Keppinger Video

I was in contact with Mark Keppinger today and mentioned I had found a picture of him on the internet. I did a search to try and find out where I found it and stumbled across something wonderful. I don't remember anyone ever posting anything about this (but that's not to say they haven't).

I found a series of 14 short videos of Mark himself talking about the theremin and his tube theremin in particular. While about half are of the usual fare, I found the ones about the construction and function of his theremin to be especially interesting. In the last one he even describes and demonstrates his coil winding machine. I recommend videos 1 through 5, 8, and 14.

Mark Keppinger (http://homegarden.expertvillage.com/interviews/theremins.htm)

Thanks Jeff! It was cool to see these.

I emailed Mark a while ago asking about the winder Steve used to repair Maunette, and he responded with some detailed info about the coil winder, but was too busy to send a photo along (he sounded very busy, so I don't blame him). Though he didn't send a picture, his description was clear enough to visualize it. Here's what he wrote me:

"I work at our local science museum (www.omsi.edu) as an electronics designer, and Roger, one of my co-workers who is a machinist extraordinaire, helped me build the winder. It consists of a wooden platform, a double ended arbor with 5/8" bronze bushings, an old foosball rod (5/8" diameter!), a flywheel with a crank handle on one end (off of an old Singer sewing machine), a few wooden cones with 5/8" holes drilled through the centers, a few springs to allow for the various lengths of coil forms, a pin that keeps the cones / springs from slipping off the end (the pins go through the foosball men holes), a microswitch, a "P" clamp around the 5/8" rod that acts as an actuator that hits the microswitch each time it rotates, a mechanically resettable electrical counter connected to the microswitch, and a power supply that runs the counter. Want me to take a picture of it tomorrow and e-mail it to you? Please feel free to pass this info along to the other good folks on LevNet... "

Is it correct that the classic theremin sound is basically a fully rectified sine wave, plus a bit of amplifier colour, as mentioned in the clip "what makes the theremin sound special?"

Well, I was initially under the impression that the detector circuit was little more than a balanced (ring) modulator along with a low pass filter to pass only the difference frequency. Assuming that the fixed and sensing oscillators are producing sine waves, then the difference frequency would be a sine wave in such an arrangement. Theremins such as the Theremax use a balanced-modulator/low pass filter arrangement.

Some theremins use Mixer/detectors. Consider a mixer that simply adds the two signals together. If you saw the result on an 'scope, you would see an amplitude-modulated radio-frequency waveform (the result of the two oscillators periodically adding and cancelling each other out). A detector would then produce a pulse corresponding to the peaks of the signal -- decidedly NOT a sine wave. (an analogy would be to sit on the edge of a pier when the water is just high enough that the tops of the waves touch your feet -- your feet are like the detector -- picking up the peaks).

Howard Mossmann (an acknowledged expert on the topic) has written about the tube detector circuitry -- and asserts that the "classic" RCA sound is largely the result of the tube detector circuit. To run a solid-state theremin through a tube amp will not produce the same effect.

Incidentally, the Keppinger Videos are excellent. His coil-winding machine demonstrates some real genius!

There are others with much more understanding of these circuits than me and perhaps they will contribute some info to this thread (and correct me if need be :) )

hi to all
i wrote to mark by a email that i found in google, but i havent had answer till now, does anyone the contact of him?, please let me know more than one, :), i am really interested to make a real theremin.
thanks

Well, I can't tell you if you have the right address, since you didn't tell us, but Mark is a busy man, so he may not respond as quickly as you might like.

He was selling what parts (chassis, etc.) he had, so I don't know if he has any left, if that's what you're looking for.

I don't know what you're looking for, but I might be able to help. I just finished redrawing the schematic for his tube theremin. I've heard it was available online, but I haven't been able to find it there.

There are also a number of other theremin schematics online. I believe Jason has links to several of them in the Theremin Construction/Schematics menu on the left side of the website.

Hello Jeff,
I'm about to complete two of the Keppinger theremin.
I made a complete part list and complete the schematic.
I will really appreciate if you can send me you redrawed copy of the schematic.
Many thanks :-)

Vincent

Vincent - You must be the one who made up the component list I used to verify the identity of some of the components I couldn't read on the schematic. If so, I owe you a big thank you!

The only issue I had was that there are TWO different resistors labeled R27. I do not feel comfortable about that. I intended to ask Mark about that before I shared the new schematic drawings with anyone. I don't think it would be a problem if I just renumbered them on my own.

I also have detailed information on the coils as well as modifications to change the range and add a pitch preview.

You can either post your email address here or send it to me at jaygeeess(at)yahoo.com if you'd prefer.