Unusual for me to look for something simple, but I can't find my bag of optos at the moment and I don't want to go the OTA route. I have seen such a VCF circuit but where???
This was on Jürgen Haible's site, the description says 'How to build a fully polyphonic instrument in 1975: thyristor VCO, one-transitor VCF and one-transistor VCA. And don't forget the single opamp that works as saw wave buffer and PWM comparator !'
http://www.jhaible.de/pe1000_1.gif
the filter looks pretty simple to me, but I'm a bit of a novice with filters.
Go PAiA.
page 11-12 here: http://www.johnnypumphandle.com/johnny/Paia/Paia_synth_manual.pdf
Wonderful, thanks very much.
Another good one here http://www.aleph.co.jp/~takeda/radio/MS20clone2E.html (http://www.aleph.co.jp/~takeda/radio/MS20clone2E.html)
Quote from: slacker on October 01, 2010, 12:07:56 PM
Another good one here http://www.aleph.co.jp/~takeda/radio/MS20clone2E.html (http://www.aleph.co.jp/~takeda/radio/MS20clone2E.html)
Many thanks
There is the passive PAiA 2720 stuff:
http://experimentalistsanonymous.com/diy/Schematics/Filters%20Wahs%20and%20VCFs/Paia%202720-3l%20VC%20LPF.gif
http://www.freeinfosociety.com/electronics/schemview.php?id=389
Quote from: Cliff Schecht on October 01, 2010, 07:26:06 PM
There is the passive PAiA 2720 stuff:
http://experimentalistsanonymous.com/diy/Schematics/Filters%20Wahs%20and%20VCFs/Paia%202720-3l%20VC%20LPF.gif
http://www.freeinfosociety.com/electronics/schemview.php?id=389
Thanks Cliff,I hadn't seen that.