# Modern Balanced Tube Amp Build



## SonicTrance (Jul 1, 2020)

Hi,

I thought I'd start a thread on my DIY project I've been building.
Comments or questions are welcomed!

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!. It's very resolving, transparent and non-fatiguing. The LTP sounds clean, crisp yet very dynamic and real.

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.

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.













































Like you see from the pics I use separate chassis for input and output stage. That's because the original plan was to only build the input stage and hook that up to the output stage of my LD MK6. But plans changed and I decided to build the complete amp instead. Hence the separate chassis. If I was building from scratch today I'd have input and output stage in one chassi and a separate chassi for the psu.

I encourage people to build it. It sounds amazing!



Final pics of version 2 with 6C8G's and 47's (full build gallery on page 4):














Pic of the SE version with C3G input and 6BG6 output (more pics and schematic on page 8 and 9)






Here's the latest edition with SE input stage using 6AT6 and balanced LTP output stage with EL81. This amp is called Oblivion.


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## HiGHFLYiN9

Nice! Lots of Russian cold war caps in there  The chassis looks great! Love the lighted VU meters too.

Over the heatsink, you might try mounting a couple of these old school phenolic terminal strips to hold the resistors and transistors, may prevent a short if you plan on traveling with the amp.







Did you wire up the stepper yourself? Nice job!!


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## SonicTrance

HiGHFLYiN9 said:


> Nice! Lots of Russian cold war caps in there


Yes, all film caps are Russian NOS caps. They're huge but does the job. Good caps.



HiGHFLYiN9 said:


> The chassis looks great! Love the lighted VU meters too.


Thanks!
I spent some time on aesthetics. Glad you like it! The VU meters look cool but are kind of useless TBH. I've not managed to calibrate them correctly. Sure, the needles are bouncing but not the way they should, if that makes sense, lol.




HiGHFLYiN9 said:


> Over the heatsink, you might try mounting a couple of these old school phenolic terminal strips to hold the resistors and transistors, may prevent a short if you plan on traveling with the amp.


I understand your concern, but I'm afraid that would complicate the assembly of the CCS's/follower's. But I assure you the construction is quite solid. This is not a amp to travel with anyway.



HiGHFLYiN9 said:


> Did you wire up the stepper yourself? Nice job!!


Yes, I bought the attenuator and resistors as a kit from hifi-collective. I did the soldering. Some therapeutic work right there!


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## Sodacose

Wew, nice build!

Do you know what the reasoning for the grid drivers is? Are they driven A2 or just there to buffer the previous stage?  

Very interesting design with the mosfet sandwich and transformer coupled output.


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## MrCurwen

> Do you know what the reasoning for the grid drivers is? Are they driven A2 or just there to buffer the previous stage?



The output tubes are not driven to A2 at least in any meaningful way. Maybe some transients; however on the other side of the waveform, there is not that much B+ available.

The buffers serve two functions:

1) Relieve the previous stage of any drive responsibilities. This includes the coupling capacitor; the capacitor is basically completely transparent if placed in front of a FET gate. 

2) Properly drive all the parasitics of the tube grid. All tubes draw some amount of grid current much before grid going positive. For best results, this must be accounted for, and the way to accomodate it is not thru a capacitor. 

A FET followers gate is a nonexistent load (provided there is enough voltage between gate and drain, easy to accomodate in a high voltage tube circuit), whereas a tubes grid is in fact not a nonexistent load, not at all. 

Sonic has listened to this amp both with and without the grid drivers, I'll let him provide his own comments on that.



> Very interesting design with the mosfet sandwich and transformer coupled output.



Thank you. My primary direct influences are Wavebourn, Tubelab-George and pmillett. Rod Coleman's work was also important for the directly heated version of this amp

What do you mean with MOSFET sandwich?

The transformers in my own and also Sonic's build are Hammond 125D. Smaller ones work just as well, like 125A. There is no real reason to use 125D or even 125E.


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## Sodacose

Hi MrCurwen,

Thanks for your thoughts.  I've also been reading up on TubeLab's A2 experiments and have seen Millett's similar CCS loaded mosfet implementation.  Even if not driving the grids to A2, it sounds like your arrangement serves a similar purpose here: dealing with the impedance inconsistency due to grids drawing current. Of course presenting the high impedance to the previous stage in the process is another advantage. Stating for the benefit of others as I'm sure you know all this. 

"MOSFET sandwich" is just referring to the CCS loaded MOSFETs between stages and at the output. Not using it pejoratively 

Couple of questions since I'm curious and you're willing to discuss:

The power supply isn't shown; how are you biasing the MOSFETs following the LTP? I see trim pots in the pics but wondering if you figured out some other kind of arrangement (servo or otherwise). 

Have you had the chance to compare the MOSFET approach to the old school cathode follower in a similar configuration? On paper a MOSFET wins in most ways, but would love to hear any thoughts.

Have you done any experimenting with "Super Triode" outputs?  That's something I'd like to try in the not too distant future and judging by this design I imagine you might have looked into it. TubeCAD and JC Labs are both websites that touch on it pretty frequently but I don't see many others actually giving it a go.


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## MrCurwen

> Thanks for your thoughts. I've also been reading up on TubeLab's A2 experiments and have seen Millett's similar CCS loaded mosfet implementation. Even if not driving the grids to A2, it sounds like your arrangement serves a similar purpose here: dealing with the impedance inconsistency due to grids drawing current. Of course presenting the high impedance to the previous stage in the process is another advantage. Stating for the benefit of others as I'm sure you know all this.



Yes. The grid drivers improve transient response, they make the sound (in my opinion) more 'fast' and dynamic. The technical reasons for this are (in my guesstimation) 70% relating to the grid and Miller capacitance and 30% related to the coupling capacitor. The follower deals with both of them in a brute force manner.



> "MOSFET sandwich" is just referring to the CCS loaded MOSFETs between stages and at the output. Not using it pejoratively



No pejorative inferred. Hmm, most people are more puzzled with the LTP configuration at first glance; high impedances at both the tail and at the top.



> The power supply isn't shown; how are you biasing the MOSFETs following the LTP? I see trim pots in the pics but wondering if you figured out some other kind of arrangement (servo or otherwise).



The output followers are biased with R1/R2 and R7/R8 voltage dividers to halfpoint between B+ and ground, minus 4.5V FET drop of course. This leaves the follower with maximum amount of symmetric voltage swing available. Bias current is determined by the bottom CCS.

The power supplies are very simple RCRC or similar (doesn't really matter) followed by a simple 2 FET regulator. 



> Have you had the chance to compare the MOSFET approach to the old school cathode follower in a similar configuration? On paper a MOSFET wins in most ways, but would love to hear any thoughts.



Not in a similar configuration. I have built some circuits with tube cathode followers, most notably tube plate loads (plate load is a follower). I am not pleased with using tubes in roles other than voltage gain. They can do ok, but not for best results in my opinion.

I used to do all tube regulators back in my tube purist ideological days. Crazy business.



> Have you done any experimenting with "Super Triode" outputs? That's something I'd like to try in the not too distant future and judging by this design I imagine you might have looked into it. TubeCAD and JC Labs are both websites that touch on it pretty frequently but I don't see many others actually giving it a go.



I haven't built any Super Triode circuits. I've played around with them in sims some time ago. 

Not a bad idea, but I don't think it would bring any benefits above my current strict roles (tubes do voltage amplification, FETs provide current). Super Triode is a FET or transistor that has a feedback loop around itself, and the tube is in the feedback loop. This way the tube 'lends' some characteristics to the FET.

Only upside would be efficiency, but as far as I'm concerned that boat sailed away a long time ago.

Serious problem would be providing a good load for the Super Triode. I guess it's supposed to be used in series feed mode, which is not for me as it requires expensive OT's and doesn't properly deal with OT parasitics.


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## Sodacose

Thanks for the lengthy responses!  All good info.

I'd encourage you to revisit the Super Triode topology when you get bored because I'd love to see what you come up with.  I don't believe there is any reason they can't be used OTL, differential, or parafeed.  With the lowered effective Rp and multiplied load impedance they should also be able to make use of lower turns ratio transformers (more power, less parasitics).  The tube determines voltage amplification (still Mu) by way of the feedback scheme.

But if one thing is true in the hobby, it's that there are plenty of ways to skin a cat.  Thanks again for sharing yours.


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## coinmaster (Jun 22, 2017)

So basically it has Mu follower driver stages with a parafeed output and some buffers in between. Overall pretty standard design but still pretty good. Chassis work is amazing. I gave up on P2P construction about a year ago..too many fried mosfets..too many power supply accidents. After a long search I've found solderless breadboards to be the bees knees for prototyping overall. I can build an amp in 30-60mins after conception, its great.
Personally I would ditch the parafeed, OTLs are easy to make with solid state no need to deal with transformer parasitics as a factor at all and you'd be able to ditch that second set of tubes in the output stage.
I'd change the RC ratio of the mu followers to something that allows a lower and higher quality cap to be used, such as 10meg/0.1uf. I'd also switch to a faster mosfet than the IRF830 for better HF response and better bandwidth.  I'd also use a current balancing bias scheme to ensure the tubes run at matching currents for better H2 cancelation.

For the output stage I'd go with a lower distortion stage like a sandman or an aleph-esk design, or at the very least I'd cascode the source follower to make it much more linear. I prefer to know where my distortion is coming from, easier to tune that way. Those source followers will introduce considerable distortion under load, depending on the load. Not that increased distortion is necessarily a bad thing but in terms of amp design I think it's better to add distortion after the fact.

As far as interstage buffers go the standard current source fed source followers are fine, the load is negligible as long as the idle current is at a much higher ratio than the expected grid draw.
I'm curious about your findings on the interstage buffers, I'm not convinced the grid current is enough to make a difference in sound if the previous stage is drawing a reasonable current, especially when you're driving the next stage with a mu follower already.

You'd need quite a few microamps or miliamps to delinearize the preceeding stage depending on the current draw of that stage. The mu follower should keep the triode at a stable current, the mu follower output itself could become slightly delinearized depending on the ratio of current delta at its source pin but I don't see how a triode under standard operation could draw enough current to matter. Maybe I'm wrong and you could enlighten me? I've never considered grid current as a factor. I'd just assumed it drew a few microamps at most depending on grid capacitances.

In either case I'm a believer in results over theory, what is your impression on the sound with/without the buffers in place?


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## SonicTrance

Sodacose said:


> Wew, nice build!


Thanks Sodacose!



Sodacose said:


> Do you know what the reasoning for the grid drivers is? Are they driven A2 or just there to buffer the previous stage?


MrC got that covered much better than I ever could. I have merely been given his design and built it. When I started I couldn't even read a schematic, lol.



MrCurwen said:


> Sonic has listened to this amp both with and without the grid drivers, I'll let him provide his own comments on that.





MrCurwen said:


> The grid drivers improve transient response, they make the sound (in my opinion) more 'fast' and dynamic.


I agree, definitely a faster sound with more weight behind the tones. Very noticeable.



Sodacose said:


> The power supply isn't shown;


I've updated first post with psu schems. Those are exact values that I've used.



MrCurwen said:


> The output followers are biased with R1/R2 and R7/R8 voltage dividers to halfpoint between B+ and ground, minus 4.5V FET drop of course.


And the grid driver followers are biased through the voltage reference at R1. It's just B+ -> 220k -> 10k trimmer -> ground. I have the grid drivers output 0VDC to output tube grids. The other trimpots, on top of the B+ decoupling caps, are to set the gyrator output voltage (anode voltage)



coinmaster said:


> Chassis work is amazing.


Thanks!



coinmaster said:


> I gave up on P2P construction about a year ago..too many fried mosfets..


I think P2P is great. I too have fried lots of FETs. It became a pain to change them since I glued them to the heatsink everytime. I now have drilled and tapped M3 holes in both heatsinks, grid driver and power buffer. If something should go wrong now its very easy to change them.



coinmaster said:


> Personally I would ditch the parafeed, OTLs are easy to make...


That would make this an entirely different design. I already have an excellent sounding OTL amp as you know. The modded LD MK6. Great thing with having the tubes do only voltage amplification is that you can use any linear tube and it'll sound great.
As far as using better caps there's no need. I've tested the input stage with Mundorf S/G/O .68µf coupling caps. Absolutely no difference compared to the russian KBG's when followed by the grid drivers. I'd rather spend a few dollars on FET's than hundreds on audiophile caps.

I've built MrCurwens design without questioning it or try to change it. I am extremely happy I did that too. The price to performance ratio is very, very good. You can, if you don't care much about aesthetics like I do, build this amp for little money.



coinmaster said:


> In either case I'm a believer in results over theory, what is your impression on the sound with/without the buffers in place?


I've listened both without the grid drivers and power buffer. Also with only power buffer and no grid drivers. I've already mentioned the grid drivers above. The power buffer sounds very clean. The sound is "muddier" without it (without sounding bad, still sounds good) I think I notice more of a difference with the use of power buffer than MrC does.
Anyway, the buffers do improve SQ by a significant amount.


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## coinmaster

.





> I already have an excellent sounding OTL amp as you know. The modded LD MK6. Great thing with having the tubes do only voltage amplification is that you can use any linear tube and it'll sound great.


Well, what I meant was simply removing the parafeed stages and using a good solid state output stage. The parafeed is effectively acting as a distortion generator in comparison, which isn't a bad thing at all in itself but personally I would forgo the mess of parasitics involved with transformers unless it offers a specific sound you like.

I don't agree with the statement that having tubes only amplify voltage makes them all the same, my experience has been far different and I've tested this a lot. 



> The power buffer sounds very clean. The sound is "muddier" without it


 I've noticed this too when using solid state in place of tubes where they are supposed to drive current.

So far I've only built 2 stage amps though, I try to avoid more. Effectively speaking in comparison my "grid driver" simply drives the headphones instead of a bunch of extra stages. I usually direct couple the whole thing, no capacitors or transformers anywhere in the signal path, talk about clean sound. 

Although my DAC blew up along with my laptop during the winter due to a mishap when my usb oscilloscope accidentally whacked against an exposed 350v power supply rail of a CLC filter I built which caused a chain reaction of destruction so I can only really compare my designs to each other now as amplifying my laptop headphone jack sucks in comparison to a real dac, there's this permanent "haze" in the sound.

That was the last time I ever touched P2P, that accident was a multi thousand dollar mistake right there in itself. Hindsight I should of spend a grand or 2 on lab power supplies and I would have saved twice the money in the long run and a whole lotta burnt components. (I've spent way to much time/money on trying to be cheap, ironically)
Only recently I discovered the ease and speed of simply using solderless breaboards, I guess the best solutions are often the simplest ones. What normally took me days now takes me less than an hour.

I will say that my designs wipe the floor with the modded MK6 when I compared, I swapped the input stage in my modded MK6 with my latest one and it improved the sound in every way possible by a very large degree. I did the same for the MK6 with a SS output stage I had at the time, it also wiped the floor with the MK6 output stage. Since then I've made those designs twice as good, I just need to get that darn dac fixed for once or buy a new one.


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## coinmaster

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## MrCurwen

> But if one thing is true in the hobby, it's that there are plenty of ways to skin a cat. Thanks again for sharing yours.



That is indeed true! 

It all depends on 

1) the design goals and priorities that are set (they cannot be vague like "good sound" but specific in technical terms, like a certain output impedance or a certain voltage gain or a certain THD etc.)

2) the practical limitations; what kinds of components will be used, funds available etc. 

3) the design principles and philosophies to be followed.

These all to an extent interact with each other in very complex ways. 

My design has been arrived at during several years. I thought I was the first to come up with it, but later found out some others had made similar efforts. Specifically the LTP configuration, the grid stuff came from George.

I assure you it's quite well thought out, the individual parts complement each other. For example the output buffer; you can say the simple one FET follower with CCS bias is too weak and will produce distortion if loaded. Well, the load for it is quite low, it can handle it with no distortion. Confirmed by sims and listening. It's super clean, no distortion, either low order or high.

As well one could think that the OT being there at all would be "less than perfect" since a real coil will always behave a bit nastily. Well, it is driven by such a low impedance, that the nasties simply are not there. However if you were to take the OT out and direct drive your load, you would end up with a situation where the follower would indeed produce a lot of distortion and would need to be a lot more complex for good results.

Here you have two imperfect solutions ('weak' follower and an OT) that in effect cancel out each others weaknesses. The OT primary is such an easy load the weak follower is overkill for the job (even a tube can manage it!) and produces no distortion, and the imperfect OT is so 'overdriven' (you get my point) that it's parasitics disappear. It doesn't produce any distortion. The idea of OT's as distortion producers is a relic from ages past where you only had very compromised ways of driving the primary.

The follower doesn't need to be more stronger or more complex, it is overkill as it is. The OT doesn't need to be of higher quality because it is driven to transparency as it is. Going OTL would destroy this design balance and introduce a whole Pandora's box of problems on it's own.

Perfect can be an enemy of the practically (doably) very good.

Same thing with the grid drivers. On another more engineering oriented forum I get a few private messages every year from people who are interested in my direct coupled circuits from years ago (back when I was a direct coupled purist). I spend a lot of time explaining the reasoning behind how and why I get better results with proper grid drive than with DC. 

DC is in the abstract 'better' but not in practise.



> The price to performance ratio is very, very good. You can, if you don't care much about aesthetics like I do, build this amp for little money.



I'm very very very cheap. I find it a virtue not a vice. This circuit can be built much simpler while achieving 85% of it's (in my opinion quite exceptionally high) sound quality. Ditch all the PSU's except one for B+ and one for B-. It can even be arranged so there's no need for B-. Output buffer can be omitted. For an even simpler version use a SE input stage; this introduces a little bit of H2 but all the dynamics, all the punch is still there. 

Very very cheap tubes can be used with sound just as good as an "audiophile tube". Just as Sonic said;



> you can use any linear tube and it'll sound great.



Quite true. Emphasis on the linear there. But, many dirt cheap unknown tubes are super linear. One of my design philosophy rules is if you hear a noticeable difference between tube types in a voltage amplification context, your design is poorly thought out. Sorry rollers...



> As far as using better caps there's no need. I've tested the input stage with Mundorf S/G/O .68µf coupling caps. Absolutely no difference compared to the russian KBG's when followed by the grid drivers. I'd rather spend a few dollars on FET's than hundreds on audiophile caps.



My thoughts exactly. The cap game is for audiophools in my opinion. Sorry rollers again...



> I've listened both without the grid drivers and power buffer. Also with only power buffer and no grid drivers. I've already mentioned the grid drivers above. The power buffer sounds very clean. The sound is "muddier" without it (without sounding bad, still sounds good) I think I notice more of a difference with the use of power buffer than MrC does.



Yes. I think it's the bottleneck thing. Sonic has much better headphones and a much better source. I do hear a very noticeable difference with regards the output buffer, but I'm quite sure Sonic hears more, because it's more of an bottleneck for him than for me.

Also I'm at the point where I'm very lazy. I have a decent enough workhorse system (no chassis... don't do this at home guys) that the effort of getting my ultimate system builts is too much to actually start doing. I've been busy with studies and work and other hobbies.


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## Sodacose

Very provocative thoughts on the 'weak' buffer driving the cheap OPT  I was wondering the same thing as coinmaster, but you make a good point. Proof is in the listening, I think.

Have you tried any similar experiments allowing the MOSFETs to provide a fixed bias to the output tubes rather than the CCS bias? I'd be interested to know how it might compare in sound.


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## MrCurwen

> Have you tried any similar experiments allowing the MOSFETs to provide a fixed bias to the output tubes rather than the CCS bias? I'd be interested to know how it might compare in sound.



That's the place where I started my balanced building originally. I then moved to a resistor tail and then a CCS tail. The CCS tail is an integral part of the way my LTPs are set up. Without the tail the signal balance (DC balance is not important within normal variation) needs to be achieved some other way. The tail is the easiest and most obvious way to achieve this balance. 

And in a balanced amp the actual signal balance is one of the most important things.


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## coinmaster

> Proof is in the listening


 Always.


I'm still a direct couple "purist" because even overdriven I don't trust OTs due to the complex reactive traits it inherent to it, it's just a big mess of potential imperfections I don't want to deal with, not that it isn't good sounding.

Same with caps, I use duelund cast caps anytime I use caps at all because I still have them from my original MK6 mod. I'd rather just not wonder if the caps are making a difference by either using the best or none at all, so far in my experiences caps have had a significant effect on the sound whenever I try a cap somewhere of lesser quality, not that my results are conclusive to all circumstances, I'll eventually do some tests when I get around to it. 
The massive improvement in sound I heard when upgrading to duelunds in my MK6 is the reason I became interested in electronic design to begin with so it left quite an impression.


As for direct drive producing more distortion then OT, it really just depends on the design.For a standard source follower, yeah the distortion would be considerable depending on the load.
I've spent most of my time designing direct drive output stages because I'd rather have the input stage producing my distortion and after endless hours in spice I've got a handful that should in theory produce next to 0 distortion, like between -120db and -200 db  peak distortion according to spice depending on the design.

No matter what parasitics I introduce or components I use or even changing component values to a large extent in spice the results are basically the same meaning the designs are solid, some to a higher extent then others. I've only built two of these types of designs so far but they sound flawless, I would need a distortion analyzer to confirm the actual THD but even if it was 10,000 times worse then spice suggests it would still be above average performance. (one of the designs stubbornly registers as 0% distortion in spice no matter what I do to it, a good sign)
It's all about error correction via non-negative feedback schemes, NFB is a subtractive process and depending on how it's used it can degrade the sound, not a variable I want to add into the mix.
However feedforward and other error correction schemes can let you have your cake and eat it too, there's many ways to approach this and when done right the performance is amazing.

At the end of the day I think distortion is a good thing and very desirable but I don't want untamed distortion to dominate my designs. After I get the time/money to test all my current distortion free output stage designs I'm going to switch things around and look into distortive output stages and distortion free input stages, I hear that's a popular concept in japan right now.
I can see the appeal due to the rising harmonic content with power of tubes under load which is the opposite of how solid state parts function and in line with how sound through air functions, this is likely one of the big reasons why tubes sound so natural over many solid state designs.



> Quite true. Emphasis on the linear there. But, many dirt cheap unknown tubes are super linear. One of my design philosophy rules is if you hear a noticeable difference between tube types in a voltage amplification context, your design is poorly thought out. Sorry rollers...


 I'm not convinced. I too use mu followers for the outputs of my input stage most of the time, it's just sensible all around, constant current on AC, constant voltage on DC, low output impedance. Low output impedance meaning able to drive reasonable loads without loading down the tube at all. Pair this with the fact that my output stages have practically no input capacitances and no current draw and you have a tube that is purely amplifying voltage under ideal conditions, I've heard differences in sound with different tubes here in their linear regions.
This alone is not conclusive evidence but I've read too many blogs or threads from people with amps using hybrid mu followers and different tubes that all have the similar ultra linear looking curves on the scope yet having their own distinct sound of their own. On the other hand MrCurwen is the only person I've seen claim otherwise. I'm putting my hat in with the majority so far. Now that I finally have a solid prototyping set-up I'll be able to do a lot more testing later this summer when I get the time.


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## Sodacose

Coinmaster, do you have a build/design posted somewhere that I can read about?  Out of respect for OP and MrCurwen, we should try to avoid hijacking this thread with discussion of other designs/philosophies.


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## coinmaster

Yeah I guess I am bordering on hijacking, sorry I never have anyone to talk to about this stuff. No I don't have any posted designs my end goal is to create a product line, I don't want some chinese guy ripping me off before then .


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## MrCurwen

Those heater DC bias resistors in the PSU schems should be 270k and 33k of course. Using the values presented (about 300 ohms in total) would make for some smoke.


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## SonicTrance

coinmaster said:


> I've heard differences in sound with different tubes here in their linear regions.


I've tried TS BGRP 6F8G's, Sylvania 6SN7W metal base and even the Mullard ECC32 and 33. They don't sound any better than a russian 6N8S in this circuit. They all sound equally good! If there's a difference it's extremely small.

I've also used different tubes in the output stage. I started with 6C5G/6J5G's and then went to EL36's and finally to the 6BG6/6P7S's. They all sound equally good too. The 6C5G/6J5G's had too much gain though. I only settled on the 6BG6's cause I like the look. The EL36's sounds just as good.



coinmaster said:


> On the other hand MrCurwen is the only person I've seen claim otherwise.


So my listening doesn't count?
I had a hard time believing this myself before I heard the amp. I've bought lots of audiophile tubes for the MK6. In that amp you can really hear the difference. 



MrCurwen said:


> Those heater DC bias resistors in the PSU schems should be 270k and 33k of course. Using the values presented (about 300 ohms in total) would make for some smoke.


Good catch! It's now fixed!

Speaking of tubes, I've made adapters for the 7193's today. I still enjoy rolling different tubes even though the SQ doesn't change. My first time building adapters.


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## MrCurwen

> I've also used different tubes in the output stage. I started with 6C5G/6J5G's and then went to EL36's and finally to the 6BG6/6P7S's. They all sound equally good too. The 6C5G/6J5G's had too much gain though. I only settled on the 6BG6's cause I like the look. The EL36's sounds just as good.



Didn't you have 6P31S as well if I recall correctly.

I'm constantly on the search for new tubes, at least mentally. However I now have about 500 tubes in my cabinet, almost neatly organized, so I have plenty already and won't buy any more. 6P36S is most interesting despite it's 2A heater. For SE duty most likely.



> Speaking of tubes, I've made adapters for the 7193's today. I still enjoy rolling different tubes even though the SQ doesn't change. My first time building adapters.



Indeed! Your top caps look very good, glad to see something else besides the white ceramic ones. I get it they're behaving nicely now?



> I had a hard time believing this myself before I heard the amp



There are popular forums with engineering minded people, where you will find more people who would assert without missing a beat that under certain conditions tubes will sound exactly interchangeable. But not everyone goes everywhere so no shame in that. Tubes are not magic, they do follow laws of nature. If the load line is linear enough in both tubes, and rp is played out of the equation (only voltage amplification); they will necessarily sound the same. SE stages will exhibit more differentiation because they are hard to get as clean as well designed LTPs.


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## SonicTrance

MrCurwen said:


> Didn't you have 6P31S as well if I recall correctly.


Correct. I bought some of those. I have not tried them since I got rid of the oscillating rectifier tubes though. They were noisy at the time but I'm sure they'd be quiet if I tried them now.



MrCurwen said:


> Indeed! Your top caps look very good, glad to see something else besides the white ceramic ones. I get it they're behaving nicely now?


Thanks!
Yes, the 7193's are behaving now! Top notch. I will say this though; if a tube is noisy/microphonic you instantly hear it in this circuit. Quiet tubes are a must.


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## MrCurwen

> Yes, the 7193's are behaving now! Top notch. I will say this though; if a tube is noisy/microphonic you instantly hear it in this circuit. Quiet tubes are a must.



That has been my experience as well. It's not an easy circuit to get quiet, it can take a lot of debugging. Sometimes it's quiet straight away, but mostly not. The circuit simply has a lot of gm and a lot of wires in a small space, so noise is bound to happen.

The SE version is much more forgiving in this regard.


----------



## MrCurwen

This is a reply to gug42 from another thread:



> 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.



Within retro confines, this is completely true. However it's not that difficult to engineer around this problem; an expensive OT is not at all necessary. 



> And it would be better to have a well designed OTL than a cheap OT.



Again, completely true within retro solutions.



> Moreover, he told me than an OTL amp can't be converted to OT easely.



Well depends on the circuit and definition of 'easy'. If the amp has two tube stages already and enough PSU capability, it's not that difficult if you just go retro.

However because the smart way to drive an OT will require such an extensive rebuild that in most (practically all?) cases it's much smarter to do a scratch build.


----------



## gug42 (Jun 27, 2017)

Hello,

Thank you for thoses replies. When you speak about "retro" you means "old fashion way" ?  

I've read a little more and well agree : more simple to design and build from scratch than modify one topology to another one.


----------



## MrCurwen

gug42 said:


> Thank you for thoses replies. When you speak about "retro" you means "old fashion way" ?



Yes. Most people who build tube circuits use the circuits that were popular back when the tubes were made. Those circuits use many compromises that modern builders don't have to use. 

For example most modern DIY builders are not or at least shouldn't be very interested in efficiency or cost. The professionals making product designs back in the 1950's were very much concerned with cost, and that heavily affected their designs.

Even if you forego cost and efficiency, and let's say you design an OTL amp using tubes. Most modern hobbyists are still mentally constrained by component choise. They want to use components that were available during the time their tubes were manufactured. 

A hobby is a hobby, I do see value in reproducing old circuits. But that is a goal in itself; if your goal is transparent sound reproduction for HIFI, then all else should flow from that main goal, and adherence to design restrictions of old times should become irrelevant.


----------



## gug42

Ok I see !
I see your point, two main goal : building an old fashion amp or building an efficient one using tubes.
By the way production cost is still really important for mass industry, but less for hobbies.


----------



## SonicTrance

MrCurwen said:


> Most modern hobbyists are still mentally constrained by component choise. They want to use components that were available during the time their tubes were manufactured.


You have successfully turned me, lol. Thanks again for the opportunity and help to build this beast of an amp! Couldn't be happier!  

Listening with my LCD-3's through the (insert a proper name for the amp here) amp. Sounds amazing, can't get enough of this amp!


----------



## coinmaster (Jul 3, 2017)

> But that is a goal in itself; if your goal is transparent sound reproduction for HIFI, then all else should flow from that main goal, and adherence to design restrictions of old times should become irrelevant.


 That's how I see output transformers, an old flawed methodology . As I mentioned in the other thread, a voltage follower buffer by definition will skew the current through the transformer due to its inductance, I think if you are going to stick with a transformer output then driving it with an active current source buffer instead would perform better because it will ignore all parasitics thanks to Kirchhoff , after all a transformer is run by current, not voltage.


----------



## gug42 (Jul 28, 2017)

Hello,

I've done some googling about a 4P1L amp. Well I found this : 
http://www.bartola.co.uk/valves/2016/03/05/russian-pse-in-steroids-4p1l-into-4p1l/
http://www.bartola.co.uk/valves/2016/03/06/russian-pse-in-steroids-6e5p-into-4p1l-part-ii/

The block "HT MU_OUT" is the gyrator card : http://www.bartola.co.uk/valves/for-sale/gyrator-pcb/

First some stupids question : 
- Did I need two blocks of thoses, one per channel ?
- Can I assume the IN where the + of the RCA ?  And I wire the - to any ground
- The ground is unique ?
- Rod Coleman : ... hum any schems/plan of this thing ???
- About outpout transformer : can I choose it depends of the load ? 4Ohms / 8Ohms / 50Ohms / 300Ohms headphones ?

An internal schem of the gyrator : 
http://www.bartola.co.uk/valves/2017/04/17/gyrator-hack-enhancement-mode-mosfet-option/

Indeed I prefer the schems of the first page, those with the blue background, more easy to read for me


----------



## coinmaster

> Did I need two blocks of thoses, one per channel


One per channel. The schematic is of one channel.


> Can I assume the IN where the + of the RCA ? And I wire the - to any ground


"IN" is the input signal. For RCA you'd want to ensure the ground connection between source and amp is connected yes.


> The ground is unique ?


I'm not sure what you mean by this.


> Rod Coleman : ... hum any schems/plan of this thing ???


 No schems that I know of but it's essentially a current source fed into a gyrator to buffer the signal from the heater PS.
If you are going to be messing with DHTs and don't want to design your own heater supply just buy his regs, they are well regarded among the DIY community.


> About outpout transformer : can I choose it depends of the load ? 4Ohms / 8Ohms / 50Ohms / 300Ohms headphones ?


 For better impedance matching it should depend on the load or you could have different taps off the transformer for different load impedances.


----------



## Sodacose

I wouldn't hesitate to try any of Rod Coleman's designs.

You'll need a gyrator for each channel.  The "In" is the "positive" of an RCA and the "negative" should be grounded. I haven't seen how Rod built this amp, but I'm certain that all the grounds are tied together in some way. There are lots of ways to do this, but "star ground" is one of the keywords.  I typically use a combination of a star ground and a bus bar when building, keeping any high current returns (eg output tube cathodes, PSU grounds) closer to the common point than grid references or input stage cathodes.  This has always worked well for me.

The output transformer can use any secondary appropriate for what you're connecting (eg a 300 ohm secondary tap for HD600s). You'll want to be sure that the impedance reflected at the primary stays in the same ballpark as designed though (3,000 ohms).


----------



## gug42

Hello,

Noted ! Thank to you !

About the design itself : I'm surpise to see so few caps and seems to be low caps isnt it ?

Regards,


----------



## coinmaster (Jul 28, 2017)

There's a cap in the gyrator and a cap between the stages, both about .22uf.
 If you really wanted, the interstage cap could be removed but it would make the design more complex and expensive, requiring higher voltages. Not worth it unless you really hate caps.
The gyrator cap must stay.


----------



## gug42

Hello,

No I'm really ok with caps. Indeed I'm suprise to see so few (and little) in this design ...


----------



## coinmaster

It's not really uncommon. You seem to spend a lot of time over at the MK9/8 mod thread and that amp only have 2 small caps per channel as well in SE mode.


----------



## gug42

Indeed you'r right.


----------



## MrCurwen

> First some stupids question :
> - Did I need two blocks of thoses, one per channel ?



The schematic is of one channel.



> - Can I assume the IN where the + of the RCA ? And I wire the - to any ground



Yes. 



> - The ground is unique ?



Electrically it will function no matter what as long as all the grounds are connected together. This can cause hum or noise problems, or it can be completely silent.

In a balanced amp where the PSU is not in the picture this is much much less critical for obvious reasons. In a SE amp you have to think in terms of current loops.

A useful and practical approach is using local grounds as I believe somebody already pointed out. For example make each gain stage or buffer stage have a local star ground, and then connect all these star grounds to the last PSU cap ground (never to the first cap ground, it's the noisiest ground in the whole circuit). This is then your master star ground.

You could also go for a ground plane approach, and just connect every ground straight to the chassis. This works really well in guitar amps and also in high frequency circuits like CRT circuits, radios etc.

I myself use the local ground method.



> - Rod Coleman : ... hum any schems/plan of this thing ???



Well he sells it, so no. Other systems that work on the exact same principle have schems floating around the technical DIY forums. Basically it's a voltage control (gyrator) on one leg, and constant current source on the other leg. High impedance on both legs; keeps the audio signal out of the PSU.



> - About outpout transformer : can I choose it depends of the load ? 4Ohms / 8Ohms / 50Ohms / 300Ohms headphones ?



Depends completely on which kind of topology you go for.

The design that this thread is about uses a 10k : 4R OT that can drive any speakers or headphones no second thoughts about it. I don't see any point in matching impedances, I'm not in the output power game at all. Overkill low impedance drive is where I'm at.

You can ask Sonic if this gross impedance mismatch causes any problems for his headphones.



> An internal schem of the gyrator :
> http://www.bartola.co.uk/valves/2017/04/17/gyrator-hack-enhancement-mode-mosfet-option/



Now that is a super overkill gyrator right there. First class work. In my experience and opinion it will however not bring any audio benefits.

There has been a pretty large consensus for years that 50x rp impedance for the plate load is about the upper limit where any audio benefits are had. Many would argue it's much lower, 20x or 30x. 

This 50x is easily had with a single FET gyrator for almost all useful audio tubes.


----------



## MrCurwen

General comments about the schematic you linked gug42:

1) I would not parallel tubes when looking for best results, especially for headphones. For power, yes, it's a smart thing to do, but for fidelity, no. It smears the microdetails quite noticeably when using headphones. Also there is absolutely no other need for it besides output power.

2) I would not operate 4P1L without proper grid drive. I found out by extensive experiments that 4P1L does in fact draw quite a lot of grid current on transients. This ruins the dynamics of the amp unless the grid is properly driven. This can be easily accomodated with a simple source follower, look at my Red Star schems. You can read Sonics comments on this grid drive subject in this thread also.

3) I would not operate an OT in series feed mode. This both ruins the output tube's load line, and introduces many problems regarding the OT quality. Using the topology described in this thread you can achieve top results using only a cheap OT.

What I mean by that is that you can get better sound quality on all metrics using a 25€ or whatever it is nowadays Hammond 125D OT in the topology described in this thread (or the Red Star) than you can using that Lundahl quality iron proposed in the schematic you linked.


----------



## baronbeehive (Jul 29, 2017)

MrCurwen said:


> Very very cheap tubes can be used with sound just as good as an "audiophile tube". Just as Sonic said;
> 
> ...
> 
> ...





SonicTrance said:


> I've tried TS BGRP 6F8G's, Sylvania 6SN7W metal base and even the Mullard ECC32 and 33. They don't sound any better than a russian 6N8S in this circuit. They all sound equally good! If there's a difference it's extremely small.
> 
> I've also used different tubes in the output stage. I started with 6C5G/6J5G's and then went to EL36's and finally to the 6BG6/6P7S's. They all sound equally good too. The 6C5G/6J5G's had too much gain though. I only settled on the 6BG6's cause I like the look. The EL36's sounds just as good.
> 
> ...



Hi Guys! It makes sense thinking about it. In simplistic terms amplifying a distorted signal with a component of idiosyncratic construction, ie. different tubes manufactured differently, would introduce a third factor ie, sound differences. Be that as it may, since I got my first tube amp with the Tungsol tube added, I've been addicted to the sound it produces. I'm not really a roller, I just know the sound I like and use tubes to get it, once it's there it's sorted!

What I'm saying is that I look at tubes as a tone control, In my Miniwatt I have 2 different Tungsol types, one produces the typical liquid, immersive sound that flows so naturally, the other has more dynamics and punch, perfect! However if the amp in Sonic's build would produce that sound I like, probably better even, then no need for the tube rolling! I would happily leave it behind.

BTW Sonic your comment that before you started your build you didn't even understand circuit diagrams has given me much encouragement lol.


----------



## MrCurwen

> However if the amp in Sonic's build would produce that sound I like, probably better even, then no need for the tube rolling! I would happily leave it behind.



My version of tube rolling is looking for tubes that perform really well but nobody has heard of, or that people think are "lower quality" and then buying a lot of them. Or, think a lot about buying a lot of them...

I now have over 500 tubes sitting in my lab. I simply cannot justify buying any more. I still browse datasheets and eBay sellers though, for fun.

TV sweep tubes were practically free up until recently. I bought a TV repairman's box (with advertising graphics and all, cardboard box with a handle) full of 6BQ6 / 6CU6 beam tetrodes. 50 pieces, cost 14 euros + 52 euros shipping from USA! They perform pretty good in my circuit, better than expected. EL36 / 6P31S are of course top notch and pretty cheap still.

For big show, 6P36S is quite cheap still. I've got around 30 of them. 

Too bad the american sweep tubes have gotten expensive. I like the fat bottles. Russian bottles are thin, because of the communism and all.



> BTW Sonic your comment that before you started your build you didn't even understand circuit diagrams has given me much encouragement lol.



We corresponded a lot, many many messages for a long time. He's really smart and a fast learner, very easy to work with. Most of this stuff is just a lot of small things to take into account, so you got to put in the hours.

Anybody can learn this stuff, just start building. I recommend building a simpler amp first, like the SE version. Then you can get the additional satisfaction of upgrading when you later build the balanced version. Also you have less frustration because simpler circuits are easier to troubleshoot.


----------



## baronbeehive

MrCurwen said:


> ....
> 
> TV sweep tubes were practically free up until recently. I bought a TV repairman's box (with advertising graphics and all, cardboard box with a handle) full of 6BQ6 / 6CU6 beam tetrodes. 50 pieces, cost 14 euros + 52 euros shipping from USA! They perform pretty good in my circuit, better than expected. EL36 / 6P31S are of course top notch and pretty cheap still.



I wondered where all those tubes went....



MrCurwen said:


> ....
> 
> Anybody can learn this stuff, just start building. I recommend building a simpler amp first, like the SE version. Then you can get the additional satisfaction of upgrading when you later build the balanced version. Also you have less frustration because simpler circuits are easier to troubleshoot.



Thanks. Look forward to that sometime.... atm most of my time is taken up with work on the house after the move, you might remember from the other thread.


----------



## SonicTrance

baronbeehive said:


> Thanks. Look forward to that sometime.... atm most of my time is taken up with work on the house after the move, you might remember from the other thread.


Get to building, baron! It's really fun and super rewarding! I'm also working on the house after my move. Haven't listened to music for about a week but I have things on order for my next build already! I'm really excited. Next build is gonna be 6C8G input and #47 output, so DHT magic! I'll update this thread with pics and whatnot when I start building.


----------



## baronbeehive

SonicTrance said:


> Get to building, baron! It's really fun and super rewarding! I'm also working on the house after my move. Haven't listened to music for about a week but I have things on order for my next build already! I'm really excited. Next build is gonna be 6C8G input and #47 output, so DHT magic! I'll update this thread with pics and whatnot when I start building.



OMG !!

I will sometime..... but your house is obviously in better condition than mine lol.


----------



## coinmaster

> 2) I would not operate 4P1L without proper grid drive. I found out by extensive experiments that 4P1L does in fact draw quite a lot of grid current on transients. This ruins the dynamics of the amp unless the grid is properly driven. This can be easily accomodated with a simple source follower, look at my Red Star schems. You can read Sonics comments on this grid drive subject in this thread also.


How much current did you measure on the grids? Bartola's gyrators in that schematic are intended to be used as mu followers so they are essentially a low impedance source follower anyway.


----------



## SonicTrance

So I'm in the process of building version 2.0 of this amp. Now with separate psu chassis and signal chassis, featuring 6C8G input and 47 output tubes. Thought I'd post a bunch of in progress pics of the build for anyone interested. It'll be like a build log.


----------



## SonicTrance

Here's where I'm at now. Psu chassis done, will probably need to adjust some R's in the filters but other than that all done. Here in the signal chassis I've mounted input stage gyrators and B+ decoupling caps as well as one parafeed cap. More to come.


----------



## gug42

Wahou really nice jobs. Beautifull works  Hope one day to be capable of doing a so nice work   

Where did you buy the enclosure for toroidal transformers  ?


----------



## SonicTrance

gug42 said:


> Wahou really nice jobs. Beautifull works  Hope one day to be capable of doing a so nice work
> 
> Where did you buy the enclosure for toroidal transformers  ?


Thanks!
I got the tranny covers from some Chinese ebay seller, of course


----------



## SonicTrance

Wiring up the 6C8G's



 
Lots of resistors in the sockets. These are 100ohm stoppers for grids, anodes and cathodes.


 
Put a 400mVpp signal through the input stage and this is what came out. One phase is grounded so the µ36 gets cut in half to µ18. Looks very good so far.


----------



## SonicTrance

Grid drivers with 0.25µF KBG coupling caps are in and tested! Works as planned. Also hooked up the VU-meters. Pretty hard not to have it look messy with all these wires! Will try to tidy up a bit later on. Next step will be gyrators and voltage reference for the #47 output tubes.


----------



## MrCurwen

It looks clean enough. Remember parallel wires are just extra parasitic C in the circuit!

What P to g2 resistor value are you going for with the 47's?


----------



## SonicTrance

Think I’ll start off with 1k and if there’s oscillation move up to 10k, or something in between. What do you suggest? Maybe go for 10k from the start?


----------



## SonicTrance

Been soldering for two days straight. All that’s left now is output wiring. Everything else is in place with all good voltages and nice sine wave at the output. Can’t wait to listen to it for the first time!


----------



## MrCurwen

Looks very good!

How's the noise floor? I'm thinking mainly considering the filament supplies on the 47's. 

The OT should eat most of it away if there's any, but it's one of the possible problem areas.


----------



## SonicTrance

So, here's how the internals looks finished! The ice cream sticks on top of the large parafeed caps are there to make the caps level with the bottom cover, to ad support. Amp sounds fantastic, I'm very happy with it. 

Signal chassis:


 

Psu chassis:


 

Will take some nice pics of the exterior and update first post later.


----------



## gug42

nice works 
I like to see your post and photos


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## Maxx134 (Dec 11, 2017)

SonicTrance said:


> So, here's how the internals looks finished! The ice cream sticks on top of the large parafeed caps are there to make the caps level with the bottom cover, to ad support. Amp sounds fantastic, I'm very happy with it.
> 
> Signal chassis:
> 
> ...


From looking at all the point-to-point wiring,
This would have taken me countless sleepless days worrying I miss a solder spot! Lol
*I like* how you used the resistors leads instead of more wiring, or making a Circuit Board.

Wow just excellent work beyond normal.
Nice big block caps you have on sides.
They look like industrial or type you see in high voltage lamps.

Nice touch using what looks like lamp sockets for connecting between PSU and amp, right?


----------



## SonicTrance

gug42 said:


> nice works
> I like to see your post and photos


Thanks gug42!



Maxx134 said:


> From looking at all the point-to-point wiring,
> This would have taken me countless sleepless days worrying I miss a solder spot! Lol


I build each module outside the case before I install (glue) them in to place. Makes it pretty easy.




Maxx134 said:


> *I like* how you used the resistors leads instead of more wiring, or making a Circuit Board.


Yes! I think point to point is the way to go.



Maxx134 said:


> Wow just excellent work beyond normal.
> Nice big block caps you have on sides.
> They look like industrial or type you see in high voltage lamps.


Thanks Maxx!
Those are the 4µF 400V KBG parafeed caps. And yes, they're huge, lol.



Maxx134 said:


> Nice touch using what looks like lamp sockets for connecting between PSU and amp, right?


No, I use two octal sockets to pass what's needed from the psu to the signal chassis.


 
I've the filament supplies for the 47's in one octal socket. Four local grounds and four hot wires.
B+ for the LTP, B+ for the power buffer, B-, 12V for the meters, chassis ground and 6.3V heaters for 6c8g's in the other.


----------



## MrCurwen

> Yes! I think point to point is the way to go.



Yes, so much more easier to troubleshoot and mod. In my opinion there's no way to do really good experiments without P2P.

This is how all amps and electronic instruments were built in the golden days of tubes. Once you get enough practise, it's much easier than dealing with a PCB.

Prettiness of the layouts do of course vary a lot, Sonic is very good at 3D layouts.



> They look like industrial or type you see in high voltage lamps.



They are in fact industrial types. Mostly military, "EMP resistant".



> No, I use two octal sockets to pass what's needed from the psu to the signal chassis.



The outer insulation makes the wire look very good. I just twist the individual wires around each other and leave it like that. Oftentimes I use different colours for the wires...


----------



## SonicTrance

I updated first post with final pics of version 2.


----------



## iTsCraig

SonicTrance said:


> I updated first post with final pics of version 2.


well done on an extremely good looking AMP
I am glad to hear it sounds good


----------



## SonicTrance

iTsCraig said:


> well done on an extremely good looking AMP
> I am glad to hear it sounds good


Thanks!
I’m glad you like it. Appreciate the feedback!


----------



## MrCurwen

That's a beautiful amp, inside and outside!

Do those dampers work? Do you have bad microphonics without them?

It is common that directly heated tubes have some microphonics, but usually it's very mild. One amp I built (with 4P1L) had a strange condition - if the music played had a big transient, that transient would cause a kind of an echo. Not repeating, but kind of like a sustain effect. With headphones no less! This would stop if you changed the tubes or damped the offending tube enough. I guess the filament was just kind of loose on that tube.


----------



## SonicTrance

MrCurwen said:


> That's a beautiful amp, inside and outside!


Thanks!



MrCurwen said:


> Do those dampers work? Do you have bad microphonics without them?


I can't tell you if they work or not as my tubes are not microphonic. I think they look cool, that's why I got them!


----------



## Maxx134 (Dec 22, 2017)

coinmaster said:


> That's how I see output transformers, an old flawed methodology . As I mentioned in the other thread, a voltage follower buffer by definition will skew the current through the transformer due to its inductance, I think if you are going to stick with a transformer output then driving it with an active current source buffer instead would perform better because it will ignore all parasitics thanks to Kirchhoff , after all a transformer is run by current, not voltage.


But then it would be in thw signal path, right?
Then it would be a hybrid design no?
I would not want that.
Why?
 I still notice with both hybrids, and fake hybrids (buffer tube stage), and solid state amps... A problem.

Problem is that they all still cannot convey as much  3 dimensiomal space as good as a tube amp..
I feel This issue is hidden with speaker amps because the room will make up the soundstage.
But when having headphones on you get to hear the true nature of amp without room and speakers to add to it.

So the amps with poor soundstage are revieled with headphones...
and so I can also see how MrCurwen states the use of paralleded tubes can blur the details.



MrCurwen said:


> Using the topology described in this thread you can achieve top results using only a cheap OT...


I would not have believed this if I didnt witness this myself on my mini amp.


It is using tiny
Japan Z11 EI48 24 Output Transformers ,

And the huge 6bg6 tubes troide strapped  ha.
It is also using a switching PSU which is interesting, and I habe noticed the SS TO-220 transistors before the driver tube which indicate to me a similar approach in using new design.

So now with the positive experience of this mini amp I am very convinced in these New approaches, instead of older & expensive  designs.


----------



## Maxx134 (Dec 22, 2017)

SonicTrance said:


> featuring 6C8G input and 47 output


Hey SonicT, what was your reasoning on the 47 tube?
I see there is also the 46 tube and the 71A tube and the 6A4 tube,
All being like the 47 as a lesser cost alternative.

I know you have very similar taste as me in tubes and I also love the  6C8G as driver tube, but that was in our LittleDot amps which (like most tube amps) is  prone to tube rolling differences to get best sound...

I need to look further into the output tube choice,
 as I was heavily under the impression that the 45 and 2a3 was best and the 300b most linear..

I had my mind set on a totally different design but am glad I waited a year to see your project first...
If (when) I go for next project I am heavily leaning on your (MrCurwen) topology,
But would still would like to implement some change like an autoformer for volume, if not too expensive.

Anyways, I would like anyone's input on the DHT output tube choices..


----------



## MrCurwen

Once again, everything is in the signal path.

At least everything you can 'hear', meaning everything that has any amount of effect on the sound quality (or, in the case of not-HIFI, tone) of the audio output. 

So, I really don't understand this "it's in the signal path" thing. What use is it to ask that? If changing some part of the amp has absolutely no effect on sound output quality, why discuss it? If it does, it's in the signal path.



> Problem is that they all still cannot convey as much 3 dimensiomal space as good as a tube amp..



Sonic do you have a comment for this?

As an aside, I have never heard the term "fake hybrid" before. Please elaborate.



> So the amps with poor soundstage are revieled with headphones...
> and so I can also see how MrCurwen states the use of paralleded tubes can blur the details.



Indeed. Parallel caps also, but this is highly context dependent. 



> I would not have believed this if I didnt witness this myself on my mini amp.



Interesting. So it's a SE parafeed amp?



> So now with the positive experience of this mini amp I am very convinced in these New approaches, instead of older & expensive designs.



Maybe I'm cheap but I cringe thinking about the cost of one build of the scheme described in this thread. I'm always finding ways to try and cut corners and make it cheaper.

Indeed with only a few changes it's possible to achieve 92% of the sound quality with significantly lowered price.



> I see there is also the 46 tube and the 71A tube and the 6A4 tube,
> All being like the 47 as a lesser cost alternative.



71A as a LESSER cost alternative to the 47? I must've misunderstood or times sure have changed from my tube buying days. I came to the 47 because I got tired of trying to find affordable 71A's for my amps.



> I need to look further into the output tube choice,
> as I was heavily under the impression that the 45 and 2a3 was best and the 300b most linear..



Again, 4P1L is the undeniable king of DH tubes. And also king of all tubes in it's mu and rp area. Only reasons to use american tubes are

1) aesthetics

2) you are building a recreation of a classic amp, i.e. aesthetics.

Not to say you can have first class results with them also; the 47 was after all ranked almost as low THD in the distortion benchmark I linked way back.




> But would still would like to implement some change like an autoformer for volume, if not too expensive.



What is your objective with the autoformer?

In any case, the volume pot / stepped attenuator is basically a non-issue. There is really zero audio gains to be made there. I don't hear any difference in sound quality between using an Alpha pot (yes, the guitar amp kind) and precision fixed resistors (unadjustable attenuator). If you have a balanced input (XLR) then stepped attenuator is more handy. Otherwise just go with the Alpha pot.



> Anyways, I would like anyone's input on the DHT output tube choices..



1) Don't go DHT. 

2) If you go DHT, use 4P1L.

3) If you have a specific aesthetic in mind, go for 33 or such. 47 if you simply must have big bottles. 2A3 is for suckers, 45 is too expensive and 300B is just pointless (although very pretty and linear). 

With big current DH tubes you are just digging a very hot hole for yourself. Unless you MUST have DH tubes, just don't. 

The sound quality difference is quite metaphysical in nature. Meaning you must really hard believe that you are hearing it to really hear it. It's not a "night and day" thing.

With some amps it can be, I know. Not with this one. The 6P31S version has "DHT sound" already built into the schematic. 

Just go with the TV sweep tubes. I myself think they're pretty.


----------



## SonicTrance

Maxx134 said:


> Hey SonicT, what was your reasoning on the 47 tube?


It was recommended to me by MrCurwen as he knows I like big bottles. I just wanted to build this amp using DH tubes and wanted to use globe tubes as I like the look. 
The 71A has much smaller envelope, so is not as impressive looking  It's also a triode rather than a pentode. Not that it matters.



Maxx134 said:


> I know you have very similar taste as me in tubes and I also love the 6C8G as driver tube, but that was in our LittleDot amps which (like most tube amps) is prone to tube rolling differences to get best sound...


The 6C8G was chosen for two reasons;

1: It has µ36 which is perfect for this amp as I need more gain than the 6SN7's µ20 for driving speakers.

2: Aesthetics, it just look sweet with the ST bottle and top grid cap! Also quite affordable still.



Maxx134 said:


> Anyways, I would like anyone's input on the DHT output tube choices..


You can use any linear tubes you want and it'll sound fantastic! If you build with the output buffer you can also use output tubes with high rp, if not then preferably use output tubes with low rp. Remember, if you look at datasheets for a pentode it will list a very high rp. You need to look for the triode curves for that tube!



MrCurwen said:


> Sonic do you have a comment for this?


Not really, no.



MrCurwen said:


> Again, 4P1L is the undeniable king of DH tubes. And also king of all tubes in it's mu and rp area. Only reasons to use american tubes are
> 
> 1) aesthetics
> 
> ...


This^^
Aesthetics is very important to me. So is SQ of course. I want the best of the two! I'm very happy with my choice of tubes. Though, the DH tubes each require a separate PT (winding) and their own reg. So it dramatically complicates the build! That being said, I have no regrets!


----------



## Maxx134

MrCurwen said:


> As an aside, I have never heard the term "fake hybrid" before. Please elaborate


Yeah sorry thats just my own opinion of some equipment that use tube for the sake of having it,
 while not even having it implemented to perform any useful amplification.
Its not a real term just an observation.



MrCurwen said:


> 71A as a LESSER cost alternative to the 47?


Yes my mistake  I really need to do more research into these tubes .



MrCurwen said:


> ) If you have a specific aesthetic in mind, go for 33 or such. 47 if you simply must have big bottles. 2A3 is for suckers, 45 is too expensive and 300B is just pointless (although very pretty and linear).


That's some real advice! much appreciated thanks.


----------



## Maxx134 (Dec 23, 2017)

SonicTrance said:


> Aesthetics is very important to me. So is SQ of course. I want the best of the two! I'm very happy with my choice of tubes. Though, the DH tubes each require a separate PT (winding) and their own reg. So it dramatically complicates the build! That being said, I have no regrets!



The more I looking at your tube choices,
 the more I see myself liking your choices.

I have same exact preference as I have same driver tubes in my littleDot now.

I have to start planning  lookiing into chassis style lol.

In really like the implementation of your
 Chassis setup,
as it remind me of the Woo Wa33 which I also heard ..

Both the Woo Wa33 and the Eddie Current Studio which I heard,
are both using 2a3 tubes,
 and its so funny to me when reading what MrCurwen stated here about the 2a3 is for suckers lol.
It definitely makes the amp more sellable.

Both of those amps, I heard,
and they have a characteristic large powerful soundstage but I do not care for 2a3 and also think it is more  for aesthetics and popularity while being  expensive.


----------



## SonicTrance

Maxx134 said:


> The more I looking at your tube choices,
> the more I see myself liking your choices.


Yes, they are good choices! 

However, you would get pretty much the exact same gain if you used triode strapped EL36's instead.
Superbly linear tube.


 



Maxx134 said:


> In really like the implementation of your
> Chassis setup


Yes, separate psu chassis seems to work very well!


----------



## baronbeehive (Dec 24, 2017)

Wonderful work Sonic!

I agree that P2P must simplify enormously any problem solving you need to carry out. The  whole thing looks complicated this way but as you say some form of modular construction lies behind all that mass of wiring fortunately lol!

I just had part of the trace come up during a repair but managed to circumvent that. I'm still trying to fix my LD!!!


----------



## Maxx134

baronbeehive said:


> I just had part of the trace come up during a repair but managed to circumvent that. I'm still trying to fix my LD!!!


I in same boat I have to check my socket pins for a cold solder joint that opens with tube heat  2min into playing music .
Just didn't have time to fix.

LD amp was a great learning experience for me and more a sentimental value but like Sonic I ready for another project.

You should post your current issues in the LD thread .
Merry Christmas guys.


----------



## SonicTrance

baronbeehive said:


> Wonderful work Sonic!


Thanks, baron!
So, when are you starting to build this amp?


----------



## SonicTrance

Maxx134 said:


> LD amp was a great learning experience for me and more a sentimental value but like Sonic I ready for another project.


I agree! The LD is where it all started and it will always be special. This is at another level though. 

Merry christmas!


----------



## baronbeehive

SonicTrance said:


> Thanks, baron!
> So, when are you starting to build this amp?



Next week!!!

Yes it's been good, I never thought I would do anything like this. Maybe this is just the start of an exciting adventure.

Merry Christmas guys,


----------



## SonicTrance

baronbeehive said:


> Next week!!!


Really?!!


----------



## MrCurwen

Happy Christmas from me too.

Regarding tube selection for this schematic specifically: 

You probably need to change your way of thinking a little bit. Instead of getting a tip of what's hot right now, simply look at some datasheets. If you don't know where to start, look at some eBay stores and start to look up tube datasheets from Frank's for example.

Any tube that has just about the right mu (3 to 20 depending on your needs; input tube mu and source level), just about right rp (800 to 6000 ohms, 1k recommended if no output buffer as Sonic explained) and just about right gm (if the two conditions mentioned before are met, this is met as well).

No need to find "a perfect tube" with regards to anything else besides good, linear curves. All else is just fine if somewhat in the parameters mentioned above.

In short: look at the curves. They tell everything.

Some beam tetrodes and pentodes don't have triode curves listed. Then you can make an educated guess based on a number of variables. This is a longer post and maybe I won't get into this here. 

I strongly recommend that you use some sweep tube. There are some with rather big envelopes as well. Make the signal chassis so that if you get the urge, you can fit other socket there later. Also leave 50% of the PSU chassis empty for this same reason.

The DH version is not sensible use of money and effort, at least for a first complicated build. Maybe second build. The 6P31S version sounds just as good, the DH part is just so you have DH, if I'm being a bit rude.


----------



## SonicTrance

Ok, so I've made my first ever power measurement on this amp:




 

Excuse the blurry pic. This is right before clipping with a 3.9R load @ 1kHz. So 0.48 Wrms of output. So quite low output power, but it's more than enough with this amp! Was planning to test with different loads but broke the output buffer on the first try! Doubt I'll do this again after repair.


----------



## MrCurwen

Great work!

I've broken a couple of amps doing this measurement.

Calculate which clips first, voltage or current. Probably current.


----------



## SonicTrance

Yes, current right before clipping is 0.35 Irms. Voltage is 1.37 Vrms before clipping.


----------



## baronbeehive

Hey Sonic, when you have the time are you going to fill us in with more detail on your design, how it differs from your earlier amp, the rationale behind it, what stage you are at etc. I gather you are testing now so let us know how it all goes.


----------



## SonicTrance

baronbeehive said:


> Hey Sonic, when you have the time are you going to fill us in with more detail on your design, how it differs from your earlier amp, the rationale behind it, what stage you are at etc. I gather you are testing now so let us know how it all goes.


The differences between this amp and the previous build are the tubes and layout of the build. Last build had input stage in one chassis and output stage in another with separate psu's. This one has one chassis for psu's and filament supplies. And one signal chassis. Much, much better layout!  

The first amp had oscillation problems in the psu's. Got rid of most of it when I took out the rectifier tubes and replaced them with diodes, but still the oscillation came creeping back. So I decided to start from scratch and build a new, more thought out amplifier. Also wanted it to drive speakers, which it does flawlessly! I have a pair of Monitor Audio Bronze 2's hooked up to it in my lab/listening room. Sounds very good!

Tube choices (6C8G + 47) were based on tube characteristics as well as aesthetics. I chose DH output tubes just because I wanted to go "all out" even though same fidelity can be had with IDH tubes. Also I'm a tinkerer and love projects and challenges!

Amp is complete. I've used it daily for a few weeks. I just now got time/energy to do the power output test.


----------



## baronbeehive

SonicTrance said:


> The differences between this amp and the previous build are the tubes and layout of the build. Last build had input stage in one chassis and output stage in another with separate psu's. This one has one chassis for psu's and filament supplies. And one signal chassis. Much, much better layout!
> 
> The first amp had oscillation problems in the psu's. Got rid of most of it when I took out the rectifier tubes and replaced them with diodes, but still the oscillation came creeping back. So I decided to start from scratch and build a new, more thought out amplifier. Also wanted it to drive speakers, which it does flawlessly! I have a pair of Monitor Audio Bronze 2's hooked up to it in my lab/listening room. Sounds very good!
> 
> ...



I see, thanks for that!

I like the layout with separate PSU, sounds ideal.

I don't know about your Monitor Audio Bronzes but I would never change my Silver's, I love the refined sound of them, nice and detailed, balanced with just a hint of warmth.


----------



## Maxx134 (Dec 27, 2017)

Hey Sonic although your measuring power that is RMS and the unit is wired in triode mode and balanced and is class A right?

I was assuming it should be as powerful as an amp using 2a3 tubes.
Edit:
Never mind 2a3 is a bit more overall power depending...


----------



## MrCurwen

Most 2A3 amps run 60mA or so current. This amp has 15mA per current buffer. In PP a 2A3 amp would have about 120mA of current capability in theory, per channel. This amp has about 30mA per channel theoretical maximum.

Also 2A3 amps usually have Va of 200 or 250V. This amp has Va of about 170V. 

Power is made of current and voltage; get more of those and you get more power. However, VOLUME is not necessarily made out of power only. Sonic's amp is probably able to provide the same amount or maybe more of CLEAN listening volume. Volume is mostly not about RMS power, rather it's about transient delivery. 

That is what this amp does incredibly well (in my opinion); transient response. I have not heard a faster sounding amp at any price point in any High End event.

If transient response is ok, RMS power is an afterthought.


----------



## Maxx134

I read in the 47 data sheet that the tube may emit some blue glow.
Is it visible?
SonicTrance it would be great to see some pics of tube glow..


----------



## SonicTrance

Maxx134 said:


> I read in the 47 data sheet that the tube may emit some blue glow.
> Is it visible?
> SonicTrance it would be great to see some pics of tube glow..


Sorry, no blue glow that I've seen. It does look pretty though with the two filament wires glowing.


----------



## MrCurwen

Blue glow is gas inside the tube. It glows when it heats up.

It's either trapped there during manufacturing or leaked in gradually after that. In the case of the first, it's rather benign, in the case of the latter, it means the tube is losing vacuum, there is a leak. Gas inside tube is one of the signs of failure.

Gas inside tube can cause problems. It is attracted to the anode and the grid. If enough foreign material attaches to the grid, it may shift the bias point and also impact linearity. To prevent this in later production tubes, some of the heavy duty (such as TV sweep tubes) types had gold plated or solid gold grids. Gold is much more unreactive, so no foreign material gets alloyed with it.

In short, the blue glow is often not a horrible thing, but it is nonetheless unwanted. If your tubes don't glow, be happy.


----------



## SonicTrance

Maxx134 said:


> SonicTrance it would be great to see some pics of tube glow..


This is the amount of tube glow you can expect from the 47's




 



 

And a pic of the backside of the signal chassis for no particular reason.


----------



## MrCurwen

Am I the only one who sees the aesthetic in metal envelope tubes? 1619 is basically a 45, superbly linear and dirt cheap. And beautiful!

Gor light effects you can always use a magic eye tube or a small CRT! Especially the small CRT showing the signal is very beautiful to watch.


----------



## SonicTrance

Do you mean a CRT tube like this?







MrCurwen said:


> Am I the only one who sees the aesthetic in metal envelope tubes? 1619 is basically a 45, superbly linear and dirt cheap. And beautiful!


Beautiful, no. I think they look like dirty old lytic caps, lol.


----------



## MrCurwen

I guess I have an engineer's eye.

Yes, there's even smaller, 1 inch screens. Smaller CRTs are easier to fit to places and they require much less complicated PSU's. Most 1 inchers can give good brightness with 300V or so, bigger ones need more voltage for decent brightness.

I've built a few CRT 'scopes', they display the music signal that is playing. Quite distortedly in HIFI terms, but who cares, it's nice to watch anyway!

Here's a couple of vids, taken with a cell phone:



Here's some theremin music by the wonderful Clara Rockmore:



At the end I put on a square wave. The scope doesn't display it as square, more like a triangle. Sine waves it did great. The CRT itself can display anything correctly, but it's about the support circuitry. I just threw something together with as little parts count as possible.

The Y axis is controlled by the music signal, amplified by EF80 in pentode mode. The X axis (refresh rate of the screen, basically) is controlled by another EF80 acting as an oscillator. If you input a music signal that is the exact same frequency as the oscillator, the wave will appear to stand completely still on the screen. In other cases, it will move left to right.

The oscillator frequency will also determine the 'resolution' of the scope. If you set the oscillator high, the screen will display high frequency information from the music signal. If the oscillator is low, it will display lower frequency information, i.e. the waveform will be smoother.

I love CRTs, I've got 11 industrial / military (radar screens) of different sizes. Biggest one is 8 inches, from USA 1940's military. Second biggest is 17 cm from West Germany 1950's I think. I've got 2 913's, I plan to make a small "robot head" with the 913's as eyes, displaying music waveform that is playing.


So many projects, so little time... I wonder when I'll ever finish half the stuff I want to build. Such is DIY I guess.


----------



## Maxx134

MrCurwen said:


> Am I the only one who sees the aesthetic in metal envelope tubes? 1619 is basically a 45, superbly linear and dirt cheap. And beautiful!


Wow that don't even look like a tube hehe.
Maybe for a driver tube the low key dark  appearance would work ,
so it wont take away from bigger output tube appearance..
Still it looks like meant for a truck.
Ha yes a shame lots of  good tubes look so ugly (to me).


----------



## MrCurwen

> Still it looks like meant for a truck.
> Ha yes a shame lots of good tubes look so ugly (to me).



Shame for you, good for the rest. No reason to bring prices up.

For me, the beauty in an amp (after considering it's sound quality and transparentness) comes in this order:

1) The schematic. How clever are the technical solutions, for example I find great beauty in the complementary approach I described earlier in this thread. "Weaknesses" canceling each other out.

2) Outsmarting audiophools, to put it in rude terms. I find an amp beautiful to look at, if it has tubes that perform superbly and cost next to nothing, because other people haven't figured out how to use them, or find them unaesthetic or some such nonsense. It really warms my heart to look at an amp like that.

3) There is some history behind the tubes. I really like to read tube lore and find out what different tubes were used for and where.


Which brings me to my next point;

Most tubes were meant for things like trucks and factory machines. Radios and radars and CRT circuitry. Only a small handful of tubes were ever designed for audio duty. Many were adapted for it, like 300B (telephone and wire transmitter amplifier, quickly adapted for some movie theater consoles) and 6SN7 (TV sweep tube / oscillator).

If I may continue my rude commenting for just a bit longer;

A modern audiophile commenting on a tube's looks as pretty is like the stereotypical woman commenting that a car is a good car because it has a nice colour paint job.

But in all seriousness, people have different aesthetic preferences. Many different tubes (and other components) can be used to achieve superb results, so it's not that serious. I explained the reasoning behind my own aesthetic views above, you may have yours.


----------



## Maxx134 (Jan 2, 2018)

I have a question about the power buffer .
Is C1, C2, acting as coupling caps?
If so how do you negate any sonic characteristics of the capacitor?
Sorry I probably overlooked this and have to read the thread again.
I am guessing only C3 would be the important cap, as it inline with the output transformer.
Its Very interesting & I have limited time to learn these new designs but will catch up reading eventually.


----------



## SonicTrance

Yes, C1 and C2 are blocking the DC coming from the gyrator outputs. 

The power buffer followers are then biased at exactly half of B+ through the voltage divider for most available voltage swing. 

When you get to building you should experiment with different caps to see if you can hear any differences. 

I use quality russian KBG's for coupling from input gyrator to grid drivers, output gyrator to power buffer and as parafeed caps. 

I did experiment with butique caps in my first build. Could not hear any difference. I havent tried butique caps in parafeed position though as it would get very expensive.


----------



## MrCurwen

> If so how do you negate any sonic characteristics of the capacitor?



A capacitor does not have an intrinsic sound. Whether or not a capacitor has a sound (or what that sound is) is determined by 

1) what is before the cap, i.e. driving the cap

2) what is after the cap.

C1 & C2 from the power buffer schematic are in such positions that they have basically no load (except on the highest transients). In follower mode the FET has a tiny input capacitance (not so in other modes). On the other side, driving the cap, is a decently low output impedance follower as well, able to deliver very good current.

These caps have their parasitic properties "flooded with current", i.e. low output impedance.

C3 is a bit different, but in many ways very much the same situation. Within this context of a high quality film cap (all but the very cheapest are in fact high quality, and any real foil with impregnated paper whether wax or oil is high quality) the output impedance and drive capability of the follower is quite overkill. The follower is more than easily able to control the primary, and has plenty of drive left to deal with the cap as well.

Anyone can play the "you haven't tried cap X yet so you cannot say anything" game. That game is for people who don't understand principles. Sure there are exceptions to any rule, but that doesn't mean the rule is not useful. Here the principle is that sufficient drive removes the capacitors 'sound', leaving it transparent. 

I did try several different kinds of caps (both soviet NOS and other kinds) in the parafeed position. You can say none of those caps were "high quality" by some standard you choose to  take, but those same caps had in my previous (quite traditional) circuits provided very variant sound quality results.

In this kind of a circuit they really didn't. For a while I used only KGB's which are the highest quality true foil paper in oil caps, very good sounding. After many tests I don't know if they sound different than the cheaper MBGO's which are true foil with waxed paper caps.


I would recommend you try this circuit out with the russian caps first. Then do your experiments. I am 99% sure you will find no sound quality related reason to not leave the russian caps in the circuit.


----------



## Detectit

Wow that's a damn sexy looking tube amp. 

If it was a PCB diy project i would have build it. 

Great work!!


----------



## SonicTrance

Detectit said:


> Wow that's a damn sexy looking tube amp.
> 
> If it was a PCB diy project i would have build it.
> 
> Great work!!


Thanks!

This might not be as straight forward as a pcb kit with step by step instructions, but as long as you are comfortable soldering and learning it really isn't hard. We'll gladly help you in this thread if you want to build!


----------



## umeng2002

Making/ getting your own PCBs made aren't tough these days. But it does add extra design work since it adds resistance, etc. over just soldering components directly to each other.


----------



## SonicTrance

But why mess with a PCB if you dont have to?
The flexability you get with p2p is unbeatable. Very easy to work with.


----------



## Detectit (Jan 9, 2018)

Soldering and some basic electrical skills i have.
But i am not confident in ordering parts. Read: quality and suitable parts. 1.000 different types of resistors and caps.

And a step by step tutorial is more or less needed.

Just finished my first humble headphone amp. Starving hybrid Millet.... Yes it's a PCB version.
3.5mm jack integrated in the enclosure to plug in the Cayin N3.

Maybe in a later stage I am more confident to build something great as yours.
Adored the pics of the silver unit a thousand times. In love....

Maybe it's not done to ask, if not forgive me. But what is the approx BOM costs..


----------



## baronbeehive

umeng2002 said:


> Making/ getting your own PCBs made aren't tough these days. But it does add extra design work since it adds resistance, etc. over just soldering components directly to each other.



All my problems with my amp mods to date have been down to problems with the PCB, P2P would have eliminated them!



Detectit said:


> Soldering and some basic electrical skills i have.
> But i am not confident in ordering parts. Read: quality and suitable parts. 1.000 different types of resistors and caps.
> 
> And a step by step tutorial is more or less needed.
> ...



Hey... I have that album lol!

Yes a guide to the build is a good idea.


----------



## SonicTrance

Detectit said:


> But i am not confident in ordering parts. Read: quality and suitable parts. 1.000 different types of resistors and caps.


I've used all Russian NOS film caps as per recommendation from @MrCurwen. He's very knowledgeable about these things. They are high quality and still cheap. All resistors , except in the psu's, are 1W carbon films, nice and cheap. No reason to go with "audiophile" caps or resistors in this circuit!



Detectit said:


> And a step by step tutorial is more or less needed.


We can help with that. Can you read a schematic?



Detectit said:


> Adored the pics of the silver unit a thousand times. In love....


Thanks!
I liked those chassis too. I need to build something in them again (the insides are ripped out now). Will need to get some new top plates though.



Detectit said:


> Maybe it's not done to ask, if not forgive me. But what is the approx BOM costs..


Very hard to answer. You can build this amp for very little money. It depends how much you're into aesthetics? Sky is the limit! Most expensive part for me was the balanced stepped attenuator. If you don't need balanced inputs you can just use a stereo pot. MOSFET's, transistors, caps and resistors are all quite cheap. You can also use cheap tubes as long as they're linear, like TV sweep tubes. One thing I bought cheap for the first amp (silver) was the tube sockets. That was a big mistake! They became quite loose after short period, not good. This time I spent more money on teflon insulated sockets with tight fit. Very happy with them!


----------



## MrCurwen

Detectit, don't be intimidated by the way a P2P build looks! IRL it's not as complicated. As Sonic pointed out it's actually less complicated. Also, if you're into it, there's the historical reason; this is how everything was made for decades.

As for component selection; the main rule is it's not that big a deal. Here are my recommendation.

For resistors, the most important thing is to observe correct wattage. Most resistors in these schems should be cheapest available 1W carbon film resistors, or 1W metal film. Either is fine, I always use carbon film myself. There will be absolutely no sound quality difference; go with the cheapest.

Capacitors; 

1) 1.5µF / 160V types are K73 types. You can buy these off eBay very very cheaply. Buy a full box.

2) 250nF high voltage types are MBGO or any OMBG (these are the same cap type for different application originally). Very cheap, buy in bulk.

3) I recommend you just buy MBGO for the parafeed caps as well. Sonic uses 12µF, but 4 or 8 µF is probably sufficient. This is dependent on your load.

4) PSU electrolytics; go with the cheapest, but if you have lots of heat (very small chassis) I'd recommend you invest a couple of pennies for 105 degree versions. 


OT's should be Hammond 125D or 125C. Either is fine, there will be absolutely no sound quality difference. 125A is also fine. There is no DC flowing thru the primary at all. Hammonds should be pretty easily available everywhere.

IRF830's can be bough in bulk (please do, you'll need them) via eBay for 14 euros per 50 or so. Get double or triple amount of what you need. 

Same goes for 2N2222(A). Get a lot of these, they don't cost much.

For wire I recommend teflon covered wire because it is great to handle and doesn't burn when touched with soldering iron. It is a bit expensive though. 


For tubes I recommend 6SL7 or 6SN7 and 6P31S for 8 pin. For 9 pin 12AX7 and EL81. There will be absolutely no sound quality differences.

If less gain is needed, E180F or 6J9P for noval input tubes.

Buy only the cheapest tubes.

You can achieve 96% of sound quality by just dumping the output buffer. You can leave room for it and add it later if you so wish. It really is a beautiful and great amp even without it.

Depending on your chassis choises, this amp can be built for 300 to 400 euros. If you leave the output buffer and go for the cheapest tubes and caps, 330 should suffice.

If you wish to save even further money, you can achieve 90% of the sound quality by making the input section single ended. I can provide easy instructions (schems) on how to do this. This adds a tiny bit of "tube sound" but the quickness, impact and realism is are still there. This simplifies building a lot, and cuts down on costs even further.

It might be worthwhile to make a set of schems that have as added text the component info (MBGO, K73, resistor wattage etc.).


----------



## MrCurwen

If you already have some tubes laying around, you can (probably) use them. Depends completely on the type. This circuit will sound very good with even less-than-perfectly-linear tubes like 6V6GT for example.


----------



## SonicTrance

MrCurwen said:


> 3) I recommend you just buy MBGO for the parafeed caps as well. Sonic uses 12µF, but 4 or 8 µF is probably sufficient. This is dependent on your load.


I actually use 4µF in the new amp as I needed to use the 400V caps. No room for more capacitance. Not needed as stated, frequency response is flat from 20Hz to 20KHz. I've no evidence (pics) of this but I did measure output amplitude from 20 - 20 000 Hz and it stayed about the same.



MrCurwen said:


> It might be worthwhile to make a set of schems that have as added text the component info (MBGO, K73, resistor wattage etc.).


I can do that and update first post!


----------



## SonicTrance

First post is now updated with schems with component types and values.


----------



## Maxx134

SonicTrance said:


> Most expensive part for me was the balanced stepped attenuator


Ok can you link me that stepped attenuator?
I did look into this a year ago with the little dot but I like that you did all those resistors yourself  haha


----------



## SonicTrance

Maxx134 said:


> Ok can you link me that stepped attenuator?
> I did look into this a year ago with the little dot but I like that you did all those resistors yourself haha


Here it is: https://www.hificollective.co.uk/ca...ed-attenuator-metal-film-resistor-p-9287.html
I got the Elma switch in kit form. They do sell it built as well for an extra £30. 
The switch feels very good when changing volume. One thing I don't like though is that there sometimes is a pop when changing volume. I've soldered an extra 10M resistor in parallell with the output of the attenuator, so from each 6C8G grid to ground. That completely removed the pop when there's no signal. It sometimes still pops when changing volume with music playing.


----------



## SonicTrance

Come on guys! Get to building! Or is someone secretly building without posting? Then post! I wanna see! 

Listening to my amp now as I'm prepping a chassis to build the SE version of this amp. Gonna be interesting to compare the two!

Inspirational pics:


----------



## Maxx134

SonicTrance said:


> I've used all Russian NOS film caps as per recommendation from @MrCurwen. He's very knowledgeable about these things. They are high quality and still cheap


Alot these russian caps are actually at a higher than average level (!).

 I would say as good as the best mundorf caps.
If I didn't hear it myself I wouldn't have believed it.



SonicTrance said:


> Very hard to answer. You can build this amp for very little money. It depends how much you're into aesthetics


I good way to see how much all will cost,
 is creating a project-parts list in the Mouser website.


----------



## SonicTrance

Maxx134 said:


> Alot these russian caps are actually at a higher than average level (!).
> 
> I would say as good as the best mundorf caps.
> If I didn't hear it myself I wouldn't have believed it.


Yeah, and as soon as you put a source follower, like grid driver or power buffer, directly after the cap, the cap becomes transparent! If good quality of course. I couldn't hear any difference between the russian KBG and Mundorf S/G/O's.


----------



## bloodhawk

SonicTrance said:


> Come on guys! Get to building! Or is someone secretly building without posting? Then post! I wanna see!
> 
> Listening to my amp now as I'm prepping a chassis to build the SE version of this amp. Gonna be interesting to compare the two!
> 
> Inspirational pics:




I really want to start building one. But im moving soon, so ill probably do it around the end of July. 

Will riddle you and McCurwen with questions lol 

In the mean meantime, how much did the parts cost? (Minus the cost of the chassis)


----------



## SonicTrance

bloodhawk said:


> I really want to start building one. But im moving soon, so ill probably do it around the end of July.
> 
> Will riddle you and McCurwen with questions lol
> 
> In the mean meantime, how much did the parts cost? (Minus the cost of the chassis)


Please ask questions! 

Parts dont cost much. Do like Maxx said and make a cart at mouser for example. The russian caps you get from ebay are also cheap.


----------



## bloodhawk

SonicTrance said:


> Please ask questions!
> 
> Parts dont cost much. Do like Maxx said and make a cart at mouser for example. The russian caps you get from ebay are also cheap.



Oh trust me there are going to be many! Now that i maxed out my MKVI+, i really am itching for the next DIY build. 

Are those Teflon sockets btw? I recently used Teflon Octal and Nine pin sockets and oh boy are these amazing. 

Gotcha, on it!


----------



## SonicTrance

bloodhawk said:


> Oh trust me there are going to be many! Now that i maxed out my MKVI+, i really am itching for the next DIY build.
> 
> Are those Teflon sockets btw? I recently used Teflon Octal and Nine pin sockets and oh boy are these amazing.
> 
> Gotcha, on it!


Yes, the sockets in the amp with 6c8g and 47's are teflon. Feels high quality compared to ceramic sockets.


----------



## SonicTrance (Jul 12, 2018)

SonicTrance said:


> Listening to my amp now as I'm prepping a chassis to build the SE version of this amp.


A little update on the SE amp build!

I'm reusing one of the silver chassis I used in the first LTP build, since that amp was in pieces anyway, and I really like the look of that chassis!
This is what I had to work with. Fortunately I have two so I can mix panels from the two to minimize drilling and unnecessary holes. 



Some new holes drilled and old superglue residue has been grinded off.


 


Tube sockets and transformers mounted! As you can see there're two loctal sockets. The amp will be C3G input and 6BG6/6P7S output. The rectifier socket in the middle will not be used for B+, but I have a plan for it!



I like the new more "busy" front plate. New additions are toggle switch to switch between speaker and headphone output. And the SE headphone jack since, well, SE amp. Will probably only use the XLR output jack anyway but nice to have both. Also gives the opportunity to listen with two headphones simultaneously.



RCA inputs and speaker outputs added to the back panel. I don't plan to have a switch between the RCA and XLR inputs, so I can only use one at a time but that's all I need.



Here's an experiment I did with the B- supply. I first built the filter using a 42 VAC PT and voltage doubler filter and this is what I got after the regulator:
The filter had about 8mV of noise but after the regulator there was 80mV of ripple.




While the above ripple probably wont hurt anything in a constant current draw amp I wanted to less noise out of principle. So I decided to get rid of the voltage doubler circuit and changed the PT to 115 VAC.
Here're the results:



Reg output on the left, filter output in the middle and AC ripple on the right.


 


I'm very happy with 3mV of noise. For some reason the two FET regulators doesn't seem to like voltage doublers. 
Those outputs are unloaded btw. Under load filter output should be around -125V and reg about -100V.


----------



## drtechno

the voltage regulator looks like a half wave, but the fets need a power supply with a lower output impedance that the uf4007 can provide. if you changed them to a lower drop diode (like a 6A10) it would work. But i would redo it so it was full wave voltage doubler...


----------



## SonicTrance

drtechno said:


> the voltage regulator looks like a half wave, but the fets need a power supply with a lower output impedance that the uf4007 can provide. if you changed them to a lower drop diode (like a 6A10) it would work. But i would redo it so it was full wave voltage doubler...


Thanks for your reply!
It's a full wave doubler like the example on the right below. With the diodes facing the other way of course since it's a negative supply.



 

The 6A10 is a beefy 6A diode. Way too big for my needs. This supply will draw about 15mA total. Anyway, I got a clean enough supply now with the 115 VAC PT. Will stick with that.


----------



## drtechno (Jul 13, 2018)

SonicTrance said:


> Thanks for your reply!
> It's a full wave doubler like the example on the right below. With the diodes facing the other way of course since it's a negative supply.
> 
> 
> The 6A10 is a beefy 6A diode. Way too big for my needs. This supply will draw about 15mA total. Anyway, I got a clean enough supply now with the 115 VAC PT. Will stick with that.


its not the amperage size, its the voltage drop (about 1/3 of a uf4007).  A much better diode to use there since you need a low impedance out.  also why have that 6.8nf cap in it? because I can see that shunting some of the current potential away n the power supply. The problem is your 10A regulator is starved for current. Alternatively, if you use something that would be more realistic, like a zfp4424A for a sub 1A regulator, you wouldn't need that high current demand (which requires a lower impedance output) on startup.. also why the high value caps since if the regulator is set up correctly, you can have 10% or more ripple coming out of the doubler, and sill be mv of ripple on its output. Parts of your circuit makes sense, others seem you are putting an elephant in a Volkswagen Beetle.


----------



## MrCurwen

drtechno, absolutely no malice implied here; either you don't know what you're talking about or I don't understand what you mean in your message.




drtechno said:


> its not the amperage size, its the voltage drop (about 1/3 of a uf4007).



This is not at all an issue. Look at the percentages of voltages; a lower voltage drop diode wouldn't change anything. UF4007 is more than able to pump the caps in that doubler or any high(ish) impedance PSU / circuit. 

Pumping the caps isn't the issue. It's oscillationl. It cannot be pumping the caps, since the measured ripple BEFORE the reg was higher than after. That means 100% certainty it's some kind of oscillation, most probably interaction between PT secondary (which has all kinds of nasty things) and the reg. If there were more R in series between these two, the problem would most probably go away. Just a theory based on experience, the cause of oscillation could be many things, but it is 100% certainly oscillation.



drtechno said:


> also why have that 6.8nf cap in it?



To increase stability. Shunt some MHz crap out before it gets into the FETs.



drtechno said:


> because I can see that shunting some of the current potential away n the power supply



No.

Look at the relations again. 6.8nF is a drop in the bucket when you are pumping current into the electrolytics. Absolutely no effect between these two.



drtechno said:


> The problem is your 10A regulator is starved for current.



Not at all. If you think so, please elaborate.

These kinds of regs are very easy to set up and very very stable. Useful tools. Absolutely no reason to run them at insane currents. Understand we are talking about a high impedance circuit driving 10k output transformers, not 4 ohm direct output transistor amp. The whole circuit draws some tens of mA.



drtechno said:


> Alternatively, if you use something that would be more realistic, like a zfp4424A for a sub 1A regulator, you wouldn't need that high current demand (which requires a lower impedance output) on startup



See this is where I definitely start to think you don't know what you're talking about. Again, no offence meant, just statement of fact.

A FET that is able to pass 10A of current does not NEED to pass 10A of current. It is 100% fine and useful (with lower gm) passing say 1mA. 

The reg doesn't try to draw 10A at startup. If you think this, please elaborate.




drtechno said:


> Parts of your circuit makes sense, others seem you are putting an elephant in a Volkswagen Beetle



I'm not sure if you mean the circuit as a whole, or this B- supply in specific, but I can kind of agree with this! It's a bit crazy circuit until you get into the details and read my stories (earlier in this thread) on how and why I put it together like this. There is a specific reason for most things in the circuit (some are just arbitrary, like most stuff before the regs in the PSUs) and all the parts fit together beautifully (in my opinion) in the end.

Of course the specific applications in the SE project are all Sonic, I just gave some ideas to him.


----------



## drtechno

some stuff looks oversize for what it does. Sometimes going too big in certain rating can cause the intrinsic flaws with a device to show up... Just saying.

oh, did you try a 1M resistor between your grid of the tube and the grid stopper and ground? Thats how I maintain bias in my 9A small signal tubes so the grid bias doesn't flop all over the place as I adjust volume in the unbalanced circuit.   

btw there shouldn't be any ground references in your signal path. This includes your attenuator,  and btw,  I don't really see your input circuit anywhere.

This woman needs chocolate now......


----------



## SonicTrance (Jul 1, 2020)

drtechno is obviously a troll. I don't feed trolls.

Build update:

I've completed one channel input stage and biased the C3G tube.
Grid bias on the left and voltage drop across R3 on the right. Operating point is 150Va, 10mA Ia and -2.48Vg (the -2.248 is to ground, not cathode)




Put a 400mVpp signal in and this came out. 19.2Vpp means a µ of 48. A bit higher than the 40 that's stated in datasheet.




Nice looking sine wave though. So far so good!


----------



## MrCurwen

Looking good!

You've got some serious measument tools there. Usually measuring grid bias at the grid is pretty useless, at least with a cheap multimeter. It doesn't give very accurate results especially with tubes where 2.2 and 2.4 V grid bias mean very different Ia.

But, this is not important. Important is that Ia us where you want it to be, and that can be very accurately measured as you've done.

10mA on a single voltage amplification stage. Whew, you sure are throwing efficiency out the window. Not that there is any efficiency to talk about in any of these designs anyway. 

Small correction; this SE amp is not constant current draw. The balanced amp is. When the output stage swings current, there is nothing to counteract that; in the balanced circuit the tubes (or the FETs above them) conduct in push-pull.

There are some schemes to make SE stages more or less constant current (most notably Broski), but I personally don't find them worth the trouble. Combination of simple but relatively effective B+ regulation and the gyrator offering high impedance load make the PSU relatively transparent compared to trad SE amps. Truth is, the SE amp is not as good as the balanced one, but it's SURPRISINGLY good if you've built a bunch of trad SE amps.

Also the CCS at the output also compensates this. That first 4mA portion of the wave IS constant current, the CCS acts as "counterweight" in that part of the wave. So microdetails get the "no PSU" treatment.


----------



## SonicTrance

MrCurwen said:


> 10mA on a single voltage amplification stage. Whew, you sure are throwing efficiency out the window. Not that there is any efficiency to talk about in any of these designs anyway.


Yes, looking at the triode curves for the C3G, 10 mA @ 150 Va looked like a good place to be. 



MrCurwen said:


> Truth is, the SE amp is not as good as the balanced one, but it's SURPRISINGLY good if you've built a bunch of trad SE amps.


Really looking forward to hear it for myself! Should be ready for first listen in the next few days.


----------



## SonicTrance (Jul 17, 2018)

More progress! Completed one channel output stage (almost, haven't wired the outputs yet)

This is at 6BG6 gyrator output. Operating point is 180Va, 20mA Ia (+4.3mA CCS) and -16.86Vg. At this operating point current and voltage should theoretically clip at about the same point.
50mVpp signal input. This is max volume:


----------



## SonicTrance (Jul 1, 2020)

The SE amp is now complete!

Here're some pics:

Overview of the inside. Yes! I have a thing for large Russian caps! Those large green ones in the middle are K75-10 10µ parafeed caps. Also used K75-10 caps for input and coupling.




To the right of the choke is the vu meter backlight ps. That's what I'm using the 274B rectifier for! I realize of course that it's completely unnecessary to take 115 VAC, rectify it with a tube/diode bridge and load it with two backlights @ 50mA a piece. The result is 8 VDC out and about 90mA current draw. That's maxing out the Sophia Princess "mesh" 274B! The lamps do get a very nice slow start anyway! Only doing this because it's fun and I wanted a use for the tube!



To the right of the speaker outputs is the ps for the fans. I have two 120mm fans on the bottom panel. See the ground lead going from the resistor lead there to chassis ground. I had to remove that as it caused hum to the amp. The fan ps is not very clean. It needs much larger caps than the 220µ that's there to make it clean, maybe 1mF. Good enough for fans though. I run them at 7V, very quiet. And with a floating ground no noise problem. The vu meter ps is also floating for the same reason. I've done one "circuit ground" and one "dirty ground". Was planning to have the first lytics in B+ and B- supply, HV centertap, meter ps and fan ps on the "dirty" point but meter ps and fan ps are now floating.




I have a pair of C3G's that I've stripped from their shield but can't use them. Way too microphonic. The shield actually grounds at the socket to circuit ground. Maybe the "naked" pair is naturally microphonic. Haven't used them in years.




















So, how does it sound? I've listened for a few hours only. To both my headphones (Audeze LCD-3 and LCD-XC) and speakers in my lab/listening room (Monitor audio bronze 2) and I'm very impressed! First thing a noticed was the lack of noise, there's none! Dead quiet! Even with my LCD-XC's which are my most sensitive cans and also my favorite. I would say the balanced LTP is a bit faster sounding and have bit more micro detail than this SE version. But the SE also sounds very crisp, dynamic and packs a punch. Bass is very pleasing indeed! I think the LTP pairs better with my speakers though than the SE.

The major advantage the SE amp has is obviously size. Only one chassis. Also much easier to build, less components. I could definitely live with only the SE version.

I've not done any power output test yet. Right now I'm just enjoying the music!

Feel free to ask questions!


----------



## MrCurwen

SonicTrance said:


> The SE amp is now complete!



Congratulations! The pictures show once again first class build quality inside and out. You've really got this P2P thing under control, I'm impressed.



SonicTrance said:


> Overview of the inside. Yes! I have a thing for large Russian caps! Those large green ones in the middle are K75-10 10µ parafeed caps. Also used K75-10 caps for input and coupling.



Have you made any noteworthy sound quality observations? These green K75-10's are later production, late 70's and 80's (some still made in the 90's), metallized plastic film with wax if I recall correctly. No oil. I've got a couple of these I've used (10µF / 400V) but as B+ caps they don't have much sonic impact anyway so I don't know how good they are.

I'm beginning to think correctly used all caps sound pretty much the same.



SonicTrance said:


> To the right of the choke is the vu meter backlight ps. That's what I'm using the 274B rectifier for! I realize of course that it's completely unnecessary to take 115 VAC, rectify it with a tube/diode bridge and load it with two backlights @ 50mA a piece. The result is 8 VDC out and about 90mA current draw. That's maxing out the Sophia Princess "mesh" 274B! The lamps do get a very nice slow start anyway! Only doing this because it's fun and I wanted a use for the tube!



List of your audiophool sins is ever growing; you've used expensive high end boutique rectifier for non-audio assistance job. Whatever will be next... (I recommend small CRTs.)



SonicTrance said:


> It needs much larger caps than the 220µ that's there to make it clean, maybe 1mF.



Or, keep 220µF and add a "filament regulator" unit. It loses a couple of volts but should take care of any ripple.



SonicTrance said:


> I have a pair of C3G's that I've stripped from their shield but can't use them. Way too microphonic. The shield actually grounds at the socket to circuit ground. Maybe the "naked" pair is naturally microphonic. Haven't used them in years.



Most tubes meant for radio actually really need their metal casings.



SonicTrance said:


> First thing a noticed was the lack of noise, there's none! Dead quiet!



I've noticed the same. I think the reason is simply that there's less gm inside the chassis; or, in other words, less FET drains connected to the same B+ regulator output.

One possible solution would be to go true dual mono. So make full one channel amps (they can be in the same chassis) with separate PSUs and PTs and everything. Maybe separate PSU raw filter section branches and separate B+ regulators for different gain stages.

Too much work.



SonicTrance said:


> I think the LTP pairs better with my speakers though than the SE.



Very possible. Most modern speakers are made for lowest possible output impedance. Your balanced amp has near-transistor amp output impedance because of the output buffer.



SonicTrance said:


> I've not done any power output test yet.



You'll be surprised how low the RMS out is. I don't remember if we've talked about why it can be so low and yet sound so loud and clean.


----------



## MrCurwen

SonicTrance said:


> I would say the balanced LTP is a bit faster sounding and have bit more micro detail than this SE version. But the SE also sounds very crisp, dynamic and packs a punch.



So now you have a feel for what the balanced version sounds like, and what the SE version sounds like. The breadboard workhorse amp I'm using has a SE input stage and balanced grid drivers and output stage. No buffer. It's "good enough" to keep using every day. Sound quality is somewhere between SE amp and balanced amp, maybe leaning a bit more towards the balanced amp.

The SE amp is by far the easiest to build for a beginner, but for a bit more ambitious builder the SE / balanced 'hybrid' could be a good solution as well. It's easier to build and set up than the full balanced version, and if chassis allows, can be extended to full balanced later.


----------



## SonicTrance

MrCurwen said:


> Congratulations! The pictures show once again first class build quality inside and out. You've really got this P2P thing under control, I'm impressed.


Thanks! Means a lot! Glad you like it!



MrCurwen said:


> Have you made any noteworthy sound quality observations? These green K75-10's are later production, late 70's and 80's (some still made in the 90's), metallized plastic film with wax if I recall correctly. No oil. I've got a couple of these I've used (10µF / 400V) but as B+ caps they don't have much sonic impact anyway so I don't know how good they are.


Not made any comparisons this time. Just decided to use the K75-10's and went with them. Mine (both the huge 10µ 250V and 680n 250V) are from the 90's. Don't know if you're thinking of some other cap? These are hybrid with both paper and lavsan in oil. There's definitely oil in them as they're very heavy and solid. Think they come in 250, 500 and 750V, not seen any other voltage ratings.



MrCurwen said:


> Or, keep 220µF and add a "filament regulator" unit. It loses a couple of volts but should take care of any ripple.


Thought about adding some regulation but meh, no room and works like a charm now anyway. Might swap those caps at some point though.



MrCurwen said:


> Most tubes meant for radio actually really need their metal casings.


Might sadly be the case! You know I love my glowing tubes! C3G's are quite pretty ones naked. I might take a chance and buy another pair and strip them. If you're very careful it can be reversed!



MrCurwen said:


> I've noticed the same. I think the reason is simply that there's less gm inside the chassis; or, in other words, less FET drains connected to the same B+ regulator output.
> 
> One possible solution would be to go true dual mono. So make full one channel amps (they can be in the same chassis) with separate PSUs and PTs and everything. Maybe separate PSU raw filter section branches and separate B+ regulators for different gain stages.
> 
> Too much work.


Mono blocks would be a fun project! If using IDH tubes there's less work. My 6C8G / 47 amp is quite complicated but then performs like a champ.



MrCurwen said:


> You'll be surprised how low the RMS out is.


Will do a test for sure. I remember the output buffer breaking in the LTP when I did the power output test. This amp should not be so sensitive to clipping I think?



MrCurwen said:


> I don't remember if we've talked about why it can be so low and yet sound so loud and clean.


I think so, a long time ago, refresh my memory.



MrCurwen said:


> The SE amp is by far the easiest to build for a beginner, but for a bit more ambitious builder the SE / balanced 'hybrid' could be a good solution as well. It's easier to build and set up than the full balanced version, and if chassis allows, can be extended to full balanced later.


I agree! If you want "super high end" full balanced is the way to go. But after spending some time with this SE version I don't think it's "worse" than the balanced but rather "different flavor" if that makes sense. I really like it!


----------



## MrCurwen

SonicTrance said:


> Not made any comparisons this time. Just decided to use the K75-10's and went with them. Mine (both the huge 10µ 250V and 680n 250V) are from the 90's. Don't know if you're thinking of some other cap? These are hybrid with both paper and lavsan in oil. There's definitely oil in them as they're very heavy and solid. Think they come in 250, 500 and 750V, not seen any other voltage ratings.



Yes I recall completely wrong. They have toxic oil inside. I should try and find the pdf of that russian cap catalogue I downloaded off some forum years ago and just post it here.



SonicTrance said:


> Might sadly be the case! You know I love my glowing tubes! C3G's are quite pretty ones naked. I might take a chance and buy another pair and strip them. If you're very careful it can be reversed!



One possibility is that if you use anti-oscillation methods, the extreme microphony might get under control. Stoppers on every pin, reduced gm etc. When used in pure voltage gain mode (input tube), gm doesn't matter at all so just toss it.



SonicTrance said:


> Will do a test for sure. I remember the output buffer breaking in the LTP when I did the power output test. This amp should not be so sensitive to clipping I think?



Probably not, but the CCS in parallel might break. Just increase volume veeery slowly and you should be ok. Use a higher f, maybe 2k or 4k; then the flat top of clipped wave is less like DC (because it's shorter in duration).



SonicTrance said:


> I think so, a long time ago, refresh my memory.



Human hearing cannot really make out the exact volume relations of peaks, unless they're grossly different in volume. If they're in the same general category of volume, you cannot tell which is louder.

Your can only produce the output power it can; after that it will clip. The output power is quite small, the amp clips a lot during transients. What matters is how the amp RECOVERS from that transient.

Now if you have a RC bias (cathode bias) somewhere, the bias circuit needs to recover from that transient. This takes time, during which the amp doesn't behave normally.

Worse yet if you have large NFB loops, spanning several gain stages; this takes a long time to stabilize again, during which time the amp behaves absolutely horribly. This is why when you use gNFB you want to have enough power capability for the loudest transients, even if your baseline power need is 0.1W RMS. That 100W transistor amp really needs that 100W in reserve, even if your baseline need is 0.1W (which it about is if you think that SE amp is loud enough).

There's lots more things inside typical tube amps that require some recovering time after a clipping transient. 

Anyway, what happens if these things are taken care of? Well, the amp just clips the top off the transient, and then carries on just normally. 

Your ears hear the music just continuing; they don't know how loud the transient was supposed to be, and even if the transient was there in full, they wouldn't be able to say in blind A/B comparison which transient is louder, the clipped one or the full one. They are both "loud", since they rise very fast up from the baseline. Ears detect the delta of the transient, (how "fast" the music sounds) not the amplitude (how high the wave peak is).

So the key to making the amp "fast" is investing in transient response and recovery. This means driving all kinds of capacitances from low impedance sources (grid, OT), not using bias methods that can be destabilized (caps need recharging time), having a flawless PSU.

If you want "fast" sound dealing with parasitic C is very important; if the signal has to "wait" while a poor current source is trying to charge a parasitic C, the crisp edge of the transient is lost. The voltage needs to be able to rise instantly. Ears detect delta, not amplitude of transient.

The last one is the biggest difference between the balanced amp and the SE amp (when talking about "speed"); since the balanced amp is constant current draw, it has a flawless PSU. The SE amp draws varying current, so it doesn't have. 



SonicTrance said:


> I agree! If you want "super high end" full balanced is the way to go. But after spending some time with this SE version I don't think it's "worse" than the balanced but rather "different flavor" if that makes sense. I really like it!



How would you place 

1) IDH balanced amp
2) DH balanced amp
3) SE amp
4) modded LD

in relation to each other regarding sound quality. In different aspects of SQ ("speed", "realism", "microdetails" etc) the order of preference might be different of course.


----------



## SonicTrance (Jul 21, 2018)

MrCurwen said:


> I should try and find the pdf of that russian cap catalogue I downloaded off some forum years ago and just post it here.


Yes, you should! Would be nice to have!



MrCurwen said:


> One possibility is that if you use anti-oscillation methods, the extreme microphony might get under control. Stoppers on every pin, reduced gm etc. When used in pure voltage gain mode (input tube), gm doesn't matter at all so just toss it.


Like you see in the schem I have stoppers at grid, cathode (both pins) and anode. Quite conservative values though.



MrCurwen said:


> Probably not, but the CCS in parallel might break. Just increase volume veeery slowly and you should be ok. Use a higher f, maybe 2k or 4k; then the flat top of clipped wave is less like DC (because it's shorter in duration).


Will try later today or tomorrow!



MrCurwen said:


> Human hearing cannot really...


Thanks! Excellent explanation!



MrCurwen said:


> How would you place
> 
> 1) IDH balanced amp
> 2) DH balanced amp
> ...


I'm comparing the DH fully balanced LTP now against the IDH SE amp!





I had to rearrange things. I'm running out of space here! Anyway...

When switching between the two you can clearly hear the LTP has more "air", instrument separation, soundstage. The LTP is the superior amp, BUT the SE is not far behind! Can't remember how the IDH LTP sounded but remember I thought the DH version was a step above. All versions of this amp beats the modded LD MK6, which in it self is a great amp but this design is a step above. Also a lot cheaper as the LD required boutique caps and expensive tubes to sound it's best, the "modern" design doesn't!

Think I'll keep the SE as my daily driver and use the LTP when I just want to lean back and listen to music and not do other things at the same time. The LTP deserves full attention! If you're not concentrating on the music you're missing the advantages of the LTP.


----------



## SonicTrance (Jul 21, 2018)

I've now done some power output tests!

These measurements are max clean amplitude for the given load. With higher output the bottom part of the sine wave starts to round off.

100 ohm load
5.4Vpp
1.9Vrms
*36.4mW rms
72.9mW peak*






20 ohm load
5.28Vpp
1.87Vrms
*174.2mW rms
348.5mW peak*





4 ohm load
4.52Vpp
1.60Vrms
*638.3mW rms
1.28W peak*





I did a power output test on the LTP in this post: https://www.head-fi.org/threads/modern-balanced-tube-amp-build.852879/page-6#post-13936396
That was with 4 ohm load and 480mW rms output. This SE amp actually outputs almost 640mW rms into 4 ohms. Also I remember that the clipping was very hard when measuring the LTP. Top part of the sine wave cut right off, very hard. When I did these measurements the bottom part just started to round off a tiny bit. So, it's possible that I could of dialed it in better when measuring the LTP.

As you can see the SE amp is no slouch and has plenty of clean power for your listening pleasure!


----------



## MrCurwen

SonicTrance said:


> That was with 4 ohm load and 480mW rms output. This SE amp actually outputs almost 640mW rms into 4 ohms. Also I remember that the clipping was very hard when measuring the LTP. Top part of the sine wave cut right off, very hard. When I did these measurements the bottom part just started to round off a tiny bit. So, it's possible that I could of dialed it in better when measuring the LTP.



Well now we get into difficult territory.

We measure power to a certain load, ok, but are they at the same THD? Certainly not.

If you do sims and use the built in THD tool (which is useful in precisely THIS kind of stuff) you can see the SE amp has a pretty linearly increasing THD, and the balanced amp has a hockey stick curve. THD is very low, very low, very low and BOOM it shoots up.

Are these two power measurements comparable? Kind of, but not really? I don't know. This is of course all academic, it's just interesting to see what results you get, this is analysis after the fact.

Visual inspection of waveform gives the point where the signal will really sound bad, hard clip. There is 'unacceptable' levels (in high end terms) of THD way before you can see it with your eyes.

The SE amp does clip much more softly, more like a trad tube amp. The reason is because it has output tube much 'closer' to the OT primary than the balanced amp. The precise reason is too longwinded to explain here, but it's all in the interaction between the OT and output tube.

In the balanced amp the top FETs handle the OT. In the SE amp the top FET AND the tube handle the OT.

FETs clip hard, tubes bend the wave. SE amp does a kind of hybrid of these.

What does all this mean for the power figures? Well, in my opinion and estimate by ear, when looking at about the same level of clean output, the balanced amp is 'louder' than any SE amp I've built. Closest to Sonic's amp would be my 6SL7 / 4P1L SE with 20mA bias (no CCS in parallel).

Output power is much more complicated than a single number.




SonicTrance said:


> As you can see the SE amp is no slouch and has plenty of clean power for your listening pleasure!



Absolutely, no question. Who needs 30W amps, pfft. Get decent transient response and 0.5W RMS is more than you'll really need unless you run a disco or listen to music in a 100 sq m hall.

Also investing in transient response is cheaper in the end than getting big big PT's and OT's and cap banks and heat sinks and all that.


----------



## MrCurwen

Also to expand a bit on the THD / Spice stuff:

I've said on a number of occasions that relating real world absolute results to Spice results is not serious stuff. Nobody who knows what they're talking about does that.

But that tool is very useful WITHIN Spice, to compare say the same schematic with different values, (if the sim THD lowers, it probably lowers also in real life, even if the absolute numbers are meaningless), or to find out the curve of the THD (does it increase linearly or exponentially or logaritmically or what).

Also the FFT results are skewed towards lowering 2H and 3H, and increasing all higher harmonics.

If you sim the FFT results of Sonic's SE amp with any significant output power, you'll see some nasty things. These nasty things don't however manifest themselves in real life. Sonic has listened to his SE amp, at high volumes as well I presume, and hasn't reported any "SS harshness" or anything like that.

This higher harmonic overreporting in Spice is a common thing, that especially tube designers come accross. Tube amps (esp. retro type) are smooth sounding (oftentimes too smooth), but Spice says there's supposedly all these higher harmonics. No there's not.


It's simply a case of understanding the limitations of simulation. It's a useful and fun tool, not something to really go by. You need to build stuff and then listen to it. You can make lots of different 'perfect' circuits on Spice, that don't work out nearly as well in real life, simply by stumbling on some kink or bug or feature in the THD / FFT algorithms.

All good design starts from basic electronic understanding and experimentation.


----------



## Maxx134

MrCurwen said:


> So the key to making the amp "fast" is investing in transient response and recovery. This means driving all kinds of capacitances from low impedance sources (grid, OT), not using bias methods that can be destabilized (caps need recharging time), having a flawless PSU.


On the point of "caps need recharging" , 
That point I have  wondered about in past.

So can you tell more, like what conditions is the bias destabilized.

 I also noticed benifits from using larger cathode caps (in an ouput tube circuit) than what was normally needed, to keep the voltage drop across the cathode more constant, 
And noticed better bass response.
Yet I havent thought about the "recharging" at that point, so maybe that would have sonic effect on the bass(?).

In my tests on my tiny tube amp  I only noted better bass sustain,  before the (cheap PSU) amp was drained in constant loud passage.


----------



## MrCurwen

Maxx134:

First you need to understand what that cap is there for, what it is doing. Read my gain stage basics: https://www.head-fi.org/threads/lit...rified-mods-are-on-first-page.782183/page-199

To bring it home I quote myself from https://www.head-fi.org/threads/lit...rified-mods-are-on-first-page.782183/page-195 :

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.



Think of current as water and the C as a bucket. Water flows from B+ via a tube (pun intended) that changes it's size constantly (according to signal applied at tube grid, no analogue comes to mind just go with it).

The cathode R is a part of the tube but it doesn't change size, it's the same circumference all the time.

Now you want to have same amount of water flowing thru the bottom R tube at all times (because if you want the bias to be stable, think Ohm's law etc etc).

If the main water tube closes off (tube clips on transient), no more water coming. The bucket starts emptying, water flows thru the bottom tube (R) to ground.

Now once the top tube opens up again (non-clipped operation continues), the bucket has lost much water. Now one of the following things must be true:

1) bottom part water pressure is different than at "normal conditions" (bias is way off)

2) some extra water must come thru the top tube and refill the bucket (messing up the normal operation of the tube, it's not just following the input signal now, it's doing this also)

In reality both of these happen at the same time for a time. This interferes with the signal reproduction, messing up transient recovery.


When designing high fidelity, always go with either CCS bias (for balanced) or grid bias (for SE). If you must have cathode bias (for DC circuits) use a capacitance multiplier. They sound as good as grid bias, but are a pain to set up.


----------



## MrCurwen

Bigger cathode C has more current stored to sustain the bias voltage normalcy thru transients, but it has other drawbacks. Mainly, parasitics. It holds more current, but is much slower to discharge, causing problems at high frequencies.

Parallel caps have their own problems, mainly the fact that they have a large area where they BOTH discharge, only at lower amplitudes and with phase shift. This can muddy up spatial information according to many (including me, I never parallel audio caps).


----------



## Maxx134

MrCurwen said:


> 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


This was exactly my thoughts, and made me wonder over the effects..

And you answered it by saying the bias Will be altered and gradually regained so the ouput will vary..

This is why, in one instance, I choose a "rediculously" large value, which should never discharge to a noticable point (in a driver stage),

And so have benifit of   more stablility..

BUT then, as you say, other issues at hand.


MrCurwen said:


> In reality both of these happen at the same time for a time. This interferes with the signal reproduction, messing up transient recovery


This also was another concern of electrolytics being slow, and I realize that it is a main reason why the popular practice of adding a "bypass cap" on top of the cathode electrolytics is done.



MrCurwen said:


> Parallel caps have their own problems, mainly the fact that they have a large area where they BOTH discharge, only at lower amplitudes and with phase shift. This can muddy up spatial information according to many (including me, I never


This is also I agree is like a "compromise", but area you speak of (lower amplitude and differing phase shift) is the area where it cuts off.
The actual area of optimal "overlap" should be same amplitude and phase just faster to respond/ delivery..(?)

In practice, it supposed to "correct" the slower delivery at high frequency, right?
 Usually these caps are small and not intended to cover a large area that I have seen.

But if the electrolytic wasn't not so bad it wouldn't need as much help.
Problem is most amps do not use "audio-quality" electrolytics, like this 
As it considered "boutique" and expensive.
I dissagre and say most designers are cheap b@$$tards because in general most electrolytics are not that expensive.

The real problem I see is the fact of trial and error to test how they actually sound and relying on more expensive parts is a real Problem that I can agree is a problem of design.
The design having to rely on parts quality is an bad design which makes amps cost $3k, $4k ,$5k and up for a tube amp, just rediculous how the tube amp market is today...



MrCurwen said:


> Bigger cathode C has more current stored to sustain the bias voltage normalcy thru transients, but it has other drawbacks. Mainly, parasitics. It holds more current, but is much slower to discharge, causing problems at high frequencies


 ...
Looks like a compromise of either smallest size and quality,
Or cheapo big caps with bypass on top..


 I believe this one big reason I hear differences in distortion between amps...

 One time I was lucky enough to compare two of the same amps, one with "upgrade" caps.
 I heard the "stock" amp have more distortion, BUT was more full and musical,
While the "better cap" amp was cleaner but also more* sterile, and lifeless *so  that was quite an "eye opener" .
It was a very expensive amp side-by-side at same time comparison.


So going this "traditional" route (of relying on component quality) is really a can of worms to get the "ingredients" right, and still be accruate enough to be end-game.
It is a hit or miss, and need of constant tuning to "optimize"..

Really not an optimal approach but no choice if playing with those "traditional" designs.



MrCurwen said:


> When designing high fidelity, always go with either CCS bias (for balanced) or grid bias (for SE). If you must have cathode bias (for DC circuits) use a capacitance multiplier. They sound as good as grid bias, but are a pain to set up.


I have been cautious to integrate Solid-state into tube circuit, because of the "purists" approach saying it also introduce effects, of which I won't state as I do not have all the info, 

But your design    implementation seems like the way to go.
Most newer tube amps I seeing using these approaches. 

Yet I am very impressed with your views on imortance of transients and also phase response.
Giving the amp more discernable power.

 I am thinking this design should give tube amp a different sound, as most vagrantly use old design for added harmonics or tube sound.

So this amp design will no longer be a traditional tube sound, while also having the benifits of tubes.


----------



## MrCurwen

Maxx134 said:


> This is also I agree is like a "compromise", but area you speak of (lower amplitude and differing phase shift) is the area where it cuts off.
> The actual area of optimal "overlap" should be same amplitude and phase just faster to respond/ delivery..(?)



In the overlapping area, they both discharge, only one cap discharges with less amplitude and altered phase. Think of this like an echo; you know how trying to carry on a conversation in a very echoing room can mask details and make it harder to understand what is said. Same thing happens to a lesser extent here; some microdetails are lost. Something which probably cannot be heard using speakers, but only with close examination on headphones. But, if looking for best results I wouldn't do it.



Maxx134 said:


> Usually these caps are small and not intended to cover a large area that I have seen.



Pick up an RC calculator and check your premises. Remember also that it's not that large an area where spatial information is transmitted.

If you take a good amp with great spatial delivery, and a good recording with 3D sound, and you play it, then turn down treble (a good amp wouldn't even have that but anyway) just a little bit. Spatial info is GONE very quickly. 



Maxx134 said:


> I dissagre and say most designers are cheap b@$$tards because in general most electrolytics are not that expensive.



I am not a basstard (I've had to be reminded by other people that 25 to 30 Hz area really matters; I used to make amps that didn't do under 30Hz and I was quite fine with it), but I truely am a cheap person, and I've got one question for you:

Why buy any electrolytic, outside of PSU? Why not simply use grid bias. It's as old as any tube, used in the 1910's, and doesn't require any SS components. Just use grid bias, never worry about cathode C again.



Maxx134 said:


> The design having to rely on parts quality is an bad design



Depends completely on what goal the designer had. Not to be cynical, but simply a statement of fact; aren't there many amps that are popular just because they respond easily to parts 'rolling'?



Maxx134 said:


> Looks like a compromise of either smallest size and quality,
> Or cheapo big caps with bypass on top..



Why not use grid bias?



Maxx134 said:


> So going this "traditional" route (of relying on component quality) is really a can of worms to get the "ingredients" right, and still be accruate enough to be end-game.
> It is a hit or miss, and need of constant tuning to "optimize"..
> 
> Really not an optimal approach but no choice if playing with those "traditional" designs.



I know a little bit of technology history (it's a hobby of mine), as you might've noticed I have a storytime about this and that quite often. These trad designs (and if a design is over 60 years old, it most surely IS traditional by that point) that are so pedestalized today, how were they designed?

The men who designed them had very very limited resources. They were simply trying to make the best of a bad deal; not get best possible fidelity.

I find if amusing that you just above lamented the fact that most modern hobbyists don't want to invest in expensive electrolytics to put inside a circuit that was originally designed to be very very cheap. It's like putting a solid gold steering wheel and hubcaps into a 1980's Honda.

The trad designs were not bad, but modern people have misunderstanding about what they were (consumer products) and how they were designed. 



Maxx134 said:


> I have been cautious to integrate Solid-state into tube circuit, because of the "purists" approach saying it also introduce effects, of which I won't state as I do not have all the info,



Remember that it matters a whole lot how you use a component or a design concept.

Modern 100W transistor amps sound bad? Why? Because of large NFB loops, on which they rely too much of their operation (all of linearity, all of output impedance).

Well, the reason a 1930's style no-gNFB SE amp with pretty ST envelope tubes sounds good is that there is a local NFB loop INSIDE the pretty big bulb tube. 

In one instance the NFB loop makes the amp sound harsh and lifeless, the other instance it makes the amp sound soft and pretty.

It all depend on how you use it, what is inside the loop etc.

This same thing applies to components. There are no magic components; no component is good or bad, it depends on how you use it, what the circuit is.

SS is not evil, it's just metals and plastic. Tubes are not good, they're just metals and glass. Rest is up to the designer.

Now it is true that components have properties, and they sometimes guide designers to use them in certain ways more than in other ways. But that is still not a law of nature, simply human choise. You can use components in other ways also.



Maxx134 said:


> So this amp design will no longer be a traditional tube sound, while also having the benifits of tubes.



I'd say that's accurate and well said. What would you say, Sonic?

To use a corny phrase, "best of both worlds". Or, to quote one of the people I've learned most from "use every component in a place they are most needed in".


----------



## Maxx134

MrCurwen said:


> I am not a basstard ....
> but I truely am a cheap person, and I've got one question for you


Haha OMG so funny! 
I wasn't referring to you or anyone in DIY,
Only to those amp makers that charge $3k and up for a tube amp, and then use $0.50 caps.
I Know it can be said they may have done that intentionally for  a specific purpose,
But still, if someone paid $3k & up, I would feel guilty to use cheapo cap lol. 



MrCurwen said:


> Why buy any electrolytic, outside of PSU? Why not simply use grid bias. It's as old as any tube, used in the 1910's, and doesn't require any SS components. Just use grid bias, never worry about cathode C again


Dammit that is a great point.
Looks like they were specifically going for distortion?



MrCurwen said:


> Modern 100W transistor amps sound bad? Why? Because of large NFB loops, on which they rely too much of their operation (all of linearity, all of output impedance)


Woah I totally overlooked the feedback effects...
Some feedback effects are crazy.
I recently heard a "feed-forward" amp and it was very strange to hear,
As it sounded so clean yet so lean and anemic.
Also a strange "processing" effect of lack of bass even when volume turned up.(!)
I don't want to name that $3k SS amp but thats enough clues as is.




MrCurwen said:


> In one instance the NFB loop makes the amp sound harsh and lifeless, the other instance it makes the amp sound soft and pretty


I guess there is something to be said for experienced designers.
Gotta get those ingredients right.



MrCurwen said:


> SS is not evil, it's just metals and plastic. Tubes are not good, they're just metals and glass. Rest is up to the designer


Great point.
Although I hate plastic, lol.
Im forever a tube guy, for amps.


----------



## MrCurwen

Maxx134 said:


> Looks like they were specifically going for distortion?



That's not a simple question.

On one hand, yes, many people prefer a distorted sound, i.e. heavy tube sound. 

On the other hand it's just practical not to have a user adjustable setting in the amp. RC cathode bias is self-adjusting, grid bias is user adjusted. If you mess up bad with that adjustment, you can release the magic smoke from the amp.

Cathode bias can use LEDs or other diodes, or batteries etc. But these are not 'traditional', so they are forbidden. You could have battery grid bias; but then the user would have to change the battery once a year or so.



Maxx134 said:


> But still, if someone paid $3k & up, I would feel guilty to use cheapo cap lol.



No but you're not thinking ahead enough!

Somebody who pays 3k for an amp has to think the designer is a very very smart person, often even a guru of sorts. Otherwise why pay that much for an amp that's made by "just some guy"?

Now after you've bought that amp and you've noticed this flaw in the genious design, YOU are now the smarter person, since you've outwitted the designer.

Now this amp is not just an product, a pile of components soldered together, it's a living testament to YOU the buyer being a smart person. This is in a nutshell the psychology behind most of the roll & mod community.

I'm sounding horribly patronising here, more than I intend to. But if a mod can be made without the modder understanding electronics 101 very basics, it's a "feel good I'm a smart person" mod, not a real mod. This is my opinion.

Some might remember this forum has seen it's share of people who are more eager to be known as "the best" designer than learning the very basics of electronics.



Maxx134 said:


> Gotta get those ingredients right.



Think of it like cooking. You wouldn't put salt into a cake, but that's no reason to say "salt is useless in cooking and shouldn't be used". Same thing, FETs are not good voltage amplifiers but that says NOTHING about their performance as followers.

Every time somebody says "SS ruins sound" or something similar I just hear "I don't know more than one topology in which to use FETs". Ok, so you don't know more than one, so what?



Maxx134 said:


> Although I hate plastic, lol.



Are you one of those guys that use cloth covered wires? My local electronics shop used to sell that for people who wanted to replicate authentic 1950's guitar amps.

I hate with a passion hitting plastic with solder iron. I don't have much excess brain cells you see. I recommend using teflon covered wire, that doesn't melt.



Maxx134 said:


> Im forever a tube guy, for amps.



I get that this is just a thing that people say casually, but what does it really mean?

The annoying first dig in this discussion is always "so do you always use vacuum rectifiers?".

Do you think the guys who made the popular topologies in the 1930 - 1960 would've not used SS devices to assist if they had them?

Let's take the job of driving current thru the OT. Tubes are pretty lousy at it; some manage ok, but none manage good. Now if Loftin and White had a 0.50 eur FET to push current thru the OT, instead of a tube, don't you think they would've taken that chance?

And guess what, their amp would've sounded BETTER, not harsher. That's because followers don't add distortion of any kind really, in any meaningful way.

Loftin and White are ripping their hair out in frustatration in the audio heaven looking at our times.


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## Maxx134 (Dec 11, 2018)

I have the honor of hearing this creation for myself today, and have to say initial impressions is that it is a seriously good amp.

SonicTrance has been very reserved about its abilities and wanted me to review it before passing onto buyer.

I am also being reserved for now as I make notes and will also do a comparison to gain more insight.
Amps chosen (for comparison) will be good ones.


----------



## MrCurwen

Exciting!

I got to get some of those black top caps, they look really nice. I like top caps on my tubes.

Sonic was very wise in being reserved, the amp will speak for itself. But one of the claims I've loudly made is that this circuit is 99% immune to tube rolling of all kinds (including between tube types as long as they have nice enough curves). Unfortunately you will not be able to test this particular claim (do not use other types, circuit could fail), but if you decide to build one for yourself, do use completely different tubes. The amp will sound exactly the same.

Of course you could try rolling different makes of those types. I'm particular to Tesla EL81's myself, I like the build consistency and ruggedness. Also they have very nice advertisement posters, that's important. I've printed some of them to use as art.

I'm rambling, just waiting for the objective evaluation!


----------



## Maxx134

MrCurwen said:


> I'm rambling, just waiting for the objective evaluation


So far, the conclusion I am forming is that your topology and methodology are genius.

I am being very reserved to say the amp is holding its own so far.

Have to organise the details & evaluate long term listening from partner with system comparisons to two other top systems to solidify observations.

Headphone used was the demanding Abyss Phi.


----------



## MrCurwen

I am a decent designer, I have my stuff figured out and ready to explain, but Sonic is a master builder. 

If that amp was put together by me, it would have a hiss or a small buzz or something. I'm too lazy to go through the final phase of debugging the layout. If it works, it's usually good enough for me. 

Sonic builds like he's making a piece of art. 

I know this is a headphone forum, but do try the amp with speakers as well. Any speaker (not electrostatic) is fine, it'll drive almost anything.


----------



## SonicTrance

Thanks for the kind words MrCurwen!
I could not wish for a better mentor!


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## Maxx134 (Dec 12, 2018)

**redacted**
I thought I was in the PM.
Just suggestions and questions for possiblities of powering most demanding cans like Susvara.

It already pushes the Abyss phi very well but wanted to volume knob position similar to other amp.

The suggestion of the driver tube is perfect solution.


----------



## SonicTrance (Dec 12, 2018)

Already answered these questions in pm but can write here as well.

Basically more power output is not possible with the cooling the amp has now and it shouldn’t be needed either. More gain on the other hand can be achieved by using a higher gain input tube. I think that’s what he’s after! That would require some modifications to the circuit.

The frequency response is dead flat from 300Hz - 20kHz, it varies a tiny amount in the bass region. So it should play any high frequencies just like they’re intended. Rolling different coupling caps don’t change the sound in this amp since there’s a source follower after the caps driving the grids of the output tubes. I’ve tried different caps and couldn’t tell them apart.

Some simple digital EQ should tailor the sound sig if you want something different.


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## Maxx134 (Dec 12, 2018)

SonicTrance said:


> Some simple digital EQ should tailor the sound sig if you want something different


Yes, your amp delivery was the most neutral of the three setups we tested.
Accuracy in various traits like FR & soundstage was a strong point.
This was very important for me.
This amp retains all the holography of tubes.

Also, not to change the topic, but so far, two of my friends suggest using Roon player for various purposes like  EQ for headphones, and/or upsampling to DSD to take advantage of dac.


----------



## MrCurwen (Dec 13, 2018)

This is the no output buffer model, yes?



Maxx134 said:


> Just suggestions and questions for possiblities of powering most demanding cans like Susvara.



I looked this up and on the surface they shouldn't be too horrible a load.

This amp is perfectly fine in powering 4 ohm speakers without any noticeable colorations. 60 ohms should be fine even with a highly reactive load.

But if not, the answer is utilizing an output buffer, a source follower - current sink system driving the OT. This lowers the output impedance of the amp ever further.



Maxx134 said:


> It already pushes the Abyss phi very well but wanted to volume knob position similar to other amp.



Do you actually run out of gain headroom (you need to put volume know to 10 or close to it) or do you simply want it to be at some specific position?

Like Sonic wrote, gain is controlled by tube choise. Any linear tube is fine to use, after small redesign.



SonicTrance said:


> Basically more power output is not possible with the cooling the amp has now and it shouldn’t be needed either.



For speaker loads, the output buffer can add an "experience of power". With loads over 20 ohms no extra power is needed.



SonicTrance said:


> The frequency response is dead flat from 300Hz - 20kHz, it varies a tiny amount in the bass region.



Inherent properties of the OT. If you use a physically very big OT, you can get closer to absolutely flat in the bass region, but then you get troubles in the high register.

Lower impedance driving the OT helps, again.

For my ears and simple 120 ohm load, the bass region is 100% fine, good separation of notes and instruments. But I'm not a bass guy.



SonicTrance said:


> Rolling different coupling caps don’t change the sound in this amp since there’s a source follower after the caps driving the grids of the output tubes. I’ve tried different caps and couldn’t tell them apart.



Yes absolute as he wrote.

One of the main design goals of the process where I came to this point originally was that cap rolling should be completely destroyed.

I was tired and frustrated with it, I didn't have the money to do it and so I wanted off the ride.

There is not going to be any audible difference with different caps in this circuit. Not worth even trying. The reasons for this have been explained in the LD thread at length; if you have the patience go and look thru my posts there. Or if you wish I can summarize it here in short, always happy to explain anything.



SonicTrance said:


> Some simple digital EQ should tailor the sound sig if you want something different.



Why?

If you want a different sound, listen to a different recording. Or, use different headphones. I'm an AKG guy, I know some guys who are Sennheiser guys. Find your preference and use that. The amp and signal chain before that should as neutral in every way as possible. This way there's the most room for the music, you get that 'live' feeling.



Maxx134 said:


> Yes, your amp delivery was the most neutral of the three setups we tested.
> Accuracy in various traits like FR & soundstage was a strong point.
> This was very important for me.



Everyone uses different terminology, I like to say transparent. What is in the signal source comes thru. Like MP3 compression artefacts...



> This amp retains all the holography of tubes.



Yes, there's no gNFB. "Tube sound" is 50% no gNFB, 50% OT inefficiencies. Here we only have 2% OT inefficiencies, so the no gNFB sound is very dominant.

Ok tube sound is also 50% high 2H and 3H. None of that here also. (Yes tube sound is so large it's 150%.)

But seriously think of it like this: gNFB is "SS sound" and open loop is "tube sound". It matters a lot HOW you lower THD.


Have you compared to a high level SS amp? Or, with speakers?

By the way, talking about OT's... Maxx do you know what kind of OT's this amp has?


----------



## SonicTrance

MrCurwen said:


> This is the no output buffer model, yes?


Yes.
You know I've praised the output buffer but it's very hard to get stable. At least that's my experience, even with separate power supply's. So any amp I build for someone else will not have the buffer for a number of reasons. It drives cost up as you need bigger chassis and separate power supply. It's too fragile. It sounds extremely good without it so it's just not worth it. 



MrCurwen said:


> Do you actually run out of gain headroom (you need to put volume know to 10 or close to it) or do you simply want it to be at some specific position?


He meant gain, not power. Classic mixup.


----------



## MrCurwen

Yes I know first hand, the buffer can be a source of troubles, in many ways. It's not worth the price of admission unless you are strictly a speakers guy, and probably not even then.

That is the only theoretically possible improvement I can think of. Any other improvement would upset the balance of design features, like I explained early in this thread. 

If you get rid of the OT, you introduce a completely new set of problems. Providing open loop solutions for a truely low output impedance are really not there. I know some people have made a source follower type direct output system (namely the legendary Wavebourne), but that is so expensive and heat intensive that I find it hard to justify. 

OT and NFB are the practical ways of achieving low output impedance. That's just how it is.


Earlier in the circuit there's not much to discuss. You cannot make the loadlines better without making the tail CCS simply crazy (the tail must be able to overpower both the tubes and both the plate loads at the same time, with ease). Anyway you can only hear improvements up to (at the most) 50x rp, after that there's nothing to be gained. With the current single FET simple gyrator we're there for most practical tubes.

There's no point in making the tail CCS more complex, it can overpower the current paths above it with ease, as Sonic's measurements have proven.

There's no point in making the regulator better. The simple 2 FET reg does it's duty decently. The amp draws pretty much completely constant current, so you wouldn't be able to hear any improvements at all.

Grid driver does 97% as well with just a resistor load (if there is enough B-), but has a CCS load as well. Not much to improve; FET source followers are clean as can be.

There are gains to be made in making the amp more stable, perhaps, probably, but I'm not very motivated in that. It's "good enough" for me.

So, the output buffer thing is the only frontier to suggest, really. I personally don't have it in my workhorse amp, not enough benefit.


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## Maxx134 (Dec 16, 2018)

MrCurwen said:


> Do you actually run out of gain headroom (you need to put volume know to 10 or close to it) or do you simply want it to be at some specific position?


Yes it was for appearance.
The EC Studio has volume on Susvara like 10oclock and that's high enough.
On the Aficionado it was around 12oclock for the Abyss, and 1oclock for SonicTrance amp.
So yeah it was more for appearance because it was loud enough.



MrCurwen said:


> Why?
> 
> If you want a different sound, listen to a different recording. Or, use different headphones. I'm an AKG guy, I know some guys who are Sennheiser guys. Find your preference and use that. The amp and signal chain before that should as neutral in every way as possible. This way there's the most room for the music, you get that 'live' feeling.


EQ was only for adjusting headphone weaknesses.
Both the stax 009 & the Abyss were more neutral once we EQ a "correction" EQ setting in Roon player.
This topic had nothing to do with the amps.



MrCurwen said:


> Everyone uses different terminology, I like to say transparent. What is in the signal source comes thru. Like MP3 compression artefacts...


 Ok but all three amps tested at the time were incredibly transparent, and mainly differed in presentation, not "resolve". Resolve and realism were all at the top level you could ask.




MrCurwen said:


> Ok tube sound is also 50% high 2H and 3H. None of that here also. (Yes tube sound is so large it's 150%.)


To me, the tube coloration adds either some richness or some other euphoric trait added, apart from the realism.
But all 3 amps had high realism.
The SonicTrance amp also had all the holographic image which I normally notice more of tube designs.



MrCurwen said:


> But seriously think of it like this: gNFB is "SS sound" and open loop is "tube sound". It matters a lot HOW you lower THD.


I am not sure if it is this or the transient speed that gives this amp a "solid" imaging.
I know my other amps with NFB sounded clearer with less NFB, but still retained the holography, but in that old design, it was easy to lose or gain both clarity & holography with change in tube & bias.
So traditional design is a nightmare minefield of tuning to do to lol.


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## baronbeehive (Dec 28, 2018)

Maxx134 said:


> I am not sure if it is this or the transient speed that gives this amp a "solid" imaging.
> ....



I am sure the transient speed is primarily responsible for this going from the previous discussion about the new amp builds, that must make a big difference to the soundstage for example.

Very interesting discussion since I was last here. I really buy into the new designs such as those of MrCurwen's and very exciting to see the progress made by Sonic here. I almost don't mind about SS versus Tube but I think I'm with Maxx about veering to the tube side..... the dark side lol. I also don't mind about balanced versus SE, they're just different design solutions not necessarily better than each other. If you can forgive my rambling I have a few points to make on the preceeding discussion.

One thing mentioned is the smearing effect of parallel bypass caps. I have had experience of both cathode caps with and without bypasses on the APPJ speaker amp I have. I tried initially with just the high quality Kaisei caps on there now with high - 1000uF capacitance hoping that this would be good enough. I found that it definately needed the bypasses to bring back the higher frequencies and sparkle which it had lost, which corroborated what other members in the LD thread found. TheAPPJ amp is also very fast and resolved and I certainly couldn't detect any smearing artifacts that have been suggested. It would be interesting to try the stock value capacitance but with the Kaisei caps without the bypasses to see what the effects were vis a vis the stock sound and the modded sound regarding smearing, liveliness etc., this is something that hasn't been done.

Another point mentioned is the ability to use all reasonable quality caps and tubes without detecting any sound differences, due to the inclusion of followers in the design. I don't know if this is relevant but I have found following the latest mods to the LD amp, including the CCS, that I can't really tell any difference now between using expensive WE 421A's or cheap RCA 6AS7G's, or fairly expensive TS 6SL7's versus cheap GE 6SL7's and was wondering if the changes to the circuitry, notably the force balanced operation were responsible. I never wanted to spend that much on tubes anyway!


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## baronbeehive (Dec 28, 2018)

SonicTrance said:


> I agree! If you want "super high end" full balanced is the way to go. But after spending some time with this SE version I don't think it's "worse" than the balanced but rather "different flavor" if that makes sense. I really like it!



In what way is it different?

I'm trying to remember the discussion about the LD when members were trying it SE and balanced, and I think that conclusion was that balanced was tighter sounding, for example bass was more defined but not necessarily more hefty, I don't know if others can remember but I think that was the gist of it.

Edit: I forgot to mention the machining of the chassis looks very good, it looks like you have smoothed the holes so that there are no sharp edges?


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## SonicTrance

baronbeehive said:


> In what way is it different?
> 
> I'm trying to remember the discussion about the LD when members were trying it SE and balanced, and I think that conclusion was that balanced was tighter sounding, for example bass was more defined but not necessarily more hefty, I don't know if others can remember but I think that was the gist of it.
> 
> Edit: I forgot to mention the machining of the chassis looks very good, it looks like you have smoothed the holes so that there are no sharp edges?


I posted this a few posts down

"When switching between the two you can clearly hear the LTP has more "air", instrument separation, soundstage. The LTP is the superior amp, BUT the SE is not far behind! Can't remember how the IDH LTP sounded but remember I thought the DH version was a step above. All versions of this amp beats the modded LD MK6, which in it self is a great amp but this design is a step above. Also a lot cheaper as the LD required boutique caps and expensive tubes to sound it's best, the "modern" design doesn't!"

So, the balanced version is superior!


Dont know which chassis you're talking about but yes, no sharp edges anywhere!


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## baronbeehive (Dec 28, 2018)

SonicTrance said:


> I posted this a few posts down
> 
> "When switching between the two you can clearly hear the LTP has more "air", instrument separation, soundstage. The LTP is the superior amp, BUT the SE is not far behind! Can't remember how the IDH LTP sounded but remember I thought the DH version was a step above. All versions of this amp beats the modded LD MK6, which in it self is a great amp but this design is a step above. Also a lot cheaper as the LD required boutique caps and expensive tubes to sound it's best, the "modern" design doesn't!"
> 
> So, the balanced version is superior!



Sorry I missed that. The LTP amp must sound good with your speakers! Your Monitor Audios look to be better than mine lol, mine are some years old now and at 87d sensitivity it is surprising that they sound so good with the 3.5 watts of the little APPJ amp. I still prefer listening through speakers but now that the LD is performing well I look forward to headphone sessions as well!



SonicTrance said:


> Dont know which chassis you're talking about but yes, no sharp edges anywhere!



Yes, compared to the LD which has those nasty edges for the transformer wires which is a worry!

Edit: Have you another project in the pipeline, or just chillin' and enjoying the amps?


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## MrCurwen

baronbeehive said:


> I almost don't mind about SS versus Tube but I think I'm with Maxx about veering to the tube side..... the dark side lol.



I veer to both the tube side and the SS side. I veer to all sides.

For example, I wouldn't have anything but good curved tubes doing voltage amplification.

I wouldn't have anything but a decent SS device like a MOSFET driving a complicated load.

Strong preferences.

It's about using the right tool for the right job. My preference is for the best tool, nothing more.



baronbeehive said:


> I have had experience of both cathode caps with and without bypasses on the APPJ speaker amp I have.



Not to sound needlessly rude, but to me the point is moot. Why have cathode caps and worry about that? If you have a SE stage, use grid bias. Simple, no need to worry about C bypass ever again, best SE sound there is.



baronbeehive said:


> I never wanted to spend that much on tubes anyway!



My thoughts exactly. Some crazy transmitter tubes in my collection are going "A-HMMM, what about us?" right now...



baronbeehive said:


> I'm trying to remember the discussion about the LD when members were trying it SE and balanced



Sonic put my thoughts into words there pretty accurately. Balanced is better, but SE is suprisingly good. I'm more agnostic on the DH question these days. 67% out of laziness to be honest. Once you've set up 4 filament supplies and keep them adjusted you'll know why.



baronbeehive said:


> Edit: I forgot to mention the machining of the chassis looks very good, it looks like you have smoothed the holes so that there are no sharp edges?



Sonic has his own tricks I'm sure. What I do is I first make the hole, the size I need it to be. Then I take a bigger drill bit and do a few rounds in that hole. Only a few, say 4 rounds. I do this on both sides of the hole. Cleans up the jagged edge, and makes a nice visual. For a 4mm hole I'd use a 10mm bit. 



baronbeehive said:


> Your Monitor Audios look to be better than mine lol, mine are some years old now and at 87d sensitivity it is surprising that they sound so good with the 3.5 watts of the little APPJ amp. I



My speakers are Whaferdale Emerald 97 Mk. 4 with 89dB/W sensitivity if I recall correctly. 0.5W RMS is just fine, more headroom than I'll ever really need. 1W for balanced amp is overkill in home use in a small room. 



baronbeehive said:


> Edit: Have you another project in the pipeline, or just chillin' and enjoying the amps?



Hey I really wish somebody would build a balanced amp of my design with 6N16B subminiature tubes. They are simply wonderful!

I had that amp (breadboard) in use for about 6 months some time back. Great amp. The subminiatures are a bit of a pain to work with, but look very nice.

Also just to prove it can be done and they are serious tubes for high end use.


----------



## baronbeehive

MrCurwen said:


> My speakers are Whaferdale Emerald 97 Mk. 4 with 89dB/W sensitivity if I recall correctly. 0.5W RMS is just fine, more headroom than I'll ever really need. 1W for balanced amp is overkill in home use in a small room.



Oh that is interesting to know what you have that works! (I know it is not power output per se but recovery from transients, but the low sensitivity was a concern).



MrCurwen said:


> Hey I really wish somebody would build a balanced amp of my design with 6N16B subminiature tubes. They are simply wonderful!
> 
> I had that amp (breadboard) in use for about 6 months some time back. Great amp. The subminiatures are a bit of a pain to work with, but look very nice.
> 
> Also just to prove it can be done and they are serious tubes for high end use.



…….anybody? I'm not looking for a project atm unfortunately, exciting though it looks!


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## SonicTrance

baronbeehive said:


> The LTP amp must sound good with your speakers!


It does! When using speakers I notice more difference between the SE amp and the LTP.



baronbeehive said:


> Edit: Have you another project in the pipeline, or just chillin' and enjoying the amps?


Ive started to build for other people! I figured since I really enjoy building amps and I can't really build amp after amp for myself, I can build for others.

You see the amp in my avatar. I call it Oblivion. Its the version of this amp with SE input stage and LTP output stage. 

To me, it sounds really good and hits the sweetspot in terms of build complexity and price/performance.


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## baronbeehive

SonicTrance said:


> You see the amp in my avatar. I call it Oblivion. Its the version of this amp with SE input stage and LTP output stage.



Great name, and great looking amp. Good luck with that!



SonicTrance said:


> Ive started to build for other people! I figured since I really enjoy building amps...



Ha ha..... "enjoy" is not the word I would use when trying to troubleshoot the LD sometimes!!

I have other priorities atm but at some point it would be fun to try to build one of MrCurwen's designs.


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## SonicTrance

baronbeehive said:


> Great name, and great looking amp. Good luck with that!


Thanks baron!



baronbeehive said:


> I have other priorities atm but at some point it would be fun to try to build one of MrCurwen's designs.


What could possibly be more important? 
Please do! Its a great learning experience and you'll get a very nice amp.


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## baronbeehive (Dec 29, 2018)

MrCurwen said:


> Hey I really wish somebody would build a balanced amp of my design with 6N16B subminiature tubes. They are simply wonderful!
> 
> I had that amp (breadboard) in use for about 6 months some time back. Great amp. The subminiatures are a bit of a pain to work with, but look very nice.
> 
> Also just to prove it can be done and they are serious tubes for high end use.



Yes but some of us are more into these monsters, 6BG6G's, lol. I don't use these on the APPJ though:


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## SonicTrance

baronbeehive said:


> Yes but some of us are more into these monsters, 6BG6G's, lol. I don't use these on the APPJ though:


I’ve used those (and the Russian equivalent 6P7S) in a couple of amps as I too am a fan of the big bulbs! Nice sounding tubes.


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## baronbeehive (Dec 29, 2018)

I have a couple of questions pertaining to the LD so sorry to post here but the subject of the questions has been mentioned and someone here might be in a position to answer.


I'm not up on the theory but could the cathode caps be replaced by grid bias in the LD
Could gyrators be used in the LD, presumably in addition to the CCS, for plate loads, and might they fit. I've looked at Sonic's pics and its difficult to tell.
I thought we had fixed the anode values in my tests recently but this is obviously a whole new thing that could be done.... I might be completely wrong, but I was just wondering if it would be feasible, or indeed advisable in the LD!


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## SonicTrance

baronbeehive said:


> I have a couple of questions pertaining to the LD so sorry to post here but the subject of the questions has been mentioned and someone here might be in a position to answer.
> 
> 
> I'm not up on the theory but could the cathode caps be replaced by grid bias in the LD
> ...


Non of the above can be used in the output stage of the LD without total redesign as it’s a white cathode follower stage.

There’s no cathode cap in the input stage and grid bias is not possible since it’s an LTP stage. Gyrator plate loads could be used but would preferably need higher B+ voltage. Also, it would be very hard to fit inside stock chassis since the FET needs heat sink (you need 4 gyrators for the LD input stage). And to get the most out of the gyrator plate loads a regulated ps would be ideal.

Its a lot of work that’s needed with external/extended chassis.


----------



## MrCurwen

Sonic addressed the other points.

About the output buffer stage in the LD:

No, unfortunately not. The top part is already using grid bias, the servo is adjusting the bias dynamically.

The WCF buffer is made up of the top and the bottom tubes. The top tube is using grid bias, and the bottom tube is using RC bias. The bottom tube grid is inside a local NFB loop, which lowers the output impedance of the WCF. This loop is what makes the WCF basically.

I would advise not to add anything inside that loop. That means no grid bias there.


By the way, how is your goat this year Sonic? It's almost end of december already, will it make it?


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## SonicTrance

MrCurwen said:


> By the way, how is your goat this year Sonic? It's almost end of december already, will it make it?


Haha, I’m surprised you know about it! I actually live in Gävle where the goat is. So far it’s doing fine. Someone tried to set fire to the little goat that’s besides the big one. Only a burnt leg though.


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## Maxx134 (Dec 29, 2018)

baronbeehive said:


> I think I'm with Maxx about veering to the tube side.....


From my observations of amps I generally found that although tubes (used traditionally) gave some extra added sound, they also *always *gave me more, in image placement and detailing.
I also noticed hybrid stuff would also try to improve in these areas, yet no hybrid I heard so far, implents this optimal approach like this  amp.



MrCurwen said:


> It's about using the right tool for the right job. My preference is for the best tool, nothing more


Your approach is the most optimal implementation of how a hybrid should be made.

It's a wonder why amps aren't done this way, and stuck on ancient designs.
Also modern solid state designs don't compare to this either.
It's as if both SS&Tube amps today are used in a compromise way.




SonicTrance said:


> You see the amp in my avatar. I call it Oblivion. Its the version of this amp with SE input stage and LTP output stage.
> 
> To me, it sounds really good and hits the sweetspot in terms of build complexity and price/performance.


Price performance is ridiculously good..
I have the amp back in my possession & decided to keep it.
Its a super transparent amp with ideal tube transients, soundstage, &  holography. Imaging is rock solid and clear.
No worries about tube being optimal in sound. No skewed image or FR signatures like yraditradit designs.. it just sounds super transparent with full tube soundstage.

Makes my MK8se an obvious example of traditional design expense, requiring tons of expensive parts & modding time to accomplish a similar route, but an unmistakably colored one, like most all other tube amps.

ALL tube amps (except for few Uber $$$ $3k & up amps) will give you an obvious signature, while this new amp SonicTrance made is just musical & holographic without the tube coloration.
Very well done and proves the design ideology, because the sound is really excellent.
I am currently using it with a new prototype HD800mod I made wich has greater soundstage and more bass than any HD800 iteration.


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## baronbeehive

MrCurwen said:


> Sonic addressed the other points.
> 
> About the output buffer stage in the LD:
> 
> ...



I see, thanks for the explanation.



MrCurwen said:


> By the way, how is your goat this year Sonic? It's almost end of december already, will it make it?



Haha, very surreal!




Maxx134 said:


> It's a wonder why amps aren't done this way, and stuck on ancient designs.



Agree, absolutely, I'm not stuck in the past.



Maxx134 said:


> I have the amp back in my possession & decided to keep it.



If you're keeping the review model, Sonic will have to make a new one lol! This all sounds very interesting indeed!



SonicTrance said:


> Haha, I’m surprised you know about it! I actually live in Gävle where the goat is. So far it’s doing fine. Someone tried to set fire to the little goat that’s besides the big one. Only a burnt leg though.



…...only a burnt leg, poor creature..... lol.

I'm guessing a sculpture!


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## SonicTrance

baronbeehive said:


> …...only a burnt leg, poor creature..... lol.
> 
> I'm guessing a sculpture!


Its the famous Christmas goat called "Gävle bocken" in Swedish!
https://en.m.wikipedia.org/wiki/Gävle_goat


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## baronbeehive

SonicTrance said:


> Its the famous Christmas goat called "Gävle bocken" in Swedish!
> https://en.m.wikipedia.org/wiki/Gävle_goat



Very entertaining read!


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## Maxx134

baronbeehive said:


> If you're keeping the review model, Sonic will have to make a new one lol! This all sounds very interesting indeed


Yes the logistics of shipping, and the fact that I am unable to make any amp until next year is why I decided to keep this sweet amp. Lol


I have posted many observations in my PMs to both Sonic and Baron that I will use to summarize in a future post here.

I was fortunate to have access to many amps in coming to impressions and will use my perspectives of other amps in past to summarize.

Bottom line is that I am keeping this amp.
That in itself should say alot.
Having had access to other amps made me have an open mind of either buying or making my own.


----------



## MrCurwen

SonicTrance said:


> Please do! Its a great learning experience and you'll get a very nice amp.



Yes. It gives me personal satisfaction to see people build stuff I've proposed and hear their impressions. So far my circuits are alive on the North American continent, the South American continent and in different corners of Europe. One guy in Hong Kong was talking about building something but I haven't heard from him in a long time.



SonicTrance said:


> Haha, I’m surprised you know about it! I actually live in Gävle where the goat is. So far it’s doing fine. Someone tried to set fire to the little goat that’s besides the big one. Only a burnt leg though.



Did they make it?

The Finnish media actually reports on this wicker goat. My girlfriend has known about it for years apparently.



Maxx134 said:


> It's a wonder why amps aren't done this way, and stuck on ancient designs.
> Also modern solid state designs don't compare to this either.
> It's as if both SS&Tube amps today are used in a compromise way.



Yes. 

Wait a few years, a lot of these kinds of things are slowly coming into production amps. I originally thought I was the only one who thought of these particular design points, I was congratulating myself day and night. Later I found out a few others had made almost identical schems earlier, but I honestly did not know about them at all. And at the time I was all over all of the bigger forums and websites (I still have most of Bob Danielak's old site stashed up somewhere).

It's not about being a genious or whatever, it's about propagating good stuff and helping other folks build and understand stuff.

So far the only one that incorporates every one of the design points in my schem is my own schem (and Sonic's via me). But more are sure to come, people who've never even seen one post by me.



Maxx134 said:


> Price performance is ridiculously good..
> I have the amp back in my possession & decided to keep it.
> Its a super transparent amp with ideal tube transients, soundstage, & holography. Imaging is rock solid and clear.



"Tube soundstage" is simply the lack of higher harmonics. Any amp with a significant amount of gNFB is going to have some higher harmonics (despite having overall lower THD), and these mask the spatial information in the signal.

It's not "tube soundstage" it's "no gNFB soundstage".



Maxx134 said:


> Having had access to other amps made me have an open mind of either buying or making my own.



There's no substitute for building your own as far as satisfaction in your listening gear goes.


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## baronbeehive

MrCurwen said:


> There's no substitute for building your own as far as satisfaction in your listening gear goes.



Yes, I really hope to do that at some point, I can really appreciate the way you've come up with your design philosophy which has become apparent with reading the thread!


----------



## Maxx134

So I have owned one of this latest iteration of SonicTrance build, which he calls "Oblivion".

As you may or may not have known, I have compared it to a few other "end-game" level amps to guage its worthyness.
In Some instances, you could say some choices  could been a preference for things besides the sound. 

There was one aspect which this amp wich was startling to grasp that it had matching or superior to others, and that was the accuracy of the soundstage.
Soundstage was laid out with a sense of certainty & delicacy.
I will get into this more in a review. 
To let the cat out of the bag, suffice to say this amp matched or beat other top amps, and the amps it did beat were amps that beat out others I compared those to.

The only parameter some of them had over this version was they had a bit more power, but there was an issue that even with more power that didn't help.

Anyways SonicTrance can you post the specific details of the "Oblivion" as compared to the other versions you have planned?

My review will not me taken easily because my style of reviewing was done by comparison to other amps, not by colorful interpretations of specific songs.
How else to tell of value , but to put amps side-by-side?


----------



## SonicTrance

Maxx134 said:


> Anyways SonicTrance can you post the specific details of the "Oblivion" as compared to the other versions you have planned?


I have two versions planned:

Oblivion: SE input stage (RCA input) and balanced LTP output stage
Citadel: LTP input stage (XLR input) and LTP output stage.

The main difference is the input stage. Both amps will have regulated B+ and B-, gyrator plate loads, CCS tails (Oblivion only in output stage as input stage use grid bias)
Citadel will rule out any “imperfections” the SE input stage brings. Those “imperfections” may not be bad though, that’s up to the listener and personal preference. Citadel will sound cleaner than Oblivion.

Both amps will have optional speaker outputs.


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## MrCurwen

Anybody bite on the DIY front?

I've got a few builds planned, I'll document them here at some point.

The circuit is not THAT difficult to set up. If you use the exact same notes as somebody else, it's very straightforward. If you want to use some other tubes, there's some extra steps.


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## bloodhawk

MrCurwen said:


> Anybody bite on the DIY front?
> 
> I've got a few builds planned, I'll document them here at some point.
> 
> The circuit is not THAT difficult to set up. If you use the exact same notes as somebody else, it's very straightforward. If you want to use some other tubes, there's some extra steps.


I was about to start ordering the parts but then my company decided to move me from LA to their Canadian office.... and i never really got the chance to setup my my workshop here :X


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## baronbeehive (Dec 28, 2019)

MrCurwen said:


> Anybody bite on the DIY front?
> 
> I've got a few builds planned, I'll document them here at some point.
> 
> The circuit is not THAT difficult to set up. If you use the exact same notes as somebody else, it's very straightforward. If you want to use some other tubes, there's some extra steps.



Interested to hear when you do that.

I did talk about it with Maxx a while back, then he got his Oblivion and I think he is happy now that he doesn't have to build. Then I got my LD back working again and was happy with it. Personally I would like to give it a try at some point, not now though. I would not be totally confident without help, especially of theory, and time and money are a factor atm, as always!

Edit: Money tends to go on the house and car, and time on playing my Stratocaster which I'm just getting back into after a long lay off... you know how it is!


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## baronbeehive

If and when I do decide to go ahead and do this I would probably do it one module at a time,   v  e  r  y     s  l  o  w  l  y...., nice and easy.

This is intriguing me.


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## baronbeehive (Dec 29, 2019)

Just been re-reading the Oblivion review thread: https://www.head-fi.org/threads/oblivion-ultrasonic-studios.902926/page-5 and the picture of Sonic's latest version of Oblivion, especially the internals on page 5 looks doable, it is so neat and tidy. I just might be able to copy that... sometime...
.

Edit: It actually doesn't look THAT complicated…. I might come to regret saying that...


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## MrCurwen

Each module when broken down is very simple. Like making one gyrator module, it's just a FET with a couple resistors and a cap. That's all. 

A CCS module is not that much more complicated. The 3D nature of the layouts makes it look messier than it is, when you actually make it yourself.

Most of the circuit is just repetition, lots of the same module over and over again. The end result has a lot of wire, but it's not hard to make.

I'm telling you, the amp you'll love the most, is the one you made for yourself.


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## baronbeehive

MrCurwen said:


> Each module when broken down is very simple. Like making one gyrator module, it's just a FET with a couple resistors and a cap. That's all.
> 
> A CCS module is not that much more complicated. The 3D nature of the layouts makes it look messier than it is, when you actually make it yourself.
> 
> ...



Yes right! That would be absolutely fine. The CCS that I did for the LD was not a problem. TBH I'm not interested in the theory, apart from general principles, so if it's an assembly job I would be happy with that.

It is tempting, I will look again at this sometime in the coming year.


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## Whitigir

where can I find more information about the schematic and the BOM ?


----------

