Freaky volume event

Posted: 9/14/2009 3:48:38 PM

From: Croxley Green, Hertfordshire, UK

Joined: 10/5/2005

Hi again Niallx.

Hmm. Things like that are usually down to big metal things being nearby - or anything that conducts electricity - and doing capacitance related stuff. (Stop me if I get too technical!)

The odd thing is that from your description it sounds like the pitch rod was working correctly. If it's tuned right you should get a wide range of pitches from deep rumbles to high squeals. And when you step away from the instrument it should go silent - not be 'on'.

I suspect it might be time to break out the manual and the little plastic screwdriver thingy that came with the etherwave and twiddle the inductors a bit.

But it is so hard to tell online. I recall you're UK based. Maybe we can find someone local to you? [edit] Googled "niallx" - Truro? There's a fair chance I'll be in Plymouth around 26 to 30 October. I'm here ( on facebook if you want to arrange something. [/edit]
Posted: 9/14/2009 8:32:00 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 . ...................................

Joined: 12/7/2007

"something new happened......the closer my hand was to the volume antenna, the louder was the

"Also, i had a significantly larger range.."

Volume getting louder as one gets closer would indicate that the 'operating point' has shifted significantly.. The response curve for volume looks a bit like a volcano - imagine the peak of the volcano as maximum volume, as one gets closer to the antenna, frequency drops, and ones position on the slope moves left.. Ideally, when one is away from the antenna, one is on the left side near the top.. as one gets closer, one moves left, and therefore down, and therefore lower, and therefore volume decreases.

If ones starting point is on the right side of the volcano, moving left causes one to go up.. If the tuning is set so that the operating point (when one is not close to the antenna) is beyond (right side) of the peak, then approaching the antenna will cause an increase in volume.

If one had something adding capacitance - pushing the operating point left - and this 'something' was removed - the operating point could shift 'right' beyond the 'peak' and cause the effect you saw..

My guess is that it was the [b]removal[/b] of some capacitance you are used to, which caused the effect you saw.. And quite likely that whatever affected the volume field so dramatically is also 'damping' your pitch field.

I may be completely wrong.. But I would try playing your Theremin in different locations and with different proximities to other objects (for example - do you have an amplifier / speaker positioned close to your Theremin, which you relocated on the event you mention?)

Only when you have determined the optimum conditions would I re-tune the Theremin.

[b] EDIT --> [/b] The above discription / analogy is certain to confuse everyone!! - Sorry - got left / right / up / down muddled a bit...

Adding capacitance moves the operating point position left..

Reducing capacitance moves the operating point position right..

Ideal position when distant from the antenna is on the left hand slope, near the top..

Coming closer to the antenna shifts the point left, moving the operating point down the slope, therefore reducing volume.

If the above conditions are obtained due to there being a big capacitance in the 'background' which imposes a large 'left shift' and the Theremin is tuned to compensate (intentionally or accidentally) for this background capacitance, such that, WITH this background capacitance present the volume operating point is on the left slope near the top when player is away from the antenna, THEN, Removal of this capacitance could move the operating point RIGHT past the peak and onto the left side slope.

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