SVF based Stereo Harmonic Chopper-Tremolo Setup

[Mr. Lime]

Some years ago I planned building a harmonic trem with wah functionalities to recreate an effect I once used on an old Zoom multieffect board. The trem LFO frequency went up when the wah shifts to highs and vice versa - I loved it. When I moved to another PC I lost my final PCB design and documentation but from todays perspective, there was room for improvement for sure.

Now when I think about it again, I would like to discuss with you guys, how the setup could be done.

I would take the highpass and lowpass outputs of a state variable filter and add a variable resistor to each path.
With a on-on-on switch, someone could choose between HP, dry or LP combinations, 2 of them are always selected and run to a stereo output for panning effects. The frequency control of the trem LFO and the frequency control of the SVF would be tied together on a wah rocket pedal or via CV input.
Obviously a MCU should be used for the LFO to add neat features with small space needed. The variable resistors get modulated antiparallel (a control for 0-180° phase shift would be awesome to blend between harmonic and classic trem, but not a must).

I always loved when percussive trems have a very wide frequency range so that they could be used as chopper/pseudo ringmod. LDRs would be the easiest way but probably not the best as they are rather slow. Some bitcrusher designs use jFETs or OTAs for ring mod sounds. The LM13700 seems interesting but I read a lot of problems setting them up without carrier bleeding, otherwise I had seen it as an elegant solution for this effect. Any suggestions appreciated!


If a MCU with high PWM rate output is used, can a CD4040 divider be used to bring the range down to usual trem rates or is that a bad idea?

Here's a circuit to show what I'm roughly looking for with the ringmod/chopper part:



I also wanted to ask about you guys opinion on this SVF which has the frequency control placed untypically in a feedback loop:



For reference, I think the Spaceman Delta II is a close commercial design (without the possibility to control the SVF frequency shift by foot or beeing stereo.

Looking forward to your experiences!