Astell&Kern SP4000T

The Astell&Kern A&ultima SP4000T is the new flagship of the A&ultima line and the first digital audio player built around four vacuum tubes. It pairs A&K's reference dual-DAC architecture with a quad Raytheon tube stage, giving listeners up to 54 ways to shape the sound, from solid-state precision to rich, tube-driven warmth.

Type and Technology

A reference digital source built on AKM's flagship silicon: dual AK4191EQ modulators feeding dual AK4499EX DACs in A&K's HEXA discrete configuration, one per channel. What sets the SP4000T apart is its analog stage, the industry's first quad-tube design, using four Raytheon JAN6418 MIL-Spec vacuum tubes in a channel-separated, fully balanced layout. It runs Android 15 with the full Google Play Store on an octa-core processor, and decodes PCM up to 32-bit/768kHz and native DSD512.

Sound Character

The SP4000T is made to be tuned. Three tube voicings (Triode, Ultra Linear, and Pentode) combine with three amplifier modes (OP AMP, Tube, and Hybrid) and adjustable tube current for up to 54 distinct presentations, from clean and linear to warm and harmonically rich. A second-generation, five-stage anti-microphonic structure keeps the tube stage quiet, and measured performance stays reference-grade, with frequency response within plus/minus 0.006 dB from 20 Hz to 20 kHz, THD+N as low as 0.0004%, and signal-to-noise up to 125 dB balanced.

Build and Finish

The SP4000T is offered in machined stainless steel and copper finishes. It ships with a cognac-colored case in Minerva leather, hand-finished by Badalassi Carlo of Florence. A 6-inch 2K touchscreen, dual-antenna Wi-Fi 6, and USB-C round out a player that also works as a USB DAC for Mac and Windows and as a Bluetooth DAC through BT Sink.

Best For

Listeners who want one reference-class portable source that can be voiced to taste, pairing the resolution of a flagship dual-DAC design with the character of real vacuum tubes, and who drive everything from sensitive IEMs to demanding planar headphones from a single device.

What's in the Box

• Astell&Kern A&ultima SP4000T
• Minerva leather case (cognac)
• USB-C to USB-C cable

Specifications