What Is a Preamp, and Do I Really Need One?

every audio system Requires amplification. In traditional hi-fi set-ups, loudspeakers are always “passive” – that is, they do not produce any power of their own. Instead, they must receive an amplified audio signal from an external source, called an amplifier, to do their job. Even in more modern, self-contained audio systems (for example, like the Sonos Era 100), the sound-producing drivers must be amplified to function—all of this happens in a single box, rather than hi-fi separates.

But if you’ve heard of amplifiers, you may also have heard of preamplifiers (often referred to as “preamps”) and wondered where they fit into an audio system, and whether you need one. Let’s answer those questions, shall we?

What does a preamp do?

An audio signal requires a lot of attention before it is ready to be amplified – so ultimately the question “What does a preamp do?” Broadly speaking, this has its own answer. A preamplifier takes care of everything that needs to be done before the audio signal (sent from the music source) is amplified and sent to the system’s speakers.

In self-contained audio systems like Sonos speakers, the preamplifier and amplifier are in the same enclosure, along with the speaker drivers that actually deliver the sound. Even in more sophisticated hi-fi separate setups, the preamplifier portion of the proceedings is still often housed within the amplifier, out of sight. This type of amp is known as an “integrated amplifier” and has both preamp and amplifier functionality.

However, some people prefer to separate this functionality, which is when you can view a preamplifier as its own piece of equipment paired with a power amplifier. In these cases, the preamplifier allows you to select the source of the music you want to listen to (most have a selection of input options to support systems with multiple sources), and also allows you to set and adjust the volume.

The preamp also ensures that the audio signal is at “line level” – that is, the standard voltage strength of the audio signal transmitted between the components – and sends it to be amplified, finally, ready to be carried forward to the speakers.

Does an external preamp improve sound quality?

Hi-fi orthodoxy says that individual functions in any system should be kept as separate as possible if the best results are to be achieved. The thinking is that, by keeping the electrical activity as protected and self-contained as possible, the audio signal has the best chance of remaining as pure and uncolored as possible.

By separating the preamplifier and amplifier functions into separate boxes, there should be a reduction in electrical noise and interference around the signal compared to having them all in a single box.