dbx 161 Manuel d'instruction - Page 4
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FRONT PANEL CONTROLS & METERING*
Fig.
1
-
Front
Panel
COMPRESSION
control
varies
the
amount
of
compression from
1
:1
(unity
gain)
up
to
infinity
(approx. 120:1).
The
unit
can be considered
to
be
limiting
at
compression
settings of
10:1 or higher.
OUTPUT
GAIN
control adjusts the gain
of
the
unit's
output
stage;
can
actually
attenuate
up
to
20dB,
or
can provide
up
to
20dB
of
gain.
This
control
is
independent
of
Threshold
and
Compression.
BELOW,
ABOVE THRESHOLD
(L.E.D.'s)
When
the
amber
indicator
is
illuminated, the
input
level
to the
compressor/limiter
is
below
the threshold
level
adjusted
by
the
THRESHOLD
control.
When
the red
indi-
cator
is
illuminated, the input
level
to the
compressor/limiter
is
above
the threshold
level
The
L.E.D.'s
do
not
measure output
level.
THRESHOLD
control
adjusts the
level
above which compression
or
limiting
occurs,
and
is
continuously
variable
from
lOmV
to
3
volts.
POWER
switch
turns
AC
power "on"
and
"off".
No
signal
flows
when
power
is
"off".
METER FUNCTION
SWITCHES
select
whether
the
meter
displays the
INPUT
level,
the
OUT-
PUT
level,
or the
amount
of
GAIN
CHANGE.
METER
Factory
set
for
0VU=+4dB,
the
meter
can
be
recalibrated to
other
nominal
OVU
levels
(+20
to -
1
0d
B
) .
The
meter
calibration
trimmer
is
on
the
rear
panel
(the
screw
beneath
the
meter
face
is
a
zero-set adjust-
ment
to assure the
needle
rests at
OVU
when
the unit
is
"off").
•
Controls
and
functions are
identical for the
Model 160 and Model
161.
INSTALLATION
The
units are
supplied
in
handsome
cabinets
that
can be
placed
almost 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-magnetic
fields,
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
single 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
until
all
signal
connections have been
made.
Signal
Connections
MODEL
160
Make
input
and output
connections
to the
barrier strip
on
the
rear panel, as
shown
in
Figure
2.
Note
that
the
160's
input
impedance
is
50k -ohms
when
connected
in
the
"balanced"
mode,
but
is
25k -ohms
if
connected
in
an
unbalanced
configuration.
When
using
an unbalanced input
connection,
reversing the
"+" and
input terminals
will
cause
the
output
signal
to
be
180
degrees out-of-phase with
the input
signal.
When
the
output
is
connected
to
an
unbalanced
load,
special circuits
in
the
160's
output
stage
sense
any
ground-
loop current (hum).
The
ground-loop compensation then
applies 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 input
and output
(avoid
"double-
grounding").
One
grounding
method
that 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
connected only
to the
output
of
device feeding the 160.
NOTE:
Connecting
the
and
"shield"
leads
together
at
the
160's
output,
instead of
at
the input of the following device,
defeats
the
ground-loop compensation
circuitry.