Shure 76B User Guide

DATA SHEET No. 140

DATE: February, 1942

SUBJECT: Model 76B Lapel Crystal

Model 76B Lapel Crystal Microphone

Added cable should be of high quality and

low capacity. The inner leads should be soldered and insulated with a good grade of rubber Metal braid sleeve or a serve of fine wire should be soldered between the shields of the cable to

complete the shielding. Longer lengths of cables with standard plug attached may be purchased at

small cost, and may be used interchangeably with

shorter cables. OPERATION:

Crystal microphones may be seriously damaged if accidentally connected to loud speaker or power supply outlets carrying high voltage. Check your connections carefully.

Crystal microphones should not be used or kept in places where the temperature exceeds 125°F.

GENERAL:

speech when attached to the lapel. The crystal used is a grafoil (high capacity) bimorph unit, moisture-

sealed to withstand adverse climatic conditions. The microphone is compact and light, weighing only 1-1/2 oz. It is provided with a 25 foot shielded rubberjacketed cable.

APPLICATIONS:

ters and all general uses where clear, intelligible

reproduction of speech is of primary importance, and where the user must be able to move freely at all

times. INSTALLATION: Model 76B is supplied with an alliga-

of the wearing apparel. A 25 foot cable iS furnished, which permits freedom of motion; the cable length

may be increased if necessary. (See Connections).

CONNECTIONS:

a load resistance of ½ to 5 megohms. Input resistance of approximately 1/2 megohms should be used to decrease the low frequency response of the Microphone, for improvement in speech transmission efficiency; but higher values are recommended if good low frequency response is desired. The shield should be

connected to the chassis.

companied by a decrease in output level as given in the table below. There is no frequency discrimina-

tion introduced by the cable, regardless of length.

*(Expressed in db below 1 volt per bar.)

margin or gain to make up for the decrease in output levels shown in the table. If the amplifier does not have the necessary gain a preamplifier at the microphone or near the main amplifier, is suggest-

ed. Preamplifiers with low impedance output are

recommended if the main amplifier system has low

impedance transformer or mixed input.

Model 76B is a pressure-actuated dia-

phragm-type crystal microphone especially

designed for high quality reproduction of

The Model 76B is designed for public address, lecturing in large halls, broadcasting from-portable transmit-

tor clip especially designed to fasten firmly to the lapel or other parts

The inner conductor of the cable should be connected to the grid of the first tube in the amplifier across

Added lengths or connecting cable will be ac-

Total cable length

25 ft.

(Standard) -61.0 db 50 ft. 75 ft.

100 ft. 150 ft. -71.5 db 200 ft.

Most modern high-gain amplifiers have sufficient

Output Level* at Cable Terminals

-65.0 db

-66.5 db

-68.0 db

-73.5 db

They should not be exposed to 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° and permanently damage the crystal.

When used near a radio transmitter, use the

minimum length of cable consistent with placement

requirements. Careful grounding of the cable shield is advisable.

ACOUSTIC CONSIDERATION:

quency response is accentuated for maximum intelligibility, and is smooth and free from undesirable peaks. The accentuation or high frequency

response is very useful because of the fact that

sounds reach the Microphone at an angle which tends to decrease transmission of high frequencies. The

low frequency response is flat, but maybe attenuated

if necessary as indicated under connections.

VOLTAGE SENSITIVITY :

equivalent to 61 db below 1 volt per dyne per sq.cm.

INTERNAL OUTPUT IMPEDANCE:

RECOMMENDED LOAD

IMPEDANCE: 1 to 5 megohms.

GUARANTEE:

date or 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.

LICENSE NOTE:

Microphone

No polarizing voltage is required for

crystal microphones.

The frequency response of the 76B

Microphone extends from 30 to 6000

cycles per second. The high fre-

SPECIFICATIONS

8.9 Millivolts for a 10 bar speech signal at the end or a 25-foot-cable. This is

Equivalent to a 1,500 micromicro-farad condenser.

Model

Diameter

Thickness Thickness, including clip Finish

Net Weight

Microphone head only Complete with cable

Shipping Weight

Code Word (25’ cable)

Each microphone Is guaranteed to be

free from electrical and mechanical defects for a period of one year from

Shure patents pending. Licensed under patents of the Brush Development Company.

Iridescent Gray Chrome

76B

1-29/32”

3/4”

1-3/16”

1-1/2 oz.

1 lb.

RULOP

Printed in U.S.A.

tape.