Seeking Advice: Playable Digital Schematic

Posted: 5/31/2010 12:46:33 AM

Joined: 5/31/2010

I'm looking to build a theramin over the summer. It kinda defeats the purpose to just buy a kit and vaccuum tubes frighten and confuse me.

I'm looking for schematics for a digital two-antena theremin that will be playable with a minimal ammount of fuss and provides some flexibility for future alteration. I thought I had found this in the Glasgow University schematics, but apparently the general consensous is that this is not (at least without alteration) a playable instrument.

Any suggestions?

Thanks in advance.
Posted: 5/31/2010 2:13:04 AM

From: Croxley Green, Hertfordshire, UK

Joined: 10/5/2005

Welcome to Theremin World, laughingfuzzball.

[i]It kinda defeats the purpose to just buy a kit[/i]

Surely that depends what the purpose is.

It will help people give you relevant advice if we know a little of what you intend to use the finished theremin for, and something of your experience with building electronic devices.

Also, why specifically digital? The consensus around here favours analog. :-)
Posted: 5/31/2010 2:54:04 AM

Joined: 5/31/2010

[i]Surely that depends what the purpose is.[/i]

The purpose is to build a theramin :p

Seriously, though, I want a project to work on through the summer and this seemed as good as any. Assembling a kit is hardly a summer-long thing and feels like cheating.

I would like to be able to play music, though it does not necesarily need to be concert quality. Basic musicality--volume control, bearable tone, some semblance of linearality-- is enough.

I went through an electronics phase in my teen years, and can still follow a schematic if I have a chart for some of the less common symbols. This will be a challenging project for me, so simpler is better, as is a minimum of fuss and adjustment. Some challenge, frustration, and experementation is good, though.

I know that the general advice is to start with a pitch-only instrument, but neither the process nor the end result would be very enjoyable.

Why digital? It seems like the easiest way to keep the project relatively simple and cheap. If analog can be done without too much fuss or specialty components, I generally preffer the sound, though I was under the impression that analogue usually meant vaccuum tubes? I have no experience with vaccuum tubes, and they seem a bit costly.

The EM Theremin certainly seems simple enough, and there don't seem to be any specific complaints about the design, though someone said some of the integrated circuits have become hard to find. Can these be found through internet suppliers? Is the EM a good candidate, or does its simplicity hamper its usefulness?
Posted: 5/31/2010 3:47:31 AM

From: Colmar, France

Joined: 12/31/2007

The EM Theremin is a good choice since it is technically a predecessor of the Moog Etherwave Theremin.

There is only one IC inside (LM13600) which can be replaced by the LM13700. The latter can be found on ebay without problems. What will be much harder to find are the adjustable TOKO inductors (2x100uH, 1x68uH) since they are out of production.That's why Moog modified the circuit:
They replaced the 100uH by fixed inductors of 47uH in series with adjustable 47uH TOKO inductors in the pitch oscillators and the 68uH by a fixed 22uH in series with another adjustable 47uH in the volume oscillator. The adjustable 47uH TOKO inductors (154ANS-T1017Z) can still be found here: (Reference EZ1017) I recently ordered some as replacement parts there.

Still later Moog replaced these TOKO inductors by Coilcraft TEN-5-10 types which have a hexagonal tuning slug and which are still in production. They don't bring any technical or musical advantage to the theremin but they require a different biasing of the oscillators which had to be done by changing most of the resistor's values around the three transistors in each oscillator. So if you can get some TOKOs, don't care about the Coilcraft problems. I have the fixed 22uH and 47uH inductors which have to be put in series in stock, so I'll be able to help you with them since they're hard to find in small quantities (I ordered 50 of each recently).

Another problem will be the linearization coils (2.5mH, 5mH, 10mH) which have to be 3Pi wound inductors with low distributed capacitance. The final values to use depend strongly from the antenna geometry, so we'll see that later.
Posted: 5/31/2010 4:11:28 AM

From: Colmar, France

Joined: 12/31/2007

Edit: Deleted double post due to network probs
Posted: 5/31/2010 3:33:11 PM

Joined: 5/31/2010

Thanks for the help, guys.

I wasn't too worried about the coil issues, since there are solutions just a couple threads down. I think I'll try to snag the ones used in the article, to minimize fiddling. If not, I'll use the alternative TOKO coils with the modifications you suggest (it seems simpler than sorting out the Coilcraft issues).

How major of an issue will the linearization coils be? is it just a matter of fine-tuning, or are significant alterations likely to be required to make it playable?

I knew Mr. Moog was responsible for the EM design, but didn't know it was so similar to the etherwave. I had assumed it was a dumbed-down version for us uneducated plebs. This is good to know.

Thanks again for the advice, guys. I'll start sourcing parts this week, hopefully you'll be laughing at my poor construction skills and electronic ignorance in a month or so.
Posted: 7/3/2010 12:56:55 AM

Joined: 5/31/2010

The first box of parts came yesterday. I might be able to work on the cabinet this weekend.

Since I'll mostly be using headphones or powered speakers, rather than a proper amp, I think I might like to have a mini-jack in there. Can I just put one in parallel with the 1/4" jack, or would I be better off leaving the circuit alone and using an adapter?
Posted: 7/3/2010 5:17:07 PM

From: Canada

Joined: 8/1/2008


The only people who are allowed to misspell the word "theremin" and get away with it (simple typos don't count) are people whose native language is NOT English. Since you are obviously an English speaker, you just gotta learn how to spell THEREMIN.

Hey, good luck with the project.

"Hallo avrybuddy, I am a parson who is in hungary living wanting to build thariman......"

Posted: 7/4/2010 5:33:11 PM

From: Colmar, France

Joined: 12/31/2007

[i]"Hallo avrybuddy, I am a parson who is in hungary living wanting to build thariman......"


"...I want to have this shpooky sound effects. BTW: my name is Vlad D."

Posted: 1/21/2011 6:55:33 PM

Joined: 1/20/2011

are you using the schematic for this one?

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