# Help needed to upgrade the capacitor in OTL tube amp



## telecaster

Hello there! I need some help to upgrade the capacitor in my La figaro 339. Please correct me as I know next to nothing appart that there are lethal voltage all around.
   
  The 4 little purple caps I think are the "lining" caps (don't know the name), they are 220µF 200V each.
  The 6 bigger purple caps are the "power filter" caps I believe 820µF 200V each.
  And there are 4 hidden "coupling" caps 63µF 350V each, I believe that they are bypassed by those rectangular blue caps. And if I swap them for MKP caps is it correct that I won't need to bypass them anymore with caps?
   

   
  I want to increase the value of the coupling caps to 100µF each as I want more bass.
  I choosed those MKP caps:

   
   
  I want to change all the electrolytics caps to MKP but the 220µF ones are problematic because of size, so for them maybe I will just use Vishay BC electrolytic of a bigger value.
   
  Is it good to increase the µF for the power filter and line capacitors?
   
  Also using these MKP instead of the lytics 220µF is it going to upgrade the sound:?

   
  I have so many questions, I hope someone will chime and help!
   
  Cheers!


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## tomb

I think you need to learn a lot more before you go trying to replace the caps with different types and sizes.  Unless I'm mistaken (I don't see a lot of transformers around), that thing is an OTL (Output Transformer-Less) amplifier.  As such, it needs some pretty huge caps at the output to keep from cutting out the bass due to the RC-cut-off frequency relationship.
   
  In other words, all things being equal, you may need as much as 220uf at the output to keep the -3db cutoff at 20Hz with 32 ohm headphones.  Even then, the actual start of the cut in bass begins somewhere between 100Hz and 1000Hz.
   
  So, what I'm saying is that attempting to replace electrolytic output caps with film capacitors at the output on an OTL amp is not going to work.  You simply can't purchase film caps with enough uf's to improve the bass.  What you should focus on is replacing the electrolytic caps with something even bigger.  If the coupling caps are truly 63uf, then I'd focus on finding some electrolytics as high as 220uf, 470uf, or even 1000uf, if you can afford them.  Bypass them with some good film caps and you won't notice the loss of quality with the electrolytics.  The film caps will carry most of the frequencies that are important.  Bass detail is not easily detectable, so you can make many cahnges while you're trying the increase the bass.


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## telecaster

I use this OTL with HD650 which are 300 ohms, that gives that I need 265µF/channel (with a calculator it gives me 2Hz -3dB point and perfect 20Hz response point). I would need to buy two 130µ to put in parallel, it's not impossible but I'm searching if going all MKP and that's regular high voltage MKP not the fancy one is going to be better than electrolytic bypassed by high end cap...
  The price in final is somewhere like 120€ for four 130µF MKP caps, or 60€ for good electrolytics and maybe 60/100€ for good bypass caps...
   
  I still wonder if bypassing the four 130µF MKP is going to help to not...


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## tomb

Well, OK - as long as you have a handle on how much uf's you need ... and it sounds like you do.  I haven't heard of anything this extreme in awhile (Ferrari did all film capacitors as the output capacitors once on a Millett Hybrid), but more power to you!  Bottom line, yes - if you can make up the uf's with film capacitors, they should almost always be better than even the best electrolytics.


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## telecaster

Those caps are huge and they fit just tight by my calculations!
   
  Do you know if bypassing the big MKP will do any good, and if yes what value would be adequate?
  I am searching for the resonnance frequency of various MKP cap and I can't find anything?! I thought I needed this info to choose the correct bypass cap value?!


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## tomb

The whole reason for bypassing is to allow a film capacitor (sounds better, faster, more detailed) to take over from an electrolytic at the higher frequencies (greater than bass) that are more sensitive to human hearing.  If you don't have an electrolytic, there's nothing to bypass.


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## telecaster

Thanks for the info. If I understand this well, adding bypass capacitors will introduce distorsion (time smear?) at the crossover points? So a single capacitor handling the whole human sensitive frequency range without any crossover point is better? So the primary purpose of those low µF exotic and really expensive capacitors are for passive loudspeaker network? That would mean that bypassing capacitor is only a last resort solution to heal electrolytic problems?


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## Zigis

If you use only 300 Ohm phones, even one 130uf or 100uf (white one in your pic) make adequate bass, no need to parallel 2.
   
  If you want upgrade PS caps, you can change only one el cap with film. I see, there is CRCRC filter, change only last C, closer to amp.
  Easy, cost free PS upgrade - wen you change output caps to film, solder remaining blue film caps parallel to power caps.


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## tomb

Quote: 





telecaster said:


> Thanks for the info. If I understand this well, adding bypass capacitors will introduce distorsion (time smear?) at the crossover points? So a single capacitor handling the whole human sensitive frequency range without any crossover point is better? So the primary purpose of those low µF exotic and really expensive capacitors are for passive loudspeaker network? That would mean that bypassing capacitor is only a last resort solution to heal electrolytic problems?


 
  Electrolytics have important applications with low-impedance headphones, too.  At 32 ohms, you need at least 1000uf to get to the same cutoff value that Zigis suggests above.  Also - IMHO, every electrolytic in the signal path should be bypassed.  The point being is that a film cap always sounds better, they're just not practical (or affordable) at the lower frequencies.  Bypassing is more of an art, too - and the size of the bypass is not really proportional to the electrolytic rating.  Usually, 0.47uf is about the limit of a good bypass, regardless of the electrolytic size.  I use 0.22uf the most, with 0.1uf being about the lower limit.  There are many schools of thought (smearing is one of them), but after much experimentation, I tend to think that a successful bypass combination results in a unique capacitance, not really two individual capacitors working on separate frequencies.
   
  Here's a good read on output coupling capacitors and the results of several bypassing combinations:
Notes on Output Coupling Capacitors


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## telecaster

Quote: 





zigis said:


> If you use only 300 Ohm phones, even one 130uf or 100uf (white one in your pic) make adequate bass, no need to parallel 2.
> 
> If you want upgrade PS caps, you can change only one el cap with film. I see, there is CRCRC filter, change only last C, closer to amp.
> Easy, cost free PS upgrade - wen you change output caps to film, solder remaining blue film caps parallel to power caps.


 

 Thanks, I will bypass the power cap then with those blue film. To be sure, they are 0.47µF 250V.
   
  And to be certain about the aforedmentionned cap, it is the cap that is the closest to the tubes? Also each of the power caps are 220µF in value, so it may not fit inside the case. Also costwise is it worthwhile considering I would spend also 120€ for changing only the both last power cap!


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## telecaster

Quote: 





tomb said:


> Usually, 0.47uf is about the limit of a good bypass, regardless of the electrolytic size.  I use 0.22uf the most, with 0.1uf being about the lower limit.


 
  Thanks a lot! One thing I still wonder, those bypassing capacitor value is for a single cap and should not be the total of all the bypass caps in the row of paralleled electrolytic caps?


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## telecaster

I don't know if it's worthwhile to increase the imput capacitor value or just replacing them with two 22µF film cap. I guess I don't know the imput impedance so I cannot calculate de frequency cut off.


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## tomb

Quote: 





telecaster said:


> I don't know if it's worthwhile to increase the imput capacitor value or just replacing them with two 22µF film cap. I guess I don't know the imput impedance so I cannot calculate de frequency cut off.


 
  Typically, the input impedance is set by the impedance of the volume pot.


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## jcx

the engineering numbers make it hard to believe in bypassing audio signal coupling electros with few % film/mica/PIO, whatever FOTM
   
  bipolar - full depth oxide on both foils is "best" on measured distortion for electrolytics - if you care you just use brick sized film caps alone - they mesure better than any electro
   
  I have measured a multichannel SACD player and found lower distortion with the "ordinary" Nichicon on the surround channels vs the Muse caps used in the R,L channels - the distortion was only just visible on the high pass "shoulder"
   
  the condition for distortion from cap dielectric is that there has to be signal drop across the cap - at filter edges - so just "supersize - make the coupling C 10-20x larger that "needed" and the audio distortion is impossible to measure
   
  the numbers for a small bypass cap shorting out a decent electro's ESR is laughable also - the corner frequency is typically 10s of MHz - no effect at audio - and there is a typically L:C resonant peak from lead inductance at lower frequency
   
  I realize there is huge audiophile belief in "Capacitor Sound" - but no "Capacitor Tasting" review I've ever seen goes into any depth about even basic Blinding, controls needed to make hearing the "only" thing used for the discrimination


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## tomb

Here's an excellent article on "Blinding":
http://www.innerfidelity.com/content/beyond-neutral-measurements-blind-testing-subjective-experience-and-personal-pleasure-headph
  Just someone's ( 
	

	
	
		
		

		
		
	


	




) opinion, but it's interesting to note this quote: _"I do not think it [blind testing] does a very good job of quantifying performance characteristics, because humans are not at all like scientific instrumentation."_
   
  I would also note that bypassing output coupling capacitors is not a FOTM fascination and has been used since well before 2000 for headphone amplifiers.  Besides Dsavitsk, Pete Millett has used bypass capacitors in many of his designs, along with Alex Cavalli, Andrea Ciuffoli, and van Waarde.  Amps are designed with either sand or glass, or a combination of both.  Those that specialize in glass and combinations with sand are very familiar with bypass capacitors.  The all-sand proponents typically don't have a clue.


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## telecaster

Input impedance for the calculation of imput cap is the volume impedance gotcha! I now have pretty much all info to mod this great little amp, danke schöne meinen herren!
  I know that electro caps in the signal is the worst and I will switch them as soon as possible. We are not debating it here!
   
  Sadly my seller doesn't have 130µF in stock and the delay is two months, a downer... I think I will use two 100µF and two 30µF(to fit the case) per channel. Isn't it to detrimental to use four caps instead of two soundwise?
  Also I want to replace the last power cap but I fear funds are not allowing it. So is it possible to only add another film cap lets say 30µF at the end of the CRCRC filter and keep the benefit?
  Lastly i will change the elec imput cap to film ones, four 22µF is cheap enough!


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## Zigis

If you really use only 300 ohm phones, for output cap one 100 uF per channel is enough. 
  For input 4.7 uF good polypropylene film cap is enough, even for 10K pot, however in tube amps usually are 50K or 100K.
   
  Math is - corner frequency for input depend on input cap and pot impedance, for output - output cap and phones impedance. Larger impedance - smaller cap required for the same corner frequency. For 32 ohm headphones 470uF is the best, with 10x larger impedance 300 Ohm (Senn) 10x smaller cap - 47uF do the same job. Your 100uF cap is even extra.


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## telecaster

I want to  have a 2Hz -3dB point, to have a perfect 20Hz response, no compromise for that! That is why I need 265µF for the output cap.
   
  I have one question, can I replace the dual electro imput caps (2X22µF) for a single film 4,7µF? So I would need to change the resistor too?. How do I calculate its value?
   
  Also when I replace the last cap in the CRCRC power filter, can I switch the last elec 220µF cap unit for a parallel 2X50µF film? Would I also need to change the resistor between this and the preceding elec cap?
  
  Another question, isn't it better to bypass the power filter elec cap with something like film 2,2µF or higher value? I read a specialist saying that it's needed to have a better impedance curve without bump...


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## jcx

the Sound Science forum is the place to debate validity of listening protocols - I simply point out that there are reasons the Scientific/Engineering communities only respect Blinded tests of "audibility", with controls for level matching, frequency response - plenty of perceptual psychology, psychoacoustics refereed journals, textbooks explaining the the problems with sighted, "just listen", naive "I am mentally honest with myself and can suppress unconscious bias" claims
   
  if the OP really wants to know "what makes a difference" he should learn some of the issues, techniques for valid listening comparisons
   
  with the Figaro he has a great opportunity because the circuit is dual mono - he can change the parts in one side only and be able to compare with the unmodified channel - albeit in mono only
   
  this requires "blueprinting" the R,L channels for any other differences - tubes must match gm, mu, gain resistors to 1% between channels
   
  a few adapters, attenuators, some free SW and much of the required measurements could be done with a PC soundcard - even typically poor internal chipsets will get you a long ways towards having some technical ground to stand on


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## Zigis

With 100uF output cap and 300 ohm phones you got -3db at 5.3Hz, do you seriously think this is not enough? 
   
  For input cap formula is the same as for output, R is volume pot. 4.7uf is oversized in almost any situation (I know, you like it
  For volume pot 10K, -3db is at 3.39Hz, volume 50K - 0.68Hz, volume 100K - 0.34Hz
  Even with 1uF input cap you got 3.18Hz with 50K volume and 1.6Hz with 100K pot


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## telecaster

About the 2Hz -3dB point, I believe that the high pass fall off is really muting the bass from my not so deep HD650... I want to be sure I have the maximum freq bandwidth, so the 2Hz point is what I will stick too, even if I have to pay for 30/40€ more.
   
  About psychoacoustic:
  I learned to trust my feelings over the years not the numbers.. Of course I know a little about the scientific side of audio but I don't fall for the audiogoofy claims thats are plaguing this hobby. Years ago I grew up with a Meridian M2 active loudspeakers and I love them... When one blew up, I had to find an alternative and ended with a system that I didn't like at all, leading to listenning less and less music, two years later seeing my departure from being a music lovers to being a music listenner I took the money under the bed and shell out for a Meridian system... I was in love again!
   
  Back to the subject! I think I gave all wrong numbers about the values of the power filter caps, they are 820µF each, and the pairs located near the tubes are 220µF! Now I seriously think there are no imput capacitors and those 220µF caps are bypass caps ??!! Could you help me and tell me where is located the imput caps? That pair of 220µF is in parallel to the power caps if that helps...
   
  So all in all, about my 4.7µF imput question, I could use only one film cap instead of the CRC imput caps, if it is that?


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## WALL-E

Updated: full schematic with my multimeter reading.
   
   
  You quoted to my post on Darkvoice 339 thread but I think here on DIY I will continue the discussion.
  I drew scheme of our LF339 (incomplete) just to better understanding how it is built.
 As you see diagram below ther is NO imput capacitors at all,  to be honest only one capacitor is in signal pach output coupling cap and thank God. The two smaller electrolite working with resistor voltage divider part of power supply actually all EL are in power supply.
  
 I checked the voltage on cathode resitor is 90V so you don't have to be worry about SCR MKP 250V you chosen, 250V cap is more then enough.

 @ Originally Posted by *telecaster* I cannot locate a good seller for caddock resistors, I will then stick with Seta brand... Now could you lead me in calculating the correct value of resistors for the imput cap?

 Orginal value of cathode resistor is 430 ohm 50 wats so you have to use 3 resistor 1.3K ohm(1300 ohm) 20 Watt each in pararell = 433 ohm 60 Watt.
   
   
   
  C1,C2,C3 820uF
  C4,C5 220uF
  C6 130uf output coupling
 R5 430 ohm 50 Watt cathode resistor


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## jcx

Quote: 





> About psychoacoustic:
> I learned to trust my feelings over the years not the numbers..


 
   
  false dichotomy - assuming you're human the results of perceptual psychology apply to you as well - "the numbers" for level matching, frequency response are necessary to establish a level playing field for effective listening for circuit, component differences
   
   
  one of the lessons from Science based psychoacoustic testing is that even 0.1 dB, ~1% SPL is heard as a "sound quality" difference - and not as "oh that's just because one's louder" - few can tell the difference is solely loudness until the difference is >1dB ~10%
   
  so to compare fairly by ear you have to match levels, and use some Blinding method to make sure the only information your brain can use is the sound entering your ears
   
  at frequency extremes the level match requirement gets much looser: http://home.provide.net/~djcarlst/abx_crit.htm
   
  the numbers in the abx threshold graph are useful to put upper bounds on "how bad" the frequency response can be without "sounding different" for the "uninteresting" reason that the level/EQ is off
   
   
  the required level matching does require measurement, "doing some numbers" - almost any soundcard or PC with analog line level in is adequate for this if you use the same channel for all measurements
   
   
  at the low end it appears that even 30-40 Hz 3 dB corner will not be "obvious" - but if concerns for subtle distortion drive you then as I mentioned above aiming for 5-20x lower corner frequency is a technical fix
   
   
  the above doesn't have anything to do with claims that something "must" sound  good just because the numbers are good - attending to these numbers are required for valid results from listening - whether you are gifted amateur, Golden Ears, Professional Musician, Sound Engineer...
   
   
   
  comparing magnitude, orders of distortion to guess relative audibility goes more like this:
   
  this doesn't address the (in)audibility of subtle capacitor dielectric distortion in a simple tube amp with 10000x higher 2nd order distortion from the tube, "simple" circuit's characteristics


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## telecaster

I agree jcx, I wasn't saying I don't believe in the science of measurement in audio, far from this. But I have no technical ability to do so. I am only an end user here!
  As for the tube distorsion, I happen to love it, and I would gladly hear it and not the electrolytic in the output. But as I have ordered some cheap bypass teflon and KP caps, I will first try to bypass those electrolytics with better caps and the filters too and see if I can improve things before going all out and going film only for the output caps.
  I had a hard time comparing sounds of different tubes, but only by hear and analysis I have achieved some findings. Going back and forth is really easier but my auditive memory is not too shabby, I am a musician.


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## telecaster

Thank you a lot WAAL-E!! I now see a lot clearer in this amp! I was sure I responded last night but here it is again! Thanks for the schematic! I'm glad the SCR 250V is right because nothing else fits in there hehe!
   
  So there is not imput cap? Isn't it strange or a genius of a design? Do you know what are the two white boxes sticking to the sides of the amp near the driver tubes?
   
  I have bought some 2200pF teflon caps and 0.5µF KP caps in order to experiment with bypassing, a lot of fun in sight!
   
  Thanks again for the diagram! I ask Yuking team about it, but they never responded...
   
  I have something that I need to ask :
   

   
  What is are the two soldering card for and what are the components on them?
   
  Also in Keph modded 339:

  What are the diodes for (on the soldering card next to the 2000pF capacitors)? I assume the tiny caps are for decoupling the power filter? The diodes are needed if I want to bypass my power filter too?
   
  Also how is called what is used to solder the resistor network? I need to order that part but I cannot find it unfortunately.
  BTW thanks for the calculation of the resistor but I remembered my high school days yesterday and found this as well. Appart from that my resistor is 470ohms 50w, not sure why he change the value except that availability of parts...
   
   
  Quote: 





wall-e said:


> You quoted to my post on Darkvoice 339 thread but I think here on DIY I will continue the discussion.
> I drew scheme of our LF339 (incomplete) just to better understanding how it is built.
> As you see diagram below ther is NO imput capacitors at all,  to be honest only one capacitor is in signal pach output coupling cap and thank God. The two smaller electrolite working with resistor voltage divider part of power supply actually all EL are in power supply.
> 
> ...


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## kevin gilmore

The schematic has errors.
  The grid of V2 is driven from the plate of V1.
  There is a resistor between the cathode of V1 and ground.
  There may also be a cap across this resistor.


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## jcx

any V1 cathode bypass would count as a "signal path" C if you're obsessing over Cap quality
   
  discrete diode bridges may be fast recovery - nowadays Schottky are available at tube B+ voltages - Schottky shouldn't need snubber C - only standard recovery diodes really need local RF bypass - questionable to be concerned here when the unshielded tubes sit out in the open


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## WALL-E

I drew it because looking on the picture of amp is difficult to descramble what is what?
 This diagram is incomplete I omitted a couple of elements I don't wont posting full schematic on public forum that would be illegal I guess?

 @There may also be a cap across this resistor.
 I think you mean local feedback, no there is not. It is pure SE design, the V2 twin power triode(two triodes in each glass envelope) is in parallel mode (not shown in  schema) to handle more current and reduce half the output impedance to better match with lower impedance load.
  Quote: 





kevin gilmore said:


> The schematic has errors.
> The grid of V2 is driven from the plate of V1.
> There is a resistor between the cathode of V1 and ground.
> There may also be a cap across this resistor.


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## telecaster

I added up all the prices for the caps I want to change and the resistors too, I came up with 230€, it's a little steep right... That is for the top of the line vishay BC electro, and 265µF of output coupling SCR MKP per channel. Oh and every elec will be bypassed by it's SCR MKP too. I am sure the price to pay won't transform the 339 radically, but I expect a good step up sonically. Oh and as a bonus I have shop teflon and KP as bypass experimentation!
   
  WALL-E, thanks for the drawing I understand way better now! May I ask you what you want to upgrade in the 339?
   
  I have an advice to ask though, I wonder if those MKP is any good for output coupling duty : Would they be good as I never heard anyone using them as such...?
   

   
  They have 3.5mOhms ESR, huge voltage rating which is good I understand, they are MKP of course, and I can have a good price.
  Downside is it doesn't fit inside the central black cover, so I thought I could tie them together, markings hidden down, with the lugs facing toward the sides symetrically and have 8 units like that sticking between the two black covers remaining in the open air. For sure I'll have to find a way to secure them to the case. Oh the and total height of this monster cap would be 9cm, so it would be 1 or 2cm higher than the black box... Thinking about it, it's not that pretty, but that way I could pack high voltage MKP which otherwise I would have to stick with 250V MKP, it's the only way...


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## jcx

> Quote:
> 
> 
> 
> ...


 
   
   
  in the US at least, for any commercially sold product, absent binding contract secrecy terms - anything you can determine by any level of inspection, reverse engineering, is considered fair game - equivalent to being published
   
  the only restriction is that you cannot publish a copyright protected exact "mechanical" copy of the manufacturer's user, service manual drawing without permission - if you derive it yourself, hand draw or enter in your own schematic software is it yours to publish freely


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## WALL-E

@Do you know what are the two white boxes sticking to the sides of the amp near the driver tubes?
 It could by resistors it have to be resistors but why he used big ceramic one ? maybe someone who have the other version of LF339 with 6c5 driver will know?
   
  @Also how is called what is used to solder the resistor network?
  Solder terminal strips.
   

 the diodes used in keph modded LF339 are very fast rectifying diode VISHAY BYW type very popular in use in switched-mode power supply, but my choice will be Schottky
  I double checked and the cathode resistor is 470 ohm, but mills 430 ohm resistor was used in one of modded lf339 too.
   
  Quote: 





telecaster said:


> Thank you a lot WAAL-E!! I now see a lot clearer in this amp! I was sure I responded last night but here it is again! Thanks for the schematic! I'm glad the SCR 250V is right because nothing else fits in there hehe!
> 
> So there is not imput cap? Isn't it strange or a genius of a design? Do you know what are the two white boxes sticking to the sides of the amp near the driver tubes?
> 
> ...


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## tomb

Quote: 





jcx said:


> any V1 cathode bypass would count as a "signal path" C if you're obsessing over Cap quality


 
  Yes, and since jcx points out that it can be "interpreted" as part of the signal path, you should also bypass it to be consistent.


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## telecaster

Ok I've been learning a little bit about CRCRC filter. I guess I understand why the 339 sound very tight in the bottom, it is because it seems it's might be filtered that way.
   
  I wonder what would be the effect if I would lower the filtering to only a CRC filter. If I understand well, if I keep the two resistors in serie, and if I move the middle cap to // of the last cap, I would achieve a last C of (820µF+820µF+440µF) while the first C is 820µF. Is it dangerous if I try it?
   
  Or maybe I should use a lower value of nominal C1? Higher C1? Yuking is using 1000µF C1 and C2 // with two 220µF with whats look like a CRC:
  It is his no cost object last project custom made for his friend. I know he is into classical music essentially, maybe that's why he's into tight bottom and presence.

   
  For the record, he is using those film cap as output coupling, and that is only 120µF per channel it seems:


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## WALL-E

I found that the aluminum-housed 470 ohms resistors have not too good tolerance the multimetr showed 514 ohm on one of them almost 10% and it could be worst when they heat up.
 I'll gonna change it for Non Inductive -1% Wirewound resistors like, MILLS - MRC50 or MRA-12 12 watt in paraller conf, in power line I think I stick with Mills or Caddock for the driver section and the rest I will use some good Metal Foil Resistors.

 In power supply I would try 4-pole electrolytic capacitors MUNDORF MLytic HV Series is especially designed for the application in innovative and demanding tube ampliﬁers.

 And for output cupling Mundof too, MTube Series M-TubeCap polyprophylene film or MKP Series Film Capacitors.

 Also will change the stock bridge for Schottky Bridge Rectifies and AC IEC Inlets only because  feling off wen connecting rigid power cords.
 That's all.
 Vishay 1845 MKP it could be anyway It be worth experimenting using different caps.
	

	
	
		
		

		
			




  Quote: 





telecaster said:


> I added up all the prices for the caps I want to change and the resistors too, I came up with 230€, it's a little steep right... That is for the top of the line vishay BC electro, and 265µF of output coupling SCR MKP per channel. Oh and every elec will be bypassed by it's SCR MKP too. I am sure the price to pay won't transform the 339 radically, but I expect a good step up sonically. Oh and as a bonus I have shop teflon and KP as bypass experimentation!
> 
> WALL-E, thanks for the drawing I understand way better now! May I ask you what you want to upgrade in the 339?
> 
> ...


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## WALL-E

This is single rail resistor voltage divider and leave it as is,  you can increase the capacity.
 The Yuking custom amp could have different transformer winding to provide two split rail.
  Quote: 





telecaster said:


> Ok I've been learning a little bit about CRCRC filter. I guess I understand why the 339 sound very tight in the bottom, it is because it seems it's might be filtered that way.
> 
> I wonder what would be the effect if I would lower the filtering to only a CRC filter. If I understand well, if I keep the two resistors in serie, and if I move the middle cap to // of the last cap, I would achieve a last C of (820µF+820µF+440µF) while the first C is 820µF. Is it dangerous if I try it?
> 
> ...


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## telecaster

Quote: 





wall-e said:


> This is single rail resistor voltage divider and leave it as is,  you can increase the capacity.
> The Yuking custom amp could have different transformer winding to provide two split rail.


 

 Ok thanks, can I lower C1 to 680uF or lower? Same 680uF for C2, then 1000uF for C3? If yes do I need to recalculate the Rn and how do I calculate R?
  I read that it's best to have a small and fast C1 and a three times bigger C3, don't know about C2... Also I read that bigger is not better in PS filter, it can make the sound in the bass sterile.
   
  C4 and C5 are // of C3 thus increasing its capacitance or not? I don't understand fully C4 and C5, could you please explain it to me?
   
  Is it ok to bypasse C1 to C5 with 10µF MKP cap then again 0.42µF bypass? If yes where do I solder the bypass caps? Do I solder the 10µF just at the bypassed big electrolytic lug?


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## WALL-E

Voltage after graetz bridge will drop about 1,2÷1,4V and will increase after C1 capacitor Uout = ~Uin * √2 - 1,4V. So the first cap after bridge shuld be bigger value and the C2&C3 could be less value of capacity if you really want.
 I measured the voltage on R1 is 179V,between R1 & R2 is 160V and between R2 & R3 is 142.6V and this is for power the V2, and between R3&R4 is 142.3 and on the end R4 we got 87V this is for power driver V1. I may suggest you C1,C2,C3 equal 1000uf and C4,C5 equal 220 or 330 or 470uF the value of R1..4 do not need to be changed.
  To bypass EL I use value between 100nF to 1uF but you choiceu will gona work well, yee solder directly to the endings of EL.
  Quote:


telecaster said:


> Ok thanks, can I lower C1 to 680uF or lower? Same 680uF for C2, then 1000uF for C3? If yes do I need to recalculate the Rn and how do I calculate R?
> I read that it's best to have a small and fast C1 and a three times bigger C3, don't know about C2... Also I read that bigger is not better in PS filter, it can make the sound in the bass sterile.
> 
> C4 and C5 are // of C3 thus increasing its capacitance or not? I don't understand fully C4 and C5, could you please explain it to me?
> ...


----------



## telecaster

Thanks a lot for the advices! I have bought 6 1000uF 200V BC for PS filter.
  About the value of Rn: I need some help my seller doesn't have 200R and 1Mohm and 30Kohm (he carries 220R though)
  R1 and R2 are 100R each right?
  R3 is 200R?
  R4 is 30Kohm?
  R to V1 grid is 10Mohm?
  I will order the 3 watts resistors so I don't want to mess it up many many thanks by the way!


----------



## WALL-E

V1(8 pin octal socket) resistor soldered to pin 1 and 4 is 1 M-ohm, resistor soldered between pin 5 and 8 his value is 1K-ohm.
 I will post complete amplifier schematic with all my multimeter readings on weekand it should be helpful anyway.

 R1,R2 100ohm/10watt
 R3 200 ohm
 R4 30K-ohm
  Quote: 





telecaster said:


> Thanks a lot for the advices! I have bought 6 1000uF 200V BC for PS filter.
> About the value of Rn: I need some help my seller doesn't have 200R and 1Mohm and 30Kohm (he carries 220R though)
> R1 and R2 are 100R each right?
> R3 is 200R?
> ...


----------



## telecaster

Could 180ohm or 220ohm replace the 200ohm resistor? Same for the 30Kohm, does the 22Kohm is ok?
  Is there a downside effect because I upgraded all PS caps to 1000µF for C1 C2 C3 and 470µF for C4 C5?
  Particulary for C4 C5, by increasing the capacitance, does it increase the current to the driver? Will it help reducing hum in certain (like the EF80) tubes?


----------



## WALL-E

The resistor values are carefully calculated by designer don't change the the value, if you don't have 200 ohms, 30K-ohm leave the original ones in place.
  The B+ power supply is a simple single polarity type, the capacitor job is store a steady amount of charge and then quickly release it most of this charge when it is needed in this aplication also is in smoothing the output of a bridge rectifier after it has converted AC electricity into DC.
   
  @is there a downside effect because I upgraded all PS caps to 1000µF for C1 C2 C3 and 470µF for C4 C5? : there is NO
  @Particulary for C4 C5, by increasing the capacitance, does it increase the current to the driver? : NO
  Will help reducking hum in general.
   Quote:


telecaster said:


> Could 180ohm or 220ohm replace the 200ohm resistor? Same for the 30Kohm, does the 22Kohm is ok?
> Is there a downside effect because I upgraded all PS caps to 1000µF for C1 C2 C3 and 470µF for C4 C5?
> Particulary for C4 C5, by increasing the capacitance, does it increase the current to the driver? Will it help reducing hum in certain (like the EF80) tubes?


----------



## telecaster

@Wall-E : So the big ceramic resistor (white plastic box) is 10K ohm? Is it possible it is damage and cause crackling noise?
   
  I change the big wirewound resistor today... They were fooked up! They are simply plastic resistor cap inside the aluminium heatsink, when I removed them they were completely loose and the plastic was desintegrated! I wondered why my amp was so hot, now that I changed it it is not hot like before! Still hot but less than before and less quickly!
  I wonder what is wrong in my amp, I still have sometimes a crackling noise when no music is playing. Metal film resistors don't make that sound do they!? I have this crackling only on left channel. Yuking sent me all the wirewound resistors to replace them so I guess while I wait for the new parts for the mod, I will change and isolate where does this crackling noise comes from...


----------



## telecaster

I am very curious about converting the 6SJ7 socket to 6J5 socket:
  It seems so easy to do! Only change the pinouts and change R3 to 100ohm... R4 is connected the same, the filaments are pin 2 and 7 also, and 3 and 6 are the same. Only need to change the resistor of grid and the big ceramic.
   
  It looks even possible to make some kind of several switches to change the grounding of the pins and to change the resistor pin, and to change the anode and cathode... It would be cool to be able to switch this. It must take some thinking to make the swtich combination idiot proof. Need also to make a switch to change R3 from 100R to 200R... hmm all in all there are no space to achieve this, but it's definately doable in design. Maybe just not worth it.
   
  Problem is I have just one tube that I love with 6SJ7, while in 6J5 there are a lot to try that looks cool! Only TS 6SJ7GT looks cool, the others are ugly!
   
  Or just change the socket to 6J5 and be done with it! There are a lot of nice tubes for those.
   
  NB: filaments are the same 2-7pin.
  6SJ7 pinout


   
   
  6J5 pinouts


----------



## telecaster

Quote: 





wall-e said:


> @Do you know what are the two white boxes sticking to the sides of the amp near the driver tubes?
> It could by resistors it have to be resistors but why he used big ceramic one ? maybe someone who have the other version of LF339 with 6c5 driver will know?


 
  In fact the 6J5 version use it too. It is the EF86 version which doesn't use that resistor.


----------



## WALL-E

I don't know the value of the"white plastic box" resistor do you ?
 I like your idea"all in one" to use switches to change the type of drivers tube, but even upgrade to 6c5,6j5 shuld be easy to do like you said.
 The aluminum-housed resistor had inside thermo protection fuse? the thing what fell off, anyway they would need replacement. May I ask what type wirewound resistor you use as a replacment?
 Do you have the cracking noise with all your driver tubes or just with them which need adapter?
 I have one faulty ef80wf which after hour or two have statick clicking noise and not always.
 When I got ef800tfk to try while ago with the adapters they humed/noise like hell and was sensitive to touch but the issue was not tubes but the adapters.
 I opened(lifted up) the adapter with sharp tool  there was twisted bundle of cables which had interference making the noise.With the headphones on head  by simply ajust (twist/turn) top plate of adapter few milimetres left or right  maked the hum/noise disappeared for good the same i did with other adapter.
   
  The second photo from the bottom it is the other version of  LF339 with 6c5,6j5 as a driver ?


----------



## telecaster

I used the same type of wirewound resistor as stock, sent by Yuking as I was experiencing crackling no matter what tube was in there.
  I had a driver tube (6SJ7WGT philip) that "red plate" on this socket (left), and even when powered off in urgency, the tube was still burning bright, so I pulled it off quickly because it was wrong! Since then I have that crackling noise wich is not always there, but it happens only when no music is playing and mostly when the amp is not warm. It may be one of the other resistor or even the capacitor I don't know, after inspection nothing is burned... weird! It was my fault, because in the beginning I was switching drivers tube without waiting the tubes to cool off, and switching a cold driver with a hot power tube is a NO NO! I learned the hard way.
   
  Since I will change all the parts, it should go away, unless it is the white box (mystery resistor) or the transformer which is highly unlikely.
   
  I will use four 1K8 16watts vitreous glass resistor in // to replace the big wirewound. First I was going for 25watt 1K8 to lower the heat but those cost 5€ each so 8 of them was kinda expensive and were very long at 65mm. The 16 watts are 45mm an can handle 400°C and are 2€ each!
  I'm waiting for the solder terminal strip to arrive from US. BTW still I can smell this 470R resistor burning the plastic again, those are crap.
   
  And the adapter are fine mostly, only the EF80 and EF800 tubes when not really knew or banged up are static! I have bought some brand spanking new mullard EF80 and they are perfect! Wish I found those at first. This should have save me a lot of time with those damaged EF80...
   
  Anyway since I have found those mullard, I don't have that urge to upgrade to 6J5. 6J5 are going expensive, and while very cool looking I'm not sure I will go the route to find good pair again. The mullard I found are so nice sounding, they make my newly arrive GEC 6080 and Bendix sounds bassy which was the only thing that were missing from them!
   
  I agree that the adapter are not great, I want to redo them with some quality gold plated socket but it's hard to separate the red base to the chrome body so I will as Yuking to sell me the parts unsoldered. And just buy some teflon gold plated 9 pin sockets.
   
  About the switches, if going for a regular bypass switches it will need at least 3 or 4 switches for each socket, plus 100R and 200R also on switch.  In the end one should be very carefull not to mess up the switch config too! But I think it's doable still!
   
  Just converting to 6J5 is pretty easy though and I might just buy another pair of socket in order to keep the 6SJ7 socket wire up stock in case I want to revert easily.
   
  The photo on the bottom is from an upgraded 339 for 6J5 driver. Just R3 is 100R instead of 200R, the 30K is connected to the same pin. It just need to modify the grounding of three pins and to change cathode and anode and that's it.


----------



## WALL-E

When one of yours 6SJ7WGT lost the vacuum and went white it could damage the 1Kohm  resistor from cathode pin5 to 8(ground) I think it is a stopper which earthed  the cathode to prevent oscillations, check the resistor and voltage on the pin5 of V1 I have 1.8V.The type of small resistor not burns this way, when they fail you  will see some crak or small piece felling off ceramic body or sometimes no marks of burn at all.


----------



## telecaster

Hi, and thanks! I don't get it! The resistor on pin 5 of V1 is the big white box!? See my photo. I will check the the voltage right now and get back to you.


----------



## WALL-E

this time i don't get it my lf339 don't have the big white box!?


----------



## telecaster

When did you buy it? I bought it in april I think... I've read a little about it, and it looks like it's called a grid stopper? Recommandation is to use a non inductive resistor like carbon com resistors, while some says modern metal film are adequate. I have even read that the best is to use some kind of choke as grid choke, maybe the white box is kind of cheap choke I dunno... Anyway I hear some radio frequency sometimes on the left channel, it seems my grid stoppers is defective! I will replace it like your 339 with a 10K grid stopper resistor...
  
  About the measurement, I have to plug the power and the tubes in order to read right? At what pin exactly I have to read? I fear because your lightbulb technique works great, but I never get into a tube amp with live power on.


----------



## WALL-E

Quote: 





telecaster said:


> When did you buy it? I bought it in april I think... I've read a little about it, and it looks like it's called a grid stopper? Recommandation is to use a non inductive resistor like carbon com resistors, while some says modern metal film are adequate. I have even read that the best is to use some kind of choke as grid choke, maybe the white box is kind of cheap choke I dunno... Anyway I hear some radio frequency sometimes on the left channel, it seems my grid stoppers is defective! I will replace it like your 339 with a 10K grid stopper resistor...
> 
> About the measurement, I have to plug the power and the tubes in order to read right? At what pin exactly I have to read? I fear because your lightbulb technique works great, but I never get into a tube amp with live power on.


 
  Now I got it. I bought my in july 2011 it seems like yuking do some modifications in production process to the current lf339.It is soldred to the same pins like my one,  pin5 and the other end of the "white box" is ground.To be shure you can swap the white box from R-Ch to the L-Ch to see if helped.Yea could be kaind grid choke, does it have symbol or serial number ? Is it possible to open if yes inside should a choke/coil , resistor and smal capacitor I guess.
  To take the reading you have to run the amp with tubes in, be cerful!, set the meter to DC, then connect ground tip(black colour) your multimeter to ground and the red tip stick to pin 5 and take the readings and compare with other channel.


----------



## telecaster

I finally got the time to do it!
  It's weird, I check all the the resistors, they seem to all be in good value appart from the resistor btw pin 1 and 4, but the value is off a little.
  Both the white boxes both are almost exactly 1Kohm.
  The R right channel pin 1 pin 4 read 3.9ohm( min vol) and 88,9Kohm (max vol), voltage brw pin 5 and ground reads 1.68V
  The left channel pin 1 pin 4 read 3,3ohm (min vol) and 82,5Kohm (max vol), voltage btw pin 5 and ground reads 1.71V
   
  Both 30Kohm read almost exactly 30Kohm, the 200ohm read 200ohm...
   
  I fear my problem comes from somewhere else, I hope it is not the transformer! Maybe it is the electrolytic. If not I am in serious trouble!
  It seems the 1Mohm in the left channel is off a little, maybe it's the culprit (btw pin 1 and 4)...
   
  Yesterday I got an almost non stop faint crackling noise from the left channel...


----------



## telecaster

I switched from left to right the 1K white box resistor, the 1M resistor, I change the 220uf lytics to new 470uF lytics and the pop noise (it sounds like pop pop pop pop") remain on the left channel!
   
  I am in the process of changing the output coupling lytics to MKP and will report  tonight if the pop noise is still there.... Damn...


----------



## nikongod

Have you changed your tubes?
  Moved them from one channel to the other?


----------



## telecaster

Of course I did change tubes! Don't you think I would have checked my tubes before changing the resistors!?


----------



## telecaster

I switched the 30K resistors, still the crackling noise in left channel...
  I changed the output capacitor to MKP, the sound is good, but still the crackling noise...
  I replaced the 100ohm resistors for the power caps.. Still the noise.
  I hope to receive the BC capacitor to change the PS caps and hope that noise will end once and for all!
   
  Is it possible it's the rectifier? Or the transformer?


----------



## nikongod

Quote: 





telecaster said:


> Of course I did change tubes! Don't you think I would have checked my tubes before changing the resistors!?


 
   
  IME that it is not safe to assume that you swapped the tubes to verify that they are not at fault. So I asked.


----------



## telecaster

No problem m8, you are right, in fact I double checked it numerous time too to be sure it wasn't the four pairs of tubes I was using.
  Anyway I have isolate the cracklin noise problem. I switched the output coupling resistors and that was the cultprit. I'm still waiting for the solder terminal strip to convert it to a parrallel bank of power resistor... Pfeww that's a relief now that I have found what the problem was!


----------



## WALL-E

Quote: 





telecaster said:


> No problem m8, you are right, in fact I double checked it numerous time too to be sure it wasn't the four pairs of tubes I was using.
> Anyway I have isolate the cracklin noise problem. I switched the output coupling resistors and that was the cultprit. I'm still waiting for the solder terminal strip to convert it to a parrallel bank of power resistor... Pfeww that's a relief now that I have found what the problem was!


 
   
   Almost all checked....weird isn't it? I thought about "Ground Loop" issue ? and to try to isolate it to see if help but
  I see you sorted out the problem with the pop noise. Good job!


----------



## telecaster

That was close I was almost beginning to forfeit!
  Anyway Wall-E what sort of resistor are you gonna use as output coupling resistors? The Mills don't seem to handle a lot of watt... I figured out my SETA are inductive so it might be a problem, what do you think?


----------



## WALL-E

Quote: 





telecaster said:


> That was close I was almost beginning to forfeit!
> Anyway Wall-E what sort of resistor are you gonna use as output coupling resistors? The Mills don't seem to handle a lot of watt... I figured out my SETA are inductive so it might be a problem, what do you think?


 
  I checked voltage and current consumption on the cathode resistor and depends of what tubes I used it is from 84-90V and current is 168mA-184mA what give the Rk wattage between 14-17Watt idle and with the load on is almost the same. Of course better oversize the resistor to hold in reserve few watts or use smaler in parallel which will disperse the heat better then single one.The Rk like output coupling caps have an effect on sound and better use good components.
 I'll use non inductive 1% Wirewound resistors like, Mills  MRC50 this one is 50Watt or go with MRA-12 series 12Watt so 3 in parrarel give me 36watt seems enough.


----------



## telecaster

Ok thanks, I have received the solder strip but unfortunately it's a small model, not like the one Yuking is using. anyway I use my seta resistor and it fits the amp, I will eventually replace the whole array when I spot a problem, but for now the sound is pretty much problemless even though those resistors are inductive...
   
  I added 30uF per channel of MKP totallizing 230uF per channel of film cap. The bass is slightly better now compared to stock, I have spotted the sound is more well rendered in the lower octave, and in general bass has more body,but it's slight.
   
  The sound of the MKP vs lytics is also a slight change but for the better. I don't bypass the flim caps at all, I find the sound detailed and more relax and in comparaison the lytics were a little scratchier in the top end, and the bass lacked the lowest octave probably due to the 130uf per channel value of stock lytics.
  The sound is more coherent and has more depth with the film cap, but it's not a night and day change, as I did the switch I know it's there, but it's not "obvious".
   
  I added 4.7uF bypass to the 470uF lytics in PS, and 9uF bypass cap to the last 820uF cap in the PS. I found the sound a little cleaner, but the change is really slight too, but I like it better that way. Costwise those are really not worth it, but in a cost non object I would say why not...


----------



## telecaster

Added 10000pF silver mica to the output, still testing, the sound is not bad...
  The 4X100µF MKP are on the other side of the board. Still waiting for the PS caps to arrive..
  Gotta find a way to fit two more 30µF MKP in there somewhere!


----------



## WALL-E

I'm glad you're happy with the results you did to modifying your lf339 anyway pleased to Do It Yourself.

 Also I would not expect huge improvement like Night & Day, look at this amp is build like tank every thing is doubled and  the performance with low-high cans & SQ are first class. It's not like my 332c which looks poor compared to lf339  in which I upgraded output caps and the result exceeded all my expectations I could tell that it was almost like Night & Day.
 But for me even small improvement will be worth to put the extra DIY wchich i like it and "£,$,€" to tweaking the amp.

 Good Job!!! telecaster.
  Quote: 





telecaster said:


> Ok thanks, I have received the solder strip but unfortunately it's a small model, not like the one Yuking is using. anyway I use my seta resistor and it fits the amp, I will eventually replace the whole array when I spot a problem, but for now the sound is pretty much problemless even though those resistors are inductive...
> 
> I added 30uF per channel of MKP totallizing 230uF per channel of film cap. The bass is slightly better now compared to stock, I have spotted the sound is more well rendered in the lower octave, and in general bass has more body,but it's slight.
> 
> ...


----------



## telecaster

Thanks for the kind word!
  I don't know if if it is a placebo effect but the sound is really better than before all the mods! The 339 highs were already very clear and relax, but now it's another level of clearness and naturalness. It is like a layer of mild distorsion has disapeard. Now there are 3X 10000pF of silver mica per channel, it's the russian capacitor CRM3.
  I think now the sound is even more clear in the upper range. I will stick with that for some days to analyse the effect of those bypasses.


----------



## telecaster

Some days have passed and I can tell now that the bass is definitely better! I suspect it is the 470µF caps in place of the 220µF.
   
  Before the mods the highs were more agressive and the bass less warm and less powerfull. Now The highs are perfect mix of detail and relax, and the bass has more power and more definition. This is surely due to the  film output coupling caps that is almost double of stock value. The silver mica cap also help opening the highs that seem more natural than without it. But this is not certain I need more time to tell the differences.
   
  That is my findings so far!

 I have ordered  some non inductive caddock to replace them in CRCRC filter and and output coupling. Also have some carbon composition to try at pin 4 and pin 5 in place of the white box...


----------



## telecaster

Quote: 





wall-e said:


> I'm glad you're happy with the results you did to modifying your lf339 anyway pleased to Do It Yourself.
> 
> Also I would not expect huge improvement like Night & Day, look at this amp is build like tank every thing is doubled and  the performance with low-high cans & SQ are first class. It's not like my 332c which looks poor compared to lf339  in which I upgraded output caps and the result exceeded all my expectations I could tell that it was almost like Night & Day.
> But for me even small improvement will be worth to put the extra DIY wchich i like it and "£,$,€" to tweaking the amp.
> ...


 

 Is this rectifier a correct replacement?
 GI2502 Rectifier bridge 200V 25A


----------



## WALL-E

Quote: 





telecaster said:


> Is this rectifier a correct replacement?
> GI2502 Rectifier bridge 200V 25A


 

 25A bridge is way too much 3A could be enough for the headphone amp but I would not worry it's doesn't matter but max voltage does matter. In theory 200V bridge could work with the 140V AC from the secondary winding of transformer but in practice could be failure. Beacouse AC from the outlets are not constans and not clear of noise the voltage can jump for fraction of a microsecond and the peak impuls (overvoltages) could  damage one of diodes in the bridge in the best case the fuse blow up but if not all the electrolytic capacitors overheats then get swollen and....Bum!  Ok all bridges over 200V seems enough.

 May I suggest  you the bridges/diodes use in critical audio applications like HEXFRED high-speed soft-recovery Bridge Rectifiers.
 IXYS FBE 22-06N1  22A 600V
 IXYS VBE 17-06NO7 27A 600V

 or you can build Gretz bridge with four BY228 (1500V 3A) the same as in keeph modded LF339 and very cheep.

 or the best of all Schottky bridge rectifiers IXYS SiC but  they are very exspensive!!! and probably not worth it.


----------



## telecaster

Quote: 





wall-e said:


> May I suggest  you the bridges/diodes use in critical audio applications like HEXFRED high-speed soft-recovery Bridge Rectifiers.
> IXYS FBE 22-06N1  22A 600V
> IXYS VBE 17-06NO7 27A 600V
> 
> ...


 
   
  Thanks for the advice! It really helped me. I have looked at the IXYS HEXFRED rectifiers and "IXYS VBE 17-06NO7 27A 600V" looks like it's not soft recovery (which seems to be the best for audio). And "IXYS FBE 22-06N1" is soft reverse recovery, don't know if it's the same as soft recovery.
   
  For the best SIC rectifier, those are 80 bux a unit, and I have the idea to make a cheaper bridge with SIC schottky using those : http://uk.farnell.com/jsp/search/productdetail.jsp?sku=1851840
  What do you think? It seems it would be the same quality using SIC schottky diode to make a bridge from scratch?
   
  I have read some terrible things about diode that blow up, are you sure if I use 4A sic schottky to make a bridge it is safe enough?
   
  Also is we use those fast schottky, will it be safe using 1000µF 200V right after it? I have read that using fast diodes increased the voltage in the PS filter...
   
  Also I have experimented replacing the white box 1K ohm with allen bradly carbon comp resistor, and I found the sound slightly inferior to the white box. But with the carbon comp I have no hum when using EF80, but I have hum in one channel using my tungsol 6SJ7GT. But using the white box I have no hum using the TS 6SJ7GT and incredible hum using EF80 in one channel... Pretty weird isn't it!
  I was unable to open this white box because it is glued.


----------



## WALL-E

HexFred diodes/bridges are fast switching but soft response,which means it has less switching(ringing) noise to provide a cleaner, faster DC voltage. The HexFred have good opinion and is often used as a replacment of standard rectifiers in audio hi-fi / hi-end power supply.
 The main difference between HexFred and Schottky is the Schottky are low forward voltage drop and no reverse recovery. So bulding the schottky diodes bridge will increase the voltage but don't worry just slightly. The general purpose single rectifier diodes will forward voltage drop about 0.7V and for Schottkthy is 0.2V.
 Transformer in the power supply give 140V with the max current about 300mA and 6,3V/3A for filament which is supply directly from AC transformer so the bridge will use only with high voltage so the 4A sic schottky are safe enoug.
 You can build the Graetz bridge and you will get the same parameters like singe bridge rectifiers.


----------



## telecaster

Thanks for the reply m8! I have finally decided on Vishay HFA08TB60, 8A 600V hexfred because I have read some people finding the SIC kinda hard sounding... Which is something I don't like in general, and also because farnell wanted 20€ shipping cost for the SIC and the only ebay seller who has them don't ship abroad.
   
  I have made a little graetz on a small heatsink that will fit nicely, here is a picture of my schematic before powering it because I don't want to make everything explode! I have found those diodes cheap hence my choice over the IXYS FBE2206N1.
   
  I have ordered four per channel 30W // caddock resistors in TO220 format to use as output resistors. They are non inductive and I hope will be reliable, less hot and good sounding. The seta works fine but I just want all the resistors to be non inductive and have a foolproof design. The PS resistors will also be change for caddock TO220 format.
   
  Do you know what is the use of the 10K near the headphone jack output? I hear using carbon composition of high value and in bad places will produce distorsion. Is this 10K replaceable with carbon comp without drawback? Also can I replace the 1M resistors across the driver tube with carbon comp?
   
  Thanks for all your help WALL-E, this is greatly appreciated!
   
  Can you please tell me if this is correct?:


----------



## WALL-E

The two 10k Ohm resistor next to headphone socket are bleeder resistor.The output of coupling capacitor is connected through a resistor to ground in order to prevent headphones from DC stored in capacitors, and the amp does have a load even with no phones connected so these two resistors bleed away the DC if no phones are connected. The 10k is a load like headphones but with 10 times more(resistance) than the higher impedance headphones I know. Probably not have a significant impact on sound quality but they are in signal patch. I would be willing to slightly increase bleeder resistor on the output something in between 10K & 22k Ohm. But increasing the resistance will increase the time to bleed away the DC.

 Formula Tsec = R Ohms * C farads
 some examplesstock lf 339) 90V, 130uF with 10K Ohm bleeder resistors the time is about 1.30 sec aftre you can conect your hedphone without pop up sound noise in your hedphones.
 90V, 260uF with 10K Ohm the time is about 2.60 sec
 90V, 260uF with 22K Ohm time is about  5.72 sec and etc.

 Your drawings of bridges are correct but if you not sure or just make a mistake u dont know I sugest to test the bridge with some small transformel low voltage like 230/12V  taking out from broken toy or something and check the bridge with mulimeter before you put it in amplifier.
   
  The caddock like a Millet are on my top list, with TO220 housing caddock you will need heatsink to disperse the heat.
  Quote: 





telecaster said:


> Thanks for the reply m8! I have finally decided on Vishay HFA08TB60, 8A 600V hexfred because I have read some people finding the SIC kinda hard sounding... Which is something I don't like in general, and also because farnell wanted 20€ shipping cost for the SIC and the only ebay seller who has them don't ship abroad.
> 
> I have made a little graetz on a small heatsink that will fit nicely, here is a picture of my schematic before powering it because I don't want to make everything explode! I have found those diodes cheap hence my choice over the IXYS FBE2206N1.
> 
> ...


----------



## telecaster

Quote: 





wall-e said:


> The two 10k Ohm resistor next to headphone socket are bleeder resistor.The output of coupling capacitor is connected through a resistor to ground in order to prevent headphones from DC stored in capacitors, and the amp does have a load even with no phones connected so these two resistors bleed away the DC if no phones are connected. The 10k is a load like headphones but with 10 times more(resistance) than the higher impedance headphones I know. Probably not have a significant impact on sound quality but they are in signal patch. I would be willing to slightly increase bleeder resistor on the output something in between 10K & 22k Ohm. But increasing the resistance will increase the time to bleed away the DC.
> 
> Formula Tsec = R Ohms * C farads
> some examplesstock lf 339) 90V, 130uF with 10K Ohm bleeder resistors the time is about 1.30 sec aftre you can conect your hedphone without pop up sound noise in your hedphones.
> ...


 

 Thanks a lot! I now understand the purpose of the bleeder resistor! But why would you want a higher value? Is the higher value safer and shunting more DC to the ground?
  So if this bleeder is in the signal path, I guess using carbon composition would introduce distorsion? I thought that only carbon comp resistance in series would be introducing distorsion.
  And as for the Graetz I'll make, that is a good advice to try on a low voltage transformer beforehand connecting to my amp!
   
  For the output coupling resistors, will you choose the 50W Mills wirewound? Or the caddock? Frankly the caddock seem expensive at this position but I did it anyway, it would look original at least. And yes I have those heatsink on order for caddock TO220, now I have to think hard how to arrange all those components in this little 339 case!


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## WALL-E

The main reason to use bleeder resistor is safety and the higher value is not safer and will need more time to discharge cap but safer not always mean "better" in audio. The audio signal flows from input to the output and it will  “hit”  the bleeder resistor too. Every commponent got some noise in that case bleeder resistor which could have impact on sound quality. It’s too risky to remove the Bleeder at all but increase the value will make the “hit” less affected.

 With the carbon resistors is like with the VDH carbon cables is known as warm and musical some people like them some dislike.
 My advise is to use metal film as much as you can.

 The stock 470ohm aluminum-housed resistor are bad they tend to drift in value with temperature, and time.
 For a cathode resistor I will choose Wirewound  Mills MRC50 or MRA-12 both are non inductive and  1% tolerance in PS i will use caddock TO220 and elsewhere precision metal film resistors.


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## telecaster

I haven't found 22K in my stach, could I use 25K without detrimental effect? It is very interesting thanks for the knowledge WALL-E!
   
  I received the BC 1000µF 200V and installed them. I added 30µF MKP caps to the output coupling, and I removed all the bypass caps too. I think it must be the brand new caps but I find the sound lacking bass. The sound is relax though but the bass quality is not there. I will let the amp burn couple dozen of hours and see if it improves.
  Overall I prefer the sound before this mod, highs were more calm, and bass were deeper stronger. i strongly suspect the caps needing burn in.


----------



## WALL-E

Quote: 





telecaster said:


> I haven't found 22K in my stach, could I use 25K without detrimental effect? It is very interesting thanks for the knowledge WALL-E!
> 
> I received the BC 1000µF 200V and installed them. I added 30µF MKP caps to the output coupling, and I removed all the bypass caps too. I think it must be the brand new caps but I find the sound lacking bass. The sound is relax though but the bass quality is not there. I will let the amp burn couple dozen of hours and see if it improves.
> Overall I prefer the sound before this mod, highs were more calm, and bass were deeper stronger. i strongly suspect the caps needing burn in.


 
  With the supply 90 VDC, 25K Ohm Bleed Resistor and  230uF(summary) output capacitor u will need wait about 6 second to connect headphones without poping noise. If after that u will hear single crack/popup noise then lower the valu of bleed resistor.

 Like you said, many parts has been changed it is now like a new amp and needing burn in, to get it best!


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## telecaster

I can wait 7 secondes no problem! I am already waiting somewhere around 10 secondes to plug my HP everytime... The thing is I found caddock MP930 in 25K so thats what I'll use.
   
  The sound is definately better after 15 hours burn! I didn't believed it but more and more I begin to think this is not psychological, the brand new cap need some votage through them that is for sure! The sound was very nice without the bypass caps.
   
  I will try with the bypass caps now and report later after some burn in.


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## telecaster

I recieve a pair of L63 (6J5) tube and I wanna try it! On the darkvoice 339 thread, Yuking said that I don't need to change any parts only the tube wiring.. But in Keph modded 339 that uses 6J5, there is a 100R between the 220µF caps while stock 339 has 200R value there.
  Do you know what specs of the L63/6J5 tubes I have to look for to know if 200R is safe?


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## telecaster

I guess 200ohms holds more voltage and current than 100ohms so I went ahead! I did the 6J5 mod! I am very happy because the bass is really better with those osram driver.


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## WALL-E

In the stock LF339 the last two resistors in series in ps filter are 200 Ohm and 30K Ohm and if u look closer on keph modded machine they are100 Ohm and 33K ohm. The input penthode 6js7,6j7gt..etc in the 339 is triode-strapped connected (grounded plate and screen as plate configuration) with the G2 as the output of a pentode that's mean pentode is used in triode mode.That's why it possible to use "real " Triode(6j5) as a driver instead of 6js7(pentode).

 back to the two resistors in ps filter in orginal unmoded 339 they are 200ohm in series with 30K ohm so after B+ rail for 6js7 the plate voltage is about 73V(mesured with 6as7&6js7gt in ) and  It's drawing about 2.19mA of plate current at idle, which means it is ok. according to the data sheets on the 6SJ7 shows typical operation at 2-3ma plate current.
  
 Characteristics and typical operationwith point of the 6j5 (Medium-Mu Triode) is ideal when running them at higher currents at lest ( 8 > or = 8mA ) It tends to run them at 8 - 10mA typically.
 I think these two resistors(100 Ohm & 33k) in keph's modded lf339 were chosen to adjust current and voltage swing to get the optimal operation point and linear characteristics with the 6j5.
  
   
  PS;
  I hope the LF boss will join to the discussion and explain it 
	

	
	
		
		

		
			





 better.


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## telecaster

Yes I hope too! But it seems the language is a barrier here!
  I bought the same 33K caddock the boss is using but I am using 200ohm resistor for B+ rail right now because I didn't receive the 100ohm resistor yet. Sound is great but I have some hum/noise which I don't know if it's the tube itself or the problem in current.. I will report back when 100ohm arrives.
   
  I have an idea to combat a problem that may or not apply here. I read that someone cured buzzing by filtering the AC filament heater supply 6,3V with capacitor (10000µF/16V) and a bridge to produce DC 6,3V. In his case he has two AC 6,3V supply, one for the power tubes, and one for the drivers. He only filtered the driver AC 6,3V and said it was much more cleaner. He said due to huge current draw - the 6,3AC was very distorted before  (individual secondary had to supply almost 4A of current) so the buzzing had many harmonics above 50 Hz.
   
  I guess this doesn't apply to LF339 because there is only one AC 6,3V supply right?


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## WALL-E

The LF339 use the common 6.3 volt AC / 3A secondary to heat the filament, but it doesn't mean it can't be DC apply to this amp, it is still possible! The rca 6as7,6080..drawing about 2.5A of filament current plus about 300mA for a 6sj7,6j5..etc. it is a lot but power tranny can handle it.
  let's see.
  Convert 6.3V AC onto DC to heat all the filaments is bad idea because the high current, but if you split the common 6.3V and let the power section be AC powered and for driver tube u went onto DC using a couple of low forward voltage drop diode(Schottky) and a couple of thousands(uF) caps with a dropping resistors it could work.
   

   
  Another option more expensive is to buy separate or custom wound transformer with the 6.3V and 9V AC secondary to heat the filaments.
 To obtain the perfect extra smoothing 6.3VDC u need about 9VAC secondary to use with low drop out regulator like LM317,LM350...etc.  
   
  AC voltage can generate an AC electric field, which affects the grid, introducing noise that gets into everything, but DC magnetic field source is the DC current! so?
 It doesn't mean you cannot use DC, but to keep AC hum low can be achieved by using standard practices like:
 1. Proper lead dress, and twisting of heater pairs, twisting the heater wires greatly reduces the magnetic field that is radiated.
 2. It is also a good idea to use a shielded filament transformer, which lf339 it already has.
 3. Shielding heater leads is only to reduce the risk of RF contamination but can be apply.
 4. Another tactics to suppress the noise on AC heaters is using small ceramic caps ( typically use a 0.1uf) from each heater pin to earth is a good idea.

 It seems that symmetrical layout of wires in lf339 work well for me but if not (during the further upgrade/mod) I will rewire the filament wires twisting the cables.
  So for now I will follow rule number one: "if it works, don't touch it".


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## telecaster

This is really interesting, I thank you for the sound advices and most likely if I build a new amp from scratch will follow thoses rules in making quiet driver PS. As for the 339, this is only one pair of tubes that hums slightly, nowhere near as my old 6SJ7 so it is really acceptable all in all! Also when changing to 470µF the C4 and C5 I noticed the noise floor lowered significantly and also the bass and control is better than with 220µF value.
  You are right for now the layout work well so I think I won't mess with it.


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## telecaster

@Wall-E : With all the left over parts I want to make another headphone amp. It seems I just need two transformer and tube sockets. Do you know what transformer should I buy? I found on ebay cheap transformer with 220V primary and 6V secondary rated 30VA...
  Or maybe it must be better to find good quality transformer to replace those in the 339?
  Will you be using the stock transfomer in you mod? I think Yuking is upgrading the transformer in his mods.


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## nikongod

Why not build something totally different?
   
  Maybe its just me, but I can never stand to build 2 of the same. For the crazy-money one could spend on "better" parts to build another of the same in the hopes of finding marginal differences one could just build something different. Like a SET amp. Or a parafeed amp. Or a Push-pull amp. Or a hybrid. Or an SS amp with transformer coupled outputs. Or any number of things that ARE different.


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## telecaster

You are completely right! I just am totally new to valve circuits, so replicating the other amp was the only straight forward thing I was thinking of.
  The thing is I have loads of 6AS7G and 6SJ7 tubes, the later being unused now that I transform my amp to 6J5 driver tube.
  Also I wasn't going for an exact same replicate, I wanted a 2000µF output capacitor coupled amp to drive low impedance cans.
   
  Maybe you have some idea to share about a louspeaker amp using 6AS7G and 6SJ7? Also I don't think OTL will I be able to use commercial loudspeaker with...
  Also the capacitor I have on hands are only rated 200V...


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## telecaster

I am thinking of making a converter to use 6SJ7GT with 6J5 socket. WALL-E you said plate current is 3ma for 6SJ7 but in this specs sheet http://www.r-type.org/pdfs/6sj7.pdf it is stated that in triode connection mode the plate current is 6ma to 9ma...
  I wonder if doing a converter to use 6SJ7 is worth it, I just have sockets on hands, and as I am rewiring the EF80 converter Yuking sold me into EF86 converter (I will post the pinouts for reference later).


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## WALL-E

Updated: full schematic with my measurements


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## WALL-E

I was quite busy for the last to months"sumer hollyday", but now back to reality. With an empty wallet, but with big intentions preparing to "mod" the amp soon, ordered most of parts, needed to order output coupling capacitors, not decide yet which one because lack of space u know for one large single capacitor for each channel.
  Telecaster u used 4 solen 100uf/250 in place of stock cap I think to use Mundorf MKP they have similar dimensions to Solen, did you have any difficulties to fit them and put the lid back?


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## telecaster

I choosed the 100uF because the retailer specs stated size within the inner size of the lid. When all finished there is no problem to fit the four caps, the heatshink over the solder ends. In reality the caps are 2mm smaller than the specs and I think I could have fitted 120uF caps for sure, and maybe even 133uf.
  My choice was just to let the lid off because it looks salty to me hehe!
  Thanks for the schematics, good works! It looks very neat and fully comprehensive. I have found great impact in bass and distorsion tuning when changing the value of R4. In my modded 339, 33K was very clean but little sterile in the bass. 10K was too much bass and very distored, and I finally use 25K with great bass and good tube bloom. I want to try 22K one day just for the fun. In my limited measurements, raising R4 lowered current on V2 and increased current on V1.


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## WALL-E

Just waiting for a output caps to arrive with some hook-up wires and bypass caps to complete all the parts I need to mods this amp.
	

	
	
		
		

		
			




   

   
   
  All complete and ready to go!


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## WALL-E

It took awhile to complete all parts and find some time to do this mods but finally I did it.
  

   
  265uf  per channel
   

   
  The DK339


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## telecaster

Wondernice! I love it WALL-E good job!


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## KimLaroux

Indeed, Wow! Very clean job, I love it. I can't even tell what you modified, but I have a feeling it's everything. It does look glorious, anyways. Any audible difference?
   
  Oh and have you got a picture of before, just for fun?


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## WALL-E

Quote: 





kimlaroux said:


> Indeed, Wow! Very clean job, I love it. I can't even tell what you modified, but I have a feeling it's everything. It does look glorious, anyways. Any audible difference?
> 
> Oh and have you got a picture of before, just for fun?


 

 Yeah it looks like but some things has not been changed, all those things make noticeable, measurable and audible difference, but the sound of this amp is heavily dependent by the choice of tubes,  with good one even unmodded sound very well. First of all, the dynamic has improved and bass extension, much lower end, tight bass, the sound is more clearer it has more details but still retained the warm tubey sounding.
   
  more details about the amp can be find on this thread     http://www.head-fi.org/t/502306/dark-voice-339/1095
   

   
                                before                                                                            after
   
  Kim your Millett "Starving Student" Hybrid amp looks really stunning! I can only imagine, how much work and effort you had to put into this project.


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## KimLaroux

Thanks, but my starving student is child's play compared to what you did to your Dark Voice, and it probably doesn't sound even remotely as good.
   
  I'm really speechless. You managed to upgrade it while at the same time making it look better. And you seem to have picked the upgrade parts with care, giving more credit to their specifications than to their brands. I'll take your experience as a lesson. I went for brands with my SSMH and the result is not very good. I think the capacitors I used in my power supply have too high ESR. I have 10 420µf of capacitance on the power rails, but I still have a lot of background noise. Makes me sick just to think about it. The problem is that most "boutique" brands don't have those specs in their datasheet. How did you go about selecting the right parts?
   
  Another thing I'm curious about, is the enclosure of the Dark Voice a ferrous material? i.e. will a magnet stick to it? I'm asking because my experience with different enclosure material is pushing me to conclude that the only real way to shield an audio circuit is to use a ferrous enclosure, like steel. And something tells me the Dark Force has a steel enclosure.


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## WALL-E

Quote: 





kimlaroux said:


> Thanks, but my starving student is child's play compared to what you did to your Dark Voice, and it probably doesn't sound even remotely as good.
> 
> I'm really speechless. You managed to upgrade it while at the same time making it look better. And you seem to have picked the upgrade parts with care, giving more credit to their specifications than to their brands. I'll take your experience as a lesson. I went for brands with my SSMH and the result is not very good. I think the capacitors I used in my power supply have too high ESR. I have 10 420µf of capacitance on the power rails, but I still have a lot of background noise. Makes me sick just to think about it. The problem is that most "boutique" brands don't have those specs in their datasheet. How did you go about selecting the right parts?
> 
> Another thing I'm curious about, is the enclosure of the Dark Voice a ferrous material? i.e. will a magnet stick to it? I'm asking because my experience with different enclosure material is pushing me to conclude that the only real way to shield an audio circuit is to use a ferrous enclosure, like steel. And something tells me the Dark Force has a steel enclosure.


 
   
  That is true most of manufactures don't have ESR in their datasheet. Before choosing a capacitor, it is worthwhile to check spec at angle of ESR and ripple current often higher voltage capacitor has lower ESR then cap on the lower voltage.

 I am familiar with some brands like wima,or mundorf used it before, especially mundorf are very good sounding caps, I planned to use the mundorf 4 pole caps in power supply but due to the high price I had to find something similar, Kendeil was just right had everything what I need.

 Background noise is the bane of almost all DIY'ers who build their amplifiers.The source of hum,noise can be anywhere, it could be power supply  but very often is the ground issue,e.g too many ground points can make ground loops, try to avoid it, ground should be as close to the signal circuits as possible, use only one point "star grounding" to connect the signal grounds to supply ground, try and keep the connection as short as possible.These are standard practices, but  proper grounding is more like kind of art.

 The enclosure is made from iron or steel the magnet will stick to it.


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## tomb

Quote: 





kimlaroux said:


> Thanks, but my starving student is child's play compared to what you did to your Dark Voice, and it probably doesn't sound even remotely as good.
> 
> I'm really speechless. You managed to upgrade it while at the same time making it look better. And you seem to have picked the upgrade parts with care, giving more credit to their specifications than to their brands. I'll take your experience as a lesson. I went for brands with my SSMH and the result is not very good. I think the capacitors I used in my power supply have too high ESR. I have 10 420µf of capacitance on the power rails, but I still have a lot of background noise. Makes me sick just to think about it. The problem is that most "boutique" brands don't have those specs in their datasheet. How did you go about selecting the right parts?
> 
> Another thing I'm curious about, is the enclosure of the Dark Voice a ferrous material? i.e. will a magnet stick to it? I'm asking because my experience with different enclosure material is pushing me to conclude that the only real way to shield an audio circuit is to use a ferrous enclosure, like steel. And something tells me the Dark Force has a steel enclosure.


 
  It's difficult to suggest for sure why you have a noise issue, but ... the proximity of the xfmr to the tubes would be a greater suspicion, IMHO, than the caps.  Still, I'm very sorry to hear it - your SSMH build was outstanding and remains so.


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## xmdkq




----------



## WALL-E

Quote: 





xmdkq said:


>


 
   
   
   
   
  Who's the gentleman in suit? My guess the La Figaro boss himself?
   
  Wow! 339 Reference, really nice!!
   
  I wish to have the Audio Precision (AP) analyzer even for one day, unfortunately  the kind of measurement apparatus is beyond my reach.
  The (Ap) graphs already shows how good the 339 Reference is, really impressive!
  The frequency response at low range band is very interesting it's slight boost the upper bass when the load is applied I had similar with my DK339. The mid and high range band is PERFECT -0.4dB on 20kHz! It's probably merit of the new adaptation of input stage (new input tube) may I ask what tubes are they?
  The spectrum graph show that mains hum is very low -91bB at 50 Hz almost not audible, THD with the highest 2nd harmonic [dB] -102 and the 3,4,5,6,7,8,9 harmonic below [dB] -110! amazing.
   
  I really appreciate it. You put a lot of thought and effort into that mod. Great work!


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## xmdkq

Was customized to overseas users 93/4


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## kramer5150

WOW... impressive!!!
   
  What OTs are these?  are they 600:32 ?  Off the shelf or custom winds?  They look like low wattage speaker OTs, 4/8/16 ohms


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## WALL-E

Quote: 





kramer5150 said:


> WOW... impressive!!!
> 
> What OTs are these?  are they 600:32 ?  Off the shelf or custom winds?  They look like low wattage speaker OTs, 4/8/16 ohms


 
  This amp is OTL construction no "iron" at all.
  The picture shows the transformer and two chokes is the parts of  PSU with the JAN 5R4WGB rectifiers.


----------



## WALL-E

Quote: 





xmdkq said:


> Was customized to overseas users 93/4


 
   

 I am completely blown away by the look of this amp!! It's High-end Output Transformer less, two-piece design.
   
  I followed the creation of this amp quite some time ago on the forum diybuy.net, but I thought that is a only special order, isn't it? You said it “Was customized to overseas users” so this is the standard version of the amp with “premium parts upgrade package” Is that correct? which allows me to wonder, if the "customized platform 9 3/4" was a special order to one of your overseas customer, what about the platform 9 3/4"unmodded" standard version, are you going to produce and sell them like your other La Figaro amplifiers?
   
  I would not be able to stretch my budget to include another amp BUT IF how much is it ?
   
  thanks


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## xmdkq

Quote: 





wall-e said:


> I am completely blown away by the look of this amp!! It's High-end Output Transformer less, two-piece design.
> 
> I followed the creation of this amp quite some time ago on the forum diybuy.net, but I thought that is a only special order, isn't it? You said it “Was customized to overseas users” so this is the standard version of the amp with “premium parts upgrade package” Is that correct? which allows me to wonder, if the "customized platform 9 3/4" was a special order to one of your overseas customer, what about the platform 9 3/4"unmodded" standard version, are you going to produce and sell them like your other La Figaro amplifiers?
> 
> ...


 
   http://www.diybuy.net/thread-461889-1-1.html


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## kramer5150

Quote: 





xmdkq said:


> http://www.diybuy.net/thread-461889-1-1.html


 
  WOW.... thats some intense amp building!!! thanks for sharing.


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## telecaster

Quote: 





wall-e said:


> Who's the gentleman in suit? My guess the La Figaro boss himself?
> 
> Wow! 339 Reference, really nice!!
> 
> ...


 
  Hey Wall-E, I believe they are EF86 ;p


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## StalkerAssassin

Hello people.
How you these capacitors *Jantzen Cross Cap* as output separation? I want to use them for DarkVoice 336SE. Will there be enough 100uF for channel?


----------



## WALL-E

Quote: 





stalkerassassin said:


> Hello people.
> How you these capacitors *Jantzen Cross Cap* as output separation? I want to use them for DarkVoice 336SE. Will there be enough 100uF for channel?


 
  I don't remember now, what is the value of output coupling cap in DV336se? What headphones will be plugged into it?


----------



## StalkerAssassin

wall-e said:


> I don't remember now, what is the value of output coupling cap in DV336se?



In stock Darkvoice 336SE - 20uF per channel, La Figaro 336C - 40uF per channel. But I will only use the circuit from 336SE, I will do all of the new in large chassis.


> What headphones will be plugged into it?



Sennheiser HD 650.

F = 1/(2 * pi * C * R)
F= 1 / (2 * 3.14 * 0.0001 * 300) = 5.3 (Hz) This means that up to 5 Hz, frequency response is linear, with no recession on the low frequency?


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## WALL-E

Quote: 





stalkerassassin said:


> In stock Darkvoice 336SE - 20uF per channel, La Figaro 336C - 40uF per channel. But I will only use the circuit from 336SE, I will do all of the new in large chassis.
> Sennheiser HD 650.
> 
> F = 1/(2 * pi * C * R)
> F= 1 / (2 * 3.14 * 0.0001 * 300) = 5.3 (Hz) This means that up to 5 Hz, frequency response is linear, with no recession on the low frequency?


 
  Well bigger enclosure, it is understood so u have a lot space to put good but large film caps, the mkp jantzen will do this job pretty well, with 100uf and 300 ohm headphones you'll get -3bB at 5Hz and the optimal frequency response is about 53Hz It means the roll off start from 53Hz to reach the point at 5Hz, but if u really want flat frequency response 20Hz at 0dB u need 265uF cap
   

  This is the frequency response graph which my measurements, the white plot show the 130uf cap with the 300 ohm load and the yellow & blue 265uf on to 300 ohm, so as you see only with the bigger cap the FR is flat up to 20Hz


----------



## kramer5150

Don't forget too the impedance (or resistance... I forget which) of the power tubes.  It gets added to the load impedance of the headphone in the high-pass cutoff frequency equation.
   
  So in a TS-5998, dual triode, paralleled output configuration its ~70ohm + ~70ohm.  together in parallel result in 35ohms... that gets added in series to the headphone load impedance.  32ohm grado thus is really 32 + 35 total in the f-Hz calcs.


----------



## WALL-E

Quote: 





kramer5150 said:


> Don't forget too the impedance (or resistance... I forget which) of the power tubes.  It gets added to the load impedance of the headphone in the high-pass cutoff frequency equation.
> 
> So in a TS-5998, dual triode, paralleled output configuration its ~70ohm + ~70ohm.  together in parallel result in 35ohms... that gets added in series to the headphone load impedance.  32ohm grado thus is really 32 + 35 total in the f-Hz calcs.


 
   
  good point Kramer!  have a look on FR graph, it is good example, the plots red and purple tung-sol 7236(mu-4.8) higher output impedance vs TS5998(mu-5.4) slightly lower, 265uf output coupling cap into 50 ohm dummy load resistor. We can see how the tube impedance affect the FR, small difference because 7236/5998 are similar but there are.
   
  I have another good example even more interesting, this is FR graph(ARTA software) taken out from my current setup LF339, tung-sol 5998, gec1067 and 325uf output coupling capacitors.

  5998, 325uf 5% tolerance on to 33 ohm dummy load, the -3dB point is about 9.5Hz, ok let's mats, for the perfect model high-pass cut-off frequency for 325uf and 33ohm load will be 14.84Hz at -3dB so we have 14.84 (calculated) - 9.5 (measured)  = 5.34
  5.34Hz is the tube impedance effect on frequency  response.
  Ok, let’s see for an amp impedance, to get the 9.5Hz at -3bB with the 325uf cap we will need load about 51.5 ohm.
  51.5(calculated) - 33(measured) = 18.5
  Does this mean the 18.5 ohm is a output impedance? hmmm...slightly too low for a amp with 5998 as a output tube. It can be concluded, that impedance has a partial (some) influence on the high-pass cut-off frequency equation IMO.
   
   
  DV337 & LF339 are cathode follower amplifiers, in this case, I think the output impedance for TS-5998 will be a little bit different.
  A cathode follower never has a voltage gain more than 1, Vin = Vout, what it does offer is current gain, that is why it is used to drive hungry current cans.
  The output from the CF is taken from the cathode, which has an impedance of approximately 1/gm(higher gm a lower output impedance) the transconductance of the tube, is also in parallel with the cathode resistor which primarily sets the idle current through the tube.
  Knowing that the (Zo) formula for a cathode follower should be, Zo = rp/(mu+1), where (rp) is the plate resistance, (mu) is the amplification factor.
  TS-5998:
                 - (rp) 350 ohm approx                                                                                                
                 - (mu) 5.4 some datasheets gives 5.5
  350/(5.4 +1) =54.68 / 2 (because parallel triode section) = 27.34 ohm.
  Does this mean the 27.34 ohm is a output impedance? hmmm...close enough, but not exactly. Data sheet shows only limited information, what will be the plate resistance for example 140V?, the (mu),(gm) can varies depending on the current flow, the 5998 wit max plate current amplification factors can rise to 6.2 which has a large impact on the final impedance of amplifier.
  Only by measuring the impedance on working amp(driving the load) can give reliable and correct number of output amp impedance!


----------

