Theremin

[Radamus]

Hello,

I'm looking to build a Theremin and I've come to find a significant gap in the available schematics. Some of the earliest designs for Theremins using tubes and a large number of inductors are available, as are really modern interpretations with Optics instead of antennas, etc.

I am looking for a schematic that has solid state electronics, two antennas, and inductive circuits that don't actually use inductors. I imagine that something like this has to exist. The closest I've come so far is this project: http://www.swtpc.com/mholley/PopularElectronics/Nov1967/PE_Nov1967.htm . It still uses inductors, and I'm not a skilled engineer so I don't know how to replace the inductors with circuits.

Does anyone out there know of a Theremin design that is more like what I'm asking for? I don't think that what I've asked for is too specific, as I can't imagine anyone these days being too crazy about inductors.

If you know of any websites where I can find some sort of formula for replacing inductors, I could try that as well.

Thanks!

[ianmgull]

Inductors in EQ circuits are sometimes replaced with gyrator circuits:

http://en.wikipedia.org/wiki/Gyrator

[linny1982]

jaycar electronics have a kit from silicon chip magazine. http://jaycar.com.au/productView.asp?ID=KC5475&keywords=theremin&form=KEYWORD i did the mk1 version a few years ago and it worked pretty well. i don't think its exactly what your lookin for but its a pretty good kit.

[Cliff Schecht]

You aren't going to get away from inductors/tuning slugs with an analog theremin. The basic principles of a theremin rely on the bodies capacitance to ground weighed against a (usually large) coil. Simply trying to replace the inductors with ANY other element is not going to work, even with simulated inductor circuits like a gyrator circuit. I can't think of a single scenario where an inductor can simply be replaced with an equivalent impedance part (assuming Q and other factors can even be matched) and give you a working circuit.

Do some googling around for the MC1496 based theremins (i.e. google "mc1496 theremin"), a few people have done them now with great success. The 1496 is a great (old!) IC that can modulate/demodulate signals with high linearity if designed correctly. This makes for a predictable and therefore easy to play theremin.

Or you could just buy a theremin. I have both Big Briar and PAiA theremins and use them both for different things. The Big Briar has a pretty standard theremin sound but is easy to play. The PAiA unit has some very cool CV and trigger outputs which allow it to be used as a synth controller. It's a good sounding theremin itself and has a lot more tonal variety than the Big Briar one although it is a bit larger and the stock antennas are a bit wobbly.

[petemoore]

The PAiA unit has some very cool CV and trigger outputs which allow it to be used as a synth controller.
  If you can figure any way to apply it.
  I have a PIaa Theramax [I like it, really cool !], and posted a number of times about using this thing in any fashion as a controller, I wanted to control something. Like a synth [Korg Triton Extreme] or even the gain on a FF, there's not enough voltage for an LED, and I couldn't find any suggestions to persue.

[earthtonesaudio]

The "Minimum Theremin" uses no inductors, is tolerant of part substitutions, and the principle is pretty straightforward.  Make one fixed RC oscillator, and then make another one variable.  For the variable one, you basically lift the grounded end of one capacitor and attach it to your antenna.  Then you mix the outputs and the resulting beat frequency is what you hear.  You could make a second one of these for controlling volume, or really just add a second variable oscillator and mix with the fixed oscillator separately (use buffers!) to make a volume CV.  Most people just use a volume pedal or knob.

The main issue with this circuit is it doesn't stay in tune very long.  But, if you're just wanting to make weird noises, that's not really an issue.

[petemoore]

  Hard to play !
  It's like making light year trips with stops at precise points across the galaxies of notes. Making the stops at any particular notes is the hard to do part, settling on 1 frequency requires concentration and one steady arm, but hitting various intervals of frequencies [playing a 'tune'] requires...
  What I started to get going. It was a mesmerizing sound, and so I would have reverb/echo and tremolo on it, this helps to hide 'errant' frequencies in the 'slur'. After a while the lights weren't needed, this is when the vision of notes down a string appeared in darkness. My mind conjured up the ruler, though everything seemed to be moving.
  Anyway, I managed to pull off portiona of Star Trek theme and Somewhere Over the Rainbow very nicely a few times, setting up and reaching for the recorder button with the light on blew all the space-vision-tone-frequency rulers visions out. Wasn't at all the same as sitting in a pitchblack room with only the frequency and your hand 'connected' to your senses.
  I took it out and other people help play it, they can't help but help.
  To play it around people you need a surround fence to keep sentients [such as people or cats] about 6' away from it, or just let the cat play it.

[Rectangular]

the only theremin circuits I've found without any inductors are chip-based theremins.  they're not digital, but using a PLL  doesn't sound particularly nice.  when I first got into building theremins I was confused about the inductor thing too.  I would recommend buying an LCR meter (they're around 30 bucks usually) so you can test various inductors and find one that the circuit calls for. you can also pre-tune it to some extent by matching the two inductors.

my problem is always that inductors are NEVER labeled. unlike just about every other passive component out there, I've never seen an inductor that has a clear, understandable label. its always some cryptic jibberish like  "TT-3304-92" stamped on the side

[JKowalski]

the only theremin circuits I've found without any inductors are chip-based theremins.  they're not digital, but using a PLL  doesn't sound particularly nice.  when I first got into building theremins I was confused about the inductor thing too.  I would recommend buying an LCR meter (they're around 30 bucks usually) so you can test various inductors and find one that the circuit calls for. you can also pre-tune it to some extent by matching the two inductors.

my problem is always that inductors are NEVER labeled. unlike just about every other passive component out there, I've never seen an inductor that has a clear, understandable label. its always some cryptic jibberish like  "TT-3304-92" stamped on the side

Yeah, inductors really annoy me that way. My fluke meter does everything but inductance, so I had to make a workaround:

1. Build one of these http://falstad.com/circuit/e-colpitts.html on your breadboard (takes two seconds, really)
2. Put your inductor in the circuit
3. Guess the approximate value of the inductor and change out caps to get an easily measurable frequency
4. Measure the frequency of your breadboard circuit
5. Change out the values of the caps in the http://falstad.com/circuit/e-colpitts.html simulation to match your own
6. Change the value of the inductor until you get the frequency that you get out of your B-board circuit
7. Thats your inductor value

The accuracy is not great (probably terrible in fact) with all the stray capacitance and inductance on the b board (especially for low value inductors) and the discrepancies with the simulation and reality but it's good enough for me in most cases. You can also go the math way instead of adjusting the simulation but I think the simulation way is quicker.

For cheap sources of inductors, old broken SMPS for computers have tons (~15, ranging from 10uH to 5H, many coupled) and old radio recievers have alot of adjustable and odd ones. If you need a particular value, you can buy a spool of magnet wire and wind it around one of the many many cores you can pull out of SMPS inductors.

[Rectangular]

the only theremin circuits I've found without any inductors are chip-based theremins.  they're not digital, but using a PLL  doesn't sound particularly nice.  when I first got into building theremins I was confused about the inductor thing too.  I would recommend buying an LCR meter (they're around 30 bucks usually) so you can test various inductors and find one that the circuit calls for. you can also pre-tune it to some extent by matching the two inductors.

my problem is always that inductors are NEVER labeled. unlike just about every other passive component out there, I've never seen an inductor that has a clear, understandable label. its always some cryptic jibberish like  "TT-3304-92" stamped on the side

Yeah, inductors really annoy me that way. My fluke meter does everything but inductance, so I had to make a workaround:

1. Build one of these http://falstad.com/circuit/e-colpitts.html on your breadboard (takes two seconds, really)
2. Put your inductor in the circuit
3. Guess the approximate value of the inductor and change out caps to get an easily measurable frequency
4. Measure the frequency of your breadboard circuit
5. Change out the values of the caps in the http://falstad.com/circuit/e-colpitts.html simulation to match your own
6. Change the value of the inductor until you get the frequency that you get out of your B-board circuit
7. Thats your inductor value

yeah there's a lot of diy circuits  for measuring inductors, but if you're going through a bucket of ones that you ripped out of old electronics,  a $30 LCR meter makes a lot of sense. most multimeters dont have a capacitor function anyway, so you're getting a good "2 for 1" deal there

if you're doing a lot of audio experimentation, especially vintage circuits, you're going to need an LCR meter eventually.

[jimbeaux]

The PAiA unit has some very cool CV and trigger outputs which allow it to be used as a synth controller.
  If you can figure any way to apply it.
  I have a PIaa Theramax [I like it, really cool !], and posted a number of times about using this thing in any fashion as a controller, I wanted to control something. Like a synth [Korg Triton Extreme] or even the gain on a FF, there's not enough voltage for an LED, and I couldn't find any suggestions to persue.

Have you tried this circuit to boost the CV & Gate ?

http://paia.com/ProdArticles/therefaq.htm#cvboost

[petemoore]

  Nope, but searching and prodding over time produces new results like this !
  Now I need to figure out what I can do to match that to a Korg Triton Extreme jack. The manual is pretty specific IIRC about mentioning Korg accessories, not much I could find about what these inputs expect other than dedicated hardware.
  So I'm waiting until I know more until I start plugging ''this'' in 'that' and hoping it works, more importantly that nothing gets damaged.

[Radamus]

Thank you guys for all of the responses.

Cliff- I probably should have assumed when I didn't see any inductorless designs that it might be critical, but I wasn't sure.

I did a little more research and I found this  schematic: http://www.thereminworld.com/pics/schematics/SiliconChip/sc-diagram.gif . It seems to be the one you were talking about, Cliff. If it isn't let me know. It uses a couple of transformers which are not easily sourced, but mouser has them: http://www.mouser.com/Search/Refine.aspx?FS=TRUE&N=4294759688+254428+4294620437+4294741289+4294620443+4294401844 . I'm not sure which one of those transformers I need, exactly, (I think it's 3 of one, 1 of another), but I can figure it out. If you guys know off-hand, let me know.

I have another schematic that I've been looking at, but it uses adjustable coils. Is this part of the tuning? Are these hard to tune?

Also, what type of antennas should I be looking at? I have this old TV thing that I was planning on building the theremin into as it already has speakers and one antenna. It's a straight, collapsible antenna. Will that work?

Thanks for the help.
Conrad

[rustypinto]

Since you're giving in to coils, i'll recommend the 145:

http://home.att.net/~theremin1/145/145.html

(i build the owl at the end of the page). Its a fairly straight forward build and well documented. Art (the guy who put the project together) sells the inductors from his shop in the next town over from me. He's a very helpful guy.

I have used salvaged inductors, as well as inductors available from Mouser (search "choke" too).

Good luck

[amptramp]

Rustypinto is right, there is a whole site on theremins including available kits at:

http://home.att.net/~theremin1/

I have it bookmarked.

[squidsquad]

petemoore reminded me of this:
http://www.youtube.com/watch?v=0ONJfp95yoE
The *WTF* look of the cat on the floor at the end slays me!

[petemoore]

  Read the Piaa on how to tune the coils, pretty straightforeward and makes sense when the coils are there, ready to tune.
I did it a few times to try it out.
  The source is produced using carrier frequencies, 'conveniently' outside the audio range, One osciallator is 'here' in frequency, the other is 'there'. Mix the two different frequencies and the difference makes a third frequency-tone, this one is mostly stays within the audio range [source for the theremin output].   
  The controller, altering the frequency of one of the oscillators is what alters the audio output frequency.

[Cliff Schecht]

Err, are you sure it isn't two higher frequency oscillators running near the same frequency? I'm sure the audible sounds you hear from just about any theremin comes from two RF oscillators operating NEAR the same frequency. The beat frequency you actually hear and control is the difference between the two oscillators (frequency wise).

I've only built the commercial kits and so my experience is limited to there but I've never had a problem getting everything tuned up IF I follow the instructions .

[sean k]

Isn't it funny how we all, at some stage, become somewhat obsessed with Theremins?

Ive done it in the past but then found the simple theremin and all my needs were answered. No coils and just two IC's and it makes quite a passable sound... bad theremins, no matter how complex, are the ones that sound like old fashioned arcade car racers... an output pure sine wave is incredibly boring.

Theremins really need to have a bunch of harmonics added to the sound otherwise they are a solution to nothing and if they need to be re-tuned for every new room they are played in... I'm glad I only use them for noise makers.

I usually chuck my simple theremin through a bunch of distortions and a delay then use the mixer for volume and just crash out a bunch of unrelated notes that stretch up and down and around.

I remember a few years ago seeing a site where the guy used the theremin concept as controllers for all his stuff. A guitar player who stood amongst a bunch of antennas and used them as CV's to control all his effects. Never have been able to find it again but it was certainly amazing and fed my obsession at the time to be master of all I survey using radio frequency... hytrodyning... thats not spelled correctly is it (rhetorical question)

If you can then listen to soundfiles of relevant Theremins. You don't want to be dissapointed by all that time and energy creating a prehistoric video game racing car engine sound

But as an exercise in interesting enclosures... thats a worthwhile avenue I think.

[Cliff Schecht]

I think that while the idea ORIGINALLY was to create a pure sinusoidal waveform (I believe the principles of the device were well understood by Leon Theremin at the time), the usage of tube devices added a certain distortion to the sound. Even the mixer tubes aren't very linear so the source signal that comes from the beat frequency is going to have some distortion. Combine these characteristics with the tube power amps, weak transformers and small speakers usually associated with a theremin and you have the recipe for a very distinct yet somehow mellow and pleasing sound. IMO nothing beats a tube theremin for sound, except for maybe a tube theremin emulation done right .