Theremin...

This one was just featured in IEEE Spectrum and you can buy it as a kit:

Here is the article:

Looks like the only thing the author didn't like was the not so exact fit of the oak enclosure parts. $359 is probably a bit steep for "doing some electronics" but it does look like a fancy instrument. Not something your wife would want out of the living room immediately. And since the Euro is pretty high and if you daughter promises not to do anything stupid or dangerous for at least six months, maybe Santa Claus has a heart ;-)

Not sure what the French authorities would think about the EMI these things generate, I think they are quite strict over there.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Chris

free.fr...

her

er

-)

Well, I can report that the University of Glasgow digital version (from that page) both uses a VCO that's more or less unobtainable these days, and the circuit was not functional when a high school student tried to toss it together for a project - but I can't swear that he got it all right - on the other hand, I couldn't find where he got it wrong, either, and we did find at least a couple of errors in the published schematic (which is still the same, as I recall, but I don't recall what the errors were at present. I might have that info in an old email, but given the VCO, it's mostly irrelevant.) I'm far from being a great designer, but I am a pretty good technician and troubleshooter.

Many, most or perhaps all ( I can't claim to have tried them all, or even throughly investigated them all) of those schematics are almost unbuildable as is, because they are old, and depend on parts which are no longer available (or not very easily.) Substitute enough sort-of-similar new parts and unstated assumptions in the original circuit go awry.

As such, that page is hardly the resource of "Things we've actually built" that Fred is looking for, unless you folks have actually built them. I sometimes suspect that the people who make the things for sale seed the net with bad schematics to keep themselves in business, but I have no proof of that, and file it mostly under paranoid delusion. But I have been keeping an eye out for something "easily buildable with obtainable parts" for the next student that wants to give it a whirl - and I haven't seen it yet.

--
Cats, coffee, chocolate...vices to live by

l?

I looked at the kit sold by PAIA Electronics earlier this year -

It's called the "Theremax Theremin". They carry other synth kits if your daughter's interest spreads...

How little? An electronic organ stylophone type thing might be a lot easier.

You could do a simple - just the frequency one with a single antennae and rely on the local oscillators entraining into lockstep as a mute.

I think you are hopelessly optimistic too. I have just built a relatively simple one for a Christmas science lecture.

Tracking down and getting the right parts will take longer than that. Almost all the once common tuned IF coils are no longer in manufacture and require careful tracking down to find suitable ones. If you still have some in a junk box then fine.

I built the Mini Theremin circuit described in the UK magazine EPE May/June 2008. They reprinted a design from Silicon Chip magazine at:

I had to bodge a 2nd IF from the ones I could get. The optocoupler is rare in the uk. Some of the bits I used came from Oz. Largely because they were cheaper there than locally sourced bits in small quantities! (and I wanted to use exactly the same part for the equalising coil)

The design works more or less as advertised. I'd recommend powering the main output amplifier off the supply rail but apart from that it is OK. You probably do not have a hope in hell of getting it to work without the detailed alignement instructions. There are a lot of things to trim before it behaves at all. The hand wound equalising coil is only 300t but must be minimum self capacitance and is tricky to get right.

If you don't mind about non-linear frequency to hand movement tuning then you could ignore the resonant equaliser.

Typically I got the tricky frequency side to work first time, but had real problems tuning the amplitude control side (where the right IF component was no longer available). Frequency side uses an MC1496 balanced mixer and a load of 445kHz IF transformers as the pullable and reference oscillators. Ceramic resonators resist being pulled off frequency too well and have almost totally displaced these IF cans from the market. You have to trawl round radioham sites to find one with the right internals and pinout.

Someone here very helpfully pointed me at a UK supplier with a stock of obsolete Toko IF transformers that fitted the bill:

You need a fair amount of tweaking to get them all to behave simultaneously without interfering in the audio band. The board layout of the project leaves a bit to be desired but works. There are still 7 knobs to play with on the front panel of this *simple* design!

You are probably best off ignoring the built in tuning test circuit as the trailing leads mess up the tuning! A bodge on a bit of veroboard on short leads works much better.

One other comment is that Australian towel rails at 15mm seem a bit weak. UK I had to use 18mm towel rail supports and pack them to take

15mm chrome tube as the two antennae.

Regards, Martin Brown

I'd be tempted to do something much simpler and much more digital, like a set of infra-red LEDs and receivers time multiplexed to create an x-y scan. This doesn't sound like a quick project to me, there may be many hours spent with your daughter gazing over your shoulder while to try hard not to swear at the box!

Mark.

perhaps a physical variation on this:

Aww, that's cute!

Mark.

$161 without case

$227 with case

Tell me about it. But the only real trouble I had building the EPE one from May/June 2008 was finding the right IF coils (one I had to bodge) and the daft trailing leads for the test set up circuit. Their design isn't perfect but it works OK on the pcb as laid out.

EPE (UK hobbyist magazine) will sell you the article and the PCB though I copied the part that I hadn't got from a public library.

The equaliser coil is a PITA to get right. But it is easy enough to have something where waving your hands makes the right sorts of noises.

I suggest you obtain the IF coils ASAP. They are hard to find now and getting harder by the day. I guess you could use ceramic resonators for the reference LO on the frequency side and the edge filter for amplitude. That still means you need two IF transformers to make one.

Regards, Martin Brown

Greetings Fred,

You may find my page, "Art's Theremin Page," of interest:

The article for my design called "The Minimum Theremin" is very popular, and the circuit may be feasible to create in a week or so, for the well-equipped hobbyist:

The Minimum Theremin is also available as a kit from Harrison Instruments:

The Minimum Theremin is NOT a high-fidelity instrument, owing to the fact that it uses relaxation (R-C) oscillators with no inherent selectivity, as opposed to the resonant oscillators of many other designs such as the PAiA Theremax or the Moog Etherwave. This fact makes the Minimum Theremin more sensitive to interference from emissive sources such as flourescent lamps, etc. However, the Minimum Theremin is really simple, and many youngsters have built it with just a little help. It is more than adequate for science projects or just an enjoyable building experience. And, if your daughter is musically-inclined, exposure to theremins at an early age might just yield a modern-day Clara Rockmore!

well?