My New Year gift to TW: A new theremin circuit

I made a version of this circuit with varicaps, and an effective tone adjustment with a variable resistor. If anyone is curious, I can provide a diagram. .

Martel, are you properly grounding it?  Could you perhaps have a ground loop (multiple grounds can cause this)?  If you post an MP3 sample of the low note problem I might be able to help.  Lots of mains hum in the typical room environment.

dewster - These theremins are small in size, even sometimes without a nut to mount on the stand. That's why I don't ground. And I don’t even have grounding in my apartment. (neither good nor bad. Only zero and phase are brought into the apartment).

But I will try to record the sound of this "triple" one of these days.

Martel, grounding is a very basic aspect of Theremin operation.  I've read you can stand on a metal plate under the Theremin, or throw enough wire on the floor (with either connected electrically to the Theremin) and get good results.  The audio connection to amplification may be enough too.

dewster - I will try to record the sound of this "triple" one of these days.

Here is a recording of the defective sounding of theremins in my apartment, where there is no grounding (on the third floor and only zero and 220 volts are brought into the apartment).
Theremin is powered by a 9 volt battery. the recording goes to the computer, which means that there is a binding by "mass" (this is not earth).
I tried to "ground" on the heating battery and on the metal box - without result.
This makes me very nervous and upset.
But here's what else you need to try - to record the sound of the theremin without connection to the electricity network.
Powered by a separate battery, and recorded on a recorder-voice recorder. To exclude the power supply. Which is probably polluted by impulse devices and does not have not only quality land, but it does not have it at all.

audio - https://cloud.mail.ru/public/xDNj/vLkxJXyi4
https://cloud.mail.ru/public/xDNj/vLkxJXyi4

"(How to upload files here? Is it completely impossible without an intermediary file hosting service?)" - Martel

I believe you can only upload pictures here (which is nice).

I listened to your file and looked at the spectra in Audacity.  Around 25 seconds in there is a fairly steady pitch area of 391Hz or so, and it is quite noisy sounding.  If you have a scope you should look at the output of each oscillator, as well as the mixed result, for any instabilities.

I like the simplicity and repeatability of this scheme. But it looks like she can show cunning).
That theremin, which was terribly "troilic", rattled at low notes, after a few months, under the same conditions, it did not rattle.
(tested both with mains and battery power)
I'm not an electronics engineer, but I'm guessing the following logic:
The gates of the transistors of the generators are on the ground (ground) and may be the influence of external influences on this ground the cause of "triples" - rattling?
Is this circuit vulnerable to external electromagnetic radiation? Because the FET gates are on ground?
And with this scheme, there is no way to fix it?

Hi Martel,
that noisy sound heard by dewster can be watched at the FFT-waterfall-diagram shown here. There are 50 Hz "combs" over the whole tone range. That possibly results from home installations and is captured via the pitch antenna and your body. In this circuit, there is no special prevention (filtering) of such incoming hum signals. You can try getting out of your house and use a large tent peg for grounding both the battery driven theremin via the amplifier in one point.

Thanks everyone for participating in the topic.
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Based on the problem I described with the sound quality of my versions of Thierry's theremin, I have a new assumption. My problematic theremins were made with 5484 transistors purchased on Aliexpress.
The sound on them is sharp, prickly, not soft and with triplets on low notes.
The other day I assembled two circuits using KP303 transistors, which, as I understand it, I bought from their manufacturer. This is an analogue of 5484. And they sound very different. Better, softer, more pleasant and seems without tripping.

So I assume that transistors purchased on Aliexpress, labeled as 5484, may not be such. And they are some kind of unclaimed, but also field-effect transistors.
Perhaps they are made on some old, preserved equipment and labeled with types for which there is demand.

This forum has gone way off topic from the true Theremin Phenomenon due to imitation.

Martel, In your situation poor earth ground is my first guess due to the added noise.

My second guess is your oscillator coils may be too close to one another so the magnetic fields are interacting or fighting with one another. Distance between the coils will improve this, not shielding. This is the killer of many early designs.

Distortion is a good thing but only if in our control

Each oscillator must not know the other one exists. I also built this circuit, the sound was ok but the pitch field using FET’s was too weak or insensitive for my experiments. I think I posted a circuit board iron-on earlier in this thread, page 17.

I posted another theremin board a while back. It can be either an analog pitch or volume board.

I wish you the best, Merry Christmas

Christopher