[sdiy] Filter strangeness.

[synth at oldmail.charlielamm.com]

> If you wanted a photo resistor to vary cutoff, how
> would you setup the input
> stage?

You can use opamp, with a transistor to up the current it can
source...examples on my site.  Look at the circuit fragment surrounding 
IC1D.

http://www.charlielamm.com/synth/vactrolvcfsch2.pdf

Vactrol filter page is here.
http://www.charlielamm.com/synth/vactrolvcf.php3

There are other ways to do this...eg, check out some of the buchla clones
for instance on Verbos site, buchla is the grand master of using
photoresistors to do clever things.

http://www.simple-answer.com/DIY.html