Astell&Kern A&ultima SP4000T Digital Audio Player

The A&ultima SP4000T is the culmination of nearly two years of dedication and exploration, beginning from the planning and development stages of SP3000T. 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?” Industry-first DAP featuring JAN6418 MIL-Spec tubes in a Quad configuration Triple Tube Mode with Triode, Ultra Linear, and Pentode operating modes Triple AMP System with OP AMP, Tube AMP, and five-stage Hybrid AMP modes Dual AK4191EQ digital processors and dual AK4499EX flagship DACs Our Take The A&ultima SP4000T combines Astell&Kern’s flagship digital architecture with an unusually flexible analog amplification system. Its Quad Raytheon vacuum-tube configuration, three tube-operating modes, Triple AMP System, and adjustable tube current provide up to 54 combinations for tailoring the presentation. Listeners can move between the clarity and expansive soundstage of OP AMP mode, the rich harmonic character of Tube AMP mode, and five Hybrid AMP stages that blend analog warmth with high-resolution output. Beyond its analog capabilities, the SP4000T is also designed to integrate seamlessly into modern streaming ecosystems with support for Roon Ready and Qobuz Connect. Together, these features complement the SP4000T's advanced hardware by providing a streamlined, high-resolution listening experience for both locally stored music and network streaming. ANALOG SOUND PALETTE The A&ultima SP4000T is the industry’s first digital audio player to use four MIL-Spec Raytheon JAN6418 vintage vacuum tubes in a Quad configuration. Independent dual-tube structures are dedicated to the left and right channels, bringing a channel-separated architecture traditionally associated with high-end home tube amplifiers into a portable player. The four tubes operate in a differential configuration, with each pair arranged in mirror symmetry. This configuration amplifies the music signal while mutually cancelling common-mode noise. Each tube is measured for its noise and gain characteristics before pairing and is isolated through independent modular flexible PCBs and a multilayer architecture. Triple Tube Mode combines Triode, Ultra Linear, and Pentode operation with the Triple AMP System and three-level tube-current adjustment, providing up to 54 possible combinations. Triode mode emphasizes rich harmonic texture and lingering decay, Ultra Linear mode balances tonal color with solid output, and Pentode mode maximizes output and dynamic range for a cleaner and more forceful presentation. “The delicacy of Triode, the balance of Ultra Linear, the dynamics of Pentode.” — Astell&Kern, SP4000T Product Development TRIPLE AMP SYSTEM Built on Astell&Kern’s Teraton Alpha technology, the SP4000T offers three distinct amplification approaches. OP AMP mode focuses on high resolution, clarity, dynamics, and an expansive soundstage, while Tube AMP mode emphasizes the warm texture and emotional depth associated with real vacuum-tube amplification. Hybrid AMP mode combines analog character with high-resolution output through five adjustable stages, allowing listeners to select the balance of tube warmth and solid-state precision that best complements their headphones, music, and personal preferences. ADVANCED AUDIO ARCHITECTURE The SP4000T uses a HEXA audio circuit structure built around two AK4191EQ digital delta-sigma modulators and two AK4499EX analog DACs. Digital and analog signal processing are physically separated to reduce noise and preserve signal integrity, while High Driving Mode, Enhanced Signal Alignment, Advanced DAR, and Astell&Kern Direct Path further support detailed, bit-perfect high-resolution playback. A five-stage second-generation anti-microphonic architecture isolates the four vacuum tubes using modular flexible PCBs, silicone cushioning, custom-fit silicone around the tube leads, suspended silicone dampers, and copper shield cans to suppress vibration-related tube noise.p> Comfort & Build The SP4000T features a stainless-steel and copper body built around Astell&Kern’s “Burst” design concept, which visually represents concentrated energy expanding outward from the volume wheel. Its 6-inch 2K touchscreen provides a large interface for navigation, while the included Cognac-colored case uses Minerva leather from the Italian tannery Badalassi Carlo and includes a rear cutout that reveals the vacuum-tube LED glow. Included + Specs What’s Included Astell&Kern A&ultima SP4000T Digital Audio Player Premium Cognac Minerva Leather Case 256GB of Built-In NAND Storage USB Type-C Charging and Data Input Key Specs DAC: AK4191EQ x2 + AK4499EX x2 Vacuum Tubes: Raytheon JAN6418 x4 (Quad Tube) Display: 6-inch 2K (2160 x 1080) touchscreen Outputs: 3.5 mm single ended unbalanced and digital optical; 4.4 mm balanced Output Level: 4.2 Vrms unbalanced; 8 Vrms balanced Output Impedance: 0.7 Ω (3.5 mm Unbalanced) │ 1.7 Ω (4.4 mm Balanced) Frequency Response: ±0.006 dB (20 Hz–20 kHz), ±0.06 dB (20 Hz–70 kHz) Signal-to-Noise Ratio (S/N): 124 dB @ 1 kHz (Unbalanced) │ 125 dB @ 1 kHz (Balanced) Crosstalk: -136 dB @ 1 kHz (Unbalanced) │ -145 dB @ 1 kHz (Balanced) Total Harmonic Distortion + Noise (THD+N): 0.0006% @ 1 kHz (Unbalanced) │ 0.0004% @ 1 kHz (Balanced) Storage: 256GB internal; microSD up to 1.5TB Wireless Connectivity: Wi-Fi 802.11 a/b/g/n/ac/ax and Bluetooth 5.2 Battery Capacity: 7,450 mAh, 3.8 V Li-Polymer Playback Time: Approximately 10 hours Weight: Approximately 19.9 oz (565 g)