Gianluca, Thanks so much for posting your pics. I found them to be very interesting. I’d like to do something similar. I tried piezo pickups (3 of them) on the inside of my P37. They worked, but there was way too much key noise. I bought a Hammond 44 and so I ended my experiment with the pickups. I WISH that Yamaha would offer an electrify kit for their P series melodicas. If it mimicked the Hammond system, it would just need to be a replacement end cap with a mic in it and a volume control. They’d sell a bazillion, I’ll bet! An incorporated pre-amp would make it even better.