Astell&Kern SP4000

Built on Legacy, Evolving Perfection

Enhanced Signal Processing Capabilities with Octa Audio Circuit Architecture

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.

[ OPAMP : Series Configuration ]

Driving range increases linearly, but with increased noise and reduced SNR. While the sound may feel more powerful, it tends to become rougher or harsher.

[ OPAMP : Parallel Configuration ]

The driving range expands horizontally, with no increase in noise or reduction in SNR. This results in increased dynamic range and enhanced sound detail.

Minimized group delay with 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, minimizing frequency distortion and dramatically enhancing sound clarity and purity.

*What is Group Delay?

In audio, group delay refers to the time differences it takes for various frequencies to pass through an internal system. In other words, each frequency reaches the output at slightly different times. Simply put, it describes a phenomenon where different frequencies within an audio signal do not arrive simultaneously, resulting in slight delays.

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.

[ Astell&Kern Direct Path Flow ]

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

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.

* The LED light can be turned on or off according to user settings.

Crossfeed, Speaker effect when listening through headphones

Crossfeed mixes parts of the original signal from one channel and sends that signal to the opposite channel with a time difference to center the sound image. Through the use of detailed settings such as Shelf Cutoff, Shelf Gain, and Mixer Level, you can set the level of crossfeed according to your listening preferences.

Adoption of 6 inch 2180x1080 2K Display

Experience the SP4000 more conveniently and comfortably with a wide 6-inch, large-screen 2180x1080 2K display.

AK File Drop to enjoy wireless transfers

The new AK File Drop function in the SP4000 makes files transfers easier and more convenient. Using AK File Drop, you can freely transfer files wirelessly through a PC, smartphone, or FTP program located on the same network. Music file management is now possible with a cableless, wireless solution.

ReplayGain Automatically and Uniformly Adjusts Playback Volume

ReplayGain for Automatic Volume Level Adjustment ReplayGain functionality, which adjusts audio sources with varying volume levels to a uniform loudness, has been implemented. Enjoy your personalized playlists with the ReplayGain feature.

* ReplayGain supports up to 24bit/192kHz audio sources.

PD 3.0 Fast Charging Supported

The SP4000 supports Qualcomm QC 3.0 fast charging, so you can charge your DAP faster and more efficiently than previous models, reaching a full charge in about 4 hours.

Wireless Hi-Fi Sound via BT Sink

The BT Sink function allows you to connect the SP4000 to an external device via Bluetooth, similar to connecting a smartphone to a BT speaker. Music being played on the external device can be transmitted to the SP4000 through the BT Sink function.

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

Body:

Color Black, 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℉)

Audio Specifications

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

S/N: 
129dB @ 1kHz, Unbalanced │ 131dB @ 1kHz, Balanced

Crosstalk: 
-136dB @ 1kHz, Unbalanced │ -145dB @ 1kHz, Balanced

THD+N:
0.0005% @ 1kHz, Unbalanced │ 0.0003% @ 1kHz, Balanced

IMD SMPTE:
0.0004% 800Hz 10kHz (4:1) Unbalanced │Balanced

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

Clock Jitter: 

25pS (Typ)

Reference Clock Jitter: 

200 Femto Seconds

Storage Capacity

Built-in Memory: 

256GB [NAND]

External Memory:
microSD x1 (Max. 1.5TB)

Battery

Capacity:
6,780mAh 3.8V Li-Polymer

Charge Time:
about 4hours (QC3.0 Charging)

Playback Time:
about 10hours (Standard : FLAC, 16bit, 44.1kHz, Vol.50, LCD Off)

Supported OS

Supported OS: 

Windows 10,11(32/64bit) MAC OS X 10.7

Etc

- Audio measurements are based on the Normal mode.
- Auto Mute is not used during audio testing.