[sdiy] Questions: Akai ewi 3020 controller to CV

[Ian Fritz]

Richard --

At 11:28 AM 2/11/2005, Richard Arntzen wrote:

>I want to DIY my Akai EWI 3020 controller into a conventional CV controller,
>and being a newbie (a measly ChemE) I have some initial scares that I have
>to overcome. I could of course go MIDI, but then I have to lug around this
>beast of a module. And it wouldn't be nearly as cool as having my own
>controller module.

You are saying, I believe, that you want to use the 3020 to drive a 
standard 1V/Oct modular synth?


>The controller is capacitive (which I still haven't figured out exactly what
>means in this intstance). It has four  voltages going in: +/- 12VDC, +5VDC -
>and ground. No service manuals available as far as my searches can tell.

The key switches are actually resistive.  Your finger resistance provides a 
leakage path that fires a comparator.


>1) Have anybody already done this :)
>2) Will I fry the controller if I apply +/- 15VDC instead of the existing
>+/-12VDC? Then I can use my MOTM-power-supply which would be really neat :)

Not sure about that.  Offhand, from the schematic, that looks OK.  Why not 
ask Nyle directly?  Here's his home page: 
<http://patchmanmusic.com/NyleSteinerHomepage.html>


>I have poked around inside the companion module (an EWI 3030m), and there is
>a circuit board that handles the signal from the controller and sends it to
>the digital synth engine PCB. One of these days I will probably have to
>dismantle the thing and check out the controller PCB - with the 7
>panel-mounted pots... But I have gotten some readings out from near the
>internal instrument connector:

The panel pots are for scaling and offset, I believe.  You could either 
find their individual outputs or make your own interface.


>The controller sends 6 signals back to the module:
>Key; 0.20 V/semitone (0.15 - 3.55 VDC)
>Octave; 0.59 V/octave (0-3.55 VDC)
>Vib; 1 - 1.2 VDC - at least with the pressure I am able to apply. It is a
>blip-signal, so my DVM may be too slow to catch the highest reading.
>Breath; 0.46 - 3.5 VDC, again with the pressure I am able to set up.
>Glide; 0.64 - 1.64 depending on the coverage of the capacitive pad.
>Pitch; -3.5  - 3.5, -0.26 in zero mode
>
>Now - it would be pretty simple to offset/scale these voltages using OpAmps
>circuits (after re-measuring for +/-15VDC first). I have prepared some
>schematics, and I am starting to get worried (...) about temperature drift
>and accuracy since (I assume that) 1 V/oct means 83 mV/semitone, and so
>believe I have to use high-specs resistors, trim-pots, and possibly
>temperature-compensation circuits in order to get some stability into this.

Should be as easy as you say.  Just be sure to use good opamps and 
metal-film resistors and you should be OK.  You will need to add together 
the octave and sub-octave signals.


>3) Is it as hard as I think to get decent reliability by analog circuitry
>alone?

I see no reason it should be hard.


>4) Does it make more sense to do this digitally - AD-DA?

NO!  :-)

Best regards,

   Ian