Shure M268n Schematic

SHUme

THE

SOUND

OF

THE WFESSIONAUB

MICROPHONES

\VORLWIDE

AND

222

EVANSTON.

ELECTRONIC

HARTREY AVENUE

ILLINOIS

60202-3696 U.S.A.

COMPONENTS

DATA SHEET

MODEL M268

MICROPHONE MIXER

GENERAL

The Shure Model M268 is a highly versatile portable
microphone mixer designed for use with sound rein­forcement, tape recording and audio-visual systems. Its
excellent operational characteristics, compact size,
and functional capabilities make the M268 a fine choice
as a primary or add-on mixer in any sound system.

M268

Features:

Wide, flat frequency response and extremely low
distortion at full output

Very low line noise and radio frequency in­terference susceptibility

Four low-impedance balanced and four high­impedance unbalanced inputs

High-level auxiliary input for tape, tuner and
accessories

Individual feedback-type active gain controls for all
five inputs

Master volume control sets overall output level

Compact and lightweight, with rugged, abrasion­resistant case

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

SPECIFICATIONS

Frequency Response

40 Hz to

Voltage Gain (at 1,000 Hz)

(Outputs terminated: mic 150 ohm133 kilohms;
aux 47 kilohms; mix bus 3.3 kilohms)

Low-Impedance
Microphone

High-Impedance
Micro~hone

Aux In
Mix Bus

Inputs

20,000 Hz, + 3 dB

INPUT

OUTPUT

Lo

Imp

Mic

+28 dB

!

+5dB r3ldB +55dB I OdB

-16dB

-8dB

Hi Imp

+54 dB

I I

+I0 dB
+18dB

Aux Out

Mic

+78 dB

+34dB
+42dB

Mix Bus

+23 dB

I

/

-21 dB

--

Phantom power for condenser microphones

High- (unbalanced) and low-impedance (balanced)
microphone-level output matches most amplifier
inputs

High-impedance auxiliary outputs for high-level

equipment inputs

Direct mix bus for simple mixer interconnection
("stacking")

Automatic muting circuit prevents speaker damage
during turn-on and -off

Regulated power supply is unaffected by line

voltage fluctuations

Copyright

1995,

27A8432

Shure Brothers Inc.

(OH)

IMPEDANCE

INPUT

Lo Imp Mic

Hi Imp Mic

Aux

Mix Bus

'

Depending on control setting

for

Bal or unbal

19 to 600 ohms

Unbal 10 to 50

100 ohms to 10

kilohms

level unbalanced

3.3 kilohms

Designed

use with

kilohms

high-

Actual

(Internal)

1,000 ohms

140 kilohms

43 kilohms

3.3 kilohms

Input Clipping

Level

-32 to -5
(25 mV to 0.56V)

-

I0 to + 18 dBV'
(0.32V to 7.9V)

+I4 to +30 dBV'

(5.OV to 32V)

+8 dBV

(2.5V)

Distortion

0.2% or less THD from 40 to 20,000 Hz with lo imp
output at 60 mV level, hi imp mic output at 1.5V

mic
level, and aux out at 7.OV level

Pr~nted ln U.S.A

dBV*

Outputs

OUTPUT

Low Imp

Mic

High Imp

Mic

Aux

Mix Bus

IMPEDANCE

Designed for

Use W

ith

Any low imp

(19 to 600

mic circuit

Unbal 10 to

50 k

10 k

greater

unbalanced

high-level cir-

 mic

circuit

cuits

3.3 k

)

 or



Actual

(Internal)

120

5 k

2.5 k



3.3 k



Output

Clipping Level

–22 dB

(10

0 m

V)

+4.5 dBV

(1.7 V)

18 dBV

(7.9 V)

–8 dBV

(0.4 V)

Dimensions

See Figure 1.

309

mm

(12 5/32 in.)

68.8mm

(2 23/

in.)

32

6.3
(1/4 in. )

mm

229 mm

(9 in.)

FIGURE 1

Weight

Net: 1.8
Packaged:

kg (4 lb 1 oz)

2.8 kg (6 lb 1 oz)

Certifications

Listed by Underwriters’ Laboratories, Inc., and listed

Canadian Standards Association as Certified

by

Noise

Equivalent

mic

150  - 300-20,000 Hz) at full gain

Input Noise:

–128

dBV (low impedance

Equivalent Input Hum and Noise: –125 dBV (low
impedance

mic 150  - 20-20,000 Hz) at full gain

Output Noise: –90 dBV (master control down). –65

(

maste

r up), (

inpu

t c

ontrol

s d

own

, 3

own

maste

, 2

00-20,00

r d

0-20,00

dBV

Output

Hum and N

oise

dBV (master up) (inpu

: –82 dBV (

t c

ontrol

s d

Common Mode Rejection

65 dB minimum with 100 mV input at 100 Hz

Control Interaction

Less than 1 dB with any control combination

Phase

All microphone inputs and outputs in phase; tips of
high-impedance
pin

3; aux input in phase with aux outputs and pin 2

inputs

and mix bus jack in phase with

Phantom Power

own)

0 H

0 H

, –

z)

60

CONTROLS AND CONNECT

ORS

WARNING

This

apparatus must be earthed (grounded)!

M268

power supply is energized when the unit
connected to an ac source; disconnect mains
(power)

z)

Inputs

A

m

ribbon

plug from supply when not in use.

aximu

m o

f four low- and four h

o

r c

ondense

r m

icrophone

s can b

igh-impedanc

e c

onnecte
tacles marked INPUT 1, INPUT 2, INPUT 3, and INPUT 4.
The

i

nput

s are d

esigne

d for l

ow-impedanc

e m
19 to 600  impedance, or high-impedance microphones.
Both

low- and h

multaneously .

igh-impedance microphone

Crysta

l o

r c

erami

c m

icrophone

s can b

mended. The input receptacles are professional three-pin
XLR

A

udio-typ

e c

onnectors

, and 1/



p

hon

4

e j
ure 2 for low- and high-impedance connections to inputs.
Note that some condenser microphones produce very high
output

s

ignal

s w

hic

h may o

verloa

d the i

nput

s o
the M268’s feedback-type active gain controls virtually elimi ­nate th

e n

eed fo

r i

n-lin

e a

ttenuator

s t

o c

ompensat

“hot” microphones.

SHIELD

2

1

3

The

e d

d t

icrophone

e used s

s are not r

acks

. See F

f many m

e for t

SHIELD

is

ynamic,

o r

ecep­s w

ecom-

ixers;

hese

ith

i-

ig-

30 Vdc open circuit, 3.3 k series resistance

Operating V

120
for

oltage

or 240 volts ±10%, 50/60 Hz, 5W

120 V

ac operation (see Service section

operation)

Temperature

Range

Operating: –18o to 57o C (0o to 135o F)
Storage: –29o to 74oC (–20o to 165o F)

, supplied wired

for 240 V

ac

LOW IMPEDANCE OUTPUT

2

MICROPHONE

1

2

3

(BALANCED LINE)

MIXER

LOW IMPEDANCE
(BALANCED LINE)

MICROPHONE OUTPUT PLUG CONNECTIONS

INPUT

MICROPHONE INPUT CONNECTIONS

SHIELD

HIGH IMPEDANCE OUTPUT

FIGURE 2

MICROPHONE

HIGH IMPEDANCE

MIXER INPUT

SHIELD