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Grounding If there should be objectionable hum, connect the
metal chassis of the mixer to a good ground such as the
metal frame of a wall outlet, or a water or steam pipe.
This is normally accomplished automatically through
the ground wire of the power cord.
INPUT CONNECTIONS
Microphones
Up to four low- or high-impedance dynamic, ribbon, or
condenser microphones can be connected to recep-
tacles marked Mic 1, Mic 2, Mic 3, Mic
4. The inputs are
designed for low-impedance microphones with 25 to
250 ohms impedance or high-impedance microphones.
Both low-impedance or high-impedance microphones
can be used simultaneously. 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 receptacles are professional
audio connectors (three-pin on the M68 and
three- socket on the M68FC)*. See Figure 2 for low- and high-
impedance connections to receptacle.
PICTORIALLY - PINS I AND 2. INPUTS ONLY,
REVERSED FOR MODEL M68FC AND M68FCE
, C:7%IEL.Qq
------ .,- - - - - 2' MICROPHONE MIXER INPUT MICROPHONE MIXER INPUT
LOW IMPEDANCE HIGH IMPEDANCE
(BALANCED LINE)
MICROPHONE INPUT CONNECTIONS
SHIELD SHIELD
c----;? m-------;TJ xu----- MIC OUTPUT----- MIC. OUTPUT LOW IMPEDANCE HIGH IMPEDANCE
(BALANCED LINE)
MICROPHONE OUTPUT PLUG CONNECTIONS
MICROPHONE CONNECTIONS
FIGURE 2
NOTE: Some condenser microphones produce very
high output signals which may overload the mixer input.
A Shure Model
A15AS Microphone Attenuator placed
between the microphone and the mixer input will
eliminate this problem.
Auxiliary
The phono jack on the rear of the panel marked Aux
lnput will accept output from a high-impedance, high-
level source such as a tape recorder, am-fm tuner, or
phono cartridge preamplifier. The Model
A68M
Microphone Preamplifier can be connected to this jack
to provide a fifth microphone input.
OUTPUT CONNECTIONS
Microphone
The receptacle marked Mic Output is a dual-
impedance output 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 microphone line or into a high-impedance
amplifier or tape recorder microphone input. The recep-
tacle is a professional three-pin audio connector*. See
Figure 2 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 0.5 to 2 volts, or the
auxiliary or tuner input to an amplifier or tape recorder.
Accessory 28-volt DC
The rear panel jack, marked Accessory 28 V.D.C. pro-
vides 28 Vdc open circuit (20 Vdc at 5
mA max.) for ac-
cessories such as the Model A68M Microphone
Preamplifier. The jack is also used as a power input
when using the Model
A67B Battery Supply.
CAUTION: The 28 Vdc input circuit of the M68 is not
fused. An external 28 Vdc source should be provided
with a
0.125A, 250V in-line fuse as a safety precaution.
OPERATION
Power
Connect the mixer power cord to the proper ac power
outlet (see Operating Voltage under Specifications).
'Designed to mate with Cannon XL series, Switchcraft A3 (Q.G.) series or equivalent connector.
Volume Controls The Master gain control and individual gain controls
for each of the five channels are identified on the front
panel. 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 counterclockwise).
CONNECTING TWO UNITS Two M68 mixers may be combined to give a total of
eight microphone channels plus an auxiliary input as
follows. 1. Connect Aux High Level Output of Unit 1 to Aux lnput
of Unit 2.
2. Connect microphones to mixers and set each
microphone input control to
"O".
3. Take output signal for recorder of PA amplifier from
appropriate output jack on Unit 2.
4. Set Master control on Unit 1 to 4. 5. Set Aux control on Unit 2 to 10.
6. Master control on Unit 2 is now Master for all inputs.
7. Advance Master control (Unit 2) to about 5 and adjust
individual microphone controls for proper level. If
overall gain is too low or too high, Master control
(Unit 2) can be adjusted.
8. If input to auxiliary channel is needed, such as for
tape recorder or tuner, use Aux lnput on Unit
1. Use
Aux control on Unit 1 for level adjustment of Aux
source. Master gain control for entire system is
Master control on Unit 2.
GUARANTEE
This Shure product is guaranteed in normal use to be
free from electrical and mechanical defects for a period
of one year from date of purchase. Please retain proof
of purchase date. This guarantee includes all parts and
labor. This guarantee is in lieu of any and all other
guarantees or warranties, express or implied, and there
shall be no recovery for any consequential or incidental
damages.
SHIPPING INSTRUCTIONS Carefully repack the unit, have it insured, and return it
prepaid to: Shure Brothers Incorporated
Attention: Service Department
222 Hartrey Avenue
Evanston, Illinois 60204
If outside the United States, return the unit to your
dealer or Authorized Shure Service Center for repair.
The unit will be returned to you prepaid.
OPTIONAL ACCESSORIES
Battery Power Supply .................. Model A67B
Locking Panel ........................ Model A68L
Rack Panel Kit ................... Models A68R, -BL
Microphone Preamplifier ............... Model A68M
Microphone Attenuator ............... Model A15AS
