Model-D help please: cv/gate IN problem

[galino]

The thing is the model-D was in really poor condition when I got it and I only recently got it serviced and partly restored by the only tech that still works on them in this country...

If it's not too personal, can I ask what country are you from ?

Also, if you disconnect everything from the Minimoog and play the keyboard on it, is it in tune ?

I'm in australia actually, there are lots of synths for sale here but not many techs will even touch analogues. The keyboard is perfectly in tune, only incoming CV plays out of tune, it's noticable but probably not so much across a small range of notes.

In a way it just wouldn't feel right to totally disconnect the keyboard. I still noddle around with it when looking for ideas or a certain timbre. Retuning the oscillators to match the mc202 would also throw the keyboard out of tune. I fiddled around with ms-02 interface for a while but can't find any way to rescale it from there either. It's quite annoying as I'm sure I had working and with both units in tune via the ms-02 at some point. I never would have thought external conrol of a minimoog would be this difficult. At least Kraftwerk made it seem so simple.

[thealien666]

Ok. I went and did some tests with my Mini. Controlling its pitch via the Oscillator Input control voltage on the back, from a MIDI-TO-CV interface on my modular. I also tried from my Korg Mono/Poly pitch CV out.

If I play the lowest C first on the Mini, to get the proper offset, then all the notes played via that external input are in tune and the scaling is good, at least from the MIDI-TO-CV of the modular. The CV coming from the Mono/Poly suffers from a slightly less than stellar scaling. But I know it's because that my Korg is not generating a very precise 1 volt per octave pitch CV.

So,

1- I would check if the MC202 is sending 1V per Octave from its pitch CV out, first.

2- If so, then I would check my connections carefully from it to the Mini (bad, or intermittent connections can cause all kinds of problems, as the relatively low pitch CV is quite sensitive to minute variations). Then, I would also check the (Bakelite) Cinch-Jones type six pins keyboard connector under the mod wheel assembly for intermittent or bad contacts. And at the same time, the Mod Wheel connector while it's accessible. The pitch bend wheel is continuously offsetting the pitch CV, even in the notch (middle) position.

Although all of the above (under item number 2) would only offset the tuning, and usually not affect the pitch scaling, it wouldn't hurt to check.

The very last thing I would do, would be to open the back of the Mini, and re-seat the oscillator board in its socket. Maybe pin 8A (ext CV in) isn't making proper contact ?

When things were working fine before and suddenly start to go wrong on their own, 90% of the time it's caused by intermittent or bad electrical contacts. The other 10% of the time, it's component failure, from my personal experiences.

Looking at the schematics of the MC-202, I noticed that there is a calibration trimpot for the D/A converter. But if the internal synth is playing and scaling fine, it's most probably okay because the output pitch CV is the same as the internal pitch CV. So if that calibration was off, the internal synth's scaling would also be off.

Pitch control voltages are so sensitive, that even a deviation of only a few millivolts can wreak havoc on pitch. That's one of the main reasons why MIDI was invented, over 30 years ago. Because controlling a synth from an external pitch CV is tricky, so say the least...

[CZ Rider]

I fiddled around with ms-02 interface for a while but can't find any way to rescale it from there either. It's quite annoying as I'm sure I had working and with both units in tune via the ms-02 at some point.

That MS-02 really seems like a very powerful interface tool. I do not have one here to actually test it, but it seems like Korg covered all the bases with the MS-02 including scaling to odd oscillator ranges.
Did you try using the summing amp to trim or add to the pitch voltage going to the Mini? Seems like a patch involving the adder section would solve the issue with not being exactly 1v/octave. I would try patching to either ch.1 or ch.2 input and tune the scale with the level knob. The setting at X1 being a starting point and see if the scaling can be tuned with that method. Depending on if you use ch.1 or ch.2 the other knob should be either a +5 (ch.1)or -5 (ch.2) voltage to offset and add or subtract to the overall tuning to get the C or whatever note you want to start at, or just leave it at zero..

If you did not have an MS-02, you would need to recalibrate the Mini somehow. But with that interface, you should be able to get many different brand oscillators to track many different voltages. So maybe it is just the way you patched it that you need to change. Just a thought.

[thealien666]

Good idea CZ Rider.

But since it's currently night time in Australia, we'll have to wait for him to try it, and get back to us...