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Here just a quick summary and the pictures. It's about using a standard 270 degree potentiometer in a musical keyboard foot expression pedal that usually needs a 45 degree type of potentiometer. The trick is to use a low-power, rail-to-rail OpAmp to compensate the small movement angle.

The original pedal:

[Bespeco Volume Pedal]

The reference, the Roland EV-5:

[Roland EV-5]

How it looks on the synth side (newer use 3.3V):

[Roland U-20]

The compensation circuit consumes only about 300uA, not more than the EV-5 10k potentiomenter:

[Schaltung zur Drehwinkelkompensation]

Prototype, here without protecting diodes:

[Platine zur Drehwinkelkompensation]
2020 Alexander Mumm