Headphones don’t always get the partnering equipment they deserve. Here’s how to change that
In the language of hi-fi, the name ‘headphone amplifier’ is more likely to raise a puzzled frown than a nod of recognition. And yet, a headphone amplifier simply does what it says on the can – it is an amplifier circuit that is specifically designed to drive headphones rather than speakers. That might sound like a simple enough task, but few manufacturers make it more than a low priority.
While dedicated headphone outputs have faded from many phones (thanks for that, Apple) they still exist on a huge array of audio and video components. And at a basic level they work; you connect your headphones and you get a sound. That might be enough for some people; but you are reading What Hi-Fi? – you care about sound quality.
Look out for the signal
How is a headphone amplifier different from a conventional amplifier? Speakers require more power than a pair of headphones, which makes sense if you think about the difference in size between a listening room and your ear cavity. That vastly lower power requirement means that a headphone amplifier circuit has to be engineered to excel at low-signal levels, and many simply are not designed to do that.
Made to measure
It is not just about muscle though, as the electrical loading of headphone drive units is different from that of speakers. Most speakers have a nominal impedance of around 8 ohms, with some falling to half of that. Headphones tend to have far more of a spread, typically going from 16-600 ohms.
The amplifier designed to drive them must be happy working with such a range of electrical loads. It isn’t uncommon to find a unit where the headphone feed is simply an attenuated version of the signal coming out of the speaker terminals. This is a cheap, easy and ultimately limited way of doing things. Poor sound is usually the result.
Buy a dedicated unit and the story is very different. Here, headphone sound is the priority and so every care is taken to get the best performance. Component quality is higher and the power supply is optimised for the task at hand. Essentially, everything is geared towards delivering the best sound quality inside the operating range of the headphones. Hand; meet glove. Good examples of this include the entry-level iFi Zen Can and, on the premium side, the SPL Phonitor xe (see main pic).
Headphone amplifiers tend to be wholly analogue devices in their most basic f
