[Re: DIY pitch/mod wheels?]

[Harry Bissell]

Yes... I can. I made my own pitch wheels for a PAiA 2720 a long long time ago
(in a far distant galaxy...) I used some 1/4" thick lexan (plexiglass) and a
hole saw (one with teeth all the way around, not the one with the little arm
{thats a fly cutter}). Use whatever size you want, but you need enough
diameter to have the body of the pot you use be beneath the panel. Probably
about 3" diameter is about right. Then, take an old plastic knob with a brass
(preferred) of aluminum insert and set screw. Cut away the plastic and save
the insert. Usually the insert will be knurled. Here's the tough part. Drill a
hole (where the hole saw pilot hole is) just slighty smaller than the outside
diameter of the insert. Then drill a hole just a little bigger than the
setscrew diameter, perpendicular to the first hole. This is hard to do by
hand, but if you have access to a drill press its easy (I didn't). Last, press
the insert into the large hole, making sure that the set screw hole lines up
with the long hole in the plastic. When you mount the wheel, have the setscrew
hole down inder the panel. You can use a half-round file to make a little
dimple for your finger.
Need a center detent. Two solutions. I ripped out the rubber capstan-idler
assembly from a cheap dead cassette player, arm and all. Use the half round
file to make a little detent in the bottom of the wheel, and make some kind of
bracket to hold the wheel so it rides on the wheel edge. when it is at the
center, it will fall into the hole. Don't go very deep or it will be HARD to
break it away from center. If you wire the pitch wheel with positive and
negative voltages, and then put back to back diodes in series with the wiper,
you can get a slight deadband effect. Sequential Circuits did this in the
Prophet V, and it will make it alot easier to calibrate. Use your full plus
minus supply, and attenuate it later so the diode drops don't chew too big a
hole in the response. Put a pull-down resistor  to groung on the far side of
the diodes (away from the wiper).
Plan 2: some hardware stores carry a cabinet (door) latch that uses a spring
loaded rubber wheel, use instead of the capstan above. It has the bracket
already attached, but it has quite a still spring, maybe TOO stiff. You could
adjust the tension by the position but DONT cut away too much of the wheel
with the file, or it will never move away from center. I hate spring-loaded
wheels SO I WON'T TELL YOU how to do that. Ha HA. Good luck :-)
harrybissell at netscape.net
    P.S. maybe you can BUY a wheel from some company as a spare part, like
Alesis synths have a pitch wheel on them, and probably some others...Or but a
really old vintage MINIMOOG and trash it to get the pitch wheel :-)

Ingo Debus <debus at cityweb.de> wrote:
M.A. Martin wrote:
> 
> Could anyone point me toward a source of information for constructing my
> own pitch/mod wheels? 

In a Doepfer keyboard I once had there were just normal potentiometers.
Of course, the whole 270 degrees range of the pot cannot be used that
way. Recently I bought a replacement pot for a foot pedal with 90
degrees range, this is certainly a better choice for a
pitchbend/modulation wheel. The 90 degrees pot wasn't very expensive.

Ingo


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