JBL GTH400 20107 User Manual

GTH400-20107 06/03/98 15:49 Side 26  
GTH400-20107 06/03/98 15:49 Side 2  
Table of Contents  
1. Introduction...................................................................................... 3  
1.1 Features .................................................................................... 4  
1.2 About Installation ...................................................................... 4  
2. Installation and use.......................................................................... 5  
3. System Design with the GTH400..................................................... 6  
3.1 Speaker Requirements ............................................................. 6  
3.2 Typical Applications.................................................................. 7  
4. Installation and Use ......................................................................... 9  
4.1 Controls and Connectors.......................................................... 9  
4.2 Internal Adjustments................................................................ 12  
Speaker-Level Input Impedance Adjustments......................... 12  
Crossover Frequency Adjustments.......................................... 12  
Custom Chip construction....................................................... 13  
Remote Chassis Installation .................................................... 13  
Unter-Dash Remote Installation............................................... 14  
In-Dash remote Installation...................................................... 14  
Power Supply Connections ..................................................... 14  
Simultaneous Speaker Stereo-Mono Connection Diagram..... 16  
Speaker-Level Input Harness - Color Codes........................... 17  
5. Adjusting the Gain .......................................................................... 17  
6. Important Characteristics ............................................................... 19  
7. In Case of Difficulty......................................................................... 21  
8. Specifications ................................................................................. 23  
Owner’s Warranty Information  
Model Number  
Serial Number  
Dealer Name  
City, State, Zip  
Sales Receipt Number  
Date of Purchase  
GTH400-20107 06/03/98 15:49 Side 3  
In addition to conventional preamp-  
level inputs, the GTH400 features JBL’s  
Universal Interface design, which  
facilitates simple connection to factory  
radios with the low distortion that is  
usually only associated with preamp  
level connection. In addition, when  
using a high-powered (BTL) radio  
through the speaker-level inputs,  
Common Sense turn-on circuitry  
senses the common-mode voltage  
present on the radio’s speaker wires,  
turning the amplifier on without an  
additional remote wire.  
1. Introduction  
Thanks for purchasing your new GT  
series automotive multichannel ampli-  
fier. Your GT series amplifier will easily  
connect to virtually any car audio  
system, whether it is factory installed or  
one purchased separately. The GTH400  
includes an abundance of unique  
features which are described in this  
manual. The most obvious feature of  
the GTH400 is its 6-channel,  
staggered-power design. This design  
provides the simplicity of driving an  
entire system with a single amplifier  
without compromise. The flexible  
design of the GTH400’s built-in  
crossover circuitry also allows elaborate  
systems to be built more simply than  
with conventional components. For  
optimum performance, the power  
amplifier circuitry is a fully discrete  
design notable for its low distortion and  
unusually clean and clear sound quality.  
3
GTH400-20107 06/03/98 15:49 Side 4  
1.1 Features  
1.2 About Installation  
Theory of Operation –  
Virtual Center Image Enhancer  
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  
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  
installation be done by your  
authorized JBL dealer.  
If you choose to install the GTH400  
yourself, read all of the information in  
this manual before you start the  
installation. Pay particular attention to  
the safety precautions and notes.  
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.  
4
GTH400-20107 06/03/98 15:49 Side 5  
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.  
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.  
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!  
7. Install the remote control in the  
desired location. Connect and run  
the cable from the remote to the  
amplifier.  
8. Connect the speakers to the ampli-  
fier according to the Wiring Diagram  
on page 18.  
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.  
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.  
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  
13. Set the mode switches to Stereo,  
Left + Right, or Left Input Only  
operation for each group.  
14. Double-check your switch settings.  
Reconnect the negative battery  
cable. Note: Incorrect switch  
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.  
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.  
16. Adjust the amplifier gain controls  
using the procedure described in  
the “Adjusting the Gain” section  
(page 25).  
4. Mount amplifier in the desired  
location using the included screws.  
17. Read the rest of the manual to get  
maximum use and enjoyment from  
your amplifier.  
5. Connect power wiring as shown in  
the Wiring Diagram on page 18.  
5
GTH400-20107 06/03/98 15:49 Side 6  
When a group of the GTH400 is in  
bridged mode, the combined  
3. System Design Using  
the GTH400  
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  
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  
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.  
overheat, activating the protection  
circuits and causing the unit to shut off  
until it cools down sufficiently.  
Parallel Wiring  
(+)  
2 ohms  
Nominal  
4 ohms  
4 ohms  
Impedance  
(–)  
Series Wiring  
(+)  
4 ohms  
8 ohms  
Nominal  
Impedance  
4 ohms  
(–)  
6
GTH400-20107 06/03/98 15:49 Side 7  
3.2 Typical Applications  
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.  
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.  
Application 1  
6-Channel Bi-Amplified System with  
Non-Fading Subwoofers  
L
Front  
L
R
L
R
Preamp or  
Rear  
R
Speaker-Level  
Input  
Group 1  
Stereo  
Group 2  
Stereo  
GR 2  
Group 3  
Stereo  
R
L
GR  
1
GR  
2
Mode  
Group 2 Input  
Group 3 Input  
Speaker Crossover  
Preamp Crossover  
GR 1+2  
High Pass High Pass Low Pass  
GTH400  
GR  
1
GR  
2
GR  
3
+
+
+
L
L
L
L
L
L
R
+
R
R
+
R
R
+
R
+
+
+
+
+
+
L
R
L
R
L
R
Front Speakers  
Rear Speakers  
Subwoofers  
Application 2  
5-Channel Bi-Amplified System with  
Non-Fading Mono Subwoofer  
L
R
L
R
Preamp or  
Front  
L
Rear  
R
Speaker-Level  
Input  
Group 1  
Stereo  
Group 2  
Stereo  
GR 2  
Group 3  
L+R  
R
L
Mode  
GR  
1
GR  
2
Group 2 Input  
Group 3 Input  
Speaker Crossover  
Preamp Crossover  
GR 1+2  
High Pass High Pass Low Pass  
GTH400  
GR  
1
GR  
3
GR  
2
+
+
+
R
L
L
L
L
L
R
+
R
R
+
R
+
+
+
+
+
L
R
L
R
Front Speakers  
Rear Speakers  
Subwoofer  
Satellite Speakers  
7
GTH400-20107 06/03/98 15:49 Side 8  
Application 3  
4-Channel Full-Range or Bi-Amplified  
L
R
L
R
Preamp or  
Front  
Rear  
R
4-Channel Full-Range  
Speaker-Level  
Input  
Group 1  
L
Group 2  
Group 3  
Stereo  
GR 3  
Flat  
L
L
L
Input Mode  
Group 2 Input  
Group 3 Input  
L
GR 2  
Flat  
GR  
3
GR  
1
GR  
2
Speaker Crossover  
Preamp Output Crossover  
Flat  
GTH400  
4-Channel Bi-Amplified with  
GR  
1
GR  
2
GR  
3
+
R
+
R
+
L
L
L
L
Fading Mono Subwoofers  
R
+
R
Group 1  
Group 2  
Group 3  
L+R  
Input Mode  
L
L
GR 2  
Group 2 Input  
Group 3 Input  
GR 3  
Speaker Crossover  
Preamp Crossover  
High Pass High Pass Low Pass  
+
+
+
+
L
R
L
R
*Stereo subwoofers may also be used by selecting “ST”  
on the group 3 input mode switch.  
Front Speakers  
Rear Speakers  
or Subwoofer  
Note: Image Enhancement cannot be used in these applications.  
Application 4  
3-Channel Bi-Amplified  
L
R
L
L
R
Rear  
4-Channel Input (Fading Subwoofer)  
Front  
Use these when  
4-channel output  
is available.  
Group 1  
Group 2  
Group 3  
L+R  
L
L
R
Input Mode  
Group 2 Input  
Group 3 Input  
L
L
GR 2  
GR  
1
GR  
2
GR  
3
GR 3  
Speaker Crossover  
Preamp Output Crossover  
High Pass High Pass Low Pass  
GTH400  
2-Channel Input (Mono Subwoofer)  
GR  
1
GR  
2
GR  
+
R
3
+
R
+
R
L
L
L
Group 1  
Group 2  
Group 3  
L+R  
Input Mode  
Group 2 Input  
Group 3 Input  
L
L
GR 2  
GR 1+2  
Speaker Crossover  
Preamp Crossover  
High Pass High Pass Low Pass  
Note: Image Enhancement cannot be used in these applications.  
L
R
Main Speakers  
Subwoofer  
8
GTH400-20107 06/03/98 15:49 Side 9  
10. Gain Controls – Use these controls  
to adjust the gain of the amplifier  
channel group. See the “Adjusting  
the Gain” section (on page 25) for  
tips on proper setup.  
4. Installation and Use  
4.1 Controls and Connectors  
1. Preamp-Level Input Connector –  
Use these connectors for line (pre-  
amp) level inputs to the amplifier.  
11. Preamp Crossover Switches – These  
switches control the built-in cross-  
overs that are directed to the  
2. Preamp-Level Output Connector –  
Use these outputs to send  
signal to additional amplifiers.  
preamp-output connectors. Set the  
switch to F (flat) for full-band  
3. Speaker-Level Input Connector –  
Use this connector for speaker level  
input signals. A wire harness is  
supplied for use with this  
operation for that group. Set the  
switch to L (low) to activate the low-  
pass filter on the pre-amp output  
group (for subwoofer use or to use  
in conjunction with a high-pass  
filtered input signal to create a  
bandpass crossover for a midrange  
or midbass driver). Set the switch to  
High-Pass to activate the high-pass  
filter for use with satellite speakers  
or tweeters on the pre-amp output  
group.  
connector. See “Audio Input  
Connections” section (page 23) for  
wiring instructions. This input also  
includes JBL’s Common Sense  
input circuitry which turns the  
amplifier on as soon as the high  
powered head unit connected to  
this input is turned on.  
4. Speaker Output Connectors –  
Connect speaker wiring to these  
connectors. See wiring directions  
for more information.  
12. Speaker Crossover Switches –  
These switches control the built-in  
crossovers that are connected to  
each group's power amplifier cir-  
cuitry. Set the switch to F (flat) for  
full band operation on a group. Set  
this switch to L (low) to activate the  
low-pass filter on the selected  
5., 6., 7., 8. Power Connector –  
Connection for power wires. See  
wiring directions for information on  
proper connections.  
9. Fuses – Two 30 Amp ATC type  
fuses.  
amplifier group for subwoofer use or  
9
GTH400-20107 06/03/98 15:49 Side 10  
to use in conjunction with a high-  
pass filtered input signal to create a  
bandpass crossover (for a midrange  
or midbass driver). Set the switch to  
H (high) to activate the high-pass  
filter for use with satellite speakers or  
tweeters on an amplifier group.  
non-fading subwoofer output on  
Group 3.  
17. Remote Bypass/On Indicator – This  
indicator is on when the Imaging  
Enhancer is engaged and off when  
the Imaging Enhancer is bypassed.  
18. Driver/All Optimizer Indicator – This  
indicator is on when the Virtual Center  
Channel circuitry is in “Driver” opti-  
mization mode and off when it is in  
the “All” passenger mode. Note: The  
enhancer on indicator must be on  
before driver’s mode can enabled.  
13. Mode Switches – These switches are  
used to set the input mode for both  
preamp and speaker-level inputs.  
Set the switch to ST(ereo) for normal  
operation on the group using  
individual left and right inputs. Set  
this switch to L to drive both the left  
and right outputs with only a single  
input on the left jack. Set the switch  
to L+R to sum the left and right  
inputs for a mono output on the  
group. These switches do not affect  
the preamp outputs.  
19. Front Ambience Control and  
On/Bypass Switch – Rotating this  
control adjusts the amount of  
ambience and front staging width  
produced by the Imaging Enhancer.  
Pulling the knob places the Imaging  
Enhancer in Bypass” mode.  
14. Bass EQ Switch – These switches  
activate a built-in Bass Boost circuit  
used to increase low-bass output on  
the selected group. These switches  
do not effect the preamp outputs.  
Pushing in the knob places the  
Imaging Enhancer in On” mode.  
20. Rear Ambience and Driver/All  
Optimizer Control – Rotating this  
knob controls the amount of rear-fill  
ambience and the “room size” of the  
acoustic environment when used in  
a system with rear speakers. Pulling  
the knob out places the Imaging  
Enhancer in All” passengers opti-  
mization mode. Pushing the knob in  
places the unit in “Driver” optimizati-  
on mode. Best results at the driver’s  
position will be achieved with the  
control in the “Driver” setting.  
15. Group 2 Input Switch – This switch is  
used to select which inputs will drive  
Group 2 of the amplifier. Put the  
switch in position “GR 1” to allow  
Group 2 to be driven by the Group 1  
inputs. Put the switch in the “GR 2”  
position to drive Group 2 with the  
Group 2 inputs.  
16. Group 3 Input Switch – This switch is  
used to select which inputs will drive  
Group 3 of the amplifier. Put the  
IMAGING ENHANCER  
ENHANCER ON  
FRONT AMBIENCE  
NHANC  
DRIVER MODE  
REAR AMBIENCE  
DRIVE  
switch in position “GR 3” to allow  
Group 3 to be driven by the Group 3  
inputs. Put the switch in the “GR 2”  
position to drive Group 3 with the  
Group 2 inputs. Put this switch in the  
GR 1+2” position to drive Group 3  
with the sum of Group 1 and 2 for a  
17  
19  
18  
20  
E
ER  
R
ON  
BYPASS  
ALL  
MIN  
MAX  
MIN  
MAX  
Power Indicator LED (on amp chassis  
top) – LED steadily illuminates for normal  
operation. LED blinks when protection  
circuitry or muting is engaged.  
10  
GTH400-20107 06/03/98 15:49 Side 11  
B A S S B O O S T  
B A S S B O O S T  
B A S S B O O S T  
C H . 2 R O U T  
C H . 2 L O U T  
C H . 1 R O U T  
C H . 1 L O U T  
C H . 2 R I N  
C H . 2 L I N  
C H . 1 R I N  
C H . 1 L I N  
11  
GTH400-20107 06/03/98 15:49 Side 12  
4.2 Internal Adjustments  
rotary-type control, not one controlled  
by electronic pushbuttons.  
Speaker-Level Input  
Impedance Adjustments  
If you are not certain of the type of  
fader control your unit has, measure the  
resistance across one set of speaker  
outputs with an ohmmeter (with the  
head-unit off). Adjust the fader control  
through its entire adjustment range. If  
there is a change in the resistance as  
the control is adjusted, set the jumpers  
to the 15-ohm position. (See step 1,  
page 16 to remove bottom cover.)  
The speaker level inputs of the GTH400  
come factory set with 100k ohm input  
impedance. This will provide the lowest  
distortion operation from the speaker  
outputs of most modern head units by  
reducing the power the amplifier in the  
head unit must deliver to practically  
nothing. On some older, or lower-priced  
head units, this load will not facilitate  
proper fader operation. To allow for  
this, we have provided the ability to  
change the input impedance of the  
speaker-level inputs to 15 ohms. This is  
accomplished by moving the jumpers  
Crossover Frequency Adjustments  
The GTH400 amplifiers include built-in  
frequency selectable crossovers. One  
crossover is connected in series with  
the amplifier circuitry and the other  
crossover is connected to the preamp  
level output jacks. These crossovers  
can be set in either the F (full bandwidth  
operation), L (subwoofer operation), or  
H (satellite operation).  
JUMPER SELECTOR  
SELECT 100K OR 15 OHMS  
100K  
150HMS  
The crossover frequencies are set by  
chips inside the amplifier. These chips  
are simply a set of resistors, connected  
across the pins and molded into a  
single package. The crossover  
frequencies may be changed to any  
value desired by changing the resistor  
network.  
100K  
L I N E I N P U T  
SPEAKE  
R
INPUT  
150HMS  
IMPEDANC  
SELECTO  
E
R
100K  
P R E A M P O U T  
150HMS  
100K  
150HMS  
shown on the diagram above. This in-  
put is also capable of directly accepting  
signals, when in the 100k ohm setting,  
from many Balanced Line Drivers such  
as those sometimes used in competi-  
tion vehicles. For best results, a  
Frequency Resistor  
Value  
JBL Part  
Number  
Balanced Line Driver capable of at least  
4V nominal output should be used.  
50Hz  
80Hz  
47k  
33k Ω  
22k Ω  
12k Ω  
10k Ω  
6.8k Ω  
4.7k Ω  
3.9k Ω  
1k Ω  
1-23-750  
1-23-817  
1-23-820  
1-23-821  
1-23-810  
1-23-822  
1-23-815  
1-23-823  
1-23-824  
1-23-816  
If the head unit has 4 channels of built-  
in amplification and/or an electronic  
fader control, you should leave the  
jumpers in the factory set position.  
120Hz  
200Hz  
250Hz  
375Hz  
500Hz  
650Hz  
2.5kHz  
5kHz  
If the head unit has 2 channels of  
amplification, with a speaker-level  
fader, the jumpers should be set to the  
15-ohm position. This will always be a  
470 Ω  
12  
GTH400-20107 06/03/98 15:49 Side 13  
Custom Chip Construction  
1. Remove the screws from the  
bottom panel as shown below.  
Regardless of whether you build or buy  
it, the necessary resistor network has  
the following configuration:  
2. Select which resistor module, high  
pass or low pass, that you wish to  
change.  
3. A chip puller, which can be  
obtained from any electronics store,  
is recommended to remove the  
resistor chip. Pull the resistor chip  
from the socket as shown in the  
figure below.  
• Each resistor in the package has the  
same value.  
• If you know the crossover frequency  
you want, you can calculate the  
resistor value necessary by solving the  
following equation:  
Resistor  
Value  
in ohms  
2,500,000  
Frequency in Hz  
=
JBNC.  
REV  
JBL GTS600  
NOHRIDGE, CA  
A
PC00108800  
FILTER  
LOW PASS  
CROSSOVER  
FREQUENMCOYDULE  
SELECTION  
C10  
• Use the following equation if you have  
a resistor pack of a known value, and  
want to find its crossover frequency:  
C13  
FILTER  
HIGH PASS  
FREQUENMCOYDULE  
SELECTION  
4. Place the new module in the socket  
making sure all pins are lined up  
with the socket holes. Press the  
module firmly into the socket.  
Frequency  
in Hz  
2,500,000  
Resistor Value  
in ohms  
=
• To build chips from discrete resistors,  
solder the resistors to a standard 14-  
pin “DIP Header” according to the  
diagram. If a DIP Header is not  
5. Replace the bottom lid.  
For further information on how to use  
the speaker output and preamp output  
crossovers for system building see the  
Typical Applications” and “Add-On  
and Upgrade Steps” sections.  
available, you may bend the leads of  
1
4-watt resistors 90 degrees, trim them  
to 18"-length, and insert them directly  
into the chip sockets.  
Remote Chassis Installation  
The wired remote of the GTH400 can be  
installed either in dash or under dash.  
To change the crossover frequency  
change the resistor network as follows:  
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GTH400-20107 06/03/98 15:49 Side 14  
Under-Dash Remote Installation  
remote control wire (included) to the  
connector on the back of the  
remote control box.  
1. Set the GTH400 remote in the  
installation location and mark two  
mounting screw hole locations.  
7. Run the wire back to the GTH400  
main chassis and plug the remote  
control wire into the “Remote In”  
connector on the main chassis.  
Note: a standard 6-pin telephone  
extension cord may be used if more  
wire is needed for remote control  
connection. These extension cords  
can be purchased at many  
2. Set the GTH400 remote aside and  
drill two pilot holes using a 1⁄16"-  
(1mm) bit. Be careful not to drill into  
any of the car’s components.  
3. Secure the spacer and faceplate  
(with the control labeling) to the  
front of the remote control panel  
using the four smaller screws  
included.  
electronics or hardware stores.  
In countries with Right Hand Drive  
vehicles, the built-in Image Enhancer  
will not operate properly with standard  
wiring. To use the GTH400 with right  
hand drive vehicles, reverse both the  
input and output wiring as shown  
below.  
4. Push the two adjustment knobs  
onto the metal shafts.  
5. Set the GTH400 remote back in  
place and secure it using two sheet  
metal screws. Continue to Step 6 in  
the “In-Dash Installation” section.  
In-Dash Remote Installation  
GTH400 Audio Signal Connection  
for Right Hand Drive Cars  
1. Choose a location for the in-dash  
installation and use the template at  
the back of this manual to mark  
hole locations as shown on the  
template.  
GTH400  
Front  
Rear  
L
R
Group 1  
Group 2  
L
R
2. Drill the holes indicated on the  
template.  
3. Using the diagram on page 15 as  
reference, install the remote behind  
the panel with the holes just drilled.  
Position the remote so the two  
knobs feed through panel and the  
LEDs are in alignment with the  
holes drilled.  
The right and left inputs and outputs of the GTH400  
must be reversed for proper functioning of the virtual  
center image enhancer when used in a right hand  
drive automobile.  
Power Supply Connections  
The power input and remote turn-on  
wires are connected to the GTH400 via  
the power connector on the end of the  
amplifier.  
4. Place the trim panel with the control  
labeling over the two shafts and  
secure it in place with the 4 screws  
provided.  
+12V Battery Wire  
• Connect a wire directly from the +12  
volt terminal of the battery to the +  
Battery terminal on the amplifier. Use  
a minimum of AWG #8. Use wire that  
5. Push the two adjustment knobs  
onto the metal shafts.  
6. Connect one end of the GTH400  
14  
GTH400-20107 06/03/98 15:49 Side 15  
FACE PLATE  
DASH PANEL  
FACE PLATE  
SPACER  
PLATE (INCLUDED)  
Cassette/CD Tuner  
Speaker Level Output Connection  
(Use only when line level ouput  
is not available)  
CD Player  
or Changer  
Cassette/CD Tuner  
Antenna Input  
CD Input  
Amplifier  
Speaker  
Level  
Power  
Antenna  
Cassette/Receiver  
Power Supply  
Inputs  
Wires  
Power  
Antenna  
Relay  
Amplifier  
Amplifier  
Power  
Cassette/CD Preamp Output  
Speaker  
Output  
Connection  
Connection  
+
Speakers  
Blue w/White Stripe - Remote On/Off  
Amplifier  
IMAGING ENHANCER  
+
+
Speaker  
Output  
Ignition Switch  
Connection  
60 Amp  
(Not Included)  
Fuse  
Speakers  
Main +12V  
+
Amplifier  
+
+
Speaker  
Output  
Vehicle Battery  
Connection  
Power Ground  
+
Speakers  
Chassis Ground  
15  
GTH400-20107 06/03/98 15:49 Side 16  
is heat- and oil-resistant whenever  
running wires through the engine  
compartment. All wire-to-wire  
connections should be soldered and  
insulated with heat shrink tubing, or  
connected through a high-quality  
insulated crimp-on connector or  
secure set-screw-type terminal  
blocks. Never leave bare wire  
exposed. Terminate wires with crimp-  
or solder-on lug terminals whenever  
appropriate.  
Simultaneous Stereo-Mono  
Connection Diagrams  
Subwoofer (Low-Pass)  
A. Satellite/Subwoofer  
(–)  
(+)  
High Pass Satellite  
Crossover Frequency: 100Hz  
Tweeter/Midrange Satellites  
(High Pass)  
Left  
Right  
C: 300µF capacitor  
100V, non-polorized  
(–)  
(+)  
C
(+)  
C
(–)  
L
Subwoofer Lowpass  
Crossover Frequency: 100Hz  
L: 6.2mH air core inductor  
GTH400  
SPEAKER LEVEL  
INPUTS  
SPEAKER OUTPUTS  
POWER  
L
1
R
L
2
R
L
3
R
REM IN  
REM OUT  
R
2
L
+
+
+
+
+
+
LINE LEVEL INPUTS  
PREAMP OUTPUTS  
2
+
+
FUSE  
30A  
FUSE  
30A  
1
2
3
1
3
L
R
+
+
+
L
R
1
_
_
_
_
BATT(+)  
GND  
*You may change the subwoofer satellite crossover frequency by using the  
Inductor and Capacitor values calculated with the following formulas:  
30,000  
High-Pass (Satellite Crossover):  
Low-Pass(Subwoofer Crossover):  
= New Capacitor Value in µF  
Desired crossover Frequency in Hz  
620  
= New Inductor Value in mH  
Desired crossover Frequency in Hz  
Center Channel  
Bridged Speaker Connection*  
B. Center Channel  
( – )  
( + )  
8 Minimum  
8 L-Pad  
(Optional but Recommended)  
GTH400  
SPEAKER LEVEL  
INPUTS  
SPEAKER OUTPUTS  
POWER  
L
1
R
L
2
R
L
3
R
REM IN  
REM OUT  
R
2
L
+
+
+
+
+
+
LINE LEVEL INPUTS  
2
PREAMP OUTPUTS  
2
+
+
FUSE  
30A  
FUSE  
30A  
1
3
1
3
L
R
+
+
+
L
R
1
_
_
_
_
BATT(+)  
GND  
* Center Channel Speaker Minimum 8 Ohms, Main  
Speakers Minimum 4 Ohms When Used Simultaneously.  
( + )  
4Minimum  
( – )  
( – )  
( + )  
Stereo, Non-Bridged  
Speaker Connection*  
4Minimum  
16  
GTH400-20107 06/03/98 15:49 Side 17  
• The GTH400 will draw as much as 60  
amps from the vehicle’s electrical  
system, enough to overload  
conventional vehicle wiring. Therefore  
the +12 volt power supply must be  
taken directly from the positive side of  
the battery.  
Speaker-Level Input Harness  
Color Codes  
Group 1 Left (+):  
Group 1 Left (–):  
White  
White with  
Black Stripe  
Group 1 Right (+): Gray  
Do not connect to the vehicle’s fuse  
block or to a wire feeding other  
accessories.  
Group 1 Right (–): Gray with  
Black Stripe  
Group 2 Left (+):  
Group 2 Left (–):  
Green  
• To prevent electrical system damage  
or fire, a fuse holder and fuse (not  
included – maximum 60 Amp) must be  
installed in the power supply wire as  
close to the battery as possible, and  
before the wire travels through the  
firewall or other metal panel.  
Green with  
Black Stripe  
Group 2 Right (+): Purple  
Group 2 Right (–): Purple with  
Black Stripe  
5. Adjusting the Gain  
Ground Wire  
Before operating the GTH400, recheck  
all wiring connections to make sure they  
are correct and secure. Be sure that a  
fuse (60 amps, not included) is installed  
in the +12V line near the battery.  
Reconnect the negative ground (–)  
terminal of the battery. Make sure that  
the mode switches, crossover switches,  
Group 2 & 3 Input switches, and  
crossover frequency modules, are  
properly set.  
• Proper grounding is extremely  
important. Use a heat- and oil-  
resistant stranded copper automotive  
wire equivalent to the size used for the  
+12V connection. Crimp or solder and  
insulate any wire-to-wire connections.  
Keep the ground wire as short as  
possible. A ground wire must be  
solidly connected to a major sheet  
metal structure of the vehicle such as  
a panel near the amp-mounting  
location. Scrape all paint and primer  
off the sheet metal at the grounding  
point to ensure a good electrical  
connection. Attach the wire to the  
grounding point with a nut, bolt and  
star washer. The high current  
• The setting of the gain controls on the  
GTH400 is important to ensure proper  
performance, low noise levels, and  
maximum reliability in the system. As a  
general rule, controls on components  
at the front-end of the system (source,  
equalizers, electronic crossovers, etc.)  
should be set as high as possible, with  
the amplifier gain control set as low as  
possible while still providing adequate  
volume levels. Using a high signal level  
from the source and a low gain setting  
on the amplifier will help keep  
demanded by high-powered amplifiers  
requires a more secure ground than  
the typical sheet-metal screw will  
provide.  
The color code for the speaker-level  
input harness is as follows:  
17  
GTH400-20107 06/03/98 15:49 Side 18  
background noise levels in the system  
low.  
the head unit’s volume control to a  
comfortable level, and adjust the  
remaining channels for the desired  
system balance. You will find this  
easiest to do by adjusting the  
• To adjust a system using a single  
GTH400, start with all three of the  
amplifier gain controls fully  
channels in the following order: 1)  
front speaker Group, 2) rear speaker  
Group, 3) subwoofer speaker Group.  
Elaborate systems incorporating tri- or  
quad-amplification can be complex to  
adjust. Your local authorized JBL  
installation specialist is the best  
person to help with such adjustment.  
counterclockwise and the Imaging  
Enhancer Remote set to Bypass”  
mode. Some head units have  
additional output level controls or  
switches. Set those to their maximum  
position.  
• Set the level controls on any  
associated equipment such as  
equalizers and electronic crossovers  
as recommended by their  
Imaging Enhancer Setup  
After the installation and set up is  
finished and all wiring is checked,  
proceed with the next few steps to set  
up the Imaging Enhancer on the  
GTH400.  
manufacturers. Set all Bass/ Treble or  
equalizer controls to their centered or  
bypassed positions. While listening  
carefully to the system output, adjust  
the volume control of the radio/tape  
deck to the point where you first begin  
to hear audible distortion. Use caution:  
excessive distortion can damage  
loudspeakers. Reduce the level just to  
the point where the distortion goes  
away. This is the maximum  
undistorted output level of your head  
unit and signal processors, and should  
not be exceeded during use. If audible  
distortion does not occur, continue to  
increase the level until the head unit is  
turned all the way up. If this setting  
does not provide adequate volume  
levels, gradually increase (turn  
Note: Since the Imaging Enhancer in  
the GTH400 is primarily designed to  
optimize the sound stage for the driver,  
all tests should be performed while  
sitting in the driver’s seat.  
1. The Power Indicator LED on the  
GTH400 main chassis should light  
up when the head unit is turned on.  
2. Make sure the “Front-Ambience/  
Bypass/On” knob and “Rear-  
Ambience/Driver/All” knobs are  
pushed in and rotated completely  
counterclockwise.  
3. Play a selection which has vocals  
and good “center” information.  
clockwise) the gain control for the  
main (usually front) speaker groups on  
the GTH400 until the system plays as  
loud as necessary or when the first  
signs of distortion are heard.  
4. Gently turn up the volume to a  
comfortable listening level. You  
should hear a very distinctive center  
image coming from the middle of  
your dashboard. If not, make sure  
the “Rear-Ambience/Driver/All”  
knob is pushed in to the “Driver”  
• After adjusting the main speaker’s  
gain control, you may then turn down  
18  
GTH400-20107 06/03/98 15:50 Side 19  
position for driver-optimized sound  
stage.  
systems with rear speakers). You  
should begin to hear an increase in  
reverberation and get a feeling of  
being in a very large auditorium.  
Note: The GTH400 converts the  
rear channels into true rear-fill  
surround channels which cancel  
all center information (vocals, lead  
instruments, etc.) and lets only true  
ambience information come out.  
This same process is used in more  
expensive Surround Sound”  
5. Proceed to push and pull the Rear-  
Ambience knob to hear the effects  
of “Driver” and “All” modes. You  
should hear imaging coming from  
the middle of the dashboard when  
the knob is pushed in (Driver”  
mode). You should hear stereo with  
ambience recovery when the knob  
is pulled out (All” mode). If you find  
that the center imaging in the  
Driver” position is slightly offset to  
the left or right side of the  
systems used in theaters.  
8. Adjust the front and rear ambience  
as desired. For optimum center  
imaging, it is recommended that  
ambience be used sparingly on the  
front channels.  
dashboard, switch the car-size  
switch located inside of the  
GTH400 under the bottom cover as  
shown below. This switch optimizes  
the Imaging Enhancer for standard  
or large cars.  
9. To bypass the effects of the  
Imaging Enhancer in the GTH400,  
simply pull on the “Front-  
IMAGING ENHANCER  
Ambience” knob until it clicks to the  
“Bypass” position. The “Enhancer  
On” LED on the remote control  
panel will turn off and your sound  
system should revert back to  
normal stereo sound without  
ambience enhancement. The  
Imaging Enhancer is also bypassed  
when the remote control is  
REMOTE PLUG  
FRONT  
PLATE  
Imaging Enhancer  
Car Size Switch  
IMAGE  
ENHANCER  
MODULE  
Standard  
Large  
unplugged from the amplifier.  
6. Slowly turn the “Front-Ambience”  
knob in the clockwise direction to  
increase ambience. You should  
begin to hear slight reverberation in  
the music and a sense of a  
6. Important Characteristics  
Overload Protection – The GTH400  
incorporates elaborate protection cir-  
cuitry to prevent damage to the  
amplifier circuitry and ensure reliable  
operation. This circuitry will turn the  
amplifier off in the event of overheating,  
a short circuit on the speaker output  
wiring, or improper power supply  
connections. If the amplifier cycles on  
widening front sound stage in both  
the “Driver” and “All” modes.  
7. Slowly turn the “Rear-Ambience”  
knob in the clockwise direction to  
increase rear ambience (only in  
19  
GTH400-20107 06/03/98 15:50 Side 20  
and off, or does not work at all, a  
problem in installation or an abnormal  
electrical condition is indicated. Check  
speaker wiring for short circuits or  
impedance loads significantly below 2  
ohms (4 ohms in bridged mode). Check  
the power supply voltage at the input of  
the amplifier to be sure that it is normal;  
between 11 and 16 volts. Check that  
the power wires are not reversed.  
20  
GTH400-20107 06/03/98 15:50 Side 21  
7. In Case of Difficulty  
Power-on light does not come on  
• Head unit not on; turn the head unit on.  
• Ground wire is disconnected or  
defective; check for continuity with an  
ohmmeter between the amplifier’s  
ground terminal and a known chassis  
ground point.  
• Battery wire is disconnected or  
defective; check for approximately +12  
volts between the amplifier’s battery and  
ground terminals.  
• Blown fuse; check amplifier’s fuses  
located on the end panel near the power  
connector. If they are blown, replace  
them with an identical one. If the new  
fuses blow immediately, then check all  
the wiring connections. If no fault is  
found, consult your JBL dealer.  
• Remote-on wire between the head unit  
and the amplifiers is disconnected or  
defective; check for +12 volts between  
amplifiers remote-on input terminal and  
the ground wire with the head unit on.  
Power light is on, but no sound is heard  
from some or all of the speakers  
• Incorrect switch settings; make sure  
that all switches (mode, input and  
crossover) are in their correct positions  
for your system configuration.  
• Incorrectly connected or shorted  
speaker wires; check for shorts in  
wiring.  
• Defective or disconnected audio cables;  
check for continuity and replace if  
necessary.  
• Incorrect gain adjustment; verify that the  
amplifier gain controls are not turned  
completely down. If they are, sound  
output level may be very low and may  
give the impression that the system (or  
part of the system) is dead.  
21  
GTH400-20107 06/03/98 15:50 Side 22  
Power light is on, but no sound is heard  
from some or all of the speakers  
• Defective head unit or signal processor;  
check each component for proper wiring  
and operation.  
• Defective GTH400; If there is audio  
signal present at the inputs of the  
amplifier and there is no output, the  
GTH400 may be defective.  
Alternator whine through the audio system • Ground loops; follow the wiring  
with the engine running  
suggestions in the section called  
Solving Noise Problems.” Also, verify  
that the chassis grounding point you  
have chosen is true ground by checking  
for continuity between the chassis  
ground point and battery ground.  
Bass output from speakers too low  
• Speaker wired out of phase; check for  
proper polarity on all speaker wiring  
(+ amp terminal to + speaker terminal  
and – amp terminal to – speaker  
terminal).  
Amplifier Power Light is on and  
• Verify that the remote control is not set  
in BYPASS” mode by checking to see  
that the “ON” LED is lit.  
sound is heard from the front and rear  
channels but the Imaging is not improved  
with the image enhancer on  
• Using the system configuration diagram,  
confirm that the audio connections are  
correct for signal path and polarity. Note  
that right hand drive car installations  
must have the Left and Right input and  
output connections reversed as shown in  
the wiring section on page 19.  
• Perform the adjustments as directed in  
the Imaging Enhancer Setup section.  
Power light is blinking and  
no sound is heard  
• Incorrectly connected or shorted speaker  
wires; check for shorts in wiring.  
• Defective GTH400; if there is no short  
on the speaker outputs, the GTH400  
may be broken. Consult your JBL dealer.  
22  
GTH400-20107 06/03/98 15:50 Side 23  
8. Specifications  
GTH400  
35 Watts x 4 + 70 Watts x 2 (4 ohms, 0.05% THD)  
50 Watts x 4 + 100 Watts x 2 (2 ohms, 0.08% THD)  
100 Watts x 2 (Bridged 4 ohms, 0.08% THD) +  
70 Watts x 2 (4 ohms, 0.05% THD)  
100 Watts x 2 (Bridged 4 ohms, 0.08% THD) +  
200 Watts x 1 (Bridged 4 ohms, at 0.08% THD)  
Signal to Noise Ratio  
Frequency Response  
100dBA  
10Hz – 50kHz (+0, –1dB)  
20Hz – 20kHz (+0, –0.1dB)  
Damping Factor  
Slew Factor  
>200  
>5  
Line Level Input Sensitivity  
(For Rated Power)  
100mV – 4V RMS  
Line Level Input Impedance  
10k ohms  
Speaker Level Input Impedance  
15 ohm or 100k ohm  
(Selectable by Internal Jumpers)  
Speaker Level Input Sensitivity  
200mV – 8V RMS  
Preamp Output Sensitivity  
Preamp Input:  
4V in for 4V out  
4V in for 2V out  
Speaker Input:  
Minimum Speaker Impedance  
Single Ended (Non-Bridged)  
2 ohms  
4 ohms  
Bridged  
Built-in Electronic  
Crossover Frequency and Slope  
18dB per Octave Low-Pass Filter,  
Frequency Chips Available from 50–5kHz  
Factory Setting 80Hz  
18dB per Octave High-Pass Filter,  
Frequency Chips Available from 50–5kHz  
Bass Boost Frequency  
and Magnitude  
+4dB at 40Hz  
23  
GTH400-20107 06/03/98 15:50 Side 24  
Power Requirement  
Fuse Size  
11 to 16V DC Negative Ground  
30 Amp ATC Type Fuse (2 per Amplifier)  
15-1/4" x 11-1/4" x 2" (387mm x 286mm x 51mm)  
13 lbs 4 oz (6 kg)  
Size (L x W x H)  
Weight  
Speaker Level Input  
Mating Connector  
Molex Mini-Fit Jr  
#39-01-2080  
Metal Pins: 39-00-0038  
Remote Control Drilling Template  
9/64" (3.5mm) in 4 places  
9/64" (3.5mm) in 2 places  
UP  
UP  
25/64" (10mm) drill in 2 places  
24  
GTH400-20107 06/03/98 15:50 Side 25  
Staple or clip your original bill of sale here.  
25  

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