The revision A power supply board in mine has a date of 11-4-22. This has been a pretty long trial run.
they have been fighting this circuit for a year already.
Maybe I can help them with a few design tweaks for preamp Revision D.
In just 16 days I have already fixed a lot:
adjusted the gain of the 2nd stage to match a balanced +4dB hot input signal.
Entirely rebuilt the 4 band EQ, while leaving the stock eq intact for a/b
Tuned the crossover to eliminate the frequency notch
Now I'm looking at the power supply to see if I can adjust the regulation to +/- 18v (not 18.6v) ... and I'm fine tuning the pot tapers on my bass and treble pots.
Then I'm done.