Shure M-64-A Service manual

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HARTREY AVENUE

EvANsToN. ILLINOIS

ELECTRONIC

60202-3696

COMPONENTS

U.S.A.

DATA SHEET

MODEL M64A

STEREO PREAMPLIFIER

The Shure Model M64A Stereo Preamplifier provides the proper input and output impedances, voltage gain and equalization necessary to operate magnetic phono cartridges and tape playback heads with audio amplifiers having no equalization. A low-noise and

lowdistortion device, the M64A permits further signal processing without appreciable degradation in signal-tonoise ratio. In addition, the preamp can be used without equalization for a microphone input or as a buffer amplifier.

Typical Applications

Permits turntable to be used with PA mixers and amplifiers without phono inputs

Converting stereo record pickup systems from ceramic to magnetic cartridges

Microphone preamplifier Low-gain buffer amplifier (where long cable lengths

are extended to a preamp input)

M64A has a single three-position slide switch for

The selecting Phono, Tape or Flat frequency compensation. The Phono position provides the standard RIAA equalization for phonograph records. In this mode, magnetic phono cartridges can operate into auxiliary level inputs, inputs without

RIAA equalization, or ceramic phono cartridge inputs. The Tape position provides playback heads on tape recorders with standard 7-112 ips NARTB equalization. In the Flat position, the M64A can be used as a flat-response microphone preamplifier, or as

a buffer (isolation) amplifier for magnetic phono cartridges when long cable lengths or switching systems are necessary between the turntable and main equalized amplifier (note that the low-level

outputs should be used when operating the

M64A as a

buffer amplifier).

The

M64A's inputs and outputs are standard phono pin jacks. Both high- and low-level outputs are provided, so that the

M64A can be connected to either high-level auxiliary inputs or low-level microphone inputs (or equalized phono or tape head inputs in buffering applications). A grounding screw is provided for hum pickup reduction.

M64A as supplied operates on 120 Vac, 50160 Hz.

The An internal selector switch (qualified service personnel only) permits operation from 240

Vac, 50160 Hz sources.

The unit can also be modified for balanced line output.

M64A is listed by Underwriters Laboratories, Inc.

The

SPECIFICATIONS

Gain

(Measured at 1 kHz; input through 680 ohms; output terminated in 47 kilohms)

Switch

Position Output

Phono

Flat

Tape

Frequency Response

Phono: + 2 dB of Standard RIAA curve from 40 Hz to

15 kHz

Flat:

Tape:

20 Hz to 20 kHz,

2 dB of 7-1/2 ips NARTB curve from 50

kHz

100 1000

TYPICAL FREQUENCY RESPONSE

Total Harmonic Distortion

Less than 1% with 2V output at 1 kHz in all switch positions. Phono position only: less than Hz with 2V output.

Clipping Level

Phono: 100 Flat: 250

Tape: 80

(at 1 kHz)

mV minimum mV minimum mV minimum

Channel Separation

50 dB or more

Channel Balance

Within 2 dB

Hum and Noise

Phono: Flat:

Better than 64 dB below 10

(20 Hz to 20 kHz)

Better than 71 dB below 10

High-Level Low-Level

34.5 dB +11 dB

27.5 dB

+37 dB

+2 dB

FREQUENCY

FIGURE

HERTZ

10,000 20.000

(at 1 kHz)

mV input

Output

+ +

13.5 dB

l0/o

4 dB

at 30

27A8086

1989.

(IF)

Shure Brothers

Inc.

lnput lmpedance (at 1 kHz)

Resistance: 50 Capacitance: 160 picofarads

Output Impedance (at 1 kHz)

High Level: Less than 2000 ohms (minimum recomLow Level: 600 ohms (any load on Low Level output

kilohms

mended load is 22,000 ohms)

will not affect input clipping level)

OPERATION

WARNING

Use of the M64A with power amplifiers of the transformerless (ac-dc) type may result in a shock hazard. A suitable power line isolation transformer should be used with such equip-

ment.

Power Consumption

5 watts

Operating Voltage

120 or 240 volts ac table)

Temperature Range

Operating: Storage: -29" to 71 " C (-20" to 160"

Dimensions

See Figure 2

Net Weight

986 grams (1

r(5-9/16

-7" to 57" C (20" to 135"

144mm 104mm

1O0/0, 50160 Hz (internally selec-

Ib 2-112 oz)

IN.

)

OVERALL DIMENSIONS

FIGURE

(4-3/32 IN.I~

INSTALLATION

To reduce the risk of fire or electric shock, do

not expose this appliance to rain or extreme moisture.

1. Set the selector switch to the desired function (Phono, Flat or Tape). This automatically selects the

proper equalization (frequency response) for both

channels.

2. For the equalized Phono

tions, connect the signal leads from the phono car-

tridge or tape head to the

lnput and Channel 2 Input. Note that the Flat

nel position can be used for phono cartridge or tape head buffering applications in which the put is connected to an equalized amplifier input.

3. For the Flat position using two high-impedance

microphones, connect each microphone cable to one of the impedance microphone is used, connect it to either lnput connector. NOTE: If low-impedance

microphones are to be used, a suitable line matching transformer such as Shure's A95 Series should be used.

4. Refer to the phono cartridge, tape head or microphone data sheet

phasing and grounding.

5. Connect the Channel 1 and Channel 2 Output jacks

(High or Low Level) to the corresponding input jacks of the power amplifier, preamplifier, tape recorder or

mixer. The High Level outputs can be connected to high-level auxiliary inputs, and the Low Level outputs can be connected to low-level microphone inputs (or equalized phono or tape head inputs in buffering applications).

6. If grounding is necessary, the associated equipment ground lead can be attached to the screw.

Insert the M64A power line cord into a proper power outlet (120 controlled by the power amplifier's on-off switch. Make certain the the unit is to be remotely turned on and off.

M64A lnput connectors. If a single high-

Vac +lo%, 50160 Hz), preferably one

(RIAA) or Tape (NARTB) posi-

M64A jacks marked Chan-

M64A out-

for details on connections,

M64A Ground

M64A Power switch is turned on if

SERVICE

M64A can be operated on any flat surface, or

The (with adequate space) be mounted to an amplifier chassis or cabinet using screws through the

mounting flanges. The unit can be mounted in any position for normal operation, but for best results, it should be located away from motors, lighting dimmers, or other hum-producing power sources and away from intense heat sources.

Should hum be encountered in a sound system or

installation, one or more of the equipment power plugs may be reversed to reduce hum. If the turntable has a grounding lead, this wire can be connected to the Ground screw to reduce hum pickup.

M64A's

M64A

WARNING

Voltages in this equipment are hazardous to life.

Refer servicing to qualified service personnel.

Balanced Line Output

For professional low-impedance balanced-line use such as broadcast systems or recording consoles, an external line matching transformer such as Shure's A95 Series can be added to each The resultant output level is approximately -32

M64A High Level output.

dBm. If

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