Very simple and useful circuit for communication between two people. The transistor Q1 is used to amplify the weak output signal of the speaker when someone pushes their side push-button to speak. The configuration of Q1 pre-amplifier is formed as so-called common-base, because of matching low impedance of speaker with the input impedance of the pre-amplifier, so that it can produce maximum gain. To drive the speaker, the circuit uses an integrated audio power amplifier LM380. The whole circuit can be built on a vero-board for simplicity and still get good result! However, if you intend to design a PCB for this circuit, you would probably get better result. Please note that, the PCB should be designed for the master side, and it should connect to the slave side via shield stereo cable.