Power Supply Bypass Caps

Of course different designers have different opinions on this but a good place to start is to bypass with a value 1/100th of the big cap. You can bypass again with another cap 1/100th of the smaller and see if that does anything.

example, original electrolytic 4700 uF bypassed by a 47 uF film cap and a .47 uF film cap.

The best thing is to get rid of the electrolytics but the alternatives are expensive and physically very large. For solid state amps using thousands of uF it is pretty much impossible to get away from electrolytics.

check out http://www.percyaudio.com/ to see a variety of film caps to choose from, some quite expensive in relative terms.

DIY HiFi Supply also has a selection.

The current issue of AudioXpress has an article on just that subject. That should help a lot. Michael

The values of bypassing caps are determined by the amount of ripple rejection desired and the frequency range. Any capacitor will have a self-resonant frequency calculated by
fr=1/2π√(LC)
Above the self-resonant frequency, the capacitor will start to look like an inductor and its impedance will increase. For optimum ripple rejection, you want the shunt impedance to be as low as possible. Impedance is calculated by

Xc=1/2πfC.

Where: f=frequency (Hz) C=capacitance (farads) L=inductance (Henrys).

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. Find the spec sheets for the capacitors you plan on using to determine their inductance and self resonant frequency and then calculate the values you’ll need for the additional bypass values. It’s better to understand why things are done instead of using “rules of thumb”. I hope this helps.

I usually just use a Wima or Rifa filmcap valued 0.1uF - 0.47uF

These values usually just do the trick with out all the spec. searching. Takes out some ugly ripple. And as Sadownic says; caps in parallel and smaller value is also to recommend, but not a have-to-do. Film cap does just fine to smoothen.

But then again - if you wanna do it like a pro - read Sadownics answer and get your calculator.

Best,
Mike