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Rockford Fosgate Prime R400-4D

4-channel car amplifier — 75 watts RMS x 4

34 Reviews | 6 questions - 11 answers


Our take on the Rockford Fosgate Prime R400-4D

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.

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

What's in the Box:

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

i used it to replace an amp that was 6 years old what an amazing difference! the clarity and power was incredible

james, Spanaway, WA


Rockford Fosgate Prime R400-4D Reviews

Average Customer Review(s):

(34 Reviews)

Rockford Fosgate Prime R400-4D

Crutchfield customer from Kapaa, HI on 1/9/2019

Crutchfield Customer Review (What's this?)

My first RockFos. I'm pretty sure that I love it. Makes my little Mazda B4000 a much better pleasure to drive. I honestly didn't think that was possible. I also got a pair of the punch triax. I am a real stickler for crisp clean sounds. I have that now. Thank you Crutchfield. I'm gonna get the head unit next, maybe you should be ready to ship it on over. Aloha Jeff from Kauai, Hi.



Good, not great

Wyatt from Livingston Tx. on 10/19/2018

Crutchfield Customer Review (What's this?)

Good starter amp. If you already have a good amp driving your system, stay away from this one. That being said, this is a good amp, not a great one. Seems to want to clip really fast according to my oscope. Will try a different tone and see if that changes anything. Does pump up the low end, and clear up the high end. Swapped out a JL Audio 50x4 for this 75x4. Didn't really live up to my expectations, but sounds good. Very clean, very quiet. Runs insanely cool. Install and wiring is not for novice. Managed to hide behind glove box. Bet they could have packed it in a smaller package. As it stands its right on the edge of limiting mounting options, and you have to get real creative if your going stealth install. but it is what it is. Punch EQ adjustment just seems to muddy the sound up, tuning is still ongoin. Bought this scratch and dent, cause they were out of brand new. When they say scratch and dent, they MEAN scratch and dent. It should be marketed as used in this shape. But I didn't buy it to look at it so ill take it. If I could go back I probably would go another direction, but overall, satisfied.

Pros: Quiet, cool, lot of amp for the money. Good highs and lows. Medium footprint allows some versatility in mounting.

Cons: If we can put 50x4 into a brick amp, feel like we could do 75x4? 4 gauge wiring seemed a bit big when there are are other 75x4 amps that use 8 guage.

Rockford Fosgate Prime R400-4D

Crutchfield customer from Burlington, NJ on 10/3/2018

Crutchfield Customer Review (What's this?)

Installed in my 2018 frontier crew can....sound is positively astounding...



Rockford Fosgate Prime R400-4D

james from Spanaway, WA on 8/21/2018

Crutchfield Customer Review (What's this?)

i used it to replace an amp that was 6 years old what an amazing difference! the clarity and power was incredible



Best Value and Price

Ed from South Florida on 7/29/2018

Crutchfield Customer Review (What's this?)

Great price and value. It runs 6 speakers in my truck without any interference or gaps. Doesn't overheat.

Pros: *Best price. *High end product. *Multiple channels.

Cons: *Could be more powerful. *Requires skill to setup with existing factory audio system.

Rockford Fosgate Prime R400-4D

Harrison from College Station, TX on 7/16/2018

Crutchfield Customer Review (What's this?)

Works Great! Provides plenty of power to my door speakers and makes them sound awesome!



Rockford Fosgate Prime R400-4D

Crutchfield customer from Fulton, KY on 7/6/2018

Crutchfield Customer Review (What's this?)

So far, so good. No complaints with this unit at all. Seems to be a very strong unit as it compares to it's rating. Very pleased so far.



Rockford Fosgate Prime R400-4D

Crutchfield customer from Grantsville, UT on 6/25/2018

Crutchfield Customer Review (What's this?)

Rockford Fosgate is the best as always




Carlos from Lajas, PR on 6/24/2018

Crutchfield Customer Review (What's this?)

Just what I was expecting Lots of Power, reliability,no overheating ; just plain Rockford Fosgate class



Clear sound, clean power, small package and price!

Eric from Mount Juliet, TN on 6/14/2018

Crutchfield Customer Review (What's this?)

Excellent amp! Lots of clean power in a small package. Doesn't get hot and has all the features I could expect for the price point. Wish it had a fuse or onboard fan for piece of mind, but other than that.... great amp.

Pros: Compact, affordable, excellent clarity

Cons: No fuse, cooling fan...

Rockford Fosgate Prime R400-4D

Wade from College Place, WA on 5/18/2018

Crutchfield Customer Review (What's this?)

Great choice for my situation, excellent amp.!

Pros: All Good


Packs a punch for the price.

Tim from Arab, AL on 1/2/2018

Crutchfield Customer Review (What's this?)

Easy set up and install. Plenty of power and good sound.

Pros: Fast delivery, good sound, and plenty of power.

Cons: Not any at this time.

Rockford Fosgate Prime R400-4D

rickie from Sherman, TX on 12/26/2017

Crutchfield Customer Review (What's this?)

I have not had time to install yet had knee replaced so I cant give review on anything yet




wesley from reading, pa on 9/30/2017

Crutchfield Customer Review (What's this?)

So far this is everything I could want in a 4 channel amp

Pros: Works

Cons: None

Rockford Fosgate R400 4D

Ryan from Fenton, Iowa on 5/15/2017

Crutchfield Customer Review (What's this?)

Great amp for the price. Easily powers my RF 5x8's and tweeters. Makes the system sound complete and has plenty of power. Been running this amp for about 4 weeks powering 4 5x8's and a set of tweeters, clean highs, powerful mids. Great amp!!!

Pros: Lots of clean power. Great price.

Cons: None to speak of at the moment

Buy with caution

willie from Port Saint Lucie, FL on 5/9/2017

Crutchfield Customer Review (What's this?)

I love the features, power is good, installation easy. The first unit I received heated up and shut it self off after about 15-30 minutes of play. The second unit quality was lacking. I read reviews on this unit and experienced a lot of the complaints I read in the reviews , I would buy with caution.

Pros: nice features

Cons: Overheats and shuts off

Rockford Fosgate Prime R400-4D

Jason from Michigan on 2/11/2017

Amazing little amp. Rated at 75W x 4. Factory cert rating was 549W RMS. Gain set at 2. Stays cool every day on my hour commute to work.

Pros: Price Size POWER

Cons: No high level line input clip

Rockford Fosgate Prime R400-4D

Jason from Michigan on 1/29/2017

Rated at 4 by 75 watts. Certified by Rockford at 549 watts. That's a lot of bang for the buck! Sounds great with the Rockford speakers.

Pros: Power Size

Cons: No high level inputs.


J.R. from San Antonio, Tx on 1/14/2017

Crutchfield Customer Review (What's this?)

Great amp for the price. I used to run RF wayyyyyyyyy back in the day of Punch 45,75 & 150. They were kind of dirty little amps but got the job done. The new amps are nice, clean, efficient, solid and have well thought out hookups, dials and switches. This amp far exceeded my expectations. Great clearance for behind the back seat of a 2011 ford f150 extended cab. It's a D class amp so it's efficiency means it runs at a much cooler temp than the old school A/B class amps. Currently running a pair of Polk Audio MM5251 component speakers up front and Pioneer 6x8 4ways in the back doors. This amp runs all of them with with the gain only up about 1/2 way. Even at this level, the volume on the stereo set at 10 will blow your doors off. No regrets.

Pros: Well priced, quality feel, easy to reach dials and switches

Cons: NONE

Great quality and sound

Ben from Woodbury, tn on 12/20/2016

I love this amplifier I have it powering 2 sets of Rockford fosgate t1650 coaxial speakers and it sounds amazing the only problem is that the amplifier has only one set of rca's out but it would be nice to have 2 sets.

Pros: Awesome product.

Cons: Only one set of rca's out.

Excellent amp!!!

Bill from Staten Island, NY on 9/27/2016

Over the years I have used nothing but RF amps in any of my cars, and never once have I been disappointed. The quality is amazing and the sound they put out is awesome. Easy install, love the small size can fit it almost anywhere. Excellent controls to set up the amp just right. Cant go wrong with RF.

Pros: Same RF quality as always, small size huge output. High quality great price. If you want to do it onxe and do it right yoy will not be disappointed with RF.

Cons: None

Great product, great instructions, great sounding!

Paintxpert from Stratford, CT on 4/23/2016

Crutchfield Customer Review (What's this?)

Product was endorsed by Crutchfield for my application. The instructions to install were right on. It was a very happy ending and a SUPERB upgrade. Thanks for all the product support.

Pros: Great sounding product that was easy to install. Thank-you for all the product support.

Cons: None so far that I can see.

Great speakers

Austin B from pittston, PA on 1/29/2016

Speakers are great! They fit perfect in my 2004 Jeep Wrangler roll bar... There being powered by a Rockford fostgate prime amp.. I am very impressed with the sound quality crisp highs! And very good mids in the stock Jeep Wrangler pods. They screw right it and fit perfectly.

Pros: Sound quality is great! Crisp highs and very good mids. Fit right in my jeep wranglers speaker pods.

Cons: Absolutely none

Cool AMP - Small But Quality

jffp from Philippines on 1/25/2016

I've setup with AVH x5750BT Head Unit, with Focal 165F and JL Audio 12" W1 v3 Subs! Great sound and clarity! feel all the bass and power !




Bill M from Georgia on 9/8/2015

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

mike88688 from Pompano beach, FL on 7/19/2015

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

DG from San Antonio on 8/12/2014

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

David from Oklahoma City on 6/10/2014

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

John D. from Chesapeake, VA on 3/18/2014

Crutchfield Customer Review (What's this?)

Worth the price for amplifier.

Pros: Can install underneath driver's seat.

Cons: None

Great amp

Kristoffer from Provo, Utah on 9/8/2013

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

DPowell from Harrisburg, Pennsylvania on 9/7/2013

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

Guest from Mentor, OH on 4/22/2013

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

Steveintexas from NE Texas on 10/21/2012

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

Marvin from CA on 6/27/2012

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

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.

Q & A

Customer Q&A

Crutchfield asked  
Why did you buy this?

I recently installed this amp in a friends hot rod wired to four RF TS1693 6x9. I experienced zero distortion at maximum volume and decided to mount one in my daily driver. [ Charles M  Dec 30, 2018 ]
Rockford is the best and I already use one of these amps in my other vehicle [ MICHAEL  Dec 18, 2018 ]
As recommended by Gil from Crutchfield [ Bertram  Mar 25, 2018 ]
Because the Reviews of this particular item [ JAIME  Jan 02, 2018 ]
Amp worked good for the new speakers i picked out. [ corey  Dec 11, 2017 ]
Christmas present for son... he picked it out. [ Marie  Dec 05, 2017 ]
I have always enjoyed the power and value from Rockford Fosgate equipment. [ Christopher  Aug 23, 2017 ]
great power output from such a small amplifier. LOVE IT!!!!!! [ Alfonso  Mar 19, 2017 ]
I am using everything Rockford fosgate I need 2 twleves a amp and a box combo [ daniel  Dec 17, 2015 ]
Is it what i need [ sergio  Dec 11, 2015 ]
Bang for the buck [ Brent  Dec 05, 2015 ]

6 questions already asked

Thanks for your question. For information on selecting the best amp for your speakers 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. [ Krissy  Dec 19, 2018 ]  Staff
Yes. And definitely one of the best amps you can buy if your powering good speakers. You won't even use half it's potential [ eric gorski  Jan 12, 2018 ]
It says to run a #4 wire which can handle 100 amps I believe it just needs capacity for flow of electricity.. I notices if voltage drops amp crackles... [ Greg  May 23, 2017 ]
In order to answer this question, there are a few variables that need to be filled in. Everyone's answer may differ ... I'd suggest using an ohms law calculator or amperage draw calculator online to give you the closest possible answer. [ Chris  May 23, 2017 ]
Hi. I'm pretty sure it doesn't go by amperage, look at the wattage. If anything, very little amperage. [ eric gorski  May 23, 2017 ]
It sure on ohms but I have mine hooked up to 4 pioneer 6 x 9s works fine [ DOUGLAS  Jan 06, 2017 ]
It will power them both for sure, the speakers that have the higher resistance will suffer for sure. Great amp for what it cist [ Joseph W.  Jan 06, 2017 ]
U won't go wrong with RF amps. I use the prime series. They put out gobs of power!! Plus They're small and don't draw much current. I didn't use a capacitor and I have no problems with lights dimming or bass cutting out and I'm running the R500x1D at 2 ohms. U won't find a better amp for the price imo. [ william  Jan 07, 2016 ]
Rockford fosgate is the only option in my opinion, I have never had issues with my amps and when it comes to getting the power from theses amps it s way to easy . Well know and depndable quality unsurpassed . Don't make a mistake and choose a cheaper brand because you won't be happy , to with the best and forget about the rest. Dave [ David  Jan 06, 2016 ]
Thanks for your question. For information on selecting the best amp for your speakers and sub 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. [ Kenny  Jan 06, 2016 ]  Staff
If you purchased the product from Crutchfield, feel free to contact our Tech Support team. They can walk you through the settings on the product and see if there may be a fix. Our toll-free Tech Support number is printed on your invoice, and is also available under the "My Orders" tab in the "My Account" section of our website. If you did not purchase the unit from Crutchfield, then you may want to contact the manufacturer. You can also post your question in our forums: Or try our online support center: [ Krissy  May 26, 2014 ]  Staff