DOWNLOAD JBL GTO 601.1 (serv.man13) Service Manual ↓ Size: 3.68 MB | Pages: 28 in PDF or view online for FREE

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

GTO Amp OM  2/3/04  3:54 PM  Page 6

5

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

GTO Amp OM  2/3/04  3:54 PM  Page 7

6

7

8