🚀 go-pugleaf

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..."