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3
CONTROLS AND CONNECT
ORS
WARNING
This
apparatus must be earthed (grounded)!
The
M267
power supply is energized when the unit
is
connected to an ac source; disconnect mains
(power)
plug from supply when not in use.
Inputs
The four inputs are professional three-pin female XLR
audio connectors located on the rear panel and desig-
nated
INPUT
1 through INPUT 4. The inputs are balanced
(internal transformer, MUMETAL shielded); pins 2 and 3
are
“hot”, and pin 1 is “ground”. For microphone operation,
the switches labeled LINE/MIC (directly above the input
connectors)
must be in the MIC position; for line level in
-
puts, the switches must be in the LINE position. For im-
pedance,
clipping
and operating signal levels, refer to the
SPECIFICATIONS
section.
Outputs
The
rear-panel connector labeled OUTPUT is a
profes
-
sional
three-pin male XLR audio
connector
. With the adja
-
cent LINE/MIC switch in the MIC position, the OUTPUT
connector is used to feed a low-impedance microphone
line
or a low-impedance
microphone input. With the LINE/
MIC switch in the LINE position, the OUTPUT connector
feeds
the line-level
input of an amplifier
, tape recorder
, or
another
mixer
.
The OUTPUT connector is a balanced out
-
put with the LINE/MIC switch in either position; pin 1 is
ground, pins 2 and 3 are “hot”, and the connector is in
phase
with the corresponding pins of the input connectors.
The rear-panel binding-post connector designated
LINE
OUTPUT is in parallel with the OUTPUT connector
and
can be used as a line-level output feed simultaneously
with the OUTPUT connector
. The terminals are numbered
2 and 3 and are in phase with the corresponding pins of
the
input connectors. While the line outputs can be used
to drive various impedance lines, the VU meter is cali-
brated
for use with a 600
W
line.
The
line output transformer will operate properly with
up
to 100 mA dc in the line. This feature permits the use of
standard
“dialed-up” telephone lines with dc across
them.
(Since
a slight
distortion increase may occur at high output
levels with maximum dc current, operation with the VU
RANGE
switch at +4 dBm is recommended.)
Input Gain Controls
The front-panel controls designated 1 through 4 are the
individual
a
ctive
g
ai
n c
ontrol
s f
o
r c
orrespondingl
y n
umbered
inputs. Note that the input connectors are located on the
rear panel directly behind their corresponding gain control.
The
c
ontrol
s s
e
t t
h
e p
reamplifie
r g
ai
n a
n
d p
rovide
p
reampli-
fier
o
utput
a
ttenuation
. A
s t
h
e g
ai
n i
s r
educed
, t
h
e p
reampli-
fier
i
npu
t c
lippin
g l
eve
l i
s i
ncrease
d f
or tha
t c
hannel.
Input
control 1 serves an additional function as the level
control for the tone oscillator when the INPUT 1/OCS 1
switch
is in the OSC 1 position.
IMPORTANT:
For optimum signal-to-noise ratio, the indi
-
vidual
input controls should be operated at as high a set
-
ting as possible, consistent with maintaining adequate
control
range and input clipping level.
Master Gain Control
The front-panel control designated MASTER is the
master gain control which sets the overall output level of
the mixed sources (including signals applied to the MIX
BUS
input).
Limiter
The
front-panel LIMITER IN/OUT switch turns on a fast-
acting, peak-responding limiter circuit that cuts overload
distortion during loud program intervals without affecting
normal program levels. When the LIMITER switch is IN
(operating), the mixer output is limited to approximately
+15dBm.
Increasing the individual or MASTER gain con
-
trols will increase the average output and the amount of
limiting. The limiter threshold can be reset to any other
output
between –4 and +18 dBm if desired. With the limit
-
er
switched OUT and tone oscillator activated, adjust IN
-
PUT 1 and MASTER level controls to produce an output
0.5
dB higher than desired. Switch the limiter IN and set
the LIMITER THRESHOLD ADJUST control (accessible
though
the bottom of the chassis) for the desired level.
The front-panel PEAK LED indicator shows limiter op-
eration
with the limiter in,
and operates when program lev
-
els approach overload with the limiter out. The indicator
is much faster than a meter and will be activated by the
shortest
transient peak, but it remains on long enough
to
provide
easy recognition.
Low-Cut Filters
The
low-cut filters provide a low-frequency rollof
f to the
response
curve as shown in Figure 2. The filters are acti
-
vated
by the LO-CUT IN/OUT switch above each individu
-
al
input gain control
and can be used individually with each
control
to reduce wind noise or undesirable low-frequency
signals
such as from condenser microphones or turntable
rumble.
500
1,00050
100
200
20
0
–10
–20
LOW-CUT FILTER ACTION
FIGURE 2