ARP 1601 Service Manual - Page 8

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The
voltages
from
the
decoder
chips are
also
supplied
to
100K
sliders
(R57
through
R103)
to
provide
a
variable
voltage
level
(0
to
+10V)
for
each
position.
Voltages
from
the
A
bank
sliders
and
the
B bank
sliders
are
summed
in
the
output
amplifier
circuit
Z19A
and
Z18A.
When
the
sequencer
is
in
the
16
X
1
position,
the
output
of the
A
and B
channels
are
summed
together
so
that the
outputs
of
Z19B
and
Z18B
will
be the same.
The
Sequencer output
voltages supplied
by
the
output
amplifiers are
routed
to the
quantizer (schematic
3).
3.10
Gate Output
Processing
Gate
Output
Processing
circuit
provides 6 outputs:
Gate Bus
1,
Gate Bus
2,
Gate Bus
3,
Clocked Gate
1,
Clock Output, and
Position
1
Output.
The
Gate Bus
1
,
2,
and 3 outputs
are
driven
from
the
3
position
slide
switches
in
the
Decoder
circuit.
Z15C
and
Z15D
are
a
flip-flop
which
supplies the
Clocked
Gate
1
Output
and
turns
on
the clock
indicator
light
(CR22).
The
position
1
output
obtains
its
signal
from
Position
1
(Q1
1
base)
in
the
Decoder
circuit
so
that
more
than
one
sequencer
can be synchronized.
QUANTIZER
3.11
Current Source
&
Semitone
Shift
Z29A
supplies
constant current through 13 equal
value
resistors
(100ohm)
located
in
resistor
pack
Z20.
The
voltage
drop
across
each
resistor
is
2/12
of
a
volt
(two semitones,
or
one whole
tone).
Q36
supplies
an
offset voltage to pin
3
of
Z29A
to "shift"
or
raise
the
output
of
the current source (and
there-
fore pins
1
through 14
of
Z20) up
1/12
of
a
volt.
etc.
one
at
a
time
sequentially.
The
remaining
bit
(LSB)
on
the
Counter output
(pin 12)
is
supplied
to the
Current Source
to
shift
the
resistor
chain
level
up
1/12
of
a
volt to
obtain
two
voljage
levels
per
resistor
in
Z20.
3.14
Comparator
The
scanner
output
(Z29B
pin
7)
is
supplied to the
inverting
input
of
the
Comparator
(Z23).
An
external
control
voltage
which
is
to
be
quantized
is
supplied to the noninverting input of the
Compara-
tor
via
the Input
Channel
Selector.
Initially,
the
Comparator
output
is
logic
1
(+15
volts)
which
permits the counter
to
be
advanced by
the
Clock through
Z24D. As
the
Counter
advances, the
voltage
on
pin
2 of
Z23
"steps"
in
1/12
volt incre-
ments
until
it
exceeds
the voltage
level
on
pin
3
of
Z23.
The
output
of the
Comparator
then changes
to
logic
which immediately
stops the
Counter.
The
voltage
on
the
Scanner output
(now
constant)
is
the
nearest
1/12
of
a
volt
level
to
the input control
volt-
age;
therefore,
it
is
supplied to the
Channel
Memory
via
Z30C
to be
stored.
3.15
Sample
Control
Z30C
is
enabled
when
the
Sample
Control provides
a
logic
1
to the clock input of
Z28A.
Z28A
then
turns
on one
of the transmission gates
(either
channel
A
or
B) for
a
time period
of
half
a
clock
cycle.
After
the
quantized
control voltage
from
Z29C
has
been
supplied to
one
of the
memory
circuits,
Z27C
resets
both
the
Sample
Control and
the
Counter.
Addi-
tionally,
the
outputs
of
Z28A
reverse state to
switch
from one
channel
to the
other
(A
to
B
for
example).
The
Quantizer
is
now
ready
to
quantize the
voltage
waiting
on
the other
input.
3.12
CV
Generator
&
Scanner
Z21
and
Z22
are digitally
controlled analog switches
which
are
connected
to the
CV
generator outputs
(Z20).
The
three binary inputs (A,
B and
C)
select
one
of eight switches to
be turned
on and connect
an
input
(pins 13, 14, 15, 12,
1,
5, 2,
or
4) to
the
output
(pin
3).
All
of the switches
are off
when
a
logic
1
is
on
pin
6
(inhibit).
The
A, B and
C
inputs of
Z21
are
driven
by Z25.
3.13
COUNTER
Z25
generates
a
binary
number
which "counts" from
00000
to
11111.
The
first
bit
(MSB)
inhibits either
Z21
or
Z22
so that
only
one
voltage
from
Z20
is
ever
on
at
the
same
time.
The
next
three
bits
(pins
6, 9,
and
11
of
Z20)
turn
on
channels
13, 14, 15, 12,
1
3.16
External
CV
Input
The
External
CV
input allows
a
control voltage
from
another
synthesizer to
be
summed
with the
output
of
the
two
Quantizer
circuits.
The
keyboard
CV
of
other instruments can be
added
to
the sequencer's
voltage to
change
the
key
in
which
the
sequencer
plays
simply by
playing
an
external
keyboard.
The
test
points
on
the
following
two
pages
illustrate
the
operation
of
the
circuits
in
the
sequencer
in
relation to
one
another.