ASSORTED QUESTIONS - CONTINUED (2)..

[i]"I am trying to find a simpler way so that I could produce a single-board Theremin I could sell as a kit, and matches the E-Pro's performance."[/i]

If you can do that and make it sound better than the E-Pro, I will be your first customer. I like the response of the Pro, but I have never been crazy about the sound of it. I wish it could make a more "classic" sound like the Standard does.

[i]"I like the response of the Pro, but I have never been crazy about the sound of it. I wish it could make a more "classic" sound like the Standard does." -Eitherspiel [/i]

And here is one of the problems - people's personal preferences regarding the sound... I could easily make it sound like the "standard" - but think most people would prefer the sound of the 'Pro. .. However, there are those who dont like the sound of the 'Pro. ... I would love to smother the surface of the Theremin with knobs, so that any sound could be made - but this adds cost and complexity.. not something I want with my single-board version... I will need to keep this as minimal as possible.

Whatever I do, I will leave expansion possibilities in the board design, so that more complex additions can be added later as upgrades. .. But, at this time, my minimal Theremin consists of a simple standard 5 octave Theremin board with buffered reference and variable oscillator outputs that I can plug into whatever I want to play with (waveshaping, octave switching, etc)..

[i]"There are simpler ways, and Moog has chosen one of them" - Thierry [/i]

Two other ways I could think of, I rejected - they would not reproduce the waveforms resulting from mixing the "real" pitch and reference oscillators.. They would grossly distort these or bear no relationship to them.

The first of these "simpler" methods is full wave rectification of the oscillator waveforms, producing a crude distorted double frequency waveform.. taking this waveform, buffering it, ac coupling it, then rectyifying it again to get the next doubling of frequency..

The above method is too horrible to think about!

The other way is using digital dividers.. Again, too horrible to think about

The only other way I can think of employ phase-locked-loops (PLL) to facilitate frequency multiplication.. This is quite simple - but one does lose the original waveforms and replace these with waveforms from the PLL VCO's.. This is a quasi-analogue solution.. Incoming oscillator waveform is first converted to square wave (digital) and fed to a phase comparator (XOR or edge triggered DMN.. Digital).. The output of this phase comparator drives an integrator (analogue) and the voltage from this drives a high frequency VCO (analogue). The Square wave output of this VCO drives a digital divider (which sets the frequency multiplication, so would be programmed for dividing by 1,2,4,8,16 from the range switch, to cover a total of 10 octaves in five 5 octave overlapping bands) and the output of this divider is fed to the other input of the phase comparator.
The output of the VCO will be at the input frequency multiplied by the divider, and the VCO could be designed to give selectable waveforms.

A standard PLL would not be able to cater for the huge frequency coverage required - The VCO for this PLL would need to be designed so that the range switch changed its timing components so that it only needed to track the frequency changes for a single band.. The integrator TC may also need to be dynamically changed by the range switch.

Although not a true heterodyning Theremin in the sense that the waveforms from the pitch oscillators are not directly used to form the audio output, I think this scheme could make a good Theremin with good sound options.

This method, in effect, results in a voltage control based Theremin.. A lot of what is being done here is quite similar to the voltage controlled heterodyning oscillator I am working on - and it overcomes many of the problems and simplifies things greatly.

Choices, choices.. ... This is probably the best balance between cost and performance for a single board E-Pro targeting Theremin.. The CV from the integrator could also drive a simple VCF for simple, smooth, comprehensive tone control, and all the pre-mixer waveshaping options are still available

Thank you, Thierry, for getting me thinking and inspiring me to come up with possibly a BETTER solution to "cloning" an E-Pro!

removed - I see my question was answered above.

Fred, thank you for writing down these thoughts. It makes me believe that the email that I've sent you this afternoon fell on fruitful ground. ;-)

I also have been seduced by the idea of using a 4046 PLL in a theremin, but on the volume side. The idea was to make the vco track the volume oscillator's frequency, convert its control voltage in a 16 bit numeric value, pass through a flash rom lookup table, feeding the output in a D/A converter in order to have a perfect linear volume CV...

[i]Wasn't the RCA only 3.5 octaves? That would be nice![/i]

And wouldn't that be great for learning classical theremin?

An affordable first theremin with a single classic tone and a limited range, but with great linearity and stability, and widely spaced notes just like Theremin's own designs, and a good volume gradient.

(Now comes the clever bit.)

Just one such theremin at first, covering the most commonly used range of pitches in classical playing (mezzo-soprano?) and a timbre to suit.

And then a double bass (?) model with the same field characteristics (for player mobility between models) and a timbre to suit the different range and to differentiate it from the other model - and with RF frequencies that do not interfere - for duets.

And so on.

The idea works just fine for a lot (http://en.wikipedia.org/wiki/Range_(music)) of other orchestra instruments.

Professional thereminists and wealthy amateurs can get the complete set! (And simple enough to modify and customise, for the owner with a soldering iron.)

Thierry, when Lydia Kavina was describing her requirements for a volume field at the workshop in Oxford, she said that she wanted it more spread out further from the loop as she used larger gestures when playing loudly, and more compressed closer to the loop for small, quiet playing and better staccato.

(For my own idiosyncratic playing style I believe I would prefer linearity and to move to different areas of the loop to vary the overall compression of the field between the loop and my hand.)

[i]"I also have been seduced by the idea of using a 4046 PLL in a theremin, but on the volume side. The idea was to make the vco track the volume oscillator's frequency, convert its control voltage in a 16 bit numeric value, pass through a flash rom lookup table, feeding the output in a D/A converter in order to have a perfect linear volume CV..." - Thierry [/i]

Thierry - I have almost exactly what you describe (doesnt ave a true PLL, but a much better 'equivalent' - and doesnt use a LUT.. it uses an analogue method of linearization which is not affected by temperature and does not require any thermal compensation components.. and has 16 bit resolution BEFORE linearization, and has auto-calibration, so you push a button, set your "null" position above the antenna, push another button, set the "maximum volume" position above the antenna.. no knobs to fiddle..) This is all embedded into a mixed signal IC, it has been designed specifically for processing the volume antenna, and it requires reasonably simple external circuitry.. It is one of the few bits which I have now signed off as complete and ready to roll.

I intend to send you boards as soon as I can - My present 'panic' is to get the whole system running before the last week in August.. I have been forced to take some contract work to pay my bills (one of the reasons I am wasting so much time here at TW - I get so bloody bored trawling through a pile of crap boring code I must fix for my client, that I divert to TW to have a break! :)

I intend to sell my ASICs to OEM's eventually - I dont really want to manufacture Theremins, I just enjoy designing them! If I can sell the custom parts and leave others to actually build the bloody things, that would suit me fine! ;-)

One other thing .. I was not thinking of using a 4046.. I doubt the VCO is fast enough for this application.. For a 300kHz input, multiplied up 4 octaves, the VCO frequency is >2Mhz.. At present I am using 455kHz pitch reference, so require > 5Mhz .. >10Mhz is a possible requirement for full 10 octave coverage.. a bit beyond the 4046 unfortunately!

Gordon, thank you for this information. Finally my design idea would allow to realize Lydia's wish, just by loading different values into the flash rom. I think that Fred, who is the microcontroller expert, could even find something which makes the circuit self-learning or self-adapting by using not only the absolute distance between hand and loop but also the velocity.

[i]One other thing .. I was not thinking of using a 4046.. I doubt the VCO is fast enough for this application.. For a 300kHz input, multiplied up 4 octaves, the VCO frequency is >2Mhz.. At present I am using 455kHz pitch reference, so require > 5Mhz .. >10Mhz is a possible requirement for full 10 octave coverage.. a bit beyond the 4046 unfortunately![/i]

The other thing is that I never would think of using a PLL in the pitch circuitry. Since I'm rather a sine wave fan, I'd consider the idea of RF frequency doubling by full wave rectification and then applying good old tuned LC circuits in order to clean up the signals.

But I finally don't know if I'll build my own theremin and if I'll do so there will be no register switch but the full 7 octave pitch boom in one heat.