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In Reply to: Re: Every capacitor has some parasitic inductance. posted by sherod on April 15, 2007 at 10:51:48:
A good rule of thumb is to have at least a 100 to 1 ratio between cap values. Why? Because the self resonance of the cap, related to value, changes as the square root of the value, so 100 to 1 in value is 10 to one in resonance range. Less separation means interaction between the caps. It can be shown with a computer simulation.
Follow Ups:
Sorry to get a bit more complicated .
What is the situation when you have parallel same sized caps..ie 2 x 100 Mf + 200 Mf ? or more?...do you bypass with 1 mf or 2 mf?.etc.
I can even see a reasons for going lower than the 1Mf or have I got it wrong...You can go higher that 2MF.
There is no HARD rule. You just should not put the values too close together, because they most often will interact. 100;1 is a good start, but in your case, maybe .1uF is better.
...(and, of course, lots lower than that) when bypassing their 'styrene coupling caps. I recall they love the sound of 0.15µF bypasses on values as small as 1s and as large as 4s.Don't know if they're doing that with/to their Teflon-film caps.
Probably every combination (of brands, types, and values) has a different sound, so what works for A plus B doesn't work as well for X plus Y. Sure am glad I'm no GEA! :-)
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Hi and thanks for explanation.
Does this also go someway towards answering my previous thread re bypassing at 50 to 1 (half decades etc) which sonivally caused some dullness at certain frequencies and or possibly highlighted others.
Based on my experience, I have heard what you are talking about when using bypasses that fall under the 100 rule. Some call it "phase anomalies". I'd like to see in a computer graph what this looks like, but nonetheless, I can still hear it.
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