[sdiy] Reply to all.. how to build a cv keyboard

[jhaible]

> One thing to remember: if you're using linear response modules, your
> keyboard needs to put out an exponential control voltage (anybody ever put
> together an old PAIA keyboard with the trim pot for each key?). Making a
> linear CV keyboard is much easier, even though it requires you use
> exponential response modules.

An exponential keyboard (V/Hz) isn't that difficult either.
Instead of equal resistor values, you build a ladder from
3 different values. Certainly no trimpot per key required.
Korg had a patent on this in the 70's.
For details, check the MS-20 schematics (or any other early
Korg synthesizer). The real tricky stuff was to derive a
good gate signal over the whole keyboard range (very different
voltage steps on both ends of the keyboard!), but this, too,
was solved with a small circuit by Korg. (And it even works
with single key contacts!) Again, see MS-20 for details.
(Or Korg Sigma for switchable retrigger/non-retrigger Gate
option.)

JH.

(Who once foolishly unsoldered a string of carefully selected
precision resistors from a Roland SH-2000 keyboard to replace
them with the Korg resistor ladder in order to get V/Hz response
for the JH-720. Not knowing that the SH-2000 was V/Hz as well.)