Tube Theremin

Posted: 1/14/2009 10:00:11 PM
antiquekid3

From: Alabama

Joined: 1/14/2009

I have been into tube radios for some time (my latest project being my great-grandmother's Philco 42-1010 radio-phonograph) and am really wanting to build a tube theremin since I have access to tubes, transformers, chassis, and countless parts from my radio repairs. Does anyone have any recommendations for schematics and plans? I would really want easy-to-wind coils, but as long as it's not too complicated, I'll be okay. I also hope the transformer isn't some rare beast, or I'll really be in trouble! Thanks!
Posted: 1/15/2009 8:48:48 AM
omhoge

From: New York, NY

Joined: 2/13/2005

Welcome antiquekid3.
I can't help much, I'm just a player, but did you check our Schematics (http://www.thereminworld.com/projects.asp) page?

We just added Jeff's Kippinger plans (http://www.thereminworld.com/news.asp?s=792 )

Try the search too, coils were discussed by several guys who've built tube theremins, and look at the Keppinger videos (http://www.thereminworld.com/news.asp?s=550), they may help too.

Good luck! Can't wait to hear it!!!
Posted: 1/15/2009 12:06:52 PM
djpb_designs

From: Escondido, CA

Joined: 2/6/2008

I think the most recent and best tube theremin project that we have seen was the one built by the Georgia Tech students.

Try searching for the GT Theremin posts here on TW.

Don
Posted: 1/15/2009 8:30:29 PM
antiquekid3

From: Alabama

Joined: 1/14/2009

Okay, cool! I have checked the schematics page, but some of the transformer and coil data is either obscure or absent.

I'm actually thinking about going to Georgia Tech in 1.5 years! How awesome! I'll have to look that theremin up!

Thanks so much!
Posted: 1/16/2009 1:15:23 PM
djpb_designs

From: Escondido, CA

Joined: 2/6/2008

When you go to do a thesis project, try to come up with something new and unique. Maybe some really cool application for gestural controllers, rather than just building a theremin.

The world needs new, original ideas!

Don
Posted: 1/16/2009 1:22:15 PM
djpb_designs

From: Escondido, CA

Joined: 2/6/2008

Regarding power transformers ...

Check out Antique Electronics Supply and Magic Parts ( www.magicparts.com ). Both of these vendors have tubes, sockets, power transformers and output transformers.

Don
Posted: 1/16/2009 5:50:35 PM
antiquekid3

From: Alabama

Joined: 1/14/2009

I will certainly try and come up with something very creative. I think GT is definitely my #1 college at this point. I still have some time to fully decide, though!

AES is one of my favorite places for parts, but I am a member of the Alabama Historical Radio Society, and we have a lot of tubes and parts there. Who knows, I might try building an original RCA Theremin if we have the right parts!
Posted: 1/16/2009 6:48:47 PM
djpb_designs

From: Escondido, CA

Joined: 2/6/2008

Here's the Georgia Tech post:

matt.britt
From: Atlanta, Georgia
Joined: Apr 2008

4/25/2008 12:46:18 AM

Hey folks, I thought I'd share a recent Theremin project completed by myself and a friend. It was built as my senior design project, but it's something I've thought about doing for awhile.

Let's begin with the end result:
* The GT Theremin
* Close up
* Closer up
* Inside
* Filament transformer, tuning caps, internal supports for antennas, etc.
* Detail on sliding contact for the removable antenna
* Detail on one of the two stacks of circuit boards separated by a copper ground plane

First of all, yes the blue glow comes from LEDs... Blackbody radiators have to be pretty darn hot to emit in the 470 nm band. :P The physical design of this Theremin was intended to create an eye-catching aesthetic to go along with such an interesting instrument. Thus the metal look, the LEDs, and the somewhat unnecessary use of a glow-discharge tube (the big tube glowing neon orange).

I wanted to build it with vacuum tubes because I had never worked with them before, they add to the aesthetic (sorry, but an op-amp design in a plastic box isn't very interesting to look at!), and I think that doing so somehow pays homage to Termen's original design and the instrument's popularity in sci-fi movie sound tracks. The design uses only vacuum tubes as active devices, though I did resort to using a single semiconductor diode in the power supply to avoid me having to build a (complicated) error-feedback voltage regulator late in the design stages. Obviously the construction methods are modern, with molded (rather than wound) inductors in the RF oscillators, protoboard and heat-shrink-wrapped header pins, lovely compact electrolytic decoupling and filtering capacitors, etc. Again, I wasn't necessarily aiming to create an authentic early-twentieth-century design.

Here is the full circuit schematic if you're interested. It's entirely original, though I was influenced by Doug Forbes' and Art Harrison's tube theremin designs (kudos to them). I prototyped all the circuitry on several breadboards, but RF coupling issues were fairly severe with that setup so it still required some tweaking once it was fully assembled and in its present form.

The Theremin as shown was assembled over the past two and a half weeks or so, with the physical design being mostly dreamed up as we went, laid out in CAD in the evenings, and built during the day. The circuit design has taken me the past couple of months to conceive, simulate, and test. Some crucial components like the oscillators were simulated in EWB Multisim with some custom tube models that I found online and tweaked for my purposes. My friend is responsible for a lot of the good construction ideas, including the stacked circuit boards and the arrangement of the top.

So how does it play?

Pretty well! The pitch range is roughly 100 Hz - 3.4 kHz over a sense distance of around 12" (just guesstimating on the distance; I haven't measured in awhile). Volume dynamic range is about 28 dB, which is sufficient to bring the output levels from 1.5 Vpp max down to a few millivolts over the noise floor. There is a lot of harmonic content at the lowest frequencies, and the highest frequencies are obviously too closely-spaced to be very useful. I'd say the useful playable range is about 300 Hz - 1.5 kHz. I could probably improve the lower frequencies somewhat with some more work on the mixer circuitry; maybe I'll have the opportunity to in the future. Sorry I don't yet have a recording to share; I'll get some audio/video of it soon and share it here.

Well that's about all for now. I'll be glad to answer any questions you might have about the GT Theremin. Thanks for reading!

Update: Sound recording
Update 2: Demo video

It's still not on the TW Schematics page, but it really should be! They did a great job on this proj
Posted: 1/16/2009 6:53:36 PM
antiquekid3

From: Alabama

Joined: 1/14/2009

I love the look of it, although I wouldn't have the flip-open chassis. I like the look of an aluminum chassis with only the bottom open.

Also, I would much rather have the circuit that decreases the volume as you get closer, just like a band director. Or that's the way it should happen in a band! :-) Sometimes it doesn't always happen in our school's band!

I really am liking the way the Keppinger tube theremin is looking. I might need some info on some variable capacitors for tuning. Thanks again!
Posted: 1/17/2009 11:05:16 AM
hypergolic

From: Richmond Hill, Georgia

Joined: 9/18/2005

Check out

http://www.neidlinger.us/keppinger.htm

You can get trimmer pots from

http://www.surplussales.com/

Keep in mind, that the pots probably need to be good quality chassis mount types. Aligning the thing with it in pieces doesn't work well. The tuning points change when reassembled.

What I did was drill holes in the shelf the oscillator chassis is sitting on, and align the trimmers so they can be adjusted from below----however, make sure they have enough room above the power supply tubes so you don't burn your hands.

Get on LEVNET and ask Mark Keppinger if he has any chassis sets left over. The project will work A LOT better if mounted on a prepunched chassis..

Good luck

Philip Neidlinger

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