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

Lev Sergeyevich Termen, best known 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.

Termen’s Harmonium was an early vacuum-tube-based polyphonic instrument, tuned to accompany and train vocal performances, built at the Laboratory of Acoustics and Sound Recording of the Moscow Conservatory from 1926 and continuously developed until the 1960s. The portable desktop instrument had a three-octave keyboard with variable tuning, allowing 1,200 microtonal divisions per octave. The sound volume can be adjusted using a dedicated volume roller at the front of the keyboard. The timbre and acoustic envelope could be varied by a “rotary timbre register with 12 different sound characteristics”. The output reached a tuning stability of 3 cents once the machine had been active for fifteen minutes and had a maximum output of 3 watts “increased by connecting a powerful amplification device with additional loudspeakers.” ¹ Termen, L. S. (1964) Harmonium for working with choirs, report, Laboratory of Acoustics and Sound Recording of the Moscow Conservatory, TOPIC Z-N, 1964. http://www.theremin.ru/archive/harmonium.htm retrieved 25/11/2023.

“The new Keyboard Theremin, which is designed in the form of a piano to produce synthetic music. […] With huge banks of vacuum tubes, Prof. Theremin conducts experiments in his laboratory, which led to a harmonious reproduction of the radio squeals.” (Popular Science, USA, Jun 1932) ² Radio Squeals Turned Into Music for Entire Orchestra, Popular Science Jun 1932, 51.

Sources:

• 1
  Termen, L. S. (1964) Harmonium for working with choirs, report, Laboratory of Acoustics and Sound Recording of the Moscow Conservatory, TOPIC Z-N, 1964. http://www.theremin.ru/archive/harmonium.htm retrieved 25/11/2023.
• 2
  Radio Squeals Turned Into Music for Entire Orchestra, Popular Science Jun 1932, 51.