Hi folks,
When I first powered these modules up one kept blowing fuses. It was wired incorrectly, with +12v connected directly to ground..!
So - after a few years of just looking at these Moog 701 drum synthesizer modules… and only ever making a couple of videos of them ‘singing away’ uncontrollably - but at least I knew that they made some noise… I have finally sat down and looked at them in depth.
First I had to build them their own dedicated power supply as the only other one I have is in the Modular. I have drawn out the circuit layout, and from those, the circuit diagrams. I’ve analysed the workings so to speak and got my head around them. Originally in my previous videos the filter and the envelope generators for both the filter & VCA weren’t doing anything.
Bearing in mind the earlier incorrect wiring I found, I investigated and found two more things… the first was a faulty transistor and once I had the EG’s doing their thing on my oscilloscope I found that the VCA was still not being controlled. The filter was now being opened and closed - but the module was still sitting there, merrily singing away. The problem, I hate to say, turned out to be what I reckon is a design fault…! The VCA on these things just doesn’t shut off.
I trawled the internet for transistor based VCA circuits and found a lot… all basically designed differently to the ones in these modules. So I built my own transistor based VCA going off the designs I found - and now it all works…!
I’ve played around with the unit and it does some interesting things using just it’s own internal oscillators. There are rear connector inputs for white, pink & red noise. I’ve yet to hook it up to some noise generators - which is where it should really come into it’s own… 
Cheers,
Tom
