Filter cap value …decimals? …multiples?

[jessenator]

Maybe a no-brainer, but figured I'd confirm

When setting up filter caps for the power section, should the multiples(?) of the the caps be multiples?

E.g. if my main filter cap is 100µF, should the second (and third, possibly) follow suit? 10n, 1n? So if I'm doing a smaller 47µ, 47n and 4n7?

[jwin615]

I think it's common practice but I don't think it is required by any means. At least practically. Theoretically, maybe there's a reason. But with a good power source, the large cap should really be redundant and ripple should be minimal to start so it is only acting as a "reservoir" at that point.

[mauman]

Rod Elliott addresses this at https://sound-au.com/articles/power-supplies3.htm

"A common recommendation is to use two or more capacitors in parallel, with each having a different value.  While you might think this could spread the resonance and reduce its effects, it does no such thing.  A 100nF cap (for example) in parallel with a 10µF cap behaves more-or-less identically to the 10µF cap by itself, even if one or both has a significantly higher/ lower ESR than the other.  You may read that the values should be 'non-harmonically related', meaning that they shouldn't be half, double, three times or any other simple multiple.

Just like any other caps in parallel, the larger (or largest) value will dominate, but the performance is much the same as you would expect of paralleled capacitors.  The total value is the arithmetic sum of the individual values used.  The only place where it's common (and useful) to use unequal value caps is when bypassing opamps and RF circuits.  A monolithic/ multilayer 100nF ceramic should be in parallel with the supply pins, and it's usually wise to include 10µF electros (usually between each supply and ground) where the DC enters the PCB.  This has nothing to do with snake oil, but compensates for the track and wiring inductance that may otherwise cause instability."

In other words, use your 100 uF for the DC supply and skip the rest.  Do, however, add 100 nF bypass caps from +V to ground right at each op amp.

[jessenator]

In other words, use your 100 uF for the DC supply and skip the rest.  Do, however, add 100 nF bypass caps from +V to ground right at each op amp.

Wow, that could simplify the boards I'm putting together for sure. Thanks! Yeah, I was definitely into the whole spreading thing.