JBL GTO755.6 Service Manual

GTO Series

755.6

755.6II

6 CHANNEL POWER AMPLIFIERS

SERVICE MANUAL

JBL Consumer Products
250 Crossways Park Dr.

Woodbury, New York 11797 Rev

2VV10/2005

Power Amplifier GTO 755.6/755.6II

1

- CONTENTS -

SPECIFICATIONS ………………………………….……..1
FEATURES/TEST CONDITIONS……..….………………2
INSTALLATION………………….……...……..…...…...…3
CONNECTIONS………………….……...……..…...…..…4
SET-UP/CONTROLS ……..…………….…..…….….…...6
INSTALLING NEON TUBES..…….……..………………..6
BASIC TROUB L E SH OO TI NG..…….….… .……… ………7
TYPICAL SYSTEM WIRING..…….……..……………..…8

EXPLODED VIEW/PARTS LIST…….….…..…………....9

MECHANICAL PARTS LIST……………………………..10
AMPLIFIER BLOCK DIAGRAM…………………….……11
P.C.B. D RAWI N G S ….………………………… ……. …….12
ELECTRICAL PARTS LIST ..……….……….…….….…16
VERSION II ELECTRICAL PARTS LIST ADDENDUM….……….20
IC/TRANSISTOR PINOUTS..……..….…….….….….…..21
GTO75 5. 6 SCHEM ATI CS……………………… ...… …...2 4
GTO7 5 5. 6I I S CHEMATICS… ……..……….……..… …...2 8

PACKING……..…………………………………………....32

GTO 755.6/ GTO 755.6II Specifications

Output Power: 60W RMS x 4 channels; 107W RMS x 2 channels
(14.4V supply) @ 4 ohms; ≤1% THD + N

80W RMS x 4 channels; 150W x 2 channels

@ 2 ohms; ≤1% THD + N
160W RMS x 2 channels; 300W x 1 channel

@ 4 ohms; ≤1% THD + N
Signal-to-noise ratio: 79dBA (reference 1W into 4 ohms)
Dynamic power: 117W (channels 1,2,3,4) @ 2 ohms
163W (channels 5,6) @ 2 ohms
Effective damping factor: 6.39 @ 4 ohms
Frequency response: 10Hz – 47kHz (–3dB) (channels 1,2,3,4)
10Hz – 302Hz (channels 5,6)
Maximum input signal: 6.0V
Maximum sensitivity: GTO 755.6 - 250mV
GTO 755.6II - 75mV
DC Offset <50mV (-50%)
Output regulation: .042dB @ 4 ohms
Idle Current 1.9A
Input Impedance 22kΩ
Max Current Draw 50A @ 4 ohms
89A @ 2 ohms
Dimensions: 18 11/16 x 12 5/16 x 2 3/8” (L x W x D)
(474mm x 313mm x 60mm)
Fuses: 30A x 2

JBL continually strives to update and improve existing products, as well as create new ones. The specifications and details in
this and related JBL publications are therefore subject to change without notice.

755.6/755.6II

2

INSTALLATION

3

755.6/755.6II

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 cut­ting 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.

Figure 1. Terminal connection end plate.

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 star­type 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.
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

Failure to adequately protect the

metal.

positive wire from potential damage may
result in a vehicle fire.

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 Turn­On 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.

Do not install the fuse at

When you are done

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 GTO series
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.

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

AWG

GTO755.6 87A #8 AWG
These recommendations assume 7' – 10'
wire runs. If your installation differs mark­edly, 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” ).

Subwoofer Rear Front

–

+

+

–

+

–

CONNECTIONS – GTO755.6/755.6II

Subwoofer Rear Front

Subwoofer Rear Front

–

+

–

+

+

–

+

–

+

–

+

–

Subwoofer Rear Front

Rear Front

–

+

–

+

+

–

+

–

+

–

4

The GTO755.6/755.6II can be configured for
6-channel, 5-channel or 3-channel
operation, as shown in

through 11

.

INPUT MODE switch:

• Use INT (internal mode) to send a
signal from the front and rear inputs
to the subwoofer.

• Use EXT (external mode) when
sending a dedicated signal to the
subwoofer inputs; e.g., if your source
unit has a subwoofer output.

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.

Figures 9

Figure 9. 6-Channel operation: GTO755.6/755.6II amplifier driving full-range front and rear speakers and a pair of subwoofers.

755.6/755.6II

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: GTO755.6/755.6II amplifier configured for 3-channel operation, where all of the channels are

bridged for a subwoofer and a pair of component speakers.

755.6/755.6II

5

INSTALLATION AND SETUP

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).

6

755.6/755.6II

NOTE:The subwoofer output of the GTO755.6
is low-pass only and does 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.

Figure 12. Control end panel.

REMOTE LEVEL CONTROL

All 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 GTO755.6/755.6II
is 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

NOTE:

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

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

7. Slide the cover back into place and re­install 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 13).

Figure 13.

GTO75.2/75.2II

GTO75.4/75.4II

GTO300.1/300.1II/600.1/600.1II/1200.1/1200.1II

GTO755.6/755.6II

INSTALLATION AND SETUP

To Neon

Power
Supply

To Neon

Power
Supply

7

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

TROUBLESHOOTING

755.6/755.6II

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)

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

Distorted audio Input sensitivity is Check INPUT

Distorted audio Short circuit in Remove speaker leads
and PROTECT speaker or wire one at a time to locate
LED flashes shorted speaker or

Music lacks Speakers are not Check speaker
“punch” connected properly connections for

regulator

not set properly, or LEVEL setting; or
amplifier or source check speaker wires
unit is defective for shorts or grounds

wire, then repair

proper polarity

755.6/755.6II

8

Grand TouringGrand Touring

A

9

B

755.6/755.6II

C

D

E

71 2 3 4 5 6 8