RAYTHEON JAN6418 Quad
The SP4000T is the industry's first portable player to feature four MIL-Spec vintage Raytheon JAN6418 vacuum tubes in a dual-channel, symmetrical Quad configuration—a design previously exclusive to high-end home audio amplifiers. To overcome the challenges of managing multiple highly sensitive tubes, Astell&Kern precisely pairs each valve by noise and gain characteristics, isolating them on independent flexible PCBs to completely eliminate microphonic interference. Operating in a mirrored differential setup, these four tubes work in perfect balance to cancel out common-mode noise while doubling sonic clarity, delivering the richest, most resonant analog harmonics ever achieved in a portable player.
TRIPLE AMP SYSTEM
Powered by Astell&Kern's exclusive TERATON ALPHA technology, the SP4000T seamlessly fuses rich analogue warmth with modern digital dynamics through its signature Triple Amp System. Users can freely switch between three distinct sonic profiles to match their music and headphones:
- OP AMP Mode: Delivers Astell&Kern's pinnacle signature clarity, massive soundstage width, and distortion-free, high-resolution dynamics across every genre.
- TUBE AMP Mode: Activates the Quad-configured real vacuum tubes, delivering the irreplaceable, emotionally deep, and velvety analog texture of classic valve amplification alongside groundbreaking low noise.
- HYBRID AMP Mode: A next-generation hybrid engine featuring a 5-stage adjustment slider, allowing you to seamlessly blend the organic soul of tube warmth with the crisp resolution of solid-state playback to dial in your perfect custom sound.
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.
HEXA Audio Circuit Structure
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 analogue 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 analogue 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
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
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.
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.
Astell&Kern Direct Path
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.
