A Brief Guide to Audio Amplifier Classes
If you’ve been shopping around for amplifiers you may have spotted Class A, B, A/B, D, G or H within the specifications. So what the heck do these classes actually mean? They aren’t any indication of performance or quality, but rather a guide to the amplifier’s circuitry and how it processes the sound input. Although these differentiations are complex we’ve put together a very brief guide to help clarify the different types and help you choose between the different Ecko, Quad and Audiolab amps on offer.
The basic job of an amplifier is to increase the size of the waveform from its source without adding or enabling distortion. In a class A amplifier, both the positive and negative output stages of the audio signal are constantly processed at full power. While that means very little distortion, class A amplifiers are also the least efficient design of all and they do tend to heat up from wasted energy.
In a nutshell: Low distortion with low efficiency (approx. 20%), this type of amplifier is also very popular and popular for radio transmitters and guitar amplifiers because of its very low distortion characteristics.
In a class B amplifier, the input waveform is split in two and each half conducted through one of two devices that are each active when the other is not, leading to the “push-pull” term you might have heard mentioned. These two halves of the signal are united once more at the output to create the final waveform. While more efficient than class A amplifiers, there can be some crossover distortion due to the delay between devices.
In a nutshell: Much more efficient than class A with some potential for crossover distortion, therefore commonly chosen for battery-operated situations.
A class A/B amplifier brings together the best features of A and B, by essentially conducting slightly more than half of the input signal to overlap output and reduce the impact of any crossover distortion. It makes sense, then, that these systems will be slightly less efficient – yet produce a smoother result – than their Class B counterparts. This makes them a popular choice for many household amplifiers, such as the excellent Audiolab 8300A Integrated Amplifier.
In a nutshell: Class A/B keeps things relatively efficient with low distortion and a smoother crossover for good all-round sound.
Contrary to popular belief, class D does not stand for ‘digital’. Unlike the previous classes with one or more output devices that are constantly on, a class D rapidly switches output devices off and on to produce a pulse width square wave. This stream of pulses rapidly alternates between low and high frequency at a proportional rate to the original input signal, then passes through a low-pass filter to produce a smooth and amplified analogue signal. The result is up to 90% efficiency, explaining its popularity for a number of applications.
In a nutshell: Typically lightweight and more efficient than traditional AB, therefore a popular choice for car systems, sub woofers and personal audio devices.
Class G and H
Class G and H amplifiers work much in the same way as an A/B amplifier does. The difference is that while an A/B design has a single voltage rail, G and H designs feature multiple supply rails at different voltages to enable a wider range of input voltage. Class G features multiple voltage rails, while class H features rails with infinitely variable voltage. What results is A/B sound quality with G and H efficiency.
In a nutshell: Heat and energy savings mean that class G and H are generally used for huge, professional power amps.
It’s impossible to delve into the endless detail of the different amplifier classes here, so if you’re still not sure what amplifier is right for you get in touch or find one of our stockists to speak with a specialist. We’d be happy to take you through the different options throughout the Quad, Ecko and Audiolab power amplifier range.