Enkelaar Mod

Hi everyone !
I'm new here. I own a Kees Theremin and there was this mod I wanted to try for a long time :

https://www.element14.com/community/docs/DOC-23047/l/enkelaar-theremin-schematic

The idea is to replace the 2 position switch (sine/square) by a variable resistor to have a tone shaping pot. I did it today but it sounds awful.
1st half of the coarse has nearly no effect on the sine wave. On the second half, there is a nasty distorted sound added, like harsh harmonics, only on a part of the range, so there's a point in the scale where it disappears. The distorion varies with the volume antenna. When I turn it full CW, I get the original "square" sound, or at least close enough

I probably missed something. I don't know electronics, I just followed the instructions. Any ideas ? Maybe it's a much more complex problem than I thought and I should step back ?

Thanks for your help !
All the best

Your theremin is excellent for learning and understanding the theremin principles. Learning how to play effectively requires a better design. The transistor can capture all the wonder of the original vacuum tube Classic Theremin. Many theremin designers today give up what is beautiful about the theremin and go digital as that is all they know.

This is an analog transistor design with a little bit of knowledge.  Sample.wav 

Currently I am working on a DIY modification for the EtherWave Standard where my Pitch module replaces the EWS pitch side completely with a plug-in $100 mod using a basic TRS jack, the EWS PCB remains un-violated and un-removed. Unplug the TRS male plug and the EWS theremin returns to normal. This approach has ideal Pitch Field linearity like the Epro or better, Pitch Preview, Mute and the Classic Sound. Let us return to what is beautiful about the theremin, that has been lost over time. The PCB to do this I have and give away at no cost, if you have pictures of your build skill and you are in the States. Your success is most important. Today is August 28, Leon Theremin's recognized birthday.

Christopher
www.Hwy79.com

Hey Christopher,
Thanks for your reply ! 

The Kees isn't very satsfactory indeed : loop range is very short, linearity isn't great and the sound is either dull or harsh. I love its look though !
I've tried an Etherwave the other day and seemed easier to play, but I'm not going to buy one (I have other machines and synths, both digital and analog to make my music)

The idea was to find infos to upgrade the Kees to the max of its design possibilities in order to get a better practice ; and to find a better instrument later when I know I can play something decent on the theremin. But perhaps the Enkelaar design is not upgradable.

About your design, at first I thought you were talking about a EWS mod module, but from your website I've understood it's a complete build. It seems really interesting ! Seems that it is the instrument I've always dreamt of. I could use the Kees antennas and build a cabinet myself (woodworking and 3D printing is not a problem)
But I'm not confident in my skills. I can (and did) unsolder/resolder wires and pots, but a complete assembly scares me as I don't have electronic knowledge. Means that I could solder everything but without knowing how to troubleshoot and monitor the progress.

I have an long-term medium-skill electronic project with my kids which may give me more confidence in the future but for now I don't know how reasonnable it would be... Tho I'd love to be one of the early birds (phoenix?) diving into your theremin design ! Your thoughts ?

— Still looking for infos to upgrade my Kees for now. Any tips about Fred modification ?

Thank you again

Hi Chritopher,
Thanks very much for your reply. I know the Kees Theremin has some flaws. The volume range is quite short, linearity isn't great and the sound is either dull or harsh. But I'm not willing to buy a more expensive instrument for now (I already have what I need for my music)
As I want to practice a bit more, my idea is to try to upgrade the kees as much as I can... but maybe it's not possible or not worth it.

What you say about your design is very interesting ! Seems it is the theremin I've always dreamt of. I was dreaming of a subscope recently... Your sample sounds very good, very classic to me.
At first I thought it was only a plug-in for an EWS, but I've discovered that it is a complete build, which is great news !
I'd be glad to accept your generous offer, but I'm not in the States and I don't think my skills would meet your expectations, I have only a little experience in soldering and not at all in electronic design and theory.
This said, I'm a curious mind and a fighter and I don't give up easily. I'm now on a big non-musical project that involves a lot of different skills (including electronics) and it's going well.
I surely would be pleased to be an early bird (phoenix?) user of your design !

(In the meantime I'm still looking for infos about the enkelaar mods)
thanks
All the best !