Astell&Kern A&ultima SP4000T DAP: The World's First Quad Tube DAP Is Here
Read Time: Approx. 8 min.
The Quad Tube DAP That Changes Everything
Just when you think the DAP Mongol Astell&Kern has pulled the last rabbit out of its hat, they continue their evolution of tube excellence with the release of the A&ultima SP4000T Digital Audio Player. As the company's third DAP to feature real vacuum tubes alongside solid-state amplification technology inside the same chassis, the SP4000T pushes the boundaries of what's technically possible in a portable device.
At $3,620, the SP4000T is the culmination of two years of dedication and exploration, taking what's been learned from the A&ultima SP4000 DAP and the SP3000T and channeling it into a single defining question: How can we bring deeper emotion through analog sound? The answer is everything you see–and hear–in this player. With support for the full Android OS, including the Google Play Store, 54 ways to shape your sound, a flagship-level DAC chipset, AK file drop support, and Astell&Kern's signature striking design, the SP4000T invites audiophiles in as the ultimate portable hi-fi companion.
Key Features
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 3 Levels
ADP (Astell&Kern Direct Path) for bit-perfect streaming
Crossfeed, ReplayGain, VSE, and DAC Filters
2nd Generation Anti-Microphonic Noise Architecture
High Driving Mode, ESA, and Advanced DAR technology (Digital Audio Remaster)
Roon Ready certified, BT Sink mode
Full Open Android (15)
10 hour battery life, 6-inch touchscreen, PD 3.0 fast charging
Enhanced Octa-Core CPU
How does the SP4000T DAP differ from the SP3000T DAP?
Unlike the SP3000T, the SP4000T is equipped with four RAYTHEON JAN6418 tubes, further enhancing its analog sound characteristics. By applying the Triple AMP system, the SP4000T perfectly harmonizes the true analog sound of Quad vacuum tubes with the dynamic sound of an OPAMP in a single chassis.
It also builds on what was learned from the A&ultima SP4000 and the SP3000M, advancing the platform's processing power, noise architecture, and connectivity in meaningful ways.
Four Tubes, One Vision: The Quad Configuration
The SP4000T stands out as the industry's first DAP to deploy RAYTHEON JAN6418 vacuum tubes in a Quad configuration: four MIL-Spec vintage tubes operating in two independent, channel-separated pairs. This isn't just doubling up for the sake of it; the four tubes operate in a differential configuration with each pair arranged in mirror symmetry. Music signals are amplified with twice the clarity while common-mode noise is mutually cancelled. The result is the richest, most resonant tube sound.
Each individual tube is measured for noise and gain characteristics before being matched with its partner, then isolated via independent modular flexible PCBs built on an Any Layer HDI PCB architecture and multi-layered design that only a company with Astell&Kern's depth of analog circuit experience could execute.
Triple Tube Mode: 54 Ways to Shape Your Sound
Just when you think one industry-breaking feat is enough, Astell&Kern does it again, making the SP4000T the first DAP to feature Triple Tube Mode. Combined with the T Series Signature Triple Amp Mode and the Tube Current level adjustment, it offers 54 possible combinations tailored to any genre or preference. Triple Tube Mode encompasses the full extensive 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 brings the richest harmonic texture the tube has to offer. Think lush, lingering reverb and an almost tactile sense of breath and string resonance.
Ultra Linear Mode splits the difference between Triode warmth and Pentode muscle. The edges are soft, the core is firm, and virtually every genre feels at home here.
Pentode Mode maximizes output and dynamic range. The warmth remains, but the reverb is stripped back in favor of clean, direct, powerful presence.
Pair these three tubes with AK's Triple AMP System — TUBE AMP, OP AMP, and HYBRID AMP modes — plus five-stage HYBRID blending and three-level Tube Current adjustment, crossfeed for natural headphone imaging, ReplayGain for consistent playback across your library, selectable DAC filters, and VSE (Vibration Suppression Engineering) for further mechanical noise control. Take all of that, put it together, and you arrive at 54 54 possible sound combinations. That's not a gimmick; it's a genuine analog sound palette that lets you tune the SP4000T to suit your headphones, your music, and your mood.
The Technical Foundation Beyond the Tubes
Beyond the tubes, the SP4000T is built on an impressive technical foundation. It uses a HEXA audio circuit architecture featuring dual AKM AK4499EX DACs paired with dedicated AK4191EQ digital processors for each channel. Astell&Kern separated the two signal paths with the digital delta-sigma modulator, reducing noise before handing off to a completely isolated analog stage.
The anti-microphonic architecture has been upgraded to a five-stage second-generation design to keep the four tubes quiet. Each tube is cushioned by a silicone base, wrapped in a custom silicone jacket around its leads, suspended in a silicone damper, and enclosed in a 99.9% pure copper shield can. This level of obsessive, layered engineering is what makes the difference between a concept and a product that actually performs.
- Separate modular flexible PCB, isolated from the main PCB
- Silicone base cushion for primary shock absorption of the tube
- Custom-fit silicone around the tube leads to absorb the impact transmitted through the leads
- Silicone damper encasing the tube, suspending it mid-air at the damper tip
- Copper shield can covering the entire tube, suppresses even the faintest micro-noise
Rounding out the technical suite are Astell&Kern's proprietary ESA (Enhanced Signal Alignment) technology and Advanced DAR upsampling technology. ESA addresses group delay, one of audio's persistent thorns, by aligning frequency signals for more uniform arrival, resulting in cleaner, purer sound reproduction. Advanced DAR routes audio through AK's virtual sound extender to restore lost harmonics before applying DAR upsampling, delivering a more complete and immersive result.
A Platform as Much as a Music Player
The SP4000T runs Android 15 and supports Astell&Kern's Direct path technology, which bypasses the Sample Rate Conversion limitation inherent to Android for bit-perfect playback in streaming environments. Native DSD512 and 32-bit/768kHz playback are on board, as well as Bluetooth 5.2 with aptX HD, LDAC, and LHDC support.
The design architecture follows suit with previous Astell&Kern models, keeping it minimal and straightforward. The 6-inch 2K touchscreen is the largest A&K has put on a DAP to date, and a new dual-antenna design roughly doubles 5GHz Wi-Fi download speeds compared to the previous generation. Battery life sits at around 10 hours under standard conditions, with a 7,450mAh battery that charges fully in approximately 5 hours via USB PD 3.0.
Preorder Your SP4000T DAP Today
At $3,620, the A&ultima SP4000T DAP sits at the top of AK's lineup as the company's new flagship. This is a player that treats the vacuum tube not as a cosmetic addition but as the centerpiece of an expertly constructed engineering system. The quad tube configuration, 54-combination sound palette, next-generation noise suppression, and HEXA DAC architecture put the SP4000T in a class of its own.
The SP4000T is available for pre-order now and is expected to ship June 30, 2026. It's available in Silver only at launch. If you have questions or want helping pairing it with the right Dragon Audio Cables or IEMs, reach out to us–we're happy to help you build the perfect system around it.
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What's in the Box
- Astell&Kern A&ultima SP4000T DAP
- Premium leather Cognac-colored case
Specifications
GENERAL SPECIFICATIONS
Model: SP4000T (PPF52)
Body Color: Silver, Copper
Body Material: Stainless Steel, Copper
Display: 6-inch 2K (2160 x 1080) touch screen
Dimensions: 3.37" W x 5.9" H x 0.76" D (85.7mm W x 150mm H x 19.5mm D)
Weight: About 19.9 oz (565g)
Input: USB Type-C input (for charging & PC & MAC)
Outputs: Unbalanced Out (3.5mm), Optical Out (3.5mm), Balanced Out (4.4mm, 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)
Feature Enhancements: Firmware upgrade supported (OTA)
Operating Temperature: 0℃ ~ + 40℃ (32℉~ 104℉)
Built-in Memory: 256GB [NAND]
External Memory: microSD x1 (Max 1.5TB)
Battery Capacity: 7,450mAh 3.8V Li-Polymer
Charge Time: About 5 hours (PD3.0 charging)
Playback Time: About 10 hours (Standard: FLAC, 16bit, 44.1kHz, Vol.80, LCD Off, Low Gain)
Supported OS: Windows 10, 11 (32/64bit) MAC OS X 10.7
CLOCK SOURCE
Clock Jitter: 25pS (Typ)
Reference Clock Jitter: 200 Femto Seconds
AUDIO SPECIFICATIONS
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 playack
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 at 1kHz, Unbalanced | 125dB at 1kHz, Balanced
Crosstalk: -136dB at 1kHz, Unbalanced | -145dB at 1kHz, Balanced
THD+N: 0.0006% at 1kHz, Unbalanced | 0.0004% at 1kHz, Balanced
IMD SMPTE: 0.0004% 800Hz 10kHz (4:1) Unbalanced | Balanced
Output Impedance: Unbalanced Out 3.5mm (0.7 ohms) | Balanced Out 4.4mm (1.7 ohm)
