Minimoog Model D modification

[Reverend Sunrise]

What's up everybody. I have had a Model D for the past several years and have never tested out the modifications it had when I bought it. (Guess this beast on it's own has been more than adequate for my needs!) I'm assuming that it is some kind of CV Gate mod, but that is unfamiliar territory for me and I was hoping somebody on this forum has experience with with such a modification. On the front panel, there is an "EXT CV" switch, and an "EXT" knob. On the rear panel, from left to right, there are inputs labeled "LFO," "MOD," "BEND," "CV" and "GATE." Anyway, just trying to figure out exactly what's going on with it and maybe the best way to go about testing it. Appreciate your time.

[Don T]

What's up everybody. I have had a Model D for the past several years and have never tested out the modifications it had when I bought it. (Guess this beast on it's own has been more than adequate for my needs!) I'm assuming that it is some kind of CV Gate mod, but that is unfamiliar territory for me and I was hoping somebody on this forum has experience with with such a modification. On the front panel, there is an "EXT CV" switch, and an "EXT" knob. On the rear panel, from left to right, there are inputs labeled "LFO," "MOD," "BEND," "CV" and "GATE." Anyway, just trying to figure out exactly what's going on with it and maybe the best way to go about testing it. Appreciate your time.

I think the first big step would be to open it up and verify what kind of jack is being used for each function. I.e., stereo vs. mono, switching vs. non switching. If they are stereo jacks, and have a wire attached to the tip, the ring, and the sleeve, they will most likely be looking for both positive and negative going control voltages. If mono, or stereo wired with no connection on the ring, you'll need to verify which kind of control voltage it'll be expecting.

Second step, before trying to feed any control voltages into the thing, trace each wire to wherever it is patched into the synth, and the method by which it is patched in. For example, does it have an added buffer, or a reverse-current protection diode, or does it go straight into the board? Once it is traced and connection method determined, make sure that each wire is connected to the correct place for its intended function (i've made good money from time-to-time by undoing other people's botched mods). Use a schematic (and make sure it is the correct schematic for the version of your Minimoog) to check this. Each function, excepting for "GATE" should be tied into its corresponding control voltage mixer, with its OWN resistor going into the mixer, not simply a wire grafted onto another input.

If in doubt on anything that has been done, feel free to post questions and or pics of anything questionable, there are plenty of folks here who can help figure out what's been done, and if it is correct. Assuming the synth is working fine, and someone actually used those functions before successfully, everything may be ok. If it was my Mini though, I'd double check if I wasn't sure.

Good luck!

[analoglsd]

What you have is a standard mod that was usually done by Studio Electronics in the 80's.
The mod was meant to interface with the Roland MPU-101 MIDI-to-CV converter so you could control all of those parameters("LFO," "MOD," "BEND," "CV" and "GATE") via an external MIDI controller.
I've had about 3 different Mini's with this mod, and at least 2 of them were total hack jobs that I ended up paying hundreds of dollars to have removed.
Hopefully the one in your possession was installed competently and is functional.

[Reverend Sunrise]

I appreciate both your responses to me quarry...that definitely helps clarify the situation. I originally got this Mini from David White up at AnalogKeys in Cambridge, Mass. I've bought several synths from him over the years and all of them worked perfectly, and I'm pretty sure that he told me that it worked back then, but h**l, I really dunno! In terms of the simplest and most straightforward way to test this mod on the MIni, would I need to have a Roland MPU-101 or would it serve any purpose at all or even be possible to test it with any other kind of midi/cv converter? I'm completely ignorant of this s**t! Thanks for your help.

[analoglsd]

If you have another synth with one-volt-per-octave CV and Trigger outs, you can at least test the CV/Gate.
You don't necessarily need an MPU-101, to test it out, that was just kind of cutting edge at the time, so it was adapted.