@aaronpk thanks! Drone and trompette (buzzing) sound are acoustic, the melody is just the synth. Magnets in the keys + hall effect sensors on a board underneath, a magnetic rotary encoder on the shaft controlling noteon/off and expression, and an arduino inside the keybox putting it all together and sending MIDI signal out. The whole thing is built into the instrument, which also works great acoustic or amplified. There are a lot of improvements to make, but I think this is a good start!