Beginner’s theremin construction/use query

Hey all!

Apologies for the basic questions but I’m very new to theremins.  To cut a long story short, I want to build a sort of moving sculpture, with a miniature theremin as part of it to be activated and played by other parts… so my questions are:

1) what would work instead of a person’s hands to manipulate the sound of the theremin?  The sculpture would be mostly clay, but if I put for example little magnets in the moving parts, would they work?  I read that the human body works because we’re made up of a lot of salty water, but the small size of the moving sculpture parts wouldn’t accommodate holding a liquid.  Any suggestions would be very welcome!  

2) what would happen if part of the conducting rod was encased in something non-conductive?  Would the whole theremin stop working, or would it still be triggered, but with less sensitivity/range?

3) I’m thinking considering my size and budget limitations to get something like the Gakken mini theremin.  If anyone has any better suggestions please let me know.

I really appreciate you taking the time to share your knowledge, and again apologies for the noob questions!

R

Hi R,

An 'antenna' of a theremin, in the circuit, is the non-movable part of an air-gap variable capacitor, of which the hand/body of the player forms the movable/variable part. The body/arm/hand is capacitively coupled to earth. Something conductive that will act as the variable part, which is connected to earth, or to the zero volt of the circuit, will work. Over which range it will work depends how you set your zero beat point, if that rage is short, small movements will have large effects o the sound.
The conducting rod, being a 'plate/electrode' of a capacitor needs to have something non-conductive between itself ad whatever acts as the variable plate, commonly air, something non-conductive as coating/encasing the rod/antenna thus won't stop it from working. 
Some put silicon tubing or shrink-wrap tubing around their antennas especially on theremins that have no built in protection against static electricity jumping to the antenna(s).

Hope that helps a few steps further.

DreadVox has answered your questions well!  I would add that the thing "playing" the antenna can be anything from a bag of salt water, to a piece of solid metal, to something non-conductive with a foil covering, etc. 

Any of these can be insulated, including the antenna, with no real effect. 

Capacitance is 90% proximity, so the closest conductive thing (connected to ground, or at least the Theremin ground) will dominate the response. 

The only thing a magnet might do is saturate the oscillator's inductive core if it is ferrite and if the magnet is placed really close to it (unlikely).

The antenna doesn't have to take the form of a rod either, a plate or screen will work too and perhaps better for certain situations.

You might look into the Open Theremin project (https://www.gaudi.ch/OpenTheremin/) they are quite reasonably priced.

Hi R,An 'antenna' of a theremin, in the circuit, is the non-movable part of an air-gap variable capacitor, of which the hand/body of the player forms the movable/variable part. The body/arm/hand is capacitively coupled to earth. Something conductive that will act as the variable part, which is connected to earth, or to the zero volt of the circuit, will work. Over which range it will work depends how you set your zero beat point, if that rage is short, small movements will have large effects o the sound.The conducting rod, being a 'plate/electrode' of a capacitor needs to have something non-conductive between itself ad whatever acts as the variable plate, commonly air, something non-conductive as coating/encasing the rod/antenna thus won't stop it from working.  Some put silicon tubing or shrink-wrap tubing around their antennas especially on theremins that have no built in protection against static electricity jumping to the antenna(s).Hope that helps a few steps further.

Thank you so much for taking the time to give such a helpful response!  Really appreciate it

DreadVox has answered your questions well!  I would add that the thing "playing" the antenna can be anything from a bag of salt water, to a piece of solid metal, to something non-conductive with a foil covering, etc.  Any of these can be insulated, including the antenna, with no real effect.  Capacitance is 90% proximity, so the closest conductive thing (connected to ground, or at least the Theremin ground) will dominate the response.  The only thing a magnet might do is saturate the oscillator's inductive core if it is ferrite and if the magnet is placed really close to it (unlikely).The antenna doesn't have to take the form of a rod either, a plate or screen will work too and perhaps better for certain situations.You might look into the Open Theremin project (https://www.gaudi.ch/OpenTheremin/) they are quite reasonably priced.

Thanks so much for your help!!  I’ll have a look at different forms of antennae for sure, thanks for the tip : ) 

Hey guys I was curious if anyone knew of a replacement for the miller 70 coil, preferably not the the PCA70 as it seems to be around 60$, If anyone could tell me how I could determine what may be a compatible replacement that would help also. I am working on the nightmare 1961 electronics illustrated theremin but I think It's so cool.

Logan,

Any RF coil will work as the magic of the theremin is not found in the coils or the mixer or old parts. I used a 1N914 diode for the mixer and a standard IF transformer for the coils. The theremin uses a phenomenon of Nature that most people are unable to figure out much less control, so they go with imitation bypassing the authentic theremin voice.

I hate to tell you this but you have years ahead of you with your current approach of learning. I have a friend Tanner Packham that just finished his 4th year at MIT and he will pick up where I left off on my theremin research. The Theremin family is excited for this to happen so people do not forget what Lev Sergeyevich Termen actually discovered (circa 1919).

His YouTube channel - https://www.youtube.com/@TannerTech

The authentic theremin has many of its own natural musical voices.

Performed by Valery Shamarin of St Petersburg Russia, my heart goes out to all of their people. Seems when world leaders get over 70 years of age their thinking gets weird.

https://www.oldtemecula.com/+lights-go-down2.wav

(I'm talking about timbre formation as always)
Tell me, what is the reason for the ineffectiveness of conventional filters, which are effective both for live sound and for oscillators on logic microcircuits, but are completely ineffective for the sound of the theremin? What is the essence, the reason?
In the presence of a high-frequency component in the signal? If so, what can be done? A filter that cuts off all high frequencies? I tried this too. But it is not very effective.
For example, this standard filter on an operational amplifier is effective for everything except the theremin.
 

What else can I try?

Timbre formation through linear filtering (high pass or low pass) requires an input signal with (too) much harmonics like a sawtooth or square wave, so that the filter can take something off.

On most analogue theremins, the mixer output ressembles to a sine wave, or a half or full way rectified sine wave as on most demodulators. These have not much harmonics, thus, there is not much which a linear filter could enhance or dampen. That's why theremin wave shaping often uses nonlinear filtering like soft clipping with a variable degree of symmetry by using the "bent" transfer function of a semiconductor. You should study the wave shaping circuit of the Moog Etherwave standard where the LM13700 is driven willingly more or less into saturation (Brightness setting) with a small variable DC offset to act on the signal symmetry (Waveform setting). The Moog Ethervox and Etherwave Pro Theremins use the same principle but with a more sophisticated technical implementation.

Thank you for your reply, Thierry. I really appreciate it. I read you and realized again that I knew it, but some time passes, I want to get a rich, variable timbre on the theremin again, and in this desire I forget again and again that the theremin signal is too poor for timbre formation. Probably the minimum is to convert it to a rectangle, via a Schmidt trigger.

(I tried (and there was a result) to get a change in timbre in the imbalance of signals going to the mixer. If you simply put a variable resistor in one of the signals, then there is an effect. But probably this worsens the stability of the circuit).