Astell&Kern A&ultima SP4000T

Astell&Kern A&ultima SP4000T

The Astell&Kern A&ultima SP4000T is the brand's flagship portable digital audio player, the result of nearly two years of development building on the SP3000T and its pursuit of a single question: how to bring deeper emotion through analog sound. Where most players treat the DAC, amplifier and any tube stage as separate ingredients, the SP4000T is engineered as a complete analog-voiced instrument, designed to be immediately comfortable to listen to while revealing more detail and character the longer you spend with it. It sits at the very top of the A&ultima line as a reference-class source for demanding headphones and in-ear monitors.

At its heart is an industry-first quad vacuum-tube stage, using four MIL-Spec Raytheon JAN6418 tubes arranged in a differential, mirror-symmetric configuration that cancels noise, with each tube individually measured for noise and gain before installation. A second-generation, five-stage anti-microphonic architecture isolates every tube on its own flexible PCB with silicone cushioning, damping and a pure-copper shield can, so the delicate tube sound stays free of mechanical interference, and a soft Vacuum Tube LED glows during tube operation. The new Triple Tube Mode lets you choose between Triode for the richest harmonic texture, Ultra Linear for a balance of warmth and output, and Pentode for maximum dynamic range and clean power, and combined with the amplifier modes and three selectable tube current levels this gives up to 54 distinct sonic combinations to tune to your taste.

Amplification is handled by a Triple AMP system built on Astell&Kern's Teraton Alpha engineering, offering an OP AMP mode for high resolution and clarity, a TUBE AMP mode for warm, analog character from the quad tubes, and a five-stage Hybrid mode that blends the two to taste, with a High Driving Mode that arranges the op-amps in parallel for extra driving power and stability into demanding loads. Digital conversion uses a HEXA audio circuit that pairs dual AK4499EX DACs with AK4191EQ modulators, one set per channel, keeping the digital and analog signal paths physically separate for the lowest possible noise. Proprietary technologies including ESA signal alignment, second-generation DAR upsampling with VSE harmonic restoration, and Astell&Kern Direct Path for bit-perfect streaming further refine the sound, and seven selectable DAC filters let you fine-tune the presentation.

The SP4000T plays virtually any file natively, supporting PCM up to 32-bit/768kHz and DSD up to DSD512, across formats including WAV, FLAC, ALAC, AIFF, DSF and DFF. Measured performance is exemplary, with a signal-to-noise ratio of 125dB and THD+N of just 0.0004% on the balanced output, which delivers a substantial 8Vrms to drive even hard-to-power headphones, alongside a 4.2Vrms unbalanced output. Outputs comprise 3.5mm unbalanced, 4.4mm balanced and a 3.5mm optical connection, with AK Cradle compatibility. Streaming and wireless are equally comprehensive: the player is Roon Ready, supports Qobuz Connect up to 24-bit/192kHz, and adds BT Sink, dual-antenna Wi-Fi 6, and Bluetooth 5.2 with LDAC, aptX HD and LHDC.

Everyday use is handled by a bright 6-inch 2K touchscreen, an octa-core processor running a full open Android 15 platform, 256GB of internal storage expandable by microSD up to 1.5TB, and a 7,450mAh battery giving around ten hours of playback and roughly five-hour USB-C fast charging. The chassis reflects the flagship status, machined from stainless steel and copper with a 99.9% pure copper shield can and an Any Layer HDI circuit board, finished in a choice of Silver or Copper and centred on Astell&Kern's signature volume wheel. Each SP4000T is supplied with a premium leather case in Cognac, hand-made from Italian MINERVA vegetable-tanned leather, with a cut-out at the rear to let the tube LED shine through.

What Astell&Kern say about the 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). 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. The tubes operate in a differential configuration, with each pair facing the other in mirror symmetry.

Triple Tube Mode. Triode: brings out the richest harmonic texture unique to vacuum tubes. Ultra Linear: blends the tonal color of Triode with the output of Pentode. Pentode: Maximizing tube amplifier output and dynamic range.

Triple AMP System. 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.

The bundled premium leather case uses 'MINERVA' leather from 'BADALASSI CARLO', a renowned leather workshop located in the San Miniato district of Florence, Italy, and features a rear pattern cutout designed to showcase the tube LED glow.

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 product. The ultra-low noise and high resolution achieved through Astell&Kern's TERATON ALPHA technology will reveal new dimensions of music you have never experienced before, 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.

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.

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.

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.

Specifications

About Astell&Kern

Astell&Kern is the ultimate digital music source that brings you Mastering Quality Sound or MQS. Astell means ‘Stars’ in Latin and Kern means ‘Center’ in German. We believe Astell&Kern is the center of music.

Today, original music performances can be captured in digital almost exactly as they were performed due to new, advanced recording technology currently available. However, these high quality recordings are mainly listened to through inferior sound formats, such as MP3 or through streaming services. With the debut of the MP3 format, music lovers sacrificed sound quality for the convenience of being able to carry their music collection wherever they went. Because the MP3 format heavily compresses files for the sake of convenience, the vocals and instruments you hear are only an inferior version of the original. The soundstage and the ambience of the original performance often disappears when listening to compressed MP3 music. After pondering these issues, Astell&Kern was our solution to poor sound quality for the sake of portability, and our way in reviving the original sound quality of music, MQS, for music artists, recording engineers, and professionals.

Astell&Kern's pursuit is to provide natural and original sound without distortion. It showcases the presence of the original recording with miniscule details you may not have noticed from other music systems, while playing back high-resolution music bit by bit, exactly as it was recorded. The ability to play back the exact recording of any live performance is what Astell&Kern is known for.

The power of true sound from Astell&Kern can now be experienced and has been part of many famous audio exhibitions around the world. Astell&Kern is now admired by music lovers from many countries, including the USA, China, Japan, UK, France, and many more around the world.