LM13700 VCF
This design is originally by René Schmitz and is (half) an MS-20 filter but with an LM13700 chip instead. I have found a pretty solid layout on a forum called "electro-music.com" by user Clack, but since that topic is from 2010 I decided to try and fix it a bit:
A couple of changes on mine: 1) R13.1 and R13.2 was originally just one 10K resister but I've found that a bit loud and got a more stable but devestating result when putting a 6.8K and 2.7K resistor in parallel with eachother. You could manage using a 10K trimpot here as well of course!
2) The transistors T1 and T2 are reversed now and are 2N3906's. There wasn't a cut between the bases before, there is now.
3) Cut was removed for IC2's pin 11 connection to -12v rail.
4) I've actually put diodes in this layout, but on my PCB it has LEDs (any diode can be used actually, and they light up a bit when you have the resonance up... Bit useless when it's hidden inside your modular of course haha..).
5) I've used an LF347 instead of TL074 because I had them laying around.
If you follow this layout your filter should be working with both +15/-15v and +12/-12v.
Will edit this post with audio clips when I can.











