Does cap voltage affect tone?

[daz]

assuming you are safely over whatever the cap needs to handle in it's context, are there any places in an amp where using say a 450v cap instead of a 50v would affect tone in any way? I seem to notice something but it's too subtle to count placebo effect out.

[Merlinb]

Usually no, but with some electrolytics, when operating under very low polarising voltages or very low signal voltages, low frequency distortion can occur.

[daz]

You mean if the caps are rated pretty high?

[Ptron]

Ceramic caps can change pretty dramatically in capacitance depending on the voltage across them. Their rated capacitance is usually given at some percentage of their rated voltage. At their rated voltage their capacitance can be tens of percent less. I'm being vague because I'm too lazy to look up the numbers. Can this be audible? I dunno. A lot of people think so. Personally, I tend to be skeptical of such things but this is the one capacitor/tone thing I find most plausible.

[daz]

Thats not what i meant. What i was asking is say you have a cap on a preamp cathode and in place of a small 10v 1uf cap you put a 450v 1 uf cap. Will the big 450v cap that can handle about 400 times as much voltage as necassary in that context cause any change in tone over using that 1uf 10v cap?

[Chuck H]

Not if all other things are created equal. And they never are. A high voltage cap will have differences in construction (spacings, etc.) from a lower voltage cap. Since electrolytics are said to have poor performance at higher frequencies I would think this only gets worse with an increase in dielectric spacing. Not really sure about that and it may not even apply to audio frequencies. But the point is that differences in construction can cause a difference in performance. But I doubt the difference would be any greater than changing from one low voltage cap to a different brand of low voltage cap. I'm pretty picky and I don't think I would hear the difference in this application. That isn't to say you can't. It's just to say the difference is really really small. And to further eliminate this difference you could take two totally different 10uf electrolytics and bridge each one of them with a 1uf film cap. This would probably eliminate any performance difference between the two. It's a neat trick to improve performance on electrolytics. But again, the difference is so tiny in this application that you will wonder if your imagining it. So I don't bother.

What merlinb said is also true. But I've never noticed a problem using 100v caps for preamp bypass so I've never reconed with it.

Something you may want to try is dry tantalum caps. Alot of guys here will poo them for their supposed high failure rate. But they may be talking about the cheap little blob looking ones that you almost never see anymore. I use the little plastic cone headed ones made by Kemet. I've abused them pretty badly with some circuit errors. Even had two installed in reverse polarity recently. The crazy thing is, not only did they not fail, they were working. I tested them and then reinstalled them correctly (re-reversing the polarity) and they still didn't fail. I've used them in a dozen projects without incident. They have much better audio performance than electrolytics. You will hear a difference. And they will last many times longer. I only use them for preamp cathode bypass circuits. I took the idea from Mesa who has been and is still using them.

Chuck

[Merlinb]

You mean if the caps are rated pretty high?

Yes. In a very low-voltage situation, a high-voltage cap is liable to give low frequency distortion. This only happens at very low polarising voltage though, or large signals voltages (I got that back-to-front in my earlier post). So if you used a 450V cap for a cathode bypass, you could expect some ugly bass.
See 'Capacitor Distortion' p175
http://books.google.co.uk/books?id=B...amps#PPA175,M1

[cbarrow7625]

Chuck, I'm with you on the dry tantalums. I use them all the time in cathode bypass applications. In many cases I find that they give me the best tone, at least the tone I am looking for. Less constrained without being irritating like poly bypass caps can sometimes be. I don't use them in all circuits but I always give them a shot and find they work very nicely a lot of the time.

[cbarrow7625]

The caps could also have very different ESR. That could account for the tone shift more than just low frequency distortion (not to discount that idea, just adding another one - I'm no expert on caps).

[daz]

Good stuff, thanks all ! I'm going to see if i can find some tants. i may even have some on old boards i save for parts, tho i likely won't be lucky enough to find tha values i need. but this sounds like a good idea.

[daz]

Thanks for the idea on the tantalums. I also heard in the past that regular caps in place of electro's is a better way to go. So i didn't have a .68uf tant for the first stage cathode, but i did have a epoxy dipped style .68uf cap and used that, and i have 1uf caps on two other stages and i DID find 1uf tants for those. Long story short it seems to have totally eliminated a certain super high end buzziness i hear when using semi clean tones via the guitar volume knbs. I have always had that isse in most every amp i've had, and it's always bugged me a bit at times. this seems to have eliminated it altogether and the tone just seems purer or something. Good call guys, this is not a real subtle improvement so i say thanks much ! (i mean, not HUGE, but certainly not subtle)

[Chuck H]

"Purer" is a good way to describe it (wow, that word looks funny spelled out).

It just sounds more natural and open. Like the gain stage is doing it's job without fighting the short commings of the componants. The great news is that the Kemet tants that I use are available in most of the common values like 1, 2.2, 10 and 22uf. Interestingly I find myself most often using values that are uncommon. You can also get 3.3, 4.7, 6.8, and 15uf values. I find the 1, 2.2, 3.3 and 15uf values the most useful for my personal amps. But I don't own a Tele or a LP. Idealizing an amp for the guitar you will most often use with it is the ultimate in tweaking.

Chuck

[daz]

I'll have to see if i can get a .68uf for the first stage. probably won't matter since i now have a epoxy cap there instead of a electro, but what the heck. By the way, do tants NOT come in values under 1uf?

Good thing i had a 10x eye loupe tho....the + sign on those tants is so small i could never have possibly seen them with anything less. I couldn't even see it thru my lighted magnifier.

[Chuck H]

I'll have to see if i can get a .68uf for the first stage. probably won't matter since i now have a epoxy cap there instead of a electro, but what the heck. By the way, do tants NOT come in values under 1uf?

1uf, .68uf, Whats the difference? I wouldn't quibble over .32uf in a cathode bypass circuit. But FWIW most of the Marshalls I've seen use a film cap in for that value and they are redily available.

Good thing i had a 10x eye loupe tho....the + sign on those tants is so small i could never have possibly seen them with anything less. I couldn't even see it thru my lighted magnifier.

The tants I use are chamfered on the + end (kind of semi cone shaped) so it's easy to tell polarity. I can't imagine trying to accuratly read the marks on the little blobs that are most dry tants.

Chuck

[daz]

1uf, .68uf, Whats the difference?

Thats what i figured too, but there really is a difference. I didn't notice much till i played it for a while with a 1uf there, but i ended up putting the .68 back in because there is just this slight difference that changes it enough to mater. It may make more difference if your amp is marshall voiced because it seems as tho it does give it a slightly more marshall sort of voice or feel. Subtle, yet not, if you know what i mean. in any case, placebo effect or real, it makes me happy so i have to remain a slave to my ears be they right or wrong.