Hammond Organ L-100 Series, Service Manual

Page: 20 / 87

Page 20
With the “Mode Switch” in the “Normal”, “Vibrato”, or “Delayed
Vibrato” position, the various pre-voiced percussions are routed
to a percussion preamplifier comprising Q314 and Q313. These
amplified signals are then routed into the regular Hammond
percussion system at the collector of Q201. With the “Mode
Switch” in the “Normal” position all percussion voices sound as
normal—that is, they have no vibrato.
NOTE 2–7–B
To obtain the following vibrato effects it will be necessary to de press
one or both of the VIBRATO tabs.
With the “Mode Switch” in the “Vibrato” position, a portion of the
percussion signal is taken from the input side of the Expression
pedal and routed through R670, the “Mode Switch”, and is then fed
to the grid of V1A (Pin 2). Here the percussion voices are amplified
and fed to the vibrato phase-shift amplifier. All voices so routed
now appear with vibrato.
With the “Mode Switch” in the ‘”Delayed Vibrato” position, a
portion of the percussion signal is taken from the input side of
the Expression pedal, and routed to a voltage divider made up
of R682 and R681. This weak signal is fed to the base of Q112.
Note that the emitter of this stage is not bypassed and the output
of this stage is relatively low. During keying, after a .5 second
delay, the charge on C631 is depleted by Q308 and Q309. With
this charge depleted, Q308 and Q309 stop conducting and their
respective collectors assume the supply pot12V. This
+12V, from the collector of Q309, is now applied to the base Q310,
thereby placing Q310 and Q311 in a state of conduction. With
Q311 now conducting, C633 is placed across the emitter resistor of
Q312. This materially increases the gain of this stage, and, as the
percussion is dying away, feeds this amplified portion of the fading
percussion signal through both the “Mode Switch” and R683 to
the grid of V1A (Pin 2). There the signal is amplified and fed to the
Vibrato Phase Shift Amplifier. All voices so routed now appear with
a vibrato tail-off.
Two positions of the “Mode Switch”, “ Vibrato” and “Delayed
Vibrato”, also affect the normal Hammond percussions when they
are in use (See
Note 2–7–B above).
2–7–2 FREQUENCY DIVIDER
When using the “Chime” voice, it is necessary to create a
1-¼ harmonic for the proper reproduction of the “Chime” tone.
This is accomplished by routing the 5th harmonic into an amplifier
made up of Q315 and Q316. Q317 rectifies and further amplifies
this pulse which is then fed to a two-stage frequency divider made
up of Q318, Q319, Q320, and Q321. The output of this second
frequency divider is then routed back to the “Selector Switch”, and
is used as one of the harmonics in the “Chime” voice.
NOTE 2–7–A
Because a frequency divider can handle only one frequency at a
time, any attempt to play two or more “chime” notes at a time will
result in distortion.
2–7–3 CYMBAL AND BRUSH
The “Cymbal -Brush” switch when in the “off” position disables the
keying functions necessary to produce the “Brush” effect. With the
“Cymbal-Brush” switch in any one of the “on” positions, the 8th
harmonic of the lower manual is disabled and this harmonic busbar
is used for keying the “Brush” effect. The pedal signal (keying)
contact is used to activate the “Cymbal” effect each time a pedal is
depressed.
2–7–4 BRUSH KEYING
With the “Cymbal-Brush” switch in any of the ON positions, the
base of Q322 is routed now to the 8th harmonic busbar in the
lower manual. Anytime a key is depressed, the base voltage of
this transistor is routed to ground, and this stage stops conducting.
The attendant rise in collector voltage is impressed on one plate