10v Capacitors - Anyone use in your 9v effects?//

[bdevlin]

Quite a few of the salvaged caps that I have gotten off of discarded electronics are rated at 10 volts.  I know a rule of thumb is to use caps rated at 2x the voltage.  Anyone thinks it's a REALLY bad idea using these 10 volters?  They are nice and small....Oh they are electrolytics.

[Mark Hammer]

Not a good idea for power supply, but there are a number of instances when they would not be that risky:

• For smoothing Vref; Vref is derived from a divided-down version of V+, so if you start with 9vdc from a battery or wallwart, chop it in half with a resistor pair to 4.5v and use a 10uf/10v cap to smooth that Vref, you're probably not in any danger
• In the signal path when you don't anticipate more than a coupla volts going through them max.  Though keep in mind that the "coupla volts" may well be superimposed on top of a 4.5V Vref.  Personally, I'd use a 1uf input cap to a circuit since I'm confident the previous pedal will have a DC blocking cap on its output so the aforementioned 1uf input cap will only see whatever the audio signal is (e.g., maybe +/-200mv), which shouldn't tax it.

[JonFrum]

You won't kill yourself, so it's not REALLY bad, but it is a bad idea to use them at 9V. That doesn't mean you can't use them in a pedal though. If the top of the cap is sitting at 4.5V in a circuit, then I'd think it's no problem to use one there. The only voltage that counts is the voltage across the cap itself, not the maximum voltage from ground in the circuit.  In a tube amp, you can use a 16v electrolytic cathode bypass cap in a preamp circuit that has a 300V plate supply. There's only about 1.5V across the cathode cap, so the other value doesn't matter.

[bdevlin]

I suppose a lot of the applications in pedals would be <9v.  But like for power supply decoupling?  I suppose that might be the biggest area where it is foolish.

[Mark Hammer]

Rule of thumb is that it is wise to have a voltage rating on the cap that's at least 25% or greater higher than the DC voltage that cap might see....IF you want to assure the cap is on spec.  You could always use a 10v cap with a 9v battery but there is no guarantee it would act like the cap it says it is (e.g., 10uf, 47uf, etc.) all the time, or for long.

So, taking any DC bias voltages into account, always ask yourself "What sort of voltage will be at THIS point?" and choose acordingly.

[markm]

Rule of thumb also states that recycled electros, especially old ones are not exactly a good idea.
Although, I've done it before!