Path: utzoo!attcan!uunet!news.larc.nasa.gov!grissom.larc.nasa.gov!kludge
From: kludge@grissom.larc.nasa.gov ( Scott Dorsey)
Newsgroups: sci.electronics
Subject: Re: How do I choose a capacitor type ?
Message-ID: <1991Feb7.145212.24656@news.larc.nasa.gov>
Date: 7 Feb 91 14:52:12 GMT
References: <64@owl.ukc.ac.uk> <10836@pasteur.Berkeley.EDU>
Sender: news@news.larc.nasa.gov (USENET Network News)
Reply-To: kludge@grissom.larc.nasa.gov ( Scott Dorsey)
Organization: NASA Langley Research Center
Lines: 25

In article <10836@pasteur.Berkeley.EDU> spp@zabriskie.berkeley.edu.UUCP (Steve Pope) writes:
>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).

>(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.

>(3) Don't use a capacitor with high hysteresis (such as a ceramic)
>as a sampling cap in a sample/hold circuit.

Don't use it for anything.  Throw it away.
--scott