HAND-FREE PHONE SYSTEM TWO-WAY SIMULTANEOUS TALKING UNIT

PURPOSE:To effectively prevent a howling by respectively connecting same phase output circuits which give voice signals from a microphone in common to both input parts of a differential amplifier and also connecting a transmission line to a connection point between the same phase output circuit and one input part of the differential amplifier. CONSTITUTION:In case of inputting a voice in the microphone M of a master machine B, the voice signals are inputted in the same phase output circuit H and the voice signals, passing through the circuit, are transmitted to the transmission line L1 for call. In this case, the voice signals outputted from the same phase output circuit of the master machine are added to both input parts of the differential amplifier on the master machine side in common but the differential amplifier does not output any signals because the inputted voice signals have same phases. Meanwhile, when the voice signals are inputted from a slave machine C to the master machine H through the transmission line L1, the voice signals are added to one input part of the differential amplifier and amplified in actuation to be outputted from a speaker SP because the voice signals have the phases different from the voice signals which are added in another input part of the differential amplifier. On the slave machine side the process is executed in the same way. Thus, since the inputs are not outputted from the speaker on the same side, the howling does not occur.