Patents are a problem when designing a theremin?

Posted: 1/6/2009 6:50:58 PM

From: Escondido, CA

Joined: 2/6/2008

Wouldn't have been nice to have been able to sit down with Bob Moog for a day or so and talk about all the things he had tried ... what worked and what didn't?

All of us builders and developers are really just repeating what Bob did.

3.14 (pi, eh?), I don't want to sound so discouraging, but I am not sure what you have in mind. There's not really any new, 21st century technology for building 2 RF oscillators. If you dive into any latest & greatest radio or TV, you'll still see bipolar transistors and MOSFETs ... maybe a phase-locked loop chip (PLL) ... nothing new there. Stripline inductors maybe? Not new either. Varactor diodes? Also not new.

The 21st century has really only brought us "faster, better, cheaper, more efficient" microprocessors and DSP chips. "Better mousetraps" as it were ... not anything earthshakingly new. These would fall under the "digital cheating" category. And if that were the route you were going (you said you were not going down that road!), you'd probably be better off to buy a MIDI synth.

The other thing "new" is the push to connect everything from cellphones to toilets to the internet ... again nothing much of interest there to aspiring theremin designers. "iTheremin", "Wii Theremin" ... uh, no thanks! A friend of mine has a harmonica simulator application on her iPhone ... cute gimmick, not all that useful!

If you stray too far from 2 RF oscillators beating against each other, you'll probably kill the timbre. Pure sinewaves tend to not sound all that musical. So PLLs or digitally-controlled oscillator chips would not be the best. Some of the "magic" is in "predistorted" (i.e. not pure sinewave) waveshapes in one or both oscillators and some non-linearity in the detector stage.

You might be able to make the oscillators more temperature-stable, but that's about it.

If you read through all the dialog that has gone on between the "professional players" on this and other forums, you might notice that what they prefer is the older, simpler technology.

Vacuum tube-based designs seem to have that nice "throaty" sound to them, but that kind of sound is not impossible with transistors. JFETs are finicky and are not used in new designs as far as I can tell. The Jaycar theremin uses JFET oscillators.

In Bob Moog's Etherwave design he used oscillators that were made from differential amps. Those are probably very stable, but you might have to match transistor pairs. You might be able to build something similar with newer opamps, but they may be "too clean" to be musical.

Maybe there are other methods in use in "modern theremins" (not everyone publishes their schematics), but I think I've pretty much covered the ground in the above discussion. Got something above and beyond these approaches? Then maybe you should build one, convince yourself if works under worst case conditions, then seek a patent.

I hope this is helpful, not hurtful information. Sometimes just being told "you can't do that" encourages amazing new things ... you never know.


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