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From: spp@zabriskie.berkeley.edu (Steve Pope)
Newsgroups: sci.electronics
Subject: Re: How do I choose a capacitor type ?
Message-ID: <10883@pasteur.Berkeley.EDU>
Date: 7 Feb 91 18:53:06 GMT
References: <64@owl.ukc.ac.uk> <10836@pasteur.Berkeley.EDU> <1991Feb7.145212.24656@news.larc.nasa.gov>
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Reply-To: spp@zabriskie.berkeley.edu.UUCP (Steve Pope)
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In article <1991Feb7.145212.24656@news.larc.nasa.gov> kludge@grissom.larc.nasa.gov ( Scott Dorsey) writes:
>In article <10836@pasteur.Berkeley.EDU> I wrote:
>>A few simple rules for audio circuits:
>>
>>(1) Always use an aluminum electrolytic as opposed to a tantalum 
>>in an audio signal path (this applies not only to coupling caps,
>>but emitter bypass caps etc.).
>
>NO NO NO!  Aluminum electrolytics are better than the tantalums, but they
>are still pretty bad.  Use a plastic film capacitor (polypropylene is
>better, but polyester is okay).

Mea culpa.  I intended to say, IF the value needed is so large
than an elecrolytic is the only choice, always use aluminum, never
tantulum.  Otherwise, don't use an electrolytic at all!




>
>>(2) Polypropylene or polystyrene are good choices for equalizers
>>and such where some precision is needed.
>
>What does precision have to do with anything.  Most of these caps are 5%.
>(Electrolytics have very poor tolerances, usually -10%, +50%, which is
>not the only reason to avoid them, but a good one).  You can get high precision
>plastic film caps for eq circuits, but most plastic film caps aren't very 
>high precision at all.

Some equalizers and filters call for precision values.  Seimens
makes some nice 2% polypropylenes that are close to ideal.
I've also seen people use dipped mica's which come n precise values
but I'm not sure audio purists would agree with this.






>--scott

steve