How to build a theremin


 The Theremin (named after its inventor Leon Theremin) is a musical instrument that dates from the early days of radio and electronics. It is a simple radio frequency device which relies on the interaction of two oscillators to produce a range of musical notes. One oscillator serves as a reference while the second oscillator is free to be influenced by the capacitance of the player’s hand approaching the instrument’s pitch antenna. To achieve control over the volume of the sound produced by the instrument another oscillator arrangement is used.

Playing the instrument is an interesting blend of electronics and theatrics. As the Theremin virtuoso gestures in space, glissandos of sound emanate from the instrument’s loudspeaker. Although the Theremin has been used for serious musical performance, it is more usually recognised for the eerie sound effects in 1950’s sci-fi movies.

I had being toying with the idea of building a Theremin since the late 60’s but never got around to actually doing so until a few of years ago. Here is a description of the results of quite a few hours spent in my backyard shed and a few useful tips for the enthusiast who might want to also have a go. 

 The Design
Although I had a strong urge to produce a traditional instrument, it is hard to ignore the benefits of the semiconductor when devising a project of this nature. The result of my labour is an instrument using the same oscillator frequencies and a similar functional arrangement as the original RCA Theremin but utilizing transistors instead of the valves (or toobs).

My Theremin is constructed using separate modules representing each functional unit of the instrument. In this way it is a simple matter to build each element of the Theremin, get it operating correctly and then finally assemble the whole instrument. The Theremin’s modules are:

  •  Pitch reference oscillator
  • Pitch control oscillator
  • Mixer
  • Volume control oscillator
  • Volume resonant circuit and voltage controlled amplifier
  • Audio amplifier
  • Power supply

Each oscillator used in this Theremin is of the Colpits type and uses a miniature ferrite core inductor and three capacitors as the frequency determining components. Two of the oscillators incorporate a means to allow the operator to adjust their frequency with a front panel control. 

 The Circuits
Each module can be built, tested and tuned so that the final assembly is the simple process of hooking everything together and performing a few final adjustments. In order to test and tune the modules, an oscilloscope is required.

Note: All capacitor values are in uF unless otherwise noted.