Question:  Does the SB-704 party-line main station support program audio feed to specific PL channels (A, B, C or D)?
Answer:  Yes, there are several ways to introduce program audio feed into the SB-704 main station and to route program feeds to specific channels on the intercom. 
Program audio can be brought in to each channel directly via the rear panel DB-15 connector.  Four different program inputs, one for each channel, are provided. These auxiliary program inputs can only be fed directly to their associated intercom line. The only controls that affect these inputs are the PGM level controls associated with each channel and the internal program interrupt switch which is active if the function has been activated with an option DIP switch and a talk is active on that channel.  Refer to the illustration for connection of the program inputs. Pins #5 or #14 can be used for connecting shields in the attached SB-704 DB-15 drawing. 













The other way to bring in audio to the SB-704 is to use the main program input 3-pin XLR connector.  From there it can be routed to specific IC channels.  PROGRAM ON/OFF Four DIP switches (one for each channel) enable feeding the main program input to the selected intercom channel.  These DIP switches are located behind the access panel on the front panel of the SB-704.  If the DIP switches that control this functionality are in the up position then program is not routed to the specific IC channel.  See the attached DIP switches and audio controls drawing.