Electronic interference when touching anything metal

Posted: 5/2/2014 8:57:30 PM

Joined: 5/2/2014

Hello all, this is my first time on the site and I looked around briefly, but didn't see an answer to this question.  MY name is Troy and I am a classical guitar major at Edinboro University (Pennsylvania, not Scotland) and have unfortunately suffered a repetitive motion injury causing me to give up on the instrument.  I've gone through significant amounts of ear training and have found myself very drawn to the theremin.  I purchased a Moog Etherwave Standard and have been playing for a few weeks, but have run into a problem.  Whenever I touch the metal part of the cable going into the jack on the front of the etherwave (or amplifier) the pitch jumps up significantly and greatly increases the range of the field (as in the lowest note is well behind me when I touch the jack, despite being perfectly in tune when not touching it.)  This is no problem, because why the hell would I touch it while playing, but it does the same thing when I touch an effect pedal...and I greatly wish to use my loop pedal for theremin.  I have rubber shoes on and am standing on a wooden floor, but this has happened in several locations outside of my apartment as well so it's not an issue with my apartment wiring.  



Posted: 5/2/2014 9:36:38 PM
RS Theremin

From: 60 mi. N of San Diego CA

Joined: 2/15/2005

I will get back to you with a better answer. What you describe almost seems normal, maybe I am missing something. You might of left out an important detail, are you connected to  earth ground with a three prong plug going into your wall. Not having this affects the RF, EM, Electric Field and what not.


Posted: 5/2/2014 10:43:56 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 Himtroy, and welcome to TW!

Quite detailed (technical) accounts of grounding can be found on this thread (its actually about battery powering a theremin) posts relevant are headed: Re: Grounding / Earthing. Much of this is about creating a "ground antenna" when its not possible to connect the theremin to ground, but its also relevant for other situations where player coupling to ground is poor - even if the theremin is connected to ground.

Having rubber soles and standing on a wooden floor is going to make matters much worse, not better! Having a grounded metal floor and wearing socks would be ideal! (provided you dont touch anything live, as this could be fatal! ;-) - (Socks is just me being a bit silly ;-)

But to sum up what I believe your problem is..

A player needs a good consistent coupling to ground, this coupling is usually capacitive (when you touch the jack its galvanic) - the players feet and body couple to ground through the floor and to grounded objects near them, and IF the theremin is grounded, then this closes a capacitive circuit which controls pitch and volume.

If, for any reason, the players capacitive coupling to ground is low, then when any part of their body comes close to some grounded object (like a grounded pedal) their bodys capacitive coupling to ground will increase - and this increase will affect pitch in the same way that getting closer to the pitch antenna does.

One needs good ground coupling - first, you need to be sure your theremin is well grounded - then you need to be sure that you have a good strong coupling which 'swamps' any additional coupling you may get from pedals or the like.

 .. A conductive mat placed under the player (which can be covered in insulation, or under a mat - even a sheet of aluminium foil under a mat, and connected to ground, works well) , or having a load of grounded wire near your feet so that your body's coupling to ground was increased, will probably fix your problems - it could be as easy as having a long (shielded) audio lead from the theremin looped 'round the area your feet are, on the way to the amp...

(you should also find a HUGE improvement in the performance of your theremin if you are correctly grounded - linearity and sensitivity should improve, making playing easier)


some related links:







Posted: 5/3/2014 1:44:19 AM

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

"would these be a viable solution?"

Depends on the resistivity of the material, and its formulation, thickness, all sorts of things.. Bench / floor static dissipation does not require low impedance, in fact, Meg-ohms is fine.. Some static dissipatives actually are non-conductive at low voltages (< a few hundred volts) and would be useless.. But some (the more expensive conductive plastic formulations) would probably work.(my antistatic bench mat works, but not nearly as well as space-blanket.. and the antistatic mat cost me >£50) .. It is REALLY difficult to predict how well any resistive mat would work - Its not just down to conductivity - its also down to capacitive distributions within the material - some have wires embedded to 'spread' the conduction, and these would be better (even if specified as high resistance) - but you dont find this sort of data in the specifications.

The easiest and most effective IMO is DIY - Metalized (aluminium) "space blanket" one can buy for a few £ - then solder a wire to a piece of copper tape having conductive adhesive (ok, a roll of this will cost more than the space blanket, and you only need a small piece) and stick this tape to the conductive side of the space blanket..

Then, over this (conductive side and tape) stick any plastic book covering or whatever - I would re-enforce both sides with some such material - 1 meter square is more than enough and makes a mat you can roll up.. Some blue-tak is useful to keep it flat on a floor, or some weights on the corners.

But if you have the theremin mostly in the same place, aluminium foil or whatever placed under a mat or carpet is fine - its really not critical - you can connect to the aluminium by stripping a lot of insulation off the wire and scrunching this into the foil (wrap a corner of the foil over the bare wire) then stapling it and taping it (this is what I did for my ground antennas in 2010 - I had no aluminium solder or conductive adhesive)

I had actually wondered about producing a mat woven with hook-up wire - just some basic course canvas or whatever, with one wire woven a few times across it.. Anything with good conductivity and area under the player will do the job - the simplest is just a long audio lead (it something you need anyway and shouldn't forget to take to a gig! ;-)


Posted: 5/3/2014 8:33:03 PM

Joined: 5/2/2014

Wow...I don't even understand what I just read.  I suppose I'm going to try to pawn this off on a friend with the intention of paying them for their time.  Thank you very much though, it's certainly my lack of knowledge that has left me confused.

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