Every audio system requires amplification. In a traditional hi-fi set-up, the loudspeakers are always “passive”—which is to say, they don’t produce their own power. Instead, they must receive an amplified audio signal from an external source, aptly called an amplifier, in order to do their thing. Even in a more modern, self-contained audio system (like the Sonos Era 100, for example), the drivers that produce the sound must be amplified in order to function—this just all happens in a singular box rather than across hi-fi separates.
But if you’ve heard about amplifiers, you may have also heard about 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 needs plenty of attention before it’s ready to be amplified—so ultimately the question “what does a preamp do?” broadly contains 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 onwards to the system’s speakers.
In a self-contained audio system like the Sonos speaker, the preamplifier and the amplifier are in the same enclosure, along with the speaker drivers that actually deliver the sound. Even in a more sophisticated hi-fi separates setup, the preamplifier part of proceedings is still often handled out of sight, within the amplifier. These types of amps are known as “integrated amplifiers” and contain both preamp and amplifier functionality.
However, some people prefer to separate out this functionality, which is when you may come across 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 music you’d like to hear (the majority have a selection of input options in order to support a system with multiple sources), and also set and adjust the volume.
The preamp also ensures the audio signal is at “line level”—that is, the standard voltage strength of an audio signal transmitted between components—and sends it on to be amplified, ready to be moved onwards, finally, 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 goes that, by keeping electrical activity as shielded and self-contained as possible, the audio signal has the best shot at remaining as pure and uncolored as possible.
By dividing the preamplifier and the amplifier functions into separate boxes, there should be a reduction in electrical noise and interference around the signal compared to having it all crammed into a single box.