Main Filter Caps/Bypass formula?

[patfont]

Hope this is the right forum for this:

I have a Marantz 2220B and am attempting to bypass the main filter caps. They are 6800uf 35V. I tried Mundorf 2.2uf 250V, and I like that it removes hash, and grunge from the sound, but at the same time the dynamics and soundstage are slightly compressed, and slightly dark sounding not to mention they make the music sound like it is slightly out of time. I did see some one who had stacked 3 caps togeather 5uf with a .47 uf and a 1000pf. Any ideas on the proper way to do this so I can get some benifits with out the draw backs. Is there specific values you use to match the size of you filter caps. Any brand or value size recommendation will be appreciated.

[!]

When you start getting specific about minute sound differences there is no formula we can apply to know what you will prefer. Generally speaking you're going to have to decide if a specific noise profile is what you find pleasing then filter all but that, or if you are attempting to remove higher frequency ripple which is better done nearer the amp output transistors. Otherwise a scope reading of the power rails there would better indicate what you need.

[DF96]

If you are going to add a bypass about the worst place to put it is directly across the main cap, yet this is what many people do. The bypass should go near the amp, not near the main cap, then the resistance of the connection can help damp the HF resonance which bypassing can create.

Calculating the value is difficult, because calculations have to be based on science but the science says that bypasses are generally a bad thing. If you can measure the stray inductance and ESR of the main caps then a calculation may be possible, if you know what you want to achieve.

[simon7000]

Put a low value (470 pf or so) on the main PS capacitors. Then place the film caps close to the output transistors. You can also put a small resistor (.05 to .47) in series with the film capacitors.

I prefer around 300 uf of film capacitors near my outputs for an 8 ohm load.

[gorgon53]

caps are more or less LCR devices. 1 cap would be a serial resonance circuit. Put an other cap in parallel and you get paralell resonance possible even at audio frequencies.

[sreten]

Originally Posted by DF96

If you are going to add a bypass about the worst place to put it is directly across the main cap, yet this is what many people do. The bypass should go near the amp, not near the main cap, then the resistance of the connection can help damp the HF resonance which bypassing can create.

Calculating the value is difficult, because calculations have to be based on science but the science says that bypasses are generally a bad thing. If you can measure the stray inductance and ESR of the main caps then a calculation may be possible, if you know what you want to achieve.

Hi, +1 for the above, bypass caps should be and usually are on the PA board, rgds, sreten.

In preamps they are very near the chips or the analogue circuit to be bypassed.

[patfont]

ok, this is sounding more and more like it is not worth it, not only does it seem hard to figure out, but putting the bypass in these other locations is kind of beyond the scope of what I can do. I have recapped this receiver, including the main filter caps and it sounds very good. When I tried to add the bypass caps to the main filter caps I loved the now dead silent back ground, but of course it had it's draw backs so I removed them. I thought maybe I put the wrong value in. I am using Nichicon KG main filter caps and will try Mundorf M-Lytics or Kendeil K05's to see if they would improve things.