MPA-46 35W PA Amplfier (320-2042) Connections Faxback Doc. # 34508 INSTALLING PA INTO PHONE SYSTEM Use isolation transformer Cat. No. 273-1374, between the phone system and PA. The MPA-46's paging port is 600 ohms. This could be set up with the KEY systems and prior Radio Shack systems by using a line transformer (to obtain Isolation), hooking up LINE IN to the PA & PAGE OUT to the phone. (IR-09/06/96)