Reimagine Analog Sound, A&ultima SP4000T
A&ultima SP4000T is the culmination of nearly two years of dedication and exploration, beginning from the planning and development stages of SP3000T.
DAC, Tube, and AMP — the essential elements of high-end audio — may be accessible to anyone. Yet even with the same elements, what is ultimately created from them is an entirely different matter. Using the canvas of SP4000, the essence of digital sound, Astell&Kern held onto one defining question over the past two years:
“How can we bring deeper emotion through analog sound?”
The answer was drawn with sincerity and endless passion, stroke by stroke. Every trace of that journey is distilled into SP4000T. Astell&Kern’s own analog sound — comfortable to listen to, yet revealing new depth and character the longer you experience it.
Discover it for yourself with A&ultima SP4000T.
- Industry-first DAP with MIL-Spec Vintage Vacuum Tube Raytheon JAN6418 in Quad Configuration
- Industry-first DAP with Triple Tube Mode (Triode, Ultra Linear, Pentode)
- T Series Signature feature: Triple AMP System
- Adjustable Tube Current with Three Levels
- High Driving Mode, ESA, and Advanced DAR for superior sound quality
- Full Open Android
- Enhanced Octa-Core CPU
RAYTHEON JAN6418 Quad — A New Standard in Tube Configuration
The SP4000T is the industry's first DAP to feature the MIL-Spec vintage vacuum tube RAYTHEON JAN6418 in a Quad configuration.
With independent dual-tube structures dedicated to the left and right channels respectively, the channel-separated design — once exclusive to home audio high-end tube amplifiers — has finally been brought to the world of DAPs.
But the essence is not the number of tubes. Managing multiple highly sensitive vacuum tubes is far more than a simple matter of addition. It demands answers to countless questions: How do you pair tubes with subtly different noise characteristics and gain rates? How do you overcome microphonic noise? How do you minimize output variation between left and right channels?
The four tubes in the SP4000T do not operate independently — they work in a differential configuration, with each pair facing the other in mirror symmetry. In this precise balance, music signals are amplified with twice the clarity, while common-mode noise is mutually cancelled and eliminated.
Each of the four tubes is precisely measured for its noise and gain characteristics before being paired, then fully isolated from noise through independent modular flexible PCBs and a multi-layered architecture — a design that only Astell&Kern, with its long experience in analog circuits and vacuum tubes, could bring to life.
When four hearts beat as one in perfect balance, the tube's signature rich harmonics resonate with the deepest, most resonant sound ever heard in the SP4000T.
The SP4000T is the industry's first DAP to feature Triple Tube Mode. Combined with the T Series Signature Triple AMP Mode and the Tube Current level adjustment first found on the SP3000T, it offers up to 54 possible combinations tailored to any genre or preference — a true Analog Sound Palette.
Because how you operate the same tube fundamentally changes its tonal character, Triple Tube Mode encompasses the full expressive range of a tube amplifier. The delicacy of Triode, the balance of Ultra Linear, the dynamics of Pentode — the extraordinary analog sound experience once exclusive to high-end tube amplifiers is now yours in the SP4000T.
Triode Mode — The Purest Voice of the Tube
This mode brings out the richest harmonic texture unique to vacuum tubes, letting the breath of a vocalist and the trembling of strings gently dissolve into a lush, lingering reverb.
Ultra Linear Mode — The Aesthetics of Balance
A design that blends the tonal color of Triode with the output of Pentode. The sound fades softly at its edges, yet carries a firm, solid core — a well-balanced mode capable of rendering every genre with authority.
Pentode Mode — The Most Powerful Voice of the Tube
Maximizing tube amplifier output and dynamic range, this mode retains the tube's signature warmth while stripping away reverb — delivering a clean, powerful presence that speaks with directness and force.
* Tube Mode applies only in Tube AMP and Hybrid AMP modes.
The Perfect Harmony of Real Vacuum Tubes and OPAMP, Astell&Kern's TRIPLE AMP SYSTEM
A&ultima SP4000T, built on Astell&Kern's exclusive Teraton Alpha technology, achieves a perfect fusion of true analog sound from the Quad-configured Real Vacuum Tubes and the dynamic sound of the OPAMP. SP4000T offers TUBE AMP mode for the authentic analog sound of a tube amplifier, OP AMP mode delivering Astell&Kern's signature clarity and expansive soundstage, and HYBRID AMP mode combining the best of both analog warmth and high-resolution output.
Experience a distinctly differentiated sound through the T Series' signature amplifier technology.
Overwhelming High Resolution and Dynamics, OP AMP Mode
High resolution that reproduces the original sound without distortion, an unparalleled sense of space, and the ultimate in clarity and dynamics — OP AMP mode delivers the pinnacle of high-quality sound that Astell&Kern has pioneered across every genre.
True Analog Sound, TUBE AMP Mode
The warm texture and unique soundstage of a Tube Amp cannot be replicated by any modern digital amplifier. Beloved since the very first appearance of tube amplifiers, they remain unmatched in conveying the emotional depth of music. SP4000T's TUBE AMP mode pairs the deep, rich analog sound exclusive to its Quad-configured Real Vacuum Tubes with groundbreaking low noise achieved through cutting-edge technology and craftsmanship — letting you lose yourself entirely in the music.
Astell&Kern's Advanced HYBRID AMP Mode
Beyond just two modes — Tube AMP and OP AMP — a next-generation Hybrid AMP mode lets you handpick your preferred tonal character. Combining the analog sensibility with the advantages of high-resolution output, the five-stage HYBRID AMP mode allows you to freely dial in the perfect sound for your taste and your music.
2nd Generation Anti-Microphonic Noise Architecture
The greatest technical challenge in applying vacuum tubes to a compact portable device is achieving low noise even at high resolution and high output. The SP4000T features twice as many tubes as its predecessor — four in total — and introduces an upgraded 5-stage 2nd Generation Architecture (up from the previous 4-stage design) to suppress microphonic noise (noise generated in vacuum tubes from even minor external vibrations). Drawing on Astell&Kern's proprietary know-how and years of experience, repeated rounds of design, testing, and verification led to the optimal solution for overcoming the structural limitations of microphonic noise.
1. Separate modular Flexible PCB, isolated from Main PCB
2. Silicone base cushion for primary shock absorption of the tube
3. Custom-fit silicone tube around tube leads to absorb impact transmitted through the leads
4. Silicone damper encasing the tube, suspending it mid-air at the damper tip
5. Copper Shield Can covering the entire tube, suppresses even the faintest micro-noise
The Most Delicate Analog Sound, Tube Current Option
We verified the safe operating range of the vacuum tubes and developed a system that adjusts the internal plate voltage across 3 levels, each of which changes the amplification of the tube amp — and with it, the tonal texture of the sound. Experience the subtle yet striking shifts in density and soundstage — the most delicate nuances a headphone or IEP can reveal — through tube current adjustment.
Vacuum Tube LED
While operating in Tube or Hybrid mode, the vacuum tube on the back of the SP4000T glows with a soft, warm light — amplifying the subtle, stylish analog aesthetic.
* Tube LED does not illuminate in OPAMP mode.
HEXA Audio Circuit Structure with Complete Separation of Digital and Analog Signals
The SP4000T integrates dual AK4499EX DACs—AKM’s latest flagship, proven across Astell&Kern devices—paired with dedicated AK4191EQ processors for each left and right channel, forming a fully discrete audio circuit architecture.
Unlike conventional DAPs that handle both digital and analog signals inside the DAC, the SP4000T's audio circuit uses a dedicated digital delta-sigma modulator (AK4191EQ) to reduce noise in the digital signal before passing it to a completely isolated Analog DAC (AK4499EX) for independent analog signal processing.
Built on this physically complete separation of digital and analog signal paths, the SP4000T's signature analog sound is realized with greater depth than ever before.
High Driving Mode for the Ultimate Sound
The SP4000T inherits the beloved High Driving Mode from the SP4000, acclaimed by audiophiles worldwide. With twice as many OPAMPs arranged horizontally, it delivers even greater sonic density. Like a four-wheel-drive vehicle conquering rough terrain, High Driving Mode channels superior driving power to produce a stronger, more stable sound — precisely articulating even the most easily missed sonic details, and designed for a deeper, more vivid listening experience.
Proprietary ESA (Enhanced Signal Alignment) Technology for Minimized Group Delay
The SP4000T dramatically improves Group Delay — one of audio's most persistent challenges — through its proprietary ESA (Enhanced Signal Alignment) technology. ESA aligns frequency signals so they arrive more uniformly, minimizing frequency distortion and delivering sound with greater clarity and purity.
*What is Group Delay?
Group delay refers to the difference in time it takes for each frequency to pass through an internal audio system. In simple terms, it describes a phenomenon where different frequencies within an audio signal do not arrive simultaneously, resulting in slight timing delays acros
Advanced DAR Support for Enhanced Sound
Advanced DAR is the 2nd-generation DAR technology, delivering even more natural and refined sound. Rather than passing audio directly to the DAR engine, it first routes the signal through VSE (Virtual Sound Extender) to virtually restore lost harmonics and enhance audio quality — then applies DAR technology in a second stage for a more complete upsampling result. This allows listeners to enjoy a deeper, more immersive sound that is truer to the original recording.
Astell&Kern Direct Path for Bit-Perfect Playback
ADP (Astell&Kern Direct Path) — Astell&Kern's proprietary customization technology — bypasses the Sample Rate Conversion (SRC) limitation inherent to the Android OS, enabling lossless Bit-perfect playback even in streaming environments for the highest possible audio quality.
Keeping pace with the shift toward streaming-centric listening, the SP4000T runs the latest Android 15 — delivering top-tier analog sound quality alongside exceptional convenience.
Precision Sound with Any Layer HDI PCB
The SP4000T uses the same Any Layer HDI PCB for high performance as the SP4000. Commonly found in smartphones and high-end electronics, this high-density circuit board enables the precise design of complex circuits within a smaller footprint — minimizing signal loss and delivering more refined sound.
99.9% Pure Copper Shield Can
The SP4000T employs a complete Shield Can design to block noise and electromagnetic interference that could affect the audio block. Using a 99.9% pure copper Shield Can, it goes beyond basic shielding to deliver an even cleaner, more vivid sound.
Sound Design Through DAC Filters
Design your own sound style with 7 DAC filters.
Enhanced Battery Protection Mode
The battery protection mode — previously fixed at 85% — now offers a wider range of options. Choose the option that best fits your Music Lifestyle.
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.
General Specification
Model
SP4000T (PPF52)
Body Color
Silver, Copper
Body Material
Stainless Steel, Copper
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 4.2Vrms │ Balanced 8Vrms (Condition No Load)
CPU
OCTA-Core
DAC
AKM4191EQ x2 + AKM4499EX x2
Vacuum Tube
RAYTHEON JAN6418 x4 (Quad Tube)
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/ax (2.4/5GHz)
Bluetooth
V5.2 (A2DP, AVRCP, Qualcomm® aptX™ HD, LDAC, LHDC, SBC, AAC)
Dimensions
3.37” (85.7mm)[W] x 5.9” (150mm)[H] x 0.76” (19.5mm)[D]
Weight
About 19.9oz(565g)
Feature Enhancements
Firmware upgrade supported (OTA)
Operating Temperature
0℃ ~ + 40℃ (32℉~ 104℉)
Audio Specification
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
124dB @ 1kHz, Unbalanced │ 125dB @ 1kHz, Balanced
Crosstalk
-136dB @ 1kHz, Unbalanced │ -145dB @ 1kHz, Balanced
THD+N
0.0006% @ 1kHz, Unbalanced │ 0.0004% @ 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)
Clock Source
Clock Jitter
25pS (Typ)
Reference Clock Jitter
200 Femto Seconds
Storage Capacity
Built-in
Memory256GB [NAND]
External Memory
microSD x1 (Max. 1.5TB)
Battery
Capacity
7,450mAh 3.8V Li-Polymer
Charge Time
about 5hours (PD3.0 Charging)
Playback Time
about 10hours (Standard : FLAC, 16bit, 44.1kHz, Vol.80, LCD Off, Low Gain)
Supported OS
Windows 10,11(32/64bit) MAC OS X 10.7
