In the 1950s, the Hohner company in Trossingen developed a range of electronic or “electrified” instruments for private music-making. Their style of playing was generally similar to that of the accordion and piano. The “Electronium Pi” was an add-on instrument for the piano and was mounted under the keyboard. The monophonic instrument had numerous electronic tone qualities, octave transposition, a controllable vibrato, and volume control. The sounds were produced by an electronic valve. Amplifier and loudspeakers were housed in a separate case.