Non-functional volume circuit and another problem

Posted: 2/21/2015 10:38:59 PM

Joined: 2/2/2015



I am currently encountering a couple problems concerning my etherwave theremin. I am building it according to the schematic drawing in this pdf


One of the problems is located in the volume circuit witch behaves as follows: volume antenna circuit oscillating at 441 kHz, VO is oscillation around 480-490kHz(should be 450kHz), these produce less than -0,1 V at R14. Any idea why?


Also, when introducing an injected, adjustable, voltage (via a potentiometer) we where able to control the volume (with the volume circuit disconnected). We also tested with another totally functioning Volume circuit producing -3V and got no sound or volume control. Why do the injected voltage work but not the functioning volume circuit?

Posted: 2/22/2015 7:30:04 PM

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014

Hey Kev,

I had never put a scope on an EWS until two weeks ago, as my own theremin research is original. Now I find blending the work of Bob Moog and my own will complement one another. This approach really simplifies what I had always hoped to achieve with theremin design. Mostly it solves some of the construction issues.

Using my EWS, which there are some differences from the EM, at the test point between D1 and C12 the minus voltage is -.65v with my hand at the loop and -15v hand away maximum volume. On the other side of C12 I measure a frequency of 528 kHz and 527 kHz with the hand at the loop. The amplitude on the scope at C12 is ~6.5 volts p-p, I am using a 10:1 probe.

You are not getting the developed –4 volts or more, this is the area of focus, your problem seems to me to be Out of Range Tuning and maybe weak oscillator amplitude. Try jumping L10 and then tune L11.

I need to go back and study Thierry's many writings on this subject.

Again I can only guess. I use to have my builders send me a picture of their construction and more often than not after spending many days with them I was terrified by the construction methods I saw. 0-:

Good Luck


Posted: 2/23/2015 2:29:23 PM

Joined: 2/2/2015

Thank you so much Christopher, our theremin are now up and running. Now it is just the tuning left. Thanks once again! 

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