Shure m68 audio

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222 HARTFIEY AVE, EVANSTON, IL, 60204 USA.
AREA CODE 312/8632200 ¢ CABLE: SHUHEMICFID
TWX: 910-231-0048 TELEX: 72-4349

MICROPHONES AND ELECTRONIC COMPONENTS

DATA SHEET

MODELS M68 AND M68FC
MICROPHONE MIXERS

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The Shure Models M68 and M68FC are five-channel,
portable microphone mixers for use with sound rein-
forcement, tape recording and audio-visual systems.

Features:

I Four microphone inputs with individual slide swit-
ches for selection of low impedance (balanced or un-
balanced) or high impedance (unbalanced)

I High-level auxiliary input suitable for tape, tuner, and
accessories

I Individual volume control to balance each input

I Master volume control to simultaneously control
level of all inputs

I High- (unbalanced) or low-impedance (balanced or
unbalanced) microphone level output. Impedance
selected to match microphone input of associated
amplifier

I High-impedance auxiliary output

I DC power supply jack supplies 28 volts do for use
with accessories or may be used as power input in
connection with Model A673 Battery Power Supply

I Facility for connecting two or more mixers together
to obtain additional microphone inputs (two mixers
connected together give a total of eight microphone
inputs and one auxiliary input)

I Listed by Underwriters Laboratories, Inc., and by
Canadian Standards Association as Certified

SPECIFICATIONS
Gain (at 1,000 Hz)

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OUTPUTS
INPUT Low Imp. High Imp. High Imp.
Mic, Mic. Aux.
Low Imp. Mic. +6 (13 +30 dB +57 dB
.5 mV produces 10 mV 15.5 mV 355 mV
High Imp. Mlc. - 16 dB +3 dB +35 dB
5 mV produces .78 mV 12.7 mV 285 mV
Aux. -38dB -14dB +13 dB
50 mV produces .64 mV 10 mV 227 mV
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(ll-318 IN.) (5-1/4 IN.)
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5.5 mm
(7/32 INII
OVERALL DIMENSIONS
FIGURE 1

Fret1uency Response
F at 13 dB, 40 Hz to 20,000 Hz
Hum-Noise

70 dB below rated output (Aux. Output)
Equivalent Input Noise

150 ohm source, 123 dB below 1 volt

Copyright 1934. Shure Brothers Inc.
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Impedance
INPUT DESIGNED FOR USE WITH ACTUAL IMPEDANCE
Low Imp. Mic Balanced or unbalanced 25 300 ohms
to 600 ohm microphones
High Imp. Mic. Unbalanced 10 to 50 60 kilohms

kilohm microphones

Auxiliary 100 ohm to 10 kllohm unbal- 40-70 kilohms
anced high-level sources
OUTPUT DESIGNED FOR USE WITH ACTUAL IMPEDANCE

Low Imp. Mic. Balanced or unbalanced 25 to 150300 ohms~
600 ohm microphone-level
circuits

High Imp. Mic. Unbalanced 10 I0 50 kIIOhm
microphone-level circuits
Unbalanced high-impedance
(1O kilohms or greater)
auxiliary circuits

'Depending upon control settings

30-40 kilohms'

Auxiliary 2.5-3 kilohms

Clipping Levels (minimum)

INPUT CLIPPING LEVEL
Low Imp. Mic. 30 mV
High Imp. Mic. 450 mV
OUTPUT CLIPPING LEVEL
Low Imp. Mic. 60 mV
High Imp. MIC. 850 mV
Auxiliary 4 volts
Distortion

Less than 1% total harmonic distortion when low-
impedance microphone output is at 20 mV level,
high-impedance microphone output is at 200 mV
level, and auxiliary output is at 2.0 volt level

Phase
All microphone inputs and outputs are in phase. Aux-
iliary input and output are in phase with each other
but out of phase with pin 3 of microphone connectors

Operating Voltage
AC Operation: 108-132 volts, 50/60 Hz, 3W
DC Operation: 28 volts do 220%, 5 mA
Dimensions
See Figure 1
Net Weight
1.8 kg (4 lb)

INSTALLATION

w A R N I N G
To reduce the risk of fire or electric shock, do not
expose this appliance to rain or extreme moisture.

Connection Between Components

For balanced-line connection use two-conductor,
shielded, low-capacity cable. For unbalanced (high-im-
pedance) connection, use single-conductor, shielded,
low-capacity cable.

Printed in U.S.A.

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Grounding

If there should be objectionable hurn, 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 highlmpedance 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.

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REVERSED For! MODEL users ANDMGaFCE

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MIXER INPUT Micaoeeou 14mm INPUT
LOW IMPEDANCE HIGH IMPEDANCE
(BALANCED LINE

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MICROPHONE INPUT CONNECTION 5

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Low IMPEDANCE
(BALANCED LINE)
MICROPHONE OUTPUT PLUG mEchONS

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 phonojack 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
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
GOO-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 zs-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 ABBM 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-Iine 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, Swltchcraft A3 (0.6.)
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 Input

of Unit 2.

. Connect microphones to mixers and set each

microphone input control to ".0

. Take output signal for recorder of PA amplifier from

appropriate output jack on Unit 2.

Set Master control on Unit 1 to 4.

Set Aux control on Unit 2 to 10.

. Master control on Unit 2 is now Master for all inputs.

. Advance Master control (Unit 2) to about 5 and adjust

individual microphone controls for proper level. If
overall galn 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 Input 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.

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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