voltage ratings that are way higher than necassary

[iknowjohnny]

I think i read something once that said using cathode caps that were rated much higher than necessary were somehow not optimal for tone. Is this true of ANY place in an amp? I have some 1uf cathode caps on a couple preamp stages that are epoxy or poly or whatever and rated for high voltage, i believe something like 400 V. Would it make any difference to go to a cap rated low even if i have to use a electro, and are there other places in an amp where not using highly over-rated voltage parts can be bad tonally?

[rdjones]

To my understanding this applies mainly to electrolytics, and in particular to power supply caps.
I'd avoid electrolytics in signal areas unless there's not much other choice due to value needed.

rd

[Firestorm]

What I remember hearing is that electros used at lower than rated voltage "get used" the lower voltage and have to be reformed slowly if they are going to be subjected to the higher voltage. That sounds kind of plausible. But I can't imagine how a cathode cap's voltage rating would have any sonic impact. With coupling caps, on the other hand, I assume that a cap rated for 400V could sound different from the same value rated for 15kV. Some people claim to be able to hear the difference between 400V rated caps and 630V rated ones. I can't (but then, my ears have been subjected to a lot of loud music over the years).

With some components, higher ratings also imply different construction: higher voltage film and foil caps have an extra metalized layer added to make them self-healing; cast "cement" resistors are typically wirewound up to a certain resistance and are made from metal oxide above that. Things like that could make a difference.

[Structo]

I've read the same thing Johnny.
I thought it had to do with the ESR.

I'll see if I can dig up what I have on it.

[iknowjohnny]

Sound like it may just be a mojo thing huh? don't go to any trouble....i was just curious but if you guys are unsure it's obviously subtle enough if even real to be negligible.

[Firestorm]

I thought it had to do with the ESR.

Oh, good thought. Actually might be something one could use deliberately in a bypass cap.

EDIT: I checked a little. It seems (to me) that ESR in an electrolytic is small enough that it shouldn't come into play with a preamp bypass cap because of the low current and voltage present (different story with PS filters and maybe bypass on output tube cathodes). The higher rated ones will have both thicker dielectric and larger plate surface area, so they sort of cancel out. But ESL may be something to consider, since it apparently rises with the cap's physical size. I also found that it's way hard to find data sheets that even list ESR and ESL.

[KellyBass]

I think I read something about this in one of merlin's articles. Something to do with the availability of different values/types of caps...and being sometimes forced to use higher voltage rated caps where they are not necessarily needed and the consequences (ESR or something).

Or did I just dream this?...

[rdjones]

In the case of the cathode bypass caps there's only a few volts at most present (preamps).
The lowest voltage rated electrolytics are many times these voltages.

What's the common voltage ratings on caps being used here, 25V, 50V ?
I know there's 16V rated electros, but mostly in higher uF capacities.

rd

[Alexo]

There's always tantalum if you want a low voltage, high UF alternative to electrolytics.