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Astell&Kern AK100 portable player
Using The Player
Sound Quality
Measured Performance
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Astell&Kern AK100



Able to play top rate digital files, the Astell&Kern AK100 is a portable player with a difference, Noel Keywood finds.


This tiny music player fitted my shirt’s top pocket, making for a short connection to a pair of headphones I could barely take off. The reason being it offers top digital quality, far better than CD or most other players on the market. The Astell&Kern AK100 is a high definition portable audio  player – think iPod – of super high quality. Although a portable to make others weep, it can also drive a hi-fi system – it’s been designed to do so – providing better sound quality than CD.
    Measuring just 80mm high, 65mm wide including the protruding volume control button, and 15mm deep, the AK100 is one small player. It plays music stored on 32GB of internal memory or from two micro-SD cards that can be inserted into slots in the player’s base, behind a small sliding door. At around 100MB per 24/96 track that amounts to ten tracks per GB, so a 32GB card (£18 or so) will hold around 320 songs, meaning the player can tote around 1000 songs maximum, using two 32GB cards in addition to its own memory. That’s plenty enough for most people.

   The AK100 is basically a portable music player with a single 3.5mm headphone socket. Controls are few. There is a big rotary volume control at right, pause/play and forward and backward skip buttons at left, plus an on/off button on top. The buttons are small and sit almost flush. The combination headphone socket contains an optical S/PDIF digital output for connection to an external hi-fi digital-to-analogue convertor. You need an adaptor to plug in an optical cable, but many leads come with them as standard. Unusually, there’s an optical input too, so the player can be used as a DAC, but it cannot record through this input.
    On the base is a micro USB port for connection to a computer and to charge the internal battery; the importers tell me that audio is available through this connection too. It takes around 5 hours to accept a full charge and the battery is not removable, so you cannot carry spares. A USB socket able to deliver enough current to support charging is needed, which usually counts out keyboard outlets and such like. Our player was reluctant to charge fully overnight on a computer hub outlet, but charged fast from an iPhone charging unit (£15). A small battery indicator icon turns from red to white when charged, but shows nothing in-between, unlike most battery indicators. After some use to cycle the battery we recorded 8hours 20mins continuous playing time, playing one song on repeat, with display off, but the importers claim 10hours and Astell&Kern 16hours. The discrepancy may be explained by variability between batteries, since the chemistry of small Lithium Ion batteries is unpredictable.
    The instructions, which you can download from, mention little of this, which wasn’t helpful, and they failed to mention many peculiarities, such as the player being switched on before it can be recognised by a computer.
        The front carries a bright touch screen that needs a quick stab to work, or it remains unresponsive. Stab it whilst playing, to move from full colour cover artwork to play controls, pause/play, skip forward or back. These duplicate the function of the play buttons, so there are two control options. There is no external remote control option in a headphone lead extension, so you have to reach into your pocket to start, stop or adjust volume.
    There is, however, a Bluetooth short range radio transmitter that enables wireless connection to the hi-fi if you have a Bluetooth receiver, but Bluetooth works at CD quality (16bit) compressed to reduce data rate. High resolution 24bit files will play but their quality isn’t maintained. Degradation from 24bit to 16bit, through word truncation, is not drastically obvious, but there is an appreciable difference between the two: 24bit is smoother, has more low level detail and sounds less ‘barren’. Bluetooth connection is a convenience; the optical S/PDIF output supports full 24/192 quality measurement showed.
    The AK100 is one of few portable players available able to play top resolution 24bit/192kHz sample rate files through its internal Wolfson DAC. Generally, 24/96 is plenty enough resolution for headphones of good quality, the advantages of 192kHz are hardly audible, but file sizes are double those for 96kHz sample rate: think 200MB or so. But some may want 24/192 when driving a top quality hi-fi system. Whatever the practical issues, the time is approaching when 24/192 is a must, simply because the hardware exists and companies like iriver are using it.
    An on-screen display flags up bit depth and data rate in small orange text, and the player also makes all high resolution music files available through a folder labelled Mastering Quality Sound, which strikes me as a nod to Apple’s requirement that studios provide 24/96 Masters for iTunes, even though Apple do not, as yet, offer such quality. The days when studios are able to provide pristine studio masters direct to listeners are here though, it’s just that the world has to catch up and the AK100 is part of this process.
    The AK100 plays WAV, FLAC, WMA, Ogg and MP3 music files now, and all future AK100s will also be loaded with Apple AAC, ALAC and AIFF files, Astell&Kern tell us, these being downloadable from the iRiver web site for older AK100 units.
    The sheer quality of the AK100’s replay circuits, from its high quality Wolfson DAC, to its unusual headphone amplifier appreciably improved sound quality I found, even from MP3s and the like; this player does improve on other portables. The reason is simple, substantial and significant: the AK100 is more a ‘CD player’ than a portable. Where portables always use cheap low quality DACs and weedy headphone amps that deliver 0.3V, the AK100 has a top quality Wolfson DAC on board and delivers no less than 1.55V from its headphone socket, little less than a CD player. And you can hear this, not just as greater volume but as vast dynamic range. Headphone amps are constrained by hiss at low levels and by distortion at high levels, and they are all the same, because group-think and aural safety make them that way. I was quickly aware, before I measured the AK100, that it doesn’t have the usual noisy headphone amp and the shaky quality they possess – more of which soon.


Initially I found the AK100 difficult to use. The instructions do not explain basic menu structure and its logic, simple operational sequences such as hooking up to a computer or even which operating systems are compatible. Providing it is switched on, the AK100 comes up on a Mac or a PC as external memory, like a memory stick. Files can be quickly saved or deleted into its folders. Neither my Macs (Snow Leopard and Lion) or Windows System 7 on a Mac’s Bootcamp sector had any problem seeing it. Music player software is available for PC only, but it installs Active X files and System 7 spewed out warnings.
    Switch on is slow as the internal DSP winds up, lasting 30 seconds, and I found operational sequences less obvious than you’d expect from an iPod for example, but this is a matter of familiarity. After learning its operational methodology I found the AK100 easy and fast to use, although if I missed the graphic screen controls it would change screens, and this is why the small hardware buttons are provided. The capture area of the screen buttons needs expanding to reduce this irritation.
    The player is beautifully built: its machined alloy case feels rigid and solid; its buttons have a short, firm action. Warnings are automatically provided for most actions. So when I plugged an optical lead (with adaptor) into the input the AK100 detected it and re-configured itself as a DAC, providing an on-screen warning. The underlying hardware/software interface is very well thought through and intelligent, but this is a specialist machine and the screens are opaque in meaning and in logic sequence.

    There are lots of nice details though, including a large on-screen digital volume readout (0-75) accompanied by a graphic display, the valuable bit depth and sample rate readout that warns of truncated or rate changed files (this happens a lot during computer processing but few realise it) and there is even a graphic equaliser.
    This player has been designed as a portable hi-fi player – think super CD player – rather than an iPod rival; it isn’t simply an upmarket portable. So I used it to drive a variety of systems, including the new Quad 2812 electrostatic loudspeakers featured in this issue, a pair of Martin Logan Electromotion electrostatics, and two home systems, one AV and the other stereo with a WAD 300B valve amplifier and WAD KLS9 loudspeakers.  The point being that to appreciate what the AK100 can do means using a top quality replay chain. But I kicked off with headphones and some properties were immediately obvious.


Initially, before measuring or spending time with the AK100, I grabbed a pair of lightweight Jays V-Jays ‘phones used when travelling, to sort out this player’s menu structure and foibles. With a slew of songs externally dumped onto a 16GB (faster than 32GB) Kingston memory card, casual listening in a quiet room made obvious the AK100 has a darkness to its silences and a sense of silky smoothness, almost a warmth. I found myself winding volume right up, the sound was so clean, then winding it rapidly back down as crescendos loomed! In this sense it is like a very clean hi-fi system that encourages the volume to be wound up – and you only realise how loud it is when someone tries to speak. This happens because the ear judges volume by distortion; lower distortion and 'loud' does not seem it.

   I found out later, during measurement, that the AK100 really does go hugely loud, arguably too loud for headbangers glued to headphones. It’s output is way above that of volume-limited portables and it is easy to turn right up. But boy is it enjoyable! (hearing damage results from continuous listening at high levels).
    I switched to a pair of Sennheiser HD650s and it all got much better, greater dynamic scale, firmer bass and more extended treble becoming obvious in particular. However, swapping between various headphones and then moving onto a Marantz SR8002 receiver in an AV system with Martin Logan Electromotion electrostatic loudspeakers up front made clear that headphones don’t fully reveal the AK100’s potential, unless you use Stax electrostatic ‘phones perhaps, – not too easy on the move. But the message is the AK100 is way above a normal portable in quality terms, in another league in fact. You can detect its ability even through budget travelling ‘phones of decent quality.
    I use my Marantz receiver as a test mule, because its internal 24/192 DACs and amps are clean and revealing, and its connectivity broad in conjunction with a Cambridge Audio Stream Magic 6 network player with BT100 Bluetooth receiver.
    Running Bluetooth first, the player paired immediately and was playing within ten seconds or so. Again its smooth, almost silky quality was obvious, characteristic of ‘digital done properly’, meaning not CD. Violins hung in space and were clear and stable, and also clearly separated from each other when playing Trondheim Soloists Divertimenti (24/192) through the Electomotions.
    Swapping over to a direct optical connection brought out greater low level filigree detailing and a stronger sense of depth and space to the sound stage, putting the many players into more easily identified positions.
    The same was true of Rock, kick drum sounding firm, brushed cymbals shimmering with fine detail in Misery, from Dave’s True Story. A set of Eagles rips from Long Journey Out of Eden sounded as gently smooth and transparent as they do through the best DACs. Even when working from internal battery power, that tends to compromise bass push, bass was firm.
    Running digitally from the optical output of the player uses the receiver’s DACs, the AK100 becoming a portable digital source. Connecting the headphone output to the receiver’s analogue inputs (using Pure Direct mode to bypass the DSPs and snuff the displays), to assess its own 24/192 DAC produced very similar results, the player’s on-board DAC sounding creamy smooth and utterly svelte.
    I later used the AK100 as a top quality digital ‘CD player’ like this to drive our Icon Audio MB845 MkIIm valve power amplifiers direct, connecting through a 3.5mm-to-phono socket headphone output adaptor and, ultimately, driving Quad ESL-2812 electrostatic loudspeakers. This demonstrated just how smooth and well separated the strings of the Trondheim Soloists were in glorious 24/192, and Rebecca Pigeon had a breathy presence between the loudspeakers singing Spanish Harlem. There was silky dark silence behind Amber Rubarth singing ‘Storms are On the Ocean’ and a lovely stable, solid feeling to her image between the loudspeakers. The AK100’s internal Wolfson DAC offers glorious results, perhaps helped by being battery driven and free from earth currents, hum and noise.
    This is a top quality, high definition music player, one that can be connected up to a hi-fi through its headphone output. The AK100 is no ordinary portable, that’s for sure.


The AK100 is at heart a wonderful digital source player, deeply engineered in a unique fashion. It’s best seen as a portable high resolution ‘CD player’, masquerading as an MP3 player. I used it as such through its headphone outlet and got spectacular sound quality from high resolution 24/96 and 24/192 digital recordings. It’s very well made and finished and it works well too, but it does have a few frustrating weaknesses.
    The issue of charging needs improvement and some useful instructions produced. A charge indicator would help.
    Such idiosyncrasies apart the Astell&Kern AK100 is an astonishing player, with fabulous sound quality and an amazing spread of ability as a source. It’s a must have in fact.

Astell&Kern AK100  £569

A portable high definition player with fabulous sound quality. Awesome, if with irritations.

- sound quality
- small size
- connectivity

- poor charge display
- brief instructions
- no charger supplied

Air Audio Distribution
+01491 629 629

Rohde & Schwarz UPV audio analyser


The headphone output of this player delivers 1.55V, close to (-2dB) the 2V of a CD player and much higher (+14dB) than the usual 0.3V of a typical portable player. The DAC and output amplifier were far quieter than the norm for portable players too, noise measuring -110dB when playing a notched out -60dB tone (24bit), to avoid output muting. These are exceptional figures for a portable and are comparable to a hi-fi DAC. As a result EIAJ Dynamic Range measured no less than 110dB with 24bit, again on par with a good stand-alone DAC.
    The headphone output performs as well as a high quality analogue line output and can be used as one. These results were from test files, but the optical input gave almost identical (a tad better) results.
    Frequency response was flat from 4Hz to 71kHz (-1dB) with a 192kHz sample rate signal, as the analysis from our Rohde & Schwarz UPV analyser shows, so again the analogue headphone output performs as well as a quality DAC.
    Distortion at -60dB was low with 16bit, measuring 0.18% and similarly low with 24bit at 0.06%, the distortion analysis shows. This result and low noise both contributed to the player’s high EIAJ Dynamic Range figures.
    Jitter on the digital output was low in all respects, low rate clock wander coming in at 40pS, uncorrelated jitter hovering at 4pS and signal related jitter (1kHz, -60dB test tone) measuring 18pS. These figures better most CD players, matching the best.
    The AK100 produced exceptional results for a portable player. It has massively greater dynamic range, lower distortion and negligible jitter than typical portables, measuring as well as a high quality stand-alone DAC. It’s a portable hi-res player that approaches the limits of what is possible. NK

Frequency response (-1dB)
192k sample rate    4Hz-71kHz
Distortion (16 / 24bit)    %
0dB        0.0006/0.0006
-60dB    0.18 / 0.06
Separation (1kHz)     108dB
Noise (IEC A)    -110dB
Dynamic range (16/24)    102/110dB
Output    1.55V


FREQUENCY RESPONSE, 192k sample rate    (what it means)


DISTORTION, 24bit, -60dB    (what it means)



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