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Rockford Fosgate M400-4D

4-channel marine amplifier — 75 watts x 4 channels

14 Reviews | 1 question - 5 answers

Item # 575M4004D

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825 Gardens Blvd

109 South Carlton

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Our take on the Rockford Fosgate M400-4D

Rockford Fosgate's compact marine amplifiers provide high-efficiency Class-D power for your marine audio system. They meet tough UV and Salt-Fog protection standards, so you can install them with confidence in your pleasure craft, whether you're blasting across inland waterways, or cruising out to your favorite salt-water fishing grounds.

High power from a compact amp

Rockford Fosgate M400-4D marine amplifier

Rockford Fosgate's compact marine amplifiers provide high-efficiency Class-D power for your marine audio system. They meet tough UV and Salt-Fog protection standards, so you can install them with confidence in your pleasure craft, whether you're blasting across inland waterways, or cruising out to your favorite salt-water fishing grounds.

Power your speakers or subs

The M400-D4 4-channel amp delivers the power you need to drive two pairs of full-range speakers in your boat, sending 75 watts continuous power to each speaker. If you want to power a pair of subs, you can bridge the amp to 2-channel mode, sending 200 watts to each subwoofer — plenty of kick if you want some bass on board.

The amp features variable frequency filters to adjust the amp's output to your system, whether you're running full-range speakers or subs. And the compact footprint makes it easy to mount the amp in a small storage locker or other tight spot.

M400-4D connection panel

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)
  • conformal-coated circuit board and UV-resistant finish
  • variable high- and low-pass filters (50-500 Hz, 12 dB per octave)
  • variable bass boost (0-12 dB at 45 Hz)
  • three auto-turn on modes
  • CEA-2006 compliant
  • preamp-level inputs and outputs
  • 4-gauge power and ground leads recommended — wiring and hardware not included with amplifier
  • 9-1/8"W x 2"H x 6-7/8"D
  • warranty: 2 years
  • Our 60-day money-back guarantee

What's in the Box:

  • 4-Channel marine amplifier
  • 3mm Hex key
  • 4 Self-tapping screws (length=1-5/8")
  • Installation & Operation Manual
  • Amplifier Verification Certificate

This is my second amp purchase for my boats and I'm using it to run 4 6.5 JL Speakers Sounds great

Kirk Hicks, Prince Frederick,MD


Rockford Fosgate M400-4D Reviews

Average Customer Review(s):

(14 Reviews)

Rockford Fosgate M400-4D

Kirk Hicks from Prince Frederick,MD on 8/15/2017

Crutchfield Customer Review (What's this?)

This is my second amp purchase for my boats and I'm using it to run 4 6.5 JL Speakers Sounds great

Pros: Sounds great


Rockford Fosgate M400-4D

Anonymous from Girard, OH on 6/23/2017

Crutchfield Customer Review (What's this?)

yea....uh not impressed, sounded good for about 2 months and then fried itself!!



Rockford Fosgate M400-4D

Anonymous from San Angelo, TX on 6/9/2017

If you want a marine amp look somewhere else! This amp is garbage had it in my boat for 2 weeks and the second time I took it out the amp quit working. So call marine that got a little water once and it quit. Rockford fosgate is supposed to be a good amp! I've had there speakers in marine and normal and have been happy but this product is trash. Do not waste your money. Would give zero starts if I could!

Pros: Sounded good for a day

Cons: Got wet once and broke Not marine

boat install

jchance from Olive Branch, MS on 7/5/2016

Crutchfield Customer Review (What's this?)

I bought two of these amps for my boat. very good size with great power. I had one amp with a problem and crutchfield sent another one out asap. great company to deal with. the only complaint is the mounting locations its hard to get a srew in the sleeved area wish it would have been mor of an open hole.

Pros: great size great power

Cons: mounting location diffulcult

Phosgate powering JL audio making speakers

TOGA from Dalton, GA on 6/30/2016

I have two of these amps in the boat powering JL audio marine speakers. The original amp is driving 4 JL's in the cockpit. The second is powering two JL tower speakers. Amp runs efficiently and drives the JL's clearly. Great set-up.

Pros: Good power and affordable



Derek from Ft Walton Beach, FL on 6/25/2016

Crutchfield Customer Review (What's this?)

Good value, good sound. Have it driving a Bazooka Tube and four Infinity 6.5s in my boat and it is more than adequate.

Pros: Value, amp size, sound quality


Great AMP.

Steve from Farmington, NM on 6/5/2016

Crutchfield Customer Review (What's this?)

Great amp. We installed this in our boat. Smaller size was easy to mount. It puts out plenty of power. We are running two JL Audio 6" and two infinity 6X9. The sound is great.

Pros: Size and power.

Cons: none

Strong Amp

Greg H from Florida on 8/11/2015

Crutchfield Customer Review (What's this?)

This is very strong & clean amp that is running my JL's 6.5's & 8.5's. Everything sounds great and it delivers plenty of power to my boat

Pros: Very affordable


Polaris Slingshot

Jeff Mc from Nashville on 8/2/2015

Crutchfield Customer Review (What's this?)

This amp is perfect if it's in the Dash behind the radio and I wired it in to the existing radio works great

Pros: Fits my Slingshot - Sounds great with JL audio speakers

Cons: No cons to say

Amp is great

Baja from Westminster on 6/1/2015

Crutchfield Customer Review (What's this?)

Great amp easy to install and tech help if you need it great price

Pros: It came with every thing I needed



Jvassion from North Bend, OR on 11/16/2014

Crutchfield Customer Review (What's this?)

Great power and sound and handles rough ride of my jeep.

Pros: Easy to install and set up Waterproof Solid component.

Cons: None

Fosgate Amp

TEDIII from Nashville on 5/21/2013

Crutchfield Customer Review (What's this?)

Great amp. Easy install. Actually came certified it tested at 553 amps. Would buy again.

Pros: Solid product, small footprint, easy to install


Rockford Fosgate M400-4D

Nicholas L from Birmingham, AL on 5/11/2013

Crutchfield Customer Review (What's this?)

Perfect match for the 4 JL Audio 6.5s it's working, amp is easily tuneable, doesn't get hot in my dry storage, can blast music all day and the amp never gives up.

Pros: Compact, easily tuneable, and can't seem to overwork amp.


rf m400 4d

bob from omaha ne on 6/29/2012

Crutchfield Customer Review (What's this?)

good sound and output, runs way cooler than the 2 amps next to this one.and smaller




Hands-on research

Product Research



Overview: The Rockford Fosgate Prime Marine M400-4D is a 4-channel full-range Class D marine amplifier. It is optimized to power a full-range front/rear speaker system. You can also bridge the front and/or rear channels to run a subwoofer or two. The Class D design is very efficient with a cast aluminum heatsink to keep it in a small footprint.

Marine Amplifier: The M400-4D is designed for the harsh marine environment. The amplifier features a conformal-coated PCB and UV-resistant finish, and conforms to UV and Salt-Fog protection standards.

CEA-2006 Compliant: CEA-2006 is a system of testing and measurement methods for mobile audio amplifiers. This voluntary standard advocates a uniform method for determining an amplifier's RMS power output and signal-to-noise ratio. The criteria for measuring power uses a DC input voltage of 14.4 volts and the RMS power output is measured into a 4-ohm load with 1% or less Total Harmonic Distortion plus noise (THD+N). Signal-to-Noise ratio is measured in weighted absolute decibels (dBA) at a reference of 1 watt into 4 ohms. CEA-2006 allows consumers to compare amplifiers and receivers on an equal basis. The CEA-2006-rated RMS power output is as follows (measured with a 14.4 volt input, <1% THD+N, 20 Hz-250 Hz):

  • 4-Ohm: 75 watts x 4
  • 2-Ohm: 100 watts x 4
  • Bridged (4-Ohm): 200 watts x 2

LED Indicator: The amplifier is equipped with a top-mounted LED indicator which illuminates blue when the unit is turned on. The LED illuminates red when a protection circuit engages (short circuit or too low an impedance is detected at the speaker connections). The amplifier automatically turns off if this occurs.

Mounting: The amplifier can be mounted vertically, horizontally, or inverted using the supplied mounting screws; horizontal mounting (right side up) will provide the best cooling.


Independent Controls: The M400-4D has independent, top-mounted controls for the front and rear channels. The controls include:

  • Gain Control: The amplifier has rotary gain controls (0 to 11) for front and rear channels.
  • Crossovers: The amplifier features independent Butterworth crossovers for the front and rear channels. Each crossover can be set for low-pass, high pass, or all-pass (full range). The crossover frequency is continuously variable from 50-250 Hz with a slope of 12 dB per octave.

Punch EQ: The rear channel has an independent Punch EQ (bass boost) control that works with the crossover switch. When the rear channel crossover is set to low-pass, the Punch EQ can add a bass boost, centered at 45 Hz, from 0 dB to +18 dB.

2/4 CH Switch: When the 2/4 CH switch is set to the 2 CH position, the inputs are switched to a 2-channel mode. The signal on the front input feeds all four output channels, however, you lose front to rear fading capability. In the 4 CH position, the amp uses both front and rear inputs and fading capability is restored.


Power Terminals: The power and ground terminals are nickel-plated set-screw terminals, and will accommodate up to 4-gauge wire. The set screws can be tightened/loosened with the supplied 3mm hex key.

Fuses: The amplifier does not have on-board fuses. A 40A fuse should be placed on the power wire within 18" of the battery.

Remote Turn-On Terminal: The remote turn-on terminal is a nickel-plated set-screw terminal that will accommodate up to 8-gauge wire. The set screws can be tightened/loosened with the supplied 3mm hex key.

Speaker Terminals: The speaker terminals are nickel-plated set-screw terminals that will accommodate up to 8-gauge wire. The set screws can be tightened/loosened with the supplied 3mm hex key.

RCA Input Jacks: There are two pairs of RCA input jacks for the front and rear channels. They are nickel-plated to resist signal degradation caused by corrosion.

RCA Pass-Thru Jacks: The nickel-plated RCA pass-thru jack provides a convenient source for daisy-chaining an additional amplifier without running an extra set of RCA cables from the front of the vehicle to the amplifier location.

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?

Experience with RF products, customer ratings and price for quality. [ Douglas  Sep 06, 2017 ]
Good value, great brand [ Derek  May 14, 2016 ]
It was available [ jeffrey  Apr 12, 2016 ]

1 question already asked

I'm getting this amp for my sidexside. I will be running the front left / right to the 2-way mids I have and the rear channel's left - to the sub - and then amp's right + to the sub's + Per Fosgate's manual, this will run the rear channel in mono, bridging the left & right into 1 to the speaker (sub) and keep the front channel in stereo. Pg 9 on the right: 4-Channel (2ch Stereo & 1ch Mono-Bridged) (Crutchfield won't let me link to the manual) [ justin  Mar 07, 2016 ]
I bought this amp but unfortunately havent had the time to install it. I plan to use the same 3 channel setting. I think that as long as you keep the same ohms and avoid overheating, you should have no problem. [ ANTONIO  Aug 02, 2014 ]
Yes, just wire the 7.7s to the two front channels then wIre the subs to one of the rear channels and leave the other channel empty. Or you could try running double wires from the rear channels to the sub get more power. [ jeff st  Aug 01, 2014 ]
Yes I would say you could as long as the amp has enough power for what your speakers and sub are rated for. Just check to make sure the amp can produce enough power for what your running. [ CAREY R  Aug 01, 2014 ]
Thanks for your question. For information on selecting the best amp for your subs I would recommend reaching out to an Advisor by phone (1-800-324-9695) or online chat. They will be able to help determine the differences between the amp models and help you make the best choice for your system. [ Greg  Aug 01, 2014 ]  Staff