The Keyboard Electric Harmonium . Lev Sergeyevich Termen, USA/Russia, 1926

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Lev Sergeyevich Termen most famous for creating the ‘Theremin’ also invented many other electronic instruments based on the heterodyning vacuum tube technology of the day – including the Keyboard Theremin, Theremin Cello, Terpsitone, Rhythmicon and the ‘Electric Harmonium’ or ‘Theremin Harmonium’.

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Termen’s Harmonium was an early vacuum tube based polyphonic instrument designed to accompany vocal performances. The instrument had a three octave keyboard with a variable tuning that allowed 1,200 micro-tonal divisions per octave. The timbre and volume of the sound could be varied using twelve dials fixed to the front of the instrument.

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Sources:

(1) Theremin Center for Electroacoustic Music