Follow-Up March 2014
After I reviewed the Astell&Kern AK100 portable media player in August 2013, rather than return the review sample to A&K, I bought it. Yes, I very much liked what this little gem of a player didmuch as I appreciate how much music I can store on my 160GB iPod, it sounds harsh and lacking in detail compared with the AK100. However, one thing the iPod does that the AK100 didn't was support gapless file playback, which is essential for such works as through-composed operas and symphonies, or even albums like Sgt. Pepper and Abbey Road, where there is no pause between movements.
Astell&Kern addressed this omission in June 2013, after I had submitted my review text for publication, with the release of the v.2.01 firmware. This is supplied as a binary hex file that you copy into the AK100's root folder with the player connected to your computer as an external USB drive; when you disconnect and reboot the AK100, it installs the new firmware. (Don't do what I inadvertently did when I installed the new firmware and set the default language to Koreanit took me a long time trying to decipher Korean messages in order to reset the default to English!)
The next upgrade, in July 2013, was v.2.10, which added the capability of using the AK100 as a USB DAC, offered as a menu item when you connect the player to a computer via USB. Then, in December 2013, Astell&Kern released the v.2.30 firmware, which allows the AK100 to play DSD64 files in both .dff and .dsf formats. I was somewhat puzzled by this new functionality; according to its datasheet, the Wolfson WM8740 DAC chip used by the AK100 doesn't support DSD input data, just PCM data with word lengths of from 16 to 24 bits and sampling rates up to 192kHz.
Nonetheless, I copied some DSD64 files to my AK100, which duly recognized them and added them to its library. When I selected one of these files for playback, "DSD" appeared on the AK100's display and I heard music through the headphones, as expected. However, when I connected the AK100's TosLink output to an Auralic Vega DAC, which I reviewed in February, it became apparent that the AK100 was outputting 24-bit PCM data sampled at 88.2kHz. So while I appreciated its new ability to play DSD64 files, the AK100 is actually transcoding DSD data to high-resolution PCM, in order to be able to present them to the Wolfson DAC.
Is this anything to be concerned about? Not from my auditioning. Acoustic Sounds now offers DSD downloads, and I purchased some favorite albums in the format, including Shelby Lynne's Just a Little Lovin' (DSD64, Lost Highway). Played through the AK100, that little sob in Lynne's voice in the title track was just as heart-wrenching, and the sense of space in this superb recording was just as convincing as they'd sounded with the Auralic Vega, whose ESS Sabre32 9018 DAC supports native DSD decoding. The space around Joe Morello's drums in his solo in "Take Five," from the Dave Brubeck Quartet's Time Out (DSD64, Columbia), was palpable with the upgraded AK100, even though, in this early stereo recording, Morello remains firmly planted in the left channel.
One thing I did notice was that the touchscreen was slower to respond when the AK100 was playing a DSD file than it was with PCM files, presumably because the conversion of DSD to PCM uses more of the player's processing power. Astell&Kern warns that playing DSD files will shorten the time between battery charges, which also suggests that greater processing overhead is involved.
The v.2.30 firmware upgrade brings the $699 AK100 closer in its capabilities to Astell&Kern's top model, the AK120, which costs $1299. The AK120 offers twice the internal memory (64GB vs 32GB), and the ability to accept 64GB Micro-SD cards; it uses two WM8740 DAC chips rather than one to increase resolution, flanks the exposed volume-control knob with flanges to provide it with some physical protection, and offers a significantly lower output impedance: 3 ohms vs the AK100's 22 ohms. (In December 2013, A&K introduced the AK100 Mk.2, with the same 3 ohm output impedance as the AK120.)John Atkinson