Envelope Filter
My take on the classic Mutron envelope filter using a single supply (the Mutron uses dual +9/-9V). The envelope follower is quite different, but it’s easier to implement with the single supply. The Vactrols I used were the homemade shrinking tube LED/LDR kind. Didn’t include the “wah/wow” switch in the diagram, but it’s easily doable. I also omitted the High Pass output, but that was just a matter of only having SPDT switches instead of SP3T one. I also included a Frequency potentiometer and separate Gain and Sensitivity controls for more versatility. There are Attack and Release pots also, but they are maybe kind of control overkill. Fixed resistors can be chosen, or even trimpots instead of pots, with no great loss of sonic possibilities.
REV: the actual opamps used were LM324’s. The TL’s wont have enough current output to drive the LED’s.