[URGENT] need a help with my theremin build

Posted: 3/12/2017 2:24:24 AM
Art Harrison

Joined: 3/17/2010

This theremin is described at http://www.theremin.us/200/wien.html. It is a design I did in 1999 to evaluate a number of non-resonant circuit topologies for pitch theremins, and it works fairly well. Several of these have been built in the 18 years since publication. There are detailed drawings in the article, such as http://www.theremin.us/200/top.gif that show the recommended layout with Vectorbord(TM) and push-in terminals. The schematic presented above is a copy someone made, sans my name. If there is interest in a sound sample, I would be happy to post one.

Posted: 3/12/2017 2:44:47 AM

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014


I am not the sharpest marble but I don't think you mentioned what the sudden awakening is about? I will always think of you as one of the great ones, you demonstrated stuff that actually worked. I found outside of the USA circuit design is often a secret or it does not work and here in the states everything is over analized. What makes theremin design special it is actually simple or as complicated as someone wants to make it. As I have learned over the years everyone is an expert.


Posted: 3/12/2017 1:28:45 PM
Art Harrison

Joined: 3/17/2010

Hi Christopher! 

I hadn't been looking around the Internet for things-theremin lately, but someone who recognized the design as being one of mine brought this thread to my attention. I responded (about 880 days late!), although I realize it is essentially a forgotten topic.

If the fellow having the trouble with this design had contacted me, I would have been happy to help, but such is the nature of these circuits when the schematics are stripped away from their articles and construction advice is ignored.

I noticed that 2N5457s JFETs replaced my recommended 2N5484s, so I would first 'scope-out the oscillators to make sure that their AGC loops are functioning. The two types are similar, but some differences may prevent the 2N5457s from working they way I intended. Also, as someone mentioned, the neat-looking white board layout may be a detriment due to numerous stray couplings.

Posted: 3/12/2017 1:40:32 PM

From: Northern NJ, USA

Joined: 2/17/2012

"Also, as someone mentioned, the neat-looking white board layout may be a detriment due to numerous stray couplings."  - Art Harrison

That was me.  There's nothing nearly as convenient as a plastic breadboard when it comes to trying things out, and there are ways to minimize stray C when doing so (use a raw breadboard without a metal plate backing; lift the breadboard a few inches off the workbench with a plastic box or spacer of some sort; when C is really critical leave every other row blank and wire "in the air" rather than close to the board, etc.).

It's quite instructive to take a very sensitive C meter and roughly measure the various items that might come in contact with Theremin circuitry.  I think budding developers too often work in the dark when it comes to these kinds of basics, and end up rather superstitious.  For example: wood very close is surprisingly kind of bad, metal doesn't need to be brass nor kept >2m away.

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