Kees Enkelaar Theremin

Posted: 5/22/2013 2:33:49 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 . ...................................

Joined: 12/7/2007

The Kees is about as simple as a theremin can get - its just a SC (Jaycar) theremin kit with modifications.. $1000 is absurd for this $50 kit with a few modifications and a nice box.. Anyone wanting one, contact me! I will happily build one for $500! (perhaps even less if you twist my arm ;-) .. With the disclaimer that, IMO, this is not a "good" instrument .. and not worth $500 IMO...

I know some people like Uncle Howie have praised it and said it sounds like an RCA, but I really cannot see anything about it to merit this commendation - Its sound is entirely derived from using its horrible power amplifier (The original SC drives a horrible small speaker - this particular amplifier is well known amongst the "Stomp-Box" community as a useful distortion component)

Kees used this amplifier to change the tonal character of the SC so his theremin gives line-out with a "waveshape" switch and exploiting this amplifier distortion mechanism - he also did some modification to the front-end to facilitate tuning and other minor improvements - But nothing was done with care or attention to detail.. It is, bluntly, hobbyist.

Full details (schematic, photos etc) of the innards can be found in my documents page on my Element-14 Theremin group.. See all documents starting with "Enkelaar".

This is an extremely simple re-build of the SC theremin.. The schematic etc were "decoded" by me from Gordon C's Enkelaar.. Any competent constructor could buy the S/C kit and modify it based on the data I have provided.. probably about $10 extra components and a good cabinet and antennas are the only extras needed.

Sorry Dana - But if one looks at whats inside a Moog 91A, and the fact that these are not selling for even $500.. And one looks inside a Kees - Well, getting $50 for a Kees would be a comparative over-charge.. Ok, I know it doesnt work like that - But IMO if you got more than $400 you would be doing well. In terms of performance, the Kees is usable - As usable as the other SC theremins, but cannot be compared to an EW or 91 or any other theremin which is designed by someone who knows what they are doing..

At its original low price, the Enkelaar was fair, IMO.. The modifications Kees made to the S/C theremin were needed and improved it (Some of these modifications are the same or similar to those published by Max Baars here on TW - I dont know who was first..) And Kees is not responsible for the worst aspects of the S/C design.. IMO, the S/C design is simple - but that is the only thing it has going for it! 


Posted: 8/30/2020 12:28:13 AM

Joined: 8/28/2020

Hi Fred, I know this post is old but it led me to think I can make few simple mods on my good old Enkelaar.
Fisrt of all, thank you very much for having provided these infos about the Kees theremin.

I've replaced the tone switch by a variable 100k resistor as you suggest here, but it doesn't sound good. The non-extreme porsition are unevenly distorted.  Am I missing something, should I have done something else ?

If I may ask, on the Max Baars page about the S/C it is suggested that replacing the 1MOhm by 220k (or 100k in your drawing) would improve the behaviour of the volume antenna, extending its range. Would it work on the Kees ? (Maybe it's more complicated than that...) The part about adding a coil to linearize the pitch field seems interesting too.

Thank you for your help !
All the best

Posted: 8/30/2020 12:44:20 AM

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014

Fred is dead long ago as is Max and Uncle Howie, they were great to debate with. Yes a pitch antenna coil is one of the secrets of linearity. You want the pitch antenna circuit to resonate with the variable oscillator. You tune the variable oscillator to be slightly "above" the resonant frequency of the antenna circuit with series tuning.

In my own theremin design my antenna circuit resonates in parallel with the variable oscillator. This method surprisingly is much more forgiving. When you have linearity from a resonant antenna circuit the musical notes snap into place, there is no almost linear.

This should be a fun experiment for you.

How the beautiful sound comes about is so simple yet not obvious. I am considering mounting the best transistors for it to happen as I mount IC sockets on the boards that are given away. The Classic Sound begins at the Pitch Antenna if not in the Pitch Field. It seems her voice has been elusive to most engineers.

When I tell many generous details it is because I am looking for that local young hot shot builder to embrace my research as I have special knowledge. Also looking for a good local Thereminist and I would make her day. Most theremin designers are engineers who in their old age are so smart they become stupid to analog design so they go digital as that is what they know.


Posted: 8/30/2020 8:09:10 AM

Joined: 8/28/2020

Oh sorry to hear that. It is a faux-pas from a newbie, my apologies. 
Thank you for the info, I’ll do my best to understand what I can and experiment a bit. 
As said I’m no engineer so I can’t really debate with you on the process, nor be the local researcher you’re looking for. Just trying to get a fun way to enhance my instrument and my playing. 
I’m not expecting miracles, but making a few mods that work would be a great satisfaction for me. 
I look forward to get more confident In my skills and maybe one day try to build your design !
Thanks again

Posted: 8/30/2020 4:21:36 PM

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014

PcXT no need for apology as we all take our turn.

Each morning in the hour before I get out of bed I have a moment of clarity. Today it told me your theremin could have ideal linearity which is what makes the theremin musically playable. This is a major aspect why many pay so much for the Moog Epro.

This could be a fun experiment. What you would need is a frequency counter and access to the spring coil I use. This is the antenna circuit for Ideal Linearity.  C20, L4, L5 and the pitch antenna which is a spring coil resonator. Does this look like something you could tackle?

What frequency does your theremin work at, it may need adjustment, maybe near 450 khz.

When I tried this on the Thierrymin at 450 kHz using FET's it did not have the horsepower to drive the circuit properly, maybe two octaves.

Edit: Looking at the Jaycar schematic I have my doubts this will work, the JFET's.

LT Spice by dewster
  needs update                            More Electrodeum Info


Posted: 8/30/2020 7:43:09 PM

Joined: 8/28/2020

Thanx man, this is awesome. 
I think I could manage to build that circuit.
What I don’t know is if I can connect it to my existing board haha !
I’ll try tomorrow to fix my tone problem. I’m not sure if it’s worth the hassle if my instrument has still a sound that isn’t satisfying. 
In fact you almost made me want a better instrument!

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