Hammond clone using Hammond keyboard

[Bob.Schrum at harpercollins.com]

I've never known anyone to do so, but if you have a real Hammond keyboard 
assembly, it would be certainly do-able.  All you need is a wave generator to 
produce seven octaves (or so) of equal-tempered sinewave outputs (A 
high-frequency CMOS oscillator clocking a Top-Octave Generator chip with a six- 
or seven-stage binary divider on each of the 11 outputs. Tap off the TOG outputs
and each binary divider stage into RC Lowpass filters to shape the square wave 
into something sinusoidal.)

The mass of outputs from the tone generator are wired to various spots along the
keyboard which connect to flexible contact fingers.  Each key has nine of these 
contact fingers which contact nine silver bus bars which extend the length of 
the keyboard.  Each bus bar corresponds to a harmonic and goes to a drawbar, 
essentially volume controls with their outputs summed together to determine the 
harmonic content of the resulting timbre.  The harmonics are, in order: 

        Bus 1 - one octave below the fundamental pitch (16' brown drawbar)
        Bus 2 - the fifth above the fundamental (5 1/3' brown drawbar)
        Bus 3 - the fundamental (8' white drawbar)
        Bus 4 - one octave above the fundamental (4' white drawbar)
        Bus 5 - one octave above the fifth (2 2/3' black drawbar)
        Bus 6 - two octaves above the fundamental (2' white drawbar)
        Bus 7 - two octave above the third (1 3/5' black drawbar)
        Bus 8 - two octave above the fifth (1 1/3' black drawbar)
        Bus 9 - three octaves above the fundamental (1' white drawbar)

The tricky part would be the fact that the keyboard assembly includes a network 
of fine wires that interconnect the flexible key contacts to route each 
generator output to the key/harmonic that requires it.  For example, the 440Hz 
output of the generator would go to the fundamental (bus 3) of Middle A, but 
also to the subharmonic (bus 1) of the A one octave up, the subharmonic fifth 
(bus 2) of Middle D, and so onto the other busses down the keyboard.  At a 
glance this may seem to make things really easy, but you need to know what model
organ the keyboard assembly was designed for, because these interconnects also 
produce the foldback idiosyncracies of certain Hammond models.  Check out the 
Hammond Grounds (http://www.webcom.com/groove/hg/) and Goff Professional's web 
page for info on this stuff.  

As far as tone generators go, I have schematics for the Hammond X5, which 
contains a CMOS-based tone generator.  If you send me your address, I can 
snail-mail the pertinant pages, if you wish to roll your own based on a Hammond 
design.


______________________________ Reply Separator _________________________________
Subject: Hammond clone using Hammond keyboard
Author:  Robert May <wfrb at miworld1.miworld.net> at Internet-Server
Date:    7/23/96 5:35 PM


     
     Has anyone ever experimented with using an actual Hammond keyboard to
key electronically created near-sinewave tones (as in the Hammond X-2 
portable organ)?
     
  Rob