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Rockford Fosgate Prime R400-4D

4-channel car amplifier — 75 watts RMS x 4

20 Reviews | 4 questions - 9 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.

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!!!

Ryan, Fenton, Iowa

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")

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

Rockford Fosgate Prime R400-4D Reviews

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(20 Reviews)
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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.

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Q & A

Customer Q&A

Crutchfield asked  
Why did you buy this?

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 ]

4 questions already asked

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