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Rockford Fosgate Prime R300X4

4-channel car amplifier — 50 watts RMS x 4

Outlet: Open Box

Item #: 575R300X4

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6 Reviews | 3 questions - 4 answers


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Rockford Fosgate power for your speakers

Rockford Fosgate performance in a small package. The Prime Series R300X4 4-channel amp can drive your speakers with 50 watts RMS each, so you'll really feel your tunes rockin'. Or, you could switch the R300X4 to 2-channel mode to run a couple of subs with 150 watts RMS each — when you buy a bigger amp for your subs later on, you can still use this 4-channel to drive all your speakers. Smart move.

You can use the high- and low-pass filters and Rockford Fosgate's famous Punch boost to get maximum performance from the speakers in your vehicle. And speaker-level inputs let you hook this amp up to almost any system, even a factory stereo.

Rugged performance and value

The R300X4's heavy cast-aluminum chassis efficiently draws damaging heat away from its internal components, ensuring reliable, long-term play. The amp's built-in sensors keep track of the output current and power supply temperature, ensuring that plunging speaker impedances (they change constantly during play) or even a short circuit won't hurt anything. Your driver's seat will become your favorite place for listening to music once this Prime amp goes to work.

Product Highlights:

  • 4-channel car amplifier
  • 50 watts RMS x 4 at 4 ohms (75 watts RMS x 4 at 2 ohms)
  • 150 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) on front and rear channels
  • selectable bass boost (0, 6, 12 dB at 45 Hz)
  • Class-AB amplifier design
  • MOSFET power supply
  • frequency response: 20-20K Hz
  • preamp and speaker-level inputs
  • 8-gauge power and ground leads and a 50-amp fuse recommended — wiring and hardware not included with amplifier
  • no onboard fuses — when installing multiple amps in a system, an additional 50-amp in-line fuse between the distribution block and this amplifier is recommended
  • 13-1/4"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 R300X4 Reviews

Average Customer Review:

6 Reviews


Written by: r chapa from san antonio, TX on January 30, 2016

Crutchfield Customer Review (What's this?)



Cons: NONE

Terrific amp

Written by: Jontyrees from austin, TX on January 29, 2016

Just installed this to replace an alpine MRPF300 tht never impressed me. Night and day difference. This RF is sooo much better, finally the system sounds like I thought it should. I blamed head units, speakers, previously, but the problem was the two alpine amps, mrp500 and MRPF300. I replaced both with similar rated and priced RF Prime units, and the difference is staggering. Simply switched out the amps, changed nothing else. I'll never use another brand of amp than RF from now on. Oh, and the birth certificate showed 416w RMS, vs 300w rating.

Pros: Great sound, great price, good looking, adjustments on top

Cons: I didn't buy it soon enough

Great amp

Written by: Barto from New Jersey on January 17, 2016

Crutchfield Customer Review (What's this?)

Great amp, very flexible with different setups, using it to drive 6x8 Polk coaxials front and rear and has more than enough power. Very happy with this amp, Install was very easy nice size gives you lots of choices.

Pros: Great power,very clean,very flexible with different setups

Cons: None

Works great

Written by: Dennis D. from Sarasota, Florida on January 11, 2016

Crutchfield Customer Review (What's this?)

Works great. Easy setup.



Rockford Fosgate Prime R300X4

Written by: 808xN8 from Hawaii on January 4, 2016

Crutchfield Customer Review (What's this?)

Excellent amp. Provides more than enough power for 6 1/2 inch front and rear component speakers that I have in the doors. Also allows me flexibility to change/ upgrade the speakers in the future if wanted. I Have the gain set at half power right now.

Pros: Small and powerful. Looks good and simple to hook up. Sound comes out clear at high volume.

Cons: Not many I can think of yet. To be picky , it could have bigger connections for wire inputs and outputs. They seem small for the power of the amp.

best amp to get for your car speakers clear sound amazing!

Written by: eddie from whittier ca on August 9, 2014

best amp to get for your car speakers clear sound amazing!



Hands-on research

What's in the box?

Download owner's manual

  • 4-Channel amplifier
  • Two 6" Speaker level input harnesses
  • 3mm Allen wrench
  • Four 3/4" Self-tapping screws
  • 4 Flat washers
  • Installation & Operation manual (English/ French/ Spanish/ German/ Italian)
  • Amplifier verification certificate

Product Research



Overview: The front and rear sections of the Rockford Fosgate Prime R300X4 4-channel amplifier are bridgeable, so it can be wired in 4-channel, 3-channel, or 2-channel mode.

CEA 2006 Compliant: The R300X4's power ratings and signal to noise ratio are measured according to the uniform standards advocated by the Consumer Electronics Association (CEA). This allows you to accurately compare these specifications for all CEA 2006-compliant amplifiers, even from different brands. Manufacturers who adhere to these standards can display the CEA 2006 logo on their products and packaging. CEA2006 Specifications for this amplifier are:

  • 4 Ohms: 50 watts RMS x 4 at 4 ohms, 14.4 volts, and less than 1% THD+N
  • 2 Ohms: 75 watts RMS x 4 at 2 ohms, 14.4 volts, and less than 1% THD+N
  • Bridged: 150 watts RMS x 2 at 4 ohms, 14.4 volts, and less than 1% THD+N
  • S/N: 80 dB, measured at 1 watt output (100 dB measured at rated power)

LED Indicator: The amplifier is equipped with an LED power/protect indicator. The LED illuminates blue when the unit is turned on. It illuminates red if the thermal or short circuit protection circuit is engaged, and the amplifier will automatically turn off.

Mounting: The amplifier can be mounted vertically or horizontally using the supplied mounting screws. The amplifier should never be mounted in an engine compartment as this will void the warranty.


Gain Controls: The front and rear amplifier channels have independent gain controls. Each rotary control is labeled 1 to 11 and has a sensitivity range of 150mV to 4V when using the RCA inputs, 450mV to 12V when using the speaker level inputs.

Crossover: There are also independent 12 dB/octave crossovers for the front and rear channels. Crossover switches allow you to choose low-pass, high-pass, or full-range operation. The crossover points are continuously variable from 50 to 250 Hz.

Punch EQ: The Punch EQ bass boost circuits are individually selectable, 0 (flat), +6 dB, or +12 dB and centered at 45 Hz.

Input Switch:

  • 2-CH: when using only the front inputs
  • 4-CH: when using the front and rear inputs


Power Terminals: The power and ground terminals are nickel-plated set screw terminals and will accommodate up to 4 gauge power and ground wires.

Fuse: An external 50-amp fuse (not included) must be installed on the power wire at the battery. If a wiring kit is used which includes a fuse with a value other than 50-amps, the original should be replaced with a 50-amp fuse.

Remote Terminal: The remote turn-on terminal is a nickel-plated set screw terminal that will accommodate up to an 8 AWG wire. It's used to remotely turn the amplifier on and off.

Speaker Terminals: The four pair of speaker outputs are nickel-plated set screw terminals what will accommodate up to 8 AWG speaker wire.

RCA Input Jacks: Front and rear RCA input jacks provide an easy connection for preamp level inputs. They are nickel-plated to resist signal degradation caused by corrosion.

Speaker Level Input: Two speaker level input harnesses are included, making it easier to add the amplifier to a factory radio or to a receiver with no preamp outputs.

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.

Customer Q&A

3 questions already asked

How much watts you need depends on the speakers you plan on using. This amp is 75x4 rms. I'm no expert but usually the peak output is about double the rms. I have the gain set at about 1/2 for front and rear components that rate 50watts rms. it's way more than enough, but allows for future upgrades [ Nathan  Dec 28, 2015 ]
I don't think so. [ JESSE  Sep 24, 2014 ]
We have not received any answers from other customers on your question. I would recommend reaching out to an Advisor by phone (1-800-324-9695) or online chat. They should be able to help answer your question. [ Krissy  Sep 16, 2014 ]  Staff
I forwarded your question to an Advisor and they responded with the following: The amplifier has speaker level inputs, so you do not "need" an LOC. It can still help if you want to get the cleanest signal to your amplifier from the factory radio. If you would like to discuss further you can contact an Advisor directly by phone (1-800-324-9695) or online chat. [ Krissy  Aug 06, 2014 ]  Staff