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JL Audio M400/4

4-channel marine amplifier — 75 watts RMS x 4

7 Reviews | 2 questions - 11 answers

Item # 136M4004

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825 Gardens Blvd

109 South Carlton

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Our take on the JL Audio M400/4

The M400/4 is small — less than 9" wide — but it delivers a massive amount of power from its compact chassis — up to 100 watts from each of its four channels. It owes these impressive specs to JL Audio's Class D NexD™ ultra-high-speed switching design, which eliminates the traditional drawbacks of a Class D amp design to deliver full-bandwidth performance, excellent efficiency, and very low distortion levels.

JL Audio Built In USA

Small footprint, big kick

The M400/4 is small — less than 9" wide — but it delivers a massive amount of power from its compact chassis — up to 100 watts from each of its four channels. It owes these impressive specs to JL Audio's Class D NexD™ ultra-high-speed switching design, which eliminates the traditional drawbacks of a Class D amp design to deliver full-bandwidth performance, excellent efficiency, and very low distortion levels.

Great for a variety of applications

You can use this 4-channel amp for a variety of applications. Run two sets of high-performance coaxial or component speakers, or bridge the amp to 2-channel mode to get a couple of subs thumping. Or enjoy the best of both worlds by going 3-channel, and powering a sub plus your full-range speakers.

You can run the built-in variable frequency filters in high- or low-pass mode, depending on whether you're powering speakers or subs. JL Audio's optional wired remote lets you adjust the amp's level from the helm, while the preamp outputs make it easier to get signal to another amplifier in your system.

Product Highlights:

  • 4-channel marine amplifier
  • 75 watts RMS x 4 at 4 ohms (100 watts RMS x 4 at 2 ohms)
  • 200 watts RMS x 2 in bridged mode (4-ohm stable in bridged mode)
  • Class-D design
  • white and gray powder-coat finishes, gasketed control cover, and stainless steel hardware
  • variable high- and low-pass filters (50-500 Hz, 12 dB per octave)
  • optional remote level control
  • preamp-level inputs
  • preamp outputs
  • 4-gauge power and ground leads recommended — wiring and hardware not included with amplifier
  • 8-1/2"W x 2-1/16"H x 7-1/8"D
  • warranty: 2 years
  • Our 60-day money-back guarantee

What's in the Box:

  • 4-Channel Class-D marine amplifier
  • 2.5mm Allen wrench
  • JL Audio emblem
  • Owner's Manual

This a smokin little amp ! Incredibly small yet powerful, very flexible in the way amp can be set up. Clean detailed music when matched to quality speakers like JL MX series marine. Amp seems expensive but worth the price in terms of quality and music reproduction.

Bill, Chambersburg, PA


JL Audio M400/4 Reviews

Average Customer Review(s):

(7 Reviews)

Powerful little amp.

Bill from Chambersburg, PA on 7/9/2017

This a smokin little amp ! Incredibly small yet powerful, very flexible in the way amp can be set up. Clean detailed music when matched to quality speakers like JL MX series marine. Amp seems expensive but worth the price in terms of quality and music reproduction.

Pros: Sound quality and flexibility.

Cons: None

JL Audio M400/4

Stephen from Taylorsville, NC on 7/5/2017

Crutchfield Customer Review (What's this?)

Only had my new system a week but WOW, sounds great. JL is a leader in marine sound technology and the best part ,made in USA. I'm going to add their 8'' subwoffer to my system.

Pros: Extremely well made and out performs my expectation .

Cons: None


Joe from Lenoir city, TN on 3/6/2016

Crutchfield Customer Review (What's this?)

Easy installation, the unit will handle just about any input signal including line out from the stereo unit. The wire terminations are very secure and solid all included tools (allen wrench) are provided to terminate wires and secure them. Great clarity and very easy to set up for all audio sources, as long as you have a multi-meter to read the AC voltage.

Pros: Easy of installation Easy to configure Very well thought out design

Cons: None so far but had the unit only a couple of weeks.

Great amp for rzr1000 xp4

Anonymous from Scottsdale, az on 5/16/2015

Crutchfield Customer Review (What's this?)

Great amp for my rzr. Small with lots of power. Easy to install



Outstanding couldn't be happier

Fourwinns from Wichita Falls TX on 4/17/2015

Crutchfield Customer Review (What's this?)

I bought this item as scratch and dent.. I couldn't find a scratch not dent on the amp. Wired 4 JL MX650's to my head unit first and was disappointed (obviously) then plugged in the speaker wire I had run for the amp. 100x better clearer and LOUD! I probably have the perfect amp for those particular four speakers but the difference was incredible, not to mention the sound is amazing. I highly recommend ALL JL AUDIO MARINE products they're in my opinion the best you can get.

Pros: Good power, no noise, great sound

Cons: Haven't found any cons so far

Awesome tiny-mite!

Chris from Katy, TX on 3/13/2014

Powering two jl 7.7 coax's and two channels bridged to power the 10" open baffle sub in our little ski boat and it plays detailed, soft and load, and it puts out clean undistorted full range watts!

Pros: Small easy to hide

Cons: Forget it's there!

M400/4 amp

Oz from Frankfort, Ky. on 9/8/2012

Crutchfield Customer Review (What's this?)

Installed JL amp for my boat , sounds great and after 5 hours of playing music, the amp wasn`t hot. Will tell family and friends.




Hands-on research

Product Research



4-Channel Full-Range Amplifier: The JL Audio M400/4 is a four-channel, full-range audio marine amplifier utilizing NexD ultra-high speed switching technology to deliver outstanding fidelity and efficiency. The M400/4 can be operated with a wide variety of source units and system configuration.

Marine Amplifier: The JL Audio M-series marine amplifiers are specifically designed for marine applications. These amps are not waterproof, however, and should not be mounted where they are likely to get wet.

Amplifier Rating: The JL Audio M400/4 Class D 4-channel marine amplifier is rated at 75 Watts RMS x 4-channels in 4-ohm at 20 to 20,000Hz with a signal-to-noise-ratio of 104 dB and a total harmonic distortion of 1% while receiving 14.4 Volts.

NexD Class D Technology: NexD is a state-of-the-art switching amplifier design that combines exceptional audio quality with excellent efficiency and less complexity. This results in an affordable compact amplification with exceptional audio quality and unsurpassed total efficiency.

Advanced Rollback Protection: The M-series amplifiers employ advanced thermal and low-impedance protection to virtually eliminate annoying amplifier shut-down events. Should any M-Series amplifier ever overheat, its intelligent, unregulated power supply reacts by limiting available peak voltage until the amplifier returns to a safe temperature range. Likewise, if an impedance lower than optimal for the amplifier is present at the outputs, the M-series amplifier will roll back peak voltage to protect itself without shutting down.

Differential-Balanced Inputs: The JL Audio amplifier features differential-balanced input architecture to effectively control noise and ensure compatibility with a wide variety of source units, including many OEM systems. Without resorting to line output converters, you can directly connect most OEM source units to the JL Audio amplifier without creating any noise or compatibility issues. Unlike conventional single-ended inputs, the differential-balanced design does not connect one side of the audio signal to chassis ground. This eliminates any voltage sensitivity between one input terminal and ground and greatly reduces the incidence of alternator whine in a typical 12-volt installation.

Note: You will need two speaker wire to RCA adaptors (136XDCLR2S, sold separately) to connect this amplifier to your headunit via speaker-level.

Protection Circuitry With Status Indicator Lights: There is a single multi-color LED on the top panel of the amplifier to indicate the amplifier's operating status.

  • Flashing Green: When the LED is flashing green, the amplifier is powering up and audio output is muted.
  • Constant Green: This LED lights green to indicate that the amplifier is turned on and operating normally.
  • Constant Red: This Red LED lights to indicate that the amplifier has exceeded its safe operating temperature, putting the amplifier into a self-protection mode, which reduces the power output of the amplifier. The red light will shut off and the amplifier will return to normal, full-power operating mode if the heat sink temperature drops back to a safe level.
  • Constant Amber (Yellow): The Amber (Yellow) LED light indicates that an over-current condition has occurred and is accompanied by a muting of the amplifier's output. Over-current condition 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.
  • LED Off: The only condition that will shut down an undamaged M400/4 completely is if battery voltage or remote turn-on voltage drops below 10 Volts. The amplifier will turn back on when voltage climbs back above 11 Volts.

Cooling System: The outer shell of the 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.


Control Panel Cover: The M400/4 features a Control Panel Security Cover which protects and hides the amplifier's controls. When installed, the cover ensures that the amplifier's settings are not accidentally changed while creating a clean aesthetic look for the amplifier and your installation. The control panel security cover is pre-installed at the factory and must be temporarily removed for access the amplifier's controls. The security cover is secured by two 2.5mm Allen-head screws.

Simplified Gain Setting: The M-series amplifier makes setting the gain level of the amp via the input sensitivity control very simple. All you need is Digital AC Voltmeter (142TK12V, sold separately) and a Test CD Disc (503CD104, sold separately) 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).

Note: The M400/4 is equipped with a independent gain controls for the Front (1&2) and Rear (3&4) channels.

Flexible Input Section And Active Crossover Network: The JL Audio M-series amplifier provides a flexible input section and a comprehensive crossover network to fine tune your system effectively and accurately. The variable filter design employed in the JL Audio M-series amplifier crossover sections allow you to seamlessly switch slopes, easily change filter frequencies and address what frequencies the preamp inputs will pass. The M400/4 offers the following independent crossover adjustments for the front and rear channels along the unit's top panel, behind a removal cover plate.

  • Input Mode: This switch allows operation of all four amplifier channels with only one pair of input signals (2-CH Input Mode) or with independent front and rear input signal pairs (4-CH Input Mode). You will only need to connect the front RCA inputs when placing the amplifier in 2-CH input mode.
  • Filter Mode: The amplifier allows you to select either a Low Pass, High Pass or Full-Range operation of the amplifier's 1 & 2 channels and 3 & 4 channels.
  • Variable Frequency: You can set the amplifier's Low Pass or High Pass crossover from 50 to 200 Hz for channels 1 & 2 and channels 3 & 4.


Power/Ground/Turn-On Terminals: The amplifier features set-screw terminals for the power, ground, and remote turn-on connections.

  • Power and Ground: The JL Audio amplifier's set-screw Power and Ground connections are designed to accept 8 to 4 AWG power wire. A 2.5mm Allen wrench is supplied for making connections.
  • Remote Turn-On: The JL Audio M-series amplifier's set-screw turn-on lead will accept 18 to 8 AWG wire. The same 2.5mm Allen wrench is supplied for making connection.
Note: The Amplifier is not equipped with a fuse. An external 40-amp AFS, AGU, or MAXI fuse (not included) must be installed on the power wire. If a wiring kit is used which includes a fuse with a value other than 40-amps, the original should be replaced with a 40-amp fuse.

Speaker Output Terminals: The M400/4 amplifier's eight set-screw speaker terminals will accept 16 to 8 AWG speaker wire. A 2.5mm Allen wrench is supplied for making connections.

Preamp Inputs: The amplifier features two sets of differential-balanced RCA jack inputs. The amplifier features a dedicated Input Sensitivity gain control for the front and rear channels of the amplifier. These controls are designed to match the input sensitivity of the M400/4 to the specific signal source that is feeding it. The amplifier's input level can be set independently for the front and rear channels between 100mV-4V.

Preamp Outputs: The M400/4 incorporates a pass-through preamp output sections, so that additional amplifiers can easily be connected to the same signal(s) feeding the M400/4. These preamp output signals are buffered to prevent noise and are always preamp level, regardless of the level of signals feeding the M400/4's inputs. The amplifier's set of preamp outputs can be configured two different ways.

  • Front (1&2): The preamp output delivers the same signals that is connected to the M400/4's front RCA inputs. This mode is useful for feeding a subwoofer amplifier when the M400/4 is being used to drive front and rear speaker system. In this mode, the preamp output level will track with the signal level of the front input signals, allowing you to fade the rear channels in and out, without affecting the subwoofer level.
  • Sum (F+R): This mode delivers a sum of the signals being fed to the front and rear RCA inputs of the amplifier. When the M400/4 is being used to drive front and rear speaker systems, this preamp output mode will deliver a summed front/rear signal to the subwoofer amplifier, while permitting fading of the front and rear speaker system from the source unit.

Remote Level Control: The amplifier features a standard telephone connector for adding an optional wired remote level control. With the addition of the optional wired Remote Level Control (136HDRLC, sold separately), you can control the volume of one or both channel pairs of the M400/4 form the front of your vehicle. This is useful for subwoofer level control or even as a master volume control for your system. If desired, multiple M-series amplifiers can be controlled from a single HD-RLC controller using a simple phone line splitter and multiple phone cables (all sold separately).

Note: All inputs and outputs are located on one side of the amplifier to make installation of the amplifier simple and neat.

Our Product Research Team

At Crutchfield, you'll get detailed, accurate information that's hard to find elsewhere. That's because we have our own in-house Product Research team. They verify what’s in the box, check the owner's manual, and record dimensions, features and specs. We stay on top of new products and technologies to help people make informed choices.

Q & A

Customer Q&A

Crutchfield asked  
Why did you buy this?

Recommended by my marine electronics installer to add to existing system [ Jorge  Jul 18, 2017 ]
Highly recommended by other boaters [ Steven  Apr 25, 2017 ]
Ringo recommended Ringo's Bio: [ Anton  May 12, 2016 ]
Best bang for the buck with great reviews. [ Randy  Apr 30, 2016 ]
Great power [ Corey  Mar 13, 2016 ]
to power two jl audio 10 inch subs [ Keith  Mar 07, 2016 ]

2 questions already asked

No [ Kevin  Jun 28, 2016 ]
No internal fuse that you should have to replace. These units are designed to have customer supplied fuse that is installed near source of power [ woody  Jun 28, 2016 ]
Not that I am aware of ; instructions are specific about installing one ahead of the unit in the power feed [ NEIL  Jun 27, 2016 ]
YEs [ ROBERT A  Jun 27, 2016 ]
Yes [ JOHN  Jun 27, 2016 ]
No, I mounted it a a vertical 'wall'. [ Gregory  Jul 27, 2015 ]
i mounted mine vertically in side a closet [ DAVE  Jul 27, 2015 ]
No it can be mounted anywhere [ Steven  Jul 26, 2015 ]
You can mount this amp pretty much anywhere you want. Just make sure it won't get wet. I mounted the amp in my electronics box in my T top. Very happy with amp [ richard  Jul 26, 2015 ]
no. it can be bulkhead mounted.. in ur instructions manual it will tell you it is the preferred mount.. mine is under my m600.6 n over my m600.1.. [ GEORGE  Jul 26, 2015 ]
No [ Jesse  Jul 26, 2015 ]