Astell & Kern A&K PD20

Under the hood.

To my surprise, the PD20 broke from A&K’s traditional AKM chipset design, this time implementing a quad-DAC architecture with four ESS ES9027Pro 32-bit HyperStream IV DACs. Each of the DACs is configured to operate independently, with a dedicated op-amp circuit, to deliver R+, R-, L+, and L- signals that are precisely separated while minimizing inter-channel interference. Everything is still under TERATON Alpha FPGA control, inherited from their other releases, including the implementation of Enhanced Signal Alignment (ESA) technology to minimize group delay between different sound frequencies, introduced in their flagship SP4000.

The touch display remained the same as in SP4000 too, at 6” with 2160×1080 resolution. To me, a bigger display usually unlocks a more common smartphone user experience with an easier-to-access interface. The GUI seems to carry the same upgraded design as in the SP4000, and the speed of the interface under Octa-core Snapdragon processor operation was no different. While A&K didn’t officially disclose how much RAM it was packing inside their PD-series DAP, I did find a reference to 4GB RAM, along with 256GB NAND storage, further expandable with microSD card support of up to 2TB.

While the DAP still features a typical, optimized closed Android A&K interface, just like in SP4000, you can also access the Google Play Store to download and install any app. There should be plenty of processing power to do audio decoding while supporting all the popular lossy and lossless formats, such as WAV, FLAC, WMA, MP3, OGG, APE, AAC, ALAC, AIFF, DFF, and DSF, with PCM rates up to 32bit/768kHz and native DSD support up to 22.4MHz (DSD512).

The output voltage/power seems to be pretty high, especially the balanced output. The single-ended 3.5mm PO has an output impedance of 0.7 ohms and 5 Vrms, whereas the balanced 4.4mm (5-pole, ground connected) has an output impedance of 1.7 ohms with a maximum of 10 Vrms based on unloaded measurements. Each port can be changed to Line Out, and 3.5mm also supports optical out. The dual-band wifi (2.4/5GHz) remains, and Bluetooth (BT5.3) support includes not only aptX HD but also LDAC protocols for 24-bit playback over Bluetooth (Rx and Tx).

The battery capacity remained the same as in PD10, with 5,770mAh, 3.8V LiPo, capable of running for about 14 hours (according to A&K), under local playback with display, wireless, and DAR off, and in Class AB amp mode. Once you start enabling more features, such as switching to Class A and the high-current setting, battery performance will decrease, as expected. It’s one of the reasons the Hybrid amp mode was very welcome here. Enabling Advanced DAR takes an even higher toll on the battery. In real-life performance, with the most optimized local playback setting, realistically you can get close to 12 hours of playback. Then, with Class A and high current, you can lose up to 2 hours, and with Advanced DAR enabled, another hour.

You have to keep in mind that A&K’s newly adopted Advanced DAR utilizes a combination of software (Restoration) and hardware (Upsampling) technology for upsampling, in both PCM and DSD modes. I covered DAR functionality in depth in my SP4000 review, and the same will be applicable here. Also, just like in SP4000, it applies to both LO and PO, and drains more battery. At the same time, with support for PD3.0 charging, the PD20 battery can quickly bounce back in about 4 hours under fast charging.

GUI.

The PD20 GUI, which is probably the same as SP4000 v4.5, feels and performs very similarly to their SP-series flagship. And overall, when it comes to A&K DAPs’ user interface, once you are familiar with one, you will feel at home using the rest because they share a similar interface, from the 6” PD20/SP4000 down to their smaller 3.6” display SR35 models. The 4th-gen interface update marked a significant improvement in ergonomics, while the 4.5th-gen further refines it.

When you start the player, the greeting screen has a carousel where you can swipe through and access your songs in alphabetical order. It’s a fun way to view the song’s artwork along with other info, and it is very fast as you swipe through it. As you swipe right->left above or below the carousel of artworks, you have a Media Category Browser screen to view your Songs, Album, Artist, Genre, Playlists, Folder, Favorite, HD Audio, and CD Library. Then, Settings and Category allow you to rearrange the order of categories above and turn off the home screen carousel. By the way, when enabled, the Home button at the bottom of the screen takes you to this home screen carousel, and every time you touch the Home button, it randomly brings up another song. I wish there were a way to assign a different screen to the Home button, but if you turn off the Home carousel view and rearrange Media Categories, touching the Home button will always bring you to the first selection in that list. I know it is probably hard to visualize just by reading this, but playing with it is a lot of fun, especially since the GUI is quite responsive.

In the carousel screen, below the carousel itself, there is an App Drawer shortcut which I wish were at the bottom of the screen, like in the previous 4^th-gen GUI. At the bottom of the screen, you have four shortcut buttons: open App/Screen to close any of them (as part of the “open” Android functionality), a Home button which I already talked about above, the VU meter button (the same three selection of VU meters as in SP4k), and a Back button. Above it in the Main Home screen, you have a Playback control strip with the name of the currently playing song/artist and Play/Pause and Skip controls. Tapping it or swiping it up brings up a familiar Playback screen window where the embedded artwork occupies the top half of the screen, and tapping it expands the view and shows lyrics if one is available. Swiping this window down brings you back to the main home screen. Below it, you get a summary of the song format (bit depth, sampling rate, file type) and a shortcut to tag the song as Favorite or another 3-dot shortcut with additional functions. Then, you have a song artist/title and a scrub bar to advance through the song. Playback touch controls are underneath that, along with Play mode controls.

Swiping down the notification bar gives you shortcuts to various controls, which you can toggle on/off or long-press to get to their corresponding Settings screen, if available. Here you have wifi, Bluetooth, DAR (Digital Audio Remaster), Gapless, Crossfeed, AK Connect, Line Out, XLR, Replay-Gain, Car Mode, Settings, and more. You can edit which shortcuts are displayed here and change their order. At the bottom of the open notification bar, you also have Brightness control. The full Settings window has more controls, partitioned into sections. Other controls you can find here include selecting Bluetooth Codec, the Roon Ready switch, AirPlay, Crossfeed, DAR setting, DAC filters, L/R balance, Gapless, ReplayGain, Line Out, and Playback setting. Other usual controls for A&K CD Ripper, USB Mode and Audio output format, S/PDIF Conversion, Car Mode, Notification panel editing, Setting Control lock, setting Volume limit, enabling Double-Tap Screen to wake and Screen Timeout in Display setting, and enabling/disabling LED indication. Also include typical date/time changes, language and keyboard selection, timer settings, FW update, System info, and System Reset.

Sound Studio.

Sound Studio is the main selling point and the most important new feature of the PD20. There are 2 ways to access it. From the carousel screen, right under the carousel on the left, there is a shortcut icon with “ear”, or when you press and hold the Sound Master wheel for 3s. In there, you have access to Personal Sound, Equalizer, Audiosphere DSP effects, and Acura DSP effects. One very important thing to note: Sound Studio effects apply to both PO (phone out) and LO (line out) outputs.

Personal Sound was developed in collaboration with a well-known Audiodo audio solution company. Once this feature is enabled, you can create a custom personal sound profile when you click on “+” to start the audio test. The hearing test takes about 3 minutes; you can only use 3.5mm SE output, and it is highly recommended to use the provided IEMs. The test is performed separately with sound pings to your left and right ears, which you have to acknowledge during the test that determines your hearing level and creates a customizable EQ correction curve for your Left and Right ears. Once you save your profile, you can create another one, even try different IEMs, as long as they connect to a 3.5mm port. Plus, you can have other people create their own profile to access when sharing PD20 with your family or friends.

Next is the Equalizer, also developed by Audiodo. This EQ, originally with 3 bands, but later updated to 5 bands, has a GUI where you can move each band (left-right) within a limited allocated frequency range, and up/down to adjust the gain. Each band is linked to the Sound Master wheel, where you can cycle through by pressing it continuously and turning the wheel to adjust the gain. You can also save the EQ profile, but as of now, once you start tweaking the EQ setting, it autosaves the changes. My suggestion to A&K is not to auto-save the preset, allowing the user to save the EQ profile only when you are done tweaking the EQ. Also, below the EQ, there is a tilt slider to adjust/tilt the EQ setting to the left, toward the heavier (bassier) sound, or to the right, toward the brighter (more revealing) sound.

Audiosphere is a DSP surround sound effect that enhances spatial audio, and it comes in 4 presets: Subtle, Balanced, Immersive, and Echoic. Personally, when listening to music, regardless of the genre, it made the sound too artificial, so I wasn’t too crazy about it. Maybe when watching movies or playing games, it could be useful, but I found it to be a bit too distracting. One thing I would recommend is to add something like a mix control to adjust the amount of the effect applied. That could give a user more control in fine-tuning the effect.

The newly added DSP effect, after the fw 1.02 update, is Acura. This effect is based on real-time spectrum analysis to enhance detail retrieval and bass boost. Each of these controls is individually enabled and adjusted on a 0-100 scale for the amount of the effect applied. These effects are not that bad, and I found them more useful. However, I personally prefer to use EQ to adjust the clarity. But the bass boost worked quite well.