If the phrase ‘100 Watt Class A/B Amplifier’ has you scratching your head, you’re not alone. For the beginning or novice guitar player there are a lot of concepts that will be totally foreign when you are just starting out. One of the main ones is the specifications of the guitar amplifier. There are many different aspects to this and for the purposes of this article I will concentrate on guitar amp class designations. Most of this revolves around how the amp handles electrical current. You don’t really have to know this to buy your first practice amp, but the knowledge will make you a more well-rounded musician.

A class
In a class A amplifier, current flows inside the amplifier at all times, even when it is idle (no music is playing). What this means is that the response of the amplifier is very fast because the current can be transferred to the speakers immediately. There’s also less crossover distortion, which is a type of distortion that occurs when switching between devices that drive a load, like transistors. The bottom line is that Class A guitar amps sound better, are more responsive, and are more expensive to build as a result. An example of a Class A device would include the Orange AD30HTC 30 Watt Dual Channel Amplifier.

Class B
Class B amps differ from Class A amps in that no current flows when the output devices are inactive. What this means is that they actually have to power up from a dead state when a signal is presented. Class B designs tend to have slower slew rate (maximum rate of change of a signal at any point in a circuit) and higher crossover distortion, but are more affordable than Class A as a result.

Class AB
A combination of Class A and B, basically these amps have different parts of their output operating in either class A or B. You’ll find that the vast majority of guitar amps are in this class because it’s simply a more efficient way to operate. Pure Class A amps need large power supplies and tend to get very hot. This is the tradeoff for the ability to instantly send a current flow to the speakers upon receiving an input signal. An example of a Class A/B guitar amp is a Mesa Boogie Dual Rectifier.

Class D
In this case, the output transistors work as switches. These amplifiers have higher efficiency and as a result require less robust power supplies and smaller heat sinks. These are important advantages in portable and battery-powered equipment.

H-class
Class H devices are very efficient and allow for a lightweight amplifier design. However, there is a drawback as distortion is more apparent at lower volumes.