Voltage rating question ...

[MartyMart]

When a circuit calls for between 16v DC and 21v DC ( Studer comp/limiter rack )
would 24v DC be a tad too much ?
Best to regulate down or stick a suitible large resistor in series ....
IC's are MC1539G's and a HC8A101
Thanks,

MM

[petemoore]

  use of 1/4w resistors'll be fine.
  The caps and IC's should be checked for voltage ratings, then, any voltage less than that can be applied to them safely.
 

[R.G.]

I would take into account what the cost would be if there was a problem. Presumably they are doing something inside that they don't want as much voltage on, and while it might just be a bias shift problem, it could be that there's a regulator or something in there that will overheat, possibly burning out if you put 24V on it.

If the device was a piddly pedal where you could debug and replace anything that burned easily, I'd go ahead. As it's a studio rack unit, it is going to be a tad more complicated and expensive to fix it if it does break.

So ask yourself - do you feel lucky?

Besides, dropping voltage is so easy. Each silicon diode drops a relatively fixed 0.6V. the 3V down to 21V is only five diode drops. I would string together five or six 1N400x diodes and have done with it. You could use a series zener, or an amplified zener, or a single transistor Vbe multiplier, lots of ways to drop voltage.

[MartyMart]

Thanks chaps, great advice .... as always !
I found an 18v DC PSU, which seems to power them up fine, they only need 180ma
and this is a 300ma regulated, so fine for one of them at a time.
( old answering machine PSU )
Need to wire up some balanced insert cables and see if they're alive !

MM.