Class D and Class AB amplifiers: which should you choose?
Audible Pakistan · Updated
When you compare amplifiers, you will see letters such as “Class AB” and “Class D” in the specifications. They describe how the amplifier works inside, and they affect size, heat, power use and sometimes price. For most installed sound systems, both can do a good job. This guide explains the difference in plain words so you can pick the one that suits your project.
What the class means
An amplifier makes a small signal bigger. The “class” is the method it uses to do this.
Class AB amplifiers use output parts that stay slightly active all the time, passing the signal smoothly from one half of the wave to the other. This method has been used for decades, is well understood, and is simple. The trade-off is that some of the electrical power is turned into heat, so Class AB amplifiers are usually bigger and heavier and often need cooling.
Class D amplifiers work by switching their output parts on and off very quickly, many thousands of times a second, and then smoothing the result back into the audio signal. Because the parts are either fully on or fully off, very little power is wasted as heat. Class D amplifiers are typically lighter, smaller and run cooler.
Side by side
| Class AB | Class D | |
|---|---|---|
| How it works | Output parts stay slightly active | Output parts switch on and off quickly |
| Heat | More heat, often with a fan | Much less heat |
| Size and weight | Larger and heavier | Smaller and lighter |
| Power use | Higher for the same output | Lower for the same output |
| Familiarity | Long-established design | Now common in installed sound |
| Typical fit | Where size and heat are not a concern | Where space, heat or power use matter |
Does one sound better?
In the early days, Class D amplifiers had a reputation for harsher sound. Modern designs are much better, and for speech and background music in a school, shop, mosque or office, you are unlikely to hear a difference that matters. What does matter is that the amplifier has enough power, suitable inputs and reliable protection. A well-built amplifier of either class will serve well.
When to choose Class D
- Limited space. A compact amplifier fits easily on a desk or in a small rack.
- Hot rooms. Less heat means less stress in an enclosed cabinet or a warm utility room.
- Power-conscious sites. An efficient amplifier draws less from the mains.
- Battery backup. Efficiency helps when running from a battery during a power cut.
When to choose Class AB
- You prefer a traditional design with a long track record.
- Space and heat are not a problem, such as a well-ventilated rack.
- You need many zones and inputs in one unit, which some Class AB models offer.
Audible amplifiers and their class
The SPA-60/150W is a compact Class D amplifier. It gives 150W, three speaker channels, three microphone inputs, a USB and SD player, and a 12V DC input for battery backup. It can be mounted on a desk or in a rack.
The LPA-150EC is a Class AB amplifier with 280W of rated output, five independent zones, three microphone inputs, two AUX inputs and a built-in fan for cooling. It also has echo and delay controls.
The USB-80A is a Class AB amplifier of 80W with two independent zones. It offers USB, Bluetooth 5, FM and AUX sources, with priority on microphone 1 for announcements.
See the full range, including the A-2120H, A-2240H, PA-260 and PA-380, on the PA amplifiers page.
Power cuts and battery backup
In places where mains power can drop out, a sound system that keeps running can be valuable for announcements and safety messages. Because Class D amplifiers draw less power for the same output, they suit this job well. The SPA-60/150W has a 12V DC input for battery backup, so it can keep working from a battery during a power cut. Ask us about the battery and charger you would need for your site, because the right size depends on how long you want the system to run.
More important than the class
Before you decide on class, check these things, because they affect your system more:
- Power. Add up the speakers’ power taps and choose an amplifier with 20 to 30 percent spare.
- Zones. Make sure there are enough for your building.
- Outputs. Check for the 100V, 70V or 4 to 16Ω output that your speakers need.
- Inputs. Count the microphone, AUX and music inputs you will use.
- Protection. Look for protection against short circuit, overload and overheating.
A quick way to decide
If you are choosing for a small to medium room and want a compact, cool-running unit with battery backup, the Class D SPA-60/150W is a good place to start. If you need five zones and more power in a ventilated rack, the Class AB LPA-150EC fits. For a small office or shop that wants Bluetooth and two zones, the USB-80A is a simple choice. If you are unsure, tell us about your project and we will suggest one.
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