Shure M-61 Owners manual

TRANSISTOR STEREO PREAMPLIFIERS

General: The Shure M61 Series Transistor Preampli-

fiers are designed to furnish the voltage gain and equal­ization necessary to operate magnetic phono cartridges
(such as the Shure Dynetic Cartridges) and tape playback
heads with standard audio amplifiers. One of the primary
uses of the M61 is in conversion of Stereo systems from
ceramic cartridges to magnetic cartridges. It can also be
used without circuit modification as a preamplifier for
microphones. Advantages include complete freedom from
microphonics, extremely low noise, the use of 50 feet or
more of output cable in “phono” and “tape” positions,
and years of maintenance-tree performance. The operat­ing temperature range is from 32°F. (0°C.) to 140°F.
(60°C.).

The Model M61-1 operates on 105-125 volts 50-60

Hertz power line.

The Model M61-2 operates on 210-240 volts 50-60

Hertz power line.

The Model M61-3 operates on battery power.

The Model M61 Preamplifiers feature a single slide
switch for selection of either phono (RIAA), tape (NAB),
or a microphone (MIC) f

vides the Standard Equalization for phono records. The
NAB position provides the Standard Equalization for
tape and the MIC position provides a flat amplifier for
microphones.

The preamplifier has dual input and output jacks which

will

accept standard phono pugs.

The input impedance is optimized for Dynetic and

magnetic phono cartridges, for tape heads, and for low
or medium impedance microphones.

The output load will typically be the 500,000 ohm
Tuner or Ceramic input of an Amplifier. Earphones of
4,000 ohms or more nominal impedance can be con­nected directly, or through a 1,000,000 ohm control, to
the M61 output with the following specifications obtain­ing down to 250 Hertz or lower.

Gain: RIAA (Phono) 46 db (5

NAB (Tape) 41 db (2 millivolts input produces 0.225 volt)
MIC 63 db (2 millivolts input produces 2.8 volts)

Frequency Response and equalization:

Phono: Standard RIAA equalization

Tape: Standard NAB equalization

MIC: Response ±2 db from 20 Hz. to 15,000 Hz.

Input Impedance:

Phono end tape: Approximately 50,000 ohms at 1,000 HZ.

Microphone: Approximately 20,000 ohms at 1,000 Hz.

Output Impedance:

LOW output impedance (less than 1,000 ohms at 10,000 Hz. for

phono end tape functions)

Channel Separation:

50 db or better (at 1,000 Hz.)

unction. The RIAA position pro-

SPECIFICATIONS

millivolts input produces 1.0 volt)

DATA SHEET

MODEL M61 SERIES

Channel Balance:

2 db at 1,000 Hz. (for Phono end Tape functions)

Hum and noise:

76 db below IO millivolt input, unweighted

Distortion:

Less than 1%. Measured at I volt output

Output Clipping level:

More than 4.5 volts (at 1,000 Hz.)

Available power supplies:

1. 105-125 volts 50-60 Hertz (included in Model M61-1)

2. 210-240 volts 50-60 Hertz (included in Model M61-2. Avail­able separately as Model PS220).

3. Battery [included in Model M61-3. Available Separately as
Model PSB30).

The battery (Burgess type K20 or Eveready type 430) provides

170 hours minimum of operation.

Overall Dimensions: Preamplifier or power supply

Length 5¼ inches (133.4 mm)
Width 2-7/16 inches (61.9 mm) preamplifier has plug pins ex-

tending en additional ½ inch (12.7 mm)

Height 2-5/16 inches (58.7 mm) over switch button

Weight: Net weight (M61-1) 1¼ pounds (567g)

Packaged weight (M61-1) 2½ pounds (1133.8g)

Installation: The M61 Preamplifiers and power sup-

ply may be mounted on an amplifier chassis or cabinet
by using the wood screws or machine screws provided.

The Preamplifier can be mounted in any position for

normal operation;

should be located away from motors or other hum pro-

ducing power sources and away from intense heat
sources. Should hum be a problem in a given system or
installation, one or more of the power plugs may be re­versed to reduce hum.

but for best results, the Preamplifier

Copyright, 1962, Shure Brothers, Inc.

27A206 (4-68)

Printed in U.S.A.

Caution: The use of the M61 Stereo Preamplifier

with other power amplifiers of the transformerless (AC-

DC) type may be a shock hazard.

A suitable power line isolation transformer should

be used.

Connections: a. Set selector switch to the desired

function. This automatically selects the proper equaliza­tion or frequency response for both channels.

b. For the Phono (RIAA) position, connect the signal
leads from the phono cartridge to the jacks marked “IN”
at channel “A” and channel “B”. For the microphone

position using two separate microphones, connect the
cable from one microphone to jack marked “IN” at
channel
should connect to the jack marked “IN” at channel “B”.

For single microphone application connect to either
channel “A” or “B”.

the data sheets of the phono cartridge, tape head, or
microphone regarding their connections, phasing, and
grounding.

“A” and “B” to the corresponding input jacks of the
power amplifier or preamplifier or to the earphones.
(Parallel the outputs for monaural earphones). If it is

“A”. The cable from the other microphone

Attention must be given to information contained in

c. Connect the jacks marked- “OUT” of channel

found necessary to “ground” the M61 Preamplifier
chassis, a wire can be connected to one of the screws
holding the bottom plate to the chassis.

d. If AC power operated, insert the M61 power

line cord in a proper power outlet preferably one con-

trolled by the power amplifier’s On-Off switch. Be sure

power switch on preamplifier is in the ON position. If

the battery power supply is used, an ON-OFF switch is

provided.

SWITCH IN

“RIAA” POSITION

SWITCH IN

“MIC” POSITION

SWITCH IN

“NAB” POSITION

Guarantee: This Shure High Fidelity Component is

guaranteed to be free from electrical and mechanical

defects for a period of one year from date of shipment
from the factory, provided all instructions are complied
with fully. In case of damage, it is essential that you
carefully repack the unit and return it to the factor for
repair. Our guarantee is voided if the assembly has been
subjected to unreasonably rough handling.

CIRCUIT DIAGRAMS

OF POWER SUPPLIES

The M61 Preamplifier has been designed to operate
satisfactorily with most magnetic phono cartridges. How­ever, certain cartridges having very high output may
cause overloading and distortion.

This distortion can be eliminated by using a simple
resistor network at the input of the preamplifier. See
“Optional Network.”

The network must be used in both channels and can be
inserted inside the preamplifier case or can be made up
as an external attenuator between the phono cartridge
and the preamplifier inputs.

CIRCUIT DIAGRAMS

OF PREAMPLIFIER SECTION