GTO 504 - JBL Car Audio Service Manual (repair manual). Page 5

Installation Warnings and Tips:
• Always wear protective eyewear when using tools.
• Disconnect the negative (–) lead from your vehicle’s

battery.

• 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.

• If the amplifier’s fuse must be replaced, use only 

the same type and rating as that of the original. 

• Choose a mounting location in the trunk or cargo

area where the amplifier will not be damaged by
shifting cargo. 

• Make sure there is sufficient air circulation at the

mounting location for the amplifier to cool itself.

• 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.

What’s in the Box?
(4) #8 x 2-1/2" Philips panhead screws for mounting

the amplifier

(2) 20A ATC-type fuses
(1) Owner’s Manual

Specifications
• 55W RMS x 4 channels @ 4 ohms and 

≤1% THD + N*

• 70W RMS x 4 channels @ 2 ohms and 

≤1% THD + N*

• THD+N: 0.02% (rated power @ 4 ohms)
• Signal-to-noise ratio: 90dBA 

(reference 1W into 4 ohms)*

• Signal-to-noise ratio: 105dBA 

(reference rated power into 4 ohms)

• Frequency response: 10Hz – 100kHz (–3dB)
• Max Power: 280 Watts
* CEA-2006A compliant

0 Speaker Output Connectors

• Connect the speakers to these terminals observ-

ing proper polarity.

• Four-channel operation: Connect the front left

speaker to the Front L+ and L– terminals, and
the front right speaker to the Front R+ and R–
terminals. Repeat for rear speakers using the
Rear R+ and R– terminals.

• Three-channel operation: Connect the stereo

speakers to the Front terminals as above.
Connect the single speaker into which the
amplifier’s rear channels will be bridged to the
Rear R+ and Rear L– terminals. 

• Two-channel (bridged) operation: Connect one

speaker to the Front R+ and Front L– termi-
nals. Connect the other speaker to the Rear
R+ and Rear L– terminals.

• Minimum speaker impedance for stereo opera-

tion is 2 ohms. Minimum speaker impedance for
bridged operation is 4 ohms.  

1 Fuses

• Replace only with same type and rating.

2 Power Input Connectors 

• +12V: Connect to the positive terminal of the

vehicle’s battery. 8 AWG wire is recommended.
Install an appropriate fuse holder and fuse (40A
minimum) within 18 inches of the battery. Make
sure the wire is not damaged or pinched during
installation. Install protective grommets when
routing wires through the firewall or other sheet
metal. 

• GND: Connect to the vehicle’s chassis. Clear

away the paint from the chassis location where
you will connect the ground wire. Use a ring 
terminal, tapping screw and star washer.

• REM: Connect to the “Remote Out” lead from

source unit or to a source of switched 12V+
(ACC).

3 Aux Output Connectors (RCA)

• Summed, nonfiltered pass-through output. 

Front right and rear right inputs are combined
and sent to the right AUX output. Front left 
and rear left inputs are combined and sent 
to the left AUX output. Connect to the input 
of an additional subwoofer amplifier. 

4 Front Input Connectors (RCA)

• Connect to front RCA outputs from the source

unit or signal processor.

5 Front Input-Level Control

• Used to match the front input level of the 

amplifier to the output level of the source unit.

• See F for adjustment procedure.

6 Front Crossover-Frequency Control

• 12dB/Octave crossover, variable from 

32Hz to 320Hz.

• See G for adjustment procedure.

7 Front Crossover-Filter Selector

• LPF – Select for subwoofer(s).
• Flat – Select for full-range speakers when 

no subwoofer will be used in the system.

• HPF – Select for midrange speakers or 

full-range speakers when a subwoofer is 
used in the system.

8 Rear Bass-Boost Control

• Set the Bass-Boost control according to your 

preference, being careful not to apply 
enough boost to damage your speaker(s).

9 Rear Crossover-Filter Selector

• LPF – Select for subwoofer(s).
• Flat – Select for full-range speakers when 

no subwoofer will be used in the system.

• HPF – Select for midrange speakers or 

full-range speakers when a subwoofer is 
used in the system.

A Rear Crossover-Frequency Control

• 12dB/Octave crossover, variable from 

32Hz to 320Hz 

• See adjustment procedure in G.

B Rear Input-Level Control

• Used to match the rear input level of the 

amplifier to the output level of the source unit.

• See 16 for adjustment procedure.

C Power On LED

• Illuminated when the amplifier is on.

D Protect LED

• Illuminated under any of the following fault 

conditions: Battery over/under voltage, short 
circuit in speaker wires, amplifier is too hot,
amplifier’s output circuit has failed (DC voltage
present in the amplifier’s output).

E Rear Input Connectors (RCA)

• Connect to rear RCA outputs from the source 

unit or signal processor.

F Setting Input Level

A Turn all Input-Level controls counterclockwise

to 6V (minimum).

B With a dynamic music track playing, turn head

unit’s volume control to the 3/4 position.

C Turn Front Input-Level control clockwise until

the music is so loud that it no longer sounds
clear (distortion is present in the output).

D Turn Front-Input-Level control counterclock-

wise gradually, just until the music sounds
clear, once again.

E Front-level input is now adjusted correctly.
F Adjust Rear Input-Level control so that the 

level of the rear speakers is proportionate to 
the level of the front speakers according to 
your preference.

G Setting the Crossover

A Crossover setting for 5" or larger full-range

speakers when no subwoofer is included in 
the system.

B Crossover setting for midrange and/or 

full-range speakers when a subwoofer 
is included in the system.

C Crossover setting for subwoofers.
Note: Acceptable frequency ranges indicated 
in gray.

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