PMA450B Audio Panel: Impressive Feature Set
The panel will come on with the master avionics power, but the small rotary knob serves double duty as a power control (its a push-in-and-hold switch to eliminate inadvertent power cycles) and pilot/copilot intercom volume. The larger knob is for passenger volume. Green LED bars to the left of the knobs illuminate when you turn the knobs, showing relative volume. The volume controls are linear throughout the range and there was more than enough gain through our Bose A20 headset.