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Ken Ball of ALO Audio is a Portland/Oregon-based retailer and manufacturer of headfi kit. Having bought from him many upscale headphones and replacement harnesses over the years, Ken has become a trusted fount of knowledge in this sector: "I've used the AK100 for over a month now. We do sell it so I can't claim no bias. On the other hand we don't carry products we don't thoroughly love. And the iriver I thoroughly love for several reasons. I think it's somewhat of a transformative portable hifi product. I have a large collection of 16/44 Apple lossless files. When on the go I use those. I also have a collection of 24-bit FLAC files. Because I've had no access to a FLAC player that didn't come with an assortment of disagreeable complications, I didn't really use those files for personal audio. When the guys at iriver popped into my shop a few months ago and let me kick the tires out of the AK100, I was able to load up my 24-bit FLAC files along with similar 16-bit material. The benefits of 24 over 16 bits were apparent and quite enjoyable. Moreover the GUI of the player was intuitive and satisfying. To edit meta data for FLAC files I like Swinsian which is also an excellent high-res player. There's also this.
AK100 + Rx MkIII
"With the AK100 my giant triple-decker portable brick of iPod, Algorhythm Solo and ALO Audio MkIII headphone amp is significantly reduced. Now I use the iriver with the RxIII or our new International DAC/amp. I've found 24-bit files off the iriver to best all 16/44 files from an iPod/Solo combo. Plus it's a less bulky setup with one less interconnect and one less battery to worry about. I have all of my album art loaded to my AK100. I use 2 x 64GB microSD cards plus the internal 32GB for 160GB of 24-bit action.
"The iriver lets me know what resolution and type of file is playing and easily sorts files by resolution. Basically it's all of the ease of working with an iPod in a smaller package and at 24 bits. IMO the AK100 really shines on such material. The only real present prohibition is the shortage and expense of 24-bit music. But I bet we'll be seeing a lot more released in the near future. Incidentally Vinnie at Red Wine Audio is doing a mod* for this player to improve its headphone output stage. The stock output is good but won't get loud enough for some of my 'phones. So I use the player's headphone output with the volume turned up all the way, then send the signal to my RxMkIII amp via a right-angle mini-to-mini link. That's awesome."

*"We bypass the 22Ω resistors in the output stage and hard-wire Cardas copper litz solid core wire from the output FETs directly to the pins of the headphone jack for the shortest cleanest path.
AK100 + International

"This also bypasses tiny circuit board traces and the header connecting main board to smaller headphone jack board. Output impedance is now <1Ω. This is by far the most natural sounding DAP I've heard! It's smaller and lighter than an iPod and super quiet. The built-in head amp drives all IEMs with ease and most full-sized 'phones to adequate levels. There are layers and layers of detail and nuance unraveled. The AK100 also is a fine source for a portable headfi amp. Its volume sets the output level of the Wolfson chip outside the signal path and the mini 24/192 Toslink output blows away the mini Toslink of the Macbook Pro. Be sure though to use proper glass-fiber and not cheap plastic optical cable."

"I think it's going to be an interesting 2013 to see how these small high-resolution players battle each other. The $829 iBasso DX100 is the iriver's strongest competitor. It has more output power but its battery life is pretty bad and it's another massive brick. The AK100 is a true portable. Its board layout is fantastic. The headphone output stage uses surface-mount discrete FETs which are very nice. Even at max volume it doesn't ever distort to make for a great fixed-output source!"

As Michael Goodman of Centrance learnt during R&D for his $699 Hifi-M8 portable DAC/amp, going loud in style—having sufficient gain at high SQ for full-size headphones from a portable device—means high-spec opamps whose stiffer appetite for voltage drains batteries more quickly.

This is yet another steep barrier of entry into the sector. Not only must a designer work with very restricted real estate, he must get the most mileage from batteries and come up with a reliable fast way to recharge them. Time now to lay eyes on the Astell&Kern AK100 and inspect how iriver handled expectations for compact form factor, sleek lines and noble materials like Steve Job's iconic aluminum and elephant-glass iPod.
Hifi-M8 with two optional front panels

Except for the protruding volume click wheel apt to catch in trouser or jacket pockets, very well. Fang Bian's competing $999 HifiMan HM-901 arguably integrates its volume wheel better to be easier accessible inside a pocket without playing catch'n'twist with thin linings. On overall industrial design many could give the nod to iriver. Unlike at Apple, the dress code for Astell&Kern is formal black only. Dimensions are 3.11 x 2.33 x 0.57" HxWxD, weight is 4.3oz.

The 2.4" touch screen serves up 320 x 240 pixel resolution well below current 720p and Retina displays. The bane of regular hifi sockets is size once migrated to portable fi. Here a coaxial S/PDIF output wouldn't have fit. iriver cleverly incorporated a mini Toslink inside their 3.5mm stereo headphone port, then added another mini Toslink as digital input. Communication with PC or Mac to import files to internal memory, upgrade firmware and to charge the battery happens via a standard micro rather than full-size USB cable. Where the HM-901 gets dual Sabre 9018 DACs, iriver opted for Wolfson's 8740 with fully differential voltage outputs for a claimed S/N ratio of 110dB, -120dB of crosstalk and 0.00009% of THD. Max output is 1.5Vrms and response is claimed to be linear within 0.002dB from 10Hz to 20kHz. Clock jitter is 90ps and as such quite a bit higher than what one expects from a full-size stationary converter these days.

The internal battery is a 2.000mAh 3.7V Li-Polymer cell with a long 5 hours of recharge and a claimed 16 hours of playtime if volume is set to 37 and both display and EQ are off. The latter is a five-band affair with hinge points at 60, 179, 310 600 and 16.000Hz. Like many tablets the machine's CPU runs off a Telechips TCC 9201.

With a $699 retail to which one must add a c-note or more for memory cards to match the biggest iPod's capacity, it's fair to say that the AK100 is aimed squarely at audiophiles just as its posh Astell&Kern badge would suggest. Such a focus seems quite inevitable. Thus far market leader Apple has shown zero commitment to give us high-rez support.

Rather than create another iPod—what a losing proposition that would be—iriver has upped this game and aimed higher. Their focus on sound quality strategically cuts out wifi, telephony and a camera. Those are counterproductive when you're seriously crippled on raw hardware space and mean to do just one thing well. Clever because it can be done in the digital domain to linearize headphone response**, the 5-band EQ sports precision ±10dB adjustments. Whilst audiophiles snub equalizers, tweaked carefully they can be very useful. If you disagree, don't use it!

** On that topic Swedish company XTZ has developed a custom EQ curve for the freebie Apple earbuds which embeds in iTunes via an app; and one for their own IEMs.