What Does A Car Amplifier Do? understanding how it works

If you’ve ever dabbled with car audio systems, chances are you’ve heard of some of the basic parts: stereo, speakers, bass box, amps. You may have heard about car amplifiers – but do you really know what they do?

In this article, I hope to give you a better understanding of what exactly a car amplifier does, why it’s important and how to choose the right one for you.

When I bought my first car stereo – I bought a Blaupunt ACR 3231 headunit – but because i didn’t know what i was doing It turned out to be a bit of a let down. I wired the unit up and turned it on expecting the speakers to blow the windows out of my car – but instead it was just sort of similar to the old standard radio.

I then checked the user manual to see if there was someway to make it louder – It told me there were 2 channels each with 6.5 watts RMS of power. After asking someone where i bought the unit, i found out my new radio had very little power – major downer!. This is when I began to learn all i could about car sound systems.

What Does A Car Amplifier Do?

In short, an amplifier in an audio system does exactly what it sounds like it does: it takes an audio signal and boosts it, literally amplifying the sound. But there’s a little more to it than that, and that’s why it’s important to have the know-how to make an educated choice for your system.

Every basic car sound system has an amplifier built-in so it provides sound. But often these amps aren’t sufficient for powering added or upgraded speakers. These standard amplifiers are usually mounted inside the radio, which means they are small and not very powerful.

This small amp within your radio only provides a basic sound that gets the job done, it is not an amp that brings your sound truly to life. Trying to force that amp in your radio to handle a newer, bigger, better speakers wouldn’t result in the clarity, quality, or volume your new speakers are capable of.

A separate amplifier, however, solves these problems. This allows you to increase your music’s overall quality, lowers the distortion from spikes in volume, and allows you to add things like a subwoofer that your built-in amp wouldn’t be able to handle alone.

How Does A Car Amplifier Work?

So, we know an amp takes an audio signal and boosts it. But the mechanisms behind that process are worth learning about so you know what to look for.

Power Supply

You might be wondering how, exactly, it takes the signal and amplifies it when the amp still only uses 12 volts like the car stereo. That’s because inside the amp the voltage is increased to provide more power for your speakers.

Inside an amplifier, the voltage is increased using special circuitry called a switched mode power supply to provide the extra volts the speakers need to boost the sound signal from your stereo and deliver it to your speakers with more power.

The magic this internal power supply provides is that it allows you to boost your 12V power supply to around 28V. This helps the amp send a higher powered audio signal to your speakers. This works because of two things: resistance load (impedance) and a switched-mode power supply (SMPS).

Resistance Load

Speaker resistance load, known as impedance– which is measured in ohms- defines how much resistance a speaker has. The smaller the speaker the higher the resistance and therefore the higher the ohms rating it will have. For example a tweeter will typically be rated 8ohms, 6″ x 9″ speakers are around 4 ohms and a 10″ subwoofer will typically be around 2 ohms.

Large low ohm powerful speakers like subwoofers require a lot more current than small tweeters. This puts a higher load on the amplifier, meaning it will draw on more amps from its power supply. This is why it is very important that you use the correct rated power cable for your amp – a thin power cable can overheat and burn.

Switched-Mode Power Supply

In order to get a larger amount of power from a 12V power source, amplifiers use what’s called a switched-mode power supply, or SMPS. This is the most important part of the amp.

What makes an SMPS special is its ability to efficiently increase electrical power.A SMPS works by rapidly switching the input voltage on and off. This sounds weird but it I will explain it more in depth in another article.

Im short -this means that an SMPS can create more power out of a 12V source than a standard or “linear” power supply would, this increases the performance of your amplifier.

Audio Input And Amplifier Output

The two other important parts of car amplifiers are the audio input stages – where the signal from the stereo is received and is processed (noise filtering and crossover circuits). This audio signal is then sent to the amplifier section where it is boosted before being sent to the speakers.

Audio Input Stages

The input stages take care of quite a few jobs for the amp. A lot of these seem like small or subtle tasks but they’re just as crucial. I’ll list these briefly:

  • Connecting the amp to stereos both with and without RCA inputs
  • Eliminating “alternator whine” or “ground loop noise” when you accelerate or decelerate
  • Crossovers, which prevent distortion and speaker damage
  • Gain levels to maximize sound clarity

Amplification Stages And Output Section

The amplification stages and output section of an amplifier hold the final steps between the original input audio signal and the new, amplified output signal. Car amps have large output transistors that are designed for higher current to account for the extra power you need. These transistors are fed by the SMPS and go on to transmit the larger, higher-power output signal to your speakers.

What Are Channels On An Amp?

Amplifiers come in a variety of options, the most common of which you’ll see are 2 channel and 4 channel amps. It’s important to know what this means when picking an amp so you get the right product for your project.

Channels are important because they are the paths your audio signal will take to create an output signal. In stereo, these channels dictate the sound that comes from the left and right speakers.

Some stereos also support forward and rear outputs, using the sound system to provide a fuller, surround-sound experience. Matching up the number of channels to your system’s particular needs is important to make sure you get the sound quality and diversity you’re looking for.

Bridging an amplifier

Bridging an amplifier is when you take the positive from one channel and the negative from another channel and connect them to a speaker. This essentially doubles the power (watts) output to the speaker. This can be good if your existing amp is being used to drive a new larger speaker – which means you don’t need to buy another amp, or if you are tight for space but need a more powerful, larger amp.

How Are Car Amplifiers Beneficial?

Now that we’ve taken a look at the nitty-gritty of how an amplifier works, you can clearly see how this piece of equipment will enhance your audio experience.

The multitude of things an amplifier takes care of is absolutely essential when you’re considering building, upgrading, or adding to your car’s audio system. Without a separate amplifier, you’d be working with the limitations of whichever one is already built-in, which is often less than ideal.

Without the power and versatility of a quality amplifier, there are many things that can go wrong when you feel like upgrading your sound system by only buying better speakers. Your system might suffer from distortion, you could damage your new speakers, or you might hear some unwanted noise such as the “alternator whine.”

By properly designing your sound system and including a separate amplifier, you’ll be able to get the most out of every piece of equipment you add to your system.

Typical Car Amp Connections And Controls

There are many connections and controls on a standard amplifier. Being familiar with them is essential both when choosing an amplifier and when installing it.

The good news is that most amps are set up essentially the same. Your power connectors will be on one end and your audio and gain controls will be on the other.

Power connections

You’ll want to use larger gauge copper wires for your power connections. These can typically be found in an amplifier’s wiring kit, or you can pick some up on your own if you got a used amp that didn’t come with one.

Audio connections

To connect your amp to the audio outputs and speakers, you’ll want to use RCA cables. The connectors for these should be on the end opposite of the power connections. These connections are for the speakers, which you’d use to bridge the amp if you so desired.

No RCA connections

The final set of inputs you’ll see on most amps are the speaker level inputs. A lot of pre-installed stereos don’t have RCA jacks, so you’ll need to use speaker level inputs, or “high level inputs.”

These connections will take the high voltage from speaker wiring and reduce it into a voltage your amp can actually use. If, for some reason, speaker level inputs are unavailable, you could use a speaker level adapter instead.

How Car Amps Are Installed

Making sure you have the appropriate gauge and type of wire for your connections is the most important part of amp installation. The original wiring of your car can’t handle the kind of power an amp needs or produces.

The wiring you need to install an amplifier can typically be found in an amplifier wiring kit. Your amp may come with one of these, or you might need to purchase one. Either way, it should provide you with the following:

  • A fused, large-gauge power wire (12V)
  • A negative connection to either the battery terminal or car body to ground it
  • A remote-start wire to turn the amp on or off with the stereo or your ignition
  • RCA and/or speaker level input cables
  • Speaker wiring and connectors

The basic steps for installing an amp are as follows:

  • Connect the fuse holder to the positive battery clamp, keeping it within roughly one foot of wire from the post.
  • Route the positive cable through the firewall and rubber seal. You can use a coat hanger to pull the wire through if need be.
  • Run the wire down the side of the interior on the battery side of your car.
  • Connect the remote lead to the remote-out wire or your car’s 12V switched wire.
  • Connect the RCA cables and jacks or the speaker level wires.
  • Mount your amp to your subwoofer box or another board mounted to your car.
  • Connect your subwoofer’s speaker wire to the amp, bridging as necessary.
  • Connect the ground wire securely to bare metal on your car’s body, using self-tapping screws and a drill if you can.

2 Channel Vs. 4 Channel Amps

There are a variety of amplifiers out there, some of which have a different number of channels. The most common you’ll see are 2 channel and 4 channel amps. Both of them serve different purposes, so it’s important to know which one will suit your needs.

A 2 channel amp is what most people have or will choose. This is because it suits basic needs quite well, taking care of powering one pair of speakers and providing you with good stereo sound.

A 4 channel amp, on the other hand, is great for when you want to also control front and rear sound, allowing power to go individually to all four speakers. Alternatively, a 4 channel amp can be bridged so that it powers speakers in stereo with a subwoofer, using two of the four channels for the sub.

You can also make use of a 4 channel amp in future upgrades, as you could always use it to power two more speakers, getting your hands on a separate amp for the subwoofer altogether.

Do I Need A Car Amplifier?

Well – this depends. If you want to upgrade the speakers in your car without using a car amp then this can work – but the speakers will most likely underperform by using the small amp built into your car stereo. You will not get the clarity, volume or power that added a separate amp will give you. You may be wasting your money by buying just the speakers on their own.

This is especially true if you’re planning on adding a subwoofer to your system. Bass waves need a lot of power, particularly if you want them to sound good, and your car’s built-in amp just won’t provide that kind of power for you.

If you do decide to upgrade your cars sound system a good amp is essential for any new sound system.

How Do I Choose A Car Speaker Amplifier?

When picking out an amplifier for your sound system, there’s a number of things you should take into consideration.

  1. Number of speakers and their location (number of channels – front and back and if you need a subwoofer or not).
  2. Type of speakers and their power requirement. Tweeters, 6″x9″ or subwoofers all require different amounts of power.

The power of your amplifier is the wattage it sends to your speakers. Since you’re using the amp to power the speakers you need to add up the power requirement of all the speakers and select the appropriate size of amp for them..

A great 4 channel amp is the Alpine MRV F-300. I have written an in depth review of it here.

RMS power rating

When choosing an amp you sould only pay attention to the RMS figure (Root Mean Square) quoted in the specification section. This is the measured amount of continuous power the amp produces when in operation. Your amplifier’s RMS should match the power handling of your speakers, which will be unique to your setup.

The best RMS to shoot for is between 75% and 150% of the power your speakers can handle. More is better here because, if the amp doesn’t match the RMS power of the speaker, you’re not going to get the most out of your speaker

Max power

The “max power” figure or “peak power” is the maximum power the amp or speaker can handle in a very short burst. It is a misleading figure and should not be used when designing your sound system.

Many poorer products will bum up the performance of their products using this figure “max power” rating. If the product does not list the RMS figure i would advise you not to buy it.


  • A car amp takes the small signal from your car stereo and boosts it which allows you to run larger more powerful speakers
  • A car amplifier will also “filter noise” and improve the quality of the sound to your speakers
  • Your standard car stereo does not have the power to run upgraded car speakers effectively.
  • Car amps have different numbers of channels or outputs which can be used in “bridged mode” to operate very large, powerful speakers such as subwoofers.

See the next article How to bridge a car amplifier


1 thought on “What Does A Car Amplifier Do? understanding how it works”

  1. The next time I read a blog, I hope that it doesnt disappoint me as much as this one. I mean, I know it was my choice to read, but I actually thought youd have something interesting to say. All I hear is a bunch of whining about something that you could fix if you werent too busy looking for attention.

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