Pro Intercom AD903 2-to-4 Wire Adaptor Active Transformer Isolation Audio In & OutThe AD903 has many functions for getting various levels of audio into an intercom circuit, or getting the intercom audio "traffic' out to an amplifier or recorder. It is also useful as a 2 to 4 wire adaptor for connecting 4 wire communications into and out of a standard intercom circuit. Both the input and the output are transformer isolated from whatever devices are connected. The wide range of level adjustments will accommodate almost any audio