Guitar amps go hand in hand with electric guitars. No matter how well you play, your sound won’t project without an amplifier. So, if you are an electric guitarist, chances are you have an amp. But how does a guitar amp work? It isn’t magic that projects your guitar at loud volumes!
In this article, I will go over the basics of a guitar amplifier and its components. By the end of this article, you will have a clear understanding of how a guitar amp works and what components make it up.
The guitar signal: how do pickups work?
When you strum or pick your electric guitar strings, you won’t get much volume unless you plug it into an amp. When plugged in, the vibrations of your strings are turned into an electrical signal by the pickups on your guitar. These pickups are electromagnetic devices that are the first step in transferring the sound of your guitar to your amp.
What are pickups made of?
There is a magnet and a coil of copper wire in a pickup. The magnet is usually made of a magnetic material like alnico or ceramic, creating a magnetic field. The coil of wire is wrapped around the magnet. When your guitar strings vibrate, they disturb the magnetic field, which causes an electric current to flow through the coil.
How does the signal go from the pickup to the amp?
The pickup produces a very faint electrical signal that must be amplified before being heard. This is where your guitar amplifier comes in.
Your guitar pickups send a signal down the cable to the amplifier’s input jack, which has been calibrated to match and accept the impedance of your guitar pickups. The amplifier picks up the sound signal sent from the pickup and boosts (or amplifies) the sound tenfold. Now you can actually hear the sound coming from your guitar.
How does a guitar amp work?
A guitar amplifier is an electronic device that amplifies the small electrical signals generated by a guitar’s pickups into an audible sound that can be heard through its speakers. These are complex devices with lots of circuitry and electrical components, so I have broken this down in the simplest way possible.
Preamp & power amp
Besides the speakers, which are the largest part of an amp, any guitar amplifier is primarily made up of two main components: the preamp and the power amp.
When you plug your guitar into your amp and play a note, the signal from your pickups first passes through the amp’s preamp section, which brings it up in level and shapes the guitar’s tone.
The signal then passes from the preamp to the power amp, which amplifies it further and transmits it to the speakers. The electrical signal is subsequently converted into sound by the speakers.
The preamp section
While there are many different configurations in preamp design, these are the main stages your signal goes through within the preamp:
1. The buffer circuit
Upon entering the preamp, your guitar signal first goes through a buffer circuit. The buffer separates the guitar from the rest of the circuitry.
This prevents signal loss or tonal degradation, which would occur if the guitar’s impedance is directly connected to the input of the amplifier.
2. Gain staging
After the buffer circuit, your signal passes through a succession of gain stages. Depending on your amp’s gain setting, each gain stage amplifies the signal by a specific amount.
Gain stages are typically implemented with tubes or transistors, which add the analog warmth and color that preamps are known for.
3. Tone stack
After the gain stages, the signal is routed to the tone stack, which gives you a chance to shape your guitar tone. The tone stack is comprised of dedicated knobs for bass, mid, and treble.
Some preamps have additional tone-shaping circuits like presence and contour. The tone stack allows you to shape your primary guitar tone without additional effects or pedals.
Power amp section
The power amp section is made up of several parts that work in tandem to amplify the signal from the preamp to a driveable level at the speakers:
Transformers are generally found at the beginning of the power amp. These transformers change the high-current, low-voltage signal from the preamp into a high-voltage, low-current signal that is needed to power the speakers.
The transformers not only keep the preamp and power amp parts of the amplifier electrically separate and isolated, but they also help reduce noise and hum.
2. Output tube
The power amplifier’s output tubes are considered to be one of the most important components in the design of a tube amplifier. This is because the signal from the transformers is amplified by them so that it can power the speaker.
Different types of tubes produce different tones, and most experienced guitarists have strong opinions about which ones they prefer in their amplifier circuit.
These are some of the most well-known output tubes:
EL34: Pentode tube design famously found in British amps like the Marshall JTM45 and Vox AC15C1 provides classic tube warmth with a compressed mid-range.
6L6: Beam tetrode tube design famously found in American amps like the Fender Twin Reverb (4 x 6L6 tubes in the power amp section) and Mesa Boogie Dual Rectifier (matched pair of 2 x 6L6 tubes).
While these tubes are known for their famous “open-sound” in the Fender Twin, they tighten the low end and add definition to the high frequencies in the Mesa Boogie.
KT88: Beam tetrode tube design found famously in the Hiwatt 100. It was also found in the Marshall 200 series. While they provide excellent dynamic range and add fullness to the low end, they’re not as common as the EL64 or the 6L6.
3. Bias Circuit
Bias is the amount of current that goes through the power tubes in the output stage of an amplifier. The bias circuit is in charge of setting the correct operating point for the power tubes.
Setting the bias accurately ensures that the power tubes will work at their most efficient level. This makes sure that the amplifier generates the best tone and sound that it is capable of.
Most guitar amplifiers use a fixed-bias circuit, in which the power tubes are biased to their optimal working position using a negative voltage source.
4. Filtering Capacitors
The power amp generates noise and distortion at high frequencies that must be filtered out. Filtering capacitors eliminate this noise and ensure the output is clean and free of distortion.
5. Output Transformer
The impedance of the power amplifier must be matched to the speaker’s impedance, which is the output transformer’s job. It also keeps the power amp and the speaker from touching each other electrically. This provides isolation which helps cut down on noise and hum.
The last part of the guitar amp is the speaker, which turns the electrical signal into sound waves you can hear. Usually, the speaker is housed in the wooden frame of the amp. The size of the speaker is important because even a high watt amp won’t be very loud with a small speaker.
The speaker cabinet’s size and design configuration can significantly impact the amplifier’s overall tone and sound, affecting the amp’s low-end EQ slope, mid-frequency response, and decibel levels. Most guitar amp speakers are 12 inches in diameter and come with either one, two, or four speakers.
- 1×12” cabinet: The sound is concentrated and focused, with less low-end response than a 4×12. It’s generally found in practice amps and is highly portable.
- 2×12” cabinet: It generates a fuller, more nuanced, and more complex sound than a single-speaker cabinet. It’s generally preferred by blues rock guitarists and works well for small-sized gigs.
- 4×12” cabinet: A 4×12 cabinet produces a large, powerful, deep sound with ample volume and a powerful low end. It’s generally preferred by metal and hard-rock guitarists who want their guitars to cut through the drums in the mix. These are bulky, heavy, and generally only used in large venues.
While 12-inch speakers are the most popular in guitar amps. You can find speakers of many different sizes.
- 10” speakers: These are favored by some guitarists because they have more mid-range and have a punchy tone. They are fairly common to find in guitar amps.
- 8” speakers: This is a much smaller speaker that is really only found in small beginner amps and practice amps. It is difficult to get much volume or a full tone with this size speaker.
- 15” speakers: These bigger speakers are the standard size for bass amps and are not very common for guitar amps. Some guitarists prefer to use bass amp speakers because they have more low-end and a deeper tone.
Aside from size, the speakers’ design configuration also has a massive impact on the sound:
- Open back design: Open and airy sound that suits the guitar’s mid-range frequencies.
- Closed back design: Tighter low end with an overall focused sound.
Difference between a guitar amp and a speaker
Even though your guitar amplifier and your set of speakers may look similar, and in theory, they do similar things, several key differences separate the two:
Guitar-specific EQ curve
A guitar amplifier’s EQ curve is designed to specifically amplify the mid and high-mid frequencies while shelving off the low frequencies of the electric guitar. On the other hand, a speaker is made to play back sound from a microphone or stereo system. So its EQ curve isn’t made to match that of a guitar. Guitar amps have a more limited frequency range as they are designed specifically to handle guitar tones, not the entire sound spectrum. In general, speakers have a better overall sound quality, especially when it comes to bass frequencies.
The output jack on the guitar connects to the guitar amp’s input which is usually a 1/4″ jack that can take a mono cable. A speaker usually has 1/4″ phone jacks, RCA jacks, and XLR connectors as it plays back sound from a microphone or a stereo system.
Power amp section
A guitar amplifier has a power amp section, which boosts the signal from the guitar so that it can be heard through the speakers. A speaker doesn’t have its own amplifier built in. Instead, it needs power from an external amplifier or source.
Different types of guitar amps
There are a few different types of guitar amps that work very differently from each other.
Vacuum tubes are used to boost the guitar signal in tube amps, which lend the guitar a natural warmth and tonal character that is highly sought after. When cranked, the tubes compress and drive the signal, creating the “crunch” or “overdrive” tone that is heavily used in rock and blues. Tube amps were the only amps around until the mid-60s, so these amps have the classic rock sound.
Check out my article that covers tube amps in detail.
Besides the preamp and the power amp sections, which I have already covered, the tube amp has a rectifier section.
Rectifiers convert AC power from the wall outlet (power source) into DC power that the amp can use to power various components. This DC power is also needed to bias the tubes correctly and give the speaker the voltage it needs to work efficiently.
Advantages of tube amps
- Low-watt tube amps are louder than solid state amps of the same wattage.
- They have a better overall sound than solid state amps and are preferred by most guitarists.
- Have a natural overdrive sound due to the tubes being pushed to their limit.
Disadvantages of tube amps
- Need regular maintenance. Tubes will need to be replaced every 5-10 years.
- More expensive than solid state amps.
- Need frequent “biasing” to ensure the tubes run at the right voltage.
Solid state amp
Solid state amps boost the guitar signal with the help of transistors and other solid state parts. They generate a flatter frequency response than tube amps. This generates a clean, clear, and round tone that works well for jazz and country.
Solid state amps consist of a preamp and a power amp section and usually have more built-in effects and features, like reverb, chorus, and distortion.
Advantages of solid state amps
- More affordable than tube amps.
- Clear, clean tone.
- Require less maintenance than tube amps.
Disadvantages of solid state amps
- Lack of the organic tone and warmth you get with tubes.
- Don’t react as well as tube amps when they are overdriven.
Hybrid amps take the best parts of both tube amps and solid state amps and put them together in one unit.
A tube preamp section is used for tonal sculpting, and a solid state power amp section is used to amplify the guitar signal. This gives the amp a warm, organic sound like a tube amp, but it is more stable and cheaper than a tube amp.
Most hybrid amplifiers are versatile and work well with a variety of playing techniques and musical styles.
Advantages of hybrid amps
- Similar to tube amp overdrive and tone.
- Low maintenance type of amp. Fewer repairs are needed.
Disadvantages of hybrid amps
- Unable to match the warmth of an all-tube amp as they only use 1-2 tubes.
- More complex than tube and solid state amps, making them harder to repair.
- Generally more expensive than their solid state counterparts.
How guitar amp controls work
The controls on your guitar amp allow you to control the tone, volume, gain, and reverb of your output sound. Some modern amps even have built-in effects or amp models.
The guitar amp’s tone control lets you sculpt your guitar signal’s overall EQ curve by increasing or decreasing the bass, mid, and treble frequencies.
The volume control changes how loud the amplifier is as a whole. However, turning up the volume also makes it more overdriven and saturated if there isn’t a separate master volume.
The overdrive channel is meant to sound similar to the cranking of a tube amplifier’s preamp tubes, which makes it go into saturation. This kind of distortion is called “soft clipping.”
As the input signal goes up, the output signal starts to compress and saturate, resulting in a smooth, warm analog-sounding tone with organic decay.
The dirty channel is meant to emulate the heavy distortion heard in heavy metal music. Known as “hard clipping,” it is achieved by utilizing diodes or transistors to clip the input signal, resulting in a more compressed distortion tone with excellent sustain.
The reverb control on a guitar amp lets you change how much reverb is added to the sound. This can make it sound like you are in a much bigger room with better acoustics. The amount of reverb can range from barely noticeable to fluttering echoes.
Guitar amps are an integral part of a guitarist’s sound. Knowing how a guitar amp works from the inside, from the preamp to the power amp to the speaker, will go a long way in getting the ideal tone you’re looking for.
Have more questions about which amp to go for? Feel free to reach out. I am always happy to help!