Kustom Theremin 1966

It's been about 6 years since I tuned it, and I don't remember everything. I do remember that I was able to tune it by ear, without any test equipment. It is a simple design, and I'm surprised that it works so well.
I'll open it up again, make some notes, and post a procedure and a few photos.
Shoot me an e-mail. randkg (at) att dot com
I wrote my address that way to avoid spam, but anybody on this forum is welcome to send me one.
I've been looking for information on this old beast for a long time, and this forum is the first hit I've had.
I was beginning to think it was home made, and stuffed in a Kustom case, or maybe a prototype.

I'd be glad to see pictures of the instrument...

I took some pix, I just gotta figure out how to post them........Sigh.
I'm also drawing a schematic while I have it open.
This will take a while.

The easiest way to post pictures is to use one of the many photo hosting websites to host the photos and post a link to them here. Here are a few of the most popular...

photobucket.com (http://photobucket.com)

imageshack.com (http://imageshack.us)

flickr.com (http://www.flickr.com)

Theremin World has a photo gallery, but it hasn't been updated in years, and I don't think very many people even look at it. You could ask John or Jason if they'd care to host the photos.

W0ttm -

If you want, I can put your pictures up on Element-14 (http://www.element-14.com/community/groups/theremin-general-resources) and link them to here.. I might even be able to embed the images in this thread..

<-- My email is in my picture.. Just email the pics to me and I will be happy to do the rest.

Fred.

I took a bunch of photos of the internal parts of the Kustom Theremin and posted a zip file at Kustom Theremin Photos (http://www.lightshow.cc/download/Kustom Theremin.zip)

FredM- Thanks. I'll probably send you some.
Digitalrust- Great pictures! It looks like your volume oscillator is set at a lower frequency than mine. The coils are near maximum inductance. I don't think that maters much.
I measured my volume oscillator frequency at about 400 khz and my pitch oscillator was at 138 khz.
I have a schematic now, and I'm writing a tune up procedure.
The schematic is hand drawn, so I'll post it when I've finished transferring it to my schematic editor.
My avatar is the beast we are discussing.
More to come..........Rob.

Kustom (http://s1090.photobucket.com/albums/i368/w0ttm/)
Let's see if that works.
On the schematic, some parts have no value because they were not marked.
I think the trimmer caps are about 10 pf.

Thanks W0ttm -

Another schematic ;-) .. This one is quite inductor laden - and they are not, as far as I can see, standard parts.. So take great care not to damage them!

The design? - well, crude is something of an understatement (I just love the diode connected directly to the output - LOL! - Now that REALLY is taking component minimization to an obscene extreme! ;-).

I doubt that the 'diode' setting will be bearable to listen to - wasp in a jar, I suspect.. The 'sine' tone could be ok, particularly if there is good coupling between the VFO and Ref oscillators - and the mixer looks like it will provide this..

The mixer is similar to that on the EW, but MUCH cruder, and the "VCA" is so crude I am surprised it works! - There will be severe "distortion" as the volume is changed - particularly at the low volume end.. but this could be ok - The EW deliberately causes the volume to affect the harmonics.

I doubt this theremin will play well in the bass register - I suspect the oscillators will go into lock at quite a high frequency, and probably jitter on the border. There is an EQ inductor, and oscillator coupling, so linearity might be reasonable.

Apart from the inductors, this is one of the simplest pure analogue theremins I have seen - The whole thing could be thrown together for about £15 if one costs each inductor at £1.50.

On the left bottom corner (DSCF0009.jpg) there seems to be the tuning capacitor .. Dont know if this is accessible from the front (should be) but this would be the first thing to try adjusting.

There are two tunable transformers shown at the top of the schematic - Left-hand one is the pitch oscillator tuning, right hand one is the reference oscillator tuning.. One wants to tune the antenna capacitor and VFO inductor for optimum linearity - this is the tricky part... Then you want to adjust the reference oscillator for null when hand is withdrawn from the antenna, hopefully you wont need to adjust the volume oscillator.

Best to find someone who has done this sort of thing before, if you can.. But if not, look over tuning instructions for the EW and any other theremins you can before you start fiddling.

Fred.

Thank you W0ttom,
I really appreciate the schematic and I look forward to your procedure for tuning the coils.

Thanks FredM,
Very helpful observations. Even though the design is not up to standard, you would be surprised by the tone and playability of the Kustom Theremin. Back in 1967, I found it very easy to play in pitch and I loved the tone of both the sine and distorted sounds. With a little splash of reverb it was a very rewarding instrument to play. It fit perfectly with the psychedelic sounds of the day. On-the-other-hand, I never liked the volume control; it had too steep a curve. But, a Morely volume pedal solved that problem.

As to the dependability of the parts, well my theremin worked hard in 1967 and 1968 then it just quit. Recently I put it on the bench and checked the components looking for the part or parts that had failed. I found a bad 6 mfd capacitor. Unfortunately thirty years ago when the theremin stopped working, being young and full of confidence beyond my skill, I changed the settings of the tuning inductors, ignorantly trying this and that to make the thing work without understanding anything about the circuit or electronics for that matter. Looking back it makes me want to laugh ... and cry.