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Old 1st December 2005, 03:52 AM   #1
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Default Best caps for signal passing

If one had to put a capacitor in the signal path of an audio amp, what is the best kind of capacitor to use (poly, tantalum, ceramic, etc.)?
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Old 1st December 2005, 04:07 AM   #2
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an air cap.....
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Old 1st December 2005, 06:30 AM   #3
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While placing capacitors in the signal path should be avoided if at all possible, I got the following advice from "Picking Capacitors" by Walter G. Jung and Richard Marsh (Do a search on Google and you can find this very revealing article about capacitors and how they relate to audio). Anyway,

"Up to values of about 10,000 pF, polystyrene is the best all around choice, as it has reasonable size and is readily available in many sizes, with tight tolerances available. Above 10,000 pF, and up to 0.1 u F, it still can be used but is much harder to obtain. Above, 0.1- u F polypropylene (or metalized polypropylene) is the dielectric of choice, as it has nearly the same relative qualities of DF and DA as polystyrene. Tight tolerances are available (but will be special order), and you can get capacitors up to 10 u F or more. Teflon may well be the best dielectric of all for audio, but is produced in limited volume and is generally not practical. Parylene is an excellent dielectric also, but limited in electrical size ( 1 uF or less) and not widely available. Polycarbonate is perhaps the next best all-around choice behind these and is generally available in a wide range of values. Polyester types are the most widely available for all the films and are already widely used in many audio circuits. There is no doubt that this is due to the generally low cost of these capacitors, but convenience and low cost should not be primary selection criteria to a critical audiophile. Polyester capacitors can be readily heard in good systems, with defects similar to those described for tantalum but, of course, reduced in magnitude. In our opinion, polyester capacitors should be very carefully applied in an audiophile's system, and any system using them in the signal path may potentially benefit by the substitution of (equal value, voltage and tolerance) polypropylenes or polycarbonates. We have done this ourselves on different items of equipment, tube and transistor, with always the same result—a stunning upgrade in sound quality. Further, we have observed others do similar things, either completely independently or at our direction, with the same type of results."

Hope this helps.
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Old 1st December 2005, 04:22 PM   #4
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Found the article:

http://www.capacitors.com/picking_ca...rs/pickcap.htm
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Old 1st December 2005, 06:39 PM   #5
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Just as an FYI, Jung's article is a bit out of date. These days you can get polypropylene caps up to 200 uF, so long as you dig deep in your wallet.


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Francois.
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Old 1st December 2005, 06:43 PM   #6
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Quote:
Originally posted by DSP_Geek
Just as an FYI, Jung's article is a bit out of date. These days you can get polypropylene caps up to 200 uF, so long as you dig deep in your wallet.
And even more than that (which means even deeper into your wallet).
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Old 2nd December 2005, 12:20 AM   #7
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Originally posted by Christer


And even more than that (which means even deeper into your wallet).
Really? Where? I'm only acquainted with the selection at PartsExpress and Madisound. Not that I need such things as my crossover of choice is electronic, but it's nice to keep up with available parts.

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I remember the ARRL book telling me that a farad was an almost impossibly large unit of capacitance that nobody could have a use for. My, how times have changed.
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Old 2nd December 2005, 03:06 AM   #8
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Quote:
Just as an FYI, Jung's article is a bit out of date. These days you can get polypropylene caps up to 200 uF, so long as you dig deep in your wallet.
Good to know. I am kinda a newb at DIY electronics. Where do most people go for their capacitor needs? I do not have a deep (or a deeper) wallet, as I assume most DIYers do not, and I can't find any good deals on capacitors. In any case it seems from reading many threads on this forum that DIY audio becomes somewhat of an addiction at some point and spending nearly needless amounts of money on parts becomes almost common hat. Call me crazy, but I think thats exactly where I am heading, which is ok with me, I love this stuff .
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Old 2nd December 2005, 05:46 AM   #9
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Originally posted by DSP_Geek


Really? Where? I'm only acquainted with the selection at PartsExpress and Madisound. Not that I need such things as my crossover of choice is electronic, but it's nice to keep up with available parts.

Maybe I gave you false expectations, but at least SCR makes them up to 330 uF. I suspected they might make even higher values which were just not available at "my" supplier, but checking the datasheets, 330 uF seems to be the biggest they make. Still, they may have other series, and there might be other manufacturers, perhaps.
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Old 2nd December 2005, 05:02 PM   #10
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Im seeing polypropylene (non oil) motor start caps in the 250uF range cheap, wide tolerance, but its still better than elco where you can tolerate the size.
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