Model 10 Calibration

[PaulLawler]

I've had my Model 10 for a couple of years now and pretty much gave up on the oscillators because of the poor tracking, even with the scaleable tracking on my Kenton Pro.

Last night I saw a Model 10 youtube video and the tuning over several octaves seemed pretty good, even matching well between the 901 and 901b, and mine dont get close.

This made me think that mine actually might need some kind of recalibration and I wondered how that's done, and if its technically easy enough to do myself ?

Thanks.

[ProspectHillMusic]

The Technical Service Manual for the Moog Modular System can be downloaded from several sources and it contains the adjustment procedure for tuning the 901A and 901Bs. If you follow the tuning instructions exactly I think that you will be OK but the more knowledge and experience in electronics you have the easier it will be.

I'm curious, do you have a Model 10 reissue or a vintage system? If you have a reissue I would have assumed that it would have been tuned at the factory and wouldn't have drifted as much as you indicate since it was shipped to you.

[PaulLawler]

It's the re-issue yes, but not the very latest one with improved tuning from last year.

My 901 can be in tune on middle C - one octave above that is +23 cents, and one octave below is -39, anything beyond there is pointless. That's with the Kenton Pro 2000 Mk2.

The 901 a+B combo can be ok for around 4 octaves after many hours warming up, although I tend to bypass these for the Synth-Werk clones if I'm in a rush.

I'll check for these resources. I have very limited electronics knowledge but if it can tell me which pots to turn then I'll be fine.

[PaulLawler]

Just a bit more info for anybody wanting the same solution :

The 3 pots on the left hand side seem to be for tracking and I managed to extend the range from less than one octave to 3.5. Oddly this morning that had extended to 5 octaves while completely cold, but seems to be getting less and less while warming up, currently around 2 octaves .... so no idea about that sorcery.

Moog tech support suggested I use a Kenton, or their 953 keyboard. They seemed to have ignored my request for trim pot information. Maybe they don't understand it ?

[analogmonster]

I think the 953 won't help you. I cloned the original circuits of the 60th with more or less original parts and got the same problem. See http://www.analog-monster.de/mmt901_en.html. Forget the part of the Conclusion. The temperature drift came back later. The calibration of the 901* is very nonpermanent due to the CA3019 diode array compensation circuitry in the 901A. I calibrated it more than once, but doing this repeated is an anoying pain in the a$$.
Do you have a service manual of your system? Does your 901A still use this original technology? In this case I would say that there is not much you can do. I use my 901* clone with my T960 sequencer clone. With an analogue sequencer you have to adjust each note anyway. For playing with my T950 keyboard clone I use my MINI oscillator clones which use a CA3046 based heated transistor array for temperature compensation. This works much better and is still stable. I keep my 901* oscillator clones though because they have a wonderful wave shaper which sounds very nice.
My recommendation is: Play the 901* oscillators with an analogue sequencer like the 960 or similar. If you want to play your system with a keyboard only, replace the 901 oscillators with other oscillator types or clones.

[ummagumma]

I wonder if there is a way to build a temperature box around that part of the circuit? Seal it off & add some kind of temp sensor that would keep it stable

[analogmonster]

I wonder if there is a way to build a temperature box around that part of the circuit? Seal it off & add some kind of temp sensor that would keep it stable

Some people do that indeed, but this is only a part of the show. The point is that you have two different and independent temperature curves in your VCO. First is the circuit itself which heats up due to current consumption. Next is the outer temperature of the room your modular resides in. If you use a TempCo solution to compensate it is nearly impossible to lay the compensation curve exactly on the circuit curve, and the outer temperature is not considered neither. So the Temp isolation solution with sensor and compensation circuitry is only the half of the rent.
A better solution is to use a heated transistor array. Standard VCO circuits use an array of 5 like the CA3046 or CA3086. Two transistors of the chip are used for the exponentiator, one is the sensor for the compensation circuitry and two just consume a defined current without any technical or electronic function. They just heat up the transistor array chip to a configurable temperature. And this artificially created temperature is independent from circuit heating up and outer studio temperature.
The time until your VCO is "online" and stable is maximum the heating up time of the array. That is very fast. And it works in weird temperature ranges. I know a guy who freezed a VCO in his freezer to minus degrees, took it out and connected it to his modular immediately, and it worked stable and in tune.
So I recommend this as the temperature compensation solution for any VCO.

[ummagumma]

Good info: is that what the Voyager uses?

Maybe I'll build a modular cab that doubles as a beer fridge

[analogmonster]

Good info: is that what the Voyager uses?

At least: nearly. The Voyager oscillators use the MAT04 transistor array with 4 transistors, not 5. But the components "exponentiator", "heater" and "sensor" are implemented according to the schematics. So the VCO stability should be similar.

[ummagumma]

Good info, thx!

Do we know what Moog did to improve tuning on the rev2 RI model 10?

[analogmonster]

Do we know what Moog did to improve tuning on the rev2 RI model 10?

I don't have any info, unfortunately I really would like to know whether they replaced the CA3019 diode array solution of the 901(A) with something that works. So if anybody of the Model 10 RI owners could provide a service manual and / or the schematics, that would be great.

[ummagumma]

Or maybe a gut shot would reveal which IC's they used?

[analogmonster]

Or maybe a gut shot would reveal which IC's they used?

Well, seems that someone did this with Gene Stopp, who is one of the Moog Modular Reissue architects and techs and whom I wanted to ask about the 901(A) reissue:

https://forums.musicplayer.com/topic/18 ... ene-stopp/

Very sad to read this. We communicated some years ago because he was interested in my inductor sets I build for my T914 Fixed Filter Bank clones for the new 914 of the Moog Modular Reissues.

[ummagumma]

Yes that was terribly sad news to hear. I'm surprised there wasn't more forum activity about it.

I posted about Herb Deutsch & there wasn't much of a response here either.

RIP both...

[analogmonster]

Yes, Herb and Bob - the pioneers of modular synthesizers. They gave inspiration to all of us.

I found an old post of noddyspuncture where he answered my question concerning temp stabilisation:
viewtopic.php?f=18&t=35289
where he says that there is a tempco solution nowadays.

That is better than the diode array, but still not that efficient like a heated transistor array.