My New Year gift to TW: A new theremin circuit

Posted: 2/25/2020 8:06:44 PM

Joined: 2/24/2020

Hello Thierry, I followed the Keystones video and build this circuit but havent get sound from the antenna. I used J113 instead of 2N5484 and all the other components are identical. I got some strange radio like sound from amplifier but the antenna is not function at all. 

Btw, is your C13 1.5nf? 

Posted: 3/18/2020 10:21:42 PM

Joined: 3/18/2020

Hi all! I am using this design for my senior project and have unfortunately hit a block. I am using a guitar amp as the audio out and an currently only getting static. If I unground the audio jack connected to the guitar amp, I can get a slight pitch variation in the feedback if I pinch the antenna. I don't know what I'm doing wrong and have re built the circuit three times on a breadboard. Any help would be much appreciated as I need to fix this to graduate!

Posted: 3/18/2020 11:22:27 PM

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014

Tune your Analog AM Radio to around 900 khz and you will find two blank spots in the static on the AM band if both oscillators are working. This is 2 x 450 khz or whatever it is.  If you find the two blank spots tune to overlap them. This is fun stuff. Thierry a genius but I got the edge. I have a pdf toner transfer print out for this circuit I can share if you know what that is.

Your coils are probably 10% so the oscillators could be out of tuning reach of each other, you might need to add a few PF's to one side. Also have a length of wire for the antenna mounted. This should drive your amplifier for the experiment.

In my graphic below I added a spot for a LDR volume control.

There is a lot to learn from this design, like why I avoid using FET's.


70 mm x 100 mm

Posted: 3/20/2020 7:49:39 PM

From: Germany

Joined: 8/30/2014

The beauty of the layout almost rivals that of the bird.

(no, I don't like the sight of P-to-P tube amp circuits, either )

Posted: 7/28/2020 3:30:33 PM

From: Russia

Joined: 9/8/2016

I haven't been here for a long time. And once again I went to say thanks to Thierry for the circuit and especially for patience and participation in the topic :-) you do not leave us with our problems) on my own I can add that both the transistors and the 6-volt power supply in this circuit are fundamental. (And even, probably, not every copy of the recommended transistors may not fit, the range of parameters is too wide for field-effect transistors. But I could be wrong here))
Having collected several theremins according to different schemes, I was disappointed in the weak possibility of forming a timbre. During all this time, new ideas have appeared in this area, and I plan to return to the theremin to implement these new ideas.

Posted: 8/12/2020 2:45:21 PM

Joined: 8/12/2020

Hi Thierry,
I hope you are well during the pandemic.
Thank you for a nice simple design, and thanks for putting so much effort into answering everybody's questions ! This is much better than most internet blogs !

I could see the selected FETs were different to any I had in stock, but had no problem ordering the correct ones from ebay.
It would've been useful if your suggested PCB layout was a black & white image ready for photo etching, but It didn't take me long to reverse-engineer it.
With the reccommended components, the circuit was up and running in no time, with nice clean sine waves :-)

I have a general question - so maybe other readers could answer...
I'm using this circuit as a proximity detector - as opposed to a musical instrument.
My aerial is a 10cm flat plate, I want it to react nicely to a persons hand, in the (rough) range 30cm - 10cm.
I dont have the option to change the aerial plate design, as its part of a sculpture, but in theory I should be getting between 0.2pf and 1pf plate capacitance.
The output of the mixer is bufferred and driving a TTL divider chain, so it doesn't matter if the output is tens of kHz or just a few kHz, I just need a range of > 1 octave spread nicely over the distance.
At the moment, I'm only getting a noticable frequency variation if my hand is very very close to the antenna.

To improve the response, 
* should I be raising, or lowering the frequency of the oscillators?
* is it worth tuning the fixed frequency oscillator to match the aerial / plate ? - for example by adding a trimmer cap and adjusting for max amplitude.

many thanks,

You must be logged in to post a reply. Please log in or register for a new account.