Abstract: The inputs of an operational amplifier are connected across a telephone line and bridged by a capacitor. The output of the operational amplifier drives the coil of a relay via an intermediate amplifier. The relay is of the make-before-break type, and is interposed between an audio source, audio speakers, and dummy load resistors. When the voltage across the telephone line indicates an on-hook condition for a telephone, the audio source is connected to the speakers through the relay. When the voltage across the telephone lines indicates an off-hook condition of the telephone, the audio source is connected to the dummy resistors and disconnected from the speakers and is thereby muted, enabling telephone conversation to take place.