New member; Sussex, UK

Hi all,

Just to introduce myself to the forum.
I couldn't yet call myself a thereminist, as I have very little time under my belt as a player so far. I have a home-made theremin which I built several years ago, and now I'm looking to learn how to play it.

Anyway, best wishes to all,

Peter

Hello Peter and welcome! I'd like to hear about your homemade instrument.

I started practicing seriously three months ago - about an hour a day.  I do a daily pitch & interval etc exercise with an app called Vanido and then I play along with a bunch of pieces - Autumn Leaves, In A Monastery Garden, On The Street Where You Live, Summertime, Somewhere Over The Rainbow, All Of Me, Sunrise Sunset, Happy Birthday, starting a few Christmas carols, Star Trek theme etc.

Hello Peter and welcome! I'd like to hear about your homemade instrument.I started practicing seriously three months ago - about an hour a day.  I do a daily pitch & interval etc exercise with an app called Vanido and then I play along with a bunch of pieces - Autumn Leaves, In A Monastery Garden, On The Street Where You Live, Summertime, Somewhere Over The Rainbow, All Of Me, Sunrise Sunset, Happy Birthday, starting a few Christmas carols, Star Trek theme etc.

Hi Daniel,
Thank you for the welcome.
The theremin is basic, but a little unorthodox: it uses a pair of 24 MHz crystal oscillators; one (reference osc) is part of a mixer / oscillator device (SA602), and the other (tunable osc) is a conventional Colpitts circuit feeding into one of the mixer's inputs. The audio is the difference product, which is amplified to headphone level by an LM386 device. I chose to use this scheme for stability reasons. The pitch antenna is a telescopic rod about 90 mm tall, and the volume control is by a light-dependent resistor in the audio line between mixer and amp. It runs on a 9 V battery, and lives in an old 2 oz tobacco tin. My profile picture gives an image. The compass (A2 to G7) is compressed into a 33 mm range, making the usual finger-gesture playing very awkward; I prefer to view it as a single-string violin with a 1-1/2 inch fingerboard. The range does extend downward, and I can attain single-figure Hz tones, before it stops beating altogether.
I admire your practice regime. I have a busy life, and my music time is dominated by fiddle practice; I want to spend more time on the little theremin, and perhaps build another of more conventional size (big enough to have a decent physical / musical range), and with an osc / BPF / VCA level control. I am still very much at the learning-the-scales stage as a player.

Welcome from another new player in the UK - look forward to hearing more.

Welcome from another new player in the UK - look forward to hearing more.

Hi @scifigene,

Thank you for the welcome. Things are moving quite quickly; I'm now into the build of my next theremin. This one will use the 'conventional' oscillator / filter / VCA volume control, which is far more proportional in character than my LDR-biased VCA, and definitely better than the LDR pad of my original 2009 design. I've reached the point where I'm evaluating how many crystals I need in the filter to get a reasonable slope in the response, when married to the 2 MHz free-running volume oscillator. The oscillator uses a physically large (T05 can) bipolar, driven softly to limit heating (and hence drift) and has a one-stage buffer to match it to the filter.

Some 'fun fact' observations:
(1) The pitch generator of a theremin is known in the radio world as a 'direct-conversion receiver'.
(2) The level control system in a theremin is an example of a 'slope detector'.
Search these terms for circuit ideas. Full disclosure: I'm also a radio amateur.

Who knows, I may even pluck up the courage to post some audio from the new theremin. I'm a very shy musician.

libraquarius said: Who knows, I may even pluck up the courage to post some audio from the new theremin. I'm a very shy musician.

I enjoy sound bytes, not so much the ability to play... rather listen and observe the harmonics.

Home builds are the best because you can comfortably make changes to improve it. Also I like building in a modular fashion so sections are easily swapped out.

Most of my knowledge comes from my amateur radio days my call  WD6EDZ, back around 1970 the test to pass was half transistors and half vacuum tubes. Then you had to interpret morse code at least 5 words per minute. Here in the states it is much easier to get a license today.

I think you mentioned using a crystal for the fixed oscillator, when I tried this noise and thermal drift were an issue.

If you are going to build another theremin you might stop by and maybe get some ideas from my approach.

I like your T05 oscillator idea, I use 300 volt T092 oscillator transistors as they improve the sound, discovered this by trial and error. (1000 volt NPN would not easily oscillate)

Christopher
Hwy79.com

libraquarius said: Who knows, I may even pluck up the courage to post some audio from the new theremin. I'm a very shy musician.I enjoy sound bytes, not so much the ability to play... rather listen and observe the harmonics.Home builds are the best because you can comfortably make changes to improve it. Also I like building in a modular fashion so sections are easily swapped out.Most of my knowledge comes from my amateur radio days my call  WD6EDZ, back around 1970 the test to pass was half transistors and half vacuum tubes. Then you had to interpret morse code at least 5 words per minute. Here in the states it is much easier to get a license today.I think you mentioned using a crystal for the fixed oscillator, when I tried this noise and thermal drift were an issue.If you are going to build another theremin you might stop by and maybe get some ideas from my approach.ChristopherHwy79.com

Hi Christopher,
Thanks for the encouraging reply. In my first theremin, both pitch control oscillators were crystal; I used an SA602 Gilbert-cell mixer / oscillator as the fixed pitch oscillator and mixer, and fed this with a variable crystal oscillator which had the pitch antenna connected to the junction of the pulling reactances via a trimmer capacitor. Tuning is effected by varying the length of the telescopic antenna. This system requires effectively zero warm-up time, and the stabilised supply assures no audible drift. This may appear to be cheating, but I see it as an application of Occam's Razor, edged with quartz. The theremin is very compact, and a battery is included. The equally simple volume control circuit is another cheat: it requires ambient light to activate the light-dependent resistor. This is in the gate bias of a FET which shunts the audio from the mixer to ground progressively as it 'turns on'; the result is soft, even-harmonic distortion as the FET pinches the sound off. This is not authentic-sounding, but it has a character of its own.

There are aspects of the design which I wish to improve. I've mentioned the intended use of 'traditional' volume control in a previous reply to this thread, and I also want to use a different audio output (headphone) amplifier in the next theremin. My first theremin used an LM386 device; this is noisy, has a high quiescent current and I have a much better design in mind which uses a high-quality dual audio opamp, one section as gain block and the other as closed-loop output driver. I also want to have a switchable 'leak' which partially bypasses the volume control to one earphone channel; this allows the player to hear the pitch even when the left hand is on the volume antenna. This gives the player a chance to find the next note before exposing it to the audience (who hear what the other ear hears).

Thanks once again, Peter G1INF