My homebuilt theremin

[i]"Stuff with more mass seemed to work better"[/i]

Thank you, Andreas.. This has certainly given me something to think about (and experiment with).. At this time I can see no possible connection between mass and any relevant parameter - but the proof of the pudding, as they say, is in the eating thereof..

[i]"It's nice to see that you know much about the electronics :-).[/i]

I have been in electronics for 28 years, 20 of which as a designer, and spent the last year working almost exclusively on Theremin designs.. I have prototyped Theremins quite similar to your voltage controlled design (but focussed on providing 1V/Octave output over a larger sensing range, and getting perfect linearity).. Your posting and the sounds came like a smack in the gob.. Particularly as the circuitry you present is so simple compared to my prototype assemblies..
But I am targeting a somewhat different market / specification.. I want minimum 5 linear octaves and sensing field of at least 60cm ..
But perhaps I should have gone into production with my original 30cm Theremin products first.. (and perhaps adding a roll of solder would have helped things, LOL!)


The sound of your Theremin is superb.. The sine wave is certainly not a sinewave though! it has lots of other harmonics, and these are musically wonderfully balanced.. I am inclined to think that there are some things going on here which you are not telling us! - it sounds almost like a Tvox! ;)

No problem, it's nice to give you some ideas! I also learned a new expression, proof of the pudding... Had to google it.

Ah sounds nice! I've been in electronics for about 8 years when i started electrical/electronic-school.

Getting a playable linear distance of 60cm sounds like a tough task, but very intrestning. One thing that is nice with the XR2206 is that is can be configurated as ratio 1:1 in voltage to frequency conversion, like 1V beeing 1kHz, 2V - 2kHz and so on, but also in a logarithmic way decided by two simple resistors on the input voltage control when configurated in sweep mode. I think my ratio is about 1:1,41 which compensates some of the unlinearity in the capacitance/voltage circuit.

[i]and perhaps adding a roll of solder would have helped things...[/i]

:-D

It's nice to hear you think the sound is good! I was really happy with the sound also. It's true it isn't a clean sinewave. It is however quite clean sinewave out from the VCO, with the timbre at minimum - but much of the magic happens in the vacuum tube VCA. Im using the good old 12AX7 doubletriode which in regular HIFI tubeamps are ran at 250V-300V anode voltage (supply voltage) for maximum linearity. Im running my on about 90V. This makes it terribly unlinear, meaning the output doesn't really correspond to the input. I also have a pot for anodecurrent and with this set low, it makes alot of difference to the sound.

Here is the circuit board by the way:
link (http://img413.imageshack.us/img413/8929/91777912.jpg)

Here is a picture while measuring "as good as it geets sine"

link (http://img149.imageshack.us/img149/2180/47389788.jpg)

And here is what a tube can do but what transistors just would cut off and cause distortion. But that maybe sounds cool? :D

link (http://img26.imageshack.us/img26/3953/98378463.jpg)

Another intresting thing about the tube-VCA is that with low anode current the more i damp the signal with the velocity/volume antenna the more timbre or treble it gets in the sound. Im not sure exactly why this happens but im gessing is has to be the tube creating lots of harmonics when driven so low..

That "good as it gets sinewave" is already showing some of the non-linear response at the top peaks of the signal. I'd say since it is not responding as fast as the input, you are getting what used to be called "transient intermodulation distortion". Another name for that was "slewing-induced distortion".

Now that nobody cares much about "hi-fi" that sort of thing is hyped in "high-end audio" circles when they rave about how great low-power, single-ended power amps are. Those are the guys raving about $25,000 tube amps.

"We" (in theremin design circles) tend to refer to this as "timbre". In guitar amp circles, "we" call this "tube distortion effects". Adding harmonics tends to make the resulting output sound "fuller". In either event, it seems that the earlier in the signal chain this effect can be created, the better.

Since the theremin is all electronics, we have the ability to put it before the detector in the RF stage.

As for "mass" being a significant factor in the antenna ... I wonder if it is not so much mass as more surface area. In essence a bigger capacitor.

I guess we will have to wait for Thiery's research paper :)

Don

Yes, Andreas, mine is a homebuilt theremin ... or at least it will be a "theremin" when it starts behaving better.

Lack of time and inclimate weather is keeping me from getting the thing done.

Don

Don said: [i]"I am using a vactrol device in my volume loop circuit. This is a LDR + yellow LED packaged into a single part."[/i]

If you want these, probably best to buy some now.. I understand that they may not be manufactured for much longer, as they contain cadmium and are therefore restricted under the 'new' ROHS laws being applied.. Many products one could obtain easily are now being discontinued.. I have found no equivalent component for the Vactrol part (Siliconix NSL-32SR3) or the opto-coupled FET isolators (H11F1).. And both of these parts have applications which cannot be replaced by OTA's (LM13700 etc).. I do not know of any opto-coupled resistive part which is not on the 'discontinued or to be discontinued' list.
The NSL-32SR3 is a great component for audio - it has good linearity, an a large resistive range allowing 80db control.. Its only 'problem' is slow response - it is fine for audio, but no good for HF modulation.

RoHS is the bane of my existence these days!

Hadn't thought about that one, but you are right and every cadmium photocell would have to be removed from the market.

I wonder if the environmental problem is anywhere near worth the logistics problem RoHS has created world-wide?

Don

[i]"RoHS is the bane of my existence these days!

... every cadmium photocell would have to be removed from the market.

I wonder if the environmental problem is anywhere near worth the logistics problem RoHS has created world-wide? "[/i]

Don, I agree with every sentiment here!

My opinion on ROHS is that it has been the biggest con and most useless counter-productive 'green' legislation ever implemented by morons.. I also believe that the electronics industry has been complicit in this scam.

I can go out and buy a roll of roofing lead - one roll probably represents more lead than all the circuits I have got to market... BUT.. This lead is far more toxic than solder, Why? Because the mixture of lead and tin reduces the alloy toxicity hugely (I remember 95% reduction being quoted, but this may be incorrect) .. It is the same principle as mercury in tooth filling alloy - the mercury content on its own would kill you within 5 years, but the alloy neutralises it. The funniest farce was the drama over gallum arsenide, because it contains arsenic - Yeah! A single green potato contains more arsenic than the Ga-As diodes in 10 mobile phones!
So we have hundreds of tons of perfectly functioning ROHS 'waste' which will be disposed of.. How? The replacement compliant parts will add to the total electronic waste eventually dumped.. Who wins? NOT the environment, Not the consumer, Not the engineers who must deal with the new and UNTESTED technology.. Products will NOT be as robust - the brittle solder will cause premature failures, so MORE (slightly less toxic)electronic product will be dumped sooner.

There was a real answer - Legislation should have been introduced based on product lifetime - High tax on product which was dumped within 10 years of manufacture.. This would have forced manufacturers to put a high price on junk, making junk uneconomic.. I bet the industry would have fought that proposal! - But they made money from ROHS..
Banning components like cadmium photocell's is utterly ridiculous - the total volume of these manufactured is miniscule, and there are no compliant replacements.. But the cost of trying to get specific exemption makes it uneconomic for manufacturers to even try. Most of RoHS is utter Bo****ks, and might even end up being more costly to the environment in the long run - it will certainly reduce product lifetimes and increase electronic waste in the short term.

All sorts of highly toxic stuff is used in EVERY semiconductor's manufacturing process. They are used as "doping" agents to make "semiconductors" more "conductive" in a given way ... ie. to create "N type" and "P type" from same basic, generic stuff whether it be germanium, silicon or whatever else.

They are used to etch away the unwanted part of the wafers. To clean the finished wafers, etc. Sorry, you can't just legislate away every thing you think might be "bad for you" and still be able to make ANYTHING!

Greed always finds a way ... all the vendors have found a way to turn low-volume items into higher-volume by obsoleting the old parts in favor of RoHS and jacking up the prices on the standard stuff to force manufacturers to go RoHS compliant.

ARGH!!!

Don

... and now back to your regularly-scheduled topic ...

Sorry about RoHS rant. Now back to topic ...

Are you planning on sharing schematics with us Andreas? You have some very interesting circuits there.

Don

Sorry to hijack the thread again, but this just cracks me up! Antique Electronic Supply sells RoHS compliant vacuum tubes!

http://www.tubesandmore.com/


Don