Why does my Etherwave make funny noises when I touch the volume loop

Hallo! My name is Thomas Zunk, I am a thereminist from Berlin/Germany.
This is my first post and I hope you can help me.

I don´t know whether this has been discussed here before. I certainly did not find any answer here nor anywhere else nor on Moog´s site.

I own an Etherwave standard bought new 2008. It works fine and reliable but...
whenever I touch the volume loop, it makes a crackling noise. This was there right from the start.

Is that a common thing? I saw pictures on the net where thereminists had covered parts of the volume loop with plaster, I think I saw it in videos by Randy George (? correct me) and maybe even on some old pictures of RCA theremins??
So I tried that in between and it seemed to work.

And did not Thomas Grillo (if I remember right)offer a special kind of "Coat" made from some fabric for the loop (like a glove)for the same reason??

You understand: It would already satisfy me to hear that my Etherwave is not defect (or at least that I am not the only one:))

Thank you very much for your answers and best regards from Berlin
Thomas Zunk
www.myspace.com/thomaszunk

Hello Thomas, and welcome to thereminworld.

Many, but not all Etherwave Standards have this charactoristic audio artifact when the volume loop is touched. Even the Wavefront Travel Case I have does this. But not the Etherwave Pro, or the other theremins I have.

A friend in the UK has an Etherwave which does not do this.

Currently, the only work around is to cover the volume loop with either shrinkwrap, cable sleeve, or vinyl tubing, ect. Some have even tried painting the loop with transparent paint.

Good luck with your theremin.

Thank you very much for your reply, Thomas.

Right, I too have other theremins that do not produce that artefact when touched.

So I will return to covering a small portion of it the size of a hand with some piece of plaster. Somehow I prefer doing that instead of touching the cabinet to shut it down.
Only thing is that it looks as if the loops is broken :))

Thanks again. Apart from these chirpy artefacts my Etherwave works fine with me. I could by no means afford a Professional anyway, even if they were still made.

cheers from Berlin

You're welcome Thomas.

I had this same problem with mine, and Moog said this is just the nature of the curcuitry. Its intermittant and it doesn't bother me at all. I set it where I never have to touch the Theremin anyway, so it is alright.

Id love to own a Pro.


Eric

Perhaps I don't quite understand, but "plaster" seems to be an extremely impractical material choice for this purpose.

I also have this issue and I use plastic spiral wrapping intended for bundling electrical wires. It is a milky, transluscent plastic; most likely polyethylene.

One interesting feature is that, when I quickly squeeze it at certain points, the theremin lets out a "chirp" or "bark" depending on the frequency. This may be a useful feature for those who enjoy using a variety of sound effects in their compositions (or, just for fun).

[edit 05/14/10]
You're right Brian. As I said, "Perhaps I don't quite understand".

I used to think I spoke (and wrote) "English", but over the last year or so, I've come to learn that English is actually a foreign language (to me).

It's also difficult to make that determination when people do not supply any personal information, such as their general location, next to their avatar. [end edit]

Jeff: In Britain (and so, I take it, in European English), an adhesive bandage is a "plaster" ... so, Thomas is probably using some sort of plastic tape. (Yes, I had the same bizarre mental image when I first read his post.)

I think it is the extreme change in sensed capacitance when an 'antenna' physically connects to the player (as in, the connection is galvanic not capacitive - which effectively makes the player an extension of the antenna) which causes the problems.

Adding electrical insulation to the antenna prevents this galvanic connection, and forces the coupling between player and antenna to always be purely capacitive.. This limits the player/antenna coupling to probably 100pF maximum (still a high capacitance) for an antenna coated in a thin layer of epoxy paint.

I have used both epoxy paint and heat-shrink sleeving to coat antennas.. It is possible to achieve the same result from uninsulated antennas by placing a capacitor between the antenna and the circuit - for example, adding a 220pF NPO capacitor between the EW volume antenna and its equalizing inductor fixed the problem on an EW volume circuit I was evaluating.. Effectively, this mod makes it impossible for the circuit to 'see' a capacitance > 220pF, even if the antenna was shorted to ground - but only slightly reduces sensitivity under normal conditions.

Doing this mod does require re-tuning the volume circuit.. The 'seen' capacitance of the antenna is reduced (12pF would reduce to 11.4pF) and a change in capacitance of 1pF would be seen as a change of 0.9pF.

Insulating the antenna is the better solution, as this will not require re-tuning, and will not decrease sensitivity.. But adding a capacitor is probably cheaper and simpler. The best value of the capacitor would need to be determined experimentally if (as indicated in other posts) different EW's have different charactaristics - The higher the value one can get away with, the better - so start with perhaps 470pF, and reduce this if required, down to a minimum of perhaps 68pF.. Values below 100pF will probably cause sensitivity to be decreased to an unnaceptable level.

I purchased a length of clear plastic tubing and slid it onto my volume loop -- I used a little WD40 to make the plastic slide around the loop.

However, there is another issue with the volume loop -- namely that when one's hand is close to the volume loop the pitch may change as much as 50 cents. This is not consistant and I suspect it is related to the grouding. During my sound checks I test this... it can be very unnerving to fish for a pitch and then have a different pitch sound when one brings the volume up.

And yes, to physically touch the loop greatly impacts the pitch.

[i]"However, there is another issue with the volume loop -- namely that when one's hand is close to the volume loop the pitch may change as much as 50 cents. This is not consistant and I suspect it is related to the grouding. During my sound checks I test this... it can be very unnerving to fish for a pitch and then have a different pitch sound when one brings the volume up." - Kevin [/i]

This is really interesting (and a little bit worrying..) - I did some quick tests on my prototype, and this has the same problem..

On my prototype, it is not the antenna itself which causes the problem, it is the fact that, as the hand gets closer to the volume loop, it also gets closer to the grounds of the Theremin circuitry - this coupling is 'interpreted' by the pitch oscillator in the same way as if the hand was moving closer to pitch antenna.

With my Theremin, the entire assembly is screened (grounded foil coating the box on the inside) so ground coupling from the volume hand is severe - about 1st ... Arrghhh!!!

I never noticed this before - but I can see that this could be a real problem.. I can see a way to fix it (buffer the volume antenna signal, and connect this buffered signal to a seperate isolated screening layer placed over the ground screening layer, so that the hands proximity to the box has no grounding effect) but this adds another mechanical/construction hassle..

Oh well - it needs to be done. Thanks Kevin.. Far better to find this now, than to find it when customers start complaining!