The FiiO WARMER is a desktop digital-to-analogue converter that brings together a true R2R resistor-ladder DAC architecture and a vacuum tube buffer stage in a single, compact unit. Where most desktop DACs use conventional delta-sigma chips, the WARMER employs a fully differential R2R design built from 192 high-precision thin-film resistors — 48 per channel — each matched to 0.1% tolerance with an ultra-low 30ppm temperature coefficient. The result is a more linear, measured conversion that many listeners describe as distinctly natural and analogue in character.
R2R Ladder DAC Architecture
The four-way fully differential R2R array operates in two modes selectable by the user. Non-oversampling (NOS) mode processes your music at its original sample rate, preserving the timing and transient character of the source file. Oversampling (OS) mode upsamples to 384kHz for those who prefer additional high-frequency reconstruction filtering. Both modes draw on the ES9068AS chips, one per channel, for left/right channel management alongside the resistor arrays.
Vacuum Tube Buffer Stage
Following the DAC stage, the analogue signal passes through four JJ Electronic E88CC vacuum tubes imported from Slovakia. These double-triode valves are powered by a dedicated ±28V supply — significantly higher than the token voltages found in some budget tube designs — giving them enough headroom to operate in a genuinely linear part of their characteristic curves. Each tube is rated for 10,000 hours of service, and spares are included in the box. The tube stage adds a degree of harmonic richness and tonal warmth that complements the already natural presentation of the R2R front end.
Linear Toroidal Power Supply
Rather than a switching supply, the WARMER uses a 46W low-noise toroidal transformer wound on a non-oriented silicon steel core. The linear supply keeps mains-derived noise and ripple well clear of the sensitive DAC and tube stages, which is particularly important in an R2R design where power rail quality directly influences DAC linearity.
Inputs, Outputs and Display
Three digital inputs are provided: USB-C (supporting UAC1.0 and UAC2.0 for driverless operation on most platforms), optical, and coaxial. Both balanced XLR and single-ended RCA line outputs are available simultaneously, making it straightforward to run the WARMER into an integrated amplifier or headphone amplifier of your choice. A pair of backlit mechanical VU meters — driven by a dedicated control IC — gives the front panel an elegant, vintage-inspired character while providing a practical indication of output level.
Design and Build
The WARMER is styled around a blend of classic square and round forms, with a grille that allows adequate airflow around the tubes. It is available in Black or Silver to suit a range of system aesthetics. In the box you will find the unit itself, an AC power cable, a USB cable, a spare fuse tube, a quick-start guide, and a warranty card.
