# Headphone output capacitor size



## grenert

I want to replace the DC blocking capacitors in some portable audio devices of mine with better quality ones (I did test DC offset to see if they were necessary, and they definitely are). It is difficult to find 330uF or larger caps that will fit, but I can probably cram in some 220uF ones. Would I be better off with non-audio 330uF low ESR caps, or "audiophile" 220uF caps such as Silmic or Cerafine? Thanks!


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## n_maher

Are the stock caps 330uF? If not, what are they?


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## grenert

Stock are 220uF. I'm going on the typical modder's (maybe incorrect) assumption that the stock caps are both too small and poor quality.


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## Pars

220uf is pretty large for a coupling cap. There is usually a resistor to ground after these. The formula f = 1/2 * Pi * R * C (where C is in farads) determines the -3dB frequency. This is a high-pass filter. If for example the resistance is 100K ohms, the cutoff (-3dB point) would be 1/2 * 3.14159 * 100000 * 0.000220 = 1/ 138.22996 = 0.0072 Hz, which is really close to DC. Even a resistance of 1000 ohms is going to give a pretty low value (0.7Hz).

 I would go better cap, but maybe smaller value. Out of curiosity, are 220uf caps used elsewhere in the device? Sometimes manufacturers will just use or reuse parts that they are already using elsewhere because it is easier and cheaper for the to do so.


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## jcx

depends on your cans too, some are as low as 16 Ohms while others are sensitive enough to be OK with DAPs despite 70 Ohm impedance

 thats > 4x range in C for the same low frequency cutoff


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## holland

There may be an output resistor to bring the load up, such as 120ohms so that a smaller C can be used.

 For the resistor to ground, wouldn't that parallel with the headphone Z in the RC circuit for a single ended amp?

 I know some amps, based on chip amps, like the uAmp107 has a 1000uf coupling cap.


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## AudioCats

I vote for better quality. The last thing you want is muddy boomy sound from the headphone out....


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## ericj

Quote:


  Originally Posted by *Pars* /img/forum/go_quote.gif 
_220uf is pretty large for a coupling cap. There is usually a resistor to ground after these. The formula f = 1/2 * Pi * R * C (where C is in farads) determines the -3dB frequency. This is a high-pass filter. If for example the resistance is 100K ohms, the cutoff (-3dB point) would be 1/2 * 3.14159 * 100000 * 0.000220 = 1/ 138.22996 = 0.0072 Hz, which is really close to DC. Even a resistance of 1000 ohms is going to give a pretty low value (0.7Hz)._

 

470uf is quite common for output coupling in DIY headphone amps. 

 And yes, there is often a resistor to ground after the coupling cap, but it's there to allow the cap to charge and discharge normally whether or not headphones are plugged in. 

 And you've forgotten that the impedance of the headphone driver is in parallel with this resistor. 

 So lets say that you have a pair of Grados at 32-ohms and a charging resistor of 10k, which is a totally believable charging resistor value. The effective impedance 'seen' by the capacitor is 31.8 ohms. We'll just say 32 ohms because .2 ohms is irrelevant here. 

 A 470uf capacitor thus gives us a corner frequency of about 10hz for grados, though bass starts rolling off at about 40hz. 

 That's only half the issue, though. You also have phase distortion to consider. If the output cap is too small relative to the impedance of your headphones, there will be significant smearing of bass frequencies. With 32-ohm grados and a 470uf output cap, there will be some phase distortion as high as, oh, 80hz or so. 

 The downside: a larger output capacitor takes longer to charge, so the turn-on 'thump' that occurs while the cap is charging takes longer the bigger the cap is. if this is bad enough, it could potentially harm some headphones if they are plugged in when the device is switched on.


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## regal

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_That's only half the issue, though. You also have phase distortion to consider. If the output cap is too small relative to the impedance of your headphones, there will be significant smearing of bass frequencies. With 32-ohm grados and a 470uf output cap, there will be some phase distortion as high as, oh, 80hz or so. 

 ._

 


 Phase "distortion" is a misnormer, it just means there is a shift in phase relative to the other frequencies up to 10x the cutoff freq. On headphones I believe it is a non issue. I have used VST plugins to purposely change the phase below 80 hz and it is completely inaudible. I could be wrong but I think this is a bit of a head-fi myth.


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## grenert

Thanks for all of the information and the equation. The players do use the same 220uF caps elsewhere. Most of my headphones for portable use will be 60 ohms or more, so that helps somewhat. The problem with larger value caps is the diameter. However, I could probably parallel two good-quality 220uF caps (which have smaller diameter) to get 440uF. Any problem with this solution?


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## tomb

Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_Phase "distortion" is a misnormer, it just means there is a shift in phase relative to the other frequencies up to 10x the cutoff freq. On headphones I believe it is a non issue. I have used VST plugins to purposely change the phase below 80 hz and it is completely inaudible. I could be wrong but I think this is a bit of a head-fi myth._

 

While I generally agree with eric's last post, I think you have a point, there. I've used the term, too (phase distortion), but the actual _start_ of the corner frequency fall off may be more important.

 I published this graph way back in July of last year in the Millett MAX thread (Post #479):






 It's easy to see in this case that if someone is pursuing flatline amplifier response (why wouldn't we?), then you have to take into account where that -3dB cutoff slope starts deviating from the flatline. To do that, you have to push the cutoff frequency lower so that the _start of the fall off_ occurs at 20Hz or below. Whether the start of the response deviation can be called "phase distortion" seems a bit iffy, I guess, but the desired effect is similar: you want the cutoff frequency almost less than half of 20Hz.

 Note -3dB cutoff frequencies:
 470uf w/32ohms ~10Hz,
 680uf w/32ohms ~ 7Hz,
 1000uf w/32ohms ~ 5Hz.

 This and the graph shows that 680uf might be a minimum to ensure a flat response with Grados down to 20Hz. That said, no one has ever reported issues with bass rolloff using Grados on a Millett or MAX with 470uf output caps. I think that has most to do with the fact that Grado's own response curve peaks at 50Hz and rolls off under that.

 Disclaimer: I _am not_ saying that Grados' bass response is limited. When you get below 50Hz, you're talking about feeling rather than hearing, anyway.


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## regal

Good post tomb, Also remember the reason we use -3dB, because no one can hear the less than 3dB difference in sound levels.
 So in effect the -3dB point _is _where the bass starts to roll-off ( to human ears anyway.)


 Edit: I guess an argument could be made that if the headphones themselves start to roll-off before the corner freq the combo w/ the cap could be percieveable before the -3dB point!


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## luvdunhill

Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_Good post tomb, Also remember the reason we use -3dB, because no one can hear the less than 3dB difference in sound levels.
 So in effect the -3dB point is where the bass starts to roll-off ( to human ears anyway.)_

 

I don't know if I agree with this. When dealing with speaker crossovers, differences in fractional decibels are definitely perceivable, especially in the upper-midrange. Anyone who has dialed in a number of crossovers in their day will be able to do this blind-folded. 

 Do you have a source for this claim? Here's mine:

Decibels


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## ericj

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_While I generally agree with eric's last post, I think you have a point, there. I've used the term, too (phase distortion), but the actual start of the corner frequency fall off may be more important._

 

I think that, due to the swampy nature of bass waves, as long as phase distortion stays in the bass range it is probably not easily perceived. It's when it reaches up into the midrange that things get ugly.


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## nikongod

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_I don't know if I agree with this. When dealing with speaker crossovers, differences in fractional decibels are definitely perceivable, especially in the upper-midrange. Anyone who has dialed in a number of crossovers in their day will be able to do this blind-folded._

 

in multi-driver crossovers, the phase shifts &turnover points of a crossover are essential to get right. in reality though, it does not matter if BOTH are at exactly 3khz, or both are at EXACTLY 2.9khz. As long as they mesh properly they will work. the problems come when things DONT mesh up properly. the sounds from the 2 drivers can cancel or partially cancel (I agree) which is all sorts of screwy.

 In a single driver system this whole issue is less important. there is nothing else to reference the mis-phased sound to, and you just go with the flow.


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## luvdunhill

Quote:


  Originally Posted by *nikongod* /img/forum/go_quote.gif 
_in multi-driver crossovers, the phase shifts &turnover points of a crossover are essential to get right. in reality though, it does not matter if BOTH are at exactly 3khz, or both are at EXACTLY 2.9khz. As long as they mesh properly they will work. the problems come when things DONT mesh up properly. the sounds from the 2 drivers can cancel or partially cancel (I agree) which is all sorts of screwy.

 In a single driver system this whole issue is less important. there is nothing else to reference the mis-phased sound to, and you just go with the flow._

 

good examples, but I was thinking more along the lines of padding down a tweeter, not crossover points. 

 Point being that human hearing has much greater resolution than 3dB.


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## tomb

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_good examples, but I was thinking more along the lines of padding down a tweeter, not crossover points. 

 Point being that human hearing has much greater resolution than 3dB._

 

... but as an industry standard, 3dB is the convention used for "barely perceptible"


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## luvdunhill

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_... but as an industry standard, 3dB is the convention used for "barely perceptible"_

 

I'm not trying to be a donkey here, but I'd like to see a reference to this claim.. Half-power bandwidth has history that preceeds audio. 

 It's easy to test... see if you can distinguish +- 3dB, I'd wager that you'd find the difference much more than "barely perceptible".


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## tomb

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_I'm not trying to be a donkey here, but I'd like to see a reference to this claim.. Half-power bandwidth has history that preceeds audio. 

 It's easy to test... see if you can distinguish +- 3dB, I'd wager that you'd find the difference much more than "barely perceptible"._

 

Well, I'm not trying to be persnickety here, either, but the North Avenue Trade School* down the street might have something to say about using your reference of Georgia State's HyperPhysics data in a licensed engineering practice setting. 
	

	
	
		
		

		
			








 Regal may have stated it a bit strongly, but as stated, 3dB is the recognized industry standard intensity level change for a "Barely Perceptible" subjective loudness change (else why the focus on *3dB* for "cutoff?"). My own reference may be dated (I've only used it since 1980), but the 6th Edition of "Mechanical and Electrical Equipment for Buildings" by McGuinness, Stein, and Reynolds has the following table in their chapter on "Fundamentals of Architectural Acoustics". It's "Table 26.3" (facsimile-reconstructed here to save me from scanning):






 At the same time, you are no doubt correct. It's no stretch to say that someone in the audiophile community building, testing, and critically listening to audio equipment can tell the difference at a much smaller interval than 3dB - especially at certain frequencies. Your reference for the HyperPhysics confirms this - stating that variable frequency sensitivity by the human ear must be factored into the sound intensity if one is looking for an absolute difference. Nevertheless, industry has to pick a convention for a common frame of reference outside of the niche audiophile community. That table summarizes it for many cases.


 *Georgia Tech


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## tomb

Quote:


  Originally Posted by *FAQ* /img/forum/go_quote.gif 
_May I ask a question not related directly to the thread topic?


 I have a DAC with a .15uF output capacitor (I had to keep the value small for it to be high quality), and an amp with a 50K input impedance.

 I have calculated that the high-pass corner frequency (-3 dB) is at 21 Hz. So where can I expect the response curve to "start to fall", like for instance with a 1 dB attenuation (which I suppose to be barely audible)?

 Thanks in advance!_

 

You can model it from the curve I published a few posts back - it's probably going to be somewhere between 90 and 100Hz where the curve starts. I think most of us size an ouput cap for connection to a 50K input pot on an amp at ~ 0.47uf to 1.0 uf. You don't want to lose anything off of a DAC. It gets a little less critical at the other end at the connection to the headphone.


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## dsavitsk

Quote:


  Originally Posted by *FAQ* /img/forum/go_quote.gif 
_hear the difference in low bass performance_

 

A lot of people would be surprised at what actually constitutes "low bass". It is worth your (and everyone's) while to find a signal generator, or download some test tones, and get a feel for what 20Hz, or 60Hz, or 120Hz actually sounds like. Oh, and for the record, I don't buy this new claim that phase distortion caused by a high pass filter are inaudible, or that they aren't distortion. True, it is probably a bigger issue with crossovers where it can lead to waves canceling, and it is not harmonic distortion as such, but I'll stand by it being an issue with the 3dB point.

 Oh, also, as to whether 3dB is audible, like everything, this is more complicated and less understood, than it should be. A 3dB drop caused by a inductor attenuator, while it measures the same, seems to sound smaller than a 3dB drop caused by a resistive attenuator. I don't think anyone has a clue why, but the perception is different.


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## holland

Hmm, interesting post dsavitsk. FWIW, I can't actually hear 20Hz, but I sure as hell can feel it...a bit hard with headphones though as most roll off before that. You do have a good point. Some people perceive low bass as a higher frequency than they think it is.

 Regarding caps and inductors. Does that imply that one is subjectively better than another (i.e., inductive filter vs the typical RC)? I know many people are against such networks, but this leads somewhat towards zobel RLC networks at the outputs of amps. I view them as a necessary evil since I'm not constantly monitoring if I'm causing adverse effects or not with various loads.

 @ FAQ, hehe, yeah, uAmp107, one of my favorites for sure...not. Some people seem to like them, though. I recall it ranked fairly high in Skylab's initial viewing of it, but it's slunk down towards the bottom over time.


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## regal

Quote:


  Originally Posted by *dsavitsk* /img/forum/go_quote.gif 
_A. Oh, and for the record, I don't buy this new claim that phase distortion caused by a high pass filter are inaudible, or that they aren't distortion. 

 Oh, also, as to whether 3dB is audible, like everything, this is more complicated and less understood, than it should be. A 3dB drop caused by a inductor attenuator, while it measures the same, seems to sound smaller than a 3dB drop caused by a resistive attenuator. ._

 

Great discussion.

 This stuff is all very easy to test with a set of phones, a tone generator and a VST like Ozone.

 With my rig I cannot hear any difference between a 40 hz tone at 78hz and 81 hz. Also no difference in music played with up to 180degrees phase distortion (a cap doesn't get near this amount of phase distortion.)

 I think dsavitsk has high end equipment (I think even a DC coupled tube amp with no output transformers or caps) so he may be able to pick up on small nuances like this that those of us with more common equipment wouldn't. Most of us have bigger issues with our equipment like opamps and S-D chips in our DAC's.


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## philodox

I think that the bass rolloff with output caps is a little over stressed. For instance, my amp has 50uF caps on each of the 4 outputs [balanced] and my RS-1's still sound lovely. From what I understand, if you have a cap on all 4 channels of a balanced amp [rather than one on each side of the amp] you require twice the capacitance... so effectively that is only 25uF that the RS-1's are seeing. I plan on raising the value of these caps in the future, but it is definately not an urgent change.

 Any idea what would be an ideal value for my amp given that it will primarily be used for K340's and RS-1's?

 I've been looking at the Mundorf M-Cap 250V and 400V MKP lines as well as the Mundorf M-TubeCap line since they have values ranging from 100uF to 330uF. Would these be good choices?

 EDIT: Looks like Solen has some caps ranging from 100uF to 220uF as well. I think they are the same motor run style that I am currently using, so I wouldn't need to change much. Havent been able to find pics of teh Mundorf caps yet, so I'm unsure if they are radial or axial...


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## dsavitsk

Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_Also no difference in music played with up to 180degrees phase distortion (a cap doesn't get near this amount of phase distortion.)_

 

Even with phase distortion on only part of the signal? I would think that 180 degrees out of phase for the hole thing is fine, but on not hearing it when just the bass is this much out of phase, and where the change is gradual, would be surprising.

  Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_I think dsavitsk has high end equipment_

 






 I like to think so, but then, it is only high end to me. Someone else might not like it at all. I don't make any claims on actual measured performance, only my subjective preference.

  Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_(I think even a DC coupled tube amp with no output transformers or caps)_

 

Actually, everything is pretty much transformer coupled -- two digital pulse transformers (on each end of the spdif cable), transformer on the output of the DAC, and transformer on the input and output of some of the amps (just output on others). Some of these are parafeed, too, which means cap coupling in a sense, though it is a little different than RC cap coupling. But, no opamps for whatever that's worth.

  Quote:


  Originally Posted by *philodox* /img/forum/go_quote.gif 
_I think that the bass rolloff with output caps is a little over stressed. For instance, my amp has 50uF caps on each of the 4 outputs [balanced] and my RS-1's still sound lovely. From what I understand, if you have a cap on all 4 channels of a balanced amp [rather than one on each side of the amp] you require twice the capacitance... so effectively that is only 25uF that the RS-1's are seeing. I plan on raising the value of these caps in the future, but it is definately not an urgent change._

 

Most pop music doesn't go as low as people think, and most stereos don't really produce much true bass -- more like lower midrange, so we aren't really used to hearing it. Also, higher harmonics can be interpreted as bass by the ear, so you'll sometimes hear what isn't actually there. That said, you are probably in that range where even just doubling up on the caps would make a difference. Shooting for 2Hz as a 3dB point is anal retentive, but shooting for 40Hz to 60Hz is probably minimal -- especially with your phones. Years ago, I used my original Millett with the stock 100uF output caps, and I thought everything was fine. Moving to bigger caps did give a little deeper bass, but it wasn't a huge change.


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## nikongod

Quote:


  Originally Posted by *philodox* /img/forum/go_quote.gif 
_I think that the bass rolloff with output caps is a little over stressed. For instance, my amp has 50uF caps on each of the 4 outputs [balanced] and my RS-1's still sound lovely. From what I understand, if you have a cap on all 4 channels of a balanced amp [rather than one on each side of the amp] you require twice the capacitance... so effectively that is only 25uF that the RS-1's are seeing. I plan on raising the value of these caps in the future, but it is definately not an urgent change._

 

With some OTL tube output stages you can "get away with" an undersized output cap because of the fact that the amp puts more POWER into a higher impedance load. As the load impedance as seen by the amp RISES (the impedance of the cap at LF plus the headphones) the power goes up too. most calculations for bass rolloff through a cap assume that power decreases as load impedance increases. 

 Although you can get power to the headphones through an undersized cap, im not as sure about the effects on phase. 

 There is another school of thought that DELIBERATELY rolls off deep bass so that an amp which may be slightly underpowered (or one which has transformers that can only play to 40hz) in this area can perform better everywhere else.


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## tomb

Quote:


  Originally Posted by *dsavitsk* /img/forum/go_quote.gif 
_<snip>Shooting for 2Hz as a 3dB point is anal retentive, but shooting for 40Hz to 60Hz is probably minimal -- especially with your phones. Years ago, I used my original Millett with the stock 100uF output caps, and I thought everything was fine. Moving to bigger caps did give a little deeper bass, but it wasn't a huge change._

 

Anal retentive? OK, but maybe it's anal retentive to sweat about the difference between a 100uf cap and a 470uf one. 470uf is all we're talking about to assure flat bass down below 20Hz for almost all major cans. The difference is in pennies for many caps. Spend a few extra of those pennies and then just forget about even having the discussion.
	

	
	
		
		

		
		
	


	




 Spend that effort on worrying about which brand of cap or how to bypass it for best sound - starting with reading your Notes on Output Coupling Caps.


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## regal

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_ the difference between a 100uf cap and a 470uf one. 470uf is all we're talking about to assure flat bass down below 20Hz for almost all major cans. The difference is in pennies for many caps. Spend a few extra of those pennies and then just forget about even having the discussion.
	

	
	
		
		

		
		
	


	




 [/URL].
	

	
	
		
		

		
		
	


	


_

 

Negative, the idea is to avoid electrolytics. A 120uF Solen is $35 , while a 330 uF is $95, so the difference in price for a pair is $120. And Ill bet money a $35 120uF Solen will sound better than a $15 470uF Blackgate on the end of a Maz or Bijou. Well I'm going to bet as I plan on ordering a pair today.


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## tomb

Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_Negative, the idea is to avoid electrolytics. A 120uF Solen is $35 , while a 330 uF is $95, so the difference in price for a pair is $120. And Ill bet money a $35 120uF Solen will sound better than a $15 470uF Blackgate on the end of a Maz or Bijou. Well I'm going to bet as I plan on ordering a pair today._

 

Personally, I would take that bet. By the time you deal with the size, the Solen's bad rep, and the price difference that you incur, I don't think it would be a good choice - but admittedly, that's just my opinion.

 Work the numbers - bypassing with a high quality film cap on an electrolytic will have the film cap seeing most frequencies down to the last few octaves where the electrolytic doesn't sound that bad anyway.


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## regal

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_Personally, I would take that bet. By the time you deal with the size, the Solen's bad rep, and the price difference that you incur, I don't think it would be a good choice - but admittedly, that's just my opinion.

 Work the numbers - bypassing with a high quality film cap on an electrolytic will have the film cap seeing most frequencies down to the last few octaves where the electrolytic doesn't sound that bad anyway._

 



 It is an expensive experiement, several of the european Bijou builders are reporting good results with the Solen's. I know you like by-pass caps but many don't believe in it. I think Runelight is one. Have you done any A-B comparisons w/ vs w/out a bypass?


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## tomb

Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_It is an expensive experiement, several of the european Bijou builders are reporting good results with the Solen's. I know you like by-pass caps but many don't believe in it. I think Runelight is one. Have you done any A-B comparisons w/ vs w/out a bypass?_

 

Yes, absolutely I have A-B'd with and without bypass. However - quite honestly, you're into voltages I'm not familiar with. My original reference up there was because Doug used the example of 100uf caps on his Millett. You can read in his excellent reference, though, that Solens are not up there with the best. So, that was the basis of my perspective. As stated, I would take the bet whether a Solen would be better than a Black Gate NX at a larger size rating _at low voltages_.

 At higher voltages, though, things change. Electrolytics - especially Black Gates - might not be as cheap as the $15 you quoted, either. A 330uf N (NX is not even available at higher voltages) at 100V is $43. It gets worse from there.

 So, it may very well be worth a try if you're talking Bijou. 
	

	
	
		
		

		
			





 P.S. Cap bypassing is a very inexact science. I've had more failures than success. As a for instance, though, a Muse ES bypassed by a Vitamin Q comes scarily close to a Black Gate NX in performance. Whereas, the ES is noticeably deficient in highs by itself. On the other hand, bypassing a Muse ES at 470uf and higher with a Sonicap GEN II was not a good combination, but it works quite well at DAC sizes around 47uf/0.1uf. RMAA analysis also shows that adding a cap bypass can lower distortion/noise for entire regions of the electrolytic's response. Strangely, Black Gates appear to be so fast that many film caps have no effect at all when bypassing them.

 Bottom line, it would be easy to see how one could give up by trying a few combinations - convinced that there was nothing to it.


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## dsavitsk

I'd be of the opinion that a good step down transformer, assuming you have too much gain (and with Grados you always have too much gain), with a small coupling cap sized for the reflected impedance, is actually the best way to go. It will sound way better than similarly priced big Solens. Take a look at the Lundahl LL1930 as an example. They are affordable and quite good. Along these lines, here's what I am working on these days, though the final project is not yet done: ecp.cc


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## grenert

When people talk about "film" capacitors, they seem to be referring specifically to polypropylene. For portable applications, polypropylene is way too large. I have a line-out that can use a coupling cap of 5-10uF. I can either use polyester or electrolytic. Actually, I did use polyester (Wima MKS-2), but I wonder if it's worth taking out and re-doing with an electrolytic. Is polyester generally better than electrolytic?


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## regal

Tomb, thanks for the reply. You are correct that with the Bijou the high voltage is the issue, there are no 250V boutique electrolytics on the market.


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## philodox

Thanks for the tips and info guys. I think I'll try 'doubling up' on the caps [increase them to 100uF each] and see what happens. Will probably shoot for a quad of motor run metal can type caps so that I don't have to change much... if I go for a big axial film cap I'll basically need to rebuild my amp. I plan on doing that at some point in the future anyways, but I don't think I'm quite there yet.


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## luvdunhill

Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_Tomb, thanks for the reply. You are correct that with the Bijou the high voltage is the issue, there are no 250V boutique electrolytics on the market._

 

what about Jensen and Mundorf electrolytics? They more than qualify IMHO...

 also, you can always stack caps... I've done this for smaller voltages (like 250v) and it's worked quite well... haven't had the guts to do it for the 550v-600v I need these days...


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## Pars

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_what about Jensen and Mundorf electrolytics? They more than qualify IMHO...

 also, you can always stack caps... I've done this for smaller voltages (like 250v) and it's worked quite well... haven't had the guts to do it for the 550v-600v I need these days..._

 

BG VKs in 350V are still available (22uf and 150uf) are still available... I think these qualify.


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## luvdunhill

IMHO, the Xicon HV caps should be labeled as boutique, as they sound really nice. Same with the snap-in United Chemi-Con...


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## regal

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_IMHO, the Xicon HV caps should be labeled as boutique, as they sound really nice. Same with the snap-in United Chemi-Con..._

 

Boutique at $2.50 each ?


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## ericj

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_IMHO, the Xicon HV caps should be labeled as boutique, as they sound really nice. Same with the snap-in United Chemi-Con..._

 

Xicon and CDE I think don't get enough credit for their product lines, I think. I haven't tried UCC caps lately. 

 The CDE caps i used on the output of my bijou sound quite good to me, paralleled with a 1uf Wima MKP10. 

 I was ordering parts for my Stacker II prototype the other day and the nichicon parts for the 1st HV cap and for the cap on the buffer boards were out of stock, so i started digging through datasheets of what mouser did have in stock. 

 Of the parts that were available - picking between nichicon, xicon, and CDE, I ended up with a CDE cap on the high voltage supply because it was rated for 150ma surge and the best nichicon mouser could offer (including the one that was out of stock, iirc) was rated at 105ma. Similar situation with the xicon cap i ordered for the buffer board.

 As DIYers we look down on some brands of capacitors, and i'm stating to think that it's because the labels look dull.


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## Pars

I am just about ready to order some coupling caps for the line stage of my preamp (Counterpoint SA5.1). The stock caps are per the schematic, 8uf Wondercaps, bypassed. Per Mike Elliot (former Counterpoint CEO and designer), I thought I would use Dynamicaps, not necessarily because they get the best reviews, but partially because they are what altavista uses in their rebuilds, and it shouldn't hurt resale value (maybe help).

 8uf Dynamicaps are a bit low voltage rating wise, and physically too large. This pre has cap shields around the caps, so ~17-18mm is the largest diameter that will fit if i retain them. Which means 2uf at the most. One pre I pictured on altavista site used 1uf, and that is probably what I will do. If I don't use Dynamicaps, I thought I would try Sonicap I.

 At any rate, I attached the schematic and a couple of pics.

 Schematic:






 Modified pre:






 Another modified pre (user):


----------



## dsavitsk

Lots of people have good things to say about the Dynamicaps. I don't think they'll be a bad choice. 1uF is probably fine on the output, and you should shrink C8 to that size as well. In fact, make R17 larger (like 500K) and you can shrink C8 even more.

 Does this really run with 42V on the plate of a 6DJ8? Remind me not to buy a Counterpoint.


----------



## Pars

Quote:


  Originally Posted by *dsavitsk* /img/forum/go_quote.gif 
_Lots of people have good things to say about the Dynamicaps. I don't think they'll be a bad choice. 1uF is probably fine on the output, and you should shrink C8 to that size as well. In fact, make R17 larger (like 500K) and you can shrink C8 even more.

 Does this really run with 42V on the plate of a 6DJ8? Remind me not to buy a Counterpoint._

 

Closer to 70 (60 something IIRC when I checked it). B+ at C is 250-255 Vdc. What is ideal on a 6922? Also, I can just increase R17 with no ramifications?


----------



## dsavitsk

Quote:


  Originally Posted by *Pars* /img/forum/go_quote.gif 
_What is ideal on a 6922?_

 

60 is okay ... better than 40. Not sure what ideal is, but more like 90V is pretty common.

  Quote:


  Originally Posted by *Pars* /img/forum/go_quote.gif 
_Also, I can just increase R17 with no ramifications?_

 

Not quite, but the datasheet says that 1M is max, so 500K is certainly fine. This resistor just connects the grid to ground usually (here to the bias supply, but ground as far as the tube is concerned) to reference it. There isn't any current flowing through it.

 By the way, a CCS on the plate would be a nice improvement.


----------



## Pars

Quote:


  Originally Posted by *dsavitsk* /img/forum/go_quote.gif 
_60 is okay ... better than 40. Not sure what ideal is, but more like 90V is pretty common.



 Not quite, but the datasheet says that 1M is max, so 500K is certainly fine. This resistor just connects the grid to ground usually (here to the bias supply, but ground as far as the tube is concerned) to reference it. There isn't any current flowing through it.

 By the way, a CCS on the plate would be a nice improvement._

 

That would be replacing R20 (the 2 Mills resistors in bottom photo are R20 and other ch. R20)? Sorry, toob noob somewhat (can't even reference plate to the schematic part, etc. other than heaters 
	

	
	
		
		

		
		
	


	




). I just assumed that is where a CCS would go... 

 Also, am I viewing this right as a high pass filter? For example, C8/R17 forms a filter with a -3dB point of 1/2 * Pi * 100000 * 0.000008 = .19Hz versus if I went 1uf it would be 1.59Hz?

 Thanks for your input

 Chris


----------



## nikongod

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_As DIYers we look down on some brands of capacitors, and i'm stating to think that it's because the labels look dull._

 

it would be exceptionally nice if any of these guys posted a linearity graph that applied to the audio band.

 there are almost certainly some "diamonds in the rough" out there, but with the trends to *only* publish specs at 10khz and higher, how are we to even from an educated guess (aside from trusting our ears, which gets expensive...)
  Quote:


  Originally Posted by *Pars* /img/forum/go_quote.gif 
_That would be replacing R20 (the 2 Mills resistors in bottom photo are R20 and other ch. R20)? Sorry, toob noob somewhat (can't even reference plate to the schematic part, etc. other than heaters 
	

	
	
		
		

		
			





). I just assumed that is where a CCS would go..._

 

yes, R20 should (if you want to...) be replaced with a CCS.
  Quote:


 Also, am I viewing this right as a high pass filter? For example, C8/R17 forms a filter with a -3dB point of 1/2 * Pi * 100000 * 0.000008 = .19Hz versus if I went 1uf it would be 1.59Hz? 
 

yes, C8&R17 form a high pass filter. 

 C10, and whatever you are driving also from a high pass filter.

 To kind of agree with davitisk's points before on high-pass filters cut-off-points even though i think the whole thing is still a little overblown, I have seen a couple recommendations to only have 1 filter ANYWHERE near 20hz in the system, as multiple "crossovers" in the same area can cause a smear. cathode bypass caps can have an effect, interstage coupling caps, etc. The idea dosnt seem so far-fetched to me, and in this case is not really all that difficult to execute.


----------



## Pars

Resistor selection for R17, R21 and an unmarked (and not shown on this schematic) resistor used for gain switching? If I were to replace/increase R17 from 100K to 500K, and wanted to replace the 1M R21 with another resistor type for lower noise, what would you recommend? The preamp stock uses Roederstein Resistas, which in general I like. In the altavista rebuilds, he uses some Caddock TF020s, the 1M R21 being one of them I can see from pics, and it wouldn't surprise me if R17 was one as well.

 The gain resistor was a change from the SA5 to the SA5.1, and basically sits between the line/RIAA switch and the balance control (I ohmed it out and have it drawn in on a schematic copy around here somewhere). The preamp is noisier in the low gain position (resistor in circuit) than in the high gain position.

 Any other resistor you would recommend? Tantalum? I will be ordering from partsconnexion, so might as well get those while they are 15% off as well.


----------



## luvdunhill

Quote:


  Originally Posted by *Pars* /img/forum/go_quote.gif 
_Any other resistor you would recommend? Tantalum? I will be ordering from partsconnexion, so might as well get those while they are 15% off as well._

 

It's strange, as I've been playing with a lot of resistors of late. In addition to the usual suspects, I'd like to recommend something a bit of the wall: Texas Components TX2352 or TX2575. I've compared them to the Vishay S102 and they are quite comparable. If you don't want to bother tracking these down (I buy direct), then I really like Caddock MK132.

 edit:

 data sheets, found under the "audio resistor" section of their website

http://www.texascomponents.com/pdf/tx2352.pdf
http://www.texascomponents.com/pdf/tx2575.pdf


----------



## luvdunhill

Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_Boutique at $2.50 each ?_

 

yup.. I did some insane product comparison a while back looking for HV caps, and I think the best performing caps I found were some super expensive CDE caps (edit: these were "computer grade" caps... what the heck kinda computer needs 450v rails? they were like $25 for 10uF/450v) followed by the Xicon $2 caps. I choose the Xicon and put them in a HV power supply and was very impressed. Now, I was looking for 400V+ caps, but these two handily beat all other caps that I could get specs on. I think I compared around 50 'lytics. 

 I think I might have found the OEM for the Jensen caps, and they offer very competitive prices for custom caps and I have a bit out on some 600 VDC compatible caps.


----------



## luvdunhill

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_As DIYers we look down on some brands of capacitors, and i'm stating to think that it's because the labels look dull._

 

well-said.


----------



## Pars

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_It's strange, as I've been playing with a lot of resistors of late. In addition to the usual suspects, I'd like to recommend something a bit of the wall: Texas Components TX2352 or TX2575. I've compared them to the Vishay S102 and they are quite comparable. If you don't want to bother tracking these down (I buy direct), then I really like Caddock MK132.

 edit:

 data sheets, found under the "audio resistor" section of their website

http://www.texascomponents.com/pdf/tx2352.pdf
http://www.texascomponents.com/pdf/tx2575.pdf_

 

Hi Marc,

 Roughly what do these run? You must have added the pdf links while I was reading... I had gone to the site and looked at these. Looks like the resistance range doesn't go high enough (tx2352 goes to 250K). Unless I were to change out the 1M for something lower (and quieter). It appears that I could also change R21 (the 1M) as it is in parallel with the tube output impedance, which probably dominates.

 I think Elliot now uses naked vishays (are those the S102s?) instead of the Caddock TF020s. You like the MK132s? Those go up to 1M or higher, and partsconnexion has them for ~$5+ each. WHich is better than the TF-020 1M at $11.


----------



## Pars

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_As DIYers we look down on some brands of capacitors, and i'm stating to think that it's because the labels look dull._

 

Pretty cap labels do have a large effect on "desirability"... good point.


----------



## luvdunhill

Quote:


  Originally Posted by *Pars* /img/forum/go_quote.gif 
_Hi Marc,

 Roughly what do these run? You must have added the pdf links while I was reading... I had gone to the site and looked at these. Looks like the resistance range doesn't go high enough (tx2352 goes to 250K). Unless I were to change out the 1M for something lower (and quieter). It appears that I could also change R21 (the 1M) as it is in parallel with the tube output impedance, which probably dominates.

 I think Elliot now uses naked vishays (are those the S102s?) instead of the Caddock TF020s. You like the MK132s? Those go up to 1M or higher, and partsconnexion has them for ~$5+ each. WHich is better than the TF-020 1M at $11._

 

Well, the TF020s are physically larger and have lower power ratings than the S102. Honestly, I haven't never had a chance to use the TF020, 'cause of these two "limitations". If you buy the S102 from Percy, most of his have the casing removed. Percy also sells a cheaper Vishay bulk foil (VSH is it? it's almost like a footnote to the S102 section) and the prices are comparable to MK132. I haven't tried these yet. FWIW, Percy gets his Vishays from Texas Components, and I'm not really sure what the difference is between the Vishay S102 and the TXxxxx parts. Since Texas Components OEMs these resistors for Vishay, the line is even blurrier. With regards to pricing and this confusion, here's a good link:

diyAudio Forums - Is it worthwhile to buy Bulk Metal Resistors?


----------



## rds

I can sell you some resistors at $100 a piece, and when you're trying to figure out how you'll pay the rent you'll swear they are the best resistors you have ever heard.


----------



## regal

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_I think I might have found the OEM for the Jensen caps, and they offer very competitive prices for custom caps and I have a bit out on some 600 VDC compatible caps._

 


 Do you know the OEM for the Jensen 100+100/500VDC ?


----------



## Pars

Quote:


  Originally Posted by *rds* /img/forum/go_quote.gif 
_I can sell you some resistors at $100 a piece, and when you're trying to figure out how you'll pay the rent you'll swear they are the best resistors you have ever heard._

 

???

 Good stuff...


----------



## luvdunhill

Quote:


  Originally Posted by *rds* /img/forum/go_quote.gif 
_I can sell you some resistors at $100 a piece, and when you're trying to figure out how you'll pay the rent you'll swear they are the best resistors you have ever heard._

 

I'm thinking about making my own resistors for I/V duty. I need around 50 feet of silver wire... they'd be much more than $100 each. 

 Is this what you're referring to?


----------



## nikongod

I dont think that R17&21 are particularly significant to the sound. they should be good, but dont have to be great.

 R18,19,30 should of course be great 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_I'm thinking about making my own resistors for I/V duty. I need around 50 feet of silver wire... they'd be much more than $100 each._

 

resistor loading an I/V stage? Or resistors in an active I/V stage?


----------



## luvdunhill

Quote:


  Originally Posted by *nikongod* /img/forum/go_quote.gif 
_I dont think that R17&21 are particularly significant to the sound. they should be good, but dont have to be great.

 R18,19,30 should of course be great 
	

	
	
		
		

		
		
	


	





 resistor loading an I/V stage? Or resistors in an active I/V stage?_

 

the former.

 DIY resistors are the new Singlepower... says me. Just a major PITA to wind.

 BTW, I figured out that the resistors Percy sell are the TX2352... says so on my invoice at least. Who woulda thunk. I guess they do indeed sound very favorable.... as in, pretty much identical. Silly me.


----------



## rds

Quote:


 I'm thinking about making my own resistors for I/V duty. I need around 50 feet of silver wire... they'd be much more than $100 each.

 Is this what you're referring to? 
 

Yeah


----------



## Pars

Back to the coupling caps for the SA5.1...

 I sent an email to the designer today:
_I am about to replace the stock line stage coupling caps and wanted to use 1uf Dynamicaps in order to retain the shields if possible. I was a bit concerned with the frequency response issues posed by R17 of 100K ohms. Would you recommend increasing the value of R17 or is a -3dB point of 1.6Hz normally acceptable? Or do you think that using an 8uf cap here is a better solution_

 Reply:
_*The SA-5's line stage is a two-pole design with input and output coupling capacitors. Proper selection of capacitors needs to be done by loading the SA-5 into the power amplifier's input impedance (or resistor of same value) and then adjusting the poles to achieve as long a bass step as possible with as little overshoot as possible. *_ 

 Goes on to explain that explaining what "bass steps" are and how to measure them is beyond the scope of this "freebie" email... OK 
	

	
	
		
		

		
			





 I've never heard of the term bass steps, but seems like a bit of BS to me? Any thoughts or illumination appreciated.


----------



## luvdunhill

Quote:


  Originally Posted by *Pars* /img/forum/go_quote.gif 
_Back to the coupling caps for the SA5.1...

 I sent an email to the designer today:
I am about to replace the stock line stage coupling caps and wanted to use 1uf Dynamicaps in order to retain the shields if possible. I was a bit concerned with the frequency response issues posed by R17 of 100K ohms. Would you recommend increasing the value of R17 or is a -3dB point of 1.6Hz normally acceptable? Or do you think that using an 8uf cap here is a better solution

 Reply:
*The SA-5's line stage is a two-pole design with input and output coupling capacitors. Proper selection of capacitors needs to be done by loading the SA-5 into the power amplifier's input impedance (or resistor of same value) and then adjusting the poles to achieve as long a bass step as possible with as little overshoot as possible. * 

 Goes on to explain that explaining what "bass steps" are and how to measure them is beyond the scope of this "freebie" email... OK 
	

	
	
		
		

		
		
	


	




 I've never heard of the term bass steps, but seems like a bit of BS to me? Any thoughts or illumination appreciated._

 

sounds like BS to me... you mean that you have to adjust xover poles in the preamp to a specific power amplifier? how ridiculous is that...


----------



## nikongod

Quote:


  Originally Posted by *Pars* /img/forum/go_quote.gif 
_Goes on to explain that explaining what "bass steps" are and how to measure them is beyond the scope of this "freebie" email... OK 
	

	
	
		
		

		
		
	


	




 I've never heard of the term bass steps, but seems like a bit of BS to me? Any thoughts or illumination appreciated._

 

as a scientific wild ass guess, that may mean that they tune the coupling cap size with a low-frequency square wave. 

 my mildly useless, totally speculative drivel to follow. 

 Obviously a larger coupling cap will have a lower -3db point, but they may have the idea that using a cap which is too large brings its own problems to the system. I dont know if there is any factual basis for this idea or not. With an oscilloscope and square-wave generator you could see whether this has any merit or not in like 5 minutes.

 after writing that, I pondered why they would not use it to tout the technical superiority of their products were it the case. to add to that, it may not *really* depend on the fact that the input impedance of the amp being driven is within a certain range, but that the actual size of the cap does not exceed a certain value.


----------



## Pars

You have to remember that he is now basically modding or servicing his old equipment, plus has his new company Aria. Seems as if he has become more defensive when dealing with DIYers (such as ermm, me) and protective of his revenue stream, so he isn't going to give me a clear answer. And I completely understand that, not dissing him at all. I had talked to him 2-3 times in the past and he had been pretty approachable, so I figured it was worth a shot. 

 Thanks for your input (Marc and nikon).


----------



## Pars

Quote:


  Originally Posted by *dsavitsk* /img/forum/go_quote.gif 
_<snip>
 Not quite, but the datasheet says that 1M is max, so 500K is certainly fine. This resistor just connects the grid to ground usually (here to the bias supply, but ground as far as the tube is concerned) to reference it. There isn't any current flowing through it.

 By the way, a CCS on the plate would be a nice improvement._

 

Regarding a CCS, something along these lines? It appears that the board run for this did not materialize? Nice answer to the one insistent poster btw 
	

	
	
		
		

		
		
	


	




 Is there a particular one of the 6 circuits (if I counted right) that would be the preferred one for my application? I was thinking about using the IXYS FETs (I think I have 1 or 2 laying around, the 10m45 is it?).


----------



## regal

Yes the IXYS 10m45, I am actually modifying a DAC to use these for a CCS, it is recomended to use 2 as a cascode on the plate. You can set the current using a 9V battery and a pot before you hook it up.


----------



## dsavitsk

Quote:


  Originally Posted by *Pars* /img/forum/go_quote.gif 
_It appears that the board run for this did not materialize? Nice answer to the one insistent poster btw 
	

	
	
		
		

		
		
	


	


_

 

I actually ran the group buy that did happen which was for the IXYS boards. The boards can be seen in regal's post above. (_Edit: actually, those aren't the ones that were used as the design as revised a bunch._) The answer I gave to b.f. was a hint for him to send me an email as I had some extra boards I could have supplied him with. But, he was so insistent on getting angry that I guess he didn't get it. Oh well. The boards ultimately were sold off to someone else.

  Quote:


 Is there a particular one of the 6 circuits (if I counted right) that would be the preferred one for my application? I was thinking about using the IXYS FETs (I think I have 1 or 2 laying around, the 10m45 is it?). 
 

I think the one shown above is a good option. But, even a single IXYS chip is a big improvement from a resistor and worth experimenting with first.


----------



## regal

These are easy to build on a RadioShack perf board. I am fitting 2 casscodes for the plate and 2 singles for the sinks on a single little clad ratshack board.


 Question I have is when using the CCS on the cathode as a sink do you have any improvement on PSRR vs a resistor?


----------



## Pars

I etch alot of my own boards, so I could start with that. Do the IXYS parts require heatsinking? The size of those look like they could be implemented rather easily as the current resistors are Mills MRA-12s (R20, schematic in post 41, page 5). Possibly stand these boards on edge and drop them right in. I assume I would replace R20 with a CCS? Or would it be better to replace each of the 51 ohm resistors with a CCS?


----------



## dsavitsk

Quote:


  Originally Posted by *Pars* /img/forum/go_quote.gif 
_Do the IXYS parts require heatsinking?_

 

Not always, but often. It is pretty easy to figure out how much heat is dissipated. As an example, a CCS loaded 6dj8 with 10mA of current and biased to 2V will have about 100V on the plate. With a 200V supply, this means dropping ~100V across the CCS at 10mA. W = VI = 100 * 0.01 = 1W. You need a sink for that. Lower voltage, or lower current, you might not. For the version with 2 IXYS chips, it is a little more complicated, but most of the heat is dissipated across the top chip.


----------



## regal

Where are getting 1W=heatsink from the data sheet? I am looking at 0.5W and wasn't planning on using a sink, what's the limit?


----------



## luvdunhill

Quote:


  Originally Posted by *dsavitsk* /img/forum/go_quote.gif 
_Not always, but often. It is pretty easy to figure out how much heat is dissipated. As an example, a CCS loaded 6dj8 with 10mA of current and biased to 2V will have about 100V on the plate. With a 200V supply, this means dropping ~100V across the CCS at 10mA. W = VI = 100 * 0.01 = 1W. You need a sink for that. Lower voltage, or lower current, you might not. For the version with 2 IXYS chips, it is a little more complicated, but most of the heat is dissipated across the top chip._

 

I didn't realize that the CCS would drop voltage in this case. I suppose just sourcing 10mA of current without a voltage drop would perhaps violate some fundamental law, but I assumed this is how these 3 legged devils worked. Can you explain?


----------



## Pars

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_I didn't realize that the CCS would drop voltage in this case. I suppose just sourcing 10mA of current without a voltage drop would perhaps violate some fundamental law, but I assumed this is how these 3 legged devils worked. Can you explain?_

 

In my case, between R20 (10K ohm) and the 51 ohm resistor(s), B+ is ~250Vdc and the V at the tube is ~70V, so it is dropping ~180Vdc. The current is therefore ~18mA. The IXYS device has to have some effective resistance, and any current thru it is going to result in a voltage drop across it (Ohms law). Add in RTEST (or is this jumpered?) and R3 and the pot || R2.


----------



## regal

Guys the voltage drop is determined by the tube. You are setting current fixed via the IXYS and cathode bias via your cathode resistor, so the tube pushes its plate voltage to match. Based on the plate curve. Its backwards of how we were originally taught biasing tubes but this is how it works.


----------



## dsavitsk

Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_Guys the voltage drop is determined by the tube. You are setting current fixed via the IXYS and cathode bias via your cathode resistor, so the tube pushes its plate voltage to match. Based on the plate curve. Its backwards of how we were originally taught biasing tubes but this is how it works._

 

Yes. You can read my more thorough description at my MEHA Page.


----------



## luvdunhill

Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_Guys the voltage drop is determined by the tube. You are setting current fixed via the IXYS and cathode bias via your cathode resistor, so the tube pushes its plate voltage to match. Based on the plate curve. Its backwards of how we were originally taught biasing tubes but this is how it works._

 

ah, that's what I thought, but I was confused by the terminology used, i.e. "this means dropping ~100V across the CCS" all is good and the world is still round...


----------



## regal

It is dropping across the CCS, the tube just determines how much.



 Dsavitsk, just noticed that new DAC on your site, can't wait for the details.


----------



## Pars

So in terms of calculating what I would want to set the CCS up for (mA), what I posted would be correct (~18mA)? Or that is the correct way to do it?


----------



## regal

Pars if I read your post correctly you currently have 18 mA bias on your tube (pre CCS.) R3 in the ciruit I posted is just there to ensure that if you mistakenly turn the pot to zero the chip won't fry.

 Rtest is just used when you hook of the CCS to a 9V battery and dial in the current you want (18 mA). Use a 100 ohm resistor and measure the Vdrop across Rtest. So dial the pot to 1.8V. Then remove or jumper Rtest.

 You are now ready to sub for the existing plate resistor. You will need a big heatsink if you stay with 18mA (*180V) 3W. You can add a big 3W 5K resistor at the end of the CCS to share the load and reduce the heatsinking requirements.


----------



## dsavitsk

Quote:


  Originally Posted by *Pars* /img/forum/go_quote.gif 
_So in terms of calculating what I would want to set the CCS up for (mA), what I posted would be correct (~18mA)? Or that is the correct way to do it?_

 

I think you are thinking about this wrong. You are not dropping voltage due to Ohm's law. The CCS does not have "resistance" per se. Rather, it has a changeable resistance determined by need. 

 The tube has an operating point. Usually you set plate voltage and bias, and the current is determined by the tube. With a CCS, you set current and bias, and the plate voltage is set by the tube. The CCS will then drop the correct amount of volts -- this is what it means to be a CCS: the current is constant regardless of outside influences. The CCS circuit will adjust what voltage needs to be dropped to met the constant current requirements. Really, go read the MEHA page. The notes on the Bottlehead CCS page might help a little, too.


----------



## Pars

OK. I read the MEHA page and started in on the Bottlehead page as well as the boozehound labs page, and will spend some more time going over this. About time to learn tubes I guess 
	

	
	
		
		

		
			





 A couple of questions:
 1) Initially, with a plate resistor(s), current flowing thru the tube can be calculated by the voltage drop across the resistor(s) divided by the resistance, or 250 - 70 = 180 / 10,051 ohms = ~18mA... correct? So this would be the approximate current the design is looking for on the plate?

 2) Looking at your MEHA page, the second load graph, you drew a load line thru the point. I don't quite understand how you determined the slope of this line. You say:
_In the figure below, this line passes through our operating point, and contacts the X axis at ~23V (which is the plate voltage at 0mA of current) and the Y axis at 6mA (which is the plate current at 0 ohms)._ 
 Huh? Where did you get the 6mA and the 23V from? It takes two points to determine slope and you have 1 point defined. Or is this what is really going on:

_The first is that the load line contacts the X axis at ~23V. *I am assuming that we are using a 24V power supply.* The 23V is to allow for the fact that that the cathode is biased up about a volt._

 I'll do some more reading... thanks for the hints and help!

 Chris


----------



## dsavitsk

I picked an operating point at 2mA/16V. Then, I knew that I had a 24V supply. When the tube is not conducting, when current flow is 0, the voltage on the plate will be the same as the B+ since there is no current flowing across the loading resistor and thus no voltage drop. So, 0mA/24V is the second point. Draw a line that connects them and extend it to the Y axis. It will contact 0V at some point -- 6mA in this case. So, this is when the tube is conducting 6mA all of the voltage will be dropped across the load leading to 0V on the plate. Now, it can't ever really reach these two extremes, but this is sufficient for estimation purposes. Then, you can use V = IR to determine the size of this resistor. The V is the change in voltage (24 - 0 = 24) and the I is the change in current (.006 - 0 = .006). Thus, 24/.006 = 4000.


----------



## Pars

Gotcha. The way the text read it didn't really explain where you came up with the points from. And reading the boozehound text, it appears the key is the change in voltage over the change in current to determine slope.


----------



## TimmyMac

I went to the dump today to take some junk, and I couldn't help noticing air conditioners people had thrown out with HUGE caps in them... looked like oil caps. Checked the specs on one - 45mfd 370VAC - would this be good to use in an amplifier somewhere? Film or oil caps that large are tough to find normally.


----------



## Pars

Quote:


  Originally Posted by *Pars* /img/forum/go_quote.gif 
_<snip>
 At any rate, I attached the schematic and a couple of pics.

 Schematic:





 Another modified pre (user):



_

 

I spent the weekend changing out the line stage coupling caps (the center 4 in the picture). Running RMAA on this, there is more rolloff below 50-30 Hz than there used to be (down 1.5dB at 20 Hz) but the graph looks much more rolled off than before. I did not change R17 form the 100K yet. A couple of questions:

Looking at R17, it is attached to the wiper that is used for biasing. If I increase R17 to say ~500K, will this have an effect on biasing (i.e., will I be able to adjust it)? This is adjusted for lowest THD.
As in the pictured modified unit, I have seen another one done like this that uses what I presume to be 8uf Dynamicaps (the big pair) which matches the stock value. The position these are in however is C10... not C8? C10 is followed by a 1M resistor to gnd. C8 by the 100K to gnd. Any reason you can think of for doing this, as it would seem that even with a 1uf / 1M on C10, the -3dB point is 0.16Hz?

 Any other comments welcome.


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## regal

1. R17 is a grid leak resistor , it doesn't affect the tube bias. The pot doesn't either, it just sets gain. Increasing R17 isn't going to lower your -3dB point either. There is no reason to increase it.

 2. C8 is an input coupling cap.

 C10 may be followed by a 1M resistor but it will be in parralell with your amp's input impedance (meaning the 1M becomes negligible.) So just ignore that the 1M is there and calculate your -3dB for C10 using your amp's impedance.


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## Pars

Quote:


  Originally Posted by *dsavitsk* /img/forum/go_quote.gif 
_Lots of people have good things to say about the Dynamicaps. I don't think they'll be a bad choice. 1uF is probably fine on the output, and you should shrink C8 to that size as well. In fact, make R17 larger (like 500K) and you can shrink C8 even more.

 Does this really run with 42V on the plate of a 6DJ8? Remind me not to buy a Counterpoint._

 

 Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_1. R17 is a grid leak resistor , it doesn't affect the tube bias. The pot doesn't either, it just sets gain. Increasing R17 isn't going to lower your -3dB point either. There is no reason to increase it.

 2. C8 is an input coupling cap.

 C10 may be followed by a 1M resistor but it will be in parralell with your amp's input impedance (meaning the 1M becomes negligible.) So just ignore that the 1M is there and calculate your -3dB for C10 using your amp's impedance._

 

Seems like R17 should still function as part of a high pass filter... at any rate the pot is used in adjusting for lowest THD.

 The actual plate voltage is 52V in one channel and 57V in the other, from a B+ of 237V. I should probably raise the B+ a bit (schematic shows 253V). I'm not sure if raising the B+ would also raise the plate voltage or force R10 to dissipate more voltage drop across it (has 180V across it now).


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## Pars

Put the preamp on the bench today because the L channel went out for some reason... haven't found a problem as it is working fine 
	

	
	
		
		

		
		
	


	




 At any rate, Regal, you were absolutely right. I patched one of the 8uf caps in parallel with C8 and then C10 and ran RMAA on it. C8 had no effect. C10 took it out flat to 10Hz or less, down 0.2dB IIRC at 20Hz (vs 2.6dB previously). I think I will order bigger caps for C10 / C110. I had failed to remember that the output impedence with the 1M resistor was in parallel with the next device input impedence.


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## regal

You didn't believe me?


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## Logistics

I vote keeping the stock value in microfarads, but upgrading to a non-polarized (bipolar) capacitor from a known quality manufacturer. I don't mean something like a BlackGate, I mean something like a Panasonic SU.


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## Pars

I would think the Dynamicaps that I am using would qualify... I'm not sure why I would use an electrolytic unless I needed such a large value that film was out of the question. 8uf is not in that territory.


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## Logistics

Quote:


  Originally Posted by *Pars* /img/forum/go_quote.gif 
_I would think the Dynamicaps that I am using would qualify... I'm not sure why I would use an electrolytic unless I needed such a large value that film was out of the question. 8uf is not in that territory._

 

I was replying to the author of the thread who requires at least 220uF.


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## Pars

Quote:


  Originally Posted by *Logistics* /img/forum/go_quote.gif 
_I was replying to the author of the thread who requires at least 220uF._

 

Ahh. Yes, this thread has been threadjacked a couple of times


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