The public address amplifier shall provide simultaneous mixing of two low-impedance balanced microphones and one telephone input; or one microphone, one auxiliary input, and one telephone input. The unit shall have a front panel selector switch which shall allow one of the input channels (MIC 2/AUX) to be selected for use as a microphone or an auxiliary input. It shall be possible to mute the auxiliary input when a customer-supplied SPST switch is attached to the AUX MUTE terminals on the rear panel. The TEL input shall provide signal-activated paging with muting of the AUX channel. A VOX threshold control shall be included to eliminate activation of the channel by noise on the telephone line. The threshold control and TEL volume control shall be located on the rear panel.