The DAPs from AK run on Android. However, it is a highly customised variant to provide a fully optimised system and user interface, designed to give users a smooth, fluid musical playback experience, which also means that it lacks Google Play Services. For those who play music from streaming services, the SR25 supports 2.4 GHz Wi-Fi (802.11b/g/n) with Deezer, TIDAL (without off-line storage support) V-Link apps pre-installed. Music streaming service apps validated by AK can be added via the Open APP service. At the time of writing, there is a total of 33 validated apps. For more information about the Open APP service, you can visit AK’s support page.
Equipped with a faster Quad-Core CPU and based on Android 9.0, the usability of the SR25 is significantly enhanced compared to the SR15, particularly evident in the UI’s responsiveness as well as software compatibility with the music streaming apps. Comparing to the SR15, there are also a few minor but significant improvements to the UI during the local music playback, made possible by the higher display resolution. The ‘A’ logo of Astell&Kern which appears at the top left-hand corner to provide accessibility to the main menu, is now ever-present. One also does not need to tap on the album art to bring up the accessibility buttons; it now sits just below the album art, allowing one to access the recent menu list, add to playlist, add to favourites, toggle between shuffle and repeat modes, and display current track information respectively.
Let’s talk about the battery life on the SR25. On paper, AK has stated battery life of 21 hours based on the following parameters; FLAC, 16-bit/44.1kHz, 3.5 mm single-ended, Volume 50, EQ OFF, LCD OFF. Using the same parameters, we were able to register an average battery life of 22 hours, 39 mins, and 12 seconds over three cycles of testing, which is impressive, noting that it is equipped with the same 3,150 mAh 3.7 V lithium polymer battery as the SR15.
One of the most exciting aspects of the SR25 is that it is the first DAP from the brand to include support for the LDAC Bluetooth codec on top of the aptX HD Bluetooth codec. At the time of this review, AK has announced two other DAPs: the A&futura SE200 and the KANN ALPHA. Only the KANN ALPHA includes support for the Sony Bluetooth codec; thus, the jury is still out on whether LDAC will become a permanent feature on AK’s future DAP releases. The SR25’s support for Bluetooth 4.2 and not 5.0 as well as its lack of 5 GHz Wi-Fi are chinks in the SR25’s amour.
Like all good DAPs, the SR25 can be used as a USB-DAC, supporting up to 24 bit / 192 kHz and DSD256, a feature that will allow one to experience an enhanced audio experience when working on the PC, be it a laptop or desktop, simply connecting it to the DAP via USB.