Understanding Amplifier Classes
Amplifiers can be an intimidating topic for the average guitar player to delve into. Which is actually kind of unfortunate considering that, other than to the guitar itself, there is not much else that impacts your tone more. One of the main issues for people with amps is just how much is going on electronically. With a guitar, all you really have to understand is how magnets and signal work. Amps introduce all kinds of electrical components and concepts that go right over the average person's head. One of these concepts that you likely have come across is the idea of amplifier classes. Whether it be from a manufacturer or in a forum, the terms A, AB and D get used often when referencing different brands and models. Why don’t we take a look at what these classes mean both technically and to you as a player? Let’s get you one step closer to better understanding amplifiers.
The best place to start when looking at amp classes is class A. In this method of amplification, the process is completely analog and done inside the context of tubes. Class A amps have the highest amount of clarity (more accurately called linearity) when it comes to the signal of your guitar. However, there are two major drawbacks to these amps. Firstly, they are very inefficient, getting as low as 15%. This efficiency is how much of the amplification process is actually going to the speakers. So, where does all that other power go? Heat. The other major issue you have to deal with in class A amplification is the heat dispersion. This means things like heat sinks must be added to the chassis interior. These elements all add up to a more expensive amp in the end.
Many will refer to Vox amps being the standard idea of a class A guitar amp. This is a very good general idea for what this amp class can be thought of. In fact, many attribute their class to being one of the parts that make up that signature sparkly tone. While this is really not all that true it does have some degree of merit according to other designers. Other than AC15s your likely going to be hard-pressed to find another class A amp under a grand. While nearly all companies have some class A amps, Vox is definitely the brand most associated with them.
Class AB amps are fairly comparable to that of the class A amps in the idea of them being mostly analog designs. Exceptions to this do exist however, the most notable being the Boss Katana. But most of the time AB amps are going to be full tube amps. The real pro of AB over A is the large jump in efficiency (up to 80%). This efficiency also means less heat and fewer components to handle the heat. However, don’t go thinking that this means all AB amps are going to be cheaper than A amps. No, there are actually quite a few factors that go into the price of an amp, but generally, this part of the amp is more affordable within the AB class.
Class AB amps make up the majority of tube amplifiers on the market. Pretty much any brand you can think of, Fender, Marshall, Orange, etc. all predominantly use class AB amps. Most manufacturers have found this class to be the perfect compromise between efficiency and single throughput.
While there are a lot of similarities between class A and class AB amps, class D amps are quite a bit different from either. Essentially when we say class D, as a guitar player your brain should go straight to solid-state. Yes, in D amps we are negating the tube technology that so many players have come to love. These D circuits are using digital pulses to try and match up with the analog waveforms that your typical tube amp would have. This process has a lot of involved factors having to deal with feedback and filtering. Unfortunately, because of these factors, designing a great class D amplifier is no easy task. If you look back to the ’80s in the early days of solid-state guitar amps, you could definitely hear these amps were not up to par with… anything really. Thankfully, in 2019, amp makers are sitting on decades of research and development on how to make great amps in this form.
Looking at some of the examples of class D amps, you realize that there are plenty of great tones to be pulled out of this type. Just look at the Fender Mustangs or any of the affordable offerings from Blackstar. Solid-state technology has come a long way.
Does it Matter?
Honestly, while all this (and all) information about gear and amps is good to understand, it kind of ends up being not that important to the end-user. Nearly every major amp maker today, including the three mentioned previously, have class A, AB, and D amps in their line. The truth of the matter is, regardless of what class you are talking about, whether or not the amp sounds good is in the hands of the designer. Even when talking about a classic sound from a beloved manufacture, the tone is not all that reliant on solely the amp class alone. But this fact should not be news to anyone who has been around the guitar long enough, the sound is impacted by a LOT of factors. So, while it is good for you to be aware of what these classes mean, also don’t let them be a major part of why you buy an amp. As with all the gear, the single most important factor in getting a great tone is your ears.