The truth about caps

[guitician]

I thought overkill was the driving force behind all of this, no?

Na....just a lot of fun

[hasserl]

Regarding the OP: The best way to find out is to try it yourself....

Place a high quality polypropylene in parallel across an interstage coupling capacitor and see if you can hear a difference (maybe even solder just one end so you can "switch" it in and out, provided the voltages are safe enough). My experience has been that there is often a perceptible increase in clarity, particularly if the capacitor being bypassed is a large electrolytic. Everything in the circuit makes a difference, down to the solder and traces themselves. The question is whether or not the differences are significant.... and that can be a subjective matter.

Of course, if you parallel caps the total capacitance adds up, so there should be an audible difference. Also, I'm not aware of any guitar amps that use electrolytic caps for coupling stages, are you?

[12Bass]

Of course, if you parallel caps the total capacitance adds up, so there should be an audible difference. Also, I'm not aware of any guitar amps that use electrolytic caps for coupling stages, are you?

Definitely found coupling using electrolytics in solid-state bass amplifiers. They can also be found in some consumer audio amps. I don't think it is the increased capacitance so much as the better dielectric which makes an audible difference. Electrolytics have high inductance and resistance at high frequencies.

[Steve Conner]

No they don't. Well, some really cheap and nasty ones do, but you get premium low ESR parts.

I'm designing a DC-DC converter board at work just now, and I'm using some Nichicon 330uf 16V electrolytics that have 14 milliohms ESR at 100 kHz. I believe they're similar to the Panasonic FC series mentioned earlier.

You pay for it though, they cost about $1.50 each in the small quantities I'm using. That's still pin money in audiophile terms, though. :-)

On ESL: I once worked with electrolytic caps the size of soup cans, and they had 26 nanohenries ESL. If anything went wrong, they could launch pieces of the circuit over 10 feet. Smaller caps should have proportionately less ESL.

As far as the importance of ESR/ESL: Depends on the circuit. In a cathode bypass cap, the tube has an internal cathode resistance of its own, equal to 1/gm: somewhat under 1k ohms for a 12AX7. You have to ask yourself what percentage of that the ESR of your cathode bypass cap forms, and whether it'll make 3dB of a difference to anything. You also have to ask how many ohms of reactance the ESL adds to the circuit at 20kHz.

A guideline given by Douglas Self is: Electrolytic capacitors should never be used as part of RC filters that shape frequency response. The reason being that they have very wide tolerances, and generate measurable distortion if a high audio voltage ever appears across them. They are widely used for coupling in solid-state gear, but they should always be sized so big that they don't roll off in the audio band.

[R.G.]

What's really fun is to make up your own glass plate caps.

For this you need a large number of thin sheets of glass and a large quantity of tin foil. No, not aluminum foil, *tin* foil. You intersperse one plate of glass, one sheet of tinfoil, and repeat as needed. You leave the tin foil extended out of opposite sides on alternate layers. When you have enough capacitance (easy to calculate how much you have, it's a beginning physics problem), you fold all the protruding tabs on one side down and solder a wire to each of them. Same for the alternating foils on the other side. Now you have a capacitor which will withstand lots of volts, several thousand at least, and which has vanishing small ESL. You can pull some real current pulses out of it, as well as storing a lot of energy in there. The energy stored goes up linearly with capacitance but by the square of the voltage, so things get very charge-y.

A really good source of thin sheets of glass is the face plates for welding helmets. These are consistent in size and shape, and come in boxes of 100's.

Glass plate caps like this will hold lethal charges for months or years. They're quite dangerous because the energy storage is so high and the leakage is so low.

Eh? Heavy and fragile? Not enough capacitance? Pooh. Nothing succeeds like excess.

[guitician]

That reminds me of an idea I had to make the cabinet out of dielectric and use it as the PSU filter. I like trying the unusual sometimes, just for fun.

[R.G.]

That reminds me of an idea I had to make the cabinet out of dielectric and use it as the PSU filter. I like trying the unusual sometimes, just for fun.

That would certainly make picking which of the leads was the ground lead versus hot lead important...

[J M Fahey]

Hi guitician.
Your idea

That reminds me of an idea I had to make the cabinet out of dielectric and use it as the PSU filter. I like trying the unusual sometimes, just for fun.

is neither that preposterous nor that new, since it was used some 4000 years ago.
Just read your Bible or simply search for "Ark of the Covenant".
It was a cabinet built of "the driest wood that could be found in the hottest desert", great dielectric (for the age) if you ask me.
It was covered in gold foil, inside and out.
It was carried averywhere enveloped in a piece of blue cloth, which must naturally have been wiping it all the time, because of movement, and given the desert conditions must also have been *very* dry.
Do I hear the phrase "electrostatic buildup"?
It usually runs into KiloVolts, as the 1/2 inch sparks show.
No wonder "everybody who touched it died"
Please be sure that what I state above is written with the maximum respect, and, besides, I am one of those who believe that the Bible *is* based in fact, even if sometimes those who transmitted such facts to us by word of mouth sometimes used different words than what we *might* have used.

[tedmich]

No wonder "everybody who touched it died"

I believe everyone who didn't touch it also died, hardly a miraculous claim.

Didn't Moses gets all pissed about the Golden Calf and then his followers end up worshiping a golden box? From ROTLA it could hold quite a charge though, enough to melt Nazi's apparently.

[Steve Conner]

Do I hear the phrase "electrostatic buildup"?
It usually runs into KiloVolts, as the 1/2 inch sparks show.
No wonder "everybody who touched it died"

I swear this is true! It was originally called "Arcs from the covering", but it got mangled in translation.

[guitician]

Hmm, I always thought of my amps as of being a little divine in nature....

Organic polymer sheet may work.....now were do I get some samples?

[cminor9]

I am going to order some spragues, and just for fun, some Solens for my Matchless clone.

I am no expert as I have only been doing this a couple of years, but I have always been a parts-is-parts person simply for the fact that guys like Jim Marshall and especially Leo fender cared about economics. It just makes more business sense. I cannot see those guys debating the merits of various manufaturers' components. They were running a business. That's my theory and I am sticking to it. So I am what you could call a bit of a skeptic.

I'll post the results. I ought to record these amps and post them for you all to hear, sort of a before and after thing. The after will be with no changes other than filter caps, so it will be somewhat scientific (though I have no cap tester). Maybe I'll do just that.

As promised (well, about 25% of what I had wanted to do)... I got a couple of F&T caps and dropped them into my spitfire clone. I replaced Xicon caps of the same value and voltage (well, maybe the xicons were rated for 25v lower, but the amp in question has a B+ of about 350v) No other changes. plugged in, and?

Didn't notice much if any difference in the overall tone of the amp at normal playing volumes. That's a good thing, cause it sounded fine. The only thing I didn't like was the tone of the amp when driven full tilt. So I cranked it up, and I did actually notice some improvement. It didn't get all muddy and sucky when I hit a bunch of palm muted power chords.

As for the 6G3 with all four filter caps being Xicons...I didn't work on that one. I'm selling it to someone who really likes it (he begged me not to salvage it and made a 5G9), so I am not really going to mess with it. But that would have been a *really* good test. Sorry, guys.

So perhaps not a conclusive test in the sense that I did a double blind test, but in my mind it was ten dollars well spent. Really, it comes down to a bit of an edge case: in reality I am not gonna play that amp *that* hard cause I don't play much metal these days (Master and Volume full on.) But if I ever want to, it'll sound the way I like it to.

Would the Xicons have been good enough? Probably, because this amp isn't being run that hard regularly. It's the 80/20 rule, of which Steve Conner's 3db rule seems to be a corollary: in most cases the 80% is good enough. But it made an audible difference, albeit in an edge case, so I think in this instance I am happy with the results (sometimes, 80% isn't good enough, sorry Pareto.) F&T caps are about $5 apiece for the common 22uf/500V value. I can get Xicons for about a buck apiece. I could pay $8 for spragues. Is $4 extra per cap a lot of money? I don't think so. If I were mass producing amps, it most certainly would be. But for building amps I can gig/record with I am willing to spend a *little* extra in the right places. My next amp will be a 5G9 or a clone of a boutique amp I found a schematic for (though I am grappling with the question of do I *really* need any more amps?) For something like a boutique knockoff or a tweed, if I don't buy one of those CE Manufacturing cans for space reasons, I think I'd do the F&Ts. For recapping my hot rod deville, I'd use the Xicons.

I wish I had a scope so I could provide hard data. I don't so I can't. This is as good as it gets from me. The bottom line: It didn't make a different amp, but for the edge case I was testing for it helped enough to satisfy me. For $10, the cost/benefit ratio was good enough.

[R.G.]

I replaced Xicon caps of the same value and voltage

Given that most film caps are either 10% or 5% tolerance, how closely did the two sets match in actual, measured value as opposed to the 10%-20% they could have mismatched and still been within tolerance?

So perhaps not a conclusive test in the sense that I did a double blind test, but in my mind it was ten dollars well spent.

I believe that every part of this statement is literally true.

[Prairie Dawg]

I love this quote from their "specifications":
Fuses always carry high electric current thereby causing metal fatigue. This would then adversely alter the conductivity behavior of the fuse element and hence the performance of the equipment.

Well, I'm a metallurgist, and I was never taught that electricity causes metal fatigue, and I never read about that possibility before. So, I guess we should also tear out the wiring inside our house after some period of time because the copper has been fatigued by the electrical current. I think I'll go purchase some stock in the copper mining industry. Maybe we should ask them why their gold plated fuses aren't fatigued by the electrical currents. This is fascinating science...

You're the second metallurgist I've met. The first one was my old man and his BS is from MIT, class of 1941. He sure knew his stuff-about metals anyway.

[cminor9]

Given that most film caps are either 10% or 5% tolerance, how closely did the two sets match in actual, measured value as opposed to the 10%-20% they could have mismatched and still been within tolerance?

I have no cap tester. I don't know.

I believe that every part of this statement is literally true.

Zing! You're funny, I see what you did there. Literally, it made me laugh. Good one.

Maybe it is in my own mind. Keep in mind I entered this as somewhat of a skeptic. So while perhaps there is a bit of a confirmation bias in my mind since I did pay money for the caps and wanted them to work, I certainly didn't expect to hear a difference. Perhaps if someone were to reimburse me for the caps, then things would change?

A double blind A-B test would have been ideal, but then of course I'd need an exact replica of the clone I built (with parts that measure all the same, natch.) Or I could have come up with some complex system of switches to switch the new ones out and the old ones in. Also ideal would have been measuring each cap to ensure they were of the same value, and then viewing the signal on a scope and providing the traces for everyone.

It starts to get pretty absurd, doesn't it? Even then someone would make the claim that I slightly rerouted some wire or fixed a bad solder joint or heated a component one too many times. That's the way it is with these sorts of things. Believers believe and skeptics doubt, and there's nothing little ole me can do about that. Yes, caps are a holy war.

I got crap to do and a life to live and certainly not enough time or resources to do a proper scientific test or deal with people's faith in the mighty high-end cap. I just wanted to post my subjective, anecdotal results for everyone to see. I am starting to wonder why, though, see previous paragraph.

This is why I work in software development. Testing is so much easier. Just write a unit test and execute against the actual code and you're done. No double blind, no subjectiveness. Oh, there are still holy wars (coding style, development methodology, language, platform), but I guess I have the good sense to stay out of them.

Jeez.