What is a headphone amplifier and why should you buy one?

What is a Headphone Amplifier? It is an amplifier circuit designed specifically to drive headphones rather than speakers. That might sound like a simple enough task — after all, headphones are just little speakers, right? But perhaps because the job seems so simple, it turns out to be a bit of a blind spot for many manufacturers and is usually given a low priority.

While dedicated headphone outputs have faded from many phones (thanks for that, Apple), they still exist on a huge array of components that span the audio and video fields. And at the most basic level, they work. You plug in your headphones and you get sound. That may be enough for some people. But, you are reading Which Hi-Fi? and you know performance matters.

How does a headphone amplifier differ from a conventional amplifier? Speakers require more power than headphones, which makes sense when you consider the difference in the size of the room they operate in – consider a listening room compared to just your ear cavity. That vastly lower power requirement means that a headphone amplifier circuit must be designed to excel at low signal levels, and many simply aren’t designed to do that.

Wired over-ear headphones: Austrian Audio Hi-X15

Even affordable offerings like Hi-X15 from Austrian Audio benefit from a dedicated headphone amplifier (Image credit: Austrian Audio)

It’s not all about muscle, though, as the electrical load of headphone drive units is different than that of speakers. Most speakers have a nominal impedance of about 8 ohms, with some dropping as much as half. Headphones tend to have a lot more spread, usually from 16 – 600 ohms.

The amplifier designed to drive them should be happy with such a range of electrical loads. It’s not uncommon to find a device where the headphone input is simply a weakened version of the signal coming out of the speaker terminals. This is a cheap, easy, and ultimately limited way of doing things. Bad sound is usually the result.

iFi Zen Kan

iFi’s talented and affordable Can headphone amplifier (Image credit: iFi)

Buy a special unit and the story is very different. Here, the sound of the headphones has priority and therefore everything is done to get the best performance. The quality of the components is higher and the power supply is optimized for the task at hand. Essentially, everything is geared towards providing the best sound quality within the headphone’s operating range. Hand meets glove. Good examples of headphone amplifiers are the entry-level iFi Zen Can and the SPL Phonitor xe on the premium side.

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