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6
FRONT PANE
L
CONTROLS & METERING*
Fig.
1
-
Front
Panel
COMPRESSION
control varies the
amou
nt
of compression
fro
m 1
:1
(unity
gain)
up to i
nfini
ty
(approx. 120: 1 ).
Th
e
unit can be considered to be
limiting at
compression settings
of
OUTPUT GAIN control
adjusts the gai
n
of
t he
unit's
o
utput
stage; can actually attenuate
up
to
20dB,
or can provide
u
p
to 20dB of gain.
This
control
is
inde pendent
of Threshold
and
Compression.
10:1 or higher.
BELOW, ABOVE
THRESHOLD
(L
.E
.D
.'s)
Wh
en
the
amber i
ndicato
r
is illuminated,
the
input level to the compressor
/
l
imi
ter
is
below
the threshold
leve
l
adjusted by
t
he
THRESHOLD
control. When the red
indi-
cator
is i
llum
i
nated
,
the
inpu
t leve
l to
the
compressor
/
li
m
iter is above
the
thresho ld
level.
The
L.E.D.'s do
not
measure
output
level.
TH
R
ESHO LO
control
adjusts the level
above
wh
ich
compression
or li
mi
ti
ng
occurs,
and is continuously
variable
from
1
OmV to 3
volts.
1V
3V
POW
ER
2
1.5
1
t
6
-10
10
20
-
20
•
20
(D
GAIN
INPUT OUTPUT CHANGE
i
i
I
I
METER
dbx
COMPRESSOR/LIMITER
POWER switch turns
AC
power
"on"
and "off".
No
signal
f
lows
when power
METER FUNCTION
SWITCHES
select whether
the rnet
er
disp
lays
th
e
INPUT level, th
e
OUT
-
PUT level,
or the amount
of GA
IN
CHANGE
.
METER
Factory set
f
o
r
OVU
=+4
dB,
the
meter
can
be
recali
br ated
to other
nom
inal
OVU
levels
(+20
to
-10dB).
The meter calibration
trimmer
is
on the rear panel (the screw
beneath
t
he meter
face
is a
zero-set adjust-
ment to assure
t he
needle
rests at
OVU when
the
uni
t is
"off"}.
is
"off".
•controls
and functions
are
identical
for the
Mod
el
160
and
Mod
el
161.
INSTALLATION
The units are
supplied in handsome cabinets that can
be
placed
almo
st anywhere
.
Self-adhesive rubber feet
are
supplied
for
protection
of
delicate finishes that might
otherwise be marred
by the
compressor/limiter's
wood
cabinet.
Avoid
mounting a
unit above any source
of
heat
or
strong electro-magnet ic fie
lds,
such as
those generated
by power
amplifiers or vacuum tube
equipment.
Two dbx
compressor/limiters can be mounted
side-by-side
in
a
standard 19-inch rack
with
a dbx Rack Mount Kit RM
-
150-C, or a
sing le
unit can be rack mounted
in a
19"
rack
with a
dbx Rack Mount Kit
RM-
150-D.
AC
Power
Connect the Model
160
or 161 to a 117V AC, 50 or 60Hz
AC power source only.
Models
for use with
foreign
power
sources
are available. Contact
the
dbx factory
for
informa-
tion. The Model 160 or 161
requires
8 watts of
AC
power
(Maximum). As a precaution, do not connect the AC power
cable unti
l
all signal connections have been made.
Signal
Co nnect ions
MODEL 160
Make
input and
output
connections to the
barrier
strip
on the rear
panel, as shown
in
Figure
2. Note that
t
he 160's
input
impedanc
e
is 50k -ohms when conn ected in
the
"balanced" mode,
but
is
25k-ohms if connected in an
unba lanced configuration.
When
using an
unbalanced input
connection, reversing
the
"+"
and
"-"
i nput
terminals
will
cause
the output
signal
to
be 180 degrees
out-of-phase
with
the input
signal.
When the
output is
connected
to
an
unba lanced
load,
special
circuits
in the
160's output
stage sense any
ground
-
loop current (hum). The ground-loop
compensation
then
appl ies a
precise correction
signal
to
the
160
output,
at
the
proper level and phase
to reduce
hum in
the
output
signal
by up
to
40dB. For
maximum
hum reduction,
avoid com-
mon grounding at the
inp
ut
and
output
(avoid
"double-
grounding").
One grounding method
t
hat
usually works
is
to
ground the
shield at the
160's
output
"Gnd"
terminal
and also
ground
it
at the
input
of the following device. Do
not
connect
the shield
at
the
160'
s input
"Gnd"
terminal.
Leave
the
input shield connect ed only
to the output
of
device
feeding
the
160.
NOTE: Connec
ti
ng
t
he
"-"
and
"shield"
leads
together at the
160
's
output,
i
nst ead
of
at
the input of
the
following device,
defeats
th
e
ground-loop compensation circuitry.
7