Astell&Kern A&ultima SP4000 Review: The Pinnacle of Portable Audio Performance

October 7, 2025 4:35 pm

When it comes to luxury portable audio, few names carry the same weight as Astell&Kern. The company’s latest flagship digital audio player continues its tradition of pushing technical and artistic boundaries in equal measure. Crafted for discerning listeners who value both aesthetic refinement and uncompromising sound quality, this device represents the next step in high-end personal listening. Let’s take a closer look at how Astell&Kern elevates the experience of digital playback, refining every aspect of design, performance, and usability.

What You Get

A&K SP4000 High-Resolution Digital Audio Player
Leather Holding Case
Protective Case
USB-C Charging Cable
Micro USB Cable
Screen Protectors
User Guide
Warranty Info

Build

If you’ve used Astell & Kern products, then you’re familiar with their premium design that is structurally flawless while also being a bit unwieldy. The stainless steel chassis and 6-inch screen make up a beautiful piece of design, but I never see myself carrying it around with me everywhere. That’s not what these high-end players are to me, and the SP4000 is a testament to that with its jewel-like architecture. Otherwise, the SP4000 is an exceptionally built device that wears its bold price on its sleeve. Not much has changed from the SP3000 to the SP4000, but A&K seems to be confident enough with this build standard to continue with it without much tweaking.

Design

The Astell & Kern A&ultima SP4000 is built around several premium components. It uses a real quad-DAC configuration combining four AKM AK4191 digital processors paired with four AKM AK4499EX DACs for a true 1:1 signal processing architecture, achieving high precision and low noise. Its power and output stage incorporates enhanced op-amps in parallel (“High Driving Mode”), an ultra-low-noise LDO regulator, and a 99.9 % pure copper shielding to suppress interference. The SP4000 also features advanced signal alignment via ESA technology, a high-density Any-Layer HDI PCB, a Snapdragon octa-core CPU with 8 GB RAM, and a full Android OS with proprietary DAR (Digital Audio Remaster) and ADP (Astell & Kern Direct Path) audio path technologies.

User Interface

Using the SP4000’s Android-powered interface is snappier than ever, featuring its streamlined design. It’s what differentiates Astell and Kern players from other players, but sometimes I wonder if the interface is too streamlined. One change that the SP4000 makes is allowing the Google Play Store to be available, adding more options for third-party apps. Tidal is available from the get-go, but now everything is downloadable right from the device, rather than the “open source” folder.

Sound Impressions

From my experience with Astell & Kern players, including past versions of the SP4000, I know that the sound profile of these devices goes for reference-level purity. Sometimes this can result in a cold and clinical sound, but the SP4000 is slightly different. While listening to the Dan Clark Audio E3, I found the timbre of the frequencies to be a lot more delicate and wispy. You still have a very neutral tone, but the texture can break through in exciting ways that elevate certain performances. Listening to Olafur Arnalds’ “Some Kind of Peace” had a weightlessness to it that gave me the most artifact-dense upper-mids and highs. Microscopic detail was given raw power, providing a surreal level of depth to instruments like strings and piano. The soundstage propels everything outward, but also provides intimacy when necessary.

Weightless doesn’t mean the SP4000 lacks body and impact for notes. In fact, the SP4000 has tons of strike to it, just not a very bass-focused one. Switching over to the HiFiMAN HE1000 revealed a lot more possible cut and sharpness from individual notes that felt highly physical. There’s so much finesse and velocity to these transients that the tracks can feel like they’re being recorded live in the studio as you sit there listening in the control room. Activating DAR mode on the player really makes that come true. Converting my TIDAL tracks into DSD right on the device breathed such an uncanny life into the sound, with every buzz and pluck from Jim O’Rourke’s acoustic guitar on “Happy Trails” delivering unparalleled definition compared to any other portable music player.

Summary

The Astell&Kern A&ultima SP4000 is less a portable player and more a statement of audio mastery. Every element, from its stainless steel chassis to its advanced DAC configuration and digital remastering capabilities, reflects Astell&Kern’s relentless pursuit of sonic perfection. Its neutral yet emotionally resonant tonality, expansive soundstage, and ultra-clean resolution set a new benchmark for what digital playback can sound like. While its size and cost may place it beyond the reach of casual listeners, the SP4000 exists for those who want the pinnacle of portable hi-fi, a device that doesn’t just play music but recreates it with breathtaking authenticity.