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I'm looking at a theremin listed for sale on Craigslist, and am tempted to buy it.

I have musical skill and knowledge, but am entirely unfamiliar with theremins. When presented with the instrument, what should I look for/what tests can I perform to ensure the instrument is in (relatively) good working order?

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This is a great example of how to ask this kind of question! – Matthew Read Feb 13 '12 at 15:59
up vote 3 down vote accepted

The theremin is actually a really simple instrument to test - there are different models, but the core idea is that one antenna controls volume and the other controls pitch (generally the vertical antenna is for pitch, and the horizontal loop antenna for volume).

There are no tuning rules, so as long as the frequency range covers a few octaves you should be fine from a frequency perspective.

So, testing:

  • move your hands close to the antennae until you generate a tone (or more likely, a squealing of banshee-like horror) and wiggle one hand. If the pitch changes, that is your pitch antenna.
  • move your hand from really close to far away - the pitch should start really high and drop off the further you get from the antenna
  • for volume, as you raise your hand higher off the loop, the volume will increase to its maximum about a foot above the loop
  • if you use the same settings on your amp as you would for a guitar, volume should be at a reasonable level
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In addition to the tests Dr Mayhem suggested, I'd also suggest checking that there is no noise when your hands are away from the antennae.

Some cheaper models have a residual 'hum' which requires constantly recalibrating to get rid of. A bit like radio interference or feedback through a mic<->amp. I've used one in very close proximity to a keyboard before which picked up interference along the line out - as I say, a cheaper model.

Along the same lines, also test that there is no 'wobble' in pitch or volume when you hold your hand at a constant distance. Harder to test accurately I know, as you may not have that steady a hand of course!

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