This Envelope Follower PCB was developed for use in the cellF synth, it is based on the design in the Buchla Easel. Obviously it has a few changes; a gain pot rather than a hi/lo switch and a gate output. It is a wonderfully sensitive and expressive EF, that works nicely with regular microphones and guitars.
The 1/4" jack connects to the switch of the 3.5mm input jack, the outputs are pre-amp (20x gain), envelope and gate. The LED indicates when the gate is on.

These kits and assembled modules are offered on demand, click the link to learn more.