Kosmo 1222 source a reasonable LM4040AIZ 4.1?

In our application (the #1222), as you say the precision doesn’t matter thanks to the REF trim pot.
The main difference between the A, B & C parts and the D&E, is the temperature stability (±100ppm/°C vs ±150ppm/°C), but if you intend to keep the temperature mostly constant or are willing to re-tune when temperature changes significantly, it probably doesn’t matter all that much.

If my calculations are correct, the difference isn’t huge.
If you had a worst case of going from 0°C in a van to 45°C in a concert like Sam had:
The change in voltage would be ±100ppm/°C x 45°C = ±4500ppm
For the top octave at 4V, you get a drift of ±4500/1000000x4V= 0.018V
In musical terms, that is 0.018 octave x 12 semitone/octave x 100 cent/semitone = 21.6 cents
For the D&E parts, multiplying by 1.5 gives us 32.4 cents

Chances are that with such a large temperature change, you may need a tuning anyways due to other components’ temperature coefficient.

EDIT: I had missed the factor of 4 for the top octave in the first multiplication.

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