Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!uwvax!astroatc!nicmad!kunert From: kunert@nicmad.UUCP (Dick Kunert) Newsgroups: sci.electronics Subject: Re: Appropriate use of capacitors Message-ID: <1849@nicmad.UUCP> Date: Thu, 6-Aug-87 18:29:53 EDT Article-I.D.: nicmad.1849 Posted: Thu Aug 6 18:29:53 1987 Date-Received: Sat, 8-Aug-87 18:06:32 EDT References: <1108@rtech.UUCP> Organization: Nicolet Instrument Corp., Madison, WI Lines: 50 Keywords: capacitor Summary: Good magazine article In article <1108@rtech.UUCP>, jchan@rtech.UUCP (Jeff Chan) writes: > > Here's a question for you old farts, audiophiles, and EEs: > > What are the appropriate uses and benefits/disadvantages of all the > various types of capacitors? For example, electrolytics are often > used in power supplies. I suspect that polycarbonates are thermally > quite stable. > > I am curious about ceramics, tantalums, electrolytics, metallized and > foil film capacitors with mylar=polyester, polystyrene, polypropylene, > polycarbonate, teflon, etc. Please post to the net. In February and March, 1980, "Audio" magazine published a two part article on picking capacitors. See if your local library can get it for you. Without going into too much detail, for audio applications you want the lowest possible dielectric absorption and dissipation factor. Polystyrene, teflon and polypropylene caps are among the best, polycarbonate nearly as good, and polyester (mylar) caps not as good but still much better than electrolytics or ceramics. The article went into a fair amount of detail on why you should never, never put any kind of electrolytic or ceramic cap in your signal path. Basically, dielectric absorption is a "memory" effect- when the cap is discharged it doesn't *stay* discharged, but builds up to some percentage of its previous voltage. This causes a sort of low level "grundge" in the signal. A high dissipation factor will cause phase and amplitude to vary non-linearly with frequency. Most mid-fi audio gear has aluminum electrolytics liberally sprinkled throughout the signal path. Some of the more enlightened manufacturers bypass the electrolytics with small film caps; this is sort of a compromise. High end manufacturers often use polypropylenes , etc. but this is directly reflected in the price (look up pricing for a 10 uF, 35 volt polypropylene cap sometime). The film caps are also quite LARGE. > P.S. not to start any controversies, but I have heard audio differences > between electolytic and polypropylene dc blocking caps in disc players. > The film caps were pretty close, and the 'lytics did bad things to sound. > You can *easily* test this yourself. Just put some big caps on a switch > in series through a tape loop and switch them. Electrolytics do sound bad, but to be fair you really need to supply sufficient DC bias so the signal doesn't reverse-voltage the caps. -- ihnp4-\ "I'm looking for a lifestyle Dick Kunert seismo!uwvax!nicmad!kunert that doesn't require my decvax-/ presence..."