JBL GTH 400 (serv.man2) User Manual / Operation Manual ▷ View online
4
1.1 Features
Theory of Operation –
Virtual Center Image Enhancer
Virtual Center Image Enhancer
JBL’s breakthrough “Virtual Center”
circuitry is the result of the
understanding of how the human ear
responds to timing, frequency, and
amplitude cues to determine the
apparent direction of a sound source.
Virtual Center circuitry manipulates the
analog signal in real time to provide
each of the driver’s ears with the signal
they would receive if the driver was
seated in the center of the vehicle. This
provides a stable, centered image to
the driver much like that obtained with
a dedicated center-channel
loudspeaker.
circuitry is the result of the
understanding of how the human ear
responds to timing, frequency, and
amplitude cues to determine the
apparent direction of a sound source.
Virtual Center circuitry manipulates the
analog signal in real time to provide
each of the driver’s ears with the signal
they would receive if the driver was
seated in the center of the vehicle. This
provides a stable, centered image to
the driver much like that obtained with
a dedicated center-channel
loudspeaker.
To restore the spaciousness that is
generally lost in the small confines of a
car interior, the rear channels utilize
differential-mode ambience recovery to
restore the ambience information pres-
ent in all conventional stereo
recordings. Unlike DSP, the JBL
circuitry does not add synthetic reverb,
but recovers real information that is
masked in conventional systems. As a
result, the overall effect from the Virtual
Center circuitry of the GTH400 is
incredibly realistic, yet simple to adjust
and use. Best of all, the “Virtual Center”
and ambiance recovery circuits do not
require specially encoded recordings
and work with virtually all conventional
stereo tapes, discs, and broadcasts.
generally lost in the small confines of a
car interior, the rear channels utilize
differential-mode ambience recovery to
restore the ambience information pres-
ent in all conventional stereo
recordings. Unlike DSP, the JBL
circuitry does not add synthetic reverb,
but recovers real information that is
masked in conventional systems. As a
result, the overall effect from the Virtual
Center circuitry of the GTH400 is
incredibly realistic, yet simple to adjust
and use. Best of all, the “Virtual Center”
and ambiance recovery circuits do not
require specially encoded recordings
and work with virtually all conventional
stereo tapes, discs, and broadcasts.
1.2 About Installation
Although the GTH400 is designed to
make installation as easy as possible, it
is an extremely sophisticated product
that requires proper installation and
setup to realize its full performance
potential. If you feel you do not have
the necessary knowledge and skills, we
strongly recommend that the
installation be done by your
authorized JBL dealer.
make installation as easy as possible, it
is an extremely sophisticated product
that requires proper installation and
setup to realize its full performance
potential. If you feel you do not have
the necessary knowledge and skills, we
strongly recommend that the
installation be done by your
authorized JBL dealer.
If you choose to install the GTH400
yourself, read
yourself, read
all of the information in
this manual before you start the
installation. Pay particular attention to
the safety precautions and notes.
installation. Pay particular attention to
the safety precautions and notes.
GTH400-20107 06/03/98 15:49 Side 4
5
2. Installation and use
Refer to the “Crossover Frequency
Adjustments” and “Speaker-Level Input
Impedance Adjustments” sections of
this manual to see if you will need to
make alterations to their factory
settings.
Adjustments” and “Speaker-Level Input
Impedance Adjustments” sections of
this manual to see if you will need to
make alterations to their factory
settings.
1. Disconnect the negative cable from
the battery. Note: If the vehicle’s
radio features a code type security
system, make certain you know
the code before disconnecting the
battery!
radio features a code type security
system, make certain you know
the code before disconnecting the
battery!
2. Run a minimum AWG #8 power
cable complete with a 60 amp fuse
(not included) directly from the
positive +12V battery terminal to
the desired amplifier location. Keep
the fuse within 6" of the battery
terminal, and position it before the
wire runs through any metal
partition.
(not included) directly from the
positive +12V battery terminal to
the desired amplifier location. Keep
the fuse within 6" of the battery
terminal, and position it before the
wire runs through any metal
partition.
3. Note: All wiring connections should
be made either by soldering with
heatshrink tubing insulation or with
high quality crimp-type insulated
connectors installed with a
professional-type, articulated
crimping tool. Soldering crimp-type
terminals is recommended for
additional
security. Never use wire nuts,
insulation-displacement connectors
(i.e. ScotchLok type), or twist and
tape connections. Do not use
electrical tape; it will loosen with
age and extreme temperatures.
heatshrink tubing insulation or with
high quality crimp-type insulated
connectors installed with a
professional-type, articulated
crimping tool. Soldering crimp-type
terminals is recommended for
additional
security. Never use wire nuts,
insulation-displacement connectors
(i.e. ScotchLok type), or twist and
tape connections. Do not use
electrical tape; it will loosen with
age and extreme temperatures.
4. Mount amplifier in the desired
location using the included screws.
5. Connect power wiring as shown in
the Wiring Diagram on page 18.
6. Connect the outputs from the head
unit to the appropriate inputs of the
amplifier according to the Wiring
Diagram (page 18) with either (or
both) high quality low-level signal
cables with RCA plugs, or the
supplied speaker-level input
connector.
amplifier according to the Wiring
Diagram (page 18) with either (or
both) high quality low-level signal
cables with RCA plugs, or the
supplied speaker-level input
connector.
7. Install the remote control in the
desired location. Connect and run
the cable from the remote to the
amplifier.
the cable from the remote to the
amplifier.
8. Connect the speakers to the ampli-
fier according to the Wiring Diagram
on page 18.
on page 18.
9. Turn the gain controls to the
1/4-position for all groups.
10. Set the bass boost of each group to
the desired position.
11. Set the crossover switches for each
group as desired.
12. Set the Group 2 Input and Group 3
Input as desired.
13. Set the mode switches to Stereo,
Left + Right, or Left Input Only
operation for each group.
operation for each group.
14. Double-check your switch settings.
Reconnect the negative battery
cable. Note: Incorrect switch
settings can damage your speakers!
cable. Note: Incorrect switch
settings can damage your speakers!
15. Turn on the signal source at a low
volume level, and check for the
correct output from each speaker.
correct output from each speaker.
16. Adjust the amplifier gain controls
using the procedure described in
the “Adjusting the Gain” section
(page 25).
the “Adjusting the Gain” section
(page 25).
17. Read the rest of the manual to get
maximum use and enjoyment from
your amplifier.
your amplifier.
GTH400-20107 06/03/98 15:49 Side 5
3. System Design Using
the GTH400
the GTH400
3.1 Speaker Requirements
When used in the non-bridged mode a
group-channel of the GTH400 can
easily drive two 2-ohm speaker loads.
When only one speaker is connected to
the left and right outputs of a group,
virtually any conventional speaker may
be used. When two speakers are
connected in parallel to a single output
(left or right) of a given group, each
speaker must have a minimum
impedance of at least 4 ohms. This
ensures that the combined load will not
drop below 2 ohms. Although the
amplifier will not be damaged, load
impedances lower than 2 ohms will
eventually cause the amplifier to
overheat, activating the protection
circuits and causing the unit to shut off
until it cools down sufficiently.
group-channel of the GTH400 can
easily drive two 2-ohm speaker loads.
When only one speaker is connected to
the left and right outputs of a group,
virtually any conventional speaker may
be used. When two speakers are
connected in parallel to a single output
(left or right) of a given group, each
speaker must have a minimum
impedance of at least 4 ohms. This
ensures that the combined load will not
drop below 2 ohms. Although the
amplifier will not be damaged, load
impedances lower than 2 ohms will
eventually cause the amplifier to
overheat, activating the protection
circuits and causing the unit to shut off
until it cools down sufficiently.
When a group of the GTH400 is in
bridged mode, the combined
impedance of the speaker (or speakers)
connected to the bridged channels
should be at least 4 ohms. As in the
example above, sustained operation of
the GTH400 in bridged mode with less
than 4 ohms will likely cause
overheating.
bridged mode, the combined
impedance of the speaker (or speakers)
connected to the bridged channels
should be at least 4 ohms. As in the
example above, sustained operation of
the GTH400 in bridged mode with less
than 4 ohms will likely cause
overheating.
The GTH400 must not be used with
speakers that have either one of their
input terminals wired to the frame of
the speaker or to the chassis of the
vehicle.
speakers that have either one of their
input terminals wired to the frame of
the speaker or to the chassis of the
vehicle.
(+)
(–)
(+)
(–)
Parallel Wiring
Series Wiring
2 ohms
Nominal
Impedance
Nominal
Impedance
8 ohms
Nominal
Impedance
Nominal
Impedance
4
ohms
4
ohms
4
ohms
4
ohms
6
GTH400-20107 06/03/98 15:49 Side 6
7
3.2 Typical Applications
The diagrams on pages 8 & 9 show
the most common basic system
configurations of the GTH400. One
or more of these building blocks may
be combined to form elaborate system
designs.
the most common basic system
configurations of the GTH400. One
or more of these building blocks may
be combined to form elaborate system
designs.
The GTH400 uses the terminology
“Group 1,” “Group 2” and “Group 3” to
indicate the three main signal paths
within the amplifier. Each “group” may
consist of a mono bridged signal or a
stereo pair of L+R signals depending
on the system configuration.
“Group 1,” “Group 2” and “Group 3” to
indicate the three main signal paths
within the amplifier. Each “group” may
consist of a mono bridged signal or a
stereo pair of L+R signals depending
on the system configuration.
R
L
R
L
–
+ –
+
–
+ –
+
L+
L–
R+
R–
L+
L–
L+
L–
R+
R–
R+
R–
–
+ –
+
Application 1
6-Channel Bi-Amplified System with
Non-Fading Subwoofers
Non-Fading Subwoofers
GTH400
GR 1
GR 2
GR 1
GR 2
GR 3
R
L
R
L
R
L
Front Speakers
Rear Speakers
Subwoofers
Group 1
Group 2
Group 3
Mode
Stereo
Stereo
Stereo
Group 2 Input
–
GR 2
–
Group 3 Input
–
–
GR 1+2
Speaker Crossover
High Pass
High Pass
Low Pass
Preamp Crossover
–
–
–
–
+
–
+
–
+
L+
L–
R+
R–
L+
L–
L–
R+
R–
R+
–
+ –
+
Application 2
5-Channel Bi-Amplified System with
Non-Fading Mono Subwoofer
Non-Fading Mono Subwoofer
R
L
R
L
Preamp or
Speaker-Level
Input
Front
Rear
R
L
R
L
GR 1
GR 2
GR 1
GR 2
GR 3
R
L
R
L
Preamp or
Speaker-Level
Input
Front
Rear
GTH400
Front Speakers
Satellite Speakers
Rear Speakers
Subwoofer
Group 1
Group 2
Group 3
Mode
Stereo
Stereo
L+R
Group 2 Input
–
GR 2
–
Group 3 Input
–
–
GR 1+2
Speaker Crossover
High Pass
High Pass
Low Pass
Preamp Crossover
–
–
–
R
L
R
L
GTH400-20107 06/03/98 15:49 Side 7
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