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BRIEF OPERATIN
G I
NSTRU CT
IONS
Fig. 1
-
Front Panel
Threshold Indicators There
are three LED's
which
indicate
the relationship of the input
signal level to the threshold of compression.
The green LED is ON when the signal is
below threshold, the red LED is ON when the
signal is above threshold, and the amber
LED
is ON when the signal is in the Over Easy
threshold range.* (
Refer
to Figure 4 .) Since
the LED's indicate the contents of the gain
control signal, their response time will be
affected
by the selection of automatic or
manual
operation,
and
by the attack/release
rates selected in manual operation.
Meter
Function
Switches
These three interlocking
pushbuttons determine whether the meter
displays Input
level,
Output level or the amount of Gain Change. Input level metering is
useful
in
deciding how much compression may be needed. Output level metering is
useful
as a check to
ensure that the levels are not exceeding the desired
maximum
and the over-all gain of the 165 is
set properly.
I
nput and output
levels
are displayed on an RMS basis, with fixed time constants
which are unaffected by the front panel attack and release controls. Gain change metering pro-
vides a more precise
indicatio
n
of how
much
of the program is being compressed than can be
determined from the
Threshold Indicator
LED's.
The
meter, when
displaying gain change,
indicates the contents of the gain control signal, so its response time will be affected by the
·
setting of the front panel manual/automatic
switch and, in manual
mode,
by the attack and
release rate controls. ( Fixed gain changes commanded by the output gain control are not
displayed by the meter's gain change function.)
NOTE
:
Even though
no
input signal is
applied, it is normal
for
the Above Threshold
and Over Easy™ LED
indicators
to flicker ON
when the power is turned ON or OFF.
Compression Control
Clockwise rotation of
this control increases the maximum amount of
compression from 1:
1
(unity gain)
up
to
infinity.
The
unit
can be considered to be a
limiter at compression settings of
10:
1 or
higher, especially with a fast attack rate
Meter
The
meter
is factory set so that O VU
is
equivalent to+
4
dB
input
or output
level,
as
selected
with the Meter
Function
switch.
The
nominal
O
VU
level may be changed to
anywhere from
-
10
dB to
+10
dB by
adjusting the rear panel Meter Calibration
trimmer.
In Gain Change
mode, the meter
pointer
moves
down scale from
O
VU to
indicate
how many dB of compression the
165 is
providing.
(above
100
dB/mS).
Auto Attack/ Release Indicator
Power
ON/OFF Switch
Engage this
switch to apply AC power to the unit.
The LED (Light Emitting
Diode)
indicator above will be illuminated
when the power is ON.
No
signal
flows
when the power is OFF, unless the
System Bypass button
is
engaged.
This
LED
is illuminated
when the
165
is in
Auto Attack/Re lease mode.
NOTE: The screw beneath the meter face is a
zero-set adjustment
to
assure the needle
rests
at
O
VU when
the
unit is
OFF; it
is not
intended
for
calibration.
See page
8 for
meter rei;al
ibration
instructions.
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Stereo Coupler
For single-
channel (monaural) operation,
this switch determines
whether the
unit
will be the
master (controlling
unit) or
the slave.
The
unit becomes a
slave when the button is
pressed IN,
and the
LED
above the button turns ON to
indicate the slave status.
In
stereo operation, all gain,
attack/release, compression
and threshold adjustments are
made
.wit
h
the
Master unit's
controls.
The
Slave
follows
the
Master's
commands with
the exceptions of Meter
switching,
System
Bypass
switching and
Power
switch-
ing
which remain
independent
and must be done on both
units.
Threshold Control
Adjust th
is
knob
to set
the threshold of
compression from
-
40
dB
(7.8 mV) to
+
10
dB (2.45 V).
••
The
threshold of compression
I
/
Attack Rate Control
Clockwise
rotation of this contro
l
adjusts the
maximum
attack rate from
400
dB
per
millisecond to
1
dB
per
millisecond.
The control
setting only affects the 165's
operation when the unit is
in
manual
mode; it has no effect
when the
165
is
in
Auto Attack/
Release mode.
Auto Sw itch
Engage this switch to
place the 165
in
the Auto
Attack
/
Release
mode.
The compressor's
attack rate and release
rate
then
automatically
vary to suit the
volume envelope of the
input
signal. The attack
and
release
characteristics may be set
manually
with the adjacent front panel con-
trols when the switch is not engaged.
is defined
as the approximate
middle of the Over Easy TM region.
Release Rate Control
Clockwise
rotation of this control adjusts the
maximum
release
rate from 4,000 dB
per second to 10 dB
per
second.
The
control setting only affects the 165's
operation when the unit is in manual
mode;
it
has
no effect when the 165
is
in
Auto Attack/Release
mode.
-••
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OUTPUT
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N
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INPUT OUTPUT
GA.,N
1's
vsHM
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BYPASS
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0
0
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ut
put Gain Con
)
o
l
This
control
adjusts the amount
/
~f
gain in the 165's output amplifier
stage. The
signal
can be attenuated or boosted by a ful
I
20 dB
relative
to a "O" center setting (unity gain).
This
control is
independent of
the
threshold of compression.
Because 20 dB of gain can be added at
the
165
output, it is possible to cause clipping
even
when the
input
level is
with
in
the
specified range. Especially
when
the
COMPRESSION
RATIO
is
set
at a low
number
(a low "factor"),
extreme clockwise rotation
of
the OUTPUT GAi
N may cause the
165
output
stage to clip
program
peaks.
Therefore, for normal
operation we suggest
setting OUTPUT GAi
Nat
"O
dB" (12 o'clock
position). Where the
circuit
fed
by the 165
has
a high input
sel]sitivity,
lowering the
165's OUTPUT
GA
i
N
setting can avoid
the
need for
an attenuation
pad.
System Bypass Switch
Engaging
this button creates a hard-
wired bypass of the 165's circuitry
by connecting the
input
directly to the output. The
Bypass is
useful
for A-B
com
parisons
of the compressed and
the
"straight"
program, or
for
rapid
restoration of signal flow
in
the event of a
165
c1rcu1t problem.
NOTE: Since
the system output
is
normally single-ended,
in normal operation the (+) output carries the signal, while
the(-}
output is connected to ground.
In
the
System
Bypass
mode, the(+) signal
input
is
directly connected to the(+)
signal output, and the (-) signal input
is
directly connected
to the (-) system output. Thus, in Bypass mode,
the
output
is single-ended when the input is single-ended, and balanced
when the input connection
is
balanced.
*"Threshold"
is defined as the point of 6 dB gain reduction when the unit is set for a
maximum (infinite)
compression ratio.
**O
dB is referenced to
0.775
V
RMS.
"dbx"
and
"Over
Easy" are trademarks of dbx
Inc.
3
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