What are the components that costs hundreds and why they broke.


 
 Opamps, transistors and the occasional resistor. All of that is eliminated by disconnecting the PS during troubleshooting.
 Aside from the fact the PS needs to be disconnected with issues involving current anomalies due to the incorrect readings it causes at the key measuring points
  
 Sure you can just try to figure it out and hope for the best, with the PS plugged in but I had just about every problem the MK6 can physically last year and the majority of the time I saved myself a whole lot of trouble by just disconnecting the PSU. Plus over half the time the problem was undiagnosable with the meter when I didn't want to disconnect the PSU due to current draw.
 I've since parted from the stock MK6 at the beginning of the year and my experience has allowed me to troubleshoot every strange and unusual problem I've come across building my new, much more complex amplifier.


> This is not a sound science thread to post massive speculations without stating they are your speculations and not fact.


 
 I was discussing my skepticism, which I stated multiple times. No harm would have come from me being right or wrong since it obviously makes a difference either way.
 And guess what. I came to the proper conclusion on both of the matters I was discussing, what do you know, that's the point of discussing.
  


> You think those resistors are applying feedback in a traditional sense.
> They are not.


 
 They are a series global negative feedback loop. Verified in Spice.


> Why did you tell him to add diode?


 
 If actually read you would know. I told him to make more headroom for his 421a and then I came to the conclusion that it wasn't needed. Reading is a wonderful thing.
  


> Do you know why the PSU is set that way to begin with?


 
  
 Because it was designed to be a 100v bipolar supply with a 25v vdrop for the specified point on the load line, the load line operating point is under biased, more than likely to save power supply costs, which is why the NFB is needed.
 The extra 15v is headroom for the regulator, yet there is some squeeze room if you wanted more.
  


> Your not giving tube headroom.
> Only changing the parameters while diminishing the PSU headroom.


 
 The only parameter that is changing is the B+/- supply. Which would obviously be compensated with the proper resistors.
 I said to use 105 or 110v zeners to account for error and to bring it a bit lower than the 115v line.
  
 But if you actually read the things I say you would know I said it's not needed given the worst case V swing of the amp unless you like to have it at 100% volume with 421a tubes and unusual resistor values.
 Quote:


> We just but heads from time to time.


 
 No harm no foul. I'm bored and have too much time on my hands.
  


> Maybe we should open a different thread on "analysis of MK6&8 design".


 
 I would if it wasn't already demystified for me except for the 2k resistors. After reviewing the details of the original schematic I made last year I learned the how the delay circuit and the protection circuit work and the rest of the amp is just a basic SE input stage with WCF output stage and a servoed output. The remaining details of which I've discovered over the last few pages. My new amp WCF design is not load dependent nor does it need a bunch of NFB or an analog timer/protection circuit so I haven't really cared about the extra details until now.
 I wouldn't make a thread explaining the details of the MK6 unless there was a demand for it cuz it's sort of a waste of time.
  


> The bickering on this thread has a way to go before it reaches the lofty heights of other audio forums! Thank god for that


----------



## SonicTrance

maxx134 said:


> To be fair, I am always impressed with Coinmaster determination and injenuity and growth.
> I do expect nice DIY future from him.
> We just but heads from time to time.
> Maybe we should open a different thread on "analysis of MK6&8 design".


 
 Also, I did ask Coin for his thoughts about biasing the 5998/421A's and he went all in with his answers, lol.
  
 I personally think we should be able to discuss potential mods in this thread and have all verified and tested mods on first page. A second thread would kill this one I think. But I know that was not your and TS Redge78 intention with this thread so I will respect that.


----------



## Maxx134

Quote:
*"They are a series global negative feedback loop. Verified in Spice."*
Is the DC servo included in Spice?
Because that is what I see the resistors feeding. 
I see the opamps controlling the gain.
That is not a direct traditional NFB signal loop.
I see a NFB in the opamp, but they are DC servo.

Edit :
OK, now I remember that diagram I was supposed to verify, 
So I will check this weekend if the output tube is feeding the driver thru those resistors.


----------



## coinmaster

maxx134 said:


> Quote:
> Is the DC servo included in Spice?


 
 Yes, I regularly use them in spice and in real life and they have been invaluable for my upcoming designs. I don't know why you think I'm so incompetent lol.


> Because that is what I see the resistors feeding.


 
 It's not. I've done a continuity test a thousand and 1 times on the actual board. They are feedback resistors linked directly to the gain switch between the output and the input. 
  
 The more NFB you have the lower the gain. Which is why people claim a difference in distortion between the switches. They are wired in parallel for an 80k/390k switch.
  
 I always thought they were an NFB shunt because of the 2k resistors to ground but they are actually a series NFB, the 2k resistors are quite a mystery to me since they don't really do anything other than draw a bit more current from the load.


> I see the opamps controlling the gain.


 
  For someone who keeps baselessly claiming that I assume everything, you sure do make a lot of assumptions.
  
 The opamps do not control the gain, they are integrators with their non-inverting input connected to ground
 https://en.wikipedia.org/wiki/Integrator
 If I didn't verify what they were already I wouldn't have been able to build my MK6s or design the bias circuits for my upcoming amp which requires much more complex opamp configurations.
 The only reason I have't had an "official" mk6 rebuild yet is because I don't feel comfortable connecting my HD800s for very long to a direct drive amp that is essentially a bunch of flimsy wires on my desk.
 I'm waiting on custom PCBs for my new design.
  
 Quote:


> I see a NFB in the opamp, but they are DC servo.


 
 There's no NFB connected to the opamp. The 100k resistor that connects to the opamp is a part of the low pass filter to prevent the integrator from canceling out the audio signal.


----------



## Maxx134

Hello I'm just reading this now yet I won't agree with anything until I look at this over myself later 

Edit :
Oh and thanks for the compliments .


----------



## Maxx134

Apart from traditional configuration of opamp,

 we have to see how it is is implemented because it is can be a multiple solution going on at once.

I still see the opamps being fed from those resistors and yes thru a 100k, and controlling the power tubes gain thru their grids. 
The 1uf cap is the opamp feedback I saw.

You say "cancel the signal", and I say gain..


Also what led me to my assuptions was actual hands on occurance, 
Not guesswork.
I am more a hands on guy,
While Redge78 is very sharp, but he has been away.


I have observed sometimes an opamp can get loose from it's socket connections, and you will hear the volume go down. 
I pressed on it and volume came back up. .


I also don't trust the stock opamps on my amp, because the pins were thinner than the replacements,
And when I replaces them I had to adjust the blue trim pot noticably, yet there was no observable difference in performance. 

Remember my amp was constructed from stratch, direct from the company last year.
 So it contains more cost cutting in parts than older units which had higher quality parts..

Anyways I base most my assumptions on observations with solid theory before any changes,
And my amp has been a testing ground for every mod and I haven't blown anything up yet,
Except for occasionall breaking things from impatience.


----------



## coinmaster

> The 1uf cap is the opamp feedback I saw


 
 The 1 uf cap is part of the RC filter.
  


> You say "cancel the signal", and I say gain.


 
  Lol, that's like saying the sky is blue because I want it to be. You can say gain all you want but the opamps *are* integrators, a basic fact that is so basic I have a hard time putting it into words how ridiculous it is that you continue to think otherwise.
 The integrators take feedback from the output and bias the top triode until the opamps negative input (also the amplifiers output) matches its positive input, which is grounded. Integrator 101, the RC filter between the input and the output prevents it from compensating for the music signal. The 100k resistor /1uf capacitor forms a cutoff of 1.59 HZ which is just next to DC, meaning it won't compensate for any signals above 1.59 HZ.
 Quote:


> And when I replaces them I had to adjust the blue trim pot noticably, yet there was no observable difference in performance.


 
 That's because the trimpot only compensates for the natural offset between the opamp inputs.
  


> Anyways I base most my assumptions on observations with solid theory before any changes


 
 Yet you ignore the fact that I've literally torn this amp apart and put it back together more times than you ever will (which will probably be 0) and I've built much more advanced systems at this point. 
 I have nothing more to say to you if you still think that you can dispute me on such elementary matters of the design. You completely disregard everything I say as if I'm ignorant and incompetent and as if I haven't already proven these theories by actually building the mk6 from the ground up multiple times, which by the way required me to have sufficient understanding of the details behind the opamps operation and function before I could even do it the first time which I learned by countless hours of research, trial, and error.
  
 The only part of the amp I haven't officially built is the NFB because I had the volume very low and I had no intention of having long listening sessions with my HD800s connected to flimsy proof of concept mock ups that can fry my headphones with one wrong move. But even then you can't deny the facts that it is a series NFB because the physical design, the simulations, and basic logic prove it. Plus the fact that 1% volume was still pretty darn loud without the NFB resistor.
  


> I have observed sometimes an opamp can get loose from it's socket connections, and you will hear the volume go down.
> I pressed on it and volume came back up. .


 
 You should have used a multimeter to test it then, if the connection truly was loose then it was probably pumping -36 volts of bias into your tube in an attempt to match its negative input to ground. Which would cause a decrease in volume at the very least. Then again, depending on how it was loose it could just break your headphones. 
 The opamps are not something you want to have loose in this amp.
 The protection circuitry should prevent an offset failure at the output so I'm suspicious that it was even the opamp at all, although I don't know the threshhold at which the relay trips. I coded an arduino to handle my offset and timer circuits so I haven't bothered much with the analog versions.


----------



## Maxx134

Like I said,
 I am impressed with your knowledge growth,
But I still feel the past few pages of your posting was a waste.
EXCEPT this last post of yours...
 you finally give some decent information,
with a liberal amount flaming on me, 
 which I hope you enjoyed.


----------



## Maxx134

I like to discuss the protection circuit...

The protection circuit is not fast enough in every circumstance to protect your headphones. ..


On one occasion I had the blue trim pot shorted due to a solder overlap of excess solder,
 and there was a huge pop to my HD800 (!) before protection kick in!

 Also, in another circumstance, 
The stock WCF cap dislodge from its weak soldering joint and created and slight hum and a pop up on Startup...

This totally blew my one of the drivers of my cheap headphones on the single ended Jack...

Edit these events happened way back when I did the cap upgrade,
That's why patience is more than a virtue here.


----------



## Maxx134

I believe there is a small capacitor right next to the chip which is responsible for the timing of the protection trigger..
Coinmaster, can you verify that?

Edit, yes I know it seems like I am being a bit lazy in not looking up the chip data myself,
But what is actually the case is that I am having less time for this lately..


----------



## SonicTrance

maxx134 said:


> Edit, yes I know it seems like I am being a bit lazy in not looking up the chip data myself,
> But what is actually the case is that I am having less time for this lately..




Hope you get more time soon, Maxx. We need you back in the game, modding!


----------



## coinmaster

> with a liberal amount flaming on me,
> which I hope you enjoyed.


 



> On one occasion I had the blue trim pot shorted due to a solder overlap of excess solder,
> and there was a huge pop to my HD800 (!) before protection kick in!


 
 I guess it's not surprising considering the fact that the relay is mechanical. Plus the protection IC is from like, 1990. How long did it take to kick in? My aduino kicks in instantly so any DC would only be on the line for a fraction of a second. Although I do question the reliability of a digital protection circuit that runs on code. I am considering using an analog set-up instead.
  


> The stock WCF cap dislodge from its weak soldering joint and created and slight hum and a pop up on Startup..


 
 The cap itself is only meant to pass AC so it possibly shorted B+ or B- to something since it is connected to both. I guess I can't really blame the protection circuit for not being able to prevent a possible power supply short to the output but I'm not inspired with confidence at this point.
 Thankfully I've only had a few light pops back before I understood the purpose of the opamps and I had about 1 volt DC on the output when I was rebuilding my amp initially. At least yours survived some loud ones.
  


> I believe there is a small capacitor right next to the chip which is responsible for the timing of the protection trigger..
> Coinmaster, can you verify that?


 
 No they all seem to be filter caps. The 33uf cap has a time constant of 2 seconds so it could be a timer but I have no idea what "VCC ON mute" is.
 The 5k1 and one of the 56k resistors seem to determine the offset threshhold value but I haven't cared enough to determine how and what value is.
  
 Here's the  pinout for the IC 

 and here's the crappy schematic I made way back
  

 Hot and cold wires should actually be reversed.


----------



## Redge78

Guys,
  
 I'm a little confused here ... are you talking about the "Burr Brown OPA445AP" chip here (the only ones in the MK8) ? Or is there another one for the MK6 ?
 Because if it's the OPA445AP, the pinout above is vastly different from the official datasheet :
  
  

  
 And without the correct pinout (and therefore the correct schematic around it) it may be a triffle difficult to calculate what this opamp is really doing.
  
 From what I have read, the OPA445 is modelled in Spice, that may help.


----------



## Maxx134

Hi Redge78, coin posted the protection circuit relay .
Thank you Coin. 
Believe me, you wouldn't want the pop Is heard shooting thru an hd800 so loud that it instantly make you rip it off your head and throw it in a reflex motion!
Lol
It happened to me twice long ago and is a testimony to how strong the hd800 are.
The hd800 can burst your eardrum!
That's why I am suggesting we decrease the response time of the protection circuit.


----------



## coinmaster

The MK6 uses the OPA445AP as well.
 Don't worry about what the opamp is doing. I verified it long ago and I ordered my own custom versions for my experiments
  
  

  
 This is a straight up copy of the configuration on the MK6.
 My initial trials were P2P construction but I did not feel comfortable having the opamps flimsily dangling around.
  
 The jist of it is that the opamps positive terminal is connected to ground. 
 The negative terminal is connected to the output.
 The opamp will try to do what it can to make both inputs the same.
 This means that the output of the opamp will bias the top triode of the WCF so there is ground level dc (0v) on the output of the amplifier (also negative opamp pin).
 The 100k resistor/1uf cap is an RC filter so the opamp ignores frequencies above 1.6HZ.
 The 470k resistors/ .22uf cap is another RC filter at 1.6HZ presumably to get rid of any noise the opamp creates and it is also a high impedance buffer from the signal.
 The 1uf caps are just bypass caps to stabilize the supply voltage.
 The 20k trimmer adjusts the offset error between the inputs of the opamp so when the opamp tries to keep both inputs the same they actually both measure the same. Basically you use this to tweak the DC at the output of the amp.
  
 I've used what I've learned from the MK6 integrator to come up with much more complex and useful designs.

 This is the upcoming PCB for the biasing circuits that will allow me to fully adjust the load line vertically and horizontally while in operation. It's not finished cuz these software designs are a P.I.T.A to make within the "design rules" of the manufacturer but I should have it done soon.
  
  
 The pinout of the OPA445AP datasheet is correct.
 Refer to my schematic for the MK6 design which now that I look at it again is kind of crappy but it works
  



> That's why I am suggesting we decrease the response time of the protection circuit.


 
 R75, R5, and C4 in the relay schematic form a 2 second time constant to the "VCC ON mute" pin which from my short reading on "mute" seems to simply mean off/disconnected.
 So effectively it seems to just delay the power to the IC for 2 seconds on startup to give the servos enough time to stabilize so you don't blow your headphones. It doesn't seem to be a timer for the protection relay in active duty and I don't see why there would be a timer.
  
 That's actually a good point though, I didn't code my arduino to protect the headphones on startup. Glad I caught that before I used it on the real thing.
  
 I've verified that my arduino protection circuit reacts instantly to offset above the set threshhold so If the analog circuit is really as slow as you think then my arduino solution would work, but I think such a thing is beyond the scope of this modding thread and probably a horrible idea to have people playing around with.
  
 Keep in mind that the IC in the amp a 1990 model. Whether that's relevant or not I don't know.


----------



## Maxx134

sonictrance said:


> maxx134 said:
> 
> 
> > Edit, yes I know it seems like I am being a bit lazy in not looking up the chip data myself,
> ...



Since I remember you trying out various tubes for the MK6 I would like to know if there was any to you wish you could use which the MK6 does not use,
to see if it is possible.

 I am just wondering what are considered the best tube types, besides "300b" 


It may be that we already have the best choices, but I don't know.
I do know that in each type there are favorites, but probably hard to get.


----------



## coinmaster

I've actually designed a circuit that will allow the use of DHTs such as the 300B in a Servoed WCF such as the MK6/MK8. The problem is it would be expensive to implement not counting the cost of the tubes so I'm hesitant to try it unless I know there will be improvements over just buying a 5998 which has similar linearity to the 300B (sort of). 
  
 I've tested the Mullard, Geck, Bendix 6080s and a few others I can't think of off the top of my head. Bendix is good but Mullard and 5998s are amazing. Geck was boring and unspecial. Bendix was pretty solid, just not as good as the Mullard or 5998.


----------



## Maxx134

Ok, although I have not heard any pop on startup on my amp now which is normal functioning,
I think best to not leave headphones plugged in.

I asked about the tubes but it was too general.

Yes those 300b use too high voltage.
I was looking at 6sn7 types and was wondering what is general concensus for best tube types...


----------



## coinmaster

> Yes those 300b use too high voltage.


 
 Well the MK6/8 has enough voltage to run the 300b, especially if you use it as an input tube but biggest problem with the 300b is the fact that the filament is also the cathode. This makes it complicated to implement in designs such as a WCF especially if you want to servo it. As an input tube it...could work actually.
 The MK6 input stage B+ is 220v and the 300b is extremely linear across its entire operating range so if you drop like 70v across the plate resistor it would run pretty well at 150v.
  
 The problem is you would want to run them at like 20ma which could be pushing the 3A limit of the PS especially considering a 6SL7/6SN7 uses a fraction of an amp of heater current and a 300b uses 1.2 amps of heater current so you would probably want to use an external filament transformer.


> I was looking at 6sn7 types and was wondering what is general concensus for best tube types...


 
 The Tung Sol round plate 6SN7 is the consensus to be the "holy grail"  of 6SN7 tubes.
 I have these and the PSVANE CV181-TII. The psvane ones are a technical upgrade to the stock but the stock is more "musical".
 The Tung Sol round plates are better than both in every way and is easily noticeable as an upgrade. Too bad they are rare and expensive.


----------



## Maxx134

What about the Sylvania silver top?
I heard those are good ones. 
Have you considered the 
Shuguang "treasures" CV-181-Z ??


----------



## coinmaster

Haven't heard them. The TS round plates are considered the undisputed best from every source I've looked at so I haven't been interested in replacing. They are at least twice an improvement over my psvane t2s which are considered high end.


----------



## Maxx134

I will now look to see why the MK8 is using 12at7 types instead of 6sn7 types..

Probably a heat issue or cosmetic change as the power tubes are smaller .

But the power tubes in the mk8 are considered one of the best tubes..


----------



## Maxx134

coinmaster said:


> Haven't heard them. The TS round plates are considered the undisputed best from every source I've looked at ...



I only see one on ebay for $375. (!)


----------



## coinmaster

> I will now look to see why the MK8 is using 12at7 types instead of 6sn7 types..


 
 The 6SN7 tubes are considered the most linear small triode so maybe they used a less linear input tube to counter balance the linearity of the output tubes in the MK8 to avoid an overly linear sound?.
  


> I only see one on ebay for $375


 
 I paid $200 for mine (each)


----------



## Redge78

coinmaster said:


> The 6SN7 tubes are considered the most linear small triode so maybe they used a less linear input tube to counter balance the linearity of the output tubes in the MK8 to avoid an overly linear sound?.


 
 or they needed the extra amplification of the 12AT7 to achieve a decent voltage swing for the Hi-Rez headphone ...
 or it was just cosmetic ...
 or it was just to cut costs ...
  
 The 12Ax7 family has never been thaught for audio anyway and can easily be upgraded by ... anything else really.


----------



## Maxx134

redge78 said:


> ..or they needed the extra amplification of the 12AT7 to achieve a decent voltage swing...
> 
> 
> The 12Ax7 family has never been thaught for audio anyway and can easily be upgraded by ... anything else really.




I believe resistors by the gain switch can be adjusted for gain into the power tubes. 

I am now thinking the 12a*7 family is a compromise compared to the 6sn7 type ,
and was done so for cosmetic and tube rolling purposes since they are so popular. 

That's an area where I will be looking into..


----------



## baronbeehive

I believe the 12ax7's were used In audio because they are predominately used in Fender guitar amps and so are one of the most ubiquitous tubes out there. They are said to have a slightly fuzzy quality and that therefore they are not perfect in audio amps but the direct replacement of 5751's are a step up in this respect giving a more accurate sound.
  
 Not everyone likes the TS 6SN7, some in the 6SN7 thread say that the treble roll off is unacceptable which I suppose it may be to treble freaks, I think it is just nice and balanced. Also the silky sound is not liked by live music freaks because it doesn't have the raw edges of say the Shugangs.
  
 The Sylvanias are very brittle and sparkly tubes with a rather light sound so they do not have the depth for my of, say the TS's but in the 6SN7 thread there are one or tow Sylvanias above all others, some metal bases and the 1952 dated tube. Personally I wouldn't bother with any of them.
  
 If you want to see what other tubes are used in audio you could look at the Yamamoto amp site which has various models using different tube types, such as 45's which are very linear sounding compared to the very tubey 300B, then there are the 2A3, 205D, 316A and AD1, most of which I've never heard of.


----------



## Maxx134

Aha thanks guys my mind is now set on some driver tube replacements. .


----------



## SonicTrance

maxx134 said:


> sonictrance said:
> 
> 
> > maxx134 said:
> ...


 
 I've tried many different 6AS7G/6080 types for output and found that the GEC 6AS7G are superior. Chatham 6AS7G/6520 are also very good at a much cheaper price. Then there's the 5998's, which I find to be similar in terms of SQ to the GEC 6AS7G, but the GEC's are warmer sounding. Then my favorite, WE421A. A 5998 on steroids I'd say. Expensive and rare, you get what you pay for basically regarding power tubes IMO.
 I do not like any of the 6080 I've tried, especially the Mullard 6080. Way to warm and almost grainy sound.
  
 For driver tubes my favorites are the Mullard ECC family, ECC32/33/35. They all sound similar to me with slight differences. Again expensive and rare. To my ears they beat the Tung-Sol round plate tubes which I also like. I have all TSBGRP except for the 6SN7. I have the 6F8G which basically is an early version of the 6SN7 with different pinout, ST bottle and grid cap. Also have the 6C8G, 6SL7 and 6SU7GTY and they all sound similar to me.
 Ken-Rad black glass 6SN7 are also very nice tubes.
 I have a few different types of Sylvania 6SN7GT and do not really care much for them. Though I'm currently looking for the Sylvania metal base 6SN7W, just to hear what all the fuss is about.
  
 Those new production Psvanes and Shuggies are not that great I think if you compare to old stock tubes. 
  


maxx134 said:


> I will now look to see why the MK8 is using 12at7 types instead of 6sn7 types..
> 
> Probably a heat issue or cosmetic change as the power tubes are smaller .
> 
> But the power tubes in the mk8 are considered one of the best tubes..


 
 Yeah, I don't understand what 's different in the input stage in the mk8 vs mk6? From what I remember all resistors are same value in both amps in input stage.
  


redge78 said:


> coinmaster said:
> 
> 
> > The 6SN7 tubes are considered the most linear small triode so maybe they used a less linear input tube to counter balance the linearity of the output tubes in the MK8 to avoid an overly linear sound?.
> ...


 
 The 12AT7 has a mu of 60 and the 6SL7 (which is the tube the mk6 is based on) has a mu of 70
  


maxx134 said:


> Aha thanks guys my mind is now set on some driver tube replacements. .


 
 And lucky for you there's nice gold plated pin adapters to buy:
 http://www.ebay.com/itm/1piece-Gold-plated-6SN7-6SL7-TO-12AU7-ECC82-12AX7-ECC83-tube-adapter-6-3V-Heat-/201506915612?hash=item2eeabf851c:g:KecAAOSwqYBWngU7
  
 You need to remove the tube cages though.


----------



## SonicTrance

coinmaster said:


> The problem is you would want to run them at like 20ma which could be pushing the 3A limit of the PS...




What is this 3A limit you speak of? 3A limit for what?


----------



## coinmaster

I think moral of the story is, you won't know what you will like until you try it. However for output tubes I've found mixing always produces a superior sound to any single type. Just make sure to try both positions because one position always sounds better than the other.
  
  


> or they needed the extra amplification of the 12AT7 to achieve a decent voltage swing for the Hi-Rez headphone


 
 These amps don't need voltage swing, especially into hi-Z headphones.
  


> What is this 3A limit you speak of? 3A limit for what?


 
 The transformers have a 3A fuse on them and seeing as they were custom made for the MK6 that more than likely means 3A is at or near the current limit of the transformers.


----------



## SonicTrance

coinmaster said:


> I think moral of the story is, you won't know what you will like until you try it. However for output tubes I've found mixing always produces a superior sound to any single type. Just make sure to try both positions because one position always sounds better than the other.
> 
> 
> 
> ...


 
 You wouldn't happen to know the exact heater current limit for the driver tubes in mk6? There has to be a separate winding for driver tubes as the heater wires are much thinner than for the power tubes. I've used ECC32's for extended periods without issues and those pull close to 1A. Would be interesting to know the actual limit though.


----------



## coinmaster

I couldn't tell you. The 3A fuse is connected to the neutral pin at the wall though so if the the amp draws more than 3A including the heaters it will blow.


----------



## SonicTrance

coinmaster said:


> I couldn't tell you. The 3A fuse is connected to the neutral pin at the wall though so if the the amp draws more than 3A including the heaters it will blow.


 
 That's not possible as each power tube draw 2,5A, that's 10A just for power tubes. If you add a couple of ECC32's the total heater current becomes close to 12A.


----------



## coinmaster

Hmmm, good point. Not sure what's going on there, except it's an undeniable fact that there's a 3A fuse at the wall connection. I've had to replace a bunch of them so I know for sure.
 The current has to travel through the that fuse before it reaches the transformers.


----------



## MrCurwen

Understanding transformers basic idea is entry level learning. You shouldn't be poking around electronics without understanding the basics.

Current doesn't work like that. 

3A at 120V can deliver 360W of power. One 2.5A / 6.3V heater draws 15.75W of power. So you could heat up 22 such tubes and be under 3A current draw on the primary side.


Looking at the pictures in this thread I'd just like to say based on my experience many of you are asking for serious trouble with heat damage down the road. Too much stuff in too small a space. At least your caps seem to be well overrated; that'll help. I've learned this the hard way, I've had my earlier amp builds returned to me for fixing after a year or two because of this.

6SN7 is not the most linear small signal triode commonly available. It is very good though. Tubes like 6E5P, 6C45P or 4P1L deliver an order of magnitude better results. Proper design of course matters the most in any case. A first class design with second class tubes will pretty much always outperform a sloppy or antiquated design with any tubes.

12AX7 has first class curves, every bit as good as 6SN7. Implemented with a proper plate load (1M or so) it'll deliver high end results no problem.


----------



## MrCurwen

Transformer example is theoretic, it assumes ideal materials, no resistance in the wires. Real transformers have a limit on the output, it is stated in the transformer specs. 

Current does not pass thru the transformer from primary winding to secondary. That is one of it's most important functions, galvanic separation.


----------



## coinmaster

Oh hello MrCurwen. I was wondering if you were going to pop in at some point.
 I admit your usage of watts confuses me as watts signifies total power, not the individual components of V/I/R that make it up.
  
 The filament resistance of the 6080 tube should be about 2.52 ohms @ 2.5A each so with 4 in parallel the draw from the source would be 10 amps. I'm not sure how the transformer is able to bypass this fact.
 I guess my understanding of transformers is not up to par because I am not sure where the current is coming from.


----------



## MrCurwen

Current doesn't pass thru the transformer from primary to secondary. Instead, current goes thru the primary from one end of it to the other. This current causes a magnetic field around the wire. 

This magnetic field is concentrated by having a very long lenght of wire in a physically small space. This is why it's a winding, not just a piece of wire. One end of the winding is connected to one of the pins on the wall socket, the other end is the other pin on the wall socket. No electrons leave this wire either to the core, or to the secondary winding.

The concentrated magnetic field is picked up by the core, which is made of a highly magnetic material.

The magnetic field around the core causes electrons to flow in the secondary. A negative field repulses electrons in the secondary wire, and a positive field attracts them.

The impedance ratio between primary and secondary is determined by the number of windings on each side. The total energy (minus losses) of the magnetic field must find a way to release itself; how it manifests itself with regards to current and voltage is determined by the secondary (number of windings, wire gauge).

Let's say you have a 6.3V heater winding. If 1A of current flows in it, then about 52mA of current flows in the primary (assuming 120V wall voltage). 

This is also how OT's work. A large voltage swing with a small current swing on the primary is transformed to small voltage swing and large current swing on the secondary.

Sometimes a transformer doesn't provide a different voltage than the wall voltage. It is simply used as galvanic separation since current doesn't pass thru it.


----------



## SonicTrance

Thanks for the explanations @MrCurwen Most of us are beginners here so bare with us, lol.
  
 Regarding heat damage;
 Yes, all caps are overrated and we also use active cooling. I use a pair of 120mm static pressure fans from underneath. Still think we could have problems with heat?


----------



## Redge78

mrcurwen said:


> Looking at the pictures in this thread I'd just like to say based on my experience many of you are asking for serious trouble with heat damage down the road. Too much stuff in too small a space. At least your caps seem to be well overrated; that'll help. I've learned this the hard way, I've had my earlier amp builds returned to me for fixing after a year or two because of this.


 
 You have to remenber that all our amps have mecanical fans, some with adjustable fan speed. It helps tremendously to remove heat out of the box, stopping the slow building up on some areas.
 We are very conscious that we have to take care of our $$$ boutique caps if we don't want to change them twice a year.
  
 The more "enlightened" of our modders also have multicolor diodes on their fans ... they say it helps fluidify the air stream, or something like that ...


----------



## SonicTrance

redge78 said:


> mrcurwen said:
> 
> 
> > Looking at the pictures in this thread I'd just like to say based on my experience many of you are asking for serious trouble with heat damage down the road. Too much stuff in too small a space. At least your caps seem to be well overrated; that'll help. I've learned this the hard way, I've had my earlier amp builds returned to me for fixing after a year or two because of this.
> ...


 
 They do, no joke!


----------



## Maxx134

Hey hey now, I'm not getting involved with that...

I have enough diodes on top my amp as it is. .
Actually I took down the LED cubes for some simple solar tubes that spin in sun... 


Anyways, all joking aside, 
I do plan to extend the bottom and address the air flow in mine...

As for now, I have been rolling almost every 12a*7 available, with my stock and help of another friends rare stockpile..
I even have the tall 12BH7A, 12BZ7,
And even up to the mega tall of 9-pins..
The e80cc pinch that is not even any 12a*7 type.


So far I have to agree with MrCurwen,
That the circuit matters heavily.

Ever since implementation of all the caps upgrades, almost every tube sounded full of life.(!)

But to complete my tube journey I need to test the 6sn7 in my amp like Sonic suggested, 
And which I already had odered 2 pair hehe! 
have some Ken-Rad black glass, & Shuguang treasures on the way..


----------



## SonicTrance

Nice Maxx!
 Be sure to let us know how they sound once you get them! I think you'll enjoy the Ken-Rads much more than the Shuggies, though the Shuggies *look* nice.


----------



## baronbeehive

Guys, tomorrow's the big day, I'm getting the amp back! I don't know what to expect, I'm not expecting much and I'm not going to exaggerate, I'm just going to say it as it is.
  
 I don't think there were any problems............. apart from getting the PCB back in as Redge said, but I will find out later. That's why I only put the cathode by pass RIFA's on the reverse side to make it easier to get back in. Apparently everything fitted OK.
  
 This is all a bit strange, I wasn't originally going to mod the amp at all, I was pretty happy with it but why wouldn't you want to get the most out of it lol. I'll keep you posted.


----------



## SonicTrance

baronbeehive said:


> Guys, tomorrow's the big day, I'm getting the amp back! I don't know what to expect, I'm not expecting much and I'm not going to exaggerate, I'm just going to say it as it is.
> 
> I don't think there were any problems............. apart from getting the PCB back in as Redge said, but I will find out later. That's why I only put the cathode by pass RIFA's on the reverse side to make it easier to get back in. Apparently everything fitted OK.
> 
> This is all a bit strange, I wasn't originally going to mod the amp at all, I was pretty happy with it but why wouldn't you want to get the most out of it lol. I'll keep you posted.


 
 That's good news Baron! Looking forward to hear your impressions!
  
 Also, having the Rifa caps on top side of board does not make it any harder to put the board back in. The hard part is to get the tube sockets in the case holes. On my amp that's impossible to do by hand. I use a insulated screwdriver which I poke through the sockets and pop them in place one by one, that's the only way to do it, at least on my amp. I must have taken the board out and back in again 10-15 times while troubleshooting when the amp broke. I do it in about 2 minutes now, lol.


----------



## baronbeehive

sonictrance said:


> That's good news Baron! Looking forward to hear your impressions!
> 
> Also, having the Rifa caps on top side of board does not make it any harder to put the board back in...................


 
   
 Oh now you tell me 
	

	
	
		
		

		
		
	


	




.
  
  


> ..........The hard part is to get the tube sockets in the case holes. On my amp that's impossible to do by hand. I use a insulated screwdriver which I poke through the sockets and pop them in place one by one, that's the only way to do it, at least on my amp. I must have taken the board out and back in again 10-15 times while troubleshooting when the amp broke. I do it in about 2 minutes now, lol.


  
 Ha ha, well done, I remember you saying you never wanted to get it out ever again lol!
  
 I've just remembered that I don't have a decent music player on my PC atm because I've just installed windows 7 and its taking for ever to update so I may not have foobar installed by tomorrow damn.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > That's good news Baron! Looking forward to hear your impressions!
> ...


 
 I did say that, lol. But now it's pretty easy after having done it so many times.
  
 Get on it Baron. If your PC takes until tomorrow to update it's time to upgrade, lol.


----------



## baronbeehive

The amp's back 
	

	
	
		
		

		
		
	


	




.
  
 Apparently my soldering was OK, except for getting one cap the wrong way round, well alright give me a break! Also one of the heater wires was too close to one of the power resistors and melting so be warned. You guys were right, those resistors do get hot and need to be well away from everthing and well ventilated.
  
 I was right to be cautious about the pads, the PSU pad was fixed in the same way Sonic fixed one of his with wire.
  
 Looks like there was a bit of a problem fitting everything in on the underside of the PCB because I will either have to redo something when I have a closer look or fit a spacer round between the chassis and the bottom plate where there is now a gap, it could be the new resistor I fitted under the WIMA caps for the driver stage, because when I checked with the original resistor everything fitted........ just!
  
 Only one thing though, the second meter to come on on power up stays at max and doesn't appear to auto bias, but the engineer said that both channels sounded OK! So it's just that that might need something doing about, and then there's the new larger fans to fit.......... oh, and the LED lighting effects obviously!!
  
 Edit: I still can't try it though, I'm still having problems with windows 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

baronbeehive said:


> The amp's back
> 
> 
> 
> ...


 
 This is not good. Have you tried switching the tubes around from left to right to see if it's the tubes? Or does the meter get stuck when it overshoots, ie it's stays above max? That sometimes happens. It has happened to me a couple of times when starting the amp with low value plate resistor. Not at stock value though.
 You could always measure the voltage across the cathode resistors to be sure.


----------



## baronbeehive

sonictrance said:


> This is not good. Have you tried switching the tubes around from left to right to see if it's the tubes? Or does the meter get stuck when it overshoots, ie it's stays above max? That sometimes happens. It has happened to me a couple of times when starting the amp with low value plate resistor. Not at stock value though.
> You could always measure the voltage across the cathode resistors to be sure.


 

 Yes, it's not the tubes. The meter just goes straight to max when it comes on and makes no attempt to autobias. The only thing I did to that meter is resolder 2 wires. The engineer said that the light on that meter goes off and on, I don't know about the readings. So which resistors do I measure voltage?


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > This is not good. Have you tried switching the tubes around from left to right to see if it's the tubes? Or does the meter get stuck when it overshoots, ie it's stays above max? That sometimes happens. It has happened to me a couple of times when starting the amp with low value plate resistor. Not at stock value though.
> ...


 
 Ok, sounds like the needle gets stuck then? Is the needle on 100mA or is it past the 100mA mark? If the light goes on and off there has to be a bad connection. The backlight and meter readings should not have anything to do with each other as there's different connections. 
  
 Here's the connections for the lights inside the meters, circled in red:

 The meter gets its readings from the other two points, which are connected to the two .68 ohm resistors on component side.
  
  
 You can measure the voltage drop across the cathode resistors. With amp on measure DC voltage here:


----------



## Maxx134

I am thinking it is his meter wires incorrectly connected,
Maybey switched wiring of light to the meter..
I assume if meter was disconnect and reconnected maybe wires mix up


----------



## baronbeehive

maxx134 said:


> I am thinking it is his meter wires incorrectly connected,
> Maybey switched wiring of light to the meter..
> I assume if meter was disconnect and reconnected maybe wires mix up


 

 I don't think that was it, it was just one red and one black wire and I reconnected them just as they were, I'll double check just to be sure, I still have my wiring diagram!
  
 I've managed to find the multimeter in the bottom of a box - I'm still in transit between homes - so I will take off the bottom plate again and switch on and then measure the voltage between the 2 legs of each Mundorf E cap cathode bypass?


----------



## SonicTrance

baronbeehive said:


> maxx134 said:
> 
> 
> > I am thinking it is his meter wires incorrectly connected,
> ...


 
 Yes, do that and also check the meter if it's past the 100mA mark, ie stuck. I think the needle gets stuck when it overshoots.


----------



## Maxx134

I believe if the meter is "zero" in the front with the screw, 
It may solve the needle sticking problem,

That is, if it is stuck.

Could be probably the meter wire at the board solder at incorrect spot.

If amp is performing normal, then it must be one of these reasons.


----------



## baronbeehive

sonictrance said:


> Yes, do that and also check the meter if it's past the 100mA mark, ie stuck. I think the needle gets stuck when it overshoots.


 

 It had to be the most difficult to get at lol. They all read 24 - 25v except one which reads 30v. Any significance In this? I think this was a joint that came apart and I resoldered and it seemed OK then. I will just have a tug at it to see.
  
 Re: the meter it does attempt to autobias from 100ma to 80ma on startup and settles at around 90ma so it isn't stuck. The other reads around 60ma constantly which is normal.
  
 The 2 red and 2 white wires connecting to the meter are in the correct position.
  
 BTW it's great to have the amp back even if I can hardly lift it these days!
  
 Edit: I checked the joint and it stays put, but I noticed that it might not be making good contact the heatshrink may have melted into the joint.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Yes, do that and also check the meter if it's past the 100mA mark, ie stuck. I think the needle gets stuck when it overshoots.
> ...


 
 Ok, now that we have those readings we can see that one tube bias completely different from the others. You say it's not the tubes but those readings say otherwise. That 30v reading indicates a tube going bad. I guess that the cathode resistor that measured 30v is in the 90mA channel? If so, try a different tube in that socket. If you don't have replacement try it in the other channel that reads 60mA on the meter and see if that channel then reads 90mA instead.
  
 If that don't work, the cathode resistor that reads 30v may be out of spec (by a lot), but that's not likely I think.


----------



## baronbeehive

sonictrance said:


> Ok, now that we have those readings we can see that one tube bias completely different from the others. You say it's not the tubes but those readings say otherwise. That 30v reading indicates a tube going bad. I guess that the cathode resistor that measured 30v is in the 90mA channel? If so, try a different tube in that socket. If you don't have replacement try it in the other channel that reads 60mA on the meter and see if that channel then reads 90mA instead.
> 
> If that don't work, the cathode resistor that reads 30v may be out of spec (by a lot), but that's not likely I think.


 

 OK, but I reversed the 2 tubes on the right channel to the left channel yesterday and the same meter was still at max but I will try the different combinations again and check the voltage at the cathode bypasses again and see if it changes round. So you don't think the joint is bad?


----------



## SonicTrance

Ok, I didn't realize you already swapped the tubes. Then I really don't know to be honest. Measure the resistance across that bypass cap, amp off, it should measure 330 ohms. It shouldn't matter if some heatshrink has melted into the joint as long as the lead is connected.


----------



## baronbeehive

sonictrance said:


> Ok, I didn't realize you already swapped the tubes. Then I really don't know to be honest. Measure the resistance across that bypass cap, amp off, it should measure 330 ohms. It shouldn't matter if some heatshrink has melted into the joint as long as the lead is connected.


 

 It is 330 ohms. I don't know if this was the cap that I put in the wrong way, the engineer said it was one of these, but if I did perhaps it could have been damaged so maybe I should replace it?


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Ok, I didn't realize you already swapped the tubes. Then I really don't know to be honest. Measure the resistance across that bypass cap, amp off, it should measure 330 ohms. It shouldn't matter if some heatshrink has melted into the joint as long as the lead is connected.
> ...


 
 The Mundorf E-Caps are bipolar, so it doesn't matter which way you put them. But something is not right as you got that 30v reading and if it isn't the tube it has to be something else. Question is what? I don't know now..
  
 Usually, a meter reading that's off tells you that a tube is going bad,  but since you swapped the tubes and the same meter still reads 90mA and (I guess) about 30v across the cathode resistor something else must be wrong. If the circuit is working as it should you would not get 5-6v difference like you get now.


----------



## baronbeehive

sonictrance said:


> The Mundorf E-Caps are bipolar, so it doesn't matter which way you put them. But something is not right as you got that 30v reading and if it isn't the tube it has to be something else. Question is what? I don't know now..
> 
> Usually, a meter reading that's off tells you that a tube is going bad,  but since you swapped the tubes and the same meter still reads 90mA and (I guess) about 30v across the cathode resistor something else must be wrong. If the circuit is working as it should you would not get 5-6v difference like you get now.


 

 No, I agree somethings out, and I'll check the voltage again with swapped tubes. But the lytics caps are polarized, I missed that on page 1, and this is what the engineer said so it could be damaged and they're cheap to replace so I think I will order a replacement, at least that will eliminate that possible cause.
  
 There is a resistor that sets the voltage, maybe that needs to be checked?
  
 Finally I did resolder the 2 wires for that meter and found it quite difficult to get the solder to stick for some reason, I mention this as the only things I can think of that could be a possible cause.
  
 Edit: I just looked up the Ecaps and they are bipolar as you said but on page 1 it says they have a positive and a negative so I don't understand that.


----------



## SonicTrance

Most lytics are polarized but bipolar caps have no polarity.


----------



## baronbeehive

I've just switched tubes and you were right there is a faulty tube causing the reading at the caps. So that means that the meter problem is a separate problem because the same meter is reading 90mA, so perhaps it is my soldering!


----------



## baronbeehive

sonictrance said:


> Most lytics are polarized but bipolar caps have no polarity.


 
  
 The Ecaps look like they've got a positive and negative end and maybe that was what confused everybody including the engineer.


----------



## Maxx134

Edit.


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## Maxx134

baronbeehive said:


> sonictrance said:
> 
> 
> > Most lytics are polarized but bipolar caps have no polarity.
> ...


take a pic to see if yours is different from ours


----------



## Maxx134

baronbeehive said:


> I've just switched tubes and you were right there is a faulty tube causing the reading at the caps. So that means that the meter problem is a separate problem because the same meter is reading 90mA, so perhaps it is my soldering!



It could be that resistor feeding your meter that Sonic disconnected last time..


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## Maxx134

Actually I would also be sure by swapping the tubes yet again.
Don't keep the same two on each side together ...


----------



## SonicTrance

baronbeehive said:


> I've just switched tubes and you were right there is a faulty tube causing the reading at the caps. So that means that the meter problem is a separate problem because the same meter is reading 90mA, so perhaps it is my soldering!




Did you put the faulty tube in the other channel or in same channel but different socket? You need to test the bad tube in the other channel. The left meter should give you the high 90mA reading if the bad tube is in one of the two left sockets.


----------



## baronbeehive

OK, I'll check that, but it was one of the caps in the other channel that read 30v this time, yet it was still the same meter that read 90mA, which suggest a separate problem.
  
 Got to watch it changing tubes too quickly if that was what was causing the transistor problem.
  
 The E Caps look like a battery with a flat end and a slightly pointed end.


----------



## Maxx134

Looking for any marking on the Ecaps indicating polarity, like a white line or "minus" symbol,
 not how it is shaped.


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## Maxx134

I highly doubt your problem are the Ecaps


----------



## Maxx134

Show us also a pic of where the meter is connected on your board.

No rush, enjoy the amp.


----------



## MrCurwen

Why use a bipolar electrolytic as a cathode resistor bypass (if I understood correctly the position you are talking about)?


Good thing you have active cooling. I've never used active cooling myself, so I can't comment on it's efficacy. You're probably ok with it.

I had to make my comment because seeing those tight builds just gives me bad vibes from my own experiences. Also brings back memories of burning my fingers soldering while making too tight 3D point to point layouts...


Your amp does in fact very clearly implement NFB. The same node feeds the global loop from output to input (audio circuit feedback) and the op amp controlling the DC offset. So essentially two different feedback loops (for two different purposes), starting from the same node (output node). The 2k resistor from that node to ground is to provide a voltage refence to ground for the servo feedback. The audio feedback terminates to ground via the input transformer secondary, but the servo feedback has no other ground reference. For brevity, it is not wise or possible to have the servo also referenced to ground via the input transformer secondary, so a 2k resistor is provided for that reference. It cannot be left floating.

One of the big selling points of widespread implementation of NFB in audio circuits back in the 50's was that it maked component selection (quality) much less important, inside the loop. Saying that NFB ratio setting resistors have audio impact is not just wrong, it shows a clear lack of understanding what NFB actually is. 

If for the sake of argument resistors have sonic impact; the NFB ratio setting resistors would be at the bottom of the list of spots to consider upgrading the resistors. 

This is a component rolling thread, not a design thread, but I can't help wondering why would an amp that uses decent tubes (looking at the curves) need to use NFB?


----------



## Maxx134

I too wonder, and could not believe the resistors involved in NFB, 
As I only thought those resistors were for gain switch. 
But coinmaster is adamant about it,
So my fault for not verifying it in my amp.

So I will check this weekend my MK8 amp. 

I only looked as far as the resistors being implemented in parallel by the gain switch,
so I did not check to see if it also connected to the power tube anodes, according to coinmaster diagram...
It was a great undertaking for him to make a schematic from scratch, 
As Little Dot did not help with giving us a schematic.


----------



## MrCurwen

maxx134 said:


> I too wonder, and could not believe the resistors involved in NFB,




What do you mean, you didn't believe the resistors were involved in NFB loops or that they should be changed to another type of resistor?




> As I only thought those resistors were for gain switch.




Changing the amount of NFB actually is the gain switch. More NFB = less gain, less NFB = more gain.

Posting a schematic without part names and unlegible layout is not a good idea.


----------



## Maxx134

Yes I was unaware the resistors were involved in a NFB loop..

In general I understand the use of feedback as implemented in opamps for linearity, but didn't know it was implemented here for gain setting.

The power tubes in both mk6&8 amps are under-biased,
 and so maybe another reason why NFB was used.

I would rather like to eliminate NFB on this amp 



As for type of resistor, 
 I never changed mine as I didn't think they were in direct signal path.


----------



## MrCurwen

Eliminating NFB would require a comprehensive redesign not fitting under the purpose of this thread. NFB is keeping this amp afloat. It cannot simply be eliminated without designing out the problems it was utilized to sweep under the rug.

For the benefit of whoever might be interested, I drew up clean versions of MK6 audio circuit schems.


----------



## SonicTrance

Hi MrCurwen,
  
 Thanks for the schematic. I'm still learning how to properly read schematics but seems you have wrong values for cathode and plate resistors for power tubes, they're 330 ohms. Also, what does "NHSV" mean?


----------



## MrCurwen

sonictrance said:


> Hi MrCurwen,
> 
> Thanks for the schematic. I'm still learning how to properly read schematics but seems you have wrong values for cathode and plate resistors for power tubes, they're 330 ohms.




You're welcome. If more mistakes come up, I'll repost.




> Also, what does "NHSV" mean?




No Heater SVetlana

NH means it's the Spice model with no heater included, and SV refers to the source of the curves used for the Spice model. They were apparently taken out of Svetlana datasheet.


----------



## Maxx134

Very nice schematics. 
How refreshing and clear,
 as the old diagram was difficult to read and there is no input transformer in our amps.


----------



## Maxx134

mrcurwen said:


> NFB is keeping this amp afloat. It cannot simply be eliminated without designing out the problems it was utilized to sweep under the rug.



You have peaked my interest as I am very curious to learn about the design issues and choices made by designer.

I always curios to know why design choices are made with any design.

If not too off topic, 
maybe a bit of comments would be greatly appreciated.


----------



## baronbeehive

Yes, this is why I would like to have involved the electronics man who designs and builds his own tube amps for some contribution to the theory, if I get the chance I will sound him out.


----------



## baronbeehive

maxx134 said:


> Show us also a pic of where the meter is connected on your board.
> 
> No rush, enjoy the amp.


 
  
 Ha ha, I nearly got the board out again, this is it I think. If it doesn't show it I may have another pic. Haven't tried the amp yet, win 7 installed and foobar but I now have a bad tube and no replacements 
	

	
	
		
		

		
			





.


----------



## Maxx134

mrcurwen said:


> Why use a bipolar electrolytic as a cathode resistor bypass (if I understood correctly the position you are talking about)?



It was same design choice as designer. 
Mainly because it fits better by laying down on side, due to the amp slim design.
 Plus it is an audio grade cap instead of a generic electrolytic. 
But the fact that it was a bipolar only made it dummy proof during installation.


----------



## baronbeehive

Trying to find the best pic of the wire connection from the board to the meters
  

  
 or
  

  
 or
  

  
 or:
  
 This one and the next show where the 2 red and white wires broke off and I resoldered them back in the same place. Unfortunately I can't remember if that was the wire coming from the meters. I think it was because it came in from the centre by the meters and was made up of 2 lots of 2 grey wires, that's all I can tell with the board in, I don't know if anyone can help me on that.
  
 So those were the only 2 wires that came off, apart from the 2 red and white wires going into the meter on the one side.
  

  
 or
  

  
 or


----------



## SonicTrance

*5998 / WE421A Bias switch mod for the MK6*
  
 This mod is only for MK6 users and is a mod that optimizes the MK6 to use the 5998's and WE421A's power tubes. Sure, you can use those tubes without doing this mod and it'll sound good. But when your done and the mod is complete you wont regret doing it. That's a promise! 
  
 The sonic gain is incredible. Especially the low end gets improved with much more weight and slam. Also overall dynamics and clarity improves. I rate this mod as one of the big ones for the MK6, if you’re using these tubes that is. 
  
 You may have noticed, if you’re using 5998’s or 421A’s as power tubes in your MK6, that the amp runs much cooler and bias meters only reads about 30mA, while the 6080/6AS7G’s gives you 60mA on the meters and amp runs hot? That’s because the 5998/421A’s bias differently and doesn't get enough current in a 6080/6AS7G circuit.
  
  
*What are we doing here?*
  
 The goal with this mod is to cut the stock cathode resistor value in half, which in turn will double the amount of current to the tubes. The MK6 has 330 ohm cathode resistors, so 165 ohms is what we're looking for here.
  
 To do this you could either just swap the stock cathode resistors for some 165 ohm ones. But then you can’t use any 6080/6AS7G’s. So we implement a bias switch. That way we can use all our favorite power tubes.
  
 Basically what we do is get a 4 pole switch (one pole/tube) and 4 additional 330 ohm cathode resistors. Then connect the new resistors in parallel to existing resistors through the switch.
 As the stock cathode resistors are on top side of the board it’s easier to connect the new ones on component side in parallel to the cathode bypass caps. When the switch is on the cathode resistor value will be 165 ohms which is the new 5998/421A setting. And when switch is off the cathode resistor value will be stock 330 ohms for the 6080/6AS7G’s.
  
*These are the cathode bypass caps*
  

  
*Here's pics of the finished mod*
  

  

  

  

  

  
*How do we do this?*
 You can see from above pics that I've soldered the resistors on one end of the cathode bypass caps, and a wire from the other end. Then run the wires to the switch which makes them parallel to the stock cathode resistors. It is that simple. 
  
 I chose to have my bias switch through the bottom cover as the case is 10mm thick and it was hard to find a switch that would fit. Plus it was handy to be able to take the bottom cover off and drill the hole for the switch and not worry about getting metal residues inside the amp.
  
  
*What parts do we need?*
  
 - 4 x 330 ohm resistors, Mills MRA5
  
 - A 4 pole switch, the higher the voltage rating the better. Be sure to measure size first as well. A lot of switches are huge and wont fit depending on where you're planning to put it. 
  
 - Wire. I used 22awg silver plated copper with PTFE insulation. Decent size and easy to work with.
  
  
*It’s only recommended to switch while amp is off. If you have to switch while amp is on then be sure to unplug your headphones first!*
  
  
 Big thanks to user and amp builder @2359glenn for help and information about this mod!


----------



## Maxx134

sonictrance said:


> *5998 / WE421A Bias switch mod for the MK6*
> 
> ....
> 
> ...



Just repeating the thanks.
 Always appreciate a helping hand. 

Also,
I doubt anyone would want to switch while amp on,
As they have to turn off anyways to pull out / swap tubes!


----------



## Maxx134

In case anyone wondering, 
SonicTrance has been helping in PMs,
And so posting his new mods.


----------



## SonicTrance

maxx134 said:


> Also,
> I doubt anyone would want to switch while amp on,
> As they have to turn off anyways to pull out / swap tubes!




Yes, but I was referring to switching with amp on and 5998/421A tubes installed to compare the sound.


----------



## Maxx134

Since both the MK8 & MK6 have same driver stage voltage parameters to tube,
I decided to try a few MK6 driver tubes to see how they match with my amp, and how they really stack up against the 12a*7 family tubes, which are very popular in general use but not as popular in audiofile choices.
Edit*
Yes I realize feeding different output tubes in MK8 so my observations will generally pertain to MK8.

 I will see for myself and maybe blow away this myth that 12a*7 types are a lesser tube than a 6SN7GT type.. 
So far it is true that most 12a*7 are nothing special except for rare mullard or GEC or yellow T brimar, 
Yet the 12BZ7 & 12BH7 are above most other in that catagory, along with the e180cc pinch type. 
So far the best tube I have is the e80cc pinch,
A tube wich is clearly not a 12at7 type.

So I already have the Ken-Rad 6SN7GT black plate, and the pretty new type CV181-Z "treasures" with me know.
 Just waiting on the adapters to try them.
Also waiting for the ECC40 to arrive. .

Never thought this amp would have such a large tube rolling ability for driver tubes.

I have to concede though that the MK6 has the advantage in tube roll with some incredibly beautiful tubes.


----------



## SonicTrance

@baronbeehive
 Wasn't it your right meter that read 90mA? The wires that you broke are for the left meter. 
  
 Here's a pic of my amp to compare. Looks like the wires for the backlight for right meter are reversed on your amp.


----------



## SonicTrance

maxx134 said:


> Since both the MK8 & MK6 have same driver stage voltage parameters to tube,
> I decided to try a few MK6 driver tubes to see how they match with my amp, and how they really stack up against the 12a*7 family tubes, which are not very popular in use but not as popular in audiofile choices.
> 
> I will see for myself and maybe blow away this myth that 12a*7 types are a lesser tube than a 6SN7GT type..
> ...


 
 I'm looking forward to hear your findings on this Maxx!
  
 What I've learned though is that a particular driver tube can sound boring or dull with a certain power tube and good and lively with another. I know you're not planning on rolling power tubes though.


----------



## baronbeehive

sonictrance said:


> @baronbeehive
> Wasn't it your right meter that read 90mA? The wires that you broke are for the left meter.
> 
> ...............


 
  
 Are you sure? The wire coming in from the top left in my pic which ends in the broken red and white wires would surely be coming from the right meter wouldn't it? (The second meter to come on on power up).
  
 Quote:
 ..............
  
 Here's a pic of my amp to compare. Looks like the wires for the backlight for right meter are reversed on your amp.
  

  

  
 Yes the wires look reversed where you've circled in red but they must be right because they didn't break. Maybe they're reversed in the meter connections, mine are 2 red and 2 white looking from the back of the meters, that's why I don't think I could have got wrong when I soldered them back.


----------



## baronbeehive

sonictrance said:


> I'm looking forward to hear your findings on this Maxx!
> 
> What I've learned though is that a particular driver tube can sound boring or dull with a certain power tube and good and lively with another. I know you're not planning on rolling power tubes though.


 
  
 Absolutely right! I've been trying a friend's amp while I'm staying at his place. He has ECL 82's for power tubes, (Mullard and RCA's mixed), and new issue JJ's for drivers, (12ax7's). So I thought I would try my favourite TS5751's in their place. Surprisingly I didn't like them as much as the JJ's. I think that was because he already has musical sounding power tubes and needed a more analytic driver tube to go with them, whereas on my miniwatt amp I have quite analytical power tubes, (amperex),  and therefore the TS's sound better.


----------



## SonicTrance

I'm sure Baron.
  
 Here's the connections. Red circles for right meter, green circles for left meter.


----------



## baronbeehive

sonictrance said:


> I'm sure Baron.
> 
> Here's the connections. Red circles for right meter, green circles for left meter.


 
  
 OK, thanks, so that's ruled out the resoldering as a cause then, unless it is where I resoldered to the back of the meter,  so it must be something else.
  
 BTW Maxx there's not + or - markings on the E caps so they are bipolar as you said.


----------



## coinmaster

Sorry I've been busy lately
  
 Quote:


> For brevity, it is not wise or possible to have the servo also referenced to ground via the input transformer secondary, so a 2k resistor is provided for that reference. It cannot be left floating.


 
 Hrrm. Will the opamp be damaged if the inverting input is left floating? The voltage reference should be reached via the feedback between the inputs of the opamp so doesn't it just create its own "ground"?
 What am I missing?
 The servo reads fine on the bench although I don't recall if I had the 2k resistor soldered in since I thought it was a part of the NFB at the time.


> Saying that NFB ratio setting resistors have audio impact is not just wrong, it shows a clear lack of understanding what NFB actually is.


 
 I was mostly referring to the fact that if there is some distortion differences or whatever between resistors then the higher quality less distortive resistors would provide a more accurate feedback signal.


> OK, thanks, so that's ruled out the resoldering as a cause then, unless it is where I resoldered to the back of the meter,  so it must be something else.
> 
> BTW Maxx there's not + or - markings on the E caps so they are bipolar as you said.


 
 It would be better if you just unsoldered the meter and used your multimeter to test the current.
 I don't know the resistance of the internal ammeter on the multimeter so the .68ohm resistor might override it but if you disconnect one of the legs of the meter on the .68ohm resistor that is connected to the problem meter and then use the ammeter between the legs of the resistor you can get a proper reading.
 Leave your headphones unplugged while doing this and don't disconnect the .68ohm resistor if it doesn't work as bad things can happen if you test that way.


----------



## baronbeehive

coinmaster said:


> ...............
> 
> It would be better if you just unsoldered the meter and used your multimeter to test the current.
> I don't know the resistance of the internal ammeter on the multimeter so the .68ohm resistor might override it but if you disconnect one of the legs of the meter on the .68ohm resistor that is connected to the problem meter and then use the ammeter between the legs of the resistor you can get a proper reading.
> Leave your headphones unplugged while doing this and don't disconnect the .68ohm resistor if it doesn't work as bad things can happen if you test that way.


 
 Thanks, as I will probably resolder to the meter that's a good idea to check that first. I'm checking DC current not AC I assume?


----------



## coinmaster

DC.


----------



## Maxx134

baronbeehive said:


> resoldered to the back of the meter...



Ug Damn you disconnected that end too?!


----------



## baronbeehive

maxx134 said:


> In case anyone wondering,
> SonicTrance has been helping in PMs,
> And so posting his new mods.


 
 Very ingenious Sonic! It's shocking to think that your mod _*improves*_ the 5998 type even further!


----------



## baronbeehive

maxx134 said:


> Ug Damn you disconnected that end too?!


 
 Not voluntarily though! Those blasted wires have a life of their own lol.


----------



## SonicTrance

baronbeehive said:


> maxx134 said:
> 
> 
> > In case anyone wondering,
> ...



It sure does, and not by a little!


----------



## Redge78

sonictrance said:


> *5998 / WE421A Bias switch mod for the MK6*
> 
> This mod is only for MK6 users and is a mod that optimizes the MK6 to use the 5998's and WE421A's power tubes. Sure, you can use those tubes without doing this mod and it'll sound good. But when your done and the mod is complete you wont regret doing it. That's a promise!
> 
> ...


 
  
 Excellent job SonicTrance. Exactly what i like.
 The text/pics have been copied in page 1 under section 3 ("around the Power cathode").
  
 If you want to make changes, plz PM me.


----------



## SonicTrance

Thanks Redge! Appreciate it!


----------



## Redge78

mrcurwen said:


> Why use a bipolar electrolytic as a cathode resistor bypass (if I understood correctly the position you are talking about)?
> 
> 
> Good thing you have active cooling. I've never used active cooling myself, so I can't comment on it's efficacy. You're probably ok with it.
> ...


 
 It may be a bit late to answer that ... but here it is (the subject is interesting anyway)
  
*"Why use a bipolar electrolytic as a cathode resistor bypass" *
 That was our first mods, we were experimenting and changing from a crap 2p component for a "audio grade" Silmic (+RIFA bypass) was already an already a significant imporvement.
 Why a Lytic ? ... The film/PIO alternatives are MUCH more expensive and are taking a LOT of space.
 At that time, my Silmic were 470µF ... think of what would have been that capacity in some russian PIO ... for each of the 4 power channels !
  
 One year latter, this is something that I have been considering (exchanging for a 220µF MKP, maybe ... some SCR PA/PB). Or I have my monstruous TPC 100µF I can try, I'll raise a bit the cut freq. but who cares ... for a test. 
  
_* "cooling"*_
 yes, we have an efficient cooling system. Before that, the amp case was "burning hot" (difficult to keep on the case after 10s). With the cooling, the case is a bit colder that the hand temperature, and can be adapted if the room temperature rises (summer !).
  
_*"NFB"*_
 Thanks for the tech insights. That's a part of the amp I didn't bother to study.
 As for why they have implemented an NFB, the "lower quality components" reason makes sense. This is an 1K$ amp after all, not an AudioNote ... And we ahve already realised that some few components may be worth replacing.
 That being said, I have seen "full" NFB on much more ambitious tube amps. Like five times more ambitious ...
  
 So, could NFB be also used for something else, a more dignified function ? like counter-acting some sonics drifts when the tubes are aging ?
  
 What would be interesting to know is how much NFB is sent back in the Input ... 1% ? 10% ?  More ? Less ?
 From what I understand, this NFB ratio will be (roughly) dependant of the amplification factor of the driver stage and of the voltage drop by the resistance bridge after the output (around the swich).
 So ... what happens to the NFB when we change our original 12AT7 driver tubes (amp: 60) to some (much better sounding) E80CC (amp: 27) ... And could a part of the better sound caused by a diminished NFB ratio ?
  
*"the NFB ratio setting resistors would be at the bottom of the list of spots to consider upgrading the resistors"*
 I didn't pay much attention to it at the time, but I have read something about it where the guys were not that affirmative. Actually, they were setting the importance of this NFB resistors between the Anode resistor (most impact on sound) and the Cathode resistor (no significant impact on sound). But that's just one feedback amongst many what may vary. 
  
 Finally (for tonight) I have seen some schematics were they are adding some RC filters on the NFB loop to be used as "Bass boost". That's something I may have a look into, if equalisation in the digital domain doesn't work well enough.


----------



## Redge78

mrcurwen said:


> For the benefit of whoever might be interested, I drew up clean versions of MK6 audio circuit schems.


 
  
 Great ! A schematic we can read ! Nice !
  
 What is missing most is around the Load and how it is wired when used in Single-Ended (with a 3pin jack, I mean) where both chanels share the same "ground" and 2 power channels out of 4 are unused.
 Again, I didn't pay much attention to it as I don't use the SE output at all, but from what I remember, the "ground" at the jack plug goes to the "middle ground" of the Power PSU ... the rail that I referenced as "0V" on my PSU drawing page 1.


----------



## Mogos

Sonic T very nice finding. Thank you for sharing and instructions. I imagine you are in haven listening to the music with anode and catode resistors optimisation and the W421 
	

	
	
		
		

		
		
	


	




. I decided to do for now optimisation of the USB signal path out of a computer. The purchase of the 5998 or W421 will be postponed for some time. I belive that with the resistors optimisations and the W421 the amp is reaching now the top-notch performance you could not find any other one.


----------



## SonicTrance

mogos said:


> Sonic T very nice finding. Thank you for sharing and instructions. I imagine you are in haven listening to the music with anode and catode resistors optimisation and the W421
> 
> 
> 
> ...


 
 Hi Mogos! Long time no see!
  
 Yes, well actually I took my Ra switch out when troubleshooting the amp when it broke. So I still have some optimization to look forward to. This time I'll follow your advice that you told me long time ago. Measure my tubes gm to get a more fine tuned Ra, instead of calculating from datasheet spec. I'll take an average reading though, I wont go crazy with different Ra for different tubes.
  
 Remember that I sold all my 5998's before? Well, after I heard what this bias optimization did for my WE421A's, I bought some 5998's once again, lol. They haven't arrived yet, but I'm looking forward to hear the improvements on the 5998's as well.


----------



## baronbeehive

mogos said:


> Sonic T very nice finding. Thank you for sharing and instructions. I imagine you are in haven listening to the music with anode and catode resistors optimisation and the W421
> 
> 
> 
> ...


 
  
 Hi Mogos, sounds like your amp is trouble free now? Are you separating the power line in the USB or just getting a cable upgrade then?
  


sonictrance said:


> Hi Mogos! Long time no see!
> 
> Yes, well actually I took my Ra switch out when troubleshooting the amp when it broke. So I still have some optimization to look forward to. This time I'll follow your advice that you told me long time ago. Measure my tubes gm to get a more fine tuned Ra, instead of calculating from datasheet spec. I'll take an average reading though, I wont go crazy with different Ra for different tubes.
> 
> Remember that I sold all my 5998's before? Well, after I heard what this bias optimization did for my WE421A's, I bought some 5998's once again, lol. They haven't arrived yet, but I'm looking forward to hear the improvements on the 5998's as well.


 
  
 Well that's handy, the 5998's are more plentiful so if we buy them all up before Mogos has a chance......................
	

	
	
		
		

		
		
	


	




.


----------



## Mogos

Baron to satisfy your curiosity about the USB subject I will do the offtopic record 
	

	
	
		
		

		
		
	


	




. I hope it will be forgiven.
 There would be not to much to write about if it will be only a cable upgrade.
 See how looks my USB connection on the computer side.
 The USB card is PAUL PANG AUDIO GRADE V2 USB CARD.

 and below final "product"

 On the way are Wyred 4 Soound Recovery and Intona High Speed USB Isolator.
 I will also use JCAT cable and Corning USB 3.Optical™ Cable in the chain.
 I know it looks or even is complicated. The assumption is to have mobile setup and that is the reason for laptop computer as a player.
 I hope the galvanic isloation and femtoclock reckloking will pay back in the better sound. I will see 
	

	
	
		
		

		
		
	


	




.
 I do have some doubts about the improvment results as I am experiencing now one of the best sounding headphone rigs I have ever herd. But if I will not try it then curiosity will ate me.
 I was swallowed by the music and the addiction is deepening. 
 Will see 
	

	
	
		
		

		
		
	


	




.


----------



## MrCurwen

redge78 said:


> It may be a bit late to answer that ... but here it is (the subject is interesting anyway)




Yes, I don't have much to contribute regarding component rolling, I design and build amps and that's my focus. If people find value in more technical discussions in this thread, I'm very happy to participate. It is very interesting!

Regarding bipolar caps:

As a rule, bipolar caps are not as good as regular electrolytics. Basically, a bipolar is two electrolytics in series. Anyway, some bipolars will surely be better than some (or many) polar electrolytics.

What I myself would do, for best results, is utilize a capacitance multiplier. It gives out heat (a lot) and is a bit tricky to set up, but it is the most transparent solution in my experience. It basically uses a FET and a small capacitor (say a 250nF or 1µF film cap) to simulate thousands of µF's of capacitance with pretty close to ideal "capacitor performance specs" (in quotes because the system is not a cap, but a simulation of a cap). In both sims and my listening tests, it performs as good as fixed grid bias when compared to RC bias (with large film caps) or LED bias.




> yes, we have an efficient cooling system. Before that, the amp case was "burning hot" (difficult to keep on the case after 10s). With the cooling, the case is a bit colder that the hand temperature, and can be adapted if the room temperature rises (summer !).




I live in Finland in a 109 year old stone building in the capital city. During winters the 70cm thick stone walls radiate cold; if you put your hand on the wall inside the apartment, it's quite cold. I have my workhorse amp in the corner, touching the walls. It's happy and cool in the winter.

During summers, the text prints on the power resistors fade a bit, from heat exposure... I have some power resistors with no visible text left, even though they have never been operated electrically more than 50% of specs. You must remember that the 10W or whatever it is rating is in a specific ambient temperature. So even if grossly overrated, some components may be working at or closer to their max specs in some situations.

Heat is a complicated and sometimes hard to predict nuisance. Active cooling probably is the way to go.

Me as a DIY guy who only uses self designed and self built amps, I've resigned to just building a few new amps every year with not much though spent on longevity. However when making amps for other people, I've had to adapt a much more conservative outlook on heat.




> Thanks for the tech insights. That's a part of the amp I didn't bother to study.
> As for why they have implemented an NFB, the "lower quality components" reason makes sense. This is an 1K$ amp after all, not an AudioNote ... And we ahve already realised that some few components may be worth replacing.




Well the whole picture, technically, is complex.

NFB does "equalize" components to a large degree.

However the real issue with the coupling caps for example, is not their inherent poor quality, but the way in which the circuit is set up. I'm talking about the 1µF cap between the input stage and the output followers.

The source, the input stage output, is of such very high impedance and outlandishly poor current capability (the 6SL7's are running at something like 400 to 600 µA), that it most certainly bring out all the parasitics of the coupling cap that it is feeding.

On the other side, that same cap is supposed to feed and satisfy the parasitics of the output tube grid. Those big power triodes have 

1) large electrode surface areas 

2) high pulse capability, meaning a large pool of 'vacant' electrons humming around the cathode, hitting the grid

These properties lead to a large grid current. Now the cap cannot supply more current on the output side than is provided on the input side. Then if the cap itself has parasitic properties (being a real physical capacitor, it most certainly does), you have a recipe of 1) poor sound 2) capacitor mattering a lot.

Now if you have a situation where the source impedance is a lot lower, you will alleviate some of these conditions.

The only way to really alleviate the output tube grid parasitics (besides the all around solution of NFB) is to provide a good low impedance direct coupled source driving the grids.

These reasons are also the reason why these amps don't utilize an output capacitor. The follower system serving as the output of this amp is not that good; if you put a capacitor between the amp and the load (headphones) it's parasitics would affect the sound, it would not be sonically transparent.

The solution to these problems is not universal direct coupling. Instead it is to use low output impedance drivers in strategic places. Practically, it means source followers. Using capacitors, even cheap ones, in front of source follower FET gates (gate capacitance is manifested differently in source followers than gain stages), is completely transparent. 


Having a 500µA 6SL7 with resistor plate load driving a large cap and a high pulse capability power triode on the other side is like having a weak old lady holding a wobbly 5 meter pole in her hand and trying to write some text with the pole that she is reading. Now make the pole a bit less wobbly, and sure, the text she is writing will probably resembe the input (text she is reading and copying with the pole) more. But change the weak old lady to a strongman, you have a different situation. Or, maybe change her to an industrial robot holding and controlling the pole...

You are focused on the cap. All the sonic properties of any of these caps are 100% dependent on the circuit. Caps themselves do not - above a certain point - have any inherent sound to themselves.

Same goes for tubes.




> So, could NFB be also used for something else, a more dignified function ? like counter-acting some sonics drifts when the tubes are aging ?




I don't know what is or is not dignified in this context. The way the NFB loops are set up, they do nothing for balance. Each side of the balanced circuit (per channel) has it's independent NFB loop. This means that tube selection may indeed matter. This is not a good thing, it's a very bad thing. You are not going to hand or ear match the tubes to any great degree. Some matches will sound better than others, but it's a needle in a haystack kind of situation.

The main point of the NFB in this amp seems to be to lower output impedance. I did some sims with the circuit, and I got the following results (the exact numbers are trivial, the comparison is the point);

Low gain mode (using 100k NFB resistor): output impedance about 23 ohms.

High gain mode (using 390k NFB resistor): output impedance about 54 ohms.

Open loop (no NFB): output impedance about 83 ohms.

Using the 6AS7 as a pure cathode follower (no NFB, CCS load underneath): output impedance about 266 ohms.

These numbers are well within expectations. As demonstrated by comparing to the pure cathode follower, the White Cathode Follower does benefit the output impedance a lot. NFB benefits it further.

I also dropped in a CCS loaded source follower. FETs not optimized to the task, just any common general purpose high voltage n-channel FETs:

Open loop (no NFB): output impedance about 2.3 ohms.

That's 2 point 3 ohms. With no NFB, or distortion added. 


So, the main point of the NFB seems to be to lower the output impedance. Secondary point is to clean up some distortion caused by bad load lines on the input tubes. Third, alleviate the sonic impact of poorly driven caps and other parasitics.



> What would be interesting to know is how much NFB is sent back in the Input ... 1% ? 10% ?  More ? Less ?




I put a 100mV input signal into the sim circuit, and looked at what is the level on the input tube grid after NFB is applied.

Low gain mode (using 100k NFB resistor): about 69mV

High gain mode (using 390k NFB resistor): about 35mV




> From what I understand, this NFB ratio will be (roughly) dependant of the amplification factor of the driver stage and of the voltage drop by the resistance bridge after the output (around the swich).




Yes.



> So ... what happens to the NFB when we change our original 12AT7 driver tubes (amp: 60) to some (much better sounding) E80CC (amp: 27) ... And could a part of the better sound caused by a diminished NFB ratio ?




Less gain to swap for lower output impedance, and lower distortion.

Distribution of harmonics: more low order distortion, and less high order distortion.

Most dramatic change is caused by the tube types and their respective curves. Look at the curves. That's the first place to look at when thinking about using a specific tube type.

I would not use 12AT7 in a HIFI amp. 12AX7 properly loaded and buffered is good for even the best amps, 12AT7 is not. Again, look at the curves, and think about the load.

ECC80 is ok. Proper circuit design of course matters.



> I didn't pay much attention to it at the time, but I have read something about it where the guys were not that affirmative. Actually, they were setting the importance of this NFB resistors between the Anode resistor (most impact on sound) and the Cathode resistor (no significant impact on sound). But that's just one feedback amongst many what may vary.




I use 1W carbon film resistors for general purposes. I don't know the maker. I would recommend those to anyone, for any purpose (wattage allowing). I would not recommend loading any tube in a serious HIFI amp, with resistors. 



> Finally (for tonight) I have seen some schematics were they are adding some RC filters on the NFB loop to be used as "Bass boost". That's something I may have a look into, if equalisation in the digital domain doesn't work well enough.




In my opinion this is 100% completely outside of any serious HIFI ambition. I wouldn't even consider it.

A flat frequency response can be had without any equalization at all. Simply nonsense, in my experience and opinion.


A bit of a long post, I hope other participants find value in this.


----------



## coinmaster

> On the other side, that same cap is supposed to feed and satisfy the parasitics of the output tube grid. Those big power triodes have
> 
> 1) large electrode surface areas
> 
> ...


 
 I thought a grid leak resistor takes care of electron build on the grid?  I also thought the grid has a high input impedance, something like 50Mohms, how does any current flow between stages?


----------



## Redge78

Quote:


mrcurwen said:


> Yes, I don't have much to contribute regarding component rolling, I design and build amps and that's my focus. If people find value in more technical discussions in this thread, I'm very happy to participate. It is very interesting!
> 
> Regarding bipolar caps:
> 
> ...


 
 Sorry, I jumped at the "Lytic" part, missing the "bipolar" ... and yes, bipolar is not electrically required here, I didn't used any of those. If someone did it, it must be linked to some listening feedback, I suppose.
 And I was under the impression that the bipolar was 2 Lytics in parallel and head/tailed ...
  
 The capacitance multiplier is interesting, but that's kind of "level 3" mod.
 We have done "level 1" (the Silmic/RIFA change), I'm currently experimenting the "level 2" mod (much larger capacity bank with Silver/Mica-MKP-FKP ... and possibly a large MKP to end).


----------



## Redge78

mrcurwen said:


> A bit of a long post, I hope other participants find value in this.


 
  
 Don't worry about that, I am pretty confident when saying that we all found this post very interesting and we appreciate the time and effort you put to do it.
  
 I'll "answer" bit by bit, I have to think about a lot of things, and learn even more.
  
 The "NFB reduces the Output resistance" is pretty neat and is sufficient a reason to explain why they have inserted it in the design, I think. Especially for the MK6 that is given to be able to drive 20 ohms headphones ...
  
 And I'm not sure to be ready to follow you in the "no inherent sound of the cap" ... not saying that I don't believe you but it's very far from what we have been experimenting over the past year.
  
  
_Low gain mode (using 100k NFB resistor): about 69mV
 High gain mode (using 390k NFB resistor): about 35mV_
  
 Funny I would have thaught it would be the other way round ... "High gain" => less NFB => higher input voltage.


----------



## MrCurwen

Redge78 you are correct, it is in fact the other way around. I should've been more careful in copying the results from where I put them down.

Also to clarify my poor wording regarding NFB changes with tube type change:



> Less gain to swap for lower output impedance, and lower distortion.




Means:

Less gain to swap for lower output impendance and to lower distortion.

Reducing NFB (all other things equal) increases distortion. In a tube type change, all other things are not in fact equal, of course. 


I think I must take back the capacitance multiplier recommendation. For normal SE operation it still stands, but I'm not sure it's good in a WCF. Probably worth experimenting though; it is the best not-fixed-grid-bias biasing method known to me.

For best results... WCF will never be best results.

I used to be a cap guy. Unfortunately I don't have the money to spend on expensive caps, so I had to engineer around the cap problem. Now I use caps that withstand heat the best. 

The best caps I found were SSG silver micas. I still have a bunch of them in 144nF or so. I don't really feel the need to use them over the MBGO film caps, since they don't provide any benefit in a properly designed circuit. In a lacking circuit they sure did, like night and day.

But I don't want to be the guy in this thread telling everybody they're wrong. Not everybody can DIY a whole amp, or wants to.


----------



## Maxx134

mrcurwen said:


> "A bit of a long post, I hope other participants find value in this."




Wow 
Yes this excellent, because it is alot of info to chew on,
 and start ideas for perfecting things further.



mrcurwen said:


> "I would not use 12AT7 in a HIFI amp. 12AX7 properly loaded and buffered is good for even the best amps, 12AT7 is not. Again, look at the curves, and think about the load...
> ECC80 is ok. Proper circuit design of course matters."




I completely agree here and whish I also had LOOKED AT THE CURVES earlier...!

I have tried all thee 12a*7 types, 
and the least impressive were the 12at7's and other variants of same mu output.
The best were surprisingly (to me) the 12ax7 types.
I thought the higher mu would make distortion but missed the point to LOOK at the linearity curves.
Those 12at7 types probably made to have those curves for guitar amps. 

So yes the best ones I found were the Silvania & GE 12ax7 black plates.

Yet the best driver tube in my amp was the large e80cc type.
Best, untill recently that is.
After trying a 1950 RCA 12BH7A black plate with tallest plates I seen in a 9pin tube, matching the e80cc with a bit more lively presentation.
I account this to the curves and circuit design as McCurwen states.

Although in the MK8 I will now look into eliminate the NFB as my output power tubes are already practically the most linear tubes ever made, (original russian "supertube").
So yes parts can sometimes overcome circuit design limitations. 

In my MK8 I believe the NFB was left also implemented so my tubes run below optimal bias.
Maybe for heat issues?

I will optimize the correct bias level ans see what changes occur.



mrcurwen said:


> "I use 1W carbon film resistors for general purposes. I don't know the maker. I would recommend those to anyone, for any purpose (wattage allowing)."



I partially agree, yet choose a different approach:

For general purposes yes .
Carbon film are very solid choice general resistors,
but for Anode/plate or any other signal path resistors I would not never want to use them in heat conditions generated in a TUBE amp.

What is generally stated as a fact about carbon film having thermal noise, 
Actually materialized sonically, and came to pass in our hot amps of the old thread. 
A user reported a sonic warmth to the sound upon replacing his 330ohm anode/cathode resistors, with big carbon film ones,
 in the old MK6 thread.
He still preferred the change because the stock resistors were burnt out of spec values, so less equal.

Because of this, I would never use carbon resistors in a final product in a tube amp, although it makes sense financially for a company. 

Being a consumer, I can spend a bit more and get superior non-inductive wirewound resistors for signal path,
 and best metal film for low watt signal path.




mrcurwen said:


> "The only way to really alleviate the output tube grid parasitics (besides the all around solution of NFB) is to provide a good low impedance direct coupled source driving the grids."



Yes.
I really whish we could do this in future mod.
It would have been great if we could have a direct coupling instead of this coupling cap between the two stages.

Especially since our amp is now dependent on a quality Cap ,
 because as you say it is a non-optimal design of this driver stage feeding the power stage thru a coupling capacitor. 


To put things in perspective, there are compromise in all amps and none are optimal. 

So far we dealt with this using an expensive copper film cap, or highly rated mundorf caps.



mrcurwen said:


> "The way the NFB loops are set up, they do nothing for balance. Each side of the balanced circuit (per channel) has it's independent NFB loop."




I too was wondering about this and remember coinmaster mentioning the 56k resistors tied between the channels, 
Which I am now assuming may be their frame of reference, or balance as you say, so not independent NFB?.

Similar to the opamps having a 2k resistor to ground for a "reference point"..

*Quote Coinmaster*:


> Quote, Coinmaster :
> "Will the opamp be damaged if the inverting input is left floating? The voltage reference should be reached via the feedback between the inputs of the opamp so doesn't it just create its own "ground"?
> What am I missing?"




 Your missing what McCurwen said about a common reference point for the opamps so they won't be independent of each other.




mrcurwen said:


> " if you put a capacitor between the amp and the load (headphones) it's parasitics would affect the sound, it would not be sonically transparent."




Yep, Completely agree here with any amp.
That's why I prefer this OTL design.
Unfortunately this "purest" approach is limit to higher output impedance.

So the compromise here is higher output impedance of our OTL amp,
Wich you stated the choices made to lower it's impedance :
1-The NFB
2- the white cathode follower 
3- output tube choice

 4- then your suggestion of NOT using direct tube output(!) :
Using an FET "follower", 
 So end result is a hybrid tube amp!:

"The solution to these problems is not universal direct coupling. Instead it is to use low output impedance drivers in strategic places. Practically, it means source followers. Using capacitors, even cheap ones, in front of source follower FET gates (gate capacitance is manifested differently in source followers than gain stages), is completely transparent."
[/quote]

Actually I think that choice would mean that it is no longer a "tube" amp..
For me, " the jury is still out " for a hybrid amp being a best choice.

To me it depends on what is it that your looking to hear...

I base preference from my own listening experience as everyone does.

First off,
 I havent heard yet a SS or hybrid with greater soundstage or micro detailing than tube amps.

Secondly,
 Although I certainly heard very beautiful powerful sound from a hybrid amp like a Cavali amp,
It still didn't measure up to a top tube amp, with coupled output transformers like an Eddie Current amp.

Why?

Foe me the test is still soundstaging. 
In this area, to me nothing I have heard beats tube amps, and I believe it has to do with the capacity to retain low level micro information. 
This is confused with the bad rap that tubes generally have with higher harmonic distortion figures,
 when just looking at specs and not the whole picture.

 Regardless of the type distortion measured,
 the micro detailing & ambiance is preserved in tubes,
 Unlike the solid state amps I have heard.

The problem here is that these differences are mostly noticable in headphone amps, 
which is of recent popularity.

They don't have ambient room acoustics to help which speaker amps have had and get away with.
So it is my opinion that this has gone largly unnoticed in past. 

 I believe tube amps will always have larger soundstaging.
As example, my mk8 2yr ago at a NY meet had obviously greater depth and layering of soundstaging next to the monster amp which was being fed the same source.

Like most SS amps, it's background hit a wall, while my amp extended beyond those boundaries. 
Wasn't even about my amp.
It did not even have any internal super mods at the time..
Only Tube majic.
A similar observation was noted with the same SS amp alongside a "Torpedo" tube amp, we're the listeners were surprised to prefer the tube amp.




mrcurwen said:


> But I don't want to be the guy in this thread telling everybody they're wrong. Not everybody can DIY a whole amp, or wants to.



Haha yep this is alot of work as it is.
Importance is being satified with the outcome, 
untill the next mod.


----------



## Maxx134

I have originally not wanted to post images of the modded amps,
Because the focal point is about the interior mods,
But realized recently had a change of heart, 
Looking thru the tube amp images thread,
We should not deny our amps beauty..
So *edit*
posted some pics first page.


----------



## SonicTrance

mrcurwen said:


> But I don't want to be the guy in this thread telling everybody they're wrong. Not everybody can DIY a whole amp, or wants to.


 
 First off, thanks for the detailed information you post, very informative!
  
 Second, even with all the design flaws and the WCF topology as a whole not being optimal. I think that if you got to hear one of our modded amps you'd enjoy it, a lot.


----------



## coinmaster

> mrcurwen said:
> 
> 
> > "The only way to really alleviate the output tube grid parasitics (besides the all around solution of NFB) is to provide a good low impedance direct coupled source driving the grids."
> ...


 
 It's not too hard to direct couple but it's also not something you can do simply by modifying the original product. At least not to the level of the other mods. I plan on testing the sound quality of direct coupling soon enough.
 MrCurwen claims that parasitics and low current are responsible for cap sound but I don't get how any current can flow into the grid due to its high impedance.
  
  


> I too was wondering about this and remember coinmaster mentioning the 56k resistors tied between the channels


 
 The 56k resistors at the output are dummy load resistors I think.
  


> Your missing what McCurwen said about a common reference point for the opamps so they won't be independent of each other.


 
 Maybe I'm stupid but all of the opamps are referenced to the same ground via the non-inverting input of the opamp, that means they will all attempt to reach the same potential at the output. I still don't understand the need for a reference to ground on the inverting input.
  


> For me, " the jury is still out " for a hybrid amp being a best choice.


 
 I feel the same. I've heard that when using fets as followers they don't impart any sonic impact but that seems too good to be true since that would make solid state followers the end all of HI-FI. As usual I'm going to take everything with a grain of salt until I test it for myself.


> Second, even with all the design flaws and the WCF topology as a whole not being optimal. I think that if you got to hear one of our modded amps you'd enjoy it, a lot.


 
 Yeah, it's mind blowingly realistic and euphonic.. First amp I've experienced both realism and euphony together especially on my HD800s.
 The first few months I was going mad with withdrawals 
	

	
	
		
		

		
		
	


	




 I was actually addicted to it.
 I've since forced myself to forget how amazing it sounds so I can continue with my R&D without going crazy.
  
 I'm building my amp modular so I can easily make more iterations without too much trouble.
 Variable power supply box
 Output stage box
 Input stage box
  
  
 The output stage box will initially be my modded MK6 in a more suitable custom chassis.
 The next output stage box will be the new output stage Broskie and I created.
 The input stage box will be switchable between the stock SE input stage and a couple of other more complex designs.
  
 Unfortunately it's always a waiting game on components and cash. I should finally have all the official components here in a week or so.


----------



## Maxx134

sonictrance said:


> mrcurwen said:
> 
> 
> > But I don't want to be the guy in this thread telling everybody they're wrong. Not everybody can DIY a whole amp, or wants to.
> ...



Haha that because what is considered a flaw in general, is actually a solution in this amp.

Consider the makn coupling cap.
In general all coupling caps are a flaw, 
But in practice used in the MAJORITY of tube amps I have seen.
In our amp this "flaw" is actually the "solution" for combining the driver & output stages.

We "compensate" this flaw by using the best cap attainable to the owner. 

This will usually be a huge improvement over the stock caps which all manufacturers are limited to because of financial profit reasons.

So the end result is an improvement. .


----------



## Maxx134

coinmaster said:


> [CONTENTEMBED=/t/782183/little-dot-mk8se-mk6-super-mods/1340_20#post_12550285 layout=inline] [/CONTENTEMBED]
> 
> 
> 
> ...




Hmm, yes we need to know if any sonic gains are worth the effort over simply upgrading the cap!




coinmaster said:


> MrCurwen claims that parasitics and low current are responsible for cap sound but I don't get how any current can flow into the grid due to its high impedance.




Hmm again, I think the .22uf caps all around the output circuit were overlooked..
They are supposed to deal with parasitics.
It is obvious we don't have any when listening to amp.
I have zero noise at full volume..



coinmaster said:


> > Your missing what McCurwen said about a common reference point for the opamps so they won't be independent of each other.
> 
> 
> 
> Maybe I'm stupid but all of the opamps are referenced to the same ground via the non-inverting input of the opamp, that means they will all attempt to reach the same potential at the output. I still don't understand the need for a reference to ground on the inverting input.



Listen we all know you are intelligent yet comprehension of topology is not something learned overnight.
 If he already saying what those 2k resistors are for , then that's what it is .
I get your trying to understand "why" and that's a good thing. 
Sorry I can't explain it other than the fact that in real world the opamps will not always behave exactly as you want, so we have the trim pots and the 2k to ground resistors to make sure.

Also is the other fact that SonicTrance 2k resistors burned in another scenario just as example not easy to see all the variables in a design all at once.



coinmaster said:


> > For me, " the jury is still out " for a hybrid amp being a best choice.
> 
> 
> 
> I feel the same. I've heard that when using fets as followers they don't impart any sonic impact but that seems too good to be true since that would make solid state followers the end all of HI-FI. As usual I'm going to take everything with a grain of salt until I test it for myself.



Well, even the best FET can impart something to sonics.
It has been discussed in yggy threads as a limiting factor the the yggy, and a future project I put on hold to bypass the FET buffer stage.
That's why I covered up the mod nameplate on my yggy as the mod not done yet..





coinmaster said:


> Yeah, it's mind blowingly realistic and euphonic.. First amp I've experienced both realism and euphony together especially on my HD800s.
> The first few months I was going mad with withdrawals   I was actually addicted to it.
> I've since forced myself to forget how amazing it sounds so I can continue with my R&D without going crazy.
> 
> ...



Yes must have patience, 
I remember making my own circuit boards in college projects and it was really fun.
Don't loose the fun of this hobby with the obsession to finish.
There is no rush or race, and remember compromises is not always a bad thing.


----------



## MrCurwen

maxx134 said:


> Wow
> Yes this excellent, because it is alot of info to chew on,
> and start ideas for perfecting things further.




Great!




> I have tried all thee 12a*7 types,
> and the least impressive were the 12at7's and other variants of same mu output.
> The best were surprisingly (to me) the 12ax7 types.
> I thought the higher mu would make distortion but missed the point to LOOK at the linearity curves.
> Those 12at7 types probably made to have those curves for guitar amps.




12AT7, along with 12AU7, 12AV7 and 12AY7 were all designed for radio frequency operation. Linearity is not important in all applications.




> Although in the MK8 I will now look into eliminate the NFB as my output power tubes are already practically the most linear tubes ever made, (original russian "supertube").
> So yes parts can sometimes overcome circuit design limitations.




I don't know about your system, but I very much doubt your output section has very good output impedance without NFB. 

Is your output tube 4P1L? =) That is the most linear tube ever made. 6E5P and some TV sweep tubes come close.

Anyway, what is your output tube? Is the schematic similar or maybe identical to the other model, which I posted?


Tubes simply are not current devices. Some of them can deal with some amounts of current, but they will only be less bad at it, none of them are good in the current domain.

Providing current to a low impedance load (yes, even 300 ohm headphones are low impedance if you compare to most tubes' plate resistances) is hard hard work for tubes. They only barely manage it, and none, not a single one, manages it without smearing the sound a great deal. That's why NFB is needed to save the day.

Talk about voltage amplification, then tubes win running circles around all the competition. (The ones with good curves.)

NFB is a crutch to have tubes do something they are not designed to do, and are very bad at doing.


Regarding resistors:



> What is generally stated as a fact about carbon film having thermal noise,
> Actually materialized sonically, and came to pass in our hot amps of the old thread.




I'm a headphone guy mainly, and as all of us know, headphones reveal ALL. Pretty much no mistakes allowed in the noise department.

All my amps use 1W CF for all purposes. No hiss, no noise, no nothing. I'm not alone in this.

There's other things going on in your amps.

Thermal noise is not an issue regarding resistors. You will have other things go wrong before resistors start making hiss because of temperature.




> A user reported a sonic warmth to the sound upon replacing his 330ohm anode/cathode resistors, with big carbon film ones,
> in the old MK6 thread.




I don't know what was there before, but the CF probably stopped some oscillation. Usually with all other things being equal, a "softer sound" due to a single replacement is an oscillation either stopping or moving bandwidth.



> He still preferred the change because the stock resistors were burnt out of spec values, so less equal.




What burned the resistors? Was there something wrong with the amp, resistors shouldn't just burn.



> Because of this, I would never use carbon resistors in a final product in a tube amp, although it makes sense financially for a company.




I just yesterday delivered a high end amp (my flagship circuit, original design) to a customer and it has all 1W no name CF resistors. No hiss, no nothing. Very great transparency though, even if I say myself.

He has Sennheiser HD800.



> best metal film for low watt signal path.




Throughout this thread there's been a lot of very technically unsound statements being made about what is or isn't on the signal path. It's not always so obvious what is on the signal path, unless you know electronics. 




> I really whish we could do this in future mod.
> It would have been great if we could have a direct coupling instead of this coupling cap between the two stages.




DC itself wouldn't solve the problem. The output impedance of the input stage would still remain very high.



> That's why I prefer this OTL design.
> Unfortunately this "purest" approach is limit to higher output impedance.




By no means. Like I simmed, 2 ohms is achievable. Many people have built such outputs.

Also, properly driven OT is just as transparent as a bit poor output follower direct driving a load directly. There is no magic in direct drive, it's all just a matter of how do we get decent drive to the load.

Designer of this amp realised that (relatively) high plate resistance tubes driving OT's are not going to be able to make the OT parasitics disappear, so: get rid of the OT.

This doesn't mean OT's are dirty and cannot be used in a pure design. It just means the designer was for whatever reason unwilling or unable to engineer around the problem. Probably the first, since he wanted to make a product for a specific audience, looking at the input stage also.




> 4- then your suggestion of NOT using direct tube output(!) :
> Using an FET "follower",
> So end result is a hybrid tube amp!:




Yes, a FET can be used in a follower (a source follower) just as a tube (cathode follower). The topology of follower is not owned by any component, it is a topology. A FET source follower is no less a follower than a tube based WCF. Actually it's much more of a follower; the WCF output resembles the input much much less than the source followers output.


This discussion of HYBRID comes up often. I find it silly and unproductive.

They are all just components. None of them are inherently good sounding, or inherently dirty.

Some components are good for some jobs, others for other jobs. Use the wrong component in the wrong job and you're going to have not-so-good results.

Tubes are just components. FETs are just components. Both have their strenghts and weaknesses.



> Actually I think that choice would mean that it is no longer a "tube" amp..




I don't see why that would be. It would still have 100% of voltage amplification done by tubes, so ... it's a tube amp?




> For me, " the jury is still out " for a hybrid amp being a best choice.




Being a "hybrid amp", whatever that means (are you utilizing vacuum diodes in the PSU? Is it still a "tube amp"?), that is sold at the shops, has really nothing to do with the proposition at hand. I am 100% sure you have not heard an amp that has tubes doing voltage amplification, and a source follower driving the load, directly or via OT. I've heard of one (1) commercial product like that. 




> First off,
> I havent heard yet a SS or hybrid with greater soundstage or micro detailing than tube amps.


 

You have not heard the stuff that is being designed and built in the DIY community. As I said above, you have not heard that kind of an amp. 



> Foe me the test is still soundstaging.
> In this area, to me nothing I have heard beats tube amps, and I believe it has to do with the capacity to retain low level micro information.
> This is confused with the bad rap that tubes generally have with higher harmonic distortion figures,
> when just looking at specs and not the whole picture.




There is no need to throw out technical info OR listening impressions. 




> I believe tube amps will always have larger soundstaging.
> As example, my mk8 2yr ago at a NY meet had obviously greater depth and layering of soundstaging next to the monster amp which was being fed the same source.




Again, none of these things have anything to do with proposition at hand.

I call "a tube amp" any amp that has tubes doing voltage amplification. These titles are pretty useless once you start designing own equipment that is not similar to stuff being sold at shops.


----------



## MrCurwen

sonictrance said:


> First off, thanks for the detailed information you post, very informative!




Thanks!



> Second, even with all the design flaws and the WCF topology as a whole not being optimal. I think that if you got to hear one of our modded amps you'd enjoy it, a lot.




I'm sure. Most amps are enjoyable in some way.


----------



## MrCurwen

maxx134 said:


> Haha that because what is considered a flaw in general, is actually a solution in this amp.
> 
> Consider the makn coupling cap.
> In general all coupling caps are a flaw,
> ...




Please elaborate. 

Every single coupling cap in every single amp that uses them is "the solution" to connecting the preceding stage to the next. How is this different?


----------



## MrCurwen

maxx134 said:


> Hmm again, I think the .22uf caps all around the output circuit were overlooked..
> They are supposed to deal with parasitics.
> It is obvious we don't have any when listening to amp.
> I have zero noise at full volume..




All real components have parasitic properties. Some are relevant to application at hand (audio reproduction in a specific circuit topology), some are not. 

Parasitics don't usually manifest as noise. They can, but it is not the bulk of what I meant.

For example when a transient occurs in the signal, and the output followers upper triode has it's grid approaching positive (with regards to it's cathode), a large amount of electrons hit the grid. This is not how the tube is supposed to operate, it is totally unwanted. It is a parasitic property.

This current has to find a way out of that node, and the only route is via the grid leak resistor. What happens when current passes thru a resistor? A voltage appears over the resistor.

This voltage is summed with the signal voltage at the grid node. Is this new signal that is formed 100% the same form as the signal that is put into the amp? No it is not.

This effect is pronounced in tubes with high pulse capability, since they have a large electron cloud around the cathode, ready to accomodate a pulse. They are not trying to hit the grid, but since the grid must physically be in the path and also close vicinity to cathode, to perform it's function, this happens.

When looking at tube datasheets, they give the max grid - cathode resistance (max value of grid leak resistor). It is usually different for fixed grid bias and cathode bias, since cathode bias has some inherent self-adjustability to compensate.

If the grid voltage is changed enough thru this method, the tube may self destruct due to having too positive a bias. This is not relevant in most cases, but the max value of grid leak resistor must be observed.


Also the electrodes (anode, grid(s), cathode/filament) have capacitance between them. The larger the surface areas and/or the closer they are spaced, the larger this effect is. Imagine it as a capacitor that must be filled with current, before the actual signal can be applied. Each cycle it must be charged and also discharged. 

In RC coupling, the current that charges this parasitic capacitance must come from the capacitor. The discharge happens thru the grid leak resistor.

In a situation where that node simply doesn't have enough current to satisfy everything in time each cycle, the signal is corrupted.

Drive the grid with a source follower, and it can simply flood all the parasitics with current. This is why it's very very noticeable how much transient response improves with this approach.

Anyway, a less complicated solution would be to simply use a driver tube with a lower plate resistance and larger current capability. Less than 1mA is not going to drive anything at all properly.



> Yes must have patience,
> I remember making my own circuit boards in college projects and it was really fun.
> Don't loose the fun of this hobby with the obsession to finish.
> There is no rush or race, and remember compromises is not always a bad thing.




Well said!

Oh, the amount of unfinished electronics around my apartment... Like a couple of from-scratch radar CRT monitors and a RIAA corrector, and who knows how many breadboard tube guitar amps I have lying around ...

Compromises must be made with real world components (and money). The trick is finding out which compromises to make!


----------



## MrCurwen

> Drive the grid with a source follower, and it can simply flood all the parasitics with current. This is why it's very very noticeable how much transient response improves with this approach.




To clarify:

When the anode voltage of the input stage changes, let's say it rises, the voltage potential between the plates in the coupling cap is increased.

The coupling capacitor is a container, that has a certain amount of current stored inside it at a certain voltage between the plates.

When the voltage potential changes, the amount of current that must be stored inside the capacitor (the charge of the capacitor) changes.

That current must come from somewhere; in this application, it comes from B+ via the plate resistor. This movement of current from B+ to the cap actually causes the plate voltage to change; there is a voltage drop.

This is how load lines operate.

On the other side, the same amount of current moves the opposite direction, from the plate via the grid leak resistor to ground. When this current moves via the grid leak resistor, a voltage appears over the resistor, according to Ohm's law.

This is how RC coupling produces the signal accross the capacitor.

Anyway.

The standing current of the input tube is let's say 500µA. Let's say all of it goes to the capacitor (it doesn't, and it can't, but for simplicity of example).

Some of this current is spent satisfying the parasitic properties of the coupling capacitor. We must substract this amount from the amount that is moved on the other side of the cap, via the grid leak to produce the signal there.

Then, on the grid side of the cap, some of that signal current must be spent satisfying the parasitics of the tube and it's grid. This must be substracted from the current that is left to form the signal (by moving thru the grid lead and producing a voltage differential across it).

These parasitics are in the grand scheme of things pretty small and some would say insignificant. They do however affect transients and micro details of complex audio signals. The fact that better quality caps affect the sound that much, means they are significant for the application at hand.

If you feed a capacitor with poor quality (much parasitics) with a low impedance source, it can instantly provide enough current to the capacitor to satisfy it's parasitics (they no longer affect the sound signal then).


----------



## Maxx134

Wow MrCurwen I really appreciate your posts!



mrcurwen said:


> Anyway, what is your output tube?




I have the Russian 6n30p-dr 

I will look up the data sheet later as I am now operating on my amp!
Hehe!



mrcurwen said:


> "...but the CF probably stopped some oscillation."...




OMG your right about the oscillation!
 I actually experience this a bit as a shiny airy signature on my old wirewound resistors, 
 so I was had to read up and figure out whatvthia shiny sound was.
I read up about this oscillation and I got rid of them.
I had them in Anode/ Cathode resistors. 
I mentioned this somewhere in the thread.




mrcurwen said:


> "Was there something wrong with the amp, resistors shouldn't just burn."




Yep it was the stock garbage resistors probably not being a true 2 watt rated on board.
OR,
It was an MK6 amp, so most likely He probably tube rolled the wrong tube as there so many octal tubes that fit.



mrcurwen said:


> "I just yesterday delivered a high end amp (my flagship circuit, original design) to a customer and it has all 1W no name CF resistors. No hiss, no nothing. Very great transparency though, even if I say myself."




Oh dam, don't make me salivate..
You don't know, I whish I could buy every tube amp out there..
I live to check the tube amp pictures thread .
Have you posted pics somewhere I like to seee




mrcurwen said:


> "This doesn't mean OT's are dirty and cannot be used in a pure design. "



I Agree fully here.
Some Best tube amps I heard using OT.
Actually that's the majority I have seen.
They using OT..
Maybey its easier to design using Output Transformers?



mrcurwen said:


> "are you utilizing vacuum diodes in the PSU?"




Haha!
Wow great point.
Your right again.
Yep my PSU is all SS..

Also,
Just Saturday I was at a friends and his dac had an rectifier tube and it was amazing to hear differences swapping the rectifier tube..(!)

Similar scenario when I had my Woo WAA7TP..

Reading your explanations on tubes really insightful to these observations as well..

In my amp, I swapped out my garbage 25 cent rectifiers to put better ones in but didn't think much about this till today..
It's like opening another discussion though..



mrcurwen said:


> "I am 100% sure you have not heard an amp that has tubes doing voltage amplification, and a source follower driving the load, directly or via OT. I've heard of one (1) commercial product like that...
> **
> Drive the grid with a source follower, and it can simply flood all the parasitics with current. This is why it's very very noticeable how much transient response improves with this approach."



Dammit now I am very interested in this! 
But for now just Source follower in driving the load. .


----------



## Maxx134

Update:
 Ever since SonicTrance did his bias mod, it made me curious about my bias settings..

It is now clear that the designer made many choices that can be optimised and I cannot blindly overlook, like the NFB..

Anyways 
I looked into my amp power tube bias and found that it is alarmingly low.
28ma when my tubes are designed for 40ma.

Even older photos SonicTrance showed me had the bias at 32 ma, 
 So I am currently increasing the bias and hopefully will improve the output..

Also,
Last night I did the driver tube replacements and there is no denying that in the MK8 amp the driver section has better sound when using different tubes other than any 12a*7 type.


----------



## Redge78

mrcurwen said:


> I don't know about your system, but I very much doubt your output section has very good output impedance without NFB.
> 
> Is your output tube 4P1L? =) That is the most linear tube ever made. 6E5P and some TV sweep tubes come close.
> 
> ...


 
  
 Basically, the MK8 has the same "White Cathode Follower" output stage than the MK6, maybe the value of the anode resistors and cathode resistors may change between the two, but that should be it.
  
 The 6H30 are very linear, with lower Rplate than 4P1L and high Pulse plate current ... it's widely used as output stage on high end preamp (AR) and CD (Ayon). It's military specced so it's supposed to be long-lasting and the modern ones (not NOS) are all built in the same russian factory (through two brands) so you don't have to bother with tube rolling as they don't have any direct replacement. My wallet appreciate that !
  
 The overall output impedance of the amp should be in the low 2 digits (without considering NFB but with cathode Bypass), Long time ago I calculated it, I found a impedance below 20 ohms above 20Hz. But I have never been able to really verify it.
 Anyway, to drive a 300 ohm load, that gives a decent damping factor. For a 20 Ohm load, that's an another story ...
  
 I understand the "current" situation, but we're powering high impedance headphone with (most of the time) some few mW, the current needed is very small and far within the specs of what a WCF of 6H30 can easily produce.


----------



## Redge78

mrcurwen said:


> Also, properly driven OT is just as transparent as a bit poor output follower direct driving a load directly. There is no magic in direct drive, it's all just a matter of how do we get decent drive to the load.
> 
> Designer of this amp realised that (relatively) high plate resistance tubes driving OT's are not going to be able to make the OT parasitics disappear, so: get rid of the OT.
> 
> ...


 
  
 With all due respect, I think that on that OTL thing, you are missing the main point which is "money" !
 You cannot really put some crap OT in the amp, too much impact on the sound.
 A pair of decent OT wil cost (some) hundreds and you have to take into account the "commercial multiplier" on the overall price of the amp.
  
 And for what ? After all, an (low end) OT is always source of noise, parasitics, reduced freq. band, saturation, low level signal lost ...
 And if you can feed your headphone directly from the farm tube, why adding a costly component that will degrade your sound ?
  
 Obviously, an OTL is a dangerous beast, and you'll have to design some security features (or not ...) but that will be cheaper than an OT anyway.
  
 As for the WCF topology, in my mind that's not a coincidence that a lot of head-amp manufacturers have gone this route. The circuit has a lot of advantages for the "high Z low W" niche our headphones are into.  
  
 [EDIT] Some of the best of us are a bit on the tube fetishist path of the force. But that's OK, it has never been easy to do mods on CMS anyway !


----------



## MrCurwen

redge78 said:


> Basically, the MK8 has the same "White Cathode Follower" output stage than the MK6, maybe the value of the anode resistors and cathode resistors may change between the two, but that should be it.




Okay, good to know.

My experience has been that I can sense improved fidelity up to about the point where amp output impedance is about 50 times lower than the load impedance. So with my 120 ohm headphones the response gets better down to about 2 or 3 ohms or so of amp output impedance. My flagship circuit has an output impedance of below 1 ohm. It has source followers (4 of them, two per channel balanced) driving an 10k : 4 ohm OT.

Anyway I don't mean to make this thread about my own stuff, but just to provide my reasoning for the statement that it's not smart to remove NFB from a direct drive system that doesn't have that low of an output impedance.

It is true, that not all people like the improvement in dynamics and transient response that lower output impedance brings. Some like mellower, more compressed and warm sound etc.

I am by no means a fan of NFB, I don't utilize it myself because I don't like the sound it makes. But the designer put it there in these amps for a reason; it is needed. Probably not a good idea to take it out without some redesigning.




> The 6H30 are very linear




Kind of true. Not bad, depends on what you compare to. Ale Moglia made some interesting comparison measurements which were posted on his great blog. That blog seems to be offline ATM for some reason. 

Anyway, 6H30 has ok linearity. Not top class.



> with lower Rplate than 4P1L and high Pulse plate current .




True and true.



> .. it's widely used as output stage on high end preamp (AR) and CD (Ayon).




Many not so good tubes have been used in many an amp well regarded... This is not one of them, it's a good tube, but not the best by any means.



> I understand the "current" situation, but we're powering high impedance headphone with (most of the time) some few mW, the current needed is very small and far within the specs of what a WCF of 6H30 can easily produce.




True, depending on what is the standard being used. 

If the standard is that of preserving micro details and super elusive spatial information and very small level dynamics... 

The hammering that 20 ohm output impedance does to micro details in the signal is much much more than what any cheap film caps do to the signal earlier in the amp. 

But, again, I do realise not everyone wants to or can DIY a whole new amp. I'm simply providing perspective.


----------



## MrCurwen

redge78 said:


> With all due respect, I think that on that OTL thing, you are missing the main point which is "money" !




Oh? =)

I made my designs only because I didn't have money to buy decent OT's. Necessity is the mother, father and best friend of invention.




> You cannot really put some crap OT in the amp, too much impact on the sound.




I in fact, can. No impact. =)

My analysis of the capacitor situation is 100% the same as the OT situation. It's a matter of drive. Think it through and think about why changing caps matters. If my analysis of cap shortcomings is lacking or wrong, please elaborate how so.

Why, in the technical sense, does changing caps matter to the sonic impressions the amp produces?




> And for what ? After all, an (low end) OT




What I use is most certainly considered low end, yes.



> is always source of noise




No. Only when applied with unnecessary compromises.



> parasitics




No. Parasitics disappear when drive impedance is low enough. Why use high drive impedance?



> reduced freq. band




No. Look above.



> saturation




Why would you have DC thru the OT?



> low level signal lost




Why is it lost? If you can answer that, then ask yourself: is it necessary to operate the OT in such a way?



> And if you can feed your headphone directly from the farm tube, why adding a costly component that will degrade your sound ?




In my flagship model, each of the OT's cost as much as each of the (Hammond alu) chassis'. =)





> A pair of decent OT wil cost (some) hundreds and you have to take into account the "commercial multiplier" on the overall price of the amp.




Well, no. Only if you use old 1950's and 1960's topologies. I don't see why that should be the case.

I do realise there is absolutely no way to convince any of you about these claims. I sense we are drifting off topic and I do not wish to derail this thread. Best not to discuss them further in this thread. I assure you no magic is involved; also you do not know how my designs sound. This thread is not about my designs, but I do hold them as standards when discussing other schematics as well.

I'm not a genious by any stretch, and I was able to engineer around a cheap OT to get it to do the disappearing act. It can be done. Several people from the forums have built my designs also.




> As for the WCF topology, in my mind that's not a coincidence that a lot of head-amp manufacturers have gone this route. The circuit has a lot of advantages for the "high Z low W" niche our headphones are into.




Yes, I agree.

It performs significantly better than pure cathode followers for example. It is not the best follower however.

[EDIT] Some of the best of us are a bit on the tube fetishist path of the force. But that's OK, it has never been easy to do mods on CMS anyway !
[/quote]

After using a device for a couple of nights, it gives me no good feelings to know it has very luxorious (and getting up in price, slowly) silver mica caps. First night it might.

After a while all that matters is how good the transparency is, how much of a live experience the music provides. The silver doesn't matter at all. Neither does anything else about the amps insides.


----------



## Maxx134

mrcurwen said:


> "Kind of true. Not bad, depends on what you compare to. Ale Moglia made some interesting comparison measurements which were posted on his great blog. That blog seems to be offline ATM for some reason.
> 
> Anyway, 6H30 has ok linearity. Not top class."




That's not what I heard.

I checked and they have almost same linearity curves..

*



*

So yeah the 6n30p-dr is actually a top class "dual triode",
 So if my 6n30p-dr can match the best "pentode", 4P1L, 
And also have more disirable traits 
of lower Rplate and high Pulse plate current, which Redge78 mentioned,
and than also two amplification sections, compared to one in the 4P1L ..
Then I would have to say wait, thats cheating...

Since your comparing the best in a different catagory (pentode).

Nobody here is saying the MK8 output tube is the best output tubes in the world, or even the best choice.
But the 6n30p-dr was/is clearly one of the best.

 Maybe old news, but you Google 6n30p-dr and easily get the story of why the tube was branded the "supertube".




mrcurwen said:


> "I am by no means a fan of NFB, I don't utilize it myself because I don't like the sound it makes. But the designer put it there in these amps for a reason; it is needed. Probably not a good idea to take it out without some redesigning.



Yep, 
that's why the mods take time.





mrcurwen said:


> "The hammering that 20 ohm output impedance does to micro details in the signal is much much more than what any cheap film caps do to the signal earlier in the amp."




I am all about micro details and soundstaging..

My latest trials I discovered more ambient cues in the actual detailing, 
 More more "dimensionality perception" of distant sounds in background..
This was exciting discovery. 
This is why super modding is fun.

Now if I had a "perfect" amp that was already reached its max potential,
Then I would never have enjoy this experience of gaining more..

Ahh what am I saying, no amp is that perfect that it can't be helped with a mod..

Our next mods will include the upcoming headphone impedance matching mod.





mrcurwen said:


> "Why, in the technical sense, does changing caps matter to the sonic impressions the amp produces?"




Just because they can function the same, doesn't mean they will "sound" the same.
That question is too general as there are all types of caps...
So how could they, if we change the size, the specs/limits, the choice of internal compositions and type?

I am thinking your point is to avoid coupling caps to begin with.
Unfortunately this design has one so we must make the best of it,
And using a top quality cap like the Copper foils may be "good enough". 




mrcurwen said:


> "Why use high drive impedance?"




Good question.
Answer is I didn't do it..

But,
 There is the experience of heavenly beauty when listening to the HD800 on a high impedance tube amp..

Then crashing back to earth,
with the hd800 turning into your worst shrill nightmare on a low impedance (SS) amp.


Theres reality again, slapping us in the face.




mrcurwen said:


> "Best not to discuss them further in this thread. I assure you no magic is involved; also you do not know how my designs sound. This thread is not about my designs, but I do hold them as standards when discussing other schematics as well."




I would love to see/hear your designs.
Maybe open a thread here so others can maybe aquire/build your design if possible. 
This site is seems the best for exposure. 
When you say no majic, does that mean no tubes?
If not, I won't go.





mrcurwen said:


> "After a while all that matters is how good the transparency is, ...."




That is what we all striving for.


----------



## coinmaster

> If he already saying what those 2k resistors are for , then that's what it is .
> I get your trying to understand "why" and that's a good thing.


 
 Except I *need* to understand since my I'm spending thousands of dollars on R&D for my new designs using this mechanism. I'm combining several different opamp configurations to create the biasing circuits which is expensive, I don't recall ever having an issue on the bench not having the 2k resistor connected and the simulations always work without it but I can't go on if there is a variable I'm missing.
  


> Also is the other fact that SonicTrance 2k resistors burned in another scenario just as example not easy to see all the variables in a design all at once.


 
 They burned because the grids went positive and the b+ wasn't connected so the grids became a pseudo anode.
  


> a less complicated solution would be to simply use a driver tube with a lower plate resistance and larger current capability. Less than 1mA is not going to drive anything at all properly.


 
 Wouldn't running 6SN7 tubes at 10ma solve the issue? How much current is enough?
  


> looked into my amp power tube bias and found that it is alarmingly low.
> 28ma when my tubes are designed for 40ma.
> 
> Even older photos SonicTrance showed me had the bias at 32 ma,
> So I am currently increasing the bias and hopefully will improve the output..


 
 Use a wirewound potentiometer. They come in high wattage and they are commonly used for this exact purpose. Just make sure you have a minimum resistance in series with the pot so you don't have 0 bias if the contacts come lose or if turning the pot too low. Using a dual gang wirewound pot for each channel or a quad for both channels and have two for the B+/- is a simple way to adjust the load line where you want it, assuming you're loading the tubes with resistors.
  


> Hmm again, I think the .22uf caps all around the output circuit were overlooked..
> They are supposed to deal with parasitics.


 
 They only affect the parasitics between the PS and the anode/cathode resistors. I'm pretty sure they just offer a capacitance to cancel out the trace inductance.


> Why, in the technical sense, does changing caps matter to the sonic impressions the amp produces?


 
 There's a lot of different theories on that with different data presented. I won't even consider forming an opinion because it's such open water. For now it all comes down to the simple fact that in my experience capacitors do make a difference and that remains the case until I personally try a different method in the same circuit and find different results.
 You say that OTs can be driven to have no affect on sound but didn't you say yourself that you haven't actually tried a direct drive approach? How can you say for sure.
  


> After a while all that matters is how good the transparency is


 
 Yeah which is why I feel kind of foolish tearing my amp apart in search of something better since my modded MK6 was already orgasmic but alas, it's too late now 
	

	
	
		
		

		
			





 
  
 Good stuff MrCurwen. Amazing replies.


----------



## Maxx134

Thanks for suggestions with the pot coinmaster. 

What I need to do now,
Is fine tune my NFB,
Because changes made to the bias and driver stage..


----------



## Redge78

mrcurwen said:


> I do realise there is absolutely no way to convince any of you about these claims. I sense we are drifting off topic and I do not wish to derail this thread. Best not to discuss them further in this thread. I assure you no magic is involved; also you do not know how my designs sound. This thread is not about my designs, but I do hold them as standards when discussing other schematics as well.
> 
> I'm not a genious by any stretch, and I was able to engineer around a cheap OT to get it to do the disappearing act. It can be done. Several people from the forums have built my designs also.


 
 Don't get me wrong. I understand that your knowledge and experience is far behond mine, and I am happy you contribute.
 I'm a grown-up man and I can take criticisms and suggestions, as long as they are given in a positive mind-spirit (which I believe is the case).
 So, no worry about that, at all. Half the fun in this thread is trying to understand things.
  
 You have talked a bit earlier of "unsound assertions" ... please, do not hesitate to tell us where we may have been be wrong (and why ...), especially if this has a direct impact on one of the previous mod we've done.
  
  
 As for the "convincing" part ... At the end of the day, I suppose that a good listening session would do more that a hundred pages of explanations. 
 And please, believe that if the DIY amps are half as good as what I understand, you'll have a very interested audience here. 
  
  
 But yes, this is not a "full DIY" thread here, we never had this ambition. Maybe one day, when we'll have learned enough ...
  
  
 About your schematics...if you have published them somewhere, I would be pleased to have a look at them.
  
  
_And one last thing ... my english is not that good, I miss most of the nuances I would be able to put in a french writing, that may make my sentences more affirmative that I intended them to be._


----------



## coinmaster

> As for the "convincing" part ... At the end of the day, I suppose that a good listening session would do more that a hundred pages of explanations.


 
 I'm on board with this. There are so many factors and unknowns in creating good audio that data will never be able to tell you what sounds good. If "technically" perfect sound reproduction was the goal then solid state amps would probably be the go-to.
 Then there's things like LDR pots and capacitors and all that in which no one can seem to agree on why they sound the way they do.
 I don't think there is any mention on the internet that LDR pots for example sound anything less than totally amazing yet the readings suggest they should sound totally horrible with extremely high distortion and such. 
 Things like this beg the question as to what really affects sound quality and how it all fits together. If THD was the end all of good sound then even cheap solid state amps should wipe the floor with tube amps by orders of magnitude.
  
  


> But yes, this is not a "full DIY" thread here, we never had this ambition. Maybe one day, when we'll have learned enough ...


 
 I'm being the guinea pig for that. I'm striving for a "better" MK6 and I've already spent almost 6 grand in the process. 3 of it was the 'boutique' components and the industrial AVX caps I bought for the original mod, the other 3 is for R&D materials, never new R&D was this expensive..
 I'll be testing all sorts things that are a "technical" improvement over the stock design, so we will see what works and what doesn't.
  
 I'm hoping to come up with something worthy of sale that isn't ripping somebody else off, so far its going pretty good. 
  
 If I achieve my goal maybe I'll post a DIY guide or sell a DIY kit or something. Preferably something that gets me a return on my investment at least 
	

	
	
		
		

		
		
	


	




 it's rending a hole in my heart spending this much money on something this inefficient.


----------



## MrCurwen

Regarding 6N30P:

I must take back my previous statements about this tube. I made an error; I mixed it up with the 6N6 medium mu low rp double triode.

I've tried to memorize by heart the catalogue of russian tubes, but I apparently still have gaps in places.

Ale's blog is online again: http://www.bartola.co.uk/valves/2012/06/17/thd-benchmark/

Every time anyone makes these kinds of measurements, the methodology can be questioned. This is no exception, and I myself am skeptical of a couple of participants here. Anyway, it's always good to look at measurements and comparisons; certain tubes come at or near the top pretty consistently, just like here.

People who try almost all russian tubes seem to go back to 4P1L and 6E5P the most often. I'm one of those people. 6S45P is top of class also, but getting too expensive for me. I bought a lot of 24 4P1L's a few years ago, and I've been using those in my builds. That tube is also getting up there in price. 5€ for a tube is too much in my opinion to pay for tubes. 2 or 3 euros is better.

I probably should keep my mouth shut here about those tubes. Well, lucky for me there are a lot of gems still out there that are known and used only in small and weird DIY circles at the moment...




maxx134 said:


> I checked and they have almost same linearity curves..




Not to my eye. Also the actual measured 4P1L curves are better than those drawn by hand by a soviet engineer. This is quite often the case with the datasheets unfortunately (or maybe fortunately?).

Also measured 6E5P curves are better:

http://www.hagtech.com/blog/images/6e5p.jpg

Don't get me wrong, I'm updating my assesment (after getting un-mixed-up about the types) from ok to very good. Actual value of tube is of course always application dependent; I would not ever use 4P1L in a WCF. 6E5P maybe, but probably not. 6N30P is very good in a follower, but it is NOT, and I quote from this thread: 



> practically the most linear tubes ever made




Not at all. I made my original challenge to this statement 20% in jest. This is what audiophiles and audiophools do; argue about tube types...

But, looking at the curves, 6N30P cannot be in all earnestness said to be the most linear. That is just asking for arguments!

Compare for example to 6P36S TV sweep tube with very low rp and extremely high pulse capability (and the troubles that go with that, as I explained earlier);

http://www.bartola.co.uk/valves/wp-content/uploads/2013/02/6P36S-triode-model-SMALL.png

A lot depends of course on the load line and intended area of operation (where on the curves the load line will set).

I've got 20 or so of 6P36S's waiting for use. They're very pretty and I like to look at them (I enjoy top caps very much), but the heater current is a real hurdle since I'll need 4 of them for balanced stereo operation. 8A of current is liable to make the neighbours HIFI system hum as well as mine. Not to mention the heat, always the heat.




> So yeah the 6n30p-dr is actually a top class "dual triode"




It is, agreed.




> So if my 6n30p-dr can match the best "pentode", 4P1L




It cannot.

Besides just looking at the curves, there is also the issue of DH vs. IDH. DH's seem to always win the day in the end. I must grudginly agree myself; four regulated filament supplies per amp is a pain to deal with. The amount of wiring alone.



> And also have more disirable traits of lower Rplate and high Pulse plate current




Depends, not necessarily desirable in every scenario. Pulse capability brings need for grid drive, such as source followers etc. 

But, 4P1L has quite hungry grid also, as I've experimentally found out the hard way. Customer complained that his test track song didn't sound 'right', it was 'lazy' even though very detailed and everything else seemingly very good. Well, grid drive fixed that, dynamics increased quite noticeably. So it does eat a lot of current on transients, not in steady state operation or normal signal.



> Then I would have to say wait, thats cheating...
> 
> Since your comparing the best in a different catagory (pentode).




What do you mean? Why would it be cheating to compare two components that clearly can fill the same job?




> Nobody here is saying the MK8 output tube is the best output tubes in the world, or even the best choice.




I quote from this thread:



> practically the most linear tubes ever made







> But the 6n30p-dr was/is clearly one of the best.




Agreed.




> Yep, that's why the mods take time.




Indeed.

I must say I'm unsure where DIY and modding go their separate ways. They clearly have a common area, but they are not the same thing. It's problematic. For DIY I find the best scope is the largest scope. 




> Now if I had a "perfect" amp that was already reached its max potential,
> Then I would never have enjoy this experience of gaining more..




Indeed. I've designed and built THE BEST AMP for a number of times now. I am running out of ideas to improve my flagship design, other than using more expensive parts in some places. The swaps I've made have made 0 improvements. For example I did a build (which is my workhorse amp at the moment) with russian film caps in the PSU, no electrolytics. 50µF / 1000V filtering caps. I listened very carefully for a few weeks, and then switched in the cheapest electrolytics I have (and normally use in PSUs). After careful listening... absolutely no change.

The reasons for this are obvious; the amp has a simple B+ reg, nothing before the reg is audible in any way. Also the amp is constant current draw down to the microamperes, so the caps don't need to discharge any current for the signal. Why would their quality matter? Well, it doesn't. 

Same for coupling caps; if you use coupling caps in front of source follower gate, it becomes completely impossible to hear differences between decent quality caps. With traditional circuits in the past, the differences were very clear, often like night and day. KBG oil caps would sound very different from metallized film polyprops or MBGO waxed paper or SSG silver mica (the best)... Now I just use MBGO for it's robustness and cheap price. Sound is as good as SSG.

I used to buy a bunch of tubes to mix and match and do the rolling thing. I've still got a couple of dozen cardboard boxes full of tubes around here, annoying my girlfriend.

I got tired of that game, mostly the cost of it, and I designed my circuits so that it's not important to match tubes any closer than 10% or so. Easily achievable. No further benefit is available in my circuit from matching tubes.

Also rolling is out; any properly functional 6SN7 (with 10% tolerance between section) will sound exactly the same. Before giving out the amp to my customer earlier this week, I had to change one 4P1L out because it was 20% off in plate current. The replacement was like 5% off, and thus sonically 100% identical to the others in my circuit.

This is not a DIY thread and I should probably take this kind of talk elsewhere, but it really is about design. All of it.

If I were making an amp to sell to "the wide audience" (my customers are weird high end eccentrics I know personally), I would make it so that it does have audible differences if you switch the caps or tubes. Of course. People like to do that stuff. I don't mean this as an insult, even though it's coming out very dangerously close to that, but think about it.




> Ahh what am I saying, no amp is that perfect that it can't be helped with a mod..




True, with the caveat that one can successfully only mod things that one truely understands.

For example, there are schems on DIY forums that I simply don't understand. I'm sure I will once I get to studying them, but there's so very much different things in DIY that it takes years to get around to all topologies and all things. My schems have been met with "how does it even work" or "this will not work, will not produce sound" from many people as well, simply from not understanding them. The senior members did get it right away though.

For example, I would not poke around an amp utilizing a FET driven modern Schade feedback system because outside of abstract concept I don't understand how it practically works. Not utilized in any commercial products as far as I know. 


Regarding the caps and why they sound different:

My answer would be that different caps have different parasitics, and some caps fit some circuits with inadequate operating conditions (parasitics are not fully satisfied) better than others. "The sound" is not an abstract thing. It is made up of material used in construction of caps, and circuit design and natural laws. 




> I am thinking your point is to avoid coupling caps to begin with.




No no. My 'solution' to the cap problems I experienced (described above) was to go direct coupled. This brings it's own set of compromises, such as requiring RC cathode bias on the output section. So now I've swapped a good quality small film cap to a bad quality (in comparison) large electrolytic. Not a good trade, capwise. So, the young aspiring DIY man I was I used LED cathode bias. I still have the 200 LEDs per channel boards somewhere, nice room lighting, not to smart design!

It did sound ok though. Light on the bass, unsurprisingly (LEDs have a low impedance, but they do have impedance and it stacks up).

I don't avoid coupling caps. Like I said, they are transparent in front of the FET gate. FET drives (direct coupled) the output tube grid. Takes out cap problem, and output tube grid problems. Transient response through the roof, kicking you in the ear!




> Then crashing back to earth,
> with the hd800 turning into your worst shrill nightmare on a low impedance (SS) amp.




It's not the low output impedance making your dreams bad. It's other things.




> When you say no majic, does that mean no tubes?




No it does not mean that. Like I've consistently stated, tubes make the best voltage amplifiers there are. No magic means things are in fact explainable and predictable to an extent (complex systems...).


----------



## MrCurwen

Maxx134, that is some serious chassis work! 

My stuff looks like an engineer designed it, and a child did the actual work. Not pretty at all, very boring.


----------



## MrCurwen

redge78 said:


> Don't get me wrong. I understand that your knowledge and experience is far behond mine, and I am happy you contribute.




Glad to hear it! 

I write on different DIY audio and instrument amp forums. I have this thing of trying to help people who don't have the technical info they'd like to have, since I myself have received such a huge amount of help from these forums over the years. I feel obliged to give back. 

Sometimes it's too easy to mumble on about something that's not really helpful to anyone...




> I'm a grown-up man and I can take criticisms and suggestions, as long as they are given in a positive mind-spirit (which I believe is the case).




Indeed.




> You have talked a bit earlier of "unsound assertions" ... please, do not hesitate to tell us where we may have been be wrong (and why ...), especially if this has a direct impact on one of the previous mod we've done.




I had a bunch in mind when I read thru this thread some time ago. I forgot them all, aside from the signal path thing (and I dont' remember specifically what that was about). I should look again sometime.



> As for the "convincing" part ... At the end of the day, I suppose that a good listening session would do more that a hundred pages of explanations.
> And please, believe that if the DIY amps are half as good as what I understand, you'll have a very interested audience here.




DIY is where it's at. Most stuff for sale (not all), even the boutique stuff, is not very impressive. A lot of people have been innovating all along, but that stuff tends to 

1) stay in small circles

2) be difficult to understand

1 is of course in large part caused by 2. If it takes some years of fiddling around with building amps from scratch, and studying the operation in theory, most people just find a more easily fullfilling hobby. The people who go thru this process are oftentimes a bit eccentric by personality, and don't really care about communicating with the larger public. I'm more than a little bit in this camp.

Most audio hobbyists are unaware of anything thought up after 1970, or if aware, too lazy to find out how it works. It's easy to say "nothing new under the sun" while not understanding what other people are cooking up.




> About your schematics...if you have published them somewhere, I would be pleased to have a look at them.




Parts of them have been published on these forums (I don't recall if in this very same thread also), badly drawn and without credits.

Maybe I'll make a thread at some point. Experience tells me the response is going to be 2% very enthusiastic, and 98% grossly dismissing. =)

My track record with actual auditions is impeccable though, thus far. If you happen to come by Helsinki, do drop by. =)




> _And one last thing ... my english is not that good, I miss most of the nuances I would be able to put in a french writing, that may make my sentences more affirmative that I intended them to be._




In finnish, we have no nuances. Also no facial expressions. No fun without alcohol and no kidding. 

Just kidding. We do in fact nuances in describing different kinds of snow. Not as much as the eskimos though.


----------



## baronbeehive

Very interested in MrCurwen's contributions. I am not happy doing anything without confirming the validity first, and this could lead to new interesting things.
I do think though that LD have done a great job for a relatively cheap amp, NF and all.


----------



## Maxx134

mrcurwen said:


> Maybe I'll make a thread at some point. Experience tells me the response is going to be 2% very enthusiastic, and 98% grossly dismissing. =)



We would be your 2%


----------



## Maxx134

mrcurwen said:


> Maxx134, that is some serious chassis work!
> 
> My stuff looks like an engineer designed it, and a child did the actual work. Not pretty at all, very boring.



My insides look like spaghetti haha


----------



## coinmaster

> For example I did a build (which is my workhorse amp at the moment) with russian film caps in the PSU, no electrolytics. 50µF / 1000V filtering caps. I listened very carefully for a few weeks, and then switched in the cheapest electrolytics I have (and normally use in PSUs). After careful listening... absolutely no change.


 
 I don't think not hearing a difference between cheapo russian film caps and cheapo lytics is very conclusive.
 Time and again when people do comparison of cap sonics the expensive ones usually sound decisively better. Usually concocted in an active switching mechanism to prevent placebo.
 I remember reading an article about  Duelund caps and the reason they are considered the best. It had something to do with the fact they are a pure copper capacitor and they don't use the shortcuts and workarounds that most film caps use, I don't remember I'll have to find the article again.
 You need to test with high end caps before you can say anything, even if you _think_ high end caps are a waste of time, otherwise it's just an eternal assumption.
  
  


> > I'm a grown-up man and I can take criticisms and suggestions, as long as they are given in a positive mind-spirit (which I believe is the case).
> 
> 
> 
> ...


 
 Yet giving me the silent treatment is real mature


----------



## SonicTrance

mrcurwen said:


> I bought a lot of 24 4P1L's a few years ago, and I've been using those in my builds. That tube is also getting up there in price. 5€ for a tube is too much in my opinion to pay for tubes. 2 or 3 euros is better.


 
  No 300B amps for you then. 
	

	
	
		
		

		
		
	


	



 Seriously though, tube rolling for me is a big part of owning a tube amp. So I don't think I would want a tube amp that didn't respond to tube rolling. Takes the fun away from it IMO. It would be cheaper though, I've spent more money on good sounding NOS tubes than I'd like to admit, lol. 
  
  
 Quote:


> If I were making an amp to sell to "the wide audience" (my customers are weird high end eccentrics I know personally), I would make it so that it does have audible differences if you switch the caps or tubes. Of course. *People like to do that stuff.* I don't mean this as an insult, even though it's coming out very dangerously close to that, but think about it.


 
 Yes we do!


----------



## baronbeehive

mogos said:


> Baron to satisfy your curiosity about the USB subject I will do the offtopic record
> 
> 
> 
> ...


 
  
 Thanks Mogos. I will look up some of that equipment, some of which is similar to the Audiophilleo USB interface that I have to reduce jitter and isolate the power supply. The extent to which it will actually improve the sound will depend on how good your system is atm in those areas. The reviews are great, I haven't seen a massive improvement but I keep the system in place just in case.
  
 Great discussion in this thread now, honest and open, just what we need. Could be some interesting developments following this!


----------



## Maxx134

baronbeehive said:


> ..
> Great discussion in this thread now, honest and open, just what we need. Could be some interesting developments following this!



Great discussion?
yes.. 


Honest?
 I don't know about that, haha!
After all, I'm accused of sayn something like my tubes are best in the world! heehee..
 until I find a way to squeeze some 2a3 in there!

But at least you know where my interest are..
 fixing these damn amps!


I am actually behind schedule in my mods.

SonicTrance bias mod actually made me put the switch mod on hold,
 to try out fine tuning my bias points.

Also testing new driver tubes..


----------



## Maxx134

Coinmaster I have a theory as to why when you were using to different tubes in power stage,
It gave you a sonic benefit..

 My theory is that in order for the DC offset to work between two different tubes, 
The opamps grid control had to alter the bias in those tubes by a sonically noticeable amount.
Edit* in other words, one of those tubes bias points weren't optimal.
I am sure you already addressed this in your prototype amp.

I am finding that optimal bias maximizes soundstage and overall realism..


----------



## coinmaster

The different tubes are two sections of the balanced stage so the DC offset only applies to each tube individually.
 Both sides of the load would have 0VDC either way.
  
 When one tube goes positive the other tube goes negative
 The diaphram in the headphones go back and forth depending on polarity which vibrates the air and creates sound.

  

  
  
  
  
 So when you use different tubes the "signal" is traveling through both tubes.
  
  
  
 Meaning if you use two different tube types it would travel through two different tubes which shifts the overall linearity of the signal.
  
 I don't understand why one slot always sounds better than the other though. When you mix the tubes you have to try both positions because way one is always the clear winner and the other way will either sound bad or unimpressive.


----------



## Maxx134

coinmaster said:


> > a less complicated solution would be to simply use a driver tube with a lower plate resistance and larger current capability. Less than 1mA is not going to drive anything at all properly.
> 
> 
> 
> Wouldn't running 6SN7 tubes at 10ma solve the issue? How much current is enough?



You answered it yourself.
Seems that post was not to solve, only to get a point across.


----------



## Maxx134

coinmaster said:


> The different tubes are two sections of the balanced stage so the DC offset only applies to each tube individually...



Ok I am trying to understand this further..
I am thinking, although the opamps are individually working.
But we use the blue trimpots so that the differences between the two tubes or opamp sections are "zeroed".
So the two opamps are set to have 0v to each other.
Then you throw a different tube with different gain & plate & grid resistance,
and the opamp now has to adjust the tube bias at the grid to maintain this 0v difference you set between them with the blue trim pots. .

That's what I am thinking. .


----------



## Maxx134

Another thought is that the opamp reaction time is different with each tube.

And another thought is the two impedance difference between the tubes once in complete circuit with headphone.


----------



## MrCurwen

Are the output stage tubes configured so that (looking at the schem I posted), the bottom row shares an envelope, or vertically so that both phases have their own envelopes?

So basically is it so that 

1) the bottoms are in same envelope and the tops are in the same envelope

2) one envelope contains one top and one bottom?


----------



## coinmaster

> But we use the blue trimpots so that the differences between the two tubes or opamp sections are "zeroed".


 
 The trimpots are to fix the error between the inputs of the opamp because they aren't perfect components.
  


> Then you throw a different tube with different gain & plate & grid resistance,
> and the opamp now has to adjust the tube bias at the grid to maintain this 0v difference


 
 Yeah I've mentioned this like 10 times. It was the main reason I was skeptical about the impedance mod initially because it is essentially creating a new load line curve when you mix tubes and when you change plate resistors.
 Then I realized that while the triodes load lines become unbalanced using the impedance mod, the current becomes balanced because the top triode has to take in both the current from the bottom triode and the current from the other tube so increasing the impedance of the top triode balances it out.
  


> Another thought is that the opamp reaction time is different with each tube


 
 It wouldn't matter because it's below the audio range anyway, the 100k resistor and the 1uf capacitor create like a 1.5 HZ reaction time.
  


> And another thought is the two impedance difference between the tubes once in complete circuit with headphone.


 
 Well let's assume the left triode has an impedance of 1 ohm and the right triode has an impedance of 2 ohms across the spectrum. The impedance would be 3 ohms either way.
 But since they don't have perfectly linear curves I assume either triode type acts as a bottleneck of impedance across its curves shifting the curves to the lowest point of either.
  

  
  


> 2) one envelope contains one top and one bottom?


 
 This
  


> You answered it yourself.
> Seems that post was not to solve, only to get a point across.


 
 He told me not to use direct coupling on multiple occasions, specifically because it would be "replacing my good caps with bad ones in the power supply". He already knew I was going to be running my input tubes at 10ma. 
  
 But he doesn't like me and is giving me the silent treatment so


----------



## MrCurwen

maxx134 said:


> My insides look like spaghetti haha




Mine as well.

But spaghetti is not necessarily a bad thing! 

If you route all wiring in parallel lines, like in a properly drawn schematic, you have maximum amount of capacitive coupling between wires (surface area next to each other).

Visually it is best to route wires 'beautifully', but for technical considerations there is a point to be made about simply using the shortest possible wire route and having every wire in a different angle. Of course certain spots should be avoided, such as excessive heat sources, etc.

My biggest sin regardin wiring and layout is having the output wiring coming in too close contact to input wiring. This is asking for trouble. But, you do what you can in the space you have, and then deal with suppressing oscillations afterwards.


----------



## MrCurwen

> No 300B amps for you then.




No 300B amps for me, yes.

I have been toying around making a 2A3 or 300B amp for aesthetic reasons, and to sell it. I could no in way justify spending that much money for my own amp. 

There simply is no benefit (for me) to these tubes. If you want linear high current (high power), you can use 6P36S (which is curvewise exactly as good as 300B) for next to nothing.

If you want directly heated magic vibes, there's 4P1L and other less known tubes. Combine that with a current buffer, and you've got the vibes and the power (much cleaner power at that).

None of my potential customer base (which is tiny, not really a base at all) care about looks, so it looks like I'm not going to build a 300B amp anytime soon.

Back before my balanced topology days, when I was doing mostly trad stuff still, I bough a bunch of classic american tubes. I have 12 globe 47's made in 1920s and 1930s. I have some 46's, and a bunch of 71A's (my favourite soundwise, also easy to heat). A whole bunch of different globe tubes, 27, 24A etc. A dozen of ST envelope 76's.

I'm going to use these globe tubes for an timeperiod authentic 1929 theremin replica for my girlfriend. One more project unfinished!

But for HIFI, no. Too expensive, too fragile (I don't have the money to buy genuine completely unused tubes from the prewar era). The new production american classic tube clones are 

1) too expensive
2) too hard to heat
3) meant for too high a current to implement in my circuit without big big heat problems
4) because of 3, meant for unnecessarily high output power

I don't see a need for a 3W amp. 0.9W RMS of first class transient response (this is the catch here) power is too much for everyday use.




> Seriously though, tube rolling for me is a big part of owning a tube amp. So I don't think I would want a tube amp that didn't respond to tube rolling. Takes the fun away from it IMO. It would be cheaper though, I've spent more money on good sounding NOS tubes than I'd like to admit, lol.




Yes exactly. 

It's not as though these things (component selection) have to matter at least to the extent that this thread has found they do (I do believe they matter in this circuit); it's a matter of pleasing the customer base.

When you DIY an amp, even from a complete schematic taken from the internet, the connection you feel to your equipment is a heart warming thing. I am sure, that rolling components gives a small amount of that same pride, of seeing your own handiwork doing something beautifully. It connects the user to the equipment.

Your own kids' artwork is the most nice looking artwork, and the amp you helped create, even if by changing a component or two, will sound nicer than something just bought and then used as such.


----------



## MrCurwen

maxx134 said:


> Honest?
> I don't know about that, haha!
> After all, I'm accused of sayn something like my tubes are best in the world! heehee..
> until I find a way to squeeze some 2a3 in there!




Honest mistake in interpretation between two people who don't speak english as a first language!

Anyway, one thing I remembered from when I read this thread thru the first time (I'm going to do a reread when I have time) was that somebody said (again, could have been offhand) that the 6SN7 is the most linear small signal tube there is.

Splitting hairs about this issue is a pet peeve of mine; most hobbyists don't really know of that many tube types, and still the internet is full of these kinds of statements, however lightly said.

2A3 is not the best tube, or the most linear tube, it is very good but it is simply not. It's just WELL KNOWN.

Also, it suffers from the inherent problem of having two separate triodes parallel inside it. There are some obscure single plate 2A3's which cost both arms and both legs and a piece of your brain (the piece which makes good financial investments).

6SN7 is very good, I use it, but it is not the best. It is just well known and easily available.

I get that most people make these statements offhand, in a light manner, but for the advancement of our hobby I feel the need to clarify this issue. 


Same with the caps. Well known and by extension well regarded by magazines, blogs and forums with users that have a very light understanding of electronics (nothing wrong with that, but it's a fact) does not mean a cap is objectively good.

If you go by the route of popularity (which components are most well regarded by consensus), then it depends a lot on which group you are listening to.

For example, there are a lot of technical forums that have gone completely bananas over the russian components (the OTK ones, not the civilian crap) in recent years. Judging from the lack of SSG or teflon enthusiasm on this thread I'm guessing you guys are simply from another faction, another tribe.

None of those things actually says anything, nothing at all, about the objective quality of the russian components. Nothing.

Neither does their price.

Saying that the selling price or the "these components are not popular in my group as of yet" is an objective measurement, is simply buffoonery. 


It comes down to two philosophical routes to this question;

1) "You can't really say anything unless you've physically tried this component yourself", in which case nobody can say anything about russian components unless they have tried them themselves.

2) It is possible to have (to some degree, maybe a lot) knowledge of a components quality before trying it out yourself. The way in which to get this knowledge is to have technical understanding. For example one does not need to try out an electrolytic cap to know beforehand that it is not probably going to be as good as a high impedance node signal coupling cap as any film cap. 

Which is it?

Don't say it's crap unless you've tried it, or look at the specs and then you simply cannot say it's crap.

The OTK (for military use) caps are super high quality. They are some of the best caps ever made.

For example, how many american paper in oil caps there still are on the market? Not many, for various reasons, but most of them have degenerated by now, even if NOS in storage. The russian OTK paper-in-oils (KBG for example) are actually in NEW condition still, even if made in the 50's.

The big K73 film caps (50µF / 1000V) I use in my PSU were made for industrial laser PSUs. They are still in new condition, and the specs are quite impressive.

One cannot be a subjectivist and an objectivist at the same time. Or, if one is, then one must be an agnostic consistently. Making categorical claims without 

1) experience

2) technical knowledge

is simple idiocy.


----------



## MrCurwen

maxx134 said:


> Another thought is that the opamp reaction time is different with each tube.




I'm going to tease you by asking you that if the opamps control the bias and furthermore the operation of the tubes to this extent, is it still A TUBE AMP?


No but seriously; You are right that a proper bias ie. op point is very very important to good operation. It absolutely is.

However I think in this amp the main point with regards to tube selection and rolling is the lack of balance.

It is in name a balanced amp; it has a balanced input and a balanced output. It is in the technical sense, as in actual electrical operation, not balanced at all.

There is nothing balancing the amp.

In most retro circuits the NFB is set up so that it helps with the balance. In old days, there was nothing practical available to force the balance; there was only

1) tube matching

2) NFB

In this amp, NFB is set up one loop per phase, so it cannot help with the balance between the phases. There is only tube matching available.

As speculated earlier, this was a smart choise because people actually do like tube rolling, a lot.

From a technical point of view, with regards to achieving the best possible fidelity, this is not very smart.


----------



## MrCurwen

If people are interested in going further into the "why caps matter in this amp" and by extension the theoretical "how could you make them not matter", I'll ramble on a bit about it. Stop me if this is off topic.

I mentioned my experience with my current workhorse amps PSU. I'll use it to demonstrate some things that can be applied to the amps of this thread.

How can one know that caps in that particular PSU don't matter? Even without auditioning all the different caps available. 

Real caps have parasitic properties. They are caused by the materials of the cap (the plates, the dielectric, is it soaked in oil, what kind of oil), and the construction of the cap (planar, rolled, stacked, etc.).

These properties cause the cap to charge and discharge in different ways. A cap that is in DC steady state (disregarding leak current) is "just as good" regardless of properties, because it is not charging or discharging.

Now my workhorse amp is forced balanced. Each stage has a CCS tail with several megaohms of impedance. What this means, is that it draws the exact same amount of current all the time.

Confirmed by theory, confirmed by sim, confirmed by oscilloscope measurement. 

Let us disregard the simple B+ reg (output impedance of around 20 ohms; it's basically there to set the voltage, and suppress oscillation) and just look at the PSU filtering caps.

If the amp draws the same amount of current at all times, the PSU caps do not charge and discharge with the signal.

How can they exhibit any sound?

If they were to exhibit any sound, it would mean they are charging and discharging with the signal. 

Now one could ask, what about the filtering of rectified AC coming from the PSU. Well, that is another issue. But, film caps are not best for this; they produce too sharp a residual ripple. The output from the PSU filters (the ripple component on top of the DC component) looks more like a triangle wave or a sawtooth wave. With poor filtering caps, like cheap electrolytics, it looks a bit more like a sine wave, at least not as sharp.

Less headaches for the regulator and/or the actual audio circuit.

A statement that one cannot know that caps don't matter in a constant current draw amps PSU is idiotic and buffoonery. A beginner with an honest outlook would ask how can this be, or why is this. 

Beginner level understanding of electronics turns the question on it's head; how could cap quality matter in a constant current draw PSU?


Now this amp in question in this thread;

Like I mentioned earlier, it is not balanced in operation. At least not very well. There will absolutely be a variable current draw from the PSU. This means the caps will have to charge and discharge in accordance with the signal. This will most certainly make them audible, they are in the signal path.

A cheaper and more sensible alternative to big film caps in the PSU would be to add even a simple 2 FET regulator. I'm not sure if there is enough voltage headroom for that (10 to 15 volts), but even arranging for that headroom is probably cheaper than big film caps.

A more invasive mod would be to add forced balance at least to the input stage. This would in practise be a CCS tail, with a negative supply (12 to 15 volts or so). This would have other benefits as well.


To clarify; the bulk of current draw delta is of course coming from the high current output followers. However if the input stage were balanced, it would no longer have the PSU caps in it's signal path.

Think of it this way; if you're the input stage, and trying to bounce up and down following a specific wave (like a friend next to you jumping up and down) as exactly as you can, would you rather jump on

1) a trampoline

2) a padded soft mat at a judo dojo

3) concrete

Number 1 is an electrolytic cap in the PSU, 2 is a film cap in the PSU, and 3 is with a CCS tail, PSU completely out of the picture.


Thinking up analogues is not always succesful. Please ask clarification if this subject is of interest.


----------



## MrCurwen

Previous rambling was about PSU caps. Let's have a quick look at signal caps.

Again, charging and discharging the caps is where the differences come about. They do these things differently on account of different materials and different construction. 

Some of these properties are static, ie. they aren't dependent on the signal amplitude (or only to an extent dependent). Some are dynamic, ie. they change depending on the voltage potential between the plates, or how fast the cap is 'asked' to charge or discharge, etc.

Once again, imagine the parasitics as a pool of water, and current (charge) as water. The parasitic pool needs to be filled before the signal pool can be filled.

Now let's say we have an anode signal of 10 VPP. So now the anode potential goes up 10 V, and so does the potential between the cap plates.

The dielectric absorbs some current. This is unwanted, but it happens. The amount of current it absorbs is partially dependent on how big the potential between the plates is.

If the potential increases, the dielectric becomes hungry. It need a certain amount of current per centain amount of volts of potential increased.

This property does not care how much current is available from the thing, whatever it is, that is driving the cap. It is hungry. Not polite.

If the driving system has a very very small current capability, it cannot satisfy this hunger to full extent. The amount of water cannot fill both parasite pool and signal pool.

This is a small phenomenon, but it does affect the micro details etc. 


Like I went thru earlier, a similar effect happens on the other side of the cap, and the output followers grid also.


For the charging and discharging of the cap it matters

1) what is charging the cap, and can it effectively charge the cap and it's parasitics

2) what the cap is discharging to, and can the cap discharge what the load wants/needs


So have a thing charging the caps that able to satisfy the cap, any cap, and have the cap discharge to a load that doesn't ask anything. Then the cap quality becomes moot; nobody will hear any difference.

In real world these ideal drivers and ideal loads don't exist, but there are lots of alternatives that come a lot closer than these traditional designs from the 50's.


----------



## baronbeehive

Hey guys there's some food for thought in the last 2 posts, any ideas for Implementing? I will rule myself out of it on lack of knowledge grounds!


----------



## coinmaster

> You can't really say anything unless you've physically tried this component yourself", in which case nobody can say anything about russian components unless they have tried them themselves


 
 Lots of people have tried russian caps and have reviewed them against many other caps. My own experience is limited to Duelunds VS junk but there are quite a few capacitor "showdown" reviews out there and the consistency between their claimed sonic signature and the consistency behind the claims that for the most part the more expensive caps sound better lead me to believe that it is unlikely to be a faslehood. Claiming russian caps are the best caps ever made when you haven't tried all the caps ever made is just an opinion. Especially since you refuse to ever try the expensive caps.
 I'm not going to sit here and say it is one thing or the other but the consistent consensus of claims lead me to believe that more expensive caps are usually better.
  


> If the amp draws the same amount of current at all times, the PSU caps do not charge and discharge with the signal.


 
 As far as I understand capacitors will draw current in order to maintain voltage. So if a CCS changes its resistance to maintain a constant current then the voltage must fluctuate. So if the voltage fluctuates then the capacitors will react to the change in voltage and try to increase the current, however I assume this extra current from the capacitors is dissipated as heat in the regulator/CCS. I'm not really sure where this leaves things.
  


> So have a thing charging the caps that able to satisfy the cap, any cap, and have the cap discharge to a load that doesn't ask anything. Then the cap quality becomes moot; nobody will hear any difference.


 
 You still haven't tried an expensive cap to confirm this fact.
  


> Hey guys there's some food for thought in the last 2 posts, any ideas for Implementing?


 
 I've been over all the angles of implementing those mods months ago and there is no good way to go about it since the stock design uses a pcb which means it uses copper traces and the actual implementation would be a mess. If you were to implement these mods you should be prepared to accidentally ruin your amp.
 This is why I am forced to build from scratch, it's easier and more reliable in the end.


----------



## Maxx134

mrcurwen said:


> p
> Judging from the lack of SSG or teflon enthusiasm on this thread I'm guessing you guys are simply from another faction, another tribe.




As far as caps I think we are open minded for whatever works best.
Caps and tubes preferences are not vigorously determined. 




mrcurwen said:


> "... If you want linear high current (high power), you can use 6P36S (which is curvewise exactly as good as 300B) for next to nothing..."
> 
> "...If you want directly heated magic vibes, there's 4P1L and other less known tubes. Combine that with a current buffer, and you've got the vibes and the power (much cleaner power at that).."



the question of Tubes was going to be my next one.
But not the single triode types.
I was wondering which "dual triode" types tubes would be best for our amps, in which space is the limiting factor. .




mrcurwen said:


> "There is nothing balancing the amp
> A more invasive mod would be to add forced balance at least to the input stage. This would in practise be a CCS tail..."




You re-made the diagram so you should know instead of asking coinmaster..
It is incorrect to say nothing is balanced.

We already have force balanced in driver stage by the "common cathode tail".

Then, the "tuning" of the opamps controlling DC offset also means power tubes are balanced. 


Also everyone forgetting the two 56k that I believe help the opamps achieve zero offset before the headphones are plugged in.




mrcurwen said:


> "film caps are not best for this; they produce too sharp a residual ripple."




Yes, I agree and why Electrolytics are optimal in PSU stage.
So I was wondering why would you put film caps in your PSU to try hear any difference.

I assume your just experimenting PSU topologies?
Too much PSU & cap rambling in your posts so whatever cap works for you is fine with me.

Not shure why you explaining so much about the caps though, because the FIRST PAGE explains specifically the goals we wanted to achieve for this amp, 
and the cap review links posted there are very useful..


"...to big film caps in the PSU would be to add even a simple 2 FET regulator..."
Interesting ideas but hard to follow your point because it seems you are not referring to our amps.

We are only using film caps for specific purposes in "Decoupling" close to the tubes, and coupling..
 not in PSU stage.
In PSU stage we boosted the "reservoir" of capacitance but that's it.
And we already have 2 power transistors operating in our PSU. 




mrcurwen said:


> "Number 1 is an electrolytic cap in the PSU, 2 is a film cap in the PSU, and 3 is with a CCS tail, PSU completely out of the picture."




This is Interesting for other designs and should be made more clear that, that is what it is.
A bit off topic, but interesting as we are open minded so nothing to say, just opening our minds to your designs.




mrcurwen said:


> Previous rambling was about PSU caps. Let's have a quick look at signal caps.



Oh ok...




mrcurwen said:


> there are lots of alternatives that come a lot closer than these traditional designs from the 50's.



Ok now you peaked my interest. 
So then, what alternatives can we implement for coupling?





baronbeehive said:


> Hey guys there's some food for thought in the last 2 posts, any ideas for Implementing? I will rule myself out of it on lack of knowledge grounds!



Hmm not yet..


----------



## coinmaster

> We are only using film caps for specific purposes in "Decoupling" close to the tubes, and coupling..
> not in PSU stage.


 
 I replaced the 300uf bypass cap in the PSU with films and they made a massive difference in bass quality.
  
 I'm also going to replace the cathode bypass caps with the industrial AVX films which is technically part of the PSU.
  


> Hmm not yet..


 
 Don't bother there's no way to do it, I went through it in December/January. It's a bad idea to mod the "force balanced" input stage and the CCS tail output stages in this amp. It's beyond the level of the other mods in this thread, especially given the layout of the PCB and the overall design of the stock product.


----------



## Maxx134

Getting back on topic,

For better matching/coupling/driving of the driver to the powertube stage :

Using the 6sn7gt I have half the plate resistance of a 12a*7 type to feed the powertube's input stage with lower impedance..

This theoretically should have an improvement,
 and so far the answer is yes, 
as results are excellent. 

Yet this also brings up topic me and SonicTrance have been discussing,
Whether the driver stage tube stage is optimally biased for the tubes being used. ..


----------



## coinmaster

> Whether the driver stage tubes are optimally biased for the tubes being used. ..


 
 The MK6 is biased well for the 6SL7 which is what comes with it stock.
 For the 6SN7 it is being starved. Which is interesting because the 6SN7 still sounds better on all the tubes I've tried.
  
 A wirewound cathode bias pot would be really nice here if you wanted fine tune the input stage bias for best sound. You would need to make sure you do not exceed the current limit of the tubes you are using though. 6SN7 can take up to 20ma I think while 6SL7 can only take like 2.3ma.


    
 You would probably want a switch for different tube types toswitch between a current limiting resistor for each tube type. You would want to have the resistor series with the pot so you always have a minimum resistance for the max value you want to current to go to.


 Not sure where you would fit more pots and switches though. Would probably require an "under" box.
  
 Speaking of boxes, finally got my official build on the way

 That doesn't even include the input stage box 
 The entire thing is on hold again because I don't have enough washers/bolts to keep things in place.


----------



## Maxx134

coinmaster said:


> I replaced the 300uf bypass cap in the PSU with films and they made a massive difference in bass quality.



That's good.
That is the tail end of the PSU after the power transistors. 

But for the initial caps in PSU right after the bridge, film caps are not optimal. .


----------



## Maxx134

Yeah so the issue now is, 
When tube rolling
 is a specific tube sounding better because it is actually better?
Or it it because it is more optimally biased.


----------



## coinmaster

It is said often that 6sn7 tubes like to run at high current so I suspect an improvement by increasing the bias to 10ma. 
  
 Tungsol round plate vs psvane cv181-tii vs stock tubes, the tung sol wipes the floor with the other two in every way. It's possible that a shift in bias would make certain tubes sound better or worse, more of a reason to have a bias pot to find out. I have no plans to test this in the forseable future since I have many other things to test first so if anyone wants to do the bias pot mod that would benefit us all.


----------



## Maxx134

coinmaster said:


> > Whether the driver stage tubes are optimally biased for the tubes being used. ..
> 
> 
> 
> ...


 wow this is an excellent post.


----------



## baronbeehive

coinmaster said:


> The MK6 is biased well for the 6SL7 which is what comes with it stock.
> For the 6SN7 it is being starved. Which is interesting because the 6SN7 still sounds better on all the tubes I've tried.
> 
> A wirewound cathode bias pot would be really nice here if you wanted fine tune the input stage bias for best sound. You would need to make sure you do not exceed the current limit of the tubes you are using though. 6SN7 can take up to 20ma I think while 6SL7 can only take like 2.3ma.
> ...


 

 Maxx you should do something like this then I could finally stop worrying about the airflow through yours which lets face it is pretty choc a block with components!


----------



## Maxx134

Naw I'm like the heat.

Bedides, I keep a fire extinguisher by my bed..

More changes soon so it will look different again.


----------



## SonicTrance

coinmaster said:


> The MK6 is biased well for the 6SL7 which is what comes with it stock.
> For the 6SN7 it is being starved. Which is interesting because the 6SN7 still sounds better on all the tubes I've tried.
> 
> A wirewound cathode bias pot would be really nice here if you wanted fine tune the input stage bias for best sound. You would need to make sure you do not exceed the current limit of the tubes you are using though. 6SN7 can take up to 20ma I think while 6SL7 can only take like 2.3ma.
> ...


----------



## coinmaster

A 6sl7 @ 20ma would self destruct.
 It's way beyond the thermal limit of the tube which can only dissipate 1W.
 This means the Woo amps are being run at a low bias. Possibly to allow tube rolling, possibly because it sounds better in the design, who knows.
 I don't recall ever reading anything where 6SN7s sound better at low current though. The claims are always that they should be run at high current.


----------



## SonicTrance

coinmaster said:


> A 6sl7 @ 20ma would self destruct.
> It's way beyond the thermal limit of the tube which can only dissipate 1W.
> This means the Woo amps are being run at a low bias. Possibly to allow tube rolling, possibly because it sounds better in the design, who knows.
> I don't recall ever reading anything where 6SN7s sound better at low current though. The claims are always that they should be run at high current.


 
 So, you think the 6SL7 and 6SN7 gets same amount of current in same type of circuit? That they bias exactly the same? I'm thinking that's not the case. They're very different tubes spec wise. The only thing they have in common is plate voltage (for typical operation) and same pin-out.
 Perhaps @MrCurwen knows something about this?


----------



## coinmaster

Hmmmm, now that I look at the load lines of both tubes more closely you are right. 
  
 Let's say you wanted to put 10ma @150v across a 6sn7, a 400 ohm resistor should do the job. The same 400 ohm resistor would put the 6sn7 at about 2ma.
  
 The situation is not the same for the MK6 though, the resistor values are too high and the voltages are too low.
 The 6sl7 is running at about .5ma and the 6sn7 should be running at about .8ma which is garbage.
  
  

 .8ma would be those squished lines at the bottom, very non linear.
  
 In order to fully traverse the load line with pots you would need a pot for both cathode and anode.
 If you picked a stable plate voltage and just used a cathode pot you could traverse the load line vertically, but in order to traverse horizontally you would need to adjust both the anode and cathode pots and you would have to know what the operating points were in real time for it to be safe.
  
 Luckily vertical traversal is more important here.
 You would want the current limiting resistor switch to also switch the plate resistors when switching tubes which means a 2 deck 2 pole rotary switch.
  
 I would say that a 7k resistor would be near what you want for the 6sn7 plate resistor but I've read that you want a resistor that is multiple times the plate resistance of the tube for the input stage which I know nothing about so I won't comment on what the official value of the 6sn7 plate resistor should be since several times plate resistance doesn't leave much plate voltage.
  
 A current source would probably be better but that's a whole nother can of worms in terms of sound and implementation.


----------



## MrCurwen

maxx134 said:


> As far as caps I think we are open minded for whatever works best.




That's a good attitude to have!

However, there was a categorical claim made about russian caps being poor. At least the categorical claim of them being good has (in addition to a growing pool of DIY guys with extensive history of comparing caps getting on board with them) actual technical specs supporting that at least they are very good.

Anyway I should not be getting more people into the MBGO / KBG / SSG / K73 stuff. The prices are slowly but steadily climbing, and that's not good.




> the question of Tubes was going to be my next one.
> But not the single triode types.
> I was wondering which "dual triode" types tubes would be best for our amps, in which space is the limiting factor. .




I think what you have is good. There are better ones, but they would basically need a lot of redesigning and a bigger chassis. These are very good tubes anyway. Tubes are not the bottleneck; the design is.




> You re-made the diagram so you should know instead of asking coinmaster..




What did I ask? I don't understand, please clarify.



> It is incorrect to say nothing is balanced.




Alright, a clarification;

It is not very well balanced. It is not balanced to the degree that I would consider "high end". Whether or not that matters to you is up to you, but I'll present my opinion with some reasoning.




> We already have force balanced in driver stage by the "common cathode tail".




No.

Forced balance means that the outputs are of exactly equal amplitude in antiphase, even if 

1) the inputs are not of exactly equal amplitude (the other input could be grounded for example, so completely nil)

2) the tubes (or tube sections) are not identical in specs (they never really are, +-10% is the norm, +-20% not hard to find)


Without going into a long explanation of how a LTP works (unless there is interest), the forcing of the balance is dependent on what are the relations between

1) the tail impedance

2) the tubes' plate resistance

3) the plate load impedances

Three main rules;

1) the more dominant the tail impedance is, compared to all other impedances in the current route, the better the balance

2) the branches from the shared cathode node (top of the tail) must be as closely matched as is possible

2) considering the previous, the more dominant the plate load impedance is compared to the tube plate resistance, the less the tubes' spec variance matters to the balance


So let's round up and say the plate load impedances are about 4.5 times the plate resistance. The tail is 1.5k, so each branch on top the tail is about 180 times the impedance.

Even guitar amps which don't look for fidelity of any kind, have better ratios. Guitar amps are conserned with balance in some cases, but not because of fidelity but because of power efficiency. 


Looking at guitar amps;

Using similar enough tubes like 12AX7 you have 100k plare resistor (bad for linearity, but good for guitar amp) and 10k or 22k or 47k tails!

This amp has 1.5k tail.

It is relying heavily on the fact that the input is perfectly balanced. And, of course, tube selection.

If you put into your amp an signal that is 100% on the other side, and 80% amplitude on the other side, the balance is not going to be pretty.

And also, if you put in a tube that has a (very normal) 10% section mismatch, the balance is not going to be high end pretty.


If you want forced balance, the tail impedance must be AN ORDER OF MAGNITUDE bigger than the COMBINED impedances of both the branches.

Also the plate load impedance should be the dominant one in each branch; 50 or so times greater than the plate resistance. This plays the tube variance out of the picture completely; increases fidelity significantly.

As I said, if this general tube theory is ok in this thread, I can elaborate.




> Then, the "tuning" of the opamps controlling DC offset also means power tubes are balanced.




The servos don't contribute to the signal balance between the phases in any way. The servos control DC conditions, they don't affect the signal in any way.

Also they are looped one servo feedback loop per phase. Not connected.



> Also everyone forgetting the two 56k that I believe help the opamps achieve zero offset before the headphones are plugged in.




They are dummy loads. They are there for stability and to prevent pops in turn on and turn off conditions and like you said plugging the headphones. Not relevant in any circuit analysis.



> Yes, I agree and why Electrolytics are optimal in PSU stage.
> So I was wondering why would you put film caps in your PSU to try hear any difference.




Indeed. I used film caps just because I happened to have them (I bought them for a +800 or +900 V supply, so for the voltage rating). I did not expect to hear any difference, for reasons I explained earlier. 

A lot of people use very expensive film caps in PSUs because "they are better". A smarter and a lot cheaper solution would be to understand electronics and design, and design around the problem; such as not having the PSU in the signal loop.

If you throw a rock up into the air, and close your eyes, you don't have to see it fall down to know it is in fact going to fall down.

A cap that doesn't charge and discharge in accordance to the signal doesn't affect the sound. One doesn't need to try this out to understand it.

If it happens to affect the sound, then you know you do not in fact have a constant current draw amplifier.




> Too much PSU & cap rambling in your posts so whatever cap works for you is fine with me.




I'm sensing I'm going off topic and losing your interest. I'm sorry.




> Not shure why you explaining so much about the caps though




Well, when I was trying out different caps for my traditional DIY stuff (mostly single ended and some old timey push pull amps) I was very much interested in how and why the caps seemed to do what they did. General knowledge is applicable to many situations, including modding your amp. This could be off topic though so I'll stop.



> "...to big film caps in the PSU would be to add even a simple 2 FET regulator..."
> Interesting ideas but hard to follow your point because it seems you are not referring to our amps.




Your amps could have regulators in the PSU. At least designwise, maybe not in the space that is available. Line between DIY and modding is drawn in water. I will of course respect the purpose and confines of the thread so please just say if it's of not enough relevance.




> And we already have 2 power transistors operating in our PSU.




Yes. It is a voltage setter, not a regulator.




> This is Interesting for other designs and should be made more clear that, that is what it is.




It could be that none of this stuff can be made with the space available or with the PCB. It is for general interest and increased knowledge on how your amp works. If it's off topic I'll leave it alone.


[qoote]So then, what alternatives can we implement for coupling?[/quote]

Output from input stage -> cap (of maybe only modest quality) -> source follower -> direct coupled to output follower grid

This is probably not practically possible in the available space. Anyway if there is interest I'll elaborate.


----------



## MrCurwen

sonictrance said:


> So, you think the 6SL7 and 6SN7 gets same amount of current in same type of circuit? That they bias exactly the same? I'm thinking that's not the case. They're very different tubes spec wise. The only thing they have in common is plate voltage (for typical operation) and same pin-out.
> Perhaps @MrCurwen
> knows something about this?




Misusing equipment by installing tubes that it was not designed for is possible in circuits with autobias i.e. cathode bias done with resistors and using a resistor as a plate load.

Let's say you have such a circuit set up with 6SN7 and 10mA bias current. The plate resistance of the 6SN7 is part of the equation that establishes the op point (ie. plate voltage & plate current).

Once you change the tube to another type (or, even, another piece of the same type with +-20% variance in specs!) the plate resistance of the tube in the circuit is different. So the equation works out differently, and the plate current is not the same anymore.

If the plate resistance is substantially larger, the plate current will drop substantially. 

This kind of misuse (or misdesign) might be damaging to the tubes, or it might not. It might result in exiting new kind of distortion for the effects-seeker, or it might not. If the original stage was horribly designed, it might even lead to an objective improvement.

If you have a system that doesn't have this autobias function (ie. set plate voltage, fixed grid bias) you can not do this kind of thing. There will be smoke and sparks. The op point is fixed, it's set.

With the resistors on the plate and the cathode, ohms law will do it's thing. This might be enough to land the new tube into a safe operating area, or it might not. Depending on all the variables (resistor values, B+, tubes in question etc.).

Do you understand load lines SonicTrance?


----------



## coinmaster

> the more dominant the tail impedance is, compared to all other impedances in the current route, the better the balance


 
 So if we used a very high value resistor between B- and the the cathodes it would make it more balanced?
  
 Let's say I ran a resistor between B- (-100v) and the cathodes using the 6SN7 with the goal of 10ma@150v. 
  
 I would need a 10300 ohm resistor on the cathode and a 7k resistor on the anode. This works well in spice, however if I wanted to use a plate resistor that is 4.5x plate resistance then all of the voltages would go negative except for the grid because the plate resistance would be too high to allow that current to flow in series with the plate resistor.
  
 The only solution that I see in this situation is to increase the B+ to around 500v or something similar. Or obviously a current source since they are effectively an "infinite" impedance but a current source, at least your version, probably isn't a good idea as a general mod here. It depends on how far people here want to go into circuit creation and alteration, if they even have the space for it.
  


> the branches from the shared cathode node (top of the tail) must be as closely matched as is possible


 
 I assume you're talking about wire resistance?
  
 Quote:


> Yes. It is a voltage setter, not a regulator.


 
 It's a series pass regulator by definition.

 Never heard of a voltage settler and google hasn't either, is that some slang?
  


> Output from input stage -> cap (of maybe only modest quality) -> source follower -> direct coupled to output follower grid
> 
> This is probably not practically possible in the available space. Anyway if there is interest I'll elaborate.


 
 Probably doable, all you'd have to do is solder in the source pin where the cap leg was and solder the cap to the gate with a resistor and some wire. Should be a relatively easy and safe mod, there should be enough space even in a build like max is using. Although I imagine max would dread the thought of it given all that hot glue and 3D architecture he already has in there


----------



## SonicTrance

> If you want forced balance, the tail impedance must be AN ORDER OF MAGNITUDE bigger than the COMBINED impedances of both the branches.
> 
> Also the plate load impedance should be the dominant one in each branch; 50 or so times greater than the plate resistance. This plays the tube variance out of the picture completely; increases fidelity significantly.


 
 Hmm, we have 220K Ra in our amps, which is spot on 5 times 6SL7 44K. However, if we use 6SN7 it's about 31-32 times the internal Rp of the tube.
  


> Misusing equipment by installing tubes that it was not designed for is possible in circuits with autobias i.e. cathode bias done with resistors and using a resistor as a plate load.
> 
> Let's say you have such a circuit set up with 6SN7 and 10mA bias current. The plate resistance of the 6SN7 is part of the equation that establishes the op point (ie. plate voltage & plate current).
> 
> Once you change the tube to another type (or, even, another piece of the same type with +-20% variance in specs!) the plate resistance of the tube in the circuit is different. So the equation works out differently, and the plate current is not the same anymore.


 
 Yes, I'm beginning to understand this now.
  


> If the plate resistance is substantially larger, the plate current will drop substantially.


 
 Yes, I recently modded my amp to give the 5998/421A output tubes more current by reducing the cathode resistor value from 330 ohms to 165 ohms. With the lower cathode resistance the current doubled. From 30mA to 60mA (same amount of current that the 6AS7 gets with stock resistors)
 However, I didn't change the plate resistors, only cathode resistors. We have another mod for the plate resistors. 
  


> This kind of misuse (or misdesign) might be damaging to the tubes, or it might not. It might result in exiting new kind of distortion for the effects-seeker, or it might not.* If the original stage was horribly designed, it might even lead to an objective improvement.** *


 
 Easy now MrC. That's like saying most of the head-amps that's discussed on this forum are horribly designed. Just look at the different tube rolling threads for different amps, you'll see that many prefer non-stock tubes with adapters and so on.
  
 I'll give you an example.
 I have four different types of Tung-Sol driver tubes. 6SL7, 6SU7GTY, 6F8G and 6C8G, all with same construction with the round plates and black glass. To me they all sound identical in my amp. Sure, I notice the increase in volume when using the tubes with higher mu, but that's it.
  
 Also, the Mullard ECC35/33/32. I did a comparison of these tubes some time ago and found them to sound very similar in my amp. Yet, spec-wise they're very different. Perhaps the ECC33 for example would outclass the ECC35's with proper biasing. I don't know.  
  


> Do you understand load lines SonicTrance?


 
 Yes, well for the most part. Honestly, I find that those graphs in old datasheets can get confusing and hard to read. But then again, I'm a newbie after all.


----------



## coinmaster

> However, I didn't change the plate resistors, only cathode resistors. We have another mod for the plate resistors.


 
 The plate resistors on those tubes are too low to limit the current, it's only an issue if the plate resistor value is too high, such as my above example. As a general rule the cathode resistor sets the current.
  


> Easy now MrC. That's like saying most of the head-amps that's discussed on this forum are horribly designed


 
 In all fairness, they probably are. It doesn't take an amazing design to create an expensive product, a running theme I've noticed as I've looked around as popular amps.
 A lot (most?) of the commercial tube amps run a generic, commonly known design that has been used for ages without any true innovation.
  
 Like in the MK6 amp, it's just a basic resistor loaded SE input stage, it doesn't get any simpler than that. I have to admit, after modding the amp sounds mind blowingly good and I can't help but wonder whether MrCurwen has an idea of just how good it actually sounds, but from a technical perspective the input stage is not that impressive and the output stage is an ancient design other than the servo usage.


> Yes, well for the most part. Honestly, I find that those graphs in old datasheets can get confusing and hard to read. But then again, I'm a newbie after all.


 
  




 The horizontal numbers on the bottom are the voltage difference between the plate and the cathode.
 The vertical numbers on the left is the current flow through the tube.
 The curves indicate the voltage difference required between the grid and the cathode in order to achieve the desired current at the desired voltage.
  
 So if you want 10ma @ 150v then you imagine a diagonal line between 10ma and 150v and see where that lands you on the grid voltage. This is the line that the signal will follow.
 With a current source it will be a horizontal line because the current would remain constant. You always want your grid to be more negative than the cathode otherwise the positive grid potential will sling shot more current to the plate and possibly destroy the tube among other bad things.
  
 I'm unsure what happens if you run a tube with positive grid voltages and still stay within the thermal limit of the tube since the charts don't have that data. However it does seem to be a typical theme that the more positive the grids are relative to the cathode, the more linear the tube is. In order to run positive grids you would need to use a source follower or something on the grids because the grids will draw current at that point.


----------



## SonicTrance

> The horizontal numbers on the bottom are the voltage difference between the plate and the cathode. The vertical numbers on the left is the current flow through the tube.
> The curves indicate the voltage difference required between the grid and the cathode in order to achieve the desired current at the desired voltage.
> 
> So if you want 10ma @ 150v then you imagine a diagonal line between 10ma and 200v and see where that lands you on the grid voltage. This is the line that the signal will follow.


 
 Yes, that much I know. Was more referring to graphs like this one. Which can be messy and hard to read.


----------



## baronbeehive

coinmaster said:


> ..............
> Like in the MK6 amp, it's just a basic resistor loaded SE input stage, it doesn't get any simpler than that. I have to admit, after modding the amp sounds mind blowingly good and I can't help but wonder whether MrCurwen has an idea of just how good it actually sounds, but from a technical perspective the input stage is not that impressive and the output stage is an ancient design other than the servo usage.
> 
> ...............


 
 I was wondering the same. It would be interesting if MrCurwen had a listen and told us what he thought compared to one of his amps for example. We can carry on with the component mods for a while yet and then perhaps switch to some circuit mods if possible. Obviously the circuit is the critical thing but the component changes have been positively compared by Maxx for example to some of the top amps out there I believe. Maxx may like to respond if I have made an error in my last statement.
  
 BTW MrCurwen, please carry on with your theoretical posts, I don't know about the others but I don't see them conflicting with the aim of the thread at all and should throw up some good ideas.
  
 Below is a pic of the finished mods on my amp carried out by the engineer who tested it. As you can see some rearrangement of one of two components had occurred with the board back but I can see that I could redo these to make everything fit properly including rerouting the wire below the wimas. Then with the bigger fans the cooling should e sufficiet, hopefully! It will be interesting to see whose amps are still working in a years time!


----------



## MrCurwen

sonictrance said:


> Hmm, we have 220K Ra in our amps, which is spot on 5 times 6SL7 44K




Rp is dependent on the op point that is in use.

The op point that your amp has for the input stage 6SL7's is about 400µA at 85 or so volts Va. This op point has rp of about 75k quickly calculating from the curves. Real tube sections will have anything from 60k to 90k.



> . However, if we use 6SN7 it's about 31-32 times the internal Rp of the tube.




If you look at 6SN7 curves, you wouldn't want to use it under 4mA or so. 5mA with a flat loadline is very good though. Depends on the load line, always.




> Easy now MrC. That's like saying most of the head-amps that's discussed on this forum are horribly designed.




Well, I said I'm not going to be that guy so I guess I'm not going to defend my assertion further in this thread. But I will say this; if the design sounds better with another type, why didn't the designer use it in the first place? What does that say about the designer?



> Just look at the different tube rolling threads for different amps, you'll see that many prefer non-stock tubes with adapters and so on.




Adapters don't necessarily mean you'll be using "another type" in the sense that I meant. 

For example take 6SN7 and it's military rugged brother, 2C22 or 7193. They are basically the same tube, except different envelope and connections. 2C22 fits just fine into any circuit with 6SN7 despite having a bit lower rp (I don't remember by heart what the datasheet says, but all the 2C22 I've got are lower than 6SN7). 

There are plenty of examples like these.

But if the tube is really dissimilar, one must ask again; why didn't the designer use that tube to begin with?

Of course some very simple designs can accomodate a number of tubes that have a similar enough op point available. 




> Yes, well for the most part. Honestly, I find that those graphs in old datasheets can get confusing and hard to read.




It's all about the curves. The secret life of tubes!


----------



## MrCurwen

sonictrance said:


> Yes, that much I know. Was more referring to graphs like this one. Which can be messy and hard to read.




What's hard about it, looks fine to me? =)

Quite the pulse capability that tube has.


----------



## coinmaster

> It would be interesting if MrCurwen had a listen and told us what he thought compared to one of his amps for example.


 
 Yeah, that would save me a lot of skepticism. Plus all the time I've been putting into tests of progressive technical improvement over the modded MK6, using the MK6 as a standard.
  


> We can carry on with the component mods for a while yet and then perhaps switch to some circuit mods if possible


 
 My tests will tell us what mods are worth doing. I'll be testing many different changes to the design including a variation of MrCurwens suggestions.
 It's annoying how my project keeps getting put on hold by small things like the wrong size washer and such though.
  


> Obviously the circuit is the critical thing but the component changes have been positively compared by Maxx for example to some of the top amps out there I believe


 
 I can't speak for Max but I've listened to the flashship amps of Moonaudio, Hi-Fi man, Mcintosh, and some I forget the name and they all sound garbage compared to the modded MK6. I remember one of them costing over 10k and my MK6 still wipes the floor with it.
  
   





> BTW MrCurwen, please carry on with your theoretical posts, I don't know about the others but I don't see them conflicting with the aim of the thread at all and should throw up some good ideas.


 
 Indeed, this is good stuff and is filling in the gaps of my understanding, which saves me time and money, plus it is good for potential mods.
  
  



> if the design sounds better with another type, why didn't the designer use it in the first place? What does that say about the designer?


 
 Cost I'd imagine, the MK6 is extremely cheap for what it is and so are the tubes they come with. Plus it's china


----------



## MrCurwen

baronbeehive said:


> I was wondering the same. It would be interesting if MrCurwen had a listen and told us what he thought compared to one of his amps for example.




I was thinking about what route to take with this one.

I have in fact built "all of the classics" (not really all, but sufficient amount to know different most used topologies from the retro times), such as maybe a dozen or so circuits with the kind of input stage that this amp has. 

I've done a number of things with tubes attempting to handle current like in the WCF output of your amp. An excellent analogy is the road I took with regs; I started out with different tube regs.

I've built a number of cathode followers, and also the Aikido.

While I have not heard your amp, I have built and listened to most of it's constituent components. I am sure that the amp does in fact "good sound", but I am as sure it is not high end as such. Of course all of these titles depend on what is the comparison. 

The engineer always sees the weak points, and thinks of ways to improve them. The customer wants to think highly of his investment. These two can cause friction.

But, again, not everybody wants to or even can DIY a whole amp. 


I'm not going to go on the route of explaining the transparency of my amp via words. I should probably just build a rugged build and mail it to someone in Europe. I don't know, sounds like a lot of trouble for small gain. The flagship amp is way too big to mail, but maybe one of the smaller ones with IDH tubes (6SL7 & 6SN7 and a current buffer)...



> We can carry on with the component mods for a while yet and then perhaps switch to some circuit mods if possible.




Is the amp in one or two chassis'?



> BTW MrCurwen, please carry on with your theoretical posts, I don't know about the others but I don't see them conflicting with the aim of the thread at all and should throw up some good ideas.




Thanks. Alright!


----------



## coinmaster

> While I have not heard your amp, I have built and listened to most of it's constituent components. I am sure that the amp does in fact "good sound", but I am as sure it is not high end as such. Of course all of these titles depend on what is the comparison.
> 
> The engineer always sees the weak points, and thinks of ways to improve them. The customer wants to think highly of his investment. These two can cause friction.


 
 I've been disappointed the majority of times I've tried a high end product, including thing's I've spent a lot of money on, like the HD800 and TH900 initially, plus numerous other things. I'm not afraid to call my investment crap if it is because I don't want to waste money on crap.
  
 However, from an objective standpoint, after modification, the MK6 sounds unspeakably good, like my brain actually gets confused because it sounds like the singer is standing in the room but I cannot see them. After upgrading to my Duelunds alone all aspects of the sound quality increased hugely and the sound stage went from frontal to almost 360 degrees. The Bypass cap upgrade increased the bass quality 5-10x.
 I cannot find fault in the sound it's full, it's fast, it's holographic, it's realistic, it's euphonic, yet still neutral, even with my HD800s the base quality and quantity is like wow.
 Obviously you can't imagine a color you have not seen so maybe it is "bad" compared to what you have heard but I cant imagine it getting much better, I didn't even upgrade the WCF cap either before I tore my amp apart and that is supposed to be a huge improvement.
  
 I'm comparing it to the standard of real life non-reproduced sound and it sounds in some ways even better than real life. However, there are soundstage and bass limitations due to it being headphones.
  


> Is the amp in one or two chassis'?


 
 One, some of us have been using wooden/metal extensions to create more space.
  


> Thanks. Alright!


 
 Yes, moar, _moar_.
  
 At the very least the source follower mod on the grid seems easily doable without annoying complications and should probably be one of the first things looked into at this point, especially if we want to test the "good caps are better" theory.


----------



## Maxx134

Hey!
I dissappear for 2 days and now I have all this to read? !





> Quote :
> "BTW MrCurwen, please carry on with your theoretical posts, I don't know about the others but I don't see them conflicting with the aim of the thread at all and should throw up some good ideas."




We will plan to tune these amps further with these long winded discussions on tubes & bias.


I agree with MrCurwen about the attention our balance amp needs to be made optimal.
The design on driver stage is autobias and common cathode.
Driver tube Cathode resistance is low, for a different reasons like PSU voltage & input *edit "tube type" & impedance of the driver stage.

Yet for driver stage such small signal, we actually only looking at a tiny part of those big graph/curves..

So we need to put things into perspective.
Your driver tube is not going to change in tonality with volume adjustment, 
and 
A coupling cap in a high impedance part of a circuit is not going to a be a "bad choice".
Yet they will be more dependant on quality, to perform as intended.

So it's not the design as flaw,
As reading MrCurwen posts may imply.
But the cost cutting measures used to carry out the design objectives in our amp.

Yet,
The idea of designing out component dependancies is the clever/interesting topic that MrCurwen provides. 




mrcurwen said:


> "Output from input stage -> cap (of maybe only modest quality) -> source follower -> direct coupled to output follower grid
> 
> This is probably not practically possible in the available space. Anyway if there is interest I'll elaborate."




Hmm .. 
yes there is interest but let's keep the modest quality out and at least say "good quality" !
Lol

So..
A cheapo cap > to transistor > to the grid...
Blasphemy!.. Lol

I do not want any SS device in my signal path! (as a choice.)

Although I do not disagree the theory I don't know, 
just the components.
Looks complicated :

http://www.bartola.co.uk/valves/tag/schade-feedback/




mrcurwen said:


> "Quite the pulse capability that tube has."




One of the many many reasons I have read tubes are a superior devices to SS.
That's another topic offtopic,
but a reason we like tube amps.



coinmaster said:


> > "At the very least the source follower mod on the grid seems easily doable without annoying complications and should probably be one of the first things looked into at this point, especially if we want to test the "good caps are better" theory."



It will probably be one of last things attempted, 
Only because we are backed up with focusing on optimal tubes and bias now, and finishing overdue mods.

We are currently testing what works best, not just in theory.

Also, and as example,
 is coinmaster's real world testing and discovery of an occurrence of " a sonic improvement", of "mixing powertubes", but only "in one direction". 

You see I don't dismiss anything that is found in real testing.



So far I am establishing data about which sonic characteristics are being affected, and which sonic characteristics are predominant in each tube socket position.
Which is not easily explainable on paper, 
But nevertheless easy to find out in testing.

So far, I have successfully tried and noted coinmaster observations as a true occurrence. 
There "can" be sonic benifit of combining strengths of two slightly different tubes based on socket position, 
But,
Having better tubes in general is optimal solution "in theory"..

So far have not done anything crazy, Only with same parameter tubes to decipher the "predominant" traits according to the "positive or negative signal" socket position. 

Further testing is needed so I am in process ordering more tube types.




coinmaster said:


> > "I can't speak for Max but I've listened to the flashship amps of Moonaudio, Hi-Fi man, Mcintosh, and some I forget the name and they all sound garbage compared to the modded MK6. I remember one of them costing over 10k and my MK6 still wipes the floor with it."




I made it a choice to never talk about such controversial topic of which tube amp actually sounds best, as it is non-productive.
Simply because they all have different levels of euphoria and realism.

People like to have choice.
I chose this amp as a hobby.
I wanted a fully balanced tube amp.
Although I can afford a top tube amp "now", 
I have no reason to with this one.

So far,
 I what "best" amps I did hear were similar in high realism, 
yet different tonalities...

Also, of interest to me, is Soundstage...
They all have great separation, 
But I found Soundstage to be the key in separating the best amps from the others. 

So far I must say this amp always had great Soundstage, 
But the latest sonic improvements I have noted in tuning powertube bias & tube selection was the "realism within" the soundstaging...
The "holography"...





mrcurwen said:


> It is relying heavily on the fact that the input is perfectly balanced. And, of course, tube selection...:




Exactly, and is testament to the designer that is works this well..

Actually, driver tube selection is not even a choice,
As only one dualbtriode tube per channel makes it already up to the circuit to balance the two triode sections within ONE tube, 
which are by default already close to matching being identical within the same tube,
 and so should be easier for the common cathode tail to achieve.




coinmaster said:


> "MK6 is extremely cheap for what it is and so are the tubes they come with. Plus it's china  "




The Chinese market has much competition and a lot of very beautiful looking designs.
Yet they all seem to have their main goal on price over anything else.




mrcurwen said:


> I have in fact built "all of the classics" (not really all, but sufficient amount to know different most used topologies from the retro times), such as maybe a dozen or so circuits with the kind of input stage that this amp has.




Impressive! but wondering, 
have you built a balanced tube amp? 
Not many balanced amps out there.
I realize it is mostly a customer preference, but
This is the only balanced tube at the thousand mark in cost.




mrcurwen said:


> "I should probably just build a rugged build and mail it to someone in Europe. I don't know, sounds like a lot of trouble for small gain. The flagship amp is way too big to mail, but maybe one of the smaller ones with IDH tubes (6SL7 & 6SN7 and a current buffer)"




That does sound excellent. .
The "thread starter" is in Europe 
and we had played around with the idea last year,
about what topologies would be of interesting for a future project.

But so far, these MK6 & MK8 amps keeps getting better with mods,
 so I stopped looking for at least another year to enjoy..


----------



## Maxx134

baronbeehive said:


> ..
> Below is a pic of the finished mods on my amp carried out by the engineer who tested it. As you can see some rearrangement of one of two components had occurred with the board back but I can see that I could redo these to make everything fit properly including rerouting the wire below the wimas. Then with the bigger fans the cooling should e sufficiet, hopefully! It will be interesting to see whose amps are still working in a years time!



Very nice!
 have you tested it yet?


----------



## coinmaster

> just the components.
> Looks complicated :


 
 The source follower grid drive mod would be simple and easy to implement unless MrCurwen has some fancy pants version of it.
 I would be extremely interested in someone trying this out because I am very interested to see if the claims that a source follower does not effect sound are true. Source follower have often been said to sound better than cathode followers as well.
 I won't be able to test this my self until next month since I've realized that I'm missing about $100 in components I need for my power supply and I can't pay for it atm.
  


> but a reason we like tube amps.


 
_Technically_ it is current that drives headphones and transistors are as good at current duties as tubes as at voltage duties.
  


> It will probably be one of last things attempted,
> Only because we are backed up with focusing on optimal tubes and bias now, and finishing overdue mods.


 
 Force balancing tubes is an even worse idea to try first. If we want to use 4.5x resistor value of plate resistance then that doesn't leave us an easy option with our 6SN7 either.
  


> So far I am establishing data about which sonic characteristics are being affected, and which sonic characteristics are predominant in each tube socket position.


 
 Every aspect of the sound can be affected. One socket position can sound bland and boring and the other can sound lively and realistic. It's best to try with as many different tubes as you can because the variation in improvement is large between them. Since the signal must travel between both tubes I suspect it is shifting the over all linearity of the "curves" to the highest impedance of either tube at any one point on the load line.
  


> but maybe one of the smaller ones with IDH tubes (6SL7 & 6SN7 and a current buffer)"


 
 I'm curious to how those sound, it seems like a common cathode input stage with a simple current buffer is a really good design for its simplicity.


----------



## Maxx134

coinmaster said:


> > just the components.
> >
> > Looks complicated :
> 
> ...




Well...
To answer first two,
I wil post a reason why I do not want any hybrid or transistors in this design:
Look here:




http://www.theaudioarchive.com/TAA_Resources_Tubes_versus_Solid_State.htm

Read it and weep.

Of course out of curiosity, nothing will be overlooked including this.

Also, you are mistaken I am not forcing anything with the tube circuits.
We are simply reviewing limits and ideal parameters for all the tubes, 
Since this thread is turning into a complaint thread about bias without giving suggestions.

Edot*:
More info:

http://kenrockwell.com/audio/why-tubes-sound-better.htm


This show *triode* as best device over SS or pentode:
http://www.vac-amps.com/sciam.html


----------



## coinmaster

> Also, you are mistaken I am not forcing anything with the tube circuits.


 
 I'm not sure if you understood what I meant. Go back to MrCurwens explanation of force balancing.
  


> Since this thread is turning into a complaint thread about bias without giving suggestions


 
 Are we reading the same thread? It's the opposite of that.
  
  


> Read it and weep


 
 There's an eternal argument on both sides. You shouldn't make opinions based on a few sources. There's always more to it then that. As MrCurwen said it's about the right component for the job, among other factors.
 I really don't care about the theory at this point, for every person claiming one thing there's another person claiming another thing.
 I'll believe what I hear.
 There's a whole lot of people that claim source followers sound really really good, even compared to tubes, coming from people that build tube amps, therefore it is worth looking into.
 Also you should let the people on the forum decide what mods they want to do instead of dictating it. 
  
 My bias pot idea is a bust due to the high RA requirement for the 6sn7. The only way to optimally bias the 6sn7 is to create bulky complex circuits or increase the power supply voltage by a few hundred volts which is unlikely to happen.
  
 This leaves out input stage optimization unless or until we have another idea.
 We've already dealt with the output stage other than CCS tails like Mrcurwen suggested but that is delving into circuit creation again. 
 Current source tails could be doable without too much issue in theory given the layout of the board but it would take some effort to create an official guide for it and I question what happens when the signal is moving horizontally on the bottom triode and diagonally on the top triode, you might need to use a gyrator or inductor on the plate of the top triode which turns it into a whole nother mess of things.
  
 The only mod suggested so far that is easily doable and explainable is the source follower grid drive mod.
 Let people decide individually what they want to do.


----------



## MrCurwen

baronbeehive said:


> Then with the bigger fans the cooling should e sufficiet, hopefully! It will be interesting to see whose amps are still working in a years time!




Looking at this picture really _chills_ my soul! Good luck!

Every day I'm nerveous for 5 seconds when I think about how the components are cooking in my amp builds, especially the flagship one I delivered last week. The power buffer could be used as a grill...


----------



## coinmaster

Active cooling does wonders.


----------



## MrCurwen

maxx134 said:


> The design on driver stage is autobias




Yes.



> and common cathode.




No.

Common cathode gain stage is a gain stage that has it's tubes cathode at AC ground. Either it is outright grounded, or it has a direct AC path to ground via a large enough capacitor.

A long tailed pair has a tail that cannot be bypassed with a capacitor. If it is bypassed, you do not have a LTP anymore, you have something else.

What this circuit has, is a LTP. Not a common cathode.

The fact that the cathodes are connected together at the cathode does not make it a topology named common cathode gain stage. This nomenclature was in use before WWII, and still is.




> So it's not the design as flaw,
> As reading MrCurwen posts may imply.
> But the cost cutting measures used to carry out the design objectives in our amp.




Potato, potato.




> yes there is interest but let's keep the modest quality out and at least say "good quality" !




Modest quality not good enough, eh?

In soviet russia you don't choose the cap, the cap chooses you!

In future, I propose only use cap of very cheap price and horrible aesthetics. No pretty boy caps anymore!




> So..
> A cheapo cap > to transistor > to the grid...
> Blasphemy!.. Lol




All just components. The question is, which one performs best in which role? You wouldn't go hunting with a housecat, and you wouldn't have a Lapland husky at your bedside inside house while sleeping. 

No one component type is good at everything. Even everything it could possible be used for.



> I do not want any SS device in my signal path! (as a choice.)




Well you do at the moment. Several.




> Looks complicated :
> 
> http://www.bartola.co.uk/valves/tag/schade-feedback/




Schade is not applicable in any way here.




> One of the many many reasons I have read tubes are a superior devices to SS.




They most surely are not. Depends a lot on what you are doing.

Try filtering a 11V rectified supply to get superclean 4.2V DC for heating of directly heated 4P1L. It takes only tiny tiny 320mA of current. 

Try getting best possible output impedance for direct drive system driving headphones. You say you don't like low output impedance amps you've heard (SS amps); well, like I said earlier NOT ONE OF THEM had a linear voltage amp and a source follower driving the output (making the output impedance low). 

Talking about the curves I commented; 

It's a tube made for low powered radar pulse oscillator, or possibly small TV sweep duty. 6SN7 could be, or similar.

So it can pulse a few hundred milliamps? That's quite impressive for a tube, very impressive, but it's childs play for pretty much any FET costing 50 cents (I buy bulk).

Again, I would never ever ever use an SS device to do voltage amplification. That's another story. Just as I would never use a tube to control any meaningful amount of current in a "best results" amp.




> We are currently testing what works best, not just in theory.
> 
> You see I don't dismiss anything that is found in real testing.




It could be the language barrier, or whatever, but just to clarify in any case; all of the things I'm talking about have been succesfully built a number of times. I'm not sure by any means you were directing that at me even, but just to say it. There, it's said.




> Also, of interest to me, is Soundstage...
> They all have great separation,
> But I found Soundstage to be the key in separating the best amps from the others.




I completely agree.

I tease my friend who has a surround system that surround sound is for people with low fidelity.




> Actually, driver tube selection is not even a choice,
> As only one dualbtriode tube per channel makes it already up to the circuit to balance the two triode sections within ONE tube,




Yes. It does this sloppily. Have the tail impedance be at least 1 megaohm, with the 220k plate resistors, and then you've got balance.



> which are by default already close to matching being identical within the same tube,




Not at all.

No no no. Not in any tubes that are actually made and sold. Sure they can be matched, but that's an anomaly that has to be laboriously looked for. Really well matched tubes cost a lot more. (Not all sold as matched are very well matched in actuality. A lot of dishonesty.)

+-10% is the norm. +-1% is like one in a thousand tubes manufactured. 




> Impressive! but wondering,
> have you built a balanced tube amp?
> Not many balanced amps out there.




My original designs for the past three, maybe four years, have all been balanced. (I did do two SE amps as well, one this year, one last year.)

I've mainly built balanced amps for years.

I've also built balanced direct drive ESL amps, two of them. The DIY ESL elements need a lot of work, but the amp was fine. Direct drive was nice at the time, but later I achieved the same things other ways.


I catch your drift, I'll make a new thread for general tube theory. There's a lot of forum sections here, could somebody tell me where it might be smartest to put it?


----------



## coinmaster

> I catch your drift, I'll make a new thread for general tube theory. There's a lot of forum sections here, could somebody tell me where it might be smartest to put it?


 
 In the DIY section most likely.


----------



## Redge78

mrcurwen said:


> In soviet russia you don't choose the cap, the cap chooses you!
> In future, I propose only use cap of very cheap price and horrible aesthetics. No pretty boy caps anymore!


 
  
 For the record, my three first coupling cap replacements were russian :
*K75-10* (0.33µF/500V) ... nice upgrade from the horrific SCR-PA 0.22µF MKP
*K73-16* (0.47µF/630V) ... I really liked those ones, very lively
*TF-3 *(0.22µF/600V) ... but I probably didn't have the time to break them properly
  
 And to be honest, none of those could not stand a chance against the *Jupiter Copper/Wax*, the difference is just cruel.
  
  
 But the K75-10 ar still in my amp, as WCF cap, bypassed by small *K72P-6*
 And I have plenty of *SGM-4* in my new cap banks, alongside some WIMA FKP-1 and other stuff
 Oh ! I didn't mention the *K71-7* I still have to test sometime ...
  
  
 So, yes, I would tend to agree with you. No need to break the bank to have more than decent caps.
 But the best (Duelund, Jupiter, AN, V-cap, ...) are in an another league, pretty much like the transformers from what I have understood (think "amorphous" ...)


----------



## john57

Does the Jupiter Copper/Wax caps require a operating temp of 80°C to sound best?


----------



## Maxx134

john57 said:


> Does the Jupiter Copper/Wax caps require a operating temp of 80°C to sound best?



The Jupiter are in another league..
A SERIOUSLY huge jump.

Imagine, thinking you have a really great cap in a mundorf silver/gold/oil..

Then you switch to this Jupiter copperfoil cap,
And suddenly the mundof sound unnatural and artificially sweet in treble? 

The treble and whole sound of this cap is so natural and clean, it is a seriously transparent cap.

Edit*
I am only describing the coupling cap position. 

Not the WCF position where the Mundorf are my second choice.

Also I feel jupiter in the WCF position is not needed and a waste of money there, base on past descriptions of WCF sonics I posted .


----------



## baronbeehive

maxx134 said:


> Very nice!
> have you tested it yet?


 

 No! I tried to test it about a week ago and my DAC didn't work, maybe something to do with changing over to windows 10. I can't replace bad tubes or test it further atm because I'm still in temporary accommodation. So I still have to wait for another few weeks until I'm in my new permanent home unfortunately 
	

	
	
		
		

		
		
	


	




.
  
 But I will give my impressions as soon as possible.


----------



## Maxx134

I hate having to make these clarification posts,
But here we go again. .





coinmaster said:


> I'm not sure if you understood what I meant. Go back to MrCurwens explanation of force balancing.



Yes I understood, but I agree the force balancing won't work in our amp.




coinmaster said:


> > Quote:
> > "Since this thread is turning into a complaint thread about bias without giving suggestions.."
> 
> 
> ...




 Sorry, but I called it as I saw it...

No values,
 just shedding light on general design limitations.

 The driver stage cathode resistor issue & bias issues are common amp design compromises brought to light without any solutions.

I didn't say it was a bad thing.
Shedding light on any weaknesses is a good thing, as it makes us think more,

So we have more things to look over and fine tune. 
For instance, this helps to narrowing down what are the best choices for driver tubes to match the circuit. 

So far we dealt with our limitations by otimization of the circuit with higher tolerance quality matched components. 
And Mods that are sonically verified. 




coinmaster said:


> "..you should let the people on the forum decide what mods they want to do instead of dictating it. "




Ugh!
*HUGE MISUNDERSTANDING!!
*

Now *YOU'RE* the one reading differently!


Since when have I actually told anyone WHICH mods to do.???

In fact it's the opposite..

I enthusiastically accepted SonicTrance bias mod..!
Even to impementing similar into my own amp..!

THEN,
 Redge78 posted SonicTrance mod on first page..(!)


You want to do any mod on this amp go right ahead and be my guest!

You want to specifically suggest a mod,
then go right ahead be my guest!

Don't confuse things.





coinmaster said:


> "The only mod suggested so far that is easily doable and explainable is the source follower grid drive mod.
> Let people decide individually what they want to do.."



Easy?
Where would you come off a "common cathode tail"?
You would have to eliminate the balanced input stage,


Just because I have my doubts on implementation.
If it will benifit ME,
over what I currently have..
Which is a top quality over-spec jupiter copperfoil as coupling cap of highest clarity...
Doesn't mean it I disagree it will be working perfectly in other designs.
So sorry if your misunderstanding me.

Also,
 I am not stopping anybody..
I only stated I am backed up on mods..
I have 3 other things to do.
So Who is going to try this "easy" mod? 

There are only two others here that might try it besides me.
You wanna help with specifics & answers to speed it up?..
Instead of complaining about me?






coinmaster said:


> I'll believe what I hear.



At least we can agree on this.





mrcurwen said:


> No pretty boy caps anymore!



Haha!
I gave up some of those "pretty" caps for "Vitamin Q" caps in my WCF cap area.
I go for the sound over the looks,
Yet in these amps, the pretty white caps are actually very inexpensive .




mrcurwen said:


> Well you do at the moment. Several.



Potato / potato..
No,
 I don't have any SS device *"IN"* my *signal path*.




mrcurwen said:


> Yes. It does this sloppily.
> Have the tail impedance be at least 1 megaohm, with the 220k plate resistors, and then you've got balance.




So you admit It works...

I wish your general suggestion was applicable in our amp, 
But as Coinmaster pointed out,
the issues are PSU voltage limitations before those 220k plate resistors. 





mrcurwen said:


> "Schade is not applicable in any way here."




I will take it a step further and say not much in these past topics thus far is applicable here.





mrcurwen said:


> "They most surely are not. Depends a lot on what you are doing."



Agreed I was too general.
Specifically, I am referring to this amp for now.
So my point and links count.





mrcurwen said:


> I tease my friend who has a surround system that surround sound is for people with low fidelity.



Oh!
 I never thought about that!
Haha good point 




mrcurwen said:


> NOT ONE OF THEM had a linear voltage amp and a source follower driving the output (making the output impedance low).




Don't get me wrong.
I actually find this idea VERY interesting.
I have not looked at other hybrids to see whats the common implementations, but this sounds unique.
I'm a hobbiest who is learning all the time so it's interesting to see new things.




mrcurwen said:


> I catch your drift, I'll make a new thread for general tube theory. There's a lot of forum sections here, could somebody tell me where it might be smartest to put it?




To clarify;
The only "drift" I am making is to clarify whether ideas presented are applicable to this amp.

They are nevertheless interesting and others like your posts and no one is telling you not to post.




mrcurwen said:


> My original designs for the past three, maybe four years, have all been balanced..




Now your talking...
Have you compared yours sonically to the usual popular top amps around?

There are a few popular amps in threads here like the "torpedo" and "bottlehead" amps,
 which users can build kit or order, but 
Those amps are only upper mid-tier amps.. 
Not TOTL type..
I personally heard them in quiet settings so I know.

I have not heard the Feliks-Audio ELISE amp yet and that would be interesting to hear as I love all tube amps.

So far I haven't heard anything to pull me away from this amp in its current highly moded form.


Do you have kits? Or just build?
That would be a better thread to start.


----------



## Redge78

john57 said:


> Does the Jupiter Copper/Wax caps require a operating temp of 80°C to sound best?


 
 To answer that specific question ... NO
  
 Actually, you should try to be as far as possible from the "max temp" of the cap.
 A generic rule of thumb ("Arrhenius law") is that you double the life expectency of each 10° decrease from the Max Temp. Originaly, this law is for chemical caps, but you can never be too careful.
_For a cap given for 5000H @80°, you can expect to keep it for 10000H @70° or 20000H @60° ... _


----------



## coinmaster

> The driver stage cathode resistor issue & bias issues are common amp design compromises brought to light without any solutions.


 
 There are solutions, we discussed them.
  


> Now *YOU'RE* the one reading differently!
> 
> 
> 
> ...


 
   
 Here:


> coinmaster said:
> 
> 
> > > "At the very least the source follower mod on the grid seems easily doable without annoying complications and should probably be one of the first things looked into at this point, especially if we want to test the "good caps are better" theory."
> ...


 



> Easy?


 
 Yes, the source follower mod would require a few tiny components and a wire, the other proposed mods would require many many times more effort to implement due to the bulk and complexity and the layout.


> Where would you come off a "common cathode tail"?
> You would have to eliminate the balanced input stage,
> 
> 
> ...


 

 Those sentences were not in good english, mind repeating?
  


> Just because I have my doubts on implementation.
> If it will benifit ME,
> over what I currently have..
> Which is a top quality over-spec jupiter copperfoil as coupling cap of highest clarity...
> ...


 
 I have no clue whether it will sound better either I have Duelund Cast caps which are considered the best of the best of the best. Still though, after doing some reading and rereading some grid driving posts it does seem to be proven that the source follower mod can improve transients greatly, whether that is applicable here with high end caps in place I don't know. In either case if the theory behind it is correct then it wouldn't surprise me if it worked given the abysmal current the input stage runs at.
  
  


> You wanna help with specifics & answers to speed it up?..


 
 I'm waiting to see if there is interest, also MrCurwen said he would go into it more if there was interest. I'm a ways off from testing it, I've got other priorities and the waiting game on cash and delivery is creating more of a delay than I had hoped for my build.
  


> Instead of complaining about me?


 
 Where's the fun in that? 




  


> I don't have any SS device *"IN"* my *signal path*.


 
 Well, technically the regulator is solid state and it most certainly affects the sound due to inherent impedances on the signal if nothing else. I would rather go with a shunt regulator due to the supremely low impedance they have, in either case solid state is helping rather than hurting here unless you want the warm, "old school" tube rectifier/regulator sound.
  


> I wish your general suggestion was applicable in our amp,
> But as Coinmaster pointed out,
> the issues are PSU voltage limitations before those 220k plate resistors.


 
 There is hope, a current source should pose effectively the same impedance as a 1 meg resistor with the added bonus of a horizontal load line.
 Plus a gyrator load which negates the issue of the power supply voltage being too low and also provides super high impedance.
 I already have a nearly complete PCB board for the both of them
 I chose a different variation of gyrator then MrCurwen but in general it's the same.

 It wouldn't be too difficult to implement assuming you could find the space(it's smaller then it looks). You would need to create your own -15v supply though. I could make it so you can plug it in to the B- of the amp but I don't see a safe way to prevent disaster in case of some sort of malfunction putting -100v on the cathode. 
  
 If there's interest I can create a PCB model for the 15v supply as well using the 2 fet design MrCurwen was talking about, or you can just buy an IC for it which will be much smaller and is way cheaper. I wouldn't recommend perf-boarding it, I fried many a component with those accursed things and they are a P.I.T.A to get working.
 There's no way to fit these inside the case unfortunately, at least I don't think so.
  
 This PCB can be used on the output stage as well which gives the tubes CCS tail and gyrator load which should keep both tubes on a horizontal load line, unlike simply using a CCS tail which seems like it would unbalance the current between the tubes.
  
 Also you can fully traverse the load line horizontally and vertically with it although you would want to be able to read voltage/current levels while doing it and traversing the load line of a WCF is more effort then it is worth over just picking a good spot on the load line.
  
 Once I have the file ready I can upload it and you send it to https://oshpark.com and spend $30 or something for a few copies. I've used them a few times and they make really nice PCBs.
  


> The only "drift" I am making is to clarify whether ideas presented are applicable to this amp.


 
 That depends on the individual. They are all applicable if you put in the effort.


----------



## baronbeehive

Nice ideas. So maybe we could make a list of potential mods together with supposed benefits, difficulties in implementing and so on to give everyone an idea what to go for?


----------



## Maxx134

coinmaster said:


> There are solutions, we discussed them.
> 
> Those sentences were not in good english, mind repeating?




Coin 
you didn't answer me.
Instead you say it's not good English. 
Since when are you an English teacher? 

1-Yet again you didn't admit your wrong about slandering me.
2- your trying to "grasp straws" by highlighting my use of the word "we"..
The word "we", could mean me and my dog...

3- Your blatantly avoiding my points about the driver stage.

You cant implement this without loosing the "common cathode" connection, responsible for keeping the balanced operation. 

You forget this is a balanced amp?

Basically I see you would have to separate the cathodes for that "idea" so there is no balanced driver stage.

Thanks for the info in that post for the boards,
But that doesn't make you right.

It be nice to have some help from you for a change without trying to be right all the time. 



> QUOTE :
> "Oh, well *if* there enough interest. ."



That's not the point.
The point is if it is viable to even try.


----------



## Maxx134

baronbeehive said:


> Nice ideas. So maybe we could make a list of potential mods together with supposed benefits, difficulties in implementing and so on to give everyone an idea what to go for?



Name the viable ideas.


----------



## Maxx134

I'll go further and say there is not one viable idea to implement in these amps. 

The only thing this has done is:

1- make me think (good)
2-give me headache (bad)
3- make me listen to off topic ideals and designs (interesting)
4-have to answer coinmaster nonsensical accusations (bad)
5- force me to merge the mk6 & mk8 on a design level mentally (good)
6-review areas that are not of concern (waste of my time)
8-try to understand why I am read 3-4pages of posts with next to nothing pertaining to *actual* mods.


----------



## coinmaster

> Coin
> you didn't answer me.
> Instead you say it's not good English.
> Since when are you an English teacher?


 
 I'm not an english teacher by I do speak the english language and I have no idea what you said.
  


> Yet again you didn't admit your wrong about slandering me.


 
 I call things as I see it, don't get upset about it. Feel free to slander me all you want.
  


> 2- your trying to "grasp straws" by highlighting my use of the word "we"..


 
 Further questioning your understanding of proper english, you consistently say things which grammatically imply you are the one who calls the shots around here, extending far beyond a single post.
 You seem to do this without noticing it and appear to forget that this is a public forum where things don't have to be run by you for approval.
  


> You cant implement this without loosing the "common cathode" connection, responsible for keeping the balanced operation.


 
 Yes you can, it doesn't change it at all.
 You are either replacing the resistors with different value resistors and higher supply voltages or replacing the tail resistor with a mosfet and the plate resistor with a gyrator.
 The "common cathode" connection doesn't change.


> It be nice to have some help from you for a change without trying to be right all the time.


 
  Yup, I've contributed nothing so far





  


> I'll go further and say there is not one viable idea to implement in these amps.


 
 To you maybe, it depends on the individual.
 The PCBs I'm ordering could very well be used to apply most of the suggested mods and they greatly reduce the hassle involved. The main issue is space, only people utilizing an "under-box" would realistically be able to use them.
 On the other hand the grid-drive mod should be able to be implemented easily with little space consumed.
  


> Nice ideas. So maybe we could make a list of potential mods together with supposed benefits, difficulties in implementing and so on to give everyone an idea what to go for?


 
 The PCB above solves the complexity issue with force balancing on the input and current source tails on the output. It doesn't really solve the size issue as much but I'm sure you can get creative.
 It also removes the need for the bias pot mod since it is a better version anyway.
 Even though the PCB should work just dandy I never intended to use it for public modding, I might wait until I use it in my own design first to account for any unintended issues like heat problems or something.
 The input stage will be one of the last things I build since the power supply and output stage is way more of a time sink, so I don't know how long it is going to be until I can test it. It will probably be june by the time I can afford the odds and ends I need to finish off the power supply/output stage and then another 2-3 weeks before I even get the PCBs in the mail so it could be July by that time (damn that sucks actually).
 The gyrator on the output stage anode would negate the need for the impedance mod pot and instead you would adjust the plate voltage to whatever voltage the impedance mod would have imposed.

 So that takes care of 
 Impedance mod
 Force balance mod
 CCS tail mod
 The PCB is probably going to be half the size of the picture I posted and you would need 4 of them, not including the -15v supply that would need to be created.

 So what's left is
 Grid Drive mod
 and that's it?
 I don't know what Maxx had in mind he seems to be interested in finding optimal tube types. The CCS/Gyrator mod would allow you to use whatever tube you wanted within the limits of the power supply (even 300B) with very little hassle to bias it (turning knobs)
 The problem is you really should have some way of displaying voltage and current of the plate of each tube otherwise it will be difficult to get to the point you want on the load line (and dangerous)
 Perhaps Maxx should replace those tempurature meters for volt/ammeters.

 Oh right I almost forgot, the input stage power supply is unregulated. Meaning the voltage does not remain stable during operation. This could be a good thing or a bad thing or both sonically, as they both have advantages/disadvantages but from a pure technical and HI-FI perspective unregulated is bad.
 This means another circuit, maybe something simple like another series regulator like we have in the output stage power supply or a 2 fet regulator like MrCurwen suggested which is a bit more complex. 
 Or you could spend $60 on a Salas Shunt Regulator which is well renowned and a go-to regulator in the DIY community. 
 Either way there's no way it's gunna fit inside the chassis.
  
 So that leaves us with 
 Grid drive mod
 Regulated input supply
 and maybe a better output supply if you want to go that far.

 Shunt regs are generally better then series regs especially when using a constant current load. They have far lower output impedances, usually. Lower impedance power supply = better sound.
 So 
 Grid drive mod
 Regulated input supply
 Improved output supply
  
 At this point it might literally be easier to order a custom PCB for the entire amp and replace the one you have.
 The problem is I have no idea how the sound would differ with all these changes, for example regulating the input stage supply could refine the sound but also take away some life and possibly reduce transient response.
 Or It could make things 10 times better, who knows. If you're going to use a CCS/Gyrator load then I suspect regulated supply will outweigh any potential downsides,
 In any case this is all theory at this point, at least in my eyes. From a technical perspective they are all improvements, and on paper they should sound way better. People that make and use these methods claim how good they are, For example the regulated power supply and Gyrator/CCS input stage has been touted over and over to sound amazing, but I still stand by my way of "I'll believe what I hear when I hear it".
  
 I don't recommend any attempt on force balance/CCS tail mod unless you use a custom PCB unless you want to get involved with circuit creation which requires time and money for materials, experience, and getting things to work.
  
 The Source follower grid drive mod can be done pretty easily, I'll have to make some sort of guide somehow, unless MrCurwen wants to chime in.


----------



## john57

redge78 said:


> To answer that specific question ... NO
> 
> Actually, you should try to be as far as possible from the "max temp" of the cap.
> A generic rule of thumb ("Arrhenius law") is that you double the life expectency of each 10° decrease from the Max Temp. Originaly, this law is for chemical caps, but you can never be too careful.
> _For a cap given for 5000H @80°, you can expect to keep it for 10000H @70° or 20000H @60° ... _


 
 Maybe there is a misunderstanding here. I am not talking about max temp but operating temp. These caps have wax inside not outside and seems to _require_? the wax in a melted state to work best. The same company also makes caps with bee wax with a operating temp of 70C according to the manufacture.  I have paper in oil metal case caps in tube amps. These caps do not have paste that can dry out with heat. Like I noticed tube amps need to warm up a bit and in my experience takes about 35 to 40 minutes at 90% best with the various tube amps I have in the past.


----------



## Maxx134

baronbeehive said:


> Nice ideas. So maybe we could make a list of potential mods together with supposed benefits, difficulties in implementing and so on to give everyone an idea what to go for?





******



Sorry if I came off rude.
But the Ideas presented to me can only apply to coinmaster unfinished amp which can change in design however he wants.

It would have been nice to have an actual mod to implement instead of nice ideas.

But "*we*" (me and my dog) are coming up with actual solutions. .

. .


----------



## Maxx134

john57 said:


> redge78 said:
> 
> 
> > To answer that specific question ... NO
> ...



It is true that they changed the wax on their Copperfoil version.
Edit* 
I only responding to the material change & sound.
Nothing else can comment. 

I used both on this amp and I can say first hand I did not like the regular "HT" cap because it had a sonic characteristic of heavier bass and the treble was soft.


----------



## coinmaster

> But the Ideas presented to me can only apply to coinmaster unfinished amp which can change in design however he wants


 
 Or anyone using an extension box. I don't know who other then Redge is currently using one. At first I wasn't going to recommend the mods due to the layout and construction issues but using a custom PCB actually makes it relatively easy to implement other then the space requirements.
  
 Like I said the impedance mod pot would not be needed so that frees up one space for a voltage/current pot, however you still need more pots and meters so no matter how you look at it you need an extension box.
  
 I actually have no intention of modding my MK6 output stage much after building it, I need something to listen to in between mods, Most of my effort will go into messing with my new design which solves the problem the "impedance" mod tries to solve from the get-go.
  
 As for the MK6 output stage I'll mod it when people here have shown that it is a proven upgrade, maybe other then the "grid drive" mod since it is easily applied and the results can have huge implications for me.


----------



## Maxx134

> Quote: Coinmaster]
> *"The "common cathode" connection doesn't change.
> ..
> The Source follower grid drive mod can be done pretty easily, I'll have to make some sort of guide somehow, unless MrCurwen wants to chime in."
> *



OK, 
I will be civil and try to be productive here...

Convince me and I will do it...


Where exactly will you connect the source follwer..
Doesn't each one have to go on a cathode? 

Aren't the two triode cathodes connected directly together? 

So how will you separate the positive & negative cathodes without eliminating the common cathode design?

Me and my dog *(we)* would like to know. .

Edit**
I do have a dog..
Here he is guarding my amp above him:

He seems bored when I mention modding my amp..
He says coin ideas are more exciting than mine.


----------



## Maxx134

coinmaster said:


> > But the Ideas presented to me can only apply to coinmaster unfinished amp which can change in design however he wants
> 
> 
> 
> ...



For space for the pots,
There is enough space inside the huge transformer covers we have..


----------



## Mogos

In my amp after power is on the ventilators doesn't work. The amp is heating up for approximately 40 min (winter/spring conditions) and when temperature reaches 50 degrees the ventilators turns on cooling down the temperature to 40 degrees.
 When I was planing the modification one of the priorities was to have good ventilation. Just to remind some photos of the casing done by me.


----------



## Maxx134

Mogos, your talking Celsius correct?


----------



## coinmaster

> OK,
> I will be civil and try to be productive here...
> 
> Convince me and I will do it...
> ...


 
 Okay so this is what the input stage of the MK6 looks like stock
  

 The current flows through the tail resistor and sets the bias voltage for the current you want.
 The two plate resistors sets the plate voltage.
  
 It turns out you were right about the "common cathode connection" While technically you can do it, the current source will be fighting the antiphase signals of either tube as well as the different tolerances of the tubes and you will not end up with constant current at the cathodes.
  
 On the other hand it doesn't matter because the current sources will make sure they are both running at the same current anyway and maintain balance. Even with different tolerances the balance will be the same since both current sources will be individually ensuring that the tubes operate the same.
  
 So this is what the individual triodes would look like after the mod

 The current source maintains a constant current and the gyrator maintains a constant voltage at DC but a constant current at AC. Both of them present an extremely high impedance which as MrCurwen said will provide good balance.
  
 R8 and R6 in the picture would be where you would place the pots. R6 sets the anode voltage and R8 sets the current.
  
 As for the Grid drive mod
  

  
 This is the usual configuration for grid drive with source follower
  
 Just replace one leg of the cap with the source pin and place the cap on the gate and find a ground point for R9. I have no idea if R9 is a good value I just picked a random one.
  
 The problem is the grid resistor is effectively 1 meg between the opamp and grid and 470k between the grid and the cap to ground which is too high for the source follower to function, it will need to be lowered drastically. 470k seems to be the proper grid leak value so I don't know the effects of doing this, I feel like I am missing something obvious. Will need to wait for MrCurwens input.


----------



## Mogos

Yes Celsius. I forgot that it is an international thread. And celcius was so obvious for me. I live in Poland Europe 
	

	
	
		
		

		
		
	


	




.


----------



## Redge78

john57 said:


> Maybe there is a misunderstanding here. I am not talking about max temp but operating temp. These caps have wax inside not outside and seems to _require_? the wax in a melted state to work best. The same company also makes caps with bee wax with a operating temp of 70C according to the manufacture.  I have paper in oil metal case caps in tube amps. These caps do not have paste that can dry out with heat. Like I noticed tube amps need to warm up a bit and in my experience takes about 35 to 40 minutes at 90% best with the various tube amps I have in the past.


 
 No misunderstanding here.
 The temp you have on the datasheet will be the *max *operating value, not the *best *operating value. Same than all the other caps from all the other brands.
 This is one point that is utterly important if you want to put those Jupiter in a tube amp. The life expectancy of those caps may be (very) short if you don't have the proper ventilation (natural or forced).
  
 Me, myself and my Jupiters have decided to stick to the "Arrhenius law" and always try to have the cooler temp possible inside the amp. I'm not ready to spend $400 every 6 months on my coupling caps.
  
 And I have never heard/read anywhere that the wax would need to be melted (which would be pretty difficult when you use those caps in a filter speaker .... the 100V version, I mean).
  
 [EDIT] _70°C is just bloody dreadfull for a component in a tube amp ... Funnily, the famous Mundorf Silver/Oil are also rated 70°C Max (but the upgraded S/G/O version are rated 85°C Max)_


----------



## MrCurwen

Liquid or semi-liquid or partially liquid forms don't have the same voltage rating as solid forms of the same material.

Take a DESILITER of water and put a current thru it, measure how much resistance.

Now freeze that water solid, and try to put a current thru the ice cube. Measure resistance.


This is a serious problem with some dielectrics and some applications. I've got some polystyrene caps that haven't been potted in plastic casing, or any kind of casing. That type have been raported to suffering shorts in a hot guitar amp (intended use for me as well). Really good tone though. Polystyrene colours the sound very excitingly in a high impedance, poorly driven system! Not harsh like HIFI silver mica (treble cap in tone stack).


----------



## Redge78

mogos said:


> In my amp after power is on the ventilators doesn't work. The amp is heating up for approximately 40 min (winter/spring conditions) and when temperature reaches 50 degrees the ventilators turns on cooling down the temperature to 40 degrees.
> When I was planing the modification one of the priorities was to have good ventilation. Just to remind some photos of the casing done by me.


 
 Mogos, I really like the aesthetic of your amp.
 The only thing is that bothers me are the little holes you've got on the bottom box, they must **** up your ventilation path. The air is supposed to exit from the holes around the tubes ... Pretty sure we already talked about that earlier on, when Maxx sealed his bottom plate (and lost 10° (Celsius ?) ) in the process.
 But maybe you already took care of that, told me and I forgot ... would not be that surprising !
  
 Anyway, when my large mods are completed, I may come back to you and copy you shamelessly. 
 That is if my plans of a fluorescent acrylic box is too complex/expensive to do.
  
@Mogos
 Anothe subject : I have read that you have a paul Pang V2 USB card. I was planning to buy one myself. Can you tell me what you think of it ? That would be much appreciated/helpfull.
  
 [EDIT] _The potential problem you may have is that some areas of the amp may be significantly hotter than where you're taking your temp. I would (warmly 
	

	
	
		
		

		
			





 ) recommend to always have at least a bit of forced air through the amp. It's noiseless and good preventive maintenance. _


----------



## coinmaster

Okay I solved the plight I was having with the Grid drive mod implementation. It seems my memory of transistor biasing has gone to trash.

  
 Same as before but you connect R3 to the opamp output instead of ground. 
 The 20v battery indicates the opamp and the two 470k resistors are the grid leak/buffer resistors in the amp between the opamp and grid.
  
 So essentially like I said before, switch out the capacitor leg and the source leg and connect the capacitor leg to the gate of the mosfet.
 Connect the drain to B+ of whatever stage and connect R3 between gate and the opamp output (pin6).
  
 I could have sworn R4 and R2 are too high of a value for it to work but spice is telling me the otherwise. 
  
 Of course it might actually be better to connect it to C2 as an AC path to ground for the gate current like this
  

 But you're going to have to ask MrCurwen for the fine details like that, I only know the overall concept.
 He is giving me the silent treatment so you're going to have to ask him directly.
  
  
  
 As for the force balance mod you would have to splice apart or rip out the copper trace between the cathodes in the input stage for it to work but it's not hard to reconnect them whenever.


----------



## Maxx134

john57 said:


> I have paper in oil metal case caps in tube amps.



I use vitaminQ caps as my second choice cap after the Jupiter copper.





mogos said:


> Yes Celsius. I forgot that it is an international thread. And celcius was so obvious for me. I live in Poland Europe  .



The amp doesn't have to suffer in heat with the "warm-up" time you like to give your tubes. ..

Personally I want the whole amp to be as cool as possible inside and have my fan on even before I turn on the amp.

The tube are far away on top and are not affected by the fan.

The PSU generate a lot of heat, as does the sockets.
So we need the inside as cool as possible. 
I would never wait for insides to get hot..

My fan is blowing directly onto my caps.
The air is forced out top because I taped holes on bottom I had...
Only way to remove heat buildup because of lack of easy air flow.


----------



## Mogos

Maxx your assumptions are correct. In case of my solution the temperature reches level wich I have observed when I had the stock solution (smaller fans turn on from the begining). The 50 Celcius 
	

	
	
		
		

		
		
	


	




 degrees is a temperature measured in hottest points. I have two sensors. So the conditions around the precious caps are better then in the stock solution. Additionaly the ventilators does not stop after the power is turned off. They are turned off automaticaly when the temperature reaches 35 Celcius degrees. With this solution I see two advantages. The amp as a whole heats up faster (and as john57 pointed out the tube amp needs to heat up to spread the wings). Second maybe not so relevant is that if I am listening to the music for not so long then the ventilators don't start at all (winter time).


----------



## Mogos

redge78 said:


> Mogos, I really like the aesthetic of your amp.
> The only thing is that bothers me are the little holes you've got on the bottom box, they must **** up your ventilation path. The air is supposed to exit from the holes around the tubes ... Pretty sure we already talked about that earlier on, when Maxx sealed his bottom plate (and lost 10° (Celsius ?) ) in the process.
> But maybe you already took care of that, told me and I forgot ... would not be that surprising !
> 
> ...


 
 It may look like the airstream may be disturbded by the holes. But the effect is different. The heated air always run upstream and the tubes are the motoric force for it. The little holes act for suction of the air not dissmisal of it especcialy when the ventilators are off. I don't have any measuring devices but I have used very thin paper to check which way the air may travel trough the wholes and it looks like the chimney effect is working 
	

	
	
		
		

		
		
	


	




 with fans off. (of course it is very weak effect but at least telling me that the air is not pushed out). The air stream forced by the vetilators bounces against the PCB and for sure there may be tendency to run side ways and run away trough the wholes. But the same measuring with the thin paper dose not show it. Any way when the ventilators are on the temperature is stable and reaches the 40 Celcius degrees. As I have alredy written I have placed the sensors in the hottest points so I have good control of the temperature inside the amp 
	

	
	
		
		

		
		
	


	




. And this is what it shall be.
  
 I can recomend the use of the Paul Pang V2 USB card. Maybe sonically it is not day and night but you are gaining few advantages with it for the further components. I will not go for the highest model and invest this money for adding eg. Wyred 4 Sound reclocker just in front of a DAC or USB-SPDIF converter. With Paul's card you have digital audiooutput separated from the computer USB bus. You can power it with dedicated PSU and this current may be used by the DAC or other reciver if it is needed DC for comunication (it dose not give you isolation). And you are sure that the signal going out of the computer is reclocked with audiofile grade clock with stable powering and not just "something"


----------



## Mogos

Olny one thing is in minus in the whole casing design considering it from the viewpoint of cooling. The cage over the tubes is not recomended. But looks sooooo gooood for me that I am willing to accept the consequencec of using it. Tubes have not an easy life conditions and the whole amp could run even cooler.
 I think that for hot days I will take it off.


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## Maxx134

My room is always very warm 29 celsius , 84 Fahrenheit, 
so I do not have advantage of effective cooling,
But I like your automatic and temp sensor solution.

Do you have specifics on these components?

I rather not look myself, if you already done it..


----------



## SonicTrance

mogos said:


> In my amp after power is on the ventilators doesn't work. The amp is heating up for approximately 40 min (winter/spring conditions) and when temperature reaches 50 degrees the ventilators turns on cooling down the temperature to 40 degrees.
> When I was planing the modification one of the priorities was to have good ventilation. Just to remind some photos of the casing done by me.


 
 You really did a beautiful job with your amp Mogos!
 If I ever decide to extend my amp I would (try to) hire you to make the extension! 
	

	
	
		
		

		
		
	


	



  
  


maxx134 said:


> My room is always very warm 29 celsius , 84 Fahrenheit,
> so I do not have advantage of effective cooling,
> But I like your automatic and temp sensor solution.
> 
> ...


 
 29C, really? I would die!! We try to keep a steady 20C at home.


----------



## baronbeehive

maxx134 said:


> ******
> 
> 
> 
> ...


 

 Agreed! And I thought it would be best to stick to realistic solutions rather than theoretical at least at this stage, hence the need for more info on what the proposed mods actually are. I'm not at the same technical level as the others anyway so wouldn't be able to implement the more exotic ideas.


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## baronbeehive

Quote: 


mogos said:


> ................ As I have alredy written I have placed the sensors in the hottest points so I have good control of the temperature inside the amp
> 
> 
> 
> ...


  
 Sorry Mogos, which is the hottest part?


----------



## Mogos

baronbeehive said:


>


 
 Measuring points of temperature.


----------



## Mogos

Maxx the temperature controler I use is ESCO company DC-20. Powered with 12V (there are options 230v and 24V). And has two measuring probes. 
  
 Below Google translation:
  
 2 CONTROLLERS in one housing
 2 measuring inputs
 2 control outputs
 View T1 and T2 alternately
 Mathematical functions (measurement of average, differential)
 REGULATORS can be associated with each other (eg. WYJ1 = on when WYJ2 = disabled)
 Digital input for manual or cat. failure
 Built-in beeper (buzzer)
 One controller for adjusting the temperature of heating systems:
 - Electric heaters, stoves,
 - Heating cables, deicing systems
 - The incubators, terrariums, aquariums
 - Boilers, heaters, etc.
 - Pump C.O. and hot tap water
 - solar panels
 - Fireplaces with water jacket
 - Servo valve 2, 3, 4 way valve
 and cooling:
 - Refrigerators, freezers, refrigerated counters
 - Fans, coolers
 - Units for automobiles (version for 12V or 24V), etc.
 DC-20 stands. Abbreviation "double controller" is a de facto two temperature controllers placed in one housing with the possibility of any configuration of input-output and linking both regulators. The device has 2 inputs and 2 control outputs, which can operate in either heating or cooling, and the measurement is measured from the sensor T1 or T2, or both sensors simultaneously.
 With mathematical functions measurement with two sensors can be calculated as the difference [T1-T2] (used in systems with solar collector) or average [T1 + T2] / 2.
 The controller can perform both simple single or double heating system or cooling and more extensive application.
 The controller has a digital readout of the temperature and calibration function display. The value of the sensor T1 and T2 is displayed alternately every 3 seconds. You can be set to control display only one reading.
 Built-in beeper can be set to sound when switching outputs and alarm states.
 The digital input can be used as an alarm input or manual output control. It can signal a failure of the activation of an external pressure switch or temperature limiter STB connected to a digital input. In case of failure disconnect the whole system with the ability to sustain the fault state until manual reset button.
 The controller is equipped with 1 relay output high power 20A (4500W maximum resistive load) and Output 2 with max. Load 8A. Mounting in a panel or enclosure hermetic, wall-mounted.
  
 
  

 


 Zdjęcia Do góry​  

 Entrance:
 2 NTC temperature sensors 5kOhm at 25 ° C
 digital input (normally open or closed)
 Measurement range:
 -50 ... + 150 ° C
 Accuracy:
 +/- 0.5 ° C
 Sampling period:
 330 ms
 Display resolution:
 0.1 ° C over the range of
 Resolution settings:
 0.1 ° C over the range of
 display:
 LED, 4 digits with a height of 11mm with graphical icons
 Control method:
 ON-OFF with hysteresis
 Accuracy of adjustment: adjusted in the range 0.1 ... 20.0 ° C
 Control outputs:
 1 relay 20A 4,5 kW, durability of 100 thousand. cycles
 1 relay 8A 1.5kW, durability of 100 thousand. cycles
 Additional features:
 - Mathematical functions (differential measurement, average)
 - Channel selection temperature read
 - The audible alarm signaling
 - The possibility of connection of both outputs (application conditions)
 Montage:
 in the hole dimensions: 71 x 29mm
 Degree and class of protection:
 IP65 / II
 Power supply:
 230 VAC +/- 15% or 12VAC / DC or 24AC / DC
 Power consumption:
 max 3 VA
 Working conditions:
 -5 ... 60 ° C; 0 ... 85% RH (non-condensing)
 Storage conditions:
 -40 ... 85 ° C; 0 ... 85% RH (non-condensing)







 
	

	
	
		
		

		
		
	


	

  
 I think you can find somthing similar localy.
  
 Below how it was fitted in the amp casing.


----------



## Maxx134

sonictrance said:


> maxx134 said:
> 
> 
> > My room is always very warm 29 celsius , 84 Fahrenheit,
> ...




Well  actually right now it says 28.1c





That's at night with amp off so coldest it gets..


----------



## coinmaster

> It turns out you were right about the "common cathode connection" While technically you can do it, the current source will be fighting the antiphase signals of either tube as well as the different tolerances of the tubes and you will not end up with constant current at the cathodes.
> 
> On the other hand it doesn't matter because the current sources will make sure they are both running at the same current anyway and maintain balance. Even with different tolerances the balance will be the same since both current sources will be individually ensuring that the tubes operate the same.


 


> As for the force balance mod you would have to splice apart or rip out the copper trace between the cathodes in the input stage for it to work but it's not hard to reconnect them whenever.


 
 So I was thinking, if you cant keep the "common cathode connection" with the current source because it would be fighting anti-phase currents then what does the situation look like when a single 1.5k resistor is fighting the antiphase currents?
  
 This is our stock input stage with the 1.5k tail.

  
  
 This is what the voltage swing looks like with this

 Almost a sawtooth wave.
 The current swing through each tube seems fine
  
 Now let's see what happens when we separate the "common cathode connection" independently bias them.
  

  
 Let's take another look at the voltage when the two were connected

 and now when they are separated

 Much better until you realize the voltage swing of the top one is a couple milivolts and the bottom one is hundreds of milivolts.
  
 This results in lower current and voltage swing at the cathode and anode because the voltage swing on the separated version is following the input to an extent, meaning there's less cathode-grid voltage differential, meaning the tube is not turning on/off as hard.
  
 The reason the "common cathode connection" is maintaining a stable voltage must be due to the constant antiphase currents canceling out changes in voltage.
  
 So it seems that the balanced design has a unintended bonus of creating a stable voltage reference.
  
 Although you get more gain by having a stable cathode voltage, using a single resistor for each tube generates its own local negative feedback so it could still possibly be better.
  
 Another option is a current source for each cathode but that is another can of worms.
  
 So if the cathodes have a stable voltage reference via the resistor then another option for that route is a LED biasing, yes as in 




  
  

 They are constant voltage devices and are often praised for superior sound to resistors, they are often used in input stages.
  
 You'd want to use an infared LED with a forward voltage drop of 1.5v and strap a 4.5k resistor (depending on max current of the LED) between cathode and B+ so it has enough current to maintain linear voltage regulation.
 Will this resistor affect tube operation? No, the excess current will flow from ground to B+ and voltage will be maintained.
  
 The last option is also highly praised, perhaps more so then the LED option. It is often considered very musical.
 It is battery biasing. 
  
 Yes as in this
  




 Batteries are also constant voltage sources. If you connect the positive terminal to the cathodes and the negative terminal to ground it will maintain a constant voltage and many people like it for its musical sound.
 Different battery types sound different, lithium/alkaline/life/etc,etc, all have their own sound. 
 There was a contest once in vegas and the winner was some sort of phosphurous airliner backup deep cycle battery or something, in any case you can "roll" them like tubes.
 Luckily 1.5v batteries and battery holders are everywhere.
  
 Another voltage source is a solar cell, as far as I know it's never been tried but I have a stack of cells I got on the cheap for a rainy day.


----------



## Maxx134

You mean for a sunny day..


----------



## coinmaster

After looking into proper mosfet biasing and source follower configurations I learned that my above example of the grid drive mod would work but it is far from optimal.
  
 This is a better way to do it.

 M10 is the source follower mosfet
 M11 is another source follower
 M12 is a constant current source (maintains a constant current)
 The zener diode D3 puts the gate of M11 at a set voltage above the output, in this case 27v.
 This makes M11 produce 20v at its source (depending on the mosfet and its bias). So the voltage difference between the drain and the source of M10 is always going to be 20v at DC.
 The capacitor C12 feeds the output signal to the gate of M11 so the voltage difference between drain and source of M10 will be the same at AC as well. 
 The end result is that as far as M10 is concerned, it is sitting at a stable 20v even though the the source and drain voltages are all over the place.
  
 M12 feeds M10 a constant current.
 As current is drawn through R31 a voltage drop is produced which after a certain voltage thresh hold turns on the transistors Q12 and Q13 which brings the voltage on the gate of M12 to ground level.
 After the the current decreases from this the transistors turn off, the end result being an equalibrium of current is maintained.
  
 Typically transistors turn on at about .7v differential between the emitter (pointy end) and the base but if you add more like I did in the above example it makes them more sensitive and they turn on at a lower voltage which means they react faster and a more stable current is maintained.
  
 So what does it all mean in the end?
 Well the current source and M11 maintain a constant voltage and current across the source follower (M10) which means it is locked in place on the load line, no change in transconductance or linearity can occur, this also reduces the effective input capacitance since input capacitance is the sum of the capacitance between gate-source and gate-drain.
 A source follower has pretty much no difference between gate and source voltage so there is no need to charge/discharge the capacitance between them and the voltage difference between gate and drain stays stable also meaning there is no need to charge/discharge the capacitance between them.
  
 In the real world there will be small variations but this way the overall distortions remain minimal.
  
 This means you should still probably choose the most linear part of the load line for the mosfet just to eek out every last bit of linearity.
 Meaning you should probably have M10 and M11 be the same mosfet since you are feeding them the same current and preferably the same voltage so they will act the same which will prevent phase shifts,
  
 I'm choosing the BUZ901 because I don't know the meaning of restraint and it is probably the most linear mosfet in existence and I'm going to feed it 3.5 amps @ 20v which gives an insanely linear performance even if the voltage/current wasn't locked.
  
 I've learned a lot from this source follower design and I've already been able to greatly improve my upcoming designs with the technique.
 However it is not a simple mod and it will not fit in case (especially if you want to run BUZ901s @ 3.5 amps).
 This design can actually be used as the output stage itself and could drive speakers, which I fully intend to try next month. Paypal Credit, what would I do without you.


----------



## Maxx134

Coin,
Have you looked into balanced designs and topologies? 
Now that you have your CCS I believe you should bring your attention to possible clever ways to achieve the effects a balanced topology does


----------



## coinmaster

Not sure I catch your drift. As far as I know the main advantage of balanced designs is EMI rejection.
 Technically I am _only_ looking into balanced designs because I see no reason not to and its better to be safe then sorry since balanced is often claimed better sounding.
  
 Not sure where the CCS falls into that or what you mean by "effects" of balanced design.


----------



## Maxx134

Not sure what you mean by not sure.

I barely have time to push out my latest mods and now I have to explain things..


----------



## coinmaster

A balanced design uses anti phase signals on each side of the load, I''m not sure what a CCS has to do with it.


----------



## Maxx134

Exactly the point, now you have to address how will you maintain the force balace of the two triodes.
When one triode changes gain due to age, we need the other to adjust accordingly in relation to the other side.
Maintaining CCS on each side does not address this..
Edit:
Maybe a regulator to force both ccs to be fed equally.


----------



## coinmaster

A CCS does maintain balance with age. If the tube ages and its specs change the CCS changes with it. That's why it's called a constant current source. You can do whatever you want with the tube specs and it will maintain the same operating point on the load line assuming the voltage is the same.
  
 But, for a WCF the top triode will not maintain a constant current unless you use a gyrator or inductor load. Just verified that in spice. But it also seems to cancel out the signal so there may not be a way to maintain top triode balance without a change in design, at least not with a CCS. 
 The servo maintains the impedance of the top triode over its lifetime in order to keep a 0vDC output so that helps.
 Also the auto biasing on the bottom triode helps counteract aging as well. 
 I think that's about as good as you are going to get.
  
 Since you mentioned gain I assume you are mainly referring to the input stage, in which case a CCS will maintain a balance between the two regardless of age/tube type/etc.
  
 For example, lets say one tube is half dead and one tube is new.
 The new tube requires the cathode to be 2V more positive then the grid and the half dead tube requires the cathode to be 3v more positive then the grid in order to maintain a 10ma current.
  
 The current sources will put 2v and 3v on the triodes cathodes and 10ma will be maintained through both.


----------



## Maxx134

OK I see,
So you will need at least this CCS to stabilize the triodes, in order to implement the cathode follower / grid drive mod...

Now count the amount of components (maybe custom chip, or mosphets, transistors, diodes,caps , and their separate PSU stage) in order to implement this. 

While I am not going to say anything until I try for myself, and in fact once I extend my bottom case, I would be open to try, especially once you do it ha. 

But...

Remember this is all to replace one coupling cap and one cathode resistor in our current amp..

Now our coupling caps are large enough, and of highest order (copper foils), 
as is anode/cathode resistors in driver stage (zfoil resistors) .

Now this is where design choices are made.

Wich path will we decide to choose?.
And will we gain a sonic benifit specifically where implemented,
Not in a general sense .

Will our driver/power tubes benifit from these changes?
As they can handle such a wide range of variables.
And which tubes will benifit most?
And which tubes will sound best regardless of these changes? 

This is the whole problem at hand that we are dealt with here, wich will take some more time to sort out.

I am currently in a different project to test all options of tube types in my amp.
I almost covered testing most all 9pins and 8pin types from both MK6&8, in my amp, 
In various configurations in both driver and power areas.

My current goal is to see for myself what types works best in current design configurations.

So coinmaster you must have even more choices to make because you has more options on tube types to use.
I assumming basically you want that sweet spot that you heard in past.


----------



## coinmaster

> So you will need at least this CCS to stabilize the triodes, in order to implement the cathode follower / grid drive mod.


 
 Grid drive mod doesn't need it, using it in conjunction with the "bootstrap" source follower just locks its load line into a single point on the load line so the overall distortions are minimal if any.
  


> Now count the amount of components (maybe custom chip, or mosphets, transistors, diodes,caps , and their separate PSU stage) in order to implement this.


 
 Component count is probably the biggest problem other then size, mainly because you need to have a decent electronics setup in order to build and troubleshoot the circuits which from my own experience can be a huge pain.
 The best way to do it is simply by ordering PCBs which saves space, time, and probably money, and its safer.
 I have the PCB files mostly done already other then labeling the values on the board but I still need to test them to make sure they are public ready first so unless someone else wants to take that job they will have to wait until I have the time and money plus the 2-3 weeks wait for shipping.
  


> Remember this is all to replace one coupling cap and one cathode resistor in our current amp


 
 The coupling cap doesn't go anywhere, assuming you are talking about the grid drive mod.
 You still need to separate B+ and the servo voltage.
 The grid drive mod just turns the high impedance output of the input stage into a low impedance one so it can quickly and easily overcome the capacitances of the output tube which should increase dynamics.
  
 I tried simulating this but I'm not sure the proper way to go about it.
 Instead I simulated the input stage feeding a 6080 cathode directly and nothing really worked, the 6sn7 with a resistor on anode/cathode produced a few ma into the 6080 but the CCS/gyrator did not.
 So I cannot say what will happen if I directly couple the input and output stage, perhaps at a minimal it will sound as good as the duelunds but in order to directly couple the stages the input stage plate voltage needs to be at the grid voltage level meaning the servo would have to adjust the B+ of the input stage instead of just the grid voltage, but that also means that the grid of the input stage triodes needs to be below ground level so unless you float your entire dac to that level or unless your dac has an output capacitor it won't work.
 My dac is direct coupled so I would need to float the entire thing to whatever voltage I need on the grid which is project in itself (and one I'm not sure I'm willing to try).
  
 I do have an idea though, if a low output impedance is needed to overcome grid capacitances of the output tubes then why not use a Jfet in cascode with a low RP tube like a 6080/6as7 or more preferably the 300b.
  
 Jfets are commonly used in input stages because they are so quiet and they are very tube-like in sound and operation. Normally they are difficult to use because of low voltage requirements but they would work for this purpose.
 The problem with this idea is that a jfet/tube cascode would have so much gain you would never be able to use it, but then again I don't know much about Jfet biasing, perhaps there is a way to reduce the gain.
  
 Such a mod would theoretically be relatively easy to implement.

  


> And which tubes will benifit most?
> And which tubes will sound best regardless of these changes?


 
 That's a can of worms I don't intend to open, you can break the bank and use up all your time trying to find out. There's a lot of tubes out there.
  


> Will our driver/power tubes benifit from these changes?


 
 The driver tubes are by far the weakest link in the amp, even as skeptical as I am I can't ignore the fact that at the very least the technical improvement would be huge with the mods.
  


> This is the whole problem at hand that we are dealt with here, wich will take some more time to sort out.


 
 Yeah unfortunately, I already have the materials needed to do all of the testing but I need to wait to order a few more odds and ends so I can properly finish up my diy build which is modular and will allow me to switch between different stage designs fairly easily but then again while I do intend to test different input stage designs I want to leave my MK6 output stage alone for now.
 I haven't actually listened to the modded MK6 since early september or something so even if I do test the mods I can't speak too much about how they improve over the original.
  
 I'm secretly hoping someone else will take on some of the load because at the end of the day I just want to listen to my music 
	

	
	
		
		

		
			





 I suspect my drive to design and innovate will go down once I finally have an amp to use.
 But I do have 3 more output stages to test, a solid state and 2 hybrids. One is a modified version of what MrCurwen recommended me a while back, one is a modified version of the WCF that always maintains equal current balance between the triodes at all frequencies, something the impedance mod cannot do, and one is push pull version of the "common cathode" input stage (real common cathode, not the one we have which isn't really common cathode) which seems to be the universally accepted "best" input stage topology since it cancels out all distortion and gets heavenly claims from everybody.
 The push pull "output stage" version of this that I have been working on does the same thing but is able to be used as a output stage for driving headphones however it is insanely complex, so far it needs 20 opamps per channel to bias 4 tubes. It works well in spice but can still use some optimizations, I would like to get some second hand advice on it but I am banned from DIY-audio website which is sadly the only place where people have the experience to comment on such a design.
  


> So coinmaster you must have even more choices to make because you has more options on tube types to use.


 
 Sadly if I want to keep an OTL/OCL output stage my tube choices are very limited, I was thinking of using 300b tubes which would be very complicated to make into OTL and may or may not be better given the fact they have more then twice the output impedance of our tubes.
  
 As for input tubes I do have a lot of choice but my Tungsol RP 6SN7 "holy grail" tubes blew away the competition I tried so I will probably stick to them for now although I would like to try 300b at some point.
 I am for sure going to try the "common cathode" input stage since it is so often considered to be unspeakably good due to its distortion canceling capabilities but since it is  distortion canceling it may not matter what type or quality of tube I use.
  

  


> I assumming basically you want that sweet spot that you heard in past.


 
 I'm going on the assumption that what I heard in the past can be improved on, otherwise I would be listening to an MK6 right now. It really was that perfect sound that I didn't think actually existed.
  I truly cannot imagine it sounding better then it did. This was before the WCF cap mod was introduced which is almost on the level of the coupling cap mod right? Wow.
  
 I have a sub goal of creating a new product, or at least something that I can recoup the thousands (around $7,000 so far, ouch) I've spent on materials for R&D so far.
 I've already helped create a new output stage which I was praised for by broskie, the tubecad guy, which I've made further improvements on and I'm hot on the trail of another design that seems to be really good so I have some material to work with, it all depends on how they actually sound in the end. I want to avoid using known designs.


----------



## Maxx134

coinmaster said:


> I am for sure going to try the "common cathode" input stage since it is so often considered to be unspeakably good due to its distortion canceling capabilities but since it is distortion canceling it may not matter what type or quality of tube I use.




This is exactly the point I am trying to make about the distortion cancelling abilities of the common cathode design.

Which takes on more importance and effect in the low level signal driver stage.

As far as I have checked,
this driver stage implement almost textbook spec.

Yet you and MrCurwen kept pointing out amp by stating the driver stage is poor and non optimal.

In reality nothing is optimal.
We have to deal with what we have.

So our amp driver stage may not be perfect, but I have not notice anything poor in driver circuit except the tubes themselves.

Many preamp circuits run tubes at lower power than optimal so running at 250v or less is not uncommon. 

So hopefully we can look over this driver stage to see how we can fine tune and optimize it's performance further.

Edit:
Looking over the values it does seem this circuit is more for triode balance than the "common cathode" benifits of noise cancelling.
Edit2
I changed some words to be more polite so not take me wrong way. 
I do realize We need to expose weaknesses .


----------



## coinmaster

> This is exactly the point I am trying to make about the distortion cancelling abilities of the common cathode design.
> 
> Which takes on more importance and effect in the low level signal driver stage.
> 
> ...


 
 We do not have a common cathode input stage(this has been said multiple times including once in my above post). A common cathode input stage is a cathode follower feeding a grounded grid amplifier, the cathode follower distorts one way and the grounded grid distorts the opposite way, the end result being the distortion is canceled out.
  
 It would require 2 dual triode input tubes per channel to do this with a balanced amp.
  
 The purpose of the two triodes in our amp is to amplify a pair of anti phase signals because the output requires the signal to be anti phase on each side of the load in order for it to be a balanced design.
 It is basically two SE amplifier tubes that are amplifying two different signals, this is why balanced designs require two sets of dacs and amps because they have an in phase and an out of phase signal (opposites).
  
  


> In reality nothing is optimal.
> We have to deal with what we have.
> 
> So our amp driver stage may not be perfect, but I have not notice anything poor in driver circuit except the tubes themselves.
> ...


 
 The technical improvements that can be had to the input stage are huge, you can use word play all you want but that is still the truth.
 The input stage is, from a technical point of view, garbage.
 Will it sound better by "improving" it? I'd be surprised if it didn't. The only way I see otherwise is if the suboptimal implementation is creating "good" distortions. Everything about the input stage is poorly implemented, obviously to save on costs.
  
 If you have an extension box then you can optimize the input stage without too much trouble, the problem is creating the CCS/gyrator/power supplies.
 Like I said I'm already ordering PCBs for the CCS/gyrator so you can just leech off my design for that and order your own which makes things a whole lot easier.
 The problem is the power supply for the B+ and CCS.
 It may be worth it just to order a Salas shunt regulator for $60 since they are the bees knees in the diy community and they come in kits. This shunt regulator can also improve on the output stage power supply and will no doubt improve the sound due to lower output impedance.
 As for the CCS power supply, I may have to create a PCB design for that unless people want to make it themselves. It would be a -15v supply to have enough headroom for the CCS to regulate.


----------



## Maxx134

coinmaster said:


> We do not have a common cathode input stage(this has been said multiple times including once in my above post). A common cathode input stage is a cathode follower feeding a grounded grid amplifier, the cathode follower distorts one way and the grounded grid distorts the opposite way, the end result being the distortion is canceled out.




Depends which version your looking at..
The actuall name is different here but the objective and schematic is exact same as in our amp.







You say input stage is, from a technical point of view, garbage..


Why does simplicity lose out over complexity with you?



I believe this is what makes the tube rolling more noticeable.


----------



## coinmaster

It's a fancy way of saying two SE amplifier tubes that amplify opposing signals with the downside that if they are not perfectly matched they will draw uneven current.
 There is no distortion cancelation in the design, it is not a common cathode input stage.
  
 This is a common cathode input stage




 The right triode counteracts the distortion of the left triode.
  
 It doesn't "depend" on which version I'm looking at. 
 You don't take the words "balanced" and "common cathode" literally when discussing topologies. 
  
 Here is a read on common cathode stages http://www.tubecad.com/2005/April/blog0042.htm
  
  
 Quote:


> You say input stage is, from a technical point of view, garbage..
> 
> 
> Why does simplicity lose out over complexity with you?
> ...


 
 Has nothing to do with simplicity or complexity.
  
 The input stage power supply is unregulated.
 The resistor values are poor
 The bias is poor, depending on the tube you use
 The balance between the tubes is poor
 Resistor loading in general is poor due to the impedances and the way the signal travels along the load line.
  
 The ideal load for a triode in order to get the most linear impedance and transfer characteristics is an infinite impedance and resistance, something a resistor can not do and still have current running though it unless you want to run a 10KV power supply.
 That's why CCS/gyrator is good because a CCS is the closest you can get to such a situation and puts an effectively infinite impedance on the cathode and the gyrator puts an effectively infinite impedance on the anode while maintaining a constant voltage.


----------



## coinmaster

Edited the above post to be a little more clear on common cathode.
  
 Did anyone ever find out if changing the pot made a difference in sound? People kept talking about it a while back but I don't think anyone ever reported on the findings.
  
 I have a 32 bit dac so I should have a good range of digital attenuation via the PC before I get into any bit compression.
 So I don't intend to use any pot but I am curious to know whether it makes a noticeable difference either way.


----------



## Maxx134

I am thinking the values on the driver resistors to was set that way because of the Limited PSU so I will look into that

Edit
 I was told that using a pot was a bad idea


----------



## coinmaster

> I am thinking the values on the driver resistors to was set that way because of the Limited PSU so I will look into that


 
 Yeah, if you want proper voltages with high impedance resistors then you would need more then double the voltage the power supply offers (minimal). I think this was the best balance of efficiency and sound while maintaining a price point. The power supply is usually the most costly part of the amp.
  


> I was told that using a pot was a bad idea


 
 Oh, did you take your stock one out?


----------



## Maxx134

coinmaster said:


> The input stage power supply is unregulated.
> The resistor values are poor
> The bias is poor, depending on the tube you use
> The balance between the tubes is poor
> Resistor loading in general is poor due to the impedances and the way the signal travels along the load line.



Just because you say it's poor doesn't make it so..
Edit :
If you give it an F,
I will give it a C+

Obviously it looks like it could be better..

I already showed you the diagram of what's happening in our stage ..

You keep sidetracking being stuck on my words that's why I had to show you the diagram.

Also certain driver tubes datasheet actually makes note & specify same values we have for resistors with near same voltage,

So This needs to be looked into further


----------



## Maxx134

*
Quote:
, did you take your stock one out?*

That was not attempted by me,,
 but definitely looking into this,
because experienced to designers know where the sweet spots are,
 when dealing with limited PSU..


----------



## Maxx134

Yesterday I was sidetracked with a WCF cap not making connection causing a slight hum...


----------



## coinmaster

> Just because you say it's poor doesn't make it so.


 
 Unless you ignore the facts of electronic design it is poor. Of course everything is relative.
  


> I already showed you the diagram of what's happening in our stage ..
> 
> You keep sidetracking being stuck on my words that's why I had to show you the diagram.


 
 I've already showed you that diagram so many times and explained how it works.
 That explanation on that diagram literally just explains how two individual SE tubes function when they are fed by anti phase signals, because that's what it is, two amplifiers feeding two signals.
  
 As I went over previously the anti phase currents maintain a stable voltage on the cathode but that's only true if they are both drawing the same current, which isn't the case in real life when tubes cannot be perfectly matched and are often 10-20% different from each other.
  
 This is why it explains that you lose gain when the signals are not antiphase because it starts acting more like a cathode follower and you lose cathode-grid potential.
 Plus there's the fact that they will be operating at slightly different points on the load line.
  
 As MrCurwen and I have been saying, a current source cleans this mess up and balances them unconditionally with other benefits.
  


> Also certain driver tubes datasheet actually makes note & specify same values we have for resistors with near same voltage


 
 Depends on tube and design. For a 6sl7 the plate resistors are okay but it doesn't change the impedance ratio issue of the cathode resistor that MrCurwen was explaining, no practical design with resistors is going to beat a CCS here because a CCS is close to a 1meg impedance to AC.


----------



## Maxx134

As an example about Sweet Spots in tubes,

 I was able to increase my tube performance in sound stage with a slight increment of bias to rear power tubes..

They are different tubes than MK6,
butt just showing an example.

The bias point is still below what datasheet states optimal,
 but I am finding out that the tubes Heat and longevity is compromised with higher setting ...

We only need what works.
We don't need what datasheet states..


----------



## coinmaster

> As an example about Sweet Spots in tubes,
> 
> I was able to increase my sound stage with a slight increment of bias to rear power tubes..


 


> We only need what works.
> We don't need what datasheet states..


 
 You have to remember there is a reason why things improve when you do things. It's not magic.


----------



## Maxx134

*
QUOTE:

As MrCurwen and I have been saying, a current source cleans this mess up and balances them unconditionally with other benefits.

no practical design with resistors is going to beat a CCS here because a CCS is close to a 1meg impedance to AC.
*

As a solution, 
I will repeat the words "current source" till it sinks in..
That may take a while. .

Edit:
Meanwhile,
 I will listen to my amp, 
which "shouldn't work" as good as it does.
I remember you stating Yours was excellent also..


----------



## Maxx134

coinmaster said:


> > As an example about Sweet Spots in tubes,
> >
> >
> > I was able to increase my sound stage with a slight increment of bias to rear power tubes..
> ...



**,
Of course.
I placed bias point more in midde of the optimum part of the curve,
But optimal value, was stated higher,
And the datasheet doesn't tell me what sonic gains were to be had. .

edit:
 Also the decision of the designer to a place the bias point lower. .
 why?
 I think because of heat and longevity and no fans on bottom MK8 unit!


----------



## coinmaster

> Of course. I placed bias point more in midde of the optimum part of the curve, But optimal value, was stated higher,


 
 Datasheets and reality are far different from each other. Most datasheets were done almost a century ago and some were hand drawn. This is why the only way to really know what your curves are is with a curve tracer.
 Even a tube tester has a considerable margin of error so even when you buy matched tubes you aren't really buying matched tubes most of the time.
  
 Datasheets are a general reference, even if they were accurate they would only be accurate for the tube that was tested since tube specs vary between each other.
  
 I've been contemplating building a tracer but I am not yet sure the extent to which bias shifting affects the sound so I don't want to go overkill for no reason.
   





> and the datasheet doesn't tell me what sonic gains were to be had. .


 

 Well, maybe not down to the last detail but it does give you an idea. More linear parts of the load line = more accurate reproduction. Less linear = more distortion.
  


> Also the decision of the designer to a place the bias point lower. . why?I think because of heat and longevity and no fans on bottom MK8 unit!


 
 I don't know what your tubes are biased at stock but I don't think it the designer would compromise bias rather then buy some fans.
  


> Meanwhile,
> I will listen to my amp,
> which "shouldn't work" as good as it does.
> I remember you stating Yours was excellent also..


 
 Yeah I can't argue with how good it sounds, I'm detaching myself from what I heard and am looking for design improvements regardless.
 The amazing sound is why I became interested in improving it to begin with since a few component upgrades made such a huge huge difference.
  
 Although technically I have no real passion for the subject of electronic design and I'll be glad when its over. But since I'm already down the rabbit hole I might as well explore.


----------



## Maxx134

coinmaster said:


> There is no distortion cancelation in the design, it is not a common cathode input stage.





Just to clarify your statement with some corrections..


Yes it is not a common cathode, 

So misunderstanding of names on my part. 

But the design our amp has does cancel distortion
Look here: 
http://www.atma-sphere.com/Resources/Our_Basic_Circuits.php

Optimally, it would have these advantages:


----------



## coinmaster

> But the design our amp has does cancel distortion


 
 You're right, it does cancel second order harmonics which is sometimes considered the "good" kind and is responsible for SE sound but the common cathode topology cancels out all harmonic distortion. It's on another level.


----------



## Maxx134

Hmm. 
Also this seems to match why the driver PSU is not so well executed. .

Also;
Common Cathode like you say would require double the tubes! 
Ha!


----------



## Maxx134

Something tells me this may have been it.. (!):


----------



## coinmaster

Yeah I was thinking about that when you showed it to me a while back.
 But it has 1 tube too many for common cathode per channel.
  
 I'm not really sure what that's about.


----------



## Maxx134

I bet the middle is same as our front end differential, 
Then it feed two common cathode. .


----------



## coinmaster

No because you only need 4 triodes to create a balanced common cathode stage and the common cathode stage would not counteract the distortions caused by the differential amplifier.
  
 I suspect it is not a common cathode because putting any other tube in the path would only add distortion rendering the common cathode stage pointless.
 I'm willing to bet one of those tubes is a phase splitter.


----------



## coinmaster

I think for the time being someone should try the battery or LED bias mod since it is so easy anyone and their mom can do it.
  
 The battery mod consists of simply replacing the 1.5k resistor with a AA battery. Positive terminal to cathode negative terminal to ground.
 The LED mod consists of replacing the resistor with an LED with a 1.5v forward voltage drop (infared probably) and throwing a resistor between cathode and B+ so the LED gets the current it needs.
 Both are claimed to sound better then resistor.
  
 Edit: That only counts for the Mk6. I don't know what bias voltage the MK8 needs.


----------



## Maxx134

Bias voltage I measured at 2v for mk8 with a 6sN7 on driver stage.
The resistor values are the same on both amps.


----------



## coinmaster

2v LEDs and batteries can be found as well. LED will probably be red or green, the best ones are the vintage "dim" variety. The new bright ones get mixed reviews.
 Overall batteries get better reviews, I've only heard good things. Lead acid batteries come in 2v and so do deep cycle batteries if you want to go balls to the wall.
 Both are among the best sounding batteries if I recall.


----------



## Maxx134

This weekend will let you know how much fire 





coinmaster said:


> 2v LEDs and batteries can be found as well. LED will probably be red or green, the best ones are the vintage "dim" variety. The new bright ones get mixed reviews.
> Overall batteries get better reviews, I've only heard good things. Lead acid batteries come in 2v and so do deep cycle batteries if you want to go balls to the wall.
> Both are among the best sounding batteries if I recall.



I will see this weekend how much of an explosion I can make..
Ha


I have heard a rumor little dot prototype amp using 300b tubes. .

Also, look at the tube types used by Eddie Current (my only choice if not DIY)

6sL7, 6sN7, 2a3, 300b 

Those are the popular tubes of choice. 

Something to think about. ..


----------



## MrCurwen

maxx134 said:


> Coin,
> Now that you have your CCS I believe you should bring your attention to possible clever ways to achieve the effects a balanced topology does




I don't get this. As far as I know all of the recent examples in this thread have been of balanced topology. No SE designs at all.

The source follower systems driving output tube grids I've discussed would necessarily be SE, but since they have a gain approaching 1, it's inconsequential. One buffer per phase, so... it's a balanced topology as a whole. 

Anyway. Please explain.


----------



## coinmaster

He explained earlier that he was mixing up balanced topology and balance by definition. Which lead to the last few pages of discussion.


----------



## MrCurwen

maxx134 said:


> OK I see,
> So you will need at least this CCS to stabilize the triodes, in order to implement the cathode follower / grid drive mod...




I'm not entirely sure what you are talking about.

The grid drive system I was talking about is input stage output -> cap of soviet quality -> source follower loaded by a CCS -> direct coupled to output tube grid.

It has nothing to do with the input stage as such, other than relieving it of all responsibilities to provide current to cap, or output tube grid.




> Now count the amount of components (maybe custom chip, or mosphets, transistors, diodes,caps , and their separate PSU stage) in order to implement this.




Yep, it's much.




> Remember this is all to replace one coupling cap and one cathode resistor in our current amp..




Just to re-emphasise: These are 100% different mods or designs.

1) The tail CSS

2) Source follower driving output tube grid

Number 2 doesn't in fact replace the coupling cap. It needs to be there. It just makes it's quality rather irrelevant (or, supercharges it's quality to glorious heights, however you wish to look at it).

Also the issue of the facts at hand on the grid side of the coupling cap. Currently they are left completely unaddressed. Of course there is NFB...



> Now this is where design choices are made.
> 
> Wich path will we decide to choose?.




Yep, that's DIY. =)

Many paths.


----------



## MrCurwen

maxx134 said:


> This is exactly the point I am trying to make about the distortion cancelling abilities of the common cathode design.




No common cathode designs being discussed in this thread. Please use universal terminology for ease of understanding of everyone.

LTP is even faster to type out! In addition to being factually correct.




> As far as I have checked,
> this driver stage implement almost textbook spec.
> 
> Yet you and MrCurwen kept pointing out amp by stating the driver stage is poor and non optimal.




Tube textbooks are not HIFI, and by no means high end (whatever that means to anybody).

1% distortion is ok and actually incredibly good, if you live in 1960 or 1950.

To my ears it's bad. 

Not as bad as 0.001% achieved via NFB, but still bad.

Open loop 0.001% (which none of you have heard unless you go to DIY meets) on the other hand, is good.




> In reality nothing is optimal.
> We have to deal with what we have.




True. But, some things are more optimal than others. 




> So our amp driver stage may not be perfect, but I have not notice anything poor in driver circuit except the tubes themselves.




I see. Well, 'poor' is a subjective term. Hard to argue.

Put a 10% mismatched signal into the input LPT and see what comes out.




> Looking over the values it does seem this circuit is more for triode balance than the "common cathode" benifits of noise cancelling.




Please elaborate.


----------



## MrCurwen

maxx134 said:


> As an example about Sweet Spots in tubes,
> 
> I was able to increase my tube performance in sound stage with a slight increment of bias to rear power tubes..




I do believe that. I remember using a lot of time optimizing bias points and I did on a number of occasions obtain great sonic benefits. They did of course vanish quite fast if I changed the tube and got unlucky.

The sonic differences in bias points are not because of the curves. Sometimes you get these optimization benefits even if you move within the linear regions of the curves.

They are because of plate resistance changes.

Imagine the tube is a resistor inside the circuit. A variable resistor with a center point it returns to when there is no signal.

When you move the bias point, or op point, you change the center point of the virtual resistor. This might make it fit the circuit more, or make it fit the circuit less.

The trick to eliminating this effect is to design the circuit so, that the tube's rp has no significant importance to the function of the circuit.

As it is, if you can hear benefits from op point optimization (inside the linear regions of the curves) it means your circuit is designed so that it is just barely able to fullfill it's current demands, and any change to the rp is thus critical.

I no longer like to do that stuff, so I make the rp irrelevant. Best just have the tube doing voltage amplification and that's it. That's what it was designed to do, and it does it superbly. Have it provide current to load, and it starts to fail at it's main job, voltage amplification.


----------



## MrCurwen

maxx134 said:


> *
> Meanwhile,
> I will listen to my amp,
> which "shouldn't work" as good as it does.
> *


*


No, it works just as well as it's supposed to. A collection of good solutions and bad solutions, design compromises which leads to the level of fidelity that it leads to.

Pride of the customer and engineer mentality are not, as I said earlier, very compatible.

If you do DIY long enough, you will build several THE BEST amps you've ever heard, and spend many nights marveling how you couldn't even imagine how any sound reproduction system could sound any more realistic and musical. Then you design a couple of failed things, and then you design the thing that is again THE BEST, even better than the last one. Then you spend many nights.... etc. Continue until you run out of cognitive ability to understand more electronics. That will be your best then. For many people it will be the classic schem with one or two mods they copied off of internet.

Good and best are two different things.

Your amp is no doubt good. Is it special in the grand scheme of things? Not at all in my opinion. I haven't heard it, but simply looking at the output impedance, I can tell I wouldn't be super impressed with it, even though I'm sure I'd enjoy listening to it.

Any previous systems with that high (or even much lower say 10 ohms) output impedance have sounded unimpressive in the long run.

These are my opinions and yours may vary. I haven't stated you shouldn't be able to enjoy your amp, you totally should be able to enjoy your amp. If you find criticism of it unbearable, I don't know what to tell you. Why mod if improvement is not interesting?*


----------



## MrCurwen

maxx134 said:


> Also the decision of the designer to a place the bias point lower. .
> why?
> I think because of heat and longevity and no fans on bottom MK8 unit!




No, he didn't want to pay for parts to a higher voltage B+ for the input stage. 

Calculate the differences in heat. Completely insignificant, not an issue in the slightest.

Also longevity not an issue at all in the case of 6SL7. Again, calculate the watts and compare to datasheet.


----------



## MrCurwen

A common cathode tube stage is one where the cathode is at AC ground. 

In a LTP the cathode is not at AC ground. 

The Broskie circuit should be called a cathode coupled stage. Common cathode was in common use before WWII and still is. 


A LTP is not a LTP unless the cathode node voltage (top of the tail) can float. It cannot be biased with a fixed or semi-fixed voltage system such as LED or battery.

If you prevent the cathode node from floating, you have something else, not a LTP anymore. 

The balance of LTP is dependent on the impedance ratio of the tail versus the brances that leave from the cathode node upwards (tube, plate load, on both sides). If you put a LED as the 'tail', it has an impedance of around 10 to 100 ohms, depending on make of LED. What's your ratio then? 

The tail then ceases to be the tail, since it cannot do the functions of the tail. The functions of the tail (forced balance or attempted balance, power supply noise reduction) are dependent on the impedance ratio. The tail impedance must be the biggest impedance in the whole system.

The CCS in my schems, with the 2N2222 darlington pair and the FET, achieves a 2 to 6 megaohm impedance, depending on FET choise. The gyrators are about 500k, tubes' plate resistances are so small you can leave them out of the equation (bye bye tube rolling, not missing you personally).

500k + 500k = 1M total both of the brances combined. Tail let's say 4M. Perfect balance.


I've done stuff with battery bias. Batteries do have a sound. Some sound better than others. They always colour the sound, so I quit using them at the cathode. Grid bias can be provided with batteries, but it's too much of a hassle for no added benefit.

An ideal battery cannot be used as the 'tail' in a LTP. It has constant voltage, so the cathode node cannot float. Impedance 0 ohms.

In reality it is at least hundreds of ohms, and very highly 

1) current

2) frequency dependant

This is how it colours the sound. Good for effects seekers, bad for transparency and realism.

Also it changes with age, a lot. Batteries are only good (in HIFI) for fixed grid bias, nothing else.


----------



## coinmaster

> The trick to eliminating this effect is to design the circuit so, that the tube's rp has no significant importance to the function of the circuit.


 
 Unfortunately this can't be done in the MK6, or with any tube output stage where the tube feeds the load, at least not that I can think of.

  


> If you do DIY long enough, you will build several THE BEST amps you've ever heard, and spend many nights marveling how you couldn't even imagine how any sound reproduction system could sound any more realistic and musical. Then you design a couple of failed things, and then you design the thing that is again THE BEST, even better than the last one. Then you spend many nights.... etc. Continue until you run out of cognitive ability to understand more electronics. That will be your best then.


 
 I hope I don't end up like this. I want the best *now *






.
 I certainly hope my upcoming designs function like they do in spice. Way to expensive for failures and the common cathode inspired design I'm working on has 20 feedback loops per channel for biasing, I don't even want to think about troubleshooting it.
  
  


> Open loop 0.001% (which none of you have heard unless you go to DIY meets) on the other hand, is good.


 
 I would love to know how you do that with open loop.
  


> The balance of LTP is dependent on the impedance ratio of the tail versus the brances that leave from the cathode node upwards (tube, plate load, on both sides). If you put a LED as the 'tail', it has an impedance of around 10 to 100 ohms, depending on make of LED. What's your ratio then?


 
 Yeah I was thinking about that, but since it's an easy experiment to try regardless I thought it might be something to experiment with. A learning experiment if nothing else.


----------



## MrCurwen

maxx134 said:


> This weekend will let you know how much fire
> I have heard a rumor little dot prototype amp using 300b tubes. .




I just shake my head and wonder why would anybody use 300B as direct coupled output tube in a WCF. Other than looks and brand recognition.

I assume the topology would be same.

It would contribute to a more traditional tube sound, catering to many people who enjoy that. Transients more compressed etc. 

DHTs have a certain 'magick' to them, I don't deny that. For best results I use 4P1L partly because it is DH. But higher output impedance makes the sound slower, the transients lazier and the bass less controlled and more boomy. Not good for long term use in my opinion.




> Also, look at the tube types used by Eddie Current (my only choice if not DIY)
> 
> 6sL7, 6sN7, 2a3, 300b
> 
> ...




Yep, most designers and hobbyists don't go outside popular waters. If you use a good tube that nobody knows about, you have to design around it's specs all by yourself, understand all of the stuff on the datasheet and more... That takes effort. Most people don't like spending effort, too much.


----------



## coinmaster

> I just shake my head and wonder why would anybody use 300B as direct coupled output tube in a WCF. Other than looks and brand recognition.
> 
> I assume the topology would be same.
> 
> ...


 
 Higher output impedance is the only downside other then design complications right?
  


> Yep, most designers and hobbyists don't go outside popular waters. If you use a good tube that nobody knows about, you have to design around it's specs all by yourself, understand all of the stuff on the datasheet and more... That takes effort. Most people don't like spending effort, too much.


 
 I'd rather do what works best. But I don't want to bite off more then I can chew, I learned that lesson the first few months I tried to learn electronics. Slow and steady is better,
 I know how 6080s and 6SN7s sound in my circuit so I'm going to focus on design before I focus on tubes instead of blowing more money on uncharted waters.


----------



## Maxx134

mrcurwen said:


> *Quote:
> If you do DIY long enough, you will build several THE BEST amps you've ever heard, and spend many nights marveling how you couldn't even imagine how any sound reproduction system could sound any more realistic and musical. Then you design a couple of failed things, and then you design the thing that is again THE BEST, even better than the last one. Then you spend many nights.... etc. Continue until you run out of cognitive ability to understand more electronics. That will be your best then.*




I agree with your statement here 100%
This is why I held back on a next project for another year, 
To decide which design to use. ..

I know my strengths and weaknesses, 
Which places me as a builder and modder,
NOT a circuit designer.
Although this hobby has me made lots of reading and discovering. .

I rather enjoy the idea to make a future DIY amp in a rediculously spectacular case..
 hehe.


----------



## MrCurwen

I am in awe of your casing work!

My amps look horrible. I don't have paint skills, or much of woodwork skills in the aesthetic department. I go for engineer look, that's hard to fail at.


----------



## coinmaster

> This is why I held back on a next project for another year,
> To decide which design to use. ..


 
 Smart. I don't trust the internet and peoples all too similar claims that everything sounds "amazing" so I'm going to design my own thing.
 If I heard MrCurwens amp for example I'd have a reference to go off of but for now all I have is his word that it sounds amazing. Unfortunately "amazing" is all relative and subjective.
  
 Apart from modding the MK6 design and the current balancing version of it I helped design I am going to start looking into distortion canceling designs from here on out.
  
 Odd harmonics are really hard to get rid of so canceling out distortion with distortion seems to be the best way to go. 
 This requires a predictable distortion source of equal and opposite measures and thus far the only way I know to go about this is to feed a cathode follower into or from a grounded grid or grounded cathode amplifier.
 One of the big questions I have is what the difference in distortion "correction" is between the two types of amplifiers as it has a large effect on design since one is a low impedance input and one is a high impedance input.
  
  



> I rather enjoy the idea to make a future DIY amp in a rediculously spectacular case..
> hehe.


 
   I'm not surprised. You seem to have spent more on your case then on the rest of it 
	

	
	
		
		

		
			




 DIY is the way to go if you know how to do it. I'll never buy another amp again.


----------



## MrCurwen

Completely off topic, sorry for that, but just to illustrate what I meant by not having much aesthetic skills:

http://kalleria.org/livejournal/Kuva1339.jpg

This is my flagship amp, not in my possession anymore. Unfortunately I didn't take a 'final' picture of it; here the buffer (sitting on top) is not yet operational, as you can see from the indicator light not being on. Also the PSU and signal chassis indicator lights are of very different brightness. I fixed this later, important mod!

Not very mailable, unfortunately. But I am thinking more and more about mailing a smaller amp for audition, first to one man in Denmark who I've been tutoring and then onwards to somebody else in Europe. Preferably somebody who has very expensive caps to try out. I don't know, I should make another thread for this, sorry for the off topic.


----------



## coinmaster

I'd be tempted to buy it since it would finally give me a sonic reference to attach to your words but last I recall you said it was like $1300 or more? I don't remember. That doesn't include shipping. I've already invested too much into a DIY set-up and I'm reaching the threshold of my comfort zone.
 I'd pay for the schematic but I wouldn't blame you for not sharing that with people. I would no doubt learn a lot from it though.


> Preferably somebody who has very expensive caps to try out


 
 I do! Too bad I'm not in europe.


----------



## MrCurwen

I find it utterly dishonorable to publicly mention facts talked about in private conversations. Again.


----------



## coinmaster

Something wrong with talking about the expense? You get offended way to easily as usual.


----------



## Maxx134

Coin has the best caps, Deuland.
Although there are I believe three best and Jupiter & I believe "V-Cap" is the other.

And about caps :
It has been generally stated in past, that a cap can alter the depth perception of an instrument within the sound field accordingly to the dynamics. 

 I have not noticed this on new copper foil caps.
They are on another level & also entirely free of treble colorations..
They make the best Mundorf sound very colored.


----------



## Maxx134

mrcurwen said:


> I find it utterly dishonorable to publicly mention facts talked about in private conversations. Again.



Coin has done this in the past to me and another guy from another thread he posted here..

Coin, maybe you need to learn the word discretion. 
 lol


----------



## Maxx134

coinmaster said:


> Something wrong with talking about the expense? You get offended way to easily as usual.



Hey, I thought I was the only one you said that too!
Now I don't feel special..


----------



## coinmaster

> Coin has the best caps, Deuland.
> Although there are I believe three best and Jupiter & I believe "V-Cap" is the other.


 
 I can't speak for Jupiter (yet) or v-caps but Duelund is definitely the most finely crafted and expensive one, at least from a materials perspective. The thing is like a lead weight, it's solid copper and is as big around as my palm.
  
 The only review I've found of Duelund vs Jupiter claimed them to be very similar. I have some Jupiters ready for use and they look like tiny axial versions of duelunds without the weight. I suspect they were Jupiter's attempt at recreating Duelund tech for cheaper.
  


> It has been generally stated in past, that a cap can alter the depth perception of an instrument within the sound field accordingly to the dynamics.


 
 The sound stage went from conal to almost 360 degrees after upgrading to duelunds from stock, among the many many other delicious sonic benefits.
 For the first few hours there was this incredibly "sweet" sound on the highs it was orgasmic, I kept waiting for the high notes so I could keep experiencing it. It was actually high inducing. Sadly after letting it burn in over night the sweet sound went away 
  


> Coin has done this in the past to me and another guy from another thread he posted here..
> 
> Coin, maybe you need to learn the word discretion.
> lol


 
 True, but I never mentioned your name, it was on another website with no reference to you in particular. I only mentioned your advice to me.
 As far as I see it I did him a favor by mentioning the price of his amp. Marketing is what sells and $1300 is pretty darn good for what it is (assuming that was the price, I don't recall correctly) and he sounds like he wants to sell.
  
 MrCurwen easily gets upset at the drop of a hat over the internet no less. Such things are way beneath me. Progress is either being made or it's not, people that get mad about petty nothings are probably miserable irl and make wonderful bait for internet trolls.
  


> Hey, I thought I was the only one you said that too!
> Now I don't feel special..


 
 No actually you adjusted pretty quickly, Redge on the other hand seems to be in the same boat as MrCurwen. He hasn't spoken to me in quite awhile.


----------



## Maxx134

OK let's change topic..

Another thing I have learned that you won't hear too often.


On the subject of capacitors. 

In my WCF you will see I replaced one cap for three in parallel. .





 


I did this for other reasons, 


But sonically I have noted improments over single cap.


I have to do a future test to give more accurate description of benifits, 


But so far I can say I have more liquid and better Soundstage. 


I am currently using three "VitaminQ" caps which are now my preferred choice over both the Mundorf (silv/gold/oil) and the "plain" Jupiter HT ..

Edit*
The "VitaminQ" cap is similar to the Russian oil caps in a heavy metal case,
So I had to tape them to cover the metal!


----------



## coinmaster

> But sonically I have noted improments over single cap.


 
 More caps equal less ESR and inductance. It's like putting resistors or inductors in parallel. Caps in parallel increase capacity as well.
 More caps is usually better then one assuming you implement them correctly. I forget the details but there is a proper way to solder them for best performance. I'll have to find that thread again.
 This is actually really important if what you say is true.


----------



## coinmaster

Here it is http://www.diyaudio.com/forums/power-supplies/214869-single-vs-parallel-capacitor.html
 It's a long thread and I'm too lazy at the moment to look for it but there was mention of making sure the impedance paths are aligned properly or some such.
  
 If lends favor to MrCurwens argument if you are hearing a sonic gain via this method. Which means the grid drive mod may be something important to try. Although honestly I don't see how an active device is going to beat a capacitor in the end in terms of low distortion.


----------



## Maxx134

Yes the WCF cap is directly affecting the tonality .
 I also inadvertently had one disconnected on the left channel negative tube , and the result was about a 10% loss of some treble and focus.
 That was only with one tube,  so not full signal.


----------



## coinmaster

You may want to try a bundle of $1 caps and see what happens. The more you parallel the closer to a perfect cap it becomes.
 But you have to take into account that parallel caps add capacitance.
 So you can buy like 10 100nf caps instead of 10 1uf caps.
 You should also make sure that the increase in capacitance is not playing a part in better sonics.


----------



## Maxx134

mrcurwen said:


> Completely off topic, sorry for that, but just to illustrate what I meant by not having much aesthetic skills:
> 
> http://kalleria.org/livejournal/Kuva1339.jpg
> 
> ...



The amp looks clean,
 and I bet if the case was black it would look sleek and very professional.

Plus it would need your signature in gold ink on the corner for finishing touch..


----------



## Maxx134

coinmaster said:


> You should also make sure that the increase in capacitance is not playing a part in better sonics.



I have made sure I feel a .33uf sounds best and any more will lead to a thickening of sound in cheaper caps which I do not like.
Only The .47uf Mundorf was able to pull it off and sound very sweet and energetic,
But my caps choice is for natural trebles and I believe I have that with the VitaminQ in that position.


----------



## coinmaster

I'll end up using Duelund interstage and Jupiter WCF caps but if parallel caps really do sound better then a single jupiter then there is some valuable information to be gained here.
 Technically speaking multiple caps are better in pretty much every way but I never considered it would be as big of an improvement as you say unless I'm misreading.


----------



## MrCurwen

I find cap parallelling smears the finest details away. This is contingent on the rest of the amp being able to reproduce those finest of the fine details. 

Well, out of necessity I parallel caps of same type. I prefer to use same production batch if it is possible (often not).

But two different types are definitely out. 

The guitar amp DIY guys (which I also am) actually found that they can create exciting new sounds by doing dissimilar parallels with caps. So not for HIFI, at least the dissimilar parallel.


I just recalled I never responded to the message about russian caps. I've not used the ones in that post, except for K73-16 which is for assist duties. The different russian caps are as different as different American or European or Japanese caps.

SSG is best, KSG second best, KBG best in big numbers, MBGO good for all.

Some of the PIOs other than KBG have a lousy retro sound, which many like but I don't consider HIFI. Excellent for guitar amps, though.


But, in the end, if the circuit responds a lot to cap rolling, it's probably not a very good circuit. General rule, has served me well thus far. There are some exceptions.


----------



## Maxx134

I like to mention of note last night listening session.
I was laying down and a usual track I played scared the crap out of me!

I was hearing treble/air movement of a person passing by,
that in past did not notice as the detail or ambient cues was not resolved enough for my brain to interpret it in the past.

It literally scare the crap out of me for a second!

The problem is that I do not know which mod is responsible:
1- the bias to powertubes,
2- the change in driver tubes (6sn7)
3- using EH & DR powertube pair
4- Bypassing my ygggy USB with the "F1" spdif converter, in this thread:

http://www.head-fi.org/t/803111/xmos-xu208-usb-bridges-the-latest-gen-has-arrived/0_20


Oh, forgot new tube burn in!


----------



## MrCurwen

maxx134 said:


> Plus it would need your signature in gold ink on the corner for finishing touch..




Me and the owner of the amp I linked a picture of go to high end shows and shops to audition things.

After one of those outings we actually laughed around that maybe I should do that signature, since all the BIG LEAGUE amps seem to have it. =)

The speaker posts are gold though so technically it still is eligible in HIGH END, despite it's other sins.


----------



## Maxx134

My topic on the cap paralleling was specific to the WCF position,

And it is good to know about possible smearing which I would not choose to do in a coupling position.


----------



## claverocks

maxx134 said:


> I like to mention of note last night listening session.
> I was laying down and a usual track I played scared the crap out of me!
> 
> I was hearing treble/air movement of a person passing by,
> ...


----------



## coinmaster

> I was hearing treble/air movement of a person passing by,
> that in past did not notice as the detail or ambient cues was not resolved enough for my brain to interpret it in the past.
> 
> It literally scare the crap out of me for a second!


 
 That happened to me a few times after upgrades. Spooky realism. Depends on the quality of the recording though.


----------



## MrCurwen

The WCF caps are 100% as much in the signal path as the coupling cap between input and output stages.

Of course, it is inside a local NFB loop, so it's not so critical. If the devices inside NFB loop had more gain and transconductance, the quality of the cap would become irrelevant.

Comparing to the gyrator cap. I use "assist duty quality" K73-16 there, because it is inside a very very strong full degeneration NFB loop (from FET output straight to FET input basically). I used to use very good quality caps there but they don't really make any difference inside the loop.

It is the local NFB loop inside the WCF that lowers the output impedance of the WCF and of the amp. If you can hear any difference between caps inside that loop, you know the performance of the output stage is not optimal or very impressive.

That doesnt' mean it's not GOOD. It just means the rabbit hole in fact is more deeper whether you wish to go there or not.


----------



## coinmaster

> Of course, it is inside a local NFB loop, so it's not so critical. If the devices inside NFB loop had more gain and transconductance, the quality of the cap would become irrelevant.


 
 Hmm, not sure I understand this. The WCF cap is required for proper push pull operation, good signal integrity ensures that the bottom triode conducts oppositely to the top triode allowing proper current flow through the load.
 How does more gain make the cap matter less? The WCF ensures less then unity gain anyway right?


----------



## MrCurwen

One of my test tracks (I have many for different purposes and qualities) for the creep factor is Violenza Domestica by Mr.Bungle:

https://www.youtube.com/watch?v=-qVjAFCHoaI

My girlfriend really enjoys the musical crazyness of Mike Patton. Towards the end of the track (maybe 4 mins in) there's a section where he talks directly to your terrified soul. How horrifying it sounds is a measurement of the amps fidelity. 

Some decent transient tests in that one as well. 


Then there's the position of singers head with regards to the microphone. There's many good tracks for this, but one to mention is Gun Street Girl by Tom Waits. I don't know if he's actually drunk while singing, but it sure seems so. =)

Also the physicality of the instruments is one way to describe realism. Every decent studio recording is much more of a live performance (if done well).

Good song though, much more pleasant than the Mr.Bungle song.


----------



## Maxx134

mrcurwen said:


> The WCF caps are 100% as much in the signal path as the coupling cap between input and output stages.
> 
> Of course, it is inside a local NFB loop, so it's not so critical. If the devices inside NFB loop had more gain and transconductance, the quality of the cap would become irrelevant.
> 
> ...



I am going to go there by changing my powertubes which are already on the way. .


----------



## coinmaster

Here's an interesting article by Nelson Pass, the jesus of audio.
  
 http://www.6moons.com/industryfeatures/distortion/distortion.html
  
 He explains why NFB is bad and why THD is a load of BS.


----------



## claverocks

maxx134 said:


> I was laying down and a usual track I played scared the crap out of me!
> 
> I was hearing treble/air movement of a person passing by,
> 
> It literally scare the crap out of me for a second




Lmao! That was me, about to stage an intervention haha


----------



## coinmaster

Lol.


----------



## Maxx134

Look at these nice tubes!



The VT-99 look sweet and smaller..

Alot testing to commence.


----------



## coinmaster

> Look at these nice tubes!


 
 Wow nice, how much did those set you back? Are those the new PSvane treasure tubes?
  
  
  
 I have news as well, I did a nice long simulation of the Mk6 with the impedance mod vs my new design I'm working on.
  
 Here is the simulated distortion of the MK6 up to 20khz

  
 This is the simulated distortion of my design, it took half the day to simulate due to the complexity of it and there is still room for plenty of optimizations I think.
  
  

 Dayyyuuuum 
	

	
	
		
		

		
			




 It looks almost like the MK6 without all the distortion. That's with the triodes slightly out of balance too and very little NFB was used.
 I'm confident I can improve it further without the use of NFB but the damn simulations for it take ages to load .


----------



## Maxx134

What type of distortion display was that?
And can you run a stock version as well?
It would have been better to test against stock as we don't know what parameter you chose to do impedance mod.

Only the bias mod was posted. 
The impedance mod may vary upon setting.


----------



## coinmaster

> What type of distortion display was that?


 
 FFT analysis
  


> And can you run a stock version as well?


 
 Yeah, I'll load it up and post it when it's done.
  


> It would have been better to test against stock as we don't know what parameter you chose to do impedance mod.


 
 I used 800 ohm resistor for 400 ohm load.
 The simulation is showing perfect balance between triodes so it is working as intended.
  
 Interestingly I can't remember how I originally came up with the value of 800 but it does seem to be correct.
 I went back to the cavalli papers and redid the calculation but I can't seem to come to the same conclusion, hmmm. Maybe I just suck at math 
	

	
	
		
		

		
		
	


	



  
  
 I did another sim of my amp, strangely it loaded quickly this time, only about 30 minutes to load the sim and about 1 second to actually do the simulation, it's almost comedic.
  
 I removed all NFB and this is what I got

 Interestingly a lot of the slant is gone but the the harmonics are back. Still a great improvement over the MK6 though since the MK6 has a lot of NFB and this has none and it's still better.
  
 The design still has some kinks to be fixed so I suspect it will get reasonably better, hopefully I can get the .0001% open loop distortion MrCurwen spoke of 
	

	
	
		
		

		
		
	


	



 Unfortunately as soon as I removed the NFB it started clipping balls, it seems I inadvertently created a cascode between stages, I'm going to have to reduce gain majorly or end up using autoformer pots for gain reduction.


----------



## MrCurwen

NFB as a theoretical concept is not bad for audio signal reproduction, not bad at all.

For example, the reason a triode with good curves is linear, is because of NFB inside the tube.

The electron stream traveling in vacuum and different electric fields (such as the field around the control grid) has a feedback loop in it. This is what linearizes a triode.

The strenght of this NFB inside a triode is dependent on the geometry of the tube; how the electrodes (cathode/filament, control grid, anode) are placed in relation to each other. 

There are triodes with "tetrode like curves" that don't have the screen grid. This is because the distance between the cathode and anode is so great that the feedback effect is very weak. (Very very high rp)

There are even triodes with pentode like curves (although a weak pentode); they even have beam plates! They are called beam triodes. They are usually for some extremely high voltage duties. The distance between the electrodes is so great, the tube can withstand something like 10kV of voltage. Good for some radar and large screen CRT applications.

For audio use triodes have a lot of NFB inside them. This is not bad, because what makes NFB bad is WHAT IS INSIDE THE LOOP. In a triode, there is vacuum. 

Put a resistor inside a NFB loop. Not bad. (For example a CCS)

Put a capacitor inside a NFB loop. Not bad (if decent film cap).

Put a resistor and a capacitor inside NFB loop; not bad at all. (Say, the gyrator.)

Put a complex system of voltage and/or current gain stages inside a NFB loop, and you've got big big problems. This is the SS SOUND.

A regulator is a 100% degenerated NFB loop. The loop is local, very short, and doesn't contain any significant amount of reactive elements. No SS nastiness or problems.

The Little Dot's 'regulator' in the PSU (it's really a voltage setter, since the feedback loop is only (mainly) affecting the PSU ripple, not the audio side of the circuit; it sets the voltage, it doesn't REGULATE the B+) has a 100% degenerated NFB loop. Does it bring SS nastiness into the sound?

SS is not bad inherently. If you put SS inside a local, small and simple NFB loop, it's just as un-nasty as a triode with it's local, small and simple NFB loop.

This is a rudimentary explanation of the subject, but just to illuminate a bit about these things.


A tetrode or a pentode don't have triode curves because the screen grid breaks the NFB loop between the plate and the cathode. It breaks it by having an independent electric field in the path of the electron stream. If you want to have your pentode behave more like an ideal pentode (so, more like a MOSFET in essence), you regulate the screen supply, making it very sturdy. This makes the screen grid electric field more independent of the anode conditions, and breaks the feedback loop in the electron stream more, thereby making the curves more horizontal and flat.

If you connect the screen to the plate, you no longer break the NFB loop, therefore you have more linear curves. After you do that, the linearity of the system is again dependent on the inner geometrics of the tube. Most tetrodes, beam tetrodes or pentodes are not designed with triode operation in mind, so they have rather poor geometry for triode operation linearity. There are a notable number of exceptions, such as 4P1L.

4P1L was actually designed by nazi scientists. It was probably meant for a very wide variety of applications, and that is why it was designed with geometry suitable for triode operation as well.

Most pentodes were not. Linear triodes were around, so why bother? The nazis were operating under very severe shortages, and couldn't afford to make that many different types (each needing their own factories etc.) Same goes for the soviets. 



People think because SS doing voltage amplification necessitates a LOT of NFB to make it linear, thereby causing A LOT of SS nastiness, that all SS components by nature produce this nastiness in all circuits, no matter what they are used for.

A general rule; if the SS component has 100% degeneration, meaning it exhibits no voltage gain, it WILL NOT PRODUCE ANY NASTINESS. At all. No more than your 1930's triodes. Actually, less than that if the 1930's triode is exhibiting voltage gain, it will produce some harmonics. The 100% degenerated SS component will not produce any harmonics, because 100% degeneration means just that.

If you have 97% degeneration, you will have harmonics. 


In short, it's simply idiotic to compare SS with voltage gain to SS with no voltage gain. Any articles discussing the first and reaching a conclusion IT'S BAD FOLKS is not applicable to source followers or 100% degenerated regulators and such. They are different things.

A CCS is not exhibiting any voltage gain to the circuit. There is gain inside the loop, but it's 100% degenerated. This means 100% of the gain is dissipated in the loop, in audio frequencies. Sometimes there is gain with radio frequencies (oscillation) and that needs to be dealt with.

A CCS will not contribute any signature to the audio, other than by correctly organizing the circuit for example balancing a triode pair in a LTP, or sinking grid current from a power tube grid.


----------



## MrCurwen

So in short: NFB is totally ok or completely crap depending on what is inside the loop.

SS is totally ok or completely crap depending on if it has voltage gain or not.


There is a feedback loop inside the voice coil of your headphones. The current traveling inside the coil is producing an electric field that is affecting the other parts of the coil, giving the coil IMPEDANCE. 


Partial NFB (not 100%) over gain stages, worst case over multiple gain stages or worst possible case over multiple gain stages, multiple electrolytic caps, and a transformer ... You've got problems.

NFB from FET source via a resistor and a film cap to it's gate; no problems, no sonic impact. Unless cap is electrolytic, cap quality is irrelevant.


A NFB loop exchanges gain / transconductance to linearity.

Increase the gain and/or transconductance inside the loop, and you've got a better loop, assuming you're operating under 100% degeneration.

For example; add a darlington pair of 2N2222 inside the CCS feedback loop, thus introducing voltage gain of like 15 000, thus increasing the FET transconductance to nearly infinite. Now you have a CCS that is behaving more like an ideal CCS.

Replace the gyrator plate load FET with a weak triode (weak in transconductance) like a 6SN7. You've got less transconductance inside the loop, you've got a weaker loop.

It behaves much much less like an ideal gyrator. Impedance provided to the tube underneath it much much less. More distortion.

Replace the 6SN7 with a strong triode, like a 6S45P with very high transconductance. Now you have more transconductance inside the loop, stronger loop. More impedance, less distortion. Better plate load.

Ok, so now replace the 6S45P with a pentode. More transconductance, more impedance. Less distortion.

Replace the poor FET-lookalike pentode with a real FET; you've got more transconductance and you get the rest.


CCS's can be made with triodes or pentodes. There's no point really, outside of for giggles.


The progression I described is what I personally went thru. Although I skipped the pentode and went straight for the FET. And I did try more different types of tubes. More transconductance inside the gyrator 100% NFB loop --> better sound.


----------



## coinmaster

> People think because SS doing voltage amplification necessitates a LOT of NFB to make it linear, thereby causing A LOT of SS nastiness, that all SS components by nature produce this nastiness in all circuits, no matter what they are used for.
> 
> A general rule; if the SS component has 100% degeneration, meaning it exhibits no voltage gain, it WILL NOT PRODUCE ANY NASTINESS. At all. No more than your 1930's triodes. Actually, less than that if the 1930's triode is exhibiting voltage gain, it will produce some harmonics. The 100% degenerated SS component will not produce any harmonics, because 100% degeneration means just that.


 
 Yeah, I'm beginning to understand that now between nelson pass's article and yours.
  
 What about source followers? They have no gain but they do produce harmonics, plenty of data around to suggest that.
  
 Nelson pass said the NFB decreases total harmonic distortion but increase high order harmonics which are the non-musical kind. Does that not apply to 100% degenerated local NFB?
  
  
  
 Also it seems the above FFT analysis of my design was of an older version with a major imbalance in the output tubes. Spice refuses to load when I apply a solution.
 Plus I ran the MK6 stock in simulation at a 1 ns timestep all night and it produced a way too perfect distortion reading.
 I'm thinking there is some sort of optimization I need to make on both ends, need to look into it before I post MK6 stock vs impedance mod vs my design.


----------



## Maxx134

You may need to break down / interpret info to mainly worry about odd order harmonics ,
and also the level I see is already over minus 120db down so it is of questionable importance, unless I am not interpreting correctly


----------



## coinmaster

Reading from pass's article 2nd and 3rd harmonics are plentiful in real life music which is why they are more acceptable and considered musical, even if they do have downsides.
 The higher harmonics sound bad.
  
 I'm not sure what the deal is with the -120db on the FTT response.
 I'm trying to set up some THD addon to LTspice that does all the complicated work of THD analysis for you since apparently it's not as simple as clicking on FFT after simulation but it wants to run the simulation 3001 times for different frequencies. We'll be in the space age by then 
	

	
	
		
		

		
		
	


	




 Where's a super computer when you need it.


----------



## MrCurwen

maxx134 said:


> You may need to break down / interpret info to mainly worry about odd order harmonics ,
> and also the level I see is already over minus 120db down so it is of questionable importance, unless I am not interpreting correctly




It would seem he doesn't know how to use the program. 1nS timestep is useless, info provided on low levels not realistic. FFT is of current thru load, the scale is wonky and unreadable... I'm guessing the improved accuracy math setting is not on (it's off by default) as well.

Proper way to measure distortion is voltage over load. For 1kHz signal proper scale is 800 Hz to 10 kHz since 9 first harmonics are the ones of interest. At least in open loop circuits. The further you go up, the less realistic the simulation is anyway.

Proper Y axis scale is about top of 1kHz signal minus 100 dB, since that's the absolute bottom of any importance. I've found that as far as distortion goes, my ears (and my friend the high end hobbyist with golden ears and Sennheiser HD 800) tell me -80dB from signal peak is "not there anymore", and -70dB is "excellent".

Spice overestimates 2nd and 3rd by a varying degree. With tube models, usually a great degree. Some things that model as "distortion free" are not distortion free in real life. Simulation has it's uses and also it's problems.

With 1µS timestep and improved accuracy math on it takes a couple of minutes to do a 100mS sim of a complex circuit. And my computer is made of potatoes from 2004.

Spice has inbuilt THD measument, usable by one line;

.four 1000 9 V(n002)

Results in Spice Error Log Ctrl + L

I just simmed a source follower with unoptimized FETs (general purpose); CCS load under it, set for 15mA, +310V B+, a very very demanding 5k load and 100VPP signal.

Total Harmonic Distortion: 0.000389%

These numbers are for entertainment purposes really, but a source follower really has no THD. I've never heard it myself. If there is any, it is way down on list of distortion contributants.


----------



## MrCurwen

If somebody is still scratching their head thinking "an SS circuit module with no real THD and no high or odd order harmonics? How could that be, every single SS amp I've heard have had that tiring, shrill sound to them!" 

There is not one single SS amp on the market that doesn't have global NFB (NFB over the whole amp, multiple gain stages). It is the gNFB that produces the "SS sound". There are some tube amp designs that have more than a little bit of the "SS sound"; they utilize very high gNFB.

It's gNFB sound, not SS sound.

Even if you have an SS amp with source followers or other followers as the output, the low / no distortion output doesn't negate the nastiness made in the preceding sections. They will have gNFB if they are SS based.


So once again, it's about topology and circuit design. It pretty much always is.


----------



## MrCurwen

I'm an open loop guy all the way.

There's no way to know at the moment, but my amp probably has LESS of an "SS sound" than The Little Dot, since my amp is open loop. Despite the 20 or so FETs that reside in it.

Sorry off topic. Couldn't resist.


----------



## Maxx134

mrcurwen said:


> I'm an open loop guy all the way.
> 
> There's no way to know at the moment, but my amp probably has LESS of an "SS sound" than The Little Dot, since my amp is open loop. Despite the 20 or so FETs that reside in it.
> 
> Sorry off topic. Couldn't resist.



Is it the one you pictured?
how many tubes and what are they?
The past picture shows a straight line of tubes..
Just curious to know the layout


----------



## coinmaster

> With 1µS timestep and improved accuracy math on it takes a couple of minutes to do a 100mS sim of a complex circuit. And my computer is made of potatoes from 2004.


 
 Even my overclocked 4770k takes a while to even begin the simulation.
 I think LTSpice hates all the integrator/comparator feedback loops I'm using. Feedback loops seem to be the enemy of load times.
  


> Spice has inbuilt THD measument, usable by one line;
> 
> .four 1000 9 V(n002)


 
 Okay I loaded that up and this is the MK6 stock, sorry about the scale, not much I can do about it. 

 The THD is 0.136160% stock
  
 This is the MK6 with impedance mod

 THD is 0.062541% modded
 Which is weird because it looks like it actually has more distortion.
  
 Still trying to get my design to load


----------



## MrCurwen

maxx134 said:


> Is it the one you pictured?
> how many tubes and what are they?
> The past picture shows a straight line of tubes..
> Just curious to know the layout




Since you asked, I'll answer despite off topic!

The pictured one was my flagship amp. Forced balanced from input to output. 

The two rightmost tubes are input stages; 6SN7 russian eq.

The four left side tubes are 4P1L, each grid driven by a source follower buffer.

The power buffer on top is 4 source followers with CCS loads driving parafeed OT's. Each follower has about 15mA bias current.

It has 4 PSU:s, each regulated with a simple 2 FET regulator;

1) +290V for the input stage and the grid buffers
2) +356V for the output tubes
3) +305V for the power buffer
4) -14V for the input stage tails.

The signal parts have 28 FETs, the regs have 8. Also 4 low rdson FETs regulate each of the 4P1L filament supplies. The amp has a pitch black background despite having DH tubes (not a given by any means).


My current (not in any casing, just breadboard) workhorse amp is similar topology. 12AX7 input stage, grid buffers feeding 6E5P output tubes. Single B+ of 310V with a two FET reg, no output buffer. 

This one has some problems, some background noise. The super high transconductanse tubes such as 6S45P and 6E5P can be a pain to deal with. They do provide excellent dynamics though, even without a FET power output buffer. Not as good, but pretty great.

Anyway it has good sound quality, so I'm too lazy to work on it. I'll build another amp for myself later, identical to the flagship amp I made earlier. I already have the chassis worked and painted and also most of the woodwork done. 

I've made a number of variations on the theme with different tubes. Next I'll make a fully forced balanced 6SL7 -> grid buffer -> 2C22 -> power buffer, for one person I know.

2C22 is in my experience the most linear and sturdy 6SN7 variant there is. It should be, since it was made to be just that.

The amp I'm thinking about sending out to the gentleman in Denmark and possibly further on from there would be fully forced balanced 6SL7 -> grid buffer -> 6SN7 -> very small power buffer, kind of a stripped version of the previous model. I must make it yet smaller or it's not going to be possible...


----------



## Redge78

For the record, I have (slightly) changed the tittle of this thread, and made an addition in the first post.
  
 For the last 20 pages or so, the discussions have severely drifted from their original purpose.
 Personally, I find that interesting, even if I would have preferred to have some practical suggestions to work on.
 But for a newcomer it may be only useless technical garbage.
  
 And our initial aim was to help the newcomers, remember.


----------



## coinmaster

My initial aim was just to make an awesome amplifier 
	

	
	
		
		

		
			





 
 We've hit a wall on simple mods anyway so this is the next step to more mods.
 Plus this is valuable information.
  


> even if I would have preferred to have some practical suggestions to work on.


 
 CCS/gyrator/grid drive/power supply/LED/battery mods are all practical.
 It depends on how far you wana go. Like I said I'm ordering PCBs for them for myself anyway so you can just take the file and order your own. Not difficult to screw them onto an extension box with standoffs and the implementation to the board is simple.


----------



## Maxx134

coinmaster said:


> We've hit a wall on simple mods anyway so this is the next step to more mods.



Not me,
I have to push out:
1- bias adjustment refinement for MK8 powertubes
2- impedance switch mod 
3- driver tube change & refinement 
4-DE-coupling caps refinement
5- parasitic red caps upgrade 
6- power tube rolling with corresponding bias adjustment.

Future mods:
7- Extend bottom chasis
8- PSU upgrades


----------



## coinmaster

> Future mods:
> 7- Extend bottom chasis


 
 That should be your top priority lol.


----------



## Redge78

coinmaster said:


> We've hit a wall on simple mods anyway so this is the next step to more mods.


 
  
 You may have but I don't. I have enough new mods to keep me busy for the rest of the year, not speaking of the mod that I have already implemented and are in test right now.
  


coinmaster said:


> Plus this is valuable information.


 
  
 I don't deny that, even if the term 'information" may be a bit strong.
 There is a large community of (european ?) DIYers that would be less than enthousiast on those CCS and FET schematics.
 So until  I have actually listened to those SS things, I will remain cautious. 
  
 Anyway, my concern is more about "the new guy" whose main hobby is to listen to music and not to understand the electronic finesses. Let say he has 25 hours (?) to read/understand/order/solder/test our mods and he will go back to listening ... not sure those last pages of thread will be of a great help.
  
  
  


coinmaster said:


> CCS/gyrator/grid drive/power supply/LED/battery mods are all practical.
> It depends on how far you wana go. Like I said I'm ordering PCBs for them for myself anyway so you can just take the file and order your own. Not difficult to screw them onto an extension box with standoffs and the implementation to the board is simple.


 
  
 Don't get me wrong, all that may be very good.
 But until you can give us an actual "MK6" listening feedback _(corroborated by someone else would be a must)_, with a list of components, some nice pictures and an "How to" ... this is not "practical" in my book.
  


coinmaster said:


> It depends on how far you wana go. Like I said I'm ordering PCBs for them for myself anyway so you can just take the file and order your own. Not difficult to screw them onto an extension box with standoffs and the implementation to the board is simple.


 
  
 You're right, my ambition never was to rip the amp off and to modify 90% of it. 
 I want to keep a sensible "time spent" to "SQ increase" ratio.
 Even if the thread has impacted badly this ratio ... it also brought us some new joy.


----------



## Redge78

coinmaster said:


> That should be your top priority lol.


 
  
 Tell him that he would have more room to new decorating ideas !


----------



## coinmaster

> There is a large community of (european ?) DIYers that would be less than enthousiast on those CCS and FET schematics.


 
 I've done a lot of reading over the last 6 months, I've heard both sides of the story and the "tube purist" ideology has been debunked a thousand times. That's putting aside the science, data, experiences, and overall design logic behind it. Even if all SS devices were evil they aren't always in the "signal path" like the gyrator for example, depending on how picky you are going to be on your idea of "signal path".
  
 I'll be the first to say that all SS amps I've tried are garbage, even the big heavy expensive ones but you might as well ditch the opamp in the MK6 since it's SS right?
 Way too many claims from people that laugh at audiophoolery and design tube amps for decades that SS can sound good with proper implementation for me to dismiss it, coupled with the design knowledge I've gained and data I've seen I doubt it's untrue. In the same way I doubted high end caps can't make a difference even though so many people claimed that was BS, and here I am after blowing 800 bucks on duelund caps and heard an amazing difference.
  
 I think ignorance and stubbornness is the enemy of innovation and progression.
  

  


> Anyway, my concern is more about "the new guy" whose main hobby is to listen to music and not to understand the electronic finesses. Let say he has 25 hours (?) to read/understand/order/solder/test our mods and he will go back to listening ... not sure those last pages of thread will be of a great help..


 
 No they won't, that's why I've been saying for months now you should put a disclaimer saying the front page is where the tried and tested mods and instructions are at, that way we can discuss and progress in the thread without resorting to inefficient PM secrecy that only a select few can get in on and learn/contribute. Much better this way for a lot of reasons.
  
 Although I do agree it was good that most of our earlier conversations were kept in pms. At least now we can discuss things intelligently knowing what the design is and not having me be a clueless newby to electronics pestering you for information 
	

	
	
		
		

		
		
	


	



  


> Don't get me wrong, all that may be very good.
> But until you can give us an actual "MK6" listening feedback _(corroborated by someone else would be a must)_, with a list of components, some nice pictures and an "How to" ... this is not "practical" in my book.


 
 I'm workin on it. If anyone wants the PCB design I can finish up the last details and upload the file now, there's no reason it should not work the design is functional and the PCB layout has minimal inductance but other then that it will probably be july before I do my own tests at this rate.
  


> I want to keep a sensible "time spent" to "SQ increase" ratio.


 
 Indeed, but from a technical point of view, the mods are such an upgrade that it is likely they will be worth it. At the very least you can rest knowing you have the best 
	

	
	
		
		

		
		
	


	




 That's kind of my goal.


> Tell him that he would have more room to new decorating ideas !


 
 Indeed he would. I can only imagine..


----------



## Maxx134

redge78 said:


> coinmaster said:
> 
> 
> > That should be your top priority lol.
> ...




Haha!

I already had body / chassis idea ready for next amp,
Which will be never made at this rate haha .

but you're right looks like it's time to extend my bottom especially since I can use that space for switch mods haha

** edit:
 at this rate looks like my Amp may not be ready for the upcoming New York headfi meet,
 but at I least I will bring my newly-modded headphones..
Hd800
HE1K
PM2
All modded. 
Finally I went a bit off-topic


----------



## coinmaster

> Finally I went a bit off-topic


 
 How dare you
  


> at this rate looks like my Amp may not be ready for the upcoming New York headfi meet


 
 Oh right...forgot about that. I don't think I will be going, the last thing I need is to relapse on good sound while my amp is still in progress.


----------



## Maxx134

http://www.head-fi.org/t/788652/official-new-york-spring-meet-saturday-june-11-2016/0_20


----------



## SonicTrance

I've been reading recent posts regarding biasing the driver stage but did not find any useful info.
  
 What I'd like to try is to bias the ECC32 more optimally in the MK6 by altering the Ra and Rk.
  

 According to the above chart, a 47K Ra and 1K2 Rk would give me 1.9mA. That'd be a significant decrease in Ra though compared to stock 220K.
  
 Thoughts? @MrCurwen


----------



## Mogos

mrcurwen said:


> ...........
> 
> 2C22 is in my experience the most linear and sturdy 6SN7 variant there is. It should be, since it was made to be just that.
> 
> .................


 
 So the 2C22 can be used in place of 6SN7. No problems if pluged in MK6? There is no where any information that it can replace the 6SN7. At least I could not find it.


----------



## Maxx134

I believe that is a single triode,
 and not sure if adapter will fit,
 as would be two tubes on one socket.


----------



## MrCurwen

mogos said:


> So the 2C22 can be used in place of 6SN7. No problems if pluged in MK6?




Yes it is a direct equivivalent in specs. Like Maxx134 said it's a single triode, not a double triode, so it's not a plug and play -eq.

Of course one could make a thing like this: http://www.ebay.com/itm/1pcs-Tube-Amplifier-2C22-2C22-Replace-6SN7-Tube-Socket-Adapter-Suzier-C7-/281951474429?hash=item41a59e12fd:g:vrMAAOSwyQtV5rmU

I wouldn't recommend it. This is another thing in the "good to know on a general level" category, not practically applicable to your chassis as it is.

If you do a scratch build, and wish to get "the best", then get 2C22 / 7193. 

It's ratings are well underspec'd. I've ran mine in various amps for long time with both anode dissipation and anode voltage rating exceeded (a bit), and they're just fine. They were made for very hard pulse duty, and in audio operation they are overspec'd.

Also the curves are - at least for the ones I've had - much better than drawn in the datasheets. I got perfectly linear 700 VPP swing out of a LTP for my TV experiments. I visually checked the waveform on the 8 inch CRT, it was completely symmetric.



> There is no where any information that it can replace the 6SN7. At least I could not find it.




Not replace as such, in an existing amp, in the meaning of tube rolling. If you design your own, it's an eq. Plenty of DIY forum posts about this to be found.

Anyway, not applicable to this amp. The 220k plate resistors aren't for the 2C22 or similar 6 to 7 k anode impedance tubes.


----------



## SonicTrance

> Anyway, not applicable to this amp. The 220k plate resistors aren't for the 2C22 or similar 6 to 7 k anode impedance tubes




It's not hard to change plate resistors.


----------



## Mogos

mrcurwen said:


> .........
> 
> Of course one could make a thing like this: http://www.ebay.com/itm/1pcs-Tube-Amplifier-2C22-2C22-Replace-6SN7-Tube-Socket-Adapter-Suzier-C7-/281951474429?hash=item41a59e12fd:g:vrMAAOSwyQtV5rmU
> 
> ...


 
 Whay do you not recomend the adapter. I understand that it will simulate the 6SN7 tube so it should be no problem.


----------



## MrCurwen

mogos said:


> Whay do you not recomend the adapter. I understand that it will simulate the 6SN7 tube so it should be no problem.




If you use a premade adapter (as opposed to making it yourself) it is very likely to not fit, unless you are able to change the orientation of your octal sockets on the chassis.

Furthermore, for the same price, you can buy a new blank aluminium chassis and a couple of octal sockets, and make proper chassis for 2C22 use.

And more, with the op point and load line in the circuit as it's sold, you will not be able to hear any positive improvement. It's would be just an elaborate way to starve a 6SN7 basically.


Mogos:

You basically need a higher B+ for any proper implementation of 6SN7 family tubes. It can sound ok or decent with lacking implementation, if you're lucky, but best results require a more suitable load line and op point, and they require higher B+.

SS assistance could come a long way, 170V B+ might just about barely cut it for my LTP but it's probably not going to fit inside stock chassis. Regulated 250V and you're good to go for my LTP, and for pretty good results with retro resistor loads (for the retro sound) you'll need a good 350V.


----------



## SonicTrance

mrcurwen said:


> mogos said:
> 
> 
> > Whay do you not recomend the adapter. I understand that it will simulate the 6SN7 tube so it should be no problem.
> ...


 
 We have about 200V on the rail and the 220K resistors eats most of it when using 6SN7's. I measured about 50V on the plates. Wouldn't lowering the Ra value increase the plate voltage?


----------



## Mogos

I have used Electroharmonix 6SN7 and they have sounded decently. For sure not inferior to the 6SL7. I don't understand all the technicalities connected with proper tube aplication. I am the assembly guy 
	

	
	
		
		

		
			





.
 I understand that the stock solution is optimised for the 6SL7 driver tubes. The same story we have had with driver tubbes 5998 solved by Sonic Trnace with the switch and resistors. So maybe there could be another switch to make more optimised conditions to work for the 6SN7 tubes ?. I have still some free space in the casing 
	

	
	
		
		

		
		
	


	




. But I will need a schematic how to do it.


----------



## SonicTrance

mogos said:


> I have used Electroharmonix 6SN7 and they have sounded decently. For sure not inferior to the 6SL7. I don't understand all the technicalities connected with proper tube aplication. I am the assembly guy  .
> I understand that the stock solution is optimised for the 6SL7 driver tubes. The same story we have had with driver tubbes 5998 solved by Sonic Trnace with the switch and resistors. So maybe there could be another switch to make more optimised conditions to work for the 6SN7 tubes ?. I have still some free space in the casing  . But I will need a schematic how to do it.




Yeah, 6SN7's still sounds really good in our amps even though it only gets about 50v on the plates. It doesn't matter what MrCurwen thinks, it's a fact. I've also measured the plate voltages using ECC35's and it was 100-105v. So by lowering the Ra we should get higher plate voltage, but will it sound better? That's the question. Only testing can verify that. We also have that 1k5 cathode resistor that's shared between the two triodes...


----------



## Mogos

sonictrance said:


> Yeah, 6SN7's still sounds really good in our amps even though it only gets about 50v on the plates. It doesn't matter what MrCurwen thinks, it's a fact. I've also measured the plate voltages using ECC35's and it was 100-105v. So by lowering the Ra we should get higher plate voltage, but will it sound better? That's the question. Only testing can verify that. We also have that 1k5 cathode resistor that's shared between the two triodes...


 
 SonicTrance it looks like you are already pointing in a good direction 
	

	
	
		
		

		
		
	


	




. To check if it will sound better is not a problem. I can invest in the required parts. The tuebes are alredy there. I am gona also have any way the adapter for the C2CC and a set of Ken-Rads. If we could create more suitable enviroment for the 6SN7 tube then the effect can be very interesting. Few guys on the net reports that the C2CC sounded for them better then any other 6SN7 even the most appreciated ones . Can you Guys think about that subject and prepare some solution with assembly instruction for an assembly guy like me. It has to be done by somebody who has knowlege about it to make it safe 
	

	
	
		
		

		
		
	


	




. I don't know if I could survive one more time amp break down.  I am afraid it will also break me down 
	

	
	
		
		

		
		
	


	




.


----------



## MrCurwen

You should disconnect the stock input section, and connect long wires to the output points (and heaters and B+ / ground) of the input section, and build the new input section (experiment) outside the chassis.


This is what I always do when I have to experiment on something that's not expendable.

Experiments always need troubleshooting. Better to do it in good space.


So what's the input section B+ under load? What is the current delivery capability of it? Can it support 10mA? 15mA?


----------



## Mogos

mrcurwen said:


> You should disconnect the stock input section, and connect long wires to the output points (and heaters and B+ / ground) of the input section, and build the new input section (experiment) outside the chassis.
> 
> 
> This is what I always do when I have to experiment on something that's not expendable.
> ...


 
 Thank you MrCurven. What you have written says something to me but you have to remember there are here not only a pro guys. There is a need to create an instruction with photos, connection points etc. Like it is done on the first page (thank you Redge,Maxx for you understending of the need for simple instructions for guys like me). From what you have written I understand that it will be necessary to build separate circut capable to deliver appropriet voltage and current. Or maybe there is simpler but not perfect solution just improving the conditions and simple in it's implication. Question is will it be possible to switch between the stock solution and the added circut like in case of just adding the resistors like SonicTrance has done for the 5998 and 6080 power tubes. I think it will be to difficult for me with the whole new circut to perform the necessary experiments and trouble shutting if problems occure.


----------



## MrCurwen

I see.

I could provide more detailed information on how to build a separate input section box (thus leaving the stock circuit alone as a backup). However my personal philosophy is that it's not wise to give TOO detailed info. That's not responsible, it's like handing a gun to a child after explaining (with good detail) how the gun works.

Basically just get an aluminium box (Hammond is cheap), drill some holes to it (figure out all the things you need to attach to it), put four octal sockets on top in a pretty row, look up datasheet and tube pinout, connect heaters, then connect everything else in accordance to a schematic you wish to test out and you're set. All the info is readily available (such as tube datasheets) and the gaps can be filled with asking specific questions. If a builder needs an all encompassing full build guide with pics then DIY is not for him. Pics are ok for layout suggestions, but anybody can make their own layout.

The space and PSU constraints of the stock amp are a hard limit on experiments. Chassis expansion basically is the only way to do any substantial modding (in DIY circles modding means not component rolling (that is referred to as component rolling) but changing the actual operation of the circuit) is to have more space, and a better PSU.

The stock input section PSU could have current delivery capability, but it could just as well not have it. Why spend extra money on a 40mA winding, when a 5mA winding is well overspecc'd for the 4 x 400µA stock circuit.

Is the power transformer marked with specs such as voltage and current capabilities?


If there is interest somebody other than coinmaster start a new thread with title something like Little Dot expansion chassis experiments or something and I'll give my weird suggestions there. Schems only, no pic tutorials.


I myself got into tube DIY by doing a THOUSAND different mods to a Epiphone guitar amp head. The small one, with only a single volume control and two tubes; 12AX7 and EL84. When I had over 50% of the circuit outside of the stock chassis, I thought maybe I'll just start making scratch builds...

Same thing ended up happening when I got into tube HIFI. I made a FINAL BUILD of a 12AU7 direct coupled to EL84 triode strapped (SE) amp (for headphones mainly). I continued reading up on electronics, and kept on modding the amp. When more than 50% of the amp was outside the original chassis I had made, I just decided to go full breadboard. Now I'm just starting to make chassis builds again; the circuits have been sufficiently perfected for now.


----------



## Maxx134

*Quote:
So maybe there could be another switch to make more optimised conditions to work for the 6SN7 tubes ?. I have still some free space in the casing . But I will need a schematic how to do it.*

The issue at hand is that the MK8 powertubes prefer a different gain than the MK6 powertubes. 

The driver stage is currently our concern at the moment.

The 6sN7 tube is very popular so we like it to be sounding as good as the 6sL7 type.

I have a 205v plate voltage.
David at Little dot PM me long time ago that the change of resistors was intentional.

I am talking about the 3k3 resistors on the sides which feed the driver stage.

They have been lowered in my amp to 2k2.
This gives me an almost 10v boost.

Also, old versions of these Amps had 200k plate resistors,
Which would also give a bit more plate voltage to tube.

The issue is whether we want to try to adjust for a compromise setting,
Or stay with the circuit as is , which is set for the 6sL7 type.

So now, which tube is better sonically?
That should be the direction. 
Just to mod the cicuit to have more options is not the ideal goal..


----------



## Maxx134

Personally, on my MK8 ,
I am finding the 6sN7 gain to not be as lively as the 6sL7 type.

On the MK8, you would have to remove the guards to try 8pin types with adapters, 
Which is what I have been doing to look into the MK6 driver tube types.
And as stated,
The MK8 presents another issue of driver tube matching to powertubes stage.


----------



## Maxx134

We(me & my dog) will probably look for a better 6sN7 setting but that means trying different plate resistors and testing.


----------



## Maxx134

@Mogos,
 if you like,
you can try 200k resistors on your driver tube plates and report back. 

This was the older setting so still should be valid.


----------



## MrCurwen

Tubes don't have an inherent sound at all. Aside from the curves.

Both 6SN7 and 6SL7 have quite large linear areas in their curves, so they are exactly equally good sounding. They are both indirectly heated.


All the rest is a matter of: How well does the circuit accomodate the tube in question?


----------



## Maxx134

mrcurwen said:


> ..
> 
> 
> So what's the input section B+ under load? What is the current delivery capability of it? Can it support 10mA? 15mA?




Surprisingly the PSU for the driver uses the left transformer, 
While the powerstage uses the right transformer.
The servo and protection circuits ate fed from the left transformer,
So I assume the PSU, although not as refined, is actually as robust as the other PSU.
*edit*
Same bridge rectifier as well.
Both transformers are nice big heavy types.
For detailed info on the transformers,
Little dot has to be contacted, 
Because the details are not printed on the toroidal transformers.


----------



## Maxx134

mrcurwen said:


> ..
> .Aside from the curves.
> 
> Both 6SN7 and 6SL7 have quite large linear areas in their curves, so they are exactly equally good sounding. They are both indirectly heated.
> ...



I know this..
Yes that is the question at hand because the circuit is not operating in the most linear range at all


----------



## MrCurwen

If the input section PSU can support decent amounts of current, then there are more options for the expansion box even without buying a new transformer. That's good.

In that scenario I would still recommend building a simple raw supply and a simple reg in the expansion box, just leave the stock PSU unconnected as a backup. Cost is like 20 to 30 euros at most.

The biggest question mark in this approach is the NFB. The output stage probably really needs the NFB (as per my output impedance sims). I'm an open loop guy, so I'm not entirely sure if my schem would be compatible (i.e. behave nicely inside a global NFB loop).

Anyway.


----------



## Maxx134

No need to start from scratch, *for me*
Only need try some different well decided points.
We don't need more gain though.

Also will have to be aware of the wattage of the Cathode resistor,
if tube bias set higher.


----------



## SonicTrance

maxx134 said:


> No need to start from scratch, *for me*
> Only need try some different well decided points.
> We don't need more gain though.
> 
> ...


 
 I feel the same way. It doesn't seem worth it to me with a external psu as the 6SN7's already sounds great + I use the ECC35's most of the time anyway. Right now though I'm enjoying the Sylvania 6SN7W metal base, which to me is the best 6SN7 I've heard.


----------



## Mogos

maxx134 said:


> *Quote:
> So maybe there could be another switch to make more optimised conditions to work for the 6SN7 tubes ?. I have still some free space in the casing
> 
> 
> ...


 
 Maxx I don't want to compromise the existing set up for 6SL7. But if it is possible to add eg pararel resistor to change the current and have it on the switch than why not. SonicTrance has done it for power tubes. But I don't know if it could be just so simple to eg. add resistor in pararell.


----------



## Maxx134

mogos said:


> maxx134 said:
> 
> 
> > *Quote:
> ...



Yep that looks to be the path to choose.
First must find an optimal value for 6sN7. 
Unknown it possible to improve it yet.
More testing to do .


----------



## Mogos

maxx134 said:


> We(me & my dog) will probably look for a better 6sN7 setting but that means trying different plate resistors and testing.


 
 I count on your dog. My told me that this area of subjects is not in the circle of his interests otherwise he will help me.


----------



## Maxx134

Well, 
so far I have had my MK8 power tube running at a higher bias, which improved transparency. 

I have had it running for over a month but today will refine the settings for a MK8 only upgrade post.

This is following the lead of Sonic,
 who recently posted that power tube bias switch mod upgrade,
And was posted on first page.

Future upgrades on two other sections coming..

They are not my mods to divulge but should be sweet. 

I am only fine tuning the MK8 power tube bias,
 and also looking into a possible optional tube roll with another tube which I have not received...

But so far the best combination for the MK8 is:
EH tube left side negative socket.
Sovtek tube right side positive socket.

This combination will surpass the expensive DR Super Tubes, which I also have.

Will post further details and write up for first page later.


----------



## coinmaster

Haven't been reading this thread lately, been at the beach.
  


> If there is interest somebody other than coinmaster start a new thread with title something like Little Dot expansion chassis experiments or something and I'll give my weird suggestions there. Schems only, no pic tutorials.


 
  Lol, you're pettiness knows no bounds. Perhaps I'll make this thread just to mess with you 
	

	
	
		
		

		
		
	


	



  
 Quote:


> > Maxx I don't want to compromise the existing set up for 6SL7. But if it is possible to add eg pararel resistor to change the current and have it on the switch than why not. SonicTrance has done it for power tubes. But I don't know if it could be just so simple to eg. add resistor in pararell.
> 
> 
> 
> ...


 
 Won't work for the mk6, the 220k plate resistors limit the current. You will barely get any increase in current if at all. 
 Which means you have to lower the plate resistors first which can reduce the linearity of the tube. Higher voltage B+ is really what's needed here.


----------



## Maxx134

coinmaster said:


> Haven't been reading this thread lately, been at the beach.





> Won't work for the mk6...




Haha ..!
We will see about that...


----------



## Mogos

coinmaster said:


> .
> 
> Won't work for the mk6, the 220k plate resistors limit the current. You will barely get any increase in current if at all.
> Which means you have to lower the plate resistors first which can reduce the linearity of the tube. Higher voltage B+ is really what's needed here.


 
 I agree that the parallel resistor is not a good solution. It has to be done with switch and two sets of resistors (one for 6SL7 and one for 6SN7). But why you are saying that lowering down the plate resistors will reduce the linearity of the tube. The lower value of the plate resistor shall improve the linearity of the 6SN7 tubes. Right now they are working in the unfavorable conditions. Can somebody explain what is B+ voltage. How it is controled in the mk6 circut?


----------



## SonicTrance

mogos said:


> coinmaster said:
> 
> 
> > .
> ...


 
 You're right Mogos.
  
 Here you can see the load line we would get for the 6SN7 with a 35K Ra (red line), 220K Ra (blue line)

 Then we would have to choose cathode resistor to set the grid voltage.
  
 B+ is the rail voltage, which we have measuring point on the board for 170VAC for driver stage. Which becomes about 200VDC once rectified.
  
  
 Also got the spec for the mk6 transformers now.

  
 The 85v winding is for driver stage, connected in series with the other transformer, which gives us 170V and 50mA. So we have plenty of current we can use!


----------



## Mogos

Ok it is very concrete information. For me it is the way to go but I am an layman in the subject. Your comments, sugenstions and instructions will be very valuable. Can you tell what are the rules to choose the catode resistors having all the information above.


----------



## coinmaster

> Haha ..!
> We will see about that...


 
 I did simulations of this a few weeks ago and I don't think I got passed .9ma with 220k plate resistors in place without increasing B+.
 A change in bias resistor will probably just shift the tube into different non-linear areas. Whether this will sound good or not is anyones guess. Good thing you are testing it.
  


> But why you are saying that lowering down the plate resistors will reduce the linearity of the tube. The lower value of the plate resistor shall improve the linearity of the 6SN7 tubes.


 
 If you delve into tube theory and operation an infinite impedance load will produce the most accurate signal.
 For example a 1 meg plate resistor would create the least distortion but you would need like a 10KV power supply in order to get enough current though that.
  
 This is why the CCS/Gyrator mods are good because they pose an effectively infinite or near infinite impedance to the signal without the need for crazy power supplies.
  
 The rule of thumb for plate resistors is 4-5 times RP because it is a balance between high impedance and practicality.
  
 Therefore if you lower the plate resistor you will get more current but you will also be reducing linearity.


> Also got the spec for the mk6 transformers now.
> 
> 
> The 85v winding is for driver stage, connected in series with the other transformer, which gives us 170V and 50mA. So we have plenty of current we can use!


 
 Thanks for that, I've been wondering what the limits of the transformers are. David never responded when I asked as usual.
  
 Also the B+ of the input stage is 220v not 200v.


----------



## Mogos

Coinmaster I am traying to delve in to the tube theory but I may not be able to make such a huge progress like you. Some help will be appreciated 
	

	
	
		
		

		
		
	


	




. So looking at the plate characteristics chart posted by SonicTrance for me it looks like the red line is showing better operating conditions. Voltage is something what we have and we have to work around with. Current is what we can change (for the tube).
 So simple questions:
 Will lowering the plate resistor value improve the working conditions of 6SN7?
 What value of the plate resistor will be the best choise?
 How to choose the catode resistor to match the change in plate current?


----------



## coinmaster

> So looking at the plate characteristics chart posted by SonicTrance for me it looks like the red line is showing better operating conditions


 
 Those load lines are a reading of the tubes operating point under the conditions it was tested in.
 The datasheet will probably tell you what load resistor was used.

  


> Will lowering the plate resistor value improve the working conditions of 6SN7?


 
 I don't know. Lowering the plate resistor should decrease linearity and increasing current should increase linearity, depending on where it is on the load line. 
 So you might end up with a wash although if you want to decrease the plate resistor value to 4-5x RP of a 6sn7 tube then the non linearity might take over as a factor since it's a huge jump down from 220k.
 No way to really know without trying it, but technically you will get better fidelity from higher impedance loads. I'd just slap a gyrator on there and solve the whole problem, they really aren't that hard to make and you don't need an extra power supply.
  

 just a mosfet a few resistors and a small capacitor.
 It is not in the signal path, all it does is pose a high impedance to the signal.
 I suppose I could post some sort of guide on building it if anyone is interested in actually building it, or MrCurwen could do so.
 I still have my MK6 board lying around, perhaps I can find an optimum way to jerry rig it.
  


> What value of the plate resistor will be the best choise?


 
 30-35k plate resistor would work if you wanted to go that route.
  


> How to choose the catode resistor to match the change in plate current?


 
 Plate resistors don't set the current but they can limit it if they get too high.
 Current flows up through ground from the cathode resistor first so as long as the plate resistor has headroom for whatever current you want to draw you just choose the cathode resistor the old way which is Ohms law cross referenced with the tube data sheet.
  
 Let's say you wanted the plate voltage to 100v @ 5ma. That puts it at about the 2v grid curve. So the grid needs to be 2v lower then the cathode.
  
 a 2v drop at 5ma would mean a 400 ohm resistor.
  
 But you would want to go to 10ma since 6sn7 tubes like high current.
 So 150v@10ma would be better which just happens to also equal out to 400 ohms.
  
 Since the cathode are connected it would be 200 ohms instead because the current is split between them.


----------



## Mogos

In the stock solution for 6SL7 we have 220k plate resistors and 1,5k catode resistors. Is it correct?
  
 And thank you Coin what you have written let me better picture what is going on.


----------



## Mogos

coinmaster said:


> ........
> 
> Let's say you wanted the plate voltage to 100v @ 5ma.


 
 Yeah. The problem is I don't know what I want 
	

	
	
		
		

		
		
	


	




. According to the 6SN7 data the plate current is max 9 ma. I think we shall not go so high and use 70% of this value


----------



## coinmaster

> In the stock solution for 6SL7 we have 220k plate resistors and 1,5k catode resistors. Is it correct?


 
 Yeah
  


> Yeah. The problem is I don't know what I want
> 
> 
> 
> ...


 
 The tips of the curves show the maximum dissipation points.
  
 You could run the tube at 150v @ 25ma if you wanted, just don't expect the tube to live that long.


----------



## coinmaster

> Yeah. The problem is I don't know what I want


 
 I find myself wondering too. There is a hole in my understanding of tube linearity.
  
 To me it seems like the -24 grid curve is the most linear since it requires almost 100v of change in order for the tube to change a few ma, while the 0v curve changes almost 20ma over the same voltage range. I would think less change in current equals better transfer characteristics, after all it's not current we're amplifying it's voltage.
 I am unclear on what exactly it is that is desired, I haven't been able to find a clear answer.
 I've been going off of the notion that " the more spaced out lines are better" but I'm not seeing the reason behind this. If the grid voltage is fixed then it's going to follow its assigned curve regardless.


----------



## coinmaster

Nevermind, I see my flaw. The grid curves aren't indicative of DC only voltage.
 If you determine the plate resistor value and follow the line like here

 The line shows you the path the signal can follow. The grid curves along the line show how much input signal translates into how much voltage amplification at the bottom. So 10v of input swing would be about 200v of output swing at low current.
 So I guess if the curves aren't evenly spaced out then the output signal will get weird aka distorted.
 I guess that's even more reason to use a CCS because it's more linear across a horizontal line then a diagonal one.
 The increased curviness at the bottom is due to the fact that tubes have a harder time shutting off then turning on. A CCS can avoid that area.
 WoW that clears up a lot actually.


----------



## Maxx134

We don't need 10 milliamps for driver Stage.

This is a small signal input stage therefore Manny linearity points can be chosen.

I have already completed listening tests with real components.

I am waiting for Sonic to follow my lead and tune it for the MK6 because the power tubes make the difference in fine tuning..


----------



## Maxx134

This has proven to be an area that can give you better gains than buying the best tubes


----------



## coinmaster

> We don't need 10 milliamps for driver Stage.


 
 Above 8ma gives the most linearity.
 Not just on the curves but it's also well known that 6SN7 tubes sound better with lots of current.
  


> I have already completed listening tests with real components.


 
 You've tried 6SN7 @ 10ma?


----------



## Maxx134

This is an area not usually covered,
 because choosing an operating point for your driver tubes is a designer decision.


It is actually a fun but tedious thing to do and I'm just waiting for other guys to catch up.

Going there actually is no wrong operating point.
 it depends what you want out of the circuit.

Better linearity can be obtained from stock settings without complexity


----------



## Maxx134

I do not intend to run driver tubes at 10ma


----------



## Maxx134

My goal was finding an operating point of which the majority of tubes would benefit from,
 not just the 6sn7


----------



## coinmaster

> I do not intend to run driver tubes at 10ma


 
  
 Well then you can't really say we don't need it 
	

	
	
		
		

		
			




  
 All facts and claims point to a better sounding tube at higher currents.
 The MK6 can't get passed 1 ma on its own.
 Anything below 8ma is a distortion generator for 6sn7.
  


> My goal was finding an operating point of which the majority of tubes would benefit from,
> not just the 6sn7


 
 Ah okay. I still say just get a wirewound pot if you want to go that route. I hope you aren't using fixed resistors to do it 
	

	
	
		
		

		
		
	


	




 that would take ages.


----------



## Maxx134

It is true that there are if you look at the graph you can make msny lines and choosing the right one that actually sounds the best Within the limits of your PSU and and circuit design is the goal ..

Simply picking a linear point it's not enough,
 because you need to actually listen in combination with the power tubes that you have chosen.

remember we have a input stage which is not a common one, but more like a differential balanced input with s common tail cathode,
so that,
 plus the PSU voltage limits,
 placed limitations on my choices


----------



## Maxx134

coinmaster said:


> > I do not intend to run driver tubes at 10ma
> 
> 
> 
> ...



This is actually incomplete thinking because the stock settings do not give you that much.
Sorry I am unable to elaborate further as I'm leaving from work


----------



## Maxx134

The graph supposed to mostly show second-order Distortion and not actually sound as bad as it looks haha because we have been in the non-linear curve the whole time with these amps haha


----------



## coinmaster

> Simply picking a linear point it's not enough,
> because you need to actually listen in combination with the power tubes that you have chosen.


 
 More reason to use a wirewound pot.
 Also you can't go off of datasheet curves for actual testing because it's not accurate.
  


> This is actually incomplete thinking because the stock settings do not give you that much.


 
 I know I've said that a zillion times  that's not that point though, we do have the ability to bypass the power supply limits in order to get the 10ma of current using a CCS/gyrator.
  


> because we have been in the non-linear curve the whole time with these amps haha


 
 Which makes me wonder why it sounded so damn good..


----------



## Maxx134

I like to give a shout out to publicly thank Redge78 & SonicTrance 
for the help in understanding these graphs properly (designer viewpoint)..

So in tuning my driver Stage for MK8, no one else helped me, 
except maybe my dog haha


----------



## coinmaster

Hey hey hey! I've been belching out information and suggestions on the input stage for weeks!
 Plus we wouldn't even know what the schematic to the amp is without my tedious efforts!
  




  
 Just messin with ya 
	

	
	
		
		

		
		
	


	




 
  
 But no really I've covered everything and then some over the last few weeks along with MrCurwen.
  
 I can understand why people keep asking questions that have already been answered though. Things don't register well when they are gibberish. I find myself going back and rereading things often when I gain a better understanding of things.


----------



## Maxx134

Oh yeah!
 I like to publicly thank *COINMASTER* for the schematic of course!

*HUGE* help..
That goes without saying..

But...

 I didn't use a damn thing about those suggestions in last twenty or so Pages!
 haha!


----------



## coinmaster

> I didn't use the damn thing about those suggestions in last twenty or so Pages!
> haha!


 
 Yet 
	

	
	
		
		

		
		
	


	



  
 Although I did explain in detail the workings of the input stage and all of the available options of modification and the methods behind them and explained how the input stage would react to each of the mods including resistor value changes.
 I think most of it got glazed over by people though 
	

	
	
		
		

		
		
	


	




.


----------



## coinmaster

I'm currently in a position where I can afford to purchase the remaining items required to finally finish my DIY amp build and test all of these mods but I'm torn between amplifier and this baby http://www.ebay.com/itm/Hobie-Mirage-Outback-Kayak-2016-See-Options-For-Available-Colors-/162083826712?
 Tough choice........
 I live at the beach now so..


----------



## Maxx134

I do think the implementation of a CCS to replace our Cathode would be optimal solution in future for better circuit.

I am more an application and test person,
 and that's why I gave thanks to Sonictrance & Redge78 for the graph interpreting,
and so I leave it up to them to explain/disclose it.

I was just impatient and went ahead and did my testing and listening to fine tune my amp before them.

So mogos you will have to wait for SonicTrance to fine tune the MK6.

I still have to solder in the final choice replacement plate/anode resistors!


----------



## Maxx134

coinmaster said:


> I'm currently in a position where I can afford to purchase the remaining items required to finally finish my DIY amp build and test all of these mods but I'm torn between amplifier and this baby http://www.ebay.com/itm/Hobie-Mirage-Outback-Kayak-2016-See-Options-For-Available-Colors-/162083826712?
> Tough choice........
> I live at the beach now so..



Get it for the summer and the sell it in August one month B4 summer ends.
Then you can finish amp after ..


----------



## SonicTrance

coinmaster said:


> > So looking at the plate characteristics chart posted by SonicTrance for me it looks like the red line is showing better operating conditions
> 
> 
> 
> ...


 
   
  
  
 Quote:


coinmaster said:


> Nevermind, I see my flaw. The grid curves aren't indicative of DC only voltage.
> If you determine the plate resistor value and follow the line like here


 
 I drew those load lines. I also stated which Ra values I used to draw them. 35K Ra (red line), 220K Ra (blue line).
  


> Also the B+ of the input stage is 220v not 200v.


 
 Perhaps it is if you measure directly at the rectifier bridge pin. Once it reaches the anode resistors it's not. I measured 190v on the rail when using 6SN7's and 198v using ECC35's. Don't really know why the rail voltage decrease when using 6SN7's though.
  


coinmaster said:


> > I do not intend to run driver tubes at 10ma
> 
> 
> 
> ...


 
 Yes, it can. Look at the chart I posted again. Using the 35K Ra we can easily get above 1mA plate current.
  
 Say we choose to have the grid at -2v, the curve looks good there. We would get about 3.5mA @ 85Va. For this we should use a cathode resistor 286 ohms (2/0,0035*2).

 I have no idea if there's downsides to use such low value cathode resistors though. Again, it needs to be tested to hear how it sounds, as that's what matters in the end, not these damn curves, lol.





  
  


maxx134 said:


> I like to give a shout out to publicly thank Redge78 & SonicTrance
> for the help in understanding these graphs properly (designer viewpoint)..
> 
> So in tuning my driver Stage for MK8, no one else helped me,
> except maybe my dog haha


 
 Thanks Maxx! I'm glad to be of help to you (and your dog) for a change!




  
 Anyways, despite all this talk about 6SN7, my goal for now is to optimize the bias for ECC32 as it's the best tube I've heard in the MK6. Now that I know it's safe to run it as we got the transformer specs.
  
 Here's what the load line using 68K Ra should look like with ECC32:

 The 68K Ra should also work nice with the 6SN7. I agree with Maxx, I would prefer not to have a switch for this. Speaking of switches, I need to install my Ra switch for power stage again, that's top priority now.


----------



## coinmaster

> I drew those load lines. I also stated which Ra values I used to draw them. 35K Ra (red line), 220K Ra (blue line).


 
 I know
  


> Perhaps it is if you measure directly at the rectifier bridge pin. Once it reaches the anode resistors it's not.


 
 Mine always measured 220v before the plate resistors.
  


> Yes, it can. Look at the chart I posted again. Using the 35K Ra we can easily get above 1mA plate current.


 
 I'm the one who originally said that 35k resistor would allow 10ma of current through the 6sn7 many pages ago, that doesn't change the fact reducing the load impedance is a bad way to go about it.


----------



## Maxx134

I need to look over my notes on the Cathode.
I have it at 1030ohm now.
Sonic what is your cathode value for that graph?


----------



## SonicTrance

coinmaster said:


> > I drew those load lines. I also stated which Ra values I used to draw them. 35K Ra (red line), 220K Ra (blue line).
> 
> 
> 
> ...


 
 I wonder why you have 30v more than me? What value are these resistors in your amp?

 Maxx has lower value than me in his amp, and he gets more voltage than I do. But not as much as you get.
  
  
 You can't get 10mA with a 6SN7 using 35K plate resistors in the MK6. Even if you calculate using your 220V you only get 6.3mA on the load line.


----------



## SonicTrance

maxx134 said:


> I need to look over my notes on the Cathode.
> I have it at 1030ohm now.
> Sonic what is your cathode value for that graph?


 
  
 In this chart for 6SN7 I used 286 ohms cathode resistor, but like I said, I don't know the downsides of using such low value.


----------



## Maxx134

Probably without the tube in he got higher voltage


----------



## Maxx134

3k3 resistors are creating a voltage drop to the plate according to the tube


----------



## Maxx134

*Quote :
I don't know the downsides of using such low value.
*
Theoretically the downside would be less effects of having a common Cathode.

This is not exactly a differential circuit because it does not have a negative B- voltage at the cathode, 
But nevertheless should be performing all that a differential circuit supposed to do, which is noise reduction and balancing triodes.

This is a logical circuit input stage for a balanced design.


----------



## Maxx134

Coin master you keep thinking stuck on not lowering the Anode resistor.
You thinking anything less than testbook linearity. 
No such amp in existence. 

Many points in the curves will give positive results because the stock settings are the most non-linear.

The design gets away with it thru finesse. 
Designer tricks.

The fact that we are using a small area of the curves due to small signal stage,
and high Ra of 220k..


----------



## coinmaster

> I wonder why you have 30v more than me? What value are these resistors in your amp?


 
 Not sure, mine were 220k last I measured before I completely ripped the amp apart.
 It's entirely possible that the input stage was not 100% functional at that point when I measured it. The input stage is not regulated so it would be no surprise that the b+ gets dragged down.
  


> You can't get 10mA with a 6SN7 using 35K plate resistors in the MK6. Even if you calculate using your 220V you only get 6.3mA on the load line.


 
 You're right. I was thinking of when I said 7k plate resistor, which is far far worse.
 Now I remember why I said more B+ is unavoidable, even with 4-5x rp resistor value, optimal performance can't be achieved with reasonably high impedances.
  
 I'd love to give an explanation into why higher impedances = more linear amplification but it's all steeped in heavy math that I don't even want to attempt to understand. So far I haven't been able to find a laymens explanation. However it's common fact and is a part of the basics of tube design.
  
 What you guys need to remember is those curves you are plotting off of will change when you lower anode resistance.


----------



## Maxx134

I believe the two 3k3 resistors feeding the input stage from PSU,
are part of a "RC Ripple Filter" set up using the 33uf electrolytics we took out..


----------



## MrCurwen

mogos said:


> I agree that the parallel resistor is not a good solution. It has to be done with switch and two sets of resistors (one for 6SL7 and one for 6SN7). But why you are saying that lowering down the plate resistors will reduce the linearity of the tube. The lower value of the plate resistor shall improve the linearity of the 6SN7 tubes. Right now they are working in the unfavorable conditions. Can somebody explain what is B+ voltage. How it is controled in the mk6 circut?




Setting up a tube one needs to consider the dynamic conditions, meaning signal swing. It's not just a matter of choosing the singular op point (bias current, plate DC voltage). This is why load lines are used.

http://www.head-fi.org/content/type/61/id/1646228/width/500/height/1000/flags/LL

Looking at SonicTrances load lines here, the red one. Let's say the op point (DC conditions) is chosen at -4V grid.

When the grid voltage changes, let's say it moves up to 0V and then the same amount down (from the op point), so -8V.

When you look at how much the plate voltage changed when going up from the op point (plate voltage decreases) and from going down from op point (plate voltage increases).

It's clear that the left side of the load line is longer than the right side. Op point being the middle.

So grid signal swinged +4 and -4 from DC conditions, perfectly symmetrically. Did the plate voltage follow this signal with fidelity? It did not.


Now it could be said that in this application such large swings are not present. It's true. However, one must imagine an infinite amount of grid lines BETWEEN the ones that are printed on the data. They follow the trends that the widely spaced lines indicate.

It's clear, that even if you expect to use +-15V (on the plate) of the load line, around that op point the left side is longer than the right side. I.e. the right side is beginning to bunch up.

Is this meaningful? Is it harmful or not? That's up to you. But this is how load lines function on a rudimentary level.


----------



## Maxx134

In other words the driver PSU was not as bad or "naked" as Coin says haha


----------



## Maxx134

*Quote:
Maxx has lower value than me in his amp, and he gets more voltage than I do. But not as much as you get.*

I have 2k2ohm resistors in the MK8, which is giving me approximately 10 more volts..


----------



## MrCurwen

mogos said:


> Yeah. The problem is I don't know what I want  . According to the 6SN7 data the plate current is max 9 ma. I think we shall not go so high and use 70% of this value




It most surely is not. Where do you get that?

http://www.mif.pg.gda.pl/homepages/frank/sheets/093/6/6SN7GTB.pdf

For DC operation 20mA is the max current, this will have the tube perform for years (provided max dissipation is not exceeded) just fine.

For signal conditions, at 50Hz (vertical sweep duty in a TV) it can do 70mA peak for years. For shorter pulses at 15kHz (horizontal sweep) it can do 300mA.

If you look at page 4 you can see the pulse curves. They show quite the current capability. I believe this is the picture of curves posted earlier in this thread when talking about curves in general. I forget by whom.

6SN7 is not designed to be an audio tube. It was

1) TV sweep tube
2) general purpose

Audio enthusiasts picked it up because it has good curves and is readily available. In audio use it's doing light duty, so don't worry about current. No crazy sweep pulses in your music, I hope. Unless you listen to full blast dubstep.

2C22 was the rugged military version, for small radars to generate sweep pulses. It has even greater current capability (exceeding datasheet specs).


If you have a horizontal load line, 5mA for a +-30 V signal is good for best results. At least with the tubes (russian) I've been using. No distortion at all in a perfectly balanced LTP. Anyway, off topic.


----------



## coinmaster

> In other words the driver PSU was not as bad or "naked" as Coin says haha


 
 Where did you get that idea? The driver psu is nothing other then a simple unregulated RC filter and the B+ is free to be bogged down by the signal as it pleases.
 So yeah, it's pretty bad. 
  
 Here's an old schematic I made of the driver PSU. It's pretty poorly laid out now that know what it is.
 It's a CRCR filter with heater bias thrown in to avoid hum in the input tubes.


----------



## Maxx134

mrcurwen said:


> Setting up a tube one needs to consider the dynamic conditions, meaning signal swing.
> 
> ..



This is what I just pointed out.

Line level signals going to the grid should be no more than 1-2 volts maximum..

This is how the driver stage gets away with sounding good in a non-linear range.
Using only in driver stage with small signal levels.

You are generalizing what I am pointing out.


----------



## coinmaster

> Line level signals going to the grid should be no more than 1-2 volts maximum..


 
 My dac outputs 5v to the grid.


----------



## Maxx134

coinmaster said:


> > In other words the driver PSU was not as bad or "naked" as Coin says haha
> 
> 
> 
> ...



You forgot to add that 33 uf capacitor after the 3k3 resistor...


----------



## coinmaster

Oh yeah, true. So CRCRC with a film bypass on the last c


----------



## Maxx134

coinmaster said:


> > Line level signals going to the grid should be no more than 1-2 volts maximum..
> 
> 
> 
> My dac outputs 5v to the grid.



Did you measure at the Grid,or at the dacs output?


----------



## coinmaster

I did not measure but that is what it says in the dac specifications.


----------



## Maxx134

coinmaster said:


> Oh yeah, true. So CRCRC with a film bypass on the last c


 yep but I'm wondering if an electrolytic was more optimal for that position, as I didn't know what it was doing before. .


----------



## Maxx134

coinmaster said:


> I did not measure but that is what it says in the dac specifications.



Okay so okay so what does 5 volt peak-to-peak equal in RMS haha


----------



## MrCurwen

maxx134 said:


> This is what I just pointed out.
> 
> Line level signals going to the grid should be no more than 1-2 volts maximum..
> 
> ...




I explained the very core of basics how load lines operate, since Mogos and others seem to have some questions regarding that.


Even at small signal levels, looking at the op point(s) under discussion, there is significant bunching. The drawn lines on datasheet are not reliable under 2mA, not at all. Near cut off there are some weird things happening inside the tube.

What sounds 'good' or "not good" is a subjective matter. I don't think I'll be commenting on that anymore. It all depends on what your goals are.


----------



## MrCurwen

maxx134 said:


> yep but I'm wondering if an electrolytic was more optimal for that position, as I didn't know what it was doing before. .




Why do you say that?


----------



## Maxx134

mrcurwen said:


> maxx134 said:
> 
> 
> > yep but I'm wondering if an electrolytic was more optimal for that position, as I didn't know what it was doing before. .
> ...




Because it being an RC Ripple filter,
and electrolytics are best for "ripple current"


----------



## MrCurwen

Regarding "te(s/x)tbook perfection":

It all depends on what you are looking for. Low distortion open loop is not at all the same 'sound' as low distortion with massive NFB. When you get into effects-seeking, yes, some distortions sound nicer than others. But, not HIFI any more by any definition.


----------



## coinmaster

> yep but I'm wondering if an electrolytic was more optimal for that position, as I didn't know what it was doing before. .


 
 Film is the right choice. The film bypass was to filter the high frequencies without needing a bulky film cap. Lytics have a higher impedance at higher frequencies.
  


> Okay so okay so what does 5 volt peak-to-peak equal in RMS haha


 
 I don't know if it is RMS or P2P it just says "output level 5v"
 In either case it's still at least a 5v swing across the load line.


----------



## MrCurwen

maxx134 said:


> Because it being an RC Ripper filter,
> and electrolytics are best for "ripple current"




The last cap is the least involved in ripple rejection. It is however the most involved in delivering (varying) current to the audio circuit. If the audio circuit is not perfectly (forced) balanced, the current draw will vary, and the LAST cap will deliver it. It is COMPLETELY in the signal path.


----------



## Maxx134

mrcurwen said:


> maxx134 said:
> 
> 
> > This is what I just pointed out.
> ...




I can agree here this is where listening tests is very important.


----------



## coinmaster

> The last cap is the least involved in ripple rejection. It is however the most involved in delivering (varying) current to the audio circuit. If the audio circuit is not perfectly (forced) balanced, the current draw will vary, and the LAST cap will deliver it. It is COMPLETELY in the signal path.


 
 Interesting. I was wondering what the point of high frequency filtering was, you're explanation makes more sense.


----------



## Maxx134

mrcurwen said:


> maxx134 said:
> 
> 
> > Because it being an RC Ripper filter,
> ...




I disagree.
 this was an RC ripple filter.
It does exactly what it states it is.

The driver tubes are not taking more than a few milli amp at these settings.

The PSU is capable of delivering 50ma without sweating. 

Regardless, we replaced it with nice larger film caps.



coinmaster said:


> > The last cap is the least involved in ripple rejection. It is however the most involved in delivering (varying) current to the audio circuit. If the audio circuit is not perfectly (forced) balanced, the current draw will vary, and the LAST cap will deliver it. It is COMPLETELY in the signal path.
> 
> 
> 
> Interesting. I was wondering what the point of high frequency filtering was, you're explanation makes more sense.



 I'm not seeing this..


----------



## coinmaster

The current through the input tubes aren't balanced due to spec differences and other things, equal and opposite currents will maintain a voltage but unequal and opposite currents will cause changes in the voltage. A capacitor increases current through it in order to maintain its stored voltage.  A film cap works better throughout the audio frequency range then a lytic does.
 Therefore a film cap will be better at maintaining AC B+ voltage with unequal antiphase currents.
  
 At least that's my understanding of it. So I guess it's still technically a ripple filter unless MrCurwen had a different meaning,


----------



## Maxx134

Two Different issues..
 Quicky delivering B+ is film cap strength,
 and Ripple current is electrolytic strength..
 Two different issues but solved with large enough film capacitor haha.

Yet what you are alluding to is an issue covered by our *DE-COUPLING CAPS*.


----------



## Maxx134

We have large decoupling caps for the power tubes power rail..
Similar for driver tube.


----------



## coinmaster

> two Different issues..
> Quicky delivering B+ is film cap strength,
> and Ripple current is electrolytic strength..
> Two different issues but solved with large enough film capacitor haha.


 
 Not quite, read my above post again.
 I went over a similar phenomenon with the cathode currents of the input stage remember?


----------



## Maxx134

coinmaster said:


> > two Different issues..
> >
> > Quicky delivering B+ is film cap strength,
> >
> ...



Nope don't Remember you post too much to remember haha

It is a decoupling cap


----------



## coinmaster

> Nope don't Remember you post too much to remember haha


 
 That's the problem 
	

	
	
		
		

		
			





 people keep coming to conclusions way after I already stated them. It seems a lot of what I say is skimmed over.


> It is a decoupling cap


 
 It depends on what your idea of a decoupling cap is. A decoupling cap is usually used to shunt unwanted noise into another part of a circuit, so I guess it is a decoupling cap in the same way a capacitor in an RC filter is a decoupling cap.
 But the point is it counteracts the AC voltages caused by uneven currents through the tubes because a film cap has a low impedance a high frequencies.
 Since capacitors don't have perfectly flat impedances across all frequencies the cap is in the signal path.


----------



## coinmaster

Someone needs to man up and make a gyrator.
 The simple one that MrCurwen uses is supposedly a 500k impedance, simulates the same as a 60H inductor, and you can go as high as you want with the plate voltages as long as you leave room for the signal.
 It won't solve the balance problem but it will solve the bias problem.
 I have a working gyrator sitting around but it's pointless since I can't listen to it and I'm forced to deal with design theory until I decide to throw in the cash to finish my amp.
  
 I'll make a guide if someone steps up.


----------



## Maxx134

I want to boost the cathode impedance for circuit benifits of canceling distortion and more control of triode drift.

I am assuming I can use a CCS in place of the cathode, so I can set the bias higher current without lowering the cathode resistance. ..


----------



## coinmaster

A CCS is the closest to ideal the real world has to offer when it comes to high impedance.
 It floats the load line above the nastiness at the bottom of the curves.
 It maintains a set current through the tube no matter the make model or age which means both tubes will be balanced.
 It also means you never have to adjust resistor values again.
 It also has other benefits that go into the mathematics of tube theory and 2/3 power law and stuff that I don't care to understand.
  
 A gyrator is also sort of like a a CCS but instead of producing or sinking a set amount of current it simply resists changes in current. It also poses an extremely high impedance that would not be practical otherwise and it allows you to easily set the plate voltage with a pot all the way up to B+ voltage if you wanted without lowering the impedance.
  
 So basically with the gyrator will allow you to use whatever current/voltage you want while also increasing linearity due to higher impedance and more stable current
 The CCS will also increase linearity on the load line and solve the issue the film cap tries to solve as well as keep both tubes operating the same.
  
 The gyrator is relatively easy to make. The CCS is more complicated due to the need for an extra power supply. Worst case scenario you could use a regulator IC and cheat your way out of that.
 You could use the output stage power supply as a CCS power supply but if you screw something up with the CCS all hell will break loose plus higher voltage mosfets = worse CCS performance usually.


----------



## Mogos

Guys I would like to report back strange behavior of my amp. I decided to run it for few days with the russian new production Tung Sols 6SN7 tubes. I want to do it before I will use an adapter/converter and the 2C22 tubes. I was using the 6SN7 tubes since three days. Till now nothing unusual did happend. I was just turning on the amp and listening to music. Today I have switched off the amp after listening to it for around two hours. I need to go with my doog for a walk. So approximately after 30 minutes I have turned the power on. And there was one pop sound (a little strange different than usual) and .... and nothing happend. The right meter stayed dead. I have trayed two times to switch on the amp. No awaking result. I have changed the tubes for the russian 1579. And it helped to bing it back. Well no idea what was going wrong. After some time I will tray the 6SN7's again. The 1579 are much better than the Ting Sols.


----------



## coinmaster

> I want to do it before I will use an adapter/converter and the 2C22 tubes


 
 Glad you're deciding to test those. From what I've read they blow 6SN7s away in sound. I was thinking of ordering some.


> Till now nothing unusual did happend. I was just turning on the amp and listening to music. Today I have switched off the amp after listening to it for around two hours. I need to go with my doog for a walk. So approximately after 30 minutes I have turned the power on. And there was one pop sound (a little strange different than usual) and .... and nothing happend. The right meter stayed dead. I have trayed two times to switch on the amp. No awaking result. I have changed the tubes for the russian 1579. And it helped to bing it back. Well no idea what was going wrong. After some time I will tray the 6SN7's again. The 1579 are much better than the Ting Sols.


 
 It's difficult to say without testing it with a multimeter.
 The right meter is the one that turns on after a few minutes right?
 It turns on when current flows into B+ so if it is dead that means no current flow. Faulty tube perhaps?
 Did the light turn on?


----------



## Mogos

No light on the right meter. Totaly dead. Now I am lstening to music like nothing happend. Strange, isn't it? Maybe faulty tube I will test with another 6SNt tubes. But not today 
	

	
	
		
		

		
		
	


	




.


----------



## coinmaster

Can't remember what the light was connected to. I think it was B+ and ground. In any case no right meter = no current flow between B- and B+ so it's probably a faulty tube although you might want to make sure there wasn't a condition from your mods that destroyed the tube like a voltage/current spike from something.
 If the light is connected to B+ and ground then something else might be amiss because that means B+ itself wasn't working.


----------



## coinmaster

No wait I remember, the light was connected to the delay capacitor in the delay circuit. So it seems B+ was not switching on.  I have a feeling the 6sn7 may not have been the cause since the delay circuit is isolated from the rest of the amp.
 If the 6sn7 was the cause then it might have been that the output relay tripped which would probably mean a faulty valve but I don't recall any reason why that would prevent the delay capacitor from charging.


----------



## SonicTrance

If the protection circuit kicked in with one tube and not the other it has to be a faulty tube. Just goes to show the quality of these new production tubes
:rolleyes:

I've never had a tube die on me and I only use old stock tubes. I've bought a few that arrived leaky/shorted though.


----------



## coinmaster

Can't seem to find any 2c22 tubes anywhere, at least not many. Mogos did you find any? They seem to be rare.


----------



## SonicTrance

coinmaster said:


> Can't seem to find any 2c22 tubes anywhere, at least not many. Mogos did you find any? They seem to be rare.


 
 Here you go:
 http://www.ebay.com/itm/10-coppie-7193-2C22-Ken-Rad-triodo-anno-1942-made-in-USA-tube-valve-Valvula-/272239668439?hash=item3f62bfacd7:g:bOoAAOSwgkRVSOMV
  
 Or you can buy China made Shuguangs, seems to be the only alternative on ebay if you want more than a pair.


----------



## Maxx134

mogos said:


> Guys I would like to report back strange behavior of my amp. I decided to run it for few days with the russian new production Tung Sols 6SN7 tubes. I want to do it before I will use an adapter/converter and the 2C22 tubes. I was using the 6SN7 tubes since three days. Till now nothing unusual did happend. I was just turning on the amp and listening to music. Today I have switched off the amp after listening to it for around two hours. I need to go with my doog for a walk. So approximately after 30 minutes I have turned the power on. And there was one pop sound (a little strange different than usual) and .... and nothing happend. The right meter stayed dead. I have trayed two times to switch on the amp. No awaking result. I have changed the tubes for the russian 1579. And it helped to bing it back. Well no idea what was going wrong. After some time I will tray the 6SN7's again. The 1579 are much better than the Ting Sols.



The sound was your relay kicking in, triggered by the protection circuit,
Because of your garbage "New Production" tubes. ..

Throw them out, or better yet out your window to hear a nice crash.

For the tube to trigger the protection, it has to have a near dead short.

Do not buy new production tubes of any kind ever again,
 or I will throw my pretty Chinese tube at you.


----------



## Maxx134

Looking for 1579 tube all I see is 6n9s tubes...


----------



## Mogos

Yes it is tube from the family: 6C8G 5691 6SL7 6N9P 6H9C ecc35.
 Maxx don't say that all new production tubes are bad. You are breaking my heart. There are some manufacturers worth to give them a tray 
	

	
	
		
		

		
			





.


----------



## coinmaster

Maxx have you tried the 6ax7 tubes? I need a high gain signal tube.


> Or you can buy China made Shuguangs, seems to be the only alternative on ebay if you want more than a pair.


 
 Can you point me to an example? I don't see them.


----------



## SonicTrance

mogos said:


> Yes it is tube from the family: 6C8G 5691 6SL7 6N9P 6H9C ecc35.
> Maxx don't say that all new production tubes are bad. You are barking my heart. There are some manufacturers worth to give them a tray
> 
> 
> ...


 
 6C8G is in a family of its own. Very different from the 6SL7.
  


coinmaster said:


> Maxx have you tried the 6ax7 tubes? I need a high gain signal tube.
> 
> 
> > Or you can buy China made Shuguangs, seems to be the only alternative on ebay if you want more than a pair.
> ...


 
 http://www.ebay.com/itm/2pc-NOS-Shuguang-Tube-6C8P-6C8C-2C22-7193-/191553524632?hash=item2c997ad398:g:q-IAAOSwBLlVI9uM


----------



## coinmaster

> http://www.ebay.com/itm/2pc-NOS-Shuguang-Tube-6C8P-6C8C-2C22-7193-/191553524632?hash=item2c997ad398:g:q-IAAOSwBLlVI9uM


 
 Those are *6C8P *and they have garbage linearity.


----------



## SonicTrance

coinmaster said:


> > http://www.ebay.com/itm/2pc-NOS-Shuguang-Tube-6C8P-6C8C-2C22-7193-/191553524632?hash=item2c997ad398:g:q-IAAOSwBLlVI9uM
> 
> 
> 
> Those are *6C8P *and they have garbage linearity.


 
 Get the Ken-Rads I linked then!




  
 Search for 7193, you'll get more hits.


----------



## coinmaster

I'll probably get the ken rads, I'm still wondering if I should just go with a 4P1L input tube instead. People say that the 6c22 tubes are the closest thing to DHT in sound from a IDT but then again a 4P1L is the most linear DHT. Hmmmmmmm.


----------



## Mogos

sonictrance said:


> 6C8G is in a family of its own. Very different from the 6SL7.


 
 Please don't listen to me. As I am like child in the fog. I will stop writing any kind of technical statements. Sorry for causing a stir 
	

	
	
		
		

		
		
	


	




. I have drawn the conclusion about the family just looking at the listing from the seller 
	

	
	
		
		

		
		
	


	




. Thank you SonicTrance for your vigilance.


----------



## Maxx134

sonictrance said:


> Get the Ken-Rads I linked then!
> 
> 
> Search for 7193, you'll get more hits.



I have noticed that the single triode tubes are really good maybe the best,
 but our amp uses dual triode,
so I get fooled many times when I see a link for really good tube,
 and then find out is not a dual triod..


Anyways, I never tried the 6ax7 tube but my mind is set on rolling larger tubes for now..


----------



## Maxx134

mogos said:


> Yes it is tube from the family: 6C8G 5691 6SL7 6N9P 6H9C ecc35.
> 
> Maxx don't say that all new production tubes are bad. You are breaking my heart. There are some manufacturers worth to give them a tray
> .



Yeah I was kidding as I actually really like my ShuGuang "50years Treasures" a lot. 
It's just some brands don't last ..


----------



## SonicTrance

maxx134 said:


> sonictrance said:
> 
> 
> > coinmaster said:
> ...


 
 Yeah, I don't know. Dual triodes sounds pretty damn good to me. I have done zero research on single triodes though. I've read people using the 6J5G/GT's with good results, which is also half of a 6SN7.


----------



## coinmaster

I've seen many people on different sides of the internet that say the same thing.
 They say that 2c22/7193 tubes are better then 6sn7 by a lot but DHT tubes are way better then 2c22/7193.
  
 Quite a few of them have the same story too. They say that they started out with 6sn7 tubes and then after trying 2c22/7193 tubes they were amazed and then after trying DHT tubes they never used the 2c22/7193 anymore.
  
 I guess DHT is the way to go...but I'm stuck with the 10 7193s I just blew 200 bucks on


----------



## coinmaster

So I just found out why changing the capacitor 300uf bypass capacitor in the power supply offers such a huge upgrade.
  
 After fiddling in LTspice trying to create an all-in-one prototyping power supply I realized that the amplifier draws its signal current from the last capacitor in the power supply, like all of it.
  
 If you remove the 300uf cap the current would be drawn from the 1200uf cap and would be subject to the frequency response of the regulator.
 So in other words the 300uf cap is 100% in the signal path. This would explain the massive increase in bass quality and quantity among other things I experienced after upgrading to super low ESR MKP caps in that area.
  
 So in other words the 300uf cap should be as high quality as possible because all of the signal travels into and out of them.


----------



## coinmaster

After deciding to not use the "decoupling" mod in my amp rebuild I started to wonder about it.
 What does it really do? It certainly doesn't "decouple" anything maybe other then decoupling stray signal on the B+/B-.
 Decoupling is used to shunt a signal into another part of a circuit.
  
 When I implemented the decoupling mod with industrial film caps there were two things I noticed.
 The sound got a little faster and less slurred and it also got a lot more distance and less intimate.
 It was like on stage vs in the middle of the crowd.
  
 The 300uf bypass cap in the power supply is where the audio signal current comes from, all of the transients and everything are handled by that cap.
 I suspect that since the "decoupling" cap was so close to the tube pins vs the 300uf bypass cap replacement it was acting as an extension of the bypass cap. The bypass cap is far enough away for inductance to interfere but I'm pretty sure the .22uf red caps are there to help counteract that.
  
 In any case I simulated the distortion with the "decoupling" caps in place and this is what I got
   


 Seems legit.


----------



## MrCurwen

maxx134 said:


> I disagree.
> this was an RC ripple filter.
> It does exactly what it states it is.




Sure, because it is on the B+ rail, no matter what position, it technically does contribute to ripple filtering. Every cap that is on the rail does.

However, like I said, the cap cap contributes the LEAST amount to ripple filtering. It is not important in the ripple filtering.

It is highly important in the signal current delivery business.

When your audio circuit needs current, it comes from the last filter cap. If that cap is not good at delivering it fast enough, and with good enough accuracy, you will be able to hear it.

That's the point of making the last cap a film cap.

Also there's oscillation prevention. At least one cap in the PSU (if you have a reg, one before the reg and one (the only one) after the reg) should be a film cap for stability reasons.

Electrolytics don't do oscillation prevention well, or at all in most cases I've found.

So, these are the two reasons for making the last cap in a retro type circuit such as under discussion, a film cap. Delivering current to audio circuit and stability.




> The driver tubes are not taking more than a few milli amp at these settings.




By that logic, calculate the currents that go around in the coupling circuit current paths (between input stage and output stage grid). Tell me again does the component quality there matter at all and why does it matter or not matter?


It's not the amount of current asked; if the electrolytic cap cannot physically deliver the sharp corner of a transient waveform, it cannot, no matter if 400µA or 40mA.


Once again we come back to circuit design. EVERYTHING is in the signal path that isn't behind a 100% NFB loop (regs, gyrators, CCSs etc.). I've gone thru this in this thread, if interested read those messages again.




> The PSU is capable of delivering 50ma without sweating.




At what speed? At what output impedance?

By the same logic, any 50 cent polyester cap is capable of delivering a "correct" waveform thru it; however you don't seem to want to use those for coupling between stages.

Both of those PSUs have - in my personal opinion as a designer and builder - quite poor and unimpressive performance. I wouldn't say they deliver anything without sweating.

Ask that PSU to deliver a +-25 mA square wave and see what happens to the rail voltage. 



> I'm not seeing this..




Okay, so you do understand that not-fully-balanced circuits draw varying amounts of current from the PSU, right? We've talked around this in this thread a number of times. Your circuit is not fully balanced, it does just this.

What delivers that current?

It is the last cap. Then the caps before that try to refill the last cap thru later on. This kind of a system has a fluctuating voltage; some of the audio signal 'rides' on the rail voltage.

Where else would the current come from? I don't get it, please explain.

How could the last cap NOT be in the signal path?

Well, if the audio circuit draws the exact same amount of current at all times, then it certainly is not. But that's not applicable to your amps.


----------



## MrCurwen

I don't know what these special decoupling caps are. Post a legible version of the schem (I posted one earlier but I don't have it at hand anymore) and refer to the part names.

If they are the 220nF or so caps between rail and ground, those are for stability. They don't deliver much of anything under about 10 or 15 kHz.

Offtopic but as an example I personally use one 4µF 400V MBGO film cap (hermetically sealed waxed paper) after each B+ reg. I place it as close as possible to the circuit parts that the B+ rail in question is feeding. This is not important for audio, but for the megaherz range it can be important, i.e. stability reasons, oscillation prevention. For audio it doesn't matter at all where you place it.


----------



## MrCurwen

General theory for general understanding of circuit operation, figure out application yourself;

If you put a decent at least somewhat strong regulator between the last filter cap and an audio circuit that draws varying current, then the quality of the last cap is not important or audible in any way, even though it still does deliver the varying current to the circuit.

The 100% NFB loop in the reg (with an error amp, so at least 2 FET) makes all the difference. If there's enough brute force inside the loop, it can "eat away" all of the stuff preceding the reg (the raw PSU).

Indicated by electronics theory, and confirmed by DIY builders around the world. No brainer.


The voltage setter in your B+ and B- rails is a single device system. It doesn't have an error amp to increase the force of the NFB loop. It mostly tries to keep the voltage steady at DC.


----------



## MrCurwen

sonictrance said:


> Here you go:
> http://www.ebay.com/itm/10-coppie-7193-2C22-Ken-Rad-triodo-anno-1942-made-in-USA-tube-valve-Valvula-/272239668439?hash=item3f62bfacd7:g:bOoAAOSwgkRVSOMV
> 
> Or you can buy China made Shuguangs, seems to be the only alternative on ebay if you want more than a pair.




Apparently the Chinese tubes are not equivivalent as stated earlier by someone. Hadn't heard of them myself.

However, even if they were, the point of the 2C22 being a good tube is that it's special quality for military service, making radar sweep pulses. (JAN, Joint Army Navy second WW)

I doubt any chinese these days go thru the kind of quality control the JAN contractors had to go thru.


Well well well, it seems the larger circles have found this tube. When I got mine they were only a fraction of these prices. I haven't paid that much for all my 2C22/7193 combined, and I've got maybe 35 pieces I forget the exact amount. The last batch I bought were 25 pieces for something like 30 euros with delivery. 

Haven't bought them for a long while now though. 

That's the thing, if want to buy good quality stuff for cheap, you need to know what you're doing, and not care about other people's consensus opinions. Then when everybody else catches on, you've got your stash.


2C26A is a bit higher anode resistance, but just as linear by my tests. They do have a very high heater current which might make them hard to use for headphones. Shame. I've got 12 of them, and they sound excellent, but I couldn't shake off the 100Hz heater hum, and going regulated with that high current is a pain, a hot pain.


There's still some first class catches to be found, mostly in the Russian tubes. I've mentioned some here, though I probably shouldn't have. Not very DIY oriented forum, so probably safe though. Either take risks and know how to read datasheets (even in russian... I got the hang of the important words after a while), or spend a lot of stupid money buying audiophile approved tubes.


----------



## Maxx134

*So in other words the 300uf cap should be as high quality as possible because all of the signal travels into and out of them.
*
OMG...
Why are you acting as if you never read first page?
Read it again .
You are late to the party to discover this and it is certainly why we using film cap decoupling mod to supplement and "decouple" the tube dependance to the PSU.


*After deciding to not use the "decoupling" mod in my amp rebuild I started to wonder about it.
What does it really do? It certainly doesn't "decouple" anything*
Again you need to refresh by reading what we are doing.
What is going on with "Decoupling"
exactly described on first page.
Don't waste time trying explain away things already explained and verified. 

Furthermore, I remember that "Decoupling" has been used in past by top amps in long winded stereofile reviews I used to read many years ago.
They also placed Cap banks right by the output transistors for transient speed.

You decided whatever you want.
This what happens when you teach yourself . 
You can do it your way.
It doesn't mean your right when your wrong.





coinmaster said:


> In any case I simulated the distortion with the "decoupling" caps in place and this is what I got
> 
> 
> 
> ...



The legitimacy of your posts seem to have gone down by 12381.193822%..!!! 
Lol!

In any case, I have posted an article and there should be another one in first page on calculating "layers" of decoupling as there are some issues of ringing to neutralize. 

Redge78 will also come out with a refinement of that mod.

I am currently enjoying superior sound on my new bias settings.
This mod will be as good as buying the best tube.

The sound is upgraded in Every possible 
Way, as I am out of the non-linear range with no drawbacks. 
I also increased voltage average of 14v (depending on tube) by decreasing the RC filter resistor to 1k and still have over 25db ripple attenuation. 

Anyways still "real world" testing and waiting on resistors for tuning last settings on the driver tubes, 
But it has been very promising and will be a major mod!


----------



## Maxx134

mrcurwen said:


> maxx134 said:
> 
> 
> > I disagree.
> ...



Thanks for explaining,
And also why we need the "Decoupling caps"
Coinmaster, listen to him


----------



## Maxx134

mrcurwen said:


> General theory for general understanding of circuit operation, figure out application yourself;
> 
> If you put a decent at least somewhat strong regulator between the last filter cap and an audio circuit that draws varying current, then the quality of the last cap is not important or audible in any way, even though it still does deliver the varying current to the circuit.
> 
> ...




I like this regulator idea


----------



## coinmaster

> OMG...
> Why are you acting as if you never read first page?


 
 Probably cuz I haven't since the thread was made and I knew not what I was doing.
 This is my reaction when people keep asking questions and coming to conclusions that MrCurwen and I already discussed.
  


> The legitimacy of your posts seem to have gone down by 12381.193822%..!!!
> Lol!


 
 Why am I not surprised you took that seriously 
	

	
	
		
		

		
		
	


	



  


> And also why we need the "Decoupling caps"
> Coinmaster, listen to him


 
 I see nothing in the first page that explains what they are decoupling. For the purpose stated on the first page they should be connected to ground and considered bypass caps because what you explained is the same job as the bypass cap.
 What's the point in decoupling the B+/B- rails? All it does is average together the signals on the B+ B- rail which probably increases distortion.


----------



## MrCurwen

maxx134 said:


> Thanks for explaining,
> And also why we need the "Decoupling caps"
> Coinmaster, listen to him




You're welcome!

Terminology can be confusing. A cap in a certain place can act as a 

1) ripple filter
2) decoupling cap
2a) decoupling megaherz oscillations 
2b) decoupling voltage drops caused by PSU output impedance delivering current to audio circuit

Some of these functions in that specific spot are incidental but beneficial, some are highly necessary. The cap itself doesn't know what it is supposed to do, the circuit designer must know.


A cheaper and sonically more pleasant option for a large film cap is to have CAPS OF POOR QUALITY in the PSU, and then a simple reg with decent output impedance, and then a single film cap, maybe 1 to 5 µF to prevent oscillation. I use 4µF as I mentioned. Cheapest, and best of all worlds.

I'll draw an example of a simple reg later today.


Coinmaster and myself have agreed (on his suggestion) to not interact. I don't know why he doesn't honor that agreement.


----------



## coinmaster

> Coinmaster and myself have agreed (on his suggestion) to not interact.


 
 Whoa whoa dude, when did this happen?
 I simply recall saying that if you don't like me there is no need to respond to my messages.
 I have no beef with you, I don't take the internet seriously. It's all in good fun.


----------



## MrCurwen

maxx134 said:


> This what happens when you teach yourself .
> You can do it your way.
> It doesn't mean your right when your wrong.




I don't know if you mean 'you' as in passive, when somebody teaches themselves, or 'you' as in the specific person in question.

Teaching yourself things in general is a very good thing to do.

I've got a couple of years of university training in electronic engineering, and I've been reading the largest and best DIY tube audio forum for maybe 10 years, I've even posted some 600 messages, most of which in the early times were very stupid questions.

The expertise and innovation available there are of such quality (if you know how to seek them out and talk to them among all the LET'S BUILD A 2A3 AMP threads) that it's kind of like a "tube university" of sorts.

But, like in all things, in the end it's you yourself who has to teach yourself things. The most important thing is to have a humble and respectful attitude; both to the craft itself, laws of nature and people helping you. When somebody has something you want, you don't get to make the rules. This is true in every thing in life, tube audio not excluded.

I didn't come by my original schems in a few months, it took years of building the retro stuff and really understanding what goes on inside them. I still don't understand everything, like the Schade thing and some others. But I've got the basics covered.

The person you are referring to is by his own words not at all interested in doing things I described above. So, in that regard, you are correct I believe.



> The legitimacy of your posts seem to have gone down by 12381.193822%..!!!
> Lol!




I find it disturbing that somebody didn't make this comment when in this thread were described (multiple times) how current flows from negative to posive and how plate loads "sink current". Or when CCS tailed LTPs cause varying current draw from PSU. Or when CCS tails were multiple times referred to as affecting the load lines of tubes above it. Or when decoupling caps increase distortion ...


I really from the bottom of my heart believe general electronics and tube theory is always useful if not directly applicable to some situation at hand. "Trying things out" didn't get me anywhere, but making educated guesses and design risks based on theory really has.


----------



## coinmaster

> > The legitimacy of your posts seem to have gone down by 12381.193822%..!!!
> > Lol!
> 
> 
> ...


 




 Looks like someone is finally warming up to responding to me directly!
 For starters current does flow from negative to positive, you get so mad when people adopt true current rather then conventional current 
	

	
	
		
		

		
		
	


	



 I never said plates sink current (but you obviously did since you cling to conventional current for dear life).
 I never said CCS tails draw varying current (why would they do that).
 I never said CCS tails affect load lines (other then making it horizontal).
  
 Damn dude did you even read? lol
  
 I'll give you that I could be wrong on the "decoupling cap" mod because I still don't see the point in close proximity decoupling between B+ and B-, the only "decoupling" there that I see is going to be the rail signal.


----------



## MrCurwen

About keeping the rail voltages regulated i.e. stable in AC signal current draw conditions;

Somebody has a white screen of canvas and a laser pointer. He is moving the laser pointer light up and down on the canvas. You are supposed to follow that light as closely as possible jumping up and down with your feet.

Now imagine you doing this in a small row boat on the lake. (Don't jump in a boat it's dangerous folks.) How well are you going to be able to follow the light signal? Not well at all, because the boat, your reference point, is floating up and down.

Not imagine doing the same thing on a waterbed. Maybe a bit better, still not very good, because reference point is moving again.

Now if your reference point is steady, like a concrete floor, you can do this task much better.


If your B+ is fluctuating with the signal... Figure out the rest.

The signal itself is the ONLY THING that is supposed to move the op point of the tube. If at the same time the signal and some other thing (such as a poorly regulated PSU with high output impedance) are moving the point of the tube... The signal will not be reproduced 100% or even close.

Now these are very small effects you are talking about, I hear some saying. True. 1950's designers were not at all concerned with any of this.

However, the effect of PSU output impedance on overall fidelity in signal reproduction is several orders of magnitude higher than any coupling caps or such. When talking HIGH FIDELITY we are in fact focusing on fringe issues.


----------



## coinmaster

> About keeping the rail voltages regulated i.e. stable in AC signal current draw conditions;
> 
> Somebody has a white screen of canvas and a laser pointer. He is moving the laser pointer light up and down on the canvas. You are supposed to follow that light as closely as possible jumping up and down with your feet.
> 
> ...


 
 Which is why I question the "decoupling" mod.
 The cathode of the WCF probably acts like a terrible cathode follower in terms of signal reproduction especially considering the 330 ohm load posed to it.
 So when you "decouple" B+ and B- you average the waveforms.
 At least without the decoupling cap the rail reference is in line with the output signal but if you average the B+ and B- signals it probably gets weird. Sort of like moving the boat side to side as well as up and down.


----------



## Maxx134

coinmaster said:


> > > The legitimacy of your posts seem to have gone down by 12381.193822%..!!!
> > >
> > > Lol!
> >
> ...



Lolo loll! !!!!
OMG that is so funny! Look!
That facial reaction!
I can see that happen to you!
Lol.

Edit :
Sorry dude I couldn't help repost it.
But I couldn't stop laughing looking at that ..
Edit2:
I forgot to add 5% more to above figure for your last subsequent posts!


----------



## Maxx134

mrcurwen said:


> Terminology can be confusing. A cap in a certain place can act as a
> 
> 1) ripple filter
> 2) decoupling cap
> ...



Really good point!
There are multiple things going on here. 

Edit the oscillations is also an important issue...


----------



## MrCurwen

maxx134 said:


> I like this regulator idea




Here's an example schem taken from instructions to one man I correspond with. 



Zener string D5 & D6 determine output voltage. For 100V output I'd start out with a 75V zener and add 9V zeners until close enough.

Use 0.5W zeners. They operate more stable (i.e. closer to spec'd voltage) under current starving conditions than higher wattage. The zener string takes up under 1mA.

The protection zeners should be directly on the pins and before any stopper resistors. 

This reg needs about 10V headroom to operate, 15 to 25 volts recommended for best results.

If best possible ripple rejection is needed, feed top of R4 from a separate feed; take raw B+ and put an RC branch from it, use that. I've tried this out, but never used it since. No ripple in B+ anyway, so not needed. 

IRF820 / 830 give something like 15 ohm output impedance across entire audio range. Improves transient response in SE circuits especially. In your amps, the amount of improvement is contingent on how unbalanced they happen to be. If some of you were able to hear improvements by changing the last PSU cap to film, then I'd guess you would probably hear some improvement with this reg.


----------



## coinmaster

maxx134 said:


> Edit :
> Sorry dude I couldn't help repost it.


 
 I love how you edited out the important bits.
  


> I forgot to add 5% more to above figure for your last subsequent posts!


 
 You sound desperate.
 The pettiness from you and MrCurwen is gut wrenching.
 For starters Mrcurwen is as bad as you at reading comprehension since he claimed I said all this stuff I did not.
 If you think I am wrong about something state it and give reasoning 
	

	
	
		
		

		
		
	


	




.
 So far my logic about the decoupling cap seems to be sound. If you know something I don't let's hear it.


----------



## Maxx134

coinmaster said:


> maxx134 said:
> 
> 
> > Edit :
> ...




Hey it was your pic.
I don't meant to offend.
Just trying to lighten the subject.

If you want serious discussion then fine but you are the one not reading,
as MrCurwen already posted info to help understand and I already told you the Decoupling info is on first page.

I realize you may think/solve/understand differently,
So you take the word "Decoupling" differently..

So this crazy percentage you came up with must have to do with something you found that you believe will be a factor.

The problem is you need to stop focus on the word and explain what it is this percentage, which could be any type of measurement/result. 

Maybe your trying to explain why there is a sonic difference with the film caps?


----------



## coinmaster

> If you want serious discussion then fine but you are the one not reading,


 
 I read everything carefully.
  
 Quote:


> MrCurwen already posted info to help understand and I already told you the Decoupling info is on first page.


 
 I read Mrcurwens info and the explanation on the first page states the same operating as the bypass cap.
 Still don't see the point in decoupling B+ and B-. Especially due to the reason I posted earlier. Seems to make more sense just to ground it.
  

  


> So this crazy percentage you came up with must have to do with something you found that you believe will be a factor.


 
 That crazy percentage was a joke. I thought that was pretty obvious.
 LTspice likes to bug out sometimes when it comes to distortion analysis.
  
 My problem with the decoupling mod is posted near the top of this page.


----------



## SonicTrance

mrcurwen said:


> However, even if they were, the point of the 2C22 being a good tube is that it's special quality for military service, making radar sweep pulses. (JAN, Joint Army Navy second WW)
> 
> I doubt any chinese these days go thru the kind of quality control the JAN contractors had to go thru.


 
 There's lots of military JAN 6SN7's also, most are branded VT-231. Can't say they sound better than the non-JAN tubes from same manufacturer though. I've also heard 5998's and 6F8G(VT-99) both JAN and non-JAN, without being able to tell the difference. So, JAN branded tubes doesn't mean they will sound better.
  
 And yes, I don't think those Shuguangs are very reliable, though they are sold as NOS so not new production.


----------



## Maxx134

coinmaster said:


> > MrCurwen already posted info to help understand and I already told you the Decoupling info is on first page.
> 
> 
> 
> ...



OK then .
There are many things going on in the circuit. 
We are not decoupling the B+ & B- rail.
We decoupling the tubes and using the caps as a fast transient delivery of power for tube.

You can't put the cap on the tube plate. 
So you place it on top the Anode resistor. 

You are thinking something else of another issue if you don't understand what was posted on first page.

Your problem with decoupling stems from not looking at the schematic the way it is posted on first page.
Edit :
To clarify , it's not that you didn't see it,
But I notice your schematics are circular, 
Whereas normally it would be up and down, right and left. ..
This may alude to your thinking more "outside the box"..


----------



## Maxx134

coinmaster said:


> When I implemented the decoupling mod with industrial film caps there were two things I noticed.
> The sound got a little faster and less slurred and it also got a lot more distance and less intimate.
> It was like on stage vs in the middle of the crowd.



I will try to be helpful now..

I have noticed this occurance before,
But it was when I was testing tube parameter changes of bias and Ra and voltage changes...

Edit:
Sorry for the edits haha.
Anyways my point is once coin master bias testing commences that will be an observation


----------



## coinmaster

> We are not decoupling the B+ & B- rail.


 
 But we are though.
 It's connected between B+ and B- at the load resistors.
 This means it will be decoupling the signals on the power rails.
 The cathode of the WCF is effectively a really bad cathode follower so if you mix that signal with the anode signal the voltage references get distorted, probably with higher order harmonics. If you refer to MrCurwens analogy of the white board and the boat this would be like moving side to side as well as up and down.
  
 That's the way I see it anyway, it is logical.
 I don't doubt that it gives better transients, I myself heard this, but it seems to just be an extension of the bypass cap in performance and I did hear a vivid "distancing" of the music which was not pleasing. (non pleasing distortions are usually high harmonics and look ugly on oscilloscope.)

  


> You can't put the cap on the tube plate.
> So you place it on top the Anode resistor.


 
 Yeah I know, but 330 ohms doesn't pose much of an impedance to the signal and the regulator doesn't regulate AC. Refer to MrCurwens white board and boat analogy.
  


> But it was when I was testing tube parameter changes of bias and Ra and voltage changes...


 
 Maybe it's the same possible high order harmonics I was referring to before.


----------



## Maxx134

Sorry, but Just because I haven't looked at this thread in a day doesn't mean your right.
Your wrong again.
Sorry I will try explain tomorrow


----------



## Maxx134

1-No signal on power rails
2-signal is on plate from volt drop of anode resistor. 
3-the "white cathode follower " needs to be looked at as a whole, TWO TRIODES, ONE TUBE, ONE DECOUPLING CAP BANK PER TUBE.
4- multiple issues going on
5- I not able to explain now but I just post how it should be viewed.

Edit :
Forgot to point out that we need remember this is OTL and output not going into transformers, which is a parameter considered in having 300 ohm anode resistors


----------



## coinmaster

> No signal on power rails


 
 Yes there is, the question is how much.
  


> the "white cathode follower " needs to be looked at as a whole, TWO TRIODES, ONE TUBE, ONE DECOUPLING CAP BANK PER TUBE.


 
 I'm aware of how a WCF works.

  


> Forgot to point out that we need remember this is OTL and output not going into transformers, which is a parameter considered in having 300 ohm anode resistors


 
 The fact they are so low is my point. They are low because there needs to be signal attentuation in order for the WCF to work. Some of the signal is shunted into the rails.
 The regulator does not regulate AC so it depends on how well the 300uf cap regulates.


----------



## MrCurwen

sonictrance said:


> There's lots of military JAN 6SN7's also, most are branded VT-231. Can't say they sound better than the non-JAN tubes from same manufacturer though. I've also heard 5998's and 6F8G(VT-99) both JAN and non-JAN, without being able to tell the difference. So, JAN branded tubes doesn't mean they will sound better.
> 
> And yes, I don't think those Shuguangs are very reliable, though they are sold as NOS so not new production.




Yes I agree. Let me clarify;

Comparing the same type between JAN and civilian, you are not likely to get any linearity benefits. You could get longevity benefits.

However, as far as I know 2C22 was specifically designed for military (and later industrial) applications. It is not 100% eq with 6SN7. It has a much larger linear area - larger than the printed curves imply, by my tests both visual and audio.

One does not simply make a tube with a larger linear area (and keep µ same, rp a bit lower). It is difficult, and requires more rigorous quality control. It is a different, more difficult to manufacture tube type.

In manual labour manufacturing you need better workers to man that line, you need to disqualify more units etc.

As discussed earlier, tube linearity is mostly contingent on electrode geometry, for example grid pitch and distance of grid from cathode, is the cathode 100.0% perfectly in the middle of the two anode sides, are the anode sides pressed together symmetrically etc.

You can make a tube more rugged, meaning it will last longer, or withstand more vibration or heat, without making it more linear. These are separate (not completely, but large parts) manufacturing concerns.

Most JAN types were made to be more rugged, some were completely same as civilian, but ordered in bulk batches for military. Some types were designed specifically for military purposes, some with extraordinary qualities. 

There's this french guy on youtube who has a lab where he manufactures his own tube types from materials. Wonderful stuff, very exciting! But on his website the curves he traces are quite ... not-HIFI to be polite. It's quite the task to make an actually linear tube by hand. No offense to the chinese, but the best of the best in tube manufacturing might still be out of their league. Or perhaps not, but these are my guesses.

Simply looking at the amount of resources available; the worldwide new tube market wouldn't cover even 10% of the training budget of a single major tube manufacturer in USA back in the 50's. The expertise doesn't just appear out of thin air, it takes a pool of people and money and effort, not justified by current market conditions (by my guesses).


----------



## MrCurwen

coinmaster said:


> I love how you edited out the important bits.
> 
> You sound desperate.
> The pettiness from you and MrCurwen is gut wrenching.
> ...




There is no need to give serious detailed responses to person using childish pictures, rolling eyes like a teenage girl and saying things like somebody is a miserable person. This is not 4chan or reddit and acting like a brat is not "how the internet is", it's how you are. 

The way you write and communicate is a signal as to how good your amp is going to be. As of now, it's garbage. Why should anyone serious help you.

If you think CCS tails make tube load lines horizontal in an LTP, you haven't grasped even the beginner basics of tube operation and basic topologies. Not an 'oopsie' level mistake, fundamental mistake.


Normal, adult respectful behavior is not an unreasonable request. Plenty of people of our age manage it, for example everyone I correspond with about electronics.


----------



## MrCurwen

maxx134 said:


> The problem is you need to stop focus on the word and explain what it is this percentage, which could be any type of measurement/result.




The LTSpice inbuilt THD measurement tool compares the output point (given as a parameter on the .four line) to the AC signal generator output (amp input in sim). If the output point is correct, it gives an estimate of the THD correctly.

However, if the output node is wrong, you get very strange results. It could be a node with an AC signal that is not related to the audio signal or even DC (which will surely give a very high number if I recall correctly). 

So a simple typo can get you 12k % THD from that tool. If properly set up, it can be a useful tool.


----------



## coinmaster

> There is no need to give serious detailed responses to person using childish pictures


 
 I don't think you're the one to be talking about being childish.
  


> saying things like somebody is a miserable person


 
 If you get upset over petty matters then you are more then likely a miserable person. 
  


> This is not 4chan or reddit and acting like a brat is not "how the internet is", it's how you are.


 
 You still don't get it 
	

	
	
		
		

		
			





 I'm amazed at the ignorance. It's not about "acting like a brat" It's about not taking everything seriously like a life and death matter. Aside from the fact it's the *internet, *if you don't understand what I mean by that then you should probably continue to stay within the boundaries of diyaudio.cm and head-fi.com.

  


> If you think CCS tails make tube load lines horizontal in an LTP, you haven't grasped even the beginner basics of tube operation and basic topologies. Not an 'oopsie' level mistake, fundamental mistake


 
 I never once said the CCS tail makes load line horizontal in a LTP. I went out of my way to say that it wouldn't. Reading helps.
 I was talking about individual CCS for each triode. I went over that like 4 times.
  


> Normal, adult respectful behavior is not an unreasonable request. Plenty of people of our age manage it, for example everyone I correspond with about electronics.


 
 Yes and 99% of them are 50+ years old with no sense of humor. One day you might understand how to lighten up 
	

	
	
		
		

		
		
	


	




.


----------



## MrCurwen

maxx134 said:


> 1-No signal on power rails




Correct, with an ideal PSU feeding the circuit, with 0 ohms output impedance.

With the PSU you have there, there is signal riding on the rails as I've explained. Ohm's law; where there is impedance and current drawn thru the impedance, there is voltage drop. 




> 3-the "white cathode follower " needs to be looked at as a whole, TWO TRIODES, ONE TUBE, ONE DECOUPLING CAP BANK PER TUBE.




Now this is the heart of the matter. This is the correct viewpoint to look at this in my opinion.

Voltages are relative. If you have fluctuating B+ and B- underneath the WCF system, you have less stable op point.

Put a cap directly between B+ and B-, and they both are - from the viewpoint of the tube and it's op point - more stable.

It's a cheap and easy way to make the PSU more stable and 'regulated' using only retro style means. 

It can change some MHz oscillations' bandwidth, thus bringing it closer to audio range, causing harshness. In my experience ALL circuits oscillate at VHF or UHF if not actively regulated. The grid stoppers (300 ohms) don't do much.


Extending (and partially breaking) my boat metaphore; decoupling the rails as closely as possible, it's like both the guy with the laser pointer and the canvas are on the same boat as you are, jumping with the light.

Without decoupling, the canvas and the laser guy are on another boat, that is moving with the waves differently from your boat.


Decoupling both to common ground can work, but less efficient; caps in series is not as good as one cap directly between points. Double the colorations, half the capacitance. Less stability.


----------



## coinmaster

Ah yeah, good point. Even if the signal on the rails does get averaged and distorted it will ideally still be seen by the WCF as a stable voltage between anode and cathode.
 That's assuming the waveforms are equal on both ends, LTspice is telling me a different story. Wave forms on B+ and B- seem to be quite different and quite distorted with the decoupling cap in place, not sure why. Phase issues? Or perhaps LTspice being a pita again.


----------



## MrCurwen

> Or when CCS tailed LTPs cause varying current draw from PSU.






> I never said CCS tails draw varying current (why would they do that).




Discussing amp with only CCS tailed LTPs;



> > If the amp draws the same amount of current at all times, the PSU caps do not charge and discharge with the signal.
> 
> 
> 
> ...




There's many different ways to interpret that piece of gobbledygook right there, and all of the ones I come up with are wrong on a level showing fundamental lack of basic electronics understanding.

Only way for the PSU capacitor voltage to fluctuate (assuming wall AC is resonably steady, but that's not at all what you are talking about here) is to draw varying amounts of current to the circuit. The only way possible by physics agreed on by everybody for 200+ years. So you are for all intents and purposes saying here either that

1) CCS tails don't draw constant current
2) you have no idea of how stuff works, such as Kirchof's and Ohm's laws, and/or CCSs.
Bonus:
3) you have no idea how current paths work (as evident by multiple statements elsewhere as well)

Again: Ohm's law; where there is impedance and current drawn thru the impedance, there is voltage drop. If each stage (as was the case explicitly in the amp I was describing) has a CCS tail (all LTPs), so the total current draw of the amp circuit is not varying at all... how can there be at the last PSU cap (disregarding wall AC ripple, but again, you're not talking about that here) a varying voltage?

Not an oopsie level mistake from person making the best amp, or making any original design at all.




> Or when CCS tails were multiple times referred to as affecting the load lines of tubes above it.






> I never said CCS tails affect load lines (other then making it horizontal).




So by your above quote you do think CCS tails in an LTP affect load line angle?

'Tail' in audio electronic design refers to LTPs. One could imagine a case where somebody could use it to describe a CCS load of a follower. No such reference made in this thread.

When you talk about tails, you always talk about LTPs. It is the long TAILED pair. Only topology to use this word 'tail'.

The tail, whether CCS or otherwise, does not affect the angle of the tubes' load line AT ALL. Never. It chooses the op point on the load line, to satisfy it's own current rule.



> I was talking about individual CCS for each triode.




Nobody who knows what they are talking about calls those CCSs 'tails'. An LTP has a tail. No other topologies. If you called separate CCS cathode bias 'tails', that's shows fundamental lack of understanding of topologies, and why the tail has to be separately named in the topology. 

Nowhere in post 1746 do you mention even once that by 'tail' you are actually refering to separate CCS bias. I do not care to dig up the earlier instance which first caught my eye.

Not an oopsie whichever way you look at it.


Current and electrons are not synonymes. If you draw a picture showing schematic symbols, the automatic assumption is that the picture shows 1) voltages 2) current. These are the things electronics are about. Electrons are mostly in physics. You can design the best amp in the world and not really think about electrons at all.

If you draw a picture with schematic symbols, you must 100% of the time explicitly explain you are not talking about current here, but electrons. Why you should wish to discuss electrons rather than current in a discussion of electronics design is beyond me.


There's absolutely no need to make remarks about other people's personal properties in the manner coinmaster does even if one were the chillest person on this planet. He apparently simply likes to make these remarks.


There's all kinds of kooky stuff said by coin but I don't care to hash this any further. Either act like a honorable normal person, or respect the agreement of not receiving any help from me.


----------



## coinmaster

> If each stage (as was the case explicitly in the amp I was describing) has a CCS tail (all LTPs), so the total current draw of the amp circuit is not varying at all... how can there be at the last PSU cap (disregarding wall AC ripple, but again, you're not talking about that here) a varying voltage?


 
 Good point. You're right, I haven't fully integrated ohms law into my understanding. I'm learning what I need to learn for each specific problem I encounter instead of taking everything on at once. IT's much more effective then what I was doing last year trying to learn everything with no practical application.
  


> So by your above quote you do think CCS tails in an LTP affect load line angle?


 
 Not in a differential amplifier, at least not horizontally which is what I was referring to at the time.
  


> The tail, whether CCS or otherwise, does not affect the angle of the tubes' load line AT ALL. Never. It chooses the op point on the load line, to satisfy it's own current rule.


 
 Datasheet curves say differently, and you yourself have said this multiple times, not to mention there's plenty of people across the internet that say it.
 If the current is constant then it can only follow the horizontal line of the specified current on the datasheet.


> Nobody who knows what they are talking about calls those CCSs 'tails'.


 
 I don't recall calling it a tail at the time, and if vocab = understanding then english masters would rule the world.
  


> that's shows fundamental lack of understanding of topologies, and why the tail has to be separately named in the topology.


 
 Big whoop. I'd rather learn how they work then learn what theya re called.
  


> Nowhere in post 1746 do you mention even once that by 'tail' you are actually refering to separate CCS bias


 
 That's because you weren't reading when I spent a couple of pages going over input stage operation and what LTspice had to say about it. Anything after that was a reference to that. Don't make bold claims if you weren't paying attention.
  


> He apparently simply likes to make these remarks.


 
 Only because pettiness is a pet peeve of mine. Lifes too short for that garbage.
  


> or respect the agreement of not receiving any help from me.


 
 There was never such an agreement, you made that up in your own mind. I simply said if you don't like me you have no obligation to talk to me.
 Playing the whole " I refuse to talk to you because I don't like you" game is childish and way beneath me. I learn much from you and would prefer to stay in communication but that's not my decision, that's yours. I'd rather have a proper discussion then all this fighting and bickering. Post questions, discuss questions, come to conclusions. No need for the attacks against each other. That being said if you attack me I'm not going to ignore it.


----------



## Maxx134

coinmaster said:


> if you don't understand what I mean by that then you should probably continue to stay within the boundaries of diyaudio.cm and head-fi.com.



I realize you were in a rant,
But please refrain from discouraging ANYONE who chooses to post and contribute here.

No one should be discouraged or intimidated to post here, just because they would have to worry of having to play "ping-pong" rebuttals to you.





> > or respect the agreement of not receiving any help from me.
> 
> 
> 
> There was never such an agreement, you made that up in your own mind. I simply said if you don't like me you have no obligation to talk to me.




Instead of littering this thread, you also don't have to respond to him here,
You can take it to PMs. .



> Playing the whole " I refuse to talk to you because I don't like you" game is childish and way beneath me. I learn much from you and would prefer to stay in communication but that's not my decision, that's yours. I'd rather have a proper discussion then all this fighting and bickering. Post questions, discuss questions, come to conclusions. No need for the attacks against each other. That being said if you attack me I'm not going to ignore it.



This is a discussion taken off topic now.
Ignoring things is a sign of maturity.
Let us now move on to better topics at hand. 

Like the possibility that what you heard with your Decoupling caps were what MrCurwen aluded to as high frequency Oscillations. ..


----------



## Redge78

_*[...Extending (and partially breaking) my boat metaphore; decoupling the rails as closely as possible, it's like both the guy with the laser pointer and the canvas are on the same boat as you are, jumping with the light.
 Without decoupling, the canvas and the laser guy are on another boat, that is moving with the waves differently from your boat...]*_
  
 I like this Boat Metaphore (even if I didn't see it before, I have been busy lately).
  
 Can I add my little contribution to it ?
 - Larger decoupling caps (energy-wise) => larger boat ?
 - Faster decoupling caps (pulse rate / impedance on a Freq. band) => the laser guy with better "aiming" capability ? or a larger beam laser ... ?
  
 I have been working on that particular area for some weeks now, with some significant audio benefits. 
 I will be pleased to share/exchange on that matter when this thread is back to a more peaceful mood.
 I was aware of this oscillation problem, I was kind of experimenting them (not sure of that) but I have been unable to find any comprehensive stuff on that subject.


----------



## MrCurwen

maxx134 said:


> Instead of littering this thread, you also don't have to respond to him here




I'm sorry. You are correct. I will contain my future comments to be more closely related to topic at hand with some general theory. 

I skimmed thru the new first page, and to my eye it seems you've got the entry level mods very expertly covered. As I've said, in other circles the term 'modding' refers to also actual circuit changes. The line between 'modding' and 'creation' or 'scratch design' is drawn on water. However I do not wish to define this line for you, you define it. General understanding of what it is you've got there and how it actually works is bound to be beneficial, intellectually interesting at least, I hope.



> Ignoring things is a sign of maturity.




Indeed.



> Like the possibility that what you heard with your Decoupling caps were what MrCurwen aluded to as high frequency Oscillations. ..




This is quite common. Not necessarily the cause, but easily could be.

I'm at the moment corresponding with a gentleman from Hong Kong, about some russian tubes and circuit design. He's done some things with 6E5P and found it to sound "harsh" despite being highly linear so no higher order harmonics should be there.

My first experiences with 6E5P years ago were a deep disappointment as well, I found it to sound harsh.

When I started to become aware of just how much EVERYTHING I build seems to like to oscillate, and took a number of steps to prevent that, I found the high gm tubes such as 6E5P no longer sounded harsh at all!

Later hunting for oscillations with a cheap USB scope (very useful tool) this whole picture became even more clear. 

Very very high oscillations don't usually disturb the sound, but the ones closer to audio range disturb it a lot. That's because of wave physics; when you sum two waves together, you get intermodulation distortion. If this new frequency component is inside the audio range, it can interfere. Usually by sounding harsh.

As an aside, this is how the theremin works; you have two oscillators at the same frequency. You have a mixing node where you get as output |f1 - f2| . So if they are the same, output is 0 Hz. If they are 1kHz apart, output is 1kHz. Then you make the pitch antenna part of the other oscillator circuit (one oscillator is fixed), and there you have it! By introducing a capacitive element (your hand) next to the antenna, you can control the instruments pitch. The volume control is a bit more complicated.

Anyway. The above mentioned theremin type oscillation is also possible in an audio amp. If you have two sections oscillating very close but not at the same frequency, this theremin effect can happen.

I've had it happen in my amp builds, and it usually manifests not as harshness, but an actual sound, high pitch squeling (like a theremin out of control...). Comical to remember, but at the time not fun at all.


The way an oscillation finds it's frequency is a mess of different things. It could be for example a megaherz signal riding on the wall AC, coming thru the transformer parasitics (imagine a small value cap from the primary to the secondary), finding a new energy minimum in the parasitics of the PSU caps, and then it's on the B+. The 'reg' that's there might not be operational at that frequency level.

The oscillation can only exists at a frequency where there is sufficient impedance to ground. A cap has an impedance plot, usually it starts at the highest point (infinite impedance at 0 Hz) and then drops as frequency rises, until it levels and starts to slowly rise again.

Within certain limits, the bigger the cap, the smaller the impedance it has at the bottom of the impedance graph, and the lower the frequency of the bottom.

So by increasing size of decoupling cap, you might be forcing the oscillation to move down in frequency, thereby interfering with audio reproduction via the intermodulation effect.

It could be this, or a number of other things. This came to mind, now whenever I hear 'harshness' especially after a change which should lower distortion not add to it, I automatically think oscillation.


----------



## MrCurwen

The issue of how an electronic oscillation finds it's frequency is fascinating. 

How does an oscillation of water mass find it's frequency and amplitude? 

It is dependent on the force causing the oscillation, let's say you drop something in the water. It also depends on the total mass of the water in the container, and the dimensions of the container.

It just seems to 'know' these things. The water molecules that the object actually hits don't know what the size of the container or it's dimensions are. Or, how much there are other water molecules.

It self organizes in a way as to provide the least expenditure of energy to produce the waves.

Now let's say the object dropped into the water is an electric signal, and the water is the electric energy inside the circuit (electrons with potential). The container is the circuit; all of the components and their parasitics.

The signal could be simply the AC 'sine' wave (not actually sine usually, contains all kinds of garbage) coming from the wall outlet. Or, it could be the actual audio signal coming from amp input. Or, it could be your amp picking up a local radio station or cell phone signal.

Or it could be the neighbours computer PSU sending back pulses (they do that a lot), or a fluorescent lamp PSU from your house, or your refridgerator compressor PSU or a number of things... 


The analogue is not perfect, but hopefully gets somebody thinking.

If you put lots of small walls inside the water container, you could significantly limit the amount of waves happening when you drop an object there.

That would be a whole bunch of C and R added in the appropriate places in a circuit. Like the grid stopper R and decoupling C.

Or, if your water system is actively controlled, let's say it's not standing water but an open halfpipe with a powerful pump at the other end, moving the water forcefully. If you drop a small object into that moving water, it will not produce significant waves at all.

This would be the sufficiently powerful regulator.


This is not directly applicable to your amp, but general information;

If you have two high transconductance devices operating closely together, they could start to spontaniously oscillate together.

Let's say the force of the water pump is analogous to gm (transconductance). If you have two strong pumps pumping the water (towards same direction), and there is only a small distance of halfpipe between them;

If they don't pump at the exact same frequency there will be a component of backwave coming from the second pump back (against stream) to the first one. If they are 90 degrees out of phase, the backwave is very big. 

If you have a high gm tube, like 6E5P, and you put a high gm module underneath it (like a CCS tail in a LTP), the same thing could happen electrically. I had to deal with this by putting a 47 ohm resistor between cathode and CCS.

Also, on the top side; the plate load FET and the 6E5P could start oscillating together. There is a resistor at DC between source and plate, but the gyrator cap from plate to gate makes the AC impedance close to zero.

So, again, I put a 100 ohm anode stopper on the anodes, so the AC path from tube to FET gate has more impedance.


Messy business, oscillations. Your amp probably has a reasonably small amount of them, since no high gm devices except transistors in PSU.


----------



## Maxx134

mrcurwen said:


> Simply looking at the amount of resources available; the worldwide new tube market wouldn't cover even 10% of the training budget of a single major tube manufacturer in USA back in the 50's. The expertise doesn't just appear out of thin air, it takes a pool of people and money and effort, not justified by current market conditions (by my guesses).




I have read that many secret techniques that 1950s tube companies had in competition with each other, went to the grave with them when they closed down...
Very sad scenario for our precious tubes. .




> That's because of wave physics; when you sum two waves together, you get intermodulation distortion. If this new frequency component is inside the audio range, it can interfere. Usually by sounding harsh.




Also,
Very interesting posts on circuit oscillation potentials, Thanks for those analogies MrCurwen,
 as good to view circuits very liquid and not static.






redge78 said:


> :
> 
> I have been working on that particular area for some weeks now, with some significant audio benefits.
> I will be pleased to share/exchange on that matter when this thread is back to a more peaceful mood.
> ...





I remember this thread was conceived because of your decoupling ideas in PMs, but
what I have seen from you lately,
 is something I believe never attempted/researched/addessed in such a intensive manner on an amp before.


----------



## MrCurwen

redge78 said:


> I like this Boat Metaphore (even if I didn't see it before, I have been busy lately).
> 
> Can I add my little contribution to it ?




Thanks! Sure.



> - Larger decoupling caps (energy-wise) => larger boat ?
> - Faster decoupling caps (pulse rate / impedance on a Freq. band) => the laser guy with better "aiming" capability ? or a larger beam laser ... ?




Now this really got me scratching my beard.

Let's find out how long the analogue can stretch before breaking.

Mass = current;

Vertical position = voltage;

Strenght/speed of your legs = tube gm

Okay, so the person holding the laser pointer is not a person, it's a ghost. It moves the light but has no mass (except tiny mass made of ectoplasm ghost material ( = grid parasitics), which you can ignore unless you wish to be reticulously exact, i.e. high end HIFI enthusiast).

It's the gm of the tube, i.e. the jumping strenght (and your mass) that moves the boat the most, i.e. fluctuates rail voltages. So by making the rails stiffer, by decoupling better, your analogue of making the boat bigger (or, heavier) is good and applicable.

As for the laser ghost's aim and the quality (size) of the light being moved; I'd think they are properties of the preceding stage and the coupling between them. I.e. how well it is able to deal with coupling cap parasitics and/or grid parasitics. The light that is actually on the canvas is the charge, the electric field on the grid that manages to get thru the things in the previous sentence. The light that hits the fog that is floating over the lake is lost to the parasitics.

Yes, it's a foggy lake.

The quality of the decoupling hmmmmm.

I'd think that since being on the same boat i.e. having the rails at the same AC potential is the decoupling, the quality of the decoupling would be the stiffness of the boat itself. 

Maybe the boat is made of rubber. Maybe it's made with thin, bendable wood. Maybe it's made of stiff solid plastics, or metal. Or, good quality tarred finnish wood.




> I have been working on that particular area for some weeks now, with some significant audio benefits.




I would be interested to see what your approach is. Mine is basicly brute force. Regulate everything and then don't ask questions later, since it's irrelevant. All is taken care of. All rails stiff as steel beams. 

It's so cheap and easy to regulate everything these days, why not. In 1950 it was very clumsy and expensive. Why do we care?




> I was aware of this oscillation problem, I was kind of experimenting them (not sure of that) but I have been unable to find any comprehensive stuff on that subject.




I was surprised to find that EVERY SINGLE ONE of my circuits had some oscillations inside the circuit. Usually somewhere in the 4 to 10 megaherz range. Unless there's many of them (thus creating intermodulation components) they don't usually cause any trouble and are completely inaudible.

Then there was this:




Unless you hear something out of the ordinary (what is ordinary is another question) you're probably pretty good. If a mod causes harshness, you might have a problem.


There also are people who regard fidelity as harshness. A LOT of people enjoy saccharine sound, the retro sound. This once again presented with the NFB caveat. Not all low THD is created equal.


----------



## Redge78

mrcurwen said:


> I would be interested to see what your approach is. Mine is basicly brute force. Regulate everything and then don't ask questions later, since it's irrelevant. All is taken care of. All rails stiff as steel beams.


 
 I'm afraid you'll find it "old-fashioned" but it has 2 strenghts : it's easy to implement (not so easy after some thaughts tho) and I can understand it.
  
 I took the "energy" viewpoint, how much do I have of it and how fast it can be delivered ...
  
 Our (power) PSU is basically an "average quality" transformer > "average quality" bridge > a "half decent" C-R-C filter > Transistor/Zener voltage regulator > a "small" Lytic as energy reservoir
  
 1 - I have changed this "small lytic" for the largest *RIFA/KENET PEH200* I could find (12000µF/250V). It is given for extra-low ESR (around 10mOhm in the Freq. Band) and ESL (17nH) 
 It will serve two purposes :
 - It will feed the following Decoupling Caps
 - In the lowest freq. band, it will directly feed the tubes with fast energy (a huge Capacitance and how it impacts the overall impedance via the "Zc=1/*C*w" rule)
  
 2 - I have installed "as close as possible to the tubes" (on the Ra/Rk leads effectively) a Cap Bank for each tube.
 The bank is composed of 4 caps, with different capacitances ( 100µF / 4.7µF / 0.15µF / 4700pF) that should be addressing each a separate Freq. Band.
 Each cap has been chosen to be "the best" tech in its range, focusing on their "pulse rate" values and focusing on the energy stored via their max Voltage. Needless to say that cost and availability was also prime factors, as we were in some kind of experiments.
 So, for the time being, my caps Banks are donne like that :
*- 4700pF/500V SGM-4* (Silver-Mica)  _Teflon and Polystyrene were also considered_
*- 0.15µF/1250V WIMA FKP1*  ...  _Probably the center piece of the bank (11000 V/ms Pulse rate)_
*- 4.7%F/500V WIMA MKP10 *..._ to make the bridge between the FKP1 and the following TPC_
*- 100µF/1100V TPC/AVX FFVE* (Industrial MKP "DC filtering" caps) .. _ultra-low ESR (1mOhm) and low ESL (40nH) ... I bought them "used" with the idea that they could be very useful in a next 300B/845 amp too. Lots of energy stored and ultra-fast delivery.  _
 The 4700pF/0.15µF/4.7µF have also been used to the "Cathode Resistance Bypass" Cap Banks (the "CRBCB") alongside the large _but Lytics_ Elna Silmics (should be exchanged for some RIFA MKP5 sometime soon).
  
 Not sure the chosen cap values are the best possible, this "USB oscillo" thing should help, indeed. I'll have a look into that. Any recommendation/brand would be welcome.
  
  
  
 I have installed the Cap Banks and the CRBCB first, with a very significant impact on sound, more dynanic, better detail, reverb ...
 The RIFA has been installed 2 weeks ago with great benefits too. I have gained mostly on bass, with a 25Hz I can really hear now, better texturing and impact on sub-bass and bass.
  
 I am not very good at writing about what I hear, it's MAxx's job, but my feeling is that it's VERY cost effective mod.
  
  
 Some pics :
  
*WIMA FKP1 + WIMA MKP10 (2 channels)*
  

  
  
*The CRBCR !!!*
  

  
  
*The Overall view :*
 Front : all Power tubes decouplings + CRBCP
 Back (below and including the big black round caps) : Driver tubes decouplings
  

  
  
*And the same with the TPC Industrial caps (in the Extra-box) ... *_sorry for the bad pic_
  

  
  
*The RIFA "White Monster" and its "inrush current limitation" apparatus (with bypass)*
  

  
  
  
_I suppose that when this mod has been validated by somebody else (and we have improved how to handle the White Monster) ... plus the oscillo thing, we'll move that post in Page one_


----------



## MrCurwen

redge78 said:


> I'm afraid you'll find it "old-fashioned" but it has 2 strenghts : it's easy to implement (not so easy after some thaughts tho) and I can understand it.




Looking at the pictures I'd say the implementation is not so easy! Very small space, lot's of capacitance. Well done.

As for the second point; smart thinking. Want to stay out of trouble (smoking components and money lost)? Only build things you actually understand. 

My financial losses have gone down so much, down to manageable (and to some extent unavoidable, there's always human error) after I reached some understanding of how stuff works. Also audio results; like I said earlier, just "trying things out" didn't get me too far.




> I took the "energy" viewpoint, how much do I have of it and how fast it can be delivered ...




Yes. This is bound to improve function.

However, adding C to the end of an RCRCRC or whatever it is, is not going to lower the total R along the way at all. 

If your end game caps (closest to the audio circuit) can deliver very fast, the current that resupplies the caps must go thru that earlier system with it's impedances and parasitic properties (slower caps).



> *- 4700pF/500V SGM-4* (Silver-Mica)  _Teflon and Polystyrene were also considered_




I've never tried the SGM. One would guess it's as good as the SSG and KSG; silver micas are top notch usually.


There's no clear scientific consensus on this, but a largish minority of DIY guys think that parallel caps is a bad idea. I'm somewhat in this camp as well.

The resoning goes, that in the cap system you create overlapping areas, and when they discharge, the smaller cap has a phase error in discharging.

Exactly the same as in a speker crossover. The overlapping areas are problematic. Some people prefer full range speakers despite them having problems in high treble and low bass. Also many people cite the lack of a crossover system as a big benefit in using headphones.

Did you try out and compare single cap and multicap solutions and come to find you prefer this system?

My opinion on this matter is undecided, leaning strongly in favour of single caps where possible.



> Not sure the chosen cap values are the best possible, this "USB oscillo" thing should help, indeed. I'll have a look into that. Any recommendation/brand would be welcome.




I'm sure any decent one is fine. They have their uses, but meaningful THD analysis will costs you a lot. A useful USB scope capabable of finding oscillations and measuring frequency response will cost only like 120 euros.

Also it's fun to put a square wave into the amp and look at what comes out, at different frequencies. Also useful is to input a strange signal, like a triangle wave, and have a look at what different places that signal ends up in (for example, the B+ rail...).

They usually have a measurement range of like +-30V and max DC rating of 100V or so. You'll need to do most measurements thru a RC buffer. A decent cap of 600V rating, and a 1 meg resistor.



> I have installed the Cap Banks and the CRBCB first, with a very significant impact on sound, more dynanic, better detail, reverb ...
> The RIFA has been installed 2 weeks ago with great benefits too. I have gained mostly on bass, with a 25Hz I can really hear now, better texturing and impact on sub-bass and bass.




That means the PSU is severely lacking in unmodified condition. In other words IT'S IN THE SIGNAL PATH. All of it.



> I am not very good at writing about what I hear, it's MAxx's job, but my feeling is that it's VERY cost effective mod.




Yes.

Maybe next try out the simple 2 FET reg? I can write up a post explaining in detail how it works. It's quite simple really. Reg parts cost like 15 to max 20 euros.


----------



## baronbeehive

mrcurwen said:


> Thanks! Sure.
> Now this really got me scratching my beard.
> 
> Let's find out how long the analogue can stretch before breaking.
> ...


 
  
 Those last 2 points are true. I was thinking about this after reading some of the recent posts and I know that I go for a certain kind of sound, not necessarily transparency, but also warmth as well as fidelity. I'm not sure for example that I would like out and out transparency if it was unpleasant to listen to, maybe, maybe not. I was rather shocked when I heard a friends amp which had more SS sounding driver tubes and I really liked the sound.
  
 Great metaphors in these recent posts! There's also some good stuff going on lately, looks like some good mods to come. I have to say I'm struggling with it but its all good.


----------



## SonicTrance

Hey @baronbeehive  !
  
 Have you listened to your modded amp yet?


----------



## Maxx134

Re-doing bias on both driver and power stage has been a "rabbit-hole" journey leading to many , many tube rolling choices.

Tried 5 differeent power tubes on my MK8 so far,
And not even using 6h30 right now look my meter:

Bias has not beeen optimized for tube and it seems the best way to test a tube is to first make sure bias pionts are decent.

Still have more tubes to try , especially on driver stage,
But just when I feel Im getting close, it seems another bias parameter to decide throws all my tube rankings different.

Settling on the best driver tube for this amp not easy when bias point and powertube choice are now variable.

Looks like I now have MK6 issues lol


----------



## SonicTrance

maxx134 said:


> Re-doing bias on both driver and power stage has been a "rabbit-hole" journey leading to many , many tube rolling choices.
> 
> Tried 5 differeent power tubes on my MK8 so far,
> And not even using 6h30 right now look my meter:
> ...


 
 Yeah you do! This tube rolling business is a never ending story! Ha!


----------



## baronbeehive

sonictrance said:


> Hey @baronbeehive  !
> 
> Have you listened to your modded amp yet?


 
  
 No, I'm still waiting to move into my new house. Things take for ever here, most of my stuff is in store. I promise to say when I've listened to it at last !!
  


maxx134 said:


> Re-doing bias on both driver and power stage has been a "rabbit-hole" journey leading to many , many tube rolling choices.
> 
> Tried 5 differeent power tubes on my MK8 so far,
> And not even using 6h30 right now look my meter:
> ...


 
  
 Nightmaresville Arizona, 
	

	
	
		
		

		
		
	


	




, things are getting soooo complicated.


----------



## Maxx134

Thanks to SonicTrance for showing me more tubes!

Ha

Edit one thing for sure I will no longer be using 6h30 tubes!
But not mk6 tubes either.


----------



## Maxx134

Time for periodic update. 

In case anybody wondering, 
This thread is quiet for a reason..

Like a volcano quiet until ready erupt and cause havoc, 
There will be massive changes to driver stage(!).

Massive testing underway on search for the best driver tubes for our amps!
(Within current model design limitations).

Plus new bias settings for all tubes tested,
 to add even more calculations and sorting ..

*Here are the candidates:
(Various versions of each being tested):
*
*6sn7
6sn7gt
6sn7gta
6sn7gtb
6sn7W
6sL7
6su7gty
6sc7
6n7 
7n7
7f7
6f8g
6c8g
VT-99
ECC33
ECC35 
ECC32/CV181
CV181-Z*

 This is not an easy task to find which tubes will be the top pick,
 due to our amp driver PSU limitations,
So not all will be *"optimally" biased.
Edit: 
The term "optimally biased" is actually a variable choice, as one could even say the stock settings were not optimally biased (!)..


And small PSU optimizations being tested simultaneously, 
Whith future idea discussions welcomed due to this PSU being in general being such a weak point.

OK so that's one of the various mods underway which has seemed to jump in front of all other projects for now.


----------



## baronbeehive

Massive task Maxx. How are you going to rank them because each person will prefer a different type of sound like I was saying. Difficult to say which is best. Perhaps if you give an indication of each tube's characteristic SQ? That might enable us to choose which ones we may like best.


----------



## SonicTrance

maxx134 said:


> The term "optimally biased" is actually a variable choice, as one could even say the stock settings were not optimally biased (!)..


 
 I can certainly attest to that. I have the ECC35's @ 1.3mA of plate current now and the sound is much, much better than the stock setting which is 0.4mA.


----------



## Mogos

Guys I have a problem. I have bought lately some 6C8G NOS tubes and used them for few days with an adapter. No problems at all, very good sonicaly. Today I have recieved another 6C8G tubes for rolling. First I have checked them for short time if they are at all turning on. All were ok. So I decided to put one pair for heat up and longer listening sesion. After 20 minutes of listening I have herd sharp pops in the left channel. But shortly everything came back to normal. After another period of time (around 30 min) there was pop and the sound dissaperd for few seconds in both channels ( I think relay had worked). I have turned of amp and replaced the tubes with the ones I have been listening for few days (6C8G). After turning on the amp I can hear in the left channel hum and pops and the volume of the signal is lower than in the right channel. I have switched the position of the adapters but the left channel still had problems. I have installed back the 6SL7's and everything is ok. There was some noise and slight crackles just after turning on the amp with the 6SL7's but now evrything is ok. No issues at all but no great sound also . Question what is going wrong. For few days everything was ok. I have been listening for long periods. Right channel seams to perform correctly.


----------



## Maxx134

mogos said:


> Guys I have a problem. I have bought lately some 6C8G NOS tubes and used them for few days with an adapter. No problems at all, very good sonicaly. Today I have recieved another 6C8G tubes for rolling. First I have checked them for short time if they are at all turning on. All were ok. So I decided to put one pair for heat up and longer listening sesion. After 20 minutes of listening I have herd sharp pops in the left channel. But shortly everything came bak to normal. After another period of time (around 30 min) there was pop and the sound dissaperd for few seconds in both channels ( I think relay had worked). I have turned of amp and replaced the tubes with the ones I have been listening for few days (6C8G). After turning on the amp I can hear in the left channel hum and pops and the volume of the signal is lower than in the right channel. I have switched the position of the adapters but the left channel still had problems. I have installed back the 6SL7's and everything is ok. There was some noise and slight crackles just after turning on the amp with the 6SL7's but now evrything is ok. No issues at all but no great sound also . Question what is going wrong. For few days everything was ok. I have been listening for long periods. Right channel seams to perform correctly.



My guess is that it had nothing to do with your tubes,
 but instead it had to do with moving the adapters in and out of the stock socket.

Adapters have thinner pins than tubes,
 and do not make good connections at times. 

Slightly bend the pins and try again.


If you are using adapters on your power tubes, you must check/clean and slightly bend those pins as well.

Just because they are shiny gold pins do not mean they are making great contact.
They are pretty thin.


----------



## Maxx134

Also,
The top plug on your adapter needs to be tight not too loose.
Make sure that it making good contact


----------



## SonicTrance

maxx134 said:


> mogos said:
> 
> 
> > Guys I have a problem. I have bought lately some 6C8G NOS tubes and used them for few days with an adapter. No problems at all, very good sonicaly. Today I have recieved another 6C8G tubes for rolling. First I have checked them for short time if they are at all turning on. All were ok. So I decided to put one pair for heat up and longer listening sesion. After 20 minutes of listening I have herd sharp pops in the left channel. But shortly everything came bak to normal. After another period of time (around 30 min) there was pop and the sound dissaperd for few seconds in both channels ( I think relay had worked). I have turned of amp and replaced the tubes with the ones I have been listening for few days (6C8G). After turning on the amp I can hear in the left channel hum and pops and the volume of the signal is lower than in the right channel. I have switched the position of the adapters but the left channel still had problems. I have installed back the 6SL7's and everything is ok. There was some noise and slight crackles just after turning on the amp with the 6SL7's but now evrything is ok. No issues at all but no great sound also
> ...


 
 Remember that we are using octal adapters in the MK6 rather than the 9-pin adapters for the MK8. The octal adapter pins are, from my experience, not thinner than tube pins. Also, Mogos has new, tight, sockets in his amp.
  
 Have you done any work on the amp lately Mogos? Other than rolling tubes?


----------



## Mogos

My sockets and the adapter have the tight type of pin sockets. I will put attention doing next change to that possibility. Maybe there is a problem. But there is a continuation of the story. I have inserted the 6SL7's and listened for around 30 min. As I said just on the begining I have herd some weak noises (with 6SL7's) but later on everything was in perfect order. So I decided to tray the first set of 6C8G I have been using on the begining for few days without issues again. I have turned off the amp for ten minutes and inserted the 6C8G tubes. Now I am listening for 30 minutes and everything works as previously. The same tubes inserted just after the other pair of 6C8G (I think one of the tube in this pair is faulty) behaved like the faulty pair. I know it sounds strange. I decided to listen to the present configuration for longer time. And than I will do a change for another pair of 6C8G. I will report back.
 I have to apologize to baronbeehive and Sonic Trance for beeing so sceptical about thier good advises to get some NOS tubes. I have strated ackwardly with the 6C8G tubes and adapters. But the difference is huge. My experience in tube rolling is almost none. The only NOS tubes I have used are the russians 1579. And they have brought a chnge, positive change but small. So I imagined that the tube known for nice performance will bring just another slight change to that one with russian ones. But I was so wrong. 
 See what I have got.


----------



## Mogos

Sonic I haven't touch the amp. I was just enjoying the music. I know that what is happening is strange. Could that be that the faulty tube charged some capacitors or could done temporary damage. I am still listening to the music as nothing has happend (with 6C8G and adapters).


----------



## SonicTrance

mogos said:


> Sonic I haven't touch the amp. I was just enjoying the music. I know that what is happening is strange. Could that be that the faulty tube charged some capacitors or could done temporary damage. I am still listening to the music as nothing has happend (with 6C8G and adapters).


 
 Don't know what happened here to be honest. Good thing it's working fine again! I wouldn't use the tubes that first caused the problem though.


----------



## Mogos

Yes I will not use the suspicious tube. We see what will hapend when I tray the other pairs. The amp is still working without problems.


----------



## Maxx134

The symptoms you posted also can describe condition of a tube starting to fail..

I had a 6sn7 start to give static noise and I knew it was ready to go


----------



## MrCurwen

Mogos' problem sounds very much like a contact problem as pointed out already. There's no socket expensive enough (high price is no guarantee of high quality) to not be susceptible to contact problems, I've found that out many times.

Tube failure by heater - cathode (partial) short will also cause pops and hiss.

The problem could also be inside the adapter; a partial or near-short.


----------



## Mogos

It looks like all the strange problems are connected with the tubes. One RCA tube is totaly dead. One National Union has only one rod glowing and one Ken-Rad does not show any visiual signs of failure but after some time starts poping, ckracling. I have another pair of National Union and they are working ok. For awile I thought it is the adapter causing problems. But changing positions and lamps shows that with the adapters everything is ok. I am using them now for already few hours with another pair of Ken-Rads and everything is ok. So adapters and contacts can be exculded from suspicion. I thought it may be some shortage in current supply from the amp. For shure with the stock solution there is limited supply of current. So Maxx good news that you are preparing a remedy for it.


----------



## baronbeehive

mogos said:


> It looks like all the strange problems are connected with the tubes. One RCA tube is totaly dead. One National Union has only one rod glowing and one Ken-Rad does not show any visiual signs of failure but after some time starts poping, ckracling. I have another pair of National Union and they are working ok. For awile I thought it is the adapter causing problems. But changing positions and lamps shows that with the adapters everything is ok. I am using them now for already few hours with another pair of Ken-Rads and everything is ok. So adapters and contacts can be exculded from suspicion. I thought it may be some shortage in current supply from the amp. For shure with the stock solution there is limited supply of current. So Maxx good news that you are preparing a remedy for it.


 

 Looks like you've had some problems with NOS tubes I'm assuming you're getting, always a problem. Fortunately I've largely escaped this problem, I don't know if you are getting tubes advertised with good test results, although that does not guarantee a good tube.


----------



## Mogos

Yes, you alredy know that I had been prejudiced to NOS tubes. And it seams I had correct feelings. Buying a NOS tubes is a lottery 
	

	
	
		
		

		
			





. But you know what. It is worth to risk!!. 
	

	
	
		
		

		
		
	


	




 I will tray to replace the out of order tubes (it shall be no problem). And for now I have ednded up with three pairs of NOS tubes changing the amp in exceptional instrument. I am still wating for the 2C22/7193 adapter and the 7193 Ken-Rads. I hope the amp will provide sufficient current to run the setup. I am very curious of the sonic effect of the setup.


----------



## Maxx134

mogos said:


> I thought it may be some shortage in current supply from the amp. For shure with the stock solution there is limited supply of current. So Maxx good news that you are preparing a remedy for it.



The driver PSU, is separate from the heater current demands,
 and that comes straight off the transformers in AC,
So there is no worries about having enough power for the driver tubes,
 as the transformers have the power,
 as SonicTrance posted the schematic LittleDot gave him.

Also,
I was cautious and modified driver PSU resistors to only get an extra 10v out of it. 

A far cry from a real modification like earlier suggestions. 

Anyways, I realize what we are doing is kind of late to the party,
As I been reading threads 5-10years ago and it's all been tried before with tube choices. 

Also,
The 2c22 tube is a good idea. 
Yet even that not the final say as there is even higher.
Looks like the future seems to say DHT is way to go..
Dam, this really doesn't end..


----------



## MrCurwen

An ok tube with the best circuit design will every time beat the best of the best tubes with mediocre circuit designs.


----------



## Maxx134

mrcurwen said:


> An ok tube with the best circuit design will every time beat the best of the best tubes with mediocre circuit designs.



That is welcome news.

Also I have come to conclusion that the driver stage on this amp was limiting performance and holding back the power tube stage .

Also, side note:
 I really really really do not like the usage of super tiny zener diodes in the power stage PSU...

The resulting narrow parameters from a small watt zener (and accompanying tiny resistor) ,
*edit*
 is not conducive to longterm reliability. .

I edit long winded post.


----------



## Maxx134

Not sure if this is OK to post but I found this very good research report on amplifier design and if possible anyone could post some opinions about it:

http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

One of my future plans is to look into these points about the amp global NFB:

Why is it there in this amp.
How much is being used percentage wise.
Whether it is necessary 
What parameters can be adjusted if possible to eliminate or minimize the need for it at all.


----------



## Redge78

*You've got your Quest, Sir Galaad !  **Go find the Truth !*


----------



## Redge78

mrcurwen said:


> An ok tube with the best circuit design will every time beat the best of the best tubes with mediocre circuit designs.


 
  
  
 OK, you've got your boundaries here, let's say a 3000$ for a "pair of Output Transformers" Vs 3000$ for a "pair of 300B" (just an exemple).
  
 I'm pretty convinced that the real difficulty is to find the right balance between the "circuit design", the associated costs and the final sound quality.
 We have seen so many start-up companies selling "over the top" audio stuff (with "over the top" prices) that didn't live very long. 
  
 And I suppose we could have a 200 pages of discussion of what is the "best circuit design" and still not agree (I mean, not "me" personnaly, I don't have this expertise... but some "enlightened" dudes).


----------



## Redge78

_Sorry for the late answer, i have had a busy personal/professional life these last weeks. It will be more calm during summer, I hope. _
  
  
 Quote:


mrcurwen said:


> However, adding C to the end of an RCRCRC or whatever it is, is not going to lower the total R along the way at all.
> 
> If your end game caps (closest to the audio circuit) can deliver very fast, the current that resupplies the caps must go thru that earlier system with it's impedances and parasitic properties (slower caps).


 
  
 The overall idea is not to lower the total R, but to "decouple" as much as possible the Signal loop (Energy provider > Tube > Headphone) from the PSU.
  
 The PSU is there only to refill the Decoupling Banks. As long as the PSU can provide more energy than what is used in the Signal loop (which is the case obviously), the Energy Balance of the cap banks between what goes in and what goes out is OK.
  
  


mrcurwen said:


> There's no clear scientific consensus on this, but a largish minority of DIY guys think that parallel caps is a bad idea. I'm somewhat in this camp as well.
> 
> The resoning goes, that in the cap system you create overlapping areas, and when they discharge, the smaller cap has a phase error in discharging.
> 
> ...


 
  
 Yes I have tried a lot of different setups :
 Setup 1 :no caps : original
 Setup 2 : 1 cap : 33µF Clarity Caps
 Setup 3 :2 caps : same as above + 0.33µF RIFA PME271
 Setup 4 :3 caps : same as above + 10nF polystyrene (not good at all ... maybe not enough burning)
 Setup 5 :3 caps : 0.15µF FKP1 + 4.7µF MKP10 + 100µF TPC
 Setup 6 :4 caps : my current setup (with the White Monster)
  
 And yes, I have heard significant changes between each of those setups, not all were good. The current setup (the 3 and 4 caps) is the one which provided the more benefits by a large margin.
  
  
 I have been trying to see if a "one cap" could be enough too. It would have make my life much easier. But I could not reconciliate the few parameters I wanted to play with in a single cap.
 I wanted :
 - fast transient
 - low impedance
 - high energy
 - form factor that could fit the amp and allow to put the bank as close as possible to the tubes (not that easy)
 - not a bank breaker
  
 The problem I had with the "single cap" is that it could not satisfy all the criterais at the same time.
 You can't have a low impedance with a small cap, especially on the audio freq. band due to the "Zc = 1 / jwC" part of the impedance law. 
 You can't have a fast transient on a very large cap which will most probably be a Lytic
  
 A middle ground between those could have been some large industrial FKP "laser pulse" caps, but they are incredibly hard to find (B2B most exclusively) and expensive.
 And "large" means that you'll have to put then some inches away from your tubes, adding some inductance in the process and killing your "high freq response". 
 And even then, you can't expect to have the almost infinite transient of a silver/mica and the low impedance at 100Hz ...
  
 So, maybe the "phase error" you're talking about can have an sonic impact, I honestly don't have a clue. If this is an area for improvements (better values scale ?), I'm really open to suggestions/discussion. 
  
 But I suppose this is always a mater of cost/benefit. I'll have my transient and my low impedance at the cost of some phase error and maybe oscillations too.
 But overall, when I listen to it, it's a clear improvement for me.
 I don't say it's final or it's the best way, just saying that in this context it works, it's easy to implement (sort of) and it's cheap.


----------



## Maxx134

I find hard to imagine different discharge rates in cap being a phase error because it is not in a signal position, like a speaker crossover, 
 but instead, in a replenishing&discharging power condition. 

So the result should be the response of the energy available(at a given point in time).
That should be the only parameter, plus any ringing associated,
Which would be taken care of with successive paralleled cap additions. .

Why would phase difference in psu suppy transients matter when each successive cap will mask the others response time?


----------



## MrCurwen

maxx134 said:


> Not sure if this is OK to post but I found this very good research report on amplifier design and if possible anyone could post some opinions about it:
> 
> http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php




It says:



> Robert Fulton was emphatic that the quality of the topology came first, then quality of components, and if everything was right, the distortion would already be low. Negative feedback could be reduced or eliminated.




Yep. My designs are super low distortion and open loop. Best way to go, in my opinion.




> One of my future plans is to look into these points about the amp global NFB:
> 
> Why is it there in this amp.
> How much is being used percentage wise.
> ...




I discussed these at lenght earlier in this thread. In short: the output impedance will skyrocket if you do away with the NFB. If you like the retro sound, you might like it. If you like fast transients and wide soundstage, you will probably not like it.


----------



## MrCurwen

redge78 said:


> OK, you've got your boundaries here, let's say a 3000$ for a "pair of Output Transformers" Vs 3000$ for a "pair of 300B" (just an exemple).




Circuit design that is contingent on high $€ OT's is not very good in my opinion. Or one that is contingent on expensive tubes.

That's component choise, not circuit design. (I get they are intertwined, but there is a difference.)




> And I suppose we could have a 200 pages of discussion of what is the "best circuit design" and still not agree (I mean, not "me" personnaly, I don't have this expertise... but some "enlightened" dudes).




Yep.

Even if there is no Holy Grail, some positions are easier to defend than others. Very few DIY guys go back from regulated supplies to unregulated etc.


----------



## Maxx134

mogos said:


> ...
> I am still wating for the 2C22/7193 adapter and the 7193 Ken-Rads. I hope the amp will provide sufficient current to run the setup. I am very curious of the sonic effect of the setup.



Let us know how that goes as I am very interested to know about them 
but the adapters plus tubes is a considerable change to try


----------



## MrCurwen

redge78 said:


> The overall idea is not to lower the total R, but to "decouple" as much as possible the Signal loop (Energy provider > Tube > Headphone) from the PSU.
> 
> The PSU is there only to refill the Decoupling Banks. As long as the PSU can provide more energy than what is used in the Signal loop (which is the case obviously), the Energy Balance of the cap banks between what goes in and what goes out is OK.




Yes the PSU can provide more current, but think in terms of timeframe.

If you want the sharpest high end transients; 

Ok so the decoupling cap discharges because output section asks for current. So now the cap is less charged, it must recharge. 

Can it recharge fast enough for stable rail voltage?

Can the PSU chain before the decoupling cap recharge the last cap fast enough?


Sure, the quality of the last cap is most important, but this arrangement only lessens the PSU imperfections, it doesn't eliminate them. 

Active regulation does (in practical terms) eliminate the problem.

It could be that your PSU is now "stiff enough". I'm just bringing another perspective to the table. I personally like to go brute force and just use active regulation. Then it's a non-issue anyway.



> Yes I have tried a lot of different setups :




Really good work. You should go DIY all the way, you've clearly got the proclivities and beginner skills.



> And yes, I have heard significant changes between each of those setups, not all were good.




Yes. One of the reasons I went regulated B+ (first with tube regs, then FETs) because I got tired of thinking where to get money for more caps.




> I have been trying to see if a "one cap" could be enough too. It would have make my life much easier. But I could not reconciliate the few parameters I wanted to play with in a single cap.
> I wanted :
> - fast transient
> - low impedance
> ...




Sounds like you're looking for 20 euros worth of active regulation there.



> A middle ground between those could have been some large industrial FKP "laser pulse" caps




My 50µF / 1500V film caps are for laser PSUs. I bought them for CRT monitor build.



> And "large" means that you'll have to put then some inches away from your tubes, adding some inductance in the process and killing your "high freq response".




Unless you're thinking of oscillation prevention... Just calculate the inductance and HF pole there and then think again.



> But I suppose this is always a mater of cost/benefit. I'll have my transient and my low impedance at the cost of some phase error and maybe oscillations too.




Your current setup is very good for oscillation prevention.



> But overall, when I listen to it, it's a clear improvement for me.
> I don't say it's final or it's the best way, just saying that in this context it works, it's easy to implement (sort of) and it's cheap.




Indeed.


----------



## MrCurwen

maxx134 said:


> I find hard to imagine different discharge rates in cap being a phase error because it is not in a signal position, like a speaker crossover,
> but instead, in a replenishing&discharging power condition.




It's completely in the signal loop. I don't understand how it could not be?

Answer this; if it's NOT in the signal loop, why does changing the decoupling cap improve transient response?

It is exactly like a speaker crossover, only with higher impedance (less current involved) and better quality caps. Whether or not it is an actual issue in a specific circuit and with a specific set of ears listening, is up to you.




> Why would phase difference in psu suppy transients matter when each successive cap will mask the others response time?




Let's pick a frequency, and call if f.

At f, cap A has no phase shift (A is a big cap). At f, cap B has 5 deg phase shift (it's at the low end of it's freq response in the specific circuit it's in).

So the audio circuit asks for some current at f.

Cap A discharges, with correct phase.

Cap B also discharges, but with wrong phase.

The current going into the circuit has this error component as well. The fact that cap A can deliver the asked current correctly, doesn't stop cap B from ALSO discharging (of course they deliver current in a specific ratio, it's not 50/50 but use Ohm's law there).

So there is extra information in the 'response' current. It's a phase shift.

Same thing happens with sound waves in the air.

Just because the bass element in the speaker can deliver the energy of the sound wave correctly, doesn't stop the mid element from delivering a mutated version (if f is at the overlapping point). This is a known problem with wave systems of all kinds.

Think of the water pumps and how they must be perfectly synchronized, or there will be a "backwave" in the water pipe.


----------



## Maxx134

mrcurwen said:


> maxx134 said:
> 
> 
> > Not sure if this is OK to post but I found this very good research report on amplifier design and if possible anyone could post some opinions about it:
> ...




Yes thank you for refreshing my memory which I have problems with at times.

I have also noted the MK6 having higher resistances, so less NFB than the MK8,
Which is interesting as I would have thought the MK6 should have more Global NFB as it is supposed to be lower output impedance & more power output.
So I am assuming it is dependent on the type of power tubes .


----------



## MrCurwen

maxx134 said:


> I have also noted the MK6 having higher resistances, so less NFB than the MK8,




Please elaborate.



As for the signal loop;

Every component and circuit part that has 

1) a varying voltage across it

2) a varying current thru it

, in relation to the input signal, is on the signal path.

If the current output of a cap varies in direct relation to the input signal, then IT IS ON THE SIGNAL PATH.


No ifs ands or buts about it. 


The definition of signal path used in for example this thread on multiple occasions is completely absurd in electronics terms. If the last PSU cap (or, decoupling cap as it's called here) only "charges and discharged energy" or whatever the phrase was, then what about this;

The coupling cap between input stage and output WCF is not on the signal path. It only charges when the input receives a negative signal, and discharges when the input receives a positive signal. It there only to transfer some energy, nothing more.


----------



## Maxx134

I can see that the PSU voltage needs to be rock stable,
So that only the Anode resistor volt drop & plate voltage are making the signal,
As your "boat in still water" analogy.

So I can see how any possible fluctuations of the PSU will directly be a part of the signal.
I have noted this actually happening with extreme volumes with low impedance headphone loads.

So in our amp design, the PSU needs to be rock stable, and we have no choice but to strengthen the PSU traditionally with more capacitance, as there is not precise regulation with the existing transistor voltage regulation,
Unless we adopt an additional type regulation.
Correct?


----------



## MrCurwen

maxx134 said:


> I can see that the PSU voltage needs to be rock stable,
> So that only the Anode resistor volt drop & plate voltage are making the signal,
> As your "boat in still water" analogy.




Yes, when searching for best possible results, PSU is what you are essentially listening to as the old saying goes. (Except of course in constant current draw amps as discussed.)

As demonstrated by Redge78 and his well documented decoupling cap mods. The caps he's using are making the PSU stiffer.



> So I can see how any possible fluctuations of the PSU will directly be a part of the signal.
> I have noted this actually happening with extreme volumes with low impedance headphone loads.




Please tell more! What exactly did you hear?




> So in our amp design, the PSU needs to be rock stable, and we have no choice but to strengthen the PSU traditionally with more capacitance, as there is not precise regulation with the existing transistor voltage regulation,
> Unless we adopt an additional type regulation.
> Correct?




Essentially yes.

Different regulator with more power.

If you wish to be a tube purist for non-technical and non-auditory reasons, you could get a new PT with higher voltages and use a more powerful tube regulator. 

Or, try out a simple 2 FET reg. There are also more powerful regulators with more parts and better performance. Whether or not they'd provide any benefit is contingent on how unbalanced the amp is.


----------



## Maxx134

mrcurwen said:


> Please tell more! What exactly did you hear?
> 
> .





My MK8 which using 6h30 or 6n6p tubes, with a low impedance planar such as the hifiman, 
Would create a dip in the bias meters once volume is 3/4 way up.
Noticeable sound difference was a type of distortion somewhat like clipping. 

I prefer the 6n6p tube as it sounds superior and yet the bias meters go from the normal position of 60 down to 40ma.
And With stock settings I expect them to read around 30ma.

I do not believe these meters as accurate anyways, but it is interesting that the bias meters are at much less milliamp. 
So the PSU now supposed to have less of a load, which means the zener diodes have to dissipate more to control the power transistor PSU output voltage at around 100v each.

I realize the zener diode is controlling the whole PSU regulation, and that a zener is not a great regulator but that is another story.

The point is I should have plenty of power but my power tube settings are not optimized to show it.


Redge78 told me the meters should not have moved as they are bias meters and so the cicuit could have been driven out of the class A operation,
Because the MK6 does not have that problem with its different power tubes using planar headphones. 

I don't know, as I don't usually play at such loud volume,
But I can tell it is not as much power as it could be. 

So I looking to squeeze a bit more powerr out of them, by probably adjusting the bias point yet again.

One issue is the op-amp DC Servo controlling the voltage at the grid,
Which could be the problem.
The blue trim pots can adjust a wide range.
I believe they can move the bias meter a difference of 5-10ma on the meters.
I currently testing the range on the op-amp blue trim pots.

So I adjusted the cathode resistor. 
The bias was increased previously for the 6h30 tubes by dropping the total Rk resistance from 150ohm stock setting to 110ohm total, with a 402ohm paralleled addition.

This made the 6h30 tubes come alive and more dimensional, making stock settings sound like colored crap. 
The bias meters went from 60ma position to almost 75ma.

Yet I am no longer using the 6h30.
I am currently only using 6n6p type. 
I have not changed any parameters for the 6n6p tubes yet, as they already sound superior with an Rk of 110ohm.

But the meters are at 40ma instead of 60ma, and I do not believe the meters to be accurate, because from measuring the other 6h30 tubes I got a 3.6v volt drop across the cathode and the meters incorrectly read 70ma bias.
3.6v & 110ohm is only about 33ma bias.

So I am starting to think that the optimal setting would be to have the meters in stock position of "60ma",
For the circuit design & opamps grid voltage control. 

That would mean increasing my current bias point, which is at 40ma position using the 6n6p tubes.
Something I will try next and see if it performs better..
Also I must test the voltage drop to get the true reading for the bias.

Also I realized another reason why my bias meters may have dipped when blasting music,
 was because I lowered my Anode resistors from stock 150ohm to 82ohm.

It was for my WCF circuit impedance to match better my planar headphones at the time I was using the Ether headphones.

Right now I been using the HifiMan HEK almost exclusively but I switch to my HD800 at times, which sounds much better at the stock 150ohm anode (Ra) setting.


----------



## Maxx134

As for the global NFB, the MK6 uses a higher value resistance than the MK8,
Which means it uses less NFB.
I forget as usual, but I will look up the values.


----------



## Redge78

The MK8, even more than the MK6 due to its specific power tubes, being OTL is a "High voltage swing" / "Low current" amp.
 It fits perfectly the low power & high impedance receivers (our Senn headphones are a blessing for the OTL community).
  
 When you decrease the impedance of your receiver, you hit the "current limit" and that dictates the max power you can acheive (simple Ohm law).
  
 Even with the Ra swich to have the best balance between the 2 triodes of the White Cathode Follower which will allow both triode to produce their max current, you'll have that 50mA (?) current limit.
  
 Best (easiest ?) way to solve the problem would be to add some output transformers, with something like a 1:4 ratio. I wouldn't be surprised about MrC proposing a JFet stage


----------



## MrCurwen

maxx134 said:


> My MK8 which using 6h30 or 6n6p tubes, with a low impedance planar such as the hifiman,
> Would create a dip in the bias meters once volume is 3/4 way up.
> Noticeable sound difference was a type of distortion somewhat like clipping.




Do you mean the meters move if there is a transient in the music, and then move back to normal?

Or, do you mean they permanently moved position and stayed there?


The overall big picture problem with a low impedance load is that the amp simply runs out of current to deliver. To add to that, because of it's highish output impedance, it starts to "run out" even before it's actually out. Outputting current thru impedance changes the voltage waveform, distorts it. More current, more distortion. This can make transients distort even before the amp is out of current.

There is no easy solution; this kind of amp probably is just for higher impedance headphones.


I like to drive my 120 ohm headphones with something like 1 ohm output impedance. Followers driving (parafeed) OT's. There is no change in sound, headroom or volume with headphones if I switch speakers (6 ohm) on and off and on. 


As per tube selection, have you considered 6S19P?


----------



## MrCurwen

maxx134 said:


> As for the global NFB, the MK6 uses a higher value resistance than the MK8,
> Which means it uses less NFB.
> I forget as usual, but I will look up the values.




It's the ratio that counts, and the amount of gain inside the loop.

To pick arbitrary numbers, 100k / 2k will provide less feedback than 500k / 22k.

It's the voltage divider in the insertion point that matters with regards to amount of NFB. The value of the series resistor in itself does not tell you which amp has more NFB.


----------



## MrCurwen

redge78 said:


> The MK8, even more than the MK6 due to its specific power tubes, being OTL is a "High voltage swing" / "Low current" amp.
> It fits perfectly the low power & high impedance receivers (our Senn headphones are a blessing for the OTL community).
> 
> When you decrease the impedance of your receiver, you hit the "current limit" and that dictates the max power you can acheive (simple Ohm law).
> ...




All correct.

Simply adding OT's in the retro way is not smart though, unless you want to pay yourself senseless.


----------



## Maxx134

I have noted the higher impedance headphones do not sound better with lowered output impedance for this amp. 

The best sound came from impedance matching the WCF circuit to the headphones. 

Especially with the HD800, but even with the Ether at 30ohm .


----------



## Maxx134

mrcurwen said:


> Do you mean the meters move if there is a transient in the music, and then move back to normal?



Yes.
It starts to wiggle/dip slightly at 80% volume.

I usually never listen past the 50% though with the HEK,
And at 40% volume with the HD800.

So you see it is not bad, but I just want to squeeze more out of it.

So it seems the limitation is my tubes.

Since I am choosing a more inexpensive power tube, 
I will not worry about the life, and try maximize the bias,
 but first I must measure to see at what bais it truly is at.
Then I need to also make sure any new bias point actually sounds better .



I am currently altering the PSU so this will take some time.
Just got my new parts today for working on amp this weekend,

 so I will have an update on the bias over the weekend. 
Progress is a bit slow when not have the time on weekdays.


----------



## Maxx134

mrcurwen said:


> maxx134 said:
> 
> 
> > As for the global NFB, the MK6 uses a higher value resistance than the MK8,
> ...



Oh, OK.
 so now I have a new quest to figure out the :
*"the voltage divider in the insertion point "*


----------



## MrCurwen

maxx134 said:


> I have noted the higher impedance headphones do not sound better with lowered output impedance for this amp.




This is a very peculiar statement to make; unless you like less defined bass, slow sound and compressed dynamics. (Some people do.)

How was the output impedance lowered, please be very specific.




> The best sound came from impedance matching the WCF circuit to the headphones.




When you say impedance matching, does that mean that the output impedance of the amp was exactly the same as the load (headphone) impedance? 

Or, does it mean that the output impedance was at some value that was deemed 'optimal' to drive the specific load? If so, what was the logic by which this was arrived at?


----------



## MrCurwen

maxx134 said:


> Yes.
> It starts to wiggle/dip slightly at 80% volume.




Yep, just as Redge78 pointed out; the amp is running out of current.




> So it seems the limitation is my tubes.




Well, yes, but I don't think you can find a tube with significantly less plate resistance than 6AS7 and similar.

For low impedance load operation you can either

1) go with MOSFET output (I'm not a JFET guy BTW Redge78!)

2) go with an OT, preferably driven with low impedance driver for best results

Other than that, this kind of circuit simply cannot drive low impedance loads very well or at all (say, speakers).

There is one more option;

3) Parallel a whole bunch of tubes; this is what most OTLs do. Gets very crazy very fast.


----------



## MrCurwen

maxx134 said:


> Oh, OK.
> so now I have a new quest to figure out the :
> *"the voltage divider in the insertion point "*




The insertion point is the input tube's grid. The other resistor in the NFB voltage divider is the 10k resistor next to the insertion point.

I just did some simming, and with 100k series resistor for NFB (low gain) the attenuation seems to be:

When putting into the circuit 100 mVPP signal, the signal at the grid is about 40 mVPP. I leave it to you to calculate the dB amount, but it's a pretty significant amount of NFB for a tube amp in my opinion (opinions may vary).


----------



## SonicTrance

mrcurwen said:


> Or, does it mean that the output impedance was at some value that was deemed 'optimal' to drive the specific load? If so, what was the logic by which this was arrived at?


 
 I can answer this!
  
 We have calculated specific values for Ra at a given load after reading the Cavallis WCF paper.
  
 It's this formula we used:
  

  
  
 This mod gave great results for me. Especially when using my LCD-XC (20 ohms)!
  
 The output impedance does not change much though. I used this formula to calculate the Zo:
  

 For example;
  
 With WE421A's
  
 Mu = 6
 rp = 310
 Ra = 330 (stock)
 Rk = 165
 Zo = 37.9 ohms
  
 Change Ra to 100 ohms:
  
 Zo = 40.4 ohms
  
 I realize that the Zo calculation is not exact as the rp changes with the operating point, but there you go.
  
 So, this mod is about balancing to WCF at a given load. Not so much about the amp output impedance.


----------



## MrCurwen

sonictrance said:


> We have calculated specific values for Ra at a given load after reading the Cavallis WCF paper.
> 
> It's this formula we used:




Ah, that clears it up. When you optimize a circuit like this, it usually needs to operate with the specific load used in the optimization calculations. So no wonder Maxx134 reported high impedance phones sounding off with "lower" output impedance. 

Lowering the output impedance of the amp, as opposed to optimizing it for a specific load, should benefit all loads. As I've said, my own amps have only a couple of ohms or less output impedance, and my headphones are 120 ohms. I specifically made it like this; the sound became more fast and more dynamic the lower the output impedance became.



> So, this mod is about balancing to WCF at a given load. Not so much about the amp output impedance.




Yes exactly. 

These optimizations can work fine. Some people like the SRPP things; I got really tired of optimizing them really fast, and went with brute force actual drive capability.


----------



## Maxx134

mrcurwen said:


> maxx134 said:
> 
> 
> > Yes.
> ...




Oh, I do not believe there is a problem with the 6as7 tubes as that is the MK6.

Who knows, I might try 6as7 on the MK8,
But I really like the 6n6p tubes which I am currently using for power tubes.

The issue does not occur with the higher impedance cans like the HD800, which the amp was designed for.


Thanks for the NFB info I will calculate with actual resistance on high gain which is what I always use. 
I believe around 300k but I have to check.


----------



## SonicTrance

mrcurwen said:


> sonictrance said:
> 
> 
> > We have calculated specific values for Ra at a given load after reading the Cavallis WCF paper.
> ...




Yes, that's why we use a switch for different headphones and tubes! 
I have four different settings,
6AS7 - 110 ohm load
6AS7 - 20 ohm load
421A - 110 ohm load
421A - 20 ohm load


----------



## baronbeehive

sonictrance said:


> Yes, that's why we use a switch for different headphones and tubes!
> I have four different settings,
> 6AS7 - 110 ohm load
> 6AS7 - 20 ohm load
> ...


 

 Have you reinstalled the switch? I'm struggling to keep up atm but I knowing you had problems with it I just wondered what the position was now? Also I wasn't sure about the status of this mod in view of the problems of optimising the settings for the HD800 when balancing the WCF for a given load.
  
 BTW Maxx, slightly off topic, but I seem to remember you saying you would not be using the HEK because too expensive!


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Yes, that's why we use a switch for different headphones and tubes!
> ...




Yes, switch is back in, working no problems. I had a short last time.


----------



## Maxx134

Edit :
Further testing required.


----------



## Maxx134

baronbeehive said:


> .
> 
> BTW Maxx, slightly off topic, but I seem to remember you saying you would not be using the HEK because too expensive!



Well, I don't remember saying that,
But I had to try it.


What I found is that it is my preferred headphone. 

I am currently liking the combo of just 2 headphones (HD800 & HE1000).


----------



## baronbeehive

maxx134 said:


> Well, I don't remember saying that,
> But I had to try it.
> 
> 
> ...


 
  
 Excellent - getting rid of the Senns.........just joking Redge!
  


maxx134 said:


> ............
> 
> Edit:
> Here is an old quote from Regldge78 in PM,
> ...


 
  
 So is page1 being upgraded with the info.


----------



## MrCurwen

maxx134 said:


> Oh, I do not believe there is a problem with the 6as7 tubes as that is the MK6.
> 
> Who knows, I might try 6as7 on the MK8,
> But I really like the 6n6p tubes which I am currently using for power tubes.




The point was that there are very few options to improve the performance further, within your circuit topology and component preferences.

WCF topology with it's local NFB and the gNFB of the whole circuit provide a lower output impedance than the intrinsic output tube plate resistance.

However, there is no way to escape the fact that those factors only work as a leverage, a coefficient, the intrinsic plate resistance of the output tube is still at the center of it all.

(Quoted rp is datasheet value for "common op points", actual in-circuit rp is dependent on op point. Still a useful comparison tool.)

6AS7 and 6080 and eq have rp of about 280 ohms. 

6N6P has about 1.8 k, which is quite high. There are a number of dirt cheap TV sweep tubes that can easily provide better results. That version must have a lot more gNFB to compensate for this high rp!

Common pre-war tube designs like 2A3 and 300B have 800 and 700 ohms rp respectively, but they have their other disadvantages.

Only common tube that has lower rp than 6AS7 that comes to mind would be the 6S33S with 130 ohms. That one is quite a monster.


Of course there's always parallelling. That's the way OTL guys usually go. That has it's own set of problems as well; the designer of your amps could've easily gone this route but didn't, probably for good reasons.

I've found parallel tubes to always provide a bit less microdetail than singles. This goes for 2A3 as well, since it's internally parallel'd.


So,

1) Leave it be with it's restrictions and compromises (make no mistake, higher output impedance and/or gNFB do leave a sonic imprint)

2) more gNFB

3) go source follower

4) parallel several tubes

5) 6S33S


----------



## Maxx134

Thank you. 
What do you think about choice of DC over AC heaters? 
I have considered to go DC, which would increase my range of tube choices that require more heater current..

Edit:
Also I have looked at how the AC heater ground was elevated, and wonder if that was necessary for the AC
Heater feed.


----------



## MrCurwen

maxx134 said:


> What do you think about choice of DC over AC heaters?




Depends a lot on the situation at hand.

For directly heated tubes, well regulated (not with an IC, but discreet circuit) DC is mandatory, not optional.

For mic preamps and RIAA correctors and other very low signal level stuff (possibly DAC output analogue parts); recommended. Again, well regulated, just "DC" is not a good idea.

For most indirectly heated middle and high level signal circuits? Not a particularly good idea, unless there is audible 50 Hz hum.


A simple PSU for heaters that has transformer -> diode bridge -> cap (-> maybe R / L + C) -> heaters is not a step up in most cases. Unless the filter section is very well filtered and feeding a low current heater system (like a single 6SN7 with 600mA heater), you're going to end up with a worse looking wave on the heater.

Let's assume an AC heater system has a perfect sine wave. It doesn't, since wall AC is full of garbage in most places. 

The way electromagnetic waves go to places they don't belong to (tube cathode, other wires close to heater wires etc.) is reliant on the waveform. The closer the waveform is to DC, the less there is induction (just like inside all transformers). The more sharp corners there are, the bigger the pulses that are inducted.

Get PSU designer tool from Duncan, very handy program. Simulate the PSU you'd have, and look at the ripple amount and shape.

A rectified "DC" heater supply will have a 1 volt or even more of a sharp triangle wave riding on top of the DC component, unless there are several filter sections not just one or two. So RCRCRCRC.

This gets pretty stupid very fast; so smarter route is to regulate the supply properly. A single gyrator kind of FET, voltage controlled impedance, kind of sort of mimicing a huge L, and you only need one RC filter section before it.

Even several amps of current thru it, and no hum. Very small ripple measured with oscilloscope.

However, this system has a drawback; heat. Always with the heat. The FET has a 4 or 5 volt drop, and say you have 1.5 A current needed; that's 7.5 W of heat inside chassis. 

So no, unless there is audible hum, I personally would not recommend using a sloppy "just rectified high pulse 'DC'" approach, and even the regulated one needs a good reason to be used, in my opinion.



> I have considered to go DC, which would increase my range of tube choices that require more heater current..




How would it increase your range of tubes? Are you looking for tubes with more heater current, and afraid it will cause hum (it sure might)?



> Also I have looked at how the AC heater ground was elevated, and wonder if that was necessary for the AC
> Heater feed.




Short answer; yes, it's a good idea.


----------



## Maxx134

mrcurwen said:


> How would it increase your range of tubes? Are you looking for tubes with more heater current, and afraid it will cause hum (it sure might)?



Yes that is correct,
 The Transformer winding for the driver tubes is the weak point, according to the transformer schematic posted by Sonic trance earlier.


----------



## MrCurwen

How much heater current are you looking to have?


----------



## Maxx134

I have been rolling anything I could fit in my amp, even getting rediculous with two adapters(!)...


Searching for the elusive addictive excitement of trying a new and different tubes, 
and then afterwards playing with the anode/cathode resistors to totally throw it's operation/bias points differently to see how it sounds...





Even comparing different tubes on right and left channels ..



It has been very fun,
And scary because I can tell I am pushing the transformer windings beyond its safe limits. 
I recently realized the "start rush current" on initial turn on is what may be killing my transformer heater windings!

That and the fact that I fall asleep with my amp on all night and my room get quite hot at 28 degree celsius(!),
So there is high heat condition.



Anyways, another point is,
The realization is that tube rolling is not the same to me anymore...







I have come to a different conclusion on how I am viewing things. 
I am no longer viewing "tube rolling" as important as other aspects, notably the circuit design choices. . 

Tube choice is important, 
But circuit design and tube operating point has the most noticeable benifits and of higher importance,
Not tube rolling. 

As a consumer we are limited by the design so only have the choices of tube rolling. 
It can be a huge waste of money as well.

Now that I am modifying the circuit, and so not as much bound by circuit design limitations,
 I am seeing a sea of bewildering choices to make in terms of design choices, to jump in the DIY.

But for now I will settle on this little dot parameters while I learn.
I already have taken steps to solve my tube heater current limitations.

 I plan to use separate DC supply for the tube heaters, so I won't strain the stock transformers, 
 and at same time while I have unit circuit board open,
I will upgrade transistors and diodes rated at much higher currents. 

Once it is done I will post.


----------



## Maxx134

Anyways
 to answer the question,
For this MK8 amp, 
I think I will settle with the 9pin 6h6p for powertube so that is not a problem.

The main change will be my choice of driver tube which will be an 8pin, and so I like to have over 1amp for each tube heater current in case I try an ecc31,
But most likely be using the same tube SonicTrance likes, the ecc35 at his bias settings. .


----------



## Maxx134

The tube rolling madness has passed. ..
For now..
Look:




























Ugg,
Wew!


----------



## coinmaster




----------



## Maxx134

Well at least your alive!
I Remember there is one member in old thread (SoundEngineer) that dissappeared after sayn he was going to replace all his caps..
I hope he comes back but I fear he didn't make it..


----------



## coinmaster

I've gotten 2 shocks so far, a 200v one from the filter caps when my solder wire touched it which caused convulsions in my arm and painful contraction in my chest but I didn't think much of it and I actually thought it felt kind of cool. The other shock was form my big 150uf red caps that were charged to 350v from weeks before. I forgot they were charged and I picked them both up in each hand to move them, again I didn't think much of it, it took me a second to realize what was happening.
 Needless to say I make sure neither of these things happen anymore. 
  
 I wonder how current can even flow through the body with no ground connection? There is a third time that I should have been shocked but I wasn't. One time when I had my ghetto rigged power supply up and running I leaned over and accidentally touched a connection with 165v on it but all I felt was warm metal. I wonder what the conditions are for a shock to occur and a lethal shock. I know current through the heart is bad and being grounded is bad but I wasn't grounded in any obvious way the two times I was shocked and that other time I felt no shock.


----------



## Maxx134

Usually we touch with our hands, 
But just were the shock goes thru is very variable. 
Across the chest most dangerous of course.

But thru 2 fingers only will go thru one hand and send shock feel up arm.
AC is always shocking, 
But DC can hold or repell you for the shock duration .

They say only a small amount of current can kill, but I am assuming it would have to go thru the heart.

Then there are all those stories of people getting hit by lightning, 
Ha


----------



## Maxx134

I used to touch 9 volt batteries with my tongue to check it if it's good,
and my friend used to use his two fingers to test for house 110v AC,
Ha


----------



## coinmaster

maxx134 said:


> and my friend used to use his two fingers to test for house 110v AC,
> Ha


 
 Wow lol.


----------



## Maxx134

coinmaster said:


> maxx134 said:
> 
> 
> > and my friend used to use his two fingers to test for house 110v AC,
> ...



You know the mechanic type guys with super rough callous dried out hands, lol


----------



## baronbeehive

maxx134 said:


> You know the mechanic type guys with super rough callous dried out hands, lol


 

 I'm back again after the house move!
  
 What you said reminds me of the car maintenance class I went to and this old chap started up the engine and pulled out the high tension leads and proceeded to stick one finger up it and sparks flew out of his remaining 9 fingers!


----------



## coinmaster

http://spectrum.ieee.org/semiconductors/devices/introducing-the-vacuum-transistor-a-device-made-of-nothing
 https://www.nasa.gov/sites/default/files/atoms/files/arc-17130-1_nanostructure-based_vacuum_channel_transistor.pdf
 http://spectrum.ieee.org/semiconductors/materials/how-a-microscopic-supercapacitor-will-supercharge-mobile-electronics


----------



## Maxx134

Need.
More..
More testing...


----------



## Mogos

Finnaly arrived. The guy just forgot to send them after my payment . He has done it two months later after the dispute on the PayPal had been opened. It can happend but why he did not respond to my messages? 
	

	
	
		
		

		
		
	


	



 Now the 7193 are runing and it looks like this:
  

 Compared to 6C8G they are in the same league. There is no jaw dropping effect as I had encounter substituting the new production Tungs Sols with the 6C8G tubes.
 The 7193 are giving more foucused and tight sound. Better sound stage imaging with very good separation of the instruments. Less spontaneous and colorfull presentation than the 6C8G but also very interesting. They need more hours and most probably the sound signature will change. But I don't know which direction. 
 I have to do the mod on the driver stage resistors. I had planned to make a switch for the 6SL and 6SN tube types but I will do optimisation only for the 6SL type and it will be enought also for the 7193. What I hear now is very good so no need to go for extreme solutions 
	

	
	
		
		

		
		
	


	




.
  
 Thank you MrCurven to pointing out the 2C22 tubes. You have mobilized me to get finnaly good tubes for the drive stage. Now I understand how mutch I had been missing till now.


----------



## coinmaster

Just don't buy the lot of 10 2C22 tubes from the italian ebay guy. He stiffed me.


----------



## Mogos

I have got at last 2 pairs from him. But it looks like I had been lucky. PayPal helped 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

I think you got "lucky" Mogos, to at least get the tubes. Just look at the guys recent feedback. 

Great that you're enjoying them as well!


----------



## Maxx134

Mogos, 
Remember your stock settings on driver section are set very small/low. ..
All your tube have hidden potential.

Once you open up the bias more, 
It will be the biggest improvement over any tube choice. 
You will be blown away, guaranteed! 


I have had some delays, and will be finishing up my amp on my Vaca next week.


----------



## Maxx134

For those interested, 
I was looking into this issue of "feedback" in the mk6 & mk8 circuits. .

There is an attenuation or gain switch inside ,
Which introduces Global feedback into the overal amp design...

It seems like a more significant amount in the MK8...

Also it has been PM to me that reduction of this feedback makes the MK6 worse.
This is opposite of what normally would be assumed.


It is generally assumed that Feedback will allow and intoroduce more higher harmonics and sideband distortions that were not originally present,
 while only basically lowering the 2nd harmonic to make specs look good. .

But the testing was not fully covered as it introduced low amounts of feedback...

What we have in the little dots amps are (by my assumption), relatively high amounts of feedback...

This in turn poses both an intellectual problem and a real one,
Because the amp literally sounds fantastic with the gain on low, which translated to higher global feedback. ..

So this got me to do a little searching and I immediately found this issue explained which our amps prove in actual use of higher feedback amounts...

Quote :
*
"...it is normal for an experimenter to experience that if you take a good-sounding zero-feedback amplifier and add 6dB of feedback, the result sounds worse. They heard that right. But had they been in a position to add 60dB, well then, suddenly they would have been confronted with a sound that is little short of magical."*

Here is the link to the page for an interesting read:

http://www.soundstageultra.com/index.php/features-menu/general-interest-interviews-menu/455-searching-for-the-extreme-bruno-putzeys-of-mola-mola-hypex-and-grimm-audio-part-one


Looks like the designer of these little dot amps is still "one step ahead ",
As we discover his design goals..

Edit :
Actually I believe the primary reason for the feedback was to bring down the output impedance. .

Looks like yet another topic to experiment. ..


----------



## coinmaster

Negative feedback increases high order harmonics unless you use a lot of it. That is why adding only 6db of NFB would make a good zero feedback amp sound worse. High order harmonics are the bad stuff.


----------



## Bruch

2 stupid questions:

1) Is the negative feedback in the system the single most limiting factor in this amp - even more so than the limiting factors that the mods on the first page are trying to solve?
2) Is it even possible to achieve reasonable levels of impedance in this amp without a negative feedback loop?


----------



## coinmaster

The main purpose of the negative feedback is to lower the output impedance. The higher the output impedance of an amplifier the more the headphones imperfect frequency curves are exaggerated. Tubes all have too high of an output impedance even as a cathode follower. Negative feedback sacrifices gain for linearity, lower impedance drop, better phase alignment.
 So no, negative feedback is not the most limiting factor unless you are part of the crowd that thinks all NFB is evil, which it may or may not be, I haven't built an open loop amp yet.
 Also no, you can't get reasonable levels of output impedance without changing the design. Unless you use planar headphones, then output impedance doesn't matter anyway because they have a flat impedance curve.


----------



## Maxx134

The MK6 really doesn't have any problems with any headphones and I would say it actually hard to beat..


----------



## Maxx134

I had some delays both electronically and in personal life,
So ow back to refining driver stage.

So far I am liking the soundstage of the 6f8g,



But my best driver stage tubes consist of the ecc35, and the Silvana 6sn7W..


Those top choices I assume will be similar to the MK6, because the driver stage is the same..


----------



## baronbeehive

*SMLD MODS:* *Final stage*.
  
*Stage 6 -* Testing, testing......
  
 Guys, I've just spent the last hour or so with goose pimples going up and down my neck.
  
 I've finally replaced the dodgy tube in order to have a first listen after all this time! And what you have been saying is right there are improvements across the board. Everything is more realistic, more transparent, more 3 dimensional. The sound is fuller and draws you in more to be nearer to the music. It was a similar feeling to when I tried out a new DAC, everything stood out more, all the instruments were better defined. The treble is not quite so artificially bright, the bass is fuller, but everything we like about the LD, the sound, is still there, it just adds to it. I don't know what that is down to because I've done all the mods at once so I can't say its the wiring, or the caps or whatever.
  
 At this level I think we realize that any improvements are going to be fairly small, and I don't want to exaggerate them, and I've always thought the basic LD was good, but taken together they add up to something that's difficult to describe because its just what good music should be, you can't say the bass is mind boggling or the guitar is amazing because it's just how it should be. I can't see how it could be improved further yet you say the impedance switch does just that, but I think it is now down to matching headphones to get exactly the sound you want, and I'm looking to getting the HE1K's when I can.
  
 I've had to limit listening time because the bottom plate doesn't fit on properly so next is to reroute some wiring and parts to make everything fit better, then the bigger fans and finally the disco lighting he he...... Also I have to try to find out why the right hand meter is reading high now. Then there's still the WE 421A's and ECC35's to look forward to..... it goes on........


----------



## Maxx134

High meter reading only correspond to the power tubes.

Usually one slowly dying tube will be the cause.


----------



## Maxx134

baronbeehive said:


> *SMLD MODS:* *Final stage*.
> 
> ...., and I'm looking to getting the HE1K's when I can...




Price dropped under 2k because of Version 2 announcement.
Good deal, especially with upcoming mods to make them better


----------



## nuport

Hello,
  
 I would like to start modding my MK VI. Can someone help with my parts order list below? I don't have an electronics background and I'm a bit unsure if I have the quantities of each part are correct:
  
 Coupling caps: (2) Jupiter 0.47uf 600v
 Decoupling caps: Wima 0.47uf 600v film cap do I need 4 or 6? 
 Cathode bypass caps: (4) Elna Silnic II  0.47uf 50 v and (4) Kemet PME271M 0.1uf 275v
 PSU caps: (2) Mundorf M-Lytics 1500µF Where can I buy these in the US?
 Power Stage Resistors (8) Mills MRA-5 330ohm
 Driver Stage:  (4) 220k ohm _TKD CM2 Series 2 Watt - __1% Metal Film Resistors _
_                      (4) 10k ohm Vishay Z-Foil resistors_
_                       (2) 1.5k ohm Vishay Z-foil resistors_
 WCF coupling caps: (4) WIMA FKP1 0.22uf 400v
  
  
 Do I have this right? Your help is appreciated.


----------



## baronbeehive

nuport said:


> Hello,
> 
> I would like to start modding my MK VI. Can someone help with my parts order list below? I don't have an electronics background and I'm a bit unsure if I have the quantities of each part are correct:
> 
> ...


 
  
 Hi nuport. Re: your parts list, you need *4* x Jupiter coupling caps, 4 x Elna Silmic II  *470uf,* *not* *.47uf *or Mundorf E-cap 220uf cathode bypass caps, also it is recommended to go for *.33uf* WCF caps. Your decoupling caps will depend on whether you're going for the compact version which will fit in the existing chassis or whether you want to build a new chassis bottom to fit everything in. You will need 6 x PME-140: 0.33uF 275 Vdc Evox Rifa PME271M bypass caps anyway, then for the compact version 4 x Mundorf Mcap *47uf, not .47uf, *and you could do what I did and have 2 x MKP 40 µF Wima. Everything else is fine.
  
 If in doubt go to page 73 where I finished my build which lists all the relevant mods pages of mine and Mogos and SonicTrance and you can check everything from there.
  
 Good luck and keep us informed of progress, always nice to see someone else go through it like we did 
	

	
	
		
		

		
			





.
  
 Edit: you will have to think your way into this before starting anything...... I just remembered that if you are going to use the 2 x 40uf WIMA's then they will not fit if you use your 2 x 1.5k Z-foils unless you can lay them flat.


----------



## baronbeehive

maxx134 said:


> High meter reading only correspond to the power tubes.
> 
> Usually one slowly dying tube will be the cause.


 
  
 Not in this case as I've swopped them all round and it's always the right meter that reads 90ma.
  


maxx134 said:


> Price dropped under 2k because of Version 2 announcement.
> Good deal, especially with upcoming mods to make them better


 
  
 Sounds good, are you still happy with yours? Only thing with those is being willing to look like an idiot when wearing them 
	

	
	
		
		

		
		
	


	




.


----------



## Maxx134

baronbeehive said:


> maxx134 said:
> 
> 
> > High meter reading only correspond to the power tubes.
> ...




First off,
1st Topic:
 I tip my hat off to you.
I could not have answered parts list question better mysel, and shrewd insight on option to lay the zfoils,
AlthoughI no longer recommend any zfoils for cathode resistor as our latest driver stage testing shows we will go with larger resistor at lower resistance.
So anyways, maybe Ridge should link your parts post as a good example...
I can link it as well .

2nd topic:
If yout right meter remains higher, is it from beginning, or after a while?
Check meter calibration screw in front middle when unit off it shod be pointing nicely zero.
Also,
The DC offset opamps are known to control the bias slightly, which is what the meter is showing.
If not off by much, like 10 more I would not worry but you said 90 so I must assume should you check your Anode / cathode resistors just in case.

3rd topic:
The HEK being used at home so it doesn't matter how it looks,
But I likes my first older unit which was very loose and broken in.
It broke due to an accident and I almost died on the spot when that happened ...
My replacement unit is stiffer and needs burn in as well, sonot at the level of ease my old unit had.


I not sure if you know this but I am the one who made the first HEK mods.

I have since made new mod on them and will post soon,
As I believe they should be as good as V2 now.
I will compare mine this week to another member stock HEK.
I will call it the V2 mod.

Sorry guys for off-post topic as just wanted to respond to the question.


----------



## Benny-x

maxx134 said:


> 3rd topic:
> The HEK being used at home so it doesn't matter how it looks,
> But I likes my first older unit which was very loose and broken in.
> It broke due to an accident and I almost died on the spot when that happened ...
> ...




I find it interesting how no one has heard the HEK V2s yet, but they're already making their way into comparisons... I'm hanging on tightly to my V1s, I'm a huge fan and doubt there will be much difference, if any; pending both versions have the V2 earpads.

About your mods though, I'm looking forward to seeing the thread, I enjoyed the first one quite a bit. It was very interesting to do my own trials and heat the sound changes right before my eyes/ears. So, colour me interested!


----------



## baronbeehive

maxx134 said:


> First off,
> 1st Topic:
> I tip my hat off to you.
> I could not have answered parts list question better mysel, and shrewd insight on option to lay the zfoils,
> .........


 
  
 You forget, I've been through the pain and suffering lol!
  


maxx134 said:


> .........
> 2nd topic:
> If yout right meter remains higher, is it from beginning, or after a while?
> Check meter calibration screw in front middle when unit off it shod be pointing nicely zero.
> ...


 
  
 So is it just a continuity check on the resistors?
  


maxx134 said:


> ......
> 3rd topic:
> The HEK being used at home so it doesn't matter how it looks,
> But I likes my first older unit which was very loose and broken in.
> ...


 
  
 I didn't know about V2, I'll have a look at that but sadly money is flowing one way only atm due to the house move so I'm unlikely to get my hands on them any time soon 
	

	
	
		
		

		
		
	


	




.
  
 Edit: Next up is a LED Cluster Advance 120mm fan that Sonic recommended, I think I can just afford that!


----------



## Maxx134

benny-x said:


> About your mods though, I'm looking forward to seeing the thread, I enjoyed the first one quite a bit. It was very interesting to do my own trials and heat the sound changes right before my eyes/ears. So, colour me interested!



What people do not know yet is..**redacted** due to off topic & "TMI".
Hehe.
There is a ""battle of the headphone giants" going on with all these new headphones coming out and as a customer it can only spell good news for us.


----------



## Maxx134

baronbeehive said:


> So is it just a continuity check on the resistors?
> 
> Edit: Next up is a LED Cluster Advance 120mm fan that Sonic recommended, I think I can just afford that!



Not continuity, but you can measure the resistance to make sure they read the resisor value.

Sonic has the best fans,
as I believe they move more air than my single jumbo fan.


----------



## nuport

baronbeehive said:


> Hi nuport. Re: your parts list, you need *4* x Jupiter coupling caps, 4 x Elna Silmic II  *470uf,* *not* *.47uf *or Mundorf E-cap 220uf cathode bypass caps, also it is recommended to go for *.33uf* WCF caps. Your decoupling caps will depend on whether you're going for the compact version which will fit in the existing chassis or whether you want to build a new chassis bottom to fit everything in. You will need 6 x PME-140: 0.33uF 275 Vdc Evox Rifa PME271M bypass caps anyway, then for the compact version 4 x Mundorf Mcap *47uf, not .47uf, *and you could do what I did and have 2 x MKP 40 µF Wima. Everything else is fine.
> 
> If in doubt go to page 73 where I finished my build which lists all the relevant mods pages of mine and Mogos and SonicTrance and you can check everything from there.
> 
> ...


 
 Baron,
  
 Thanks so much for your reply, it was very helpful. Please do not give me too much credit, I'm not going to do the install myself  I went to page 73 of this thread but couldn't locate any parts lists (I also checked all your posts around March and couldn't seem to locate one either). Below is my revised parts list with some additional questions.
  
 I couldn't follow this comment: _"You will need 6 x PME-140: 0.33uF 275 Vdc Evox Rifa PME271M bypass caps anyway, then for the compact version 4 x Mundorf Mcap *47uf, not .47uf, *and you could do what I did and have 2 x MKP 40 µF Wima." _Which mod is this referring to?
  
 I would like everything to fit in the existing chassis, so please let me know if I have selected anything that would not fit. Also, for those of you who have upgraded the fans in the existing chassis with these mods, what is the height of your fans?
  

ModQtyPartQuestionCoupling Caps4​Jupiter 0.47uf 600v Decoupling caps4​Wima DC Link 47uf 700vHow many do I need? If I want to fit in existing chassis what values do I need?Cathode bypass4​Elna Simic II 470uf 50vIs this correct?Cathode bypass4​Kemet PME271M 0.1uf 275vIs this correct?PSU Caps2​Mundorf MLytics 1500ufWhat voltage do I need? US source only has 100vPower Stage Resistors8​Mills MRA-5 330ohm Driver Stage Resistors4​TKD CM2 Series 2 watt 1% metal film Driver Stage Resistors4​Vishay Z-foil Driver Stage Resistors2​Vishay Z-foil 1.5k ohm NakedAre naked ok? I can't find these in a non-naked version in 1.5k ohmWCF Coupling4​WIMA FKP1 0.22uf 400vI cannot find these in 0.33uf online
  
 Is changing the volume pot worth it? Mine can get a bit scratchy when I move it. The knob feels kinda chinzy too.  I did read in a post that it is the same as the Oppo HA-1. I wonder if they would be willing to sell me just the volume knob and if it would fit. Anyone else have ideas for a nicer knob too?
  
 I will happily clean this table up and include links to everywhere I bought the parts once I have this finalized so that it can be added to the thread


----------



## Maxx134

We will be going with a lower than 1k resistor and at higher wattage so right now haven't decided.

There are two different values we are testing so I would NOT get any zfoils for driver stage Anode cathode as they are expensive and will be replaced.

You can either leave stock for now, or try new values we have not yet determined which is optional yet.


Also for the WCF coupling, try using a non- plastic type cap.
Paper in oil type cap (vitaminQ or Russian caps) is what I have to compliment my main coupling cap Jupiter copper foils.

the WCF caps Sonic traits must compliment the main coupling caps.

First page has link to cap types .

Wima caps excellent at size and value, but WCF is an area which influence sound, so best sound types are favored.
Mundorf is actually a fav pic there.


----------



## Maxx134

If in USA, 
I would check mouser electronics and 
Soniccraft..

For the power supply caps go here:

http://www.soniccraft.com/index.php/electrolytic-capacitors-mundorf-c-23_318


----------



## baronbeehive

maxx134 said:


> What people do not know yet is..**redacted** due to off topic & "TMI".
> Hehe.
> There is a ""battle of the headphone giants" going on with all these new headphones coming out and as a customer it can only spell good news for us.


 
  
 Maybe I will sell my house so that I can afford them then!
  


maxx134 said:


> Not continuity, but you can measure the resistance to make sure they read the resisor value.
> 
> Sonic has the best fans,
> as I believe they move more air than my single jumbo fan.


 
  
 Yes but I like the lights mainly 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

nuport said:


> Baron,
> 
> Thanks so much for your reply, it was very helpful. Please do not give me too much credit, I'm not going to do the install myself  I went to page 73 of this thread but couldn't locate any parts lists (I also checked all your posts around March and couldn't seem to locate one either). Below is my revised parts list with some additional questions.
> .................


 
  
 On page 73 I gave all the pages that have my mods on, one of which was page 53 which has the parts list which you could refer to along with page 1. It takes a while to take in, I had to study it for a while before it began to sink it but in certainly helps to become as familiar as possible, even if you are not going to do it yourself.
  


nuport said:


> .............
> I couldn't follow this comment: _"You will need 6 x PME-140: 0.33uF 275 Vdc Evox Rifa PME271M bypass caps anyway, then for the compact version 4 x Mundorf Mcap *47uf, not .47uf, *and you could do what I did and have 2 x MKP 40 µF Wima." _Which mod is this referring to?
> 
> ...................


 
  
 The 6 x .33uf bypass caps are for bypassing the other 6 decoupling caps to compliment them in sound qualities that they may be lacking on their own. We have therefore decided to have the main 6 decoupling caps with the bypass caps soldered on to them. For them all to fit you will have to have the 4 Mundorf Mcaps I mention, not the 4 Wimas you mention. Then you need another 2 decoupling caps for the driver stage which could be the ones I mention, (which are WIMA's).
  
 For PSU caps you should get 160v, not 100v.
  
 The fans will not fit unless you reverse the bottom plate with the fans outside, for this you will need longer legs to clear the table.
  
*This is my parts list below:* Have a look at it again together with the diagrams on page 1 to get an idea of how everything will fit inside.
  
*SMLD: Parts List*
  
 This is my parts list so that if you think there is anything missing you can let me know now, perhaps you could tell me before I start. I'm only going for the minimum necessary resistors as recommended by Maxx and what I think I need, for example I wasn't going to get any new driver stage resistors - the 2 groups of 3 on the other side of the driver tubes from the 220k ohm ones. These could be the zfoils. If you think I ought to have them let me know because I only want to do this once 
	

	
	
		
		

		
			





.
  
*Capacitors:*
  
  - Output stage decoupling     - Mundorf Mcap 47uf, 250V x 4
  - Driver stage decoupling      - MKP 40 µF Wima  800V 10 % x 2
  - Decoupling                          - PME-140: 0.33uF 275Vdc Evox Rifa PME271M x 6
  - Cathode bypass                  - PME-080: 0.1uF 275Vdc Evox Rifa PME271M x 4
  - Cathode bypass                  - Mundorf E-cap 220uf, 63V x 4
  - PSU caps                            - Mundorf M-Lytics AG 1500µF 160V x 2
  - Coupling, or WCF coupling - Audyn True Copper 0.22uF 630VDC x 4
  - WCF coupling, or coupling  - Mundorf Silver in Oil 0.33 UF 1200V 2% x 4
  
*Resistors:*
  
  - PSU stage    - Mills MRA5 8K2 x 2
   - Power stage - Mills MRA5 330R x 8

   - Driver stage  -TKD 2w 220K metal film x 4
  

*Wires:*
  
 - Chassis cable runs - 4 x 2-foot long cables, 3 core 22 AWG silver plated PTFE 19 strand wire
 - Output cables - Neotech 20 AWG, UP-OCC copper single core wire, RED teflon
  
*Misc:*
  
  - AMR Audio 90% Silver Alloy Fuse Tube 5x20mm 3.15A (Slow Blow) x 1
 - AMR Audio 90% Silver Alloy Fuse Tube 5x20mm 0.5A  (Slow Blow) x 2
  
 ......Oh, and there's the soldering video.............or soddering as you call it in the US .........most essential part of all!!
  
 Finally we recommend you have 2 Mills PSU resistors as above but don't bother with the Z-foils as Maxx has suggested, you could leave the stock until  you know what ones to replace. 
	

	
	
		
		

		
		
	


	




.
  
 Post your parts list when you're ready and we will check it again just to be sure
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

baronbeehive said:


> *SMLD MODS:* *Final stage*.
> 
> *Stage 6 -* Testing, testing......
> 
> ...


 
 Long time no see Baron!
  
 Congrats on getting to finally listen to your modded MK6! And like you say, it only gets better from here with tube rolling and MORE mods!


----------



## baronbeehive

sonictrance said:


> Long time no see Baron!
> 
> Congrats on getting to finally listen to your modded MK6! And like you say, it only gets better from here with tube rolling and MORE mods!


 
  
  
 Hi Sonic!
  
 I've been a while with no internet connection what with the house move but things are getting back together now at last. Couldn't wait to try the amp! Then I had problems waiting for the new tubes which went to my old address and I couldn't get hold of them 
	

	
	
		
		

		
		
	


	




, but I'm so happy now that everything's working ok apart from the problem with the right meter. And its great to know that our LD is right up with the best out there after the mods so looking forward now to just enjoying it and watching those LED's when the fan arrives 
	

	
	
		
		

		
		
	


	




.


----------



## Maxx134

nuport said:


> Is changing the volume pot worth it? Mine can get a bit scratchy when I move it. The knob feels kinda chinzy too.  I did read in a post that it is the same as the Oppo HA-1. I wonder if they would be willing to sell me just the volume knob and if it would fit. Anyone else have ideas for a nicer knob too?



A long time we considered this and I also have an extra volume knob I never tried.
The issue was the fit.
There is no easy replacement.


Any truley high quality volume are too big.
Your money & resources are much better spent on other areas..






baronbeehive said:


> ...
> Not in this case as I've swopped them all round and it's always the right meter that reads 90ma.





To get to the bottom of this ,
I would like to know if the meter shows norm reading at first, and how long does it take to go to 90?
 Slow or quickly?

Also do you hear any tiny pop sound when inserting headphones?

We have to take in the role the DC servo is doing to keep a zero DC offset so should be zero pop .

My guess is if the meter always read 90, one of your resistors are incorrect value or slightly off,
But my first guess is always the power tubes.


----------



## baronbeehive

maxx134 said:


> ..........
> 
> To get to the bottom of this ,
> I would like to know if the meter shows norm reading at first, and how long does it take to go to 90?
> ...


 
  
 The meter needle starts off at zero and quickly goes to 100mA when the right meter lights up and quickly settles at around 90mA as part of the normal biasing except that it doesn't equalize at 60mA like the left meter. I don't insert the headphones, I keep them in because the manual says to keep a load, the headphones, before switching on so no I don't hear any pop, which is different from what you do by inserting yours after you switch on.
  
 The next thing is to check the resistors as you say which I will do. I think we can rule out the power tubes because I have swopped them all round.
  
 Thanks for your help, I will check the resistors next.


----------



## Maxx134

Ok so from what you have said,
I must assume it is an incorrect resistor on one or two of your tubes.
Compare them to the other side/channel..

Also , I must disagree with leaving the headphone in the amp before turn on.

The amp already has two very high resistors at output to equalize the DC offset,
So it does already have a load.

The problem is that you are risking your headphones IF there is an abnormal issue occurring, 
And that goes with any a amp..

Which is exactly what you do have..

In my own experience and scenario 
I lost an Ultrasone ED8 driver to this amp this way when it had an issue in testing with the output...
I had mistakenly put solder across two pins and connected to points by the blue trim pot(!),
 so it was not an actual issue with the amp, but instead my mistake...
$90 for am ultrasone driver..


----------



## baronbeehive

maxx134 said:


> Ok so from what you have said,
> I must assume it is an incorrect resistor on one or two of your tubes.
> Compare them to the other side/channel..
> 
> ...


 
  
 Yes I take  your point, I have a tube amp for speakers as well and I was a bit worried about my speakers if a tube should go.
  
 I've taken readings for the 4 330R power stage resistors accessible from the component side of the PCB. They are: 328, 330, 356, 330, so all look good except for the one reading 356 which is on the right channel!!! Could that be the culprit? I haven't taken readings of the 4 resistors underneath the board because I couldn't access them from the top and I couldn't undo the screws to remove the board because they are so tight!


----------



## Maxx134

baronbeehive said:


> maxx134 said:
> 
> 
> > Ok so from what you have said,
> ...



There is no need to open the board to read the resistor on the other side because they are in parallel with the bypass caps..

So just read across the bypass caps..

Yes that one resistor can be the culprit..
Edit: or a result of the culprit!


----------



## SonicTrance

I'm getting the feeling of Deja Vu here guys 
	

	
	
		
		

		
		
	


	




 Look at page 87-88. But yes, replace that plate resistor asap.


----------



## baronbeehive

maxx134 said:


> There is no need to open the board to read the resistor on the other side because they are in parallel with the bypass caps..
> 
> 
> 
> ...


 
  
*........or a result of the culprit!*.................. aaaaaaaaaaghhhh.......... spooky.
  


sonictrance said:


> I'm getting the feeling of Deja Vu here guys
> 
> 
> 
> ...


 
  
 That* was *a long time ago....... but going back to that:
  
 1 - It's not the tubes, I've switched them all round, the 30v reading on one of the cathode resistors changes from right to left channel with the faulty tube but the right meter stays at 90mA
 2 - It's not a sticking needle, it does attempt to autobias
 3 - I've measured the voltage across the cathode resistors and replaced the duff tube as a result and the readings across the resistors are now all the same, however the right meter still reads 90mA
 4 - Although the engineer said the light to the right meter goes off and on I haven't seen this happen at all, anyway is a separate problem if at all
 5 - The wires to the meter are soldered correctly but the soldering may be faulty, I will try that as a last resort
 6 - Measure the resistance across 330R resistors/bypass caps, this is the point I got to before and measured 330 ohms which is correct, but I can't remember if I measured all resistors or just the one with the 30v reading
  
 Anyway I've measured the 4 on the component side and identified a possible cause, so now to measure the other 4 as Maxx says and thank goodness I don't have to remove the board............... yet!
  
 Edit: another resistor on order as we speak.
  
 Edit2: I've just measured the other 4 resistors across the cathode bypass caps and they all read within the same range of 327 - 328 ohms so there is obviously one which is at fault, I'm hoping it is a cause and not a symptom!


----------



## baronbeehive

maxx134 said:


> ......
> 
> Looks like the designer of these little dot amps is still "one step ahead ",
> As we discover his design goals..
> ...


 
  
  


bruch said:


> 2 stupid questions:
> 
> 1) Is the negative feedback in the system the single most limiting factor in this amp - even more so than the limiting factors that the mods on the first page are trying to solve?
> 2) Is it even possible to achieve reasonable levels of impedance in this amp without a negative feedback loop?


 
  
  


coinmaster said:


> The main purpose of the negative feedback is to lower the output impedance. The higher the output impedance of an amplifier the more the headphones imperfect frequency curves are exaggerated. Tubes all have too high of an output impedance even as a cathode follower. Negative feedback sacrifices gain for linearity, lower impedance drop, better phase alignment.
> So no, negative feedback is not the most limiting factor unless you are part of the crowd that thinks all NFB is evil, which it may or may not be, I haven't built an open loop amp yet.
> Also no, you can't get reasonable levels of output impedance without changing the design. Unless you use planar headphones, then output impedance doesn't matter anyway because they have a flat impedance curve.


 
  
 I was interested in all this talk about negative feedback since MrCurwen brought it up in talking about tube amp theory. I wanted to put in my twopenny worth from a layman's point of view, ie who knows nothing. I appreciate MrCurwen is an open loop guy but I didn't really understand all the negative vibes on the subject. After all negative feedback loops are everywhere in control systems such as central heating etc., working  well, solving problems. And in audio have been pretty well indispensable, getting rid of noise, much like balanced design does, and setting bandwidths and frequency spectrums to well defined limits etc. Everywhere they are they are solving problems. I don't think their effect is negative on sound necessarily although obviously open loops are the ideal, they must be extremely difficult to achieve. Everywhere I look I see design compromises, for example use of filters, digital sampling interpolations, very little of the actual music remains after all this processing. Obviously open loops and bit perfect reproduction are ideal, but even there the higher bit rates are either not as high as stipulated or are beyond human hearing. My point is that it is all a balance or compromise even. Sorry to go off the thread slightly but much discussion has been about this.


----------



## coinmaster

> After all negative feedback loops are everywhere in control systems such as central heating etc., working  well, solving problems.


 
 Control systems don't need perfect signal reproduction as they don't enjoy listening to music and typically they only deal with a few selection of voltagesfor biasing and to signify on and off as a way of digital communication, not an entire audio spectrum.
 Basically for 99.99% of applications transistors and the negative feedback that is needed to control their gain and poor linearity is "good enough".
  
 Sadly this is why tubes are no longer produced even though unlike transistors they tend to distort in the 2nd and 3rd harmonics instead of the higher stuff (anything beyond 3rd is bad).
 2nd and 3rd harmonics are present in live music and are generally responsible for euphony. This is much of the reason why tubes sound better, because they distort pleasingly, transistors do not.
  
 While negative feedback reduces total harmonic distortion it can also increase high order distortion which can affect the sound even at very low distortion levels. A lack of 2nd and 3rd harmonics or the presence of higher harmonics can drain the life out of the sound which is what solid state sound is.
 In other words, THD is just marketing BS, not useful.
  
 I guess people who have compared open loop vs feedback designs prefer open loop. I've read quite a few instances where long time engineers or respected amp builders mention how something sounds better under X circumstance yet they have never been able to deduce why with their test equipment. There is clearly still unknowns in the field of audio.


----------



## baronbeehive

Another unknown in the audio field.......... does anybody know or care why or if directionality of fuses is important in SQ..... I haven't put mine in yet.


----------



## coinmaster

A fuse is just a piece of wire, any direction is fine. Assuming fuses affect SQ to begin with.


----------



## baronbeehive

coinmaster said:


> A fuse is just a piece of wire, any direction is fine. Assuming fuses affect SQ to begin with.


 
  
 Thank you! I've never heard such a load of b$*&)%&"(^*t connected with a piece of wire before I mistakenly went on some of the relevant sites.


----------



## Maxx134

All that "nit picking" about special fuses,
is of course to make something special to sell you...

They will make it out of "unobtanium" and have it perform special tests to amaze you...

Bottom line these things are all about dealing with phenomena on a micro level,
 where you have to be in a state of yoga levitation to appreciate it...

Regardless, I'm not one to be left out of the euphoria, 
so I bought the expensive ones myself.


----------



## coinmaster

I'm a long way away from caring about cables and other unobtanium at this point. I've been breadboarding amps with cheap chinese clamp cables. Sounds pretty good regardless. There may or may not be an improvement with better cables but I'm a ways off from that. Although since I've satisfied my desire for methods of amplifier prototyping I may just order another MK6 to actually listen to, in fact I probably will. I can't believe it's been a year since I listened to my mk6


----------



## baronbeehive

maxx134 said:


> All that "nit picking" about special fuses,
> is of course to make something special to sell you...
> 
> They will make it out of "unobtanium" and have it perform special tests to amaze you...
> ...


 
  
 Ha ha...... shame on you 
	

	
	
		
		

		
		
	


	




, I only bought the cheap silver ones.
  


coinmaster said:


> I'm a long way away from caring about cables and other unobtanium at this point. I've been breadboarding amps with cheap chinese clamp cables. Sounds pretty good regardless. There may or may not be an improvement with better cables but I'm a ways off from that. Although since I've satisfied my desire for methods of amplifier prototyping I may just order another MK6 to actually listen to, in fact I probably will. I can't believe it's been a year since I listened to my mk6


 
  
 Get it now, you must be in serious withdrawal!!
  
 I'm going to solder the replacement resistor in from the component side despite originally soldering the other 3 on this side from the other side, I don't suppose this will matter? I can't get the board out it must have been screwed in with a monkey wrench!
  
 I should have tested all the replacement parts myself before putting everything together again but this was what I was not confident enough to do.
  
 Congratulations on the revamped first page guys!
  
 BTW Maxx how do you dust your amp?


----------



## coinmaster

> Get it now, you must be in serious withdrawal!!


 
 Bah! but it's so much money! Especially when I can just built it, although I've learned how an
 noyingly hard it is to breadboard an otl white cathode follower. This is an SE version of an mk6 with a common cathode input stage

  

  
 if I built it balanced it would be twice as big. I've come to the realization that the only practical way to prototype is by ordering pcbs. At least for the output stage if using tubes. However I kinda just want to lay low for the rest of the year and pay off some stuff before I go designing and buying pcbs for different stage designs. 
 I could buy a full on mk6 for now, mod it, and resell it later when I no longer need it. Do you think anyone would buy such a thing? I could stomach it if it was an investment but almost 900$ is a lot for something I could build for 1/3  as much if I wasn't lazy about it.


----------



## Maxx134

Probably better to buy used. 

If you still have the board just fill it in.


----------



## coinmaster

Board is toast. I beat it up pretty good. I fry an opamp every time I use it so there is probably a short in the copper layers. Those opamps are expensive to replace. Where to buy a used mk6?


----------



## baronbeehive

Guys, I'm really disappointed. I replaced the power resistor and it now correctly reads 329 like the others and it was obviously fried, but after waiting what seemed like an age for it to power on and nearly having a heart attack, the right meter still reads about 95 as before 
	

	
	
		
		

		
		
	


	




. I was hoping to get on to the next stage and fit the fans and do the mod by Sonic but that will probably have to wait until I've found the fault. Everything else is working fine which is very surprising given all the mods I did all in one go 
	

	
	
		
		

		
		
	


	




.
  

  
 Everything fits! But I think I will put a spacer between the chassis and bottom plate to prevent the Mcaps bearing down directly on the power resistors.


----------



## Maxx134

It looks great.
So what is the reading on the left side?

So the right side says you have a high bias and the resistor was a casualty of it, then we have to figure what that could be the reason for the increased current to cause cathode resistor to fry.

Maybe check your grid resistors for proper installation.

Does the right channel sound any different!

My guess is the issue has to be a parameter change around that power tube.

The opamps only deviate the bias about 5-10m, and if blue pots were untouched, then they cannot be the cause , so I would look elsewhere,
 like at all the connections surrounding the tube that had the burnt resistor.


----------



## Maxx134

baronbeehive said:


>



Man this is really nice work!
I like the layout and the wiring.


----------



## baronbeehive

maxx134 said:


> Man this is really nice work!
> I like the layout and the wiring.


 
  
 Thanks! I had to reposition some things when I got the amp back to make everything fit nicely and now it all fits.......... just! The engineer repositioned the wires to either side of the pot presumably because of the 2 WIMA's but luckily I left enough slack to move them slightly so that they didn't get in the way of the bottom plate when closed.
  


maxx134 said:


> It looks great.
> So what is the reading on the left side?
> 
> So the right side says you have a high bias and the resistor was a casualty of it, then we have to figure what that could be the reason for the increased current to cause cathode resistor to fry.
> ...


 
  
 The reading on the left side is 60mA.
  
 No I didn't notice any difference in sound.
  
 I've checked all the power stage Mills MRA5 330R resistors, I will check the others starting with the resistors I changed first: the PSU stage Mills MRA5 8K2, the driver stage TKD 2w 220K metal film, and finally the 2 driver stage 1.5k ohm resistors. I didn't put in any new WCF grid resistors or power tube 300 ohm resistors.
  
 What do I need to measure, resistance as before? I don't really know what I am looking for.
  
 Do I need to check the caps?
  
 The only thing I can think of that may be causing a problem is the pads which lifted when I was soldering:
  
 1 - The pad on the 330ohm power resistor on the extreme right, not the problem resistor which is second from right.
 2 - The pad on the 1.5k driver stage resistor
 3 - The pad on the WCF cap connection right by the problem resistor.


----------



## coinmaster

The first thing you need to do is measure the bias voltage on the grid, which would be located anywhere between the bottom half of the coupling capacitor and the 300 ohm resistor to the tube. Not sure where those are specifically as I don't have my board anymore. Or use this as a reference http://wooaudio.com/docs/tube_data/6AS7GA(6080).pdf The voltage should be  around -20 to -25V under proper biasing conditions assuming you are using a 6080 or similar.
  
 Measure the grid of both tubes as the bias meter only shows the total average current of the channel by splitting current with the .68 ohm resistor for 1/2 current measurement through two WCFs.
 The tube with a lower negative voltage will be the problem tube. Also you should measure the cathode/anode voltage on the tube side of the 330 ohm resistors. They should read in the range of +/- 70-80v with stock biases. I don't know which mods you implemented so.
  
 The input stage won't have anything to do with it as it is not DC coupled with the output stage so the 1.5k resistor would not cause it and the WCF cap would not cause it either because it just transmits the AC signal from the plate to the bottom grid, unless there is a short between the bottom grid and the cathode, that would be a problem.


----------



## baronbeehive

coinmaster said:


> The first thing you need to do is measure the bias voltage on the grid, which would be located anywhere between the bottom half of the coupling capacitor and the 300 ohm resistor to the tube. Not sure where those are specifically as I don't have my board anymore. Or use this as a reference http://wooaudio.com/docs/tube_data/6AS7GA(6080).pdf The voltage should be  around -20 to -25V under proper biasing conditions assuming you are using a 6080 or similar.
> 
> Measure the grid of both tubes as the bias meter only shows the total average current of the channel by splitting current with the .68 ohm resistor for 1/2 current measurement through two WCFs.
> The tube with a lower negative voltage will be the problem tube. Also you should measure the cathode/anode voltage on the tube side of the 330 ohm resistors. They should read in the range of +/- 70-80v with stock biases. I don't know which mods you implemented so.
> ...


 

 Alright, I am away for a week, I will follow this up when I get back thanks. You don't think it might be anything to do with the PSU caps then, as there are 2 of them I wondered if there was one for each channel.


----------



## Maxx134

No those PSU caps feeds all power tubes same time.


----------



## Maxx134

Coins also correct that driver stage has nothing to do with it.

The problem is very localized.

My guess it has to do only with the connections around by the socket in which has the burnt resistor.. each dual triode tube is it's own WCF circuit.

The other tubes values can be compared but problem should be that one tube circuit including its WCF cap. unless the two stacked Cathode bypass caps are crossed.

Maybe a bad solder or a component wire touch, or pushed too far in and touch the chassis.

So the yes I agree with Coinmaster to check each powerube bias by reading their voltages to compare the left good side against the right side.


----------



## nuport

Please see my revised parts list below:

ModQtyPartQuestionCoupling Caps4​Jupiter 0.47uf 600v Output stage decoupling4​Solen Fastcap 47uf 400vdcWill these fit? A lot cheaper than MundorfsDriver decoupling2​Wima MKP4 40uf 900v Decoupling6​PME-140: 0.33uF 275Vdc Evox Rifa PME271M Cathode bypass4​Elna Simic II 470uf 50v Cathode bypass4​Kemet PME271M 0.1uf 275v PSU Caps2​Mundorf MLytics 1500uf 160v Power Stage Resistors8​Mills MRA-5 330ohm Driver Stage Resistors4​TKD CM2 Series 2 watt 1% metal film 220k PSU Stage Resistor2​Mills MRA5 8k2x2 WCF Coupling4​Russian K75-10 0.22uf 1000v Is 0.22 uf ok? Only value I can find for the Russians

  
  
 Also, when I turn my volume knob past halfway, I hear a hum. This is my first tube amp, is this normal? I bought this amp used so I want to be sure everything is working ok before I commit to upgrading it.


----------



## Maxx134

Since this is a balanced amp,
You should use the balanced output to gain the benefits of full power and zero hum.

If you have hum on balanced oit Itwould be surprised.

Sometimes my single ended output is nice and quiet and sometimes it has a very low level hum.
It depends o. How solid the board to ground I Assuming.

The balanced output was always quiet.
Right now it's dead quite at full volume.


----------



## Maxx134

Your list looks very good!
Although I would not buy the driver stage resistos now.
This weekend I will compare my settings with SonicTrance to decide on settings..
The consensus is that lowering theses values placed the tube in a more linear part of its bias curve,
And the impact on sound was rather HUGE(!)...

Anyways, for the "Solen Fastcap 47uf 400vdc",
Just pull out the data's sheet for it,
and there is a chart with the dimensions based on size.

Also, if a bit too large, no worries, as you can extend the bottom.

I am looking at extending it only about an inch.


----------



## nuport

I am using balanced but get hum when more than 50% volume, even when the input is disconnected. I bought this used on ebay, maybe I should return it and get a new one to mod...


----------



## nuport

maxx134 said:


> Your list looks very good!
> Although I would not buy the driver stage resistos now.
> This weekend I will compare my settings with SonicTrance to decide on settings..
> The consensus is that lowering theses values placed the tube in a more linear part of its bias curve,
> ...


 
 Ok thanks for the tips, I will pass on the driver stage resistors for now. Too bad I don't live in NYC anymore, would love to compare notes


----------



## baronbeehive

coinmaster said:


> The first thing you need to do is measure the bias voltage on the grid, which would be located anywhere between the bottom half of the coupling capacitor and the 300 ohm resistor to the tube. Not sure where those are specifically as I don't have my board anymore. Or use this as a reference http://wooaudio.com/docs/tube_data/6AS7GA(6080).pdf The voltage should be  around -20 to -25V under proper biasing conditions assuming you are using a 6080 or similar.
> 
> Measure the grid of both tubes as the bias meter only shows the total average current of the channel by splitting current with the .68 ohm resistor for 1/2 current measurement through two WCFs.
> The tube with a lower negative voltage will be the problem tube. Also you should measure the cathode/anode voltage on the tube side of the 330 ohm resistors. They should read in the range of +/- 70-80v with stock biases. I don't know which mods you implemented so.
> ...


 
  
 Using the 6AS7G data sheet pins 1 and 4 are connected to the grid so this is where I take a voltage measurement? I took voltage readings already from the cathode bypass caps which are now all reading 24-25v since I replaced the faulty tube so if the cathode bypass caps are connected to the grid then the readings are good. If not I will have to locate it on the board from the traces from the pins1 & 4?
  
*The voltage measurement on the tube side of the 330ohm resistors*, surely I have already done that with the readings from the cathode bypass caps which are in parallel to the 4 330ohm resistors on the reverse side? As I said they read 24-25v not 70-80v that you say? That leaves the anode 330 ohm resistor for that tube which I haven't measured yet?
  
 Am I missing something? Probably!
  


maxx134 said:


> Coins also correct that driver stage has nothing to do with it.
> 
> The problem is very localized.
> 
> ...


 
  
 The cathode bypass caps are not crossed. I will check the connections of the components in the relevant circuit but what am I looking for is it voltage differences between adjacent circuits, and left/right channels?


----------



## baronbeehive

Sorry for the duplicate post which didn't display properly the first time.


----------



## coinmaster

> As I said they read 24-25v not 70-80v that you say?


 
 I was referring to ground reference not voltage across resistors. 25v seems right. As for the grids just measure the bottom end of the coupling cap. From ground.


----------



## baronbeehive

coinmaster said:


> I was referring to ground reference not voltage across resistors. 25v seems right. As for the grids just measure the bottom end of the coupling cap. From ground.


 
  
 I've no idea how to do that. I just watched a video that warned against connecting a live circuit to any metal to measure voltage which is what I was going to do. I've measured all 330 ohm resistors in situ and they all read the same for resistance so overall the 4 circuits match. I just have to measure the 4 resistors on the component side for voltage which should show differences according to the resistor.


----------



## coinmaster

Just touch the black probe to the chassis or stick it in one of the big holes in the board where the big psu caps are then measure with the red probe.


----------



## baronbeehive

coinmaster said:


> Just touch the black probe to the chassis or stick it in one of the big holes in the board where the big psu caps are then measure with the red probe.


 
  
 Outside left 104v, inside left 102v, inside right 111v, outside right 112v. The same resistor is smoking, quite alarming!
  
 I can't see any leads touching and from my pics of the reverse of the board everything looks good with nothing apparently touching the chassis.
  
 This is soooo annoying..... all I want to do is listen to it, but then you guys have had your problems as well. Just have to be patient!


----------



## Mogos

baronbeehive did you change the PSU transistors or you are using the stock ones?


----------



## coinmaster

> This is soooo annoying..... all I want to do is listen to it, but then you guys have had your problems as well. Just have to be patient!


 
 It's been a year for me. The first 6 months of withdrawals sucks hard. It's difficult to justify the cost of a new mk6 when I can build one but building one has its own annoyances. I haven't decided what to do yet. At the moment I'm just waiting on some source follower pcbs I ordered to greatly reduce the complexity of the output stage so I can experiment with input stages. In the end I will need to have an mk6 though cuz that is so far the best amp I have ever heard so I need it for reference.
  
  


> Outside left 104v, inside left 102v, inside right 111v, outside right 112v. The same resistor is smoking, quite alarming!


 
 Need more specifics, left/right of what, where. Also you need to measure grids,the bottom end of your couple cap that connects to the output tubes or preferably directly on the grid pin itsef, use the link I gave toy before to see where it is located on the pins. Unless you mean the grids are at 100+v then u have a serious problem.


----------



## baronbeehive

mogos said:


> baronbeehive did you change the PSU transistors or you are using the stock ones?


 
  
  
 Stock.
  


coinmaster said:


> It's been a year for me. The first 6 months of withdrawals sucks hard. It's difficult to justify the cost of a new mk6 when I can build one but building one has its own annoyances. I haven't decided what to do yet. At the moment I'm just waiting on some source follower pcbs I ordered to greatly reduce the complexity of the output stage so I can experiment with input stages. In the end I will need to have an mk6 though cuz that is so far the best amp I have ever heard so I need it for reference.
> 
> 
> Need more specifics, left/right of what, where. Also you need to measure grids,the bottom end of your couple cap that connects to the output tubes or preferably directly on the grid pin itsef, use the link I gave toy before to see where it is located on the pins. Unless you mean the grids are at 100+v then u have a serious problem.


 
  
 Looks like you have to have a mkvi lol! Interesting though to see what you can come up with, I wait with interest, but, yes the wait is hard, I finished the mods back in march!
  
 Those were the measurements you said to take from bottom of coupling caps to ground from left (good) to right side (bad) meter readings. I can confirm that if necessary by taking readings from the grid pin 1 or 4 which are connected to the grid according to the data sheet but looks like the right side is affected by some fault manifesting in the burnt resistor, just have to find what.


----------



## coinmaster

Are you waiting for the relays to kick in before you measure? Which resistor is burnt? In any case the voltages seem more in line with B+ then grid. Either you are measuring something wrong or you got a major wiring issue.


----------



## baronbeehive

coinmaster said:


> Are you waiting for the relays to kick in before you measure? Which resistor is burnt? In any case the voltages seem more in line with B+ then grid. Either you are measuring something wrong or you got a major wiring issue.


 
  
 Yes, after they come on.
  
 Middle/right resistor.
  
 I will measure from the grid pin to ground tomorrow to check.
  
 The left meter reading is normal at 60mA for 6AS7G tubes.


----------



## Maxx134

if possible take some close up pictures of the resistor in question that is burning I like to know what is the exact location of this resistor so I can know which anode resistor, and also the surrounding socket and connections.

In order for that resister to be burning, there has to be an incorrect connection, excess solder connection, or other variables like if you using tube adapter sockets.

The fact that your measurements are similar only shows that the PSU is feeding the resistors.
You need measure the Anode(plates) from chassis ground to each anode which ia the other end of the resistors.
Did you measure with tubes in place?
The burning resistor must be having a problem from the Anode connection or the bias for that specific triode section, or a wrong connection by that specific triode cathode connection.
We talking only three points for that specific triode (anode-grid-cathode)section of the circuit and socket area. 
Coin is right an incorrect bias is a possibility meaning a wrong connection on its grid.
all other sections are fine don't start looking at the unit as a whole board with 4 powrtube sections , as you only have to focus in that one specific tube section.


----------



## coinmaster

Burning resistors mean too much current, an incorrect bias voltage is the only thing that would push the tube to draw more current unless your cathode/anode voltages are way off. Check both grids of each tube in the faulty channel and let us know the voltages.


----------



## nuport

maxx134 said:


> Since this is a balanced amp,
> You should use the balanced output to gain the benefits of full power and zero hum.
> 
> If you have hum on balanced oit Itwould be surprised.
> ...





>


 
 After speaking to the ebay seller I have decided to return the amp. I will be purchasing a new one but I guess I have to wait now for delivery.


----------



## baronbeehive

maxx134 said:


> if possible take some close up pictures of the resistor in question that is burning I like to know what is the exact location of this resistor so I can know which anode resistor, and also the surrounding socket and connections.
> 
> In order for that resister to be burning, there has to be an incorrect connection, excess solder connection, or other variables like if you using tube adapter sockets.
> 
> ...


 
  
 I'll take some pics tomorrow. I'm not using adapter sockets, and I don't think there is an incorrect connection, I've looked everywhere, including pics of the reverse of the board, and as you know I've been pretty sparing with the solder!
  
 Yes I measured with tubes in place.
  
 Just after I took the last lot of voltages the heat melted the solder and a wire from the Mcap came off and shorted to the chassis ground via one of the screws. I'll have to solder that on again first.
  
 Does it matter which end of the resistor to measure when measuring from it to ground?
  


coinmaster said:


> Burning resistors mean too much current, an incorrect bias voltage is the only thing that would push the tube to draw more current unless your cathode/anode voltages are way off. Check both grids of each tube in the faulty channel and let us know the voltages.


 
  
 I'll check the 2 grid pins, pins 1 and 4, for each of the 2 tubes, tomorrow, its getting late here.


----------



## baronbeehive

nuport said:


> After speaking to the ebay seller I have decided to return the amp. I will be purchasing a new one but I guess I have to wait now for delivery.


 
  
 That's a good move. I don't know if they still do the modded version with Mundorf coupling caps and silver wiring but the wiring would save you some work!


----------



## baronbeehive

Here's the  pics:
  

  
 Shows the burnt resistor. The yellow wire coming in from the left is connected to the Mcap and came off after I took the voltage measurements when the solder melted with the heat and shorted through the screw. I've got to reconnect it.
  

  
  

  
 The black and red wires go to the WCF cap. The 2 black wires to the right of the red wire go to the coupling cap and bottom Ecap respectively.
  

  
 The 3 wires going to the cathode bypass cap joint are connected to the RIFA for that circuit, the bottom Ecap and the Mcap.
  

  
 A pic of the reverse of the board when I finished it, there look to be no problems from the pic. (I put in new heater wires).
  
 Readings to follow.


----------



## Mogos

maxx134 said:


> ........
> This weekend I will compare my settings with SonicTrance to decide on settings..
> The consensus is that lowering theses values placed the tube in a more linear part of its bias curve,
> And the impact on sound was rather HUGE(!)...
> ...


 
 Guys I am also very interested in the outcome of your findings.
 Did you manage to discuss the optimal values of the resistors?
 Is there any mathematical or good practice rule connecting the values of the cathode and anode resistors?


----------



## baronbeehive

mogos said:


> baronbeehive did you change the PSU transistors or you are using the stock ones?


 
  
 You changed yours when you had your problems didn't you? I don't know whether to change them, they are not on the list of mods on page 1 yet.


----------



## Mogos

Yes I have changed them. But in my case and also Sonic Trance the resistors and diodes in the PSU section get burnt and our meters did not move on.


----------



## baronbeehive

I think these are better pics:
  

  
 1 - Circuit with burnt resistor
  

  
 2 - Circuit with burnt resistor
  

  
 3 - Circuit with burnt resistor
  

  
 4 - Circuit with burnt resistor
  

  
 1 - The other right hand side circuit next to it
  

  
 2 - The other right hand side circuit next to it
  

  
 3 -   The other right hand side circuit next to it
  

  
 4  - The other right hand side circuit next to it
  
 I tried to get readings today but some were all over the place and then I noticed the burnt resistor leg had come out of hole so I'll have to put it back in and try to get the readings again.


----------



## Maxx134

I am not understanding why the components are coming out of your board...

 what type of solder low flash point cheap ***** solder you use?

 another problem is shorting out that Cap 2 chasis..
hopefully you didn't exceed you power transistors rating, but if you get the same normal readings on other tubes you should be fine.

 PSU feeds all tubes the same time.

As coinmaster stated, check the grid area of circuit, as it should be reasons why your tube is behaving to burn your anode resistor.


----------



## baronbeehive

maxx134 said:


> I am not understanding why the components are coming out of your board...
> 
> what type of solder low flash point cheap ***** solder you use?
> 
> ...


 

 It was the burnt resistor that melted the solder on the leg causing the (temporary) lead to come off. I think I made a mistake soldering the resistor in too far with one leg and not far enough with the other one (which came out). I checked pretty thoroughly all other joints to be satisfied they were ok but not this one because I was in a hurry to get the readings. All my solder joints have to pass the "tug test" before I'm satisfied, a good joint will not come out.
  
 The solder is good - cardas solder so no problems there. The readings I managed to get before I noticed the resistor leg had come out looked good so hopefully no damage done 
	

	
	
		
		

		
			





. I'll try again tomorrow.


----------



## Maxx134

Although you said you replaced heater wiring, 
I like to know if this was the side of resistor burn. 
It is super easy to make a mistake soldering back heater wires to wrong pin!


----------



## MrCurwen

PCBs and tube amps: not a good combination in my experience. P2P all the way.


----------



## baronbeehive

maxx134 said:


> Although you said you replaced heater wiring,
> I like to know if this was the side of resistor burn.
> It is super easy to make a mistake soldering back heater wires to wrong pin!


 
  
 I was wondering this too. The engineer said that one of the heater wires I replaced was too close to the resistor and burned when he tested it and he said he moved it. I don't know the answer to your question without contacting him or getting the board out again and I will probably have to get him to do that because the board is screwed in so tight. I did wonder if what he said had burned was the resistor or the heater wire, if it was the resistor then it was a preexisting problem, if it was the heater wire then as you said it could be this put in wrongly.
  
 Anyway I have the readings from left good side to right bad side:
  
 1 - Grid pin 1 to ground -20.2, Grid pin 4 to ground -106.3
      Grid pin 1 to ground -18.7, Grid pin 4 to ground -105.9
      Grid pin 1 to ground -0.6,   Grid pin 4 to ground -104.8
      Grid pin 1 to ground -17.4, Grid pin 4 to ground -105.3
  
 2 - Cathode -88.3
      Cathode -87.5
      Cathode -86.3
      Cathode -86.4
  
 3 - Anode 72.1
      Anode 70.9
      Anode 44.3
      Anode 69.8
  
 The 4 cathode 330ohm resistors are the ones in the cathode bypass joints on the component side I believe.
 The 4 anode 330ohm resistors are the ones in the reverse side I believe.
 I'm  assuming it doesn't matter which leg of the resistor I measure to?
  
 BTW Maxx the problem resistor is overheating so much that the solder is melting again so it isn't my soldering that's the problem!


----------



## baronbeehive

mrcurwen said:


> PCBs and tube amps: not a good combination in my experience. P2P all the way.


 
  
 Absolutely!


----------



## Maxx134

I'm going to take a guess here and say that one of your heater wires are connected to the grid or wrong pin..

Edit :
Why?
Your grid voltage is elevated about amount of heater voltage amount.


----------



## Maxx134

You don't have to pull out board to test.
Test for continuity with amp off.
The two tubes on each side should have continuity on same pins for heater.
Edit:
So the point is, 
NO other pins should read continuity with the heater pins!
Pull out tubes with amp off for this test.


Also, side note, never turn on amp without tubes.
As this power supply likes to see a load with tubes,
 or the zenner diode gets more hot.


----------



## baronbeehive

maxx134 said:


> I'm going to take a guess here and say that one of your heater wires are connected to the grid or wrong pin..
> 
> 
> 
> ...


 
  
 OK thanks Maxx, that sounds possible. So I'm either going to have to get a large handled screwdriver - the cordless shredded one of the screw heads, or take it back from whence it came.


----------



## baronbeehive

maxx134 said:


> You don't have to pull out board to test.
> Test for continuity with amp off.
> The two tubes on each side should have continuity on same pins for heater.


 
  
 I don't get how to do that, continuity from a pin to where?


----------



## Maxx134

baronbeehive said:


> maxx134 said:
> 
> 
> > You don't have to pull out board to test.
> ...



1-Locate the heater pins.
2-Set your tester to ohm meter at lowest setting only.
3- touch one end probe on either heater pin,
And other probe to other pins, one at a time,
 to see if any low reading which would indicate continuity...


----------



## baronbeehive

maxx134 said:


> 1-Locate the heater pins.
> 2-Set your tester to ohm meter at lowest setting only.
> 3- touch one end probe on either heater pin,
> And other probe to other pins, one at a time,
> to see if any low reading which would indicate continuity...


 

 There are 2 heater pins - 7 & 8 so touching 7 at one end and 8 at the other would indicate continuity of a circuit? Then if there is continuity at another pin other than those 2 pins the heater circuit has been connected up wrongly to the other pin which indicates continuity? Sorry if that's garbled!


----------



## baronbeehive

I've just checked for continuity between pins 7 & 8, and others, and the wiring is correct on all tubes ie. continuity only with pins 7 & 8.
  
 So it's back to square one!
  
 What does that grey 2 core wire do on the reverse of the board?


----------



## SonicTrance

baronbeehive said:


> The 4 cathode 330ohm resistors are the ones in the cathode bypass joints on the component side I believe.
> The 4 anode 330ohm resistors are the ones in the reverse side I believe.
> I'm  assuming it doesn't matter which leg of the resistor I measure to?


 
 Hi Baron!
  
 Its' the other way around. The anode resistors are on component side. One of them is mysteriously burnin. Cathode resistors are on top side of board. You have them soldered in parallel to the Rifas and Mundorf E-Caps.
  
 It does matter from which resistor leg you measure. If you measure before the voltage has passed the anode resistor you are measuring B+. If you measure after the resistor you are measuring plate voltage.


----------



## baronbeehive

sonictrance said:


> Hi Baron!
> 
> Its' the other way around. The anode resistors are on component side. One of them is mysteriously burnin. Cathode resistors are on top side of board. You have them soldered in parallel to the Rifas and Mundorf E-Caps.
> 
> It does matter from which resistor leg you measure. If you measure before the voltage has passed the anode resistor you are measuring B+. If you measure after the resistor you are measuring plate voltage.


 

 Hi Sonic!
  
 Of course that's what I meant ha ha 
	

	
	
		
		

		
		
	


	




.
  
 I'm beginning to slowly realize what it's about, voltage is bound to be affected by resistance, thanks for your patience 
	

	
	
		
		

		
		
	


	




.
  
 OK, so have you any ideas why its burning?


----------



## coinmaster

> Grid pin 1 to ground -0.6


 
 That would do it. Check the area around that pin for shorts, etc.
 Learn how to use a continuity tester. Most multimeters haver a contuity setting that will beep on continuity, if not just measure resistance and very low ohms means continuity. 
 Check everything from the bottom of the coupling capacitor up until it hits the grid resistor and the grid and make sure nothing is connected that should not be.
 Also check the continuity from ground to the opamp pins. The small circle on the opamp indicates pin 1. Only pin 3 should show continuity, if any of the others are then the opamp is toast or there's a short.


----------



## Maxx134

Yes if looks like there is some type of short on the grid pin and if that is the main grid, not the WCF grid,
 then need to check all coimmaster said.

If it is the WCF grid, then check the WCF cap wires that may be touching, or not on proper position..

My guess s(yes again) is a mistake with cap connection..
Make sure solder joints are not covering two different points
.


----------



## baronbeehive

coinmaster said:


> That would do it. Check the area around that pin for shorts, etc.
> Learn how to use a continuity tester. Most multimeters haver a contuity setting that will beep on continuity, if not just measure resistance and very low ohms means continuity.
> Check everything from the bottom of the coupling capacitor up until it hits the grid resistor and the grid and make sure nothing is connected that should not be.
> Also check the continuity from ground to the opamp pins. The small circle on the opamp indicates pin 1. Only pin 3 should show continuity, if any of the others are then the opamp is toast or there's a short.


 
  
 Thanks Coin. I'm guessing that the black thing marked "OPA..." with 8 contacts is the opamp? So I check each of these 8?
  
 The grid resistors are the 2 brown 300ohm ones at top right with the red wire near and bottom left by the red wima?
  

  


maxx134 said:


> Yes if looks like there is some type of short on the grid pin and if that is the main grid, not the WCF grid,
> then need to check all coimmaster said.
> 
> If it is the WCF grid, then check the WCF cap wires that may be touching, or not on proper position..
> ...


 
  
 Can't see visually any shorts on the trace from the grid pin but haven't used the continuity check yet.
  
 The WCF wires look OK, (red and black wires in pic), and in correct position. There is a question about the pads on this WCF cap though that I remember from the original mods.
  
 The only solder covering two different points is on the cathode bypass joints which is OK. Maybe something like that on the reverse of the board possibly?
  
 Thanks guys for giving up your Saturday evening 
	

	
	
		
		

		
		
	


	




.


----------



## coinmaster

> Thanks Coin. I'm guessing that the black thing marked "OPA..." with 8 contacts is the opamp? So I check each of these 8?


 
 Yeah only with continuity, not with voltage so leave the amp off. Just measure the pins from ground. Pin 3 should be the only one with a continuity reading.
  
  


> The grid resistors are the 2 brown 300ohm ones at top right with the red wire near and bottom left by the red wima?


 
 Not sure but with a continuity test you can find out, just measure from grid.
  


> If it is the WCF grid, then check the WCF cap wires that may be touching, or not on proper position..


 
 From his previous statements it is the top grid that is the issue, the wcf grids look fine. Plus it's the anode resistor that's burning which would make since if the top triode is running at near 0v grid.


----------



## baronbeehive

So far everything appears to check out visually, and with continuity test comparing the bad circuit with the other right hand circuit: grid to grid resistors, *and to other modded components*, and opamps check out. There's continuity where there should be and no continuity where there shouldn't be. I haven't compared to the left hand side circuits.
  

  
  

  
 Just out of interest I looked at the pic of the reverse. I don't see how anything could have pierced the new blue heater wires. It looks like the right hand circuit heater wires were the ones that were moved being closer to the resistor. Do the wires have to go from pin 7 of one tube to pin 7 of the other because that could have been mixed up. It looks like on the stock, (red wires), they were connected pin 7 on one tube to pin 8 on the other and visa versa.
  
 I also checked the 2 output wires coming from pin 3 of each of the 2 right hand circuits in case that was wrongly connected. The output wires were about the only change on the reverse side from stock apart from the resistor/rifa combo. The left hand circuit wire was connected to one of the output pins on the left 3 pin xlr* however the right hand circuit wire was connected to one of the output pins on the left 3 pin xlr as well as all the 3 pins on the right 3 pin xlr which can't be right can it?*
  
 It looks from the pic like the output wires are coming from pin 4 not pin 3.
  
 That's weird they are definitely coming from pin 4 which is correct looking at the old pics, so I don't know what I measured from pin 3, it says r-out and l-out on the component side. I've had enough for now.


----------



## SonicTrance

baronbeehive said:


> Just out of interest I looked at the pic of the reverse. I don't see how anything could have pierced the new blue heater wires. It looks like the right hand circuit heater wires were the ones that were moved being closer to the resistor. Do the wires have to go from pin 7 of one tube to pin 7 of the other because that could have been mixed up. It looks like on the stock, (red wires), they were connected pin 7 on one tube to pin 8 on the other and visa versa.


 
 It doesn't matter.
  
  


baronbeehive said:


> I also checked the 2 output wires coming from pin 3 of each of the 2 right hand circuits in case that was wrongly connected. The output wires were about the only change on the reverse side from stock apart from the resistor/rifa combo. The left hand circuit wire was connected to one of the output pins on the left 3 pin xlr* however the right hand circuit wire was connected to one of the output pins on the left 3 pin xlr as well as all the 3 pins on the right 3 pin xlr which can't be right can it?*
> 
> It looks from the pic like the output wires are coming from pin 4 not pin 3.
> 
> That's weird they are definitely coming from pin 4 which is correct looking at the old pics, so I don't know what I measured from pin 3, it says r-out and l-out on the component side. I've had enough for now.


 
 No that's not right. Left channel connects to left output and right channel to right output. The correct output pin is 5 (plate).


----------



## baronbeehive

sonictrance said:


> It doesn't matter.
> 
> 
> No that's not right. Left channel connects to left output and right channel to right output. The correct output pin is 5 (plate).


 
  
 I just checked pin 5 as well and I get the same result as for pin 3 so there must be a short there somewhere, it doesn't do that on the good side.


----------



## coinmaster

If the grid is really showing -.6 volts then that remains the issue. Test continuity between opamp pins instead of from opamp pins to ground. Make sure there are no shorts between the pins.
 Ignore the other tubes, focus on the one with the -.6 volts on it.


----------



## baronbeehive

coinmaster said:


> If the grid is really showing -.6 volts then that remains the issue. Test continuity between opamp pins instead of from opamp pins to ground. Make sure there are no shorts between the pins.
> Ignore the other tubes, focus on the one with the -.6 volts on it.


 
  
 Just tested the opamp pins and everythings OK.


----------



## coinmaster

Try switching the the opamp for one of the other ones. If it still shows -.6v on that grid then the opamp is not the issue and the problem lies with wiring.
 Just be careful taking them out, try not to ruin them they are a bit expensive to replace.


----------



## baronbeehive

coinmaster said:


> Try switching the the opamp for one of the other ones. If it still shows -.6v on that grid then the opamp is not the issue and the problem lies with wiring.
> Just be careful taking them out, try not to ruin them they are a bit expensive to replace.


 
  
 OK. That may be a bit of a problem getting the board out again, I'll try getting that screwdriver but may have to get the engineer out again for that, so unless there is anything I can do in the meantime that may be a while.


----------



## coinmaster

Until then try testing pin 4 and 7 of the opamp for voltages. pin 4 should be -36-ish pin 7 should be +15.


----------



## Maxx134

You don't have to pull out board to swap opamps.

Also if your output wires are incorrect then that can B the problem,

 but your issue should have caused the output relay to open


----------



## Maxx134

baronbeehive said:


> * however the right hand circuit wire was connected to one of the output pins on the left 3 pin xlr as well as all the 3 pins on the right 3 pin xlr which can't be right can it?*



You need to make sure the output wires are not mixed up on the output sockets.
From the board they go to the rear XLRs.
From there they then tap off and go to the front 4pin xlr.

The wires from the tube sockets are the minus signal of each side.
The wires from the center board are the two positive signal wires for each side.

No output pins should have continuity with each other.


----------



## baronbeehive

maxx134 said:


> You don't have to pull out board to swap opamps.
> .......


 
  
 How do they come out then?
  


maxx134 said:


> ......
> but your issue should have caused the output relay to open


 
  
 So what effect would that have?
  


maxx134 said:


> You need to make sure the output wires are not mixed up on the output sockets.
> From the board they go to the rear XLRs.
> From there they then tap off and go to the front 4pin xlr.
> 
> ...


 
  
 .....no that's clearly wrong! I'm scratching my head.
  
 I'm glad that I've found what could be the cause of the problem but pretty annoyed after checking, and double checking the wiring at the time, unless it was a slip up I didn't notice. Something has clearly happened, I don't know what.
  
 I don't know if the grey centre wire was connected back wrongly or whether it would have the effect on continuity that was found if it was. Both of the wires in the core came out so I might have forgotten which was which. So it looks like I will have to try to get the board back out to check everything on the reverse. I just can't see what could be wrong on the component side so that's what I will have to do next.
  
 I'll let you know what happens, until then if you think of anything let me know.
  
 Modded:
  

  
 Modded:
  

  
 Modded:
  

  
 Modded:
  

  
 Modded:
  

  
 Stock:
  

  
 Stock:
  

  
 Stock:
  

  
 Stock:
  

  
 My feeling is that since it is that tube circuit which is causing the abnormal readings at the outputs then I must have maybe got one wire wrongly connected on the reverse of the board, I can't think of anything else.


----------



## Maxx134

1- What grey wire do you speak of?

2- Opamp chips are right on board bottom where the components are.. you already saw them and pointed them out.

3-the relay protection in the middle of board cuts/ disconnect the two positive signal output to safeguard the headphone out if any DC offset unbalance...
This is why I doubt it is the opamps..

TEST THIS FIRST..
OUTPUT WIRING:
SOMETIMES THE CONNECTIONS GETS SHORTED BY HANDLING AND PRESSING ON ALL THOSE WIRES TOGETHER...

4- just test with meter your xlr output pins.
Easy to do from the rear.
Touch with probes in any order.
None should have continuity with each other, except the two ground pins on those two 3-pin xlr out.

If one of the signal outputs(positive&negative pins) makes continuity with any other pins, you have short or incorrect wiring.

Compare the good side xlr, to the bad side.
If you touch the chassis you will get incorrect false continuity which may have been what happened last time you measured.


----------



## baronbeehive

This is stock.
  

  
 My connections are as stock - blue, brown, blue, brown, black from left to right. The black is only one wire from one of the 2 cable runs isn't it? I cut off the black off the other cable, which means that the right hand output black wire isn't connected to the XLR headphone jack. I'm sure that was how the stock wires were connected as shown in the pic.
  

  
 Are the WIMA legs connected correctly? I have joined the 2 legs correctly but does it matter which of the legs connects to which of the 2 sets of resistors?


----------



## Maxx134

Caps are not polarized so no.
Only have to make sure it is at the cathode resistor ground end , not the anode side.

Anyways, you are asking about driver stage decoupling caps ,
when the issue is in your output stage tube area.
I am not concerned with the color coding of your wires.
Or how you did it.
I am sure it's OK.
What I am taking about is using your meter to test for connection problem with output.
A short or error can definitely be your actual problem .
So test those dam rear output connections.

I spoke of the rear output pins,
Because they are easy to get to and test without opening the amp


----------



## baronbeehive

maxx134 said:


> Caps are not polarized so no.
> Only have to make sure it is at the cathode resistor ground end , not the anode side.
> 
> Anyways, you are asking about driver stage decoupling caps ,
> ...


 
  
 OK, OK!! I posted that before I got your last post. I was just checking the connections yet again and they look good into the XLR output side.
  
 I'll do as you say now 
	

	
	
		
		

		
			





.


----------



## baronbeehive

maxx134 said:


> 1- What grey wire do you speak of?
> 
> ...................


 
  
 This one in the middle which is brittle and breaks off:
  
 You can see the red wire has come off but in the end both came off.


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## baronbeehive

pin


maxx134 said:


> Caps are not polarized so no.
> Only have to make sure it is at the cathode resistor ground end , not the anode side.
> 
> Anyways, you are asking about driver stage decoupling caps ,
> ...


 

*There is a short or bad connection - *between all 3 pins on the right hand side outputs and the first pin on the left hand side outputs looking at the pic going clockwise. Also* - there is a short or bad connection *between all of the 3 pins on the right hand side outputs.
  
 Whereas there is no continuity between all 3 pins on the left hand side outputs which is correct.
  

  
  
 Could this be the problem??


----------



## coinmaster

> How do they come out then?


 
 Pull or wedge them out, they are in sockets.

  


> Could this be the problem??


 
 I've been glazing over this issue since your text seems hard to decipher and I'm too lazy to look at it at the moment. Perhaps u can give more specific information on where and what is shorted.
  
 http://www.kirkeo.org/sites/default/files/images/node15/XLRpinout.png
 https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcTTKuGz5E5tFaujULP9HYCZ_MY_0_3wLLDRKhJiOyQOW_bXYzu3uw


----------



## baronbeehive

coinmaster said:


> ............
> I've been glazing over this issue since your text seems hard to decipher and I'm too lazy to look at it at the moment. Perhaps u can give more specific information on where and what is shorted.
> 
> ...........


 
  
 Sorry coin, while trying to be clear I ended up confusing everybody lol.
  
 I got as far as the opamp and was going through other possible things I may have done wrong to cause the problem hence my recent posts.
  
 Ignore this next post, I think everything here's fine:
  
 Quote:


baronbeehive said:


> This is stock.
> 
> 
> 
> ...


 
  
 Initially I wanted to test the 6 red output wires in one of the pics below so I tested for continuity from the tube pins to the output XLR's and this is was when I found the problem.
  
 This is the problem I found:
  


baronbeehive said:


> *There is a short or bad connection - *between all 3 pins on the right hand side outputs and the first pin on the left hand side outputs looking at the pic going clockwise. Also* - there is a short or bad connection *between all of the 3 pins on the right hand side outputs.
> 
> Whereas there is no continuity between all 3 pins on the left hand side outputs which is correct.
> 
> ...


 
  
 As I said here there is continuity between all 3 pins on the right hand XLR outputs. Also there is continuity between all 3 pins on the right hand XLR outputs and one pin on the left hand XLR outputs. Both test results clearly indicate a wiring problem. I don't know what as yet.
  
 The next post I flagged up as a possible problem but may be OK. The reason was because both wires of the 2 core grey wire in the middle reverse of board came off and I may have soldered them back wrong, though I don't think so. I don't know what this wire does but the 2 cores indicate the 2 circuits on left and right sides.
  


baronbeehive said:


> This one in the middle which is brittle and breaks off:
> 
> You can see the red wire has come off but in the end both came off.


 
  
 The bottom line is there is a wiring issue which may be the cause of the problem.
  
 Next I'm going to do a continuity test again on the 4 tube circuits, as you suggested, to look for problems in the bad right hand circuit to check if the problem is somewhere there. I'll let you know when I have the results.


----------



## baronbeehive

These are the results of the continuity test having tested a good left hand circuit, and both right hand circuits where the problem lies:
  
 The tests all agree with each other except for the following results:
  
 1 - The suspect middle right hand circuit shows continuity between pins 5 and 6
  
 2 - The suspect middle right hand circuit shows continuity between pin 3 and the 330 ohm resistor
  
 3 - The outside right hand circuit shows continuity over its coupling cap
  
 I've double checked this and this appears to be somewhere where the problem must be if anyone has any ideas.
  
 This is in addition to the wiring anomalies at the output XLR's identified earlier.


----------



## hakiu1980

very nice tube amp, did someone try ting feng 6 pro ?


----------



## Maxx134

I was not around yesterday but seems to me like this short wire issue is causing your resistor to burn so bottom line you're wiring maybe crossed.

Test again without the tubes.
 Pull out the tubes and see if you still getting continuity.
Remember this is a test with the amp off nothing is on or connected


----------



## Maxx134

Disconnect any input sources to the amp as well and then try


----------



## SonicTrance

baronbeehive said:


> > As I said here there is continuity between all 3 pins on the right hand XLR outputs.


 
 You have shorted outputs!
 Pin 1 on the XLR outputs are suppose to connect to ground (on both output jacks) and then be joined together at the 4 pin XLR headphone output ground.
 If you have continuity between all pins on the output jack, they're all grounded! Fix that as number one is my suggestion.
  


> Also there is continuity between all 3 pins on the right hand XLR outputs *and one pin on the left hand XLR outputs*. Both test results clearly indicate a wiring problem. I don't know what as yet.


 
 Probably (hopefully) pin 1, which is suppose to be grounded and have continuity to pin 1 on the other jack.


----------



## baronbeehive

maxx134 said:


> I was not around yesterday but seems to me like this short wire issue is causing your resistor to burn so bottom line you're wiring maybe crossed.
> 
> Test again without the tubes.
> Pull out the tubes and see if you still getting continuity.
> Remember this is a test with the amp off nothing is on or connected


 
  
  


sonictrance said:


> You have shorted outputs!
> Pin 1 on the XLR outputs are suppose to connect to ground (on both output jacks) and then be joined together at the 4 pin XLR headphone output ground.
> If you have continuity between all pins on the output jack, they're all grounded! Fix that as number one is my suggestion.
> 
> Probably (hopefully) pin 1, which is suppose to be grounded and have continuity to pin 1 on the other jack.


 
  
 Thanks Sonic and Maxx! I will get on with that after I've considered... ie. after I know what I'm doing 
	

	
	
		
		

		
			





.
  
 I've spent a fair bit of time today looking at pics of the wiring and I'm 99% convinced that if there is a wiring problem it could only be from crossed wiring with one of the output wires.
  
 One last thing, can you tell me if both black wires of the 3 core runs ending in the XLR headphone out are connected. As I said recently only one is connected with mine because I'm sure that was how it was originally. I remember taking the stock wires off and being surprised that one of the black ones was cut off before reaching the socket.


----------



## SonicTrance

baronbeehive said:


> maxx134 said:
> 
> 
> > I was not around yesterday but seems to me like this short wire issue is causing your resistor to burn so bottom line you're wiring maybe crossed.
> ...


 
 They're suppose to be connected, joined together at the headphone output. They're not signal but ground wires giving the headphone output jack a ground reference. I doubt that it would make much difference if only one is connected.
 I would connect them both though just because.


----------



## Maxx134

I used to look at my wiring in the old days but after my amp started turning more complex & looking like spaghetti, I use my meter as my eyes instead


----------



## baronbeehive

maxx134 said:


> I used to look at my wiring in the old days but after my amp started turning more complex & looking like spaghetti, I use my meter as my eyes instead


 
  
 Good point! No use looking at yours, I'm already cross-eyed from trying to figure out mine 
	

	
	
		
		

		
		
	


	




 
  
 The problem is made worse by replacing 3 colours of wire with just one lol.


----------



## Maxx134

If there was a problem with the opamp or area of the DC offset servo controlling the balance of the tubes, then the protection relay would have kicked in.

Therefore it is another clue that was not the case, and you did find the culprit of the burning resistor in the output wiring.

You don't have to pull out board to fix or trace wiring.
Just unsolder wires from board at the XLR plugs.

On the board (component side) , you will see the markings on the negative tube pins.
The will say "left-" and on other side "right-" .. for the negative side of signal.

On the middle of board you will see the positive signal markings left & right "+" positives..

The remaining wires are "ground".
So you use your tester to touch each point labled on board and then check the wires one at a time to identify which is which.

If all seems correctly positioned, then look to the wiring at the headphone socket.

Most probably it was a simple mistake of the male & female plugs having to be oppositely wired and just a mixup.
Edit*
At least we hope that's all that's wrong for now..


----------



## baronbeehive

baronbeehive said:


> These are the results of the continuity test having tested a good left hand circuit, and both right hand circuits where the problem lies:
> 
> The tests all agree with each other except for the following results:
> 
> ...


 
  
 I've just checked the circuits again with tubes out and everything is as before with tubes in, but there are a couple of addtional points to add to the above which I missed yesterday:
  
 4 - The suspect middle right hand circuit shows continuity between pins 3 and 6
  
 5 - the suspect middle right hand circuit shows continuity between pins 2 and 6
  
 6 - the suspect middle right hand circuit shows continuity between pin 5 and cathode bypass/330 ohm cathode resistor
  
 7 - the suspect middle right hand circuit shows continuity between pin 3 and cathode bypass/330 ohm cathode resistor
  
 8 - the suspect middle right hand circuit shows continuity between pin 5 and 330 ohm anode resistor
  
 9 - the suspect middle right hand circuit shows continuity between pin 6 and 330 ohm anode resistor
  
 If anyone can see a pattern in this let me know!
  
 Now I'm going to test the wires.
  
 Edit: I've just seen a pattern, the problems are in both plates and cathodes, apparently not the grid.
  
 Edit 2: Just tested the output XLR's from the positive and negative points on the board. All good except the right hand negative. I've revised my results yesterday so they are as follows now:
  
 1 - There was continuity with pin 1 of right hand XLR output from right hand -ive on the board.
 2 - There was continuity with pin 2 of right hand XLR output from right hand -ive on the board.
 3 - There was continuity with pin 1 of left hand XLR output from right hand -ive on the board.
 4 - There was continuity with pins 1 and 2 of right hand XLR output testing just the XLR's (not from the board).
  
 This post summarizes the test results to date, I've spent most of the day on this.
  
 What makes me think it's the output wiring is because I've checked the 4 runs of 3 core wires and they are connected correctly, (except for the lack of an earth wire in one of them as I mentioned earlier which was the same as stock wiring). That leaves the 6 output wires............. HOWEVER the left and right hand +ives are correct and the left hand -ive is correct and the left hand ground is correct and therefore the continuity with the right hand pin probably indicates ground on the right hand pin therefore the other right hand pin is probably correct .......... so the output wires are probably correct? (Or these 2 pins could be reversed).
  
 I believe the connections are all correct so if I can find out where the short is that could be the answer because it is all the power in the right -ive connection that is draining out and could explain why there is practically no voltage going through the middle right grid pin 1.
  
 You can compare the above anomalies with the good circuit:
  
 1 - pin 3 has continuity with pin 5
 2 - pin 7 has continuity with pin 8
 3 - pin 2 has continuity with 330 ohm anode resistor, WCF and cathode bypass/cathode 330 ohm resistor
 4 - pin 6 has continuity with cathode bypass/cathode 330 ohm resistor
 5 - cathode bypass/330 ohm cathode resistor has continuity with cathode bypass/330 ohm cathode resistor and 330 ohm anode resistor
 6 - WCF has continuity with 330 ohm anode resistor
  
 I don't know what to do next to try to find the short if it is that.


----------



## baronbeehive

Quote:


> Originally Posted by *baronbeehive* /img/forum/go_quote.gif
> ..................
> 
> What makes me think it's the output wiring is because I've checked the 4 runs of 3 core wires and they are connected correctly, (except for the lack of an earth wire in one of them as I mentioned earlier which was the same as stock wiring). That leaves the 6 output wires............. HOWEVER the left and right hand +ives are correct and the left hand -ive is correct and the left hand ground is correct and therefore the continuity with the right hand pin probably indicates ground on the right hand pin therefore the other right hand pin is probably correct .......... so the output wires are probably correct? (Or these 2 pins could be reversed).
> .......


 
  
  Sorry if that sounded garbled, I've just corrected some faulty reasoning.
  
 Quote:


baronbeehive said:


> .................
> 
> I believe the connections are all correct so if I can find out where the short is that could be the answer because it is all the power in the right -ive connection that is draining out and could explain why there is practically no voltage going through the middle right grid pin 1.
> ..........


  
 Therefore the short is somewhere _*between pins 1 and 2 from the right hand -ive connection on the board.*_


----------



## Maxx134

You will have to check the headphone jacks in front for wiring issue.
It may even be something as simple as the single ended jack having the center right contact and the last contact (ground) reversed..


----------



## baronbeehive

maxx134 said:


> You will have to check the headphone jacks in front for wiring issue.
> It may even be something as simple as the single ended jack having the center right contact and the last contact (ground) reversed..


 
  
 Just checked:
  
 1 - Right hand headphone to right hand XLR output, brown has continuity to brown
 2 - Right hand headphone to right hand XLR output, blue has continuity to blue
 3 - Right hand headphone to right hand XLR output, blue has continuity to black (ground) - _*therefore short here.*_
 4 - Right hand headphone to left hand XLR output, blue has continuity to black (ground) - _*because of short.*_
 5 - Left hand headphone to left hand XLR output, brown has continuity to brown
 6 - Left hand headphone to left hand XLR output, blue has continuity to blue
 7 - Left hand headphone to left hand XLR output, black has continuity to black
 8 - Left hand headphone to right hand XLR output, black has continuity to black
 9 - Left hand headphone to right hand XLR output, black has continuity to blue -* because of short.*
  
 All correct except nos. 3, 4, and 9.
  
 This all appears to be down to the fact that the right hand ground, or black, wire hasn't been connected to the ground pin on the headphone jack because I didn't think that it was originally. Anyway, now to connect the ground wire and see what happens........!!


----------



## baronbeehive

maxx134 said:


> You will have to check the headphone jacks in front for wiring issue.
> It may even be something as simple as the single ended jack having the center right contact and the last contact (ground) reversed..


 
  
 I haven't touched the SE jack.
  
 Quote:


baronbeehive said:


> .........
> This all appears to be down to the fact that the right hand ground, or black, wire hasn't been connected to the ground pin on the headphone jack because I didn't think that it was originally. Anyway, now to connect the ground wire and see what happens........!!


 
  
 Well, I've done that and still got the problem!
  
 It can't be the 3 core wiring which I've checked again and it can be seen visually whereas the 6 output wires can't be seen visually all the way. The problem is the continuity between XLR pin 1 - ground, and XLR pin 2, -ive, right hand side. The connections on the board look straightforward from the pics, just one connection to one of the tube pins. I haven't checked the ground wires because they are inaccessible. So what combination of negative wires or ground wires crossed could cause that?
  
 Ground and -ive wires crossed possibly, or wrong connection at the tube pin which is not likely given that there is a similar connection on the left hand side and I didn't get that wrong. 
  
 Or could the problem be back in the right hand middle circuit somewhere?


----------



## Maxx134

To find the location of the error,
you simply have to divide and separate the two sections...

 first section is the board to the XLR ..
second section is the XLR to the front headphone Jack's..

 so you simply disconnect and label wires at the XLR Jacks in the rear ..

Then test with those connections apart..

so you can find out if the short is on the side eminating from the board,

 or the wires going to to the front...

Remember the wires are twisted so easy to mix up if not color coded..

 the rear XLR are your midpoint to disconnect,
because they joined both board outputs and front jacks together ..


----------



## baronbeehive

The problem seems to be with the right hand -ive output which is going to ground. I disconnected the wires and its not that so there must be a short somewhere from the right hand -ive output tube pin.
  
 Looks like I'm going to have to get the board out to see what's going on there 
	

	
	
		
		

		
			





.


----------



## Maxx134

baronbeehive said:


> The problem seems to be with the right hand -ive output which is going to ground. I disconnected the wires and its not that so there must be a short somewhere from the right hand -ive output tube pin.
> 
> Looks like I'm going to have to get the board out to see what's going on there  .



You tested each wire individually (separate) and other prob to chasis?

So are you say the wire from board negative wire grounded?

There is one positive tube(circuit) and one negative tube(circuit).

The tube that had the burnt resistor should be the wire but we tracing the location of the short by disconnecting the wires from the XLR jacks.

You only needed to do this on the side you had problems (right).

Anyways we cannot rule out that there could be a soldering mistake there.

The reason for testing wires is to locate the area of short so if the wire grounded is coming from the board side then ,
Before you pull out, recheck the soldering and connections on the resistor anode area.


----------



## baronbeehive

maxx134 said:


> You tested each wire individually (separate) and other prob to chasis?
> 
> So are you say the wire from board negative wire grounded?
> 
> ...


 
  
 I disconnected the ground and -ive output wires from the right hand XLR, these were the 2 wires that were showing continuity at the XLR when there shouldn't be continuity.
  
 I then tested at the right hand XLR with the other probe at the +ive output connection on the board.:
  
 1 - The +ive pin tested correctly. This output wire was left on because it was not causing the problem.
  
 I then tested at the right hand XLR with the other probe at the -ive output connection on the board, the connection from pin 3 of the faulty tube circuit.
  
 2 - The ground pin only showed continuity. This indicates that it wasn't the output wire causing it, because I had disconnected it. So the right hand -ive output connection from the board was obviously going to ground.
  
 I then tested at the right hand ground XLR pin with the other probe at the chassis ground:
  
 3 -  It showed continuity correctly and none of the other pins showed continuity which was correct.
  
 I then tested the ground output wire at the XLR end with the other probe at the chassis ground. This wire I had disconnected:
  
 4 - It showed continuity correctly showing ground.
  
 Then I tested the right hand -ive output wire at the XLR end with the other probe at the chassis ground. This wire I had disconnected:
  
 5 - It showed continuity indicating a short somewhere before, or at the board -ive output connection.
  
 Then I tested the disconnected right hand -ive output wire at the XLR end with the other probe at the -ive output connection on the board:
  
 6 - It showed continuity which is what you would expect in a correct circuit but....
  
 Then I tested the distconnected right hand ground wire at the XLR end with the other probe at the -ive output connection on the board:
  
 7 - It also showed continuity indicating that the -ive wire was grounded.
  
 Not much point checking the soldering around the anode resistor because it melts every time I switch on due to the power draining out. But this was a pre-existing problem, it was not the soldering that caused it. The other connections look good.
  
 Edit:
  
 I also tested the suspect right hand circuit tube pins 3 and  5 with the other probe at chassis ground, and both pins were grounded which was incorrect.
  
 These results taken with the tests on the bad circuit continuity I did on the last page indicating continuity on many parts of the bad circuit which should not have been the case, I believe indicate that *somewhere on the circuit on the board is the problem, not in the wiring.* That could explain the incorrect continuity readings in the bad circuit that I found during testing.


----------



## Maxx134

I believe pins 3&5 go together in WCF circuit, and so should read same.

The question is if the output wire from that board was connected when you performed that continuity test.
The output wire from board needed to be disconnected at the XLR.

You have a grounded output but maybe only grounded for the instance of the time it take the big coupling cap to charge.
That is, if the big coupling cap is improperly connected at wrong side of the resistor..

Compare that big coupling cap connection point to the others.

Also verify the output wire from board is disconnected at XLR when doing checking those pins 3&5.


----------



## baronbeehive

maxx134 said:


> I believe pins 3&5 go together in WCF circuit, and so should read same.
> 
> The question is if the output wire from that board was connected when you performed that continuity test.
> The output wire from board needed to be disconnected at the XLR.
> ...


 
  
*Yes there is continuity *between pins 3 and 5 in the good circuits.
  
*Yes I disconnected the ground and -ive wires *from the XLR's when I did the continuity test.
  
 So to check the connections around the cap, *which big coupling cap do you mean?*
  
 So to sum up, it can't be a wiring problem because I disconnected those -ive and ground wires and then tested at the XLR's.
  
 Therefore I think I'm right in saying that somewhere on the bad circuit is a short, or bad connection and that would explain all the false continuity readings that I was getting on the bad circuit only. I've looked at some of these readings and I can't see what could be shorting without actually looking on the reverse side. For example the only possible thing may be a wrong connection of the -ive wire at the wrong tube pin indicated by continuity between pins 5 and 6, but I can't think of anything else. Nothing seems to be physically close enough to cause a short.
  
 I've discounted the opamps for the moment because the grounding issue looks more likely.
  
*So I think I need to look somewhere around grid pin 1.* This had a wrong reading of  -0.6v, measured from ground to pin1.* Also the anode resistor*, which had a wrong reading of  44.3v. All other voltage readings were good.
  
 So how would I find the exact location of the short?
 Do I need to take more voltage readings?
 Will capacitance readings tell me anything?


----------



## Maxx134

baronbeehive said:


> So to check the connections around the cap, which big coupling cap do you mean?
> ....
> 
> So how would I find the exact location of the short?
> ...



The wire soldered to the negative pin must be touching ground if your reading ground.
You reading ground on the pins.
Leave meter on it and see if the value changes.
If it stays near zero there is a ground connection, as the amp it not on so the grid can't control that.

Disconnect any tube AND tube socket .
Extra Tube sockets are known to short.

Test again those pins without tube to verify it is the connection.

Also,
I was talking about the huge Decoupling cap.
It's the only "large" one there, and supposed to be connected as in pic.

If the cap was connected on wrong end of resistors (either end - anode resistor or cathode resistor)
Then you would initially see ground, but value would change as cap charges.

Anyways, just a visual look at the big caps (47uf I think you have)
Would easily tell you if one Cap is misplaced.


----------



## baronbeehive

maxx134 said:


> The wire soldered to the negative pin must be touching ground if your reading ground.
> You reading ground on the pins.
> Leave meter on it and see if the value changes.
> If it stays near zero there is a ground connection, as the amp it not on so the grid can't control that.
> ...


 
 Yes.......
  
 I'm reading ground on the ground pin with other probe on negative output on board with wire disconnected, which indicates short around that negative connection somewhere.
  
 I'm also reading ground on the end of the disconnected negative wire with other probe on ground with wire disconnected which indicates short around that negative connection somewhere.
  
 I'm also reading ground on the end of the disconnected ground wire at the XLR end with the other probe at the -ive output connection on the board which indicates short around that negative connection somewhere.
  
 The meter stays at or near zero.
  
 I've removed the tubes so the readings are with them out.
  
 All decoupling caps are connected at the same ends of the resistors, therefore if it was that it could only be the solder joint.


----------



## Maxx134

Have you doubled up on the wiring?
If so maybe make sure they not mixed/crossed.


----------



## baronbeehive

maxx134 said:


> Have you doubled up on the wiring?
> If so maybe make sure they not mixed/crossed.


 
  
 No.
  
 Looks like I will have to take the board out and you think that whatever is wrong should be able to be traced fairly easily?
  
 If I do have to take the board out, do I need to do any more tests first?


----------



## baronbeehive

maxx134 said:


> The wire soldered to the negative pin must be touching ground if your reading ground.
> ................


 
  
 Not sure because...........
  


baronbeehive said:


> ...........
> 
> Then I tested the disconnected right hand -ive output wire at the XLR end with the other probe at the -ive output connection on the board:
> 
> ...


 

 Therefore it is connected to the -ive output on the board. How can it be connected correctly to the board at that end and connected correctly to the XLR end as well yet be shorting out. Possible I suppose but I think it must be something else in the circuit.


----------



## Maxx134

If you pushed your leads of caps or resistors or the wire in the board too far they will extend and touch the metal surfaces on other side such as frame or screws .
Especially when you insert wires soldering they will slip in far if not Careful.

Something is creating contact,
But just to have continuity from one side to the other (board to XLR end) should not be confused with continuity from any point of testing, to the metal frame (ground)..


----------



## Maxx134

It could even be a pinched wire on underside.


----------



## baronbeehive

maxx134 said:


> It could even be a pinched wire on underside.


 

 Yes, it could be all of those, so looks like the board will come out and that's not going to be easy!


----------



## Maxx134

Check wiring just that one negative signal wire.

you need to see if possible to observe if that wire is pinched or soldered on two points instead if one.
Use a dentist mirror and flashlight to look inside..


----------



## baronbeehive

maxx134 said:


> Check wiring just that one negative signal wire.
> 
> you need to see if possible to observe if that wire is pinched or soldered on two points instead if one.
> Use a dentist mirror and flashlight to look inside..


 

 I was thinking of using a dentist's drill to remove those tight screws lol. I finally managed to loosen them with a new screwdriver so hoping to remove the board tomorrow now so I can have a look and see what's what. It must be something like that wire!
  
 I won't be using the dentist's mirror and flashlight....... too many painful memories 
	

	
	
		
		

		
			





.


----------



## Maxx134

Must be careful with those black screws as they can strip easily with a screwdriver that not exactly right size.
I have two on bottom cover I had to drilled out the screws on.


----------



## colliedoggy

How many differences are there between the mk vi+ and the mk viii se please?
  
 Is the pcb layout the same, greatly different or slightly different?
  
 What are those differences?
  
 Thanks
  
 James


----------



## baronbeehive

Just checked everything on the reverse and it's all looking good, including the wire, soldering, nothing touching, connections are good.
  
 I checked the pins again and pins 3 and 5 are grounded on the bad circuit. Given that pins 3 and 5 are connected in the same circuit on the good side then then clearly if one of these is grounded in the bad circuit it will affect the other. So I'm trying to investigate further to find out where the grounding is.


----------



## Maxx134

Post a pic of the area on both sides so we can compare solder joints for irregularities.
If not the wire and tube is not connected, then most likely a soldering issue..


----------



## Maxx134

Signal output of that tube goes only to output wiring,
and also runs in board back to the gain switch,
 thru the resistors next to it, 
So that gain switch area also needs observation.


----------



## baronbeehive

Inside right hand (bad) circuit : cathode bypass/resistor, coupling cap, WCF, anode resistor connections.
  


 Inside right hand (bad) circuit : -ive output connection.
  


 Both right hand circuits : cathode bypass/resistor connections.
  


 Both right hand circuits : heater wire connections.
  


 Outside right hand circuit : cathode bypass/resistor, WCF, coupling cap, connections.
  


 Outside right circuit : anode resistor connections.
  


 Inside right hand (bad) circuit : anode resistor, WCF connections.
  

  
 Inside right hand (bad) circuit : cathode bypass/resistor, anode resistor, WCF, coupling cap connections.
  

  
 Headphone output socket
  


 Outside right hand circuit : WCF, anode resistor connections.
  


 Outside right hand circuit : anode resistor connections.
  

  
 Outside right hand circuit : cathode bypass/resistor, coupling cap connections.
  


 Gain switch.
  


 Let me know if you need more info.


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## SonicTrance

> Outside right hand circuit : anode resistor connections.


 
 Looks like the Rifa cap lead is shorting, or very close to it, with the 300 ohm grid resistor.
  
 Other than that I can't see anything off.


----------



## baronbeehive

sonictrance said:


> Looks like the Rifa cap lead is shorting, or very close to it, with the 300 ohm grid resistor.
> 
> Other than that I can't see anything off.


 
  
 Thanks Sonic. It's quite well clear from a different angle, although the insulation could be better.
  
 I've checked the 4 mods in the path of the bad circuit, and of the coupling, WCF caps, anode resistor and cathode bypass, both the anode resistor and cathode bypass are grounded, but so are they in the OK left hand circuit so I'm still wondering!
  
 Edit: I just looked again and you can see by the curve of the bottom wire a tiny blob of solder, but it is only touching the board so could not short I don't think.
  
 To summarize: everything is the right way round, connected up correctly, soldering looks good and there's no touching wires or anything, so what do I do now 
	

	
	
		
		

		
		
	


	




 ???


----------



## baronbeehive

baronbeehive said:


> These are the results of the continuity test having tested a good left hand circuit, and both right hand circuits where the problem lies:
> 
> The tests all agree with each other except for the following results:
> 
> ...


 
  
 Quote:


baronbeehive said:


> I've just checked the circuits again with tubes out and everything is as before with tubes in, but there are a couple of addtional points to add to the above which I missed yesterday:
> 
> 4 - The suspect middle right hand circuit shows continuity between pins 3 and 6
> 
> ...


 
  
 Just speculating, but if there was a short between tube pins 5 & 6 that would explain most of the test results above. For example:
  
 Point 1 (above) - _The suspect middle right hand circuit shows continuity between pins 5 and 6_* (because I think there may be a short there)*
  
 Point 4 (above) -_ The suspect middle right hand circuit shows continuity between pins 3 and 6 _*(because pin 3 has continuity with pin 5 in the good circuit and pin 6 may be shorting with pin 5)*
  
 Point 6 (above) -_ the suspect middle right hand circuit shows continuity between pin 5 and cathode bypass/330 ohm cathode resistor _*(because pin 6 has continuity with cathode bypass/cathode 330 ohm resistor in the good circuit and pin 6 may be shorting with pin 5)*
  
 Point 7 (above) -_ the suspect middle right hand circuit shows continuity between pin 3 and cathode bypass/330 ohm cathode resistor _*(because pin 6 has continuity with cathode bypass/cathode 330 ohm resistor in the good circuit and pin 6 may be shorting with pin 5 which is connected to pin 3 in a good circuit)*
  
 Point 8 (above) -_ the suspect middle right hand circuit shows continuity between pin 5 and 330 ohm anode resistor _*(because cathode bypass/330 ohm cathode resistor has continuity with cathode bypass/330 ohm cathode resistor and 330 ohm anode resistor in a good circuit and pin 6 has continuity with cathode bypass/cathode 330 ohm resistor in a good circuit and pin 6 may be shorting with pin 5)*
  
 Point 9 (above) - _the suspect middle right hand circuit shows continuity between pin 6 and 330 ohm anode resistor _*(because cathode bypass/330 ohm cathode resistor has continuity with cathode bypass/330 ohm cathode resistor and 330 ohm anode resistor in a good circuit and pin 6 has continuity with cathode bypass/cathode 330 ohm resistor in a good circuit)*
  
 Point 2 (above) - _The suspect middle right hand circuit shows continuity between pin 3 and 330 ohm anode  resistor _*(because cathode bypass/330 ohm cathode resistor has continuity with cathode bypass/330 ohm cathode resistor and 330 ohm anode resistor in a good circuit and pin 6 has continuity with cathode bypass/cathode 330 ohm resistor in a good circuit and pin 6 may be shorting with pin 5 which is connected to pin 3 in a good circuit)*
  
 Sorry to be repetitive but I'm trying to be as clear as possible. I'm only speculating because I don't know about circuit diagrams and don't know which way it goes through the circuit. But I'm sure a circuit diagram could be drawn to make sense of this.


----------



## SonicTrance

> Sorry to be repetitive but I'm trying to be as clear as possible.


 
 I'm struggling to read your posts to be honest, baron. 
  
 I can say this though. Only the heater pins, pin 7 and 8, should have continuity between them. If any other pins show continuity it's not good. Now that you have the board out you could start de-soldering suspect components around the problematic tube until there's no more short.


----------



## baronbeehive

sonictrance said:


> I'm struggling to read your posts to be honest, baron.
> 
> I can say this though. Only the heater pins, pin 7 and 8, should have continuity between them. If any other pins show continuity it's not good. Now that you have the board out you could start de-soldering suspect components around the problematic tube until there's no more short.


 
  
 Ha ha.... thanks for trying anyway Sonic, I can't understand what I said either!
  
 My point was that if there was a short between tube pins 5 & 6 then it would explain the test results I had for the bad circuit. However I can't quite see how there could be a short there.
  
 Edit: There's also continuity between tube pins 3 and 5 in a good circuit, not just 7 and 8.


----------



## colliedoggy

I have just been checking the power supply in the Mk viii SE against the schematics posted by coinmaster for the mk vi+. For the main section of power supply, there are a few differences with the values shown:
  
 'R12' is two 120_Ω_ 5W resistors in parallel (and likewise on the other side).
  
 Instead of one 5k1_Ω _there are two 5k1_Ω _in parallel. (On the board is printed '3k9 2w'!) 
  
 Instead of one 8k2_Ω _there are two 8k2_Ω _in parallel. On the board is printed '5k6 2w'!)


----------



## colliedoggy

The stock power stage resistors in my mk viii se are not 150 Ohms. They are actually 180 Ohms.
  
 How will this change the operation of the circuit from the 150 Ohms it seems other people have?


----------



## Maxx134

All resistors are an approximate.
The zener diodes will make sure the voltages are correct.
The anode resistors being 180 ohm is not a big deal either.

My phone died so I was away for a few days.

As for the problematic output tube stage of member baronbeehive,
Do what sonic says (disconnect),

Remember very importance to realize that the amp DOES NOT have a mirror image of both sides,
So comparing sides you should realize that the pins of the good side are exact copy to other side, NOT a mirror image where things are reversed,

So yes there should be continuity on the heater pins, 
And another separate continuity of two pins from cathode of one triode to plate of other, but neither of those should have continuity to chassis ground.
I suspect an error in solder or connection.

Focus on area of the burnt resistor.
A short on your cathode area would have caused it to slowly burn.
Look at where you connected everything on your cathode area.

The reason to disconnect the large cap (decoupling) is to verify it not a error in connection, and also disconnect one end of the gold rifa cap to make sure it not a shorted bypass cap.
Also check the normal bypass caps for proper connection, and also disconnect one end to test if shorted.


----------



## Maxx134

When testing caps they will briefly show some continuity as they charge up, but then go up into infinity ohm.

You can leave one end installed, total removal unnecessary


----------



## baronbeehive

maxx134 said:


> All resistors are an approximate.
> The zener diodes will make sure the voltages are correct.
> The anode resistors being 180 ohm is not a big deal either.
> 
> ...


 
 Yes, I intend to do what Sonic says, but it's finding the time atm.
  
 I hope to have another look in the next couple of days. I've satisfied myself that it's nothing obvious, I've gone over and over the connections and pretty sure they're good but I have some suspicions of the solder around the cathode bypass like Maxx says. So I intend to have a very close look at that area, there are some solder spots which could cause tracking around the board and a dubious area of possible shorting like Sonic said. I will look at that and clean up the area very thoroughly before trying again. I noticed this with having moved some of the parts out of the way so it's easier to see around that area.
  
 One thing, I'm quite surprised at how good the reverse of the board looked, and the engineer remedied the problems with the pads which was good. So I'm able to dismiss some possible causes, like the wire, for example.


----------



## Maxx134

baronbeehive said:


> ...
> One thing, I'm quite surprised at how good the reverse of the board looked, and the engineer remedied the problems with the pads which was good. So I'm able to dismiss some possible causes, like the wire, for example.



I gotta admire your interest and persistence in checking and learning,
 instead of just bringing it to your engineer..


----------



## baronbeehive

maxx134 said:


> I gotta admire your interest and persistence in checking and learning,
> instead of just bringing it to your engineer..


 
  
 When I've got you guys behind me, it's easy! I hadn't got a clue at first but I know there had to be a logical explanation for the problem, it's just a case of finding it. This is no more than others on this thread, it's good learning new things. I surprised myself at how good the work on the reverse of the board was but I had feeling that there was nothing wrong there, I followed the advice of Redge when he said check everything, and then check again.........and again!


----------



## coinmaster

Wait you still haven't fixed it yet? Have you tried switching the opamps like I suggested or are we beyond that issue now?


----------



## baronbeehive

coinmaster said:


> Wait you still haven't fixed it yet? Have you tried switching the opamps like I suggested or are we beyond that issue now?


 
  
 No, I haven't forgotten that. I'm leaving that for the moment until I've fixed the short because there is an obvious issue there. Assuming I can fix it then if there is still a problem then that's next on the list.


----------



## Maxx134

I have an extra opamp if you wanna try regardless...
Hey why don't you just pull the opamp out while unit off to make sure it not a shorted opamp over there?


----------



## coinmaster

Can you explain to me in simple terms what is shorted? I don't want to decrpyt the previous messages  Any issue with this amp should be easily troubleshootable unless it's high density like Maxx's in which case it would probably be annoying.


----------



## baronbeehive

coinmaster said:


> Can you explain to me in simple terms what is shorted? I don't want to decrpyt the previous messages  Any issue with this amp should be easily troubleshootable unless it's high density like Maxx's in which case it would probably be annoying.


 
  
 That's what you get for trying to be clear and simple lol! This is not like Maxx's but it is annoying!
  
 Initially I noted that there was continuity between XLR output pins 1 and 2 right hand circuit, indicating possible bad connection/shorting of wires - *BAD!*
  
 After disconnecting the wires I found that XLR output pins 1 and 2 no longer had continuity - *GOOD!*
  
 When I got the board out I found the wires and connections OK - *GOOD!*
  
 So following this up to look for the problem somewhere else in the faulty circuit I found that there was continuity between tube pins 5 and 6 and they were also grounded - *BAD!*
  
 That's what led me to think there may be a short between tube pins 5 and 6 or if not there then somewhere in the faulty circuit
  
*Crucially* I tested from the -ive output connection on the board and there was continuity from there to the end of the -ive output wire - *GOOD!*
  
*However *there was also continuity from the -ive output connection on the board to ground, *clearly indicating a short!*
  
 I know of no simpler way to say that......... wait.......... there's a boo boo in the works and sparks are flying and I don't like it one bit................... 
	

	
	
		
		

		
		
	


	




.


----------



## colliedoggy

So is the continuity between pins 5 and 6 on only one of the 6N30P sockets in the right hand circuit, or both of them? 
  
 If only one, is it the +ve or -ve socket?
  
 Presumably, this short is with no valves in the sockets, is it?


----------



## Maxx134

Just look at the board trace in the center of the socket it clearly shows two pins connected I don't have time to pull up pics but it is from first triode of WCF circuit to second triode.
As long as they don't have continuity to chassis ground you should be good .


----------



## colliedoggy

Those are pins 3 and 6 that should be connected. Check.


----------



## colliedoggy

Could someone help me with what components are soldered and what values on the top side of the pcb for the mk viii se?
  
  
 I believe that there may be a resistor on the top side of the board of value 180 Ohms in parallel with each cathode bypass cap. This is the value I get with my DMM rather than the 330 Ohms marked on coinmaster's schematic for the mk vi+ .
 Is this correct?
  
 What other components are not visible without removing the board?
  
 Thanks


----------



## SonicTrance

colliedoggy said:


> So is the continuity between pins 5 and 6 on only one of the 6N30P sockets in the right hand circuit, or both of them?
> 
> If only one, is it the +ve or -ve socket?
> 
> Presumably, this short is with no valves in the sockets, is it?


 
 Just so you know, Baron has a MK6. So no 6N30P sockets there.


----------



## Maxx134

Yep different pins that's why I not stated the pins, but a OK as same idea


----------



## SonicTrance

colliedoggy said:


> Could someone help me with what components are soldered and what values on the top side of the pcb for the mk viii se?
> 
> 
> I believe that there may be a resistor on the top side of the board of value 180 Ohms in parallel with each cathode bypass cap. This is the value I get with my DMM rather than the 330 Ohms marked on coinmaster's schematic for the mk vi+ .
> ...


 
 The cathode resistors are on top side of board. Also some ceramic resistors in the psu and a couple by the relay.
  
 As far as I know the MK8 usually has 150 ohm cathode and plate resistors. 180 ohm will also work of course. Tubes will run cooler at lower current.


----------



## colliedoggy

Ahh!
  
 In my unit the plate resistors actually fitted are 180 Ohms, so that explains things.
  
 Thanks


----------



## Maxx134

The anode/cathode resistor values are the only difference between amp components to get that I recall,
 and all extra components to install are same.


----------



## baronbeehive

colliedoggy said:


> So is the continuity between pins 5 and 6 on only one of the 6N30P sockets in the right hand circuit, or both of them?
> 
> If only one, is it the +ve or -ve socket?
> 
> Presumably, this short is with no valves in the sockets, is it?


 
  
 Hi colliedoggy, welcome!
  
 The continuity is on only one, the suspect right hand circuit. I don't know if it is the +ve or -ve but it is the one with the -ve output going from it.
  
 Yes tubes are out.
  


maxx134 said:


> Just look at the board trace in the center of the socket it clearly shows two pins connected I don't have time to pull up pics but it is from first triode of WCF circuit to second triode.
> As long as they don't have continuity to chassis ground you should be good .


 
  
 I can't see the connection from the board trace but it is definitely pins 3 and 5 that are connected as confirmed by the other good circuits. On the bad circuit they are grounded, as I said by a possible short with pin 6.
  


colliedoggy said:


> Those are pins 3 and 6 that should be connected. Check.


 
  
 No, pins 3 and 5. Pin 6 is only connected in the bad circuit as indicated by continuity check, not in the other circuits.
  
 Thanks for the help, I'm getting nowhere, having checked again the connections, joints and so on and I can't see anything amiss, and I've run checks to try to see as well. Maybe I should just send it back and stop wasting everyone's time.
  
 Before doing that I will of course try to wrench out the opamps, how do I test them to check they're OK? I still don't see how they could cause a grounding issue though.


----------



## colliedoggy

baronbeehive said:


> Hi colliedoggy, welcome!
> 
> The continuity is on only one, the suspect right hand circuit. I don't know if it is the +ve or -ve but it is the one with the -ve output going from it.
> 
> ...


 
 Apologies about the pin numbers but now I realise that you have the mkvi+ and I have the mk viii se which have different output valve pin outputs
  
 Chin up and keep going! 
  
 I haven't got enough acquaintance with the circuit and your problem yet to be able to judge whether the op amps could be the source. But you could always try swapping them from one left to right channels and see if the problem moves. There is a cheap tool to pull them from their sockets cleanly and without fear of damage.to the pins, which is referred to as an 'IC puller'. Essentially they are just a pair of tweezers with right-angled, inward-pointing tips. They cost a couple of quid..Before I had a pair of those I used to just carefully prize up one end a tiny amount, then the other, etc,. incrementally, until the chip could easily be pulled out with forefinger and thumb.


----------



## coinmaster

A short between 5 and 6 would immediately blow the fuse on startup. The only way that could be shorted is a broken WCF cap or some really bad wiring or a tube short. 
 What is this -ive you are referring to?


----------



## baronbeehive

colliedoggy said:


> Apologies about the pin numbers but now I realise that you have the mkvi+ and I have the mk viii se which have different output valve pin outputs
> 
> Chin up and keep going!
> 
> I haven't got enough acquaintance with the circuit and your problem yet to be able to judge whether the op amps could be the source. But you could always try swapping them from one left to right channels and see if the problem moves. There is a cheap tool to pull them from their sockets cleanly and without fear of damage.to the pins, which is referred to as an 'IC puller'. Essentially they are just a pair of tweezers with right-angled, inward-pointing tips. They cost a couple of quid..Before I had a pair of those I used to just carefully prize up one end a tiny amount, then the other, etc,. incrementally, until the chip could easily be pulled out with forefinger and thumb.


 
  
 Hey, thanks for the tip about the opamp tool, I was wondering if I had anything suitable in the cutlery drawer and was contemplating getting an ice lolly and using the stick to lever it out! With all the mods it would be difficult to do by hand because everything else is in the way.
 Are you modding your MKVIII then?
  


coinmaster said:


> A short between 5 and 6 would immediately blow the fuse on startup. The only way that could be shorted is a broken WCF cap or some really bad wiring or a tube short.
> What is this -ive you are referring to?


 
  
 Well there is definitely continuity there such that I was thinking about removing the tube socket to see if there was any solder or anything stuck there, but first I wanted to be sure it was nothing else in the circuit. I've tried looking underneath the socket and it all looks clear. Looks like the tube short is ruled out because I'm testing with tubes out.
  
 So would the amp still work with a blown fuse, because if it's just that it would save a lot of hassle.
  
 The -ive is the -ive output marked on the board by the tube pins of the faulty tube circuit going from there to the output XLR, and the other one is the output on the board just by the fuses, (-ive and +ive).


----------



## SonicTrance

> So would the amp still work with a blown fuse, because if it's just that it would save a lot of hassle.


 
 No, with a blown fuse no AC enters the amp.


----------



## coinmaster

I take it back, 5 and 6 being shorted is normal. I forgot they wired it a little funky from the way I look at the diagram. It's just the output to the WCF.


----------



## coinmaster

I pulled my mk6 board out of the trash and I don't see any -ive marked anywhere so I have no idea what you are talking about if you can take a picture that would be great.
  
 Other then that start with what you know. The grid voltage is grounded which would cause the original symptoms you were having. Switch the opamp in the problem area out with one of the other ones and see if the issue moves around with it.


----------



## coinmaster

Today is a glorious day, I finally purchased another MK6 lol. I turned off my brain and just clicked the buy button before logic and reason returned to me 
	

	
	
		
		

		
		
	


	



 Also the fact that I'm constantly waiting on parts made me realize that my prototypes will never be a good way to just listen, at least not anytime soon. Dear god help my bank account.


----------



## baronbeehive

coinmaster said:


> I pulled my mk6 board out of the trash and I don't see any -ive marked anywhere so I have no idea what you are talking about if you can take a picture that would be great.
> 
> Other then that start with what you know. The grid voltage is grounded which would cause the original symptoms you were having. Switch the opamp in the problem area out with one of the other ones and see if the issue moves around with it.


 
  
 Mk VI - trash - you have no respect lol.
  
 This pic shows the right -ive board output to the XLR, the other 2 outputs are just down below the 2 fuses.
  

  
  


coinmaster said:


> Today is a glorious day, I finally purchased another MK6 lol. I turned off my brain and just clicked the buy button before logic and reason returned to me
> 
> 
> 
> ...


 
  
 I gave up worrying about my bank account long ago 
	

	
	
		
		

		
		
	


	




.


----------



## coinmaster

I still don't see what you're talking about there's no -ive label nor do I see any XLR exits.


----------



## baronbeehive

coinmaster said:


> I still don't see what you're talking about there's no -ive label nor do I see any XLR exits.


 
  
 Where it says R_OUT - with a (3) underneath indicating pin 3, that is the right hand negative point on the board circuit which goes to the right hand negative pin on the XLR output on the chassis back panel. It goes there via pin 5 which is where the output wire to the XLR's is connected. There is also a R_OUT + which is on the board just below the fuses, and a ground point also.


----------



## baronbeehive

coinmaster said:


> Today is a glorious day, I finally purchased another MK6 lol. I turned off my brain and just clicked the buy button before logic and reason returned to me
> 
> 
> 
> ...


 

 What have you been using for music listening then? At least I've got my speaker amp 
	

	
	
		
		

		
		
	


	




.


----------



## coinmaster

The R_OUT -  is the cathode. The output to XLR should be on 5 or 6. If the cathode is reading ground then you have a problem. If the XLR out is outputting from this ground you also have a problem. Show me pictures of the backside of this area. Also make sure you are measuring from the proper ground. I usually just stick the probe in the big metal hole between the large psu caps for convenience as it is directly tied to ground.


----------



## coinmaster

> What have you been using for music listening then? At least I've got my speaker amp
> 
> 
> 
> ...


 
 Nothing 
	

	
	
		
		

		
		
	


	



  
 Also I take it back again, I was going off the top of my head before, 3 and 5 should be connected not 5 and 6 so if 5 and 6 are connected then you got probs. Remove tube and test again and check backside of board.


----------



## baronbeehive

baronbeehive said:


> Inside right hand (bad) circuit : cathode bypass/resistor, coupling cap, WCF, anode resistor connections.
> 
> 
> 
> ...


 
   



coinmaster said:


> Nothing
> 
> 
> 
> ...


 
  
 As before, pins 3, 5 and 6 are grounded and connected.


----------



## coinmaster

6 shouldn't be grounded. The only thing that should be connected to 6 is the cathode resistor and bypass cap.


----------



## baronbeehive

coinmaster said:


> 6 shouldn't be grounded. The only thing that should be connected to 6 is the cathode resistor and bypass cap.


 
  
 No, it shows continuity with the cathode bypass and resistor but is grounded. I've looked at the tube sockets and there doesn't seem to be any way that there could be a short between pins 5 and 6 so it must be somewhere else in the circuit. I keep on checking the wiring, connections etc. and can't see anything relevant at all.


----------



## colliedoggy

Did you change the wiring to the rear pre-amp out sockets at all?
  
 Is there any possibility it could arise from that?
  
 (Yes, I am in preparation for modding. I am still putting together a parts list.)


----------



## colliedoggy

Have you done anything with the volume pot?


----------



## baronbeehive

colliedoggy said:


> Did you change the wiring to the rear pre-amp out sockets at all?
> 
> Is there any possibility it could arise from that?
> 
> (Yes, I am in preparation for modding. I am still putting together a parts list.)


 
  
 Yes I've changed the wiring, and I did think initially that it was that as that was when I first spotted the grounding issue at the XLR's. But I've disconnected the wires and there's still the same issue so it must be somewhere in the circuit, not the wiring.
  
 BTW good luck with the mods 
	

	
	
		
		

		
		
	


	




.
  


colliedoggy said:


> Have you done anything with the volume pot?


 
  
 No.


----------



## Maxx134

-ive = negative...

I did not realize this abbreviation at first either.
Lol

Check out coinmaster suggestion as he has the MK6 not me


----------



## Maxx134

I would like to point out at this time for the importance and necessity and cooling the amp not because of the tubes,
 but mainly and specifically because of the Transformers winding for the driver stage...

 If you look at the Transformer schematic (posted in thread), you will see that the winding for the driver Stage is the weakest link..

In other designs, if you do not have enough heater current,
it just simply Taps out..

 But in this design, the driver tube heaters are connected direct to the Transformer without any type of protection.

So what we have is a circuit in which a Transformer tries to deliver whatever the current demands,
 no matter tube so increased heat until shorting/failure of the Transformer heater windings..

Only the driver Stage has this potential possibility when using rolling tubes not designed for the amp but a similar effect can be accomplished with letting the amp Transformers overheat.


So make sure your Transformers are not blazing hot,
 or you risk a short in your driver coil windings..

I had this unfortunate incident a few months ago,
of using an adapter which shorted out my driver Stage..
 I fell asleep and woke up with a non-working left side.


 I didn't even know it failed because my ground fault protection Outlet was triggered and shut down AC..
 I use and recommend a hospital-grade isolation transformer for all audio equipment.

Anyways, the point is you don't want to have to order a replacement Transformer,
As then you will and end up waitIMG almost a month for replacement Transformer,
Which is nice heavy item:


It's alot of wires too.
 So take care of any heat issues.

Replacement need access to covers and inside bolt holding it.


Anyways I have taken a break from completing my mods to actually enjoy the amp.

Too much testing of driver stage was problem.
Anyways if you want to roll any tube, then a separate PSU for the heaters would be optimal, 
Which is another uncompleted mod lol.


----------



## coinmaster

> > it shows continuity with the cathode bypass and resistor but is grounded. I've looked at the tube sockets and there doesn't seem to be any way that there could be a short between pins 5 and 6 so it must be somewhere else in the circuit. I keep on checking the wiring, connections etc. and can't see anything relevant at all.


 
 Are you saying there is continuity between 6 and ground? How are you measuring ground?


----------



## Maxx134

coinmaster said:


> > > it shows continuity with the cathode bypass and resistor but is grounded. I've looked at the tube sockets and there doesn't seem to be any way that there could be a short between pins 5 and 6 so it must be somewhere else in the circuit. I keep on checking the wiring, connections etc. and can't see anything relevant at all.
> 
> 
> 
> Are you saying there is continuity between 6 and ground? How are you measuring ground?



Good question.
He needs to be sure of what is just continuity, from what is "being grounded"..


----------



## baronbeehive

coinmaster said:


> Are you saying there is continuity between 6 and ground? How are you measuring ground?


 
  
 Yes, there are 2 separate things:
  
 1 - continuity with ground with each of pins 3, 5 and 6 ie. each is grounded
 2 - continuity between pins 3, 5 and 6 in whatever order ie each is connected with each of the others
  
 I'm measuring ground by putting one probe in a screw hole in the chassis, or when the board is in, by putting it in a screw hole or in one of the 2 big holes near the PSU caps. The other probe touching the tube pins in turn.
  
 BTW coin, I'm going out tomorrow to get the opamp extractor tool.
  
 BTW Maxx, the engineer said that he didn't like all of the bunch of wires going in the small hole to the transformer, very tight fit and the hole has sharp edge.


----------



## coinmaster

If 3/5/6 is showing continuity with ground and there are no visual indicators  you may have damaged the board and shorted the pins to the ground plane as I did with mine.


----------



## baronbeehive

coinmaster said:


> If 3/5/6 is showing continuity with ground and there are no visual indicators  you may have damaged the board and shorted the pins to the ground plane as I did with mine.


 
  
 Yes, that's why I was concerned about the pads, but the engineer did repair those. Is there any way of testing to find that out, by for example testing at different points along the plane?
  
 One thing puzzles me, that is the intermittent nature of some of the test readings which has made testing quite tricky. For example when testing pins 3 and 5 to ground they give off continuous signals but when testing pin 6 it only gives a bleep of a few seconds before stopping and then will not give a reading again unless I reverse the probes. It looks like the short of whatever it is is only intermittent. I don't understand things like the direction of the current through the circuit but I know that diodes only allow current through one way only for example.
  
 But to be sure I didn't make a mistake I made sure I repeated the tests several times until I was satisfied they were consistent.


----------



## coinmaster

> but when testing pin 6 it only gives a bleep of a few seconds before stopping and then will not give a reading again unless I reverse the probes.


 
 That's what happens when u test continuity across a capacitor. You are charging the plates of the capacitor and they will not respond once fully charged unless the polarity is reversed. This means the B- connection is where the ground issue is which could be anywhere between the bottom of the cathode resistor to a bunch of places in the power supply. Although this would mean the fuse would trip after the relays kicked in so unless you broke it since u last had it on I'm not so sure. Check the bottom of the cathode resistor for continuity to ground.
  
  
 As for 5 and 6 check the 2k resistor by the opamp.


----------



## colliedoggy

baronbeehive said:


> BTW coin, I'm going out tomorrow to get the opamp extractor tool.


 
 Wait!
  
 It just occurred to me that each op amp is adjusted for offset by its trimmer capacitor, which is the blue box nearby with the small screw on top of it. 
  
 Whenever you change the position of one of the op amps, the op amp offset ought to be corrected for by adjusting the trimmer potentiometer (the blue box with the screw on top). 
  
 Do you understand how that works?
  
 ( At the very least please label each IC so that you know which position it came from in the first place.)


----------



## colliedoggy

maxx134 said:


> I would like to point out at this time for the importance and necessity and cooling the amp not because of the tubes,
> but mainly and specifically because of the Transformers winding for the driver stage...
> 
> If you look at the Transformer schematic (posted in thread), you will see that the winding for the driver Stage is the weakest link..


 
 I finally found the Transformer schematic which was posted by SonicTrance in post #1621 on page 109 of this thread.
  
 Are the same transformers used in the mk viii se?
  
 Thanks


----------



## Maxx134

baronbeehive said:


> coinmaster said:
> 
> 
> > Are you saying there is continuity between 6 and ground? How are you measuring ground?
> ...







colliedoggy said:


> baronbeehive said:
> 
> 
> > BTW coin, I'm going out tomorrow to get the opamp extractor tool.
> ...



*Correct... * 
Forget swapping opamp. 
Each pot is adjusted individually for each opamp. 
So if you swap, You *WILL* get a DC offset resulting in a tiny pop sound when plugging in the headphones.
Also, marking the pots is useless because these trim pots have MANY turns... 



Also, Coin is right, Baron does not have a problem with pin 6.







colliedoggy said:


> maxx134 said:
> 
> 
> > I would like to point out at this time for the importance and necessity and cooling the amp not because of the tubes,
> ...



You are right again...


----------



## coinmaster

The trimmers adjustments aren't critically important. They are there to adjust the 0 point of the opamp because the 100k RC resistor on pin 3 will draw a small current that will move the ground reference above ground but seeing how all the trimmers are already adjusted the offset won't be much if any. I've had 530v across my headphones for a few seconds as well as a couple hundred and a couple dozen volts dissipated through it. The 530v one had such a strong current that you could see the current flowing through the air when I pulled the alligator clip off it up until about 2 inches away.
 My headphones still sound fine and still measure a perfect 311 ohms on both drivers, they are just metal coils afterall. The biggest problem with DC offset in headphones is the fact that with a high enough DC offset the coil gets displaced which screws with the sound. 
 As for headphones not having any ability to dissipate heat, that's a load of bologna.
 The pop sound always happens when any dc appears across the coil.


----------



## colliedoggy

So, just to be clear, the same transformers ARE used for both models. Check?
  
 (I just corrected my error above where I referred to the trimmer pot as a trimmer cap!)


----------



## baronbeehive

colliedoggy said:


> Wait!
> 
> It just occurred to me that each op amp is adjusted for offset by its trimmer capacitor, which is the blue box nearby with the small screw on top of it.
> 
> ...


 
  
 I think I understand now that you've explained it. So how do you adjust it?
  
 I assume that I could still check by swapping the opamps to see if it resolves the grounding issue nevertheless because the adjustment would not be critical, and so long as I put them back the same way they came out all would be well?
  


maxx134 said:


> *Correct... *
> Forget swapping opamp.
> Each pot is adjusted individually for each opamp.
> So if you swap, You *WILL* get a DC offset resulting in a tiny pop sound when plugging in the headphones.
> ...


 
  
 So don't bother removing opamp after all?
  
 So I do not have a problem with a grounded pin 6? I am thinking if coin is right about the board I may have to take it back and see if the engineer can fix it otherwise I'm not sure what to do now.


----------



## coinmaster

Nah, read my statement again. I said your reading of pin 6 meant you were reading continuity through the bypass cap, meaning the short is coming from the B- supply. Check the bottom of the cathode resistor for ground continuity. Don't bother adjusting the trimmers, the offset won't hurt and you won't be plugging in your headphones for it to matter anyway.
  
 Switching out the opamp was to test if the opamp was defective because your grid voltage is 0. For now, just check the cathode resistor for ground and let me know because a 0v grid is irrelevant if your b- is grounded. 
 Unless there's more to this picture or you are doing/understanding something incorrectly that is confusing us, I strongly suspect your board is defective (I blame your "engineer" 
	

	
	
		
		

		
		
	


	




)


----------



## baronbeehive

coinmaster said:


> Nah, read my statement again. I said your reading of pin 6 meant you were reading continuity through the bypass cap, meaning the short is coming from the B- supply. Check the bottom of the cathode resistor for ground continuity. Don't bother adjusting the trimmers, the offset won't hurt and you won't be plugging in your headphones for it to matter anyway.
> 
> Switching out the opamp was to test if the opamp was defective because your grid voltage is 0. For now, just check the cathode resistor for ground and let me know because a 0v grid is irrelevant if your b- is grounded.
> Unless there's more to this picture or you are doing/understanding something incorrectly that is confusing us, I strongly suspect your board is defective (I blame your "engineer"
> ...


 
  
 The cathode resistor is connected to ground, correctly I assume because the other circuits are the same. (I am measuring the resistor through the cathode bypass connection).
  
 Edit: to clarify that the cathode bypass/resistor is connected to ground while the caps are charging but then when they are charged I no longer get the continuity to ground reading. This is the same for all the circuits not just the bad one.
  
 NB: This may affect my previous test readings now that I know about the caps charging so if you need to clarify anything I did previously I can do a retest if necessary. (I don't think you will need to clarify anything because nobody understood what I said before 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

Sorry about this guys, I didn't understand why I was getting that intermittent bleep on the tester before, now it is beginning to make sense. I've just tested pin 6 again and it's OK, an initial bleep while the cathode caps is charging and then no bleeps and longer grounded, same as other circuits and all OK!
  
 So it's pins 3 and 5 now that *are grounded!*


----------



## colliedoggy

Great!
  
 I have deleted my comment about adjusting the offset as I may have misunderstood how the circuit is working.


----------



## coinmaster

Hold up, the problem with pin 6 is that if your black probe was connected to ground as it should be and you are getting beeps while the cap is charging this means you have continuity to ground through the cap. The cathode resistor should not be connected to ground, the amp uses a bipolar supply.
 Make it clear to me if the bottom of the cathode resistor is connected to ground.


----------



## Maxx134

baronbeehive said:


> Sorry about this guys, I didn't understand why I was getting that intermittent bleep on the tester before, now it is beginning to make sense. I've just tested pin 6 again and it's OK, an initial bleep while the cathode caps is charging and then no bleeps and longer grounded, same as other circuits and all OK!
> 
> So it's pins 3 and 5 now that *are grounded!*



LOL yes that's the area to check k. 
Unsolder your extra caps there one at a time and then check to see if short goes away. 

Also I am not in agreement about board being damaged.. 
The copper pads are not critical I ha e pulled them out on component side where they connect to nothing. 
It is impossible for a board to be shorted, it must be your components or connections. 

Missing connections are more likely a cause for board failures...


----------



## Maxx134

coinmaster said:


> Hold up, the problem with pin 6 is that if your black probe was connected to ground as it should be and you are getting beeps while the cap is charging this means you have continuity to ground through the cap. The cathode resistor should not be connected to ground, the amp uses a bipolar supply.
> Make it clear to me if the bottom of the cathode resistor is connected to ground.



Also he had the tube out, so it was most likely just a charge of cap regardless of which cap. 

The PS is working fine for the other tubes, 
So it has to be specific component in that area. 

The two pins connected should have no other components connected, 
Is there any wire or connection on these pins, not pin 6,
But the other two...


----------



## Maxx134

colliedoggy said:


> Great!
> 
> To adjust the offset, with no audio input, the input to the op amp needs to be connected to ground and the output at pin 6 is read with a voltmeter. Adjust the trimmer pot until this reads zero.
> 
> Question I have is at what point along the chain towards the - input of pin 3 should the ground be made?



I never did it this way so it news to me... 

The meter methods are not enough... 
Especially digital meters which keep moving. 
Final trim pot adjustments need be tuned by ear for absolute zero micro pop.


----------



## colliedoggy

So how exactly did you do it Maxx?
  
 Thanks


----------



## baronbeehive

coinmaster said:


> Hold up, the problem with pin 6 is that if your black probe was connected to ground as it should be and you are getting beeps while the cap is charging this means you have continuity to ground through the cap. The cathode resistor should not be connected to ground, the amp uses a bipolar supply.
> Make it clear to me if the bottom of the cathode resistor is connected to ground.


 
  
 Yes but it isn't the only component to be connected to ground, and the ones in the other good circuits are the same.
  
 Yes I am clear that both ends of the cathode resistor are connected to ground initially before the cap charges and then no connection to ground after so it must be normal.
  


maxx134 said:


> LOL yes that's the area to check k.
> Unsolder your extra caps there one at a time and then check to see if short goes away.
> 
> Also I am not in agreement about board being damaged..
> ...


 
  
 Should I desolder and resolder before checking for continuity or check with them out of the circuit?
  
 Re: the board, it is very well built and would be difficult to break I would have thought compared to some I've seen and I have wondered if it was some faulty component that was contributing to the problem. Other than that a possible cold solder joint lacking in conductivity.
  


maxx134 said:


> Also he had the tube out, so it was most likely just a charge of cap regardless of which cap.
> 
> The PS is working fine for the other tubes,
> So it has to be specific component in that area.
> ...


 
  
 Exactly. The other circuits are working fine so unless I have a test reading which is not replicated on the other circuits then only that is significant. No there is no wire or anything else between these 2 pins, and it would be difficult to see how a piece of wire that long could have got in there by accident.
  
 Just to be clear, I always repeat a test before I report it to be sure and I always check against a good circuit before I consider it significant. If there is something I am not sure about I will ask.


----------



## Maxx134

colliedoggy said:


> So, just to be clear, the same transformers ARE used for both models. Check?
> 
> (I just corrected my error above where I referred to the trimmer pot as a trimmer cap!)



Although the two transformers have different stickers on them. 
They have exact same windings and markings.
But I would rather have the MK6 transformers just to be on safe side. 





coinmaster said:


> As for headphones not having any ability to dissipate heat, that's a load of bologna.
> The pop sound always happens when any dc appears across the coil.



LOL I like bologna... 
I would not risk a headphone, as unlike you, I blew out an Ultrasone Ed8 because of the DC offset. 
Plus I use an HD800 to test and tune away the DC offset micro small pop once it close with meters. 
Basically you need use any sensitive dynamic driver headphone (at balance out better), and quickly insert and remkve to listen for pop with insertion, 
While you simultaneously adjust blue trim pot. 
Do not leave headphones plugged in or the pop will disappear as the opamps adjust. 



coinmaster said:


> I strongly suspect your board is defective (I blame your "engineer"  )



I strongly suspect either a missing connection or wrong connection. 
The problem is that baron cannot detect any visual connection error, 
So I must assume component failure, 
But my gut feeling is that one cap lead is in wrong place, as I cannot believe a new component failing. 
I hope baron was testing with tubes and any socket adapters removed. 

My guess is that his engineer friend will be need 
because if he actually has no short, it may would be a bias issue . 

I would:
1- disconnect the large decoupling cap. 
2- test resistance across the cathode resistor. 
It will vary like zero at first as cathode cap charges, but needs to read the full 330ohm. 
3 - test the two grids, 
One at a time from grid- to- metal casing ground.. Should read infinite or very high in ten or hundreds of K-ohm both. 
The opamps are connected to the WCF grid, so that area would be suspect after all else test Ok.

Edit: test with unit off and tubes out.
Edit2: gotta give Baronbeebive credit. 
He tested a lot, 
 but his engineer friend is the one who did the job, 
 and so he should have gone back to him for this error as he may been able to solve much easier since he did it... 


Edit: 
I had to turn off my keyboard auto-correction it keeps putting dumb words when I type, lol


----------



## Maxx134

baronbeehive said:


> But to be sure I didn't make a mistake I made sure I repeated the tests several times until I was satisfied they were consistent.




Do you remember the last time you used the unit... 
Question :
1- how long it was playing 
2-what were the symptoms 
3-was the volume low
4- what headphones were you were using 
5-did you switch different headphones to make sure it was not a short in the headphones?
6-sometimes can be an adapter wiring short or planar headphone defect. 

We can't rule out anything for sure without you finding out.

Because a unit playing while anode resistor burning is usually a load at the headphone output end..


----------



## baronbeehive

maxx134 said:


> Do you remember the last time you used the unit...
> Question :
> 1- how long it was playing
> 2-what were the symptoms
> ...


 
  
 Yes I remember, I've only really used it once when I got all the hifi gear set up again. It was playing for about half an hour because I already had the preexisting issue with the burning resistor and I didn't want to risk it.
 I didn't notice any audio symptons.
 The volume was medium, about a quarter to.
 I was using my HE-500's
 No I didn't switch, that's my only cans.
 May be adapter wiring, but don't forget I had this problem before I even tried the amp out with headphones and it showed itself again when I was testing for voltage and that's after I changed the resistor, and it started smoking again due to the problem.
  
 Also if it was a headphone effect why did it only affect that circuit?
 And it was smoking with the headphones disconnected if I remember rightly.
  
 Thanks for your help, looks like I may have to resort to professional help again, unless you have any other ideas but I'll just try coins and your suggestions first.


----------



## baronbeehive

maxx134 said:


> ..............I strongly suspect either a missing connection or wrong connection.
> The problem is that baron cannot detect any visual connection error,
> So I must assume component failure,
> But my gut feeling is that one cap lead is in wrong place, as I cannot believe a new component failing.
> ...


 
  
 Yes I was.
  
 He he, everytime you say it must be a wrong connection I go and check again and again, and everythings still in the same place, I'm starting to feel very insecure lol !


----------



## baronbeehive

coinmaster said:


> .................. I've had 530v across my headphones for a few seconds as well as a couple hundred and a couple dozen volts dissipated through it. The 530v one had such a strong current that you could see the current flowing through the air when I pulled the alligator clip off it up until about 2 inches away.
> ................


 
  
 Hmmmm, I just might try that with headphones on as a cure for my current depression 
	

	
	
		
		

		
			





.


----------



## baronbeehive

maxx134 said:


> ..........
> You have a grounded output but maybe only grounded for the instance of the time it take the big coupling cap to charge.
> That is, if the big coupling cap is improperly connected at wrong side of the resistor..
> ..........


 
  
 This does seem to be what is happening. How do you mean "connected at the wrong side of the resistor". I have checked repeatedly and all looks good, and the same on the 4 circuits.


----------



## Maxx134

When testing before you pulled out board, it could have been grounded, and now that wires are disconnected, test the headphone jack wiring while board not connected, to see if any shorts


----------



## baronbeehive

Can you tell me which way round the current flows through the circuit, giving the parts the current flows through in sequence to give me an idea which end of the caps etc to disconnect to check for shorts. Or maybe it doesn't matter?


----------



## Maxx134

Direction is not needed for what your checking for (shorts, wire connections, & identifying wires).


----------



## baronbeehive

I was just thinking if, say current flows starting at A then goes to B, C and finally D, if I put one probe at A and test to D and there is a short, then I could test to C to see if the short is still there, if not it will be between C and D.
  
 Or maybe I could just test between any 2 components, yes I think that is what I will do.


----------



## coinmaster

> Yes but it isn't the only component to be connected to ground, and the ones in the other good circuits are the same.
> 
> Yes I am clear that both ends of the cathode resistor are connected to ground initially before the cap charges and then no connection to ground after so it must be normal.


 
 Either your board is really messed up or there is a big misunderstanding somewhere. in any case just ignore it for now. Switch out the opamp, and tell me the voltages of the faulty area on the plate/cathode/grids as before.
  


> the board, it is very well built and would be difficult to break I would have thought compared to some I've seen and I have wondered if it was some faulty component that was contributing to the problem.


 
 Abuse it enough and it will break. I have a short to ground plane on mine, hence why i just ordered a new mk6.
  


> Exactly. The other circuits are working fine


 
 That assumes you didn't break it since your last test. There's no reason you should measure ground on the B- supply. If the fuse blows next time it turns on you'll know why.
  


> I strongly suspect either a missing connection or wrong connection.
> The problem is that baron cannot detect any visual connection error


 
 That's what I thought but those pictures look pretty good. If it's a wrong connection it's very subtle.
  


> He he, everytime you say it must be a wrong connection I go and check again and again, and everythings still in the same place, I'm starting to feel very insecure lol !


 
 Faulty connections are usually the problem with these things but between the pictures and your thoroughness I don't think that's the problem here.
 The thing you need to understand is checking connections can only help so much. Operating parameters are the best way to know where the issue is. I've successfully troubleshooted every circuit I've ever made or used which is more then I can count at this point. I've also successfully troubleshooted the mk6 about a dozen and a half times.
  
 Forget current flows and capacitors. If the capacitor was broke it would result in other symptoms then it is.
  
 Go back to the last known issue. The grid was at 0v in the faulty circuit. This would cause the burning resistor you had. A grounded output would also cause the resistor to burn but it would cause have caused both resistors to burn not just one. The only thing that is connecting ground to the output by default is the 2k resistor by the opamp. Test that first.


----------



## Maxx134

coinmaster said:


> > The only thing that is connecting ground to the output by default is the 2k resistor by the opamp. Test that first.
> 
> 
> 
> Would be interesting if there was something touching that resistor or by the gain switch


----------



## colliedoggy

I have just bought this laptop fan:
  
AVANTEK CP172 15''-17'' Laptop Cooling Pad with Dual 160mm Fans at 1000RPM (2 Fans)  
The amp fits perfectly over the top of this with the fans covering almost the whole of the pcb area (just the corners aren't covered because the fans are round, obviously.)


----------



## baronbeehive

In the light of the the fact that cap charge up affects continuity momentarily I've revised my previous test results which are now:
  
 1 - Headphone jack - no shorts
  
 2 - WCF/CBP/Anode grounded _only while cap charging_* in all circuits*
  
 3 - CBP has continuity with Anode _only while cap charging _*in all circuits*
  
 4 - WCF has continuity with Anode *in all  circuits*
  
 5 - Pin 2 has continuity with Anode/WCF *in all circuits*
  
 6 - Pins 3 and 5 grounded *only in bad circuit*
  
 7 - Pin 5 has continuity with Pin 6 _only while cap charging _*only in bad circuit*
  
 8 - Pin 2 had continuity with Pin 6 _only while cap charging _*only in bad circuit*
  
 9 - Pins 3/5 had continuity with CBP _only while cap charging _*only in bad circuit*
  
 10 - Pins 5/6 had continuity with Anode _only while cap charging _*only in bad circuit*
  
 I've distinguished between "grounded" and having "continuity" for clarity hopefully.
  
 I appreciate the operating parameters are crucial but I want to correct my previous readings initially. Also I hope it confirms what I said about certain parts being grounded even in the good circuits. I need to concentrate now on the results only affecting the "bad circuit"
  
 Next I will get on to answer coin's questions.


----------



## baronbeehive

colliedoggy said:


> I have just bought this laptop fan:
> 
> AVANTEK CP172 15''-17'' Laptop Cooling Pad with Dual 160mm Fans at 1000RPM (2 Fans)
> The amp fits perfectly over the top of this with the fans covering almost the whole of the pcb area (just the corners aren't covered because the fans are round, obviously.)


 
  
 Great idea 
	

	
	
		
		

		
			





.


----------



## baronbeehive

maxx134 said:


> ..................
> I would:
> 1- disconnect the large decoupling cap.
> 2- test resistance across the cathode resistor.
> ...


 
  
 I've disconnected one leg of the Mcap on that circuit:
  
 1 - The resistance across the CBP reads 330 ohm.
  
 2 - The resistance across the anode resistor is 345 ohms, not surprising if its fried.
  
 3 - The measurement from grid pin 1 to ground is infinite, and across grid pin 4 to ground is 550 ohms
  
 Both of these results read the same as for the good circuit so I assume they're good.
  
 4 - I'm using grid pins 3 and 5 as a test for whether there is still a short because they are grounded and the finding is that they are still grounded so the short is still there. I think this is a correct interpretation as I'm new to all this.
  
 Edit:
 I've repeated the above tests having removed one leg also of the CBP and Mcap rifa bypass. The results are the same. I won't do anymore yet in case I'm not doing the testing correctly.


----------



## baronbeehive

Originally Posted by *Maxx134* 


  
 Quote:


coinmaster said:


> > The only thing that is connecting ground to the output by default is the 2k resistor by the opamp. Test that first.
> 
> 
> 
> Would be interesting if there was something touching that resistor or by the gain switch


 
  
 Which resistor is that?
  
 I've tested the 2 outer ones of the set of 2 each on either side of the blue trim pot and both of the 2 outer ones are grounded, which includes the one right next to the opamp. The same resistors in the good circuit are not grounded.
  
 Edit: I can't see anything touching any resistors by the gain switch either on top or underneath the board.
  
 If that 2k resistor has been fried could it cause a permanent grounding issue like I have until it's changed?


----------



## Maxx134

find out what is connected to pins 3&5 .
 check board trace for any solder job that is touching/overlapping onto the CB trace for those pins.


----------



## coinmaster

Just got my mk6. I forgot how much I hate these screws, those chinese don't mess around when it comes to cost savings. Haven't even gotten inside yet and I've already stripped 3 screws.
 After some brief listening it seems my last experiment may have messed up my left driver, the volume in left driver goes down with frequency. Not too noticeable except on bass notes though.
  
 I spose I was asking for it eventually with all the OTL experiments and no relay circuit.
 Don't spose sennheiser can replace the drivers for me can they?


----------



## colliedoggy

Sennheiser do sell replacement drivers.


----------



## colliedoggy

Do check the cables and connectors first though as the drivers are quite dear.


----------



## Maxx134

coinmaster said:


> Just got my mk6. I forgot how much I hate these screws, those chinese don't mess around when it comes to cost savings. Haven't even gotten inside yet and I've already stripped 3 screws.
> After some brief listening it seems my last experiment may have messed up my left driver, the volume in left driver goes down with frequency. Not too noticeable except on bass notes though.
> 
> I spose I was asking for it eventually with all the OTL experiments and no relay circuit.
> Don't spose sennheiser can replace the drivers for me can they?



Hey , back in the game I see, excellent. 
I also hadbto drill out three bottom plate screws just to get into my unit as welll!!!
Maybe we need advise about this issue, that those black screws are soft and you really need an exact fit screwdriver with a large handle for torque power..

Also, call sennheiser I believe the drivers for their popular units can't cost much...


----------



## coinmaster

> I also hadbto drill out three bottom plate screws just to get into my unit as welll!!!


 
 Dremel came in very handy this time.
 I'm inside and unsoldered all the yucky components. It's funny how it took days to mod it when I first started but now it's like a 30min project start to finish. It would only take me a couple mins to solder in the good components since I can care less about replacing the crap solder with magic solder but I'm gunna wait and order some banana plugs because I need my expensive caps for other projects as well. 
 I have cathode coupled and differential DHT input stages that will be up and running soon and I have gyrators, current sources, and source followers ready for use on whatever so I will test the source followers as grid drive/output stage/ and maybe even as a current buffer to the tube output stage.
 Although I admit I probably won't bother with a gyrator or current source on the stock input stage because who needs 6sn7s when you have DHTs.
  
  


> Also, call sennheiser I believe the drivers for their popular units can't cost much...


 
 Don't you require matched drivers though?


----------



## colliedoggy

Their drivers are all made to the same close specification so they are all matched by default.
  
 For the HD800 the product code is 534409.
  
 It would be interesting whether they have the HD800S driver available. The only difference would be the anti-resonant plug for the 6kHz spike in response. Obviously you would need the pair, but then you could upgrade the Hd800 to the HD800S (minus the black paint job.)


----------



## coinmaster

Got myself a temporary setup. I didn't bother puting in the decoupling caps because it would be exceptionally annoying and the antiphase currents of each channel should cancel out the majority of ripple anyway.
 Changing the stock russian driver tubes to holy grail tungsol rp tubes is in itself a life changing experience. Also  the amount of bass this amp can deliver to the hd800s is crazy after putting the 275uf film caps in the supply and putting in a good driver, my head vibrates. The high frequencies are magical as well.
 The midrange is good but not organic sounding however it wasn't like that last september so it may have something to do with the fact I had about 10 seconds of DC dissipation through my headphones during my last bench experiment ( I was like 
	

	
	
		
		

		
		
	


	




 when I realized what I had done). Something does sound a bit off and I hear slight vibrations in the drivers that shouldn't be there.
  
  
  
 However I'm glad my amp broke last Sep, cuz there was no way I would have had the discipline to not listen to my headphones, I already reinjured it 3 times by that point cuz I was addicted to this awesome sound.
  
 Can't wait to try the DHTs out, if they are half as good as everyone claims they are it should be good stuff.
  
 The sound is so lively, punchy, dynamic that I can barely tell that my left driver is totally screwed with the tungol drivers in place. I soo don't have the money to repair it right now 
	

	
	
		
		

		
		
	


	




 At the very least they are still in good enough condition to enjoy the music well and compare my designs. My years worth of money wasting and learning is finally all starting to come together, next month I'll finally have a stable, reliable working hybrid amplifier (waiting on transformer stock)  and I have a a few more designs and many experiments planned after that, no more half baked proof of concept bench experiments and short listening sessions finally.
 I'm gunna recoup the money I've blown with a sellable product or become a hobo trying. (I've already spent over $10k 
	

	
	
		
		

		
		
	


	




)
  
 Also as I finish writing this I just have to emphasize again how insane the bass is on my HD800s right now, they aren't even the same headphone. Made even better by how tightly they control the bass.


----------



## colliedoggy

I have just bought some NOS 6N2P-EV s cheap as (silicon) chips and would like to try them as the drivers. They need rewiring pins 4, 5 and 9 of the driver sockets to do this and I am hoping that this will be possible on the top side of the pcb, which I haven't yet seen. Would that be possible without having to cut the pcb? 
  
 I realise that they take 40mA more heater current than the 12AT7 s, but I am using 6N6P s in the WCF which take 75mA less heater current per tube than the 6N30P s, so I should be fine. (If I don't like them, I can always use adapter sockets and use 12AT7 s, but this is not possible _cleanly_ the other way round.) 
 I am using 6n6p's for the WCF tubes, which take 750mA heater current rather than the 825mA of the 6N30P, so I should have the reserve in the transformer filament winding for the extra 40mA that each 6N2P takes over the 12AT7.


----------



## baronbeehive

maxx134 said:


> Hey , back in the game I see, excellent.
> I also hadbto drill out three bottom plate screws just to get into my unit as welll!!!
> Maybe we need advise about this issue, that those black screws are soft and you really need an exact fit screwdriver with a large handle for torque power..
> 
> ............


 
  
 The only way I could get the screws out was with a screwdriver with a right angled handle so I could use sheer brute force!
  
 Quote:


> Originally Posted by *coinmaster* /img/forum/go_quote.gif
> 
> ............
> However I'm glad my amp broke last Sep, cuz there was no way I would have had the discipline to not listen to my headphones, I already reinjured it 3 times by that point cuz I was addicted to this awesome sound.
> ...


  
 Sounds pretty awesome. What were the 275uF caps?
  
 A lot more listening could be in order from now on 
	

	
	
		
		

		
		
	


	




. Maybe you should break your amp more often lol!
  
 I've got my IC extractor tool so ready to go, I will report back!


----------



## coinmaster

The caps are the big red industrial AVX caps you see on the first page. They have effectively no esr/inductance to speak of, best technical specs I could find on any cap so great for high capacitance bypass caps. I'm not sure what you guys are hearing with your improved lytic caps but seeing as I haven't seen anyone mention head shaking bass on HD800s I'd guess it's no where near as good as films which of course isn't surprising. Much of the bass does seem to come from my driver tubes as well, however the stock power supply bypass caps are a bottleneck for the entire signal path so it should really be the best cap possible. This applies to the cathode caps too which I have yet to change to film caps although I do have 220uf films on the ready for when I figure out how to mount the massive caps and when I stop using them as bypass caps in my other supplies.
  


> Maybe you should break your amp more often lol!


 
 Couldn't if I wanted to anymore, I've been pretty good at troubleshooting every circuit I've used over the last year and there is always always a bunch of issues due to the fact I usually build p2p or perfboard. No matter how careful I am always manage to make one tiny mistake that causes a chain reaction of issues.
 I've only very recently been converting to custom PCBs which has solved all my plights and allowed me to actually move forward. Hindsight it was probably a good thing that I didn't convert to pcbs til now cuz I really needed the time to develop my knowledge and experience.


----------



## Maxx134

colliedoggy said:


> I have just bought some NOS 6N2P-EV s cheap as (silicon) chips and would like to try them as the drivers. They need rewiring pins 4, 5 and 9 of the driver sockets to do this and I am hoping that this will be possible on the top side of the pcb, which I haven't yet seen. Would that be possible without having to cut the pcb?
> 
> I realise that they take 40mA more heater current than the 12AT7 s, but I am using 6N6P s in the WCF which take 75mA less heater current per tube than the 6N30P s, so I should be fine. (If I don't like them, I can always use adapter sockets and use 12AT7 s, but this is not possible _cleanly_ the other way round.)
> I am using 6n6p's for the WCF tubes, which take 750mA heater current rather than the 825mA of the 6N30P, so I should have the reserve in the transformer filament winding for the extra 40mA that each 6N2P takes over the 12AT7.




Sorry it doesn't work that way.
The power supplies are separated for the WCF output tubes , 
And the input tubes..
And also the heaters for the driver tubesare independent of the PSU.

Anyways, about your tubes, just get an adapter for those cheapo russian tubes. 
Try with adapters before you mess with the board or socket design. ..
I tried just about every type for the MK8 but those I have not tried .

Regardless, if you want better driver tube in your MK8, then you need to go with MK6 driver tube selections with adapters. 
Then you can also use pretty bottles like these :



You will get better sound on mk8 with these or 6sn7 or 6sl7 or 6f8g or 6c8g or ecc35 or vt99 or ...etc..
Point is they all match or surpass the 12a*7 types in the mk8 stock bias settings...





coinmaster said:


> The caps are the big red industrial AVX caps you see on the first page. They have effectively no esr/inductance to speak of, best technical specs I could find on any cap so great for high capacitance bypass caps. I'm not sure what you guys are hearing with your improved lytic caps but seeing as I haven't seen anyone mention head shaking bass on HD800s I'd guess it's no where near as good as films which of course isn't surprising.



We haven't implemented that yet..

Redge78 did test some higher values of flimcap,
 and yes, you are correct as we confirmed similar results of your experience where thw HD800 gains incredible / unspeakable bass power ..

 I suspect not many amps have been able to do this,
 because there are not many tube amps with high current as well as just voltage into 300-600ohm load of HD800.

Anyways the problem is if too large a cap value, the stock "obsolete " voltage regulating power transistors will get hit with a huge current draw on start up (charge ),
Enough to kill the transistors. 

A transistor upgrade to the newer stronger ones would be in order,
So you just let "cat outa da bag" and "can of worms" by suggesting jumbo caps without protection. ..
Hehe


----------



## Maxx134

coinmaster said:


> Got myself a temporary setup. ..
> 
> I Changing the stock russian driver tubes to holy grail tungsol rp tubes is in itself a life changing experience...



Oooo tell me which type tungsol tube you are using for driver tubes?


----------



## coinmaster

> Anyways the problem is if too large a cap value, the stock "obsolete " voltage regulating power transistors will get hit with a huge current draw on start up (charge ),
> Enough to kill the transistors.


 
 True but these are lower capacitance then the stock and the leakage resistors in the delay circuit helps as well.
 It would be very expensive to go higher then stock value with films and I am unsure of how to calculate the the holdup time of the capacitance for the optimum value.
  


> I suspect not many amps have been able to do this,
> because there are not many tube amps with high current as well as just voltage into 300-600ohm load of HD800.


 I've heard a bunch of very very expensive high power solid state amps with and they didn't give this kind of bass. Before I modded last september I resigned to the HD800s being low bass headphones. Sadly I only had the full mod going before a few weeks before I broke it so I forgot how much bass it really has, it outshines all other frequencies in punch and power.



> Oooo tell me which type tungsol tube you are using for driver tubes?


 
 Tungsol black glass round plate but they are $200+ each if you can find them.
 However in the stock settings it would be biased very low, like really really low. Plate voltage was like 50v last time I checked and the current would be very low but I don't care enough to get up and check right now.
 Looking at the curves it seems the distortion created by this would be mostly even order distortion but the differential input stage cancels out even order distortion anyway presumably. I'll increase the bias eventually when I get my THD analyzer and move on to understanding the relationship between distortion and good sound.


----------



## baronbeehive

maxx134 said:


> find out what is connected to pins 3&5 .
> check board trace for any solder job that is touching/overlapping onto the CB trace for those pins.


 
  
 Just done that as far as possible with visible traces. Actually I already did that before when I checked all the components in the bad circuit see below:
  


baronbeehive said:


> Which resistor is that?
> 
> I've tested the 2 outer ones of the set of 2 each on either side of the blue trim pot and both of the 2 outer ones are grounded, which includes the one right next to the opamp. The same resistors in the good circuit are not grounded.
> 
> ...


 
  
 These resistors were on the board trace from pins 3 and 5, as well as 3 others also connected to pins 3 and 5 and therefore also grounded, not much point pointing them out because you would expect them to be connected when they're all on the same trace.
  

  
 Is that 2k resistor which coin mentioned as being connected to earth significant? I don't know which one that is.
  
 Also only one of these resistors that I mentioned above has continuity with itself, could that be the one that is shorted? Possibly this may have happened when the heater wires were accidently pierced, before I replaced the wires.
  
 When I've exhausted these possibilities I will swap over the opamps after I've resoldered the other parts.


----------



## coinmaster

> I don't know which one that is.


 
 Multimeter is your friend. Test the resistors next to opamp until you find 2k. Test it on the unbroken circuit next to it and then on broken one and see if there are any irregularities. The 2k resistor is the only natural connection to ground so if the resistor is shorted somehow that could be the issue.


----------



## baronbeehive

coinmaster said:


> Multimeter is your friend. Test the resistors next to opamp until you find 2k. Test it on the unbroken circuit next to it and then on broken one and see if there are any irregularities. The 2k resistor is the only natural connection to ground so if the resistor is shorted somehow that could be the issue.


 

 I can't get a consistant reading from the one that has continuity over itself, ie it reads as an open circuit, I think it must be this one. The others don't read  as 2k.
  
 Don't know if I've done this right but I tested it again for continuity to pin 3, for continuity over itself and tested for ground, this is what I found:
  
 1 - It has continuity with pin 3 so could be relevant to the problem as it's on the trace
 2 - it has continuity over itself so could be shorted
 3 - It is grounded on both legs, not in itself a problem if it's connected to earth anyway
  
 Then I tested on the good left hand circuit after locating the 2k resistor again for that circuit and found the following:
  
 1 - It does not have continuity with pin 3 of that circuit
 2 - It does not have continuity over itself
 3 - It is grounded on one leg only
  
 When you mentioned that there was a resistor with a connection to ground I felt we could be on to something. It only needs a fault there and then everything else on that circuit with connections to it could be also grounded, which is exactly what my problem is!!!
  
 I'm not holding my breath.....
  
 Edit: ..... but maybe I will just go ahead and order another 2k resistor 
	

	
	
		
		

		
		
	


	




.


----------



## colliedoggy

If you disconnect the leg of the offending 2k resistor which isn't grounded in the good circuit, does the ground problem go away at the valve or does the resistor then measure at 2k?


----------



## coinmaster

Continuity over itself is normal if there is a short to ground anyway. The fact it doesn't read as 2k means for sure there is a direct short to ground. Check the other side of the board where the 2k resistor is, look for solder shorts, it only takes a tiny splat of solder to short it out.


----------



## baronbeehive

colliedoggy said:


> If you disconnect the leg of the offending 2k resistor which isn't grounded in the good circuit, does the ground problem go away at the valve or does the resistor then measure at 2k?


 
  


coinmaster said:


> Continuity over itself is normal if there is a short to ground anyway. The fact it doesn't read as 2k means for sure there is a direct short to ground. Check the other side of the board where the 2k resistor is, look for solder shorts, it only takes a tiny splat of solder to short it out.


 
  
 I think I will get a new resistor anyway, I think it may be at fault. I'm going away for a few days and want to have it for when I come back just in case!
  
 I already checked and there's no trace of any solder or wrong connection, it would have to be between 2 components to short and there's nothing there. This is what's made it so difficult to find out the problem. That's why I thought it could have been shorted by the old heater wire, not likely but possible, I did pierce it when I put in the WCF cap although that's not really near to the resistor location. Also the engineer did mention the wires burning near to the heat generated by the power resistors, which is why he moved them.
  
 Thanks guys!


----------



## baronbeehive

That's a nuisance, the resistor tests at 2K now that I've taken it out so its not that, I give up.
  
 Does anyone know what resistors to get to replace the 2K anyway?
  
 Pins 3 and 5 are *still* grounded, with no resistor in there, I'm totally hacked off.


----------



## Maxx134

coinmaster said:


> Continuity over itself is normal if there is a short to ground anyway. The fact it doesn't read as 2k means for sure there is a direct short to ground. Check the other side of the board where the 2k resistor is, look for solder shorts, it only takes a tiny splat of solder to short it out.



Tiny splat or even a thread of heater wire over the wrong pin which can be highly probable IF the heater wiring was replaced or moved..





baronbeehive said:


> That's a nuisance, the resistor tests at 2K now that I've taken it out so its not that, I give up.
> 
> Does anyone know what resistors to get to replace the 2K anyway?
> 
> Pins 3 and 5 are *still* grounded, with no resistor in there, I'm totally hacked off.



Resistors usually never short,
They only burn open open.

Check the socket pin solder connections on top board side for DEBREE between socket and board


----------



## Maxx134

coinmaster said:


> . (I've already spent over $10k :blink



Think of that as tuition for your learning


----------



## baronbeehive

maxx134 said:


> Tiny splat or even a thread of heater wire over the wrong pin which can be highly probable IF the heater wiring was replaced or moved..
> Resistors usually never short,
> They only burn open open.
> 
> Check the socket pin solder connections on top board side for DEBREE between socket and board


 

 Right I think I will have to desolder the socket to see underneath. At least we know that the problem must be between that 2k resistor and the pins somewhere.


----------



## Maxx134

Desoldering socket is not a great idea unless you have a new one in case of damage from removal.


----------



## colliedoggy

How are you getting on Baron?


----------



## baronbeehive

colliedoggy said:


> How are you getting on Baron?


 
  
 Fine thanks. Just been away awhile. I've got some work to do outside then it's back to the amp!
  
 What's the situation with your mods, are you doing it yourself? Keep us posted 
	

	
	
		
		

		
			





.


----------



## baronbeehive

Normal service has been resumed, I'm now back working on the amp!
  
 I have now tested the circuit with one leg removed of all the modded components. Also I have removed the opamp. Then I tested tube pins 3 and 5 and, yes, they're still grounded. The only thing I haven't done that you recommended is to check the tube pins. I found it impossible to see underneath so it looks like I will have to desolder.
  
 What else can I do, and what else could be causing it other than a fault in the board?
  
 Edit: Oh and one of the black wires has come off on the reverse, I believe it has only just come off due to being very brittle.
  

  
 The wire between the green and yellow wires toward the centre.
  
 Also I haven't tested voltages on the opamp, I may have to remove other components before I put it all back together again so that will have to wait. If there's nothing else I can do myself the last resort is to take it back to a professional and hope he can fix it 
	

	
	
		
		

		
		
	


	




.


----------



## Maxx134

baronbeehive said:


> Normal service has been resumed, I'm now back working on the amp!
> 
> I have now tested the circuit with one leg removed of all the modded components. Also I have removed the opamp. Then I tested tube pins 3 and 5 and, yes, they're still grounded. The only thing I haven't done that you recommended is to check the tube pins. I found it impossible to see underneath so it looks like I will have to desolder.
> 
> ...



I dont like how those cathode resistors were soldered to board.
They supposed to be over the vent holes.
Also those caps leads are squashed into the hot resistors.
Make sure there is no touching of the cap leads onto those resistors.
For longevity of unit, have this redone as suggested in beginning thread unless you like potential heat issues,
Edit: especially for those small PIO caps, high heat from Cathode resistor not a good thing.


----------



## baronbeehive

maxx134 said:


> I dont like how those cathode resistors were soldered to board.
> They supposed to be over the vent holes.
> Also those caps leads are squashed into the hot resistors.
> Make sure there is no touching of the cap leads onto those resistors.
> ...


 
  
 Sorry Maxx, that pic was the best I had to point out the black wire I was talking about, the cathode resistors were resoldered after you pointed out the heat problem before, they are in the correct position now.
  
 I'm just thinking that if I don't have any more leads about the next step to take I've no option but to try the professional again, I seem to be in a dead end.


----------



## Maxx134

Well, you could check under socket for possible solder or extra wire filaments from old heater wiring that you replaced, or board trace pad detached, or socket pin irregularities


----------



## baronbeehive

maxx134 said:


> Well, you could check under socket for possible solder or extra wire filaments from old heater wiring that you replaced, or board trace pad detached, or socket pin irregularities


 
  
 I've done that as far as possible and it's revealed nothing, and the pads are fine. Can't find any pin irregularities, don't know what you mean really. Also I've given the whole area a shot of compressed air.
  
 I've checked the CB resistances, the grid resistances, all good. I've checked the circuit trace connected to pin 3 to find out why pin 3, (and pin 5), are grounded and found 3 resistors, including the 2k resistor are also grounded. The  2k resistor also has continuity over itself but I can't find out why the grounding issue persists. Having removed the 2k resistor and the grounding is still there, and the solder points of the 2k resistor *still* have continuity with each other which I don't understand. I'm at a complete loss and I think I'm at my limits now, there doesn't seem to be any obvious cause.
  
 Also I removed the opamp as Coin suggested and still the grounding issue is there so I don't think there's much point looking at voltages. Maxx, you said the opamp/WCF area could be problematic?
  
 If neither of you have any more suggestions then it's going back to the engineer as a last resort.


----------



## MrCurwen

baronbeehive:

Pin 3 on the output tube is cathode, I'm assuming it's the top cathode (looking at the schematic I posted).

This node is connected via 56k (the dummy load) to the other side top cathode, meaning other output tube of the channel, and from there via that sides 2k to ground. Could this be the route?

Is the resistance 0 ohms or something else?

Pin 5 is the bottom triode anode, which (again, looking at the schem) is connected to top triode cathode. So if the above mentioned route is there, then this pin is grounded as well.


----------



## baronbeehive

mrcurwen said:


> baronbeehive:
> 
> Pin 3 on the output tube is cathode, I'm assuming it's the top cathode (looking at the schematic I posted).
> 
> ...


 

 Thanks for your help MrCurwen, I was just on the point of contacting a professional about this when I got your post!
  
 Just to go over what you said: pin 3 (cathode) is connected to pin 3 (cathode) of the other tube in the channel via the 56k resistor and to the 2k resistor and ground. Yes that is the route but as far as my testing has gone, pin 3 of the other tube in the channel is reading OK, ie not grounded, I haven't tested the 56k resistor. The 2k resistor was not reading as 2k until I removed it from the circuit then it tested correctly. Before that it was fluctuating. There was continuity over the 2 contacts on the PCB for the 2k resistor with it removed which I found strange. Also both legs of the 2k resistor were grounded when it was in place, against only 1 leg in the good circuit.
  
 The resistance over the cathode resistor was 330 ohms, across the burnt anode was 345 ohms. The resistance for grid pin 1 to ground is infinite, and across grid pin 4 to ground is 550 ohms. Both of these results for the grid pins read the same as for the good circuit so I assume they're good.
  
 Yes, pin 5, like pin 3 is grounded.
  
 Does this answer your question? Let me know if I can provide any other measurements.
  
 I find it odd that having found what I thought was a short in the 2k resistor possibly causing the grounding issue in the tube pins that having removed the resistor the issue remains.


----------



## MrCurwen

> Yes, pin 5, like pin 3 is grounded.




Just to make sure, when you say grounded you mean 0 ohms to ground?


----------



## coinmaster

Last I checked he's using a beeper which means it would be close enough to zero to register the beep. 
 Pin 3 and 5 are both the output to the white cathode follower.
 From your pictures and statements the board seems fine. 
 The output wire from the board to the pre-amp jack and then to the output of the amplifier. Desolder the wire from the output of the cathode follower and then check to see if it is still shorted, this is the most likely suspect area at the moment.


----------



## baronbeehive

I'm using the continuity setting, not the resistance setting on the multimeter, yes. Just to check I've just used the resistance setting on pins 3 and 5 and the reading varied from zero to above zero, fluctuating continuously, which I suspect is normal, it did the same on a check for ground with both wires on the chassis.
  
 I've removed the WCF cap from the bad circuit and pins 3 and 5 are still grounded.


----------



## coinmaster

Do what I said above.


----------



## baronbeehive

Sorry I misunderstood you. Do you mean the output wire to the preamp jack? If so I've already desoldered the right hand negative and earth wires to the preamp output, these were the ones that I originally found were grounded and were continuous with each other which alerted me to the problem.


----------



## coinmaster

The problem area must be located away from the circuit area, there's no other point of entry unless you did not correctly measure something. The 56k resistors Mr Curwen mentioned are the only other point of entry. They are located next to the protection IC in the center, check these as well, there should be 2 of them.


----------



## Maxx134

Yep it's frustrating when you know you can do this quickly if you had the board in front of you.
It has been very difficult to explain and you know the issue has to be right there.


----------



## Maxx134

baronbeehive, trace the board and use the meter in ohmmeter setting, not continuity.
That way you can see low resistances that may trigger your bleeper and make you believe you have ground when you actually don't.
And like MrCurwen pointed out continuity is not same as zero ohms to board/chassis ground ( grounded ).

I always use resistance setting.
Also resistance varying from zero to above zero is just the caps charging and you have to Wait for it to settle.

Many times it easier to test for voltages with unit on but baronbeehive if you decide to have the guy fix it , tell him to show you the problem so you will understand.
Good luck.


----------



## coinmaster

> Yep it's frustrating when you know you can do this quickly if you had the board in front of you.
> It has been very difficult to explain and you know the issue has to be right there.


 
 Yeah 
	

	
	
		
		

		
			





> baronbeehive, trace the board and use the meter in ohmmeter setting, not continuity.
> That way you can see low resistances that may trigger your bleeper and make you believe you have ground when you actually don't.


 

 Unless his multimeter is incompetent I doubt using an ohmmeter will help because none of the components are low enough value to set off a false alarm. The continuity setting should beep at a value low enough to be accepted as wire resistance.
  


> Also resistance varying from zero to above zero is just the caps charging and you have to Wait for it to settle.


 
 That or not enough pressure on the contact point.  





> Many times it easier to test for voltages with unit on


 
 Assuming you know it won't burn up more stuff. In this case it's guaranteed to since the output is grounded.


----------



## baronbeehive

maxx134 said:


> Yep it's frustrating when you know you can do this quickly if you had the board in front of you.
> It has been very difficult to explain and you know the issue has to be right there.


 
  
 Yes, anyway good to know you guys are on it!
  
 I've located one 56k resistor, the blue one in the centre, to its right is a brown resistor but this reads 5.6k not 56k. So I've checked the blue one which I assume is the one you mean and it is not grounded. The resistances to ground from each leg are 5.7k from one leg and 61k from the other. As I haven't located the other 56k resistor I can't compare the readings to that but they will be different anyway because of the disconnected parts from the circuit I'm measuring.
  
 The fact that I can get a resistance reading from this resistor is in contrast to the 2k resistor which I couldn't get a reading from at all due to it fluctuating, I could only get a proper reading when I removed it.


----------



## coinmaster

Just do it the easy way and make sure none of those resistors in that area are grounded on either side.


----------



## baronbeehive

Right, as I said the 56k resistor is not grounded, and if that is the only way in for the circuit then it looks like it is a circuit not a wiring problem. I looked at the others in that central area and of the 2 just above the fuse the top resistor, nearest to the smaller of the round caps on its own, is grounded on one leg, the others are ok.
  

  
 I looked at all the resistors in the circuit a while ago and some are grounded but as it means nothing to me, not knowing the circuit, I don't know what to say about it. This is why I feel it will have to go back to be looked at by someone who knows.


----------



## coinmaster

There are 2 56k resistors per channel. None of the resistors in that area should be grounded. Can you give a better description of the resistor that is grounded on 1 leg? Or a picture.


----------



## baronbeehive

These are the resistors that are grounded in that circuit, indicated by an arrow to the relevant leg. The 56k resistor isn't grounded. The 2k resistor is and is now removed and both contacts on the PCB are grounded still. Maybe that info will help you find the path of the short.


----------



## coinmaster

The 56k on the bottom looks correct considering your situation. The 56k on the top is not right because it should not be grounded but I don't have my old schematic and I can't recall what it does exactly, it's some sort of bias for the protection IC I think.
 My recommendation would be to unsolder all of those circled components on 1 leg and see if the circuit is still grounded, if it is then you may want to consider contacting your engineer because I'm running out of ideas, there's only so much we can do over the interwebs.


----------



## baronbeehive

Ok, thanks for your help. Which is the 56k resistor on the bottom, only the one I've marked reads 56k.


----------



## coinmaster

All 3 of those resistors be the protection IC are 56k


----------



## baronbeehive

Since we're all at the end of the line with this, I've decided to take it in tomorrow to see if it can be fixed 
	

	
	
		
		

		
		
	


	




.


----------



## Maxx134

To me, I could not be certain what you found as actually grounded, or just common ground, or just continuity, or just cap charging from tester to show grounded...
I never use a bleeping or lighted continuity tester.
An Oscilloscope would been a huge help as well.
Anyways it will be interesting to find out what was the cause of your issues,
So find out and let us know.


----------



## baronbeehive

maxx134 said:


> To me, I could not be certain what you found as actually grounded, or just common ground, or just continuity, or just cap charging from tester to show grounded...
> I never use a bleeping or lighted continuity tester.
> An Oscilloscope would been a huge help as well.
> Anyways it will be interesting to find out what was the cause of your issues,
> So find out and let us know.


 
  
 Yep, I tried to distinguish between all that later when I was learning about that with the help of all you guys. It was kind of a mystery to me at the beginning but I think I've picked up quite a bit, but not enough to find the cause of the problem, I kept thinking I found what it could be and it kept biting back and saying no keep looking! I needed a knowledge of what the circuitry does which I don't have.
  
 I'm hoping to find out soon, assuming it is not as bad as I fear, and I'll get back to you.
  
 It will be nice to actually listen to it for a change instead of cursing it!
  
 Edit: The point about the grounding issue is that tube pins 3 and 5 were grounded (ie to chassis ground) *only* on the bad circuit, and that's the only way I could tell it was significant, by comparing to good circuits, given that I did not have any knowledge of how the circuit works or of the operating parameters as coin said. I hope I have not missed anything by using the beeper, next time I will have to get used to using the ohmmeter.
  
 NB. pins 3 and 5 also have continuity with each other in all circuits but that is a different issue to the grounding issue and is OK if it is in all circuits. I was only interested in finding continuity if it indicated a possible problem such as a short, or finding components in a trace.
  
 Anyway, enough of that it's outta my hands thank goodness!


----------



## Maxx134

baronbeehive said:


> These are the resistors that are grounded in that circuit, indicated by an arrow to the relevant leg. The 56k resistor isn't grounded. The 2k resistor is and is now removed and both contacts on the PCB are grounded still. Maybe that info will help you find the path of the short.



Here is a possible reason for your measuring continuity of points:


----------



## baronbeehive

Is that on that trace?
  
 Explain please!
  
 Do you mean continuity between points on either side of the on switch when its off?


----------



## Maxx134

baronbeehive said:


> Is that on that trace?
> 
> Explain please!
> 
> Do you mean continuity between points on either side of the on switch when its off?




 yes when testing around the switch when cloed position


----------



## coinmaster

Good point, almost forgot about the relay.


----------



## baronbeehive

I've got some preliminary news on the fault from the engineer............. and its good news 
	

	
	
		
		

		
			





! The fault was a short over the 2k resistor and was found under the valve socket. So we were on the point of finding it ourselves but I just couldn't see anything under the socket but it was extremely difficulty to see under there and I didn't want to go to the trouble of desoldering and wrecking it.
  
 I now realize that investing in a magnifying glass might be a useful idea!

 Cheers guys 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

coinmaster said:


> Good point, almost forgot about the relay.


 
  
 Explain please. What is the relay and under what circumstances would all the points be continuous with each other?


----------



## Maxx134

baronbeehive said:


> I've got some preliminary news on the fault from the engineer............. and its good news  ! The fault was a short over the 2k resistor and was found under the valve socket. So we were on the point of finding it ourselves but I just couldn't see anything under the socket but it was extremely difficulty to see under there and I didn't want to go to the trouble of desoldering and wrecking it.
> 
> I now realize that investing in a magnifying glass might be a useful idea!
> 
> ...



Haha I told you so...

Just kidding.
Glad to hear good news.


The relay in middle board is controlled by the protection circui and really not need to get into ,
But it would be triggered to shut output to protect headphones if there was any problems


----------



## baronbeehive

maxx134 said:


> Haha I told you so...
> 
> Just kidding.
> Glad to hear good news.
> ...


 
  
 Yeah, I suppose most faults fall into the category "solder splats etc", I just wish it was easier to find them.
   

 Quote:


> ...........
> The relay in middle board is controlled by the protection circui and really not need to get into ,
> But it would be triggered to shut output to protect headphones if there was any problems


 
  
 I see, so when the circuit closes the connections all switch on, but it wouldn't have affected my tests because it would not be local to any one of the tube circuits.
  
 Anyway I've picked up quite a bit about testing now and as I said we were just in sight of the finish when I gave up! Maybe I should have stuck it out though. Thankfully the board was OK!


----------



## SonicTrance

Thats great news Baron! I hope you get the amp back soon!


----------



## baronbeehive

sonictrance said:


> Thats great news Baron! I hope you get the amp back soon!


 
  
 Cheers Sonic! Can't wait to get it back after about 9 months without it. Have you made any changes in equipment lately?
  
 Your mods next!


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Thats great news Baron! I hope you get the amp back soon!
> ...


 
 9 months is a long time to be without the LD!
  
 I've actually built a amp from scratch with the help of MrCurwen, it's his design (with small alterations to suit my needs). It sounds very, very good! Right now I'm having some issues with oscillation though. It's a big learning experience for me.


----------



## baronbeehive

sonictrance said:


> 9 months is a long time to be without the LD!
> 
> I've actually built a amp from scratch with the help of MrCurwen, it's his design (with small alterations to suit my needs). It sounds very, very good! Right now I'm having some issues with oscillation though. It's a big learning experience for me.


 
  
 WOW! Very exciting, keep us informed.
  
 Good luck 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

I've just got back from the engineers and while I was there I had a sound check on the repaired amp.............. and all I can say is....... *OMG* ......... *simply stunning!* I'll stop there but the hairs are going up on the back of my neck again. One track started with an unbelievably life like kick drum and proceeded making me think I was there right next to the band in the studio during recording. The quality of the bass has gone up incredibly not to mention everything else. I just want to get back and have a long listen for the first time.......
  
 The fault was traced from the 2k resistor further on the board trace to the tube pin 3 and the solder joint of the output wire which was going to ground. If only I had desoldered it from that end and not the XLR end the problem would have been traced.
  
 Now all I need is the HEK's for that immersive soundstage, the HE-500's are not up to it now 
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

I just wanted to say that this forum has been really great. From the mods page and discussion, everybody's experiences with the mods, the experiences of the beginners........... me ..........., the tube amp theory and the troubleshooting pages. Very comprehensive. I hope that they may encourage others to give it a go too, it's been fun 
	

	
	
		
		

		
		
	


	




.
  
 Now that Sonic is building his own amp where is it going to next I wonder.........


----------



## coinmaster

Grats baron, hope you learned a few things from your experience.
 You should check out the MK6 schematic if you want to learn more about it, troubleshooting is hard when you don't know what does what.
 The schematic doesn't seem to be on the first page though, it's probably lost in the depths of these pages somewhere. Just P.M. me if you want it.
  
 I recently blew up both my dac and my laptop when a loose ground clip on my usb oscilloscope touched my 275v supply, so Instead of shipping it to china for repairs I'm going to do the same thing I did when I originally broke my MK6 and reverse engineer it and learn from it. After I'm done with that I'll just order a new USB and DAC module which I suspect are problem, however this means once again I'm without music for a while 
	

	
	
		
		

		
			





.
  
  
 My amp project is almost done though, I've completed the input stage and it performs beautifully, at least on the scope, I haven't heard it yet sadly although because of what it is it should make the MK6 input stage sound like garbage in comparison.
 My higher end scope revealed a dead silent background and revealed only a very small 100Mhz+ oscillation which is good and possibly only due to the fact that the whole thing is exposed, last time I listened to a DIY amp in here I could hear radio broadcasts though it.
 It passes the square wave test perfectly and the amplified waveforms look beautiful which is no surprise because the distortion should be stupidly low.
  
  
  
 The output stage is not fully built yet but the one I've concocted simulates at 0.000016%  with 30v p-p into 8 ohms (yes really) which is many orders of magnitude better then any other design I've ever simulated. Even if the real life results were 100 times worse (which will never happen) it would still be 0.016%..
 I called BS at first but the simulations are accurate as long the the component models are good and the parasitics are realistic. No matter what component models I use, what voltages I use, or what reasonable parasitics I add or even if I use mismatched components the results are pretty much the same, which means the topology itself is solid and the real life results should be close.
 I'm pretty excited to try this one out in real life and overall I'm pretty proud of the overall amp design right now. Can't wait to get some actual listening in.
 I've got about a half dozen other interesting and/or unique amp designs I am going to build as well, using either designs of my own or alterations and improvements on other known designs.


----------



## baronbeehive

Is that PCB in the top pic the LD one or your modded one because it looks a lot different to the old one?
  
 Good luck with your build, hopefully at least one of your designs will live up to expectations!


----------



## coinmaster

> Is that PCB in the top pic the LD one or your modded one because it looks a lot different to the old one?


 
  
 The top one is the Audio-GD NFB-1 DAC that I broke. I doubt they will lend me a schematic so I have to do through the tedious process of reverse engineering it if I don't want to ship it out to china.
  
  
  


> Good luck with your build, hopefully at least one of your designs will live up to expectations!


 
 It better, I've spent the every day for a year contemplating and simulating these designs. But from an engineering perspective they are the bees knees so I"m not too worried about it. In a few days I'll have what I need to finish my output stage and I'll probably use an ipod or something as a dac replacement for a listen.


----------



## Mogos

baronbeehive great that you have your amp back to live!


----------



## baronbeehive

mogos said:


> baronbeehive great that you have your amp back to live!


 
  
 Hi Mogos! Yes I'm going to be doing a lot of listening to catch up now 
	

	
	
		
		

		
		
	


	




. You guys with your working amps are having all the fun!
  
 Any changes to your system? I would like to get the HEK's, are you still happy with your V1 and how would you describe the soundstage I imagine it works well with the LD.


----------



## Mogos

HEK's amaze with the sound qualities in every aspect. Especially after some minor mods. They have the same huge soundstage as HD800 but deeper and better filled with instruments. I have folowed some of the mods from these instructions but a little different way
 And I have replaced crappy 50 cents minijack socket. With the minijack there is a problem to use different connection wires and the plug tend to get loosend from the socket very easily. It almost costed me loss of one driver as one of the connection wires broke off and I had big dificulty to resolder it. So be very cearfull with those wires.
 But there is another side of HEK's. Avarage comfort and ergonomics and poor quality built materials. Eg. the pads have plastic rings for attachment to the driver housing. You have to take them off from time to time to clean hairs comming through the fabric screen (at least I have to do it). Even if you are very cearful with removing the pads it is very easy to broke the plastic mounting rings as they are made of poor quality material. In my case the pads are pushing against the head to mutch. It has also impact on the sound qualities. With original head band solution I cant lessend the clamping force.
 Sorry for offtopic record.
 To be at least a little to the subject I am addting the amp photo with the 7193 Kan Rads tubes.

 And the very special edition of the HEK's


----------



## Maxx134

mogos said:


> HEK's amaze with the sound qualities in every aspect. Especially after some minor mods. They have the same huge soundstage as HD800 but deeper and better filled with instruments. I have folowed some of the mods from these instructions but a little different way
> And I have replaced crappy 50 cents minijack socket. With the minijack there is a problem to use different connection wires and the plug tend to get loosend from the socket very easily. It almost costed me loss of one driver as one of the connection wires broke off and I had big dificulty to resolder it. So be very cearfull with those wires.
> But there is another side of HEK's. Avarage comfort and ergonomics and poor quality built materials. Eg. the pads have plastic rings for attachment to the driver housing. You have to take them off from time to time to clean hairs comming through the fabric screen (at least I have to do it). Even if you are very cearful with removing the pads it is very easy to broke the plastic mounting rings as they are made of poor quality material. In my case the pads are pushing against the head to mutch. It has also impact on the sound qualities. With original head band solution I cant lessend the clamping force.
> Sorry for offtopic record.
> ...




That is excellent info on HEK you should also post in HELV1 thread.
Did your HEK come with that rear grill??

Also, how do you like those power tubes with adapters?
Are they similar, or better than normal MK6 power tubes??


----------



## Maxx134

baronbeehive said:


> I've just got back from the engineers and while I was there I had a sound check on the repaired amp.............. and all I can say is....... *OMG* ......... *simply stunning!* I'll stop there but the hairs are going up on the back of my neck again. .



Yep, I have been looking around for a second amp to use as backup for burn in tubes and burn in my headphones...

The realization hit me that the greatest strength of these amps are that they are BOTH OTL & OCL design...
They WAY surpass the other amps which use heavy transformer or huge capacitor coupling...

DIRECT OUTPUT TUBE COUPLING = most pure sound..


That is their advantage, over all these other tube amps in this category...

Yet, I also believe other factors in stock MK6/8 are a compromise, 
Like what I would agree with Coin that the driver stage could be better.
As is, the driver tubes are sipping power and not optimally biased, BUT,
They are very clean sounding, with the elevated heater ground and some clever design of common cathode on the pos&neg inputs.

I abandoned MK8 driver tube choice of 12a*7 tube and bias points,
And instead went for an 6c8g with increased bias...
It is a much livelier tube.
I prefer this to ALL the normal 6sn7 variants of MK6.
,


----------



## Mogos

maxx134 said:


> That is excellent info on HEK you should also post in HELV1 thread.
> Did your HEK come with that rear grill??
> 
> Also, how do you like those power tubes with adapters?
> Are they similar, or better than normal MK6 power tubes??


 
 It is not a grill. I have installed material similar to the one used for the speaker screens from outside. It is similar solution metioned in the other instruction but done without opening the headphones. To mask the edge of the material I have glued decorative string around.  After the problem with the broken wire I wish never erver again to open the headphones . The mod is very recomended as it helped midrange frequenciec to be more pronounced. Now there is a great balance over the whole frequency spectrum.
 The tubes are for driver stage. They are far better than the normal MK6 driver tubes. Similar to 6C8G. 6C8G are slightly warmer and with fuller body but the 7193 KenRads have better transients reproduction.


----------



## coinmaster

> and some clever design of common cathode on the pos&neg inputs.


 
 The common cathode is actually necessary to reject common mode noise picked up by the cables, this is one of the main advantages of balanced design other than the distortion being cut in half.
  
 I will be selling my MK6 soon because I need the money (knew I shouldn't have re-bought that thing 
	

	
	
		
		

		
		
	


	




) so if anyone wants an mk6 for sale I can pre-mod it for you or whatever.
  
 Maxx, I ordered a chassis for my latest and greatest design so I can move it around. We will have to meet at some point so I can try your headphones and yggy and compare amps since you are relatively close to me.


----------



## Maxx134

mogos said:


> maxx134 said:
> 
> 
> > That is excellent info on HEK you should also post in HELV1 thread.
> ...



Wow ok great,
 but I assume your running stock bias,
 Increasing bias should also get more benifits since stock setting so low.

PM sonic for his optimal values as I have not finished my bias testing.


----------



## baronbeehive

Maxx, a bit off topic but a few words please about why the HEK is so good, it looks like end game. There are only a few slight issues for me but would not be important. Could you link to the that HEK thread.
  
 I forgot to mention when I heard the amp at the engineers that he used only a cheap £10 CD player bought off ebay as a source which was then put through a Soundcraft Folio mixer, no DAC, and it still sounded amazing!!


----------



## baronbeehive

Hey.......... what's Sonic's amp doing over here? Wait a minute......... that's mine 
	

	
	
		
		

		
		
	


	




. Spot the difference.
  
 There are now 5 or so very happy LD owners on this forum, fantastic 
	

	
	
		
		

		
		
	


	




.
  
 Edit:
  
 In case there is anyone else out there thinking about doing the mods, what are you waiting for? Just look at page 1 and my mods pages: 50, 53, 55, 57, 62, 65, 66, 68, 69, 70, 71, 72, which include pics. Also Mogos mods are here; 33-38, and SonicTrance here: 23, 43, including some great pics.
  
 For troubleshooting and fault finding you can look at pages 126-143 where a common fault in circuits was tracked down up to the point of fixing it. I was a complete beginner in electronics work and circuit testing before I did this and was not confident at all but I feel much better at it now and have picked up a lot with the excellent help of forum members.
  
 I'm having to find an excuse to go in the room to look at the amp now every 5 minutes and its getting ridiculous!


----------



## SonicTrance

baronbeehive said:


> Hey.......... what's Sonic's amp doing over here? Wait a minute......... that's mine
> 
> 
> 
> ...


 
 If you want yours to look like mine you're gonna have to make some aesthetic mods too!
  










  
 Good to hear that you're finally enjoying your MK6 the proper way with mods in place!
  
 Now, go ahead and do the Ra switch mod and 5998/421A bias mod!


----------



## colliedoggy

Baron
  
 What was your final build composed of please and where did you source them from here in the UK?  
  
 What were all the elements you replaced, including wiring?
  
 I note that HiFi Collective has a seasonal reduction running up to New Year, which is where I assume you got at least some of your components.
  
 I have had to delay my mods due to family matters, but now want to finally get down to sorting it out.
  
 Thanks


----------



## baronbeehive

colliedoggy said:


> Baron
> 
> What was your final build composed of please and where did you source them from here in the UK?
> 
> ...


 
  
 Hi colliedoggy!
  
 My parts list is essentially the same:
  


baronbeehive said:


> *SMLD: Parts List*
> 
> This is my parts list so that if you think there is anything missing you can let me know now, perhaps you could tell me before I start. I'm only going for the minimum necessary resistors as recommended by Maxx and what I think I need, for example I wasn't going to get any new driver stage resistors - the 2 groups of 3 on the other side of the driver tubes from the 220k ohm ones. These could be the zfoils. If you think I ought to have them let me know because I only want to do this once
> 
> ...


 
  
 ............ except for:
  
 1 - Coupling caps are now Jupiter copper foil in wax .47uF 600v.
  
 2 - I also added Shinkoh 1w 1k5 resistors x2 to make it easier to solder the wires from there to the driver stage decoupling Wima.
  
 3 - Enermax 120mm fans: http://www.enermax.co.uk/cluster/
  
 4 - Variable 12v fan speed controller and power supply, if using an external supply:
https://www.amazon.co.uk/gp/product/B01N2NNFT6/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
  
 Most of it from hificollective except for:
  
 1 - Mundorf PSU caps, they don't do the 160v, I can't remember where I got mine, I think it was from the same place I got the Wima below.
  
 2 - Driver stage decoupling Wima's: http://www.conrad.com/ce/en/product/451208/MKP-thin-film-capacitor-radial-lead-40-F-800-V-10-375-mm-L-x-W-x-H-415-x-31-x-46-mm-Wima-DCP4L054007ID4KYSD-1-pc
  
 3 - Chassis cable runs were from ebay, several sellers on ebay.
  
 4 - 6 output wires were from hificollective
  
 5 - Fuses from ebay: http://www.ebay.com/itm/AMR-Audio-90-Silver-Alloy-Fuse-Tube-5x20mm-0-5A-Slow-Blow-/291957152867?hash=item43fa009c63
  
 I think that covers it.
  
 Nice to see another poor guinea pig putting himself on the line, keep us informed and good luck 
	

	
	
		
		

		
		
	


	




.
  
 Edit: I forgot the tube heater wires on the reverse, but if you're careful putting in the WCF caps you won't damage the wires 
	

	
	
		
		

		
		
	


	




.
  
 Edit 2: I see by your join date that you joined the same time as me so your LD will have the same high quality resistors that the first batch of amps had so will probably not need to change any of the others!


----------



## baronbeehive

sonictrance said:


> If you want yours to look like mine you're gonna have to make some aesthetic mods too!
> 
> 
> 
> ...


 
  
 I don't know about the impedance mod but I'm doing your tube bias mod very soon, that looks straightforward, but...........
  
 Having had the dubious pleasure of rereading some of the previous posts in an idle moment to find out where we're at with the impedance mod I gather Maxx's dog hasn't come up with the goods yet and I see it hasn't made it to page 1. I don't have the technical details to do this yet, what resistors and where etc? What was the result with the listening tests? I know that you have put in the switch again but that's all I know about it. I thought that there was a problem for the HD800 implementation and things were on hold, although I believe Maxx is still working on perfecting the bias figures.
  
 I suspect the dog is heavily involved with all the donkey work while Maxx is having a nice time laid back with the listening tests and his feet on the table, and his favourite band playing through those shutter blind headphones!
  
 Edit: BTW should I be worried about uprating the diodes and transistors? Looks like I may have been lucky to only oven bake a resistor.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > If you want yours to look like mine you're gonna have to make some aesthetic mods too!
> ...


 
 Yes, the bias mod is very straightforward!
  
 Impedance mod hasn't made it to first page, but it is done! If you want, tell me what output tubes you'll be using and what headphones (impedance) and I'll tell you what additional resistors you need.
  
 I recommend at least a 5 position switch. That way you can have settings for different output tubes and headphones!
 I use this one: http://www.ebay.com/itm/Rotary-Switch-4-pole-5-positions-NOS-Lot-of-1-/262524365430?hash=item3d1fabea76:g:iasAAMXQRkdR5ngl
  
 No need to replace the diodes and transistors as long as they work IMO. It is kind of a week spot in the amp though but requires board removal. You can always do it next time you need to remove the board for some reason.


----------



## baronbeehive

sonictrance said:


> Yes, the bias mod is very straightforward!
> 
> Impedance mod hasn't made it to first page, but it is done! If you want, tell me what output tubes you'll be using and what headphones (impedance) and I'll tell you what additional resistors you need.
> 
> ...


 
  
 OK, thanks!
  
 I will be using the HE-500, 38 Ohm, for the foreseeable future, unless I can acquire the HE1K, (when Mogos upgrades to V2 and gives me his old V1 
	

	
	
		
		

		
		
	


	




), same impedance, somehow, so perhaps include this as well. Tubes will be RCA 6AS7G and WE 421A, possibly TS 5998.
  
 I've bought these 2 switches for your tube bias mod:
  

  
 I would prefer to use the bottom one but it will need the hole in the chassis drilling out to fit. They are slightly different, the top one has 3 banks of 4 poles, the bottom 2 banks of 4 poles. How would I wire them? The top one is on/on, apparently on the 2 outer banks of 4 poles. I assume the middle bank is off, but there is no off position on the switch.
  
 You said that the tube bias mod is very good sonically, is the impedance matching mod the same? Also I'm assuming it will not be used for the HD 800's?
  
 Your dog is clearly working harder than Maxx's 
	

	
	
		
		

		
		
	


	




.


----------



## Maxx134

baronbeehive said:


> Hey.......... what's Sonic's amp doing over here? Wait a minute......... that's mine  . ...



Hey! I see same baby amp that I have here:

  



baronbeehive said:


> Maxx, a bit off topic but a few words please about why the HEK is so good, it looks like end game. ...



To Me it is .
I have HD800 & HEKV2.
Need nothing else with these two. 
Listened more to Utopia yesterday. 
Actually am blessed to have heard them all except LCD4 & ZMF models.
Utopia may be flavor of the month, but not a replacement for my preferred two.
They are the most well rounded headphones approaching the top realism factor.
HD800 modded of course but HEKV2 is my go to headphone used most at home. 
At that level it is mostly a preference whether you want an energetic can (Utopia) or a refined can (HEK & HD800).
You will see in long run most cans won't live in limelight long enough to hold up to status of HD800..


----------



## baronbeehive

maxx134 said:


> Hey! I see same baby amp that I have here:
> 
> 
> 
> ...


 
  
 WHAT IS THAT AMP??? It's slightly different to mine 
	

	
	
		
		

		
		
	


	




. Mine has been keeping me going through all the bad times without my LD.
  
 I don't think I could live with the Utopia after what I've heard, after the HE-500 I really need something with a realistic soundstage such as appears to be the case with the HEK.
  
 What is the HEK thread you use please?
  
 I've just been looking at the HEK Upgrade Discussion thread where there is some wonderful bitching going on, and some very unhappy bunnies!!!
  
 Edit: You, of course were the voice of reason 
	

	
	
		
		

		
		
	


	




.


----------



## Maxx134

baronbeehive said:


> WHAT IS THAT AMP??? It's slightly different to mine . Mine has been keeping me going through all the bad times without my LD.
> ...




I can't believe this little amp has been so overlooked, but it is fairly new...
Lookhiw nice!




It is a baby headphone amp,
Not a speaker amp like yours..

It is a perfect compliment to our bigger amp.
I can burn in my driver tubes (with adapters) and headphones with it, 
So I won't have to use up the MK8(or 6), which has the valuable power tubes...


Here is the link here:
http://www.head-fi.org/t/780178/any-opinions-reviews-on-gemtune-appj-pa1502a/0_20

I plan to mod it of course..
Replace caps mainly..
It's using some bland coupling caps..
Lol


----------



## baronbeehive

Oh, thanks! It may be a baby amp but if it's anything like mine, and it looks like it is, it's the best bang for buck out there with the right tubes!
  
 I looked into modding it but very limited space inside is a problem.


----------



## Maxx134

baronbeehive said:


> Oh, thanks! It may be a baby amp but if it's anything like mine, and it looks like it is, it's the best bang for buck out there with the right tubes!
> 
> I looked into modding it but very limited space inside is a problem.


 
You could always expand the bottom...


----------



## baronbeehive

maxx134 said:


> You could always expand the bottom...


 
  
 Oh yes of course, I forgot ............
	

	
	
		
		

		
		
	


	




.
  
 When I got mine there was a company offering a mods package consisting of caps, pot, fuses I think but I haven't been able to find anything out about it now. Could you PM me if you do mod yours with the details, cap etc.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Yes, the bias mod is very straightforward!
> ...


 
 I've made a chart for you:
  

  
 It's the "addit. Ra" resistors you need to buy. Obviously the closest value you can find. Wire them in parallel to stock Ra, through the switch, and you'll get the "Total Ra". The values are calculated with tube gm according to datasheet, so NOS tubes are preferred. 
	

	
	
		
		

		
		
	


	



  
 If you're not sure about the pinout of your switches, just measure with your ohmmeter. Measure continuity between the pins with the switch in both positions. That will tell you how to wire the switch. I also used a ON/ON switch for the bias mod. Just leave one pole disconnected for your OFF setting.
  
@Maxx134
 That little amp looks impressive with those KT66's!


----------



## baronbeehive

Quote:


sonictrance said:


> I've made a chart for you:
> 
> 
> 
> ...


 
  
 Thanks Sonic, I see in your pic below the added Ra resistors:
  


sonictrance said:


> ...........
> 
> 
> 
> ...


----------



## SonicTrance

baronbeehive said:


> Thanks Sonic, I see in your pic below the added Ra resistors:


 
 Yes, exactly!


----------



## baronbeehive

sonictrance said:


> I've made a chart for you:
> 
> 
> 
> ...


 
  
 Just to confirm before I order, I will need 4x8R MRA05(180 Ohm) for 5998, 4x2R7 5w MRA05(130 Ohm) for 421A, and 4x22K 5w MRA05(500 Ohm) + 4x3K9 5w MRA05(430 Ohm) for 6AS7G?
  
 How are those figures calculated?
  
 I'm waiting for the 330 ohm resistors for the tube bias mod which I will do straight away, and then later the impedance mod when I've decided finally on tubes. I've already ordered that rotary switch. I take it your 3 different resistors are for your WE's and GE's?


----------



## SonicTrance

> Just to confirm before I order, I will need 4x8R MRA05(180 Ohm) for 5998, 4x2R7 5w MRA05(130 Ohm) for 421A, and 4x22K 5w MRA05(500 Ohm) + 4x3K9 5w MRA05(430 Ohm) for 6AS7G?


 
 The values in parentheses are correct. But 8R means 8 ohms, 2R7 means 2.7 ohms and 22K means, well, 22k ohms. So not sure what you mean by that?
  
 You have these 910 ohm R's. http://www.hificollective.co.uk/catalog/mra05375-910r-mra05-mills-resistor-p-8191.html
 I'd go for those instead of the 500 + 430 for simplicity.
  


> How are those figures calculated?


 
 Ra is calculated using this formula from the Cavalli WCF paper.
  



> I'm waiting for the 330 ohm resistors for the tube bias mod which I will do straight away, and then later the impedance mod when I've decided finally on tubes. I've already ordered that rotary switch. I take it your 3 different resistors are for your WE's and GE's


 
 I have my Ra switch configured like this:
  
 1 - Open (330) - 6AS7G 110 ohms
 2 - 225 ohms - 6AS7G 20 ohms
 3 - 103 ohms - 421A 20 ohms
 4 - 136 ohms - 421A 110 ohms
 5 - Open
  
 I went the extra mile by testing all my tubes for gm and then calculating the new Ra from that.


----------



## baronbeehive

sonictrance said:


> The values in parentheses are correct. But 8R means 8 ohms, 2R7 means 2.7 ohms and 22K means, well, 22k ohms. So not sure what you mean by that?
> 
> You have these 910 ohm R's. http://www.hificollective.co.uk/catalog/mra05375-910r-mra05-mills-resistor-p-8191.html
> I'd go for those instead of the 500 + 430 for simplicity.
> ...


 
  
 Yes, pity I don't have a tube tester and nobody around here has one.
  
 People ought to be aware it's a bit confusing on hificollective. It so happened that the 330 Ohm Mills resistors have the same SKU identifier ie. MRA05-*330* but this isn't the case with all the resistors so don't get confused like I did.
  
 So it's back to the drawing board with my order!


----------



## Maxx134

baronbeehive said:


> ...
> 
> I'm waiting for the 330 ohm resistors for the tube bias mod which I will do straight away, and then later the impedance mod when I've decided finally on tubes. I've already ordered that rotary switch....




I consider the output tube bias mod and future driver tube bias adjustment more important for the MK6, than the impedance mod. 

Optimal bias is one of the most substantial improvements, as you can literally liven up the tubes and improve soundstage holography.. 

With any amp, we are limited to the designer choice of bias point, which is always a compromise of many things. 

But we are going for optimal sound... 
So for sure you will need to change these settings, especially for the driver tubes... 

The impedance mod selector I have only done to one low setting for my planar, yet I still plan to complete the switch next year, lol


----------



## baronbeehive

maxx134 said:


> I consider the output tube bias mod and future driver tube bias adjustment more important for the MK6, than the impedance mod.
> 
> Optimal bias is one of the most substantial improvements, as you can literally liven up the tubes and improve soundstage holography..
> 
> ...


 
 Ah, right, now I know where we are at with this impedance mod!
  
 So there's now a driver tube bias mod, I was only wondering about that the other day, but for sure matching impedance for tubes and headphones will end up with a fantastically personalized system which the designers strive for but cannot achieve for obvious reasons, as you say. Keep up the good work...... and give the dog a well deserved rest 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

maxx134 said:


> baronbeehive said:
> 
> 
> > ...
> ...


 
 I agree. Tube bias mod has more affect than the impedance mod.


----------



## Maxx134

baronbeehive said:


> maxx134 said:
> 
> 
> > I consider the output tube bias mod and future driver tube bias adjustment more important for the MK6, than the impedance mod.
> ...



I have to thank member "*SonicTrance*" for huge help early on in driver stage bias info and work. 

Although our findings are not finalized, 
they are mostly corroborated as being in agreement and in right direction.. 

I PMed him, and we both are very busy now, 
 but for new year we will pickup where we left off with these upgrades and hopefully more from Redge78.


----------



## baronbeehive

*OMG............... ha ha ha ha........!!!*





 
  
 Edit: I'm just sitting here speechless ............ grinning............. so good........... sorry............ can't talk now............... see below for why!!


----------



## baronbeehive

................


----------



## Maxx134

Swap out the driver tubes for some 6c8g with adapters.. 
You get even better looks/glow and livelier sound.. 
Your too happy! 
Just kidding, enjoy every level before you consider more, lol


----------



## Maxx134

sonictrance said:


> ....
> If you want yours to look like mine you're gonna have to make some aesthetic mods too!
> 
> 
> ...



I don't know if any owners of MK6 realize, 
 but I see member SonicTrance is possibly "cheating" by having the absolute best tube combo I have ever seen on this amp, if you look closely... 
 

So, end result is basically, 
An OTL & OCL fully balanced amp, 
 with double bias mods, impedance mod, plus all other mods done, while topping off with ultra rare Holy grail tubes... 

That makes for an extremly end game level, hard to beat, and one of a kind amp SuperMod amp...
 We gona have to think up something else for you to add now lol.


----------



## SonicTrance

maxx134 said:


> sonictrance said:
> 
> 
> > ....
> ...


 
 Thanks Maxx!
 I'm very happy with the sound of my MK6 as it is now. I'll do some coupling cap experiments with russian KBG's in the next couple of months though.


----------



## baronbeehive

Has anyone had the nightmare experience of seeing a 5mm piece of wire disappear just when you were trying to pick it up from the PCB very carefully? It must have rolled underneath through one of the holes so I've decided to remove the board again because it could short out everything again which obviously I don't need right now. It may be alright but I know it is there somewhere and I couldn't sleep at night worrying 
	

	
	
		
		

		
		
	


	




. I won't be happy until I see that blasted piece of wire again and remove it.
  
 Re: the tube bias mod, I've connected up the wires to the switch one tube for each of the 4 poles and the corresponding pole to complete the circuit for that tube. I've tested for continuity and the off position is correct ie no continuity. In the on position I thought that only each tube circuit would have continuity but in fact each tube circuit has continuity with itself *but also* with the other 3 tube circuits as well. I assume this is right because the whole thing would be on, but I just wanted to check with you first to be sure before blowing it up again! I'm obviously not understanding this but before the switch and wires were in place, ie in the stock arrangement, I don't think there was continuity with the 4 circuits for example when measured at the cathode bypass caps.
  
 I'm sure I've managed to wire up the switch correctly.


----------



## SonicTrance

baronbeehive said:


> Has anyone had the nightmare experience of seeing a 5mm piece of wire disappear just when you were trying to pick it up from the PCB very carefully? It must have rolled underneath through one of the holes so I've decided to remove the board again because it could short out everything again which obviously I don't need right now. It may be alright but I know it is there somewhere and I couldn't sleep at night worrying :mad: . I won't be happy until I see that blasted piece of wire again and remove it.
> 
> Re: the tube bias mod, I've connected up the wires to the switch one tube for each of the 4 poles and the corresponding pole to complete the circuit for that tube. I've tested for continuity and the off position is correct ie no continuity. In the on position I thought that only each tube circuit would have continuity but in fact each tube circuit has continuity with itself *but also* with the other 3 tube circuits as well. I assume this is right because the whole thing would be on, but I just wanted to check with you first to be sure before blowing it up again! I'm obviously not understanding this but before the switch and wires were in place, ie in the stock arrangement, I don't think there was continuity with the 4 circuits for example when measured at the cathode bypass caps.
> 
> I'm sure I've managed to wire up the switch correctly.




I'm having a hard time following what you mean, Baron. 
Before you power ON just measure resistance across each cathode resistors/bypass caps (amp off obviously). It should measure 165 ohms across each cathode resistor when you have the switch ON and 330 ohms with switch OFF.


----------



## baronbeehive

sonictrance said:


> I'm having a hard time following what you mean, Baron.
> Before you power ON just measure resistance across each cathode resistors/bypass caps (amp off obviously). It should measure 165 ohms across each cathode resistor when you have the switch ON and 330 ohms with switch OFF.


 
  
 Sorry again!
  
 Yes the resistances are correct as you say.
  
 What I mean is, for example when measuring from each pole to each of the other poles on the switch they are all continuous with each other when in the on position. I assume it is because the 4 tube circuits are all connected up through the switch that is the reason for this.
  
 Edit: BTW, are the resistors wired in series for the impedance matching mod? I will be ready to do that when the resistors and switch arrive.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > I'm having a hard time following what you mean, Baron.
> ...




The resistors are wired in parallel for the impedance mod also. When you put resistors in series the resistance adds up, so two 100 ohm resistors would be 200 ohms in series for example. Different story when connected in parallel. That's why I made that chart for you.


----------



## baronbeehive

sonictrance said:


> The resistors are wired in parallel for the impedance mod also. When you put resistors in series the resistance adds up, so two 100 ohm resistors would be 200 ohms in series for example. Different story when connected in parallel. That's why I made that chart for you.


 
  
  Yes, thanks. I can't work it out from the pic though:
  
 Quote:


sonictrance said:


> .........................
> 
> 
> 
> ...


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > .........................
> ...




I have my lowest setting resistors connected to the poles of the switch, from ground side of Ra. The other R's, on B+ side of Ra, are then connected in series to that pole resistor. Can't remember why I did it like that but it doesn't matter. You can also just solder a wire to the poles, from either side of Ra, and then your different "addit Ra" from the other side of Ra to the different positions on the switch.


----------



## baronbeehive

*SMLD MODS: (continued)*
  
*6AS7G/421A Tube Bias Mod - By SonicTrance.*
  
 4 x 330ohm resistors connected in parallel to cathode resistors via switch to double current when using 421A's.
  

  
 Still plenty of space for more mods 
	

	
	
		
		

		
			





.
  
 Next, the impedance mod for tube/headphone matching!
  
 Quote:


sonictrance said:


> I have my lowest setting resistors connected to the poles of the switch, from ground side of Ra. The other R's, on B+ side of Ra, are then connected in series to that pole resistor. Can't remember why I did it like that but it doesn't matter. You can also just solder a wire to the poles, from either side of Ra, and then your different "addit Ra" from the other side of Ra to the different positions on the switch.


 
  
 Thanks Sonic!
  
 You didn't mention if 6AS7G's sound better on their impedance setting, as well as the 421A's?
  
 Also the current to 6AS7G's would be double the stock setting if the switch was on the 421A setting, is that OK?
  
 Looking forward to try out the mod when I get the full set of 421A's 
	

	
	
		
		

		
		
	


	




.


----------



## SonicTrance

baronbeehive said:


> Still plenty of space for more mods
> 
> 
> 
> ...


 
 Nicely done! Have you measured to see if the cathode resistances are correct for the different settings? If not, please do so before power on.
  


> You didn't mention if 6AS7G's sound better on their impedance setting, as well as the 421A's?


 
 They do sound better. The Ra switch is not a night and day difference though, but clearly noticeable and an important mod! I noticed most improvement with my LCD-XC's at 20 ohms.
  


> Also the current to 6AS7G's would be double the stock setting if the switch was on the 421A setting, is that OK?


 
 That's definitely *not *OK, baron! The amp will overheat very quickly. Very important that you don't use 6AS7/6080's in 5998/421A setting!
  
  Quote:


> Looking forward to try out the mod when I get the full set of 421A's
> 
> 
> 
> ...


 
 Looking forward to hear your impressions too!
  
 Remember to control measure the different settings on your Ra switch (and bias switch) before power on. Also check for shorts and things like that.
  
 Happy modding!


----------



## baronbeehive

sonictrance said:


> Nicely done! Have you measured to see if the cathode resistances are correct for the different settings? If not, please do so before power on.
> 
> They do sound better. The Ra switch is not a night and day difference though, but clearly noticeable and an important mod! I noticed most improvement with my LCD-XC's at 20 ohms.
> 
> ...


 
  
 Thanks!
  
 I have measured the resistances in the different settings and they're good.
  
 I thought I would mention that about the doubled current for 6AS7G's because no mention has been made of this, so I think it would be best to have a stock setting for the 330ohms and *only* change this when using 421A's. Perhaps mention could be made of this as a warning on page 1?
  
 As my headphones are only 38ohms and your LCD's are 20ohm it would appear that low impedance headphones are most affected by the impedance mod.


----------



## SonicTrance

baronbeehive said:


> sonictrance said:
> 
> 
> > Nicely done! Have you measured to see if the cathode resistances are correct for the different settings? If not, please do so before power on.
> ...


 
 Yes, it would be good to mention that on first page. It's been a long time since I heard anything from @Redge78 though...
  
 I believe your 38 ohm cans will improve greatly with the Ra mod.


----------



## baronbeehive

BTW how does tube bias mod at the cathodes affect the impedance mod at the anodes? Is there any interaction? Does the change at the cathodes cause a change at the anodes?
  
 I've taken some readings and the switch doesn't appear to affect it.


----------



## SonicTrance

baronbeehive said:


> BTW how does tube bias mod at the cathodes affect the impedance mod at the anodes? Is there any interaction? Does the change at the cathodes cause a change at the anodes?
> 
> I've taken some readings and the switch doesn't appear to affect it.


 
 No relation. The cathode resistors only sets the cathode/anode current.
  
 You can take measurements once you have a complete set of 421A or 5998's;
  
 Measure voltage across cathode resistors, with unit on obviously. 
  
 Should be around 10V with 165 ohms resistance which equals about 60mA of current.


----------



## baronbeehive

maxx134 said:


> Swap out the driver tubes for some 6c8g with adapters..
> You get even better looks/glow and livelier sound..
> Your too happy!
> Just kidding, enjoy every level before you consider more, lol


 
  
 Happiness, short lived unfortunately 
	

	
	
		
		

		
		
	


	




.
  
 I've just had the time to test the amp for the first time with the switch in and I've got a problem again! The right hand meter this time is only showing about 40mA, and I've taken voltage readings at the cathode bypass and the voltage is up on that same right hand circuit compared to the others.
  
 All I have done since it was working perfectly was to try to find that annoying piece of wire which involved taking the board out again to no avail. Everything looked OK on the reverse when I put it back after a good old clean with air and isopropyl alcohol. That and the switch was all I did! Maybe something was disturbed in the process?


----------



## Maxx134

Hey guys been away. 
All stock cable used especially for both heater and PSU to the transistors are brittle and prone to disconnect with even one time opening board so check there...


----------



## baronbeehive

maxx134 said:


> Hey guys been away.
> All stock cable used especially for both heater and PSU to the transistors are brittle and prone to disconnect with even one time opening board so check there...


 
  
 Hi Maxx, yes I was careful to check the wires after what happened last time before putting the board back but it's such a struggle to get it back in you are always wondering if something happened during the process. Sonic said that he used a special screwdriver to pull down the tube sockets and I tried using a tool with a bent end which didn't work well, so I think next time I will have to make sure I have the right tool for the job to avoid forcing it.
  
 Anyway I will check everything starting with the board in to see if there is anything obvious, but I'm not in a rush, other things to do. I can keep in touch by PM's if you would rather, or keep posting as I go, whatever!


----------



## SonicTrance

baronbeehive said:


> maxx134 said:
> 
> 
> > Hey guys been away.
> ...


 
 Nothing special about my screwdriver other than it has insulation on the shaft, but that's not important. I just poke the screwdriver through the center of the socket, where the guide pin goes, and pop the sockets in place one by one. I start with the driver tube sockets. I need to force it in place though, no getting around that as there's virtually no extra clearance at all.


----------



## baronbeehive

sonictrance said:


> Nothing special about my screwdriver other than it has insulation on the shaft, but that's not important. I just poke the screwdriver through the center of the socket, where the guide pin goes, and pop the sockets in place one by one. I start with the driver tube sockets. I need to force it in place though, no getting around that as there's virtually no extra clearance at all.


 
  
 Oh I see. I ended up doing much the same thing with an ordinary screwdriver and the force needed is a bit of a concern when pushing against those ceramic sockets. I tried several things one of which was a dentist type tool with a bent end which kept slipping out so I threw that away. I did think of a right angled screwdriver but unless it had a smallish end would not have fitted up the central hole.
  
 I haven't had time yet to look at the amp, it can't be much and the resistances and continuity readings for the switch are fine.


----------



## Maxx134

Check your tiny gain switch.
Flip them from high to low, or low to high.
Check that they in same position.
I am thinking about abolishing this stupid gain switch, in any position.
Another untouched path to look into..


----------



## coinmaster

The gain switch is part of the NFB loop. Nothing good will come of removing it.


----------



## baronbeehive

OK, thanks, I could flip it to high/low gain to check. I'm working on the house atm so I will get back to the amp later.
  
 The amp was working fine after getting it back from the engineer. So what could have happened?
 Since then I removed the board to try to find that piece of wire but couldn't find it. The board was a struggle to put back as ever but I made a point of checking the wires on the back first.
 Then I fitted the switch and as I said the readings were fine and the switch was out of the way of anything underneath it. The solder joints were good.
 Then I fitted the fans, one of the nuts on the inside was close to the top of one of the 4 1200uF 220v power caps, the other nuts cleared everything.
 The I cleaned inside with air and isopropyl alcohol.
 Then I rearranged the parts inside and fitted cable ties etc so that the parts inside were in their final position.
 Finally I put 2 new 3 amp fuses inside.
  
 Could that piece of wire be causing a problem, or something happening when putting the board back, or the switch, or the fans, or cleaning it, or the rearrangement inside, or the fuses?
  
 My feeling is that maybe rearranging the parts inside might have done something. For example I noticed that the engineer must have had 2 1k resistors handy because he fitted them in series to replace the 2k resistor so possibly the fact that they are pointing upwards might have caused them to come in contact with a wire when I rearranged everything. I feel it must be something like that that has happened, but I will look into it more later.
  
 Edit: I meant 0.5 amp fuses.


----------



## Maxx134

coinmaster said:


> The gain switch is part of the NFB loop. Nothing good will come of removing it.



Sorry I did not mean to change the circuit, just solder a position of either low or high gain...
I do not like or trust these switches,
 and believe they may cause volume imbalance if one of them lessen contact.
I personally don't need it.


----------



## Maxx134

Since we are talking hundreds of kilohms involved with the switch,
 switching in resistors.. 
 I could see how the tiny dip switches themselves may become a factor if the switch is defective or tarnished..


----------



## Benny-x

I've been keeping one eye on this thread and the other out for a MK6+. I'm talking to a seller right now of one that says it's his 2nd and that both have exhibited some external transformer hum and some noise through the 1/4", SE headphone jack.

Now the noise through the SE headphone jack I've read a lot about, and I just plan on using this balanced anyway. But the external transformer hum is something I don't recall reading about and I'm wondering if all you guys in here also have this issue with your Mk6s and Mk8s?


----------



## baronbeehive

benny-x said:


> I've been keeping one eye on this thread and the other out for a MK6+. I'm talking to a seller right now of one that says it's his 2nd and that both have exhibited some external transformer hum and some noise through the 1/4", SE headphone jack.
> 
> Now the noise through the SE headphone jack I've read a lot about, and I just plan on using this balanced anyway. But the external transformer hum is something I don't recall reading about and I'm wondering if all you guys in here also have this issue with your Mk6s and Mk8s?


 
  
 No, and I haven't heard of this before. I doubt the others have experienced it either or I would have known about it. Maybe you could get a new one under warranty? It can't be much more expensive.
  
 I just remembered that when I sold my mkivse the person that bought it insisted there was a hum and sent it back and when I tried it there was no hum so it's possible this is peculiar to one's system maybe.


----------



## Benny-x

baronbeehive said:


> No, and I haven't heard of this before. I doubt the others have experienced it either or I would have known about it. Maybe you could get a new one under warranty? It can't be much more expensive.




Hmm, maybe he just has a ground loop and that's causing transformer hum?

Anyway, holy shiit am I were glad you said I should just check out a new amp, as the cost shouldn't be too different! I forgot that the exchange rate had changed vs. the Chinese Yuan. Now I can get a new Mk6+ for about $660USD, shipped to my door... I never realised that at all, so no more worries about trying to snag a deal on some classifieds, I can just buy from LD or an authorized dealer! Haha

Thanks for the heads up! Now if only I could find a matched quad of Tung-sol JAN CTL 5998s or WE 421a for some ridiculously low price~


----------



## baronbeehive

benny-x said:


> Hmm, maybe he just has a ground loop and that's causing transformer hum?
> 
> Anyway, holy shiit am I were glad you said I should just check out a new amp, as the cost shouldn't be too different! I forgot that the exchange rate had changed vs. the Chinese Yuan. Now I can get a new Mk6+ for about $660USD, shipped to my door... I never realised that at all, so no more worries about trying to snag a deal on some classifieds, I can just buy from LD or an authorized dealer! Haha
> 
> Thanks for the heads up! Now if only I could find a matched quad of Tung-sol JAN CTL 5998s or WE 421a for some ridiculously low price~


 
  
 Yes you beat me to it re: the ground loop hum - see my last post!
  
 But l assume you're joking about the cheap TS's/WE's, if not let me know!
  
 Of course if you do get a new mkvi you might be thinking of voiding the warranty 
	

	
	
		
		

		
			





.


----------



## Maxx134

If I bought an MK6,
The tube type is actually an ideal choice for me,
 and I definitely would have spent more money to get those great tubes.

I bought the MK8 instead since I had an HD800.
I almost never heard a better tube amp for the hd800.
Using 6h30dr Supertubes was not cheaper either.

Yet now I settled on rolling tubes to a 6n6p (at higher bias) which is quite inexpensive which save me a ton money,
 and actually more holographic than the expensive Supertubes I still have.

Since the MK8 is set for higher impedance cans, I needed to lower it for my choice of planar cans.
The output impedance switch mod testing solved that Problem.
 Since I didn't install the switch yet,
 I currently have the amp I one setting to match a 20ohm can, since my best headphone is the HEKV2.

So, my point is, I went for the more expensive amp, which turns out using cheaper tubes than MK6..

Yet if I knew what I know now, I would have choosen the MK6,
Both for my power needs with planar heaphones,
And for the magic of the output tube choice (WE tubs).

I am guessing my MK8, in its current tube choice,
 is less tube sounding and definitely less powerful than MK6,
 but enough juice for my HEKV2.

Yet for either MK6 & MK8 amp, I am strongly convinced on using same driver tubes.

The 6C8G tubes with adapters. ( a 6sL7 equivalent type).

Since the 6C8G have more gain (mu), I get close to the fabled ECC35 type I also have.

The 6sn7 types weren't as lively in comparison,
 since they played better with higher bias.
Yet the best one was the Silvania 6sn7W.

Since the driver stage for the MK8 is almost identical, I am convinced this applies to both, regardless of the powerube stage.

On the MK8, I tried literally every 9pin driver tube possible, regardless of spec.

The best were the tall e80cc pinch, yet for all the 9pin tubes, 
Literally No 9pin, not even one, could beat the best 8pin tubes.
Most probably because of this the amp design.

It was actually a great thing for me to be able to try all types of 8pin types, and I rolled so many different types.

Then one day I put in a different type with a bad adapter.
I fell asleep before I could test and left the amp on...

Long story short,
I end up waiting a dam long time over a month for a replacement Transformer,
as my driver tube "heater winding" was burned.

That put a halt to my modding ,
And left me pretty sore about Little Dot customer service.

I lost my motivation after that.
I recently got my motivation back with the tiny cute tube amp I use for headphone break in.
It all tubes:


http://www.head-fi.org/t/780178/any-opinions-reviews-on-gemtune-appj-pa1502a/260_20#post_13145720



This tiny amp is a jewel in that it is running class a triode mode, 
And has Japan output transformers, and implement a modern PSU design to the tubes with Constant Current, and DC heaters.


----------



## baronbeehive

maxx134 said:


> ..............
> 
> Then one day I put in a different type with a bad adapter.
> I fell asleep before I could test and left the amp on...
> ...


 
  
 Hey, don't worry about falling asleep on the job, we all have our off days 
	

	
	
		
		

		
		
	


	




.
  
 I too have been kept going by my little amp and continue to be amazed by it. I first heard about it through Steve Guttenberg and it's kept me going ever since I got it when my mkvi has been offline!
  
 I'm also looking forward to trying those WE's, I've got 3 atm so looking for a cheap one to complete the set. They're not matched so it's a bit or a gamble. I have yet to try my ecc35's as well.
  
 It's a pity about the LD customer service. Their good reputation was a big reason I got my LD in the first place.


----------



## SonicTrance

baronbeehive said:


> Hey, don't worry about falling asleep on the job, we all have our off days
> 
> 
> 
> ...


 
 http://www.ebay.com/itm/Western-Electric-421A-Tube-NOS-Dated-11-21-67-/142263860185?hash=item211f963bd9:g:1BYAAOSw44BYkNyM
  
 Cheap but untested^^
  
 Might be worth a shot.


----------



## baronbeehive

sonictrance said:


> http://www.ebay.com/itm/Western-Electric-421A-Tube-NOS-Dated-11-21-67-/142263860185?hash=item211f963bd9:g:1BYAAOSw44BYkNyM
> 
> Cheap but untested^^
> 
> Might be worth a shot.


 
  
 Thanks. I'll follow it just in case.......


----------



## Maxx134

Hey guys,
I was reading about the virtual sea of caps out there , and found out a few points good to know, 
So this just an update about caps.
Specifically, our cathode Electrolytic caps..

There are instances where using bipolar caps are superior to polarized.

If the amp has split supplies , bipolar 
since there is no voltage to bias the cap.


varying amounts of bias distortion can change on a polarized electrolytic, causing bias distortion for polarized Electrolytic.
So it can be twice or more than the distortion of the bipolar electrolytic capacitor. 

To qoute Batemen's summary:

" In every case, the bipolar capacitor produced much lower levels of distortion than measured on similar value and voltage polar capacitors."


So the bottom line is a better sounding lyctics in general using bipolar,
So better to use in areas of signal , and my choice of mundorf have also been noted better sounding than popular Elma silmic.

 This was a decision taken by the original designer which, puzzled me at the time.
 I did not know the reason why, at the time that the choice of a bipolar cap for cathode caps,
 was a choice made for a better sounding cap.

I bet those stock blue caps were specifically chosen for the job.


----------



## baronbeehive

maxx134 said:


> Hey guys,
> I was reading about the virtual sea of caps out there , and found out a few points good to know,
> So this just an update about caps.
> Specifically, our cathode Electrolytic caps..
> ...


 
  
 Very interesting.............ever get the feeling that you're getting into the heads of  the designers?
  
 Glad I didn't go for the Elna Silmics, the Mundorfs are dirt cheap as well!


----------



## Maxx134

Actually the general consensus I read Elna Silmic2 as very good sounding.

The topic of how they sound was one point,
And the distortion aspects was another.

There is also the "Audio Note" KAISEI Electrolytic Capacitors that supposed to be superior sounding and from the makers of famous "blackgate" caps.

Anyways, in our amp, that is not too critical as we added the smaller .1uf "paper in oil" paralleled caps to help out the Electrolytic.


----------



## MrCurwen

I find parallel caps create "crossover distortion". I use this effect in guitar amp builds; parallel two caps of different types and create a different sound.

I personally never use parallel caps if I can avoid it. Or electrolytics. Then again, if your design calls for a cathode bypass cap, you've got to use something.


----------



## Maxx134

mrcurwen said:


> I find parallel caps create "crossover distortion". I use this effect in guitar amp builds; parallel two caps of different types and create a different sound.
> 
> I personally never use parallel caps if I can avoid it. Or electrolytics. Then again, if your design calls for a cathode bypass cap, you've got to use something.




Agreed, this design takes advantage of using an electrolytic for cathode bypass in powertubes section. Pretty standard.

Distortion lowering is most probably why the original designer used a bipolar cap per cathode.

Also, fortunately the distortion scenario you describe, is not happening here, 
AS I also would not recommend to parallel COUPLING CAPS, unless they are exactly the same type/brand/amount.
Even then it not a good idea, (for coupling).

Yet for most other purposes, especially across an electrolytic,
They are actually improving the Electrolytic performance with an added cap.


For this amp scenario, the cathode cap selection was briefly explained first page, and also a known practice to do for the Electrolytic.

Also, the selection of bypass using the specific PIO choice made at the specific value of.1uf for bypass on the cathode Electrolytic was not guess work.
 It was a researched decision from Ridge78 with help of an old authority and author of tubes. 

Also, another type of cap usage we know that helps is the decoupling cap methods,
 by bypassing caps with paralleled ones at a higher order/ multiplier, not in similar range like what MrCurwen noted can happen.

 There was a link which was deleted which covered this multiplier at another site.
In essence, We benifit from the smaller cap's higher set impedance curves, 
so we still have the capacitive part of smaller caps its impedance curve where the larger cap would not be as effective as it get close to Inductive.
So at higher 100khz plus range it would help with any possible intermodulation distortion that could arise from this amp, being that it use NFB.

Anyways, testing this and other ideas was put on hold.

Another curious note about caps,
 is that they can have same voltage and capacitance spec, yet still sound different and why we have the links to caps in first page.

I must agree that even though caps technology has gained ground with better Electrolytics like "Audio Note KAISEI" , and better "film caps" like copper foils,
In general Caps still are to be avoided in signal path if possible and why you see some expensive tube amplifiers using interstage Transformers instead of coupling caps.
Quality Transformers are fairly expensive though,
And why such advantage to use hybrids designs.

I bet MrCurwen is familiar with such designs/solutions.

There are still those that choose the old fashioned tried and true pure "less is more" way.
I really appreciate both.


As I can also appreciate the implementation of solid state to solve issues in my mini tube amp, for example.

My tiny tube amp uses SS very effectively to eliminate the PSU Transformer for a switching one.
It is a huge cost savings.

I still playing around with it to see if I can optimize the somewhat limited PSU.


It is a great conversation piece because it is so dam small a full tube amp:


----------



## baronbeehive

mrcurwen said:


> ..............
> 
> My tiny tube amp uses SS very effectively to eliminate the PSU Transformer for a switching one.
> It is a huge cost savings.
> ...


 
  
 A bit off topic but I remember reading somewhere that the amp was so small it was difficult to keep it from jumping up and down with the music. I think this is where some mods might come in handy, perhaps using my spare Jupiter caps and then extending the bottom.... possibly with some lead shielding to hold it down 
	

	
	
		
		

		
		
	


	




!! I think if the makers made it bigger it would be taken more seriously as a proper amp. I would be very interested to hear it with something like the Jupiters, because it is already so good with NOS tubes.
     
 I believe the SMPS has advantages and disadvantages: any noise tends to be beyond the range of human hearing - mine has a  very quiet background, but it can be liable to sudden failure with disastrous results.
  
 Edit: I have had mine for years with no problems, but my engineer told me about the failure rate so he must have seen examples of this.
  
 I have been told that with only 3.5w power output it shouldn't work in my system but obviously the *quality* of those watts is a major factor.


----------



## Maxx134

I have finished upgrading that mini amp, 
And suffice to say it is now top notch.

With most tube amps, if there is a signal "coupling" between stages,
You can bet that is going to be the most critical and most obvious upgrade.

I still NOT seeing manufacturers of tube gear acknowledging the usage of highest quality in that area.
They all still using cheapo parts for maximum cost effectiveness.

But if you wanna be the best, you gotta stop being cheap.

While it is great so many cheap amps are affordable, 
It is not so often known you can make many a cheap design dam good just upgrading for less than buying a top notch amp.
That's why DIY will always rule as best.

Yet, the expensive tube manufacturers have no excuse going cheap on coupling cap when they command prices beyond $1k.
Some amps use Transformers because of this cap issues.

 But today's best caps have come a long way.
So you get a simple amplification design and it can have the edge at purity thru simplicity,
And just need some upgrading.

I also see new designs having great merits with SS helping tubes with CCS, regulation and in PSU. 
I have notice tube rectifiers changing outcome of sound before, 
Yet I still think it not necessary and SS in PSU can be made better.


Anyways I edited my last post to clarify what was mentioned about paralleled caps..

Cheers


----------



## Maxx134

I been testing some Electrolytic types at the cathode of another amp,
and found these to be superior for a "Cathode bypass" cap:

Audio Note "Kaisei" 
So far I believe those are tops for Cathode caps.

*****

I also testing some other caps as coupling.
Although my PIO caps tried sound both lively and musical.
I did notice that both transparency in mids and depth and Soundstage was the determine factor.

The Jupiter copper is still my best choice.
Simply the best cap I ever heard, 
although I didn't try expensive Duelunds or Vcaps.

I did try the "Audyn True Copper"...


They are the cheapest copper foil cap I have seen and a true value.
Excellent sound even above mundorf best in natural realistic tonality. 
Still waiting to see how it breaks in on Soundstage it almost even so far but it is new.

It give same realism as the other top copper caps,
But just a touch below the Jupiters in depth and holography.
I am expecting it to open up more as they are new and need burn in.
Most caps do need substantial burn in.


----------



## SonicTrance

^^
Nice caps Maxx! It's nice to see your still modding! We're just getting settled after moving house and I'm going to get my workspace setup soon.


----------



## Maxx134

sonictrance said:


> ^^
> Nice caps Maxx! It's nice to see your still modding! We're just getting settled after moving house and I'm going to get my workspace setup soon.



Me too I have moved into new place and setup my new work space too lol!


Check out this nice cabinet I setup all my Electronic parts on top and tools and tubes in bottom tool boxes:


----------



## baronbeehive

sonictrance said:


> ^^
> Nice caps Maxx! It's nice to see your still modding! We're just getting settled after moving house and I'm going to get my workspace setup soon.


 
  
 Quote:


maxx134 said:


> Me too I have moved into new place and setup my new work space too lol!
> 
> 
> Check out this nice cabinet I setup all my Electronic parts on top and tools and tubes in bottom tool boxes:


 
  
 Hey guys...... can I join in on the party...... BTW... I thought of the move first 
	

	
	
		
		

		
		
	


	




.
  
 Maxx... your workspace looks way too tidy lol!
  
 This is mine

  
 Better acoustics after my last place but not an ideal room shape.
  
 Edit:
 Check out that optical illusion with the speakers.
 NB. Those speakers are actually the same height and level and the same distance from the camera but the shape of the room looks weird.


----------



## Maxx134

Nice...


----------



## baronbeehive

Sorry to gatecrash your party guys 
	

	
	
		
		

		
		
	


	




.
  
 I was wondering if  Mogos has also moved?
  
 Edit:
 I hope someday to have the setup looking more like Maxx's, at present the working area is in another room...... the kitchen in fact!


----------



## MrCurwen

maxx134 said:


> Agreed, this design takes advantage of using an electrolytic for cathode bypass in powertubes section. Pretty standard.




Indeed. My experience has been - and I'm being a bit devilish here - that standard solutions only produce standard sound quality, not exceptional.




> Also, fortunately the distortion scenario you describe, is not happening here




It is. Each cap has a falling phase response when you go down in frequency. The smaller cap has a significant phase distortion occuring inside audio range, most probably inside the most easy to hear middle range.

In essence, the smaller cap still discharges and charges in the frequency range where it is "not supposed to", only it does so 

1) with a diminished signal (higher impedance, but signal output still there)

2) with a significant phase distortion.

I personally find this effect smears the soundstage a little bit. Not as much as some other things, but with the lower distortion models I built it was noticeable.




> AS I also would not recommend to parallel COUPLING CAPS, unless they are exactly the same type/brand/amount.




No, same effect applies to all uses of capacitors. Some applications more than others, but cathode caps most surely.



> Yet for most other purposes, especially across an electrolytic,
> They are actually improving the Electrolytic performance with an added cap.




Yes, that is true, they improve the output impedance of the cap system, but at the same time that phase distortion applies. In PSU supplies that are behind a regulator this is not an issue, but inside the actual audio circuit it is.

Once again whether or not this is at all audible in a particular circuit depends on the overall circuit. If there are bigger performance bottlenecks, then it will not be audible.



> Another curious note about caps,
> is that they can have same voltage and capacitance spec, yet still sound different and why we have the links to caps in first page.




First thing I think when reading this: not a very robust design if it's performance is so contingent on small component variations. I don't mean to be impolite about it, just another perspective to be argued (as I have previously; component choise should not be very important).



> I bet MrCurwen is familiar with such designs/solutions.




I am indeed familiar with different transformer coupling and hybdrid (SS coupling) topologies. Not sure if exactly those you mean.



> It is a great conversation piece because it is so dam small a full tube amp:




That is one pretty little amp! What are the tubes?


----------



## MrCurwen

baronbeehive said:


> I have been told that with only 3.5w power output it shouldn't work in my system but obviously the *quality* of those watts is a major factor.




I'll continue your off-topic a bit!

3.5 W RMS is in INSANE amount of power, depending on topology of course. 

The smallest HIFI amp I've built:







Single ended 6S45P -> source follower direct coupled to 6E5P triode strapped. About 0.2 W RMS output power. Meant to be used with speakers.

It has surprisingly good punch. My girlfriend uses it for background listening in her reading room.


----------



## MrCurwen

Your work spaces are so neat and organized. I'm just sad now.

We moved august of last year, and I still haven't got my electronics laboratory set up for actual use. I parsed most of the stuff thru once, put it in boxes in a bit more condensed manner, but... Well, see for yourselves:



The big cardboard box marked FRAGILE contains my CRTs, well padded. Most are very small, two are 18 and 21 cm in screen diameter. All round, radar CRTs.

The blue boxes are full of tubes. The tube boxes on the left are all empty, I collect the ones I like aesthetically. 

The empty chassis' are on top of my work table. I was supposed to build two amps during the winter...

The small boxes on the shelf are full of russian caps. There's more underneath, not in picture.



There's the work table. The boxes on it contain tubes.

On the far left, just barely in the picture there are two (the other one is not in the picture) 5 inch radar CRTs in boxes, in a tower.

The boxes that are on the floor contain miscellaneous components.



More boxes full of tubes and misc tools and components.

The cabinet on the left is packed full of unfinished projects.


So, be happy about your work areas. May this serve as a warning for you to not buy more components.


----------



## baronbeehive

mrcurwen said:


> I'll continue your off-topic a bit!
> 
> 3.5 W RMS is in INSANE amount of power, depending on topology of course.
> 
> ...


 
  
 I'm aware that all the hype about 100 + watts is balderdash, my friend has a tube speaker amp rated at 8W and I've been regularly deafened by it on half volume or less. The recommended speaker system for my small amp would be around 95db or more that's why I'm surprised it sounds so good on 87db speakers! But I'm amazed that 0.2W works!


----------



## Maxx134

mrcurwen said:


> That is one pretty little amp! What are the tubes?



This is the APPJ PA1502A mini tube amp.
Although the audio path implement triode mode class a design, the rest is very smart solid state PSU and other areas in it so it is almost like a hybrid.

It's a "class A" single ended desing, 
But using a "switching" power supply,
 and tiny surface mount parts by tubes which look like they implementing some type regulation feeding them.
Maybey a CCS circuit.
It also uses two dedicated output Transformers which have many terminals on them when I peaked inside. 

Yes those are "Brimar" mini version of 6v6 to match it size.
Surprisingly good!

I have upgraded what I can on this thing but have not touched the PSU as it is a "switching" type and there is no schematic available that I know.

It sounds dam good now too lol.
It was used to test caps.
I tried different types and also test impact on areas.
You were right I noticed sonic thickness with paralleled caps, but only in coupling stage.

In the cathode position I tried a few types.
I have also used a bypass Wich is common to do for the Electrolytic in that position.

I recently found an electrolytic cap that is very good and just recently posted here.
The Audio Note KAISEI Electrolytic Cap.

I do see and agree that use of capacitor or Transformer coupling, will have to rely on the quality and is a cost issue.




mrcurwen said:


> Single ended 6S45P -> source follower direct coupled to 6E5P triode strapped.



Wow that looks like a dam nice tube on the data sheets!
Wired triode nice!

I notice you say you use "source follower direct coupled" which is using Solid State device to couple and may consider it a hybrid, or not(!)

That is very smart move to avoid expensive passive coupling of either cap or Transformer, while maintaining any aplification to the tube, and using Solid State job just in in followers and power supply functions.
That's probably the future of optimizing tube gear.
The mini amp I have proved this to me once I removed some limiting areas in the caps.
Yet it still relied heavily on them because of traditional coupling cap design.


----------



## Maxx134

mrcurwen said:


> Your work spaces are so neat and organized. I'm just sad now.
> 
> We moved august of last year, and I still haven't got my electronics laboratory set up for actual use.
> .



Haha we all moved recently.
It not bad cluttered if you know where everything is, and it keeps others away! lol
I whish I had that much space!


----------



## MrCurwen

baronbeehive said:


> I'm aware that all the hype about 100 + watts is balderdash, my friend has a tube speaker amp rated at 8W and I've been regularly deafened by it on half volume or less. The recommended speaker system for my small amp would be around 95db or more that's why I'm surprised it sounds so good on 87db speakers! But I'm amazed that 0.2W works!




If you have "normal sensitivity speakers", you only ever use about 0.1 to 0.2 W RMS power 90% of the time. That is true whether your amp has 100 W of reserve power or 0.3 W.

It's all about the transients. More specifically, how your amp deals with them.

In an amp that uses heavy gNFB to achieve linearity or a low enough output impedance to be useful as an amp, you have a situation where the amp's power must accomodate the full extent of the transient peaks.

That is because the loop will destabilize if it clips, causing very nasty audio products to occur at worst for tens of milliseconds after the transient clip. 

On the other hand, if the amp is designed in a way that it can instantly recover from clipping transients, the signal following the transient is reproduced correctly.

The human ear cannot detect the transient missing it's top, if the signal right after it resumes fully correctly. I.e. you don't sense the difference between a transient being 10x the base level and 35x the base level.

So if you only need about 0.2 W RMS at most (that's already too loud for me in most situations) then a 0.5W or 1W amp will provide all the volume and dynamics necessary.

I do admit that a 1W RMS amp does sound better than a 0.2 W amp, but by a surprisingly low margin. A 2W amp doesn't sound any better really.

Keep in mind I am all the time talking about amps with first class impeccable transient response here. An amp using even small amount of gNFB or other 'classic' or 'standard' topologies is not going to sound good at 0.2 W RMS.


To bring it back to the amp this thread is about; 

The LD is grossly overpowered (in my opinion) to driving most ordinary headphones. This is because it is utilizing solutions that trade power to linearity and better output impedance.

Many ways to achieve different goals.


----------



## MrCurwen

maxx134 said:


> It's a "class A" single ended desing,
> But using a "switching" power supply,
> and tiny surface mount parts by tubes which look like they implementing some type regulation feeding them.
> Maybey a CCS circuit.




Could it be it is utilizing some sort of Schade feedback? That can provide outstanding results from SE circuits. I haven't seen any commercial products based on that, but it's been popular in the DIY circles for some time now.



> Yes those are "Brimar" mini version of 6v6 to match it size.
> Surprisingly good!




Mini? I'd think those nice fat ST bottles are much bigger than the G type bottles that 6V6 tubes usually have!

What's the preamp tube?



> Wow that looks like a dam nice tube on the data sheets!
> Wired triode nice!




I assume you mean the 6E5P. It is super linear, yes. Unfortunately it is a real pain to get to behave; it tends to oscillate very easily. Other than that it's supercheap and sounds nicer than most "known audiophile tubes" by an embarrasing lead.



> I notice you say you use "source follower direct coupled" which is using Solid State device to couple and may consider it a hybrid, or not(!)




I don't know, what's the point? Call it whatever. Properly implemented source followers are 100.0% transparent sonically, so whatever. We've been thru this before in great detail. They're just components.

6E5P has a frame grid made out of gold. It is super close to the cathode, allowing for the (almost solid state level) high transconductance and high mu (45 or something like that), but at the same time it catches a LOT of grid current. So if you want good performance you basically have to use a proper grid driver such as a source follower. No-brainer.

Anyway I'm sorry if this is too much off-topic, but here's the schem if anybody is curious:



For further questions on this schem write a PM to me or start a new thread (and link it to me) so there's no hijacking of this thread. Anyway throwing around different ideas can bring some inspiration to your mods as well, or at least more general understanding of electronics and what goes on inside your amp.


----------



## MrCurwen

maxx134 said:


> Haha we all moved recently.
> It not bad cluttered if you know where everything is, and it keeps others away! lol
> I whish I had that much space!




Only problem is I cannot use my work desk because the space in front of it has 1+ meters of boxes stacked on the floor! Plus half of my tools are scattered in whatever boxes... Oh the horror.


----------



## SonicTrance

Here's my new work space/listening room!
 Got a new work desk (to the right) that you can set the height on electrically. Very nice as I often stand up when soldering. Those drawers are filled with tubes, caps and misc amp parts. Tube tester on top. 
	

	
	
		
		

		
			





  

  
 An LED lamp with magnifying glass.

  
 Amp rack. Bottom two are my DIY amp that I did with the help of MrC. Those are going on the bench very soon as they still need some tweaking!

  
 The room is not complete yet as we just moved in, but it's getting there! No more kitchen soldering for me!


----------



## MrCurwen

SonicTrance wow that is some wonderful workspace / listening area / chassiswork!


----------



## baronbeehive

sonictrance said:


> Here's my new work space/listening room!
> Got a new work desk (to the right) that you can set the height on electrically. Very nice as I often stand up when soldering. Those drawers are filled with tubes, caps and misc amp parts. Tube tester on top.
> 
> 
> ...


 
  
  


mrcurwen said:


> SonicTrance wow that is some wonderful workspace / listening area / chassiswork!


 
  
 Yes, you've put down a new standard for sure........... and....... respect for standing up and soldering without the aid of an iron brace 
	

	
	
		
		

		
		
	


	




. Actually I do the same, sitting is childs play!


----------



## Maxx134

sonictrance said:


> Here's my new work space/listening room!
> Got a new work desk (to the right) that you can set the height on electrically. Very nice as I often stand up when soldering. Those drawers are filled with tubes, caps and misc amp parts. Tube tester on top.
> 
> 
> ...



That is sweeet!
A desk that lifts up!

But sweeter are those amps.


----------



## Maxx134

mrcurwen said:


> > Yes those are "Brimar" mini version of 6v6 to match it size.
> > Surprisingly good!
> 
> 
> ...



Haha yes I noticed the 6v6 tubes are already small but these mini 6v6 from Brimar fit in same box as a standard 6sn7.!

The driver tube in that pic was a e80cc which was nice but the amp was designed for an 12ax7 type.
At least it can handle higher heater draw types like the e80cc or a 12BH7 type because the amp really use 12v instead of 6v.


I still looking for a better tube combo.
I think I should have measured all the tube pins to see what bias settings are...


----------



## SonicTrance

mrcurwen said:


> SonicTrance wow that is some wonderful workspace / listening area / chassiswork!


 
  


baronbeehive said:


> Yes, you've put down a new standard for sure........... and....... respect for standing up and soldering without the aid of an iron brace
> 
> 
> 
> ...


 
  


maxx134 said:


>





> That is sweeet!
> A desk that lifts up!
> 
> But sweeter are those amps.


 
 Thanks guys!
  
 Today I'm finally back to modding! I'm going to test some new output tubes, EL36 triode strapped.


----------



## MrCurwen

sonictrance said:


> Today I'm finally back to modding! I'm going to test some new output tubes, EL36 triode strapped.




I think we're hijacking here, but: what value resistor are you using between screen and anode? I'd err on the high side here rather than low, given that the tube stage is operating into a nonexistent load so rp and gm are not very important. 4.7k maybe, then try 10k if oscillation is present?


----------



## SonicTrance

mrcurwen said:


> sonictrance said:
> 
> 
> > Today I'm finally back to modding! I'm going to test some new output tubes, EL36 triode strapped.
> ...


 
 I was gonna use 1k, but I could go higher. Thanks!


----------



## baronbeehive

My kitchen workspace setup:
  

  
 Sadly not up to scratch 
	

	
	
		
		

		
		
	


	




.


----------



## MrCurwen

baronbeehive, still more functional than mine.


----------



## Petyot

Guys,
  
 I need your help... A few weeks ago, I bought a LD MKVI+ on this forum. When I received it, I had a noticeable hiss sound coming from the SE output on both channels in my headphones and a small hiss on the left channel with the balanced output (but each output were functionnal).
  
 I bought it with the original tubes and a complete set of other tubes (including 4 6AS7G). 
  
 Since the hiss was only on the left channel, I suspected that it was coming from a bad tube. I swapped the tubes and I finally found the faulty tube. Since I didn't have an extra 6AS7G, I put back two 6080wc. One of each on each channel (6AS7G + 6080wc for each channel). After the swap, everything was working perfectly for the balanced output with no hiss and since I was using it mostly with my HD800/HD600 balanced, I was happy!.
  
Yesterday, I decided to try again the SE output with my LCD-2 and I realized that there was almost no sound coming from the right channel (I tried with my TH900 with the same result so the problem is not coming from the headphones). The ratio between the left and right channel is like 10 to 1. I hear no sound from the right channel at low volume (knob at 9) and I hear a faint music sound with the knob at 12... and the balanced output is still perfectly functionnal!! 
  
The only changes I have made since I received it with a functionnal SE output was to swap the tubes! The amp was not moved, knocked, opened or modified...
  
Any idea of what the problem could be ? Do the SE output and the balanced output have completly separate circuits? Any risk for the balanced circuit with the SE output dysfunctionnal? Could the change or the mix of tubes have broken something ?
  
 Any help would be much appreciated!
  
 Thanks
  
 Pierre


----------



## Maxx134

First determine if it the amp by switching the rear input cables..


----------



## Maxx134

Next ​to do is swap the right side driver tube
.


----------



## Maxx134

Single ended uses only one side of each output section, 
So again,

Lastly swap output tubes but not between channels, 


Only swap the output tube pair pair on right side.


----------



## Petyot

maxx134 said:


> First determine if it the amp by switching the rear input cables..




I have two amp connected (via y cables) to my balanced Dac and the other amp is working fine.


----------



## Petyot

maxx134 said:


> Next ​to do is swap the right side driver tube
> .




I did it, no change


----------



## Maxx134

petyot said:


> maxx134 said:
> 
> 
> > First determine if it the amp by switching the rear input cables..
> ...



That don't mean anything.
We wanna know if your specific cables going in thw little dot has issue


----------



## Petyot

maxx134 said:


> Single ended uses only one side of each output section,
> So again,
> 
> Lastly swap output tubes but not between channels,
> ...




I will try that

Thanks!


----------



## Maxx134

Sounds to me like one of your rear right side output tube going bad.


----------



## Petyot

maxx134 said:


> That don't mean anything.
> We wanna know if your specific cables going in thw little dot has issue




Would that not impact both SE and balanced outputs?


----------



## Maxx134

Balanced can get away with one of the positive pins not working at a diminish volume on this amp


----------



## Petyot

maxx134 said:


> Balanced can get away with one of the positive pins not working at a diminish volume on this amp




But my balanced output is working well, only the SE is dysfunctionnal


----------



## Maxx134

maxx134 said:


> Single ended uses only one side of each output section,
> So again,
> 
> Lastly swap output tubes but not between channels,
> ...




How do the meters look?
Right side may be higher which is an indication of bad tube.


----------



## Petyot

maxx134 said:


> How do the meters look?
> Right side may be higher which is an indication of bad tube.




Left is around 60 and right is at 62. Is that a big difference?


----------



## Petyot

Could il be a bad tube socket?


----------



## Maxx134

No..
Usually bad tube.
I asked you to switch the two rear power tubes on the right side with each other...


----------



## Maxx134

Single ended socket only use the left tube on each side, as I recall


----------



## Petyot

maxx134 said:


> No..
> Usually bad tube.
> I asked you to switch the two rear power tubes on the right side with each other...


 
 I will try that tonight (I am at work right now), but from what I remembered doing last night, I have tried to go back to the 6080wc for both channel, I have tried to mix the the 6AS7G and the 6080wc on both channel with the same result : SE non working.
  
 When I put back the defective 6AS7G tube the hiss come back (on the channel it is connected with) with the balanced output and the SE is dysfunctionnal. When I put all 6080, the hiss is not there on the balanced output, but the SE is still dysfunctionnal. The only thing I didn't try (I think) is to swap the tube on the same side (not on different channel)
  
 Thanks again for your help, this is really appreciated.


----------



## Petyot

maxx134 said:


> No..
> Usually bad tube.
> I asked you to switch the two rear power tubes on the right side with each other...


 

 I went home for lunch. Did some swapping between tubes on the same side... No change for the SE output. Balanced output still functionnal. Again, there is some sound on the left channel but I have to crank the volume to hear it...
  
 Weird... 
  
 Could it be the wiring under the left socket of the right channel ?


----------



## MrCurwen

I'd say your next best bet is the output wiring. The way you describe your problem it very much sounds like you have one phase disconnected. Could also be the ground pin.


----------



## Petyot

mrcurwen said:


> I'd say your next best bet is the output wiring. The way you describe your problem it very much sounds like you have one phase disconnected. Could also be the ground pin.


 
  
 Thanks. Anything I can do to check that easily ?


----------



## MrCurwen

Well, the way I would do it would be to look up the tube socket pins that are supposed to be connected to the output, then put one ohmmeter probe in the output socket and other probe on the pin and check for continuity. I don't know if this is very easily done with this amp. Maxx134 or some of the other guys can tell you.

The ground pin should be easy enough to check though.


----------



## baronbeehive

maxx134 said:


> Check your tiny gain switch.
> Flip them from high to low, or low to high.
> Check that they in same position.
> I am thinking about abolishing this stupid gain switch, in any position.
> Another untouched path to look into..


 
  
 Quote:


baronbeehive said:


> OK, thanks, I could flip it to high/low gain to check. I'm working on the house atm so I will get back to the amp later.
> 
> The amp was working fine after getting it back from the engineer. So what could have happened?
> Since then I removed the board to try to find that piece of wire but couldn't find it. The board was a struggle to put back as ever but I made a point of checking the wires on the back first.
> ...


 
  
 To refer back to my post above, I'm now looking into the problem with the amp again.
  
 After having successfully modded the cute baby amp that Maxx and I both have and loving the sound I thought it was time to see if I could see what was wrong with the LD.
  
 I said that "Could that piece of wire be causing a problem, or something happening when putting the board back, or the switch, or the fans, or cleaning it, or the rearrangement inside, or the fuses?" The reason being that those things were the only things disturbed since it was working perfectly last.
  
 - I've ruled out the wire because I found an identical piece, near where I turned the amp upside down, lying on the carpet,
 - then I ruled out the fans because the same thing happens without the fans on and the bottom off,
 - then I ruled out cleaning it because I don't think I disturbed anything just cleaning it,
 - then I ruled out the fuse change because it was in correctly and anyway would have affected both right hand circuits,
 - I don't think it could be the switch, all the resistances are correct in both switch positions,
 - I also don't think it could be rearranging all the internal components in their final position because I've moved them out checked for any problems with the insulation. I noticed that where the tube pins come out of the board to their solder points they come through quite sharply but I moved all wires out of the way when I tested it,
 - that leaves a possible problem when getting the board out and putting it back.
  
 I don't know what you think?
  
 These are the voltages I took:
 Grid Pin 1 to ground
 Anode to ground
 Cathode to ground
  
 Looking left to right with pot at bottom:
  
Circuit 1               Circuit 2               Circuit 3             Circuit 4
  
 Pin 1 = 18v          Pin 1 = 65v          Pin 1 = 20v        Pin 1 = 21v
  
 Anode = 73v        Anode = 103v      Anode = 74v      Anode = 75v
  
 Cathode = 91v    Cathode = 109v    Cathode = 91v   Cathode = 93v
  
 The right meter reading is about 38ma, the left meter reading is about 70ma with 6AS7G's.


----------



## coinmaster

Damn bro, your still having trouble with that thing? It would be faster to simply teach you how the mk6 works at this point lol. I'd help but I'm way too busy for text analysis at the moment. May the force be with you.


----------



## baronbeehive

coinmaster said:


> Damn bro, your still having trouble with that thing? It would be faster to simply teach you how the mk6 works at this point lol. I'd help but I'm way too busy for text analysis at the moment. May the force be with you.


 
  
 No worries my friend! I really must teach myself how this thing works 
	

	
	
		
		

		
			





. My APPJ/Miniwatt is running well and the sound on it is pretty awesome so I usually have this as my main amp these days anyway, this is just a side project as long as it's limping along.
  
 Anybody else for text analysis? I'll try to keep it simple 
	

	
	
		
		

		
		
	


	




.
  
 Edit: The Miniwatt has Jupiters in now as well, I reckon even a tin of baked beans with these in would sound amazing.


----------



## baronbeehive

maxx134 said:


> Check your tiny gain switch.
> Flip them from high to low, or low to high.
> Check that they in same position.
> I am thinking about abolishing this stupid gain switch, in any position.
> Another untouched path to look into..


 
  
 I've done that and no difference, the right and left meters are still reading 38mA, and 70mA.


----------



## Maxx134

baronbeehive said:


> baronbeehive said:
> 
> 
> > OK, thanks, I could flip it to high/low gain to check. I'm working on the house atm so I will get back to the amp later.
> ...




All four power output tube should have close to identical voltages so clearly your circuit 2 shows off...

 I have not open my unit up so long I don't remember which section or side this correspond to, but should be same area of problem. 

 Check the cathode resistor area for any short.
Check the cathode bypass cap leads in that area that may be touching each other incorrectly..

Actually woops it look like increase voltages to ground would means a cathode resistance burnt or at a higher resistance .
So with unit off,
Measure your cathode resistor and connection there..

Edit**:
 Measure both the cathode , and the anode resistors on circuit 2...


Resistors can burn slightly, causing increase resistance and result in higher volt drop to ground and lower ouput...


----------



## SonicTrance

Sorry baron. But I haven't opened the LD for a long time, but yes your circuit 2 is obviously off. 

Swap the tubes around and see if problem stays at same channel/phase. Also measure the cathode resistors like Maxx said.


----------



## baronbeehive

sonictrance said:


> Sorry baron. But I haven't opened the LD for a long time, but yes your circuit 2 is obviously off.
> 
> Swap the tubes around and see if problem stays at same channel/phase. Also measure the cathode resistors like Maxx said.


 
  
 Tubes swapped, the problem remains in same circuit.
  


maxx134 said:


> All four power output tube should have close to identical voltages so clearly your circuit 2 shows off...
> 
> I have not open my unit up so long I don't remember which section or side this correspond to, but should be same area of problem.
> 
> ...


 
  
 OK, yes. The problem doesn't appear to be anything around the resistors, either cathode or anode:
  
 1 - Anode resistors all at 330 ohm give or take a couple of ohms.
 2 - Cathode resistors also are all at 330 ohm give or take, measured at either end of the cathode bypass caps
 3 - Cathode resistors are all at 660 ohm give or take measured at the end of the additional 330 ohm resistor, soldered on the end of the cathode bypass cap for the switch.
 These readings for the cathodes are with the switch in the 6AS7G position.
  
 For switch in 421A position:
 4 - Cathode resistors are all at 165 ohm give or take, measured at either end of the cathode bypass caps
  
 I've checked the all leads in the circuit and the only slight suspect is a coupling cap lead that is very close to a screw head, I can imagine this could cause problems as it is so close to the lead, but I will make sure it isn't touching and test it.
 Edit: There's no continuity between the screw head and the coupling cap lead.
  
 BTW how do you actually check for shorts, visually or what because if you don't know where it is how do you do continuity checks until you know roughly where to do it?
  
 I'm going to disconnect the 6AS7G/421A switch to see if there's any wrong connection there to the cathodes. This is the only soldering I did since it was last working.


----------



## coinmaster

I heard putting your amp in a bathtub filled with water and turning it on helps.


----------



## Petyot

coinmaster said:


> I heard putting your amp in a bathtub filled with water and turning it on helps.


 

 Do you have to be in the bath at the same time ?


----------



## Maxx134

baronbeehive said:


> ....
> 
> I'm going to disconnect the 6AS7G/421A switch to see if there's any wrong connection there to the cathodes. This is the only soldering I did since it was last working.




I am now wondering if your switch is fully correctly wired. .


----------



## baronbeehive

maxx134 said:


> I am now wondering if your switch is fully correctly wired. .


 
  
 That's what I was thinking, but I now think it is correct because all the tests are right, however I have found something which I will investigate tomorrow!


----------



## baronbeehive

coinmaster said:


> I heard putting your amp in a bathtub filled with water and turning it on helps.


 
  
  


petyot said:


> Do you have to be in the bath at the same time ?


 
  
 After you!


----------



## baronbeehive

I noticed it looked like a lot of heatshrink had melted into one of the wire ends on the switch mod, but on closer look it is OK.
  
 However .......... I think I've found the problem which probably arose with the rearrangement of the parts inside before putting the bottom back on, it was a bit of a tight squeeze! One of the WCF leads in circuit 2 was loose and came out of the hole along with the pad so I'm looking into how to fix it. Either push the wire right back into the hole and hope there is enough solder on both sides to hold it, or glue the pad back, or get the board out again to solder it properly on the other side and possibly fix wire across the hole as well.
  
 Edit:
 I've decided on what to do. I'm not going to glue it because I don't know what that will do to the board conductivity, I've going to try to solder it from the component side and hope enough solder runs through to the other side to hold it firm. I know from past experience that plenty of solder usually does go through the hole, so that might do it. If not I will have to get the board out again and run some wire past the hole, or get the engineer out to do a proper repair to the pad.


----------



## baronbeehive

Oh well, I've done that and the joint seems solid ..... but the 2 meters are still reading the same. Could it be the lack of a pad on the component side is still affecting it, or is it something else, I don't know. Maybe something on the reverse of the board?


----------



## SonicTrance

Which pad is loose? Where does the trace go? Check for continuity from the cap lead to where it's suppose to connect.


----------



## baronbeehive

sonictrance said:


> Which pad is loose? Where does the trace go? Check for continuity from the cap lead to where it's suppose to connect.


 
  
 Thanks Sonic! I've checked the trace and it is continuous with tube pin 2 which is where the trace goes so it seems to be alright.
  
 I've turned my attention to the switch and here's a pic just to make sure it's OK, I'm sure it is but I may be missing something.
  

  
 It would probably have been quicker to take a photo of the board!


----------



## baronbeehive

Oooops, I tested the amp after checking everything was in place as usual, but forgot I had been testing the switch and it was on the 421A setting so I quickly switched off and no harm done I think. I will check the resistors when it's cooled down but this is so easy to do - that's about the only time I left the switch in the 421A setting.
  
 I did notice something interesting though, the right hand meter always reads half of the left hand meter reading, this time the right hand meter reads around 55mA and the left hand meter was off the scale at 100+mA. When the switch was in the 6AS7G setting the right hand meter reads 38mA and the left hand meter reads 70mA.
  
 Is there any significance in this and is there any fault that you know of that would explain this?
  
 I've thoroughly checked that circuit again and resoldered the cap connection which appeared faulty but the problem remains and I don't know what to do now other than take the back off again. I'm thinking of desoldering the switch but I don't see how it can possibly be wrong.


----------



## SonicTrance

baronbeehive said:


> Oooops, I tested the amp after checking everything was in place as usual, but forgot I had been testing the switch and it was on the 421A setting so I quickly switched off and no harm done I think. I will check the resistors when it's cooled down but this is so easy to do - that's about the only time I left the switch in the 421A setting.
> 
> I did notice something interesting though, the right hand meter always reads half of the left hand meter reading, this time the right hand meter reads around 55mA and the left hand meter was off the scale at 100+mA. When the switch was in the 6AS7G setting the right hand meter reads 38mA and the left hand meter reads 70mA.
> 
> ...


 
 It just means the switch is working as it should. Lower cathode resistance suppose to give an increase in Ia, which is clearly did.
  
 It's hard to give advice on this now other than to check every connection in the faulty channel and compare to the working channel.


----------



## baronbeehive

sonictrance said:


> It just means the switch is working as it should. Lower cathode resistance suppose to give an increase in Ia, which is clearly did.
> 
> It's hard to give advice on this now other than to check every connection in the faulty channel and compare to the working channel.


 
  
 Yes, that's what I thought, at least my mistake showed the switch was working correctly! I've checked the resistors and no harm done.
  
 This is baffling when all I've done since it was last working flawlessly is to solder the switch, apart from other minor things.


----------



## SonicTrance

Here're the schems drawn by MrCurwen. Some values, like anode, cathode resistors and coupling caps are not correct. But you'll get the idea. Study these easy to read schems and then check each and every corresponding connection in your amp. Might seem like a big job but you'll have a much greater understanding on how the amp works.


----------



## Maxx134

baronbeehive said:


> sonictrance said:
> 
> 
> > It just means the switch is working as it should. Lower cathode resistance suppose to give an increase in Ia, which is clearly did.
> ...




The Meters correspond to the bias level which is what those voltage measurements that you measured .

Somehow your one tube not have correct voltages. 

also,
 just because the switch is functional doesn't mean it's wired it totally correctly ...

there's a lot of wires there,
And I thought you disconnected the switch....

you supposed to disconnect the switch ...

To remove any doubt from that area , 
You need to remove and then put the back if it's no difference ...

you're beating around the bush by not ruling the switch wiring out...

 Think of one tube having both triode in series which is what a WCF circuit has...

You already narrowed it down to the tube and the triode section of the tube, by comparison to other tube voltages. .


----------



## Maxx134

Actually wire disconnection of just the tube in question should be all that necessary to find out (if wiring is culprit).


----------



## baronbeehive

maxx134 said:


> The Meters correspond to the bias level which is what those voltage measurements that you measured .
> 
> Somehow your one tube not have correct voltages.
> 
> ...


 
  
 OK. I've disconnected the switch, and we can rule out that as the problem because the 2 meters are still reading as they were.
  
 I'm convinced that there isn't a problem with the circuit, the joints and wires are all good although I haven't thoroughly tested the whole circuit yet, so if it isn't that could it be something loose on the back of the board?
  
 Edit: I've checked most of the resistors on that circuit and they seem to be good, ie they read what they say. I also tried taking resistance measurements at various points round the circuit but rapidly lost patience due to having to wait for the values to stabilize.


----------



## coinmaster

Bro just move to Connecticut in the USA and I got u covered. EZ fix.


----------



## coinmaster

I'm currently thru-hiking the AT so I haven't had time to read your problems but I'm chillin out today so I will offer some help.
From your previous post stating voltages, circuit 2 does not appear to be drawing much or any current.
Pin 1 should be showing around -20v. However it seems to be nearly at what the cathode voltage should be, assuming it is actually a negative and not a positive like you posted, but if it was a positive we would be seeing excess current rather than no current.
-65v on grid 1 would certainly cause the issue.

In either case the opamp is not capable of supplying 65v so check your grid connection for shorts.


----------



## coinmaster

I should probably have worded that better. Dont check the grid connection for shorts per se, check anything connected to pin 1 and see if you can find the source of the -65v. Also make sure that the opamp is functioning properly, test pin 6 on the opamp, find the little dot next to one of the pins on the opamp, that would be pin 1. Count the pins counter clockwise from there until you reach 6. Let me know the voltage.


----------



## coinmaster

Also keep in mind that the -65v is probably being dropped across a resistance so don't specifically look for 65v as the source voltage is probably lower. Your cathode voltage is pretty much at B- so I suspect some current flow between B- supply and grid 1.


----------



## baronbeehive

coinmaster said:


> Bro just move to Connecticut in the USA and I got u covered. EZ fix.


 
  
 OK, great, good to know!

 Get back to you later ..... when I'm packed.


----------



## coinmaster

But for real I may not be within range of a cell tower for the next week or longer after tomorrow, not to mention I'm supposed to get rained on all week so if you can't get those results soon I may not respond back for a while. In any case if your posted voltages were reliable then I should have given you sufficient information to isolate the problem assuming you haven't created any more variables since then.


----------



## baronbeehive

coinmaster said:


> But for real I may not be within range of a cell tower for the next week or longer after tomorrow, not to mention I'm supposed to get rained on all week so if you can't get those results soon I may not respond back for a while. In any case if your posted voltages were reliable then I should have given you sufficient information to isolate the problem assuming you haven't created any more variables since then.


 
  
 No worries!
  
 I've been pretty busy here myself for the past few months and the amp has had to take second place. I'll check out what you said and get back to you when I can, no rush. Those voltages were reliable, they were the same every time.
  
 Hint ......check out those golf brollies, they're pretty good in the rain 
	

	
	
		
		

		
			





.


----------



## baronbeehive

This is my new baby ......... the cute little amp! It has the Jupiter and Kaisei caps inside, and sounds amazing.
  
 Edit: Unlike the LD the mods only took about 1 hour
	

	
	
		
		

		
		
	


	




.


----------



## baronbeehive

coinmaster said:


> But for real I may not be within range of a cell tower for the next week or longer after tomorrow, not to mention I'm supposed to get rained on all week so if you can't get those results soon I may not respond back for a while. In any case if your posted voltages were reliable then I should have given you sufficient information to isolate the problem assuming you haven't created any more variables since then.


 
  
 Hi coin, sorry for the delay, I can't work on this when I would like.
  
 I've looked for a trace from tube pin 1 and there isn't one, so I tested for continuity and nothing seems to be connected to pin 1.
  
 The voltage from pin 6 on the opamp is 15v. Those opamp pins are difficult to test without the probe slipping off all the time.
  
 You were correct when I said earlier that the voltage on tube pin 1 was 65v, I meant -65v.
  
 Also if there was no current going through circuit 2 that would explain the bias meter reading which would double if there was a current. I wondered if there was perhaps a separate wire input for each circuit on the reverse of the board which might have come off on that circuit?
  
 You still hiking? What's "... the AT?"


----------



## coinmaster

Pin 1 is connected to the coupling capacitor and two 470k resistors and a small red capacitor which connect to the opamp. The traces are probably on the other side of the board.
I'll see if I can post you my schematic, it's difficult on the phone.
As expected pin 6 is swinging to the positive rail trying to compensate for the connection to b-, thus creating a voltage divider.
Some voltage dividing math might reveal the culprit but I don't know if I have time for that.
The "AT" is the Appalachian trail, a 2100mile trail that goes through the Appalachian mountains. I finally managed to snag a signal at the top of an annoyingly tall mountain


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## coinmaster

Here is an old schematic I made, it's not as legible as it should be but it has all the connections

Just poke around the opamp area until you find something with suspiciously low voltage and follow it, preferably starting from pin 6 of the opamp. 
It's possible that the voltage short to b- is between the 470k resistors outputted from the opamp, or perhaps your WCF cap on the b- side is touching something in that area, but who knows.


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## baronbeehive

coinmaster said:


> Pin 1 is connected to the coupling capacitor and two 470k resistors and a small red capacitor which connect to the opamp. The traces are probably on the other side of the board.
> I'll see if I can post you my schematic, it's difficult on the phone.
> As expected pin 6 is swinging to the positive rail trying to compensate for the connection to b-, thus creating a voltage divider.
> Some voltage dividing math might reveal the culprit but I don't know if I have time for that.
> The "AT" is the Appalachian trail, a 2100mile trail that goes through the Appalachian mountains. I finally managed to snag a signal at the top of an annoyingly tall mountain


 
  
  Hey ..... climbing up the nearest mountain top just to get a signal .... you shouldn't have 
	

	
	
		
		

		
		
	


	




.
  
 Right, I'll check out what you said thanks.
  
 The great outdoors ... fantastic! The nearest we've got near me is Dartmoor National Park, BUT ... it's nothing like that!
  
 Edit: Maybe take the cable car down...


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## coinmaster

Nah I wasn't going out of my way. The idiots who created the AT did it with the intention of going over every mountain peak possible. Every day is a constant trek up and down 3000ft mountains.
I should have just went fishing in Yellowstone or something I would probably enjoy myself a lot more


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## baronbeehive

coinmaster said:


> Also keep in mind that the -65v is probably being dropped across a resistance so don't specifically look for 65v as the source voltage is probably lower. Your cathode voltage is pretty much at B- so I suspect some current flow between B- supply and grid 1.


 
  
 So I'm looking for a voltage of -65v or lower than -65v, ie -66v onward?
  


coinmaster said:


> Pin 1 is connected to the coupling capacitor and two 470k resistors and a small red capacitor which connect to the opamp. The traces are probably on the other side of the board.
> I'll see if I can post you my schematic, it's difficult on the phone.
> As expected pin 6 is swinging to the positive rail trying to compensate for the connection to b-, thus creating a voltage divider.
> Some voltage dividing math might reveal the culprit but I don't know if I have time for that.
> The "AT" is the Appalachian trail, a 2100mile trail that goes through the Appalachian mountains. I finally managed to snag a signal at the top of an annoyingly tall mountain


 
  
 OK, I've found a connection with one 287ohm resistor only. There is no continuity between pin1 and the coupling caps either on this circuit or the others. Also I can't measure continuity with the red cap on this side of the board
   
 Quote:


coinmaster said:


> Here is an old schematic I made, it's not as legible as it should be but it has all the connections
> 
> Just poke around the opamp area until you find something with suspiciously low voltage and follow it, preferably starting from pin 6 of the opamp.
> It's possible that the voltage short to b- is between the 470k resistors outputted from the opamp, or perhaps your WCF cap on the b- side is touching something in that area, but who knows.


 
  
 So, to confirm what to do, I'm assuming I measure voltage from pin 6 of the opamp to any other components around that area, not from each of the components to ground?
 Then if I find a voltage of around -65v from the opamp pin to some component then I measure from that component to another to see if I can find the source of the -65v. Correct?


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## Maxx134

Hi here is a separate question... 
Hey did you say pin 1 of the tube? 
That should be the Plate/anode & should be connected to the anode resistor. Check connection.


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## coinmaster

Don't look for continuity, continuity means a dead short. You need to understand what Connects to what and move down the line. The 287 ohm resistor is just the grid stopper resistor. Test continuity from the other side of the grid stopper until you find the leg of the 470k resistor, then go to the other leg of that resistor and move down the line until you get to pin 6 of the opamp and test the voltages as each point between the tube's grid and the opamps output, somewhere between those points you have a connection to B-.
Nothing in that area should be below what the opamp is pushing out which right now is 15v.
Just look for the point where the lowest voltage is along that line and then look to see what is touching it that shouldn't be. It may just be easier to poke around the opamp area with the voltmeter.


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## baronbeehive

maxx134 said:


> Hi here is a separate question...
> Hey did you say pin 1 of the tube?
> That should be the Plate/anode & should be connected to the anode resistor. Check connection.


 
  
 Yes tube pin 1. I just tested it and there is no continuity between pin1 and the anode resistor, either on this circuit or on the others.


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## baronbeehive

coinmaster said:


> Don't look for continuity, continuity means a dead short. You need to understand what Connects to what and move down the line. The 287 ohm resistor is just the grid stopper resistor. Test continuity from the other side of the grid stopper until you find the leg of the 470k resistor, then go to the other leg of that resistor and move down the line until you get to pin 6 of the opamp and test the voltages as each point between the tube's grid and the opamps output, somewhere between those points you have a connection to B-.
> Nothing in that area should be below what the opamp is pushing out which right now is 15v.
> Just look for the point where the lowest voltage is along that line and then look to see what is touching it that shouldn't be. It may just be easier to poke around the opamp area with the voltmeter.


 
  
 So I test as follows: atm I have continuity between pin 1 and 287 ohm resistor.
  - I then test for continuity from other leg of 287 ohm resistor to find 470 ohm resistor then..
  - I test for continuity anything in between the other leg and opamp pin 6 then...
  - having noted anything that has shown continuity I then test the voltage between each of those points and ground.
  
 I assume that the continuity test gives me the line the circuit takes through the connections, sorry if that's garbled.


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## coinmaster

If you look at the schematic I posted you, you will notice that the grid of the tube connects to two 470k resistors in series with a .22uf capacitor between them, they are laid out in the opamp area along with the 2k and 390k resistors. You could just use an ohmeter to test each resistor value in the area and hope the cap doesn't mess with your readings, in either case just find the lowest voltage in that area of the circuit.


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## coinmaster

Also something you might try is using and ohmmeter between pin 1 and the b- supply. You might want to try that first and see what it says.


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## baronbeehive

coinmaster said:


> Pin 1 is connected to the coupling capacitor and two 470k resistors and a small red capacitor which connect to the opamp. The traces are probably on the other side of the board.
> I'll see if I can post you my schematic, it's difficult on the phone.
> As expected pin 6 is swinging to the positive rail trying to compensate for the connection to b-, thus creating a voltage divider.
> Some voltage dividing math might reveal the culprit but I don't know if I have time for that.
> The "AT" is the Appalachian trail, a 2100mile trail that goes through the Appalachian mountains. I finally managed to snag a signal at the top of an annoyingly tall mountain


 
  
 I've traced the circuit from pin 1 to the coupling cap via the 287 ohm resistor but can't find any continuity from the other leg of the coupling cap to anything so I'm assuming it goes to the red cap.
 I've tried tracing it the other way from pin 6 of the opamp and this goes to the 561 ohm resistor and again I can't trace it from here on.
 Anyway I can check this out from your circuit diagram later.
 I've take a whole bunch of readings which I'm trying to make sense of and while I was doing that I noticed a large solder splatt that suddenly appeared by a resistor near those 8 red stock wima caps, not near the opamp. The other thing I thought about was that coupling cap lead that was almost touching the screw head on the board, and I resoldered it. It could well have been something like that causing a short again.
  


maxx134 said:


> Hi here is a separate question...
> Hey did you say pin 1 of the tube?
> That should be the Plate/anode & should be connected to the anode resistor. Check connection.


 
  
 When I said there was no continuity between pin 1 and the anode I meant no direct connection, I didn't try following the circuit all the way from pin 1.


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## Maxx134

Not to side track on your troubleshooting, 
But it is funny how the two amps (MK6 & MK8) 
Reverse roles when modding for TOTL level... 

Best tubes for MK6 remain same as if not molded, and can be quite expensive for the power tubes. . 

While best tubes for MK8 reverse from the very expensive 6n30dr supertubes, 
To the ultra low costing 6n6p tubes talked about here :

 http://www.lampizator.eu/UPGRADE/upgrade%20noval%20tubes%20to%206H6P.html

Those tubes I run at a slightly higher bias... 

For the driver stage, the MK8 is the same circuitry as the MK6, except for using 9pin tubes (probably for looks). 

So I after alot of testing, switched to MK6 choices of using 8-pin driver tubes... 
I finally settled on the 6C8G (6SL7 equiv) type for driver stage:

And this is after trying many many many 9pin and 8pin varieties of types, not just brands...
For this amp driver stage, the best 8-pin always were better than the best 9pins.


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## baronbeehive

maxx134 said:


> Not to side track on your troubleshooting,
> But it is funny how the two amps (MK6 & MK8)
> Reverse roles when modding for TOTL level...
> 
> ...


 
  
 Hey, great work Maxx! These are pretty cheap too!
 Which ones do you like, KenRad, RCA, National Union... not the TungSol's at $2000 I hope 
	

	
	
		
		

		
			





.
 As soon as the amp is up and running......


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## Maxx134

I found the tung-sol to be one of best at in all 8pin (driver tube) types.


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## Maxx134

baronbeehive said:


> ...
> Which ones do you like, KenRad, RCA, National Union... not the TungSol's at $2000 I hope  .
> As soon as the amp is up and running......



Oh!, haha I seen that sale. 
It was for 100 NOS tubes. 
That seller would have sold all by now, if he sold them separately.. 
It was also posted months ago. 
When I saw it I offered to buy a few. 
Seller agreed but then backed out. 
So too bad for them. 
I have my own tung-sol which is older production and better than that seller has.


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## baronbeehive

I'm struggling to understand this. I've looked  at the circuit diagram. I've also taken readings from every component that can be reached in the circuit.
  
 Nearly every component has very low readings, ie. minus something, including nearly all tube pins. The anode resistor is about the only thing with positive readings which I suppose is encouraging.
  
 I've tried to trace the circuit from pin 1 and opamp pin 6 and I get so far only.
  
 The problem I have is knowing which reading is significant. Also I can't seem to find 2 resistors that read around 470 ohms.
  
 Therefore I will give you a couple of readings in that circuit ie. the circuit from pin 1 to coupling cap to 470 ohm resistor to .22uF cap to opamp pin 6:
  
 Pin 1    -62v     to:
    287 ohm resistor    -62v both legs     to:
        coupling cap      -61v      +193v other leg
  
 Then from opamp pin 6     +15v      to
    .561 ohm resistor      15.5v       -22.4v other leg
  
 I know opamp pin 7 is not in that circuit but it is also reading high ie 16v.
  
 I don't know if that helps or if it is garbled.
  
 Also I don't know what B- is or where it is on the board.


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## coinmaster

Yeah there's too much nonsense in that. Okay Here's what's gunna happen. Download skype on your phone, create a skype account if you don't have one. P.M. me your skype name and I'll help you out on skype.


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## Mogos

Maxx good to hear that you like the 6C8G. I have bought few pairs of them. I did not have an opportinity to test to many types of the driver stage tubes. So hearing from you that I just have done one of the best choices make me feel good . Very simiral are the 7193 KenRad with adapter. They are faster and tighter than 6C8G but less musical. Recently I have 7193 pluged in.


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## baronbeehive

Quote:


mogos said:


> Maxx good to hear that you like the 6C8G. I have bought few pairs of them. I did not have an opportinity to test to many types of the driver stage tubes. So hearing from you that I just have done one of the best choices make me feel good . Very simiral are the 7193 KenRad with adapter. They are faster and tighter than 6C8G but less musical. Recently I have 7193 pluged in.


 
  
 Hi Mogos, don't buy up all those 6C8G's, leave some for me 
	

	
	
		
		

		
		
	


	




.
  
 Quote:


coinmaster said:


> Yeah there's too much nonsense in that. Okay Here's what's gunna happen. Download skype on your phone, create a skype account if you don't have one. P.M. me your skype name and I'll help you out on skype.


 
  
 Hey, thanks coin, I'll set it up!


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## MrCurwen

> While best tubes for MK8 reverse from the very expensive 6n30dr supertubes,
> To the ultra low costing 6n6p tubes



6N6P has Pa of only 4.8W. How low current is this direct drive output stage using?

6N6P and variants don't have the top notch linearity: 

https://i2.wp.com/www.bartola.co.uk/valves/wp-content/uploads/2012/06/THD-analysis.png

Of course in your application this is not very important; as a follower inside a NFB loop. The low Pa puzzles me though.



> I finally settled on the 6C8G (6SL7 equiv) type for driver stage:



The 'king' of the 6SL7 / 12AX7 high mu high rp product line was the special quality 6SF5. It's got pretty much perfect 4P1L level curves, and a mu of 100. The top cap can be a pain though, I personally never got it completely quiet. Pretty tube though.



> Maxx good to hear that you like the 6C8G. I have bought few pairs of them.[...] Very simiral are the 7193 KenRad with adapter. They are faster and tighter than 6C8G but less musical. Recently I have 7193 pluged in.



Wha...what? 7193 has a nominal rp of 6 to 7 k, 6C8G is at 22.5 k. They are similar like aeroplanes and boats, both can be used to get to places. Very different rides though.

In serious terms they require very very different circuitry around them to function properly.

Different tube types used the same pinouts because of tube testers, not because they should be used in the same circuit.


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## coinmaster

I like turtles.


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## Maxx134 (May 23, 2017)

Maxx134 said:


> Not to side track on your troubleshooting,
> But it is funny how the two amps (MK6 & MK8)
> Reverse roles when modding for TOTL level...
> Best tubes for MK6 remain same as if not molded, and can be quite expensive for the power tubes. .
> ...


I have tested as many driver tubes as I could before I blew out my transformer heater coil output winding to get that opinion.
So just recently I went online to see if any correlation to this,
And  I found out that my findings actually did correlate to what was known already in general about some 9pins and Octal pin tubes.
Specifically the tubes used for these amps driver stage...


baronbeehive said:


> Hey, great work Maxx! These are pretty cheap too!
> Which ones do you like, KenRad, RCA, National Union... not the TungSol's at $2000 I hope .
> As soon as the amp is up and running......


I am finding out a right combination is best...
Like brighter driver tube will liven a thicker powerube down the line...
So its a balance .


baronbeehive said:


> I'm struggling to understand this. I've looked  at the circuit diagram. I've also taken readings from every component that can be reached in the circuit.


There is another way...
If you really want to see if it is your opamp,
Just swap that specific one which controls your defective stage,
To the other channel on the same stage (positibe or negative stage)
Then try and see if the meters are different .


Mogos said:


> Maxx good to hear that you like the 6C8G. I have bought few pairs of them. I did not have an opportinity to test to many types of the driver stage tubes. So hearing from you that I just have done one of the best choices make me feel good . Very simiral are the 7193 KenRad with adapter. They are faster and tighter than 6C8G but less musical. Recently I have 7193 pluged in.


And


MrCurwen said:


> The 'king' of the 6SL7 / 12AX7 high mu high rp product line was the special quality 6SF5. It's got pretty much perfect 4P1L level curves, and a mu of 100. The top cap can be a pain though, I personally never got it completely quiet. Pretty tube though.


I am specifically not dealing with single triode tubes,
 because for me the only gain would be more linearity(non issue becaue, as MrCurwen stated we have feedback),
And the slight improvement from possible isolation of triodes.
The issue is that in this driver circuit it doesn't really apply because we are still within the same channel.
So the theoretical & possible gains of triode isolation would result in maybe better noise cancellation ,
wich is already non detectable..
And in this specific amp " balanced " design,
the driver tube actually NEEDS the two triode sections as similar as possible , so within the same tube glass,
 is actually a better chance of uniformity.
Better still would be a driver tube with common cathode.
 I tried some but haven't found any noticeably  good ones.


MrCurwen said:


> Of course in your application this is not very important; as a follower inside a NFB loop. The low Pa puzzles me though.


Yes, you are correct as usual lol.
I am glad your interest about the tube.
Yes there is lower power output, although I am running them near max bias.
What I found was that although all these type tubes have the annotation of "P" for pulse,
Which is an advantage for increased power output..
In my trials upon listening, the music dynamics & on transient attacks, it seemed exaggerated ..
I found that the music dynamics seemed artificially expanded in minute levels at times.
Of all the 6n6p or 6h30 or 6n30dr types I tried,
The bottom line was the russian 6n6p (oldest version without the gold grids)
Were the most natural sounding... In this amp.
They had both the most natural, realistic and most holographic sound of the bunch... Even over the "supertube" version.... All hype.
But you are absolutely correct in that the 6n6p are a weaker tube for power output.
  I lost a few DB of power as a result in my amp.
Remember since we are powering headphones , my application is not as critical to have lots of power,
So I still have just enough power on tap for my HEKV2(20ohm) to be acceptably loud , but not tremendous...
 And my HD800 can play tremendous loud still.
I have the amp on high gain as well, with higher bias on both driver and power stages, and using the higher gain type driver tubes.. All to help with "gain".
It just all works out, lucky for me.
Also the increase MU of the 6SL7 type or 6C8G type , for me gives more life and detailing , wich would or could be lost in any non-optimal circuit or bias situations..
Remember the stock design is using a super low bias point which is already not optimal.. 
So I prefer the choice of a higher gain driver tube .


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## Maxx134 (May 23, 2017)

I am going to give you MY OPINION, not law,  but based soley on MY OWN RESEARCH....
About....
My..

TUBE SELECTION.. (! heh)

Ok here it is,  and remember I am convinced mainly because it's what I was able to verify on my own... Yet only on this amp,  so on another amp design it may not apply..

Quote:


I have personally tested and tried many variations of the *dual triode *driver tubes,
 both nine-pin and eight pin...
As my MK8 uses nine pins over the octals that MK6 uses..

So,
These are the the reasons (both read about afterwards,   and verified beforehand  in my testing)
 I will always go with an octal tube over any nine-pin, for the  driver stage:

6SL7 is a more linear tube, than a 12AX7 ( which has spikes and dips in it's EQ )...
So you get get a better tonality out of the octal tube!

 Octals were more popular with hifi DIY'ers for RIAA phono preamps,
 because the 12AX7 is a horrible match with RIAA correction(!)..

Smaller 9pin tubes may also be  vunerable to problems such as cross talk between the two sections and the heater.

Also the  plates of the two sections are closer together because of the narrow confines of smaller tube...

So, to combat this, on some tubes
 they decided to add a "shield' between the two triode sections, and bring it out on the extra pin, as done with MK8 power tubes.

This was used to keep the two sections more isolated,
which can also be especially useful for high frequency use or issues  (oscilations)..

Still, the smaller size and higher gain factor and headroom of the 12AX7 type increased its popularity over the Octals, in guitar amps in the '60's.

But that's were advantages end and there more bad news ...
The square plates in tubes,
 are found in the later (cheaper) constructed tube years, which
is why they usually don't command as high a price as the rectangular
or *"round plates"*.

_*Round plates are more desireable*_ ...
 Although the round plates don't have as much maximum power handling as the rectangular or square plates of same type,
 the focus is sound quality...

The round plates have a more "even distribution" between the cathode, grid and plate,
 which improves the  amplification quality and details of the tube...

I have personally verified this with many, many, many driver tube trials on my MK8,
Before finally settling on the MK6 choice of driver tube of...

Of the 6SL7 but *especially 6C8G*, _as it has the superior characteristic of both greater triode  separation *and* round plate..._


*Thats why an Octal (8pin) tube with round plates is best to me, IMHO...
*

There you have it.
Truths exposed hehe.

Don't tell me,  you  already knew,  lol


----------



## MrCurwen

> I am specifically not dealing with single triode tubes,
> because for me the only gain would be more linearity(non issue becaue, as MrCurwen stated we have feedback)



I'm sure most have heard me quote the old "NFB is trading gain for linearity". There is another level to this; within this linearity that is acquired via NFB. It trades lower overall THD to higher proportion of higher order products.

So let me clarify.

If you have a circuit that produces 1% THD consisting of only 2H and 3H and you apply gNFB, you then get lower (let's say 0.1%) THD, but the spectrum of harmonics changes so that you now have very small amounts of 4H, 5H, 6H, and 7H.

What this means to you is up to your ears and brains. Just something to think about. (I'd like to reiterate that "the SS sound" in my opinion is not caused by SS, but by NFB.)

To bring it back to the quote above, it's not completely irrelevant how inherently linear your gain stages are, even if they are inside a loop. It is mostly irrelevant, but not completely, and for BEST RESULTS HIGH END AUDIO it definitely is not at all irrelevant.

My personal opinion is that is is always best to not create any distortion in the first place than to try to fix it after the fact.



> The issue is that in this driver circuit it doesn't really apply because we are still within the same channel.
> So the theoretical & possible gains of triode isolation would result in maybe better noise cancellation ,
> wich is already non detectable..
> And in this specific amp " balanced " design,
> ...



For balanced SS circuits it is very important to have the devices heat coupled (same heat sink is best). For tubes, heat does change the specs a bit, but not as much as SS components. Having the tubes inside the same glass envelope is not important at all for the matching, especially since 99.99% of the heat inside a high rp low current tube is from the heater anyway, not the actual Ia or Pd.

I'd say single triodes are for best results in circuits where tube matching is critically important, because you cannot get double triodes with identical tube sections. 

I don't think in practise this makes much difference in your circuit, but just a thought.



> Better still would be a driver tube with common cathode.
> I tried some but haven't found any noticeably good ones.



6SL7 has a shared cathode version (for radio duty) 6SC7. 

http://www.mif.pg.gda.pl/homepages/frank/sheets/093/6/6SC7.pdf

http://www.mif.pg.gda.pl/homepages/frank/sheets/127/6/6SC7.pdf

It has essentially identical specs and identical linearity.

Very nice metal envelope, JAN, super high quality for military: http://www.ebay.com/itm/1-x-Ken-Rad...894410?hash=item5b349f88ca:g:2mIAAOSwMTZWR08f

These are a bit more expensive than I'd like to pay for a tube, since they are common in early 1950's Tweed style guitar amplifiers. I love tweed amps, I simply use russian 6SL7 for sensible price. Quality just as good.

Russians also make a copy of 6SC7, it's 6N10 but it's not available for sale. Probably only a few were ever made.

Why do you think having the cathodes connected together inside the tube envelope makes any difference compared to connected on the outside?



> I am finding out a right combination is best...
> Like brighter driver tube will liven a thicker powerube down the line...
> So its a balance .



Yep. My own philosophy would be "don't mess with the frequency response in the first tube stage, so you don't have to try to fix it in the second tube stage".




> Yes there is lower power output, although I am running them near max bias.



What's your Ia?



> What I found was that although all these type tubes have the annotation of "P" for pulse,
> Which is an advantage for increased power output..



Kind of. Pulse capability doesn't increase RMS power at all, but it can (in a properly designed circuit) increase transient response which brings about the sensation of power in the listener.

In a circuit that doesn't speficically take into account the pulse capability, they will probably sound worse. Let's go into that:



> In my trials upon listening, the music dynamics & on transient attacks, it seemed exaggerated ..
> I found that the music dynamics seemed artificially expanded in minute levels at times.
> Of all the 6n6p or 6h30 or 6n30dr types I tried,
> The bottom line was the russian 6n6p (oldest version without the gold grids)
> Were the most natural sounding... In this amp.



Yes. I find this easy to believe.

Back some time ago I wrote about the grid parasitics, with specific mention to high pulse capability tubes (such as these russian tubes and also TV sweep tubes which I've been dealing with).

Basically the bigger the pulse capability of the tube, the bigger the electron cloud hovering around the cathode. Now there electrons hit the grid, and they must find a way to escape then. The circuit around the grid must accomodate this.

Worst case scenario, there is a large resistor from grid node to ground (or other reference that is applicable). This trapped current must then go thru that resistor to escape; current thru resistor causes voltage (Ohm's law). So that shifts the voltage at the grid.

What is the voltage at the grid? It's the audio signal. 

This grid current phenomenom happens a little bit on zero signal situations, depending on bias point. In high mu high gm supertubes like 6E5P and other frame grid tubes it most definitely happens even at zero signal conditions. This is because the frame grid is positioned very very close to the cathode.

But of course with signal peaks you understand is where most of this grid current happens. In audio terms it affects transient response. 

Now your circuit is not feeding the grid from a low impedance source (i.e. a source that is able to deal with the current easily) so it is no wonder that pulse tubes cause transients to sound 'wrong'. What you are probably hearing is extra distortion on transients, this makes your ear catch them more, not in a good way.



> They had both the most natural, realistic and most holographic sound of the bunch... Even over the "supertube" version.... All hype.



100% circuit dependent.

I find that pulse types (such as TV sweep tubes) make THE BEST audio output tubes, provided they have adequate grid drive. Source followers in practise. If the transients are clean, they don't catch your ear in a bad way, instead they make the music more 'lively' and dynamic.

My current workhorse amp has 6E5P output tubes. Incredibly dynamic and also superbly clean. Have a look at the triode curves, sure is a sight for sore eyes aren't they.



> I have the amp on high gain as well, with higher bias on both driver and power stages, and using the higher gain type driver tubes.. All to help with "gain".



I always tend to end up either with too little or way too much gain. Current amp has a voltage gain of 3500 (12AX7 -> 6E5P) which is simply stupid and an invitation for oscillation problems. I need my lab set up so I can build a new amp...



> Also the increase MU of the 6SL7 type or 6C8G type , for me gives more life and detailing , wich would or could be lost in any non-optimal situations..
> So I prefer the choice of a higher gain driver tube .



Yes all things being equal everybody prefers the louder one. That's why A/B tests need to be strictly volume matched.


----------



## gug42

Hello,

Sorry if i interrupt your discution .... hard for me to follow. I'm a future owner of a mk6+ and I was looking for tube.

I have ask the question on the mk6/mk8 thread, but someone told me to ask here for confirmation and explanation :
Can it be a probleme to not have closely matched 6SL7 driver tube ? Around 15-17 % of differences between the anode ?


Thank you by advance !


----------



## MrCurwen

> TUBE SELECTION.. (! heh)



One of my most favourite subjects! Always on the lookout for new tube types.



> 6SL7 is a more linear tube, than a 12AX7 ( which has spikes and dips in it's EQ )...



Could be in your circuit, but in general; no, not at all. There is no inherent difference in linearity in the most commonly used op point area of these tubes. Possible differences in EQ and linearity come from poorly matching the resistor values to the tube rp, and from poor output impedance. 12AX7 does have a bit higher rp and so if it is used to drive a load (such as a capacitor with parasitics or a hungry tube grid) it will do worse. A decent buffer solves this.



> Octals were more popular with hifi DIY'ers for RIAA phono preamps,
> because the 12AX7 is a horrible match with RIAA correction(!)..



Not in DIY circles, not at all. Where are you getting this?



> Smaller 9pin tubes may also be vunerable to problems such as cross talk between the two sections and the heater.



Possibly. Not in practise in my experience. At RF these things matters, not so much at audio frequencies.

Also the plates of the two sections are closer together because of the narrow confines of smaller tube...



> This was used to keep the two sections more isolated,
> which can also be especially useful for high frequency use or issues (oscilations)..



Yes these things do matter a bit, but the most significant difference with regards to oscillation is mu, which is distance of grid to cathode. Closer to cathode, higher mu, higher parasitics, higher coupling and chance of oscillation.



> Still, the smaller size and higher gain factor and headroom of the 12AX7 type increased its popularity over the Octals, in guitar amps in the '60's.



No. Guitar amps used 12AX7 because it was plentiful and cheap. It had become plentiful and cheap because of NFB. Early 1950's saw the onslaught of gNFB audio circuits, which necessitated a lot of gain. So, 12AX7 became hugely popular. Also it was hugely popular because it was the tube of choise for jukebox RIAA correctors, and jukeboxes became very common.



> But that's were advantages end and there more bad news ...
> The square plates in tubes,
> are found in the later (cheaper) constructed tube years, which
> is why they usually don't command as high a price as the rectangular
> or *"round plates"*.



Ah, tube electrode geometry! One of my most favourite subjects! 



> _*Round plates are more desireable*_ ...
> Although the round plates don't have as much maximum power handling as the rectangular or square plates of same type,
> the focus is sound quality...



It's not so simple as round = better and not round = not so good.

Some of the best tubes have all planar construction. Think of the directly heated classics; 45, 47, 300B, even the 2A3. 

Or, the most linear tube; 4P1L: all planar.

Then again, some of the most linear tubes also have all round construction (think especially directly heated transmitter tubes and also these small signal tubes you talk about here).

The most important thing for linearity is that the electrodes are the same form. The reason for this becomes obvious once you visualize what is going on inside the tube.




> The round plates have a more "even distribution" between the cathode, grid and plate,
> which improves the amplification quality and details of the tube...



What does this mean, I didn't understand?

Placing of the grid between cathode and anode determines mu of the tube. The closer the grid is to the cathode, the higher the mu. 

But, the closer you put the grid to the cathode, the more dense the grid wires must be. Each wire emits an electric field that is stronger near the wire and weakens when going outwards.

If you look at the electric field made by the grid assembly standing on the cathode; the further away the grid is, the more uniform the field is.

The closer to you the grid is, you begin to see weaker spots in the electric field: between the grid wires!

This causes the effect in the curves where when you go left, the curves are wide apart (each grid wire has a small negative charge, close to 0V, between the wires there are openings with almost no charge, many electrons rush thru them) and going right they bunch up (the openings close because of strong negative field from each wire).

Solution? Make the grid more dense. This causes massive grid current (electrons accidentally hit grid wires and get trapped in the grid node) and capacitive parasitics (capacitance is determined by the area of the grid relative to the area of the cathode; more wires means more area). These bring all kinds of nasty problems.

Real solution? Frame grids. Not made of wire, but one single piece, usually needs to be solid gold. Super thin with a mesh like texture, so maximum electric field coverage with maximum routes for electron stream to physically pass the grid without hitting it.

Frame grids allow the grid to be placed super close to the cathode, making some pretty extreme tubes such as 6E5P and D3a and the like. They still eat up A LOT of grid current though.



> Don't tell me, you already knew, lol



Indirectly heated small signal tubes usually have a round cathode, so as to heat it most effectively. I.e. the heater is about as close to all points of the cathode. This means for uniform geometry the plate should also be round.

The grid is not round though. Some transmitter tubes have round frame grid grids.

This is probably why the ultimate linear tubes such as 4P1L and 47 have all planar construction; each element, grid included, can be planar. Uniform.


So I guess, yes, I already knew. =) I'm being silly but I love tube geometry.


----------



## MrCurwen

> Sorry if i interrupt your discution .... hard for me to follow. I'm a future owner of a mk6+ and I was looking for tube.



Not at all, it is me who is interrupting so no need for you to apologize. Let me try to help you.



> I have ask the question on the mk6/mk8 thread, but someone told me to ask here for confirmation and explanation :
> Can it be a probleme to not have closely matched 6SL7 driver tube ? Around 15-17 % of differences between the anode ?



What do you mean a problem? What are your goals?

It will work just fine, just not with best sound quality.


----------



## gug42

Hello. Thank you to take time. Well i'd like to know the impact.
 I was thinking mostly about channel imbalance between left and right. But some ine says to me that the op will auto adjust.... Strang thing for me but why not ...


What did you mean by sound quality  ?  Please i need a little bit more explanation   

Thx


----------



## baronbeehive (May 23, 2017)

Maxx134 said:


> I have tested as many driver tubes as I could before I blew out my transformer heater coil output winding to get that opinion.
> So just recently I went online to see if any correlation to this,
> And  I found out that my findings actually did correlate to what was known already in general about some 9pins and Octal pin tubes.
> Specifically the tubes used for these amps driver stage...
> ...



Very nice work, I really like this experimetal approach.

You are right about the driver/power tube matching. My friend has a mix of RCA and Mullard EL34 power tubes which are quite thick, and JJ driver tubes, 12AX7's,which are very lively sounding. The combo works really well. When I replaced the JJ's with my favourite TS5751's, which are a bit more tubey it didn't work as well as on my other amp which has Amperex EL84 power tubes which are very clear sounding and the TS driver tube, and the JJ's were too SS sounding on mine.

I can check out the opamp as you suggest however I would have thought it would affect both right hand circuits not just one. I have not done anything yet because I'm still too busy and the amp is having to take second place for the moment.
Edit: Oh wait I didn't realise there was one opamp on each tube, sorry.

But coin is ready and waiting as soon as I can get around to it I think!!

Edit: Oh, and turtles are really great,  just waiting  to book my holiday in the  Galapagos!


----------



## baronbeehive

gug42 said:


> Hello. Thank you to take time. Well i'd like to know the impact.
> I was thinking mostly about channel imbalance between left and right. But some ine says to me that the op will auto adjust.... Strang thing for me but why not ...
> 
> 
> ...



You needn't worry as MrCurwen says it will work fine, and will autobias within limits. You are correct in that the only effect you might notice is channel imbalance which will affect the sound quality by making one channel louder than the other. More important is for the power tubes to be more closely matched.


----------



## Maxx134

MrCurwen said:


> One of my most favourite subjects! Always on the lookout for new tube types.
> 
> 
> 
> ...



Good stuff to digest,  thanks for info...
: popcorn:
 



MrCurwen said:


> What's your Ia?


Yes I wrote it in my notes I will find much later I have to go for now.


----------



## baronbeehive (May 23, 2017)

........ incidently I think that bit about the archbishop on page 1 should have been left in........... how can we mod without all the facts?


----------



## gug42

baronbeehive said:


> You needn't worry as MrCurwen says it will work fine, and will autobias within limits. You are correct in that the only effect you might notice is channel imbalance which will affect the sound quality by making one channel louder than the other. More important is for the power tubes to be more closely matched.



Thank you. Good news. Well 15% could be in thoses "limits" or not ?

I suppose channel imbalance could be compensed by equalizer or by my unbalanced ear (true by the way ) !


----------



## baronbeehive

gug42 said:


> Thank you. Good news. Well 15% could be in thoses "limits" or not ?
> 
> I suppose channel imbalance could be compensed by equalizer or by my unbalanced ear (true by the way ) !



If I remember right you're out by 5%, so not a problem!


----------



## gug42

Yes, generally admited that matched pair is under 10% of differences.
Thx


----------



## MrCurwen

If I recall correctly it's one envelope (one double triode) per tube, so that each tube section inside the envelope handles one phase of that channel.

That being the case, having a 15% mismatch in transconductance  (that is how tubes are matched) between two triodes that share an envelope will not be affecting channel balance, meaning relative volume between channels. Not at all.

It will affect linearity of that channel, meaning more gm mismatch -> more distortion. It's mostly 2H but as discussed above the NFB then spreads the harmonics around a bit. 

I get that gug42 you won't probably be understanding a lot of this stuff so let me make it clear; having a normal 10 to 15 % mismatch between triodes inside a double triode is not going to be the sound quality bottleneck of your amplifier. It is not good for the sound quality in objective terms, but some people even prefer mismatch and the distortion it causes. It's often called "tube sound". Whether or not this sounds good or bad to you, only you can tell. So try it out.


As an aside, the percentages are in fact gm, not mu. Gm does by proxy affect gain a little bit (depending on circuit), but not that much. Tubes are usually not matched by mu.

Most human ears are 100% ok with 10% or even more volume mismatch, they simply adjust to it. 30% or more, ok you might have a problem then.


----------



## MrCurwen

> If I recall correctly it's one envelope (one double triode) per tube, so that each tube section inside the envelope handles one phase of that channel.



What I meant to write was:

If I recall correctly it's one envelope (one double triode) per channel, so that each tube section inside the envelope handles one phase of that channel.


----------



## gug42 (May 29, 2017)

Hello,

@MrCuren : Thank you for thoses explanations. 
=> Internal mismatch can be more anoying than tube Left/Right mismatch 


Another point : Can you point me to a fan model that fit in ?  Need a 80x80x*20*
Noctua doesn't enter in 

Thx !


----------



## SonicTrance

Ive never seen a aftermarket 80x80x20 fan. Just get 25mm thick fans and mount them on the outside. Also get some taller feet to give them airflow. 
Preferably you should use bigger fans for lower noise and higher airflow. I use 120mm fans. Then you'll need to cut the bottom cover though.


----------



## SonicTrance (Jun 16, 2017)

I thought I'd make a post comparing the MK6 to my DIY project I've been building.
For the last year or so I've been experimenting and building @MrCurwen 's LTP design. It has been many ups and downs along the road but the amp is finally finished!

Granted, I've not heard many top dollar amps but this LTP is the best amp I've heard!. When comparing to the LD it practically blows it out the water. It's very resolving, transparent and non-fatiguing. The modded LD is also all of those things, but this is on another level! The LTP sounds cleaner, crisper yet very dynamic and real. The LD has a layer of dirt that the LTP don't have.

Tubes do only voltage amplification and cheap russian tubes sounds just as good as the premium audiophile tubes in this circuit!
All tubes have gyrator plate loads and CCS tails. B+ and B- are regulated.

Circuit goes like this:

Input LTP - grid drivers - output LTP - power buffer - OT/parafeed caps.

Schematics (@MrCurwen 's design):

Input stage:





Grid drivers:




Output stage:




Power buffer:


 

I can also share psu schems if someone is interested.

Pics of the completed amp:
Input stage:




Grid drivers:




Gyrators/CCS.




Output stage:




Power buffer:




Gyrators. I doubled up on their heatsinks in output stage as they need to dissipate about double wattage compared to input stage.











































If someone wants to build this design we can start a new thread. I encourage people to build it. It sounds amazing!


----------



## baronbeehive (May 27, 2017)

Fantastic Sonic, congratulations! Must be a great design of MrCurwen's.

That layer of dirt would be the NFB?

How much do you reckon it would cost?

Difficult to imagine any improvement on the SMLD but hey......

Edit: looks like there are 2 amps?

Has that design been implemented before now?


----------



## SonicTrance

baronbeehive said:


> Fantastic Sonic, congratulations! Must be a great design of MrCurwen's.


Thank you!




baronbeehive said:


> That layer of dirt would be the NFB?


Different designs. The LD needs feedback. This LTP does not. 



baronbeehive said:


> How much do you reckon it would cost?


The parts alone are not that expensive. I have used all russian film caps, which are cheap. And just regular lytics. As the psu is regulated and doesn't fluctuate with the signal, cap quality doesn't matter as they're not in the signal. I have not calculated how much I've spent on it. Most expensive part is probably my Elma 4 pole 24 way attenuator.



baronbeehive said:


> Difficult to imagine any improvement on the SMLD but hey......


Yes, I felt the same way! The LD is still very good, of course.



baronbeehive said:


> Edit: looks like there are 2 amps?


One input stage and one output stage. I have two separate chassis because my initial plan was to only build an input stage and hook that up to the LD output stage. But plans changed and I ended up building the complete amp and left the LD as is.
If I was going to build again from scratch I would probably have both input and output stage in one chassi and a separate chassi for the psu. I could never fit everything in one case, unless huge of course.



baronbeehive said:


> Has that design been implemented before now?


What do you mean?


----------



## baronbeehive (May 28, 2017)

That attenuator looks impressive, as does the whole amp I will leave the more technical aspects to others to comment on.

Excellent idea to separate the PSU chassis for noise isolation.

Could the input stage be bolted on to the LD then?

I meant, has this design been built by others, or just yourself?

BTW, does it still sound "tubey", what I mean is, is it liquid, and warm sounding, or just very transparent?


----------



## SonicTrance

baronbeehive said:


> Could the input stage be bolted on to the LD then?


Yes, you could build the input stage and connect it to the LD (output tube grid would be where you connect it)



baronbeehive said:


> I meant, has this design been built by others, or just yourself?


MrCurwen has obviously built it, and some others I believe.



baronbeehive said:


> BTW, does it still sound "tubey", what I mean is, is it liquid, and warm sounding, or just very transparent?


If by "tubey" you mean slow,  warm and creamy? Then, no. It sounds fast, punchy and clean. Very non-fatiguing. You hear it's a tube amp though as clean as SS. No harsness or other fatiguing sounds!


----------



## MrCurwen

SonicTrance said:


> Pics of the completed amp:



Wow the work quality is so much better than anything I've ever done. 

I'm a circuit design guy, not a chassis design guy, and these pictures sure drive the point home.



> That layer of dirt would be the NFB?



Sonic's reply is correct, it's not the NFB, it's a combination of many things. Basically it's just distortion, LD produces more distortion even with NFB. The reasons for this have been written out in this thread.



> I meant, has this design been built by others, or just yourself?



It's the same circuit that was inside the amp I linked a picture of here. Small black wooden shelf with two white chassis' (PSU & signal chassis) and black wooden open-top power buffer on top of the shelf. Different tubes only; Sonic didn't have space for directly heated tubes' filament supplies. TV sweep tubes (BEAM TETRODES, think about that, not even real triodes) are superbly linear though.

I've built it a number of times. One gentleman in Denmark has the schems and a lot of info, he wanted to build it to use with speakers only, but I haven't heard from him in some time.

My SE design is very similar in nature, but since it's much simpler more people have built it. One gentleman in Peru, one in South Carolina USA, one in Hong Kong. There may be others that simply built it from schems and never messaged me, I don't know.



> BTW, does it still sound "tubey", what I mean is, is it liquid, and warm sounding, or just very transparent?



Sonic gave his comment, mine is more pedantic; if the recording has a warm and liquid sound, then a truely transparent amp will reproduce the warmth and the liquidness. If the recording doesn't have these things, a transparent amp will not reproduce these things.

I'm guessing you are using 'transparent' to mean "low THD achieved via soul killing amounts of NFB". I object to that; the common english meaning of 'transparent' would be what I explained above.



> How much do you reckon it would cost?



Depends on how many FETs you burn during building and setup. Not kidding, they can easily make a serious dent in your budget.

Sonic went the elegant route with really good aesthetics, that increases cost. Also the stepped attenuator could be replaced with a 2.5 eur pot with not much harm. 

The power buffer at the output is not necessary, it is basically for "best results only" builder. The amp sounds (in my opinion) extremely good without it. 

The OT's in Sonics build are Hammond 125D if I recall correctly. My local shop doesn't carry them anymore (tragedy for me) but I paid 25 euros per piece for them originally. 

All in all if you cut some corners the design can be simplified (cheapened) a lot without too much loss of HIGH END POINTS. This build Sonic made is the ultimate version.


----------



## baronbeehive

MrCurwen said:


> ......
> 
> Sonic gave his comment, mine is more pedantic; if the recording has a warm and liquid sound, then a truely transparent amp will reproduce the warmth and the liquidness. If the recording doesn't have these things, a transparent amp will not reproduce these things.
> 
> ...



Sorry I was generalising after having used tube amps forever! Of course you are quite correct.



MrCurwen said:


> ......
> 
> .... This build Sonic made is the ultimate version.



Sure looks like it to me .


----------



## gug42

SonicTrance said:


> Ive never seen a aftermarket 80x80x20 fan. Just get 25mm thick fans and mount them on the outside. Also get some taller feet to give them airflow.
> Preferably you should use bigger fans for lower noise and higher airflow. I use 120mm fans. Then you'll need to cut the bottom cover though.


Ok sniff bad news 

@* SonicTrance  @MrCurwen *https://www.head-fi.org/f/members/mrcurwen.442227/
Wow Impressive peace of works ! Wishes I have a such amp !
https://www.head-fi.org/f/members/mrcurwen.442227/

Other subjects about super moding Little Dot mkVI+ : Any one try to add some outpout transformers on the mkVI+ ?


----------



## Maxx134 (May 31, 2017)

MrCurwen said:


> Ah, tube electrode geometry! One of my most favourite subjects!


Hi! I been away and nice surprises here..
I like to ask what you think about silver plates.
I realize it too general question so to specify,
I found that for my 12sl7, I feel the silver plate gave me better treble and air.

It not seem to make sense as I thought black plates were best.
For instance, my raytheon & kenrad with silver plate sounded better than the black kenrad and also Sylvania wich seemed a Touch less resolving,
So i am just curious if the silver plate helped, or maybe the year produced instead.





gug42 said:


> Yes, generally admited that matched pair is under 10% of differences.
> Thx





gug42 said:


> => Internal mismatch can be more anoying than tube Left/Right mismatch


I believe the MK6 & MK8 don't have to worry as the tube configured in common cathode circuit so the triodes within the tube are  forced to perform similar.







SonicTrance said:


> If someone wants to build this design we can start a new thread. I encourage people to build it. It sounds amazing!


Wow buddy how you keep all that majestic work from us?
Lol excellent work!
 I like the choice of tubes!
So how much power we talking here?
How is the soundstage?





MrCurwen said:


> This build Sonic made is the ultimate version.


Thats what I would do...
If your going to do a project, 
might as well go all in haha.


----------



## MrCurwen

> I like to ask what you think about silver plates.
> I realize it too general question so to specify,
> I found that for my 12sl7, I feel the silver plate gave me better treble and air.
> 
> ...



Material of the anode has 0.0% effect on sound quality, in any audio circuit.

It has an effect on longevity; different metals (or rather metal compositions) react differently to heat, some expand more than others. Also different metals store different amounts of residual gas; this gas is trapped inside the metal while the tube is constructed. Then it is released when the anode is heated during normal operation. This gas then disrupts the normal operation of the tube by attaching itself to either the grid or the cathode, changing their chemical composition, and thereby altering their electric behavior. This is normal ageing of the tube, leading to eventual end of life.

Some anode materials trap more gas than others. This effects tube reliability and lifetime, but not sound quality (while the tube is young in hours operated).

Two main routes of tube wear are

1) heat expansion warping the elements

2) gas damages.




> So i am just curious if the silver plate helped, or maybe the year produced instead.



The silver plate had no effect. The production year could have had an effect. Linearity is determined by tube geometry, construction and alignment of the electrodes, i.e. how regular is the grid wire pitch etc.



> So how much power we talking here?



Into a 4 ohm load (speakers) about 0.5W RMS, enough to fill a decent sized room to deafening sound levels with normal sensitivity speakers. Power is not an issue for headphones with any amp really, I think.



> I believe the MK6 & MK8 don't have to worry as the tube configured in common cathode circuit so the triodes within the tube are forced to perform similar.



Forced by what? There is 1.5 k ohms of impedance in the tail, let's say 250k to 350k impedance in each branch above the tail. What is the dominant component, is it the tail?



> I like the choice of tubes!



Even the beam tetrode?


----------



## gug42

Maxx134 said:


> Hi! I been away and nice surprises here..
> I like to ask what you think about silver plates.
> I realize it too general question so to specify,
> I found that for my 12sl7, I feel the silver plate gave me better treble and air.
> ...



Well from your local expert : for a same brand, it's more a matter of factory, production line and quality control ... 




> I believe the MK6 & MK8 don't have to worry as the tube configured in common cathode circuit so the triodes within the tube are  forced to perform similar.



Sorry ... I did'nt understand ... perhaps my english ... perhaps my knowledge


----------



## SonicTrance

MrCurwen said:


> Wow the work quality is so much better than anything I've ever done.
> 
> I'm a circuit design guy, not a chassis design guy, and these pictures sure drive the point home.


Thanks! Really appreciate it!



MrCurwen said:


> Depends on how many FETs you burn during building and setup. Not kidding, they can easily make a serious dent in your budget.


I've learned this the hard way! Ha! 



MrCurwen said:


> The power buffer at the output is not necessary, it is basically for "best results only" builder. The amp sounds (in my opinion) extremely good without it.


I agree it sounds great without the buffer. But I noticed a cleaner sound with the buffer so I wouldn't cheap out on that. Just my opinion.



MrCurwen said:


> Also the stepped attenuator could be replaced with a 2.5 eur pot with not much harm.


Remember you need a balanced 4 pole pot. They are usually stereo so you'd need one for each channel, which is a pain. Maybe there's cheap balanced pots, I haven't seen any? The pot could be completely taken out though, replaced by some resistors and then adjust volume digitally.



Maxx134 said:


> Lol excellent work!
> I like the choice of tubes!


Thanks, Maxx!
Yes, I experimented with some different tubes and ended up with this combo. The input stage takes either a pair of 6SN7's or two pairs of 6C5G/6J5G (with 20min of soldering it can take any input tube you wish, within limits of course) 
Output stage takes two pairs of 6BG6's or 6P7S's (pictured). I also experimented with EL36's which sounds just as good but I chose the bigger ST bottles as they're nicer looking, ha!

You may notice I have a empty socket in the middle of both stages. That's where the rectifier tube would go. I wanted to use a rectifier tube only for aesthetics. A rectifier tube will not have any impact on sound when followed by a reg as the voltage is constant and doesn't fluctuate.
I had severe oscillation problems and it turns out the rectifier tubes caused 95% of that oscillation for some reason. Which does not make much sense but I now use UF4007 diodes instead and oscillation is gone!  



Maxx134 said:


> How is the soundstage?


Compared to the LD I'd say it's wider and more realistic. As you know I'm kind of awful at describing sound with words. You really need to hear it!


----------



## MrCurwen

> I agree it sounds great without the buffer. But I noticed a cleaner sound with the buffer so I wouldn't cheap out on that. Just my opinion.



My whole design came out of the necessity of not wanting to buy expensive parts (especially OTs)! I am very cheap! I don't buy tubes that cost over 4 or maximum 5 euros per piece, I prefer tubes that cost 3 euros per piece.

Thus far there are two functioning builds of the whole things (with output buffer) and neither of them is in my own use. There are more builds without the output buffer. I really need to build one for myself also, I enjoyed the output buffer as well. 

But, it is not necessary for superb high end audio. I bring this point out to lower the threshold for inexperienced builders; leaving the buffer out simplifies things, think about PSUs etc. It is possible to add later also.

People who are not cheap like me, can also try buying better OTs. Once you have the output buffer there, OT quality is not important, but without it, you can improve sound by simply spending money on a better OT.



> Remember you need a balanced 4 pole pot. They are usually stereo so you'd need one for each channel, which is a pain. Maybe there's cheap balanced pots, I haven't seen any? The pot could be completely taken out though, replaced by some resistors and then adjust volume digitally.



Yes of course for balanced DAC output. I'm thinking about SE sources all the time. For SE input you can just use an Alpha double pot, but I do believe they cost more than 2.5 eur nowadays.



> Compared to the LD I'd say it's wider and more realistic



Distortion masks microdetail. Lower (open loop) distortion -> more detail, larger soundstage.


----------



## gug42

I'm a total newbe about amp conception, but well I'm really curious why anyone try to add outpout transformers to the mkVI+ ?
For some people it is the only "flaw"  of the mk6 ?


----------



## MrCurwen

> I'm a total newbe about amp conception, but well I'm really curious why anyone try to add outpout transformers to the mkVI+ ?



I assume you mean why anyone hasn't added OTs to the LD.

Why would anyone add OT's there? One of the main points of sale for the LD is that it's OTL. The same (or very similar, following the same retro style of circuit design) circuit with an OT wouldn't sound very good, whereas the LD sounds probably pretty decent.

If you can't drive an OT properly (because of retro), you'll achieve much better results by going OTL.



> For some people it is the only "flaw" of the mk6 ?



Really? Who? I find this hard to imagine.


----------



## gug42 (Jun 27, 2017)

Hello,

Sorry for my late reply : A french specialist told me that an amp with an output transform will drive more easely headphones with low/medium impedance BUT a good one is really expensive. And it would be better to have a well designed OTL than a cheap OT. Moreover, he told me than an OTL amp can't be converted to OT easely.

Ok well, now back to this thread 

About bias adjusting for 5998A : I have buy four 5998A and I'd like to adjust the bias.

At first, a point surprise me, the thread talk about vu metter @60 with 6080. Mine is around 75 with 6080. Is it important or not ?

The idea to use a switch really interest me. But can you give me more information or pics to do it please ?

On the first page, the red circle is around the caps but we are talking about resistors. 
Moreover I didn't see or imagine how to wire the switch, the old resistor and the new one together. On the photos there is too much things ... and I can't find any "story books" ( intermediate photos between steps).

Thank you in advance for your help.


----------



## gug42 (Jun 27, 2017)

Ok well I've re-read multiple time this stance :


> As the stock cathode resistors are on top side of the board it’s easier to connect the new ones on component side in parallel to the cathode bypass caps.



So well did I need to solder the resistors in parallele to the caps ? where I add the green circle ?






Thank you !



> - 4 x 330 ohm resistors, Mills MRA5
> - A 4 pole switch, the higher the voltage rating the better. Not too huge
> - Wire. I used 22awg silver plated copper with PTFE insulation. Decent size and easy to work with.


[/quote]


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## coinmaster (Jun 27, 2017)

> A french specialist told me that an amp with an output transform will drive more easely headphones with low/medium impedance BUT a good one is really expensive. And it would be better to have a well designed OTL than a cheap OT.


From a theory standpoint, I agree. Transformers have all kinds of inductance and capacitance and leakage currents and phase issues and the list goes on and on. Mr Curwen seems to think that because he has source followers driving them that all these issues go away.
I seriously doubt that, having a low impedance voltage follower helps but a voltage follower doesn't ignore the parasitics and having a low impedance only lessens the blow compared to a higher one.
Mr Curwen claims that driving it with a source follower makes it sound completely "transparent" but unless he compares his low end transformer to a high end one in his design then that is just an opinion.
If he insists on using a transformer output driver I would switch to an active current source buffer rather then a voltage one. At least a current buffer will ignore the parasitics in the transformer and it's the current that drives the transformer not the voltage. A voltage follower will produce a skewed current into such a load no matter how good it is which means a skewed current transfer.

On another note I spent the afternoon upgrading my MK6 since I had nothing else to do. I've spent the last year or so learning and designing I completely forgot the original mission of upgrading the MK6 to the ultimate verison of itself.
I implemented a mod that keeps the current between both the triodes in the WCF stages equal regardless of the load impedance at any frequency. It's basically a "perfect" version of the "impedance mod" The Impedance mod tries to optimize the WCF across as wide a frequency range as it can but mathmatically it is optimized for a single impedance so it only improves the averages of frequencies that it can perform well. My mod works at all frequencies no matter the load.
Thanks to John Brosky for helping me perfect this mod way back when I was first trying to solve this issue a year and a half ago, damn that feels so long ago now, I knew so much less about electronics then.
It's funny how quickly I came upon the solution after searching for it though, I was looking into the effects of using cathodes/plates as input with grids as feedback inputs and it turned out to be just what I was looking for. Although I just sat on it since then and never actually implemented it.
Here is a blog post he made about the circuit https://www.tubecad.com/2016/02/blog0339.htm

I'll update this post when I get a pic of the mod, I literally have no camera of any kind right now.

Sadly I only have my ipod to use for an input since my dac is fried but it sounds really good even in SE mode, can't wait to get a balanced dac again.
I spent a bit of time mixing tubes again, it's amazing how much of an improvement in sound there is when mixing tubes. In my current SE configuration the stock 6080s mixed with 6as7s seems to sound best although I have quite a few configurations left to try.
As usual mixing tubes between the slots of each channel reveals that one configuration is always far superior to the other, I still don't know why this can be since both triodes in each tubes are conducting current in series with each other, the only difference being which triode type conducts first.
Switching between the cheap russian stock input tube that came with the unit to my holy grail 6SN7 RP tubes reveal a life changing improvement in sound. The MK6 is truly a great distortion generation machine.

Next is to replace the 1.5k cathode resistor in the input stage with a current source, an extremely easy mod that should already be posted on the front page. I don't recall if the transformer can handle the increase from a few mA to 20+mA. I know it was posted somewhere in this thread, does anyone know the answer to this?
Upgrading the input stage load resistors to a gyrator or Mu follower is a slightly more annoying, I'll have to use some mu follower pcbs I have lying around for it, but other than upgrading the power supply to a super regulator or something (which I will probably do) I will have created the ultimate version of the MK6 strictly speaking.
If people care enough I might post a beginner friendly how-to guide. First let's get someone other than me to listen to these mods since amplifying an ipod in SE configuration isn't exactly the best benchmark of sound not to mention the fact that I haven't really listened to the MK6 in a long long time so I'm not the best person to give judgements upon its state of sound compared to many others here who I'm sure are much more intimately familiar with its sound using the current mods.


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## coinmaster (Jun 27, 2017)

This new mod is awesome. Can't stop listening to it, even amplifying a grainy,hazy sounding ipod it's like sweet sweet candy to my ears. Euphonic heaven. It's like a continuous "high" in my brain, this is why distortion rules. I wish I had a distortion analyzer so I can do tests on harmonic structure vs euphony.


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## coinmaster (Jun 28, 2017)

So this is what a permanent orgasm feels like..




6 hours later and I still can't get the goofy smile off my face. It's like sugar and chocolate being poured all over my brain.


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## Maxx134 (Jun 28, 2017)

coinmaster said:


> Next is to replace the 1.5k cathode resistor in the input stage with a current source, an extremely easy mod that should already be posted on the front page.


I remember you stating this and was interested & planning to try this specific mod you suggested,
As MrCurwen stated in past the non optimal low resistance, but we needed the bias up and only way was to actually lower that cathode resistor even more,
which surprisingly sounded much better anyways as the tube bias point was increased to much better linear higher setting.




coinmaster said:


> I implemented a mod that keeps the current between both the triodes in the WCF stages equal regardless of the load impedance at any frequency. It's basically a "perfect" version of the "impedance mod" The Impedance mod tries to optimize



I have my impedance mod set to one setting because of my choice of low impedance headphones,
 and so never got around to implementing the switch I made, like member SonicTrance did.

So I am curious to know about your mod.
 If it can be combined with resistor settings
or is a total replacement of the static resistors selection with switch.

Looks like two SS devices to implement on top and bottom of the WCF, essentially replacing the anode and cathode resistors??


----------



## gug42

Hello, 

What's new mod  ? 
And please can you check the soldering point for resistors for the 5998 mods ?


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## Maxx134 (Jun 28, 2017)

gug42 said:


> Hello,
> 
> What's new mod  ?
> And please can you check the soldering point for resistors for the 5998 mods ?


I assume you are referring to the output tube bias switch mod,
As I do not think we posted the output impedance switch mod?

Yes there are two switch mods.
The bottom plate switch mod is for the optimal output tube bias points,
And adjusts by adding parallel resistor to the cathode resistor.

The Cathode resistors are in parallel to the Cathode bypass caps, so the actual soldering points are same points that the cathode bypass caps are on component side.
They are the blue caps on the original board.
Use those points.
The switch is 4 pole, so 4 separate switches inside.
Each switch connected in series with the new additional 330ohm resistor and that  goes across each cap so solder points are the cap leads


There should have been posted a schematic to make it easier but I didn't post it.
That is SonicTrance mod.
He was able to get the optimal values for the MK6 two powertube selections.

You can try PM him for any detailed info.
Goodluck and nice to see another ok interested member.


----------



## coinmaster (Jun 28, 2017)

> So I am curious to know about your mod.
> If it can be combined with resistor settings
> or is a total replacement of the static resistors selection with switch.


The mod replaces the resistors. It forgoes the sense resistor all together and balances the whole thing in a different and better way with lots of extra bonuses. So it's not really a WCF anymore.
The current sharing between the triodes is equal regardless of the load assuming your cathode resistor is close to the optimum value for the tubes you are using.
So it's like having every value resistor in the "impedance mod" all at once, effectively.

I soldered together little discreet "modules" and put them in place of the resistors. It's doable for beginners, it would just require a step by step guide.

Maxx what current are you using on your input tubes? Before I place a current source in there I wana make sure I won't blow the transformer.


----------



## gug42

Hello,

Thank you. 
Yes I was talking about the bias point.  Thank you for the complement of information.
Ok that basicly I was right, the soldering point are in green in my pics 
For me the switch is a little refinement, I surely can live without it if I am lazy 

By the way If you have any schematics of the little dot mkVI+, I'am really interested. Because I could show it to a friend 


Regards,





Maxx134 said:


> I assume you are referring to the output tube bias switch mod,
> As I do not think we posted the output impedance switch mod?
> 
> Yes there are two switch mods.
> ...


----------



## gug42 (Jun 28, 2017)

And moreover can I use other resistors than "Mills MRA5" ? Have you some references ?
I found them here :
http://www.soniccraft.com/product_info.php/330-ohm-mills-mra-p-599
or
http://www.partsconnexion.com/resistors_mills_mra5.html#19160

Any recommandation please ?


----------



## Maxx134

For resistors, there's so many choices..
I picked mills mr5 mainly because its a non-inductive wirewound which can handle stress/heat/surge much better than crap fake weak metal films,  and cheapo heat/noise carbon ones, 
But the issue is nit picking.
You should just pick whichever ones you want as it's your choice and the sound choice is yours. Nothing is really bad when your tubes will be much greater difference


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## gug42 (Jun 28, 2017)

I have look at mousers and digikeys ... so many choice (in 330Ohms / 5W) ... I'm totaly lost ... so I prefer to take the references already tested 
Ok found it in europe, so no question, i will take them 
https://www.hificollective.co.uk/catalog/mra05235-mra05-mills-resistor-p-8163.html

Well need a 4 pole switchs now


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## Maxx134 (Jun 28, 2017)

Redge78 said:


> As the stock cathode resistors are on top side of the board it’s easier to connect the new ones on component side in parallel to the cathode bypass caps.


See here it was already describe how to connect that bias mod.

Since I only using one type powertube, I not need a switch and just reduced my cathode resistor to increase my bias as well.

I will look up the details in my notes.
Basically the setting made my powertubes sound better, with more life and holography.
I assume the designer chose to go for lowest good bias setting for longevity of tubes and heat consideration.



coinmaster said:


> Maxx what current are you using on your input tubes? Before I place a current source in there I wana make sure I won't blow the transformer.


Ok I will go check my notes but SonicTrance posted the Transformer winding schematic way back..


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## Maxx134 (Jun 28, 2017)

gug42 said:


> I have look at mousers and digikeys ... so many choice (in 330Ohms / 5W) ... I'm totaly lost ... so I prefer to take the references already tested


Oh, I forgot to state that most other resistors of same watt as the Mills will be much fatter/larger,

So I would just go for the slimmest which is the ones suggested ( Mill MRA5)...


----------



## SonicTrance

coinmaster said:


> Before I place a current source in there I wana make sure I won't blow the transformer.





 

You have 50mA to play with in the driver stage psu. I don't think you'll have much voltage left if you pull 50mA though.


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## gug42 (Jun 28, 2017)

Maxx134 said:


> See here it was already describe how to connect that bias mod.
> 
> Since I only using one type powertube, I not need a switch and just reduced my cathode resistor to increase my bias as well.
> 
> ...



You mean for 5998A or 7236 powertubes ?
Well I have buy two quad of 5998A ... so I'm really interested by this mod   (but don't want to cook my amp of course )

A switch to swap between 5998A and 6AS7G could be a nice to have, but :

For now, I like the tung-sol 6AS7G black plates ... but well when I will heard 5998A, did I use again 6AS7G or 6080 ? ... good question !
Perphas a simple wire between the resistor and the caps  could do the tricks : when I want to back to 6AS7G I just remove a soldering point on the wire ... more easy than wiring a switch for sure.



Maxx134 said:


> Oh, I forgot to state that most other resistors of same watt as the Mills will be much fatter/larger,
> 
> So I would just go for the slimmest which is the ones suggested ( Mill MRA5)...



Ok Thank. I found an Europe reseller :
https://www.hificollective.co.uk/catalog/mra05235-mra05-mills-resistor-p-8163.html


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## Maxx134 (Jun 28, 2017)

SonicTrance said:


> You have 50mA to play with in the driver stage psu. I don't think you'll have much voltage left if you pull 50mA though.



That seems like enough t play with.

As I recall, the bias on the driver tubes were extremely lower than ideal,
So me and Sonic were testing higher bias points and we came up with similar settings.
I had my cathode around 1k ohm while I believe Sonic you went further down to 800ohm or 500ohm?

My plate settings I think were similar but also a bit higher than yours.
I have my plate resistance down from 220k to around 70k

So 70k ohm plate and 1kohm Cathode was sweet spot for my driver stage,
But for MK6 using different power tubes, (so a different input matching between stages)
 I believe SonicTrance even lower resistor settings for a higher bias point on the driver tubes were more benificial for him due to his different tube choice of ecc35 I think.

We did this to bring bias setting to more linear part of its curve.

Anyways I believe we pushing driver tubes at around 2ma current each so there should be room for the current source circuit that Coinmaster mentioned..


----------



## gug42

Well another question, this time about coupling mod caps : 
In the little dot mkVI+, I didn't see any "small black "SCR PB" cap" for the coupling cap. I only see a pink little box cap, am I right ?
Is there still a huge improvement to change this little pink box cap ? I suppose it could be tricky (or long time taking) because I need to unmount the all pcb ?

Regards,


----------



## gug42

Maxx134 said:


> That seems like enough t play with.
> 
> As I recall, the bias on the driver tubes were extremely lower than ideal,
> So me and Sonic were testing higher bias points and we came up with similar settings.
> ...



Oh really ? Sorry to ask so quickly, did you have modify it ? Any big improuvement ?

Thx


----------



## coinmaster

> You have 50mA to play with in the driver stage psu. I don't think you'll have much voltage left if you pull 50mA though.


 Yeah plus the regulation will be worse as the current goes up since it's just a CRCR filter. Which reminds me I need to put a regulator there in order for it to be respectable. Luckily I have a shunt reg sitting around that is already set to 150v. 
I guess I'll go wire up that current source in a few minutes and see whats up.


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## Maxx134 (Jun 28, 2017)

gug42 said:


> Oh really ? Sorry to ask so quickly, did you have modify it ? Any big improuvement ?
> 
> Thx


Stock driver circuit has tubes running at very low bias points,
Using high resistance values.
220k ohm anode/plate
1.5k ohm Cathode

The increased driver tube bias changes I noted in previous post,
 were our optimal bias settings for the limited PSU voltage we have.

Of course the change made everything better...
in terms of sound and linearity and liveliness and holography..
We did not post this mod yet.

Also I like to see how the "Current source" added in place of the cahode resistor works out, because of the benifits of high Cathode impedance to force the two  triodes to behave similar while adjusting optimal bias point better.
So it would replace my low resistor settings..

Anyways 
yes, all the mods may require you to open and pull out board,

So think hard your own strategy on what mods you want to and plan ahead accordingly to get as much done so you won't have to pull out board so much.





coinmaster said:


> Yeah plus the regulation will be worse as the current goes up since it's just a CRCR filter. Which reminds me I need to put a regulator there in order for it to be respectable. Luckily I have a shunt reg sitting around that is already set to 150v.
> I guess I'll go wire up that current source in a few minutes and see whats up.


Wait a minute, as I recall my own measurements there was over 190v from the PSU to the anode resistors so your regulator may not be optimal..


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## SonicTrance (Jun 28, 2017)

Maxx134 said:


> I believe SonicTrance even lower resistor settings for a higher bias point on the driver tubes were more benificial for him due to his different tube choice of ecc35 I think.


These are the settings I ended up with for the ECC35's. Major sound improvement over stock 220K Ra and 1K5 Rk.
*
ECC35*

*Ra: 33K
Rk: 390R*

Rail: 169,0V
Plates: 124,7V, 124,5V
Rk drop: 1,020V
Ia: 1.3mA




Same settings for the 6SN7, see the rail voltage drop when you start pulling more current:

*6SN7W:*

*Ra: 33K*
*Rk: 390R*

Rail: 143,5V
Plates: 70,5V, 66,7V & 65,6V, 71,1V
Ra drop: 73,3V, 76,9V & 77,9V, 72,3V
Rk drop: 1,77V & 1,78V
Ia: 2.27mA


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## gug42 (Jun 28, 2017)

Hello,

Wow really interesting indeed !!
If you get a camera and have some time, a friendly guide would be really appreciate 
(perhpas a big blue circle around the resistors to change on one of the pics of the  fist parge could be really appreciate and enough to do the trick)

I suppose you use mills ra5 resistors again ?

Ok well I will read all the thread, but for me, 3 mods I'd like to do by proprity order :
- 5998A bias current mods with a 330 Ohms resistors in //
- Adjust the bias on the driver tubes
- Changing the coupling

Well this we I will try to mix the thomson csf 6080 and the Tung Sol 6AS7G to heard what could appends 

Thank you !


----------



## SonicTrance

gug42 said:


> If you get a camera and have some time, a friendly guide would be really appreciate
> (perhpas a big blue circle around the resistors to change on one of the pics of the fist parge could be really appreciate and enough to do the trick)



I'll repost some of my pics for you. You can find them here: https://www.head-fi.org/f/threads/l...re-on-first-page.782183/page-23#post-12052225





Here are the Plate R's. They're TKD 2W metal film.





Cathode resistor is the z-foil to the right (1K5). I believe I use Takman there now. That that important.


----------



## coinmaster

Maxx134 said:


> Also I like to see how the "Current source" added in place of the cahode resistor works out, because of the benifits of high Cathode impedance to force the two triodes to behave similar while adjusting optimal bias point better.
> So it would replace my low resistor settings..


They won't behave similar with a current source tail alone, they will just behave _more_ similar because it's easier to match curves horizontally.

I just implemented the current source mod, it only took like 3 minutes to build and install. unfortunately I totally forgot that the load resistors are 220k and my current source was set to 10ma which would require a 2.2KV supply. I don't really know what current it was running at since the load resistors were choking it but I will say the sound was cleaner and overall improved regardless, because I quickly swapped the 1.5k resistors back in and it sounded dirtier and lower volume.

It's been a long while since I even thought about the MK6 so I totally forgot that a sufficient current source can't be implemented without a gyrator or mu follower as well. It would take me an hour or so to build and implement but I'm afraid of fixing what isn't broken. Currently the amp is amazingly euphonic. The euphony isn't frequency dependent either it's like a passive "something" in the sound that just gives me a "high". A distortion analyzer would be really nice to have right now so I can log the harmonic structure and maybe figure out what harmonics are having play in this.
The euphonic distortion is actually a result of a very specific tube configuration I'm using right now. I'm mixing 6080Wa tubes with 5998s in the output and using 6H9C tubes in the input.



> Wait a minute, as I recall my own measurements there was over 190v from the PSU to the anode resistors so your regulator may not be optimal..


The supply should sit at around 200v, so if I tweak the shunt reg for like 180 or something that gives 30v headroom for the input stage if I run the tubes at 150v. I just remembered that I literally don't have any more mosfets to use, I'm running of stock on a lot of things.
So I can't make anything if I wanted to. If someone with 250v+ N channel mosfets, some spare film capacitors and assorted resistors lying around I can instruct via skype, it's simple and easy to make.


----------



## coinmaster

> Well this we I will try to mix the thomson csf 6080 and the Tung Sol 6AS7G


Just remember when mixing output tubes there is always a "wrong" configuration, as in it will sound a lot worse  in X Y configuration then in Y X configuration so try both positions.


----------



## SonicTrance

coinmaster said:


> Just remember when mixing output tubes there is always a "wrong" configuration, as in it will sound a lot worse in X Y configuration then in Y X configuration so try both positions.


And definitely don't mix 5998 and 6AS7/6080 after doing the 5998 bias mod. Running 6AS7 with 165 ohms cathode resistance would be running the tube at about 120mA. Won't hurt the tube but the MK6 would overheat very quickly.


----------



## coinmaster

Yeah that would be bad.
My new mod would fix that issue since the cathode/anode voltage would remain constant regardless of the tube implemented.


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## gug42 (Jun 28, 2017)

Thank you a lot !

I will abuse of your knowledge  

- why not use evry where mills resistor ?
- when you talk about takman resistor in place of z-foil, did thoses one ?
https://www.hificollective.co.uk/components/takman_resistors_metal.html
- strange Z-Foil are realy expensive, dunno why
https://www.hificollective.co.uk/components/car_resistors.html



Ok, for now my top rating mod for me will be :
1/ 5998 Bias mod without switch
2/ The latest driver bias mod
3/ Changing if I can the coupling cap. <= Did you know if I can only change the caps without adding stuff around it ? Any cap recommendation for  one to one replacement ?

Any opinion about them ? Any other really efficient mods ?
Perhaps replace the fuse on the board ?

Thank you !





SonicTrance said:


> I'll repost some of my pics for you. You can find them here: https://www.head-fi.org/f/threads/l...re-on-first-page.782183/page-23#post-12052225
> 
> 
> 
> ...


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## coinmaster (Jun 28, 2017)

Personally I would hold out on all of those mods until the people of the thread decide what to do with my current mods, which are all major improvements over the existing ones.
From an sound improvement perspective upgrading the power supply is likely to be your biggest game changer along with the interstage cap upgrade. Just buy the jupiter PIO caps and be done with it. Or go crazy and buy duelund cast caps like I did. Don't bother with the mundorf crap.


But the power supply is crap and is a high priority for upgrade, it's one of the if not the biggest bottlenecks in the sound of the amp from stock.
Unfortunately I had to use gigantic high value film caps to really get a respectable result from the power supply upgrade. The optimal capacitive value of the PS caps would probably be something like 100,000uf to be on par with a decent regulator which aint never gunna happen
Therefore a regulator would be the best option. Now that I think about it something like Mr Curwens simple two transistor regulator could be easily rigged into the power supply, just replace the zener with a mosfet and a couple resistors and a capacitor., it wouldn't be an ideal supply but if the amp is being run balanced then it would be sufficient enough to bring the power supply output impedance pretty low, at least much lower then it was and it would be easy to implement.
If the tubes were all perfectly matched then the power supply would be ideal without the need for a regulator since in balanced mode the currents cancel each other out but alas that isn't the case. This is why the amp sounds better in balanced then in SE (which is sad because I don't have a dac anymore  )
I'd prefer if someone volunteered to test these mods out, I could apply them easily but I don't think my opinion is as relevant as someone like Maxx or Sonic because they are more intimately familiar with the sonic traits of the existing mods then I am so they can better compare.
I've no doubt that my proposed mods will improve sound quality so simply saying "it sounds really good" doesn't offer much.
I could show whoever volunteers how to do it over skype.


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## gug42 (Jun 28, 2017)

Hello,

I found your opinion really right : find the worst composent and upgrade it.
But well, for my part
- I've lost the mathematical ability to do it  and don't have the time and will to get it again
- Not lot's of time, so I'd like to do simple and quick win modification  with some aftermarket stuff

Moreover, from what I read, buying a  balanced  DAC could be a big improvement ... for now I use a modi multibit ... Probably my next dac could be the Ares R2R.

Well on a french forum, some quick win :
- Replace the 3 fuses by some high quality (Padis fuse)
- Replace the coupling cap by PIO K75-10 en 0.33µF
    => but I want to be sure where is the place of this cap on the mk6 .... On the pics Ididnt see any more the ping cap boxes on the 0,22 / 250v slot between AOP and gain switch ... Is it here ? Can you confirm me this point please  ?  Well If you have better cap, juniper references for exemple, i'm interested.

Some more operations but simple one :
- Replace the chemical 330 µF by PIO  or propylos
- Add decouplings caps (red arrow) but you already now that mods 
- Mills RA5 seems to be a very good resistors !


About quick wins, what I read about bias point convince me : simple and efficient.
So this two mods seems to be quick win :
- use 5998A / 7236 tubes, and adjust the bias by adding a resistor (really simple to do because don't need to unmount evrything)
- replace some resistor to adjust the bias for 6SL7.
- use better resisotr

Well on exploring stuff from the french forum :
- Put 8x Wima DC-link en 200 µF for output cap ... well to much work for me

But bad thing ... I don't understand half of what they speak  ...


And from this thread a schema of the mk8 :
https://drive.google.com/file/d/0BzC3Mc-BjWN6Q2tDMDYzTTZMVUE/view
http://forum.elektor.com/download/file.php?id=2703096&mode=view

And about some other repors :
- Rise the alimentation caps
- Replace half of the cehmical cap by some Mundorf M-lytic HC (less F capacity), sound could be better
- Replace the other half chemical by big polypro Wima DC-Link : better end

If anyone want to read french stuff :
http://forum.elektor.com/viewtopic.php?f=223119&t=2710181
-


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## coinmaster (Jun 28, 2017)

If your not using a balanced dac then that should be your highest priority. Balanced operation provides the biggest upgrade to the performance of the power supply and lowers the distortion while increasing the power. It may be the biggest upgrade you can do initially.
Don't bother with fuse upgrades. I wire my amps together with the crappiest wire imaginable and still get amazing results. Not saying that wire definitively can't make a difference but it's the lowest priority of upgrade.
For the coupling caps just get jupiter PIO, they are considered to sound close to duelunds and duelunds are the best of the best.
Don't bother with decoupling caps if you plan on going balanced operation, the audible difference will be slight if any.
If you want ease and bang for buck just get a balanced dac, get better coupling caps, and use a current source tail on the input stage to some low Ma value. Personally I haven't found upgrading the power supply caps to be that worth it without using film caps and film caps are massive so it's not a simple easy mod.


----------



## gug42 (Jun 28, 2017)

Thank you !
Ok I will go that way   (appart i will add the 5998A bias mods).
But I'm not really sure where are the coupling caps ... if a good soul can point them on pic, i will really apreciate 

Well if you have any opinion about theses DAC are possible :
- DENAFRIPS ARES R2R DAC : 760€ here. possibly the best cost effective dac around
- schiit Gungnir Multibit : 1350€


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## coinmaster (Jun 28, 2017)

Personally I would go with http://www.audio-gd.com/Pro/dac/NFB1.38/NFB1.38EN.htm
Audio-GD is world renowned for their stuff and they put a lot of attention into their power supplies. Plus you get chinese prices for high quality goods.
If the DENAFRIPS ARES R2R DAC  is really 760€ then I wouldn't buy it over the NFB1 since the NBF1 is using the best dac chip available and even at chinese prices it costs nearly the same at $750 there's no fancy features it's just a DAC.
The DENAFRIPS ARES R2R looks like a lot of the cost went into features, not a good sign.

Also if I were you I'd try mixing the 6080s with the 5998s before appling the bias mod.
The order of installment from left to right being  6080/5998/6080/5998


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## gug42 (Jun 28, 2017)

Really another good competitor : 875€ from a local seller ... You may have right.
Well i found R2R beautiful looking ... but it's not the main purpose here.



> Also if I were you I'd try mixing the 6080s with the 5998s before appling the bias mod.
> The order of installment from left to right being 6080/5998/6080/5998



Thank you ! I will try !


----------



## gug42

Please can you explain (or translate) this sentence : "use a current source tail on the input stage to some low Ma value." ?
Really i don't understand, sorry


----------



## coinmaster

Replace the cathode resistor with a 10M45S that has a resistor soldered between gate and source. It takes minutes to build and install, easy peasy.


----------



## baronbeehive (Jun 28, 2017)

coinmaster said:


> .............. amplifying an ipod in SE configuration isn't exactly the best benchmark of sound not to mention the fact that I haven't really listened to the MK6 in a long long time so I'm not the best person to give judgements upon its state of sound compared to many others here who I'm sure are much more intimately familiar with its sound using the current mods.



You are right... an ipod definitely IS NOT a good benchmark. I used to use one before I got a proper source and at the time I quite liked it, but changing to a good source made a world of difference. The frequency spectrum was now flat, not artificially boosted in the bass or treble regions like it is to get a half decent sound out of an ipod - a contradiction in terms since ipod users are not supposed to be interested in SQ, only listening to the latest music stream while making to wherever they are going.....

...so for your mod to sound good from an ipod... it must be pretty amazing lol!


----------



## coinmaster

> ...so for your mod to sound good from an ipod... it must be pretty amazing lol!


I was foolish enough not to listen to the amp before I modded it, so I really don't know the exact difference in sound, but yeah I'm impressed too. The sound is hazy and almost LF but there's "something" in the sound that gives a passive euphony.
I'm not sure how much of it has to do with the mod and how much has to do with my tubes.
Unfortunately after 6 hours of listening last night I felt a sharp spike of pain in my left ear, it seems even though it's been like 2 years since i severely injured my ear at a concert my ear till isn't healed yet. My left ear may be permanently damaged. It's been 1.5 years since I sat down and listened to my headphones for any reasonable length of time and it still isn't healed.
Unfortunately this means I can't listen to my headphones for a few weeks at least, I don't want to take any chances. Damn it all.


Other than using an ipod and using SE configuration my only headphones, the HD800s are damaged, the frequency response is awry in the bass and at around 15k and bass rattles in the left ear. The left driver is particularly jacked up. So much money down the drain because I never bothered to get a proper lab power supply. Don't repeat my mistakes, if you start designing electronics do it the right way, get a good programmable lab supply and use solderless breadboards for typical circuits. I've rigged some of my tubes to fit into the solderless breadboard slots now as well, but I've run out of component stock to actually build much of anything right now ironically. I need like 900 bucks to continue my quest. The MK6 is nothing compared to the amp I've spent the last year designing. For the brief time I had a earlier prototype version up and running it completely obliterated the MK6 in all aspects. Now If I can just master the art of distortion generation I will be the king. I think the MK6 is an excellent device for studying euphonic distortion for when I manage to get my hands on a distortion analyzer.
My core philosophy is that an amp should sound both euphonic and extremely realistic, usually a contradiction but my original MK6 mod had these traits, it was perfection. At least until I realized that from an engineering perspective it still could be improved greatly.


----------



## coinmaster (Jun 28, 2017)

Here's a couple pictures of the mod 

 


Kind of a messy implementation but I'm not known for elegance. I'm sure Maxx could make it clean as a whistle.

Here's a pic of the current source tail for the input stage

If you want to use it without using a mu follower instead of plate resistors then you can just use a resistor to meet whatever current value you expect to use, it should still be an audible improvement over a resistor. Just don't expect to get more then a few mA without replacing the plate resistors.


----------



## Maxx134

SonicTrance said:


> the ECC35's. Major sound improvement over stock 220K Ra and 1K5 Rk


Yep and I was going to try your values when I blew my Transformer due to an unrelated driver tube adapter..




gug42 said:


> Ok well I will read all the thread, but for me, 3 mods I'd like to do by proprity order :
> - 5998A bias current mods with a 330 Ohms resistors in //
> - Adjust the bias on the driver tubes
> - Changing the coupling


Those should be best and easiest to try without need of pulling out board.

If you do pull out board take pics of wires to board,
As the stock wiring of the regulators may break off from board.



SonicTrance said:


> Cathode resistor is the z-foil to the right (1K5). I believe I use Takman there now. That that important.


How the hell you get those zfoils to look so perfectly installed?!?!



coinmaster said:


> Kind of a messy implementation but I'm not known for elegance. I'm sure Maxx could make it clean as a whistle.


No way, look at SonicTrance work above!



coinmaster said:


> Just buy the jupiter PIO caps and be done with it. ... Don't bother with the mundorf crap.


I agree here.
I only recommend copper foil caps for coupling caps.




coinmaster said:


> Just don't expect to get more then a few mA without replacing the plate resistors


.
We dont need more than 2 ma currently


----------



## Maxx134

coinmaster said:


> Replace the cathode resistor with a 10M45S that has a resistor soldered between gate and source. It takes minutes to build and install, easy peasy.


I will look into parts needed for that ,
As I plan to try,

but would like to also see a schematic or parts list of the other mod for the powerubebstage.


----------



## gug42 (Jun 29, 2017)

Thank you everyone for your advise and explanation !
I resume my point, mods and questions here.

Ok I'd like to do thoses mods :

*Changing coupling caps*
Please can you point me with a big green circle *where as they on the board *? I didn't find any black SCR capacitor ... For me they was replace by some chemical pink boxes capacitor ...? Blue cirle on this photos : https://cdn.head-fi.org/g/9934408_l.jpg

Can I use K75-10 500V 0,33 uF ? Well perhaps the jupiter PIO JCW-080 could be the best but 70€ each one (0,33uF version)... 

Or is It better to use 0,43 uF or higher capacity ?

Stuff : https://www.hificollective.co.uk/catalog/jcw070-033uf-600vdc-jupiter-copper-foil-paper-p-9972.html or https://tubes-store.com/product_info.php?cPath=35_41_84&products_id=439


*5998A bias mods *
Material needed : 4 resistors mills RA5 330 Ohms https://www.hificollective.co.uk/catalog/mra05235-mra05-mills-resistor-p-8163.html

Mount resistor in parallel of cathode bypass caps, red circle on this picture : https://cdn.head-fi.org/a/8680852.jpg
Mount one in vertical position on a side and wire it to the other side. Easy to do.


*Driver bias mods *
Material needed* : *
4 x TDK 2W 33KOhms metal film : https://www.hificollective.co.uk/catalog/cm2510-correctohm-metal-film-resistor-p-9651.html

6x Charcroft Z-Foil 0,4W  390 Ohms : https://www.hificollective.co.uk/catalog/car200-390r-charcroft-zfoil-resistor-p-5049.html
You mention takman resistor ? but well sorry to ask which one ? https://www.hificollective.co.uk/catalog/rey50280-390r-takman-metal-film-resistor-p-4840.html

Replace Z-foil 1,5K Ohms by 390 Ohms   Image here : https://cdn.head-fi.org/a/7963645_thumb.jpg
Replace 220KOhms Resistor by TDK 2 W 33KOhmsmetal film Image here : https://cdn.head-fi.org/a/7963651_thumb.jpg


*Replace the cathode resistor with a 10M45S*
Please can you point me on the PCB where it is ?


Perphaps changing the fuse : simple operation. From a french guy, not day and night but can be heard
*=> *And  you mention the ability to thoses modes without pulling the board .... how did you change resistors and capacitors from the front of the board ?


Thank you everyone !


----------



## gug42 (Jun 29, 2017)

My bad ... there was a pic on first page 
WCF is for White Cathod Follow.

The bad news is : I don't see how to replace them without unmount evrything and pull the board out.



> *
> MK6 Overview :*
> 
> 
> ...


----------



## baronbeehive

gug42 said:


> Thank you everyone for your advise and explanation !
> I resume my point, mods and questions here.
> 
> Ok I'd like to do thoses mods :
> ...



Hi gug42!

Coupling caps are the pink ones you mention in the blue circle.
You can use K75-10 500V 0.33uF, 0.47uF is probably best but you can go higher to about 0.68uF. Best bass response is probably around 0.47uF. You could also use Audyn True Copper for the very best sound, cheaper than Jupiter but very big. If so you need to see about extending the bottom of the chassis.



gug42 said:


> ......
> 
> *5998A bias mods *
> Material needed : 4 resistors mills RA5 330 Ohms https://www.hificollective.co.uk/catalog/mra05235-mra05-mills-resistor-p-8163.html
> ...



You need 4 Mills mra05 330R here: https://www.hificollective.co.uk/(MRA05-330) - 330R 5W MRA05 Mills Resistor
Yes mount in parallel to cathode bypass caps in red circle as you said using 4 pole switch.



gug42 said:


> ......
> 
> 
> *Driver bias mods *
> ...



You need 4 TKD 220K 2W here: https://www.hificollective.co.uk/catalog/cm2610-220k-correctohm-metal-film-resistor-p-9712.html
Replace them in the position you say, correct in picture.

I don't know about the Z-foils or Takman resistors.



gug42 said:


> ......
> 
> *Replace the cathode resistor with a 10M45S*
> 
> ...



I think you mean cathode bypass cap as there is a separate cathode power resistor which we are not talking about here. The cathode bypass caps are in red in the picture.
I don't know what you mean by a 10M45S

Yes, change the fuses by all means, you never know if it might make a difference.

You need to solder parts from the reverse of the board so you will need to remove it by unscrewing the screws and the nut holding the pot and gently wiggling the board away from the pot and at the same time pressing the tube sockets out. Be carefull when you have got it out because the wires on the reverse can easily break.
When you put the board back check that the wires are still in place and use a screwdriver in the tube socket holes to pull the board back in position. This is very tricky and has us all swearing lol.....

Good luck and before you are ready you can let us know a final version of your parts to check everything is OK!

Hey guys gug42 has WIMA coupling caps in his LD!


----------



## MrCurwen

> Perphaps changing the fuse : simple operation. From a french guy, not day and night but can be heard



Are you being serious?


----------



## baronbeehive (Jun 29, 2017)

MrCurwen said:


> Are you being serious?



Ha, ha, probably not I think!

Edit: Of course the fuses need to be put in the right way round...... also joking.. probably!


----------



## baronbeehive

BTW gug42 you might like to think about replacing all 8 of your Mills MRA5 330R power resistors, 4 are on the back of the board, because they get very hot and the Mills replacement would therefore be advisory.

Also I forgot to mention that when you replace the cathode bypass caps you will need to add bypasses to those caps such as these: PME-080: 0.1uF 275Vdc Evox Rifa PME271M x 4, because it puts the treble frequencies back in that you lose. I know that adding bypasses is not always advised but I found it necessary on another amp, without them you do notice something missing.


----------



## gug42

baronbeehive said:


> Hi gug42!
> 
> Hi  ! Thank you for your answear.





baronbeehive said:


> Coupling caps are the pink ones you mention in the blue circle.
> You can use K75-10 500V 0.33uF, 0.47uF is probably best but you can go higher to about 0.68uF. Best bass response is probably around 0.47uF. You could also use Audyn True Copper for the very best sound, cheaper than Jupiter but very big. If so you need to see about extending the bottom of the chassis.


Ok thank you  !  



baronbeehive said:


> You need 4 Mills mra05 330R here: https://www.hificollective.co.uk/(MRA05-330) - 330R 5W MRA05 Mills Resistor
> Yes mount in parallel to cathode bypass caps in red circle as you said using 4 pole switch.



Thx for this confirmation !  


baronbeehive said:


> You need 4 TKD 220K 2W here: https://www.hificollective.co.uk/catalog/cm2610-220k-correctohm-metal-film-resistor-p-9712.html
> Replace them in the position you say, correct in picture.
> 
> I don't know about the Z-foils or Takman resistors.



I was talking to have better bias point for the driver tube like mentionned in the previous pages. 

Is there any intetest to replace existing resistor ?  



baronbeehive said:


> I think you mean cathode bypass cap as there is a separate cathode power resistor which we are not talking about here. The cathode bypass caps are in red in the picture.
> I don't know what you mean by a 10M45S



Hum well i will not try this mode in fine ... Too much stuff and thing  




baronbeehive said:


> Yes, change the fuses by all means, you never know if it might make a difference.
> 
> You need to solder parts from the reverse of the board so you will need to remove it by unscrewing the screws and the nut holding the pot and gently wiggling the board away from the pot and at the same time pressing the tube sockets out. Be carefull when you have got it out because the wires on the reverse can easily break.
> When you put the board back check that the wires are still in place and use a screwdriver in the tube socket holes to pull the board back in position. This is very tricky and has us all swearing lol.....
> ...



Ok thank you about soldering .... A difficult operations to pull out the board  well sweating for sure.


----------



## gug42

baronbeehive said:


> BTW gug42 you might like to think about replacing all 8 of your Mills MRA5 330R power resistors, 4 are on the back of the board, because they get very hot and the Mills replacement would therefore be advisory.



You mean replace the existing resistor by better aftermatket stuff



baronbeehive said:


> Also I forgot to mention that when you replace the cathode bypass caps you will need to add bypasses to those caps such as these: PME-080: 0.1uF 275Vdc Evox Rifa PME271M x 4, because it puts the treble frequencies back in that you lose. I know that adding bypasses is not always advised but I found it necessary on another amp, without them you do notice something missing.


----------



## gug42

Did you know how to remove WIMA MKS withtout pull the board ?


----------



## SonicTrance (Jun 29, 2017)

gug42 said:


> Did you know how to remove WIMA MKS withtout pull the board ?


I believe he does and it's not pretty, lol. My advice is to remove the board and de-solder the caps from top side of board. While you have the board out replace the cathode resistors. The stock ones are not good.
Read the first page of this thread until you memorize it!

Remember if you do the 5998 bias mod without the switch, you can't use any other power tubes (such as stock 6080/6AS7G) The amp will overheat!

I advice you to do ALL mods! Why not if you're pulling out board anyway? If not here's a priority list for you.

Coupling caps + WCF caps!
5998 bias mod
driver stage bias
Ra switch (not presented on first page yet, can be messy to fit. As far as I know I'm the only one that has done it)


----------



## coinmaster (Jun 29, 2017)

> but would like to also see a schematic or parts list of the other mod for the powerubebstage.









The original schematic by comparison.




Fore a more official version I would up the value of resistors for R5 R3 R12 R1 while maintaining the ratio for better performance with .22uf caps so you can use .22uf instead of 1uf on the extra input cap. Getting the proper value resistors for that will require an assortment of resistors in the megaohms tho.
You can also improve the performance of the source followers by using a cascode follower which is what I would do if I was serious about it.





> Can I use K75-10 500V 0,33 uF ? Well perhaps the jupiter PIO JCW-080 could be the best but 70€ each one (0,33uF version)...


I wouldn't skimp on this one.



> Replace Z-foil 1,5K Ohms by 390 Ohms Image here





> *Replace the cathode resistor with a 10M45S*
> 
> Please can you point me on the PCB where it is ?


The 10M45S goes in place of the 1.5k resistor, don't bother with the Zfoil.


----------



## baronbeehive

gug42 said:


> You mean replace the existing resistor by better aftermatket stuff



Yes, all 8 Mills MRA5 330R power resistors, don't forget the cathode bypass  and its cathode resistor bypass soldered on to the reverse of the board.

I would advise you to follow SonicTrance's advice and decided carefully what mods you want and then after studying page 1 make up a parts list such as we have done eg. page 53, then put it to us for approval. Then you're ready to go.

Probably best to limit yourself to the tested mods on page 1, because, for example, the driver tube bias mod hasn't been tested, or at least hasn't made it to page 1 yet, although if you want to, go for it by all means.



gug42 said:


> Did you know how to remove WIMA MKS withtout pull the board ?



Er ..... yes .....


----------



## gug42 (Jun 29, 2017)

SonicTrance said:


> Remember if you do the 5998 bias mod without the switch, you can't use any other power tubes (such as stock 6080/6AS7G) The amp will overheat!
> 
> I advice you to do ALL mods! Why not if you're pulling out board anyway? If not here's a priority list for you.
> 
> ...



Thank you.
I will go for the "best" : jupiter PIO.
I haven't follow the RA switch mod, what is it ?



coinmaster said:


> The 10M45S goes in place of the 1.5k resistor, don't bother with the Zfoil.



Hum ok well but the 10M45S seems to have 3 pins, isn't it ?



baronbeehive said:


> Yes, all 8 Mills MRA5 330R power resistors, don't forget the cathode bypass  and its cathode resistor bypass soldered on to the reverse of the board.
> 
> I would advise you to follow SonicTrance's advice and decided carefully what mods you want and then after studying page 1 make up a parts list such as we have done eg. page 53, then put it to us for approval. Then you're ready to go.
> 
> ...



Ok good advice ! Read carefully, take notes, choose mods and stuff ! Thank you for your proposal to read my future list 
Well by the way I will not replace resistor stuff for better one 

Thank you again !


----------



## coinmaster

> Hum ok well but the 10M45S seems to have 3 pins, isn't it ?


Yeah just solder a resistor between the gate and source pins and use the drain/gate pins as +/-, bend the souce pin up so it doesn't get in the way. You could also solder a trimmer resistor on there for manual bias adjustment to whatever current you want. I would use a trimmer of 1-2k value for that.


----------



## gug42

Ok thank you for the explaination. Well for a fist run of modification I will stay simple ... hum seems a bit to far away from my knowledge


----------



## baronbeehive (Jun 29, 2017)

gug42 said:


> .....
> I haven't follow the RA switch mod, what is it ?
> 
> .....



I'm beginning to lose track of all the mods but this is the* impedance mod, *the idea is to match the impedance of the amp to your particular headphones.
Then there is the *driver tube bias mod, *to operate the amp in the most linear part of the frequency curve of the driver tube
Then there is coinmaster's version of the impedance mod using the 10M45S parts, which better matches the impedance to a whole lot of headphones at once I believe.
He also has other ideas which he will explain no doubt.

This is where we're at atm with the mods. The ones above haven't been included with the 10 items in the contents list on page 1 for a number of reasons,  mainly due to lack of thorough testing.

Edit:
BTW could you give a link or picture of the 5998A's you intend to use, they may not be the same ones we have implemented the power tube bias mod for, there are several different 5998A's, and I believe the 7236 is also a version of these.


----------



## coinmaster (Jun 29, 2017)

> Then there is coinmaster's version of the impedance mod using the 10M45S parts


Two different mods, the 10M45S are an improved version of the "driver bias" mod.

Although to have the ultimate upgrade to the driver stage you'd have to include a mu follower in place of the load resistors along with the 10M45S mod which is easy enough for anyone that wants to do it, I'd be happy to show you how, but I won't hold my breath. It seems like enthusiasm has waned for the MK6 mods.

The Improved "impedance mod" is a different beast.


> which better matches the impedance to a whole lot of headphones at once I believe.


The impedance mod doesn't match the impedance to a single headphone or lots of headphones per se. The WCF topology can only be optimized for a single load impedance in which the current sharing between both triodes are equal.
Unless you are using planar headphones this means that the existing impedance mod will not work throughout the entire frequency range, the goal of the existing impedance mod is to find the a sweet spot to try to hit as many frequencies at once as it can but dynamic headphones have varying impedance with frequency so it will never be optimal.
My improved impedance mod does a few things at once, it gives a lot better PSRR, lowers the input capacitance, and keeps the current through both triodes balanced no matter what the load is.
The end result being less loading on the input stage as well as improved sound throughout the entire frequency range.


----------



## gug42

Hello, 

Thank you for thoses explanation. 
Indeed The switch mode is to adapt the bias point of the push pull to the charge. 

So well i understand it could be really interesting to do it ... But i don't have the knowledge to do the math and calculation....

Lucky i m mainly use a planar of 50 ohms, a zmf.  If you say the value of the resistor to use i will do the mod   

When i receive the tube I can post some picture. 5998A are electricaly identical to 5998. 7236 are a little different.
http://tubedata.milbert.com/sheets/127/5/5998A.pdf

Regards


----------



## baronbeehive

coinmaster said:


> Two different mods, the 10M45S are an improved version of the "driver bias" mod.
> 
> Although to have the ultimate upgrade to the driver stage you'd have to include a mu follower in place of the load resistors along with the 10M45S mod which is easy enough for anyone that wants to do it, I'd be happy to show you how, but I won't hold my breath. It seems like enthusiasm has waned for the MK6 mods.
> ......



I wouldn't say that, I think everybody is just taking stock atm and enjoying the results of their work, like I'm doing with my other amp.

I'm still interested in the mods but not in any position to do anything for a while. Also I'm not too familiar with the sound of the modded LD because I've only had it up and running for a short while, so I would need to re acquaint myself with it first. But I would certainly be interested in trying out your mods. I would like to see something along the lines of the first page with each mod, its purpose, what parts are needed and how to do it and the expected results. We could maybe take it from there and do the necessary testing to flesh out any problems?



coinmaster said:


> .....
> 
> The Improved "impedance mod" is a different beast.
> 
> ...



Right! I can see that keeping the current through both triodes balanced would help with the problem of varying impedance when using a range of dynamic headphones, if it does do this it should be interesting trying that out!


----------



## coinmaster

> Right! I can see that keeping the current through both triodes balanced would help with the problem of varying impedance when using a range of dynamic headphones, if it does do this it should be interesting trying that out!


Keeping the current sharing between balanced doesn't help the issue of varying impedance in dynamic headphones, it's the other way around, the varying impedance of dynamic headphones breaks or weakens the push pull operation of the WCF at frequencies it is not optimized for.
In other words my mod ensures proper push pull operation regardless of the load, while the existing impedance mod only tries to find a sweet spot for your particular headphones so it can attempt to maintain push pull at at many frequencies as it can.


----------



## gug42 (Jun 30, 2017)

Oh really interesting indeed  !
Ok i will read some post back to know what soldering where


----------



## gug42 (Jun 30, 2017)

Hello,

What could be the most size effective capacitor for 0,47uF / 250V ?
Any advice on this site please ? https://www.hificollective.co.uk/catalog/components/capacitors.html

For the power/driver coupling caps I will go with the big/large  and expensive jupiter PIO because they are the best !

But for the WCF power tube coupling cap I can't spend so much ... and I'm concern by the place left in the boxe ...  Perphaps I go with K75-10 250V 0,47uF ... really cost effective ....  ?



Regards,


----------



## coinmaster

The optimal capacitor size would be about 2uf all around. Just buy the biggest size you're comfortable with with the highest quality capacitor you can afford. Don't get too obsessed over the details.


----------



## gug42

Yes aggree about details  
Indeed my concern is  related to physical size  for 0,47uF / 250V


----------



## baronbeehive

gug42 said:


> Hello,
> 
> What could be the most size effective capacitor for 0,47uF / 250V ?
> Any advice on this site please ? https://www.hificollective.co.uk/catalog/components/capacitors.html
> ...



Yes, these are the ones we used from hificollective: https://www.hificollective.co.uk/catalog/jcw080-047uf-600vdc-jupiter-copper-foil-paper-p-9973.html
They are 21x52mm and if in doubt check out the ones we have used in the compact version of the mods on page 1 because then you know they fit OK.
The K75-10 should be fine, I'm not sure of size but they look like they will fit OK.


----------



## gug42 (Jun 30, 2017)

Hello I was looking for the WCF coupling cap between the power tubes.
Because physically place will be important indeed 

So well What do you think about thoses one : 
https://www.hificollective.co.uk/catalog/jcw080-047uf-600vdc-jupiter-copper-foil-paper-p-9973.html


----------



## coinmaster

I never actually implemented the WCF cap upgrade, how does it sound?


----------



## baronbeehive (Jun 30, 2017)

The compact version used Mundorf MCap Supreme Silver/Oil 0.33uF 1000V but you could try the ordinary Mundorf Supreme if you wanted a cheaper cap.

I don't know how it sounded because I did all the mods at once, all I know is that Maxx really went for the Mundorf SiO as the best WCF replacements with a really strong treble sound.

Edit:
Please let me have quoted Maxx correctly lol!


----------



## gug42

coinmaster said:


> I never actually implemented the WCF cap upgrade, how does it sound?



Redge tell me that is a really important upgrade for sound quality, ahead Bypass cap and coupling cap.
For Redge the order are :
- 5998A bias mod
- Output impedance bias mod adapted for the headphones (but to hard for me !  so I will not do it  )
- Coupling cap between
- WCF   cap inside the power stage (between power tubes)
- Bypass cap
- Decoupling cap on the power tubes (I will not do this one)



baronbeehive said:


> The compact version used Mundorf MCap Supreme Silver/Oil 0.33uF 1000V but you could try the ordinary Mundorf Supreme if you wanted a cheaper cap.
> 
> I don't know how it sounded because I did all the mods at once, all I know is that Maxx really went for the Mundorf SiO as the best WCF replacements with a really strong treble sound.



Well I'm looking mainly by a soft/mellow/laid back trebble. So I don't know how to understant your stance .... perhaps K75-10 will be a really good choice.

Thank you evryone ! Tomorrow i will post my shopping list


----------



## coinmaster

> Redge tell me that


 Redge is still alive?


----------



## baronbeehive

gug42 said:


> ......
> 
> Well I'm looking mainly by a soft/mellow/laid back trebble. So I don't know how to understant your stance .... perhaps K75-10 will be a really good choice.
> 
> Thank you evryone ! Tomorrow i will post my shopping list



BTW have you seen this: http://www.humblehomemadehifi.com/Cap.html
It may help you make up your mind about caps.



coinmaster said:


> Redge is still alive?



Redge???...... who????


----------



## baronbeehive

This is a pic of my mods to show how everything fits:


----------



## coinmaster

> Redge???...... who????


The guy who made the thread.

I just implemented the "5998 bias mod" on my new output stage where I had the 5998s installed (consisted of changing out a 1 meg resistor with a 10meg resistor, easy) and while there was an improvement in holography and bass the vocals went to crap. Terrible mid range.
I switched it back and it was way better, far more realistic and intimate vocals. No doubt this anomaly is due to the tube mixing I'm doing. If only I had distortion testing equipment, the things I could learn.


----------



## baronbeehive

coinmaster said:


> The guy who made the thread.
> 
> ......



I know .....sorry, bad joke...... sorry Redge, if you're there.. I do know who you are!


----------



## coinmaster (Jun 30, 2017)

Well isn't that interesting.
I don't have a 5998 spice model but I simulated my above situation running 6as7 tubes with the follower on the left half of the load @ 75ma and the right half running @9ma and the distortion of the output (no nfb) went from 1.9% to 0.7%, quite an interesting result, that may explain why the 5998 mod sounded bad when I implemented it in mixed tube configuration. I may be onto another potential mod here.
I simulated it with the original white cathode follower and my "leamy follower" topology (Named it after myself, a bit pretentious and I feel uncomfortable doing it since broskie did all the tough maths for me but broskie already has a "broskie follower" and the concept was my idea plus this mod has no name so I gotta call it something, maybe the leamskie follower? )

The distortion was lower on both topopogies when one of the stages was running on low current, although mine was maintaining push pull while the WCF was not, which is good because it means mine does what it's supposed to.

Someone that doesn't have the 5998 bias mod in place try out this configuration and let me know what you hear 6080/5998/6080/5998 left to right.



"edit" It looks like the distortion reduction may be assisted by the load dissipating around 1/4 less power due to the lower current in one of the follower stages, interesting how the distortion got cut by 65% and not 25%.


----------



## gug42

baronbeehive said:


> BTW have you seen this: http://www.humblehomemadehifi.com/Cap.html
> It may help you make up your mind about caps.



Nice website ! I wasn't thinking the Caps could be tested (in heard way) as tubes ! First for me.
Thank you for sharing  

Anyone try the "Intertechnik Audyn True Copper Max MKP 630VDC - 2% tolerance" ?
Seems really close the Jupiter PIO for more than half the price, so could be really interesting ! Need x4 for coupling caps (driver  stage <=> power stage ), and x4 for WCF coupling caps (inside power stage) ...




baronbeehive said:


> This is a pic of my mods to show how everything fits:



Nice peace of work ! impressive !
Did you remember what's stuff/composents did you use ?




coinmaster said:


> Well isn't that interesting.
> Someone that doesn't have the 5998 bias mod in place try out this configuration and let me know what you hear 6080/5998/6080/5998 left to right.
> 
> 
> ...



Can I try with TS 6AS7G insteed of 6080 ? 
Really I found the stock thomson to be a little too much bright and agressive ...


----------



## coinmaster (Jul 1, 2017)

The rules get thrown out when you mix tubes. I found the stock 6080WAs to sound superior when tube mixing in nearly all combinations, although mullards are also really good.
Rather then being bright the stock thomsons add low end heft and lushness to the sound.
I think adding 6as7 with the 5998s will actually be on the bright side but you can try both and see what you like more.
Unfortunately I've forbid myself from listening to my headphones until august to give me ear a chance to heal.


----------



## gug42

I have try stock thomson 6080WA and Sylvania 5998A in this oder, left to rigt : 6080 5998A 6080 5998A.
- There was a little hum  
- I found the sound a little too bright, a little bit aggressive. Like it was with the 4x thomson 6080A.

Indeed I prefer my 4x Tung sol 6AS7G.
Well, now, I'm hopping that 4x Sylvania 5998A will do a good job .... I'm waiting for the other matched pairs


----------



## baronbeehive (Jul 1, 2017)

gug42 said:


> Nice website ! I wasn't thinking the Caps could be tested (in heard way) as tubes ! First for me.
> Thank you for sharing
> 
> Anyone try the "Intertechnik Audyn True Copper Max MKP 630VDC - 2% tolerance" ?
> Seems really close the Jupiter PIO for more than half the price, so could be really interesting ! Need x4 for coupling caps (driver  stage <=> power stage ), and x4 for WCF coupling caps (inside power stage) ...



Yeah, they were what I was going to try but didn't because of the size. What I've heard is that they are practically as good as you say. I know Maxx has these in his other amp, so he might tell you, but they are BIG!



gug42 said:


> .....
> 
> Nice peace of work ! impressive !
> Did you remember what's stuff/composents did you use ?



Yes my parts list is on page 53.



coinmaster said:


> The rules get thrown out when you mix tubes. I found the stock 6080WAs to sound superior when tube mixing in nearly all combinations, although mullards are also really good.
> Rather then being bright the stock thomsons add low end heft and lushness to the sound.
> I think adding 6as7 with the 5998s will actually be on the bright side but you can try both and see what you like more.
> Unfortunately I've forbid myself from listening to my headphones until august to give me ear a chance to heal.



Agreed about the tubes but I think 6AS7G RCA's might give the mellowness gug42 is after.

That concert you went to must have been LOUD, sounds like you might have damaged your eardrums.

Edit:
I think you will find Sylvanias a bit on the bright side, TS5998's would be much mellower if you can get hold of any at a fair price.


----------



## coinmaster (Jul 1, 2017)

Hmm, maybe its the difference in our headphones, mine isn't bright at all. Try mixing them like this 5998/6080/5998/6080. I encourage you to try with the 6as7s too.



> That concert you went to must have been LOUD, sounds like you might have damaged your eardrums.


 It was so loud it should have been illegal.


----------



## gug42 (Jul 1, 2017)

baronbeehive said:


> Yeah, they were what I was going to try but didn't because of the size. What I've heard is that they are practically as good as you say. I know Maxx has these in his other amp, so he might tell you, but they are BIG!



Audyn Body dimensions: 30mm (diameter) x 45mm (length)
Jupiter Dimensions: 21mm (diameter) x 52mm (length)

Duno if it's a problem within the mk6 ... did it feet in the boxe  ?!?

But Well  did you have some caps in the same price range ? 
Ineed 80€ for a jupiter is a bit high 



baronbeehive said:


> Yes my parts list is on page 53.


Thank you !
https://www.head-fi.org/f/threads/l...re-on-first-page.782183/page-53#post-12280541



baronbeehive said:


> Agreed about the tubes but I think 6AS7G RCA's might give the mellowness gug42 is after.
> 
> That concert you went to must have been LOUD, sounds like you might have damaged your eardrums.
> Edit:
> I think you will find Sylvanias a bit on the bright side, TS5998's would be much mellower if you can get hold of any at a fair price.



I have a quad cetron whos coming (the plate looks like Tung Sol 7236 but without the third mica and the added support for this third mica).
Well RCA 6AS7G is on my test list ...but well can't test evrystuff in the world 



coinmaster said:


> Hmm, maybe its the difference in our headphones, mine isn't bright at all. Try mixing them like this 5998/6080/5998/6080. I encourage you to try with the 6as7s too.
> 
> It was so loud it should have been illegal.



Why not !
Sorry to read about your ear problem bad news


----------



## baronbeehive

gug42 said:


> Audyn Body dimensions: 30mm (diameter) x 45mm (length)
> Jupiter Dimensions: 21mm (diameter) x 52mm (length)
> 
> Duno if it's a problem within the mk6 ... did it feet in the boxe  ?!?
> ...



No I went for the Jupiters in the end.

The dimensions you give 30mmx45mm are for Audyn True Copper Max, the True Copper are 40mmx36mm for 0.47uF so be careful. They would not fit. The True Copper Max might if you arranged them like this but it would be tight:







I didn't do this in the end because I had to get 2 large Wima caps in for the driver stage!


----------



## coinmaster

I'm surprised no one here has tried that "bathtub" mod.
If you fill your bathtub halfway with water and make sure the water temperature is about 50c and put your amplifier in it, it makes the sound so much more "liquid", you should try it.


----------



## gug42 (Jul 1, 2017)

Thank you for this nice photos ! Impressive jobs by the way (blow job ? )
I was talking about the max version 

Well indeed if you a good cap, small physical size, money value (=< 30€), I  will go for it


----------



## gug42

And after some more readings, the "antzen Audio Superior Z-Cap" could be the better money value ... any opinions ?


----------



## coinmaster

You're getting caught up in the details, don't mess with success. The jupiter caps are almost as good as duelund caps meaning if you like transparent sound then just go with the jupiters. If you wana roll the dice with sound shaping then try something else.


----------



## Maxx134 (Jul 3, 2017)

gug42 said:


> For me they was replace by some chemical pink boxes capacitor ...? Blue cirle on this photos :


Yes those are the coupling caps,
And as you can see the manufacturer went with really cheap caps!
This is due to pricing competition in Chinese market, and for profits.




gug42 said:


> is It better to use 0,43 uF or higher capacity ?


No!
.33uf is good enough and .47uf is way good enough and anything higher for this amp coupling caps is over-kill overboard to gain a few db on 2-5hz is rediculous when size of cap and space is limited.



gug42 said:


> Can I use K75-10 500V 0,33 uF ? Well perhaps the jupiter PIO JCW-080 could be the best but 70€ each one (0,33uF version)...
> 
> Or is It better to use 0,43 uF or higher capacity ?


No, use the dam Jupiter or you wasting your hard earned miney and hard work installing.



gug42 said:


> *5998A bias mods *
> 
> Material needed : 4 resistors mills RA5 330 Ohms


For a beginner I suggest not do a "powertube" bias mod unless you stick with one type,
Like me.
I did the bias change for one type of powertube and not have to worry about changes to bias.

Same with the impedance output mod.
I set it to match a 20ohm headphones amd left it there as most my headphones are low impedance.
That is not a mod covered on first page yet anyways I believe.
Only the powerube bias mod is for now.



gug42 said:


> *Driver bias mods *
> 
> Material needed* : *
> 4 x TDK 2W 33KOhms


This settings was for the ecc35 tube that member SonicTrance was using.
Not for the more common 6C8G/6SL7 type I am using.
I did not get to try this settings yet.
Also I plan to try Coinmaster chip design in place of the driver tube Cathode resistor,
But not have time yet.



gug42 said:


> 6x Charcroft Z-Foil 0,4W 390 Ohms


No!
Don't buy any Z-foils as you need larger watt resistors.
Plus they expensive.
Plus I not sure where you're putting them.



gug42 said:


> *Replace the cathode resistor with a 10M45S*
> 
> Please can you point me on the PCB where it is ?


NO!
This is advanced mod and your a beginner.
You Better off with resistor values I posted for the 6SL7 driver tube.



gug42 said:


> Perphaps changing the fuse :


NO! That is waste of money !
I did on mine and put top of the line synergistic fuses for nothing.
PSU upgrades are real improvement, not fuse.



gug42 said:


> And you mention the ability to thoses modes without pulling the board .... how did you change resistors and capacitors from the front of the board ?


By breaking them to pieces with a dam pliers and side cutter...



baronbeehive said:


> Best bass response is probably around 0.47uF. You could also use Audyn True Copper for the very best sound, cheaper than Jupiter but very big. If so you need to see about extending the bottom of the chassis.


YES! They excellent and cheaper but they too big going over .33uf




baronbeehive said:


> You need 4 TKD 220K 2W here:


.
NO,
That is stock setting I DO NOT RECOMENDED STOCK SETTING IS CRAP.

So if possible, change to lower settings for a higher bias ...
I like 70k ohm, and it not need to be 2watt
Although member SonicTrance went lower .
I found going lower than 50k ohm for anode gave me compressed dynamics,
Unless I lowered the anode lower than 1k ohm.

Also I like 1kohm Cathode, although member SonicTrance went lower than 500ohm for cathode..
You can experiment if you can.




baronbeehive said:


> I know that adding bypasses is not always advised but I found it necessary on another amp, without them you do notice something missing.


YES IT IS ADVISED ON MANY OTHER PLACES I READ.



gug42 said:


> Did you know how to remove WIMA MKS withtout pull the board ?


YES BREAK THEM TO BITS!!




SonicTrance said:


> Remember if you do the 5998 bias mod without the switch, you can't use any other power tubes (such as stock 6080/6AS7G) The amp will overheat!


YES LISTEN TO THIS.
If you stay with one type your ok .
If you switch tubes, you need install a switch to flip for other tube needs.



baronbeehive said:


> because, for example, the driver tube bias mod hasn't been tested, or at least hasn't made it to page 1 yet, although if you want to, go for it by all means


It has been tested to work and be a HUGE improvement so we do need to eventually place it  there,
And also with comparisons to Coinmaster suggested mod.



gug42 said:


> Hum ok well but the 10M45S seems to have 3 pins, isn't it ?


This is too much for beginner.



coinmaster said:


> Yeah just solder a resistor between the gate and source pins and use the drain/gate pins as +/-, bend the souce pin up so it doesn't get in the way. You could also solder a trimmer resistor on there for manual bias adjustment to whatever current you want. I would use a trimmer of 1-2k value for that.


See... Too much for beginner and would be nicer with trimpot too.



gug42 said:


> Ok thank you for the explaination. Well for a fist run of modification I will stay simple ... hum seems a bit to far away from my knowledge


I agree you don't need to bite off more than you can chew.
We don't want you to feel overwhelmed and get discouraged.



baronbeehive said:


> This is where we're at atm with the mods.


You forget powertube bias mod?

Yeah we not post drivertube bias mod or
Output impedance mod.
I have mine set at one setting as I never got around to installing my switch.




baronbeehive said:


> I wouldn't say that, I think everybody is just taking stock atm and enjoying the results of their work, like I'm doing with my other amp


Yes we all have busy lives and we all still like to upgrade.



gug42 said:


> What could be the most size effective capacitor for 0,47uF / 250V ?
> Any advice on this site please ? https://www.hificollective.co.uk/catalog/components/capacitors.html


Audyn true copper.

The best coupling caps are the "copper film" caps...
Do NOT waste your money on anything else or you will regret.



gug42 said:


> But for the WCF power tube coupling cap I can't spend so much ... and I'm concern by the place left in the boxe ... Perphaps I go with K75-10 250V 0,47uF ... really cost effective .... ?


NO!
Those WCF "coupling" caps need to be bright or lively caps.
DO NOT USE THICK/HEAVY/DARK/BASSY sounding caps.
You need *spacious* lively fast neutral quality caps.



coinmaster said:


> The optimal capacitor size would be about 2uf all around.


NO, we don't want to burden the amp with subsonic or ultrasonic frequencies, or unkown feedback oscillations.



gug42 said:


> Hello I was looking for the WCF coupling cap between the power tubes.
> Because physically place will be important indeed
> 
> So well What do you think about thoses one :
> https://www.hificollective.co.uk/catalog/jcw080-047uf-600vdc-jupiter-copper-foil-paper-p-9973.html


YES, AND NO!!
YES FOR JUPITER COPPER ALWAYS..
NO FOR ANY SIZE ABOVE .33UF OPTIMAL.
LARGER SIZE REDUNDANT HERE, for this WCF "coupling" 



baronbeehive said:


> This is a pic of my mods to show how everything fits:


DAM BEAUTIFUL WORK!!




coinmaster said:


> Someone that doesn't have the 5998 bias mod in place try out this configuration and let me know what you hear 608


My own testing gave me this observations:
The LEFT SIDE of each group (right or left channel/ group) was responsible for leading edge, air, and details.

The right side of each group was responsible for decay, sustain, tube sound, and bass output.

Those were my own personal observations, your observations may vary..
So put the clearer tube on the left socket each side (right or left).




gug42 said:


> Anyone try the "Intertechnik Audyn True Copper Max MKP 630VDC - 2% tolerance" ?
> Seems really close the Jupiter PIO for more than half the price, so could be really interesting !


YES! IT IS JUST AS REALISTIC AND TRUE SOUND, with 8% LESS Soundstage, which still SUPERIOR TO MUNDORF silver/gold/oil . ..



coinmaster said:


> The rules get thrown out when you mix tubes.


As long as you mix only different manufacturers within same tube type.(!)



baronbeehive said:


> . I know Maxx has these in his other amp, so he might tell you, but they are BIG!


I made foolish mistake to get the .68uf jumbo size, which I did not need, but it was on sale.
Bigger not optimal in size.
Remember coupling not need any bigger than.47uf with .33uf just fine.



gug42 said:


> And after some more readings, the "antzen Audio Superior Z-Cap" could be the better money value ... any opinions ?


No, noo NO!
ONLY COPPER FOILS OR YOU WASTING YOUR MONEY!!!




coinmaster said:


> You're getting caught up in the details, don't mess with success. The jupiter caps are almost as good as duelund caps meaning if you like transparent sound then just go with the jupiters. If you wana roll the dice with sound shaping then try something else.


YES, GO WITH JUPITER , don't roll the dice!

Well that's all for now..
Lol


----------



## coinmaster

> This is too much for beginner.


It's really not, a few example pictures and a few sentences would be enough even for a complete novice.



> NO, we don't want to burden the amp with subsonic or ultrasonic frequencies, or unkown feedback oscillations.


Nonsense, that's vodoo. None of those things are going to happen. A lower corner frequency lessens phase deviation, a 2uf cap with the 470k resistors in place at the end of each cap would mean 2uf would be the overkill ideal, but .16uf is sufficient mathematically.



> ONLY COPPER FOILS OR YOU WASTING YOUR MONEY!!!


What he said. Duelund caps sound the same as direct coupling so you can really beat them, they are solid copper caps. The one test I did with jupiters revealed they are close to duelunds. No need to buy anything else on a budget.


----------



## MrCurwen

> My own testing gave me this observations:
> The LEFT SIDE of each group (right or left channel/ group) was responsible for leading edge, air, and details.
> 
> The right side of each group was responsible for decay, sustain, tube sound, and bass output.



What do you think causes this in your circuit?



> So put the clearer tube on the left socket each side (right or left).



Which property inside the tube makes it clear?



> So if possible, change to lower settings for a higher bias ...
> I like 70k ohm, and it not need to be 2watt
> Although member SonicTrance went lower .
> I found going lower than 50k ohm for anode gave me compressed dynamics,
> Unless I lowered the anode lower than 1k ohm.



Did you draw the load lines for these anode loads? What did you find and how do you think it relates to your listening experiences?



> No, noo NO!
> ONLY COPPER FOILS OR YOU WASTING YOUR MONEY!!!



KBG's are copper foil with oil impregnated paper (the real good sounding old time toxic oil, not the limp wristed "solid state sounding" oil they use these days) as insulation. All this time I've used audiophile approved components without realising it! Copper is not that expensive, KBG's are quite cheap luckily.



> LARGER SIZE REDUNDANT HERE, for this WCF "coupling"



The WCF cap determines frequency pass just as much as any other cap on the signal path. Your point stands though, there's no benefit to increasing the capacitance.



> .33uf is good enough and .47uf is way good enough and anything higher for this amp coupling caps is over-kill overboard to gain a few db on 2-5hz is rediculous when size of cap and space is limited.



I forget, what is your (meaning the thread participants in general) standing theory of what causes the differences you hear between caps and cap types?

If rolling some copper foil and let's say plastic in a roll together causes some properties that are harmful to the sound reproduction that you prefer, what does it mean for your preferred sound quality when you roll much more copper foil and plastic into the roll?


----------



## gug42 (Jul 3, 2017)

Maxx134 said:


> Well that's all for now..
> Lol




Lot's of informations, so well what's I  hold back :
- Stay with simple mods, so thoses one are out :
    * output impedance matching
   * Decoupling cap :  could be a good thing .... but well I will pass on it  sorry. The caps are huge and what I read there is only a slight improvement

- For 5998A Bias mod, better to hadd a switch. Any opinion about some "pins socket connection". Less than a switch better than a soldered cable ?

- To remove the ping cap :


> "By breaking them to pieces with a dam pliers and side cutter..."


Ok thank you !


- You say that driver tubes bias mods could be huge improvement, but well the R value mentionned is for ECC35 and taht Z foils are not good.
Can you give me some more informations ?
Well perhaps for better to wait that this mods go in the first page with lot's of informations and details.
Or Perhaps only buying 4x TDK 70kOhms resistor and wait to see.



> Don't mix 5998A and 6AS7G. Mix only within the same tube familly.


Ok it's seems logical.



> The LEFT SIDE of each group (right or left channel/ group) was responsible for leading edge, air, and details.
> The right side of each group was responsible for decay, sustain, tube sound, and bass output.


When I receive all my 5998A tubes, i will do the testing to mix cetron and sylvania.


Then about caps, the most complicated part because too many choices :


Jupiter PIO  : the best around, but for me far too expensive.
Size are 21mm (diamter) x 51mm (length) for both 0,33uF and 0,47uF

Intertechnik Audyn True Copper Max MKP :
Same size 31mm (diamter) x 45mm (length) for 0,47uf and 0,33uF
The non max version are 33mmx36mm for 0,33uF and 40mmx36mm for 0,47uF
The problem with them : they can be huge ... too huge to go in the chassis
For wcf coupling cap I will go with 0,33uF (the stock one are poor quality 0.22uF /250V)
For coupling cap between driver/power, is 0,33uF will be ok ? (The stock one are poor 0.22uF / 600V)
They are not PIO  ??  

@MrCurwen : you are talking about KBG caps, for me they are not really "thin" no ? K75-1O could be the most effective one  and indeed I'm looking for rolled off trebble (But from my window, I prefer a clean neutral amp, and if I need, play with a software equalizer)
jantzen Audio Superior Z-Cap : some people says they are the best money values caps ...
Any other options ?
30€ by cap is a budget because 8 of them are needed


http://www.ebay.ca/itm/KBG-MN-600V-...751318?hash=item43d2576396:g:FZ8AAOSwibFUYEqY



> > ONLY COPPER FOILS OR YOU WASTING YOUR MONEY!!!
> 
> 
> What he said. Duelund caps sound the same as direct coupling so you can really beat them, they are solid copper caps. The one test I did with jupiters revealed they are close to duelunds. No need to buy anything else on a budget.



Dunno why but ok !!




> KBG's are copper foil with oil impregnated paper (the real good sounding old time toxic oil, not the limp wristed "solid state sounding" oil they use these days) as insulation. All this time I've used audiophile approved components without realising it! Copper is not that expensive, KBG's are quite cheap luckily.
> 
> The WCF cap determines frequency pass just as much as any other cap on the signal path. Your point stands though, there's no benefit to increasing the capacitance.
> 
> .33uf is good enough and .47uf is way good enough and anything higher for this amp coupling caps is over-kill overboard to gain a few db on 2-5hz is rediculous when size of cap and space is limited.



Then I will stay with 0,33uF ! no need for 0,47uF great 



> I forget, what is your (meaning the thread participants in general) standing theory of what causes the differences you hear between caps and cap types?
> 
> If rolling some copper foil and let's say plastic in a roll together causes some properties that are harmful to the sound reproduction that you prefer, what does it mean for your preferred sound quality when you roll much more copper foil and plastic into the roll?



Interested too


----------



## baronbeehive (Jul 3, 2017)

gug42 said:


> Lot's of informations, so well what's I  hold back :
> - Stay with simple mods, so thoses one are out :
> * output impedance matching
> * Decoupling cap :  could be a good thing .... but well I will pass on it  sorry. The caps are huge and what I read there is only a slight improvement
> ...



*You are right!*



gug42 said:


> .....
> 
> - For 5998A Bias mod, better to hadd a switch. Any opinion about some "pins socket connection". Less than a switch better than a soldered cable ?
> 
> ...



*You are right!

For the impedance mod and power tube bias mod you can just put in another resistor anyway if you are using one set of headphones and one set of power tubes. You need to know the headphones  and power tube types and then ask someone for the appropriate resistor value.*



gug42 said:


> ......
> 
> 
> - You say that driver tubes bias mods could be huge improvement, but well the R value mentionned is for ECC35 and taht Z foils are not good.
> ...



*Again decide what drier tubes and ask someone for the resistor value*



gug42 said:


> ......
> 
> Then about caps, the most complicated part because too many choices :
> 
> ...



*Your problems would be solved if you:*

*Use Audyn True Copper, or True Copper  Max  .33uF for both coupling, and WCF.
They are one of the best and compare favourably with Jupiter caps.
They fall within your budget.
They would fit, especially if you are not doing the decoupling cap mod, they are smaller in size than the decoupling caps.
They would give you a neutral sound.
You could then alter the sound by your tube choice and so wouldn't need a software equalizer either!!

Problem solved!
.
*


----------



## baronbeehive

coinmaster said:


> .....
> 
> 
> What he said. Duelund caps sound the same as direct coupling so you can really beat them, they are solid copper caps. The one test I did with jupiters revealed they are close to duelunds. No need to buy anything else on a budget.



That's what I find so amazing about Jupiter caps! As we know any interstage component would have detrimental effects to some extent, yet the Jupiter's manage to sound totally transparent, how they do this is beyond me!


----------



## gug42

baronbeehive said:


> *You are right!*
> 
> 
> 
> ...



Ok thank you. Is there anyone who can give me the value please ? 
For 6SL7 (mostly Sylvania 6SL7WGT or Ken Rad from 1940/45)  and a 50Ohms planar.
Redge tell me for this mod there is no hurry because I could be in the sweet spot already. I don't know...
In the future I will get an hd-6xx (sen hd-650) 300Ohms but it will be in 6 month so don't worry ...



baronbeehive said:


> *Your problems would be solved if you:*
> 
> *Use Audyn True Copper, or True Copper  Max  .33uF for both coupling, and WCF.
> They are one of the best and compare favourably with Jupiter caps.
> ...



Ok thank you


----------



## Maxx134 (Jul 3, 2017)

MrCurwen said:


> What do you think causes this in your circuit?


This is a very interesting topic to try to discover about the WCF circuit.
For now, I can only tell you my observations which hold true for me,

But as to why is very interesting and I can only assume is how it reproduce the signal.

The issue of the WCF effects using two same type, but different manufactured tubes of different materials indeed have different performance , just like having to non-matched tubes.

The left side tube produce the leading edge of the negative signal.
 I *edit* do not know is why it has the advantage or predominance in making the channel sound good or not.

The second tube on right side is leading edge for the positive side of the signal.

This effect is probably not happening  due to the WCF design, 
because instead the "balanced" design of this amp, which is also DC offset protected so the difference of tubes still behave as one balanced signal.

I used two tubes which I very much knew their different signatures.
The Electro Harmonic was the thicker tube,
And the Russian Supertube was the clearer more neutral tube.

The circuit *ALWAYS* sounded better with the more clearer tube on the left side..
Maybe its a "bottleneck" effect..
But the left side characteristics were the predominant ones.

Also, another reason why this happens without harm is because the amp opamp circuit controlling any DC offset by a mismatch of tubes..



MrCurwen said:


> Which property inside the tube makes it clear?


We know regardless of design that some tubes sound better , and I *do* believe that * you *can design a circuit which is less affected by tube rolling as SonicTrance amp has proven, but in this and MANY current amps out there,
The sad case is that all are using old simpler designs which do not use SS devices to help and so are very much affected by tube rolling.



MrCurwen said:


> Did you draw the load lines for these anode loads? What did you find and how do you think it relates to your listening experiences?


Yes!
The load lines were drawn and SonicTrance load lines were at a higher position than mine but I did not test it because my amp heater circuit burned,
Which was totally unrelated occurance due to using some bad adapter sockets.

The reason I like to listen before I accept another nicer looking load line ,
Is because I also found that the bias affects not only the linearity,
But shrinks the Soundstage and increases the liveliness of the tube.
I did not want a tube that has smaller Soundstage than what should be.

As far as the load line, I felt the effects were more in the Dynamics effects.
Some settings increased livelinness and yet had effect on dynamic range.
I also feel the PSU for that stage was not optimal and very weak.
This must have played a big issue.
Also why I agree with Coinmaster that the PSU may not be able to handle too much changes as so only interested in trying the changes to the Cathode resistor replacement.

So for now since I haven't had much time,
 I keep my driver settings at 70k for anode and 1k for cathode which brings life to the driver tubes..



MrCurwen said:


> KBG's are copper foil with oil impregnated paper (the real good sounding old time toxic oil, not the limp wristed "solid state sounding" oil they use these days) as insulation. All this time I've used audiophile approved components without realising it! Copper is not that expensive, KBG's are quite cheap luckily.


This is excellent to know, but I still believe the Jupiter caps cannot be beat by anything older.
Even the mundorf silver/gold/oil cannot reach the realism and tonality ofbthe Jupiter copper foil.
The cheaper normal Jupiter beeswax on the other hand is a POS garbage that give a thicker less Soundstage and duller sound.
The mundorf exceed them easily.
I do not understand why Decware using them in their thousand dollar amps.
But so so many these amps are just really limited by the cheap choices in coupling caps.



MrCurwen said:


> If rolling some copper foil and let's say plastic in a roll together causes some properties that are harmful to the sound reproduction that you prefer, what does it mean for your preferred sound quality when you roll much more copper foil and plastic into the roll?


Too big a cap is a waste of size and money.
Too many differences in caps.
The best caps give tremendous upgrade in all important coupling stage.
I prefer large holographic Soundstage with natural timbre that only copper foil give.
The others will give a plastic or different tonality.
I like PIO caps too.
I using them in WFC coupling as they are smooth, natural and great tonality,
But no cap I tried approach the Soundstage and details of a great copper foil cap.
That's why they so dam expensive Because they great.
I haven't tried any silver foil due to being expensive but they say its not as natural as the copper anyways.




gug42 said:


> Any opinion about some "pins socket connection". Less than a switch better than a soldered cable ?


NO,
You can't use a tiny switch Because that area need a heavy duty switch.



gug42 said:


> Well perhaps for better to wait that this mods go in the first page with lot's of informations and details.
> Or Perhaps only buying 4x TDK 70kOhms resistor and wait to see


If you buy the 70k ohms, then also need to have two 1k ohm for cathode resistors.

You can also try SonicTrance choice of resistors ,
But the point is to change BOTH the anode and the cathode resistors  to get the "load lines" that worked nice.
Or else you may end up with a distorted or compressed signal.



gug42 said:


> The problem with them : they can be huge ... too


Look for .33uf  is good




gug42 said:


> For coupling cap between driver/power, is 0,33uF will be ok ? (The stock one


Yes , .33uf is good!



gug42 said:


> Then I will stay with 0,33uF ! no need for 0,47uF great


Yes!



baronbeehive said:


> *Your problems would be solved if you:*
> 
> *Use Audyn True Copper, or True Copper Max .33uF for both coupling, and WCF.
> They are one of the best and compare favourably with Jupiter caps.
> ...


LISTEN TO THIS QUOTE AS HE SAYS IT ALL.


----------



## SonicTrance

gug42 said:


> you are talking about KBG caps, for me they are not really "thin" no ?


There's axial versions too. Like these: http://www.ebay.com/itm/0-25MF-10-2...e=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649
I've been meaning to try these in my MK6 to compare them to the Jupiters and Mundorfs but haven't gotten around to it yet.



gug42 said:


> Redge tell me for this mod there is no hurry because I could be in the sweet spot already. I don't know...


Why isn't he posting in the thread??



Maxx134 said:


> The left side tube produce the leading edge of the signal as it is the positive.


The "positive" and "negative" markings are only there for convenience. It's just two phases that are anti-phase towards each other. There's nothing that makes the "positive" phase more positive than the "negative" phase. They're both equally positive and negative.
I don't know why the different tube placements sound different when mixing tubes. I've never mixed myself.


----------



## gug42 (Jul 3, 2017)

Ok thank you ! I will go for Audyn True Copper (Max ?) 0.33uF

Ok last check about the others mods and my shpping list

Bias 5998A power tubes mods :
4 resistor mills MRA 05 330 Ohms 5W
https://www.hificollective.co.uk/(MRA05-330) - 330R 5W MRA05 Mills Resistor

Bypass caps
4 x Elna Silmic2 470µF/50v 
https://www.hificollective.co.uk/ca...lna-silmic-electrolytic-capacitor-p-6229.html
4 x RIFA PME 0,1µF/250V 
https://www.hificollective.co.uk/catalog/0-1uf-275vdc-evox-rifa-pme271m.html

Driver bias mods for 6SL7WGT
Can you confirm that thoses with orange circle please ? 
http://www.hostingpics.net/viewer.php?id=218114LDmk6.jpg

Option 1
*4 x *TDK 2W 70Kohms (can I go with 68KOhms ? or did i mount resistor in serial to have 70K ?)
https://www.hificollective.co.uk/catalog/cm2550-correctohm-metal-film-resistor-p-9706.html

*2 x* Takman metal film 1kohms * 0,5W *
https://www.hificollective.co.uk/catalog/rey75330-takman-metal-film-resistor-p-6154.html

Option 2
*4 x *TDK 2W 33Kohms

*2 x* Takman metal 390 Ohms *0,5w*

*Option 3 : Add resistance in //  *(insteed of replace). I need to do some math to acheive 70k and 1k. *Can you confirm please *?
From 220K to 70K, I need a 104K.  *Did 100Kohms will ok *?
https://www.hificollective.co.uk/catalog/cm2570-100k-correctohm-metal-film-resistor-p-9708.html
From 1.5K to 1K,*  Did I need a 3K ?*
https://www.hificollective.co.uk/catalog/rey75-385-3k-takman-metal-film-resistor.html

All Coupling caps
8 x caps 0,33uF 630V  Audyn True Copper Capacitor. If Max version can fit (go in) I will take the max
https://www.hificollective.co.uk/catalog/1603021-0-33uf-630vdc-audyn-true-copper-max.html




Spoiler



And for the balanced DAC, I will wait to have more money in bank and go for the schiit gungnir multbit. Really appreciate by evryone, evrytime in competition against new one. Simple solution with any disappointment at the end.



Thank you every one !

Regards,


----------



## SonicTrance

gug42 said:


> Can you confirm that thoses with orange circle please ?


Yes, but not all of them. The three small resistors on each side of the pot are two grid resistors (10k) and one cathode resistor (1k5).



gug42 said:


> 6 x Takman metal film 1kohms * 0,5W or 1W* ?


Don't get 1W! You'd need to file down the leads for them to fit the holes in the board! You don't need any more than .5W anyway.
Don't change the value of the grid resistors (10K).

Personally I've found that 33K anode resistors and 390R cathode resistors gave me best all round SQ. That includes ECC35's as well as 6SN7's.


----------



## coinmaster (Jul 3, 2017)

> What do you think causes this in your circuit?


I wish I knew this.
In operation both triodes types are in series with each other regardless of which direction the current is flowing.
The only difference being which tube type it enters first but the curves must average either way. But there must be another difference because one configuration always sound clearly worse then the other by a large margin.




> Don't mix 5998A and 6AS7G. Mix only within the same tube familly.


Unless you applied a mod that prevents you from doing it, there's literally no reason not to mix different tube families within the acceptable electrical parameters of the circuit, mixing 5998s, 6080s, 6as7, or similar is fine.



> I've never mixed myself.


You're missing out.


----------



## Maxx134 (Jul 3, 2017)

SonicTrance said:


> The "positive" and "negative" markings are only there for convenience. It's just two phases that are anti-phase towards each other. There's nothing that makes the "positive" phase more positive than the "negative" phase. They're both equally positive and negative.
> I don't know why the different tube placements sound different when mixing tubes. I've never mixed myself.


Yes they're both equall levels of positive and negative, but all due to the opamp DC servo control.

The reason why these outputs are "equally positive and negative" is because of the opamp "DC offset"  (servo) circuit  making the tubes equal output regardless of different tube or output strength ..

This is why we can mix same type tubes  without worry of output imbalance.

The markings on the board do signify importance, and not for convenience,
 as you can get one channel out of phase if  improperly wired.

XLR out has four pins,
 left Neg, left pos, right neg, right pos.
Four separate signals corresponding to the four separate output tubes.

So yes in balanced amp this is four outputs from four separate tubes adding separately to different part of signal, not working together like in your LTP amp.
That's how I see it.




gug42 said:


> Bypass caps
> 
> 4 x Elna Silmic2 470µF/50v


It does not pay to get these caps, or even the mundorf I haf used,
When there is better electrolytic cap available.
The Audio Note Kaisie caps, said to be technology derived from famous "blackgate" caps :



Use recommended values on first page
Not the size shown in pic,
But if you can squeeze larger electrolytics then that's fine,
 as long as you have at least a 50v rating or higher..




gug42 said:


> Driver bias mods for 6SL7WGT
> 
> Can you confirm that thoses with orange circle please ?


Ok:

Orange circled


All else you quoted in your post was fine..


----------



## coinmaster (Jul 3, 2017)

> The reason why these outputs are "equally positive and negative" is because of the opamp "DC offset" (servo) circuit making the tubes equal output regardless of different tube or output strength ..
> 
> This is why we can mix same type tubes without worry of output imbalance.


That's not how it works, I believe I made a visual illustration of the WCF operation a while back on this thread.
The opamp servo just makes sure you don't blow up your heaphones with the OTL output, it applies the necessary grid voltages so the impedance between the two triode are at a ratio where the output is at 0v. Therefore no need for output transformer or capacitor.
In operation the signal flows from the bottom triode of the WCF to the opposing top triode for each phase (true current not conventional). There's no "channel imbalance" by mixing different tube types. The signal is in series with both tubes either way.


----------



## Maxx134

coinmaster said:


> But there must be another difference because one configuration always sound clearly worse then the other by a large margin.


I believe the reason is that :
1-Either both plus& minus oitput tubes are overlap near the zero mark, or
2- there is more difference in sound Because using different tubes for each half of the signal, like using two different amps.
This makes for greater differences detected in sonic image and is an added effect.
I liked effect as for me it combined the clarity of one tube with the increased bass of another,   but only worked better one way,
And switching I lost the clarity of the better tubes..
So I do not use mix tubes myself as I moved onto nicer tubes, but now I wonder if I should try again lol.


----------



## Maxx134 (Jul 3, 2017)

coinmaster said:


> That's not how it works


I am not talking about the WCF circuit.
I am talking about how each tube corresponding to each pin of the XLR and so each part of signal...
Nothing to do with the dam WCF and everything to do with the DC servo which you already mentioned..
SonicTrance LTP design didn't have this "separation of tubes" issue and not need a DC servo as his tube went to an output Transformer.


----------



## coinmaster (Jul 3, 2017)

> -Either both plus& minus oitput tubes are overlap near the zero mark





> there is more difference in sound Because using different tubes for each half of the signal, like using two different amps.


They both overlap during the entire signal. They criss cross between each other during each phase.

I don't know, the curves should average out no matter how you splice it. But there's something else going on.


> So I do not use mix tubes myself as I moved onto nicer tubes, but now I wonder if I should try again lol.


In my experience mixing always sounds better.



> Nothing to do with the dam WCF and everything to do with the DC servo which you already mentioned.


 Because of the above reasons the servo is not that cause. The servo only DC biases the tube so you have a 0v output. Sure this may cause a bias difference between its top and bottom triode within the WCF but it's in series with the other WCF anyway.


----------



## Maxx134 (Jul 3, 2017)

coinmaster said:


> The signal is in series with both tubes either way


I disagree we have a misunderstanding..

The signal is in series with both TRIODES WITHIN ONE TUBE..only...
 per each half of the signal!
Hehe..
EACH POWER TUBE being fed independent with XLR inputs and each separate triode within driver tube..


----------



## gug42

SonicTrance said:


> Yes, but not all of them. The three small resistors on each side of the pot are two grid resistors (10k) and one cathode resistor (1k5).
> 
> 
> Don't get 1W! You'd need to file down the leads for them to fit the holes in the board! You don't need any more than .5W anyway.
> ...



Thank you ! So only need 2 of them ! Didn't see it ....
Are you sure about 6SN7 ? Because I mostly have 6SL7.




Maxx134 said:


> It does not pay to get these caps, or even the mundorf I haf used,
> When there is better electrolytic cap available.
> The Audio Note Kaisie caps, said to be technology derived from famous "blackgate" caps :
> 
> ...



Why not ! But I didn't find a 470uF with 50V
https://www.hificollective.co.uk/catalog/-c-61_68_462.html

In the standard version, there is a HUGE one, too huge  
https://www.hificollective.co.uk/ca...dio-note-standard-electrolytic-capacitor.html



Maxx134 said:


> Ok:
> 
> Orange circled
> 
> ...



Sorry but can't read what you have write on the pic
Thank you about point me the right resistor to change .... !

By the way what did you think about my option 3 for bias driver ? (// mounted resistor)


----------



## coinmaster (Jul 3, 2017)

> The signal is in series with both TRIODES WITHIN ONE TUBE.


No, they are in series with the opposing tube. How do you think current flows through the load?

As the top triode goes low the bottom triode goes high, the other WCF being the inverse of this means the current flows from the bottom triode to the opposing tubes top triode for each phase.

However current is still shunted into the opposing triode within the same tube during these phases, I'm beginning to think that this is the cause behind tubes sounding different in different slot configurations.
Without a perfect current balance the current being shunted on each side (or not) is going to affect the end result of the curve averaging.
I didn't think much of it then, but I noticed on my new output stage that ensures equal current balanced between the triodes in the WCF that when I mixed tubes there wasn't much or any difference in either slot
This seems to make sense as the stock WCF is not going to maintain push pull across all frequencies.
I'll have to test it again because l wasn't thinking much of it at the time.


----------



## MrCurwen

> Yes they're both equall levels of positive and negative, but all due to the opamp DC servo control.
> 
> The reason why these outputs are "equally positive and negative" is because of the opamp "DC offset" (servo) circuit making the tubes equal output regardless of different tube or output strength ..



No.

The DC offset servo removes DC offset from the output. It does NOTHING else. As the name suggests, it only operates on DC.

Again, it does NOTHING to the AC audio signal (except some amount of low freq phase distortion which means nothing).

Think about the signal. At point A phase 1 (one side of the circuit) is positive, the other is negative. At point B phase 1 is negative, and phase 2 is positive. 

The reason they are marked is because the left and right channels need to have the same phase once the audio is reproduced (actual air waves). You can figure this out yourselves I'm sure. The phases could be marked A and B or green and yellow, it has no significance to the electric operation.

The circuit operates in class A, meaning both phases reproduce the whole wave. Both reproduce the positive side and the negative side.

As to this part:



> making the tubes equal output regardless of different tube or output strength ..



There is nothing in this circuit that makes the tubes output equal. They are roughly equal, but it's a gamble as to how much. This is why tube rolling produces different results. 

I've gone over these things before I won't ramble on about them anymore. But false statements simply are false. 

It is a matter of opinion what sounds good to somebody, but you are making factual claims here.



> So yes in balanced amp this is four outputs from four separate tubes adding separately to different part of signal, not working together like in your LTP amp.
> That's how I see it.



No, your amp does in fact operate in class A. All tubes conduct signal at all times, unless the amp is clipping.


----------



## Maxx134

Ok , so the opamp is changing the bias to each WCF to keep a zero DC between tubes but how that in series?


----------



## coinmaster

I made a bunch of visual descriptions a ways back explaining all this.
Basically the servo samples the output DC and strives to bias the top triode of the WCF at whatever DC voltage is needed to keep the output of the amplifier at 0v.

Think of tubes as variable resistors. When you change the grid bias, whether AC or DC the resistance changes.
The WCF is basically a resistor divider, so if we have +100v on the top, -100v on the bottom, and two equal resistors in between then the middle point is going to be 0v.
However the supply voltages aren't perfectly at +/- 100v and the triodes within the tube aren't perfectly matched not to mention that the bottom triode in the WCF is stuck at the mercy of the bias that the cathode resistor gives it.
So basically the opamp keeps the ratio of impedance between both tubes at a value where there is 0v at the midpoint.


----------



## MrCurwen

Maxx134 do you remember my ramblings about what a vacuum tube (triode in specific) is and what it does?

Think of a triode as an adjustable resistor. The voltage at the grid adjusts the ohm value of the resistor. The more negative the grid voltage, the higher the ohm value, and the more positive the grid voltage, the lower the tube equivivalent ohm value.

Now the two sides operate antiphase, meaning while the left side receives a positive input signal, the right side receives a negative input signal.

The WCF complicates this story a bit. The top tube receives the input signal, the bottom tube is operating antiphase to the top tube, on each side.

So while the left side top tube is getting a positive input, it's resistance is lowering. It conducts more current.

Meanwhile the left side bottom tube is receiving a negative input and cutting off current.

At the same time this same thing is happening to the other direction on the right side; the top tube is cutting off current, and the bottom tube is lowering plate resistance.

The extra current that is flowing thru left side top tube, thru the load (headphone coil), then thru the right side bottom tube. So the current finds a "lower resistance path" like this.

Once the waveform turns, this happens to the other direction.

"Plate or anode resistance" is not actually caused by the anode at all. The anode is as conductive as anything. It is a 'virtual' impedance caused by the negative electric field around the grid. Electrons that try to fly from cathode to anode are repelled by this field, so it emulates resistance.

So a triode is a dynamically adjustable resistor in essence.


----------



## coinmaster (Jul 3, 2017)

What he said, the current criss crosses between the bottom triode and the top triode of both tubes because when one end of the load goes negative, the other one goes positive resulting in a current flow between them, therefore both tube types are in series with each other when mixing.

The WCF should ideally have 50% of the AC current go into the opposing triode within the same tube and 50% of the AC current going into the load, this is why the sense resistor exists, it's to attenuate the signal to the point where the bottom triode isn't overamplifyng into the load, trying to achieve a 50% ratio. So while the bottom triode is in series with the top triode on the other end of the load, it's also in series with the top triode in the same tube, ideally 50/50. I'm using true current terms, if it makes it easier think in conventional current, top triode to bottom triode.


----------



## baronbeehive

gug42 said:


> .....
> 
> Why not ! But I didn't find a 470uF with 50V
> https://www.hificollective.co.uk/catalog/-c-61_68_462.html
> ...



If not Elna Silmics you have 2 options:

1 - https://www.hificollective.co.uk/catalog/audio-note-kaisei-220uf-100v-bipolar.html

Must be bipolar. The downside - these are expensive, £30.50.

2 - https://www.hificollective.co.uk/catalog/ecap63030-220uf-63vdc-mundorf-ecap-electrolytic-p-4010.html

These are what we used and are cheap.


----------



## gug42 (Jul 3, 2017)

Maxx134 said:


> Ok:
> 
> Orange circled



Sorry to anoy you and ask again  but well what you write seems important, at least for my eyes 
Can tell what have you write please ? And what to do with thoses two resistors ?  (Mout other in // or replace them ?) 

Thx !



baronbeehive said:


> If not Elna Silmics you have 2 options:
> 2 - https://www.hificollective.co.uk/catalog/ecap63030-220uf-63vdc-mundorf-ecap-electrolytic-p-4010.html
> These are what we used and are cheap.



Mundorf better than Elna SilmicsII ?


Thank you again !


----------



## baronbeehive

gug42 said:


> Sorry to anoy you and ask again  but well what you write seems important, at least for my eyes
> Can tell what have you write please ? And what to do with thoses two resistors ?  (Mout other in // or replace them ?)
> 
> Thx !
> ...



No, but the most important for sound quality are probably the coupling and WCF caps. If the Audio Note Kaisei are too expensive for you then the Mcaps are a cheap alternative to them and the Elna Silmics.

BTW You need 8 Mills MRA5 330R 5W resistors, 4 are on the reverse of the board!

Are you doing the mods yourself?


----------



## gug42

Hello 

Ok thx for the bypass cap. 

 On the first page only 4 in // of the 4 bypass caps are mentionned .... Are se talking for this mod  ?  

Perhaps the bias driver mod is a little out of my capability ...

Yes i will take my time to do it. I have a little experience in soldering and i have done recently... But elec math and calculation is too far away in my memory


----------



## coinmaster (Jul 3, 2017)

Just remember, if you wire those Mills resistors in the wrong way around your amp will explode with enough force to kill you on startup. Make sure you get the + / - end of the resistor correct.


----------



## baronbeehive (Jul 3, 2017)

gug42 said:


> Hello
> 
> Ok thx for the bypass cap.
> 
> ...



No.... EASY!!

Oh you mean 4 MRA5 resistors for the tube bias mod? Yes that is for that mod. However you may like to think of replacing all 8 of the power resistors, up to you.

Maths is not my strong point either lol !!




coinmaster said:


> Just remember, if you wire those resistors in the wrong way around your amp will explode with enough force to kill you on startup.



Cheerful chappie... seriously take note of safety, always disconnect and allow 30 minutes for the caps to discharge before touching anything inside.... Please *OBSERVE PROPER SAFETY PRECAUTIONS.*

With the mods you are doing you will notice a MASSIVE DIFFERENCE.......

Edit:
I forgot we don't like to raise expectations too much but leave it to you to discover for yourself these very worthwhile mods, as you will no doubt do!


----------



## coinmaster

Damn no one likes my jokes  I was trying to scare and confuse the poor guy.


----------



## gug42 (Jul 3, 2017)

of Course.  I'm not discouraget at all thx 

I will put this for  protection, safety first ! 


>


By the way .... well I'm in doubt about the "big" resistor cercled in orange ... replace them but what value ? (driver bias mod for 6SL7)


Maxx134 said:


>



You are my only hope guys !


----------



## gug42

Ok too easy to loose track of message here my bad 

So Maxx134, you go with 70k (4x resistors of 70k) and 1K (2x resistors) with your mk8

And SonicTrance for his mk6 and 6SL7 (==ECC35 ) go for 33K (4x resistors of 33k) and 330.

Well good, but what I don't understant here, is why there is two resistor for each anode of driver tubes ? They re un mountend in // ?
Thant's really disturbed me ...

Thx all !




Maxx134 said:


> That seems like enough t play with.
> 
> As I recall, the bias on the driver tubes were extremely lower than ideal,
> So me and Sonic were testing higher bias points and we came up with similar settings.
> ...





SonicTrance said:


> These are the settings I ended up with for the ECC35's. Major sound improvement over stock 220K Ra and 1K5 Rk.
> *
> ECC35*
> 
> ...





SonicTrance said:


> I'll repost some of my pics for you. You can find them here: https://www.head-fi.org/f/threads/l...re-on-first-page.782183/page-23#post-12052225
> 
> 
> 
> ...


----------



## Maxx134 (Jul 4, 2017)

Hey guys I was away and thanks for all these explanations helping me while I was away.



coinmaster said:


> The opamp servo just makes sure you don't blow up your heaphones with the OTL output, it applies the necessary grid voltages so the impedance between the two triode are at a ratio where the output is at 0v.


Ok I see my mistake each tube out at 0v
So accordingly to how old and unmatched the triods are within each tube, they will be biased separately to have Ov dc output each..
The trim pots at opamps for each tube assures both tubes are calibrated equally, whether they both be at 0v or at 1v , as the trim pot allow a variable setting around the 0v so both tubes can be adjusted very closely and probably more exact than the opamp circuit can without the trim pot.




coinmaster said:


> In operation the signal flows from the bottom triode of the WCF to the opposing top triode for each phase (true current not conventional). There's no "channel imbalance" by mixing different tube types. The signal is in series with both tubes either way


I see now thnx.



coinmaster said:


> Sure this may cause a bias difference between its top and bottom triode within the WCF but it's in series with the other WCF anyway.


Ok!



coinmaster said:


> No, they are in series with the opposing tube. How do you think current flows through the load?


I was not thinking of any load!
thats why lol my bad.




coinmaster said:


> However current is still shunted into the opposing triode within the same tube during these phases, I'm beginning to think that this is the cause behind tubes sounding different in different slot configurations


I see now, with the load connecting both different tubes in series,
the difference in the tubes resistances and volt drops will affect the signal across the load.



MrCurwen said:


> The DC offset servo removes DC offset from the output. It does NOTHING else


I am now curious to know if the op-amp has to adjust bias to achieve zero DC offset within the tube ,
Then with a slightly different tube (when mixing) it would do same but would need to adjust at different amount for the different tube.
Then that different tube is set at a different bias to preserve the Zero DC, so it should have a different load line too.



MrCurwen said:


> No.
> The DC offset servo removes DC offset from the output. It does NOTHING else.


 but it needs to change/regulate  the bias in doing so.



MrCurwen said:


> It is a matter of opinion what sounds good to somebody, but you are making factual claims here


Yes I am when it counts lol.
I trying to spare newcomers headaches so I explain less when I should explain more so I won't sound like that.

I made you feel I making claims.
The mix up is We were talking about  mixing tubes so my assumptions were just that which you and coin helped me understand more...

I was trying to explain some reasoning for my factual observations.
I did observe, (when mixing tubes) the left tube of each side determine the quality or have predominant role..

 I did observe a better bias points for driver stage..
Very much  so..

I did observe better caps than the Russian PIO which I still have..



Observation and testing is what proves theories as it is what actually occurs,
and so it is not matter of opinion.
So when a test shows an improvement then it is so.

Also,
I can agree about preferences not being improvements, but just preferences..
Like preference for more intimate sound, or more euphoric tube sound, or more Soundstage is all matter of opinion.
Yes that's true.

Amplifiers should be as resolving as possible..
So For me it needs to sound true to source, not altered with those  preferences.

So for me its not a matter of opinion if I observe an improvement,
because I base it on being more accurate.
That's why I stayed with my driver tube bias settings.

That's also why first page only has mods thats were tested, observed and verified to have actuall Improvement.

I can also agree many amps are easy to improve because they are not using modern techniques you and Coin  describe.




MrCurwen said:


> So a triode is a dynamically adjustable resistor in essence


I like this explanation very much  thanx.



coinmaster said:


> What he said, the current criss crosses between the bottom triode and the top triode of both tubes because when one end of the load goes negative, the other one goes positive resulting in a current flow between them, therefore both tube types are in series with each other


Ok so they both in series but not behaving with same "dynamically adjustable resistance" , so we also hearing the summed "difference" between them!





gug42 said:


> By the way what did you think about my option 3 for bias driver ? (// mounted resistor)


Yes, that is currently the easiest way to go,
Just add a parallel resistor to change the anode resistor and cathode resistor,
Which is what I did.
Just use the parrellel resistor formula.



baronbeehive said:


> allow 30 minutes for the caps to discharge before touching anything in


You not have to wait 30 minutes if you unplug, and press power button on..
It should take only a few min, 3- 5 the most.



gug42 said:


> So Maxx134, you go with 70k (4x resistors of 70k) and 1K (2x resistors) with your mk8



Yes and it does not matter which amplifier as both the MK6 and the MK8 have same driver stage,
But different power tubes.
So you can try both mine and SonicTrance values as he use the same mk6.
The difference would be the mu gain of the different power tubes, but as I recall both amps sounded great with the 6SL7 over the 6sn7.


----------



## coinmaster (Jul 4, 2017)

> I am now curious to know if the op-amp has to adjust bias to achieve zero DC offset within the tube ,
> Then with a slightly different tube (when mixing) it would do same but would need to adjust at different amount for the different tube.
> Then that different tube is set at a different bias to preserve the Zero DC, so it should have a different load line too.


Yeah I mentioned that earlier and the more I think about it the more I think it could be another big candidate for why tubes could sound different in different slots, but it would only affect which phase gets distorted by which tube.

For example if we have the tubes in X/Y position then we would get the average of both tube curves but if the top triodes in X/Y are at a different bias then the bottom triodes then the positive half of the waveform would have a different distortion figure then the bottom half. Let's call this distortion A distortion on the positive waveform and B distortion on the negative waveform.

So if we switched the tubes from X/Y to Y/X then A and B distortion would switch places. Creating a sort of inverse distortion. I guess I could actually test this theory on my oscilloscope.



The bottom triode grid is stuck at B- voltage so the biasing of the bottom triode is fixed based on the cathode current.
However, the opamp adjusts the top triode to compensate so there is 0v on the output. This means in a typical configuration the top and bottom triode are probably not biased the same.
Meaning if the top two triodes in each WCF are biased differently then the bottom triodes then that would mean the averaged curves of both the WCF top and bottom triodes in series during each phase would be different on both the positive and negative phase even though the current is technically flowing through the same tube types during each phase.



> Ok so they both in series but not behaving with same "dynamically adjustable resistance" , so we also hearing the summed "difference" between them!


Yeah, that's why when mixing tubes you often get the best traits of both tubes in the sound. Which is why I always find it better to mix tubes then to use all the same tubes.



> You not have to wait 30 minutes if you unplug, and press power button on..
> It should take only a few min, 3- 5 the most.


I wait about 3 seconds. My amp takes about that long to discharge. With hot tubes it shouldn't take more then a few seconds to drain the PSU caps. Check with a multimeter and see.


----------



## gug42

Maxx134 said:


> Yes, that is currently the easiest way to go,
> Just add a parallel resistor to change the anode resistor and cathode resistor,
> Which is what I did.
> Just use the parrellel resistor formula.
> ...




Ok thank you for this confirmation ! 
I wiil mount resistor in parallel.  I will buy resistor for both value, yours and SonicTrance.

So I modify my shopping list to get the two possibility with parallel mounted resistors  

Without modification, and with a RCA dac, I already found that the mk6 is a really good amp !

*Options 1 70k anode et 1K cathode :*

4 x TDK 2W 100KOhms  (*ok the result will be 68,5K ...* close enough to 70K isn't it ?)
https://www.hificollective.co.uk/catalog/cm2570-100k-correctohm-metal-film-resistor-p-9708.html

2 x takman metal 0,5W 3Kohms
https://www.hificollective.co.uk/catalog/rey50385-takman-metal-film-resistor-p-4861.html
*Options 2 33K anode et 390R cathode :*

4 x TDK 2W  39KOhms  
https://www.hificollective.co.uk/catalog/cm2520-correctohm-metal-film-resistor-p-9703.html

2 x takman metal 0,5W 560ohms  (*the result will be 407R)*
https://www.hificollective.co.uk/catalog/rey50300-560r-takman-metal-film-resistor-p-4844.html

Thx for you


----------



## SonicTrance

gug42 said:


> So I modify my shopping list to get the two possibility with parallel mounted resistors


Shopping list looks good! Though for future mods you'll probably need to get rid of the parallell resistors. Especially the anode resistors as they take up a lot of space.
Look at mine how cramped it is.


----------



## MrCurwen

> I did observe better caps than the Russian PIO which I still have..



Those are not KBGs. I have those ones you have there as well; I wouldn't use them in a HIFI build myself. Soviet union produced a number of quite different caps for different purposes and different quality standards.



> Observation and testing is what proves theories as it is what actually occurs,
> and so it is not matter of opinion.
> So when a test shows an improvement then it is so.



I am starting to get the point that many of your goals are quite divergent from my own. To put it bluntly, many people here seem to be after an effects filter, not transparent sound reproduction.

To each their own, but if we speak completely different languages it's maybe not very productive for me to ramble on about things which don't really mean anything to most readers.

I personally find absolutely no dissonance between theory and practice. Or, if I do, it disappears in due time as I learn more. That's why I think it's important to understand what actually go on inside electronics circuits; otherwise it's just shooting in the dark. True, sometimes you hit the mark, but that's not for me.

If you are still in the place "low THD == nasty and dead SS sound" then ok I guess effects producers are nicer to listen to.

If the music has IT (whatever 'it' may be; wide soundstage, powerfull dynamics, kick, ambience, personal presence, whatever), a low THD open loop transparent system WILL provide it. 

Adding stuff to the signal as opposed to letting it pass most uninterrupted is another hobby from mine in my opinion.


----------



## MrCurwen

> You not have to wait 30 minutes if you unplug, and press power button on..
> It should take only a few min, 3- 5 the most.



I personally always measure before touching. It takes no extra effort and you don't have to wait any extra time because you know instantly when it's ok to touch.


----------



## gug42 (Jul 4, 2017)

Thx a lot ! really appreciate 
Indeed nice works very impressive  

Forget the switch ... damned



SonicTrance said:


> Shopping list looks good! Though for future mods you'll probably need to get rid of the parallell resistors. Especially the anode resistors as they take up a lot of space.
> Look at mine how cramped it is.


----------



## coinmaster (Jul 4, 2017)

> To put it bluntly, many people here seem to be after an effects filter, not transparent sound reproduction.


The issue is you are preaching about transparent sound reproduction on a thread about an amplifier whos main advantage is to be a distortion generator.
I think the thing you are missing is that a distortion generator can "sound" transparent, and even better. Our brains aren't offended by low order harmonics because it is the same type of distortion as mechanical distortion present in real life sounds.
Higher order distortion is electrical distortion, it does not exist in nature.
If you have an amplifier of a certain harmonic structure at a very low THD and you simply level shift the distortion upward to a higher THD, the odds are it will sound similar yet more pleasing to the ear.


----------



## SonicTrance

MrCurwen said:


> I personally always measure before touching.


+1
Always measure. Better safe than sorry.


----------



## gug42

Is this enough for the toggle switch of 5998 bias mod : 

Contact rating (AC): 5A 120VAC/28VDC 2A 240VAC 

Contact rating (DC): 5A@120V
http://www.ebay.fr/itm/131171914389

Thank you ! Want to be sure


----------



## SonicTrance

gug42 said:


> Is this enough for the toggle switch of 5998 bias mod :


Yes, no problem.


----------



## MrCurwen

What is the consensus opinion of this thread:

Is the LD a top quality world class HIFI amp or a distortion generator?

Excluding audiophoolery (the gold and (snake) oil magic fuses part of the scene), these two are mutually exclusive. A distortion generator can be a so-so HIFI amp at the most if you're being charitable.


----------



## baronbeehive (Jul 4, 2017)

MrCurwen said:


> What is the consensus opinion of this thread:
> 
> Is the LD a top quality world class HIFI amp or a distortion generator?
> 
> Excluding audiophoolery (the gold and (snake) oil magic fuses part of the scene), these two are mutually exclusive. A distortion generator can be a so-so HIFI amp at the most if you're being charitable.



I don't think its aim is to be totally transparent, no. I do think however that the makers have produced a competitive amp which is extremely pleasing to listen to, I've had 2 as well as other amps, including SS, which by the way was extremely pleasant also. I don't think it sounds old school either. Take together with the parts upgrades I think it's even more competitive and I love the sound. I said that the Jupiters make it "sound" more transparent, even if it isn't and so I think we have achieved our aims. I appreciate the stock design leaves a lot to be desired.

I'm very interested in other designs as well but for me I'm happy atm! Maybe I'm not the one to comment on the theoretical side, interesting though it is.

On the subject of transparency I was interested to hear Sonic say that the amp he has built from your design though transparent is also non fatiguing, so transparency does not imply overwhelming detail and painful listening. The little SET amp I have is also quite transparent yet not at all difficult to listen to, on the contrary. It also provides a comparison to the LD, and both perform at a high level now.

Also we wouldn't have rock 'n roll without Jim Marshall don't forget!


----------



## Maxx134 (Jul 4, 2017)

MrCurwen said:


> I am starting to get the point that many of your goals are quite divergent from my own. To put it bluntly, many people here seem to be after an effects filter, not transparent sound reproduction


Just because an amp has a "flavor" does not make it less transparent.

The last few pages We are just trying to understand effects of tube mixing.
Not have to do with the quality of the amp.

Many top amps have way much more THD, because the designers know that the actual measurement of "THD",
 is skewed... To have low numbers...

We now know after so many years that  all orders of Harmonics are not equal, as  we know that "lower order" Harmonics are way less harmful to sound than the higher and odd order Harmonics that are mostly produced by SS  at lower amounts.
I realize you also advocate zero feedback which is source of such problems.


I do agree that The newer designs which implement amplification only in triodes while having the SS controll other aspects like PSU & current and buffer are excellent choices of design I am realizing,
 and are rarely implemeted in todays top tube amps so I do appreciate all your insights.




MrCurwen said:


> I personally always measure before touching. It takes no extra effort and you don't have to wait any extra time because you know instantly when it's ok to touch


Best practice!


----------



## coinmaster

> Is the LD a top quality world class HIFI amp or a distortion generator?


 Who cares if it is Hi-Fi, Distortion generator, or a piece of cheese as long as it sounds good.
A distortion free amp is bound to sound boring, the worldly consensus is that distortion sounds good, I think you are biased too much toward infinitely low distortion, harmonic structure and harmonic behavior is more important then THD. 

From your obsession with whatever your version of "transparency" is it seems you have not had the pleasure of listening to a highly euphonic amp yet.
If you play around with the MK6 and get the distortion "just right" you can achieve scarily realistic sounding music (like the person is in the room with you) and at the same time mind melting euphony. 
Who cares whether it is by definition "transparent", my ears aren't listening to the philosophical concept of transparency, they are listening to the music.


----------



## MrCurwen

The reason I asked that question is quite practical; you need to know what you are doing to go about it in any sensible way. If you're going swimming you need different stuff with you than when you're going hunting.

It's also not to promote my own circuits or any other circuits, but to understand what it is that you're doing here, in light of some recent messages here. 



> I don't think its aim is to be totally transparent, no. I do think however that the makers have produced a competitive amp which is extremely pleasing to listen to



Transparent and pleasing are not mutually exclusive, assuming you are listening to recordings you appreciate.

A circuit can be less than totally transparent (which is an unattainable goal in strict terms but let's just get past that) while still striving to be as transparent as possible within some limitations. These limitations can be philosophical ("I only use X components" or "I only use X topology") or practical ("I don't think that is worth doing because of cost / benefit") or whatever ("that's not going to fit in my chassis"). 

It still matters what the context is with regarding what it is you think you are doing. Are you making a HIFI reproduction system (within some limitations) or are you making an effects producer (not HIFI)?

Name of this forum contains the word 'fidelity'. I assume this is referring to fidelity towards the reproduced material, as it is commonly understood in the phrase HIFI. 



> Take together with the parts upgrades I think it's even more competitive and I love the sound. I said that the Jupiters make it "sound" more transparent, even if it isn't and so I think we have achieved our aims. I appreciate the stock design leaves a lot to be desired.



That is fine. My question isn't meant to be framed as "your amp is crap", which I don't think it is. I think it's a decent amp, but not nearly as good as some earlier messages set it out to be. What I'm after is the goals of the modifications and discussion. Is it to reproduce sound with fidelity (within factual and perhaps ideological constrains) or is it to produce effects filters using semi-random trial and error?



> On the subject of transparency I was interested to hear Sonic say that the amp he has built from your design though transparent is also non fatiguing, so transparency does not imply overwhelming detail and painful listening.



I don't mean to continue hijacking this thread further with this particular topic but again on the definition of transparent; 

If the recording is produced to be painful to listen to, a transparent amp should reproduce a painful listening experience. If it is produced to be pleasant to listen to, a transparent amp should reproduce a pleasant listening experience. Same thing with detail, and soundstage and everything.



> Also we wouldn't have rock 'n roll without Jim Marshall don't forget!



Indeed. I got my distortion shaping stripes building and eventually designing a couple dozen guitar amplifiers. First it was quite painstaking trial and error, but in the end I got really good at designing guitar amps that have just that pleasant, juicy distortion that I myself prefer. That experience really helped me to make HIFI amps; as a main rule simply do the opposite of what you would do when designing a guitar amp.

Think of it like this; I understand the guy who spent X hours designing the guitar amp used in a recording (let's skip the studio stuff here for simplicity). If my HIFI amp were to ADD something to that, it would ruin the sound of the guitar on the recording.

I want to listen to the recording, not my HIFI equipment. I like the recording, that's why I'm doing HIFI.

Further on this path;

There is no 0% THD amp available, but if you have an amp that adds a SIGNIFICANT (and it's 100% up to you to decide what constitutes significant for you) amount of let's say just 2H and a fraction of 3H (so the 'natural' waterfall FFT pattern). Let's say you are listening to a beautiful recording of an acoustic instrument with a nice natural complex harmonic structure like a flute.

Your amp adding those harmonics to the flute causes IMD with the original harmonic content on the recording, causing those UNNATURAL odd harmonics. Furthermore this then MASKS micro level detail, ruining spatial information (that coveted soundstage).

What about when you listen to a recording with non-natural instruments or effects? Why should a 80's synth or a 60's flanger effect have the harmonic signature of a flute or a piano added on top of it? Should everything sound more the same? Also the IMD and masking effects ("the dirt" or "the veil" on top of the sound) would apply.

Back in my early days I was big on euphonics and I read all the SE stuff advocating for the benefits of 2H and 3H. I used to be "SE for life".

When I got on and found ways to lower distortion open loop, I realised I enjoy listening to music more than I enjoy listening to my HIFI equipment. 



> Just because an amp has a "flavor" does not make it less transparent.



Let's say you have a painting. You put a glass in front of the painting. No glass can be 100% transparent, but if you put a clear glass in front of the painting you can see painting better than if you put a stained glass (like in churches) window in front of it. Sure you might enjoy the stained glass artwork a lot, but a person who came to see the painting might be a bit disappointed.

Just because an amp has a flavour does make it less transparent by definition. Striving for higher fidelity means removing any interfering (good or bad) flavours. The flavours you must have (because cannot get rid of them) should of course be as benign as possible (i.e. whatever THD you have should be concentrated on the 2H and 3H area).



> Many top amps have way much more THD, because the designers know that the actual measurement of "THD",
> is skewed... To have low numbers...



2H is less bad than 7H. Having more 2H is worse than having less 2H.



> We now know after so many years that all orders of Harmonics are not equal, as we know that "lower order" Harmonics are way less harmful to sound than the higher and odd order Harmonics that are mostly produced by SS at lower amounts.
> I realize you also advocate zero feedback which is source of such problems.



Yes I read this stuff ten years ago back when I was building direct coupled SE amps. The question was about the fundamental premise of:

Do you prefer to have an amp with X amount of 2H, rather than an amp that has the least possible (within practical and perhaps ideological constraints) amount of 2H?

The first is an effects filter, the latter is a HIFI amp of some quality, depending on the success of the design and build.




> I do agree that The newer designs which implement amplification only in triodes while having the SS controll other aspects like PSU & current and buffer are excellent choices of design I am realizing,
> and are rarely implemeted in todays top tube amps so I do appreciate all your insights.



Thank you. This tends to sound like you prefer fidelity and transparency more than adding effects. 

I must - tongue in cheek - remind you that Sonics new build doesn't have all triode tubes. The second gain stage is TV sweep beam tetrodes! My upcoming builds have all pentodes. Of course these are all triode strapped but just to put a point accross, in case anyone thinks triodes are somehow magical.

Bit of a long post but I think this topic is quite relevant. What is your goal in doing these modifications?


----------



## gug42 (Jul 5, 2017)

Hum thank you all. Last question, how did you fix thoses bigs caps ? glue  between the board and the caps ? patafix ? scotch ? nothing, just the pin ?


----------



## baronbeehive

MrCurwen said:


> ......
> 
> 
> I don't mean to continue hijacking this thread further with this particular topic but again on the definition of transparent;



Not a problem for me!



MrCurwen said:


> .....
> 
> I want to listen to the recording, not my HIFI equipment. I like the recording, that's why I'm doing HIFI.



Agreed, I really don't like listening to my HIFI for its own sake.



MrCurwen said:


> ....
> 
> Further on this path;
> 
> ...



Absolutely agree! However very few recordings get the soundstage right due to bad production and unnecessary microphone placement etc. so it's rare to hear a pure soundstage without artefact.



MrCurwen said:


> What about when you listen to a recording with non-natural instruments or effects? Why should a 80's synth or a 60's flanger effect have the harmonic signature of a flute or a piano added on top of it? Should everything sound more the same? Also the IMD and masking effects ("the dirt" or "the veil" on top of the sound) would apply.



Sorry to agree again!



MrCurwen said:


> ........
> 
> Bit of a long post but I think this topic is quite relevant. What is your goal in doing these modifications?



As I said I think we have realized our goals in this thread. My LD is a "value" piece of kit, part of the fun was to achieve what we have without spending a fortune. It does have a flavour which I like but I think it has         eenough transparency.  It can sound stunningly real. 

Doesn't mean I might not change my mind later! I think the circuit mod points you raise are interesting points for future projects but I can't really see that we would be able to substantially alter the circuitry of the LD. I    may be wrong.


----------



## baronbeehive

gug42 said:


> Hum thank you all. Last question, how did you fix thoses bigs caps ? glue  between the board and the caps ? patafix ? scotch ? nothing, just the pin ?



You can glue or use cable ties.

I think we mainly just used the legs of the caps. You can use wire also. I used Neotech 20 AWG, UP-OCC copper single core wire, RED Teflon wire for the large PSU caps for example. This is stiff enough to hold them in place!


----------



## coinmaster (Jul 5, 2017)

> The reason I asked that question is quite practical; you need to know what you are doing to go about it in any sensible way. If you're going swimming you need different stuff with you than when you're going hunting.


That's kind of a moot point since making an amp with low THD is relatively straightforward and there are a near infinite ways to create distortion so there's no way to intentionally create a hi-fi sounding "effects" amplifier without understanding the science behind distortion and euphony and how they interact. So far there's not much officially known or documented about it. At least not that I've ever seen.
And no I'm not talking about guitar style distortion.

Fidelity isn't a virtue, good sound is a virtue.



> I think it's a decent amp, but not nearly as good as some earlier messages set it out to be


Nonsense, just because it's not your definition of "transparent" electrically does not mean it doesn't sound that way. The if realism and euphony aren't the goals then what would be? The problem is because it is basically a distortion "rolling" device, there are many many ways to "roll" the distortion so I'm sure a lot of people here haven't even maxed their system out yet.
You really ought to try the amp before forming any official opinions.



> What I'm after is the goals of the modifications and discussion. Is it to reproduce sound with fidelity (within factual and perhaps ideological constrains) or is it to produce effects filters using semi-random trial and error?


Strictly speaking fidelity means the output signal is faithful to the input signal. We are not after fidelity, we are after good sound, perceived fidelity is all that matters.. Why bother listening to a THD meter when you can listen to the music?
Honestly if I didn't know any better I would have thought that he MK6 is very high fidelity by definition.



> Let's say you have a painting. You put a glass in front of the painting. No glass can be 100% transparent, but if you put a clear glass in front of the painting you can see painting better than if you put a stained glass (like in churches) window in front of it. Sure you might enjoy the stained glass artwork a lot, but a person who came to see the painting might be a bit disappointed.


You got it all wrong dude, the modded MK6 does not sound like a guitar amp. It sounds as clear and real as real life with the right set-up, but with euphony added in. Even with that being said, this amp is certainly not an ultra low THD amp, meaning it must be a distortion generator in some way. It's clear that is the case due to how easily I can adjust all aspects of the sound by mixing tubes and doing parts mods.



> What about when you listen to a recording with non-natural instruments or effects? Why should a 80's synth or a 60's flanger effect have the harmonic signature of a flute or a piano added on top of it? Should everything sound more the same? Also the IMD and masking effects ("the dirt" or "the veil" on top of the sound) would apply.


The music I listen to is a combination of classical, EDM, rock, and vocals mixed into one song.
I'm not sure what you call that kind of music but I really like it. I guess it's unique to touhou so I guess it would simply be touhou music.

Basically it's got every kind of natural and non-natural mixed into it, yes including flutes sometimes.
I hear nothing but crystal clear sound and tight sound separation throughout. Of course this was before my DAC broke, not really the case using an ipod.
In any case no "dirt" or "viel".




> 2H is less bad than 7H. Having more 2H is worse than having less 2H.


Only if you are a robot. If the original recording had more 2H in it would it matter then? You seem to imply the original recording is perfect and knows all.
Fidelity for the sake of it is good for robots not humans.



> It can sound stunningly real.


What he said. If it sounds real does it really matter whether it is electrically "transparent" or not?
I'm not listening to the philosophical concept of transparency when I listen to music, I'm listening to the music.

In short I think a hifi sounding "distortion generator" will please more then simply listening to the fidelity of your DAC or the raw recording.
In fact I tested this by using a low distortion power buffer in front of my DAC. (dac output voltage is usually enough to drive headphones without amplification)
The result was clean and clear and boring sound.

I did compare one of my prototype amps to the MK6 in a stage by stage comparison I.E. input state to input stage, output stage to output stage.

Mine won out easily against the individual stages of the MK6 but I used my headphone out jack on my PC as a source during this so it sounded not that great in general, I could only really compare between the two.

The jury is still out on how that prototype would have compared to the MK6 with a proper balanced set-up, good power supplies, and compared with all stages intact. 

For example, if I were to replace my input tubes with my ipod (which I did initially recently) it would sound "okay" (keep in mind this is in reference to me having no DAC in SE mode)
but adding in the input tubes makes it sound way livelier and more enjoyable.

Now if I were to switch out my 5998s with some Gec 6080 tubes it would sound a lot worse.
The point being the MK6 has a complex array of distortions that all meld into the end result.

 Meaning while my prototype did beat out the MK6 stages individually, more testing is needed.
I'm working on upgrading my "lab" to a more respectable one so I can do proper testing and prototyping.


----------



## baronbeehive (Jul 5, 2017)

I meant to say a couple of other points in my last post as to why I like my LD especially post mods:

1 - There is the question of substandard recordings which can sound horrendous but are much better to listen to if some sort of rounding off process occurs.
2  - Then there is the point about "artificial" software equalizers which I don't like, therefore if the house sound of the amp is sufficiently to your liking that you can listen to poor quality recordings and you don't feel you need an equalizer that's all to the good.
3 - Finally I've been to many live concerts and for me to get 90% of the sound of the live concert is OK. I get this with the LD with Tungsol tubes. I know they are not accurate in sound reproduction but to have a near enough reproduction of a live concert, albeit with the edges rolled off, which I personally like, is fine.
I also prefer some roll off for headphones because it makes listening less fatiguing.
My other amp is a speaker amp and also has Tungsol tubes but the leading edges are much more sharp and defined with a lot of textural information and give me an extra 5% of the live sound, still not perfect, or accurate but I really like it. I feel it is more transparent than the LD, and probably approaches the sound of the Decware amps such as the ZEN which are famously transparent. BUT.... they cost an arm and a leg!


----------



## coinmaster

Edited a few things into my last post.


----------



## Maxx134

MrCurwen said:


> I must - tongue in cheek - remind you that Sonics new build doesn't have all triode tubes. The second gain stage is TV sweep beam tetrodes! My upcoming builds have all pentodes. Of course these are all triode strapped but just to put a point accross, in case anyone thinks triodes are somehow magical


Wait a minute,
 triodes are not magical?
Aren't they supposed to be the pest form of amplification??
 damn!  haha yeah I noticed as I have the same design in my mini amp running  with been power tubes (6v6) in " triode strap" mode in my mini amp
Nice truck to run them as triodes.





MrCurwen said:


> Bit of a long post but I think this topic is quite relevant. What is your goal in doing these modifications


My goal is to liven up the driver Stage to perform better than it was...

It was running at a super low bias which was lifless and also very tube rolling  dependent...

So basically I wanted to improve it ,
even though there's PSU limitations with that stage.
That is why I increased bias point and did achieve a mich more resolving, alive and dynamic  sound.
The load line was in a much better and linear spot on the curve.

I have been very happy with this new bias point, but  I remember you specifically made note that the common cathode resistance is way too low to have the triodes performing equally..

So now I want to try member coinmaster suggestion to try with a CCS at the Cathode.




gug42 said:


> Hum thank you all. Last question, how did you fix thoses bigs caps ? glue  between the board and the caps ? patafix ? scotch ? nothing, just the pin ?


Plastic ties , but hot glue is my fav .
Nice and messy haha.




baronbeehive said:


> approaches the sound of the Decware amps such as the ZEN which are famously transparent. BUT.... they cost an arm and a leg!



Don't believe this hype!
 inside the Deckwere they're using way less quality of modest coupling caps (Jupiter Beeswax) than what we are using, and that makes a huge difference!

This is an example of deliberate sound manipulation by using these caps which are thicker sounding and have a more natural tone than most.
They probably wanted to get away from the plasticy trebles of most caps.

So although they have a thicker sound,
 they don't have the same sound stage. Even if the tubes can be adjusted for Soundstage,
 the clarity will never be as good what we havr with these MK6&8, because of thier usage of modest level capacitors for critical coupling of the driver to the power stages.

I've heard Decware amps,
 both in private homes and n meets,
There is nothing special about them except that they are nice upper level amps.
don't be fooled by the hype.


----------



## MrCurwen

> As I said I think we have realized our goals in this thread. My LD is a "value" piece of kit, part of the fun was to achieve what we have without spending a fortune.



Indeed. 

I personally wouldn't spend a thousand dollars or euros on an amp, but I can understand that DIY is not for everybody. Surely the LD has a recognizeable name, so there is resell value.



> It does have a flavour which I like but I think it has eenough transparency. It can sound stunningly real.



Not sure if this applies to you specifically (the above quote would suggest no), but just to bring the point home;

Transparency and realism are not mutually exclusive in any way. In fact if the recording sounds 'real', then a transparent amp will convey a most convincing amount of realism.

Just to bring an example, back when I was still in possession of my flagship amp, I had a cello player friend of mine listen it. He brought a recording of his cello master. The recording was very well made, and very lightly produced.

When we played it, he was stunned at how much it sounded like he was playing in the same room with us. He even recognized the cello his master uses, by sound. He said he hasn't been able to hear that specific signature on any other system.

Now that I call transparency. The realism was there in the recording, and the system allowed it to be played back, to be reproduced without destroying it somehow.

The easiest way to destroy a delicate signal with complex spatial and harmonic signatures (i.e. realism) is to splash some extra harmonics (no matter how benign or natural) on top of it. But more on that later.



> I think the circuit mod points you raise are interesting points for future projects but I can't really see that we would be able to substantially alter the circuitry of the LD. I may be wrong.



I suspect you are not wrong. Chassis size is the biggest constraint. If you start a new chassis, why not go for a different, fundamentally better design anyway.



> You can glue or use cable ties.



Superglue is my most important material after solder and wire. Look at Sonics great quality pictures, he has adopted the superglue approach as well. What superglue cannot fix cannot be fixed.




> 1 - There is the question of substandard recordings which can sound horrendous but are much better to listen to if some sort of rounding off process occurs.
> 2 - Then there is the point about "artificial" software equalizers which I don't like, therefore if the house sound of the amp is sufficiently to your liking that you can listen to poor quality recordings and you don't feel you need an equalizer that's all to the good.
> 3 - Finally I've been to many live concerts and for me to get 90% of the sound of the live concert is OK. I get this with the LD with Tungsol tubes. I know they are not accurate in sound reproduction but to have a near enough reproduction of a live concert, albeit with the edges rolled off, which I personally like, is fine.
> I also prefer some roll off for headphones because it makes listening less fatiguing.



This message could've been written by past me, I've been in this place. I listen to a lot of old stuff that is recorded quite poorly. One of the best examples is the catalogue of Robert Johnson. While I thoroughly enjoy his music, the sound quality is so rough it can be quite taxing to listen to.

Fortunately I found a way around this.

What the last sentence of point 3 tells me is that your system produces some amount of harmonic content, more than it should according to your ears. Let's go back to this:

The easiest way to destroy a delicate signal with complex spatial and harmonic signatures (i.e. realism) is to splash some extra harmonics (no matter how benign or natural) on top of it.

Distortion measurements are usually done using as pure a sine wave as possible, then looking at the output and it's harmonic content. Let's say the output at 1kHz has some 2H and less 3H, no higher harmonics. 

Ok then, what happens when you input into this hypothetical amp a signal with equal amounts of 1kHz and 3kHz. What comes out?

Both of these signals produce their 2H and 3H. Then these 4 newly created harmonics also SUM TOGETHER, creating 4H, 5H, 6H and 7H at lower levels. So now we have quite a complex mat of harmonics from these two (1kHz and 3kHz) inputs.

Now imagine you input a complex signal with multiple instruments into this amp.

You are going to have a mess. Granted these sum harmonics are at a low level, but the higher you go, the nastier they are even at low levels.

Incidentally this sum effect is how and why great amounts of gNFB produces a complex mat of very low level harmonics. It's an "infinite sum loop" to simplify a bit.

Wave physics 101. I remember this part from my days in EE university (I changed majors since). Think about a still surface of water. You drop a perfect round object into water; it creates a ripple. The ripple waves are bigger the closer they are to the point of impact (W1 and W2 are biggest, rest are quite small in comparison).

Now if you drop two round objects of about same size simultaneously, they will exhibit the same ripple behavior close to the impact site, but where the waves meet each other, they produce a lot of very small erratic ripples (higher harmonics of the wave), because the waves sum.

This metaphor is not 100% applicable to electric waves, but in essence the same thing happens with them.

For this reason alone (to avoid complex IMD products) I personally would like to minimize the amount of harmonics my amp adds to the signal.

My SE amps have a substantial amount (depends on what's the comparison I guess?) of 2H and some 3H. While they sound very nice, there is a 'something' on top of the sound at all times. The dynamics ("the kick") largely compensates for this when using speakers, and I wouldn't make a SE headphone amp anymore.

This is also the 'dirt' / 'veil' that Sonic described in comparing amps in another thread.

Distortion (however 'benign') always masks detail. Detail conveys realism; the subtle cues that come from the room, or from the instrument. One consistent comment I get from people who listen to open loop low THD amp for the first time is that they become suddenly hyperaware of the fact that the instrument they are listening to has a physical form. Like you cannot stop imagining the acoustic guitar you are listening, because you hear these subtle audio signatures that come from the body of the guitar.

This effect is most pronounced on human voices for understandable reasons.

These audio cues are transmitted in the higher register. You can rough test this by cutting frequencies above 12kHz and see what happens to spatial information. Now if your amp has even a tiny amount of higher harmonics, you cannot hear these, they are drowned in these harmonics.

Now to bring it back to your quote;

A rough recording with quite high distortion is going to sound bad when EVEN MORE distortion is added, because it will further mask the "realism information" and it will produce nasty IMD products. Get a cleaner OPEN LOOP amp and these problems are greatly alleviated. At least this has been my finding.


My experiences with shaping distortion back in the instrument amp world are about 60 to 70% on CLEAN guitar. Plug a guitar to a HIFI amp and play clean. It's horrible. The 'clean' guitar sound, whenever nice sounding, is in fact quite distorted (in HIFI terms). There is no reason to add any distortion during reproduction, if a nice guitar amp was used; a transparent amp will make it sound every bit as nice as it was in the studio. Unless the engineer was an idiot.


----------



## gug42

Hello 

Thx. The problem with glue is unmount sruff.... Well fist i will try patafix ... 

The other point  : don't what bias driver mod to use for 6SL7WGT the one with 33kr/400r or 77k/1k and which method (// soldering or dirty replace with cutting the legs) ....


----------



## coinmaster (Jul 6, 2017)

> Transparency and realism are not mutually exclusive in any way. In fact if the recording sounds 'real', then a transparent amp will convey a most convincing amount of realism.


You are probably right. What I like about the LD that I haven't seen anywhere else is that it sounds both "real" and euphonic at the same time. Those are two seemingly contradictory traits. I can enjoy both worlds where usually I have to pick.


> The easiest way to destroy a delicate signal with complex spatial and harmonic signatures (i.e. realism) is to splash some extra harmonics (no matter how benign or natural) on top of it. But more on that later.


Hmmmm, this may be strictly true technically, but I think the gain in euphonics is worth the slight loss in detail, the micro detail is still very apparent. That's part of what makes it sound so real. Like you said if the recording is well done even more so it sounds like the person is real and you can hear all the spatial information.
 I'd say you lose 5% micro detail and gain 40% euphony with this amp in the right set-up if I had to guess. I think it's the perfect balanced of "transparent" and euphonic. I mean like I said, subjectively speaking I thought it sounded like real life on many recordings so that's real enough for me.



> What the last sentence of point 3 tells me is that your system produces some amount of harmonic content, more than it should according to your ears


His statement about "rounded" sound really depends on what tubes you are using and in what combination.
It can sound rounded, it can sound rigid, it can sound "guitar" like, it really just depends on what kind of distortion you are "rolling" in.
I will say that I don't think the amp can be as fast sounding as a solid state amp though.
But all in all at the end of day, with the right configuration I think it gives the best of both worlds of realism and euphony.


----------



## SonicTrance

MrCurwen said:


> Superglue is my most important material after solder and wire. Look at Sonics great quality pictures, he has adopted the superglue approach as well. What superglue cannot fix cannot be fixed.


Haha! Yes! Though I didn't use any superglue in the MK6, only cable ties. I would not recommend superglueing something to the PCB. That stuff is so strong and could possibly rip some copper trace if you have to remove the glued part.


----------



## baronbeehive (Jul 6, 2017)

MrCurwen said:


> Transparency and realism are not mutually exclusive in any way. In fact if the recording sounds 'real', then a transparent amp will convey a most convincing amount of realism.
> 
> Just to bring an example, back when I was still in possession of my flagship amp, I had a cello player friend of mine listen it. He brought a recording of his cello master. The recording was very well made, and very lightly produced.
> 
> ...



Yes, one of the ways I test out an amp is to see what a violin sounds like, and if you can almost feel the sound of the bow going across the strings you know its not bad! As a violinist used to practice at our house I'm familiar with the sound! My other amp has all this information in the leading edge of the music and lends a lot to the transparency. The LD is good but mellower without that incisive edge, some of that if not all I put down to it being a speaker amp and the sound is much more visceral. But with more information in that leading edge it all goes to build up the texture more realistically.



MrCurwen said:


> This message could've been written by past me, I've been in this place. I listen to a lot of old stuff that is recorded quite poorly. One of the best examples is the catalogue of Robert Johnson. While I thoroughly enjoy his music, the sound quality is so rough it can be quite taxing to listen to.
> 
> Fortunately I found a way around this.
> 
> ...



Yes to all that! My grandmother was a piano teacher and I'm familiar with the sound of a piano being moved around and all the complex harmonics being produced whenever it was moved on the floor! Also what you said reminds me of the use of the sustain pedal which is OK to use for single passages of music to produce more harmonics but must be lifted after that passage of music otherwise the whole thing rapidly becomes a mess.

Its a shame there is so much bad recording around, even now. I have some old jazz recordings, for example "Milt Jackson" the vibes player from the 1950's and the sound quality is superb although the technique of instrument placing is a little dated.



MrCurwen said:


> Now to bring it back to your quote;
> 
> A rough recording with quite high distortion is going to sound bad when EVEN MORE distortion is added, because it will further mask the "realism information" and it will produce nasty IMD products. Get a cleaner OPEN LOOP amp and these problems are greatly alleviated. At least this has been my finding.
> 
> ...



Yes, right. The main way I test out the sound of the amp, for example when changing tubes is if I get the incredible sound of the guitar right. The Fender sound twangs, and the Gibson sound sustains, and both these sounds are what gives me most pleasure in music.


----------



## baronbeehive

gug42 said:


> Hello
> 
> Thx. The problem with glue is unmount sruff.... Well fist i will try patafix ...
> 
> The other point  : don't what bias driver mod to use for 6SL7WGT the one with 33kr/400r or 77k/1k and which method (// soldering or dirty replace with cutting the legs) ....



Yes glue pads are quite useful, to fix together adjacent caps for example.

I don't know what the others think but really I would always desolder, and solder properly, unless you are attaching a parallel resistor. Some large caps, or ones that need longer legs might be done with wire such as I mentioned but you still want to solder properly, its good practice and I don't like the sound of too many cut legs and reattached parts etc.

Desolder, get rid of as much old solder as possible to avoid cold solder joints. I always used extra flux for resoldering but if you use Cardas solder it has plenty of flux and is easy to work with.

Desoldering is what I hated most lol !!


----------



## Maxx134

gug42 said:


> Hello
> 
> Thx. The problem with glue is unmount sruff.... Well fist i will try patafix ...
> 
> The other point  : don't what bias driver mod to use for 6SL7WGT the one with 33kr/400r or 77k/1k and which method (// soldering or dirty replace with cutting the legs) ....


Easier to add resistors to test before buying exact value and remove old resistors..

If you like closer imaging I believe SonicTrance lower settings will do.

My higher settings seemed more balanced to me.




SonicTrance said:


> Haha! Yes! Though I didn't use any superglue in the MK6, only cable ties. I would not recommend superglueing something to the PCB. That stuff is so strong and could possibly rip some copper trace if you have to remove the glued part.


That's why I use hot glue as it goes on fast, and you can pull off i need.



baronbeehive said:


> The LD is good but mellower without that incisive edge


I am almost certain that is due to your extremely low stock driver tube bias settings...
You really need to try what me and Sonic did to increase bias.
Just add some parallel resistors to test before settling on a value.
It is a noticable improvement!


----------



## baronbeehive (Jul 7, 2017)

Maxx134 said:


> ..........
> 
> I am almost certain that is due to your extremely low stock driver tube bias settings...
> You really need to try what me and Sonic did to increase bias.
> ...



OK, that's quite possible. Also I'm using RCA 6AS7G's as well, I haven't tried the 421A's yet which will add more dynamics!

I'm not saying the Miniwatt is better, just better at some things, and the LD is better at others, but as you know I've been shocked at the improvement in the little amp after the mods!


----------



## baronbeehive

My other amp, the Miniwatt N3:






Jupiter coupling caps, Kaisei cathode caps and now Audyn True Copper cathode bypass caps. Chassis extended to fit.


----------



## MrCurwen

baronbeehive, that's a pretty little amplifier! What are the tubes you have there? Do you have a schematic?



> Haha! Yes! Though I didn't use any superglue in the MK6, only cable ties. I would not recommend superglueing something to the PCB. That stuff is so strong and could possibly rip some copper trace if you have to remove the glued part.



Yeah, no, that's not good. No glue on PCBs.

The safest thing to do would probably be to extend the chassis downwards, put the caps on P2P soldering posts (like the one somebody linked to Sonic in his modern balanced amp build thread), and just connect the caps to the LD chassis with wires. That way you can also easily change the caps for experiments.


----------



## coinmaster

> Also I'm using RCA 6AS7G's


 Eew, no wonder. At least mixem with the stock 6080s, 6AS7s alone are meh.


----------



## baronbeehive (Jul 9, 2017)

MrCurwen said:


> baronbeehive, that's a pretty little amplifier! What are the tubes you have there? Do you have a schematic?
> 
> 
> 
> ....



Its similar to Maxx's headphone amp, the APPJ PA1502A. Mine is the APPJ PA0901A, or Miniwatt.
I've just got adapters for Russian 6F6C Kobra's on the recommendation of APPJ thread members. The driver tube is a Tungsol 12SL7. The original tubes I used are Amperex EL84 power tubes and Tungsol 5771 driver tubes.
I don't have a schematic.  I have continuity tested every component to check on the traces, so I know what's connected to what, but don't know how to do the schematic. This amp was so much easier than the LD to test parts because the left and right channels are laid out virtually identically.



coinmaster said:


> Eew, no wonder. At least mixem with the stock 6080s, 6AS7s alone are meh.



Alright, alright, I will give that a try!

Edit:
Sonic, can you give me the link to your balanced amp build thread?


----------



## coinmaster

> Alright, alright, I will give that a try!


Just remember to try both positions.



> Sonic, can you give me the link to your balanced amp build thread?


https://www.head-fi.org/f/threads/modern-balanced-tube-amp-build.852879/


----------



## coinmaster




----------



## coinmaster (Jul 13, 2017)

Finally got my "ultimate" amp up and running.
Well technically it's only my "ultimate" input stage design, the output stage is a standard sandman but you can't really go wrong with a sandman in a pinch. My real "ultimate" output stage is next on my list.

My efficiency went up like 5000% ever since I bought these solderless breadboards a week or so ago, I shoulda been using these for prototyping from the start I would have never been able to build this on anything else.

 
It was one seriously noisy beast when I first got it up and running, almost 10v of noise from 0-10Mhz all over. I managed to quell most of it but the solderless breadboards aren't the best thing to use for this.
Part of the reason for all the noise is the distance between the components and the power supply. It can't regulate all 3 boards effectively and my low bandwitdth opamp in the reg isn't helping things.

Even with semi-unregulated to unregulated supplies I still get this beauty



Blue is the input signal to the input stage, yellow is the output signal of the input stage through the other end of my duelund cap shrunk down. Not too bad for a poorly regulated input stage. This is my first time seeing such a good copy of a complex signal since I got my oscilloscope and it can be further improved with better supply regulation and a few other tweaks.
Actually the input stage is only using a C filter of a few thousand uf on the B+, no resistors or regulation which isn't good because the design is susceptible to poor power supply regulation and output impedance (so much for ultimate?)

Although to be fair I've yet to measure an amp with a regulated supply which may be why I often see way more imperfections in the amplified signal (you don't even want to see what the mk6 looks like in SE mode) but considering how this isn't regulated it's pretty darn good.

The sound is clear as a bell, micro detail galore. Nowhere near the euphony of the MK6 though which is unsurprising considering it should be very low distortion, although the clarity, dynamics, and effortless sound separation is in itself mesmerizing.
Either way I'm satisfied that the results meet my expectations and my design goals.
In theory as far as tube input stages go this really is the ultimate theoretical design if the goal is linear amplification. The only way to improve it is to use better matching tubes but even then I built circuits to compensate for unmatched tubes as best as can be done without some sort of digital software curve analysis and algorithmic matching or something crazy like that (which I would love to do).

All I have to use for a DAC right now is my ipod, interestingly it still sounds amazingly good, unlike my MK6 which is in euphony only mode right now since its power supply is a piece of garbage without balanced operation

I'm going for a DHT and a nutube version next before I build my "ultimate" output stage. I built filament regulators that should in theory far outperform the coleman regs so even the filaments will be ultimate.

Then I can put my focus into mastering distortion generation rather then distortion elimination. Which reminds me I should probably connect this new stage to my mk6 output stage.


----------



## coinmaster (Jul 13, 2017)

So I connected my new input stage to the mk6 and it was the most celestial thing I've ever heard, even better then my modded MK6 in its prime, even though I'm using an ipod "dac" in SE mode.
It was like that for about 5 seconds anyway, until I accidentally ripped the ground cable out of my input tubes which caused some sort of voltage anomaly in the mk6 which was apparent due to the relay kicking in for a few moments. Afterword the sound was garbled and terrible in both channels. I've deduced that my input stage is fine, it's just the mk6 that is busted.

I'm a bit stumped on what I did exactly though, the DC conditions are all normal which makes it unusually difficult to figure out that I did.
Damn it, I was so close to audio nirvana too! God keeps screwing with me.

In any case there is something to take away from the fact that my SE mk6 sounds that good with my new input stage and terrible without balanced operation with the stock input stage.

It seems that the input stage really is the downfall of the mk6. Balanced operation is the only way to regulate the input stage beyond some minimal amount. It seems regulation via matched tubes and balanced operation and/or using an actual regulator is the only way to make it work decently with the stock circuit.

The output stage clearly isn't as bothered by the lack of regulation due to how clear and amazing it sounded by just replacing the input stage.


----------



## Maxx134

baronbeehive said:


> My other amp, the Miniwatt N3:
> 
> 
> 
> Jupiter coupling caps, Kaisei cathode caps and now Audyn True Copper cathode bypass caps. Chassis extended to fit.


Hey I see you finally have the Russian tubes..
Nice Right?




baronbeehive said:


> I've just got adapters for Russian 6F6C Kobra's on the recommendation of APPJ thread members


So what you think?



coinmaster said:


> I built filament regulators that should in theory far outperform the coleman regs so even the filaments will be ultimate


I read also high frequency to the heaters is a good idea..



coinmaster said:


> Afterword the sound was garbled and terrible in both channels.


Sounds like the driver PSU...


----------



## coinmaster

> I read also high frequency to the heaters is a good idea..


High frequency solves noise issue but wont sound as good as a current source filament because it doesn't isolate the heater PS from the signal.



> Sounds like the driver PSU...


 Nah the driver PSU is fine, it seems to be a pretty robust circuit overall.
The issue was some of the mosfets in my new output stage mod were partially but not completely fried. I guess I should start adding zeners or TVS diodes to my mosfets, I usually neglect that.

Now I'm going to wait until next month to do some real listening so my ear gets a chance to heal. I also need to repair my dac and my headphones, my headphones are all kinds of messed up at this point, too many times have I shot DC through them. 

I need to use a DC sense relay circuit between them and my prototypes from now on after I put new drivers in them.


----------



## baronbeehive (Jul 20, 2017)

coinmaster said:


> So I connected my new input stage to the mk6 and it was the most celestial thing I've ever heard, even better then my modded MK6 in its prime, even though I'm using an ipod "dac" in SE mode.
> ...



Sounds promising! I always liked the sound of my iPod Classic, but am surprised that it scales up to that extent. I don't remember what the verdict was on the DAC they used.
Can't wait for your results on the input stage, (for the MKVI), when you've got it fixed.
I had a Graham Slee Voyager with a bass boost function, and not only did it boost the bass but also it was incredibly euphonic, so much so that although very interesting to use it occasionally, it did not give a true representation by any means, it had massive echo, reverb and such like. But this is a distortion feature you could incorporate once the basic circuitry is producing the sounds you seem to have now with that good output signal you now have.



Maxx134 said:


> Hey I see you finally have the Russian tubes..
> Nice Right?
> 's
> 
> ...



I wish I could comment but sadly they don't work, either due to poor impedance or power matching. However the 12SL7 is fantastic! I've been on a euphoric high ever since from which I'm not coming down any day soon, due to that wonderfully immersive flowing experience. It takes you on the same ride you get taken on with the 6 volt tungsols.
I get less of the live sound now, but I've got that with the 5751's so it's all covered!


----------



## coinmaster

> when you've got it fixed


It's already fixed. After a bit more listening one thing I did notice that was inferior to my original super modded MK6 over a year ago was the lack of "wrap around your head" 360 degree sound and questionable realism on high quality recordings that would have fooled my brain into thinking the singer was in the room was me on my original modded mk6.
On the other hand I've never heard such clean and effortless sound separation and dynamics using my current set-up.

I blame the shortcomings on using an ipod instead of a proper dac in balanced mode and the fact that my headphones are damaged. Neither of which were the case when I had my original modded MK6 up and running.
If not I'll easily discover the culprit by recreating my original modded mk6 and using process of elimination but my current version is technically superior and I doubt an inferior mechanism like distortion was the cause of those traits in my original mod.

Currently headphones are approaching the point of unlistenability due to rattling on low frequencies and an increasingly distorted and mismatched frequency response. I'm dedicating next month to fixing my dac and replacing my headphone drivers.
Then I need to put my new designs into PCB form so I can use my poor excuse for power supplies to use for continued development. If only I had like $5000 to blow on proper lab equipment.


----------



## baronbeehive

coinmaster said:


> ..........
> I blame the shortcomings on using an ipod instead of a proper dac in balanced mode and the fact that my headphones are damaged. Neither of which were the case when I had my original modded MK6 up and running.
> ......



I would think that's definitely the case. You're amplifying a basically crap signal which is fine for the crap headphones you use with an iPod, but not up to it for anything else. The iPod could have been more than acceptable if it had let third parties unlock the the true digital signal within to develop superior applications, but of course Apple does not do this kind of thing.


----------



## Maxx134

coinmaster said:


> The issue was some of the mosfets in my new output stage mod were partially but not completely fried


Yeah looks like mosphets need care.
If I recall correctly Sonic also had issues with his mosphet implementation but he solved it.



coinmaster said:


> and the fact that my headphones are damaged


What were your headphones?


----------



## coinmaster

> What were your headphones?


HD800


----------



## Maxx134 (Jul 21, 2017)

coinmaster said:


> HD800


Yep they will hurt your ear.
Not only from stock treble levels,
But from the super fast bass and high dynamic range.

I hurt my ear once from listening to the "1812 overture" which had cannons at the end and the HD800 re-created them with transients and I put at high volume they can hurt your ear so clean and fast sound.

800S gives more satisfying lower end resulting in less need for volume elevation, which can hurt your ear without knowing,
 as the stock hd800 bass is so fast your not noticing and it can hurt you over time with certain bassy types of music.


----------



## coinmaster

I'm a treble junkie so I don't mind the supposed "treble issue" of the HD800s. If people didn't talk about it I wouldn't know it exists.
I actually like the HD800s bass. I've never heard bass so prominent yet so tightly controlled as in the HD800. The issue is it's rare to find an amp that will allow them to produce bass in good quality and quantity.
The MK6 can do it but only if you use huge ultra low esr film caps in the power supply.


----------



## gug42 (Jul 22, 2017)

Hello,

Good news I have receive the stuff !  Well it will be some time and work to get evrything in place.

Bad news, I forget one thinks : I need to put the fan outside the chassis.
Can you please indicate me the feet you use to raise up the little dot please ?

The TDK resistor are more thick than I though and it can be a problem ... 
And the only way I found to put  all the caps are this one :






Little dot mkVI+ with audyn caps by gug42 on Head-Fi.org

We can see the 8 Audyn true copper max and only one set of bypass caps. The resistor are not here.


----------



## gug42 (Jul 22, 2017)

And for internal hook up wire, did you think this one is ok : http://www.audiophonics.fr/fr/fils-...-multibrin-silicone-033-mm-blanc-p-11952.html
22AWG, 0,33mm², copper multistrand, 600V, 8A, 200°C


----------



## Maxx134

gug42 said:


> The TDK resistor are more thick than I though and it can be a problem ...
> And the only way I found to put all the caps are this one :


The wire is not an issue.
The only issue is the placement of the caps.
You need extend the bottom and can leave open until you do.
Caps need to be close to there associated circuits.
Placement matters and you don't want caps far away with the leads over the PSU area.


----------



## baronbeehive (Jul 22, 2017)

gug42 said:


> .....
> 
> Bad news, I forget one thinks : I need to put the fan outside the chassis.
> Can you please indicate me the feet you use to raise up the little dot please ?
> ...



These are the ones I use. The height can be adjusted if you use washers: http://www.underwoodaudio.co.uk/performance/isofee02-turntable-speaker-spikes/

Also, the TDK resistors should not be a problem.




gug42 said:


> And for internal hook up wire, did you think this one is ok : http://www.audiophonics.fr/fr/fils-...-multibrin-silicone-033-mm-blanc-p-11952.html
> 22AWG, 0,33mm², copper multistrand, 600V, 8A, 200°C



You should have heat resistant PTFE insulation so this is what I used: https://www.hificollective.co.uk/catalog/stdct22-neotech-upocc-copper-wire-7025mm-teflon-p-8455.html
This is pure copper multi strand,  a bit expensive but you don't need much.
Or you could use this which is cheaper and take apart the 3 strands: http://www.ebay.com/itm/25-feet-22-...hash=item35dce0a54a:m:m23Ub6Kj8Kt_V0Lfvef5S3w
That is silver plated copper wire.

Then I used this solid core pure copper for a stiffer wire to hold large caps in place: https://www.hificollective.co.uk/catalog/soct20-neotech-upocc-copper-wire-1085mm-teflon-p-8452.html


----------



## gug42 (Jul 22, 2017)

Maxx134 said:


> The wire is not an issue.
> The only issue is the placement of the caps.
> You need extend the bottom and can leave open until you do.
> Caps need to be close to there associated circuits.
> Placement matters and you don't want caps far away with the leads over the PSU area.



Hum ... so can put the caps where they are in my pics 
What is the problem ? The psu could "disturb" the caps ?

I will try to find another placement ... but well seems a bit hard   Well I will look how to extend the chassis in a quick and dirty way 



baronbeehive said:


> These are the ones I use. The height can be adjusted if you use washers: http://www.underwoodaudio.co.uk/performance/isofee02-turntable-speaker-spikes/
> 
> Also, the TDK resistors should not be a problem.
> 
> ...



Thank you for all this references ! really appreciate


----------



## gug42

baronbeehive said:


> I think we mainly just used the legs of the caps. You can use wire also. I used Neotech 20 AWG, UP-OCC copper single core wire, RED Teflon wire for the large PSU caps for example. This is stiff enough to hold them in place!



Sorry miss this !


----------



## MrCurwen

> What is the problem ? The psu could "disturb" the caps ?



Caps contain large conductive surfaces, wires act as antennaes. Put too much stuff close to each other and you have an oscillation system. Especially with an gNFB loop like the LD has.

I'd say the input tube area is the most dangerous wrt oscillation and loose wiring. Anyway, you have very little space, so... hope for the best?


----------



## baronbeehive (Jul 23, 2017)

gug42 said:


> ...
> 
> And the only way I found to put  all the caps are this one :
> 
> ...








Try something like this: Your WCF caps where the white MCaps are and the Coupling caps where the Jupiter caps are. You might have to juggle them around a bit, maybe put some vertically instead of horizontally. With the black caps not there in yours you should have plenty of room.
The soldering points where your red coupling caps are should be as close to your new Audyn coupling caps as possible.

To see what myself and others have done see page 73 where I have listed my mods pages and the others mod pages also. We all did it slightly differently and have a look at this to see why you don't have a problem:


Mogos said:


> Is getting bigger and bigger. Heavy also.



Sorry Mogos . Here's how it looked when finished: 
	

	
	
		
		

		
		
	


	




Not bad eh!

Edit:
Hey Mogos, I've just noticed you have yours on pretty loud !


----------



## gug42 (Jul 23, 2017)

Ineed, nice stuff !  Well what your black M cap for bypass ? the elmicII is a bit too high ...
Moreover the little dot in silver case seems to have a little more space than the black version, isnt it ?


Mogos, if you came here, can you tell me the references of the underlying "silver" case ? It can be good option to add an underlying case 

Edit : found this : http://www.conrad.fr/ce/fr/product/...tage-extrieur-M6-Hauteur-25-mm-1-pcs?ref=list

Can help to add the little missing space inside the box ??


----------



## baronbeehive

gug42 said:


> Ineed, nice stuff !  Well what your black M cap for bypass ? the elmicII is a bit too high ...
> Moreover the little dot in silver case seems to have a little more space than the black version, isnt it ?
> 
> 
> ...



My black Ecap is 16x39mm, what dimensions are your Elna Silmics?

I think Mogos built the case himself, perhaps he will tell you.

Yes you could use something like a spacer to raise the bottom of the chassis.

Are you sure you cannot fit everything inside. My WIMA caps are 31mm high, the same as your Audyns, I have mine either side of the pot like this: 




There is plenty of room for everything.


----------



## gug42 (Jul 23, 2017)

I will try again with aother placement, you are right. Put the caps around the psu is indeed a bad idea ...

For the bypass caps I have the Elma selmicII 470uF and RIFA PME 0,1µF (first page).
The elma are a little bit taller : 16mm (diameter) x 35.5mm (height). Their standard position are the standing one ... I could try to laid them down and connected them with wire.
Or perhaps I could buy some more smaller (220uF are 16x25)  or the Mundorf Ecap 220uf.
More over the Rifa caps have 24mm (length) x 7mm (depth) x 14mm (height)

And perhaps, when I order, I have make a mistake to buy the audyn maxx 0.33uF. They are a little too large perhpas (31mm diameter ... i was thinking it was ok ... but ....)
The 0.22uF version is much smaller (21mm diameter).   Or buying the murdoff 0.47uF would have been a better choice ....

Edit : stop complain ! I must retry ! And I will find a nice solution    Rubber spacer is another good option ! And when your MKP goes i can put some audyn for sure !

Thank you for you advice and help.


----------



## baronbeehive (Jul 24, 2017)

gug42 said:


> I will try again with aother placement, you are right. Put the caps around the psu is indeed a bad idea ...
> 
> For the bypass caps I have the Elma selmicII 470uF and RIFA PME 0,1µF (first page).
> The elma are a little bit taller : 16mm (diameter) x 35.5mm (height). Their standard position are the standing one ... I could try to laid them down and connected them with wire.
> ...



All your caps are fine, and you will be able to fit them in nicely, believe me, just experiment in the  MKP area, and the space below them up to where the pot is,

Don't forget to follow the pages where we have done the same and any problems let us know, we   have all been there and made the same mistakes lol!!


----------



## gug42 (Jul 24, 2017)

Thx you  i will ask if i have trubble 

Well I have made another "simulation", I will buy 4x "220uF 63V Mundorf ECap AC RAW electrolytic".
And mount them the way you did. Then I will have the place to put the audyn maxx (where you put the white mkp cap).

Another question : what are the value and brand of the stack of double resistor you use in the PSU (top left corner, left to the big caps) ?  I'm asking myself if mine doesn't have some brown traces ...


thx again !


----------



## baronbeehive

gug42 said:


> Thx you  i will ask if i have trubble
> 
> Well I have made another "simulation", I will buy 4x "220uF 63V Mundorf ECap AC RAW electrolytic".
> And mount them the way you did. Then I will have the place to put the audyn maxx (where you put the white mkp cap).
> ...



Hey gug42..... you don't need to replace your Elna Silmics for Ecaps, they Elna Silmics *DON'T NEED TO BE MOUNTED VERTICALLY!* Just mount them the same way as I mounted the Ecaps, they are the same size and will go in the same way!! Also they are better than Ecaps! Redge did them that way because he had a lot of *LARGE* components to fit and was short of space!

The resistors are Mills MRA5 8K2 x 2.

Keep us informed gug42!
.


----------



## gug42

Ok I will go this way  Hope for a good operation 
Thx for the resistor. 

Well I have ordered the feet and will order the neotech cable soon.


----------



## gug42 (Jul 26, 2017)

nothing sorry. Research


----------



## gug42 (Jul 31, 2017)

Ok find it. I will try to do the same work for the stock value and for Ra = 70k and Rk = 1K




SonicTrance said:


> These are the settings I ended up with for the ECC35's. Major sound improvement over stock 220K Ra and 1K5 Rk.
> *
> ECC35*
> 
> ...


----------



## gug42 (Aug 2, 2017)

Flash news, I'm on the move.
Take more time than expected, but well I'm a newbe 
Well a little scratch with soldering iron   (thx to my girl who asking me about vegetables or something like that) Hope for the best .... not worst than someone before me so ...





LD6_Bypass_left by gug42 on Head-Fi.org - Headphone forums and reviews for audiophiles





LD6_Bypass_right by gug42 on Head-Fi.org - Headphone forums and reviews for audiophiles

And well, I'm sure to stay with my 5998A tubes, never back to TS 6AS7G or ThomsonWCF 6080 stock.
Did you think it's ok to solder/mount the parallel resistor like this, between the two legs of the caps ?
For me it's the same ... but I prefer to ask 





LD6_Bypass_right_with_R by gug42 on Head-Fi.org - Headphone forums and reviews for audiophiles





LD6_Bypass_left_with_R by gug42 on Head-Fi.org - Headphone forums and reviews for audiophiles

If it's ok tomorrow I solder this // resistor for 5998A bias point, and this we I go for soldering on the board.  Little scared about soldering on the board ....

Well it will take month before I destroy the WCF and coupling caps and soldering the Audyn caps ...
I have buy a couple of pink/red wima caps, I found them pretty hard to destroy .... can't easy cut through ... so I  doubt about this move .... 

Thx in advance for advice !

Regards,


----------



## SonicTrance

gug42 said:


> Did you think it's ok to solder/mount the parallel resistor like this, between the two legs of the caps ?


Yes, you can solder the parallel cathode resistor like that. You should wrap the leads of the resistor around the cap legs so there's a mechanical connection as well. And cut the leads do they don't stick out like in the pics. It's nice to see you're making progress.


----------



## gug42

SonicTrance said:


> Yes, you can solder the parallel cathode resistor like that. You should wrap the leads of the resistor around the cap legs so there's a mechanical connection as well. And cut the leads do they don't stick out like in the pics. It's nice to see you're making progress.



Thank you. Indeed the red wire is wrap around the leg, but the legs of the caps aren't wired .... did I need to restart, I'm sure the legs are physcally in contact.

I will cut the leg at the end, after remove the stock caps from the board, and just before soldering them.


----------



## gug42

I have'nt twist the legs of the two caps.... Did you think I must re-make the soldering work  ?


----------



## SonicTrance

You dont have to redo it if it has good connection. I would have wrapped them around the cap leads just for peace of mind.


----------



## gug42

Thank you. I'm sure the legs are physically in contact. I can pull the leg without breaking the soldering point.
Next time I will do it for  sure ... I've done it for the wire, indeed logical to do it for legs.


----------



## baronbeehive

gug42 said:


> Thank you. I'm sure the legs are physically in contact. I can pull the leg without breaking the soldering point.
> Next time I will do it for  sure ... I've done it for the wire, indeed logical to do it for legs.



Yes, that's a good test, pull and if it comes apart you probably have a cold solder joint, if not it's good. Your joints look good, if they don't look shiny you might be in trouble, coming on nicely !

BTW, your Elna Silmics are polarized so make sure you connect them the right way round to the board.


----------



## gug42

Thx. Yeah evrything stay in place !

Ready for next move  I will check and re-check the - and +


----------



## gug42 (Aug 5, 2017)

Hello Guys,

Job done ! Happy to have make it.

Scarry time, cut the leg :






Left side :









right side :









So  a long moment when I push the power button. Seems to me a very long time before the warm up finish.
The vu metter are now at 65 for the left and 70 for the righ (not a quad matched ... only two pairs for this set .... I will try with a quad matched set.)

I think it's a little more detailled and the bass seems to be more deep and clean (the difference between two instruments seems more clear). I'm pretty sure to head a clear diffence, but don't wan to over react 

Thank you every one !
Hope my albums could help someone, really it's not hard to do ! Just time !


----------



## gug42

Hello,

A quick question : did you know a small sized MKP for bypass ?
Well It will be really easy to solder if I can have the space inside  ... (you warn me for the size of the audyn true copper max indeed ... )
Thank you in advance !


----------



## baronbeehive

Good work Gug42!

I think however you have 165 ohms now at the cathodes  - 2 x 330 ohm resistors in parallel, one new one and the other one on the back of the board? Was that your intention?

Why do you need bypasses now?

Are you going ahead with the Audyns? You will certainly notice the sound difference with those in place!!

Now go ahead and destroy your old Wima coupling caps lol .


----------



## gug42 (Aug 5, 2017)

baronbeehive said:


> I think however you have 165 ohms now at the cathodes - 2 x 330 ohm resistors in parallel, one new one and the other one on the back of the board? Was that your intention?


Bias mod for 5598 (I have 5998A that I prefer over stock 5998A or TS 6AS7G)



baronbeehive said:


> Why do you need bypasses now?


Because they are easy to install and can improve the sound quality ?



baronbeehive said:


> Are you going ahead with the Audyns? You will certainly notice the sound difference with those in place!!


Place inside is still a problem ... Perphaps I can install them outside and drill the the bottom aluminum plate for cables.
There is still some place between the chassis and my desk, thx to the feet.



baronbeehive said:


> Now go ahead and destroy your old Wima coupling caps lol .


To be honnest I found very hard to destroy a wima caps ... So a little be scarred to do this mod .... more easy if it was only to cut some leg (like bypass).
I will try to find a better tool, more sharp ... if you know a very good one


----------



## SonicTrance

gug42 said:


> To be honnest I found very hard to destroy a wima caps ... So a little be scarred to do this mod .... more easy if it was only to cut some leg (like bypass).
> I will try to find a better tool, more sharp ... if you know a very good one


I still recommend to remove the board and simply de-solder the caps. It can be a bit tricky the first time but once you get the hang of it you're removing the board in a couple of minutes. If you go this route do be careful with the wires on top side of board. They are very brittle and WILL break if you're not careful. Take pics of the wires so you know where to connect them if they come loose.
Once the board is out it's very easy to de-solder the coupling caps.


----------



## baronbeehive (Aug 7, 2017)

gug42 said:


> Bias mod for 5598 (I have 5998A that I prefer over stock 5998A or TS 6AS7G)
> 
> 
> Because they are easy to install and can improve the sound quality ?
> ...



Ok for the resistors and the bias mod, I forgot!

You only need bypasses for the high capacitance cathode bypass caps.

I don't see why you can't find space for the Audyn  caps inside but if you really don't have space then you could use longer screws and spacers to extend the bottom plate and the fill roud the gap with something. An idea I got from Maxx was to use heat sink such as this: https://www.amazon.co.uk/130mm-Heat...UTF8&qid=1502045222&sr=8-17&keywords=heatsink

This amp uses heatsink to extend the bottom:






You should follow Sonic's advice but if you can't then I destroyed my WCF wima caps with these, for your wima coupling caps perhaps a bigger pair? Then you can cut down to the legs and use these to solder on to.






Do you have a picture of your amp showing the Audyns inside where I suggested so that I can see if they fit?

Edit:
I don't think he wants to remove the board Sonic!!


----------



## baronbeehive

.......something like this:





but surely you can fit those Audyns in OK?


----------



## gug42

Hello,

Thank you all !  Nice trick about the spacers indeed, thx.
I will try to find a better tool to cut. 

Thx


----------



## gug42

MrCurwen said:


> Eliminating NFB would require a comprehensive redesign not fitting under the purpose of this thread. NFB is keeping this amp afloat. It cannot simply be eliminated without designing out the problems it was utilized to sweep under the rug.
> 
> For the benefit of whoever might be interested, I drew up clean versions of MK6 audio circuit schems.



Great schematics thx you


----------



## Mogos (Aug 27, 2017)

gug42 said:


> Ineed, nice stuff !  Well what your black M cap for bypass ? the elmicII is a bit too high ...
> Moreover the little dot in silver case seems to have a little more space than the black version, isnt it ?
> 
> 
> ...



The "silver" extension was done by me. To do that I have to order the corner elements to be done by CNC processing from aluminium bar 10x40 mm. Having the corner elements I have assembled the extension frame usin perforated steel plates and prefabricated aluminium corner elements. Then painted all together. If I will do it again it will be a little higher/dipper. Extension shall have at least the hight of the stock frame.


----------



## Mogos

Hey baronbeehive, don't be sorry for to show my work. The position of my pot dose have nothing to do with the volume regulation. When I had  problems with hum I dicided to dismantle the pot and use the tantalum 2W resistors. And it stayed like this. I am controling the volume digitaly in the scope of +- 6 db. And It works for me perfectly.


----------



## gug42

Thank you for thoses informations and photo ! Really nice work indeed ! 
Well don't find the time to work on my amp ... hope for soon !


----------



## baronbeehive

Mogos said:


> Hey baronbeehive, don't be sorry for to show my work. The position of my pot dose have nothing to do with the volume regulation. When I had  problems with hum I dicided to dismantle the pot and use the tantalum 2W resistors. And it stayed like this. I am controling the volume digitaly in the scope of +- 6 db. And It works for me perfectly.



No,indeed I think you should show it off at every available opportunity lol!! I was only saying to gug42 not to be put off by the amount of work to do by showing him what you did to yours inside, massive job indeed!


----------



## gug42

I still watn to add some modifications   Really  I have 8 nice audyn capp waiting !
Your post and pictures are really apreciate because give me some exemple ! thx


----------



## coinmaster




----------



## baronbeehive

gug42 said:


> I still watn to add some modifications   Really  I have 8 nice audyn capp waiting !
> Your post and pictures are really apreciate because give me some exemple ! thx



What's up?? Is there nowhere that you can pick up a set of pliers lol?

Jump in your batmobile this minute to your nearest neighbourhood DIY shop and get one............ or bring in Superman to finish the job!


----------



## gug42

Hello,

Thank you for asking news 
Well I've done nothing on the little dot  

But I have design my own amp : an SE of 4 Watt, based on KT66 and E186F  
Building will start next month !


----------



## baronbeehive

gug42 said:


> Hello,
> 
> Thank you for asking news
> Well I've done nothing on the little dot
> ...



That's good news..... Good Luck!


----------



## gug42

If you need plan or peace of gears used, don't hesitate to ask


----------



## 3ggerhappy

Hi all posting it here: 
Just found out my little dot mk viii has channel imbalance just realize this when I use it as a pre on my speaker setup. Volume pot issue I think, problem is the volume does not equalize when I turn the volume up. Now Can anyone point me(link if posible) for a compatible replacement for the pot? stepped attenuator if posible? Is it even possible to replace it? Please advise to those with the know how


----------



## SonicTrance

3ggerhappy said:


> Hi all posting it here:
> Just found out my little dot mk viii has channel imbalance just realize this when I use it as a pre on my speaker setup. Volume pot issue I think, problem is the volume does not equalize when I turn the volume up. Now Can anyone point me(link if posible) for a compatible replacement for the pot? stepped attenuator if posible? Is it even possible to replace it? Please advise to those with the know how


Hi @3ggerhappy 
You wont fit a balanced stepped attenuator inside the mk8 without some modifications. Easiest thing to do is to replace the pot with fixed resistors and change the volume digitally from your PC/Mac or music player.


----------



## Maxx134 (Oct 15, 2017)

SonicTrance said:


> Hi @3ggerhappy
> You wont fit a balanced stepped attenuator inside the mk8 without some modifications. Easiest thing to do is to replace the pot with fixed resistors and change the volume digitally from your PC/Mac or music player.


Maybe Easier to check the tiny (10k I believe)  input grid resistors after the volume and possibly change them out to either adjust or correct difference.

IMO, changing out the volume is going to be really small advantages if any.
Money better spent elsewhere in this Amp..


----------



## MrCurwen

> Maybe Easier to check the tiny (10k I believe) input grid resistors after the volume and possibly change them out to either adjust or correct difference.



Absolutelu do not do this. The 10k resistor is a voltage divider for NFB insertion. It's value is not trivial.

I second Sonics proposal.


----------



## Maxx134 (Nov 16, 2017)

I thought I answered this.
I strongly disagree to change the volume pot.
It is a sore waste of money as it is hard to find  better replacement without expense.

My initial intention and suggestion was to correct the imbalance of the channels,
Not remove them.
Yet if the NFB is to also be of concern,
Then it may very well be the NFB resistors that are off, as they are at such a high value that they can most likely be the culprit of mismatch.
And so should be checked for similarity of both sides.

Another likely problem area could also be the tiny gain switch as well?
It sets gain by changing value of the NFB resistors with parallel resistors .
I am contemplating to bypass this gain switch,
 since I do not use both settings.


----------



## Mogos

Hi Guys!
I have a question.
Lately one of the current meters started to show higher values than usual.
On the start the value is the same on both meters (as below).




After around 2 minutes the value reises up to




It is connected with the tubes. That's for sure. But what can this mean?


----------



## SonicTrance

Probably a tube thats going bad. Have you switched left channel to right channel and see if the problem moves with the tubes?


----------



## baronbeehive (Dec 22, 2017)

Pleased to say my LD is up and running again!

I haven't bothered to see what was wrong up to now because I've been enjoying my little speaker amp too much but there are times when headphones come in handy, like in the middle of the night for example, and I was missing my LD!

I found out the problem which was another of those little annoying problems like the last time with the wire, only this time it was a bad solder joint which I noticed pretty much straight away, in fact I remember mentioning it before, on one of the WCF caps. I checked the trace to tube pin2 which revealed the problem was a lifted pad. I fixed this but the problem was still there so I took out the board again, getting good at that and putting it back again with Sonic's tip using an insulated screwdriver. The reason I didn't fix it properly first time is because the board is multi layered and has a different trace on the back with one leg of the WCF cap being connected to one leg of the 330ohm resistor, this couldn't be seen from the component side! Confusing LOL!

What obviously caused it was when I rearranged the parts inside into their final positions which probably disturbed the dodgy solder joint. Suffice it to say problem sorted, and thats 2 amps that I've fixed now, this one and my speaker amp. Feeling pretty good and its thanks to you guys, you've trained me well!

Just got to get the switch back in and the the driver tube bias adjusted and we're away!

.......

Edit:

Well not quite...... I've rectified the fault with the faulty circuit, and the amp powers up with both meters showing equal current..... however having plugged in the headphones, there's no sound. I suspect the safety protection circuit kicked in when I had the problem with the amp. I've checked the fuses and it's not that so I need to know about this protection circuit.

How do I locate and fix it?


----------



## gug42

Sorry to  ask here ... but you've been so helpfull ....and seems you are the guys for this question 

Well I have a MKP 4 pins capacitor for bypassing an electrolytic one, and I don't know how to wire the 4 pins  .. I don't want to take risk .... and I don't find any clear schematics  on google ..
The capacitors are : https://www.mouser.fr/productdetail/871-b32778p6356k000

Any help please ? Did I wire the two left legs and the two right legs ?  An another options ?

Really hope you can answer me ... don't want to blow things  

Well a little schematics, the second would be my guess :
 
Thank you  in advance !


----------



## gug42

Or another option ?

 

Well sorry to ask .. i'm a little lost ...


----------



## baronbeehive

gug42 said:


> Sorry to  ask here ... but you've been so helpfull ....and seems you are the guys for this question
> 
> Well I have a MKP 4 pins capacitor for bypassing an electrolytic one, and I don't know how to wire the 4 pins  .. I don't want to take risk .... and I don't find any clear schematics  on google ..
> The capacitors are : https://www.mouser.fr/productdetail/871-b32778p6356k000
> ...



Hi gug42, my guess is that the second pic is correct as you suggest, except that the negative terminal of the blue cap should go to ground which is the other terminal to the one in the pic I believe. *However I'm not certain, you must PM one of the others to confirm before you go ahead*, I'm sure they will give you a quick answer.


----------



## gug42

Hello,

Thank you to have take time to answer me.
I have ask on a french forum too. I will pm people if no more answer  

Thank you.


----------



## baronbeehive (Dec 27, 2017)

gug42 said:


> Hello,
> 
> Thank you to have take time to answer me.
> I have ask on a french forum too. I will pm people if no more answer
> ...



That's ok. See here: https://www.head-fi.org/threads/lit...erified-mods-are-on-first-page.782183/page-70
(Second post down the page)This shows how I did it with the WIMA caps which are non polarized, with RIFA bypass caps which are also non polarized. I think your square caps are non polarized also? But the round caps are polarized by the looks of it and that's why I wasn't sure.
Sorry I can't be more help.


----------



## gug42

Hey,

Thank you ! exactly what I m looking for  
For sure the round one is polarized, I manage it. Don't focus on it for the picture !

So great I connect the legs like i was guessing. Thank you


----------



## baronbeehive

gug42 said:


> Hey,
> 
> Thank you ! exactly what I m looking for
> For sure the round one is polarized, I manage it. Don't focus on it for the picture !
> ...



Yes, and if you are not sure about the square cap just test the pairs of legs with an ohmmeter, and connect the 2 lets that have zero ohms, ie no connection, if they are at opposite ends of the cap then there will be an ohm reading.


----------



## gug42

I repost the link for quick reserch about wima cap wiring : https://www.head-fi.org/threads/lit...re-on-first-page.782183/page-70#post-12402649

Thank you. 



baronbeehive said:


> Yes, and if you are not sure about the square cap just test the pairs of legs with an ohmmeter, and connect the 2 lets that have zero ohms, ie no connection, if they are at opposite ends of the cap then there will be an ohm reading.



Oh well of course, obvious but wasn't thinking about this trick


----------



## gug42

Connection of the blue MKP cap confirmed on a french forum.

By the way some electro caps have special 4 pins connection. Note the case for mkp.

Thank you again.


----------



## baronbeehive

gug42 said:


> Connection of the blue MKP cap confirmed on a french forum.
> 
> By the way some electro caps have special 4 pins connection. Note the case for mkp.
> 
> Thank you again.



Good glad that's sorted!

Just mine to fix now. As I've said the problem with the faulty circuit was fixed due to a bad solder on the WCF cap. Both gauges read the same at about the right current, all appears well, except for no sound.

I've been re reading this forum and I noticed that others had had a similar problem. Mogus had problems with his transistors, fixed them then had no sound and eventually traced it back to his faulty pot. I haven't touched the pot so I'm now wondering if the problem is more than just the headphone protection circuit kicking in. If this happens does it correct itself because I still have no sound and am wondering if it is anything more now.
Before this happened everything was working perfectly so it can only be an effect of the problems associated with that faulty circuit that I had before it was fixed.

Any ideas guys.


----------



## gug42

Follow the track with a multimetters  ?  First in Ohmeters ?   No need of power for this.


----------



## baronbeehive

gug42 said:


> Follow the track with a multimetters  ?  First in Ohmeters ?   No need of power for this.



Thanks, I might have to do that, I already did it for the problem connection. What I really need is someone who has experience of this type of problem to point me in the right direction otherwise it is difficult to know where to start.


----------



## gug42

Sorry never face this type of problem .... perhaps in a near futur but not now.
Hope you find it quickly


----------



## SonicTrance

baronbeehive said:


> Just mine to fix now. As I've said the problem with the faulty circuit was fixed due to a bad solder on the WCF cap. Both gauges read the same at about the right current, all appears well, except for no sound.


So the problem you had before with one bias meter reading was off, was caused by a bad solder joint on one of the WCF caps?

Do both meters read about 60mA now? And you have no sound in any channel?



baronbeehive said:


> I'm now wondering if the problem is more than just the headphone protection circuit kicking in.


Don't really remember but I believe if the protection circuit kicks in, it shuts the B+ off so you wouldn't get any meter readings at all (meters at 0 mA). This is not what happens I assume?



baronbeehive said:


> Before this happened everything was working perfectly so it can only be an effect of the problems associated with that faulty circuit that I had before it was fixed.


Was the amp working flawlessly after you repaired the bad solder joint and then just stopped producing sound, without you fiddling with the amp?


----------



## baronbeehive (Dec 29, 2017)

SonicTrance said:


> So the problem you had before with one bias meter reading was off, was caused by a bad solder joint on one of the WCF caps?
> 
> Do both meters read about 60mA now? And you have no sound in any channel?
> 
> ...



....thought you might be sitting in front of your latest creation drooling!!!

You may remember me way back getting the amp back from the engineer and firing it up and enjoying it for a day or so...... until I rearranged the parts inside and aggravated a bad solder connection in one of the WCF caps which no longer had contact with the board trace, resulting in one meter reading 40mA and the other reading 80mA. Prior to this everything was working perfectly with both meters reading around 60mA. Well when I noticed the bad connection recently, I fixed this and the 2 meters now read the same, however they both read around 80mA. Then when I plugged in the headphones there was no sound in either channels.

I now think it is not the protection circuit because that should switch back on I think. I think that when there was a faulty circuit it might have affected something giving rise to the no sound problem.

I have had no sound since I did the repair. I can't remember if there was sound the first time I switched on the amp after I did the rearranging of parts inside, tying up the caps etc. This was when I noticed the meters giving different readings therefore I may have switched off the amp straight away I don't know but before this it was working flawlessly.

I'm using 6AS7G's.

Edit: I had the board out again to check the trace on the back but I was super careful when I put it back to make sure the wires were OK first so I'm confident nothing happened there.


----------



## baronbeehive

Just soldered the switch back again to see if it made any difference, but it didn't.


----------



## SonicTrance

Very hard to know whats wrong here, unfortunately. Can't come with any advice except check all connections with your ohm meter (amp off). You can also measure the anode voltages (amp on). There should be about 80 V on the anodes of the 6AS7's. 100 V on the B+, then a 20 V drop across the 330 ohm anode resistor. Also measure voltages on the input stage. If all voltages are good you should have sound.


----------



## baronbeehive (Jan 3, 2018)

I've measured the voltage at either end of the 330 ohm anode resistors:

B+ side = 98v, other side = 62v on previously faulty circuit
B+ side = 98v, other side = 67v on previously good circuits
I hope I've done this right
I don't know where on the input stage to measure?

I did find a likely touching wire which I thought might have triggered the protection circuit but I've corrected this now and so the readings are taken after this.
Still no sound.


----------



## baronbeehive (Jan 5, 2018)

I've checked all the resistors and all are OK except for one on the previously faulty circuit which reads 1.9k ohm and should read 106k ohm. This one:





It's the brown one on the right, next to the red cap, just under the Mcap, it's a Dale as well, damn and blast, they're the good ones! Must have blown with the last fault I had.

Do I need to check the resistors in the centre by the fuses I couldn't get stable readings from them as they are connected to caps.

I will order a replacement for the Dale,


----------



## baronbeehive

I'm going to assume that the replacement of the bad resistor will stop the headphone protection circuit tripping* ..... I hope....* and go ahead and finish the rest of the mods:

This is my order for this, and the rest of the resistors:

*To replace the bad 106k Dale resistor in the pic above:*
 - Takman metal film 110k .5W *or* .25W

*Impedance mod:* (figures from the table by SonicTrance - no switch, I will decide on one or the other for now like Maxx)
 - Mills MRA05 120R 5W x 4 - for 421A's (38 ohm headphones)
 - Mills MRA05 910R 5W x 4 - for 6AS7G's (38 ohm headphones)
To be soldered in parallel to the 330R anode resistors

*Driver Bias mod:*
 - TKD metal film 33K 2W x 4 to replace existing anode resistors in driver stage.
 - Takman metal film 390R .5W *or* .25W x 2 *or:*
 - Shinko 390R .5W *or* .25W, x 2 to replace existing cathode resistors in driver stage

Does that look OK?

*NB: *I know how to measure the resistances in a parallel circuit but is there an easy way to calculate what resistor needed to parallel with the 220k, and 1.5k driver stage resistors, I'm struggling with the maths!


----------



## SonicTrance

baronbeehive said:


> 've measured the voltage at either end of the 330 ohm anode resistors:
> 
> B+ side = 98v, other side = 62v on previously faulty circuit
> B+ side = 98v, other side = 67v on previously good circuits


That is 109 mA and 94 mA / tube. It should be around 60-70 mA. Are the anode resistors 330 ohms? Have you measured? Are these measurements on the same channel? If so, have you measured the other channel?



baronbeehive said:


> I don't know where on the input stage to measure?


You can measure rail voltage at top of driver stage anode resistors to ground, yellow circle. Also measure across those anode resistors to see the voltage drop. Cathode resistor circled in red, measure across it. Do the same for other channel.



 



baronbeehive said:


> I've checked all the resistors and all are OK except for one on the previously faulty circuit which reads 1.9k ohm and should read 106k ohm. This one:


How do you know that that resistor belongs to your "faulty circuit"? Also, 106k seems very strange. Does it say 106k on the board below the resistor? I think it's a 100k.
I don't know the purpose of that resistor but it's located close to a OPamp so probably have something to do with it. Have you measured DC offset at the outputs?



baronbeehive said:


> I'm going to assume that the replacement of the bad resistor will stop the headphone protection circuit tripping


I still think that if the protection circuit is active you should read *0 mA *on the meters, i.e. B+ shut off. I don't think your protection circuit kicks in at all.



baronbeehive said:


> Does that look OK?


It looks good but I would get the amp working before changing any more parts.



baronbeehive said:


> *NB: *I know how to measure the resistances in a parallel circuit but is there an easy way to calculate what resistor needed to parallel with the 220k, and 1.5k driver stage resistors, I'm struggling with the maths!


http://www.sengpielaudio.com/calculator-paralresist.htm


----------



## baronbeehive (Jan 5, 2018)

SonicTrance said:


> That is 109 mA and 94 mA / tube. It should be around 60-70 mA. Are the anode resistors 330 ohms? Have you measured? Are these measurements on the same channel? If so, have you measured the other channel?



Thanks Sonic! I measured at the anode power resistors, yes they measure 330ohms, same on the other circuit on that channel, I will measure them all again.



SonicTrance said:


> How do you know that that resistor belongs to your "faulty circuit"? Also, 106k seems very strange. Does it say 106k on the board below the resistor? I think it's a 100k.
> I don't know the purpose of that resistor but it's located close to a OPamp so probably have something to do with it. Have you measured DC offset at the outputs?



I measured each group of 6 resistors in that position for each circuit: each group of 6 measured - .56k, .56k, 10k,10k, 1.9k and 106k, except for the previously faulty circuit where the resistor that should read 106k measures 1.9k or 1.8k near enough. I can't see what the board says but the resistor is marked 107 so that sounds right. As they are all the same ie. 106k I am wondering if I need another resistor with that exact reading rather than, say 100k, or 110k?

This resistor is on the previously faulty circuit I'm sure because it is close to the problem solder joint that I had to repair, when one leg of the WCF cap became disconnected from the trace.

I will take some more measurements where you suggest later.

Edit: Hey thanks for that parallel resistor calculator, just the job lol!


----------



## klnglim (Jan 5, 2018)

I bought MK8SE 6 months ago, unlucky it come out smoke & smell burn, so now I have to modify & change some circuits.
After change all those circuits, have noticed sound signature & bass improvement, the amp run more stable, better performance & lower temperature.


----------



## SonicTrance

Looks like you still have the stock coupling caps and then put the RIFA 330n caps in parallell? Why?

Good thing you got it working again! From the looks of one of the old cathode bypass caps there has been some serious heat inside that amp! I would also replace those burnt resistors in the ps.


----------



## klnglim

Myself actually is not very good with solder or unsolder iron on board, so I have to spend few days to watch & learn from youtube channel and other electronic websites regard about  calculatie and change electronic component. 
RIFA caps is for bypass which I read from the first page, I understand some people may be disagree with my idea, please explain to me or correct my mistaken anytime as I like to learn and want to know more. 
In my opinion the caps is so cheap, why not have a try & experience with it?
I've been already using this amp about 6 months without any mod, run with the original high quality Electro Harmonic "Gold pins" (Driver tube & Power tube).
When notice smoke & smelling bad burn happened from inside the amp, that means is time to upgrade.

So I Replaced all the Power Resistor from original 150 Ohm / 3Watts with wirewound 150Ohm / 5Watts, upgrade Capacitor 220uF/63Volt to Audio Grade Nichicon 220uF/100Volt
Install 2 x silent PC fan cooler with blue LED under the case, I used and modified my very old EXT HDD 12Volts  adaptor to drive those fans.
Swap the original Electro Harmonic driver tube with Russian's Gold Lion tube (12AT7)
Totally, I spent less than 2 week began since channel,  then slowly try replace every bad burn circuits inside the board.
May b this mod is not perfect sound for everyone, but I m still satisfy with the sound audio performance improvement, since after few hour's amp burn in, then next day I used high gain & run balance connection to my HD800S, I get smoother + stronger + more bass , notice the amp runs very stable and well balance when read from the from meter.

Unluckily, within 2 days of 10 hours used, half way there seeing a little bit lite smoke come out from inside the amp again but no bad burn smell no over heat happen this time. 
Now I have to get involve deeper to investigate where and why the hell smoke still there.


----------



## Maxx134 (Jan 6, 2018)

klnglim said:


> I bought MK8SE 6 months ago, unlucky it come out smoke & smell burn, so now I have to modify & change some circuits.
> After change all those circuits, have noticed sound signature & bass improvement, the amp run more stable, better performance & lower temperature.


Very nice job regardless of having paralleled coupling caps.
Think about replacing the cathode follower caps also..
Break the red caps with a cutters to expose thier legs, then solder the new caps to them.
That's if you not want to remove the board.
For fun buy a pair of different brand power tubes and mix.
My favorite on the MK8 was Sovttek on left & EH on right of each side.(all 6n30 type just different brand)





klnglim said:


> Unluckily, within 2 days of 10 hours used, half way there seeing a little bit lite smoke come out from inside the amp again but no bad burn smell no over heat happen this time.
> Now I have to get involve deeper to investigate where and why the hell smoke still there.


Most likely it is from the resistors in your PSU after the caps and they can get burnt over time they should be replaced with the 5w wirewound as stock resistors are fake asss 2w garbage resistors that can't even hold 1watt without gettn Brown so over time they will burn.
No worries though just check and replace whenever but be careful if taking board out as the cheap adds garbage tin stranded wire that connects board to power transistors will detach...
So take pics when opening up...

I replaced all these things and just because I complain , dont think I am putting this amp down...
I can name ALL tube amps out there and call them out for using cheap non-optimal parts for cost cutting.
I'm not talkin about quality, I'm talking about parts that not as design intended like 2w resistors that are probably 1w capacity or stranded wire which should be copper but instead using cheaper tin or other garbage.

I seen $2k-$8k amps using lowly $10 caps in critical bypass areas.

The problem is the design. Most amps is using old topologies,
not like Sonic modern amp which not old school design.


----------



## Maxx134

baronbeehive said:


> How do I locate and fix it?


You don't fix a resistor that has lowered in value.
Something in the circuit made it lower in value.
Resistors can only increase and burn open,
They never go down in value..
Check your dip switch gain to make sure it is not stuck in middle ..



baronbeehive said:


> Edit: I had the board out again to check the trace on the back but I was super careful when I put it back to make sure the wires were OK first so I'm confident nothing happened there.


The garbage stranded tin wire is guaranteed to break off after about two times opening board out..
Even so, you would not have proper voltage if any problem there.



baronbeehive said:


> I've checked all the resistors and all are OK except for one on the previously faulty circuit which reads 1.9k ohm and should read 106k ohm. This one:


You probably "over" soldered and spilled solder somewhere there,
Or a bit of solder can be lodged in all that wiring...
Go get a can of  compressed air to blow out debris from the board...

*********


*Now to test if the protection circuit actually engaged..*.:::


1-Make sure all ready to turn on, have amp off.

2-have source already continuously playing before turning on amp.

2-Have a cheapo headphone (that not worry about breaking ) already plugged into the balanced socket before turn on amp...

3-Place headphone on head but NOT directly on your ear, in case you hear a pop..

Turn on amp...!
It Will warm up.
Listen for music from driver stage to travel thru the output tubes before they get their power, when the second meter clicks on.

The amp should have weak music playing on both sides evenly..

Once the delay finish and the second meter clicks in , try to notice if a second relay immediately clicks in (protection circuit).

If the protection circuit actually did click in,
There may be a loud  pop sound before this that may or may not damage your headphones lol.

A pop sound is not enough to damage a high impedance headphone but can damage a small portable...

So the point in this test is to verify if the driver stage is working and if the protection circuit actually engaged to shut off the power tubes..

*OR...

You can just buy an oscilloscope ha..*


----------



## klnglim

Yes, the picture shown is just temporary as I m planning to get some good quality capacitors & resistors. 
Can you write me the quantity needs and list of brand capacitors & resistors recommendation for replacement?
Anyway, I appreciates & Thanks for your kindly help


----------



## Maxx134 (Jan 6, 2018)

klnglim said:


> Yes, the picture shown is just temporary as I m planning to get some good quality capacitors & resistors.
> Can you write me the quantity needs and list of brand capacitors & resistors recommendation for replacement?
> Anyway, I appreciates & Thanks for your kindly help


Did you check the first page instructions?
Much info there.
You did great and I would not bother with the resistors right now...

Just the WCF bypass caps replace with same size & brand gold Square ones you used for coupling cap to make match...

Then I would skip all else and do the driver bias mod upgrade.
It is talks about but I haven't checked if we posted it.

An optimal mod would be a CCS there but haven't tried it yet.

Those are sound quality mods that are immediate.

As for the rest,
Don't bother with output mod on your mk8 yet but can try as a last mod to do to match to your headphones..


----------



## coinmaster

Oh boy, so many words to read through on this page. Baron I told you a long time ago I would skype you to help you fix it. My offer still stands. It would be very simple to deduct where the issue is if I could guide you in real time.


----------



## klnglim (Jan 7, 2018)

I have read the first page at least 10 times more, still confusing a bit cause the mod between MK6 & MK8SE are mix up togather, that's why I only replace all those burnt capacitors & resistor
Before I had changed resistors 150R 3W to 300R 5W (Vishay brand), the amp turn on like normal but no sound receive from headphone, then again I changed to 150R 5W (Vishay brand as well)
at last, the amp run very stable and heat temperature is lower compare with the original brand new out from factory.
The reason I bought this amp is to drive my headphone HD800S as I didn't like the sound drive by solid state amp, which missing low end bass. Honestly, I like the design of the amp but very disappointed with some crap components inside the board.
In my opinion, modding this amp will improve the performance and get the better sound quality more than I expected especially the bass


----------



## klnglim

I turned on the amp again after few hours rest, now it runs very stable and lower temperature without smoke or bad smell


----------



## baronbeehive (Jan 7, 2018)

klnglim said:


> I turned on the amp again after few hours rest, now it runs very stable and lower temperature without smoke or bad smell



There's something funny going on there, try to look to see if you can see which resistor is burning, those by the PSU look off, you could check the resistances with a multimeter, look especially around the area where the burnt cathode caps were.

It's odd that you had a problem before you did the mods, and the burnt cathode caps look suspicious. If you can remember which of the 4 output tube circuits the burnt cap was on check that circuit for anything odd. Also I would check all the solder joints I did with a multimeter for continuity on the trace that the joint is connected to. They look ok but it's difficult to tell. Check solder joints and any loose or touching wires.

The Rifa bypasses on  the coupling cap are not recommended in this area, only where the caps they are bypassing are high in capacitance and need a smaller value bypass cap to add back the lost treble frequencies.


----------



## baronbeehive

coinmaster said:


> Oh boy, so many words to read through on this page. Baron I told you a long time ago I would skype you to help you fix it. My offer still stands. It would be very simple to deduct where the issue is if I could guide you in real time.


Thanks coin, I'll be in touch!


----------



## klnglim (Jan 7, 2018)

I have just cut off Rita bypass from coupling cap, checked the whole board & there's no sign of burn.
The amp has been turned on, both meter show stable, heat temperature normal, tube light brightness normal, no smoke and no burn smell so far.
Now I just let the amp run for few hours so to confirm its 100% great performance.


----------



## baronbeehive (Jan 7, 2018)

klnglim said:


> I have just cut off Rita bypass from coupling cap, checked the whole board & there's no sign of burn.
> The amp has been turned on, both meter show stable, heat temperature normal, tube light brightness normal, no smoke and no burn smell so far.
> Now I just let the amp run for few hours so to confirm its 100% great performance.



Right!

Glad you went back to stock 150 ohm power resistors!

What coupling caps did you use? I'm guessing they were in before you got the amp?
Did you solder from the other side of the board? It looks like it, that's good.

If someone modded the amp before you got it that could cause a problem as removal of the board can cause wires to break. Also your cathode caps should not have burnt!


----------



## baronbeehive

coinmaster said:


> Oh boy, so many words to read through on this page. Baron I told you a long time ago I would skype you to help you fix it. My offer still stands. It would be very simple to deduct where the issue is if I could guide you in real time.



Ha ha, for once not all the words are by me!

Coin, before I get in touch I mentioned the 107k resistor, previous page, next to the red cap next to the opamp, it is connected to tube pin 3 and opamp pin 2, (second from left on side nearest pot). It is reading 1.9k now, all others on the other 4 circuits read 107k. As everything was ok before I found that 1 leg of the WCF cap had come out from board, I am assuming that this caused the problem and burnt out that resistor. I've rectified the WCF connection and both meters read the same now, therefore I will replace this resistor and check everything again to see if everything is ok. Does that resistor have to be 107k, will 110k be ok as I can't find a new one that is of that value.


----------



## coinmaster

> Coin, before I get in touch I mentioned the 107k resistor, previous page, next to the red cap next to the opamp, it is connected to tube pin 3 and opamp pin 2, (second from left on side nearest pot). It is reading 1.9k now, all others on the other 4 circuits read 107k.


Sounds like a parallel connection to me. Resistors don't burn closed and the resistor in that picture does't look bad at all.


baronbeehive said:


> As everything was ok before I found that 1 leg of the WCF cap had come out from board, I am assuming that this caused the problem and burnt out that resistor.


 The WCF not being connected would not cause the problems you describe unless it was touching something it shouldn't. Don't replace or order anything. Replacing parts blindly is a good way to waste money and burn more parts.


----------



## coinmaster

Looking at the original schematic I made, the 100k and 2k resistors in the opamp area paralleled would give the value you describe. Did you measure the 2k resistor to see if it was the same value?


----------



## baronbeehive (Jan 7, 2018)

coinmaster said:


> Looking at the original schematic I made, the 100k and 2k resistors in the opamp area paralleled would give the value you describe. Did you measure the 2k resistor to see if it was the same value?



Thanks for the schematic.

The 2k resistor is 2k, 1.9 actually. Al other resistors in that circuit are all OK.

Surely going from 106k to 1.9k means it has gone open, ie. less resistance?

Edit: I did notice one other possible problem looking at the circuit, the WCF cap lead appeared to be touching the coupling cap lead.


----------



## coinmaster (Jan 7, 2018)

No, open means higher resistance.
So you're saying the 2k resistor is the same value as the "broken" 107k resistor? See if they are the exact same value or not.


----------



## baronbeehive (Jan 7, 2018)

coinmaster said:


> No, open means higher resistance.
> So you're saying the 2k resistor is the same value as the "broken" 107k resistor? See if they are the exact same value or not.



Yes.

Edit: 2k is 1.83, broken one is 1.91


----------



## coinmaster (Jan 7, 2018)

That is likely a parallel connection and would cause the issues you are having.  Check if either side of the broken "107k" resistor is grounded.


----------



## baronbeehive

Neither side of the 107k resistor is grounded.


----------



## coinmaster

Now check if either side of the 2k resistor is grounded.


----------



## coinmaster (Jan 7, 2018)

Oh just noticed you updated your other post on the values. Probably not a parallel connection then, at least not with the 2k resistor, unless trace resistance makes up the difference. Do you want to skype? Would be a lot easier and faster to get to the bottom of it.


----------



## baronbeehive

The side of the 2k resistor nearest the pot only is grounded


----------



## baronbeehive

Yes if you want to skype now fine.


----------



## klnglim (Jan 7, 2018)

baronbeehive said:


> Right!
> 
> Glad you went back to stock 150 ohm power resistors!
> 
> ...




I bought this amp brand new from Taobao.com 6 months ago, since used from first day, the amp is quite hot and that's why I install 2 DIY PC blue LED quiet fan under the case.
Past few weeks suddenly smoke and bad smell burnt came out from inside the amp, noticeable one from the four power tube was too bright, I unplug electric  cable away from the amp ASAP
When the amp cooling down I opened the bottom case, some leaking melt liquid spread over some parts of the board from original Philips blue capacitors & 2 resistors burnt black are clearly seen.
During that time I suspected transformer may be provided over current but the fuse looked normal, so I ordered some resistors and capacitors for replacement. I took out the whole board solder both side which apply. The coupling caps are original (PB-MKP-FC 0.68uF 400V) made in France 96.
Now those replacement seen from picture is just for temporary, as I plan to upgrade better quality parts soon. Please feel free to give any adavise or recommendation for further improvement?

Already more than hour the amp operate now, so far no burnt, no bad smell, meter show stable (left is 50mA & right is 60mA), heat temperature whole case isn't very hot but I have seen very little smoke out from  inside.
Is this look normal?


----------



## baronbeehive

klnglim said:


> I bought this amp brand new from Taobao.com 6 months ago, since used from first day, the amp is quite hot and that's why I install 2 DIY PC blue LED quiet fan under the case.
> Past few weeks suddenly smoke and bad smell burnt came out from inside the amp, noticeable one from the four power tube was too bright, I unplug electric  cable away from the amp ASAP
> When the amp cooling down I opened the bottom case, some leaking melt liquid spread over some parts of the board from original Philips blue capacitors & 2 resistors burnt black are clearly seen.
> During that time I suspected transformer may be provided over current but the fuse looked normal, so I ordered some resistors and capacitors for replacement. I took out the whole board solder both side which apply. The coupling caps are original (PB-MKP-FC 0.68uF 400V) made in France 96.
> ...



Oh I see you got it from new therefore the problems was before you modded it. I hadn't seen those coupling caps before. Unlikely to be a faulty cathode cap to cause them to burn out, and not an overheating problem with the MKViii. Which resistors were burnt?


----------



## Maxx134

baronbeehive said:


> This resistor is on the previously faulty circuit I'm sure because it is close to the problem solder joint that I had to repair, when one leg of the WCF cap became disconnected from the trace



I bet that  resistor once taken out (carefully) would read proper resistance .
If it not not b burnt it most likely good.

I bet the trace to that resistor goes to your problem solder areas and its there not by the resistor..

I bet there is an error in connection by your socket


----------



## klnglim (Jan 7, 2018)

baronbeehive said:


> Oh I see you got it from new therefore the problems was before you modded it. I hadn't seen those coupling caps before. Unlikely to be a faulty cathode cap to cause them to burn out, and not an overheating problem with the MKViii. Which resistors were burnt?


The burnt resistors & capacitors was found near third & fourth power tube (Right side) during that time.
Now I notice those very lite smoke actually is look like steam from the power tube, beside that, all look great, sound from HD800S not bad too


----------



## baronbeehive (Jan 7, 2018)

klnglim said:


> The burnt resistors & capacitors was found near third & fourth power tube (Right side) during that time.
> Now I notice those very lite smoke actually is look like steam from the power tube, beside that, all look great, sound from HD800S not bad too



Were they the 150 ohm power resistors?

If you swap around the tubes you may find a faulty tube causing the different meter readings.



Maxx134 said:


> I bet that  resistor once taken out (carefully) would read proper resistance .
> If it not not b burnt it most likely good.
> 
> I bet the trace to that resistor goes to your problem solder areas and its there not by the resistor..
> ...



Right I'll have a closer look. So difficult to see properly under all these mods!


----------



## klnglim (Jan 7, 2018)

baronbeehive said:


> Were they the 150 ohm power resistors?
> 
> If you swap around the tubes you may find a faulty tube causing the different meter readings.
> 
> ...


The power tube is brand new like original, all light up normal.
The resistors are new 150R 5Watts
*Vishay AC05 Series Axial Wirewound Resistor 150Ω ±5% 5W -80 → -10ppm/°C*

Now The sound is great, clear details, wide sound stage, bass improvement is most noticeable


----------



## baronbeehive (Jan 7, 2018)

klnglim said:


> The power tube is brand new like original, all light up normal.
> The resistors are new 150R 5Watts
> Vishay AC05 Series Axial Wirewound Resistor
> 
> Now The sound is great, clear details, wide sound stage, bass improvement is most noticeable



Those resistors did have a nasty habit of burning, lets hope now that you've put in better ones the problem will stop.

Fan cooling alone might not have been enough with those crap resistors, but now that you've installed fans to keep it cool that should be fine.


----------



## Maxx134

klnglim said:


> Honestly, I like the design of the amp but very disappointed with some **** components inside the board


Don't be because ALL commercial amps have such problems of cutting costs and using cheapo parts.
The fact remains that this amp has a great balanced design and Luke any amp needs work to elevate it.



klnglim said:


> I turned on the amp again after few hours rest, now it runs very stable and lower temperature without smoke or bad smell


Then don't worry.
It was probably your PSU resistors they always slow burn to a higher amount and balance out.

You must keep each over any power tube glowing brighter which means a tube going bad.



baronbeehive said:


> There's something funny going on there, try to look to see if you can see which resistor is burning, those by the PSU look off,


Yeah he could have had thermal runaway on one tube which caused that cap failure.
I assume new parts keeping all in check.



baronbeehive said:


> The Rifa bypasses on the coupling cap are not recommended in this area,


It didn't matter and those caps he had are better then the French caps that are there...

It should be noted that MANY amps are using these same cheapo  French caps,
 because they are cheap and look fancy..

Still. the RIFA he had on top are better.



klnglim said:


> I have just cut off Rita bypass from coupling cap


You could have left them on for a lower frequency response cut off, so deeper bass..



coinmaster said:


> Don't replace or order anything. Replacing parts blindly is a good way to waste money and burn more parts


Exactly... Coin is right.



baronbeehive said:


> Surely going from 106k to 1.9k means it has gone open, ie. less resistance?


Your terminology is off:

*Open*=high resistance = burnt

*Short*= Low or zero resistance= closed




klnglim said:


> The coupling caps are original (PB-MKP-FC 0.68uF 400V) made in France 96.


That is the nice looking cap which is supposed to be a good buy for manufacturers..
You will notice big improvement upgrading here..



klnglim said:


> Is this look normal?


Yes



klnglim said:


> The burnt resistors & capacitors was found near third & fourth power tube (Right side) during that time.
> Now I notice those very lite smoke actually is look like steam from the power tube, beside that, all look great, sound from HD800S not bad too


The new wirewound resistors can withstand more power and would give of a bit smoke if tube was faulty.
Keep an eye on the meters of one goes higher.
Otherwise don't worry


----------



## klnglim

baronbeehive said:


> Those resistors did have a nasty habit of burning, lets hope now that you've put in better ones the problem will stop.
> 
> Fan cooling alone might not have been enough with those crap resistors, but now that you've installed fans to keep it cool that should be fine.


Can u give me the website where to order those caps and resistors for upgrade?
I m from Sydney, Australia by the way


----------



## baronbeehive

Sorry in Europe we mostly use hificollective.co.uk I don't know anywhere in Australia, but if you want to know exactly what to order we can help when you decide exactly what you need.


----------



## Maxx134

klnglim said:


> Can u give me the website where to order those caps and resistors for upgrade?
> I m from Sydney, Australia by the way


For you better to look for local parts seller you probably can find on Google a parts company


----------



## klnglim

baronbeehive said:


> Sorry in Europe we mostly use hificollective.co.uk I don't know anywhere in Australia, but if you want to know exactly what to order we can help when you decide exactly what you need.


I plan to ugrade PSU caps to MUNDOLF brand  
4 x coupling with *K75-10* 
8xMills MRA5 150R/5W resistors
A lot of cables I have own so cable upgrade is skip
After some times self learn and pratice, soldering isn't any issue anymore.
Since last mod experience, take off the whole board out from the amp is not hard at all
Myself already own some drivers tubes & NOS, so skip  tube row


----------



## baronbeehive (Jan 7, 2018)

klnglim said:


> I plan to ugrade PSU caps to MUNDOLF brand
> 4 x coupling with *K75-10*
> 8xMills MRA5 150R/5W resistors
> A lot of cables I have own so cable upgrade is skip
> ...



Sounds good, those are important upgrades, you already have upgraded cathode caps so good luck!


----------



## Maxx134 (Jan 7, 2018)

klnglim said:


> I plan to ugrade PSU caps to MUNDOLF brand
> 4 x coupling with *K75-10*
> 8xMills MRA5 150R/5W resistors
> A lot of cables I have own so cable upgrade is skip
> ...



Everything you do with this design will make a difference(!)...

 but the PSU improvements are the lesser,
  compared to the most important noticeable upgrades,
 which are:
1- the coupling caps
2-the WCF caps
3- and the bias adjustment to the driver tubes...

 those are three areas of concern that I would do first,
 because they will give you your most noticeable improvements currently....

 The psu stage upgrade is also an improvement...
But the other mods we do to the rail voltage stated in first page also does same.


 Although it is true that the PSU in every amp will interact with its load, the design of the PSU for the powerubes in this amp has already been stated as "musical" as is from a designer..
And yes it is a simplistic but beefy PSU.


----------



## baronbeehive (Jan 9, 2018)

Maxx134 said:


> I bet that  resistor once taken out (carefully) would read proper resistance .
> If it not not b burnt it most likely good.
> 
> I bet the trace to that resistor goes to your problem solder areas and its there not by the resistor..
> ...



I've checked the trace, the end of that resistor that goes to tube pin 3 and on to the XLR output is fine, no soldering done there anyway..*..... HOWEVER..... *the end that goes to opamp pin 2......... I swopped opamps within one channel and ..... as you said the problem resistor was now OK, and the corresponding resistor in the other channel was now reading 1.9k instead of 106k ohms, therefore the opamp is messed up, probably was called on to channel too much power during that fault I had, what do I do now get another one?

I think they're drop in replacement, but don't know what type, I'm assuming I need audiophile type?

The problem with the opamp would explain the lack of sound I think. When I know what to get I can take voltages again after I've put it back into the socket if necessary.


----------



## coinmaster

> I've checked the trace, the end of that resistor that goes to tube pin 3 and on to the XLR output is fine, no soldering done there anyway..*..... HOWEVER..... *the end that goes to opamp pin 2......... I swopped opamps within one channel and ..... as you said the problem resistor was now OK, and the corresponding resistor in the other channel was now reading 1.9k instead of 106k ohms, therefore the opamp is messed up, probably was called on to channel too much power during that fault I had, what do I do now get another one?
> 
> I think they're drop in replacement, but don't know what type, I'm assuming I need audiophile type?


That would explain why the measurement between the broken 106k resistor and the 2k resistor were so close and yet not exact. The opamp was amost completely shorted at pin 2, making an effective parallel connection.
Just buy another opa445ap.


----------



## Maxx134

baronbeehive said:


> what do I do now get another one?





coinmaster said:


> That would explain why the measurement between the broken 106k resistor and the 2k resistor were so close and yet not exact. The opamp was amost completely shorted at pin 2, making an effective parallel connection.
> Just buy another opa445ap.


Do what he said...
 and also dont get anything different or "better"...

From what I remember in past,
This just used as a DC servo control Opamp, and is fine for what it does.

Glad you found your problem.


----------



## klnglim (Jan 10, 2018)

For fun buy a pair of different brand power tubes and mix.
My favorite on the MK8 was Sovttek on left & EH on right of each side.(all 6n30 type just different brand)[/QUOTE]


Just Received a pair Sovtek 6H30 tube, I plug in as Sovtek on left EH on right, unfortunately after one hour Sovtek suddenly become too bright, then I turn off the amp ASAP, let it cool down and checked inside the board, found nothing burnt, no caps leaking, all look good.
Then I was thinking If mix with pair EH 6H30 tube, possible try roll the same brand tube each on left and right? (Mean Sovtek on 1st + 3rd, EH on 2nd + 4rd)
I turn on the amp and let it long run, already 3 hours , the amp temperature stay normal, meter and tube brightness very stable, the sound stage background become clearer and more nice crispy.
Sometimes I find this amp quite funny, just a little bit adjustment, miracle happen


----------



## klnglim

Maxx134 said:


> Everything you do with this design will make a difference(!)...
> 
> but the PSU improvements are the lesser,
> compared to the most important noticeable upgrades,
> ...




I m not sure where about driver tube BIAS adjustment? Can You show me the picture?


----------



## baronbeehive

coinmaster said:


> That would explain why the measurement between the broken 106k resistor and the 2k resistor were so close and yet not exact. The opamp was amost completely shorted at pin 2, making an effective parallel connection.
> Just buy another opa445ap.



Yes, looks like the values are correct for a parallel circuit.
Thanks, opamp opa445ap on order!



Maxx134 said:


> Do what he said...
> and also dont get anything different or "better"...
> 
> From what I remember in past,
> ...



Correction.....I found...*a*...problem, I hope you're right!


----------



## baronbeehive

Just beginning to get a handle on these schematics, what is the one circled on the left I assume that ps = power source but what is the symbol and is the letter "E" just a label
Also I assume that the second symbol is a tube socket.


----------



## coinmaster

I had another schematic where "E" led to for the input stage power supply...somewhere.
That schematic is really old though, I made it back when I was using some crappy software.
Is there some special reason you are trying to understand it?


----------



## baronbeehive (Jan 10, 2018)

coinmaster said:


> I had another schematic where "E" led to for the input stage power supply...somewhere.
> That schematic is really old though, I made it back when I was using some crappy software.
> Is there some special reason you are trying to understand it?



No, I was just trying to get a general understanding of electrical circuits so that I can see what's going on in the LD.

What you always telling me to do lol!


----------



## baronbeehive (Jan 10, 2018)

klnglim said:


> For fun buy a pair of different brand power tubes and mix.
> My favorite on the MK8 was Sovttek on left & EH on right of each side.(all 6n30 type just different brand)
> 
> 
> ...



That tube configuration should be fine, the tubes will autobias, and that combination of positions is what others have found works best.
I quite liked Sovtek's on my other amp!

"Sometimes I find this amp quite funny, just a little bit adjustment, miracle happen"

Yes, that's why we are having fun with the mods!!

Glad the amp's working now.



klnglim said:


> I m not sure where about driver tube BIAS adjustment? Can You show me the picture?


----------



## coinmaster

> No, I was just trying to get a general understanding of electrical circuits so that I can see what's going on in the LD.
> 
> What you always telling me to do lol!


 Yeah I was making sure, I can explain the MK6 to you, but not on here. Would be too annoying. Shouldn't be too hard for me to explain it over skype or something though.


----------



## klnglim

baronbeehive said:


> That tube configuration should be fine, the tubes will autobias, and that combination of positions is what others have found works best.
> I quite liked Sovtek's on my other amp!
> 
> "Sometimes I find this amp quite funny, just a little bit adjustment, miracle happen"
> ...




Thanks A lot for the picture. I've already ordered K75-10 from Russia, "0.33uF 630V" out of order, I guess "0.33uF 500V" should work, that's the next step for the mods


----------



## baronbeehive

coinmaster said:


> Yeah I was making sure, I can explain the MK6 to you, but not on here. Would be too annoying. Shouldn't be too hard for me to explain it over skype or something though.



OK, right, I have to sort out the setup problems I had yesterday. I have a friend on Skype, I can try it out there first. Should be interesting.


----------



## Maxx134 (Jan 11, 2018)

klnglim said:


> Sovtek suddenly become too bright


That is called "thermal runaway"!
Not sure why your Sovttek could not handle it but no worries ,
Maybe later get some tube socket extenders to lift tubes up for better cooling.



klnglim said:


> Then I was thinking If mix with pair EH 6H30 tube, possible try roll the same brand tube each on left and right? (Mean Sovtek on 1st + 3rd, EH on 2nd + 4rd)


That is exactly what I wanted you to do.
The Sovttek give the detail edge and the EH tube give the fullness and bass.
Perfect combo.
Switching tubes around you will find not as good as that specific order...




baronbeehive said:


> That tube configuration should be fine, the tubes will autobias, and that combination of positions is what others have found works best.
> I quite liked Sovtek's on my other amp!
> 
> "Sometimes I find this amp quite funny, just a little bit adjustment, miracle happen"
> ...



MK6 users like you don't have to be left out.
 I would also try it (same tube model type, just different name ) ...
putting your brighter/clearer tube on left and your thicker/richer tube on right (of each channel) as done above.
Get the best from both tubes..


----------



## baronbeehive (Jan 11, 2018)

OK. I have sound. It was panic stations when I inadvertently used the volume knob of the other amp and still couldn't hear anything. Then I realized my mistake!

Everything appears to be working OK, both meters are reading normal, about 65mA, all good. So I assume when they were both reading around 80 previously the current was being shared somehow between circuits compensating for the bad circuit.

Now for the rest of the mods, then maybe I can actually listen to it for more than a minute before something else happens lol.

I plan to add resistors in parallel to the driver stage rather than resolder the whole shooting match, so that resistor calculator has been invaluable Sonic, it would have taken me days to work that out by hand!


----------



## coinmaster

> but the PSU improvements are the lesser,
> compared to the most important noticeable upgrades,
> which are:
> 1- the coupling caps
> ...


I would argue that the power supply cap upgrade is one of the biggest upgrades *if* you use film caps. The power supply bypass caps are basically giant coupling capacitors for the entire amplifier. The current loops for the whole shebang have to go through those bypass caps in the supply.
Lytic caps have measurable distortion, they are just bad for audio. Especally if you use off the shelf power supply lytics like the stock mk6 has.
Replacing mine with film improved every aspect of the sound and gave my HD800s powerful bass.
That being said, there's no way you're going to fit film caps of similar value inside the chassis.


----------



## baronbeehive (Jan 11, 2018)

Maxx134 said:


> ......
> 
> MK6 users like you don't have to be left out.
> I would also try it (same tube model type, just different name ) ...
> ...



No I plan to try that with my RCA 6AS7G's combined with some 6080's, probably Thomson, I like the RCA's but they need livening up a bit. But I still have 3 matching 421A's and looking forward to trying those out when I get another one to complete the set.


----------



## coinmaster

Just make sure to check both positions when you mix.


----------



## baronbeehive

Wonderful to have the amp back!

The baby amp however has held it's own while the LD was out of action, it is shockingly good for practically no money.


----------



## coinmaster

Do you know what the schematic for the "baby amp" is?


----------



## Maxx134 (Jan 12, 2018)

baronbeehive said:


> I plan to add resistors in parallel to the driver stage rather than resolder


That's what I did..
Just added parallel resistors to increase bias..
Going to have to add it to first page eventually..



baronbeehive said:


> No I plan to try that with my RCA 6AS7G's combined with some 6080's


I dunno if they are equivalent to mix ask Coin.



coinmaster said:


> Do you know what the schematic for the "baby amp" is?


There is some of the schematic in the APPJ thread.
It using a switching supply, triode strapped pentodes(beam-power tetrode) surface mount parts...
There are TO-220 transistors by each of the driver tubes which not in the schematic here:
https://www.head-fi.org/threads/any...une-appj-pa1502a.780178/page-24#post-13480908


----------



## baronbeehive (Jan 12, 2018)

Getting the LD back again has had one undesirable side effect after being used to listening though speakers. The soundstage of my HE-500's is not so good so everything is now pointing to the HEK V2's at some point in the distant future. This is the one area that is so much worse than listening with the APPJ. The other thing that the APPJ does better IMO is the bass response is slightly sharper, although quantity and impact is similar. However that could be down to the RCA power tubes because they do have that characteristic sound.

It's difficult to compare speaker amps with headphone amps though but they are remarkably similar in performance, and the APPJ is single ended of course.


----------



## MrCurwen

> There are TO-220 transistors by each of the driver tubes which not in the schematic here:
> https://www.head-fi.org/threads/any...une-appj-pa1502a.780178/page-24#post-13480908



Interesting. The FET in the output tube cathode node is part of a "fixed bias" system. It's there to make sure the output tube conducts the same DC bias current at all times. However it does nothing at AC, and therefore does not in any way improve or decrease sound quality.

Sound quality of that particular module is determined by C10.

The extra transistors you mention are probably doing something similar, since if the amp has anode resistors included, that part is taken care of, and the input tube grid is the least likely place to utilize grid drive. So, PSU related probably.

It's a nice retro amp, I've built several of these. 6V6 however is not that linear in SE mode; I guess that's why there's NFB included (not usually used in SE amps).



> It's difficult to compare speaker amps with headphone amps though but they are remarkably similar in performance



They are both retro type circuits in essence (elaborate DC bias schemes notwithstanding), and while dissimilar in topology, after NFB is applied they are bound to sound more than a little bit alike.


The most interesting part for me is this:



> However that could be down to the RCA power tubes because they do have that characteristic sound.



That amp uses 6V6 type tubes. The LD does not, nowhere near even. By what is this "RCA sound" transferred?


----------



## MrCurwen

Oh how did I miss this, the 6V6 is operated in TETRODE MODE, so NFB is required, not optional. THD will be thru the roof otherwise.

Just for fun, here's what I'd do to improve sound quality of that amp:

1) Remove NFB. This will decrease sound quality by increasing THD and output impedance, and worsening freq response. 

Now then to gain back these things and possibly much more:

2) 6V6 goes triode mode.

3) Cathode bias of output tube goes out the window. No reason to play with C10 rolling. Instead use fixed grid bias; cathode is connected to ground, negative bias voltage is delivered to the other end of R15.

4) 6V6 is found too unlinear in SE mode without NFB. So, go for a linear tube. True triode 1626 is perfect replacement (even if more expensive these days) if 12V heaters can be supplied (which are apparently available). Others are available, such as EL36 / 6P31S, which is linear enough in SE and takes 6V heaters.

5) Fixed grid bias for input tube as well. It really is the most transparent bias method. Cathode bias always messes up dynamics to some degree, esp. bass.

6) Change R19 - 22 to one FET, two resistors and one cap. A simple gyrator costing a few pennies.

At this point sound quality is probably significantly better as a whole then at the start. Further improvements would be regulated B+ (very important in SE amps, those two 100µF caps at B+ are bound to be very slow and dusty sounding) and grid driver for output tube.

Parafeed cannot be arranged without completely redesigning the PSU (more voltage would be needed), so that would be the end of that road.


I realise there is no space inside the chassis for any of this, but if that amp is found to sound good, why not go adventuring on a new build, starting from about the same place as that amp.


----------



## baronbeehive (Jan 12, 2018)

MrCurwen said:


> ..........
> 
> The most interesting part for me is this:
> 
> ...



Just to be clear in case of misunderstanding, my LD has RCA 6AS7G power tubes whereas my APPJ, the speaker version, has EL84's. I've found that for the circuits I've used them in, the RCA's pretty much in general have good quantity bass but are characteristically quite a soft smooth, balanced sounding tube, hence my comment that the APPJ has a slightly tighter bass sound whereas the LD is slightly softer and smoother sounding. I've found in the 2 or 3 circuits I've used them in that these tubes have a characteristic sound regardless of circuit. For example I prefer Tungsols on both amps for their sound. Also I found that in may cases tube makes have a similar sound, for example I can tell a Tungsol from a Sylvania regardless of whether it is a 12AX7 or a 6SN7, therefore tubes by the same manufacturer but completely different construction. This doesn't always hold true but I find that quite strange, especially in view of your comments that in a well designed circuit tube types should have no effect on sound assuming equal load lines characteristics and such like.

BTW I like your ideas to mod the APPJ.... where does it all end!


----------



## baronbeehive

MrCurwen said:


> .......
> 
> I realise there is no space inside the chassis for any of this, but if that amp is found to sound good, why not go adventuring on a new build, starting from about the same place as that amp.



Maybe there is room, another extension maybe.....

Chassis already extended:










The insides of the APPJ speaker amp to show circuit layout.


----------



## baronbeehive

I've tried the Mullard ECC35's today, nice tubes!

Next is driver bias mod when I get the resistors, then after that the impedance mod when I get the last 421a.


----------



## MrCurwen

> Just to be clear in case of misunderstanding, my LD has RCA 6AS7G power tubes whereas my APPJ, the speaker version, has EL84's



Oh, ok. Why is this? The schematic you linked has 6P6 which is soviet 6V6GT.



> I can tell a Tungsol from a Sylvania regardless of whether it is a 12AX7 or a 6SN7, therefore tubes by the same manufacturer but completely different construction.



Both in a circuit with a resistive anode load of less than 10x rp --> very small rp differences will be altering the function of the circuit. 


Theory time:

Everybody understands how a voltage divider works, right? You have two resistors between + and ground, and the junction node voltage is determined by the resistors.

Now imagine you make the bottom resistor a potentiometer. You wire it as an adjustable resistor. You take your hand and you turn the wiper; the junction node (which is above the pot of course) voltage then varies, because the top resistor stays the same.

Are you following so far? Simplest ohm's law stuff, nothing to worry about.

Now if you make the + voltage really big, let's say 300 volts, and the top R 100k, and the pot max value is 100k. You now have a certain adjustment area.

Let's say your hand moves in tandem with a sine wave you see somewhere. Now as you move the pot wiper, you are in fact controlling the R / pot junction node voltage.

Let's say you move the pot all the way from open to max value during the sine cycle. You get junction voltages between 0V and 150V.

Now if you keep the R same value, and change the pot to a 90k max value pot, you get junction voltages from 0V to 142.105 V. Same input, your hand moves the same amount, but different output.


A tube is actually just an adjustable impedance. The above example can be expanded and clarified to apply more to an actual tube, but it would become much more complicated when you take into account resistance vs. impedance etc. It's a good enough analogy as it is.


So the principle is that if you have anode R that is not very big in comparison to rp, then if rp varies (it varies during operation, I mean statically between different tubes) it will cause the circuit to operate differently.

If anode R (or rather, Z) is large enough to drown out the influence of rp (remember, they are always in series between + and ground, one of them is by necessity dominant in determining the current thru that node and the junction node voltage), then variations in static rp (between different tubes) is meaningless.


What you are hearing is that some manufacturers are "over spec" in some specs, and some are "under spec". Whether or not these are consistent across different tube types within a manufacturer seems a bit odd, but not completely out of possibility.


Anode resistance is key here. A reason why some tubes sound "dark" and some "bright" is because a small variation in rp changes the R in an RC lowpass or highpass filter somewhere in the circuit. Why somebody would want to make a circuit that is so vulnerable to small variations is beyond me. I try to eliminate them.

The tube itself isn't "dark", you just dropped in a component that had "the wrong value". Let's say you'd have an RC highpass filter. You have a C of 100nF. Now you solder in as the R a random resistor. You cannot see it's value. What frequency pole ("sound") will you get? This is tube rolling in an essence.


----------



## baronbeehive (Jan 12, 2018)

MrCurwen said:


> Oh, ok. Why is this? The schematic you linked has 6P6 which is soviet 6V6GT.
> 
> .....



The confusion arises from the fact that there are 2 APPJ's, the headphone version which Maxx linked to the schematic, and the speaker version which I have, both with different power tubes, in fact I believe there is a third version now.




MrCurwen said:


> Oh, ok. Why is this? The schematic you linked has 6P6 which is soviet 6V6GT.
> 
> .........
> 
> ...



Yes I get that, and it's interesting how that translates into sound, ie, every GE I've heard sounds thin and clean, nearly every Tungsol sounds silky smooth, every RCA I've heard sounds very smooth and laid back, etc. What I wondered about the similarities between same manufacture tubes was something in the manufacturing process that is only known to the manufacturers themselves but it seems a bit esoteric.

Edit:I see there are now 2 new APPJ's, one with 2x 6AD10 tubes, the other has 2x6 JI+ 2x6P14's.


----------



## coinmaster (Jan 12, 2018)

> Getting the LD back again has had one undesirable side effect after being used to listening though speakers. The soundstage of my HE-500's is not so good so everything is now pointing to the HEK V2's at some point in the distant future. This is the one area that is so much worse than listening with the APPJ. The other thing that the APPJ does better IMO is the bass response is slightly sharper, although quantity and impact is similar. However that could be down to the RCA power tubes because they do have that characteristic sound.
> 
> It's difficult to compare speaker amps with headphone amps though but they are remarkably similar in performance, and the APPJ is single ended of course.


 I hope you weren't trying to drive speakers with the mk6 lol.
Also keep in mind the MK6 can sound like apples or oranges depending what you do to it.
Personally I highly recommend putting film caps in the power supply of the MK6 if you want much improved bass quality and quantity and just an overall quality improvement across the range.
And I got the best sound when mixing tubes as well, so I recommend that, 5998s with mullard 6080s were my best combo, I think. But the stock 6080s with 6as7 is also good if you don't have 5998s. The stock 6080wa tubes sounded much better than all the other 6080s I tried by a large margin when mixing, only barely beat by the mullards.


> I dunno if they are equivalent to mix ask Coin.


 You can use 6080, 6as7, 5998, other equivalents. I would recommend mixing different types rather than the same type with different brands.


> There is some of the schematic in the APPJ thread.


 Ah okay so it's nothing too fancy then. Not something I would ever build..too many flaws as MrCurwen said.


> Why somebody would want to make a circuit that is so vulnerable to small variations is beyond me. I try to eliminate them.


 From a pure engineers point of view yeah, but if you manage to tweak such an amp just right then it can blow you away like the MK6 did to me. I guess that can be seen as an advantage since a "well designed" amp will not be capable of sounding like much else than you designed it.


----------



## baronbeehive

It's really great to switch on the amp and wait for the meters to light up without the agonising worry about whether they're going to read OK now.

Thanks everyone for their help!


----------



## Maxx134 (Jan 14, 2018)

baronbeehive said:


> The soundstage of my HE-500's is not so good


Have you done any bias mods yet?.

Remember your speaker amp is actually using your room as an added
soundstage which not in the source music ..




MrCurwen said:


> Oh, ok. Why is this? The schematic you linked has 6P6 which is soviet 6V6GT.


My fault I forgot to state we have similar but different amps in that "APPJ" thread.



MrCurwen said:


> Anode resistance is key here. A reason why some tubes sound "dark" and some "bright" is because a small variation in rp changes the R in an RC lowpass or highpass filter somewhere in the circuit. Why somebody would want to make a circuit that is so vulnerable to small variations is beyond me. I try to eliminate them.


I have also noted and mentioned in past it was surprising to discover the very low bias setting of the driver tubes...
I am talking about the little dot mk6&8 having same driver stage.
The anode resistor was high at 220k ohm,
But the bias was at a very low point .

I  believe it will promote and guarantee sonic changes in tube rolling,
Because the load lines measured by Sonic where plotted in lowest non linear areas of the driver tube..

I have to believe it was an intentional design to introduce tube sound into the driver stage,
and then the reliance on using feedback...

My guess for another strong reason of bias point,
would be for cutting costs on a lower voltage PSU for that driver stage.
So staying competitive  in cost, while still making profit may have  been a factor..


----------



## Maxx134

baronbeehive said:


> everything is now pointing to the HEK V2's at some point in the distant future.


Dam..
That reminds me to post the 
*HEKV2 Feilian Port Mod*
Here along with original V1 mods.
While I was away from amp playing I was modding alot headphones lol.


----------



## klnglim

Maxx134 said:


> Everything you do with this design will make a difference(!)...
> 
> but the PSU improvements are the lesser,
> compared to the most important noticeable upgrades,
> ...




I have just checked my amp and notice all those original red colour caps are WIMA MKP10 (0.22/250V), are those good quality caps?


----------



## baronbeehive (Jan 14, 2018)

Maxx134 said:


> Have you done any bias mods yet?.
> 
> Remember your speaker amp is actually using your room as an added
> soundstage which not in the source music ..
> ...




The power tube bias, and driver stage bias mods are finished, just the impedance mod to go, waiting on getting another 421A before I do that because I want to bias it initially for those tubes. I am must about to take some pics of the mods.

The soundstage is not a problem of the LD but of the HE-500's. At the time I got them they had probably the best soundstage of the HiFiMan's but by todays standards it is not very good, and after being used to listening to speakers for a year or more the difference is very striking, I must say my preference is always for listening through speakers but I realized that is not possible for some people, such as those living in apartments in NY for example lol, or for me all of the time.



Maxx134 said:


> ...........
> 
> 
> My fault I forgot to state we have similar but different amps in that "APPJ" thread.
> ...



They have 2 new APPJ's out now, one of which replaces mine!! That one only has 2 power tubes to replace the EL84's so I don't know how it works!



Maxx134 said:


> .........
> 
> I have also noted and mentioned in past it was surprising to discover the very low bias setting of the driver tubes...
> I am talking about the little dot mk6&8 having same driver stage.
> ...



Oh, I wondered how Sonic came to his preferred values for his driver stage.




Maxx134 said:


> Dam..
> That reminds me to post the
> *HEKV2 Feilian Port Mod*
> Here along with original V1 mods.
> While I was away from amp playing I was modding alot headphones lol.



Must check out that thread again to see what's up!


----------



## baronbeehive

klnglim said:


> I have just checked my amp and notice all those original red colour caps are WIMA MKP10 (0.22/250V), are those good quality caps?



They are OK for what they do, the mods only replace those that are important for SQ.


----------



## baronbeehive (Jan 14, 2018)

*SMLD MODS: (continued)*

*Driver Bias Mod *- The idea is to optimize bias on driver stage. The total resistance at the anodes was changed to 33k ohms, the total resistance at the cathodes was changed to 390 ohms, as suggested by SonicTrance for the MKVi+, to change the operating point to a more linear part of the driver tube load line.

Like Maxx134, I decided to add resistors to existing. The alternative is to remove existing resistors and solder in new ones.

New resistors soldered in parallel to existing anodes:





New resistor soldered in parallel to existing cathodes:




You can follow my mods pages: 50, 53, 55, 57, 62, 65, 66, 68, 69, 70, 71, 72, 147, 179 which include pics. Also Mogos mods are here; 33-38, and SonicTrance here: 23, 43, including some great pics.


----------



## klnglim (Jan 14, 2018)

baronbeehive said:


> They are OK for what they do, the mods only replace those that are important for SQ.



Is it better idea to replace some important resistors (below) before on going the next mod?
8 x Mills MRA 150 R/5 W
4X 220K Ohm (Anode resistors) - _TKD CM2 Series 2 Watt - 1% Metal Film Resistors - High quality (Japanese) Audio grade resistor._
4 X 10k ohm ("Grid stopper" resistors)
2 X 1.5k ohm ("Common" Cathode resistors)

Do you know what Capacitance/Watts & type of resistors to be replace from picture below?


----------



## klnglim

Did anyone know what Capacitance/Watts & type of capacitors to be replace?


----------



## Maxx134 (Jan 14, 2018)

klnglim said:


> I have just checked my amp and notice all those original red colour caps are WIMA MKP10 (0.22/250V), are those good quality caps?


Do not change all caps.
Only the caps mentioned in first page.
The caps to change are :
1-Coupling caps
2-cathode caps
3-What caps.
Nothing has changed since first page, only the added extras of changing the bias points of the driver and powertube stages.
That means the driver tube anode resistors of 220k ohms and the 1k cathode resistor should be lowered .
You can use baronbeehive settings.
I myself did not need to  go as low and kept my anode & cathode at higher settings,
Because I increased tge PSU voltage by lowering the last 3k3 resistor that feeds the driver stage circuit.
The PSU was a RcRc filter and the reason I could lower the last resistor was because we increased the last capacitance feeding the anodes.



klnglim said:


> Do you know what Capacitance/Watts & type of resistors to be replace from picture below?


Those should have been power resistors there.
There is no capacitance there.
The designer get away with using cheapo garbage resistors which cannot take the current so they slowly burn over time as you can see...
He try get away with using two resistors in parallel to try dissipate the wattage created there which makes more heat...
They are garbage 1-2watt resistors and is why they cannot take the power so they burn.

This in effect also lower the rail voltage to the powertube over time.

You need one power resistor here.
It is explained in first page.
The best to use here ie Mills wirewound resistor.
They are non inductive wirewound and take alot of punishment without burning.
Only thing to be careful with wirewound resistors is not to damage outer surface when soldering.

It is also recomended in first page to replace all your powertube anode & cathode resistor with Mills wirewound resistors as they are superior .
This is mentioned in first page.
Nothing has changed.



klnglim said:


> Did anyone know what Capacitance/Watts & type of capacitors to be replace?


There are no capacitors you circled .
You circled the resistors.
If You wanted to change any capacitors in the PSU,
It has been mentioned by coinmaster and also recomeneded on first page .
They are the last two caps of the PSU stage mentioned on first page.


----------



## SonicTrance

klnglim said:


> Do you know what Capacitance/Watts & type of resistors to be replace from picture below?


I would replace those, yes. They are already quite burnt and wont get any better, lol. The Mills 5W wirewound is perfect for that position.



klnglim said:


> Did anyone know what Capacitance/Watts & type of capacitors to be replace?


You don't measure caps in W. But all cap mods are on first page.


----------



## SonicTrance

baronbeehive said:


> SMLD MODS: (continued)


I'm glad that your amp is finally working again, baron! Go easy with the soldering iron!


----------



## klnglim

Maxx134 said:


> Do not change all caps.
> Only the caps mentioned in first page.
> The caps to change are :
> 1-Coupling caps
> ...




Sorry my mistaken for typing capacitors, actually what I meant was resistors..
As before make an order, just want to confirm replace all resistors with Mills wirewound, thanks again!


----------



## baronbeehive

klnglim said:


> Sorry my mistaken for typing capacitors, actually what I meant was resistors..
> As before make an order, just want to confirm replace all resistors with Mills wirewound, thanks again!



Only the 8 x 150 ohm power resistors, and the ones you have circled:





I replaced the bottom pair with 2 x 8K2 MRA5, and you could replace the burnt pair with whatever value they are on your board. No use looking on the first page for these, they aren't mentioned!


----------



## Maxx134 (Jan 14, 2018)

baronbeehive said:


> No use looking on the first page for these, they aren't mentioned!


I didn't know this...
Also I believe in both this thread and the other mk6 thread there were owners with slightly different values...
I don't believe exact value is critical.

Just read or measure them by disconnecting one side from board to test...
The reason I don't say remove totally before test, is because there is a strong chance these resistors will break once removed.

Anyways they should still be visible to read their values,
AND the PSU schematic on first page should have the values,
Which were taken from an MK8.


----------



## baronbeehive

Maxx134 said:


> I didn't know this...
> Also I believe in both this thread and the other mk6 thread there were owners with slightly different values...
> I don't believe exact value is critical.
> 
> .....



I just reread the first page to check if I was mistaken, but it's not there. I remember it coming up way back and I can't remember why it was mentioned except to say that it was decided to replace the existing resistor with 2 in parallel to double the wattage. I believe there was some uncertainty about the values on our boards, due to someone having a different one or something.


----------



## SonicTrance (Jan 16, 2018)

Hi guys!

I had some time today so I took some measurements of the MK6. Thought I'd post them here for you guys to see!

*Amp in question:*





I started by measuring all important voltages of course (I haven't used this amp in quite some time). All voltages were good!

As some of you know I've built @MrCurwen LTP design which is a forced balanced design by the CCS (constant current source) tail. If I inject a signal in one phase of one channel in the LTP and ground the other phase, both phases output the exact same amplitude!

So, I thought it'd be fun to do just that with the mk6. I had to leave one phase input floating or disconnected for this to work. Could barely get a reading with one phase grounded.

Input signal is 700 mVpp @ 1kHz



A 100 ohm resistor as load across the right channel outputs. Scope and DMM probes hooked up across it.




This is what came out at full volume. 2.28 Vpp from a 700 mVpp input signal gives me a total gain of 3.26. Remember, the ECC35 has µ68 and 6AS7G has µ2, so full gain would be 136. That's the NFB. *Oh yes, I have the gain set to low, so maximum amount of NFB!*



Here's the measurement from the phase without input signal (same channel). I just flipped the scope leads on the load R.


 As you can see there's barely any signal there at all.

Also thought it'd be fun to do a power output measurement. Remember, gain still set to LOW!


This is right before the sine wave starts to round off at the bottom.



 
7.1 Vrms ^2 / 100R (load) = *0.5 Wrms *or.....
10 Vp ^2 / 100R (load) = *1 Wpeak
*
I don't know how much the low gain setting affected power output but for fun I also simmed the MK6 in spice:

Also with low gain setting. If I drove it any harder than this the signal would clip. This is about 15 Vpp with 100 ohm load. I don't know how accurate spice is when doing these types of measurements but use it as entertainment at least.



Both phases have input signal here as you can see. Nice and balanced outputs. The voltages at V4 and V5 are adjusted to get 0 VDC at output. Don't know how accurate those are either. 
*Edit: I got curious and measured the voltage at the top triodes grids. It was in fact very accurate at -23 V!*

I did not post this to bash on the MK6 in any way. I still think it's a great sounding amp!


----------



## MrCurwen

Excellent work Sonic! Really interesting to see.

This kind of amp would be quite perfect for driving a pair of high impedance horn speakers. Plenty of output power for any kind of speakers really, but the output impedance is too high for normal speakers.

Regarding balance; 

Exactly as theory would predict. The biggest impedance in the series (between B+ and ground or B-) determines the balance in any LTP (which the LD input stage has, there's two triodes and a common tail in series with both triodes), so which is it? It's not the 1.5k tail, it's the tubes.

So the tubes determine the balance. This is why tube rolling works, and also why it's not a good solution.



> This is what came out at full volume. 2.28 Vpp from a 700 mVpp input signal gives me a total gain of 3.26. Remember, the ECC35 has µ68 and 6AS7G has µ2, so full gain would be 136



I think the WCF has a negative gain with any real load, something like 0.8 if I remember correctly from way back when I simmed this circuit a lot. Doesn't change the point though, gain is suppressed to a significant degree (within tube amps, SS amps have a lot more NFB).


By the way, I recommend running sims for at least 100mS preferably 200mS if you wish to have any degree of accuracy in FFT or THD results. The longer the sim runs the better the resolution becomes. But, as you said, these are for entertainment purposes only. You can make a lot of 'perfect' sims that come out less than perfect or even unuseable (Spice is suspiciously stable from a builders perspective). Only way to become a decent designer is to build build build, sim afterwards for entertainment and food for thought.

If you sim that very LTP balance test with my circuit, you will not get nearly as good a result as you will in real life measurements. Sometimes sims give worse than real results, sometimes better than real results. Oftentimes the fault lies in tube models; they are very much simplified. In reality a tube doesn't have a set of curves that are set in stone and static. Spice tube curves are static.


----------



## SonicTrance (Jan 16, 2018)

MrCurwen said:


> By the way, I recommend running sims for at least 100mS preferably 200mS if you wish to have any degree of accuracy in FFT or THD results. The longer the sim runs the better the resolution becomes.


Thanks!

Edit: Miss information. Correct info in later post.


----------



## SonicTrance

If any of you guys need me to take any measurements of the MK6 now is the time! Just let me know and I'll do it!


----------



## MrCurwen

Did you use the .four statement that is visible in the schem you posted? If so, it's invalid. It's "SE output" THD, not the actual balanced signal. I'd suggest changing node 10 to I(RL).


----------



## SonicTrance

MrCurwen said:


> Did you use the .four statement that is visible in the schem you posted? If so, it's invalid. It's "SE output" THD, not the actual balanced signal. I'd suggest changing node 10 to I(RL).


You're right! I didn't think about that.

With 1.6 V signal (near clipping) THD = 0.5%, 15 Vpp
With 0.5 V signal, THD = 0.045%, 4.85 Vpp

With gain set to high (low NFB) 0.5V signal, THD = 0.40%, 10 Vpp

So, THD increases with lower NFB and gain increases. To be expected.


----------



## Maxx134

SonicTrance said:


> If I inject a signal in one phase of one channel in the LTP and ground the other phase, both phases output the exact same amplitude!
> 
> So, I thought it'd be fun to do just that with the mk6. I had to leave one phase input floating or disconnected for this to work. Could barely get a reading with one phase grounded.


I believe the single ended output jack is also giving this signal.



SonicTrance said:


> I did not post this to bash on the MK6 in any way. I still think it's a great sounding amp!


Thanks for info and it would ne interesting to see how iy looks at high gain setting which uses leads NFB which I use.
I believe this setting you can offset gain with a lower MU tube choice,

But chose not to.
I balanced it another way by different choice of output tube.



MrCurwen said:


> there's two triodes and a common tail in series with both triodes), so which is it? It's not the 1.5k tail, it's the tubes.
> 
> So the tubes determine the balance. This is why tube rolling works, and also why it's not a good solution.


I agree and also want to still keep optimising this amp, so I have planned to place CCS at the driver tube cathode which is probably the last things I could do,
Except for putting a lot in the place of the gain switch, to see how low NFB I can go without messing up the sound .




SonicTrance said:


> If any of you guys need me to take any measurements of the MK6 now is the time! Just let me know and I'll do it!


That would be great not only to fill in the schematic with measurements, but to analyze and learn both the flaws and compromises in these designs.
I am interested in how MrCurwen also thinks about designs.
It is great to get you thinking.



SonicTrance said:


> So, THD increases with lower NFB and gain increases. To be expected


If possible take in high gain as it would be interesting to see what type of distortion increases with less NFB.
Probably dependant on type of tube and makes this amp "tube rolling" sensitive...


----------



## SonicTrance

Maxx134 said:


> I believe the single ended output jack is also giving this signal.


I don't have any SE jacks in my MK6.




Maxx134 said:


> I agree and also want to still keep optimising this amp, so I have planned to place CCS at the driver tube cathode which is probably the last things I could do


Yes, might try this myself just for fun. I'm wondering how much it would lower the B+ though. I definitely think that we should go for 6SL7/ECC35 or 6C8G which doesn't require much current to be linear. About 2mA. Otherwise we wouldn't have much B+ left! We got plenty of B- for FET voltage headroom, so should not be a problem there. Not sure how the CCS would interact with retro style resistor plate load though.



Maxx134 said:


> If possible take in high gain as it would be interesting to see what type of distortion increases with less NFB.


What measurements would you like to see with high gain? Same as above or something in particular?


----------



## coinmaster

> Not sure how the CCS would interact with retro style resistor plate load though.


 As long as the cathodes are current source loaded it won't matter much, the cathode feedback is what matters if you want amplitude matching. The stock plate resistors can only handle less than 1ma before the b+ gets too low, so that needs to be taken into account.


----------



## SonicTrance (Jan 17, 2018)

coinmaster said:


> The stock plate resistors can only handle less than 1ma before the b+ gets too low, so that needs to be taken into account.


If you pull 1 mA through 220k you drop 220 V. That's more than the available voltage.

We need to use something like 33k as I'm using now. From previous experiments I've found that if I pull 3.5 mA / tube, so 7 mA total from the driver stage psu I get a B+ of 160 V. If we draw more current than that we loose to much voltage swing.

0.00175A * 33k = 58 V drop across Ra

Operating point would be:
101.4 Va
-0.6 Vg
1.75 mA


----------



## coinmaster

> If you pull 1 mA through 220k you drop 220 V. That's more than the available voltage.


 Indeed, that's why I said "less than", I think the tubes run at like 700ua stock or something. It wouldn't be overly difficult to just use a gyrator. Bartola sells gyrator pcbs that can be slotted right into the chassis. A p2p gyrator should be doable without too much difficulty as well. Just gotta be careful how much current you draw, the RC filter might need to be adjusted and I don't remember the current rating on the winding.


----------



## SonicTrance

Here's a schem using a CCS tail and ECC35's with the above operating point. It sims very well. Ground one input and both phases output same amplitude.


----------



## coinmaster (Jan 17, 2018)

A simple low voltage jfet current source would be simpler and more practical than a scheme like that for a current source implementation in the mk6. I'm not sure how good of an idea it is to attach it to B- either since it won't be clean and will hurt the impedance of the current source to some extent and introduce some measure of crosstalk.

It would probably be better to simply attach it to ground, as long as your tubes aren't wildly unmatched the voltage at the cathodes should have enough swing to not need a b- connection if you run them balanced. If the tubes are perfectly matched there will only be pure DC at the cathodes during balanced operation, so 1.5v+ grid bias should be plenty of theoretical headroom for voltage swing with mismatched tubes, 0.6 is probably okay too but I wouldn't want to place a bet on that especially if you account for the headroom required for the jfet if you're grounding it. I'm not sure how low the LV jfets can go.
1.5v would need a gyrator to work as well. Something for you to think about.


----------



## SonicTrance

The MOSFET needs 10 V+ headroom to function properly and as the operating point is only 0.6 V it needs B-. Don't know about your JFET though. This is the CCS I'm familiar with.


----------



## coinmaster (Jan 17, 2018)

Something like this only requires 0.8v to operate and costs less than a dollar.
http://www.ti.com/lit/ds/symlink/lm334.pdf
Considering the voltage drop across the trimmer, you'd probably want a 1.5v grid bias with that.


----------



## Maxx134 (Jan 17, 2018)

SonicTrance said:


> Otherwise we wouldn't have much B+ left


Sonic do you remember the PMs long ago where I was able to increase the B+?



SonicTrance said:


> . If we draw more current than that we loose to much voltage swing


Thats why I did not need To choose your slightly lower anode resistor settings,
 and I probably got similar bias increase with the higher B+ I had,
by lowering the value of the last 3k3 resistors (sides of board) in the PSU RC filtering.
I got away with this as the added caps we put made up more filtering for the  decreased resistor which gave me a higher B+
I forgot how much I believe it was about over 10v more but I have to check...

The bottom line is that anyone who increased the caps by the driver tubes can effectively lower their 3k3 resistor to gain some more precious needed voltage..



coinmaster said:


> the RC filter might need to be adjusted


Yep,
That's what I did!




coinmaster said:


> Something like this only requires 0.8v to operate and costs less than a dollar.
> http://www.ti.com/lit/ds/symlink/lm334.pdf
> Considering the voltage drop across the trimmer, you'd probably want a 1.5v grid bias with that.


That is BRILLIANT IDEA!!


You have grown very strong in the force...
Don't mind me,
 I just watched the last star wars movie..


----------



## coinmaster

Actually you can get 3ma for about 20 ohms on the trimmer so you can get away with a 1v bias using that jfet.


----------



## MrCurwen

SonicTrance said:


> Not sure how the CCS would interact with retro style resistor plate load though.



In practise, very well. There's less likelihood of instability than with gyrator anode loads, for obvious reasons. The first CCS tail balanced HIFI amp stage I made had resistor plate loads, and I also made a few for CRT driving purposes (700VPP output, very clean visually observed on radar CRT).



SonicTrance said:


> We need to use something like 33k as I'm using now.



Yes, I'd recommend this.



SonicTrance said:


> The MOSFET needs 10 V+ headroom to function properly and as the operating point is only 0.6 V it needs B-. Don't know about your JFET though. This is the CCS I'm familiar with.



Doesn't the amp already have a B- supply or am I remembering wrong? 

Oh, I guess it's for the output section only. Well, if you want any good results from this experiment, you are going to need 10+ volts of B-. It is not necessary to regulate this, since there will be so many megaohms of impedance between B- and ground / B+.



Maxx134 said:


> by lowering the value of the last 3k3 resistors (sides of board) in the PSU RC filtering.



Yes, this is the smart route, after applying forced balance to the input section that section's PSU requirements drop to zero pretty much. You can decrease filtering by 50% or more. This includes decreasing R and C.



Maxx134 said:


> The bottom line is that anyone who increased the caps by the driver tubes can effectively lower their 3k3 resistor to gain some more precious needed voltage..



This is very very stupid. 

You should NEVER decrease R and increase C, unless you are absolutely sure your PT can take it. Do you know the currents ratings of your PT? If you decrease R by 20% and increase C by 20% you can in some cases quadruple the current pulses the PT needs to supply. Even if this doesn't lead to instant dramatic smoke and fire, you will be shortening your PT lifespan by a lot.

Anyway it's bad design. There is no point in having big C in a PSU for CCS tailed LTP stage.



Maxx134 said:


> That is BRILLIANT IDEA!!



I would not be using a chip CCS for a serious HIFI or even high end build. When looking for best results, always always always go discreet.


----------



## SonicTrance

MrCurwen said:


> Doesn't the amp already have a B- supply or am I remembering wrong?
> 
> Oh, I guess it's for the output section only.


Yes, it has B- for the output stage, -100 V. You can see from the schem I posted, with the CCS tail in place, that I connected the CCS to -100 V. I don't see a problem with that? We would only pull about 10 mA more from the B- supply. Makes for a very easy installation. Just take out the cathode resistors and replace with CCS, hook up B+ and B- and you're done!



MrCurwen said:


> Do you know the currents ratings of your PT?


We have two of these:



 
Driver stage psu are the 85 V windings in series, so 50 mA rating.


----------



## coinmaster (Jan 18, 2018)

> It is not necessary to regulate this, since there will be so many megaohms of impedance between B- and ground / B+.


 Non regulated current sources introduce unwanted harmonics.
The last place you want these to appear is at a sensitive feedback location like the cathodes of a LTP with a mu of 100 where it only takes milivolts to correct large variations of output amplitude mismatch.
Also the impedance between b- and ground would simply be the impedance of the bypass cap, an unregulated CCS will provide less impedance as a current source.


> I would not be using a chip CCS for a serious HIFI or even high end build. When looking for best results, always always always go discreet.


True but using a jfet is the simplest method for modding a ccs into the amp since it's so cramped as it is, and you don't need a perfect current source for a LTP,  0.02% current variance is plenty.


----------



## SonicTrance

Ok, so I tried it!

Cathode resistors out. You can see I've lifted a soldering pad there. That's because I've jammed the leads of 1W resistors in holes made for 0.25W R's. You live and you learn!


 
Soldered the CCS right on a cathode pin. Also put 100R between the CCS and cathodes.


 
B+ taken from top of Anode load resistors.




B- taken from the resistor lead here.


 


 

It works and sounds very, very good so far. Haven't had much time to listen yet. All voltages are stable and amp is dead silent as usual!

Will return with more measurements and listening impressions later!


----------



## baronbeehive (Jan 18, 2018)

SonicTrance said:


> Ok, so I tried it!
> 
> Cathode resistors out. You can see I've lifted a soldering pad there. That's because I've jammed the leads of 1W resistors in holes made for 0.25W R's. You live and you learn!
> 
> ....



Ha ha, tell me about it......and you tell me to go easy with the soldering lol!
P2P has it's advantages!



SonicTrance said:


> ....
> 
> It works and sounds very, very good so far. Haven't had much time to listen yet. All voltages are stable and amp is dead silent as usual!
> 
> Will return with more measurements and listening impressions later!



Nice work Sonic! Look forward to more of your impressions.

Edit: You realise I've just put in the driver stage mod, oh well never mind!


----------



## coinmaster (Jan 18, 2018)

You might want to scope the b-  to see the extent of the harmonics you are feeding the ccs.


----------



## SonicTrance

baronbeehive said:


> Ha ha, tell me about it......and you tell me to go easy with the soldering lol!
> P2P has it's advantages!


Yes, well to my defense it must be a couple years ago by now I made that mistake. 
I even filed the ends of the resistor leads on the other channel to make them fit! Haha!


----------



## SonicTrance (Jan 20, 2018)

I've experimented with different operating points for the ECC35's and also different values for the last R's in the input stage psu. I wasn't getting enough B+ with the settings I used above, so bias voltage was very low. The goal here was to get as much B+ as possible, give the tubes as low current as possible without any SQ drawback. We work with what we have here, though 250+ V B+ would of been much better, of course.

These are the settings I ended up with:

B+: 155 V
Ia: 1.2 mA (no reason to go lower, this gave me enough voltage and sounded just as good as 1.75 mA)
Va: 114 V
Vg: 900 mV

For the last 3k3 R's (after psu splits) I used 750R.

Total current draw / channel is 3.44 mA (2.4 mA for the tube and about 1 mA for the 220k R that bias the darlington pair 2N2222 transistors.

Here's the operating point:



The curves are pretty accurate to real life measurements as you can see.

These settings should work well with ECC35's, 6SL7's and also 6C8G's. However 6SN7 would still be in non-linear area of the curves as it requires at least 4 mA (/ triode) to be linear. That would bring the total current draw per channel up to about 9 mA, which in turn would bring the B+ way down. So, it would be basically impossible to bias the 6SN7 optimally with this psu. Lucky for us there's no need to use the 6SN7 when we have other tubes.


Now that I'm satisfied with the operating point, I'll go ahead and do some more testing and listening! It's quite fun to be working on this amp again, haha!


----------



## baronbeehive (Jan 20, 2018)

SonicTrance said:


> I've experimented with different operating points for the ECC35's and also different values for the last R's in the input stage psu. I wasn't getting enough B+ with the settings I used above, so bias voltage was very low. The goal here was to get as much B+ as possible, give the tubes as low current as possible without any SQ drawback. We work with what we have here, though 250+ V B+ would of been much better, of course.
> 
> These are the settings I ended up with:
> 
> ...



Yes, that's great!

I am also doing some comparisons between this amp and the APPJ out of interest, which I thought you might also find interesting. I have a splitter going from the DAC so can compare directly. I found that as I said they perform at a similarly high level but that the APPJ is slightly more articulate in the bass and across the board. However I'm burning in the upgrades atm as I believe the Jupiters need a lot of burnin. I have only used the LD for a hour or so since doing the mods a year or so ago, and already it is increasing in holography and space around the instruments. I believe when I replace the...some say crap RCA's... with the full set of 421A's it will go through the stratosphere! Also I'm going to test in high gain to see what the effects of feedback are.

Please note, I want to be as objective as possible I am in no way criticising the LD, on the contrary it is sounding absolutely wonderful, and still getting better, as far as I can see it is top notch and I love it, but there's no denying other amps have their different sound signatures and one of the APPJ's is speed and sharp transient leading edges which the LD does not quite have, not far behind, but the LD has it's own areas which it excels in, and I believe will knock spots off most of the amps out there, at least until you start spending mega bucks, and I'm loving it.


----------



## SonicTrance

baronbeehive said:


> but the LD has it's own areas which it excels in, and I believe will knock spots off most of the amps out there, at least until you start spending mega bucks, and I'm loving it.


No need to spend mega bucks! Just build the modern LTP!


----------



## baronbeehive

SonicTrance said:


> No need to spend mega bucks! Just build the modern LTP!



Ha,ha,much as I would like to, now is not the right time unfortunately, but sometime soon yes!!

Edit: Oh you mean the CCS mod, I don't know if that's part of a LTP on the LD, waiting to hear more!


----------



## coinmaster (Jan 20, 2018)

> The goal here was to get as much B+ as possible, give the tubes as low current as possible without any SQ drawback. We work with what we have here, though 250+ V B+ would of been much better, of course.


 Just make a voltage doubler. Only requires a few parts.


> APPJ's is speed and sharp transient leading edges which the LD does not quite have,


 Film caps in the mk6 power supply solves this.


> Oh you mean the CCS mod, I don't know if that's part of a LTP on the LD, waiting to hear more!


 it is.


----------



## baronbeehive

coinmaster said:


> ...
> Film caps in the mk6 power supply solves this.
> ...



....yes but I have no heavy articulated truck to deliver it.....!


----------



## MrCurwen

I don't exactly recall what was in the PSU, but I'm sure it could just be tossed and put a simple RCRC with small R (like 100 or 200 R) and a simple 2 FET reg. Then you'd have more or less about the same B+ voltage, which is fine.

Use cheapest resistors and 105 degree 47µF electrolytes. Absolutely no difference in sound quality either theoretically or observably is going to be happening. It's a constant current draw stage at that point and behind a regulator. Put one 1 to 4 µF film cap after the reg for stability. Russian MBGO 4µF recommended. No observable sound quality difference either way, this cap is for stability and nothing else.

Then just put the gyrators in there. The input stage only needs to provide a small voltage output because of the nature of the amp as a whole. No need for 70V voltage headroom, 10 or 20 will suffice, 50 will be overkill.

With gNFB and adding stuff inside the loop stability is always a concern. But I guess there's only one way to find out; stability cannot be simmed.


----------



## MrCurwen

After the mods described in my previous post having the input stage inside the loop is actually only hurting the sound quality of the input stage. It is however still required for making the output stage have a useable output impedance.


----------



## SonicTrance

baronbeehive said:


> Edit: Oh you mean the CCS mod


No, I mean this: https://www.head-fi.org/threads/modern-balanced-tube-amp-build.852879/

But, yes. I also recommend the CCS mod for the MK6!

I guess this is one of those which simmed better in spice than it performed in real life. 
If I inject a signal in one phase and say the output is 2 Vpp. Then the output of the phase without input signal is about half, so 1 Vpp. Still much better than before but not "forced balanced". But when listening to music we have input signal in both phases, of course.

All in all I think it sounds much better than before! As it should.


----------



## baronbeehive

MrCurwen said:


> After the mods described in my previous post having the input stage inside the loop is actually only hurting the sound quality of the input stage. It is however still required for making the output stage have a useable output impedance.



Thanks, we will look into this. As I said it is not a problem for me because I like a non fatiguing sound over  headphones, nevertheless to get the most definition it may need to  be done.


----------



## SonicTrance

MrCurwen said:


> I don't exactly recall what was in the PSU, but I'm sure it could just be tossed and put a simple RCRC with small R (like 100 or 200 R) and a simple 2 FET reg. Then you'd have more or less about the same B+ voltage, which is fine.


Have you looked at any of the pics I've posted? There's absolutely no room for any reg's or gyrators and most definitely not any russsian caps, lol! Sure, I could rebuild the psu filter, but without the reg there's no point.


----------



## coinmaster

> Have you looked at any of the pics I've posted? There's absolutely no room for any reg's or gyrators and most definitely not any russsian caps, lol! Sure, I could rebuild the psu filter, but without the reg there's no point.


 You wasted all the space using an elaborate ccs scheme instead of a 2 terminal scheme. I also said there are low profile gyrator pcbs you can buy. You seem to be ignoring me so I'll just leave it at that.


----------



## SonicTrance

coinmaster said:


> You wasted all the space using an elaborate ccs scheme instead of a 2 terminal scheme.


Well, I had all parts on hand so...And I trust MrCurwen's advice as it has worked out great for me so far.



coinmaster said:


> I also said there are low profile gyrator pcbs you can buy.


Do you have any pics with these boards fitted inside the MK6?



MrCurwen said:


> After the mods described in my previous post having the input stage inside the loop is actually only hurting the sound quality of the input stage. It is however still required for making the output stage have a useable output impedance.


My goal is not to mimic the modern LTP. I already built my dream amplifier so there's no point in trying to make the mk6 sound just like it (I realize it never will with the WCF output stage). If other people are willing to extend the bottom of the chassis or make a separate box for the input stage, that's totally understandable. After all that was my initial goal before I built the modern LTP.


----------



## coinmaster (Jan 20, 2018)

> Well, I had all parts on hand so...And I trust MrCurwen's advice as it has worked out great for me so far.


 It's an upgrade to be sure, I still don't trust the b- connection though. Any harmonics that get through the current source will be heavily amplified. Like I said you might want to scope your b- supply to see how dirty it is. The dirtier it is the less impedance the current source will provide and the more unwanted harmonics will leak into the input stage.


> Do you have any pics with these boards fitted inside the MK6?


 I only applied my improved wcf mod to my mk6 a while back. My headphones bit the dust after years of abusing them in experiments so I didn't see the point in doing any more mods. I'll soon be repairing them while I build full scale prototypes of one of the amps I designed.
That being said the PCBs are mostly flat, the mosfet is the exception but it can be bent back. http://www.bartola.co.uk/valves/for-sale/gyrator-pcb/ I would be surprised if you couldn't squeeze it in there.


> My goal is not to mimic the modern LTP. I already built my dream amplifier so there's no point in trying to make the mk6 sound just like it (I realize it never will with the WCF output stage). If other people are willing to extend the bottom of the chassis or make a separate box for the input stage, that's totally understandable. After all that was my initial goal before I built the modern LTP.


 The WCF may not be technically optimal but it does a lot of things well in OTL and has the hidden advantage of how it sounds when mixing tubes. There are ways to make the wcf and the "modern LTP" perform much better without the need for feedback, I'll soon find out how this better performance translates into sound in the next few weeks.


----------



## SonicTrance

coinmaster said:


> Any harmonics that get through the current source will be heavily amplified. Like I said you might want to scope your b- supply to see how dirty it is.


I have looked at the B- using FFT on the scope. Looked very clean.



coinmaster said:


> I would be surprised if you couldn't squeeze it in there.


Remember, you need four of those for the input stage. Probably heatsinks on the FET's as well. I could most likely build p2p gyrators smaller than that pcb, especially if not using a heatsink. Anyway, I'm not all that interested in installing gyrators and grid drivers in the mk6. I might hook something up externally because it's fun to experiment. 


When listening to music I have my other amp.


----------



## coinmaster (Jan 20, 2018)

> Remember, you need four of those for the input stage. Probably heatsinks on the FET's as well.


 No need for heatsink. I have 4 of those pcs I used for other projects. They would fit nicely even with 4.



> I have looked at the B- using FFT on the scope. Looked very clean.


What are you using to read fft? Oscilloscope ffts are not designed for audio work.


> Anyway, I'm not all that interested in installing gyrators and grid drivers in the mk6. I might hook something up externally because it's fun to experiment


Voltage doubler would probably work for you then.


----------



## SonicTrance

coinmaster said:


> No need for heatsink.


Yes, I realized there’s no need for heat sinks as the dissipation would be very low in the mk6



coinmaster said:


> Oscilloscope ffts are not designed for audio work.


Yes, FFT on the scope is what I use. Range is from 1Hz to many MHz. 



coinmaster said:


> Voltage doubler would probably work for you then.


It would definitely fit inside if I take out the existing filter. Question is how the PT(s) would react to a doubler.


----------



## coinmaster (Jan 20, 2018)

> Yes, FFT on the scope is what I use. Range is from 1Hz to many MHz.


 Only the most expensive scopes have FTTs that aren't garbage, they are added to the scope as an afterthought. FTTs are process intensive, you need a dedicated audio spectrum analyzer to get a good reading, or at the very least a sound card. What scope are you using?
It may be easier to just look at the B- in AC scope mode. You don't need an FFT reading to know if the supply is clean or not.



> It would definitely fit inside if I take out the existing filter. Question is how the PT(s) would react to a doubler.


 They wouldn't. At the current you need the caps don't have to be huge.


----------



## SonicTrance

coinmaster said:


> It may be easier to just look at the B- in AC scope mode.


There's only about 100 mVpp of ripple on the B-. Same on the B+ for the output stage as well as the B+ for the input stage. About 100 mVpp of ripple on all of them.


----------



## coinmaster (Jan 21, 2018)

I'm looking at a 0.73% increase in THD with a 100mv b- in spice, and even worse if the B+ is as bad since it's also feeding the current source.
If the ripple in the supply is non harmonic that makes it worse still.
You're basically relying on the GNFB to clean this mess up, that is just a bad way to design. Like I said, the cathodes are too sensitive for this kind of implementation without a regulated supply. Use a jfet and be safe in the knowledge your feeding it with an "ideal" supply (ground).


----------



## SonicTrance

coinmaster said:


> I'm looking at a 0.73% increase in THD with a 100mv b- in spice, and even worse if the B+ is as bad since it's also feeding the current source.


Increase in relation to what? The 1.5 k resistor tail?
Anyway, even if your numbers are accurate it can't be heard! Nothing beats listening tests. 
I'll stick with the MOSFET CCS. Might actually put in a voltage doubler for the driver stage B+ though. Ive made some sims in psud and I can do it with parts on hand. Ideally it should be a reg also of course, but as stated before theres no room. 
Higher B+ would let me use higher plate load and potentially more voltage swing.


----------



## coinmaster (Jan 21, 2018)

> Increase in relation to what?


 The equivalent circuit powered by a clean supply.


> Anyway, even if your numbers are accurate it can't be heard!


 Um, yeah a nearly 1% increase in distortion (2% if b+ is dirty) is pretty audible. The GNFB is cleaning it up but if you think using NFB to solve a messy design is a good plan...I guess you'll be satisfied with any amp on the market.


> Nothing beats listening tests.


 That statement means nothing when you haven't compared the two.


----------



## SonicTrance

coinmaster said:


> The GNFB is cleaning it up but if you think using NFB to solve a messy design is a good plan...I guess you'll be satisfied with any amp on the market.


Well thats the way this amp is built so... Ive never said that its optimal design. Like I said I already built my dream amp! I'm only messing with the mk6 for fun! Give me a break, man! And learn to quote like normal people!


----------



## coinmaster

> Well thats the way this amp is built so... Ive never said that its optimal design.


 You're missing the point. Using a current source that increases the distortion in the amplifier by a potential 1-2% before feedback is not a good idea if you care about the sound at all. A current source should not increase distortion. The MK6 GNFB is is not cleaning up such a careless mess, it's only reducing the flaws in the inherent design.


----------



## Maxx134 (Jan 21, 2018)

coinmaster said:


> Voltage doubler would probably work for you then.


I like this idea as I feel the single most important improvement would be having enough voltage for optimal tube operation instead of starving the tubes...




coinmaster said:


> It may be easier to just look at the B- in AC scope mode. You don't need an FFT reading to know if the supply is clean or not.



Sonic MK6 is the most heavily moded MK6 I seen and so I can't imagine the B- not being clean, unless the power tubes are modulating the B- because of dynamic load of music..

Edit:
Woops I didn't see thia last page of comments ok now I understand..


----------



## coinmaster (Jan 21, 2018)

> Sonic MK6 is the most heavily moded MK6 I seen and so I can't imagine the B- not being clean, unless the power tubes are modulating the B- because of dynamic load of music..


Since the mk6 power tube supply is not actively regulated it relies on the balanced operation of the amp to perform the regulation (which is a big reason why balanced sounds better in this amp) Since both phases of each channel are 180 degrees out of phase, the currents drawn by the supply are canceled out, making for a perfect AC voltage null resulting in pure DC at the power supply. At least in theory. This requires that the tubes are perfectly matched and the currents drawn by everything in the amp is equal and opposite. Drawing X amount of current from the B- supply to feed a current source scheme isn't helping this either, as it will increase the imbalance of currents.
Since the amp isn't perfectly symmetrical there's leftover AC in the supply.
100mv is pretty dirty by any "hifi" standard. Depending on the harmonics involved in the supply ripple it could be more or less okay, I still suspect some level of harmonious ripple can be a good thing although I haven't tested this yet myself, but I have reasons to believe in the possibiltity, at least under certain conditions. However it reduces channel separation in this amp, and feeding any of it into the input stage cathode is not good. If there's non harmonic content in the ripple its not good at all.


----------



## Maxx134 (Jan 22, 2018)

SonicTrance said:


> Anyway, even if your numbers are accurate it can't be heard! Nothing beats listening tests


I recently listened to a stock headphone and appreciated how nice it sounded...
Only until I compared it side by side with a same model moded headphone was I able to realize how much faults it had...

The point is you can't tell without the side by side comparison,
Which I remember I PM you a while back how I did it to compare tubes..




SonicTrance said:


> Higher B+ would let me use higher plate load and potentially more voltage swing.


I wanted to voice my concerns about the voltage swing...
In my testing,
When Using too low an anode resistor.
I noticed a loss of voltage swing which audibly resulted in less dynamics ...
I did this with *"comparative testing"* ,
Which is the same testing I PM you about last year when I was comparing tubes...

So if possible, try revert one side(channel)
 to compare to other,
So as to compare both sides ( one side to the other.) Using a mono sound source.

That is why I chose *NOT to *use the low anode resistor settings that you chose..
For me It reduced the dynamics (on comparison testing) and was not compatable with the other tubes I was testing.

I understand you chose this setting for the ecc35 tube, and remember. that I also bought those excellent tubes thanks to you.

I should have lowered my cathode to increase bias further and test that low voltage swing.
Yet,
I did lower my 3k3 to 1k to increase the B+ and voltage swing..
So the volt drop swing was higher at my settings.(while bias was lower but similar due to increased B+).

The anode volt swing is a totally different sonic sound effect/characteristic ,
than the increased bias  (by cathode resistor lowering.)

The parameter effected from changing the bias (with cathode resistor change)"
 was the aspect of tube liveliness and also a difference in soundstage ...
I adjusted the bias to still be in the good sounding range of the curves, even though it wasn't more higher like yours it still sounded in that lively sounding  range.

My setting made the 6SL7 (6C8G) sounded best.
They also they had more *soundstage* than the ecc35 which I liked,
and ended up being my best bias tubes within this amp limited PSU .

I Highlighted the word "*soundstage" *above for a reason..
The single most telling aspect for me, when comparing amps,
is the ability to portray soundstage holography...

Its the only area where I can separate the really good amps, and I have heard many of the latest and best already.

So I expect our amps to be resolving and have different flavors in sound.
But You have not yet mentioned the aspect of holography and soundstage in your amps, so that to me would be the interesting thing to do.




coinmaster said:


> That statement means nothing when you haven't compared the two.



The problem is how can SonicTrance compare his amp "before" and "after" the CCS he applied....

I mentioned this long ago.
Side by side comparison is best way to compare a "before and after"  modification.

It is how I verified every mod, and how I kept what worked..
It is also how I compared my tubes.
It is also how I compared all my headphone modifications.
Sometimes I was lucky to have two of same headphone to compare.

So SonicTrance you can continue to improve upon both your amps and verify any upgrade by changing one side (left or right channel) at a time to compare to the other side...


----------



## Maxx134 (Jan 22, 2018)

It's a shame no one mentions the sonic characteristics according to what is changed.
I havent read anyone commenting on how the tube sound changes with bias...
 or the dynamics with volt swing.

It may be assumed readers might know,
but I believe everyone should know these little technical details that designers seem to "hide".
I had to find out for myself to tune my tubes bias to their "sweet spots"..

Also I realize the NFB setting of the amp also has a huge role to play and affects the driver stage so my setting of higher gain (less NFB) probably played a factor in my different bias settings.
The less NFB may have made my range of acceptable setting more noticable or narrow.

My Optimal Driver tube  settings were:
*1k* for the last resistor PSU (3k3 resistor)
*69k* for anode resistors
*1k* for cathode

I would Also disregard MrCurwen error in commenting that it is "very very stupid" to lower the 3k3 resistor down in this amp,
 to my setting of 1k,
Or  SonicTrance *750R* setting without issue.
As you see we both benefit with higher B+ and no issue in the RCRC filtering.

I would not agree blindly like MrCurwen for a *33k* for anode setting,
 as that is a way lower voltage swing.

I would never choose that setting,
but as I said, member SonicTrance was using higher NFB setting (low gain) in past , (which can mask issues)...
 So unless he do a comparison (right vs left) we won't know if the lowered anode resistor lost some dynamics from the lower volt swing.

I am being soft.
I already tested less than optimal conditions.

In my past tests,
With *41k* anode setting,
The 6c8g sound lost some of its dynamics and vitality.
 ECC35 had same problems, muted dynamically, only slightly better than the 6c8g...

So SonicTrance, there is a strong possibility for your MK6 to climb up to your other LTP amp in dynamics,
By using higher anode resistor settings,
Which you can find out.


----------



## baronbeehive

Maxx134 said:


> I recently listened to a stock headphone and appreciated how nice it sounded...
> Only until I compared it side by side with a same model moded headphone was I able to realize how much faults it had...
> 
> The point is you can't tell without the side by side comparison,
> ...



I quite agree about this, we mustn't lose the thing that has made this thread great, the reliance on rigorous testing. I wouldn't have done the mods without being certain of the benefits. We all know that audiophile forums are littered with snake oil remedies for this and that so we must't fall into this trap. I didn't hear any differeces whatsoever for example with tube mixing, so I have to say that, of course it could be that the tubes I tried were too similar to each other to discern their combined effects but I don't think I will be pursuing that.

I don't think I'm losing it quite yet because I've been able to tell all the different tube types I've tried on the other amp. Also, I've been able to do the direct tests with the 2 amps side by side and this did confirm suspicions I had, but without the direct comparison I couldn't have been sure.

Lets be clear everyone on this thread has done great work, and I think Maxx should have a pat on the back.... no a distiguished medal at the very least.... for all his hours spent in testing on the couch, which would have scrambled my brain frankly, it's no wonder that he kept falling asleep with all that lol!


----------



## SonicTrance

Maxx134 said:


> I like this idea as I feel the single most important improvement would be having enough voltage for optimal tube operation instead of starving the tubes...


They're not starved with the CCS in place together with the lower anode loads. They were only starved for current before, not voltage. Of course, more voltage would give a better operating point. 



Maxx134 said:


> The point is you can't tell without the side by side comparison,
> Which I remember I PM you a while back how I did it to compare tubes..


I also did this exact same thing. Just look at the tube comparison PM's. It did not work well for me listening with only one ear. I thought everything sounded bad like that. I need stereo. To do a fair comparison of anything I would need to have two MK6's side by side, volume matched, both connected to some kind of splitter and be able to switch between the amps in a second. Everything else is comparing by memory. I don't see that happening, unfortunately. 



Maxx134 said:


> I should have lowered my cathode to increase bias further and test that low voltage swing.


To be clear though. The B+ and anode load sets the load line, which the grid voltage can swing up and down across, and the cathode R sets the operating point on that load line.



Maxx134 said:


> The anode volt swing is a totally different sonic sound effect/characteristic ,
> than the increased bias (by cathode resistor lowering.)


Say you have bias (grid) voltage of -1 V. Like the operating point below. The signal is then 2 Vpp * µ68 (it's not really 68 in this circuit, in my sims µ is about 14, low gain)  = 136 Vpp (28 Vpp). That's the voltage the anode's are trying to swing.
Look at the load line below and see if it's possible. You can see that 136 Vpp is in fact not possible. But 28 Vpp is. With Va at 110 V, positive peak would be at 124 V and negative peak at 96 V. Tube will be down in non'linear region at positive swing though.



 



Maxx134 said:


> But You have not yet mentioned the aspect of holography and soundstage in your amps, so that to me would be the interesting thing to do.


As you know I'm nowhere near as good at describing sound as you are. But I think micro detail increases soundstage and there's lots of that in the modern LTP. 



Maxx134 said:


> So SonicTrance you can continue to improve upon both your amps and verify any upgrade by changing one side (left or right channel) at a time to compare to the other side...


Like stated above. This does not work for me, unfortunately. I can only make comparisons by memory and measurements. 



Maxx134 said:


> It's a shame no one mentions the sonic characteristics according to what is changed.
> I havent read anyone commenting on how the tube sound changes with bias...
> or the dynamics with volt swing.


This is because no one is doing any modding except for me, lol




Maxx134 said:


> As you see we both benefit with higher B+ and no issue in the RCRC filtering.


He did say not to increase C and lower R at the same time. I actually lowered both last C (15µ) and R (750R) Don't think it matters anyway as the PT is rated at 50 mA, so plenty of current headroom.


----------



## MrCurwen

Ok, so Sonic has built the CCS tail mod in the LD, measured it with scope and ears, and found it an improvement. No report of flood of nasty high order harmonics. That's the practical part. What about theory?

I drew up a similar schem, don't worry about RC coupling values etc. they don't effect these results in any way. 

 

B+ is 160V DC, B- is -100 VDC, input signals are 100mVPP. CCS is of very powerful type.

I added just a pinch of trouble in the PSU supplies, just to prove a point for people who haven't read their beginner electronic theory. No shame in that, not everybody has time for everything me included. Demonstrations and tests are just as good of a way to learn, maybe better.

So here's B+:

 

Auts, that's a doozie. Not clean at all. I don't know what the PSU designer was drinking while making that one.

 

No better there. 

The frequencies are 5kHz and 6kHz for added problems. Quite close, but not too close, for maximum IMD. 

So let's have a look at the inputs and the output;



Output is about 10VPP and the oscillations were several volts, so they should be showing up here. I don't see them. Let's have a look at the THD of the output.

Total Harmonic Distortion: 0.010390%

Hmm that's not bad at all, quite spectacular actually considering the 33k anode loads (which are grossly insufficient for best results as everybody agrees).

But maybe there's lot's of high order harmonics there, let's have a look at the FFT:



Let's analyze that.

H5 and H6 which were inserted into the circuit about 20 times larger than the input signal are both below oh let's just say -80dB level. That's quite incredible. 

H2 is missing completely, and H3 is below -90dB. This is in my opinion and experience unhearable. 

There's some IMD products, H4 and H7. If somebody says H8 at -120dB is relevant to anything, I'm going to wish them good luck in their building endevours.


I would personally say that CCS tailed LTP's, even semi-retro types like this, are incredibly resistant to both tube related distortions and PSU related distortions. 

Most people look at the LTP as two SE gain stages, bolted together. In some ways it is true, if that doesn't describe the actual functioning of the forced balanced pair. But I've gone thru this many times and don't want to hijack this thread more than I already do, so if somebody is interested read my old stuff or ask about it. I'll be happy to elaborate.


Empirical experience is completely in line with theory.


----------



## MrCurwen

Let's run the sims again with more realistic disturbances. Everything else stays the same, but B+ and B- oscillations are reduced from 4VPP to 200mVPP. This is still quite bad, I wouldn't have this in any amp I build or design for serious listening.

Output amplitude is the same, THD is reported as Total Harmonic Distortion: 0.002355%.

This is of course Spice fantasy, but these numbers are useful in comparisons between one simulation and another. Meaning this circuit will not give this THD in reality, but in reality it will be a lot better than the previous conditions simulated.

Let's look at the FFT:

 

H3 is generated by the tubes, because their anode loads are grossly insufficient. The rest are inserted via PSUs and IMD.

All the PSU and IMD related harmonics are below -100dB. This is well below hearing, and oftentimes well below noise floor.

Now in reality the high order harmonics would be lower (in both sims) and H2 and especially H3 would be a lot higher. This is because of the anode loads.

H2 and H3 are not horrible to listen to ("tube sound"), but of course for best results you will need to get rid of them, as explained earlier. 


Most people consider lower order (below H5) harmonics -70dB below signal peak to be so good it's meaningless.


----------



## Maxx134

baronbeehive said:


> Lets be clear everyone on this thread has done great work, and I think Maxx should have a pat on the back.... no a distiguished medal at the very least.... for all his hours spent in testing on the couch, which would have scrambled my brain frankly, it's no wonder that he kept falling asleep with all that lol!





SonicTrance said:


> This is because no one is doing any modding except for me, lol


I re-read my posts sounded a bit harsh so just want to clarify.

I like to thank SonicT for continuing where I stopped when my amp broke (I fell asleep with bad tube adapter in place lol),
And carrying on with more mods....

And commend  MrCurwen for both his input for learning,
and for motivating Sonic further to build new amp.

Sonic been motivating me to also lately move on to new amp.

In this thread it not matter that we don't always see eye-to-eye,
I still value & admire  everyone who participates and contributes to learning, that goes for coin as well.

They say too many cooks spoil the pot,
But I admire the ideas that come from it.
All this is good stuff for me.
Cheers.


----------



## coinmaster (Jan 22, 2018)

> Let's analyze that.


Yeah good job measuring the current distortion across R1 to get a better result...

If I did a fourier analysis with current as the parameter I would get 0.000001% thd on any respectable design.
My sim is identical to yours and the _voltage_ distortion is far worse. Were feeding headphones, not a ribbon, and not into a 200k load.
Also it's the FFT equivalent of a horror movie. It's comprised of purely high order harmonics.

I would never make something with such high order harmonics. You say they are inaudible, well that may be true with at normal headphone SPL levels if comodulation unmasking wasn't a thing and if higher order harmonics weren't much more detectable by our ears on top of that. Besides if DB at that level is inaudible then "tube sound" is also inaudible, guess there's no point in using tubes anymore eh? Plus you said it yourself, spice is too perfect, reality will be worse.\
It's not good to design this way when a simple Jfet current source sidesteps the whole issue.


----------



## Maxx134

SonicTrance said:


> I also did this exact same thing. Just look at the tube comparison PM's. It did not work well for me listening with only one ear. I thought everything sounded bad like that. I need stereo. To do a fair comparison of anything I would need to have two MK6's side by side, volume matched, both connected to some kind of splitter and be able to switch between the amps in a second. Everything else is comparing by memory. I don't see that happening, unfortunately


Haha ok it will take about $300 round trip to ship to you and back lol.
Problem is mine is mk8 & all my diamonds would fall off in transit lol.

I love your new amp tube selection but will hold off yet .
My Next amp will be all plain and black.
I am in no rush tho.
I still don't have a scope yet which worries me.
Also,

Yes Using one ear is a trained thing.
My teacher in studio engineer was a microphone placement guy.
He taught me his technique was to use one ear to find the "sweet spot" for microphone placement of music bamd & orchestra.
So you see it is a technique they teach, not my idea.


----------



## baronbeehive (Jan 22, 2018)

Maxx134 said:


> Haha ok it will take about $300 round trip to ship to you and back lol.
> Problem is mine is mk8 & all my diamonds would fall off in transit lol.
> 
> ...



No need to worry about that, you would never get it through customs anyway...



Maxx134 said:


> ...
> My Next amp will be all plain and black.
> ...



..... yeah, right!



I can check out the effects of feedback on the anode-cathode values now that I've done that mod with the lower values, when I test it in high gain....with or without your amp......


----------



## MrCurwen

Science and engineering have a lot in common, yet they also have a lot of differences. In abstract, science is about the search for truth; to make all things fit simply and beautifully together. In abstract, engineering is about making the best possible machine (whether physical or not) with the resources that are reasonably available.

Now in reality both are about small incremental improvements and they do resemble each other more than not.

I get we are talking about a hobby; selling amps is actually 99% thinking about available resources and what makes sense for other people (customers), not you. Hobbyists are not scientist or engineers. 

But whenever you get a wannabe amp builder with the mindset that there is a truth to be found, you are going to have trouble. The wannabe is going to have a bad time, and so is everybody else around them.

Amp design is about what works, and what is better than what you had before. All amp builds and designs that perform better than what the designer made previously, are respectable. 

Not respecting this process of incremental betterment is the hallmark of the wannabe. These guys show up regularly on different places. Everybody deals with this "perfect problem" to some extent, but some get an obsession with it. 


The ones that get an obsession of perfection never do the work; they are lazy, often arrogant to people who are willing to do the work. 

Going thru the process of building simple stuff, then improving it bit by bit, sometimes going into a dead end and turning back; this is what gives a designer the instinctive knowledge of "what probably works". Sure this doesn't make you a god among men, but without it you have no way to interpret Spice results. Sometimes Spice is very misleading, sometimes it's not. You have do the solderwork to have a clue which is which.

Sonic did the solderwork; it worked. It was better than before. That's respectable. 

Nothing is perfect nor ever will be. Work is respectable.


----------



## coinmaster (Jan 22, 2018)

> Sonic did the solderwork; it worked. It was better than before. That's respectable.
> 
> Nothing is perfect nor ever will be. Work is respectable.


 Respectable? Sure. I can be respected for getting out of bed in the mourning. Comparative praise is not the kind that matters if results are the goal.
I prefer to go with the more logical choice from the get-go, in this case there's only downside to be had from the current source implementation he chose over the alternative I suggested, often I withhold judgement because of possible alternative factors but there's just nothing good about this one. Does this make him a bad person? No, but it's not wise if the goal is sound improvement.


----------



## MrCurwen

Spice does not give the automatic THD number for an expression, as far as I know (if there's a way to do that I would appreciate the tip), so there's no other way to measure THD for differential circuits except at the output of OT where the OT has reintegrated the signal.

However FFTs can be done with expressions, as I did in my previous sim posts. The graphs are accurately titled on the top of the graph. This shows the FFT for the actual output signal you will be listening. Any other FFT analysation would be quite pointless to look at or talk about.


----------



## Maxx134 (Jan 22, 2018)

coinmaster said:


> Yeah good job measuring the current distortion across R1 to get a better res


Umm ok, so what your saying is that he needed to use the voltage distortion measurements, for more realistic results,
Instead of the "current distortion" measurement, which ends up giving a "better" result...

We Will probably need to compare CCS eventually, but one jfet does sound more convincing just to be on the safe side..

The good news is that it can be done and I also like the idea of the voltage doubler but the effort involved may not be worth any actual results compared to what we have already.




baronbeehive said:


> I can check out the effects of feedback on the anode-cathode values now that I've done that mod with the lower values, when I test it in high gain


Please do so...
If not too much trouble.
Would help to also find out wether the lower gain setting mask and help any problem,
As low gain a
Setting is actually higher feedback setting..


----------



## coinmaster (Jan 22, 2018)

> Umm ok, so what your saying is that he needed to use the voltage distortion measurements, for more realistic results,
> Instead of the "current distortion" measurement, which ends up giving a "better" result...


 Even by my cautious standards, I can get truly inaudible distortion out of any good design using current measurment as an indicator. 0.0000000% spice distortion by this standard is achievable.
So if he was getting 0.01% with current measurement, that is actually a really terrible result.
I copied his sim to the T and got the same result I got before in voltage distortion.


> so there's no other way to measure THD for differential circuits except at the output of OT where the OT has reintegrated the signal.


 That doesn't mean it's the right way. Current measurement in spice is only good comparatively, the results are far too good for reality into a headphone load.
Also, even though the distortion of the current source will be in phase at both ends of the differential circuit, do you really trust tubes to keep them perfectly symmetrical? Yeah......there's just no good side to this.
So with that theme here are the results for a jfet current source vs the sonic is using measuring the current across the load of a fully simmed mk6.






Jfet




Discreet

Keep in mind, these spice tubes are perfectly matched with each other.
The more unmatched their distortion and amplitude is the worse this graph would be. This is triply true for the discreet version since the jfet will only have its own operational distortion to worry about, no extra power supplies.
Under these comparative tests the jfet wins. It's better in every conceivable category I can think of.


----------



## Maxx134 (Jan 22, 2018)

MrCurwen said:


> Sonic did the solderwork; it worked. It was better than before. That's respectable.
> 
> Nothing is perfect nor ever will be. Work is respectable.



SonicT build of his new amp I amazing to me I instantly absolutely fell in love with the amp and tube selection lol.
I am very visual biased lol.
So doing the solder work I agreee is respectable and motivated me to try one build from scratch .
Trickle down motivation from you !

Anyways, all said and done, I will plan to try the CCS using one Jfet as I feel Coin post is more persuasive to apply a  more safe approach .

I actually was excited about using that single cheapo chip as well, but not sure if it could be plugged into a sim.
Although it is not a new device either ..


----------



## baronbeehive

MrCurwen said:


> Science and engineering have a lot in common, yet they also have a lot of differences. In abstract, science is about the search for truth; to make all things fit simply and beautifully together. In abstract, engineering is about making the best possible machine (whether physical or not) with the resources that are reasonably available.
> 
> Now in reality both are about small incremental improvements and they do resemble each other more than not.
> 
> ....



I've been thinking about this and was wondering if the guys at LD are not even more savvy than we already think, and maybe they designed an imperfect machine because they knew it would sound great, maybe they even tried it out step by step in varying degrees to get just that sound that they thought we would like.

Sorry you guys are way ahead of me but it is obvious that they didn't design a perfect machine but we love what they did!


----------



## Maxx134 (Jan 22, 2018)

baronbeehive said:


> Sorry you guys are way ahead of me but it is obvious that they didn't design a perfect machine but we love what they did!


They certainly knew how to make better:




But like MrCurwen stated its about what will sell..

I like this amp.
Actually not sure if it was any better.
Too bad they never produced it commercially...


----------



## coinmaster

> I've been thinking about this and was wondering if the guys at LD are not even more savvy than we already think


 Based on what I know and the amount of improvements I can make even within the same design I question how savvy they actually are.


> and maybe they designed an imperfect machine because they knew it would sound great, maybe they even tried it out step by step in varying degrees to get just that sound that they thought we would like.


 I would not doubt the possibility. But also keep in mind, typically tube amp designers are lazy and unimaginative. Why? Because its very easy to get a good result from a tube design. I think most people try not to fix what isn't broken. It's rare I see a tube amp schematic that doesn't bore me with mediocrity, from an engineers perspective.
It seems more likely they just found a cost effective biasing solution for the 6sl7 which conveniently allows 6sn7 operation as well, and just threw in a WCF output stage for OTL/OCL operation.
Sadly, this concept is pretty novel in the market. The lack of engineering creativity in the market makes me want to claw my eyes out.


> Sorry you guys are way ahead of me but it is obvious that they didn't design a perfect machine but we love what they did!


The word "perfect" requires a goal. To the person engineering the amp, we can only use functional theory to design. Unfortunately psychoacoustic audio theory and electronic audio theory are not complete, so we can't make the "best" amp using only theory.
The MK6 may not be technically perfect, but it can be perceived that way depending on what you do to it, within limits. My point is, theoretical engineering is not the end all, what matters is the end result. I could go much deeper into this but I have no desire to write an article.


> They certainly knew how to make better


Yeah those tubes are not good for mass production design, sadly.


----------



## baronbeehive (Jan 28, 2018)

OK, so out of interest where are we with the proposed new mods:

I'm speaking of:
1 - CCS tail to better balance operations to improve transients, remove dirt from the system - would probably fit in the chassis
2 - Force balance, same as above, don't know how this differs from CCS tail balancing - would probably not fit in the chassis
3 - Source follower, to optimise impedance, all round improvement due to lowered output impedance - would probably fit in the chassis
4 - Regulated power supply, to remove power disturbances, all round improvement due to removing power supply fluctuation - would probably not fit in the chassis
5 - Redge's decoupling mods mark 2 to improve cap functions in the power supply, supposed to improve detail, transients, bass - would not fit in the chassis

Burn in is proceeding apace.... apart from forgetting to switch on the fan yesterday.... and amp holography, instrument separation is fantastic now.
If we could discuss the latest proposed mods we could be in a better positon to see how we can proceed possibly. Also what is the status of testing of these mods.


----------



## Maxx134

baronbeehive said:


> OK, so out of interest where are we with the proposed new mods


Your asking a lot...
Lol

Basically all of that post involve same area,
Namely, the Driver stage upgrade.

I am in the camp of the single jfet idea.

Also I am not convinced 33k anode will give optimal voltage swing.

We Will have to compare.

Both me and Sonic and probably you have the tubes in question.
Bias settings will vary on tube.

The only difference is that I am using a different powertube stage, which may be why my higher gain setting(less NFB) is preferred.

So what setting(high/low) do you have your gain?


----------



## baronbeehive (Jan 29, 2018)

Maxx134 said:


> Your asking a lot...
> Lol
> 
> Basically all of that post involve same area,
> ...



Ha, ha, just trying to make sure noone's trying to sneak ahead without me knowing!

Yes I like the sound of the single jfet, but it's not tested is it, also the source follower looks ok, what I'm not sure about is how these mods work with each other, for example is the force balance mod needed if the CCS is already done

All I know is that the sound is great atm, don't know how it's changed from before the driver stage mod, as you probably know I didn't have the amp working long enough to compare.

I don't have the ECC35 Mullards anymore, I decided to stick with the TS 6SL7's for the LD, whereas I love the Mullards on the APPJ, (and the Mazdas I told you about!!!).

I have low gain setting atm and will probably try high gain next, probably when I have got the last 421A to match my other 3, so that I also do a comparison with the LD with the RCA's. Burn in has not finished yet due to a failure with the fan controller, I have a new one on order.


----------



## MrCurwen

Maxx134 said:


> The point is you can't tell without the side by side comparison,



This is regarding the supposed increase in high order harmonics in Sonic's latest mod. These harmonics are easily heard. Either they're simply not there (as is in fact the case), or they are not as bad as previously thought, in which case no harm done by them.



Maxx134 said:


> I wanted to voice my concerns about the voltage swing...
> In my testing,
> When Using too low an anode resistor.
> I noticed a loss of voltage swing which audibly resulted in less dynamics ...



With dynamics I assume you are talking about transient response, i.e. "how fast the amp sounds". 

Most common reason for muddling these is distortion. Distortion masks all kinds of details in the sound.

Now if you have both 1) poor balance and 2) poor load lines, you are going to have bad dynamics. If you correct the balance to perfect, you can have a poor load line and still come out way ahead distortionwise.

It would be preferred to have a flat load line and perfect balance, but we are working with practical limitations.




Maxx134 said:


> I would not agree blindly like MrCurwen for a *33k* for anode setting,
> as that is a way lower voltage swing.



I adressed the dynamics part above, but regarding the voltage swing;

This is a direct coupled output amp. You do not need or want to output more than a few volts, 20 or so at most. You are not going to need a lot of voltage swing unless you plan to break your headphones.

This is one of the saving graces of this amp design; if you were to travel long distances on the load lines, be they 220k or 33k, you are would have a lot of distortion. But, since the distance is tiny, you can get away with things.



Maxx134 said:


> With *41k* anode setting,
> The 6c8g sound lost some of its dynamics and vitality.



You simply need to look at the situation as a whole, as stated above. There is no special quality that a certain value of anode resistor imparts on the sound. It's all about how the circuit performs as a whole.



Maxx134 said:


> So SonicTrance, there is a strong possibility for your MK6 to climb up to your other LTP amp in dynamics,



Not adressed to me, but no. No possibility without complete redesign.



SonicTrance said:


> It did not work well for me listening with only one ear. I thought everything sounded bad like that. I need stereo.



I'm the same. Actually whenever I try this, I find that if I listen with only one ear, I only hear sounds, noises, but my brain doesn't analyze these noises as music even if I'm listening to my favourite songs.



SonicTrance said:


> You can see that 136 Vpp is in fact not possible. But 28 Vpp is. With Va at 110 V, positive peak would be at 124 V and negative peak at 96 V. Tube will be down in non'linear region at positive swing though.



28 Vpp is more than enough. gNFB influence is already present at the grid input signal, and WCF is let's say 0.8 gain, so with 28Vpp at tube anode you'll have 70 Vpp across the headphone! That's crazy loud, unuseable.



Maxx134 said:


> Umm ok, so what your saying is that he needed to use the voltage distortion measurements, for more realistic results,
> Instead of the "current distortion" measurement, which ends up giving a "better" result...



There's some weird notions floating around here.

First of all, my FFTs are all voltage. Every single one. Look at the headers on top, they're all clearly visible in the pictures I posted. V means voltage in Spice.

The THD measurement is taken on current thru a makeshift load. The load is much harsher than would appear in reality. Since there is some misunderstanding about this still, let me be blunt; Spice THD measurements are a joke. If you look at my messages in this thread, I have tried to always include a side note of this whenever I mention it. It is common knowledge, but since I don't know what you know or don't know, I've but some kind of remark on many occasions.

They do have their place in some things, but that is after the designer has done X Y and Z, and knows to take these things into account. Build a trad SE circuit with H2 at -50dB, listen to it a lot. Then make a simple change to it, rinse and repeat. That is the only way to get real understanding of what you are looking at when you see a THD measure or a FFT screen.

-100dB is the event horizon. At that level the harmonics are not there, they don't make IMD, they don't anything.

At -80dB all but the highest order harmonics are "not there". At -70dB they're "excellent, very clean and clear, superb performance". 

Spice can give you whatever, solderwork and earwork give you understanding of what you're really dealing with. Spice doesn't even model correctly that CCS that Sonic is using; this has been confirmed by measurements (look at his modern LTP thread). In reality that CCS is much more powerful, meaning it offers even greater protection against both PSU and tube distortions. I alluded to this when I wrote here that in reality H2 and H3 would be higher and the higher harmonics wouldn't really be there.

But that's Spice. There's even more disturbing problem in that quote. Let's get into that.


You cannot evaluate a differential circuit's performance any other way than by looking at the differential output.

Let's take a second and really think about that. You cannot evaluate a differential circuit's performance any other way than by looking at the differential output. 

This is audio circuit topology 101 first 4 minutes. Basics of the basics. Not high level genius stuff.

One of the main reasons for adopting the differential topology (in addition to increased power with the same B+ as compared to SE circuits) was that it offers protection against PSU distortions.

Look at pre WW2 scopes. They were the important measuring tools of their day, scientific equipment. They had open loop differential circuits controlling the CRT. Why? Because this offered improved signal quality without having to improve the PSU.

Chokes and capacitors were very expensive then, so this was a big big plus. Even with the increase in tube cost (you need two now), the advantage of removing some tube made distortions as well is there. So you come out ahead.

Of course they had very limited ways to balance the circuit, but still this proved a very good improvement. You can test this yourselves by comparing LD performance in balanced versus SE mode. LD only has 1.5k tail, which doesn't really balance anything, still it performs better balanced than SE.

Common mode noise rejection has been a known thing for about 100 years. Yet in this thread we are supposed to forget it, and take SE measurements from balanced circuits? Why?

The point of the balanced topology is that the topology itself removes these PSU and tube related problems (to the extent that balance is maintained). Increase tail impedance, decrease PSU problems and tube created distortions.

For anyone to claim to understand anything at all about circuit design and then proceed to take SE measurements from balanced circuits is quite arrogant and foolish.


So. I posted a differential voltage FFT previously. THD joke measurement was from current. Let's look at the FFTs, current vs. voltage. Anybody who understands the very basics of Ohm's Law and FFT knows already what's up:

Here's the schem;

 


I forget what the output amplitude was in the last experiment, here it's 12 VPP which is quite well enough. Crazy 400mV ripples on both B+ and B-, at different frequencies. Quite a mess.

I put a voltage controlled voltage source with unity gain as a load. It actually doesn't present a load at all for the circuit, giving way less realistic results than a simple 100k load. 100k load is pessimistic, no load is optimistic. 

So this voltage box integrates the differential signal, just like your headphones ultimately would. Meaning, this is what you'd actually be listening for.

Let's have a look at the FFT:



To avoid confusion among the less experienced people (no insult, what you don't know, you don't know) I limited the results to about -100dB. As you can see, there is some H3. In reality there would be a tiny amount of H2 and some more H3. This is caused by the tubes' load lines (the 33k anode resistors).

Then I changed the load to 100k resistor instead of the virtual voltage box. This approximates reality, little bit pessimisticly.



It's basically the same, just a couple dB worse. In this scale it's 100% the same.

Just to avoid some extra confusion, FFTs are always read in relation to the main signal. So it's always minus X dB lower than the main signal. The absolute scale is meaningless.

Now, if you knew Ohm's Law even a little bit, is this not the result you would be expecting? Learning the basics really comes in handy at all stages of the design process. Cannot be overstated.




Maxx134 said:


> We Will probably need to compare CCS eventually, but one jfet does sound more convincing just to be on the safe side..



I don't know what this safety is. Please elaborate?

Let me explain my own thoughts about this subject.

PSU problems related to this tail topology have been adressed (not by me, but engineers 100 years ago). But what about other things?

First of all, the point of the CCS is to float the cathode node voltage up and down, whenever needed, to control the tubes' bias points. This is how it actually maintains the balance. 

For this, the tail needs adequate room for adjustment. This means voltage across itself.

Now if you have a device that claims to maintain a constant current at a certain voltage headroom, it will fail to do so if it dips below that. In practise this is quite catastophic for the sound signal being reproduced. In Spice it just lags down, but in reality some pretty nasty things happen.

The CCS I use can operate at around 6 volts, but I maintain that it shouldn't be used unless 10V or preferably more is available. This gives enough headroom for several volts to dynamically (along with the signal) adjust the op points of the tubes.

This chip lists 0.9V as minimum opeating headroom when dealing under 1mA of current. If you put this chip as your LTP tail with bottom connected to 0V, you have absolutely no room for any operation.

It works out fine if you are only expecting DC conditions. However it is quite useless if you understand what the LTP is actually for, and what it is doing to achieve that. The cathode node must be able to float up and down without breaching the tail CCS headroom requirements.

The chip is meant for close to DC applications, not dynamic applications.

Furthermore, a simpler device, especially when there is a NFB loop inside it, is usually better. Have the least amount of components to achieve your goal, and no more. Looking at the chip schematic (on page 16) this chip is unnecessarily complex for the task at hand.




baronbeehive said:


> I've been thinking about this and was wondering if the guys at LD are not even more savvy than we already think, and maybe they designed an imperfect machine because they knew it would sound great, maybe they even tried it out step by step in varying degrees to get just that sound that they thought we would like.



Maybe. I think it's more likely they wanted to 'trap' some guys into tube and cap rolling by making the amp susceptible to small variations in these components. Makes for a fun hobby for many people.



baronbeehive said:


> 1 - CCS tail to better balance operations to improve transients, remove dirt from the system - would probably fit in the chassis
> 2 - Force balance, same as above, don't know how this differs from CCS tail balancing - would probably not fit in the chassis
> 3 - Source follower, to optimise impedance, all round improvement due to lowered output impedance - would probably fit in the chassis
> 4 - Regulated power supply, to remove power disturbances, all round improvement due to removing power supply fluctuation - would probably not fit in the chassis
> 5 - Redge's decoupling mods mark 2 to improve cap functions in the power supply, supposed to improve detail, transients, bass - would not fit in the chassis



CCS tail is what is used to force balance. Source follower has no chance of fitting inside the chassis.



Maxx134 said:


> I am in the camp of the single jfet idea.
> 
> Also I am not convinced 33k anode will give optimal voltage swing.



Why?

As to the 33k; what amount of swing are you looking to get and why?



baronbeehive said:


> I have low gain setting atm and will probably try high gain next, probably when I have got the last 421A to match my other 3, so that I also do a comparison with the LD with the RCA's. Burn in has not finished yet due to a failure with the fan controller, I have a new one on order.



Are you actually using NOS never-been-plugged-in tubes? You guys must be rich. 

Once a tube has had the cathode emitting some dozens of hours, there is no more burning in that can ever be done.

By the way; if you make the circuit not dependent on tube gm, burn in doesn't matter anymore.


----------



## coinmaster

Looks like MrCurwen is sidestepping any point that I made. Not even going to repeat myself.


----------



## baronbeehive (Jan 29, 2018)

MrCurwen said:


> Maybe. I think it's more likely they wanted to 'trap' some guys into tube and cap rolling by making the amp susceptible to small variations in these components. Makes for a fun hobby for many people.



You said that.... I didn't want to! I also didn't want to mention Chinese tubes!!

My point was that their circuit design was done knowingly and no attempt was made to produce a perfect circuit, if you look at the nano technology adopted in headphone manufacture nowadays by the Chinese I know that they are well able to produce cutting edge design if they want to.



MrCurwen said:


> CCS tail is what is used to force balance.



Thanks, that's what I thought. This is probably the next mod then... a little bit of circuit design never comes amiss! The balance issue is important along with the PSU issue.



MrCurwen said:


> Are you actually using NOS never-been-plugged-in tubes? You guys must be rich.
> 
> Once a tube has had the cathode emitting some dozens of hours, there is no more burning in that can ever be done.
> 
> By the way; if you make the circuit not dependent on tube gm, burn in doesn't matter anymore.



I'm using NOS testing tubes, more by luck than by design. I don't mind trying my luck with tubes with no test data, they often turn out fine, but its a bit risky. The burn in is more for the Jupiter caps, I never bother to burn in tubes.

Rich, not a chance!!I wanted to try the Western Electric's, but chances are they will have to go at some point to pay for the car to be serviced unfortunately. That's why I am in fact quite happy with the RCA's, I've always said that I prefer the cheaper tubes on the whole, some of the expensive ones are ludicrously overpriced and under perform as well, yet they have a massive following. As an example I've always used the TS6SL7's, quite cheap when I bought mine but they sound exactly the same as the very expensive "holy grail" TS 6SN7 and the same goes for the extremely tight tolerance and expensive 6SU7GTY's.

Edit: Hmmm, that's a idea, sell the Western Electrics, and buy the parts for the LTP amp, and still have enough left over for another 3 amps, or an assortment of headphones, and speakers...


----------



## MrCurwen

baronbeehive said:


> Thanks, that's what I thought. This is probably the next mod then... a little bit of circuit design never comes amiss! The balance issue is important along with the PSU issue.



If you force balance, PSU disappears. You can have potatoes as filter caps after that.



baronbeehive said:


> Edit: Hmmm, that's a idea, sell the Western Electrics, and buy the parts for the LTP amp, and still have enough left over for another 3 amps, or an assortment of headphones, and speakers...



Unless you really have money to burn, spending big bucks on tubes is madness in my personal opinion. Just go Russian; they're usually fully NOS never seen a tube socket. Cheap as bread and perform very well. 6P31S is a gem.

Also EL81 is fantastic, and still affordable. That's my new favourite tube to use. I've grown tired of making filament supplies for 4P1L, even though it is the best of the best. The difference is fleeting, and probably nonexistent.


----------



## MrCurwen

6E5P is superbly linear as well, just as good as 4P1L, but it's a bit tricky. It tends to oscillate while still in the box. Too high gm even after degeneration, and too high µ. Really great linearity though, one of the best in the whole world.

My current breadboard workhorse has 6E5P finals. Great sound but there's some background noise. Too small to get me off my ass to really fix it, so it just keeps annoying me. That's why EL81 is my new favourite.


----------



## SonicTrance

MrCurwen said:


> 28 Vpp is more than enough. gNFB influence is already present at the grid input signal, and WCF is let's say 0.8 gain, so with 28Vpp at tube anode you'll have 70 Vpp across the headphone! That's crazy loud, unuseable.


I found the gain formula for WCF:
*
Gain =               mu² + murp/Ra                 * * 
                (mu² + mu + 1)  + (mu+2)rp/Ra*

If we use the 6AS7/6080 tube we get about 0.55 gain. But how do you calculate? How do you get 70 Vpp from 28 Vpp with 0.8 gain? Probably a stupid question but I don't get it, lol.


----------



## baronbeehive

MrCurwen said:


> If you force balance, PSU disappears. You can have potatoes as filter caps after that.



So.... cheap as chips..... sorry you probably didn't want to say that either!

I was wondering that about balancing and the PSU, I thought they were separate issues, so how does balancing the signal avoid the need for PSU regulation for example? Do any perturbations cancel out  or what?


----------



## MrCurwen

SonicTrance said:


> If we use the 6AS7/6080 tube we get about 0.55 gain. But how do you calculate? How do you get 70 Vpp from 28 Vpp with 0.8 gain? Probably a stupid question but I don't get it, lol.



By calculating wrong, apparently. I guess my brain was still a bit foggy after lifting weights just before writing that...

0.55, that's lower than I recalled. Anyway you still shouldn't need that much voltage swing on the input section anodes. At the load you sum the individual swings together.



baronbeehive said:


> I was wondering that about balancing and the PSU, I thought they were separate issues, so how does balancing the signal avoid the need for PSU regulation for example? Do any perturbations cancel out or what?



For starters look at my previous few messages, especially the experiments. 

Any signal that is present at the cathode node does not appear in the output. Also if current draw is constant, PSU ripple decreases significantly. PSU is played out of the equation.

For best results I would still strongly advocate using a simple 2 FET reg that I've posted. It's strong enough to provide a decent output impedance even for SE use, and simple enough to be cheap, easy to build and set up. Only use the least level of complexity required. 

Reg also significantly improves stability. That's the #1 reason I use it.

Probably wouldn't fit in the chassis though.


----------



## MrCurwen

Differential means that the only signal that is taken into consideration is the DIFFERENCE between the phases. If something is shared, it's called common mode signal, and it doesn't appear in the differential output.

PSU is shared, it's distortions are shared, so they don't appear in the output.


----------



## Maxx134

MrCurwen said:


> Why?
> 
> As to the 33k; what amount of swing are you looking to get and why?


Why..

Because One jfet sounds better to me than one mosfet plus 2 transistors.


As for the 33k anode,
I already tested that setting , but with slightly higher B+ & cathode resistance.
That setting was too low voltage swing and gimped/neutered the dynamics.
The overall sound was still very euphoric and nice with the tubes in question (ecc35) so it may have not been noticed without comparison.

I will have to test the whole thing again with same cathode setting,
But the whole thing may be a waste if we use CCS anyways.

Also that low anode reaistor setting was much worse on other tubes so really depending on which tube.
Bottom line listening,
And I chose 68k.

Oh well the real topic is what choice of CCS is best for this admittedly compromised driver stage.


----------



## MrCurwen

Maxx134 said:


> Because One jfet sounds better to me than one mosfet plus 2 transistors.



I agree as a principle to go with the least complicated solution that gets the job done good enough. The CCS I and Sonic use is that; small component count, small loop (only one loop). Still insanely powerful.

That chip you are talking about has much more stuff inside it. Look at the datasheet page 16, there is a schematic of the insides.


----------



## baronbeehive

MrCurwen said:


> Differential means that the only signal that is taken into consideration is the DIFFERENCE between the phases. If something is shared, it's called common mode signal, and it doesn't appear in the differential output.
> 
> PSU is shared, it's distortions are shared, so they don't appear in the output.



Right so it looks like the CCS tail mod is most important, and moreover probably makes the other 4 mods I mentioned: Force balance, Source Follower, Regulated PSU, and Redge's decoupling mods, rather redundant. Regulated PSU becomes less important, Redge's decoupling mods no longer needed, and the Source Follower mod I'm assuming is no longer needed if we already have the impedance mod.


----------



## MrCurwen

baronbeehive said:


> Right so it looks like the CCS tail mod is most important, and moreover probably makes the other 4 mods I mentioned: Force balance, Source Follower, Regulated PSU, and Redge's decoupling mods, rather redundant. Regulated PSU becomes less important, Redge's decoupling mods no longer needed, and the Source Follower mod I'm assuming is no longer needed if we already have the impedance mod.



Pretty much yes, except for the source followers. If you mean the grid drivers by these, then there is nothing performing that particular function.


----------



## Maxx134 (Jan 29, 2018)

baronbeehive said:


> so it looks like the CCS tail mod is most important, and moreover probably makes the other 4 mods I mentioned: Force balance, Source Follower, Regulated PSU, and Redge's decoupling mods, rather redundant. Regulated PSU becomes less important, Redge's decoupling mods no longer needed, and the Source Follower mod I'm assuming is no longer needed if we already have the impedance mod.



The decoupling in the driver stage is actually not an optional "add-on", but instead a substitution.

Remember the tiny 33uf electrolytic caps we took out?
They were part of the driver stage PSU "RCRC" filter..

So you already replaced them with nice film caps,
 which perform way better, so I would not say it is not needed..

Take it out and you loose the last part of your PSU RCRC filter(!).

Plus since they are larger, you can lower the 3k3 resistor to my suggested value of 1k (or lower like SonicT did),
To get a higher B+ out of the anemic driver stage PSU.

It is sorely needed, and depending on the tube used you will have a different B+ because of the last R volt drop of the PSU RCRC design, (since there is no SS regulator).

So for driver tubes,
you like 6SL7,
and I preferred the (similar) 6C8G,
And SonicT like the Mullard ecc35, right?

They all higher "mu" than the 6SN7,
but different plate resistance & different load lines.

I guess we should find some optimal bias settings for each of these tubes to list in first page what bias for which tube (a can of worms lol)

My situation is that I have not implemented the CCS yet.
So I will order parts now.

Notice that although I have MK8 (which use 9pin tubes),
I preferred the use of  adapter for the 6pin tube types,
 as they sounded best to me (on this same  MK8&MK6 driver stage).


Another thing I noticed is that Both you and SonicT prefer the lower gain setting on MK6.

For my MK8, the higher gain setting worked better, and I believe it is because of the different output tubes used on MK8 (9pin 6h30 type but I currently using cheaper 6n6 which actually more realistic for me).
It funny that the MK8 cost more but use cheaper tubes.


----------



## Maxx134

SonicTrance said:


> Just look at the tube comparison PM's


Yes, it was massive improvement I don't think is stated enough.

You should post the stock settings on these tubes.
I remember you made them .
They were absolutely dismal compared to your final load lines.

Show a before and after so everyone can realize the HUGE improvement you made just on bias alone.

Also of interest would be noting any audible changes of  your CCS implementation.


----------



## Maxx134

Here is an article showing how setting bias boils down to what sounds good, instead of what looks good:

http://www.diyparadise.com/variation.html


----------



## baronbeehive (Jan 30, 2018)

Maxx134 said:


> The decoupling in the driver stage is actually not an optional "add-on", but instead a substitution.
> 
> Remember the tiny 33uf electrolytic caps we took out?
> They were part of the driver stage PSU "RCRC" filter..
> ...



Yes, I had forgotten we had decoupled the driver stage as well, I was thinking more of the power stage which Redge was talking about here in his more recent modifications of the power stage decoupling in order to provide a large, fast energy bank in reserve for the PSU, using a large fast cap feeding the decoupling banks made up of different value caps of different construction to cater for different frequencies.

It would be this arrangement that would be made redundant with the CCS in place, the reason being that however elaborate the cap bank, and however fast the fasted cap is to replenish the power supply, it is still limited by the slowest cap in the bank, whereas with a CCS doing the force balancing any irregularities in the power supply would largely be cancelled out and the PSU ripple would be decreased by the constant current draw anyway if I have understood correctly:



Redge78 said:


> I'm afraid you'll find it "old-fashioned" but it has 2 strenghts : it's easy to implement (not so easy after some thaughts tho) and I can understand it.
> 
> I took the "energy" viewpoint, how much do I have of it and how fast it can be delivered ...
> 
> ...



Re: my use of the lower gain setting, it was more of a practical use with the higher gain 6SL7's. With the higher setting there would not be much useable volume without it going too high.


----------



## SonicTrance

baronbeehive said:


> Re: my use of the lower gain setting, it was more of a practical use with the higher gain 6SL7's. With the higher setting there would not be much useable volume without it going too high.


I've only tested high gain setting once and it was very noisy. Never tried again.


----------



## Maxx134 (Jan 30, 2018)

baronbeehive said:


> whereas with a CCS doing the force balancing


That is done in the driver tube stage.



Powertube output stage has the WCF topology and the different the different  tasks like bringing  impedance down.

Wow that was an old PM post from Ridge78 if I recall...
I had those white monster caps..





They needed meters to monitor the charge from the PSU so I could know when to engage without the series resistors, so the surge current would not fry the Power transistor/diode combo.

I chose not to implement, then I got married and that stopped the crazy fun experiments.


----------



## MrCurwen

If you're worried about connecting the tail to a dirty B-, just do this:

 

Since the current is only below 2mA, no heat sink needed. This can be put into very small space.

C3 should be 105 degree type, cheapest you can find.

C4 can be very small electrolytic, or alternatively if you've got the space and feel like being fancy, use 2µF 160V MBGO.

This kind of a active filter (not really a regulator) is super effective if the load is drawing a constant current. Look at this experiment:

 

Green wave is the B- rail (before R6). It has 10 Vpp ripple. Blue wave is at the source of M1, the "tail supply".

Suppression is such that any real world 200mV ripple becomes DC. I've built a million of these, they actually work very well in real life. Simple and effective where actual regulation is not necessary or possible.


----------



## MrCurwen

Maxx134 said:


> I had those white monster caps..



What were those caps supposed to do? PSU filtering?


----------



## bloodhawk

Gonna be joining you guys in the mod party soon 



ViKiD(TM) said:


> Got my Little Dot VI+ today. And boy even with the stock tubes (Thomson JAN 6080WA + OTK 6H9C) this amps sounds so much better than the Crack. (Single Ended)
> 
> So i before i start tube rolling tomorrow, i thought id try some weird things with the HD800S...
> 
> ...





ViKiD(TM) said:


> Oh yeah totally agreed. Already ordered some Audyn True Copper caps (0.68 uF 630V) (Not really a fan of Mundorf Supreme SGO's for what they cost). Will do the caps first over the weekend, next will be the resistors and the bias switch along with replacing the wiring with silver coated single core 600V wire.
> 
> Got a bunch of 5998's, RCA 6AS7G's, Tungsol 6080's and a few Winged C 6H13C's. Along with some really nice Sylvania Bad Boys. So im pretty covered on the tube end of things
> 
> Will post in the mod thread soon.


----------



## baronbeehive

Maxx134 said:


> That is done in the driver tube stage.
> 
> 
> 
> ...



Ha ha, I see!

Thank you for putting me right about the driver stage, I was totally mixed up there, so would the source follower be needed at the power stage, with our impedance mods?

BTW I really love that pic!


----------



## baronbeehive

ViKiD(TM) said:


> Gonna be joining you guys in the mod party soon



Hi ViKiD(TM)
Come on in to the mod party!
Good to have someone with obviously good taste, I see that you're going to use the Audyn's which is what I would have done if it hadn't been for their size!


----------



## bloodhawk

baronbeehive said:


> Hi ViKiD(TM)
> Come on in to the mod party!
> Good to have someone with obviously good taste, I see that you're going to use the Audyn's which is what I would have done if it hadn't been for their size!



Yeah that was one reason why i almost went with the Mundorf's myself. But a few measurements later, im sure i can fit these in there using some single core silver coated copper wiring.
Need to find some thin / low profile silent fans though.

Worst case i mod the bottom cover and  move the fans outside


----------



## baronbeehive

ViKiD(TM) said:


> Yeah that was one reason why i almost went with the Mundorf's myself. But a few measurements later, im sure i can fit these in there using some single core silver coated copper wiring.
> Need to find some thin / low profile silent fans though.
> 
> Worst case i mod the bottom cover and  move the fans outside



Yes, that's what we did here, you'll need some higher feet obviously.

Best of luck with the Audyn's, you might just make it, I hope that the dimensions are correct this time, when I bought mine they turned out to be much larger than specified.


----------



## Maxx134 (Jan 30, 2018)

MrCurwen said:


> What were those caps supposed to do? PSU filtering?


They were placed after the last two caps, and feeding the rails of powertubes.
I realize it was overkill bit did give results.
They gave the amp more bass authority, plus the sheer size meant way way low ESR . Read Ridge78 quote in Baronbehive post above.



bloodhawk said:


> Yeah that was one reason why i almost went with the Mundorf's myself.


You chose well, as I tried both,
And the copper are most true in trebles.

They both have great  soundstage,
 but mundorf is not as neutral in trebles(sweeter).

I do think the (Audyn true copper) took longer to reach full potential than the Jupiter copper foils I have,
But it is too subjective to say for sure.
I still think the Jupiter have a slight edge in soundstage depth,
But those Audyn true copper have a really clear live presence.
Again, this is subjective as I didn't place the Audyn in same amp,
Like I did with the top Mundorf .


I would not have bothered with .68uf though..
Not higher than .47uf on this amp,
 as you could gain any bass extension benefits on the (Powertube) cathode caps instead, by increasing size there.
No matter it still excellent.

I really think (for coupling caps on these more traditional designs) the copper type caps finally reach level of quality as  great interstage transformers you see in some expensive tube amps.
Most of the time in most amps you see (cheap) coupling caps instead.

Also I have to agree that for those on budget, old caps in oil are great.
I like "Vitamin Q"  and Russian PIO caps which I still have but haven't used yet.

I am using "Vitamin Q" caps in my amp now.
I like them a little better than the top Mundorf they replaced in the "WCF  coupling cap" position (powertube stage from first to second triode),
But they probably at similar level.
Mundorf add a sweet treble so not a bad choice.

I hated the Jupiter beeswax caps which give a thick dull presentation in that position.
I can't believe that a famous tube amp I will not name (ZMF likes) uses that dam dull cap.
Yet to each his own.
That amp is a traditional design so parts play a role in sound,
Unlike newer designs like which SonicTrance made (MrCurwen design) to have less reliance on parts.

My APPJ mini amp is also an example of cheap but with newer designs implemented into tube amp.


----------



## Maxx134

I mention all that cap comment because I rather not see anyone go thru alot expense.

Also with tube rolling we never made list of favs.


----------



## bloodhawk (Feb 1, 2018)

Maxx134 said:


> You chose well, as I tried both,
> And the copper are most true in trebles.
> 
> They both have great  soundstage,
> ...



Personally i didnt like the Jupiters at all. Dunno why, but i found that a tad too boring.

But i definitely agree with the Audyn vs Mundorf observations. They behave very similarly when i tested those in my Crack. The main reason i went for the .68uF was because the diameter was the same and the only thing that changed was the length. Went with the 33uF caps for the decoupling caps ( haven't been able to find the 47uF Mundorfs).

A nice list of Tubes and their respective Sound Signature effects in this Amp would be freaking awesome, if someone was inclined to make one that is 

Im loving the TS 5998 + 6H13C + TS 5998 + 6H13C with RCA 6SN7 GTB combo for now. Next ill be trying the Bad boys and the CV181-TII's with the same power tubes. 

Been trying to find the GEC 6080 / TungSol 6AS7G for reasonable prices, but its been almost impossible.


----------



## baronbeehive (Feb 1, 2018)

bloodhawk said:


> Personally i didnt like the Jupiters at all. Dunno why, but i found that a tad too boring.



....SHARP INTAKE OF BREATH....... such heresy on this thread lol.

We go for the realistic type sound here not the artificially sweet sound of some other caps. I don't know how they do it, they're only an intertage component after all and do not affect the underlying circuitry b but they manage to impart a wonderful transparency to the sound, no matter, I'm sure others are good too.



bloodhawk said:


> A nice list of Tubes and their respective Sound Signature effects in this Amp would be freaking awesome, if someone was inclined to make one that is
> 
> Im loving the TS 5998 + 6H13C + TS 5998 + 6H13C with RCA 6SN7 GTB combo for now. Next ill be trying the Bad boys and the CV181-TII's with the same power tubes.
> 
> Been trying to find the GEC 6080 / TungSol 6AS7G for reasonable prices, but its been almost impossible.



I did a list of tubes a long time ago on the other LD thread, when I was trying out some  combinations just after I got the LD, I don't do tube rolling now. I will see if I can find it. I already like the RCA 6AS7's you mention and the  combo with the TS5998's would be awesome. I assume you mean Psvane CV181-T11's which I haven't tried but would be interested in what out think about them, they're supposed to be the best of the new issues.

Most guys here like the TS6SL7's which are typical TS, liquid, magical sound and cheaper than the other TS's but just as good IMO, and  the  ECC35 Mullard, which are nice and full sounding in  the mid rage.

For power tubes you have the Svetlana's which I haven't tried but Ibelieve are very clear and detailed, RCA's, typically RCA sounding, nice balanced warm, cheap, I would avoid the TS7236's which are cold and analytic and boring.

Edit: I used the Jupiter caps in my small and cheap APPJ speaker amp and together with different tubes it was transformed into a top level sounding amp.

Most of what we have done here has been well tested so you can be pretty sure that the results are reliable.


----------



## bloodhawk

baronbeehive said:


> ....SHARP INTAKE OF BREATH....... such heresy on this thread lol.
> 
> We go for the realistic type sound here not the artificially sweet sound of some other caps. I don't know how they do it, they're only an intertage component after all and do not affect the underlying circuitry b but they manage to impart a wonderful transparency to the sound, no matter, I'm sure others are good too.



haha, let me put it this way..it feel that they normalize the "signature" 



baronbeehive said:


> I did a list of tubes a long time ago on the other LD thread, when I was trying out some combinations just after I got the LD, I don't do tube rolling now. I will see if I can find it. I already like the RCA 6AS7's you mention and the combo with the TS5998's would be awesome. I assume you mean Psvane CV181-T11's which I haven't tried but would be interested in what out think about them, they're supposed to be the best of the new issues.
> 
> Most guys here like the TS6SL7's which are typical TS, liquid, magical sound and cheaper than the other TS's but just as good IMO, and the ECC35 Mullard, which are nice and full sounding in the mid rage.
> 
> ...



Oh wow, i gotta go find it! 

Yeah, the TS 5998's really bring out the Mid's and a nice extension on the high end. The 6H13C's are bass monsters 
The RCA 6AS7's on their own are really really well balanced tubes, but i didnt like them when paired up with the 5998's. But im sure there are people who will prefer that combination. I wont be using the TS 7236's without the 6H13C's at all. I remember when i last tried my friends 7236 in my crack, the high was super sharp, good extension, but way too sharp. 

Yeah Jupiter are definitely great Speaker caps, for headphone amps and for my tastes, i just find them bit too flat.


----------



## baronbeehive (Feb 1, 2018)

Here you go, found it, near the beginning luckily:

"Hi Guys I've just found this thread so I've copied my post which I put on the mk vi thread which has now ceased.

I thought I would throw in my tuppenny worth because there seems to be so little information on the mkvi and would like to contribute something to the discussion on this fantastic amp having been helped by forum members previously. My set up is: PC>FOOBAR>USB to TOSLINK>CHANNEL ISLANDS AUDIO BALANCED DAC>ALO AUDIO SILVER COATED COPPER RCA'S>LD MKVI+>AUDIO TECHNICA ATH AD2000'S and SENNHEISER HD600's. I'm going to go ahead and assume this is the correct thread so here goes!

Previous to the mkvi I owned a mkiv se and always loved it with the standard power tubes and Tung Sol 6ak5w driver tubes which gave a much clearer warmer and less overpoweringly tubey sound than with the original m8100 driver tubes. The only upgrade I could think of from there was to go balanced to get the next step in up in SQ therefore I went for the mk vi a year ago. So far I've only used it single ended due to financial constraints! Since owning it I wanted to get the mkiv sound back which I loved and came close to it with raytheon vt231 6sn7 tubes. However I liked the slightly more tubey sound that the 6sn7 driver tubes gave me over the mkiv sound whilst still retaining the detail, it is a tube amp after all! This is why I like the amp so much, but if any one wants to know how it sounds then refer to the mkiii or mkivse review for close approximation as the sound signature is similar according to others, with the mkiii slightly warm and the mkiv slightly clearer but taking the sound up a notch again.

TUBE ROLLING. What follows are my observations from memory on the other tubes I've tried, and how they affect the sound of the amp. There is a good choice with the 6sn7 tube family which are suited to this amp and are all great tubes. The rca 6sn7 gtb are beautifully rich, detailed and balanced, whereas the vt123 grey glass tubes are musical, very balanced and exceptionally smooth and easy to listen to. The sylvania 6sn7 gtb are warm, detailed, balanced, crisp and slightly solid state sounding. The tung
sol 6sn7 gtb sound clear, detailed and analytical. Brimar cv1988 tubes are very dynamic, punchy, tubey and fantastic for mid range vocals, especially female. Finally the tung sol oval plate tubes are about the best I've tried with a beautiful balance, detailed base and magical silky treble and 3d soundstage. If anyone wants any further elaboration please let me know as I have had to find most of this out for myself with a little help and I would be pleased to respond with my own observations. I've also tried some tung sol 7236 power tubes which are very clear, detailed and analytical sounding. The only tubes I would like to try now are the sylvania 6as7g power tubes which are supposed to be warm, detailed with a good soundstage and I would like to contrast these with the rca 6as7g power tubes that I've been using up to now. I've tried examples from the main tube families so I would think that within these families the tubes all have a similar sound signature eg sylvanias are all warm and crisp sounding whereas rca's are smooth and rich sounding etc. I've also tried all the main construction types eg flat plate, round plate, t plate etc so have got a rough idea of these sound signatures. Anyone can get an overall picture from various tube sites.

I hope this gives and indication of characteristics of the mkvi. I love it and for the value and also the customer experience I am really impressed. I can't see me ever changing the set up - possibly!  In the future I do want to go balanced however with some HiFiMan HE500's which can be easily recabled unlike my Audio Technicas. It they are as good as the reviews say then I will have the perfect set up - great sounding amp with no faults that I can detect, and one of the best sets of headphones around!!!

Finally regarding the hum, I did think that it had been sorted with the later mkvi's. Mine is a mkvi+ and I don't get this humming noise, all I get is the quiet whirring of the fans which is not a problem. Just occasionally I do get a slight hum on one or other channel which I put down to interference of some sort, either my own system or from other networks possibly, or the tubes. I'm not an expert on this but this noise never lasts and is never intrusive.

Great to come across this thread at last, carry on the good work!"

Edit: so if you like smooth, live type sound you could try Raytheons, refined, balanced sound -RCA's, light, crisp type sound - Sylvanias, Silky, liquid sound -Tungsols, finally dynamic, euphonic sound try the Brimars.
I think I updated this post later but this should give you some idea.
Oh and Bendix 6080WB's are one of he best power tubes, open, detailed, smooth, dynamic sounding.


----------



## SonicTrance

baronbeehive said:


> The only tubes I would like to try now are the sylvania 6as7g power tubes...


So, did you ever find those? Most Sylvania 6AS7's I've seen are RCA rebrands.


----------



## baronbeehive (Feb 1, 2018)

SonicTrance said:


> So, did you ever find those? Most Sylvania 6AS7's I've seen are RCA rebrands.



No, I gave up looking, from what I heard about them from other members they were not all that detailed anyway so I forgot about them!

Edit:

I have just one other tube I'm going to try, the 12SL7 GE, and this came about because I have it on the APPJ and found it to be very transparent sounding but a bit thin and slightly harsh on that amp. It made me think though that because the modded LD is very rich sounding it might work well on that so as I already have one I decided to order another at the princely sum of $5, very cheap so I think I can get away with it.

The thing about the GE6S7's is that none of them seem to have very good reviews so I overlooked these at the time but the 12SL7's are different construction with rounded centre flat silver plates which made them slightly different from standard.

Anyway I will report back when I've tried them.


----------



## Maxx134

bloodhawk said:


> Yeah Jupiter are definitely great Speaker caps, for headphone amps and for my tastes, i just find them bit too flat



Just to be clear which version of Jupiter where you using?
 the bees wax,
 or the copper foil?

I found the beeswax to be a bit thick and not as good as any others mentioned here.


----------



## bloodhawk

Maxx134 said:


> Just to be clear which version of Jupiter where you using?
> the bees wax,
> or the copper foil?
> 
> I found the beeswax to be a bit thick and not as good as any others mentioned here.


Copper Foil.


----------



## bloodhawk

ooooh boy, TS5998+6H13C+TS5998+6H13C with the Sylvania VT-231's makes the amps soooo much better. And this is without the mods. Cant wait to try out the CV181-TII's once they get here next week.


----------



## MrCurwen

Just as a sidenote;

In cyrillic script H is N (en) and C is S (es), so 6H13C is 6N13S using latin letters.

How's your soldering skills, bloodhawk?


----------



## bloodhawk (Feb 3, 2018)

MrCurwen said:


> Just as a sidenote;
> 
> In cyrillic script H is N (en) and C is S (es), so 6H13C is 6N13S using latin letters.
> 
> How's your soldering skills, bloodhawk?



Pretty awesome 

I have done a lot of SMD soldering, modding GPU's for LN2 / Power mods etc. The BH Crack was pretty much a piece of cake.

Caps should be here Monday.

Some observations regarding the Tung Sol 7236 tubes ( I grabbed 4 of these NOS)

- 3 are dual round getters (Horse shoe?)

- 1 of these is a dual rectangular getter.

- All 4 are grey plates.

Observations -

- Out of the 3 round getter tubes, 2 have orange text printing. One is the standard Black text. Here is the interesting part, the orange text tubes, sound way more dynamic than the black text ones. They even Bias higher.
Black Text tubes Bias @ about 50-52 ish. Orange tubes are Biasing around 55-58ish.

- The Orange tubes actually sound better to me than the standard 5998 (NOS) that i have been using.

- The mids are definitely a tiny bit more forward, but there is more texture to the low end, and there is bit of more added mid/sub bass. This is without sacrificing the treble clarity / texture or the openness.


Also the order the tubes are placed in matter way more with the 7236's. Im guessing because of the
lower trans-conductance vs the 5998's.
With the 5998's i couldn't tell any difference. (2 x 5998's + 2 x 6H13C)
But with the 7236's, the 6H13C's need to be first in order - 6H13C + 7236 + 6H13C + 7236


----------



## baronbeehive

bloodhawk said:


> Pretty awesome
> 
> I have done a lot of SMD soldering, modding GPU's for LN2 / Power mods etc. The BH Crack was pretty much a piece of cake.



You should be good for the mods then. I see you've done the Speedball mod to your Crack, we're doing a similar mod to the LD atm!

Re: your tube choice, I get the feeling you like the really in your face detail type tubes, in which case you will love the Winged "C", and the Psvanes. The RCA's are not liked by everyone, I associated their sound with the first time I got the LD and was blown away by it. You might be interested in the GE's when I eventually get the last one, they have a really clean sound and extended treble. I will post on them. I much prefer them to the Sylvanias which I don't like, the sound of the GE's is much purer for me.


----------



## bloodhawk

baronbeehive said:


> You should be good for the mods then. I see you've done the Speedball mod to your Crack, we're doing a similar mod to the LD atm!
> 
> Re: your tube choice, I get the feeling you like the really in your face detail type tubes, in which case you will love the Winged "C", and the Psvanes. The RCA's are not liked by everyone, I associated their sound with the first time I got the LD and was blown away by it. You might be interested in the GE's when I eventually get the last one, they have a really clean sound and extended treble. I will post on them. I much prefer them to the Sylvanias which I don't like, the sound of the GE's is much purer for me.



NICE! Really interested in seeing how those mods turn out and a worklog if possible. 

Umm kinda. But i do love a spacious soundstage as well. Im right there with you about the RCA's they were highly disappointing for me tbh.  Specially when compared to my Crack running a 5998+E80CC or 5998 + Mullard / Telefunken 12AU7. 

Do you mean the GEC 6080 / 6AS7 ? I have been looking for both and its been really hard find a pair for a reasonable price, let alone matched. The normal GE's sounded very plain to me, definitely a step over the RCA's and very balanced when compared to the bass monster 6H13C's. but way down the chain vs the 7236 / 5998.

Cant wait to try out the Psvanes on Monday.


----------



## baronbeehive

bloodhawk said:


> Do you mean the GEC 6080 / 6AS7 ? I have been looking for both and its been really hard find a pair for a reasonable price, let alone matched. The normal GE's sounded very plain to me, definitely a step over the RCA's and very balanced when compared to the bass monster 6H13C's. but way down the chain vs the 7236 / 5998.
> 
> Cant wait to try out the Psvanes on Monday.



No the GEC's are an entirely different kettle of fish and are very good I believe, SonicTrance has them. I was talking about the 12SL7 GE's which I had on my APPJ, I agree that GE's are not particularly exceptional in general but I have a feeling that the transparency of the 12SL7's would be good in the LD post mods. BTW I hope your wallet recovers quickly from the Psvane purchase....

I kept a work log of my mods for anyone trying them here:



baronbeehive said:


> *SMLD MODS: (continued)*
> 
> *Driver Bias Mod *- The idea is to optimize bias on driver stage. The total resistance at the anodes was changed to 33k ohms, the total resistance at the cathodes was changed to 390 ohms, as suggested by SonicTrance for the MKVi+, to change the operating point to a more linear part of the driver tube load line.
> 
> ...


----------



## baronbeehive (Feb 4, 2018)

Do I need to change any other resistors next time I get the back off?

I've changed the 8x330ohm power resistors, the 4x220kohm anode resistors, and the 2x1.5kohm cathode resistors as part of the mods. As for the resistors near the PSU, I changed the 2x8k2ohm resistors but one resistor near these is going burnt and looks like it needs changing, not sure which one this is, possibly the 2x5k1ohm resistors. I can't check it until I next get the back off to do the CCS mod, but last time I checked it was still reading fine.


----------



## baronbeehive (Feb 4, 2018)

This one here:






On some boards this one is paralleled.


----------



## bloodhawk (Feb 6, 2018)

baronbeehive said:


> No the GEC's are an entirely different kettle of fish and are very good I believe, SonicTrance has them. I was talking about the 12SL7 GE's which I had on my APPJ, I agree that GE's are not particularly exceptional in general but I have a feeling that the transparency of the 12SL7's would be good in the LD post mods. BTW I hope your wallet recovers quickly from the Psvane purchase....



Ahhh i totally got them confused for the Power Tubes, i haven't tried the 12SL7's yet though.

The wallet should recover once i finish the porting over my Crack into a new 10"x10" chassis and sell it  I have a feeling with all my mods and the convenient driver tube bias switches, it should fetch a decent amount.

Hoooly Shiitt... PSVane CV181-TII's.

I dont even know how much more better things can get...


----------



## baronbeehive

bloodhawk said:


> Hoooly Shiitt... PSVane CV181-TII's.
> 
> I dont even know how much more things can get...



Ha, ha, I've heard about them!!


----------



## SonicTrance

baronbeehive said:


> This one here:


I would replace if it's getting burnt. It will only get worse.


----------



## baronbeehive

SonicTrance said:


> I would replace if it's getting burnt. It will only get worse.



Right, thanks. I remember way back that the some of the PSU resistors were replaced, for example the 8K2 parallel ones and I think some of us replaced the other ones in that area as well, everyone appeared to have different value ones there. The burnt one I have is OK and has been like that for some time but as you say better safe than sorry.


----------



## bloodhawk (Feb 8, 2018)

So the Audyns are going to be going in like this, one lead on each cap will be extended by an inch or so using silver plate single core wire. And ill stick them to the board using Velcro. I might extended both leads actually since that will make things even easier.   -
	

	
	
		
		

		
			







Ill flip over the fans to the outside of the panel and use taller feet instead of the stock ones. The fan wire might need a bit of extending.

In the meantime i realized i accidentally ordered 400VDC 33uF Mundorf MKP's instead of 250VDC. Welp, they will probably end up on the FS forums


----------



## baronbeehive

bloodhawk said:


> So the Audyns are going to be going in like this, one lead on each cap will be extended by an inch or so using silver plate single core wire. And ill stick them to the board using Velcro. I might extended both leads actually since that will make things even easier.   -
> 
> Ill flip over the fans to the outside of the panel and use taller feet instead of the stock ones. The fan wire might need a bit of extending.
> 
> In the meantime i realized i accidentally ordered 400VDC 33uF Mundorf MKP's instead of 250VDC. Welp, they will probably end up on the FS forums



That should work fine, just try to keep the leads as short as  possible to keep the impedance down.

The fans would be better to have an external controller to limit any PSU noise.

The 400vdc will be fine, the higher the voltage the better the safety margin.

Also don't forget that you might be adding in extra mods later so leave room for these so that you don't have to keep desoldering the work you've already done.


----------



## baronbeehive (Feb 8, 2018)

I've just tried the 12SL7 GE's and it looks like I was right. First impressions are they work very well, with great transparency and absolutely wonderful extended treble that rings out like a bell. They are not refined like the Tungsols this is a different sound that I first heard when I tried them on the APPJ, more of a live type sound and it looks like I will be spending a lot more time with them. Well worth a try.


----------



## MrCurwen

baronbeehive said:


> That should work fine, just try to keep the leads as short as possible to keep the impedance down.



Wire impedance matters only at MHz range, and in this application (HIFI amp) it's a plus, not a minus.

Well, extra wire can pick up noise and oscillations via coupling (especially if you route wires parallel), so that's a minus. So plus minus zero. But impedance is not a problem.


----------



## bloodhawk

MrCurwen said:


> Wire impedance matters only at MHz range, and in this application (HIFI amp) it's a plus, not a minus.
> 
> Well, extra wire can pick up noise and oscillations via coupling (especially if you route wires parallel), so that's a minus. So plus minus zero. But impedance is not a problem.



Basically instead of running point to point wires parallel / straight, twist em around?


----------



## MrCurwen

I usually do wiring so that the shortest amount of wire is needed. This results in a horrible looking plate of spaghetti, but electrically it's just fine.

The goal is to have the least amount of parallel surface area between the wires, to minimize capacitive and inductive coupling. Also don't put the wires close to each other; if this requires using a little bit more wire than shortest distance, that's fine. Also a good idea to try to steer past 1) large amounts of gm 2) large amounts of gain 3) magnetic components like chokes, OT's, PT's.

Wiring very rarely causes any problems. I've wired half of my amps quite lazily after I found that out. My latest SE amp a few years ago even had straight heater wires, not twisted, next to signal wires. No pickup.

But wire inductance is not an issue in any way at all on audio frequencies. That is just foolery.


----------



## baronbeehive

MrCurwen said:


> I usually do wiring so that the shortest amount of wire is needed. This results in a horrible looking plate of spaghetti, but electrically it's just fine.



I go for the tagliatelle look!



MrCurwen said:


> The goal is to have the least amount of parallel surface area between the wires, to minimize capacitive and inductive coupling. Also don't put the wires close to each other; if this requires using a little bit more wire than shortest distance, that's fine. Also a good idea to try to steer past 1) large amounts of gm 2) large amounts of gain 3) magnetic components like chokes, OT's, PT's.
> 
> Wiring very rarely causes any problems. I've wired half of my amps quite lazily after I found that out. My latest SE amp a few years ago even had straight heater wires, not twisted, next to signal wires. No pickup.



No, I was a bit concerned about all the extra wiring going in but, so far I've found the same, no noise at.

How close is close, for the wiring?


----------



## bloodhawk (Feb 10, 2018)

Just finished installing the Audyn's -

https://imgur.com/a/y6gZP


Spoiler: Pictures






















And wow didnt know better caps make so much of a difference in higher end amps. In the BH Crack all the upgrades maybe made about 5-10% difference at the MOST. Same with my friends Mainline, high end components barely made any super apparent difference. (And im talking Jupiter caps / Mundorf Supreme SGO caps)

In my LD VI+ running - 6H13C-TungSol 7236-6H13C-TungSol 7236 + PSVane C181-TII's , the soundstage is audibly wider with the Audyn 0.68 uF 630V caps. I will be honest, i really wasnt too optimistic about hearing any major differences. Since the VI+ already has decent WIMA MKP's which are almost as good as Mundorf MCap MKP's.  With the stock caps, the AMP sounded super lively, maybe overly lively i guess, but it was super fun to listen to. Now its sounds smooth and lively, while retaining all the resolution and micro-dynamics.

But damn, glad to be proven wrong, now i cant wait for the Mundorf Mcap MKP 33uF 250V caps to come in, the going to complete all the mods, along with swapping out the stock Panasonic caps and the resistors.

Thank for all the helpful posts guys, almost pretty went through the whole thread, and lots of great info in there.

My flipping over the fans job could be done better, but these are cheapo fans, so i just cut a small hole to route the wire through. Ideally i would drill holes next to each fan and route the wires inside for a cleaner look. But i have something else panned for that 

Question - Is there anything like "Burn in" for caps?


----------



## MrCurwen

bloodhawk said:


> And wow didnt know better caps make so much of a difference in higher end amps.



When you put together the drive capability of the input stage (not very good at best) and the hungry hungry grid of the power triode 6N13S, it's like you're putting a magnifying glass on the caps.

6N13S and similar have such huge cathodes and huge heater currents that they have a very large electron cloud around the cathode. Even though µ is small (grid is not very close to cathode), the cloud is so large that grid current is a very serious phenomenom.

6N13S grid eats current, 6SN7/6SL7 input stage cannot deliver it. Whatever parasitics the cap has, are not satisfied and therefore remain to be heard.

Increase drive capability, decrease cap disturbances.


This amp was made purposefully for cap/tube rolling.


----------



## baronbeehive (Feb 11, 2018)

bloodhawk said:


> Just finished installing the Audyn's -
> 
> And wow didnt know better caps make so much of a difference in higher end amps. In the BH Crack all the upgrades maybe made about 5-10% difference at the MOST. Same with my friends Mainline, high end components barely made any super apparent difference. (And im talking Jupiter caps / Mundorf Supreme SGO caps)
> 
> Question - Is there anything like "Burn in" for caps?



Good work! The upgraded caps work really well in the LD circuitry, it has the capacity to take the improvements and make the most of what is already there, which lower end systems wouldn't be able to do. This is the strange thing about adding better caps, there can be perceived increase in transparency despite the fact that caps really shouldn't do that as an interstage component, what they do is optimize the functioning of the existing circuitry I think, better parasitic treatment - despite that magnifying glass - for example.

Re: burn in, reviewers say anything up to 500 hours, I myself have noticed improvements in both my amps up to and after about 100 hours mainly in soundstage becoming more open and spacious with improved resolution. In my LD/HE500 combo the soundstage due to the cans is not large but burn in has noticeably improved it despite these limitations and I'm much happier with the headphones now, (my other amp is a speaker amp, so doesn't have the same problems).

Good luck with the rest of your mods.


----------



## SonicTrance

MrCurwen said:


> How's your soldering skills, bloodhawk?





bloodhawk said:


> Pretty awesome
> 
> I have done a lot of SMD soldering, modding GPU's for LN2 / Power mods etc. The BH Crack was pretty much a piece of cake.


Have a look over here: https://www.head-fi.org/threads/modern-balanced-tube-amp-build.852879/

You seem to have the skill and more importantly the drive to complete a scratch build! You'd not regret it. Just a tip


----------



## bloodhawk

MrCurwen said:


> When you put together the drive capability of the input stage (not very good at best) and the hungry hungry grid of the power triode 6N13S, it's like you're putting a magnifying glass on the caps.
> 
> 6N13S and similar have such huge cathodes and huge heater currents that they have a very large electron cloud around the cathode. Even though µ is small (grid is not very close to cathode), the cloud is so large that grid current is a very serious phenomenom.
> 
> ...



Ahh gotcha. Makes more sense now! 

Definitely worth the effort to upgrade the other components as well, if that is the case.!



baronbeehive said:


> Good work! The upgraded caps work really well in the LD circuitry, it has the capacity to take the improvements and make the most of what is already there, which lower end systems wouldn't be able to do. This is the strange thing about adding better caps, there can be perceived increase in transparency despite the fact that caps really shouldn't do that as an interstage component, what they do is optimize the functioning of the existing circuitry I think, better parasitic treatment for example.
> 
> Re: burn in, reviewers say anything up to 500 hours, I myself have noticed improvements in both my amps up to and after about 100 hours mainly in soundstage becoming more open and spacious with improved resolution. In my LD/HE500 combo the soundstage due to the cans is not large but burn in has noticeably improved it despite these limitations and I'm much happier with the headphones now, (my other amp is a speaker amp, so doesn't have the same problems).
> 
> Good luck with the rest of your mods.



Thank you good sir!! 

Now im really curious to see how much these open up.



SonicTrance said:


> Have a look over here: https://www.head-fi.org/threads/modern-balanced-tube-amp-build.852879/
> 
> You seem to have the skill and more importantly the drive to complete a scratch build! You'd not regret it. Just a tip



WHAI MAN WHAI... WHAI would you do this...!? I ... must... be .. content with... the VI+!! 

But one a serious note, damn that is some impressive stuff. I have a feeling i WILL end up building one based on the schematics a few months down the line... just to satisfy the itch!


----------



## baronbeehive

SonicTrance said:


> Have a look over here: https://www.head-fi.org/threads/modern-balanced-tube-amp-build.852879/
> 
> You seem to have the skill and more importantly the drive to complete a scratch build! You'd not regret it. Just a tip



....and it took him half the time it took me lol...



bloodhawk said:


> Ahh gotcha. Makes more sense now!
> 
> Definitely worth the effort to upgrade the other components as well, if that is the case.!



Yes, roll on the CCS mod, that should take care of the input stage limitations



bloodhawk said:


> Thank you good sir!!
> 
> Now im really curious to see how much these open up.



Yeah, I don't know the science behind burn in for caps but it worked for me



bloodhawk said:


> WHAI MAN WHAI... WHAI would you do this...!? I ... must... be .. content with... the VI+!!
> 
> But one a serious note, damn that is some impressive stuff. I have a feeling i WILL end up building one based on the schematics a few months down the line... just to satisfy the itch!



Haha, maybe you should just scratch that itch for now....


----------



## bloodhawk (Feb 11, 2018)

baronbeehive said:


> ....and it took him half the time it took me lol...
> 
> 
> 
> ...




LOL

Things are still a bit rough around the edges, and i really need to take care of all the dust that got collected in there over the past week, since i was cleaning other things around the amp.

Also the bottom panel currently has the extended feet, super glued to it :>

Im ordering a new bottom panel with additional holes for 120mm fans and a fan controller (if the need be). Along with a few extra ventilation holes.Though this will only go through once i finish working on the 10"x10" panel for my BH Crack, really need to get off my lazy ass :S

Though the next time i open up the VI+ ill be adding in the remaining mods. Really need to figure out a way to easily remove the giant ass PCB out of the chassis though. It really feels like the wires are going to snap, if i slip even a tiny bit. Might just end up replacing the each and every wire with 22 AWG and 18 AWG single core silver plated copper wiring.

I dont know if its just my brain adjusting to the slightly newer sound signature, but vs. what i heard right after the cap replacement, and now after about 10 hours of operation, its sound a bit more fluid and maybe with a bit more separation ? This could probably just me placebo though. End of the day im definitely more than happy...


I will definitely need to set that itch aside for now, since work  is a tad bit too busy to be able to accommodate time for something that i would really love to pour my heart and soul into.


----------



## baronbeehive (Feb 11, 2018)

bloodhawk said:


> LOL
> 
> Things are still a bit rough around the edges, and i really need to take care of all the dust that got collected in there over the past week, since i was cleaning other things around the amp.



You think you have problems, I had the bottom off for the best part of a year, but a quick shot of compressed air, and plenty of isopropyl alcohol sorted it.




bloodhawk said:


> Im ordering a new bottom panel with additional holes for 120mm fans and a fan controller (if the need be). Along with a few extra ventilation holes.Though this will only go through once i finish working on the 10"x10" panel for my BH Crack, really need to get off my lazy ass :S



Hey look here, if it's not too late:



Maxx134 said:


> Massive Hole punch:
> 
> 
> Insulating bottom with plastic paint:
> ...





bloodhawk said:


> Though the next time i open up the VI+ ill be adding in the remaining mods. Really need to figure out a way to easily remove the giant ass PCB out of the chassis though. It really feels like the wires are going to snap, if i slip even a tiny bit. Might just end up replacing the each and every wire with 22 AWG and 18 AWG single core silver plated copper wiring.



That's the trickiest bit, there's an Allen key to loosen in the volume knob, and a nut and washer. Then once you've removed all the screws you carefully snap out the PCB pushing the tube sockets and when they're out gently wiggle the board away from the pot side until its out. The wires on the other side are very brittle and you need to check these are still there before you put the board back. Most of us are old hands at that trick now we've done it so often!



bloodhawk said:


> I dont know if its just my brain adjusting to the slightly newer sound signature, but vs. what i heard right after the cap replacement, and now after about 10 hours of operation, its sound a bit more fluid and maybe with a bit more separation ? This could probably just me placebo though. End of the day im definitely more than happy...



We've all had problems describing the changes, my way is to note initial impressions because if there is a change it usually hits you straight away, then I go away and listen a bit more to try to confirm what I heard!


----------



## bloodhawk

baronbeehive said:


> You think you have problems, I had the bottom off for the best part of a year, but a quick shot of compressed air, and plenty of isopropyl alcohol sorted it.
> 
> Hey look here, if it's not too late:



I actually, already have a nice fan controller  And extra silent maglev fans.

The reason why im waiting on the Panel thing is because im making the new front plate i mentioned for the BH Crack using the Front Panel Express tool, so was thinking if i should order this one from there as well. But need to put some more though into it.



baronbeehive said:


> That's the trickiest bit, there's an Allen key to loosen in the volume knob, and a nut and washer. Then once you've removed all the screws you carefully snap out the PCB pushing the tube sockets and when they're out gently wiggle the board away from the pot side until its out. The wires on the other side are very brittle and you need to check these are still there before you put the board back. Most of us are old hands at that trick now we've done it so often!



Ahhh, didnt know i had to push on the tube sockets. I got the know out easily, and was actually pretty surprised that it was made out of Aluminium LOL.It felt like plastic. Yeah that brittle ness of the existing wires is one of the reason why i want to swap them out for sturdier single core wires.

One thing i did notice recently was that my pot has this scratchy noise when going all the way up around 95-100%. Which is only audible when i wiggle / twist the knob around that point, and then it goes away. is this a 4 Gang pot or 2 gang? From what i could see there are no terminals /  circuitry to make use of the motor, i might just swap it out for a 4Gang TKD pot.


----------



## bloodhawk

Question for the folks here , what power rating resistors is everyone using? Or if anyone has a picture of the board with the resistors pulled out. So that maybe the required values are readable on the board.  IM in the process of ordering a bunch of stuff for further upgrades and dont really want to get the Z-Foils, which from i have been able to find for values like 10k Ohm and 1.5k ohm are only available in 0.4W ratings. 
Correct me if i am wrong, but as a good practice for ratings under 1W the higher the better, but over 1W we need accurate power ratings on the resistors? 

Would really be helpful if someone and list out what the power ratings on the resistors are needed. The only solid info i found in the thread is for the heavy duty 5W resistors and there are multiple place where people are using a few 12 W resistors? 

This post was super helpful - https://www.head-fi.org/threads/lit...re-on-first-page.782183/page-21#post-12046254  - But i havent been able to find any power ratings for most of the resistors. Or are we going with the higher the better rule, while maintaining decent size?


----------



## baronbeehive (Feb 14, 2018)

bloodhawk said:


> One thing i did notice recently was that my pot has this scratchy noise when going all the way up around 95-100%. Which is only audible when i wiggle / twist the knob around that point, and then it goes away. is this a 4 Gang pot or 2 gang? From what i could see there are no terminals /  circuitry to make use of the motor, i might just swap it out for a 4Gang TKD pot.



If I remember right one member had this problem and tried the old compressed air trick and it cleared it from dust. Failing that quality resistors in the drier stage should cure it.

I don't know about the pot, no one here has replaced theirs, it would be interesting if you tried that. I'm not sure myself how to test the accuracy of the 2 channels within the pot it would be interesting to test them to see how accurately matched they are. We think that the fact that it's motorized is simply that they had a supply of those and chose to use them, it's not wired up for remote use as you say.



bloodhawk said:


> Question for the folks here , what power rating resistors is everyone using? Or if anyone has a picture of the board with the resistors pulled out. So that maybe the required values are readable on the board.  IM in the process of ordering a bunch of stuff for further upgrades and dont really want to get the Z-Foils, which from i have been able to find for values like 10k Ohm and 1.5k ohm are only available in 0.4W ratings.
> Correct me if i am wrong, but as a good practice for ratings under 1W the higher the better, but over 1W we need accurate power ratings on the resistors?
> 
> Would really be helpful if someone and list out what the power ratings on the resistors are needed. The only solid info i found in the thread is for the heavy duty 5W resistors and there are multiple place where people are using a few 12 W resistors?
> ...



Don't get the z-foils, use the Takman Rey or Shinkoh Tantalum in these 3 positions. I had an early PCB which had quality Dale resistors in so I didn't replace all the ones you mention but I can tell you what to get. For the 220K ohm use 2W, for the driver stage 10K ohm and 1.5K ohm use 0.5W, or you could go with 1W but it's not necessary to go higher here because not much power is being channelled in this position.

The important ones are the 8x330 ohm power resistors. These are basically crap in stock form and burn even without mods so it's important to go for quality, so we use 5W Mills wirewound here as they get hot easily. The other ones you mention I would go with the values Sonic has, perhaps he will confirm that. It wouldn't do any harm to go higher value, generally the higher the better, one member here went over the top slightly for safety's sake but it might make your build more difficult due to their size. There's only one 12W so stick with that.


----------



## SonicTrance

bloodhawk said:


> This post was super helpful - https://www.head-fi.org/threads/lit...re-on-first-page.782183/page-21#post-12046254 -


I've stated the power ratings for all resistors I replaced in that post. The Mills resistors are 5 watt. The 5 in mra5 is the power rating. I only used 12w for the 56k drain resistors as I could not get proper value of the 5w.


----------



## SonicTrance

baronbeehive said:


> Don't get the z-foils


Why no love fod the z foils? Yes, theyre very expensive and possibly unnecessary but they're good resistors. I use them as grid resistors.


----------



## MrCurwen

bloodhawk said:


> Correct me if i am wrong, but as a good practice for ratings under 1W the higher the better, but over 1W we need accurate power ratings on the resistors?



I don't quite understand this sentence, please explain.

Old engineers rule of thumb is to calculate the expected power dissipation, multiply by 3 or by 5 if in a critical spot (very close to capacitors esp. electrolytics) and you're good.

Using oversized resistors like 5W for every spot won't do any good, and in some cases it can introduce some small amount of hiss. Mostly just waste of money.

If a resistor has a lot of AC across it, then you need to multiply by 5 or 10 because the heat generated during positive peak doesn't have time to dissipate during the negative cycle. Heat moves in a solid material a lof slower than electricity. Especially since it has to move phases from solid to gas (dissipate to air).


If a chassis has a lot of heat overall, it might be prudent to use bigger wattage resistors. In most spots this still comes out as 1W because most spots don't dissipate much at all.


----------



## baronbeehive

SonicTrance said:


> Why no love fod the z foils? Yes, theyre very expensive and possibly unnecessary but they're good resistors. I use them as grid resistors.



Quote".....theyre very expensive and possibly unnecessary"....and they get in hte way...but they do look good!!


----------



## bloodhawk

baronbeehive said:


> If I remember right one member had this problem and tried the old compressed air trick and it cleared it from dust. Failing that quality resistors in the drier stage should cure it.
> 
> I don't know about the pot, no one here has replaced theirs, it would be interesting if you tried that. I'm not sure myself how to test the accuracy of the 2 channels within the pot it would be interesting to test them to see how accurately matched they are. We think that the fact that it's motorized is simply that they had a supply of those and chose to use them, it's not wired up for remote use as you say.



Weirdly enough i gave the pot a little outward tug and the scratchiness went away :S



baronbeehive said:


> Don't get the z-foils, use the Takman Rey or Shinkoh Tantalum in these 3 positions. I had an early PCB which had quality Dale resistors in so I didn't replace all the ones you mention but I can tell you what to get. For the 220K ohm use 2W, for the driver stage 10K ohm and 1.5K ohm use 0.5W, or you could go with 1W but it's not necessary to go higher here because not much power is being channelled in this position.
> 
> The important ones are the 8x330 ohm power resistors. These are basically crap in stock form and burn even without mods so it's important to go for quality, so we use 5W Mills wirewound here as they get hot easily. The other ones you mention I would go with the values Sonic has, perhaps he will confirm that. It wouldn't do any harm to go higher value, generally the higher the better, one member here went over the top slightly for safety's sake but it might make your build more difficult due to their size. There's only one 12W so stick with that.



Gotcha. Yeah i have the Takman 0.5W ones sitting in the cart right now. Thank you for the confirmation on the rating! I have quite a few Kiwame 330R 5W's sitting with me from some other build i was working on. Might give those a shot instead of the Mills. 



SonicTrance said:


> I've stated the power ratings for all resistors I replaced in that post. The Mills resistors are 5 watt. The 5 in mra5 is the power rating. I only used 12w for the 56k drain resistors as I could not get proper value of the 5w.



Yeah just realized im blind Oo
I think i just got confused because of the zFoil ratings 



SonicTrance said:


> Why no love fod the z foils? Yes, theyre very expensive and possibly unnecessary but they're good resistors. I use them as grid resistors.



I personally really dont want to spend that much on resistors. Im sure they are worth the cost, but a bit over the top for me. The most im willing to spend on resistors would be what the Mills cost.



MrCurwen said:


> I don't quite understand this sentence, please explain.
> 
> Old engineers rule of thumb is to calculate the expected power dissipation, multiply by 3 or by 5 if in a critical spot (very close to capacitors esp. electrolytics) and you're good.
> 
> ...



I think i misunderstood something i read elsewhere that, for power ratings upto 1W it is better to get the maximum rating upto 1 W, but if you need to go higher its always better to stay within <2 times the required power rating. Which somewhat confused me as it didnt make a whole lot of sense. 

Thank you for the clearing that up!


----------



## baronbeehive

bloodhawk said:


> Gotcha. Yeah i have the Takman 0.5W ones sitting in the cart right now. Thank you for the confirmation on the rating! I have quite a few Kiwame 330R 5W's sitting with me from some other build i was working on. Might give those a shot instead of the Mills.



We recommend the wire wound sonically rather than the carbon film resistors, and tolerance is important too along with wattage which is why we went with the types specified on the first page.


----------



## MrCurwen

bloodhawk said:


> I think i misunderstood something i read elsewhere that, for power ratings upto 1W it is better to get the maximum rating upto 1 W



If you mean there's no point in getting lower than 1W resistors even if the resistor in question wouldn't dissipate anything; well, yeah. No point in using lower wattage. x2 is not good for tube circuits or AC components, x3 is minimum.


----------



## bloodhawk (Feb 15, 2018)

So i did some tests last night with different 330Ohm Resistors - Dale 330Ohm 5W 1% (20ppm) RS variant that are supposedly Inductive (NS is the Non Inductive variant) / Mills MRA5 330Ohm (20ppm?) / Kiwame 330Ohm 5W

My observations -

Dale - Ran kinda hot, and initially did not have any hiss/noise. But after about 30 mins of constant music at 60% volume, when i maxed out the pot there was a very faint hiss audible above 95% volume. Other than that super silent. I did not sense any change in Sound Signature over stock.

Mills - Super Silent. Maybe sounded a clearer than the Dale, but could be the cost of these things poking me in the head. Weren't too hot.

Kiwame - Super silent, and sounded exactly the same as the Mills. And after 30 mins, they were just as cool as the Mills.

So im kinda confused if it takes ALL the mods together to make the Mills Resistors to sound the best, or im probably not capable of hearing the changes.

I wanted to test these 8 resistors out before i swapped out all the other resistors out long with the additional cap changes and maybe the output wiring.

One thing is for sure though, Sonic improvements or not, the stock resistors are garbage. Even the Dale improved the background a lot, it was much darker than with the stock resistors. I havent been able to find the Dale Non Inductive variants though, so kinda curious how well they stack up vs the Mills.

Another thing to definitely note is that im using different caps (Audyn's) and slightly different tubes than most peeps here. So maybe that makes a difference. End of the day im going to stick with the Kiwame's. Going to use the MIlls for a DIY project or something.


----------



## Maxx134 (Feb 15, 2018)

MrCurwen said:


> 6N13S grid eats current, 6SN7/6SL7 input stage cannot deliver it. Whatever parasitics the cap has, are not satisfied and therefore remain to be heard.


The cheapo red wine caps have a parasitic soft dull small stage sound.

The upgrade in changing the bias point really solved that issue for me.

You are correct I would not use plan 6sn7 or in MK8 plain 12at7 type.

The amp sounds much better with the higher output 6SL7 (or 12AX7 in MK8).
I find with the change done to increase the bias point really sovled that issue and also used the higher gain setting,
But for MK6 the higher gain is stated by others to not sound as good.
I am now thinking it probably due to what you mentioned with the output tubes, as my MK8 using different ouput tubes.



MrCurwen said:


> Whatever parasitics the cap has, are not satisfied and therefore remain to be heard.
> 
> Increase drive capability, decrease cap disturbances.
> 
> ...


I just think this amp had a good design in mind  which was stripped down in production phase for cost.

The driver stage PSU and choice of cheapo components all look to me, that they needed to lower cost to make the amp more competitive,
and if you look at the China market there is a sea of tube amps out there..

Anyways,
I have not yet noticed any tube amp different.
All benefited to some extent from upgrade,
and the extent can be more or less noticable on the person's setup and sensitivity to the changes.

I guess this is were your design of Sonic amp takes a better approach to mitigate this.



bloodhawk said:


> Definitely worth the effort to upgrade the other components as well, if that is the case.!


Yes it just keeps climbing with every tweak mod listed.

What's still not listed is the driver stage choice of new bias points we are using.
That was the most significant upgrade to the driver stage.



bloodhawk said:


> Now im really curious to see how much these open up.


The .68uf  Audyn copper foils I had in my other amp took about 200hrs to settle.



bloodhawk said:


> Might just end up replacing the each and every wire with 22 AWG and 18 AWG single core silver plated copper wiring.


I replaced all my internal input (small signal)  wiring to silver plated,
And my (larger signal) output wiring to OCC copper.

Plus, I got carried away and re-tinned every solder point on the circuit board(!) with Cardas Solder...

In the process I temporarily broke my  amp by soldering two pins together by mistake.
So don't go crazy like me lol.

And keep an eye on the thick rear wires that go from the power transistors on the top of amp to the board.
They are guaranteed to break upon second to third time you open board,
Simply because they are cheap garbage stranded tin wires.



bloodhawk said:


> I dont know if its just my brain adjusting to the slightly newer sound signature, but vs. what i heard right after the cap replacement, and now after about 10 hours of operation, its sound a bit more fluid and maybe with a bit more separation ?


Yes those caps get more articulate as time progress to about 200hrs I did notice.




bloodhawk said:


> This post was super helpful - https://www.head-fi.org/threads/lit...re-on-first-page.782183/page-21#post-12046254 - But i havent been able to find any power ratings for most of the resistors. Or are we going with the higher the better rule, while maintaining decent size?


Don't forget that the quality of the Mills wirewound resistor is superior to a film or carbon or other composition resistor as the the electrons don't have to pass thru different materials with their inherent impurities.

It was mentioned in the other thread one user used carbon resistors when upgrading the power stage and noticed some different added aspect to the sound.

I myself tried another older wirewound and noticed an odd thinness as they were Inductive.

The Mills are non-inductive so they are the best choice in the ouput powertube stage.

Takmans or other film resistors are just fine in the driver stage the resistor upgrade was negligible.
It was the bias change that made the biggest massive difference there.



bloodhawk said:


> I have quite a few Kiwame 330R 5W's sitting with me from some other build i was working on. Might give those a shot instead of the Mills.


 They are probably good but also probably carbon type and will not be best choice. Mills MR5 best choice for that output stage.


----------



## Maxx134 (Feb 15, 2018)

bloodhawk said:


> or im probably not capable of hearing the changes.


Do not decieve yourself,
You will ALWAYS hear all and any changes when you are using your own system in your own home that you are familiar with.
Familiarity and knowing ones own system is the key to distinguish things.
This is why "_having it at home_" is the best way to evaluate a product.


----------



## Maxx134

bloodhawk said:


> I wanted to test these 8 resistors out before i swapped out all the other resistors out long with the additional cap changes and maybe the output wiring.





bloodhawk said:


> One thing is for sure though, Sonic improvements or not, the stock resistors are garbage.


Yes because they are most probably low cost low grade resistors, but only the resistors around tubes (grid,anode,cathode) were worth changing, not *all *the resistors..


----------



## bloodhawk

Maxx134 said:


> Don't forget that the quality of the Mills wirewound resistor is superior to a film or carbon or other composition resistor as the the electrons don't have to pass thru different materials with their inherent impurities.
> 
> It was mentioned in the other thread one user used carbon resistors when upgrading the power stage and noticed some different added aspect to the sound.
> 
> ...





Maxx134 said:


> Do not decieve yourself,
> You will ALWAYS hear all and any changes when you are using your own system in your own home that you are familiar with.
> Familiarity and knowing ones own system is the key to distinguish things.
> This is why "_having it at home_" is the best way to evaluate a product.




Perhaps. I swapped in the Mills 330Ohm MRA5 again today and have been listening to music for about 3 hours now. Still sounds exactly the same as the Kiwame 5W Carbon Film resistors. The background is pretty much blank with both Kiwame and Mills. One thing i noticed with all the Kiwames is that they read much better on my Fluke Multimeter. The Mills seem to be 1-1.5% tolerance. Kiwame's are under 0.75% tolerance and mostly around 0.5%, going as low as 0.4%.

End of the day im happy with either, so will probably with Kiwame's , since i like the color haha. Mills will be used in another high end project.

Also when i mentioned i will be replacing all the resistors, i meant all the resistors that were mentioned by you guys!


----------



## SonicTrance

Im sure the Kiwames are fine. The nr 1 reason for changing the anode and cathode resistors is to get rid of the crap stock resistors that burn under normal use.


----------



## baronbeehive

Maxx134 said:


> The amp sounds much better with the higher output 6SL7 (or 12AX7 in MK8).
> I find with the change done to increase the bias point really sovled that issue and also used the higher gain setting,
> But for MK6 the higher gain is stated by others to not sound as good.




Maye the gain settings combined with other tweaks is another area to look at, I think Sonic tested his gain settings prior to doing the mods, I could test it after the mods to see if it still sounds crap with the different driver bias setting for example. The amp might benefit from less feedback if we could overcome the problems that might cause somehow as you seem to have found.



Maxx134 said:


> Plus, I got carried away and re-tinned every solder point on the circuit board(!) with Cardas Solder...



Hey, I thought I was the perfectionist around here, but I didn't go to those extreme lengths!

Have you found the problem with one of your bias meters dropping after warmup?



Maxx134 said:


> It was mentioned in the other thread one user used carbon resistors when upgrading the power stage and noticed some different added aspect to the sound.
> 
> They are probably good but also probably carbon type and will not be best choice. Mills MR5 best choice for that output stage.



Yes I remember someone saying that. I had them fitted before the mods too and I didn't notice anything bad about them.


----------



## baronbeehive

SonicTrance said:


> Yes, I use a psu like this, with a 4-pin molex plug:
> 
> 
> And then I connect it to this:
> ...



That's for a dimmer switch isn't it?

Is the WiFi receiver in the 3 plugs or do you need anything else with this kit?

I was looking into this because I'm still waiting on my replacement speed controller from Hong Kong. I think the SMPS must have failed with my existing one, I can't see how the rheostat could have failed because it's sealed in.

That's why I was looking into the remote. The other option would be to have a power supply with a fixed 5v output rather than the 1-12v. I think 5 volt would be enough for a speed somewhere in the mid range of operation.

Failing that I could always knock up one myself I suppose.


----------



## SonicTrance

baronbeehive said:


> That's for a dimmer switch isn't it?


No, just power on or off. There's a reciever in the plug. You dont need anything else. The remote can control three plugs. Ive had an entire power strip on one plug. Very handy if you want to power on/off a lot of devices at once. 

Some fans wont run at 5V. Check specs before buying.


----------



## baronbeehive

SonicTrance said:


> No, just power on or off. There's a reciever in the plug. You dont need anything else. The remote can control three plugs. Ive had an entire power strip on one plug. Very handy if you want to power on/off a lot of devices at once.



How do you control your fan speed then?

These fans are so powerful that max speed is too much, and the noise of the air flow replaces the bearing noise we had with the old fans.


----------



## Maxx134

bloodhawk said:


> End of the day im happy with either, so will probably with Kiwame's , since i like the color haha. Mills will be used in another high end project.


That is great.
Go with what you like.
Most performance issues are only at extremes.
Carbon Resistors do generate thermal noise.
Our amp gets hot, but with fan and
The 5W rating ,
It Most likely make it negligible as you have noted.
Still for impulse and other heavy duty characteristics, wirewound is Superior.




baronbeehive said:


> Maye the gain settings combined with other tweaks is another area to look at,


Yes, so I encourage bias testing for both high and low gain (NFB) settings,
as it should be slightly different sweet spots depending also on which tubes used. 

Also I did notice a difference in sensitivity with change of power tubes, as I am not using stock tube type in output stage either, (I using old cheap Russian 6h6 at higher bias),
So I must agree what MrCurwen aludes to the input grid sensitivity of the power stage will affect your settings on the driver output.
So you should use the new bias points as a place to start, and adjust the Anode lower untill you find a good spot.

Then setup a CCS after you find your best bias points.

Yet I remember both me and Sonic found massive improvement with higher bias so you can't go wrong.

For my MK8,
I use tubes that worked well on high gain setting (less nfb), and then adjusted bias.
In general, both stages did better with higher bias settings.

I remember Sonic changed his output tube  bias right?
Not the impedance mod.
We need find write good bias settings for output tubes of mk6



baronbeehive said:


> Have you found the problem with one of your bias meters dropping after warmup?


It was not meter , it was a "cold solder" point in the driver stage socket.


----------



## SonicTrance (Feb 16, 2018)

baronbeehive said:


> How do you control your fan speed then?


I use fan speed reducer adapters. They have a dropping resistor on the +12V wire. That's easiest for me as I really don't need to change the speed. I just want it to be quiet and at the same time cool the components.



Maxx134 said:


> I remember Sonic changed his output tube bias right?


That's the 5998 bias mod you're thinking about. That one actually made it to the first page! Ha! 



bloodhawk said:


> Might just end up replacing the each and every wire with 22 AWG and 18 AWG single core silver plated copper wiring.


If you replace the wiring from the transistors on top side of board (recommended as they're going to break loose at some point) you need to use a flexible wire. If you use single core wire there it will also be prone to break from solder connection when you put the board back in. I used 20 awg stranded silver plated PTFE wire. Pretty stiff but OK to use, have no issues.


----------



## bloodhawk

SonicTrance said:


> If you replace the wiring from the transistors on top side of board (recommended as they're going to break loose at some point) you need to use a flexible wire. If you use single core wire there it will also be prone to break from solder connection when you put the board back in. I used 20 awg stranded silver plated PTFE wire. Pretty stiff but OK to use, have no issues.



Gotcha, yeah i realized for a lot of the wiring at the back that doesnt need to be routed around using flexible wiring would be better. I might still end up using single core wire routed around the board for the output. But ill know more once i take the whole board out. 

Thanks again for the helpful replies guys!


----------



## Maxx134

SonicTrance said:


> That one actually made it to the first page! Ha!


Good!
Let me know if you wanna put anything else first page,
If Ridge78 not available (as he been MIA here),
I can squeeze in my old posts.

Basically only need some topics baronbeehive mentioned.


----------



## baronbeehive (Feb 17, 2018)

Maxx134 said:


> Yes, so I encourage bias testing for both high and low gain (NFB) settings,
> as it should be slightly different sweet spots depending also on which tubes used.
> 
> Also I did notice a difference in sensitivity with change of power tubes, as I am not using stock tube type in output stage either, (I using old cheap Russian 6h6 at higher bias),
> ...



MrCurwen did suggest removing NFB from the APPJ and went on to suggest other tweaks to mitigate that, that's why I thought about trying to optimize the high gain setting on the MKVI.

I've lowered the driver bias to the Sonic settings near enough with the parallel resistor add on. So I would start with this new setting and maybe try another setting intermediate between this and the stock 220K ohms. I'm not sure how less feedback affects other component settings, generally I would think that some components need to be higher and some lower, sorry if that's pretty vague.

Then on to the CCS mod. This should have a big effect on the amp. As you know I have already said that one area, the only area, that the MKVI is slightly down on comparisons with the APPJ is on articulation, especially transients, at least with my tube setup, and this could change a lot with the CCS mod. Also a different tube type, power or driver would help, the GE's that I got recently are much sharper in sound so should be better in this respect.

You are ready to do this mod right?





Maxx134 said:


> For my MK8,
> I use tubes that worked well on high gain setting (less nfb), and then adjusted bias.
> In general, both stages did better with higher bias settings.
> 
> ...



Yes Sonic has optimized power tube bias for the 6AS7G's/421A's, and I have also done this mod. I don't plan on using any other power tube types so power tube bias is already done for me. The optimum point on the tube load line does not change with differing NFB does it?

If so all I need to do is adjust the driver bias again with the high gain setting

As I said I'm going to continue using my existing power tube types so I don't know if I can find a more optimum type to work well on high gain as you have done. How would I do this anyway?

ATM I will continue with burn in when I get my speed controller from HK probably next week, only after burn in can I do the sound tests when the system has settled down. But I don't plan to do any more mods until I get the last 421A because then I can fix the resistor value for these tubes, and go on then to complete the mods.


----------



## bloodhawk

Anyone ever try the RIFA Class X1 caps ? The PME-271E.

From the information i could find they are the 300V variants, and have higher voltage tolerances. I haven't been able to find a solid way to find the proper capacitance tolerance though. Since the Class X2 PME271M' have both a 10% and a 20% variant.


----------



## MrCurwen

Are there any capacitance critical spots in these amps? Coupling cap values are not at all important within 20% ranges.


----------



## bloodhawk

MrCurwen said:


> Are there any capacitance critical spots in these amps? Coupling cap values are not at all important within 20% ranges.



I honestly do not know the answer to that. But from what i do know, these are being used to bypass the 220uF Cathode bypass Caps in parallel.


----------



## MrCurwen

Well that is certainly not a capacitance critical spot, so don't worry about tolerances. Doesn't matter at all.


----------



## baronbeehive (Feb 19, 2018)

My experience with the APPJ made me think about the LD. I have a favourite tube on the APPJ, a Philips, similar to Mullards, but from the Herleen factory. It has an ultra realistic sound and that was what I was comparing to the LD. So I noticed that the 12SL7 GE's sounded good on the APPJ and that's why I thought of trying them on the LD.

Anyway I've just done a comparison again with the GE's in the LD. Now that I've had a listen I can tell that, as I thought, the articulation that I noticed on  the APPJ is on the LD also, thanks to the sharper sound of the GE's. The only drawback is I've lost that magical  sound of the TS 6SL7's, however I must say I like this GE sound also. I don't think they would work in the LD before the mods but because  the amp has such a full sound now they work a treat. Very nice transparency in the soundstage, and very clean sound now, and more on a par with the APPJ in terms of articulation. Probably the best $5 I've spent!

I think the reason it works is that I needed that sharpness in combination with the RCA power tubes I've got. They were a bit soft with the Tungsols in as well. I still like the Tungsols but they would probably work better with some sharper power tubes in.

As I said I'm not tube rolling now that I'm very happy with the sound but I can't say that it hasn't been interesting seeing all the different sounds you can get out of the same amp!

Edit: All the same it would be nice having the Sonic amp and not have to worry over tubes any more.


----------



## bloodhawk

Question - How are the Mlytics being wired? 

From what i understand, join the in- and the pin right under, same with in+ and out+ pin (right under in+) , then hook up to the boards + (solid color) , - (dashed) pins?


----------



## SonicTrance

bloodhawk said:


> Question - How are the Mlytics being wired?
> 
> From what i understand, join the in- and the pin right under, same with in+ and out+ pin (right under in+) , then hook up to the boards + (solid color) , - (dashed) pins?


Yes.


----------



## bloodhawk

Pictures of the under side of the stock board along with the stock wiring if anyone is interested - https://1drv.ms/f/s!AtHvY3vY0T9YgpZBVIj4oNuf82e_1A

I would strongly suggest downloading the images, just in case i move them to a private folder in the future.


----------



## baronbeehive (Feb 23, 2018)

Just trying to figure out from Sonic's pics of the CCS mod and MrCurwen's schematic what parts to get in order to be ready for doing the mod. I've decided on MrCurwen's CCS implementation with his active filter add on, to get rid of any residual ripple, because its a reliable and effective mod by all accounts.






My understanding is still somewhat sketchy but from what I can gather from the input schematic this is the CCS above and that plus the 2 caps, C3 ad C4 are what provides the filter which Sonic didn't do I think.

Going by this it looks like I need a transistor - Q4, 2 Mosfets - M1, M3, 2 caps - C3, C4, and 6 resistors - R6, R7, R8, R9, R18, R19. The same again for the other channel.

I don't know if some of the resistors in the schematic are existing or not, for example R18, R19.

I don't understand how the thing works and so I have to go on what others have done. I will go back and look again at the information. I've looked at Sonic's pics but it's really difficult to see all the connections. No doubt you will tell me where I've gone wrong.

My anode resistors are 33K atm but I haven't decided on a final value, they could be anything between that and the stock 220K.

Edit: I might not change that because the amp is sounding unreal atm, not bad for a flawed design!


----------



## baronbeehive

bloodhawk said:


> Pictures of the under side of the stock board along with the stock wiring if anyone is interested - https://1drv.ms/f/s!AtHvY3vY0T9YgpZBVIj4oNuf82e_1A
> 
> I would strongly suggest downloading the images, just in case i move them to a private folder in the future.



Great pics!


----------



## MrCurwen

baronbeehive said:


> Going by this it looks like I need a transistor - Q4, 2 Mosfets - M1, M3, 2 caps - C3, C4, and 6 resistors - R6, R7, R8, R9, R18, R19. The same again for the other channel.



Q3 and Q4 are 2N2222 or 2N2222A or similar. Buy bulk, at least 10. They're very cheap.

You only need one PSU filtering section. Both channels can share; M1 source is then connected to both channels.




baronbeehive said:


> I don't know if some of the resistors in the schematic are existing or not, for example R18, R19.



R18 and R19 are not in the stock amp. Ask Sonic for detailed pictures of the 3D layout for the CCS. It looks frightening but is quite easy to make.

Buy IRF830 in bulk also.

C4 value is not important, it can be anything from 2µF up. Shouldn't be too big, no more than 22µF I think. If you have extra space use a film cap if you wish; it's not going to affect sound quality either way.


----------



## baronbeehive

MrCurwen said:


> It looks frightening but is quite easy to make.



Thanks. It doesn't look difficult, just trying to see what goes where from Sonic's pic!

Really looking forward to doing this.


----------



## bloodhawk

Is it normal for the board to be as harder to put back in as it is to take it out?
The tube sockets were really lining up properly, so had to put a bit of downward pressure on the board and make sure they moved into their respective holes.


----------



## bloodhawk (Feb 24, 2018)

75% done -







I might finish the other side tonight it self. In total have spent about 7 hours on the amp so far.

Progress images are in the One Drive folder shared in the previous post.

The 2 most annoying things so far -

Taking the board out, and putting it back in, closely followed by taking the PSU Electrolytic caps out.



EDIT ---

ANNNNDDD DONE ! - https://imgur.com/a/AOysB







First impression , WHERE IS MAH BASS?  

On the bright side the separation seems better, low end extension is definitely better. Sound Stage is wayyyy wider.

I guess things might change once the caps settle in a while.

One thing im not sure is a good thing or not, but the amp is running wayyy cooler than it was before. I remember right as the right channel meter kicks on the amps is usually much hotter / warmer than it is now.

Alright , 15 mins in and.. the thump seems to be coming back.. phewww...


----------



## SonicTrance

baronbeehive said:


> I've looked at Sonic's pics but it's really difficult to see all the connections.


These are the best pics I got on the CCS module:


 

 



Hopefully you can see all connections from these pics?
Middle pin (Drain) of the IRF830 connects to one cathode. There's a trace in the board between the cathodes so doesn't matter which one you connect. I also added a 100 ohm R between drain and cathode, mainly because I needed the CCS module to sit a bit higher up. I would actually advice against the 100R as the bias voltage is so low already and that R is going to drop it some more.


----------



## SonicTrance

bloodhawk said:


> First impression , WHERE IS MAH BASS?


Great work bloodhawk! Looks very clean!
Don't know if you read my first impression in this thread but it was similar to yours, ha! No one else that I know has noticed a decrease in bass. As I listened some more and both the components and my ears settled to the new sound it was very, very good though!


----------



## SonicTrance

bloodhawk said:


> 75% done -


Just now noticed that the "fuses" right above the volume pot has been replaced with solid wire (maybe something like 1000A fuse?, lol) Wonder why that is?



bloodhawk said:


> Is it normal for the board to be as harder to put back in as it is to take it out?
> The tube sockets were really lining up properly, so had to put a bit of downward pressure on the board and make sure they moved into their respective holes.


I poked a screwdriver through each socket and pulled it in place (with force!) my board is a very tight fit. But after you've done it a few times it becomes easy. Be sure to replace the transistor wires as they WILL brake.


----------



## bloodhawk (Feb 24, 2018)

SonicTrance said:


> Great work bloodhawk! Looks very clean!
> Don't know if you read my first impression in this thread but it was similar to yours, ha! No one else that I know has noticed a decrease in bass. As I listened some more and both the components and my ears settled to the new sound it was very, very good though!



Thanks! Not as clean as yours though haha.
If took some more time to finish this up, i could have just used used some black wires / heatshrink for a better look.

Yeah, seems like in the mean time while i was soldering everything in, i had the 6XX running off of the NFB 11. I just need to re adjust. But everything sounds much CLEANER now. Like a thin shroud has been lifted or something.



SonicTrance said:


> Just now noticed that the "fuses" right above the volume pot has been replaced with solid wire (maybe something like 1000A fuse?, lol) Wonder why that is?
> 
> 
> I poked a screwdriver through each socket and pulled it in place (with force!) my board is a very tight fit. But after you've done it a few times it becomes easy. Be sure to replace the transistor wires as they WILL brake.



Yeah im not sure why that is, i really am not comfortable with those wires tbh. Specially since i dont know what they are rated for, if anything. Ill replace them with actual fuses next week.

Exactly what i did ! 
Glad im not the only one with the ridiculously tight fit, was really worried if i accidentally moved  a wire or something that was blocking the board.

Yeap wiring is on the menu next time i open this up. Probably going to be in a couple of week once work isn't as busy.


----------



## MrCurwen

The schematic I posted is missing the 100 ohm gate stopper for the FET in the CCS. It can clearly be seen in Sonic's photos. Be sure to put that in, it is required. It also helps construction a lot.

100R between CCS and cathode node is not needed. A resistor is a good binding post, but maybe get a 1R resistor for that. Or 10 or something.


In some circuits you need a cathode stopper between cathode and CCS to prevent oscillations.


----------



## baronbeehive

bloodhawk said:


> The 2 most annoying things so far -
> 
> Taking the board out, and putting it back in, closely followed by taking the PSU Electrolytic caps out.



Welcome to the club!

Very nice job, I am in awe of your desoldering/soldering skills!



bloodhawk said:


> First impression , WHERE IS MAH BASS?



The bass on the MKVI actually has more thump than on my speaker APPJ, and that is no slouch!It does take a while to get used to the new sound and for me the refinement is one thing that makes it so much better, you notice much more happening than before when you really start to listen, it really draws you in.

I'm sure you're aware of this but just watch those 3 points highlighted because parts can move around when opening and shutting the chassis and I have the same problem with the third circle at the bottom, the wire is very near to the screw and you might not have noticed that!

So what about the WCF caps?


----------



## baronbeehive

SonicTrance said:


> These are the best pics I got on the CCS module:
> 
> Hopefully you can see all connections from these pics?
> Middle pin (Drain) of the IRF830 connects to one cathode. There's a trace in the board between the cathodes so doesn't matter which one you connect. I also added a 100 ohm R between drain and cathode, mainly because I needed the CCS module to sit a bit higher up. I would actually advice against the 100R as the bias voltage is so low already and that R is going to drop it some more.



Thanks Sonic, they look very good pics. I will study them some more.
.


----------



## klnglim (Feb 24, 2018)

After few weeks waiting for those components, just finshed all mod except decoupling caps, this is a low budget Russian Caps and bypass, Mundolf MKP Caps, 150R Mills resistors mod, the amp run very stable, sound stage wide, nice  and natural comfort, after few hours run, tide bass improvement noticeable, hopefully more improvement in next 200 hours of burn in, may be will do decoupling in future soon, any suggestion for further improvement please give advise, thanks


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## gug42 (Feb 24, 2018)

@ klnglim : you can't go really further thant what you did. 
If you want, you need to build a total different amp ... a SE one with good output transformer (lundhal or toroidy for cheaper one).


Please can you remind me the specs of the power transformers ? 
Perhaps I will do an another amp with thoses parts 

Thx !


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## baronbeehive (Feb 25, 2018)

klnglim said:


> After few weeks waiting for those components, just finshed all mod except decoupling caps, this is a low budget Russian Caps and bypass, Mundolf MKP Caps, 150R Mills resistors mod, the amp run very stable, sound stage wide, nice  and natural comfort, after few hours run, tide bass improvement noticeable, hopefully more improvement in next 200 hours of burn in, may be will do decoupling in future soon, any suggestion for further improvement please give advise, thanks



Hey, great day for mods from members!

That is looking fantastic, good work!

Re further mods you might be limited due to the size of the Russian caps unless you want to extend the chassis.

Here's my suggestions roughly in order of sonic benefits, any or all of these:
1 - WCF cap, might be a problem with space
2 - Driver tube bias mod
3 - CCS mod, think about his before doing the driver tube bias mod. I'm not sure but this might mean you don't need to bother with the decoupling for driver stage Also means that it's not so important to upgrade the PSU caps I think. I'm not sure yet as I haven't done it but could be one of the most important mods Also the fact you have Kasei cathode caps means that you gain on sonic benefits so PSU mods not so important.
4 - Power tube bias only if you are plannig on using 5998's/4221A's
5 - Wiring
6 - At least these resistors which are looking worse for wear and are important:


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## baronbeehive

gug42 said:


> @ klnglim : you can't go really further thant what you did.
> If you want, you need to build a total different amp ... a SE one with good output transformer (lundhal or toroidy for cheaper one).
> 
> 
> ...



Hey gug42, how is your build going?


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## gug42 (Feb 24, 2018)

Great ! Jobs done, and really working well   Impressive dynamique, really powerfull bass and lots of details with evry headpones.  Far better than the little dot. Perhaps a little bit too expressive in the trebble area. In comparaison the little dot sounds life less ....

My amp, well, take the headphone in their hand with strengh, power and authority. And I have'nt use high end materials : Toroidy for iron (transformers and choke), chemical capacitor bypassed with basic mkp (some blue boxes epcos), total  14 Kg 
I have used simple but high end design : two powerlines, one by channel, an really carefull electrical ground implantation.
Tubes are Sylvania 6SN7WGT and JJ KT88

I'm waiting for an oscillo to mesure it.

In the future I will :
- Rebuild it to have a more compart form factor ! Perhaps with using a 6SL7 SRPP gomez
- Build one with theoretical better stuff :  lundhal output transformers, hammond choke, full mkp and PIO capacitor (huge beasts), SRPP gomez for input, and DHT tubes for output (2A3 ? 45 ? 300B ? others ?)


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## klnglim (Feb 24, 2018)

baronbeehive said:


> Hey, great day for mods from members!
> 
> That is looking fantastic, good work!
> 
> ...


I agree with you is changing most of the resistor, just want to know can those resistors (from the pictures with yellow circle) change to wirewound 150R 5W instead of
original show is 120R 5W ? 
I understand space inside this amp.is limited, just try my best to find tiny, low cost and better quality if possible as I like the original design case and look weird when extend it.
Another question is about cathode bypass caps, I still some caps (same brand same type) left over, can I add extra as parralel caps coupling?Will that cause sound badly?
Thanks


----------



## klnglim

gug42 said:


> @ klnglim : you can't go really further thant what you did.
> If you want, you need to build a total different amp ... a SE one with good output transformer (lundhal or toroidy for cheaper one).
> 
> 
> ...


Sorry I m not very sure about the power transformer specs and I never open the cover take a look too


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## bloodhawk (Feb 24, 2018)

baronbeehive said:


> Welcome to the club!
> 
> Very nice job, I am in awe of your desoldering/soldering skills!
> 
> ...



Thank you for the compliments 

All the info in this thread by you, Max, Sonic, Redge has been invaluable!

Ah those wires won't move. The one on the top is much lower than it looks in the picture, from the terminal of the other cap.

And other ones are super stiff Cooper , they won't move even if I drop the amp lol. Plus the copper strands have this really strong and sturdy coating on them.

I might swap out the WCF caps in the future with some MKP's.

For some reason i kinda felt the thump was much more with only the Audyn's in. But it could also because the lower frequencies weren't rolling off as much, and now because of the extension they are rolling off much further down. End of the day not a deal breaker. Some of it has already come back, i have a feeling things will get even better over time as the caps settle in.


----------



## baronbeehive

klnglim said:


> I agree with you is changing most of the resistor, just want to know can those resistors (from the pictures with yellow circle) change to wirewound 150R 5W instead of
> original show is 120R 5W ?



If you mean the WCF grid resistors I think you should stick to your board values, and not necessary for wirewound there, but you could since they are 5W. I'm not sure I can't remember what mine are there.



klnglim said:


> I understand space inside this amp.is limited, just try my best to find tiny, low cost and better quality if possible as I like the original design case and look weird when extend it.
> Another question is about cathode bypass caps, I still some caps (same brand same type) left over, can I add extra as parralel caps coupling?Will that cause sound badly?
> Thanks



Ha ha, yes it does look a bit weird!!!

No, that will degrade sound. You need the smaller capacitance value here because it is putting back the high frequencies that are lost due to the larger type upgrade caps. The smaller value caps as bypass are necessary, I found that with my other amp, without these type caps the sound becomes lifeless and others here have experimented and found just the right size and value caps which you should use.



bloodhawk said:


> Thank you for the compliments
> 
> All the info in this thread by you, Max, Sonic, Redge has been invaluable!
> 
> For some reason i kinda felt the thump was much more with only the Audyn's in. But it could also because the lower frequencies weren't rolling off as much, and now because of the extension they are rolling off much further down. End of the day not a deal breaker. Some of it has already come back, i have a feeling things will get even better over time as the caps settle in.



Great, I would have got nowhere without the help here.....apart from up the creek
.

That's an interesting point which I brought up recently with my comparisons with my other amp and found that the MKVI was less articulate in the bass regions. It's something we have tried to address here as a known aspect of the LD's bass being somewhat lacking in transient attack which I believe would elevate the LD to top level status.
I am holding out for the results of the CCS mod before I decide on this because it could do the trick. I believe it had similar results in your BH Crack speedball mod from what I've heard.


----------



## baronbeehive

gug42 said:


> Great ! Jobs done, and really working well   Impressive dynamique, really powerfull bass and lots of details with evry headpones.  Far better than the little dot. Perhaps a little bit too expressive in the trebble area. In comparaison the little dot sounds life less ....
> 
> My amp, well, take the headphone in their hand with strengh, power and authority. And I have'nt use high end materials : Toroidy for iron (transformers and choke), chemical capacitor bypassed with basic mkp (some blue boxes epcos), total  14 Kg
> I have used simple but high end design : two powerlines, one by channel, an really carefull electrical ground implantation.
> ...



Very interesting! What design did you use, was it DIY


----------



## gug42

Yep a DIY, a really standard SE with the spirit of "less is more", juste the usefull stuff :
- only R and C
- Two power line, one by channel
- Classical filter CLCRC
- One ground line by channel

Well if you wan i can send you the schematic


----------



## baronbeehive

gug42 said:


> Yep a DIY, a really standard SE with the spirit of "less is more", juste the usefull stuff :
> - only R and C
> - Two power line, one by channel
> - Classical filter CLCRC
> ...



I think we would all be interested, thanks!


----------



## bloodhawk

baronbeehive said:


> Great, I would have got nowhere without the help here.....apart from up the creek
> .
> 
> That's an interesting point which I brought up recently with my comparisons with my other amp and found that the MKVI was less articulate in the bass regions. It's something we have tried to address here as a known aspect of the LD's bass being somewhat lacking in transient attack which I believe would elevate the LD to top level status.
> I am holding out for the results of the CCS mod before I decide on this because it could do the trick. I believe it had similar results in your BH Crack speedball mod from what I've heard.



Oh yeah with the Crack, it made everything super clean. Like the background was super dark/blank, but after that it pretyy much pitch black. Made the amp cooler as well. The low end was more audible / had better texture as a result of that.


----------



## gug42

Here it is


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## gug42 (Feb 24, 2018)

And, well, a point I have learn : a real one watt is very loud for a headphone !

So if you want a really good quality for money my advice would be :
- lundhal LL2765 60 mA or 80 mA
- Toroidy power transformers with the ability to use regulated heater (needs 7 V and x3 A)
- hammond  or toroidy self 10H
- chemical + MKP capacitor
- One 5998A tubes can power  the two channel. But you can use other stuff 
- Input tubes depends what you want, there is multiple options


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## baronbeehive

bloodhawk said:


> Oh yeah with the Crack, it made everything super clean. Like the background was super dark/blank, but after that it pretyy much pitch black. Made the amp cooler as well. The low end was more audible / had better texture as a result of that.



Right!

The CCS should rule out pretty much PSU artifacts in the audio signal, resulting in a cleaner signal. The balanced output of the LD is generally agreed to improve bass quality and detail over the SE output, and force balancing, which is what the CCS does, should further improve this because the LD balance depends very much on the tubes and can be in or out of perfect balance quite considerably.


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## gug42 (Feb 24, 2018)

The CCCS has one advantage : infinite equivalent resistance, BUT the CCS has one flaw : provide some disruption, some noise, by the principe of the ccs ... instability ...
The most simple way to go : use one R by triode (not by tube but by triode), for sure less fun than a cccs ...  
And moreover, if you find that you have enough gain, no obligation to use a bypass cathode capacitor. Less distortion.

A+


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## SonicTrance

gug42 said:


> BUT the CCS has one flaw : provide some disruption, some noise, by the principe of the ccs ... instability ...


This is exactly what the CCS doesn't do. The CCS provides balance and stability to the signal. Not sure where you got that info?

You should look into building the "modern LTP"!
https://www.head-fi.org/threads/modern-balanced-tube-amp-build.852879/

No reason to use pricey Lundahl transformers in that amp


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## baronbeehive

SonicTrance said:


> Ok, so I tried it!



I tried to find correct values, hope I haven't read wrong way round.


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## baronbeehive (Feb 25, 2018)

SonicTrance said:


> These are the best pics I got on the CCS module:
> 
> Hopefully you can see all connections from these pics?






That's very clear!

The brown black black black brown resistors are 100R.

OK. Could I connect to the cathode where the cathode resistor was, or better to connect direct to socket pin? I'm not sure of the board trace atm.


----------



## SonicTrance

baronbeehive said:


> I tried to find correct values, hope I haven't read wrong way round.


The 270R is in series with a 220R for a total of 490R. I didn't have a 470R .6w 1%.
That is called the sense resistor and is the resistor that sets the current. The formula is: Iccs = 1.16 / sense R. So, in my case its 1.16 / 490 = 2.37 mA. Thats the total current. Each triode will get half, about 1.2 mA.

The gate stopper is 100R, not 2k like you wrote in the pic. Look at IRF830 datasheet to learn which pin is gate, drain and source.

It doesn't matter if you connect the ccs where the cathode resistor was or directly at a cathode pin. It's the same thing. Just make sure to connect the ccs on the cathode side of the resistor holes and not the ground side. Use ohm meter to test.


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## baronbeehive (Feb 25, 2018)

SonicTrance said:


> The 270R is in series with a 220R for a total of 490R. I didn't have a 470R .6w 1%.
> That is called the sense resistor and is the resistor that sets the current. The formula is: Iccs = 1.16 / sense R. So, in my case its 1.16 / 490 = 2.37 mA. Thats the total current. Each triode will get half, about 1.2 mA.
> 
> The gate stopper is 100R, not 2k like you wrote in the pic. Look at IRF830 datasheet to learn which pin is gate, drain and source.
> ...



OK, thanks for that, don't know why I wrote 2K, I've got 100R in my notes!


----------



## MrCurwen

gug42 said:


> Here it is



Yes I've built a bunch of different kinds of SE amps in my day. This is quite typical retro type SE amp; not bad to listen to, but not very good either if I'm being honest. Fun to build though, and very very informative if you go thru the trouble to find out what happens inside it.

As drawn, the output section doesn't pass any kind of audio signal thru the OT. There's a mistake somewhere.

Either it's meant to be a parafeed type amp, in which case it needs a plate load of some kind between KT66 anode and B+. Resistor, choke or a SS module of some kind.

Or, it's meant to be ultrapath amp, in which case B+ needs to be inserted at the junction of the OT primary and C704 (the ultrapath cap). Then the OT primary can act as a plate load in the usual way for series feed OTs.

It's probably the ultrapath one. The voltage markings are just made somewhat misleadingly. In that case the cathode caps are 100% completely unnecessary. Ultrapath trades cathode bypass caps for the ultrapath cap; it's a higher impedance node, so you can get by with a smaller capacitance, 30µF film cap in this case. Easier to use film caps than 100µF cathode bypass cap.



SonicTrance said:


> This is exactly what the CCS doesn't do. The CCS provides balance and stability to the signal. Not sure where you got that info?



Indeed. I suspect gug42 is talking about some other thing, not a CCS used as a tail. Or, he doesn't understand what goes on inside a balanced pair.



gug42 said:


> The most simple way to go : use one R by triode (not by tube but by triode), for sure less fun than a cccs ...



If you are talking about your SE amp that's another thing. Separate cathode resistors in a balanced (or using the old terminology, push-pull) stage is just counterproductive.



gug42 said:


> And moreover, if you find that you have enough gain, no obligation to use a bypass cathode capacitor. Less distortion.



Ok I'm pretty sure you're talking about a SE amp here, right?


I'm very happy there is excitement to try the CCS tail mod. It's not a fix-everything magick pill for the LD, but Sonic reported it as a noticeable improvement. Also it'll help ease some underlying worries about "THAT SS SOUND" that a lot of people might still have.


----------



## baronbeehive (Feb 25, 2018)

MrCurwen said:


> Ok I'm pretty sure you're talking about a SE amp here, right?



I think so. I suspect that gug42's amp might exaggerate the transients somehow to get that alive sound that he has, especially in the treble frequencies,


----------



## bloodhawk

MrCurwen said:


> I'm very happy there is excitement to try the CCS tail mod. It's not a fix-everything magick pill for the LD, but Sonic reported it as a noticeable improvement. Also it'll help ease some underlying worries about "THAT SS SOUND" that a lot of people might still have.




Yeah that is something i have been noticing post mods, that the amp sounds very close to an SS amp now. Would love to try out the CCS in the VI+ once Sonic posts some more info.


----------



## baronbeehive

bloodhawk said:


> Yeah that is something i have been noticing post mods, that the amp sounds very close to an SS amp now. Would love to try out the CCS in the VI+ once Sonic posts some more info.



What do you mean by SS sound? To me it means more exaggerated transients, hotter, splashy sound and not so rich or holographic as tube sound.

Of course the best SS systems are not like this!


----------



## bloodhawk (Feb 26, 2018)

baronbeehive said:


> What do you mean by SS sound? To me it means more exaggerated transients, hotter, splashy sound and not so rich or holographic as tube sound.
> 
> Of course the best SS systems are not like this!



I personally feel that SS amps sound very analytical and transparent. When we get Tube amps we get them for the musical/euphoric nature. And to me post mods the VI+ sounds very analytical. Which isnt really a bad thing, as it still sounds amazing. But it just seems to not have that warm tube sound anymore.

Ill have access to a VI+ running similar tubes like mine, later this week and ill be able to do some accurate A/B comparisons then.


----------



## baronbeehive

bloodhawk said:


> I personally feel that SS amps sound very analytical and transparent. When we get Tube amps we get them for the musical/euphoric nature. And to me post mods the VI+ sounds very analytical. Which isnt really a bad thing, as it still sounds amazing. But it just seems to not have that warm tube sound anymore.
> 
> Ill have access to a VI+ running similar tubes like mine, later this week and ill be able to do some accurate A/B comparisons then.



Really! I don't find that about being analytical. I think that may be down to the choice of tube. The TS 6SL7, for example, is very magical sounding, no way is it analytical except that it does have great detail as well as musicality.

Interesting to hear your comparisons.


----------



## baronbeehive (Feb 26, 2018)

I don't know if this makes any sense:






Edit: Booboo 1 - I think the binding post should go down between the 2 nodes above the transistor.


----------



## MrCurwen

baronbeehive all good with following notes;

1) Why do you need a binding post between R19 and the Darlington pair / FET gate circuit? Just use R19 as the binding post?

2) If instability occurs, put a 10R or more resistor between each CCS bottom and M1 source. Don't add these resistors "just in case", only if instability occurs. Probably won't, the active filter doesn't have that much gm.

3) You might need a binding post between M3 and the cathode node. As Sonic mentioned, preferably use a small value like 10R. If instability occurs, increase to 47 or 100 R.


----------



## baronbeehive

MrCurwen said:


> baronbeehive all good with following notes;
> 
> 1) Why do you need a binding post between R19 and the Darlington pair / FET gate circuit? Just use R19 as the binding post?


I don't, that was supposed to be the one that Sonic mentioned which I think I got correct in the first draft but deleted it between M3 and the cathode node, it looked wrong when I looked at Sonic's pics.


----------



## gug42 (Feb 26, 2018)

Hello Guys,

And thx to reply to me 



MrCurwen said:


> It's probably the ultrapath one. The voltage markings are just made somewhat misleadingly. In that case the cathode caps are 100% completely unnecessary. Ultrapath trades cathode bypass caps for the ultrapath cap; it's a higher impedance node, so you can get by with a smaller capacitance, 30µF film cap in this case. Easier to use film caps than 100µF cathode bypass cap.



Here, it be call "transversal capacitor" Noted Ci. Don't know if it help.

I use a mkp capacitor. 35 uF because I have thoses in my box ... so more simple than order a another 30uF  The schematics is correct about the wiring. The objectif is to provide a little power boost in the bass  (if I have understand everything)



MrCurwen said:


> Indeed. I suspect gug42 is talking about some other thing, not a CCS used as a tail. Or, he doesn't understand what goes on inside a balanced pair.



Yep SE amp. Sorry If I misunderstand something ...
cascode constant current source ?  and not used to provide some balance in a push-pull but for define a constent current in place of Rk.



baronbeehive said:


> I think so. I suspect that gug42's amp might exaggerate the transients somehow to get that alive sound that he has, especially in the treble frequencies,



Please can you develop ?  How to check this ? Can I see it with an oscilloscope ? Really interested indeed 

Well at the end, I'm pretty happy with it, and yes, it's a fabulous learning tool. I have learn lots of thing  for sure !

thx


----------



## MrCurwen

gug42 said:


> I use a mkp capacitor. 35 uF because I have thoses in my box ... so more simple than order a another 30uF  The schematics is correct about the wiring. The objectif is to provide a little power boost in the bass (if I have understand everything)



Kind of. The objective of the Ultrapath topology is to trade cathode bypass cap (of big capacitance value, electrolytic by necessity) to the Ultrapath cap between cathode node and B+. This cap can be of much smaller value to provide adequate bypass, therefore a good quality film cap can be used instead of electrolytics.

Think of it like this; the cathode node needs to be at AC ground. This is achieved by letting all AC pass thru from cathode node via a capacitor. Now usually it passes to ground; the amp does have one more DC rail, the B+ rail. There is no reason not to 'ground' the other end of the cap to B+ instead of ground.

The only meaningful thing for the cap is that the other end is at an steady DC rail. Both B+ and ground (in theory) are just that.

Now why can the cap be of smaller capacitance if it is tied to B+ instead of ground? Well, the capacitance is determined by the R (or Z) component of the highpass filter. If the cap is tied to ground, the R is the cathode resistor, usually not of very large value. Therefore the cap must be of large value (Google RC highpass calculator and try out some values to see what frequency response you get).

If the cap is tied to B+, the R component is made up of the impedance (Z) of the tube and the OT. These easily come up much larger than a typical cathode resistor, therefore less C is required to achieve the same frequency response. 

There's also some current loop stuff going on but it's less consequential. This is the meaningful point.



gug42 said:


> cascode constant current source ? and not used to provide some balance in a push-pull but for define a constent current in place of Rk.



No cascode, only one CCS. I'm not sure what you are saying there, please elaborate?

In a long tailed pair (LTP), which is what the LD has, the tail is supposed to provide balance for the pair by acting as a current sink. The larger the impedance (compared to the tubes' anode resistances and plate loads), the better the balance.

Now a strong CCS such as I and Sonic propose provides so many megaohms of impedance that it's practically infinite, therefore balance is practically perfect.

Please elaborate on the harmful effects you mentioned.



gug42 said:


> Please can you develop ? How to check this ? Can I see it with an oscilloscope ? Really interested indeed



If we are indeed talking about the Ultrapath type retro SE amp, there is absolutely nothing in there that provides superclean transients. If by 'exaggerate' you mean slightly distorted transients then that's another thing.

The simplest way to improve transient response in that amp would be 

1) Fixed grid bias. Trade big cathode bypass electrolytics to small good quality grid coupling caps.

2) Regulate B+ with simple 2 FET regulator. This plays out most of the PSU electrolytics and most of all the tube rectifier. You do realise guitar amp guys actually deliberately put in tube rectifiers to get a compressed sound? Tube recs are ANTI TRANSIENT RESPONSE, big time.



gug42 said:


> Well at the end, I'm pretty happy with it, and yes, it's a fabulous learning tool. I have learn lots of thing for sure !



That's great! Do you plan to keep it as is, or experiment and mod?


----------



## baronbeehive

gug42 said:


> Please can you develop ?  How to check this ? Can I see it with an oscilloscope ? Really interested indeed
> 
> Well at the end, I'm pretty happy with it, and yes, it's a fabulous learning tool. I have learn lots of thing  for sure !
> 
> thx



I was only speculating, I suspected some kind of bass/treble boost such as you find in ipods and such like which is there to make the sound acceptable for mini headphones. It can sound great but for me the frequency spectrum is too unbalanced.

Glad you are liking your amp, well done for achieving this.


----------



## gug42

MrCurwen said:


> That's great! Do you plan to keep it as is, or experiment and mod?



For sure I will do some modification, but not before the end of march ... no time before.
Well I have some test in mind :
- tests 6SL7 
- tests some interstage capacitors (I have some russian caps) And I can I would like to refactor the amp. 
- DC regulated heaters (LM317 or LT1084)

And well in a galaxy far away : 
- tests some lundahl opt, 
- tests DHT tubes like 45 or 2A3 : Really I would prefer 45 but hard to find ... And in new production only emission labs ... costly ....
- tests a full mkp dc link power supply line

And I must read and understant more stuff about tailed stuff.

And By the way I wait my usb scope to mesure the amp 



baronbeehive said:


> I was only speculating, I suspected some kind of bass/treble boost such as you find in ipods and such like which is there to make the sound acceptable for mini headphones. It can sound great but for me the frequency spectrum is too unbalanced.
> 
> Glad you are liking your amp, well done for achieving this.



You think the bass/trebble boost can be in the recorded tracks ?? I mainly use tidal in hifi quality.
I use a schiit modi multibit dac.

Yeah I'm pretty happy to acheive this, a challange for me  And of course, now, I want more ! 

Thanks guy !

Regards,


----------



## baronbeehive (Jun 5, 2021)

Parts List for CCS mod:

1 - 2 x transistor (Q3) 2N2222 - NPN
2 - 2 x transistor (Q4) 2N2222 - NPN
3 - 2 x mosfets (M3) IRF830 - Vishay IRF830APBF N-channel 5 A 500V 3-Pin TO-220AB
4 - 1 x mosfet (M1) IRF9640 - Vishay IRF9640PBF P-channel 11 A 200V 3-Pin TO-220AB
5 - 1 x cap (C3) Nichicon Aluminium Electrolytic 22uF 160V +105C
6 - 1 x cap (C4) Nichicon Aluminium Electrolytic 10uF 160V +105C
7 - 2 x resistor (R19) Takman Metal Film 220K 0.5W 1%
8 - 2 x resistor (R18) Takman Metal Film 470R 0.5W 1%
9 - 2 x resistor (R20) Takman Metal Film 100R 0.5W 1%
10 - 2 x resistor (R21) Takman Metal Film 10R 0.5W 1%
11 - 1 x resistor (R6) Takman Metal Film 1K 0.5W 1%
12 - 1 x resistor (R7) Takman Metal Film 1K 0.5W 1%
13 - 1 x resistor (R8) Takman Metal Film 10K 0.5W 1%
14 - 1 x resistor (R9) Takman Metal Film 220K 0.5W 1%


----------



## bloodhawk

baronbeehive said:


> Parts List for CCS mod:
> 
> 1 - 2 x transistor (Q3) 2N2222 - NPN
> 2 - 2 x transistor (Q4) 2N2222 - NPN
> ...



NICE!

Does any one have images of the CCS modules installed in the MK VI+?


----------



## SonicTrance (Feb 28, 2018)

baronbeehive said:


> I haven't decided the value of the 470R sense resistor yet, I'm not sure if it is taken from board measurement of the B+ or calculated from the B+


I answered this on the previous page. There’s a formula to calculate the current. The CCS will keep that constant current at all times. Has nothing to do with B+.
Only R18 needs to be metal film 1%. The rest can be 5% and 1w. Especially R19 should not be 0.5w, at least 1w.
Otherwise it looks good. Binding post also not necessary.


----------



## SonicTrance

bloodhawk said:


> NICE!
> 
> Does any one have images of the CCS modules installed in the MK VI+?


I posted some very clear and detailed pics a few days ago.


----------



## bloodhawk

SonicTrance said:


> I posted some very clear and detailed pics a few days ago.



Interesting, i only saw the ones of the modules themselves, but not wired up in the amp. I might have totally missed the post though, will go back and double check. Thanks!


----------



## MrCurwen

baronbeehive said:


> I was only speculating, I suspected some kind of bass/treble boost such as you find in ipods and such like which is there to make the sound acceptable for mini headphones. It can sound great but for me the frequency spectrum is too unbalanced.



Series feed OT amps pretty much always have an anti-loudness frequency response, meaning at least some depression in bass and high treble. It's the "sweet mids tube sound" thing.

Add grid current and RC cathode bias and you've got a pinch more loudness filter.



gug42 said:


> For sure I will do some modification, but not before the end of march ... no time before.



I'll comment very shortly here. If you're interested in some suggestions and further comments, please PM me or make a new thread and link it to me. I'm very happy to provide suggestions and info. I started out with SE amps, I've gone thru quite a lot with them.



> Well I have some test in mind :
> - tests 6SL7



Tube types aren't the important thing (up to a point, they need to have nice curves). Simple changes in circuitry bring back so much more in sound gains than any tube type change.



> - tests some interstage capacitors (I have some russian caps) And I can I would like to refactor the amp.



Same here. I'd suggest trying to go around the problems with the caps.

But do use russian caps. They're very rugged, real NOS, and if nothing else they can be used as binding posts in P2P layouts. That's a big plus. Cheap also.



> - DC regulated heaters (LM317 or LT1084)



Unless you've messed up with the wiring, this will do nothing for the sound quality. No need for it at all. Badly filtered DC WILL sound worse than clean AC, because it has spikes in the voltage (triangle wave or similar).



> And well in a galaxy far away :
> - tests some lundahl opt,



Why pay for iron? I'd suggest engineering around it. A cheap Hammond will sound better in the right circuit than your Lundahl. 



> - tests DHT tubes like 45 or 2A3 : Really I would prefer 45 but hard to find ... And in new production only emission labs ... costly ....



DH tubes will sound horrible unless filament supply is actively filtered. This is a real hassle once you go up in current. If you want to taste the DH magick, I suggest you use 4P1L.

It's the most linear and best output tube there is anyway. Why go for second rate tubes like 2A3? 45 is crazy expensive; if you want Golden Age Americana, go for 47 or 1619 or similar.



> - tests a full mkp dc link power supply line



Crazy crazy expense. A simple 2 FET reg will solve these issues AND sound better.




baronbeehive said:


> 1 - 2 x transistor (Q3) 2N2222 - NPN
> 2 - 2 x transistor (Q4) 2N2222 - NPN
> 3 - 2 x mosfets (M3) IRF830 - Vishay IRF830APBF N-channel 5 A 500V 3-Pin TO-220AB
> 4 - 1 x mosfet (M1) IRF9640 - Vishay IRF9640PBF P-channel 11 A 200V 3-Pin TO-220AB
> ...



All good, except you need to use 1W for all except the sense resistor. Also just use carbon films. 

Don't buy 4 FETs, buy at least 10. Same for 2N2222. Trust me.



baronbeehive said:


> I haven't decided the value of the 470R sense resistor yet, I'm not sure if it is taken from board measurement of the B+ or calculated from the B+



Sonic gave the formula for that value; 1.16 / R = desired I

I use 1.13 as the factor. It varies, it's determined by the base voltage of the 2N2222(A) you happen to get. Use whatever, it's not that sensitive. Basically the formula comes from keeping the Darlington pair at the exact threshold of conductance. That's where the CCS stabilizes.



baronbeehive said:


> I'm not sure how to put 2 resistors between each CCS bottom and M1 source if there is instability, given that both the CCS's are joined, surely only 1 resistor will be possible here?



In that scenario the CCS bottoms would not be joined, except via the two resistors. That's the point. Don't worry about it, I don't expect there to be instability, so just don't use them unless there is.


----------



## SonicTrance

bloodhawk said:


> Interesting, i only saw the ones of the modules themselves, but not wired up in the amp. I might have totally missed the post though, will go back and double check. Thanks!


Right. I misread your post. I did post pics on them installed in the LD also some time ago when I did the testing and measurements.


----------



## gug42 (Feb 28, 2018)

Hello,

MrCurwen, When I will get more time, I will realy be interested !  My first amp is what it is : a first amp, a starting point, a learning machine 
Now I'm confident in myself to be able to  build an amp 



MrCurwen said:


> Series feed OT amps pretty much always have an anti-loudness frequency response, meaning at least some depression in bass and high treble. It's the "sweet mids tube sound" thing.
> 
> Add grid current and RC cathode bias and you've got a pinch more loudness filter.



Sorry I don't understant what you want to say / explain 



MrCurwen said:


> Tube types aren't the important thing (up to a point, they need to have nice curves). Simple changes in circuitry bring back so much more in sound gains than any tube type change.



I'm totally agree.  I have a good stock of 6SL7 and only two paris of 6SN7 .... I start with 6SN7 for timing reason .... Shipping delay for some resistor ....



MrCurwen said:


> Unless you've messed up with the wiring, this will do nothing for the sound quality. No need for it at all. Badly filtered DC WILL sound worse than clean AC, because it has spikes in the voltage (triangle wave or similar).



Yep I know. But it's to have exactly 6,3V whatever my local voltage could be 



MrCurwen said:


> DH tubes will sound horrible unless filament supply is actively filtered. This is a real hassle once you go up in current. If you want to taste the DH magick, I suggest you use 4P1L.
> 
> It's the most linear and best output tube there is anyway. Why go for second rate tubes like 2A3? 45 is crazy expensive; if you want Golden Age Americana, go for 47 or 1619 or similar.



I know that DHT tubes needs a careful filament supply. Planning one : filtered and regulated.

I really want to heard thoses golden age tubes. I'm open to other stuff. 47 could be an option, in triode strapped modes. Indeed that's not the "good" or "best" approche, but ... well .... it's a pleasure, and, at the end pleasure is the objectif (if you see my point ?)

Did you have some triode strapped curves for the 47 ?




MrCurwen said:


> Crazy crazy expense. A simple 2 FET reg will solve these issues AND sound better.



Ok I will please to talk about this with you 

Thank you again


----------



## gug42

Hello,

Just to post a wonderfull page : http://lilienthalengineering.com/100-amplifiers-chapter-1

And for the Western Electric 32A, you'v got the "grid to cathode coupling" trick


----------



## baronbeehive (Feb 28, 2018)

SonicTrance said:


> I answered this on the previous page. There’s a formula to calculate the current. The CCS will keep that constant current at all times. Has nothing to do with B+.
> Only R18 needs to be metal film 1%. The rest can be 5% and 1w. Especially R19 should not be 0.5w, at least 1w.
> Otherwise it looks good. Binding post also not necessary.



Yes I know, sorry I put this post together rather hastily  after searching out  the parts all afternoon and looking for the best deal I just didn't know if the formula applied to a measurement from the board or to the type of part that was installed which MrCurwen answered. And yes I knew I needed the sense resistor 1% so just got the others the same

Right thanks for the information, beginning to understand the functionality of the CCS.



MrCurwen said:


> Series feed OT amps pretty much always have an anti-loudness frequency response, meaning at least some depression in bass and high treble. It's the "sweet mids tube sound" thing.
> 
> Add grid current and RC cathode bias and you've got a pinch more loudness filter.



Ah, interesting. In that case gug42 should notice the missing frequencies. Strange that he said that the treble was almost too much.



MrCurwen said:


> All good, except you need to use 1W for all except the sense resistor. Also just use carbon films.
> 
> Don't buy 4 FETs, buy at least 10. Same for 2N2222. Trust me.
> 
> In that scenario the CCS bottoms would not be joined, except via the two resistors. That's the point. Don't worry about it, I don't expect there to be instability, so just don't use them unless there is.



OK about the  resistors.

No I  was intending  to get 5 or 10 of the transistors as you suggested, but I was just saying what I needed for this mod.

Thanks  for  the help!


----------



## baronbeehive (Feb 28, 2018)

Just having a listen since burn in and I think the bass articulation problem seems to be much improved surprisingly, even with the TS 6SL7 in. I'm glad about that, it's  my favourite tube, it has such great  definition on drums for example. There is a very slight treble roll off with this tube on high  hat type cymbal for example which I only just noticed when comparing it to the APPJ but on the  whole the treble definition is superb  as well.

Also the soundstage problem, not a problem if  you've got the right headphones, seems to be  much improved, it seems much more spatial,  even on my HE-500's.


----------



## bloodhawk

baronbeehive said:


> Just having a listen since burn in and I think the bass articulation problem seems to be much improved surprisingly, even with the TS 6SL7 in. I'm glad about that, it's  my favourite tube, it has such great  definition on drums for example.
> 
> Also the soundstage problem seems to be  much improved, it seems much more spatial,  even on my HE-500's.



Is this with CCS? or just general amp burn in since the mods?


----------



## baronbeehive

bloodhawk said:


> Is this with CCS? or just general amp burn in since the mods?



Ha, no, I'm not that fast a worker! Just general  burn  in for those caps.

Here you go bloodhawk,  post 2708.

https://www.head-fi.org/threads/lit...rified-mods-are-on-first-page.782183/page-181


----------



## baronbeehive

OMG.... the sound of Gibson Les Paul, and the Strat on this amp, sounds equally amazing on the other amp, to die for!


----------



## MrCurwen

gug42 said:


> MrCurwen, When I will get more time, I will realy be interested ! My first amp is what it is : a first amp, a starting point, a learning machine
> Now I'm confident in myself to be able to build an amp



That is exactly as it should be.

Do you plan to mod your existing amp or build a completely new one?



gug42 said:


> Sorry I don't understant what you want to say / explain



OT means output transformer. Series feed OT means a topology where the OT primary is in series with the output tube. So it is between B+, the tube, and ground, having the same DC current pass thru it that passes thru the tube.

Loudness filter means a frequency response with some degree of added highs and lows. Anti-loudness filter is the opposite of that, some degree of less highs and lows.

Series feed OT amps almost always have some anti-loudness filter going on, that is because of the properties of the OT. With DC bias the OT has difficulty reproducing low frequencies. The DC "drowns out" any nearby (like 50 or 100 Hz) action. Also the windings have a lot of parasitic capacitance; think about it, lots and lots of wire stacked up right next to each other. This capacitance - if not satisfied with current - forms a low pass filter, depressing high frequency response.

These problems can be satisfied by

1) not having DC current thru the OT (fixes the bass issue completely)

2) driving the OT primary from a low output impedance source (fixes the high frequency issue).

Grid current is the umbrella term for parasitic properties of tube control grids. They generally require some current to satisfy. Imagine there is a capacitor inside the tube between control grid and cathode, and also control grid and anode. These capacitors in conjuction with other circuitry around the control grid act as low pass filters, dampening transients and often dampening high frequency response.

The most common comments people give upon fixing this grid current insufficiency problem are that the sound is "more airy", "more 3D" and "faster". So, high frequency response and transient response are improved in technical terms.

RC cathode bias does a similar thing but on the bass side of the frequency response. Point of the cathode C is that it is supposed to keep the cathode node at a steady DC and drown out all AC by charging and discharging accordingly.

Now once the C has discharged some, it can only be recharged by current that arrives thru the tube from B+. This doesn't happen instantly; think about Ohm's law. There is a tube with impedance of X ohms between B+ and the cathode node. This impedance limits the amount of current that can be transported.

So it doesn't charge instantly. While the C is not charged, the DC bias point of the tube (cathode node voltage) is different. What happens is the cathode node voltage floats up and down with the signal, a little bit. Now since the tube only amplifies the VOLTAGE DIFFERENTIAL between cathode and the control grid, this means that if the cathode node voltage is floating in sync with the signal, there is less amplification. This effect happens most on the biggest amplitude frequencies, because they resemble DC the most.

If the cathode C has to discharge a long long time, it takes a long long time to recharge it, allowing the cathode node voltage lag.

Why does the cathode node voltage fluctuate in the first place? Well, same reason as the anode node voltage fluctuates. The tube doesn't know which resistor - anode resistor or cathode resistor - is supposed to be the output.




gug42 said:


> Yep I know. But it's to have exactly 6,3V whatever my local voltage could be



That's understandable. I'd go for 6.1V instead; doesn't hurt operation in any way and doubles lifespan of the tube.



gug42 said:


> I really want to heard thoses golden age tubes. I'm open to other stuff. 47 could be an option, in triode strapped modes. Indeed that's not the "good" or "best" approche, but ... well .... it's a pleasure, and, at the end pleasure is the objectif (if you see my point ?)



So what I'm hearing is you like the way the ST envelope tubes look? That's fine. Go for the 47 then, it's every bit as linear as any 45 or similar.

But I'd suggest testing new circuit topologies with ugly TV sweep tubes first. After you've got them working, then bring in the pretty tubes with difficult PSUs.



gug42 said:


> Did you have some triode strapped curves for the 47 ?




 

Please note 0V is not at the origo, but rather at the point where the first curve begins. Individual tubes will differ +- 15 % on anode resistance.



gug42 said:


> And for the Western Electric 32A, you'v got the "grid to cathode coupling" trick



Yes it's basically the "Ultrapath solution" applied to the grid. You can trade a large (and in those times very poor quality) electrolytic for a nice high quality film cap (or paper in oil in those days).



baronbeehive said:


> Right thanks for the information, beginning to understand the functionality of the CCS.



The FET needs about 4.5V positive on the gate to start conducting. The higher the gate voltage, the more it conducts.

The Darlington pair needs a certain positive base voltage to start conducting.

Remember Ohm's law. Look at the resistor above the Darlington pair, let's call it the R. At rest the FET gate is at B+; since there is no current thru the R (the Darlington pair is basically 'open', not conducting) there is no voltage drop across the R.

Once there is current thru the pair, and thus, thru the R, there is a voltage drop across the R. 

So, the gate voltage lowers. FET conducts less current. There is a smaller voltage drop across the sense R underneath the FET.

This means the base voltage for the pair is lower, meaning it conducts less current. Less current thru the R means FET gate voltage rises -> FET conducts more -> more current and thus voltage across the sense R -> higher Darlington pair base voltage -> Darlington pair conducts more -> more current thru the R -> FET gate voltage drops -> FET conducts less current etc etc ad infinitum.

It doesn't actually oscillate like this (best case scenario...), but rather it stabilizes so that any change in the feedback loop is very strongly resisted.

Every feedback loop contains a time paradox, so it's rather difficult to fully imagine. Don't think about how the loop is first set up, at power on. You'll hurt your brain; I know I cannot imagine it. Which component needs to conduct first?

The Darlington pair and the FET work in a see-saw. If one begins to conduct more, the other conducts less. But each has their input at the output of the other (the pair is set up like a normal gain stage, with 'anode' output, the FET is a source follower).

This is inside the loop; looking in from outside all you can see is the FET changing the voltage across itself. When the FET gate voltage changes, this also changes the voltage across the FET as well as how much current it is conducting. This effect is what makes the CCS useful in a LTP circuit. It floats the cathode node voltage to achieve constant current. Cathode node voltage changes tubes' biases. Tube biases change the voltage conditions inside the tube.



baronbeehive said:


> Ah, interesting. In that case gug42 should notice the missing frequencies. Strange that he said that the treble was almost too much.



Possibly some high frequency distortion.


----------



## baronbeehive

MrCurwen said:


> Every feedback loop contains a time paradox, so it's rather difficult to fully imagine. Don't think about how the loop is first set up, at power on. You'll hurt your brain; I know I cannot imagine it. Which component needs to conduct first?
> 
> The Darlington pair and the FET work in a see-saw. If one begins to conduct more, the other conducts less. But each has their input at the output of the other (the pair is set up like a normal gain stage, with 'anode' output, the FET is a source follower).
> 
> This is inside the loop; looking in from outside all you can see is the FET changing the voltage across itself. When the FET gate voltage changes, this also changes the voltage across the FET as well as how much current it is conducting. This effect is what makes the CCS useful in a LTP circuit. It floats the cathode node voltage to achieve constant current. Cathode node voltage changes tubes' biases. Tube biases change the voltage conditions inside the tube.



I'm trying not to think about it lol, not hard for me.

Yes, I thought there must be some sort of dynamic interplay going on inside the CCS to achieve balance, but it's interesting having the filter part of it coming into play to clean up anything bad at the source of the driver stage as well.



MrCurwen said:


> Possibly some high frequency distortion.



Yes, way back in the beginning.... ah 10 years ago now, when I got the LD I used it to amplify my ipod classic and was impressed, but it in no way compares with a proper clean source that I got some time after that. I realised I was amplifying garbage, noise and distortion! Anyway all that's prehistory now.

I will go on putting my order together today with the proper parts for when I'm ready to implement it. Nothing much else to do atm we're snowed under, something that rarely happens here!


----------



## gug42 (Mar 1, 2018)

Hello,



MrCurwen said:


> Do you plan to mod your existing amp or build a completely new one?



Hum, If  I can, economically speaking, I'd like to start a new one.



MrCurwen said:


> 1) not having DC current thru the OT (fixes the bass issue completely)



So a Push-Pull in class A ? 
But loosing some microdetails when the signal cross the tubes ?



MrCurwen said:


> 2) driving the OT primary from a low output impedance source (fixes the high frequency issue).



I have read that a requirement is a x3 ratio between tube impedance (Ri) and Z presented at the tube by the transformer ?


MrCurwen said:


> Grid current is the umbrella term for parasitic properties of tube control grids. They generally require some current to satisfy. Imagine there is a capacitor inside the tube between control grid and cathode, and also control grid and anode. These capacitors in conjuction with other circuitry around the control grid act as low pass filters, dampening transients and often dampening high frequency response.
> 
> The most common comments people give upon fixing this grid current insufficiency problem are that the sound is "more airy", "more 3D" and "faster". So, high frequency response and transient response are improved in technical terms.
> 
> ...



Thank you, I will need to re-read this multiple time 



MrCurwen said:


> Yes it's basically the "Ultrapath solution" applied to the grid. You can trade a large (and in those times very poor quality) electrolytic for a nice high quality film cap (or paper in oil in those days).



I'm using a 35 uF mkp (so PP film capacitor)

Thank you for the graph. 
Well I will think but after some reflexion ... the 4P1L could be a very good option for my need ! 
Evryone says that's a damm good tube. What is the internal impedance of the 4P1L in triode ?

Thank you I will take some times and find the times to work on the next one. I will surely post a thread  

Regards


----------



## MrCurwen

gug42 said:


> Hum, If I can, economically speaking, I'd like to start a new one.



I'm cheap, so my specialty is getting maximum sound quality at the lowest possible price. Best results can be had much cheaper than you probably think at the moment! 



gug42 said:


> So a Push-Pull in class A ?
> But loosing some microdetails when the signal cross the tubes ?



Retro push-pull class A still has DC current thru the primary, only in a kind of sort of balanced way so as to cancel the magnetic bias. What I mean is no DC current at all. 



gug42 said:


> I have read that a requirement is a x3 ratio between tube impedance (Ri) and Z presented at the tube by the transformer ?



Yes that's the old time rule. What I prefer is about 20 to 50 ohms output impedance driving a 10k primary. Sounds like there's no OT there at all!



gug42 said:


> Thank you, I will need to re-read this multiple time



Basically it's this: grids eat current, especially at transients. If sufficient current is not available, transients sound lazy. 

RC cathode bias (with a resistor and a cap bypassing it) always takes some definition and force (transient impacts) out of bass register.

Solutions: drive hungry grids with a low output impedance; use fixed grid bias.



gug42 said:


> Well I will think but after some reflexion ... the 4P1L could be a very good option for my need !



Yes. I'd still suggest going with 6P31S. It is a very very good sounding linear tube. You can upgrade to 4P1L later if you wish.



gug42 said:


> Evryone says that's a damm good tube. What is the internal impedance of the 4P1L in triode ?



Anode resistance is about 1k, maybe 1.2k or something like that.


----------



## baronbeehive (Mar 2, 2018)

Just trying to get a handle on this CCS.

I've looked at the FET specs for the IRF830APBF and I'm assuming they're the same for that type of FET. They all seem to list the specs slightly differently but from what I can gather the max gate source voltage is 30V, min is 2V, and the threshold voltage is 4.5V, as MrCurwen said.

For the Transistor, specs for the 2N2222 are, collector-emitter voltage: 40V, collector-base voltage: 75V, and emitter-base voltage: 6V. I'm assuming the transistor pair start conducting at 6V then.

The formula for the resistance value is 1.16 / R = desired I, or 1.13/R = desired l. I don't know how this is related to the base voltage of the 2N2222. I see that the formula comes from keeping the transistor pair at the exact threshold of conductance to stabilize the CCS, where it stops oscillating I assume. This is the point I was making about whether to take the desired CCS current value from a measurement from the board or from the parts spec ie from the CCS requirements. Anyway MrCurwen said that the current at the CCS is below 2mA, which is at each CCS I assume. This doesn't agree with what Sonic said about his I value being 2.37mA. So do I take the Sonic value, or if not where do I get the value from on my amp?

I'm a lot happier about the interaction between the transistor pair and the FET now after MrCurwen's explanation!


----------



## MrCurwen

baronbeehive said:


> For the Transistor, specs for the 2N2222 are, collector-emitter voltage: 40V, collector-base voltage: 75V, and emitter-base voltage: 6V. I'm assuming the transistor pair start conducting at 6V then.



These are breakdown voltages.



baronbeehive said:


> The formula for the resistance value is 1.16 / R = desired I, or 1.13/R = desired l. I don't know how this is related to the base voltage of the 2N2222



Look at page 2: http://www.farnell.com/datasheets/296640.pdf (don't worry, it's the same part, just the old metal envelope)

Saturation voltage 0.6V at 15mA, and it decreases when current decreases (we're looking at 1mA or so here). Also Darlington is configured so that the saturation voltages are stacked (both transistors need to be turned on), so that adds up to about 1.13 or so. It does depend a bit on what production batch and manufacturer you get.

Once again, it's not so sensitive. Just use 1.14 or 1.15 or whatever. Even if you use 0.1% resistors, the FET and the transistors have temperature coefficients, so the current is never going to be 100.00% where you plan it to be. Close enough is good enough.



baronbeehive said:


> Anyway MrCurwen said that the current at the CCS is below 2mA, which is at each CCS I assume. This doesn't agree with what Sonic said about his I value being 2.37mA. So do I take the Sonic value, or if not where do I get the value from on my amp?



I don't know what the context is for my statement. But you can just pick a current you like, and use the formula. It'll be ok. 0.3mA here or there is not going to matter much.



baronbeehive said:


> I'm a lot happier about the interaction between the transistor pair and the FET now after MrCurwen's explanation!



I'm very happy to hear that! 

Have you thought about the external functioning of the CCS? As in, imagine it's a module, a box dropped in the circuit; what does it do, what is it's function in the circuit?


----------



## baronbeehive

MrCurwen said:


> These are breakdown voltages.
> 
> 
> 
> ...



I don't want to hog this thread too much so I'll keep it simple.

Not sure what saturation voltage is, is it max voltage handled, is it optimum voltage for the stabilization of current, I don't know. The ImA or 1.13mA, is that the amount of current the CCS can use to keep everything stable, I don't think so because the test condition specified up to 500mA, so I will stop babbling, until I know more I'm at my limits atm, sorry.

I've tried several options for calculating R:

1.15/3.0=.38
1.15/2.0=.58
1.13/3.0=.38
1.13/2.0=.57
1.16/2.0=.58
1.16/3.0=.39

You're right they don't diverge that much, at least it doesn't look like it to me so I will probably pick a value of R somewhere between .38 and .58.

I have only thought superficially about the CCS in a circuit, obviously it needs to iron out differences when the balanced signals are combined, and it does this within the limits defined by the sense resistor. When the current changes the voltage also changes in the same direction after it passes through the CCS, and when this change is noted in the circuit it adjusts again to keep the current the same.


----------



## SonicTrance

I don’t think MrCurwen gives the CCS enough credit. In my experience it’s very accurate and sensitive. I use 1.16 when calculating and it’s always very close IRL. Also, baron, you need to calculate in amps, not mA. So move your comma three places to the right and you have your sense R.


----------



## bloodhawk

SonicTrance said:


> I don’t think MrCurwen gives the CCS enough credit. In my experience it’s very accurate and sensitive. I use 1.16 when calculating and it’s always very close IRL. Also, baron, you need to calculate in amps, not mA. So move your comma three places to the right and you have your sense R.



Weird ass question, but what type of sonic change did you notice after adding the CCS module?


----------



## SonicTrance

bloodhawk said:


> Weird ass question, but what type of sonic change did you notice after adding the CCS module?


Can’t really tell you, unfortunately. I only listened for a short while after I did the mod. I believe I wrote some impressions, not sure. The LD doesn’t get any use. I only use my DIY amp, the modern LTP.


----------



## bloodhawk

SonicTrance said:


> Can’t really tell you, unfortunately. I only listened for a short while after I did the mod. I believe I wrote some impressions, not sure. The LD doesn’t get any use. I only use my DIY amp, the modern LTP.



Ah gtocha. Ill go back and see if i can find anything. I have been reading up on the LTP schematics and trying to plan things out. Wish i got some time off from work ... sigh...


----------



## baronbeehive (Mar 2, 2018)

SonicTrance said:


> I don’t think MrCurwen gives the CCS enough credit. In my experience it’s very accurate and sensitive. I use 1.16 when calculating and it’s always very close IRL. Also, baron, you need to calculate in amps, not mA. So move your comma three places to the right and you have your sense R.



Right!

But he's correct the sensitivity is such that the potential R's only vary slightly whether you use the lower of the higher figure:

0.00113/0.003 = 0.38
0.00113/0.002 = 0.57
0.00116/0.003 = 0.39
0.00116/0.002 = 0.58

Ha, must be something wrong with my maths, R is still .38 etc!

So why did you arrive at a figure of 2.37mA for your desired CCS current value? I still can't make this out.


----------



## MrCurwen

baronbeehive said:


> I don't want to hog this thread too much so I'll keep it simple.



I think since several people are considering doing the CCS mod, it's beneficial to iron this thing out in full. I just got some ideas on how to explain this LTP scheme while taking my evening walk along the frozen solid seashore. I'll do that tomorrow.



baronbeehive said:


> Not sure what saturation voltage is



Just think threshold voltage. No need to complicate this too much; let's just say the Darlington pair needs 1.16V between top base and ground to conduct current and leave it at that.



baronbeehive said:


> The ImA or 1.13mA, is that the amount of current the CCS can use to keep everything stable, I don't think so because the test condition specified up to 500mA, so I will stop babbling, until I know more I'm at my limits atm, sorry.



I have no idea what you wrote here. Let's just stick to basics and move from there.



SonicTrance said:


> I don’t think MrCurwen gives the CCS enough credit. In my experience it’s very accurate and sensitive. I use 1.16 when calculating and it’s always very close IRL



You're right. 

I'm just trying to move past this issue of base voltage threshold, because if we are to go deep on it, there's a lot that goes into it. For example the threshold voltage changes if you change

1) B+

2) the R above the pair

because the threshold voltage is dependent on current thru the pair. You've had about similar conditions always, so it's stable.

It's not relevant at all to this discussion, but when I had an amp with a B+ of 650V, the CCS formula was way off. Circuit functioned just fine though. That's when I learned not to be too alarmed if it's a bit off.

Also I used to use the retro metal envelope 2N2222's, because I got a bunch of them in a sale way back. They have a bit different ratings; one of the base max voltages is 5V instead of 6V etc., also the threshold is a few percent off. 


Long story short; if you use brand new 2N2222A with normal range B+ and normal range Ic, you're going to be spot on with 1.16V base threshold. This is a non-issue. Let's just call it 1.16 and be done with it. If somebody comes back with "I got 10% different current in this one circuit I tried, your formula is bunk" they can find this message.

Sonic already pointed out the error in the calculations. It's just Ohm's Law; voltage / resistance = current, units are V, ohm, A.


----------



## SonicTrance

baronbeehive said:


> Right!
> 
> But he's correct the sensitivity is such that the potential R's only vary slightly between lowest and highest desired CCS current:
> 
> ...


Yes, your math is wrong. Formula is 1.16 / Iccs (A) = senseR. 1.16 / 0.0024 = 483 ohms. 
I tried different currents and arrived at 1.2 mA of bias current. That gave me enough B+ while still being in the linear part of the ECC35 curves.


----------



## MrCurwen

baronbeehive said:


> Ha, must be something wrong with my maths, R is still .38 etc!



Yes.

Use volts; 1.16V, amperes; 0.0024A, and you get ohms; 483.3 ohms. You could for example use 470 ohms, or parallel 2 1k and get 500 ohms.



baronbeehive said:


> So why did you arrive at a figure of 2.37mA for your desired CCS current value? I still can't make this out.



1) Draw a load line with the anode loads you plan to use.

2) Find a nice bias point with as symmetric swings to both sides (left and right) from the bias point.

3) There you are.


----------



## baronbeehive

bloodhawk said:


> Weird ass question, but what type of sonic change did you notice after adding the CCS module?






SonicTrance said:


> Can’t really tell you, unfortunately. I only listened for a short while after I did the mod. I believe I wrote some impressions, not sure. The LD doesn’t get any use. I only use my DIY amp, the modern LTP.



Ha ha, you don't expect Sonic to tell you after he's spent so much time building his LTP do you?


----------



## baronbeehive

SonicTrance said:


> Yes, your math is wrong. Formula is 1.16 / Iccs (A) = senseR. 1.16 / 0.0024 = 483 ohms.
> I tried different currents and arrived at 1.2 mA of bias current. That gave me enough B+ while still being in the linear part of the ECC35 curves.



Oh, right I thought the 1.16 value was mA as well.


----------



## MrCurwen

baronbeehive said:


> Ha ha, you don't expect Sonic to tell you after he's spent so much time building his LTP do you?



I certainly do. Why wouldn't he?

My experience from building and modding all kinds of things predicts this;

1) transients stayd about the same (sound is "as fast" as it was before)

2) a little bit more ambience, "3D / holographic"

3) mostly just a bit more clean overall, more definition.

Well, these things can be difficult to put into words. One mans definition is anothers ambience.

How about this: The sound gets cleaner.


----------



## bloodhawk

MrCurwen said:


> I certainly do. Why wouldn't he?
> 
> My experience from building and modding all kinds of things predicts this;
> 
> ...



LOL just what i was looking for!


----------



## baronbeehive

MrCurwen said:


> I certainly do. Why wouldn't he?



I think he's discarded his LD like an old raincoat lol !


----------



## bloodhawk

baronbeehive said:


> I think he's discarded his LD like an old raincoat lol !



If the LPT build had wiring instructions, i would build it within 2 weeks 

But the best things in life need more effort put in


----------



## baronbeehive (Mar 2, 2018)

MrCurwen said:


> Saturation voltage 0.6V at 15mA, and it decreases when current decreases (we're looking at 1mA or so here). Also Darlington is configured so that the saturation voltages are stacked (both transistors need to be turned on), so that adds up to about 1.13 or so. It does depend a bit on what production batch and manufacturer you get.



I think I've found the source of one of my confusions, where I thought that the 1.16 value was mA, when you said "we're looking at 1mA or so here"... then you said "so that adds up to about 1.13 or so"..... sorry I'm easily confused. I should have realized we're dealing with Ohm's Law!


----------



## baronbeehive

bloodhawk said:


> If the LPT build had wiring instructions, i would build it within 2 weeks
> 
> But the best things in life need more effort put in



If you can wait till I've done it, at least you'll know how not to do it!


----------



## bloodhawk

baronbeehive said:


> If you can wait till I've done it, at least you'll know how not to do it!



LOL.

Im sure ill end up building one within the next 2 months at the most


----------



## baronbeehive (Mar 2, 2018)

MrCurwen said:


> I think since several people are considering doing the CCS mod, it's beneficial to iron this thing out in full. I just got some ideas on how to explain this LTP scheme while taking my evening walk along the frozen solid seashore. I'll do that tomorrow.



Better you than me! We're not used to the -10 centigrade figures we're getting atm, some places here are colder than in the Arctic, hoping to go into positive territory sometime tomorrow then I can venture out again!



MrCurwen said:


> Yes.
> 
> Use volts; 1.16V, amperes; 0.0024A, and you get ohms; 483.3 ohms. You could for example use 470 ohms, or parallel 2 1k and get 500 ohms.
> 
> ...



Thank you, now I know.

Edit: Oh so we might need another switch for different tubes, the whole thing will end up look like the cockpit of an airliner.

Just joking, so it looks like we're limiting ourselves to one set of tubes.


----------



## baronbeehive (Mar 2, 2018)

bloodhawk said:


> LOL.
> 
> Im sure ill end up building one within the next 2 months at the most



It looks a piece of cake, it's just getting the values right.

I don't intend to do it just yet because as I said I will be hard wiring the impedance mod in for 421A tubes and I can't do that until I get the full set so I intend to do all the remaining mods at the same time.


----------



## baronbeehive (Mar 5, 2018)

OK, so I'm trying to do some load lines for the upcoming CCS implementation and also for experimenting with the anode values for the driver stage, I think I'm Ok on that but I can't figure out how to calculate or set B+ for the load lines, until I know that I can't make any progress. I can set a value easily enough, for example 100V which I think it is for the power stage, but I really want to know what the specific value is on both stages and how it varies with different tubes. I can't see the value anywhere on the schematics.

Sorry for the simple question.


----------



## bloodhawk

Question for the peeps who know the workings of this amp way better than i ever will -

How do track channel imbalance ?

A friend of mine recently did the same mods as i did (Just used Supreme SGO's instead of the Audyn's). And he is having a very slight channel imbalance with the right channel being about 2-3% lower in volume. I tested the following thugs out so far -

- Tubes, multiple sets of power and driver tubes. Biasing is working fine and is always matched.
Along with testing the tubes in my amp.

- Different cables for his HD800's. 

- The imbalance isn't as audible on the SE output , only on balanced out is it very apparent. 

- Before he swapped out the stock parts he made sure to measure all the caps and resistors to make sure the values are well within the tolerances. 

- I opened up his amp to double check that all the wiring was fine. 

- ONE THING he did good up on was with one it the Mlytic AG+ caps. When he was bending on of the out leads, it snapped off. Now since those leads seems to be welded or soldered using really high temperature , he didnt want to use a soldering iron. So he soldered it with the appropriate lead and made sure it was making a decent physical contact with the caps pad. 
When I measured the capacitance values on that cap they came out fine. 

Any idea what could be the reason for the I'm balance ? 

Also which one of those Mlytic caps is handling the right channel ? Top( close to the connectors?) Or bottom ?


----------



## MrCurwen

My very easily understandable LTP theory post is late, but still forthcoming.



baronbeehive said:


> OK, so I'm trying to do some load lines for the upcoming CCS implementation and also for experimenting with the anode values for the driver stage, I think I'm Ok on that but I can't figure out how to calculate or set B+ for the load lines, until I know that I can't make any progress.



I think it was 170V. Are you using some calculator or drawing by 'hand' in Paint? 



baronbeehive said:


> I really want to know what the specific value is on both stages and how it varies with different tubes



B+ should not vary at all with different tubes. Or, do you mean with different tube types? Still, it shouldn't vary by more than a few volts.



bloodhawk said:


> And he is having a very slight channel imbalance with the right channel being about 2-3% lower in volume.



2 or 3 % volume difference is not audible by anybody. But, if you have an audible difference I hope somebody can help you.


----------



## baronbeehive (Mar 5, 2018)

bloodhawk said:


> - ONE THING he did good up on was with one it the Mlytic AG+ caps. When he was bending on of the out leads, it snapped off. Now since those leads seems to be welded or soldered using really high temperature , he didnt want to use a soldering iron. So he soldered it with the appropriate lead and made sure it was making a decent physical contact with the caps pad.
> When I measured the capacitance values on that cap they came out fine.
> 
> Any idea what could be the reason for the I'm balance ?
> ...



If I remember right both caps feed both channels, if I'm wrong someone will correct me, I don't want to give you false information.

You probably just need a good soldering iron to handle the thicker wires there. I'm assuming that the trace hasn't come up from the board when that happened. You should check that the pad is still making contact with the trace with a multimeter. I think we all had problems with removing these caps.

But the first thing I would do to eliminate things would be check cables leading from your gear to make sure it's making good contact, not loose or fraying. Then swap headphones, then if you've tried swapping tubes between channels it is possible to check the strength of the 2 channels inside the amp but I hesitate to recommend this unless you know what you are doing because it's potentially lethal, so I will leave that to others to suggest. But if both bias meters are reading the same then I don't know.

So how good are you guys on circuit fault finding and testing. Did you do the work yourselves?


----------



## baronbeehive (Mar 5, 2018)

MrCurwen said:


> My very easily understandable LTP theory post is late, but still forthcoming.



I'm holding my breath!



MrCurwen said:


> I think it was 170V. Are you using some calculator or drawing by 'hand' in Paint?


I intend to draw in Paint. I thought I would work backwards and draw some sample lines and calculate from that, mixing in a few "odd" looking operating points, ie. not obviously linear looking just for fun.




MrCurwen said:


> B+ should not vary at all with different tubes. Or, do you mean with different tube types? Still, it shouldn't vary by more than a few volts.



The reason I ask was because I was not sure that B+ is always the same, I thought that once it was coming into the amp from the power supply it would change as it traversed the resistors in the way for example. Given that I would assume this, it must be important where you measure B+. Also is it the same for the driver and power stage

I've looked at examples in this thread and noticed that the load lines are all coming from a different B+. Also something Sonic said about choosing a value for the CCS that gave him enough B+ implying that it would change.


----------



## bloodhawk

baronbeehive said:


> If I remember right both caps feed both channels, if I'm wrong someone will correct me, I don't want to give you false information.
> 
> You probably just need a good soldering iron to handle the thicker wires there. I'm assuming that the trace hasn't come up from the board when that happened. You should check that the pad is still making contact with the trace with a multimeter. I think we all had problems with removing these caps.
> 
> ...



Yeah we tried used a pretty beefy soldering iron to try and solder it back. But didnt really want to make contact for too long with fear of damaging the capacitor. 

The trace is perfectly fine on both sides, as i myself removed the stock capacitors for him. Even tested the traces to make sure nothing was damaged. For good measure i told him to solder the single core wire through the holes on both sides, which he did and continuity was perfect. 
All cables have been verified unfortunately none of them was loose or frayed. Even tried different headphones to rule the headphones and the respective cable as being the cause. Im pretty decent at finding faults, but have been out of touch with hardcore circuit building and troubleshooting for a whole, and have not been able to find voltage references for this amp that i can use to check if everything is as it should be. 
From the amount of trouble shooting i did on his amp, i re tinned all his joints, double check resistor and capacitor values, etc. Everything seems to be on points. He himself isnt new to electronics or soldering , but neither of us know this amp inside out as much as some of the more knowledgeable members here.


----------



## baronbeehive (Mar 5, 2018)

bloodhawk said:


> Yeah we tried used a pretty beefy soldering iron to try and solder it back. But didnt really want to make contact for too long with fear of damaging the capacitor.
> 
> All cables have been verified unfortunately none of them was loose or frayed. Even tried different headphones to rule the headphones and the respective cable as being the cause. Im pretty decent at finding faults, but have been out of touch with hardcore circuit building and troubleshooting for a whole, and have not been able to find voltage references for this amp that i can use to check if everything is as it should be.
> From the amount of trouble shooting i did on his amp, i re tinned all his joints, double check resistor and capacitor values, etc. Everything seems to be on points. He himself isnt new to electronics or soldering , but neither of us know this amp inside out as much as some of the more knowledgeable members here.



OK, fine I know you've worked on your BH Crack, I just don't want to encourage beginners to do something dangerous lol!

So you could check the voltages on each of the 4 anode resistors, that's the 330R resistors, on the bottom of the board, ie. when you take the bottom off, and the cathode bypasses. You should be able to see at once if one of them is  out.

*Safety Note!!!!! You  know you don't touch anything inside while it's on except with a  multimeter.... I have to say that with new members!
*
Edit: The tubes are self biasing but if there is something wrong it would show up.


----------



## bloodhawk

baronbeehive said:


> OK, fine I know you've worked on your BH Crack, I just don't want to encourage beginners to do something dangerous lol!
> 
> So you could check the voltages on each of the 4 anode resistors, that's the 330R resistors, on the bottom of the board, ie. when you take the bottom off, and the cathode bypasses. You should be able to see at once if one of them is  out.
> 
> ...




Totally understandable 

Gotcha ill try and stop by at his place either today after work, if not then definitely over the weekend. Thank you for the pointer on what to check for first. 

Always! While doing these type of live readings i hook up insulated alligator clips and then use those to measure the terminals after turning on the amp.

Thanks again.


----------



## MrCurwen

baronbeehive said:


> The reason I ask was because I was not sure that B+ is always the same, I thought that once it was coming into the amp from the power supply it would change as it traversed the resistors in the way for example. Given that I would assume this, it must be important where you measure B+. Also is it the same for the driver and power stage



In this amp it's not the same for the driver and the power stage. Power stage has B+ of 100V and also B- of 100V. 

B+ is measured at node of the last cap feeding the circuit. Any resistors after that are part of the audio circuit and not the PSU. They do not change B+, they change some other voltage inside the circuit.



baronbeehive said:


> Also something Sonic said about choosing a value for the CCS that gave him enough B+ implying that it would change.



He meant voltage headroom for the tube to operate well enough.


One of the main goals of PSU design is to make the B+ not change at all. It's very important for a good sounding amp to have solid B+ (and other supplies if applicable).


----------



## Maxx134 (Mar 5, 2018)

baronbeehive said:


> The reason I ask was because I was not sure that B+ is always the same,


Sadly, because of the driver stage RCRC filter,
There is a voltage drop which varies with the different tubes plate resistance (Rp),
So there are slightly different B+ voltage at the anode resistors and the range of difference of the tubes I tested was around 10v .

That's when me and Sonic and Ridge78 were in PMs almost 2 yrs ago....
Dam, has it been that long??

Oh well, that's around the time we decided that the last driver stage PSU resistor can be lowered from 3k3 to 1k with no adverse effects and gain some precious little voltage gains...
At the time, we all had upgraded the stock 33uf electrolytic (by the anode resistors) with film caps, which can do better job with less capacitance.
I dunno why I even open that "can of worms" discussion, but replacement of those caps already described in first page of thread.




bloodhawk said:


> Yeah we tried used a pretty beefy soldering iron to try and solder it back. But didnt really want to make contact for too long with fear of damaging the capacitor.


This can be simpler...
If you want to rule out the caps, simply swap them around to other channel.(right to left & vise versa)
Caps are usually durable but never know if the casing is compramised by accidentall side melting of a soldering iron.

If you want to rule out the circuit,
Use tester and measure the good side voltages against the bad side on same points,
As the circuit is not mirrored, but same layout on both sides.

If all turns out well I would then look into the wiring to the volume pot.
Re-tinning the solder spots there or anywhere can have made tiny solder droplets splatter on board.
Airgun is a good tool for cleaning out debree.


----------



## bloodhawk

Maxx134 said:


> This can be simpler...
> If you want to rule out the caps, simply swap them around to other channel.(right to left & vise versa)
> Caps are usually durable but never know if the casing is compramised by accidentall side melting of a soldering iron.
> 
> ...



Hmm thats something i want to avoid doing. Since what he told me it was a real pain for him to solder the wires into the bent leads and make sure that the detached lead also made contact with the capacitor pad. Ill see if i can use one of my caps. 
Yeah, thats also one thing im very unsure off. How much abuse these can handle outside of a circuit. 

Ill do the measurements in a day or 2 asa i get some time after work to stop by at his place. Any specific terminal points you suggest that i should check the voltages between ?

I actually thought of the same thing, and did a through check to make sure there weren't any shorts or stray solder droplets between caps/resistors etc. Everything was clean.

Thanks for all the suggestions Max! Ill check and post update you guys.


----------



## SonicTrance

baronbeehive said:


> I think I'm Ok on that but I can't figure out how to calculate or set B+ for the load lines





SonicTrance said:


> These are the settings I ended up with:
> 
> B+: 155 V
> Ia: 1.2 mA (no reason to go lower, this gave me enough voltage and sounded just as good as 1.75 mA)
> ...


To draw a load line like this you first measure B+. It's easiest to measure at top of anode resistors (the lead closest to the front of the amp). I measured 155 V as you can see above. There's your point on the Va horisontal axis. Then calculate the maximum plate current. Ohms law: B+ / plate resistor = 155 / 33k = 4.7 mA, there's your point on the mA vertical axis. Then simply draw a line between the two points and there's your load line.

Plate current is set to 1.2 mA through the CCS. Mark that point on the mA axis. Measure or calculate the Va. Remember that Va is the DIFFERENCE between anode and cathode, NOT anode to ground. Same thing with the grid voltage, Vg. It's the difference between grid and cathode. I measured about 114 V between anode and cathode. There's your second point on the Va axis. Now simply draw a line from the 1.2 mA point until you hit the load line, then go straight down. You should then hit the measured Va (these curves are not exact so ballpark is enough)



baronbeehive said:


> Also something Sonic said about choosing a value for the CCS that gave him enough B+ implying that it would change.


Yes! Since this ps is not regulated it drops significantly when more current is pulled. That's why I lowered the last R in the ps to 750R. I would not recommend you pull anymore current then this. But feel free to experiment, nothing bad is going to happen from that, except maybe bad sound, lol.


----------



## baronbeehive (Mar 6, 2018)

bloodhawk said:


> Hmm thats something i want to avoid doing. Since what he told me it was a real pain for him to solder the wires into the bent leads and make sure that the detached lead also made contact with the capacitor pad.



I had this problem with my other amp trying to solder the thick Audyn leads. I nearly bought another soldering iron but as a last resort I thoroughly cleaned the solder tip, tried again with a huge dollop of solder which was enough to transfer the heat so that I could do the job this time, and I only have a 25W iron so you should be able to manage lol.

Re: the load lines, thanks for the replies guys, I've done some already but was stuck at the start getting B+ right.

I intend to do lines for the TS6SL7 and my new favourite the GE 12SL7 which has same specs as the 6SL7. I'm not planning on getting any other driver tubes now.Then for power tubes, the RCA 6AS7G, WE 421A, Thomson 6080WA and Svetlana 6AS7. The main point of doing lines for power tubes is to see what they look like as potential candidates for the high gain setting. Does anybody know of any very linear power tubes that could work on high gain setting? I'm thinking that the closer we can get  to open loop and then try the anode values the better sound we can get..... maybe!


----------



## MrCurwen

I've finished making the sims and pictures for my thing. I'll write it up later tonight.

baronbeehive if you are doing loadlines for the output tubes, what load are you using? The WCF is a cathode follower system, the load is the bottom tube. You cannot simply use a static anode resistance or something like that.

Or, maybe you're just using arbitrary loads, just to see what they look like. That's another thing then.


----------



## Maxx134 (Mar 6, 2018)

bloodhawk said:


> Hmm thats something i want to avoid doing. Since what he told me it was a real pain for him to solder the wires into the bent leads and make sure that the detached lead also made contact with the capacitor pad. Ill see if i can use one of my caps


Woops I forgot to mention that you can use a capacitance tester on them , probably without even having to disconnect from board (in that coupling capacitor stage.)
Although it wont read accurate in board, you can compare any difference to other side...




baronbeehive said:


> I intend to do lines for the TS6SL7 and my new favourite the GE 12SL7


The TS6C8G was my top tube for MK8,
And the 12SL7 was my top tube for the APPJ amp.
Really great tubes.
I tried a bunch.



baronbeehive said:


> potential candidates for the high gain setting.


I not sure why,  but MK6 has more distortion on high gain than MK8,
 because mine sounds better on high gain.
The only difference is the output tubes.

This aludes to both tube choice, and their grid resistor , so if that changed, then the Cathode must change appropriately to keep similar bias...
Hmmm
Not sure how less NFB would change the whole amp.
Looks like another project idea lol.


----------



## Maxx134

MrCurwen said:


> baronbeehive if you are doing loadlines for the output tubes, what load are you using? The WCF is a cathode follower system, the load is the bottom tube. You cannot simply use a static anode resistance or something like that.


Yeah, I believe he was doing the driver tube but did make mention of output tube which I assume was a different question about using less NFB


----------



## baronbeehive

Maxx134 said:


> Yeah, I believe he was doing the driver tube but did make mention of output tube which I assume was a different question about using less NFB



Yes, maybe I could just try some different output tubes to see if any are linear enough to work on high gain then. Perhaps it won't work on the MKVI.


----------



## MrCurwen

The output section is not doing any amplification. Gain of the stage is 0.55. 

It's a follower, not a gain stage.


----------



## baronbeehive (Mar 6, 2018)

Maxx134 said:


> The TS6C8G was my top tube for MK8,
> And the 12SL7 was my top tube for the APPJ amp.
> Really great tubes.
> I tried a bunch.



I'm not changing my Philips and Mazdas, they sound wonderful on the APPJ ...and they've finally knocked my Tungsol off top spot, just like the GE has done on my LD!

Re: the 12SL7's, I found the Tungsol just a bit too laid back, and the GE too sharp on the APPJ, whereas the Philips and Mazda are both extremely musical.



Maxx134 said:


> Not sure how less NFB would change the whole amp.
> Looks like another project idea lol



Maybe, yes.

So if it's only a follower, no point on doing load lines then.

Edit: The idea of working on the power tubes in high gain, as well as the CCS, was just to up the level of articulation and snappyness as much as possible within the limits of the LD. It already has improved with the GE, the sound is that much cleaner now and if that can go up a notch, all well and good.

Forgot to mention, it might help if you use a bit of extra flux on old solder bloodhawk , may seem obvious but you need to try everything.


----------



## Maxx134

I believe the mk6 has greater potentiaI of trying output tubes..

was lucky that my MK8 had one other tube to try that was 9pin.
The Russian 6h6 tubes worked nice but had less output.
Regardless once I increased the bias it was more realistic and holographic over both my stock sovtek & Electro-Harmonic tubes,
And also my uber expensive 6h30dr tubes..

So I stayed with this combination that matches well...

So you could do similar to get a good match.
I would stay with the driver selection you have and then try what output tubes are to your liking.
Then find out what is optional bias for it.

I believe stock bias settings on output tubes may not be most optimal..


----------



## MrCurwen

baronbeehive said:


> So if it's only a follower, no point on doing load lines then.



Well, let me clarify:

It's completely normal and useful to draw load lines for a cathode follower, exactly in the same manner as for a common cathode gain stage ('normal' gain stage with grid input and cathode at AC ground). 

However once you add an extra local feedback loop, you cannot draw a load line anymore, at least not very easily. It's now a complex (at least when compared to a normal follower) circuit. 

Basically it boils down to this; what ohm value of load would you use? It's not the static rp of the bottom tube, it's not the "anode resistor", what is it?

There's a solution to this but it's mathematical and complex, and I don't know it.


----------



## baronbeehive (Mar 6, 2018)

MrCurwen said:


> Well, let me clarify:
> 
> It's completely normal and useful to draw load lines for a cathode follower, exactly in the same manner as for a common cathode gain stage ('normal' gain stage with grid input and cathode at AC ground).
> 
> ...



You might be surprised to hear I don't know either!

I can see the problem of trying to formulate a value for something that's virtually undefinable.

But I assume that it's still possible to try to find a good linear power tube? Or do you think it's a waste of time trying to adjust the amp properly for the high gain setting? I appreciate the feedback is there for a reason but there may be a chance that the setting works well.


----------



## bloodhawk

Heya,

Anyone know to test if the channel imbalance is because of the pot without having to take the whole pot out? 

Also turns out the imbalance on my friends amp is also through the SE output as well.


----------



## MrCurwen

baronbeehive said:


> But I assume that it's still possible to try to find a good linear power tube and the adjust the grid resistor accordingly for a good fit? Or do you think it's a waste of time trying to adjust the amp properly for the high gain setting? I appreciate the feedback is there for a reason but there may be a chance that the setting works well.



Waste of time? Well, I don't know.

I don't understand what this grid stopper optimization is all about. It's a grid stopper?

I guess it could have some small effect on grid current, but not without drastic changes in values.

A follower is better with lower rp tubes, and grid current effects are smaller in some tubes than others. These are the two variables I see in play there. Not very big gain to be had all in all, I predict.

bloodhawk, could it be that the channels have different gain settings, i.e. different amounts of gNFB? Although that would lead to a much more audible balance difference than 2 to 3 percent.


----------



## baronbeehive

bloodhawk said:


> Heya,
> 
> Anyone know to test if the channel imbalance is because of the pot without having to take the whole pot out?
> 
> Also turns out the imbalance on my friends amp is also through the SE output as well.



Was is there before doing the mods?


----------



## bloodhawk

baronbeehive said:


> Was is there before doing the mods?



From what he told me, probably. But he didnt think much of it as he was really enjoying the amp. But once he noticed the imbalance, its super apparent.


----------



## bloodhawk (Mar 7, 2018)

So i had done some more testing last night at his place, and the right channel is definitely biasing lower than the left channel by 10-15mA .Not sure why the right channel meter was not showing this over the weekend. 

This is irrespective of 4 x tube sets that we tested.

Can someone tell me what to check for and exactly at what terminals?

 That would super helpful and appreciated


----------



## MrCurwen

bloodhawk:

If the bottom tube cathode resistor and capacitor are ok, it pretty much leaves the biasing chip.


----------



## MrCurwen

Ok so time to get into it. 

I really hope this explanation is easily understandable, so that everyone who is planning to try the CCS mod out can understand it. Please point out unclear points and I'll be happy to try and find another way to explain that part.

I've tried to explain the functioning of LTP a few times in this thread, but I think it's less than successful because one cannot jump in the middle of things, so to say. So I'll start from really basics and build on it. This is all good to know information anyway; all of it leads up to the final LTP scheme.



 

This is a triode stage. Without the resistor values we cannot know if it is a gain stage or a cathode follower.

If there is more resistance above the anode (R1) than below the cathode (R2), then it's a gain stage.

If R2 is bigger than R1, then it's a cathode follower.

When set up as a gain stage, the triode amplifies the voltage difference between control grid and cathode. 

This means that the triode has two (2) inputs; the grid, and the cathode. This is very important, we'll get back to this later.


First we'll set the stage up as a cathode follower:

 

R1 is unnecessary for the cathode follower, it is here to make a point. Sometimes anode stoppers are used for stability reasons or for some NFB reasons like in the White Cathode Follower in the LD.

So, most of the resistance that is in series with the tube is beneath the cathode, and there is a signal output taken from the cathode.

Let's look at the anode voltage:

 

It changes some 100mV. This is of course explained by Ohm's law; the 33k cathode load causes a load line with a lot of current variation, and the anode resistor is in series with the tube so Ohm's law dictates that since current is changing along with the tube's input signal, voltage across the anode resistor is changing.

But, of course it changes a lot more across the cathode resistor:

 

Cathode follower is supposed to follow the input signal, not amplify it. So, here we see an output of about 80+% of input signal. This is because of the 33k loadline, it's not that good.

The anode and cathode waves are from the same timeframe. You can see that they are antiphase; the anode wave is 180 degrees inverted in relation to the grid signal, and the cathode wave is not inverted, same phase as grid signal. This is very important later.

So, that's a cathode follower. Next we'll make a gain stage:

 

So basically we've just flipped the resistors top to bottom and vice versa. This scheme is very familiar for everybody I'm sure.

Is there amplification now? Let's look at the anode output:

 

Yes there is. The model I used here has a µ of about 20, and we can see the gain of this circuit is about 8. The 33k loadline is steep, but it's not that steep. What happened to the gain?

Let's look at the cathode:

 

It's swinging about 200mV. 

Now you have to understand that the tube does not know what is supposed to be it's output. Ohm's law produces these signals at the anode and cathode simply because there is resistance in series there.

We noted a bit earlier that the anode output is inverted phase, and the cathode output is non-inverted phase. So that means there is 2VPP at the grid, and 200mVPP at the cathode. Let's look at these superimposed:



Blue wave is cathode, green wave is grid, and red wave is anode output. 

The difference between grid and cathode is about 800mVPP, which is amplified to about 16VPP.

This effect is called cathode degeneration. It is known to affect frequency response, because the bigger the wave amplitude, the bigger the effect (on account of Ohm's law). Bass typically has bigger amplitude waves and treble has smaller amplitude waves, so this eats up some bass. It also affects dynamics (adds compression) because of the same thing.

Unbypassed or partially bypassed cathodes are used in guitar amps to add these things; compression and cut bass (prevents farty bass distortion).

The important thing here is to understand the way phase works here, and that the tube doesn't know what it's output is supposed to be.


Let's fix the cathode degeneration:

 

C2 should keep the cathode node at AC ground. It charges and discharges when needed to achieve this. Let's look at the cathode node now:

 

The wave has shrunk from 200mVPP to about 1mVPP. But, this is frequency dependent: these sims are all done at 1kHz, at 50Hz or 30Hz the results would be different (much worse).

We can also see there is some DC drift. This is because the capacitor has to charge thru the triode and the anode resistor. That's a lot of series resistance (and impedance) to feed thru. I even added some 50mS of simtime before Spice starts to record results, and it still isn't fully charged. 

This is a symptom of the reason why C2 cannot handle bass frequencies perfectly. Once it's discharged during a bass peak, it cannot instantly recharge. This means there is some cathode degeneration still going on, it's just (a lot) less than before. 

Now that the difference between grid signal and cathode wave is much bigger (because cathode is now at 'DC'), the anode output signal is also bigger:

 

About 30VPP, giving a gain of about 15. Sounds about right with the 33k anode load.

The important thing to understand here is WHY the gain is now bigger.


----------



## bloodhawk

MrCurwen said:


> bloodhawk:
> 
> If the bottom tube cathode resistor and capacitor are ok, it pretty much leaves the biasing chip.



Gotcha, so these would be the 330R resistors and the 220uF caps?


----------



## MrCurwen

bloodhawk, yes.

Back to tube theory:

So we've gone thru stages using cathode as output and anode as output. I've also said that the tube doesn't know which output it's supposed to use. Let's look at an extreme case of this:

 

This is called a concertina phase splitter, or alternatively a cathodyne phase splitter. (I think both of these come from HIFI manufacturer brand names.)

There is equal amount of resistance in series both above the tube and below the tube. Nothing is bypassed with a cap. Knowing what we just went thru in my previous message, what kind of an output do you now predict this produces?

Think about it for a second before looking at the next picture.

 

Did you get it right? This is exactly as theory would predict. Anode output is inverted, cathode non-inverted, and equal resistances produce equal amplitudes.

So it really is just a matter of Ohm's law, and the ratio between the anode and cathode resistances. The tube changes transconductance (meaning alters the amount of current that goes thru it), and the rest is just Ohm's law.

The concertina has very good properties on paper, (pretty much perfect balance), but it has some shortcomings. As you can see, the amplitude is compressed; 2VPP at grid produces 1.6VPP outputs. This reduces dynamics.

Also the anode and the cathode don't have equal output impedances (meaning they don't have equal ability to output current to load). This sim has 470k load on the other side of the capacitors, but in many real life cases there is a much harsher load there (especially on transients), and then bad things happen to the balance.

So this type of phase splitter is not ideal for transparent high fidelity sound reproduction. It's very commonly used in guitar amps though.


We know that triodes amplify the difference between grid and cathode voltage. In the previous part I stated right in the beginning that a triode has two inputs; grid and cathode.

We looked at a situation where cathode is at AC ground, so essentially grounded for signal purposes. What about this:

 

Would it work? There is a difference between grid and cathode voltage after all!

Let's look at the waves:

 

Grid is grounded of course, green is cathode at 2VPP and blue is anode at 36VPP! This gives a gain of about 18.

Works just as theory predicted. Triode amplifies difference between cathode and grid voltage. I keep banging on this particular drum because it is essential to the LTP operation.

As an aside, this kind of grounded grid amplifier was very common in radio frequency amplification as the first stage amplifying input from an antenna. The cathode resistor was replaced with a small choke, giving high impedance at very high frequency while having a low DC resistance to bias the tube right. The point of it was that capacitance between cathode and anode was almost nonexistent; this is important because the antenna produces pretty much no current at all to drive this parasitic capacitance. So while a grid input would have a high Miller capacitance, cathode input doesn't. 

We noted earlier that the cathode OUTPUT is non-inverting. This is also true of the cathode INPUT. If you look at the waves above, they are in phase.


So, let's move closer to the goal:

 

Here we have a pair of single ended gain stages. They are not connected to each other in any way except via the B+, which here is pure DC. Left side receives a grid input of 2VPP, and right side receives no input with grounded grid.

No surprise what the outputs look like:

 

I'm sure you can guess that was the right side.

 

Left side has some cathode degeneration (green wave), but there is a decent output still.

This type of circuit is of course quite pointless. Let's see what happens when we connect the cathodes:



Now this is starting to look a lot more familiar now! Based on the previous examples, predict what happens here after the cathodes are connected together.

Since they now share a cathode node, there is only one voltage there:

 

It is of course produced by the left tube; it is in phase with the left tube grid signal. 

Now this is where it might get a bit tricky, keeping all the phase in your brains.

So left tube grid gets signal. Let's call it's phase as 0. There is an unbypassed resistor at the cathode, so there appears "cathode output" voltage. It also has phase 0.

Now left tube anode output is at phase 180 since grid to anode output is inverted phase. 

Right tube receives a cathode input, when using cathode to anode input phase is not inverted. So right tube anode output signal has phase 0.

So what do we end up with?

 

Green wave is left anode, and blue wave is right anode. Left output is about 24VPP, right is about 7VPP.

Of course left output is much bigger; left tube input (at the grid) is 2VPP. There is some cathode degeneration, but not that much, about 600mVPP as was seen above.

This 600mVPP is the whole of the input signal for the right side tube, so naturally it's output is much smaller.

Why is the cathode signal (parasitic output for left side tube, input signal for the right side tube) so small?

Well because of Ohm's law; the 750 ohm cathode resistor (the tail) is not that big. So what happens if we make it a lot bigger?

 

Now if we make the tail resistor bigger, we must make the bottom of the tail voltage much lower, negative. I tried to keep the current about the same, so the bias points are about the same; if the same current flows thru a resistor, there needs to be a voltage across it. Ohm's law again.

So about -1000V B- there. Easy to build, at least in Spice!

But now the tail is 120k instead of 0.75k. Based on what we've gone thru here, predict what happens and why.


Well, first of all, the left tube experiences a lot more cathode degeneration. 

Because of that, the right side receives a much bigger input signal via cathode input.

So, outputs should be much closer to amplitude.

Let's look at the outputs then:



Almost same in amplitude! With only one input into the whole circuit!

Anode output amplitudes are now about 16VPP. But, since the signal is now balanced, we don't have to think in terms of SE signals anymore; the DIFFERENTIAL output amplitude is both waves added together, so 32VPP.

When we look at the previous example with the 750 ohm tail, the outputs were about 24 and 7 VPP, together about 31 VPP, this tells us that the sum of the output amplitudes is pretty much always the same (with the same anode resistors).

If we were to increase anode resistance, we'd get an overall larger differential output (increased gain).

Let's look at the left grid voltage and the cathode node voltage:



Blue is left grid input, and green is cathode node, which has of course some DC component also (bias voltage for the tubes).

You can see the cathode wave is 50% amplitude of the left grid wave. This causes two things:

1) it suppresses left tube gain (cathode degeneration); we can see this by looking at the individual outputs and comparing to the previous scheme with the 750 ohm tail

2) increases right tube input signal via cathode input; this increases right side anode output amplitude.

Balance achieved!


But how does the circuit 'know' how to stop the cathode degeneration at 50% of left grid amplitude? After all, there is now 120k beneath the left side cathode, and only 33k above the anode. Shouldn't the left side be much more of a cathode follower, yet there is a big anode output?

Think about it and give your suggestions. We'll go thru this at a later time.

This is the essentials; the same way that this topology can compensate for missing input signal on one side, it can compensate for tube differences.


----------



## MrCurwen

The first gainstage example, the one with the unbypassed cathode, should read about 800mVPP of swing at the cathode. I mistakenly only looked at the numbers after the decimal point and missed that the volt had changed. Doesn't affect the point though.


----------



## baronbeehive (Mar 8, 2018)

bloodhawk said:


> So i had done some more testing last night at his place, and the right channel is definitely biasing lower than the left channel by 10-15mA .Not sure why the right channel meter was not showing this over the weekend.



Do you mean the meters are showing this?

You could rule out the opamps by swapping the one in the possibly faulty circuit with another one. But first you could just check those resistors in the area around the gain switches and compare with the other circuit or channel to the possibly faulty one. It doesn't look a massive difference to me so probably not a grounded connection like I had, but also possibly a pot imbalance, if you say the difference was there before, don't know how you would check that though.

I would also check those new connections you have done to make sure they're making good connections with their traces if you haven't already done so.

Also check for possible signs of excess heat anywhere.


----------



## bloodhawk

baronbeehive said:


> Do you mean the meters are showing this?
> 
> You could rule out the opamps by swapping the one in the possibly faulty circuit with another one. But first you could just check those resistors in the area around the gain switches and compare with the other circuit or channel to the possibly faulty one. It doesn't look a massive difference to me so probably not a grounded connection like I had, but also possibly a pot imbalance, if you say the difference was there before, don't know how you would check that though.
> 
> ...



Yeap the meters.
Gotcha ill try that tomorrow. 

Will do. I do trust his soldering skills, but will ask him to check the solder joints again to be triple sure , just in case.


----------



## baronbeehive

bloodhawk said:


> Yeap the meters.
> Gotcha ill try that tomorrow.
> 
> Will do. I do trust his soldering skills, but will ask him to check the solder joints again to be triple sure , just in case.



Yep, just check component leg to board trace not just the pad.

....and you could take voltages at the anode resistors, should be about 75v and cathode bypass caps, about 90v give or take. That will help you zero in on the possible faulty circuit.


----------



## bloodhawk

baronbeehive said:


> Yep, just check component leg to board trace not just the pad.
> 
> ....and you could take voltages at the anode resistors, should be about 75v and cathode bypass caps, about 90v give or take. That will help you zero in on the possible faulty circuit.


Aye sir!


----------



## baronbeehive (Mar 8, 2018)

Sorry those voltages were from my faulty circuits! I should have said 100v on the B+ side and 80v on the other side of the 330ohm anode resistor.


----------



## bloodhawk

baronbeehive said:


> Sorry those voltages were from my faulty circuits! I should have said 100v on the B+ side and 80v on the other side of the 330ohm resistor.



Tool late, amp blew up.


Jk


----------



## baronbeehive

bloodhawk said:


> Tool late, amp blew up.
> 
> 
> Jk



Hey, what're you doing following my advice anyway, you should know better lol.


----------



## bloodhawk

baronbeehive said:


> Hey, what're you doing following my advice anyway, you should know better lol.



I really dont know this amp as well as you guys. If i could find a schematic for this thing, it would be a different story. 

Plus since its not my amp that im fiddling with here, id rather get a second opinion to be sure of whats up and fix it.


----------



## SonicTrance

bloodhawk said:


> I really dont know this amp as well as you guys. If i could find a schematic for this thing, it would be a different story.
> 
> Plus since its not my amp that im fiddling with here, id rather get a second opinion to be sure of whats up and fix it.


I’ve posted schematic of the audio circuit and psu schematic is posted on first page, hand drawn.


----------



## bloodhawk

SonicTrance said:


> I’ve posted schematic of the audio circuit and psu schematic is posted on first page, hand drawn.



Yeah found the PSU schematic, but havent been able to locate the audio circuit, do you by any chance remember which page it would be on? (or maybe a close enough guess)


----------



## SonicTrance

Here you go https://www.head-fi.org/threads/lit...e-on-first-page.782183/page-180#post-13978373


----------



## bloodhawk

SonicTrance said:


> Here you go https://www.head-fi.org/threads/lit...e-on-first-page.782183/page-180#post-13978373



You are awesome! <3 <3


----------



## bloodhawk

Does anyone have picture of the board without these resistors installed / list of the values in the order they are installed on the board - 







Mainly the circled ones - 
	

	
	
		
		

		
		
	


	





I am not able to confirm on my own amp, since there are a lot of wires/caps in the way.


----------



## bloodhawk

So kind of about to give up on troubleshooting his amp. Tested all the 330R resistors, and all of them check out just fine. Swapped around opamps, and the results were the same. 

I didnt test out the voltages, since im not exactly sure which terminals to test the voltage between, now since this isnt my amp im trying to troubleshoot, i dont want to start poking and prodding terminals based on what i understand. 

Will someone here be able to point me to exactly what to check for and in between what terminals?


----------



## baronbeehive

bloodhawk said:


> Does anyone have picture of the board without these resistors installed / list of the values in the order they are installed on the board -
> 
> 
> 
> ...



I can go better than that!
Left to right: 0.56, 106, 0.56, 1.9, 10, 10 - 10, 10, *106*, 0.56, 0.56, *1.9* - - 106, 0.56, 0.56, 10, 10, 1.9, 10, 10, 1.9, 0.56, 106, 0.56
They're not mirrored between channels so that makes it slightly awkward.

I think they're all K ohms, I will check. Also the 2 values in bold might be reversed, I'll check that too.


----------



## baronbeehive

bloodhawk said:


> So kind of about to give up on troubleshooting his amp. Tested all the 330R resistors, and all of them check out just fine. Swapped around opamps, and the results were the same.
> 
> I didnt test out the voltages, since im not exactly sure which terminals to test the voltage between, now since this isnt my amp im trying to troubleshoot, i dont want to start poking and prodding terminals based on what i understand.
> 
> Will someone here be able to point me to exactly what to check for and in between what terminals?



Just check voltages on the 4 330R resistors, not the drop over the resistors. They should read around 100v on one side and 80v on the other. Then compare readings for the 4 circuits to see which one is out.


----------



## bloodhawk

baronbeehive said:


> I can go better than that!
> Left to right: 0.56, 106, 0.56, 1.9, 10, 10 - 10, 10, *106*, 0.56, 0.56, *1.9* - - 106, 0.56, 0.56, 10, 10, 1.9, 10, 10, 1.9, 0.56, 106, 0.56
> They're not mirrored between channels so that makes it slightly awkward.
> 
> I think they're all K ohms, I will check. Also the 2 values in bold might be reversed, I'll check that too.



Damn ! Thanks a lot! 

From some more troubleshooting, i have a feeling on of the bypass RIFA caps might not be upto spec or working properly. I cant test the capacitance with the cap installed the board, but tomorrow ill start take the bypass caps out one by one to see if thats the cause.


----------



## bloodhawk

baronbeehive said:


> Just check voltages on the 4 330R resistors, not the drop over the resistors. They should read around 100v on one side and 80v on the other. Then compare readings for the 4 circuits to see which one is out.



Voltages on the 330R's were matched up across left/right sections. SO that pretty much rules out the resistors. Even their values were consistent.


----------



## baronbeehive

bloodhawk said:


> Voltages on the 330R's were matched up across left/right sections. SO that pretty much rules out the resistors. Even their values were consistent.



That pretty much rules out channel imbalance then. One thing, the soldering looks to be OK. So that leaves the pot as far as I can see, don't know how you go on from here, someone else might have some ideas, at least it doesn't look serious!


----------



## bloodhawk (Mar 11, 2018)

baronbeehive said:


> That pretty much rules out channel imbalance then. One thing, the soldering looks to be OK. So that leaves the pot as far as I can see, don't know how you go on from here, someone else might have some ideas, at least it doesn't look serious!


 
I doubt its the pot since, from what i understand, the pot come after the bias circuit.

I brought his amp back to my place today, and did some listening for a few hours, and seems like its not exactly a channel imbalance, but feels more like there is a hard roll off of the high end. Im not sure how to explain this properly.

But the main thing that really concerns me right now is the tube bias being 10-15mA lower on the right channel OR higher on the other one.

Im really leaning towards a bad / faulty cap. Probably one of bypass RIFA caps.

Also anyone know what exactly the TRIMPOTs are doing? Are they being used as a offset for the OPAMP auto biasing resistance?


----------



## baronbeehive (Mar 11, 2018)

bloodhawk said:


> I doubt its the pot since, from what i understand, the pot come after the bias circuit.
> 
> I brought his amp back to my place today, and did some listening for a few hours, and seems like its not exactly a channel imbalance, but feels more like there is a hard roll off of the high end. Im not sure how to explain this properly.
> 
> ...



The pot and biasing circuit are independent.

That roll off, would you describe it as a high frequency imbalance of some sort, seems even more likely to be the pot!

So what do the 2 meters read, also what tubes is he using

I believe the trimpots are for providing a baseline for the biasing.

Edit: Try flipping the gain switches, they're known to be problemmatic as well.


----------



## klnglim (Mar 11, 2018)

My MK8SE just burnt again, any idea what happened? This is the third time already, may be bad luck for me. When begin turn on, look normal but after the second meter turn on the amp sound like something is burning and I straight turn it  off immediately, the bulb seen normal, I have checked all the other component fine but the amp inside burn,cant find any reason what is going on?


----------



## baronbeehive

klnglim said:


> My MK8SE just burnt again, any idea what happened? This is the third time already, may be bad luck for me. When begin turn on, look normal but after the second meter turn on the amp sound like something is burning and I straight turn it  off immediately, the bulb seen normal but the amp inside burn,cant find any reason what is going on?



I see you changed the layout, was it alright before and when did this happen, did  it happen just after you did something?


----------



## klnglim

baronbeehive said:


> I see you changed the layout, was it alright before and when did this happen, did  it happen just after you did something?


Before it was turn on, after second meter jump but meter show 0 with light and amp not working, that's why I changed take out the bypass cap


----------



## baronbeehive (Mar 11, 2018)

klnglim said:


> Before it was turn on, after second meter jump but meter show 0 with light and amp not working, that's why I changed take out the bypass cap



If it was not something you did just before this happened you should check your solder joints, wires. Something is not making connection or is touching something else and shorting out.

Do you have a multimeter. If so you should check every solder joint you have made and make sure it is making proper connection with the board trace. That will rule out any problem solder work. Also check there is no solder particles lying around.

Finally make sure everything is connected up correctly.

Edit: Check especially the circuit which is reading zero, there is a faulty connection there somewhere.

This is disheartening kinglim, I'm sure it is something simple that can be put right!


----------



## klnglim

baronbeehive said:


> If it was not something you did just before this happened you should check your solder joints, wires. Something is not making connection or is touching something else and shorting out.
> 
> Do you have a multimeter. If so you should check every solder joint you have made and make sure it is making proper connection with the board trace. That will rule out any problem solder work. Also check there is no solder particles lying around.
> 
> ...


I m taking off everything, check all the connection now and will replace new resistor and Mosfet tomorrow


----------



## klnglim

baronbeehive said:


> If it was not something you did just before this happened you should check your solder joints, wires. Something is not making connection or is touching something else and shorting out.
> 
> Do you have a multimeter. If so you should check every solder joint you have made and make sure it is making proper connection with the board trace. That will rule out any problem solder work. Also check there is no solder particles lying around.
> 
> ...


The solder joint check fine, may be Mosfet cause problem?


----------



## baronbeehive

klnglim said:


> I m taking off everything, check all the connection now and will replace new resistor and Mosfet tomorrow



Great, I had a similar problem, you might need to check that the opamp hasn't shorted out when you put everything back.

Good luck!


----------



## baronbeehive (Mar 11, 2018)

SonicTrance said:


> To draw a load line like this you first measure B+. It's easiest to measure at top of anode resistors (the lead closest to the front of the amp). I measured 155 V as you can see above. There's your point on the Va horisontal axis. Then calculate the maximum plate current. Ohms law: B+ / plate resistor = 155 / 33k = 4.7 mA, there's your point on the mA vertical axis. Then simply draw a line between the two points and there's your load line.
> 
> Plate current is set to 1.2 mA through the CCS. Mark that point on the mA axis. Measure or calculate the Va. Remember that Va is the DIFFERENCE between anode and cathode, NOT anode to ground. Same thing with the grid voltage, Vg. It's the difference between grid and cathode. I measured about 114 V between anode and cathode. There's your second point on the Va axis. Now simply draw a line from the 1.2 mA point until you hit the load line, then go straight down. You should then hit the measured Va (these curves are not exact so ballpark is enough)



Yes, I get all this. We start off with a measured B+ from the LD driver stage, We can then vary the anode resistor to arrive at a value for the plate current. What I would like to know is:

1 - Is there an optimum value, or range of values for the plate current?

2 - Is there an optimum value, or range of values for the current through the CCS?

3 - Is there an optimum value, or range of values for the plate voltage?

I've looked at the tube datasheets but don't really see how we relate our values to what is on the datasheets.

I realise that we can set our operating point on the grid which will tell us what the grid voltage is and this should be set at the most linear part of the grid ideally.



SonicTrance said:


> Yes! Since this ps is not regulated it drops significantly when more current is pulled. That's why I lowered the last R in the ps to 750R. I would not recommend you pull anymore current then this. But feel free to experiment, nothing bad is going to happen from that, except maybe bad sound, lol.



The last R in the PS is the cathode resistor, or the 3k3 resistor?

Edit: I think you mean the 3k3 resistor. Which resistor is that?


----------



## SonicTrance

baronbeehive said:


> 1 - Is there an optimum value, or range of values for the plate current?


Just look at the curves in the datasheets. You want to be in the linear part. That is where there is equal amount of space between the grid lines both left and right. 



baronbeehive said:


> 2 - Is there an optimum value, or range of values for the current through the CCS?


Plate current is current through the CCS / 2, since there’s two triodes. Plate current is what you are setting with the CCS. 



baronbeehive said:


> 3 - Is there an optimum value, or range of values for the plate voltage?


Again, look at the curves. 



baronbeehive said:


> I realise that we can set our operating point on the grid which will tell us what the grid voltage is and this should be set at the most linear part of the grid ideally.


The grid in the LD input stage are always at 0 V, in relation to ground. We’re setting the load line with the anode resistors and we’re setting the operating point with the CCS. 



baronbeehive said:


> The last R in the PS is the cathode resistor, or the 3k3 resistor?


It’s the 3k3. The cathode resistor is not part of the power supply but the audio circuit. Cathode resistors are also taken out when you install the CCS’s.


----------



## bloodhawk (Mar 11, 2018)

baronbeehive said:


> The pot and biasing circuit are independent.
> 
> That roll off, would you describe it as a high frequency imbalance of some sort, seems even more likely to be the pot!
> 
> ...



Interesting.

The meters read -  60 on the left and 45 on the right.  With 6080's and the stock driver tubes.

This shifts to 55 and 40 if he uses 4 x 5998's.

Tried the gain switches, the bias imbalance stays the same.

The reason im rather skeptical its the pot is because the imbalance wasn't there before when he only swapped out the coupling caps, so im highly leaning towards the Cathode Bypass/Decoupling caps/bypasses.

Any idea on how to measure the values the trimpots are set to without taking the board out? I want to make sure he didnt accidentally nudge either of those. Also what the stock values should be on the trimpots.


----------



## baronbeehive (Mar 11, 2018)

bloodhawk said:


> Interesting.
> 
> The meters read -  60 on the left and 45 on the right.  With 6080's and the stock driver tubes.
> 
> This shifts to 55 and 40 if he uses 4 x 5998's.



Those bias values are out, there's something up here, but I can't make out what. The left meter is reading correctly for 6080's, but for 5998's the reading of 40 is more likely correct. So I'm at a bit of a loss here. I can't quite understand why your voltage readings didn't show up any differences in the circuits.

I'm at my limits here, I'll have to leave it to the others, hope you can sort it bloodhawk!

Edit: you need to be able to tell if there is a defective circuit, and if so which one so that you can concentrate your efforts on that circuit. My guess is a connection fault somewhere.


----------



## bloodhawk

baronbeehive said:


> Those bias values are out, there's something up here, but I can't make out what. The left meter is reading correctly for 6080's, but for 5998's the reading of 40 is more likely correct. So I'm at a bit of a loss here. I can't quite understand why your voltage readings didn't show up any differences in the circuits.
> 
> I'm at my limits here, I'll have to leave it to the others, hope you can sort it bloodhawk!



Just to confirm the voltages on the 330R's are to be tested against ground right?


----------



## baronbeehive (Mar 11, 2018)

bloodhawk said:


> Just to confirm the voltages on the 330R's are to be tested against ground right?



Yes.

Edit: You could try the power tube pin sockets as well, especially pin1.
I edited my previous post.
Maybe a pic of the inside would help with a close up of the connections.


----------



## bloodhawk (Mar 11, 2018)

baronbeehive said:


> Yes.
> 
> Edit: You could try the power tube pin sockets as well, especially pin1.
> I edited my previous post.
> Maybe a pic of the inside would help with a close up of the connections.


ANNND fixed it !

Its was the .33 uF RIFA Bypass caps. Removed the ones from the left channel, and it instantly went back to normal.Removed it from the right channel and they are almost perfectly matched now. I might swap the ones being used as the decoupling cap bypass as well, with some better film 0.33uF ones.

For now since i have 2 x MK VI+'s at hand with slightly different upgrade components im really interested in doing blind A/B testing to see if i can the difference each component makes. Specially since i already need to rearrange the shoddy placement job my friend did.

One thing i instantly noticed between my amp and his without the .33uF RIFA bypass caps across the coupling caps , is that low end is much richer and not sharper. Which is exactly what i prefer. And i have a feeling @SonicTrance Might also like.
Its has the right amount of texture and smoothness and feel much "fuller". In a way one can say that , instead of being - Oh hey, there was the low end nice. You literally go - HOLY crap the low end FEELS awesome.


----------



## bloodhawk

@baronbeehive I spoke too soon . The bias balanced out for only a few minutes. 

I went back and started taking a few voltage readings and this time- 

Tube 4 pin 1 to 330R (on the left, with the amp upside down) reads 45V , while all other Tube Pin 1's to their respective 330R 's read 55V. 

However from socket / common ground to any of the 330R's the voltage reads at 80V. 

I removed all the resistors and checked their values.. they we're exactly on point. Even the capacitors read  perfectly fine out of the circuit. So the issue seems to around this region - https://i.imgur.com/Z3kcdKg.jpg


----------



## baronbeehive (Mar 12, 2018)

bloodhawk said:


> @baronbeehive I spoke too soon . The bias balanced out for only a few minutes.
> 
> I went back and started taking a few voltage readings and this time-
> 
> ...



Correct.

I know Maxx had this problem and it turned out to be a colder solder around his cathode bypass I think. It seems your circuits are OK up to the tube sockets, at least until warm up. I'm not sure of the board trace but you could check the other pins and anyone that is out check the trace and see where it goes.

What mods has he done, has he done any wiring. In any case I would think that if you redo the connections for the modded parts on this circuit you will probably sort it. I very much doubt that it is the tube sockets themselves, but it might be a wire connected to it.

Also check 330R resistors voltage again after warm up.


----------



## baronbeehive

SonicTrance said:


> Again, look at the curves.
> 
> It’s the 3k3. The cathode resistor is not part of the power supply but the audio circuit. Cathode resistors are also taken out when you install the CCS’s.



Yes right!

I didn't realise you had altered the 3k3 resistor, that's something I must do, which one is it

I will get round to doing some load lines next.


----------



## bloodhawk

baronbeehive said:


> Correct.
> 
> I know Maxx had this problem and it turned out to be a colder solder around his cathode bypass I think. It seems your circuits are OK up to the tube sockets, at least until warm up. I'm not sure of the board trace but you could check the other pins and anyone that is out check the trace and see where it goes.
> 
> ...



So i redid all the solder joints, and tested the amp. Bias looked good. But now there is another issue, where the left channel is only has a buzzing sound lol. 

Another thing i tried was to match the Trimpot resistance values to 0.89 (k Ohm?, dont remember exactly), since my friend mentioned that he did actually try to turn the dial thinking he accidentally nudged one (for the left channel) and that was causing the bias issue. 

The buzzing in the left channel could actually because of a wire being dislodged or stuck between something under the board which ill confirm later tonight after work. But not knowing how and what to set the trimpots to is somewhat worrying me.


----------



## baronbeehive

bloodhawk said:


> So i redid all the solder joints, and tested the amp. Bias looked good. But now there is another issue, where the left channel is only has a buzzing sound lol.
> 
> Another thing i tried was to match the Trimpot resistance values to 0.89 (k Ohm?, dont remember exactly), since my friend mentioned that he did actually try to turn the dial thinking he accidentally nudged one (for the left channel) and that was causing the bias issue.
> 
> The buzzing in the left channel could actually because of a wire being dislodged or stuck between something under the board which ill confirm later tonight after work. But not knowing how and what to set the trimpots to is somewhat worrying me.



OMG.... bias  good, buzz most certainly not good lol. Just when you think you're getting someplace, the amp turns round and bites you.

I'll have to hand you over to someone who knows more, I'm at my limits here. The trimpot issue is not important it only allows you to manually adjust any imbalance.

Got to hand it to you for the work you're putting into someone else's amp!


----------



## bloodhawk

baronbeehive said:


> OMG.... bias  good, buzz most certainly not good lol. Just when you think you're getting someplace, the amp turns round and bites you.
> 
> I'll have to hand you over to someone who knows more, I'm at my limits here. The trimpot issue is not important it only allows you to manually adjust any imbalance.
> 
> Got to hand it to you for the work you're putting into someone else's amp!



Haha exactly what i felt lol. If its not one thing its the other.

Thanks a bunch for trying!! Hopefully @Maxx134 or @MrCurwen can help me out here. 

Well hes a really good and super old friend of mine with very limited knowledge of how to work around electronics. Good thing is that he isnt afraid of taking chances with expensive gear knowing well that things can always go sideways, being super patient also helps!


----------



## SonicTrance

bloodhawk said:


> So i redid all the solder joints, and tested the amp. Bias looked good. But now there is another issue, where the left channel is only has a buzzing sound lol.


I thought I read you fixed the amp? 
Anyway, the trimpots are to set 0 V at output. Hook voltmeter probes up to one output at a time and adjust the trimpots. You can also try plugging in your headphones while they're on your head. If you don't have 0 V at output there's a pop when you insert the headphones. If there's 0 V it should be quiet.


----------



## bloodhawk

SonicTrance said:


> I thought I read you fixed the amp?
> Anyway, the trimpots are to set 0 V at output. Hook voltmeter probes up to one output at a time and adjust the trimpots. You can also try plugging in your headphones while they're on your head. If you don't have 0 V at output there's a pop when you insert the headphones. If there's 0 V it should be quiet.



Ahh.. gotcha. So 0 V per channel vs ground , correct? Apologies if this is a dumb question :S

Well i thought i fixed it, until 25 minutes later where the bias imbalance landed back where it was. Currently the bias are very much close, but all that comes out of the left channel is a buzzing noise. Right channel sounds clean. Could this buzzing noise be because of non 0 output voltage?


----------



## SonicTrance

bloodhawk said:


> Ahh.. gotcha. So 0 V per channel vs ground , correct? Apologies if this is a dumb question :S
> 
> Well i thought i fixed it, until 25 minutes later where the bias imbalance landed back where it was. Currently the bias are very much close, but all that comes out of the left channel is a buzzing noise. Right channel sounds clean. Could this buzzing noise be because of non 0 output voltage?


Yes, well 0 V / phase vs ground. You have four phases in total, two / channel.
Not sure if the DC offset is the cause of your buzz. But since you know you have messed with the trimpots I would definitely adjust them first thing.


----------



## bloodhawk

SonicTrance said:


> Yes, well 0 V / phase vs ground. You have four phases in total, two / channel.
> Not sure if the DC offset is the cause of your buzz. But since you know you have messed with the trimpots I would definitely adjust them first thing.


Aye, ill test this out tonight after work and report back.

Would you know what the reasons might be for the bias imbalance? I tested each of the resistors and caps individually, and they all seem to be fine.


----------



## SonicTrance

bloodhawk said:


> Aye, ill test this out tonight after work and report back.
> 
> Would you know what the reasons might be for the bias imbalance? I tested each of the resistors and caps individually, and they all seem to be fine.


If the bias is drifting over time it sounds like a bad tube. You have switched the tubes around to see if the problem follows the tubes, correct? If the cathode resistors and caps are fine and the tubes are good it should bias correct.


----------



## bloodhawk

SonicTrance said:


> If the bias is drifting over time it sounds like a bad tube. You have switched the tubes around to see if the problem follows the tubes, correct? If the cathode resistors and caps are fine and the tubes are good it should bias correct.



Thats the first thing i tested, i used his set of 5998's , his stock set of 6080's , my set of 5998's, 7236's and then stock 6080's. Along with his stock driver tubes, my stock driver tubes, along with the extra VT231's that i had. All show the same behavior.

Even tried swapping the opamps over. Same behavior.


----------



## SonicTrance

bloodhawk said:


> Thats the first thing i tested, i used his set of 5998's , his stock set of 6080's , my set of 5998's, 7236's and then stock 6080's. Along with his stock driver tubes, my stock driver tubes, along with the extra VT231's that i had. All show the same behavior.
> 
> Even tried swapping the opamps over. Same behavior.


Then my best bet is a bad connection. I know you just re-soldered a bunch of joints. Have you checked them to make sure proper connection? It's a quick check. Just use continuity on your meter and check the connections. Something has to be off if there's no component failure.


----------



## Maxx134

Sorry guys I don't get notifications in my email so wasn't around this thread...



klnglim said:


> My MK8SE just burnt again, any idea what happened? This is the third time already, may be bad luck for me. When begin turn on, look normal but after the second meter turn on the amp sound like something is burning and I straight turn it  off immediately, the bulb seen normal, I have checked all the other component fine but the amp inside burn,cant find any reason what is going on?


Have you found your problem?
The garbage stranded tin wiring going to the PSU power transistors are always at fault for sparking.
Check continuity of wires.



bloodhawk said:


> I spoke too soon . The bias balanced out for only a few minutes


This is strong indicator of tube .



bloodhawk said:


> The buzzing in the left channel could actually because of a wire being dislodged or stuck between something under the board which ill confirm later tonight after work. But not knowing how and what to set the trimpots to is somewhat worrying me.


Tube.
Otherwise check driver PSU transformer wires as one elevates the ground reference.



bloodhawk said:


> Well i thought i fixed it, until 25 minutes later where the bias imbalance landed back where it was. Currently the bias are very much close, but all that comes out of the left channel is a buzzing noise. Right channel sounds clean. Could this buzzing noise be because of non 0 output voltage?


Denfinitely sounds like tube.



SonicTrance said:


> If the bias is drifting over time it sounds like a bad tube. You have switched the tubes around to see if the problem follows the tubes, correct? If the cathode resistors and caps are fine and the tubes are good it should bias correct.


Yep I agree , you could check voltages same on both sides, but because meters were reading correct initially that tells me bias on both sides were same but tube drift over time and is bad.
Sometimes when bias is run high the tube can have thermal run away..
This happened with the MK8 powertubes a few times with me.


----------



## bloodhawk (Mar 12, 2018)

SonicTrance said:


> Then my best bet is a bad connection. I know you just re-soldered a bunch of joints. Have you checked them to make sure proper connection? It's a quick check. Just use continuity on your meter and check the connections. Something has to be off if there's no component failure.



Yeah right there with you, im thinking of redoing all the wire connection, just to be on the safe side and make rule those out as a reason.



Maxx134 said:


> Yep I agree , you could check voltages same on both sides, but because meters were reading correct initially that tells me bias on both sides were same but tube drift over time and is bad.
> Sometimes when bias is run high the tube can have thermal run away..
> This happened with the MK8 powertubes a few times with me.



Any way to test what the bias is at and if its safe/correct value? From what i understand, the 330R's are the main resistors that can alter the bias easily. Since those are just fine, i took them off the problem list. 

Tested different types of tubes to make sure those weren't the problem, ill check the transformer grounds tonight and report back.


----------



## Maxx134 (Mar 12, 2018)

bloodhawk said:


> Thats the first thing i tested, i used his set of 5998's , his stock set of 6080's , my set of 5998's, 7236's and then stock 6080's. Along with his stock driver tubes, my stock driver tubes, along with the extra VT231's that i had. All show the same behavior.
> 
> Even tried swapping the opamps over. Same behavior.



Wow dam that sounds like cold solder connection.
Stock soldering is sparse and cheap so when you pulling on the board sockets swapping tubes, these things can happen.

Check for any loose socket pins by looking and wiggle with a Needle,
Or just go ahead and re-tinn the sockets on the offending side with generous solder but beware it likes to splatter..


----------



## bloodhawk

Maxx134 said:


> Wow dam that sounds like cold solder connection.
> Stock soldering is sparse and cheap so when you pulling on the board sockets these things can happen.
> 
> Check for any loose socket pins by looking and wiggle with a Needle,
> Or just go ahead and re-tinn the sockets on the offending side with generous solder but beware it likes to splatter..



Aye! Will do!


----------



## Maxx134 (Mar 12, 2018)

The Problem is to heat good because the other side of board needs to make contact as it is double sided.

Also the trim pots have nothing to do with hum ...
Dont mess with the trim pots as they are perfectly set to only adjust the "DC offset" which, when not adjusted well , will be noticable with a slight tiny click/pop sound when you plug in Headphone...

So when adjusted properly, there is zero pop/click sound when inserting Headphone..

This must be tuned by ear, as your meter can only read so tiny milivolts, unless you have more expensive equipment..

I posted a how-to a super long time ago but once have time will try again.

A curious effect is that
You can basically lift or lower your power-tube meter bias setting (slightly), by turning both trimpots equally on same side..


----------



## bloodhawk

Maxx134 said:


> The Problem is to heat good because the other side of board needs to make contact as it is double sided.
> 
> Also the trim pots have nothing to do with hum ...
> Dont mess with the trim pots as they are perfectly set to only adjust the "DC offset" which, when not adjusted well , will be noticable with a slight tiny click/pop sound when you plug in Headphone...
> ...



Yeah i made sure the solder flows to both sides, ill triple check again tonight.

Gotcha, my multimeter is a nice super sensitive one, so i think i should be able to read those. Will do additional testing with the trimpots once i have an idea of whats causing the other issues.


----------



## klnglim

baronbeehive said:


> Great, I had a similar problem, you might need to check that the opamp hasn't shorted out when you put everything back.
> 
> Good luck!


Just find out one cable behind the board (direct right side output) is broken, also I notice that the original wires from factory are suck, unbelievable super thin low quality copper!
That's one of the reason cause my amp burnt 4 times (include today burnt again), my advice is never ever buy their product, better spend a bit more to get high quality one!
Now have to decide to buy some Teflon cables and some thick tinned copper wires to replace all the wires inside the amp.


----------



## Maxx134 (Mar 12, 2018)

bloodhawk said:


> Will do additional testing with the trimpots once i have an idea of whats causing the other issues


You read it by the output to ground...
 Not anywhere near the trimpots.



klnglim said:


> unbelievable super thin low quality copper!


Guess again.
Some of the wire is also cheap tin(!)
There is probably huge pressure to be competitive in China market so this result in materials cost cutting.



klnglim said:


> Now have to decide to buy some Teflon cables and some thick tinned copper wires to replace all the wires inside the amp.


I would stay with thin stranded OCC type because you need wire flexible, not thick.

Check first page as you also need many wires running along side, so a multi conductor cable is optimal.


----------



## klnglim

Maxx134 said:


> You read it by the output to ground...
> Not anywhere near the trimpots.
> 
> 
> ...


I have used Teflon wires to connect those Russian & Mundolf Caps, very good quality. May be will replace some thin wires with this Teflon wires (18 awg thickness), another 16 awg tin copper thick cables is to replace those 3 pin & 4 pin output.Is this good idea?


----------



## bloodhawk

Maxx134 said:


> You read it by the output to ground...
> Not anywhere near the trimpots.



Yeah i have been using the power sockets ground for the most part. 

Im also thinking of taking my whole amp apart and redoing every single wire inside the amp, specially so that its much easier to take apart without tugging and pulling the wires soldered to the board, or even implementing sockets/plugs so that the board is easier to take out entirely. 

But first i need to fix my friends amp, on the bright side, this is a good exercise for me to learn more about its inner workings and the common issues.


----------



## baronbeehive

klnglim said:


> Just find out one cable behind the board (direct right side output) is broken, also I notice that the original wires from factory are suck, unbelievable super thin low quality copper!
> That's one of the reason cause my amp burnt 4 times (include today burnt again), my advice is never ever buy their product, better spend a bit more to get high quality one!
> Now have to decide to buy some Teflon cables and some thick tinned copper wires to replace all the wires inside the amp.



Yeah, but we're not really supposed to be messing around inside with this amp are we? There is much about these wires on the first page, including warnings. Whatever amp you buy will be compromised in some way, for example so called quality amp but with nasty caps inside, you might know who I mean.....

Don't complain about the product, they produced a product to meet a certain sector of the market, the value sector, and what you lose in crap components like wires you gain in superb SQ so we can't complain.


----------



## Maxx134 (Mar 12, 2018)

baronbeehive said:


> or example so called quality amp but with nasty caps inside, you might know who I mean.....


Haha no I don't as that cover most amps lol.

The design of this amp is the advantage tho.
A fully balanced tube amp using popular tubes,
Just not optimally done.
You dont see too many fully balanced Headphone tube amps.
Very, very Few out there.

At least this not an ancient design that rely on output caps or ouput transformers to muck up the sound, and instead using nice idea of op-amp servo.
So it has a high clarity potential.
Too bad it rely on some NFB,
Yet most still do.


----------



## baronbeehive

Maxx134 said:


> Haha no I don't as that cover most amps lol.



....oh you won't hazard a guess then.....



Maxx134 said:


> So it has a high clarity potential.
> Too bad it rely on some NFB,
> Yet most still do.



We don't get the hifi meets here like you do in NY city so I haven't heard the absolute top quality amps but from my own imagination I would say that we're about 95% there with that extra 5% only of dust on the glass in between us and the music. And I think we could get as near as dammit once the CCS is in place, the there's always other mods.......


Really I'm completely happy with it, just one or two more tweaks, but that soundstage is wonderful!


----------



## klnglim (Mar 12, 2018)

baronbeehive said:


> Yeah, but we're not really supposed to be messing around inside with this amp are we? There is much about these wires on the first page, including warnings. Whatever amp you buy will be compromised in some way, for example so called quality amp but with nasty caps inside, you might know who I mean.....
> 
> Don't complain about the product, they produced a product to meet a certain sector of the market, the value sector, and what you lose in crap components like wires you gain in superb SQ so we can't complain.


Actually I didn't plan to mod this amp since the day I bought it, however after 6 months of using, the smoke show up & smell bad burnt, then I have to open fix it.Unlucky is after fixed, less than a month another smoke show up 
again, this time getting worst as the amp spark and smoke everytime try to turn on, now it become my nightmare


----------



## baronbeehive

klnglim said:


> Actually I didn't plan to mod this amp since the day I bought it, however after 6 months of using, the smoke show up & smell bad burnt, then I have to open fix it.Unlucky is after fixed, less than a month another smoke show up
> again, this time getting worst as the amp spark and smoke everytime try to turn on, now it become my nightmare



Yes I appreciate that, I also had a problem with it and was without it for a year or so, but it's really all been worth it now, and I hope you will feel the same when you've got it fixed lol! Just replace those bad wires with good quality OCC and it will sound soooo good!


----------



## bloodhawk

baronbeehive said:


> Yes I appreciate that, I also had a problem with it and was without it for a year or so, but it's really all been worth it now, and I hope you will feel the same when you've got it fixed lol! Just replace those bad wires with good quality OCC and it will sound soooo good!



Part of the reason why im really trying to have this amp fixed, want to pry that WA22 out of his hands that he is soo happy with. :S


----------



## klnglim

baronbeehive said:


> Yes I appreciate that, I also had a problem with it and was without it for a year or so, but it's really all been worth it now, and I hope you will feel the same when you've got it fixed lol! Just replace those bad wires with good quality OCC and it will sound soooo good!


Hopefully no more smoke after replace all the wires


----------



## baronbeehive

Maxx134 said:


> The Problem is to heat good because the other side of board needs to make contact as it is double sided.



This is  a  problem, with my last issue it would not  have helped if I tested one side of the board necause there was a different trace on the other side which I hadn't noticed which also needed testing for continuity.



bloodhawk said:


> Part of the reason why im really trying to have this amp fixed, want to pry that WA22 out of his hands that he is soo happy with. :S



Haha, no  you  don't want  that lol,  The LD is better!

Also, I would suggest you test the resistances with the resistors in situ because they point to the problem, if you take them out they will read OK usually anyway.

So the meters are correct on switch on but drift later?


----------



## bloodhawk

baronbeehive said:


> Haha, no  you  don't want  that lol,  The LD is better!
> 
> Also, I would suggest you test the resistances with the resistors in situ because they point to the problem, if you take them out they will read OK usually anyway.
> 
> So the meters are correct on switch on but drift later?




For the first few power cycles they read fine, and then if left turned they drift apart, and after a few time they start showing different bias.

The resistors read fine in the circuit as well. Just that the voltage is off on the area that i circled in the image earlier. Ill double check the wiring in that region today. But the main concern right no is the left channel buzzing.


----------



## baronbeehive

bloodhawk said:


> For the first few power cycles they read fine, and then if left turned they drift apart, and after a few time they start showing different bias.
> 
> The resistors read fine in the circuit as well. Just that the voltage is off on the area that i circled in the image earlier. Ill double check the wiring in that region today. But the main concern right no is the left channel buzzing.



That can't be tubes, you've tried it and the same happens with different tubes.

More likely a cold solder perhaps, when heated up it expands and the poor connection suffers as a result possibly. But you've resoldered everything in that circuit?

And the voltage readings are the same as before, so something around that area, which is why I asked you about the wiring. Still might help to check all the tube pins with the other circuit and see if that leads to anything unusual.


----------



## bloodhawk

baronbeehive said:


> That can't be tubes, you've tried it and the same happens with different tubes.
> 
> More likely a cold solder perhaps, when heated up it expands and the poor connection suffers as a result possibly. But you've resoldered everything in that circuit?
> 
> And the voltage readings are the same as before, so something around that area, which is why I asked you about the wiring. Still might help to check all the tube pins with the other circuit and see if that leads to anything unusual.



Yeah thats the next thing ill try tonight, to triple check the wiring in that area and resolder the socket pins. I could be that a stock solder joint was damaged when putting the board back in as it goes in super tight into the socket holes.


----------



## baronbeehive (Mar 12, 2018)

bloodhawk said:


> Yeah thats the next thing ill try tonight, to triple check the wiring in that area and resolder the socket pins. I could be that a stock solder joint was damaged when putting the board back in as it goes in super tight into the socket holes.



Yep, and  checking all the pins would show up a bad connection to one of them as well.

Also you could check the pads on the reverse of the board if you get it out again.


----------



## bloodhawk

baronbeehive said:


> Yep, and  checking all the pins would show up a bad connection to one of them as well.



Gotcha!

Thank again for all the help guys! Really really appreciate it! Maybe one day i can return the favor somehow.


----------



## baronbeehive

bloodhawk said:


> Gotcha!
> 
> Thank again for all the help guys! Really really appreciate it! Maybe one day i can return the favor somehow.



OK, and I edited my last post....... just to keep you busy tonight lol!


----------



## bloodhawk

baronbeehive said:


> OK, and I edited my last post....... just to keep you busy tonight lol!



haha , im sure i will be.

I checked the pads yesterday and all of them are perfect. He took a lot of care when removing all the components, and only took the parts out after the solder melted. The only dodgy pad was on one of the PSU caps, where the via came out with one of the caps legs. To fix that i told him to pass a sold silver plate 20 awg wire through and bend it on the other side. And then solder it on with  generous amount of solder. The continuity was showing no issues after that.

But just in case ill double check the pads again.


----------



## Maxx134

bloodhawk said:


> Yeah thats the next thing ill try tonight, to triple check the wiring in that area and resolder the socket pins. I could be that a stock solder joint was damaged when putting the board back in as it goes in super tight into the socket holes.


Careful with the heater wires on top board that they not get disturbed.


----------



## bloodhawk

Maxx134 said:


> Careful with the heater wires on top board that they not get disturbed.



Will you be to point out which one those are, so that i can make sure i dont mess those up by accident?


----------



## bloodhawk (Mar 13, 2018)

@Maxx134 @baronbeehive @SonicTrance

So fixed the buzzing issue, it was a ruptured solder joint under the tube 1 socket.

Now gotta figure out the bias issue.

Update - So after checking the wires again, and re tinning a bunch of joints, but the bias is still higher on the left channel.

Does switching the gain to HI, change the BIAS at all ?

Im out of idea now lol. The only thing left to try is to remove the decoupling caps and put the stock ones back in to see if that is the issue.


----------



## baronbeehive (Mar 13, 2018)

bloodhawk said:


> @Maxx134 @baronbeehive @SonicTrance
> 
> So fixed the buzzing issue, it was a ruptured solder joint under the tube 1 socket.
> 
> ...



Oh great! That must have been tricky to find that problem under the socket.

No, the bias is not changed, just the NFB.

I really think it unlikely to be new components. I can only suggest removing all the new parts in that circuit, bit of a nuisance, but not many there anyway, and resolder.

BTW, don't forget the traces are different on both sides of the board, just because you have continuity on one side doesn't mean you will have on the other side with different connections, so check both sides of the PSU cap connections for example. Also giving wires and joints a gentle pull can expose cold solder joints which look OK from the outside and wires that look OK too. Also a magnifying glass comes in handy for close ups of joints etc. Check no wires broken or loose, and no solder joints overlapping.

If you say that voltages are OK at the anodes, 330R's all equal, try to find where they are not eg at the tube pin sockets, or cathode bypasses to isolate the problem. Might even be an output problem.

Edit: So what mods has he done?


----------



## baronbeehive

bloodhawk said:


> Will you be to point out which one those are, so that i can make sure i dont mess those up by accident?



The 2 twisted blue or red wires to tube sockets on the reverse of board, easy to pierce by accident when fitting WCF caps on other side.


----------



## bloodhawk (Mar 13, 2018)

baronbeehive said:


> Oh great! That must have been tricky to find that problem under the socket.
> 
> No, the bias is not changed, just the NFB.
> 
> ...





baronbeehive said:


> The 2 twisted blue or red wires to tube sockets on the reverse of board, easy to pierce by accident when fitting WCF caps on other side.




Yeah, probably going to resolder everything. And this time going to solder small pieces of solid core silver wire through each hole first and then solder components onto those. That should rule out any damaged via issues along with solder not reaching pads on the other side of the board.

I resoldered all the wire joints just to be sure they are in good condition.

By output problem do you mean the wiring to the jacks?


But one thing im still very much curious about is why the bias drifts overtime, irrespective of the tubes. It definitely seems to be heat related as @Maxx134 suggested earlier.

Ill hook up some probes to the 330R's tonight and see if their values are drifting as they heat up. Other than the 330R's which other resistors are directly contributing to the bias? 
I dont this is related to anything in the PSU, since the voltages are changing only after the driver stage. Mainly when i measure from tube pin 1 to after the 330R's. Im seriously feeling that one of the Mills MRA5's that he using is either faulty or not upto spec, and is dropping its resistance value with heat.


----------



## Maxx134 (Mar 13, 2018)

bloodhawk said:


> So fixed the buzzing issue, it was a ruptured solder joint under the tube 1 socket.


Thats from pulling and swapping out tubes.
Original Solder prob was laid too thin.

Need to describe your issue more detail.
The left meter rises after 20min?
When I had issue of meter going up, it was due to the tube being at a high bias and then thermal runaway.

Is that amp using stock bias settings?
If that MK6 had a bias mod done, it is for one tube type, not both.

Also check the resistance of the upgrade resistors.
It probably not correct or connection at wrong point.

Those mills wirewound usually just go bad if their surface area is scratched.

Make sure that any cap  mod done to that side if connected in right spot.

No need to change parts.
Disconnect one side of cap & then check across it with continuity to see if it has leak.
Should be a short rise as it charges and then goes to unfinity (when using visual needle meter).


----------



## Maxx134

Were the grid resistors changed?
If so must check them.


----------



## bloodhawk

Maxx134 said:


> Thats from pulling and swapping out tubes.
> Original Solder prob was laid too thin.


Probably.



> Need to describe your issue more detail.
> The left meter rises after 20min?
> When I had issue of meter going up, it was due to the tube being at a high bias and then thermal runaway.



So after a cold start (amp being completely cold for a few hours), the bias start out matched and then drifts apart within about 10-15mins.



> Is that amp using stock bias settings?
> If that MK6 had a bias mod done, it is for one tube type, not both.



Yep stock bias, no bias mod.



> Also check the resistance of the upgrade resistors.
> It probably not correct or connection at wrong point.



Individually all upgraded resistors read perfectly fine. I need to check the grid resistors making proper connection once again though.


> Those mills wirewound usually just go bad if their surface area is scratched.



Interesting, i dont remember seeing any scratches or damage. But ill check again.



> Make sure that any cap  mod done to that side if connected in right spot.



Im 99% sure they are all connected to the right spot, but ill double check.



> No need to change parts.
> Disconnect one side of cap & then check across it with continuity to see if it has leak.
> Should be a short rise as it charges and then goes to unfinity (when using visual needle meter).



I have done a capacitance check on all the caps, and they read good. Will the continuity check reveal a separate issue with the caps?



Maxx134 said:


> Were the grid resistors changed?
> If so must check them.



Yeap they were swapped with better resistors, ill re tin them again tonight just to be triple sure. So they also effect the bias?


----------



## Maxx134

bloodhawk said:


> Yeap they were swapped with better resistors, ill re tin them again tonight just to be triple sure. So they also effect the bias?


Check for overlapped solder and correct connection as well as correct resistor value in case a mix up .

When meter rise does one of the tubes looks brighter or run hotter?
If so that is the socket area to check.


----------



## bloodhawk

Maxx134 said:


> Check for overlapped solder and correct connection as well as correct resistor value in case a mix up .
> 
> When meter rise does one of the tubes looks brighter or run hotter?
> If so that is the socket area to check.



Gotcha.

Left side meter it is.


----------



## baronbeehive (Mar 13, 2018)

bloodhawk said:


> Yeah, probably going to resolder everything. And this time going to solder small pieces of solid core silver wire through each hole first and then solder components onto those. That should rule out any damaged via issues along with solder not reaching pads on the other side of the board.



Yes, I still think you should check the continuity from the soldering to the trace on both sides of the board though. What would happen if you put in the wire through the hole to the other side and the pad was faulty on the other side. I mention this because I had this when I had a problem with a WCF cap pad, I fixed it so that it had continuity with the trace to pin2, but still not working so on the reverse of the board the trace went to the 330R resistor so that needed to be fixed as well, if you see what I mean, this board is so confusing.

Really all you need do is check continuity on both sides after you've done the soldering.



bloodhawk said:


> By output problem do you mean the wiring to the jacks?



Yes, that's why I asked what mods has he done, if he's done wiring then the output wire to the tube pin could be at fault.



bloodhawk said:


> But one thing im still very much curious about is why the bias drifts overtime, irrespective of the tubes. It definitely seems to be heat related as @Maxx134 suggested earlier.
> 
> Ill hook up some probes to the 330R's tonight and see if their values are drifting as they heat up. Other than the 330R's which other resistors are directly contributing to the bias?
> I dont this is related to anything in the PSU, since the voltages are changing only after the driver stage. Mainly when i measure from tube pin 1 to after the 330R's. Im seriously feeling that one of the Mills MRA5's that he using is either faulty or not upto spec, and is dropping its resistance value with heat.



It definately seems heat related so bad connection somewhere.

Good idea bloodhawk! Might just work!


----------



## SonicTrance

bloodhawk said:


> Ill hook up some probes to the 330R's tonight and see if their values are drifting as they heat up. Other than the 330R's which other resistors are directly contributing to the bias?
> I dont this is related to anything in the PSU, since the voltages are changing only after the driver stage. Mainly when i measure from tube pin 1 to after the 330R's. Im seriously feeling that one of the Mills MRA5's that he using is either faulty or not upto spec, and is dropping its resistance value with heat.


Do not do that. Never measure resistance with amp ON. You’ll ruin your meter. Only measure voltage with amp ON. When you say 330R resistors which resistors do you mean? Anode or cathode? It’s the cathode resistors that sets the bias. They’re located on top side of board.


----------



## bloodhawk

SonicTrance said:


> Do not do that. Never measure resistance with amp ON. You’ll ruin your meter. Only measure voltage with amp ON. When you say 330R resistors which resistors do you mean? Anode or cathode? It’s the cathode resistors that sets the bias. They’re located on top side of board.



I meant Anode, since the voltage is lower after Tube 1's anode resistor. The voltage difference is 10V at the least.


----------



## baronbeehive

bloodhawk said:


> Ill hook up some probes to the 330R's tonight and see if their values are drifting as they heat up. Other than the 330R's which other resistors are directly contributing to the bias?
> I dont this is related to anything in the PSU, since the voltages are changing only after the driver stage. Mainly when i measure from tube pin 1 to after the 330R's. Im seriously feeling that one of the Mills MRA5's that he using is either faulty or not upto spec, and is dropping its resistance value with heat.



Did you mean voltage or resistance?


----------



## bloodhawk

baronbeehive said:


> Did you mean voltage or resistance?



Voltage. Dont think resistance can be measure properly in live circuit unless im wrong.

Or maybe the current across the resistor, but i dont know how to do that across the Anode/Cathode resistors.


----------



## baronbeehive

I  really wouldn't try to measure current, bit risky.

I think your crocodile clips idea is good, there is every chance you will see some voltage drift, but I'm convinced that complete resolder of your parts in that circuit will do the trick!


----------



## bloodhawk

baronbeehive said:


> I  really wouldn't try to measure current, bit risky.
> 
> I think your crocodile clips idea is good, there is every chance you will see some voltage drift, but I'm convinced that complete resolder of your parts in that circuit will do the trick!


Yeah, this time i will do it in a way that literally guarantees both sides of the pads are properly connected no matter what.


----------



## baronbeehive (Mar 14, 2018)

I've drawn some speculative load lines for my 2 preferred driver tubes , the TS6SL7 and the GE12/6SL7. I'm not likely to change them for any other tubes now - the GE is my current favourite on account of its transparency and extended treble.
Some of the load lines will not be feasible because plate voltage and current might be outside of normal values.
I chose a range of B+ of slightly above and below what is probably correct to allow for a range of values, Maxx said that his different (power) tubes varied by about 10V on the B+, for example. As yet I haven't measured the actual B+ in my amp.

I haven't taken plate dissipation into account at this time.

I've indicated the ones that look worth exploring further with a red circle, no need to calculate anode/cathode values yet. You can see the grid, plate voltage and plate current. What do you think and are the values realistic? It's interesting that the Tungsol is not very linear at all yet it's one of my favourites. Maybe we should reverse our usual thinking!














































I intend to do the same for some power tubes although I realise from MrCurwen that calulating the values is not straight forward due to the intrusion of feedback into the equation. The only power tubes I would like to be using are the RCA 6AS7G and WE421A.

If anyone knows of any ultra linear power tubes to try for the high bias setting let me know.


----------



## baronbeehive (Mar 13, 2018)

Phew,I didn't think that would  load properly!

Here's the Tungsol 6SL7's.














































Edit: I had to shrink them to fit the page lol.


----------



## baronbeehive (Mar 14, 2018)

I thought it would be interesting to see what the operating point looks like on our amps.
Again I've estimated the B+ at 170v, and 150v to cover all possibilities.
Red and yellow lines are for stock settings: 220k anode, 1.5k cathode.
Green and blue lines are for mine and Sonic's settings: 33k anode, 390R cathode

Tungsol 6SL7 on left, GE 12/6SL7 on right. (GE is approximate due to going off scale at top).







The new setting on the TS looks slightly more linear but neither operating point looks ideal.
The new setting on the GE also looks slightly more linear and again neither operating point looks ideal. The stock load line looks quite good though.
The plate current looks high on the GE on the modded settings.

Edit: Looks like a better operating point would be on the -1v line for both tubes. I will bear this in mind when I've measured B+ accurately.

The higher plate current due to the mods at least allows you to get out of the non linear region.


----------



## baronbeehive

I measured the 1.2mA for the plate current through the CCS, (purple line), and for the GE, the Va reads 120v, blue line, 140v, green line.
For the TS Va reads 110v, blue line, 130v, green line.
i just noticed that this gives a good operating point coincidentally.
Sense resistor would be 833R, blue line, 1k, green line for GE
For TS sense resistor would be 666R, blue line, 1k, green line.


----------



## MrCurwen

baronbeehive said:


> What do you think and are the values realistic?



I don't see any values mentioned. It's easy enough to calculate them from your pictures but why not simply mention them if you wish to get comments?



baronbeehive said:


> It's interesting that the Tungsol is not very linear at all yet it's one of my favourites. Maybe we should reverse our usual thinking!



What do you mean, I challenge you to find a tube with µ over 10 and better curves.

If you mean the load lines instead of the tube, then that's another thing. But then what would the make of the tube have to do with it. I don't see what you're talking about.



baronbeehive said:


> If anyone knows of any ultra linear power tubes to try for the high bias setting let me know.



Please don't use that phrase. Ultralinear is a thing, it's a topology invented to decrease distortion from pentode and beam tetrode output stages.

Once again, your output stage is a WCF, emphasis on the follower. It is not a gain stage.

Pentodes make good followers, very unlinear as gain stages. 

FETs make supreme followers, very unlinear as gain stages.



baronbeehive said:


> Tungsol 6SL7 on left, GE 12/6SL7 on right. (GE is approximate due to going off scale at top).



I don't understand what's the point in presenting the same load lines on the same tube but two different manufacturers? If you don't like the graphics or the scale on one set of curves, simply use some other version of the curves. But why present more than one version of the same curves?



baronbeehive said:


> The new setting on the TS looks slightly more linear but neither operating point looks ideal.



Define ideal.

Once again you have to look at the situation, the circuit, as a whole. 

1) You only need about +-10V swing on the anode, maybe +-30V max on huge transients. Consider that when looking at the load line.

2) You have gNFB; distortion is lowered via that. Balance is not corrected AT ALL via gNFB since the loops are within phases.

3) Because of point 2 even if you have a slightly worse load line you still come out ahead as a whole if you take care of the balance problem.


----------



## MrCurwen

baronbeehive said:


> I measured the 1.2mA for the plate current through the CCS, (purple line)



You have the CCS tail built and operational?

I don't understand what it is you're doing at the moment.


----------



## SonicTrance

baronbeehive said:


> The higher plate current due to the mods at least allows you to get out of the non linear region.


Yes, this was the whole point of the driver stage bias mod.



baronbeehive said:


> Sense resistor would be 833R, blue line, 1k, green line for GE


You have not understood how to calculate the sense resistor. Both your graphs have a plate current of 1.2 mA. That's 2.4 mA through the CCS. 1.16/0.0024=483 ohms, a standard 470R would do just fine. A 1k sense R for example would give you 1.16 mA through the CCS, that's 0.58 mA for each triode.

I also second everything that MrC wrote. Even though different makes of the same tube sounds different in the LD, the curves are all the same. So you only have to use one set of curves for a specific tube.


----------



## baronbeehive

MrCurwen said:


> I don't understand what it is you're doing at the moment.



My limited goals are to look again at the anode and cathode values that we changed in the driver bias mod. Maxx chose one set of values and Sonic chose another.

Re: CCS mod I will be following Sonic's design for the CCS closely because we have both made similar mods with similar values




MrCurwen said:


> I don't see any values mentioned. It's easy enough to calculate them from your pictures but why not simply mention them if you wish to get comments?



Sorry, just preliminary attempts to elicit very general comment as to plate current values etc which I'm not sure about.



MrCurwen said:


> What do you mean, I challenge you to find a tube with µ over 10 and better curves.



Thank you, I meant where the load line was in relation to the curves, my mistake.



MrCurwen said:


> Please don't use that phrase. Ultralinear is a thing, it's a topology invented to decrease distortion from pentode and beam tetrode output stages.
> 
> Once again, your output stage is a WCF, emphasis on the follower. It is not a gain stage.
> 
> ...



OK.

I didn't know about the specific phraseology "ultralinear"



MrCurwen said:


> I don't understand what's the point in presenting the same load lines on the same tube but two different manufacturers? If you don't like the graphics or the scale on one set of curves, simply use some other version of the curves. But why present more than one version of the same curves?



I was not absolutely sure that same tubes by different manufacturers were identical in every respect.




MrCurwen said:


> Define ideal.
> 
> Once again you have to look at the situation, the circuit, as a whole.
> 
> ...



OK, I understand.

Just first faltering steps!


----------



## baronbeehive

SonicTrance said:


> Yes, this was the whole point of the driver stage bias mod.
> 
> 
> You have not understood how to calculate the sense resistor. Both your graphs have a plate current of 1.2 mA. That's 2.4 mA through the CCS. 1.16/0.0024=483 ohms, a standard 470R would do just fine. A 1k sense R for example would give you 1.16 mA through the CCS, that's 0.58 mA for each triode.



Right, thanks for pointing that out.


----------



## Maxx134

baronbeehive said:


> Thank you, I meant where the load line was in relation to the curves, my mistake.


Don't thank him for being a crab.
He should know your still learning.



baronbeehive said:


> I was not absolutely sure that same tubes by different manufacturers were identical in every respect


Yes and no..

They are not identical in every parameter,
 & that's why we all have favorites og brand or year, in every type.

There supposed to be same specs & graphs,
 but if you see one slightly different it would be interesting to post.


----------



## baronbeehive (Mar 14, 2018)

Maxx134 said:


> Don't thank him for being a crab.
> He should know your still learning.



Ha ha, trying to be polite lol.

Edit: I was only trying to get past 1000, don't care about this hifi at all!


----------



## baronbeehive (Mar 14, 2018)

Just out of interest I thought I would see what Maxx's settings looked like, here they are in 2 shades of brown:






They look good, but it's all in the listening.

(I think your B+ is 150v so the light brown will be more accurate).


----------



## MrCurwen

baronbeehive said:


> My limited goals are to look again at the anode and cathode values that we changed in the driver bias mod. Maxx chose one set of values and Sonic chose another.



I see. 

Because B+ is so low, none of the load lines are not so good. Luckily the swing needed is not that big. Always good to practise drawing load lines.

A gyrator load would allow for a flat load line, combined with CCS tail at desired anode current, even at 150V B+. Not sure about stability inside a gNFB loop, also probably wouldn't fit inside the chassis.



baronbeehive said:


> Re: CCS mod I will be following Sonic's design for the CCS closely because we have both made similar mods with similar values



Good idea. 



baronbeehive said:


> Sorry, just preliminary attempts to elicit very general comment as to plate current values etc which I'm not sure about.



I would shoot for 1 to 1.3 mA of Ia in your scenario. Enough to get the tube really conducting, and to offer at least some drive to the following coupling cap.



baronbeehive said:


> I didn't know about the specific phraseology "ultralinear"



Here's a schematic:



So g2 (screen grid) is not connected to a DC supply (pentode mode), it's not connected to the anode (triode mode), but rather somewhere inbetween. UL requires a special tap on the OT primary, usually at 17% of the primary turns. 

Curves are somewhere between triode and pentode (or beam tetrode) mode. Compare the different mode curves: http://www.audiomatica.com/tubes/6l6.htm

17% was more or less arbitrarily chosen as a nice point, there have been also different tap arrangements. The closer you move the tap to the anode side, the more the curves resemble triode mode, and the closer you move it to B+, the more the curves resemble pentode or beam tetrode mode.

In technical terms you are introducing a local feedback loop that has part of the primary in it. The point of this was to achieve some better THD performance of the triode mode while retaining some of the higher power output of the pentode mode.

It's still used in some bass guitar amplifiers and retro type PA amplifiers, but I wouldn't recommend UL for serious best results HIFI use. It still has lots of pentode mode odd harmonics present. (Adds 'bite' to bass guitar sound.)



baronbeehive said:


> I was not absolutely sure that same tubes by different manufacturers were identical in every respect.



Not in every respect, but for voltage and current purposes and load line purposes, yes, they are identical.

Or, as identical as any tubes of the same type, within one manufacturer. Remember these curves say AVERAGE for a reason. They were made as composites, typically taking readings from a hundred different tubes.

If the type was meant for home use, they might include tubes with +-20% specs in that average. If it was special quality for industry or military, maybe only +-10%.

There is bound to be great variance in anode resistance and sometimes even µ (though that is a bad sign for quality) among any tubes, within or between manufacturers.

Modern people think with modern standards. These were not the standards when tubes were developed and mass manufactured.

The reason tube rolling works in some circuits, is just that; there is a lot of variance. If the circuit is "balanced on a tipping point", small variance one way or another can change the behavior of the circuit. Smart design avoids this.

Anode resistance is the big one usually, it affects distortion behavior, but different capacitances can affect 'tone'. If your circuit can deal with the capacitances, all tubes "sound the same".



Maxx134 said:


> He should know your still learning.



Yes I know. The way you learn is that somebody points out the correct information when you use terms incorrectly. Leaving somebody in a state of mistake is not a favor to that person.



Maxx134 said:


> Don't thank him for being a crab.



My posts are written more or less like an engineer. Aside from clear joking, any emotional tone you infer is your own projection.

Do not use such language in the future to refer to me or my writing.


----------



## Maxx134 (Mar 15, 2018)

baronbeehive said:


> Edit: I was only trying to get past 1000,



You did post allot of graphs lol




MrCurwen said:


> and to offer at least some drive to the following coupling cap


I agree  as I  have noticed the 6SL7 type and other  higher gain (6C8G) was always Better sounding to me.




MrCurwen said:


> The way you learn is that somebody points out the correct information when you use terms incorrectly. Leaving somebody in a state of mistake is not a favor to that person.


Yes we have different ways.
I rather try explain first rather than afterwards.
You just now explained a day later.

Although it may give them time to think,
 it also may negatively discourage if they don't have time or ability to figure it out as this remains a hobby to most so time is limited.

Anyways point taken on your egineering approach.

I will also make clear  that I do appreciate all your posts regardless,
 as well as all seasoned experienced members,
And shown that with likes to your older posts.


----------



## baronbeehive

MrCurwen said:


> My posts are written more or less like an engineer. Aside from clear joking, any emotional tone you infer is your own projection.



He was joking, we try not to be too serious on this thread!

Anyway no worries, I've made my intentions clear and thanks for that information, I'll study it later. I'm excited to try the CCS, but trying not to expect too much , so that I can seriously evaluate it later.



Maxx134 said:


> You did post allot of graphs lol



I meant 1000 posts!

Nobody congratulated me LOL.


----------



## bloodhawk (Mar 16, 2018)

So i think the bias issue is fixed. He has 2 bad 330R resistors whose values would go up by about 25Ohms as the amp started to heat up.

Im still now too confident though, usually with the 6080's it seems fine on when the amp is upside down on my workbench, but once i put it back together and set it up properly the bias deviates. Ill finish and test it again tomorrow.

For not the bias's match even after leaving the amp running for about 20 mins.


If someone can do me a favor... Can you please the continuity between the R+ and L- terminals next to the pot ? 
When I test that I get this really grainy beep. I'm starting to believe that the pot has been the cause this whole time for slightly channel imbalance. 

Or if someone can tell how to bypass the pot all together.. 
I do have a 100k stereo pot with me if there is any way to use that to test things.


----------



## klnglim (Mar 16, 2018)

klnglim said:


> Hopefully no more smoke after replace all the wires


After changing cable , check connection no error, still same burning happened, have no idea what is wrong


----------



## bloodhawk (Mar 16, 2018)

klnglim said:


> After changing cable , check connection no error, still same burning happened, have no idea what is wrong



Will you be able to post a well lit picture of where exactly the burning is happening?

@baronbeehive @Maxx134

Are these voltages normal from common ground to PSU side of Anode / Cathode resistors? (From Right , tube 4, to Left, tube 1)
75 - 75 - 79 - 79  -  79 - 79 - 79 - 79
 And Pin 1's to driver / output side cathode / anode resistors -
52 - 45 - 53/55 - 55 - 55 - 55 - 53-55 - 55


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## klnglim (Mar 16, 2018)

bloodhawk said:


> Will you be able to post a well lit picture of where exactly the burning is happening?


Always same place burning, this is Right side error, Left side has no problem, but I have checked every where no connection error, fuse no broken.
When turn on left side light on and after few minutes right side light on, straight burning happen.
Confusing about what has happened now. Can anyone tell me what is the exact amount of resistor there


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## klnglim (Mar 16, 2018)

bloodhawk said:


> Will you be able to post a well lit picture of where exactly the burning is happening?
> 
> @baronbeehive @Maxx134
> 
> ...


Tube light show normal while turn on and after burned tube still light up normal but the BOTH SIDE meter show '0'


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## bloodhawk

klnglim said:


> Always same place burning, this is Right side error, Left side has no problem, but I have checked every where no connection error, fuse no broken.
> When turn on left side light on and after few minutes right side light on, straight burning happen.
> Confusing about what has happened now. Can anyone tell me what is the exact amount of resistor there





klnglim said:


> Tube light show normal while turn on and after burned tube still light up normal but the BOTH SIDE meter show '0'



That looks like something is burning on the other side of the board or shorted. By any chance do you have an image of the same spot on the other side with the board flipped over?
I dont have a MK8 so cant be of too much help, i would definitely check if the resistor/diode pins are by chance penetrating a wire on the other side.


----------



## klnglim

bloodhawk said:


> That looks like something is burning on the other side of the board or shorted. By any chance do you have an image of the same spot on the other side with the board flipped over?
> I dont have a MK8 so cant be of too much help, i would definitely check if the resistor/diode pins are by chance penetrating a wire on the other side.


         

All seen normal


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## SonicTrance (Mar 16, 2018)

bloodhawk said:


> Are these voltages normal from common ground to PSU side of Anode / Cathode resistors? (From Right , tube 4, to Left, tube 1)
> 75 - 75 - 79 - 79 - 79 - 79 - 79 - 79


No, if you’re measuring from psu side to ground it should read +100 V from anode resistors and -100 V from cathode resistors, ei full B+ and B-. If you’re talking about the output stage. 



bloodhawk said:


> And Pin 1's to driver / output side cathode / anode resistors -
> 52 - 45 - 53/55 - 55 - 55 - 55 - 53-55 - 55


Don’t understand what it is you’re measuring here? Pin 1 is one of the grids.


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## SonicTrance

klnglim said:


> Always same place burning, this is Right side error, Left side has no problem, but I have checked every where no connection error, fuse no broken.
> When turn on left side light on and after few minutes right side light on, straight burning happen.
> Confusing about what has happened now. Can anyone tell me what is the exact amount of resistor there


This has happened to me as well! Check the 100 V zener diodes, they’re most likely open. You’ve circled the B- zener but replace both. I used 3w zener s there followed by 5w resistors. Also check the voltage setting transistors. The one for B- is more than likely broke! Again, replace both. I can give you part number tomorrow when I’m at the computer as the transistors LD use are no longer used.


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## bloodhawk (Mar 16, 2018)

SonicTrance said:


> No, if you’re measuring from psu side to ground it should read +100 V from anode resistors and -100 V from cathode resistors, ei full B+ and B-. If you’re talking about the output stage.
> .



Damn, then im way off. Any idea what to check for, to figure out what is causing the discrepancy? By the Anode/Cathode resistors i mean the 330R's .. Am i mistaken here or does this need to be measured at the 220R's?

All the connections /  wires were resoldered to make sure things were in place. 



> Don’t understand what it is you’re measuring here? Pin 1 is one of the grids.



Hunh, i was under the impression Pin 1 was ground / NC ?


----------



## SonicTrance

bloodhawk said:


> Damn, then im way off. Any idea what to check for, to figure out what is causing the discrepancy? By the Anode/Cathode resistors i mean the 330R's .. Am i mistaken here or does this need to be measured at the 220R's?
> 
> All the connections /  wires were resoldered to make sure things were in place.
> 
> ...


You’re probably measuring from anode and cathode side of the resistors in which case the 79 V readings are normal (the readings at the cathode should be negative). 75 V are a little low as that would mean a 25 V drop across 330R, that’s 76 mA of bias. 

Don’t know of any 220R resistors?

Yes, pin1 is grid. 6sn7/6080/6as7 has easy to learn pinout: grid, plate, cathode, grid, plate, cathode, heater, heater.


----------



## baronbeehive

bloodhawk said:


> So i think the bias issue is fixed. He has 2 bad 330R resistors whose values would go up by about 25Ohms as the amp started to heat up.
> 
> Im still now too confident though, usually with the 6080's it seems fine on when the amp is upside down on my workbench, but once i put it back together and set it up properly the bias deviates. Ill finish and test it again tomorrow.
> 
> For not the bias's match even after leaving the amp running for about 20 mins.



Ha, I had exactly this problem. Fortunately there is usually a simple solution. What that suggests to me is a bad connection somewhere which might look ok on the surface. The thing is when you put the parts back in their positions you have to bend wires and push caps back in place etc putting pressure on the joints. So what I would suggest is to check continuity on those areas you suspect on that problem circuit but this time wiggle the wires as you do the check, I suspect you might find continuity is disrupted on the problem areas. Those resistors going off is also a result of the problem, not the cause I suspect.  Also I bet they are on that problem circuit.


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## bloodhawk (Mar 16, 2018)

SonicTrance said:


> You’re probably measuring from anode and cathode side of the resistors in which case the 79 V readings are normal (the readings at the cathode should be negative). 75 V are a little low as that would mean a 25 V drop across 330R, that’s 76 mA of bias.
> 
> Don’t know of any 220R resistors?
> 
> Yes, pin1 is grid. 6sn7/6080/6as7 has easy to learn pinout: grid, plate, cathode, grid, plate, cathode, heater, heater.



Ah gotcha. So im guessing one of the PSU components isnt properly soldered. Any tips on what to check for the bias drop? Pretty much covered all the basic things like re tinning, making sure both sides of the via/pads are properly soldered along with checking each of the components out of the circuit.

I meant the 220k resistors, at the driver stage.

Really appreciate it!


baronbeehive said:


> Ha, I had exactly this problem. Fortunately there is usually a simple solution. What that suggests to me is a bad connection somewhere which might look ok on the surface. The thing is when you put the parts back in their positions you have to bend wires and push caps back in place etc putting pressure on the joints. So what I would suggest is to check continuity on those areas you suspect on that problem circuit but this time wiggle the wires as you do the check, I suspect you might find continuity is disrupted on the problem areas. Those resistors going off is also a result of the problem, not the cause I suspect.  Also I bet they are on that problem circuit.



Will do ! Im literally this close to taking the whole thing apart and rewiring everything to my liking.. but only if this was my amp lol.


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## baronbeehive

bloodhawk said:


> Will do ! Im literally this close to taking the whole thing apart and rewiring everything to my liking.. but only if this was my amp lol.



Probably no need to go to those lengths lol.

Check every connection there, not just wires, all new parts, legs etc, give them a good wiggle because if they come off then they were not soldered properly anyway!It's possible that the solder looks good on the pad but the pad might have come unstuck with too much heat and just making feeble contact. Also people make the mistake of using too much solder which just  hides the problem from view.


----------



## bloodhawk

baronbeehive said:


> Probably no need to go to those lengths lol.
> 
> Check every connection there, not just wires, all new parts, legs etc, give them a good wiggle because if they come off then they were not soldered properly anyway!It's possible that the solder looks good on the pad but the pad might have come unstuck with too much heat and just making feeble contact. Also people make the mistake of using too much solder which just  hides the problem from view.



I resoldered all the new parts properly with continuity checks 2 days back. Only solder joints i havent  checked are of the PSU side components. Guess i should do that as well.


----------



## baronbeehive

bloodhawk said:


> I resoldered all the new parts properly with continuity checks 2 days back. Only solder joints i havent  checked are of the PSU side components. Guess i should do that as well.



If the bias is fine upside down but not when you put  it back together, it's got to be what I said, that's the only thing that's changed.


----------



## klnglim

SonicTrance said:


> This has happened to me as well! Check the 100 V zener diodes, they’re most likely open. You’ve circled the B- zener but replace both. I used 3w zener s there followed by 5w resistors. Also check the voltage setting transistors. The one for B- is more than likely broke! Again, replace both. I can give you part number tomorrow when I’m at the computer as the transistors LD use are no longer used.


The transistor is L7812CV, I have just changed brand new, the original resistor show 2k2 ohm / 0.5 watts


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## bloodhawk

klnglim said:


> The transistor is L7812CV, I have just changed brand new, the original resistor show 2k2 ohm / 0.5 watts



You should check the Diode on top of it as well.


----------



## klnglim

SonicTrance said:


> This has happened to me as well! Check the 100 V zener diodes, they’re most likely open. You’ve circled the B- zener but replace both. I used 3w zener s there followed by 5w resistors. Also check the voltage setting transistors. The one for B- is more than likely broke! Again, replace both. I can give you part number tomorrow when I’m at the computer as the transistors LD use are no longer used.


ok thanks


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## bloodhawk

Annnd yeap the issue is with the tube sockets. Now the issue has moved to socket 2 xD

FML.


----------



## klnglim

bloodhawk said:


> You should check the Diode on top of it as well.


every where checked no problem except the place which resistor was burnt


----------



## SonicTrance

klnglim said:


> The transistor is L7812CV, I have just changed brand new, the original resistor show 2k2 ohm / 0.5 watts


That transistor is for the fan 12 V power supply. I'm talking about the transistors that are located between the power transformers, MJ15020 and MJ15021. 
Check the wires that's coming from those transistors first as they're notorious for breaking. If connection is good check the transistors, the MJ15021 (B-) is probably broke. If so replace both with these:
MJ15024G (NPN) for B+
MJ15025G (PNP) for B-
Also, the zeners are more than likely open if there's smoke! You can use higher wattage resistors in that posistion for the 2k2 and 2k7. It's a week spot in this amp.


----------



## bloodhawk

SonicTrance said:


> That transistor is for the fan 12 V power supply. I'm talking about the transistors that are located between the power transformers, MJ15020 and MJ15021.
> Check the wires that's coming from those transistors first as they're notorious for breaking. If connection is good check the transistors, the MJ15021 (B-) is probably broke. If so replace both with these:
> MJ15024G (NPN) for B+
> MJ15025G (PNP) for B-
> Also, the zeners are more than likely open if there's smoke! You can use higher wattage resistors in that posistion for the 2k2 and 2k7. It's a week spot in this amp.



LOL talk about timing, one of the zeners blew on the amp i was working on because of the brittle ass wires (black one to be exact). (The top one to be specific, going to MJ15020 )


Any way to test if there was damage to the transistors?

Also do you have a link to where you got the 3w Zeners from ? Im ordering the transistors from mouser..

Once the new ones are here, ill just replace the garbage wire with some extended better quality wiring. 

@baronbeehive I think the issue was party the heater wiring between the sockets as well. I swapped out the wires and the voltages were matching across both sides, at least before the diode went kablowie. xD


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## SonicTrance

bloodhawk said:


> Any way to test if there was damage to the transistors?


Here's how you test transistors on a DMM:

Step 1: (Base to Emitter)

Hook the positive lead from the multimeter to the to the BASE (B) of the transistor. Hook the negative meter lead to the EMITTER (E) of the transistor. For an good NPN transistor, the meter should show a voltage drop between 0.45V and 0.9V. If you are testing PNP transistor, you should see “OL” (Over Limit).

Step 2: (Base to Collector)

Keep  the postitive lead on the BASE (B) and place the negative lead to the COLLECTOR (C).

For an good NPN transistor, the meter should show a voltage drop between 0.45V and 0.9V. If you are testing PNP transistor, you should see "OL" (Over Limit).

Step 3: (Emitter to Base)

Hook the positive lead from the multimeter to the to the EMITTER (E) of the transistor. Hook the negative meter lead to the BASE (B) of the transistor.

For an good NPN transistor, you should see “OL” (Over Limit).If you are testing PNP transistor, the meter should show a voltage drop between 0.45V and 0.9V.

Step 4: (Collector to Base)

Hook the positive lead from the multimeter to the to the COLLECTOR (C) of the transistor. Hook the negative meter lead to the BASE (B) of the transistor.

For an good NPN transistor, you should see “OL” (Over Limit).If you are testing PNP transistor, the meter should show a voltage drop between 0.45V and 0.9V.

Step 5: (Collector to Emitter)

Hook the postitive meter lead to the COLLECTOR (C) and the negative meter lead to the EMITTER (E) – A good NPN or PNP transistor will read "OL"/Over Limit on the meter. Swap the leads (Positive to Emitter and Negative to Collector) – Once again, a good NPN or PNP transistor should read “OL”.

If your bipolar transistor measures contrary to these steps, consider it to be bad.



bloodhawk said:


> Also do you have a link to where you got the 3w Zeners from ? Im ordering the transistors from mouser..


Just use any 2 or 3w 100 V zeners, nothing special. Would also recommend higher wattage resistors for the 2k2 and 2k7. Mills MRA5 is a tight fit in those holes. Here's mine.


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## bloodhawk

SonicTrance said:


> Here's how you test transistors on a DMM:
> 
> Step 1: (Base to Emitter)
> 
> ...




Thanks a bunch for the detailed reply Sonic! 

So the transistors are also dead :S 

All the values that are supposed to be between 0.45-0.9 V keep on rising way past that. 

I ordered  5W 100V zeners that should be here tomorrow, i think i might have a  2.2k MRA5 with me, but might need to just hook up a 2k7 1W for the other resistor for the time being.


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## SonicTrance

The new transistors I recommended also have higher spec, so they will not fail as easily. Hope you get the amp going soon!


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## baronbeehive

SonicTrance said:


> The new transistors I recommended also have higher spec, so they will not fail as easily. Hope you get the amp going soon!



x2


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## klnglim

SonicTrance said:


> This has happened to me as well! Check the 100 V zener diodes, they’re most likely open. You’ve circled the B- zener but replace both. I used 3w zener s there followed by 5w resistors. Also check the voltage setting transistors. The one for B- is more than likely broke! Again, replace both. I can give you part number tomorrow when I’m at the computer as the transistors LD use are no longer used.


Can u tell me how to  check the voltage setting transistors?


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## SonicTrance

klnglim said:


> Can u tell me how to  check the voltage setting transistors?


Look at first post on this side. In my quote in bloodhawks post.


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## klnglim

SonicTrance said:


> That transistor is for the fan 12 V power supply. I'm talking about the transistors that are located between the power transformers, MJ15020 and MJ15021.
> Check the wires that's coming from those transistors first as they're notorious for breaking. If connection is good check the transistors, the MJ15021 (B-) is probably broke. If so replace both with these:
> MJ15024G (NPN) for B+
> MJ15025G (PNP) for B-
> Also, the zeners are more than likely open if there's smoke! You can use higher wattage resistors in that posistion for the 2k2 and 2k7. It's a week spot in this amp.


ok, now I understand, just ordered NPN & PNP transistor, 5W Zener Diodes & 5W resistors, thanks a lot


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## SonicTrance

klnglim said:


> ok, now I understand, just ordered NPN & PNP transistor, 5W Zener Diodes & 5W resistors, thanks a lot


No problem!


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## bloodhawk (Mar 17, 2018)

SonicTrance said:


> The new transistors I recommended also have higher spec, so they will not fail as easily. Hope you get the amp going soon!



Yeah i think i could have prevented this from happening, but i was so excited to see matching voltages that i i didnt realize that they were higher than usual. Instead of the normal 2.5 to 3.2 V (before the relays kick in) they were at 2.7 to 5.5V. Asa the relays kicked in there was a pop and bye bye Zener. All because of a brittle B- Base wire.


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## klnglim

SonicTrance said:


> No problem!


The resistors value 2.7K ohm I ordered may be temporary out of stock, can I connect value 5.6K ohm as parallel as replacement?


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## SonicTrance

klnglim said:


> The resistors value 2.7K ohm I ordered may be temporary out of stock, can I connect value 5.6K ohm as parallel as replacement?


Yes. Dont see any problem with that. That would be 2k8, close enough.


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## baronbeehive (Mar 18, 2018)

bloodhawk said:


> Yeah i think i could have prevented this from happening, but i was so excited to see matching voltages that i i didnt realize that they were higher than usual. Instead of the normal 2.5 to 3.2 V (before the relays kick in) they were at 2.7 to 5.5V. Asa the relays kicked in there was a pop and bye bye Zener. All because of a brittle B- Base wire.



That's the problem we have, usually a faulty connection that then goes on to cause collateral damage before we realise something's up. I never lose the excitement of seeing the meters reading the same current lol.


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## klnglim (Mar 22, 2018)

SonicTrance said:


> Yes. Dont see any problem with that. That would be 2k8, close enough.


All Z-diodes, resistor and transistor had been replaced, now the amp power on as normal, no more burn and all tube light up look normal however no sound and the meter show '0' , did I miss something not yet troubleshoot?


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## SonicTrance

klnglim said:


> All Z-diodes, resistor and transistor had been replaced, now the amp power on as normal, no more burn and all tube light up look normal however no sound and the meter show '0' , did I miss something not yet troubleshoot?


Sounds like the protection circuit is kicking in if the meters read 0 mA. Hard to say why? A short somewhere or a bad tube maybe? Have you measured voltage at all key points? Rail, anode, cathode voltage for output stage and input stage.


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## klnglim (Mar 22, 2018)

SonicTrance said:


> Sounds like the protection circuit is kicking in if the meters read 0 mA. Hard to say why? A short somewhere or a bad tube maybe? Have you measured voltage at all key points? Rail, anode, cathode voltage for output stage and input stage.


may I know how to measure?Do I need to turn on power while taking measurement?>Tube valve is brand new and look good when light up,I guess may be something wrong with resistor in somewhere else


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## baronbeehive

klnglim said:


> may I know how to measure?Do I need to turn on power while taking measurement?>Tube valve is brand new and look good when light up,I guess may be something wrong with resistor in somewhere else



First, do you have a multimeter, if so have you checked continuity with the board trace on your connections?

I don't think it is this but to rule it out you could check the continuity from ground to the opamp pins,  if more than one of the pins is showing continuity then the opamp has a short and you will get no sound.

Also have you checked the 2 fuses?


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## baronbeehive (Mar 23, 2018)

I wanted to try to put to rest the difference of opinion over the driver stage anode and cathode values. Maxx and Sonic have already experimented so I wanted to get into the mix.

I've produced a graph showing stock values, Sonic's values and Maxx's values together with my proposed values. The values are ball park figures.

I've also shown on the graph some values required for the CCS as suggested by Sonic and MrCurwen.

As you can see all the operating points on the graph fall below the 3.5mA/tube that Sonic recommended. Also the CCS would not fit with the stock values.

My proposed operating points shown in green are shown in several positions of differing linearity. I intend to pick some of these points to experiment with SQ. I especially like the points on or just over the -1v grid line because the voltage swing is more equal either side of zero volts while still remaining linear. However that depends on how much voltage swing there is, the larger the swing the better the operating point on the bias voltage further to the left of the -1 grid line is because the positive swing would approach the non linear region. Obviously it's not necessary to put precise values yet as I've not decided anyway but these operating points are suggestions. The values I propose are realistic. I could go outside the range of values suggested by Sonic, but I don't think I know enough to try it and he has already defined some operating limits. I'm open to suggestions. What do you think?

So now I will order some resistors at the same time I get the CCS parts, so I can experiment, and have fun.

Edit: To avoid confusion, the CCS is a separate issue from the anode/cathode resistors. Once I have decided on optimum resistors for anode and cathode then I intend to go on to fit the CCS at the best operating point for the CCS, so I don't want to confuse issues. The anode/cathode experiment is just for anyone doing the driver bias mod, not the CCS mod.








The graph on the bottom shows the proposed cathode values.


----------



## klnglim

baronbeehive said:


> First, do you have a multimeter, if so have you checked continuity with the board trace on your connections?
> 
> I don't think it is this but to rule it out you could check the continuity from ground to the opamp pins,  if more than one of the pins is showing continuity then the opamp has a short and you will get no sound.
> 
> Also have you checked the 2 fuses?


Yes I have Digital Multi Meter, I have looked surround the PCB board cabling several times, cant find any error, resistor and Fuse checked all good. As I m new to this that's why many IC component measurement need guidance, I remember this amp suddenly come out very fast light sparkling outside the case while half way listening to music, that was first time make me so scary crap in my experience, later on no matter how I try to fix, the amp keep burning and smoke while the right side VU meter start ligfht on,luckily after change transistor, resistor and Z diodes, the worst scary nightmare smoke and burn problem solve, all tube light up normal, unfortunately the both side VU meter light up with value '0' and no sound , plug in headphone hear nothing at all,   any help is much appreciated, thanks anyway!


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## baronbeehive (Mar 24, 2018)

klnglim said:


> Yes I have Digital Multi Meter, I have looked surround the PCB board cabling several times, cant find any error, resistor and Fuse checked all good. As I m new to this that's why many IC component measurement need guidance, I remember this amp suddenly come out very fast light sparkling outside the case while half way listening to music, that was first time make me so scary **** in my experience, later on no matter how I try to fix, the amp keep burning and smoke while the right side VU meter start ligfht on,luckily after change transistor, resistor and Z diodes, the worst scary nightmare smoke and burn problem solve, all tube light up normal, unfortunately the both side VU meter light up with value '0' and no sound , plug in headphone hear nothing at all,   any help is much appreciated, thanks anyway!



OK. You should do what Sonic says and check your voltages... *but first I have to repeat the safety warning on page1 for all new members:*

*It is very dangerous, you could be killed if you touch anything inside the amp while it is switched on so only go ahead if you understand and are aware of the dangers. Also after you switch off wait some time, I usually wait about 30 minutes, until the parts inside have discharged because the danger is still there until then.*

You need to measure the voltages to ground at:
power stage anode - 330R resistors, the 4 resistors you can see when you open up the bottom,
cathode - at cathode bypass,
driver stage anode - 2 groups of 2x220K resistors near bottom corners,
cathode 1k5 resistor, the resistor in a group of 3 nearest the pot,
the bias at tube pin 1.

Are you OK with that?


----------



## klnglim

baronbeehive said:


> OK. You should do what Sonic says and check your voltages... *but first I have to repeat the safety warning on page1 for all new members:*
> 
> *It is very dangerous, you could be killed if you touch anything inside the amp while it is switched on so only go ahead if you understand and are aware of the dangers. Also after you switch off wait some time, I usually wait about 30 minutes, until the parts inside have discharged because the danger is still there until then.*
> 
> ...


Yes , I understand the dangerous of electric shock, normally I will wait at least 30min before open the bottom cover. Did u mean measure the DC voltage ?


----------



## SonicTrance

klnglim said:


> Yes , I understand the dangerous of electric shock, normally I will wait at least 30min before open the bottom cover. Did u mean measure the DC voltage ?


Yes, measure DC volts. Put the black, ground, lead of your DMM in one of the ground holes between the filter caps. Then measure voltage at both sides of anode and cathode resistors with the red lead.


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## bloodhawk (Mar 24, 2018)

@baronbeehive @SonicTrance

Swapped out the faulty transistors and the diodes. All good on the PSU end.

But the bias issue still persists.

Here are the voltages across the anode / cathode resistors (Tube 1 to tube 4 respectively) -

79V / 79 V / 78.75V / 79V  - 78 V / 78V / 76V / 77 V

- I re soldered all the wire soldered points at the back
- Redid the tube socket soldering for the right channel tubes
- Checked for shorts/lifted pads (none were bad)
- Checked out put wiring (dont think this will affect the bias though)
- Checked voltages across driver stage anode resistors and the 1k5 resistors.

Dont know how to check the bias at tube pin one though?

Also the left side bias meter now shows 0  , even though the audio is fine and same as usual. The wiring to and from the meter is also fine. I have a feeling the meter might be busted since the last time when the transistors/diodes went bust, one of the wires for the left meter also snapped off. Resoldering that didnt help.

Here are few images of the problematic region in the amp im trying to fix - https://imgur.com/a/AsIY9

Also could it be that im looking at the problem entirely wrong and the left channel is biasing higher because of an issue there?


----------



## baronbeehive

bloodhawk said:


> @baronbeehive @SonicTrance
> 
> 
> Here are the voltages across the anode / cathode resistors (Tube 1 to tube 4 respectively) -
> ...



Goddamit!

That's not a massive difference, but I see it's on the same side though. I don't think it's a bad connection now, could be just some resistor that's off or something. Could be tube now. Swap the tubes and see if the problem moves with the tubes.

Then take voltages on both sides of anode/cathode resistors at both power and driver stages and let us know what they are.

Also at tube pins1 and 4 to check grid voltage.



bloodhawk said:


> @baronbeehive @SonicTrance
> 
> Also the left side bias meter now shows 0  , even though the audio is fine and same as usual. The wiring to and from the meter is also fine. I have a feeling the meter might be busted since the last time when the transistors/diodes went bust, one of the wires for the left meter also snapped off. Resoldering that didnt help.



Possibly, or could be stuck. Could check with an ammeter or swap wires, bit of a faff though.



bloodhawk said:


> @baronbeehive @SonicTrance
> 
> Also could it be that im looking at the problem entirely wrong and the left channel is biasing higher because of an issue there?



No that channel looks to be reading with correct values.


----------



## bloodhawk

baronbeehive said:


> Goddamit!
> 
> That's not a massive difference, but I see it's on the same side though. I don't think it's a bad connection now, could be just some resistor that's off or something. Could be tube now. Swap the tubes and see if the problem moves with the tubes.
> 
> ...



Its definitely not the tubes, since i tried the swap last night. Ill check the resistors again tonight.


----------



## bloodhawk

baronbeehive said:


> Goddamit!
> 
> That's not a massive difference, but I see it's on the same side though. I don't think it's a bad connection now, could be just some resistor that's off or something. Could be tube now. Swap the tubes and see if the problem moves with the tubes.
> 
> ...



Hey @baronbeehive , wanna know how big a retard i am ?? And how happy my friend is right now?


----------



## baronbeehive

bloodhawk said:


> Hey @baronbeehive , wanna know how big a retard i am ?? And how happy my friend is right now?



Yeah.......!!


----------



## bloodhawk

baronbeehive said:


> Yeah.......!!



He accidentally swapped the 300R / 470R resistors :\


----------



## baronbeehive

bloodhawk said:


> He accidentally swapped the 300R / 470R resistors :\



Oh, that...... we've all done it lol!

So is everything OK now....


----------



## bloodhawk

baronbeehive said:


> Oh, that...... we've all done it lol!
> 
> So is everything OK now....



Bias is back to normal, but the highs on the right channel dont seem to be as clear as the left channel.

But for now he seems to be happy as it isn't as extreme as it was before.


----------



## SonicTrance

bloodhawk said:


> He accidentally swapped the 300R / 470R resistors :\


Which resistors are you referring to? Only 300R resistors I can think of are the grid resistors and the 470R are ground references for the grids. Got nothing to do with bias?



bloodhawk said:


> Here are the voltages across the anode / cathode resistors (Tube 1 to tube 4 respectively) -
> 
> 79V / 79 V / 78.75V / 79V - 78 V / 78V / 76V / 77 V


You're measuring those voltages to ground. When you say "across" you mean from one end of the resistor to the other. In other words the voltage drop across the resistor, which would be about 21 V. Also, please remember to ad (-) when voltages are negative. Im thinking about people who might be reading this thread and are doing mods based on recent posts.


----------



## bloodhawk (Mar 26, 2018)

SonicTrance said:


> Which resistors are you referring to? Only 300R resistors I can think of are the grid resistors and the 470R are ground references for the grids. Got nothing to do with bias?



Weirdly enough, putting the those 2 in the correct places, instantly improved the bias gap.



> You're measuring those voltages to ground. When you say "across" you mean from one end of the resistor to the other. In other words the voltage drop across the resistor, which would be about 21 V. Also, please remember to ad (-) when voltages are negative. Im thinking about people who might be reading this thread and are doing mods based on recent posts.



Yes, to ground. I have not tried across yet. Since the resistance values were on point

Im sure its getting confusing for most. Since there arent particular resources consolidated enough for people to be able to troubleshoot on their own. And most senior members are super busy to be able to help. I can move this over to PM's if it helps?

For newer members or ones who arent really experienced in troubleshooting issues like this, would greatly benefit from the most common voltage reference points and the appropriate values. Or what the most common causes of such issues might be. I personally know at least one person who has managed to mess up a few things with the mods, and literally didnt know what to do or what to check to find the cause. Even though it seems that other have had similar problems, but none of those were mentioned here or documented.

End of the day im  most grateful for whatever help i can get here. If im able to fix this amp for his, it will be awesome, other wise he will just go back to his WA22 and ask me to either dump it or sell it for parts here.

I can also volunteer to do a full write of these things, with pictures and warning, if anyone is willing enough to guide me and explain things.


----------



## SonicTrance

bloodhawk said:


> Weirdly enough, putting the those 2 in the correct places, instantly improved the bias gap.
> 
> 
> 
> ...


That is kind of strange. 

No reason for PMs. Its good to keep the thread alive. Just think we should be as accurate as we can when we post. Im glad the amp is working, finally!
Now you can go back to work on your own amp.


----------



## bloodhawk

SonicTrance said:


> That is kind of strange.
> 
> No reason for PMs. Its good to keep the thread alive. Just think we should be as accurate as we can when we post. Im glad the amp is working, finally!
> Now you can go back to work on your own amp.



Yeah, next on the agenda is adding better quality sockets, along with swapping out the transformer and output wiring! 

Before that though i need to swap out the pot and the busted left channel ammeter in his amp. At least for now the gap in voltages has dropped down all the way from being 5-7V apart to 1.3-3V at the most.


----------



## baronbeehive

SonicTrance said:


> Im glad the amp is working, finally!



+1



bloodhawk said:


> I can also volunteer to do a full write of these things, with pictures and warning, if anyone is willing enough to guide me and explain things.



That's quite a good idea, I get tired of repeating warnings all the time. Also it takes a while to familiarize yourself with the insides of the amp and a quick guide would help. See what Maxx thinks.



bloodhawk said:


> Before that though i need to swap out the pot and the busted left channel ammeter in his amp. At least for now the gap in voltages has dropped down all the way from being 5-7V apart to 1.3-3V at the most.



So did you take voltages, if you took them on both sides of the reference points it would help to pinpoint issues.


----------



## bloodhawk (Mar 26, 2018)

baronbeehive said:


> So did you take voltages, if you took them on both sides of the reference points it would help to pinpoint issues.



Yeap, new voltages are 80V / 79.8V / 79V / 79.8V / 77.8V / 78V / 79.6V / 80V

For now hes super happy with the amp , i have 2 new ammeters coming in along with a new pot and new better quality tube sockets. Ill be replacing those in a week or 2, plus the heater wiring coming from the transformers. I really feel that those need to be better.


----------



## baronbeehive

bloodhawk said:


> Yeap, new voltages are 80V / 79.8V / 79V / 79.8V / 77.8V / 78V / 79.6V / 80V
> 
> For now hes super happy with the amp , i have 2 new ammeters coming in along with a new pot and new better quality tube sockets. Ill be replacing those in a week or 2, plus the heater wiring coming from the transformers. I really feel that those need to be better.



That's looking good bloodhawk!!

What pot are you going to use? Did you check if it would fit?


----------



## bloodhawk

baronbeehive said:


> That's looking good bloodhawk!!
> 
> What pot are you going to use? Did you check if it would fit?



Its the same Pot, just pretested to make sure that there is not channel imbalance. However for my own amp im getting a TKD 4CP-2500, that ill mount on a custom PCB. I wanted to go with a stepped attenuator, but i really prefer granular control.


----------



## SonicTrance

SonicTrance said:


> Which resistors are you referring to? Only 300R resistors I can think of are the grid resistors and the 470R are ground references for the grids. Got nothing to do with bias?


Sorry, my mistake. There's no 470R resistor that I'm aware of? The ground (B-) reference resistors is of course 470K. So you only had 300R to B- instead of 470K. That must be what messed up the bias. The actual grid resistor should not affect the bias at all.


----------



## bloodhawk

SonicTrance said:


> Sorry, my mistake. There's no 470R resistor that I'm aware of? The ground (B-) reference resistors is of course 470K. So you only had 300R to B- instead of 470K. That must be what messed up the bias. The actual grid resistor should not affect the bias at all.


These are the ones im referring to - https://imgur.com/a/JHfT2

He had the 2 on the far left swapped around.


----------



## SonicTrance

bloodhawk said:


> These are the ones im referring to - https://imgur.com/a/JHfT2
> 
> He had the 2 on the far left swapped around.


The ones you circled are not the same type. Look at this pic from first page:





The resistors circled in yellow are 300R grid resistors. The 470K's are not circled but are the other ones right above the tubes.


----------



## bloodhawk

SonicTrance said:


> The ones you circled are not the same type. Look at this pic from first page:
> 
> 
> 
> ...



Whoops yeap my bad. Dunno why i always mistake the layout as mirrored/symmetrical. 

But the ones of the far left top of the tube were in swapped positions.


----------



## Maxx134

bloodhawk said:


> Asa the relays kicked in there was a pop and bye bye Zener. All because of a brittle B- Base wire.


Yeah but its interesting to see the board is now black..
Ha maybe they don't want it traced ha.



klnglim said:


> plug in headphone hear nothing at all, any help is much appreciated, thanks anyway!


You are only one left with Problem.
I am pretty sure the protection circuit kicked in.
This means you need to re-check everything that you did before.
What did you replace?



bloodhawk said:


> Yeah, next on the agenda is adding better quality .....along with swapping out the transformer ....


NO,
nobody mentioned anything about a transformer here...
There are no output Transformers,
And these transformers as PSU only and are specific.
SonicTrance posted a schematic of it.
They cost about $80 US from Little dot and take almost a month in shipping.
You don't want to mess with them.
You can upgrade your PSU other ways if you like but all most noticable upgrades would be the ones mentioned already,
And the driver bias setting(depending on tube) that hasn't been settled on.



baronbeehive said:


> That's quite a good idea, I get tired of repeating warnings all the time. Also it takes a while to familiarize yourself with the insides of the amp and a quick guide would help. See what Maxx thinks.


Sure as I have way less time now,
Whoever feels they like to contribute I would paste it in first page.


Baronbeehive I see your doing a nice work in finding out best bias points, just remember there are many points that will sound good .
Your going to have to get a bunch of reaistors to test your bias points with listening.


----------



## bloodhawk

Maxx134 said:


> NO,
> nobody mentioned anything about a transformer here...
> There are no output Transformers,
> And these transformers as PSU only and are specific.
> ...



Wiring coming from and going to the transformer. Not the transformer itself. I actually checked with LD a while back and they said they can ship replacement transformer through DHL which take about 3 days to get here and costs under $20 (for shipping).


----------



## baronbeehive (Mar 26, 2018)

Maxx134 said:


> Yeah but its interesting to see the board is now black..
> Ha maybe they don't want it traced ha.



No.... it's so you can't tell if it's burnt lol.



bloodhawk said:


> Wiring coming from and going to the transformer. Not the transformer itself. I actually checked with LD a while back and they said they can ship replacement transformer through DHL which take about 3 days to get here and costs under $20 (for shipping).



Looks like Maxx got a bum deal there!



Maxx134 said:


> Baronbeehive I see your doing a nice work in finding out best bias points, just remember there are many points that will sound good .
> Your going to have to get a bunch of reaistors to test your bias points with listening.



Well just trying to catch up on what you and Sonic did a year or two ago, when most of that stuff went over my head!

I've put my order in for the parts for the CCS mod and the driver bias tweaks. The load lines and operating points are pretty much as I put in the last graph, I will reuse the 1.5K cathode R, try a 1K like you did but with different load lines, and a 390R that I have in atm, like Sonic, but again with different load lines. That should give a reasonable spread as you can see in the graph.

I'm hoping to hear differences now that I'm reacquainted with the sound of the amp after some time.

Edit: Probably won't be using your 1 ear trick though.

BTW how much extra B+ did you get with a 1K 3K3 R?


----------



## Maxx134 (Mar 26, 2018)

baronbeehive said:


> BTW how much extra B+ did you get with a 1K 3K3 R?


This is an important aspect as the driver tubes are essentially staved for B+ so I strongly recommend to swap out your 3k3 to the 1k ohm that both me and I believe Sonic using.

Also interesting to note is that on my stock unit it was already droped to 2k2 and when I asked "Little Dot" US rep,
 it took a while, but my response was "_for stability" , _
Which now we know is not really the case at all but instead to give slightly more B+

The actual PSU voltage at the anode Resistors is dependent upon the driver tube plate resistance, or to view another way, it is the load the tube imposes onto the PSU which is not regulated in any way, will vary.

As I stated before,
 The fact that you already upgraded your driver stage by replacing the tiny 33uf with some nice decoupling film caps will offset any changes to the 3k3 Resistor which is performing the function of a RCRC filter for PSU.
The stock 33uf electrolytic was the last "C" of the RCRC circuit and the 3k3 is the second "R".
The first "RC" is located in the driver PSU.
Very old school design bu hey it is clean and works.


----------



## Maxx134

Forgot to add the voltage varied in my testing about 15v,
So not a huge increase, but did make a difference sonically as changes to the B+ affect the bias points


----------



## klnglim

Maxx134 said:


> Yeah but its interesting to see the board is now black..
> Ha maybe they don't want it traced ha.
> 
> 
> ...


----------



## SonicTrance

baronbeehive said:


> BTW how much extra B+ did you get with a 1K 3K3 R?


Just use ohms law and calculate. As the 3k3 resistors are located after the psu splits, so its one 3k3 / channel, you calculate using the current drawn / channel. 

Example:
Say you bias the tubes at 1.5 mA. Thats 3 mA total / channel. 
A 3k3 will drop 0.003 × 3300 = 9.9 V
A 1k will drop 0.003 × 1000 = 3 V

So, if you pull 3 mA / channel you gain about 7 V of B+ / channel.


----------



## bloodhawk (Mar 27, 2018)

SonicTrance said:


> Just use ohms law and calculate. As the 3k3 resistors are located after the psu splits, so its one 3k3 / channel, you calculate using the current drawn / channel.
> 
> Example:
> Say you bias the tubes at 1.5 mA. Thats 3 mA total / channel.
> ...





Maxx134 said:


> This is an important aspect as the driver tubes are essentially staved for B+ so I strongly recommend to swap out your 3k3 to the 1k ohm that both me and I believe Sonic using.
> 
> Also interesting to note is that on my stock unit it was already droped to 2k2 and when I asked "Little Dot" US rep,
> it took a while, but my response was "_for stability" ,_
> ...





Maxx134 said:


> Forgot to add the voltage varied in my testing about 15v,
> So not a huge increase, but did make a difference sonically as changes to the B+ affect the bias points



Interesting. What kind of improvements did you and Maxx notice after this? Im guessing the gain on the driver tubes goes up ? (Please be gentle if im being dumb)

But will the increased B+ negatively effect the power tubes?


----------



## SonicTrance

bloodhawk said:


> Interesting. What kind of improvements did you and Maxx notice after this? Im guessing the gain on the driver tubes goes up ? (Please be gentle if im being dumb)
> 
> But will the increased B+ negatively effect the power tubes?


The amp has two separate psu's. One B+ for the driver stage and both B+ and B- for output stage. All totally independent. 

Increasing B+ for driver stage is done to give the tubes higher anode voltage and be in a more linear part of the tube. Of course you also need to adjust anode load resistors when messing with the this.


----------



## baronbeehive

SonicTrance said:


> Just use ohms law and calculate. As the 3k3 resistors are located after the psu splits, so its one 3k3 / channel, you calculate using the current drawn / channel.
> 
> Example:
> Say you bias the tubes at 1.5 mA. Thats 3 mA total / channel.
> ...



Right, thanks Sonic, I was trying to figure that out yesterday and gave up!


----------



## bloodhawk

SonicTrance said:


> The amp has two separate psu's. One B+ for the driver stage and both B+ and B- for output stage. All totally independent.
> 
> Increasing B+ for driver stage is done to give the tubes higher anode voltage and be in a more linear part of the tube. Of course you also need to adjust anode load resistors when messing with the this.



Ah the 220R's?


----------



## baronbeehive

I'm wondering about this voltage doubler that has been mentioned by Coin and others recently.

If I'm understanding this right at the moment Maxx is getting 2v of total swing, and so is Sonic with the CCS, without the CCS at Sonic's and my settings we are only getting 1v total swing.

The reason I mention this is because Maxx wondered about the dynamics due to voltage swing and I have also noticed in my comparisons with the APPJ amp that the APPJ sounds more lively in certain frequencies. That lead me to thinking about this.

So does the voltage doubler double the B+ If so we could get 5.5v of swing with 320v B+.

The bass articulation problem that I mentioned recently has largely been solved by the sharper driver tubes I use now and the only thing now that I would like to do something about is this other aspect of the sound.

I wondered what you thought about this. Has anyone noticed this themselves because I don't know if it is down to my headphones or tubes or something other than the amp.

If you think it would be a good idea to implement, how would you build the voltage doubler?


----------



## SonicTrance

bloodhawk said:


> Ah the 220R's?


No, the 220k's above the driver tube anodes.



baronbeehive said:


> If I'm understanding this right at the moment Maxx is getting 2v of total swing, and so is Sonic with the CCS, without the CCS at Sonic's and my settings we are only getting 1v total swing.


Your graph is too small, I can't read the numbers, lol.

Anyway, the voltage the tubes are trying to swing at the anodes is the bias voltage (*difference in voltage between the grid and cathode) ** µ of the tube. In my case, with a bias voltage of about -1 Vg. The voltage swing would be 2 Vpp * 68 µ = 136 Vpp

Here's my post from before where I explained it.


SonicTrance said:


> Say you have bias (grid) voltage of -1 V. Like the operating point below. The signal is then 2 Vpp * µ68 (it's not really 68 in this circuit, in my sims µ is about 14, low gain) = 136 Vpp (28 Vpp). That's the voltage the anode's are trying to swing.
> Look at the load line below and see if it's possible. You can see that 136 Vpp is in fact not possible. But 28 Vpp is. With Va at 110 V, positive peak would be at 124 V and negative peak at 96 V. Tube will be down in non'linear region at positive swing though.


----------



## bloodhawk

SonicTrance said:


> No, the 220k's above the driver tube anodes.



Damn it i need to pay attention to the R's and k's. Thanks though, ill read up more into this.


----------



## baronbeehive (Mar 28, 2018)

SonicTrance said:


> No, the 220k's above the driver tube anodes.
> 
> 
> Your graph is too small, I can't read the numbers, lol.
> ...



Ha, and I just read your post before writing that lol! I'll try again with my head screwed on this time!

In the graph - (suitably resized!):





....the theoretical voltage swing is 136 Vpp for you with CCS.... I forgot to multiply bias voltage by amplification factor.

The swing for your operating point before you implemented the  CCS, ie with your 390R cathode would be 1 Vpp*amplification factor of 68 = 68.

If we could get a doubled B+ of 320V, with an operating point in the middle of the grid voltages we could get a swing of 5.5*68 = 374.


----------



## MrCurwen

I'm not trying to be difficult here, but I don't understand what you're talking about. Please elaborate.

Why would you want or need to have more than a few volts of signal swing (at the anode as Sonic mentioned)? It's a direct drive output amp, sure the output stage has a negative gain of 0.5 or what was it, but still; you don't want more than maybe 10VPP max at your headphones. And, in a differential amp the phases are added together at the load, so 5VPP per phase would produce that.

As for the voltage doubler, it can be a useful tool for many places, but it shouldn't be used in a situation where PSU performance matters at all. If it doesn't matter at all, sure, use a doubler, it cannot hurt.

If you totally play out the PSU from the circuit, then you can start thinking about using a doubler, not before. Ask Sonic about his recent findings on this subject.

Gain and µ are two different things. µ is theoretical, gain is the voltage gain achieved in a specific real world circuit. It can approach µ, then you can use them as synonyms. With resistor anode loads, gain is usually much lower than µ. Sonic mentioned this in his post quoted in recent posts. 


I again point out my personal opinion that the linearity within a single phase is not as critical in this amp as is the balance between the phases. There is intra-phase gNFB, but there is nothing delivering the balance reliably. Weakest link is balance, not intra-phase linearity. Of course it is good to study and look at all kinds of things, I'm not discouraging that not at all. Just my overall perspective.




baronbeehive said:


> The swing for your operating point before you implemented the CCS, ie with your 390R cathode would be 1 Vpp*amplification factor of 68 = 68.



Might be miscommunication, but;

CCS  tail only sets Ia. It doesn't affect the load lines in any way, it doesn't affect gain in any way.

Also if you have resistive anode load that is less than 10x rp, you are not going to get gain anywhere near full µ.


----------



## baronbeehive (Mar 28, 2018)

MrCurwen said:


> Why would you want or need to have more than a few volts of signal swing (at the anode as Sonic mentioned)? It's a direct drive output amp, sure the output stage has a negative gain of 0.5 or what was it, but still; you don't want more than maybe 10VPP max at your headphones. And, in a differential amp the phases are added together at the load, so 5VPP per phase would produce that.



This is what I was throwing up for discussion, I know several here are concerned about the small voltage swing and have thought that it might be related to lack of perceived dynamics. I thought that this was possible, that's why I related it to my observations on comparing the amp to the other amp, but I take your point about the max voltage at headphones.



MrCurwen said:


> If you totally play out the PSU from the circuit, then you can start thinking about using a doubler, not before. Ask Sonic about his recent findings on this subject.



Yes I know Sonic mentioned the voltage doubler and I don't know if he has done any more work on it, but yes the idea would have been to use it after implementing the CCS ie after the PSU has been "regulated". Or if not regulated then as near as we can with the CCS/filter mod as you said so yourself. (Of course the PSU has not been regulated, only to all intents and purposes).



MrCurwen said:


> Gain and µ are two different things. µ is theoretical, gain is the voltage gain achieved in a specific real world circuit. It can approach µ, then you can use them as synonyms. With resistor anode loads, gain is usually much lower than µ. Sonic mentioned this in his post quoted in recent posts.



Yes, right I am aware that he did mention that which is why I emphasised "theoretical" because I did not want to confuse the calculated swing which might not be actually possible as Sonic mentioned, with the actual gain in the circuit.



MrCurwen said:


> I again point out my personal opinion that the linearity within a single phase is not as critical in this amp as is the balance between the phases. There is intra-phase gNFB, but there is nothing delivering the balance reliably. Weakest link is balance, not intra-phase linearity. Of course it is good to study and look at all kinds of things, I'm not discouraging that not at all. Just my overall perspective.



No I absolutely agree about this, why have a balanced amp when you are not getting perfect balance out of it, that is the priority, that's why I'm looking forward to implementing the CCS.



MrCurwen said:


> Might be miscommunication, but;
> 
> CCS  tail only sets Ia. It doesn't affect the load lines in any way, it doesn't affect gain in any way.
> 
> Also if you have resistive anode load that is less than 10x rp, you are not going to get gain anywhere near full µ.



No absolutely agree, this is really why I raised the question of voltage swing because the anode load is so small on Sonic's amp prior to his fitting the CCS and on my amp atm with the 390R anode. I wondered if we could compensate in any way for that by having a larger swing, perhaps you could advise on this or tell me that I'm wasting my time as I don't know the answer to this.(I'm not talking about the CCS here I'm talking about the driver bias mod with anode/cathode values that we are trying to optimize).

Edit: What it boils down to is, does voltage swing affect dynamics?


----------



## Maxx134 (Mar 29, 2018)

baronbeehive said:


> Edit: What it boils down to is, does voltage swing affect dynamics?


It will depend on the following circuit it is driving.
The driver tubes are driving the powertube stage with that coupling cap in between.
So it depend what the powertubes need.

You have MK6 and from SonicTrance testing he was able to get away with smaller anode resistor and also using amp on low gain.

On my trials I am using MK8 with different output tubes and on high gain.
I needed the anode Resistors higher to not get what resulted in comoressed dynamics for the driver tubes I chose.

I would suggest this method to tune your driver tube bias:

Select the tubes you want to use.

Calculate and buy the Resistors needed to test the different settings.

A bundle of cheapo resistors for testing.

With both left and right channel having same tubes, leave unit upside down and solder one side/channel/driver tube with added paralleled reaistors to lower thier values to your graph settings you picked.

Then try amp on and listen comparing one side to the other with your player (foobar has settings) in mono..

It easy to compare that way .

Your end results may prove to be different settings than both me and Sonic,
 easily because of your preference and also your fav tube selection...

Also be ready to change your mind on your favorite tube as that has happened to me with me settling on the 6C8G Tung-Sol for driver tube.

I still have alot others and also my MK8 was supposed to use small 9pin variety tubes,
Which I went thru rolling almost ALL variations I could find and STILL settled on the 6pin 6C8G as my favorite driver tube for this amp...

The point is your MK6 already using 6pin driver tube variety and I feel it a better choice.

But your power tubes are way more expensive than the MK8 tubes..

Plus I tried all possible type for my MK8 amp, and settled on 6n6 type at higher bias point, over the uber expensive 6h30dr tubes..

Anyways the bottom line is you need test..


----------



## baronbeehive (Mar 29, 2018)

Maxx134 said:


> I would suggest this method to tune your driver tube bias:
> 
> Select the tubes you want to use.
> 
> ...



Right, thanks.

I will try that method, should be interesting to see what the best settings for anode and cathode are finally for my tube selection.

Edit:
When I've done that I intend to fit the CCS at Sonic's settings because I'm afraid to go outside the operating limits of the CCS inadvertently.


----------



## bloodhawk (Mar 29, 2018)

Maxx134 said:


> It will depend on the following circuit it is driving.
> The driver tubes are driving the powertube stage with that coupling cap in between.
> So it depend what the powertubes need.
> 
> ...





baronbeehive said:


> Right, thanks.
> 
> I will try that method, should be interesting to see what the best settings for anode and cathode are finally for my tube selection.
> 
> ...




Question.. How do i test the tube bias using a multimeter?

The points that go out to the ampmeters, the combined average bias? Or for the driver tubes?

And are there any other changes that are necessary for the CCS tail?


----------



## SonicTrance

baronbeehive said:


> Yes I know Sonic mentioned the voltage doubler and I don't know if he has done any more work on it


I’ve found that voltage doublers are noisy and needs to be followed by a reg. Even with a regulator in place it brings quite a lot of psu noise. IMO we don’t need higher B+ for the input stage if we use 6SL7/ECC35/6C8G and a CCS tail. It can drive the output stage no problem and bias points are good. The main benefit would be the ability to use higher anode loads. 



bloodhawk said:


> Question.. How do i test the tube bias using a multimeter?


Measure voltage drop across the anode resistor. Use ohms law to calculate the current. The current is chaired between the triodes in the output tubes. Input stage has one anode resistor / triode.


----------



## bloodhawk

SonicTrance said:


> Measure voltage drop across the anode resistor. Use ohms law to calculate the current. The current is chaired between the triodes in the output tubes. Input stage has one anode resistor / triode.



Gotcha yeah, kinda clicked a bit later.


----------



## baronbeehive (Mar 29, 2018)

SonicTrance said:


> I’ve found that voltage doublers are noisy and needs to be followed by a reg. Even with a regulator in place it brings quite a lot of psu noise. IMO we don’t need higher B+ for the input stage if we use 6SL7/ECC35/6C8G and a CCS tail. It can drive the output stage no problem and bias points are good. The main benefit would be the ability to use higher anode loads.



Oh, very interesting. Yes I noticed the bias points looked good on your ECC35 graph.

The CCS has certainly solved the balance issue too by all accounts.

Re: the 6SL7's I remember people on the other LD thread liking the Tungsol 6SN7 better than the 6SL7 for example, and I could  never understand why I always preferred the 6SL7's so I think you're right about the better tubes for the LD. You've got to have high gain on this amp.


----------



## baronbeehive

bloodhawk said:


> And are there any other changes that are necessary for the CCS tail?



Just replace the 2x3k3 resistors in PSU with 1k or 750R to get a bit more voltage.

The other thing is the last C caps in the RCRC filter in the driver stage should not be higher than stock 33uF but I see yours are 15uF so that's alright.

So are you thinking of doing it any day soon?


----------



## bloodhawk

baronbeehive said:


> Just replace the 2x3k3 resistors in PSU with 1k or 750R to get a bit more voltage.
> 
> The other thing is the last C caps in the RCRC filter in the driver stage should not be higher than stock 33uF but I see yours are 15uF so that's alright.
> 
> So are you thinking of doing it any day soon?



Yeah probably next weekend. This weekend im redoing my wiring, with better routing and swapping out tube sockets with better ones.


----------



## baronbeehive

bloodhawk said:


> Yeah probably next weekend. This weekend im redoing my wiring, with better routing and swapping out tube sockets with better ones.



Hey, wait a minute...... I forgot to tell you new members aren't allowed to beat me LOL.

So be careful with that wiring.......


----------



## bloodhawk

baronbeehive said:


> Hey, wait a minute...... I forgot to tell you new members aren't allowed to beat me LOL.
> 
> So be careful with that wiring.......



Haha trust me even i beat you with speed, im not even close to having the amount of know how you guys have. Im pretty learning how to read amp schematics and recall whatever i learnt during my undergrad and makes sense of things. 

The only hard part being, locating traces and the right test points on the black PCB. 

Ill keep you posted for sure and post pictures, plan is to swap out wires one by one (or in pairs) so that i dont have to keep track of a bajillion things.


----------



## baronbeehive (Mar 30, 2018)

Guys, this is a great tip for desoldering I got from an electronics man: https://uk.rs-online.com/web/p/cable-sleeves/3031748/
They fit on the end of the solder sucker. I could never get on with the solder sucker but these give a better suction on the end and you can change them when they get burnt.


----------



## Maxx134

baronbeehive said:


> The other thing is the last C caps in the RCRC filter in the driver stage should not be higher than stock 33uF but I see yours are 15uF so that's alright.


In the mods we actually removed and replaced the stock 33uf for more space.

They are tiny electrolytics at last end of PSU.
In this location they would be more useful as film or pulse-type film caps instead.

If you can fit higher capacity than what we used, then all the better for you.

No one said you can't go higher than stock.
Its just the limitation of internal space.
It's hard to fit anything bigger than what we put in.

They not have to be expensive audio caps either,
 as their function is for speed/transients/current delivery.
Further Comments were on first page.


----------



## MrCurwen

baronbeehive said:


> Edit: What it boils down to is, does voltage swing affect dynamics?





Maxx134 said:


> They not have to be expensive audio caps either,
> as their function is for speed/transients/current delivery.



Why do you think that?


----------



## baronbeehive (Apr 1, 2018)

Maxx134 said:


> In the mods we actually removed and replaced the stock 33uf for more space.
> 
> They are tiny electrolytics at last end of PSU.
> In this location they would be more useful as film or pulse-type film caps instead.
> ...



OK, I know you have higher and so do I, and Sonic has only 15uF. I was thinking of changing mine for 33uF because I didn't want to stress the PSU when I lower my last R to around 1k.


----------



## bloodhawk

baronbeehive said:


> OK, I know you have higher and so do I, and Sonic has only 15uF. I was thinking of changing mine for 33uF because I didn't want to stress the PSU when I lower my last R to around 1k.



So questions -

What are the draw backs of swapping out the 3.3k R's with 2.2k or 1k R's without the CCS Tail installed?

Also Advantages / Drawbacks of doing both the 3.3k R swap to 2.2k/1k along with having 33uF instead of the 15uF caps?


----------



## baronbeehive (Apr 3, 2018)

bloodhawk said:


> So questions -
> 
> What are the draw backs of swapping out the 3.3k R's with 2.2k or 1k R's without the CCS Tail installed?
> 
> Also Advantages / Drawbacks of doing both the 3.3k R swap to 2.2k/1k along with having 33uF instead of the 15uF caps?



All I know about this is that one recommendation on this thread is not to decrease the second R in the RCRC filter at the same time as increasing capacitance in the last C due to possible adverse effects on the PSU, unless we are sure the PSU is strong enough to handle it. As I'm not sure it is then you might like to follow that advice. However I'm sure Maxx has increased his last C with no adverse effects so maybe the PSU can handle it alright.

33uF should be fine though because that is the stock value, and also someone here said that Little Dot had advised of a decrease in the second R themselves so no problem with decreasing that R.

The advantage of dropping the resistance of the that R is to gain a few precious volts to put the tubes in a better operating region on the load lines potentially.


----------



## baronbeehive (Apr 3, 2018)

baronbeehive said:


> All I know about this is that one recommendation on this thread is not to decrease the second R in the RCRC filter at the same time as increasing capacitance in the last C due to possible adverse effects of the PSU, unless we are sure the PSU is strong enough to handle it. As I'm not sure it is then you might like to follow that advice. However I'm sure Maxx has increased his last C with no adverse effects so maybe the PSU can handle it alright.
> 
> 33uF should be fine though because that is the stock value, and also someone here said that Little Dot had advised of a decrease in that R themselves so no problem with decreasing that R.
> 
> The advantage of dropping the resistance of that R is to gain a few precious volts to put the tubes in a better operating region on the load lines potentially.



The fact is that the need for filtering when you have forced balance with the CCS decreases so that is the reason that you can drop values in the filter.


----------



## bloodhawk (Apr 8, 2018)

Finished rewiring stuffs ended up not touching the transformer wiring, since it was being wayyyy too difficult to remove the existing wires and didnt seem worth the trouble.
Swapped out the tube sockets for better ones as well. Along with routing some annoying wires properly so as to make things more accessible. Sure its not pretty , but it avoids the potential issues that might creep in with straight/parallel wiring.
Also putting those tiny 0.22uF caps at the bottom, might just let me use the 33uF 450V caps instead of the 250V ones.

Going to add in the RIFA's and the mills resistors tomorrow, maybe the other components on the other side of the board as well.

https://imgur.com/a/vxoJS (Album)


----------



## SonicTrance

@bloodhawk 
Nice progress pics! One thing I’d do though is put insulation on the leads of the tiny .22 uF caps. Just to avoid future shorts.


----------



## bloodhawk (Apr 9, 2018)

SonicTrance said:


> @bloodhawk
> Nice progress pics! One thing I’d do though is put insulation on the leads of the tiny .22 uF caps. Just to avoid future shorts.





SonicTrance said:


> @bloodhawk
> Nice progress pics! One thing I’d do though is put insulation on the leads of the tiny .22 uF caps. Just to avoid future shorts.



Thanks!

Its kinda baffling how some of the wiring is just routed so poorly.

On another note, one of my 100Ohm 5W resistors went up in smoke... any idea what could cause this ? I turned off the amp instantly and have ordered 10W Mills resistors instead. But im rather curious what could be the reason, everything else looks perfectly normal.

EDIT - Well found my idiotic mistake that cause one of the filter caps to go bye bye -







In case anyone new is wondering, that circled wire need to goto the ground pad to the left.

Sad i have to wait 2 more days now, everything was looking so pretty -


----------



## klnglim

bloodhawk said:


> Thanks!
> 
> Its kinda baffling how some of the wiring is just routed so poorly.
> 
> ...


That's impressive details and very helpful idea. Unfortunately, my mk8se still cant find out the error yet even after change NPN & PNP transistor, Zener diode and resistors, the amp still read '0' after right side VU Meter light up while turning on


----------



## bloodhawk

klnglim said:


> That's impressive details and very helpful idea. Unfortunately, my mk8se still cant find out the error yet even after change NPN & PNP transistor, Zener diode and resistors, the amp still read '0' after right side VU Meter light up while turning on



What were your voltage checks like ?


----------



## klnglim

bloodhawk said:


> What were your voltage checks like ?


The problem is I don't know how to check the voltage, need guidance


----------



## bloodhawk (Apr 9, 2018)

klnglim said:


> The problem is I don't know how to check the voltage, need guidance



So as its been stated before_ *BE VERY VERY CAREFUL BEFORE MEASURING VOLTAGE ON A LIVE / ACTIVE AMPLIFIER or any electrical equipment!!!!*_

Make sure the tubes installed are good, and the amps is upside down propped up on something stable! You do not want, it moving around or sliding/falling when turned on. Before plugging in the mains cable, double check everything and the surrounding area has plenty of space, and nothing interferes when you are moving around or moving the multi-meter leads around.

Next, switch the Multi-meter to DC Voltage mode and put the Black / Negative lead from your multi-meter into one of the holes circled BLACK , this way you can freely move around your other hand.

You want to first measure your voltage to the terminals circled red. If all of these are consistent, then your PSU stage is fine. On the MK VI+ , they are @ 100V for me. @Maxx134 or @SonicTrance might know what they should be for the MK VIII.

Next if those are fine and the PSU stage is indeed OK , then you should measure the voltages, at the terminals circled white. Im not sure how much they should be on the MK VIII , as that amp uses different tubes. So someone else like @Maxx134 will have to chime in. and tell you if the values that you report are in line or not and that will help in tracking down the issue.

After if the voltages at the terminals marked red and white are consistent, and seem normal. Check at the terminals marked yellow.








Once you take the readings, post them here. And make sure you mentioned what value is from which point to which point.


*AGAIN>>> BE VERY VERY VERY CAREFUL!!!! IF YOU FEEL THIS IS A LITTLE TOO DANGEROUS OR DO NOT KNOW WHAT TO DO/HOW TO DO.... STOP! And Maybe find someone else around you who knows their way around electronics to do it for you. 

A shock from a live equiment like this can kill you, SO BE CAREFUL!!*


----------



## klnglim (Apr 9, 2018)

*While turn on the amp, I heard sound 'pop' like short explosion after second VU meter light up. However when I open the case, fuse show normal. can't find any circuit, resistor and wire burn even after check with DMM,
I understand it's a bit risky but will have another try with your method as the mention above, thanks*


----------



## klnglim

bloodhawk said:


> So as its been stated before_ *BE VERY VERY CAREFUL BEFORE MEASURING VOLTAGE ON A LIVE / ACTIVE AMPLIFIER or any electrical equipment!!!!*_
> 
> Make sure the tubes installed are good, and the amps is upside down propped up on something stable! You do not want, it moving around or sliding/falling when turned on. Before plugging in the mains cable, double check everything and the surrounding area has plenty of space, and nothing interferes when you are moving around or moving the multi-meter leads around.
> 
> ...


*While turn on the amp, I heard sound 'pop' like short explosion after second VU meter light up. However when I open the case, fuse show normal. can't find any circuit, resistor and wire burn even after check with DMM,
I understand it's a bit risky but will have another try with your method as the mention above, thanks*


----------



## baronbeehive

bloodhawk said:


> EDIT - Well found my idiotic mistake that cause one of the filter caps to go bye bye -
> 
> 
> In case anyone new is wondering, that circled wire need to goto the ground pad to the left.
> ...



Nice work bloodhawk...... apart from that blasted wire LOL. That's the way it is with this amp, 2 steps forward, 1 step back. Seriously though, that's so easy to do!


----------



## baronbeehive

klnglim said:


> The problem is I don't know how to check the voltage, need guidance



That's good advice from bloodhawk, just remember not to touch anything while the amp is switched on, except with your multimeter, also leave it to discharge after you switch it off for about 30 minutes before touching anything.

I am wondering if your headphone protection circuit kicked in. If so there must be something causing that to happen.

Have you taken values of every resistor in the orange circle below, I can give you the proper values if you want.


----------



## klnglim

baronbeehive said:


> That's good advice from bloodhawk, just remember not to touch anything while the amp is switched on, except with your multimeter, also leave it to discharge after you switch it off for about 30 minutes before touching anything.
> 
> I am wondering if your headphone protection circuit kicked in. If so there must be something causing that to happen.
> 
> Have you taken values of every resistor in the orange circle below, I can give you the proper values if you want.


what's the value?  thanks


----------



## baronbeehive

Here you go kinglim: (I used one of Sonic's pics hope he doesn't mind, mine were too blurry lol)


----------



## baronbeehive (Apr 9, 2018)

....might be easier to read....









Edit: I'm pretty sure they're the same on the MKViii.


----------



## klnglim

baronbeehive said:


> ....might be easier to read....
> 
> 
> 
> ...


That's a bit different resistors value between mk6 and mk8, I had checked all those resistors and nothing wrong.
However I will double check again before turn it on to take the voltage value


----------



## klnglim

bloodhawk said:


> So as its been stated before_ *BE VERY VERY CAREFUL BEFORE MEASURING VOLTAGE ON A LIVE / ACTIVE AMPLIFIER or any electrical equipment!!!!*_
> 
> Make sure the tubes installed are good, and the amps is upside down propped up on something stable! You do not want, it moving around or sliding/falling when turned on. Before plugging in the mains cable, double check everything and the surrounding area has plenty of space, and nothing interferes when you are moving around or moving the multi-meter leads around.
> 
> ...


I assembly back to simple setup and just got all the voltage reading now, seem like something error on right side output.
Read from picture above shown:
Red first left to right : (151.5) (-108) (-108) (151.5) (151.5) (1.0) (1.0) (151.5)
White left to right : (149) (-105) (-94) (149) (149) (1.0) (1.0) (149)
Yellow left to right (213) (213) (214) (214)
Help needed for the negative reading, thanks


----------



## bloodhawk

klnglim said:


> I assembly back to simple setup and just got all the voltage reading now, seem like something error on right side output.
> Read from picture above shown:
> Red first left to right : (151.5) (-108) (-108) (151.5) (151.5) (1.0) (1.0) (151.5)
> White left to right : (149) (-105) (-94) (149) (149) (1.0) (1.0) (149)
> ...



First think would be to double check and reflow the joints in this region - 
	

	
	
		
		

		
			





Next double check the tube socket solder joints and reflow those 

(Be careful with the heater wiring, as it loves to come right off if you dont hold it down while reflowing the solder joints) - These are the 2 thick grey wires coming from the transformer at the back and then branching off to the second tube socket.


----------



## baronbeehive (Apr 9, 2018)

klnglim said:


> I assembly back to simple setup and just got all the voltage reading now, seem like something error on right side output.
> Read from picture above shown:
> Red first left to right : (151.5) (-108) (-108) (151.5) (151.5) (1.0) (1.0) (151.5)
> White left to right : (149) (-105) (-94) (149) (149) (1.0) (1.0) (149)
> ...



Not sure what's happening here, you should be getting 100v on the B+ and a 25v drop across the 330R resistors.

Check the voltage drop across the 330R's, put one probe of your multimeter on one side and the other probe on the other side of the 330R's to check the voltage drop.

Also could you post a pic with your resistor values like I have done.

Edit: How many 330R resistors have you installed? I can only see 4.


----------



## klnglim (Apr 9, 2018)

baronbeehive said:


> Not sure what's happening here, you should be getting 100v on the B+ and a 25v drop across the 330R resistors.
> 
> Check the voltage drop across the 330R's, put one probe of your multimeter on one side and the other probe on the other side of the 330R's to check the voltage drop.
> 
> ...


There are 8 150R  mills resistor, that's the different between mk6 & mk8se


----------



## bloodhawk (Apr 9, 2018)

klnglim said:


> There are 8 150R  mills resistor, that's the different between mk6 & mk8se



@baronbeehive

There seems to something wrong with the PSU side feeding the right channel anode as well. Some sort of short around there .



Also.. anyone know what value of resistor is being in the ampmeter lighting circuit ? I measured it as 68Ohm.. but on my friends amp where the left meter is busted , with a new replacement ampmeter the light doesn't seem to be turning on.


----------



## baronbeehive (Apr 9, 2018)

bloodhawk said:


> @baronbeehive
> 
> There seems to something wrong with the PSU side feeding the right channel anode as well. Some sort of short around there .



Yes, somewhere between anode and cathode something's up, I leave it to someone else to fathom that one out. When the problem there is found it might rectify the other wrong readings I mentioned.

If we can have the resistor values, that might point to something unless you say they are correct, otherwise you will have to check connections and components in that area on the trace between anode and cathode, both circuits right side.

BTW, sorry I forgot the MKViii has 150R's, not 330R's.


----------



## bloodhawk

baronbeehive said:


> Yes, somewhere between anode and cathode something's up, I leave it to someone else to fathom that one out. When the problem there is found it might rectify the other wrong readings I mentioned.
> 
> If we can have the resistor values, that might point to something unless you say they are correct, otherwise you will have to check connections and components in that area on the trace between anode and cathode, both circuits right side.
> 
> BTW, sorry I forgot the MKViii has 150R's, not 330R's.



yeap!

Ill look into this more tonight after work and try to help him out. 


Onto the next thing, any idea what the rating for the amp meter lighting is? I found a 68Ohm in series with the positive lead going to the amp meters. Was wondering if those are super necessary or can be removed as its super hard to solder those on.


----------



## baronbeehive

bloodhawk said:


> yeap!
> 
> Ill look into this more tonight after work and try to help him out.
> 
> ...


Right! My guess is a short or a grounded connection somewhere, difficult to know when you don't know what has been done.

Re: the meter, sorry I do't know about that.


----------



## bloodhawk

baronbeehive said:


> Right! My guess is a short or a grounded connection somewhere, difficult to know when you don't know what has been done.
> 
> Re: the meter, sorry I do't know about that.



Yeah my guess right now is that the wiring on the B- transistor. 


On another note, i have a crap ton of extra PNP and NPN transistors that @SonicTrance had recommended, mouser had goofed my order and thought they sent the wrong pair even though i received the correct ones. A week later 4 more pairs showed up lol.


----------



## SonicTrance

bloodhawk said:


> Onto the next thing, any idea what the rating for the amp meter lighting is? I found a 68Ohm in series with the positive lead going to the amp meters. Was wondering if those are super necessary or can be removed as its super hard to solder those on.


I don’t understand what exactly it is you mean? Where did you find a 68R resistor?


----------



## bloodhawk

SonicTrance said:


> I don’t understand what exactly it is you mean? Where did you find a 68R resistor?



The amp meters positive terminal for the yellow lamp.


----------



## SonicTrance

bloodhawk said:


> The amp meters positive terminal for the yellow lamp.


Ok, I didn’t know there was a resistor there. Where is it? On the board, soldered on the wire or inside the meter? Sounds like a current limiting resistor and is there to prolong the life of the bulb.


----------



## bloodhawk

SonicTrance said:


> Ok, I didn’t know there was a resistor there. Where is it? On the board, soldered on the wire or inside the meter? Sounds like a current limiting resistor and is there to prolong the life of the bulb.



My bad i should have specified. Its heatshrinked between the wire and the meters terminal. I didnt even know it was there until i took out the old meter out .

Ahh that would make sense.. im guessing to drop the voltages from 12V to about 8-10V?


----------



## SonicTrance

bloodhawk said:


> My bad i should have specified. Its heatshrinked between the wire and the meters terminal. I didnt even know it was there until i took out the old meter out .
> 
> Ahh that would make sense.. im guessing to drop the voltages from 12V to about 8-10V?


I don’t remember how much current the bulbs draw. Therefore I don’t know how much voltage a 68R resistor would drop. I would definitely use some resistor there though as to not cook the bulbs at turn on when voltage is higher.


----------



## klnglim (Apr 10, 2018)

bloodhawk said:


> Yeah my guess right now is that the wiring on the B- transistor.
> 
> 
> On another note, i have a crap ton of extra PNP and NPN transistors that @SonicTrance had recommended, mouser had goofed my order and thought they sent the wrong pair even though i received the correct ones. A week later 4 more pairs showed up lol.


Hey Guy! I just find out what's the problem when double checked the NPN & PNP , although both nothing wrong but I notice those transistor's Collector touching ground, I guess that's the reason why the amp short circuit after 2nd VU meter light up.
I will change some problem circuit and confirm again later


----------



## baronbeehive

klnglim said:


> Hey Guy! I just find out what's the problem when double checked the NPN & PNP , although both nothing wrong but I notice those transistor's Collector touching ground, I guess that's the reason why the amp short circuit after 2nd VU meter light up.
> I will change some problem circuit and confirm again later



Sounds like that could be the problem. That would probably explain why the headphone protection circuit kicked in too, you were getting very high voltages in the other circuit but I think this may right itself when you've fixed the ground issue.

I would like to know what voltage triggers the protection circuit.


----------



## bloodhawk

klnglim said:


> Hey Guy! I just find out what's the problem when double checked the NPN & PNP , although both nothing wrong but I notice those transistor's Collector touching ground, I guess that's the reason why the amp short circuit after 2nd VU meter light up.
> I will change some problem circuit and confirm again later



Interesting. I guess it was a good move on my part to have insulated the transistor shield with some thick double sided tape. 

Hope fully this solves your issue.


----------



## klnglim (Apr 11, 2018)

baronbeehive said:


> Sounds like that could be the problem. That would probably explain why the headphone protection circuit kicked in too, you were getting very high voltages in the other circuit but I think this may right itself when you've fixed the ground issue.
> 
> I would like to know what voltage triggers the protection circuit.


The actual ground error connection with transistor is due to serious bad damage of circuit board. It happened since the day when amp start sparkling light and burnt in a sudden when I listened to music..
Now I have to find the way to fix the PCB carbon conducting ground shortage.



Watch this amp repair video,   where I have just learned some knowledge from his playlists


----------



## bloodhawk

And all done -


----------



## Whitigir

This amp do look like a mod heaven,  is it worth all the troubles over spending on some real high-end one guys ?


----------



## baronbeehive

klnglim said:


> The actual ground error connection with transistor is due to serious bad damage of circuit board. It happened since the day when amp start sparkling light and burnt in a sudden when I listened to music..
> Now I have to find the way to fix the PCB carbon conducting ground shortage



Hi kinglim, sorry to hear that, I will check out the videos when I have time.

I'm assuming that the copper trace has melted from that area you indicated to ground. If it isn't too much damage you could probably use wire to and from the affected area as a solution.

The circuit board has to put up with a lot of punishment and several of us have had to do this when we have had similar problems including me when I accidentally lifted a trace.
.


----------



## baronbeehive

Whitigir said:


> This amp do look like a mod heaven,  is it worth all the troubles over spending on some real high-end one guys ?



I definately think so!

The amp, post mods is approaching TOTL. It has wonderful euphonic tone, soundstage and detail. Pretty much all deficiencies can be fixed with the mods. Whether you like the sound is probably an individual preference of course. I have this amp and a Miniwatt amp, also modded, and both are equally good but each has it areas where it scores better slightly.

Only thing is difficulty working in a confined space when you are adding quality parts inside the chassis!

Others on this thread would probably agree with me about the great qualities of the amp.


----------



## baronbeehive

bloodhawk said:


> And all done -



......and all working!!

Very nice clean job bloodhawk! I see you have decided on the "standard" layout lol.
.


----------



## bloodhawk

baronbeehive said:


> ......and all working!!
> 
> Very nice clean job bloodhawk! I see you have decided on the "standard" layout lol.
> .



Haha thanks!
I have a feeling my friend is going to want me to do the same to his amp now xD

Figured after moving the caps at the top of the otherside of the board, I'll have more space to slap in the 450V 33uF caps. Sonic's layout really helped along with adding a few standoffs in screw holes to add a gap in the bottom panel mounting.


----------



## klnglim

bloodhawk said:


> And all done -


That's nice job and great idea, how it sound like now?


----------



## klnglim

baronbeehive said:


> Hi kinglim, sorry to hear that, I will check out the videos when I have time.
> 
> I'm assuming that the copper trace has melted from that area you indicated to ground. If it isn't too much damage you could probably use wire to and from the affected area as a solution.
> 
> ...


That damage area has carbonize conductive which cause ground shorted PNP transistor, all other circuit has no issue at all after checked with DMM


----------



## bloodhawk

klnglim said:


> That's nice job and great idea, how it sound like now?



The changes weren't as dramatic as the ones i had before, as i basically rearranged things around and changed the wiring from before. 

But the most apparent and biggest changes were to the separation and the blackness of the background when nothing is playing. Before this, the soundstage had a nice bump going from stock to the new resistors/caps, with the wiring everything is much more "clearer". And the low end is so much more well defined. When compared to my WA22, it sound like this has a layer of cloudyness removed, whereas the WA22 feels like it has something in front of it. (if this makes any sense)



klnglim said:


> That damage area has carbonize conductive which cause ground shorted PNP transistor, all other circuit has no issue at all after checked with DMM



I had this issue once with one of my desktop motherboards, the only way i could fix it was to first clean the affected area with isopropyl alcohol and then to scrape all the carbon off. Which in turn ruins a lot of traces coming into the affected region, so i had to run wires on both sides of the board. Luckily these amps dont have as many traces as a motherboard, and you seem to have the blue PCB so traces will be easier to spot.
A well lit workbench will go a long way to help you in spotting the affected the traces.


----------



## bloodhawk

@baronbeehive Any idea if its sensible to use 33uF instead of the 15uF driver decoupling caps? If you have tried this, what type of improvement does this yield?


----------



## Whitigir

So, the amp is easily taken apart to work on the PcB guys ?


----------



## baronbeehive

Whitigir said:


> So, the amp is easily taken apart to work on the PcB guys ?



Haha, yes. Don't know quite what to say here. The first time you try it it is difficult, but after one or two efforts you get the hang of it. The PCB slides out but not completely due to the wires on the back.


----------



## baronbeehive

bloodhawk said:


> @baronbeehive Any idea if its sensible to use 33uF instead of the 15uF driver decoupling caps? If you have tried this, what type of improvement does this yield?



Yes that would be alright, sorry I thought that was what you meant when you were probably talking about the power tube decoupling. I have 40uF driver decoupling caps atm. Don't know what effect they have though because I've only ever had those caps.


----------



## bloodhawk

baronbeehive said:


> Yes that would be alright, sorry I thought that was what you meant when you were probably talking about the power tube decoupling. I have 40uF driver decoupling caps atm. Don't know what effect they have though because I've only ever had those caps.



Ahh gotcha. I wanted to confirm before i swap the 15uF's for 33uF's in my friends amp. Ill see if i can compare, once everything is done.


----------



## Whitigir

Out of interests, I checked some of those Caps, and quickly add up to Thousands....LoL!

So, is the sound performances up to par ? Can it be said to be top of the line that can compete against very expensive one ?  How about output impedance?


----------



## bloodhawk

Whitigir said:


> Out of interests, I checked some of those Caps, and quickly add up to Thousands....LoL!
> 
> So, is the sound performances up to par ? Can it be said to be top of the line that can compete against very expensive one ?  How about output impedance?



Its a balancing game tbh. Like some of the caps that @SonicTrance is using have great value for money.But its upto you if you want to spend that much, after a certain price you reach a point of diminishing returns.

The most i spent on my upgrades was $350.


----------



## baronbeehive

bloodhawk said:


> Ahh gotcha. I wanted to confirm before i swap the 15uF's for 33uF's in my friends amp. Ill see if i can compare, once everything is done.


Right.

My view is that the CCS mod will do more than the driver stage decoupling but I can't say for sure because we haven't tested or compared these properly in this amp. But the idea of a film cap in the driver stage is to provide a fast response reservoir to tighten things up a bit.


----------



## baronbeehive

Whitigir said:


> Out of interests, I checked some of those Caps, and quickly add up to Thousands....LoL!
> 
> So, is the sound performances up to par ? Can it be said to be top of the line that can compete against very expensive one ?  How about output impedance?



I think the cost of mine was £300 or so, not bad considering the amp wasn't particularly expensive for a balanced amp can't say exactly because it kept changing but for example the Audyns are quite cheap compared to the Jupiter caps but with very similar performance. The quality caps do make a massive difference together with tubes etc. My preferred set of tubes atm cost $5 each!The output impedance is one of our mods to tailor the amp to your desired set of headphones.

I will leave the question of whether it's TOTL or not I think others here might like to say what they think but some members have had access to various hifi meets in which the very best amps were on show.


----------



## klnglim

bloodhawk said:


> The changes weren't as dramatic as the ones i had before, as i basically rearranged things around and changed the wiring from before.
> 
> But the most apparent and biggest changes were to the separation and the blackness of the background when nothing is playing. Before this, the soundstage had a nice bump going from stock to the new resistors/caps, with the wiring everything is much more "clearer". And the low end is so much more well defined. When compared to my WA22, it sound like this has a layer of cloudyness removed, whereas the WA22 feels like it has something in front of it. (if this makes any sense)
> 
> ...


I guess sound stage will be better after 100 hours run


----------



## bloodhawk

klnglim said:


> I guess sound stage will be better after 100 hours run


All the parts have been run for way more than 100 hours already. I just rearenaged them recently and changed the wiring.


----------



## klnglim

klnglim said:


> That damage area has carbonize conductive which cause ground shorted PNP transistor, all other circuit has no issue at all after checked with DMM


After checked cabling, ground connection, at last the amp turn on peacefully however still read "0" on the vu meter, no idea what's wrong, the DC voltage reading :
(106) (3.5) (3.5) (106) (106) (3.5) (3.5) (106)
(106) (3.5) (3.5) (106) (106) (3.5) (3.5) (106)
(215) (215) (215) (215)


----------



## baronbeehive (Apr 17, 2018)

klnglim said:


> After checked cabling, ground connection, at last the amp turn on peacefully however still read "0" on the vu meter, no idea what's wrong, the DC voltage reading :
> (106) (3.5) (3.5) (106) (106) (3.5) (3.5) (106)
> (106) (3.5) (3.5) (106) (106) (3.5) (3.5) (106)
> (215) (215) (215) (215)



Your voltages at B+ side at 106v are nearer to the correct value so if we assume that everything is alright up to there then the problem is after the anode and around the cathode area, but you are getting no voltage drop across the 150R resistor which I can't understand. I'm assuming that you have checked the resistance across your 150R resistors. All your voltages are the same at either side of the anode and cathode resistors. I'm assuming that because both your channels show equal values that the problem is higher up the chain. I believe the 2 channels are linked by the 680R resistor but  I'm at my limits here, hopefully someone who is more knowledgeable than me will chime in.

In the meantime, it's a long shot but you could do a continuity check with one end of your multimeter to ground and the other on various components: each leg of the 680R resistor in the middle near the fuses, each of the pins in the output XLR sockets, then each of the pins in the power tube sockets and note down the results. That should show up anything going to ground that shouldn't be.

Edit: Did you manage to fix the carbonize issue? And are you board traces through that burnt area OK now?


----------



## klnglim

baronbeehive said:


> Your voltages at B+ side at 106v are nearer to the correct value so if we assume that everything is alright up to there then the problem is after the anode and around the cathode area, but you are getting no voltage drop across the 150R resistor which I can't understand. I'm assuming that you have checked the resistance across your 150R resistors. All your voltages are the same at either side of the anode and cathode resistors. I'm assuming that because both your channels show equal values that the problem is higher up the chain. I believe the 2 channels are linked by the 680R resistor but  I'm at my limits here, hopefully someone who is more knowledgeable than me will chime in.
> 
> In the meantime, it's a long shot but you could do a continuity check with one end of your multimeter to ground and the other on various components: each leg of the 680R resistor in the middle near the fuses, each of the pins in the output XLR sockets, then each of the pins in the power tube sockets and note down the results. That should show up anything going to ground that shouldn't be.
> 
> Edit: Did you manage to fix the carbonize issue? And are you board traces through that burnt area OK now?


Sorry for the late reply, the damage board area fixed already but the amp still reading "0" on VU meter , totally silence to headphone, still can't find out what's the problem yet


----------



## bloodhawk

klnglim said:


> Sorry for the late reply, the damage board area fixed already but the amp still reading "0" on VU meter , totally silence to headphone, still can't find out what's the problem yet





baronbeehive said:


> Your voltages at B+ side at 106v are nearer to the correct value so if we assume that everything is alright up to there then the problem is after the anode and around the cathode area, but you are getting no voltage drop across the 150R resistor which I can't understand. I'm assuming that you have checked the resistance across your 150R resistors. All your voltages are the same at either side of the anode and cathode resistors. I'm assuming that because both your channels show equal values that the problem is higher up the chain. I believe the 2 channels are linked by the 680R resistor but  I'm at my limits here, hopefully someone who is more knowledgeable than me will chime in.
> 
> In the meantime, it's a long shot but you could do a continuity check with one end of your multimeter to ground and the other on various components: each leg of the 680R resistor in the middle near the fuses, each of the pins in the output XLR sockets, then each of the pins in the power tube sockets and note down the results. That should show up anything going to ground that shouldn't be.
> 
> Edit: Did you manage to fix the carbonize issue? And are you board traces through that burnt area OK now?



Are these voltages with the default caps? 

One thing i would definitely do is check if the via's are not damaged.


----------



## klnglim

bloodhawk said:


> Are these voltages with the default caps?
> 
> One thing i would definitely do is check if the via's are not damaged.


I can't get any result right now include output XLR pin, cause the meter show unstable big differential DC voltage reading, I just got the input pin reading all same 133.5 mV


----------



## baronbeehive

klnglim said:


> I can't get any result right now include output XLR pin, cause the meter show unstable big differential DC voltage reading, I just got the input pin reading all same 133.5 mV



OK, have you continuity tested everything you have done to the next point on the trace on *both* sides of the board, very important as the board is double sided just to confuse us.

I don't believe your 150R resistors are at fault so the only way that I can see that the voltage is the same on both sides of the 150R resistor is that the signal is taking a short cut and bypassing the resistors there. So I suggest to do what I said in my last post and check for shorts or ground on every component, so just run a continuity test with one end of the multimeter in ground and the other on every leg of every component including the output XLR's, tube socket pins etc., amp off, and let us know the result.


----------



## klnglim (Apr 20, 2018)

baronbeehive said:


> OK, have you continuity tested everything you have done to the next point on the trace on *both* sides of the board, very important as the board is double sided just to confuse us.
> 
> I don't believe your 150R resistors are at fault so the only way that I can see that the voltage is the same on both sides of the 150R resistor is that the signal is taking a short cut and bypassing the resistors there. So I suggest to do what I said in my last post and check for shorts or ground on every component, so just run a continuity test with one end of the multimeter in ground and the other on every leg of every component including the output XLR's, tube socket pins etc., amp off, and let us know the result.


I had checked the ground short earlier, that's why I found problem with transistor before. After transistor problem solve, the amp turn on no more crack sound, no more circuit burn, however both VU Meter now light up togather at the same time, I suspect either zener diodes, diodes, bridge retifier, N channel J-Fet and Mosfet having some issue, may be going to change those parts later. I also ordered some eyelets to fix those damage area. (https://www.aliexpress.com/item/100...ular-Rivets-DIY-Double-sided/32841162429.html)


----------



## baronbeehive

Oh, right!

Not sure how that circuit works on switch on. There is a diode near the fuses in that area, I don't know if you've checked that. Anyway good luck!!


----------



## klnglim (Apr 21, 2018)

baronbeehive said:


> Oh, right!
> 
> Not sure how that circuit works on switch on. There is a diode near the fuses in that area, I don't know if you've checked that. Anyway good luck!!


The Diodes u mention about show 0.245 V under diodes read  in DMM, this one seem like unnormal?
I also just found one of the bridge rectifier has an issue so as j fet n channel


----------



## baronbeehive

klnglim said:


> The Diodes u mention about show 0.245 V under diodes read  in DMM, this one seem like unnormal?
> I also just found one of the bridge rectifier has an issue so as j fet n channel



Yes, that sounds off, it's a 100v diode, same as the others.


----------



## klnglim

baronbeehive said:


> Yes, that sounds off, it's a 100v diode, same as the others.


There is something I dont understand, when i took off those diodes from PCB, the DMM reading normal and no error, then I put it back, the DMM show 0.245V, that makes me confuse?
Do you know why ?


----------



## klnglim

klnglim said:


> There is something I dont understand, when i took off those zener diodes from PCB, the DMM reading normal and no error, then I put it back and checked again, the diode near fuse DMM show 0.245V, right side UV meter diode show 0.15V, both diodees become no polarity, that makes me confuse?
> Do you know why ?


----------



## baronbeehive

klnglim said:


> There is something I dont understand, when i took off those diodes from PCB, the DMM reading normal and no error, then I put it back, the DMM show 0.245V, that makes me confuse?
> Do you know why ?



I don't know, I hope somebody here can help with that.

Just to recap to before you had your latest problem:

1 - Your amp was working fine after your mods then...
2 - After a while the burning to the 2k2 resistor started again - did you do anything before this happened, I think you changed the layout. Also you found a broken wire at the back
3 - Since then you had more burning and have then replaced the transistors and diodes and fixed the carbonization issue and your traces are back to normal.

Is all that true?

You seem to be saying that all the connections and wires are good, but there must be something wrong, it is easy to miss something. Are you sure you have fixed the grounding issue, I feel something like this is still affecting your amp, you could begin by checking the output XLR's to see if anything at that end of the amp is grounded that shouldn't be.

Also check the traces going to and from the 2k2 resistor to see what could be causing the burning.

It's difficult to advise because we don't know exactly what's been happening.


----------



## baronbeehive

Might be a problem here?


----------



## bloodhawk (Apr 24, 2018)

So stuff happened, my friend spilled beer on his amp xD
Tripped breaker and a full disassembly later, he ended up buying my amp minus my parts and we ended up salvaging most of the high end upgrades from his board and i installed those on my board. All in all after about 8 hours of work and a bunch of cash in my pocket later, i bought another MK VI+ from the HeadFi market for $722 

Another 8 hours later and this is the result -  https://imgur.com/gallery/hO0rZ9X















Now this kinda threw a wrench into my plans of adding the CCS tail and bias switch . But was a blessing in disguise as i was thinking about things, and realized that i like use 2 x 6AS7G's / 6080's along wtih 2 x 5998/7236's most of the time. Here is a question for @baronbeehive @SonicTrance @Maxx134 , how bad of an idea is it to have individual switches for each of the power tubes? I can easily tuck 2 switches to the far left end (left tubes) , next to the power button with drilled holes out front and the other 2 for the right side tubes on the far right next to the headphone jack. Making them super symmetrical and might actually look cool.
This will give me the freedom of choosing which sockets i plug the 5998's/7236's in.


----------



## baronbeehive (Apr 25, 2018)

bloodhawk said:


> So stuff happened, my friend spilled beer on his amp xD



Careless!!



bloodhawk said:


> Now this kinda threw a wrench into my plans of adding the CCS tail and bias switch . But was a blessing in disguise as i was thinking about things, and realized that i like use 2 x 6AS7G's / 6080's along wtih 2 x 5998/7236's most of the time. Here is a question for @baronbeehive @SonicTrance @Maxx134 , how bad of an idea is it to have individual switches for each of the power tubes? I can easily tuck 2 switches to the far left end (left tubes) , next to the power button with drilled holes out front and the other 2 for the right side tubes on the far right next to the headphone jack. Making them super symmetrical and might actually look cool.
> This will give me the freedom of choosing which sockets i plug the 5998's/7236's in.



Goddamit, bloodhawk, you like your music LOUD!

I'm not sure of the fine detail of the circuitry so you will have to wait to see what Sonic says but I don't think you could do that. ATM the tube mix is on uniform power from the amp and the different tubes make the best of it, but if you change each tube's power requirement that will feed back into the circuit giving effectively 2 different power requirements in the same circuit which I don't think would work.


----------



## SonicTrance

bloodhawk said:


> how bad of an idea is it to have individual switches for each of the power tubes?


If you think that mixing tubes sounds better than running same tube types its not a bad idea. Nothing bad is going to happen. I think its unnecessary with four switches though. Why not settle for one / channel?


----------



## baronbeehive

SonicTrance said:


> Nothing bad is going to happen.



Of course, the 5998 setting just doubles the current to the tubes but doesn't affect the circuitry thereafter.


----------



## klnglim

baronbeehive said:


> Might be a problem here?


Make me no choice so I have to take out the board and check all the broken traces, take off all the burning area components, clean out with alcohol, put some flux then refill the eyelets every single hole.
It needs some times to finish all the process, I also repaint the front display as dislike the Little Dot logo.


----------



## klnglim (Apr 25, 2018)

klnglim said:


> Make me no choice so I have to take out the board and check all the broken traces, take off all the burning area components, clean out with alcohol, put some flux then refill the eyelets every single hole.
> It needs some times to finish all the process, I also repaint the front display as dislike the Little Dot logo.


----------



## baronbeehive

klnglim said:


> Make me no choice so I have to take out the board and check all the broken traces, take off all the burning area components, clean out with alcohol, put some flux then refill the eyelets every single hole.
> It needs some times to finish all the process, I also repaint the front display as dislike the Little Dot logo.



Yes, I can clearly see your problem now with your close ups!


Looks like your PC has been in the wars LOL.

Don't worry I don't know anyone here who hasn't lifted a pad or two. I was in your situation but I decided to get an engineer to check my mods before switching it on because I wasn't confident. Lucky for me he fixed all dodgy areas before sending it back.

Got to hand it to you for sticking at it. Good luck, those eyelets should help you to do a professional job which I'm sure you will. Keep us informed of progress.


----------



## bloodhawk

baronbeehive said:


> Goddamit, bloodhawk, you like your music LOUD!
> 
> I'm not sure of the fine detail of the circuitry so you will have to wait to see what Sonic says but I don't think you could do that. ATM the tube mix is on uniform power from the amp and the different tubes make the best of it, but if you change each tube's power requirement that will feed back into the circuit giving effectively 2 different power requirements in the same circuit which I don't think would work.



LOL That 0 dB is because the DX7s is in DAC mode. And my Music players are all set to 50% volume with windows being set to 75%. 

But yeah really careless on his part. There is a reason why i never let people drink around my electronics or even let anyone into the room if there is a party at my place. 




SonicTrance said:


> If you think that mixing tubes sounds better than running same tube types its not a bad idea. Nothing bad is going to happen. I think its unnecessary with four switches though. Why not settle for one / channel?



Wanted to do 4 just for the freedom of tube positioning. Because for example, this order of tubes - 6AS7G/5998/6AS7G/5998 does not sound as good as 5998/6AS7G/5998/6AS7G. Same with the 7236's. 



baronbeehive said:


> Yes, I can clearly see your problem now with your close ups!
> 
> 
> Looks like your PC has been in the wars LOL.
> ...



Yeap definitely lifted pads. The black boards actually have suuper stury traces and via, this older board has much more brittle traces. I lifted 2 pads even after being super careful. 

@klnglim if the traces are super messed up, then i would definitely run 20 AWG solid core wire from one side of the board to the other, to make sure the continuity is perfect. This might be a little bit overkill. But it will ensure a perfect connection.


----------



## Maxx134 (Apr 25, 2018)

bloodhawk said:


> how bad of an idea is it to have individual switches for each of the power tubes?


Use four double throw switches. 
Each switch to switch bias setting for each tube.

Then you will have ultimate freedom of mixing tubes in amp.

Just make sure your in correct switched position...

Double check switch with Sonic as we went over looking for high current switches in past.

I believe the switches should also be double throw, if you are only changing the cathode resisitor (bias mod).
I forget as I have an MK8 and did not need this bias mod.

I only adjusted bias for one tube type.





klnglim said:


>


Wow that's a big project now.
Will be a big sense of accomplishment once done.


----------



## bloodhawk (Apr 25, 2018)

Maxx134 said:


> Use four double throw switches.
> Each switch to switch bias setting for each tube.
> 
> Then you will have ultimate freedom of mixing tubes in amp.
> ...



Gotcha, yeah thats the plan.

I have 125V 6A / 250V 2A switches. Should be plenty.

@klnglim If you can the board outside (in better lighting and take a few pictures of the board, i can try and tell you which pads will need fixing with a wire.


----------



## Maxx134 (Apr 25, 2018)

bloodhawk said:


> Gotcha, yeah thats the plan.
> 
> I have 125V 6A / 250V 2A switches. Should be plenty.


What is the configuration?
Is it a double pole , double throw?
You need at least double pole for the two triodes per tube.

I like that idea better than original , for geater freedom of tube selection.

That means all power  tube types can be mixed in the mk6..

Sometimes I feel like buying an mk6 to compare to my mk8..
But I am currently lack of time and planning a major amp project next.


----------



## bloodhawk (Apr 25, 2018)

Maxx134 said:


> What is the configuration?
> Is it a double pole , double throw?
> You need at least double pole for the two triodes per tube.
> 
> ...



I have ONON SPDT's / ON ON DPDT's. Along with a bunch of 3PDT'S and 4PDT's. 

Arent we just trying to add resistors in parallel ? So a Single pole should just work fine?

The pictures on the first page arent exactly clear. From what i can see, we are just switching and dropping the resistance for the cathode by half.


----------



## SonicTrance

bloodhawk said:


> I have a ONON SPDT's . ON ON DPDT's.
> 
> Arent we just trying to add resistors in parallel ? So a Single pole should just work fine?
> 
> The pictures on the first page exactly clear. From what i can see, we are just switching dropping the resistance for the cathode by half.


Yes, correct. Only the bottom triode has a cathode resistor. The plate of the bottom triode then connects straight to the top triodes cathode. So one resistor per tube.


----------



## klnglim (Apr 25, 2018)

baronbeehive said:


> Yes, I can clearly see your problem now with your close ups!
> 
> 
> Looks like your PC has been in the wars LOL.
> ...


Never give up till the miracle happen. LOL

Thomas Edison Quotes : I have not failed. I’ve just found 10,000 ways that won’t work.


----------



## klnglim (Apr 25, 2018)

Maxx134 said:


> Use four double throw switches.
> Each switch to switch bias setting for each tube.
> 
> Then you will have ultimate freedom of mixing tubes in amp.
> ...


A lot lessons learnt during process, good for self improvement. LOL

Thomas Edison Quotes : I have not failed. I’ve just found 10,000 ways that won’t work.


----------



## Maxx134

klnglim said:


> After checked cabling, ground connection, at last the amp turn on peacefully however still read "0" on the vu meter, no idea what's wrong, the DC voltage reading :
> (106) (3.5) (3.5) (106) (106) (3.5) (3.5) (106)
> (106) (3.5) (3.5) (106) (106) (3.5) (3.5) (106)
> (215) (215) (215) (215)


Your supposed to have B+ & B- voltages.
This tell me one of the transistors are bad.




klnglim said:


> Sorry for the late reply, the damage board area fixed already but the amp still reading "0" on VU meter , totally silence to headphone, still can't find out what's the problem yet


0 on the bias meters is a result of the protection circuit kicking in, 
Due to the Problem with PSU giving the output circuit error .



klnglim said:


> After transistor problem solve, the amp turn on no more crack sound, no more circuit burn, however both VU Meter now light up togather at the same time, I suspect either zener diodes, diodes, bridge retifier, N channel J-Fet and Mosfet having some issue, may be going to change those parts later.


The issue is that the diodes are performing as zener diodes to stable the power going thru the power transistors.
The problem lie that they can burn (with their series resisitor next to them), when there is "no tubes" in the sockets .
This will cause chain reaction to blow your transistors.
Replacement of both the pnp&npn power transistors simultaneously is recomended, 
As well as the crappy tiny diodes for greater amperage versions (100v and higher amperage for durability).
Change all four at same time, and you won't have one component blowing out the other..
Swap out the garbage tiny series resistor that is with the (zener) diodes as well to greater wattage.

I always use Mills MR5 wirewound for these applications where the current can get high.
They can give ofd smoke for a few seconds  an still perform like new.
This is from my own  experience on same PSU.



klnglim said:


> The Diodes u mention about show 0.245 V under diodes read  in DMM, this one seem like unnormal?
> I also just found one of the bridge rectifier has an issue so as j fet n channel


Just change out those tiny baby diodes for some heavy duty and not have to worry .



klnglim said:


> There is something I dont understand, when i took off those diodes from PCB, the DMM reading normal and no error, then I put it back, the DMM show 0.245V, that makes me confuse?
> Do you know why ?


The diodes supposed to perform a zener voltage regulation to the base of the power transistors which handle the PSU current.

Without the diodes you will not have regulation and I am not sure but I believe the transistors are configured to fully conduct .
When there is less load on PSU, the diodes will conduct more to absorb the voltage headroom of the PSU , which in return biases the power transistor to put out lower voltage and less demand.
Yet the diode will get super hot and burn their accompanying series resisitors.
This is hottest area of amp.
The heat also travels thru the traces to the last two caps that are suggest upgraded.

So I would replace the zener diodes with larger and with longer leads to help dissipate heat further away from board.

If not done already, I would extend the bottom of the amp for more component space.

Good luck!


----------



## bloodhawk (Apr 25, 2018)

Something interesting I came across today while talking to a friend who works as engineer in the USAF,

All of Tlthe MILLS resistors are made my VISAHY / DALE. MRA5 / MRA12 are exactly the same as the 5W/12W Dale's (black / brown doesn't matter) .
Vishay / Dale produces a RS (basic variant) and a NS (NON inductive) variant. These are then colored / labelled for different markets. The specs on both of these are much better than the MILLS branded ones. And all of them are made in Mexico.


End of the day they are all the same, just make sure you get the correct non inductive variant. 

 Hope this saves a few people some money.


----------



## Maxx134 (Apr 25, 2018)

bloodhawk said:


> And all of them are made in Mexico.
> 
> 
> End of the day they are all the same. Hope this saves a few people some money.


Agreed, my MR5 come from Mexico, and are all matched.

The main thing to make sure of, is that they state they are "non-inductive" types...

The older ones that dont state this,  are usually slightly inductive..

 There was a sonic difference noticed,
Which was in the upper FR spectrum having a "shiny, glossy, wet,metalic" type ring,
 or ambiance to the circuit.

I believe this due to some type of high freq oscillations going on,
 because of the added inductance to the circuit.

The actual possible issues can be googled, so I am only noting sonic observations made from this ouput circuit only, 
so only applies to this amp.

Results can vary wildly to no issues, or anything depending the the amp and circuit.

Also, on another topic,

The stock bridge rectifiers look like tiny little round things,
 but are super durable..

 I replaced mine with  some fancy Shockey rectifier thats supposedly better, but with the amount of capacitance in the main PSU, I heard no benifits.

Still they probably good for component logevity.

Also if I werr to do it again,
I only would only  change the driver stage PSU rectifier, as it has less capacitance and no regulation, but since it is an rcrc circuit I really doubt upgrading the rectifier does any benifits here.


----------



## klnglim

Maxx134 said:


> Agreed, my MR5 come from Mexico, and are all matched.
> 
> The main thing to make sure of, is that they state they are "non-inductive" types...
> 
> ...


I notice so far, Other than those bridge rectifier, volume controler, tube sockets, op-amp chips and fuse, the rest of the components are garbage include the PCB itself


----------



## bloodhawk

klnglim said:


> I notice so far, Other than those bridge rectifier, volume controler, tube sockets, op-amp chips and fuse, the rest of the components are garbage include the PCB itself


The blue PCBs seem to be of much poorer quality than the newer black PCBs.

Even after a lot of care while pulling the larger caps and a few of the smaller resistors , I pulled 3 pads. On the amp with the black PCB , 0 pads got pulled no matter hoq many times I soldered / applied heat to the same pads. And I did that a bunch of times on my friends amp.

Probably one of the reasons why they switched to the black boards. And partly to hide the traces.


----------



## klnglim (Apr 25, 2018)

bloodhawk said:


> The blue PCBs seem to be of much poorer quality than the newer black PCBs.
> 
> Even after a lot of care while pulling the larger caps and a few of the smaller resistors , I pulled 3 pads. On the amp with the black PCB , 0 pads got pulled no matter hoq many times I soldered / applied heat to the same pads. And I did that a bunch of times on my friends amp.
> 
> Probably one of the reasons why they switched to the black boards. And partly to hide the traces.


The board is quite strong but the printed silver eyelets & traces are very easy to come off, need to be careful when desolder.
That's why I ordered eyelets cooper replacement and slim cooper lining sticker to fix those damage area


----------



## Maxx134

klnglim said:


> Other than those bridge rectifier





 
Too bad all this hype sold me and I did not hear any benifits,
Which may have actually occurred in the driver  stage PSU, 
But I cannot verify, so cannot recomend unless you really want to try.


----------



## klnglim

Maxx134 said:


> Too bad all this hype sold me and I did not hear any benifits,
> Which may have actually occurred in the driver  stage PSU,
> But I cannot verify, so cannot recomend unless you really want to try.


Yes , I have seen that before, i felt this overkill


----------



## Maxx134

klnglim said:


> The board is quite strong but the printed silver eyelets & traces are very easy to come off, need to be careful when desolder.
> That's why I ordered eyelets cooper replacement and slim cooper lining sticker to fix those damage area


I forgot who it was that had their trace broken in the main PSU, right underneath the PSU caps around the diode area..
One side supposed to connect to the other thru a hole wherr two caps join(!).
You should check that area as well..


----------



## Maxx134

I meant the top board connect with the bottom board to bring the center ground potential to the transistors.
It basically depends on the board trace..
I don't know who it was  and there are soo many pages here lol


----------



## klnglim

Maxx134 said:


> I forgot who it was that had their trace broken in the main PSU, right underneath the PSU caps around the diode area..
> One side supposed to connect to the other thru a hole wherr two caps join(!).
> You should check that area as well..


This picture with circle red color is the worst issue, that area was where explosion happened, I believe that damage area cause ground shorted


----------



## baronbeehive

klnglim said:


> Never give up till the miracle happen. LOL
> 
> Thomas Edison Quotes : I have not failed. I’ve just found 10,000 ways that won’t work.



He sounds like my kinda guy LOL.



Maxx134 said:


> I meant the top board connect with the bottom board to bring the center ground potential to the transistors.
> It basically depends on the board trace..
> I don't know who it was  and there are soo many pages here lol



To save you wading through 200 or so pages... not a whole lot of fun by any means..... I had this problem but I don't think I told anyone, the engineer fixed it for me. I think Sonic had a problem fixed with wire there, I don't think Mogos had any problems like that, lucky person!


----------



## bloodhawk

baronbeehive said:


> He sounds like my kinda guy LOL.
> 
> 
> 
> To save you wading through 200 or so pages... not a whole lot of fun by any means..... I had this problem but I don't think I told anyone, the engineer fixed it for me. I think Sonic had a problem fixed with wire there, I don't think Mogos had any problems like that, lucky person!



I should have probably taken pictures. Since i had 2 larger ripped pads and (PSU caps) and 1 smaller pad with the via ripped out. But this was on the blue board. The black PCB had 0 issue even after multiple pulls and solder sessions.


----------



## baronbeehive

bloodhawk said:


> I should have probably taken pictures. Since i had 2 larger ripped pads and (PSU caps) and 1 smaller pad with the via ripped out. But this was on the blue board. The black PCB had 0 issue even after multiple pulls and solder sessions.



Yeah, I noticed your black board looked remarkably clean. Do you desolder before pulling out the components, that is the best way to avoid pulling pads......... or so I'm told!


----------



## klnglim

baronbeehive said:


> Yeah, I noticed your black board looked remarkably clean. Do you desolder before pulling out the components, that is the best way to avoid pulling pads......... or so I'm told!


I just found something interesting and I think I can copy the whole original PCB and build the second MK8SE or may be more. LOL


----------



## baronbeehive

klnglim said:


> I just found something interesting and I think I can copy the whole original PCB and build the second MK8SE or may be more. LOL



Wow..... have you thought about going P2P? Might be easier!


----------



## klnglim

baronbeehive said:


> Wow..... have you thought about going P2P? Might be easier!


what's P2P?


----------



## bloodhawk

baronbeehive said:


> Yeah, I noticed your black board looked remarkably clean. Do you desolder before pulling out the components, that is the best way to avoid pulling pads......... or so I'm told!



Yeap. But i did the same with this board as well. 


klnglim said:


> I just found something interesting and I think I can copy the whole original PCB and build the second MK8SE or may be more. LOL



Do share


----------



## baronbeehive (Apr 26, 2018)

klnglim said:


> what's P2P?



Point to point, ie you reproduce the traces from the PCB using wires instead..... no more lifted pads! You just need to know where to put everything in a custom chassis.

Or if you're thinking of going down this route ask Sonic about his LTP amp. Might be cheaper to start from scratch if you've got to get a whole lot of new components.


----------



## klnglim (Apr 26, 2018)

baronbeehive said:


> Point to point, ie you reproduce the traces from the PCB using wires instead..... no more lifted pads! You just need to know where to put everything in a custom chassis.
> 
> Or if you're thinking of going down this route ask Sonic about his LTP amp. Might be cheaper to start from scratch if you've got to get a whole lot of new components.


Now I try to figure out how to copy the board traces layout so can DIY own cooper PCB, The method is very simple, just use the bright cool white colour light focus at the bottom of the PCB,  then U CAN  see all the traces from both side the board crystal clear  , also very helpful when try to find and fix the damage area and broken traces


----------



## klnglim (Apr 26, 2018)

bloodhawk said:


> Yeap. But i did the same with this board as well.
> 
> 
> Do share


Sure will do if I can find out the way to draw out all the traces from both side of the board

Sharing is wonderful, LOL


----------



## klnglim

Here is MK8SE high quality transformer


----------



## baronbeehive

Anyone know how to remove the low/high gain switch?

Since using this switch I noticed that the resistor right next to it, the 390K resistor which reads 10K on low gain, has gone off so I checked the switch itself and found one of its resistors is not right probably causing an abnormally high reading on the 390K resistor.


----------



## bloodhawk

baronbeehive said:


> Anyone know how to remove the low/high gain switch?
> 
> Since using this switch I noticed that the resistor right next to it, the 390K resistor which reads 10K on low gain, has gone off so I checked the switch itself and found one of its resistors is not right probably causing an abnormally high reading on the 390K resistor.



I swapped the ones on my friends board using a solder sucker.


----------



## SonicTrance

baronbeehive said:


> Anyone know how to remove the low/high gain switch?
> 
> Since using this switch I noticed that the resistor right next to it, the 390K resistor which reads 10K on low gain, has gone off so I checked the switch itself and found one of its resistors is not right probably causing an abnormally high reading on the 390K resistor.


Hm, it should read about 80k on low gain as it then has a 100k in parallell with it. And obviously 390k on high gain. As for removing the switch you can just desolder it and then use fixed resistors.


----------



## klnglim (May 5, 2018)

baronbeehive said:


> Anyone know how to remove the low/high gain switch?
> 
> Since using this switch I noticed that the resistor right next to it, the 390K resistor which reads 10K on low gain, has gone off so I checked the switch itself and found one of its resistors is not right probably causing an abnormally high reading on the 390K resistor.


May be the resistor and the switch is parallel connection, the switch itself has resistance, that's why u will see the different reading in between high and low gain, but 390K is too high.I also notice my MK8se resistor 470K around that area all have to replace the new one, u need to desolder the resistor to read the right value. The switch is very easy to take off if u don't like it

Just finished fix all the damage parts, now need some times to wait for some replacement component to arrive


----------



## SonicTrance

Looking at those pics the feedback resistors for the mk8 are 100k and 68k. So 100k for high gain (low NFB) and 40k for low gain (high NFB). That’s a fair bit more NFB than the mk6’s 390k and 80k.


----------



## klnglim

SonicTrance said:


> Looking at those pics the feedback resistors for the mk8 are 100k and 68k. So 100k for high gain (low NFB) and 40k for low gain (high NFB). That’s a fair bit more NFB than the mk6’s 390k and 80k.


However after solder back 100k on PCB, the reading isn't 100k anymore from DMM and will have little bit differential of value as well if switch between high & low gain.  (The rest of the resistor's value remain unchange even after solder back on PCB)


----------



## baronbeehive

klnglim said:


> However after solder back 100k on PCB, the reading isn't 100k anymore from DMM and will have little bit differential of value as well if switch between high & low gain.  (The rest of the resistor's value remain unchange even after solder back on PCB)



Correct, sorry if I mislead you when I gave you those resistor readings, they were the measured values, the board values are sometimes different as you say.

Glad to see you are making progress with the repairs, looks like you've got those eyelets in and traces fixed nicely!


----------



## baronbeehive (May 6, 2018)

SonicTrance said:


> Looking at those pics the feedback resistors for the mk8 are 100k and 68k. So 100k for high gain (low NFB) and 40k for low gain (high NFB). That’s a fair bit more NFB than the mk6’s 390k and 80k.



My 390K resistors are in fact 360K but are quite a bit lower than that when measured out of the board. The 390k and 80K in parallel give the 66K that I see in the 80K resistor on high gain but the 390K is connected to the gain switch because it reads 27K in high gain. In low gain the readings for those 2 resistors are both 10K. The 2 resistors in the gain switch appear to be both 100k, (from readings), but the faulty one causing the bad reading in the 390K resistor reads 125K.

Thanks guys for the info on the gain switch, I thought it might clip in like the opamps. I believe Maxx said that those switches were suspect and I agree after what I've found after changing from the gain.

All this has put back my listening tests with the different anode/cathode/gain settings. However after trying high gain I agree with Maxx that high gain sounds slightly better so I will be using that setting from now on. The volume knob settings are still useable, you only have to turn down a couple of notches to get the same level as on low gain.... bloodhawk will not notice as he likes extreme volume levels lol.

I've take inspiration from the hard work of kinglim and bloodhawk and decided it was time to renew the PSU resistors, diodes and transistors..... (I had to do this anyway because I stupidly shorted out the amp when taking voltage readings with a shaky hand..... I should have taken Maxx's advice and inhaled the solder smoke to steady myself LOL!

Edit: can you correct a possible misconception, is going from 100K to, say, 50K lower, or higher, I might be using the wrong terminology.


----------



## baronbeehive (May 6, 2018)

Sorry, double post.


----------



## klnglim

baronbeehive said:


> Correct, sorry if I mislead you when I gave you those resistor readings, they were the measured values, the board values are sometimes different as you say.
> 
> Glad to see you are making progress with the repairs, looks like you've got those eyelets in and traces fixed nicely!


As myself just have a knowledge of the basic electronic and never study deeply, so need some times to understand everything inside the amp.
It's part of my hobby, I really enjoy to spend lot of times to learn and is great experience for self improvement.
Anyway, thanks for all the members from this mods forum for their wonderful sharing experience.
I also plan to build another P2P MK8se as I have all the spare component left behind


----------



## SonicTrance

baronbeehive said:


> Edit: can you correct a possible misconception, is going from 100K to, say, 50K lower, or higher, I might be using the wrong terminology.


Higher feedback resistance is lower NFB and lower feedback resistance is higher NFB. Its logical when you think about it  If there’s lower resistance more of the signal gets fed back, hence higher NFB.


----------



## baronbeehive (May 6, 2018)

I've desoldered the switch and am trying to figure it out.

Below are the connections to the switch which is ON-OFF.

My values for high gain for the 390K and 68K resistors are 27K and 68K, the values for low gain are 10K and 10K.

My problem is seeing how these values are arrived at from the connections below, can anybody see how to arrive at the above values which I believe are correct because they are the same for 3 of the 4 circuits, wheras the values for the 4th circuit are 37K and 68K!!!

There is also resistance in the switch position but it must be built into the board because I measured 100K from the 2 points on the board with the switch out.





I believe my problem with the 390K resistor reading is due to the switch not fully opening or closing properly, but until I know how to arrive at the correct values I can't bypass the switch with fixed resistors.

I'm just having trouble seeing what is in parallel to what here!

However I think with the switch out the connections are configured to high gain because on low gain the switch is on and without the switch in place it would be off.


----------



## klnglim (May 6, 2018)

baronbeehive said:


> I've desoldered the switch and am trying to figure it out.
> 
> Below are the connections to the switch which is ON-OFF.
> 
> ...


I hope below pictures might help soft your problem?
If need anymore info let me know, hope u can figure out the way


----------



## SonicTrance

baronbeehive said:


> My values for high gain for the 390K and 68K resistors are 27K and 68K, the values for low gain are 10K and 10K.


My amp uses 390k and 100k, not 68k like you say? 390k is for high gain and 390 parallell with 100 = 80k is for low gain. I have not measured these resistors when soldered on the board though.



baronbeehive said:


> I believe my problem with the 390K resistor reading is due to the switch not fully opening or closing properly, but until I know how to arrive at the correct values I can't bypass the switch with fixed resistors.


If you have a connection problem like that you'd hear it.



baronbeehive said:


> However I think with the switch out the connections are configured to high gain because on low gain the switch is on and without the switch in place it would be off.


Yes, just measure resistance from input tube grid to the output. Look at my schem here:


----------



## klnglim

SonicTrance said:


> My amp uses 390k and 100k, not 68k like you say? 390k is for high gain and 390 parallell with 100 = 80k is for low gain. I have not measured these resistors when soldered on the board though.
> 
> 
> If you have a connection problem like that you'd hear it.
> ...


May I know how many watts recommendation for the resistor to put there?


----------



## baronbeehive

Thanks guys! More of this in the morning.

Hey kinglim, that lighting idea is good, I was wondering if it might help all of us if you could take some good closeups of the board top and bottom to reveal the traces. This was a problem are for us at the start of this thread and with all the components in place it isn't easy to see them all.

Maybe Maxx would let you put them on the first page.


----------



## MrCurwen

klnglim said:


> May I know how many watts recommendation for the resistor to put there?



Let's say the signal swing at the junction of RL and R16 is 50VPP. This would mean the differential (meaning, actual voltage seen by the load) voltage across the load would be an astounding 100VPP, completely crushing your ears and burning to death your headphone speaker coils. So in other words, enough voltage.

This voltage is between the mentioned junction and circuit ground. The path to ground from that junction that goes thru the feedback resistor R16 is either 390k + 10k or 80k + 10k depending on the setting. So 400k or 90k.

Let's use Ohm's Law: 50V divided by 400k means current of 0.125 mA. Combined dissipation thru that path is then 0.125 mA times 50V which means 0.00625 W. Divide that by 400k and multiply by 390k and you get the dissipation for R16 at 390k as 0.006 Watts.

For the 90k scenario: 50 divided by 90k means current of 0.55 mA. Combined dissipation thru that path is then 0.55 mA times 50V which means 0.0275 W. Divide that by 90k and multiply by 80k and you get the dissipation for R16 at 80k as 0.0244 Watts.

In both cases you'll be more than fine with 0.25W resistors. However I recommend simply using 1W no-name carbon film resistors for all spots that dissipate under 0.75 W. That covers usually 95% of resistors inside any circuit. Why mess with different types.


----------



## klnglim

baronbeehive said:


> Thanks guys! More of this in the morning.
> 
> Hey kinglim, that lighting idea is good, I was wondering if it might help all of us if you could take some good closeups of the board top and bottom to reveal the traces. This was a problem are for us at the start of this thread and with all the components in place it isn't easy to see them all.
> 
> Maybe Maxx would let you put them on the first page.


That's the way how I search and fix those damage parts of the board. What you need is LED flash light with flat surface like glass


----------



## klnglim

MrCurwen said:


> Let's say the signal swing at the junction of RL and R16 is 50VPP. This would mean the differential (meaning, actual voltage seen by the load) voltage across the load would be an astounding 100VPP, completely crushing your ears and burning to death your headphone speaker coils. So in other words, enough voltage.
> 
> This voltage is between the mentioned junction and circuit ground. The path to ground from that junction that goes thru the feedback resistor R16 is either 390k + 10k or 80k + 10k depending on the setting. So 400k or 90k.
> 
> ...


As I am lack of electronic experience especially calculation,further more there are too many choices of resistor to replace and confuse about which is the best. Anyway, thanks for the answer.


----------



## MrCurwen

klnglim said:


> As I am lack of electronic experience especially calculation,further more there are too many choices of resistor to replace and confuse about which is the best. Anyway, thanks for the answer.



Indeed.

Equations used in my post were Ohm's law, dissipation, and simple proportional calculation.

Ohm's law in conjunction with Kirchof's law are the most important to understand, they will come up everywhere all the time. Luckily they are very simple and easy to understand.

Ohm's law is simply 1A of current flowing thru a 1 ohm resistor will cause 1 V of voltage to appear across the resistor.

Or, if you apply a 1 V voltage across a 1 ohm resistor, you will cause 1 A of current to flow thru the resistor.

Or, if you have 1 A flowing thru a resistor and you have 1 V of voltage across the resistor, the resistor must be 1 ohms.

These three variations will help you determine a great number of things in electronics. Memorize them. 


Dissipation is simply voltage (in volts) times current (in amperes, so 1mA is 0.001 A), and the result is watts. If you have AC, you must first calculate RMS values. DC is most useful though, you rarely need to calculate AC dissipations.


Kirchof's law simply means that the same amount of current that leaves the power supply must return to the power supply.

A common application of this is that if you have a current path within a circuit, let's say you have two resistors in series between B+ and ground, they both must have the same amount of current thru them.

No extra current cannot appear in the middle of that resistor series, and no current can disappear.

So let's say you have a B+ of 100V, and you two resistors in series between B+ and ground. Let's call them R1 and R2. R1 is 50k and R2 is 12k.

So we have a total of 62k of resistance between B+ and ground. Ohm's law says that means about 16mA of current flows thru that series. The same amount of current must flow thru both these resistors, since they are in series. That's pretty much the point of Kirchof's law.

From the point of view of the PSU (PT?) the whole of the circuit is just a bunch of stuff in series and in parallel between the PSU terminals. So equal amounts of current must flow in as flows out of the PSU. It's just a matter of parallel currents paths then.


----------



## klnglim

MrCurwen said:


> Indeed.
> 
> Equations used in my post were Ohm's law, dissipation, and simple proportional calculation.
> 
> ...


I understand that resistor in series = R1+R2, 50k+12K=62K, let say if power rating both resistors are 0.5W, so in series is 1W?


----------



## MrCurwen

klnglim said:


> I understand that resistor in series = R1+R2, 50k+12K=62K, let say if power rating both resistors are 0.5W, so in series is 1W?



Power rating is Pd + Pd like that only when you parallel two resistors of same resistance value.

Dissipation is always voltage times current.

So in my example you now know the current from using Ohm's law. Now you can again use Ohm's law to determine the voltage drop across each resistor.

There was a mistake in my current calculation, current is 1.6 mA not 16 mA. Anyway; the variation of Ohm's law we'll use next is this: 

Ohm's law is simply 1A of current flowing thru a 1 ohm resistor will cause 1 V of voltage to appear across the resistor.

So we have 1.6 mA or 0.0016 A of current. Multiply this by 50 000 ohms, and we get a voltage drop of 80 volts for R1.

For R2 it's 0.0016 A times 12 000 ohms, 19.2 volts. 

As we can see, the combined voltage drops equal (after taking rounding into consideration) 100 volts, so we know the calculations are correct since there is 100 volts between B+ and ground.

So now we know both voltage drops and current thru the resistors, and we can calculate dissipations.

1.6 mA times 80 volts means 0.128 W for R1.

1.6 mA times 20 volts means 0.032 W for R2.


This is how you calculate dissipations for components. Same process applies for tubes and FETs and all kinds of components that pass current.


----------



## baronbeehive

Anyone any idea where I could get an ammeter for the LD, one of the contacts is dead on one of mine, I believe a wire has come off inside it and it doesn't come apart to fix it.


----------



## bloodhawk

baronbeehive said:


> Anyone any idea where I could get an ammeter for the LD, one of the contacts is dead on one of mine, I believe a wire has come off inside it and it doesn't come apart to fix it.



I have 2 extra if you want. Just shoot me a shipping label and ill drop em off.

Otherwise i got them from here - 

https://www.ebay.com/itm/Backlight-...e=STRK:MEBIDX:IT&_trksid=p2060353.m2749.l2649


----------



## baronbeehive

bloodhawk said:


> I have 2 extra if you want. Just shoot me a shipping label and ill drop em off.
> 
> Otherwise i got them from here -
> 
> https://www.ebay.com/itm/Backlight-100mA-DC-Current-Panel-Meter-Amperemeter-34mm-Header-for-Amplifier-New/132327543572?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m2749.l2649



Thanks bloodhawk, I'll have 'em both if you don't need them. Where are you UK or US?


----------



## klnglim

baronbeehive said:


> Anyone any idea where I could get an ammeter for the LD, one of the contacts is dead on one of mine, I believe a wire has come off inside it and it doesn't come apart to fix it.


You can get more choices from Alibaba.com
https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20180508030118&SearchText=+vu+meter


----------



## klnglim

MrCurwen said:


> Power rating is Pd + Pd like that only when you parallel two resistors of same resistance value.
> 
> Dissipation is always voltage times current.
> 
> ...


Now that's what I have learn, Thanks a lot!


----------



## baronbeehive

SonicTrance said:


> My amp uses 390k and 100k, not 68k like you say? 390k is for high gain and 390 parallell with 100 = 80k is for low gain. I have not measured these resistors when soldered on the board though.
> 
> If you have a connection problem like that you'd hear it.



Yes, it must have happened after trying the gain settings which I did for the first time recently. The switch could have been stuck or not working properly because it hasn't been used for 10 years or so! After that I haven't listened anymore because of the PSU upgrades so it could have happened without my knowing,

There is definately variation with resistor values. My 390K's are actually 330K, doesn't affect the parallel calculations much, and where you have 100K I have 68K, therefore the 68K I measured for high gain must be this resistor on only. Also there is 100K in the board somehow between the 2 switch terminals. I will not put the switch back now so that means permanent high gain from now on.

My board is earlier than yours with the "quality" Dales LOL!

BTW, I've changed the 5K1 to 2K55 as was specified in the update from LD, but there is one other 5K1 resistor nearby which I have kept at 5K1 as I believe others have done, hope that is OK.


----------



## bloodhawk

baronbeehive said:


> Thanks bloodhawk, I'll have 'em both if you don't need them. Where are you UK or US?



Yeah you can have em both. 
Im in the US.


----------



## SonicTrance

baronbeehive said:


> therefore the 68K I measured for high gain must be this resistor on only.


No, your 68k are in parallell with your 330k for low gain. Again, high gain = high resistance feedback R (low NFB), low gain = low resistance R (high NFB). Your 330k is for high gain (low NFB) 
Where exactly are you measuring from? Did you measure like I said? From input tube grid to the output?


----------



## baronbeehive

SonicTrance said:


> No, your 68k are in parallell with your 330k for low gain. Again, high gain = high resistance feedback R (low NFB), low gain = low resistance R (high NFB). Your 330k is for high gain (low NFB)
> Where exactly are you measuring from? Did you measure like I said? From input tube grid to the output?



I'm still struggling with schematics, I'm finding it difficult to see what is in parallel to what frankly. I don't see a 390K there, could you elaborate?






I tried measuring from the points in red.


----------



## baronbeehive

bloodhawk said:


> Yeah you can have em both.
> Im in the US.



Right. If you can PM me with the price inc postage I will let you know my details.


----------



## MrCurwen

baronbeehive he means the output of the whole phase, meaning junction of R16 and RL, and input of the whole phase, meaning junction of R5 and control grid of U1.


----------



## klnglim (May 9, 2018)

baronbeehive said:


> Correct, sorry if I mislead you when I gave you those resistor readings, they were the measured values, the board values are sometimes different as you say.
> 
> Glad to see you are making progress with the repairs, looks like you've got those eyelets in and traces fixed nicely!


I just found out the original WIMA caps install from factory is incorrect and load of garbage component they did put in!
What I have seen from MK8SE layout ,  all those 15 pieces of red WIMA caps should be model: WKP10 0.22uF/250V, however they put 11 pieces MKP10 0.22uF/250V; 3 pieces MKP10 0.22uF/160V & 1 MKP4 0.1/630V.
I guess may be they out of stock some caps so just find other look similiar garbage put into the PCB. Although the design of this amp is very great but the job they've done and most of component include PCB board out from Little Dot company is rubbish!
Be aware & better double check all those red WIMA caps !!!


----------



## SonicTrance

baronbeehive said:


> I'm still struggling with schematics, I'm finding it difficult to see what is in parallel to what frankly. I don't see a 390K there, could you elaborate?
> 
> 
> 
> I tried measuring from the points in red.


R16 and R17 are feedback resistors. I put in 80k as that’s what the low gain setting is. 390k in parallell with 100k. Doesn’t matter which phase you measure. Input grids are pin 1 and 4. Don’t remember which one is ”negative” and ”positive”, should be easy to trace which grid belongs to which output. Then just measure from a input grid to the output of that same phase.


----------



## Maxx134 (May 11, 2018)

Wow alot passed me by I was away.
I will try to help.



klnglim said:


> This picture with circle red color is the worst issue, that area was where explosion happened, I believe that damage area cause ground shorted


No that is the resistor which burn as a result  from either the diode failure or the power transistor.
Regardless, once this happens, it is very likely you will need to replace the associated power transistor that the (zener) diode was regulating.
My stong suggestion is to upgrade BOTH the "PNP" &"NPN"  transistors  (on the chasis) a set with the upgraded version as those stock units are not made anymore but replaced with higher amperage units.
Also replace both the (100v) zener diodes and the resistors next to them with higher wattage as that I already mentioned is the hottest area of the amp (besides the sockets).




baronbeehive said:


> Edit: can you correct a possible misconception, is going from 100K to, say, 50K lower, or higher, I might be using the wrong terminology





The switch is a double pole (two circuit),
Single throw (on off)

If you look carefully, you will realize that switching "on",
 will place an added resistor in parallel.
An added paralleled resisitor will drop the  total resistance.

Lowering total resistance will increase feedback,
AND then, that
Increased feedback will end up give you a "cleaner" LOWER volume output.
This is "NFB".
NFB is not liked because, although it corrects some distortions, it is a compromise solution for this application (in an amp)
So,
Less feedback equals louder volume.
More feedback will reduce volume.

Remember, more feedback (less volume) is a result of that lower resistance that feeds it..



baronbeehive said:


> (I had to do this anyway because I stupidly shorted out the amp when taking voltage readings with a shaky hand


If amp is not functional, You most likely caused the stock "power transistors" to blow.
Shorting "Should" not have damaged the diodes, but I would definitely upgrade them as a damaged transistor can definitely blow the diode..
Just swapping these out remove the necessity of headaches and prolonged testing .
Athough testing is supposed to be a necessary tool to learn the PSU.
I believe this thread had extensive posts on PSU problems, in past.



SonicTrance said:


> Higher feedback resistance is lower NFB and lower feedback resistance is higher NFB. Its logical when you think about it  If there’s lower resistance more of the signal gets fed back, hence higher NFB.


I believe he not fully grasp because
You forgot to mention the volume into how the unit behave for complete picture to understand.
The louder setting is less feedback, so more resistance to achieve that setting.



klnglim said:


> May I know how many watts recommendation for the resistor to put there?


Quarter watt, just like mentioned and what you removed.



MrCurwen said:


> In both cases you'll be more than fine with 0.25W resistors. However I recommend simply using 1W no-name carbon film resistors for all spots that dissipate under 0.75 W. That covers usually 95% of resistors inside any circuit. Why mess with different types


That is an excellent idea,
_*In general,
*_
But *NOT* for this board, as the resistors are spaced too close together, and *no way*  are they going to fit.

Not only that, but the leads from the resistors  won't fit into the tiny holes...

Plus, the reccomended resisitors to place here are film resistors.
Preferably dale.

I will never ever recommend carbon resisitors because when you look at the data sheets, they have highest noise of all type resisitors.

You will NEVER see carbon resisitors used in volume comtrols.
They will always use best.

Depending on application you may never notice,
But even in high power applications, the best is wirewound.
The question is would it matter, and probably wouldn't in many instances.

In this amp that is confined with heat I would not recommend.
Also remember these old school designs are admittedly very dependant on components selection and quality in certain areas.

In most other amps I would not disagree with your choice, in high watt or PSU areas.




klnglim said:


> As I am lack of electronic experience especially calculation,further more there are too many choices of resistor to replace and confuse about which is the best. Anyway, thanks for the answer


Use quarter watt high quality resisitors here.
Larger will not fit in the hole.



baronbeehive said:


> I'm still struggling with schematics





You may have different values, but same circuit trace.



klnglim said:


> Be aware & better double check all those red WIMA caps !!!


Unfortunately you pulled all those out, and I not sure if they re-usable,
Buy there "purpose" was not critical, if you implememted the cap mods.

They are parasitic caps to keep circuit clean and "may" have helped with transients as they buffered the PSU.
They are not expensive so its ok.
Its just that you are changing way more than necessary,
And you may not notice much.

Also, I would encourage you to change the (switch area) resistors values a bit...
On the MK8, it is agreed that it sounds better on high gain,
Which is less feedback thru the higher resistor.
I would encourage you to try slightly higher resistance if you like.
You would get more gain as well.

On the MK6, high gain setting is so high, that it is reported to not sound as good, probably from too high resisitor, introducing distortion from to low feedback.

Yet, I am _*assuming*_ that could be remedied by a larger grid resistor at the powertubes.
Then you could implement less feedback.
Correct me if I am wrong (MrCurwen & Sonic & Coin).
I am guessing that the power tubes may end sound with a bit more harmonics (more euphoric, thicker), but the bias mods may also alter that.

Anyways, maybe I should try myself hopefully will have time this month.


----------



## SonicTrance (May 11, 2018)

Maxx134 said:


> You will NEVER see carbon resisitors used in volume comtrols.


Hificollective sells stepped attenuators with Takman carbon films. They're 2% though compared to 5% you normally see in carbon films. I use metal film 1% in my stepped attenuator but the rest of my amp (modern LTP) is full of carbon films and don't generate noise. I have some small noise that can only be heard with my sensitive LCD-XC's. Amp is completely quiet with LCD-3 and speakers. It's some kind of ground problem. Will try matching input transformers next, actually have all the parts but I've been busy and amp sounds great as it is so. I'm rambling 



Maxx134 said:


> Yet, I am _*assuming*_ that could be remedied by a larger grid resistor at the powertubes.


Not really, a larger grid resistor will not lower the gain but potentially hurt transient response if too large. Remember the WCF output stage already has negative gain. I think the stock 300R is about right.

Anyway, great to see you posting again Maxx!


----------



## klnglim (May 11, 2018)

Maxx134 said:


> Wow alot passed me by I was away.
> I will try to help.
> 
> 
> ...


I decide replace all those red WIMA caps with Mundolf caps, but still not sure which model  is the best fit?
I see board show 2k, 68k, 100k, 470k near the switch, any recommendation resistor value for that area? I also decide to replace them with Dale


----------



## Maxx134 (May 11, 2018)

SonicTrance said:


> the rest of my amp (modern LTP) is full of carbon films and don't generate noise


Yes I agree your amp is an excellent example of design choices to offset need better or expensive parts.



SonicTrance said:


> Not really, a larger grid resistor will not lower the gain but potentially hurt transient response if too large. Remember the WCF output stage already has negative gain. I think the stock 300R is about right.
> 
> Anyway, great to see you posting again Maxx!


Dam, do you know what this means?.....

I may have to give up my higher gain tubes for the lower "mu" versions...

I was using 6SL7 high gain equivalent in the 6C8G.
The good thing is that there are more of the 6sn7 gain type.
I will swap a 6F8G type there, as I like the bottle shape and they are similar performance.
You liked that high "MU" mullard type,
 and I bet you could switch amp to high gain with normal "MU" tube.

There is no reason why your loaded MK6 cannot reach sonic clarity of your new amp.
Although I do not know how "colored" it is, the realism should still be high.
I doubt the mk6 as colored as a 300b amp.
Probably a bit more than a 2a3 amp.



klnglim said:


> I decide replace all those red WIMA caps with Mundolf caps, but still not sure which is the best fit?


The best fit would be same style WIMA, and high pulse type.
Look in data sheets for best "pulse" capacitor.
They will look exactly the same.
I have seen blue caps in other designs which may be even higher voltages, but I don't know as I haven't researched it.



klnglim said:


> I see board show 2k, 68k, 100k, 470k near the switch, any recommendation resistor value for that area


For optimal feedback resisitor, that may depend on tube selection.

Yet,
One thing already noted is that the MK8 sounds good on "high gain"  selection, which, at 100k, is similar to the MK6 preferred "low gain" select of (80k)..

Let's look at the resulting resistance when switch closed:
  Paralleled:
 Mk6 390k & 80k = 68k
 Mk8 100k & 68k = 40.5k

So the two Settings of the switch Results are:
  Mk6 = 390k & 68k
  Mk8 = 100k & 40.5k

I Notice my preferred setting of higher gain (less feedback) is very close to Sonic preference of low gain (more feedback) .
They are at similar setting, wish we both prefferred over other setting.

So I would try Having 100k for both,
As the default(combined resisitors) lowest point,
instead of the lower values of 40k & 68k,  which result in way higher NFB...

Then you notice 390k is a point debatable as being prefferred in the mk6 as a choice.
That value is up in the air, and may be too high.

So up to you what to use, but what looks to be the same for both amps,
Is to get a combined low of around 100k.
That would be a good start point as the most NFB to use.

Also, for the other (high) setting,
A useful compromise of 300k (not as high on MK6) should be a good starting point to try.

So For both MK6 & MK8,
I would actually use same resisitors to try first.

Try 300k for the higher spot(close to switch), and 150k for the lower spot.

For MK8, the high gain setting may sound higher, but is unknown how clear it would get as these are different tubes.
 I feel this is a good start point to try,
Because actuall stock values are set higher in MK6 and debated as too much.

Overall, changing resisitors to try these values will still get you the desired less feedback for both amps.

Any suggestions welcome here.
The future would be to try to eliminate the NFB more,
 but that may require more changes in tube selection & tube settings.
So a whole new set of Problems, lol.

I have not even been able to get my CCS installed yet, and I would still have to "dial in" the sweet spot setting I have now.

Hope all that long post helps.
I hope to start working on projects again this month.


----------



## klnglim

Maxx134 said:


> Yes I agree your amp is an excellent example of design choices to offset need better or expensive parts.
> 
> 
> Dam, do you know what this means?.....
> ...




From the picture below, can i replace those red colour circle resistors with 150R/5W instead of 120R/5W & replace those yellow colour circle resistors with 2K2/5W wirewound instead of 3K3/2W?


----------



## Maxx134 (May 11, 2018)

Yes it's not critical.
Going up to 150 from 120 means an easier surge current for caps when turn on.


The 3k3 was lowered to 2k2 for less volt drop and more voltage to circuit.
I am unsure if these are the resisitors the same
we talked about earlier in thread ,
That both me and sonic lowered it to 1k (!)
Ask Sonic or Barron as I been away too long.


----------



## klnglim (May 11, 2018)

Maxx134 said:


> Yes it's not critical.
> Going up to 150 from 120 means an easier surge current for caps when turn on.
> 
> 
> ...



I have just upgraded those Diode:
Green circle 1N4001 replace with 1N4007
Yellow circle 5.1V replace with 5.1/5W
Blue circle 15V replace with 15V/5W
Red circle 36V replace with 36V/5W
1N4148 next to Yellow circle replace with 1N4007
Those 2 Diodes near transistors 100V/1W replace with 100V/5W


----------



## MrCurwen

klnglim said:


> What I have seen from MK8SE layout , all those 15 pieces of red WIMA caps should be model: WKP10 0.22uF/250V, however they put 11 pieces MKP10 0.22uF/250V; 3 pieces MKP10 0.22uF/160V & 1 MKP4 0.1/630V.
> I guess may be they out of stock some caps so just find other look similiar garbage put into the PCB. Although the design of this amp is very great but the job they've done and most of component include PCB board out from Little Dot company is rubbish!



What's the issue here? They're all the same capacitance, and even the same type.



Maxx134 said:


> That is an excellent idea,
> _*In general,
> *_
> But *NOT* for this board, as the resistors are spaced too close together, and *no way* are they going to fit.



Oh alright. Well, luckily 0.25W is more than plenty. 

PCBs, what a pain. Always go P2P.



Maxx134 said:


> I will never ever recommend carbon resisitors because when you look at the data sheets, they have highest noise of all type resisitors.



You are probably thinking about carbon composition, which is the retro type resistor that has high noise and drift. I am talking about carbon film, which is modern type and has no mentionable noise and no drift. Completely different types.



Maxx134 said:


> On the MK6, high gain setting is so high, that it is reported to not sound as good, probably from too high resisitor, introducing distortion from to low feedback.
> 
> Yet, I am _*assuming*_ that could be remedied by a larger grid resistor at the powertubes.
> Then you could implement less feedback.
> ...



I am asking in all honesty, please explain your reasoning as to why this would be the case. Understanding your preconceptions would help a lot as to how to approach explaining things.

I am especially referring to the role of the power tube grid resistor here.



Maxx134 said:


> Dam, do you know what this means?.....
> 
> I may have to give up my higher gain tubes for the lower "mu" versions...



Why?



Maxx134 said:


> There is no reason why your loaded MK6 cannot reach sonic clarity of your new amp.



There's plenty of reasons it cannot reach the THD, the transient response or the output impedance of that amp. What this means in terms of 'clarity' is up to debate. My own view is that all of these things (low THD without gNFB, first class transient response, very low output impedance) constitute 'clarity'.



Maxx134 said:


> I doubt the mk6 as colored as a 300b amp.
> Probably a bit more than a 2a3 amp.



SE, balanced, gNFB / open loop...? AC filaments or regulated filaments?



Maxx134 said:


> One thing already noted is that the MK8 sounds good on "high gain" selection, which, at 100k, is similar to the MK6 preferred "low gain" select of (80k)..



Knowing one resistor in the NFB loop doesn't mean anything if you don't know the other one. They form a voltage divider. One resistor is in series and one is in parallel, forming a voltage divider. Unless one of these resistors is the same value in both cases, they cannot be directly compared like this.



Maxx134 said:


> Overall, changing resisitors to try these values will still get you the desired less feedback for both amps.



I am not sure less gNFB is necessarily desireable in this amp. Lower NFB means higher output impedance, meaning less control over the load. This would bring out the differences of headphones by exaggerating their flaws.


----------



## klnglim

MrCurwen said:


> What's the issue here? They're all the same capacitance, and even the same type.
> 
> 
> 
> ...


Among within those 15 pieces of red WIMA caps, 1 of them is different model (MKP4 instead of MKP10) & another 3 pieces are different power rate 160V (should be at least 250V)


----------



## baronbeehive

Maxx134 said:


> Try 300k for the higher spot(close to switch), and 150k for the lower spot.
> .....
> Overall, changing resisitors to try these values will still get you the desired less feedback for both amps.
> 
> ...



Hi Maxx!

My listening testing has been delayed due to PSU upgrades to put right the short I had during measurements, and other problems with the ammeters and gain switch. I've also had a broken leg of one of the Jupiter caps with all the messing around inside so when this phase is finished I don't expect to do anything more....probably!

However I have got one result and that is that the high gain setting sounds very good to me, I did not hear any deficiencies in sound and have therefore decided to keep it on high gain from now on so I don't necessarily agree that the MKVl feedback values mean having to use low gain. I will only change back now if I have tubes or headphones which sound bad with high gain.

My 390K resistor is in fact 330K and I've been looking into removing the switch completely to keep the high gain setting with the help of Sonic and MrCurwen.

I wonder if bloodhawk could try high gain with his tube/headphones and see what he thinks



Maxx134 said:


> I have not even been able to get my CCS installed yet, and I would still have to "dial in" the sweet spot setting I have now.



Neither have, I was hoping to have it done by now but I've said why I've been delayed.




klnglim said:


> From the picture below, can i replace those red colour circle resistors with 150R/5W instead of 120R/5W & replace those yellow colour circle resistors with 2K2/5W wirewound instead of 3K3/2W?



Yes, replace the yellow colour resistors with 2K2, or less, Maxx, Sonic and myself have all gone to around 1K for more voltage and without issues so far.


----------



## Maxx134

MrCurwen said:


> What's the issue here? They're all the same capacitance, and even the same type.





klnglim said:


> of them is different model (MKP4 instead of MKP10) & another 3 pieces are different power rate 160V (should be at least 250V)


This is the difference... The be "MKP" designation, which is the ability for pulse voltages, and that translates for us to have better transients delivery in the PSU.
Even when same spec type (MKP), the higher voltage unit is better.
This is usefull for designs that are reliant on the parts performance.




MrCurwen said:


> PCBs, what a pain. Always go P2P.


That is a goal I want to do in a future amp I still hope to do.



MrCurwen said:


> I am talking about carbon film, which is modern type and has no mentionable noise and no drift. Completely different types.


Excellent info to know.



MrCurwen said:


> I am especially referring to the role of the power tube grid resistor here.


Yes that was a brain-fart in my rusty thinking. The grid resistor was error to think of.



MrCurwen said:


> Why?


For the usage if the amp  in a higher gain setting (of lower NFB), I would complimet with use of a tube with less gain (MU), so wont distort the driver stage.
In other words, I am compensating and adjusting one thing for another.
I know my amp sounds better with less NFB.
 I rolled many many 12pin and 6pin in both high and low settings, to get my "fav" tube choice.
It turned outmy FAv tube is an 6C8G in higher gain(less NFB),
and I do not know how much less NFB will sound good,  untill I try.




MrCurwen said:


> There's plenty of reasons it cannot reach the THD, the transient response or the output impedance of that amp. What this means in terms of 'clarity' is up to debate. My own view is that all of these things (low THD without gNFB, first class transient response, very low output impedance) constitute 'clarity'.


I agree it is not a clear cut simple thing.
For instance, I have heard some tube amps sounding:
 "euphoric", 
"colored", 
"dirty", 
"clean",
 "lifeless"....
Yet all had high resolve and realism...




MrCurwen said:


> SE, balanced, gNFB / open loop...? AC filaments or regulated filaments?


Getting into specifics do not discount the generality of a 300b tube amp still having more harmonics over a 2a3 tube amp ,
because they are all still using old-school traditional designs, unlike your unique modern approach.
That does put a spotlight, on the fact that there are rarely any new design approaches to tube amp design.
This is a sad reality.
Your design is so far the only new or different approach I have seen.

Although the implementation of new parts, like CCS, Gyro, and now switching PSU are new tech, 
but  they are still being implemented, into what is essentially still all old-school designs(in amps). 



MrCurwen said:


> they cannot be directly compared like this.


Yes they can as the MK6&8 have same driver tube circiut and I already noted the resistances.
Also I took note already the added paralelled resistor only added when switched in for more fedback.
I figured that the existing amounts were way tooo low a resistance, as the higher gains all sounded better.



MrCurwen said:


> I am not sure less gNFB is necessarily desireable in this amp. Lower NFB means higher output impedance, meaning less control over the load. This would bring out the differences of headphones by exaggerating their flaws.


I do agree that this would increase amp output impedance, but unknown for now how much and to what extent.
The WCF output stage basically is in charge of lowering impedance, so how it handles lower NFB is to find out. 



baronbeehive said:


> so I don't necessarily agree that the MKVl feedback values mean having to use low gain. I will only change back now if I have tubes or headphones which sound bad with high gain.
> 
> My 390K resistor is in fact 330K and I've been looking into removing the switch completely to keep the high gain setting with the help of Sonic and MrCurwen.


This is good to know, as that means we can try higher values for the resistors (less NFB).
I would assume that *one* of the sonic changes of less NFB is a more tube harmonics,or thicker sound, so I would be on the lookout for this effect.
Also the amp output impedance as MrCurwin stated.



baronbeehive said:


> Yes, replace the yellow colour resistors with 2K2, or less, Maxx, Sonic and myself have all gone to around 1K for more voltage and without issues so far.


Ok, so have you verified this is the resistor location right?
I would definitely reccommend going to 1k...


----------



## baronbeehive (May 12, 2018)

Maxx134 said:


> If you look carefully, you will realize that switching "on",
> will place an added resistor in parallel.
> An added paralleled resisitor will drop the  total resistance.



Ah, yes now I see the parallel connection, of course!




Maxx134 said:


> On the MK6, high gain setting is so high, that it is reported to not sound as good, probably from too high resisitor, introducing distortion from to low feedback.



I didn't hear any distortion at all on high gain.



Maxx134 said:


> Yes I agree your amp is an excellent example of design choices to offset need better or expensive parts.
> 
> There is no reason why your loaded MK6 cannot reach sonic clarity of your new amp.
> Although I do not know how "colored" it is, the realism should still be high.



This is interesting, the amp manages to sound very clear yet at the same time has a wonderful euphonic type sound, that has been mentioned before on this thread. I don't think this euphonic, or euphoric sound is distortion, or feedback going by what has been said about this previously on this subject so I can't account for how the amp manages to sound so good frankly.


----------



## baronbeehive

Maxx134 said:


> I do agree that this would increase amp output impedance, but unknown for now how much and to what extent.
> The WCF output stage basically is in charge of lowering impedance, so how it handles lower NFB is to find out.
> 
> This is good to know, as that means we can try higher values for the resistors (less NFB).
> ...



To be determined experimentally perhaps!

I took notes as I went along when I started the listening tests and I have written down for high gain, "defined", "resolved", "taut", "real", "transparent", etc.



Maxx134 said:


> Ok, so have you verified this is the resistor location right?
> I would definitely reccommend going to 1k...



Yes, same location as in the MKVI.


----------



## klnglim

baronbeehive said:


> Hi Maxx!
> 
> My listening testing has been delayed due to PSU upgrades to put right the short I had during measurements, and other problems with the ammeters and gain switch. I've also had a broken leg of one of the Jupiter caps with all the messing around inside so when this phase is finished I don't expect to do anything more....probably!
> 
> ...


Do u know where to buy those 2 transformers? I have been search everywhere but can find any similiar


----------



## klnglim

baronbeehive said:


> Ah, yes now I see the parallel connection, of course!
> 
> 
> 
> ...


As I have spare 150R/5W & 2K2R/5W good quality wirewound resister, at least replace those garbage first. 
I've just finished replace those resistors and also upgraded those small tiny Diodes


----------



## Maxx134

klnglim said:


> Do u know where to buy those 2 transformers? I have been search everywhere but can find any similiar


The two PSU Transformers are custom made.
They must be ordered direct from Little Dot.

Otherwise you may have one Custom made by a "third party" at probably double the price.
Or you can buy a general Transformer which will not have all the "secondary windings" needed.

Best approach is to just buy from the company which is what I did and it may be a slow process.
I believe the price was around $80 US dollars for me, but don't quote me as it most probably not same price.

To me the transformer seems ok except for the secondary made for the driver stage heater.
Thats the thinnest and the wire that burnt on me once, because I put in an adapter socket that went bad while I fell asleep lol.


----------



## klnglim (May 13, 2018)

[QUUnOTE="Maxx134, post: 14236772, member: 161988"]The two PSU Transformers are custom made.
They must be ordered direct from Little Dot.

Otherwise you may have one Custom made by a "third party" at probably double the price.
Or you can buy a general Transformer which will not have all the "secondary windings" needed.

Best approach is to just buy from the company which is what I did and it may be a slow process.
I believe the price was around $80 US dollars for me, but don't quote me as it most probably not same price.

To me the transformer seems ok except for the secondary made for the driver stage heater.
Thats the thinnest and the wire that burnt on me once, because I put in an adapter socket that went bad while I fell asleep lol.[/QUOTE]
As I have too many spare parts left behind, so I decide try build another diy p2p MK8SE 
Unfortunately, can't get suitable transformer


----------



## Maxx134

klnglim said:


> As I have spare 150R/5W & 2K2R/5W good quality wirewound resister, at least replace those garbage first.
> I've just finished replace those resistors and also upgraded those small tiny Diodes


You have to think "3D".
You should have those 150 ohm resisitors on the other side of the board as originals were, for easier heat dissapation.

Also, the 2k2 wirewound do not look like the "non-inductive" type.
That is ok as it is in PSU position as part of the RCRC filter stage, and any small inductance there (in series with PSU) can be viewed as a "choke".

Yet the plate resistors for the powertube stage, should have the newer "Mills MR5" which are noticably smaller for the same wattage and are non-inductive...


----------



## klnglim (May 13, 2018)

Maxx134 said:


> You have to think "3D".
> You should have those 150 ohm resisitors on the other side of the board as originals were, for easier heat dissapation.
> 
> Also, the 2k2 wirewound do not look like the "non-inductive" type.
> ...


Yes I do have MR5 resistor, will solder in later, those 2k2 wirewound actually is anti surge resistor, Flame resistant coating, I thought might be better for PSU. When I took off the whole PCB board out from the case, found out one of the caps not worked (May be cause of internal error's  shortage by a sparking lighting) and those caps are average level Panasonic brand, I decide surround that PSU area will place all brand new top range NIchicon caps when after  all the resistor being finish install. I still wait for Dale resistor arrive within next few days. By the way, other than PCB board, 90% of all the circuit chip or component are brand new replacement LOL


----------



## Maxx134 (May 16, 2018)

baronbeehive said:


> I didn't hear any distortion at all on high gain.


This is quite excellent news... for future refinement.




klnglim said:


> By the way, other than PCB board, 90% of all the circuit chip or component are brand new replacement LOL


I do realise that was your descision to make your amp as a "start over" kit,
But I do not agree to have replaced so much.
Most of improvements can be done without too much trouble.
There will be a greater room for error and troubleshooting, in your replacement,
but also greater reward as I myself have done similar, but haven't gone that far...
I did re-solder the whole board with best Cardas solder, and made a mistake in soldering two pins together...
So be careful, patience is the key.

Also, while your at it,
Since you DO have the MK8, I must reccomend higher value cathode caps than I initially am using.
They are not sufficient for using planars at higher volumes, as the bias meters dip.

So,_ If your littledot MK6 or MK8 amp bias meters budge at all at high volumes,_ 
then that is a situation where the cathode cap _should be upgraded with higher value._

It was initially set for low end frequency range cuttoff, but that was not taking into account this different parameter ..
We need the Cathode cap to hold the cathode voltage constant, in relation to the "current" demands in the tube.
So the tube can retain it's optimal gain.

That being said,* I am going change my cathode caps (mundorf), to "Audio Note Kaisei" caps at 1000uf capacity...*
This is about twice the maximum capacitance initially recomended ( From 220µF up to 470µF which would set the cut-off frequency from 5Hz to 2,5Hz).
So remember the reason in this scenario is not the cut-off freq, but instead the stability of the cathode voltage in high current demands, such as sustained bass notes from planar load.
This change probably not needed unless you have hungry planar headphones lol.

The second paralleled " bypass cap" will remain the same and will be more needed than before,
 as the "Kaisei" caps are supposed  to be similar to its predecessor, the "blackgate" caps .
 Remember we need a second Bypass cap for practically all large size electrolytics,
as treble and microdynamics are the weak points of electrolytics.

...


----------



## Maxx134

Actually there are more stable solutions like CCS applicattion.
i just going with simplicity here.
The 1000uf cathode cap value increase has already been tested on a different smaller amp.


----------



## klnglim (May 17, 2018)

Maxx134 said:


> This is quite excellent news... for future refinement.
> 
> 
> 
> ...


I do agree with your opinion, so now I replace some resistors, upgrade some Diodes with higher power rating, replace those faulty caps with better Nichicon caps & also replace same brand new relay. I also found all the replacement parts for this amp except transformer and there are not expensive, anytime can build another prototype MK8SE 
I owned many headphones like Sony Z7, Senn HD800s, LCD-X, Fortex TH-X00, Fidelio X2....etc, some are moded but not hungry planar, so I stick with same value capacitance caps.
The purpose to mod this amp is try to get excellent match with HD800s if possible, because isn't easy to get lower bass from HD800s although it's the best sound stage I have ever heard


----------



## Maxx134 (May 17, 2018)

klnglim said:


> The purpose to mod this amp is try to get excellent match with HD800s if possible, because isn't easy to get lower bass from HD800s although it's the best sound stage I have ever heard


The mk8 is one of the few amps that are tailored exactly for the HD800 impedance.
They make  the HD800 sound more alive and luscious,  different from normal low impedance amps.
I do remember the WCF caps sounded great with mundorf in upper range and soundstage,
but I had changed those to some "vitamin Q" caps,
 which I feel are adding a bit of richness to sound.
I need to clean it up a bit in the low end, so those will go, in place of some jupiters.

I have been listening to other TOTL-end game amps, like the Cayin HA-300 and a few others.
They have top-notch sound and I feel my mk8 is a bit loose in bass area, in comparison.
The Mk6 should do bettter in that regard since it has more power.


----------



## klnglim

Maxx134 said:


> The mk8 is one of the few amps that are tailored exactly for the HD800 impedance.
> They make  the HD800 sound more alive and luscious,  different from normal low impedance amps.
> I do remember the WCF caps sounded great with mundorf in upper range and soundstage,
> but I had changed those to some "vitamin Q" caps,
> ...


Earlier before the amp short spark happen, I coupling those Russian Caps n decoupling Mundolf caps, mixing 4x EH power tube, 2x gold lion driver tube
Only listen with HD800s, heard very nice treble, the best female vocal, sound stage absolute clear details, smooth light bass but still lack of low end and punch.
I guess those original coupling french mkp caps provide better bass but darker background


----------



## klnglim

I just found out those 2 groups resistors actually connect togather in parralel


----------



## Maxx134

klnglim said:


> but still lack of low end and punch.


That is what cap value upgrade is for.



klnglim said:


> I just found out those 2 groups resistors actually connect together in parralel



My simplified schematic of the PSU did not go that far to show that section.
 
I believe that section is for power to the opamp circuit.
I would check with Coinmaster diagrams:
testing a paralled connection not change importance of different values as they are most likely branching out to different circuit areas of board.
Its still good that you noticed as you become more familiar with the circuits.


----------



## baronbeehive (May 20, 2018)

Maxx134 said:


> Actually there are more stable solutions like CCS applicattion.
> i just going with simplicity here.
> The 1000uf cathode cap value increase has already been tested on a different smaller amp.



Yes, the Kaisei's work wonders in that amp, it's just sensational to me and I have no further need to change it in any way. I appreciate that other mods would be an interesting way to go with this amp, perhaps as a basis for a future build though.



Maxx134 said:


> I have been listening to other TOTL-end game amps, like the Cayin HA-300 and a few others.
> They have top-notch sound and I feel my mk8 is a bit loose in bass area, in comparison.
> The Mk6 should do bettter in that regard since it has more power.



I found that the MKVI has plenty of bass heft at least for me, the problem is the looseness as you say, that's why I recommend having sharp sounding driver tubes which all but solve the problem. After the CCS mod I don't see if anything else can be done about this. I know that Coinmaster swears by his massive industrial film caps but that's not practical for me in the stock chassis. I think he also said it provided huge bass for his HD800's. We can't ask his because he doesn't seem to be around atm.

My only other area of interest is the frequency band around the sybillant sounds of vocals and cymbals and so on. This area needs a boost to make the sound more alive. The sound atm is very smooth and deep and rich but I just feel it is slightly too smooth with not quite enough attack. I think I might have made a mistake with the OCC copper output wires to eliminate sybillance completely so I'm going to replace these with OCC silver which might be just the job for that particular problem to give it that bit more edge, which the other amp has got.

I don't know what you think with your comparisons with other amps?

I will be able to resume the listening tests when I get the amp upgrades finished, the anode/cathode settings will be comparing the Sonic settings, your settings and an intermediate setting.

An interesting aspect of the high gain setting is that it made the TS 6SL7's sound sharper and clearer and less smooth, but I felt that that was an improvement.

Edit: Ha, I see the Cayin has selective impedance matching LOL! It looks to be well received, "Enjoy The Music" like it. I remember reading a review of the Cayin A50-t a while ago and slobbering over it, it looked great at $1295.


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## Maxx134 (May 21, 2018)

baronbeehive said:


> I'm going to replace these with OCC silver which might be just the job for that particular problem to give it that bit more edge, which the other amp has got



Up to you...
Silver may make some benifits,
But the main problem of stock amp wiring,
 was the thin guage output wire from board to sockets.

There are many more informed members over at other DIY forums,
But I haven't seen any give info about how circuit choices affect sonics yet.

So, I will tell from my experience::

*** Tube and bias selection help with clarity, dynamics, and soundStage..

***Coupling cap deal with overall signature and tonality plus soundStage.

***Cathode cap electrolytic  boosts ouput, strengths bass when increased, and also can affect upper range signature detrimentally so need a bypass cap to help.

***WCF caps will make a  slight difference in tonal balance, by adding harmonics and limiting soundstage , which is why I will be looking for some brighter and better caps there.

For example, The Mundorf I had at WCF position, made the amp sweeter with a slight larger stage over my "Vitamin Q" caps which gave a more dynamic livelier sound with smoother top and less sparkle.

So, unfortunately, any amp that uses caps will have to deal with and are limited by them.
Yet the "realism" level on this amp, I found is has more to do with tube selection and bias points.

I believe the driver stage in stock form is holding the amp back.
IMHO it needs the bias increase.

Hopefully we will find out just how much NFB we can reduce without adverse affecting sound.

My guess is that the driver tube choice will make the difference here.

Hopefully will start testing soon.


----------



## Maxx134 (May 21, 2018)

baronbeehive said:


> I don't know what you think with your comparisons with other amps?




(Correction) "Some" of the best tube  amps I heard.
They had a bit more soundstage over mine.
They had a more controlled bass over mine.
They had more power as I have an MK8.
As far as realism, I could not make a call as mine falls at same level, and they all vary in harmonic signature (euphony).

This is why I believe the MK6 moded can achieve a top status potential.

If it not as "resolving" , and bias points were already adjusted, then I would say the caps are holding it back.


----------



## klnglim

Maxx134 said:


> That is what cap value upgrade is for.
> 
> 
> 
> ...


This amp so far what I have noticed is build into 2 section, there are PSU B+ B- stage and tube driver sound stage. 
It's not very difficult to build DIY prototype, the parts are quite cheap and easy to get replacement and upgrade 
The amp is amazing design, I have learned a lot after get into deeper, look inside all of it and not much $$$ spending overall total but spend a lot of time to study or to understand
Most important is thanks to this forum's members for their sharing, knowledge and support, really help a lot and wonderful experience


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## baronbeehive (May 21, 2018)

Maxx134 said:


> Up to you...
> Silver may make some benifits,
> But the main problem of stock amp wiring,
> was the thin guage output wire from board to sockets.
> ...



Yes, its a long shot but for the specific thing I mention about those sybillant frequencies it just might help bringing the qualities of OCC silver wiring. As you know I rave about the other amp and it is in comparisons with it that I picked up this about the LD, which in other respects is top class.



Maxx134 said:


> So, I will tell from my experience::
> 
> *** Tube and bias selection help with clarity, dynamics, and soundStage..
> 
> ...



I agree with you about all of this from my experience of modding both amps. I have the S/O Mundorf caps in WCF position so I think I have the best choice there for what I want.



Maxx134 said:


> (Correction) "Some" of the best tube  amps I heard.
> They had a bit more soundstage over mine.
> They had a more controlled bass over mine.
> They had more power as I have an MK8.
> ...



That's interesting, that is pretty much what I would expect from what I can imagine not having heard these top class amps. I'm not sure of the SS aspects of the circuitry in the APPJ but the bass is very controlled in that amp and the newer driver tubes really make it special, both the Philips and the Mazda are tight in bass, in comparison with the Tungsol for example, which is still pretty damn good. Don't know what you think about this with your APPJ.


----------



## baronbeehive

klnglim said:


> This amp so far what I have noticed is build into 2 section, there are PSU B+ B- stage and tube driver sound stage.
> It's not very difficult to build DIY prototype, the parts are quite cheap and easy to get replacement and upgrade
> The amp is amazing design, I have learned a lot after get into deeper, look inside all of it and not much $$$ spending overall total but spend a lot of time to study or to understand
> Most important is thanks to this forum's members for their sharing, knowledge and support, really help a lot and wonderful experience



You will soon be designing and building your own custom amps LOL!


----------



## Maxx134

baronbeehive said:


> . I have the S/O Mundorf caps in WCF position so I think I have the best choice there for what I want


Actually, the bypass cap of the cathode cap would change top end tonality for you.


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## klnglim (May 22, 2018)

Maxx134 said:


> Actually, the bypass cap of the cathode cap would change top end tonality for you.


Just want to know if I use Mundolf Evo Oil in coupling, and decoupling, Mundolf Evo in WCF, are there suitable? The idea use all Evo is because of the caps are a lot cheaper and size fit perfectly inside the amp


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## Maxx134 (May 22, 2018)

klnglim said:


> Just want to know if I use Mundolf Evo Oil in coupling, and decoupling, Mundolf Evo in WCF, are there suitable? The idea use all Evo is because of the caps are a lot cheaper and size fit perfectly inside the amp


They are very good.

They are all above average nice caps:


Good choice.
Coupling & WCF is more noticable than Decoupling..


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## klnglim (May 23, 2018)

Maxx134 said:


> They are very good.
> 
> They are all above average nice caps:
> 
> ...


yes, those are the caps size fit perfectly and price a lot cheaper, That's why I asked before order


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## baronbeehive (May 23, 2018)

Maxx134 said:


> Actually, the bypass cap of the cathode cap would change top end tonality for you.



Funnily enough I was only thinking about that yesterday, as I have the Audyn True Copper in the other amp, same as you. I didn't think the tone difference in the 2 amps was because of the Jupiter caps because I have the same in both amps. Also when I put the Audyn bypass caps in after a while without them the sound difference in the treble was massive. Don't know if they would fit though.

I might change the cathode caps to Kaisei as well if you note any differences, I have 2 spare.

Listening to the other amp yesterday, the guitar sound really rings out wonderfully, especially the treble register, but it is in no way sybillant. And there is a real edge to the transients which you can almost feel.


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## Maxx134 (May 23, 2018)

baronbeehive said:


> I didn't think the tone difference in the 2 amps was because of the Jupiter caps


That's because coupling cap position not supposed to affect FR.

The Cathode caps, on the other hand,
  does affect tonality.

Just place another smaller cap in area, like a .01uf-.02uf so it is a decimal point over from your existing .1uf Rifa that we chose in beginning to bypass.

I don't want to affect the natural presentation that cap gives, only to give more top end air.

So I will be doing the same to get  more sparkle,
 because I want to expand soundStage detail cues, but naturally so I will a carfully  choosen cap.

So caps uograde, and NFB reduction will be my next challenge.

My MK8 currently has holography in spades, and only needs more tweaks to be comparable to what I have been hearing from top amps,
Which is soundstage presentation and cleaner lower end.

That being said, I still plan to try make another amp this summer.


----------



## baronbeehive

Maxx134 said:


> That's because coupling cap position not supposed to affect FR.
> 
> The Cathode caps, on the other hand,
> does affect tonality.
> ...



Right I will try that later. Should be interesting!



Maxx134 said:


> My MK8 currently has holography in spades, and only needs more tweaks to be comparable to what I have been hearing from top amps,
> Which is soundstage presentation and cleaner lower end.
> 
> That being said, I still plan to try make another amp this summer.



Yes, holography.... front to back, side to side, top to bottom is excellent in this amp, as soon as you put on those headphones to experience this you notice it..... and the spatial seperation.

Good luck with your build, summer is not the time for me to attempt something like that though LOL.


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## klnglim (May 24, 2018)

Maxx134 said:


> That's because coupling cap position not supposed to affect FR.
> 
> The Cathode caps, on the other hand,
> does affect tonality.
> ...


Good to know u have plan to build another amp, interest to learn from yours. My MK8 still waiting for the parts to arrive which order some resistors and Mundolf EVO caps n EVO oil caps.
2 days ago, I have heard my friend's newly bought IFI PRO ICAN HEADPHONE AMPLIFIER, that's the best amp I have ever  heard to drive HD800s, the background low end very clear punch, soundstage very clear details, I think U should have a try if have any chance


----------



## Maxx134

baronbeehive said:


> I know that Coinmaster swears by his massive industrial film caps but that's not practical for me in the stock chassis


That may be because the caps were keeping the cathode voltage stable, as well as also keeping the signature high quality.  



klnglim said:


> 2 days ago, I have heard my friend's newly bought IFI PRO ICAN HEADPHONE AMPLIFIER, that's the best amp I have ever heard to drive HD800s, the background low end very clear punch, soundstage very clear details, I think U should have a try if have any chance


I owned the IFI Micro BL that is basically same with a built in dac.
They are excellent amp but still do not provide the soundstage holography of a tube amp.
The MK8 is still better for the HD800.


----------



## klnglim

Maxx134 said:


> That may be because the caps were keeping the cathode voltage stable, as well as also keeping the signature high quality.
> 
> 
> I owned the IFI Micro BL that is basically same with a built in dac.
> ...


Actually this is totally different, it has 3 internal choices to run this amp, there are solid state, hybrid and individual tube.
I have heard IFI micro BL, it's ok for me but I felt it still too big and heavy as portable use


----------



## Maxx134

Yes I was confused on the model.
That unit is nice.


----------



## klnglim

Maxx134 said:


> Yes I was confused on the model.
> That unit is nice.


I just finished assembled all the circuit parts, unfortunately the amp won't turn on except only those six tubes light up, also can't take the DC voltage result as unstable reading.
Is that something wrong with transformer? I have repeated checked the connection many many times, no idea what's went wrong?


----------



## Maxx134

klnglim said:


> unfortunately the amp won't turn on except only those six tubes light up,


Check the electrolytic  capacitors by the AC input.

If you changed them for higher capacitance OR higger voltage, then it will take longer for cap to charge up to turn on.

Does one meter light up?


----------



## Maxx134

The tubes heater will light up regardless if amp work or not because its a direct feed from Transformers,
So don't worry about that.


----------



## klnglim (Jun 5, 2018)

Maxx134 said:


> Check the electrolytic  capacitors by the AC input.
> 
> If you changed them for higher capacitance OR higger voltage, then it will take longer for cap to charge up to turn on.
> 
> Does one meter light up?


So far Only tubes light up as normal, the amp and meter are not active at all. I m still figure out what's went wrong. Do You have schematic of mk8se?
Electrolytic caps is brand new Nichicon and all resistor are upgraded to Mills and Dales but capacitance, voltage and resistance still same as usual..
Coupling Caps are Mundolf EVO OIL 0.68uF/450 Volt and WCF are EVO OIL 0.22uF/450 Volt


----------



## Maxx134

So none of the meters light up?
The left should have turned on immediately.

You may have similar Problem as another here who had lost connection of PSU center ground to other side of board under area where the big caps and zener diodes are.

The power was at the first  big caps, but missing further down.

I most likely the PSU area your Problem.


----------



## klnglim

Maxx134 said:


> So none of the meters light up?
> The left should have turned on immediately.
> 
> You may have similar Problem as another here who had lost connection of PSU center ground to other side of board under area where the big caps and zener diodes are.
> ...


How to test the PSU? Do I need replace the new one?


----------



## Maxx134

If you are not skilled enough to test PSU, 
Read back about 10 pages where many here discussed and repaired the PSU.

If you still feel not up to it, 
Simply bring to your nearest repair shop to fix.
The rebuilt schematic of this amp (by Coinmaster)  is somewhere in this thread.

I will try look for it to post on first page.


----------



## Maxx134

klnglim said:


> Do I need replace the new one?


No, in most cases this is either a board trace open or a single component issue, like the power transistors or the wiring to the board is of, like the transformers.

If you disconnected the transformer, then you may have reversed one of the primary windings, so that they are in parallel instead of series.
I did that by mistake when swapping out a transformer..

So check that the transformer primary are in series, if you disconnected them from board.

Also, be careful to not get shock when testing. check the bridge rectifiers if you replaced them wrong way..

Check for power at the PSU.
Use the PSU schematic in beginning of thread as it shows the estimated proper voltages.


----------



## klnglim (Jun 6, 2018)

Maxx134 said:


> No, in most cases this is either a board trace open or a single component issue, like the power transistors or the wiring to the board is of, like the transformers.
> 
> If you disconnected the transformer, then you may have reversed one of the primary windings, so that they are in parallel instead of series.
> I did that by mistake when swapping out a transformer..
> ...


Yeah! I suspect PSU problem, will check later. I also found NPN transistor Collector short with ground, cant find out why?
I remember few months ago, this amp turn on after few minutes, there was suddenly striking light short clearly seen in front of me.
When open bottom case, found one of the resistor explode which cause around that PCB area damage, since then can't proper turn on till now. Do u know what cause amp strike lightning?
Begin I thought wire connection error so I change those garbage thin wire with better one, follow by  changed both transistors twice, then upgrade all to  similiar amount  readinhg new caps, resistors, diode and relay, Can be said 90% of the parts inside this amp are brand new.


----------



## Maxx134

The power transistors have tiny washers on the metal case which prevent the body to touch.
It may have broke if you ddn replace.
Or they may be fine as you can only find out by checking voltages .

Checking for short may not be correct if another conpocomp like the diodes are connected.
Plus caps charging.

So best way is to test unit upside down, for checking voltages with unit on & tubes installed.
Must be careful to not cause a short when testing.

If your components are installed correctly and not higher value electrolytics by the delay circuit , then it would be the board trace.

Only way to check it to use volt meter for proper voltages and see where the power stops.

Read back on the PSU issues.


----------



## klnglim (Jun 9, 2018)

Maxx134 said:


> The power transistors have tiny washers on the metal case which prevent the body to touch.
> It may have broke if you ddn replace.
> Or they may be fine as you can only find out by checking voltages .
> 
> ...


Transistors washers has been replaced brand new earlier, both have no problem after diodes reading checked several times.
 I just found out the transformer garbage wire ground connection broken, the original wire is very thin and just replaced thicker one.
I also have checked transformer wiring the Voltage and Ohm is normal except green color Ohm reading is 46.8R, too high?


----------



## Maxx134 (Jun 9, 2018)

I never checked the ohm of the transformer so I dunno.
I forgot what the green was for but you can check the schematic that SonicTrance posted.


----------



## klnglim

Maxx134 said:


> I never checked the ohm of the transformer so I dunno.
> I forgot what the green was for but you can check the schematic that SonicTrance posted.


Transformer at last fixed, amp meter light work normal however 0 reading and no sound LOL


----------



## Maxx134

klnglim said:


> Transformer at last fixed, amp meter light work normal however 0 reading and no sound LOL


Observe if you hear relay click when second meter turns on.

Will need to test volatges of PSU.


----------



## klnglim

Maxx134 said:


> Observe if you hear relay click when second meter turns on.
> 
> Will need to test volatges of PSU.


meter 2nd light turns on later as usual after 1st light on awhile, still 0 reading and no volume.
Where to test PSU voltage U meant?


----------



## SonicTrance

klnglim said:


> meter 2nd light turns on later as usual after 1st light on awhile, still 0 reading and no volume.
> Where to test PSU voltage U meant?


Measure B+ for output stage. Start by measuring at the bridge rectifier + pin, black probe to a ground point between the filter caps. 
Then work your way from there to the filter caps, transistors and last caps of the psu.


----------



## klnglim

SonicTrance said:


> Measure B+ for output stage. Start by measuring at the bridge rectifier + pin, black probe to a ground point between the filter caps.
> Then work your way from there to the filter caps, transistors and last caps of the psu.


Sorry , is it AC or DC voltage?


----------



## SonicTrance

klnglim said:


> Sorry , is it AC or DC voltage?


DC. The bridge rectifier turns AC to DC so there's only DC after the rectifier.


----------



## klnglim (Jun 11, 2018)

klnglim said:


> Sorry , is it AC or DC voltage?





SonicTrance said:


> DC. The bridge rectifier turns AC to DC so there's only DC after the rectifier.


I got the reading 110volt DC, from rectifier both side , the other rectifier is 10 vDC both side, not sure is correct or not?


----------



## SonicTrance (Jun 11, 2018)

klnglim said:


> I got the reading 110volt DC, from rectifier both side , the other rectifier is 10 vDC both side, not sure is correct or not?


What do you mean by 'both side'? You suppose to have your negative lead to ground when measuring DC. Please explain.

Also, what do you mean by other rectifier? Do you mean for the driver stage? Dont worry about driver stage for now. But no, 10V is not right.

You should have about 135 - 140VDC at + pin and -135 - -140VDC at - rectifier pin.


----------



## klnglim (Jun 11, 2018)

SonicTrance said:


> What do you mean by 'both side'? You suppose to have your negative lead to ground when measuring DC. Please explain.


There are 4 pin , positive pin read OL, negative pin cant get reading as voltage jump up n down , the other 2 pin 110VDC, thats what i get. I hope u can show me the picture which component voltage i suppose to measure, that would be easier I guess


----------



## klnglim

SonicTrance said:


> What do you mean by 'both side'? You suppose to have your negative lead to ground when measuring DC. Please explain.
> 
> Also, what do you mean by other rectifier? Do you mean for the driver stage? Dont worry about driver stage for now. But no, 10V is not right.
> 
> You should have about 135 - 140VDC at + pin and -135 - -140VDC at - rectifier pin.


I double check again , + pin 238VDC, - pin OVDC, the other 2 pin 110VDC, Thats mean something wrong with the rectifier or connection error?


----------



## SonicTrance

klnglim said:


> I double check again , + pin 238VDC, - pin OVDC, the other 2 pin 110VDC, Thats mean something wrong with the rectifier or connection error?


Cant show picture now as Im at work. Based on your measurements I think you're measuring the driver stage rectifier. In that case voltages are good there. 

Measure output stage rectifier. Its located by the relay and the big filter caps. It looks just like the driver stage rectifier. 

Only measure the + and - pins. The other pins are AC voltage input.


----------



## klnglim

SonicTrance said:


> Cant show picture now as Im at work. Based on your measurements I think you're measuring the driver stage rectifier. In that case voltages are good there.
> 
> Measure output stage rectifier. Its located by the relay and the big filter caps. It looks just like the driver stage rectifier.
> 
> Only measure the + and - pins. The other pins are AC voltage input.


The other +pin read 21.5VDC and -pin 0VDC, the other 2 pin both read 10.35VDC


----------



## SonicTrance

klnglim said:


> The other +pin read 21.5VDC and -pin 0VDC, the other 2 pin both read 10.35VDC


Is that before or after the second meter light up? You must wait for that and then measure.


----------



## klnglim (Jun 11, 2018)

SonicTrance said:


> Is that before or after the second meter light up? You must wait for that and then measure.


after all light up result, I know that suppose to be 135VDC, I will check the connection again make no error


----------



## SonicTrance

Be sure to have your negative probe at ground between the filter caps. There're two holes there. Just stick the probe in one of them.


----------



## Maxx134

klnglim said:


> Where to test PSU voltage U meant?


Measure at same points that were measured on the PSU picture posted first page.
Check for similar voltage. 
If you need help someone to show you it would be wise to get help from any electrical engineering student or electronics person.
Its ok to try yourself as long as you are carful.


----------



## klnglim (Jun 11, 2018)

Maxx134 said:


> Measure at same points that were measured on the PSU picture posted first page.
> Check for similar voltage.
> If you need help someone to show you it would be wise to get help from any electrical engineering student or electronics person.
> Its ok to try yourself as long as you are carful.


I have checked all the AC in wire n perfect match:
White 6.81 VAC (Tube 12AT7)
Grey 6.81 VAC (Tube 6H30P)
Green 172.8 VAC
Blue 116VAC X2 or 235VAC
Yellow 15.5VAC X2 or 30.9VAC
The PSU u mention should be blue 235VAC which connect to relay I guess?
I just received Teflon wire so going to upgrade some wire & double check all the connection, will measure DC volt later if still not working


----------



## Maxx134

klnglim said:


> I double check again , + pin 238VDC, - pin OVDC, the other 2 pin 110VDC, Thats mean something wrong with the rectifier or connection error?


The issue is that your not supposed to be touching the AC pins when have your tester setting on DC..

Same goes other way.
You really need some brush up on basics so I really suggest having someone to talk in person who is available to see the unit as it is way faster/easier that way..
Based on what you said, the voltages are off after the rectifier.
I keep telling you to read up on last member who has this issue in this thread to learn much on the PSU.
It can't be more than 10 pages back.


----------



## klnglim (Jun 13, 2018)

Maxx134 said:


> The issue is that your not supposed to be touching the AC pins when have your tester setting on DC..
> 
> Same goes other way.
> You really need some brush up on basics so I really suggest having someone to talk in person who is available to see the unit as it is way faster/easier that way..
> ...


Yes , I have read that many times already. I have checked all the connection for every component, non issue include rectifier, so I decide keep going to try another method
, hard wire most of the component part of this amp, as I know hard wire connection is a big sound improvement.
The place I m using  to Mod this amp is my private place, unfortunately  nobody has any iidea about the electronic stuff, I have never attend any electronic class or school,
I learned everything  by myself without any guidance from anyone else. I like experiment or test try always, that's why my amp picture taken always look a bit different everytime. So far what I have learnt and experienced, I believe myself can make this amp alive and show improvement soon


----------



## Maxx134

Ok so when you get a chance, measure voltages of PSU and post.


----------



## klnglim

Maxx134 said:


> Ok so when you get a chance, measure voltages of PSU and post.


Sorry for the late reply as busy on work  and study other diy project. About my MK8SE, still wait for some resistors for replacement, I also just found some broken traces inside the PCB board, those damage areas are very tiny and need 
a magnifying glass to check carefully. Sure will post after complete fix all those problem and replacecment.


----------



## klnglim

Maxx134 said:


> Ok so when you get a chance, measure voltages of PSU and post.


Hi! Massdrop on sale MK6+ & MK8SE
https://www.massdrop.com/buy/little-dot-mkvi-mkviii-se-headphone-amp/talk#discussions


----------



## baronbeehive

Not sure I'm understanding this, I'm just trying to get the amp up and running after various mishaps and upgrades, finally putting in a new ammeter. I've just take some measurements and the 2 terminals are continuous with each other, ie the positive and negative terminals are connected inside the ammeters which is obviously wrong. The result is that the 680ohm resistor pictured is continuous over itself.






I checked the other new ammeter and that is the same, whereas the old one is not continuous, what is up here!!


----------



## SonicTrance

baronbeehive said:


> Not sure I'm understanding this, I'm just trying to get the amp up and running after various mishaps and upgrades, finally putting in a new ammeter. I've just take some measurements and the 2 terminals are continuous with each other, ie the positive and negative terminals are connected inside the ammeters which is obviously wrong. The result is that the 680ohm resistor pictured is continuous over itself.
> 
> 
> 
> I checked the other new ammeter and that is the same, whereas the old one is not continuous, what is up here!!


Hi baron! Those resistors are .68 ohms, not 680. That’s why they show continuity. Nothing’s wrong.


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## Maxx134 (Jul 16, 2018)

baronbeehive said:


> I checked the other new ammeter and that is the same, whereas the old one is not continuous, what is up here!!


Aside from the resisitor.
If you're testing  continuity,
The new meters would read "continuous",  like a very low resistance,
 as the meters are basically aa working coil over a magnet.
But the old one that you replace that not work is most probably because it is burn "open" and so it wont read "continuous" (which is low resistance ).


----------



## baronbeehive

SonicTrance said:


> Hi baron! Those resistors are .68 ohms, not 680. That’s why they show continuity. Nothing’s wrong.



Ha...…..!!! Thanks Sonic, I think you may have saved me another 6 months of searching..... sometimes you can't see whats right there in front of your eyes LOL. I have the wrong resistor there, .68K, not .68R, don't know quite how that happened, school boy error!


----------



## baronbeehive

Maxx134 said:


> Aside from the resisitor.
> If you're testing  continuity,
> The new meters would read "continuous",  like a very low resistance,
> as the meters are basically aa working coil over a magnet.
> But the old one that you replace that not work is most probably because it is burn "open" and so it wont read "continuous" (which is low resistance ).



Yes, that occurred to me so I measured resistance. I made another mistake when I thought that there was a dead terminal on the ammeter. I just remembered what bloodhawk said about there being a resistor in the backlight wire, so that's obviously why I couldn't measure continuity through that wire, probably nothing wrong with the blasted meter after all.

But as a warning to anyone buying  new ammeters the new ones I got which displayed continuity across the terminals must be a different batch. Both the new ones showed continuity across the terminals,  whereas both old ones didn't. The old meters measured 200 on the board and 300 ohms out of the board, which disagreed with the new ones, therefore I would conclude that the new meters may have different ratings which may vary according to which ones you buy.


----------



## baronbeehive (Jul 18, 2018)

Looks like HiFiCollective only do 5% tolerance Mills wirewound atm, is that OK for this resistor, (the 0R68 resistor)?

Edit: I'll go for the 5% anyway. 5% might be significant for a lower value resistor such as this one but as far as I can make out all this does is to send the output to the left meter after some parasitics are cleaned out via the red caps on the left channel.


----------



## SonicTrance

baronbeehive said:


> Edit: I'll go for the 5% anyway. 5% might be significant for a lower value resistor such as this one but as far as I can make out all this does is to send the output to the left meter after some parasitics are cleaned out via the red caps on the left channel.


The meter actually measures the voltage drop across the .68R resistor and displays it in mA. I'm sure 5% is fine though.


----------



## klnglim (Jul 22, 2018)

Maxx134 said:


> Ok so when you get a chance, measure voltages of PSU and post.


Hi there! It's been a long time as I m busy, how are u? Finally I just finished put all the parts inside the board.but no luck as the amp smoke come out from resistor which make me confusing again about what went wrong?
When I began to turn it on, left meter light up and everything look fine. However, when 2nd light from right meter start to turn on till max, the smoke come out from the resistor (red arrow from picture below), the left side meter reverse back to zero and right side meter straight to maximum,
I turn off the amp immediately.
At this moment, I need some advise and help which from your experience,I have no idea why the amp still cant turn on like normal, also can u draw the circle from the picture below where should I take the voltage reading?
I'll appreciate if u can tell me about what I need to  do next, so the amp can be fixed?
Thanks a Lot and hope to hear from u soon.


----------



## baronbeehive

klnglim said:


> Hi there! It's been a long time as I m busy, how are u? Finally I just finished put all the parts inside the board.but no luck as the amp smoke come out from resistor which make me confusing again about what went wrong?
> When I began to turn it on, left meter light up and everything look fine. However, when 2nd light from right meter start to turn on till max, the smoke come out from the resistor (red arrow from picture below), the left side meter reverse back to zero and right side meter straight to maximum,
> I turn off the amp immediately.
> At this moment, I need some advise and help which from your experience,I have no idea why the amp still cant turn on like normal, also can u draw the circle from the picture below where should I take the voltage reading?
> ...



Hi kiglim!Good work so far, don't give up now looks like you're nearly there. Your work looks OK. I'm assuming you've gone through the usual checklist, continuity, resistor values, wires checks, parts positions soldering etc. I don't need to tell you this now, you're probably way ahead of me after all you've done.

I'm hoping to get mine up and running again this week but need to go to an engineer to solder a wire back on the ammeter terminal, my soldering iron is not powerful enough for that job. But one resistor which was incorrect caused a problem so make sure you haven't made any stupid mistakes like me LOL. I also had a cap leg break off unkown to me at the time.

I can't advise you so wait for someone that can.
.


----------



## klnglim

baronbeehive said:


> Hi kiglim!Good work so far, don't give up now looks like you're nearly there. Your work looks OK. I'm assuming you've gone through the usual checklist, continuity, resistor values, wires checks, parts positions soldering etc. I don't need to tell you this now, you're probably way ahead of me after all you've done.
> 
> I'm hoping to get mine up and running again this week but need to go to an engineer to solder a wire back on the ammeter terminal, my soldering iron is not powerful enough for that job. But one resistor which was incorrect caused a problem so make sure you haven't made any stupid mistakes like me LOL. I also had a cap leg break off unkown to me at the time.
> 
> ...


Just found one caps problem and replaced, then try to on again, however bad luck still, this time another resistor smoke (Red arrow from picture below), so have to turn off immediately.


----------



## baronbeehive

klnglim said:


> Just found one caps problem and replaced, then try to on again, however bad luck still, this time another resistor smoke (Red arrow from picture below), so have to turn off immediately.



Just a shot in the dark but it could be wiring. You could approach the problem from that end and check the XLR output jacks on the rear panel, check each pin to ground to see if there is a grounding problem. This can happen and be difficult to see. Only pin 1 of each output, left and right, should be connected to ground.


----------



## klnglim

bloodhawk said:


> Thanks!
> 
> Its kinda baffling how some of the wiring is just routed so poorly.
> 
> ...


I have same mistake as u mention picture above , can u tell me what went wrong?


----------



## bloodhawk

klnglim said:


> I have same mistake as u mention picture above , can u tell me what went wrong?



I wired the one on the right incorrectly -


----------



## klnglim

bloodhawk said:


> I wired the one on the right incorrectly -


ok, now I got it. Will go back and check  my  amp later. Hopefully will work this time, thanks a lot anyway!


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## baronbeehive (Jul 26, 2018)

baronbeehive said:


> Yes, that occurred to me so I measured resistance. I made another mistake when I thought that there was a dead terminal on the ammeter. I just remembered what bloodhawk said about there being a resistor in the backlight wire, so that's obviously why I couldn't measure continuity through that wire, probably nothing wrong with the blasted meter after all.
> 
> But as a warning to anyone buying  new ammeters the new ones I got which displayed continuity across the terminals must be a different batch. Both the new ones showed continuity across the terminals,  whereas both old ones didn't. The old meters measured 200 on the board and 300 ohms out of the board, which disagreed with the new ones, therefore I would conclude that the new meters may have different ratings which may vary according to which ones you buy.



Just quoting myself because I wanted to correct something I said: there was nothing wrong with the ammeters, it was the wrong value resistor that Sonic pointed out that was causing the problem. Both meters do display continuity over their terminals which reads as a low resistance on the ohmmeter as Maxx said, that's OK now that I've changed the resistor…... BUT.... I've switched on after upgrading the PSU resistors and others totalling 10 in all, plus a new Jupiter cap, diodes and transistors. Now there is no smoke like kinglim but one meter reads 60mA correctly and the other reads 30mA so something needs looking at again. At least the meters aren't behaving erratically like before!

Anyway next step take some voltages etc etc…..

Bit of a bummer that, I tried to be so careful, checked everything in triplicate but this amp just likes to bite back.


----------



## klnglim

bloodhawk said:


> I wired the one on the right incorrectly -


Well, I have checked all connection, nothing's wrong. When turning on, the left side meter light up follow by right side meter warm up slowly, unfortunately reading '0' and totally silence. 
From what I have seen, the meter lights are too bright so I turn off the amp immediately to avoid component smoke again, I guess need to add small resistor to dim the meter light, by now 
 still searching for the cause of silence


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## baronbeehive (Jul 29, 2018)

That's pretty weird, I've just taken voltages and they're all good:

power cathodes all read -80v/-104v give or take on respective sides of the cathode cap
power anodes all read 76v/101v give or take on respective sides of the 330R
driver cathodes all read 0.1mv/1v give or take on respective sides of the 377R
driver anodes all read 140v/186v give or take on respective sides of the 33K

...… yet the right hand meter reads 30mA only. This meter was not the one that was changed.

Only thing I've done on this circuit was to desolder the gain switch but the resistors all read good, and a desoldered switch is the same as a switch in place in the "off", (high gain), position, so it can't be that.

My reasoning now is that if the driver and power stages are OK I need to look elsewhere, after the power stage in the circuitry, or check out the connections from the meter back, any bright ideas anyone?


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## baronbeehive (Aug 12, 2018)

I don't know if these voltages mean anything to anyone If so say now before I take the PCB out again!

1 & 2 are the red and white wires going to the left meter on the .68R
3 & 4 are the red and white wires going to the right meter lighting circuit, marked "right meter" on board
5 & 6 are the white and red wires going to the left meter lighting circuit
7 & 8 is the resistor marked "left meter" on board





I also measured 100v on each of the meter terminals.

Both channels sound fine and equal volume so without taking the board out, I'm not sure of the problem. I'm speculating that a meter resistor could have fried when a leg broke on one of the Jupiter caps, or maybe something on the back of the board.

Edit: Thanks Sonic for the pic, better quality than mine..... also his amp LOL.

The lighting circuit terminals were difficult to get at but measure 3.0mV each in the meter with the correct reading of 60mV, whereas the other 2 terminals read 0.26v (white wire), 11.7v (red wire), so something not right here.

*I've made some corrections to this since first posting.*


----------



## baronbeehive

*OMG...…. just been listening to one of my fav tracks with the complete set of 421A's...… all I can say is simply stunning.... I'm speechless.... I'm going to have to have some time getting used to this!*

On a side note there doesn't seem to be anything wrong with the amp, must be just a meter issue.


----------



## SonicTrance

baronbeehive said:


> *OMG...…. just been listening to one of my fav tracks with the complete set of 421A's...… all I can say is simply stunning.... I'm speechless.... I'm going to have to have some time getting used to this!*
> 
> On a side note there doesn't seem to be anything wrong with the amp, must be just a meter issue.


Do you have the 5998/421a bias mod in place? I can't remember. That also makes a huge difference in the LD! Great sounding tubes .


----------



## SonicTrance

Sad day, but it's time....
https://www.head-fi.org/threads/little-dot-mk-vi-super-modified-we421a.885848/


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## baronbeehive (Aug 6, 2018)

SonicTrance said:


> Do you have the 5998/421a bias mod in place? I can't remember. That also makes a huge difference in the LD! Great sounding tubes .



Yes I have the bias mod in place..... but haven't used it yet as I'm concerned about the amp atm, it seems ok but until I sort the issue with the meter I won't use it, or the 421A's, the next step is to try the various cathode-anode settings on SQ.... and finishing with the CCS some way down the line!



SonicTrance said:


> Sad day, but it's time....
> https://www.head-fi.org/threads/little-dot-mk-vi-super-modified-we421a.885848/



Sad indeed... I have considered this also, it makes sense for you though now that you have your other main amp.

Stay on the thread though Sonic!
.


----------



## Maxx134

SonicTrance said:


> Sad day, but it's time....
> https://www.head-fi.org/threads/little-dot-mk-vi-super-modified-we421a.885848/


Wow, Dumbfounded...
Sale of the century(!)..

Will never see such a moded beauty for sale like this again...

Not sellin mine, but I like to follow SonicTrance footsteps into making one more amp in the fall...

Damm that amp is sweet.


----------



## SonicTrance

Thanks guys!
I really love this amp but I'm having too much fun with my DIY amps. Can't keep everything sadly, too little time.


----------



## baronbeehive (Aug 9, 2018)

I just wanted to mention a few observations about the amp with the 421A's in, I know one or two of you will be interested. I've tried it twice briefly now and so I'm able to say one or two things:

I had two slight reservations about the amp before which were:

 - bass lacking slightly in articulation - the bass is now very lively, good definition and balance, just the right amount

 - some treble frequencies missing - these frequencies are back and the amp now performs at a very high level indeed. I had suspected all along that this was down to the RCA's which are a bit lacking in extension, I still like them however.

Also I noticed straight away the resolution and transparency has gone up massively and contributes to the soundstage accuracy and intimacy which was good before and is now top notch. I can't say about the size of the soundstage because my HE500's don't do massive soundstage unfortunately.

Everything else is spine tingling to the extent now that I can't imagine anything better. The only slight thing is that with a top level system the bass would be slightly tighter and snappier sounding, Maxx will know what I mean because I feel it's still better on the other amp. If the problem is down to the PSU and balance then the CCS mod could sort this, when I get round to it, but I suspect this is down to the amp design and probably the NFB. Possibly those massive film caps of coinmaster might do the trick - but I haven't got room in the house for them.

These are brief impressions but I would say now I'm pretty well totally satisfied with the amp, it has certainly come alive for me!!

Just a pity these WE's are so damn expensive and there's nothing really in between the RCA's and them sadly.


----------



## SonicTrance

baronbeehive said:


> Just a pity these WE's are so damn expensive and there's nothing really in between the RCA's and them sadly.


Yes, there is! The 5998!


----------



## baronbeehive

SonicTrance said:


> Yes, there is! The 5998!



Yes I know, I was keeping quiet about them, I know where I can get some. I dare say I will probably end up with those as a compromise..... with the bias mod suitably adjusted!

I think you said you liked them but they were not quite as dynamic as the 421A's.


----------



## SonicTrance

baronbeehive said:


> Yes I know, I was keeping quiet about them, I know where I can get some. I dare say I will probably end up with those as a compromise..... with the bias mod suitably adjusted!
> 
> I think you said you liked them but they were not quite as dynamic as the 421A's.


Right! I still have a NOS quad (+ 1 spare) WE421A.

If you're interested shoot me a pm.


----------



## baronbeehive

SonicTrance said:


> Right! I still have a NOS quad (+ 1 spare) WE421A.
> 
> If you're interested shoot me a pm.



Thanks Sonic, but it's not the right time. I intend to live with these 421A's for a while, then decide between these and some 5998's. I think I can get the 5998's for one third the price of 421A's,that will probably clinch it for me!

Another interesting tube is the TS 6080 and 6AS7 but they're impossible to get hold of.


----------



## baronbeehive (Aug 12, 2018)

Still trying to find the problem and I have a couple of questions:

- The amp meters read 60mA, left meter, and 30mA, right meter with 6AS7G's in
- Power/driver anode/cathode readings all good
- Both terminals on the meters read 100v
- Both legs of the .68R in the middle of board going to left channel read 100v
- The sound appears to be all good
- the only discrepancies in voltage readings appear to be in the meter lighting circuit and so surely that is not important

Bearing that in mind where could the problem be and where on the board are the 2 circuits for the right channel connected?

Could the meter itself be a problem? This is not the meter that I changed.

I'm wondering if the output of only one circuit is getting through. I'm at a bit of a loss here.

Edit: I did notice that the resistance over the terminals of the right meter is twice that of the left meter, which could indicate a fault further down the line but I can't find any faults anywhere.


----------



## baronbeehive

I've drawn a conclusion about this:

The voltages at the anodes/cathodes are good
The voltages at the meter terminals are both the same
The resistance across the meter terminals with the faulty reading is way higher than the other, new, meter
I can't find any fault with anything else.. so...

... the meter must be faulty, probaly gone open due to a voltage surge either when the capacitor broke off or due to the mistake with the resistors

I was probably right about a meter fault before but for the wrong reason - so the amp is off to the engineer again to get the other new meter soldered in place...... hope I'm right about this…..


----------



## bloodhawk

baronbeehive said:


> I've drawn a conclusion about this:
> 
> The voltages at the anodes/cathodes are good
> The voltages at the meter terminals are both the same
> ...



Did you check if the new meter has a resistor soldered in line?


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## baronbeehive (Aug 15, 2018)

bloodhawk said:


> Did you check if the new meter has a resistor soldered in line?



Do you mean the resistor on the end of the red lighting wire?

That one is still there, haven't checked the value though. But I measured across the terminals above that resistor, not from the other end of the 2 wires going into the terminals.


----------



## bloodhawk

baronbeehive said:


> Do you mean the resistor on the end of the red lighting wire?
> 
> That one is still there, haven't checked the value though. But I measured across the terminals above that resistor, not from the other end of the 2 wires going into the terminals.



Nope there is a resistor in line with one of the terminals on the ammeter. If i remember correctly its a 68Ohm resistor in series on the positive terminal of the meter. Its pretty well heat shrunk, so hard to notice.


----------



## baronbeehive

bloodhawk said:


> Nope there is a resistor in line with one of the terminals on the ammeter. If i remember correctly its a 68Ohm resistor in series on the positive terminal of the meter. Its pretty well heat shrunk, so hard to notice.








You mean this one?


----------



## bloodhawk

baronbeehive said:


> You mean this one?



Looks like it yeap.


----------



## baronbeehive (Aug 16, 2018)

bloodhawk said:


> Looks like it yeap.







Yes, that's the low voltage backlight circuit, with the resistor to lower the voltage, which you found when you were working on your amp. The other circuit is the power circuit coming off those 2 x 0.68R resistors, which I mistakenly thought were 0.68k, which could have blown open the meters. The fact that the resistance across those terminals is different must result in the different current at the meter.... I hope!

Edit: you were right the resistor under the heatshrink is 68R.


----------



## SonicTrance

The 68 ohm resistor is a current limiting resistor. So not to damage the backlights at startup.


----------



## baronbeehive

Well.... it was the meter, 2 new meters installed and everything's fine now thankfully!


----------



## SonicTrance

baronbeehive said:


> Well.... it was the meter, 2 new meters installed and everything's fine now thankfully!


I’m glad you got it sorted Baron!


----------



## baronbeehive

SonicTrance said:


> I’m glad you got it sorted Baron!



Thanks!

Looking forward to getting in some serious listening with those WE's….. and finishing the mods!

Modding can be a problem, constantly rearranging the components inside the amp, that's what caused the cap leg to break off, unknown to me.


----------



## baronbeehive (Jan 24, 2021)

*SMLD MODS: (continued)

Anode/cathode trials *-  

ANODE/CATHODE listening tests: The Results...







The graph above showed my proposals in green.





I've recalculated the graph with my revised B+ of 185v. The graph shows the region of interest where we are looking for the best operating points.

I tested 20 positions in all including 2 types of 6SL7 driver tubes and high/low gain settings.

I've got my amp up and running again I've been able to finish the anode/cathode experiments for the driver stage that I had started previously so here's what I did for these tests:

I've stuck with the RCA 6AS7G's for the purposes of the experiment because I had already started the experiments using them, before getting the full set of WE's, and I'm used to the sound. For driver tubes I used TS 6SL7's and GE 12SL7's, which are my favoured sets now.

I used the same test tracks, including some high res tracks, for all the tests and the same volume level as far as possible.

I made notes as I went along in brief comprising soundstage, bass, midrange, treble. Initially I also compared high/low gain settings but as I preferred high gain, I decided to stick with this and not evaluate it further after the initial results because I believe there is enthusiasm to see how high we can go with the gain settings in future, I found no downsides with high gain. I desoldered my gain switch due to its unreliability. By the time I had nearly finished the tests I wrote more abbreviated notes referring to other positions rather than repeating myself over and over.

I found that pretty much all of the settings sounded good, with the exceptions of those with scores of -1, and would not discourage anyone from using any of these settings, the difference is mostly a matter of personal preference, and at this level differences are not that great, I used a numerical evaluation, for example starting at 0 for the baseline - Sonic's and my settings - with anything at 1 indicating a preference over the 0 level but with this not indicating a massive difference such as a score of 2 would indicate. I've indicated why I thought one setting was better than another but you have to bear in mind that where there is a difference of only 1 point there is a subjective element in all of this. Only a score of 2 would indicate a definate, objective, indisputable difference. I didn't think any differences justified a score of 2 because there were no massive differences such as is the case for example when changing RCA power tubes for the WE's. Having said that there was one position that I nearly gave a score of 2 to!

One reason all settings sounded pretty good I think was because the voltage swing on this amp is not great as MrCurwen said before, so that even if an operating point was chosen for a tube which was close to a non linear region on the graph it would be unlikely that the swing would go near to the non linear part of the grid curves. This is probably a strength and a weakness of this amp. Another reason is that we are already in the good regions and trying to find the optimum points but I decided not to test the extremes because I wanted to stay in the linear parts, so for that reason there would not really be a huge difference. Anyone who would like to look into those non linear regions, feel free!

We have now looked at a range of operating points and currents for the tubes, we are limited by the voltage we can get so I don't think there's much we have missed concerning the tube operation now. One thing, I believe that the amp sounded better with the 2 last R, 3K3 resistors lowered in value to give a B+ of 185v on my amp.

To summarize my results there was one stand out position which hit me the moment I started listening, the sound was full, palpably real with good clarity and texture which you could almost feel. The sound had a presence, transparency, resolution and dynamism. This for me was the obvious setting to use. I was a bit surprised that my proposed intermediate settings in between Sonic and Maxx's settings were not my favourite, probably because it fell in the middle it was neither one thing nor the other. The best operating point was with an anode of 69K and cathode of 380R, point 7 in the graph. I will scan in my notes page later so you can see in more detail.

The tests also confirmed my choice of driver tubes, I've gone from preferring the TS 6SL7 to the GE 12SL7 because my experience with the other amp made me prefer a sharper, more lively sound which the GE does well, for only a couple of dollars too! The sound of the GE is better for hearing things such as the sound of the plectrum on the guitar string, whereas the TS 6SL7 has a smoother, more liquid yet still detailed sound. The surprising thing about my preferred position is that it happened with the RCA 6AS7G's in, so if it's that good I can't wait to try the new setting with the WE's!

I hope this has been useful for others trying to find the settings which suit them.


----------



## baronbeehive (Jan 24, 2021)

*SMLD MODS: (continued) *-  

*Anode/cathode trials*







The baseline was at my current settings of 33K - anode, and 380R - cathode, which was a setting that Sonic and myself had chosed to be very good for sound quality. The scores of 0, or higher were therefore at least as good as this. Going through the anode settings as follows:

33K - good baseline score, with cathode of 380R, as above, however at 2 of the cathode settings, 1K and 1.5K, I felt that the sound was somewhat flat and lifeless. High gain sounded better, slightly more transparent, with both 6SL7 tubes.

46K - again, good baseline score or thereabouts, with cathode of 380R, but with the GE tube with scores of 1 for bass, mids, treble, and soundstage I felt that this justified a second place position for SQ. Very good transparency and detail. With the 1.5K cathode the scores fell to -1 with a flat rather lifeless sound.

69K - here with all 3 cathodes I felt was the best sound with all 3 cathodes the sound was considerably above baseline. With the 1.5K cathode I felt that with the GE tube it justified second equal position in SQ. With the 1K cathode and with both 6SL7's I felt that second equal position was justified with full bodied, incisive, real and transparent sound. However as soon as I started listening with the 380K cathode in I knew straight away that I would be very happy with this setup. The sound was full bodied, had a real presence, and had the most texture to the transients and treble which gave it a dynamism. For example piano had weight and attack, guitar notes stood out, vocals sounded real, bass had weight and definition and drums had attack, you could almost feel the kick drums.

I don't want to overplay this, as I said all settings sounded good, except for the ones with scores of -1 which were a bit lifeless sounding, but anything on 0 or over sounded good but I felt that some with scores of 1 sounded just that bit better and the best position I liked immediately, but those scores in second place were not much different to first place. Interestingly I thought that all the positions in the anode setting of 69K were best so I wondered if the anodes were more important for sound, while for the other anodes nearly all positions apart from the baseline position, scores were worse with the most lifeless sound.

I would recommend that overall it would be best not to use the 33K anode setting, or the 1.5K cathode settings and go for the first place or one of the second place settings.


----------



## NNewman

Hello. Sorry to ask in this thread, but in other places I have already got nothing...
And the maasdrop drop time counts down and I need to make a choice quickly.
I m looking for a good pair to my SS headphone amp in the tube field. Currently I m choosing between LD Y1,  LD mk6+ and LD mk8 se. Tube pair is seems to be "working" only with HD800, AKG k340 and LCD4.
LD mk6 is not preffered as it has an active cooling and for a bed time setup it might be crazy bad idead. My wife might send me out to sleep on the coach.  But I must be 100% sure if MK8se is really good pair for LCD4... 

Please share with me your oppinion about this 3 variants.
Thanks in advance.


----------



## baronbeehive

NNewman said:


> Hello. Sorry to ask in this thread, but in other places I have already got nothing...
> And the maasdrop drop time counts down and I need to make a choice quickly.
> I m looking for a good pair to my SS headphone amp in the tube field. Currently I m choosing between LD Y1,  LD mk6+ and LD mk8 se. Tube pair is seems to be "working" only with HD800, AKG k340 and LCD4.
> LD mk6 is not preffered as it has an active cooling and for a bed time setup it might be crazy bad idead. My wife might send me out to sleep on the coach.  But I must be 100% sure if MK8se is really good pair for LCD4...
> ...



No worries, the other thread is grinding to a halt now!

Sorry I can't be much help, I don't have the headphones you mention, and I've never heard of the LD Y1 and had to look it up.

Re: your headphones, the HD800 I think does work with the MKVI, I've heard people say so but obviously the MK8 is preferred, probably also for your LCD4. I don't think you would go wrong with the MK8, but it's only my opinion based on what others here have said.

The type of sound you get is good balance, refinement, resolution, and great soundstage. The sound is not tubey but clear and musical, I would say it falls between the tubey 300B and the hotter SS type sound. I don't want to say more because someone with those cans may come on.

Hope that has helped with your choice.


----------



## NNewman

baronbeehive said:


> No worries, the other thread is grinding to a halt now!
> 
> Sorry I can't be much help, I don't have the headphones you mention, and I've never heard of the LD Y1 and had to look it up.
> 
> ...


Hello. Thanks for the answer. LD Y1 was a flagship for some years, until now when Y2 was out. Y2 is just an upgraded version of Y1: new traffos, DACT volume control and many many more. If somebody is interested I can post a detaild photos of Y1 here...
To MK8SE: I think that I have read any where that change of the power tubes to another type brings a noticable power boost... is it right? Or I have messed smthg?
One more question: tho OPamps in MK6 and MK8 are out of the sound path?


----------



## baronbeehive

Nearly ready to implement to CCS.

NB: this is a dummy run, the resistors etc are not correct so I labelled the correct values. I've compressed it as much as possible so that it will fit!



 







Does that look right?

I'm a bit worried that the amp might go up in flames....


----------



## MrCurwen

baronbeehive said:


> I'm a bit worried that the amp might go up in flames....



No, the worst that could happen is the CCS self-destructs. 

What FET are you using, why didn't you go for the standard IRF8x0 types?

In the future don't bend the pins so close to the body. When bending a pin always keep part of the pin closest to the body completely straight.

3D construction looks decent enough, with TO-220 body FETs you can get much better and clearer construction. Use the FET body as a main binding post.


----------



## baronbeehive

MrCurwen said:


> No, the worst that could happen is the CCS self-destructs.
> 
> What FET are you using, why didn't you go for the standard IRF8x0 types?
> 
> ...



Thanks!

Yes, bending the pins close to the body was the reason a leg broke on a coupling cap.

I'm about to go ahead and build the CCS now and will post pics when I've done it.


----------



## Maxx134 (Sep 4, 2018)

NNewman said:


> Hello. Thanks for the answer. LD Y1 was a flagship for some years, until now when Y2 was out. Y2 is just an upgraded version of Y1: new traffos, DACT volume control and many many more. If somebody is interested I can post a detaild photos of Y1 here...
> To MK8SE: I think that I have read any where that change of the power tubes to another type brings a noticable power boost... is it right? Or I have messed smthg?
> One more question: tho OPamps in MK6 and MK8 are out of the sound path?


I would not reccomend the LDMK8 for that planar.
If it is a double sided magnet, they require lots of power..
I myself have had to increase bias and plan to increase cathode cap to offset the drain planars give on this design since it is OTL.

Anyways, I never noticed that other LDY1 amp and it does looks powerful enough...


----------



## baronbeehive (Jan 24, 2021)

*SMLD MODS: (continued)

CCS mod *-  

I think I'm ready to install the CCS now.



 



Using all 1w resistors made it a bit more difficult with the size, and thickness of the leads, however it will still fit, I can stick the FET with 3m sticky tape onto the board.

I will test it before putting in the active filter to see  what it's like before and after.


----------



## MrCurwen

Decent 3D layout there baronbeehive. Pretty symmetry. I would go for smaller size and less pretty but that'll work just as well. Remember the FET metal tab is connected to the drain, so make sure it touches absolutely no metal anywhere.


----------



## baronbeehive (Sep 5, 2018)

MrCurwen said:


> Decent 3D layout there baronbeehive. Pretty symmetry. I would go for smaller size and less pretty but that'll work just as well. Remember the FET metal tab is connected to the drain, so make sure it touches absolutely no metal anywhere.



OK, thanks!

Having made one that I knew would fit both sides I didn't want to chance my luck and do the other one any differently!

Edit: As I'm removing the cathode resistors where I currently have the driver stage decoupling cap connected to the cathode side, can I simply connect the cap direct to a cathode tube pin and ignore the ground connection which was there on the other side of the cathode resistor?


----------



## SonicTrance

baronbeehive said:


> Edit: As I'm removing the cathode resistors where I currently have the driver stage decoupling cap connected to the cathode side, can I simply connect the cap direct to a cathode tube pin and ignore the ground connection which was there on the other side of the cathode resistor?


No, because the cathodes are not grounded. Cathode node will be at about 1V.
You can connect the decoupling cap lead in the same ground hole as the cathode resistor was, if it fits?


----------



## MrCurwen

I just looked at your connections in the picture.

There is no anode connection, only B+.

B- and filter are the same thing, B- for the CCS is the filter output (I realise you plan to try the CCS before adding the filter). Just making sure you understand to not connect unfiltered B- after you have the filter.

Not to be annoying, but precision is very important.


----------



## SonicTrance

Baron is referring to top of anode resistor, so B+.


----------



## baronbeehive (Sep 6, 2018)

SonicTrance said:


> No, because the cathodes are not grounded. Cathode node will be at about 1V.
> You can connect the decoupling cap lead in the same ground hole as the cathode resistor was, if it fits?



Ah, right, I didn't realize the decoupling cap connection on the cathode resistor was ground, I thought it was the cathode side, so we are just providing the ground connection to the anode decoupling circuit, but wouldn't that circuit be broken without the cathode resistor in situ?



MrCurwen said:


> I just looked at your connections in the picture.
> 
> There is no anode connection, only B+.
> 
> ...



Right, I didn't realise that the filter was B- for the CCS, I thought it was cleaning up the existing B- going by that previous circuit diagram, so the filter provides a clean B- as an alterative to the existing. I haven't looked at the filter construction yet so I'll post pics on that just to be sure.

Thanks guys.


----------



## SonicTrance

baronbeehive said:


> so we are just providing the ground connection to the anode decoupling circuit, but wouldn't that circuit be broken without the cathode resistor in situ?


Yes, ground connection for driver stage B+ decoupling.
No, its connected to the pcb ground plane. Measure with ohm meter if you're unsure.


----------



## baronbeehive (Jun 5, 2021)

*SMLD MODS: (continued)

CCS mod *-

These are the connections - CCS and revised driver stage decoupling:

Cathode ground decoupling                                                                                                                         




 

CCS cathode connection





Anode decoupling, CCS B- connection, CCS cathode connection                                                                  



 

CCS cathode connection, CCS B+ connection





CCS1 to CCS2 connection, CCS cathode connection, CCS B+ connection, CCS B- connection - other end.




.


----------



## MrCurwen

Looks pretty good to me, I don't know about the connections to the board though, not my expertise.

So how's it sound?

I predict the extra B- filter has no effect on sound quality. The improved balance should take care of all common mode noise, as per explained earlier in great detail. I originally added it to the schematic as a "final blow" to the doubts about the efficacy of the balanced common mode noise rejection. (Common mode noise rejection has been known for over a 100 years so shouldn't be too controversial.)

It's possible though it might, taking the circuit as a whole. Unknown interactions in a (semi)complex circuit are always a possibility. Interesting to hear results!


----------



## baronbeehive

MrCurwen said:


> Looks pretty good to me, I don't know about the connections to the board though, not my expertise.
> 
> So how's it sound?
> 
> ...



I haven't switched on yet!!!!

Just double... triple checking everything, cleaning the board etc. I always get stressed out at this time, so probably leave it for the moment, see what Sonic thinks.

No I agree about the effects of the filter, not expecting any change, just good to know that there's no dirt in the system.

I'll update you as soon as I think it's safe to do so...…!


----------



## SonicTrance

baronbeehive said:


> see what Sonic thinks.


Switch it on! 

I can't see if all connection are correct though as I'm on thr phone. But I'm sure you're fine if you double and triple check!

I too want to hear your impressions!


----------



## SonicTrance

Measure bias voltage at cathode node. Should read slightly higher at boot before the B- supply starts, then go to normal.

Wheres your B- connection btw? Cant see it?


----------



## baronbeehive

SonicTrance said:


> Measure bias voltage at cathode node. Should read slightly higher at boot before the B- supply starts, then go to normal.
> 
> Wheres your B- connection btw? Cant see it?



It's here:

5K1 resistor.... to ……                                                                                                                                      opposite end of 470R from FET.


----------



## SonicTrance

baronbeehive said:


> It's here:
> 
> 5K1 resistor.... to ……                                                                                                                                      opposite end of 470R from FET.


Ok, all good then!


----------



## baronbeehive (Sep 8, 2018)

SonicTrance said:


> Switch it on!
> 
> I can't see if all connection are correct though as I'm on thr phone. But I'm sure you're fine if you double and triple check!
> 
> I too want to hear your impressions!



.... actually I quadruple tested everything.... just to be on the safe side, I can't be doing with all this stress waiting for the meters to come on!

Massive relief, it works.... and it sounds damn good, in keeping with this thread I don't want to exaggerate, I want to be as objective as possible, so these are my first impressions:

I would say that the sound is of the same order as the best setting I found with the anode/cathode settings which is a relief because I was so impressed with this. I didn't want to exaggerate my impressions of this change of anodes/cathodes but looking back now I may have underestimated the improvement, I now think that the improvement of those changes was of the same order as a change of tubes from RCA to WE's, I don't mind having RCA's in now because they sound so good. This is what I said about these changes at that time:_ "To summarize my results there was one stand out position which hit me the moment I started listening, the sound was full, palpably real with good clarity and texture which you could almost feel. The sound had a presence, transparency, resolution and dynamism. This for me was the obvious setting to use."_

Anyway back to the CCS, again we're at a very high level now, and I'm having trouble picking differences, and also I'm having to rely on memory. The initial and main impression is one of total clarity, I may be imagining this but I felt that some harmonic distortion had disappeared. Overall the sound was of the same order as the best anode/cathode setting but totally free of distortion, it was like listening to the same notes but without any reflections or reverberations. Re: bass, mids, treble and soundstage I felt there was no difference, again all at this previous high level. One could not say that the bass had changed or was any sharper, or that the mids and treble stood out more or were more resolved, I didn't think this was the case. Also I couldn't hear any difference in soundstage, again at a high level as before.

My recommendations on this change are: If you like maximum clarity go for it, if you are more romantically inclined and prefer a slight sheen to your music, then maybe stick with the existing design. Whatever you decide you will be pretty happy!

So those are my intial impressions, I'm going to have to live with this for a while before I decide on what to do next, so the filter can wait until then. One thing is for sure, the level we are at now it's not going to be easy looking for yet more improvements..... or maybe.... !


----------



## MrCurwen

baronbeehive, good work!



baronbeehive said:


> The initial and main impression is one of total clarity, I may be imagining this but I felt that some harmonic distortion had disappeared.



You are not imagining it, assuming you built the thing correctly it has lower distortion. To understand why I recommend you reread the big topology theory / experiment post from this thread. I tried my best to make it understandable but it takes some time and revisiting.

When you take out distortion, there is EXTRA stuff underneath, music signal details. Add distortion and you mask stuff in the signal.



baronbeehive said:


> Overall the sound was of the same order as the best anode/cathode setting but totally free of distortion



Much more efficient to make the circuit do the balance, not to try and find a tube that is decently balanced. Have you tried different tubes with the CCS? Do they sound significantly different?

Not totally free of distortion, there's a long way to go still. You'd be surprised.



baronbeehive said:


> So those are my intial impressions, I'm going to have to live with this for a while before I decide on what to do next, so the filter can wait until then.



So I'm guessing no harsh IMD from B- ripple then? No 7H and up tearing your sweet music signal to shreds?

Understand theory and topology. Makes this hobby less poking around in the dark and more fun.



baronbeehive said:


> One thing is for sure, the level we are at now it's not going to be easy looking for yet more improvements..... or maybe.... !



In the LD the limiting factor is physical space. Also the direct drive topology is problematic to improve. 

Since the output follower has such a high output impedance and no way to force fully balanced operation (you cannot use a CCS there since it's a pair of followers), PSU improvements would be the way to go. 

I'd go for actual (even very simple) regulation, not crazy C. Now there is just a voltage setter there. It sets the voltage and not much more. If the decoupling cap (right at the B+/- nodes) has a noticeable effect on sound quality, you are not dealing with any degree of PSU regulation.


----------



## baronbeehive

MrCurwen said:


> baronbeehive, good work!



Thanks!



MrCurwen said:


> You are not imagining it, assuming you built the thing correctly it has lower distortion. To understand why I recommend you reread the big topology theory / experiment post from this thread. I tried my best to make it understandable but it takes some time and revisiting.
> 
> When you take out distortion, there is EXTRA stuff underneath, music signal details. Add distortion and you mask stuff in the signal.



I think that was the post with a lot of ripples in water metaphors, if so I remember it well! I will check it out.

What  needs to be done to compliment the cleaner signal is to boost resolution somehow so that we can hear more of these microdetails, I didn't really feel that resolution had gone up.



MrCurwen said:


> Much more efficient to make the circuit do the balance, not to try and find a tube that is decently balanced. Have you tried different tubes with the CCS? Do they sound significantly different?
> 
> Not totally free of distortion, there's a long way to go still. You'd be surprised.



Not yet. I only have the TS 6SL7's for drivers apart from the GE's. I will try them next, possibly with the WE's, the resolution is better with the WE's for power tubes.

I am trying to imagine a totally distortion free system.

This might be something for Maxx to look at, I think he wants to do the CCS mod, and he has a stash of tubes to try, I will wait to see what he thinks. He has also heard top level systems which I haven't so he will have a better idea of how far we can go with this.



MrCurwen said:


> So I'm guessing no harsh IMD from B- ripple then? No 7H and up tearing your sweet music signal to shreds?
> 
> Understand theory and topology. Makes this hobby less poking around in the dark and more fun.



No I don't think so, there was certainly nothing obviously objectionable like IMD would suggest. Also no higher order harmonics that I could discern. As I said it would be interesting to see how much microdetail we could reveal.

We have a problem here though, the gain, and how high we can go with it. We could probably go a bit  higher than the high setting but I don't know how high.



MrCurwen said:


> In the LD the limiting factor is physical space. Also the direct drive topology is problematic to improve.
> 
> Since the output follower has such a high output impedance and no way to force fully balanced operation (you cannot use a CCS there since it's a pair of followers), PSU improvements would be the way to go.
> 
> I'd go for actual (even very simple) regulation, not crazy C. Now there is just a voltage setter there. It sets the voltage and not much more. If the decoupling cap (right at the B+/- nodes) has a noticeable effect on sound quality, you are not dealing with any degree of PSU regulation.



Maybe the PSU improvements could be followed up. As I understand it we have a brutish PSU atm which performs quite well. I did wonder if the fact that we have the driver stage decoupling reduces the impact of the CCS, because the decoupling is helping stabilize fluctuations in power supply already.

IMO the amp could possibly go a bit higher in resolution, soundstage, and bass performance to reach absolute top level, but it's already excellent in these areas now.


----------



## SonicTrance

Good work baron!


I don't think there's anything you can do to the ps(s) without extending the chassis or have a external chassis for the ps(s), unfortunately.


----------



## baronbeehive

SonicTrance said:


> Good work baron!
> 
> 
> I don't think there's anything you can do to the ps(s) without extending the chassis or have a external chassis for the ps(s), unfortunately.



Thanks Sonic!

Yes, that's what I thought about the PSU.

Re: tube experimentation, we're looking for very linear tubes now, I assume, to extend the possibility of extra microdetail, but we already have the 6SL7/6SN7's. Anyway I'll leave that open to discussion, I'm very happy with the amp now, it's come alive!
.


----------



## SonicTrance

baronbeehive said:


> but we already have the 6SL7/6SN7's


Only 6SL7 with the CCS installed. ECC35 and 6C8G (with adapter) would also work, but 6SN7 would not be happy at 1.2mA of bias current.

It's good to hear that the CCS implement was a success.


----------



## baronbeehive

SonicTrance said:


> Only 6SL7 with the CCS installed. ECC35 and 6C8G (with adapter) would also work, but 6SN7 would not be happy at 1.2mA of bias current.
> 
> It's good to hear that the CCS implement was a success.



Yes of course!

I believe Maxx has the 6c8g.


----------



## MrCurwen

baronbeehive said:


> I think that was the post with a lot of ripples in water metaphors, if so I remember it well! I will check it out.



No, I mean the actual technical guide. It's in my posts on this page: https://www.head-fi.org/threads/lit...e-on-first-page.782183/page-199#post-14089563



baronbeehive said:


> We have a problem here though, the gain, and how high we can go with it. We could probably go a bit higher than the high setting but I don't know how high.



I understand you are talking about gNFB here, not gain. The amp has plenty of gain, that's not a problem. Please use precise language for ease of understanding.

The built-in problem with gNFB in this amp is that lowering it would be good for the input stage (leave room to build clean open-loop structures) but at the same time it would destroy the performance of the output stage.

The output stage needs the gNFB. 



baronbeehive said:


> I did wonder if the fact that we have the driver stage decoupling reduces the impact of the CCS, because the decoupling is helping stabilize fluctuations in power supply already.



In one aspect, yes. The CCS improves the function of the input stage in two ways:

1) it forces balance, improving the THD of the signal amplification

2) it makes the input stage current draw almost completely constant, thus taking out any PSU problems there might be.

Very efficient decoupling can make point 2 appear less important. No amount of decoupling can balance the signal though.



baronbeehive said:


> IMO the amp could possibly go a bit higher in resolution, soundstage, and bass performance to reach absolute top level, but it's already excellent in these areas now.



Bass performance bottleneck is the output impedance of the amp. Lower gNFB, and you destroy the output impedance. Higher gNFB will tighten bass performance.

What you call soundstage is probably hindered by gNFB. Most people think open loop amps sound more 'airy' and '3D'. I've gone over the harmonics stuff a few times here, big loops cause higher order harmonis, which mask spatial information because it is mostly in the higher register.


----------



## baronbeehive

I've tried the TS 6SL7's and again, fantastic clean sound, I think these work better than the GE's because they have that slight mellow edge which I like without any loss of detail.


----------



## baronbeehive

It's getting mighty crowded... but here's a possible space for the filter MrCurwen! It shouldn't take up much space if and when I decide to do it.




 



On the right is the CCS under the coupling caps.


----------



## MrCurwen

baronbeehive I recommend you construct the B- filter outside the chassis, connect via long wires (yes it's a possible stability risk but sometimes you take risks).

If you find zero sound quality improvements, remove filter. If there is some, then find a place for it inside chassis.

Reason for this is that there is only a low probability for sound quality improvements. There could be some though, not impossible.

No reason to construct experiments inside very crammed chassis.


----------



## baronbeehive

MrCurwen said:


> baronbeehive I recommend you construct the B- filter outside the chassis, connect via long wires (yes it's a possible stability risk but sometimes you take risks).
> 
> If you find zero sound quality improvements, remove filter. If there is some, then find a place for it inside chassis.
> 
> ...



Right, good idea!

I've had time to fully appreciate the upgrades now, and I must say this is stunning!

I did the impedance mod at the same time as putting in the CCS....., and I felt that possibly there was yet another improvement..... but I haven't controlled the volume like I did when I was doing the tests. So with that proviso I would just say that after the sum total of the mods to date the amp now has a power and authority and fullness of sound, noticeable with drums now, for example, and bass has a real heft.

I might have been nitpicking before because I think that the real limitation is probably my headphones which I know aren't the most resolved of headphones, and doesn't have the best soundstage or tight bass, so  I can only say we are at a top level now for me with this amp.

Thanks to MrCurwen and Sonic, I couldn't have done it without their help.
.


----------



## Maxx134 (Sep 15, 2018)

baronbeehive said:


> This might be something for Maxx to look at, I think he wants to do the CCS mod, and he has a stash of tubes to try, I will wait to see what he thinks. He has also heard top level systems which I haven't so he will have a better idea of how far we can go with this.


Yeah I spent alot of money on tubes way back before all the mods, I went thru alot of 12pin types and then moved onto the 6pin tubes to settle on the Tung-sol 6c8g which you all know is equivalent of 6SL7.

Yeah I have heard a few great amps at around the $4k price setting from good friends, so yeah I like other amps as well.

I am almost done relocating to start back on this hobby, and was content with my bias settings, but now after seeing this I also want to try!



baronbeehive said:


> We have a problem here though, the gain, and how high we can go with it. We could probably go a bit higher than the high setting but I don't know how high


I think we should try reduce the NFB after you settle on your top tube choices and also the impedance mod would help offset the output impedance changes, but may need some hard calculations unless you wanna just try experiments.



baronbeehive said:


> I'm very happy with the amp now, it's come alive!
> .


That is a big change in the driver section I noticed from dismal dull stock setting.



baronbeehive said:


> Yes of course!
> 
> I believe Maxx has the 6c8g.


I believe they were a bit more neutral than the 6SL7 type for me.
The Tung-sol was most resolving for me, while other great tubes I tried  (different type) where actually adding more tube sound which I felt was a bit too euphoric.
I wanted a clean sound.

For greater resolve I am looking at tinkering one last time at the output stage. Specifically those WCF caps.

 Also, its sad these  "traditional" designs are so component dependant.
The market is almost all traditional designed, just like some top tube amps I played with.
No real advancement in the tube amp market.

So I am going to try the CCS, then swap out the output tube cathode caps with some others (Muse caps), and then WCF caps I have (are to romantic) for more clear ones .

Then give up lol.

I would say the output tube bias change is also what made a huge difference for me.
I no longer use stock output tube type there either.

So this thread is still not finished , but Baronbehive did a HUGe push with testing here.


Also thanks MrCurwen for your knowledge and input.
 I really think its great and valuable .
I think Sonic amp will be great because of this.


----------



## MrCurwen

baronbeehive said:


> I did the impedance mod at the same time as putting in the CCS



It's best to do one major mod at a time, to know where the possible sound quality differences come from.



baronbeehive said:


> Thanks to MrCurwen and Sonic, I couldn't have done it without their help.



You're welcome. Have you tried the filter yet?



baronbeehive said:


> I might have been nitpicking before because I think that the real limitation is probably my headphones which I know aren't the most resolved of headphones, and doesn't have the best soundstage or tight bass, so I can only say we are at a top level now for me with this amp.



With superb output impedance your current headphones could have top quality tight bass response.



Maxx134 said:


> 12pin types



TV special tubes?



Maxx134 said:


> I think we should try reduce the NFB after you settle on your top tube choices



Bass will become more boomy and overall distortion will rise.



Maxx134 said:


> Also thanks MrCurwen for your knowledge and input.
> I really think its great and valuable .



Thank you.



Maxx134 said:


> I think Sonic amp will be great because of this.



He's on his fourth scratch build amp already I think!


----------



## SonicTrance

baronbeehive said:


> Thanks to MrCurwen and Sonic, I couldn't have done it without their help.


No problem baron!



MrCurwen said:


> He's on his fourth scratch build amp already I think!


You're right! Started my forth build just recently.


----------



## Maxx134

MrCurwen said:


> TV special tubes?


12at7 family variants.



SonicTrance said:


> You're right! Started my forth build just recently.


Nice.
Do you still have tube type preferences?

I gotta get rid of some tubes but there is no section for tubes in this site.


----------



## baronbeehive

Maxx134 said:


> I am almost done relocating to start back on this hobby, and was content with my bias settings, but now after seeing this I also want to try!



Your  bias settings were good, as verified by me LOL! You could possibly have gone down to under 500 ohms for cathode setting. I found that the CCS setting that Sonic chose was good, it preserved the liveliness of the cathode setting I had previously liked best but added a touch of good clean sound which together with some really linear tubes could further enhance SQ.



Maxx134 said:


> I think we should try reduce the NFB after you settle on your top tube choices and also the impedance mod would help offset the output impedance changes, but may need some hard calculations unless you wanna just try experiments.



Could try experiments, I'm a bit skeptical after what MrCurwen said. The soundstage is already excellent  with high gain and I wouldn't want to jeopardise the bass quality.

My top tube is still the GE 12SL7, it has the most clean sound.



Maxx134 said:


> The Tung-sol was most resolving for me, while other great tubes I tried  (different type) where actually adding more tube sound which I felt was a bit too euphoric.
> I wanted a clean sound.



You should get that with the CCS, as clean as we can get with a closed loop design.

I feel we are more or less at the finish now because of the NFB problem, interestingly the other amp is also  closed loop and has superb bass response.

I was looking again at some tube reviews and they have mentioned that the soundstage is largest with GE and Mazda tubes, I wondered if you have tried them yet, I know you are interested in soundstage. If you are interested I can give you the links. They mention 12ax7, which I believe you use, and 6V6 which you use on the other amp.



Maxx134 said:


> So I am going to try the CCS, then swap out the output tube cathode caps with some others (Muse caps), and then WCF caps I have (are to romantic) for more clear ones .



I may do this too, after the improvement they've made to the other amp I think those Kaiseis must be something special.



Maxx134 said:


> I would say the output tube bias change is also what made a huge difference for me.
> I no longer use stock output tube type there either.


Yes, I found that some of this might be due to increased volume, that's why I tried to be careful to keep the volume constant.



MrCurwen said:


> It's best to do one major mod at a time, to know where the possible sound quality differences come from.



Yes, I did the CCS before the impedance mod, but then did the impedance mod when I soldered in the CCS in it's  permanent position.

I felt that the CCS kept the liveliness we now have after the other changes, and the impedance mod added a touch of fullness to the sound and bass heft. But as I said I didn't keep the volume the same for this so I can't be absolutely sure.



MrCurwen said:


> You're welcome. Have you tried the filter yet?



No I'm looking at the connections but no further than that atm.



MrCurwen said:


> With superb output impedance your current headphones could have top quality tight bass response.



Oh, great. Just that the reviews said at the time I bought it, that the HE500 was designed primarily to be musical, not the last word in resolve. For example, they mentioned that the bass was of good quantity if not the most articulate such as was available with the HE6's.



MrCurwen said:


> He's on his fourth scratch build amp already I think!



…..  ???????


----------



## SonicTrance

Maxx134 said:


> Nice.
> Do you still have tube type preferences?


Now I choose tubes based on linearity, gain and looks. I don’t build amps for tube rolling.


----------



## SonicTrance

Maxx134 said:


> I gotta get rid of some tubes but there is no section for tubes in this site.


I’ve seen tubes for sale here https://www.head-fi.org/forums/cables-speakers-accessories-for-sale-trade.6553/page-2


----------



## MrCurwen

Maxx134 said:


> 12at7 family variants.



Are there 12 pin 12AT7 variants? I guess there could be, why not. 12 pin tubes are pretty much all either TV special purpose tubes or radar tubes.



baronbeehive said:


> You should get that with the CCS, as clean as we can get with a closed loop design.



If there were space, and if the loop didn't become unstable, you could add proper plate loads. That would increase linearity very drastically. It's not a subtle change.



baronbeehive said:


> I feel we are more or less at the finish now because of the NFB problem, interestingly the other amp is also closed loop and has superb bass response.



Yes.

If I understand you at all I think your other amp has an OT. That OT is the primary determinant in output impedance, the gNFB simply helps it a bit. In this LD amp the gNFB is the primary motor in providing a decent output impedance. 

If you drive the PRIMARY of an OT with a decently lowish output impedance (some hundreds or tens of ohms is overkill level sufficient), then the OT secondary will have an output impedance lower than 1 ohm. Talk about tight bass then, let me tell you.



baronbeehive said:


> Oh, great. Just that the reviews said at the time I bought it, that the HE500 was designed primarily to be musical, not the last word in resolve. For example, they mentioned that the bass was of good quantity if not the most articulate such as was available with the HE6's.



Yes, that basically means that the coil inside the element has a tricky impedance curve. Flood it with current, and it's as good as any. Of course there are other overall limiting factors in the quality of the headphone, but you would be surprised at what can be dug out of those cans.



baronbeehive said:


> ….. ???????



You originally wrote in the future tense. Sonic has already built a number of amps based on my design principles.


----------



## MrCurwen

SonicTrance said:


> Now I choose tubes based on linearity, gain and looks. I don’t build amps for tube rolling.



Good criteria.

If I may add, maybe also variance. Meaning, trying something different for a new build. Choose a less known tube type and take it as a challenge.


If you have the space, why sell tubes! I have thousands in my shelf. Someday I might need them for a project. Maybe I'll build a hundred guitar amps or something.

As an ironic sidenote, my workhorse uses 6E5P tubes. They've been in the amp about a year now, they see over 10 hours of use every day. I just have the amp on most of the day (turn-on and turn-off cycles are worst on the tubes). Anyway, the op point is pretty harsh for them, especially since the triode mode 'anode' is just a tiny tiny mesh grid.

It's started to get microphonic, sometimes if there is a loud transient in the sound there is an echo after it. It comes from electrostatic movement of the grids and their support structures. 

I've got thousands of tubes in my shelf, but no more 6E5P. I have to buy some more soon or find time to solder another configuration. Maybe EL81, I've got dozens of them and they should be more rugged anyway...


----------



## baronbeehive

Maxx134 said:


> So I am going to try the CCS, then swap out the output tube cathode caps with some others (Muse caps), and then WCF caps I have (are to romantic) for more clear ones .
> 
> Then give up lol.



I just came across this link, don't know if you've see it questioning the Muse caps soundstage:
http://funwithaudio.blogspot.com/2011/12/capacitors-brief-review.html

While I'm here, these are the other links on 6v6's and 6L6's:
https://www.watfordvalves.com/cgi-bin/documents/testreport_45.pdf
https://www.watfordvalves.com/cgi-bin/documents/testreport_44.pdf
https://www.watfordvalves.com/cgi-bin/documents/testreport_36.pdf

The authors are mainly involved in valves for guitar but also mention audio in their reviews. They put Mullards at the top invariably, but also like the GE's for clean, Fender type sound, and also soundstage, and Mazdas which I love on the other amp.


----------



## Maxx134 (Sep 16, 2018)

baronbeehive said:


> I may do this too, after the improvement they've made to the other amp I think those Kaiseis must be something special


I have recently been experimenting with various caps on the Eddie Current Aficionado...


 and it was instrumental to me finding out exactly how the popular different electrolytic (cathode) caps affected the sound.

I ended up removing the Kaisie due to characteristics of slight lower end bloom & richness, and slightly lowered but liquid trebles.
Overall a good choice but not for ultimate transparency.



baronbeehive said:


> I just came across this link, don't know if you've see it questioning the Muse caps soundstage


That was an error on part of the writer.
His negative observations were on the lower FG line, not the Muse (KZ) line.
The Nichion Muse is not affected in soundstage.

Also those impressions did not state the Elna Silmic2, only the original Silmic.
Posts from around the web referring to the Silmic2 better than original, but having treble edge or elevation, so I stayed away.

I also tried the latest Jensen audio grade caps and found them to be clear and authoritive in lower range, but also very dark and so not suitable for the cathode cap position.

So far the Nichion Muse (KZ) cap gave me most neutral sound and clarity so they are used in place of stock caps, and jupiter cap for coupling .

This elevated the Aficionado above the Cayin HA300, and the solid state Benchmark HPA4 amp in different ways.

In stock form, all of these amps are a "lateral-move" preference choice.
All over $3k and with tubes over $4k.
I do not own any so had unique perspective of testing without owner bias.

I could not compare to my own amp as I am not finished my relocating of residence.
But from memory its not far off lol.


----------



## baronbeehive

This is a stab at establishing the connections for the filter. It's the best I can do with my present (lack of) understanding, I hope you can put me right.






the existing connection to B- is disconnected and the new B- goes from M1 drain to CCS instead
the M1 gate stopper is 1K R7
the voltage source is connected to M1 source via 10K R8
the ground connection is indicated by the down arrow
I'm not sure how to connect to the voltage source.


----------



## MrCurwen

V4 is the old B-.

Ground is ground, 0V.

From the CCS point if view simply substitute new B- (output of filter) in place of old B-.

Look up FET pinout from datasheet. From memory it's "the same" as n-channel FETs, simply think of the middle pin as 'drain' (rail voltage, raw voltage input) and right pin as 'source' (output of filter). Left pin should be gate.


----------



## Maxx134

baronbeehive said:


> they have mentioned that the soundstage is largest with GE and Mazda tubes


Yeah I tried the Mazda very nice yes but nothing special.




MrCurwen said:


> V4 is the old B-.
> 
> Ground is ground, 0V.
> 
> ...


Where does the R6 go?
So V4 (old B-) goes to R6 then, correct?
That diagram has V4 typed on the bottom of the symbol..


----------



## MrCurwen

Maxx134 said:


> Where does the R6 go?
> So V4 (old B-) goes to R6 then, correct?



Yes. 

R6 is between unfiltered (old) B- and R8, C3 and M1.



Maxx134 said:


> That diagram has V4 typed on the bottom of the symbol..



Yes? V4 is the whole symbol, not for example for some pin. Ground is ground, so it cannot be input for B- filter.

I should've just left V4 out and put a text there. It's not that complicated.


----------



## baronbeehive (Sep 17, 2018)

The yellow and green symbols in the diagram, for some reason I thought the direction of travel was reversed in the P-channel FET, that's why I crossed out drain and source and reversed them. I think that I was right in the first place, no doubt you will say if I'm wrong.

So the bullet points should be changed as well:

the existing connection between B- and CCS is disconnected and the new B- goes from M1 *source* to CCS instead. The old B- is connected to the filter via R6.

the M1 gate stopper is 1K R7

the voltage source is connected to M1 *drain* via 10K R8

the ground connection is indicated by the down arrow
I will try to knock up a dummy filter out of odd resistors just to get the connections.


----------



## baronbeehive (Sep 18, 2018)

These are the connections for the filter I think....

It's a dummy run so I've labelled the parts:





…. you can tell me where I've gone wrong.


----------



## MrCurwen

Looks about right. Remember to orient the electrolytics so that + terminal is connected to ground. Capacitance values are not important, you can double them or halve them, makes no difference. If you have the space (which you don't, but in theory) C4 could be for example 4µF / 160V MBGO capacitor.

Increasing C3 doesn't really help, it simply increases turn-on time. It's there more as insulation (between raw supply and the active filter FET) and oscillation control than as a filter. C4 shouldn't be too big also since that can increase turn-on time too much.


----------



## baronbeehive

MrCurwen said:


> Looks about right. Remember to orient the electrolytics so that + terminal is connected to ground.



Shouldn't that be negative to ground like in the pic below, or is it different for a filter?





How do I connect the whole filter circuit itself to ground?
Also do I need to connect the 2 points marked with a question mark to complete the circuit or just have the B- coming out from old B- to R6?


----------



## MrCurwen

baronbeehive said:


> Shouldn't that be negative to ground like in the pic below, or is it different for a filter?



Polarized capacitors should always connect the - pin to the more negative side. Which side is more negative here, ground (0V) or the negative rail?



baronbeehive said:


> How do I connect the whole filter circuit itself to ground?



You take a wire, connect one end to the filter module ground, and the other end to the circuit ground. Doesn't really matter where, just as long as it's after the B+ decoupling cap. Any ground within the audio circuit itself is fine.



baronbeehive said:


> Also do I need to connect the 2 points marked with a question mark to complete the circuit or just have the B- coming out from old B- to R6?



No, disregard that part completely. Once again, V4 is just for the Spice simulation. Forget it once and for all. V4 symbolizes the whole of the original B- supply, with a big ripple voltage included. That's all.


----------



## SonicTrance

MrCurwen said:


> Looks about right. Remember to orient the electrolytics so that + terminal is connected to ground. Capacitance values are not important, you can double them or halve them, makes no difference. If you have the space (which you don't, but in theory) C4 could be for example 4µF / 160V MBGO capacitor.
> 
> Increasing C3 doesn't really help, it simply increases turn-on time. It's there more as insulation (between raw supply and the active filter FET) and oscillation control than as a filter. C4 shouldn't be too big also since that can increase turn-on time too much.


Hey, now I recognize it. It's basically a filament reg with a different FET and fixed resistors instead of trimmer. Also much lower value for C4.


----------



## MrCurwen

SonicTrance said:


> Hey, now I recognize it. It's basically a filament reg with a different FET and fixed resistors instead of trimmer. Also much lower value for C4.



Yep. Fixed resistors because output voltage exact value is not important, like a filament voltage is. FET difference reasons are obvious; p-channel for negative side operations and low Rds for high current operations.

Actually it's the same as the plate loads, just a high value for C4.


----------



## baronbeehive

MrCurwen said:


> Polarized capacitors should always connect the - pin to the more negative side. Which side is more negative here, ground (0V) or the negative rail?



Ah, so I've got it the wrong way round in the pic. Of course the negative rail is more negative than 0V.




MrCurwen said:


> No, disregard that part completely. Once again, V4 is just for the Spice simulation. Forget it once and for all. V4 symbolizes the whole of the original B- supply, with a big ripple voltage included. That's all.



OK, just wanted to check that.


----------



## baronbeehive (Jan 24, 2021)

*SMLD MODS: (continued)

Active filter Mod *-  

Nearly ready to fix in place, I might test it outside first but it will fit alright anyway:


----------



## Maxx134

baronbeehive said:


> Nearly ready to fix in place, I might test it outside first but it will fit alright anyway:


Hey Baron is it possible to do only one side (right or left) so you can compare sides ?
Is the expected improvement  just noise floor ?


----------



## MrCurwen

Not adressed to me, but I'll chime in:



Maxx134 said:


> Hey Baron is it possible to do only one side (right or left) so you can compare sides ?



Yes.



Maxx134 said:


> Is the expected improvement just noise floor ?



No, the expected improvement is no difference at all.


----------



## baronbeehive (Jan 24, 2021)

*SMLD MODS: (continued)

Active filter Mod *- 

I decided to go ahead and fit the filter in place, it just might provide yet more improvements! I think everything is the right way round, caps etc. Haven't switched on yet though, if anyone can see why I shouldn't then say so now....


new B- goes out from M1 source to CCS
ground connection goes from opposite end from B- to ground on board which I've taken from the original driver stage cap negative where some of us put the driver stage decoupling caps. I measured this at under .5 ohms.
old B- is the board circuit input from the 5K1, which we used for the CCS without the filter, to filter via R6


----------



## baronbeehive (Sep 21, 2018)

Maxx134 said:


> Hey Baron is it possible to do only one side (right or left) so you can compare sides ?
> Is the expected improvement  just noise floor ?



As MrCurwen said I don't think there will be any improvement, I didn't hear any nasty harmonic distortions needing cleaning up, but they might be hiding there somewhere lol. But it's nice to know the filter is there anyway just in case!

Re: your suggestion to try one side at a time, I tried this originally but was unable to get along with that method so I used my own method of first impressions which works for me. I think you need to practice at that to get used to it, but maybe you could try this when you do your implementation.

Edit: When I tried that method back with the listening tests I found it very difficult to get any impression of soundstage with one ear, also I think my ears are each slightly different so can't compare very easily!

I don't think I will be able to tell any difference atm anyway due to an ear infections so I'll have to put off any impressions for now.


----------



## baronbeehive

….. so in the meantime here's a pic showing how well it fits:


----------



## SonicTrance

Good job baron! It’s nice to see that you’re going at it!


----------



## baronbeehive

Massive relief..... active filter + CCS works! The caps haven't blown... which is always a good sign. I can't say what it sounds like atm though.



SonicTrance said:


> Good job baron! It’s nice to see that you’re going at it!



Yes, I'm a complete nervous wreck lol. Always worried about the circuit board when I make any changes.
.


----------



## baronbeehive

Maxx134 said:


> I ended up removing the Kaisie due to characteristics of slight lower end bloom & richness, and slightly lowered but liquid trebles.
> …..
> So far the Nichion Muse (KZ) cap gave me most neutral sound and clarity so they are used in place of stock caps, and jupiter cap for coupling .
> 
> This elevated the Aficionado above the Cayin HA300, and the solid state Benchmark HPA4 amp in different ways.



I'm very happy with the LD now but if the Nichicon Muse does this to bass and treble compared to the Kaisei's then I'm interested, but I'm not changing anything in the other amp, including tubes!



Maxx134 said:


> I could not compare to my own amp as I am not finished my relocating of residence.



Good luck with your move, I hear that New York apartments are getting mighty expensive lol.


----------



## Sam-Fi

The mk8SE is one of my favorite amps. Keep up the great discussion guys. I'm watching all this intently. 

Interesting mod baronbeehive


----------



## baronbeehive

Sam-Fi said:


> The mk8SE is one of my favorite amps. Keep up the great discussion guys. I'm watching all this intently.
> 
> Interesting mod baronbeehive



Hi Sam-Fi!

Yes the CCS. We've been talking about this for ages, better to make sure the amp is balanced properly than rely just on the tubes to do this.

So what other amps have you  got, and are you modding yourself?


----------



## baronbeehive (Jan 24, 2021)

*SMLD MODS: (continued)

OCC Silver output wires *-  

I made another alteration to the amp at the weekend, and first impressions are very positive!

I swopped out the OCC copper output wires for OCC silver in an attempt to sharpen up the sound so that it was more like the other amp, the APPJ in that respect. I didn't really think that changing the wire composition from copper to silver would have any effect on the component side within the amp.

At first I didn't think there was much difference, maybe a slightly brighter sound perhaps because I noticed some high frequencies that I hadn't noticed before. Well after comparing it with the other amp I can confirm that the sound is indeed brighter in the higher frequencies and that has the effect of opening up the sound somewhat.

I compared the 2 amps, the LD and the APPJ and they are now performing surprisingly similarly. Bear in mind that they are both pretty well top level to me but the main superiority in the APPJ was in bass and treble performace with these having a sharpness that was slightly deficient in the LD by comparison. Well to summarize the 2 amps now:

Resolve - the same
Soundstage - pretty similar, the LD having a slight superiority
Bass - pretty similar, the APPJ possibly slight superiority in articulation but the LD having slightly more heft
Midrange - pretty similar, the LD possibly slightly richer sounding still, but now with a brighter sound in the higher frequencies making it sound a bit more open
Treble - pretty similar, the APPJ possibly slight superiority
Textural details, the same
The differences are now so slight that to all intents and purposes they sound the same which is a very positive result to me.

Bearing in mind the APPJ is a SET headphone amp and the LD is a push pull speaker amp this is quite a surprising result I think. The increase in brightness in the treble frequencies is the right thing for the LD I think because before it was very refined sounding but possibly at the expense of some dynamics and articulation to the sound.


----------



## baronbeehive (Jan 24, 2021)

*SMLD MODS: (continued)

Cathode bypass caps change *-  

Hey Maxx, I just tried those Nichicon Muse KZ's! I was going to wait for  your impressions but as you're still relocating I decided to go ahead and give them a try, very cheap upgrade so what's not to like. First impressions are that we are now in another level of transparency as you said, sharper bass and treble. This on top of my OCC silver wire upgrade and things are really looking good. I will have some time with this to acquaint myself with the new sound and come back with some observations, I really want to be sure about the sound before I comment.

For now though the OCC silver wire upgrade from the OCC copper that I had in originally is highly recommended, the change is most definitely for the better. I think the quality of silver is key here, I don't think the sound would be the same with the cheapo silver plated wire.


----------



## Maxx134 (Nov 9, 2018)

baronbeehive said:


> For now though the OCC silver wire upgrade from the OCC copper that I had in originally is highly recommended


So far from my, what I would call average experience, I feel the headphone cables are more critical than rest.

For internal small signal stage wiring, it seems fine to go with many choices, but for output & especially headphone cable, it gets very demanding.

The only place I felt silver plated was advantageous was in small signal(line level) stage.

The circuit board's output wire to connectors, is very thin & anemic, (and it ends up being an extension of your headphone cable, once plugged in.)

Silver plated for larger signals like headphone cable always gave me slight adverse effects like slight upper spectrum shift, confusion or fatigue, or general change of perception to excessive brightness due to a "change")

 I myself installed OCC copper, but doubled & twisted


Another point I like to mention, is wire type.
 For my best choice of internal wiring of a headphone (an HD800 I had switched internal wire three times besides stock).

 I am convinced the Neotech stranded AG/GD in PE (OCC Silver with slight Gold blend mix, insulated in teflon) was the best wire for that application.

For me it gave the positive  benifits of both silver & copper(!), (even tho it used gold).

I also switched from the excellent cardass solder (which flows smoothest), to the mundorf silver/gold solder, to closer match that wire type.

These cable type benefits were noticeable in that specific application ( in the headphone.)
I do not know if these characteristic ,, carry onto  other applications.




baronbeehive said:


> Hey Maxx, I just tried those Nichicon Muse KZ's! I was going to wait for your impressions but as you're still relocating I decided to go ahead and give them a try, very cheap upgrade so what's not to like. First impressions are that we are now in another level of transparency as you said



Yes it is actually both a good and yet sad thing that the cathode cap position has ability to affect the sound, because of the traditional designs used... Yep...

A general design "reliance" on parts quality, that 99.999% of all current tube circuit designs based on.

Then you have the 0.0001% newer design approach, getting away from those designs, like the SonicTrance design approach (based on Mr.Curwen).

I am grateful to have an opportunity to hear such a design.


----------



## baronbeehive

Maxx134 said:


> The only place I felt silver plated was advantageous was in small signal(line level) stage.
> 
> The circuit board's output wire to connectors, is very thin & anemic, (and it ends up being an extension of your headphone cable, once plugged in.)
> 
> Silver plated for larger signals like headphone cable always gave me slight adverse effects like slight upper spectrum shift, confusion or fatigue, or general change of perception to excessive brightness due to a "change")



Yes, that accords with what Atlas cables themselves said about the interference that you get when mixing different metals in the same cable. I was surprised that the pure silver Neotec wires that I used for the output wires, not the silver plated, had such a good effect at line level but the change was definately for the better over OCC copper, if you value transparency, on the high frequencies which the LD was previously somewhat deficient at. I compared the 2 amps after this change and can vouch for the improvement. I remember you saying that the silver plated output wires added a touch of harshess which is why you added the OCC copper. Some top level amp manufacturers use pure silver internally so I thought about trying it. I was concerned about losing the refined sound the LD has but pure silver is raved about by many. This change alone was an improvement but this was added to by the increased extension in treble that came about with the Nichicon caps.

Having noted the beneficial change with the OCC silver 6 output wires to the line level XLR outputs, I wondered why you stopped there at the XLR lineouts and I am therefore considering completing the wire run from the XLR's on to the headphone socket with 6 more pure silver wires, I think it is perhaps possible to achieve yet more transparency.



Maxx134 said:


> Another point I like to mention, is wire type.
> For my best choice of internal wiring of a headphone (an HD800 I had switched internal wire three times besides stock).
> 
> I am convinced the Neotech stranded AG/GD in PE (OCC Silver with slight Gold blend mix, insulated in teflon) was the best wire for that application.



That's interesting. I also am considering this change to headphone cable, atm I just have the standard HiFiMan copper cable, incidently their silver headphone cable was crap which is why I think you have to go pure silver, or silver/gold. However having changed the output wires this has become less of a necessity now, but maybe in the future I could gain yet another increase in SQ!


----------



## baronbeehive (Nov 10, 2018)

Maxx134 said:


> Then you have the 0.0001% newer design approach, getting away from those designs, like the SonicTrance design approach (based on Mr.Curwen).
> 
> I am grateful to have an opportunity to hear such a design.



Wow, so good luck with your modern amp build!

.

Edit:
I myself would be interested to try a modern tube amp such as that. With the way we've got the LD now it's difficult to conceive of anything better, if pushed I suppose I could imagine something super realistic especially in the soundstage. I've heard a friends top speaker system and the only way it is superior is possibly in neutrality and resolution of very fine detail, but in may respects I prefer my system for SQ.


----------



## baronbeehive (Nov 11, 2018)

As I've lived with the recent changes for a while now I just thought I would summarize where I'm at with the last mods which have been tested against the other amp as a control, because I think it would be interesting to discuss. We've all pushed this baby quite a way from stock... travelled to distant galaxies to seek out new life and new civilisations... and all that.

I highly recommend the last 3 mods: CCS with improved operating point over stock, OCC silver output wires, and the Nichicon Muse KZ cathode caps. This has brought the sound up to a very high level. The CCS has made the sound a touch cleaner, and more lively with the revised operating point, the silver wires made the sound brighter and more transparent, and the Nichicon caps made it sharper and more extended. The combination of the silver wires and the Nichicon caps on the high frequencies has brought the high hats and cymbals into the foreground now whereas before they were very much in the background which is a very positive improvement I think. To compare the 2 amps, my APPJ, and the LD, they now sound very similar, due to the mods, in a good way.

For anyone thinking of doing this the APPJ cost virtually nothing, as amps go, but the cost was doubled with the mods. Both amps now are very highly resolved, the APPJ with the 14AF7 tubes, and upgraded caps has been pushed to a high level. The 14AF7 cost a few dollars, the EL84 Amperex tubes are not expensive. For the LD the Nichicon caps are cheap, the CCS was pretty cheap, the OCC silver wire was a bit more expensive but not much was needed. The LD uses RCA 6AS7G tubes which are cheap, and 12SL7 GE's which cost a few dollars. I see now that the 6SL7 GE's have the same silver round plate construction and so would be preferred because they don't need adapters obviously, but I already had the 12SL7's from the APPJ.

To sum up the sound signature, both amps are very resolved, have good soundstage, good rich open sounding mids, tight bass and extended treble with good textural details. The sound is neutral to warm sounding, I would suggest if you wanted a warmer sound to use OCC copper wires instead of OCC silver, this will make it slightly smoother and less incisive sounding. With the OCC silver the sound is more transparent and sharper.

Needless to say both amps sound fantastic! The amps do have slight differences but nothing major. I wanted to increase the resolution and soundstage of the APPJ and for the LD I wanted to get it to sound more dynamic and lively with a heightened treble and tighter bass and I think I've finally managed to lick the problem! It's a tad brigher and sharper, but not harsh, especially in the high frequencies which is the main reason for the improvement, and transients are very lively. Having the 2 amps was good for comparison especially as the APPJ is a speaker amp.


----------



## MrCurwen

It's been a while since I bummed everybody out so here goes:

If you can hear differences between output wires (or any wires) you have some serious issues in your amp design. Not good.

That basically means you have an unreasonably high output impedance in the 10kHz and over range. NFB should help with that but if you hear a difference, it doesn't. Very troubling.

I've done a tiny bit of RF work, and that's where wire inductance can make or break your circuit. Different wire types have different inductances; look up the specs, calculate impedance from inductance, do your RC low pass calculation and see where you're at with regards to output impedance at 15kHz.


----------



## baronbeehive (Nov 11, 2018)

MrCurwen said:


> It's been a while since I bummed everybody out so here goes:



You're welcome!

I can hear high hats and cymbals now so I'm very happy. I don't think it's affected by the NFB in the design because it's something I've been talking...… boring people about for a while, and I've tried high and low gain, if anything high gain sounds better.

Edit: This is recording dependant, some recordings sound muffled and dull, but the best recordings now exhibit all the frequencies very well, so you're right about the wire inductances affecting this design.


----------



## Maxx134

I believe that's why the wires from input socket in back, to the front of amp (input stage) was of a shielded design.

I replaced this also with a better shielded cable.

Also I see the many red caps to be placed along the output stage (power to ground)for this purpose.

So I do think this amp would have an issue because I did notice a slight difference when I used old wire-wound inductive power resistors at the anode of the output stage.

I since replaced them with non-inductive wire-wound type.

So yeah this I beleive is a common issue that plagues most designers in many circuits and why circuit board trace design is sometims critical.


----------



## Maxx134

baronbeehive said:


> I wondered why you stopped there at the XLR lineouts and I am therefore considering completing the wire run from the XLR's on to the headphone socket with 6 more pure silver wires, I think it is perhaps possible to achieve yet more transparency


Agree, from the output jacks to the front headphone socket is a good idea which I actually did replaced as well..

All my wiring was replaced.
The only issue here was space concerns.
No stock internal cabling was left inside. All was removed because they are all of a very low grade.
On unit I had, none looked to be copper(!).

Especially the wiring from the PSU power transistors to the board.
They were brittle and can  break off solder joint very easily.

After inspection, the wire has what looks like a high tin content. No copper at all (visually, maybe it was the dark stuff).

Although the input wiring was nicely shieled, it too was of a poor tin composition and strands looked dirty inside(copper?).

I replaced with a "shielded" silver plated cable, as that was the best shielded that I saw the purpose called for.

I suppose you can use other cable, but as MrCurwen states there can be interference.


----------



## baronbeehive (Nov 17, 2018)

Maxx134 said:


> Although the input wiring was nicely shieled, it too was of a poor tin composition and strands looked dirty inside(copper?).
> 
> I replaced with a "shielded" silver plated cable, as that was the best shielded that I saw the purpose called for.
> 
> I suppose you can use other cable, but as MrCurwen states there can be interference.



No, I haven't been able to find any copper wires either.

I might try the shielded wire, or maybe experiment with this or the silver. I only intend to go from the XLR outputs to the headphone socket, I'm not replacing the wires from the inputs, because I imagine the benefit will be greatest to the signal travelling from the tube sockets direct to the output sockets, ie after amplification. I would rather stick with what I have already tried, ie. silver wires than use shielded copper as you did, at least in this area, because of what I have already found though.

But the improvement to be had just from changing wires and cathode caps to Nichicons is such that it has now solved the remaining things that needed improving with the amp IMO all in one go, which is surprising. The Nichicons were a really great find of yours!

Edit: The wire inductance problem on the LD must have been known by Sword-Yang which is probably why he suggested the wire upgrade as part of the factory mods originally.


----------



## baronbeehive

Maxx134 said:


> Agree, from the output jacks to the front headphone socket is a good idea which I actually did replaced as well..
> 
> All my wiring was replaced.
> The only issue here was space concerns.
> ...



This looks like another area of potential upgrade that I've not bothered about, maybe I should. I've still got existing, resoldered, wire to the transistors.

Did you notice any sonic improvements with your wire changes? I imagine the input wires would benefit from upgrading to make sure the signal from the DAC is clean.

After the improvement I've had with the silver output wire, this looks like it might be worth doing for all stock wire as you said.


----------



## klnglim

Maxx134 said:


> Agree, from the output jacks to the front headphone socket is a good idea which I actually did replaced as well..
> 
> All my wiring was replaced.
> The only issue here was space concerns.
> ...




Hi Maxx! It's been a long time, I m still troubleshoot and hard work on my MK8SE. I had completed several times unsoldered, resoldered and cleaned the board, unfortunately till now still fail to turn it on. 
Left meter light on with "0" reading, Right meter no response at all, of course no sound at all, furthermore unstable voltage reading everywhere and sometimes one 120R/5W resistor near power supply smoke. 
Now I try to do PCB on board prototype connection, have already done half way, the whole board seen wire spaghetti all around (By the way, never give up! Just keep on search for the issues)  LOL

May I ask can *Tube NOS Voskhod 6N1P-EV replace those 6H30P tube?
Here's the website  https://www.partsconnexion.com/nos-6n1p-6h30-vacuum-tubes.html*


----------



## MrCurwen

No, not at all. 6N1P has anode resistance of 11k, and 6N30P has anode resistance of under 1k. They are meant for completely different things.


----------



## MrCurwen

Why do you need to replace the 6N30P?


----------



## klnglim

MrCurwen said:


> Why do you need to replace the 6N30P?


I didn't want to change 6H30p, just want to get some knowledges differential among those tubes


----------



## MrCurwen

When looking for an equivivalent tube, first look at anode resistance (plate resistance, rp). It's expressed in ohms. For the tube to work properly in the circuit as intended, the rp should be not too far off. 1k and 11k are worlds apart.

Second look at µ or mu. It should be in the same area. 20 and 30 can be close enough, but 11 and 30 are not. 8 and 20 probably are not. This is not as critical though as the rp.

Of course the physical constraints of the tube; which base, pinout, heater specs etc need to be considered. 

If you are concerned with fidelity (low THD), you should of course make sure the new tube has as good curves (or better) as the one being replaced. The goodness of the curves is determined by how evenly the grid lines are speced. Pick a horizontal line at a reasonable current level and go from left to right on that line. See how evenly the grid lines are spaced.

Of course often the curves are drawn poorly, and the real tube performs much better. This is quite common, especially with non-audio tubes like TV sweep tubes. The curves were not considered important so they were made just "close enough, good enough".


6N1P is a small signal tube, use for input stage. 6N30P is low rp low µ output tube. Use anti-oscillation precautions, both were meant for radio frequency duty also.


----------



## baronbeehive

klnglim said:


> Hi Maxx! It's been a long time, I m still troubleshoot and hard work on my MK8SE. I had completed several times unsoldered, resoldered and cleaned the board, unfortunately till now still fail to turn it on.
> Left meter light on with "0" reading, Right meter no response at all, of course no sound at all, furthermore unstable voltage reading everywhere and sometimes one 120R/5W resistor near power supply smoke.
> Now I try to do PCB on board prototype connection, have already done half way, the whole board seen wire spaghetti all around (By the way, never give up! Just keep on search for the issues)  LOL



Hi klnglim!

I see you are still trying to sort out your amp. I can't be much help as I don't know exactly what you've done but I would go back to basics and double check a few things:

your traces new and old - your repairs to the board look excellent
your parts - are the specs the same. It is easy to misread some parts names, for example I mistook a .68R for a .68K resistor, also I used the wrong type of diode, both of which could have stopped the amp working. Are your parts all up to spec, the right way round etc.
wires all connected correctly.

I double and triple checked mine recently and still missed a few things!

All pretty basic but a mistake at this stage will be critical. It is difficult to know what's wrong when you have done so much.

When you've got the amp up and running you must complete all the upgrades to date, that way your amp will be pretty spectacular lol!
.


----------



## baronbeehive

MrCurwen said:


> If there were space, and if the loop didn't become unstable, you could add proper plate loads. That would increase linearity very drastically. It's not a subtle change.





MrCurwen said:


> If I understand you at all I think your other amp has an OT. That OT is the primary determinant in output impedance, the gNFB simply helps it a bit. In this LD amp the gNFB is the primary motor in providing a decent output impedance.
> 
> If you drive the PRIMARY of an OT with a decently lowish output impedance (some hundreds or tens of ohms is overkill level sufficient), then the OT secondary will have an output impedance lower than 1 ohm. Talk about tight bass then, let me tell you.





MrCurwen said:


> Yes, that basically means that the coil inside the element has a tricky impedance curve. Flood it with current, and it's as good as any. Of course there are other overall limiting factors in the quality of the headphone, but you would be surprised at what can be dug out of those cans.



I am interested in what you have said here with these points, could you go into a bit more detail?


----------



## klnglim (Nov 24, 2018)

baronbeehive said:


> Hi klnglim!
> 
> I see you are still trying to sort out your amp. I can't be much help as I don't know exactly what you've done but I would go back to basics and double check a few things:
> 
> ...



Now I try other method, use good quality jumper cable as prototype style, there are a lot spaghetti wiring around, this project will finish soon.
All the resistors have changed to Dale & Mills, some electrolytic caps replaced with Nichicon audio grade, only power supply caps remain unchanged
Some Diodes have replaced with 5 Watts instead of 1 Watts, 2 rectifier changed to brand new 2W10 model
Mundolf EVO & EVO oil replace all WIMA caps, coupling and WCF
WIMA MKS2 replaced all the mini caps artound op-amp and gain switch
Overall Can be said 90% of components  include gain switch, op-amp, potentiometer, fuses, Voltage regulator, MOSFET, NPN PNP transistors, headphone protector relay & 2 sets uA meter inside this tube amp is brand new
May be sound like I m a bit over spend all those parts, actual reason is I can get those parts replacement with very low price.
Because of those super cheap low cost parts, so why not replace all with brand new, right?
Beside new parts replacement, the ground shortage issue inside the PCB also had already been fixed.
The board have already been cleaned with Methal Spirit few times as well. The reason I seldom use ISO Alcohol is the board felt a bit sticky after dry and uncomfort with finger touch. 
Hopefully, If this amp is successful to turn on, of course I will post to share.
If still no luck cant turn it on, then I'll have to work and study harder again until successful result show
Have to learn from Edison spirit : There are no failure in entire life but only to learn and find the best way to work it out! That means never give up! LOL


----------



## baronbeehive (Nov 24, 2018)

klnglim said:


> Now I try other method, use good quality jumper cable as prototype style, there are a lot spaghetti wiring around, this project will finish soon.



Sounds like you have a handle on the situation!

Do you have a new chassis for the all that wiring, at least this method will allow easier fault finding and rectification.

I don't know why you have fluctuations in power, the only thing I can think of is a broken connection, or diode or transistor faults. Do you have the correct diode in for the headphone relay for example.

I hope you can get help to fix this soon.

.

Edit: Quote by *Albert Einstein*: “Failure is success in progress”


----------



## klnglim (Nov 24, 2018)

baronbeehive said:


> Sounds like you have a handle on the situation!
> 
> Do you have a new chassis for the all that wiring, at least this method will allow easier fault finding and rectification.
> 
> ...


May be u are right about the Diode broken connection, since last time I found one of the 100V/5Watts Diodes which near transistor PNP trace was disconnected, I guess that's the reason to cause one of 120R resistor began smoke and right side uA meter malfunction then damaged.
All 3pin in/output have replaced with silver twisted cable and later all power cable from transformer will be rearranged as those are the worst thin crap quality cable inside the amp.
I had repainted the chassis with few level of shinny piano black finish colour as well as clear polish spray paint protection, so there will be no more LD MK8SE logo, no more any number or letter word will be seen
By the way, this whole tube amp machine and all the component has been tear apart, solder/desolder and PCB board taken in /out a lot of  times by my own hand.
The original PCB board is quite strong and really good quality except all the copper traces & lines 
are too weak, come off very easily
Since started troubleshoot from the sparkly short suddenly seen till now whole machine already been tear apart and  re-assembly, the cost of spending actually not much (roughly around AUD100 I guess) but a lot of clock time wasted. I also learned a lot of electronic knowledge and very familiar about almost every single piece of component inside this amp. (I even can tell every parts has been soldered inside the PCB. LOL)


----------



## Maxx134

baronbeehive said:


> I would rather stick with what I have already tried, ie. silver wires than use shielded copper as you did, at least in this area, because of what I have already found though


Yeah but for me I wanted change that input wire so best shielded was a silver plated. I only recommend for input stage.
For output cable it was best to with no plated types.



baronbeehive said:


> Did you notice any sonic improvements with your wire changes?


No.
No sonic changes for those power tramsistor wires as expected. 



klnglim said:


> May I ask can *Tube NOS Voskhod 6N1P-EV replace those 6H30P tube?
> Here's the website*


No.
Easiest way to check tube comparability & similarity is Google the data sheet.



klnglim said:


> Hi Maxx! It's been a long time, I m still troubleshoot and hard work on my MK8SE. I had completed several times unsoldered, resoldered and cleaned the board, unfortunately till now still fail to turn it on.
> Left meter light on with "0" reading, Right meter no response at all, of course no sound at all, furthermore unstable voltage reading everywhere and sometimes one 120R/5W resistor near power supply smoke


Very obvios sign of PSU problem.
Most likely not full voltage.
Must test voltage.
Key areas of concern are break in the trace from top board to bottom, completing a center groundpoint from big power resistor area to the power transistor area.

Most likely failure are diode burn & resistor burn when the PSU not have proper voltage (half the PSU power reaches the power transistor area).

The second meter will never kick in if the PSU is at fault.



klnglim said:


> I didn't want to change 6H30p, just want to get some knowledges differential among those tubes


For you I only recommend rolling driver tubes, not power tubes, but there are differences still with the power tubes from the sovtec (more neutral) compared to the other ones (more bassy).



klnglim said:


> May be u are right about the Diode broken connection, since last time I found one of the 100V/5Watts Diodes which near transistor PNP trace was disconnected, I guess that's the reason to cause one of 120R resistor began smoke and right side uA meter malfunction then damaged


This area always a concern.
If the trace ia not broken from that area to the 4 big caps & power resistors (full voltage should be measured), then  the issue usually solid-state failure(diode or power transistor).
Also check proper "NPN/PNP placement and wiring.


----------



## klnglim (Nov 28, 2018)

Maxx134 said:


> Yeah but for me I wanted change that input wire so best shielded was a silver plated. I only recommend for input stage.
> For output cable it was best to with no plated types.
> 
> 
> ...


PNP NPN, diodes and resistors brand new checked,however this time both meter light on togather, left side reading 30 and right side over maximum,
then the right side meter damage  when I shut off the amp straight away.
After found the problem and fixed for the cause of meter damage, I tried to turn on the amp again, another problem come again, both meter light on togather and only left meter read 30, right meter read nothing, then suddenly smoke come out from PSU caps 330uF/250V..
I turn off the amp again then later checked on all those diodes and resistors, none of those components have any error.
I had also already checked all the wiring, cant find any shortage and no error connection.
Unfortunately I cant take any voltage reading as I turn off the amp immediately when seeing smoke out from the caps 
Have any idea what is wrong or why the PSU caps smoke?


----------



## Maxx134

klnglim said:


> Have any idea what is wrong or why the PSU caps smoke?


Yes
Heat & smoke is usually from the resistor.
Caps usually bulge and blow up so be careful.

So check to see that those  polarized caps are in the right direction, as well as those diodes.
I personally never seen smoke caps .
If you upgraded the diodes higher at watt, check also  they are 100v I recall or they may not act like zener at designed voltage.


----------



## Maxx134

PSU pic:


----------



## baronbeehive (Dec 1, 2018)

klnglim said:


> PNP NPN, diodes and resistors brand new checked,however this time both meter light on togather, left side reading 30 and right side over maximum,
> then the right side meter damage  when I shut off the amp straight away.
> After found the problem and fixed for the cause of meter damage, I tried to turn on the amp again, another problem come again, both meter light on togather and only left meter read 30, right meter read nothing, then suddenly smoke come out from PSU caps 330uF/250V..
> I turn off the amp again then later checked on all those diodes and resistors, none of those components have any error.



I think you have a problem on the left side as well, that left meter reading of 30mA doesn't sound right.

What diode are you using for the headphone relay?

Edit: While you have the amp switched off it might be an idea to work backwards from the output XLR's to see if there is any grounding issue, grounded wire connections are very difficult to see.


----------



## klnglim

baronbeehive said:


> I think you have a problem on the left side as well, that left meter reading of 30mA doesn't sound right.
> 
> What diode are you using for the headphone relay?


From PSU, I Have changed Diodes 15V, 36V & 100V from 1 Watts to 5 Watts power handling, both relay are using Diodes1N4007.
Both rectifier remain the same 2W/10 & transistors are MJ15024/MJ15025 (All brand new and no problem so far)
All the meter nearby red caps are original WIMA MKP10 0.22uF/250V.
All meter & caps polarity installed & checked are 100% correct. 
Yesterday try to turn on, both meter light up togather but left meter read from 30mA jump to Max after a few seconds and right meter OmA.
When seeing the meter act unnormal, I straight turn off the amp immediately to avoid the current damage my meter again.
After a while, I desoldered & checked PSU every each of component, have just found one capacitor 100uF/450V leg is broken from deep inside, not sure whether is this cap cause an issue yet? 
The funny thing is everytime I try to turn on the amp always cause me feel scarry & worry as both meter act strangely, make myself confuse & question why?


----------



## baronbeehive

klnglim said:


> From PSU, I Have changed Diodes 15V, 36V & 100V from 1 Watts to 5 Watts power handling, both relay are using Diodes1N4007.
> Both rectifier remain the same 2W/10 & transistors are MJ15024/MJ15025 (All brand new and no problem so far)
> All the meter nearby red caps are original WIMA MKP10 0.22uF/250V.
> All meter & caps polarity installed & checked are 100% correct.
> ...



That rectifier diode sounds right from memory, that is the one I misread from the board markings.

Yes, every time I switch on after modifications I have a nervous breakdown lol!

Have you switched on again after your cap leg issue? I also had this issue which caused me some problems similar to you with meter readings going haywire. When you bend cap or resistor legs don't bend them near to the cap body or else they may break.

If you still have problems you could try checking the grounding issue I mentioned in the previous post, also check the resistances of everything while your amp is off. Can help to highlight the problem areas.


----------



## klnglim

Maxx134 said:


> PSU pic:




 

HI Maxx, from picture above, can I upgrade those 2 caps 330uF/250V to 1000uF/250V ? Cause I have those big caps size fit perfectly


----------



## baronbeehive

klnglim said:


> HI Maxx, from picture above, can I upgrade those 2 caps 330uF/250V to 1000uF/250V ? Cause I have those big caps size fit perfectly



Yes, and they will be better.


----------



## Maxx134

klnglim said:


> The funny thing is everytime I try to turn on the amp always cause me feel scarry & worry as both meter act strangely, make myself confuse & question why?


If both meter come on then definitely error in the area near the time delay for the second meter.
It is at bottom corner.
Check that it is same exact value as the original tall cap.

Also,
Check the relay by that rectifier (that switch power) for a mistake in resistors connection that is under it.




klnglim said:


> HI Maxx, from picture above, can I upgrade those 2 caps 330uF/250V to 1000uF/250V ? Cause I have those big caps size fit perfectly


Bigger cap will cause slight current surge for the NPN&PNP, but they should be able to handle it if you upgraded them to the latest versions which I assume you did as they do not make the original power transistors anymore..
You should be ok since you upgraded the watts of the doides & resistors..

Make sure the Dale wirewound resistors have continuity with unit off and ohmmeter.

Then you need to check the bridge rectifiers for proper rectification because your cap got burned(?)
Whichever one that was should be check & or replaced.


----------



## klnglim (Dec 4, 2018)

Maxx134 said:


> If both meter come on then definitely error in the area near the time delay for the second meter.
> It is at bottom corner.
> Check that it is same exact value as the original tall cap.
> 
> ...





baronbeehive said:


> Yes, and they will be better.


Hi guys! I would like to introduce capacitors discharger which is very useful for DIY members,
this built is come from my own idea several months ago, it just need multimeter voltage test, connect with a piece of resistor in parallel so to show the caps is fully discharge, 100% accurate and safe.
It costs cheap, simple and easy to make, all you need is multimeter, 2 pair banana plugs and a piece of 56K/5 Watts resistor. (Picture example below)


----------



## klnglim (Dec 5, 2018)

Maxx134 said:


> If both meter come on then definitely error in the area near the time delay for the second meter.
> It is at bottom corner.
> Check that it is same exact value as the original tall cap.
> 
> ...


Yes those PNP/NPN transistors was upgraded to higher voltage handling 250 volts, model number 15024 & 15025
Those 2 rectifier is brand new same as original model 2W/10
Those 15V, 36V & 100V diodes was upgraded to 5 watts
All resistors around PSU have upgraded to DALE wirewound 5W, 7W & 10W
The PSU caps 2 x 100uF/450V (Brand New Nichicon), 2 x 1000uF/250V (Brand New Nichicon), 4 x 1200uF/200V
Those 2 relays are brand new and 2 diodes upgraded to 1N4007
Those 2 meter caps remain unchanged WIMA MKP10 0.22uF/250V
I have just changed all those 0.1uF, 0.22uF & 1uF RC filter to red WIMA 100V voltage handling.
As I have soldered & desoldered components on board too many times, many traces was seriously damaged, so I have used some insulated copper & Teflon wire as jumper wire.
Now, I m keep on learning during installation & non stop do double or even triple check every component connection to make sure no short circuit and error grounding.
By the way, after several months of hard working and learning, about 80% of components from this amp had been upgraded and replaced brand new and is going to be completed soon. After so much time had been wasted, the failure of this mod has become a terrible nightmare, even though feel exciting, scary & nervous but I still believe this amp will successfully turn on to show its sound quality improvement in one day. 

Lesson Learn from the mistake and Failure is the Beginning of Success LOL


----------



## baronbeehive

klnglim said:


> ... both meter light on togather and only left meter read 30, right meter read nothing, then suddenly smoke come out from PSU caps 330uF/250V..



Sorry when I said your 30mA looks wrong, I forgot you are using 7236's in which case the reading is OK for the left channel.


----------



## klnglim

baronbeehive said:


> Sorry when I said your 30mA looks wrong, I forgot you are using 7236's in which case the reading is OK for the left channel.


I have just found the both driver tube socket (12at7) has ground short issue, I guess this is the other reason cause the amp not working


----------



## Maxx134

Make sure it's not the caps charging when you use your ohmmeter meter you have to leave it connected for a while


----------



## klnglim

Maxx134 said:


> Make sure it's not the caps charging when you use your ohmmeter meter you have to leave it connected for a while


Hi! What do u think about the amp's  Spaghetti wire from picture below? Are there any risk of short circuit, dangerous of high heat, burn smoke smell or over current explosion?
So far I have never seen anyone will do this way and I guess no one will agree or accept this type of ugly mod as well. LOL


----------



## MrCurwen

klnglim said:


> Hi! What do u think about the amp's Spaghetti wire from picture below?



What's the reason for this?



> Are there any risk of short circuit



Some risk.



> dangerous of high heat



Very unlikely.



> burn smoke smell



Use teflon wire in the future.



> or over current explosion?



Absolutely not.



> So far I have never seen anyone will do this way and I guess no one will agree or accept this type of ugly mod as well. LOL



PCBs, never again. P2P forever. Sorry not useful comment.


----------



## klnglim (Dec 13, 2018)

MrCurwen said:


> What's the reason for this?
> 
> 
> 
> ...


Yes, those are Teflon wire and some Enamel copper wire on the op-amp gain resistor.
The reason is because most of trace on this board are damaged and seriously broken.
I understand shouldn't work this way, just want to get some opinion & advice.
I think is time to learn P2P and prototype method


----------



## SonicTrance

klnglim said:


> Yes, those are Teflon wire and some Enamel copper wire on the op-amp gain resistor.
> The reason is because most of trace on this board are damaged and seriously broken.
> I understand shouldn't work this way, just want to get some opinion & advice.
> I think is time to learn P2P and prototype method


I’m sorry but that board just look like... well...
If you ever get that amp working I’d be impressed let’s put it that way. Please don’t take offense I don’t mean to be rude but it looks like you have set that board on fire, more than once! 

I also see a mills 5w cathode resistor that looks burnt. Those should not look like that.


----------



## klnglim

SonicTrance said:


> I’m sorry but that board just look like... well...
> If you ever get that amp working I’d be impressed let’s put it that way. Please don’t take offense I don’t mean to be rude but it looks like you have set that board on fire, more than once!
> 
> I also see a mills 5w cathode resistor that looks burnt. Those should not look like that.


I had tried to fix many times however still never work, as the components had been taken in & out a lot of times during troubleshooting
and cause the PCB trace damaged.
The Mills resistor is not burnt, actually is the surface get heat from soldering gun accidentally, all components have been checked 
before put into PCB.


----------



## MrCurwen

If you like this amp a lot (and it's a decent amp I'm sure), why not make a scratch build of it?

That would work as an excellent springboard towards a DIY hobby (since you've already got one foot in that hobby), and then you'd have a working backup amp always, and a good enough reference amp for your future endevours.

Get a bit bigger chassis, and go P2P. Only portion that really 'needs' to be on PCB is the servo section. Rest is just fine P2P if done properly.

It's not that complicated a schematic.The Modern amp designed by me and presented here by Sonic is much more complicated and it can be done P2P no problem. Take it as a challenge.


----------



## klnglim

MrCurwen said:


> If you like this amp a lot (and it's a decent amp I'm sure), why not make a scratch build of it?
> 
> That would work as an excellent springboard towards a DIY hobby (since you've already got one foot in that hobby), and then you'd have a working backup amp always, and a good enough reference amp for your future endevours.
> 
> ...


Yes, I have studied P2P quite some times already, looked for samples of pictures & videos everywhere, learned how other people design their works.
However I still can't find any suitable chassis yet, beside that, most of the spare parts and component I already have in hand


----------



## MrCurwen

This should do it: https://www.hammfg.com/part/1444-17123?referer=1236

I don't know about your local availability, but it's cheap enough with overseas shipping. It should be available locally also; if Hammond has a direct sales rep even in Finland (Uraltone, 100m from my home), I'm sure you do as well.

If one is not enough, get two; one for PSU, one for signal. Final looks are determined by your own efforts, I am personally satisfied with just a coat of spray paint and spray laquer. Maybe some wood around it.


----------



## klnglim

MrCurwen said:


> This should do it: https://www.hammfg.com/part/1444-17123?referer=1236
> 
> I don't know about your local availability, but it's cheap enough with overseas shipping. It should be available locally also; if Hammond has a direct sales rep even in Finland (Uraltone, 100m from my home), I'm sure you do as well.
> 
> If one is not enough, get two; one for PSU, one for signal. Final looks are determined by your own efforts, I am personally satisfied with just a coat of spray paint and spray laquer. Maybe some wood around it.


I have just ordered one exact same size as original chassis,plan to extend its height https://au.element14.com/hammond/1444-14103/enclosure-chassis-alum-unfinished/dp/2493435
Thanks for the info anyway


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## Maxx134

Spaghetti wiring is no problem and indeed you should have twisted your heater wiring as twisting is good.

As long as resistor work it but also be careful not to scratch surface of those wire-wound resistors as that can break them.


----------



## Maxx134

There is a thru-hole connection in middle of power supply that gets easily broken when replacing parts, leaving the PSU broken.
It is in the center connections and was talked about here with another member..
So check you have continuity in PSU from the big caps to before the diodes section in center trace.


----------



## Maxx134

That looked like alot of unnecessary wiring as the board trace still there...


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## baronbeehive (Dec 16, 2018)

Maxx134 said:


> That looked like alot of unnecessary wiring as the board trace still there...



Yes, but I bet he's learning a lot about the amp, and his soldering work looks much improved! Yes P2P would be the way to go though eventually. Less hassle.



Maxx134 said:


> There is a thru-hole connection in middle of power supply that gets easily broken when replacing parts, leaving the PSU broken.
> It is in the center connections and was talked about here with another member..
> So check you have continuity in PSU from the big caps to before the diodes section in center trace.



I think you mean the pads on the big caps we put in. I think Sonic broke his and I did the same. We were all too keen to do the mods to bother to desolder properly LOL and get every last bit of solder out before pulling out the cap.

Hey Maxx when will you be able to put those Nichicon caps in, they really make a big difference, both bass and treble are improved nicely!

Edit: I've even got a half decent soundstage with my HE-500's now, after all the latest mods!


----------



## Maxx134

baronbeehive said:


> Hey Maxx when will you be able to put those Nichicon caps in, they really make a big difference, both bass and treble are improved nicely!


I started to fix another friend's Cary 300b tube amp before I finish work on mine.

I own two amps in my pic that still need a bit more tunning to squeeze final improvements to compare to others, but it is unclear what my future plans are with them and what will be my next amp.


----------



## klnglim

baronbeehive said:


> Yes, but I bet he's learning a lot about the amp, and his soldering work looks much improved! Yes P2P would be the way to go though eventually. Less hassle.
> 
> 
> 
> ...


Just almost finish PSU prototype, still need upgrade from  the picture?Can anyone give simple info about grounding?
I m just a bit unsure about grounding


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## baronbeehive (Dec 19, 2018)

klnglim said:


> Just almost finish PSU prototype, still need upgrade from  the picture?Can anyone give simple info about grounding?
> I m just a bit unsure about grounding



I don't know about that in your prototype PSU.

Only issue I had was one of the wires from the tube sockets to the output jacks was grounded when compared with the other wires and the other channel. This is the only way I found out. So I suggest you do that and look at resistors also to check the correct end is properly grounded etc.

Edit: You could also look at the LD schematics.


----------



## baronbeehive

Maxx134 said:


> I started to fix another friend's Cary 300b tube amp before I finish work on mine.



So how does the Cary compare with the other amps you've heard, the Eddie Current and the Cayin? All great amps so I hear.



Maxx134 said:


> I own two amps in my pic that still need a bit more tunning to squeeze final improvements to compare to others, but it is unclear what my future plans are with them and what will be my next amp.



Really happy with my 2 amps now!


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## SonicTrance

klnglim said:


> Just almost finish PSU prototype, still need upgrade from  the picture?Can anyone give simple info about grounding?
> I m just a bit unsure about grounding


If you look at the schematic here you'll see that both B+ and B- rails share a ground (0 V)





You also need to connect the power transistors. Don't see them in your pics?


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## Maxx134 (Dec 30, 2018)

I have not mentioned this, but my MK8se has had a stubborn lingering issue I have not address all summer because of personal issues of moving to new location.

I know the problem is a cold-solder joint in one of the left side op-amp chips.
I had solved it temporarily with replacement chip, then bending pins, then trying to heat the socket pins from the top, because I did not want to remove the board as it is such a pain in the *$$ to do with all mods, but anyways I still plan some last changes.

1- I plan to upgrade the cathode caps to to Nichion KZ / Muse at larger size so meters won't dip at high volume with planars (remember I have the lesser current MK8)

2- Then the caps WCF caps to jupiter (expensive) or actually the "Clarity Cap CMR"

3- install the impedance selector for using the HD800 optimally again (currently is not set at stock setting but at a low impedance setting)

Since I have manually tuned my driver stage, I am holding back on the CCS for the driver cathode.

4- last is to compare the unit to see if I can get it to perform like SonicTrance new "Oblivion" amp (which is a single ended design) .

In truth I already know the answer, from recent upgrading of other amps.
I know I can get the performance level up to top-level, but these designs will always be "colored" in some tube (or capacitor!) way...

The plan, is to try and help another member single out just what are the most desired harmonic traits that tubes give which make a person love a thicker sounding amp, like say a 300b amp.

My LDMK8SE is tuned to not have any tube "flavor" at all, but still cannot get away from having tube characteristics.
For example, its bottom end is a tiny bit wolly and rich compared to a totally clean SS amp, or SonicTrance new amp.

The "modern amp" build of SonicTrance amp is truley ALL it was said and speculated to be.
We are talking true MODERNIZING the tube amp market which is HEAVILY old school designed.


So thats the plans for the new year lol.

I also have to verify today's recent improvement in my new HD800 experiment.
Measuring is key to solidifying listening observations.


----------



## SonicTrance

Maxx134 said:


> 4- last is to compare the unit to see if I can get it to perform like SonicTrance new "Oblivion" amp (which is a single ended design) .


Just so there's no confusion. Oblivion has SE input stage but balanced LTP output stage.


----------



## baronbeehive

Maxx134 said:


> I have not mentioned this, but my MK8se has had a stubborn lingering issue I have not address all summer because of personal issues of moving to new location.
> 
> I know the problem is a cold-solder joint in one of the left side op-amp chips.
> I had solved it temporarily with replacement chip, then bending pins, then trying to heat the socket pins from the top, because I did not want to remove the board as it is such a pain in the *$$ to do with all mods,



Yes, I've done this too and mostly got away with it. However when I do remove the board I find either the joint is flooded with solder which could touch nearby joints, or might be an issue with the trace not making good contact, so I too at some point will have to make a couple of repairs to make good properly. I intend to do this when I finish putting in the OCC silver output wires to the headphone socket.



Maxx134 said:


> 1- I plan to upgrade the cathode caps to to Nichion KZ / Muse at larger size so meters won't dip at high volume with planars (remember I have the lesser current MK8)



I think we are both agreed on this that the nichicons improve the bass and treble in the following ways: the bass bloat that was there before is gone and the bass is tightened up considerably while still having the desired heft so that I can at last say that I'm happy with bass response, but it will never reach the very highest level I don't think, which isn't a problem. Also the treble is now more extended and sharper which makes treble transients stand out more so that high hats are more prominent and plectrum strikes on the guitar come through with good textural detail. 

I used 330uF's btw, good enough because I don't listen at high volumes.... I have speakers for that! Also the 1000uF's are larger.

The effect of the change is to elevate listening to a new level of pleasure and realism, though that included the change from OCC copper output wires to OCC silver internally as well which I believe increased transparency and neutrality also.



Maxx134 said:


> The plan, is to try and help another member single out just what are the most desired harmonic traits that tubes give which make a person love a thicker sounding amp, like say a 300b amp.



I can't remember which new 300b amp that a member mentioned which was reviewed recently did not have the usual 300b characteristics at all, on the contrary it was apparently a very fast, neutral sounding amp so, as we've been saying for sometime now the circuitry is key to understanding how a particular tube works in the amp.


----------



## Maxx134

SonicTrance said:


> Just so there's no confusion. Oblivion has SE input stage but balanced LTP output stage.


I really like this approach of a single ended driver stage, rather than worrying about dual triode differences and balance input circuits. 
Balanced output is always desireable because many preefer to use XLR balanced cables.
So that topology I really like.


----------



## SonicTrance

Maxx134 said:


> Balanced output is always desireable because many preefer to use XLR balanced cables.


And, more importantly, it also sounds better than the SE output stage!


----------



## MrCurwen

baronbeehive said:


> The effect of the change is to elevate listening to a new level of pleasure and realism, though that included the change from OCC copper output wires to OCC silver internally as well which I believe increased transparency and neutrality also.



I'm sorry I can't help myself.

How is it that changing the material of the internal wiring changes audible outcomes? What causes this in your opinion or knowledge?


----------



## baronbeehive

MrCurwen said:


> I'm sorry I can't help myself.
> 
> How is it that changing the material of the internal wiring changes audible outcomes? What causes this in your opinion or knowledge?



I was as suprised as you, I didn't expect to hear any difference due to the internal wires... but I did have expectations regarding silver, ie. better high frequency sound. But my finding was observational, by comparing the LD to a fixed reference.... the other amp.

Because we are comparing 2 wires of identical construction and only a different conductor we can rule out most of the factors which might affect sound such as microphony, topology, capacitance, conductor types eg OFC or OCC and so on.

I think conductor resistance is the main relevant force, we are talking about similar types of wires for a given cross sectional area but different materials, so I would put it down to lower resistance of silver, so a more efficient signal, if that is the case. If I was comparing say solid conductors with silver plated copper or stranded I could say that solid conductors would be better for high frequencies due to larger area in the wire , the signal meets with less resistance,  but I am not comparing different types only different conductors.

Oh... I just looked up a couple of things and have found that the difference in resistance is small, only 2 ohms higher for copper... *but...* silver has the highest thermal conductivity and the highest number of free electrons therefore making it a better conductor.

I don't know about inductance for the higher frequencies but I suspect, as you said before, that inductance of the silver wire could lower impedance at that high frequency band, I don't know however if inductance varies in the same types of wires but with different conductors ie. copper vs silver.


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## MrCurwen

When you talk about "higher frequency band" you get that you're actually talking about radio frequencies? Not even bat territory, but radar and FM radio and such? Lower conductivity in these regions is BETTER for a HIFI amp, not worse.


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## baronbeehive (Jan 9, 2019)

MrCurwen said:


> When you talk about "higher frequency band" you get that you're actually talking about radio frequencies? Not even bat territory, but radar and FM radio and such? Lower conductivity in these regions is BETTER for a HIFI amp, not worse.



Yes of course, I've heard cases of RFI interference with the amp, therefore RFI needs to be taken into account at the 20khz limit for human hearing also, as the conduction, or induction of RfI could cause noise from various sources nearby. Therefore it would be necessary to block this RFI by various methods such as shielding, which Maxx mentioned.

But regarding the better high frequency sound I heard due to the silver wires this obviously isn't affecting it, presumably the same would occur with the copper wires I had in before, neither the copper nor the silver wire  was shielded.

So if lower conductivity is better at high frequencies how is silver wires leading to increased perception of these high frequencies?

Edit: Seems like wire conductivity is a complicated subject from what I can see!


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## gavincurtis (Jan 10, 2019)

Hi guys, my first post here at this forum.

I am using my little dot Mk6+ with the ESS SABRE DAC that is built into my LG G7 phone.  I added a non-balanced to balanced adapter to my amplifier as shown.  Being a noob, I learned that even though my headphones are balanced, when using the RCA inputs, only one side of each amplifier push-pull is used...what a waste!!  So I did what the manufacturer should have done.... install the proper converter.





I am using Texas Instrument's DRV134 precision audio balanced driver chip and powering off the +15v AND -36v rails from the amplifier.  The DRV134 is actually powered off +12V and -12V rails provided by the regulators as shown.  The chip also offers additional gain so the conventional non-balanced RCA signal is raised to that of balanced, allowing me to keep the gain of my Mk6+ to a minimum.  I will be adding a DPDT switch so when I use the balanced input, the signal will not back-feed into the output of the DRV134.




After 8 hours of use, my power resistors for the regulated +15v and -36v rails were very discolored.  So that part of the faulty design of the amp had to be upgraded to handle the additional current draw of the DRV134.

The 4.2K resistor I replaced with a 10 watt 1.5K resistor and increased my zener diode to a 1.5 watt.  The -36V rail resistor I replaced with a 1.2K 10 watt resistor and upgraded to a 5 watt -36V zener.  Now I have sufficient power for the DRV134 and more stability for the MK6+namplifier's op amps. I have chassis mount 20W versions to mount on the base plate on order to clean things up.


One problem I am encountering regardless of tubes I install.... my right channel drops all the way to ZERO..... still plays...but voltage drop across the .27 ohm resistor for the mA meters verifies my meter is working.  I have bias and it makes no difference.  This was a factory problem before my modification.  Any ideas?  Moving tubes around, even trying my Tung Sols.... nothing changes on the right.  It hovers between 0-20mA.  The left channel is 60-80 mA.  The meters themselves are good, so this is something in the circuitry.

On order are all new .22uF capacitors in case one is leaky... my capacitors in my amp appear to be pulls...the are all different lot numbers, even the WIMA housings vary from unit to unit.  They do appear to be genuine WIMA, just a mishmash of manufacturing dates.?.  Replacing with new and also installing PPS (Polyphenylene Sulfide) capacitors for the 1uF coupling stage.

Also, being that I am not a tube expert, what are the bias voltages supposed to typically be from the Op Amp to get me in the ballpark?  I can go from one extreme to the other on the trimmer and current drain does not change, but at some point the audio does drop out.  Tube Noob here and I have yet to see left and right meters agree.


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## baronbeehive (Jan 11, 2019)

gavincurtis said:


> After 8 hours of use, my power resistors for the regulated +15v and -36v rails were very discolored.  So that part of the faulty design of the amp had to be upgraded to handle the additional current draw of the DRV134.
> 
> The 4.2K resistor I replaced with a 10 watt 1.5K resistor and increased my zener diode to a 1.5 watt.  The -36V rail resistor I replaced with a 1.2K 10 watt resistor and upgraded to a 5 watt -36V zener.  Now I have sufficient power for the DRV134 and more stability for the MK6+namplifier's op amps. I have chassis mount 20W versions to mount on the base plate on order to clean things up.
> 
> ...



Hi gavincurtis!

I used to use my ipod as source single ended and it sounded pretty good, but a lot of bass and treble boost!

I'm not familiar with that type of adapter you're using but were those power resistors discoloured before you used the adapter because this is a common problem. Did you smell burning?

The upgraded wattage resistors is what we've done on this thread but why did you replace the 4.2k with a 1.5k?

The burnt resistors in the power stage could be a cause of the bad meter readings on the right channel. Was it like this from new?

Were the burnt resistors just on the right channel or both?

The other meter reading of 60mA would be right for 6AS7G's.

Also when does the audio drop out, after a while or after you adjusting the trimmers?

Sounds to me like a bad connection somewhere on that right channel, has it been soldered recently?


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## gavincurtis (Jan 12, 2019)

baronbeehive said:


> Hi gavincurtis!
> 
> I used to use my ipod as source single ended and it sounded pretty good, but a lot of bass and treble boost!
> 
> ...






The resistors were discolored before I did any modifications (I also had the bad reading on my mA meter BEFORE my mod as well).  The sound is definitely superior with the addition of the unbalanced to balanced converter.  Correct me if I am wrong, but if you are using your amp strictly on RCA inputs alone aren't 2 of your 4 output tubes are doing nothing?  You have to use the balanced inputs and have balanced wired headphones to take full advantage of your investment?  Problem with some RCA non-balanced to XLR balanced coverters out there is they use cheap electrolytic capacitors in the signal path and fail at subsonic frequencies, which is what the Mk6+ is all about being able to do.  The DRV134 is a DC coupled device and has no capacitors of any kind in the signal path.  Just the power rail capacitors for stability.  I tried to attach photos, but I don't understand how that works here.

The 4.2 K resistor was the one that discolored as well as the other one used for negative voltage rail of -36 volts.  They used 2 8.4 K in series in my amp.  But when you run 3 watts of resistors at 3 watts like the Chinese love to do in their designs.....you get very hot resistor that will not be long for this world.  Those resistors are not part of the sound, they are part of the power supply for the op amps that bias the outputs.  You need +15V and a -36V.  To power my DRV134, I need more current.  When using the stock resistors and zeners, the voltage dropped down to 5V and -3V.... so I upgraded the zener diodes to higher power units and lower value resistors to increase the current delivered to the more capable zeners.  That way the voltages are stable at +15V and -36V, even with the DRV134 at full load in the system.  Also the heat of the resistors is away from those adjacent electrolytics.

No other resistors in my amplifier are discolored, just the ones near the zener diodes in the power supply section.  The big 330 ohm units are perfect as are the 300 ohm.  The solder is not terrible, but the WIMA capacitors are all from different years and seem as if they were used or pulled from something else as well as a couple being deformed where the leads enter (too hot of soldering).  Just in the slight even that one is compromised, I have brand new WIMA replacements as well as 1.0uF PPS audio coupling capacitors.

My left channel audio drops out after the amplifier has about 30 minutes of use.  The mA meter doesn't change on that side...just no audio.  The right channel seems to sound okay, albeit a little thin and meter shows 0-30 mA and moves around over time...often hovering around 10mA.  Swapping tubes does absolutely nothing!  The needle will be completely at zero at times, yet the channel works.... the meter itself and its shunt resistor resistance/voltage drop did collaborate they are working correctly and the problem is in the circuit.

What is the typical bias voltage for these output tubes?  Just a ballpark... and can I damage the output tube if I wander too far off the correct bias voltage during adjustment?

Anybody know what the chip is in the center of the circuit board?  Output protection?  The schematic provided at this forum was a life saver, but is there any additional of the power supply, power up delay and protection circuits?

Thanks!


----------



## Maxx134 (Jan 13, 2019)

gavincurtis said:


> nothing changes on the right. It hovers between 0-20mA. The left channel is 60-80 mA. The meters themselves are good, so this is something in the circuitry.


Yes, the meters corresponding to the bias setting only.



gavincurtis said:


> . Replacing with new and also installing PPS (Polyphenylene Sulfide) capacitors for the 1uF coupling stage


Not sure where on the board yiu see 1uf unless its PSU stage.



gavincurtis said:


> can go from one extreme to the other on the trimmer and current drain does not change, but at some point the audio does drop out. Tube Noob here and I have yet to see left and right meters agree.


There is first mistake.
The trimmers by the opamps are NOT for any bias settings.
They are only for DC servo, so you won't get any small DC offset at the output of your headphones, because since this is a "OTL" (output transformerless) output, the tubes ouput going direct to your headphones without any caps or Transformers in between.

I am getting away from the point that you messsed up and must now adjust the trimpots (trimmers) to get zero DC offset between pos &neg output of each channel..
Get DC meter and adjust. Both trimmers can be elevated or lowered equally to cause the corresponding meter for that channel to move up or down slightly by a few points.
A final test for zero dc is having your headphones on and listening for any tiny click/pop sound as you insert into the balanced socket (not the single-ended as that by default always pops in any unit).




gavincurtis said:


> The resistors were discolored before I did any modifications (I also had the bad reading on my mA meter BEFORE my mod as well).


The resistors are usually cheap made china parts so its normal to see a burn which also meansthe resistance probably not the same anymore, but have not to do with your meters anyways.
If They are by the diodes, they are in series and taking current because of opposite what your thinking, not enough of a load on them(!)
Due to either the low bias of one side, or if you ever turned the unit in without the power tubes installed.

When there isn't enough load, the diodes acting as zener try to Control the higher voltage drop and so they take on more current which burn resistors.



gavincurtis said:


> Correct me if I am wrong, but if you are using your amp strictly on RCA inputs alone aren't 2 of your 4 output tubes are doing nothing?


Sorry wrong.
You basically went thru alot of trouble to make that front end balanced, but it doesn't matter to the driver stage.

It is ONLY at the single ended output jack that you are getting half the tubes output.
Yet it IS true that the balanced inputs give a different stronger better sound anyways.




gavincurtis said:


> The 4.2 K resistor was the one that discolored as well as the other one used for negative voltage rail of -36 volts. They used 2 8.4 K in series in my amp.


You mean they were side by side so in parallel, correct?
Cheap way for them to solve the wattage issue without using larger sized resistors that take up space.



gavincurtis said:


> No other resistors in my amplifier are discolored, just the ones near the zener diodes in the power supply section.


Yeah just replace them.



gavincurtis said:


> My left channel audio drops out after the amplifier has about 30 minutes of use


It is probably because of your opamp DC servo circuit.
Check the setting of the trimpots and then check sockets of the opamps, as sometimes they loose connection.
Also check your tiny dip switch gain setting by flipping up and down a few times to clear that.




gavincurtis said:


> The right channel seems to sound okay, albeit a little thin and meter shows 0-30 mA and moves around over time...often hovering around 10mA. Swapping tubes does absolutely nothing! The needle will be completely at zero at times, yet the channel works..


The issue here is your meter is telling you your bias is off.

The main culprit are the anode and cathode resistors, as they set the bias in this type circuit.
You need to replace those anode resistors especially as when they burn the value goes up, decreasing the current, so decreasing your bias, so posing less load on the PSU, so causing the zeners to overwork, to cause the resistors there to burn, to give more heat and burn to then give you stress and grey hair, to you not getting sleep, to affecting your personal life, to affecting those around you, wich may add to global warming, which then I get as a snow storm approaching next weekend...





gavincurtis said:


> Anybody know what the chip is in the center of the circuit board? Output protection? The schematic provided at this forum was a life saver, but is there any additional of the power supply, power up delay and protection circuits?


No chip in middle.
There is a relay in middle to cut sound, and another relay by bottombot beginning of PSU stage to delay power to ouput stage when first turned on.


----------



## gavincurtis (Jan 14, 2019)

Thank you for all the help.  No problem for me to readjust the zero set point.  I have all the tools and knowledge for that.  I have built and designed solid state amplifiers of many kinds, but tube theory I am not overly familiar with.  Now that I know what the op amps are doing (I figured either bias or voltage offset), I will proceed with setting them using proper equipment that I have and zero out the voltage offset that I have obviously messed up.

I would have never gone into the thing, but it stopped working after 8 hours of use.  Upon opening my amplifier, all of the WIMA caps were old pulled units....plier marks on them and all different lot numbers/date codes.  Even the colors of red varied from deep red to light pink and sizes varied...my amp was apparently built from a used parts pile.

I have replaced them all with brand new WIMA now.  The 1.0uF coupling capacitors were 4 variants of wima (all 4 were different sizes) I replaced with 1.0uF KEMET audio PPS now.  I upgraded all zeners to 5 watt units to keep their temperatures in the long life zone.  Chinese engineers don't care about reliability and always run components way too hot.


*"Sorry wrong.
You basically went thru alot of trouble to make that front end balanced, but it doesn't matter to the driver stage.

It is ONLY at the single ended output jack that you are getting half the tubes output.
Yet it IS true that the balanced inputs give a different stronger better sound anyways."*

Thank you for that knowledge.

So does the front end tube also double as a phase inverter when using single ended RCAs as the inputs?  In the schematic, the RCA only goes to one "input" side of the front end tube which goes to the appropriate output tube.  Only the balanced XLR input uses both inputs of the front end tube.  So when using only one input of the front end tube, does the other half of the front end tube take on the function as a phase inverter for the 2nd output tube?  Otherwise, that 2nd output tube just sits idle wouldn't it?  When mine was working and using the RCA inputs, I noted no obvious difference in output between my headphones with their balanced cable (4 pin XLR) and same headphones using the 1/4" unbalanced plug harness.

With my DRV134 modification, there is a significant improvement now between the 4 pin XLR harnes and the weaker sounding 1/4" unbalanced.....as I would expect.

It would have been nice if a $1000 retail price boutique headphone amplifier that people would potentially modify/service came with a real owners manual, proper schematics and theory of operation! Instead, I received a folded pamphlet of useless and upside down printed nonsense.  VERY disappointed with my Mk6+ so far and regret selling my Mk4.
*
"No chip in middle.
There is a relay in middle to cut sound, and another relay by bottombot beginning of PSU stage to delay power to ouput stage when first turned on"
*
On my amplifier there is indeed a chip in the center of the circuit board.  It is a 9 pin SIP device with 3 capacitors around it with its audio cut out relay.  I suspect that is the DC offset protection perhaps....?

That reminds me, does your Mk6+ have fuses installed?  I have jumper wires....no fuses in mine... completely bypassed with those 2 jumper wires.

I would like to replace them with fuses as I have some pretty expensive headphones.   What are the fuses supposed to be?  100mA?  150mA? something other?  Any reason why the "factory" would bypass the fuse protection?  I got a lemon it seems, unless they are all like this.

One final question, are there any rules regarding powering up without tubes?  I am now going to check my bias resistors as I still have the right channel bias current averaging 15mA or so... it goes all over the place actually.  Those resistors of interest are the higher power 330 ohm and 300 ohm ones correct?

Thank you again all for your help, time and knowledge.


----------



## baronbeehive (Jan 17, 2019)

gavincurtis said:


> I would have never gone into the thing, but it stopped working after 8 hours of use.  Upon opening my amplifier, all of the WIMA caps were old pulled units....plier marks on them and all different lot numbers/date codes.  Even the colors of red varied from deep red to light pink and sizes varied...my amp was apparently built from a used parts pile.
> 
> I have replaced them all with brand new WIMA now.  The 1.0uF coupling capacitors were 4 variants of wima (all 4 were different sizes) I replaced with 1.0uF KEMET audio PPS now.  I upgraded all zeners to 5 watt units to keep their temperatures in the long life zone.  Chinese engineers don't care about reliability and always run components way too hot.



Sorry to hear about your quality control problems. None of us to my knowledge have had any complaints about the amp build quality, in fact my amp, an early version had high quality Dale resistors installed. Where did you get your amp?

The amp operates a White Cathode Follower circuit, check out page 1 to see how that works.



gavincurtis said:


> On my amplifier there is indeed a chip in the center of the circuit board.  It is a 9 pin SIP device with 3 capacitors around it with its audio cut out relay.  I suspect that is the DC offset protection perhaps....?



I think that is the headphone protection circuit.



gavincurtis said:


> That reminds me, does your Mk6+ have fuses installed?  I have jumper wires....no fuses in mine... completely bypassed with those 2 jumper wires.
> 
> I would like to replace them with fuses as I have some pretty expensive headphones.   What are the fuses supposed to be?  100mA?  150mA? something other?  Any reason why the "factory" would bypass the fuse protection?  I got a lemon it seems, unless they are all like this.



Yes someone on the thread had jumper wires also. The fuses are 2 fuses in the middle are 0.5amp.



gavincurtis said:


> One final question, are there any rules regarding powering up without tubes?  I am now going to check my bias resistors as I still have the right channel bias current averaging 15mA or so... it goes all over the place actually.  Those resistors of interest are the higher power 330 ohm and 300 ohm ones correct?



Not really. But you definitely have a problem with the circuit that's showing the 15mA, possibly down to the resistors you mention, especially the 330 ohm ones. I would do a thorough check on the connections in that circuit.

Hope that helps!

Edit: Voltages at the anode 330R's should be about 101v and 76v at either side of the resistor, and at the cathode 330R's should be about -104v and -80v.


----------



## Maxx134

gavincurtis said:


> Even the colors of red varied from deep red to light pink and sizes varied...my amp was apparently built from a used parts pile.


Those caps are not critical to be same as they there to prevent any high freq oscliation.



gavincurtis said:


> So does the front end tube also double as a phase inverter when using single ended RCAs as the inputs?


Sadly no, thats why you noticed a louder better sound with balanced input.
Probably a decision to leave out in order to compete in price with market.



gavincurtis said:


> On my amplifier there is indeed a chip in the center of the circuit board. It is a 9 pin SIP device with 3 capacitors around it with its audio cut out relay. I suspect that is the DC offset protection perhaps....?


Yes I forgot about this as well.




gavincurtis said:


> That reminds me, does your Mk6+ have fuses installed? I have jumper wires....no fuses in mine... completely bypassed with those 2 jumper wires.


I didn't remember see this on mine but do remember buying three replacement fuses .
the main fuse on mine is inside the AC socket.



baronbeehive said:


> Yes someone on the thread had jumper wires also. The fuses are 2 fuses in the middle are 0.5amp.


I need to see pics its been so long I haven't looked inside mine lol.


----------



## Sage Encore

Hi Guys,
I changed out my fuses 2 x 500mA and 1 x 3A (3.15A actually) to SR 20 Quantum fuses and its really very good. I have a Simaudio HAD 430 as well and it too uses this fuse. Immaculate, I love what they do. Thanks for reading.


----------



## baronbeehive

Sage Encore said:


> Hi Guys,
> I changed out my fuses 2 x 500mA and 1 x 3A (3.15A actually) to SR 20 Quantum fuses and its really very good. I have a Simaudio HAD 430 as well and it too uses this fuse. Immaculate, I love what they do. Thanks for reading.



I've got cheapo fuses lol!

Hey, Sage Encore how are you getting on with your LD, are you still using those Russian Melz tubes and what do you think about them? Are they the cheap ones?


----------



## Sage Encore (Jan 30, 2019)

baronbeehive said:


> I've got cheapo fuses lol!
> 
> Hey, Sage Encore how are you getting on with your LD, are you still using those Russian Melz tubes and what do you think about them? Are they the cheap ones?


Hi sir,
I love my LD, sometimes I do think of getting something "Branded", I turn her on and wonder why the hell I would want to, she is so lovely, especially with the SR 20 Quantum fuses now after the upgrading I did with the Caps and resistors. I am rocking some Melz 6H8C and 6H9C tubes now. Looking to get the hole version of the 6H9C Metal base (Melz factory). These Russian babes play in a league of their own. My Ken-rad and Sylvanias are collecting dust now, that's how good they are. Exceptional value for money. They are not exactly cheap, these MELZ ones, the Hole version goes for about USD200 a pair and the metal base ones go for USD60-80 a pair made in the 50s". Foton ones are the cheapo ones, but they are not bad, not bad at all.

Get the MELZ factory ones, I tried the Foton ones as well and they are not bad, but the MELZ metal base is really very good, best 6SL7 I have heard thus far. You should give it a try, and ya, change those fuses out, u will be mightliy impressed I am sure.


----------



## Maxx134

Wow i totally overlooked these Melz tubes!
 The metal base ones from the 1950s just has to be very good (!)
Reminds me of the rare Sylvania metal base(!)

I also see there is a 6H7C tube type which has common  cathode.
That is basically what this amp does on the circuit board it combines the cathode, so that tube can be used too.
 

Dam i need to try those tube type next as I have currently settled on some tungsol...
That will be my last upgrade.
I must replace my cathode caps and cathode folllower caps to have last weakness parts replaced.
Hopefully this will elevated it further.
This amp will compliment my current amp, (made by SonicTrance) the "Oblivion" (aa hybrid) amp, which is a highly accurate & almost colorless amp.

Remember our MK6 & MK8  amp design responds & relies tremendously on upgrades, more so than other amps I upgraded, but climbs in performance the most I have seen.
The other amps I worked on also benefited from upgrades, as they also use  traditional designs.
I upgraded a stax amp, a tube speaker amp, an EC Aficionado, the small APPJ PA1502A, and I forget what else lol.
Currently troubleshooting a Cary 300b amp, but after that will come back to this amp.
I think this thread still needs updating on last mods done, but the thread starter (Ridge78) is MIA.


----------



## baronbeehive (Feb 1, 2019)

Maxx134 said:


> Wow i totally overlooked these Melz tubes!
> The metal base ones from the 1950s just has to be very good (!)
> Reminds me of the rare Sylvania metal base(!)
> 
> ...



Yes, somebody mentioned these way back on the original LD thread, ozaudio I think, whatever happened to him!

Pretty sure these are the type mentioned here: http://www.audiotubes.com/6sn7.htm

I also came across a thread discussing them and there are a few variations some of which may or may not be genuine, I can't elaborate anymore on that other than they have the valve type, a number, 1578, on the glass envelope. The participants were sure that some were genuine and others were not.

Unfortunately these are that other type of Russia tube…. expensive!




Maxx134 said:


> Dam i need to try those tube type next as I have currently settled on some tungsol...
> That will be my last upgrade.



Those Tungsols are way too expensive for me, I still like my GE's, very transparent, maybe not the last word though. This amp as it is now seems to make any tube sound good



Maxx134 said:


> I must replace my cathode caps and cathode folllower caps to have last weakness parts replaced.
> Hopefully this will elevated it further.
> This amp will compliment my current amp, (made by SonicTrance) the "Oblivion" (aa hybrid) amp, which is a highly accurate & almost colorless amp.



It will believe me, it doesn't really have a weakness anymore, it's lively, transparent, great frequency response, a joy to listen to basically

I think you might need to take a look inside your LD again if you can't remember if it has fuses or not LOL, so go on and dust those cobwebs off. You just might be putting off opening it up afraid what you might see in there….sphagetti wire, hot glue... loads of the stuff, not a pretty sight haha!!
.



Maxx134 said:


> Remember our MK6 & MK8  amp design responds & relies tremendously on upgrades, more so than other amps I upgraded, but climbs in performance the most I have seen.
> The other amps I worked on also benefited from upgrades, as they also use  traditional designs.
> I upgraded a stax amp, a tube speaker amp, an EC Aficionado, the small APPJ PA1502A, and I forget what else lol.
> Currently troubleshooting a Cary 300b amp, but after that will come back to this amp.
> I think this thread still needs updating on last mods done, but the thread starter (Ridge78) is MIA.



Yep, the recent mods have pushed the envelope tremendously to the point where I no longer am interested if it sounds good.... I know it does so I think we should get those mods posted sometime,

Edit: This is the thread I was talking about where they discuss whether the Melz 1578's are genuine: https://www.diyaudio.com/forums/tub...entic-russian-military-1578-vacuum-tubes.html

Incidently I just came across a quote from skylab where he says that the Melz 1578's are "massively overrated."

…. and if you're interested in the Melz tubes there's also this thread which goes into this subject: https://www.audioasylum.com/cgi/t.mpl?f=tubes&m=212173 …. and a lot of mass hysteria over who is right and who is wrong... obviously they all think they're right.... the usual stuff!


----------



## Maxx134

Thanks for links!


baronbeehive said:


> if you can't remember if it has fuses or not LOL,


Oh, I remember because I remember paying alot for the replacement fuses!
 
Lol


----------



## MrCurwen

W...why?


----------



## baronbeehive

Not guilty...!


----------



## Maxx134

That was a "rabbit hole"..
The box said "never compromise" lol.
Lets forget that topic! Lol


----------



## baronbeehive

Maxx134 said:


> That was a "rabbit hole"..



I've been down a few of those in my time... and managed to find my way out LOL.

Hey, the important thing is this thread is based on theory, experimentation and observation, that is it's great strength. I am confident of all our findings. I think we've managed to avoid all…. well most of the pitfalls!


----------



## Maxx134

I just have not done a comparison of the fuse.
I decided not to go there because the purchase was enough.
It was for piece of mind to cover all the bases of either real or Psychoacoustic perceptions, which in turn becomes real to the mind lol.
Just knowing I covered all the bases was enough at the time because that's when I first started on this hobby of amp upgrading.


----------



## gavincurtis (Mar 22, 2019)

Still having bias problems with the right channel.  It goes from 5mA to 40mA and anywhere between.  Does not change when I swap tubes.  Even my new Tungsol graphite tubes behave the same.  Each tube on the right is exactly 1/2, so they are malfunctioning identically on the right channel.  So one tube will draw about 2.5mA is all, left or right position on the right channel with 8 brand new tubes.

Replaced all resistors and capacitors I thought were critical to the bias, but nothing has changed.  I did zero out the offset voltages etc.  Replaced the meter shunt resistors even.  Verified meters are 100% good.

Using Nichicon MUSE audio grade electrolytics.  Non-inductive Mills resistors.  Polyphenylene Sulfide audio film capacitors in the audio coupling.  These are as close to polystyrene capacitors as I will ever get and keep the bottom cover plate on.  All new WIMA capacitors on the power rails.  Power rails are correct and stable.  Premium Teflon silver plated wire instead of the chinesium grade stuff that was originally in there.  Going to connect the volume motor to a remote control eventually, just trying to figure out how to add a jack for it on those thick 1/2" beams of aluminum and keep it all clean.

The blue PCB mod that I added to my amp is a unbalanced to balanced converter so I can use my LG G7 with the ESS SABRE DAC and still take advantage of the bridge-tied push pull.  it is a crime to only use 2 of the 4 output tubes on a $800 headphone amp otherwise.  I had to increase the zener diodes to higher power units and add heatsinks to keep them cool to the touch.  Also changed the zener current resistors to 1K and 1.5K respectively to supply the additional current required by the DRV134 converter chips and their voltage regulators.  Those resistors are no longer on the PCB and installed on the bottom panel to assist with heat dissipation, although they are not hot at all.

So any ideas as to what else I can replace to stop the problem with my right channel? There isn't much left original on my amp anymore.


----------



## Maxx134

Very impressive job.
You must set your attention on the bias circuit though.
An improper setting comes from the voltage values  at the tube.

Compare & make note of the voltage values at each tube  (anode, cathode & grid ) to ground.

You will find that the offending tube area has different voltages.
Then you check the resistors to it, because they are what affecting the bias.
Could be an improper value resistor or a mistake, or a broken circuit board where the resistor was pushed in.
Do not rely on that board as the pads around the holes will break when removing/replacing resistors...


----------



## baronbeehive (Mar 23, 2019)

gavincurtis said:


> Still having bias problems with the right channel.  It goes from 5mA to 40mA and anywhere between.  Does not change when I swap tubes.  Even my new Tungsol graphite tubes behave the same.  Each tube on the right is exactly 1/2, so they are malfunctioning identically on the right channel.  So one tube will draw about 2.5mA is all, left or right position on the right channel with 8 brand new tubes.



The problem I have is understanding why the meter readings keep varying over time. You obviously still have a problem with that right channel. I would check the 2 big black PSU resistors circled, also you could check all the resistor values, including the gain resistors, circled, for that right channel and compare with those on the left. Also did you try switching the opamps from left to right channel.

I understand that you say the power rails are fine, did you check the voltages with those I gave previously for anode and cathode values. If they are good then the problem must lie further in the circuit around the tube sockets and on to the outputs, possibly an intermittent grounded wire connection or something.





Edit: You say the meters are good, it's not likely to be a problem anyway if the right meter varies, must be a channel imbalance because the right meter has never read correctly, you could just check the resistance between the 2 terminals. To check readings I would wiggle the component while taking readings, this might show up an intermittent connection.

Otherwise do as Maxx says and concentrate around the tube sockets, and check and compare readings from the pins.


----------



## Maxx134 (Mar 23, 2019)

baronbeehive said:


> The problem I have is understanding why the meter readings keep varying over time. You obviously still have a problem with that right channel. I would check the 2 big black PSU resistors circled, also you could check all the resistor values, including the gain resistors, circled, for that right channel and compare with those on the left. Also did you try switching the opamps from left to right channel.
> 
> I understand that you say the power rails are fine, did you check the voltages with those I gave previously for anode and cathode values. If they are good then the problem must lie further in the circuit around the tube sockets and on to the outputs, possibly an intermittent grounded wire connection or something.
> 
> ...


There problem with checking to many areas is that your not "zeroing-in"  in on the problem and will get frustrated.

He needs to post & compare his voltages against yours.
The reason for variance over time is heat related .
Also, the board is thin tracing and easy to have issues at points where one side suppose to connect to the other.


----------



## baronbeehive

Maxx134 said:


> There problem with checking to many areas is that your not "zeroing-in"  in on the problem and will get frustrated.



Yeah!

He's got a few things to check atm, strange that he's had this problem from the time he got the amp, probably something simple but overlooked though.


----------



## SonicTrance

gavincurtis said:


> The blue PCB mod that I added to my amp is a unbalanced to balanced converter so I can use my LG G7 with the ESS SABRE DAC and still take advantage of the bridge-tied push pull. it is a crime to only use 2 of the 4 output tubes on a $800 headphone amp otherwise. I had to increase the zener diodes to higher power units and add heatsinks to keep them cool to the touch. Also changed the zener current resistors to 1K and 1.5K respectively to supply the additional current required by the DRV134 converter chips and their voltage regulators. Those resistors are no longer on the PCB and installed on the bottom panel to assist with heat dissipation, although they are not hot at all.


The mk6 will still operate in push pull with all output tubes when you use SE input. The LTP input stage splits the phase. It's when you use SE output there's no push pull.


----------



## gavincurtis

SonicTrance said:


> The mk6 will still operate in push pull with all output tubes when you use SE input. The LTP input stage splits the phase. It's when you use SE output there's no push pull.



Interesting.  I was told that the input stage does not split the phase.  I am a solid state guy so this is alien tech to me, so be patient with my abilities.

I'll break out the O-scope and find out once and for all as well as get voltages on all the tubes and will report back.


----------



## gavincurtis

baronbeehive said:


> The problem I have is understanding why the meter readings keep varying over time. You obviously still have a problem with that right channel. I would check the 2 big black PSU resistors circled, also you could check all the resistor values, including the gain resistors, circled, for that right channel and compare with those on the left. Also did you try switching the opamps from left to right channel.
> 
> I understand that you say the power rails are fine, did you check the voltages with those I gave previously for anode and cathode values. If they are good then the problem must lie further in the circuit around the tube sockets and on to the outputs, possibly an intermittent grounded wire connection or something.
> 
> ...



Next time I post, I will have thorough voltage readings to report.  Are voltage readings to be taken with headphones connected and no audio signal?


----------



## SonicTrance

gavincurtis said:


> Interesting.  I was told that the input stage does not split the phase.  I am a solid state guy so this is alien tech to me, so be patient with my abilities.
> 
> I'll break out the O-scope and find out once and for all as well as get voltages on all the tubes and will report back.


So, you dont believe me? But yeah, it’s always a good thing to look at the signal on an oscilloscope. I made a post a while back when I replaced the cathode resistor with a CCS. That mod makes a huge difference especially when using SE input.


----------



## MrCurwen

Not smart to use a converter to get balanced signal. Just add the CCS tail, you will always have balanced signal then. As theory would predict, and as measured and posted here.

Basically that's what's inside the converter; an extra unity gain buffer stage with a CCS tail. Why have an extra stage muddying up the signal when you can eliminate it.


----------



## baronbeehive

gavincurtis said:


> Next time I post, I will have thorough voltage readings to report.  Are voltage readings to be taken with headphones connected and no audio signal?



No need to connect headphones, there is a load resistor for protection. Yes, no audio signal, you will probably have to take readings over time if you are getting varying readings. As Maxx said probably due to heat and cold solder joints. That should show where your problem is.

Also important to keep tubes in when needing to switch on the amp for whatever reason such as taking voltages.


----------



## Maxx134 (May 5, 2019)

gavincurtis said:


> So any ideas as to what else I can replace to stop the problem with my right channel? There isn't much left original on my amp anymore



Unfortunately no matter how good and excellent and neat you can be, (as your pics show beautiful work) the issue that cannot be avoided is the circuit board.
In some places, like the anode/cathode resistors at the output stage the holes have a connection to the other side.
The trace on this board is rather easily damaged when using parts with thicker leads, like the resistors have.
You must check and compare both sides of amp for discrepancy in the board trace there.
My guess is that you may have a thru-hole "cold solder" point which disconnect as it gets hot.

Don't get distracted looking all over the dam place when the problem is at that one side of the output tubes.
Check voltages, and when off check continuity for sinilarity  to the other side as reference.

I am currently doing same on another amp.


----------



## metamorph63 (Oct 13, 2019)

Hi and Good day to all. I have a question about MKVIIISE: on the circuit board, the sockets of 12AT7 tubes is at 6,3V or 12,6V? I need of an adaptor for install the 6SN7/CV181 tubes instead of 12AT7's and so it's important to know what is voltage...


----------



## Maxx134 (Oct 13, 2019)

metamorph63 said:


> Hi and Good day to all. I have a question about MKVIIISE: on the circuit board, the sockets of 12AT7 tubes is at 6,3V or 12,6V? I need of an adaptor for install the 6SN7/CV181 tubes instead of 12AT7's and so it's important to know what is voltage...


6.3v
I tried about $2k worth of the tubes, and already went there with tube rolling of every kind, and feel the best selection was using 6SL7, or 6c8g tube, both with adapter...
If you look at my pic, I am using those type.


----------



## metamorph63 (Oct 14, 2019)

Maxx134 said:


> 6.3v
> I tried about $2k worth of the tubes, and already went there with tube rolling of every kind, and feel the best selection was using 6SL7, or 6c8g tube, both with adapter...
> If you look at my pic, I am using those type.


Thank you very much, I will try those tubes...where did you bought the adapters?


----------



## Maxx134

Ebay..
The 6c8g is the prettier bottle type over the 6SL7..
Both are the higher gain version of the 6sn7.

I still have my mk8 amp but now have another more neutral reference amp  in my link.

And for desktop level  portability, which is what I am focused on currently, is the Sony WM1A/WM1Z


----------



## metamorph63 (Oct 18, 2019)

Maxx134 said:


> Ebay..
> The 6c8g is the prettier bottle type over the 6SL7..
> Both are the higher gain version of the 6sn7.
> 
> ...


I've bought the adaptor for 6sn7/6SL7, I have not found an adaptor from 12at7 to 6c8g, but only from 6sn7/6SL7 to 6c8g...anyway, I'm satisfied. I have also an other amp, not a tube amp, a SS, more neutral and powerful, but the sound of the tubes is very interesting...thanks for the advice...


----------



## baronbeehive

Maxx134 said:


> And for desktop level  portability, which is what I am focused on currently, is the Sony WM1A/WM1Z



I used to be heavily into my IPOD classic 5 or so years ago! Mainly for work, it was permanently glued to my ears. At the time I used to discuss with friends about the lack of a high res portable player, now they are all over the place! Very interesting, I don't really have a need for such a player now though. These Sony's look very high end.

BTW are you doing any work on the other 2 amps now, I know you said you were thinking of finishing the upgrades to your satisfaction. I've not had any need to do anything to mine now, it's good to just be able to enjoy them without having to fault find all the time for a change lol.


----------



## baronbeehive (Oct 18, 2019)

metamorph63 said:


> I've bought the adaptor for 6sn7/6SL7, I have not found an adaptor from 12at7 to 6c8g, but only from 6sn7/6SL7 to 6c8g...anyway, I'm satisfied. I have also an other amp, not a tube amp, a SS, more neutral and powerful, but the sound of the tubes is very interesting...thanks for the advice...



Anything like this will do: https://www.ebay.co.uk/itm/6SN7-To-...758378?hash=item286536706a:g:TrkAAOSwBqpdpY~Z

12Au7 can be substituted for the 12At7 but has lower gain, 12Ax7 could also be used with this adapter as it says.


----------



## metamorph63 (Oct 19, 2019)

baronbeehive said:


> Anything like this will do: https://www.ebay.co.uk/itm/6SN7-To-...758378?hash=item286536706a:g:TrkAAOSwBqpdpY~Z
> 
> 12Au7 can be substituted for the 12At7 but has lower gain, 12Ax7 could also be used with this adapter as it says.


But the bottom pins are for 6SN7/6SL7 tube sockets (correct me if I'm wrong). I have already bought the adapter from 12at7 (bottom socket, Mk8se mount 12at7 sockets) to 6SL7/6SN7 tubes...


----------



## baronbeehive

metamorph63 said:


> But the bottom pins are for 6SN7/6SL7 tube sockets (correct me if I'm wrong). I have already bought the adapter from 12at7 (bottom socket, Mk8se mount 12at7 sockets) to 6SL7/6SN7 tubes...



OOPS.... sorry!

You must have used the link I posted before I corrected it. The link in my post above is correct now. Your adapter is correct.


----------



## Maxx134 (Oct 21, 2019)

baronbeehive said:


> BTW are you doing any work on the other 2 amps now,


I haven't had time to finish but I already know the preferred caps I want to change all the cathode caps the same nichion and keep the WCF caps same as coupling caps .
Keeping them same and using those  nichion for the cathode s should give me most transparency.

The choice of cathode caps was actually from testing various caps on another tube amp, the EC Aficionado.
It's a more straight forward design to test caps..


----------



## metamorph63

baronbeehive said:


> OOPS.... sorry!
> 
> You must have used the link I posted before I corrected it. The link in my post above is correct now. Your adapter is correct.


Don't worry....


----------



## baronbeehive

Maxx134 said:


> I haven't had time to finish but I already know the preferred caps I want to change all the cathode caps the same nichion and keep the WCF caps same as coupling caps .
> Keeping them same and using those  nichion for the cathode s should give me most transparency.
> 
> The choice of cathode caps was actually from testing various caps on another tube amp, the EC Aficionado.
> It's a more straight forward design to test caps..



Yes, right, good luck with that! Good quality caps should do well in those positions. Personally I feel the advice on page 1 for bright sounding caps in WCF position is ideal to push out those higher frequencies so I feel the Mundorf is good there but your opinion is good also. I am interested to see if you can get both amps performing similarly like I managed to do, when you get around to it. I feel that your higher end gear might show up the deficiencies that do not register so much with mine.

I see you are still working on the HD800S mod, this is something I might be interested in future, not now though. The priority is to finish with the silver output wires to see if I can squeeze the most transparency out of the amp. That will be the last thing I do on the LD when I get around to it!
.


----------



## Maxx134

The silver plated wire both I used and the designer had as an upgrade was used, but ONLY in the input stage, which is a high impedance input.
The wire I used I placed in beginning thread had also shielding which, like stock wire uses.
This is the suggested method for input wire... A shielded one.

Different job than output amp section which I used twisted OCC copper.

The output wires are a shorter run to output Jacks, and you don't have to go from back there to front.
You can run straight from board to front too.

Anyways you are correct to try brighter/leaner or faster WCF  caps in that section.


----------



## baronbeehive

Maxx134 said:


> The silver plated wire both I used and the designer had as an upgrade was used, but ONLY in the input stage, which is a high impedance input.
> The wire I used I placed in beginning thread had also shielding which, like stock wire uses.
> This is the suggested method for input wire... A shielded one.



I used silver plated unshielded for input wires, maybe shielding is an option there when I also finish the output wires, I didn't realise the stock wire was shielded. I concentrated on pure copper originally for output wires and changed partially to pure silver on the basis that the signal from the output tubes was the more important to preserve maximally. I don't know if sound is affected by the input wires, probably is if it was shielded but there are no EMF effects or the like that I can hear, only a completely black background, maybe there is some signal degradation though.


----------



## Maxx134

If you have quiet background then it should be fine.
The chassis is a good shield too.


----------



## baronbeehive

Maxx134 said:


> If you have quiet background then it should be fine.
> The chassis is a good shield too.



What sort of shielding did those input wires have?

Also I was wondering about the diode bridge mod, did anyone try this?

There was a diode mod for the APPJ amp which reportedly had a positive effect. Maybe having fast recovery diodes would impact positively on sound, and speed of recovery.


----------



## Maxx134

baronbeehive said:


> What sort of shielding did those input wires have?
> 
> Also I was wondering about the diode bridge mod, did anyone try this?
> 
> There was a diode mod for the APPJ amp which reportedly had a positive effect. Maybe having fast recovery diodes would impact positively on sound, and speed of recovery.


The 4 wires was in one with aluminum coax type braided shielding..


Haven't heard of diode mod so if possible  post link.


----------



## baronbeehive

Maxx134 said:


> The 4 wires was in one with aluminum coax type braided shielding..
> 
> 
> Haven't heard of diode mod so if possible  post link.




I never noticed that shielding when I took out the input wires, don't know if the MK8 is different.

You mean this:

*Diode Bridge :* _(Optional)_

IXYS FRED Rectifier Bridge FBE22-06N1 ( High performance 600v/22amp rectifier bridge with fast recovery diodes). Sonic improvements were not verified at time of installation.
http://www.mouser.com/ds/2/205/FBE22-06N1-6885.pdf

on page 1 this thread?

I mentioned the diode mod for the APPJ as both you and I have this amp and I had heard about this mod that was offered on the APPJ by an APPJ distributer way back when it first came out some years ago. I haven't been able to find out any details about it despite a full search. So I assume it involved fast recovery diodes, and was wondering if this was likely to be sufficient to cause sonic improvements for the LD, as it was said to do for the APPJ when I first heard about it.


----------



## Maxx134 (Oct 26, 2019)

baronbeehive said:


> and I had heard about this mod that was offered on the APPJ by an APPJ distributer way back when it first came out


Can you tell me if that is the same thing we already mentioned in first page?

If so, and you want to try it... it mostly benefits the power supply caps.
I could not compare to verify differences and so would have to go off memory.
And My memory tells me I don't know, ha


----------



## Maxx134 (Oct 26, 2019)

Little dot amp design  was based on a heavily buffered capacitance  PSU.

 In contrast, the appj is very small lean switching PSU so probably heavily reliant on specific parts...
So unless you actually  seen another one successfully using that bridge in place of stock parts, I would not mess with it's PSU, as those parts are pretty specific.


----------



## baronbeehive (Oct 27, 2019)

Maxx134 said:


> Little dot amp design  was based on a heavily buffered capacitance  PSU.
> 
> In contrast, the appj is very small lean switching PSU so probably heavily reliant on specific parts...
> So unless you actually  seen another one successfully using that bridge in place of stock parts, I would not mess with it's PSU, as those parts are pretty specific.



Yes.

That SMPS has held up well over the years, I wasn't sure about it at the time, I've heard of them going up in smoke, but seems to be a good design solution.

I can't say whether the diode mod for it is the same as mentioned in the first page for the LD as I haven't been able to find out anything about it annoyingly. Whenever anyone has mentioned it it is always along the lines of "people have said it is a noticeable improvement" but the trail goes dead from there when it comes to what the mod actually is... I'm beginning to wonder if it actually existed! In any case people at the time also said that putting in silver fuses was an improvement which we know is pure unadulterated snake oil... which is why I only put in a cheapo silver fuse LOL!

I was thinking that a faster acting diode would be good for the LD. Not so sure about the APPJ as the SET design is already very fast and open sounding, and I have no issues with it. Can't see the diode making much difference though.

As I said the 2 amps are performing comparably now post mods... but there are slight differences not surprisingly, such as speed and attack but frequency response is very similar. The LD is slightly warmer and fuller sounding with more bass heft, the APPJ is a tad leaner.


----------



## baronbeehive

Can't see if the wires are shielded here:


----------



## SonicTrance

baronbeehive said:


> Can't see if the wires are shielded here:


My mk6 used shielded wire on the input but the shield was not connected, so effectively useless. You suppose to ground one end of the shield. Anyway, it's not needed in the mk6 as I replaced the input wire with non-shielded wire and had no noise issues.


----------



## baronbeehive

SonicTrance said:


> My mk6 used shielded wire on the input but the shield was not connected, so effectively useless. You suppose to ground one end of the shield. Anyway, it's not needed in the mk6 as I replaced the input wire with non-shielded wire and had no noise issues.



Right! I thought so, I remember seeing yours. Anyway we bunched up the wires into 2 groups and tied up each group together so if there were any issues that would have showed up.


----------



## Maxx134 (Nov 8, 2019)

Maxx134 said:


> 1- I plan to upgrade the cathode caps to to Nichion KZ / Muse at larger size so meters won't dip at high volume with planars (remember I have the lesser current MK8)
> 
> 2- Then the caps WCF caps to jupiter (expensive) or actually the "Clarity Cap CMR



I finally got around to  ordering replacement caps.
** Nichion KZ (1000uf)f replacement of my small cathodes.
I like the balance and extension of this specific electrolytic.
It doesn't need any help with any bypass cap.

** Audyn true silver  for my WCF position caps.
I feel for this area of the circuit, we need a lively cap that is bright, fast, immediate and detailed and is *least* thick or harmonic, so no copper or mix caps.

The WCF position is  coupling and in between the triodes which react with each other, so a pronounced speed and clarity type of cap would be best.

I noted in the past that normal caps sounded thicker & duller here, so it is more critical to get a brighter and lean cap( least harmonics added sounding) cap.

This is the weakness of old school designs.
That you must know about the parts you put in, to a specific area, which is like choosing ingredients to a chef.

An experience designer in this type area (where parts are critical to sound) would know which brand caps or other parts to use.


----------



## baronbeehive

Really interested in hearing how you get on... if you can manage to fight your way past those sphagetti wires lol!
.


----------



## Maxx134 (Nov 11, 2019)

baronbeehive said:


> if you can manage to fight your way past those sphagetti wires lol!


Haha yeah I'm a bit sloppy but the mess doesn't phase me...
The caps finally came in:


I had initially planned on buying from US & Canada vendors, and I checked three, but they didn't have all the caps I wanted.
Only this site had everything I needed in one place.
Indeed they have the most complete selection of caps and I now prefer them over any other supplier for name brand stuff..
I needed caps for three different amps.


----------



## baronbeehive

Maxx134 said:


> The caps finally came in:



Maybe you could warm up on the APPJ before getting up to speed for the LD.

When you've finished you can use the monster caps as doorstops, or an occasional stool!

So far so good...
.


----------



## baronbeehive

Guys, I've looked again at the tube operating point I recommended back a while ago.

This graph shows the operating points Sonic and Maxx chose, with the stock operating point show also.





The graph below shows the point I chose, "my operating point", together with another point which I have now called "new operating point."

The reason I chose "my operating point" was that the voltage swing area is evenly spaced on either side, with the same slope on the grid curves. However this only results in a voltage swing of 40V which I was resigned to having. However you can see that if the operating point was at point 9 on the graph then the swing would be 110V, considerably more.

Therefore if we are to get maximum transparency and liveliness this could be a better operating point. The only problem stopping me from choosing that before was the problem area indicated which is where the curves become nonlinear.

In light of the discussion on the Oblivion review thread I now know a bit more about tube operation.





Therefore I was wondering about seeing if there would be a different tube that would be better in this problem region that would enable us to get more anode voltage swing for a more lively sound. I rather doubt it because the problem area is much the same in different tubes, and since we can't draw a horizontal load line we might be stuck with it.

Having said that I was pleased with my choice, but was wondering if there could be an even better solution.


----------



## Maxx134 (Jan 30, 2020)

baronbeehive said:


> Therefore if we are to get maximum transparency and liveliness this could be a better operating point.


Some of the main differences I noted in various bias points, when listening, were more of image distance and liveliness, rather than distortion.

Sometimes a livelier tube bias settling, was also a more forward sound, so selecting bias points always needed listening  observations.




baronbeehive said:


> Therefore I was wondering about seeing if there would be a different tube


What tubes are you using now?
I tried so many, I lost count.
Not only the 6pin varieties, but also of the 12pin variety..
 My tube of choice was also limited to the fact I did not use CCS.

Anyways, my pick ended up being the 6SL7 variety, not the 6SN7.
My fav being the "coke bottle" version, with top anode(6C8G):




I also preferred the 6pin types overall, over the 12pin that came stock on my MK8 version.


----------



## baronbeehive (Jan 30, 2020)

Maxx134 said:


> Some of the main differences I noted in various bias points, when listening, were more of image distance and liveliness, rather than distortion.
> 
> Sometimes a livelier tube bias settling, was also a more forward sound, so selecting bias points always needed listening  observations.



Yeah, I know you looked into this at he time. I expect distortion might be masked by the fact that we have a slightly slower, more tubey sounding amp than the Oblivion, which can still sound pleasant under different operating conditions, so long as the harmonics are lower order ones.

I just wondered if there were tube varieties we haven't tried yet that could fit the bill.

This amp runs such a low voltage and current, it needs a bit of help. I suppose that's the downside for having an OTL amp. Having said that though it's still TOTL for me.



Maxx134 said:


> What tubes are you using now?
> I tried so many, I lost count.



Haha, I would love to see your stash lol.

I'm back with the TS6SL7's, can't beat 'em. Its less of a problem now though, the amp sounds so good whatever I've got in, also different power tubes don't seem to matter now.




Maxx134 said:


> My tube of choice was also limited to the fact I did not use CCS.



If I were to change tubes now I would have to recalculate resistor values for the CCS. I'm very happy with it in though.



Maxx134 said:


> Anyways, my pick ended up being the 6SL7 variety, not the 6SN7.
> My fav being the "coke bottle" version, with top anode(6C8G):



I like the look of them, I bet they sound good. but you know me, I'm a skinflint so could not justify splashing out that sort of money for tubes...having said that I will have to justify spending out for some OCC silver to complete the silver wires inside soon... I believe I can get a slightly edgier sound closer to the APPJ.

I heard you were finishing the upgrades soon...
.


----------



## baronbeehive

Having looked again at the 6SL7 operating point tests I did on page 230 I realised that it might have been difficult to understand to anyone looking at it... if there was anyone there, so I will just summarize my findings so that anyone can easily see what to do to make the changes.

This graph shows Sonic's, in brown, Maxx's, in red, and stock, in black, operating points








This graph shows the points I picked, in green to test.





Below were my comments:

_To summarize my results there was one stand out position which hit me the moment I started listening, the sound was full, palpably real with good clarity and texture which you could almost feel. The sound had a presence, transparency, resolution and dynamism. This for me was the obvious setting to use. I was a bit surprised that my proposed intermediate settings in between Sonic and Maxx's settings were not my favourite, probably because it fell in the middle it was neither one thing nor the other. The best operating point was with an anode of 69K and cathode of 380R, point 7 in the graph. I will scan in my notes page later so you can see in more detail.

33K - good baseline score, with cathode of 380R, as above, however at 2 of the cathode settings, 1K and 1.5K, I felt that the sound was somewhat flat and lifeless. High gain sounded better, slightly more transparent, with both 6SL7 tubes.

46K - again, good baseline score or thereabouts, with cathode of 380R, but with the GE tube with scores of 1 for bass, mids, treble, and soundstage I felt that this justified a second place position for SQ. Very good transparency and detail. With the 1.5K cathode the scores fell to -1 with a flat rather lifeless sound.

69K - here with all 3 cathodes I felt was the best sound with all 3 cathodes the sound was considerably above baseline. With the 1.5K cathode I felt that with the GE tube it justified second equal position in SQ. With the 1K cathode and with both 6SL7's I felt that second equal position was justified with full bodied, incisive, real and transparent sound. However as soon as I started listening with the 380K cathode in I knew straight away that I would be very happy with this setup. The sound was full bodied, had a real presence, and had the most texture to the transients and treble which gave it a dynamism. For example piano had weight and attack, guitar notes stood out, vocals sounded real, bass had weight and definition and drums had attack, you could almost feel the kick drums._

 Below is my recommendation:

_ I would recommend that overall it would be best not to use the 33K anode setting, or the 1.5K cathode settings and go for the first place or one of the second place settings._

So, the 69K anode and 380R cathode are the best values to use, when using 6SL7 tubes. But, interestingly the 69K anode, and the 1.5K cathode, point 9 on the graph, is the position with the most voltage swing so, that might be worth a try also, however in my tests I put it in second equal position, most likely because with that amount of voltage swing the load line entered into the nonlinear region of the grid.


----------



## coinmaster (Feb 1, 2020)

Oh I forgot about this thread, Sup losers.


baronbeehive said:


> Below is my recommendation:
> 
> _I would recommend that overall it would be best not to use the 33K anode setting, or the 1.5K cathode settings and go for the first place or one of the second place settings._
> 
> So, the 69K anode and 380R cathode are the best values to use, when using 6SL7 tubes. But, interestingly the 69K anode, and the 1.5K cathode, point 9 on the graph, is the position with the most voltage swing so, that might be worth a try also, however in my tests I put it in second equal position, most likely because with that amount of voltage swing the load line entered into the nonlinear region of the grid.


Just use a horizontal or vertical load line. No need to muck around if linearity is the goal.
You should probably keep in mind the extreme lack of voltage swing required for headphones too, you're not gunna need 200v of swing. Even the worst offenders don't use more than like 30v p-p at ear splitting volumes. My HD800s only use a few volts.


----------



## baronbeehive

coinmaster said:


> Oh I forgot about this thread, Sup losers.



Hey!!

Is that *THE* coin?

Welcome back to the losers thread.

Does Frankenstein live?



coinmaster said:


> Just use a horizontal or vertical load line. No need to muck around if linearity is the goal.
> You should probably keep in mind the extreme lack of voltage swing required for headphones too, you're not gunna need 200v of swing. Even the worst offenders don't use more than like 30v p-p at ear splitting volumes. My HD800s only use a few volts.



We can't use horizontal load lines without grid drivers, and probably gyrators and a couple of other things to provide current in that area of the grid. I seem to remember you banging on about this way back at the start of the thread... when nobody was listening lol! Don't forget this amp is old school. It's sounding great though, I know you liked yours.

I must say the point I chose with 40V of swing was very linear and sounded good, probably better than the grid area with 110V swing which may have started to distort.

Stick around!
.


----------



## baronbeehive

This site has gone bananas, no wordwrap, or something…, can't get anything down properly.

That was supposed to say I seem to remember you banging on about this way back at the start of the thread... when nobody was listening lol!

Don't forget this amp is old school, its sounding great though, I know you liked yours.


----------



## baronbeehive

The website maintenance appears to have introduced a bug that only affects me, most of my post is cut off at the right hand side of the page which is pretty weird!


----------



## coinmaster (Feb 3, 2020)

> Hey!!
> 
> Is that *THE* coin?


The one and only 



> We can't use horizontal load lines without grid drivers


  I think it was the other guy that was insisting on grid drive. The grids of the following stage will draw some current but we're talkin like micro amps, the load line will still be effectively horizontal for all intents and purposes.
You could use a mu follower gyrator to drive all of the current in the next stage or apply my leamskie follower mod to ensure the next stage requires practically no current to drive and doesn't have frequency dependent current sharing on the push pull operation like the stock design does but those are a bit more complex to implement than just applying a simple current source.
A vertical load line is another option and it will greatly increase the gain of the first stage which can allow for extra feedback and will have no issues driving the next stage since it functions purely on the current axis. Implementation involves just a simple source follower between the tube and the plate resistor.
There's a zillion mods that can be done here, I design vastly superior amps at this point so the MK6 is just a paper weight for me nowadays.


----------



## baronbeehive

coinmaster said:


> the MK6 is just a paper weight for me nowadays.



I hear you can get cheaper paperweights than that!



coinmaster said:


> The grids of the following stage will draw some current but we're talkin like micro amps, the load line will still be effectively horizontal for all intents and purposes.
> You could use a mu follower gyrator to drive all of the current in the next stage or apply my leamskie follower mod to ensure the next stage requires practically no current to drive and doesn't have frequency dependent current sharing on the push pull operation like the stock design does but those are a bit more complex to implement than just applying a simple current source.



Could you demonstrate a horizontal load line, I only know the old style ones
that go from 0mA/max B+ to desired plate current.

What is the Leamskie follower?



coinmaster said:


> A vertical load line is another option and it will greatly increase the gain of the first stage which can allow for extra feedback and will have no issues driving the next stage since it functions purely on the current axis. Implementation involves just a simple source follower between the tube and the plate resistor.



The nearest I've got to the vertical load line is the brown line on the graph
in the previous post that Sonic used. But even then there is the same problem 
right near to 0mA, are you saying the line stops before you get to this region? 
And how do you get voltage swing on a vertical line?



coinmaster said:


> I design vastly superior amps at this point



So your Frankenstein monster *IS* alive.. and getting ready to get off of your workbench...


----------



## coinmaster (Feb 4, 2020)

> I hear you can get cheaper paperweights than that!


Yeah I need to sell it at some point.



> Could you demonstrate a horizontal load line, I only know the old style ones
> that go from 0mA/max B+ to desired plate current.


A horizontal load line is another way of saying constant current.
A vertical load line is another way of saying constant voltage.



> What is the Leamskie follower?


It's a more elegant name for the improved WCF design that broskie helped me complete when I first started designing amps.
https://www.tubecad.com/2016/02/blog0339.htmIt's essentially the idealized version of the MK6. I believe I mentioned my impressions after implementing it into the mk6 quite a while back in this thread somewhere.

I also designed a balanced input stage that uses one tube to cancel the distortion of the other tube using anti phase currents across the same load line, 4 triodes total for balanced, but it sounded just as good as my good SS circuits so I decided against using it due to cost and complexity of implementation into a finished design when a much cheaper and smaller SS circuit sounds just as perfect.

I was building a balanced version of the follower using 6c33c tubes years ago but couldn't finish it due to lack of funds. Coincidentally I'm going to finish it soon because I found a way to finish it without spending money.
It's more of a novelty project now since I can design way better stuff but it uses 8 6c33c tubes so it looks cool in any case.
It will have an adjustable output impedance and a feedback configuration that allows a pot to let it adjust between from 100% tube sound to 100% SS sound, the SS portion of the dial will cause the amp to produce unmeasurable distortion.



> And how do you get voltage swing on a vertical line?


 You don't, as far as the tube is concerned. You put a source follower on the plate of the tube so the tube just sees a DC voltage. Then you put the "plate" resistor on the drain of the source follower. The current of the vertical load line flows right through the source follower into the plate resistor.
This means that the gain of the circuit is set by the plate resistor resistance and the current swing of the tube rather than the gain of the tube.



> So your Frankenstein monster *IS* alive.. and getting ready to get off of your workbench...


No that stuff is garbage compared to what I make now.
I've been working for a while on an amp that has distortion well below -300db and never produces any measurable distortion under any load until clipping.
I designed a PCB for it that can pump out 25W into 8 ohms, True class A, balanced,can fit in your hand, and would sell for roughly $150.
Need to get a reputable third party measurement lab to "officially" verify the specs first before I can go to investors, that is a cost I can't incur any time soon so I'm kind of sitting on it at the moment.

That's just the tip of the iceberg though, I've developed headphones that can loudly and powerfully produce a 20hz signal and make the HD800 sound like toy in comparison and has insanely larger soundstage.
I also have a slew of other equally cool circuits that are tube based and SS based but they will never leave prototype stage until I can fund them somehow.
I tried fishing for investors on DIYaudio but god most of those guys are insufferable and mostly a colossal waste of my time. So much ego, emotion, lack of reading comprehension, and a painful lack of interest in real innovation going on over there it truly boggles the mind.


----------



## baronbeehive

Hats off for sticking with it.

I will check out all that later, I remember you doing a lot of that stuff a while back.

My opinion, for what it's worth, why don't you take a few of your best ideas and build a complete amp, and bring it to one of the threads with a following and watch it take off from there. You may have already done that, but that would be a way of getting going without needing a lot of funds. And it would demonstrate the potential of your amps.

Re: the LD, the upgrades we have done have transformed it totally. Despite the pushpull - WCF design, which is rather clever actually, it's really good now, very transparent sounding with a lot of textural detail, but still euphoric. I probably wouldn't want to change it as it stands now. As far as I can make out it doesn't have any harmonic distortion, certainly not the unpleasant kind but difficult to say, anyway it sounds good!


----------



## coinmaster (Feb 4, 2020)

> My opinion, for what it's worth, why don't you take a few of your best ideas and build a complete amp, and bring it to one of the threads with a following and watch it take off from there. You may have already done that, but that would be a way of getting going without needing a lot of funds. And it would demonstrate the potential of your amps.


Not a whole lot I can effectively demonstrate in a thread without giving too much away.


> My opinion, for what it's worth, why don't you take a few of your best ideas and build a complete amp, and bring it to one of the threads with a following and watch it take off from there. You may have already done that, but that would be a way of getting going without needing a lot of funds. And it would demonstrate the potential of your amps.


 The WCF has many intrinsic flaws that are only solved in the leamskie follower version.
I agree that the amp is transformed with the mods on this thread as I also went overboard with the modding if you recall. However, it simply can't compete with the stuff I currently make. Not even close.
The main issue is the output stage, a tube can be made sonically transparent in the input stage without too much problem but using tubes in the output stage in the way the MK6 does can only go so far sonically.


----------



## baronbeehive

coinmaster said:


> Not a whole lot I can effectively demonstrate in a thread without giving too much away.



No, but if you had a working version and got it reviewed the message would get out.



coinmaster said:


> The main issue is the output stage, a tube can be made sonically transparent in the input stage without too much problem but using tubes in the output stage in the way the MK6 does can only go so far sonically.



The CCS and filter I put on mine went a long way to cleaning up the sound, and I don't have to worry about achieving balance anymore.


----------



## coinmaster (Feb 6, 2020)

> No, but if you had a working version and got it reviewed the message would get out.


 I'm meeting Maxx today. You can ask for his opinion.


----------



## baronbeehive (Feb 5, 2020)

coinmaster said:


> It will have an adjustable output impedance and a feedback configuration that allows a pot to let it adjust between from 100% tube sound to 100% SS sound, the SS portion of the dial will cause the amp to produce unmeasurable distortion.



I'm impressed that you managed to get good distortion free SS sound.



coinmaster said:


> You don't, as far as the tube is concerned. You put a source follower on the plate of the tube so the tube just sees a DC voltage. Then you put the "plate" resistor on the drain of the source follower. The current of the vertical load line flows right through the source follower into the plate resistor.
> This means that the gain of the circuit is set by the plate resistor resistance and the current swing of the tube rather than the gain of the tube.



Did you implement this? It could overcome the problems of the nonlinear part of the grid curves.



coinmaster said:


> That's just the tip of the iceberg though, I've developed headphones that can loudly and powerfully produce a 20hz signal and make the HD800 sound like toy in comparison and has insanely larger soundstage.



20hz, wow, I want these when you've built them... while I can still hear down there... if I can still hear down there.



coinmaster said:


> ... So much ego, emotion, lack of reading comprehension, and a painful lack of interest in real innovation going on over there it truly boggles the mind.



...tell me about it... I hate all that.


----------



## coinmaster (Feb 5, 2020)

> Did you implement this?


 Never got around to it.


> It could overcome the problems of the nonlinear part of the grid curves.


So would a horizontal load line. A horizontal load line would likely give lower distortion than a vertical one on most tubes.
A vertical load line would allow more feedback and provide a bit more linear current response into the non linear input capacitance of the next stage assuming that is an audible issue.


> 20hz, wow, I want these when you've built them... while I can still hear down there... if I can still hear down there.


 You'd be surprised how audible 20hz is.
99% of speakers can't play 20hz well which is why it sounds so low or inaudible if you try. Technically you can hear way below 20hz. The commonly known theory that a person cannot hear below 20hz is only because nothing can typically play that low without impractically large drivers.  Mine doesn't have that issue.
I got it measured yesterday. The LF response is essentially flat and begins to rise as it approaches 0hz. So in other words it's loud all the way to 0hz.
The rest of the FR is similar to other high end headphones. The sound stage is in another league from the HD800 though and the sound quality makes the HD800 remind me of a phone speaker.
The prototype is essentially a first blind attempt, further testing revealed that it can be optimized much much further than it is now. But alas I have no monies it's probably gunna sit there for quite a while before I can get back to it.


----------



## stvn758

Are they still in business, I am having a hard time finding the link to their site.

Anyone help, please?


----------



## baronbeehive

stvn758 said:


> Are they still in business, I am having a hard time finding the link to their site.
> 
> Anyone help, please?



I noticed this a while back, I don't know what has happened. They have had one or two good reviews recently too!

If you want their products you could try this website: https://www.china-hifi-audio.com/en/little-dot-audio-headphone-amp-dac-c-59

I will try to email David and see what happens.


----------



## stvn758

baronbeehive said:


> I noticed this a while back, I don't know what has happened. They have had one or two good reviews recently too!
> 
> If you want their products you could try this website: https://www.china-hifi-audio.com/en/little-dot-audio-headphone-amp-dac-c-59
> 
> I will try to email David and see what happens.



Thanks.


----------



## baronbeehive

I've had no response from my email so I don't know what has happened. I don't know if they're still making products, or whether they are selling through another company or what.

Does anyone know what's happened to Little Dot?


----------



## stvn758

baronbeehive said:


> I've had no response from my email so I don't know what has happened. I don't know if they're still making products, or whether they are selling through another company or what.
> 
> Does anyone know what's happened to Little Dot?



https://www.china-hifi-audio.com/en...c-c-59?zenid=eec872e3780cb95361b034b5522c65ba

Perhaps this is them now, or they bought them. Last time I checked their forum there £900 balanced tube amp was the most expensive thing they made.


----------



## Yaska729

stvn758 said:


> https://www.china-hifi-audio.com/en...c-c-59?zenid=eec872e3780cb95361b034b5522c65ba
> 
> Perhaps this is them now, or they bought them. Last time I checked their forum there £900 balanced tube amp was the most expensive thing they made.




I have no idea why their website is down, but the owner Mr. Yang is pretty easy to reach through a Chinese forum. They are still in business and little dot actually came out with couple of new products after MK viii (LD-Y1 & Y2). Preparing to show his new amp in Shanghai conference I believe (LD-Z1). Anyways, I guess you could either buy their product through taobao, amazon, or AliExpress.


----------



## baronbeehive

Yaska729 said:


> I have no idea why their website is down, but the owner Mr. Yang is pretty easy to reach through a Chinese forum. They are still in business and little dot actually came out with couple of new products after MK viii (LD-Y1 & Y2). Preparing to show his new amp in Shanghai conference I believe (LD-Z1). Anyways, I guess you could either buy their product through taobao, amazon, or AliExpress.



Thanks for that information, do you have the link to the forum?

Or could a Chinese speaker ask what is the current position with Little Dot now. I would have thought that to be able to contact them on their website would be important if they are launching new products to try to get it out there.


----------



## Yaska729

I also have some thoughts that I wanted to talk to him about, it seems like he is only doing little bit of marketing through taobao or release his product info on erji.net lately. Anyways, I am actually giving my mk8 to him to fix some little stuff and upgrade, and I’ll let him know about his website and the horrible customer service his reseller has been providing. I got pictures of the LD-Z1 for people to check it out



The price is at 16800 yuan, which is around 2370 USD.


----------



## Maxx134

I'm unloading a stash of 12 pin driver stage tubes for the MK8.
You can check out my list of tubes here

I will also gather my extra 6pin driver tubes for the MK6 soon.

I still have my MK8 which I held off until I decided on my choice to retune/refine the signature, so I settled on  "Audionote kaisie" for the cathode caps position, & some silver  film caps for the WCF position.

will post once underway hopefully this month.


----------



## Yaska729

stvn758 said:


> https://www.china-hifi-audio.com/en...c-c-59?zenid=eec872e3780cb95361b034b5522c65ba
> 
> Perhaps this is them now, or they bought them. Last time I checked their forum there £900 balanced tube amp was the most expensive thing they made.



Not sure if you are still looking for their products, but Mr. Yang just posted in his group that they have a new distributor who can actually speak English and provide services. This is the site Mr. Yang post https://littledotus.com


----------



## baronbeehive

Yaska729 said:


> Not sure if you are still looking for their products, but Mr. Yang just posted in his group that they have a new distributor who can actually speak English and provide services. This is the site Mr. Yang post https://littledotus.com



The site is blank atm!
.


----------



## baronbeehive

Maxx134 said:


> I still have my MK8 which I held off until I decided on my choice to retune/refine the signature, so I settled on  "Audionote kaisie" for the cathode caps position, & some silver  film caps for the WCF position.
> 
> will post once underway hopefully this month.



For the Kaisei caps, don't you mean Nichicon Muse? They made a massive difference over the Mundorf's we used for the original modding. The bass tightened up considerably. I don't know what the Kaisei's would be like in the LD. I have them in the APPJ. The bass on the APPJ is nice and tight anyway due to other factors so I don't know how much the Kaisei's affected it.


----------



## Yaska729

baronbeehive said:


> The site is blank atm!
> .


Hey Baron,

It just takes a while to load, but it does have all of their stuff in it.


----------



## Maxx134 (Jul 8, 2020)

baronbeehive said:


> For the Kaisei caps, don't you mean Nichicon Muse?


Yes, although I do have the muse(kz), which are very good, I decided to go for what I feel may have more depth.

In this cathode position, we had already placed nice paper/oil bypass caps for upper end, so my goal instead, was to increase capacitance for bass sustain, and then pick a brand that I feel will give me unique attributes.

The elna is known for smoothness which I not need. Then, the Nichicon KZ-muse is known for clarity and balance, which I already have.
But Then this kaisie is supposed to be closer to "blackgate" in attributes, plus in my research it was said to have more depth and life.
So we will see.


----------



## baronbeehive

Yaska729 said:


> Hey Baron,
> 
> It just takes a while to load, but it does have all of their stuff in it.



Ah, yes I had to google it, your link didn't work for some reason!
.


----------



## baronbeehive

Maxx134 said:


> Yes, although I do have the muse(kz), which are very good, I decided to go for what I feel may have more depth.
> 
> In this cathode position, we had already placed nice paper/oil bypass caps for upper end, so my goal instead, was to increase capacitance for bass sustain, and then pick a brand that I feel will give me unique attributes.
> 
> ...



I am interested to hear your findings. I went for stock values, 220uF, purely because they fitted in without yet more modification!

I certainly wouldn't change the Kaisei's in my APPJ.., I continue to be shocked by it, and I see the APPJ thread is still going strong. The APPJ and LD MKVI make a great combo, with similar performance levels. The APPJ for speakers, and the LD for headphones.

Hope you can remember where you left your LD lol!
.


----------



## baronbeehive

... probably gathering dust in the broom cupboard... .


----------



## Maxx134

baronbeehive said:


> ... probably gathering dust in the broom cupboard... .


Nope, my unit 


is safe in a drawer at my mom's house.

I learned a lot with this amp.
Changed/altered  every stage, but main thing was the realization of all the choices that a designer picks & chooses, for their recipe of design and parts.
That's why I am being selective this last time.


----------



## Maxx134 (Jul 10, 2020)

I should & will eventually update my choice of main coupling cap, from Jupiter, to the *MIFLEX KPCU Film Capacitors.*

Although it lies in the realm of preference, as both are in same league,  I am enjoying it's delicacy.
I consider the "Jupiter" being more natural, and the "Miflex" being with a hint of signature.
It has been mentioned in past to be between the Jupiter & the Deulund.
They all already at top level resolve in this circuit position.

The main advantage is cost.
The Milflex are less than the rest, and even bring a hint of the mundorf in sweetness.

I consider the mundorf to be very nice in sound, but a touch artificiall in trebles and a slight lower in absolute image resolve.

I have noticed that the mundorf are the most common used in tube amps because of their sound and popularity.
I only preferred the mundorf in the "WCF" position.
In that specific position, they imparted their sweetness majic there without any loss of resolve.


----------



## baronbeehive

Maxx134 said:


> The main advantage is cost.
> The Milflex are less than the rest, and even bring a hint of the mundorf in sweetness.



They look very good value!




Maxx134 said:


> I have noticed that the mundorf are the most common used in tube amps because of their sound and popularity.
> I only preferred the mundorf in the "WCF" position.
> In that specific position, they imparted their sweetness majic there without any loss of resolve.



By a roundabout process I eventually used Mudorf SIO in the WCF position. Originally they were for coupling, then as the capacitance and composition was ideal for WCF I decided on that together with Audyn True Copper for coupling, then as they were too big to fit I went with Jupiters for coupling... my wallet has only just recovered... glad I did, but might well have used Miflex had they been around at that time.

I think the amp does need something which will emphasize trebles such as the Mundorfs do in WCF position. That's also why I went for OCC silver output wires, eventually I will finish replacing the wires to the headphone socket. I realised this when comparing to the APPJ which to my mind has a perfect bass-treble balance and just the right amount of treble presence. I feel that pure silver wires just might make all the difference to the treble register.. but this is already good.


----------



## baronbeehive

Maxx134 said:


> Nope, my unit
> 
> is safe in a drawer at my mom's house.
> 
> ...



I apologise lol!

...not a trace of dust in that cupboard... but looks like your mom left the amp on all that time!

Good to see that amp again...

It should be interesting to see what effect your choices have made on the amp.


----------



## baronbeehive

Maxx134 said:


> I learned a lot with this amp.
> Changed/altered  every stage, but main thing was the realization of all the choices that a designer picks & chooses, for their recipe of design and parts.
> That's why I am being selective this last time.



Yep, quite right!

I feel that the mix of upgraded parts is just about right. It has pushed the amp right up there with the big boys. I realize that there are amps out there that do this or that better, but the LD and APPJ do nothing wrong and pretty much everything right for me. ottom line is that when you have reached the sound signature that you really like it would be silly to change anything so I'm very happy. The amp has great resolve, clarity, airy soundstage, great balanced frequency range and extension, liveliness, euphoria, everything you could want. Only thing I will do is go for a top level cable such as the one you have for a few percentage points increase but I'm enjoying this so much I haven't bothered as yet. Of course if I had limitless finance available on tap....

I don't think there's anything else that could be done to the amp without completely rebuilding it, same goes for the APPJ, so I think we've reached the end of the line... probably...!

When I took the amp to the engineer after I had done the first lot of mods to check there was nothing wrong his mind was boggled when he saw what we had done inside lol!
.


----------



## Maxx134

baronbeehive said:


> When I took the amp to the engineer after I had done the first lot of mods to check there was nothing wrong his mind was boggled when he saw what we had done inside lol!
> .


Haha that would've been great to see.

I believe you did the CCS mod in the driver stage, correct?

I didn't because of all the work and trial to manually tune my bias point for a specific tube.

After all my tube roll(which I did initially), I was in effect bias point rolling on a few of my favorites tubes to tune in my selected bias point. So it was alot to tuning and listening.

Then the topic of  applying a CCS, I was afraid because I would probably loose any tube characteristics that I had tuned in, from the traditional design.

So although the CCS makes is full-proof and easy to have more optimal parameters for the tube, I chose to not use it on my amp.

Why?
Because I essentially rolled  every 12pin variant that existed, then went thru many 6pins that the MK6 was using.
I spent easily over $1.5k of tube rolling, before I settled on a 6pin, on an MK8, which is normally designed  for the much smaller 12at7 tube type.
So I'm pretty much settled on my combo of tube and bias circuit setting, for that amp.


----------



## baronbeehive

Maxx134 said:


> Haha that would've been great to see.



The only problem with that was that it means they don't want to work on the amp because of the difficulty level. But they said that they were mightily impressed that a relative beginner did that, many experienced engineers would have had difficulty with work of that sort!

Looking back it certainly wasn't easy and especially wouldn't be for those of a nervous disposition not to burn out the insides with a slight tremor of the hands!


----------



## baronbeehive

Maxx134 said:


> I believe you did the CCS mod in the driver stage, correct?
> 
> I didn't because of all the work and trial to manually tune my bias point for a specific tube.



Yes, and the active filter MrCurwen suggested using to clean up the PSU.



Maxx134 said:


> After all my tube roll(which I did initially), I was in effect bias point rolling on a few of my favorites tubes to tune in my selected bias point. So it was alot to tuning and listening.
> 
> Then the topic of  applying a CCS, I was afraid because I would probably loose any tube characteristics that I had tuned in, from the traditional design.
> 
> So although the CCS makes is full-proof and easy to have more optimal parameters for the tube, I chose to not use it on my amp.



That was exactly what I was afraid of losing. I had already tuned in the operating point in the listening tests and found my preferred one which was close to yours. However the operating point chosen by Sonic for the CCS retained the characteristics that I had already preferred for the 6SL7 so that was a massive relief. All the liveliness and impact, and the signature of the LD, were still there.

The other thing I found with the CCS was a total lack of the negative harmonics which can spoil listening... HOWEVER... this was very difficult to detect and I wasn't sure that I was just imagining it until MrCurwen said that this was a characteristic of the CCS and force balance. So I have kept the CCS mainly because I don't need the tubes to do the balance for me now. Bottom line is that the amp sounds great with it in, and I am reassured that the sonic benefits of the CCS and balance will always be there.

The filter didn't affect the sound in any way, but again I am reassured that it will keep the PSU clean.



Maxx134 said:


> I spent easily over $1.5k of tube rolling, before I settled on a 6pin, on an MK8, which is normally designed  for the much smaller 12at7 tube type.
> So I'm pretty much settled on my combo of tube and bias circuit setting, for that amp.



You're still using the TungSols? I forget which one.

I'm still using the bog standard TS GRP's. I did think of trying the Brimars again which are so euphoric but having decided on keeping the TS's a while back I will probably stick with those, they are also euphoric with a cleaner and more balanced sound IMO.


----------



## baronbeehive

Just been looking at the new LD website. They have an interesting range of new products including a mono block amp.

A couple of interesting quotes from the site:

_*"Good sound comes from good electronic components"*_
*
"listening to any music will give you a refreshing and transparent feeling."

"The own enthusiast can replace the op amp of the decoder part, the coupling capacitance of the amp part, etc., but it is not recommended for the novice DIY."*

Looks like they've been pretty busy!

... maybe I shouldn't have tried to mod the amp according to the last quote, underlined, lol!


----------



## Yaska729

Maxx134 said:


> I should & will eventually update my choice of main coupling cap, from Jupiter, to the *MIFLEX KPCU Film Capacitors.*
> 
> Although it lies in the realm of preference, as both are in same league,  I am enjoying it's delicacy.
> I consider the "Jupiter" being more natural, and the "Miflex" being with a hint of signature.
> ...



Hello Maxx, do you use the same spec 600v 0.47uf with the Miflex? It seems quite large compare with the Mundorf and Jupiter, does it fit into the original chassis? Thank you


----------



## Maxx134

n


baronbeehive said:


> Yes, and the active filter MrCurwen suggested using to clean up the PSU


ugg, I forgot to add that post!


baronbeehive said:


> That was exactly what I was afraid of losing. I had already tuned in the operating point in the listening tests and found my preferred one which was close to yours. However the operating point chosen by Sonic for the CCS retained the characteristics that I had already preferred for the 6SL7 so that was a massive relief. All the liveliness and impact, and the signature of the LD, were still there


This is really, really good to know... I should also add it also to beginning posts... Still not going to do it though lol.


Yaska729 said:


> Hello Maxx, do you use the same spec 600v 0.47uf with the Miflex? It seems quite large compare with the Mundorf and Jupiter, does it fit into the original chassis? Thank you


Nope it not needed as .33 still good for the coupling and the WCF caps... there is a calculator to calculate the low end cutoff point,(https://www.v-cap.com/coupling-capacitor-calculator.php) which is already lower than stock .22uf cap.
I would also mention what is not mentioned, which is not the size, but the voltAGE... higher is better for film cap in this position (in contrast, not for electrolytic types which works best at an optimal value).
Anyways, to me, anything past .33-47uf max in the coupling here is not really any gains. the 47uf was a bit too enthusiastic and not that practical. sub bass will be just fine with .33uf..


----------



## CopperFox (Sep 24, 2020)

Hi everyone,

As my first mod for the mkVI+, I installed 0.68uf 600V Miflex KPCU-01 caps as coupling caps...



...so I needed to build a case extension as well.



The difference in sound is certainly not small. More detail, clarity, dynamics and dimensionality everywhere.

I'm thinking of adding the decoupling caps and possibly silver wires as well.
Are there some good recent options or recommendations for the decoupling caps that aren't  mentioned in the early posts in this thread?


----------



## Maxx134

CopperFox said:


> Hi everyone,
> 
> As my first mod for the mkVI+, I installed 0.68uf 600V Miflex KPCU-01 caps as coupling caps...
> 
> ...


Yep those Miflex are tops with any others.

The decoupling caps should be small sized like the Rifa.
Yet they won't give you as much improvement as the WCF caps...
Do the WCF caps first for larger gains in sound clarity.
Use your choice of cap.


----------



## Maxx134

Also don't forget the cathode caps.
Also a direct affect on the sound.
I would suggest try the Audionote kaisie...
That or the Nichicon KZ are tops for electrolytic caps.
Then add a good small .1uf bypass for sparkle/air.

The "decoupling" caps do not change the signature like all the caps I mentioned above.
They only help with Dynamics/transients delivery.

Many tube amps simply do not use them because they use newer circuit delivery (gyro&CCs), or want a smoother attacks & more tube like sound.
It's all a choice, and now your choice to make as you see fit.


----------



## Maxx134 (Sep 24, 2020)

For those that plan to use a plannar headphiu with the MK6, I suggest boosting the cathode caps to alt least about 1000uf..
I am actually able to use those type headphones on my MK8, but the bias meters dip slightly at high bolumes from the smaller cathode caps, even though I have huge "decoupling" caps.
So larger "Cathode" caps are the way to go.
Do not confuse them with the "WCF" cap position.
The "WCF" position acts more like a "coupling" cap.


----------



## CopperFox

Maxx134 said:


> Yep those Miflex are tops with any others.
> 
> The decoupling caps should be small sized like the Rifa.
> Yet they won't give you as much improvement as the WCF caps...
> ...





Maxx134 said:


> Also don't forget the cathode caps.
> Also a direct affect on the sound.
> I would suggest try the Audionote kaisie...
> That or the Nichicon KZ are tops for electrolytic caps.
> ...





Maxx134 said:


> For those that plan to use a plannar headphiu with the MK6, I suggest boosting the cathode caps to alt least about 1000uf..
> I am actually able to use those type headphones on my MK8, but the bias meters dip slightly at high bolumes from the smaller cathode caps, even though I have huge "decoupling" caps.
> So larger "Cathode" caps are the way to go.
> Do not confuse them with the "WCF" cap position.
> The "WCF" position acts more like a "coupling" cap.




Thanks for the advice! Ordered 0.33uf 600v Miflexes for the WCF position and 470uf 50V Nichicon KZ and 220v 0.1uf Kemet/Rifa for the cathode bypass position. 1000uf KZ's were not in stock (1000uf Nichicon FG was but I heard those aren't as good). I've been using the amp in stock configuration mostly with planars (M1060C and LCD2CCB) and balanced cables and even with the stock 220uf cathode bypass capacitor, I've only had fluctuations on the bias meter on some rare tracks with very extreme bass slam (see "Freqs Galore" by Bass Mekanik) with the volume turned very high. Maybe I'll try the 1000uf later, perhaps with the Elna Silmics.


----------



## baronbeehive

CopperFox said:


> Thanks for the advice! Ordered 0.33uf 600v Miflexes for the WCF position and 470uf 50V Nichicon KZ and 220v 0.1uf Kemet/Rifa for the cathode bypass position. 1000uf KZ's were not in stock (1000uf Nichicon FG was but I heard those aren't as good). I've been using the amp in stock configuration mostly with planars (M1060C and LCD2CCB) and balanced cables and even with the stock 220uf cathode bypass capacitor, I've only had fluctuations on the bias meter on some rare tracks with very extreme bass slam (see "Freqs Galore" by Bass Mekanik) with the volume turned very high. Maybe I'll try the 1000uf later, perhaps with the Elna Silmics.



The 470uF's should be fine, I doubt that power would be compromised on the LD, the issue we have tried to address mainly is the speed of bass, as well as bass heft. I have the KZ 470uF's, together with HE-500''s and it sounds great, was very impressed with the change from the Mundorf ECaps. The wire changes you mention are well worth it as well.

Your chassis extension looks nice!

Have you upgraded the resistors too, especially the power oes? They get very hot and burn out, so they need to be replaced.

BTW your ears will be grateful for using less than max volume LOL!


----------



## Maxx134

CopperFox said:


> Thanks for the advice! Ordered 0.33uf 600v Miflexes for the WCF position and 470uf 50V Nichicon KZ and 220v 0.1uf Kemet/Rifa for the cathode bypass position. 1000uf KZ's were not in stock (1000uf Nichicon FG was but I heard those aren't as good). I've been using the amp in stock configuration mostly with planars (M1060C and LCD2CCB) and balanced cables and even with the stock 220uf cathode bypass capacitor, I've only had fluctuations on the bias meter on some rare tracks with very extreme bass slam (see "Freqs Galore" by Bass Mekanik) with the volume turned very high. Maybe I'll try the 1000uf later, perhaps with the Elna Silmics.


All excellent choices, well done.
Good luck!


----------



## baronbeehive

Maxx134 said:


> All excellent choices, well done.
> Good luck!



... you forgot to mention those really.. really.. *really..* expensive gold plated fuses that he *really ought to use*... just joking!
.


----------



## baronbeehive

BTW, a little forward planning might be useful, so that you don't need to pull the board out more than once for example!


----------



## Maxx134 (Sep 28, 2020)

TBH, you can probably not have to pull the board unless you want to rewire the bottom fragile wiring that gets detached from the power transistors used in PSU for regulation.
Looking back, we did alot of work on this unit and it is like the "mold" and/or "standard", of how to boost a tube unit, to end game status.
For the cost savings, It really does put many stock units to shame.


----------



## baronbeehive

Maxx134 said:


> TBH, you can probably not have to pull the board unless you want to rewire the bottom fragile wiring that gets detached from the power transistors used in PSU for regulation.



It's certainly not for those of a nervous disposition to work on this amp because of that. Every time you switch on after working on it your heart is in your mouth in case that fragile wiring has come adrift after moving the board!




Maxx134 said:


> Looking back, we did alot of work on this unit and it is like the "mold" and/or "standard", of how to boost a tube unit, to end game status.
> For the cost savings, It really does put many stock units to shame.



Yes, exactly! I can see no reason to change it now, of course there are other amps that might do this or that a tad better, or differently, but this amp has such a sweet sound signature that why bother to look at anything else. Of course if I had money to burn I could have an amp for every occasion, but I'm out of all that. The amp can't make badly made music sound good but it certainly can make good music sound amazing.
.


----------



## Maxx134

Having much money to spend on gear is like a double edge sword, because your less likely to determine what is best for you, and end up collecting many beautiful choices..


----------



## baronbeehive (Sep 29, 2020)

Maxx134 said:


> Looking back, we did alot of work on this unit and it is like the "mold" and/or "standard", of how to boost a tube unit, to end game status.



And maybe we did a few things that were "non standard", like breaking the transistors way back at the beginning... .





Maxx134 said:


> Having much money to spend on gear is like a double edge sword, because your less likely to determine what is best for you, and end up collecting many beautiful choices..


Yes, and a few surprises along the way no doubt!

A big shock for me was how good the little APPJ could be made to sound .


----------



## Maxx134

baronbeehive said:


> A big shock for me was how good the little APPJ could be made to sound .


Haha size doesn't matter when it comes to sounds quality.
Smaller signal path could be an advantage, once bottleneck areas resolved..


----------



## baronbeehive (Sep 30, 2020)

Maxx134 said:


> Haha size doesn't matter when it comes to sounds quality.
> Smaller signal path could be an advantage, once bottleneck areas resolved..



Yes that was an area of concern with me re: all the additional wiring from the larger caps, I know it is probably unimportant in terms of relative lengths and impedances and so on, but I was never really happy with all that additional wiring on the LD!

Saying that, I couldn't pick up any adverse effects, the background remains dead quiet, and no interference.


----------



## CopperFox (Sep 30, 2020)

Maxx134 said:


> All excellent choices, well done.
> Good luck!



Aaand it's done. (Got to love tme.eu and their two day delivery at no extra cost).




Had the time to burn-in for +10 hours as well. These mods - replacing the WCF coupling caps and cathode bypass caps also had a massive overall effect. This is the most detailed, lively, impactful and airy sound I've heard. Lows, mids and highs all sound awesome. It's like being a room with the music playing around and not coming from headphones - on many tracks where I haven't noticed such effect before.

(Using Shuguang 6SL7-T "Natural Sound" driver tubes and sixties RCA 6080's running from a "summit-fi" R2R dac.)

After removing the stock cathode bypass caps, I noticed that they were not Philips 220uf 50v caps but Vishay 470uf 40v instead. Well I think I'll try those +1000uf caps there then at some point.


----------



## CopperFox (Sep 30, 2020)

baronbeehive said:


> The 470uF's should be fine, I doubt that power would be compromised on the LD, the issue we have tried to address mainly is the speed of bass, as well as bass heft. I have the KZ 470uF's, together with HE-500''s and it sounds great, was very impressed with the change from the Mundorf ECaps. The wire changes you mention are well worth it as well.
> 
> Your chassis extension looks nice!
> 
> ...




Thanks, I made the case extension by sawing pieces from 20*40mm pine wood and drilling (or actually dremeling) holes for the bottom plate screws in them. The screw holes for the bottom plate are for standard 3M screws so I got those in 50mm length. That is actually too long for most of them as the screw holes are less deep on the sides and front than in the rear so the correct lengths would probably be something between 44 and 49 mm. (The local nuts and bolts store had nothing between 40mm and 50mm so I went with the latter. Will look into ordering the correct lengths soon.).

Also had thought that I'd use some sort of wax or varnish finish on the wood. It does look quite nice unfinished though.

Haven't replaced any resistors yet. By power resistors do you mean those near the front or something near the transformers?


----------



## CopperFox

baronbeehive said:


> ... you forgot to mention those really.. really.. *really..* expensive gold plated fuses that he *really ought to use*... just joking!
> .



I think I have those in my dac. Silver wires too.
Heard that silver plated wires were recommended for the LDmkVI. Why not pure silver? What kind of effect does the different wiring have on sound?


----------



## baronbeehive

CopperFox said:


> Aaand it's done. (Got to love tme.eu and their two day delivery at no extra cost).
> 
> 
> 
> ...



WOW, fast work! You should notice even more effect after more burn in!

As you are using 6SL7 tubes you could also go for the anode/cathode mod which will increase liveliness and impact yet further...

Interesting about the stock caps, looks like they noticed that we had optimised those ourselves for better power performance and transit recovery, especially in bass frequencies!

Did you remove the PCB, looks like you soldered from the component side?


----------



## baronbeehive

CopperFox said:


> Thanks, I made the case extension by sawing pieces from 20*40mm pine wood and drilling (or actually dremeling) holes for the bottom plate screws in them. The screw holes for the bottom plate are for standard 3M screws so I got those in 50mm length. That is actually too long for most of them as the screw holes are less deep on the sides and front than in the rear so the correct lengths would probably be something between 44 and 49 mm. (The local nuts and bolts store had nothing between 40mm and 50mm so I went with the latter. Will look into ordering the correct lengths soon.).
> 
> Also had thought that I'd use some sort of wax or varnish finish on the wood. It does look quite nice unfinished though.
> 
> Haven't replaced any resistors yet. By power resistors do you mean those near the front or something near the transformers?



The blue ones to the left and right of the cathode caps (circled), from page 1. There are 8 in all, 4 on the reverse side. 330 ohm in the MKVi.


----------



## baronbeehive

CopperFox said:


> I think I have those in my dac. Silver wires too.
> Heard that silver plated wires were recommended for the LDmkVI. Why not pure silver? What kind of effect does the different wiring have on sound?



That was meat to be an in joke between us... but if you feel positive about those fuses why not!!

We went for silver plated copper mostly as that was recommended by the manufacturers. But we went a stage further for the output wires coming from the power tubes to headphone sockets. Some preferred OCC copper, I decided to go for OCC silver. I felt that silver produced a slightly cleaner, sharper sound, whereas copper was smoother and warmer. I know this is controversial as the resistances of silver and copper are not that dissimilar though.


----------



## Maxx134 (Oct 1, 2020)

CopperFox said:


> replaced any resistors yet. By power resistors do you mean those near the front or something near the transformers?


If your unit is new, it will take a while (months) before the stock resistors start to show burn marks from the heat they cannot handle. This will eventually change their values and alter performance.
So eventually it should be redone with wirewound resistors, but not imperative.




CopperFox said:


> What kind of effect does the different wiring have on sound?


It has greatest effect on headphone cables because of the lengths and windings.

Silver "plated" usually not recommended as, in general, it excites the sound somewhat, but in low level signal (line level or less) wiring (short runs) on the circuits & boards, it is actually beneficial in my experience, as low level signal will ride the surface, so beninfit is as if it was all silver wiring.


----------



## CopperFox

baronbeehive said:


> That was meat to be an in joke between us... but if you feel positive about those fuses why not!!
> 
> We went for silver plated copper mostly as that was recommended by the manufacturers. But we went a stage further for the output wires coming from the power tubes to headphone sockets. Some preferred OCC copper, I decided to go for OCC silver. I felt that silver produced a slightly cleaner, sharper sound, whereas copper was smoother and warmer. I know this is controversial as the resistances of silver and copper are not that dissimilar though.




Well, I don't really know how the fuses would affect sound since those came with the dac. Read some article web-translated from Japanese that gold plated fuses would sound slightly warmer.

Also don't know what effect the different wirings would have - in internal wiring. I know that in headphone/iem cables copper is usually more warm/smooth sounding and silver more sharp and less warm. It's more difficult to compare internal wirings than iem cables 



> As you are using 6SL7 tubes you could also go for the anode/cathode mod which will increase liveliness and impact yet further...
> 
> Interesting about the stock caps, looks like they noticed that we had optimised those ourselves for better power performance and transit recovery, especially in bass frequencies!
> 
> Did you remove the PCB, looks like you soldered from the component side?




Removed the PCB while removing the WIMAs for the coupling caps, but didn't bother removing it while removing the WIMAs for WCF coupling caps. Which mod is the anode/cathode mod, one of those on the first page?


----------



## CopperFox

Maxx134 said:


> If your unit is new, it will take a while (months) before the stock resistors start to show burn marks from the heat they cannot handle. This will eventually change their values and alter performance.
> So eventually it should be redone with wirewound resistors, but not imperative.
> 
> 
> ...




Ahh. Think I remember seeing some brownish discoloration on one of those resistors, possibly on the other side of the PCB. Did buy the amp used from Ebay so don't know exactly how long it has been used.


----------



## baronbeehive

CopperFox said:


> It's more difficult to compare internal wirings than iem cables



Yes, exactly. We only did this for the output wires to preserve the signal leaving the output tubes, because this amounts to an extension of the headphone cable, from inside to outside the amp. The rest of the internal wires are silver plated copper as Maxx said.


----------



## baronbeehive (Oct 2, 2020)

CopperFox said:


> Removed the PCB while removing the WIMAs for the coupling caps, but didn't bother removing it while removing the WIMAs for WCF coupling caps. Which mod is the anode/cathode mod, one of those on the first page?



You managed that alright obviously .

Just to sound a note of caution, the PCB is double sided and the traces are different on both sides so you could run into trouble. It would be best to check both sides of the board after any mods.

I summarized the testing of the anode/cathode mod here: https://www.head-fi.org/threads/lit...e-on-first-page.782183/page-243#post-15446810

It's well worth it! It involves changing the values of the 2 sets of resistors to optimise the operating point of the tube. This is for 6SL7's only, other tubes will have different ideal operating points.
.

Some high end amps have pure silver wire internally now.


----------



## CopperFox

baronbeehive said:


> You managed that alright obviously .
> 
> Just to sound a note of caution, the PCB is double sided and the traces are different on both sides so you could run into trouble. It would be best to check both sides of the board after any mods.
> 
> ...



Thanks, I'll have a look at it. Not sure if I'm able to figure out what to do from this data. Although I probably won't be using 6SL7's exclusively. The other mods are apparently still having a burn-in effect, as today the Shuguang Natural Sound 6SN7 sounds better than the 6SL7 version. Those two are my favorite driver tubes followed by the Tung-Sol 6SL7 reissue and some PSVane CV181 / 6SN7s. Haven't tried the original Tung Sols yet.


----------



## baronbeehive

CopperFox said:


> Thanks, I'll have a look at it. Not sure if I'm able to figure out what to do from this data. Although I probably won't be using 6SL7's exclusively.



No worries! If you do decide let us know and we can tell you which are the anodes/cathodes to change.



CopperFox said:


> The other mods are apparently still having a burn-in effect, as today the Shuguang Natural Sound 6SN7 sounds better than the 6SL7 version. Those two are my favorite driver tubes followed by the Tung-Sol 6SL7 reissue and some PSVane CV181 / 6SN7s. Haven't tried the original Tung Sols yet.



NOS tubes any day! I think the Chinese tubes are good nowadays, but the reissue TS's sound brittle compared to the NOS IMO.


----------



## baronbeehive

Re: the 6SL7 operating points on the graph, the new recommended is point 1 with Anode 69K, and cathode 380R. The stock position is at point 2. You can see that point 1 outputs a higher current at 1.2 mA than the stock point at 0.5mA. A further point about this is that the line where the tube operates is much closer to the bottom of the graph and you can see that the voltage lines are more curved in that region indicating less linearity. This means that the sound quality will be more distorted and therefore poorer.

The reason LD did this was probably because they chose a point that would sound as good as possible with various tube types as they didn't know what the owners would prefer to use. So tube rolling would be alright in this stock situation.


----------



## CopperFox

baronbeehive said:


> No worries! If you do decide let us know and we can tell you which are the anodes/cathodes to change.
> 
> NOS tubes any day! I think the Chinese tubes are good nowadays, but the reissue TS's sound brittle compared to the NOS IMO.




Okay, after a bit more burn in and considering/testing the options, I've decided it would be best to optimize the LD for 6SL7's.
I've got another desktop amp that's built for 6SN7s so those will go there. It's not balanced but has a separate power block and point to point wiring.

Next up I'll be ordering the replacement Mills 330 ohm power resistors so to get the anode/cathode resistors at the same time would make sense. Are they the small ones near the front of the board?

Also got some Wima MKP4 DC Link 500V 100uf capacitors (part nr.  DCP4H161007J ) to try out as decoupling caps. Haven't used 4 pin capacitors before. What would be the correct way to connect/solder those - is it to first connect two pins on one side (as in this photo) and then add a wire from the connecting wire to the cap positions on the pcb?



(Photo taken from Klipsch community forums)


----------



## baronbeehive

CopperFox said:


> Okay, after a bit more burn in and considering/testing the options, I've decided it would be best to optimize the LD for 6SL7's.
> I've got another desktop amp that's built for 6SN7s so those will go there. It's not balanced but has a separate power block and point to point wiring.
> 
> Next up I'll be ordering the replacement Mills 330 ohm power resistors so to get the anode/cathode resistors at the same time would make sense. Are they the small ones near the front of the board?
> ...



Yes connect the pins as in the photo negative to negative, positive to positive,

then connect to the PCB as in the pic below,(caps omitted):





Cathode1.5k's circled in red, anode 220k's circled in yellow below:


----------



## baronbeehive

CopperFox said:


> Okay, after a bit more burn in and considering/testing the options, I've decided it would be best to optimize the LD for 6SL7's.
> I've got another desktop amp that's built for 6SN7s so those will go there. It's not balanced but has a separate power block and point to point wiring.



You can still use the amp with 6SN7's, but the tube operating point will not be ideal.




CopperFox said:


> Also got some Wima MKP4 DC Link 500V 100uf capacitors (part nr.  DCP4H161007J ) to try out as decoupling caps.



Interesting, those high values, they should work well. There is a trade off between high value and speed of the charge-discharge cycle, I don't know what the optimum value would be.

I didn't test the amp before and after adding the decoupling caps, so I would be interested in your observations. The point of adding them is to stabilize the PSU, and increase operating speed by adding in a reservoir of fast acting power. Anything done to aid the working of the PSU will benefit the signal carrying the sound, I don't know if the effects will be discernable in the same way that coupling caps and so on aid the sound production but a proper functioning PSU is important.


----------



## CopperFox (Oct 19, 2020)

baronbeehive said:


> Cathode1.5k's circled in red, anode 220k's circled in yellow below:



Thanks! I assume the recommended values (from the previous graph) are 46K for the both two yellow-circled position resistors (on each side) and 390R for the one circled in red on each side.

Edit: What is the "Last R" 3K3 resistor/value?


----------



## baronbeehive

CopperFox said:


> Thanks! I assume the recommended values (from the previous graph) are 46K for the both two yellow-circled position resistors (on each side) and 390R for the one circled in red on each side.



The best values I found were 69K and 380R. Maxx also preferred 69K but he went with 1K for cathode. I had 500R before I put in the CCS, so anything between 380R and 1K would suffice.

When you have done this you should find that the sound and liveliness is pushed to end game, and the impact and textural detail is fantastic, violins scratch, drums crash, piano notes come out forcibly, guitar picks hit you palpably, and vocals are stunning, all have that detail that says the sound is real and "in your room"!


----------



## baronbeehive

Re: decoupling caps, we felt the need to add them to the output tubes as well as the driver tubes.

This is a quote from page 1.. always a handy reference LOL! "To improve this PSU, we have decided to add to the original design a "decoupling" cap near each power tube. The current feeding the headphones will be provided by the PSU and/or the decoupling cap, depending on the respective impedence at this time."


----------



## baronbeehive

CopperFox said:


> Edit: What is the "Last R" 3K3 resistor/value?


We went down to 1K for the last resistor in the CRC power supply filter. This boosted B+ to around 185V.


----------



## CopperFox

baronbeehive said:


> We went down to 1K for the last resistor in the CRC power supply filter. This boosted B+ to around 185V.



Should I replace that too now, or should the default resistor stay there if it's part of another mod?
Oh, and where is this resistor located


----------



## baronbeehive

CopperFox said:


> Should I replace that too now, or should the default resistor stay there if it's part of another mod?
> Oh, and where is this resistor located








You can replace them now, it won't interfere with anything else.

So how far do you want to go with the mods? It might be an idea to figure that out beforehand so that, for example you can do everything you want if you have to remove the PCB again. LD obviously didn't want anyone to interfere with the insides of their amp because they fitted such flimsy wires that they were bound to break the moment you opened it up, unless you were extremely careful, they have no sense of fun! Make sure you check these before you put the board back, or better still replace some of the wires perhaps. We have all torn our hair out many times over this!

The further you go with the mods the more you need to think about uprating other components eventually, for example you should uprate the resistor wattage from stock values anyway. Being slightly off the wall, we went the extra mile and uprated much of the insides, just for something to do, especially around the PSU area where the stock garbage resistors are likely to cook eventually.

One other thing switch over to high gain, with less negative feedback the sound is better.

Good luck, and happy modding!


----------



## Maxx134

There has been allot of changes and variations to the mods later in this thread, and so I see that the first page needs a bit of updating, so I will try to update things next week.

I do not believe @Redge78 is around to do it.


----------



## CopperFox (Nov 1, 2020)

Okay, so I replaced the power and anode/cathode resistors, added decoupling caps for the driver tubes and before those did some cathode bypass cap rolling.
Also re-soldered the Miflexes with 3% silver solder.

With the cathode bypass caps I tried Elna Silmic RFS 1000uf 50v and Nichicon KZ 1000uf 50v. Both with the same Kemet/Rifa 0.1uf 220v bypass added.
Both of the 1000uf caps sounded worse than the 470uf Nichicon KZ. The 470uf had clearly more bass slam and dynamics than the larger capacities. The Elna had better mids but less bass slam than the 1000uf KZ. Did about one week of burn in on both of the larger caps and there was almost no change in sound in them. The 470uf KZ had had a clearly perceivable gradual change during burn in. So I got tired and put them back in.

For the power resistors used the Mills 330ohm 5Ws. Most of the brands/products that were recommended on the first page for the anode/cathode positions were not available so I used Kiwame resistors for those since they seemed to be both highly rated and affordable and could not find any descriptions of negative experiences with them. used 68K for anode (69K was not availabe) and got three different values to try for the cathode position, which were 1k, 470 and 390. The 1k sounded very flat and the 390 had very low amount of bass, but the 470 brought a clear improvement in dynamics and detail. Would be interesting to try the next two values, which would be 510 and 430.

EDIT: Saw some old posts that stated that the impedance of headphones used would have an effect on the correct value here. Mine are modded Monolith M1060Cs whose rated impedance is 18 ohm.


The old power resistors were in good condition. There were some other resistors which had discoloration though:



Those four stacked resistors at the top which are near the power capacitors. Are there any recommendations/mods as to how those should be replaced?

The driver tube decoupling capacitors, where I used the 100uf 500v Wima MKP4s, did have effects on sound. Less noise/distortion, more definition, more nuance. Also the sound seems to have less difference at different volumes. Installed those just two days ago though so they're probably still burning in. Will need to see what happens and also to do more tube rolling. Will try the decoupling caps on power tubes later as well. But first I need to figure out where to put them so that they stay in one place and don't get too hot. I'll probably add one or two more fans to the bottom plate as the rear middle part of the amp can get pretty hot.

The various mods have also changed the way the different tubes sound. Looks like the larger bottle-shaped power tubes have improved the most (Svetlana 6N13S and Shuguang 6N5PJ).

Also tried some 6SN7 tubes after the latest changes and they sounded ok at least. Made me wonder if there is some way to "optimize" the amp for 6SN7's by changing the resistor values.


----------



## CopperFox

baronbeehive said:


> So how far do you want to go with the mods? It might be an idea to figure that out beforehand so that, for example you can do everything you want if you have to remove the PCB again. LD obviously didn't want anyone to interfere with the insides of their amp because they fitted such flimsy wires that they were bound to break the moment you opened it up, unless you were extremely careful, they have no sense of fun! Make sure you check these before you put the board back, or better still replace some of the wires perhaps. We have all torn our hair out many times over this!
> 
> (...)
> 
> ...



Well that's a tough question as I'm not sure if I'm aware of all the mods that can be done. 
Replacing all the wires with spc sounds too tedious at the moment.

The stock wires haven't felt brittle or come loose yet. They're thicker and and have more solder on them than DAP wirings for an example.

By high gain do you mean the high gain mode that the manual only recommends for use with the AKG K1000s?


----------



## baronbeehive

CopperFox said:


> With the cathode bypass caps I tried Elna Silmic RFS 1000uf 50v and Nichicon KZ 1000uf 50v. Both with the same Kemet/Rifa 0.1uf 220v bypass added.
> Both of the 1000uf caps sounded worse than the 470uf Nichicon KZ. The 470uf had clearly more bass slam and dynamics than the larger capacities. The Elna had better mids but less bass slam than the 1000uf KZ. Did about one week of burn in on both of the larger caps and there was almost no change in sound in them. The 470uf KZ had had a clearly perceivable gradual change during burn in. So I got tired and put them back in.



Really good work CopperFox!

That is very valuable observation and backs up what I said about the tradeoff between capacity and speed. You said that the 470uF had more dynamics and this is very similar to what I found with another amp. In that amp the high capacity caps sounded dull and flat, but were relieved by putting on the bypass cap. It may be that a lower capacity bypass cap on the cathode bypass would work well here and bring out the higher frequencies more to make for a more lively sound. This is something that we haven't experimented with atm.


----------



## baronbeehive

CopperFox said:


> For the power resistors used the Mills 330ohm 5Ws. Most of the brands/products that were recommended on the first page for the anode/cathode positions were not available so I used Kiwame resistors for those since they seemed to be both highly rated and affordable and could not find any descriptions of negative experiences with them. used 68K for anode (69K was not availabe) and got three different values to try for the cathode position, which were 1k, 470 and 390. The 1k sounded very flat and the 390 had very low amount of bass, but the 470 brought a clear improvement in dynamics and detail. Would be interesting to try the next two values, which would be 510 and 430.



That's another great observation! You say the 1K cathode was flat. I suspect there is an interaction with headphones and personal preference. Maxx has a 1K cathode and used to use Sennheiser HD800's. He likes the 1K, I don't know if he has tried lower like I did. I couldn't tell much difference between 390 and 500R, and there shouldn't be a massive difference because it wouldn't change the operating point that much. I felt that a cathode somewhere around those values produced the ideal amount of impact and texture.The point on the graph where the 6SL7 operating point is is clear of distortion but has less voltage swing. Again this is something we haven't one into in detail. It may be an idea to trade some linearity for some more voltage swing, although you don't need much swing with headphones.

I will post again with the graph to illustrate this.


----------



## baronbeehive

CopperFox said:


> The drive tube decoupling capacitors, where I used the 100uf 500v Wima MKP4s, did have effects on sound. Less noise/distortion, more definition, more nuance. Also the sound seems to have less difference at different volumes. Installed those just two days ago though so they're probably still burning in. Will need to see what happens and also to do more tube rolling. Will try the decoupling caps on power tubes later as well. But first I need to figure out where to put them so that they stay in one place and don't get too hot. I'll probably add one or two more fans to the bottom plate as the rear middle part of the amp can get pretty hot.



More interesting observations LOL!

I think we were of the opinion that driver tube decoupling woun't have much effect because the signal is so small, and therefore decoupling would have more of an effect on the power tubes.

Did you install the larger fans or the same size as stock?


----------



## baronbeehive (Nov 1, 2020)

We put our white decoupling caps here without any issues:






...they are very close to the hot 330R power resistors, but so long as you have good air flow.

Also you could put in a switch and resistor combo to change from 6SL7's to 6SN7's like here with a switch to change from 6AS7 to 421A power tubes.

We didn't optimise for 6SN7's ecause the higher gain of the 6SL7's is a better match for this amp, which is relatively low in power.

Edit: Sonic's amp is the most beautiful.


----------



## baronbeehive

CopperFox said:


> Well that's a tough question as I'm not sure if I'm aware of all the mods that can be done.
> Replacing all the wires with spc sounds too tedious at the moment.



I thought the same but for the few that are most important, like output wires and any that look fragile, it actually is quite a quick operation!



CopperFox said:


> By high gain do you mean the high gain mode that the manual only recommends for use with the AKG K1000s?



Yes. It means less negative feedback in the loop so better transparency in theory, provided there is no distortion.


----------



## SonicTrance (Nov 1, 2020)

baronbeehive said:


> We put our white decoupling caps here without any issues:
> 
> 
> 
> ...


I recognize this amp!  It seems like forever ago now. Brings back memories =) I see that I hadn't completed all the mods yet in this pic. Here's a pic with the Ra mod and CCS tail completed as well. I think the Ra mod is what @CopperFox is talking about here:


CopperFox said:


> EDIT: Saw some old posts that stated that the impedance of headphones used would have an effect on the correct value here. Mine are modded Monolith M1060Cs whose rated impedance is 18 ohm.


That is where we optimized the white cathode follower output stage for a specific load, using the Cavalli formula Ra = (1/Gm*(1/Ka*(1+Ka)/(1+Kr)*(Rp+Rl)/Rp+Rl/Rp))
I even went so far as to test my own tubes for actual gm, using my heathkit tester, and then calculate the different values to optimize the WCF for different tubes and loads.
I found this chart, this is for "stock" gm though:


----------



## baronbeehive

SonicTrance said:


> I recognize this amp!  It seems like forever ago now. Brings back memories =) I see that I hadn't completed all the mods yet in this pic. Here's a pic with the Ra mod and CCS tail completed as well....


... good times!

As I said your amp is the most beautiful... hope Maxx didn't hear that lol!
 .


----------



## baronbeehive (Nov 2, 2020)

Here you see several possible 6SL7 load lines, with bias point 1 having a voltage swing of 40v and point 3 having a swing of 100v. Therefore it would seem that point 3 would offer the best in terms of dynamics, but point 3 is also lower down towards the bottom of the graph where the grid lines are starting to curve indicating distortion, whereas point 1 lies on straighter more vertical grid lines indicating no distortion.

It would be interesting to try 2 or 3 extreme points to see what the auditory effects are. I didn't do this but concetrated on the positions where there would be near zero distortion for maximum transparency.

Edit: I see I did try quite a few varied positions after all, I forgot, but there's still a chance for some adventurous person to try more extreme positions just out of curiosity.


----------



## baronbeehive

CopperFox said:


> Well that's a tough question as I'm not sure if I'm aware of all the mods that can be done.
> Replacing all the wires with spc sounds too tedious at the moment.


In fact, you've already carried out the main mods, there's also the impedance mod matching output impedance to headphone impedance, which is a minor mod not resulting in much sonic benefit, there's also a power tube mod that allows you to switch between different types of tube, like 6AS7G's and 421A's. I've found since doing all the mods here that the humble common or garden RCA 6AS7G's sound so good that you don't need anything fancier than that.

So the only thing really would be to replace key wires with good quality wire, silver plated copper, and either OCC copper or OCC silver for the 6 output wires from the board to the output XLR jacks and the headphone socket.


----------



## baronbeehive

CopperFox said:


> Those four stacked resistors at the top which are near the power capacitors. Are there any recommendations/mods as to how those should be replaced?



The pair on the right should be 2x8k2 Mills MRA5, making a combined value of 4k1. The board value should read 8k2. You may have a more recent board in which case the value should read 4k1.
The pair on the left should be 2x5k1 Mills MRA5, making a combined value of 2k55. The board values should read 5k1. You may have a more recent board in which case the value should read 2k55.

The old boards had the wrong value which has probably been updated now

What values do you have on the board

These are the important resistors to change as you can see by the fact that they are partially cooked already, but the other resistors around that area would benefit from uprating as well.


----------



## CopperFox

baronbeehive said:


> Did you install the larger fans or the same size as stock?



80mm Noctuas, so it is the same size as stock except thicker of course. There would still be room for one or two more on the bottom plate.



baronbeehive said:


> We put our white decoupling caps here without any issues:
> 
> 
> 
> ...



Mine looks like this before putting the case extension and bottom plate back on now that I've installed the power tube decoupling caps:





It took some rearranging of other caps to put the middle Wima in its right place.
It would have fit between the four largest electrolytic caps on top of the white 100R 5W resistors as well, but I had some concerns about heat in that particular spot as it's the part of the amp where at least the exterior gets hottest during extended use. The two fans are not blowing directly into that spot even if they were a bit larger. So that's why it would seem reasonable to add one or two more fans.

A 6SL7 / 6SN7 switch would be interesting. What would be or how would one determine the correct resistor value range for 6SN7s?


----------



## CopperFox

SonicTrance said:


> I recognize this amp!  It seems like forever ago now. Brings back memories =) I see that I hadn't completed all the mods yet in this pic. Here's a pic with the Ra mod and CCS tail completed as well. I think the Ra mod is what @CopperFox is talking about here:
> 
> That is where we optimized the white cathode follower output stage for a specific load, using the Cavalli formula Ra = (1/Gm*(1/Ka*(1+Ka)/(1+Kr)*(Rp+Rl)/Rp+Rl/Rp))
> I even went so far as to test my own tubes for actual gm, using my heathkit tester, and then calculate the different values to optimize the WCF for different tubes and loads.
> I found this chart, this is for "stock" gm though:



Thanks for the chart, I don't remember having I've seen it before. Is the RI in the Cavalli formula the headphone impedance value?


----------



## CopperFox

baronbeehive said:


> The pair on the right should be 2x8k2 Mills MRA5, making a combined value of 4k1. The board value should read 8k2. You may have a more recent board in which case the value should read 4k1.
> The pair on the left should be 2x5k1 Mills MRA5, making a combined value of 2k55. The board values should read 5k1. You may have a more recent board in which case the value should read 2k55.
> 
> The old boards had the wrong value which has probably been updated now
> ...



My board says 8K2/2W and 5K1/2W. Thanks for this clarification, thought the board readings could be misleading somehow. How old is my board?


----------



## baronbeehive

CopperFox said:


> My board says 8K2/2W and 5K1/2W. Thanks for this clarification, thought the board readings could be misleading somehow. How old is my board?



There was a mismatch between the actual values of those resistors and the board values. LD confirmed this, and were to put this right which they haven't done for your board obviously. I don't know how old yours is because I don't know if the board still reads the same on the newer amps.

The actual values should be as I said earlier, which involves putting in the 2 resistors in parallel to make the final value of 4k1 for the 8k2 resistors. And go for 5watt resistors here.

Great work!


----------



## baronbeehive

CopperFox said:


> 80mm Noctuas, so it is the same size as stock except thicker of course. There would still be room for one or two more on the bottom plate.



The Enermax fan I got a while ago has been superseeded but one like this would tick the box: https://www.enermaxeu.com/products/fans/silent-fans/cluster-adv/
The 120mm one pushes a high volume of air silently which would find it's way throughout the chassis and up the sides to the top, that's what we have done. You would have to bore bigger holes in the bottom plate but if you wanted to fit additional fans you would have to do that anyway.

Better to have an external speed controller and power supply to take this out of the amp, something like this: https://www.amazon.co.uk/Cooling-co...94&sr=1-125&keywords=3+Pin+to+4+Pin+fan+Cable

The fan has LED's which look very pretty!


----------



## SonicTrance

CopperFox said:


> Thanks for the chart, I don't remember having I've seen it before. Is the RI in the Cavalli formula the headphone impedance value?


Yes, Rl is the headphone impedance.


----------



## baronbeehive

CopperFox said:


> A 6SL7 / 6SN7 switch would be interesting. What would be or how would one determine the correct resistor value range for 6SN7s?



You would have to draw the load line for the 6SN7 tube using it's datasheet, and most likely test different values for SQ like I did for the 6SL7, I might get back to you but haven't the time atm.

Keep us posted!
.


----------



## baronbeehive

Thanks to Yaska729 who has said that the revamped LD website is back up.. and here it is: http://www.littledot.net/


----------



## Yaska729

baronbeehive said:


> Thanks to Yaska729 who has said that the revamped LD website is back up.. and here it is: http://www.littledot.net/


Not a problem, but honestly it might be easier just go to their new site, if the customer service is needed.


----------



## baronbeehive (Nov 3, 2020)

Here's 2 suggested load lines for the 6SN7 tube.

Line 1 - outputs 18mA, with a 10K anode and 280R, or 888R cathode
Line 2 - outputs 5mA, with a 35K anode and 666R, or 2K cathode

I think points 1 and 3 would be the most transparent.


@CopperFox you could try these values. If you wanted you could try an intermediate anode of around 22K also.

If you didn't want to be bothered with too many resistors, I would go for a compromise and try around 250R, 500R, 1K and 2K for cathodes, along with the 2 or 3 different anodes, it would still be ear enough.

Guys... look at the stock bias point right in there amongst the curved grid lines. I suppose it's ok because the voltage swing is so small, that it might not get into the distortion areas. But it's pretty weird down so low, and I know that a lot of people preferred the 6SN7, maybe for its possibly more tubey qualities?

It would be interesting to try those more extreme areas of the grid for different sonic qualities.


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## baronbeehive (Nov 8, 2020)

Out of interest I have included on the graph the ideal bias point I found for the 6SL7 tube, (in green). You can see why the amp is better for 6SL7's, at least with the stock bias point. Another factor is that the 6SL7 has an amplification factor of 70 whereas the 6SN7 is 20.

@CopperFox I would ignore the points on line 1 and just go for the points on line 2 or points on an intermediate line given by an anode of around 22k as I said previously. The reason is that the max rating for the 6SN7 is 20mA with a typical operation of 10mA.


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## baronbeehive (Nov 4, 2020)

...and the 2 blue bias points correspond to points 1 and 2 on line 2 on the previous post, which showed the graph for 6SN7's, just out of interest.

I hope that's clear, maybe not!






So it appears that both the stock amp and the amp optimised for 6SL7's will work with 6SL7 *and* 6SN7 tubes. But the amp optimised for 6SN7's will *not* run on 6SL7 tubes so that should be born in mind. That's obviously why LD chose their tube parameters.


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## baronbeehive

I should have said.. the amp optimised for 6SN7's will not run on SL7 tubes.. *unless* it has a switch much like Sonic's switch that selects between 2 different power tube types.

I haven't used 6SN7's for ages but they sounded perfectly fine when I first tried them. Though the gain is much less on them, if the amp is on high gain that would compensate for that. So it would be interesting to try these different values for the 6SN7 just to see how good it would sound optimised for them. I couldn't tell any difference between the 6SL7 and the 6SN7's but I know that some did prefer the 6SN7's.


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## baronbeehive

@CopperFox if you do want to go ahead with your 6SN7 optimisation you can do that with the values I gave, *if you're only going to use 6SN7's*. Let me know if you want to try the switch and I will find out about that before you go ahead.


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## metamorph63

I don't know if this is the right place to ask this question...anyway, If you wanted to change the potentiometer to a little dot mkviii se, what would be the best choice?


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## baronbeehive

metamorph63 said:


> I don't know if this is the right place to ask this question...anyway, If you wanted to change the potentiometer to a little dot mkviii se, what would be the best choice?



I don't know. Nobody on the thread thought it worthwhile to replace theirs, except for one that tried a stepped attenuator, I don't know any details though, sorry.


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## CopperFox

baronbeehive said:


> @CopperFox if you do want to go ahead with your 6SN7 optimisation you can do that with the values I gave, *if you're only going to use 6SN7's*. Let me know if you want to try the switch and I will find out about that before you go ahead.



Hi and thanks again for all this information.

Building the switch would be interesting as I have lots of 6SN7 tubes from my other amp. If I'm doing that it would be some time next year as I'll still be trying some things with the 6SL7s (and as the amp already sounds really good as it is). Such as trying 400uf 400v MKP Wimas for the PSU output caps since I still have room for large caps in the case and also rolling some cathode resistor values, WCF decoupling caps and possibly different resistor brands/materials as well. And buying different chinese power tubes from the 11.11. sale on AE. There have been some popping up there that I haven't seen before, not current production though.

Have also been busy with other stuff recently - ordered a new car last weekend.


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## baronbeehive

CopperFox said:


> Hi and thanks again for all this information.
> 
> Building the switch would be interesting as I have lots of 6SN7 tubes from my other amp. If I'm doing that it would be some time next year as I'll still be trying some things with the 6SL7s (and as the amp already sounds really good as it is). Such as trying 400uf 400v MKP Wimas for the PSU output caps since I still have room for large caps in the case and also rolling some cathode resistor values, WCF decoupling caps and possibly different resistor brands/materials as well. And buying different chinese power tubes from the 11.11. sale on AE. There have been some popping up there that I haven't seen before, not current production though.
> 
> Have also been busy with other stuff recently - ordered a new car last weekend.



No worries!

I was interested in the 6SN7 optimisation, since you mentioned it, and might have been interested in trying it myself. However as that would involve disconnecting my CCS I won't be trying that atm. No one here has tried that as it would involve not being able to use our 6SL7's at the same time. Little Dot used a compromise solution that enabled both 6SL7's and 6SN7's to be used albeit not at their ideal operating points so that tube rollers would be happy.

As maintaining a stable and efficient PSU is vital, your idea of upgrading to Wima MKP for the output caps should have great benefits. As I have the compact version of the mods that was something I couldn't do but I believe those who extended outside the chassis also had great benefits from this.

What values are you going to try for the cathode resistors? It would be useful to everyone here if you could keep a note and give us your impressions of the differences. If you want I can check the values you want to try. For instance nobody has tried more extreme values in the lower part of the grid on the graph, that might be interesting.

Also what power tubes have you tried? Impressions would be interesting as well!


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## baronbeehive

CopperFox said:


> Have also been busy with other stuff recently - ordered a new car last weekend.



I would have thought that a sledge would be more useful in the Arctic lol!


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## baronbeehive

CopperFox said:


> ... and also rolling some cathode resistor values,






That area circled would likely offer a different type of sound with different possibilities in distorted, or tubey sound!


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## CopperFox

baronbeehive said:


> No worries!
> 
> I was interested in the 6SN7 optimisation, since you mentioned it, and might have been interested in trying it myself. However as that would involve disconnecting my CCS I won't be trying that atm. No one here has tried that as it would involve not being able to use our 6SL7's at the same time. Little Dot used a compromise solution that enabled both 6SL7's and 6SN7's to be used albeit not at their ideal operating points so that tube rollers would be happy.
> 
> ...







Here are the 400uf 400V Wimas in place as PSU output capacitors, making the other capacitors look small. These are the fastest capacitors in the Wima MKP4 line with ESR at 1.0 mOhm and  Irms at 43 A. The 100uf 500v have 1.9 mOhm and 23 A.

Shortly after installing these I removed the 0.1uf Kemet/Rifas as there was too much treble sparkle (which I sensed was not due to low burn-in) but that fixed it entirely. I think @Maxx134 also said in some post he doesn't use them and he also has upgraded PSU output caps and the Nichicon KZs in use.

I've been using many different power tubes which have been 60's and 70's RCA 6080 (these have different sound and construction from different years/decades), 80s GE Jan 6AS7G, Thomson WA 6080, Chatham/Tung-Sol 6080, Svetlana 6N13S and Shuguang 6N5P.

With installing the decoupling caps and PSU output Wimas, the Svetlanas and Shuguangs have improved the most. The Shuguangs in the stock configuration have very liquid mids and very soft treble but great bass and excellent soundstage, which many people would almost like but the softness in mids/treble leads to an overall too fuzzy sound. That excess softness has gone away with the decoupling caps and psu cap upgrade so now they sound really good. The Svetlanas in the stock configuration have  the biggest soundstage but loose and un-solid bass and somehow thin-sounding highs as well and some unbalance in the mids toward upper mids. These negatives have also much improved with the PSU output and decoupling caps.  For the last three days the Shuguangs have sounded the best, but today it is the Svetlanas. I think the latest upgrades are still settling in and I'll know the eventual outcome in some weeks' time.

The PSU output caps have made the largest difference here but they were also installed last so I don't know how it would go in some different installation order.

Also with the Shuguang 6N5PJs the sound with the driver tube decoupling caps but without power tube decoupling caps was quite interesting and pleasant. It was more detailed and layered than before but still with a lot of softness. A bit like a watercolour or oil painting. Will maybe try that again some time later. A "softness switch" to connect/disconnect the power tube decoupling caps could be fun.

Noting that the large bottle-shaped power tubes have now sounded the best I ordered Nanjing 6N5Ss (6H5Cs) and Shugugang 6N13PTs from the 11. 11. sale to try out and some Shuguang WE6SL7 Pluses as well.

The resistor values I could try are 510, 430 and also the 390 that I tried before.


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## CopperFox

baronbeehive said:


> That area circled would likely offer a different type of sound with different possibilities in distorted, or tubey sound!



How are positions on the chart coverted into resistor values?


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## baronbeehive

CopperFox said:


> Here are the 400uf 400V Wimas in place as PSU output capacitors, making the other capacitors look small. These are the fastest capacitors in the Wima MKP4 line with ESR at 1.0 mOhm and  Irms at 43 A. The 100uf 500v have 1.9 mOhm and 23 A.



Really excellent work!

There is much of interest here. You have gone for the fastest PSU caps which should make a massive difference. I think you have the fastest and highest capacity MKP's of anyone here. It would be interesting to compare with the 1500uF lytics that we have got for the compact version. I suspect that yours would be much the superior cap.


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## baronbeehive

CopperFox said:


> Shortly after installing these I removed the 0.1uf Kemet/Rifas as there was too much treble sparkle (which I sensed was not due to low burn-in) but that fixed it entirely. I think @Maxx134 also said in some post he doesn't use them and he also has upgraded PSU output caps and the Nichicon KZs in use.



Haha.. too much treble sparkle! I have spent a lot of time trying to increase it to get more highest frequencies for added textural detail! However I don't want too much, I hate sybillant vocals or cymbals for example.


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## baronbeehive (Nov 15, 2020)

CopperFox said:


> With installing the decoupling caps and PSU output Wimas, the Svetlanas and Shuguangs have improved the most. The Shuguangs in the stock configuration have very liquid mids and very soft treble but great bass and excellent soundstage, which many people would almost like but the softness in mids/treble leads to an overall too fuzzy sound. That excess softness has gone away with the decoupling caps and psu cap upgrade so now they sound really good. The Svetlanas in the stock configuration have  the biggest soundstage but loose and un-solid bass and somehow thin-sounding highs as well and some unbalance in the mids toward upper mids. These negatives have also much improved with the PSU output and decoupling caps.  For the last three days the Shuguangs have sounded the best, but today it is the Svetlanas. I think the latest upgrades are still settling in and I'll know the eventual outcome in some weeks' time.



Yes the MKP's should improve all of that by tightening up the sound, especially bass. I am interested in what you say aout the power tubes. I haven't tried the Svetlanas and am thinking of giving them a try, perhaps in combination with the RCA's in a configurartion of Svetlana +'ive phase, with RCA's for -'ive phase in each channel.

Keep us informed of your impressions as you proceed.


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## baronbeehive

CopperFox said:


> Also with the Shuguang 6N5PJs the sound with the driver tube decoupling caps but without power tube decoupling caps was quite interesting and pleasant. It was more detailed and layered than before but still with a lot of softness. A bit like a watercolour or oil painting. Will maybe try that again some time later. A "softness switch" to connect/disconnect the power tube decoupling caps could be fun.



A softness switch, now you're talking! I was thinking about that switch for the 6SN7/6SL7 you were interested in. We could end up with several switches for different sound qualities! Might be a great idea!

Wonder why LD haven't thought of that!
.


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## baronbeehive

CopperFox said:


> The resistor values I could try are 510, 430 and also the 390 that I tried before.



You mean for the 6SL7's, I will get back to you on that.


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## baronbeehive

CopperFox said:


> How are positions on the chart coverted into resistor values?


You need to use the tube datasheet, draw the load line for your amp, and calculate the values using Ohm's law.


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## baronbeehive (Nov 16, 2020)

This graph shows the values we used and some suggested values using 6SL7 tubes:

The suggested anode/cathode values are ones either we used or values I proposed to test. I settled on an anode value of 69K, and cathode value of 380R as being the best sonically. So @CopperFox I suggest you use my anode value and try different cathodes, anything between 380R and 10K but I wouldn't use values that are too close like 380R and 450R for example because they won't be at much different points on the load line.

The graph shows Maxx's, Sonic's and stock values plus my proposals shown in different colours.

Below I also said that you could try 5K and 10K suggested values in blue. These are points that haven't been tried but would take you into interesting points on the grid which should be sonically quite different.... possible points to use in a switch!!

You could try 5K and 10K with any of the anode values, including stock as shown.


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## Maxx134 (Nov 17, 2020)

Reason I chose my values was because the anode setting gave me most Dynamics & least compression (listening impression with 6sl7mu types) and the cathode resistance value could have been lower, but instead kept at highest setting that  sounded optimal, as I felt lower values would lose the design intention of using a "common Cathode",  forcing the triodes to perform evenly.
Ideally the CCS mod on the cathode would have solved this, but the  advantage to tunning resistor settings for bias points, is that you instead can  highlight the added tube harmonic characteristics of the tube model/brand you choose.
In other words, retaining  euphoric tube coloring.

Although I owned the MK8 model, wich uses 12a**7 types in driver stage, I did not test bias points with them.
I instead choose to use 6pin types, and settled on the 6sl7 type.
It be a touch too much gain for the MK6 output tubes, as I am using MK8, so someone with MK6 would be better to comment on that.


Yet, another main reason why you should test, tune, and choose your own the bias point, is because of the output stage.
Using different tube type on output stage, will respond differenly to the input tube choice.
Synergy between both tube stages.
So I preferred the higher MU output of the 6sl7 types, as the output tubes I chose accepted that higher amplification.

So choosing the driver tube choice depending on the output tube choice, depending on which gain setting you choose...
Hehe nobody said being a designer was easy... And that's exactly what role you are choosing, in performing bias changes...


So, to summarize:
I chose higher gain for less global feedback, then choice of output tubes for most clarity, (over output power), then chose the driver tube type (mu/gain) that sounded best, with the newer bias settings...


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## baronbeehive

Maxx134 said:


> Although I owned the MK8 model, wich uses 12a**7 types in driver stage, I did not test bias points with them.
> I instead choose to use 6pin types, and settled on the 6sl7 type.
> It be a touch too much gain for the MK6 output tubes, as I am using MK8, so someone with MK6 would be better to comment on that.



Yes the gain is high but I feel the transparency it provides is worth it, but I rarely get past a quarter to on the dial.




Maxx134 said:


> Yet, another main reason why you should test, tune, and choose your own the bias point, is because of the output stage.
> Using different tube type on output stage, will respond differenly to the input tube choice.
> Synergy between both tube stages.
> So I preferred the higher MU output of the 6sl7 types, as the output tubes I chose accepted that higher amplification.
> ...



Well we've messed around with this amp for too long.. but it's worth it in the end!

The response of the output tubes to the bias point changes had been noted by CopperFox, he has provided much valuable information with those changes, and his PSU cap upgrades. He may do more testing and possibly go down in the distortion region of the grid.. on my recommendation..!!! to see what the sonic effects there are like. If he decides to try out the 6SN7 bias changes he expressed interest in using a switch to change between 6SL7 and 6SN7. Obviously LD chose the bias for both tube types in a compromise but if the amp was optimised for both tube types there would have to be a switch. That would enable you to tailor the amp to your own preferences, and change from one to the other to suit your mood!!

We could end up with more switches than the NY telephone exchange haha!




Maxx134 said:


> So, to summarize:
> I chose higher gain for less global feedback, then choice of output tubes for most clarity, (over output power), then chose the driver tube type (mu/gain) that sounded best, with the newer bias settings...



Yes that's what I prefer too. (It's what I did on the APPJ amp too, with the highly regarded Amperex power tubes for clarity and warmth, and the Philips driver for detail and soundstage and it works very well on that amp).

I was also interested in trying the Svetlana power tubes on the LD for detail in the +'ive phase of each channel and keep the warmer RCA's in the -'ive phase for that reason.


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## baronbeehive (Nov 17, 2020)

Just out of interest.. and for fun.. for anyone that would like to try optimising *for 6SN7 tubes only* the following graph gives a reasonable spread of values to test:

Disregard line 1

Lines 2 and 3 read off the values for anode (Ra) and cathode (Rk)

Stock values are there (black line).

I think the most transparent bias point would be at point 5 or thereabouts.

Bias points 7 and 8 are the more extreme bias points on the grid nearest to the nonlinear areas so might provide some interesting distortion (tubey) effects! If you want to test these 3 points you could try cathode values of around 2K - 4K. If you had a 5K or 10K lying around you could try the most extreme areas right down the bottom of the grid somewhere near the stock points but further to the right near the bottom.

Any values in between could also be tried.

*Remember, this will only work for 6SN7 tubes and if you try this you cannot then use 6SL7's.*


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## Maxx134 (Nov 17, 2020)

baronbeehive said:


> Just out of interest.. and for fun.. for anyone that would like to try optimising *for 6SN7 tubes only* the following graph gives a reasonable spread of values to test:
> 
> Disregard line 1
> 
> ...




I actually would recommend your settings over mine, as you have the MK6, while my MK8 has different output tubes so their input characteristics are different.

I am not even using MK8 type output tubes, but instead another, lower output, but more holographic tube, which I preferred.

So it's preferred to select your favorite driver tube, and then test its bias around those recommended settings, to complement your output tubes.

the no matter which driver tube you use is going to sound vastly different (better) once you get the bias up to the recommended levels.

The stock bias points are so low, it's like not even having it work to give any gain, hehe


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## baronbeehive

Maxx134 said:


> The stock bias points are so low, it's like not even having it work to give any gain, hehe



...yes right, that has lead me to revise my recommendations for the optimisation too!
.


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## baronbeehive

*Re: my recommendations for the optimisations for both 6SN7's, and 6SL7's* I think the 10K cathode I suggested to get right down there in the nonlinear regions of the grid should be ditched, it goes down too far and as Maxx said the bias is so low it wouldn't be worth bothering.

So stick with the 5K as the highest value cathode, that will go far enough!


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## CopperFox (Jul 1, 2021)

Ok, so I have now tried 510R and 430R resistors for the cathode position. Previously, I had tried 1K, 470R and 390R. Out of those, the 470R sounded best while the 390 was very low on bass, low on mids and quite airy. 1K sounded like it lacked dynamics and extension in both ends.

When compared to the 470R, the 1K and 510R have similar characteristics, but the 510R deviates less from the 470R than the 1K.
Similarly, when compared to the 470R, the 390R and 430R have similar characteristics, but the deviation is smaller on the 430R.

However - after having tried the 430R for five days I was planning to put the 470R back on. After opening the amp I noticed that one of the cathode bypass (470uf 50v Nichicon KZ) had bulged and leaked. So I put the 1000uf Nichicon KZ's back there and also left the 430R back in. ( I had tried the 1000uf caps before when I didn't yet have the decoupling caps, but they just didn't work then. )

The 1000uf + 430R sounded less different from the 470R + 470uf combination than the 430R + 470uf combination did. Bass and treble were both good but mids were still sounding too thin compared to the 470R position.

It was also obvious that the 1000uf caps sounded better than the 470uf caps now that I have the decoupling caps installed (edit: but only in high gain).

So what can be taken from this is that the effect of the resistor value changes is linked to the capacity of the cathode bypass  - whose effect seems linked to the decoupling caps. And at least the 430R seemed to produce too much current with my planars for the 470uf caps to handle.

I'm planning to put the 470R back on and try larger cathode caps still. The Nichicon KZ and FG and Elna Silmic series are not available in +1000uf/+50V, so I ordered some 2200uf and 3300uf 100v Nichicon FWs. The Audio Note Kaiseis are also available in 2200uf and 4700uf 63v rating but they are very expensive. The FW actually has quite good specs in the 2200uf 100v capacity.


----------



## CopperFox

I do have a bigger problem now though. I decided to replace one of the UV meters after having damaged it on my first try of taking the pcb out months ago. Should not have done that in a hurry - I miswired the meter and the 12v light wires got mixed with the wires for the current meter, resulting in the light exploding in a bright cyan flash and two charred resistors near the power supply capacitors. There's no other visible damage though - I wonder what other components in the 12V circuit might have been damaged and/or need replacing, if any. Will replace the resistors once I get them.

Surprisingly, the wires going to the UV meters had at least one resistor in them as well. Anyone else have a more complete idea what is/should be inside those cables? Guess I could remove the heat shrink from the other meter's cables to see for myself.


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## baronbeehive (Jan 7, 2021)

CopperFox said:


> Ok, so I have now tried 510R and 430R resistors for the cathode position. Previously, I had tried 1K, 470R and 390R. Out of those, the 470R sounded best while the 390 was very low on bass, low on mids and quite airy. 1K sounded like it lacked dynamics and extension in both ends.
> 
> When compared to the 470R, the 1K and 510R have similar characteristics, but the 510R deviates less from the 470R than the 1K.
> Similarly, when compared to the 470R, the 390R and 430R have similar characteristics, but the deviation is smaller on the 430R.



Yes, pretty much as expected. I agree with you about this, the lower values are best for dynamics. I wouldn't have thought there was much difference between cathodes of fairly similar values but it could be that you have managed to hit the "sweet spot". Also there will be small differences in other things, such as the B+ which will depend on the last resistor at the end of the CRC filter mentioned before.

With too low a cathode value there would be a disadvantage because it is usual to load the plates at several multiples of the plate resistance.


----------



## baronbeehive

CopperFox said:


> However - after having tried the 430R for five days I was planning to put the 470R back on. After opening the amp I noticed that one of the WCF coupling caps (470uf 50v Nichicon KZ) had bulged and leaked. So I put the 1000uf Nichicon KZ's back there and also left the 430R back in. ( I had tried the 1000uf caps before when I didn't yet have the decoupling caps, but they just didn't work then. )
> 
> The 1000uf + 430R sounded less different from the 470R + 470uf combination than the 430R + 470uf combination did. Bass and treble were both good but mids were still sounding too thin compared to the 470R position.
> 
> ...



Yes, I've found the caps can leak sometimes especially if they are squeezed into position up against other components so care is needed.

That's another interesting finding about cathode cap capacitance, I assume you mean cathode caps not WCF caps. I imagine that because you have very fast acting MKP film decoupling caps that this interacts with cathode cap capacitance to give a better overall frequency response, especially with the higher capacitance caps.

With the higher capacitance caps, the higher you go the more likely you will need to put back in the small capacitance bypass caps to restore the treble frequencies. The higher you go potentially the better transient response you will get, but at some point there will be a trade off with speed of the charge/discharge cycle.


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## baronbeehive (Jan 7, 2021)

CopperFox said:


> I do have a bigger problem now though. I decided to replace one of the UV meters after having damaged it on my first try of taking the pcb out months ago. Should not have done that in a hurry - I miswired the meter and the 12v light wires got mixed with the wires for the current meter, resulting in the light exploding in a bright cyan flash and two charred resistors near the power supply capacitors. There's no other visible damage though - I wonder what other components in the 12V circuit might have been damaged and/or need replacing, if any. Will replace the resistors once I get them.
> 
> Surprisingly, the wires going to the UV meters had at least one resistor in them as well. Anyone else have a more complete idea what is/should be inside those cables? Guess I could remove the heat shrink from the other meter's cables to see for myself.



I also had to replace my meters after using a wrong value resistor in the wrong place! I don't expect there will be other damage.. except your pride . The resistors near the power supply need upgrading anyway as they are prone to cooking.... and that will be a good opportunity to do that. You need to use uprated Mills in that area, I will post a picture.

Is your amp still working alright?

Yes there is a resistor hidden inside those wires, I can't remember the value. but it adjusts the voltage to 12v. If I can remember I will let you know, but you can read off the resistance from the other wire.


----------



## baronbeehive

These are the main PSU resistors circled to upgrade with 5 watt Mills, read off board values. Also at point 3 in the pic upgrade the Zeners as well as MIlls too as they can be a bottleneck, to make sure you don't run into problems down the line.


----------



## CopperFox

baronbeehive said:


> Yes, I've found the caps can leak sometimes especially if they are squeezed into position up against other components so care is needed.
> 
> That's another interesting finding about cathode cap capacitance, I assume you mean cathode caps not WCF caps. I imagine that because you have very fast acting MKP film decoupling caps that this interacts with cathode cap capacitance to give a better overall frequency response, especially with the higher capacitance caps.
> 
> With the higher capacitance caps, the higher you go the more likely you will need to put back in the small capacitance bypass caps to restore the treble frequencies. The higher you go potentially the better transient response you will get, but at some point there will be a trade off with speed of the charge/discharge cycle.



Yes, meant the cathode bypass caps and not the wcf caps. Edited the post.


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## CopperFox (Jan 9, 2021)

baronbeehive said:


> I also had to replace my meters after using a wrong value resistor in the wrong place! I don't expect there will be other damage.. except your pride . The resistors near the power supply need upgrading anyway as they are prone to cooking.... and that will be a good opportunity to do that. You need to use uprated Mills in that area, I will post a picture.
> 
> Is your amp still working alright?
> 
> Yes there is a resistor hidden inside those wires, I can't remember the value. but it adjusts the voltage to 12v. If I can remember I will let you know, but you can read off the resistance from the other wire.




The amp isn't starting properly. Tubes light up, UV meter lights turn up but the meters didn't move, sound came through to headphones but at a very low volume. After further looking around I noticed that some of the eight power resistors (Millls 5w 330ohm) were also darkened and/or cracked. So I took the board out and replaced those eight with 10W Ohmite Audio Gold 330ohm resistors, which I had lying around. Haven't yet tried again after that.

I noticed that some earlier posts stated that the resistor in the uv meter light wire would be 68 ohm or 0.68 ohm. But it looks like 8 ohm to me.


Edit: added photo of resistor on uv meter light wire:


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## CopperFox (Jan 9, 2021)

baronbeehive said:


> These are the main PSU resistors circled to upgrade with 5 watt Mills, read off board values. Also at point 3 in the pic upgrade the Zeners as well as MIlls too as they can be a bottleneck, to make sure you don't run into problems down the line.




Yeah, the two blue resistors in point 3 were the ones that got charred. Will be replacing those with something. - what would be the best here? There are two other components inside that circle too, which are smaller and black/gray and have a letter Z on them. The board has the text "100V 1W" on those spots. What are those components and is there any recommendation for their replacement?

Although the two blue resistors there got literally charred, those two Z components at least look alright. Maybe it would still be good to replace those.


Edit: reading back on the thread, there were advice also to replace the PNP / NPN transistors in cases where those two blue resistors were burned. Where would these transistors be located?

 Edit #2: Below that middle hump on the case?


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## baronbeehive

CopperFox said:


> The amp isn't starting properly. Tubes light up, UV meter lights turn up but the meters didn't move, sound came through to headphones but at a very low volume. After further looking around I noticed that some of the eight power resistors (Millls 5w 330ohm) were also darkened and/or cracked. So I took the board out and replaced those eight with 10W Ohmite Audio Gold 330ohm resistors, which I had lying around. Haven't yet tried again after that.
> 
> I noticed that some earlier posts stated that the resistor in the uv meter light wire would be 68 ohm or 0.68 ohm. But it looks like 8 ohm to me.
> 
> ...



It looks from your pic that the resistor bands are: brown, black, gold and red in which case it would be 1R, so probably .68R would be right. You can check resistor values here: https://www.allaboutcircuits.com/tools/resistor-color-code-calculator/


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## baronbeehive (Jan 10, 2021)

CopperFox said:


> Yeah, the two blue resistors in point 3 were the ones that got charred. Will be replacing those with something. - what would be the best here? There are two other components inside that circle too, which are smaller and black/gray and have a letter Z on them. The board has the text "100V 1W" on those spots. What are those components and is there any recommendation for their replacement?
> 
> Although the two blue resistors there got literally charred, those two Z components at least look alright. Maybe it would still be good to replace those.
> 
> ...



You should replace all those resistors around the PSU area with uprated Mills 5w which will insure against future problems like we have all done. Looks like yours have burnt out with a surge in those zener diodes, which are those black components with a z on them. You should replace these with uprated zeners also. When you replace them make sure you put in the new ones the right way round, check out the line going round one end.

Yes I would definately advise to change the transistors as well as the originals were prone to failure with increased loads. It sounds a lot but once you have done all this, and now would be a good time to do it, you shouldn't have to touch the PCB again, hopefully .

Yes they're under those covers if I remember right, look for 3 wires going into that area from the inside of the top chassis. Make sure you replace PNP with PNP and NPN with NPN and make sure there is no contact with the metal on the chassis, there should be an insulated pad there between the transistors and the chassis!

We mentioned what are the replacement transistors back in the thread, the originals are superseeded now with better ones.


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## baronbeehive (Jan 10, 2021)

We've all been through this BTW .

Have you got a multimeter? It would come in handy if you need to check resistor values to find the fault you have with no sound.


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## baronbeehive

CopperFox said:


> Edit: reading back on the thread, there were advice also to replace the PNP / NPN transistors in cases where those two blue resistors were burned. Where would these transistors be located?



We like you.. you actually read the thread, most people think it's too boring lol!


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## CopperFox

baronbeehive said:


> It looks from your pic that the resistor bands are: brown, black, gold and red in which case it would be 1R, so probably .68R would be right. You can check resistor values here: https://www.allaboutcircuits.com/tools/resistor-color-code-calculator/



Hmm. To me that looks clearly gray, black, gold and brown which would be 8R. That's what I put there and the meter did light up. Looked more bright than the other side though, could be from having a newer light. Or something else.


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## CopperFox

baronbeehive said:


> We've all been through this BTW .
> 
> Have you got a multimeter? It would come in handy if you need to check resistor values to find the fault you have with no sound.



No, but those are not expensive. Think I haven't used a multimeter since elementary school


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## baronbeehive (Jan 11, 2021)

CopperFox said:


> Hmm. To me that looks clearly gray, black, gold and brown which would be 8R. That's what I put there and the meter did light up. Looked more bright than the other side though, could be from having a newer light. Or something else.



You can always check with the other side, if I can find out I will let you know.

If it's the old meter it might need replacing.


----------



## baronbeehive

CopperFox said:


> No, but those are not expensive. Think I haven't used a multimeter since elementary school



It's very useful to have around, if you need to fault find. Really you should check the circuit after every time you work on it on the components you have worked on, before you switch back on. It might save a lot of grief later .


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## baronbeehive

I documented my mods fairly exhaustively, but so much has  happened along the way I can't remember it all unfortunately .

These are the transistors to get if you decide to replace them:

1 x MJ15024G (NPN) for B+
1 x MJ15025G (PNP) for B-

You're right the resistor in the ammeter wire is 68 Ohm, I think it was measured at each end of the wire so the wire's resistance will be taken into account also. There is a strong possibility that you have fried that ammeter.. or at least partially cooked it.. that's another good reason to have a multimeter lying around, you could have checked it on the terminals to see if the resistance matches the other one.

Re: the lack of sound, the current surge could have triggered the headphone protection circuit.


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## Maxx134 (Jan 13, 2021)

CopperFox said:


> sound came through to headphones but at a very low volume.


That's the driver stage your hearing and a good sign only your output stage is off. Most likely cause you already pointed out is the PSU.
No prob, It needed upgrading anyways.



baronbeehive said:


> Re: the lack of sound, the current surge could have triggered the headphone protection circuit


For sure the output stage is not working, and most likely due to the power supply failure.

The protection circuit can also be enabled because of this.



baronbeehive said:


> Yes I would definately advise to change the transistors as well as the originals were prone to failure with increased loads


Yes and as I recall, the diodes die first, causing the transistors to die next.
Hopefully they didn't blow if he caught in time.



CopperFox said:


> Edit: reading back on the thread, there were advice also to replace the PNP / NPN transistors in cases where those two blue resistors were burned


I was going to replace mine, but I haven't, as they didn't blow up on me yet.
They blow up easier and are obsolete and mouser parts have the updated version which will not easily die.
I would advise to first change the resistors and *especially* the diodes, because the transistors will die again if those cheap diodes are dead, as usually the case.

For the diodes, get higher rated wattage, but same voltage. I believe they were 100v, and you can even add two in parallel for better heat dissipate and better current.
So regardless of the burnt looking resistors, which most probably went up in value, you must change the diodes which are first to blow and cause the transistors to go right after.
If your lucky the transistors are ok but would need to check on a multi meter with a transistor tester built in.
That's allot of trouble to take out, so try the diodes first, and if the resistors start to cook, your know it's the transistors.
You must buy as a set of two (pnp& non)

Another BIG issue is that upon moving the board, it is booby-trapped with garbage tin wires that run from the board to the transistors (located on unit body ).
TAKE PICS to remember and replaced these short wires as it is essential. They break off easily and then sparks fly!
Even when hit or board closed, they can just call off thru vibration. They crumble because they're brittle, like stranded tin. Just replace them.


----------



## Maxx134

Last advice is that you must be careful with the board trace when pulling out the diodes.
If I recall correctly, there is a bottom trace in that area that goes from one side to the other, so very important not to pull the pads of the board there. 
You could do a search in thread for that.


----------



## baronbeehive

Maxx134 said:


> Another BIG issue is that upon moving the board, it is booby-trapped with garbage tin wires that run from the board to the transistors (located on unit body ).
> TAKE PICS to remember and replaced these short wires as it is essential. They break off easily and then sparks fly!
> Even when hit or board closed, they can just call off thru vibration. They crumble because they're brittle, like stranded tin. Just replace them.



Yes those wires are probably *THE* most fragile of all the other *very* fragile wires! I think he would benefit from changing the other wire runs as well especially the output wires. ATM I have OCC silver to the outputs and OCC copper to the headphone socket, and at some point will replace the whole run to the headphone socket with silver. I want to maximise the treble textures and so this is the last thing I will probably do when I can face opening it up again .

I will also change a couple of resistors in the PSU area and check circuits at a couple of points I noticed last time I opened it up.

@CopperFox you would benefit from this in improved SQ definately. The existing wires are crap.


----------



## baronbeehive

Maxx134 said:


> Last advice is that you must be careful with the board trace when pulling out the diodes.
> If I recall correctly, there is a bottom trace in that area that goes from one side to the other, so very important not to pull the pads of the board there.
> You could do a search in thread for that.



Definately check runs on *BOTH* sides of the board, but then he probably knows this.. he reads the thread lol!


----------



## Maxx134

baronbeehive said:


> Yes those wires are probably *THE* most fragile of all the other *very* fragile wires!


Yep, there was one owner who was simply rolling alot power tubes, and then a pop & Smoke! 
He got scared & turn off immediately, then opened up to find that one of those transistor wires had poped off.
He was lucky because when he soldered it back and it worked.


----------



## baronbeehive

Maxx134 said:


> Yep, there was one owner who was simply rolling alot power tubes, and then a pop & Smoke!
> He got scared & turn off immediately, then opened up to find that one of those transistor wires had poped off.
> He was lucky because when he soldered it back and it worked.



I have to own up and level with you.. I haven't replaced those wires.. BUT I'm somewhat OCD about checking them before putting the board back in. Maybe next time I open it up... .


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## CopperFox

So I replaced those transistors, resistors and diodes. Now both the UV meters and their lights work, but there isn't sound output of any kind. 

I'm thinking in the process I might have broken the relay behind the volume pot by touching it with my soldering iron - would that have this kind of effect? Will replace that next. (What else could/would cause this? Don't really see any signs of something else being wrong on the board)

If relays are mechanical, does it matter what orientation it will be installed in (I'd assume not)? Would want to mount it sideways so I wouldn't have to take the PCB out again.


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## baronbeehive (Jan 17, 2021)

CopperFox said:


> So I replaced those transistors, resistors and diodes. Now both the UV meters and their lights work, but there isn't sound output of any kind.



Good work! If you've uprated those components to higher wattage then that more or less eliminates the PSU area as the problem for now and in future!

What do the meters read?



CopperFox said:


> I'm thinking in the process I might have broken the relay behind the volume pot by touching it with my soldering iron - would that have this kind of effect? Will replace that next. (What else could/would cause this? Don't really see any signs of something else being wrong on the board)



You mean you've touched the black plastic cover? That shouldn't have an effect if that's all. Do  you have a picture?

I think you are going to have to get that multimeter and start checking the resistances of some components because you won't be able to tell by just looking. I will post a pic for you to take some measurements.

Also have you done the  usual checks after work on the amp such as checking for solder splatts, touching wires, broken wires, loose connections. You can tell that a connection is bad often only by checking continuity with neighbouring connections on the trace with a multimeter.

A broken wire can be difficult to see if it's covered by heatshrink for example, or if it's on the reverse of the board that you've just put back.


----------



## baronbeehive

The resistor in the centre that feeds the meters with current might have gone open.

Also by checking the resistances of the resistors in the bottom row you can check if there are any that look out. There are 12 resistors on each side and their values repeat so you can see by checking if any are out. If one of them is out it might also point to an opamp failure connected to that resistor.

There are other ways to check the output is ok but you need to be experienced with the multimeter.


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## CopperFox (Jan 18, 2021)

baronbeehive said:


> Good work! If you've uprated those components to higher wattage then that more or less eliminates the PSU area as the problem for now and in future!
> 
> What do the meters read?
> 
> ...



The UV meter on the right says about 38-45 ma and on the left it's between 25-40 ma (with the M1060C phones). That's the way it had been before so it looks normal to me.
With higher impedance headphones the readings had been going higher to about 60, but I only tested with the M1060Cs after replacing the transistors.

Here's a picture of the relay:



AFAIK, these relays' function is based on mechanical movement so I'm thinking any change in its physical form could be interfering with its function.



EDIT: Update: now I have sound working in the left channel but nothing on the right. So maybe it wasn't the relay after all. Not sure if I did anything to fix the left channel.


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## baronbeehive

I don't know about the relays, I don't think they are mechanical and I don't think a burn on the outside would hurt.

You have sound on one side now, if that came back all by itself it suggests to me that there is an intermittent fault with a connection, that can happen, as it did with me when I re-arranged components inside. When you have a lot of new components jostling for space a movement of one can interfere with the circuit if there is a fault with a solder joint, the only way you can tell is to wiggle it from side to side and see if it causes the problem. Of course you cannot do this while the amp is on or you might not be around long enough to appreciate the wonderful SQ of the Little Dot! This is another reason you will have to get that multimeter. If you had one you could test the continuity while wiggling the connection - with the amp off - and you would be able to tell straight away if there was a fault. Without that it's a bit like a fiddling around in the dark and hoping you find something.

The ammeters should read about 60mA with 6AS7 power tubes, and about half that with 5998 tubes. Both meters should read the same to indicate that both channels are functioning normally. They will only vary under extreme volume intermittently. If they don't read at those values or both read differently then something's wrong with either, or both channels.

From what you say I can't tell what the trouble is specifically, but as you have done the right thing and renewed the PSU components then at least that shouldn't go wrong again. So we are left with trying to zero in on the fault(s). You will also need to check that everything is ok visually like I said before because that could cause problems as well.

I suggest you get a multimeter and then you can test each component, that way you should be able to tell fairly quickly where there is a fault. We can help when you are ready.

That shouldn't put you off because it's easy getting the hang of using the multimeter, and you will have to use it to check both channels are functioning properly, that is the only way to know.


----------



## CopperFox

baronbeehive said:


> I don't know about the relays, I don't think they are mechanical and I don't think a burn on the outside would hurt.
> 
> You have sound on one side now, if that came back all by itself it suggests to me that there is an intermittent fault with a connection, that can happen, as it did with me when I re-arranged components inside. When you have a lot of new components jostling for space a movement of one can interfere with the circuit if there is a fault with a solder joint, the only way you can tell is to wiggle it from side to side and see if it causes the problem. Of course you cannot do this while the amp is on or you might not be around long enough to appreciate the wonderful SQ of the Little Dot! This is another reason you will have to get that multimeter. If you had one you could test the continuity while wiggling the connection - with the amp off - and you would be able to tell straight away if there was a fault. Without that it's a bit like a fiddling around in the dark and hoping you find something.



Now I got sound in both channels. The fault was that the right side cathode resistor was somehow loose without looking or feeling like it was. 
Replaced one of the coupling capacitors on the left side as well due to one leg snapping so that will now need some burn-in.

Next I'll be trying those +2000uf Nichicon caps for the cathode bypass position.


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## baronbeehive

CopperFox said:


> Now I got sound in both channels. The fault was that the right side cathode resistor was somehow loose without looking or feeling like it was.
> Replaced one of the coupling capacitors on the left side as well due to one leg snapping so that will now need some burn-in.
> 
> Next I'll be trying those +2000uf Nichicon caps for the cathode bypass position.



Excellent .

You see what I mean about checking, saves a lot of hassle later. When you bend the capacitor leg bend it away from the body of the cap otherwise it's liable to snap, I've done it too.. we've all done that!

Keep us posted on progress!


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## baronbeehive (Jan 23, 2021)

Guys, I had almost forgotten what an emotionally challenging experience for the nerves it was sitting waiting for that other meter to light up after working on the amp ! As it was I made a schoolboy mistake with 2 or the connections the wrong way round , and that was despite checking everything in triplicate.

I've finally got around to fitting some OCC silver output wires from the output XLR's right through to the headphone socket in an effort to boost the top end slightly, I'm talking of high hats, cymbals mainly, everything else sounds so good on this amp, and so does that but I feel it could be slightly more emphasised to make everything stand out on the sound stage that bit more. I don't mean sybillant sounds though.

Those silver wires are expensive though, so I compromised and fitted 24AWG to supplement the silver plated copper that were already there, rather than going for say 20AWG from scratch. The copper should complement the silver and as they are silver plated I don't think adding silver wires will smear the sound or anything like that.

That should be my last foray into the guts of the amp hopefully, I never want to see them again lol.

I will report back on my impressions when I compare it to my APPJ which is already slightly more emphasised in the treble frequencies.


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## baronbeehive (Jan 26, 2021)

*SMLD MODS: (continued.. er.. finished)

Silver output wires *-

The finished amp.. at last!

I don't envision doing anything else, changes to PSU would entail building it in another chassis, not necessary.

The SQ is truly endgame, airy expansive soundstage, highly resolved, transparent yet euphonic too, I can't think of ever getting rid of it.

I've yet to trial it with the silver wiring.





You can follow my mods pages: 50, 53, 55, 57, 62, 65, 66, 68, 69, 70, 71, 72, 147, 179, 230, 231, 234 which include pics. Also Mogos mods are here; 33-38, and SonicTrance here: 23, 43, including some great pics.

Edit: Anyone want a soldering iron.. surplus to requirements .

Edit: There's still some room in the upper end of the amp for something.. any ideas anyone lol!


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## AngryTank

Anyone got any recommendations for tubes for my Mk8 SE?


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## baronbeehive

Wow! I really didn't expect this.. but the silver wires have made a major difference.. in the direction I was hoping! First impressions are very favourable. I didn't expect to hear much difference, maybe a slight sharpening, but the difference is fantastic. I don't think I am being influenced by my expectations here.. but I was certainly hoping..!

Comparing with the APPJ as a baseline which I was able to switch between it and the LD side by side, the LD now is level in terms of treble texture which is there at high levels to add to the realism especially the soundstage, the APPJ is good but the LD's soundstage is second to none and gives the impression of greater resolution which may or may not be the case in reality. Guitars ring through with incredible clarity for example. Not only that the whole frequency band seems to be tighter, bass as well which is very welcome. Transparency is at the highest level, probably slightly higher than the APPJ although I put that down to room reverberations through speakers.

Anyone who wants clarity and texture to their music should really go for these OCC silver wires, the image is still very full bodied but compared to the OCC copper wires I had in originally the copper wires are much warmer and smoother, a little too much for me perhaps. One reason I didn't expect much difference, the 24 AWG wires were very thin and I thought that the lack of girth in the cross sectional area might have adversely affected the fullness of the sound. Also adding wires to those already in place might have affected SQ. but none of these concerns actually came about.

Both amps are pretty much how I like the sound to be and both perform at the highest level. I still can't really get over the shock of how good the modded APPJ is considering the mods were very simple to do, whereas the LD needed much more in the way of mods to bring out the best end game level.

So all in all a very worthwhile addition and the final touch to my LD, true to say silver wires and silvery sound!

.


----------



## CopperFox

baronbeehive said:


> I would have thought that a sledge would be more useful in the Arctic lol!




Well... it was announced by the FIA some days ago that this will be on the WRC calendar this year... so there is at least some use for cars. Trying to figure out how to apply to be a marshal there.

Then there is reindeer dodging as well!

Fun fact: the WRC is currently sponsored by Asahi Kasei corporation, which is best known on these forums for their subsidiary Asahi Kaisei Microdevices (AKM).


----------



## baronbeehive

CopperFox said:


> Well... it was announced by the FIA some days ago that this will be on the WRC calendar this year... so there is at least some use for cars. Trying to figure out how to apply to be a marshal there.
> 
> Then there is reindeer dodging as well!



Haha!

So you're in Finland.. in the arctic! One of the guys on the forum lives in Sweden.

I'm a  huge fan of WRC, always watch it on TV. Elfin Evans narrowly missed out on world champion when he slid off in Monza leaving Seb Ogier champion.. again!! There is usually a rally in UK, in Wales but cancelled this year, I really must go and see it when it comes back. I'm interested if you get to be a marshall, PM me if you have any interesting pics to share .

I have a Mini Cooper S, so driving is a bit of an addiction!


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## baronbeehive

I've spent some time with this amp now and all I can say is "the veil has been lifted", "the window has been polished clean".. and any other metaphors you can think of. The "finished"..  .. amp is transparent to the music after the sum total of mods done. I didn't really think it would be possible with the design of this amp to push it to such limits.. but no.. it was!

The beauty of it is you can alter the sound to suit your preferences, I like transparency so long as it has euphony also. If you wanted a different sound then vary the wiring, tubes, caps and tube operating point to get clarity or lush sound, dynamics or softness. With the CCS and filter I have achieved extreme clean sound, and the soundstage with the silver wires is very defined, violins, for example screech with the bowing of the gut strings.. in a good way..! Another advantage of the CCS is I no longer have to worry about achieving balanced operation, the current is kept constant by the CCS. If you wanted to try to achieve fast transients and sharp bass you could try using those huge MKP film decoupling or cathode caps that some here have done. I wanted to keep everything in the chassis so that wasn't possible, maybe I was too sensible to try!


----------



## coinmaster

Add water and it will sound more liquid. Trust me.


----------



## baronbeehive

coinmaster said:


> Add water and it will sound more liquid. Trust me.



Hey coin, and a Happy New Year to you too!! Always there with the helpful suggestions .

Really this amp is great, the SQ is fine for me. How's progress over there? I shudder to think what new designs you've come up with over the past few weeks!


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## CopperFox (Jan 31, 2021)

CopperFox said:


> Next I'll be trying those +2000uf Nichicon caps for the cathode bypass position.




Ok, now I've tried four different +2000uf Nichicon caps there and I found one of them, which would be the 2200uf 100V KW series, to be an improvement over the 1000uf 50V KZ series.

The ones that I tried were the 2200uf and 3300uf options from both the FW and KW series, all with the 100V rating.

The 3300uf caps from both series just did not work and had a strange hollow sound that didn't improve over time. So I'd think the capacitance value was too large.

I didn't like the FW series sound. It had some emphasis on midbass, lowed mids and low treble and was relatively dark. This would match what I've read about the FG series which has the same gold-black colour scheme as the FW series. I haven't actually heard the FG series myself though.

The KW series is also similar to the KZ series both in name and their black-gold colour scheme. The overrall sound presentation of the KWs is also very similar to that of the KZs.

I'd say to my ears the improvements with the 2200uf 100V KW over the 1000uf 50V KZ are not small. Bass is more controlled and detailed and there is more detail and better transients overall. With the KZ series there was some slightly unnatural metallic edge to stringed instruments (smearing from overly fast attack?). It was reduced when moving from 470uf to 1000uf though. But with the 2200uf 100V KW it's not there anymore.

Having the 2200uf 100V KW once again changes how the output tubes sound. I had been looking at the various chinese tubes with the KZs but now it's the RCAs that are sounding the best. For some reason the Svetlanas now have a mad bass sound which they never did before.

With the right output tubes these don't need the 0.1uf Rifa bypasses. If you want to try the KWs,  it's a good idea to get the 100V version ( part number UKW2A222MRD ) even though the voltage in itself isn't needed, as that one has better specs otherwise as well than the lower voltage versions.


----------



## coinmaster

baronbeehive said:


> Hey coin, and a Happy New Year to you too!! Always there with the helpful suggestions .
> 
> Really this amp is great, the SQ is fine for me. How's progress over there? I shudder to think what new designs you've come up with over the past few weeks!


Mainly just a waiting game for me. Despite having objectively better stuff than anyone else I am still not in a position to sell anything due to lack of connections and funds.
Funding the finalization of my projects is taking  a really long time and coronavirus came along right when I was supposed to get my prototypes professionally tested and reviewed so that really screwed me.
I haven't worked on amps in quit a long time though because its a problem that is completely solved  for me. I can demonstrably make cheap amps as good, or better than the best amps no problem. However the airlines destroyed my only high power prototype of my best design so...yeah.

 I'm currently finishing my headphone design, should hopefully have a finalized prototype next month (knock on wood). It takes forever because of the cost and lead-times of custom parts. However the headphones are so far above any other headphones it is laughable, so as long as I can get these done it will be easy to finally get investment since all someone has to do is place it on their head unlike the amp where I need to spend a zillion dollars for the privilege of getting a third party lab to officially measure it before I can bring it to investors. 

Also if you want to make the LD MK amp much better just delete the output stage and replace it with a simple DC servo controlled source follower. The output tubes are nothing but a detriment to the SQ regardless of how you arrange them. Although like most mods that 'solve' the issues of this amp there isn't really a clean way to do it.


----------



## baronbeehive

Yeah, this coronavirus business has knocked us all for six, as I hear you have in the States, the best that can be said, most of us are all still here.. at least as I write this. We are in the middle of a vaccination programme here. Maybe now that you have someone moderately sane as President (IMO) you might make some progress!!

I still feel you might have trouble getting patents for what amounts to changing the components around into new configurations, but I don't know where you are at atm.

Those ribbon headphones  you mentioned a while back sounded ahead of their time and exciting, and with the headphone market constantly changing it could be a winner for your prototypes. I reckon people are clammering for anything new, and that won't stop. Any forum like here would spread the word fast and a review or two, even if you don't go into details of your designs would help massively.. and a website too?

I haven't worked on my amp for ages until the last week or so I decided to finish it for once and for all. Before that I was just massively relieved it worked at all lol! Yes I thought about source followers but quite honestly the changes I have done have got the SQ just right for me and I don't really want to mess with it anymore.

Look forward to hearing from you when you next demo at Maxx's again.
.


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## baronbeehive (Feb 1, 2021)

CopperFox said:


> Ok, now I've tried four different +2000uf Nichicon caps there and I found one of them, which would be the 2200uf 100V KW series, to be an improvement over the 1000uf 50V KZ series.
> 
> The ones that I tried were the 2200uf and 3300uf options from both the FW and KW series, all with the 100V rating.
> 
> ...



Yeah, you could be getting some sort of oscillation. The whole business of choosing caps is massively complicated, I just happened to get the right type of improvements from previous recommendations. But it depends on what the caps are  used for, and the rest of the system configuration, and really you need to know some of the theory as well.



CopperFox said:


> I'd say to my ears the improvements with the 2200uf 100V KW over the 1000uf 50V KZ are not small. Bass is more controlled and detailed and there is more detail and better transients overall. With the KZ series there was some slightly unnatural metallic edge to stringed instruments (smearing from overly fast attack?). It was reduced when moving from 470uf to 1000uf though. But with the 2200uf 100V KW it's not there anymore.



Again, different people say different things so it's difficult to say, the best you can say is that you think it's better "*in your setup." *For example I know the Miflexes you use are more forward sounding than the Jupiters I use and that the Jupiters are more natural sounding so that I don't believe I have the problem of metallic sounding strings, guitars really ring out beautifully, even acoustic guitars with just the right level of attack to bring out the soundstage nicely.



CopperFox said:


> Having the 2200uf 100V KW once again changes how the output tubes sound. I had been looking at the various chinese tubes with the KZs but now it's the RCAs that are sounding the best. For some reason the Svetlanas now have a mad bass sound which they never did before.



Those RCA's are great! People dismiss them but they would give most tubes a run for their money. I think the natural sound and balance of these tubes would make them a good match for anything. And what you say about the Svetlanas is what has been putting me off trying them as I've heard that the bass can sound unnatural with them.



CopperFox said:


> With the right output tubes these don't need the 0.1uf Rifa bypasses. If you want to try the KWs,  it's a good idea to get the 100V version ( part number UKW2A222MRD ) even though the voltage in itself isn't needed, as that one has better specs otherwise as well than the lower voltage versions.



Thanks for this information. This has got to be very useful for anyone wanting to try this out.

I've most likely finished modding now on the LD, it sounds the way I like and it's not worth screwing me up anymore wondering if all the wires are still there in the back of the amp when I've put the board back again LOL


Have you finished the operating point tests?

How are you finding the amp sounding now after all that great work?

Edit: I'm interested in how  you would describe the sound to see if it tallies with what we have found here.


----------



## coinmaster (Jan 31, 2021)

> I still feel you might have trouble getting patents for what amounts to changing the components around into new configurations


 The problem with patents is the expense of purchasing one and defending it if it is infringed upon.
Despite the original design I'm no longer concerned with patents because it is effectively pointless since china or powerful companies in the US can steal whatever they want anyway.


> but I don't know where you are at atm.


 That entirely depends on the context of what you mean.



> Those ribbon headphones you mentioned a while back sounded ahead of their time and exciting, and with the headphone market constantly changing it could be a winner for your prototypes. I reckon people are clammering for anything new, and that won't stop. Any forum like here would spread the word fast and a review or two, even if you don't go into details of your designs would help massively.. and a website too?


 They aren't really ribbons per se. But yeah, if people knew what I've created, it would be a big deal. I'm not exaggerating when I say that they make all other headphones sound like a toy in comparison. (which makes it all the more frustrating), but my first prototype weighed 15 LBs and was fragile..(made of wood blocks and steel lol)  I barely managed to get it  safety to NY once to show Maxx and compare against a bunch of other top-enders.
My latest version is of normal weight in a finished design but the parts are all custom and expensive to purchase in low volume. So essentially when I finish this version of the prototype it will be the first time I've made something that can be moved around and used and reviewed like normal.

But I'm moving to Japan for a couple years starting in April because I'm sick of constant R&D that just eats up my time and money without financial return so I'm getting some "fresh air" for a change. With my typical luck I could cure death and not be able to monetize it so I'm going with the mindset of "if it happens it happens" at this point.
Maxx and I are formulating some sort of a coordinated effort to begin making and selling the headphones on different fronts within our respective regions, but there are some things to be done before that point.
Eventually if I get the headphone business off the ground I will be able to fund the selling of my amps as well.


----------



## baronbeehive

coinmaster said:


> .. but my first prototype weighed 15 LBs and was fragile..(made of wood blocks and steel lol)  I barely managed to get it  safety to NY once to show Maxx and compare against a bunch of other top-enders.



Really surprised you were worried about that, when the HiFiMan HEK's came out it looked like you were carrying around miniature speakers on your head, very silly..




coinmaster said:


> But I'm moving to Japan for a couple years starting in April because I'm sick of constant R&D that just eats up my time and money without financial return so I'm getting some "fresh air" for a change. With my typical luck I could cure death and not be able to monetize it so I'm going with the mindset of "if it happens it happens" at this point.
> Maxx and I are formulating some sort of a coordinated effort to begin making and selling the headphones on different fronts within our respective regions, but there are some things to be done before that point.



Curing death.. now you are talking.. a good idea for once!

Anyway stay in touch, hope the move goes well, that is one of my life's ambitions to go to Japan, especially when the Cherrys are in blossom.


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## coinmaster (Jan 31, 2021)

> Really surprised you were worried about that, when the HiFiMan HEK's came out it looked like you were carrying around miniature speakers on your head, very silly..


 It was more of the fact that the driver is a complex structure and they were super fragile and a pain to transport. They needed to be hung from some sort of apparatus because they were too heavy to put on your head for long and the headband was just a bunch of wood blocks lol.


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## CopperFox (Mar 4, 2021)

baronbeehive said:


> I have a Mini Cooper S, so driving is a bit of an addiction!



I assume that would be the 2000s new Mini  I remember wanting one of those in British racing green when they came out. Now I decided to go electric though and got a new Renault Zoe GT R135... in blueberry purple.




baronbeehive said:


> Again, different people say different things so it's difficult to say, the best you can say is that you think it's better "*in your setup."*
> 
> I've most likely finished modding now on the LD, it sounds the way I like and it's not worth screwing me up anymore wondering if all the wires are still there in the back of the amp when I've put the board back again LOL
> 
> ...



Yes, we all do have some varying components in the amp and also different sources and headphones. Knowing when to stop is admirable and knowledge many people in hifi do not possess. And as you wrote before, these LDs can be modded to various preferences. Even if it would be difficult to settle on one specific kind of sound, it would be possible to add some adjustability with switches. It would be interesting to have switches for the decoupling caps and 2-3 different cathode bypass caps. And even then, it could be hard to enjoy music without thinking if it would sound better with the switches in another position  I don' t really feel that I have enough knowledge and/or experience from electronics though to build those switches.

Looks like headphone modding is more straightforward than amplifier modding. Less variables and more clearly defined targets.

What are the operating point tests?

I might still be trying the Audio Note Kaisei for WCF caps. They are available in 680uf which the others aren't.


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## baronbeehive (Mar 6, 2021)

CopperFox said:


> I assume that would be the 2000s new Mini  I remember wanting one of those in British racing green when they came out. Now I decided to go electric though and got a new Renault Zoe GT R135... in blueberry purple.



Yep, that's the one, I will PM you a pic!



CopperFox said:


> Yes, we all do have some varying components in the amp and also different sources and headphones. Knowing when to stop is admirable and knowledge many people in hifi do not possess. And as you wrote before, these LDs can be modded to various preferences. Even if it would be difficult to settle on one specific kind of sound, it would be possible to add some adjustability with switches. It would be interesting to have switches for the decoupling caps and 2-3 different cathode bypass caps. And even then, it could be hard to enjoy music without thinking if it would sound better with the switches in another position  I don' t really feel that I have enough knowledge and/or experience from electronics though to build those switches.



You wouldn't believe how many amps some of the guys have on other threads! I stopped for several reasons, the main one being I am happy with the sound signature, also I know that the modding has pushed the amp to end game, so the only reason to change would be that you want some other kind of sound, not that another amp would be better necessarily.

The amp now is really transparent sounding, yet has the tube euphonics still, a perfect combination for me. The mods have brought out all the good points like soundstage and resolution to the highest level. The frequency band is in balance and extended and all the instruments sound real, emphasised by the mods we have done now. And the dynamics are good, whereas before it was a bit on the polite side. If I was to change anything it might ruin what has been achieved!

Yes decoupling caps especially would be interesting to vary. A switch would be easy.. if you're in doubt check out sonic's 5998 bias switch mod on page 1. Basically all you do is connect the switch in parallel to the existing circuit with the added on bit comprising an alternative part of the circuit. You could always get back to us on this if you decide to give it a go.

You've done a great job with testing the cathode caps and so on, I would have tried those you liked but as I have the compact version there wouldn't be any more space inside for bigger caps!




CopperFox said:


> What are the operating point tests?
> 
> I might still be trying the Audio Note Kaisei for WCF caps. They are available in 680uf which the others aren't.



The operating point tests are what you've been doing experimenting with different anode/cathodes for the driver tubes.

Kaiseis are excellent caps, I have them in my other amp, the APPJ Miniwatt speaker amp, however I stuck with the Nichicons for the LD because I believe they tightened up the bass sound a lot, whereas the bass on the APPJ was already tighter.


----------



## CopperFox

baronbeehive said:


> Yep, that's the one, I will PM you a pic!
> 
> 
> 
> ...



I see. As I'm not done with the mods I'm not sure if I will still try different cathode resistor values. Still leaning towards the 470R as it had more prominent mids than lower values. 

But for the anode resistor I remember you recommended 69K and I have 68K. What resistor brand do you have there? It seems most brands have 68K available but not 69K.

Today I started wondering what would happen with more than one cathode bypass cap in parallel... for example both a Nichicon KZ and an Elna Silmic.


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## baronbeehive (Mar 10, 2021)

CopperFox said:


> I see. As I'm not done with the mods I'm not sure if I will still try different cathode resistor values. Still leaning towards the 470R as it had more prominent mids than lower values.


I don't know what anode you are using, but if you are using 68k then I agree that 470R, or thereabouts, had the liveliest sound.



CopperFox said:


> But for the anode resistor I remember you recommended 69K and I have 68K. What resistor brand do you have there? It seems most brands have 68K available but not 69K.


Don't get too hung up on that difference. The reason is that it will not have much, if any effect because the operating point will not move with that much of a difference in values. Also other factors will come into play, your amp will most probably have a slightly different B+, depending on the components you have put in, making the calculation different as well.

I didn't fully document my mods so I can't remember if 69k was what I arrived at in doing the calculation or if it was a specific value that had been used. I suspect that the 69k value was calculated from the load line and I then found the nearest resistor to that value to put in. Also I kept the stock 220K anode resistors in place and added another resistor in parallel to arrive at the 69k value. I think I added a 10k to get the final value of 69, or 68k or whatever was nearest.

For the anode plate load it is usual to load it many times its plate resistance which is done for the stock amp. This is good because the resulting operating point allows 6SL7 and 6SN7 tubes to be used, neither being at the optimum point though. Also the output current is low. So we tried different anode resistor values to boost the current and change the operating point to arrive at the optimum value for the operating point. I think that's why the 69/68k anode works best because it doesn't go as low as the 33k that I tried which was too low a plate load.

There's still scope to try different values to vary the operating point still though if you want different sounds as I suggested. The lower the point on the graph the more distortion the sound will have which may or not be pleasant to try giving a more tubey sound. I prefer a more transparent sound with just a touch of tubes in there.

I used TKD resistors.



CopperFox said:


> Today I started wondering what would happen with more than one cathode bypass cap in parallel... for example both a Nichicon KZ and an Elna Silmic.


You can add as many bypasses as you like but we don't recommend it. The main purpose of the cathode caps is to help transient recovery which will affect bass frequencies. The fastest cap you can have will  be best to do this and avoid clipping as much as possible. Apart from this it won't have that much effect on overall sound signature, that is where the coupling and WCF caps come in, they will have greatest effect on sound.

If you imagine several batteries of different types all connected then the electrical signal coming out will be mashed up because of the differing discharge rates. This won't matter ordinarily but for the music signal it needs to be as pure as possible so smearing will inevitably occur as the signal is affected by the differences in the charge/discharge cycle. The signal at one point in the chain will be trying to move on but at another part it will be waiting for another cap to finish it's part of the cycle.

Your findings on the different cathode cap values was very useful and proved that going even larger in capacitance than we did had a beneficial effect on bass responsiveness! I suspect that going even larger than that would have negative returns possibly.

The whole point of much of the mods is to get as stable PSU as possible. The large fast capacitance MKP decoupling caps you put in will help as does the fact that the amp is balanced in the first place. Also we uprated the PSU caps to be as beefy as possible to provide a good reservoir of power on tap. Apart from that we can't do much with the PS without completely rebuilding it which would involve adding on an extra stage to the amp as it is now.

Where we did go for a bypass to the cathode cap was because we swopped the stock caps for higher capacitance, musical grade caps, which meant that we needed to add some very small bypasses to complement the lytic cathode cap techno. So we added some small fast film caps to restore the high frequencies that were lost.

So I would suggest if you want different sounds to try different coupling and WCF caps. Due to their position in the push/pull cycle the WCF caps we feel need to be the fastest and responsive to the high frequencies as you can go for, I have Mundorf SIO which I feel complement the more natural sounding Jupiters in the coupling position.

The switch you mentioned before would be easiest to implement for the different anode/cathodes by adding a supplementary circuit with other anode/cathode resistors in parallel. With a switch for different coupling caps that would be more complicated to implement though.


----------



## baronbeehive

I feel that the most interesting area of upgrade to go in now would be to do the same as has been done for the 6SL7 tube but for the 6SN7. This would need a switch because the optimal operating point for both tubes would not work together without it because they are so different with different load lines. I've heard both tubes on the stock amp and couldn't tell the difference but with both tubes optimised that would be entirely different and I would be interested to hear what the 6SN7 sounded like on it's optimum operating point. We haven't done this because we settled on the 6SL7 as being the best tube for the amp because of the higher gain so we didn't bother experimenting with the 6SN7. But I'm waiting for someone to do it! The anode/cathode tests are what I feel would bring about the most variance in sound.

A switch could also switch between different anode/cathodes with the same tube and could produce a different sound. For instance I have been wondering what sound the operating point low down in the distorted area of the grid would be like. I didn't do this because I was trying to find the best operating point, ie. the least distorted sound. It's possible that the sound would be very tubey therefore you could switch between transparent/tubey sounds depending on your mood, or what type of music you were listening to.

A switch would be simple to do by connecting in parallel the desired anode/cathode resistor to move the operating point to where you wanted it to be. It would be better to have 2 switches, one for anode and one for cathode, this would give 4 different combinations.. and if you had a similar switch for the 6SN7.. well that would be where it would start to get very interesting!


----------



## talan7

Some crazy looking mods on here


----------



## CopperFox (Apr 28, 2021)

Well I haven't posted for a while. This is because I realised the PCB on my MKVI+ had gotten into a bad enough condition that it needed replacing.

While doing extensive component rolling it is a good idea to try and preserve the PCB from excess wear, tear and heat (instead of doing this for the various new components by carefully removing any older solder from the PCB before installation). It is also probably a good idea to solder extension leads to the joints on the pcb for any components-to-be-rolled. And solder those components to the extension lead instead to keep the pcb in good condition (particularly on the components where the solder joints/pads on the pcb are small). This will probably actually save some time and pain too as it is easier to solder/desolder from the ends of extension leads than directly to the pcb when there is a lot of large added components in the way.

I figured I wouldn't have the time and patience to actually replace the PCB at the moment so in mid-february I decided to order a complete new amp. So I did that... and four weeks later got notified that the black version of the amplifier is not available and not in production and the order was cancelled on my behalf. I asked by email from Little Dot if there was any particular reason for the black version not being produced and if it was to resume production at a later date. But received no response whatsoever even though they had been responsive before that.

So I actually decided to start looking at other amplifiers that would fit the all-black aesthetic of my desk setup. But a few weeks later the silver color MKVI+ was on sale for a good enough price and I ordered that (too !!!). Then, again, for three weeks nothing happened but then the package showed up in tracking and genuinely looks to be arriving soon.

I don't really understand why there was no response from LD about the black version. Even if there are many kinds of bizarre shortages from garden gnomes to bicycle repair parts and shipping containers going on, it would be nice to have some response to queries about future availability of listed products.


The last thing I was doing on the black MKVI was testing the big cathode bypass caps. Even though I had initially positive impressions about the 2200uf FW series caps, it was looking like they were still burning in and the sound was getting worse - flatter, less dynamic, less soundstage and there were less power tubes that would sound ok with them.

The general trend with going from 470uf to 1000uf to 2200uf seemed to be that the sound got more detailed but slower and less dynamic with the larger caps. Also, with the 470uf caps, the high gain mode was _too fast_ to use, with too many things sounding like hits from a hammer. Still, the low gain mode with 470uf sounds better to me than 1000uf with high gain. The latter has more detail but less dynamics, less soundstage and is slower. I do prefer dynamics and speed over detail. Still I feel that it would be interesting to have and test something between 470uf and 1000uf from the Nichicon KZ line.


----------



## CopperFox

baronbeehive said:


> You can add as many bypasses as you like but we don't recommend it. The main purpose of the cathode caps is to help transient recovery which will affect bass frequencies. The fastest cap you can have will  be best to do this and avoid clipping as much as possible. Apart from this it won't have that much effect on overall sound signature, that is where the coupling and WCF caps come in, they will have greatest effect on sound.
> 
> If you imagine several batteries of different types all connected then the electrical signal coming out will be mashed up because of the differing discharge rates. This won't matter ordinarily but for the music signal it needs to be as pure as possible so smearing will inevitably occur as the signal is affected by the differences in the charge/discharge cycle. The signal at one point in the chain will be trying to move on but at another part it will be waiting for another cap to finish it's part of the cycle.



Hmm. Well, I did get a different similar idea. Since I would want to try Nichicon caps between 470 and 1000 uf, I will try using two similar 330uf 100v Nichicon KZ caps there. They obviously should not have very different discharge rates. I did some googling about parallel capacitors in audio circuits and the consensus seemed to be that using two capacitors instead of one larger capacitor is ok and should have lower esr even if the specifications of the larger and smaller caps were similar. With these Nichicons however, the smaller capacitors are also faster in specification. Maybe the combination of being both faster and larger (combined) capacity than the 470uf could be good.



baronbeehive said:


> So I would suggest if you want different sounds to try different coupling and WCF caps. Due to their position in the push/pull cycle the WCF caps we feel need to be the fastest and responsive to the high frequencies as you can go for, I have Mundorf SIO which I feel complement the more natural sounding Jupiters in the coupling position.



I've been thinkin about that too... might try Rike Audio Q-Caps or something else later.


----------



## CopperFox

baronbeehive said:


> I feel that the most interesting area of upgrade to go in now would be to do the same as has been done for the 6SL7 tube but for the 6SN7. This would need a switch because the optimal operating point for both tubes would not work together without it because they are so different with different load lines. I've heard both tubes on the stock amp and couldn't tell the difference but with both tubes optimised that would be entirely different and I would be interested to hear what the 6SN7 sounded like on it's optimum operating point. We haven't done this because we settled on the 6SL7 as being the best tube for the amp because of the higher gain so we didn't bother experimenting with the 6SN7. But I'm waiting for someone to do it! The anode/cathode tests are what I feel would bring about the most variance in sound.
> 
> A switch could also switch between different anode/cathodes with the same tube and could produce a different sound. For instance I have been wondering what sound the operating point low down in the distorted area of the grid would be like. I didn't do this because I was trying to find the best operating point, ie. the least distorted sound. It's possible that the sound would be very tubey therefore you could switch between transparent/tubey sounds depending on your mood, or what type of music you were listening to.
> 
> A switch would be simple to do by connecting in parallel the desired anode/cathode resistor to move the operating point to where you wanted it to be. It would be better to have 2 switches, one for anode and one for cathode, this would give 4 different combinations.. and if you had a similar switch for the 6SN7.. well that would be where it would start to get very interesting!



I actually have some new interest in the 6SN7 switch as I've been re-rolling 6SN7s and the various chinese big bottle power tubes I got late last year in my Cern Tube amp and some of those combinations have been interesting. Could get back to that in the future.

Another thing on my mind has been the "softness switch" for the power tube decoupling caps. I wonder if it would be possible to control the amount of power from those with some sort of potentiometer.


----------



## baronbeehive

talan7 said:


> Some crazy looking mods on here


Hello talan7!

Thanks . Not really crazy though, just trying to make an already good sounding amp even better lol! We feel a combination of crazy and sensible has pushed the amp to end game.


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## baronbeehive (May 1, 2021)

CopperFox said:


> Well I haven't posted for a while. This is because I realised the PCB on my MKVI+ had gotten into a bad enough condition that it needed replacing.


Ha! I was wondering when that curse would strike, you seem to have been in luck up to now. Most of us have had those problems in one way or another and have had to remedy the situation by patching up the PCB. It's not that difficult where the pads have lifted to patch them up by scraping away to expose the trace and then solder a piece of wire across to make the connection good. This is where having a DMM becomes an essential tool to check on your repairs.



CopperFox said:


> While doing extensive component rolling it is a good idea to try and preserve the PCB from excess wear, tear and heat (instead of doing this for the various new components by carefully removing any older solder from the PCB before installation). It is also probably a good idea to solder extension leads to the joints on the pcb for any components-to-be-rolled. And solder those components to the extension lead instead to keep the pcb in good condition (particularly on the components where the solder joints/pads on the pcb are small). This will probably actually save some time and pain too as it is easier to solder/desolder from the ends of extension leads than directly to the pcb when there is a lot of large added components in the way.


Yes, good idea, especially where you are repeatedly changing components such as your experiments with the cathode caps. Having to repeatedly take out the PCB is a bit of a nightmare as well.


----------



## baronbeehive

CopperFox said:


> I figured I wouldn't have the time and patience to actually replace the PCB at the moment so in mid-february I decided to order a complete new amp. So I did that... and four weeks later got notified that the black version of the amplifier is not available and not in production and the order was cancelled on my behalf. I asked by email from Little Dot if there was any particular reason for the black version not being produced and if it was to resume production at a later date. But received no response whatsoever even though they had been responsive before that.


Where did  you order from? China or US? The LD site in US, littledous.com, has told me that they place great value on customer relations and test each amp thoroughly before sending out, and their warranty looks good. Whereas the China site have been undergoing changes recently.



CopperFox said:


> The last thing I was doing on the black MKVI was testing the big cathode bypass caps. Even though I had initially positive impressions about the 2200uf FW series caps, it was looking like they were still burning in and the sound was getting worse - flatter, less dynamic, less soundstage and there were less power tubes that would sound ok with them.
> 
> The general trend with going from 470uf to 1000uf to 2200uf seemed to be that the sound got more detailed but slower and less dynamic with the larger caps. Also, with the 470uf caps, the high gain mode was _too fast_ to use, with too many things sounding like hits from a hammer. Still, the low gain mode with 470uf sounds better to me than 1000uf with high gain. The latter has more detail but less dynamics, less soundstage and is slower. I do prefer dynamics and speed over detail. Still I feel that it would be interesting to have and test something between 470uf and 1000uf from the Nichicon KZ line.


Yes that's my preference too. Your findings are pretty much what I would expect from the larger caps, I found similarly. You might see some improvement in the KZ's up to 1000 uF but that would probably be it. And I feel that if you do go to 1000uF you might need the small bypass cap again. although you seem to have good higher frequencies, that's maybe down to your Miflex coupling caps.


----------



## baronbeehive (May 1, 2021)

CopperFox said:


> Hmm. Well, I did get a different similar idea. Since I would want to try Nichicon caps between 470 and 1000 uf, I will try using two similar 330uf 100v Nichicon KZ caps there. They obviously should not have very different discharge rates. I did some googling about parallel capacitors in audio circuits and the consensus seemed to be that using two capacitors instead of one larger capacitor is ok and should have lower esr even if the specifications of the larger and smaller caps were similar. With these Nichicons however, the smaller capacitors are also faster in specification. Maybe the combination of being both faster and larger (combined) capacity than the 470uf could be good.
> 
> 
> 
> I've been thinkin about that too... might try Rike Audio Q-Caps or something else later.


You could certainly try that. We feel that bypass cap use should really be limited and only used where necessarily due to the phase differences that would result which may or may not be detectable. Would be interesting to see if you can hear anything like that going on.

With WCF caps the consensus is that if you don't  use the faster silver type caps in that position the sound would become more dull sounding. The WCF cycle goes on in sequence with the top triode operation and as such needs to be quite a distinct sound to avoid becoming muddled up. This is a particular feature of the design of the LD.


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## baronbeehive (May 1, 2021)

CopperFox said:


> I actually have some new interest in the 6SN7 switch as I've been re-rolling 6SN7s and the various chinese big bottle power tubes I got late last year in my Cern Tube amp and some of those combinations have been interesting. Could get back to that in the future.
> 
> Another thing on my mind has been the "softness switch" for the power tube decoupling caps. I wonder if it would be possible to control the amount of power from those with some sort of potentiometer.


Yes that could be interesting. It means setting up the biases for whatever tubes you use and being able to switch between them if you intend to use 6SN7's with 6SL7's for example.

Not sure if anything would come of a softness switch in the way you mention. We have done a switch for the power tube output to double it if using 5998 tubes. Personally I didn't find it of much use other than in increasing the volume.

I still think the best way to adjust the sound characteristics from slow/soft to fast/hard would be via, tubes, wires, operating points, or caps. Wires could be copper or silver internally or externally, operating points could be set to be transparent or distorted, choice of caps could be for lush or transparent sound, the same for tubes. For example a soft lush sound was easily achieved by using RCA 6SN7 grey glass tubes, whereas GE tubes will be much more transparent.

Edit: probably best to set the amp up for transparent sound and then vary that when required to softer by using tubes or distorted (lush, tubey) operating point.


----------



## talan7

baronbeehive said:


> Hello talan7!
> 
> Thanks . Not really crazy though, just trying to make an already good sounding amp even better lol! We feel a combination of crazy and sensible has pushed the amp to end game.


I ordered a MK VI from Shenzhen Audio and haven’t heard anything from them for almost two weeks since they asked me what color I wanted. Picked up a DT 990 600 ohm while waiting. Can’t wait to hear them on the MK VI, when it comes.


----------



## baronbeehive

talan7 said:


> I ordered a MK VI from Shenzhen Audio and haven’t heard anything from them for almost two weeks since they asked me what color I wanted. Picked up a DT 990 600 ohm while waiting. Can’t wait to hear them on the MK VI, when it comes.


Best of luck with your order. I know from the other LD forum that certain LD distributors have been getting a bad name so I hope that you have no problems with yours. It seems that customer relations and QC are not what they used to be now unfortunately, I hope they improve.


----------



## talan7

Would a good tube preamp to a solid state amp give a really good tube sound or do I need tube amp? Is there any benefit using tube preamp


----------



## baronbeehive

talan7 said:


> Would a good tube preamp to a solid state amp give a really good tube sound or do I need tube amp? Is there any benefit using tube preamp


It could do yes, but personally I don't think there is a need for preamps these days. Apart from imparting a tubey sound a tube preamp could cause problems with direct coupled amps if a tube were to blow which is something to consider.


----------



## talan7

Does anyone on here do mods for others? Let me know what you do and what you charge.


----------



## baronbeehive

talan7 said:


> Does anyone on here do mods for others? Let me know what you do and what you charge.


No, there's not enough people here to do that. Best thing would be if you could find a friendly electronics engineer and ask him if he could do it. I have had a TV repair man do some circuit testing for me in the past on my initial build.


----------



## CopperFox

baronbeehive said:


> Where did  you order from? China or US? The LD site in US, littledous.com, has told me that they place great value on customer relations and test each amp thoroughly before sending out, and their warranty looks good. Whereas the China site have been undergoing changes recently.



It was littledotus who did not respond to my question about the black color resuming production. Ordered from Shenzenaudio.


----------



## talan7

CopperFox said:


> It was littledotus who did not respond to my question about the black color resuming production. Ordered from Shenzenaudio.


How long did it take before Shenzhenaudio shipped out your amp? I ordered a MKVI from them almost 2 weeks ago. I received an email from them the day after I placed my order asking what color I wanted. I said silver, and that was that.


----------



## baronbeehive (May 3, 2021)

I hope you guys do alright with Shenzenaudio. Sorry to say from what I've heard on the other LD forum that people have experienced problems which is why I contacted littledotus.com to see what was happening because littledot.net couldn't be contacted, but they have now got their website back up. The US site were very friendly and helpful and said that they had upgraded their testing prior to shipping, and their warranty seemed to be good. I hope this is the case, because if not I fear many will give up on Little Dot which is a shame as the amp itself is good, and I never used to hear of problems unlike what seems to be happening now.


----------



## CopperFox

talan7 said:


> How long did it take before Shenzhenaudio shipped out your amp? I ordered a MKVI from them almost 2 weeks ago. I received an email from them the day after I placed my order asking what color I wanted. I said silver, and that was that.


Three weeks.


----------



## talan7

CopperFox said:


> Three weeks.


Oh ok 👍🏾 thanks. I feel much better


----------



## baronbeehive

CopperFox said:


> Three weeks.


Glad to hear it arrived safely!


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## Maxx134 (May 6, 2021)

The slow shipping is probably because of the weight.
I remember when I ordered just one replacement transformer and it took about 4weeks...



baronbeehive said:


> I feel that the most interesting area of upgrade to go in now would be to do the same as has been done for the 6SL7 tube but for the 6SN7


So the issue with the different tube is not the optimal bias point, but the fact that it has a different output level to the output stage.
The gain switch may be needed to switch to get an optimal gain for the next stage (output tubes) but the question is, how much gain or output would be optimal for which output tube type?
The stock setup has basically such a low driver output to not matter, but not so with these moded setups.

So my point is that you should consider which output tubes your settling on, and also the gain switch setting, before settling on a driver tube choice.

My amp is not the mark6 , so I would rather let others chime in with optimal combos for that unit..


Ideally, we would want least global feedback, which would mean the higher gain switched.
Then a driver tube that outputs it's level in the sweet spot to drive the output tubes.


For me, I first tested and settled on an output tube type, then I rolled tubes untill I found my fav driver tube to compliment the output tube.
For instance, my choice of output tubes were none of the recommended types, and they required more input gain, so the higher "MU" type 6SL7 was preferred, for my setup.
I am assuming the LD mark6 output tubes, would be better off with a lower gain 6SN7 type.


The variability of the mark6 to use more output tube types than the Mark8, makes it a bit more effort in  rolling to find what you like.

While both the tube and cap upgrades   basically overlap, help & compliment each other, in general:
The tubes basically are the sonic image, depth and richness, while the cap characteristics are basically the clarity, style & finesse..

Just mentioning these points, from a designer's perspective, because at this stage, we stopped modding long ago. 
Basically this thread has actually been redesigning.


----------



## CopperFox

Feels great to have the amp running again... in the black chassis. I put the new PCB and vu meters there .

Now with the 8* parallel 330uf 100v Nichicon KZ caps as cathode bypass. They will need to burn in along with the rest of the caps.


----------



## baronbeehive

CopperFox said:


> Feels great to have the amp running again... in the black chassis. I put the new PCB and vu meters there .
> 
> Now with the 8* parallel 330uf 100v Nichicon KZ caps as cathode bypass. They will need to burn in along with the rest of the caps.


Haha.. it's getting mighty crowded in there! The amp looks great, glad it's all up and running again. You took the PCB out of the new silver amp and put it in the black amp? Good work .

Check in again when you have an idea of what the cathode bypasses sound like.


----------



## baronbeehive (May 8, 2021)

Maxx134 said:


> So the issue with the different tube is not the optimal bias point, but the fact that it has a different output level to the output stage.
> The gain switch may be needed to switch to get an optimal gain for the next stage (output tubes) but the question is, how much gain or output would be optimal for which output tube type?
> The stock setup has basically such a low driver output to not matter, but not so with these moded setups.
> 
> So my point is that you should consider which output tubes your settling on, and also the gain switch setting, before settling on a driver tube choice.



Hey Maxx, great to hear from you again, I've been trying to hold the fort while you've been away .

Yes I'm going to look again at my graphs showing load lines and optimal bias points for 6SN7 and 6SL7 to see if I might have missed something. The issue is that it would be impossible to draw the load line for 6SN7's with their optimal bias point on the graph for 6SL7's which had also been optimised, I will check back in when I have re-examined this. On the stock amp both tube types worked with no problem because neither were at their optimal point which was obviously a compromise by LD to enable tube rolling.



Maxx134 said:


> Just mentioning these points, from a designer's perspective, because at this stage, we stopped modding long ago.
> Basically this thread has actually been redesigning.



Haha, yes *you* might have stopped modding ages ago, I just finished mine recently by putting in those Neotech OCC silver output wires to try to sharpen up things as much as possible, first time I've been inside for ages.. and the last time lol.

Edit: Redge was back on the Oblivion thread recently!!


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## baronbeehive (May 10, 2021)

@Maxx134 I've looked again at the graphs for 6SN7's, below, and 6SL7's, bottom. I've included my comments at the time.

To summarize:

I've drawn 2 load lines, line 1 and line 2, on the 6SN7 graph which could be used to try different bias points. The lines show tube output current - l, anode resistor - Ra, and cathode resistor - Rk. Ra and Rk are the values to be tried experimentally.


The max rating of 20mA on the datasheet is well above the values that could be experimented with, and the typical operating value is 10mA so values on either line 1 or line 2 would be OK to try as the highest output is 7mA on point 3, line 1.





baronbeehive said:


> Out of interest I have included on the graph the ideal bias point I found for the 6SL7 tube, (in green). You can see why the amp is better for 6SL7's, at least with the stock bias point. Another factor is that the 6SL7 has an amplification factor of 70 whereas the 6SN7 is 20.
> 
> @CopperFox I would ignore the points on line 1 and just go for the points on line 2 or points on an intermediate line given by an anode of around 22k as I said previously. The reason is that the max rating for the 6SN7 is 20mA with a typical operation of 10mA.



Where I might have slipped up is in including the 6SL7 ideal bias point on the 6SN7 graph and visa versa the 6SN7 ideal bias point on the 6SL7 graph because that doesn't work.

So ignore the green point above and the blue points below, and what I commented about them. They were just there to indicate where they were in relation to the other tube type if that makes sense.



baronbeehive said:


> ...and the 2 blue bias points correspond to points 1 and 2 on line 2 on the previous post, which showed the graph for 6SN7's, just out of interest.
> 
> I hope that's clear, maybe not!
> 
> ...



So my conclusion about optimised points for 6SL7 and 6SN7 not working without a switch was wrong, clearly you can't superimpose a bias point for one tube type on another tube type's grid curves because the electrical characteristics are different, silly of me ! No one spotted my deliberate mistake lol. You are right that it is the outputs that might need to be switched, but only to adjust the gain appropriately.

The output from 6SL7 has gone up from about 0.5mA - stock, to around 1.5mA - ideal point.

The output from 6SN7 has gone up from about 0.5mA - stock, to around 7mA - ideal point, well within operating parameters.

I hope that's cleared that up .


----------



## Maxx134 (May 8, 2021)

I read years ago, where the designer was explaining about testing load lines, and how, across the linear portion of the bias point, you can still have a preferred point..
A point that may not be exactly in the middle of the linear portion, but as long as the  + & - amplitude of the signal lies inside that area, you won't have signal compression distortion.

So the point is, that's your preferred bias point, ideally, should be tested and listened to.

In my own experience, I have noted slight differences or both liveliness and image distance, with different bias points within usable range.
At the non-linear range, I did notice some dynamics compression.

That's why I feel it is sometimes an art, to design tube amps, and that, for instance, I view the stock driver tube bias points, an intentional design choice, rather than a compromise. A choice for wider tube rolling.
They could have increased the voltage supply for better bias points, but chose to retain a lower voltage.
Another reason why I lowered those last PSU resistors (to increase plate voltage) on the sides of the board, that are in series just before the tube anodes & "Decoupling caps"..


----------



## baronbeehive (May 12, 2021)

Maxx134 said:


> So the point is, that's your preferred bias point, ideally, should be tested and listened to.



Yes, exactly! A point that looks good on paper might not be that good and visa versa. You only know after you have tested it. There could be many points that sound better than the ones we've tried yet!



Maxx134 said:


> They could have increased the voltage supply for better bias points, but chose to retain a lower voltage.
> Another reason why I lowered those last PSU resistors (to increase plate voltage) on the sides of the board, that are in series just before the tube anodes & "Decoupling caps"..



Yes, that definitely helped with an extra 20 volts or so.

I think the reason that the stock point works is that there is very little voltage swing in that position so that the swing either side of zero signal is linear because it doesn't swing far enough to reach non linear areas.. clever of LD !

The whole area of bias points is a compromise between output current, voltage swing, linearity.. and chance as well! For example when I was testing this I didn't test the differences in voltage swing at all, so that might also have yielded interesting results.

I think this area of experimentation is the only interesting one left after the other mods have been done, that's why I've been going over it with @CopperFox .There could be interesting results if some of the different points are tried. I certainly felt, as you did, that liveliness and transparency were affected so it's well worth pursuing this.


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## baronbeehive (May 9, 2021)

@Maxx134 I'm very happy with the amp as it is now and that's my mods finished lol!

I tested it on some high res music such as this: 

and this one by Dire Straits: 

The thing about these speaker demos, you get the sound as it is coming out of the top end speakers which sounds sensational both through my HE-800's and my Monitor Audio Silver speakers! I really can't imagine anything better than this, the clarity is simply stunning which I think might be partly due to the CCS. And.. there is scope for further improvements in this aspect with a Neotech headphone cable which you have I believe. I haven't bothered with one up to now because there is not really any need. 

Also the fact that the little APPJ is right up there too is quite amazing, so I will never get rid of them.. ever .


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## baronbeehive (May 16, 2021)

Following on from the previous discussion where it was stated that there could be many tube bias points that need to be listened to, not just drawn on the graph. I've got together my final say on the points that could be tried, because I don't really want to bother plotting any more load lines for the moment. These are points that I would have tried had it not been for the fact that I've finished experimenting, so I've go this together for others who might like to try. Hopefully it can be understood what to do now!!

This is for 6SL7 tubes:






The brown load line is the one drawn by sonic, red by Maxx, and the black is the stock line. On the brown, red and green lines I have already tried 3 different cathodes and have picked my best ones. The remaining points - 1, 2, 3 and 4 I have added to try now if anyone wants. They represent the extremes of values and also a good spread of values.

All that remains to say about these new points is that 2 of the points, that is points 3 and 4 are extreme values going into non linear regions where compression or distortion should be heard which may or may not be pleasant, for people that like tubey sounds for example.

The values are in red top right of page, Ra is the anode, Rk is the cathode.

If anyone wanted to try intermediate values you could do that, for example, the Rk at point 1 is 1K and the Rk at point 3 on the black line is 5K so any intermediate value between these could be tried if that is what you want. I haven't bothered to plot these intermediate points.

Edit: It doesn't matter if the values you choose are not exact or if  you can't get the exact resistor, near as dammit will do.


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## baronbeehive (May 16, 2021)

This is for 6SN7 tubes:






Again the values are in red top right of page, Ra is the anode, Rk is the cathode.

I've drawn 2 load lines, line 1 and line 2 each with 4 bias points along the line, the points represent a good spread of values and go from extremes left to right meaning that pretty well all relevant values have been drawn, but if anyone wanted to try intermediate values you could do that, for example, the Rk at point 8, line 2 is 250R and the Rk at point 7 is 5K so any intermediate value between these could be tried if that is what you want. I haven't bothered to plot all possible intermediate points.

On the extreme top right are some other points I have calculated without bothering to draw the load lines, for example at top right I have given the values for Rk of 166R and 5K3. These are values that would lie on a line half way between line 1 and line 2 with a current of 10mA. Any value between 166R and 5K3 could be tried for any points that you would like to try along that load line.

The values of Rk of 1K and 16K are along the black line which is the stock load line. Again any values between these extremes could be tried.

Again the values at the extremes are values which could sound compressed or distorted which tubey sound lovers might actually like.. maybe a lot!

Edit: As before, doesn't matter if the values you choose are not exact or if  you can't get the exact resistor, near as dammit will do as it won't affect the bias point much.

This graph might explain why some people picked up differences between, say TS6SL7 and TS6SN7. You can see for the 6SN7 the load line is very low in the graph going in to the non linear regions in contrast to the graph for 6SL7's, so the resulting sound might be more tubey sounding which some people might like. I don't think the difference is huge though as I couldn't detect much difference myself.

*NB:* As a final note on this I would recommend only using bias points along line 2 and stock if you are going to try to ideally bias 6SL7's AND 6SN7's, that is if you want to use both tube types ideally biased at the same time. Only use bias points on line 1, or the line I didn't draw between line 1 and line 2, if you are only going to use 6SN7's and not mix with 6SL7's. The reason is that the output current might be too high for one tube type which could be damaging, as you can see line 1 is fixed at 18mA and  this is way too high for a 6SL7 tube whose typical operating current is around 2mA. If in doubt only ideally bias for one tube type and don't mix them.

That is why a switch would be necessary if you want to use both tube types at the same time, and make sure that the output current doesn't go above 2.3mA for 6SL7's if  you do mix tubes without a switch. Therefore you should double check the figures before implementing them to make sure of the output current limitations in case of error, but you should be ok anyway if you stick with line 2 and my figures.


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## baronbeehive (May 12, 2021)

@Maxx134 This modded amp is truly end game, those high res speaker demos show what it can do. I know that the demos are varying distance from the speakers resulting in varying sound, when they're close the sound really is great, obviously you don't normally listen that close, but further field listening is still pin sharp on my speaker amp, APPJ.

The fact that this amp, and the LD can go to these levels in sound reproduction has shown me that the LD is well and truly there! Before, the only way I thought that the sound could be bettered is the sharpness of soundstage and the way the instruments jump out, but those demos showed me that I can reproduce that sound on the amp. Not only that but the sound signature is perfect for me, so it's good to just concentrate on the music and not on how the amp can be improved now.. that also goes for the baby amp lol!

So the only dependant factor now on how good the amp sounds is how good is the source material. Good high res music will show the amp off to its best, right up there with the top end gear IMO.

I won't go on any further about the SQ but people who have done the mods specified here will know what I'm talking about.

All that good work you did on trials and testing all that time ago certainly paid off,  you got it spot on .


----------



## talan7

Finally received confirmation of my MK V1 shipping from Shenzhen audio, coming next week.


----------



## talan7

Amp arrived early, about to go in now!


----------



## talan7

Listening now with my Heddphone, very spacious sound. How do I turn up the gain. Manual says some hole at bottom of amp but I don’t see it


----------



## AngryTank

talan7 said:


> Listening now with my Heddphone, very spacious sound. How do I turn up the gain. Manual says some hole at bottom of amp but I don’t see it


If it’s like the mk8, you have to open it on the bottom  unless you have something that fits In the vents to turn up the switch.


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## baronbeehive (May 15, 2021)

talan7 said:


> Listening now with my Heddphone, very spacious sound. How do I turn up the gain. Manual says some hole at bottom of amp but I don’t see it



Excellent!

Open the bottom plate and find the 2 red boxes, 1 is circled:





Slide both white switches on both red boxes. You now have high gain.

We recommend high gain for even greater spaciousness and transparency with less negative feedback.

Edit: For anyone new to this we always warn that if you have had the amp on *always give the amp 15 minutes or so for the caps to discharge* first to make sure you don't kill yourself poking around inside!


----------



## talan7

How powerful are the caps? Can’t be to much


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## baronbeehive (May 15, 2021)

talan7 said:


> How powerful are the caps? Can’t be to much


Enough to kill you, seriously, there is high voltage inside the amp, but so long as  you observe the precautions as I said you will be fine. If you have had the amp on that is the time to be careful. If you haven't had it on before you open it up then that will be fine. If you have had it on always unplug the power and wait 15 minutes or so and it will be safe.


----------



## talan7

Opened up and raised the gain. My DT990 600 ohm sound wonderful. They sound even more open. This is a good amp. In time, I look forward to rolling tubes. Any recommendations?


----------



## baronbeehive

talan7 said:


> Opened up and raised the gain. My DT990 600 ohm sound wonderful. They sound even more open. This is a good amp. In time, I look forward to rolling tubes. Any recommendations?


Excellent, congrats !

What type of sound do you like, tubey or clear, what sort of budget do you have, expensive or cheapo like me lol?


----------



## CopperFox

baronbeehive said:


> Haha.. it's getting mighty crowded in there! The amp looks great, glad it's all up and running again. You took the PCB out of the new silver amp and put it in the black amp? Good work .



Yes. Well at first i put everything in the silver case, but there was an unlikely short circuit caused by two different pcb mounting screws partially piercing two different cables coming from one transformer - and the screws remaining in contact with those cables - which resulted in a smoked transformer. Never had any issue with cables getting stuck on or even damaged with screws before so didn't know to look out for that. 

So it was either put the old transformers in the silver case or put the pcb in the black case, the latter looking more simple to do (and giving me a black amp). It was quite easy in the end as I could just desolder wires from the old pcb and solder them to the same spot on the new board one by one.




baronbeehive said:


> Check in again when you have an idea of what the cathode bypasses sound like.



They're probably now settled in after two weeks in there.

Here's how the 2*330uf cathode bypasses sound:

-Compared to the single 470uf, there is a lot more detail and nuance and the sound is smooth without the metallic bite/edge. With the 470uf the primary problem was excess attack which could make some tracks such as for example the 3:30-4:00 part on Sultans of Swing sound uncomfortable.
-Dynamics are good, not flat like it was with 2200uf and also better than with 1000uf. Sounds like it is still less than with 470uf though.
-2*330uf works well in both high gain and low gain. I like low gain better, primarily because bass gets loose and less extended in high gain. It sounds like something that could be caused by difference in output impedance.
-Out of the single 470uf, single 1000uf and 2*330uf, the last one sounds most refined.
-I'm now feeling the sound could actually use some more edge/bite.
-One obvious possible confounding factor is that the pcb and most of the components on it are fresher than when I had the 470uf/1000uf there.

This mostly fits in with the notion that higher capacitance here has more detail and less dynamics and vice versa. Nonetheless, I'm feeling that the 2*330uf 100v has more treble detail than 1000uf 50v.

I will still experiment with 550uf formed from one 330uf 100v and one 220uf 100v capacitor later. Possibly 2*220uf 100v as well.

However, it is fine tuning at this point. The differences could be small enough that the effect of impedance mismatch should be considered. So perhaps the impedance matching mod would be quite in place now.

There are several posts with mentions about the impedance mod back in the thread, but there doesn't seem to be a post where this mod would be described. What would be needed here to match the output impedance to my headphones, which are modded Monolith M1060C with 18 ohm impedance?

(I've also given some thought to getting an external impedance matcher such as the Raphaelite B10.)


----------



## talan7

baronbeehive said:


> Excellent, congrats !
> 
> What type of sound do you like, tubey or clear, what sort of budget do you have, expensive or cheapo like me lol?


I like deep, hard hitting bass, soundstage and lots of details.


----------



## baronbeehive

talan7 said:


> I like deep, hard hitting bass, soundstage and lots of details.


I can't really recommend hard hitting bass tubes, all I can say is that the best you could probably do would be to try Bendix 6080WB graphite tubes which have a hard hitting bass and airy detailed soundstage, but they are getting very hard to get hold of. Tungsol 5998 are probably best for soundstage and liquid detail, again expensive.
So perhaps you could look into Chinese tubes such as Psvane/Shugang and look up some of their reviews.

Also for driver tubes Tungsol 6SL7's are excellent for soundstage and liquid detail, and Mullard ECC35 and ECC32, or ECC33 which I think have stronger bass as well.

The amp doesn't really do hard hitting basshead type sound although the bass is quite powerful, so I would suggest you could try some headphones which do really hard hitting bass.


----------



## baronbeehive

CopperFox said:


> Yes. Well at first i put everything in the silver case, but there was an unlikely short circuit caused by two different pcb mounting screws partially piercing two different cables coming from one transformer - and the screws remaining in contact with those cables - which resulted in a smoked transformer. Never had any issue with cables getting stuck on or even damaged with screws before so didn't know to look out for that.
> 
> So it was either put the old transformers in the silver case or put the pcb in the black case, the latter looking more simple to do (and giving me a black amp). It was quite easy in the end as I could just desolder wires from the old pcb and solder them to the same spot on the new board one by one.


Wow I haven't heard about screws piercing the transformer wires before, I don't know how that could have happened unless the wires were wrongly positioned, don't know what chassis screws could have done that.

You might have missed an opportunity to change the wiring for some better quality wires there!


----------



## baronbeehive (May 17, 2021)

CopperFox said:


> Here's how the 2*330uf cathode bypasses sound:
> 
> -Compared to the single 470uf, there is a lot more detail and nuance and the sound is smooth without the metallic bite/edge. With the 470uf the primary problem was excess attack which could make some tracks such as for example the 3:30-4:00 part on Sultans of Swing sound uncomfortable.
> -Dynamics are good, not flat like it was with 2200uf and also better than with 1000uf. Sounds like it is still less than with 470uf though.


Yes, more or less to be expected, seems like you've hit the sweet spot! Sounds like the right combination of transient attack and power on tap for those details.



CopperFox said:


> -2*330uf works well in both high gain and low gain. I like low gain better, primarily because bass gets loose and less extended in high gain. It sounds like something that could be caused by difference in output impedance.
> -Out of the single 470uf, single 1000uf and 2*330uf, the last one sounds most refined.


Interesting finding, again expected to some extent. With high gain there's less negative feedback in the loop which has the positive effect of opening up the soundstage but at the same time risks losing some bass control.



CopperFox said:


> -I'm now feeling the sound could actually use some more edge/bite.
> -One obvious possible confounding factor is that the pcb and most of the components on it are fresher than when I had the 470uf/1000uf there.
> 
> This mostly fits in with the notion that higher capacitance here has more detail and less dynamics and vice versa. Nonetheless, I'm feeling that the 2*330uf 100v has more treble detail than 1000uf 50v.
> ...


You are right, and yes it is fine tuning now. The cathode cap upgrades are mainly for the ability of the amp to recover from strong transient clipping. The impedance matching mod only applies planar to planar headphones and not to Sennheiser HD's for example as the impedance varies with these headphones. I think the conscensus from what I have found on this thread and others is that impedance matching has very little effect on sound in spite of the fact that matching impedance with headphones would seem the correct thing to do.

18 ohms, wow that's a very sensitive headphones, more so than my HE-500's. I will see if I can find the table of values for the power resistors for the impedance mod.

I think it is quite difficult to get more edge/bite without spoiling the sound in some way, and this comes down to the interaction of the components. You might have to think about you components and what is said about them and  how they might work together. For example most of us here decided to put in Jupiter coupling caps because of their realism, whereas other caps such as Mundorf's, fore example might be sharper and more metallic. I've been trying to get a more transparent, clear, tighter sound but without the harsh sound. In the end I decided to try using Neotech OCC silver wires internally and I believe they had the desired effect. Although silver, their internal crystal structure meant that they were not harsh at all.

I can only suggest perhaps to replace the Miflexes in the coupling position in favour of Jupiters to try to get rid of the metallic edge, but it could be an expensive mistake if you don't like them!

I just mention that to give you an idea of what you might need to do to get the sound you want. Also other components in the chain such as headphones might need to be changed like for talan7.

All this can be a bit hit and miss, and you can only do what the amp is capable of.

NB. it also depends on the source media, for example if you checked out the speaker demo I posted above that shows what this amp can do in terms of transparency and sharpness and so on.


----------



## talan7

baronbeehive said:


> I can't really recommend hard hitting bass tubes, all I can say is that the best you could probably do would be to try Bendix 6080WB graphite tubes which have a hard hitting bass and airy detailed soundstage, but they are getting very hard to get hold of. Tungsol 5998 are probably best for soundstage and liquid detail, again expensive.
> So perhaps you could look into Chinese tubes such as Psvane/Shugang and look up some of their reviews.
> 
> Also for driver tubes Tungsol 6SL7's are excellent for soundstage and liquid detail, and Mullard ECC35 and ECC32, or ECC33 which I think have stronger bass as well.
> ...


thanks, I already have my RME ADI2 dac eq'ed for an additional 3-4 dbs in the bass so I'm good there. I'll probably try Tungsol 5998 and Tungsol 6SL7 to keep it all Tungsol.


----------



## talan7

Maxx134 said:


> *COSMETIC MODS:*
> 
> SonicTrance MK6 transformer mod:
> http://www.head-fi.org/t/782183/little-dot-mk8se-mk6-super-mods/80_20#post_11966905
> ...


What kind of tubes are these? They look wonderful


----------



## baronbeehive

talan7 said:


> What kind of tubes are these? They look wonderful


They look good don't they . They're Western Electric 421A's, the even more expensive version of the Tungsol 5998's I mentioned earlier. They are distinct from the 5998 and have 2 getters compared to the TS. They are said to have an even punchier bass but I believe the differences are fairly slight.


----------



## CopperFox (May 17, 2021)

talan7 said:


> I like deep, hard hitting bass, soundstage and lots of details.



Out of the driver tubes I tried in the stock configuration the made in Russia Tung-Sol 6SL7 reissue were among the bassier ones. They're somewhat more bassy than the original which in turn is smoother in mids/low treble. They're also easier to find and relatively inexpensive.

In the stock configuration the amp can take both 6SN7 and 6SL7 tubes (not at the same time though) and can be optimized for either through mods.


----------



## CopperFox

baronbeehive said:


> You are right, and yes it is fine tuning now. The cathode cap upgrades are mainly for the ability of the amp to recover from strong transient clipping. The impedance matching mod only applies planar to planar headphones and not to Sennheiser HD's for example as the impedance varies with these headphones. I think the conscensus from what I have found on this thread and others is that impedance matching has very little effect on sound in spite of the fact that matching impedance with headphones would seem the correct thing to do.



Well, the M1060Cs are large planars... and large bassy closed planars to be more specific.

And to be even more specific, here's a measurement graph from my MiniDSP EARS. The black line is the M1060Cs with my mods on them, pink is stock and a couple of other phones for reference.



They are fairly Harman-correct with the mods I have on them, possibly more so than other large planars despite some others using DSP. That might mean that they could need more current than some others. And the current output on the MKVI depends in part on the impedance matching between amp and phones.

I've also seen that with some other amplifiers that have an output impedance switch the sound does audibly change on different output impedances so it would be interesting to see if the effect is similar here or something else.




baronbeehive said:


> 18 ohms, wow that's a very sensitive headphones, more so than my HE-500's. I will see if I can find the table of values for the power resistors for the impedance mod.



Thanks, that'd be nice (again). Couldn't find much information about the actual contents of the mod from the thread yet. There was something on it in Post #3720 but that doesn't yet translate to what actually should be done or where the extra resistors should be added.


----------



## baronbeehive (May 18, 2021)

CopperFox said:


> Well, the M1060Cs are large planars... and large bassy closed planars to be more specific.
> 
> And to be even more specific, here's a measurement graph from my MiniDSP EARS. The black line is the M1060Cs with my mods on them, pink is stock and a couple of other phones for reference.
> 
> ...


Hmmmmm your headphones look quite bassy! You've smoothed out the curve a tad with your mods and got that bit more bass, very nice.

Yes current hungry, but shouldn't be a problem with the MkVI+. As they are so sensitive that is a very good test on the amp and it's mods, if you don't pick up any background noise.

I think we began to grind to a halt by the time the impedance mod was discussed, we all did it but nobody mentioned it's effects. As I said from what I've heard there is very little difference which tallies with my own experience, certainly it isn't one of the big mods. It might make a difference in your case with your headphone's sonic characteristics though.

Re: the actual mod, sonic was the only one that implemented a switch, I hard wired it in because by then I had settled on the final choice of power tube You need to do a switch if you are going to use several power tubes. As you can see on sonic's amp on the link you gave the wiring is pretty involved for the switch. I can then let you know what resistors values you need if you decide on which tube you are going to use. It is simply a case of connecting them in parallel to your existing power resistors on the component side of the PCB.


----------



## baronbeehive (May 18, 2021)

Impedance mod:






So you require 4 Mills MRA05 resistors soldered in parallel to existing 330R power resistors as above. For example if you are using 6AS7G power tubes you will require 4x930R resistors soldered on to your 330R resistors to arrive at a total Ra or 244R. That is for my 38 ohms impedance  headphones, yours will be 18 ohms so that will affect the total Ra figure obviously.

I can't find this table anywhere and don't know how to calculate it myself so I suggest you PM SonicTrance, I'm sure he will be happy to help.


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## CopperFox (Jun 9, 2021)

baronbeehive said:


> Impedance mod:
> 
> 
> 
> ...




Ok, from @SonicTrance's comments in Post #3720, the Cavalli formula is  Ra = (1/Gm*(1/Ka*(1+Ka)/(1+Kr)*(Rp+Rl)/Rp+Rl/Rp)) .

Here with 6AS7G tubes the values would be

Gm=0,007
Rp=286
RI=18 (headphone impedance)
Ka=0,7
Kr=0,75

So the equation is Ra = (1/0,007*(1/0,7*(1+0,7)/(1+0,75)*(286+18)/286+18/286))

Which results in 219,719056 so it is roughly 220.

Looking at some parallel resistor calculators, a resistor at roughly 660Ω resistance would be needed in addition to the existing 330Ω resistors to reach 220Ω.


So I'll get some 650Ω or 680Ω 5W resistors and solder those on top of the 330Ω Mills resistors.


----------



## baronbeehive (May 20, 2021)

CopperFox said:


> Ok, from @SonicTrance's comments in Post #3720, the Cavalli formula is  Ra = (1/Gm*(1/Ka*(1+Ka)/(1+Kr)*(Rp+Rl)/Rp+Rl/Rp)) .
> 
> Here with 6AS7G tubes the values would be
> 
> ...



Yes that looks good. I couldn't find out what Ka and Kr is? I can't find the original Cavalli paper to look it up.


----------



## baronbeehive

Sonic has PM'd me with the Cavalli paper which has some quite complicated maths in it to show the WCF function and calculating the load for headphones. The Ka and Kr are assumed constants so they stay the same. As far as I can gather the calculations are not an exact science.

IF you would like a copy of the paper and can understand the maths lol, let me know.


----------



## Maxx134

baronbeehive said:


> Excellent!
> 
> Open the bottom plate


Oh, everyone, remember those bottom case screws strip easy! So best to use the right fitting screwdriver.



CopperFox said:


> Here's how the 2*330uf cathode bypasses sound


This is something we never experimented with enough, so thank you for leading the way here.
Normally one would not expect differences to happen in this location, but the realization is that we are not dealing with a regular circuit, but a WCF circuit, so this has not been explored much.


CopperFox said:


> -Out of the single 470uf, single 1000uf and 2*330uf, the last one sounds most refined


This is good to know!  I plan to change my cathode caps anyways, so will take this into consideration.

We do know that the both the ESR and speed is benefitted from paralleled caps, but I was curious to know what was there a reason why the designer  chose a non-polarized cap in that position, and I never dug deeper as to why.
I am starting to think it was for speed.

So currently, my issue is that I do not have enough capacitance there, and have seen the meter dip on bass hits, when using hungry planars.



CopperFox said:


> which resulted in a smoked transformer.


If you ever want to replace a transformer they are specific to each side, and you cannot find anywhere so have to order from little dot. Took me about 2 months to get mine(!).



baronbeehive said:


> For example most of us here decided to put in Jupiter coupling caps because of their realism, whereas other caps such as Mundorf's, fore example might be sharper and more metallic


I think the are to get it more attack is the WCF caps. I remember it had an effect on clarity.

Also in the main coupling position, those mundorf not metallic, but add a sweetness on top that's nice but not actually accurate.
They do well in that WCF position to add liveliness.
😊

It's great to see guys still choosing this amp, because it's still so unique.
You simply can't find a balanced OTL amp. Especially one with solid state control over the output (for dc offset).
This is close to having hybrid without being hybrid, unless you do the driver stage mod with CCS.
😊

I noticed that first page is not updated with many of recent findings, so think best to insert links for all the latest stuff we did.
@baronbeehive , many thanks for keeping up to date on everything. I will need your help to please let me know which posts to include.
I remember we PMed about it but I been away so whenever you have time, feel free to PM or post here.

Cheers
👍🙂


----------



## talan7

Any cages fit the MKVI? I need something to put on to protect tubes from my son when he playing around.


----------



## baronbeehive (Jun 1, 2021)

Maxx134 said:


> Oh, everyone, remember those bottom case screws strip easy! So best to use the right fitting screwdriver.
> 
> 
> This is something we never experimented with enough, so thank you for leading the way here.
> ...



I don't think Copperfox tried a single cap of value about 660uF though, so it may be that this would suffice to get the same effect as 2x330's.


Maxx134 said:


> It's great to see guys still choosing this amp, because it's still so unique.
> You simply can't find a balanced OTL amp. Especially one with solid state control over the output (for dc offset).
> This is close to having hybrid without being hybrid, unless you do the driver stage mod with CCS.
> 😊
> ...



I originally thought that the WCF solution for low output impedance and double power output was not an ideal solution but now I think it is a clever move and something that benefits that amp being OTL. I believe that is what gives the sound that sweet quality, the downside is we have been trying to improve bass response as a result of no transformer on output, and I believe we have largely succeeded.

It would appear that it gave Cavalli a few problems trying to calculate the load in the WCF .

Re: my holding the fort... no problem, good to see you around again though. I did have a list somewhere of the additions but don't know what happened to that. But it will be easy to look up so I'll get back to you. We can discuss it first because we might not agree on everything though lol !


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## Maxx134 (Jun 1, 2021)

baronbeehive said:


> We can discuss it first because we might not agree on everything though lol !


Naaa lol I am very open to new stuff.
Remember in this thread when we had alternative approaches which led to @SonicTrance making the new design amps?
Well I also found out that the WCF design compromises were also resolved by member @coinmaster in a design collaboration called "leamski follower".
So see this thread led to alot of diverging directions.
😊


----------



## coinmaster

The leamskie follower does solve the design flaws of the WCF but it's not a mod that is easy to do or that I would recommend someone try to do. It would be easier to design it from scratch at that point. 
I have 8 6c33c tubes and custom wooden chassis for balanced leamskie follower that I haven't really bother to assemble yet because it would essentially be a novelty project and I've designed amps that are vastly better than the MK6 so I wouldn't really use it, and I'm working on new headphone tech right now among other things.


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## baronbeehive (Jun 2, 2021)

coinmaster said:


> The leamskie follower does solve the design flaws of the WCF but it's not a mod that is easy to do or that I would recommend someone try to do. It would be easier to design it from scratch at that point.
> I have 8 6c33c tubes and custom wooden chassis for balanced leamskie follower that I haven't really bother to assemble yet because it would essentially be a novelty project and I've designed amps that are vastly better than the MK6 so I wouldn't really use it, and I'm working on new headphone tech right now among other things.


Yeah, absolutely. No point flogging a dead horse! I have to say that the amp atm is sounding very sweet, not saying that there couldn't be better amps though.. or better  headphones come to that.

Edit: Those wood blocks might be a possible design issue lol . Saying that I don't mean single to you out... those HiFiMan headphones for example look pretty bonkers!


----------



## Maxx134

coinmaster said:


> I'm working on new headphone tech right now among other things


Not to sidetrack, but I was fortunate to hear his prototypes, and it is in another league from anything I have heard, so hopefully the future looks ripe with possibilities.

Also, I will be posting updates to first page in coming days, with @baronbeehive  help.
🙂


----------



## Maxx134

I am currently researching into the designer's choice of "non-polar" on cathode section, for instance any "esoteric" clues/reasons for his choice.


----------



## baronbeehive

Maxx134 said:


> I am currently researching into the designer's choice of "non-polar" on cathode section, for instance any "esoteric" clues/reasons for his choice.


The cathode caps do appear to be more significant than I originally thought, although I know from my other amp how relevant they are to SQ.


----------



## CopperFox

Maxx134 said:


> This is something we never experimented with enough, so thank you for leading the way here.
> Normally one would not expect differences to happen in this location, but the realization is that we are not dealing with a regular circuit, but a WCF circuit, so this has not been explored much.
> 
> This is good to know!  I plan to change my cathode caps anyways, so will take this into consideration.
> ...



One thing I noticed after installing the 2*330uf 100V caps was that the vu meters still fluctuate with some bass hits, but they move _upwards_ instead of down. I don't remember them ever doing that before, not even with the 2200uf. Whether or not this change comes from these caps still needs further confirmation though as I'm sure some of the improvements I'm hearing must come from the new pcb and new components on it. Don't know how much though. I did test the new amp before installing any mods on it but didn't really pay attention to the vu meters' movements then.

I now have 2*220uf 100V Nichicon KZ's installed as cathode bypass (the resistors I ordered for the impedance mod have been stuck in customs for a week). I'll refrain from commenting on how they sound until they've been there for about two weeks.


----------



## CopperFox

baronbeehive said:


> Sonic has PM'd me with the Cavalli paper which has some quite complicated maths in it to show the WCF function and calculating the load for headphones. The Ka and Kr are assumed constants so they stay the same. As far as I can gather the calculations are not an exact science.
> 
> IF you would like a copy of the paper and can understand the maths lol, let me know.



I found this which seems to be a compilation of articles about the WCF that includes the Cavalli paper?


----------



## baronbeehive

CopperFox said:


> I found this which seems to be a compilation of articles about the WCF that includes the Cavalli paper?


Thanks for that! This might explain why, at least in the WCF circuit, there is not much difference in sound, at least to my ears, regardless of what the Ra is in the Cavalli equation to calculate headphone load. It seems there are difficulties in this calculation before Cavalli finally arrived at his value, and possibly even after that. Or maybe there actually isn't much difference in sound as I originally thought. I have a speaker amp with adjustable outputs, 4, 6 and 8 ohms and I found the same there, not much difference if any. So I will be interested in your findings, especially as you have a very low impedance headphone which the paper you found mentions the difficulties with such difficult to drive headphones in the WCF, and the small current available within the WCF.


----------



## Maxx134

CopperFox said:


> I found this which seems to be a compilation of articles about the WCF that includes the Cavalli paper?


This is excellent for understanding the WCF design. Thanks! I will look up what info I have on it as well.

The impedance mod, is basically what is already done in the MK8, to be set for higher impedance Headphones.


----------



## Maxx134

For instance, on the HD800, it actually made the headphones more open in the midrange. So no modding was needed for the HD800 to sound great.
It was optimal for these higher impedance Headphones.

Yet I changed my MK8 to be set for a 50ohm load instead of the 300ohm of the Sennheiser headphones.
This made the HD800 revert back to it's "brighter" nature, with less open mids.

So the differences heard were from extreme differences in the impedance mod change.

From my limited testing on planars, I do have notes in which I still observed some tunning differences on the output tubes. It made a slight difference for me so I will find them.


----------



## CopperFox (Jun 29, 2021)

Ok I have now tried 2*220uf 100V and 330uf 100V + 220uf 100V in addition to the 2*330uf 100v (and single 470uf, 1000uf, 2200uf and 3300uf).

The 2*220uf had much in common with the single 470uf in that it had great dynamics and also similarly suffered from excess attack / edge on certain kinds of passages. It did have more detail than the single 470uf though and it also sounded brighter in comparison.

However, the best overall is the 330uf 100V + 220uf 100V (550uf in total). This combination has great dynamics and detail and there is neither too much edge/attack or smoothness. In my use of low gain and very low impedance planars it is just about right in many respects.

This combination also seems to have the overall widest range of usable different power tubes. I'm now using a combination of Tung-Sol 6080WB and Shuguang 6N5PJ... and those Tung-Sols hadn't really sounded right to me before, and the chinese power tubes didn't really combine well with western tubes before.

If I had to rank the cathode bypass capacitors/capacitances it would be like this (first five Nichicon KZs, 6-7 are Nichicon KW) :
(Note that I don't even have high impedance headphones so I don't know how they would work with those. I also use the low gain setting.)


1. 330uf 100V + 220uf 100V (does most things (everything?) right, overall the best sound I have heard)
2. Single 470uf 50V  (good dynamics and crunchy mids <--- those sound fun to me. Also excess attack and relatively low detail/resolution.)
3. 2*330uf 100V (good but overly smooth, not best dynamics)
4. 2*220uf 100V (good dynamics but excess attack and obnoxious slight brightness)
5. Single 1000uf 50V (sound is... ok)
6. Single 2200uf 100V (very flat, not usable, long burn in)
7. Single 3300uf 100V  (fails to burn in)

(EDIT: 1000uf+ needs high gain to burn in and function properly. Many prefer that but I prefer low gain so that does affect my ranking. My impression is that high gain needs higher capacitance than low gain. High gain with the 470uf had the worst excess attack I've heard.)

At some point with the single 470uf I was considering to stop experimenting as it was a sound that I liked but I did also want to find something to fix some of its flaws. Although it took a long time I'm now happy that I did.


----------



## baronbeehive (Jun 29, 2021)

CopperFox said:


> If I had to rank the cathode bypass capacitors/capacitances it would be like this (first five Nichicon KZs, 6-7 are Nichicon KW) :
> (Note that I don't even have high impedance headphones so I don't know how they would work with those.)
> 
> 
> ...


Thanks to your work on this we are getting a comprehensive picture on the amp's function. I will discuss this with Maxx when we update page 1.

We have ideal values for Coupling, WCF and now cathode bypass caps. It looks like you have found the sweet spot. I would suggest though that your finding of 330uF + 220uF would be replicated if there was a 570uF value caps, which there isn't. So it looks like we are looking at a value of 570uF achieved by bypassing the 2 caps you mention.

Your results concur with much of our findings and look pretty consistent. The larger values being rather dull sounding while the smaller values being brighter, to generalize.

The reason for all this is that the cathode resistor and the cathode bypass cap form a high pass filter, increasing the capacitance lowers the cutoff frequency which increases gain at low frequencies. A cathode bypass cap is used to maximize gain which would be lower due to the negative feedback loop from the cathode resistor.  Negative feedback decreases gain and promotes linearity. Because the cathode bypass cap eliminates the negative feedback loop, the amp will have more gain with the cap than without it. The capacitance of the bypass cap determines which frequencies are boosted. If a smaller capacitor is used, only higher frequencies will be bypassed. A large arbitrary value cathode cap would ensure proper cathode decoupling well below audible frequencies so that there would be no hiss, or other noise as this would be cutoff by the cutoff frequency. The higher the capacitance would increase the bass response by lowering the cutoff frequency of the filter and therefore increases gain at low frequencies. That may or may not make sense!

Edit: another problem with large value electrolytics is the increase of ESR that can be helped by using smaller value bypasses to the cathode bypass which we have done.


----------



## baronbeehive

CopperFox said:


> This combination also seems to have the overall widest range of usable different power tubes. I'm now using a combination of Tung-Sol 6080WB and clear top Shuguang 6N5PJ... and those Tung-Sols hadn't really sounded right to me before, and the chinese power tubes didn't really combine well with western tubes before.


I never did manage to get hold of those Tungsol power tubes because they were very difficult to get hold of now apparently!

So did you manage to evaluate the impedance mod yet? I was interested to see if you could hear any difference.


----------



## Maxx134 (Jun 30, 2021)

baronbeehive said:


> Because the cathode bypass cap eliminates the negative feedback loop, the amp will have more gain with the cap than without it. The capacitance of the bypass cap determines which frequencies are boosted



This is why some tube circuit do not have any cathode caps, in order to not have any added gain, so as to be more linear with less THD.
 So in this position (cathode cap) we can effect and produce the tube harmonics and "thickness".
There are manufacturers that intentionally use this area to increase their tube harmonics, by choosing their choice of cap. Not talking about size/value, but cap type. They would purposely put in a low or non-audio grade cap in that position.





CopperFox said:


> At some point with the single 470uf I was considering to stop experimenting as it was a sound that I liked but I did also want to find something to fix some of its flaws. Although it took a long time I'm now happy that I did.



I am glad you did as well. This gives us great insight into the variables to making a preference choice.
I will be using your posts for updating first page soon

This adds complexity on what choice I will make. I tend to think you found the optimal value/values, and proportion, so now we can focus on cap brand sound trait effects on the tubes..

I have already researched a few different electrolytic cap brands and will post some general consensus of thier character type soon.


----------



## Maxx134

baronbeehive said:


> I would suggest though that your finding of 330uF + 220uF would be replicated if there was a 570uF value caps, which there isn't. So it looks like we are looking at a value of 570uF achieved by bypassing the 2 caps you mention.


It seems his observations are more about some interactions going on, with smaller combined values affecting performance of the dynamics.
So the total capacitance value is another aspect.


----------



## CopperFox

baronbeehive said:


> I never did manage to get hold of those Tungsol power tubes because they were very difficult to get hold of now apparently!
> 
> So did you manage to evaluate the impedance mod yet? I was interested to see if you could hear any difference.



I did try the impedance mod by installing four 680ohm resistors on top of the component side 330ohm power resistors. 
The sound did change, but only the bass improved slightly and everything else sounded overly smooth and veiled. The bass was getting distorted at clearly lower volumes than before too. I did not have patience to keep them there for more than a couple of days before removing them though. Don't know why that mod didn't work for me. One thing that I had been wondering was that whether or not the decoupling caps would somehow affect the parameters in the Cavalli formula, or are those on an entirely different part of the circuit?

And I also did order the Raphaelite B10 impedance matcher from the latest AE sale. This is because I've had some good results with using 3.5mm impedance adapters on some amplifiers so I've been wanting to play with an XLR impedance adapter even before that was released.

My Tung-Sols are from this box. Was a good buy as I didn't have any of those particular brands' tubes before (had some Chathams though which surprisingly sound _exactly _the same as the Tung-Sols).


----------



## CopperFox

Maxx134 said:


> I am glad you did as well. This gives us great insight into the variables to making a preference choice.
> I will be using your posts for updating first page soon
> 
> This adds complexity on what choice I will make. I tend to think you found the optimal value/values, and proportion, so now we can focus on cap brand sound trait effects on the tubes..
> ...



It probably should be mentioned there that things like high/low gain and also other components such as decoupling caps will have an effect on how the cathode bypass caps will function, possibly headphone type as well? 

I didn't test the 550uf combination in high gain yet but might do that later too.


----------



## CopperFox

Maxx134 said:


> It seems his observations are more about some interactions going on, with smaller combined values affecting performance of the dynamics.
> So the total capacitance value is another aspect.



The smaller than 470uf capacitors are available in the 100V specification as well, which has lower esr (or "Tangent of loss angle") on the Nichicon KZ series data sheet. It seems to me that the faster capacitors means more detailed sound there.

Perhaps it would be interesting to test something like the Wima MKP line in ~500uf there as well but I have no plans to do that in the near future ☠️. That would certainly require a bigger case...


----------



## baronbeehive (Jul 2, 2021)

CopperFox said:


> I did try the impedance mod by installing four 680ohm resistors on top of the component side 330ohm power resistors.
> The sound did change, but only the bass improved slightly and everything else sounded overly smooth and veiled. The bass was getting distorted at clearly lower volumes than before too. I did not have patience to keep them there for more than a couple of days before removing them though. Don't know why that mod didn't work for me. One thing that I had been wondering was that whether or not the decoupling caps would somehow affect the parameters in the Cavalli formula, or are those on an entirely different part of the circuit?
> 
> And I also did order the Raphaelite B10 impedance matcher from the latest AE sale. This is because I've had some good results with using 3.5mm impedance adapters on some amplifiers so I've been wanting to play with an XLR impedance adapter even before that was released.
> ...


OMG that is somwhere very near me, I could have gone over there, might try contacting him!

I can't remember but it would be easy to find out if the Chathams are  just rebranded Tungsols.

I doubt that the decoupling caps would have any effect, their function is to provide a reservoir of fast power close by to help the PSU which isn't regulated. That's their only function, not to influence SQ as such.

It may be that the Cavalli formula isn't that precise, I saw in the paper that another factor was added in the equation last minute as a correction but I don't know how effective it is for WCF circuits.


----------



## baronbeehive (Jul 2, 2021)

CopperFox said:


> The smaller than 470uf capacitors are available in the 100V specification as well, which has lower esr (or "Tangent of loss angle") on the Nichicon KZ series data sheet. It seems to me that the faster capacitors means more detailed sound there.
> 
> Perhaps it would be interesting to test something like the Wima MKP line in ~500uf there as well but I have no plans to do that in the near future ☠️. That would certainly require a bigger case...


Yes, not sure if WIMA would be worth trying because of their SQ. They seem fairly bog standard in that department.

I'm thinking of trying for a combined value of near to 550uF after your observations.

One thing that should be mentioned though that I don't think you use smaller bypasses? If so that would influence our choices because we do. I was wondering if that was because you don't like bright(er) sound? We have found bypasses to be necessary.


----------



## Maxx134 (Jul 2, 2021)

Okay so I discovered the reason why stock amp uses bipolar capacitor in the cathode position.
It is for better frequency response on the trebles end, so therefore a second "bypass cap" is not needed for the upper end, like what we have on first page.
Although is not verified here yet, it has been discussed elsewhere, on how a non-polarized can notice better tonality, when used in places like as a "coupling cap" (which of course we're not going to do.)
So in general, it is stated as being a bit better for tonality.
here is a statement by a manufacturer.




So anyways, we know that all ectrolytics have a weakness in the upper end trebles and details area, which is why we "bypass cap"(using the paralleled paper refa cap), but also why member copperfox noted tonality differences in details area, as he chose not to use a "bypass cap" on his lyctics.
So if not, then you have more tonality differences.

So I believe there were (three) multiple issues going on: tonality, dynamics, and detailing.

So since member copperfox is not using a any small "bypass cap" on his lyctic cathode caps (for even tonality),  it was good choice for him instead select the nichion audio grade caps for his test to be more successful on tonality/detailing, and to use the smaller values in parallel for more dyamics.

Also, we read from member copperfox, that although 2x330uf did give the detailing, it did not give increased dynamics to the level of the other  solutions.
This leads me to assume that going higher than multipled 220uf caps (paralleled) does not give more dynamics.
That was the only curious aspect that didn't work out as expected.

We can expect that the much higher single cap values (1000-2000uf) to not perform as well as the smaller multiple caps, and that a "single cap" solution should not be more than the 470uf observed by copperFox.

So with all this in mind, I decided to keep my 330uf and add the 220uf to it, as member copperfox optimally suggested.
The only difference is that I also decided to use non-polar since I am already using non-polar.
This can vary my results somewhat, but I expect it to be better regardless.

In order to keep the electrolytic caps as quality or audio grade as possible, I chose some kaisie 220uf caps.
Any differences in the tube harmonics from adding two  different brand caps, would only add to the richness of the sound.
 It's still a  more optimal choice for richness, than cheaper solutions the other brands I discovered (using computer grade Nichicon cap).
It can swing both ways with good or bad quality choices.
I have also observed another manufacturer make an upgraded amp using higher grade caps, only to have a more sterile harder, darker, grittier sound!!
They were not nichicon audio caps, but instead a change from low-grade to mid-grade types. You will rarely see top grade caps even in $5000 amps.
So the point is, real world  observation matters.


AudioNote kaisie caps are way more expensive for arguably little difference, but it is general concensus that they have good depth and tone.
The nichion caps have a general consensus of being more upfront clarity, while the silmic have the consensus of having detailed smoothness.
Being that these are all general consensus observations, they are to be taken lightly and not critically.

Bottom line, lots of things going on. Nothing is as simple as it seems when it comes to the variability of design  choices.


----------



## baronbeehive (Jul 3, 2021)

Maxx134 said:


> Okay so I discovered the reason why stock amp uses bipolar capacitor in the cathode position.
> It is for better frequency response on the trebles end, so therefore a second "bypass cap" is not needed for the upper end, like what we have on first page.
> Although is not verified here yet, it has been discussed elsewhere, on how a non-polarized can notice better tonality, when used in places like as a "coupling cap" (which of course we're not going to do.)
> So in general, it is stated as being a bit better for tonality.
> here is a statement by a manufacturer.



Right! I have polar cathode caps for both amps, if we are to use bipolar we need to be looking at Nichicon ES in the Muse range instead of KZ for example. That means I can't parallel a 100uF to my existing for example, damn!

You could test this on the LD, just remove the bypasses from the Mundorfs to see before you parallel the 220uF's.



Maxx134 said:


> So I believe there were (three) multiple issues going on: tonality, dynamics, and detailing.



Perhaps we should define these terms to make sure we are talking about the same thing? For example I think of dynamics as large changes in volume in bass and mids frequencies handled well, I would think that for example fairly large caps around the 550uF range would bring dynamics out with the emphasis on lower down frequencies. But also I think of liveliness which is more of a treble thing. I would think of attack and so on which Copperfox noted on the smaller value caps up to 470uF.


Maxx134 said:


> Also, we read from member copperfox, that although 2x330uf did give the detailing, it did not give increased dynamics to the level of the other  solutions.
> This leads me to assume that going higher than multipled 220uf caps (paralleled) does not give more dynamics.
> That was the only curious aspect that didn't work out as expected.



From what we know about the high pass filter bypassing certain frequencies I would have thought that around the 2x330uF value dynamics in the sense of powerful bass and mids would be around the maximum. But liveliness in the sense of treble sparkle and upfront sound the smaller than the 2x330uF values would be more relevant. That may be why this wasn't expected. I know that on my other amp the 470uF Kaisei caps without a smaller bypass was much duller sounding and lacking in treble response and liveliness but the bass frequencies were good.

I don't know what you think, just trying to understand the findings. I know what I prefer.

Anyway I will have to try either 470uF + around 100uF polar Nichicons, or go bipolar around the same values to test this out.

Edit: Knowing what we know about the high pass filter in the cathode bypass I would think that the possibilities of tonality are pretty much endless. For example a single cap would get the tonality of the make of cap, if there were to be several makes of caps in parallel the tonality would take on characteristics of both caps, also the more the caps were paralleled together the more the tonality would be affected, possibly adversely due to the different harmonics coming out of the different caps, and possibly some THD would be involved as well. This could partly explain the smearing that can sometimes affect paralleled caps. And the cap values affecting the different bypassed frequencies would also be involved. Also as you say the linearity of negative feedback would iron out these effects so I can see that to use cathode caps or not to use them, or to use them in different combinations would produce interesting results which we may not have got to the bottom of yet!

So whether to use single or multiple caps looks to be a bit of a minefield, to be determined experimentally perhaps.


----------



## baronbeehive

Maxx134 said:


> In order to keep the electrolytic caps as quality or audio grade as possible, I chose some kaisie 220uf caps.
> Any differences in the tube harmonics from adding two  different brand caps, would only add to the richness of the sound.
> It's still a  more optimal choice for richness, than cheaper solutions the other brands I discovered (using computer grade Nichicon cap).
> It can swing both ways with good or bad quality choices.
> ...


Should be interesting combining 2 different makes, Mundorf and Kaisei. I know that in my other amp combining Kaisei with small Audyn True Copper bypasses produced a remarkably good tone, I believe due to the mix of Kaisei and especially the Audyn bypass. I think there was a mix of the qualities of both types.



Maxx134 said:


> AudioNote kaisie caps are way more expensive for arguably little difference, but it is general concensus that they have good depth and tone.
> The nichion caps have a general consensus of being more upfront clarity, while the silmic have the consensus of having detailed smoothness.
> Being that these are all general consensus observations, they are to be taken lightly and not critically.


I agree with this, I think the Kaisei worked well with the other amp and complemented it's qualities with a fuller sound whereas the Nichicons worked well with the LD bringing out the clarity more which is what I was looking for.


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## CopperFox

baronbeehive said:


> Yes, not sure if WIMA would be worth trying because of their SQ. They seem fairly bog standard in that department.
> 
> I'm thinking of trying for a combined value of near to 550uF after your observations.
> 
> One thing that should be mentioned though that I don't think you use smaller bypasses? If so that would influence our choices because we do. I was wondering if that was because you don't like bright(er) sound? We have found bypasses to be necessary.



I was thinking of the large film Wimas such as the 400v 400uf that I have on the psu output position, along the lines of @Redge78 's comments about the cathode bypass on the first page that "This 220µF value starts to be a significant value if you want to switch technology to some MKP or PIO caps. It's even worse if when you want to push the values two steps up (470µF). Those huge MKP/PIO caps would weight pounds (or even kilogrammes) each. It's feasable, it would be expensive, hard to manage ... but it could be better than even the best Lytics."

The Wima line seems to top at the 400uf value, but some other brands such as Vishay have 560uf 63V (part nr MKT1820756065 ). Those are quite large and expensive at $100 each and there is not much actual indication as to how they would actually sound so it would be an expensive blind experiment if it was possible to fit those in the case.

I haven't had the smaller bypasses installed after installing the decoupling and psu output wimas as after that they would make the sound way too trebly. So I would think that whether or not the smaller bypasses are useful depends on the other components like the psu output and decoupling caps as well.


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## baronbeehive (Jul 3, 2021)

CopperFox said:


> I was thinking of the large film Wimas such as the 400v 400uf that I have on the psu output position, along the lines of @Redge78 's comments about the cathode bypass on the first page that "This 220µF value starts to be a significant value if you want to switch technology to some MKP or PIO caps. It's even worse if when you want to push the values two steps up (470µF). Those huge MKP/PIO caps would weight pounds (or even kilogrammes) each. It's feasable, it would be expensive, hard to manage ... but it could be better than even the best Lytics."


Yes, you're right I forgot that one or two members did use those huge film caps in the cathode position, as well as for decoupling. From what I can gather the Wima sound is fairly soft I think, BUT, as film caps, in the cathode position they should be worth trying. I remember the favourable comments of the members that had used them.. in a MASSIVE custom chassis lol! The cathode position is one where speed is good and this is where film caps score above lytics.

Edit: Yes I would definitely think in your case these would be well worth trying. As I said the cathode position really needs fast caps and I think that it would benefit enormously if you did try them, bass would be snappier and transients also. This is the area that the amp would improve massively potentially as previous members have noticed.


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## baronbeehive

CopperFox said:


> I haven't had the smaller bypasses installed after installing the decoupling and psu output wimas as after that they would make the sound way too trebly. So I would think that whether or not the smaller bypasses are useful depends on the other components like the psu output and decoupling caps as well.


Yes I thought so, I remember your description after using those fairly huge, fast decoupling caps which would obviously make a difference in your case. I believe your system set up is optimised to the max to get the best possible sound from the amp!


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## CopperFox (Jul 16, 2021)

baronbeehive said:


> Yes, you're right I forgot that one or two members did use those huge film caps in the cathode position, as well as for decoupling. From what I can gather the Wima sound is fairly soft I think, BUT, as film caps, in the cathode position they should be worth trying. I remember the favourable comments of the members that had used them.. in a MASSIVE custom chassis lol! The cathode position is one where speed is good and this is where film caps score above lytics.
> 
> Edit: Yes I would definitely think in your case these would be well worth trying. As I said the cathode position really needs fast caps and I think that it would benefit enormously if you did try them, bass would be snappier and transients also. This is the area that the amp would improve massively potentially as previous members have noticed.



Hmm, maybe I could be able to fit those 560uf Vishays into the case. It would be quite a puzzle though. They are actually of similar 35mm thickness as the 100uf 500V Wimas but larger in height and width.

For comparing the speed of capacitors that have it specified in ESR and those that have it specified in tangent of loss angle I found an useful and informative post on the DigiKey support forum that has an equation to convert ESR into tangent of loss angle and vice versa.

By that equation the 0,07 tangent of loss angle at 120Hz of the Nichicon KZ capacitors would equal an ESR of ~422mOhm for the 220uf and ~281mOhm for the 330uf. That is probably not entirely accurate though as the Nichicon datasheet says "tan δ (MAX.) 0.07" for the <470uf caps, so it is a maximum value for all caps smaller than 470uf and so it is possible that the smaller caps could have lower than 0.07 tan δ at 120Hz.

Those Vishays' datasheet says that the 560uf version has 0,007 tan δ at 100Hz so by that equation their ESR would be ~20mOhm which is a lot less than the Nichicons but more than those film Wimas which have about 1 to 10 mOhm. So even there it might be beneficial to use two 275uf Wimas to reach ~550uf but no store seems to stock those and a minimum order to have them produced is 40 units.


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## baronbeehive (Jul 4, 2021)

CopperFox said:


> Those Vishays' datasheet says that the 560uf version has 0,007 tan δ at 100Hz so by that equation their ESR would be ~20mOhm which is a lot less than the Nichicons but more than those film Wimas which have about 1 to 10 mOhm. So even there it might be beneficial to use two 275uf Wimas to reach ~550uf but no store seems to stock those and a minimum order to have them produced is 40 units.



No those Wima's can be tricky to get hold of, the only thing I could find would be this: https://www.conrad.com/o/film-capacitors-0245680?ATT_NUM_ELECTRIC_CAPACITY_any=100 µF,150 µF

which would be 3x150uF + 1x100uF, which is a lot of capacitors!

I can't remember what film caps the other member for cathode bypasses used, I don't know if anyone else could help.

So the Vishays might be OK.

Edit: I've also seen these 330uF :https://eu.mouser.com/WIMA/Passive-...s/_/N-9x371Z1yzvvqx?P=1z0zldhZ1z0x7p2&FS=True

to which you could add the 220uF's also at mouser.

I've just checked the member who used film caps and he mentioned AVX.

If I remember right you are using film caps for PSU as well as decoupling? What capacitance are you using for those caps?


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## baronbeehive (Jul 4, 2021)

@CopperFox sorry, copying the search results at mouser didn't work properly, try this: https://eu.mouser.com/ProductDetail/WIMA/DCP4G064009JD4KSSD?qs=RB4whv9F6rxb7mMvMPxktA==

or enter WIMA in the search box with the 400uF filter and then the 120uF, or 3x115uF.


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## Maxx134 (Jul 4, 2021)

I think its too much efforts on cathode cap position.
The size determine the bass cutoff frequency.
Adding bypass cap (film type)will even out the larger electrolytic's frequency response issues (which would have reduced trebles without it).

So the issue in the beginning of this thread was only focused on the issue of the low end bass cutoff frequency.
That was determined to be 220-300uf.

what is being discussed now are including more different aspects:

1-The perceived dynamics using smaller paralleled electrolytics.
2- the perceived tonality changes with these smaller electrolytics.
Makes sense the smaller ones don't have the treble weaknesses that the larger electrolytics do.
3-clarity due to better (lower) ESR and tangent loss.

Using the bypass cap (as a film cap) negates the issues of points 2 & 3, but not the issue of increased Dynamics, (point 1) pointed out by member copperfox. In fact, this possibility was overlooked until now.

Then there is the other solution of not needing a bypass cap for the electrolytic, if using a non-polarized cap, which would have much less treble issues, so said to be bit better.

To me the Bottom line is, using no bypass cap, will be relying on the electrolytic. The issue here is that no electrolytic, will ever be as good as a film cap.
So, to me, using the bypass cap (for the treble end tonality) will be superior to the other solutions.

Yet I still want the increased dynamics of multi caps pointed out by copperFox.

Lastly is any harmonics added with usage of any and all electrolytic cathode caps.
Thats the reason I chose to stay with the mundorf and kaisie for _*more*_ tube harmonics, as my output tubes are different than yours.

Harmonics from the cathode position add to tube sound, and does not directly affect clarity or realism, which are areas of direct signal path (coupling cap & WCF cap).
Usage of good Nichicon caps like what copperFox used, should give least amount of harmonics into the cathode position.

Finally as always, since all these aspects not totally tested, yet I cannot say for certain these points into the first page, so for now these are my own conclusions.
👍🙂


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## baronbeehive (Jul 5, 2021)

Maxx134 said:


> Lastly is any harmonics added with usage of any and all electrolytic cathode caps.
> Thats the reason I chose to stay with the mundorf and kaisie for _*more*_ tube harmonics, as my output tubes are different than yours.
> 
> Harmonics from the cathode position add to tube sound, and does not directly affect clarity or realism, which are areas of direct signal path (coupling cap & WCF cap).
> ...


Yep, agreed on these points. I just wanted to point out that the area of cathode cap/resistor is more complex than initially appears. Clarity and detail is is excellent now with my 470uF's though going by what CopperFox has said it could be improved further by a final value of 550uF. The reason I chose to keep Nichicons in this position is probably because of this relationship to the power tubes. I like and use RCA's which do need a bit of a boost in those areas whereas a clearer tube would most likely benefit from cathode caps with more harmonics. So we have sampled these issues and any sonic effects that members note now can probably at least be explained on this basis, even if they aren't thoroughly tested "a priori."

My other amp is the opposite to this, I have put in very clear sounding Amperex power tubes and richer Philips driver tubes, and the end result is more or less the same in both amps sound signature which is the way I like it.

A further agreement in your conclusions is that the use of Kaisei caps in the other amp which has a slightly thinner tonality and therefore is better augmented by Kaisei caps rather than Nichicons for example, and the tonality is richer as a result. I certainly found dynamics improved with the caps in the other amp as well as in the LD with cathode values of 470uF which agrees with CopperFox.

I believe CopperFox has implemented more and higher value film caps than us in the compact version and so what he  has noted, in the way of attack, (or dynamics), and clarity can be explained by this in part due to lower ESR, faster response and better trebles.



Maxx134 said:


> Finally as always, since all these aspects not totally tested, yet I cannot say for certain these points into the first page, so for now these are my own conclusions.
> 👍🙂


Agreed! I don't particularly want to do an exhaustive testing of all these factors but at least we know on the basis of the high pass filter effects what should be occurring!

🤪🧐.


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## baronbeehive (Jul 5, 2021)

CopperFox said:


> The 2*220uf had much in common with the single 470uf in that it had great dynamics and also similarly suffered from excess attack / edge on certain kinds of passages. It did have more detail than the single 470uf though and it also sounded brighter in comparison.
> 
> However, the best overall is the 330uf 100V + 220uf 100V (550uf in total). This combination has great dynamics and detail and there is neither too much edge/attack or smoothness. In my use of low gain and very low impedance planars it is just about right in many respects.


@Maxx134 this is my explanation which I think concurs, at least partially with yours!

The 2x220uF and 470uF "great dynamics, excess attack" - reason - higher frequencies bypassed so were more in evidence. Also Nichicons have great clarity in sound.
The 2x330uF "overly smooth, not best dynamics" - reason - high pass filter set lower down bypassing lower frequencies so higher frequencies less in evidence and more of the lower frequencies result in smoother sound.
The 330uF + 220uF "great dynamics and detail, not too smooth or too edgy" reason - this is the sweet spot for the high pass filter getting the balance of frequencies just right, resulting in more perceived detail due to all frequencies being heard properly and resulting also in even dynamics!

So it would seem to get the right amount of detail *and* dynamics you need to hit that sweet spot somehow. Tonality would be more about the use of single caps without bypasses on the cathode caps because using bypasses would cut out some of the natural frequencies of that capacitor type. And some capacitor types would have more natural harmonics affecting tonality than others. I hope I have understood!

But a different capacitor type with a different sound might not respond in the same way at those cutoff frequencies so we need to watch out for these things.

I still think my point about dynamics is relevant because I believe that dynamics in this case are perceived as being stronger with more of the treble because this enables us to separate out the sounds and gives the sounds more of that edge that CopperFox mentions. Probably not important but I still think of dynamics as being more of a great contrast between volume of the stronger frequencies involving mids and bass more... whatever!


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## baronbeehive (Jul 5, 2021)

There is a further factor in all this. CopperFox has said that he prefers low gain. All this points to his system with, I believe, the larger faster film caps, being possibly more treble oriented with fast attack on the leading edge. The fact that he prefers low gain means that he prefers the more linear, damped attack, that low gain with it's higher negative feedback provides. As we know GNFB loops are for linear frequency response.

And the members that have used those large fast film caps for decoupling, PSU and cathode which CopperFox is implementing say what a massive sonic difference they make.

I myself have been trying to get more treble for liveliness and more attack because my system doesn't have enough of that, at least not until the recent mods. And I prefer high gain and a more open soundstage and less linearity because there is enough of this as it is on my system.

All of this means that we can assess the effects of individual changes, but when taken together all the changes we do will have different effects and we have to take all this into account when evaluating effects of changes.

This is interesting because we now have at our disposal a means of tailoring the sound from a darker more LCD type sound to a brighter more HiFiMan type sound. So that we can now advise members on the basis of what type of sound they would like and the results can vary widely making the amp very versatile indeed!


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## Maxx134 (Jul 6, 2021)

baronbeehive said:


> Clarity and detail is is excellent now with my 470uF's though going by what CopperFox has said it could be improved further by a final value of 550uF


I do not believe that the final capacitance value, is the key.
I believe the key is in usage of multiple smaller caps, when achieving the  total capacitance value

The treble variations are the result of the manufacturer design, and inherent weaknesses of using larger electrolytics. This is the common knowledge reason for using bypass caps on electrolytics.

Also, Technically, on paper and in design, the capacitance value in the cathode position theoretically should only affect the bass cut-off frequency, not the trebles.
 It is the issue of using electrolytics design at higher capacitance values, that thier design limitations is what affect the trebles.

Also, is well known that adding a cathode capacitor in a tube circuit is going to give us increased gain in that circuit, over just using a resistor alone. This would help explain the observation of increased dynamics.


----------



## CopperFox

Could not resist. 
Have the amp up and running and they will need burn-in.


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## CopperFox

Maxx134 said:


> I have also observed another manufacturer make an upgraded amp using higher grade caps, only to have a more sterile harder, darker, grittier sound!!
> They were not nichicon audio caps, but instead a change from low-grade to mid-grade types. You will rarely see top grade caps even in $5000 amps.
> So the point is, real world  observation matters.
> 
> ...



That's the problem with buying high end products... there may not even be ones available that would have the best components (or tuning) and modding naturally carries a higher cost/risk with high prices.

Most places on earth also don't have showrooms for testing expensive headphones/amplifiers beforehand.


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## baronbeehive

CopperFox said:


> Could not resist.
> Have the amp up and running and they will need burn-in.


Haha, oh wow, you might need a bigger box next time! You still have the Nichicons in though? And what are those big black caps?

Look forward to your impressions,  you've done much work there.


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## baronbeehive (Jul 10, 2021)

Following on from the discussion on cathode caps, I checked the value of my Kaiseis' in the baby amp, (APPJ), I had forgotten they are 1000uF. A couple of things about this, first, due to the amp's measly 3.5W having to feed speakers I believe the extra capacity is justified for that reservoir of power for transient recovery in this case, second the slightly thinner tonality of the stock amp benefits from the bassier bypassed frequencies, also the fuller Kaisei tonality and harmonics also benefit the amp in a complementary way.

The upshot of this is I think it would be difficult to generalize about cathode caps, because every amp is different and every cap is different and some thought needs to be given to the synergy of the amp and the components.

So despite the findings about capacitance, re: the APPJ, I  hit on a rich vein of luck with those caps because the end result is end game sound, not dull or overly smooth sounding - although it was until I put the small bypass cap on! On the contrary, also the amp has all the attack, and detail it needs. In many ways the LD has been having to keep up with the APPJ as the APPJ has always been slightly edgier in attack and textural detail due to the sharper sound signature, whereas the LD was slightly smoother. That's why I've been trying to give a small boost to the higher frequencies in the LD with the silver wires and Nichicon caps. Therefore as I have said previously the APPJ compares almost identically to the LD now which is already end game and there are no worries about components, capacitances and such like.

I'm very happy and wouldn't change anything now with these 2 amps.


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## CopperFox

baronbeehive said:


> Haha, oh wow, you might need a bigger box next time! You still have the Nichicons in though? And what are those big black caps?
> 
> Look forward to your impressions,  you've done much work there.



Those are the 560uf 63V film Vishays. They were actually the fastest delivery I've ever had from the US, just 4 days including customs processing. Quite surprising as it was the standard delivery option and with both covid and a large EU customs regulations change going on at the same time. 

(The customs regulations changed on the first of July so that now all packages from outside of EU will be processed. Before that, packages with value less than 23€ were exempt from customs processing. This practically meant that any packages that appeared to be of low value were exempt, such as any earphones or lightbulb-shaped objects from China,)


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## CopperFox (Jul 10, 2021)

I now have the Raphaelite B10 xlr impedance matcher as well. I tested it a bit before putting the Vishays in.

The results that I had with it on the MKVI mirror the experience with the impedance mod earlier. I dialed the output setting of the B10 at 16Ω to match the M1060Cs' 18Ω impedance and tried several different settings for the input, which included 16Ω, 32Ω, 50Ω, 60Ω, 120Ω and 150Ω. Presenting a higher impedance load to the MKVI at first (at 32Ω) caused a slight improvement in sub-bass, but higher impedance progressively made the treble more distant and veiled and also the bass would have less punch going higher than 32Ω.

IMO this seems to point to two things. First, the output impedance of the MKVI may not be linear across the frequency spectrum, but a rising curve toward the lowest frequencies, as with for example the Darkvoice 336SE output impedance measurements at ASR. That would explain why the bass and sub-bass in particular shows some improvement with higher impedance.

Secondly, it seems to me that for planars, the MKVI or at least my unit with my mods on it and in low gain mode produces its best treble with low impedance planars. Already with the B10's input impedance setting at 32Ω and more markedly so at 50Ω, the treble was less clear and became more veiled.

So it could be that the MKVI's output impedance is fairly low at higher frequencies and rises steeply at the lowest frequencies.

These observations could also explain why for example the small bypass capacitors for the cathode bypass would be useful for higher/medium impedance planars but not for very low impedance planars.


The B10 is a product that I like. My other tube amplifier with an XLR output is the Original OPA-5A which is a transformer output SET amp with 12AU7 and KT88 tubes and a fixed output impdance of 50Ω. With this amp and the M1060Cs, the B10 produces massive improvements all across the FR spectrum so I'm happy with the use I'm getting out of the B10 even if it were less useful with the MKVI.


Edit: I didn't test it with the MKVI's high gain mode yet, which is said to have higher output impedance.

Edit #2: Now I have tested it with the high gain mode too and its'a completely different story. More on that later.


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## baronbeehive (Jul 11, 2021)

CopperFox said:


> I now have the Raphaelite B10 xlr impedance matcher as well. I tested it a bit before putting the Vishays in.
> 
> The results that I had with it on the MKVI mirror the experience with the impedance mod earlier. I dialed the output setting of the B10 at 16Ω to match the M1060Cs' 18Ω impedance and tried several different settings for the input, which included 16Ω, 32Ω, 50Ω, 60Ω, 120Ω and 150Ω. Presenting a higher impedance load to the MKVI at first (at 32Ω) caused a slight improvement in sub-bass, but higher impedance progressively made the treble more distant and veiled and also the bass would have less punch going higher than 32Ω.
> 
> ...


I'm not familiar with impedance matchers such as the Raphaellite B10, and there don't appear to be any reviews, so I'll just reply in brief initially to your findings, maybe Maxx will reply with his input on this.

From what I found with the impedance mod, I detected a slight hump in bass as you said but it was very insubstantial and I could be imagining it.

The linearity of impedance response as far as I know is only an issue with dynamic headphones such as Sennheisers but not with planars.

However the answer I suspect lies somewhere within the Cavalli paper if only I could understand it in detail. There are several points in there that make calculating the Ra difficult, and there look to be several things that could affect linearity as you might have found. I know for example that the initial Ra calculation didn't agree with Spice simulations and had to be modified. I won't go into all of the points in the paper on my limited understanding.

You could be right though in your observations about impedance changes, especially bearing in mind we are talking about the WCF. The WCF has advantages in terms of lowered output impedance and raised power, but also probably has disadvantages and this could be one of them. My HE-500's are 38ohms, so not very high, except in comparison to yours and I haven't noticed veiling in my case, also I have small bypasses on the cathode bypass caps, but didn't test them without. But you could indeed by right about small bypasses due to you having your 18 impedance cans. However the need for smaller bypasses was the subject of extensive testing at the beginning of the mods thread, which I wasn't involved in.

All I can say atm about this is that it would be interesting in view of what you have found to test the amp with low and high impedance phones with the different B10 settings. Unfortunately I only have the one set of headhones, I sold my HD600's a while ago.

Edit: There is one factor in my case that might affect this, I have put in a CCS which ensures that there is a constant current output from the driver tubes regardless of voltage, this might affect the possible lack of linearity in the output impedance of the amp that you have found.

I don't have any frequency spectrum analysing equipment but that would be interesting to look at if anyone has.

A final point, this could also explain LD's 2 models in this range, the MKVl+ and the MK VIII, the later having an output impedance to match high impedance headphones like the Sennheisers, not only to adjust the power requirement but also to adjust tonality in line with your findings on frequency/impedance variation.


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## baronbeehive (Jul 11, 2021)

CopperFox said:


> My other tube amplifier with an XLR output is the Original OPA-5A which is a transformer output SET amp with 12AU7 and KT88 tubes and a fixed output impdance of 50Ω. With this amp and the M1060Cs, the B10 produces massive improvements all across the FR spectrum so I'm happy with the use I'm getting out of the B10 even if it were less useful with the MKVI.



My APPJ amp is also an OT SET amp!

What driver tubes do you use on the SET amp?




CopperFox said:


> Edit #2: Now I have tested it with the high gain mode too and its'a completely different story. More on that later.



Interesting!
.

Edit: Maybe greater variability?


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## baronbeehive

@CopperFox I don't want to second guess your results with the impedance matcher, but just so I can't be accused of being right... or wrong... after the event! I'm guessing that because you are now testing in high gain, ie less GNFB, I would think that the impedance matcher would have greater effect due to the higher output impedance in high gain.

Soundstage is more open in high gain, but the corollary of that is less control over bass frequencies. Therefore I would expect greater variation in soundstage, and greater variation in bass. Specifically some impedance settings resulting in more open soundstage and looser bass control, and some other settings resulting in more closed soundstage and tighter bass. Probably also greater or lesser control over treble frequencies due to the GNFB variation. Therefore dynamics would also be affected.

This would be the predicted effects, I remain to see if I'm right. If I am then we have verified what would be expected which is a positive.

Looking forward to your results anyway, and there would be an element of surprise due to what you have predicted about the frequency curve of the LD MKVl.


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## Maxx134 (Jul 18, 2021)

baronbeehive said:


> Edit: There is one factor in my case that might affect this, I have put in a CCS which ensures that there is a constant current output from the driver tubes regardless of voltage, this might affect the possible lack of linearity in the output impedance of the amp that you have found


Your CCS was mainly for the driver tube output to be better biased, so whatever quality came out goes thru the coupling cap, wich doesn't see or let the output stage be affected by anything, as it couples but also separates the stages from each other.
👍🙂


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## CopperFox (Aug 18, 2021)

Those 560uf film Vishays ended up not working. They had the same kind of issues as the 2200uf Nichicons before - slow burn-in and sound becoming flat and distant with burn-in. So I inferred the 560uf capacity is too high for film caps and now have 200uf 400v DCL-MKP film Wimas there.

I've been only doing burn-in for those sporadically so far as I was on summer vacation for the past two weeks and have been clubbing, festival-ing and driving around the country with any domestic covid restrictions having been lifted... some of them were reinstated last saturday though. It's a surreal experience after having not done any of those things for about 17 months.

Edit: will post more about the 200uf 400V wimas after they've had enough burn-in.


----------



## Maxx134

I think it aludes to not relying on one physical cap. 👍


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## baronbeehive (Aug 21, 2021)

CopperFox said:


> I've been only doing burn-in for those sporadically so far as I was on summer vacation for the past two weeks and have been clubbing, festival-ing and driving around the country with any domestic covid restrictions having been lifted... some of them were reinstated last saturday though. It's a surreal experience after having not done any of those things for about 17 months.


Ha! Glad you managed to enjoy some time off! It has been surreal, we had a short period in June after lockdown when things were beginning to return to normal, only to find the infection rate soaring again due to relaxing of restrictions. We may just be saved from another lockdown by our high vaccination rate, 80% have had both jabs, 90% have had one jab .

Festivals are out for me atm unfortunately until the rate goes down. We have the big one here, Glastonbury, which you've probably heard of, I've been many times.


----------



## Maxx134

Here is a link on bias load lines, from a "designer" point of view. He will joke about "bogus designer", but his article is actually one of the most informative:
http://www.diyparadise.com/tubeloadline/tubeloadlines.html
👍🙂


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## baronbeehive

Maxx134 said:


> Here is a link on bias load lines, from a "designer" point of view. He will joke about "bogus designer", but his article is actually one of the most informative:
> http://www.diyparadise.com/tubeloadline/tubeloadlines.html
> 👍🙂


Yeah, that's my go to source for load lines, very amusing article!
🙂 .


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## CopperFox (Aug 27, 2021)

baronbeehive said:


> Ha! Glad you managed to enjoy some time off! It has been surreal, we had a short period in June after lockdown when things were beginning to return to normal, only to find the infection rate soaring again due to relaxing of restrictions. We may just be saved from another lockdown by our high vaccination rate, 80% have had both jabs, 90% have had one jab .
> 
> Festivals are out for me atm unfortunately until the rate goes down. We have the big one here, Glastonbury, which you've probably heard of, I've been many times.



The name is familiar from some live albums' names. Haven't done any non-domestic festivals yet. Actually I haven't ever been to the UK either, but did visit Dublin and Galway in the 00s. Now I have a friend moving to Scotland next month and I might go visit him sometime in the near future. I've noticed that in the winter months in recent (normal) years there's been some rather cheap direct flights to London from my current home town as this is a popular holiday destination, so there's a fair amount of air traffic in many directions. Perhaps you'd be knowledgeable about the best and/or cheapest way to get to Edinburgh from London? I remember that the ~150km bus trip from Dublin to Galway took over four hours.

The festival that I went to was Qstock festival in Oulu, with attedance about fourty thousand. Didn't take many photos as it was raining all day on the first day, but on the second day there was nearly enough sunshine to render the darkness invisible.




What I was most looking forward to though was Oranssi Pazuzu which I had only gotten into during the pandemic (I'd describe as Hawkwind meets Emperor and Philip Glass in a _groovy_ dark winter forest). Talking about which, two weeks later it was estimated that the festival was linked to no more than 60 new covid cases.

I'm getting my second vaccine shot next month... so then I'll be able to  leave the country  go shopping in Sweden without needing to quarantine/get tested on return.


To not go completely off topic here's a photo of the 200uf 400v DCL-MKP wimas in the amp too.


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## baronbeehive (Aug 28, 2021)

CopperFox said:


> The name is familiar from some live albums' names. Haven't done any non-domestic festivals yet. Actually I haven't ever been to the UK either, but did visit Dublin and Galway in the 00s. Now I have a friend moving to Scotland next month and I might go visit him sometime in the near future. I've noticed that in the winter months in recent (normal) years there's been some rather cheap direct flights to London from my current home town as this is a popular holiday destination, so there's a fair amount of air traffic in many directions. Perhaps you'd be knowledgeable about the best and/or cheapest way to get to Edinburgh from London? I remember that the ~150km bus trip from Dublin to Galway took over four hours.


I don't personally know of train times to Scotland, actually I've never been but am looking forward to one day as it is a fantastic place, very far from me in the SW. If I do find out I will let you know but I don't think there are many options as the rail lines are few to there. I can tell you that atm it is best to look to break the journey up into smaller trips which link up if you are looking for the cheapest method when booking tickets. I know this doesn't make a lot of sense but it is the way we run our railways here, but I understand they will review this practise at some point in future. If you are looking at train travel while there, there are several very scenic lines around the Scottish coast.

You say the festival didn't result in many new covid cases, we have had the Boardmaster Festival in Cornwall, which did, and what with that and the fact that Cornwall is a popular holiday destination has resulted in Cornwall having the highest rate in the country so things are still not normal here.

Let me know if you do come to the UK!


CopperFox said:


> What I was most looking forward to though was Oranssi Pazuzu which I had only gotten into during the pandemic (I'd describe as Hawkwind meets Emperor and Philip Glass in a _groovy_ dark winter forest). Talking about which, two weeks later it was estimated that the festival was linked to no more than 60 new covid cases.
> 
> I'm getting my second vaccine shot next month... so then I'll be able to  leave the country  go shopping in Sweden without needing to quarantine/get tested on return.


I will check these out, I'm always looking at finding new music, I've certainly never heard of them, but you mention Hawkwind which are a favourite of mine from way back. I like the "Live Chronicles" live album, also others like "Choose Your Masques".


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## CopperFox (Oct 18, 2021)

CopperFox said:


> To not go completely off topic here's a photo of the 200uf 400v DCL-MKP wimas in the amp too.




These eventually did burn in, requiring eight weeks of active use during which they showed gradual but slow improvement.

It was worth the wait as these do work and they sound better than the electrolytics.

There is more air / high treble and more sub-bass detail/control and things like separation, layering, clarity and soundstage perception are better.

There is more realism to low treble and mids impact. There isn't additional edge where it does not belong, meaning an improved variety here – a mellow rock lead guitar can more clearly have both that bell-like sound or sharpness depending on how it is picked. And things like industrial metal do not suffer from lack of edge either.

I'm not a firm believer in transparency as the goal for audio equipment, but I would describe these as more transparent, allowing the other components in the amp such as the tubes to further show their character.

I needed to switch to the high gain mode to get these to work though. Fortunately they do not have any of the problems with high gain that I had with the electrolytics before (loose bass and overly soft sound). The bass control and detail is now better in the high gain mode than it was in low gain with the electrolytics.

(I saw one quote on some forum that discussed film capacitors as cathode bypass and it went something like "_all_ electrolytic capacitors have an edgy sound to them that you're not aware of until it's gone". I think that's what I was hearing before when talking about a metallic edge to the sound.)


So now I probably have the cathode bypass position settled. Although if the 200uf DCL Wima works here, it does raise the question if a lower value film cap such as 100uf could work there as well. (Some of those could fit into the standard case.) Also, how much voltage is there going through the cathode bypass capacitors with the low or high gain modes?

Seeing that the Wima DCL doesn't work with the low gain here afaik it also means that the 6SN7s would have too low gain to work with them – so if some other brand/model did, it would be interesting in that respect as well.


Next I will try some different resistor brands for the cathode resistor position such as Shinkoh and Audio Note and Ohmite. Having the extension leads there helps with that.

I might later try some other brand for the coupling capacitors as well and it would most likely be the Duelunds since I can get those for about the same price as the Jupiters (roughly 100€ each). The CAST Cu-Sn has been out of stock for months at the Nordic distributor though and they said it would be restocked Q4 this year. They did suggest trying the Duelund JDM Cu-Sn and said it is the same as the CAST Cu-Sn except with higher tolerance (5% vs 2%) and different leadout (2*0,8mm vs 1*1mm) and lower price (75€ vs 100€) and currently better availability. I wonder how different that would make them. Thinner wire means slightly higher resistance, but the lead lenghts could be quite short as they come from the same end of the cap. And 2*8mm doesn't fit into the solder joints either and my extension leads here are 0,75 and/or 1mm anyway.

The JDMs are also available in a 0,56uf capacitance which is not available in the CAST line. What exactly would be the most appropriate capacitance here and why, if I wouldn't want any bass roll-off, and are there any other advantages or disadvantages to higher/lower capacitance here? Looking back at the thread opinions seem to vary from 0,33uf to 1uf. I've seen some people say lower capacitance may have higher risk for phase oddities and that higher capacitance would put more strain on the output stage.


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## baronbeehive (Oct 19, 2021)

CopperFox said:


> These eventually did burn in, requiring eight weeks of active use during which they showed gradual but slow improvement.
> 
> It was worth the wait as these do work and they sound better than the electrolytics.
> 
> There is more air / high treble and more sub-bass detail/control and things like separation, layering, clarity and soundstage perception are better.


That's some incredibly useful work you've done there, I was wondering if you were still experimenting! To improve the already sweet treble is a good achievement, it's already sweet because there is nothing in the signal path from output tube to headphone, no caps, no OT's nothing. That can be an advantage, but the corollary of that is a potential lack of control. So the bass improvement you mention is something worth having. Members who have also put in film caps there have confirmed this, and I feel tempted to try it also now, the only thing stopping me is having the compact version, not wanting to extend the chassis, although I did do this for my other amp, the APPJ.


CopperFox said:


> There is more realism to low treble and mids impact. There isn't additional edge where it does not belong, meaning an improved variety here – a mellow rock lead guitar can more clearly have both that bell-like sound or sharpness depending on how it is picked. And things like *industrial metal do not suffer* from lack of edge either.


Ha! I wouldn't know about that anyway, it's not my bag frankly lol! But you're right there should not be more edge, film caps should be superior in every way.


CopperFox said:


> I needed to switch to the high gain mode to get these to work though. Fortunately they do not have any of the problems with high gain that I had with the electrolytics before (loose bass and overly soft sound). The bass control and detail is now better in the high gain mode than it was in low gain with the electrolytics.


That's not surprising as high gain would open up the soundstage more allowing the different elements to come through, the greater NFB in low gain would most likely obscure the effect. That's very interesting that you manage to get better soundstage *and* better bass control with the film caps, I'm getting really tempted now! The softer bass sound is something that the stock LD suffers from in not having an OT so anything that fixes this is well worth doing. Some of my mods were an attempt to do something about that as it's the only area I think in which the LD suffers.


CopperFox said:


> (I saw one quote on some forum that discussed film capacitors as cathode bypass and it went something like "_all_ electrolytic capacitors have an edgy sound to them that you're not aware of until it's gone". I think that's what I was hearing before when talking about a metallic edge to the sound.)


I believe this is due to the phase effects of a slower charge/discharge cycle, it is probable that the signal is affected by the slower cycle whereas a fast cycle will allow transients to occur naturally faster with less problems of clipping.


CopperFox said:


> So now I probably have the cathode bypass position settled. Although if the 200uf DCL Wima works here, it does raise the question if a lower value film cap such as 100uf could work there as well. (Some of those could fit into the standard case.) Also, how much voltage is there going through the cathode bypass capacitors with the low or high gain modes?


That raises the question about the different capacitance caps you experimented with together with their effects on sound, I would hypothesize that any film cap would be better regardless of size.

You could measure voltage but I always hesitate to recommend this unless you know what  you are doing and you say you haven't used a DIMM. *It is extremely dangerous and could be fatal if you don't know what you are doing!! *You have been warned.


CopperFox said:


> Seeing that the Wima DCL doesn't work with the low gain here afaik it also means that the 6SN7s would have too low gain to work with them – so if some other brand/model did, it would be interesting in that respect as well.


We like 6SL7's on the thread because of this. However a lower gain tube can have a higher headroom so it doesn't always follow. I've just started using a lower gain 12AT7 Brimar on my APPJ in place of the higher gain 12AX7 despite the lower power of the APPJ it works well.


CopperFox said:


> I might later try some other brand for the coupling capacitors as well and it would most likely be the Duelunds since I can get those for about the same price as the Jupiters (roughly 100€ each). The CAST Cu-Sn has been out of stock for months at the Nordic distributor though and they said it would be restocked Q4 this year. They did suggest trying the Duelund JDM Cu-Sn and said it is the same as the CAST Cu-Sn except with higher tolerance (5% vs 2%) and different leadout (2*0,8mm vs 1*1mm) and lower price (75€ vs 100€) and currently better availability. I wonder how different that would make them. Thinner wire means slightly higher resistance, but the lead lenghts could be quite short as they come from the same end of the cap. And 2*8mm doesn't fit into the solder joints either and my extension leads here are 0,75 and/or 1mm anyway.


The shorter the lead length the better due to the lesser impedances. If you are concerned about higher resistance in thinner wires you could use something like Neotech OCC silver wire going from the cap leads , silver has a slightly lower resistance than copper but not a great deal less but the crystalline structure of the Neotech wires means a very smooth flow through it. Also the silver doesn't have the sharpness that very cheap silver wires have but has a gloriously resolved sound


CopperFox said:


> The JDMs are also available in a 0,56uf capacitance which is not available in the CAST line. What exactly would be the most appropriate capacitance here and why, if I wouldn't want any bass roll-off, and are there any other advantages or disadvantages to higher/lower capacitance here? Looking back at the thread opinions seem to vary from 0,33uf to 1uf. I've seen some people say lower capacitance may have higher risk for phase oddities and that higher capacitance would put more strain on the output stage.


We've found by experiment that anything from about .33uF to .47uF is probably best for powerful bass with the higher capacitance the best. You can go higher up to around 1.0uF but the higher you go the more likely there could be issues with resonances coming back down the line, nothing to stop you if you want to try.

BTW did you come to any conclusions about the impedance curve on the LD which you said was probably curved. It would need an oscilloscope to prove this and would be interesting to know. Have you made any more observations about impedance matching?

Edit: I think what you are referring to re: phase problems with low capacity caps is when using them as bypass caps with the differing charge/discharge rates having an adverse effect when coupled with the caps that are bypassed.

Not sure about voltages at the cathode bypass cap, I do have figures but not sure what they refer to after all this time, but I think you have plenty to play with for cap voltages, but always the higher the better.


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## baronbeehive (Oct 19, 2021)

CopperFox said:


> Seeing that the Wima DCL doesn't work with the low gain here afaik it also means that the 6SN7s would have too low gain to work with them – so if some other brand/model did, it would be interesting in that respect as well.


If you mean other brands/models of tubes Maxx is the one who has tried them all, he would be able to let you know his choices.



CopperFox said:


> I might later try some other brand for the coupling capacitors as well and it would most likely be the Duelunds since I can get those for about the same price as the Jupiters (roughly 100€ each). The CAST Cu-Sn has been out of stock for months at the Nordic distributor though and they said it would be restocked Q4 this year. They did suggest trying the Duelund JDM Cu-Sn and said it is the same as the CAST Cu-Sn except with higher tolerance (5% vs 2%) and different leadout (2*0,8mm vs 1*1mm) and lower price (75€ vs 100€) and currently better availability. I wonder how different that would make them. Thinner wire means slightly higher resistance, but the lead lenghts could be quite short as they come from the same end of the cap. And 2*8mm doesn't fit into the solder joints either and my extension leads here are 0,75 and/or 1mm anyway.


Should be very little difference between the Duelands and Jupiters they are made in almost exactly the same way. The Jupiters/Duelands we feel give out the most realistic sound possible, whereas for example Mundorfs can sound a little unreal to some although they are excellent and were recommended in the factory upgrade by LD before they stopped doing that. I have Mundorf SIO in the WCF position to boost treble there.

Edit: Correction I should have said Jupiters and Black Gate are made in almost exactly the same way.

I think the Jupiters would be less forward sounding than your Miflexes but the realism is there in spades. I have them in both my amps and they have upped the game in my APPJ which is a sub $150 amp to end game level!


----------



## Maxx134

CopperFox said:


> Also, how much voltage is there going through the cathode bypass capacitors with the low or high gain modes?


From my memory, the voltage drop across the cathode caps was low .. maybe 25v maximum.
And, the caps used were about 50v.
Higher gain switch setting should not affect the voltage drop across the cathode caps, as that is part of the  bias circuit setting. 

So my guess as the reason for longer break in time of your caps is pertaining to how high their voltage rating is.
Higher rating will take longer to break in with lower voltage.



CopperFox said:


> Seeing that the Wima DCL doesn't work with the low gain here afaik it also means that the 6SN7s would have too low gain to work with them – so if some other brand/model did, it would be interesting in that respect as well


I believe that would depend also on the choice of output stage tube your using.
For my amp (mk8), I required higher "MU", so my choice was going for 6SL7 types.

Don't be confused because the stock MK8 is using 12pin, as I used adapters for 6pin, and the input stage circuit is exactly the same.




CopperFox said:


> Next I will try some different resistor brands for the cathode resistor position such as Shinkoh and Audio Note and Ohmite. Having the extension leads there helps with that


The resistors paralleled for cathode caps are even less affecting, and indirectly sound, unlike the input stage resistors by the volume.
The general consensus is that they will be subject to affecting sound only with resistor "thermal noise". A nice wire wound resistor would eliminate that nicely, but I have not felt even that was necessary, Because stock supposed to be "metal films" already, which are ideal over cheap carbon resistors. So check your unit.




CopperFox said:


> The JDMs are also available in a 0,56uf capacitance which is not available in the CAST line. What exactly would be the most appropriate capacitance here and why, if I wouldn't want any bass roll-off, and are there any other advantages or disadvantages to higher/lower capacitance here? Looking back at the thread opinions seem to vary from 0,33uf to 1uf. I've seen some people say lower capacitance may have higher risk for phase oddities and that higher capacitance would put more strain on the output stage


Because early on in thread we went with the online calculator which calculated anything over .33uf would already be passing the 20hz range and below. Stock was .22uf for good reason they didn't want to go lower.
So it wasn't phase oddities, but oscillations. I have also replicated this effect by using too large coupling cap in another smaller amp.




baronbeehive said:


> from about .33uF to .47uF is probably best for powerful bass with the higher capacitance the best. You can go higher up to around 1.0uF but the higher you go the more likely there could be issues with resonances coming back down the line


Although not conclusively tested here. I was general consensus that going higher than 1uf in the coupling stage gave rise to possible circuit oscillations. It was also mentioned in the original mk6 thread, and I did replicate this effect on the "APPJ" amp.




baronbeehive said:


> but I think you have plenty to play with for cap voltages, but always the higher the better


Not so for electrolytics.
They have an optimal range.
Too high, and cap performance changes (less) with longer burn in times.

Too low volt rating, and may premature damage cap, or just blow up.

I trying to remember the optimal voltage, but I believe minimum is around 25% over max circuit voltage is fine (lower voltage circuits). 
Depends also on how high or low the circuit voltage is. 
So yeah higher is better, but too high (for electrolytics) actually decrease performance slightly.



baronbeehive said:


> If you mean other brands/models of tubes Maxx is the one who has tried them all, he would be able to let you know his choice.


I have spent at least $2k  back then on every 12pin and 6pin, and even some 8pin with adapters, rolling everything into the driver stage.

The problem was that the stock bias was set so low, that all the tubes were away from there ideal performance. The result was a more pronounced tube differences when rolling.

That being said, only one tube rose from the ashes... The Tung-sol 6c8g tube (with adapter for top). My choice anyways. 
It is older version tube than 6SL7, and had the higher "MU" output level.
I had also optimize my bias at that point.




baronbeehive said:


> The Jupiters/Duelands we feel give out the most realistic sound possible, whereas for example Mundorfs can sound a little unreal to some although they are excellent and were recommended in the factory upgrade by LD before they stopped doing that. I have Mundorf SIO in the WCF position to boost treble there


I agree. Although (the best) mundorf can also sound resolving, they add that signature mundorf trebles which are not as natural compared to the others.



baronbeehive said:


> Correction I should have said Jupiters and Black Gate are made in almost exactly the same way.


I have noted that even if they are from same company with minor internal change, it will make a audible difference.
Tonal changes may be most obvious, but there are other aspects like depth or liveliness.

In the thread I remember "Redge78" mentioning that when replacing an electrolytic with a film cap, you can effectively go much lower in capacitance. We can Google the optimal percentage, but for sure you can go less capacitance. The reason we could not fit these things as they would still be huge, but member @CopperFox  has discovered a positive aspect of increased dynamics/headroom/transients by using film in Cathode cap stage....
This can be the missing link to raise the unit performance in transients, to another level. 👍
Now I must decide what to do here myself, lol.


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## baronbeehive (Oct 21, 2021)

Seriously thinking about it too:





A new chassis extension like this perhaps... 🤓.

Edit: @CopperFox a further point, go for non polarised cathode bypass caps, they are supposed to have better sound characteristics. This is because you don't want backwards voltages on half of every cycle of audio.

Edit: I think film caps are non polarized in any case.


----------



## baronbeehive

@CopperFox here is a quote showing how important the cathode bypasses are in an audio circuit from a cap manufacturer: "_I'd go as far as saying that the *cathode circuit of a tube is usually the most critical*, as this circuit carries the whole signal current in the tube and because any distortion etc. in this circuit will appear in series with signal and will thus be amplified by the tube!"_

So your work has been important, we didn't quite get this far when looking at cathode caps as we had come to the end of what we thought were the important mods. But clearly if the cathode caps are important in transient recovery then we want to get this as good as we can.

Re: your query about whether to use 100uF or 200uF film caps in place of the lytics I've been trying to find out what the equivalents are to substitute lytics for film. All I've come up with so far is that there are opinions ranging from a ratio of 2:1 right up to 10:1 so it would be worth trying out those 100uF's to see if it makes any difference because going by those ratios that could substitute for any lytics between 200uF to 1000uF which is as high as we've gone with the lytics. There is an opinion that going too high would be detrimental to sound.
.


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## Maxx134

baronbeehive said:


> so it would be worth trying out those 100uF's to see if it makes any difference because going by those ratios that could substitute for any lytics between 200uF to 1000uF which is as high as we've gone with the lytics.



Going to look around at latest films for something suitable. 
👍


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## CopperFox (Oct 23, 2021)

baronbeehive said:


> BTW did you come to any conclusions about the impedance curve on the LD which you said was probably curved. It would need an oscilloscope to prove this and would be interesting to know. Have you made any more observations about impedance matching?



Haven't used the impedance adapter in a while as it was starting to look like the mkVI+ doesn't like having it attached to it. The vu meters were beginning to show imbalance with one channel rising in output and the other decreasing.

I now have 60 ohm headphones too (Monolith M1070 which I converted to closed phones with 3D printed cups and other mods) and they don't cause that imbalance so it wasn't the load level in itself causing that.


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## CopperFox (Oct 23, 2021)

Maxx134 said:


> Going to look around at latest films for something suitable.
> 👍



There are some things I learned while looking at those that may be useful here. The film caps with these capacitances come in some different dielectric materials and they have clear differences between them in thermal-electric properties which sets them apart from each other. Polypropylene caps are the best and the rest have higher temperature dissipation which causes both higher signal loss and also possible further degradation from internal overheating. Polypropylene caps are also slightly larger than polyethylene or polyester caps.


Here's a list of some current caps in the ~100uf mark, most of which are currently availabe. Sorted by dimensions from largest to smallest.






The polypropylene caps should have no problems with heat or varying levels of AC signal.

For some of the caps the manufacturers have specified limits as to how much AC voltage they can handle without overheating (which is defined as higher than 10C temperature rise from internal heating). As an example, here's a clip from the TDK B3252X series data sheet:



Here the 63V version is specced as being able to handle AC signals up to 10kHz - with declining voltage - but the 100V version (which I didn't find in stock anywhere) looks like it can do two volts at 20kHz.

And here is the similar graph(s) from the Vishay MKT1820 data sheet:



The graph for the 63V version lacks the 100uf capacitance but it looks like it would slot in somewhere slightly below two volts at 20kHz. The graph for the 100V version is not much better and neither is the 250V version.

The film caps with appropriate specifications here are designed for DC linkage and not high frequency AC signal passthrough as that will apparently cause more heat to be dissipated by the capacitor. The polyproplene caps however are mostly immune to this as their dissipation factor (and therefore internal heating) is an order of magnitude lower than the polyethylene or polyester caps (<0,1% vs <1% vs  <1,5%). The lower dissipation factor by itself also will cause them to have better sound in audio use. Conversely, the non-polypropylene caps' sound may be actually be worse than some electrolytics at least in some respects/aspects (They might result for example in a sound that is smooth but otherwise lacking).

So from the available options the 100uf or 90uf 400V DCL Wima would seem the option of choice taking into account dimensions and thermal-electric properties. The 90uf is not stocked anywhere though and the 100uf is slightly larger. By the Wimas' spec sheet, the 400V 100uf has the exact same dimensions as the 800V 40uf version which has been observed to fit inside the standard case a few pages back here . So that could be doable.

In any case, the main point here is that polypropylene caps should be far better than the other film options in audio use so they should be used here if at all possible despite their slightly larger size.

(After having ordered the 560uf Vishay film caps which also were from the MKT1820 series, I noticed that the graph in the data sheet shows they should be able to do about 0.2V at 20kHz without overheating. While having them in the amp I did notice there was at least slightly more residual heat in them than the other components an hour after switching the amp off. I'm not sure if the amount and duration of heat from my use would be enough to make a difference in performance as the data sheet also defines a "maximum operating temperature for limited time" as 200 hours at 150C at 30% of rated DC voltage. However, I did also notice that the Wimas were clearly better sounding right from the start.)


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## CopperFox (Oct 23, 2021)

baronbeehive said:


> I believe this is due to the phase effects of a slower charge/discharge cycle, it is probable that the signal is affected by the slower cycle whereas a fast cycle will allow transients to occur naturally faster with less problems of clipping.



I had been thinking inductance (the tendency to resist changes in voltage due to magnetic effects caused by the component's structure) may have an effect there as well. It sounds like something which may cause a burst-like or jagged characted in audio use.


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## baronbeehive (Oct 24, 2021)

CopperFox said:


> In any case, the main point here is that polypropylene caps should be far better than the other film options in audio use so they should be used here if at all possible despite their slightly larger size.


Yes, I was going to bring up this point about film construction, it seems there is no agreement about which material is best but this is useful information here.


CopperFox said:


> However, I did also notice that the Wimas were clearly better sounding right from the start.)


Good information, I think the Wimas are also the smallest size, anyway it's good to know what you've found, I'm already thinking along these lines.

The one thing I've drawn a blank on so far is the ratio of lytic to film capacitance but as you say 100uF would seem to satisfy all conditions whatever the ratio. I was thinking along the lines of a compromise of 150uF just in case the ratio is right at 2:1. But from what I can find out, together with your findings with your caps it seems that almost any size would work although it would not be good to go too high as various factors could affect sound, not to mention size.

The point about whether it would fit in the chassis is irrelevant to me as my chassis is choc full anyway, so I would have to extend it .

Edit: It would seem that film caps would be better in practically any use over lytics, however lytics are good at storage so that points to lytics being OK for PSU functions so maybe film would not be necessary here. A further point is that film caps might have problems dealing with the ripple through the PSU, this would need further investigation to confirm, which might make them not ideal for PSU functions which you alluded to by the post above where you said film caps were designed for DC not AC, although I'm sure you can still use them for PSU.

One more point worth mentioning is that there can be interference betweem caps if placed to near to each other, so maybe bear that in mind when trying to squeeze them into a crowded chassis!


----------



## baronbeehive (Oct 24, 2021)

Maxx134 said:


> Going to look around at latest films for something suitable.
> 👍


I've tried to find the blue Wimas but it seems the FKP1 only go up to 4.7uF, at Mouser at least.


----------



## baronbeehive

CopperFox said:


> I had been thinking inductance (the tendency to resist changes in voltage due to magnetic effects caused by the component's structure) may have an effect there as well. It sounds like something which may cause a burst-like or jagged characted in audio use.


Yes, also their behaviour is not linear unlike film caps, and also they can be rather unstable in output under some conditions.


----------



## Maxx134

Redge78 said:


> *Voltage :*
> Not much voltage here, the "original" 50V is more than enough


Last time I measured (years ago) I found it lower than half that rating.



CopperFox said:


> The vu meters were beginning to show imbalance with one channel rising in output and the other decreasing


Them meters will show according to the bias of the output tubes. Sometimes old tubes will make it vary.



CopperFox said:


> so it wasn't the load level in itself causing that


Yep I noticed lower impedance or planar headphones will affect the meters a bit more also (White Cathode follower design).



CopperFox said:


> Here's a list of some current caps in the ~100uf mark, most of which are currently availabe. Sorted by dimensions from largest to smallest


Nice list.



CopperFox said:


> I'm not sure if the amount and duration of heat from my use would be enough to make a difference in performance


I am so very impressed by all this research and this is the type of depth that actual dedicated designers do when planning.

That being said, I like to add some more observations which help in determining parameters.
Being that the caps will be on the underside of the circuit board, and below the amp, I do not forsee the tube ambient temp (around 100C avg) affecting the ambient temperature below its socket too much.

I do not believe the ambient temperature of the caps on the board to rise above 40C with all the resistors & PSU heat combined in there.

Also, the voltage drop measured across the Cathode cap is actually fairly low, so I believe we can also go for lower ratings.
The test would be to observe the performance difference "audibly", and also by checking if the bias meters dip when bass peaks hit(recovery)...

I thinking to try doing one side (not both) and then compare the other side any differences, with a monural source.


----------



## baronbeehive (Oct 25, 2021)

According to Mouser their DC Link are all Polypropylene whereas their other capacitor types are Polyester, Polyetheline and Polypheneline. Not sure they have all the sizes atm, only the MKP6 go up to and beyond 215uF so might need to shop around.

Edit: On the wima website the MKP6 and MKP4 DCL go up to and beyond 200uF.

NB: I just reread page 1 and I see that the ratios of lytic to film are from 2:1 up to 10:1 according to Redge, so either I was right or we were both reading from the same... hopefully correct sources!


----------



## CopperFox (Nov 8, 2021)

baronbeehive said:


> Yes, I was going to bring up this point about film construction, it seems there is no agreement about which material is best but this is useful information here.
> 
> Good information, I think the Wimas are also the smallest size, anyway it's good to know what you've found, I'm already thinking along these lines.
> 
> ...



Yes the DCL Wimas seem to have the most capacitance for size in the poplypropylene caps.  (edit: removed mistaken quote of current ratings)



> According to Mouser their DC Link are all Polypropylene whereas their other capacitor types are Polyester, Polyetheline and Polypheneline. Not sure they have all the sizes atm, only the MKP6 go up to and beyond 215uF so might need to shop around.



The 400uf 400V seems to be out of stock but can be backordered also in small quantities at mouser. The 200uf 400V can be found in stock at tme.eu where I got mine from.
Two of those in parallel would also be 400uf but take more space. Perhaps there might be some other brands that could fit in an extended case as well? Haven't yet looked at that.


----------



## Whitigir

So what amp is to buy in order to have all this fun? There are non on Amazon


----------



## CopperFox

Whitigir said:


> So what amp is to buy in order to have all this fun? There are non on Amazon



littledotus.com is the US/EU distributor and it's also available at shenzenaudio.com and from various sellers at Aliexpress. 11/11 is coming up in two and a half weeks and there will probably be discounts from the Chinese sellers so that might be a chance to save some cash.

The black colour variant has not been available for the first half of the year, don't know about the current situation on that. Silver is the other option and that has been steadily available.


----------



## Whitigir

This is OTL correct ?


----------



## baronbeehive

Here is an online tool I've found that will show ideal values for the cathode bypass cap which should take the sweat out of decision making on the size of cap: https://www.ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/calculator/

So whether to use 100uF or 200uF should become obvious and we might be able to dispense with guesswork on ratios. However it doesn't deal with the differences between lytics and film caps but it should show the point at which it is overkill in going any higher in values of microfarads for example. For example it would show up on the graph whether there would be anything to gain having reached an optimum point, on going any higher in value because the graph would stay much the same if that makes sense. It would also show optimum values for bass, mids and treble so depending on your preferences you could see instantly what cap to use.


----------



## baronbeehive (Oct 25, 2021)

Whitigir said:


> This is OTL correct ?


OTL and OCL.

Edit: Be careful who  you buy it from, littledotus has said that they take care in testing thoroughly before sending out and also offer better redress, but you could check the other LD thread where this has been discussed recently due to some bad experiences that some have had:https://www.head-fi.org/threads/little-dot-mk-vi-little-dot-mk-viii-se-owners-unite.522099/page-181


----------



## baronbeehive

CopperFox said:


> The 400uf 400V seems to be out of stock but can be backordered also in small quantities at mouser. The 200uf 400V can be found in stock at tme.eu where I got mine from.
> Two of those in parallel would also be 400uf but take more space. Perhaps there might be some other brands that could fit in an extended case as well? Haven't yet looked at that.


Sounds good! I know that member coin, used 470uF cathode film caps without any problems and raved about them if I remember right! But there is some doubt about going too high, the higher the value the more bass and the less treble, and visa versa.


----------



## baronbeehive

CopperFox said:


> Yes the DCL Wimas seem to have the most capacitance for size in the poplypropylene caps.  The RMS ripple current rating for the 400uf 400V is 43A in the datasheet which probably should be enough?


That should be way over the top on a 170 odd volt B+ but I will get back to  you on that.


----------



## CopperFox

baronbeehive said:


> Sounds good! I know that member coin, used 470uF cathode film caps without any problems and raved about them if I remember right! But there is some doubt about going too high, the higher the value the more bass and the less treble, and visa versa.



I was thinking here about the PSU output cap position, which is where I have  the 400uf 400Vs.


----------



## CopperFox

I'm now preparing to do the wires upgrade as some silver and SPC wires that I had ordered have arrived. Looking at the case without a PCB in it,




I'm planning to replace the signal wires marked with the green stars and the transistor wires marked with the red lightning. But what surprised me are the resistors inside the wires in the pink capsule. 

Stripping one of those revealed this:



Those colours look like brown, black, black, black and brown to me which would make it a 100Ω resistor with 1% tolerance. And they are in the wire that goes from the PCB to the 2 * 3-pin XLR output in the rear, which is also the starting point for the wires that go to the XLR headphone output. 

So these resistors are in the signal path output wires from the PCB to the output connectors which means they will highly probably have an effect on sound. 

Are these perhaps some sort of protection resistors and what have people done with them? Upgrade to audio resistors or something else? I couldn't find any earlier discussion on this after some searching and browsing the thread.

Also, if there is no intention to use the 2 * 3-pin XLR output which is in the rear, wouldn't it make sense to route these wires directly to the four-pin XLR headphone output?


----------



## baronbeehive

CopperFox said:


> I was thinking here about the PSU output cap position, which is where I have  the 400uf 400Vs.


Don't know what coin used in his PSU but 400uF should work OK, with enough capacity for surge protection. You also uprated your transistors and diodes anyway so that looks good. That's where we have the 1500uF lytics which is more than enough.


----------



## baronbeehive

CopperFox said:


> The 400uf 400V seems to be out of stock but can be backordered also in small quantities at mouser. The 200uf 400V can be found in stock at tme.eu where I got mine from.
> Two of those in parallel would also be 400uf but take more space. Perhaps there might be some other brands that could fit in an extended case as well? Haven't yet looked at that.


Redge mentioned AVX FFVI on page 1.


----------



## baronbeehive (Oct 26, 2021)

CopperFox said:


> Those colours look like brown, black, black, black and brown to me which would make it a 100Ω resistor with 1% tolerance. And they are in the wire that goes from the PCB to the 2 * 3-pin XLR output in the rear, which is also the starting point for the wires that go to the XLR headphone output.
> 
> So these resistors are in the signal path output wires from the PCB to the output connectors which means they will highly probably have an effect on sound.
> 
> Are these perhaps some sort of protection resistors and what have people done with them? Upgrade to audio resistors or something else? I couldn't find any earlier discussion on this after some searching and browsing the thread.


Don't know, sorry, maybe Maxx knows. I didn't know they were there and there was no discussion about them. I even changed my wires here. Perhaps I'm speculating that they modify the signal for preamp outputs as compared to headphone outputs, although I don't know why.


CopperFox said:


> Also, if there is no intention to use the 2 * 3-pin XLR output which is in the rear, wouldn't it make sense to route these wires directly to the four-pin XLR headphone output?


Again, don't know. I don't see why you couldn't do this but there maybe other wires going into the XLR's which I don't know about without looking, you should check this. I wouldn't like to say though, I would prefer to leave it as is.

The only wires that need to be of the highest quality where we have put in Neotech OCC copper or silver are the 6 output wires, look for the words "output" on the PCB and trace them to the XLR's. When  you have done that you will have a wire run which effectively is an extension of your external headphone cable, you should notice a big difference as the stock wires are c**p 🙂.

Good luck with the wiring though, I  hope your notes are accurate 👍.

Edit: One thing to note, if you find any wires with shielding to replace with shielded wires for interference suppression.

One further point is to route the wires higher up so that they don't block the gap between the chassis sides and the edge of the PCB to allow the air flow unobstructed movement with all those extra caps in place.


----------



## Whitigir (Oct 26, 2021)

CopperFox said:


> I'm now preparing to do the wires upgrade as some silver and SPC wires that I had ordered have arrived. Looking at the case without a PCB in it,
> 
> 
> 
> ...


The chassis look so thick , but why resistors going toward preamp out to the rears ? Are they parallel to the headphones out ?

Do we have the schematic of this amplifier?


----------



## baronbeehive

Whitigir said:


> So what amp is to buy in order to have all this fun? There are non on Amazon


Fun?????

BTW there was a schematic, but it got lost due to all the picture links being broken on the thread, sorry.


----------



## CopperFox

Whitigir said:


> The chassis look so thick , but why resistors going toward preamp out to the rears ? Are they parallel to the headphones out ?
> 
> Do we have the schematic of this amplifier?



There is a schematic of the audio circuit drawn by @SonicTrance in the other thread in this post. Maybe someone has the PSU schematic as well?


----------



## Whitigir

CopperFox said:


> There is a schematic of the audio circuit drawn by @SonicTrance in the other thread in this post. Maybe someone has the PSU schematic as well?


Thanks !! So the Amp is designed around  NFB


----------



## baronbeehive

CopperFox said:


> There is a schematic of the audio circuit drawn by @SonicTrance in the other thread in this post. Maybe someone has the PSU schematic as well?


Haha, don't know how you managed to come up with this!

If there is a PSU schematic I will let you know if I find it.

It's unfortunate that all the diagram links have broken, makes it difficult to replicate what we have done here.


----------



## baronbeehive

Whitigir said:


> Thanks !! So the Amp is designed around  NFB


Yes, is that something that you are happy with? I don't think open loop is possible with an OTL design although the power output is low.


----------



## Whitigir

baronbeehive said:


> Yes, is that something that you are happy with? I don't think open loop is possible with an OTL design although the power output is low.


Yes, I understand for sure.  There are no perfection , and I am actually not much a fan of NFB


----------



## baronbeehive

Whitigir said:


> Yes, I understand for sure.  There are no perfection , and I am actually not much a fan of NFB


No, but the amp still manages an excellent soundstage and resolution, especially after the mods 👍.


----------



## baronbeehive (Oct 29, 2021)

Been playing with the cathode bypass calculator. Below is the frequency curve for 6SN7 with stock LD values.




... and below is the frequency curve for the optimum values I found when trying out bias points, and with my uprated cathode bypass caps at 470uF.




... and below is the same frequency curve except with a cathode bypass cap of 1000uF




You can see that the frequency curve gets slightly flatter each time until with a cathode bypass value of 1000uF it is extremely flat and linear at all frequencies from 10Hz to 10kHz! The 10Hz doesn't really matter because it is way below human hearing, and certainly mine...

Looks like in all cases the frequency curve is pretty linear at most frequencies but listening tests must have the final say which we have done with caps of up to 470uF. This doesn't mean that film caps wouldn't be better due to their linearity and response speed.

Edit: Just so you can see, below left is the frequency response using my figures except that the capacitance is 1uF instead of 470uF. You can see there is no bass response at all and the frequency response only starts to come in after you get to 100Hz and beyond.

Bottom right is the frequency response using my figures except this time the tube is a 5751. The calculator is meant for guitar amps so there is no 6SL7 option but I have been told by someone on their website that the 5751 is practically the same in response as the 5751 as they both have the same amplification factor of 70. So there is practically no difference between the 6SN7 and the 6SL7 in frequency response as you can see by comparing the last graph and the second graph above.



 



The straight line we see is ideal as all frequencies respond in a linear way along the line from bass to treble.


----------



## Maxx134 (Oct 30, 2021)

Straight line in graph is not advisable as that would not taper off below 20hz so your in now suspectable to circuit  oscillations or anything outside the audible range.



CopperFox said:


> Stripping one of those revealed this:
> 
> 
> 
> ...


I don't remember seeing this before, but suspect it has to do with the DC offset circuit. There needs to be a load, but I believe it is already in the board, so why these resistors?

If they are in series to the balanced outputs, a possible explanation could be output level... or to make the output impedance to be high, as the output circuit impedance is low for the headphones out.


----------



## baronbeehive (Oct 30, 2021)

Maxx134 said:


> Straight line in graph is not advisable as that would not taper off below 20hz so your in now suspectable to circuit  oscillations or anything outside the audible range.


OK, this is the best I could come up with, still a bit of a slope at around 100Hz which may or may not affect mid bass:





Same figures but for 6SL7, (5751):



 May be possible to refine it but listening tests would be key here.

I have a feeling that the cathode bypass cap is even more important than I originally thought which makes the work of CopperFox that much more useful. I certainly found it made a big difference when I swopped to the Nichicons.
.


----------



## baronbeehive (Oct 30, 2021)

I've tried to relate what @CopperFox found here: https://www.head-fi.org/threads/lit...e-on-first-page.782183/page-259#post-16430754
The problem is that with the calculator you need to enter quite large differences in capacitance to see differences, either that or the frequency curve is not that fine grained as it appear in the graph. For example below are 3 settings, on the left with a low capacitance of 100uF, in the middle is 440uF, and to the right is 570uF and as you can see the curve is more pronounced in the first graph with little differences between the second 2 graphs.



 

 



The overall gain, (vertical axis), is unchanged.

I don't remember what figures @CopperFox is using for his anode/cathode resistors.


----------



## Maxx134

baronbeehive said:


> OK, this is the best I could come up with, still a bit of a slope at around 100Hz which may or may not affect mid bass:


From what I recall, usually the average design is to start roll off at 20hz.

Also, another point is that the 
 formula is showing for frequency responses. It is not showing the main parameter we are also looking for to decide on the cathode cap size. ..
Which is to keep the volt drop stable across the cathode resistor with varying load.

So we know film cap will respond faster than electrolytic (better transients)
So we know effective size would be smaller than electrolytic.

There should be a minimum size.
I don't know what formula is available for that. Would have to  calculate the drain over time according to the load resistance. 
Then again we don't need to reinvent the wheel and can assume and test real world usage.


----------



## CopperFox (Oct 30, 2021)

Well that was a lot of work. I now have replaced the signal wires with SPC wires and all of my extension leads with pure silver wires. 14 meters of wire in total, some of which was bound together.

The output signal wires going from the PCB (or actually some of them from the tube sockets?) to the 2*3 pin XLR outputs and from those to the 4 pin XLR headphone out were not connected to anything else so I also routed the output wires straight to the headphone out, skipping the XLR outputs in the rear. Also removed the single ended headphone output as I'm not using that for anything. I will probably later remove the RCA inputs as well but decided to let them stay there for now. I decided to keep the old transistor wires as well.

Edit: Removing the rear XLR connectors and/or RCA inputs would also make some extra room inside the case for switches/capacitors/whatever.

Sound is improved but no more comments on that for now as I've been changing the cathode resistors with different brands/models as well and on Friday got a package with four 0.56uf Duelund JDMs and I'll still be changing those (and likely more different resistors) soon. The amp probably also needs some re-burn-in and such after having been largely dismantled for days.

It is surprising that the 100R resistors in the output leads were not mentioned before in the thread and I also now removed them.

Last year I rembember modding a Zishan DSDs dap that also had 100R resistors in the signal path just before the outputs. It was thought that they were there for some sort of protection but people would just remove them or replace them with far lower value resistors (resistance in the single digits). With that particular dap I put them back in there as I felt sound would be too brigh twithout them. But that's off topic of course.


----------



## CopperFox

baronbeehive said:


> The point about whether it would fit in the chassis is irrelevant to me as my chassis is choc full anyway, so I would have to extend it .



How large a chassis extension are you planning on?



baronbeehive said:


> Fun?????



Isn't modding fun? If doing hifi stuff is like wine tasting, then modding would be like wine tasting where the wines can be made from lego bricks.



baronbeehive said:


> Haha, don't know how you managed to come up with this!



Google image search with "little dot mkvi+ schematic"


----------



## CopperFox (Oct 31, 2021)

baronbeehive said:


> Here is an online tool I've found that will show ideal values for the cathode bypass cap which should take the sweat out of decision making on the size of cap: https://www.ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/calculator/
> 
> So whether to use 100uF or 200uF should become obvious and we might be able to dispense with guesswork on ratios. However it doesn't deal with the differences between lytics and film caps but it should show the point at which it is overkill in going any higher in values of microfarads for example. For example it would show up on the graph whether there would be anything to gain having reached an optimum point, on going any higher in value because the graph would stay much the same if that makes sense. It would also show optimum values for bass, mids and treble so depending on your preferences you could see instantly what cap to use.



That calculator seems interesting. Its website states that its function is based on the page 484 of Radiotron Designer's Handbook from 1953, which can be found in its entirety as .pdf here. On the previous page (483), there is also a formula for the voltage drop caused by the cathdode bypass capacitor, which includes the total impedance of the capacitor where its resistance would also be a factor.

As for the results of that calculator, it seems the 200uf would not have a lot of bass roll-off and it would be something in the 0,1 to 0,2 dB range. With the 100uf it would be higher than that... and to lower it perhaps something higher could be also tried but that would probably not fit in my extended chassis.


----------



## Maxx134

CopperFox said:


> so I also routed the output wires straight to the headphone out, skipping the XLR outputs in the rear.


That's what I did as well. A straight run from the tube pin to the headphone XLR socket.



CopperFox said:


> Also removed the single ended headphone output as I'm not using that for anything


That actually good place for putting your switch (impedance or tube change switch)



CopperFox said:


> I decided to keep the old transistor wires as well


Nooooooooowaaaa!..
Actually I don't know if they changed the wire, but in past the transistor (in power supply) wire used become very brittle and breaks off easily on board, causing PSU failure.
I would check/replace those wires.



CopperFox said:


> It is surprising that the 100R resistors in the output leads were not mentioned before in the thread and I also now removed them


Yeah I don't believe they were there before...


----------



## baronbeehive

Maxx134 said:


> Nooooooooowaaaa!..


Haha 👍.


Maxx134 said:


> Nooooooooowaaaa!..
> Actually I don't know if they changed the wire, but in past the transistor (in power supply) wire used become very brittle and breaks off easily on board, causing PSU failure.
> I would check/replace those wires.
> 
> ...


No I didn't come across these and I replace those wires too.


----------



## baronbeehive

CopperFox said:


> How large a chassis extension are you planning on?


It depends on the size of the cathode film caps. I was thinking of keeping the large capacity lytic PSU caps and the 47uF film decoupling caps but these may go too so when I've decided on that I will get dimensions and look for the appropriate size heatsink plates and drill through for the standoffs and screw straight into the bottom edges of the chassis.


CopperFox said:


> Isn't modding fun? If doing hifi stuff is like wine tasting, then modding would be like wine tasting where the wines can be made from lego bricks.


Yes, but my head hurt when it all went wrong, I was without the amp on two occasions initially when I couldn't find the fault and then again when if developed another fault it took me some time myself to put it right.


CopperFox said:


> Google image search with "little dot mkvi+ schematic"


Good old google 👍. I did remember after you posted it that I saw it on that thread after all.


----------



## baronbeehive

Maxx134 said:


> Also, another point is that the
> formula is showing for frequency responses. It is not showing the main parameter we are also looking for to decide on the cathode cap size. ..
> Which is to keep the volt drop stable across the cathode resistor with varying load.


Exactly! We need to know how the cap handles the transients too and as I said above the listening tests would be crucial to hear what differences in the curve have on sound, and of course to see what the transient handling is like. These might appear inconsequential on the graph but might be important.

The gain shown on the vertical axis I'm sure influences how lively and dynamic the sound is. I looked at what sonic, you and me did and you can see differences in this shown on the graph.

As I thought when I did my tests a while back the cathode resistor value doesn't affect the sound as much as the anode and so it would be more for fine tuning.

So, the cathode bypass values for the overall curve, then the anode values to modify the curve and finally the cathode resistor value for fine tuning.

Where the graph was useful was in finding the point at which no further increases in capacitance are necessary or are completely overkill.


----------



## baronbeehive

CopperFox said:


> Well that was a lot of work. I now have replaced the signal wires with SPC wires and all of my extension leads with pure silver wires. 14 meters of wire in total, some of which was bound together.
> 
> The output signal wires going from the PCB (or actually some of them from the tube sockets?) to the 2*3 pin XLR outputs and from those to the 4 pin XLR headphone out were not connected to anything else so I also routed the output wires straight to the headphone out, skipping the XLR outputs in the rear. Also removed the single ended headphone output as I'm not using that for anything. I will probably later remove the RCA inputs as well but decided to let them stay there for now. I decided to keep the old transistor wires as well.


Your wiring diagram was obviously flawless 🙂. I quite enjoyed rewiring, it wasn't so fiddly as the other work, but I still managed to make a mistake in one of the connections, easily put right fortunately. That's where the DIMM came in handy.
.


----------



## baronbeehive

Maxx134 said:


> There should be a minimum size.
> I don't know what formula is available for that. Would have to  calculate the drain over time according to the load resistance.
> Then again we don't need to reinvent the wheel and can assume and test real world usage.


The formulae for the calculator are in the book by ampbooks.com, and I think that all the formulae are there for that.


----------



## baronbeehive

CopperFox said:


> That calculator seems interesting. Its website states that its function is based on the page 484 of Radiotron Designer's Handbook from 1953, which can be found in its entirety as .pdf here. On the previous page (483), there is also a formula for the voltage drop caused by the cathdode bypass capacitor, which includes the total impedance of the capacitor where its resistance would also be a factor.
> 
> As for the results of that calculator, it seems the 200uf would not have too bad bass roll-off and it would be something in the 0,1 to 0,2 dB range. With the 100uf it would be higher than that... and to lower it perhaps something higher could be also tried but that would probably not fit in my extended chassis.


Yeah, just read your post and yes all the formulae are there, that pdf looks useful.

I think with the bass roll off it would need to be listened to to see the effects. You can see that even with the stock amp there is very little roll off and the rest of the curve is flat and linear so LD obviously thought they had got it right for the combination of tubes that would be used. A steeper bass roll off and a shallower one could be tried to see the effects on sound. As 20Hz is at the limits of hearing a steeper roll off might not be too bad and might result in a flatter curve on the rest of the frequency band.


----------



## baronbeehive (Oct 31, 2021)

CopperFox said:


> It is surprising that the 100R resistors in the output leads were not mentioned before in the thread and I also now removed them.
> 
> Last year I rembember modding a Zishan DSDs dap that also had 100R resistors in the signal path just before the outputs. It was thought that they were there for some sort of protection but people would just remove them or replace them with far lower value resistors (resistance in the single digits). With that particular dap I put them back in there as I felt sound would be too brigh twithout them. But that's off topic of course.


If you knew the current and voltage going through those wires you could calculate the voltage drop across the 100R resistor using Ohm's law.


----------



## Maxx134 (Nov 1, 2021)

From my experience, most amps have .22uf as the standard value for the *coupling cap* for many designs, and that must mean that it is so gradual a change, that many design make use of that value.

Yet the _*Cathode cap*_ is another story.
I always see wide range of values.
Just the other day I worked on a Cayin HA-300, and it has only 100uf(!):

 So there is definite intentions in the design choice of the Cathode cap.
I believe it is where most all of the tube interaction begins.
👍
Also, if you take note there are specific type of resistors for the tube stages. They are not films, as in the PSU.
This is yet another example of design choice for specific sound, like the ingredients in a soup.

I regard Cayin *the absolute best*, at making euphoric sounding amps, without the harshness of unwanted harmonics.
They are genius, when you observe their parts choices...

While I regard Little Dot path, is to use more of "design choices", rather than parts choices, for their sound. Just looking at the bias points of the driver stage, is a prime example.


----------



## Whitigir

Yeah, Cayin knows their stuff well


----------



## baronbeehive (Nov 1, 2021)

Maxx134 said:


> Yet the _*Cathode cap*_ is another story.
> I always see wide range of values.
> Just the other day I worked on a Cayin HA-300, and it has only 100uf(!):


I wonder if it is deliberately to get a certain sound signature?

The LD has 220uF and that maybe for greater transient recovery as compared to 100uF. Maybe because it doesn't have the control of an OT?

I wonder if, looking at the cathode calculator graph where 100uF looks good enough to all intents and purposes that maybe we are going in for overkill with 470uF +, yet the greater capacitance should allow for greater transient recovery, so long as it is not so high as to mask the higher frequencies with mega bass!


Maxx134 said:


> I regard Cayin *the absolute best*, at making euphoric sounding amps, without the harshness of unwanted harmonics.
> They are genius, when you observe their parts choices...
> 
> While I regard Little Dot path, is to use more of "design choices", rather than parts choices, for their sound. Just looking at the bias points of the driver stage, is a prime example.


You're probably right, different makers favour different parts choices, and I think it was Cayin that used pure silver internal wiring also? Yet LD make do with tin wire... yuck 👎.

But the earlier MKVI's, of which I have one, had better quality Dale resistors which were swopped out for cheap versions later! And the blue power and PSU resistors were abysmal .


----------



## Whitigir

I would use pure silver wiring where I can, but they are not cheap, and not all silvers are made the same.  What Cayin is using pure silver internally ?


----------



## Maxx134 (Nov 1, 2021)

Definitely for bass hits (current drain) we need more capacitance, because this is not a traditional transformer output, or even a traditional circuit, being WCF design.
So we are relying heavily on the tubes for all of the power...


----------



## baronbeehive (Nov 1, 2021)

Whitigir said:


> I would use pure silver wiring where I can, but they are not cheap, and not all silvers are made the same.  What Cayin is using pure silver internally ?


Yes internally. I can't remember if it was actually them TBH, but one of those Chinese makers, may have been Yamamoto.


----------



## Maxx134 (Nov 1, 2021)

We need to focus on the output stage caps.
The cathode cap is still before the WCF stage.... So any cathode current drain, would be from those tubes only, not the headphones load(?), hmmm


----------



## Maxx134 (Nov 1, 2021)

Ok, so on first page, according to Ridge78, half the current of the WCF push/pull design, comes from the cathode caps(!).

So now, what about the WCF cap between the triods? Have we been overlooking these?


----------



## baronbeehive

Maxx134 said:


> We need to focus on the output stage caps.
> The cathode cap is still before the WCF stage.... So any drain would be from those tubes only, not the headphones load, hmmm


@CopperFox uses 100uF Wimas there, (decoupling). Also for driver stage decoupling but I think my 40uF are adequate there.


----------



## baronbeehive

Maxx134 said:


> Ok, so on first page, according to Ridge78, half the current of the WCF push/pull design, comes from the cathode caps(!).
> 
> So now, what about the WCF cap between the triods? Have we been overlooking these?


Maybe, we haven't touched those!


----------



## baronbeehive

baronbeehive said:


> Maybe, we haven't touched those!


Also he uses 400uF PSU film caps which could be good there, I haven't decided.


----------



## Maxx134

It sucks that all the original pics are gone from first page. I have most but it will take time to find and re-upload.
😞😖😣


----------



## Maxx134 (Nov 1, 2021)

baronbeehive said:


> Maybe, we haven't touched those!


Actually we did. I believe you used mundorf there 😄.
My issue is I am wondering about current drain, as caps used as output caps are large (for current), and not have anything to do with frequency, so although as only 220uf was needed here (stock) for frequency....

I'm wondering if more capacitance would help here with transients...
Because the cap is in series with output flow, just like an output cap...


----------



## Maxx134

I'm guessing a test with a paralleled electrolytic here would find out...


----------



## baronbeehive

Maxx134 said:


> It sucks that all the original pics are gone from first page. I have most but it will take time to find and re-upload.
> 😞😖😣


I know and it's no fun reading up on all that any more .


----------



## baronbeehive

Maxx134 said:


> Actually we did. I believe you used mundorf there 😄.


Sorry for the momentary lapse.. for some reason I was thinking of those original small Wimas that were there before we replaced them. I did use Mundorf and I only realized recently that they were film caps, polypropylene metallized with silver as opposed the the MKP Mundorfs we used for decoupling which were polypropylene metallized with aluminium.


Maxx134 said:


> Actually we did. I believe you used mundorf there 😄.
> My issue is I am wondering about current drain, as caps used as output caps are large (for current), and not have anything to do with frequency, so although as only 220uf was needed here (stock) for frequency....
> 
> I'm wondering if more capacitance would help here with transients...
> Because the cap is in series with output flow, just like an output cap...


I don't like to admit it but you must be right, the WCF being just as important as the cathode caps, my problem is I don't really understand the maths behind the WCF.

So maybe bigger caps like the Mundorf Supreme SIO that I have... only bigger.... much... *BIGGER.....* 😁.


----------



## baronbeehive

Maxx134 said:


> Ok, so on first page, according to Ridge78,* half the current of the WCF push/pull design, comes from the cathode caps(!)*.
> 
> So now, what about the WCF cap between the triods? Have we been overlooking these?


This could be why we need those large cathode caps when the graph doesn't show them to be necessary above, say 100uF... blasted WCF circuitry 🥴😫

... then if we need large cathode caps... then... we also need large WCF caps to help the output 😇, unless I'm totally wrong.. again 😭😵‍💫


----------



## baronbeehive

Maxx134 said:


> I'm guessing a test with a paralleled electrolytic here would find out...


You mean to try different capacitances from the paralleled cap, and then when we have found that out, replace with equivalent high capacity film cap?


----------



## baronbeehive (Nov 1, 2021)

So really we have been treating the WCF cap mod as the coupling caps little sister when it's more important than that and the paltry .33uF should read more like 330uF?

It's an output cap, *not* a coupling cap.


----------



## Maxx134 (Nov 1, 2021)

baronbeehive said:


> You mean to try different capacitances from the paralleled cap, and then when we have found that out, replace with equivalent high capacity film cap?


No...😄
Just need to find out the circuit behavior with increased capacitance in the WCF position.
Audio quality should not be affected much because of the .33uf film that's already there. Just need to see if an increased (paralleled) capacitance there would increase the output potential.


----------



## Maxx134 (Nov 1, 2021)

baronbeehive said:


> It's an output cap, *not* a coupling cap


Well yes it is coupling the two triodes, but we want to see if any "output cap" capabilities can be had here.


----------



## Maxx134

I must have had a brain fart. The cathode caps are part of the WCF circuit, so I need to look at the  schematics again 🙃


----------



## coinmaster

The cathode caps are always going to reduce the sound quality. Which is part of the reason I got rid of them in my mod that solved every issue the MK6 has.
Hindsight, I probably should have just made a perfected version of the mk6 and sold it to members here to fuel my other research instead of going crazy and making an over the top version with 4P1Ls and 6c33cs.
Oh well.

In any case if you want to play with the cathode caps, bigger is better, and higher quality is better. Bypassing smaller higher quality caps with larger less but still good quality caps is the way to go.
The huge industrial film caps I used in my initial mk6 mod somewhere around the first pages were pretty amazing in this regard. I also used the stupidly expensive mundorf pure copper caps or whatever they were. Needed a wood box to fit it all though.


----------



## baronbeehive

Maxx134 said:


> I must have had a brain fart. The cathode caps are part of the WCF circuit, so I need to look at the  schematics again 🙃


x2 🥴. This is what I wasn't sure about, but they must be as they are involved in processing output from driver stage which obviously includes *both* triodes, first and second in WCF. That means that the cathode bypass is involved in frequency cut off for both as well. So we can't increase capacitance willy nilly without taking this into account.

I will go back and look at page 1 if I can remember where it is.

The schematic is Sonic's here: https://www.head-fi.org/threads/lit...se-owners-unite.522099/page-171#post-14709323

@coinmaster I couldn't find your schematic any more, most of the picture links are broken here.


----------



## baronbeehive

coinmaster said:


> The cathode caps are always going to reduce the sound quality. Which is part of the reason I got rid of them in my mod that solved every issue the MK6 has.
> Hindsight, I probably should have just made a perfected version of the mk6 and sold it to members here to fuel my other research instead of going crazy and making an over the top version with 4P1Ls and 6c33cs.
> Oh well.


Yes.. 😡.

... but it was great entertainment for the rest of us


----------



## baronbeehive

Stock LD without a cathode bypass cap, ie 0uF.

Gain is much reduced, obviously.


----------



## Maxx134 (Nov 2, 2021)

_*I do not *_believe cathode cap decrease sound quality at all. The interaction between the cathode cap and tube creates more gain, and _*more tube harmonics*_. This is *added* onto the sound, so doesn't take anything away. But it has to be done lightly, as if you sprinkled salt on food, not overdone.

Issues arise with using electrolytics which we have already noted and helped with film caps.



baronbeehive said:


> The schematic is Sonic's here: https://www.head-fi.org/threads/lit...se-owners-unite.522099/page-171#post-14709323
> 
> @coinmaster I couldn't find your schematic any more, most of the picture links are broken here


That link is a schematic from coinmaster's work.
Anyways, I have stumbled onto  some better schematic diagrams from an asian website.
Amp:



That is one channel, not whole amp.
👌
PSU:



👌
Driver stage PSU:




So we have a better look at what's going on.
I see that we haven't even touched the driver stage cathode area, but since you replaced the cathode resistor with
 a CCS, you can't place a cathode cap there.


----------



## Whitigir

Maxx134 said:


> _*I do not *_believe cathode cap decrease sound quality at all. The interaction between the cathode cap and tube creates more gain, and _*more tube harmonics*_. This is *added* onto the sound, so doesn't take anything away. But it has to be done lightly, as if you sprinkled salt on food, not overdone.
> 
> Issues arise with using electrolytics which we have already noted and helped with film caps.
> 
> ...


What is that OPAMP chip ? Would swapping it For another kind (discrete) be an upgrade ? Cathode caps are in series ? Interesting


----------



## Maxx134 (Nov 2, 2021)

Whitigir said:


> What is that OPAMP chip ? Would swapping it For another kind (discrete) be an upgrade ? Cathode caps are in series ? Interesting


That chip is there to control the DC offset between the the 2 tubes (for each channel). Because the 2 tubes at rest (each tube representing the "*" or "-" of the signal) must equal to zero DC at output of the headphones jack.
The op-amp control this.

If you hear a pop, in _*any*_ amp (tune or solid state, especially solid state) as you are plugging your headphones in, that is DC offset. It usually equalizes after headphones plugged in and circuit sets, but if you always have a tiny pop/click, then that's DC.

In this amp, there are very high value resistors across the output load, to have the op-amp equalize the DC offset.
But there is also an adjustment pot which is not easy to do, which was covered long ago in this thread.
I did mine for perfect reduction, as there may always be an adjustment necessary if you change your resistors and parts.


----------



## Maxx134

Ugh ugh ugh..
With help of @Whitigir , I am seeing multiple weaknesses that need to be addressed.


----------



## Whitigir

Maxx134 said:


> Ugh ugh ugh..
> With help of @Whitigir , I am seeing multiple weaknesses that need to be addressed.


Cheers!! I look forward to your results


----------



## baronbeehive (Nov 2, 2021)

Maxx134 said:


> _*I do not *_believe cathode cap decrease sound quality at all. The interaction between the cathode cap and tube creates more gain, and _*more tube harmonics*_. This is *added* onto the sound, so doesn't take anything away. But it has to be done lightly, as if you sprinkled salt on food, not overdone.


No and the gain without the cathode cap is so low as to make the sound lifeless unless other things are done to compensate


Maxx134 said:


> I see that we haven't even touched the driver stage cathode area, but since you replaced the cathode resistor with
> a CCS, you can't place a cathode cap there.


I'm thinking of taking out the CCS as the cathode research looks to be promising. I only kept it in because of the fact that the current was always constant with varying voltage so not having to worry about worn tubes. And the B- filter didn't have any effect on sound anyway.

And I was happy with the anode/cathode values that I found on sound quality before I put in the CCS.


----------



## baronbeehive (Nov 2, 2021)

One last go with the cathode calculator this time to see the effect of overkill. As you can see the stock amp curve is exactly the same with 10000uF as with lower capacitance, (500uF, right hand graph). Of course there might be oscillations with such a high capacitance.


----------



## Maxx134

It seems that ALL the schematics are from @coinmaster :


coinmaster said:


> The MK6 uses the OPA445AP as well.
> Don't worry about what the opamp is doing. I verified it long ago and I ordered my own custom versions for my experiments
> 
> 
> ...


----------



## baronbeehive

Maxx134 said:


> It seems that ALL the schematics are from @coinmaster :


Then I must have had a "moment" with my failing memory, I thought Sonic did a schematic later .


----------



## coinmaster (Nov 2, 2021)

> Anyways, I have stumbled onto some better schematic diagrams from an asian website.


An asian website?
Interesting, because those are my original schematics that I made forever ago before I started using LTspice and before I knew what I was doing really.
I guess the asians are reading head-fi.


----------



## coinmaster (Nov 2, 2021)

The question that needs to be asked is, what are you guys trying to achieve? Because it doesn't take much deviation before it's more efficient to just to a complete redesign.
The design is so deeply flawed that it's too easy to end up on something completely different when trying to solve the issues.
I can make something dirt cheap that has unmeasurable distortion and sounds as good as the best equipment.
Just ask Maxx, I used a switch to instantly swap between super expensive tube amps and my tiny, cheap but very sophisticated SS one at his place a while back and it sounded identical.
It's all about how it's designed.

I can also make pure solid state designs with tube curves







You name it, I can do it, no hype or gimmicks involved.
The question always starts with, what do you want?

But as far as this amp goes, it's actually more difficult to keep things within the scope of the original design then it is to change it completely.
Unfortunately the amp doesn't leave much physical room for modification.
So it's more efficient to ask what your goal is.



> _*I do not *_believe cathode cap decrease sound quality at all. The interaction between the cathode cap and tube creates more gain, and _*more tube harmonics*_. This is *added* onto the sound, so doesn't take anything away. But it has to be done lightly, as if you sprinkled salt on food, not overdone.


Well it's very simple. If the cathode caps could be removed without reducing the gain, then it would sound even better. The reason you think they add better sound is because without them, in the current design, the sound will indeed suck.
But the reality is, using tubes for the output stage is just terrible in general, especially with this design.
A simple source follower will sound better. In fact, that is an easy mod to do and ironically one of the best ones that can realistically be done on this design.
But then it reverts to a typical hybrid with a primitive input stage and a crappy power supply.
So I can see the appeal in not doing that.

As for the existing design. You could try using a ccs on the cathodes in place of the resistor to isolate it from the supply ripple and and tie the cathode caps of each of the opposite phases together to maintain the cmmr. I don't know the full implications of this as it's just an idea that popped into my head and I am too lazy to simulate it, but it should work. Although it will mess with the WCF current balance to some degree so the anode would need to be adjusted as well ideally.
But my gut tells me that will most likely improve the sound to some degree.
It would be a simple mod to try.


----------



## baronbeehive

coinmaster said:


> An asian website?
> Interesting, because those are my original schematics that I made forever ago before I started using LTspice and before I knew what I was doing really.
> I guess the asians are reading head-fi.


Correct.. I just found them amongst some papers which I've had for ages and they are the same!

@Whitigir sorry... I just found those schematics but didn't know what they were until I saw Maxx's post .


----------



## baronbeehive

Maxx134 said:


> Ugh ugh ugh..
> With help of @Whitigir , I am seeing multiple weaknesses that need to be addressed.


Really... 🤓. I can't see anything untoward, but then it's all Chinese to me 😲.


----------



## Whitigir

oh well, like coin master said above.  He may as well design another amp lol


----------



## Maxx134

Whitigir said:


> What is that OPAMP chip ? Would swapping it For another kind (discrete) be an upgrade ? Cathode caps are in series ? Interesting


After speaking with coinmaster, he made me realize the opamp chip having the resistors and .22uf cap at output safeguards any sonic influence from the op-amp is neutralized.
Plus this is the only op-amp listed in Mouser with a 90v limit rating.



baronbeehive said:


> And I was happy with the anode/cathode values that I found on sound quality before I put in the CCS.


Yes the bias point can be made to "sound" as good, but the CCS guarantee it can be in an optimal point.
So I would probably stayed with it if I did it. Currently I have manually found my sweet spot for a specific tube, and am done tube rolling that stage (after thousands dollars and almost all 12pin & 6pin tubes rolled in, and anything with adapters) so do not want to mess with it.



coinmaster said:


> But the reality is, using tubes for the output stage is just terrible in general, especially with this design


Yes it has a narrow range and limitation for tube out only, but it is great that it works to eliminate expensive transformer output, or expensive large cap output...
Hybrid would have been most optimal.



coinmaster said:


> A simple source follower will sound better. In fact, that is an easy mod to do and ironically one of the best ones that can realistically be done on this design


I rather have the more optimal hybrid of @SonicTrance  if I was going hybrid, or one of your new designs that no one did before.



coinmaster said:


> But then it reverts to a typical hybrid with a primitive input stage and a crappy power supply


But in this thread we juiced up the PSU greatly, so not so crappy, just old school & not modern. 



coinmaster said:


> You could try using a ccs on the cathodes in place of the resistor to isolate it from the supply ripple and and tie the cathode caps of each of the opposite phases together to maintain the cmmr


No need no supply ripple but that idea of joining the WCF cathodes sounds interesting.



coinmaster said:


> Although it will mess with the WCF current balance to some degree so the anode would need to be adjusted as well ideally


I'm wondering how this would affect the circuit...
🙂

In the meantime, optimizing the caps in this output stage is all that's left before a design change...
😳🙂


----------



## coinmaster

> I rather have the more optimal hybrid of @SonicTrance if I was going hybrid, or one of your new designs that no one did before.


Sonic's design would be more expensive and it has many redundancies and some components with flaws that cannot be overcome.
This does not mean it will necessarily have any detrimental sonic effects, but I personally I only design in a way where I have complete control over all of the performance variables and distortions. Better to not have to wonder. 
Using the loads we are using, I would be surprised if a simple class A source follower sounded any better or worse than any sufficiently designed output stage. Despite the fact that I would never use something so crude myself.




> But in this thread we juiced up the PSU greatly, so not so crappy, just old school & not modern.


Even though you beefed it up, there is not nearly enough capacitance in the supply to eliminate ripple.
The design fundamentally relies upon the usage of balanced inputs to cancel out the audio currents in the supply.
This is why balanced sounds so much better than SE with this design.
But only with perfect balance will all of the supply currents cancel.
Is the beefed up capacitance enough to deal with the remaining ripple? I honestly don't remember, probably not in the lower frequencies.
But if you use SE then you are pretty much screwed. No real regulation in the supply.


----------



## baronbeehive

Maxx134 said:


> But in this thread we juiced up the PSU greatly, so not so crappy, just old school & not modern.


Yes, and what surprised me in a good way was how sonic made his "old school" Odyssey sound so good according to one member, who apparently likes it at least as much or possibly even better than the "new school" Oblivion for example. So old school is not dead by any means apparently 🧐.


----------



## baronbeehive (Nov 4, 2021)

Maxx134 said:


> Yes the bias point can be made to "sound" as good, but the CCS guarantee it can be in an optimal point.
> So I would probably stayed with it if I did it. Currently I have manually found my sweet spot for a specific tube, and am done tube rolling that stage (after thousands dollars and almost all 12pin & 6pin tubes rolled in, and anything with adapters) so do not want to mess with it.


Yes, I just feel that if the cathode film cap upgrade can be that much better than what is there atm it might be worth jettisoning the CCS 🤞.


Maxx134 said:


> But in this thread we juiced up the PSU greatly, so not so crappy, just old school & not modern.


Yes, and what surprised me in a good way was how sonic made his "old school" Odyssey sound so good according to one member, who apparently likes it at least as much or possibly even better than the "new school" Oblivion for example. And the Odyssey relies on quality parts like we have done in the LD as opposed to new school design of the Oblivion. AFAIK it doesn't have regulated PSU, parafeed OT, source followers, for example, but it is an optimised amp which is what we are trying to do here. So old school is not dead by any means apparently 🧐.


----------



## coinmaster

"Old school" doesn't mean anything in engineering terms. It's a matter of whether X is sufficient to accomplish Y.
"Old school" power supplies can do their job just fine. Depending on the inherent regulation (or not) of the power supply, the PSRR of the amp, what type of ripple appears in the supply lines, and how the sound quality of the amp is affected by the ripple, you may have a good or bad power supply.
As for the MK6, it does not respond well to ripple and the supply is under designed considering this fact. They did this to save costs most likely.


----------



## baronbeehive

I guess the MK8 is better in that respect in that it only has to deal with much more of a fixed range of output impedance for the Sennheiser type headphone unlike the MKVI which has to deal with the full spectrum of impedances?


----------



## coinmaster

Higher impedances will be easier loads and give less supply ripple.


----------



## CopperFox

This talk about the PSU needing more capacitance for ripple current handling is interesting as on the first page it was stated that the PSU would be kind of overkill already as it is so I've only replaced the PSU output caps with the super fast 400uf 400v DCL Wimas.

But wouldn't it be quite possible to replace the four 1000uf 200v caps with bigger ones that would be specifically designed for ripple current handling, and what would be the highest sensible capacitance that could be used here? Are there some other specific components around/in the PSU that would suffer from overcurrent with a capacitance too high?


----------



## coinmaster (Nov 5, 2021)

Bigger is good. Lower esr is better.
I put 0.5 miliohm esr 100uf caps in there and it changed the amp completely.

But screw the caps. Get it regulated.
The amount of regulation that a simple regulator would provide is going to be vastly more than any capacitance you can realistically throw into it.
The issue is implementing it physically because you would really need a custom PCB to apply it, which is once again, getting into territory where it's easier just to redesign the entire thing.

If people want to make it worth my while, I can conjure up some PCBs that you can self populate that is the equivalent of an idealized version of the MK6.
But it would be quite out of my way so I would need some expressed interest.


----------



## baronbeehive (Nov 5, 2021)

CopperFox said:


> This talk about the PSU needing more capacitance for ripple current handling is interesting as on the first page it was stated that the PSU would be kind of overkill already as it is so I've only replaced the PSU output caps with the super fast 400uf 400v DCL Wimas.
> 
> But wouldn't it be quite possible to replace the four 1000uf 200v caps with bigger ones that would be specifically designed for ripple current handling, and what would be the highest sensible capacitance that could be used here? Are there some other specific components around/in the PSU that would suffer from overcurrent with a capacitance too high?


Get caps specifically designed for handling ripple.

As coin says regulation would be ideal but not feasible for the LD as it is, we have gone as far as we could with the decoupling caps which as you and others have found make a massive difference because of the speed and low ESR. I went one step further with the CCS to at least get constant current from the driver stage but as to its effect on sound I don't think it made a massive difference other than cleaning up the sound somewhat. IMO the optimisation that we did with, the bias points for example had greater effects on sound.

I don't really see that the PSU could suffer with too high a capacitance so long as peak demands were manageable, also the high capacity would be better able to handle any power surges such as at startup which is why you put in upgraded transformers and diodes.

The overkill was in the 1500uF, I think 1000uF stock, capacitance which was thought to be more than enough for a decent power supply to handle variations in signal. The tradeoff was good capacity and power against possible artifacts due to signal variation and such like, obviously regulation would be better though.

BTW the differences in impedance handling of the MKVI compared to the MK8 might be why you found the problem with the impedance matcher.


----------



## coinmaster (Nov 5, 2021)

Caps designed for handling ripple are just caps with lower ESR and better heat handling. If you want high regulation with caps you need a ton of capacitance and a low enough ESR so that capacitance isn't stifled.
You could use a capacitance multiplier which would require just a single resistor and  transistor added to each cap. But you would need to adjust some values in the supply to ensure there is enough voltage headroom or it will produce ugly ripple at the output.


----------



## Maxx134 (Nov 5, 2021)

baronbeehive said:


> Yes, I just feel that if the cathode film cap upgrade can be that much better than what is there atm it might be worth jettisoning the CCS 🤞.


No we cannot place any cathode cap on that driver tube. Sorry that was another brain fart, 😂
But you should try your calculated bias point instead of the CCS, and find out which sound you like better.
Some aspects are tangelbles not measured, such as soundstage depth or liveliness of the tube.
The internal capacitance & other factors at play should make tube rolling more noticeable without the CCS. Not saying if it's better or worse as I have not implemented the CCS to compare myself yet.
I probably will try that soon.



CopperFox said:


> This talk about the PSU needing more capacitance for ripple current handling is interesting as on the first page it was stated that the PSU would be kind of overkill already as it is so I've only replaced the PSU output caps with the super fast 400uf 400v DCL Wimas


I believe coinmaster was referring to stock implementation.



coinmaster said:


> Caps designed for handling ripple are just caps with lower ESR and better heat handling. If you want high regulation with caps you need a ton of capacitance and a low enough ESR so that capacitance isn't stifled.
> You could use a capacitance multiplier which would require just a single resistor and  transistor added to each cap. But you would need to adjust some values in the supply to ensure there is enough voltage headroom or it will produce ugly ripple at the output.


I think the dual regulation transistors with all the extra beefed up caps, with also the increased decoupling film caps already placed in this mod thread have taken care of ripple,
But definitely the driver stage is weak.

Although the driver stage's 2 driver tubes are efficient enough with the added decoupling film caps we used, it's mostly just adequate because they are not driven optimally anyways.

So I see that the "capacitance multiplier" circuit you posted could very well have been used to mitigate most the decoupling caps & driver stage.

Unfortunately the thread owner @Redge78 was against any form of solid state devices in the design at the time.


----------



## coinmaster

You're gunna want about 10,000uf capacitance to eliminate the ripple when using SE.


----------



## baronbeehive (Nov 5, 2021)

Maxx134 said:


> No we cannot place any cathode cap on that driver tube. Sorry that was another brain fart, 😂


Haha... x2... again! We've been out of this for too long LOL . Don't know about you but I can't imagine what I was thinking. I know perfectly well I have the CCS on the driver stage anode/cathode, and the cathode bypass cap on the power stage cathode, it's not that difficult... , even without a schematic... but for some reason I assumed that the cathode bypass went on the gain stage 🤯.


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## baronbeehive (Nov 5, 2021)

Following on from the work of CopperFox, and... *brain farts excepting*... I have a plan. I'm thinking of relaxing the restrictions that a compact version of the amp has and go with a chassis extension using heatsink plates, easily done and that would allow some of the huge film caps that according to members here should give the amp a boost in speed, and with that sharper bass, a weak point with the amp, and improving soundstage as well. So probably the 400uF Wimas for PSU which makes a ratio of around 3:1 film to lytic cap, seems reasonable. And up the power decoupling caps to about 100uF Wima. CopperFox already verified this. Which leaves cathode and WCF caps.

For cathode and WCF caps we need to take account of the cutoff on the rest of the frequency response, *but* also we need to have good power handling.

So for cathode caps, going from the cathode bypass calculator which is based on the mathematical formulae, probably starting at around 100uF to 500uF, figures for lytics. So for films around 50-200uF sounds about right. We will need to watch for oscillations for the higher values.

For WCF caps Maxx noted what Redge said on page 1 that half the current of the WCF push/pull design, comes from the cathode caps. Therefore the other half must come from the WCF caps? Anyway it looks like they could do with being uprated so maybe try around 1uF and possibly upwards to see the effect on the power drain, and taking account of oscillations of course here also. We may have overlooked the importance of the WCF caps before now as Maxx said.

So all of this should maximise the liveliness of the amp to a new level. I seem to remember coin, along with Redge, threw out the old chassis with his "alfresco workbench" version of the amp way back at the beginning of the thread!

How's that for a brain fart.. a huge one at that 🥴.


----------



## Maxx134

baronbeehive said:


> Following on from the work of CopperFox, and... *brain farts excepting*... I have a plan. I'm thinking of relaxing the restrictions that a compact version of the amp has and go with a chassis extension using heatsink plates, easily done and that would allow some of the huge film caps that according to members here should give the amp a boost in speed, and with that sharper bass, a weak point with the amp, and improving soundstage as well. So probably the 400uF Wimas for PSU which makes a ratio of around 3:1 film to lytic cap, seems reasonable. And up the power decoupling caps to about 100uF Wima. CopperFox already verified this. Which leaves cathode and WCF caps.
> 
> For cathode and WCF caps we need to take account of the cutoff on the rest of the frequency response, *but* also we need to have good power handling.
> 
> ...


Sounds like alotta effort for unkown performance gains.
I'm not bothering with PSU, because as coin stated, the balance design cancels PSU ripple, plus I already have film caps as decoupling..
I'm only looking to change up my cathode caps and WCF caps. 🙃🙂


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## baronbeehive (Nov 7, 2021)

Maxx134 said:


> Sounds like alotta effort for unkown performance gains.
> I'm not bothering with PSU, because as coin stated, the balance design cancels PSU ripple, plus I already have film caps as decoupling..
> I'm only looking to change up my cathode caps and WCF caps. 🙃🙂


I will let the prospect ferment in my brain for a while before doing it 🤯. If I do I might as well go the whole hog, you're probably right but might be interesting to try faster caps for PSU, I don't know. Anyway I do'nt intend to do anything more exotic as coin suggested like rebuilding the PSU for example, too much pain and maybe not enough gain, the LD already sounds pretty good to me, good enough anyway.

If the chassis is extended then I might as well fill it with something . But I agree the cathode and WCF are the interesting things to do.


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## coinmaster (Nov 7, 2021)

Well, as I said. I can build a PCB for people here of the idealized version of the mk6 where all of the theoretical flaws are already solved without changing the functional design structure (It will still act as a WCF, just without the downsides).
I'd share the schematic but I won't bother unless I decide to build it. Don't want the asian lurkers stealin it off me for nothing.

But as I said, I'll need some expressed interest for me to go out of my way.
The issue is the idealized version of the input stage requires twice the number of triodes, so it would need a new chassis and wouldn't be compatible with the existing one.
I could order a custom chassis from china but again, not worth it unless enough people are interested.
Considering the B.O.M and the time I would probably need to sell it for at least $800 if I populate the board and buy all the parts. Maybe less if I can get the expected B.O.M lower.
But I would need to order in batch to keep the cost down, so a minimum of 5 people would need to be interested.


----------



## baronbeehive

coinmaster said:


> Well, as I said. I can build a PCB for people here of the idealized version of the mk6 where all of the theoretical flaws are already solved without changing the functional design structure (It will still act as a WCF, just without the downsides).
> I'd share the schematic but I won't bother unless I decide to build it. Don't want the asian lurkers stealin it off me for nothing.
> 
> But as I said, I'll need some expressed interest for me to go out of my way.
> ...


Appreciate it!

Don't know if enough people are hanging out around this thread so for anyone who is maybe they should get in touch if they are interested.. and if that's OK with you.


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## coinmaster

Yeah, seems like a decent amount of lurkers but not many participants these days.


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## coinmaster (Nov 7, 2021)

Actually what I'd probably do is make the input stage and output stage separate entities in their own separate chassis connected via XLR.
No need to lock either section into a single design or purpose.
The input stage is probably one of the best possible designs for its purpose using tubes and would make a top end pre-amp or amp stage for speakers.
 Better to make it modular.


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## baronbeehive

Maxx134 said:


> Sounds like alotta effort for unkown performance gains.
> *I'm not bothering with PSU*, because as coin stated, the balance design cancels PSU ripple, plus I already have film caps as decoupling..
> I'm only looking to change up my cathode caps and WCF caps. 🙃🙂


I was thinking.. again.. must stop that . Don't know why that hadn't occurred to me before but we might be missing something there. We already have transformers there plus transistors and diodes, so why create what might be an unnecessary bottleneck by putting in large, slow lytics when we could have smaller, faster films. OK so we have the capacity but what might be missing is the speed? I think Copperfox got it about right with the 400uF Wimas, so I think that is definitely worth a try.


----------



## Maxx134

baronbeehive said:


> I was thinking.. again.. must stop that . Don't know why that hadn't occurred to me before but we might be missing something there. We already have transformers there plus transistors and diodes, so why create what might be an unnecessary bottleneck by putting in large, slow lytics when we could have smaller, faster films. OK so we have the capacity but what might be missing is the speed? I think Copperfox got it about right with the 400uF Wimas, so I think that is definitely worth a try.


We already placed better lyctics after the transistors, and already placed film caps as decoupling caps by the tubes.
I dunno why we running in circles here.

Copperfox was investigating films in the Cathode position so there you have your area of improvement.
Also, We already have film caps in WCF stage, so I am only changing my brand for a better film.

So this is it. There is nothing left to do, without adding in solid state and changing the design.
So to evlove from this type design would be to implement the better stages that Coinmaster has designed, or part from little dot to another design.
The problem is that there is nothing I would recommend or move to except @SonicTrance amps, or DIY a totally new design from coinmaster.


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## baronbeehive

CopperFox said:


> How large a chassis extension are you planning on?


I can probably answer your question now, most likely to accommodate those 400uF Wimas at 45mm-65mm size so it will have to take account of this, any extra space left over will leave room for the cathode bypasses easily. I really think the superfast wimas will do well in PSU area in place of the slower lytics. I will post pics when I'm ready.


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## CopperFox (Dec 3, 2021)

So in the last few weeks I've been trying out some of the different resistor brands for the cathode resistor postition... and I'd say they've had unexpectedly large differences in sound.

Perhaps I should first list some other preferences and choices I have in the system. And also for starters I haven't really understood the statements that the mkVI has a bass weakness as I've never felt that way and now it even has my favourite bass of all my amplifiers for my bassy planars.

My preferences for sound signature are that I like the Harman curve and I care most about bass, low treble/mids and high treble in this order and want them all to be good.

For the driver tubes I've been using the black and gold Shuguang 6SL7-T tubes nearly exclusively for almost 12 months. I've found these to have the best sub-bass extension, a very well balanced, detailed and smooth sound in all areas of the FR spectrum.  The other tubes I've tried in addition to the Soviet stock tubes are the Tung-Sols in both the reissue and original forms and Full Music 6SL7 tubes and some apparently quite rare Siemens tubes that came with my second hand mkVI. My experience with the various tube brands here is not extensive so I'm naturally open for suggestions too but really like these 2012-released Shuguangs.

For the power tubes I have a quite wide selection and I've found my favourites in a combination of the Tung-Sol 6080s (in the "preferred construction") and white top Shuguang 6N5PJ. The reason why the Tung-Sols are good is that they have the best sub-bass of all tubes I tried. And the way in which the Shuguang 6NP5Js are unusual is that they have both the second strongest bass and also some of that big soundstage thing like the Svetlanas do. There are (at least?) three different variants of the Shuguang 6N5PJ: (1) One with clear top and metal base, (2) one with clear top and black base and (3) one with white top and black base.

Of these, the white top has some emphasis on midbass punch and low treble, the black base clear top has emphasis on sub bass and higher treble sharpness and the metal base is most neutral of them. The white top combines well with the Tung-Sols as the midbass and low treble foci add dynamics to the sub-bass emphasized Tung-Sol sound. In some combinations I've also used a combination of two variants in the black base clear top and black base white top, using the clear top variant as a kind of substitute for the Tung-Sols if they didn't work well in some configuration of rest of the amp.  The metal base variant I use in my other OTL amp that runs two output tubes.

In the stock configuration of the mkVI, however, they did not sound very usable as despite their good bass they had an overly soft sound and they came alive only after installing the decoupling caps and film caps for the PSU output.


But back to the different resistor brands. I had had the Kiwame brand resistors for cathode and anode resistors for a year and was looking to try some other options for the cathode resistor so I got Ohmite Audio Gold ceramics, TKD metal films, Shinkoh tantalum, Audio Note tantalum non-magnetic and Audio Note Niobium non-magnetic to try out.

(For the anode resistors I have the Kiwames at 68k and most other resistors are either stock or Mills MRA.)

I had read over various forums and sources that the Kiwames have both very low tolerances (0,5%) and a "tube-like" warm, thick and bassy sound so that's probably what I had gotten used to. The first replacement I tried were the TKD metal films. I was quite surprised over their difference. The TKDs have a very crisp and clear sound that even sounds a bit artifical and they also have the lowest bass extension and quantity of these all. For my tastes I'd even say that they have a bass deficit. But they do have a certain character too that may be preferred for other people. Next I tried the Ohmite Audio Gold. It had just a bit more bass and less clarity and crispness than the TKDs. They ended up sounding a bit generic and bland. Probably not the favourite for many?

At this point I was wishing for a sound that would have the bass of the Kiwames but more clarity like the TKDs. I still had the AN tantalums and niobiums and Shinkoh tantalums. Of these I had read in advance that the Shinkoh would have been considered the best resistor at some point in the past and that they would have great mids but possibly lean-ish bass. And what I had read about the AN tantalums was that their sound was overly "tubey". The AN niobiums were the newest product of these, released only in the last year or so and there was not much information or impressions of those, but one that I remember had said they were the best of the three. So I tested the AN Niobium next and they were pretty much exactly what I had hoped for - almost exactly the kind of bass like the Kiwames except cleaner and also very good clarity and detail over the FR, a very refined, detailed and smooth high end kind of sound. Over a few days I began to notice though that they had slight recess in the mid to high treble - so I decided it might be a good time to do the input/output cable upgrade mod for the amp to see if it would fix that... and that's what it did. Afterwards I still tried the AN tantalums, but they were clearly worse than the niobiums with soft bass and muddied low treble.

So as they now worked in my system I'd rank them as follows: First, Audio Note Niobium non-magnetic - these are worth their price here and they are in a different league to the rest. Second, the Kiwames - they have good punchy and deep bass and are relatively cheap too even if they don't have the very best clarity. Third, the AN tantalums which had many things in common with the Kiwames but were worse. Fourth the TKD metal films which have a crisp character but are low on bass. Fifth and last the Ohmite Audio Golds which didn't really stand out with their characteristics.

The Shinkoh I still haven't tried but will probably do in the future. I might also re-test the Kiwames at some point as I haven't done so after replacing the wires. It would be interesting to try the Mills MRA here as well.

In any case these comparisons again show that there are many, many different possibilities with which to configure the amp to match various preferences.


(Edit: The tested resistors were in the 2W power rating except the Ohmite which was 5W.)


----------



## CopperFox

baronbeehive said:


> Following on from the work of CopperFox, and... *brain farts excepting*... I have a plan. I'm thinking of relaxing the restrictions that a compact version of the amp has and go with a chassis extension using heatsink plates, easily done and that would allow some of the huge film caps that according to members here should give the amp a boost in speed, and with that sharper bass, a weak point with the amp, and improving soundstage as well. So probably the 400uF Wimas for PSU which makes a ratio of around 3:1 film to lytic cap, seems reasonable. And up the power decoupling caps to about 100uF Wima. CopperFox already verified this. Which leaves cathode and WCF caps.
> 
> For cathode and WCF caps we need to take account of the cutoff on the rest of the frequency response, *but* also we need to have good power handling.
> 
> ...



Do the WCF caps need to be "audio caps" or just have the best electrical properties for power delivery - (how much) does the audio signal pass through them?

Also, what about the eight small Wimas that are located between the power tubes and PSU section? At least some people have replaced those with something else, such as the Mundorfs here. Is their function power delivery or something else?


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## CopperFox (Dec 2, 2021)

CopperFox said:


> Haven't used the impedance adapter in a while as it was starting to look like the mkVI+ doesn't like having it attached to it. The vu meters were beginning to show imbalance with one channel rising in output and the other decreasing.



I've been looking into this too. This effect happens with the B10 impedance matcher connected regardless of the tubes. At startup the vu meters both show 60 ma, but the left then begins slowly approaching 40 ma or lower and the right side begins approaching 80 ma or higher. This doesn't fix itself (but instead gets worse) if I leave the amp running for a long time. It also happens only with the impedance matcher attached, and is reset (so that the readings are 60 and 60) if the amplifier is turned off and on again.

Would the opamps' biasing function somehow rely on feedback from the headphone output? And if yes, could it be that having the impedance matcher attached somehow cancels some of this?


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## baronbeehive (Dec 4, 2021)

CopperFox said:


> So in the last few weeks I've been trying out some of the different resistor brands for the cathode resistor postition... and I'd say they've had unexpectedly large differences in sound.
> 
> Perhaps I should first list some other preferences and choices I have in the system. And also for starters I haven't really understood the statements that the mkVI has a bass weakness as I've never felt that way and now it even has my favourite bass of all my amplifiers for my bassy planars.


To clarify that I do think that the bass is good and powerful enough, just that as  you go down toward sub bass it gets looser which takes away a bit from the definition. My other amp has OT's and they improve the bass sharpness and definition over the LD. Interesting that you say it has the best bass of all your amps. I suspect that the film caps you have installed will make that difference, and that is why I intend to install them myself at some point later, more speed can only be beneficial.


CopperFox said:


> For the driver tubes I've been using the black and gold Shuguang 6SL7-T tubes nearly exclusively for almost 12 months. I've found these to have the best sub-bass extension, a very well balanced, detailed and smooth sound in all areas of the FR spectrum.  The other tubes I've tried in addition to the Soviet stock tubes are the Tung-Sols in both the reissue and original forms and Full Music 6SL7 tubes and some apparently quite rare Siemens tubes that came with my second hand mkVI. My experience with the various tube brands here is not extensive so I'm naturally open for suggestions too but really like these 2012-released Shuguangs.
> 
> For the power tubes I have a quite wide selection and I've found my favourites in a combination of the Tung-Sol 6080s (in the "preferred construction") and white top Shuguang 6N5PJ. The reason why the Tung-Sols are good is that they have the best sub-bass of all tubes I tried. And the way in which the Shuguang 6NP5Js are unusual is that they have both the second strongest bass and also some of that big soundstage thing like the Svetlanas do. There are (at least?) three different variants of the Shuguang 6N5PJ: (1) One with clear top and metal base, (2) one with clear top and black base and (3) one with white top and black base.
> 
> ...


I'm interested in what you say about you choice of tubes. AFAIK we haven't tried the Chinese tubes exhaustively due to some fairly negative comment initially. I've tried soviet tubes, (Sovtek), new issue Tungsols and Full Music tubes but only in my other amp, so they were 12AX7's, and although they were quite good they were not my preferred choice.

Re: your choice of power tubes I would be interested in getting hold of those Shuguang 6NP5J's if they indeed do have that Svetlana type soundstage, I steered clear of the Svetlana's also due to quite negative comments.

I'm assuming when you say you use Tungsols and Shuguangs in combination you mean having 2 Tungsols and 2 Shuguangs to make up the 4 power tubes? This is going beyond where I've gone, I haven't looked into this exhaustively, only tried a couple of combinations which weren't very promising.

You say that they did not sound very useable, do you mean the Shuguangs?

How did you manage to get hold of TS 6080's? I've been trying for ages and pretty much given up any hope of ever coming across any.


CopperFox said:


> (For the anode resistors I have the Kiwames at 68k and most other resistors are either stock or Mills MRA.)


👍.


CopperFox said:


> I had read over various forums and sources that the Kiwames have both very low tolerances (0,5%) and a "tube-like" warm, thick and bassy sound so that's probably what I had gotten used to. The first replacement I tried were the TKD metal films. I was quite surprised over their difference. The TKDs have a very crisp and clear sound that even sounds a bit artifical and they also have the lowest bass extension and quantity of these all. For my tastes I'd even say that they have a bass deficit. But they do have a certain character too that may be preferred for other people. Next I tried the Ohmite Audio Gold. It had just a bit more bass and less clarity and crispness than the TKDs. They ended up sounding a bit generic and bland. Probably not the favourite for many?
> 
> At this point I was wishing for a sound that would have the bass of the Kiwames but more clarity like the TKDs. I still had the AN tantalums and niobiums and Shinkoh tantalums. Of these I had read in advance that the Shinkoh would have been considered the best resistor at some point in the past and that they would have great mids but possibly lean-ish bass. And what I had read about the AN tantalums was that their sound was overly "tubey". The AN niobiums were the newest product of these, released only in the last year or so and there was not much information or impressions of those, but one that I remember had said they were the best of the three. So I tested the AN Niobium next and they were pretty much exactly what I had hoped for - almost exactly the kind of bass like the Kiwames except cleaner and also very good clarity and detail over the FR, a very refined, detailed and smooth high end kind of sound. Over a few days I began to notice though that they had slight recess in the mid to high treble - so I decided it might be a good time to do the input/output cable upgrade mod for the amp to see if it would fix that... and that's what it did. Afterwards I still tried the AN tantalums, but they were clearly worse than the niobiums with soft bass and muddied low treble.
> 
> ...


Again you've gone beyond where I have gone, and most others here! Incredibly interesting the differences you've found which I'm quite amazed by as I didn't think resistors would make that much differences and I think that goes for everyone here. Maybe the upgrades you have carried out have increased the sensitivity of the amp to other changes.

What wires did you put in the output position? These are the most important.

Very good work!
.

Edit: Do you intend to do any further experiments with different PSU, decoupling and cathode film cap values?


----------



## baronbeehive (Dec 4, 2021)

CopperFox said:


> Do the WCF caps need to be "audio caps" or just have the best electrical properties for power delivery - (how much) does the audio signal pass through them?
> 
> Also, what about the eight small Wimas that are located between the power tubes and PSU section? At least some people have replaced those with something else, such as the Mundorfs here. Is their function power delivery or something else?


This needs experimentation I think. The WCF caps *are* coupling caps and will have a direct sonic impact on half the power triodes. Together with their associated resistors they act to sense the current for the balanced push/pull operation of the 2 power triodes so that as one  half of the circuit is pushing with a given current the other half is pulling with the *same current* in a balanced way.

So they need to be audio type caps but they also need to have the best possible power delivery. That is something I was thinking of looking into when I do my film cap upgrades. I was intending to try values up to 1uF here to see if a higher value improved power handling without the disadvantage of unpleasant resonances which are more likely the higher you go in values.

Not sure what the function of those Wimas is. Someone here replaced theirs with Mundorfs but only for cosmetic reasons as I remember.


----------



## baronbeehive

CopperFox said:


> I've been looking into this too. This effect happens with the B10 impedance matcher connected regardless of the tubes. At startup the vu meters both show 60 ma, but the left then begins slowly approaching 40 ma or lower and the right side begins approaching 80 ma or higher. This doesn't fix itself (but instead gets worse) if I leave the amp running for a long time. It also happens only with the impedance matcher attached, and is reset (so that the readings are 60 and 60) if the amplifier is turned off and on again.
> 
> Would the opamps' biasing function somehow rely on feedback from the headphone output? And if yes, could it be that having the impedance matcher attached somehow cancels some of this?


I don't know, I can't account for this. Each channel provides a mirror image of the other channel so why one side only would increase while the other stays the same is beyond me. The opamps role is to amplify a weak signal as you probably know so I don't think that they could be involved in this. Not really sure I haven't any experience of using impedance matchers.


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## CopperFox (Dec 5, 2021)

baronbeehive said:


> To clarify that I do think that the bass is good and powerful enough, just that as  you go down toward sub bass it gets looser which takes away a bit from the definition. My other amp has OT's and they improve the bass sharpness and definition over the LD. Interesting that you say it has the best bass of all your amps. I suspect that the film caps you have installed will make that difference, and that is why I intend to install them myself at some point later, more speed can only be beneficial.



Yes the film caps as cathode bypass gave a significant improvement in sub-bass control and detail.



baronbeehive said:


> You say that they did not sound very useable, do you mean the Shuguangs?



The Shuguang 6NP5Js. Before adding decoupling caps and film PSU output caps they had nice bass but were otherwise too soft sounding. With the decoupling and psu output cap upgrades they improved a lot and got sharper so seems like they need that additional power available to sound their best.



baronbeehive said:


> What wires did you put in the output position? These are the most important.



I used this cheap SPC teflon coat wire from ebay. Bound/twisted pairs, meaning 4 wires in total for the positive and negative signal wires and a single wire for ground (should that be a pair of wires too?)

After installing them there was some interference or glitching on one channel so I routed the cables further away from the tube heater wires, shortened them and also added two different kinds of random car audio shielding (plastic tubing and nylon sheath on top of that) on the signal wires and they've worked great since.



baronbeehive said:


> Very good work!
> .
> 
> Edit: Do you intend to do any further experiments with different PSU, decoupling and cathode film cap values?



I will experiment with the four big electrolytic PSU caps. The 200uf cathode bypass caps that I now have are working great and since they took a long time to burn in I probably won't try other values there. Probably not for the PSU ouput caps either. One thing that I had thought up about those is that it might be possible to install the 200uf value caps there with shorter wires, which might or might not have lower total resistance as the wiring is probably something like 1 mOhm per centimeter. The Wima DCL-MKP datasheet specifies the 400V 400uf version as having 1 mOhm ESR and 400V 200uf having 1,2 mOhm ESR so the wiring can have higher resistance than the caps themselves.



baronbeehive said:


> This needs experimentation I think. The WCF caps *are* coupling caps and will have a direct sonic impact on half the power triodes. Together with their associated resistors they act to sense the current for the balanced push/pull operation of the 2 power triodes so that as one  half of the circuit is pushing with a given current the other half is pulling with the *same current* in a balanced way.
> 
> So they need to be audio type caps but they also need to have the best possible power delivery. That is something I was thinking of looking into when I do my film cap upgrades. I was intending to try values up to 1uF here to see if a higher value improved power handling without the disadvantage of unpleasant resonances which are more likely the higher you go in values.



It's unfortunate that the audio cap manufacturers don't bother listing the other electric properties of the different capacitance value models of the same capacitor product line.

With the datasheets of general (or other specific) purpose caps things like ESR and ESL are sometimes listed and their best values are not always consistently in the lower or higher capacitance value models. Sometimes lower capacitance is better and sometimes higher capacitance is better for those.


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## CopperFox (Dec 4, 2021)

baronbeehive said:


> I don't know, I can't account for this. Each channel provides a mirror image of the other channel so why one side only would increase while the other stays the same is beyond me. The opamps role is to amplify a weak signal as you probably know so I don't think that they could be involved in this. Not really sure I haven't any experience of using impedance matchers.



I thought it was established early in the thread that the opamps are used for biasing here?

And that the blue trimpots are there to set some sort of starting point for the biasing, which will be affected by feedback from the output? (Is any of this correct?  )

And if so, would the values from the trimpots somehow be multiplied or magnified in absence of normal/expected feedback from output?

In that case, some sort of imbalance in the trimpot adjustments could cause growing imbalance in the meters and also be redeemable by adjusting the trimpots.

But I don't know how to adjust the trimpots... how should that be done?


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## baronbeehive (Dec 5, 2021)

CopperFox said:


> I've been looking into this too. This effect happens with the B10 impedance matcher connected regardless of the tubes. At startup the vu meters both show 60 ma, but the left then begins slowly approaching 40 ma or lower and the right side begins approaching 80 ma or higher. This doesn't fix itself (but instead gets worse) if I leave the amp running for a long time. It also happens only with the impedance matcher attached, and is reset (so that the readings are 60 and 60) if the amplifier is turned off and on again.
> 
> Would the opamps' biasing function somehow rely on feedback from the headphone output? And if yes, could it be that having the impedance matcher attached somehow cancels some of this?


A further thought occurred to me while thinking about this in the night, couldn't get any sleep thinking about it! Perhaps the impedance matcher doesn't work with balanced amps, ie. that have 2 channels. It could be that it is connected to one channel only and that would explain why only one channel is changing once it is connected. You could check this be inputting a different value and see if the channel changes value correspondingly.

Edit: This may also explain why the Impedance matcher didn't work on the LD.


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## baronbeehive (Dec 5, 2021)

CopperFox said:


> I used this cheap SPC teflon coat wire from ebay. Bound/twisted pairs, meaning 4 wires in total for the left and right signal wires and a single wire for ground (should that be a pair of wires too?)


I think the one wire to ground should be alright so long as the right component is connected to ground.


CopperFox said:


> *I will experiment with the four big electrolytic PSU caps*. The 200uf cathode bypass caps that I now have are working great and since they took a long time to burn in I probably won't try other values there. Probably not for the PSU ouput caps either. One thing that I had thought up about those is that it might be possible to install the 200uf value caps there with shorter wires, which might or might not have lower total resistance as the wiring is probably something like 1 mOhm per centimeter. The Wima DCL-MKP datasheet specifies the 400V 400uf version as having 1 mOhm ESR and 400V 200uf having 1,2 mOhm ESR so the wiring can have higher resistance than the caps themselves.


We didn't do this so I will be interested in  your findings as I also wondered if uprating them would be beneficial.

I would think your cathode caps should be ok, they are high value which will ensure a linear curve and so long as they don't cause any oscillation that should be that. I was thinking of maybe a compromise of 150uF if I don't go for the 200uF there. Same with the PSU output caps if they are working well the values seem ok there.

Did you notice any difference in sound characteristics such as harmonics with the film cathode caps? The lytics may output more harmonics I don't know.

Yes it can be important to get the wires as short as possible because of the rapid rise in resistance as the distance increases, especially as we are adding components to the circuit board with a different order of size entirely. I tried to make mine fairly short. Maybe not so important with components that do not rely on speed but if you have film caps there then it makes sense to maximize their potential effects.


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## baronbeehive (Dec 6, 2021)

CopperFox said:


> I thought it was established early in the thread that the opamps are used for biasing here?
> 
> And that the blue trimpots are there to set some sort of starting point for the biasing, which will be affected by feedback from the output? (Is any of this correct?  )
> 
> ...


As I understand it the trimpots are to set the signal starting point to zero resting volts as it can go off slightly signified by a popping when you plug in your headphones. If it is not at zero then one channel will predominate over the other. The signal needs to vary either side of zero in operation. If the popping noise does happen you can adjust the trimpots by turning the screw until there is no popping noise signifying a return to zero.

If you're not sure about it you could PM Maxx. He went into how to adjust the DC offset to zero but I can't find it. I haven't had to adjust it for myself.

This is Maxx's explanation: https://www.head-fi.org/threads/lit...e-on-first-page.782183/page-267#post-16641367

Edit: I managed to find Maxx's instructions on resetting the trimmers when the zero offset has gone off: "_ adjust the trimpots (trimmers) to get zero DC offset between pos &neg output of each channel.. Get DC meter and adjust. Both trimmers can be elevated or lowered equally to cause the corresponding meter for that channel to move up or down slightly by a few points. A final test for zero dc is having your headphones on and listening for any tiny click/pop sound as you insert into the balanced socket (not the single-ended as that by default always pops in any unit)."_


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## baronbeehive (Dec 6, 2021)

CopperFox said:


> Do the WCF caps need to be "audio caps" or just have the best electrical properties for power delivery - (how much) does the audio signal pass through them?


A further point the push/pull phase/antiphase functioning of the feedback loop in the WCF circuit, between the T1 triode and the T2 triode of the power tube, is driven by the WCF cap and the plate load of the tube. Half of the power goes on the push function which then switches to the pull function due to the current sensing regulation by the plate load as I understand it. I have to say I don't fully understand the WCF functioning, especially the maths behind it and this appears to be critical especially for a high headphone load such as with low impedance headphones like you have got, and me as this is what directly drives the headphones in an OTL design.

(As a side note calculating the correct plate load is especially important according to Cavalli for 6AS7G power tubes which have an rp of 280ohms whereas, for example a 12AX7 has an rp of 80.000ohms which would swamp out any load. So given that we tried the impedance mod and most of us were unimpressed that is strange when it would seem so important to get Ra correct).

So half the power goes through the cathode bypass cap and I assume the other half also goes through it in the alternate phase but I'm not sure about this.

The coupling function of the WCF cap between the triodes is not the same as the coupling function between the coupling caps between driver stage and power stage so I'm not quite sure about what the power requirements are. We know that such requirements are critical for the cathode bypass caps but I'm assuming that the WCF caps values would be more similar to the coupling caps, especially given that they would affect the cutoff frequency in the same way so large values would not be right for the WCF caps.


----------



## CopperFox

baronbeehive said:


> I'm assuming when you say you use Tungsols and Shuguangs in combination you mean having 2 Tungsols and 2 Shuguangs to make up the 4 power tubes? This is going beyond where I've gone, I haven't looked into this exhaustively, only tried a couple of combinations which weren't very promising.



Yes, such as this:




Here's the 6SL7-Ts as drivers and Tung-sol 6080 and Shuguang 6N5PJ white top as power tubes. My most used combination although I usually have the rear tubes the other way round with the Tung-Sols on the left.



baronbeehive said:


> Did you notice any difference in sound characteristics such as harmonics with the film cathode caps? The lytics may output more harmonics I don't know.



The sound is cleaner and clearer with the film caps, without that additional edginess and without the softer bass that the electrolytics had. I don't know how those would be described in terms of harmonic distortion. Haven't seen any measurements that would have compared electrolytics vs film caps cathode bypass and don't have an oscilloscope. Would be interesting!


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## CopperFox (Dec 10, 2021)

CopperFox said:


> The 200uf cathode bypass caps that I now have are working great and since they took a long time to burn in I probably won't try other values there. Probably not for the PSU ouput caps either. One thing that I had thought up about those is that it might be possible to install the 200uf value caps there with shorter wires, which might or might not have lower total resistance as the wiring is probably something like 1 mOhm per centimeter. The Wima DCL-MKP datasheet specifies the 400V 400uf version as having 1 mOhm ESR and 400V 200uf having 1,2 mOhm ESR so the wiring can have higher resistance than the caps themselves.



I realised yesterday that with the preamp outputs removed there is now more room in the case to rearrange the 400uf PSU output caps with shorter wires so I did that:
(so will not likely put 200uf caps there)



It was also possible to rearrange the cathode bypass caps and power tube decoupling caps for shorter total wiring length. Looks almost tidy! Also used some rather thick silver wire for those. A keen eye may also notice the PSU electrolytics have been replaced... have had those there for a couple of weeks. will comment more on those later.

I also put the impedance mod back on after coming to the realisation that the reason it didn't work before were likely the 100 Ohm resistors at the output. Now with those removed it does seem to work.


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## baronbeehive (Dec 7, 2021)

Thinking of trying these, cheap for Shuguang!

https://www.ebay.co.uk/itm/265064525748?hash=item3db713afb4:g:0DwAAOSwvVxgNPXC

 I assume these are the clear tops you mention? Sound like a good replacement for Tungsols if there aren't any NOS available.

Edit: I agree with Maxx I never saw any resistors on the output wires and I replaced those.


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## CopperFox (Dec 9, 2021)

baronbeehive said:


> Thinking of trying these, cheap for Shuguang!
> 
> https://www.ebay.co.uk/itm/265064525748?hash=item3db713afb4:g:0DwAAOSwvVxgNPXC
> 
> ...



The site where they are most widely available probably is Aliexpress where they can be often found for ~$20 a pair. The reason they're sometimes listed as "Dawn" or "Dawning" tubes there is that it is the literal translation of the brand's name. And the model name is 6N5P to be specific, and the J in the end is a military-grade designation. They don't seem to be a very popular tube as they do sound too soft in most amplifiers. Seems to be more supply than demand for them.

The TS 6080s do also still seem to be available at places like ebay.

One power tube that I haven't tried are the Tung-Sol 5998s, which seem to be the most exepnsive ones here.  I also haven't tried any of the other US/EUR big bottle tubes (RCA, Philips GE etc.) yet either.


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## CopperFox

Maxx134 said:


> I have spent at least $2k  back then on every 12pin and 6pin, and even some 8pin with adapters, rolling everything into the driver stage.
> 
> The problem was that the stock bias was set so low, that all the tubes were away from there ideal performance. The result was a more pronounced tube differences when rolling.
> 
> ...



How does the Tung-Sol 6C8G sound - what makes it stand out, does it have some sort of particular emphasis, and how's the bass with it?
I could try them at some point... wonder if it would work ok with the 470R cathode resistor value or need 1K or something.


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## baronbeehive (Dec 11, 2021)

CopperFox said:


> The site where they are most widely available probably is Aliexpress where they can be often found for ~$20 a pair. The reason they're sometimes listed as "Dawn" or "Dawning" tubes there is that it is the literal translation of the brand's name. And the model name is 6N5P to be specific, and the J in the end is a military-grade designation. They don't seem to be a very popular tube as they do sound too soft in most amplifiers. Seems to be more supply than demand for them.
> 
> The TS 6080s do also still seem to be available at places like ebay.
> 
> One power tube that I haven't tried are the Tung-Sol 5998s, which seem to be the most exepnsive ones here.  I also haven't tried any of the other US/EUR big bottle tubes (RCA, Philips GE etc.) yet either.


Right, they could be worth a try to replace give my RCA's a rest! I sat up and noticed when you mentioned the soundstage! The softness agrees with some of the negative comments I have heard about Shuguangs and why I steered clear but as you say with the mods, especially the film caps then that could make the difference.

I've tried Tungsol 7236's, found them very analytic so they went straight out, also tried WE 421A's which I liked a lot. They're similar to TS5998's in that they are quite relaxed and flowing and airy but are a bit sharper in attack I think with harder hitting bass. The other ones I had were Bendix 6080WB's with graphite plates which I also liked. I had 5 or 6 sets of these but eventually sold them as I always liked the common or garden RCA's. And after the mods the sound is so good that it didn't really matter what tubes were there because they were all elevated in sound IMO.

Also tried GE 12SL7's, same as 6SL7's but with adapters, typical GE sound very clean and clear but a tad one dimensional.

GEC's are one of the best, very detailed apparently, one of the members here had them but they were incredibly pricey and rare for me to bother with.

Edit: that TS6C8G must be good if Maxx raved about it! I haven' tried it. The cathodes won't make much difference in sound just very fine tuning. I found the 470R to be the best but anything up to about 1K would be fine.


----------



## Maxx134

CopperFox said:


> One power tube that I haven't tried are the Tung-Sol 5998s, which seem to be the most exepnsive ones here. I also haven't tried any of the other US/EUR big bottle tubes (RCA, Philips GE etc.) yet either


For the WCF to perform optimally, the tubes should be if the same model number. I never mixed tubes with different model numbers, as I didn't think possible unless similar.
Also there was another mod to switch bias for other power tubes.

Check your anode resistors in case of excess burn from unbalanced tubes, but if your replacement resistors are wirewound resistors, you should be ok.




CopperFox said:


> How does the Tung-Sol 6C8G sound - what makes it stand out, does it have some sort of particular emphasis, and how's the bass with it?
> I could try them at some point... wonder if it would work ok with the 470R cathode resistor value or need 1K or something.


They had the best transparency, with lively  and balanced sound, while also being good at top and bottom FR extremes. I just used adapters for them.

As for those


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## Maxx134 (Dec 12, 2021)

CopperFox said:


> So as they now worked in my system I'd rank them as follows: First, Audio Note Niobium non-magnetic - these are worth their price here and they are in a different league to the rest. Second, the Kiwames - they have good punchy and deep bass and are relatively cheap too even if they don't have the very best clarity. Third, the AN tantalums which had many things in common with the Kiwames but were worse. Fourth the TKD metal films which have a crisp character but are low on bass. Fifth and last the Ohmite Audio Golds which didn't really stand out with their characteristics


This is excellent info! Good work! 👍 🙂



CopperFox said:


> Do the WCF caps need to be "audio caps" or just have the best electrical properties for power delivery - (how much) does the audio signal pass through them?


Yes as @baronbeehive  stated very well, they are smack in line between the output tube triodes, so they need to be quality.
A good point was made about the capacity. We have not tried larger WCF caps.  What size are yours. I only tried .33uf, but according to Baron, we might see current gains with larger size, although I do believe the current is mainly a tube limitation.



CopperFox said:


> Also, what about the eight small Wimas that are located between the power tubes and PSU section? At least some people have replaced those with something else, such as the Mundorfs here. Is their function power delivery or something else?


Those are strictly PSU caps design to keep the circuit from having any noise like hum or oscillation.  They will not affect sound, only isolation.




CopperFox said:


> Would the opamps' biasing function somehow rely on feedback from the headphone output? And if yes, could it be that having the impedance matcher attached somehow cancels some of this?


Nope. Opamps only affect DC-offset, which would result in a pop sound (when headphones insertion) if they were off by any small amount.



CopperFox said:


> I've been looking into this too. This effect happens with the B10 impedance matcher connected regardless of the tubes. At startup the vu meters both show 60 ma, but the left then begins slowly approaching 40 ma or lower and the right side begins approaching 80 ma or higher. This doesn't fix itself (but instead gets worse) if I leave the amp running for a long time. It also happens only with the impedance matcher attached, and is reset (so that the readings are 60 and 60) if the amplifier is turned off and on again


My guess is that the tubes are having a bad reaction and causing the meters to slowly change.
Check for tube thermal runaway by swapping tubes to other meter(other side).




CopperFox said:


> PSU caps


That may be a bad idea to put film caps where the 4 big PSU electrolytics are..
The reason is that we do not want such a fast load on the bridge Rectifier. This is why there are those huge resistors under PSU section, to absorb the current surge when you turn on the unit...



CopperFox said:


> I thought it was established early in the thread that the opamps are used for biasing here?
> 
> And that the blue trimpots are there to set some sort of starting point for the biasing, which will be affected by feedback from the output? (Is any of this correct?  )
> 
> ...


Check the schematic and you will see it does take a bit from the outputs as there is a very high value resistor at the output (on the board). This DC-offset it critical, as if it was off by a large amount (enough to move meters), then it would create a loud pop and trigger the output relays.
So this is not happening and most likely no one ever has to adjust the trim pots.
It can be "fine-tuned" if you hear a tiny click/pop when plugging in headphones, but try it after it is warmed up, not when just turned on as that's when circuit settles.




baronbeehive said:


> Edit: This may also explain why the Impedance matcher didn't work on the LD


I don't know why, but I have permanently installed different anode resistors to my output tubes to change the impedance out from a calculated 600 ohm to a 50ohm headphones impedance, so the calculations to change output impedance work.
 It changed the sound of a stock HD800 from a more mids, to a bit recessed mids, which is how it sounds with solid state.
At the time I changed my amp, It was tuned for the "Ether" planar, which was around 50ohms. So output was calculated for a 50 ohm load.

What impedance load have you tried set it to? It cannot be zero as it must optimally be the setting of the headphones impedance.
I thought the mk6 was already set for around 50ohm load?


----------



## baronbeehive

Maxx134 said:


> For the WCF to perform optimally, the tubes should be if the same model number. I never mixed tubes with different model numbers, as I didn't think possible unless similar.
> Also there was another mod to switch bias for other power tubes.


The only person who did that was coin I think!

Re: the power tube mod I tried this, and the only effect I found was an increase in volume which gave a perceived improvement in sound, but when the volume was adjusted back I didn't really find any difference so I would think that the primary benefit of this would be to get the tubes operating at their optimum current, but some may find it preferable to leave the 5998's to operate at half current and therefore much cooler.


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## baronbeehive (Dec 12, 2021)

Maxx134 said:


> Yes as @baronbeehive  stated very well, they are smack in line between the output tube triodes, so they need to be quality.
> A good point was made about the capacity. We have not tried larger WCF caps.  What size are yours. I only tried .33uf, but according to Baron, we might see current gains with larger size, although I do believe the current is mainly a tube limitation.


A further point we need fast acting caps here so something like Mundorf Supreme SIO because they are film caps, being metallized PP, as well as being audio caps.

I believe the MKVI is less susceptible to current fluctuations than the MK8? I never saw the meters fluctuate on power surges/dips so it would be difficult to check visually with different WCF cap sizes. Maybe though I just don't play it loud enough to see these performance effects.



Maxx134 said:


> I don't know why, but I have permanently installed different anode resistors to my output tubes to change the impedance out from a calculated 600 ohm to a 50ohm headphones impedance, so the calculations to change output impedance work.
> It changed the sound of a stock HD800 from a more mids, to a bit recessed mids, which is how it sounds with solid state.
> At the time I changed my amp, It was tuned for the "Ether" planar, which was around 50ohms. So output was calculated for a 50 ohm load.
> 
> ...


I changed mine to 38 ohm load for the HE-500's. CopperFox changed his even lower for his very low impedance Monolith headphones.


----------



## CopperFox

baronbeehive said:


> Right, they could be worth a try to replace give my RCA's a rest! I sat up and noticed when you mentioned the soundstage! The softness agrees with some of the negative comments I have heard about Shuguangs and why I steered clear but as you say with the mods, especially the film caps then that could make the difference.



Seeing that the decoupling caps and film caps for psu output improved the 6N5Ps' sound, I (only) now decided to look at their data sheet to see if there's something that might explain that. It looks like their plate resistance would be 450 Ohms and transconductance 4450 micromhos, while most 6080 / 6AS7 tubes have these these values at ~280 and ~7000. So they are not exactly the same there.

And it also means that although the resistors that I added for the impedance mod are correct for (most) 6080/6AS7 tubes, they may not be of the correct value for 6N5P - as the values for the added resistors were calculated with 6AS7 values. So as I now have two Tung-Sol 6080WAs and two Shuguang 6N5Ps for power tubes, the value may be wrong for the latter two.

As for the correct resistor values for the impedance mod, the Cavalli formula again is  Ra = (1/Gm*(1/Ka*(1+Ka)/(1+Kr)*(Rp+Rl)/Rp+Rl/Rp)) .

For the 6N5Ps in the mkVi+,

Gm = 0,00445
Rp = 450
RI = 18 (for the M1060Cs)
Ka = 0,7
Kr = 0,75

So the equation is Ra = (1/0,00445*(1/0,7*(1+0,7)/(1+0,75)*(450+18)/450+18/450))

Which results in ~333,3180 so it is roughly 333 ohms.

But... Isn't that almost exactly the default value for the power resistors here? 
Maybe I could try removing my previously added 680 ohm resistors from the 6N5P's part of the board to see if that makes a difference or not. Or could there perhaps be some reason why this wouldn't be a good idea, if I'd still have the added resistors for the TS 6080s side?

And now it looks like the 6N5Ps actually need _less_ power than the 6080/6AS7 tubes for 18 ohm impedance headphones... but they do still prefer it to be quick power?

With the impedance mod I now have in place that was calculated with the 6AS7 values (resulting in 220 ohms), the 6N5Ps now seem to be also getting more power than they need. Wonder if that is harmful in some way.


----------



## CopperFox

Maxx134 said:


> For the WCF to perform optimally, the tubes should be if the same model number. I never mixed tubes with different model numbers, as I didn't think possible unless similar.
> Also there was another mod to switch bias for other power tubes.
> 
> Check your anode resistors in case of excess burn from unbalanced tubes, but if your replacement resistors are wirewound resistors, you should be ok.



Hmm, I had been mixing the power tubes (different 6080s and 6AS7Gs) before I begun with the mods. The people in the other mkVI thread had been doing this too.
It is actually one of the reasons I like this amp. With a combination of two different power tubes on each channel it is possible to get characteristics from two different power tubes at the same time and imo the combinations also sometimes do things that the respective single tubes can't do on their own as a set of four. 

I think for now I would prefer to have this ability to over optimum WCF performance, if it works ok.




Maxx134 said:


> They had the best transparency, with lively  and balanced sound, while also being good at top and bottom FR extremes. I just used adapters for them.



Sounds good. The 6C8G's values for amplification factor, plate current and plate resistance seem to be somewhere between 6SN7 and 6SL7. Could try them in my 6SN7 amp as well. I think I'll get a couple with adapters as I'm going to be getting some new tubes next week. Also going to order some 6SL7s from the newest Chinese brand Linlai who have released three different models of them in recent weeks. Possibly the JJ Electronic 6SL7 as well.


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## baronbeehive (Dec 13, 2021)

CopperFox said:


> So the equation is Ra = (1/0,00445*(1/0,7*(1+0,7)/(1+0,75)*(450+18)/450+18/450))
> 
> Which results in ~333,3180 so it is roughly 333 ohms.
> 
> ...


👍.

As someone who hasn't done this to any extent I hadn't thought about this, so don't know about that .

So as I understand it you want to remove just one of the 2 resistors making up one of the channels. It sounds a weird thing, each channel constantly fluctuating in output impedances during the WCF loop. As the WCF function is the basis for the amps functioning I doubt this would be a good thing and thinking about it it certainly *doesn't sound a good idea**. I think this is a case of customizing gone mad, because you have to start thinking about the effects of one thing you did every time you start changing the mix. 

Sonic implemented a switch for his impedance mod but that was to change it with a change of headphones. I suppose it would be possible to have each channel output a different impedance so long as it wasn't constantly fluctuating but you wouldn't want to do that for the sake of your ears 🥴.

What do your meters read for the 6N5P's?

* Disclaimer: Of course I may be totally wrong LOL

Edit: I think I know someone who would have tried this if he could though, naming no names..., that doesn't mean you should try it necessarily 🙂.


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## baronbeehive (Dec 13, 2021)

We're getting into strange territory here because as I understand it each half of each channel operates in a phase/antiphase way so that each identical half cancels each other out regarding noise artifacts so what happens when you unbalance the channels like this.. I don't know is the short answer .

Edit: Perhaps if we both fall down that rabbit hole and meet on the other side we might see what goes on in this peculiar world where up is down and vica versa, and we can sit at the table and discuss it with the Mad Hatter who is sitting at the head of table under the grinning cheshire cat 🙂.


----------



## CopperFox

baronbeehive said:


> 👍.
> 
> As someone who hasn't done this to any extent I hadn't thought about this, so don't know about that .
> 
> ...



What I meant is remove the impedance mod (which I have installed based on calculations for 6AS7 values) from the two power rails that feed the 6N5P tubes, as the default resistor has the correct value for them and leave the mod on for the power rails that feed the 6080 tubes, so those two will have the added resistors delivering more power.

Here the idea would be to _reduce_ the imbalance between the 6080 and 6N5P on the same channel. It is also an imbalance that I've had for most of the time for the last six months as I've been using the combination of the Tung-Sol 6080WA and the Shuguang 6N5P with the same power resistor values, be it with or without the impedance mod.

As for the possible switches, the amplifier already does have individual switches (for low/high gain) leading to each of the four power tubes. Maybe it wouldn't be exceedingly difficult to also have individual 6080/6N5P/5998 switches for them as well 




baronbeehive said:


> What do your meters read for the 6N5P's?



Since starting with the new PCB in spring, the meters have been steadily at ~60 ma values on all kinds of tubes, only hopping upwards on bass hits or having some imbalance when the impedance matcher is attached. The impedance mod had no effect on the values.



baronbeehive said:


> We're getting into strange territory here because as I understand it each half of each channel operates in a phase/antiphase way so that each identical half cancels each other out regarding noise artifacts so what happens when you unbalance the channels like this.. I don't know is the short answer .
> 
> Edit: Perhaps if we both fall down that rabbit hole and meet on the other side we might see what goes on in this peculiar world where up is down and vica versa, and we can sit at the table and discuss it with the Mad Hatter who is sitting at the head of table under the grinning cheshire cat 🙂.



Well, as stated above, I have already had that kind of imbalance for the last six months. Now that I think of it, there has been this effect which could occur if I left the amp running for a longer time - above 90 minutes - where it sounded like the sound characteristics of one of the two mixed power tube types would somehow become more distant or hollow sounding. I think I had thought it is normal for tube amps to have their sound vary over time with tubes warming up and capacitors charging up, but it could perhaps possibly be better attributed to phase or impedance fluctuations in the WCF. Rebooting the amp would change it to varying degrees, not always fixing it. But putting four 6N5Ps on instead of the mix always did.

Anyways, I now have the amp back up running after removing the impedance mod resistors from the 6N5P's part of the circuit. I'll keep an eye on if there is some change on that temporal stability thing over a few weeks.


----------



## baronbeehive (Dec 13, 2021)

CopperFox said:


> What I meant is remove the impedance mod (which I have installed based on calculations for 6AS7 values) from the two power rails that feed the 6N5P tubes, as the default resistor has the correct value for them and leave the mod on for the power rails that feed the 6080 tubes, so those two will have the added resistors delivering more power.
> 
> Here the idea would be to _reduce_ the imbalance between the 6080 and 6N5P on the same channel. It is also an imbalance that I've had for most of the time for the last six months as I've been using the combination of the Tung-Sol 6080WA and the Shuguang 6N5P with the same power resistor values, be it with or without the impedance mod.
> 
> ...


Yes, you're quite right members have been doing this tube mixing for years with no adverse effects, I just don't feel qualified without detailed knowledge of how the WCF circuitry works with this kind of alteration to it to advise. As I said one member even mixed 2 completely different types of tube, and I think he survived!

Hopefully Maxx is available to comment, if not there is probably someone who will.

That power output from the meters is quite normal so no problem from those tubes, the 5998's operate at half that output so there is scope for variation, so long as it doesn't go too high to burn out any internal components.

It does seem that mixing has some effect if that problem goes when you substitute 4 of the same tubes.

Edit: Thinking about this, you have one signal from the driver stage per channel. As it goes to the output stage it gets split into 2 signals which are then recombined to cancel each other out eliminating noise. But before that, within each of the signals it is further split within the WCF into 2 in phase/antiphase manner, this is where my head starts to hurt. What happens when one of those signals outputs a different impedance than the other due to a change of Ra and then recombines with the other with a different impedance? How can the impedance be constantly changing, and if it is what effects does that have on sound and on the circuit function?

I don't know if I'm understanding it correctly, it may be that when the signal halves in the WCF are recombined any differences are cancelled out in the same way that noise would be so differences such as caused by different resistors in each half of the signal within the WCF may well not be there any more at output so impedance changes might not in fact be there. I imagine something like this must happen as it would if one of the resistors went off also.

Answers on a postcard please .


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## baronbeehive (Dec 14, 2021)

Sorry ...  ... all that is baloney. You are only proposing to change one resistor per output tube in which case I should have realised that the impedance won't be affected because it will be the same for this tube, even though it will be different for the other tube. And that is probably what is causing the sonic differences when mixing in this way.

See what happens when you make me think .

Edit: Did you get to see WRC Finland btw? I was disappointed that Elfin Evans lost out.. again.. to Seb Ogier!

Edit: When I said baloney I meant what I said, not what  you said LOL, just to avoid confusion!


----------



## Maxx134

CopperFox said:


> It is actually one of the reasons I like this amp. With a combination of two different power tubes on each channel it is possible to get characteristics from two different power tubes at the same time and imo the combinations also sometimes do things that the respective single tubes can't do on their own as a set of four


Yes this is good idea.
I was able to simulate an expensive tube, by mixing 2 lesser tubes together..🙂
As long as your anode resistors have higher wattage (like 5W), you should be ok with differences.

Im changing barons quote, ha


baronbeehive said:


> 🤔🙂





CopperFox said:


> Anyways, I now have the amp back up running after removing the impedance mod resistors from the 6N5P's part of the circuit. I'll keep an eye on if there is some change on that temporal stability thing over a few weeks


Should definitely change the tube influence levels.👍




baronbeehive said:


> Answers on a postcard please


You are correct in your assumptions for changing the resistor according to the tube, for the impedance setting from the carveli formula.

The reason is that no one ever did this before, to set impedance for different tubes.

What you essentially are doing, is optimizing the output level of that tube, for that impedance setting (for the headphones).

So your tubes are laid out :
 L~Positive + L~Negative, then other side is:
R~Positive + R~Negative

(LP)+(LN), (RP)+(RN)
So your signal should have more equal output levels per each half (positive half & negative half) of the signal.

A "skewed" level ouput would be achieved, by NOT changing the resistor according to the tube.

Part of the sonic difference would be, which tube takes over the resulting sound.

IMO,  the positive signal tube would lead the attack (wether it sounds slow or fast), while the negative signal tube would lead the decay( wether it sounds thick or not).
But that is only my general observations.
Your tubes I haven't checked which one is naturally more gain (mu) so maybe the same resistors work in lowering gain of louder one, or lower gain of lesser one.
Striking a nice balance is trial and error.

Maybe you like the greater influence of one tube over another.
I need to try this mixing tubes,  on my amp as well...


----------



## CopperFox

CopperFox said:


> Anyways, I now have the amp back up running after removing the impedance mod resistors from the 6N5P's part of the circuit. I'll keep an eye on if there is some change on that temporal stability thing over a few weeks.



It didn't require weeks to notice the difference - with the resistors for the 6080 and 6N5P tubes at the correct values, the sound was noticeably better than before right at starting the amp up... but then degraded a lot more and a lot faster than before, in less than 30 minutes.

After some initial confusion I began to suspect the reason for this would be capacitor failure of the WCF caps, which were 0,33 uf 600V Miflex KCPU-01s.

To investigate further, I removed the Tung-Sol 6080WBs from the amp and put the second bassiest of my 6080/6AS7 tubes in their place - which were GE 6AS7s from the eighties. With these in place instead of the Tung-Sols, there was noticeably less of the sound degradation over time, but there was still some of it.

So here my thought was that the Tung-Sols perhaps put out an amount low frequency current that the 0,33uf WCF caps weren't able to handle, and this amount has also been increasing with the various mods and now also with the power resistors at correct values.

The next logical step was to replace the WCF caps. I first put there some 1uf power delivery caps that were leftovers from other moddings. Those sounded stable but were bright and low on bass. Then I remembered that I have 0,47uf Miflex KPCU-01s on my shelf that I had ordered accidentally while trying to order something else at some point.

So I installed those in the WCF position and with these in place the sound seems to stay very stable over several hours and sound quality is better than before. I will now keep those there for at least some days to see if that changes or not with further burn-in. In any case, it does look like the 0,33uf capacitance perhaps is not high enough here in my use at least, unless the caps had been somehow severely damaged from being soldered on and off several times.

I could try putting the 0,68uf Miflexes in the WCF position and the 0,33uf or 0,47uf as the coupling capacitors. AFAIK there is far less current going through the coupling capacitors than the WCF caps. I do also have the 0,56uf Duelunds that I haven't given a proper burn-in yet and they might burn in faster in the WCF position because of the higher current. I have been planning to get some Miflex KFPM-01 caps to try in either position as I'm interested to see how a copper foil propylene cap would sound without the paper/oil part. There have been at least some people who said they preferred those over the KPCUs even if they are overall less hyped.

The 0,47uf KPCUs are quite large and with those installed I could only put my chassis extension back on without the side plates and if I keep the 0,47uf caps there I will need to carve those a bit to make them fit again.

Is there some kind of limit to how high a capacitance would be good in the WCF position, would the maximum be 1uf as with the decoupling caps or something else? If it is better to have high capacitance caps in the WCF than as decoupling caps, I could perhaps fit in some brand or model with 1uf capacitance.


----------



## CopperFox

baronbeehive said:


> Edit: Did you get to see WRC Finland btw? I was disappointed that Elfin Evans lost out.. again.. to Seb Ogier!



Didn't have enough experience for the marshall job, missed out on the deadline for other volunteer stuff by a couple of days and no spectators were allowed due to covid. So I watched the Arctic rally's stream from the internet. It's coming up again in a few weeks and I'll likely go watch whichever series will be ran. There's been some rumours that Sweden might get cancelld again due to legal issues with the event's relocation.

Yeah people losing narrowly to someone named Sebastian has been a recurring theme for a couple of decades. That might change next year without Ogier.


----------



## baronbeehive

CopperFox said:


> Didn't have enough experience for the marshall job, missed out on the deadline for other volunteer stuff by a couple of days and no spectators were allowed due to covid. So I watched the Arctic rally's stream from the internet. It's coming up again in a few weeks and I'll likely go watch whichever series will be ran. There's been some rumours that Sweden might get cancelld again due to legal issues with the event's relocation.
> 
> Yeah people losing narrowly to someone named Sebastian has been a recurring theme for a couple of decades. That might change next year without Ogier.


Hey, if you do get any pics in August PM me, I would be interested!

Those rally cars from last year were so fast it's getting quite scary 😲.


----------



## baronbeehive (Dec 17, 2021)

CopperFox said:


> It didn't require weeks to notice the difference - with the resistors for the 6080 and 6N5P tubes at the correct values, the sound was noticeably better than before right at starting the amp up... but then degraded a lot more and a lot faster than before, in less than 30 minutes.
> 
> After some initial confusion I began to suspect the reason for this would be capacitor failure of the WCF caps, which were 0,33 uf 600V Miflex KCPU-01s.


I would have thought unlikely. And the .33uF is the right value for the cutoff. Having said that I think it does require experimentation as we haven't been there ourselves. The power handling you mention should not be a problem, they should handle it and anyway the current output from the power tubes is small, 60mA at the meters which you can see. If the output was too high it would need an OT to handle it which is why we have a low power OTL design on this amp. Also your components are operating well within parameters. The tube could be driven by much more power, and you have uprated components to a higher wattage to avoid reliability problems.

The effect you mention is like that of a buffer filling up and then unable to disperse, or similar to a cap charging and unable to discharge properly over time.

I will have to have a think about this but the obvious things that happen due to fluctuations over time are mainly heat related. Solder, joints, wires losing, or partly losing contact when heat expands the joints. This is something that would not be noticed normally if you check the joints because they would appear OK until they heat up. I don't however think it is that because the sound of a cold solder joint for example would be more of an intermittent noise rather than a gradual decay probably.

Another obvious thought is the tubes themselves, a defective tube for example might be losing control of the electron flow and the anode might be flooded with electrons and unable to get rid of them, so the first thing is try other tubes to see if the same happens.

Another thought is interference of some sort possible due to close proximity of components such as your large PSU caps. If the problem persists I would maybe try to separate them. In some amps you will see a metal shield in between PSU components.

My initial thoughts over tube mixing a few posts back were wrong as Maxx said you are just optimising power for each tube, I got hold of the wrong end of the stick with my comments as I misunderstood what you were planning, so I don't think this would affect anything. As I said that's where my head started to hurt. I know that for class A push pull amps the signal first gets split into push and pull halves at input by the NPN and PNP transistors. Then the two halves are obviously able to retain the different signals produced by tube mixing in each of the 2 signals. But at some point they get recombined by the balanced part of the amp and this is where the noise cancellation takes place, and I'm a bit fuzzy on the exact details. But it's interesting you said the effect you found disappeared when you put in 4 of the same tubes. So I'm still not quite sure how the circuit handles this.


CopperFox said:


> So I installed those in the WCF position and with these in place the sound seems to stay very stable over several hours and sound quality is better than before. I will now keep those there for at least some days to see if that changes or not with further burn-in. In any case, it does look like the 0,33uf capacitance perhaps is not high enough here in my use at least, unless the caps had been somehow severely damaged from being soldered on and off several times.
> 
> I could try putting the 0,68uf Miflexes in the WCF position and the 0,33uf or 0,47uf as the coupling capacitors. AFAIK there is far less current going through the coupling capacitors than the WCF caps. I do also have the 0,56uf Duelunds that I haven't given a proper burn-in yet and they might burn in faster in the WCF position because of the higher current. I have been planning to get some Miflex KFPM-01 caps to try in either position as I'm interested to see how a copper foil propylene cap would sound without the paper/oil part. There have been at least some people who said they preferred those over the KPCUs even if they are overall less hyped.
> 
> ...


I would think fast acting WCF caps would be more important than high capacity there. The cathode bypass caps are already doing the power handling so what we want for WCF position is something to act fast within the feedback loop in each power tube. Those film Miflexes you mention look to be a good bet.

Anyway it looks like  you might have the problem sorted. You could also double up the .47 Miflexes, ie connect in parallel to give a combined value of .94uF and see what effect that has on power recovery after bass dips for example. That would avoid having to buy any at the 1uF value.

I have Audyn True Copper in my other amp as bypasses and I like the copper foil sound.

I would try this first before going higher but I don't think higher than 1uF would work as a coupling or WCF cap due to oscillations. Incidently I was wondering if that was what you are hearing.

Finally you need to remember what you did before the problem became apparent to narrow it down, did it happen after you put in those 200uF Wimas for example, if so maybe they may be the culprit? I think that was the last thing you did?

That's just a few thoughts thrown out there. I don't know really what the problem is, AFAIK nobody here has experienced that.


----------



## CopperFox

baronbeehive said:


> I would think fast acting WCF caps would be more important than high capacity there. The cathode bypass caps are already doing the power handling so what we want for WCF position is something to act fast within the feedback loop in each power tube. Those film Miflexes you mention look to be a good bet.
> 
> Anyway it looks like  you might have the problem sorted. You could also double up the .47 Miflexes, ie connect in parallel to give a combined value of .94uF and see what effect that has on power recovery after bass dips for example. That would avoid having to buy any at the 1uF value.
> 
> I have Audyn True Copper in my other amp as bypasses and I like the copper foil sound.



Did you try the Audyns somewhere in the mkVI at some point, how did they sound there?

I ordered 0,68uf KFPMs today so will see soon about those. Order number 666 from audiomiflex.pl !
Did some resistor upgrades today too. Put in Mills MRAs for 56k and 2k2 resistors near the psu, Audio Note niobium for the 150K resistor and finally put 1K Mills in place of the stock 3K3 "last r" resistors. Those will probably need some burn in now.

One thing I noticed while doing that was the WCF caps were the fourth warmest caps inside the amp after turning it off. Warmest were PSU electrolytics, PSU output films and power tube decoupling caps. The WCF caps had more heat in them than the coupling caps despite being right next to each other and having fans blowing directly at them. So that heat most likely comes from the caps themselves and not their surroundings.


----------



## baronbeehive

CopperFox said:


> Did you try the Audyns somewhere in the mkVI at some point, how did they sound there?


No, I actually ordered a full set because I liked the sound of them in the reviews but sadly they didn't fit for the compact version and I didn't want to extend the chassis at that point so I changed in favour of the Jupiters.


CopperFox said:


> I ordered 0,68uf KFPMs today so will see soon about those. *Order number 666* from audiomiflex.pl !
> Did some resistor upgrades today too. Put in Mills MRAs for 56k and 2k2 resistors near the psu, Audio Note niobium for the 150K resistor and finally put 1K Mills in place of the stock 3K3 "last r" resistors. Those will probably need some burn in now.


Oh dear 🙂.

When you mentioned your resistor findings I assume they were for anodes? Good job putting in Mills at those locations, they shouldn't cause trouble in future.


----------



## Maxx134

CopperFox said:


> Did some resistor upgrades today too. Put in Mills MRAs for 56k and 2k2 resistors near the psu, Audio Note niobium for the 150K resistor and finally put 1K Mills in place of the stock 3K3 "last r" resistors. Those will probably need some burn in now.


That's  excellent.  That's what I  did because wirewound has superior  capabilities.

Also,  I am glad you are addressing  the WCF cap effects  in the circuit.  
It will be interesting to know. 
I am also convinced that a larger size would be beneficial here.
In beginning  of the thread, I did first notice the importance,  and then upgrade them from their meager .22uf stock values,  to a .33uf for a noticeable  improvement.  I think  the reason I didn't go bigger  was that it was early on before I rolled  the output tubes,  and my tubes  were  smaller than the ones in your MK6.



baronbeehive said:


> But it's interesting you said the effect you found disappeared when you put in 4 of the same tubes


Yeah the first thought for me was a tube issue.  A Tube that can perform normal, can also change under stress.


----------



## Maxx134

CopperFox said:


> . So that heat most likely comes from the caps themselves and not their surroundings


Good observation. 
I too did notice all the PSU section gave off alot of heat.
I was especially  surprised how the caps took on heat, especially the last two after the power transistors. 

For those WCF caps to be warm is very good observation that I overlooked. This tells us how much more important it is than I thought.


----------



## CopperFox

While looking at the 6080 tubes' data sheets for clues about temporal stability in operation, there actually were some to be found on the second page in the Tung-sol 6080WA's data sheet.

There in the section "Additional tests to insure reliability",  it is stated that the tube's transconductance can change up to 10% from the specified 7000 micromhos in the _first hour_ of use, may drop to 5800 micromhos in the first 100 hours of use and to 5500 micromhos in the first 1000 hours of use. 

(I haven't found any data on transconductance variation by hours of use in other manufacturers' data sheets(!!))

Those changes would throw off the calculations of the Cavalli formula for the impedance mod quite a bit. If the tube spends most of its life near the 5500 micromhos transconductance rate, then the correct resistance resulting from the formula would be 280 ohms and not 220 ohms, which is the result with the specified 7000 micromhos rate.  

And that 280 ohms is closer to the stock 330 ohms value than the 220 ohms value... so the best resistance value would likely be something other than the result from the spec transconductance.

I don't know how many hours 6080 tubes are expected to last either, but from what I know it would be a lot more than 1000 hours, so the transconductance rate (and average transconductance rate across the tube's life span) may likely drop lower still.

It should be also noted that the 7000 micromhos specified transconductance only applies with specific operating conditions which are listed at the beginning of page 3 of the data sheet, which are Ef = 6.3V, Eb = 135V, Ec = 0, Rk/k = 250 Ohm. (What does that Eb voltage refer to?)

And on the last page of the data sheet there are curves of how the transconductance varies by DC grid voltage and some other variables. How should those be taken into account here?

(I've now removed the impedance mod completely myself but might put it back later on... with _some_ values).


----------



## Maxx134

CopperFox said:


> (I've now removed the impedance mod completely myself but might put it back later on... with _some_ values).


👍 🙂


----------



## Maxx134

When changing my values for impedance mod, I tried different by adding  paralleled resistors,  and noted that the specific tubes I used performed better when I  selected my new value, so I stopped at that point, bit the improvement was of both clarity and holography on the tube, so I  would suggest testing as the formula (as you have pointed out) is not perfect due to variables.


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## baronbeehive (Dec 19, 2021)

Maxx134 said:


> Also,  I am glad you are addressing  the WCF cap effects  in the circuit.
> It will be interesting to know.
> I am also convinced that a larger size would be beneficial here.


Yeah, also a cap like the Miflex film cap type would also be good bearing in mind those .22uF's were Wimas originally.


----------



## baronbeehive (Dec 19, 2021)

CopperFox said:


> While looking at the 6080 tubes' data sheets for clues about temporal stability in operation, there actually were some to be found on the second page in the Tung-sol 6080WA's data sheet.
> 
> There in the section "Additional tests to insure reliability",  it is stated that the tube's transconductance can change up to 10% from the specified 7000 micromhos in the _first hour_ of use, may drop to 5800 micromhos in the first 100 hours of use and to 5500 micromhos in the first 1000 hours of use.
> 
> (I haven't found any data on transconductance variation by hours of use in other manufacturers' data sheets(!!))


This is the trouble, data sheets are all different.


CopperFox said:


> Those changes would throw off the calculations of the Cavalli formula for the impedance mod quite a bit. If the tube spends most of its life near the 5500 micromhos transconductance rate, then the correct resistance resulting from the formula would be 280 ohms and not 220 ohms, which is the result with the specified 7000 micromhos rate.
> 
> And that 280 ohms is closer to the stock 330 ohms value than the 220 ohms value... so the best resistance value would likely be something other than the result from the spec transconductance.


I doubt if the exact figure is important, although it will be more important for 6AS7 types say, than 12AX7 types, as  you have seen tubes vary over their lifetimes so it will always be an approximation, although the Cavalli formula tried to get it right it had to provide several corrections, even then we have this problem of varying over time.

Tubes will vary and there is even the problem of using matched pairs or quads, they in fact will not be matched forever, the only way to tell would be if you happen to have a tube tester.


CopperFox said:


> It should be also noted that the 7000 micromhos specified transconductance only applies with specific operating conditions which are listed at the beginning of page 3 of the data sheet, which are Ef = 6.3V, Eb = 135V, Ec = 0, Rk/k = 250 Ohm. (What does that Eb voltage refer to?)
> 
> And on the last page of the data sheet there are curves of how the transconductance varies by DC grid voltage and some other variables. How should those be taken into account here?
> 
> (I've now removed the impedance mod completely myself but might put it back later on... with _some_ values).


Don't know what Eb is. Here are a couple of references you may or may not find useful, the first explains some of the data like maximum and working values, the second gives in intro into tube load lines and what is important, sorry I can't help more.

https://wtfamps.com/tube-data-sheets/

http://www.diyparadise.com/tubeloadline/tubeloadlines.html


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## baronbeehive (Dec 19, 2021)

Merry Christmas guys, lets hope that next year brings some improvements to all our lives .

Oh and Happy Thanksgiving... and hyvää joulua!


----------



## CopperFox

baronbeehive said:


> Merry Christmas guys, lets hope that next year brings some improvements to all our lives .
> 
> Oh and Happy Thanksgiving... and hyvää joulua!



Hyvää joulua ja onnellista uutta vuotta!

I believe thanksgiving is most often in November... but it is good to be early!


----------



## baronbeehive

CopperFox said:


> *Hyvää joulua ja onnellista uutta vuotta!*
> 
> I believe thanksgiving is most often in November... but it is good to be early!


Thanks!

You're right, I'm getting in early for next year, sorry Maxx!

Say hello to Father Christmas for me, I believe he lives in Finland 🙂.


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## Maxx134

baronbeehive said:


> Say hello to Father Christmas for me, I believe he lives in Finland 🙂.



Haha merry Christmas 🎄


----------



## CopperFox

Well I've hit a bit of trouble now. I bent and broke one of the legs on a vu meter and so decided to replace the meter thinking that would be something that is simple and easy to do. However, after trying two different replacements, apparently neither was identical to the original one and the amp hasn't started up properly since.

The original meter seemed to have a wire inside it that connected the positive and negative current terminals (?). One of my replacements didn't have that. The other one did but after checking its data it is specified to have internal resistance of 1 ohm, while some others that look similar may have for example 680 ohms.

This is rather confusing especially as the replacement meter that didn't have the terminal-connecting wire had product photos that showed it inside a MkVI+.

(Perhaps I could try removing the remaining original meter and put two similar replacement meters to see if that makes any difference. Haven't tried that yet.)

I'm also a bit surprised that my amp won't start up right without those meters in the right configuration. How is the meters' circuit connected to the rest of the system and why would it matter so much?

Looking back at the thread there seems to have been succesful cases of vu meter replacement. Where did people get those meters - from some LD representative or somewhere else?


----------



## Maxx134

Probably can get a replacement from little Dot.
I believe the turn on delay is a cap charging circuit.
Just leave the unit on longer until it switches on.


----------



## baronbeehive

CopperFox said:


> Well I've hit a bit of trouble now. I bent and broke one of the legs on a vu meter and so decided to replace the meter thinking that would be something that is simple and easy to do. However, after trying two different replacements, apparently neither was identical to the original one and the amp hasn't started up properly since.
> 
> The original meter seemed to have a wire inside it that connected the positive and negative current terminals (?). One of my replacements didn't have that. The other one did but after checking its data it is specified to have internal resistance of 1 ohm, while some others that look similar may have for example 680 ohms.
> 
> ...


Bummer . Is the amp completely dead? Could you post a pic of the damaged meter.

I've checked back and the link I used to get my meters on ebay is dead and I have no other record as the purchase history on ebay only goes back a couple of  years.

The fact that a meter isn't functioning properly shouldn't affect the amp it must be something else that happened before you did that. The meters just show the current nothing else. Before I put mine in one wasn't reading correctly, I had blown the circuitry inside, yet the amp was still functioning perfectly. The reason I blew the circuit inside the meter was I had installed a resistor feeding the meters with the wrong value. But your issue of the amp not starting is not the meters.

If I can find out any more information I will let you know but in the meantime the only thing I can suggest, apart from remembering what you did prior to the meter issue, is to search member kinglim on this thread, he might have put in new meters also, he put in virtually new everything. Apart from that try asking Little Dot what meters they use.


----------



## Maxx134

He should take the old broken meter apart to see what is going on. Maybe fix the leg and glue the meter back.
Find out if the new meter damaged or shorted the delay circuit from charging up, to turn relay on.


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## baronbeehive (Jan 30, 2022)

Yeah, if the connector is broken off there should still be something to solder on to. This is where a DIMM would come in handy to check the resistance of the 2 meters to see if they match.

Those wires going into the meters are extremely flimsy.


----------



## baronbeehive

Chassis extension underway to accommodate film caps:


----------



## baronbeehive

Nearly finished:





In case you're wondering the string will be taken off.. that's if it doesn't fall apart LOL.


----------



## baronbeehive

Nearly ready:





... will be even better when it's the right way up...


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## baronbeehive (Jan 31, 2022)

🥵🥴... Phew, now it's the right way up, and it doesn't get any easier, those 2 minutes spent waiting for both channels to come on is a nightmare. I thought I messed up again when no sound came on but then I remembered I moved the DAC and the connection on it is a bit dodgy so now everything is fine .

Following on from the excellent work of CopperFox I finally decided to go from endgame to beyond and that means chassis work as you can see. No more compact version, that's gone out of the window, this is all out for the best possible SQ! So lets see what can be achieved when you pull out all the stops.

First are WCF caps, I've paralleled my .33uF Mundorf SIO metallized polypropylene with some .68uF to take the total to around 1uF. So I will report back when I've burned them in for around 100 hours just to be sure. I'm interested not only in sound, and if there will be oscillations at 1uF, but I will also test whether the frequencies stay level, or will there be clipping on transient recovery after a heavy bass test by checking out the meters. With the existing there is a dip at max volume which I only just noticed, not having had the headphones on at max volume before ever, that's more Maxx's thing 😲.


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## baronbeehive (Feb 1, 2022)

*SMLD MODS: (finished.. er.. sorry.. resumed.. temporarily )

Chassis extension - *

Looks like the Little Dot just turned into the *Big* Dot, it dwarfs my Miniwatt, even with its own chassis extension:





You can follow my mods pages: 50, 53, 55, 57, 62, 65, 66, 68, 69, 70, 71, 72, 147, 179, 230, 231, 234, 253 which include pics. Also Mogos mods are here; 33-38, and SonicTrance here: 23, 43, including some great pics.


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## baronbeehive (Feb 7, 2022)

These are my impressions of the sound after installing 1uF Mundorf SIO metallized polypropylene caps in the WCF position. First it was unfortunate that Foobar decided to alter the order of the tracks that I had previously made some detailed notes on so I have had to listen anew and record my impressions without the notes because I didn't know which tracks they referred to so I had to guess. Fortunately at least the volume remained constant, I had left the volume knob unchanged since the last listening session.

First I have to say I didn't really expect any changes, the sound is already endgame.. but the first thing that hit me was the fuller bodied sound, both instruments and soundstage and the realism was that much greater as a result. I will go in a bit of detail because of the changes. First the bass frequencies as shown by kick drums, drum depth in general and bass guitar, these definately had more impact to the extent that in my notes where I hadn't even mentioned kick drums and bass guitar they were very noticeably more prominent whereas I hadn't noticed before. Another thing that jumped out at me this time was a track where Robben Ford switched pickups in midstream and I clearly heard it this time and the resulting change in tone of his guitar.

IMO this is yet another step up in SQ and I would recommend the change. A similar thing happened when I installed a Brimar tube in my other amp and everything suddenly got that much more powerful sounding and where the frequency band shifted somewhat toward emphasis more on bass. Maybe the cutoff has shifted toward the bass spectrum away from the treble. I would be interested in what CopperFox thinks when he fixes his amp, I know he is a bit of a basshead. The only thing I would say, if you are not so into bass as he is then maybe try an intermediate cap value somewhere between .33uF and 1uF. One thing to say is there is definately no disadvantage in going to 1uF, no oscillation or anything.

Sometime I will do a comparison with my APPJ because that would give a baseline with which to compare any changes, before both amps performed very similarly but this might now have changed.

Next are some cathode bypass Wima's, the reason for the chassis extension. I decided to go for 150uF's, the reason being that I believe the difference between them and the 200uF's that CopperFox has is probably negligable, also they are readily available from Mouser UK.

Going by the cathode bypass calculator the bass roll off starts smoothing out around 150 - 200uF, and the curve from 20hz on is pretty much horizontal anyway. I can't hear anything below 20hz. Then if we say that the equivalent film cap to lytic ratio is 3 - 5 times, if it is 3 times then that is 450 for the 150uF caps and 600 for the 200uF caps. At that capacitance the frequency curve has smoothed out completely and there is no difference between them. Also I have 450uF lytics in currently and I really like the sound atm. If the ratio is 5 times then the frequency curve is pretty much the same as for 3 times so that I believe any gains from the higher ratio capacitance is probably overkill. That means that there is no additional gain from this capacitance, although there is probably no disadvantage either, and CopperFox has not reported any oscillations or any detriment in sound.

That just about takes care of the latest mods except for the PSU. CopperFox has 400uF Wimas in there, but I will probably not change my lytics because they have sufficiently large storage to handle the PSU ripple and any spikes so I don't think there would be any advantage in changing, especially if the cathode bypass Wimas do their job.


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## Maxx134 (Feb 7, 2022)

baronbeehive said:


> One thing to say is there is definately no disadvantage in going to 1uF, no oscillation or anything


Excellent news.


baronbeehive said:


> These are my impressions of the sound after installing 1uF Mundorf SIO metallized polypropylene caps in the WCF position... First the bass frequencies as shown by kick drums, drum depth in general and bass guitar, these definately had more impact...


😮🙂


baronbeehive said:


> Robben Ford switched pickups in midstream and I clearly heard it this time


Excellent  news!

Yes, once you go beyond the frequency design aspect, there are other factors which you noted, that have nothing to do with frequency,  but of power delivery & transients, probably because of a much lower ESR from the larger cap.
Your results highlight the observation of performance gains here, exactly what I was hoping for.
Great work! 👍


----------



## baronbeehive (Feb 7, 2022)

Maxx134 said:


> Excellent news.
> 
> 😮🙂
> 
> ...


Thanks! I forgot to check on frequency response to bass dips, now I've switched off the amp, I will do that next time!

From the shift toward bass frequencies it looks like WCF caps are similar to coupling caps in their performance as has been noted already.

I'm waiting for the Wima film cathode bypass caps and will report on them then.


----------



## Maxx134

Haha I  just noticed you extended the bottom case!
Looks like I may have to do the same! 😄


----------



## baronbeehive

Maxx134 said:


> Haha I  just noticed you extended the bottom case!
> Looks like I may have to do the same! 😄


Just make sure it will still fit in your mum's broom cupboard 🙂.


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## baronbeehive (Feb 8, 2022)

Hey @CopperFox you need to get these 1uF WCF caps, the bass is really really powerful with punch and kick and makes the soundstage so all enveloping, and that's with my HE-500's, not renowned for soundstage! God only knows what symphonic rock would sound like with this mod, brain churning I would think! The sound is more speaker like. High volume is not necessary because the presentation is so dynamic with these caps.. and I haven't even installed the cathode film caps yet, can't wait!

Edit: @Maxx134 I've just done the bass test at max volume and there's no difference in the WCF cap's handling of the power dip, the meters still respond to the power fluctuation just like they did before I put in the larger caps, maybe there will be a difference when I install the cathode film caps.


----------



## Maxx134

baronbeehive said:


> *SMLD MODS: (finished.. er.. sorry.. resumed.. temporarily )
> 
> Chassis extension - *
> 
> ...


 Hey, why you using two different driver tubes?? 😮
maybe you should try some sexy driver tubes (6f8g)?🙂




🙂


----------



## baronbeehive (Feb 9, 2022)

Maxx134 said:


> Hey, why you using two different driver tubes?? 😮
> maybe you should try some sexy driver tubes (6f8g)?🙂
> 
> 🙂


Haha, they're both Tungsols, used them since the start of the amp adventure. Tungsol did do silver glass as well as black glass! That tube does have a slight emission problem so I will be looking to change, would love those sexy ones on the left!! Never liked Sylvanias though, so maybe the Tungsol version at some point.

I was really pleased with the chassis mod it could have gone horribly wrong but luckily it went well. Plenty of WIMA room now:













I was listening again last night... and LOVING the changes!! 

Edit: @CopperFox those clear top Shuguang's have arrived, looking forward to that soundstage, I will burn them in when I get the Wima's.


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## CopperFox (Feb 9, 2022)

baronbeehive said:


> Hey @CopperFox you need to get these 1uF WCF caps, the bass is really really powerful with punch and kick and makes the soundstage so all enveloping, and that's with my HE-500's, not renowned for soundstage! God only knows what symphonic rock would sound like with this mod, brain churning I would think! The sound is more speaker like. High volume is not necessary because the presentation is so dynamic with these caps.. and I haven't even installed the cathode film caps yet, can't wait!



Yes, from my experience with the 0,33uf, 0,47uf and 0,68uf Miflexes and 0,56uf Duelunds it seemed that the higher values had somehow better bass, clarity and soundstage and I have been thinking about trying the 1uf value. The problem there would be the size of the caps with the Miflexes (also price with the Duelunds). The 1uf KPCUs-01s are 44*70mm and eight of them might not fit in my chassis. However, I've been also thinking that for the WCF position maybe the 250V version KPCU-03 would work as it is 44*50mm so some of them could be mounted vertically. The stock caps in the WCF position are rated 250 volts so perhaps that could be enough. I haven't seen any information about the KPCU-03's sound but maybe it would not be very different from the 600v version.

The Duelund JDMs did sound like I've read the Duelund CASTs' sound described so it seems they could be the same as the CASTs but with lower tolerance and different leadout as their Nordic distributor had said. Which makes the JDMs also quite good value. Their sound is still more refined and coherent from the Miflexes. They have more microdetail but to my ears slightly less dynamics than the Miflexes. The bass response is slightly calmer with slightly less impact but more focus on a controlled post-impact. I might need to test them further but I think I may prefer the Miflexes for their slighly rougher and slightly more impactful sound. Or maybe it's just that I've gotten very used to them


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## CopperFox (Feb 9, 2022)

baronbeehive said:


> Chassis extension underway to accommodate film caps:



Looks nice! You went with the screw extenders, how long are those? I've also been considering installing them as the 50mm M3 screws that I have are slightly prone to bending with any lateral force so the extenders could be more stable and need less replacement. What material are those black plates?

About the Wimas I noticed that Digikey has now good stock of the 400ufs. Might get some to have spares.

My amp is still not working but now I have a multimeter and will have time to check some things over the weekend.


----------



## baronbeehive

CopperFox said:


> Looks nice! You went with the screw extenders, how long are those? I've also been considering installing them as the 50mm M3 screws that I have are slightly prone to bending with any lateral force so the extenders could be more stable and need less replacement. What material are those black plates?
> 
> About the Wimas I noticed that Digikey has now good stock of the 400ufs. Might get some to have spares.
> 
> My amp is still not working but now I have a multimeter and will have time to check some things over the weekend.



Thanks!

The standoffs are 60mm, these: https://www.ebay.co.uk/itm/19278746...var=492932372235&_trksid=p2060353.m2749.l2649
The sides were these: https://www.nationalstairnosings.co.uk/retrofit-flexible-pvc-stair-nosings/
The corners were these: https://www.nationalstairnosings.co.uk/aluminium-quadrant-corner-edge-tile-trim-2-5m/

I was looking for aluminium sides but couldn't find any the right size, and the spare computer chassis components were expensive so I went a bit creative with the stair nosings and tile edge trims! The stair nosings were a bit tricky because the corners weren't at a right angle as it looked in the picture but nevertheless I made them fit! Apart from that they were the exact depth to fit with the standoffs. I glued the corners in place with silicone. Amazing what you can do with spare DIY bits and pieces!

Glad to see you've finally got that DIMM, I can't imagine how you managed without it. You mainly need to check your connections for continuity. You can also check the resistance of the meters, check the original to see if the new ones are the same but I don't think the meters are the problem. I suspect one or more of your connections is dodgy, probably something you did just prior to the meters. You can wiggle them a bit to see if they are properly connected, and check the wires and component legs to make sure they aren't loose or broken, and make sure your board's clean.


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## baronbeehive (Feb 10, 2022)

CopperFox said:


> I think I may prefer the Miflexes for their slighly rougher and slightly more impactful sound. Or maybe it's just that I've gotten very used to them


I'm loving the sound atm with the Nichicons still in place so can't really imagine much improvement with film caps.. but if they do.. then that would be good! The bass is almost too strong for me now, nevertheless the sound with them in place has stepped up even more and is comparable to listening to a live performance with all that bass impact and drums, good depth and holography to that immersive soundstage, just amazing!


----------



## baronbeehive

*** Hey Maxx, I see you've restored all the picture links! That must have been almost as exciting as watching paint dry 😍🤩🥳👍. Now the thread is fun again!


----------



## Maxx134

baronbeehive said:


> *** Hey Maxx, I see you've restored all the picture links! That must have been almost as exciting as watching paint dry 😍🤩🥳👍. Now the thread is fun again!


I ddn do it...😮

Also, I forgot that I did extend my chassis a half inch(!) 😅




🙃🙂


----------



## Maxx134

baronbeehive said:


> almost as exciting as watching paint dry 😍🤩🥳👍....


Haha actually, I actually have been watching paint dry!



Finishing some gloss coats today... 😀


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## baronbeehive (Feb 13, 2022)

Maxx134 said:


> I ddn do it...😮
> 
> Also, I forgot that I did extend my chassis a half inch(!) 😅
> 
> ...


Haha, who the hell did then? It looks even better than before .

Hey great to see that crazy amp again 👍.

I don't think half an inch is enough for those Wimas 🙂. My extension is 60mm and even then it's a tight squeeze for the 150uF cathode bypass Wimas which I just put in today.

I'll give it a week's burn in and comment on it then .


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## baronbeehive (Feb 14, 2022)

*SMLD MODS: (finished.. er.. sorry.. resumed.. temporarily..... finished.. again!)

1uF Mundorf SIO WCF caps, 150uF Wima cathode bypass caps




*

The finished amp 🤒🥴🤕. Only just enough room for those Wimas, even with the chassis extension. That's the best position for them closest to the connections. Fortunately they are positioned right under the fans... I didn't plan that... so if they are a tad warm they should get ample cooling. (The cardboard is mounted on some silicone filler to meet up with the base when it is screwed on).

Nearly every square inch of the insides is taken up now!

Good feeling now that it is finished... well maybe some bling next, see if I can outdo Maxx with the LED flashing lights around the chassis... hmmmm.... 😅🥳

You can follow my mods pages: 50, 53, 55, 57, 62, 65, 66, 68, 69, 70, 71, 72, 147, 179, 230, 231, 234, 253, 273 which include pics. Also Mogos mods are here; 33-38, and SonicTrance here: 23, 43, including some great pics.


----------



## baronbeehive

@CopperFox I just checked the resistance of the meters while I was inside the amp, it is 0.4R in place.


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## baronbeehive (Feb 20, 2022)

I've burned in the Wima film cathode bypass caps and my impression is that the film caps have a smoother sound, less dynamic than with the lytics I had before, not as much textural detail and a tad boring if I'm honest. I was a bit surprised because I thought that film caps would provide the most changes, more so than the WCF caps that I had just increased to 1uF recently, but the opposite is the case. With that change the difference was quite striking, more weight and body to the sound and therefore more dynamics and also a more pronounced soundstage with all that going on. So I've decided to change back to the lytics because I'm really missing the sound I got after the last change. I'm slightly surprised because I'm not that much of a bass head but I've missed that lively sound.

The film caps were 150uF and it's possible that 200uF would have made more of a difference but I don't think so going by the frequency curve from the cathode bypass calculator which is virtually identical for the 200uF. Maybe it might have affected the cutoff and let in more bass but I don't think so.  I feel that this might be a characteristic of film caps that they have a flatter, more seamless sound.

The reason I wanted to try the film caps in that position was to see if the sub bass could be tightened up a bit with the increased speed and lower ESR but I couldn't really tell any difference.

The upshot of this is that maybe an extended chassis isn't necessary for top level sound so it might be preferable to save all that effort 🥴.

Edit: I also tried the dynamic test and as with the WCF caps this was the same as before, ie. there were still bass dips as shown on the meters so no increased power handling capability with the Wimas.


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## baronbeehive (Feb 20, 2022)

CopperFox said:


> The Duelund JDMs did sound like I've read the Duelund CASTs' sound described so it seems they could be the same as the CASTs but with lower tolerance and different leadout as their Nordic distributor had said. Which makes the JDMs also quite good value.* Their sound is still more refined and coherent from the Miflexes*. They have more microdetail *but to my ears slightly less dynamics than the Miflexes. The bass response is slightly calmer with slightly less impac*t but more focus on a controlled post-impact. I might need to test them further but *I think I may prefer the Miflexes for their slighly rougher and slightly more impactful sound. Or maybe it's just that I've gotten very used to them*



Yes I remembered you said something similar, (highlighted above). *That is exactly how I felt about the Wimas!*

Still you don't know until you try.

Edit: I will try the Shuguangs next while I have the Wima's in.


----------



## CopperFox

baronbeehive said:


> @CopperFox I just checked the resistance of the meters while I was inside the amp, it is 0.4R in place.



Now that I've measured the resistance of the vu meters I have, they are all slightly below 1R between 0,7R to 0,9R (stock and two kinds of replacements). So that doesn't seem to be the issue.

I've been also looking around the amp to see if there is anything that looks wrong - spent three hours on that today. Still on my latest attempt to boot the amp up there's no sound, only the left meter lights up and moves to about 10ma and the right side doesn't move.



baronbeehive said:


> I've burned in the Wima film cathode bypass caps and my impression is that the film caps have a smoother sound, less dynamic than with the lytics I had before, not as much textural detail and a tad boring if I'm honest. I was a bit surprised because I thought that film caps would provide the most changes, more so than the WCF caps that I had just increased to 1uF recently, but the opposite is the case. With that change the difference was quite striking, more weight and body to the sound and therefore more dynamics and also a more pronounced soundstage with all that going on. So I've decided to change back to the lytics because I'm really missing the sound I got after the last change. I'm slightly surprised because I'm not that much of a bass head but I've missed that lively sound.
> 
> The film caps were 150uF and it's possible that 200uF would have made more of a difference but I don't think so going by the frequency curve from the cathode bypass calculator which is virtually identical for the 200uF. Maybe it might have affected the cutoff and let in more bass but I don't think so.  I feel that this might be a characteristic of film caps that they have a flatter, more seamless sound.
> 
> ...



For me the Wimas took about eight weeks to burn in, with treble detail and sharpness improving along the way. 

The difference in bass to the Nichicons was also quite clear. The Nichicons in comparison had an elevated, higher-than-neutral midbass response/impact but were smeared below that - and also that edginess in the treble (I previously described those as "burst-like or jagged characted") . Which made me think they are designed to sound that way to be nice while masking the limitations that electrolytics have -  The Wimas' sub-bass sounds more powerful and detailed but they don't highlight midbass in a similar fashion. With the Wimas the lowest sub-bass detail was no longer markedly worse than with my solid state amps. 

There may be also some more tuning options to have some of those electrolytics' characteristics _without_ the sub-bass deficit and other issues... (While trying different resistance values for the impedance mod, I once put 2,2k 5W Kiwame resistors in parallel with the 330R Mills MRA to get to 290R... and the sound with the parallel Kiwame resistors there was quite different and reminded me of the Nichicons. That was actually one thing I was going to experiment with next - putting various audio resistors in that position).



baronbeehive said:


> Yes I remembered you said something similar, (highlighted above). *That is exactly how I felt about the Wimas!*
> 
> Still you don't know until you try.
> 
> Edit: I will try the Shuguangs next while I have the Wima's in.



Hmm, my feeling of the Duelunds so far is that they sound like they are designed to make speakers sound pleasant and refined... which they are.

I'm afraid the 6N5PJs may still have that softness without the film psu output caps - at least for me the combination of film decoupling caps and film psu output caps was what made them sound good.

While not having a working MkVi I've done some mods to my iFi Pro iCan after seeing it had six Elna Silmics in the signal path. Well they are now Nichicon KZs and the tubes are now Tung-Sols. Actually ordered more of the 200uf 400v Wimas for it too. Unfortunately its case can't be extended without being completely mangled.


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## baronbeehive (Feb 20, 2022)

CopperFox said:


> Now that I've measured the resistance of the vu meters I have, they are all slightly below 1R between 0,7R to 0,9R (stock and two kinds of replacements). So that doesn't seem to be the issue.
> 
> I've been also looking around the amp to see if there is anything that looks wrong - spent three hours on that today. Still on my latest attempt to boot the amp up there's no sound, only the left meter lights up and moves to about 10ma and the right side doesn't move.


Don't think it is the meters, probably the same as mine if you measured them in situ in the amp.

You say you have looked around the amp, what have you done, have you tested all the connections you made for continuity, especially the recent ones you did. Just look at all the connections and test them along the trace on the board with neighbouring connections which should show continuity, if not that is the fault. I know for example that a bad connection I had was only revealed when I repositioned some parts inside the amp before closing it up. That had exposed a bad connection which had moved when I repositioned the parts. I suspect something similar with your amp, it was working fine up until recently?

Keep us informed, we'll try to help.


----------



## baronbeehive

CopperFox said:


> For me the Wimas took about eight weeks to burn in, with treble detail and sharpness improving along the way.


I could try burning them in a bit more, I've spent 100 hours though. How much did you do?


CopperFox said:


> The difference in bass to the Nichicons was also quite clear. The Nichicons in comparison had an elevated, higher-than-neutral midbass response/impact but were smeared below that - and also that edginess in the treble (I previously described those as "burst-like or jagged characted") . Which made me think they are designed to sound that way to be nice while masking the limitations that electrolytics have -  The Wimas' sub-bass sounds more powerful and detailed but they don't highlight midbass in a similar fashion. With the Wimas the lowest sub-bass detail was no longer markedly worse than with my solid state amps.


That is impressive, I think your PSU film caps might have helped overall. I don't intend to change mine. I don't think my HE-500's pick up a lot of sub bass anyway.

It's possible that film caps would be as good as you say, because of the feedback from members at the beginning of the thread, but they haven't worked for me so far, at least without going the full distance and changing PSU and uprating decoupling caps. But I really liked the dynamics of the uprated WCF caps and could easily overlook the slight sub bass deficit with my current headphones.


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## baronbeehive (Feb 21, 2022)

CopperFox said:


> For me the Wimas took about eight weeks to burn in, with treble detail and sharpness improving along the way.
> 
> The difference in bass to the Nichicons was also quite clear. The Nichicons in comparison had an elevated, higher-than-neutral midbass response/impact but were smeared below that - and also that edginess in the treble (I previously described those as "burst-like or jagged characted") . Which made me think they are designed to sound that way to be nice while masking the limitations that electrolytics have -  The Wimas' sub-bass sounds more powerful and detailed but they don't highlight midbass in a similar fashion. With the Wimas the lowest sub-bass detail was no longer markedly worse than with my solid state amps.


Thinking about these Wimas I will give them a bit more burn in time and see what happens.

My feeling after that fantastic dynamic, rich tone I had before, after installing the uprated WCF Mundorf caps is that that is the sound I am happy with. If it's detail and sharpness then I have all the clarity with the CCS in place and don't really want too much sharpness in sound because I'm loving the tone from the new WCF caps now. So that is probably not the type of tone I want with the Wimas.

I agree with you about the sound with the Nichicons but could limit the elevated midbass with a slightly lower WCF value if that is what I want. And I can overlook the smearing of the subbass you mention because I don't hear that much with my headphones and I don't want too much subbass.

Speaking of that jagged treble sound I'm wondering if that could be lessened with non polar caps such as non polar Kaisei's, maybe. I'll think about whether to do that or reistall my Nichicons.

Finally I think that as you say in order to achieve the full advantages of the film caps it would be necessary to install the PSU caps as well, don't know if I want to go down that road though. And it all comes down to synergy. Your headphones are bassy I think and you like bass, whereas I don't like heavy bass, I prefer more of a balanced sound across the frequency band. So I think I may have hit on the right combination for me. I would certainly be happy with the higher value WCF caps and the overall sound as it is for good.


----------



## CopperFox

baronbeehive said:


> I could try burning them in a bit more, I've spent 100 hours though. How much did you do?



Hmm it's hard to say how much exactly but it must have been somewhere around 300 hours. I do remember that it was the treble in particular that would improve in sharpness, detail and variety over time. The burn-in took a longer time than for any other component I've installed so far. 



baronbeehive said:


> Finally I think that as you say in order to achieve the full advantages of the film caps it would be necessary to install the PSU caps as well, don't know if I want to go down that road though. And it all comes down to synergy. Your headphones are bassy I think and you like bass, whereas I don't like heavy bass, I prefer more of a balanced sound across the frequency band. So I think I may have hit on the right combination for me. I would certainly be happy with the higher value WCF caps and the overall sound as it is for good.



My feeling about the Wimas is that they are both technically proficient with their ability in bass and treble detail - and that they are also quite neutral and I hardly ever call anything neutral. And I don't really believe that people actually want a neutral sound, but a sound that they like. The advantage of a component having a neutral sound, such as here with the cathode bypass caps, would be that they would allow the other components in the system to further show their character instead, such as tubes or resistors or wiring, other capacitors and so on.

So if the goal would be have a sound with some characteristics that the Nichicon KZs there would have, it may be achieved with choice of other components such as driver and power tubes, wires, resistors etc, without some of the deficiencies that the Nichicons may have. That's one reason I'd find the Wimas preferable.


PSU output caps in general are among the components that from what I've seen on various audio devices will have the greatest effect on amount of some forms of distortion.


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## baronbeehive (Feb 21, 2022)

CopperFox said:


> Hmm it's hard to say how much exactly but it must have been somewhere around 300 hours. I do remember that it was the treble in particular that would improve in sharpness, detail and variety over time. The burn-in took a longer time than for any other component I've installed so far.
> 
> 
> 
> ...


Some good points there, I will persist a bit longer. Certainly so far the Wimas haven't really shown what I would have expected, treble not very clear and bass not improved over the lytics so far. Also being polypropylene, and especially being non polar I thought would give them a considerable advantage. So maybe as a dry construction unlike lytics that is the reason for the long burn in time.

If they do indeed allow the newly installed WCF caps to shine then it will be worth it. I had thought that the increased dynamics of the uprated WCF caps would pair nicely with cathode bypass film caps.

I have to say I do like the treble tone with the Nichicons and WCF Mundorfs atm before installing the Wimas, it is clear, extended and has a nice bite without being harsh. We shall see after some more burn in time what happens!

I looked at the Kaisei non polar but decided against trying, the 25v ones are around £11 but the price rises dramatically for anything over that, as I like the Nichicons already I might stick with that.

I do already have adequate value decoupling caps and you are quite right that PSU demands a careful design which is why regulated power is so important, and that's why I've gone some distance toward that with the CCS. After installing that I did notice a cleaner sound, but I don't want to lose all of the tube.. some would say distorted.., sound. So even without the film PSU caps I think my system should be adequate as is.


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## Maxx134 (Feb 21, 2022)

baronbeehive said:


> Thinking about these Wimas I will give them a bit more burn in time and see what happens


Noooooo... garbage! 😅



baronbeehive said:


> I have to say I do like the treble tone with the Nichicons and WCF Mundorfs atm before installing the Wimas, it is clear, extended and has a nice bite without being harsh. We shall see after some more burn in time what happens!


The red wimas were never meant for audio path.
Yes they have good pulse ratings, for PSU, but never designed specifically for audio.  
They are PSU caps, which you will see some cheapo companies use for audio path. Only the blue ones I ever saw used in expensive gear.

Sometimes you have to follow what the design intention is for.  I would not use the red ones for audio, just for the PSU.
Of course I have read that they are nice and smooth..(flat!).
BUT, You won't get any more positive impressions than that. 🥲

So since we going for top sound, I will be using silver for WCF cap and some other nice electrolytics for supplement my cathode cap.
I already have the .1uf rifa "paper-in-oil" paralleled in there on top-side of board, for the highs, so that stays for me.
🤑🙂



CopperFox said:


> I've been also looking around the amp to see if there is anything that looks wrong - spent three hours on that today. Still on my latest attempt to boot the amp up there's no sound, only the left meter lights up and moves to about 10ma and the right side doesn't move


You need to check the wiring going to the meters, because as I recall, that wiring is made of a cheap, brittle metal, so I would make sure that the wiring connections from that right meter to the board are not open or shorted. Hope that helps.



CopperFox said:


> PSU output caps in general are among the components that from what I've seen on various audio devices will have the greatest effect on amount of some forms of distortion


The PSU output caps here are large electrolytic which are then supplemented by the "decoupling"  film caps by the output tube PSU area, so I feel this is already covered enough for me. 👍


----------



## baronbeehive (Feb 23, 2022)

Maxx134 said:


> Noooooo... garbage! 😅


Hehe  😭.

I can't afford a V-Cap .


Maxx134 said:


> Only the blue ones I ever saw used in expensive gear.


I think these are the very small wimas with low values AFAIK.



Maxx134 said:


> Of course I have read that they are nice and smooth..(flat!).
> BUT, You won't get any more positive impressions than that. 🥲


Since I have gone down this path I want to see for myself so I'll give it the benefit of the doubt.



Maxx134 said:


> So since we going for top sound, I will be using silver for WCF cap and some other nice electrolytics for supplement my cathode cap.
> I already have the .1uf rifa "paper-in-oil" paralleled in there on top-side of board, for the highs, so that stays for me.
> 🤑🙂


That should be excellent. If you're going for Mundorfs they have the same construction as film caps - metallized polypropylene but the electrolytic is oil, so should be some qualities of both.

Hey what about those non polar Kaiseis for cathode bypass?


Maxx134 said:


> You need to check the wiring going to the meters, because as I recall, that wiring is made of a cheap, brittle metal, so I would make sure that the wiring connections from that right meter to the board are not open or shorted. Hope that helps.


I blew open one of my meters and it didn't make any difference to the amp the voltages were all good. I think he should check his connections first with a DIMM.


Maxx134 said:


> The PSU output caps here are large electrolytic which are then supplemented by the "decoupling"  film caps by the output tube PSU area, so I feel this is already covered enough for me. 👍


Yep, agreed 👍. The PSU lytics have a huge capacity to meet the requirements on them. But I do think that for PSU those film Wimas would provide fast power to beef up the PSU also, so you pays your money and you takes your choice as they say.


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## baronbeehive (Feb 22, 2022)

Just been looking up opinions on Wimas, I haven't done this before. It seems this one quite likes it: https://www.enjoythemusic.com/diy/1108/capacitor3.htm

whereas this one doesn't think that much: https://www.humblehomemadehifi.com/Cap.html

so in view of the fairly low ratings I've decided to give mine one more weeks burn in and if no noticeable improvement I will jettison the idea. Anyway at least I've tried but I'm still thinking of that dynamic, lively sound I heard before with the uprated WCF caps, can't wait to go back to this. I think that will be it re: cap trials.

And I now have a pretty good impression of film caps, at least the ones which don't have to be brought in on a HGV 🙂.

Edit: @CopperFox I was interested if you had done the dynamic test at full volume, if your Wima's are performing as would be expected, especially your PSU caps, then I would expect very little movement with the meters on bass dips, and this is one area I would expect the film caps to be superior to lytics. If so then we will know that the PSU is a good place to put those caps, as well as decoupling, even if opinion varies over the cathode bypass position.


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## baronbeehive (Feb 23, 2022)

Guys! I was just checking out those non polar Kaisei's and I came across this in someone's DIY build thread where he mentions putting in the Kaisei's after having no bypass caps in at all... _"The difference is pretty BIG! With the cathodes bypassed, there is a collpase in the soundstage, instrument separation suffers, there is less definition in the bass, and the high end sounds more harsh. It isn't subtle whatsoever. The amp doesn't sound bad with the cathodes bypassed, but once you've heard them unbypassed, no way you could go back. Audio quality is all relative after all. I did do some FFT measurements, bypassing the cathode resistors doesn't seem to affect distortion in a measurable way."_

I remember coin saying something similar way back in the thread.

Could this be the way to go I wonder?

Edit: OK, maybe  not. Here's another quote _"No bypass means higher output impedance (cathode resistor x mu + rp) which may or may not be an issue depending on the following stage. The reason gain is lower is because the unbypassed cathode resistor introduces degenerative feedback which like all feedback reduces gain, but also reduces stage distortion. Again this may or may not be an issue depending on the linearity of the gainstage been used. That is to say a linear triode with bypass will have lower or equal distortion than a unlinear gainstage with dengenerative feedback.

Its about the design and the choices which are appropriate to the design. As an example I would use a no bypassed input stage if the loading of the preceding stage was light - such as a cathode follower. This would give lower overall distortion at the cost of a slight loss of gain."_

I believe it  might work in conjuction with a CCS such as I have but don't know if it would be worth it.

BTW it looks as though there might be no difference between polar or non polar with small voltages of around 1 or 2v. As I remember the voltage drop over the cathode bypass is 10v so that is something that could be determined experimentally.


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## baronbeehive

Haha, I didn't expect this.

First the Wimas with Shuguang power tubes:

Hey @CopperFox I've got most of my dynamics back! Over 200 hours burn in and with the Shuguangs in, it was worth sticking with it. As you said the sound has become clearer and opened up a lot, treble is nice  and bass weight good and soundstage very good. Everything is there, I would say it's a tad warm and mellow and only the sharp edges are missing but if it's mellow you want this is it. I don't really see the sub bass tightening up that much though which is the reason for trying the Wimas.

Now with RCA's. As above except I've now got *ALL* of my dynamics back!! Not only is the sound clear as a bell and those Wimas have really opened up. The sound is seamless. Treble is back as before Wimas went in, bass is a tad tighter than before I believe and soundstage is a tad better than Shuguangs. The mellowness has gone and the attack has come back and these RCA's are really hitting the spot.

So I believe CopperFox is spot on when he says that the Wimas allow the other things in the setup to shine.

Given that there could be yet more to come after 200 hours burn in I shall stick with this for the time and live with it until deciding what to do next but I'm very happy.


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## Maxx134

baronbeehive said:


> Shuguangs


This is good to know, as the one I have  we're a bit soft/dull, so I never gave them the chance to break them in..


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## Maxx134 (Feb 26, 2022)

baronbeehive said:


> That should be excellent. If you're going for Mundorfs they have the same construction as film caps - metallized polypropylene but the electrolytic is oil, so should be some qualities of both.
> 
> Hey what about those non polar Kaiseis for cathode bypass?


Even tho Iike the mundorf very much, I am striving for treble clarity instead of sweetness,  so I  will try some others.

About the kaiseis for cathode bypass,  I am actually undecided on that area yet.
I'm worried that the kaisies might be darker than the Nichicons.




baronbeehive said:


> But I do think that for PSU those film Wimas would provide fast power to beef up the PSU also


I agree they should be perfect for using as the decoupling caps by the output circuit stage, but I (we) already have film caps there.



Remember?
That's why I keep saying this issue is moot. Any film cap ESR gains by the PSU area, is totally wasted, if not put directly next to the output tube circuit area. That's the whole reasoning for the "decoupling caps".



baronbeehive said:


> Guys! I was just checking out those non polar Kaisei's and I came across this in someone's DIY build thread where he mentions putting in the Kaisei's after having no bypass caps in at


Nah, the decision on wether a cathode cap is optimal in a given circuit, is basically depending on the design.
That's why that guy had issues.

Yet our WCF output circuit design is meant to have one 👍 

I seen single ended driver stages without a cathode cap(only the resistor), but it was designed to be that way (less gain, more linearity).

Our driver stage is devoid of one as well, but it's Totally different design.


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## baronbeehive (Feb 27, 2022)

Maxx134 said:


> Even tho Iike the mundorf very much, I am striving for treble clarity instead of sweetness,  so I  will try some others.
> 
> About the kaiseis for cathode bypass,  I am actually undecided on that area yet.
> I'm worried that the kaisies might be darker than the Nichicons.


Yep, what about V-Caps? Possibly a bit over the top for cathode bypass.

Yes but the Nichicons don't do non polar KZ's.


Maxx134 said:


> Remember?
> That's why I keep saying this issue is moot. Any film cap ESR gains by the PSU area, is totally wasted, if not put directly next to the output tube circuit area. That's the whole reasoning for the "decoupling caps".


Definately! I could not physically get them any closer!



Maxx134 said:


> Nah, the decision on wether a cathode cap is optimal in a given circuit, is basically depending on the design.
> That's why that guy had issues.
> 
> Yet our WCF output circuit design is meant to have one 👍
> ...


Yeah! 👍

Re: the cathode bypass position, I now believe that film caps.. maybe not Wimas if you don't like them.. are a good bet for this position. This is because it is not only about sound but largely about power handling which film caps excel at, as coin and others found early on in the thread with their huge monster caps. I definately think bass definition has sharpened up and the weight is substantial too. As I said above after 200 hours the sound is as I had  heard just after I put in the uprated WCF caps, and with some burn in time left it can only improve further. The sound is dynamic and flows beautifully so I'm thinking of keeping them in as there would be nothing to be gained by putting back the Nichicons. I'm a bit shocked frankly 🙂🙃.


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## baronbeehive

Well I've had time getting used to this new setup with 1uF WCF Mundorf SIO caps and 150uF Wima film cathode bypasses and I'm absolutely loving it! So I will give you a run down of the changes

Forget about the Wimas being dull and boring, I can now tell you that they are exciting and dynamic, yes you heard me right! In fact it is every bit as visceral as it was with the Nichicons in which makes me think that having film caps in the cathode bypass position shows the other parts to their best such as the WCF and Coupling caps. The difference with them in, between them and Nichicons is small but I think the resolution with Wimas is even a tad better because I'm hearing things I never noticed before.  And that soundstage is all enveloping.

The bass deficit in mid to subbass with a soft sound the lower you go down has all but gone, with the bass now it is like there is a whole new dimension to music which I really like. I listened to an album that had bass which was very difficult to hear at all originally and it sounds really excellent now, punchy, powerful, but not overly so, and good definition.

Treble is still there and the extension is excellent so there is no loss at that end of the frequency band.

So I'm very happy with the end result, I believe the amp has gone from endgame to the beyond to an unknown galaxy of audio nirvana and they let me in there for a moment to enjoy their civilization where they listen only to the highest resolution music such as you would never normally hear back on earth.

To give an example of the piano the weight is perfect to reflect the real instrument with attack and timbre, solid bass notes and treble ringing out with superb definition.

This set up is staying for me! The uprated WCF caps give excellent weight to the sound, similar to uprated coupling caps so if it's bass you want you could do either with probably the same results. The Wima's are a must in the cathode bypass position now, they allow the music to flow. Looks like the 150uF is about right although CopperFox is happy with 200uF so there is probably leeway there.

So the changes are highly recommended!


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## Maxx134

I need to add this info to beginning thread. This is excellent news.


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## baronbeehive (Mar 12, 2022)

Maxx134 said:


> I need to add this info to beginning thread. This is excellent news.



I've put together a handy one stop shop with all the finished mods gathered together in one place to save time looking through the thread, so anyone who's interested can see at a glance without having to trawl through the entire 270 odd pages. Even I started to lose interest after the first few pages! Quite a lot has happened since page 1 and the amp has been pushed to endgame and beyond since.






This is practically all the mods that can be done without a complete rebuild.

The mods (not covered in page 1 except for no 1):

1 - 5998/421A Bias switch mod (increased 5998 power) - Page 1
2 - Impedance mod (match with headphone impedance) - Conversion chart on Page 258
3 - Bias point mod (6SL7 tubes only) (optimum operating point) - Page 179, 230
4 - CCS (6SL7 tubes only) (constant current regardless of voltage) - Page230, 231
5 - Active filter (clean B- supply) - Page 234

The parts (alternatives in brackets):

Output wires - Neotech STDST-24 OCC silver (copper) wire
Main wires - 3 core 22AWG silver plated PTFE wire

Caps:

PSU caps - Mundorf M-Lytics AG 1500µF 160V (Wima DC Link MKP4 400uF (*film)) x 2
Output stage decoupling caps - Mundorf Mcap 47uF, 250V (Wima DC Link MKP4 100uF(*film)) x 4
Driver stage decoupling caps -  Wima DC Link MKP4 40uF - (100 µF Wima DC Link MKP4(*film))  800V 10 % x 2
Cathode bypass caps - Nichicon KZ 470uF 50V (Wima DC Link MKP4 150uF - 200uF(*film)) x 4
Coupling caps - Jupiter Copper Foil Paper and Wax 0.47uF 400VDC (Any other .47uF - 1uF) x 4
WCF caps - Mundorf MCap Supreme Silver in Oil 0.33uF - 1uF uF 1200V 2% (Any other .33uF - 1uF) x 4

Resistors and diodes (refer to diagram):

(See page 270 for a discussion of the SQ of different brands carried out by member @CopperFox .

1 - Mills MRA5 165R x 1 (Optimized for 6AS7 tubes) (or 330R in parallel with stock 330R's) (Left side shown)
2 - Mills MRA5 330R x 8
3 - TKD 2w 69K metal film x 4 (Optimized for 6SL7 tubes) (or 52K in parallel with stock 220K's) (Left side shown)
4 - Mills MRA5 1K x 2 (Left side shown)
5 - Mills MRA5 8K2 x 2
6 - Mills MRA5 5K1 x 2
7 - Mills MRA5 2K7 x 1
8 - 100v 2W (or higher W) Zener diode
9 - 100v 2W (or higher W)Zener diode
10 - Mills MRA5 2K2 x 1
11 - Mills MRA5 165R x 1 (Optimized for 6AS7 tubes) (or 330R in parallel with stock 330R's) (Right side shown)
12 - Mills MRA5 165R x 2 (Optimized for 6AS7 tubes) (or 330R in parallel with stock 330R's) (Centre shown)
13 - Shinkoh tantalum 1W 380R x 2 (Optimized for 6SL7 tubes) (Right side shown)
14 - Mills MRA12 56K x 2

Transistors (uprated):

1 x MJ15024G (NPN) for B+
1 x MJ15025G (PNP) for B-

* - needs chassis extension to fit

Edit:

Footnote: In keeping with the thread, like all the mods in page 1, by @Maxx134 and others, these mods have all been tested and found to add significantly to the performance of the amp. The impedance mod was not fully implemented at the page 1 stage, the same for the bias point mod, but several members have subsequently done so. The CCS was implemented by SonicTrance and myself later, and the active filter by myself only. Also changes to the WCF caps and cathode bypass caps were further modified at a later stage by @CopperFox and myself for optimum values and types of cathode caps

The performance gains of all these mods are significant and add to the gains from page 1, it has to be heard to be believed!

Finally the amp continues to perform after years without issues, and I am confident that the testing carried out had has been done to a good standard and that the outcome is enough to satisfy anyone that hears the results.


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## Maxx134 (Mar 11, 2022)

baronbeehive said:


> Right! You could stick this in if you want, might be useful to refer to.
> 
> 
> 
> ...


Thanks. I was only able to post this on my first post as I am not thread starter.

So I  posted it there.

I am a thread starter at:
https://www.head-fi.org/threads/oblivion-ultrasonic-studios.902926/
So I  also have to go over there and see what needs to update.
So yeah those are my two fav all time amps.
I still haven't side-by-side compared and when anyone ask I still recommend the other amp for not having to mod, and this thread for learning about what mods do for tube amps, and the only tube amp I would recommend to mod, as practically all other tube amps near this range are single ended and multiple times more expensive.

Actually if you wanted a balanced tube amp other than this, you literally and certainly be spending thousands..
So yeah this caliber mod I certainly would choose over all what's available in traditional design.

Yet there are different roads to get to same top level, and honestly I could not recommend any other design choice route except for the Ultrasonic amps. Otherwise your playing with mega thousand amp just to reach same peak.

Regardless, I love other tube  designs, such as the Cayin HA300 I recently moded, and right away I saw the intentional placement of specific "non-audio" version of an electrolytic brand, in the "cathode cap" placement,  which was a deliberate tunning for harmonics, proving that designers all have their own "recipes" for thier preferences/success.

But the bottom line is that once a device reaches a pinnacle, it's all a matter of signature preferences.
For instance,  I upgraded a Cary 300b speaker amp which also was fantastic and was also modded for headphones.
So yeah different paths to reach the goal.

This thread has been a huge learning and growing experience.  There is much to gain from many visitors.
If your a classic style tube enthusiasts, you will learn details on tunning amp here,  but if you not want to mod, the Ultrasonic amps are the way to go, although I assume you would not be in this thread to  begin with 😄...


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## baronbeehive

I've just added a footnote to the summary of mods above .


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## baronbeehive (Mar 12, 2022)

Maxx134 said:


> ...
> So yeah *those are my two fav all time amps*.
> I still haven't side-by-side compared and when anyone ask I still recommend the other amp for not having to mod, and this thread for learning about what mods do for tube amps, and the only tube amp I would recommend to mod, as practically all other tube amps near this range are single ended and multiple times more expensive.
> 
> ...


Yeah 👍.

The amp is superb! I'm even satisfied with the WCF design after an initial scepticism as I feel it is an excellent way of getting the Impedance down and the power up without compromising the OCL design 🤩🥳😍.

Edit: Hey.. you forgot the little APPJ!!!


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## Maxx134

baronbeehive said:


> Edit: Hey.. you forgot the little APPJ!!!


Haha yeah I still have one... it's too cute to get rid of.


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## Maxx134

baronbeehive said:


> 5 - Active filter (clean B- supply) - Page 234


I literally overlooked this..!
Ugg I don't have that one done, , lol


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## baronbeehive

Maxx134 said:


> I literally overlooked this..!
> Ugg I don't have that one done, , lol


Yeah, it's nice to know it's there but it doesn't do anything for sound as MrCurwen said. Looks like you may have a few things to catch up with .

I don't see how this amp can be improved further so that's more or less it for me . The last Wima cathode bypass mod surprised me. It really improved some aspects, mainly the bass which is now really good so I'm very happy!

Be nice to see the cash disappearing down some other pit for a change... hmmm perhaps headphones update???

Hey Maxx, so what's new in NYC, anything going on?

... and what's happened to CopperFox, haven't heard from him for a while.


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## Maxx134 (Apr 30, 2022)

baronbeehive said:


> I don't see how this amp can be improved further so that's more or less it for me



There is nothing new under the sun...

**No new amp is going to eclipse anything TOTL that's already out.
**No new headphones is going to eclipse anything TOTL that's already out.
** IEM market is starting to reach it limits with more and more approaching TOTL levels, and many IEMs already superior to most of the headphone market.
**Daps are finally reaching limits to the level that topologies don't matter anymore (R2R, Delta-sigma, discreet FPGA). Only thier amplification stages will matter.
** Desktop setups will face overlapping competition with portable DAPs performing at above desktop levels. Only TOTL setups will still have slight edge.
At this point,  a good Dap coupled with a good tube amp is all you will ever need for all solutions.
Throw away the computer setups.




baronbeehive said:


> Hey Maxx, so what's new in NYC, anything going on?


Nothing is up in NY except ghost town zombie land events. The thriving metropolis which used to be crowded in the streets, both day and night, is now a zombieland.

The NY vaccine mandate ruined the CanJam potential of more visitors.
Stupid NY libtard politics lifted the mandates only after CanJam timing, so at least now you can visit Audio stores withouta mask.

I don't see ANY closed headphones today of any value,  when it's purpose&value is totally eclipsed by IEMs.
Not one closed headphones today can match even a mid tier IEM.
I view desktop closed headphones a total waste.
The small portable headphones will always have a good market, but even cheapo Bluetooth earbuds can replace them.

So basically you can be "golden" with just a top desktop open headphones like HD800 or HEKV2, and a top IEM for closed usage.
Those two types can be all you need, if you was to narrow down the hobby with just two units.
Everything else is a futile sea of never-ending mediocrity.


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## baronbeehive (May 1, 2022)

Maxx134 said:


> There is nothing new under the sun...


Haha, my thoughts exactly 😲.


Maxx134 said:


> **No new amp is going to eclipse anything TOTL that's already out.
> **No new headphones is going to eclipse anything TOTL that's already out.
> ** IEM market is starting to reach it limits with more and more approaching TOTL levels, and many IEMs already superior to most of the headphone market.
> **Daps are finally reaching limits to the level that topologies don't matter anymore (R2R, Delta-sigma, discreet FPGA). Only thier amplification stages will matter.
> ...


Yep, will do as soon as I can! I remember discussing Daps years ago with my friend at work, who also had an iPod classic, we were moaning about sound quality, why couldn't Apple and others produce TOTL sound given they already have the bit perfect bitstream with all the data necessary for TOTL sound. Well years later they've finally caved in an done it. I think one factor was most users of the technology didn't, and probably still don't care about SQ.

As far as I'm concerned I will never use IEM's. I used them at work, and fortunately for my hearing, I couldn't get on with them. They kept dropping out, were uncomfortable and constantly getting gummed up etc etc. Pretty good technology though. The technology of some systems, which I won't name, seems so clever and to do miraculous things, but when it comes down to it I don't believe they perform any better for it.

As far as any new amps eclipsing anything TOTL I would go as far as saying eclipsing any TOTL old school technology as well. I have to admire those guys back in the day coming up with make and mend solutions to problems they had then.

I've listened to TOTL speakers and how the sound quality can ever get any better is beyond me. They are all at a level that makes them virtually indistinguishable from each other. I always think back to live performances and if it matches that then it can never get any better IMO.

I was half joking when I said I must find another money pit such as new headphones, when really I have been very happy with my existing ones for some time and would only maybe add another model for soundstage, then I would have one with up close and personal emotional sound, my HE-500, and another for 2 or 3 rows back more laid back sound such as HiFiMan 1000SE.

My modding now is transferred to my Mini Cooper S which is a whole lot of fun! I will always be interested in others though who want to achieve what we have done with our mods. That and my guitar is what I'm most interested in these days.

I expect those baby fish of yours have grown into monsters by now... .



Maxx134 said:


> Nothing is up in NY except ghost town zombie land events.* The thriving metropolis which used to be crowded in the streets, both day and night, is now a zombieland.*
> 
> The NY vaccine mandate ruined the CanJam potential of more visitors.
> Stupid NY libtard politics lifted the mandates only after CanJam timing, so at least now you can visit Audio stores withouta mask.


Wow, I can't imagine that New Yorkers have taken to that easily.

Our restrictions are lifted here but owing to the extreme high infection rates that we still have business and social life is still having to adjust. I live in a holiday area and they are having difficulties still. Last year owing to the invasion of holiday makers who couldn't go abroad and now there are difficulties with getting seasonal workers for hotels, resorts and farm produce and such like, so not back to normal any day soon unfortunately.


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## CopperFox

Hello and my apologies for inactivity here, most of my free time has gone to following the unexpected major war in Europe. Fairly historic things going on. 

Haven't done any work on the amp in the meanwhile but will do something soon. The DMM has been less useful than expected so far - tried to find out if the diodes are blown but the manual is vague on how it's done and every instruction I found online differs significantly from the others. I'll probably just replace the transistors and diodes as that appears less complicated and cheaper than another DMM.

As for the reason why the amp stopped working, I've deduced that in addition to changing the vu meter, it also coincided with some wiring changes. The pure silver wires that I had had in the amp were proving troublesome in that they were solid silver compound, so they would break off if bent and twisted long enough, and to stop having to replace those I decided to try 2.5 mm thick copper wires for even lower resistance and that is also the point where the problems started. Maybe there is something about those wires that was incompatible with the rest of the amp. Don't know what exactly. I've read that thick wires may have problematic capacitance. And also that having a resistance too low can have similar function as a short circuit.


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## CopperFox

baronbeehive said:


> Haha, I didn't expect this.
> 
> First the Wimas with Shuguang power tubes:
> 
> Hey @CopperFox I've got most of my dynamics back! Over 200 hours burn in and with the Shuguangs in, it was worth sticking with it. As you said the sound has become clearer and opened up a lot, treble is nice  and bass weight good and soundstage very good. Everything is there, I would say it's a tad warm and mellow and only the sharp edges are missing but if it's mellow you want this is it. I don't really see the sub bass tightening up that much though which is the reason for trying the Wimas.



Hey happy that the burn-in worked and you like them! Thinking back about my burn-in process for them it came back to me that there was a point in it too when the bass dynamics returned. But the treble took longer still. 

The reason why the burn-in takes such a long time with the DCL Wimas is likely to do with the 6SL7 tubes having very, very low current output at only ~2 mA. The electrolytic caps are rated for 1000-2000 mA, while these DCL Wimas are rated for 20-30 A and are certified for use in electric vehicle power trains. 

Even for the coupling caps, I noticed the Duelund 0,56uf caps would burn in a lot faster in the WCF position (30 to 70 mA current?) than as coupling caps after the 6SL7s.

(So one way to speed up the burn-in of the DCL Wimas could be to first run then in some other position with higher current, which for this capacitance could be the PSU output cap position.)



baronbeehive said:


> The bass deficit in mid to subbass with a soft sound the lower you go down has all but gone, with the bass now it is like there is a whole new dimension to music which I really like. I listened to an album that had bass which was very difficult to hear at all originally and it sounds really excellent now, punchy, powerful, but not overly so, and good definition.
> 
> This set up is staying for me! The uprated WCF caps give excellent weight to the sound, similar to uprated coupling caps so if it's bass you want you could do either with probably the same results. The Wima's are a must in the cathode bypass position now, they allow the music to flow.



These are exactly how I would describe them too - a lot more clarity and detail in the low bass without lacking punch. Also, that "they allow the music to flow" is exactly what I thought to myself about them but didn't post it here as it is something that's kind of hard to elaborate on.


Something else that I found to not be a good change/addition was replacing the PSU electrolytics. I put four 2200uf TKD caps there with the best published specs but the difference that they made was mainly a recess in the treble. So I will put the original caps back there. Interestingly, for the _majority _of applicable caps for that position on Mouser and Digikey, the specifications of most of their relevant electrical properties are _not_ published, including the stock caps of the MKVI+.


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## baronbeehive

CopperFox said:


> Hello and my apologies for inactivity here, most of my free time has gone to following the unexpected major war in Europe. Fairly historic things going on.
> 
> Haven't done any work on the amp in the meanwhile but will do something soon. The DMM has been less useful than expected so far - tried to find out if the diodes are blown but the manual is vague on how it's done and every instruction I found online differs significantly from the others. I'll probably just replace the transistors and diodes as that appears less complicated and cheaper than another DMM.
> 
> As for the reason why the amp stopped working, I've deduced that in addition to changing the vu meter, it also coincided with some wiring changes. The pure silver wires that I had had in the amp were proving troublesome in that they were solid silver compound, so they would break off if bent and twisted long enough, and to stop having to replace those I decided to try 2.5 mm thick copper wires for even lower resistance and that is also the point where the problems started. Maybe there is something about those wires that was incompatible with the rest of the amp. Don't know what exactly. I've read that thick wires may have problematic capacitance. And also that having a resistance too low can have similar function as a short circuit.


Hey... good to hear from you, I thought maybe you had managed to electrocute yourself with your new DIMM lol.

You must be concerned about the political situation, I see that Finland is looking to join NATO, the sooner the better IMO with a big bully on your border.

I would still recommend you try first to use your DIMM to test for continuity which is easy to do and will show up any problems with connections, especially with the changes you have  made to your circuit. If all is good there you can go on to test other things such as loose, broken or touching wires, resistances and such like. I have had problems with my amp at least 3 times where the amp wasn't functioning and managed to restore it eventually, we've all had similar experiences, par for the course! I haven't heard that about resistance in wires and short circuiting. I have used some thick solid copper wires in places such as the PSU caps without issue.


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## baronbeehive (May 14, 2022)

CopperFox said:


> Hey happy that the burn-in worked and you like them! Thinking back about my burn-in process for them it came back to me that there was a point in it too when the bass dynamics returned. But the treble took longer still.
> 
> The reason why the burn-in takes such a long time with the DCL Wimas is likely to do with the 6SL7 tubes having very, very low current output at only ~2 mA. The electrolytic caps are rated for 1000-2000 mA, while these DCL Wimas are rated for 20-30 A and are certified for use in electric vehicle power trains.
> 
> ...


Yes several of us here have been a tad sceptical about the use of WIMA's in positions other than PSU. BUT... you are right the changes in the sound after a very long burn in are amazing frankly. Difficult to pinpoint as you say how the sound has changed but it hits you straight away. The bass, in particular hit me with a much better definition which is something I didn't expect that just changing the cathode bypasses would be able to achieve so I am pleased that I stuck with it re: those WIMA's. I definately would recommend them if you want the best sound possible.

Let us know how you get on with any problems with the amp .


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## chezzer

Hi all, I wonder if anyone can help me, my ld mk8 has developed a rather odd problem, with one set of headphones plugged into either the single balanced output I get no sound  apart from if I turn the amp off and turn back on while the music is playing I have audio for a few seconds before it disappears again. However if I plug two sets of headphone into both the balanced and single outputs I have audio through both headphones, unplug one from either output and it disappears again, I've not changed or messed with a thing and all worked perfectly yesterday, I've tried swapping all tubes but still the same problem, any help is greatly appreciated


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