1718.1KB PDF - JBL.com

car audio 

power amplifier 

owner’s manual 

THANK YOU 

for purchasing a JBL A6000GTi or A3000GTi amplifier. 

For warranty support, please register your purchase at 

www.jbl.com. Select Car Audio, then click on Support, 

and then click on Product Registration. Also, please 

retain your original purchase receipt and packing crate 

in case you must ship your unit back for service.

INSTALLATION 

WARNING: Playing loud music 

in an automobile can hinder your 

ability to hear traffic and permanently 

damage your hearing. We recommend 

listening at low or moderate levels 

while driving your car. JBL accepts 

no liability for hearing loss, bodily 

injury or property damage resulting 

from the use or misuse of this product. 

IMPORTANT: To get the best 

performance from your JBL A6000GTi 

or A3000GTi amplifier, we strongly 

recommend that installation be 

entrusted to a qualified professional. 

Although these instructions explain 

how to install JBL amplifiers in a 

general sense, they do not show 

specific installation methods that may 

be required for your particular vehicle. 

If you do not have the necessary tools 

or experience, do not attempt the 

installation yourself. Instead, please 

ask your authorized JBL car audio 

dealer about professional installation. 

INSTALLATION 

WARNINGS AND TIPS 

• Always wear protective eyewear 

when using tools. 

•Turn off all audio components and 

other electrical devices before you 

start. Disconnect the (–) negative 

lead from your vehicle’s battery. 

• Check clearances on both sides of 

a planned mounting surface before 

drilling holes or installing screws. 

Remember – the screws can extend 

behind the surface. 

• 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. 

• Before drilling or cutting holes, use 

a utility knife to remove unwanted 

fabric or vinyl to keep material from 

snagging in a drill bit. 

• When routing cables, keep inputsignal 

cables away from power 

cables and speaker wires. Use 

grommets when passing cables 

through the vehicle’s inner walls. 

• When making connections, observe 

the amplifier’s polarity markings. 

Make sure that each connection 

is clean and properly secured. Use 

the shortest ground wire possible 

to minimize resistance and avoid 

noise problems. 

• If the amplifier’s fuse must be 

replaced, use only the same type 

and rating as that of the original. 

Do not substitute another kind. 

CHOOSING A 

MOUNTING LOCATION 

The JBL A6000GTi and A3000GTi 

amplifiers are big! Conventional 

mounting locations under driver or 

passenger seats will not accommodate 

either amplifier. Mount the amplifier in 

the vehicle’s trunk or cargo area, but 

never mount the amplifier in the engine 

compartment, outside the vehicle or 

in any location where it may get wet. 

When choosing a location, make sure 

the site’s underlying structure is strong 

enough to support the amplifier’s 

weight and drilled holes for mounting 

bolts. Also, verify that there will be 

adequate ventilation around the 

amplifier, so that airflow to its internal 

fans will not be blocked and the unit 

can properly cool itself. 

WARNING: To avoid personal injury 

and possible product damage, we 

strongly urge you to enlist additional 

help in unpacking and moving the 

JBL A6000GTi or A3000GTi amplifier 

to a desired mounting location. 

PARTS LIST 

Each amplifier is packed with the 

following parts: 

• Four (4) 1/2" x 3" socket-head cap 

screws and T-nuts. 

• One (1) Remote Level Control with 

mounting hardware 

• One (1) 15' RJ11 Cable for Remote 

Level Control 

• One (1) Logo Badge 

• One (1) Set of Performance Graphs 

• One (1) Owner’s Manual 

• One (1) Warranty Registration 

Instruction Card 

RJ45 connector on back 

MOUNTING THE 

AMPLIFIER 

We strongly recommend first mounting 

a piece of wood or medium density 

fiberboard (MDF) to the vehicle, and 

then mounting the amplifier to the 

board. The amplifier is large and heavy 

and must be mounted using all four 

screws and T-nuts provided. Using 

the amplifier as a template, mark the 

location of the mounting holes on the 

mounting surface, drill pilot holes, and 

securely attach the amplifier to the 

mounting surface with the provided 

screws and T-nuts. Make sure the 

amplifier does not pinch or smash 

power cables, speaker wires, input 

cables or any of the vehicle’s wiring. 

Install the Remote Level Control in a 

convenient location in or under the 

dashboard. The control may be 

removed from its housing for custom 

installation. Using the enclosed RJ11 

cable, connect the control to the 

amplifier, as shown in Figure 1. 

RJ11 Cable 

A6000GTi/A3000GTi 

(on input panel) 

RJ45 connector 

Figure 1. Connecting the Remote Level 

Control. 

Once the amplifier is mounted, peel the 

backing from the adhesive (on the back 

of the logo badge) and attach the 

badge in the appropriate orientation. 

2

DESIGNING A SPEAKER SYSTEM FOR THE GTi AMPLIFIER 

NOTE: Although the JBL A6000GTi or 

A3000GTi amplifier will drive a system 

made up of any subwoofers, we 

recommend using JBL GTi subwoofers 

with GTi amplifiers. 

Both the JBL A6000GTi and A3000GTi 

amplifiers provide RMS power that 

exceeds the RMS power-handling 

rating of nearly every subwoofer 

available. To use this amplifier 

optimally, you should design a speaker 

system made up of several identical 

speakers, so that the power delivered 

by the amplifier will be shared equally 

among the speakers. 

The JBL A6000GTi and A3000GTi 

amplifiers support a wide range of 

impedances, and any speaker system 

with a total or equivalent impedance of 

1 to 4 ohms will extract full power from 

either amplifier. In order to connect 

multiple woofers to the A6000GTi or 

A3000GTi, you’ll need to connect your 

speakers in series, parallel or seriesparallel. 

We’ve included diagrams for 

each connection scheme and a pair of 

formulas, which will help you. 

SERIES CONNECTIONS 

The formula for determining the 

total impedance of the two woofers 

connected in series is: 

Z total = Z 1 + Z 2 + Z 3 ... 

Where Z total is the total impedance of 

all woofers connected in series. Z 1 , Z 2 

and Z 3 (and so on) are the nominal 

impedance ratings of the individual 

speakers. The total impedance of the 

voice coils shown in Figure 2 is 8 ohms. 

4 ohms 4 ohms 

PARALLEL 

CONNECTIONS 

The formula for determining the 

equivalent impedance of the voice 

coils connected in parallel is: 

Z equivalent = 1/(1/Z 1 + 1/Z 2 + 1/Z 3 …) 

Where Z equivalent is the equivalent 

impedance of the coils connected in 

parallel. Z 1 , Z 2 and Z 3 (and so on) are 

the nominal impedance ratings of the 

individual speakers. The equivalent 

impedance of the voice coils shown in 

Figure 3 is 2 ohms. 

4 ohms 4 ohms 

Figure 3. Parallel connection of two 

4-ohm voice coils yields a total 

impedance of 2 ohms. 

DUAL VOICE-COIL 

CONNECTIONS 

Dual voice-coil subwoofers, such as 

JBL’s GTi series, may be connected 

in series, as shown in Figure 2; in 

parallel, as shown in Figure 3; or in 

series-parallel, as shown in Figure 4. 

Figure 4. Series-parallel connections 

of three W15GTi subwoofers (with a 

voice coil impedance of 6 ohms) yields 

a total series impedance of 12 ohms 

for each subwoofer, and an equivalent 

parallel impedance of 4 ohms for all 

three subwoofers. 

To determine the impedance of a 

system of three W15GTi (dual voicecoil) 

subwoofers connected in seriesparallel, 

use the series connection 

formula to determine the impedance 

of each subwoofer with its voice coils 

connected in series. Then insert the 

calculated value into the parallel 

connection formula to determine the 

equivalent impedance for the three 

subwoofers connected in parallel. 

NOTE: Each W15GTi voice coil has an 


For example, in Figure 4, each woofer 

will have an impedance of 12 ohms, by 

Z total = Z 1 + Z 2 = 6 + 6 = 12 

and the three woofers connected 

in parallel will have an equivalent 

impedance of 4 ohms, by 

Z equivalent = 1/(1/Z 1 + 1/Z 2 + 1/Z 3 ) 

= 1/(1/12 + 1/12 + 1/12) 

= 1/(3/12) 

= 12/3 = 4 

NOTE: All subwoofers connected to an 

amplifier in a system must be identical 

and, if they are dual voice-coil subwoofers, 

their coils must be wired 

identically. Do not connect the coils of 

one subwoofer together in series and 

another in parallel, since doing so will 

cause uneven power distribution, 

potential damage to the speakers, and 

poor overall performance. 

Remove 

Terminal Jumper 

ABOUT SPEAKER 

POWER HANDLING 

The RMS power handling rating of 

a speaker indicates the amount of 

power it will handle continuously. 

Although designing a subwoofer 

system by considering the RMS rating 

will ultimately provide you with the 

most reliable system, your speakers 

may be able to handle more power, 

depending on what kind of music is 

being reproduced. 

For music with extended bass notes 

(e.g., bass music, hip-hop or techno), 

you should design a speaker system 

based on the RMS power handling of 

your speakers. For music with sharp 

transient bass notes (e.g., rock, 

country or jazz), the RMS power 

handling rating is conservative, and 

you can count on your speakers being 

able to handle more power than the 

RMS rating. 

The total power output of your 

amplifier will be divided among the 

speakers connected to it. For example, 

if you are using an A6000GTi and three 

W15GTi subwoofers, each subwoofer 

will receive 2,000 watts. 

It’s important to choose a system of 

subwoofers that will handle all of the 

power. To determine how much total 

power your speaker system will 

handle, simply multiply the RMS power 

handling rating of one of your speakers 

by the total number of speakers that 

will be connected. 

Red 

Figure 2. Series connection of two 

4-ohm voice coils yields a total 


Black 

Remove 

Terminal Jumper 

3

SUPPLYING POWER TO THE GTi AMPLIFIER 

POWER IN IS 

POWER OUT 

In order to get full power out of your 

amplifier, you must provide full power 

to your amplifier. That’s a basic rule 

of physics. The A6000GTi amplifier 

can draw nearly 800 amperes when 

reproducing sine waves at full output. 

Both JBL A6000GTi and A3000GTi 

amplifiers can quickly exhaust the 

factory-installed charging system of 

any vehicle on the road today. With 

this much available amplifier power, 

you will need to beef up your vehicle’s 

electrical system to satisfy the 

amplifier’s current demands. We 

recommend adding at least two 

12-volt batteries, connected in 

parallel with cold-cranking capacities 

of at least 600 amperes each, to the 

factory-installed charging system. 

HOW YOUR CHARGING 

SYSTEM WORKS 

The battery’s job is to start your 

vehicle. Running the electrical 

accessories is the alternator’s job. 

The battery isn’t designed to be a 

continuous source of power. It is a 

renewable source and is charged by 

the alternator when the engine runs. 

Battery charging can only occur when 

the current demand from the electrical 

accessories is less than the total current 

output capacity of the alternator. 

PROGRAM MATERIAL 

AND CURRENT DEMAND 

Music is a combination of loud and 

soft sounds, with varying durations 

and rhythms that present unique 

current demands during amplification. 

For example, it may take full power 

to reproduce the sound of a kick drum. 

The peak power demand doesn’t last 

very long, but it is repeated over 

and over. 

If your charging system can’t provide 

all the power your amplifier needs on 

a continuous basis, it still may be 

adequate. During the sound of the 

kick drum, the battery can provide 

the extra current that’s necessary, 

and between kick drum beats, the 

alternator will put some of the energy 

back into the battery. 

Few stock batteries can provide the 

current required to reproduce even 

short-duration musical peaks. Adding 

a pair of batteries with cold-cranking 

capacities of 600 amperes will provide 

extra current for short music bursts, 

but reserve power may still be 

depleted over longer music intervals. 

Adding more batteries will provide 

more reserve power and current, but 

no matter how many are installed, the 

alternator will still have to recharge 

them all. 

If you plan to use the A6000GTi or 

A3000GTi in SPL competition, the 

charging system requirements will be 

much greater than those for normal 

music listening. Be prepared to add 

additional batteries and alternators to 

provide continuous current required 

for continuous duty. 

However, depending on the current 

rating of the alternator, the amplifier’s 

maximum output power, the music 

content, and the charging system’s 

capability, the alternator may not be 

able to keep up over time. In that case, 

you’ll need to install a somewhat larger 

alternator for more current, or adjust 

your driving and listening habits, to 

give the alternator time to catch up 

with the amplifier’s current demand. 

See your authorized JBL car audio 

dealer for help in designing and 

installing an upgraded charging 

system to support your GTi amplifier. 

4

MAKING THE CONNECTIONS 

POWER CONNECTIONS 

Use 0-gauge cable to connect the 

amplifier’s GND – terminal directly to 

the vehicle’s chassis (see Figure 5). 

Scrape off all paint from the metal area 

for a good, clean ground connection. 

Make sure the ground wire is as short 

as possible and is connected to metal 

on the vehicle’s body. Do not connect 

the GND – cable to the frame of the 

vehicle. It is isolated from the chassis 

using rubber shims and will not provide 

an adequate ground. Instead, use the 

trunk’s floor or cargo area as a suitable 

location. Do not connect the GND – 

cable to the battery’s negative (–) 

terminal. 

(or other 

turn-on 

signal) 

Ground 

Source Unit 

+12 V 

85 

87 87a 

no nc 

86 30 

SPDT Relay 

Remote Turn-On 

Figure 5. Power wiring 

diagram for the JBL A6000GTi 

amplifier. The A3000GTi is 

wired in a similar way. 

ANN-Type Fuse 

(500 A or more) 

Use 0-gauge cable to connect the 

BATT+ terminal directly to the vehicle’s 

battery. If the battery is located in the 

engine compartment and the BATT+ 

cable must be routed through the 

firewall or any metal obstruction, 

install a wafer-type (ANN) fuse with a 

current rating of at least 500 amperes 

and an appropriate fuse holder 

within 18" of the vehicle’s battery 

(see Figure 5). 

Connect the source unit’s remote 

turn-on lead to the REMOTE terminal 

on the amplifier (see Figure 5). Use 

any convenient gauge wire for the 

connection. 

The amplifier’s internal neon lights 

require a separate switched power 

connection with at least a 2-ampere 

current capacity. If desired, install a 

switch to turn on the neon lights or a 

relay triggered by a circuit in the vehicle 

(e.g., door switch, trunk pin switch or 

other turn-on source). If you want the 

amplifier’s neon to light when the 

amplifier is on, connect the LIGHTING 

terminal to a relay triggered by the radio’s 

remote turn-on lead (see Figure 5). 

18" 

Batteries 

A6000GTi 

Power Terminals 

0-gauge 

0-gauge 

Chassis 

Ground 

(Bare Metal) 

IMPORTANT: Do not connect a jumper 

directly between the REMOTE and 

LIGHTING terminals. Doing so may 

burn out the remote turn-on circuits 

in your source unit. 

SIGNAL CONNECTIONS 

Use high-quality twisted-pair RCA 

audio cables to connect your source 

unit’s main stereo or subwoofer RCA 

output jacks to the amplifier’s L/R 

INPUT jacks. For a single subwoofer 

output, use an RCA “Y” adapter to 

connect its signal to both input jacks. 

As a convenience, each JBL A6000GTi 

or A3000GTi amplifier is also equipped 

with a set of PASS-THRU L/R RCA 

audio jacks. They will pass incoming 

audio signals unaltered, and you can 

use them to send stereo audio signals 

to other components in your system. 

REMOTE LEVEL 

CONTROL/ACCESSORY 

GAUGE OUTPUTS 

The A6000GTi and A3000GTi use an 

RJ45 connector to output control 

signals for the Remote Level Control 

and accessory gauges. Use the 15' 

RJ11 cable to connect the control to 

the amplifier. For accessory gauges, 

use the pinouts in Figure 6 to make 

custom cables with materials found 

at most electronics supply stores or 

home centers. 

RJ45 Connector 

(GTi Input Panel) 

Ground (also use for acc. gauges) = 8 

No Connection = 7 

Remote Level Control = 6 

Remote Level Control = 5 

8 1 

For gauges, varying voltages are output 

on selected RJ45 pins to indicate 

voltage, current and temperature. 

For battery voltage, linear scale (pin 1): 

2 volts = 8 volts at the battery 

4.5 volts = 18 volts at the battery 

For temperature, linear scale (pin 2): 

0 volts = –10 degrees Celsius 

5 volts = 110 degrees Celsius 

For current, linear scale (pin 3): 

0 volts = 0 amperes current draw 

5 volts = 800 amperes current draw 

Also, you can connect a power meter 

using the pins for battery voltage and 

current. Be sure to use a power meter 

that multiplies the incoming voltage 

and current signals (i.e., P = E x I) to 

convert the data to watts. 

CONNECTING 

THE SPEAKERS 

IMPORTANT: As a safety feature 

and due to the high output voltage 

capability of the A6000GTi and 

A3000GTi amplifiers, the SPEAKER 

OUTPUTS are equipped with a cover 

that must be in place in order for the 

amplifier to operate. When the cover 

is removed, the amplifier will turn off 

and speaker connections can be 

made safely. 

1 = Battery Voltage (to acc. volt meter) 

2 = Temperature (to acc. temp. gauge) 

3 = Current (to acc. ampere meter) 

4 = Remote Level Control 

Figure 6. Pinouts for the REMOTE LEVEL RJ45 connector on the 

A6000GTi or A3000GTi amplifier. 

5


A6000GTi SPEAKER 

CONNECTIONS 

The A6000GTi is a 2-channel amplifier 

designed to drive subwoofers only. 

The left and right input signals are 

combined inside the amplifier to 

provide a mono output signal, no 

matter which output mode is selected. 

Figure 7. The JBL A6000GTi 

subwoofer amplifier is set 

to bridged mode to drive a 

subwoofer system. Only use 

this mode when the nominal 

equivalent or total impedance 

of the speaker system is 

2 ohms or greater. 

Set Output Mode 

to 2CH/BR 


A6000GTi Amplifier 

(partial output panel) 

The A6000GTi can be connected to 

two independent speaker systems in 

2-channel mode. It can be connected 

to a combination of subwoofers 

configured as a single load with its 

channels bridged or connected in 

parallel. Bridged channels will provide 

high output voltage for driving loads 

with a nominal impedance of 2 to 4 

ohms. Connecting the channels in 

parallel will provide the high current 

necessary to drive loads of 1 to 2 ohms. 

Included below are three application 

diagrams that will help you plan 

your A6000GTi installation. Figures 7 

through 9 show how to configure the 

JBL A6000GTi subwoofer amplifier for 

bridged-mono, parallel-mono and 

2-channel operation (see Setting Up 

the GTi Amplifier). 



to parallel mode to drive a 

subwoofer system. Only 

use this mode when the 

nominal equivalent or total 

impedance of the speaker 

system is less than 2 ohms. 

NOTE: A jumper is added 

between the + terminals. 

See “Setting The Crossover” 

on Page 8 

to Adjust Crossover Controls 


to PARALLEL 



on Page 8 


Subwoofer 

System 

2 ohms 

or more 



jumper 

Subwoofer 

System 

IMPORTANT: If the nominal impedance 

of the speaker system is close to 2 

ohms, you may try both bridged and 

parallel configurations to determine 

which one performs better. Remember 

to set the output mode switch to the 

appropriate setting when changing 

configurations. 

NOTE: For simplicity, Figures 7 through 

9 do not show power, remote and input 

connections (see page 5). 



to 2-channel mode to drive 

a pair of subwoofers or 

subwoofer systems with 


impedances of 2 to 4 ohms. 


to 2CH/BR 


2 ohms 

or less 




on Page 8 


Subwoofer 

System 

Subwoofer 

System 

2 to 4 

ohms 

2 to 4 

ohms 

6


A3000GTi SPEAKER 

CONNECTIONS 

Included below are three application 

diagrams that will help you plan your 

A3000GTi installation. Figures 10 

through 12 show how to configure 

the JBL A3000GTi amplifier for 

bridged-mono, parallel-mono and 

2-channel operation (also see 

Setting Up the GTi Amplifier). 

NOTE: For simplicity, Figures 10 

through 12 do not show power, remote 

and input connections (see page 5). 


amplifier is set to bridged 

mode to drive a subwoofer 

system. Only use this mode 

when the nominal equivalent 

or total impedance of the 

speaker system is 2 ohms 

or greater. 


to BRIDGE 



on Page 8 




Subwoofer 

System 

OUTPUT LOAD SWITCH 

The Output Load switch is used to 

optimize amplifier performance when 

driving a full-range signal. Set the 

switch according to the nominal 

impedance of the load: Use the 

4-ohm mode when driving loads 

with a nominal impedance greater 

than 2 ohms and the 2-ohm mode 

when driving loads with a nominal 

impedance of 2 ohms or less. 


amplifier is set to parallel 

mode to drive a subwoofer 

system. Only use this mode 

when the nominal equivalent 

or total impedance of the 

speaker system is less than 

2 ohms. 


to PARALLEL 


2 ohms 

or more 



jumper 

NOTE: A jumper is added 

between the + terminals. 


on Page 8 


Subwoofer 

System 

2 ohms 

or less 


amplifier is set to stereo 

mode to drive a pair of fullrange 

speaker systems with 


impedances of 2 to 4 ohms. 


to STEREO 





on Page 8 


L Speaker 

System 

R Speaker 

System 

2 to 4 

ohms 

2 to 4 

ohms 

7

SETTING UP THE GTi AMPLIFIER 

SETTING THE CROSSOVER 

IMPORTANT: If you plan to use the 

A3000GTi to drive full-range speakers, 

set the crossover mode switch to FLAT 

and skip to the next section, “Setting 

Input Sensitivity.” 

1. Depending on your system plan, 

set the A3000GTi’s crossover mode 

switch to LP (low-pass) or HP (highpass). 

The A6000GTi is a low-pass 

amplifier only, designed to drive 

subwoofers. No crossover switch 

is provided. 

2. The crossover slope has two 

settings: 12 (dB per octave) or 

24 (dB per octave). Select the 

slope that best suits your taste, but 

consider that a steeper low-pass 

filter will make the subwoofers 

sound less directional (since more 

midrange will be filtered from the 

signal). A steeper high-pass filter 

will reduce a small speaker’s 

unnecessary cone excursion at 

the lowest frequencies, which 

will increase power handling 

and reduce distortion. 

3. Set the A3000GTi’s HP FREQ control 

to allow the speakers to make 

as much bass as possible while 

minimizing distortion caused by 

small speakers trying to reproduce 

the lowest frequencies. The best 

setting is one where the speakers 

produce crisp, clear impact without 

being overdriven. 

4. For either amplifier, set the LP FREQ 

control so vocal information is not 

reproduced by the subwoofers, and 

the subwoofers’ sound blends with 

the sound of the midrange speakers 

without any missing information. 

NOTE: The LP FREQ control can be 

set to any frequency between 32Hz 

and 320Hz. 

SETTING INPUT 

SENSITIVITY 

NOTE: You can use the supplied 

REMOTE LEVEL control to fine-tune 

the input sensitivity or to adjust the 

level of the bass according to the 

program material after the amplifier’s 

LEVEL control has been set properly. 

Connect the remote module’s attached 

cable to the REMOTE LEVEL (RJ45) jack 

on the amplifier’s input panel. Start 

with the REMOTE LEVEL Control in its 

maximum (clockwise) position. 

1. Initially, turn the amplifier’s LEVEL 

control to the minimum (clockwise) 

position. 

2. Reconnect the (–) negative lead to 

your vehicle’s battery. Apply power 

to the audio system and play a 

favorite music track. 

3. Increase the source unit’s volume 

control to the maximum listening 

position. Slowly turn the amplifier’s 

LEVEL control counterclockwise and 

observe the I/OPT and E/OPT LEDs 

(on the amplifier’s top). 

• In the bridged or 2-channel mode, 

at the ideal setting, the E/OPT LED 

should flash on musical peaks to 

indicate the amplifier is producing 

maximum voltage. If the I/OPT LED 

flashes in bridged mode, this 

indicates the speaker system’s 

impedance is lower than 2 ohms 

and the amplifier should be 

configured in the parallel mode. 

• In the parallel mode, at the ideal 

setting, the I/OPT LED should 

flash on musical peaks to indicate 

that the amplifier is producing 

maximum current. 

If either the I/OPT or E/OPT LED is 

on steadily, the amplifier is being 

overdriven and your speakers may 

be in jeopardy. Turn the LEVEL 

control back slightly until the I/OPT or 

E/OPT LED flashes on musical peaks. 

SETTING PHASE 

1. Initially set the PHASE control to 0.° 

Play a favorite audio track that has 

significant bass output. 

2. Continue listening to the music and 

have another person slowly adjust 

the PHASE control towards 180° and 

back to 0° again. 

3. Repeat Step 2 as needed until you 

find a setting that produces the 

most mid-bass output. 

NOTE: For applications using multiple 

GTi amplifiers where the highest SPL 

is desired at a single point in the 

vehicle (i.e., SPL competition), adjust 

the PHASE controls on all amplifiers 

so all speakers are in phase at the 

microphone position. This will provide 

the highest SPL when measured with 

an SPL meter. 

DBO HP FREQ Control 

(adjusts cut-off 

frequency) 

dB 

0 

–3 

–6 

–9 

–12 

20 80 Freq. (Hz) 

DBO BOOST Control 

(adjusts boost amount 

at cut-off frequency) 

dB 

12 

6 

0 

–6 

–12 

HP FREQ 

80Hz 

BOOST 

MIN 

20Hz 

MAX 

20 80 Freq. (Hz) 

Figure 13. Frequency response curves 

show typical DBO control ranges for 

the JBL A6000GTi or A3000GTi amplifier. 

SETTING DBO 

DBO (or Dynamic Bass Optimizer) is 

a 12dB/octave high-pass filter with 

variable frequency (20Hz to 80Hz) 

and variable boost (0 to +12dB) at 

the cutoff frequency. 

NOTE: During DBO adjustment, you can 

audition the effect by setting the DBO 

switch to OFF and then back to ON. 

NOTE: The A3000GTi can be used 

to drive a pair of stereo mid-bass 

speakers. In this case, use the DBO 

to set the high-pass filter (from 20Hz to 

80Hz) and use the crossover to set the 

low-pass filter (from 80Hz to 320Hz). 

For a vented box where a subwoofer 

is prone to overexcursion below the 

tuned frequency, set DBO to ON and 

set the DBO HP FREQ control 10Hz 

below the box’s resonant (tuned) 

frequency (e.g., 30Hz for a vented 

box tuned to 40Hz). Power typically 

wasted in this region will now be 

conserved and instead be available 

for frequencies the enclosure can 

reproduce. Use the DBO BOOST 

control to boost the bass at the set 

frequency by as much as 12dB, as 

shown in Figure 13. 

For a sealed enclosure, use DBO to 

enhance the middle of the bass region. 

Set DBO to ON, and then set the DBO 

HP FREQ control to 35Hz to 40Hz. 

Adjust the DBO BOOST control for a 

big and full bass sound. Alternatively, 

for a tighter-sounding bass, set the 

DBO HP FREQ control between 45Hz to 

50Hz and also adjust the DBO BOOST 

control according to your preference. 

For an infinite baffle application, 

set DBO to ON, and then set the 

HP FREQ control to the speaker’s Fs 

value (to keep the subwoofer from 

trying to create bass below the 

resonant frequency). Adjust the DBO 

BOOST control according to your taste. 

8


REPLACING THE FUSE 

OR NEON TUBES 

The JBL A6000/A3000GTi amplifier 

is equipped with an internal fuse, a 

20-inch neon tube and two 6-inch neon 

tubes. Should the fuse or a neon tube 

fail, perform the following steps 

to replace the part: 

Figure 14. Removing bottom screws 

and the clear cover from the A6000GTi 

amplifier. NOTE: Do not remove the 

logo badge assembly. 

NOTE: For neon tube replacement, see 

your authorized JBL car audio dealer 

to purchase new StreetGlow ® neon 

tubes in 6- or 20-inch sizes. 

NOTE: Although the following 

steps discuss and illustrate how 

to disassemble a JBL A6000GTi, 

the disassembly procedure for a 

JBL A3000GTi is similar. 

1. Disconnect and unmount the 

amplifier from the vehicle. On a 

soft surface, turn the amplifier over 

to view the bottom. Using a T-25 

screwdriver, remove the four large 

Torx-head screws along the bottom 

edges and set them aside (see 

Figure 14). 

2. Turn the amplifier over to view the 

top. Using a 5 ⁄32-inch Allen wrench, 

remove the four cap screws on the 

clear cover and set them aside (see 

Figure 14). 

3. Slide the clear cover off and set it 

aside (see Figure 14). 

4. Using a T-15 screwdriver, remove 

the four Torx-head screws around 

the output panel and set them aside 


5. Repeat Step 4 for the input panel 


6. Remove the cover and set it aside 


Figure 15. Removing the input and 

output screws and the cover from the 

A6000GTi amplifier. 

9



the two Torx-head screws on the 

display board and set them aside 

(see Figure 16 below). Disconnect 

the ribbon cable from display board. 


the 16 Torx-head screws on the 

perforated shield and set them aside 


Figure 16. Removing the fuse from the 


9. Using a small flat-blade screwdriver, 

disconnect the wiring for the neon 

tubes. 

10. Remove the perforated shield and 

set it aside. 

11. Replace the fuse or a neon tube as 

follows: 

• To replace the fuse on the amplifier 

circuit board (see Figure 16), 

use a 7⁄16-inch hex-socket driver 

to remove the two fuse nuts and 

then discard the failed fuse. 

Fasten the replacement fuse 

in place using the two fuse nuts. 

• To replace a neon tube (see 

Figure 17), use a T-15 screwdriver 

and pliers to remove the two 

Torx-head screws, nuts and 

washers on the two clamps that 

hold each neon tube in place. 

Remove the failed neon tube 

and unscrew its wires. 

On the replacement neon tube, clip off 

the cigarette lighter adapter. Then strip 

the wires and screw the ends to the 

connector. Refasten the two clamps 

with hardware in place around the 

neon tube. If needed, repeat this procedure 

for another failed neon tube. 

Failed 

Fuse 

Figure 17. Neon tube locations on the 


6" Neon Tubes 

12. Reassemble the amplifier in reverse 

order, as discussed in Steps 1 

through 10. 

20" Neon Tube 

(under shield) 

10

TROUBLESHOOTING 

SYMPTOM LIKELY CAUSE SOLUTION 

No audio No voltage at power Check BATT+, REMOTE and 

(Power LED is off) or remote terminal GND – terminals with VOM for 

blown fuse or poor connection 

A6000GTi 

Power 

6000 Watts Parallel Bridge 

Thermal Signal -18 dB -9 dB E Opt I Opt Fault 

Internal fuse blown 

Replace internal fuse 

(incorrect power 

(see Replacing the Fuse 

connections) 

or Neon Tubes section) 

No audio Low or high voltage Check BATT+ terminal with 

(Power LED at power terminal VOM for voltage between 

is flashing) 

10 and 16 Vdc; if not within 

limits, check vehicle’s 

electrical system 

No audio Direct current on Disconnect cable from 

(Power and speaker output(s) REMOTE terminal; if Fault LED 

Fault LEDs 

is still on, contact local JBL 

are on) 

service center 

No audio Internal amplifier Check for blocked vents 

(Power and temperature is over or whether the ambient 

Thermal LEDs 85° C temperature is above 85° C 

are on) 

Distorted audio Amplifier’s gain is Properly adjust the 

(I OPT and/or set to High LEVEL control (see 

E OPT LED[s] 

Setting Input 

are on more 

Sensitivity section) 

than off) 

Distorted audio Defective source unit Try new source unit 

(I OPT and/or 

E OPT LED[s] Shorted speaker Disconnect wires from 

work correctly) wires SPEAKER OUTPUTS and 

check for shorts between 

wires, or between a wire and 

the vehicle’s chassis 

Music lacks Speakers are out Check speaker connections 

“punch” of phase (see sections on speaker 

connections) 

Wrong output mode 

Verify output mode setting 

(see Making the Connections 

section) 

Neon tubes do No voltage to neon tubes Check LIGHTING 

not light for +12 Vdc terminal with VOM 

A3000GTi 

3000 Watts Parallel Bridge 

CH 1 

Thermal 

Signal -18 dB -9 dB E Opt I Opt 

CH 2 

Figure 18. Display indicates Power Output and Protection status. 

Power 

Fault 

Neon tubes are dead 

Replace neon tubes 

(see Replacing the Fuse 

or Neon Tubes section) 

11

Features, specifications and appearance are subject to change without notice. 

JBL Consumer Products 

250 Crossways Park Drive, Woodbury, NY 11797 USA 

© 2004 Harman International Industries, Incorporated 

JBL and Crown are registered trademarks of 

Harman International Industries, Incorporated. 

Part No. GTIAMPOM4/04 

www.jbl.com

1718.1KB PDF - JBL.com

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