Coolidge Success - more or less - but it's really quiet

Posted: 5/20/2005 8:15:43 PM

From: Toronto

Joined: 5/5/2005

I've constructed the Coolidge theremin, with many substitutions in transistors and I made the air coils from the RS Theremin for the loopsticks. I can tune it and play it over my AM radio (which is how it's supposed to be played) but it's really really quiet - it barely comes over the noise of the set. I tried it on a different radio and had similar results.

It's not all mounted in a box yet, because I (foolishly) thought I was going to use a metal cookie tin - it looks great but it causes instability. The leads to my coils are still too long, and it's all bread-boarded, not soldered yet. Could these things affect the signal strength, or whatever makes a theremin quiet?

If anyone has any hints for a novice as to how I might improve the performance of my theremin, they would be hugely appreciated.



Posted: 5/23/2005 6:54:00 PM

From: Toronto

Joined: 5/5/2005

Golly, I was really hoping some theremin guru would have posted a simple solution to my signal strength question by now, but I have some more thoughts.

Firstly, the gentleman who maintains the RS theremin site suggests attaching the antennae to the middle of the coil, not at the end, which I shall try after I hardwire the rest of the instrument. Also, if I am a sloppy coil wrapper, would that affect the strength of the signal or just the frequency at which it oscillates?

Oh, and for people trying to build this thing, save yourselves some hassle and money - the variable capacitor allows you to tune the coils more easily than adjusting the core of the inductor, so skip the 'vari' part of the vari-loopstick. Or if you're following me and making the air coil from the RS site, you don't need the brass screws, the coupling nuts, or the end-plugs. The variable capacitors I got were from my local surplus store and salvaged from old AM radios. They are nice and big and easy to understand. They look like the things from this site: which I thought was quite interesting (being a musician and not an electronics wizard).

And sorry that this is so messy - the only other forum to which I've posted allows me to edit my posts after I've put them up, so I get second chances when I've screwed up.
Posted: 5/25/2005 2:30:59 PM

From: Sammamish, Washington

Joined: 2/13/2005

I apologize for the lame forum features... editing old posts is on the list of things to be added soon. If you have other suggestions, please feel free to post them in the suggestion box forums :)
Posted: 8/21/2005 5:39:29 PM

Joined: 7/20/2005

i am having the same volume problem with my coolige theremin as well as a problem with my volume antenna where it controlls pitch instead of volume (so i have 2 pitch antennas instead of a pitch and a volume antenna). i used some ferrite loopsticks and brand new variable capacitors. i was wondering if you had found a solution that worked yet, or if anyone else had an idea? thanks for any help.

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