theremin

how they work is based on basic RF circuitry, as you might learn in RF circuits course. heterodyning. one of my favorite documentaries is Theremin: An electronic odessey (1993)

On a sunny day (Sat, 17 Dec 2022 17:13:59 -0800 (PST)) it happened RichD <r snipped-for-privacy@yahoo.com wrote in snipped-for-privacy@googlegroups.com:

Any unscreened RF oscillator that you move your had towards will chanche frequency due to capacitive effects.

Two antennas each with their own RF oscillator and waving your hands near them alters the pitch for one and the amplitude for the other.

I recall that the amplitude section had to be very carefully isolated from the frequency or they would entrain. The amplitude was controlled by rectifying in such a way that higher frequency gave bigger voltage and modulation of the other oscillator was optically coupled (old days filament lamp, modern LED) onto an LDR.

Requires 3 or 4 RF oscillators in the same box, f_ref nice and stable and the variable ones with external antenna. The frequency you hear is the beat frequency of the oscillator pair. I made one a few years back for a lecture on sounds (Practical Electronics design from the 1980's).

They have to be located a long way away from the trombones in an orchestra. I know someone putting on an Xmas concert next week which includes both Dr Who theme tune and the Beach Boys Good Vibrations.

I learnt to approximately play mine for the lecture. Tuning drifts as the room warms up so you have to adapt quickly (or play by ear which is what I did - a bit of vibrato hides a multitude of sins).

and afaiu it wasn't a "real" theremin that was used on Good Vibrations

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