VCO hacks, tweaks

[Arthur Harrison]

On the subject of capacitors:  You can't find too many applications 
that demand more stability than theremins.  My favorites for less than 
1000pF are the silvered micas.  Good thing that they're still 
manufactured; I've recently seen them in surface mount, too.

I also like the KEMET NPOs.  I spoke with their factory the other day, 
and I was told that their CK05BX---K radials (very inexpensive!) are
actually made from NPO chips for values up to and including 220pF,
despite the "BX" (=X7R) marking.

-Art

-----Original Message-----
From: Grant Richter <grichter at execpc.com>
To: Synth-DIY list <synth-diy at mailhost.bpa.nl>
Date: Monday, November 02, 1998 10:01 PM
Subject: VCO hacks, tweaks


>A couple of odd notes:
>
>1. Main timing cap
>
>During the summer we had a problem with an ultrasonic oscillator for a
>customers product.
>The units wouldn't calibrate with the fan blowing on it. The original
>design used 1% (ouch) polycarbonate
>caps for tuning and 1% 50 ppm metal film resistors.
>
>The polycarbonates are listed at +150 ppm +/- 50 ppm per Deg. C
>
>I replaced them with KEMET ceramic COG caps and the problem went away.
>
>COG caps are rated 0 ppm +/- 30 ppm per Deg. C
>
>Something to think about....
>
>
>