The MA-485A amplifier provides audio amplification, control and power needed to operate an apartment intercom system. Extensive tests were performed to develop a reliable, long lasting intercom amplifier with precision amplifier circuits to provided crystal clear audio reception. Mircoms amplifier uses an automatic level control (ALC) circuit to ensure voice intelligibility. Built-in features include: timed door release silent door release and post office release. Also known as -Mircom Technologies - MA-485A - Speaker Type Amplifier, 4 Wire. Used with IS-489