Shure 707A User Guide

222 HARTREY AVE • EVANSTON. ILL • CABLE SHUREMICRO

MICROPHONES AND ELECTRONIC COMPONENTS

EVANSTON PHONE DA-8-9000 • CHICAGO PHONE SH 3-1600

DATA SHEETDATA SHEET

MODEL 707A

CRYSTAL MICROPHONE

General:

phragm type crystal microphone; it has a smooth re­sponse from 30 to 7000 cycles and has typical semi-di­rectional properties. Model 707A uses a moisture-proofed
Bimorph Rochelle Salt crystal.

The case is made of cast metal for good appearance
and ruggedness, and is finished in iridescent gray enamel
and chrome. The microphone is provided with a high
quality single conductor shielded cable.

Model 707A has a 5/8" - 27 thread for mounting on
a standard desk or floor stand.

Applications:

and music reproduction and is ideal for amateur com-

munication, home recording, low cost Public Address
systems, call systems, and all general purpose use.

Because the cartridge unit is mounted in rubber to
provide mechanical isolation from the case, the micro­phone can be handled with a minimum of mechanical
noise pickup.

Model 707A is a pressure-operated dia-

Model 707A is designed for voice

Connections: The inner or “hot” conductor of the

cable should be connected to the grid of the first tube in
the amplifier across a load resistance of 5 megohms. In­put resistances as low as 1 megohm may be used if neces­sary but higher values are recommended because of
better low-frequency response obtained. The shield
should be connected to the amplifier chassis or ground.
The shield, chassis or amplifier ground should be securely
grounded to a water pipe or similar ground to prevent
shock hazard during operation of the amplifying system.
The cable may be lengthened if desired; low capacity
shielded microphone cable should be used for this purpose.

Operation: No polarizing voltage is required for

crystal microphones.

Crystal microphones may be seriously damaged if

accidentally connected to loud speaker or power supply
outlets carrying high voltage. Check your connections
carefully.

Crystal

places where
not be exposed to the rays of the sun in very hot weather

for any considerable length of time-or left in closed

automobiles parked in the sun during hot weather, as the

temperature inside the automobile may easily build up to

over 125° F. and permanently damage the crystal.

When used near a radio transmitter, use the mini-

mum length of cable consistent with placement require­ments. Careful grounding of the cable shield is advisable.

microphones should not be used or kept in

the temperature exceeds 125°F. They should

Voltage Sensitivity: 3.15 millivolts r.m.s. per

microbar at the end of a 7-foot (2.1 m) cable across 1 to
5 megohms at 1000 cycles. This is equivalent to 50 db
below I volt per microbar at the terminals of the 7-foot

(2. I m) cable.

Microphone rating GM= -150 db.
RTMA Standard SE 105, August, 1949.

SPECIFICATIONS

Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707A

Length, Overall . . . . . . . . . . . . . . . . . . . . . . . . . . .

Diameter of Case . . . . . . . . . . . . . . . . . . . . . . . .

Finish

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Net Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Shipping Weight 7' (2.1m) cable . . . . . . . . . . . .

3-1/4” (82.6mm)

2-13/32" (61.1mm)

Iridescent Gray

and Chrome

7/8 lb. (360g)
2 lbs. (907g)

Internal Output Impedance: Equivalent to a

900 micro-microfarad condenser.

Recommended Load Impedance: 1 to 5 megohms.

Guarantee:

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, return the microphone to
the factory for repairs. Our guarantee is voided if the microphone
case is opened.

Each microphone is guaranteed to be free from

License Notice: Shure patents issued or pending.

I

Copyright 1949 Shure Brothers, Inc.

27-11 (8-60)

Printed in U. S. A.