Two miniature vacuum tubes, built decades ago for military electronics, running off a battery in a machine you can carry — driving headphones from a compact disc.

The tubes are the whole argument. Cayin picked Raytheon JAN6418 pentodes, subminiature valves originally made to survive being shaken around inside military gear, and suspended them in a silicone damping system. That last detail is the one that makes the thing possible rather than merely charming: tubes are microphonic, and a portable player is a device you carry, tap and set down. Without the suspension, every footstep would ring faintly through the music.

What you get for it is a switch. The Timbre Menu moves between Classic Tube, Modern Tube and Solid-State, and — unusually — the choice applies to the headphone output, the line out and the Bluetooth transmission alike, rather than only to the analogue path. Underneath sits a fully symmetrical discrete four-channel headphone amp that runs in Class-A or Class-AB, rated across an 8 to 600 ohm range, so it drives sensitive in-ears and stubborn high-impedance cans from the same box. Both 3.5mm and 4.4mm balanced outputs are on the front.

It refuses to be only a CD player. It takes USB and Bluetooth as inputs as well as discs, transmits and receives over LDAC, aptX Adaptive and aptX HD, and offers coaxial, optical and Bluetooth digital outputs. Best of all, it rips: press one button and the disc copies losslessly to USB storage, which quietly makes it the most pleasant CD ripper anybody has built in twenty years.

The limitations are the ordinary ones for the category. Battery life is roughly 7.5 hours and varies a lot with which mode you are in — tubes cost power. And the price is not casual: around $699 through US dealers, €998 in Europe, with distribution running through specialist hi-fi shops rather than the usual places. It also charges over QC and PD, so at least the power brick is not another purchase.