JL Audio XD400/4 User manual

Thank you for purchasing a JL Audio amplifier for
your automotive sound system.
Your amplifier has been designed and manufactured to exacting
standards in order to ensure years of musical enjoyment in your vehicle.
For maximum performance, we highly recommend that you have
your new amplifier installed by an authorized JL Audio dealer. Your
authorized dealer has the training, expertise and installation equipment
to ensure optimum performance from this product. Should you
decide to install the amplifier yourself, please take the time
to read this manual thoroughly so as to familiarize yourself
with its installation requirements and setup procedures.
If you have any questions regarding the instructions in this
manual or any aspect of your amplifier’s operation, please contact your
authorized JL Audio dealer for assistance. If you need further assistance,
please call the JL Audio Technical Support Department
at [phone] during business hours.
OWNER’S MANUAL
400W 2/3/4 Channel Amplier

2 | JL Audio - XD400/4 Owner’s Manual
PROTECT YOUR HEARING!
We value you as a long-term customer. For
that reason, we urge you to practice restraint in
the operation of this product so as not to damage
your hearing and that of others in your vehicle.
Studies have shown that continuous exposure to
high sound pressure levels can lead to permanent
(irreparable) hearing loss. This and all other
high-power amplifiers are capable of producing
such high sound pressure levels when connected
to a speaker system. Please limit your continuous
exposure to high volume levels.
While driving, operate your audio system in
a manner that still allows you to hear necessary
noises to operate your vehicle safely (horns,
sirens, etc.).
SERIAL NUMBER
In the event that your amplifier requires
service or is ever stolen, you will need to have
a record of the product’s serial number. Please
take the time to enter that number in the space
provided below. The serial number can be found
on the bottom panel of the amplifier and on the
amplifier packaging.
Serial Number:
INSTALLATION APPLICATIONS
This amplifier is designed for operation in
vehicles with 12 volt, negative-ground electrical
systems. Use of this product in vehicles with
positive ground and/or voltages other than 12V
may result in damage to the product and will void
the warranty.
This product is not certified or approved for
use in aircraft.
Do not attempt to “bridge” the outputs of this
amplifier with the outputs of a second amplifier,
including an identical one.
Status
LED
(pg. 11)
Ch. 1 & 2 Filter
Frequency
Selector
(pg. 8)
Ch. 1 & 2
Filter Mode
Selection
(pg. 8)
Ch. 1 & 2 Input
Sensitivity Control
(pg. 7)
Remote
Level Mode
Switch
(pg. 9)
Input
Mode
Switch
(pg. 6)
Pre-Out Signal
Selection
Switch
(pg. 9)
Ch. 3 & 4 Filter
Frequency
Selector
(pg. 8)
Ch. 3 & 4
Filter Mode
Selection
(pg. 8)
Ch. 3 & 4 Input
Sensitivity Control
(pg. 7)

3
ENGLISH
PLANNING YOUR INSTALLATION
It is important that you take the time to read
this manual and that you plan out your
installation carefully. The following are some
considerations that you must take into account
when planning your installation.
Cooling Efficiency Considerations:
The outer shell of your JL Audio amplifier is
designed to remove heat from the amplifier
circuitry. For optimum cooling performance, this
outer shell should be exposed to as large a volume
of air as possible. Enclosing the amplifier in a
small, poorly ventilated chamber can lead to
excessive heat build-up and degraded
performance. If an installation calls for an
enclosure around the amplifier, we recommend
that this enclosure be ventilated with the aid
of a fan. In normal applications, fan-cooling
is not necessary.
Mounting the amplifier upside down is
strongly discouraged. If mounting the amplifier
under a seat, make sure there is at least 1 inch
(2.5 cm) of space above the amplifier’s outer
shell to permit proper cooling.
Safety Considerations:
Your amplifier needs to be installed in a dry,
well-ventilated environment and in a manner
which does not interfere with your vehicle’s safety
equipment (air bags, seat belt systems, ABS brake
systems, etc.). You should also take the time to
securely mount the amplifier so that it does not
come loose in the event of a collision or a sudden
jolt to the vehicle.
Stupid Mistakes to Avoid
• Check before drilling any holes in your vehicle
to make sure that you will not be drilling
through a gas tank, brake line, wiring harness or
other vital vehicle system.
• Do not run system wiring outside or underneath
the vehicle. This is an extremely dangerous
practice which can result in severe damage to
your vehicle and person.
• Protect all system wires from sharp metal
edges and wear by carefully routing them,
tying them down and using grommets and
loom where appropriate.
• Do not mount the amplifier in the engine
compartment, under the vehicle, on the roof
or in any other area that will expose the
amplifier circuitry to the elements.
Remote Turn-On
Connector
(pg. 6)
Chassis Ground
Connector
(pg. 5)
Channels 1 & 2
Preamp Input Jacks
(pg. 6)
Left & Right Preamp
Output Jacks
(pg. 9)
+12 V Power
Connector
(pg. 5)
Channels 3 & 4
Speaker Outputs
(pg. 10)
Channels 1 & 2
Speaker Outputs
(pg. 10)
Jack for
Remote Level
Control Knob
(pg. 9)
Channels 3 & 4
Preamp Input Jacks
(pg. 6)

4 | JL Audio - XD400/4 Owner’s Manual
PRODUCT DESCRIPTION
The JL Audio XD400/4 is a four-channel,
full-range audio amplifier utilizing JL Audio
NexD™ ultra-high speed switching technology to
deliver outstanding fidelity and efficiency.
The XD400/4 can be operated with a wide
variety of source units and system configurations.
TYPICAL INSTALLATION SEQUENCE
The following represents the sequence
for a typical amplifier installation, using an
aftermarket source unit or OEM Interface
processor (like the CleanSweep CL441dsp).
Additional steps and different procedures may
be required in some applications. If you have
any questions, please contact your authorized
JL Audio dealer for assistance.
1) Disconnect the negative battery post
connection and secure the disconnected cable
to prevent accidental re-connection during
installation. This step is not optional.
2) Run power wire from the battery location to
the amplifier mounting location. True 8 AWG
power wire may be used for runs shorter than
18 ft. For longer runs, use 4 AWG wire. Take
care to route the wire in such a way that it
will not be damaged and will not interfere
with vehicle operation. Use 4 AWG or larger
power wire and a power distribution block if
additional amplifiers are being installed with
the XD400/4.
3) Connect power wire to the positive battery
post. Fuse the wire with an appropriate fuse
block (and connectors) within 18 inches (45
cm) wire length of the positive battery post.
This fuse is essential to protect the vehicle.
Do not install the fuse until the power wire
has been securely connected to the amplifier.
4) Run signal cables and remote turn-on wire
from the source unit to the final amplifier
mounting location.
5) Run speaker cables from the speaker systems
to the amplifier mounting location.
6) Find a good, solid metal grounding
point close to the amplifier and connect
the negative power wire to it using
appropriate hardware (use of the JL Audio
ECS master ground lug, XB-MGLU is
recommended). Use 8 or 4 AWG wire, no
longer than 36 inches (90 cm) from the
amplifier to the ground connection point.
In some vehicles, it may be necessary
to upgrade the battery ground wire.
(See page 5 for important notice).
7) Securely mount the amplifier.
8) Connect the positive and negative power
wires to the amplifier. A fuse near
the amplifier is not necessary if the
XD400/4 is the only device being run
from the fused main power wire. If
the fused main power wire is shared
by the XD400/4 and other amplifiers
or devices, fuse each amplifier/device
within 12 inches (30 cm) of wire length,
via a fused distribution block or multiple
individual fuse blocks/on-board fuses.
9) Connect the remote turn-on wire
to the amplifier.
10) Connect the input cables to the amplifier.
11) Connect the speaker cables to the amplifier.
12) Carefully review the amplifier’s control
settings to make sure that they are set
according to the needs of the system.
13) Install the power wire fuse (40A for a
single XD400/4) and reconnect the negative
battery post terminal. Install the fuse (40A)
near the amplifier (if applicable).
14) Turn on the source unit at a low level
to double-check that the amplifier is
configured correctly. Resist the temptation
to crank it up until you have verified the
control settings.
15) Make necessary adjustments to the input
sensitivity controls to obtain the right
overall output and the desired balance
in the system. See Appendix A (page 14)
for the recommended input sensitivity
setting method.
16) Enjoy the fruits of your labor with your
favorite music.

5
ENGLISH
POWER CONNECTIONS
Before installing the amplifier, disconnect the
negative (ground) wire from the vehicle’s battery.
This will prevent accidental damage to the system,
the vehicle and your body during installation.
The XD400/4’s “+12 VDC”and “Ground”
connections are designed to accept 8-4 AWG
power wire. 8 AWG is the minimum required
wire size for this amplifier.
If you are installing the XD400/4 with other
amplifiers and wish to use a single main power
wire, use 4 AWG, 2 AWG or 1/0 AWG main
power wire (depending on the overall current
demands of all the amplifiers in the system).
This large power wire should terminate into a
fused distribution block mounted as close to
the amplifiers as possible (within 12 inches /
30cm of wire length). The fused output of the
distribution block will connect to the XD400/4
with 4 AWG power wire. JL Audio ECS
fused distribution blocks are recommended
(XD-FDBU-2 and XD-FDBU-4)
Note: Smaller AWG numbers mean bigger
wire and vice-versa (1/0 AWG is the largest, 2
AWG is smaller, then 4 AWG, then 8 AWG, etc.).
To connect the power wires to the amplifier,
first back out the set screw on the top of the
terminal block, using the supplied 2.5 mm hex
wrench. Strip 1/2 inch (12 mm) of insulation from
the end of each wire and insert the bare wire into
the terminal block, seating it firmly so that no
bare wire is exposed. While holding the wire in
place, tighten the set screw firmly, taking care not
to strip the head of the screw.
The ground connection should be made
using 8 or 4 AWG wire and should be kept
as short as possible, while accessing a solid
piece of sheet metal in the vehicle. The
surface of the sheet metal should be sanded
at the contact point to create a clean, metal-
to-metal connection between the chassis
and the termination of the ground wire.
For optimal grounding, we recommend the
use of a JL Audio ECS master ground lug
(XB-MGLU). Alternatively, a sheet metal
screw or bolt can be used with a star washer.
Any wires run through metal barriers (such
as firewalls), must be protected with a high
quality rubber grommet to prevent damage to the
insulation of the wire. Failure to do so may result
in a dangerous short circuit.
Many vehicles employ small (10 AWG -
6 AWG) wire to ground the battery to the
vehicle chassis and to connect the alternator's
positive connection to the battery. To prevent
voltage drops, these wires should be upgraded
to 4 AWG when installing amplifier systems
with main fuse ratings above 60A.
FUSE REQUIREMENTS
It is absolutely vital that the main power
wire(s) to the amplifier(s) in the system be
fused within 18 inches (45 cm) of the positive
battery post connection. The fuse value at each
power wire should be high enough for all of the
equipment being run from that power wire. If
only the XD400/4 is being run from that power
wire, we recommend a 40A fuse be used.
If fusing the amplifier near its power
connections (when more than one amp is being
run from the main power wire), use a 40A fuse.
MAXI™ plastic-body fuses are recommended.

6 | JL Audio - XD400/4 Owner’s Manual
TURNON LEAD
The XD400/4 uses a conventional +12V remote
turn-on lead, typically controlled by the source
unit's remote turn-on output. The amplifier will
turn on when +12V is present at its “Remote”
input and turn off when +12V is switched off. If
a source unit does not have a dedicated remote
turn-on output, the amplifier’s turn-on lead can
be connected to +12V via a switch that derives
power from an ignition-switched circuit.
The XD400/4’s “Remote”turn-on connector
is designed to accept 18 AWG – 12 AWG wire. To
connect the remote turn-on wire to the amplifier,
first back out the set screw on the top of the
terminal block, using the supplied 2.5mm hex
wrench. Strip 1/2 inch (12mm) of wire and insert
the bare wire into the terminal block, seating it
firmly so that no bare wire is exposed. While
holding the wire in the terminal, tighten the set
screw firmly, taking care not to strip the head of
the screw and making sure that the wire (not the
insulation) is firmly gripped by the set screw.
INPUT SECTION
The XD400/4’s input section allows you to
send signals to the amplifier section through the
use of two or four differential-balanced inputs.
Input connections are via up to two pairs of
traditional RCA-type jacks.
If you wish to send four discrete channels into
the XD400/4, simply use all four inputs and set
the “Input Mode”switch in the “4 Ch.”position.
If you wish to use only two channels of
input to deliver signal to all four amplifier
channels, set the “Input Mode”switch to
“2 Ch.”and use only the inputs to channels
1 & 2. In this mode, Channel 3 will operate
with the Channel 1 signal and Channel 4
will operate with the Channel 2 signal.
Input Voltage Range:
The XD400/4’s input sections are designed to
accept signal voltages from 100mV – 4V. This
will accommodate all preamp level signals and
many speaker level signals.
To use speaker-level sources, simply splice the
speaker output wires of the source unit onto a
pair of RCA plugs for each input pair. (or use JL
Audio part XD-CLRAIC2-SW) No “line output
converter” is needed in most cases.
If you find that the output cannot be reduced
sufficiently with a direct speaker level signal
applied to the amplifier, you may use a “line
output converter” to reduce the signal level.

7
ENGLISH
INPUT SENSITIVITY CONTROLS
The controls labeled “Input Sens.” located in
each channel section can be used to match the
source unit’s output voltage to the input stage of
each pair of amplifier channels for maximum
clean output. Rotating the control clockwise will
result in higher sensitivity (louder for a given
input voltage). Rotating the control counter-
clockwise will result in lower sensitivity (quieter
for a given input voltage.)
To properly set the amplifier for maximum
clean output, please refer to Appendix A (page
14) in this manual. After using this procedure,
you can then adjust any or all “Input Sens.”
levels downward if this is required to achieve the
desired system balance.
Do not increase any “Input Sens.” setting for
any channel(s) of any amplifier in the system
beyond the maximum level established during
the procedure outlined in Appendix A (page 14).
Doing so will result in audible distortion and
possible speaker damage.

8 | JL Audio - XD400/4 Owner’s Manual
FILTER CONTROLS
Most speakers are not designed to reproduce
the full range of frequencies audible by the human
ear. For this reason, most speaker systems are
comprised of multiple speakers, each dedicated
to reproducing a specific frequency range. Filters
are used to select which frequency range is sent
to each section of a speaker system. The division
of frequency ranges to different speakers can be
done with passive filters (coils and/or capacitors
between the amplifier outputs and the speakers),
which are acceptable and commonly used
for filtering between mid-range speakers and
tweeters. Filtering between subwoofer systems
and satellite speaker systems is best done with
active filters, which cut off frequency content at
the input to the amplifier. Active filters are more
stable than passive filters and do not introduce
extraneous resistance, which can degrade
subwoofer performance.
The active filter built into each channel
section of the XD400/4 can be used to eliminate
potentially harmful and/or undesired frequencies
from making their way through the amplifier
sections to the speaker(s). This serves to improve
tonal balance and to avoid distortion and possible
speaker failure. Correct use of these filters can
substantially increase the longevity and fidelity of
your audio system.
1) “Filter Mode” Control: The XD400/4 employs
a 12dB per octave filter for each pair of
channels (one filter for channels 1&2, another
filter for channels 3&4 and a third filter for
channels 5&6). Each of these filters can be
configured independently into one of two filter
types or defeated completely by way of the
three-position “Filter Mode” switches:
“Off”: Defeats the filter completely, allowing
the full range of frequencies present at the
inputs to feed the amplifier. This is useful for
systems utilizing outboard active crossovers or
requiring full-range reproduction from one or
more of the XD400/4’s channel pairs.
“LP” (Low-Pass): Configures the filter to
attenuate frequencies above the selected filter
frequency at a rate of 12dB per octave. This is
useful for connection of subwoofer(s) to one
or more of the XD400/4’s channel pairs in a
bi-amplified system.
“HP” (High-Pass): Configures the filter to
attenuate frequencies below the selected filter
frequency at a rate of 12dB per octave. This is
useful for connection of component speakers to
one or more of the XD400/4’s channel pairs in
a bi-amplified system.
2) “Filter Freq. (Hz)” The filter frequency
markings surrounding this rotary control
are for reference purposes and are generally
accurate to within 1/3 octave or better. If you
would like to select the filter cutoff frequency
with a higher level of precision, consult the
chart in Appendix B (page 15).
Tuning Hint: If you are using the XD400/4
to drive a subwoofer system (“LP”mode), a
component satellite speaker system (“HP”mode)
or both, 80 Hz is a good baseline “Filter Freq.
(Hz)”setting. After properly adjusting the “Input
Sens.”, as outlined in Appendix A (page 14), you
can fine tune the “Filter Freq. (Hz)”control to
achieve the desired system frequency response.

9
ENGLISH
REMOTE LEVEL CONTROL OPTIONAL
With the addition of the optional Remote
Level Control (HD-RLC), you can control the
volume of one, or both channel pairs of the
XD400/4 from the front of the vehicle. This is
useful for subwoofer level control, rear channel
level control, center-channel level control or even
as a master volume control for the system.
The HD-RLC connects to the jack labeled
“Remote Level Control” on the Connection Panel
of the amplifier using a standard telephone cable
(supplied with the HD-RLC). If desired, multiple
XD (and HD) amplifiers can be controlled from
a single HD-RLC controller using a simple phone
line “splitter” and multiple phone cables.
When connected to the amplifier, the
HD-RLC operates as follows. At full counter-
clockwise rotation, the audio will mute
completely. At full clockwise rotation the level
will be the same as if the HD-RLC was not
connected at all. In other words, it operates
strictly as a level attenuator.
“Remote Level Mode” Switch: This switch
allows you to assign the operation of the
HD-RLC to one, or both pairs of channels. In
the “Al l” position, the HD-RLC knob will affect
all three channel pairs equally. In the “3&4”
position, only the level of channels 3 and 4 will
be affected by the HD-RLC knob (Channels 1 &
2 will not).
PREOUTS
The XD400/4 incorporates a pass-through
preamp output section, so that additional
amplifiers can be easily added to the system. This
pass-through pre-amp output can be configured
two different ways using the switch labeled
“Preouts From”.
1) “1&2”: The preamp output delivers the same
signal that is connected to the CH 1&2 Inputs.
This mode is useful for feeding a subwoofer
amplifier when the XD400/4 is being used to
drive front and rear speaker systems. In this
mode, the preamp output signal will depend
only on the input signal level of CH 1&2,
allowing Channels 3&4 to be faded without
affecting the subwoofer level. If CH 1&2 is
faded in this mode, the signal level of the
preamp output will change accordingly.
2) “Sum”:When the XD400/4 is being used
to drive front and rear speaker systems, this
preamp output mode will deliver a summed
front/rear stereo signal to a subwoofer amplifier,
while permitting fading of the front and
rear speaker systems from the source unit.
This method prevents a loss of signal to the
subwoofer amplifier when the system is faded to
the front or the rear by the head unit.
Note:Any signal delay between the front and rear
channels can result in a cancellation of signals
within certain frequency ranges when using the
“Sum”position. If you experience a loss of bass
output in the “Sum” position, compared to the
“1&2” position, you are likely dealing with a
delayed signal in either the front or rear outputs
of the source unit. If the front to rear delay is
desirable for other reasons or if it cannot be
defeated at the source unit, we recommend that
you use the “1&2”position.
Note: In either mode, the preamp output signal is
not affected by any crossover filter selected (if the
input signal is full-range, the preamp output will
be full-range).

10 | JL Audio - XD400/4 Owner’s Manual
SPEAKER OUTPUTS
The XD400/4’s speaker outputs are designed
to accept 16 AWG - 8 AWG wire. To connect the
speaker wires to the amplifier, first back out the
set screws on the top of the terminal block, using
the supplied 2.5 mm hex wrench. Strip 1/2 inch
(12 mm) of insulation from the end of each wire
and insert the bare wire into the terminal block,
seating it firmly so that no bare wire is exposed.
While holding the wire in place, tighten the set
screw firmly, taking care not to strip the head of
the screw.
Each pair of the XD400/4’s channels are
designed to deliver power into speaker loads equal
to or greater than 2 ohms when using a “stereo”
configuration and speaker loads equal to or greater
than 4 ohms when using a “bridged” configuration.
Speaker loads below 2 ohms nominal per
channel (or 4 ohms bridged) are not
recommended and may cause the amplifier
to initiate a protection mode which reduces
power output.
BRIDGING CONSIDERATIONS
Bridging is the practice of combining the
output of two amplifier channels to drive a single
load. When bridged, each channel produces
signals of equal magnitude, but opposite polarity.
The combined output of the two channels
provides twice the output voltage available from
a single channel. The XD400/4 has been designed
for bridging of its channel pairs without the need
for input inversion adaptors.
To bridge a pair of channels, use the “Left +”
and “Right –”speaker connectors only (the
“Left –”and “Right +”remain unused). When
bridged, each channel will deliver optimum
power into a 4 ohm load.
When a pair of channels are bridged, they
will deliver 200W x 1 into a 4 ohm load or
150W x 1 into an 8 ohm load. Operating a
pair of bridged channels into a load lower
than 4 ohms is not recommended.
Because a bridged pair of channels requires
that both channels receive input, you need to
connect both left and right inputs to the source
unit. Connection of only one input will result in
reduced power output, increased distortion and
can cause the amplifier to overheat.
Do not do this!
When a pair of the XD400/4’s channels are
operating in bridged mode, the output will be in
mono (only one channel). This mono channel
can contain right channel only information,
left channel only information or the sum of
the information from both the right and left
channels. In order to achieve one of these options,
configure the inputs to that pair of channels in
one of these two ways:
1) Left Channel Only or Right Channel Only
Information: If you wish to send a left-only
or right-only signal to a pair of the XD400/4’s
channels, use a “Y-Adaptor” to split the single
channel signal into both left and right RCA
inputs. This option is useful when using a
pair of the XD400/4’s channels to drive left
channel speakers only and the other pair of
the XD400/4’s channels to drive right channel
speakers only.
2) Left + Right Channel Information: When
bridged and fed by a stereo input, a pair of the
XD400/4’s channels will automatically combine
the left and right channels into a summed
mono (left + right) channel. This option is
useful when using a pair of the XD400/4’s
channels to drive a subwoofer system or a
summed mono center channel.

11
ENGLISH
STATUS LED / PROTECTION CIRCUITRY
There is a single multi-color LED on the top
surface of the amplifier to indicate the amplifier’s
operating status.
1 ) F l a s h i n g G r e e n : amplifier is powering up,
audio output is muted.
2) Constant Green: amplifier is on and
functioning normally, audio output is active.
3) Constant Red: Indicates that the
amplifier has exceeded its safe operating
temperature, putting the amplifier into a
self-protection mode, which reduces the
peak power output of the amplifier. When its
temperature returns to a safe level, the red
light will return to green and the amplifier will
return to full-power operating mode.
4) Constant Amber (yellow): Indicates
that an over-current condition has occurred
and is accompanied by a muting of the affected
channel(s). Because the muting behavior may be
very short in duration, it may manifest itself as
an audible, repetitive ticking noise in the output.
Over-current conditions can be caused by a
speaker impedance lower than the optimum load
impedance range for the amplifier or a short-
circuit in the speaker wiring. The latter can result
from a short circuit between the positive and
negative speaker wires or between either speaker
wire and the vehicle chassis. The “Status LED”
will remain amber for a few seconds, even if the
over-current condition is of a very short duration.
This functionality can be used to diagnose a
short-circuit by only connecting one channel at
a time. The “Status LED” will turn amber when
you connect the channel that is experiencing
the problem and turn the volume up.
5) LED off / Amplifier Shuts Off Unexpectedly
The only condition that will shut down
an undamaged XD400/4 completely is if battery
voltage or remote turn-on voltage drops below
10 volts. The “Status LED” will turn off when
this occurs. The amplifier will turn back on
when voltage climbs back above 11 volts. If this
is happening in your system, have your charging
system and power wiring inspected.
For more information on troubleshooting this
amplifier, refer to Appendix D (pages 16, 17).
SERVICING YOUR JL AUDIO AMPLIFIER
If your amplifier fails or malfunctions, please
return it to your authorized JL Audio dealer so
that it may be sent in to JL Audio for service.
There are no user serviceable parts or fuses inside
the amplifier. The unique nature of the circuitry
in the JL Audio amplifiers requires specifically
trained service personnel. Do not attempt
to service the amplifier yourself or through
unauthorized repair facilities. This will not only
void the warranty, but may result in the creation of
more problems within the amplifier.
If you have any questions about the installation or
setup of the amplifier not covered in this manual,
please contact your dealer or technical support.
JL Audio Technical Support:
(9 54) 4 4 3-110 0
9:00 AM – 5:30 PM (Eastern Time Zone)
Monday - Friday


12 | JL Audio - XD400/4 Owner’s Manual
SYSTEM CONFIGURATIONS
The XD400/4 is a flexible amplifier, well-
suited for a multitude of system configurations.
In this section, the most likely configurations for
a system with a single XD400/4 are explained in
detail.
Once you have selected your desired
configuration, you can use the amplifier panel
drawing on pages 18 & 19 to mark the required
switch positions for easy reference.
BIAMPLIFIED SYSTEMS
Bi-amplified systems are defined as systems
in which separate amplifier channels drive low-
frequency (LF) and high-frequency (HF) speakers
and are separately filtered to send appropriate
frequency ranges to each speaker system.
The most common application of
bi-amplification in mobile audio is to drive a
subwoofer system from one or more amplifiers or
channels and component speakers from separate
amplifiers or channels.
The XD400/4 can be configured to drive a
bi-amplified system by itself or with a separate
subwoofer amplifier.
Bi-Amplified System with one XD400/4
In this configuration, channels 3&4 of the
XD400/4 will drive subwoofers (stereo or bridged)
with low-pass filtering. Channels 1&2 will
drive component speakers in stereo with
high-pass filtering.
Input connection options for a bi-amplified system
with one XD400/4 are as follows:
A) No User Adjustability:
R e q u i r e d : a basic source unit or processor
with one pair of stereo outputs.
Input Connections: a single pair of stereo source
unit outputs connected to the “CH 1 (Left)”
and“CH 2 (Right)” inputs of the XD400/4
(select “2 Ch.”on the “Input Mode”switch).
R e s u l t : the relative level of the LF and HF
channels will be determined by the XD400/4’s
“Input Sens.” settings and will not be user
adjustable from the front of the vehicle.
B ) Fade Subwoofer Level vs. HF Level
R e q u i r e d : a source unit or processor with two
pairs of stereo outputs.
Input Connections: the first stereo pair of source
unit outputs is connected to the “CH 1 (Left)”
and “CH 2 (Right)” inputs of the XD400/4.
The second stereo pair of source unit outputs
is connected to the “CH 3 (Left)” and “CH 4
(Right)” inputs (select “4 Ch.” on the “Input
Mode” switch).
R e s u l t : in this mode, the user has the ability to
fade or control the level of the LF channels
relative to the HF channels via the source
unit’s fader control without exceeding the
maximum clean output level set by each
amplifier section’s “Input Sens.” controls.
C) Subwoofer Level Control Only:
R e q u i r e d : a source unit or processor with
one pair of stereo outputs and dedicated
subwoofer outputs.
Input Connections: the main stereo pair of
source unit outputs is connected to the “CH
1 (Left)” and “CH 2 (Right)” inputs of
the XD400/4. The source unit’s dedicated
subwoofer output is connected to the “CH
3 (Left)” and “CH 4 (Right)”inputs (select
“4 Ch.” on the “Input Mode” switch).
R e s u l t : in this mode, the user has the ability to
control the absolute level of the LF channels
relative to the HF channels.
Set the “Input Sens.” in the “Channel 3 & 4
Controls” section with the source unit’s
subwoofer level control set at 3/4 of full output.
See Appendix A (page 14) for details.
Crossover Setup for Bi-Amplified System
with one XD400/4:
Once the input sections have been configured
appropriately, go to the “Channel 3 & 4
Controls”. Select “LP” (low-pass) on the “Filter
Mode” switch and an appropriate “Filter Freq.”
(80 Hz is a good starting point).
Next, turn your attention to the “Channel 1 &
2 Controls”and select “HP”(high-pass) on the
“Filter Mode”switch and an appropriate “Filter
Freq.”(again, 80 Hz is a good starting point).
After proper adjustment of the “Input
Sens.” controls for both channel pairs using
the method shown in Appendix A (page

13
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14), you can fine tune filter frequencies and
attenuate either pair of channels to achieve
proper balance. For precise filter frequency
information refer to Appendix B (page 15).
MULTIAMPLIFIER SYSTEMS
Using the “Preamp Outputs” of the
XD400/4, it is easy to configure many
different multi-amplifier systems.
The most common type involves the
addition of a subwoofer amplifier, such
as the XD600/1. Common configurations
of such a system are described below.
Bi-Amplified System with one XD400/4 in
four-channel mode and a separate
subwoofer amplifier
This configuration requires that the separate
subwoofer amplifier has a built-in low-pass filter.
(All JL Audio amplifiers have this feature.)
In this configuration, channels 1&2 of the
XD400/4 will drive front component speakers
in stereo with high-pass filtering. Channels 3&4
will drive rear component speakers in stereo, also
with high-pass filtering. The separate amplifier
will drive the subwoofer system with low-pass
filtering (80 Hz is a good starting point).
Here are three possible configuration options:
A) Fade Subwoofer Level vs. HF Level:
R e q u i r e d : a source unit or processor with front
and rear pairs of stereo outputs.
Input Connections: one stereo pair of source unit
outputs is connected to the “CH 1 (Left)” and
“CH 2 (Right)” inputs of the XD400/4 (select
“2 Ch.” on the “Input Mode” switch). The
second stereo pair of source unit outputs is
connected to the subwoofer amplifier inputs.
R e s u l t : with this option, the user has the ability
to fade the level of the subwoofer amplifier’s
input relative to the HF channels, but
cannot control front-to-rear fading of the
HF channels. The relative level of the front
and rear HF channels will be fixed by the
XD400/4’s “Input Sens.” settings and will not
be user adjustable from the front of the vehicle.
B) Subwoofer Level Control Only:
Required: a source unit or processor with left,
right and dedicated subwoofer outputs.
Input Connections: The main stereo pair
of source unit outputs is connected to the
“CH 1 (Left)” and “CH 2 (Right)” inputs of
the XD400/4 (select “2 Ch.” on the “Input
Mode” switch). The source unit’s dedicated
subwoofer output is connected to the
subwoofer amplifier inputs.
R e s u l t : with this option, the user has the ability
to control the absolute level of the subwoofer
channel relative to the HF channels, but
cannot fade the front and rear HF channels
relative to each other.
Set the subwoofer amplifier’s “Input Sens.”
with the source unit’s subwoofer level control
set at 3/4 of full output.
C) Front to Rear HF Fading and Subwoofer
Level Control:
R e q u i r e d : a source unit or processor with
front and rear pairs of stereo outputs plus a
dedicated subwoofer output.
Input Connections: one stereo pair of source unit
outputs is connected to the “CH 1 (Left)”and
“CH 2 (Right)” inputs of the XD400/4.
The second stereo pair of source unit outputs
is connected to the “CH 3 (Left)”and “CH
4 (Right)” inputs of the XD400/4 (select
“4 Ch.”on the “Input Mode” switch). The
source unit’s dedicated subwoofer output is
connected to the subwoofer amplifier inputs.

14 | JL Audio - XD400/4 Owner’s Manual
APPENDIX A:
Input Sensitivity Level Setting
Following the directions below will allow the
installer to adjust the input sensitivity of each
amplifier channel pair simply and easily in just a
few minutes using equipment which is commonly
available in installation bays.
Necessary Equipment
• Digital AC Voltmeter
• CD with a sine-wave test tone recorded at
0 dB reference level in the frequency range
to be amplified for that set of channels
(50 Hz for subwoofer channels, 1 kHz for a
midrange application). Do not use attenuated
test tones (-10 dB, -20 dB, etc.).
The Nine-Step Procedure
1) Disconnect the speaker(s) from the
amplifier’s speaker output connectors.
2) Turn off all processing (bass/treble, loudness,
EQ, etc.) on the source unit, processors (if
used) and amplifier. Set fader control to center
position and subwoofer level control to 3/4 of
maximum (if used to feed the XD400/4).
3) Turn both “Input Sens.” controls all the way
down.
4) Set the source unit volume to 3/4 of full
volume. This will allow for reasonable gain
overlap with moderate clipping at full volume.
5) Using the chart on this page, determine the target
voltage for input sensitivity adjustment according
to the nominal impedance of the speaker system
connected to the amplifier outputs.
6) Verify that you have disconnected the speakers
before proceeding. Play a track with an
appropriate sine wave (within the frequency
range to be amplified by the XD400/4) at 3/4
source unit volume.
7) Connect the AC voltmeter to the speaker output
connectors of the amplifier. If the channel
pair is operating in stereo, it is only necessary
to measure one channel. If bridged, make sure
you test the voltage at the correct connectors
(L+ and R–).
8) Increase the “Input Sens.” control until the
target voltage is observed with the voltmeter.
9) Once you have adjusted the XD400/4 to
its maximum low-distortion output level,
reconnect the speaker(s). The “Input Sens.”
controls can now be adjusted downward if the
amplifier requires attenuation to achieve the
desired system balance.
Do not increase any “Input Sens.” setting for
any amplifier channel or channel pair in the
system beyond the maximum level established
during this procedure. Doing so will result in
audible distortion and possible speaker damage.
It will be necessary to re-adjust the
“Input Sens.” for the affected channels if any
equalizer boost is activated after setting the
“Input Sens.” with this procedure. This applies
to any EQ boost circuit, including source unit
tone controls or EQ circuits. EQ cuts will not
require re-adjustment.
Nom.
Impedance
Target AC Voltage
Stereo Bridged
8 17.4 V 34.8 V
6 17.4 V 32.8 V
4 17.4 V 28.2 V
3 16.4 V not recommended
2 14.1 V not recommended

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APPENDIX C:
XD400/4 Specifications
General Specifications:
Recommended Fuse Value: 40A
Recommended Fuse Type: MAXI® or AGU
Input Sections:
No. of Inputs: Two Stereo Pairs
Input Type: Differential-balanced with RCA jack inputs
Input Range: 100mV - 4V RMS
Amplifier Section:
Amplifier Topology: NexD™ Ultra-High Speed Class D
Power Supply: Unregulated MOSFET switching type
Rated Power at 14.4V with less than
1% THD+Noise (20Hz - 20 kHz)
Stereo, all channels driven:
75W RMS x 4 @ 4 ohms, 100W RMS x 4 @ 2 ohms
Bridged, all channels driven:
150W RMS x 2 @ 8 ohms, 200W RMS x 2 @ 4 ohms
Rated Power @ 12.5V with less than
1% THD + Noise (20Hz - 20 kHz)
Stereo, all channels driven:
60W RMS x 4 @ 4 ohms, 90W RMS x 4 @ 2 ohms
Rated Power Bridged, all channels driven:
120W RMS x 2 @ 8 ohms, 180W RMS x 2 @ 4 ohms
Signal to Noise Ratio:
>104 dB referred to rated power
(A-weighted, 20 Hz-20 kHz noise bandwidth)
>84 dB referred to 1W
(A-weighted, 20 Hz-20 kHz noise bandwidth)
Frequency Response: 12 Hz - 22 kHz (+0, -1dB)
Damping Factor:
>150 @ 4 ohms per ch./ 50 Hz
>75 @ 2 ohms per ch. / 50 Hz
Crossover Filters:
Filter Type: State-variable, 12dB/octave Butterworth
with continuously variable cutoff frequency selection
from 50-500 Hz.
Configurable as Low-Pass or High-Pass. Defeatable.
Dimensions (LxWxH):
8.52” x 7.09” x 2.05” (217mm x 180mm x 52mm)
APPENDIX B:
Precise Frequency Selection Chart
“FILTER FREQ”
Detent Panel Actual
Number Marking Freq.
Full counter-clockwise: 49
01 ............................49
02 ...........“50” ............49
03 ............................50
04 ............................50
05 ............................52
06 ............................53
07 ............................55
08 ...........“60” ............57
09 ............................59
10 ............................61
11 ............................63
12 ............................65
13 ............................68
14 ............................70
15 ............................73
16 ...........“80” ............76
17 ............................79
18 ............................83
19 ............................86
20 .......“12 o’clock” ........90
21 ............................95
22 ...........................100
23 ...........................105
24 ..........“120” ..........111
25 ...........................118
26 ...........................126
27 ...........................135
28 ...........................146
29 ...........................160
30 ...........................174
31 ...........................192
32 ..........“200” ..........217
33 ...........................243
34 ...........................286
35 ...........................339
36 ...........................406
37 ...........................444
38 ..........“500” ..........482
39 ...........................483
Full-clockwise: 483
Due to ongoing product development, all specifications are subject to
change without notice.

16 | JL Audio - XD400/4 Owner’s Manual
“How do I properly set the input sensitivity on my amplifier?”
Please refer to Appendix A (page 14) to set the input sensitivity for
maximum, low-distortion output.
“My amplifier doesn’t turn on.”
Check the fuse, not just visually, but with a continuity meter. It is
possible for a fuse to have poor internal connections that
cannot be found by visual inspection. It is best to take the
fuse out of the holder for testing. If no problem is found with
the fuse, inspect the fuse-holder.
Check the integrity of the connections made to each of the
“+12VDC”, “Ground”, and “Remote” terminals. Ensure
that no wire insulation is pinched by the terminal set screw
and that each connection is tight.
Check to make sure there is +12V at the “Remote” connection of the
amplifier. In some cases, the turn-on lead from the source unit
is insufficient to turn on multiple devices and the use of a relay
is required. To test for this problem, jump the “+12VDC”wire
to the “Remote” terminal to see if the amplifier turns on.
“I get a repetitive ticking or popping sound coming out of the speaker(s).”
Check the speaker wires for a possible short, either between the
positive and negative leads or between either speaker lead
and the vehicle’s chassis ground. If a short is present, you will
experience distorted and/or attenuated output. The “Status
LED” will turn Amber (yellow) in this situation. It may be
helpful to disconnect the speaker wires from the amplifier
and use a different set of wires connected to a test speaker.
Check the nominal load impedance to verify that each channel
of the amplifier is driving a load equal to or greater than
2 ohms in stereo mode (4 ohms bridged).
“My amplifier’s output fluctuates when I tap on it or hit a bump.”
Check the connections to the amplifier. Make sure that the
insulation for all wires has been stripped back far enough to
allow a good contact area inside the terminal block.
Check the input connectors to ensure that they all are making good
contact with the input jacks on the amplifier.
APPENDIX D: TROUBLESHOOTING

17
ENGLISH
“My amplifier shuts off once in a while, usually at higher volumes.”
Check your voltage source and grounding point. The power supply
of the XD400/4 will operate with charging system voltages
down to 10V. Shutdown problems at higher volume levels
can occur when the charging system voltage (or remote turn-
on voltage) momentarily drops below 10V. These dips can
be of very short duration making them extremely difficult
to detect with a common DC voltmeter. To ensure proper
voltage, inspect all wiring and termination points. It may
also be necessary to upgrade the ground wire connecting the
battery to the vehicle’s chassis and the power wire connecting
the alternator to the battery. Many vehicles employ small (10
AWG - 6 AWG) wire to ground the battery to the vehicle’s
chassis and to connect the alternator to the battery. To prevent
voltage drops, these wires should be upgraded to 4 AWG
when installing amplifier systems with main fuse ratings
above 60A. Grounding problems are the leading cause of
misdiagnosed amplifier “failures.”
“My amplifier turns on, but there is no output.”
Check the input signal using an AC voltmeter to measure the
voltage from the source unit while an appropriate test tone is
played through the source unit (disconnect the input cables
from the amplifier prior to this test). The frequency used
should be in the range that is to be amplified by the amplifier
(example: 50 Hz for a sub bass application or 1 kHz for a full
range / high-pass application). A steady, sufficient voltage
(between 0.1 and 4.0-volts) should be present at the output of
the signal cables.
Check the output of the amplifier. Using the procedure explained in
the previous check item (after plugging the input cables back
into the amplifier) test for output at the speaker outputs of
the amplifier. Remove the speaker wires from the amplifier
while doing this to prevent unpleasant noise and possible
speaker damage. Turn the volume up approximately half
way. 5V AC or more should be measured at the speaker
outputs. This output level can vary greatly between
amplifiers but it should not be in the millivolt range with
the source unit at half volume. If you are reading sufficient
voltage, check your speaker connections as explained below.
Check to ensure that the speaker wires are making a good
connection with the metal inside the terminal block. The
speaker wire connectors are designed to accept up to 8 AWG
wire. Make sure to strip the wire to allow for a sufficient
connection with the metal inside the terminal block.

18 | JL Audio - XD400/4 Owner’s Manual
INSTALLATION NOTES:
Use this diagram to document your amplifier’s switch and control positions.

19
ENGLISH

LIMITED WARRANTY  AMPLIFIERS USA
JL AUDIO warrants this product to be free of defects in materials and workmanship for a
period of two (2) years. The warranty is extended to three (3) years total if installation is performed by an
authorized JL Audio dealer using a JL Audio Premium Power Connection System for power wiring.
This warranty is not transferrable and applies only to the original purchaser from an authorized
JL AUDIO dealer. Should service be necessary under this warranty for any reason due to manufacturing
defect or malfunction, JL AUDIO will (at its discretion), repair or replace the defective product with new
or remanufactured product at no charge. Damage caused by the following is not covered under warranty:
accident, misuse, abuse, product modification or neglect, failure to follow installation instructions,
unauthorized repair attempts, misrepresentations by the seller. This warranty does not cover incidental
or consequential damages and does not cover the cost of removing or reinstalling the unit(s). Cosmetic
damage due to accident or normal wear and tear is not covered under warranty.
Warranty is void if the product’s serial number has been removed or defaced.
Any applicable implied warranties are limited in duration to the period of the express warranty as
provided herein beginning with the date of the original purchase at retail, and no warranties, whether
express or implied, shall apply to this product thereafter. Some states do not allow limitations on implied
warranties, therefore these exclusions may not apply to you. This warranty gives you specific legal rights,
and you may also have other rights which vary from state to state.
If you need service on your JL AUDIO product:
All warranty returns should be sent to JL AUDIO ’s Amplifier Service Facility freight-prepaid through
an authorized JL AUDIO dealer and must be accompanied by proof of purchase (a copy of the original
sales receipt). Direct returns from consumers or non-authorized dealers will be refused unless specifically
authorized by JL AUDIO with a valid return authorization number.
Warranty expiration on products returned without proof of purchase will be determined from the
manufacturing date code. Coverage may be invalidated as this date is previous to purchase date. Non-
defective items received will be returned freight-collect. Customer is responsible for shipping charges and
insurance in sending the product to JL AUDIO. Freight damage on returns is not covered under warranty.
For Service Information in the U.S.A. please call
JL Audio Customer Service: [phone]
9:00 AM – 5:30 PM (Eastern Time Zone)
JL Audio, Inc
10369 North Commerce Pkwy.
Miramar, FL 33025
(do not send product for repair to this address)
International Warranties:
Products purchased outside the United States of America are covered only
by that country’s distributor and not by JL Audio, Inc.