Volume Knob is Strange

Posted: 12/12/2010 2:34:04 PM

From: Florida

Joined: 12/1/2010

Hello, I recently bought an Etherwave Standard Theremin kit. I put it together all fine, and everything seemed to work right. Till I payed attention to the volume knob. For me the volume knob effects the pitch field. When moving the knob to the left, the pitch field shrinks. When going to the right, the pitch field grows. Is this supposed to happen? Or would one of my solder joints be messed up?

If someone could give me the correct voltages I'm supposed to have on the volume knob then I can compare mine to it.

Also one day I was 'very static conducting' and shocked myself a couple of times on the volume loop antenna. Would this in anyway affect the theremin?
Posted: 12/12/2010 11:35:11 PM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as WaveCrafter.com . ...................................

Joined: 12/7/2007

Hello Archez,
First - Schematics etc are all in the Etherwave Hotrodding (http://www.element-14.com/community/docs/DOC-16859) manual.

The tuning potentiometers are across Gnd and -12V, so the wiper should be adjustable from -12V to Gnd... But I think it unlikely that this is the problem.. unless you are also having problems with the pitch tuning, as there are common wires and a problem with the connector or these wires could cause strange things to happen / interactions between pitch / volume / waveform controls I guess..

Not having played with a 'real' EW, probably best to wait for Thierry! I suspect he will have seen this before, or be able to give a better guess than I can!

Welcome to TW!


ps .. "I was 'very static conducting' " - Electrostatic Discharge CAN damage Theremins (and any other electronic equipment) but the EW is not highly sensitive to ESD. The most likely component to suffer from ESD on the volume antenna would probably be Q7 as its base is directly connected via the coils.. But I do not see a mechanism by which this could cause the fault you describe - death of Q7 would stop the volume oscillator from working.

In fact, the only 'common' circuitry does seem to be in the area of the potentiometers..
Posted: 12/13/2010 7:09:27 AM

From: Colmar, France

Joined: 12/31/2007

There is a potential problem which you can't see on the cited schematics. Newer Etherwaves have an additional circuit which delays somewhat the negative control voltage through a R-C-combination and a 2N3906 pnp transistor as emitter follower/buffer (T9).

If the latter is defective, you'll not find the required stable -11.3V at the connector which leads towards the front panel, but something floating around -8 to -9V and varying depending on the potentiometer's position. So the pitch tuning knob may influence volume tuning and the other way round. Replacing T9 and its neighbored 100uF/16V electrolytic capacitor (I used a 35V version instead during the 2 repairs I had to do on Etherwaves with this fault) will fix this problem. In Europe the 2N3906 may be replaced by a BC557C. Or you may ask me for a 2N3906, I ordered a lot of 100pcs. in the US because I always prefer original spare parts.

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