Wired and Wireless connections.
In addition to being a portable DAP, you can enhance the PD20’s functionality by using it as a transport to drive an external DAC/amp, add an external amp, or convert the DAP into a wired/wireless USB DAC. Furthermore, you are not limited to wired headphones and can take advantage of a wireless Bluetooth connection.
Wireless/Bluetooth
I tested the PD20 BT Tx with the Final TWS, ZE3000 (aptX) and Tonalite (LDAC), and confirmed that it operates within 55ft (ZE3000) and 25ft (Tonalite) in open space, and enables complete remote control. Usually, Tonalite works at 50-55 ft with my S25 smartphone. With Tonalite, the stable connection was at half of that, but it was also the same as with SP4000, which I assume is specific to the design of these TWS earphones.
PD20 also features Bluetooth Sink Mode (BT Receiver) when the BT DAC is enabled, allowing you to set PD20 as a wireless DAC/amp. I tested this feature with my Galaxy S25 phone, streaming Spotify from my smartphone while using PD20 as a wireless DAC with LDAC protocol. It worked flawlessly 55ft away from my phone, displaying the name of the song I was streaming and letting me control the playback remotely from PD20.
USB DAC
I tested the USB DAC functionality of PD20 with my aging T480S Win10 laptop. Under the USB mode of the DAP, you need to switch from Media device (MTP) to DAC input, which activates USB DAC mode and brings up a menu where you can enable/disable DAR, Charge battery mode, and select a DAC filter. If you are connected to your smartphone to use PD20 as a wired USB DAC, there is no reason to drain the smartphone battery by charging the PD20, which uses the internal battery. Otherwise, keep charging the DAP when connected to the laptop. My laptop recognized PD20 as an AK Audio USB device without a problem, and I was able to control the volume from both my laptop and PD20.
One thing to note: once you unplug the USB cable, USB mode on PD20 goes back to MTP.
Line Out
The Line Out was part of my sound analysis, mentioned in the previous section of the review, where I tested PD20 LO vs PO using Brise Audio WATATSUMI amp with OROCHI IC cable.
USB Audio Out
I tested and verified this feature with a few USB DAC dongles, such as NiPO A200pro and L&P W4, and found it to work without a problem. Once connected, nothing needs to be selected, and the volume is fixed at a maximum of 150; thus, it is helpful to use it with external dongles that have a volume control. The sound quality was no different when connected to my Galaxy S25 smartphone.
Optical Out
I used the iBasso D17 DAC/amp for this testing. Nothing needs to be enabled; just connect the optical cable to the 3.5mm port and start playing. Optical output was detected automatically; the PD20 volume was set to maximum 150, and I controlled the output volume from the D17. Other than that, no surprises using PD20 as a transport to drive the external DAC/amp through the optical SPDIF interface, where I’m hearing a typical D17 tube tonality.
Conclusion.
I usually end most of my DAP reviews with: there is no such thing as the best, but rather what is the best for you, per your feature and design requirements, pair-up synergy with IEMs, headphones, and music you are listening to, and within your budget. The key here is your personal sound preference, which is often driven by your hearing ability. With age, our hearing health does change, and, as a result, we can no longer hear highs as crisp, mids as detailed, lows as tight, or background waterfall hiss as intense. In some cases, it could be a blessing if you are dealing with IEMs that have too much treble energy or high sensitivity. In other cases, we take matters into our own hands and start tweaking using EQ, often relying on our “hearing ability” to adjust it correctly.
Following the PD slogan of “Breaking Away from the Normal”, PD20 has a different approach. Besides giving you different sound tuning tools, such as triple amp design with Class A, AB, and Hybrid options, or 3-level current adjustment in Class A and Hybrid, it allows you to run a rather decent hearing test to figure out your hearing losses across the FR sweep, with individual left and right ear EQ compensation curves as part of your personal sound profile. From there, you have a dedicated EQ control to adjust it further across five bands, and then correct the “tilt” of the EQ with another adjustment, all developed in collaboration with Audiodo. And, on top of that, you also have access to the Sound Master Wheel, a hardware control wheel to step through your pre-selected EQ bands and adjust their gain up/down in 160 steps on the fly in real time during playback. Then, you can adjust the sound further with additional DSP sound effects.
But even without all this tweaking, including hearing-test EQ compensation, the baseline PD20 “unaltered” tuning has a smooth, fuller-body musical tonality, almost reminding me a bit of tube sound quality. When listening to PD20, I hear a more laid-back analog sound quality that captures the emotions of the sound, delivers fuller note weight, and gives you a more intimate musical experience that you can scale up further with many other options I mentioned above. Yes, A&K is trying to break away from normal here. And whatever they came up with is definitely unique, especially the custom Personal Sound Profile based on the hearing test, which I hope to see in more of their future releases.
