An amplifier is a necessary piece to any long-lasting car audio system. Potent, high fidelity sound is supported by this device by replicating the frequency from your music to match the voltage needed by the speakers. 

Simply put, an amplifier increases the power signal it’s being fed from the head unit. 

When sound is being played, it boosts the amplitude (size) of its signal headed towards the speakers from the stereo. The highs stay crisp, the lows are bumpin’ and the melodies flow. 

Amplifiers are engineered to convert these electrical signals by a few different methods called “classes.” The most common amplifier classes are A, B, A/B and D.

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Class A

This type of amplifier uses 100 percent of the signal from a simple circuit design. 

Planet Audio AC1500.1M

The output signal from your stereo is replicated exactly by the amp with little to no distortion or clipping. Since the amp is running the true signal, the unit is running the entire time – giving it the potential to run hot. This is why Class A Amplifiers have high sound fidelity but low efficiency. Not the best option for car audio because it lacks the ability to give good power to multiple speakers. However, they’re a great addition to someone who is happy with their system but can hear that it needs a boost. 

Class B

Most Class B Amplifiers come with two outputs which conduct signals alternately between resisters – lightening the workload between positive and negative voltage to create a unified output. 

Each transistor is on about half the time, taking half of each wave cycle to amplify. This makes them roughly fifty percent more effective than Class A Amplifiers, but it also has the potential to create “crossover distortion” as the circuits push-n-pull between one another. 

Class A/B

The most common amplifier in car audio – Class A/B is the child of Class A and B. With the double transistor circuit design out of a single input to a single output, Class A/B still functions alternatively between the two transistors. So each part is still “off” for a period of time while the other amplifies its part of the sound wave.

The dead zone that’s created by Class B amps from the switch between two transistors is reduced with each part kept on for more than half the time. It produces stable, clear music when the volume is kept at an average volume. However, if the music is turned up, it increases the volts and amperage which can create distortion. 

Sound distortion is less of an issue than with Class B – as much as 60 percent less. Installing a Class A/B amplifier is a solid choice to accommodate price point and respectable sound.

Class D

The most popular option in amplifiers are Class D. At at least 90 percent efficiency, these amplifiers don’t fall prey to frequent heat sinks so less power is drawn from your car’s charging system and overall smaller internal pieces.

Onboard circuits in the amp create high frequency pulses of DC  current. The width of this current is modified by the input signal. Through pulse width modulation (PWM), the amp can create a bigger singal with a wider pulse for a high power output. 


Before the final sound output, the signal is run through a transistor that’s either on or off, then through a low-pass filter to smooth out the PWM carrying frequency. This removes move interference and distortion before the music reaches the speakers.

Class D’s downfall is that some sound filtering is needed, perhaps beyond what’s built in.

Other Amplifier Classes

Amplifiers, alongside the rest of technology, are being developed into new classes like BD and GH. The latter is an improvement on AB and D designs – delivering the efficiency of a Class D with the quality of an AB. This is done without transistors switching on and off but through different rail voltages that swap back and forth as the signal naturally fluctuates. Class GH amps are great at reducing wasted output power, but costly to make.

Class BD have an efficiency rating like their D counterparts, around 80 percent. Filtering issues are simplified with a combination of on and off, Class B, signal relay with the distortion crossover of a Class D.

As time goes by you will see more amplifier classes appear that offer improvements over the general class A/B and class D designs. Sonic Electronix offers Class AB, AD, BD, D, H and FD.