What Should I Know About Amplifier Classes as a Guitarist?

In the world of guitar playing, understanding the nuances of your instrument is only half of the story. Equally crucial is comprehending the technology that brings your music to the ears of your audience – your amplifier. As a guitarist, getting to know different amplifier classes might seem like delving too much into technicalities, but in reality, it’s an aspect that can significantly impact your sound. From the warm, organic tones of Class A and Class AB amplifiers, to the powerful and efficient sound of Class D amps, your choice of amplifier class can shape your musical identity.

Signal Cycle

in an amplifier, an electrical signal (i. e. the sound from your guitar) starts at a certain voltage, increases to a peak, decreases to a minimum, and then returns to the starting voltage. This whole journey is a signal cycle. The amplifier’s job is to take this signal cycle and make it larger (or “amplify” it), so that it’s strong enough to drive a speaker and produce sound. Different classes of amplifiers do this in slightly different ways, which can affect the sound and efficiency of the amplifier.

Amplifier Classes: Overview

There are several different classes of amplifiers that are distinguished by the method in which they amplify signals. Here are the most common classes you should know about:

  1. Class A: These amplifiers conduct throughout the entire 360 degrees of each signal cycle. They have the highest linearity, which means they have the lowest distortion. This makes them excellent for high-fidelity audio, but they are inefficient and produce a lot of heat. This is because the transistor is always on, even if there is no input signal, causing high power consumption.
  2. Class B: Class B amplifiers only conduct for 180 degrees of each signal cycle. They are much more efficient than Class A amps, but they produce more distortion due to a phenomenon known as crossover distortion. They’re rarely used in practice due to this.
  3. Class AB: Class AB amplifiers are a compromise between Class A and Class B, providing good efficiency and low distortion. They conduct for more than 180 degrees but less than 360 degrees. Class AB amps are commonly used in guitar amplifiers due to their balance between performance and efficiency.
  4. Class D: These are “switching” amplifiers that achieve even higher efficiency by rapidly switching the output devices between the supply rails (the on and off states). This is the only active state, so there is little to no power drawn when the output devices are off. The audio signal is generated by modulating the duty cycle of the switches. Class D amps are excellent for bass amplification due to their high power and low weight.
  5. Class G and Class H: These are more complex designs that aim to improve efficiency even further by changing the supply voltage or current to the output stage dynamically. They’re often found in high-power systems.

In terms of tonal qualities and sound, Class A and Class AB are the most used and sought after by guitarists. They often produce a warm and smooth tone. Class D, on the other hand, can be great for bass or for situations where efficiency and power are paramount, although some guitarists find them to sound too “cold” or “clinical.”


Remember that the class of amplifier is just one factor in the overall sound of a guitar amplifier. The design of the preamp, the type and configuration of the speakers, the design of the cabinet, and other factors can also have a big impact on the sound.

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