This was developed for the WAMod synth building workshops, but some PCBs and panels are available
PCB - US$18
panel - US$20
shipping - US$5 per order
A fairly straightforward envelope follower and an amp circuit giving up to 20X signal gain. It means you can connect a guitar or microphone to your synth and generate a gate, an envelope and the audio signal at standard synth voltage levels.
The envelope circuit has a 'response' pot which actually greatly increases the gain on the envelope and is useful for very low level signals, there is a trade-off of some distortion on the envelope at high gain settings.