This is a Moog-inspired Voltage Controlled High-Pass Ladder Filter clone, based on the High Pass Filter by EFM (Electronics For Music).
The final circuit is also directly inspired by the comments and suggestions from Kristian Blåsol in his video Moog Highpass Transistor Ladder Filter – DIY Modular in a Week 7.5.
A couple problems have been pointed out in V0.1:
- The lower Cutoff frequency was quite high. Even when applying a negative CV and turning the “Cutoff” potentiometer, it stayed high.
- The CV input had low impact on the Cutoff frequency.
- The resonance was almost always present, even on low setting.
These are the upgrades in V0.2:
- R2 and R3 (100k) have been replaced by 10k resistors. The CV should have more effect, both on Jack input and on the potentiometer.
- Pin #1 of potentiometer R1 (“Cutoff”) was connected to GND. It is now connected to -12V, it should drastically allows a wider and lower Cutoff frequency range.