JBL GTO 75.4 (serv.man2) Service Manual ▷ View online
4
CONNECTIONS
–
GTO 75.4/75.4II
The
GTO 75.4/75.4II can be set up for stereo
4-channel, 3-channel or bridged
2-channel operation, as shown in
Figures 6 through 8.
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.
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.
for stereo operation is 2 ohms.
Minimum speaker impedance for
bridged operation is 4 ohms.
–
+
–
+
–
+
–
+
Figure 6.
GTO 75.4/75.4II amplifier in 4-channel (stereo) operation to drive front and rear full-range speakers.
–
+
–
+
–
+
Figure 7.
GTO 75.4/75.4II is set up for 3-channel operation to drive a set of full-range speakers and a subwoofer.
–
+
–
+
Figure 8.
GTO 75.4/75.4II used in bridged 2-channel mode to drive a set of components or subwoofers.
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GTO 75.4/75.4II
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6
INSTALLATION AND SETUP
SETTING THE
CROSSOVER(S)
Determine your system plans and set the
crossover mode switch accordingly. If you
plan to use the
CROSSOVER(S)
Determine your system plans and set the
crossover mode switch accordingly. If you
plan to use the
GTO 75.4/75.4II to drive
full-range speakers, set the crossover
mode to FLAT and skip to “Setting Input
Sensitivity.”
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.
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.
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.
frequency that removes vocal information
from the sound of the subwoofer.
If using the
GTO 75.4/75.4II to drive a
subwoofer(s), set the crossover mode to
LP (low pass).
LP (low pass).
SETTING INPUT
SENSITIVITY
1. Initially turn the INPUT LEVEL control(s)
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.
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.
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.
(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
GTO 75.4/75.4II amplifiers are
equipped with full-range outputs that can
be used to connect additional amplifiers.
GTO 75.4/75.4II 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.
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
(OPTIONAL)
1. Using a Phillips screwdriver, remove all
screws on the amplifier’s output/power
end panel and set them aside.
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.
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
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.
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
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.
panel and reinstall its screws.
8. Finish the installation of the neon tubes
as instructed in their owner’s manual.
Figure 12.
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GTO 75.4/75.4II
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GTO 75.4/75.4II
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7
INSTALLATION AND SETUP
To Neon
Power
Supply
To Neon
Power
Supply
Figure 13. Installing neon tubes in a JBL GTO amplifier.
TROUBLESHOOTING
SYMPTOM
LIKELY CAUSE
SOLUTION
No audio
No voltage at BATT+
Check voltages at
(POWER LED
or REM terminals,
amplifier terminals
is off)
or bad or no ground
with VOM
connection
No audio
DC voltage on
Amplifier may need
(PROTECT LED
amplifier output
service; see enclosed
flashes every
warranty card for
4 seconds)
service information
No audio
Amplifier is
Make sure amplifier
(PROTECT
overheated
cooling is not blocked
LED is on)
at mounting location;
verify speaker system
impedance is within
specified limits (see
“Specifications” on
the next page)
verify speaker system
impedance is within
specified limits (see
“Specifications” on
the next page)
No audio
Voltage less than 9V on
Check vehicle
(PROTECT
BATT+ connection
charging system for
and POWER
defective voltage
LEDs flash)
regulator
SYMPTOM
LIKELY CAUSE
SOLUTION
No audio
Voltage more than 16V
Check vehicle
(PROTECT
or less than 8.5V on
charging system for
LED is on)
BATT+ connection
defective voltage
regulator
Distorted audio
Input sensitivity is
Check INPUT
not set properly, or
LEVEL setting; or
amplifier or source
check speaker wires
unit is defective
for shorts or grounds
Distorted audio
Short circuit in
Remove speaker leads
and PROTECT
speaker or wire
one at a time to locate
LED flashes
shorted speaker or
wire, then repair
wire, then repair
Music lacks
Speakers are not
Check speaker
“punch”
connected properly
connections for
proper polarity
proper polarity
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GTO 75.4/75.4II
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