B&K Reference 4430 Owner's Manual page 8

If the control function is desired, each unit in the system must remain connected at all
times and the control must be enabled. To enable the control function, the CTRL
ENABLE button must be out for each controllable amplifier in the system. For more
information on the amplifiers output status under various control conditions, refer to the
table below.
@ CTRL IN
Signal
Signal
No Signal
No Signal
The level controls are an option that can be added to the amplifier. If your amplifier has
this option, the balanced inputs are not present.
There are three level controls on the back of the amplifier. One level control for each
channel.
When using the level controls, first start with them turned all the way up (clockwise).
Then adjust them according to your system requirements to match the sound level
coming from each speaker.
Button position
OUT
IN
OUT
IN
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Output status
Sound
Sound
Mute
Sound
@ CTRL OUT
Signal
Signal
No Signal
Signal