3101
Digital
Interface
connector provides access to the
DAC
input
latch
and
the
necessary
control signals. Instructions
for
using
the
interface
are
in
the
Operation
Manual. Briefly,
Ul13
must
be
removed,
R1182 added,
and
a
jumper
installed between
U113-2,
and 5101-7.
The
external system then connects to 3101.
tr or
details,
see
Section
5.)
Ignoring
the
Glide
circuit
for
the
moment,
U115-7
and associated resistors
form
a
1-V
Subtracter
converting
the normal
DAC
range
down
to
a
conventional
output range.
U115-1
buffers
the
KYBD
CV
sent
to
34
CV
OUT.
The
KYBD
CV
sent
to
the
oscillators
and filters can
be
bypassed
by
an
external
input
at
52,
2-13
GLIDE
The
Glide
circuit
processes the
KYBD
GV
from
the
DAC,
causing
it
to
slew between
its discrete
83-mV
steps.
U109-13
OTA
is the central
component
of
the Glide circuit,
which also contains current source
Q105/Q106
and
buffer
U110-1.
The
buffered
output
from
the
voltage follower
is
fedl
back to the
OTA
input through
R1136
so
positive
or
negative
current will
flow
into C141 if there
Is
a
difference between
the
feedback
voltage
and
the
input
voltage
through R1135.
Dl
10/11
I
protect
the
OTA
inputs.
Divider
R
1167/R1166/R
1
165
is the Glide voltage
source.
When
R1139
GLIDE
RATE
knob
is
set
to
0
(ground),
Iabc
will
be
maximum
because
diode-connected voltage
source
Q106
f
srward-biases
Q
105's
emitter
620
MV
above
ground. Transconductance
will
therefore be
maximum,
so
plenty
of
current
is available
to
charge
C141
and
the
GLIDE
output
will follow the
KYBD
CV
very closely. However
as
the
GLIDE
knob
is
raised,
Iabc
sourced
by
Q105
Is
inhibited,
reducing
the
rate
of
charge
to C141.
It
will
thus
take
longer for the
GLIDE
output
to
approach
KYBD
CV.
This
creates
a
slew
between
the
discrete
voltage
steps output
by
the
DAC.
When
5118
is
switched to AUTO,
(3149
couples
the
-GATE
signal (discussed below)
which pulls-down
the
base
of
QIO5,
enabling collector current, thus disabling
GLIDE.
When
-GATE
goes
high,
Dl12
discharges
C149 in preparation
for
the
next
-GATE.
2-14
GATE
AND
TRIGGER
LOGIC
We%e
only
left to inspect the miscellaneous circuitry which interfaces the internal
or
external clock sources
and
microcomputer. In normal modes,
the
GATE
passes
through
5
129
REPEATIEXT, and
is
buffered
by
inverter
U114-15.
The
resulting
-GATE
signal
drives
the Auto-Glide circuit, discussed
above,
and
is re-inverted
by
U114-12
for
35
GATE
OUT.
U114-10
also re-inverts
-GATE,
producing
the
signal
switched
to
the
envelope generators
by
5130,
and
driving
DS
LO
1
GATE
LED,
thorough
U114-6.
R1183
speeds-up
the
rising
edge
of
the
TRIG
signal.
It
is
switched
through
5129
and
5130.
To
trigger,
the
microcmputer momentarily pulls
TRIG
low.
This
pulse
is
coupled
through
C157
(see
SD112)
to
the
envelope generators.
1.
Switching
5130
DRONE
on
holds
both
the
TRIGGER
and
GATE
signals
high.
(Although
the
TRIG
singal is ac-coupled
to
the envelope generators.
If
5129
is switched
to
REPEATIEXT,
the
LEO,
EXTERNAL
GATE/CLK
IN,
or
-AGATE
will
also trigger and gate
the
envelopes
or advance
the
sequencer.
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