Mike Walters is a musical hardware hacking genius. He built an arm-keyboard for Devo. And a whole bunch of other sound-tastic gadgets that are impossibly beautiful. His latest is this Mellotron keyboard powered by classic Walkmans. The Mellotron was a popular 1960s instrument, and Walters has gutted one and replaced the innards with Sony cassette tape players. The first Walkman plays drum beats, the other 13 provide sampled loops of 25 different notes. The cassettes are constantly running, and pressing the key unleashes the different notes. It's all explained in loving, technical detail on his Mystery Circuits website.