TM 55-1930-209-14&P-12
APPLICATION NOTE
M3141 and M3412 HEADSET STATIONS
(Formerly Models 4S-V and 4S-VP)
INTRODUCTION
The M3141 and M3142 headset stations are communications modules which permit the connection of headset-
microphones into David Clark Company intercom systems. The M3142 is equipped with a push-to-page button.
PHYSICAL CHARACTERISTICS
The M3141 and M3142 modules are designed to fit into standard electrical wiring boxes that are at least 1-3/4 inches
deep They each occupy one "space", or the equivalent of one duplex outlet, and may be covered with any cover plate.
Any number ,f modules may be nested together using a multiple gang box.
The M3141 and M3142 modules may also be mounted in a panel in two different ways One method requires drilling
holes so that the lack and the potentiometer nuts hold the module on. The other method requires drilling clearance holes
for the jack: and the potentiometer, and holding the module to the back of the panel by using a 6-32 screw that would
normally hold the cover plate on. People using Switchcraft 298 plugs may remove the plastic caps on the front of the
modules to retain the lock-down feature, provided that the mounting panel is not more than 1/8" thick.
The rear of the M3141 and the M3142 contains an 8 terminal strip which gives access to the circuitry. The easiest crimp
terminal to use is an insulated, slotted-tongue flanged spade, such as the AMP P/N 324608 or an equivalent.
ELECTRICAL CHARACTERISTICS
The M3141 and M3142 operate into a 4-wire intercom line which has +24 volts DC, ground, a talk line (input to power
amplifier), and a listen line (output of power amplifier). The M3141 contains a mike amplifier, a DC power source for a
carbon mike or for an amplified dynamic mike, a jack for connecting a 3-wire headset/microphone, and a volume control
for the headset This volume control is after all amplifiers, and only reduces the audio going to the headset.
The M3142 has all the above mentioned characteristics, plus one other. It is equipped with a push-to-page button This
push-to-page feature allows any headset station user to push the button and be heard over an external loudspeaker
which is normally muted. A push-to-page system is particularly desirable in areas where a station may not always be
manned. When the desired person hears the page, he goes to the nearest station and uses the headset or handset at
that location
The M3142 will only retain its push-to-page feature when used in conjunction with a M3131 audio power amplifier. A
more detailed explanation of push-to-page operation is outlined in application note 17209P-03.
All David Clark Company amplifiers, and headsets using carbon or amplified dynamic mikes are designed to work with
the M3141 and M3142 modules. Sound powered headsets, and headsets using low impedance dynamic mikes are not
designed to work with the M3141 and M3142. Also, these modules cannot be operated from an external 12 volt DC
power source.
SPECIFICATIONS
The M3141 and M3142 use common emitter amplifiers with a voltage gain of 0 4 into the specified 500 ohm talk line
impedance. The input impedance of the amplifier is 420 ohms, and the output impedance is 16K ohms. The maximum
output swing is approximately 1 volt p-P. The frequency response Is contoured for best speech Intelligibility. Twelve mA
DC is supplied for the carbon mike or for the amplified dynamic mike. The volume control i: a F000 ohm audio taper pot,
wired so that the minimum impedance a power amplifier would see is 5000 ohms in parallel with the headphone
impedance. This is 640 ohms for a 600 ohm headset and 145 ohms for a 150 ohm headset.
For special applications, access is provided to the headset signal (after the volume control), and to the input node of the
amplifier. This input node can be used to provide access to the unamplifed milk signal, and it can also be used as an
input to the module
17206P-71(9-83)
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