DOWNLOAD JBL GTO 75.4 (serv.man11) Service Manual ↓ Size: 587.77 KB | Pages: 8 in PDF or view online for FREE

The GTO subwoofer amplifiers are 
single-channel amplifiers. There are
two sets of terminals to make it easy 
to connect multiple woofers. Either 
set of (+/–) terminals may be used when
connecting woofers.
To the right are two application 
diagrams to help plan your subwoofer
system installation. Figures 2 and 3
show how to configure the GTO 
subwoofer amplifiers (models GTO301.1,
GTO601.1 and GTO1201.1). 

NOTE: For simplicity, Figures 2 and 3 
do not show power, remote and input
connections.

NOTE: Minimum speaker load is 
2 ohms.

–

+

FREQ

MODE

HP

LP FLAT

+

–

+

–

–

+

Figure 2. GTO subwoofer amplifier with two woofer connections.

Figure 3. GTO subwoofer amplifier with one woofer connection.

Figure 4. GTO75.2 amplifier set up for stereo operation.

Figure 5. GTO75.2 amplifier set up for bridged-
mono operation.

The JBL GTO75.2 amplifier can be 
set up for stereo or bridged-mono oper-
ation, as shown in Figures 4 and 5.

NOTE: For simplicity, Figures 4 and 5 
do not show power, remote and input 
connections.

NOTE: Minimum speaker impedance for
stereo operation is 2 ohms. Minimum
speaker impedance for bridged opera-
tion is 4 ohms.

FREQ

MODE

HP

LP FLAT

+

–

–

+

The GTO75.4 can be set up for stereo 
4-channel, 3-channel or bridged 
2-channel operation, as shown in 
Figures 6 through 8.

NOTE: For simplicity, Figures 6 through 8
do not show power, remote and input 
connections.

NOTE: Minimum speaker impedance for
stereo operation is 2 ohms.
Minimum speaker impedance for
bridged operation is 4 ohms.

Figure 6. GTO75.4 amplifier in 4-channel (stereo) operation to drive front and rear full-range speakers.

Figure 7. GTO75.4 is set up for 3-channel operation to drive a set of full-range speakers and a subwoofer.

Figure 8. GTO75.4 used in bridged 2-channel mode to drive a set of components or subwoofers.

The GTO755.6 can be configured for 
6-channel, 5-channel or 3-channel oper-
ation, as shown in Figures 9 through 11.

NOTE: For simplicity, Figures 9 through
11 do not show power, remote and input
connections.

NOTE: Minimum speaker impedance for
stereo operation is 2 ohms.
Minimum speaker impedance for
bridged operation is 4 ohms.

–

+

–

+

+

–

+

–

+

–

+

–

Figure 9. 6-Channel operation: GTO755.6 amplifier driving full-range front and rear speakers and a pair of subwoofers.

Figure 10. 5-Channel operation: The same as Figure 9, with the subwoofer output bridged to drive a single 4-ohm subwoofer, 
providing the speaker with more power. 

Figure 11. 3-Channel operation: GTO755.6 amplifier configured for 3-channel operation, where all of the channels are
bridged for a subwoofer and a pair of component speakers.

Determine your system plans and set the
crossover mode switch accordingly. If you
plan to use the GTO75.2 or GTO75.4 to drive
full-range speakers, set the crossover mode
to FLAT and skip to “Setting Input Sensi-
tivity.”

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 or GTO75.4 to drive a 
subwoofer(s), set the crossover mode to LP
(low pass).

NOTE: The GTO301.1, GTO601.1, GTO1201.1
and the subwoofer output of the GTO755.6
are low-pass only and do not have a
crossover mode switch.

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.

The GTO755.6 and all three GTO subwoofer
amplifiers have inputs for an optional
remote level control (RLC). This will allow
the amplifier’s input level to be adjusted
from the listening position. Connect the
optional remote level control using the 
RJ-11 jack on the side of the amplifier.
Install the control module in the front of the
vehicle within easy reach of the driver.
Under the dash or in the center console are
both suitable locations.

The GTO755.6, GTO301.1, GTO601.1 and
GTO1201.1 are all equipped with a bass-
boost control. This allows you to adjust the
bass output of your system at 50Hz up to
12dB and enhance low frequency. 

GTO amplifiers (except GTO755.6) 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.

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 extru-
sion edge, as shown in Figure 13. 
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.

Figure 12. Control end panel.

GTO75.2

GTO75.4

GTOB300.1/600.1/1200.1

GTO75.6