Our Top Pick for 2018: Rockford Fosgate R500X1D Prime 1-Channel Class D Amplifier
Read our full review.
The right aftermarket amplifier provides the power you need to get bigger sound and a better listening experience out of your car stereo. If you’re adding a subwoofer (or two) to your vehicle, you absolutely need an amp – chances are, your stock sound system doesn’t have enough power to run a sub. Even if you won’t be adding a subwoofer to your system, installing a quality amplifier is an effective way to improve your stereo’s sound quality. If you’ve ever cranked the volume for your favorite song and noticed a lot of distortion, the culprit is probably an underpowered amp. High quality amps provide ‘clean’ power, boosting your CD player, aux connection, or radio’s signal without any interference or noise from other components. The right amp will give you bigger and better sound with less distortion.
#1. Rockford Fosgate R500X1D Prime 1-Channel Class D Amplifier
Don’t let the compact size fool you – this little amp is a true powerhouse. The Rockford Fosgate R500X1D is built just for subwoofers, and it excels at delivering truly big sound. If you want a heavy-hitting bass sound, this amp has you covered.
The R500X1D clocks in with a strong 500 watts RMS at 2 ohms. With a THD (Total Harmonic Distortion) of less than 1% at both 4 ohms and 2 ohms, you can expect minimal coloration to the sound. The signal-to-noise ratio is also very respectable, coming in at a rating of 80 dB when measured at 1 watt output and 100 dB measured at rated power.
Even with all that power, the R500X1D’s cast aluminum heatsink means that this amp is well-equipped to take the heat. Its class-D design offers a fantastic 89% average efficiency at 4 ohms, so you can crank things up with confidence that it can handle the job.
This single-channel amp is built for optimum bass performance, with a 12dB/octave Butterworth low-pass crossover that is always engaged. The continuously variable crossover point ranges from 50 to 250 Hz. The frequency response range is 20Hz to 250Hz, which means this amp is focused completely on lower notes for peak bass performance. And if you need to punch it up a little more, this amplifier also offers adjustable Punch EQ from 0dB (min) to +12dB (max) @ 45Hz.
Included with this unit is a wired Remote Punch Level Control, which is linked to the amp’s gain control. With this remote, you can control the amplifier output at any time from the comfort of your dashboard. Best of all, the rotary gain control is labeled from 1 to 11 – so you can say that your system truly does go to 11!
Even if you don’t have a lot of room in your car, this amp’s small footprint lets you punch up the noise without the amp intruding on your space. At just around 8.5”x7”x2”, it’s easy to mount even in a small compartment or squeezed under a seat. Note that the control panel is on the top of the unit, so you may need to slide the unit out to adjust settings out if it’s mounted beneath a seat or overhang.
The R500X1D can be mounted either vertically or horizontally (mounting screws are included), giving you maximum flexibility. Note that neither the wiring nor the fuse are included in the box, so you will need to pick up a 50-amp fuse and wires separately. While some wire kits come with fuses included, do not install the included fuse unless it’s rated for 50 amps.
The quality of this amp can be seen in the care taken in its manufacture. Included in each box is an Amplifier verification certificate, a kind of amp ‘birth certificate’ showing the actual RMS wattage tested for that individual unit. Many users report that their certificate actually rates their unit at over 600 watts RMS at 2 ohms, so you may find that you have even more power in your control than the official rating of 500 watts at 2 ohms.
While this amplifier may be all you need if you’re only adding a subwoofer to your system, it can also function as part of a larger setup. If you would like to daisy-chain an additional amplifier in your system, a pair of RCA pass-through jacks in this amp make it easy to add components without running additional cables from the front of your vehicle. With the ability to power subwoofers at both 2 and 4ohms, this unit is compatible with a wide range of speakers.
Once installed, the amplifier’s LED light will shine blue when powered on, and will change to red if it shuts down to protect itself from overheating or a short circuit. Just about the only drawback to note for this powerful and compact amp is that this LED power indicator is very bright. If you’ll be mounting this unit in the open, you may need to shield the light at night.
If you’re looking for pure power to drive hard hitting bass notes, the Rockford Fosgate R500X1D has the best combination of stats. With its high-wattage power, clean signal, and ability to power a wide range of the best subwoofers on the market, the R500X1D comes out on top.
Number of channels: One
RMS: 500 watts at 2 ohms, 250 at 4 ohms
THD+N: 4-ohm: <1.0%, 2-ohm: <1.0%
Signal to Noise ratio: 80 dB
Dimensions: Approx. 2” x 7” x 8.5”
Marine rated: No
Amplifier class: D
#2. Kenwood KAC-M1804 Compact 4-channel Amplifier
If you’re searching for a powerful amp for truly small spaces, look no further than the Kenwood KAC-m1804. Designed to boost the power and clarity of your whole stereo system, this unit offers excellent technical specifications in a tiny package.
With four channels, this Class D amplifier can power both your front and back speakers from a single unit. The KAC-m1804 offers a respectable 45 watts RMS per channel at 4 ohms, and a max power output of 400 watts. The signal-to-noise ratio comes in at a superior 90dB (measured at rated power into 4Ohms at 14.4V) and the frequency response range is a wide-ranging 20Hz-20kHz.
Best of all, the circuit board has been specially coated to protect it from moisture. You can use this marine-rated unit in your convertible, boat, or ATV with confidence, knowing it will keep powering your tunes through rain, waves, salt, and mud. A rubberized harness boot helps protect the connections for both power and speakers.
If space is at a premium in your vehicle, the M1804 is a great choice even if the amp won’t be exposed to the elements. At a truly tiny 5.5”x1 5/16”x 3 9/16”, it’s a perfect fit for motorcycles, ATVs, or any vehicle with limited space for accessories. And at just over 1.6lbs, it won’t add a lot of weight to your rig, either.
The KAC-m1804 does come with mounting hardware, but again, wires are not included. A 15-amp fuse does come in the box, so you’ll just need to pick up the wires when installing this unit.
This unit includes protection circuitry shielding it from short circuits, DC offset, and overheating. While there are no LED indicators, the amp will automatically shut itself down for any of these situations, protecting both itself and your speakers.
For those who want instant sound without the need to mess with extra buttons, this amp can be installed to take advantage of its Signal-Sensing Turn-On feature. When connected by splicing the head unit’s speaker wires to the input wires, the amp will turn itself on automatically when it detects a signal on the input.
The KAC-m1804 is a straightforward little powerhouse, with no extra settings for you to tweak or LED status lights. This unit does not include built-in controls or crossovers. If you’ll be using a small set of speakers with your amp, you may want to use the crossovers in your head unit, and you may wish to use bass blockers on the speaker outputs.
Once you have the system wired up to take advantage of your speakers’ capabilities, the lack of controls on the unit itself means that you can tuck it away wherever it will fit best, without worrying about the need to access it to tweak settings or make constant adjustments.
The KAC-M1804 is not bridgeable so it’s suitable for 4-speaker setups only, and you’ll want to consider a different unit if you need to power fewer than four speakers. Also, note that it cannot be operated at impedances less than 4 ohms, so check your speakers to ensure compatibility.
If you’re upgrading the stereo for an open vehicle of any type, the Kenwood KAC-m1804 is the best pick. This amp can provide the power you need for open-air listening over all four speakers, while still delivering crisp sound. Even if you’re upgrading an enclosed vehicle, the rugged design and super compact form factor of the KAC-m1804 makes it an excellent choice for driving your four-channel setup.
Number of channels: Four
RMS rating: 45 watts RMS x 4 at 4 ohms
THD+N: ≤1% at rated RMS power
Signal to Noise ratio: 90dB at Rated Power into 4ohms at 14.4V
Dimensions: 5.5”x1 5/16”x 3 9/16”
Marine rated: Yes
Amplifier class: D
#3. Pioneer GMA3602 2-Channel Bridgeable Amplifier
View it on Amazon: $59.79*
*Price typically updated every 24 hours. Current price may be different.
For its flexibility, superior stats, and clean signal, the Pioneer GMA3602 earns our bronze pick.
With a continuous power output of 90 watts per channel at 2 ohms (180 watts if bridged to 1 channel at 4 ohms) and a maximum power output of 400 watts, you’ll have enough juice for a very respectable boost to your system’s sound. While the power isn’t quite as high as our gold pick, this unit focuses on crispness and clarity of sound while still delivering a solid power boost. It features an excellent signal-to-noise ratio of 95 dB at rated power and a frequency response range of 10 Hz to 70 kHz.
This two-channel amp is bridgeable, and so can be used to power either a pair of speakers or a single subwoofer. A switch allows you to toggle the low pass filter on and off, so you can adjust for your chosen setup. The crossover point is fixed at 80 Hz, with a slope of -12 dB/octave.
Like our Silver pick, the GMA3602 features a speaker line input turn-on sensor, to automatically power on the unit when an input signal is detected. This unit does not offer a bass boost, but it does have an adjustable gain control (300mV-6.5V line level, 3V-26V speaker level) to accommodate the signal from whatever radio you choose.
The GMA3602 offers 3-way protection circuitry (overheating, overload, and speaker short protection) to protect itself and your speakers, but it also offers more than these normal operation guards. In addition to the regular gain control, Pioneer has developed a Gain Control Caution feature that will throttle the amplifier’s output if it’s in danger of damage, without shutting the amplifier down completely. This extra protection helps to prevent damage to both the amp and your speakers, protecting your investment from accidental or incorrect gain control adjustments without the frustration of a total shutdown.
Setup is easy, and an included speaker level input harness means you can connect this amp to your OEM radio without adapters. The amp is on the smaller side, running approximately 9.5”x2.5”x7”, making it easy to slip into tight spots. Controls are on the front of the unit, so it’s possible to position them in easy reach even if the amp is mounted beneath a seat. This unit has a single power-indicator LED, located at the back of the unit. Wires are not included, but a 25-amp fuse is already installed out of the box.
The GMA3602 is a Class AB amplifier, so it provides quality sound without the distortion of a Class B amplifier and without the inefficiency of the Class A design. While not quite as efficient as the two Class D amps above, this amp still provides reasonably efficient performance at a very affordable price.
Whether you’re looking to drive a clean signal for two speakers or boost power to a single sub, the flexible Pioneer GMA3602 is a great choice with a great price.
Number of channels: Two
RMS rating: 60 watts RMS x2 channels at 4 ohms
THD+N: ≤1% at rated RMS power
Signal to Noise ratio: 95 dB
Dimensions: Approx. 9.5”x2.5”x7”
Marine rated: No
Amplifier class: AB
#4. BOSS AUDIO R1100M Riot 1100-Watt Monoblock Amplifier
If you want to get the most out of your subwoofer without breaking the bank, the Boss Audio R1100M amplifier will give you more boom for the buck.
The R1100M is a single-channel amplifier with a peak power rating of 1100 watts at 2 ohms, and RMS of 825 watts. The rating may be a bit optimistic compared to real-life performance however, and if you’re looking for truly huge noise this unit may seem a bit underpowered. But if you are just looking to provide power and a clean signal to your new subwoofer for a reasonable price, the RM1100M is a fantastic choice.
This unit also has a surprising number of controls for its affordable price point. Subwoofer level control lets you boost or drop the sub level when connected to the subwoofer pre-amp output. A variable low pass filter control lets you set what frequencies will be sent to the subwoofer, from 35 Hz to 160 Hz. And both a variable gain control and a variable bass boost let you fine-tune the sound for your system.
The R1100M has a thermal protection unit to shut down automatically if the unit gets too hot, and speaker short protection to power down if an electrical short is detected. The unit has separate LED power and protection indicators, so you can tell at a glance what’s happening. Both indicators and all controls are found on the front of the unit, so they’re easy to view and access even if mounted beneath a seat or in a tight space.
A wired remote subwoofer control is also included in the box. This lets you easily control the subwoofer from your dash at any time. Note that the remote only works when the amp is in ‘low pass’ mode, however. If the unit is switched out of that mode, the remote won’t have any effect on the amp.
For mounting, you’ll need to find just a little extra space for this unit. At approximately 9.125″ x 10.44″ x 2.25″, it’s a bit larger than other units, but still slim enough to squeeze underneath a seat or in other tight spaces. If you mount this unit so you can view the top, you’ll be able to see the BOSS logo glowing with a cool blue backlight.
With its striking looks, cutting edge performance safeguards, and fantastic value, the BOSS AUDIO R1100M provides power without a painful price. If you’re looking to add a sub to your system and need a high-performing unit that you can afford, the R1100M definitely delivers.
Number of channels: One
RMS rating: 413 Watts x 1 at 4 ohms
THD+N: 0.01 %
Signal to Noise ratio: 102 dB
Dimensions: Approx. 9.125″ x 10.44″ x 2.25″
Marine rated: No
Amplifier class: AB
Clarity of sound and overall power
The lingo used to describe an amplifier’s performance can seem a bit confusing when you first begin comparing units. While there are a lot of stats to sort through, the major considerations are the amp’s Total Harmonic Distortion + Noise (THD +N), Signal to Noise Ratio (SNR), and RMS rating.
Total Harmonic Distortion +Noise: THD +N measures how much the amplifier impacts the final sound. The higher the number, the more distortion will likely be present in the music. The lower the number, the more the sound produced will match the original recording. Bear in mind that lower THD +N numbers are better.
Signal to Noise Ratio: SNR captures how much extra background noise is sent by the amplifier. In the same way that you might notice the refrigerator humming when standing in a quiet room, but overlook the sound when a loud party is going on, every amplifier produces a small amount of noise that will still be there no matter what volume your music is set to. The signal to noise ratio is the difference (measured in decibels) between this noise floor and the music. Since you want the noise floor as low as possible, this difference should be as large as possible. Therefore, a higher number is better here.
RMS rating: Amplifier power is measured in watts, and the RMS rating represents the amount of power the amp is capable of producing continuously. Usually this is given per channel, but sometimes the figure represents the total power of the unit. Check to make sure the amp’s output power matches that needed by your speakers. Too little power will mean weak and distorted sound, while too much can damage your gear. Many amps indicate their peak power as well, and while this can be somewhat informative, this only represents the power that can be delivered over a short period. It’s not as useful when determining an amp’s true capabilities, especially when comparing different units to each other. Check the RMS rating first, and use that as your baseline when comparing different amplifiers.
Number of channels
How many channels does your setup need? The number of channels an amp can power is equal to the number of speakers – so a one-channel (aka mono) amp is often used for adding a single subwoofer, two-channel amps can power two speakers, four-channel amps can power four, etc.
Some units can be bridged, meaning that multiple channels can be combined into one for a greater power boost to a single speaker. Be aware that not all amplifiers support this, so be sure to check that the number of channels matches the number of speakers you’ll be powering.
If you’ll be powering multiple subwoofers or if you prefer music with a strong ‘front stage’ and no rear speakers, a two-channel amp such as the Pioneer GMA3602 is perfect. If you’re looking to drive four speakers, the Kenwood KAC-M1804 will have you covered. For a single sub, the Rockford Fosgate R500X1D, the Pioneer GMA3602 (bridged), or the affordable BOSS AUDIO R1100M will all provide the power you need.
Type of vehicle and stereo
If you’re looking to add an amp to your convertible, ATV, boat, or motorcycle, the Kenwood KAC-M1804 is definitely the way to go. Its marine rating means it can stand up to the water and mud better than other units, and its extremely compact size lets you install it even in the smallest of two-wheelers.
For a regular car or truck, consider the size of your vehicle. If you’ll be installing your amp in a small car, you could get away with a less powerful unit. In fact, you may even find that more powerful units are too much for the space. If you have a larger interior space, however, consider choosing a unit with a bit more power.
If your vehicle is a compact, sports car, or standard size, any of the excellent amps above will overcome road noise and add clarity to your music. Larger vehicles may want to choose one of the units providing 50 watts per channel or more. And, of course, if you want more volume you will want to look for additional power regardless of the size of your interior space. A difference of 5-10 watts doesn’t impact the final volume very much, but jumping to the more powerful units can provide a noticeable change.
When adding a sub, more power is usually desirable. For a vehicle with its factory stereo, anything over 50 watts RMS will run the sub adequately. If you’ve installed an aftermarket receiver and want to make the most of your sub, you definitely should consider the power offered by the Rockford Fosgate R500X1D.
Remember that you need to match the impedance of your sub when choosing a sub amp. If the impedance falls too low, the amp will overheat and shut down. Bridging two channels together impacts the impedance, so it’s worth double-checking to make sure you’ll have the right numbers once everything is hooked up together.
For subs connected to a factory stereo, an amp with speaker-level inputs is your best choice since it can get its signal from the factory speaker wires.
No matter what vehicle you’ll be installing in or what stereo you’ll be using, be sure check the specifications of your chosen speaker(s) to ensure that the amp provides the power they need. Again, under-powered speakers will sound weak, while excess power or improper impedance can ‘blow out’ your speakers. Protect your investment by triple-checking first.
Class AB amps are the most popular on the market today. They’re efficient without breaking the bank, with conversion efficiencies reaching 50 to 60%. Most of all, Class AB amps provide good performance without either the inefficiency of a Class A design or the distortion that often comes with a Class B system.
Class D amplifiers are even more efficient, often achieving 90% or greater efficiency even in real world performance. They are lightweight amps that produce little heat, so they can offer more power without turning into a miniature oven. This efficiency means that Class D amps can get away with a much smaller heat sink than that that found in AB amps. Class D amplifiers are, however, generally more expensive than AB units. They are also a little more prone to producing variable sound quality depending on the speaker load at the time.
Conclusion (Wrapping it up)
Whether you want hard-hitting bass, crisp sound from your speakers, or just want to round out your music with a separate subwoofer, choosing the right amplifier to power your speakers is critical. Think about how much power you need, how many speakers you’ll be driving, what sort of vehicle you’re working with, and the tradeoffs of power vs. cost for your particular setup. With your new amp installed, you’ll be able to crank your tunes and enjoy the best possible sound in your vehicle.