So I populated my distortion/overdrive's board, and had the flying leads ready for connection to battery, pots, and jacks. Thought I'd get the 3 JFETS biased using the 100K trimmers before I installed the board in the enclosure.
'Twas an impossible task! The multimeter was hunting all over the place: I'd adjust for 4.5V, then the voltage would start decreasing, down to about 1V over the course of a minute. Turn the board over and the voltage would shoot up to 8V, 9V, and start going down again.
Surely a capacitor thing, I thought, so disconnected the big cap across the power supply. No change. Disconnected others: no change.
Anyways... finally discovered it was the flying input lead. It was about 15cm long and if I touched it, or moved it around, it affected the bias voltage . If I grounded the flying end, the voltage was rock solid.
So, indeed a capacitance thing, I guess, but not where I'd expected it.
IanG
Do you have a resistor providing a ground reference for the gate?