The 230 is part of a proud tradition starting with the 130 module. Today's modern version is the 230e.
So what does it do?
An envelope follower (or a "Tracker" as the boys at Buchla like to call it these days) is a electronic circuit that takes a signal ( audible frequencies) as input and provides an output which is the envelope of the original signal. That is, it produces control voltages & pulses that are in proportion to (or at least resemble) the amplitude of inputted signals.
It's really nice for producing CVs from drum triggers but most audio with sharp attacks will work.
To quote the official Buchla website:
"In the direct coupled mode (sustained) , pulse outputs are activated when corresponding control voltages exceed 6 volts. Transient coupling permits the detection of attack transients in the presence of background noise and over a considerable range of amplitudes.
And now for some pics of the rear PCB: