Shure M268 Schematic

Outputs

IMPEDANCE

OUTPUT	Designed	Actual	Output Clipping
	for use with	(Internal)	Level
Lo Imp Mic	Any lo imp	50 ohms	- 20 dBV
	(19 to 600 ohms)		(100 mV)
	mic c~rcuit
HI Imp MIC	Unbal 10 to 50	5 kilohms	+4.5 dBV
	kilohms mic		(1.7V)
	circuit
Aux	10 kilohm or	2.2 kilohms	+ 17 dBV
	greater unbal		(7.1V)
	high-level
	circuits
Mix Bus	3.3 kilohms	3.3 kflohms	- 8 dBV
			(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

Output noise: -90			dBV (master control		down),
-65	dBV	(master	up)	(input controls	down,
300-20,000 HZ)
Output hum and noise:				-82 dBV (master down),
-60	dBV	(master	up)	(input controls	down,

20-20,000 HZ)

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 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: 105-125volts, 50160 HZ, 5W M268E: 210-250 volts, 50160 HZ, 5Wt

Dc operation

A2688 Battery Power Supply (optional accessory): 27 volts nominal at 12.2 mA typical no-signal, 12.5 mA typical full output; 16.2 volts minimum; approximately 40 hours battery life with alkaline batteries, 4 hourslday duty cycle, simplex off

External power: 30 Vdc, 12.6 mA no-signal, 12.8 mA full output

Temperature Range

Operating: - 18O to 57OC (0° to 135OF) Storage: - 29O to 74OC ( - 20° to 165OF)

t Can be rewired for 105-125 Vac operation (see Service section)

Dimensions

See Figure 1

OVERALL DIMENSIONS

FIGURE 1

Weight

Net: 1.9 kg (4 Ib 2 oz)

Packaged: 2.8 kg (6 Ib 2 oz)

Certifications

M268 (only): Listed by Underwriters' Laboratories,

Inc. and listed by Canadian Standards Association

as Certified

CONTROLS AND CONNECTORS
I	WARNING	I
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 lowor 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 lowand 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 lowand highimpedance 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 to mate with Cannon XL series, Switchcraft A3 (Q.G.) series or

equivalent connector.

2