varying the electric field size

Posted: 5/9/2006 8:59:05 PM

Joined: 5/9/2006

hello all,

i'm a music tech student building a terpsitone variant. i need to implement a device with one channel of loading mode EF sensing, but with large field size (in the range of 2 - 6 meters), that can be varied with a potentiomemter.

because i will be using the output of the device as a control signal rather than a sound source by itself, i do not need an implementation that has good tone quality. that's why my plan right now is to use Arthur Harrison's Minimum Theremin (

but what in the schematic do i change to boost the size of the electric field? (i know the size of the antenna is a factor, and i will be using a large one). but is there anything else in that schematic that can be adjusted to maximize the field size and still be able to change it with a variable resistor?

making giant fields seems like it would be fun and useful but surprisingly i can't find much info about it.

thanks for all your help!!

Posted: 5/11/2006 4:55:15 PM

Joined: 5/9/2006

actually, what i'm looking to build is the system similar to the one bob moog developed for john cage's "Variations V"... video here:

basically a few theremin antennae on stage that can sense proximity to dancers.

is there anyone here who knows if there are schematics/technical information about this system?

Posted: 5/16/2006 10:44:13 AM

From: UK

Joined: 5/16/2006


I'm new here, and a relative n00b to electronics (majoring in computer science instead!), but here's a quote from the theory page that accompanies the 'Minimum Theremin':

"The values of the oscillators' frequency-determining components may be adjusted empirically to obtain the best compromise of sensing range and fidelity. For example, as C3 is increased, interference effects will diminish at the expense of decreased sensing range."

If you look at capacitor C3, it regulates the oscillator that the Antenna maniuplates. Whether its effect is a result of the DC filtering properties of capacitors, I'm not sure (I could have all this wrong), but by my guess, if you replace C3 with a variable capacitor whose upper limit is 100pF, then you should be able to get a good range, but at the expense of static/interference filtering, which in the case of your dancer wouldn't be too much of a problem.

Just keep the TV quite a way away ;-)

I hope this project goes well for you - sounds like a really good idea!

Have fun.


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