[sdiy] Questions: Akai ewi 3020 controller to CV

[harrybissell]

inline...

Richard Arntzen wrote:

> Hello.
>
> 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.
>
> 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.
>
> 1) Have anybody already done this :)

not me :^P

>
> 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 :)

You'd need to study it carefully. It is likely that you could up the voltage but
you need
to check WHAT they are doing with it. You might overload some parts thermally,
or mess up some bias voltages (if they did that...).   Got schematic ???

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

Temperature stability should NOT be an issue unless you are doing log or expo
converters. Linear is usually not a problem.  Modern metal film resistors are
usually
50ppm tempco or better... Opamps are as good as you want to pay for.  Watch out
for voltage references, diodes etc.

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

not unless you want you :^P

H^) harry