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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.

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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 

• Incorrect switch settings; make sure 

from some or all of the speakers

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.

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Power light is on, but no sound is heard

• Defective head unit or signal processor; 

from some or all of the speakers

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

sound is heard from the front and rear

in “BYPASS” mode by checking to see

channels but the Imaging is not improved

that the “ON” LED is lit.

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

• Incorrectly connected or shorted speaker

no sound is heard

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.

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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

100dBA

Frequency Response

10Hz – 50kHz (+0, –1dB)
20Hz – 20kHz (+0, –0.1dB)

Damping Factor

>200

Slew Factor

>5

Line Level Input Sensitivity

100mV – 4V RMS 

(For Rated Power)

Line Level Input Impedance

10k ohms

Speaker Level Input Impedance

Speaker Level Input Sensitivity

200mV – 8V RMS 

Preamp Output Sensitivity

Preamp Input:

4V in for 4V out

Speaker Input:

4V in for 2V out

Minimum Speaker Impedance 
Single Ended (Non-Bridged)  

2 ohms

Bridged

4 ohms

Built-in Electronic 

18dB per Octave Low-Pass Filter, 

Crossover Frequency and Slope

Frequency Chips Available from 50–5kHz 
Factory Setting 80Hz

18dB per Octave High-Pass Filter, 
Frequency Chips Available from 50–5kHz

Bass Boost Frequency 

+4dB at 40Hz

and Magnitude

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