Buying Capacitors: How Many Volts For Pedals?

[railhead]

I'm about to stock up on some capacitors for a boost project, and I'm wondering what volt rating I should be buying. How do you know what to buy? Is there a basic "16v or greater" rule or something?

Thanks,
Maury

[slacker]

If you're only ever going to run the pedal at 9volts, go for at least 16volts and you'll be fine. You can get away with lower voltage caps in some places because not all the caps in a circuit will have 9volts across them, but it's easier just to make sure they can all handle at least 9volts.
After that I tend to buy caps based on size, sometimes a 63volt cap in one style will be smaller than a 16volt one in another so I generally go for the smallest.

[Mark Hammer]

There are many places in circuits where voltage ratings as low as 6-10v can be "safely" used, but given the extremely small difference in price and size between 25V rated caps and those with lower voltage ratings, may as well buy the 25v ones for your parts bin and dispense with worrying about whether you have enough of the "right kind" for the next project.  That's essentially what many of the big companies do.

[railhead]

Sounds like a plan. I bought some 50v, and they're freaking huge, so I was hoping to go a bit smaller. I'll snag some 25v.

[CGDARK]

Sounds like a plan. I bought some 50v, and they're freaking huge, so I was hoping to go a bit smaller. I'll snag some 25v.

Yes, 25v will be good. They aren't too big and you have a better margin of protection in case something goes wrong.

CG

[railhead]

Huh. Searching Mouser, I can't find any 25v 10pF ceramic, .05uF film, .22uF film, or 3.3uF and 100uF aluminum electrolytic caps.

I guess I'll stick to 50v...

[Mark Hammer]

I was talking primarily about the electrolytics.  These days, it's pretty dang hard to find sub-1uf caps rated at less than 50v.

Even so, from a size perspective, you'd be surprised at the amount of variation in form factor depending on manufacturer, even for the identical voltage rating.  I've bought 25v 10uf caps that are easily the same size as some of the .22uf/25v tantalums I have, and some current-production 1uf/35v electros that are easily 3 times the size of those 10uf units..