JL Audio MHD750/1 Owner's Manual
OWNER’S MANUAL
Monoblock Full-Range Marine Amplifier
Thank you for purchasing a JL Audio amplifier for
your marine sound system.
Your amplifier has been designed and manufactured to exacting
standards in order to ensure years of musical enjoyment in your vessel.
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.
2 | JL Audio - MHD750/1 Owner’s Manual
3
PROTECT YOUR HEARING!
Input Sens itivity
Control
(pg. 10)
Power Status
Indicator
(pgs. 14-15)
Filter Mode
Selection
(pg. 10)
Filter Slope
Selection
(pg. 11)
Filter Frequency
Selector
(pg. 11)
Output Polari ty
Selection
(pg. 12)
Infrasonic Filter
Selector
(pg. 11)
Input Voltage
Selection
(pg. 9)
Remote
Level
Control
Inputs
L
R
L
R
+12 VDC Ground Remote
Preouts
+12 VDC Ground Remote
Chassis Ground
Connector
(pgs. 6-7)
Left & Right
Input Jacks
(pg. 9)
Speaker Outputs
(pgs. 13-14)
Jack for
Remote Level
Control Knob
(pg. 13)
Remote Turn-On
Connector
(pgs. 6-7)
Left & Right Preamp
Output Jacks
(pg. 12)
+12 V Power
Connector
(pgs. 6-7)
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 vessel.
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 vessel 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
vessels with 12 volt, negative-ground electrical
systems. Use of this product in vessels with
positive ground and/or voltages other than 12V
may result in damage to the product and will void
th e w ar ran ty.
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.
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 vessel’s factory
installed electronic devices. You should also take
the time to securely mount the amplifier so that
it does not come loose in the event of a collision/
sudden jolt or as a result of the repeated vibrations
the vessel is prone to during normal operation.
Stupid Mistakes to Avoid:
• Check before drilling any holes in your vessel to
make sure that you will not be drilling through
the hull, a fuel tank, fuel line, wiring harness or
other vital vessel system.
• Do not run system wiring outside or underneath
the vessel. This is an extremely dangerous
practice which can result in severe damage to
your vessel and person.
• Protect all system wires from sharp edges
(metal, fiberglass, etc.) by carefully routing
them, tying them down and using grommets
and loom where appropriate.
• Do not mount the amplifier in the engine
compartment or in any other area that will
expose the amplifier circuitry to the elements.
While this amplifier is specially designed
for marine applications, it is not waterproof
and it should not be mounted where it is
likely to get wet.
4 | JL Audio - MHD750/1 Owner’s Manual
5
PRODUCT DESCRIPTION
The JL Audio MHD750/1 is a very powerful
and compact monoblock (single channel),
full-range amplifier utilizing patented Single
Cycle Control™ Class D technology. This
groundbreaking technology delivers referencegrade sonic performance while requiring
far less current from the vessel’s electrical
system than a conventional amplifier.
Unlike most monoblock amplifiers, the
MHD750/1 is a full-range design, so it can
be used as a subwoofer amplifier or as a very
powerful full-range or satellite amplif ier,
using a second 750/1 to form a stereo pair.
JL Audio’s exclusive R.I.P.S. power supply
design optimizes the output the amplifier for any
impedance between 1.5 and 4 ohms, allowing you
to get full use of the MHD750/1’s performance
capabilities with a wide range of speaker systems.
The tightly regulated power supply design also
means that the MHD750/1’s clean power output
capability remains stable over a wide range of
vessel voltages, resulting in enhanced fidelity.
A flexible input and crossover section permits
operation with a wide variety of source units
and system configurations. The MHD750/1’s
preamp output can send pass-through signals
from the inputs to feed additional amplifier(s).
TYPICAL INSTALLATION SEQUENCE
The following represents the sequence
for a typical amplifier installation, using
an aftermarket source unit. 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 positive and negative power wire
power wire from the battery location to
the amplifier mounting location, taking
care to route it in such a way that it will
not be damaged and will not interfere with
vessel operation. 4 AWG is recommended
for wire runs greater than 72 inches (180
cm) in length. Use of 8 AWG power wire is
acceptable for shorter runs, such as from a
power distribution block to the amplifier or
from a trunk-mounted battery. Use a 2 AWG
or 1/0 AWG main power wire with a power
distribution block when additional amplifiers
are being installed with the MHD750/1 and
powered from the same main power wire.
3) Connect power wire to the positive batter y
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 vessel.
Do not install the fuse until the power wire
has been connected to the amplifier.
4) Connect negative power wire to the negative
battery post. Use the same size power
wire as the wire connected to the “+12V ”
connection (minimum 8 AWG).
5) Run signal cables (RCA cables) and remote
turn-on wire from the source unit or interface
processor to the amplifier mounting location.
6) Run speaker wire from the speaker systems to
the amplifier mounting location.
7) Securely mount the amplifier using
appropriate hardware. (See page 8 for detailed
mounting instructions).
8) Connect the remote turn-on wire and the
positive and negative power wires to the
amplifier’s power connector plug. Then insert
the power connector plug into the amplifier’s
power connector receptacle, pushing firmly.
9) Connect the RCA input cables
to the amplifier.
10) Connect the speaker wires to the speaker
connector plug and insert the plug firmly into
the speaker connector receptacle.
11) Carefully review the amplifier’s control
settings to make sure that they are set
according to the needs of the system.
12) Install power wire fuse (60A for a
single MHD750/1) and reconnect the negative
battery post terminal.
13) 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.
14) Make necessary adjustments to the input
sensitivity controls to obtain the right
overall output and the desired balance
in the system. See Appendix C (pages 16, 17)
for the recommended input sensitivity
setting method.
15) Enjoy the fruits of your labor with your
favorite music.
6 | JL Audio - MHD750/1 Owner’s Manual
7
POWER AND TURNON CONNECTIONS
Remote
Level
Control
Inputs
L
R
L
R
+12 VDC Ground Remote
Preouts
+12 VDC Ground Remote
Before installing the amplifier, disconnect the
negative (ground) wire from the vessel’s battery.
This will prevent accidental damage to the system,
the vessel and your body during installation.
+12V Battery Connection
You will need to connect a power wire to
the vessel’s positive battery terminal, using an
appropriate power ring or specialized battery
terminal connector, such as the JL Audio
XB-BTU. This connection must be tight and
corrosion-free to ensure proper connectivity.
This wire MUST be fused appropriately for safety.
Any positive power wires run through barriers
must be protected with a high quality insulating
grommet to prevent damage to the insulation
of the wire. Failure to do so may result in a
dangerous short circuit.
Power Wire Requirements
The MHD750/1’s “+12 V DC ” and “Ground”
connections are designed to accept 4 AWG power
wire. 4 AWG pure copper wire is recommended
for any power wire run longer than 72 inches (180
cm). For runs shorter than 72 inches, 8 AWG pure
copper power wire is acceptable.
If you are installing the MHD750/1 with other
amplifiers and wish to use a single main power
wire, use 2 AWG or 1/0 AWG pure copper wire
as a main power wire. This 2 AWG or 1/0 AWG
power wire should terminate into a distribution
block mounted as close to the amplifiers as
possible and should connect to the MHD750/1
with 4 AWG or 8 AWG pure copper power wire.
Please note that lower 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.).
We do not recommend the use of “copperclad aluminum wire” or “CCA” wire because
this wire is significantly less conductive than
pure copper wire. Only use pure copper power
wire, such as JL Audio’s MetaWire™. Tinned
copper wire (silver color) is acceptable as the
tin-plating is only a very minor component of
the wire.
Fuse Requirements
The installation of a fuse on each power wire,
within 18 wire inches (45 cm) of the positive
battery terminal is vital to protect the wire and
the vessel from fire in the event of a collision or
short-circuit. 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 MHD750/1 is being run from
that power wire, we recommend a 60A fuse
be used. AGU (big glass fuse). AFS (small
blade fuse) or MaxiFuse™ (big plastic-
body fuse) types are recommended.
If other amplifiers are also being powered from
a main power wire and exceed 80 amps in total
fuse rating, we recommend the use of an ANL
(large-blade) fuse and holder. Each amplifier
must be fused independently at the outputs of
the power distribution block. Use JL Audio part
XC-FOA-2PAK and appropriate MaxiFuse™ type
fuses with JL Audio distribution blocks.
Please consult with your JL Audio
dealer to make sure that the wire, fuse
holder and fuse ratings are appropriate
for your system’s needs. The safety of
your installation depends on appropriate
power connections and fuse protection.
Ground Connection
The ground connection should be made using
the same gauge wire as the power connection.
It is common for the alternator to be grounded
through its chassis. If the alternator is not
grounded through its chassis and instead employs
a small (10 AWG - 6 AWG) wire to connect to
ground, this wire should also be upgraded to 4
AWG when installing amplifier systems with main
fuse ratings above 60A.
The MHD750/1’s “Remote” turn-on connector
is designed to accept 18 AWG – 12 AWG wire. 18
AWG is more than adequate for this purpose.
To connect the remote turn-on wire to the
amplifier, first back out the set screw on the
bottom of the Power Connector Plug, using the
supplied 2.5 mm hex wrench. Strip 1/2 inch
(12mm) of wire and insert the bare wire into the
receptacle, seating it firmly so that no bare wire
is exposed. When using smaller wire, it may
be necessary to strip 1 inch of insulation from
the wire and fold the bare wire in half prior to
Many vessels employ small (10 AWG - 6 AWG)
wire to ground the battery to the vessel chassis
and to connect the alternator’s positive
connection to the battery. To prevent voltage
insertion. While holding the wire in the terminal,
tighten the set screw firmly using the supplied
2.5 mm hex wrench, taking care not to strip the
head of the screw and making sure that the wire
is firmly gripped by the set screw.
drops, these wires should be upgraded to 4
AWG pure copper wire when installing amplifier
systems with main fuse ratings above 60A.
Amplifier Power Connector Plug
To connect the power wires and the remote
turn-on wire to the amplifier, unplug the power
Turn-On Wire
The MHD750/1 uses a conventional +12V
remote turn-on wire, 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 ignitionswitched circuit.
connector plug from the amplifier chassis (pull
back firmly) and back out the set screws on
the connector plug, using the supplied 4 mm
hex wrench for the “+12 V DC ” and “Ground”
connections and the supplied 2.5 mm hex wrench
for the “Remote” connection. Strip 3/8 inch (10
mm) of insulation from the end of each wire and
insert the bare wire into the receptacle on power
connector plug, seating it firmly so that no bare
wire is exposed. While holding each wire in place,
tighten each set screw firmly, taking care not to
strip the head of the screw.
Never make power connections with a “live”
wire. Always disconnect the negative battery
post before making any connections or
adjustments to a 12V power connection!