GTO 75.2 (serv.man2) - JBL Car Audio Service Manual (repair manual). Page 6

SETTING THE
CROSSOVER(S)
Determine your system plans and set the
crossover mode switch accordingly. If you
plan to use the 

GTO75.2/75.2II to drive

full-range speakers, set the crossover
mode to FLAT and skip to “Setting Input
Sensitivity.”

Initially set the crossover frequency 
control midway. While listening to music,
adjust the crossover for the least 
perceived distortion from the speakers,
allowing them to reproduce as much 
bass as possible. 

Systems using a separate subwoofer set
the crossover mode to HP (high pass) for
your full-range speakers. Adjust the
crossover frequency to limit bass and 
provide increased system volume with 
less distortion.

For subwoofers, choose the highest 
frequency that removes vocal information
from the sound of the subwoofer.

If using the 

GTO75.2/75.2II to drive a 

subwoofer(s), set the crossover mode to
LP (low pass).

SETTING INPUT
SENSITIVITY
1. Initially turn the INPUT LEVEL control(s)

to minimum (counter clockwise).

2. Reconnect the (–) negative lead to the

vehicle’s battery. Apply power to the
audio system and play a dynamic music
track.

3. On the source unit, increase the volume

control to 3/4 volume. Slowly increase
the INPUT LEVEL control(s) toward three
o’clock until you hear slight distortion 
in the music. Then reduce the INPUT
LEVEL slightly until distortion is no 
longer heard. 

NOTE: After the source unit is on, red LEDs
(on the top panel) will light, indicating the
amplifier is on. If not, check the wiring,
especially the remote connection from the
source unit. Also refer to “Troubleshooting”
on the next page.

AUX OUTPUT
The GTO75.2/75.2II amplifiers are
equipped with full-range outputs that can
be used to connect additional amplifiers. 

NOTE: When using the high-level inputs,
the AUX outputs can be used to pass a
line-level signal to another amplifier.

INSTALLING NEON TUBES
(OPTIONAL) 
1. Using a Phillips screwdriver, remove all

screws on the amplifier’s output/power
end panel and set them aside.

2. Using a 3 ⁄32-inch Allen wrench, remove

only the screws on the amplifier’s (top)
clear cover and set them aside.

3. Remove the end panel and slide the

cover off. Set both parts aside.

4. Locate the enclosed hardware bag and

remove the four clips. Each clip has a
square end and a larger round end.
Using a round end, press two clips onto
each neon tube (e.g., Street Glow AN9 
or equivalent), as shown in 

Figure 13.

5. For each tube, align both clips so the

square ends slide onto an exposed
extrusion edge, as shown in Figure 9. 
Do not cover any screw holes. When
installed correctly, each neon tube will
sit under an extrusion and not be visible
when viewed from directly above.

6. Route each neon tube’s power cable

through its respective NEON hole on the
end panel (see 

Figure 13). 

7. Slide the cover back into place and re-

install its screws. Then, replace the end
panel and reinstall its screws.

8. Finish the installation of the neon tubes

as instructed in their owner’s manual.

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GTO 75.2/75.2II