My fire department uses a Kenwood TK690-H as a base radio. The system was used to (poorly) power 3 in ceiling speakers throughout the station.
Recently, I rewired the paging system in the station with a dedicated amplifier and 4 speakers. With Bluetooth, or 3.5mm mp3 connection to the amplifier the speakers sound good, no buzzing or hums, and is quiet when nothing is playing.
I attempted to splice the BTL output of the Kenwood to a 3.5mm cable that goes to 1/4" microphone input to the amplifier and it hums loudly and constantly.
Mic in is preferred as in paging mode it will override any other sources if our station is paged.
How can I fix this problem?