Best 4 Channel Amps for Getting Your Groove On

If you want to up your game and boost the sound quality in your car, you should invest in a quality outboard amplifier.

Nowadays, car amps come in a huge range of shapes, sizes, and power outputs. They can have anywhere from one to six channels, though four-channel amplifiers are the most common since most cars are equipped with 4 speakers.

On the other hand, there are also different classes of amplifiers, such as class A, B, AB hybrid, and D. These refer to the bias current and voltage requirements in the amplification stage. 

Lately, the super-compact class FD amplifiers have been gaining more and more followers. Theoretically, class A amplifiers offer the best performance at the expense of efficiency and size, whereas class FD models offer unparalleled efficiency and versatility.

The Best 4 Channel Amps for Your Car

Read on for my favorite 4 channel amps and tips on how to pick a car or boat amplifier.

Along with power and sound quality, size is also an important feature for a car amp. This is especially true for compact cars where space is scarce. The Alpine MRV-F300 is a class D amplifier with four channels, smart design, and quality construction. The lightweight and great ratio of price to sound quality make the F300 one of the best in its price range.

The Alpine MRV-F300 is a compact amplifier that measures only 7-7/8” (W) x 6.5” (D) x 2-3/16” (H). Its weight of around 4lbs makes it among the lightest 50Wx4 amplifiers. The black brushed stainless steel housing shows the company logo and a blue power indicator.

The back panel features speaker-level or high-level inputs for all four channels, low-level line inputs, and crossover controls. The controls are split into channels 1 and 2 (front speakers) and channels 3 and 4 (rear speakers). They are the same except there’s also a bass boost on/off switch for the rear speakers.

The F300 gives the best results with speakers that are rated up to 150W power handling. The power outputs are 50W (RMS) x4 at 4ohm or 75W (RMS) x4 at 2ohm. You can bridge two of the channels to get 150W. The peak power of this neat little amp is a quite respectable 640W. At the rated frequency response of 20Hz-20kHz and 4ohm impedance, the signal to noise ratio is over 98dB.

  • Excellent build quality
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    Very efficient
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    Compact and light
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    Elegant Design
  • Might be a bit underpowered

When shopping for a car amplifier, it is important to pick the right amplifier bias, as the different classes come with different perks and quirks. The Rockford Fosgate R300X4 is a class A/B amplifier that is more efficient than class A amplifiers and produces less distortion than class B amps.

The Rockford R300X4 Prime is a world-class example of class A/B amps. It comes in a pretty compact package. It rocks classic styling with a prominent Rockford Fosgate logo on top.

The back panel contains the connectors, while the top side has the controls. The back panel is equipped with GND, REM, and B+ connectors, and a quartet of both rear and front speaker-level connectors. The back panel also contains rear and front low-level inputs (standard RCA connectors) and high-level input connectors. On the top panel, you’ll find the back and rear speaker controls, as well as the 2/4 channel mode selector.

Sound-wise, the R300X4 offers plenty of power and a crisp tone at any sound level. It is rated at 50W x4 at 4ohm or 75W x4 at 2ohm, and the four channels can be bridged to 150W x2. At a frequency response of 20-20,000Hz, the rated total harmonic distortion is less than 1%. The total peak power is 600W and the total RMS power is 300W.

  • Class A/B bias
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    2 and 4-channel modes
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    0/6/12dB frequency punch
  • Higher distortion than class A amps

Class AB amplifiers are a good choice for car owners who would like to get the best of class A models (specs and sound quality) and class B models (higher efficiency). The ZRX616.4 Zeus by Hifonics is an affordable four-channel amplifier sporting the hybrid AB topology. This is a great solution for those who want a lot of raw power at a reasonable price.

The ZRX616.4 Zeus is a medium-sized amplifier packed in a modern metal case. The top of the amp is adorned with an illuminated Hifonics logo and laser-etched Zeus series inscription, model name, and power designation. The overall size of this amp is 12.6” (L) x 2.4” (H) x 10” (W).

Main features include low-level RCA outputs and inputs, PWM MOSFET power supply, Hifonics’ own surface mount transistor design. Safety features include overload, thermal, and short circuit protections. The ZRX616.4 Zeus can be run in 4-channel and 2-channel modes and has no provision for remote control.

This amp is rated at 150W x4 at 2ohm or 75W x4 at 4ohm. Alternatively, you can bridge two channels to get 300W at 4ohms. The frequency response ranges between 10 and 45,000Hz, while the peak power is 600W. The variable hi-pass filter can be set between 60 and 1,200Hz and the low-pass filter 30 and 250Hz.

  • 2 and 4-channel modes
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    Variable hi and low-pass filters
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    Variable bass boost
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    Variable subsonic boost
  • Heats up when played at super high gain for a long time

In situations where even class D amplifiers are too big, there are the ultra-compact FD models. Due to their super-small size, these amps usually provide a bit less power than straight-up class D models, but they compensate for in size. The Pioneer GM-D1004 is an affordable FD amplifier with 4 channels, 400 Watts of maximum power output, and minute size.

The Pioneer GM-D1004 comes in a stealthy black housing with a discrete company logo and model name inscriptions on top. The amp measures 7-1/8” (W) x 2-1/2” (D) x 1-1/2” (H). The housing is made of brushed metal, giving this amp a modern vibe.

The main features include the compact design, a wide variety of installation options, and the ability to bridge channels. Similar to some of its bigger siblings, the GM-D1004 also features high and low-pass crossovers (both fixed at 80Hz), bass boost, MOSFET output selection, as well as high and low-pass slopes (both at -12dB/octave).

This amp is rated at 45W x4 into 2ohm. Also, you can bridge two channels for 90W x2 at 4ohm. The peak power of this little amp is 400W total. At a frequency response range of 10 to 40,000Hz, the total harmonic distortion is less than 0.05% (at 1kHz). This little amp delivers a sharp, well-defined tone even at high gain settings.

  • Super-small size
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    Built-in high and low-pass filters
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    Bass boost
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    Works in 2 and 4-channel modes
  • Not suitable for power-hungry speakers

Class D amps owe much of their success to the fantastic efficiency when compared to class A, B, and AB models. Also, class D switching amps offer sufficient power for the vast majority of setups, as well as a great deal of versatility. The Kenwood KAC-M3004 is a compact class D amp with a total peak power of 600 Watts, modern design, and all the standard connectivity options expected in this class. It is a good option for all but the most powerful setups.

The KAC-M3004 can be installed pretty much anywhere and easily concealed under the seat or behind the dashboard. Its overall dimensions are 7.5” (L) x 4” (W) x 1.75” (H). The top panel sports a large Kenwood logo, triangular LED power indicator, model name, and maximum power inscriptions.

In the terminal section, this bad boy’s equipped with MOLEX connectors (speaker output), RCA connectors (line in), and screw type terminal block (ground & battery). The audio section has built-in high and low-pass filters for both A and B sections (50 to 200Hz).

This little amplifier is rated at 50W x4 at 4ohm or 75W x4 at 2ohm. In bridged mode, it delivers 150W x2 into 4ohm loads. In the tone quality area, the M3004 scores pretty high, with very low distortion at all volume levels.

  • Excellent connectivity
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    High and low-pass filters
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    Excellent sound quality
  • May not appeal to those who prefer a warmer sound

Packing a lot of power into an affordable amplifier usually means that sound quality has to suffer substantially. However, every so often there comes a model that is powerful, affordable, and performs well in a wide variety of settings. The Planet Audio AC800.4 Anarchy is a four-channel class AB amplifier with a max power of 800W and excellent sound quality.

All things considered, the AC800.4 Anarchy is pretty compact for a class AB amp. The overall dimensions are 10” (W) x 10” (L) x 2/4” (H). The housing design doesn’t bring anything revolutionary to the table, sporting the company logo, model name, max power inscription, and power indicator at the top.

Some of the main features include a variable low pass filter (35-160Hz) and a fixed high pass filter (80Hz). The variable bass boost can be 0 to 18dB, while the A-weighted S/N ratio is 102dB. The AC800.4 Anarchy also features low and high-level inputs, MOSFET transistors, and overheat and short circuit protection.

This amp is rated at 150W x4 at 2ohm and 75W x4 at 4ohm. Bridged, it delivers 300W x2 at 4ohm. The sound quality at low and medium gain levels is more than commendable, with only the slightest brightness at high gain levels. Also, you should watch out for the heat.

  • Variable low-pass filter
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    MOSFET transistors
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    Variable bass boost
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    Switchable input sensitivity
  • Can get a little hot at high gain

Sometimes, instead of a replacement, all that a car audio system needs is a little power boost. That’s where the Alpine KTP-445U comes in. This compact class D power pack is there to help underpowered head units get that extra oomph.

The KTP-445U’s “U” designation stands for “universal”, meaning that it can be paired with any brand and model of head units out there. The KTP-445A version is, however, meant to be paired only with Alpine’s own systems. The 445U can work in two and four-channel modes, similar to many other class D amplifiers.

This super-compact amp can easily fit inside or behind the glove compartment, as well as behind the dash. The highlights include independent and adjustable high and low-pass filters for the front and rear, configurable inputs, and super-low THD.

Considering its size, the 445U is relatively powerful at 45W x4 or 90W x2 at 4ohm. The sensitivity of the RCA inputs ranges from 0.2V to 4V (you need to supply 4V to get full power), while the speaker level inputs go from 0.5V to 10V.

  • Compact and light
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    Configurable inputs
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    Works in 2 and 4-channel modes
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    Adjustable high and low-pass filters
  • The bass could be a tad tighter

Class AB amps are the most popular among the car owners who want a full-range audio setup. This is mostly due to affordable prices and the best of class A and class B biases. The MTX Audio Thunder 75.4 is one of several class AB amps in the Thunder series.

MTX’s Thunder series has been around for over 20 years, which speaks volumes about its quality. The Thunder 75.4 is the smallest Thunder in current production. It comes in an elegant housing, with the company logo and the power indicator featured on top. The overall dimensions are 6-5/16” (D) x 12-5/8” (W) x 2-1/4” (H).

This amp has a surface mount design, which gives it greater vibration resistance even when driving on rocky or uneven terrain. Similar to most 4-channel car amplifiers, it has variable crossovers. The front channel high-pass filter can be set anywhere from 10 to 200Hz at a fixed slope of 12dB/octave. The rear channel low and high-pass filters range from 50 to 750Hz at the same 12dB/octave slope.

The Thunder 75.5 is rated at 75W x4 into 4ohm or 100W x4 into 2ohm. You can bridge any two channels for 200W x2 at 4ohm. The THD is 0.05% at the rated RMS power, while the S/N ratio is 78dB. This is a definitive recommendation for those who want a clean and thunderous tone at a reasonable price.

  • Very versatile
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    Variable low and high-pass filters
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    Excellent THD rating
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    Compact for a class AB amp
  • Works best with MTX subwoofers

Power and affordability don’t count for much if the amp can’t deliver quality sound in a wide variety of settings. Sure, it might be able to play loud without breaking the bank, but you might get a lot of distortion and heat at high gain. The infinity REF-704A delivers on all three fronts as a powerful and fairly affordable four-channel amp that sounds incredible at the same time.

Design-wise, this amp is a bit of a gamble, standing out from the prevalent all-black color scheme enforced by other manufacturers. The Reference 704A is a standard-sized class AB amp with bridgeable channels and a multitude of connectivity options.

The total peak power is 1,000W, or 400W RMS. The S/N ratio is 86dB or higher at the reference 1W output at 4ohm. It is rated at 100W x4 at 2ohm or 70W x4 at 4ohm, as well as 200W x2 into 3ohm when bridged. All three options have a THD+N rating of lower than 1%. This model also boasts excellent tone clarity and has adjustable crossovers and bass boost.

  • Excellent clarity at high volume levels
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    Bridgeable
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    Variable crossovers
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    Variable bass boost
  • Mounting hardware could be better

Classes

The first thing you should consider when buying an amplifier for your ride is the amplifier class or bias. Currently, there are four main classes used in consumer electronics – A, B, AB, and D. However, the super-compact FD class is becoming more and more acceptable. Let’s take a quick look at the key characteristics of each class.

Class A

Class A amplifiers have to be large because they require massive heatsinks as a result of their inefficiency. The amplification stage and transistors are always “on”, meaning electrical current is always coursing through the components.

They offer very low distortion, high fidelity, and clean output. On the other hand, they generate a lot of heat, which requires massive heatsinks to dissipate.

Class B

Class B amps can switch off when there’s no signal, making them much more efficient than their class A brethren. This is great for car owners, especially if you want to show off your car stereo without turning on the engine.

The main strengths of class B amps include higher efficiency, lower heat production (thanks to the ability to switch off), and smaller size than class A amps. However, they also have lower fidelity and are more vulnerable to distortion issues.

Class AB

Essentially, class AB models are hybrids that combine class A and B biasing. They are on the larger side as well, smack in the middle of their parent classes. The key feature is that they always have current flowing through their circuits, but they can decrease the amount when there’s no signal.

On one hand, this makes them more efficient than full class A models and less prone to distortion than the B-class models. This combination of features makes class AB amplifiers most popular among car owners.

Class D

Class D models are significantly smaller, perfect for installation inside the glove box or behind the dashboard. Also, the small class D amplifiers tend to have less power but there are also class D amplifiers that are more powerful than class AB amps. Class D amps utilize ultra-efficient switching output stages and power supply. On the downside, they have the biggest problems with distortion. There are tricks that amplifier designers can use to lower or avoid the distortion in real-world applications.

Power

This is probably the most heavily contested of all issues when it comes to picking the right car amplifier. Is more power always better? The short answer is not necessarily. You can drive your speakers to higher volume but not necessarily better at the characteristics that audiophiles care about, such as bass tightness, airiness of the high frequencies, dynamic contrast, etc.

You’ll also want to make sure to stay under your speakers’ rated power handling. A set of speakers that are rated at 100W power handling each means that they can safely handle up to 100W (per channel from your amplifier) without burning the voicecoil or experiencing other driver malfunctions.

Number of Channels

Modern car amplifiers can have anywhere between one and six channels. They are all intended for different setups and have their own ups and downs. The choice here should be based on your needs.

If you want to power just the subwoofer in the back, then you’ll probably be best off with a mono (single-channel) amp. Also, you can add a mono amp to the rig where a four-channel amp is connected to a quartet of full-range speakers (usually two in the front and two in the back) and you need a separate power source for the sub.

Some people prefer two sets of two-channel car amplifiers, one amplifier for the two front speakers and one for the back. Also, you can bridge a two-channel amp for powering a single subwoofer.

Four-channel amps offer sufficient versatility for most car systems and are currently the most popular option. Besides using a four-channel amp to power front and rear speakers, you can also use it to power a pair of high-end components speakers that come with separate tweeters and woofers.

You’d have to add a two-channel amp for the rear speakers, or another four-channel amp if you also have component speakers in the back.

Final Thoughts

All music enthusiasts can attest that having high quality sound systems in your car makes driving 100% more enjoyable. However, most cars, even some expensive ones, come with shabby stock setups.

That’s where aftermarket speakers and amplifiers come in. When shopping for an amplifier, make sure to get one with enough number of channels and power for your speakers. Also, make sure to match the amp and speaker impedance, as well as pick the right amplifier class for your setup.

Gavin Whitner
    Gavin Whitner
     

    A guitar player, songwriter, composer, and also the lead editor of MusicOomph, Gavin is one of the four musician friends behind this site. Outside of music, he's an avid sports fan and hardly misses anything from football (soccer) to F1.

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