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GROUNDING
If there should be objectional hum, ground the metal chassis of the mixer to a
good ground such as a metal frame of a wall outlet or a water or steam pipe.
INPUT CONNECTIONS
Microphones: A maximum of four low or high impedance dynamic or ribbon micro-
phones may be connected to receptacles marked MIC.
1,
MIC. 2, MIC.
3,
MIC
4.
The inputs are designed for low impedance microphones with 25 to 250 ohms im-
pedance or high impedance microphones. Both low impedance and high impedance
microphones may be used simultaneously with the M68. The unit is
not
recom-
mended for use with crystal or ceramic microphones. The impedance is selected by
a slide switch above the input receptacle. The input receptacle is a male Cannon
XLR-3-14 type (uses XLR-3-11C mate, Shure Part 95A-3176).
See Figure “A” for
low and high impedance connections to receptacle.
Auxiliary:
The jack on
the rear of the panel marked AUX. INPUT will accept
output from a high impedance, high level source such as a tape recorder, AM-FM
tuner, or output from the Model A68P Phono Cartridge Preamplifier (Accessory).
OUTPUT CONNECTIONS
Microphone: The receptacle marked MIC. OUTPUT is a dual impedance out-
put selected by the switch above the receptacle. This output is the “Mixed”
output of all the input sources and is designed to work into
a
25
to 600-ohm line
or input, or into a high impedance amplifier or tape recorder microphone input.
The receptacle
is
a male three-pin Cannon XLR-3-14 type connector.
See Figure
“A”
for output receptacle connections.
Auxiliary: The phono jack marked AUX. HIGH LEVEL OUTPUT is a high
impedance high level output designed primarily to feed a power amplifier requiring
.5
to
2 volts or the auxiliary or tuner input to an amplifier or tape recorder.
Accessory
28-volt
DC: This rear panel jack provides 28 volts DC for accessories
such as the Model A68P Phono Cartridge Preamplifier. The jack is also used as
a power input when using the Model A68B Battery Power Supply (Accessory).
OPERATION
Power:
Connect the Microphone Mixer power line cord to the proper A.C. power
outlet. See Operating Voltage under Specifications. (All Mixers except the M68-2E
come with a standard two-conductor AC plug attached).
The Model M68-2E is supplied with a three-conductor power line cord, but no plug.
The power line cord
plug
should be installed by a qualified person. The
red
and
black
leads of the power line cord should be connected to the “hot” or line voltage
terminals. The
green
lead is the grounding conductor and should be connected to
the ground or earth terminal of the plug.
If
a
different power line cord
plug
is required on the Model M68-2 Mixer, this plug
should be installed by qualified service personnel.
In the Models M68-2 and M68-2E, either operating voltage is selected by a switch
on the back panel. A switch lock plate is provided to prevent accidental switching
to the 105-130-volt position. These microphone mixers are shipped with operating
voltage selector switch locked in the 210-240-volt position. The lock plate can be
removed from the locking position by loosening (do not remove) the screw holding
the lock plate, rotating the lock plate
go”,
and re-tightening the screw. The power
ON-OFF switch is
on
the front panel.
CAUTION:
Do
Not Plug Power Line Cord of Models M68-2 or M68-2E into
Volume Controls: The Master Gain Control and the individual gain controls for
each of the five channels are identified
on
the front panel.
210-240 volts when switched to 105-130 volts.
The individual gain controls should generally be set near maximum (fully
clockwise) and the master gain control adjusted to required output. Individual
channel gain controls not being used should be kept at minimum gain (fully counter-
clockwise).
Identifying Controls
:
Pressure sensitive adhesive labels are supplied with the Mixers
as a means of identifying the control and recording the control position when opti-
mum results have been obtained. The labels are easily removed when their
use
is
no
longer required.
CONNECTING
TWO
UNITS TOGETHER
Two M68 Mixers may be combined to give a total of eight microphone channels
plus an auxiliary input.
A. Connect the AUX. HIGH LEVEL OUTPUT of UNIT
1
to the AUX. INPUT
OF UNIT 2.
position.
output jack on UNIT 2.
B.
Connect microphones
to mixers and set each microphone input control to
#O
C.
Take the output signal for recorder or P.A. amplifier from the appropriate
D.
Set Master Control UNIT
1
to position
#lo.
E. Set AUX. Control on UNIT 2 to position #4.
F.
The Master Control on UNIT 2 is now the Master for all inputs.
G.
Advance Master Control (UNIT 2) to about #5 position and adjust individual
microphone controls for proper level.
If
overall gain is too low or too high the
Master Control (UNIT
2)
may be adjusted.
H.
If
an input to the auxiliary channel is needed, such as for a tape recorder
or tuner,
use
AUX. input on UNIT 1. Use AUX. Control
on
UNIT
1
for level
adjustment of the AUX. source. The master gain control for the entire system
is the Master Control
on
UNIT 2.
The Model A68S Stacking Kit includes stacking brackets for attaching the two
mixers firmly together plus the required inter-connecting cable. The cable only, is
available separately under the Model A68SC.
Guarantee: The Shure Model M68 Mixer is guaranteed to be free from electrical
and mechanical defects for a period of one year from date of shipment from the
factory, provided all instructions are complied with fully. In case of daamge, it is
essential that you carefully repack the unit and return it to the factory or, if outside
of
the United States,
to
your dealer or authorized Shure Service Center for repair.
Our guarantee is voided if the basic assembly has been opened or subjected to
unreasonably rough handling.
SHIELD
MIXER INPUT MICROPHONE MIXER INPUT
-____-
MICROPHONE
HIGH IMPEDANCE
[BALANCED LOW IMPEDANCE LINE1
MICROPHONE INPUT CONNECTIONS
-_____
MIC. OUTPUT MIC. OUTPUT
LOW IMPEDANCE
(BALANCED LINE1
HIGH IMPEDANCE
MICROPHONE OUTPUT PLUG CONNECTIONS
MICROPHONE
CONNECTIONS
-
FIGURE
A