What value cap to bypass power supply cap?

Dracule1, Take into consideration that bypassing large inductive electrolytic caps with small non-inductive cap crates parallel resonance circuit that will ring in response to rapid current changes. Designer did not put them for a reason.

I would speculate that you might not like the result but it isn't very expensive to try.

Kijanki, thanks for that info. However, all my power supply caps are film caps which according to the manufacturer have ESR and inductance which are a fraction of electrolytic. I know the ESR is 1 mOhm at 10 kHz, but I don't know the inductance. Are film caps considered to be inductive enough to have parallel resonance?

Dracule1, I don't think so. Looks like you got great stuff there. I second 1% minimum recommendation.

Davehrab and Kijanki, I asked an experience electronics engineer who has written papers on bypass capacitors. His response to your statement:

"As you can see from above, the self-resonant frequency will vary depending on the value of capacitor used and its inherent inductance. The physical construction, size and value of the capacitor will determine the amount of inductance. So in order to maintain maximum ripple rejection across a large frequency range you’ll need to add additional (smaller value) capacitors in parallel with large value caps."

was this:

"Yes, theoretically the self resonant frequency of the capacitor can affect the ripple rejection of the power supply filter. HOWEVER, you have to remember that the amplitude of the harmonics of the rectified AC power decrease with frequency so at a few kilohertz and above, the power supply noise is pretty small."

He recommended bypassing the amplifier end (using 0.1 microF bypassed on 10-22 microF bulk bypass cap) and directly across each power supply caps (using 0.1 microF bypass caps).

Not trying to start any flames here. Just trying to learn the differing points of view on this subject.

Dracule1, I speculate that main reason to add bypass caps is to improve frequency response and to lower the noise. To combat ripples you need to increase main capacitor and/or reduce its ESR.

As for self resonance - you want it as high as possible because it is the point where capacitors starts behaving like inductor (inductive reactance larger than capacitive reactance) meaning start of impedance increase with frequency (lowest impedance point). You don't have much control over it unless you use different capacitor type.

Increasing main capacitance will reduce impedance but also reduce self resonance point. It might be necessary step to combat ripple but does nothing to improve frequency response needed to lower the noise or improve load response.

If your main capacitors are film type then you most likely won't have any problems with load response within audio frequencies hence bypass cap will be oriented toward defeating high frequency noise coming from power supply. For that you need much better capacitor with much higher self resonance point. We are not talking about harmonics of rectified AC but about high frequency noise on power line.

I'm not sure what he means by amplifier's "end"