I spent some time on the drift topic, finally!
The module I used for testing seems to have different issues. (the black edition). It already comes with a drift of 3Hz without modification and octave switch troubles in the middle position (F instead of C).
However, I replaced it with another module (yellow edition).
The results are:
| modification | drift at | drift at | drift at |
| | 130Hz (C3) | 260Hz (C4) | 520Hz (C5) |
----------------------------------------------------------
| none | -1Hz | -2Hz | -5Hz |
| R13 200k | -4Hz | -8Hz | -17Hz |
| R13 200k + 5M | +1Hz | +2Hz | +4Hz | (positive drift!)
| R13 200k + 6,6M | -0Hz | -0Hz | -1Hz | (10M and 20M in parallel)
| R13 200k + 10M | -1Hz | -2Hz | -5Hz |
| R13 200k + 20M | -2Hz | -6Hz | -11Hz |
| R13 200k + 30M | -3Hz | -6Hz | -13Hz |
RT-65B psu | saw wave used as reference |
V2 centered no CV signal
Practically, 200k // 6,6M even reduces the drift compared to no modification!
It also nice to see the drift is scaling.
EDIT: updated table with more measurements.
EDIT2: replace 7,3M with 6,6M. (my brain went off for a minute!!!)