Rockford Fosgate Prime R400-4D

4-channel car amplifier — 75 watts RMS x 4

Item #: 575R4004D

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10 Reviews

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Rockford Fosgate packs more power per square inch into their Prime Class D amps than almost any other amplifier made, so you can put more music power in your vehicle's limited space. Your music will play loud and clear with one of these reliable and cool-running amps.

4-channel versatility
The R400-4D 4-channel amp puts out 75 watts RMS to each of your full-range speakers or components, giving them plenty of juice to rock. You can also use the front channels of the R400-4D for your front speakers while using the rear channels bridged to run a sub with up to 200 watts RMS. And, of course, you can bridge the amp to 2-channel mode to drive a pair of subs.

Clean power, extensive controls
Rockford Fosgate designed Prime amps to deliver Power Output Without Excessive Regulation (POWER), which means they'll respond quickly to the peak demands that you may throw at your system. High- and low-pass filters, along with Rockford Fosgate's famous Punch bass boost, let you tune your speakers for maximum performance, so your driver's seat will become your favorite place for listening.

Product Highlights:

  • 4-channel car amplifier
  • 75 watts RMS x 4 at 4 ohms (100 watts RMS x 4 at 2 ohms)
  • 200 watts RMS x 2 bridged output at 4 ohms (4-ohm stable in bridged mode)
  • CEA-2006 compliant
  • variable high- and low-pass filters (50-250 Hz, 12 dB/octave)
  • variable Punch EQ bass/treble boost (0-18 dB at 45 Hz and 12,000 Hz)
  • Class-D amplifier design
  • MOSFET power and output stages
  • frequency response: 20-20,000 Hz
  • preamp inputs and outputs
  • 4-gauge power and ground leads recommended — wiring and hardware not included with amplifier
  • no onboard fuses — when installing multiple amps in a system, an additional 40-amp in-line fuse between the distribution block and the amplifier is recommended
  • 9-1/8"W x 2"H x 7-3/8"D
  • warranty: 1 year
  • Our 60-day money-back guarantee

My system has plenty of power. Who needs an amp?

You might think you don't need an amp because you have a 400-watt system in your car, or because your new stereo puts out 50 watts a channel. But those are peak wattage ratings, which may boil down to 15 or 20 watts per channel, using the more realistic RMS rating. An amp sends your speakers the power they need to deliver your music with clarity and impact, whether you're using factory speakers or high-performance components. And low-frequency reproduction requires lots of power, so an amp is an absolute must if you're adding a sub to your system.

Rockford Fosgate Prime R400-4D Reviews

Average Customer Review:

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Written By Bill M, Georgia on Tuesday, September 08, 2015

Crutchfield Customer Review (What's this?)

This amp makes me wish I'd never started this upgrade in the first place. I'm sure some people have had good luck with it, but I got my whole install done, hooked up the last RCAs to it, and they slipped right off. They are Stinger 6000 interconnects, and I've read a hundred reviews saying how great they are, and how tight, but on this RF amp, they come right off. I was just doing a first test of the system, engine off, listening, and the speakers cut out. The plugs had vibrated off in a matter of a couple of minutes, with just the sound causing it. When I told Crutch about it, they naturally said it was the interconnects (which I bought locally, instead of from them). Nobody I've talked to on several forums, and Amazon have had this problem. I guess the only solution is to rip out everything and start over with different RCAs. I think I'd rather just not bother, drive the car off a cliff.

Pros: The expectation of it working was great.

Cons: The reality sucked.

Rockford r400-4d

Written By mike88688, Pompano beach, FL on Sunday, July 19, 2015

Crutchfield Customer Review (What's this?)

Produces amazing sound quality when paired with Rockford subs and speaker setup

Pros: Extremely good quality and sound

Cons: Could use a little more tuning capabilities

Didn't work properly

Written By DG, San Antonio on Tuesday, August 12, 2014

Crutchfield Customer Review (What's this?)

used to power 4 speakers, had it professionally installed. 2 of the speakers didn't work at all and the problem was traced back to the amp. Ended up just buying a different one from the instaler

Pros: none

Cons: quality

do not buy

Written By David, Oklahoma City on Tuesday, June 10, 2014

Bought this amp 2 years ago. It is an awesome amp when it worked. It is hooked up with all professional wiring. I only had the front channels hooked up and were running at half gain. It is hooked up to a infinity kappa component system and sounded awesome at just half gain. Just recently it stopped working. Power light on but no sound. For this price point, with half gain, 1 channel ever used, and in a vehicle that is rarely driven this amp should not be broke. Ive had RF amps that lasted years longer at max power for extended periods of time. Purchase a different amp or get a extended warranty. Tried to get it fixed but for $150 not worth it.

Pros: Sounds great when working.

Cons: Broke after minimal use. Guess thats why its only a year warranty. Just like a car, they know how long to do the warranty because after its out you will have problems.

Rockford Frigate Amp

Written By John D., Chesapeake, VA on Tuesday, March 18, 2014

Crutchfield Customer Review (What's this?)

Worth the price for amplifier.

Pros: Can install underneath driver's seat.

Cons: None

Great amp

Written By Kristoffer, Provo, Utah on Sunday, September 08, 2013

What a great amp! First amp I've personally boughten and I've been very pleased so far! Had it for almost a year now. Love how small it is and easy to hook up. I have mine mounted to the back of my seat and it looks great! Definitely recommend!

Pros: Small Plenty of power Easy to install

Great Amplifier, Easy Install

Written By DPowell, Harrisburg, Pennsylvania on Saturday, September 07, 2013

This is a great amplifier. I used this and underrated my speakers that were able to handle 100W rms a piece. Let me tell you what, 75W a channel is perfect. Plenty of power going to my speakers, no distortion at all. Plus the high pass filters are real convenient when paired with a pair of subwoofers. Great amplifier. Crutchfield is definitely the quickest supplier you'll find, but unfortunately not the cheapest.

Pros: Easy installation All the inputs(positive and negative, power, ground, etc) are all nicely separated. Lots of power And of course, its Rockford Fosgate quality.

Cons: None that I can think of.

Great Amp, Small Size

Written By Anonymous, Mentor, OH on Monday, April 22, 2013

Purchased this amp to simplify my system in newer car, i.e. going from two amp system to one 4 channel amp. Installed along with new JVC KD-X80BT head unit, driving JBL GTO938 in rear and old Infinity reference components in the front. This amp has plenty of power. Besides breathing new life into the old Infinities, provides ample power to provide me with all the base I need from the JBLs. The small size allowed me to install under rear deck. Love the various controls and set screws for wiring.

Pros: Great Amp

Cons: None

Great Amp

Written By Steveintexas, NE Texas on Sunday, October 21, 2012

Crutchfield Customer Review (What's this?)

Installed the R400-4D in a 2009 F150 along with 4 Kenwood KFC-680C speakers. Also replaced the headunit with a Pioneer AVH 8400H receiver. The amp was easy to install and sounds great. 100% improvement over the factory radio. I've always liked the Rockford Fosgate products.

Pros: Small footprint Easy install

Cons: Should have done this sooner.

Great amp

Written By Marvin, CA on Wednesday, June 27, 2012

Great amp ive used rockford amps since the 90s and absolutely love them especially with their new style amps that have no more external fuses...

Pros: Does the trick plenty of power with a small footprint

Cons: None

Hands-on research

What's in the box?

Download owner's manual

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

Product Research



Overview: The Rockford Fosgate Prime R400-4D is a 4-channel full-range Class D 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.

CEA 2006 Compliant: The R400-4D's power ratings are measured according to the strict standards dictated by the Consumer Electronics Association (CEA). These standards allow you to accurately compare the rated power output of all CEA 2006-compliant amplifiers, even different brands. Manufacturers who adhere to the standards can display the CEA 2006 logo on their products and packaging. The RMS power output is as follows (measured with a 14.4 volt input, <1% THD+N, 20 Hz-20 kHz):

  • 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 R400-4D 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.