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What Is Gain On An Amp? Detailed Explanation

Asking many car audio enthusiasts what does gain do on an amplifier – or even just asking what does gain mean on an amp – is a little like asking people whose picture is on a $10 bill.

Nobody knows. Or very few, anyway.

We handle $10 bills on a daily basis, and yet most us are hard-pressed to say whose picture is on them. Similarly, audiophiles and bassheads use gain all the time, yet many would be hard-pressed to tell you clearly and correctly what gain on on amp is, and what does it do.

Granted, you needn’t be able to define “gain” in order to use it – you just know you turn that knob and something magic happens to your sound; usually something to do with distortion.

That’s perfectly alright, but if you’re new to car audio – more specifically, new to amplifiers – it might help to know what gain is, how to properly set it, and how it’s related to volume, as the two are closely related.

Why Do We Use Amps?

Before diving into what gain is and what does it do on an amplifier, let’s briefly mention the main reason why people use amplifiers.

Aftermarket car receivers have around 20 watts RMS maximum output power per channel, whilst standard factory car stereos usually have no more than 10 watts, in spite of what the car dealers advertise, which is usually not enough power to overcome road noise without sounding shrill. This is why we use amplifiers – to increase the power going to the speakers from the head unit.

It goes without saying that if you want your music to be loud, amplifiers are definitely part of the picture. There’s no way around it. A car amplifier will breathe life into your music, bringing out all of its excitement and detail.

A car amplifier (often loosely called an “amp”) is an electronic device that turns the low voltage signals from your receiver (about 0.5-2V on average for the most part) into a signal with enough gain to be used to power a pair of speakers or subs. Ok great to know, but what is the “gain” knob on my amplifier?

What Is Gain On An Amplifier?

Simply put, an amp’s gain refers to the input sensitivity adjustment necessary to match an amplifier’s input to the receiver’s output.

A properly adjusted gain prevents an amp from “clipping,” and reduces background noise and distortion sounds like speaker crackling, flapping, crunching, or hissing that interferes with the distinct sound of a musical instrument.

If you turn the amp’s gain up while listening to your music, the volume will increase; and likewise if you turn it down, the volume will decrease. This doesn’t mean by any means that your gain knob is a volume control knob. Got it? Confusing, right?

Well, as we’ve mentioned above the purpose of the gain control is to level match the head unit’s output voltage (around 0.5V) to the gain structure of the amplifier (how much it amplifies a signal), so that the signal is not over driven which would lead to clipping and distortion, or equipment damage.

To make it easier for you to grasp amp’s “Gain”, think of it like this: say you have two speakers, each of which is paired to a volume knob that goes from 0 to 10. One of these speakers outputs a signal at 2.5V, whilst the other outputs that same signal but at a whopping 10V. And say an amplifier is used to amplify both of those voltages by the same percentage.

If you turn the volume up to 5 (halfway) on both of these speakers, will the loudness of the music be the same for both? Of course not! The 10V speaker will definitely sound much louder compared to the 2.5V speaker. Conversely, if you turn both speakers to a volume level of 10, which is the maximum volume. The 2.5V speaker will sound quite loud, but the 10V speaker will explode or blow out or at the very least make the amplifier go into protection mode.

This is where the gain comes in. Using the gain, your speaker’s maximum volume will make the amplifier loud but not to the point of damaging your equipment.

In this case, if the amp’s gain is properly set, The 2.5V speaker will play loud and the 10V speaker will play even louder but won’t cause any problems whatsoever. That said, as a general rule of thumb, always set the gain to a point where your equipment gets loud at about 3/4th of your total volume swing (ex: 0-10).

What Does Gain Do On An Amplifier?

It must be noted that a car audio system can have its dynamic range vastly improved by simply adjusting system gains. The dynamic range on a car audio system refers to the ratio of the loudest to softest sounds reproduced without significant distortion. It’s expressed in decibels (dB). An amp’s gain primary purpose is to match the output voltage of the headunit to the input circuit of the amplifier.

If you still can’t get your head around amp’s gain, here’s a great example to make it easier for you to grasp the concept.

Imagine the gain control on your amp being the throttle adjustment on a carburetor, and your headunit’s volume knob being a gas pedal. Further, let’s assume your car comes with an engine that delivers a whopping 500 horsepower (HP). So, if the carburetor adjustment on your engine is increased, the engine will “idle” high and it will take minimal gas pedal travel to get the engine up to its full potential. Whereas, if the carburetor adjustment is decreased, the engine will “idle” low and it will take maximum gas pedal travel to get the engine up to its 500 HP potential.

That said, where the carburetor is “set” doesn’t by any means affect how much horsepower the engine can generate, just the effort required to push the engine to its full potential. Therefore, adjusting the throttle so your car engine idles at the proper RPM will – in effect – optimize the “dynamic range” of your gas pedal. Similarly, by properly adjusting your amp’s gain, your car audio system’s dynamic range will greatly improve.

How to Set Your Car Amp’s Gain for the Best Sound

So, you’ve just bought a new car amplifier, installed it, and now you’re wondering what’s next? Find the gain knob, crank it to its maximum setting and party! Otherwise you’re just under powering your gear, right?

Well, that’s completely wrong. Here’s the thing: setting your gains incorrectly doesn’t only hurt your sound quality, and lead to distortion, but it might damage your gear as well. A great car audio system requires proper tuning and gain controls are a big part of that.

In an amplified car system, you need to set your amplifier’s gain correctly in order to enjoy your music’s full range of dynamics and frequency response — hearing all the notes clearly, whether loud or soft.

It can take a little time and effort to get the gain tuning right, but the rewards of a well-tuned system are overwhelmingly cool and acoustically satisfying.

Setting your amp’s gain for the best sound remains relatively the same no matter the type of your amp. In this example, we’ll list the steps required to set the gains on a 4-channel amplifier used to drive two sets of speakers (front and rear speakers). So, without any further ado, this is how We’d tune it up:

1- Set the volume to zero on your car stereo

Turn the volume on your car stereo all the way down. It’s also highly recommended to set your receiver’s tone or EQ controls, its balance, and its fade to their middle, off, or flat positions.

If you have a subwoofer in your system, you’ll want to turn its amp gain all the way down as well.

2- Turn the gain on your amplifier all the way down

Before turning on your system, make sure you turn the gain on your amplifier all the way down, the high- and low-pass filters are off, and that any bass and treble boosts are also off.

By turning down the gain, you’re telling your amp to stop amplifying the signal coming in from the headunit.

3- Power up your stereo and play your test music (CD or a radio station)

Next, power up your headunit, and play your test music – preferably something you’re very familiar with and know what it’s supposed to sound like. And since the volume is set to zero, you will not be able to hear anything yet.

You will not be able to hear anything yet, since your volume is set to zero.

4- Set the receiver’s fade control all the way to the front speakers

Since we’re working on a 4 channel amplifier, we’ll start off by setting the receiver’s fade control all the way to the front speakers.

4.1- Turn the stereo up to 2/3 the max volume

With your amp’s gain controls all the way down, turn the receiver’s volume up to 2/3 the max volume, or until the music sounds distorted. (If you don’t hear any music at all, try turning the amp’s front gain control up a notch until you do.) If distortion starts rising, turn down the receiver’s volume until it goes away and the music sounds clean.

We use 2/3 the max volume because at this level you avoid overworking the headunit. If you overwork the latter you could end up sending distorted sounds to your amplifier.

Luckily for you, most modern headunit make it easy for you to tell when you are at 2/3 volume, but if you can’t tell when you’re at this volume level, try turning the volume all the way up (counting the number of turns) and then turn it back 1/3 of the way. For example, if you turn the volume knob 10 times to get to max volume, you would turn it back down 3 full turn to get to 2/3 volume.

4.2- Twist the gain dial on your amplifier

Now turn the front gain dial on your amplifier until the music distorts, then turn it back down until the distortion is gone and music sounds clean again.

4.3- Adjust your volume to a normal level

Turn the receiver volume down. Now that your amp’s front gain is set, you can go back to the driver’s seat and enjoy the music. But before that you need to redo the last 3 steps in order to set the gain for the rear channels.

5- Set the receiver’s fade control all the way to the rear speakers

To set the gain for the rear amp channels, we’ll start off by setting the receiver’s fade control all the way to the rear speakers.

5.1- Turn the stereo up to 2/3 the max volume

Again, turn the headunit’s volume up to ¾ full and turn up the rear gain control of your amp until distortion becomes audible, then turn it down so the music plays clean again.

5.2- Turn the receiver volume down

Congratulation, your amp and and receiver are perfectly gain-matched. You’ve properly set the gain exactly where the amp and receiver were both at their maximum clean output levels.

6- If you have no subwoofer in your system

If you have no subwoofer in your system, restore your receiver’s original tone, balance, and fade settings now. Next, engage the high-pass filter on the front channels of your 4-channel amp, and tune it to eliminate some of the low notes coming from the front speakers in order to level up your soundstage and create an accurate stereo imaging, making the music sound like a band is playing in front of you, live in your car.

7- If you do have a subwoofer in your system

If you do have a subwoofer in your system, you’ll want to adjust the receiver’s fade control to the front speakers only and turn up the volume until the music is relatively loud. Next, engage the high-pass filter of the amplifier’s front channels and adjust it so the bass notes disappear. Do the same thing to the rear speakers and after that return your receiver’s fade control to its original position.

Next, keep turning the the gain of your subwoofer amplifier slowly until the bass sounds balanced and smoothly blended with the music you’re playing. At this stage, your sub amp’s low-pass filter should already be tuned to reproduce only the low notes.

8- Adjust the sub amp’s low-pass filter

The last thing you’d want to do is to listen carefully to how the music sounds. Sometimes, after setting the gain on an amplifier, the highs and lows seem balanced but the bass sounds like it’s coming from the rear. In that case, you’ll need adjust the crossover point (also known as “de-localizing” your subwoofer).

To delocalize your subwoofer, you need to pay close attention to the “crossover area” – that small chunk of music played by both your speakers and your subwoofer. And, try to get rid of any roughness by fine-tuning the filters.

For instance, if high frequency notes, namely the vocals sound tinny, you can adjust the high-pass filters on your amp to include more low notes. Conversely, if they tend to sound a little boomy, consider raising the high-pass filters up.

Alex Brown

Hey There, my name is Alex Brown, I'm an LA-based sound engineer with over 10 years experience installing, troubleshooting, and repairing commercial, automotive, and household sound equipment. I've installed highly competitive car audio systems, and everything from navigation systems to full car stereo systems, remote starters, alarms and beyond. I enjoy creating solutions and simplifying everyday needs. I also love helping people get great sounding gear, thereby, saving the world from bad sound one customer at a time.

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