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12

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

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
Balanced Line Driver capable of at least
4V nominal output should be used.

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.

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

rotary-type control, not one controlled
by electronic pushbuttons.

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 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).

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.

50Hz

47k 

Ω

1-23-750

80Hz

33k 

Ω

1-23-817

120Hz

22k 

Ω

1-23-820

200Hz

12k 

Ω

1-23-821

250Hz

10k 

Ω

1-23-810

375Hz

6.8k 

Ω

1-23-822

500Hz

4.7k 

Ω

1-23-815

650Hz

3.9k 

Ω

1-23-823

2.5kHz

1k 

Ω

1-23-824

5kHz

470 

Ω

1-23-816

150HMS

100K

150HMS

100K

SPEAKER

INPUT
IMPEDANCE

SELECTOR

LINE INPUT

PREAMP OUT

150HMS

100K

150HMS

100K

JUMPER SELECTOR

SELECT 100K OR 15 OHMS

GTH400-20107  06/03/98 15:49  Side 12

13

Regardless of whether you build or buy
it, the necessary resistor network has
the following configuration:

•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:

2,500,000

Frequency in Hz 

•Use the following equation if you have

a resistor pack of a known value, and
want to find its crossover frequency:

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
available, you may bend the leads of

1

⁄

4

-watt resistors 90 degrees, trim them

to 

1

⁄

8

"-length, and insert them directly

into the chip sockets.

To change the crossover frequency
change the resistor network as follows:

1. Remove the screws from the

bottom panel as shown below.

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.

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.

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.

The wired remote of the GTH400 can be
installed either in dash or under dash.

HIGH PASS

FILTER

FREQUENCY

SELECTION

MODULE

LOW PASS

FILTER

FREQUENCY

SELECTION

MODULE

C10

C13

JBL INC.

NORTHRIDGE, CA

JBL GTS600

PC00108800

REV A

CROSSOVER

GTH400-20107  06/03/98 15:49  Side 13

14

1. Set the GTH400 remote in the

installation location and mark two
mounting screw hole locations. 

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.

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.

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.

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.

4. Place the trim panel with the control

labeling over the two shafts and
secure it in place with the 4 screws
provided.

5. Push the two adjustment knobs

onto the metal shafts.

6. Connect one end of the GTH400

remote control wire (included) to the
connector on the back of the
remote control box.

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
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.

The power input and remote turn-on
wires are connected to the GTH400 via
the power connector on the end of the
amplifier.

•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

Front Speakers

Rear Speakers

Subwoofers

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.

GR 2

GR 1

GR 3

GR 2

GR 1

GTH400-20107  06/03/98 15:49  Side 14

15

FACE PLATE

DASH PANEL

SPACER
PLATE (INCLUDED)

FACE PLATE

Cassette/CD Tuner

CD Player

or Changer

CD Input

Cassette/CD Preamp Output

Antenna Input

Power
Antenna

Power

Antenna

Relay

Blue w/White Stripe - Remote On/Off

Main +12V

Power Ground

Chassis Ground

Vehicle Battery

–

+

Ignition Switch

Antenna

Motor

Power

Supply

Blue (Blue/White)

Remote On/Off

Remote Antenna

Black - Power Ground

Red - Main +12V

Yellow - Back Up Power

Fuse

Fuse

Fuse

Cassette/Receiver

Power Supply

Wires

Speakers

+

–

+

Speakers

+

–

+

Speakers

+

–

+

60 Amp

(Not Included)

Amplifier

Power

Connection

Amplifier
Speaker
Output
Connection

Amplifier
Speaker
Output
Connection

Amplifier
Speaker
Output
Connection

Amplifier

Speaker

Level

Inputs

Cassette/CD Tuner 
Speaker Level Output Connection
(Use only when line level ouput
is not available)

IMAGING ENHANCER

GTH400-20107  06/03/98 15:49  Side 15