Shure M675 User Manual

222 HARTREY AVE., EVANSTON,

IL.

60204 U.S.A. AREA CODE 3121328-9000 CABLE: SHUREMICRO

0

GENERAL

The Shure M675 Broadcast Production Master is de­signed for use in conjunction with a Shure M67 or

M67-2E Professional Microphone Mixer, M63 Audio

Master, or SE30 Gated

Compressor/Mixer. The com-

bination of the two units provides a complete, compact
console permitting mixing of a number of microphones,
high level sources (such as tape or tape cartridge or
cassette machines) and turntables. By making an in­ternal jumper change, the two phono inputs may be
used for tape head or high impedance microphone

inputs.
The M675 is not a complete mixer in itself. It may be

thought of as two separate sections: a four-input mixer,
and a monitor amplifier and speaker. The mixer sec­tion adds four more inputs to the M67, M63 or

SE30.

Two inputs are line level (switchable to "Bridge" or

"Terminate"), and the other

two are switchable be-

tween "Phono" (RIAA equalized preamplifier) and

"Bridging" line level.

The primary purpose of the monitor amplifier and
speaker section of the M675 is to allow the operator
to audibly monitor the output of the M67, M63 or

SE30.
Note that the output of the associated mixer consists
of its own signals plus those from the M675 inputs.
The M675 speaker reproduces the M67, M63 or SE30
output signal, and the M675 "Monitor" control adjusts
the speaker volume. A second function of the M675
monitor amplifier and speaker is to "cue" or preview
the signals entering the M675 mixer section without
having these signals appear at the M67, M63 or SE30
output. This is accomplished using the "Cue" position
of the appropriate M675 "lnput" control knob.

NOTE: Except as noted, references to M67 refer also

to operation with M63 or

SE30.

Features

m

Provides a complete compact portable production
console when used with M67 or other Shure Micro­phone Mixers.

Adds four channels with cue provision, when used
with the M67.
Powered by either internal batteries (popular

9V

type) or by M67. Can also provide battery voltage
for powering M67.
Operator can hear program material at a reduced
level during cuing.
Wide flat frequency response and low distortion.
Extremely low noise and

RF

susceptibility.
Four balanced line inputs with individual gain con­trols.
Two line inputs switchable to magnetic phono inputs
(RIAA equalization).

Convertible line inputs are switchable at front panel.

Two line inputs are switchable between high im-

pedance, bridging, or 600-ohm terminating.
Front-panel 600-ohm headphone output jack for
program monitor and cue. Rear panel headphone

output jack for program monitor.

External &ohm speaker output jack for monitoring
program and cue, with provision for external muting.
Internal monitor speaker for program and cue.

All connections are phase-matched to M67.
Compact, lightweight.

Stacking hardware included for mounting M675 to

M67.

SPECIFICATIONS

Frequency Response:

Program Channel (measured at M67 output):

phono:
line:

Monitor Channel: response tailored to -5 dB

-3 dB

Gain

at

1

A.

Program Channel:

Input

Phono
Line 1, 2
Line 3,4 bridge

3,

4 terminate

Line

NOTE:

Gain to Mix Bus output will be approximately

than shown above if loaded with high impedance

B.

Monitor Channel (to &ohm speaker output loaded

8

with

Input Condition Gain

Headphone cable

M67)

(from

Phono This

Line 1 or 2
Line 3 or 4, bridge
Line 3 or 4, terminate

kHz:

ohms):

t2

dB of standard RIAA

+2

dB, 30-20 kHz

@

15 kHz.

Mix

Bus Output

(with

3.5k

+13.5&2dB +83.5-+2dB

k2 dB +41 t2 dB

-29

-29 f2 dB +41 *2 dB

-35 t2 dB +35 t2 dB

No pots in cue

hput only +49 +-2 dB

in

cue"

R

,I

,t

load)

@

40 Hz,

M67

Output

13

dB higher

(50k).

+

13 t2 dB

+7.5 +-2 dB
+7.5 +-2 dB
+1.5 f2 dB

NOTE: Monitor channel gain to 600-ohm output loaded

19

by 600 ohms is

dB higher than gain shown

in above table.

NOTE: Connections of M675 to M67 will reduce gain

3

on M67 inputs by

dB.

Copyright

27A1336

1976,

(PJ)

Shure

Brothers

Inc.

Printed in

U.S.A.

289 mm (11-318 IN.) 178 mm (7 IN.)

t------

Noise: Outputs:

Phono: measured at Mix bus output, at least 71 dB
below 10
output, noise depends upon M67 master gain control.
With M67 master gain at
of M67 will be -50

Line: will not add to noise of M67.

Distortion:

Program Channel: (measured at Mix Bus output)

Phono: Less than 1% THD with input level of 35
30 Hz-20 kHz.

Line: Less than 1% THD with input level of

+

Monitor Channel: measured at
with
of .56 volts to
than 2% THD with level of .31 volts at 40 Hz.

Control Interaction:
Under

Inputs:

Input

Phono

Line Bridging

Line Terminated

Monitor
(via headphone

plug)

'NOTE: The input impedance is set for

Minimum Common Mode Rejection:
80 dB with line input of 10 volts at 100 Hz.

mV input, 20-20 kHz. Measured at M67

"5%"

(-

20 dB) noise output

dBv maximum.

mV,

18 dBm, 30 Hz-20 kHz.

&ohm speaker output

Bohm load. Less than 1.0% THD with output level

8

ohms (40 mW) 100 Hz- 15 kHz. Less

1% dB with any control combination.

lmpedance

Actual

phono

phone

jack

for

(Internal)

25

kilohms*

+350 pF

75 kilohms

t10%

600 ohms

?z

1000 ohms

t

25k

(R226, R227)

10%

20%

which is the correct load

across the phono input

Designed

Use With

Magnetic

cartridges

Less than

10 kilohms

600 ohms

Input

for a stereo cartridge operating with the
parallel (monophonic mode). ~f an input impedance of 47k is
desired, the 47k resistors
jacks may be removed.

M67 head-

Input

Clipping

90

mV

Over +16

d BV

(6.3 VRMS)

Over

+

dBM

(6.3 VRMS)

Over

dBV

(2.5 VRMS)
Corresponds
to

+I8 dBM
output from
M67

L

&

R

channels

+

18

8

Output

Mix Bus

Front-Panel
Headphone Jack

Rear-Panel
Headphone Jack

8-ohm Speaker
Output

Overload and Shorting Protection:

Shorting the outputs will produce no damage. Overload
of phono inputs up to 3 volts will produce no damage.

Operating Voltage:
27 Vdc nominal supply from either internal supply

comprised of six
associated M67 or M63 Audio Master. Minimum supply
is 21.5 Vdc; maximum is 35.0 Vdc.

Weight:
Without batteries: 2.38 kg (5 Ib, 4 oz)

With batteries: 2.61 kg (5 Ib, 12 oz)

CONNECTIONS (TO M67, M63 OR
Stacking hardware is included for mounting the M67
or M63 on top of the
tions for the
sheet covering mixer and circuitry accessories. The
stacking kit is not used with the
the "Headphones" output cable at the rear of the
M675 is inserted fully into the M67, M63 or SE30
Headphones jack. The phono-type plug on the "Mix
Bus" cable at the rear of the M675 is inserted into the
Mix Bus jack on the M67 or SE30, or High Level lnput
of the M63. The red and black "30 VDC" wires at the
rear of the M675 should be connected to the 30 Vdc
connecfors on the M67, M63 or SE30.
is desired, the M67 and M675 can each be mounted in
A68R rack mount accessories. The connecting cables
on the M675 are of sufficient length to reach the M67
in this case.

t

5.5

rnm

(7/32 IN.)

lmpedance

Designed For

Use With

M67 Mix Bus

(3.5k load)

or higher

600 ohms or

greater

Low

High

(See

"Head-

phone"

section)

8 ohms or

greater

Actual

(Internal)

13 kilohms

t

20%

70 ohms

&lo%

5 kilohms

k

20%

1.1 kilohms

-c

20%

4

ohms max.

Output

Clipping

Level

-

+

17 dBV

(7 VRMS)

Same

as

M67

-2dBV
(0.8 V;

80

mW)

9V type 216 batteries or from the

CONTROLS, CONNECTIONS

AND OPERATION

SE30)

M675. See installation instruc-

A68S Stacking Kit provided in the data

SE30. The plug on

If

rack mounting

INPUTS
Line:

The four line inputs (professional three-pin female

audio

connector+) are located on the rear panel and

designated "Line

balanced (internal transformer,

1"

through "Line 4." Inputs are

mumetal shielded)
and connections are Pins 2 and 3 "hot," Pin
"ground."

Line 3 and Line 4 may be either 600 ohm line
termination or bridging, the choice being made by
the appropriate position of the "Bridge-Terminate"
switches above the Line 3 and Line 4 input connec­tors. To obtain "Line" operation for the Line
Line

2

inputs, the corresponding "Line-Phono"

switch above the lnput 1 and lnput 2 controls on the

front panel must be in the "Line" position.

Impedances and operating signal levels are shown
in the "lnput Specifications" Section.

Phono:

The two phono inputs (RCA type phono jack) are

located on the rear panel and designated "Phono
and "Phono 2." To obtain "Phono" operation for the
Phono 1 and Phono 2 inputs, the corresponding
"Line-Phono" switch above the lnput 1 and lnput 2
controls on the front panel, must be in the "Phono"
position.

The nominal "Phono" input impedance is 25 kilohms
resistive, 330

pF capacitive. In order to change the
resistive input to 47 kilohms, remove the 47-kilohm
resistors at "Phono" input terminals

(R226, R227).
When phono inputs are not being used, both "Line­Phono" switches should be left in "Line" to con­serve battery life.

CONTROLS
Individual lnput Gain Controls:

Front panel controls designated
"lnput

4" are the individual gain controls for corre-

"Input

1"

through

spondingly numbered inputs. Note that the input
connectors are located on the rear panel directly

behind their corresponding control.

The lnput
control either "Line

1

and lnput 2 controls may be used to

1 - Phono

1"

or "Line

2­2" inputs, respectively, depending upon the position
of the "Line-Phono" switch located immediately

1

above the lnput

and lnput 2 controls.

NOTE: The Line-Phono switches above Controls

and 2 are intended as SET-UP CONTROLS,
not operating controls. To conserve battery
life, these switches also control supply volt­age to the phono preamplifiers. Hence, the
Line-Phono switches should not be thrown
while "on the air" unless the input controls
are both fully CCW

("0") to avoid introduc­ing switching noise in the program material.
If phono inputs are not being used, both of
these switches should be switched to "Line"
to conserve battery life.

Monitor Gain Control:

This control is used to adjust the level of the front
panel monitor speaker, the front panel Headphone

jack, and the rear panel speaker jack. (See Cue

Operation below.)

tDesigned to mate with Cannon

series or equivalent connector.

XL

series, Switchcraft

A3

1

and

1"

Phono

(Q.G.)

OUTPUTS
Mix Bus:

The Mix Bus output is a shielded cable extending
from the rear of the M675 cabinet and terminated
with a phono plug. This cable should be connected

to the "Mix Bus" jack on the back of the M67 or

1

SE30 (use the "Aux Level Input" on the
this connection is made, the four M675 input signals
will be added and mixed with the M67, M63 or
SE30 input signals.

Front Panel Headphone Jack:

This jack provides both program and cue material to
600-ohm headphones. The "Monitor" control on the
front panel is used to adjust this headphone level.
The internal (or external) 8-ohm speaker is muted
when a plug is inserted into this jack.

Rear Panel

600

This is a two-position jack for monitoring the output

of the M67, when the "Headphone" cable at rear of
M675 chassis is connected to the M67 "Headphone"
jack. The two-position phone jack is used to provide
a choice of level. Normally, a single circuit plug
should be used. If inserted only partially to the first
detent, the output level will be less than when
pushed fully in. If stereo phones are used, the
position plug may be inserted fully and the output
will appear in both phones.

This jack is an extension of the two-level headphone
jack of the M67, and hence, it carries program
material only and its level is not controlled by the
monitor level control on the front panel.

While intended primarily for 600-ohm to
headphones, this jack may be used with 8-ohm to
50-kilohm headphones, with resultant variation in
level. Crystal phones may also be used.

The "Tip" connections of the headphone plugs and

the two phono inputs are in phase with Pin 3 of all
input connectors on both the M675 and M67, and

with the tip of the Mix Bus connector.

Rear Panel 8-Ohm Output Speaker Jack:

This jack is for an 8-ohm high efficiency speaker or
for 8-ohm high quality headphones and provides
both program and cue material. The internal speaker
on the front panel is muted when the phone plug is

inserted into this jack. Use of the front panel

1

headphone jack, in turn, will
external) speaker. A mono (2 circuit) plug should

normally be used. If a stereo (3 circuit) plug is used,
external muting of the internal speaker is possible.
See schematic.

Monitor Speaker:

The internal speaker is activated unless either the

external

&ohm Output Jack or the front-panel 600­ohm Headphone Jack is used. It monitors both
program and cue material.

OPERATION
Cue Operation:

The M675 "lnput" controls are in the Cue position
when rotated fully counter-clockwise and past the
detent.

With no M675 lnput Controls in the "Cue" position,
the monitor amplifier receives a program feed via
the connection to the M67 headphone output. The

M63). Once

Ohm Headphone Jack:

two-

2-kilohm

mute the internal (or

"Monitor" gain control can then be used to adjust
the level of this signal which appears across the
front panel monitor speaker, the front panel Head-

phone jack, and the rear panel speaker jack.
When one or more M675 lnput controls are turned to

"Cue" (fully counter-clockwise), the program feed to

the monitor amplifier is attenuated by 19 to 31 dB.

The Cue material is then routed to the monitor
amplifier, overriding the program material. When all

lnput controls are returned to normal (not in cue),

program feed is again applied at normal level to the

monitor amplifier. This provision allows monitoring

of program material at a low level while simultane-

ously cuing.

Talkback Operation:

To hear talkback material originating at the opposite

end of a two-way line connected to the M67 line

output, turn all input pots on the M675 out of cue

and turn up the monitor amp volume control. The

M67 master volume control may be turned down if
necessary.

DC Power

The M675 can be powered in two ways: by an ex-

ternal source or by internal batteries. When 30 Vdc

is applied to the "30 VDC" connectors of the

the M675 will be turned on. The power "On-Off"

switch on the front panel controls only its own
internal battery supply. Thus, if the M675 is to be
powered by an external source such as an M67,
M63 or
not be on. Note that if the M675 internal battery
supply is used to power an accessory such as the
A68M Microphone Preamplifier, the power switch
will control power to the accessory.

The M675 internal battery supply can be used to

provide automatic switchover to battery operation
when used with the M67. When the M675 batteries

are installed and the M675 is connected to an
ac-operated M67, automatic power switchover will
take
the M675 power switch is in the "On" position. The

M675 batteries will then power both the M675 and
the M67. Note that automatic power switchover is

not advisable with the M63, because some battery

drain will occur even when the M63 is operating on

SE30, the power switch on the M675 need

place if the ac line voltage fails, as long as

M675,

an acceptable ac line voltage, due to the character­istics of the M63 power supply. Automatic power
switchover is possible with the
SE30 has its own built-in battery supply for this

purpose.

Batteries (not included):

The M675 contains a battery supply requiring six
9V transistor radio batteries (Burgess 2U6, Eveready
#216 or equivalent are recommended). Access to
the steel, leak-resistant battery compartment is on
the bottom panel of the
compartment, each of the two locking screws should

'/4

be given a
then be removed. The six
into position on the printed circuit board contained

in the compartment cover. The entire compartment is

removable from the M675 by disconnecting the snap
connector (attached to the leads leaving the cover)
from the M675 receptacle. When the M675 is stacked
with an M67 Mixer, the M675 should be below the
M67 to retain access to this compartment.

Battery Check:

The nominal voltage available from the complement

of six

teries may provide a supply voltage of up to 30.5
volts. Minimum acceptable battery voltage is con-

sidered to be 21.5 volts.

The battery-check function of the M67 may be used

to indicate battery condition when the M67 and

M675 are used together.
indicates a marginal battery condition.

For best performance on battery operation at

temperatures below

Battery Check meter reading is
This is due to the operating characteristics of carbon
zinc batteries at low temperatures.

NOTE: For improved performance and longer op-

RF

When using M675-M67 combination in a high RF

location, RF pickup may occur due to the ground-

ing system of the Mix Bus on early

difficulty should occur, it may be easily remedied by

9V batteries is 27.0 volts. Initially, new bat-

Susceptibility:

turn CCW. The battery assembly may

eration at low temperatures
or lower), use manganese-alkaline batteries
(Mallory MN-1604 or equivalent).

M675. To remove the battery

"0" on the M67 VU meter

40°F, change batteries when the

SE30, although the

9V batteries are snapped

+

1.0 VU or lower.

(O0C-32"F-

M67s. If this

Current Drain and Battery Life:

Approximate Approximate

Condition Current Drain Battery Life

mA over 300 hrs

M675 only, "Phono-Line" in "Line," monitor level down
M675 only, "Phono-Line" in
M675 + M67, "Phono-Line" in "Line," M67 @ +4 dBM

+

M675
M675

M675

NOTE: Due to operating characteristics of carbon-zinc batteries at low temperatures, the useful operating
life will be noticeably shorter at lower than normal room temperatures. See Battery Check Instructions.

M67, "Phono-Line" in "Phono," M67 @ +4 dBM

+

M67, "Phono-Line" in "Line," M67 @ 4-4 dBM,

M675 monitor speaker at 10 mW 7 mA 100 hrs

+

M67, "Phono-Line" in "Phono," M67 @ +4 dBM,

M675 monitor speaker at

"Phono," monitor level down

10

mW 10

1

mA 170 hrs

4
5 mA 140 hrs

8

mA 85 hrs

mA

65

hrs

shorting the ground connection of the M67 Mix Bus
input jack to chassis. To make this modification,
which should be performed by qualified service
personnel only, disconnect ac power from the M67
and remove M67 cover. Connect a short wire from
the ground lug of the Mix Bus jack to the nearest
chassis point. The ground lug of mic. input con­nector

#2 or #3 may be used. The ground lug is
the large lug closest to the cover. This wire should
be as short as possible.

Conversion of Phono lnputs to Tape (NAB) or Flat:

Inputs 1 and 2 may be converted from

RlAA
equalization to tape (7% i.p.s. NAB) or flat. The
modification should be performed by qualified serv-

ice personnel only.

1. Disconnect M675 from M67.

2. Remove four Phillips Head Screws retaining

cover-one on front, one on back, two on

bottom.

3. Remove cover.

4. Refer to Figure of Printed Circuit Assembly

Note the jumpers on the printed circuit assembly.

5. Remove jumpers from Pin C to Pin E (Channel

and Pin S to Pin V (Channel 2).

6. Replace jumpers to achieve desired equalization.

For Channel 1, jumper C to D for "flat," or B to
D for "tape." For Channel 2, jumper S to T for

"flat" or R to T for "tape."

7. DO NOT remove any jumpers inserted through

the actual printed circuit board. Only change
jumpers between pins mentioned above.

8. Replace cover.

Specifications for Tape and Flat Equalization:

=

Gain in flat

6.5 dB to Mix Bus output, Gain in Tape

(7% i.p.s.) = 16.0 dB to Mix BUS output.

Response in flat is

Response in tape is

i2

dB, 30-20 kHz.

22 dB of the 71/2 i.p.s. NAB

curve from 50 Hz to 15 kHz.

Distortion: under 1.0% with tape input of 26

flat input of 78

mV.

mV or

lnput Clipping Level: Tape: 80 mV; Flat: 225 mV.

Conversion of Cue Circuitry:

If it is desired that the cuing action (reduction of
program level during cuing) be more pronounced
than the 19 dB-31 dB obtained in a standard

M675,

the following modification may be performed by

qualified service personnel only: Remove R115

(470k)

and change R112 (330k) to 2.2 megohms. Program

level reduction during cuing will now be 37 to 49 dB.

Adding Microphone Inputs:

The M675 line inputs may be adapted for use with

microphone inputs by the addition of one or two
Shure
phono pin output connector on the

A68M Microphone Preamplifiers. Remove the

A68M and attach

a professional three-pin male audio connector? in

its place ("hot" lead to pin 3; shield to pins

2). Connect the

A68M to Line lnput 3 or 4 of the

1

M675. Place the corresponding BridgeITerminate
switch in the Bridge position. Connect the

(-)

power cables of the A68M to the M675. Note

(+)

that the M675 power switch must be turned off to
conserve batteries when the

?Designed to mate with Cannon
series or equivalent connector.

A68M is not in use.

XL

series, Switchcraft A3

(Q.G.)

BI.

1)

and

and

DESCRIPTION OF CIRCUITRY

(Refer to Schematic)

lnput Circuitry:

Line inputs

1 and 2 are transformer coupled to
Line/Phono switches 1 and 2. Phono inputs are
amplified by the two phono preamplifiers consisting

Q1 and Q3 for channel I and Q2 and Q4 for

of
channel 2. In the phono preamps, equalization is

provided in the feedback path from the collector of

Q3 (Q4) to the emitter of

Q1 (Q2). For channel
phono equalization, gain is determined by the ratio
of the R7-C6,

R9-C10 combination versus R13. The

outputs of the phono preamps also drive the Line/

Phono switches. Setting a

Line/Phono switch to
Phono will, in addition to transferring the associated
input volume control, apply dc voltage to the pre­amplifier power supply terminal. Either switch will
apply power to both phono preamplifiers.

Line inputs 3 and 4 are directly transformer coupled
to input volume controls 3 and 4.

Bridge/Terminate
switches on these two inputs switch a 600-ohm ter­minating resistor off or onto the input of the trans­former.

The outputs of the four input pots are summed via
33k build-out resistors and carried via shielded cable
to the Mix Bus input of the associated M67.

Monitor-Cue Circuitry:

The phone plug and cable at rear of the M675 are
plugged into the associated M67 headphone output.
Program material appearing at the M67 output is
brought via this cable to the M675 where it is trans­former coupled into emitter-follower
output of the follower is applied to FET

Q106. The

Q105, which
serves only as a variable attenuator. With no input
pots in cue, the FET is "on" and presents a low
impedance in parallel with

R115 (470k). The output
of the FET (Drain) drives the monitor volume control.
When any pots are in cue, their associated 330k

resistor (R218-221) is switched to the cue bus which,

R112 (330k) turns the FET off. Hence, the resis-

thru
tance of the FET in shunt with

R115 is now very
high, and the program material fed to the monitor
volume pot is reduced in level by 19 to 31 dB. At the
same time, the cue material for the channel in cue is
fed to the cue bus and hence to the top of the
monitor volume control (for channel

1 the path is

R210, C204, C106).
The monitor amplifier is a complementary symmetry

amplifier similar to many hi-fi power amplifiers. The
gain of the stage is 40 dB, determined by the ratio
of R105 to
approximately 1

R106. The idle current of the stage is

mA. The output of the monitor amp
drives J7 directly. J7 is transformer coupled to J8
and the internal 2" speaker.

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.

1