What is a preamplifier used for?
If you’ve ever strummed an unplugged electric guitar, you’re familiar with the weak sound it produces.
But, when you plug that guitar in, it transforms into a powerful musical instrument capable of producing a wide array of sounds, from the bone-crunching power chord to the soulful notes of a blues solo.
How this works may seem mysterious, especially if you are new to electric guitars. The two obvious components in producing those distinctive electric guitar sounds are the guitar and the amplifier.
However, there is a third component you may or may not be aware of. The preamp. It’s not always a flashy piece of equipment.
As you look at your guitar and amplifier, you may not even see it. But it’s there. So, what is a preamp? How does a preamp work? And, why use a preamp?
These are important questions, and to help you out, I’ve put together some answers for you below.
What is a preamp?
Many folks think of their guitar amplifier as a single piece of equipment. However, a standard guitar amplifier is actually two separate pieces of equipment contained in the same box.
These two components are commonly known as the preamp and the power amp. So, what does a preamp do?
The preamp is the first major stop for electrical signals traveling to the speaker, and it is where your guitar really starts to build its voice. To make this easy, pick your favorite guitar great.
Whether it’s Jimi Hendrix, Stevie Ray Vaughn, Eddie Van Halen, or any other famous guitarist, they each have a signature sound. These signature sounds begin to take shape in the preamp.
In addition to the preamplifier contained in the basic amplifier, a broad selection of pedals and effect boards have been created that alter the sound of a guitar.
These pedals are also considered preamplifiers. You can even mix and match various preamps with other preamps to significantly change your guitar’s voice.
You can similarly experiment with different combinations of preamps and power amps to further expand the sound of your guitar.
This flexibility makes the preamp one of the most powerful pieces of equipment in your guitarist’s arsenal.
How does a preamp work?
To understand how a preamp works, let’s travel with an electrical signal from strum to the sound coming out of your speaker.
When you strum the strings of your guitar, the vibrations of the strings interact with the guitar’s pickups, converting these vibrations into electrical signals.
From here, these electrical signals travel through your instrument cable to the preamp. Then, these signals travel to the power amp, and finally, the speaker.
But, there is more going on here than meets the eye. These electrical signals start off weak. Remember the sound of strumming an unplugged guitar?
Amp = Amplifier
The signals produced at this point aren’t much stronger than plain string vibration. In fact, at this point, that is literally all it is.
Vibration of your strings.
That’s not much electrical strength.
These electrical signals need some help along the way to transform into a soaring solo or a tight rhythm.
These weak electrical signals make their first stop at the preamplifier, where two important things occur.
First, effects are applied to the signals by running them through specialized circuits, altering the sound these signals will eventually produce.
This can be as simple as a change in the guitar’s tone, making it deep and rich, or thin and twangy, to more complex sound variations such as distortion, chorus, or vibrato.
The second thing that occurs at the preamp is a lot like giving that weak electrical signal a shot of adrenaline. This “power boost” is the preamp’s primary job.
It’s good to keep in mind that your guitar and amp are an audio system. All audio systems have what is called a “line level.” This concept applies to more than just electric guitars.
Microphones, acoustic guitars with piezo pickups or condenser mics rely heavily on the preamp to boost their electrical signals to consistent and audible levels of sound.
Why do I have to amplify before I amplify?
Regardless of what you are using the audio system for, reaching this line level is important for creating a quality sound. And it’s up to the preamp to get the job done.
Returning to the electric guitar, If you were to plug your guitar into a pair of headphones and strum it, you’d likely hear nothing because the electrical signal isn’t strong enough.
It’s below the line level.
It’s worth noting that some guitar manufacturers have developed preamps that are installed in the guitar. If you have one of these, you will experience a different result in this experiment.
To hear what this line-level sounds like on your amplifier you can plug that same pair of headphones into the line out socket of your amplifier and you’d hear a steady hum.
On some amplifiers, you can hear this hum by simply turning up the volume until you hear it, without the need of headphones. That hum is basically the sound line-level makes.
Short Science Talk…
But remember, this is after the sound has gone through the power amplifier.
Electrical signals must be strong enough to overcome impedance.
That’s a fancy way of saying electricity gets weaker as it moves along a line, and that weak “instrument level” sound from strumming your guitar needs help.
It needs something to build its strength. That is where the preamp comes in and boosts the signal’s power to the line level.
This boost by the preamp makes the electric signal strong enough to overcome that sound of static.
And this boost makes the signal noise-tolerant, solidifying the sound and giving it consistency.
This boosted strength is also crucial for providing the power amplifier and speaker with a strong enough signal to do their jobs properly.
Without the preamp, you’d hear a sound. Still, it would be unclear, distorted, and prone to interference from stronger signals.
This inconsistency in sound is because the power amp doesn’t have a strong enough signal to work correctly.
Do I need a preamp?
Determining whether or not you need a preamp is an important question. There are several factors to consider in determining that need.
Generally speaking, if you are playing live, you will need a preamp. But, if you are recording and plugging directly into a recording setup, you do not need a preamp.
But remember, a preamp serves two purposes. So if you are recording and need distortion, chorus, or other effects, you will need some sort of preamplification to apply these effects.
You can achieve these effects using the appropriate pedals or specific recording equipment capable of creating these effects digitally.
An easy way to determine the difference between using a preamp and not using one is to plug your guitar into a speaker or PA system if available.
When you strum your guitar, you’ll immediately notice how flat and lifeless your guitar sounds without the preamp.
You may also notice unintentional distortion, or interference, and static while attempting this. This experiment is perhaps the best way to understand how a preamp affects the sound of your guitar.
If you’re looking to create a specific sound like the heavy distortion of metal, or a wah-wah infused guitar solo, you’ll need a preamp to make these sounds.
Can’t I just use a regular amplifier?
Generally, most guitar amplifiers and some guitars come with a built-in preamp.
The exception to this rule is some low-end budget amplifiers with an inadequate or absent preamp and speaker stacks that require an amplifier head.
A wide range of amplifiers with built-in preamps are available on the market, and finding the right one to meet your needs is a reasonably straightforward process.
However, if you are looking for a precise sound, this may require some trial and error. However, using a regular amplifier specifically made for use with guitars is fine in most cases.
It really depends on the kind of sound you are trying to achieve.
At their most basic level, an amplifier will be capable of producing a consistent “clean” tone without interference or unintentional distortion.
Some amplifiers come with additional effects such as distortion, vibrato, chorus, and more. As stated before, this comes down to the kind of sound you are after.
If you’re just starting out and on a budget, a basic amplifier with a built-in preamp works great.
Later, if you’re wanting to add different effects or add color to your sound, a wide variety of pedals, effect boards, and external preamplifiers are available.
It’s also good to keep in mind that a robust secondary market for guitar equipment exists, and you can often find these add-ons at a fraction of the price of purchasing an entirely new amplifier setup.
Can I just use any preamp?
Not all preamps are created equal, and the answer to the question again comes down to your needs. It’s vital to purchase a preamp that is suited to your purposes.
If you need a preamp for a microphone, it’s usually best to purchase one that is specifically made for microphones.
Likewise, if you are using an acoustic guitar with a piezo pickup or condenser mic, you’ll want to look for a compatible preamp to achieve the best sound. For more information on the best acoustic guitar amps, you can check out our article on the subject.
Outside of that, the sky’s the limit in the type of preamp you select.
So all I need is a preamp?
It’s also good to remember that you have an additional spectrum of sounds available in the interaction between your preamp and power amp.
For the guitar, the combinations you can create using pedals, effect boards, preamps, and power amps are endless.
Quality is another factor to keep in mind when making a decision about a preamp. Better made preamps will have a better sound and a wider range of effects than a low-end, poorly made preamp.
Also, some manufacturers have developed preamps with a unique sound specific to certain models.
A word of caution about Tube Preamps
It’s also important to keep in mind that some preamps are tube preamps.
Tube preamps often require additional care and maintenance as the tubes will eventually burn out and will need replacing.
If you’re a beginner and looking to keep things simple, it’s better to steer clear of tube preamps.
Plenty of solid-state preamps are available that reduce the hassle of dealing with a tube preamp while being capable of mimicking the warmth of tube preamps.
But how can I recreate that signature sound of my favorite guitarist?
If you’re just starting and are in the early stages of learning how to play the guitar, then a basic amplifier with a built-in preamp is usually sufficient.
But, if you’ve been playing a while and are looking to recreate a specific sound, like Eddie Van Halen’s “brown sound” or the transcendent sound of Jimi Hendrix’s guitar, you’re going to want to do some additional research.
For example, Eddie Van Halen’s “brown sound” was difficult to duplicate due to the massive modifications he made to his amplifier system.
Fortunately, achieving Eddie’s sound has become easier with signature series equipment. Now you can easily duplicate his sound with a Peavey 5150 stack (now called the Peavey 6505), humbucker pickups and the MXR EVH signature series pedals.
Jimi Hendrix’s sound is a bit less complicated to achieve than Eddie’s. It is less reliant on preamp acrobatics and can mostly be attributed to a reverse stringed Fender Stratocaster played upside down.
MXR has also released a Jimi Hendrix Signature series of pedals for replicating his sound and if used alongside a Marshall stack, makes a close approximation of Hendrix’s sound.
But do I need a preamp for their sound?
The first question to ask yourself when looking to create a signature sound is, do I need a preamp? That will depend largely on the guitarist you are seeking to emulate.
As with the examples above, Eddie Van Halen’s sound was heavily dependent on the preamp, while Jimi Hendrix’s sound — though dependent on the preamp — largely depended on the way his guitar was set up.
For some sounds, you will need a preamp, and for others, any preamp will work. It depends on what the artist used to create the sound in the first place.
For creating a signature sound, a preamp is frequently used for making the foundation of the sound.
Other pieces of equipment will add to this sound, but the preamp and its settings remain the core component of most signature sounds.
Some of these can even be created with a generic amplifier, with the preamp adjusted to specific settings.
If you’re after a specific guitarist’s sound it pays to do your homework before plunking down cash for new equipment.
Most of the greats have been forthcoming about the secrets of their signature sounds, and their interviews are a great place to start. You may already have what you need on hand.
If you’re planning to play a variety of cover songs by different artists, external preamps in the forms of pedals and effects boards are practically a must-have.
These preamps can be preset, making it easy to switch sounds between songs without worrying about having the settings just right in the middle of a show.
And if you’re a beginner, having access to a variety of preamps allows you to explore the different sounds an electric guitar is capable of.
Regardless of skill level, it’s always fun to play around with your guitar’s sounds. You never know. You may come up with the next great signature guitar sound.