[sdiy] GRP Genesi

[Michael E Caloroso]

> What was this element, exactly, do you recall?

>From a keyboardmag.com interview with Phil Dodds:

"The Soloist's troubles resulted from an all-analog design for both voicing
and changing preset, plus a primitive but patented method of responding to
aftertouch on the keyboard.  'Imagine a flat piece of metal about the size
of a piece of chewing gum, and another one above it' Dodds explains. 'We
took open-cell foam rubber that was impregnated with carbon and glued it to
one of the metal sticks.  There was a gap between the foam and the metal
stick above it, and there was a spring between them.  The whole keyboard
was such that when you pressed down extra hard it would bring these two
metal pieces together, compress the foam rubber, and become a variable
resistor.  The problem was that the foam rubber had a shelf life of about
eight months before it would dry out and quit working.  ...In the
ProSoloist, there was a bar running underneath all the keys with two
parallel strips of conductive material, a strip of carbon-based rubber
placed over that, and on top of that was a layer of piano felt.  When you
pressed the key hard, you'd be pressing into the piano felt, which would
cause the rubber to engage across the two conductors to create a variable
resistance [as the rubber was compressed between the metal strips].  It was
a vast improvement because the rubber had a lot longer shelf life.' "

It's worth noting that my ProSoloist is over 50 years old and
the aftertouch element still works.

On the Soloist, the element was placed between the synth base and the
bottom of the keyboard frame.  You could see the entire keyboard moving in
YT videos when pressure is applied for aftertouch.

On the ProSoloist, the element assembly was placed under the keys (the old
Pratt-Read assemblies which each key had a metal shell that the plastic
keyshell was fastened to), and fastened to a shelf on the metal assembly
that formed the combs for the key bumpers.

US patent 3,784,935 covers the ProSoloist aftertouch system, invented by Al
Pearlman and Dennis Colin.

MC

On Sat, Jul 11, 2026 at 4:52 AM Adam (synthDIY) <synthdiy at adambaby.com>
wrote:

>
>
> On 11 Jul 2026, at 08:29, Michael E Caloroso via Synth-diy <
> synth-diy at synth-diy.org> wrote:
>
> Due to premature degradation, the aftertouch element did not have a long
> life in the Soloist.
>
>
>
> What was this element, exactly, do you recall?
> I ask because the Hall sensor mechanism in my SH-2000, which gives a
> wonderful-feeling and musical aftertouch, is still working after 50
> years....
>
> A
>
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