Low ESR Caps for Filters

[Diablo]

I read about folks fussing with low ESR electrolytic caps for the main filters on guitar amps, and I'm having trouble understanding why this could be important, or how this could effect the sound/response of the amp. Low ESR caps are recommended for high frequency switching. But the line frequency for the power filters is 60 Hz, which seems fairly low to me. So, what say the techno wizards here? Are low ESR filter caps just cork sniffing? Are standard electrolytic caps just as good for this application?

[tedmich]

higher ESR will introduce some extra ripple, but IMO its corksniffing to chase low ESR ELs in HV PS filter caps (or silk and hemp dielectric...Elna Silmic II...)

sniff this:
High End Audio - Electrolytic capacitors

I will be building up my all PP film power supply soon, as the big metal oxide resistors just arrived from Mouser, at 5 x 60uf it has a total ESR at 1kHz of less than 0.01ohms...but cheap!

[Diablo]

Wow, that's some link. Geez, I wonder what wine he drinks while he's sniffing those corks.

[Chuck H]

Woah.. It's true that the low ESR thing is mostly "cork sniffing" but there are some considerations...

Low ESR is generally good. And high ESR is generally bad. But it can be design dependant also because any signal riding on the power rail is still capable of creating NFB and PFB loops. This CAN make a difference, especially when an amp is overdriven. There are some discussions at the Amp Garage forum about this and one Ampage long time members has actually done experiments with adding very small series resistors to the power filters and found the differences to be very audible. There are so many variables though that it's a hard area to generalize. The filter arrangement, series resistors, grounds, etc... So the effects of high/low ESR will be different depending on variations in these areas since they are what determine if NFB or PFB loops are created.

I just didn't want to see this subject poo poo'd too quickly. There IS something to it.

Chuck

[tedmich]

ESR is a meaningful metric, but as in many human endeavors, there is a tendency to extend sound logic to absurd lengths. (Some would observe this tendency associated with Y chromosomes, a discussion for another time and place)

ELs have relatively high ESR vs other cap designs, and low ESR ELs cost more. There is a strong audiophile bias against ELs irrespective of their amazingly high capacitive efficiency, and ESR is a handy rational number to support what may be an (largely) irrational bias.

IMO having enough actual capacitance (filtering) on a PS rail can have a bigger impact than the associated ESR of added caps. Some Carr amps go to the greatly added expense of using high $$ PP film caps in the PS and as a result have a bit of noise (with only ~60uF total filtering) in addition to the very low ESR they achieve. So add enough filtering and ideally use high quality long life ELs, but chasing the lowest ESR with disproportionate added expense is silly, as is excessive filtering. I remember an audiophile tube amp with >10mF on the rails.... come to think of it maybe all that series resistance hurt the tone...

[Chuck H]

as in many human endeavors, there is a tendency to extend sound logic to absurd lengths.

Yea brother

IMO having enough actual capacitance (filtering) on a PS rail can have a bigger impact than the associated ESR of added caps.

Amen

come to think of it maybe all that series resistance hurt the tone...

AAaah... You lost me. I could only get behind that if the the filters were too small in value. Ideally the cap at each node will do the decoupling and filtering without the need to share uf's with other caps in the rail. But it's all relevant I'm sure.

What I was talking about above was actual signal that rides on the rail, not noise or ripple. The grids do hear this signal in a less than perfectly decoupled circuit (which they all are of course). This isn't always a bad thing when you consider EL's poor HF performance and some possible scenarios. We've all heard or had personal experience with different EL filters of the same value but different brand sounding different. This, IMHO, is the reason. If you recap an amp and suddenly there's too much glassy top end, it could be that the shared grounds and filter nodes for the preamp were creating a NFB loop that is dependant on the poor ESR of the original filters.

This phenomenon has been noted and discussed as it relates to the Trainwreck Express clones the guys at The Amp Garage build and is considered one of the reasons it's hard for cloners to voice their amps like an actual Express. Glen Kuykendal (did I spell that right?) owns an actual Express but preferes to use one of his two clones on the road. Even with all parts duplicated except the film and EL caps, his clones exhibited the same harsh tone that other cloners complain about. So he tried some new EL filters that are supposedly made to sound and perform like the "old" filters, whatever that means. But his report is that the tone improved so much that he can hardly tell the difference between his original Wreck and his clone. That's a considerable difference IMO. I'm inclined to believe it too because Glen comes off as such a nice regular guy who was just trying to build some amps for himself. He certainly has nothing to gain by sharing this info. A better plan would have been to profess that 'he alone could build a proper Express clone' and then sell them for serious coin. He certaily has the clout as Trainwrecks go. And he has an original to compare each build to.


Chuck

[loudthud]

Chuck, I went looking for the thread you spoke of at Amp Garage and didn't find anything that I thought was it. Was Glen the guy who did the experiment with the ESR resistors? Can you post the name of the thread?

[dai h.]

hey LT, I think it's this one:

The Amp Garage :: View topic - Sozo electrolytics, interesting!

personally I take the info with a grain of salt. Great guitar player, but not so sure about the technical understanding (meaning that I'm not certain that something could not have been done about the reported harshness). But the stuff in there relating to series connecting filters is interesting. At times, different filters have sounded different (IME). With as much apparent high end on the Twrecks, it sorta seems differences could be more audible.

[Chuck H]

That's one of the threads I spoke of. I'll try to find the other, but not tonight. Too much work and too many beer.

Glen seems to me to be a very festidious guy. And careful about how he comes across. Since he doesn't have any kind of EE cert he's not likely to come across as "knowing" anything, as we sometimes do. But he has been working on, treaking and building his gear for a very long time. Long enough to hear any actual change instead of subliminal ones. He even has the insite in that linked post to say that the old caps were better at making amps sound right, not better quality. That's very telling about his perspective and experience. I could probably design circles around him, but I trust his opinion and believe his perceptions are from honest experience.

Chuck

[tedmich]

exhibited the same harsh tone that other cloners complain about. So he tried some new EL filters that are supposedly made to sound and perform like the "old" filters, whatever that means. But his report is that the tone improved so much that he can hardly tell the difference between his original Wreck and his clone.
Chuck

what was the magic filter? Did it have Ken Fischer's sweat on it? It seems if there was a "bad" and a "good" filter design the "good" one might sound universally better, not just in a Trainwreck, right? I mean a Wreck, for all its mystery, is a pretty simple amp. Was the secret subtle series resistance? Or low ESR caps? I love secret sauce especially if its cheap (series resistors) or just a little spendy (low ESR ELs) Voodoo is notoriously hard to steal though....

I'll always listen to learned advice, although double blinds are the only real way to know if "A" or "B" is better, as the recent Mostercable/coathanger fiasco reminds us!

[dai h.]

Chuck, I agree (and the same can be said about his apparent workmanship--looks top notch!), BUT not sure these necessarily translate into technical understanding of what to change or try to get the sound he wants or push things in the general direction. Personally, I'm not quite so convinced about the Trainwreck stuff. Is it that he (and other better-than-usual guitar players) is so good that he's MAKING the amp sound good despite itself, or is it that the amp is so special and sensitive, difficult to play but sounds like God or whatever? When I read stuff like "it was too harsh", etc. I think to myself, ("So why don't you CHANGE the damn thing!") instead of going on (what seems to be) voodoo hunting exercises (which may have SOME substance). Kinda like EQing something (that is to say 'EQ' in the sense that it could take many forms from changing the angle of a mic to shunting highs with caps or whatever) to change it if you don't like how it sounds.

[Chuck H]

They were Sozo caps. Some new, special, voodo 'just like the old ones' stuff they're making I guess.

I had no luck finding the thread at the Amp Garage about when Glen tried them his TW Express clone . I may have read it somewhere else. This is about the only forum that Glen DOESN"T post at. But I did find a thread there where Glen talks about the Sozo's becoming too "bright" and "fast" for his TW clone after breaking in. To me this sounds like lower ESR. He switched the amp back to Mallorys. He didn't say which ones.

Chuck

[tedmich]

They were Sozo caps. Some new, special, voodo 'just like the old ones' stuff they're making I guess.

I had no luck finding the thread at the Amp Garage about when Glen tried them his TW Express clone . I may have read it somewhere else. This is about the only forum that Glen DOESN"T post at. But I did find a thread there where Glen talks about the Sozo's becoming too "bright" and "fast" for his TW clone after breaking in. To me this sounds like lower ESR. He switched the amp back to Mallorys. He didn't say which ones.

Chuck

The Sozo WEB site goes into quite a bit of "creative detail" of their break in phenomenon:
SoZo Amplification
most of which sounds like total BS to me. Their highest praise is that people can hear no difference between their caps and the old "mustard" originals they replace. At least they are (a bit) cheaper than NOS mustards.....

Recapping takes time and $$ so there is an extreme probability of bias once the amp is returned. IME an audiophile equivalent of the Vulcan "Pon farr" commonly occurs after listening to the same equipment for a few months..."Must get new gear....capacitors are getting too fast and the tone is chaotic and lacking immediacy...."

Until a true double blind with designs differing only in high $$ voodoo components vs. accepted industry standard components shows a strong correlation between opinion and voodoo I will ignore most of it (voodoo that is).

PS I just picked up 10 Solen "Fast Caps" on the ebay, 22uf 630VDC, for ~$4 each. They have very low ESR (<1mOhm) and are faster...I'll try to rig an A/B switch on my next build to test if they sound markedly better than EL equivalents...

[cminor9]

Wow, that's some link. Geez, I wonder what wine he drinks while he's sniffing those corks.

Yeah, from the article:
"
Elna Silmic II is the best device of this test. Comparing with very good Black Gate, Elna sounds better. There is as difference between Sprage and Black Gate than Black Gate and Elna. It is certainly the best choice on electrolytic capacitors for top end devices. Good sound for classical, baroc, jazz and modern music.
"

Gee, you would think that someone who listens to it would know how to spell baroque. For a cork sniffer, this guy sure is a Philistine.