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Boss MR404

400W Max, 4-Channel MR Series Marine Amplifier

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Boss MR404

400W Max, 4-Channel MR Series Marine Amplifier


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4 Meters (13 ft.) 4-Channel K-Series RCA Audio Interconnect Cable


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General Features:

  • 4-Channel MR Series Marine Amplifier
  • RMS Power Rating:
    • 4 ohms: 50 watts x 4 chan.
  • Max Power Rating:
    • 2 ohms: 100 watts x 4 chan.
  • Pulse Width Modulated MOSFET power supply
  • LED power (green) and protect (red) indicators
  • Variable Bass Boost (0 to +12 dB bass boost at 50 Hz)
  • Soft start turn-on
  • 4/3/2 channel operation
  • 3-way protection circuitry (thermal, overload, and speaker short protection)
  • Heavy duty aluminum alloy heat-sink for extreme heat dissipation
  • Nickel-plated RCA level inputs
  • Nickel-plated screw terminals
  • Frequency response: 12-22000 Hz
  • 8 gauge power and ground wiring is required for installation. Contact us for information regarding a discount on select amplifier kits from our website when purchased together with this amplifier.
  • Dimensions: 9-8/10"W x 7-3/4"D x 2-3/4"H
  • Authorized Platinum Internet Dealer
  • 1 year Sonic Electronix, and 5 years Manufacturer's warranty

Power Specifications - Full Range Channels

RMS Power @ 4 ohms

The RMS power rating is the measure of continuous power that an amplifier can output, or a speaker can handle. It is the most accurate depiction of real, continuous power that the industry has so far.

If the final impedance of your speakers or subwoofers equals 4 ohms, this is how much power this amplifier will supply at that ohm level. The higher the RMS wattage, the more clean and loud your music will sound.

50 watts x 4 channels
Peak Power Output
This form of power rating refers to the maximum amount of power an electronic device can handle or output in an instant without damage occurring. Often times this maximum is achieved during a brief musical burst, such as a drum accent, or low bass hit.

Some manufacturers display peak power ratings on the face of their products to increase the appeal to consumers. The RMS power rating is more accurate, and we recommend using it for product comparison.

100 watts x 4 channels

Amplifier Specifications

Amplifier Series
This designates the series of the amplifier. Many amps are available in a litany of different wattage and channel configurations, but maintain consistent features throughout the product line.
Marine Certified
Marine certified means that the unit has been designed and manufactured with a marine use in mind. It will withstand the harsh conditions that come from marine use. Generally, they are treated against UV rays and treated with special protective coatings.
Amplifier Class

An amplifier increases the power of the signal being fed to it by taking energy from its power supply and matching the signal but increasing its amplitude. Amplifiers use many different methods for converting these electrical signals and have been categorized into classes.

Class A/B: Greater than 50% of the input signal is amplified while the other percentage is “off”. These amplifiers have a small amount of current flowing through the output transistors all the time which almost eliminates crossover distortion. Class A/B has great sound quality but is not as efficient as class D. These amps are most commonly used to drive speakers.

Class D: Also known as switching amplifiers, class D amps have output transistors that are completely turned “on” or “off”. This means that when the transistors are on, there is almost no voltage across them but when they are off there is significant voltage but no current flowing through it which makes these amplifiers very efficient at the cost of sound quality. These amps are most commonly used to drive subwoofers.

Other Classes: You may see classes such as GH, bD, X, FD, etc. by some manufactures. These amplifiers tend to be either class A/B, D or a hybrid of the two but with improvements to their designs that can make them more efficient or offer better sound quality.

Number of Channels
Each channel on an amplifier will power one speaker using a positive and negative cable. There are various types of amplifiers, each designed to power a certain number of speakers. Monoblock amplifiers, also known as single channel, are designed to power one or more subwoofers. These amplifiers often have very high power ratings. On the other hand, multi-channel amplifiers power multiple speakers, usually at lower power ratings. 2-Channel and 4-Channel amplifiers can power car speakers or low powered subwoofers. Occasionally you might see a 5 or 6-channel amplifier that can power speakers and subwoofers at the same time. The most common setup is a monoblock amp to run subwoofers and a 4-channel amp to run door speakers. Check out our Knowledge Base for more information.
Total Peak Power Output
The total peak power output is measured as the wattage per channel multiplied by the number of channels, and is calculated at the lowest level of operating impedance.

It is measured during a brief musical burst, such as a sudden drum accent. Some manufacturers display peak power ratings on the face of their products to increase the appeal.

The RMS power rating is more accurate, and we recommend using it for product comparison.

400 watts
Total RMS Power Output
Total RMS power is measured by multiplying RMS power per channel by the number of channels, and is calculated at the lowest level of operating impedance.

RMS power is the amount of continuous power, measured in watts, that an amplifier produces is called RMS power. The higher the RMS figure, the louder and cleaner your music sounds.

The RMS output figure is much more accurate than the peak rating when comparing products.

100 watts
Maximum Input Gauge Size
This is the largest gauge wire that will fit into the power and ground terminals of this device. The lower the gauge number, the thicker the wire is. For example, a 4 gauge wire is thicker than an 8 gauge wire and thus has higher current carrying capacity. Always do your best to get this size wire to reduce the risk of damage to your components.
Minimum Impedance Unbridged
The lowest impedance the amplifier will handle when it is not bridged.
2 ohms
Minimum Impedance Bridged
The lowest impedance the amplifier will handle when it is bridged.
4 ohms
THD at Rated RMS Power
The amount of change in harmonic content of the signal as it is amplified. A lower figure indicates less change and a more accurate amp. THD below 0.10% is inaudible.
Speaker Level Inputs
Speaker level inputs are commonly referred to as high-level inputs and vice versa. This input type allows you to get your audio signal directly from the speaker wire in your vehicle, instead of using RCA cables. The advantage of this is factory integration, as most stock radios do not have RCA outputs to run amplifiers.
Preamp Outputs
Many amplifiers are equipped with RCA preamp outputs which pass the original music signal from the source to additional amplifiers. This is known as daisy chaining because the source connects to the first amp, and the first amp connects to the second amp, etc. The advantage to daisy chaining is you only need one 2-channel RCA cable to transfer the signal from the head-unit to the amplifier, and then one additional cable for each amp being daisy chained.
Built-in Crossover

A crossover is a type of filtering system that permits only certain frequencies to play. A Low-Pass (LP) crossover allows only frequencies below its setting to get through which is good in the case of some subwoofers. A High-Pass(HP) filter allows frequencies above its setting to pass through, this is normally used on speakers.

When a crossover is set to FULL it means no filtering is added and the full frequency spectrum is allowed through the amplifier. Filtering is important because feeding a speaker frequencies it cannot reproduce effectively creates distortion.

Low-pass (LP)
High-pass (HP)
Signal-to-Noise Ratio
This spec compares the strength of the signal to the level of background noise. A higher value indicates less background noise.
95 dB
Bass Boost
The objective of the bass boost is to get more kick out of your subwoofer. It is a circuit that emphasizes the lower frequencies at a given point. The bass boost should always be set first before setting the gain. This feature is known for destroying subwoofers and is commonly used incorrectly, so be cautious.
0 - 12 dB
Bass/Gain Remote
If the amp comes with a bass/gain remote you will be able to control the level of your bass from your dashboard. Typically bass remotes also include a 16-20 ft. wire for installation.
Fan Cooled
A great feature to have if an amp generates a large amount of heat. Cooling fans can help regulate the temperature to prevent the amp from overheating (burning).
Fuse Rating
The amperage and the number of fuse(s) an amp requires.
20A x 1 
CEA-2006 Compliant
Amplifiers that have been tested to meet specific standards. When a car amplifier meets these standards, you can be sure that it will be able to produce the amount of power specified by the official CEA-2006 rating. Usually, these rating consist of the following items:
  • RMS Power
  • Signal-to-Noise Ratio

This rating applies to both external car amplifiers, as well as the amplifiers inside of in-dash stereos.

Sonic Certified Amplifier
Sonic Certified amplifiers have been tested by the experts at Sonic Electronix to meet or exceed the wattage ratings provided by the manufacturer. If this is marked as Yes, then you can trust the wattage ratings. If marked as No, then we have tested the amplifier and it did not meet the advertised wattage ratings. If marked as Not Tested, then the Sonic Electronix experts have not yet been able to test the amp.
Amp Bluetooth Connectivity
This feature will tell you if the amplifier has the capability to connect to a Bluetooth device.

Specials with this Item

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Warranty and Return Policy

Parts Warranty Duration
6 years
Labor Warranty Duration
6 years
Warranty Provider

Summary of Customer Ratings & Reviews

Rating Distribution

5 Star
4 Star
3 Star
2 Star
1 Star

Average Attribution Rating

Accessory Tools and Products

Accessories added

Kicker 4-Channel RCA Audio Interconnect Cable

4 Meters (13 ft.) 4-Channel K-Series RCA Audio Interconnect Cable

Your Price $19.95

StreetWires ZN7 RCA Interconnect Cable

16.4 ft. of 4-Channel RCA Cable with hyper twist construction, oxygen free copper, and precision machined tips.

Your Price $59.99

StreetWires FB8

8 Gauge Firewall Bushing

Your Price $6.95

Car/Marine Audio Installation Kit

Includes Test Light, Crimp/Splice Tool, Multi-bit Screwdriver and more.

Your Price $16.99

Browse 6 questions and 9 answers
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Why did you choose this?
Sonic Electronix Store
I Already have A Boss Head Unit And Speakers. This Amp Should Make A Big Difference. I Mine As Well Keep All The Components The Same. Boss Products Are A Affordable Way To Get Good Sound For A Cheaper Price. If This Was A Alpine Or Pioneer It Would Cost Twice As Much For A Marine Amp. Thanks
Seth A on Sep 17, 2014
had good reviews
Peter Z on Aug 12, 2014
Will this amp work well with two boss mwrt69 tower speakers?
Matt L on Feb 10, 2015
Best Answer: It should be fine. The sound from my system was muffled at first, and I thought it was an amp issue (not good quality). However, it turned out to be a speaker issue. Since switching to Alpines I have had no issues. Good looking amp too.
Reply · Report · Mark R on Feb 10, 2015
· Add Answer · I Have This Question Too (1)
Can I connect two boss tower speakers to this amp and leave factory installed speakers connected to the head unit?
A shopper on May 27, 2015
Best Answer: The low level output from the head unit should connect to the low level side of the amp and drive the towers, and the high out put speaker leads from the head unit should still power the other speakers, best and cheers
Reply · Report · Alexander A on May 27, 2015
· Add Answer · I Have This Question Too (0)
are the outputs on this amp bridgeable?
A shopper on Jun 9, 2015
Best Answer: Hello,

The manufacture does not specify on this amplifiers ability to do so. This leads us to assume it cannot. Being a fairly entry-level amplifier, it is a safe assumption that it cannot.
Reply · Report · Rick MStaff on Jun 9, 2015
· Add Answer · I Have This Question Too (0)
can I ground the amp to the battery negative post? otherwise I cannot find metal grounding location.
tim k on May 31, 2015
Best Answer: Hello Tim.

Reply · Report · Rick MStaff on Jun 1, 2015
· Add Answer · I Have This Question Too (0)
What is the physical size of the MR404? Will this unit work well with 4 MR50 Boss speakers? This is for a motorcycle application.
kawabiker on Dec 8, 2014
Best Answer: Hello Herb,

The dimensions on the website are confirmed; Dimensions: 9-8/10"W x 7-3/4"D x 2-3/4"H . The amp will be a good match for those speakers.
Reply · Report · Sonic Electronix SStaff on Dec 8, 2014
· Add Answer · I Have This Question Too (0)

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Sonic Electronix Wiring Guide

Wiring Diagram Legend

Warning: The image depicted shows the resistance change when wiring multiple subwoofer terminals. Please refer to your subwoofer's owner's manual for the proper wiring of its terminals. Sonic Electronix, Inc. is not responsible for damage caused to your audio system or vehicle due to improper installation. Please call tech support at 1-877-289-7664 if you require additional assistance.

Product Name: Boss MR404