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Re: Capacitors don't matter ...

Posted by BFitz on July 26, 2000 at 07:29:54

In Reply to: Capacitors don't matter ... posted by Dave I on July 25, 2000 at 19:03:33:

Dave -
Really interesting post. I think I heard you say film caps, perhaps even of a substantially lesser capacitance value, are far ahead of electrolytics. This jives very much with opinions from the single ended tube guys, who are using "puny" power supply caps (say, 100-200uF total) compared to typical SS PS(say,10-50,000uF). But those small value caps are BIG, film or paper in oil caps in many cases.

BTW, here are some numbers from the Jung Curl article (TAA 4/85)
I mentioned. A differential amp is set up with two caps on the two inputs, one a high quality reference, the other the cap under test. It is balanced for signal level and ESR, and a band limited pulse is used as the test signal. The "residue" is the distortion to the waveform the lower quality cap creates.
here are a few examples of the results, using a 200V polypropylene cap as the "reference".
10uF 10V aluminum electrolytic - 12% residue
10uF 25V nonpolar aluminum electtolytic - 3% residue
10uF 35V tanatalum electrolytic .9 % residue
.1uF 50V ceramic 2.4% residue
.1uF 100V polyester (mylar) .11% residue
"The residue from the test units is dominated mostly by DA errors...Not only is the basic waveform of the input pulse distorted in shape,but also note that that appreciable output is still occuring for several tens of milliseconds after the input is complete."

I would love to dive into another project, but I have way too many open now. I may see If I can duplicate the test above using an FFT analyzer with an intrumentation quality differential inputs (HP3562A)
If it is super easy I'll test what is on hand, report back, and expand it..

Very interesting discussion, has perhaps changed my perspective on caps a bit...
Bob

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