The Hammond X66 Organ
X 66 Proportional Keyer
The next item to consider in the
X66 organ is the so-called proportional keyer(s). Here is one specific
area where the X66 differs significantly from the traditional tonewheel
Hammonds. Recall that drawbar volume on a traditional Hammond is determined
by which tap on the matching transformer a particular drawbar is sending
its signal to via the drawbar busbars.
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In the
X66, the drawbar volume is determined by the output(s) of the propor-tional
keyers which are actually variable gain amplifiers. The output of a propor-tional
keyer varies with a negative DC voltage which is applied to the emitter
circuit of the transistor amplifier. Each of the nine drawbar busses carries
a higher negative DC voltage than the previous, so pulling out a drawbar
applies a progres-sively more negative voltage to the pro-portional keyer,
resulting in an increased signal output.
When you push a key, this voltage is applied to the keyer via terminal K1 through a resistance.
When you push a key, this voltage is applied to the keyer via terminal K1 through a resistance.
(For convenience, we'll use Hammond's
part numbering .) All of the proportional keyers (there are 97 of them)
are alike with the exception of resistors R1 and capacitors C3. With no
voltage applied to K1, the keyer output is zero. As in any type of circuit
where we are actually keying a DC voltage, instantaneous keying would
cause a loud bang or thump to be heard. Recall in the description of the
Wurlitzer electrostatic that the reed pickups had to be keyed through
small resistor/capacitor networks, Likewise, the proportional keyers of
the X66 must be keyed so that the audio output is not completely instantaneous.
The function of capacitor C3 is to retard the keying and eliminate keying
thumps. The capacitor values range from 0.1 uF to 0.33 uF. Terminal K3
is the keyer signal output, K5 is DC voltage in.
In the X66 console, there are preset panels similar in appearance to those of traditional Hammonds, but they are controlling DC keying voltages instead of audio signal levels. When a drawbar is pulled all the way out, the voltage is around -100V, so it is necessary to shut down the instrument when changing preset wiring combinations to prevent getting a shock.
In the X66 console, there are preset panels similar in appearance to those of traditional Hammonds, but they are controlling DC keying voltages instead of audio signal levels. When a drawbar is pulled all the way out, the voltage is around -100V, so it is necessary to shut down the instrument when changing preset wiring combinations to prevent getting a shock.
