Shure Car Amplifier M267 User Manual

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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