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Short Circuit

Article from Electronics & Music Maker, November 1984

Fancy a theremin? Paul Balfour's simple circuit should do the trick.

The start of an occasional series in which readers send in circuit details of their own music projects. This months sees a much-requested theremin circuit.

The circuit outlined below provides an excellent theramin which is both inexpensive and easy to construct. Only the pitch is proximity controlled, but if volume is controlled using a pedal, the theremin can be used whilst playing keyboards.

The circuit consists of two Hartley oscillators. One of these is fixed, while the other varies in pitch with the proximity of the player's hand to the pitch plate. The oscillators are at around 470kHz and the beats are audible. The resulting signal is picked up by the second half of the circuit - a simple medium-wave receiver. You could omit this element and use an ordinary MW radio instead, but more often than not this results in a noticeable reduction in sound quality.

Oscillator coils L1/C1 and L2/C2 are Toko YMCS 17104 IF transformers, with their screening cans removed. The sound is very much dependent on adjusting the slugs to obtain the desired effect.

If you're working on a design of your own, send it to Short Circuit, E&MM, (Contact Details).


R1 220K
R2 220K
R3 1M2
R4 4K7
R5 100K
D1 DA90
D2 DA90
C3 150pF
C4 220pF
C5 0.1μF
C6 100nF
C7 220nF
C8 10nF

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Publisher: Electronics & Music Maker - Music Maker Publications (UK), Future Publishing.

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Electronics & Music Maker - Nov 1984

Feature by Paul Balfour

Previous article in this issue:

> Modular Synthesis

Next article in this issue:

> Patchwork

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