Shure M68RM User Guide

222 HARTREY AVE., EVANSTON. l L. 6 0 2 0 4 U.S.A.

MICROPHONES AND ELECTRONIC COMPONENTS

AREA CODE 3 1 2 / 3 2 8 - 9 0 0 0 .CABLE: SHUREMICRO

DATA

SHEET

MODELS M68RM

AND M68RM-2E

MICROPHONE MIXERS

GENERAL:

The Shure Models M68RM and M68RM-2E are fourchannel, completely transistorized portable microphone mixers with built-in REVERBERATION for use with sound reinforcement, tape recording, and audio-visual systems.

The Mixers feature:

Adjustable REVERBERATION to simulate natural reverberation or echoes of a large concert hall.

Phone jack provided for use with remote reverberation ON-OFF switch.

8Four microphone inputs with individual slide switches mounted on rear panel for selection of low impedance (balanced or unbalanced) or high impedance (unbalanced).

One high level auxiliary input suitable for tape, tuner, and accessories. (Uses MIC. 4 input.) Individual volume controls to balance each of the four inputs.

Master volume control to simultaneously control level of all inputs.

High- (unbalanced) or low-impedance (balanced or unbalanced) microphone level output. Imped-

ance selected with slide switch to match the microphone input of associated amplifier.

8 High-impedance auxiliary output.

8DC power supply jack. This jack supplies 28 volts dc for use with accessories such as the Model A68P Phono Preamplifier, Model M62V Level-Loc or may be used as power input in connection with the Model A67B Battery Power Supply (accessory).

Facility for connecting two or more mixers together to obtain additional microphone inputs. For example, two mixers connected together will give a total of seven microphone inputs, or six microphone inputs and one auxiliary input.

Listing by Underwriters' Laboratories, Inc.; and by Canadian Standards Association as certified. (Applies to Model M68RM).

SPECIFICATIONS

Gain: At	1,000 Hz			OUTPUTS
				OUTPUTS		--
		Low Imp.		High Imp.		--
		Low Imp.		High Imp.		High Imp.
INPUTS		Mic.		Mic.		Aux.
Low Imp. Mic.		+4	d B	+28	d B	+56 dB
.5 mV	produces	.8 mV		13 mV		320 mV
High Imp. Mic.		- 1 8 d B		f 6 d B		f 3 4 dB
5 mV	produces	.63 mV		10 mV		250 mV
AUX.		-38	dB	-14	dB	+14 dB
50 mV	produces	.63 mV		10 mV		250 mV

REAR VIEW OF MODEL M68RM

Frequency Response:

The frequency response is flat 1-3 dB from 40 Hz to 20,000 Hz

Hum-Noise:

70 dB below rated output. (Aux. Output)

Equivalent lnput Noise:

150 ohm source, 123 dB below 1 volt, at full gain. lnput Impedance:

Microphone inputs suitable for highor low-imped- ance dynamic, ribbon, or condenser microphones. Auxiliary-50,000 ohms.

Recommended Load Impedance:

Low-impedance microphone. 25 to 600 ohms High-impedance microphone. 20,000 ohms or greater Auxiliary high-impedance. . . .50,000 ohms or greater

Distortion:

Less than l0lototal harmonic distortion when lowimpedance microphone output is at 10 mV level, high-impedance microphone output is at 100 mV level, and Aux. high-impedance output is at 1.0 volt level.

Phase:

All microphone inputs and outputs are in phase. Aux. lnput and Output are out of phase with Pin 3 of the microphone connectors.

Output Clipping Level:

Output	Min. Clipping Level
Mic. Low Impedance	60 mV
Mic. High Impedance	.85V
Aux. High lmpedance	4.OV

Operating Voltage:

Model M68RM: 120 volts & l o % ,			50/60 Hz
Model M68RM-2E: 220-260 volts, 50/60 Hz
Temperature Range:
Operating:	-7°C	to 57°C (20°F to 135°F)
Storage:	-29°C	to 71°C (-20°F	to 160°F)
Dimensions:

See Figure A.

Weight: .

2.33 Kg (5 Ib, 2 oz)

INSTALLATION:

CONNECTION BETWEEN COMPONENTS

For balanced-line connection use two-conductor, shielded, low-capacity cable. For unbalanced (highimpedance) connection, use single-conductor, shielded, low-capacity cable.

GROUNDING

5..*M	'
(7,,i.iJ	F R I C T l O N l L DIMENSIONS ilbgn
	Overall Dimensions
	FIGURE A

If there should be objectionable hum, connect the metal chassis of the mixer to a good ground such as a metal frame of a wall outlet or a water or steam pipe. This is normally accomplished automatically through the ground wire of the power cord.

INPUT CONNECTIONS

Note: Before using mixer remove shipping screw (located at top of chassis) holding small tag.

Printed in U.S.A.

Microphones: A maximum of four lowor high-imped- ance dynamic, ribbon or condenser microphones may be connected to receptacles marked MIC. 1, MIC. 2, MIC. 3, MIC. 4. The inputs are designed for low-im- pedance microphones with 25 to 600 ohms impedance or high-impedance microphones. Both low-impedance and high-impedance microphones may be used simultaneously with the M68RM. The unit is not recommended for use with crystal or ceramic microphones. The impedance is selected by a slide switch above each input receptacle. The input receptacles are professiona'lthree-pin female audio connectors.? See Figure B for lowand high-impedance connections to receptacle.

Note: Some condenser microphones produce very high output signals which may overload the input of a mixer.

pj?Fl!LQ.w		KyEIELD-m
		.,.----2
M I C R O P H O N ~	MIXER INPUT MICROPHONE		MIXER INPUT
LOW IMPEDANCE		HIGH IMPEDANCE
(BALANCED LINE)
MICROPHONE		I N P U T C O N N E C T I O N S
			SHIELD
MIC OUTPUT		MIC. OUTPUT
LOW IMPEDANCE		HIGH IMPEDANCE
(BALANCED LINE )
MICROPHONE		O U T P U T PLUG CONNECTIONS

Microphone Connections

FIGURE B

Auxiliary: The phono jack on the rear of the panel marked AUX. INPUT will accept output from a highlevel source such as a tape recorder, AM-FM tuner, or output from the Model A68P Phono Cartridge Preamplifier (accessory). In this case use MIC. 4 gain control to control volume of Auxiliary Input. (Use of this jack automatically disconnects the MIC. 4 receptacle.)

OUTPUT CONNECTIONS

Microphone: The receptacle marked MIC. OUTPUT is a dual-impedance output selected by the switch above the receptacle. This output is the "mixed" output of all the input sources and is designed to work into a 25to 600-ohm MIC. line or input, or into a high-impedance amplifier or tape recorder microphone input. The receptacle is a professional three-pin male Sudio connector.+ See Figure B for output receptacle connections.

Auxiliary: The phono jack marked AUX. HlGH LEVEL OUTPUT is a high-impedance, high-level output designed primarily to feed a power amplifier requiring 0.5 to 2 volts or the auxiliary or tuner input of an amplifier or tape recorder.

Accessory 28-volt DC:	The terminals marked 28
VOLTS DC + and (-)	provide 28 volts dc for acces-

sories such as the Model A68P Phono Cartridge Preamplifier or the M62V Level-Loc. The jacks are also used as a power input when using the Model A67B Battery Power Supply (accessory).

REVERBERATION

The blue control knob (on front panel) marked REVERBERATION is used to adjust the amount of reverberation for the desired effect.

The standard phone jack (on back panel) marked REVERBERATION REMOTE SWITCH is used to connect an ON-OFF switch which can be operated through a cable at a remote location to turn REVERBERATION on and off. See Figure C for switch connections.

1.Designed to mate with Cannon XL series, Switchcraft A3 (Q.G.) series or equivalent connector. [Shure part 95A407 (male)].

For best results the cable should be low capacity, single conductor, shielded cable with the shield connected to the sleeve of the phone plug.

	SLEEVE
SWITCH	SHIELD
SWITCH	PHONE PLUG

Remote Reverberation On-Off Circuitry

FIGURE C

CAUTION: The M68RM Mixer should not be set on or mounted against a loudspeaker, as vibrations from the speaker cabinet may cause improper operation of reverb. Avoid accidental jarring during operation.

OPERATION

Power: Connect the Microphone Mixer power line cord to a 120 volts -t lo%, 50/60 Hz power source. (220-260 volt, 50/60 Hz for M68RM-2E).

Volume Controls: Each input has a separate gain control for balancing sound levels between microphones. The MASTER gain control simultaneously adjusts the level of all inputs.

The individual gain controls should generally be set near maximum (fully clockwise) and the master gain control adjusted to required output. Individual channel gain controls not being used should be kept at minimum gain (fully counterclockwise).

Identifying Controls: Pressure-sensitive adhesive labels are supplied with the Mixers as a means of identifying the control and recording the control position when optimum results have been obtained. The labels are easily removed when their use is no longer required.

OPTIONAL ACCESSORIES

Battery Power Supply ...........................	Model A67B
Output Cable Kit ....................................	Model A68C
Locking Panel .........................................	Model A68L
Phono Preamp ........................................	Model A68P
Rack Panel Kit .......................................	Model A68R
Stacking Kit ............................................	Model A68S
HandleITilt Stand ...................................	Model A67H
Attache Carrying Case .........................	Model AC60
Interconnecting Cable ...........................	Model A68SC

CONNECTING TWO UNITS TOGETHER

1.A M68RM Reverberation Mixer and a Shure M68 series five-channel Mixer may be combined to give a total of eight microphone channels. In this case, four channels could have reverberation and four channels would NOT have reverberation.

Unit 1-M68RM

Unit 2-M68

A.Connect the AUX. HlGH LEVEL OUTPUT of UNlT 1 to the AUX. INPUT OF UNlT 2.

B.Connect the microphones to mixers and set

each input gain control to # O position.

C.Take the output signal for recorder or PA amplifier from the appropriate output jack on UNlT 2.

D. Set Master Control UNlT 1 to position #4.

E.Set AUX. Control on UNlT 2 to position #lo .

F.The Master Control on UNlT 2 is now the Master for all inputs.

G.Advance Master Control (UNIT 2) to about #5 position and adjust individual microphone controls for proper level. If overall gain is too low or too high the Master Control (UNIT 2) may be adjusted.

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