GX-A422SI - JBL Car Audio Service Manual (repair manual). Page 12

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Crossover Filter switch: When operating the amplifier in bridged mode into a subwoofer, set the Crossover Filter switch in the “LP” (low-pass) 

position. This will limit the amount of high-frequency energy sent to the subwoofer.

SET THE INPUT LEVEL

1. Turn all the Level controls on all the system's amplifiers fully counter-clockwise.
2. Play some dynamic music through your source unit and turn its volume up to 3/4 volume.
3. Slowly turn the Level control on the GX-A422SI amplifier clockwise until the music begins to sound distorted.
4. Turn the Level control counter-clockwise slightly until the music no longer sounds distorted.
5. If you're using more than one amplifier, repeat Steps 3 – 4 for all remaining amplifier Level controls.

SET THE BASS BOOST

When you’re using the amplifier in bridged mode to power a subwoofer, the Bass Boost switch can provide 12dB of bass boost at 45Hz. (Set this 

switch according to your personal taste, but if using it causes audible distortion or bottoming of your subwoofer we recommend setting it to "OFF."

CAUTION: Only use the Bass Boost switch if you're using the amplifier to power a subwoofer. Using the Bass Boost switch with full-range speakers 

can damage the speakers. 

POWER AND PROTECTION INDICATORS

• LED Illuminates orange: Normal operation (power is on).
• LED is off: Amplifier is in standby mode.

The amplifier's Protection LED should remain off during normal operation. If there is no sound from the amplifier and the Protection LED illuminates 

red, see Troubleshooting, on page 12.