Also, it’s worth noting that it took quite a long time before the wobble started for me. I suspect the 220R slowly fails over time somehow. I did check the resistance of the ones I pulled. All remained at 220R. Not sure what’s up, but the heat has something to do with it.
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I’m still seeing instability with 1k in the higher octaves (likely more noticeable). I might try swapping to 4.7k resistors next just to see.
Same here, but I didn’t watch it live, so I couldn’t say anything.
I suspect it’s the LM4040AIZ that starts acting up as it is pushed outside of its specified working area.
It is also possible that the resistance changes value as it heats up and returns close to its nominal value after cooling down but that is somewhat unlikely as we are only pushing it a bit out of its range whereas the LM4040AIZ is well out of its range (more than 2x the maximum allowed value), so it is more likely to malfunction.
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Do you think the LM4040AIZ is likely to be permanently damaged after having started to show this drifting behavior? I’m wondering if it would make sense to replace it if a module is showing residual issues.
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I don’t really know enough to say.
But it’s certainly possible.
If a module is showing residual issues, it is probably worth replacing it to find out if that is still the cause.
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Almost every datasheet says something like :
LM4040 (Texas Instruments) :
MCP4822 (Microchip) :
Do they have the same law specialist ? 
So yes, the LM4040 may have been damaged by the excessive current…
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Alright, I need to get another one in order to build my third oscillator anyway. May as well get a couple of extras to replace the old ones. One of them has started acting up again. Interestingly not the one that had it the worst before.
Good point and from the TI datasheet,
with a reverse current of 35mA the 220R resistor definitely pushes it into the no-no zone.
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Will have to get mine updated…
I have work in progress to have another 5 Custom Versions of the 1222
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Funnily enough I had already replaced the 220r resistors for all four vcos with 1k ones as per forum suggestion so that does seem to be the issue at hand. It turned out that I hadn’t switched the octave selector switch to the utmost left position before adding that little non turn washer. I fixed that and the fourth vco all of a sudden started to function just as it should. Now I have 4 vcos the sound just right but only 3 that go up to 4V at the test point the fourth one is still just stuck at roughly 3.3 V Has anybody any other ideas what could be the problem. I would be really thankful
The relevant part of the schematic is:
with of course a 1k resistor for R42. Measuring the following points with the other multimeter probe at a ground point should give you:
Left end of R42: 12V
Right end of R42: 4.1V = pin 2 of U4 and pin 3 of RV3
Pin 3 of U4: 0V
Pin 1 of RV3: 0V
Pin 2 of RV3: 4V after trimming = TP1
If you don’t have 4.0V at TP1 then either:
- You don’t have 12V going in.
- You do but you don’t have 4.1V on pin 2 of U4 which means that voltage reference is faulty or misconnected
- You do but you don’t have 4.0V at TP1 which means the trimmer isn’t set right, it is faulty, or it is misconnected
I don’t see any other possibilities.
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If your trimmer is 100R 400R instead of 100k you might get something like 3.3V there.
EDIT:corrected bad math.
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Update: I swapped out the LM4040AIZs on all my oscillators after upping the resistors to 4K7. After testing for a few hours, the wobble is gone for me. On to the next gremlins and maybe some music! 
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After a couple of days since I swapped mine, I also have stability again!
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Good to know as I’ll start building next week-end.
So up from 220R to 1K to 4K7.
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I’m sticking with 1K for now, but sure if 4K7 works, why not?
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I wonder why the 1222 outputs are not terminated with resistors to gain 1k impedance, as the kosmo specs say.
Is this already done by the 3340 IC?
The “spec” is more guidelines than spec, Sam especially is free to do whatever the hell he likes.
We tried to capture what he has been doing in the “spec” wiki so that other designers can have a chance at being compatible.
The 1K output resistor is more for output short circuit protection than for impedance matching.
(1K outputs and 100K inputs are fundamentally mismatched impedances by “spec”, but at audio frequency it doesn’t matter.)
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Mismatched for power transfer, indeed, but for voltage transfer you want output ≪ input to maximize the voltage and minimize the current (i.e. bridging, not matching).
(the TL07x’s output stage has an internal resistance of around 200-300 ohm iirc, but the effective output impedance depends on gain)
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And as has been discussed elsewhere, a TL07x can survive a short to ground or either rail indefinitely. Still, 100R to 1k output resistors are so common, their absence is a little surprising. You could always add them on the output jacks, of course.
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