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I recently stumbled onto the following comment in an article about inverse RIAA filters by Lipshitz and Jung. This is in relation to listening tests that the reader can perform by feeding their phono preamp with signals from the authors' filter design.
"You must use network components appropriate for listening use. Mica capacitors, while entirely adequate for steady state bench tests, have some dielectric absorption which is undesirable for auditioning tests. Polystyrene capacitors are preferable for listening, as are metal film resistors."
I thought this note regarding mica vs. polystyrene was interesting. I use mostly polystyrene caps in circuits like these, but the few times I've included a few micas, I don't remember hearing much difference. Anyone else noticed (or not noticed) a significant difference between them?
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Buy Chinese. Bury freedom.
Follow Ups:
i came across an article that compared various capacitor dielectrics and how they affect sound. Polypropylene was the clear winner, and PIO.
This was not a "listening" test. It was an objective test done with test equipment that displayed the distortion created by the different dielectrics. A testing methodology you can believe in, rather than people with expectation bias skewing the results.
At that time, polypropylene caps were harder to find and more expensive for reasons I cannot fathom, and now they are much more common and more reasonably priced. Since polypropylene is a cheap common plastic, to my thinking they SHOULD be cheap.
Tantalum tested poorly.
The Trainwreck guitar amp uses I believe a ceramic cap paralleled with another more audiophile quality cap to supposedly get distortion, more "crunch" as the guitarists call it. Of course, you would not want this in an audiophile amp.
While not in the phono stage, the RM-9 amp uses mica caps in the FB/gain switch-
and they replaced the early use of Polystyrenes - which can not handle heat...
Happy Listening
Yes, that's the downside to the 'styrenes. Small silver micas take heat with no problem. I wonder if the change degraded the sound.
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Buy Chinese. Bury freedom.
Just want to point out that Xicon polystyrene caps are rated to 85C. I've never had a problem with this limitation in audio work, and never had one of these caps fail.
Man, just look at those numbers for dissipation factor and Q!
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Buy Chinese. Bury freedom.
It can get hot near some tubes and polystyrene exhibits a low melting point. In a 'X7 based phono preamp 'styrene should be quite safe.
The film dielectric "pecking order" is PTFE, polystyrene, and polypropylene. Practical considerations, such as cost and heat tolerance, make polypropylene a "favorite".
Eli D.
size is also a factor. Teflons and polystyrenes tend to be bigger than polypropylene.
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