Minimum Theremin

Andreas has sent me a link to a fairly strait forward Theremin build. I’m not a Theremin guru, but the design seems easy to implement with only 2 4069 Hex Inverter ICs and other inexpensive parts. The description of the circuit operation is a nice read as well. From what I can decipher the pitch of one oscillator is controlled by the capacitance of the body’s relative position to the antenna. Another oscillator is adjusted and set to have a similar frequency of around 73kHz, that is roughly 4 times higher then the normal hearing range. What happens next is the key to Theremin operation. These 2 frequencies are actually subtracted from each other, giving a frequency that is within audible range. This typically is not the way most Optical Theremins work where a single oscillator is controlled by resistance and the resulting frequency happens to be within the audible range. Either way there are lots of cool case designs and info on this page.
An audio sample of the theremin can be heard on this arrangement.


15 thoughts on “Minimum Theremin”

  1. 18 inches playing field, according to the author! not bad. Some smaller Theremins have a tiny field of play, thereby making them hard to get very musical with. I wonder how hard it would be to rig up a audio signal kill switch, say a momentarily on pushbutton, soft spring loaded? i saw a guy with a modded Theremax and it worked out really well. Ge got really fast staccato out of the rig!

  2. Yeah a switch would be nice, but wouldn’t reaching for that switch alter the pitch?

  3. Heterodyning outputs the sum and difference of frequencies, not just the difference. We just can’t hear the sum. Optical theremins are NOT THEREMINS in any way, shape or form.

  4. To second anonymous, the above is a true theremin. Optical ‘theremins’ are simple VCOs with a CDS cell in place of a pot.

  5. CM,As far as isolating the switch from the pitch field,
    you could rig up a momentary pushbutton switch into a small enclosure at the end of a cable that plugged into the theremin,(a sort of kill switch in the audio output signal) you would hold it in the opposite hand and out of the pitch playing field. Keep in mind, Prof. Theremins first instruments were pitch only, w/primitive volume pedals. He went on to develop the volume antennae later in hid schematic design. (probably got ankle fatigue!)

  6. It seems true to the genuine definition of a Theremin, including the use of the heterodyne to generate the tone. It’s hard to tell from a recording exactly how good it is, although timbrally it’s a much better effort than most DIY Theremins are. The first problem I can see is that there appears to be no volume antenna, which is fairly essential for expressive playing, and in this case it is not true to the traditional definition of a Theremin, which has two antennas. From the recording, I’d say the timbre is a good result but you’d need an experienced player to really test the device and assess the linearity of the pitch field. Even if it’s big, the spacing of notes may be extremely skewed. It does sound vaguely playable though.

    It could be improved by adding a volume antenna, a larger chassis and upgrading the pitch antenna using Lev’s Ultimate Antenna Design as a reference.

    The “metal plate” design reminds me of the Moog/Big Briar Maestro.

  7. I see the “Maestro” theremin on the Moog Archive site, but I was under the impression that it was manufactured by some company other than Big Briar or Moog. Perhaps Oberheim(?). Alex’s comment about the plate antenna was right on the mark, because the Maestro model was the first theremin I had ever seen, and I liked the idea of plate antennas from the very start. That’s why I used a plate antenna on the “Minimum Theremin.”

  8. I constructed the Minimum Theremin and it worked OK. The only thing was..three octaves were compacted near the antenna..well, I solved that by connecting a 12 inch wire to the GROUND (MINUS) side of the output SOLDERED to a 12 X 12 inch copper plate on the floor. Of course the theremin must be on the floor with you setting in a chair with the plate on one side. Hands over the antenna…with arms resting on your knees for stability.

    I remove my shoe and put my stocking foot on the plate and that increased the capaciance, doubling the playing field to about 10 inches. I play Christian songs ie SILENT NIGHT AND SO ON. I practice about 10 songs once a day. The amp must be DC or you get hum.

    I am 85 years young and love it. Have fun and play music instead of WOW-WOWs. Practice by hitting the low starting octave and go from there. I am not a musician but can play anything I can hum. JJ

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