Shure M688 Schematic

222

HARTREY

Q

AREACOOE~https://manualmachine.com/~~E-9000

AVE..

EVANSTON.

. CABLE: SHUREMICRO

IL.

60204

u.s.A.

DATA
SHEET

MODEL M688 AND M688E

STEREO MICROPHONE

MIXERS

GENERAL:

The Shure Model M688 is a completely transistor-

portable Stereo Microphone Mixer for use with

ized,
sound reinforcement systems and tape recorders.

The Model

M688E Stereo Microphone Mixer is simi­lar to Model M688 except that it is designed to be
connected to a 120

+lo% or 240 &lo% volt ac

power line, as selected by a switch under the chassis.
Features include:

Stereo High lmpedance Auxiliary Outputs.
Mono Microphone Level Output for mixed (L

R)

monaural output.

+

Four Microphone Inputs, low impedance (bal-

anced) or high impedance (unbalanced).
Stereo, High Level Auxiliary Inputs suitable for

tape recorder, tuner, or the output of a stereo
magnetic Phono Preamp such as the Shure

Model M64.
Individual Volume Controls for each input.

A Stereo Master volume control to simu-ltaneous-

ly adjust level of all inputs.
A Mono-Stereo switch.
Left-Right switches for Mics.

1,

2 and

3.
A Pan Control used for adjusting the apparent
location of the Mic. 4 input to either left channel

or right channel position or anywhere between.
Mix Bus jacks for paralleling two or more M688

units.
Dc Power jacks to supply 27 Vdc for use with

accessories or to allow powering the M688 from
an external source, such as a Shure Model

A67B

Battery Power Supply.
Underwriters' Laboratories, Inc., listed, and listed

17/32

IN)

(M688 only).

A

by C.S.A. as certified

Dimensions:

OVERALL

See Figure A

5.5

mm

DIMENSIONS - FIGURE

Net Weight:

2.27 kg (5 Ib)

SPECIFICATIONS

Gain:

Low Imp. Mic. + 13.5 dB + 1.5 dB +25.5 dB +59.0 dB
High Imp. Mic.
Mix Bus

AUX. -31.0 dB

At 1000 Hz (Stereo Position)

INPUT

~-

Mix

Bus

Imp. Mic. Imp. Mic.

-

9.5 dB - 21.5 dB

-

-23.0dB

-43.0 dB

Low

OUTPUT

+

+

-19.0 dB

High

2.5 dB + 36.0 dB
l.OdB +34.5dB

Aux.

(High

Imp.)

+14.5 dB

Frequency Response:

Flat -c3 dB from 40 Hz to 20,000 Hz

Maximum Output Hum and Noise:

(Aux. Output, All Controls Min.) -80 dBV -68 dBV
(Aux. Output, All Controls Max.) -60 dBV -50 dBV

300-20.000

Hz

20-20,000

lnput Impedance:

Microphone inputs suitable for high- or low-impedance
dynamic, ribbon, or capacitor (condenser) microphones.

-

Auxiliary input

50,000 ohms.

Mix Bus

-

3,300 ohms.

Recommended Load Impedance:

Low lmpedance

Microphone Output

High lmpedance

Microphone Output

Auxiliary High lmpedance Output 50,000 ohms or greater

Mix Bus

...........................................

....................

....................

25 to 600 ohms
20,000 ohms or greater

2,700 ohms

or

greater

Distortion:

Less than 1% Total Harmonic Distortion when Low Im-

pedance Microphone Output is at 5
lmpedance Microphone Output is at 70

Aux. Output is at 2.0 volt level.

mV level, High

mV level, and

lnput Clipping Level:

Minimum

Clipping

Low Impedance Microphone Input
High Impedance Microphone Input
Mix Bus

.....................................................

..........

........

25 mV
350 mV
650mV

Output Clipping Level:

Output

Low Imp. Mic.
High Imp. Mic.
Aux.

Stereo
Mono

Stereo
Mono

Stereo 6.6V
Mono 5.7V

Minimum

Clipping

7

mV

14 mV

110 mV

220 mV

Phase:

The Mono Mic. Output is in phase with all microphone

inputs. The Mix Bus is out of phase with pin 3 of the
microphone inputs. The Auxiliary Output is out of phase
with pin

is in phase with the Aux. lnput and the Mix Bus.

3

of the microphone inputs. The Auxiliary Output

Operating Voltage:

MODEL

Ac Operation:

Dc Operation:

MODEL

Ac Operation: 120 or 240 volts, -t-10% at 50 to 60 Hz

Dc Operation:

power-line cord, but no plug. The power-line cord plug
should be installed by a qualified person. The brown lead
should be connected to the "live" or "hot" terminal of the

plug, and the blue lead to the neutral terminal of the plug.
The
should be connected to the ground or earth terminal of

the plug.

M688

M688E

The Model M688E is supplied with a three-conductor

green/yellow lead is the grounding conductor and

120 volts,
30 volts, 7.5

30 volts, 7.5

+-lo% at 50 to 60 Hz

mA

mA

Hz

Level

Level

Copyright

27A1009

(01)

1971,

Shure

Brothers

Incorporated

Printed

in

U.S.A.

INSTALLATION:

CONNECTION BETWEEN COMPONENTS

For balanced-line connection use two-conductor,

shielded, low-capacity cable. For unbalanced (high-

impedance) connection, use single conductor, shielded,
low-capacity cable.

p.EL!-m

MICROPHONE

-------

LOW

IMPEDANCE

(BALANCED

LINE)

MIC.

INPUT

MICROPHONE INPUT

2

MIC.

OUTPUT

LOW

IMPEDANCE

(BALANCED

MICROPHONE

MICROPHONE CONNECTIONS

LINE)

OUTPUT

INPUT CONNECTIONS

Microphones: A maximum of four low or
ance dynamic, ribbon, or capacitor (condenser) micro-

phones may be connected to receptacles marked Mic.

1,

Mic.

2,

Mic. 3 and

Mic.

for low-impedance microphones with 25 to 600 ohms
impedance or high-impedance microphones, as selec­ted by a slide switch above the input receptacle. The
unit is not recommended for use with crystal or ce­ramic microphones. The input receptacles, Mic. 1,

3

Mic. 2, Mic.

and Mic. 4 are female professional
three-pin audio connectors* (mate, Shure Part
See Figure B for low-and high-impedance connections
to receptacle.
(NOTE: Some capacitor (condenser) microphones
produce very high output signals which may overload
the input of a mixer. A Shure Model
Attenuator placed between the microphone and the
mixer input will eliminate this problem.)

Aux. Input: The left channel
phono jacks marked Aux. Input on the rear panel will
accept the output from a high-impedance, high-level
source such as a tape recorder, AM-FM tuner, or
output from a phono cartridge preamplifier, such as the

Shure Model M64 or

A68P (2 Model A68P's required

for Stereo). One or more Shure M68 Series Microphone

Mixers may be connected to these jacks to add addi­tional microphone inputs.

Mix Bus: The left channel (L) and right channel (R)
phono jacks marked Mix Bus on the rear panel are
used when paralleling M688 units to increase the
number of input channels. Use a phono pin plug

jumper cable between each L Mix Bus jack, and an-

other between each

R Mix Bus jack.

OUTPUT CONNECTIONS

Auxiliary Output: The left channel (L) and right chan-

nel (R) phono jacks marked Auxiliary Output are high­impedance high-level outputs designed primarily to

feed power amplifiers requiring 0.1 to 2 volts, or the
auxiliary or tuner inputs of an amplifier or tape re­corder.

Mono Mic. Output: The receptacle marked Mono Mic.
Output has a low- or high-impedance output selected

*

Designed to mate with Cannon

(Q.G.)

series, or equivalent connector.

p;3EG!m

\1----

MICROPHONE

PLUG

MIC.

OUTPUT

PLUG

-

--/

HIOH

CONNECTIONS

HIGH

CONNECTIONS

FIGURE

MIC.

IMPEDANCE

SHIELD

IMPEDANCE

B

high-imped-

4.

The inputs are designed

95A407).

A15A Microphone

(L)

and right channel (R)

XL

series, Switchcraft

INPUT

A3

by the switch above the receptacle. This output is the
"Mixed"

(L

+

R)

monaural output of all the input
sources and is designed to work into a 25 to 600 ohm
mic. input, or into a high-impedance amplifier or tape
recorder microphone input. The receptacle is a male
professional three-pin audio connector.' See Figure

B for output receptacle connections.

30

V.D.C.: These rear panel jacks provide

open circuit (21 Vdc at 5

mA max.) for accessories.

27

Vdc

An external battery pack, such as the Shure Model
A67B or A68B, or an external 26 to

30

Vdc source

may also be used to power the M688 via these jacks.

OPERATION
Power: Connect the three conductor power line cord
to a 120 volt,

50/60 Hertz ac power outlet. The

power ON-OFF switch is on the front panel. A neon

pilot lamp indicates that the ac power is on. (This
lamp does not light when the unit is battery operated).
If battery operation is desired, do not connect line

cord. The ON-OFF switch also controls battery input

power.

Volume Controls: The Master volume control and the

individual volume controls for each of the five channels

are identified on the front panel. Both the Aux. volume
control and the Master volume control are clutched
dual concentric controls. The left channel (L) control
is the large outer knob. The right channel (R) control
is the smaller inner knob. The relative setting of the
left and right controls may be changed by restraining
one knob and moving the other. Above the Master
volume control is a Mono-Stereo switch used for se-

lecting either monaural or stereo output at the Auxiliary

L

Output

and R jacks on rear of chassis. Individual

channel volume controls not being used should be

kept at minimum setting (fully counterclockwise).

4

Mic.

Pan Control: The Mic. 4 Pan Control on the

front panel is used for adjusting the apparent location

4

of the Mic.

Signal to either left or right positions or
anywhere between. When the Mic. 4 Pan Control is
in the maximum left position, program material on

Mic. 4 appears only at the Auxiliary Output left channel

(L); likewise, when the Mic. 4 Pan Control is in the

maximum Right position, the program material appears
only at the Auxiliary Output right channel (R). When
the Mic. 4 Pan Control is centered between Left and

Right, the Mic. 4 program material appears equally on

both left (L) and right (R) Auxiliary Output phono jacks.
The program material on Mic. 4 appears at the Mono

Mic. Output no matter where the Pan Control is set.

In making a stereo recording or with a stereo sound

reinforcement system, it may be desirable to place the

4

vocalist on Mic.

so the voice may be "centered"

between the left (L) and right (R) stereo channels
containing the orchestra.

Guarantee: This Shure product is guaranteed in normal
use to be free from electrical and mechanical defects
for a period of one year from the date of purchase.
Please retain proof of purchase date. This guarantee

includes all parts and labor.
Shipping Instructions: Carefully repack the unit and

return it prepaid to the factory. 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

M64 STEREO PREAMPLIFIER

The M64 will furnish the voltage gain and equaliza­tion necessary to operate magnetic phono cartridges
(such as Shure Stereo

Dynetic Cartridges), and tape
playback heads into stereo audio amplifiers and
mixers that have aux. level inputs with no equaliza­tion such as the Model

M688.

A68M MICROPHONE PREAMPLIFIER

The

A68M will provide a balanced line input or an

additional microphone channel to the Model

The input may be matched to a low impedance

balanced microphone, a high impedance unbalanced

microphone, or a balanced line. The Aux. Output

is terminated in a shielded cable with phono pin
plug for connection to the

M688. The A68M mounts
to the left side of the M688 and is powered by the
M688 power jacks. The

A68M's may be mounted

side-by-side to provide a stereo pair.

A68S STACKING KIT

This accessory consists of brackets for vertical
stacking of an M688 Mixer and any combination of
Shure Mixers or Controllers. An interconnecting
cable is included for connecting one channel. An
additional

A68SC (see next column) interconnecting
cable is required for connecting the second stereo
channel.

A68C OUTPUT CABLE KIT

The

A68C Output Cable Kit provides a convenient

and flexible method of connecting the microphone

level output of the M688 Mixer to the great variety
of amplifier and input receptacle configurations.

PA

Enables you to connect to virtually any

system.

Kit Includes:

One 4.6 m (15 ft) two-conductor shielded ca-

ble with male and female professional three­pin connectors.*

One 305 mm (12 in.) two-conductor shielded

adapter cable with female professional three­pin audio connector* on one end and
bell twist lock plug on other end.

One 305 mm

(12

in.) single conductor shielded
adapter cable with female professional three­pin audio connector* on one end and Am­phenol type

MC1 on the other end.

M688.

Hub-

A68SC INTERCONNECTING CABLE

This cable is a 305 mm

(12

in.) long single conductor

shielded cable with a phono plug on each end for

interconnecting an M688 Mixer in combination with
other Shure mixers or controllers.

A68R RACK PANEL KIT

The kit consists of a 483 mm x 90 mm (19 in. x
in.) precut rack panel and necessary hardware for
rack mounting of the M688 with its cover in place.

A68L LOCKING PANEL

This panel fits within the front hood of the M688
cover and locks in place to prevent tampering with

the front panel controls.

A67H HANDLEITILT STAND

A67H provides a convenient means of tilting

The
the M688 to permit better panel visibility and greater
ease of operation in some conditions. In the locked

(tilt) position, the front panel will be elevated about

20°. In the free position, the A67H serves as a

rugged carrying handle.

This case is compartmentalized and foam lined for
an M688 and accessories.

A67B BATTERY POWER SUPPLY

A67B eliminates need to connect the M688

The

Mixer to a wall outlet. The battery complement is

three

Eveready type

batteries. At room temperature, the

222, 216,

or equivalent 9 volt

A67B will oper-

ate the M688 continuously for approximately 40

hours.

31/2

e

One Phone Plug adapter for use with Am­phenol type MC1 Connector.

*

Designed to mate with Cannon

(Q.G.)

series, or equivalent connector.

XL

series, Switchcraft

A3

K

MIXER

VOLTS OR MORE UNLESS

100

VOLTS.

X

ALL CAPPCITORS IN MFD AND

MFD

OTHERWISE SHOWN. ELECTROLYTIC CAPACITORS SHOWN IN

I.

BOARD

+PC.

+WIRING

COMMON GROUND BUSSES

10%. 1/4 WATT, UNLESS OTHERWISE SHOWN.

GROUND

M~1,000.000.

1000,

,+CHASSIS

K.

THE FOLLOWING SYMBOLS DENOTE:

2. ALL RESISTORS

3.

12OU, ALL

*

IKHZ SUCH THAT LEFT

MIC4 AND MASTER CONTROLS

DENOTES D.C. VOLTAGES.

INP~T

0

OUTPUT LOADED WlTH 47K OHMS

MIC4

IVOLT.'AUX.

IS

~UTPUT

IMPEDANCE SWITCHES SET TO LO

ALL VOLTAGES MEASURED WlTH A.C. LINE

AUX.

MAX. ALL OTHERS MIN.

4.ODENOTES A.C. VOLTAGES.

MEG-

I

15%.

f

D.C.VOLTAGES MEASURED

MEGOHM V.T.V.M. A.C. VOLTAGES MEASURED WlTH

I

I

OHM LC. VT.V.M. VALUES ARE TYPICAL AND M4Y VARY

WlTH

AND MIC OUTPUT LOADED WITH 150 OHMS. ALL INPUT SWITCHES

AND PAN POT SET TO LEFT POSITION.

ALL COMPONENTS AND CONNECTIONS ENCLOSED BY DASHED

LINES ARE PARTS OF PRINTED CIRCUIT BOARD ASSEMBLY.

5.

6. ARROWS ON POTENTIOMETERS DENOTE CLOCKWISE

~106.

OF

C103 WAS.047.600V AND WIRED ACROSS PRIMARY

ROTATION.

*

7

CIRCUIT DIAGRAM

MODEL M688 STEREO MICROPHONE

PREAMP SHOWN,

I

MIC

r---------------

M688 POWER SUPPLY

---

INPUT

ACLINE

W/60 HZ.

TI06

dl

GREEN /YFI LOW

,

M6BBE POWER SUPPLY

---

PRINTED CIRCUIT BOARD ASSEMBLY

PARTS PLACEMENT

ITEM

DIOI, Dl02

PLlOl

QI-~9%

RIOI- R103, R107

R108

R113, R114
SIOJ-S104,5108
S105-S107. SllO

S109
Slll

TIOI-TI05

TI06

FlOl

SHURE

86A404
80A79
866349

46AOll
46A029
46A030
55854
55883
558103

55A66

90E2150

518252

80A155

PART

NO.

SHURE

RKC21
RKC45

RKC9

-

RKCIO

-

-

-

KIT

NO.

,PARTS LIST

Q$Y

IN

KIT

4

I

4

4

-

-

-

-

(M688E ONLY)

(M688E - HIDDEN)

(M688E ONLY)

DIODE. SILICON. IN4002 OR EQUIVALENT
PILOT LIGHT. NEON,
NPN TRANSISTOR, SILICON, SELECTED
LOW NOISE SIMILAR TO MOTOROLA
MPS 6521

POTENTIOMETER, ROTARY
POTENTIOMETER. SLIDE, IOK, SPECIAL LINEAR TAPER.
POTENTIOMETER, DUAL ROTARY.

SWITCH, SLIDE, SLOTTED BUTTON, DPDT
SWITCH, SLIDE. DPDT.

SWITCH, SLIDE. DPDT, 3 AMP
SWITCH.SLIDE, DPDT

TRANSFORMER AND SHIELD ASSEMBLY

.

TRANSFORMER, POWER

FUSE, 1/16

DESCRIPTION

A,250

WITH RESISTOR

HIGH GAIN,

50K, SPEClAL LINEAR TAPER.

50K, AUDIO TAPER.

V

*TO INSURE LOW NOISE FIGURE,

PURCHASE

REPLACEMENTS FOR QI-09 FROM SHURE BROTHERS INEORPORAED