This is an envelope follower (EF) module with mic and instrument preamplifiers.
It is a design based on the ARP 2600. Aside from changing the op amps to TL074 and reducing the output stage gain (which it seemed to need, maybe because it uses ±12 V instead of the ARP’s ±15 V) the EF core is essentially identical to the original.
The ARP EF also has a preamplifier section for input of external, non-synth level signals. Rather than try to adapt the Teledyne 1339 based design I replaced the ARP preamp with two different preamps: One to boost instrument levels to synth levels, and one to boost mic levels to instrument levels — which then goes through the other preamp as well. The mic preamp is from a design by Andy Collinson (with a mod from here ) while the instrument preamp is based on the one in Ken Stone’s Stomp Box Adapter . The mic preamp jack supplies power for a two terminal electret condenser mic. For a dynamic mic you may be able to use the instrument input, though I have not tested this.
If nothing’s plugged into the synth input it uses the output of the instrument preamp, and if nothing’s plugged into the input of the instrument preamp it uses the output of the mic preamp. And if nothing’s plugged into the input of the mic preamp it uses the condenser mic capsule mounted on the front panel! Yes, this module is always listening, so be careful what you say. Besides going to the EF input, the instrument preamp output goes to a front panel jack, so you can use this module to feed external signals (or the front panel mic) to other modules too.