Specifics?

[bucky]

In looking online for parts, I notice that there are many products that fall under the criteria that I'm looking for, but are slightly different.  For instance, I was looking on mouser for a .12uf capacitor, and there are some that are 100V, and others that are 250V.  Does it matter which ones I use?

[littlegreiger]

The voltage rating doesn't matter, as long as it's higher than the supply voltage. For a normal pedal that's 9V. Also, usually the higher the voltage rating the physically larger the capacitor becomes.

[petemoore]

  16v rating is the general minimum for running 9v effects, higher voltage caps can be used. If I think I might want to run higher voltage I'll use 25v, or when I have 'em.

[RDV]

I bought all these damn 16v caps for effects but now I'm building amps and they're all F***ing useless!!

RDV

[R.G.]

To be perfectly correct, they're differently useful...

[RDV]

To be perfectly correct, they're differently useful...

Yeah, but when you need a 50v and all you've got is 16v, they're useless!
I'm actually using some 16v in the Thomas/Vox preamp, but I'm running the thing at 18v now, so I'm "Livin' On The Edge"!

RDV

[stm]

Yeah, but when you need a 50v and all you've got is 16v, they're useless!
I'm actually using some 16v in the Thomas/Vox preamp, but I'm running the thing at 18v now, so I'm "Livin' On The Edge"!

RDV

Of course a circuit may operate for years in a limit condition, but may equally fail without previous notice in the worst situation--5 mins before a gig (as Murphy dictates).

A good design never uses a component near one of its maximum ratings.  A security factor between 20 to 50% is always desirable to insure reliable operation.  As such, even if you use a 16V capactor for a 15V supply I would consider that design "on the edge", and surely would discount points to a student that comes up wich such a design.  In this case a 25V capacitor would be a reasonable and sensible choice.

Of course sometimes we may prefer living on the edge due to space limitations and/or component availability--at our own risk.  Just wanted to clarify this for beginners to stay out of trouble.