CV....input?

I've been playing a theremin in a band for a couple of years, and while for the most part successful, I'd like to have the option of a bit more control over pitch. (I know this completely goes against the spirit of the theremin...but it's just needed for the trickier melodies).
Is there a way to control an Etherwave or Theremax (I have both) using CV inputs for a ribbon controller? Is there any way I could have a little tactile feedback without purchasing an expensive Persephone?
Any help would be greatly appreciated!

That seems to be a rather difficult task in the eyes of a circuit developer. You'd have to develop an exponential converter in order to deal with the ribbon's logarithmic 1V/Oct output. Then you'll have to find a way to control the variable pitch oscillator. Varicaps will be rather difficult to use since we're speaking in fractions of only 1pF, that means very small capacitances. A PLL would need a complete oscillator's re-design...

There are reasons for the price of a Persephone, you understand?

Finally, why don't you consider things another way round?

There are melodies which can be played on a theremin, some with more and some with less practicing. But there are naturally melodies which can't be played on the theremin, as there are others which can't be played on a trombone or on a recorder. Each musical instrument and its player have physical limitations. Accepting these limits gives better results than trying to find workarounds.

Hi Thierry! -

You are absolutely right regarding the GREAT difficulty in trying to control a Theremin from a voltage source.. Making a dedicated heterodyning VCO which tracked a 1V/Octave CV was probably the most difficult analogue design I have ever undertaken.. And I would not waste my time doing it again!

There is, however, a simpler way to do a 'ribbon' type controller for pitch - its fiddly and imperfect, but it does work.. and requires minimal electronics.. The basis of the idea was what I used on my (disasterous) 'Epsilon' prototype..

Imagine one has an 'antenna' (this is just effectively a capacitor 'plate' - as you know, Thierry - but others have strange ideas about Theremin antennas..) and this 'plate' is constructed from (say) aluminium foil laid horizontally on a non conductive dielectric (a strip of plastic).. this plate is shaped so it is narrow at one end (say 1mm) and gets wider at the other end (say 50mm) and its length is about 600mm.. One side of this plate is straight, the other is shaped with an exponential curve.

Another strip of foil about 5mm wide is run parrallel to the straight edge, seperated by a gap of about 5mm - this strip is grounded - the other (shaped) strip is taken via a small capacitor or trimming capacitor (<10pF) and connected to the Theremin antenna socket.. A strip of insulating material (tape or whatever) is placed over the foil 'plates'.

Ok - The fun bit.. Re-tuning the Theremin, trimming the input capacitor, and perhaps adding capacitance between the antenna socket and ground .. basically, fiddling about so that the action of sliding ones hand over the sensor plates (and the resulting change in capacitance due to the shaping of the plate) causes pitch change from the Theremin..

Note - the above is imperfect.. one wants to make the sensor strip more influenced by horizontal movement than by vertical movement, but pitch will change as a function of proximity of the hand to the sensor. linearity will be a function of the plate shaping.. you will never get perfect linearity.

[b]Edit->[/b]
Pitch is also directly a function of the area covered by the hand - playing with a finger only is 'best' - more capacitance = higher frequency, therefore putting ones hand flat down on the sensor will give high frequency.

Also - capacitors should be as close to antenna as possible - ALL wires connected to the antenna 'socket' ARE the antenna! .. After the capacitors, the connecting wire should be less sensitive.
[b]<-Edit[/b]
Probably be a while before I get a chance to visit again - but things are getting a little easier..

It is nice to do another long, crazy posting! ;-)


[b] Added sketch here..[/b] Crude (.jpg) sketch of above (http://www.therasynth.com/assets/images/antenna_strip.JPG) this can also be found on this page.. webpage (.html) (http://www.therasynth.com/html/temp.html)

PS.. C_TRIMM ... Wonderful name for a project like this! ;) .. Lots of C Trimming here!!

PPS.. Many years ago PAIA did the 'Gnome' (I think thats what it was called) synthesiser which used a similar capacitive pitch bender.. I just realised that I had expanded this circuit to do something like what I describe above, all those (>20?) years ago... Am I going 'round in circles? 8-(

I've got a slightly madder solution, Fred. No electronics required! (*)

Unfortunately it's not a ribbon controller, it's a keyboard. Sort of.

You can support a long metal rod in the pitch field so that the theremin is silent until you touch the end of the rod, whereupon a note of a certain pitch is played, depending on the size and position of the rod, and (I guess) the size of the player. I imagine one could arrange several such rods to each play a different note.

Disadvantage: Tuning them would be the very devil.

(*) OK, it's electronics. I admit it.

(Maybe you could combine the two ideas and add trimming capacitors to a stylophone keyboard and wire them to the pitch rod?)

"Each musical instrument and its player have physical limitations. Accepting these limits gives better results than trying to find workarounds."- Thierry

LOL! Turn the Theremin into tubular bells ?! - I think Thierry is right!

"I've got a slightly madder solution, Fred." - GordonC

If we are competing for the maddest idea - You Win! ;-) The stylophone with each pad having its own trimmer could work (for perhaps 10 minutes after tuning - until the femto-farad thermal drift from the trimmers detuned everything) but the 'tuned antennas' wont work.. the length of each antenna will make no difference to the pitch - it is the coupling between the player and the antenna conductor which determines the pitch. If one has 2 tubes connected to the antenna socket, one double the length of the other, both the same diameter, and one touched each with equal area and pressure, the resulting change in pitch will be the same.. Each would require its own trimmer (which would be the sole factor determining difference in pitch)... Alternatively, the different length tubes would not be connected to anything - they would each have an equal length conductor capacitively coupled to them, and these conductors would be commoned together and taken to the antenna socket - Then touching the unconnected tubes would allow them to play different notes..

But - The total field from even 12 such antenna would make any concept of 'tuning' quite irrelevant!

I love this place! It inspires thought processes not found anywhere else in the known universe! ;-)

This is a link to an ancient PAIA project which used a 'shaped antenna' to implement pitch bend.. A variation on this 'antenna' would probably work better than my crude triangular implementation.. but it will be a lot more difficult to construct.

PAIA 'OZ' Organ .PDF (http://www.paia.com/manuals/docs/oz-howto-article.pdf)

Just an aside.. I now have my Theremin outputting 1V/Octave over the entire audio range, tracking the Theremin voice from 16Hz with latency of 1/8th of the audio cycle (8ms for 16Hz, 125 microseconds for 1kHz)..
I also have a CV input operating on it - one can play the Theremin remotely from a CV keyboard.. You cannot, however, operate the Theremin and CV input simultaneously..
What one could do though, is use a CV->Midi converter to record, and a Midi->CV converter to play back.

Anyone who knows of any CV->Midi and Midi->CV Boards or components available at reasonable price (needs to have input / output for one high resolution controller for pitch data, and another for volume data - continuous controller stream) please let me know.. I do not really want to spend time developing this unless I must.