Astell & Kern AK HC4 review: does fourth-gen DAC bring the finesse?

Astell & Kern has been a portable digital audio hero for quite some time now, and if you're not quite ready to drop a chunk of money on one of its dedicated digital audio players the company has a plan to turn your smartphone into a valid source of music instead by making some of the best headphone DACs available. 

The AK HC4 on review here, as the name strongly implies, is not the company's first attempt at a portable USB DAC-meets-headphone amplifier, but it's definitely the most thorough yet.

So as long as the AK HC4 has what it takes to blow plenty of well-regarded and high-achieving competition out of the water, it'll be 'job done'. So, is fourth time around an all-out success? 

Astell & Kern AK HC4: Price & Availability

The Astell & Kern AK HC4 USB DAC/headphone amplifier is on sale now, and in the United Kingdom it costs £219. In the United States it sells for $219, while in Australia it will set you back AU$399.

As is usual with products like this, the AK HC4 doesn't look like an awful lot of stuff for the money. But when you bear in mind that brands as credible as AudioQuest, Creative Labs and iFi (to name just three) are ready to part you from quite similar money for a similarly compact alternative, it becomes apparent that this is simply the going rate.

Astell & Kern AK HC4 review: Features & What's New?

'If it's good enough for a digital audio player, it's good enough for a USB DAC' – this would seem to summarise the thinking at Astell & Kern where the AK HC4's feature set is concerned.

Especially where the actual DAC chipset is concerned. Admittedly there's only one AKM AK4493S here, where an A&K DAP might deploy as many as eight, but nevertheless this is a component with a powerful reputation. Its appearance in a (reasonably) affordable USB DAC/headphone amplifier is to be applauded – doubly so when you consider its compatibility with every worthwhile digital audio file type and its ability to handle content of up to 32bit/384kHz and DSD256 resolution.

Getting the digital audio information into the HC4 happens via the USB-C slot on the bottom of the device – and it's well worth noting that it supports UAC 1.0 as well as the more common UAC 2.0 standard that the majority of smartphones, laptops and tablets use. This means the HC4 is compatible with a very wide range of gaming products and audio equipment – so if you want to put a low-latency rocket up the sound of your Nintendo Switch, Sony PlayStation 5 or whatever, the HC4 is ready to do so.

Getting it out again once the AKM DAC has been at it can be done via the unbalanced 3.5mm or 4.4mm balanced outputs on the top of the device. This opens up the HC4 for use with rather more capable headphones than might be considered the norm (check out T3's best wired headphones guide for some high-end options) – but it's worth noting the balanced output is only compatible with five-pole jacks. 

Astell & Kern has also included the 'digital audio remaster' technology that features on some of its expensive digital audio players. It's designed to upsample the sample rate of the source material beyond the limits of native format – and the upshot, at least according to A&K, is "more refined playback" and "a delicate, analogue-like sound". 

Astell & Kern AK HC4 review: Performance

It's not even as if you have to go to town where your digital audio files are concerned for the AK HC4 to make a big difference to your experience. Even when given CD-standard 16bit/44.1kHz stuff to deal with, it makes its presence felt – and if you do decide to up the ante with some 24bot/192kHz content, it's capable of leaving the unassisted sound of your smartphone for dead.

It's a big, spacious listen, able to create a large and plausible soundstage – even complex, instrument-heavy recordings will find more than enough space to lay themselves out coherently. Despite all of this breathing space, though, the HC4 never sounds less than unified and 'together' – there's nothing remote or disjointed about the way it presents music. There's a wholeness and singularity that makes every recording – even a cut-and-paste hip-hop collage – sound of a piece.

Low-frequency response is substantial, but not lead-footed – for all of the body the Astell & Kern can give to bass sounds, it controls attack with real authority, and so rhythms always sound positive. The midrange is similarly confident, and the amount of detail (both broad and fine) the HC4 is able to extract at every turn means it paints a vivid and informative sonic picture.

Detail retrieval and overall insight extends to both transient information at the very edges of a recording and to the harmonic variations apparent in, say, a solo piano recording. At the opposite end of the scale, there's more than enough headroom to put significant distance between the quietest, most contemplative moments in a recording and the loudest, most intense equivalents.

For the most part, the tonality is quite carefully neutral and, also for the most part, integration of the frequency range is smooth. Problems, such as they are, are all at the top end.

The HC4's treble response lacks a lot of the substance it gives to everything below here, and top-end tonality takes a turn for the chilly at the same time. There's a rather hard, edgy character to the higher frequencies that can turn actively unpleasant if you decide to listen at properly indiscreet volume levels. And even if you're listening at realistic volumes, the glassiness of the Astell & Kern's top-end sets it at odds with the nicely balanced and realistic frequency information beneath.    

Astell & Kern AK HC4 review: Design & Usability

Astell & Kern is to be congratulated on managing to make a product that is, by necessity, as small and light as it can be and look unarguably like an Astell & Kern product (or, perhaps, like a small part that's fallen off a Tesla Cybertruck).

At 65 x 30 x 15mm (HxWxD) the HC4 is easily pocketable, and its all-aluminium construction means it tips the scales at a paltry 31g. Some trademark A&K angularity is visible on its top surface (which also includes a tiny LED to let you know if you're listening to PCM or DSD content), and the device bows inwards slightly along its sides to make gripping it a bit easier. 

Apart from a 'DAR' on/off switch and a 'volume up/down' rocker along one side, that's really it as far as design goes. And as for usability, well, I almost hesitate to tell you to plug it into a source of music at one end and a pair of headphones at the other – because that's really all there is to it.

Astell & Kern AK HC4 review: Verdict

If you've been plugging your headphones directly into your smartphone, tablet or laptop, the sonic improvements the AK HC4 is capable of delivering have to be heard to be believed. 

Yet because of its strident top-end response, it's not perfect – and it leaves the door open to quite a few price-comparable rivals as a result. 

Also consider

Yes, it's a chunk more expensive than the Astell & Kern – but iFi's GO Bar is so poised, so insightful and so across-the-board convincing that it's possible to overlook its impenetrable user interface and relatively chunky dimensions. 

If you'd rather spend a bit less, however, then AudioQuest's venerable Dragonfly Red is well worth considering. It may sound rather unspectacular on first acquaintance, but that's just because it's so nicely balanced.