I have no problem getting self oscillation anywhere further clockwise than 12:00 on the feedback knob. I don’t have an expression pedal yet, but I plugged a patch cable into the expression pedal jack and found that affects the response of the various knobs (they react differently than if nothing were plugged into the exp pedal jack). Interesting pedal, and I love it.
Memory Boy comes with a power supply, and the instructions say to use only the provided power supply. I don’t know the in’s and out’s of this, but I’d probably stick with what the instructions recommend. Have fun with your new Memory Boy!