In 1920 the Russian physicist Leon Theremin demonstrated the musical instrument that has since become known simply as the Theremin. Theremin died in November 1993, but his instrument lives on, occasionally being performed in concerts or used in soundtracks. The Theremin is unique in that it is played without there being any physical contact whatsoever between the performer and the instrument. The pitch of the instrument is controlled by the proximity of the player's hand to an antenna (mounted vertically in the original design). A second antenna (traditionally mounted horizontally) senses the proximity of the player's other hand and controls the volume of the tone.
The experience of playing the device is far removed from that of performing music using a 'traditional' instrument. There is a perpetual feedback mechanism associated with the playing of the Theremin. The feedback loop begins with the position of the player's hands, and next involves the sound produced, until finally the player processes what he/she hears and changes the position of his/her hands accordingly. A successful playing style requires the ability that a given pitch and volume of tone can be accurately converged on, and held by the player. Thus a competent Thereminist must have a good 'ear for music' and also good reflex action. Expert Theremin players have been few and far between with only a few names reflected upon when the instrument is mentioned.
We have constructed two Theremins, one based on an analog circuit and the other employing digital techniques. Photographs of our completed instruments are shown above. The visual appearance of the analog and digital versions contrast sharply, which was deliberate, in order to reflect the different design approaches used in the digital device and the more 'traditional' analog instrument.
The first Theremin circuits employed electronic vacuum tube oscillators. Vacuum tube electronics was already a fast developing field by 1920, driven primarily because of the applications in radio. However with the advent of the transistor, present day oscillators can be made considerably more stable than early designs. For our analogue theremin we used a transistor oscillator which follows a design originally developed by Colpitts. There are four oscillators in total, arranged in two pairs. Each pair forms a beat-frequency oscillator the outputs of which are modulated by the effect of a player's hand capacitance near each antenna. This is how the pitch and volume of the instrument are controlled.
To download our analogue theremin circuit, click here.
The digital theremin uses CMOS oscillators and logic gates to produce two DC levels. One DC level varies with the proximity of the player's hands from the pitch antenna, and the other DC level varies when the volume antenna is approached. This design of circuit is advantageous because it pretty much depends on the imagination of the constructer, what he/she wants to do with these DC levels.
Obviously, a basic instrument would have the DC levels controlling a voltage-controlled oscillator (VCO) and
voltage-controlled amplifier (VCA). However, such a DC level could also control a voltage-controlled
filter (VCF). There are numerous designs of such voltage-controlled circuit elements. In our circuit which you can download, it shows a VCO and VCA block based on commonly available commerical integrated circuits. Each block is controlled by a CMOS oscillator/logic gate stage, of which there are two (one for each antenna). The design has proven very successful in recording, where the signal-to-noise is of HI-FI quality, and also in playability, since the tuning and volume offset is easily trimmed by adjustable knobs on the front panel. To download our digital theremin circuit, designed and built by Lindsay Reid and Brendan Dougan for a final year project, click here.