A preamp boosts a weaker signal, bringing it to line level, and a power amp boosts the line level signal before it goes to the speakers.
In other words, a preamp increases signal strength to an acceptable level to transmit to the equipment in your chain. And by boosting the line level signal, a power amp increases the amplitude/volume of the sound you hear through your speakers.
If you ever wanted to ask, what’s the difference between a preamp and a power amp? But, you don’t want to be that guy in the conversation who isn’t technically savvy; now you don’t have to. Let’s compare the two a little more.
Many people, even those with a hobbyist interest in recording gear, assume that a preamp and power amp are two versions of the same thing. Despite both being a form of an amplifier, they are very different, indeed.
What is a preamp?
A preamp is one of the very first things in your recording chain. It takes weak signals from microphones or instruments with a low impedance and adds a specified amount of gain. Commonly, the average preamp can deliver up to 60 dB of gain.
A preamp is necessary to provide your interface, mixer, amplifier, or other equipment, with a signal it can process.
If you haven’t already, you should check out our article on preamps and what they do.
What is a power amp?
A power amp is one of the very last things, often the last before speakers, in your chain. The power amp takes the line level signal provided by the preamp and adds further gain, as desired.
As a beginner, a power amp is a little easier to understand because it’s easier to make a connection to volume/loudness.
What makes them different?
When you consider the fact that they are both amplifiers, and they are both put in place to boost a signal, it’s easy to wonder what makes them so different.
A big part of what makes them different, if we want to think of it in a simple way, is their place in the recording/playback chain. If you don’t know what we mean by chain, it just means the route the signal takes through your equipment.
For example, sound source (instrument/microphone), preamp, to an audio interface, to studio monitors, would be a typical home recording chain. As you can see, the preamp is very near the start, and the power amp is very near the end.
There can be variations, effects added to the chain, and so on, but the preamp and power amp will never stray far from their usual position.
The point is, while they both apply a gain boost to the signal, they do it for different reasons. Primarily the preamp is there to create a line level signal, but it can also add gain creatively to alter the base sound that the power amp will have to work with. Preamps can also generate distortion.
At the end of the chain, the gain added by the power amp is more about the final output because nothing else will shape the sound beyond that point.
It’s not just about the signal path and where the components are in the chain. Preamps do have other features and functions like phase invert and low-cut filters.
Do I need both?
Yes, you need both. When you look at them individually, you can see that each does the thing that the other can’t.
A preamp doesn’t have the power to drive a speaker; a power amp is needed for that.
A power amp expects a signal at line level; a preamp is needed for that.
You could technically go from a preamp, straight to active speakers without an external dedicated power amp. But, only because active speakers have built-in power amps for each driver. It wouldn’t work with passive speakers.
For more information, check out our article on differences between active and passive speakers.
Now that we can see a preamp and a power amp both have a crucial role to play, we can look at some different scenarios.
Home recording studio
If you are setting up a small home recording studio, you need a preamp and a power amp, but it’s possible you didn’t even realize it. The reason we say that is that audio interfaces have built-in preamps, and active studio monitors have built-in power amps.
When beginners think of a recording chain in it’s simplest form, it’s microphone/instrument to interface to DAW and studio monitors. So, even if you aren’t buying dedicated preamps or power amps, you still have them both.
It’s common to buy an external preamp even if your interface has built-in preamps, but the same doesn’t apply to external power amplifiers. Adding an external power amp before your active speakers could do some serious harm.
Guitar, bass, and keyboard amps all have a preamp and a power amp. In the case of an instrument amplifier, the preamp doesn’t just refer to the circuit that boosts the weak signal to line level. It refers to an entire section before the power amp that includes EQ.
So, the preamp here isn’t just a signal booster; it’s responsible for shaping the core sound of the instrument amplifier. You can see that the preamp and power amp position is still at the start and at the end of the chain, respectively.
Home stereo systems can be all-in-one or put together as a modular system through a collection of separate components. The great thing about going the separates route, is that you can mix and match components to build your dream system.
Preamps and power amps are two of the most important units, and again, the chain remains the same, with the preamp usually following the sound source and the power amp usually before the speakers.
In this scenario, you will have passive speakers, which means you have to use an external power amplifier because there is none built into the speaker.
It’s best to keep it simple; think of a preamp as the thing that preps the signal for the rest of your equipment and the power amp as the thing that prepares the signal for the speakers.
Even if you are making creative choices with your preamp, ultimately, it’s not definitive. The choices made at the preamp stage will then be affected by anything else that you have in your chain, whether that’s effects, your DAW, or just how the power amp and speakers interpret the signal.
Just know that they have some fundamental similarities and some major differences, but both are vital to any setup.