This is a Eurorack implementation of the Moog 912 Envelope Follower and trigger extractor.
The Moog
circuit is designed to work with input signal levels nominally around line
level (up to 1.4V RMS) although it will process up to 4V peak-to-peak – if using Eurorack level input signals they will
probably need to be attenuated.
The
module is unusual in that the CV output is logarithmically scaled - it
increases by 0.5V for a doubling of input signal amplitude.
I've added a V-TRIG output, and some optional additional output buffering.
This one has been on and off my workbench for about 4 years. The Norlin 1979 Schematic (Moog Modular Service Manual) contains a number of errors and inconsistencies, and I encountered some instabilities in the circuit that needed to be resolved.
Calibration was also a problem until I recently found the key information from the 1981 Moog Modular Users Manual "Control voltage drops
rapidly to -4V at levels less than -60dB" - hmm, shame they don't mention that in the service manual.
Video:
Please note while the build for this module is relatively simple, it can be very tricky to calibrate. I'll try and do a video of the calibration process soon.
