A guitar amplifier volume and gain controls

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In this article, we’re going to take a quick look at the history of the guitar amplifier and the different types of amps you’ll come across including combo amps, heads, tube amps, and virtual amps. Next, we’ll take a deep dive into the parts of the amplifier and learn what makes them tick. Finally, we’ll round it all off with some background about how to record the sound that comes out of your amp.

Iconic electric guitar amps have shaped the sound of generations of rock, blues, and metal. They are the lifeblood of any guitarist’s tone. Slash sounds like Slash not only because of his technique or his signature Les Paul, but also because of his Marshall JCM 2555. An amp gives character and depth to your sound. A good amplifier can lift your playing to the next level, adding an extra dimension to your music. A lousy amp will do just the opposite, making you sound muffled, muddy, and grating.

You might have heard terms like “EQ,” “solid-state,” “cabinet” or “gain,” but what does any of that really mean? If you’re a beginner, it’s easy to get confused. If you spend enough time fiddling around, you’ll learn about the parts of the amp through first-hand experience. However, because you didn’t take the time to learn it ‘correctly’, there might still be holes in your understanding. We’ve created this guide to give you the whole picture.

First, as a necessary pre-requisite, check out our Electric Guitar Beginner’s Guide if you haven’t already. You’ll learn about the history and parts of the electric guitar. After you’ve absorbed that information and have a solid understanding of how a guitar works, come back here and learn all about amplifiers!

Quick History of the Electric Guitar Amplifier

The history of the guitar amplifier begins a few years before the invention of the electric guitar. If you remember from our Electric Guitar guide, being heard was something of an issue for guitarists that played in bands in the early 1900s. Drowned out by the rest of the rhythm section, no one could hear the poor guitarist. There had to be a better way to stand out in a loud band.

Early 1900s

Stromberg Voisinet Electric Instruments PamphletDuring the early 1900s, the mechanics of manipulating electricity to create sound was well understood and implemented in fairly common devices like the radio and telephone. Microphone and speaker systems for public address and movie theaters were becoming commonplace, but these were far too large and expensive for the average musician of the time.

In 1928, advancements in tube technology allowed for the creation of portable amplification systems. After some experimentation, the Stromberg-Voisinet company created one of the first electric guitar and amplifier packages. Though it didn’t sell well due to issues with reliability and tone, it had one redeeming quality: the amp. It was relatively light, housing a speaker inside its wooden cabinet – complete with a carrying handle. Though no examples of it survive, its influence is seen in amplifiers even today.

In 1931, the Rickenbacker company included a 10-watt amplifier as part of a package with their now famous ‘frying pan’ guitar. Like the Stromberg-Voisinet that came before it, the Rickenbacker amp was a wooden cabinet containing electronic components and a speaker. It was the first mass-produced, commercially successful electric guitar amplifier.

Mid 1900s

Guitar amps went largely unchanged for about 15 years. A 10-watt tube amp with one speaker was par for the course. But as the electric guitar grew in popularity, so did the audiences. Larger audiences meant bigger venues. Bigger venues meant that 10 watts could no longer cut it. We needed more volume!

1947 Fender Super Amplifier
A Fender Super from 1947

In 1947, the Fender Super was born. With 18-watts of power and 2 10-inch speakers, it gave guitarists a much-needed volume boost. These higher-power amps had a bonus ‘feature’: if you cranked the volume, the sound started to distort. Though it started out as an accident, many musicians took a liking to this gritty, emotional tone. The 50s gave way to the 60s and distortion became more popular by the day.

1960s and 70s

As amps began to improve in tone and power, 10-watts became 50-watts, one speaker became four, and the number of amp manufacturers multiplied as well. In the 1960s, distortion became increasingly prevalent thanks to bands like The Kinks, who went to the extreme of slashing their speakers to try and get as much of it as they could. Fuzz became synonymous with Jimi Hendrix. In the race for heavier and heavier distorted sounds, hard rock and heavy metal were born. Effects pedals began to grow in popularity. Some of these effects, like tremolo and reverb, even found their way onto the amp itself.Jimi Hendrix with his Strat and pedals

Vacuum tube amplifiers were the standard ever since the invention of the guitar amp. The status quo began to shift in the 1970s when solid-state (transistor-based) guitar amps took the stage. Transistors were a revolution in electronic circuits. They are the reason we can have phones that fit in our pockets and computers on our desk. Solid-state amps are low maintenance, emit less heat, and consume less power than tube circuits. Sounds like a slam-dunk, right? Not everyone thought so. Tube-enthusiasts feel that tube amplifiers create more natural, superior distortion than solid-state amps, which tend to excel more at clean tones. Even today, the debate rages on.

Modern Day

Modeling amplifiers were the next advancement in the 1990s. In an attempt to capture the sounds of specific iconic amplifiers, modeling amps use a digital modeling device to change their tone to mimic the voice of a famous amp like, say, a specific Marshall or a Vox. Though they’re usually seen as a beginner’s tool, any guitarist can benefit from the versatility of a modeling amp.

Amplitube program screenshot
A screenshot of AmpliTube 3, a virtual guitar amplifier you can run on your computer or phone

One of the most recent evolutions in guitar amp technology is digital amp simulators. Since the early-to-mid 2000s, computers have revolutionized the way we record and play music. Bias and Amplitube, shown above, are programs that can convincingly simulate a guitar amplifier using a technology known as Digital Signal Processing. You plug your guitar into your computer or your phone using a digital interface, change some settings, and record! Pretty cool, huh?

Common Types of Electric Guitar Amps

Tube Amps

Vox AC30 tube amp
The legendary Vox AC30 tube amplifier

Like most other electronics of the early 20th century, tubes (also known as ‘valves’ in the UK) were ubiquitous, found in all kinds of electronics from radios to televisions. The original guitar amplifiers of the 30s and 40s all had tube electronic circuits. They were the standard for guitar amplifiers up until solid-state amps showed up in the 1970s. The overdriven tube sound defined generations of music.

Tubes are still in use today. Most professional guitarists prefer the sound of tube amplifiers due to their ‘warmer’ nature and their more natural distortion sounds. Though they need some maintenance and extra care, tube-amp owners are happy to accept a few drawbacks for superior tone.

Solid-State Amps

The increasing use of transistors in the 1950s spurred an electronics revolution and the invention of digital technology. Electronics were no longer restricted by the size, heat generation, fragility, weight, and high-power consumption of tubes. In the 1970s and beyond, more and more amps used transistor technology. Cheaper to produce and lighter in weight, solid-state amps improved on some of the drawbacks of their tube-based predecessors. However, many guitarists disagree that solid-state amplifiers sound better than tube amplifiers. Digital transistor technology, they argue, doesn’t produce as natural a tone as an analog tube-amplifier.

Modeling Amps

Vox AV30 Tube AmplifierThere is a special category of amps known as ‘modeling amps’. Inside these amps is a special digital signal processor (‘DSP’) that can mimic (or ‘model’) specific sounds. Solid-state modeling amps can convincingly replicate the sound of almost any amp.  A DSP can even model a bass guitar amp! You get a lot of bang for the buck with digital modeling technology, which is why it’s commonly found on lower-priced amplifiers.

However, don’t think that digital modeling is the only game in town. The Vox AV series of amps, for example, contains analog modeling technology. Instead of a digital signal processor, the AV series uses multiple tube-based circuits to shape its tone. However, analog modeling won’t have as much ‘range’ and versatility as a digital-based, solid-state modeling amp. And because you’re adding even more tube-based components to the amp, it weighs more and runs hotter as well. But, because the modeling is analog, some guitarists feel it sounds more natural than a digital modeling amp.

If you want authentic tube technology along with the versatility of digital modeling technology, you’re in luck. A modeling hybrid amp might be perfect for you.

Hybrid Amps

There are two main sections inside an amplifier, which we’ll talk about in detail in a later section of the article. In short, an amp consists of two separate components: a preamp and a power amp. The preamp does the tone shaping and gain response while the power amp handles the volume adjustments. In a pure tube-based amp, both of these sections are tube-based. A solid-state amp contains a solid-state preamp and power amp.

Angled view of the Vox VT20X

However, in a hybrid amp like the Vox Valvetronix VT20X, tube and solid-state technologies work together. In hybrid amps, the preamp section is tube-based while the power amp is solid-state. This gets you natural tube distortion and warmth combined with solid-state reliability. Hybrid amps are a good middle ground if you don’t want to commit fully to one technology or the other.

What about using a solid-state preamp and tube-based power amp? That’s also possible! This configuration is common in hybrid modeling amps. Because the preamp, which does the tone shaping, is solid-state, integrating a digital signal processor chip into the solid-state preamp is easy.

Digital Amp Simulators

A step beyond modeling amplifiers – amps that mimic the sound of other amps –  is the digital amp simulator. Amp simulators (or ‘amp sims’ for short) are applications that run on your laptop, desktop, or even your Android or iOS phone/tablet. These programs are entirely digital, requiring only an interface that connects your guitar to your computer or phone. By using digital signal processing (like you find in a modeling amp), amp simulators allow you to do everything you can do with a typical physical guitar amplifier and more. You can even use it to record your own music without any other gear. Some amp sims even allow you to create a virtual pedal board! Depending on the features you want, amp sims can range from anywhere between $10 up to thousands of dollars.

Parts of the Electric Guitar Amplifier

Combo Amps, Heads, and Speaker Cabinets

Fender Super Champ X2 angle view

‘Guitar amp’ generally refers to a combo amp. Combo amps, like the Fender Super Champ X2 above, are really a couple of components packaged together. It contains the electronics that do the actual amplification of your guitar’s signal, the speaker that the amplified sound comes out of, and the cabinet that holds everything together. Combo amps are great because everything you need to start rocking out is all neatly bundled together – plug your guitar in, turn your amp on, and play.

The amp’s electronics, speaker, and cabinet each have a noticeable effect on your sound. When you buy a combo amp, you get convenience and portability. You’re basically stuck with what the manufacturer has put together.

Hughes and Kettner TubeMeister 36 Amp Head

Some guitarists prefer to do things their way. They choose instead to buy an amplifier head (which houses the electronics) and a separate speaker cabinet (which houses the speaker), giving them more flexibility when it comes to molding their personal sound. Whether you pick a combo amp or a head/cabinet is up to you. Generally, combo amps are cheaper than buying a head and cabinet separately. For a beginner, combo amps are usually the easiest way to go. For the more advanced or discerning musician, buying an amp head, like the Hughes and Kettner TM36 above, and a speaker cabinet (or ‘cab’ for short) can give you more options and flexibility down the road.

Wattage

While not strictly a ‘part’ of the amplifier, the wattage of an amp affects the sound of everything you play. Wattage is a rating of how powerful an amp is. As a general rule, a higher-wattage amp can get louder than a lower-wattage amp driving the same speaker. However, we’ll touch on some of the differences between the wattage of tube and solid-state amps in the coming sections.

Preamp and Power Amp Stages

Most of the time, when we think of a guitar amplifier, we tend to picture it as a magic box. You plug your guitar in, turn a few knobs, some wizardry happens, and sound comes out! Most guitarists don’t bother to learn about what happens behind-the-scenes. What is gain? How is it different from volume? What does it mean when someone calls heavy metal ‘high-gain’ music? Let’s clear this up.

Understanding the Signal Chain

Your guitar’s pickups produce a weak, low voltage signal.  Speakers are high-impedance devices, meaning they need a lot of power to generate sound – a lot more than an electric guitar can create on its own. That’s where the amplifier comes in.

An amplifier is responsible for taking your guitar’s signal and making it more powerful in order to properly drive a speaker. An amplifier contains either solid-state components (transistors), tube-based components, or in hybrid amps, both. Transistors and tubes, when pushed to their limits, create distortion. The way they create this distortion is different, which is why tube amps sound distinct from solid-state amps. No matter if your amp is tube or solid-state, more you drive it, the more it will distort your tone.

Your amplifier actually amplifies the signal twice. These two amplification steps are commonly referred to as ‘stages.’ Each stage is controlled by a different set of electronic components built for a specific purpose. The end goal of both amp stages is the same: to amplify the signal. However, each stage amplifies the signal in a particular way for a specific purpose.

Preamp Stage

Guitar amp signal chain
The different stages of the guitar amplifier. Image courtesy of Roland UK

The first stage is the ‘preamp stage’. The purpose of the preamp is to amplify the signal’s voltage, changing it from a low voltage signal to a high voltage signal. The degree to which the signal is amplified is determined by the gain knob (sometimes labeled ‘drive’). The gain knob drives the preamp section to increase the voltage of the input signal. The higher you set the gain, the more the preamp stage amplifies and, by the nature of these electronic components, distorts the signal. Pre-amp distortion has a compressed, smooth sound that easily achieved simply by cranking the gain knob.

Power Amp Stage

The second stage is the ‘power amp stage.’ The purpose of the power amp is to take the preamp’s signal and amplify its power. The higher you set the volume, the more powerful the signal gets. A higher volume setting means your power amp section works harder to amplify the signal. As we already know, the harder these components work, the more they distort. Power amp distortion is more dynamic than preamp distortion and has a bit more punch and flavor to it.

Finally, after the power amp does its job, the signal is sent to the speaker. The electrical signals from your guitar have finally turned into sound.

From Overdrive to Fuzz

Distortion isn’t just on or off – it’s a range. The amount of distortion you’re using determines how aggressive your sound is. No distortion and your sound stays ‘clean’. Low distortion is usually known as overdrive. With overdrive, you’ve turned the gain or volume knobs just enough that the amp is starting to distort. This gives you a beautiful, bluesy tone that lends emotion to your playing. If you turn your gain knob up to 10, you get into fuzz territory. Fuzz envelopes your tone in distortion and creates a harsh, grating sound typified by Jimi Hendrix. If you’re curious about these types of distortion and the physics behind them, then check out this article to go in detail.

Headroom, Volume, and Attenuators

Remember, preamp distortion is controlled by the gain knob and power amp distortion by the volume knob. If you want to keep the volume low but still have distortion, then pre-amp distortion is what you want. It’s super easy to control. If you need more pre-amp distortion, you just turn the gain knob up. If you want less, then you turn it down. Easy-peasy. Power-amp distortion, however, is a bit more nuanced.

Power-Amp Distortion and Attenuators

Imagine you’re playing on stage at the local club and you’ve brought along a low-wattage amp. To be heard clearly, you’ll need to turn the volume up pretty high. Because you’ve cranked the volume up to 10, the power amp section is being pushed hard,  giving you plenty of power amp distortion.

Now imagine you’re playing again at the same venue, but this time you bring a higher wattage amp. With the volume knob set to just 2 or 3, you can easily fill the room with sound. Because the power amp isn’t working too hard at these low volumes, it’s not distorting your sound. If you wanted power amp distortion with your high-wattage amp, you would need to crank the volume up higher. However, because your amp is so powerful, that just might make you and everyone in the audience go deaf. In this case, you’re stuck using preamp distortion.

Bugera PS1 Power Soak
A power soak like the Bugera PS1 will help tame a high-wattage amp’s volume to bedroom levels

If you use a higher wattage amplifier and desire power amp distortion at low volume levels, you can use an attenuator (also known as a ‘power soak’). Pretend you have a powerful 50-watt amplifier, but live in an apartment. You miss that sweet power amp distortion you get on stage from turning the volume all the way up to 10 (known as ‘diming’ your amp). You know if you dime your amp at home, your ears will bleed and your neighbors will come knocking.

Attenuators

To save your hearing and avoid angering your neighbors, you buy an attenuator and hook it up between your amp and speaker. The attenuator allows you to turn up the volume on your amplifier, driving the power amp to distortion. Then, you set the volume on the attenuator to bedroom levels. The attenuator will cut the volume of the signal that reaches your speakers, but the power amp distortion will still be present. Even if you just want more control over the volume of your high-wattage amp, an attenuator can be useful. Some amps even come with a built-in attenuator!

Depending on the style of music you play, power-amp distortion may be desirable. The majority of musicians find that playing with pre-amp distortion alone serves them well enough. But, like with everything guitar, it’s up to you to decide which you like best! You might discover that a combination of preamp and power amp distortion gets you the tone you’re looking for. You’ll never know until you try.

Headroom

An amplified guitar signal
You’ll sometimes hear guitarists talk about headroom. Headroom refers to how loud your amp can get before it starts to exhibit power amp distortion. In the graph above, headroom is represented by the horizontal yellow lines. As long as your guitar signal (the dashed green wave) stays inside the amp’s headroom, the signal stays clean. As you increase the volume, the amplitude of the signal increases and it starts to look more like the solid blue wave. If you get past the amp’s headroom, the signal starts to clip and becomes distorted.

Higher-wattage amps generally have more headroom than lower-wattage amps. However, by their very nature, tube amps and solid-state amps use electronic components that have inherent differences in how they handle electrical signals. This is why a 20-watt tube amp is not always equivalent to a 20-watt solid-state amp in terms of volume and headroom. We’ll see why in the next section.

What’s in a Watt?

A scientist will tell you that a watt is a watt is a watt. It is an objective unit of measure, like a ‘degrees’ or ‘meters.’ It doesn’t change, no matter if you’re measuring a tube-amp, a solid-state amp, or a lightbulb. However, a guitarist will tell you that, in terms of headroom and volume, a 20-watt tube amp and a 20-watt solid-state amp can be drastically different.

Generally speaking, a tube amp can get objectively louder than an equivalently rated solid-state amp. However, tube amps tend to distort earlier, meaning they have less headroom. This could be good or bad depending on the style of music you play and how loud you want to get. Comparing solid-state and tube-amps in terms of wattage isn’t always a clean comparison, and many people have differing opinions on the matter. Suffice it to say, the first step in choosing an amp is to decide which type is right for you: tube, solid-state, or hybrid. Then decide on how powerful you want the amp to be: are you gonna be rocking out at home, at the bar, or in a stadium?  We go more into depth about how to choose an amp in our Guide to Buying an Electric Guitar Amplifier, but keep reading because there’s more to learn!

Many musicians who are just starting out get an amp between 5 and 20-watts, which will serve them just fine for practicing at home. Gigging musicians who play with a band may have a single high-powered amplifier with an attenuator for practicing at home at low volumes, or they might have a low-wattage amp for home and a high-wattage amp for the stage. Some guitarists enjoy having a low wattage amp that they can crank up easily and enjoy power amp distortion at relatively low volumes. When they need more volume, like at a venue, they’ll have to mic up their amp in order to keep up with the rest of the band.

Clean and Lead Channels

Peavey 6505 Channel Control Knobs
The Clean (‘Rhythm’) and Lead channel controls of the Peavey 6505

On most amps, you’ll be able to select from multiple channels. Think of channels as presets, where you can change the gain response of the amp with the press of a button. Each channel has its own volume and gain settings, and, on higher-end amps, its own EQ controls as well. Two channels are common, but some more expensive amps can have three, four, or more!

On a two-channel amp, you’ll commonly find a ‘clean’ channel and a ‘lead’ channel. The clean channel is configured to have minimal distortion. If you flip to the lead channel, the amp’s characteristics change instantly, and you’ve got more gain on tap without having to fiddle with any knobs. Each channel has separate controls for volume and gain so you can configure them separately. Many amps come with a footswitch that lets you change the channel of the amp from across the room hands-free.

EQ Controls

EQ (‘equalization’) controls shape the different parts of your sound. Musical frequencies are generally categorized as bass (low-end frequencies), mid (mid-range frequencies), and treble (high-frequency). 3-band EQs (bass, mid, and treble) are standard. EQ controls on your amp let you manipulate these different classes of frequency, increasing or decreasing their presence in your tone. Equalization and tone-shaping happen in the preamp stage of your amplifier.

Different genres of music will require you to set your EQ controls in different ways. If you play the blues, you may want to emphasize the mid and high frequencies, so turn the mids and treble up a bit. If you play 80s thrash or heavy metal, you’ll usually set the mids pretty low to get that signature sound. It’s all about experimenting and finding the right tone for the music you’re playing.

Effects and Effects Loop

Some guitar amplifier heads come with a feature known as the “Effects (FX) Loop.” Many guitarists have a set of effects pedals they use to modify their sound. They plug their guitar into the effects pedals and then connect the output of the pedals into the amplifier’s input. The effects adjust the signal of the guitar before it gets to the amp, adding compression, chorus, reverb, or even distortion.

Sadly, not all effects sound great this way. Running time-based or modulation effects like reverb or chorus into the input of the guitar amp can be a recipe for a muddy mess. Remember the preamp is what receives the signal from your effects pedals. If you’re running a reverb pedal into a guitar amp and then turn up the gain, the sound that comes out of your speakers may not be all that pleasant. The preamp will distort the reverberations and turn what you’re playing into a musical mush.

Depending on the effects you want to run, it may be smarter to utilize the amp’s effects loop. The effects loop allows you to place your desired effects in between the preamp and power amp sections of your amplifier. Placing effects ‘in the loop’ (after the preamp) allows you to avoid distorting those effects, reducing noise and creating a more pleasant sound.

Generally, because most musicians get their distortion from the preamp section, they place their time-based effects in the loop. This is not a hard and fast rule, however. As always, it’s worth experimenting. Some musicians like the sound of a distorted reverb, so they’re just fine running all their effects ‘in front.’ It’s up to you to experiment.

Speaker Outputs

Speaker outputs are located on a guitar amplifier head. Most combo amps will hide the speaker outputs within the cabinet so you won’t need to worry about them. Occasionally you’ll come across a combo amp that lets you easily plug in a different cabinet, like the Fender Super Champ X2 below.

Back of the Fender Super Champ X2

On the back of the amplifier head, there will be a place to connect one or more speaker cabinets. Using a speaker cable, you select the right speaker output for the impedance of your cabinet and plug it in. Consult your amp’s owners manual for guidelines on how to properly select the right outputs.

Never, under any circumstances, run a guitar amplifier head without a speaker connected. Your amplifier generates a lot of energy that needs somewhere to go. Without a speaker or a dummy load connected to absorb the amplified signal, it’s highly likely your guitar amp will suffer a costly injury. Don’t do it!

Speaker, Speaker Cabinet, and Cables

The speaker cabinet is the wooden enclosure that houses one or multiple speakers. In a combo amp, a cabinet houses both the head and speaker(s) and is all set up and ready to play.

Cabinet

Bugera One Speaker Cabinet
A standalone speaker cabinet, sometimes known as an ‘extension cabinet’

In a standalone speaker cabinet (sometimes called ‘extension cabinet’), like the Bugera One, you’ll find one or multiple speakers mounted to the frame and covered with a grille. The speaker cabinet plugs into the speaker outputs on an amp using a special speaker cable. Speaker cables are much thicker than the cables that connect your guitar to your amplifier (known as ‘instrument cables’). Why are they so thick? The signal outputted by your amp to the speakers is much, much stronger than the signal going into your amp from the guitar. This means extra wiring material is necessary to properly handle the amplified signal.

The cabinet itself has a lot of effect on your speaker. Some cabinets are open back, meaning they also leak sound out of the back. Open-back cabs have a room-filling effect that ‘softens’ the speaker’s output a bit. Some cabinets are closed-back and don’t allow any leakage. All the sound is sent in the direction of the speaker. This gives the bass and mid-range a boost and can make your tone more punchy and aggressive. What kind of cabinet you choose is up to you!

Speaker

Randall RG412 Speaker Cabinet
The Randall 4×12 speaker cabinet – for the metalhead who really wants to move some air

The speakers mounted inside the cabinet are usually between 6 to 15 inches in diameter. One to four speakers is standard, with smaller single speakers common for use at home and practice. Larger, multi-speaker setups are common for gigging musicians. Particular attention should be paid to picking the right speaker cabinets for your amplifier head. Be sure that your speaker cabinet has the proper impedance and can handle the wattage from your amp. We’ll go into detail about this in our Guide to Buying an Electric Guitar Amplifier.

If you’re super picky, you can even change out the speaker inside a cabinet for another that you might prefer! If you ever want to change the speaker in a cabinet, it usually isn’t too difficult a task. However, if you ever think of changing a speaker in a combo ampdon’t! Amplifiers can carry an electric charge in their capacitors even if they’re off. These electrical charges can cause death! So, don’t ever open your combo amp or amplifier head unless you have training in electronics. If you’re ever unsure, consult a local guitar technician.

Cables

Keep in mind that speaker cables and instrument cables are meant for different purposes. Swapping cable types can cause some bad things to happen. The thinner instrument cables are for connecting your guitar to your amp or your guitar to a pedal.  Thicker speaker cables are for connecting your amp to the speaker cabinet. They are not interchangeable!

Guitar Input

Fender Twin Reverb Controls

The guitar input is obviously where you plug in your guitar. However, you might come across an amplifier that has multiple inputs. The Fender Twin Reverb above has two groups of 4 inputs, each group with its own controls.

There is a group of two Normal inputs. One of these inputs is the standard input we’re all familiar with. The other provides you an immediate gain boost without having to fiddle with the gain knob. This allows you to get even higher gain sounds from the amp by raising the level of gain you start at. There is also a group of two Vibrato inputs, which are similar to the Normal inputs but are affected by the Reverb and Vibrato controls on the amp. If the amp you’re considering comes with multiple inputs, take a second to read the description to find out why! In our in-depth reviews, we’ll be sure to mention any input quirks.

Amp Classes and Biasing

If you look at tube amp spec sheets long enough, you might notice some amps come with a ‘class’ rating. Class isn’t an indication of the quality of the amplifier. Class ratings are nothing more than a shorthand description for the circuit design.  The most popular types of guitar amps are Class A and Class AB.

Class A

Class A tube amps are designed to be running all the time. As a result, they’re super responsive and react quickly to your playing. Class A tube amps are generally a lot louder than their wattage rating may lead you to believe. They are usually as loud as a solid-state amp rated at 3 or 4 times the wattage. A 5 watt Class A tube amp can get almost as loud as a 15 or 20-watt class AB amp! However, because they’re always running and ready to respond, tube life is less than an equivalent class AB amp.

Class AB

In a Class AB tube amp, two tubes share the job of amplification, so they don’t have to run continuously like a Class A amp. That means they’re a little more power efficient and the tubes last longer as well. However, this also means they’re not as powerful as an equivalently rated Class A amp.

Does class rating matter? You really can’t go wrong with either type of tube amp. These two amp classes have stood the test of time and work well for all applications. As long as you buy a tube amp you like, you’re good to go! For the majority of guitar players, it’s usually not worth worrying about amp classes.

Biasing

A tube amp’s bias setting controls the amount of electrical current set to the tubes. If the bias is set too low (‘cold bias’), the tubes aren’t receiving enough power. This is a recipe for poor tone and unpleasant crossover distortion. Crossover distortion sounds scratchy and grating, but some experimental musicians enjoy it. If you’re interested in the technical aspects behind crossover distortion, check out Aiken Amps’ superb explanation.

If a bias is set too high (‘hot bias’), then your tube amp will scream, but the life of the tubes is significantly decreased. You might even hurt your amp this way.

Tube amps are biased at the factory. Generally, you won’t need to worry about biasing unless you’re changing the tubes in your amplifier. This can be a dangerous process, so follow your owner’s manual or consult a local professional. Some modeling amps allow you to change the emulated ‘bias’ and class of the amp for even further customization of your tone. This is a safe, easy way to mess around with biasing without risking any damage to your gear.

Recording

Recording a guitar amp stack

We won’t go too much into detail about recording here. We’ll soon have a full section of the site dedicated to the subject.

Microphones

Recording an amp is something of an art and a science. For decades, using a microphone was the go-to method for recording. With a mic, it’s easy to get ‘a tone,’ but it’s harder to get ‘good tone.’ You need to take into account quite a few variables when recording with a mic. The type and model of microphone(s) you’re using, the distance from the amp and the acoustics of the room you’re playing in all have an effect. Unless you can control all these variables, like you can in a recording studio, you may find that your recordings are missing something.
Hughes and Kettner RedBox DI

Direct Recording

Luckily for musicians who don’t have access to a recording studio, technological advances have made it possible for even those with the smallest of budgets to sound like a professional. Some amplifiers have a line out so you can plug into an audio interface and record mic-free. Other amps, like the Fender Mustang GT40, even have USB outputs for connecting straight to a computer and record without any extra gear!

Direct-input boxes, like the Hughes and Kettner Red Box, are specialized pieces of hardware that can also eliminate having to use a mic. They capture the output signal of your amplifier before it gets to the speaker. Connect your amp’s speaker output to the DI-box and the DI-box to an audio interface. Now you can record the amplifier’s signal directly! Some DI-boxes even can even simulate the sound a speaker and cabinet have for an even more impressive recording.

Amp Simulators

Amp simulators can replace a physical amplifier completely. Plug your guitar into an audio interface and plug the interface into your computer. Start the amp simulator, and you have an amp on your computer! Within the program, you can modify the gain, add effects, or even change the type of emulated ‘mic’ and ‘speaker’! For a guitarist who can’t afford all that gear, this is a godsend!

Conclusion

Whew! That’s a lot of stuff. Let’s recap what we’ve learned so far.

We’ve learned about the history of the guitar amplifier and why it was invented. We saw the different types of amplifiers, including tube, solid-state, hybrid, modeling, and amp simulators. We now know about the different parts of the amp, including the pre and power amp sections and how they’re related to the volume and gain knobs. Finally, we learned what the EQ knobs do, what the effects loop is for, recording, and how different channels of the amp can affect your sound,

You now know almost everything there is to know about the guitar amplifier and how crucial it is to the electric guitarist. Now that you know all about amps, you can decide what kind of amp you want. Check out our page on Buying the Right Electric Guitar Amp for guidance about buying the best amp possible for your needs. If you prefer to skip straight to our recommendations, check out our guide for the Best Beginner Amps.


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