OWNER’S MANUAL

400W 2/3/4 Channel Amplifier

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 (954) 443-1100 during business hours.

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 PROTECT YOUR HEARING! INSTALLATION APPLICATIONS
We value you as a long-term customer. For This amplifier is designed for operation in
that reason, we urge you to practice restraint in vehicles with 12 volt, negative-ground electrical
the operation of this product so as not to damage systems. Use of this product in vehicles with
your hearing and that of others in your vehicle. positive ground and/or voltages other than 12V
Studies have shown that continuous exposure to may result in damage to the product and will void
high sound pressure levels can lead to permanent the warranty.
(irreparable) hearing loss. This and all other This product is not certified or approved for
high-power amplifiers are capable of producing use in aircraft.
such high sound pressure levels when connected Do not attempt to “bridge” the outputs of this
to a speaker system. Please limit your continuous amplifier with the outputs of a second amplifier,
exposure to high volume levels. including an identical one.
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:

Pre-Out Signal Input Remote Ch. 1 & 2 Ch. 1 & 2 Filter Ch. 3 & 4 Ch. 3 & 4 Filter
Selection Mode Level Mode Status Filter Mode Frequency Filter Mode Frequency
Switch Switch Switch LED Selection Selector Selection Selector
(pg. 9) (pg. 6) (pg. 9) (pg. 11) (pg. 8) (pg. 8) (pg. 8) (pg. 8)
Ch. 1 & 2 Input Ch. 3 & 4 Input
Sensitivity Control Sensitivity Control
(pg. 7) (pg. 7)

2 | JL Audio - XD400/4 Owner’s Manual

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 PLANNING YOUR INSTALLATION
It is important that you take the time to read
this manual and that you plan out your Mounting the amplifier upside down is
installation carefully. The following are some strongly discouraged. If mounting the amplifier
considerations that you must take into account under a seat, make sure there is at least 1 inch
when planning your installation. (2.5 cm) of space above the amplifier’s outer

ENGLISH
shell to permit proper cooling.
Cooling Efficiency Considerations:
The outer shell of your JL Audio amplifier is Safety Considerations:
designed to remove heat from the amplifier Your amplifier needs to be installed in a dry,
circuitry. For optimum cooling performance, this well-ventilated environment and in a manner
outer shell should be exposed to as large a volume which does not interfere with your vehicle’s safety
of air as possible. Enclosing the amplifier in a equipment (air bags, seat belt systems, ABS brake
small, poorly ventilated chamber can lead to systems, etc.). You should also take the time to
excessive heat build-up and degraded securely mount the amplifier so that it does not
performance. If an installation calls for an come loose in the event of a collision or a sudden
enclosure around the amplifier, we recommend jolt to the vehicle.
that this enclosure be ventilated with the aid
of a fan. In normal applications, fan-cooling Stupid Mistakes to Avoid
is not necessary. t

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.
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the vehicle. This is an extremely dangerous
practice which can result in severe damage to
your vehicle and person.
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edges and wear by carefully routing them,
tying them down and using grommets and
loom where appropriate.
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compartment, under the vehicle, on the roof
or in any other area that will expose the
amplifier circuitry to the elements.

Chassis Ground Channels 1 & 2 Left & Right Preamp

Connector Preamp Input Jacks Output Jacks
(pg. 5) (pg. 6) (pg. 9) Jack for
+12 V Power Remote Turn-On Channels 3 & 4 Remote Level Channels 1 & 2 Channels 3 & 4
Connector Connector Preamp Input Jacks Control Knob Speaker Outputs Speaker Outputs
(pg. 5) (pg. 6) (pg. 6) (pg. 9) (pg. 10) (pg. 10)

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

4 | JL Audio - XD400/4 Owner’s Manual

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 POWER CONNECTIONS
Before installing the amplifier, disconnect the The ground connection should be made
negative (ground) wire from the vehicle’s battery. using 8 or 4 AWG wire and should be kept
This will prevent accidental damage to the system, as short as possible, while accessing a solid
the vehicle and your body during installation. piece of sheet metal in the vehicle. The
surface of the sheet metal should be sanded

ENGLISH
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
The XD400/4’s “+12 VDC” and “Ground” in a dangerous short circuit.
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 Many vehicles employ small (10 AWG -
amplifiers and wish to use a single main power 6 AWG) wire to ground the battery to the
wire, use 4 AWG, 2 AWG or 1/0 AWG main vehicle chassis and to connect the alternator's
power wire (depending on the overall current positive connection to the battery. To prevent
demands of all the amplifiers in the system). voltage drops, these wires should be upgraded
This large power wire should terminate into a to 4 AWG when installing amplifier systems
fused distribution block mounted as close to with main fuse ratings above 60A.
the amplifiers as possible (within 12 inches /
30cm of wire length). The fused output of the FUSE REQUIREMENTS
distribution block will connect to the XD400/4 It is absolutely vital that the main power
with 4 AWG power wire. JL Audio ECS wire(s) to the amplifier(s) in the system be
fused distribution blocks are recommended fused within 18 inches (45 cm) of the positive
(XD-FDBU-2 and XD-FDBU-4) battery post connection. The fuse value at each
power wire should be high enough for all of the
Note: Smaller AWG numbers mean bigger equipment being run from that power wire. If
wire and vice-versa (1/0 AWG is the largest, 2 only the XD400/4 is being run from that power
AWG is smaller, then 4 AWG, then 8 AWG, etc.). wire, we recommend a 40A fuse be used.
If fusing the amplifier near its power
To connect the power wires to the amplifier, connections (when more than one amp is being
first back out the set screw on the top of the run from the main power wire), use a 40A fuse.
terminal block, using the supplied 2.5 mm hex MAXI™ plastic-body fuses are recommended.
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.

5
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 TURN-ON LEAD INPUT SECTION
The XD400/4 uses a conventional +12V remote The XD400/4’s input section allows you to
turn-on lead, typically controlled by the source send signals to the amplifier section through the
unit's remote turn-on output. The amplifier will use of two or four differential-balanced inputs.
turn on when +12V is present at its “Remote” Input connections are via up to two pairs of
input and turn off when +12V is switched off. If traditional RCA-type jacks.
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.

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.

6 | JL Audio - XD400/4 Owner’s Manual

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 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

ENGLISH
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.

7
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 FILTER CONTROLS
Most speakers are not designed to reproduce types or defeated completely by way of the
the full range of frequencies audible by the human three-position “Filter Mode” switches:
ear. For this reason, most speaker systems are “Off”: Defeats the filter completely, allowing
comprised of multiple speakers, each dedicated the full range of frequencies present at the
to reproducing a specific frequency range. Filters inputs to feed the amplifier. This is useful for
are used to select which frequency range is sent systems utilizing outboard active crossovers or
to each section of a speaker system. The division requiring full-range reproduction from one or
of frequency ranges to different speakers can be more of the XD400/4’s channel pairs.
done with passive filters (coils and/or capacitors “LP” (Low-Pass): Configures the filter to
between the amplifier outputs and the speakers), attenuate frequencies above the selected filter
which are acceptable and commonly used frequency at a rate of 12dB per octave. This is
for filtering between mid-range speakers and useful for connection of subwoofer(s) to one
tweeters. Filtering between subwoofer systems or more of the XD400/4’s channel pairs in a
and satellite speaker systems is best done with bi-amplified system.
active filters, which cut off frequency content at “HP” (High-Pass): Configures the filter to
the input to the amplifier. Active filters are more attenuate frequencies below the selected filter
stable than passive filters and do not introduce frequency at a rate of 12dB per octave. This is
extraneous resistance, which can degrade useful for connection of component speakers to
subwoofer performance. one or more of the XD400/4’s channel pairs in
The active filter built into each channel a bi-amplified system.
section of the XD400/4 can be used to eliminate
potentially harmful and/or undesired frequencies 2) “Filter Freq. (Hz)” The filter frequency
from making their way through the amplifier markings surrounding this rotary control
sections to the speaker(s). This serves to improve are for reference purposes and are generally
tonal balance and to avoid distortion and possible accurate to within 1/3 octave or better. If you
speaker failure. Correct use of these filters can would like to select the filter cutoff frequency
substantially increase the longevity and fidelity of with a higher level of precision, consult the
your audio system. 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.

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

8 | JL Audio - XD400/4 Owner’s Manual

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 REMOTE LEVEL CONTROL (OPTIONAL) 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

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“Preouts From”.

1) “1&2”: The preamp output delivers the same

With the addition of the optional Remote signal that is connected to the CH 1&2 Inputs.
Level Control (HD-RLC), you can control the This mode is useful for feeding a subwoofer
volume of one, or both channel pairs of the amplifier when the XD400/4 is being used to
XD400/4 from the front of the vehicle. This is drive front and rear speaker systems. In this
useful for subwoofer level control, rear channel mode, the preamp output signal will depend
level control, center-channel level control or even only on the input signal level of CH 1&2,
as a master volume control for the system. allowing Channels 3&4 to be faded without
The HD-RLC connects to the jack labeled affecting the subwoofer level. If CH 1&2 is
“Remote Level Control” on the Connection Panel faded in this mode, the signal level of the
of the amplifier using a standard telephone cable preamp output will change accordingly.
(supplied with the HD-RLC). If desired, multiple 2) “Sum”: When the XD400/4 is being used
XD (and HD) amplifiers can be controlled from to drive front and rear speaker systems, this
a single HD-RLC controller using a simple phone preamp output mode will deliver a summed
line “splitter” and multiple phone cables. front/rear stereo signal to a subwoofer amplifier,
When connected to the amplifier, the while permitting fading of the front and
HD-RLC operates as follows. At full counter- rear speaker systems from the source unit.
clockwise rotation, the audio will mute This method prevents a loss of signal to the
completely. At full clockwise rotation the level subwoofer amplifier when the system is faded to
will be the same as if the HD-RLC was not the front or the rear by the head unit.
connected at all. In other words, it operates
strictly as a level attenuator. 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
“Remote Level Mode” Switch: This switch defeated at the source unit, we recommend that
allows you to assign the operation of the you use the “1&2” position.
HD-RLC to one, or both pairs of channels. In
the “All” position, the HD-RLC knob will affect Note: In either mode, the preamp output signal is
all three channel pairs equally. In the “3&4” not affected by any crossover filter selected (if the
position, only the level of channels 3 and 4 will input signal is full-range, the preamp output will
be affected by the HD-RLC knob (Channels 1 & be full-range).
2 will not).

9
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 SPEAKER OUTPUTS “Left –” and “Right +” remain unused). When
The XD400/4’s speaker outputs are designed bridged, each channel will deliver optimum
to accept 16 AWG - 8 AWG wire. To connect the power into a 4 ohm load.
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 When a pair of channels are bridged, they
(12 mm) of insulation from the end of each wire will deliver 200W x 1 into a 4 ohm load or
and insert the bare wire into the terminal block, 150W x 1 into an 8 ohm load. Operating a
seating it firmly so that no bare wire is exposed. pair of bridged channels into a load lower
While holding the wire in place, tighten the set than 4 ohms is not recommended.
screw firmly, taking care not to strip the head of Because a bridged pair of channels requires
the screw. that both channels receive input, you need to
Each pair of the XD400/4’s channels are connect both left and right inputs to the source
designed to deliver power into speaker loads equal unit. Connection of only one input will result in
to or greater than 2 ohms when using a “stereo” reduced power output, increased distortion and
configuration and speaker loads equal to or greater can cause the amplifier to overheat.
than 4 ohms when using a “bridged” configuration. 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
Speaker loads below 2 ohms nominal per or right-only signal to a pair of the XD400/4’s
channel (or 4 ohms bridged) are not channels, use a “Y-Adaptor” to split the single
recommended and may cause the amplifier channel signal into both left and right RCA
to initiate a protection mode which reduces inputs. This option is useful when using a
power output. pair of the XD400/4’s channels to drive left
channel speakers only and the other pair of
BRIDGING CONSIDERATIONS the XD400/4’s channels to drive right channel
Bridging is the practice of combining the speakers only.
output of two amplifier channels to drive a single
load. When bridged, each channel produces 2) Left + Right Channel Information: When
signals of equal magnitude, but opposite polarity. bridged and fed by a stereo input, a pair of the
The combined output of the two channels XD400/4’s channels will automatically combine
provides twice the output voltage available from the left and right channels into a summed
a single channel. The XD400/4 has been designed mono (left + right) channel. This option is
for bridging of its channel pairs without the need useful when using a pair of the XD400/4’s
for input inversion adaptors. channels to drive a subwoofer system or a
To bridge a pair of channels, use the “Left +” summed mono center channel.
and “Right –” speaker connectors only (the

10 | JL Audio - XD400/4 Owner’s Manual

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 STATUS LED / PROTECTION CIRCUITRY
There is a single multi-color LED on the top 5) LED off / Amplifier Shuts Off Unexpectedly
surface of the amplifier to indicate the amplifier’s The only condition that will shut down
operating status. 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

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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
Ï system and power wiring inspected.

For more information on troubleshooting this

amplifier, refer to Appendix D (pages 16, 17).

1) Flashing Green: amplifier is powering up,

audio output is muted. SERVICING YOUR JL AUDIO AMPLIFIER
If your amplifier fails or malfunctions, please
2) Constant Green: amplifier is on and return it to your authorized JL Audio dealer so
functioning normally, audio output is active. that it may be sent in to JL Audio for service.
There are no user serviceable parts or fuses inside
3) Constant Red: Indicates that the the amplifier. The unique nature of the circuitry
amplifier has exceeded its safe operating in the JL Audio amplifiers requires specifically
temperature, putting the amplifier into a trained service personnel. Do not attempt
self-protection mode, which reduces the to service the amplifier yourself or through
peak power output of the amplifier. When its unauthorized repair facilities. This will not only
temperature returns to a safe level, the red void the warranty, but may result in the creation of
light will return to green and the amplifier will more problems within the amplifier.
return to full-power operating mode.
If you have any questions about the installation or
4) Constant Amber (yellow): Indicates setup of the amplifier not covered in this manual,
that an over-current condition has occurred please contact your dealer or technical support.
and is accompanied by a muting of the affected
channel(s). Because the muting behavior may be JL Audio Technical Support:
very short in duration, it may manifest itself as (954) 443-1100
an audible, repetitive ticking noise in the output. 9:00 AM – 5:30 PM (Eastern Time Zone)
Over-current conditions can be caused by a Monday - Friday
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.

11
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 SYSTEM CONFIGURATIONS
The XD400/4 is a flexible amplifier, well- Input Connections: the first stereo pair of source
suited for a multitude of system configurations. unit outputs is connected to the “CH 1 (Left)”
In this section, the most likely configurations for and “CH 2 (Right)” inputs of the XD400/4.
a system with a single XD400/4 are explained in The second stereo pair of source unit outputs
detail. is connected to the “CH 3 (Left)” and “CH 4
Once you have selected your desired (Right)” inputs (select “4 Ch.” on the “Input
configuration, you can use the amplifier panel Mode” switch).
drawing on pages 18 & 19 to mark the required Result: in this mode, the user has the ability to
switch positions for easy reference. fade or control the level of the LF channels
relative to the HF channels via the source
BI-AMPLIFIED SYSTEMS unit’s fader control without exceeding the
Bi-amplified systems are defined as systems maximum clean output level set by each
in which separate amplifier channels drive low- amplifier section’s “Input Sens.” controls.
frequency (LF) and high-frequency (HF) speakers
and are separately filtered to send appropriate C) Subwoofer Level Control Only:
frequency ranges to each speaker system. Required: a source unit or processor with
The most common application of one pair of stereo outputs and dedicated
bi-amplification in mobile audio is to drive a subwoofer outputs.
subwoofer system from one or more amplifiers or Input Connections: the main stereo pair of
channels and component speakers from separate source unit outputs is connected to the “CH
amplifiers or channels. 1 (Left)” and “CH 2 (Right)” inputs of
The XD400/4 can be configured to drive a the XD400/4. The source unit’s dedicated
bi-amplified system by itself or with a separate subwoofer output is connected to the “CH
subwoofer amplifier. 3 (Left)” and “CH 4 (Right)” inputs (select
“4 Ch.” on the “Input Mode” switch).
Bi-Amplified System with one XD400/4 Result: in this mode, the user has the ability to
In this configuration, channels 3&4 of the control the absolute level of the LF channels
XD400/4 will drive subwoofers (stereo or bridged) relative to the HF channels.
with low-pass filtering. Channels 1&2 will
drive component speakers in stereo with
high-pass filtering. Set the “Input Sens.” in the “Channel 3 & 4
Controls” section with the source unit’s
Input connection options for a bi-amplified system subwoofer level control set at 3/4 of full output.
with one XD400/4 are as follows: See Appendix A (page 14) for details.

A) No User Adjustability: Crossover Setup for Bi-Amplified System

Required: a basic source unit or processor with one XD400/4:
with one pair of stereo outputs. Once the input sections have been configured
Input Connections: a single pair of stereo source appropriately, go to the “Channel 3 & 4
unit outputs connected to the “CH 1 (Left)” Controls”. Select “LP” (low-pass) on the “Filter
and“CH 2 (Right)” inputs of the XD400/4 Mode” switch and an appropriate “Filter Freq.”
(select “2 Ch.” on the “Input Mode” switch). (80 Hz is a good starting point).
Result: the relative level of the LF and HF Next, turn your attention to the “Channel 1 &
channels will be determined by the XD400/4’s 2 Controls” and select “HP” (high-pass) on the
“Input Sens.” settings and will not be user “Filter Mode” switch and an appropriate “Filter
adjustable from the front of the vehicle. Freq.” (again, 80 Hz is a good starting point).
B) Fade Subwoofer Level vs. HF Level After proper adjustment of the “Input
Required: a source unit or processor with two Sens.” controls for both channel pairs using
pairs of stereo outputs. the method shown in Appendix A (page

12 | JL Audio - XD400/4 Owner’s Manual

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 14), you can fine tune filter frequencies and B) Subwoofer Level Control Only:
attenuate either pair of channels to achieve Required: a source unit or processor with left,
proper balance. For precise filter frequency right and dedicated subwoofer outputs.
information refer to Appendix B (page 15). Input Connections: The main stereo pair
of source unit outputs is connected to the

ENGLISH
MULTI-AMPLIFIER SYSTEMS “CH 1 (Left)” and “CH 2 (Right)” inputs of
Using the “Preamp Outputs” of the the XD400/4 (select “2 Ch.” on the “Input
XD400/4, it is easy to configure many Mode” switch). The source unit’s dedicated
different multi-amplifier systems. subwoofer output is connected to the
The most common type involves the subwoofer amplifier inputs.
addition of a subwoofer amplifier, such Result: with this option, the user has the ability
as the XD600/1. Common configurations to control the absolute level of the subwoofer
of such a system are described below. channel relative to the HF channels, but
cannot fade the front and rear HF channels
Bi-Amplified System with one XD400/4 in relative to each other.
four-channel mode and a separate
subwoofer amplifier
This configuration requires that the separate
subwoofer amplifier has a built-in low-pass filter. Set the subwoofer amplifier’s “Input Sens.”
(All JL Audio amplifiers have this feature.) with the source unit’s subwoofer level control
In this configuration, channels 1&2 of the set at 3/4 of full output.
XD400/4 will drive front component speakers
in stereo with high-pass filtering. Channels 3&4 C) Front to Rear HF Fading and Subwoofer
will drive rear component speakers in stereo, also Level Control:
with high-pass filtering. The separate amplifier Required: a source unit or processor with
will drive the subwoofer system with low-pass front and rear pairs of stereo outputs plus a
filtering (80 Hz is a good starting point). dedicated subwoofer output.
Input Connections: one stereo pair of source unit
Here are three possible configuration options: outputs is connected to the “CH 1 (Left)” and
“CH 2 (Right)” inputs of the XD400/4.
A) Fade Subwoofer Level vs. HF Level: The second stereo pair of source unit outputs
Required: a source unit or processor with front is connected to the “CH 3 (Left)” and “CH
and rear pairs of stereo outputs. 4 (Right)” inputs of the XD400/4 (select
Input Connections: one stereo pair of source unit “4 Ch.” on the “Input Mode” switch). The
outputs is connected to the “CH 1 (Left)” and source unit’s dedicated subwoofer output is
“CH 2 (Right)” inputs of the XD400/4 (select connected to the subwoofer amplifier inputs.
“2 Ch.” on the “Input Mode” switch). The
second stereo pair of source unit outputs is
connected to the subwoofer amplifier inputs.
Result: 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.

13
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 APPENDIX A:
Input Sensitivity Level Setting 9) Once you have adjusted the XD400/4 to
Following the directions below will allow the its maximum low-distortion output level,
installer to adjust the input sensitivity of each reconnect the speaker(s). The “Input Sens.”
amplifier channel pair simply and easily in just a controls can now be adjusted downward if the
few minutes using equipment which is commonly amplifier requires attenuation to achieve the
available in installation bays. desired system balance.

Necessary Equipment
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Do not increase any “Input Sens.” setting for
0 dB reference level in the frequency range any amplifier channel or channel pair in the
to be amplified for that set of channels system beyond the maximum level established
(50 Hz for subwoofer channels, 1 kHz for a during this procedure. Doing so will result in
midrange application). Do not use attenuated audible distortion and possible speaker damage.
test tones (-10 dB, -20 dB, etc.).
It will be necessary to re-adjust the
The Nine-Step Procedure “Input Sens.” for the affected channels if any
1) Disconnect the speaker(s) from the equalizer boost is activated after setting the
amplifier’s speaker output connectors. “Input Sens.” with this procedure. This applies
2) Turn off all processing (bass/treble, loudness, to any EQ boost circuit, including source unit
EQ, etc.) on the source unit, processors (if tone controls or EQ circuits. EQ cuts will not
used) and amplifier. Set fader control to center require re-adjustment.
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
Nom. Target AC Voltage
volume. This will allow for reasonable gain Impedance
overlap with moderate clipping at full volume. Stereo Bridged
5) Using the chart on this page, determine the target 8Ω 17.4 V 34.8 V
voltage for input sensitivity adjustment according 6Ω 17.4 V 32.8 V
to the nominal impedance of the speaker system
4Ω 17.4 V 28.2 V
connected to the amplifier outputs.
6) Verify that you have disconnected the speakers 3Ω 16.4 V not recommended

before proceeding. Play a track with an 2Ω 14.1 V not recommended

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.

14 | JL Audio - XD400/4 Owner’s Manual

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 APPENDIX B: APPENDIX C:
Precise Frequency Selection Chart XD400/4 Specifications

“FILTER FREQ”
General Specifications:
Detent Panel Actual
Number Marking Freq. Recommended Fuse Value: 40A
Full counter-clockwise: 49 Recommended Fuse Type: MAXI® or AGU

ENGLISH
01 . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
02 . . . . . . . . . . . “50” . . . . . . . . . . . .49 Input Sections:
03 . . . . . . . . . . . . . . . . . . . . . . . . . . . .50 No. of Inputs: Two Stereo Pairs
04 . . . . . . . . . . . . . . . . . . . . . . . . . . . .50 Input Type: Differential-balanced with RCA jack inputs
05 . . . . . . . . . . . . . . . . . . . . . . . . . . . .52 Input Range: 100mV - 4V RMS
06 . . . . . . . . . . . . . . . . . . . . . . . . . . . .53
07 . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
Amplifier Section:
08 . . . . . . . . . . . “60” . . . . . . . . . . . .57
Amplifier Topology: NexD™ Ultra-High Speed Class D
09 . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
10 . . . . . . . . . . . . . . . . . . . . . . . . . . . .61 Power Supply: Unregulated MOSFET switching type
11 . . . . . . . . . . . . . . . . . . . . . . . . . . . .63 Rated Power at 14.4V with less than
12 . . . . . . . . . . . . . . . . . . . . . . . . . . . .65 1% THD+Noise (20Hz - 20 kHz)
13 . . . . . . . . . . . . . . . . . . . . . . . . . . . .68 Stereo, all channels driven:
14 . . . . . . . . . . . . . . . . . . . . . . . . . . . .70 75W RMS x 4 @ 4 ohms, 100W RMS x 4 @ 2 ohms
15 . . . . . . . . . . . . . . . . . . . . . . . . . . . .73 Bridged, all channels driven:
16 . . . . . . . . . . . “80” . . . . . . . . . . . .76 150W RMS x 2 @ 8 ohms, 200W RMS x 2 @ 4 ohms
17 . . . . . . . . . . . . . . . . . . . . . . . . . . . .79 Rated Power @ 12.5V with less than
18 . . . . . . . . . . . . . . . . . . . . . . . . . . . .83
1% THD + Noise (20Hz - 20 kHz)
19 . . . . . . . . . . . . . . . . . . . . . . . . . . . .86
Stereo, all channels driven:
20 . . . . . . . “12 o’clock” . . . . . . . .90
21 . . . . . . . . . . . . . . . . . . . . . . . . . . . .95 60W RMS x 4 @ 4 ohms, 90W RMS x 4 @ 2 ohms
22 . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 Rated Power Bridged, all channels driven:
23 . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 120W RMS x 2 @ 8 ohms, 180W RMS x 2 @ 4 ohms
24 . . . . . . . . . . “120” . . . . . . . . . . 111 Signal to Noise Ratio:
25 . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 >104 dB referred to rated power
26 . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 (A-weighted, 20 Hz-20 kHz noise bandwidth)
27 . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 >84 dB referred to 1W
28 . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 (A-weighted, 20 Hz-20 kHz noise bandwidth)
29 . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
Frequency Response: 12 Hz - 22 kHz (+0, -1dB)
30 . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
Damping Factor:
31 . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
32 . . . . . . . . . . “200” . . . . . . . . . . 217 >150 @ 4 ohms per ch./ 50 Hz
33 . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 >75 @ 2 ohms per ch. / 50 Hz
34 . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
35 . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 Crossover Filters:
36 . . . . . . . . . . . . . . . . . . . . . . . . . . . 406 Filter Type: State-variable, 12dB/octave Butterworth
37 . . . . . . . . . . . . . . . . . . . . . . . . . . . 444 with continuously variable cutoff frequency selection
38 . . . . . . . . . . “500” . . . . . . . . . . 482 from 50-500 Hz.
39 . . . . . . . . . . . . . . . . . . . . . . . . . . . 483 Configurable as Low-Pass or High-Pass. Defeatable.
Full-clockwise: 483
Dimensions (LxWxH):
8.52” x 7.09” x 2.05” (217mm x 180mm x 52mm)

Due to ongoing product development, all specifications are subject to

change without notice.

15
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 APPENDIX D: TROUBLESHOOTING
“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.

16 | JL Audio - XD400/4 Owner’s Manual

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 “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-

ENGLISH
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.

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 INSTALLATION NOTES:
Use this diagram to document your amplifier’s switch and control positions.

18 | JL Audio - XD400/4 Owner’s Manual

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 ENGLISH

19
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 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: (954) 443-1100
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.

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 www.jlaudio.com

Printed in China XD400/4 MAN-02-2010

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