Shure Brothers Incorporated
222 Hartrey Avenue
Evanston IL 60202-3696 U.S.A.
Model M267 User Guide
GENERAL
•
•
All connections phased. Line output terminals phase-in
dicated
-
The
plifier
S
s
hure Model M267 is a
microphone mixer-remote am-
Compact and lightweight, with rugged, abrasion-resis-
tant case
pecifically designed for professional applications. The
excellent performance, versatility and features of this com-
•
•
Internally selectable 120 or 240 Vac, 50/60 Hz operation
plete,
mote,
expanding
audio
inputs.
c
o
ompact console make it an ideal choice f
r sound reinforcement use, a d as an add-on mixer
xisting facilities. It is also ideally suited f r u e with
nd video tape recorders to provide multiple microphone
o
r studio, re-
n
for
Underwriters’ Laboratories Listed and Canadian Stan-
dards Association listed as Certified
e
o
s
a
SPECIFICATIONS
Features:
Frequency Response
•
Wide, flat frequency response and extremely low distor-
tion up to +18 dBm output
30 Hz to 20,000 Hz, 2 dB
±
Voltage Gain (at 1,000 Hz)
•
Extremely low noise and RF susceptibility
(Outputs terminated: line 600 W, microphone 150 W, mix
Four switchable microphone- or line-level balanced-line
inputs ith individual gain controls a d low-frequency roll-
off witches. MUMETAL shielding on input transformers
•
bus
3.
3 kW, headphone 200W,
t
ip-sleeve a
nd ring-sleeve
)
w
n
s
OUTPUT
Input
•
Feedback-type input gain controls for maximum clipping
levels and dynamic range
Line
Microphone
Mix
Bus
•
•
Output switchable for line or microphone level
Low-Impedance
Microphone (150 W)
91 dB
41 dB
24 dB
Built-in switchable peak limiter cuts output overload dis
tortion, adapts to power supply voltage
-
Line
40 dB
55 dB
–9 dB
5 dB
–27 dB
– –
•
LED indicator shows limiter operation or overload with
limiter defeated
Mix Bus
Inputs
•
•
Externally adjustable limiter threshold (–4 to +18 dBm)
VU meter calibrated for +4 and +8 dBm with range
switch. Illuminated with ac operation
IMPEDANCE
Designed Actual
Input
Clipping Level
•
•
Ac or built-in battery operation. Noiseless automatic
switchover to battery in case of ac line failure. Battery
test without program interruption
for Use
(Internal)
Input
With
M
icrophone 19 to 600
–32
5 dBV∗
(25 mV to 0.56 V
dBV to
1 kW
Front-panel headphone level control and monitor jack
drives almost any stereo or mono headphones; output
W
–
)
can be additional unbalanced line feed to drive a tape re
corder or power amplifier
-
Line
Less
than10 k
66 kW
+20 dBV
W
•
•
Direct mix bus for stacking units
Mix Bus
3.5 k
W
3.5 kW
+7 dBV (2.2 V)
Automatic muting prevents speaker damage during
turn-on and -of
∗Depending on input control setting
f
•
Low distortion, high-stability tone oscillator for line test
and level checks
E1997, Shure Brothers Incorporated
27A8376 (QE)
Printed in U.S.A.
CONTROLS AND CONNECTORS
WARNING
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
-
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.
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
Inputs
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).
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
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
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.
+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
Outputs
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 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
The front-panel PEAK LED indicator shows limiter op-
eration with the limiter in, and operates when program lev
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.
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.
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-
Low-Cut Filters
The low-cut filters provide a low-frequency rolloff 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.
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.)
0
–10
–20
Input Gain Controls
The front-panel controls designated 1 through 4 are the
individual
active gain controls for correspondingly numbered
inputs. Note that the input connectors are located on the
rear panel directly behind their corresponding gain control.
20
50
100
1,000
200
500
The
c
ontrols s
utput ttenuation. As t
nput clipping level is increased for that channel.
e
t t
h
e preamplifier gain a
n
d provide
preampli-
LOW-CUT FILTER ACTION
fier
fier
o
i
a
he gain is reduced, t
he preampli-
FIGURE 2
3
Mix Bus
Direct access to the mixing bus is provided through the
rear-panel MIX BUS phono pin jack. This provision is
made primarily to facilitate stacking or “multing” M267s to
achieve additional input capacity without losing any in-
puts. With two M267s, for example, the two mixing buses
are directly connected, providing two independent master
The oscillator should be switched off (INPUT 1 position)
when not in use.
Phantom Power
The rear-panel PHANTOM OFF/ON switch controls the
application of phantom power for condenser micro-
phones, such as the Shure SM81 and SM85, to all inputs.
With the switch on and the rear-panel MIC/LINE switches
in the MIC positions, +30 Vdc is applied to pins 2 and 3 of
each input connection. Series current-limiting resistance
gain controls and two isolated line amplifiers with eight in
-
dividually controlled inputs. Since the buses are directly
paralleled, a 6 dB drop in gain will occur; and the master
or input controls must be increased to compensate. Noise
is 3.3 k, for each input. When using other condenser mi
crophones with the M267, verify that the voltage and resis
tance requirements are compatible.
-
-
specifications are not adversely affected by this intercon
-
nection. Mix bus interconnection can also be made with
other Shure mixers, such as the M268, FP42. etc.
Note that the phantom power cannot normally be ap-
plied to the inputs with the MIC/LINE switches in the LINE
position.
VU Meter
IMPORTANT Do not turn the PHANTOM switch on when
:
The VU meter is factory-calibrated for use with a 600
terminated line. The VU RANGE switch on the rear panel
selects either a +4 or +8 dBm output at 0 VU meter indica
tion. (This switch changes the meter indication but does
not change the actual output level.) Microphone output
,
using unbalanced low-impedance microphones; objec-
tionable hum will result. Turn off the PHANTOM switch
when condenser microphones are not being used.
-
Use only high-quality cable. Intermittent shorts between
broken shield wires and balanced conductors will cause
offensive noise transients in the system.
levels are 50 dB below line output. The +4 range is recom
-
mended for normal use to provide approximately 14 dB of
headroom from operating level to clipping level.
BATTERY OPERATION AND EXTERNAL POWERING
The VU meter is illuminated by two No. 86 lamps operat
-
In addition to ac operation, the M267 can be operated
from an internal battery pack. Current drain is typically 17
mA at +8 dBm output level and typically 15 mA at + 4 dBm.
ing well under their normal ratings for a life expectancy of
greater than 10,000 hours. The lamps are only lit during
ac operation. Consequently, the illumination serves as a
visual alarm if the ac is interrupted and the unit has
Battery power is recommended both for remote, on-loca
tion operation, and as an emergency backup source in
case of failure of the ac power
-
switched to battery
.
.
The VU meter is connected on the primary side of the
output transformer to assure protection from any dc level
on a telephone line.
Access to the battery compartment is provided at the
bottom of the chassis. Three 9-volt alkaline batteries pow
er the M267 at full rated output. Use alkaline batteries for
maximum life. Duracell MN1604A or Eveready 522 are
recommended. Battery life is approximately 20 hours at
+4 dBm continuos use. Note that battery operation with
-
Headphones
The headphone outlet appears at the front-panel jack
panel designated PHONES. The two-circuit phone jack
will accommodate most stereo or mono headphones. The
output level is sufficient to provide high volume for use in
noisy environments.
phantom power loads and high level headphone monitor
ing will increase battery drain.
-
With batteries in the battery compartment, the M267 will
automatically and silently switch to battery operation
should the ac voltage fall below a suitable level. If the ac
power fails completely, the VU meter lamps will go out,
providing a visual indication of line failure.
Note that the headphone output level is also high
enough to use as an auxiliary unbalanced line feed to drive
a
tape deck or a power amplifier
.
Battery condition can be determined by using the BATT
CHECK switch on the front panel. Activate the BATT
CHECK switch and observe the VU meter. A new set of
The tip and ring connections of the headphone plugs
are in phase with pin 3 of all input and output connectors,
and with the tip of the MIX BUS jack.
batteries will give about a +2 VU indication. Battery condi
-
tion is good if the reading is above 0 VU; a lower reading
means that new batteries are required for proper opera-
tion. Note that the M267 power switch must be turned on
to check battery condition.
T
one Oscillator
The highly stable, low-distortion tone oscillator provides
for line test and level checks. The oscillator is instantly ac
-
tivated by the front-panel INPUT 1/OSC 1 switch; its level
can then be controlled by the INPUT 1 gain control on the
front panel. The tone oscillator frequency is 1,000 Hz, and
the signal appears on both the line and microphone out-
puts, as well as the headphone and mix bus connectors.
Telephone Interconnection
When using the M267 connected directly to a telephone
line, check to see whether the local telephone company
requires an interface coupler between the M267 and the
4
telephone line. If a coupler is required, make certain the
240
1. Disconnect the M267 from the ac line.
2. Remove the end caps and cover
Vac, follow these steps:
coupler selected and the wiring arrangement are in com
-
pliance with the telephone company regulations.
.
When direct connection to a telephone line is not pos-
sible, acoustic coupling to a telephone handset may be
used. A Shure Model 50AC Telephone Acoustic Coupler
can be connected to the 600 , line or headphone output
of the M267 and attached to most telephone handsets.
3. Locate the voltage selector switch (S201) at the right
rear of the main printed circuit board (Figure 3). Move
SD201 to the 240V position (toward the front panel).
Telephone Line Surge Protection
WHT
120V
BLK
When using the M267 connected directly to a telephone
line subject to lightning-induced voltage surges, the fol-
lowing commercially available part can be installed across
the LINE OUT terminals to provide additional protection
for output circuit components:
T206
F202
T50/250V
S201
240V
Metal Oxide Varistor, General Electric Co., Type No.
V22ZA1
240 V WIRING
FIGURE 3
ACCESSORIES
A268R Rack Panel Kit. The Model A268R Rack Panel Kit
4. Remove fuse F201 (0.1A, 250V, time lag) and replace
it with the supplied fuse F202 (0.05A, 250V, time lag).
Note that the F202 fuse holder is at right angles to the
1
includes a 19 in. x 3-
/
2
in. (483 mm x 89 mm) precut rack
panel and necessary hardware for rack-mounting the
M267 (with its cover in place and end caps removed) in a
standard 19 in. (483 mm) rack panel.
RKC169 Rack Panel Bracket Kit. The Model RKC169
Rack Panel Bracket Kit enables owners of the Shure
A68R Rack Panel Kit (originally designed for the M67 and
M68 Mixers) to rack-mount the M267 with the A68R.
F201 fuse holder
.
5. Replace the ac line cord (if necessary) with one de-
signed for the 240 Vac source. If the M267 is to be
used outside the U.S. and Canada, local regulations
may require replacing the line cord with one having
wire insulation colors as follows:
SERVICE
“Live” or
“Hot”
Earth or
Ground
Neutral
White
Blue
WARNING
U.S., Canada
Europe
Black
Green
Voltages in this equpment are harzardous!
Brown
Green/
Yellow
Refer servicing to qualified service personnel.
240 Vac Operation
To change the M267 operating voltage from 120 Vac to
6. Replace the cover and end caps, and mark the rear
panel to reflect the new operating voltage.
5
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