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phase
inverter driving push-pull
output
tubes
V9
and
VI
0.
A
feedback
circuit
from
the
output transformer secondary
(R336
and
R337) makes
the pedal
response
more
uniform
by
reducing speaker resonance.
I
R336
is
adjusted
at
the
factory.
2-^6.
POWER
SUPPLY
(See Figure
5-4).
- The
power
supply
uses a
5U4
rectifier
tube
with conventional
filtering circuit.
2-7.
L-10QA PERCUSSION VOICING CIRCUITRY
(See Figure
5-5).
2-8.
MODE
SWITCH
-
With
the
''Mode Switch"
in
any of
the
reiteration positions,
the
harmonics
necessary to
produce
the
"Chime",
"Guitar",
and "Banjo"
are
all
fed into the
"A"
reiteration
channel
only,
while the
"Marimba"
and
"Xylophone"
effects
feed
harmonics
into
both
the
"A"
and
the
"B"
channels. This spht into the
"A"
and
"B"
channels only occurs
with
the
use
of
reiteration.
Without
reiteration,
all
effects are
routed
into the regular
percussion
system.
The two
reiteration
channels
are
identical.
You
will
note
that across the
secondary windings of
the
two
input
trans-
formers
is
located
a field-effect transistor.
These
gates
Q300
and Q303,
are fed
alter-
nating
pulses
from
a bistable
multivibrator
which
supplies alternate pulses
to
each
one
of
these
gates.
That
is;
one
is
On, while the
other
is
off.
These
gates
shunt
the
signal
to ground,
thereby
making
the channel
inoperative.
These
individual
signals are
further amplified
by
a
one
stage transistor
amplifier,
Q301
for
the
"A"
channel,
and
Q302
for
the
"B"
channel.
They
are
then
mixed
together
and
fed to
a
common
amphfier,
Q307, which
in
turn feeds
this
percussion
signal
to the input
side
of
the
swell pedal.
The
multivibrator
which
supphes
the
keying
pulse for these
two
gates
does not run
continually,
but
rather
is
turned off
and on
each time
a
key
is
depressed
on
the
upper manual.
The
multi-
vibrator consists
of
Q305
and Q306.
The
multivibrator
rate varies
with
the applied
base
voltage.
This
voltage
is
applied
through
the
"Mode
Switch" and
R684
and R685.
Q304
provides the necessary switch pulse
to
start
the multivibrator.
NOTE
Whenever
the
reiteration
is
used,
it
completely bypasses
the percus-
sion section
of
the
AO—
42
amplifier.
With
the
"Mode
Switch"
in
the
"Normal",
"Vibrato", or
"Delayed Vibrato"
position,
the various pre-voiced percussions are
routed
to a
percussion
preamphfier
made
up
of
Q314
and Q313. These
amplified
signals
are
then routed
into the regular
Hammond
percussion
system
at
the
col-
lector
of
Q201. With
the
"Mode
Switch"
in
the
"Normal"
position
all
percussion
voices
sound
as
normal;
that
is,
they have
no
vibrato.
NOTE
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 Expres-
sion
pedal
and
routed through
R670,
the
"Mode
Switch",
and
is
then
fed to the
grid
of
VI
A
(Pin
2).
Here
the percussion voices
are
amplified
and
fed to the vibrato
phase
shift
ampUfier.
All
voices so
routed
now
appear with
vibrato.
With
the
"Mode
Switch"
in
the
"Delayed
Vibrato"
position,
a
portion
of
the
percus-
sion
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
Q3
1
2.
It
will
be noted
that
the emitter of
this
stage
is
not bypassed
and
that the
output
of
this
stage
is
relatively
low.
During
keying,
after
a
predetermined time
lag
(.5
seconds),
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
potential
+
1
2 V. This
+
1
2 V.
from
the
collector
of
Q309
is
now
apphed
to the
base
Q3
1
0,
thereby
placing
Q3
1
0 and
Q3
1
1
in
a
state
of conduction.
With
Q3
1
1
now
conducting,
C633
is
placed
across the
emitter
resistor
of
Q3
1
2.
This materially
increases
the gain
of
this stage,
and
as
the
percussion
is
dying away,
feeds
this
ampli-
fied
portion of the fading percussion
signal
through
the
"Mode
Switch",
and
R683
to
the
grid
of
VI
A
(Pin
2).
There
the
signal
is
ampUfied and
fed to the Vibrato Phase-
Shift
amphfier.
All
voices so
routed
now
appear with
a vibrato
tail-off.
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