Theremin Lip-Sync Scandal

"Is that a knob and a digital tuner, or one or the other depending on the individual instrument?  Does this setup account for users with different hand geometry and people who want to tune to different intervals?  I've found that tuning to null is the first step to get you in the ballpark, then I have to fine tune to get a nice perfect fourth from my position one to position four in every playable register.  Also some people tune so the zero-beat range is very far behind them." - Jo

None of the above really apply to my scheme -

Because tuning is performed on the antenna (by electronically adjusting the equalizing inductance) the "null point" is actually tuned not to "null" but to a state where the VFO is pulled to a frequency above the antenna circuit resonance by a fixed amount, and the reference frequency is 8Hz above this.. Which gives a difference frequency of 8Hz.

When the difference frequency is lower than 8Hz, the theremin is automatically muted, it is also muted when the reference frequency is lower than the VFO frequency (wrong-side-of-null) - there is a bi-color LED which is green when difference frequency >= 8Hz, and red at all other times (when the theremin is muted)

Because the antenna circuit is always tuned for optimum linearity (regardless of background capacitances etc) and because the relationship between the free-running VFO <-> Antenna resonance <-> Reference frequency are always the same at whatever null distance the user selects (within reason - set the null point at < 40cm and the non-linearity will become bothersome - 60cm is my standard ideal distance). Due to the above, the player never needs to bother about 'hand optimising' the performance - the tuning knob is adjusted so that the tuning LED switches to red at the null distance.

There is another control I have not mentioned, because I am not sure if I would fit it - but this is a 'range' control which defines the number of octaves covered in the playing field.. 6 octaves is probably the optimum setting, this gives about 5 linear octaves over the playing field, with these octaves covering 50cm of the 60cm field - about 5cm are 'wasted' on the inaudible lowest octave, and 5cm wasted closest to the antenna.

The above is fine for a single register theremin, IMO - But for a switched register theremin (which was/is my target) better performance is, IMO, obtained by reducing the number of linear octaves to 3 or 4 - this gives larger distance available for each octave (about 12cm per octave, or 1cm / note for 4 octaves, and about 16cm/octave 1.2cm/note for the 3 octave tuned version).. Register switching alows 8 octaves to be covered with 6 register selections, or 9 octaves if the 4 octave tuning is employed.

Not really sure what you mean by "people who want to tune to different intervals" - Over the linear zone (about 50cm in a 60cm field) the intervals are evenly spaced.

But I have said far too much - I am not in a position to provide the above theremin, and not even in a position to demonstrate it yet - It is in a box in my lab, with loads of other prototypes.. My lab has been piled with assorted junk by my wife, making it impossible for me to access anything or work there.. I am looking for a new home with enough space for me to continue my R+D while my divorce goes through - but I have no money...... So, all I can do is talk about what I have done - and I have done this for about 5 years with little to show for all this hot air!  LOL!

Fred.

"Here we have a situation my understanding of word usage confuses me, you just described the Jaycar Theremin?"

"When I fitted the complex routings on my 16 theremins"

"Also what do you mean or do with theremin routing?"

 - Christopher

1.) The Jaycar uses a variable frequency oscillator for its volume - If this oscillator runs at a frequency close to the VFO or Ref osc, or if any harmonics from any of these oscillators beat in the audio range, one hears it. My design does not have a variable frequency on the volume circuit.

2.) Routing.. One has a signal source (the heterodyne audio out) which goes to the waveshaping etc which goes to the VCA which goes to the audio output - in my H1 theremins the output went to a audio pre-amp 3 band equalizer, then to the (built-in) power amplifier.

3.) Routing - the ability, for example, to take signal from before the VCA, feed this to an external effects pedal or whatever, and return thie modified signal back to the theremin for processing by the theremins VCA.

The customer (South bank arts centre) wanted (probably as a result of talking to GordonC ;-) the ability to intercept the theremin output before it went to the amplifier, and the ability to put this signal into some process (undefined - effects pedal, whatever) before returning the modified signal back to the pre-amp / amplifier in the theremin.

I agreed, as it seemed simple - and it was also a route wherebye I believed I could easily add an external volume circuit if I put these theremins into production - The reason for the extra expense was that in order to do the job well, I needed an extra buffer on the audio output and an extra out and in socket, and needed to dissassemble the amplifier modules, have the panels drilled for extra holes to mount these sockets etc..

Fred, that sounds way too neat and I want one, but I probably couldn't afford it even if you could get me one.

Not really sure what you mean by "people who want to tune to different intervals"

From a player's perspective, the interval isn't so much a set distance in space (e.g., one inch=one full step), but a ratio of the lengths of different fingering positions.  One school tunes to a perfect fourth from the first position to the last, and another school tunes to an octave, and I'm sure there are people out there who do other things.  Either way, you successfully evaded my question with your deeper description of the tuning process, so it's moot.

I've been thinking if I ever implement register switching in a design (getting way ahead of myself since I have yet to build a working design at all), the default setting should lock somewhere comfortably below 20Hz, with five, six, or however many octaves I can manage, and the other register will actually be an octave up, where I'll simply put a full-wave rectifier and a smoothing filter into the circuit. I don't see something like that affecting the linearity too much between settings, but then I had no idea putting effects modules in my signal chain would throw my theremin out of tune either until I tried it... just throwing the idea out there.

EDIT: I should add that I have run my B3 Deluxe through a breadboarded full-wave rectifier, with no filter, no extra amplifier stage, no bias adjust, and the result was a nice octave up with a little brightening, but obviously the signal was half as strong and there was a loud 60Hz hum from somewhere. It was an educational experiment anyway.

Hey Jo,

Your new to TW, so I can entertain you with a lot of sound byte junk put away as past projects. Those around TW about 8 years ago know how I did this theremin control. On the highest notes I am using an active full wave frequency doubler which give more of an accent. I have no musical talent but you get the idea.

Register Switching .mp3

Live real time register shifting I thought would have had more interest but it gets back to theremin interest falling by the way side. When ever I mention the theremin to someone today, if they heard of it, they relate it to some rock band that trashed its identity. So sad...

Other than my Tube/Valve Theremin Oscillator board, the rest of my projects use a TL082 Op amp and a TLC555. My original theremins were constructed only using Radio Shack parts to make it easy for builders so my name RS Theremin. That was during my learning period. Eventually not wanting to coil wind anymore I expanded my part choices to Mouser.

Happy Freedom from the Royal Crown!

Christopher

an active full wave bridge to double the frequency.

Register Switching .mp3

Forgive me if I'm getting too specific, but did switching in the full wave bridge add any stray capacitance or whatever else that might affect the tuning in this circuit? Did you have to add any parts to compensate in the lower register position?  Just curious as this possible problem occured to me last night as I was bringing up this method.  How would a passive rectifier work differently (since I have one breadboarded already lying around)?

Also, that is a seriously impressive tone.

My original theremins were constructed only using Radio Shack parts to make it easy for builders so my name RS Theremin. That was during my learning period. Eventually not wanting to coil wind anymore I expanded my part choices to Mouser.

Yeah the reason I know who you are is because I went looking for designs using Radio Shack parts to get started.  I still have a couple of RS stores around with a decent component selection.  I assume you don't have those old schematics published anywhere anymore? I do get parts from Mouser and Jameco from time to time, but sometimes I just don't want to wait for the delivery.

Happy Freedom from the Royal Crown!

Let's hope our great nation gets enough rain for safe fireworks shows and grilling!

Hey Jo,

"Forgive me if I'm getting too specific, but did switching in the full wave bridge add any stray capacitance or whatever else that might affect the tuning in this circuit?

No, you may be dragging down your power supply.

Did you have to add any parts to compensate in the lower register position?"

Yes, I used a 4013 to divide by 2 & 4. Then you have the fundamental and the full wave over tone. That's 4 registers to go sub-sonic or to add in full wave which adds timbre to the tone. This use to be 100% Radio Shack.

Are you Mark?  Three Joe's showed up this week related to the theremin.

Christopher

Edit: Fred we are not free in this country, it is all about money and big corporations. I have watched many small businesses including my son's collapse during these trying times. Unless you have money the brightest minds cannot climb the ladder to leadership. I wonder who or what is calling the shots as we strong arm the world!

Another Joe: "And it's one, two, three, what are we fighting for - don't ask me I don't give a damn..."

"Happy Freedom from the Royal Crown!"

I hope that some day, Britain will be able to say the same! Ohh.. I think I might even today be breaking some hidden statute by saying that!

To me, it is incredible and incomprehensible that we (in Britain) blab about equality and pretend to oppose racial and other discriminatory practices - Yet, at its heart, we have royalty - which is nothing more than saying "some people are born superior to others, some families have the right to impose their will on, and rule others - simply by merit of their genetics"

To me, a nation which embraces such obscenity has no morality at its core, and is, at heart, racist and irrational.

Ooops.. Going way off topic again! ;-) Just had to agree with your declaration, Christopher!

Fred.

Jo said: "Also, that is a seriously impressive tone."

So you moved your fingers away from the chalk board. Use the  word "simple" and you won't hear from me again. All of my work is original and brilliant not because I am a prodigy rather I listen to something few can hear.

I hate when my ideas end up in the closet so here is another sound byte using the same circuit configuration as above. This is live register slipping using a real theremin. This approach is not socially acceptable in the theremin community and over the years I have become a theremin purist but still eat meat.

Staccato .mp3 280k

People are on vacation this week so we are the entertainment. I have a tendency to delete my posts cause I get moody.

Christopher

"And it's one, two, three, what are we fighting for - don't ask me I don't give a damn..."

And its five, six, seven - open up the pearly gates..

Aint no time to wonder why - Whoopee - All gonna die!

"Edit:Fred we are not free in this country, it is all about money and big corporations. I have watched many small businesses including my son's collapse during these trying times. Unless you have money the brightest minds cannot climb the ladder to leadership. I wonder who or what is calling the shots as we strong arm the world!"

we are not free - that is the bottom line! (not even free to change this damn text colour, it would seem ;-) - But we are comparatively free, when compared to many other people.

I wonder who or what is calling the shots as we strong arm the world!?

I would be surprised if anyone was!  I think it likely that things have just got to this state, and we cannot use the same thinking which got us into this state, to get us out of it.. But old habits die hard.

Some of your soundbites are really pleasant and interesting, BTW.

Fred.

Stupid bloody editor! How is the colour / attributes coded in this? Some text can be changed, other text refuses to be modified - Is there a theremin embedded in this site somewhere? ;-)

"Stupid bloody editor! How is the colour / attributes coded in this? Some text can be changed, other text refuses to be modified..." -FredM

If the eraser and color changer don't work, try "Paste Special | Unformatted Text" into WordPad (or similar) - then copy & paste from there.