Astell & Kern HC4 review: a petite but powerful DAC that sometimes oversteps the mark

Astell & Kern HC4: Two-minute review

Astell & Kern is no stranger to digital audio in all shapes and sizes, and the A&K HC4 is its latest attempt to coax worthwhile sound quality from your smartphone or laptop – and for good measure, it’s got strong gaming credentials too.

It’s a thoroughly specified little device, from its high-end AKM AK4493S DAC chipset via its balanced and unbalanced headphone outputs to its support for UAC 1.0 as well as UAC 2.0 to ensure compatibility with as many gaming devices as possible. Its aluminium construction looks and feels smart, too – so while there’s not much of it, the AK HC4 nevertheless appears to offer decent value for money.

And when it comes to its single function – taking the digital audio information from your source device and converting it to the analogue equivalent – there’s plenty to admire here. The HC4 sounds big and organised, and extracts a lot of detail from a recording – it’s a peppy and informative listen. It overplays its hand somewhat where the highest frequencies are concerned, though, giving treble sounds a rather insubstantial and unyielding edge that is at odds with the rest of the work it’s doing. In a competitive and saturated market, then, does the A&K's plucky performance still make it one the best portable DACs going for the money? Let's see. 

Astell & Kern HC4 review: Price and release date

• Released in November 2023 
• Priced at $220 / £219 / AUS399

The A&K HC4 portable headphone amp/DAC is available now for $220 in the United States, £219 in the United Kingdom and in Australia, it'll cost you AU$399 or somewhere closely in that region.

The world is hardly short of portable USB headphone amp/DACs, though, and while the A&K refreshingly undercuts the $499 / £449 / AU$769 iFi GO Bar Kensei, it's still dearer than the five-star iFi hip-dac 3 (which can be yours for $199 / £199 / AU$349). 

So, competition is fierce at the level, and missteps will likely have repercussions. 

Astell & Kern HC4 review: Features

• AKM AK4493S DAC chipset
• 3.5mm and 4.4mm outputs
•  ‘Digital Audio Remaster’ technology

When it comes to features, you don’t have to read all that far down the HC4’s spec-sheet to realise that Astell & Kern is deadly serious. By prevailing standards, the feature-set here is formidable. 

The main business is taken care of by an AKM AK4493S DAC chipset that’s more commonly found doing its thing in (among many other devices) Astell & Kern’s well-regarded and witheringly expensive digital audio players. It’s compatible with every worthwhile digital audio file type, and is capable of dealing with content of up to 32bit/384kHz and DSD256 resolution.

Getting the information into the HC4 in the first place happens via the USB-C slot on the bottom of the device - Astell & Kern provides both USB-C / USB-C and USB-C / Lightning cables to get the job done. Getting it out again happens using either the unbalanced 3.5mm socket or the balanced 4.4mm equivalent on the top – it’s worth noting the 4.4mm output only supports five-pole jacks. 

Another feature Astell & Kern has incorporated from its pricey digital audio players is ‘digital audio remaster’ technology – it is designed to upsample the native sample rate of the source material to go beyond the limits of the source format. Sounds like quite a trick, doesn’t it? Astell & Kern reckons it delivers – and I quote – “more refined playback and… a delicate, analogue-like sound”. 

And by way of an encore, Astell & Kern has ensured the AK HC4 is compatible with as wide a selection of devices as possible by making the device’s USB-C input supports UAC 1.0 as well as UAC 2.0. Almost every smartphone, laptop and tablet supports UAC 2.0, but there are plenty of gaming devices that are still UAC 1.0 – but if you want a low-latency connection to your Playstation, Switch or what-have-you, the HC4 has you covered.   

Features score: 5 / 5

Astell & Kern HC4 review: Sound quality

• Detailed, informative sound
• Open and well-defined presentation
• Slightly skewed towards the top end

The AK HC4 is an admirably consistent device. During the course of this test I listened to 16bit/44.1kHz and 24bit/96kHz FLAC files via the Tidal app, loaded onto both iOS and Android smartphones, as well as some DSD128 stuff stored on the internal memory of a MacBook Pro. And while there are, of course, advantages to the higher-resolution stuff, the Astell & Kern doesn’t really alter its overall stance no matter what standard of content you’re listening to or the type of music you enjoy. Its fundamental attitude is always the same.

And in broad terms, it’s a revealing and explicit attitude. No matter if it’s the voice-and-guitar intimacy of Lua by Bright Eyes or the rather more complex Dirty Paws by Of Monsters and Men, the HC4 is able to see to the bottom of the mix and return with all sorts of information regarding tone and texture you may not previously have been aware of – certainly not if you’ve been listening directly from a smartphone to some wired or wireless headphones before now. 

Throughout the frequency range, detail levels are sky-high – and rather than draw attention to how clever and insightful it is, the HC4 puts everything into the correct context in order to poverty serve the recording. It’s dynamic both in the sense of ‘quiet/LOUD’ and where harmonic variations in a strummed guitar are concerned. And it creates a big, well-defined and easy-to-follow soundstage, and lays out a recording explicitly – but it doesn’t make any part of a recording sound remote from any other. There’s a singularity and idea of ‘performance’ to the sound of the HC4 that’s as enjoyable as it is impressive.

Low frequencies are substantial and properly controlled, so there’s never an issue where rhythms or tempos are concerned. The midrange is perhaps the greatest beneficiary of the A&K’s powers of analysis – there’s a stack of information about a vocalist available, and it makes for an immediate and positive description of a singer’s abilities and motivations.

It’s only at the top of the frequency range that things are anything less than fully impressive. There’s a glassiness and a rather relentless edge to the way the HC4 serves up treble information that a) puts it at odds with the rest of the frequency range where tonal balance is concerned, and b) discourages the listener from increasing volume levels much beyond ‘moderate’. The relative hardness and lack of substance to the top end makes those recordings with a high-frequency emphasis sound edgy – and overall it doesn’t make for all that relaxing an experience.  

Sound quality: 4 / 5 

Astell & Kern HC4 review: Design

• 65 x 30 x 15mm (HxWxD) 
• 31g 
• Aluminium construction

There’s usually not a lot of scope for ‘design’ to happen when a product ideally needs to be as light and compact as possible. But this is Astell & Kern we’re dealing with here – you won’t be surprised to learn that the company has given it a good go where ‘design’ of the AK HC4 is concerned.

The all-aluminium construction keeps the weight of the device down to a trifling 31g. It also allows for a hint of the trademark Astell & Kern angularity on the top surface, and for the sides to be mildly curved in order to make the HC4 easily graspable. 

One of the curved sides features a shallow rocker switch and a DAR on/off slider. At one end of the chassis there’s the USB-C input, and at the other end the balanced 4.4mm and unbalanced 3.5mm outputs. Apart from a tiny LED (which lights up in white to indicate standby, red for PCM and blue for DSD audio files), that’s your lot. And frankly, I am tempted to ask what else you might reasonably be expecting? 

Design score: 5 / 5 

Astell & Kern HC4 review: Value

• Priced in line with rivals
• Not a nailed-on winner

Just as you can’t judge a book by its cover, you can’t judge the effectiveness of a piece of consumer electronics simply by how big and/or heavy it is. The AK HC4 may not look like much, but the effect it can have on your listening experience can’t be denied – so in this respect, it represents decent value. 

When you compare it to the best of its rivals, though, it ceases to be a nailed-on favourite and becomes more of an interesting option… which probably undermines its value-for-money credentials somewhat.

Value score: 3.5 / 5 

Should I buy the Astell & Kern HC4 review:?

Buy it if...

Don't buy it if...

Astell & Kern HC4 review: Also consider

Helm Audio Bolt
The Helm Audio Bolt doesn't have the metallic style of the A&K HC4, but it’s a very effective device in its own right and a fair bit more affordable. 
Read all about it in our Helm Audio Bolt review.

iFi hip-dac 3
Now, you do get the looks; it's even styled like a hip-flask. This likeable, cheaper DAC won't fit in your pocket quite as easily as the A&K HC4 but it's nothing if not a conversation starter – and a talented one soncially at that.
Read our in-depth, five-star iFi hip-dac 3 review.

How I tested the Astell & Kern HC4

• Used for over a week (after a thorough running in)
• Tidal and Qobuz were go-tos, using various headphones/IEMs

I spent over a week listening to the Astell & Kern HC4, using Apple iPhone 14 Pro and Samsung Galaxy S23 smartphones. I connected it to Sennheiser IE900 in-ear monitors via its 4.4mm balanced output and to a pair of Grado SR80x using its 3.5mm connection. 

I used it at home, navigating traffic, and on the train. I listened to music almost exclusively from Tidal and Qobuz (since these streaming services are full of high-resolution content and 24bit/192kHz standard), and I made sure to check for connectivity and cable noise as I did so (you're fine there). 

• First reviewed: June 2024
• Read TechRadar's reviews guarantee