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.
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.
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.
Headphone amplifiers are usually all-analog devices in their most basic form. They are mostly purist units with a handful of line level inputs. Outputs can be more varied, with the traditional 3.5mm and 6.3mm jacks often complemented by various balanced options on some models.
It is certainly possible to buy digital-to-analog converters with headphone outputs (aka DAC/headphone amplifier) and the best of these can be exceptional performers. We’re thinking here of AudioQuest’s three-piece Dragonfly range (black, red and cobalt) or the great Mojo 2, Hugo 2 or the high-end Hugo TT2 from Chord Electronics. These DACs usually only have digital inputs, which range from a single USB (Type A) for the AudioQuests to the full range of coax, optical and USB for the Chords.
The advantage of this type of DAC/headphone amp combination is the potential to get better sound out of your digital sources, but that will only really happen if the device has better digital processing capabilities than the source you currently have. Something that is not always obvious.
Are there reasons not to buy a headphone amplifier? The extra cost may be a reason. It’s also another box that adds to the clutter of your system, especially if it requires additional cabling. Maybe your current setup sounds good enough, in which case you’re in luck!
It’s also fair to say that your headphones need to be of good quality before you can really enjoy the benefits of a headphone amp. Think of Austrian Audio’s Hi-X15 (£89 / $119 / about AU$160) or the similarly priced Grado SR80x as good starting points.
In most cases, we suspect that a carefully chosen headphone amp will be a significant step up from what you’ve got, and the sound improvements will easily justify the outlay.
Here are the best headphone amps out there
Or maybe you have one DAC/Headphone Amplifier combo instead?
These are the best wired headphones you can buy