Amplifiers: What do all the controls do?

Amplifiers. They come in all shapes and sizes. Some have a variety of whizzes and bangs to play with on your quest for the perfect tone, others are fairly straight forward and opt to include a limited amount of features, instead relying on the tone from the speakers and electronics. So for beginner guitarists it can often be a confusing experience and full of terminology that isn’t familiar. In this article I’m going to put some of these features into a little bit of context for you by explaining what they are, what they do and how to get the best out of them!

Master Volume or Volume

You would assume that this one would be self-explanatory, however there are some exceptions where one could run into confusion. In a nutshell, the Master Volume controls the overall loudness of the amp. It sits at the end of all the other components in your chain and raises them all together thus not affecting the components individually. Sometimes you may have a Master Volume control and two Volume controls, which usually means that your amp has two channels (the ability to switch between two sounds, for example, clean vs distortion). In this instance the Master Volume controls the output of the overall amp and the other two Volume controls adjust the loudness of the individual channels, allowing you to have one channel a different volume than the other.
Gain (a.k.a Drive)

This a good opportunity to quash a common misconception. Gain is not the same as Volume!
It actually controls how hard you are driving your amp and alters the tone of the guitar. The more gain you apply, the more distorted and dirty the sound will be. This can sound like it is making the guitar louder, which is where the misunderstanding comes from, but it’s actually just sending more of the electrical signal through your amplifier, which drives a more powerful sound through the speaker causing the sound to distort. So you can crank your gain up high but keep your amp really quiet by keeping the Master Volume low.
Equaliser or EQ (Bass/Middle/Treble)
If you have owned a stereo in your time, you may have come across Equalisers before and when it comes to guitar amps there isn’t a whole lot of difference. The most common of Equalisers on a guitar amp is called a 3-band EQ and consists of Bass/Middle/Treble (sometimes Low/Mid/High). These controls alter the frequencies that are produced from the amp across the spectrum of your sound. The bass controls how many low and deep frequencies come through, the higher you have the bass control, the more bass your sound has and vice versa. The Treble control works in the same way but adjusts the higher pitched frequencies, again the higher you have the Treble control the more high frequencies you’ll hear in your tone. And finally… the Middle control (as you’ve probably guessed by now) affects everything in between. On some bigger and more complicated amps you may even have a 5-band EQ, but this just means you have more points across the frequency spectrum to manipulate allowing you to be more detailed in your Equalisation choices. The best thing to do is experiment with the Equaliser, push it to its extremes so you can hear the differences and work back to find the tone that best suits your playing.
Presence
Not every amplifier has a presence control, so it’s function isn’t common knowledge. In simple terms, it’s an extension of the Equaliser and adds upper-mid to high frequencies to your tone. The reason for doing so is that it boosts the guitar through the mix of other instruments, in theory making your sound more present to the audience, hence the name. This can be a really useful tool if you’re lucky enough to have one on your amp and can really make the difference in having a guitar tone that stands out. If you don’t have one don’t fear, use your existing EQ to boost your mid and high frequency a little more than usual, this can produce a similar effect.

Reverb
Reverb (or reverberation) is an added ambience created by the environment of where the sound was created and occurs due to lots of small reflections bouncing around said environment in fast succession. In guitar amps you will usually have one of two types of reverbs: an analog or a digital one. Analog reverbs usually have a physical spring or metal plates built into the amplifier that conduct the electrical signal sent from the guitar and react by vibrating, simulating the reverb effect. Digital reverb is an emulation of this effect through computer simulation. Both methods can create some really interesting sounds and many guitarists usually swear by one or the other. Although I think we can all agree that any kind of reverb can really improve your guitar tone.
Delay
Delay is found mainly on modern amps. It’s a digital effect that consists of a storage medium that records the signal that goes into the amp and plays it back repeatedly, creating the effect of a decaying echo. You can manipulate the speed of the repetitions using the tempo control which is often accompanied with a ‘tap’ button which allows you to set the speed of the delay to the music you’re playing. Other parameters that you are able to alter are the depth (sometimes displayed as Dry/Wet: like 1 to 10 where dry means no effect at all and wet being saturated) which alters how much of the effect is on your tone. Feedback is how long the delay lasts for and how many repetitions you can hear. You can create some really unique sounds using delays and can create some fantastic detail into your riffs.
Ultimately, I’ve always found the best way to understand how each of these components work is to sit and play with them. Experiment with different settings and listen in detail to what is happening to the sound of your guitar, learn what sounds terrible and don’t be scared to make some noise! It could be argued that the amplifier is the most important component in any guitar chain (apart from you of course) because it’s responsible for projecting the sound. So having a good understanding of how to use it is only going to make you sound even better.