Model-D help please: cv/gate IN problem

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1

I usually control the Minimoog model-D via S-trig IN and Osc IN from an mc202 sequencer via the korg ms-02 interface. It can take a bit of fiddling around sometimes as I’m not very ‘technically-minded’ but usually I can get the model-D in tune with the mc202 sequencer and once I get the right settings I leave in so as to prevent further headaches. But now I find the model-D is way out of tune, and I haven’t altered anything. The keyboard plays fine but seeing as most of the music I would make is of triggered notes this is a big problem.

I use the same setup to trigger and an MS20 and it plays fine so I’m pretty sure the problem is in the model-D.

Has anyone had this experience or can shed some light on the situation. Also very sorry if I didn’t explain this too clearly.

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The Korg MS20 is a Hertz per Volt controlled synth, whereas the Minimoog D is Volt per Octave. They are completely different ways of controlling pitch on an analog synth, and completely incompatible.

The Roland MC202 is already a Volt per Octave device. directly compatible with the Minimoog system. The MS-20 on the other hand needs to be controlled from the Korg MS-02 adapter, to provide Hz/Volt it needs, and not directly from the Roland MC202.

If you send the signal from a Hz/Volt device to a Minimoog D it will be impossible to get notes in tune. You need to send V/Oct control signals, either directly from the MC202 or the V/Oct output from the Korg MS-02.

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Yes, the ms-02 interface converts the hz/volt signal to volt/oct. So from the mc202 sequencer a signal goes through the ms-02 interface where it is converted and then to the model-D and it usually works fine and isn’t a problem. Now overnight it will not control the pitch of the model-D, it’s all out of tune, half steps or something and not the 12 notes of a keyboard octave, if that makes any sense. The model-D keyboard conrols the pitch fine but I mostly control it with a sequencer. Many thanks for the input though I know the model-Ds are old and temperamental units and probably quite common to have this sort of problem.

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You didn’t read my last message carefully.

You don’t need to pass the CV coming out of the sequencer thru the MS-02 to control the Minimoog D.

You can control its pitch directly from the MC-202 sequencer.

Try that first, before assuming that there is something wrong with the Minimoog, and tell us if that works ?

5

Regardless of it being fed correctly scaled 1v/oct CV, it may still drift over time.
Not so much from temperature or instability, but that the ext CV is ADDED to the keyboard CV.

When a key is hit and released, the keyboard CV is held in a circuit which will not stay stable over time.
Yes, a key could be held down and it wouldn’t drift, but then it would no longer gate from the sequencer since the keyboard is also supplying a gate.

This is a problem not of the Minimoog, but of the assumption that the ext CV jack can be used from a sequencer just like the keyboard.
In truth, the keyboard transposes the ext CV and/or the ext CV transposes the keyboard.
The ext CV and gate doesn’t replace the keyboard, it only adds to it.

To get around the problem, one either needs to mod their Minimoog or use a custom cable that replaces the keyboard CV and gate entirely.

6

Right, Kevin.

I had forgotten that if he didn’t press down a key for a long time on the Mini, the pitch could have drifted enough to be untunable.

As you said:" To get around the problem, one either needs to mod their Minimoog or use a custom cable that replaces the keyboard CV and gate entirely."

Or he could also have an Opto-Key installed. That would also fix the drifting issues, since that board is generating a continuous pitch CV. And he would get MIDI to be able to control his Mini from a more versatile sequencer than the MC-202. But he might cringe at the idea of spending six hundred smackaroos on it though… Just a thought, in case he didn’t know that possibility does exist ? :mrgreen:

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It’s starting to sound like you’re the most unhappy with the price of the Opto-Key. :wink:
I can only apologize so far.
Assembly and testing one is no breeze, but the electrical, PCB and software design definitely added up.
The project has yet to pay for itself and with such a small market, may never make a profit.
If I got, say, 10 people who said they’d buy one if the price was lower, perhaps we could find some middle ground, but this is unlikely.

Regardless, he noted he wasn’t technically inclined, so either way he’d have to pay a tech to mod it.
It IS possible to mod a Mini with CV and Gate inputs that replace the keyboard signals.
No holes drilled, but still the need for a tech.

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Hey Kevin, surely by now you must know that I’m only kidding you ? :wink:

I’m probably also the most enthusiastic customer about this ! :smiley:

Anyone who can afford to buy a Minimoog D, especially at the current market prices, can surely afford your product to fix its keyboard for life. Unless one has spent his or her whole life’s worth of savings to get a Mini! :laughing:

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Pretty much. :slight_smile:
I mean.. it works and no one has complained and this is what means most to me.
But I do admit it’s a tall price, so perhaps it’s more appreciated by those that have had Minis for years and are tired of cleaning their contacts?
Anyway, I’m not too affected and DO appreciate both your business and reviews.
Thank you very much!

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Firstly I just wanted to say a big thanks for all the feedback, it has been a great insight.

Alien666, I did now send the CV directly from the mc202 to model-D and yes it works better, but still noticably out of tune when I run a sequence across several octaves (meaning the lowest note of the sequence is lower on the model-D than on the mc202 and the highest note is higher). 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, now I wish I had encountered this problem before sending it to him. I’ve tried to use it at least daily since that time.

Am I able to retune the model-D from the back panel? will that even effect the CV IN or just the keyboard? Personally I would rather not tamper with it too much.

Yes, I much prefer to use CV/gate and never use midi. It’s quite primitive but I’ve become something of an expert of programming with mc 202 sequencer.


Kevin, what is this custom cable? it sounds appealing but what does it plug into on the model-D? and are they available?

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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 ?

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The custom cables I occasionally build are at one end, two 1/8" plugs (CV and gate) and the other end, a 6 pin connector that’s the same as the keyboard has.
One unplugs their keyboard inside and plugs this in instead.
Then the keyboard no longer operates, but the new CV and gate plugs work perfectly and with no drift.
Obviously it’s a trade-off- one or the other. (keyboard OR external control; not both.)

If you scale the oscillators in back, they may be able to track the 202 better, but the keyboard will likely not be in tune any longer.
There’s no scaling or tuning just for the keyboard.
The oscillators are normally tuned to the keyboard.
Tune them to something external and the keyboard may no longer match.

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After resolving my tuning issues with you guys help (thanks) I was able to sequence the mini with the mp201 from logic with almost perfect tuning. The scaling is quite a bit off, like about 1.15, but it works. To the OP does you sequencer have scaling?

Also, not that it matters, because I don’t really sequence much, but how is it you change the scaling on the mini? I mean besides tuning the pots on the back, because the scaling turned out to not be close to 1v, yet its in perfect tune and the keys track perfectly at 1.15 or whatever. I should just leave well enough alone, just curious.

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I’m not as experienced as others at fixing Minimoog D’s, but all I can tell you is this: if you need something like 1.15 volts per octave in order to get correct scaling on yours, there must still be something wrong with it. Maybe in the exponential current converter circuit ?

Because on mine, the Opto-Key is generating an absolutely precise 1.00 volt per octave (more precise than the original keyboard resistors in fact) and I managed to calibrated it, with the scaling trim pots, exactly in tune accross the keyboard and on all octave ranges.

To my knowledge, those scaling trimpots are the only way to adjust scaling on a Mini.

But Kevin might also know something I don’t about it, as is often the case ? :mrgreen:

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In short, the Mini’s oscillators should be tuned to its own keyboard and the 202 should be calibrated to the Mini’s oscillators.
There is no adjustment for keyboard scaling on a Mini, so one has to adjust what is sending it CV. In this case, the 202.
You could tune the oscillators to track the 202, but then the Mini’s own keyboard would be out of tune.

16

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.

17

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…

18

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.

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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… :wink: