The Astell&Kern A&ultima SP4000 represents a huge advancement in portable hi-fi audio, with the introduction of an all-new Octa audio circuit architecture that uses one AK4191 digital processor and a single AK4499EX analog DAC to achieve maximum separation of signals, while also providing a lower noise floor. It is the company’s first portable player fully enabled with Android OS, which means you can download and use streaming apps natively (no side-loading!). Other technology advancements include a High Driving Mode that employs dual op-amps for improved sound detail and fidelity, proprietary Enhanced Signal Alignment (ESA) and Digital Audio Remaster (DAR) technology, and a 99.9% pure copper shield can to keep EMI at bay.
Introduction to the SP4000
“Imagine toting around a concert hall in your pocket” is what the A&ultima SP4000 aims to do. R&D and production for the SP4000 began three years after the very successful SP3000 was launched. The SP4000 is based on Astell&Kern’s work to bring maximal portable convenience without sacrificing fidelity. Audiophiles and casual listeners alike will appreciate how Astell&Kern have combined advances in hardware technologies with usable, day-to-day technologies.
Octa Audio Circuit Architecture
The SP4000 includes an entirely new Octa audio circuit architecture with eight layers of signal paths working in harmony to keep is clean. It’s like a eight-lane highway with the ability to work with the most amount of data across lanes without having vehicles (data) being bottlenecked. The Octa Circuit provides the base for the players other enhancements.
AK4191 and AK4499EX Paring
The SP4000 uses a single AK4191 digital processor paired with an AK4499EX analog DAC, instead of the dual-DAC configurations of its predecessor. Each digital signal gets a discrete path through to the DAC without any noise distribution caused by multiple DAC’s providing data..
Noise Reduction and Separation
The separation of digital and analog signal paths also ensures that less EMI and crosstalk occur through the paths, like cars and bikes having separate lanes, while they are in their lanes, they have space itself without disturbing each other. It leads to great signal separation and clarity.
Full Android OS Functionality
Gone are the days of side-loading apps: the SP4000 runs full Android OS, and has Google Play, Spotify, Tidal, and more. The player switches from being a niche audiophile product to a full-fledged streaming machine, with all of the benefits of portability and convenience.
High Driving Mode
High Driving Mode uses two op-amps in parallel, which gives richer dynamics and deeper control. Think of two engines working together in a sports car: you get solid acceleration without losing control. Audiophiles will hear increased detail in the music, particularly at lower volumes.
Enhanced Signal Alignment (ESA)
Astell&Kern’s Enhanced Signal Alignment technology (ESA) takes group delay out of the picture by guaranteeing that all frequency content arrives in phase. It’s like an orchestra conductor: everything comes together perfectly at just the right moment, leaving you with a cohesive and realistic sound staging.
Digital Audio Remaster (DAR)
The 2nd generation Digital Audio Remaster (DAR) engine takes audio quality to the next level by analyzing digital streams in real time and remastering them. Think of DAR as the master chef putting the last little bit of salt to a dish just before serving. This adds a little nuance and flavor, allowing you to get the very best out of each and every track.
Shield Can and Noise Suppression
For the first time, A&K has added a 99.9% pure copper shield can around critical circuitry to provide EMI and RFI blocking. This shield can be visualized as a fortress wall and its purpose is to protect delicate signals from anything external, allowing for ultra-clean playback.
User Interface and User Experience
A&K’s new SP4000 is launching with a robust new user interface called 4.5 Generation User Interface, that features intuitive navigation and performance. Using a responsive touchscreen, and customizable front layouts, cycling through playlists or changing user settings is as simple as using a smartphone.
Battery Life and Portability
Even with its comprehensive feature set, A&K is quick to point out, the SP4000 has remarkable battery life designed to power you during extended listening sessions from a bucket, on the go. It’s sleek, ergonomic chassis allows the SP4000 to fit in a pocket or bag, completing the transition of high res audio being portable.
Pricing and Availability
Astell&Kern showed the SP4000 during High End Munich (May 15–18, 2025) and expects a global availability this summer. Official pricing has not been released yet, but industry estimates suggest it will be priced at a premium, similar to the ~ $3,699 MSRP of the SP3000.
Final Thoughts
The Astell&Kern A&ultima SP4000 changes the game in portable audio players by offering cutting-edge design with everyday streaming capabilities. Whether you are looking for the best pure audio experience or just want easy access to your favorite apps, the SP4000 gives you both.
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