Shure M268 Schematic

222 HARTREY

AREA

TWX:

AVE..

EVANSTON.

CODE

31z/866-zzoo . CABLE: SHUREMICRO

910-231-0048 TELEX: 72-4381

IL.

60204 U.S.A.

DATA

SHEET

MODELS

~268

AND

MICROPHONE MIXERS

~268~

GENERAL

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

The Model M268E is similar to the M268 except that it is designed for connection to a 210- to 250-volt ac power line. All information applies to both units except for references to ac operating voltage, fuse and power line cord.

M268

Features:

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

Very low line noise and radio frequency interference susceptibility

Four switch-selectable low-impedance balanced or

high-impedance unbalanced inputs High-level auxiliary input for tape, tuner and

accessories

Compact and lightweight, with rugged, abrasionresistant case

M268 (only): Listed by Underwriters' Laboratories, Inc. and listed by Canadian Standards Association as Certified

SPECIFICATIONS

Frequency Response

40 Hz to 20,000 Hz, +3 dB

Voltage Gain

(Outputs terminated: rnic 150 ohm133 kilohrns; aux 47 kilohms; mix bus

(at 1,000 Hz)

3.3

kilohms)

Individual feedback-type active gain controls for all five inputs

Master volume control sets overall output level Simplex power for condenser microphones High- (unbalanced) or low-impedance (balanced)

microphone-level output matches most amplifier inputs

High-impedance auxiliary output for high-level equipment inputs

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

Ac or external dc operation. Noiseless automatic switchover to external power in case of ac line failure

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

Regulated power supply is unaffected by line voltage fluctuations

27A80ll (AE)

1981,

Shure Brothers Incorporated

Inputs

INPUT

Lo Imp Mic Bal or unbal

I I

Mix Bus

Depending on control setting

Distortion

0.2% or less THD from 40 to 20,000 Hz with lo imp rnic output at 80 level, and aux out at 8.OV level

IMPEDANCE

Designed

for use

with

(l~~~~~~l)

600

kilohms

100

ohms to

kilohms high-

unbalance(

level

3.3

kilohms

mV level, hi imp rnic output at 1.5V

,000

ohms

140

3.3

ohms

kilohms

Input Clipping

Level

(2.5V)

Printed in

dBV

U.S.A.

Outputs

IMPEDANCE

OUTPUT

Lo Imp Mic

Imp MIC

Aux

Mix Bus

Designed

for

use

with

Any lo imp

(19 to 600 ohms)

mic c~rcuit

Unbal 10 to 50

kilohms mic

circuit

10 kilohm or

greater unbal

high-level

circuits

3.3 kilohms

Actual

(Internal)

50 ohms

kilohms

2.2 kilohms

3.3 kflohms

Output

(100 mV)

-8 dBV

Clipping

Level

20 dBV

4.5 (1.7V)

17 dBV

(7.1V)

(0.4V)

Noise

Equivalent input noise:

128 dBV (lo imp mic 150

ohms-300-20,000 Hz) at full gain Equivalent input hum and noise: - 125 dBV (lo

imp mic 150 ohms-20-20,000 Hz) at full gain

dBV

Dimensions

See Figure

OVERALL DIMENSIONS

FIGURE

Weight

Net: 1.9 kg (4 Packaged: 2.8 kg (6

Ib 2 oz)

Certifications

M268 (only): Listed by Underwriters' Laboratories, Inc. and listed by Canadian Standards Association as Certified

Output noise: -90

-65

dBV (master up) (input controls down,

dBV (master control down), 300-20,000 HZ) Output hum and noise: -82

-60

dBV (master up) (input controls down,

dBV (master down),

20-20,000 HZ)

Common-Mode Rejection

65 dB minimum with 100

mV input at 100 Hz

Control Interaction

Less than

dB with any control combination

Phase

All microphone inputs and outputs and mix bus are in phase; aux input is in phase with aux output, but out of phase with pin 3 of mic connectors

Simplex Power

30 Vdc open circuit, 3.3 kilohms series resistance

Operating Voltage

Ac operation

M268: 105-125 volts, 50160 HZ, 5W M268E:

210-250 volts, 50160 HZ, 5Wt

Dc operation

A2688 Battery Power Supply (optional accessory): 27 volts nominal at 12.2 no-signal, 12.5

mA typical full output; 16.2 volts

mA typical

minimum; approximately 40 hours battery life with alkaline batteries, 4 hourslday duty cycle, simplex off External power: 30 Vdc, 12.6

mA full output

12.8

mA no-signal,

Temperature Range

Operating: Storage:

Can

rewired

for

18O to 57OC (0° to 135OF)

29O to 74OC

105-125

Vac

operation

(see Service

20° to 165OF)

section)

CONTROLS AND CONNECTORS

This apparatus must be earthed (grounded)! The M268 power supply is energized when the unit is connected to an ac source; disconnect mains (power) plug from supply when not in use.

Model

M268E

Model M268E is supplied with a three-conductor power-line cord without a plug. The plug should be installed by qualified service personnel. The brown lead should be connected to the "live" or "hot" terminal of the plug, and the blue lead to the neutral terminal. The greenlyellow lead is the grounding conductor and should be connected to the ground or earth terminal of the plug.

Inputs

A maximum of four low- or high-impedance dynamic, ribbon or condenser microphones can be connected to receptacles marked MIC 1, MIC 2, MIC 3 and MIC 4. The inputs are designed for low-impedance microphones with 19 to 600 ohms impedance or high-impedance microphones. Both low- and high-impedance microphones can be used simultaneously. Crystal or ceramic microphones are not recommended. Impedance is selected by a slide switch above each input. The input receptacles are professional three-socket audio connectors.* See Figure 2 for low- and impedance connections to inputs. Note that some condenser microphones produce very high output signals which may overload the inputs of many mixers; the M268's feedback-type active gain controls virtually eliminate the need for in-line attenuators to compensate for these "hot" microphones.

Designed

equivalent

mate

connector.

with

WARNING

Cannon

series,

Switchcraft

(Q.G.)

high-

series

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