[sdiy] Hand-matching capacitors for filter stages

[Harry Bissell]

LOL

I don't worry about 'sounding good' but whether the filter will be
stable with temperature etc. There is the matter of voltage non-linearity
with some capacitor types, I think there is a Walt Jung paper dealing with this one.

In a 'ladder filter' I have experience with using 10%, 5%, and 1% caps. The ability
of the filter to achieve resonance (oscillation) was greatly enhanced with the better
matched caps.

Probably the state-variable filter would benefit as well...

H^) harry


----- Original Message -----
From: David G. Dixon <dixon at interchange.ubc.ca>
To: 'John Mahoney' <jmahoney at gate.net>, synth-diy at dropmix.xs4all.nl
Sent: Tue, 9 Feb 2010 15:18:52 -0500 (EST)
Subject: RE: [sdiy] Hand-matching capacitors for filter stages

> >... What specific quality of polystyrene is so
> >desirable for filters, and how exactly does this enhance the filter's
> >performance?
> 
> I assume that you've read Harry's treatise?
> <http://www.musicsynthesizer.com/txt/caps2.txt>http://www.musicsynthesizer
> .com/txt/caps2.txt

Yes, several times.  It is largely silent on why a filter would sound better
with polystyrene, and says that mica is good, C0G ceramics are good, and
both polypropylene and polycarbonate are decent replacements for
polystyrene.  

None of this answers the original question, which was directed more at Tom
Wiltshire's breadboard experiments.  Specifically (and without trying to
sound too snarky), I'd like to know how the filter was better when one cap
was used instead of another.

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-- 
Harry Bissell & Nora Abdullah 4eva