Steiner-parker synth from the 70's. i ordered the PCB from ken's site http://www.cgs.synth.net/modules/cgs35_syntha_vcf.html
along with two others. this filter needs +/- 15V dual power supply which I've built on a small veroboard.
The filter is quite a simple circuit, and while you need to mod it a bit for the "right" resonance tone
(details on ken's site) this filter is a beast !!! the LP BP and HP are fat and juicy and when turning the resonance pot to the max this thing screams. you can also mix between LP BP and HP incoming signals and this sounds really special.
for the price (10$ for the PCB) and about 10 $ more for the parts this VCF is just amazing.
ken's modules are great and i will surely buy more when i'll have more time for building them. then i'll add them to my small DIY never ending modular synth . i also bought the Burst Generator PCB, and the Super Psycho Lfo which I've almost finished. great stuff!
The Super psycho Lfo and the Steiner VCF
The Steiner VCF
ken stone burst generator
Dual 15v psu