In this guide, we’re going to cover just about everything you need to know when shopping for a car stereo amplifier. Among the more misunderstood aspects of the mobile audio hobbyist sector – a list dominated by products such as crossovers and graphic equalizers – is the amplifier, though even many novices in the hobby understand that, at its most basic, the device essentially amplifies sound.

Still, there are a plethora of elements that comprise the modern-day mobile amplifier that should be understood before you begin shopping for one (or multiple amps, depending on the type of system you’re planning). Below, you’re going to see the following covered as thoroughly as possible.

See our top picks in all price ranges, buying advice, brands and FAQ below.

Monoblock Car Amplifiers

Our Pick

Pioneer GM-D9701

RMS: 500 Watts at 4 Ohms;
800 Watts at 2 Ohms;
1200 Watts at 1 Ohm
Max: 2,400W
Class: D

The new extra-efficient Class D digital amps from Pioneer mark a dramatic improvement in power output capacity, yet are 50-percent smaller in footprint than the current GM Series Class AB amplifiers.

Case in point: Pioneer’s GM-D9701 mono amp, perfect for driving a subwoofer of your choice in that this beast puts out 2,400 watts of maximum power.

2-Channel Car Amplifiers

Our Pick

Rockford Fosgate P300X2

RMS: 100 watts RMS x 2 at 4 ohms (150 watts RMS x 2 at 2 ohms)
300 watts RMS x 1 bridged at 4 ohms (4-ohm stable in bridged mode)
Class: AB

The Rockford Fosgate P300X2 Punch car stereo amplifier offers 2-channel audio, with up to 150 Watts of power at 2 ohms per channel. Incorporating Rockford Fosgate’s proprietary C.L.E.A.N. technology for crystal clear audio quality, this is a great option for anyone looking to deliver huge power to their speakers or subwoofer.

The P300x2 delivers up to 150 Watts of power to each of its 2 channels, for a total of 300 Watts across the board. We found this more than sufficient to power either our speakers or subwoofer with an impressive level of performance.

While some users have reported a seemingly higher output than listed on the spec sheet, we found the amplifier to perform just as advertised. Not that we would have complained if that were the case!

An optional high-pass filter gives you the freedom to filter out unwanted low bass and improve speaker efficiency.

Also Great

Pioneer GM-D9701

RMS: 60 watts RMS x 2 at 4 ohms (95 watts RMS x 2 at 2 ohms)
190 watts RMS x 1 in bridged mode (4-ohm stable in bridged mode)
Class: AB

Pioneer takes pride in their ability to make quality car audio equipment, which explains the focus of their GM-A3702 amplified being on the sound itself, rather than the volume.

While this amp boasts a decent 500 watts max output, the marketing speak from Pioneer is keen to point out how clean the audio coming from this amp is.

The GM-A3702 has quite a small footprint, making it ideal for vehicles where space is at a premium. It also makes an excellent amp for creating portable components, such as an all-in-one amp/subwoofer combination that can be easily removed.

1-Ohm Stable Amplifiers

Our Pick

Skar Audio RP-1500.1D

RMS @1-Ohm Stable: 1500 W
Peak @1-Ohm Stable: 1900 W
Class: D

Conservatively rated at some 1,500 watts RMS power at a one (1)-ohm load but reaching beyond some 1,900 eye-watering watts at max power output, the Skar Audio RP-1500.1D is an ideal monoblock amp solution for demanding subwoofer installations.

The oversized four (4)-gauge power and ground terminals found on the amp allow for maximum current flow and, in turn, higher power output and more efficient operation.

4-Channel Car Amplifiers

Our Pick

Alpine MRV-F300

Max Power Output: N/A
RMS: 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)
Amp Class: D
Bridgeable: Yes

This 4-channel amp (see full review) is incredibly tiny for how clear it sounds and how powerful it is. It’s actually rated at about 95 watts RMS per channel at 2 ohms, which is some 20 watts higher than Alpine advertises it.

We found it ran fantastically cool in our tests, delivering amazing sound to everything we threw at it. It’s priced VERY competitively, too — it’s cheaper than a lot of 4 channel units we looked at that delivered far less power in bulkier packages.

Also Great

Alpine KTP-445A Power Pack

Max Power Output: N/A
RMS: 45 watts RMS x 4 at 2 to 4 ohms
Frequency Response: 20-20k Hz
Amp Class: D

Looking for a simple way to kick up the power of your Alpine in-dash receiver but aren’t interested in huge, current-sucking amps?

The company’s KTP-445A Power Pack increases your Alpine receiver’s power output to 45 watts RMS by four channels and comes fully equipped as a low-profile component that can be installed anywhere.

5-Channel Car Amplifiers

Our Pick

Pioneer GM-D9705

Max Power Output: 2,000W
RMS: 100W x 4 (Main channel), 600W x 1 (Subwoofer channel) at 2 Ohms,
75W x 4 (Main channel), 350W x 1 (Subwoofer channel) at 4 ohms,
200W x 2 (Main channel), 350W x 1 (Subwoofer channel) Bridged at 4 Ohms

Amp Class: D
Bridgeable: Yes

Pioneer’s five-channel amp pumps out impressive power in an all-in-one solution designed to deliver big sound without sacrificing space. Whether it’s a cramped sports coupe or pickup truck with limited interior “real estate,” the D9705 brings installation flexibility to any type of vehicle, given its trim dimensions – as explaind in Pioneer GM-D9705 review.

There’s even a dedicated subwoofer output that’s rated at some eye-watering 600 watts RMS – so you can run your full-range speakers and sub(s) together from one amp.

Bluetooth Car Amplifiers

Our Pick

Kenwood KAC-M1824BT

Max Power Output: 2,000W
RMS: 45 watts RMS x 4 at 2 to 4 ohms;
90 watts RMS x 2 bridged at 4 ohms (4-ohm stable in bridged mode)
Amp Class: D
Bridgeable: Yes

With a small footprint and all-business finish on its chassis, the Kenwood KAC-M1824BT is built for longevity and protection from the elements, boasting connectors – including RCA jacks – that are shielded from moisture and salt/dirt by plastic covers that can be removed.

Build quality is also of the premium kind, with parts that line up correctly, and, unlike other amplifiers, Kenwood has created a cool new design in that users don’t have to install a head unit in addition to installing an amp when there’s a need for clearer, more powerful sound.

What Do I Need To Know Before Buying Car Amplifier

Why You Should Get an External Car Amplifier

Have you ever experienced what we like to call “the road noise drowned-out effect”? That is, you’re tooling down the highway with your car’s windows and sunroof open, cranking your favorite tunes, but all you hear is the nasty, loud “wooshing” of other vehicles flying by or the annoying “thump-thump-thump” of your tires hitting the pavement beneath you.

And no matter how high you twist that volume knob on the radio, the Taylor Swift CD that’s supposed to bombard you with sweet vocals and deep bass just can’t overpower the ambient sounds of the noises outside.

That is just one of the scenarios that scream out for the addition of an amplifier (or two). In fact, if you were to ask most professional car audio installers what the number one priority of an amp should be in a mobile environment – beyond powering some current-hungry subwoofers so they move enough air – they will almost always tell you “overcoming road noise.”

Car amps indeed suffer from the “out of sight, out of mind” effect, especially since most folks who never change their factory systems aren’t even aware that amplifiers are already built into their radios; speakers need to be amplified by power in order to work, so at the very least, some kind of amp is in play.

When we talk about external “power amplifiers,” we are referring to those large (ish) silver and black boxes that are installed under front seats or in a trunk/hatch area.

While those vehicles that compete in soundoff competitions are loaded from back to front with a dozen (or sometimes more) amps to drive a ridiculous array of subwoofers for SPL (sound pressure level) purposes, that’s not what we’re focusing on in this article – so don’t be concerned that what we’re suggesting is going to cost a boatload of money.

Put simply, adding an external amp can help reduce distortion while overcoming the aforementioned road noise that can make listening to your favorite music a proverbial headache. Then, there’s the power needed to drive subwoofers, if you’re adding one to your system (a car stereo radio cannot power a sub alone), in addition to getting the most out of new speakers by giving them some clean power.

In summary, the reasons to consider a separate amplifier in your mobile audio system include:

  • Louder sound without distortion
  • Power to feed a subwoofer
  • Cleanest power to feed high-quality new speakers

The Budget Factor

Depending upon where you shop, car amps are offered in an almost dizzying array of price points; of course, as you would guess, the smaller amps normally cost a bit less than their larger, more power-breathing brethren.

Still, like most things in life, if you’re working with a shoestring budget for buying a car amp, some compromises are going to have to be made.

A major factor you need to be made aware of in this area is the oftentimes misleading power-to-performance specs of amps that seem too affordable to be true.

Here’s what we mean: For far too many years, a bunch of car amp manufacturers has sold their products with ridiculously high power ratings in the marketing materials, claiming their amp puts out, say, 1,000 watts of power for a budget price; what’s more, the amp in question boasted a small footprint (size) that went against the grain of the manufacturer’s claimed power output.

We’ll get into this further in the Power and Size sections, but for now, here’s what you need to know:

Stay away from advertising that proclaims “Get 1,000 Watts for Only $99!” or “This Amp Puts Out 500 Watts for Only $59!”

Set a budget for what you’d like to spend on an amp and stick to it, shopping for the best brands that put out realistic, honest specifications.

From our experience, look for names like Alpine, Rockford Fosgate, and Kenwood when shopping for a solid amp at a good price.

Types of Amps

Understanding Channels

In the world of amplification (and this applies to home audio environments, as well) there are “multi-channel,” “mono” and “two-channel” amps, each designed to do specific jobs depending on a system layout.

The reference to “channel” in the world of audio is sometimes confusing to novices putting a system together, whether that be a mobile audio system or a home theater setup, but essentially it just means “speaker” – so, for example, a “two-channel” amp powers two speakers, while a “multi-channel” model can power multiple speakers.

While they’re a bit less common, so-called “mono” amps have been designed to power one speaker alone – normally a subwoofer, in the case of car audio.

The most cost-effective method of driving a whole set of front and back car speakers is to buy a multi-channel amplifier, which, with just one chassis, will be able to power all of them effortlessly, depending on the model you choose.

If you are looking to power just a set of front door speakers, a two-channel (or “stereo”) amp is ideal; this is also a good choice if you’re powering two subwoofers in an enclosure.

Speaking of subwoofers, many mobile audio enthusiasts feel in order to achieve the highest sound pressure levels from subs, they should be driven by multiple mono amps or by an amp that can be “bridged” (more on this in another section); bear in mind, though, that these types of installs can get complex and will probably demand additional batteries and other accessories be added to the vehicle, being that extremely high-powered amplifier models draw eye-watering amounts of current.

Amp Classes

Audio amplifiers are also broken down amongst classes, depending on what they’ve been designed to do compared to others; out of all the different amp classes, there are only four that are commonly used in mobile audio environments, and one of those is a combination variant.

These include A, B, AB and D, with the differences between them being that class A amps are “always on,” class B amps are “switched” (they use their own internal circuitry that allows them to “switch off” their output transistors when there’s no audio signal to amplify), class AB amps are a kind of hybrid in that they always have current flowing through them yet use circuitry to reduce the amount of current when no signal is present, and class D amps representing the extremely efficient variant out of all of these, and the only “switched” amp class commonly used in-car audio.

While each of these has its pros and cons, what you primarily need to know about amp classes is that A/B models are best for full-range and most component speakers, while class D amps are better for driving subwoofers.

Power

This is one of the most controversial subjects in all of the audio, be it mobile, pro or home application types, because it’s so misunderstood – but we don’t blame the consumer for this, we blame the manufacturers, because many times their power output ratings splashed across the marketing materials for their products are totally misleading.

We can’t tell you how many folks we’ve spoken to who were shopping for car amps tell us, “But that amp claims to put out 6,000 watts per channel!” only to be sorely disappointed after they installed that amplifier and it produced nothing but distortion.

Watt ratings, as we mentioned, are notoriously misleading; so much is involved in matching amps with speakers, but at its very basic, this matching depends on the number of channels (speakers) you’re trying to drive, how loud you like to play music, whether or not you’re using a subwoofer and more.

Among a speaker’s published specifications are its RMS (or “continuous”) power rating, usually in a range (five to 60 watts RMS, for example), so for your particular speakers, pair them with an amp with a top RMS output per channel no higher than each speaker’s top RMS rating.

If you drive a compact coupe or hatchback, a sports car or small cab pickup, an amp offering 50 watts RMS per channel (or smaller) will probably be able to get your music loud enough to drown out road noise; look for speakers with a top RMS rating of at least 50 watts RMS to pair with this amp.

For larger vehicles and for those who crave more volume, stepping up to an amp putting out at least 75 watts RMS per channel is ideal; amps putting out 100 watts RMS or more per channel is useful for seriously loud systems.

Because bass is much more difficult to amplify compared to other elements of the sound spectrum, subwoofers need to be powered by hefty, high-current amps; for the majority of applications, a “mono” (or one-channel) amp will provide the juice needed to power a large sub. When talking power ratings, anywhere from 50 to 1,000 watts of power can be fed to subs, depending on their specifications and your bass tastes.

Bridging

The term “bridging” refers to the process of combining two (four) channels of an amplifier into one (two) channel(s) with twice the voltage. To make it a bit clearer, a two-channel amp can be “bridged” to one channel and a four-channel amp can be “bridged” into two channels.

Essentially, bridging channels increases the power output of an amp, but it also causes it to work harder and put out more heat. For more on the subject, see this video.

Amp Wiring Kits

Installing a car amplifier is already enough work without having to worry about where to find the right wire and installation accessories. Luckily, amp wiring kits make the job easier, coming packaged with everything you need to do a basic install.

Generally speaking, a quality amp wiring kit is comprised of:

  • RCA cables of good quality, ideally around 16-feet in length or longer
  • A good remote wire
  • A positive wire with good stranded conductors in about 18-foot lengths
  • Ground wire
  • Speaker wire (may be optional)
  • Crimp ring terminals for positive and negative power wires
  • Good quality fuse holder and fuse
  • Zip ties

Crossover

We covered the basics of crossovers in car audio in a different article, but when it comes to amplifiers, here’s what you need to know: aftermarket amps typically include built-in filters that essentially act as crossovers if you’re building a basic car audio system with component speakers.

The high-pass filter (more on this below) in this type of amp enables you to drive tweeters, and the low-pass filter enables you to drive woofers without any additional crossovers.

Bass Boost

This is a feature built into some amps that can boost low-frequency response in subwoofers they’re powering, and there are many systems that boast a remote version that can be controlled from the dashboard or steering wheel.

While nice to have, they really aren’t essential; odds are, you will be getting plenty of “slam” from that sub (or subs) without the need for a bass booster, and even if you aren’t, you can always turn up the bass control at the head unit or equalizer.

Low-Pass Filter/High-Pass Filter/Band-Pass Filter

As we touched on in the crossover section above, a high-pass filter restricts bass frequencies from mid- to high-range speakers.

A low-pass filter, conversely, only allows low-frequency bass signals to reach larger subwoofers.

Band-pass filters, meanwhile, are a bit more complex, in that they play frequencies between two points by utilizing both a high-pass and low-pass in the same filter “network.”

Car Amplifiers FAQ

How Do I Match a Subwoofer with an Amplifier?

You can either buy a self-powered sub (with an amp built-in) or a separate subwoofer enclosure that needs to be powered by an outboard amp; in the case of the latter, you need to match the RMS watts the amp puts out to the number of watts a sub can handle. You also need to consider impedance, a subject we’ll cover in another article.

What Gauge Wire Do I Need For Amp?

If you are buying wires for your new car stereo setup, one of the things you want is to get your wire gauges right.

How Do I Actually Add an Amp to my Car Audio System?

This is a somewhat complex procedure that really can’t be explained in detail in this one article; if you enter “car amp wiring diagrams” into Google’s search box, you will note an almost infinite amount of sites that go into the specifics about wiring.

How Do I Bridge a Car Amplifier?

Using the negative signal of one channel of an amp with the positive signal of the other channel effectively doubles what each channel alone could put out through a two-ohm load. For more info on bridging amps.

What Are the Best Places to Install an Amp?

Traditionally and depending on the amp’s size, you’ll want to install it either under one of the front seats or in the trunk/rear cabin of the vehicle; some installers like to drill the amp directly to the subwoofer enclosure for an “exotic” look.

What Are Some Common Amp Problems?

We have seen everything from overheating and shutting down to blown channels and even fried circuitry; in general, common problems attributed to amplifier installation include sound distortion, no sound at all and even sparking issues when an amp is touching bare metal in the vehicle and it hasn’t been grounded properly.

Keep an eye out for future articles in which we will get into some of the topics mentioned here in greater detail.

Vincent Talbot

Last update on 2020-11-07 / Affiliate links / Images from Amazon Product Advertising API