Clear-Com RS-603 (No longer available) - Manual (Page 25)

2 3 R S - 6 0 3 / 6 2 3 / R B E L T P A C K S
To adjust the program audio volume, rotate the knob located on the
bottom panel of the beltpack.
To restore the connector to its “loop-through” function, slide the
switch back towards the “loop-through” connector, in the direction
labeled on the beltpack as “intercom.”
Note: In some instances, connecting a source of program audio may cause
a hum in the system. To remedy this, remove the internal jumper from
pins 1 and 2 of P2 and connect the jumper to pin 2 only. This removes
the ground and leaves only a balanced, transformer-isolated connection.
To gain access to the jumper, remove the beltpack’s back cover by removing
the four screws.