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JBL/UREI
MODEL
7110
terminals
to
the output
of
the 71
1
0.
At
turn-off,
or
loss of
power
to
the
unit,
the
relay
DC
supply
drops
quickly.
Transistor
Q6
turns
off
quickly
and removes power
from
the
relay
which
returns
to
its
rest position,
bypassing
the
unit.
4.6 Input/Qutput Display
The
Input/Output Display
circuit
is
designed
to
give the operator
a
visual
display
of
program
signal
level
as an
aid
in
setting
the
Input
and
Output
levels for
best
headroom and
signal-to-
noise,
and
to aid
in
setting
Threshold.
The
signal to
be
displayed
is
selected
by
switch
SW3,
one
half of
which
turns
on
either
LED DS3
or
DS4
to indicate
switch
position.
Output
signal
level
reference
is
adjusted
by
potentiometer
R72
and
IC9B.
The
signal
is
coupled through a
full
wave
rectifier circuit
using
IC9A and
D.
The
display
is
average
responding.
The
output
of
the
rectifier
feeds
a
multi-section
window
comparator.
The
threshold voltages
for
the
comparators
are
set
by
a
resistor
ladder
comprised
of
R107-R123.
The
outputs
of
the
comparators connect
to
a
series
string of
LEDs
which
are driven through
constant
current
source Q8.
The
comparators
are
arranged
in
such a
manner
that
an
input
voltage lower than threshold
causes
the
comparator
output
to
be
low, sinking
current
for
all
LEDs
lower
in
the
string
and
simultaneously preventing the higher
LEDs
from
illuminating.
As
the
input
voltage
exceeds
the threshold
for
an
individual
comparator
its
output
goes
high,
and
the next higher
LED
illuminates.
Ultimately,
as
the
signal
level
continues
to
increase
all
sixteen
comparators' outputs
go
high
and
the
LED
string
is
connected
to
the negative
power
supply.
4.7
Gain Reduction
Display
The
display
of
gain reduction
is
accomplished
similarly to
Input/Output
as described above,
with
the exception
that
the
DC
control
voltage
for
the
VGA
is
used
directly to
drive the
circuit.
4.8
Power
Supply
AC
mains
power
to
the 71
10
is
converted
to
DC
in
the
power
supply.
The
supply
is
a
straightforward
linear
style.
Stepdown
transformer T1 supplies low voltage
AC
to
a
bridge
rectifier
consisting
of
diodes
CR20-23.
The
full
wave
rectified
DC
is
filtered
by
capacitors
C43
and
C44
and
regulated
by
Integrated
Circuit
Voltage Regulators
VR1
and
2.
The Power
Supply
in
the
Model
71
10-EX
is
similar,
with the addition
of
a tapped
AC
Mains
transformer
and a
switch
to select
the taps
for
nominal
100,
120
or
220/240
VAC.
Page
16
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