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You are here: Home / RESOURCE LIBRARY / How Does a Car Audio Amplifier Work – The Class AB Output Stage

How Does a Car Audio Amplifier Work – The Class AB Output Stage

Class AB Amplifier

As we continue our look at how car audio amplifiers work, let’s discuss how the classic Class AB amplifier output stage works and explain why it’s still the benchmark for high-end audio systems.

How Does a Class AB Output Stage Work?

We recently looked at the power supply, the input stage and how Class D output stages work to allow your car audio amplifier to reproduce music. If you go way back to the beginning of high-power car audio amplifiers, you’ll find the Class AB design.

A Class A amplifier uses a single output transistor to add current to the output signal to drive your speaker. When no music is playing, the output device is halfway on and gets very hot. Think of the output as a resistor. If you put two small resistors in series across your power supply, a lot of current would flow through the load. A Class A amp works the same way.

Class AB Amplifier

Class B amplifiers use a pair of output devices and split the voltage delivery duties between each device. When no music is playing, both devices are turned off and no voltage is produced at the speaker. The problem with Class B amps, as the guys at BestCarAudio.com discussed in their Class AB Amplifier Distortion article, is that there a dead zone that occurs as the voltage across one of the diodes in the transistor is biased on. The result of not compensating for this roughly 0.7-volt bias requirement is called crossover distortion.

Class AB Amplifier

Class AB Amplifier Output Stage

The Class AB amplifier is a Class B amplifier with a small bias voltage applied to the output devices to get them ready to play music. Different amplifier designs use different amounts of biasing to balance between efficiency and silky-smooth operation.

Class AB Amplifier

Amazing High-Frequency Extension

Class AB AmplifierOne thing that high-end Class AB amplifiers are known for is their extended high-frequency performance. Many top-end amps can play beyond 80 kHz with ruler-flat, low-distortion performance. If you are building an audio system that is compatible with high-resolution audio, this extended high-frequency response is crucial.

Low Output Impedance

Class AB AmplifierAs compared to Class D amplifiers that use inductors and capacitors on their outputs, Class AB amplifiers, except in configurations with variable voltage power supplies (often called Class G or Class H designs), don’t need these devices. The result is less variance in output voltage relative to load impedance and more predictable response.

Image: Voce.jpg

Efficiency versus Performance

Class AB AmplifierAt low to medium power levels, Class AB amps are not as efficient as a Class D amplifiers because the output devices act like resistive voltage dividers across the power supply rail voltages. As such, AB amps need larger heatsinks to ensure their reliable operation. As you approach the upper limits of an AB amplifier’s output capabilities, their efficiency becomes similar to that of a Class D amp. The output devices are close to being all the way on or off.

Experience the Ultimate in Car Audio Amplification

If you are determined to assemble the best possible audio system for your vehicle, visit your local specialist mobile enhancement retailer and ask about using Class AB amplifiers. Yes, you’ll need to find room for them in your vehicle, but the amazing clarity and detail they provide is well worth the effort.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

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Filed Under: ARTICLES, Car Audio, RESOURCE LIBRARY

About BestCarAudio.com

BestCarAudio.com is a showcase for the very best mobile electronics retailers in the world and a place to educate and inform interested consumers about existing and emerging technologies.

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A love of sound only few can know…

Bryan has been a friend of mine for most of my life. He and I have ventured several stereo systems our entire lives. We both share a love of sound only few can know. We have worked together, installed together, learned lessons, experienced life as a whole. In my life travels, I have still never met a better man, installer, and person. I am proud to know Bryan as a friend and business owner.

Adam Francis

5.0
2016-09-27T02:12:51-05:00

Adam Francis

Bryan has been a friend of mine for most of my life. He and I have ventured several stereo systems our entire lives. We both share a love of sound only few can know. We have worked together, installed together, learned lessons, experienced life as a whole. In my life travels, I have still never met a better man, installer, and person. I am proud to know Bryan as a friend and business owner.
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Thank you for all the hard work yall are doing

I've been accessories manager at a Toyota Dealership going on 3 yrs now, and the majority of my remote starts have been done by Bryan over the years. Whenever I have questions Bryan always makes himself available to help, whenever there is an issue, he would never give me the run-around he would simply tell me to bring it by and he would fix it whether minor or major. He is extremely thorough with his installations which is the most important factor when installing aftermarket electronics in Toyota vehicles as Toyotas are very sensitive in their electrical configurations. He has won several awards for his work and his actions back up everyone.

Christopher Clark

5.0
2016-09-27T02:18:41-05:00

Christopher Clark

I've been accessories manager at a Toyota Dealership going on 3 yrs now, and the majority of my remote starts have been done by Bryan over the years. Whenever I have questions Bryan always makes himself available to help, whenever there is an issue, he would never give me the run-around he would simply tell me to bring it by and he would fix it whether minor or major. He is extremely thorough with his installations which is the most important factor when installing aftermarket electronics in Toyota vehicles as Toyotas are very sensitive in their electrical configurations. He has won several awards for his work and his actions back up everyone.
https://www.806autoworks.com/testimonials/thank-you-for-all-the-hard-work-yall-are-doing/

Very Professional

Bryan has worked on a few vehicles for me, and his work has always been very professional. Everything he has done for me looks like it came straight from the factory that way, and the service he has provided has been fantastic. I would recommend anyone needing any type of audio work to give him a call you won't be disappointed!

Mathew Miera

5.0
2016-09-27T00:49:55-05:00

Mathew Miera

Bryan has worked on a few vehicles for me, and his work has always been very professional. Everything he has done for me looks like it came straight from the factory that way, and the service he has provided has been fantastic. I would recommend anyone needing any type of audio work to give him a call you won't be disappointed!
https://www.806autoworks.com/testimonials/best-experience-ever/
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