Shure M68 User manual

The Shure Models M68 and M68FC are five-channel,
portable microphone mixers for use with sound rein-
forcement, tape recording and audio-visual systems.
snu-
@
222 HARTREY AVE., EVANSTON, IL, 60204 U S A
AREA CODE 31
2/866-2200 CABLE SHUREMICRO
.---- ---.-=--.. ---- TWX. 910-231 -0048 TELEX 72-4349
MICROPHONES AND ELECTRONIC COMPONENTS
Features:
DATA SHEET
MODELS M68AND M68FC
MICROPHONE MIXERS
Four microphone inputs with individual slide swit-
ches for selection of low impedance(balancedor un-
balanced) or high impedance (unbalanced)
w High-levelauxiliary input suitable for tape, tuner, and
accessories
Individualvolume control to balance each input
Master volume control to simultaneously control
level of all inputs
w High- (unbalanced) or low-impedance (balanced or
unbalanced) microphone level output. lmpedance
selected to match microphone input of associated
amplifier
High-impedanceauxiliary output
w DC power supply jack supplies 28 volts dc for use
with accessories or may be used as power input in
connection with Model A67B Battery Power Supply
w Facility for connecting two or more mixers together
to obtain additional microphone inputs (two mixers
connected together give a total of eight microphone
inputsand one auxiliary input)
w Listed by Underwriters' Laboratories, Inc., and by
Canadian Standards Association as Certified
SPECIFICATIONS
Gain (at 1,000 Hz)
OUTPUTS
INPUT
Low Imp. High Imp. High Imp.
Mic. Mic.
Low Imp. Mic.
.5 mV produces
High Imp. Mic.
5 mV produces
L5.5 mm
(7132 IN.)
OVERALL DIMENSIONS
FIGURE 1
Fre uency Response
Aat + 3 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 1volt
Copyright 1984, Shure Brothers Inc.
27A872 (DH)
OUTPUT
Low Imp. Mic.
High Imp. Mic.
Auxiliary
1
Impedance
DESIGNED FOR USE WlTH
Balanced or unbalanced 25 1
600 ohm microphone-level
circuits
Unbalanced 10 to 50 kilohm
microphone-level circuits
Unbalanced high-impedance
(10 kilohms or greater)
auxiliary circuits
ACTUAL IMPEDANCE
150-300ohms*
ACTUALIMPEDANCE
300 ohms
60 kilohms
40-70 kilohms'
INPUT
Low Imp. Mic
High Imp. Mic.
Auxiliary
30-40 kilohms'
2.5-3 kilohms*
DESIGNED FOR USE WITH
Balanced or unbalanced 25
to 600 ohm microphones
Unbalanced 10 to 50
kilohm microphones
100 ohm to 10 kilohm unbal-
anced high-level sources
'Depending upon control settings
Clipping Levels (minimum)
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 inputsand outputs are in phase.Aux-
iliary input and output are in phase with each other
but out of phasewith pin3of microphone connectors
OperatingVoltage
AC Operation: 108-132volts, 50160 Hz,
3W
DC Operation: 28 volts dc +.20%, 5 mA
Dimensions
See Figure 1
Net Weight
1.8 kg (4 Ib)
INPUT
Low Imp. Mic.
High Imp. Mic.
OUTPUT
Low Imp. Mic.
High Imp. Mic.
Auxiliary
INSTALLATION
CLIPPING LEVEL
30 mV
450 mV
CLIPPING LEVEL
60 mV
850 mV
4 volts
WARNING
To reduce the risk of fire or electric shock, do not
exposethis applianceto rainor 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-capacitycable.
Printedin U.S.A.

Grounding
If there should be objectionable hum, connect the
metalchassisof the mixer toagood groundsuchas 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 tofour low-or high-impedancedynamic, ribbon,or
condenser microphones can be connected to recep-
tacles marked Mic 1, Mic 2, Mic 3, Mic
4. The inputsare
designed for low-impedance microphones with 25 to
250 ohms impedance or high-impedancemicrophones.
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 receptaclesare professional
audio connectors (three-pin on the M68 and three-
socket on the M68FC)*.See Figure2 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
MICROPHONECONNECTIONS
FIGURE 2
NOTE: Some condenser microphones produce very
highoutput signals which may overloadthe 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 markedAux
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
MicrophonePreamplifier 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 microphoneinput.The recep-
tacle is a professional three-pinaudio connector*. See
Figure2 for output receptacle connections.
Auxiliary
The phono jack marked Aux High Level Output is a
high-impedancehigh-leveloutput designed primarily to
feed a power amplifier requiring 0.5 to 2 volts, or the
auxiliary or tuner input toan amplifier or tape recorder.
Accessory 28-volt DC
The rear paneljack, markedAccessory 28 V.D.C. pro-
vides 28 Vdc open circuit (20Vdc 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-linefuse 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(fullyclockwise)andthe Mastergain
control adjusted to requiredoutput. 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. ConnectAux HighLevelOutput of Unit 1toAux lnput
of Unit 2.
2. Connect microphones to mixers and set each
microphoneinput control to
"O".
3. Take output signal for recorder of PA amplifier from
appropriate output jack on Unit 2.
4. Set Mastercontrol on Unit 1 to 4.
5. Set Aux control on Unit 2 to 10.
6. Mastercontrol on Unit 2 is now Masterfor all inputs.
7. Advance Mastercontrol(Unit2) toabout5andadjust
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
Mastercontrol on Unit 2.
GUARANTEE
This Shure product isguaranteed innormaluseto be
free from electrical and mechanicaldefects for a period
of one year from date of purchase. Please retain proof
of purchasedate. 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
Carefullyrepackthe unit, haveit insured,andreturnit
prepaidto: Shure Brothers Incorporated
Attention: Service Department
222 HartreyAvenue
Evanston, Illinois60204
If outside the United States, return the unit to your
dealer or Authorized Shure Service Center for repair.
The unit will be returnedto you prepaid.
OPTIONAL ACCESSORIES
BatteryPowerSupply .................. ModelA67B
LockingPanel ........................ ModelA68L
RackPanelKit ................... ModelsA68R, -BL
MicrophonePreamplifier
............... ModelA68M
MicrophoneAttenuator ............... ModelA15AS

PRINTED CIRCUIT BOARD ASSEMBLY
WARNING
Voltages in this equipment are hazardous to life.
Refer servicing to qualified service personnel.
PARTSLIST
PRINTED CIRCUIT BOARD ASSEMBLY
UI/UUU
PARTS PLACEMENT
PART
Dl, D2
PL1
Q1-Q6
R3, R32
R24, R27
S1-S5
S6
S7
TI-T5
T6
QlY.
4
1
4
1
1
4
1
1
1
1
1
1
PART
NUMBER
RKC2l
RKC45
RKC9
46A011
46A010
RKClO
558103
55A66
90M2150
51A252
RKC6
RKC67
DESCRIPTION
DIODE, SILICON(IN4002 OR EQUIVALENT)
NEON PILOT LIGHTASSEM. (RESISTOR INTERNAL)
NPNTRANSISTOR, SILICON, SELECTED HIGH GAIN, LOW
NOISE(SIMILAR TO MOTOROLA 2N5088)
POTENTIOMETER,50K
POTENTIOMETER, 20K
SWITCH, SLIDE, DPDT
SWITCH, SLIDE, DPDT, 3A
SWITCH, SLIDE, DPDT, 3A
TRANSFORMER-SHIELDASSEMBLY
POWER TRANSFORMER
KNOB(BLACK)
KNOB(GRAY)

0
r-----------------------------------------------------------
---------
w
-I
I
TO OTHER PREAMPS-
-
PRINTED CtRCUlT BOARD ASSEMBLY
4,
I
I
CHANNEL
l
PRE- R41
I
AMPLIFIER 3.9K
MlCROHONE
'
(TYPICAL OF 'OK 470x16' C22
1 I
6
IMPEDANCE
4 CWtNNELS) c9(clo-cll-cl2r
m,.
C15
I I
8
4.71:35
I I
+
4.7X35;=C13
R24(R25-R26-R27)
C
-4)
3
ADDITIONAL MICRO-
+'
PHONE INPUTS
-4
I
-
-
-
R3 50K
NOTES:
I.
ALL CAPACITORS INbF AND
100
VOLTS OR MORE UNLESS OTHER-
WISE SHOWN. ELECTROLYTIC CAPACITORS
SHOWN
IN JIF
X
VOLTS.
2.
ALL RESISTORS 10%. IV4WATT UNLESS OTHERWISE SHOWN.
3.
THE FOLLOWING SYMBOLS DENOTE:
J,
~~~,"~~
4
WIRING
6
PC BOARD
108-132 VAC COMMON GROUND BUSES
50/60 HZ 250x40 4.
0
DENOTES AC VOLTAGES
0
DENOTES D
C
VOLTAGES
ALL VOLTAGES MEASURED WlTH A C LINE* 120V. ALL IMPEDANCE
SWITCHES SET TO
LO
MIC.1 AND MASTER CONTROLS MAX ALL
OTHERS
MIN
MIC.
I
IN'PUT
I
KHZ
SUCH THAT
AUX.
OUTPUT
is
I
WKT.
AUX. OUTWT'LOADED WlTH 47K OHMS AND MlC. OUTWT LOADED WlTH 150 OHMS. DC VOLTAGES MEASURED WlTH
II
MEGOHM VTVM
AC VOLTAGES MEASURED WlTH
I
MEGOHM A C VTVM VALUES
M68
AND
MGBFC
POWER
SUPPLY
ARE
TYPICAL
AND
MAY
VARY
?15%.
5.
ALL COMPONENTS AND CONNECTIONS ENCLOSED
BY
DASHED LINES
ARE PARTS OF PRINTED CIRCUIT BOARD ASSEMBLY.
MODELS M68 AND M68FC
MICROPHONEMIXERS CIRCUIT DIAGRAM