[sdiy] NPO caps in P08 and Andromeda

[David G. Dixon]

Would anyone care to comment on exactly which property (or properties) of
the capacitors is (are) responsible for this noticeable improvement.

>From what I can tell, the big advantages of polystyrene over other caps are
their very low leakage, which is important for holding voltages for long
periods in S&H circuits.  However, would this be a significant issue for
filters?  (I don't know; I'm asking.)

Another issue is accuracy, which I would imagine is relatively important for
filters, but is unimportant for S&H circuits.  However, there are lots of
accurate caps which aren't polystyrene.

Finally, I understand that ceramic caps can self-resonate above certain
frequencies.  This would obviously be pretty devastating to a filter.
However, the frequency for self-resonance is typically well above the audio
range (the book in front of me says 100 kHz).

Polystyrene caps are expensive and a pain to get, whereas silver mica and
polypropylene caps are cheap and widely available.  If the capacitor doesn't
have to hold a charge rock-constant for a significant period of time, then
why bother with polystyrene?

Enquiring minds are dying to know...

David G. Dixon
Professor
Department of Materials Engineering
University of British Columbia
309-6350 Stores Road
Vancouver, B.C.  V6T 1Z4
Canada
 
Tel 1-604-822-3679
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-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Dave Manley
Sent: Wednesday, December 10, 2008 11:33 AM
Cc: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] NPO caps in P08 and Andromeda

I'm a little surprised someone hasn't modded an evolver and posted some 
comparisons.  If it made a significant audio difference, you'd think 
this would be a popular mod.

With regard to the S/H caps - I believe they are being refreshed at a 
high rate, so don't need big, high quality caps.

dragons wrote:
> Hi,
> well I worked on a Jen SX 1000  two or three years ago.
> and on the list of mods I found on the web, ( which the owner wanted ) 
> was to change the filter caps from ceramic to silver mica. ( or was it 
> polyester ? )
> I wasn't sure it would make much difference, but it made a great 
> difference. I would never recommend using ceramic caps in filters.
> regards Peter
> 
> 
> karl dalen wrote:
>> The P08 uses ceramic caps in the VCF and ceramic caps in the S/H.
>> The Andromeda does the same.
>>



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