Astell&Kern A&Ultima SP4000

Astell&Kern A&Ultima SP4000

Portable digital audio player

Astell&Kern debuts its new flagship DAP, the A&ultima SP4000.

Featuring Octa circuit architecture, High Driving mode, full Android OS, and ADP technology, it delivers unmatched sound and streaming fidelity. Crafted from 904L stainless steel with a ceramic back, it’s the perfect blend of performance and luxury.

Key Features

• Full Android OS – Download and run your favourite apps with ease
• Octa Audio Circuitry + High Driving Mode – Next-level sound performance
• Enhanced Signal Alignment (ESA) – Ultra-precise, low-distortion playback
• Advanced Digital Audio Remaster (DAR) – Refined audio at any resolution
• Luxury Design – 904L stainless steel, ceramic back, and calf-leather case

Astell&Kern A&Ultima SP4000 design

‘Pierce: The force of light that pierces through the darkness.’

The SP4000 stands at the pinnacle of Astell&Kern’s flagship A&ultima line—a DAP that embodies the peak of performance and design. Like the The force of light that pierces through the darkness, the rotating volume wheel generates energy that is visualised as shards breaking through a solid wall.

This imagery is captured through sharp edges, restrained detailing, and geometric structures, expressing both explosive force and concentrated power.

The interplay of contrasting surfaces and multidimensional forms goes beyond aesthetics, serving as a visual representation of the SP4000’s high-performance audio capabilities.

Even the angle of the volume wheel’s patterns has been meticulously crafted to deliver subtle tactile resistance, offering a sensory experience that connects users to the sound itself. It’s not just about control—it’s an intuitive, emotional interaction with music.

The choice of materials in the SP4000 perfectly embodies both technology and emotion.

The front features high-gloss polished 904L stainless steel, while the rear is finished with PVD-coated ceramic, offering exceptional craftsmanship in both form and function.

The SP4000 is more than just a digital audio player—it is a work of art where technology, design, intuition, and performance converge, expressing a pure passion for the ultimate sound experience.

Breakthrough Audio Architecture Meets Powerful Sound Performance

The A&ultima SP4000 sets a new standard with its advanced Octa Audio Circuit Architecture, pairing one AK4191 digital processor with one AK4499EX DAC in a true 1:1 configuration – enabling precise signal separation and a true Quad DAC setup.

This design, which physically separates digital and analogue processing, delivers remarkably clean, detailed sound.

Combined with High Driving Mode and a parallel OPAMP setup, the SP4000 offers powerful, stable output and exceptional dynamic range for a deeply immersive listening experience.

Precision Engineering for Unmatched Clarity and Pure Streaming

The Astell&Kern A&Ultima SP4000 features Enhanced Signal Alignment (ESA) to minimise group delay for crystal-clear audio, and an Ultra Low Noise LDO Regulator that cuts noise by up to 97%.

Full Android OS with ADP tech ensures bit-perfect streaming, while Advanced DAR and VSE harmonic restoration deliver a rich, lifelike listening experience closer than ever to the original recording.

Octa Audio Circuit Architecture

In the SP3000, the digital-to-analogue signal processing structure was separated in a 1:2 ratio.

With the SP4000, it has evolved into a 1:1 architecture.

This new structure, where one AK4191 digital processor is paired with one AK4499EX DAC, allows digital signals to be delivered precisely to a single DAC without the need to distribute noise, enabling improved signal separation and processing.

Through continuous research and innovation in circuit technology, the SP4000 successfully implements a true Quad DAC—a feat previously considered impossible due to noise and other issues.

As a result, the SP4000 achieves an impressive SNR (Signal-to-Noise Ratio) of 131dB, on par with the independent dual audio circuit of its predecessor.

High Driving Mode

The SP4000 features twice as many OPAMPs arranged in parallel compared to its predecessor, delivering richer and more detailed sound. High Driving Mode provides powerful and stable output—much like a four-wheel-drive vehicle confidently navigating rough terrain.

It’s designed to reproduce even the most delicate sonic details with precision, allowing you to enjoy deeper, clearer, and more immersive music.

Proprietary ESA (Enhanced Signal Alignment) technology

The SP4000 features proprietary ESA (Enhanced Signal Alignment) technology, which significantly improves one of audio’s long-standing challenges—group delay. ESA technology aligns frequency signals to arrive more uniformly, minimising frequency distortion and dramatically enhancing sound clarity and purity.

Ultra Low Noise LDO Regulator

The SP4000 features a newly implemented LDO (Low Dropout) Regulator in its power supply, which reduces noise by up to 97% compared to previous models. LDO Regulators are high-performance components typically used in precision medical devices and 5G communication equipment. They help stabilize battery voltage and effectively suppress noise, resulting in cleaner, purer sound.

Any Layer HDI PCB

To achieve the highest sound quality, the SP4000 incorporates top-tier Any Layer HDI (High-Density Interconnect) PCB technology. Commonly used in smartphones and high-performance electronic devices, this advanced circuit board allows for the precise design of complex circuitry within a compact space. It minimises signal loss, enabling the delivery of a more refined and detailed sound.

99.9% Pure Copper Shield Can

The SP4000 is equipped with a precision-engineered Shield Can to block various types of noise and electromagnetic interference that could affect the audio block. For the first time in Astell&Kern’s lineup, a 99.9% pure copper Shield Can is used—providing not only exceptional shielding performance but also delivering sound that is clearer and more distinct than ever before.

Full Android OS Integration

Astell&Kern has overcome Android OS’s sampling limitation (SRC) through its proprietary customisation technology, ADP (Astell&Kern Direct Path). This allows for bit-perfect, lossless playback even in streaming environments, ensuring the highest possible sound quality during music listening.

In response to the growing shift toward streaming-based music consumption, Astell&Kern has integrated full Android OS for the first time.
The SP4000 not only delivers flagship-level audio quality but also offers enhanced convenience, marking its evolution into a highly refined next-generation digital audio player.

Advanced DAR

The SP4000 introduces Advanced DAR, Astell&Kern’s second-generation DAR (Digital Audio Remaster) technology, delivering sound that is even more natural and refined. Rather than sending the audio file directly to the DAR engine, the SP4000 first uses VSE (Virtual Sound Extender) to virtually restore lost harmonics, enhancing the sound quality at the initial stage.

Then, the advanced DAR engine performs a second-stage upsampling process with greater precision and completeness. This two-step approach allows listeners to enjoy a deeper, more immersive sound that comes closer than ever to the original recording.

High-End Shrunken Calfskin Case

The SP4000 is packaged with a premium leather case crafted from Shrunken Calf by Perlinger, Germany’s world-renowned leather house. Founded in 1864 and spanning five generations of craftsmanship, Perlinger supplies the finest leather to luxury brands across the globe—blending time-honoured tradition with modern techniques.

The Shrunken Calf leather used in the case is made from the soft, delicate hide of calves under one year old. It is processed using a chrome tanning method to preserve its natural texture, then uniquely shrunk using special agents—not heat—to retain its organic grain and wrinkles.

Following an aniline dyeing process, Perlinger’s proprietary pigments are added to achieve a deep, vibrant colour. Their advanced anti-aging treatment ensures that this richness lasts over time, complementing the SP4000 with a leather case that embodies lasting beauty, durability, and luxury.

Included in the box

• 1x Astell&Kern A&ultima SP4000 player
• 1x High-End Shrunken Calfskin Case
• 1x USB-C to USB-C cable (1 metre)
• 3x screen protectors
• 1x Quick start guide

Astell&Kern A&Ultima SP4000 specification

Model – SP4000 (PPF51)
Body Colour – Black or Silver
Body Material – Stainless Steel 904L
Display – 6inch 2K (2160 x 1080) touch screen
Supported Audio Formats – WAV, FLAC, WMA, MP3, OGG, APE, AAC, ALAC, AIFF, DFF, DSF
Sample rate – PCM : 8kHz ~ 768kHz (8/16/24/32bits per Sample), DSD Native : DSD64(1bit 2.8MHz), Stereo | DSD128(1bit 5.6MHz), Stereo, DSD256(1bit 11.2MHz), Stereo |, DSD512(1bit 22.4MHz), Stereo
Output Level – Unbalanced 4.1Vrms │ Balanced 8.2Vrms (Condition No Load)
CPU – Octa-core
DAC – AKM4191 x4 + AKM4499EX x4 (Real Quad DAC)
Decoding – Support up to 32bit / 768kHz Bit to Bit playback
Input – USB Type-C input (for charging & PC & MAC)
Outputs – Unbalanced Out (3.5mm), Optical Out(3.5mm), Balanced Out (4.4m, only 5-pole supported)
Wi-Fi – 802.11 a/b/g/n/ac (2.4/5GHz)
Bluetooth – V5.0 (A2DP, AVRCP, Qualcomm® aptX™ HD, LDAC, LHDC, SBC, AAC)

Dimensions – 3.34” (85mm)[W] x 5.89” (149.8mm)[H] x 0.76” (19.5mm)[D]
Weight – About 21.7oz (615g)
Feature Enhancements – Firmware upgrade supported (OTA)
Operating Temperature – 0℃ ~ + 40℃ (32℉~ 104℉)