[HAM] volume pedal mod for chopped Hammond model D

[Dave Bishop]

Its easier on the model D than on later Hammonds with air capacitors.  The 
expression pedal in the D is just a variable resistor array.  I've seen it 
done using a 250K ohm Ernie ball mono volume pedal, with another 250K+ ohm 
resistor across the poles.  You would tap off the downstream side of the .25 
mfd cap in the rheostat box, using a mic cable with the shield grounded on 
one side only.  High resistance prohibits the signal from being pulled to 
ground and the volume is high.  Low resistance shunts the signal to ground 
and the volume is low.  Its only one cable because what you are doing is 
shunting signal to ground: there is no return.

I don't know much about Morley pedals, but I think they use a photocell, 
which is not actually in the signal path.  The trick would be remove the 
transistor across the pedal output and wire the photo cell directly across 
the input jack, so it works as described above.  Maybe someone else who has 
modded a Morley pedal can jump in.

Regards,

Dave Bishop