You may have noticed when you strum an unplugged electric guitar that the instrument sounds uncharacteristically quiet.
Not exactly the sound that’s ready to rock a stadium, is it?
There is another half of the electric guitar equation that needs introducing: the Amplifier.
You may know that an electric guitar needs to be plugged into an amp to be heard, but you may be wondering… how does a guitar amp work?
What You Need Know about How a Guitar Amp Works?
Guitar amplifiers are complex and powerful pieces of machinery with many different parts working together to create the sounds you know and love.
Do you need to know all the little intricacies in regard to parts and circuitry to become a better guitar player? Arguably, no. But it certainly doesn’t hurt.
That being said, this article is going to focus on the basics of guitar amp functionality. With this information you can better understand how your amp works so that you can more easily dial in a good tone or pick out the right amplifier for your needs whether you are a beginner or a pro.
So while I will mention some major technical aspects of amps, the focus will be on how these parts interact with the amp and effect your playing.
These basics are the stuff that every guitarist should know about how guitar amplifiers work.
What Does a Guitar Amplifier Do To Your Sound?
Amplifiers take the small signal from your guitar’s pickups and amplify (make more powerful) it enough to drive a speaker. The result is a louder sound that can be distorted and tonally shaped through the amp itself.
Guitar Amps Explained
Amplifier Stages – Preamp, Poweramp, Effects Loop
Before jumping into the types of amplifiers, it’s important to know that most amplifiers share the basic design concept of two power stages: a preamp and a poweramp.
Raises your signal to Line Level. The preamp often includes a tone stack/EQ section. This is where the majority of your tone shaping occurs.
The Poweramp takes the signal from you Preamp Section and increases the level to point that your speaker moves. There is little tone shaping that happens in this portion of the amp. However, extreme settings can cause some compression/sustain. This can sometimes include a Presence feature.
This is a section of the amplifier that sits between the Preamp and Poweramp that can be utilized to create a closed loop for your effects. To learn more about how an Effects Loop works, check out this full write-up on how to use an effects loop on a guitar amp.
Power Transformer (Voltage)
This portion of the amp converts AC voltage from your wall (usually 120V AC) to the proper AC voltages for amplifier.
Types of Amplifiers
Even though all amplifiers serve the same basic purpose (to amplify your guitar signal), they go about this purpose in different ways. The easiest way to understand how amplifiers work is to break them down to their basic types, of which there are three:
- Tube Amplifiers (aka Valve amps)
- Solid State Amplifiers (aka Transistor amps)
- Amp Modelers
1. Tube Amps
The first kind of amplifier to come into existence, and the amp the remains the gold standard today in terms of tonality, is the tube powered amplifier (aka valve amps). I wrote an entire post on the best tube amps on the market and I highly recommend you read it.
As their name suggests, tube amps use a series of vacuum tubes to amplify electric guitar signals.
While vacuum tubes can be used to recreate or amplify pristine audio signals, like in the case of some vintage record players, they are often selected for guitar amplifiers because the color your guitar’s tone. Let’s take a look at how this is done.
Class A vs Class AB Tube Amps
In tube amps, there are two archetypal designs that most amplifiers fall under: Class A or Class AB.
Class A, represented well by vintage Vox amplifiers, work in such a way where each tube amplifies the entire signal in a cascading manner. The result is that Class A amps distort earlier.
Class AB amplifiers like Fender, Marshall, and Mesa Boogie, utilize pairs of tubes that work together to amplify the signal. The result is that these amps have more clean headroom and have to be pushed to louder volumes to distort. They also preserve low end frequencies better than Class A.
Types of Tubes
The type of tube that is used in an amp has a massive impact on the sound of the amplifier. Here are the most common preamp and poweramp tubes and what they sound like:
- 12AX7: Typically used in the preamp section of most amps. Originated in Fender Tweed era amps.
- 6L6: Poweramp Tubes most associated with “high headroom” sounds. Often used in Class AB amps like Fender to create warm, glassy clean tones. Not as ideal for heavy metal tones. Found in many higher wattage Fender amps.
- 6V6: Similar in design to 6L6, but breakup at lower volumes, making them a great choice for lower wattage American amps. Great for distorted blues and rock, but not ideal for heavy gain due to less pronounced bass response. Found in Tweed style amps and lower wattage British amps.
- EL34: Epitome of big British guitar tone that is most associated with Marshall style amplifiers. While they are most sought after for their saturated, high gain tones, these amps lend themselves well to clean tones as well.
- EL84: Another British tube, but this one distorts at lower volumes that makes them perfectly suited for Class A amplifiers like Vox. These provide a lot of saturation and have an emphasis on treble frequencies.
The tubes in your amplifier are non-linear, and distort more as they are pushed. While the tones that come from tube amps are highly sought after, you often have to crank them to high volume levels to achieve these tones. This makes some tube amps non-ideal for home practice, which is why some players opt to use solid state for home practice.
Changing tubes is also a fun and usually minor modification you can make to an amp, depending on the circuit. As long as the amp doesn’t require biasing, swapping like tubes is something you should learn to do on your own.
Once guitarists start down the path of looking at different tubes and realizing they provide different sounds, they often start researching swapping out tubes and making other modifications to the amp.
Can An Amplifier Kill You?
Consider this your safety warning: An amplifier holds immense amounts of voltage, even after it is unplugged, and they most certainly can electrocute and/or kill you. Unless you are an electrical engineer, take your amp to a professional for servicing.
2. Solid State Amplifiers
Great solid state amps work in a similar way to tube amps, except that they use transistors instead of tubes to amplify and distort guitar signals (similar to some overdrive and distortion pedals). This is why these amps are often called Transistor amps.
This type of solid state amp works almost identically to tubes amps in that they use a preamp and power amp section to amplify your guitar.
The tonal results can be different, however, as the transistors create a quicker response time and don’t have the “sag” or compression that some guitarists find appealing. The way that they distort also sound different, often less compressed and not as warm.
While solid state amps used to be unusable, the technology has improved over the years to where solid state amps are a real option for many players, and they are usually the ideal choice for budget friendly amps.
3. Amp Modelers
The other kind of Solid-state amplifier worth mentioning is the new Amp Modeler class of amplifier.
Instead of using transistors, amp modelers are digitally programmed to emulate both valve and transistor amps. This type of amplification has become incredibly popular for working class musicians, as they sound amazing and can offer dozens, even hundreds of amp models and effects in small enclosures.
I won’t go into the technical details of how these work here, the result is that many amp models are designed to function how traditional amps were made. This makes them a familiar, reliable, and cost effective option for working class musicians that want great sounding and flexible rigs.
Amplifier Controls Explained
Every guitar amp has different sets of controls and parameters. This can be dependent on the class of amp and may heavily impact your decision to use the amp. Here are some of the common controls you will see on all amps, no matter the type.
- Gain/Drive: controls how much a guitar signal is overdriven before going to poweramp section
- EQ: Equalization. Mix of frequencies. Typically see Bass, Mids, Treble
- Single knob: dark and bassy at one end, bright and treble at the other
- Bright Switch: adds high end boost
- Non-Master Volume amplifiers may have a Volume control, that has to be pushed in order to get distortion, but it also means your amp gets louder.
- Multi-channel Volume: may have master volumes for each channel so you can balance (or boost)
- Presence: special EQ curve to upper midrange/treble. More lively
Some amps have multiple channels, typically a clean and a dirty channel, but some even have a third channel for extreme gain tones. These are ideal if you want to have tube driven drive tones, as well as clean tones at the flick of a switch.
Some boutique tube amps have spring tanks inside them, as well as tremolo circuits. These will often have controls for the Depth, Mix, or Rate of the effect.
Solid State and Amp Modelers, on the other hand, can have any slew of effects on them. This can come in the form of an effect wheel, with controls for rate and depth. There can be digital reverbs and delays, modulation, overdrive, and more. Each amp will work differently.
Every amplifier needs a speaker.
Some amplifiers come with a built-in speaker (called Combo Amps) and some just come with a stand-alone amp (called Amp Heads). You can trust that a Combo Amp will be set up properly from the shop. Amp Heads, however, are built only to work with certain speakers and it is imperative that you match these properly, otherwise your amp could catch on fire. NO JOKE.
In short, there are two things you need to know about speakers:
Power is measured in Watts.
The total wattage of your speakers should exceed the power of your amplifier.
For example: a 100 Watt amplifier will require speakers that exceed 100 watts total. This can be done with 4 x 25 watt speakers, 2 x 50 watt speakers, etc. You can have any amount of speaker power that exceeds that of your amp, and the speaker will work great.
Impedance essentially measures the amount of load that the speakers put back on your amplifier. This is measured in Ohms.
The speaker output jacks on your amplifier will tell you what speakers the amp is rated for. Things get tricky when you use multiple cabinets, as you don’t want to drop below the minimum load.
I highly recommend you watch the video below for an in-depth look at how impedance works on your amplifier speaker cabinets. Follow your owner manual and always match up the proper speaker impedance values.
Every Electric Guitarist Needs an Amplifier
How do guitar amps work, you ask?
They all work slightly different from one another. However, you can take comfort in knowing that many guitar amps share some common design concepts.
If you’re looking to pick the right amp, but are confused on controls or specs, you can refer to these basic concepts to help you, or read my extensive post I wrote on how to choose a guitar amp.
Also if you have an amp that is making hissing, buzzing or loud humming sounds I believe it would be worth reading my post on guitar amp noise troubleshooting.
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Davis Wilton Bader is a professional guitarist/writer based out of St. Louis, MO. He plays in the bands Lumet and The Outskirts.