Thumbwheel (was:Matrix board!)

[Harry Bissell]

I designed a module that has 4 thumbwheels (decimal) selecting different
waveforms from a single oscillator (saw, pwm, tri, sine, square, /2, /3, /4,
noise, and external from a jack) Each selector goes to a two input mixer with
level, and the those two are mixed in a cross-fader stage. This allows the
module to be a single four input mixer, or two, two input mixers with
crossfade (a '70 version of "morph"). This works really well, but 1) Watch out
for crosstalk. The sine wave didn't like being in the same switch as the
squares. The switches themselves have real close artwork layout. 2) Buy spares
now and stock them forever. Thumbs used to be quite common, but not anymore.
3) Get BIG ones, the small ones don't hold up as well, and are hard to
operate. 4) Look for the ones with the pushbuttons for up and down... some
have windows so they are well sealed. I think there are still some of these on
the market. Interswitch and Digitran were popular manufacturers (but I don't
know anymore) 5) Don't overlook the bcd, or hexadecimal thumbs. If  you put
them at the summing point of an inverting op-amp, they make great mixers. Put
a resistor to ground from the summing junction so the op-amp doesn't go NUTS
when you dial in a "0". Good for summing DC voltages, too (octave switch,
anyone???) ;-) Harry Bissell
P.S. Maybe instead of having the thumbs overridden by patchcords, why not use
(like) input "9" to bring in your patch cord. Other hand, you could have the
crosstalk bug that way.



owner-synth-diy at mailhost.bpa.nl wrote:
>>All my signal prcessing modules will have two mixable inputs, with a
thumbwheel for selecting among the ten >most used signal sources

>This is an excellent idea, especially for a performance-type, non-modular
synth. What exactly is
this thumbwheel like ?

It's like the ones that are used for selecting scsi address and such. Only
that I use a decimal version, that work like a 10-way single pole switch.
So instead of one normalized connection, I have ten to choose from, for each
of the two inputs. Of course this will be overridden by inserting patchcords
in the jacks on the module.
In the bottom of the case I have two busses with headers for the ten signals.
So to connect a module, I simply plug two ribbon cables into the headers. Of
course if the output of the module is to appear on the busses, it must be
connected too.

/Jorgen



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