Cheapskate’s Headset Adapter

Here’s a cheaper and easier method of making
a telephone headset adapter. All that’s required is a cheap headset ($5
at Harvey Norman), a DPDT switch and a few
connectors. Each transducer in the headset measures about 40O. There is
also an inline volume control measuring about 500O per leg, across which
each earphone is connected. This means that each earpiece has a minimum
resistance (at maximum volume) of about 37O. 128O is the desirable
impedance. This can be achieved by wiring the earphones in series and
adding a 56O resistor. Although there is a reduction in maximum volume
due to the resistor, this was easily accommodated by the author’s
telephone, which has an amplified audio output.


Cheapskate’s Headset Adapter Circuit Diagram

The headset does not have a connection between the earphones and the
microphone, so no other modifications were required. Series connection
of the earphones is achieved by not picking up the sleeve connection at
the socket and connecting only across tip and ring. As the author’s
telephone uses an electret microphone in its hand-piece, no additional
biasing circuitry is needed for the headset’s microphone.

Author: Brian Critchley
Copyright: Silicon Chip Electronics

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