Two Wire To Four Wire Audio Converter

This converter circuit maintains 40 dB of isolation between the input and output halves of a four-wire line while permitting a two-wire line to be connected. A balancing potentiometer, Rg, adjusts the gain of IC2 to null the feed-through from the input to the output. The adjustments is done on the workbench just after assembly by inserting a 1 kHz tone into the four-wire input and setting Rg for minimum output signal. An 82 ohm dummy-load resistor is placed across the two wire terminals.

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