Simple Theremin

Dr.EM said:

Ah, right. So this can probably be built on stripboard with some care? I unfortunately can't make PCB.

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The EPE Oct 2004 article I mentioned previously gives a veroboard layout for the project!.

Ok people, thanks for your help so far. I built the "minimun theremin" on breadboard, which I know is not reccomended. Anyhow, I did get some theremin type tone from it, quite a high whitsle, and get some variation in pitch by moving my hand near the "aeriel". However, my hand has to be very near, and even then its not more than a couple semitones pitch variation. I have tried a metal box, a piece of foil and a metal number plate for ariels, the larger ones yield lower pitches, but still very little variation. Any ideas why this is? I am not using the regulator btw, as I don't have it, but am running straight from 3AA cells, giving about 4.5v. I am using a 47uf filter cap.

Makes a cool sound when you switch it off though, like an old computer game :lol:

Thunderchild, let me know how you get on with yours, I will try it if it works out well

Dr.EM said:

Ok people, thanks for your help so far. I built the "minimun theremin" on breadboard, which I know is not reccomended. Anyhow, I did get some theremin type tone from it, quite a high whitsle, and get some variation in pitch by moving my hand near the "aeriel". However, my hand has to be very near, and even then its not more than a couple semitones pitch variation. I have tried a metal box, a piece of foil and a metal number plate for ariels, the larger ones yield lower pitches, but still very little variation. Any ideas why this is?

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The amount of pitch change is dependent on the oscillator frequency, the higher the frequency the greater the change, and the more 'touchy' it will be.

Thsee simple gate oscillators are highly dependent on the exact type (including manufacturer) of gate, this can affect the frequency by a large amount - your oscillators might be running much too low?.

Then you've built it on breadboard, the high stray capacitance of a breadboard will also lower the frequency on the oscillators, probably by a considerable amount? - try reducing the values of the tuning capacitors (100pF in the diagram) - try 22pF rather than 100pF.

the thing is u act as a capacitor so if there is a lot of stray capacitance then u make little effect. i think this is why in the design i found they said to use seperate chips for the oscilators even though there r only two gates used per chip. try doing it on a seperate board with wires and try to keep it neat. putting the oscilator parts at te edge of the board may help and perhaps a bit distant from the rest.
will report how mine goes but in italy it is so damn hard to get components. u can wait months like i did for two TDA2002's that took six months to arrive. luckily i have a car now so can go to a bigger place rather that my local tv repairer :idea:

Here is what is said on the web about EPE's Minimum Theremin:
"The main problem with designing your own stripboard layout is random capacitance between tracks. As capacitance is the key to the way a Theremin operates it is highly unlikely that any stripboard layout you come up with yourself could ever work."
So I don't think a breadboard will work well.

On EPE's project index page, they have a mark indicating there is a fix or update to the project. :lol:

Ah, that doesn't sound good . It makes sense though, perhaps lowering the capacitor values will help enough, but I don't keep any below 100pf.

Just wondering then, how did they get them working back in the 1920s? I'm sure they wouldn't have very suitable constuction methods.

try msking the two oscilators in the same way physically and positioning them in the same way from the rest of the circuui this way u can try and keep them the same
also use thin wires like u would use strips of a pcb

Dr.EM said:

Just wondering then, how did they get them working back in the 1920s? I'm sure they wouldn't have very suitable constuction methods.

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They had VERY suitable construction methods, NO breadboards (worst possible method), NO veroboard (no problem for low frequency RF if constructed sensibly), NO PCB's (again, no problems if designed sensibly).

Valve construction was generally "point to point", from valve holder to valve holder, with any extra connections on insulated terminals. Certainly for the low frequencies involved in the theremin there wouldn't be any problem, and it still works well at UHF and microwave frequencies!.

Don't imagine that PCB's are the best way to construct things, they were introduced as technology moved forward for CHEAPNESS - not to improve things!. Obviously, modern techniques have introduced components specifically designed for PCB's, but it's not always been that way.

I can remember working on ITT hand wired valve colour TV sets, now that's quite a frightning thought! - a colour TV with no PCB's, all hand wired!.

if this helps as an explanantion the first theremins constructed on a large scale (1000) cost 12.000 pounds !

OK does anybody know of a substitute to the SSM-2018 chip that is a voltage controlled amplifier i think (VCA) i do not know hwre to start because i do not know of the frequenzies we r dealing with here. does anyone know where i can get the formulas to calculate the frequenzys of logic gate oscilators.

Cmos oscillator:

hm intersting but i was refering to the type of oscilators used in my diagram that have the capacitor from the inveter input to groung and the resistor from input to out all on one gate only.
thanks anyway for ur help