My New Year gift to TW: A new theremin circuit

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? 

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!

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 adjust them to overlap in frequency to hear the heterodyne tone. This is fun stuff. Thierry's 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 10" or 25 cm length of wire for the antenna mounted. This theremin should drive your amplifier for the experiment. Don't forget earth ground.

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.

Christopher
www.Hwy79.com

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 )

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))
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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.

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,
jonathan

Jonathan great detailed post.

I made that pcb before, it made me less fearful of using variable capacitors. For easier tuning you will want to add in a parallel 5pf variable capacitor. Amazon -  If you really had a 1pf change at the Pitch Antenna in theory that would be a sweep of over 4 octaves or 0 to 2500hz. What gives the Pitch Antenna response distance is how much Voltage or energy is on the antenna/electrode. The outer field will be 1 hz if no oscillator coupling occurs and next to the antenna 2500 Hz. That design will probably not give you the range you are after. The theremin has its own design rules, which most do not understand, you can not wish it to cooperate.

Any RF frequency used between 100 kHz and 1 MHz will work basically the same. The higher the heterodyned frequency used the less influence the 1pf is going to have if any.

Here is a simple method to convert Frequency to Voltage ebay  0 - 1000 hz = 0 - 10 volts

Christopher

Edit: Are you using a good earth ground? Is your sculpture conductive and swamping out the variable oscillator response? Black paint I would avoid.

Edit2: The 30cm range you're after is ideal, the Pitch Antenna begins at the circuit board so they need to be side by side.

Hi.  
Hi there and thank-you for posting these instructions on how to build a pitch only Theremin.

I appreciate the time you are taking to read this . 

I have breadboarded the project in its entirety but I had to deviate a bit, as follows:

 I used three identical, new MPF102 N-CH RF SS TO92 s. This is the datasheet I found for them:  

https://www.mouser.com/datasheet/2/149/MPF102-889956.pdf

I also used a 60pF variable capacitor, as did not have a 50pF.

The circuit does not make any buzzing noises, but it is also completely silent. I hear no sound coming out of the guitar amplifier I plugged it into.

Would it be possible to get me some advice.

I really do appreciate everyone's time and expertise.

Thank-you.

Hi.  Hi there and thank-you for posting these instructions on how to build a pitch only Theremin.I appreciate the time you are taking to read this . I have breadboarded the project in its entirety but I had to deviate a bit, as follows: I used three identical, new MPF102 N-CH RF SS TO92 s. This is the datasheet I found for them:  https://www.mouser.com/datasheet/2/149/MPF102-889956.pdfI also used a 60pF variable capacitor, as did not have a 50pF.The circuit does not make any buzzing noises, but it is also completely silent. I hear no sound coming out of the guitar amplifier I plugged it into.Would it be possible to get me some advice.I really do appreciate everyone's time and expertise.Thank-you.

SparkyCal, this is what Thierry says on the matter much earlier in the thread:

"I'm getting tired about all these people who want to use different JFETs from those for which this circuit has been designed and which have been tested and are approved...

The 2N5484 are easily available. When I search for these on eBay, I get 6 results from sellers within the EU, and 26 from sellers outside the EU. Where is the problem?"

Silverloz - I absolutely agree with this)

SparkyCal - Use the specified transistors. This is not a circuit where you can cram other transistors.