FiiO is about to release a DAC that houses the holy trinity of audiophile catnip: 1) an R2R DAC with 2) a tube-buffered output stage and 3) mechanical VU meters. The R2R Warmer puts these three features in a half-width box for an asking price that doesn’t fly in the stratosphere.

Let’s dig in.

R2R ladder

First: the R2R DAC circuit. Unlike the delta-sigma chips found in most modern DACs, which rapidly switch between voltage levels to approximate the analogue waveform, R2R (resistor-to-resistor) DACs use precision resistor ladders to convert digital bits to analogue voltages directly.

FiiO’s proprietary implementation, the same ladder (I think) found in its K13 R2R, employs 192 thin-film resistors (48 per channel) with 0.1% tolerance. The R2R Warmer defaults to NOS (non-oversampling) mode for a purist approach, but a toggle switch on the back panel engages OS (oversampling) mode, upsampling all incoming digital signals to 384kHz before decoding.

Connectivity on the R2R Warmer covers the essentials: USB-C (supporting up to 32-bit/384kHz PCM and DSD256), TOSLINK and coaxial inputs, with both single-ended RCA and balanced XLR outputs that can (apparently) be run simultaneously.

Tube buffer

Second: those four JJ Electronics E88CC tubes from Slovakia aren’t amplifying anything. They’re acting as a buffer stage, adding harmonic richness without gain. A tube buffer like this colours the sound with even-order harmonics — the pleasant kind that makes pianos sound fuller-bodied rather than skeletal.

Running on a ±28V supply, these tubes inject what FiiO calls “sweet, organic tube flavour” into the signal path. However, the tubes work in tandem with op-amps. The op-amps handle the heavy lifting of current delivery and impedance matching, whilst the tubes add their harmonic signature. It’s a hybrid approach that maintains the tubes’ character without the typical tube amplifier limitations of high output impedance or limited drive capability.

Feeding the R2R Warmer’s circuitry is a 46W ‘low-noise’ toroidal transformer — some might call this ‘proper old-school’ linear power.

VU meters

Third: the backlit twin mechanical VU meters. Digital meters might be more accurate, but they’re also synthetic. Mechanical meters move with the music’s dynamics in real-time, their needles excited by electromagnetic force (and not software).

A reality check (for some)

The combination of an R2R DAC and a tube-buffered output stage will weaken this unit’s measured performance. FiiO has already published the numbers on its website, where the R2R Warmer’s SINAD nudges 65dB: a figure that would (and will!) make measurement obsessives weep into their keyboards. FiiO isn’t pursuing that end of the market here, and grumbling about how this DAC is deliberately coloured and purposefully euphonic is like complaining that your dog isn’t a cat. But it also tacitly admits that not all DACs sound the same. And I expect the R2R Warmer to prove that beyond all reasonable doubt — but I also expect it will run warm to the touch.

Price? €464. Your choice of black or silver.

Further information: FiiO