The MSM3 adds four more circuits (C, D, E & F) to an MSM1 Master Station. Connection to the MSM1 is made via a 9-pin D-sub connector on the rear panel. The MSM3 derives all of its power from the host unit. Connections to outstations on the new circuits are made through XLR connectors on the rear panels of the add-on units. The MSM3 provides 8 connections, 2 for each of the four add-on circuits. The new circuits created by adding either of these units to the system will have access to any auxiliary program being input to the MSM1.