What value cap to bypass power supply cap?

Guys, I feel like a monkey being taught how to speak sign language. Dave, thanks for the watered down analogy of the tank filter. I'll see if this can be incorporated in my amp.

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?

Thanks! That was very helpful.

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.

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.

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.

Hi Kijanki, I think what you're talking about is putting a single cap at the input as an AC line filter. That is a great place for Mundorf Supreme. People have already tried this out and got good result:

http://www.laventure.net/tourist/caps.htm

However, as you can see in the link, there a caveat with Mundorfs as AC filter...It is note rated for use in AC application.

I have been told by several amp designers that bypassing each power supply cap with a 0.1 microF (or other small value cap) is good design practice to filter out noise in the hundreds of kHz to megaHz range, which I was told can cause unwanted oscillations in the amp.

Thanks for hanging in there to guide me.

Hi Davehrab, thank you for your input. When I started this thread, I was confusing several things about bypassing. Here is what I've learned so far from helpful people like you and Kijanki. Please correct me if I'm wrong.

1) The 1% bypass cap recommendation is to reduce ripple in the power supply. This helps with the frequency response of the amp (not exactly sure why) and decreases noise generated by the power supply.

2) Film caps have higher self resonant frequency than electrolytic caps, which is a good thing because it is farther out from audible frequency range. Film caps have much lower ESR (and ESL?) than electrolytics. Do these properties of film caps mitigate the need for the 1% bypass cap recommendation that is employed on electrolytics?

3) The 0.1 microF bypass on each power supply cap and also on the amplifier end helps filter out the really high frequency noise (hundreds of kHz to MHz) range that can cause unwanted very high frequency oscillations in the amp. Some have argued just filtering out the high freq hash may even affect sound quality (not to sure about this argument).

I hope someone will correct me if any of my statements are incorrect. I am learning so much on this forum. Thank you.

BTW, I have replaced the carbon pot on my amp with stepped resistor attenuator. A significant improvement. But the most significant improvement came from treating the room acoustics...took me over two years with various combinations of absorption and diffusion. Phase Linear?...Bob's solid state amp. I'm a fan.

Oh I see. That makes sense, but I thought you want the bypass caps as close to the power supply caps as possible? The further away the bypass cap is, the less effective the filtering, no?

I thought the 0.1 microF cap will handle those high frequency noise you just talked about.

Hi Kijanki, I will need to think about your wiring scheme to make sense of it. I'm not an experienced DIYer.

I think I will use high purity copper wiring with Teflon jacket.

As for the Hyperions, I'm not sure if I can answer that question. However, there was some controversy with phase of the midrange drivers on the 968s:

http://www.iar-80.com/page157.html

Thanks Al, for your wisdom. I will make sure I follow the guide lines provided by you, Kijanki, and Dave.

From many I have talked to, most agree to use bypass caps as close to the amplifier end as possible to filter out those ultra high freq noise in the hundreds of kHz into MHz. So can everyone agree on one sequence of capacitor values that makes sense? I'm not talking about bypass caps for ripple reduction across the power supply caps.

How about 0.01, 0.1, 1, and 10 microF?

Or even closer spacing?

Any chance of unwanted resonance creeping in using these series of values?

1/50 spacing 0.01, 0.47, and 22 microF also seems reasonable.

1/100 spacing 0.01, 1, 100 doesn't seem to reasonable because 100 microF film caps can get expensive.

Sequence of bypass caps to cover broader range of filtering from several hundred kHz to 10s of MHz. They will be at the amplifier end as you recommend.

Thanks. Will try with fewer caps to keep things simple.