What value cap to bypass power supply cap?

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"

Amplifier's end means where the output transformer goes to ground, I think.

I'm a little confused.

"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."

"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."

So, because I have film power supply caps which are nearly double the capacitance than specified in the original schematic and have very low ESR being film caps, you're saying I really don't need to worry about reducing ripple as much? Then how do I improve the frequency response needed to lower the noise or improve load response? (How does improving frequency response lower noise or improve load response?)

Do film caps in general have higher self resonance than electrolytics?

I'm going to use 0.1 microF Mundorf M-Cap Supreme as bypass caps, which are noninductive. But I have no idea what the self resonance point of these caps. Do these seem like a good choice for intended purpose?

Sorry, lots of questions, I know.

No, you most likely don't have to worry about ripple.

Film caps of equivalent capacitance have much higher self resonance point and much lower ESR than electrolytics.

Capacitor that has better frequency response offers low impedance at higher frequencies (higher self resonance point) becoming more effective filter for high frequency interference/noise. Also it can respond faster to rapid current demand having lower inductance (inductance resists current change).

Mundorf M-Cap Supreme is high quality metalized polypropylene cap. It might work fine but you can also try metal film polypropylene or Teflon. Metal foil offers lower connection resistance. Try to keep short connections since even straight wire has inductance.

You mentioned 760uF therefore it has to be low power electronics (preamp or DAC?). We might be dealing with regulated power supply greatly reducing ripple. If you have voltage regulators and plan to improve any caps behind them check first what type of regulator it is because some of them don't like low ESR load (oscillate). Give me more info.

They're not for preamp or DAC. They're for monoblock amps. However, there are a total of 12 of these. Still not a lot by electrolytic standards, but they are huge cans, each about 7 x 5 inches and weighing around 4 to 5 lbs. According to the design of the amp, huge values found in electrolytics are not needed.

The Mundorfs Supreme, although a metalized film cap, is noninductive by design (noninductive winding geometry). Shouldn't that result in very good frequency response?

Teflons are too expensive. I would need 12 of them for the power supply caps. The amp side would need only one 0.1 microF Teflon cap (I have a couple of V-Caps from another project left over). But the metal foil polypropylene caps may be viable solution for the power supply caps.