The terms sound similar, but the two devices perform different functions.
If you’re setting up a studio, whether professional or just for fun at home, you have undoubtedly come across the terms amp and preamp.
And naturally, you’re wondering what the difference is.
More importantly, do you need one, or both, of them?
Good preamps and amps are not cheap, so you definitely don’t want to end up buying equipment you don’t actually need.
So let’s get to it.
First of all, I want to clarify that amp and poweramp are interchangeable. Those two are the same thing, so there aren’t, in fact, three devices to worry about.
Let’s begin by looking at the differences.
Preamplifier Vs. Power Amplifier
The basic difference is this: a preamp boosts a weaker signal to line level, while an amplifier boosts a line level signal so that it can be sent to speakers.
For example, a microphone outputs a very weak signal that needs to be boosted to the same level as other signals by a preamplifier, before it can be processed by another device like a mixer, receiver or amplifier. Once it is at the same level it can be processed with other input signals and sent through the power amplifier to a set of speakers.
Now you’re probably wondering why you need two seperate devices for this.
Can’t you just use an integrated unit that includes both poweramp and preamp?
You can, but the reason the preamp is generally kept separate is to keep it away from the noise generated by the large transformers in a poweramp. A preamplifier uses little electricity, while a power amplifier uses a lot and generates a lot of heat as well.
If you want to know more about the function of a preamp, read this article: What Does A Mic Preamp Do?
Preamp Vs. Interface
An audio interface allows you to connect microphones, instruments and other audio equipment to a computer. Audio interfaces have built-in preamps and these usually do a perfectly fine job. If you have a quality interface, you do not need to get a separate preamp.
The only reason you might want one is if you prefer a preamp that colors the sound. The pres included in audio interfaces are always perfectly transparent, i.e. they transmit the sound faithfully and do not color it with a warmer, vintage tone like some preamps do.
Preamp Vs No Preamp
If you have a microphone or other device with a low signal strength, you need to boost that signal to line level using a preamp. If you don’t the resulting output will sound terrible.
That said, if you have an audio interface, it will already contain a preamp, so you don’t need to buy one separately. The same goes for many mixers or other devices. Chances are, they have a built-in preamp.
Where does a preamp go?
If you get a preamplifier, you need to know where to place it in the signal chain.
We are going to be using a microphone preamplifier as the example here, since it is the most common use. But the general order is always the same.
Basically, since the preamp boosts a weak signal to line level, we want to place it near the start of the chain so that it can receive that weak signal. In other words, you plug your microphone directly into the preamp’s mic input.
Any number of devices can come after the preamp. Most commonly, you might plug it into a mixer, an interface, a receiver or a power amp.
How to Connect a Preamp to an Interface
Remember, an audio interface contains a preamp, so you want to make sure you don’t run the signal through two of them.
This causes distortion and just sounds bad, but is a very common mistake with preamp to interface connection. So make sure you plug the preamp into the line input of the interface and not the mic input.
How to Connect a Preamp to a Receiver
This is the same as for the interface: the preamp plugs into one of the line inputs (sometimes labeled aux in). If you are plugging in a turntable, it goes into the phono in plug, which leads to a phono preamp in the receiver.
If the receiver does not have a phono preamp and the turntable does not either, you’ll need a separate device.
The record player then plugs into the input on the phono preamp and the output from that goes into one of the line inputs on the receiver.
You may also need to connect the turntable’s ground wire to the grounding post on the preamp (not all turntables have a ground wire).
How to Connect a Preamp to a Mixer
Again, there is no difference. The preamplifier plugs into one of the line inputs on the mixer.
How to Connect a Preamp to an Amp
This is quite simple. Plug the cable into one of the outputs on the preamplifier and into the corresponding input on the amplifier (usually marked with letters).
Preamp to Amp Cable
You can use either XLR or RCA cables to connect a preamp to an amp. For more on the different types of cables, check out this article on Yamaha’s website.
What Is Preamp Out And What Are Preamp Outputs Used For
This is a very common question, so I decided to address it here. First of all, we want to distinguish between this output on a receiver and on a guitar/bass power amp.
How Do Preamp Outputs Work On A Receiver?
On a receiver, these outputs are meant to be connected to an outboard amplifier.
If you want something more powerful than the amp built into the receiver or if you just want to take some of the load off the receiver, you can connect to a separate amplifier to power the speakers. The pre-outs are also used to connect to a powered subwoofer (and are often labeled as such).
What Does Preamp Out Mean On A Poweramp?
On a guitar/bass poweramp, the preamp out/poweramp in is meant to work as an effects loop or to daisy chain a number of amplifiers together.
Here is a video that might help explain things