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WARNING: Playing loud music in an
automobile can hinder your ability to hear
traffic and permanently damage your 
hearing. We recommend listening at low or
moderate levels while driving your car. JBL
accepts no liability for hearing loss, bodily
injury or property damage resulting from
the use or misuse of this product.

IMPORTANT: To get the best 
performance from your JBL Grand Touring

®

Series amplifiers, we strongly recommend
that installation be entrusted to a qualified 
professional. Although these instructions
explain how to install GTO amplifiers in a
general sense, they do not show specific
installation methods that may be required
for your particular vehicle. If you do not
have the necessary tools or experience, 
do not attempt the installation yourself.
Instead, please ask your authorized JBL
car audio dealer about professional 
installation.

INSTALLATION 
WARNINGS AND TIPS
• Always wear protective eyewear when

using tools.

• Turn off the audio system and other 

electrical devices before you start.
Disconnect the (–) negative lead from
your vehicle’s battery.

• Check clearances on both sides of 

a planned mounting surface before
drilling any holes or installing any
screws. Remember that the screws 
can extend behind the surface.

• At the installation sites, locate and

make a note of all fuel lines, hydraulic
brake lines, vacuum lines and electrical
wiring. Use extreme caution when cut-
ting or drilling in and around these areas.

• Before drilling or cutting holes, use a

utility knife to remove unwanted fabric
or vinyl to keep material from snagging
in a drill bit.

• When routing cables, keep input-signal

cables away from power cables and
speaker wires.

• When making connections, make 

certain they are secure and properly
insulated.

• If the amplifier’s fuse must be replaced,

use only the same type and rating as
that of the original. Do not substitute
another kind.

CHOOSING A LOCATION
AND MOUNTING THE
AMPLIFIER
Choose a mounting location in the trunk 
or cargo area where the amplifier will not
be damaged by shifting cargo. Amplifier
cooling is essential for proper amplifier
operation. If the amplifier is to be installed
in an enclosed space, make sure there is
sufficient air circulation for the amplifier 
to cool itself.

When mounting the amplifier under a 
seat, ensure that it is clear of all moving
seat parts and does not affect the seat 
adjustments. Mount the amplifier so it 
is not damaged by the feet of backseat 
passengers. Make sure that the amplifier
is mounted securely using nuts and bolts
or the supplied mounting screws.

Mount the amplifier so that it remains 
dry – never mount an amplifier outside 
the vehicle or in the engine compartment.

POWER CONNECTIONS
The GTO amplifiers are capable of 
delivering extremely high power levels,
and require a heavy-duty and reliable 
connection to the vehicle’s electrical system
in order to perform optimally. See Figure 1
for connection location. Please adhere to
the following instructions carefully: 

Ground Connection
Connect the amplifier’s Ground (GND) 
terminal to a solid point on the vehicle’s
metal chassis, as close to the amplifier 
as possible. Refer to the chart below to 
determine minimum wire-gauge size. Scrape
away any paint from this location; use a star-
type lock washer to secure the connection.

Power Connection
Connect a wire (see chart at right for
appropriate gauge) directly to the vehicle’s
positive battery terminal, and install an
appropriate fuse holder within 18" of the
battery terminal. Do not install the fuse at
this time. Route the wire to the amplifier’s
location, and connect it to the amplifier’s
Positive (+12V) terminal. Be sure to use
appropriate grommets whenever routing
wires through the firewall or other sheet
metal. Failure to adequately protect the
positive wire from potential damage may
result in a vehicle fire. When you are done 
routing and connecting this wire, you may
install the fuse at the battery.

Remote Connection
Connect the amplifier’s Remote (REM) 
terminal to the source unit’s Remote Turn-
On lead using a minimum of 18-gauge wire.

NOTE: When using the speaker level
inputs, connect the remote (REM) terminal
to the source unit. If your source unit does
not have a remote turn-on connection,
connect the amplifier’s (REM) terminal to
the vehicle’s accessory circuit.

Speaker Connections
Refer to the application guides on the
pages that follow. Speaker connections
should be made using a minimum of 
16-gauge wire.

High-Level Input Connections
The GTO75.2, GTO75.4 and GTO755.6 
amplifiers are equipped with speaker-level
inputs that allow you to add an amplifier 
to head units that do not have RCA line
outputs. The speaker outputs for the
source unit should be connected to the
amplifier using the supplied connector
(square four-wire plug). Remember to
check for proper polarity. The GTO301.1,
GTO601.1 and GTO1201.1 amplifiers are 
not equipped with high-level inputs.

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

Wire Gauge Chart
Amplifier

Maximum

Minimum 

Model

Current Draw

Wire Gauge

GTO75.2

34A #8 

AWG

GTO75.4

85A #8 

AWG

GTO755.6

87A #8 

AWG

GTO301.1

40A #8 

AWG

GTO601.1

69A #6 

AWG

GTO1201.1

115A #4 

AWG

These recommendations assume 7' – 10'
wire runs. If your installation differs mark-
edly, you will need to adjust the wire
gauge accordingly.

IMPORTANT NOTE: If you are planning 
to use optional neon tubes, install them
before making any electrical connections
to the amplifier (refer to“Installing Neon
Tubes” on page 6).

Figure 1. Terminal connection end plate.

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CONNECTIONS

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.

–

+

+

–

–

+

Figure 2. GTO subwoofer amplifier with two woofer connections.

Figure 3. GTO subwoofer amplifier with one woofer connection.

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SETTING THE
CROSSOVER(S)
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
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 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.

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.

REMOTE LEVEL CONTROL
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.

SETTING THE BASS BOOST
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. 

AUX OUTPUT
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.

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.

Figure 12. Control end panel.

GTO75.2

GTO75.4

GTOB300.1/600.1/1200.1

GTO75.6

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Figure 13. Installing neon tubes in a JBL GTO amplifier. 

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)

No audio

Voltage less than 9V on 

Check vehicle

(PROTECT 

BATT+ connection

charging system for

and POWER

defective voltage 

LEDs flash)

regulator

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 

Music lacks 

Speakers are not 

Check speaker

“punch”

connected properly

connections for
proper polarity

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