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New, Improved Theremin Mk.2

This design is an upgrade of our most popular Theremin which was featured in the August 2000 issue. We have added a voicing control, incorporated a larger loudspeaker and increased the power output. We've also changed the power supply to avoid problems with switchmode DC plugpacks.

by John Clarke

Specifications

Power requirements .........12VAC at 250mA minimum or 12V DC at 250mA 

Current draw: .................. 30mA with no sound from loudspeaker, up to 200mA at full volume.

Output frequency range .... Greater than five octaves, from 50Hz to >2kHz

Volume control range ....... >60dB

Audio output level ............. 600mV RMS 

If you are not familiar with the Theremin, we should give a brief rundown on this most unusual instrument. It is an electronic musical instrument that can be altered in pitch and volume using proximity effects. 

To play the instrument the right hand is moved horizontally toward the antenna to increase the pitch and away from the antenna to reduce the pitch. Left hand movements over the horizontal plate provide volume control. The volume is reduced as you move your hand closer to the plate. 

Click for larger image
Fig.1: the Theremin circuit comprises three virtually identical oscillators, two to generate the tone and one to control the volume.

In operation, the pitch change afforded by the antenna is infinitely variable over several octaves. In some ways this is similar to playing a trombone whereby the slide is moved back and forth to vary the pitch. Although most people can play the instrument at first attempt, an ear for pitch and fine hand control are essential requirements to become proficient at playing the Theremin. 

Several fine performances by Peter Pringle usinag a Theremin are presented at www.peterpringle.com/thereminmp3s.html. These demonstrate only a fraction of what can be accomplished with a Theremin in the hands of a skilled musician. The same website has links to YouTube performances, some of which are quite remarkable.

The fascination with the instrument, when it was first invented by Leon Theremin in 1919, was that it represented a revolutionary change in thinking about how music could be produced. It challenged traditional stringed, brass and percussion musical instruments. Its design eventually led to the development of the Moog Synthesiser and electronically synthesised music in general. Even today that fascination with producing sounds electronically is still prevalent. If you are interested in the history of the Theremin there is more information in the section headed “Theremin Origins”. 

The Theremin invention was not only instrumental in the development of electronic music; it also had an impact on a free-form style of playing music. The free-gesture hand control afforded by the Theremin was the harbinger of the modern Sensor Chair synthesiser controller where the whole body becomes a part of the musical generation process.

Before this, Jimi Hendrix was creating new sounds by generating feedback between his guitar and the amplified sound and then moving his body to modulate the amplitude. It freed him from the restriction of generating music solely by plucking the guitar strings. 

In recent times there has been quite a renewal of interest in the Theremin and there is a lot of information on the Internet. However, none of it is really helpful if you want to build your own Theremin.

This is where the SILICON CHIP Theremin comes into the picture. It uses just three low cost ICs and a handful of other components. Our Theremin is considerably smaller than the original design too, although you could build it into a larger timber box if you prefer.

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