Building a Theremin with Input for another Instrument

Posted: 4/23/2010 11:48:46 PM

From: Saskatoon, Saskatchewan, Canada

Joined: 4/23/2010

I am completely new to this challenge of building your own equipment, but I desire to create a theremin which I could plug another instrument into, specifically a bass guitar. I am keen on the Keppinger design, and I am anticipating that even this project alone will take alot of my time, but I would love to explore the possibilities of a musician being able to affect another musician's work (I am very fond of free jazz, but I am more interested in changing a bass guitar's timbre and pitch).

I have only begun my theremin project, and while I am trying to catch up with this idea, I wanted to pose this question to the experts in theremin tinkering.

good'ay mates
Posted: 4/24/2010 7:47:58 AM

From: Canada

Joined: 8/1/2008

I have never heard of anyone triggering a theremin by using some other instrument. You could certainly emulate a bass guitar using a theremin, or you could gesturally trigger a bass guitar sound by interfacing a MIDI theremin with a MIDI receiver or via CV.

Most people want to do the opposite of what you want to do - they want to use a theremin's gestural control to play other sounds.

The only theremin I know of that can be controlled in the way you describe is the Moog MIDI Ethervox. It can record to a MIDI sequencer (via its MIDI OUT port) and then the sequencer can be fed into the Ethervox (via the MIDI IN port) and its VOICE TWO can play it back. You cannot use any MIDI device to play the Ethervox other than the Ethervox itself.

I'm probably the only person here who has actually been to Saskatoon.
Posted: 4/24/2010 5:59:36 PM

From: Croxley Green, Hertfordshire, UK

Joined: 10/5/2005

[i]I'm probably the only person here who has actually been to Saskatoon.[/i]

Well, apart from Greg Clark.

I believe Fred Mundell's long awaited modular theremin will include a voltage controlled beat frequency oscillator. (AKA a heterodyning, or theremin, oscillator.)


In the meantime, if you have an old guitar you don't mind taking a jigsaw to, I did encounter an interesting guitar adaptation a couple of weeks ago.

photo (

The pitch-only theremin has a very small field, so that it is only activated when the guitarist sticks out his pinkie and produces rapid exponential chirps ( (similar to sound sample in linked page, but faster) in time with his strumming.

Not a terribly interesting effect by itself (IMO) but when we ring-modulated the guitar signal against the theremin signal at my suggestion, WOW!

Bit hard to describe, not like a guitar, not like a theremin, more melodic than you might expect, but - depending on what you want - possibly not as melodic as you'd hope for.

The point is, one way to go would be to use a theremin as the second input to a ring-mod (rather than the internal oscillator that most ring-modulators have) and use it to perturb the sound from another instrument in interesting ways.
Posted: 4/26/2010 11:22:49 AM

From: Escondido, CA

Joined: 2/6/2008

If I understand you correctly, Greg, you are looking for a way for one instrument to control another's timbre?

If you want to do something simple, you could use something like a bass effects pedal with a "control" input. An effects output, or using a Y-jack off of the other instrument's output could be connected to this control input. It might take a bit of tweaking of effects settings, but this would accomplish what I think you want.

I think if you modify a theremin to do this, it would be a lot more work, and probably won't work as well.

Posted: 4/27/2010 9:46:19 AM

From: Kansas City, Mo.

Joined: 8/23/2005

While it is possible to patch an external signal into a theremin, the only paramenter that the theremin can process is amplitude (loudness).

In order to control timbre with a theremin, you would need a theremin that produces control voltages that correspond to the pitch and volume antennas. The Etherwave Plus, Etherwave Pro, and Paia Theremax theremins all provide control voltages.

To control timbre (for example), you would run your instrument (your guitar) through a low-pass filter. You would control the filter from the output Control Voltage on your theremin.

Bear in mind that one uses the theremin as a controller -- that theremin's audio is not part of the mix.

Here is an example of an Etherwave Plus used to control the timbre of a Moog Guitar:
Posted: 5/17/2010 4:39:11 AM

From: Croxley Green, Hertfordshire, UK

Joined: 10/5/2005

Another guitar/theremin combo.

(At the time of posting this link does not work correctly - I just tested it. I think it is a synthtopia problem, and assume it will be corrected soon.)

Update: Now it works.
Posted: 5/17/2010 8:58:22 PM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as . ...................................

Joined: 12/7/2007

[i]"but I desire to create a theremin which I could plug another instrument into, specifically a bass guitar."[/i] - GregClarke

Hi Greg,
My recent 'discovery' regarding acoustic modulation of Theremin pitch, see .. here (
leads me to wonder if you could simply take a connection from the bass guitar's speaker to a small bass speaker (via a resistor) which modulates the Theremin antenna in some way.

Directly coupling the input signal to a circuit which causes this signal to modulate the Theremin frequency (circuit consisting of Variable capacitance diodes, for example .. see.. Controlling diode capacitance ( should also work.

You would want a scheme based on this circuit ( with the "DC Controlled Capacitance" connecting to the antenna, or any other point where change in capacitance alters the frequency of the reference or pitch oscillators, The input signal goes to "Variable +V" ...
I will do a quick specific design for you if you ask.

Converting the input signal to a voltage (using a pitch-Voltage converter) is not likely to be a good way of doing things.. even if I could sell you my prototype heterodyning VCO.. Particularly at low frequencies, tracking of Pitch-Voltage converters is abysmal. I am expanding my VCO design to make it closed-loop, so that it will track any input frequency - but I do not yet even have a perfect prototype, and have other greater priorities, so it will be a LONG time before this comes to market... It is easy to track Theremin frequencies when one has the high frequency components which produce the audio output, it is quite another matter to track audio signals where one needs a couple of cycles before one can determine its frequency, let alone its harmonic content!


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