Construction of a Keppinger Design Theremin

I started playing the Theremin around October 14, 2005. Like most people, my first, and current instrument is a Moog standard Etherwave. I am guessing perhaps 90% learning to play a theremin start on an Etherwave. I've been involved in electronics for most of my life. I have a degree in it, and I play with electronics in my free time via Ham Radio. You might say that learning to play this instrument is appropriate for me....I'm a techno-geek! However, I've never been particularly happy with the sound of my me it sounds somewhat harsh and buzzy. It takes a bit of digital processing to smooth it out, but in doing so I lose a bit of response in the high end registers.

After joining up with Levnet, the internet reflector for theremin enthusiasts, Mr. Mark Keppinger emailed and said that he had a pair of spare chassis left over from his vacuum tube theremin construction projects. Mr. Keppinger's theremins are highly sought after instruments, given their outstanding tonal quality. I eagerly asked for a set. Uncle Howie donated the coils. Mr. Andrew Baron sold me a bunch of parts for a good price, although I'm sure it took him quite a while to get them together from his junkbox. A lot of people have helped me from the Thereminworld and Levnet groups, and for this assistance, I am grateful. Finally, a special thanks goes out to Mr. Peter Pringle and Uncle Howie, for their encouragement, advice, and patience, answering many of my questions about playing technique and working with old style electronics.

March 11, 2007: Here is the chassis underside with tube sockets and terminal strips installed.

March 11, 2007: Here is one of the chassis pieces, freshly painted.

March 11, 2007: And, here is the top of the other chassis.

May 26, 2007: Installation of most of the capacitors on the chassis begins in earnest.

June 29, 2007: Point to Point Wiring Begun. Resistors are next in line.

July 31, 2007: I apologize. I've been a bit negligent in my updates. In a flurry of activity, I finished the power supply/audio amplifier chassis a couple of weeks ago. Everything works fine. None of the magic smoke was released when the "on" switch was thrown for the first time. The 0D3 regulator tube is particular pretty (its the one that's glowing purple).

July 31, 2007: Now, here is the underside of the power supply/audio amplifier chassis, showing all the point to point wiring. I haven't had the time to dress up all the wiring bundles with nylon ties. I also need to torque down the screws holding down the transformers and large power supply choke as they are little more than finger tight at the moment.

July 31, 2007: Here are the two of the coils Uncle Howard Mossman gave me. The large one is the tone coil. The smaller one is for the volume, or "expression loop".

August 5, 2007: Almost done with the underside of the oscillator chassis.

August 5, 2007: Here is the top of the oscillator chassis with the porcelain coil standoffs installed. Note the sockets for the jacks that will eventually plug in the two large coils. The middle jack is a test point.

August 13, 2007: Here is the top of the oscillator chassis with the coils wired up and installed.

August 13, 2007: Here is a closeup of the brass hardware connecting the wire leads to the coil windings. I soldered the windings to a brass washer, which in turn is held in place by a brass screw. We'll see how well it works. If it gives any problems we'll just solder the wires directly to the screws.

August 13, 2007: Here is a profile view of one of the coils. Red is the top of the winding; orange is the middle tap near the bottom, and black is chassis ground.

September 1, 2007: Here is the top of the completed oscillator chassis. Looking good! Let's hope it works that way!

September 1, 2007: Here is the underside of the completed oscillator chassis. Not the best solder job in the world, but I'm proud of it. Notice the abundance of cloth covered wiring.

September 1, 2007: Here is the pitch antenna coil, with a temporary coathanger antenna, and a pair of pliers attached and held by a rubber band in order to increase the mass of the array for tuning stability (really a misnomer, if you think about it). Just admire the high tech work here in the shack of KA4KOE---nuttin' but the best!!

September 1, 2007: Here is the volume antenna coil, with a temporary coathanger antenna, and an Asimov book for counterbalancing. Note the pockeknife in contact with the coathanger to add mass. Grandpappy Lev would have been proud!!

September 1, 2007: Here is the entire collage of vacuum tubes, wires, transformers, and other assorted kludges all put together on the test bench. I consider it amazing that this did not go "POOF" when all was energized as one unit for the first time.

September 5, 2007: Thoughts....The Keppinger theremin works, and is producing music, but the tone is full of odd harmonics, squeals, and strange sounds (and this is when I am not playing it!). I am having issues with the oscillators staying that way, ie oscillating. However, more troubleshooting, tweaking, and tuning is pointless at this time until I get a cabinet built and proper antennas installed. I have received a great deal of assistance from Andy Baron, Jeff Sparks, The Man himself, Mr. Mark Keppinger, Uncle Howie, and others. We'll continue our updates as progress is made on the cabinet. Sheri, my bride, has named this instrument "Gabriella", a proper Italian name, as she loves opera.

October 6, 2007: After doing some research, I reduced the grid to ground shunt resistance on the two tone oscillators to 50k Ohms (originally 100K). This modification has completely cured the intermittent oscillator operation. The instrument is now quite playable. I've been told Gabriella's voice is "stunning" by experienced players. After all of this effort, my greatest fear was that this thing would sound like a cheap penny whistle, as Uncle Howie would put it. My bride Sheri recently told me that my gift for our 7th wedding anniverary would be a custom made cabinet from a master carpenter! What a gal!!

November 14, 2007: I have completed installation of the theremin in a temporary cabinet, and will post pictures as soon as I possibly can. The theremin is working wonderfully, and has been played in my church.

December 20, 2007: Here is Gabby on top of the Fender KXR100 amplifier. This is the temporary cabinet.

April 30, 2008: Gabriella is now mostly complete. The cabinetry installation was finished after we received word about a month or so ago from our carpenter friend. The theremin was taken to Etherfest 2008 where our reception was outstanding. Lydia Kavina was the first thereminist other than myself to play Gabriella, and she also was very gracious and autographed Gabby for me. Click on the link which will take you to Flickr, where we have a lot of photos posted. Here are a couple for your enjoyment right here....

Click here for an overall schematic of the Keppinger Theremin. We will upload a clearer version of this schematic when time permits.

Click here for a sketch of the temporary cabinet shown on this page.

Click here for a sketch of the cabinet I designed, but did not build. It was a nice drafting exercise for a few winter evenings.

Click here for a sound sample of Gabriella currently on my Panelectronica MySpace site..

Click here for a parts list of the Keppinger Theremin in an Excel spreadsheet format.

Click here for Mark Keppinger's Theremin Page.

To the best of our knowledge, none of the material presented on this webpage has any copyright or other encumbrances.

Page updated on June 8, 2008 by Philip Neidlinger

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