New Silicon Chip Theremin 2009 edition

Hi Justin,
I dont want to pick any fight either! ;) ... But the whole Theremin market is cluttered with unplayable junk, and adding more junk doesnt help anyone! - this redesign is JUNK!

[i]"As for tuning controls-that's what the extensible antenna is for! :-)[/i]

This DOES NOT do the same thing as a tuning control! - Reducing/increasing the antenna area changes SENSITIVITY .. This has the APPARENT effect of changing tuning - but all it is actually doing is changing the coupling to background capacitance - and therefore ALSO changing the coupling to the player... This means that the playing field and distance between notes will change everytime one 're-tunes' by this method ... [b]ABSOLUTELY HOPELESS[/b] if one actually wants to learn to PLAY a Theremin musically!!!

Hi Fred,

Good point about changing the playing field size whenever the antenna size changes.

I guess one way to think about this one is that it's a good basis for something better-after all the much-lauded Kees Enkelaar was just a Mk1 Jaycar with equalisation coils, a better case, fixed antennas and a few dollars worth of potentiometers and resistors, and no doubt the same magic could be worked with this one...

I guess also that I'm personally biased by the fact that after being scarred by my experiences building and using the truly awful Electronics Australia 1982 design in about 1987, the original Jaycar kit made me realise what fun a theremin could be and persuaded me to actually go get that Etherwave I'd been lusting over...

Cheers

Justin

PS. Forgot to mention the Jaycar deluxe/EPE also had separate power supplies for the audio amp and the RF circuit (nice), but has no equalisation coil for volume....

Don says:
[b]"7809's would be hard to find in the US[/b][i], but it is better to use a linear regulator for something that draws so little current."[/i] -
Yes.. A SMPS is certainly not a good idea here! - a simple solution might be using an adjustable regulator such as the LM317 (http://www.national.com/ds/LM/LM117.pdf) .. 2 resistors set the voltage, and (with care) one could fit this regulator and the resistors on the board without modifying the board.

Justin -
Your expierience with your first Theremin kit is what worries me about this one (and the other junk on the market).. Ok, you got past the expierience and went on to continue with Theremins.. But how many, once put off by a bad design, never return - and so miss out on this wonderful instrument?

Equalising coils on Volume antenna - Mmmm - This is mainly due to the different method of deriving the control signal and the lower importance of volume linearity.. This whole subject is far more complicated than if first appears! -

I think the real issue about this latest design is that it is a gross degeneration of a Theremin which seemed to be evolving in the 'right' direction... The EPE version was, I think, the best yet of the Jaycar/SC Theremins - This latest is the worst!

If this had been their first Theremin, we would hope that they would learn from their mistakes and improve it.. But my feeling is that this latest design is a cynical "The punters dont know anything about Theremins, we can make more money if we sell them crap".. And this makes me angry!

Hi Fred,

is seems that you get easily angry in the last time, be it on YT or here. This may be due to existential stress (as lots of us have in the moment). Let me know if there is something that I can do in order to decrease your adrenaline level.

Back on Topic:
An equalizing coil for the volume antenna is not every time required. If the bandpass-filter and the VCA (or the VCA-like circuitry) have an adapted characteristic there may be no need for further linearisation.

BTW: A "linear" pitch theremin has never a linear but an exponential response, but I doubt that other people than mathematicians may have fun with this statement...

A 7809 may be replaced by a 7808 with a 1N4001 diode between ground pin and ground, which gives you a virtual 7808.7

Pitch tuning on the newest SC design may be done by using 2 x 1N4148 as varicaps between pins 1 and 3 of T1.

Fred-The point about quality is true, but the paradox is that the best instruments for beginners are those they are least likely to buy because of the substantial investment required-classic example is the Etherwave Pro with its excellent linearity that only sold 480 examples when the Etherwave Standard has sold thousands.

In the case of the Jaycar Deluxe/EPE, the frustrating thing was that it needn't have had so much of a premium as it did-in Australia it cost $150 and was bundled with a useless flimsy tripod (face value $19) and the design used 4 expensive multiturn trimmers to trim the range of the wave shaping controls when cheap single-turn trimmers would have done. If they'd eliminated these two things it probably could have gone for closer to $125 and would have been more viable, I'm sure.

This is an updated version of the 2000(?) Mk1 Jaycar/Silicon Chip kit Theremin.

From an initial glance, the changes seem to be the power supply and the addition of the voice control around the reference and pitch oscillators. There are some other component value changes too.

Something we should all remember is that Theremin playing or building should be about enjoyment. Fun and learning come into it too

These particular kits are aimed at the hobbyist, they offer a first step into Theremins and in some cases a first step into electronics as well and at a very reasonable price.

To build something and get it working gives one a sense of achievement. When, after using it for a while, its shortcomings become apparent and these are addressed, something has been learnt.
In this case there have been loads of articles written about how to improve the Jaycar/SC kit. As pointed out in this thread, a commercial instrument based on the kit is available and has a reputation as a decent instrument.

If people have the desire to learn an instrument, they will stick at it, regardless of what they currently use. How many of us started making music on a recorder at school?

We really should applaud Jaycar/Silicon Chip for sticking with the Theremin and its (modern) roots as a hobbyist/self build instrument.
From memory they have brought us, in less than a decade:

The Mk1 version
A MIDI Theremin
The Deluxe
And now an updated version

With pitch AND volume all in a self build kit form, which I will also point out contain EVERYTHING you need to get going, even solder. There is no need to nip out to Maplin (or wherever) to purchase additional components because it wasn’t included, its all there.
Who else offers this?

True, they are not the “best” Theremins around, we could discuss that for ever and a day. But given the price and the ease of modifications available, a lot of fun can be had.
I have really enjoyed my original Mk 1, adding some of Max’s well documented mods and also having “fixed” several for people on this forum, it makes me really happy that others are having some fun with them as well.

My advice to anyone building any one of these kits is to:

1) Get it working
2) Put it in a bigger box
3) Get a fixed pitch rod
4) Modify and experiment
5) Share your results
6) Have fun

Best wishes and regards to all

MarkT

Hello again, everyone! ;)

Thierry - Thanks for your concern.. Yeah, times are stressful - but that is not the reason for this particular reaction!

[i]>> A "linear" pitch theremin has never a linear but an exponential response[/i]

When one talks about linearity with regard to pitch, I understand it as taliking about PERCIEVED pitch linearity.. There is no other sane way of talking about it.. Yeah- in a heterodyning Theremin,this equates to an exponential change in the beat frequency - but in a voltage controlled Theremin controller it could equate to 1V/Octave(linear) which is used to drive a Linear VCO via exponential converter - If one is talking about driving a Yamaha MS20, you would need a V/Hz (exponential) control voltage..... The only common reference is our perception of pitch - As we percieve an exponential increase in frequency as a linear increase in pitch.

--------
I think that the root cause of this moment of anger, is seeing a good product get needlessly screwed up.. probably on the instruction of some bean counter. The EPE version of the Jaycar / SC Theremin was a reasonably GOOD Theremin - This new design throws away everything that made it good, and even removed the most fundamental control required by a playable Theremin.

One can say "This is for hobbyists" or "one can make modifications" - but the bottom line is this - A coil and a potentiometer have been removed - the only reason for doing this is a few 'beans' - And removal of these components turn what was a good Theremin into a useless pile of junk to anyone who is incapable of modifying it.

[i]>> I think that the root cause of this moment of anger, is seeing a good product get needlessly screwed up.. probably on the instruction of some bean counter. The EPE version of the Jaycar / SC Theremin was a GOOD Theremin - This new design throws away everything that made it good, and even removed the most fundamental control required by a playable Theremin.

>> One can say "This is for hobbyists" or "one can make modifications" - but the bottom line is this - A coil and a potentiometer have been removed - the only reason for doing this is a few 'beans' - And removal of these components turn what was a good Theremin into a useless pile of junk to anyone who is incapable of modifying it.[/i]

For me it seems perhaps not to be a bug, but a feature... why shouldn't I jump into the "Kees breach" and make some good AND affordable theremins based on this kit in order to bring happiness into the theremin universe and some strongly needed money in mine?

[i]>>"A 7809 may be replaced by a 7808 with a 1N4001 diode between ground pin and ground, which gives you a virtual 7808.7"[/i]

I cannot see any particular reason why the circuit should not work with 8V.. if 7808's are available easily in the USA, I would try this... I am a little worried about the diode Vf elevation of a 7808 to 8.7V - Vf is strongly dependent on If and temperature, so this may cause thermal stability problems (If will be inversely proportional to current demand on the regulator, and proportional to incoming supply voltage and any fluctuations thereof)

[i]">>For me it seems perhaps not to be a bug, but a feature... why shouldn't I jump into the "Kees breach" and make some good AND affordable theremins based on this kit in order to bring happiness into the theremin universe and some strongly needed money in mine?"[/i]

Why not indeed! - My comments regarding this Theremin were purely from a perspective of newcomers who lacked knowledge to (a) Realise that their Theremin was more difficult to play than it should be (b) lacked knowledge / skills required to correct the problems.I do, however, have reservations about other aspects of the design - in particular the use of the the MC1496 bias as a gain control, and the implementation of the 'voice' control.. I suspect there will be some adverse results, particularly from the bias.

If you took the kit, and with knowledge of both the playing and technical aspects, produce a real musical instrument, then you will certainly be doing everyone a service!

[i]MarkT: "With pitch AND volume all in a self build kit form, which I will also point out contain EVERYTHING you need to get going, even solder. There is no need to nip out to Maplin (or wherever) to purchase additional components because it wasn’t included, its all there."[/i]

This may have been true for past versions - With this version, in order to get a playable Theremin, I believe one would at least need to "to nip out to Maplin" to buy a tuning potentiometer, coil core, and ECW... THIS Theremin is a LEMON! - I am not detracting from its predecessors in any way.. I am simply stating that this particular mutation is rubbish... Kees could not have used THIS design for the Theremin he produced.

[b]>> OUT OF DATE:[/b][i] I have just run some simple simulations on the MC1496 mixer/VCA circuit - now, these are just simulations, and therefore depend entirely on the accuracy of the MC1496 model I am using, which I cannot easily verify.. However .. The results are similar to what I expected to see..

Feeding 2 pure sinewaves into the mixer, with 2kHz difference, I get 2kHz out - When the bias input to MC1496 is low (<1V) I get a low level sine wave out (minimum distortion) - As the bias is increased to about 4V, the amplitude of the output increases, but so does distortion - it is extreme at 4V, and above 4V there is no recognisable sine component left.

PLEASE - Dont take the above as conclusive evidence of anything.. BUT, Anyone looking to use the bias of a MC1496 as a volume control input would be advised to check distortion.. Likewise, anyone wanting to use this Theremin as the basis for a quality instrument would be advised to check this.

I may get distracted enough to quickly build the circuit - but I have more important things I should be getting on with.. I would be most interested if anyone with a 'scope has built this circuit, and can prove/disprove the relationship between distortion and the bias voltage.[/i]

[b]>>UPDATE:[/b]
I did not trust the MC1496 model - distortion was too severe to be reasonable.. As I am looking at using the MC1469 instead of the AD633 in my designs, I have now constructed an accurate simulation model for the MC1496 based on this IC's schematic.
My new model works, and the circuit using the bias to control gain appears to work - distortion over the control range is within acceptable limits. There is a big DC transfer from bias to output - this might cause 'thumps' when volume is changed / fluctuated rapidly - but this is based on feeding the control signal directly into the bias pin via the 6k8.. The real circuit has integration formed by a 10k resistor and 2u2 capacitor, which limits response time to 20ms.. so in practice thumps will not get through, but some players might find the volume response a bit sluggish.