[Scott Campbell] built a cassette-based synthesizer that sounds exactly like everything you’ve heard before. The sound generation comes straight off cassettes, but the brainbox of this synth varies the volume and pitch. It’s called the Onde Magnetique, and it is what you would get if you combined a Mellotron and Ondes Martenot.
The key component for the Onde Magnetique is a Sony cassette recorder that conveniently and inexplicably comes with a ‘tape speed input’ mini jack. By varying the voltage sent to this input jack, the speed of the tape, and thus the pitch of the sound being played, is changed. Build a box with a touch-sensitive button for volume, and a few tact switches for different speeds, and you have an electromechanical bastard child of a Mellotron and an Ondes Martenot.
By itself, the Onde Magnetique produces no sound – it only controls the pitch and volume of whatever is on the cassette. [Scott] produced a few single-note cassettes for his instrument, with ‘voice patches’ including a flute, choir, and a synth. With the CV and Gate input, these sounds can be sequenced with outboard gear, producing the wonderful sounds heard in the video after the break.