The A&ultima SP4000 is Astell&Kern’s newest flagship digital audio player, the result of three years of relentless research and innovation following the development of the SP3000.
As part of the A&ultima series—Astell&Kern’s flagship lineup combining cutting-edge technology and top-tier specifications—the SP4000 surpasses the boundaries set by the SP3000, once regarded as the ultimate reference.
Built upon an advanced Octa audio circuit architecture, the SP4000 distills the purest essence of audio engineering, delivering a sound experience unlike anything before it—refined, powerful, and remarkably close to perfection. Discover the SP4000 and experience sound on an entirely new level.
In the SP3000, the digital-to-analog 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.
Supports High Driving Mode for
Premium Sound Performance
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.
(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, minimizing frequency distortion and dramatically enhancing sound clarity and purity.
Top-Tier Noise Suppression
(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.
Precision Sound with 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 minimizes signal loss, enabling the delivery of a more refined and detailed sound.
Equipped with 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.
Sound, Infinite Possibilities
Astell&Kern’s First-Ever Full Android OS Integration
Astell&Kern has overcome Android OS’s sampling limitation (SRC) through its proprietary customization 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.
First-Ever Implementation of Advanced DAR by Astell&Kern
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.
Drive Your Music, Latest Snapdragon Octa-Core CPU for the Newest Flagship Device
A&ultima SP4000 is equipped with a Snapdragon 6125 Octa-core processor, so you can enjoy the overwhelming sound, faster system response and a redesigned generation user interface that moves comfortably and smoothly.
Featuring a high-performance CPU and improved 8GB of DDR4 memory, which is twice the amount commonly used, the more powerful system is stable with fast and fluid movement.
The CPU, memory and wireless communication parts are configured as one module, with the digital circuit parts arranged in the same area creating a single system on a chip (SoC). This maximizes the efficiency of the overall circuit configuration by providing more audio-only circuit space as well as reducing heat and noise from digital circuits.
Enhanced 4.5th-Generation UI That Blends Function and Emotion
The SP4000 features an upgraded UI that balances both functionality and emotional experience.The main screen includes an immersive animation where an LP appears to slide in and out as you swipe through albums—turning the act of choosing music into a visually engaging and tactile experience.
The interface retains Astell&Kern’s signature Crimson theme, reflecting the brand’s identity and capturing its distinct emotional sensibility in a refined, modern design.
Crimson Theme + Interation
Material Innovations, Use stainless steel 904L on DAP body material
To achieve the goal of the A&ultima series, which is 'to provide the best value that no one can imitate while using the most innovative and uncompromising design and craftsmanship', the SP4000 uses 904L stainless steel material that has never been attempted before in a portable audio player. Using this material has expanded its value from just a digital device to the realm of a luxury good.
904L stainless steel is harder and more difficult to process than general stainless steel requiring significantly more time and effort. However, due to its excellent durability and corrosion resistance, it has a characteristic that does not lose its beauty and is why it is used in expensive luxury watches where perfection in all materials and parts must be pursued with an irreplaceable and wonderful luster. Experience the uncompromising beauty and luxury of the SP4000 produced by Astell&Kern’s experienced craftsmanship.
Sound Design Through DAC Filters
With the SP4000, you can enjoy the fun of creating your own sound style by directly selecting various DAC filters provided by the DAC manufacturer. Design your own sound through 6 DAC filters.
Real-Time Information with LED Lights
The LED light surrounding the power button provides information on the Bit Depth of the currently playing song, and also adds a visually pleasing element by making it shine and stand out.
Premium Shrunken Calf Leather Case from Germany’s Finest Leather House
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-honored 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 color. 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.
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 visualized 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.
General Specifications
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Model
SP4000 (PPF51)
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Body Color
Black, Silver
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Body Material
Stainless Steel 904L
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Display
6inch 2K (2160 x 1080) touch screen
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Supported Audio Formats
WAV, FLAC, WMA, MP3, OGG, APE, AAC, ALAC, AIFF, DFF, DSF
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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
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Output Level
Unbalanced 4.1Vrms │ Balanced 8.2Vrms (Condition No Load)
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CPU
Octa-core
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DAC
AKM4191 x4 + AKM4499EX x4 (Real Quad DAC)
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Decoding
Support up to 32bit / 768kHz Bit to Bit playback
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Input
USB Type-C input (for charging & PC & MAC)
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Outputs
Unbalanced Out (3.5mm), Optical Out(3.5mm)
Balanced Out (4.4m, only 5-pole supported)
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Wi-Fi
802.11 a/b/g/n/ac (2.4/5GHz)
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Bluetooth
V5.0 (A2DP, AVRCP, Qualcomm® aptX™ HD, LDAC, LHDC, SBC, AAC)
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Dimensions
3.34” (85mm)[W] x 5.89” (149.8mm)[H] x 0.76” (19.5mm)[D]
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Weight
About 21.7oz (615g)
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Feature Enhancements
Firmware upgrade supported (OTA)
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Operating Temperature
0℃ ~ + 40℃ (32℉~ 104℉)
Audio Specifications
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Frequency Response
±0.006dB (Condition : 20Hz~20kHz) Unbalanced │ ±0.006dB (Condition : 20Hz~20kHz) Balanced±0.06dB (Condition : 20Hz~70kHz) Unbalanced │ ±0.06dB (Condition : 20Hz~70kHz) Balanced
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S/N
129dB @ 1kHz, Unbalanced │ 131dB @ 1kHz, Balanced
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Crosstalk
-136dB @ 1kHz, Unbalanced │ -145dB @ 1kHz, Balanced
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THD+N
0.0005% @ 1kHz, Unbalanced │ 0.0003% @ 1kHz, Balanced
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IMD SMPTE
0.0004% 800Hz 10kHz (4:1) Unbalanced │Balanced
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Output Impedance
Unbalanced Out 3.5mm (0.7ohm) │ Balanced Out 4.4mm(1.7ohm)
*Audio measurements are based on the Normal mode.
*Auto Mute is not used during audio testing.
Clock Source
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Clock Jitter
25pS (Typ)
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Reference Clock Jitter
200 Femto Seconds
Storage Capacity
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Built-in Memory
256GB [NAND]
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External Memory
microSD x1 (Max. 1.5TB)
Battery
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Capacity
6,780mAh 3.8V Li-Polymer
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Charge Time
about 4hours (QC3.0 Charging)
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Playback Time
about 10hours (Standard : FLAC, 16bit, 44.1kHz, Vol.50, LCD Off)
Supported OS
Etc
- Audio measurements are based on the Normal mode.
- Auto Mute is not used during audio testing.
