Discover FiiO's R2R Lineup
- FiiO's R2R DAC is built on a 24-bit fully differential resistor ladder network, made up of 192 precision thin-film resistors (48 per channel, 0.1% tolerance, 30 ppm thermal drift).
- All R2R models support both NOS (Non-Oversampling) and OS (oversampling to 384 kHz) modes, switchable between listening sessions.
- R2R DACs measure differently from delta-sigma designs — THD+N and noise floor generally higher — but produce a distinct tonal character that many describe as warmer and more natural.
- Six models currently available at Fillion Électronique: K11 R2R, K13 R2R, WARMER R2R, M33 R2R, BR15 R2R and DM15 R2R.
Most DACs use delta-sigma chips. The principle: switching millions of times per second between two voltage states, then averaging the result. It measures very well and sounds clean to most ears.
R2R is different at a fundamental level. No dedicated chip; the conversion circuit is built from a network of resistors arranged in a ladder, where each rung corresponds to one bit of the digital signal. The analogue output is directly the sum of those resistor contributions. No oversampling, no noise shaping; the signal converts cleanly or it doesn't.
FiiO launched its first R2R design in 2024 with the K11 R2R. Since then, the technology has extended to other models: the K13 R2R, the WARMER R2R, the portable player M33 R2R, the Bluetooth receiver BR15 R2R and the portable CD player DM15 R2R.
How R2R DAC Architecture Works
Delta-sigma chips oversample the input signal, sometimes several times its original rate, then use noise shaping to push quantization distortion beyond the audible spectrum. A filter then removes this residue before the output. The process is highly effective and produces excellent measurements.
An R2R DAC bypasses all of that. A network of matched resistors, one per bit of the signal, converts the digital data to analogue voltage in a single pass. The output is the sum of those contributions. In NOS (Non-Oversampling) mode, the signal reaches the resistors exactly as it was recorded.
Two conditions must be met for it to work. The resistors must be precisely matched (FiiO specifies a 0.1% tolerance) because the slightest deviation becomes a conversion error in the output. And the circuit must run fully differential, which cancels noise from both signal paths simultaneously. Together, these two factors tend to produce lower odd-order harmonic distortion than delta-sigma designs. That is what listeners often describe as a more natural sound, or one closer to analogue.
None of this means R2R measures better; it doesn't. THD+N and noise floor are generally higher than what a good delta-sigma chip produces. The question is what you prefer: better measurements, or a different kind of sound. Both answers are valid.
NOS and OS Modes: What Changes in Practice
All of FiiO's R2R models offer two playback modes:
NOS mode (Non-Oversampling) sends the signal to the resistors as is, without oversampling, without additional processing. The sample rate stays that of the source. The sound leans warm, with a softer top end. Some find this more musical for acoustic music or long listening sessions; others find it a bit lacking in precision compared to what they are used to.
OS mode (Oversampling) upsamples to 384 kHz before conversion. Measurements improve, treble extends, the overall presentation gains in precision. If you are coming from a conventional DAC, this is the mode that will feel most familiar without losing the R2R warmth.
The advantage of having both is not being locked into a choice. You can switch based on the recording, the headphones, or how you feel at the moment.
FiiO's R2R Lineup
FiiO K11 R2R — Desktop DAC/Amp 
The K11 R2R is where FiiO's R2R lineup started, and the architecture it introduced — 192 thin-film resistors, four fully differential channels, matched to 0.1% — is found in every model that followed. Output power reaches 1,300 mW balanced at 32 Ω, sufficient for most headphones, including high-impedance models. Inputs are USB-C, optical and coaxial. On the front panel, a 4.4mm balanced headphone output and a 6.35mm standard jack; on the back, RCA outputs. Compact, aluminium, powered by an external 12V adaptor.
FiiO K13 R2R — Desktop DAC/Amp with Bluetooth and XLR
The K13 R2R uses the same DAC circuit as the K11 — 192 resistors, same tolerances — but the amplifier section gains considerably in power: 2,400 mW balanced at 32 Ω, nearly double. That extra headroom opens the door to planar magnetic headphones and more demanding models. The K13 also adds Bluetooth 5.4 with LDAC, an internal 30W power supply (no more external brick), a 10-band parametric EQ, balanced XLR outputs alongside RCA, and an XMOS XU316 USB processor. The top panel has an opening — the "Skylight" — that lets you see the resistor network inside. A DC input is available for a linear power supply.
FiiO WARMER R2R — DAC with Tube Output Stage
The WARMER R2R does two things at once: R2R conversion up front, tube output stage behind it. The tubes are JJ E88CC — four in total — and two mechanical VU meters sit on the front panel. Outputs are RCA and XLR. There is no headphone output; it is a line-level component that needs a separate amp downstream. The idea is to layer the warm character of R2R conversion with the harmonic texture of valves — a proposition for speaker systems or reference headphone amp chains, not for direct listening.
FiiO M33 R2R — High-Resolution Android Player
The M33 R2R puts the same resistor network into a pocket Android player. It sits below the M27 in the lineup, but still delivers 1,100 mW balanced at 32 Ω — enough for most headphones. The R2R DAC is paired with a Texas Instruments amplifier and the XMOS XU316 USB interface. A separate power input allows it to be used in desktop mode. Ships with Android 13. Available in black, blue and gold.
FiiO BR15 R2R — Bluetooth Receiver and Desktop DAC
The BR15 R2R is the model in the lineup designed for wireless streaming. The same R2R circuit runs inside — 192 resistors, 48 per channel — but the input side is built around a Qualcomm QCC5181 chip in Bluetooth 6.0: aptX Lossless, aptX Adaptive, LDAC, LC3 and AAC. Wired inputs are USB, coaxial and optical. On the output side: two RCA, one balanced XLR, plus optical and coaxial passthrough. A 10-band EQ with AUTO EQ handles room adaptation. If your main source is a phone or a streaming device and you want R2R conversion downstream, this is it.
FiiO DM15 R2R — Portable CD Player with R2R DAC
The DM15 R2R is a CD player — a rare object at this end of the market. FiiO integrated the same 192-resistor R2R circuit found in their desktop units, which changes the nature of disc playback: same R2R warmth, same character, on physical media. The headphone amp is rated at 1,150 mW balanced, capable of driving demanding headphones directly. Connected via USB-C, it also works as a desktop DAC: PCM up to 384 kHz/32-bit and DSD256. Bluetooth is for transmission, not reception — it sends what the disc is playing to wireless headphones or speakers. There are 24 EQ presets, including a retro mode. Battery life: 7 hours. Available in black, silver, red and white.
R2R vs. Delta-Sigma: A Direct Comparison
| Criterion | R2R (resistor ladder) | Delta-sigma (integrated chip) |
|---|---|---|
| Conversion method | Direct: binary-weighted resistor network | Indirect: oversampling + noise shaping |
| Measured THD+N | Generally higher | Generally lower |
| Noise floor | Generally higher | Generally lower |
| Tonal character | Warmer, more organic (subjective) | Neutral, analytical |
| NOS mode available | Yes — inherent to the architecture | Rarely |
| Manufacturing cost | Higher (precision resistor matching) | Lower (integrated chip) |
| Harmonic profile | Lower odd-order distortion (generally) | Varies by implementation |
| Objective transparency | Implementation-dependent | Consistently high at all price points |
Frequently Asked Questions
What does R2R mean in a DAC?
R2R refers to the resistor values that make up the circuit: R and 2R, alternating in a ladder pattern. In a standard DAC chip, conversion is handled digitally; oversampling, noise shaping, filtering. In an R2R DAC, the resistors themselves do the conversion. Each bit of the audio signal controls one rung of the network; the output is the sum of those contributions. Simpler in theory, harder to build accurately.
Does R2R sound better than delta-sigma?
Not objectively. Delta-sigma measures better: lower distortion, lower noise floor. R2R has a different sound: warmer, a bit more organic, especially in NOS mode. Some strongly prefer it, others hear the measurement gap more than the tonal character. It depends on your system, your headphones, and what kind of listening fatigue affects you most.
What is NOS mode, and should I use it?
NOS sends the file to the resistors without any pre-processing. The sample rate stays that of the recording. The result sounds smoother, with less edge in the upper frequencies. OS upsamples to 384 kHz upstream, measures better and sounds more precise. There is no universally right answer; try NOS on acoustic music, OS when you want more detail and definition. The fact that FiiO offers both at no extra cost is one of the most concrete practical advantages of their R2R approach.
Why does FiiO's R2R DAC use 192 resistors?
192 total; that is 48 per channel, across four channels. Each one is matched to 0.1% tolerance, which matters because the slightest deviation becomes a conversion error. If two supposedly identical resistors differ slightly, the bit they process does not convert exactly as expected, and you hear it as distortion. Thermal drift is specified at 30 ppm, meaning the resistors remain accurate even once the unit is warm. 0.1% is the expected benchmark for a well-designed R2R design at this price range.
What is the difference between the K11 R2R and the K13 R2R?
The R2R circuit is identical; same number of resistors, same tolerances. What changes is everything else. The K13 nearly doubles the output power (2,400 mW vs. 1,300 mW balanced at 32 Ω), replaces the external power brick with an internal 30W supply, adds Bluetooth 5.4 with LDAC, balanced XLR outputs, an XMOS XU316 processor and a 10-band parametric EQ. The K11 is the right choice if you have moderately sensitive headphones and have no need for wireless. The K13 is the right call for more power-hungry headphones, speaker systems, or if you want to listen from your phone.
What is the BR15 R2R, and how does it differ from the K11 and K13?
The BR15 R2R is the only model in the lineup built around Bluetooth as the main input. The R2R circuit is the same as in the K11 and K13, but it feeds a Qualcomm QCC5181 chip in Bluetooth 6.0 handling aptX Lossless, aptX Adaptive, LDAC and LC3. One thing to note: there is no headphone output. Outputs are line-level only (RCA, balanced XLR, optical and coaxial) which requires a separate amp or active speakers downstream.
Can I use the K13 R2R with powered speakers?
Yes. The K13 offers RCA and balanced XLR outputs, with a dedicated preamp mode where volume is controlled independently from the headphone output from the front panel knob, the FiiO Control app or the remote included in the box. Connected to a power amp or active monitors, it fills the DAC/preamp role without any compromise.
Is the WARMER R2R a headphone amplifier?
No. The WARMER R2R is a line-level DAC; it has no headphone output. The RCA and XLR connections go to a separate amplifier, a power amp, or active speakers. It is not designed for direct headphone listening and is instead entirely dedicated to signal processing.
What makes the DM15 R2R different from a regular CD player?
Almost all portable CD players use delta-sigma chips, the same as in smartphones or USB dongles. The DM15 R2R replaces that with FiiO's resistor network, so discs play back with the same tonal character as their desktop R2R units. Beyond the CD transport, it accepts USB-C audio input (up to 384 kHz/32-bit and DSD256) and works as a desktop DAC. The headphone amp outputs 1,150 mW per channel. Bluetooth is transmission only; it sends what the disc is playing to wireless headphones or speakers, but does not receive.
Can I use the K13 R2R with a linear power supply?
Yes. In addition to the internal supply, a DC input is available at the back (12V, 2.5A minimum, 5.5×2.1mm connector). In DC mode, the internal supply cuts out completely; the K13 runs exclusively on what you have connected. FiiO's PL50 and PL70 linear supplies are compatible, as is any third-party model meeting the specifications.
Which headphones/earphones work well with FiiO's R2R DAC/amps?
The K11 drives most headphones up to 300 Ω without difficulty; the Sennheiser HD 600, HD 650 and HD 660S2 are typical examples. The K13 extends that to more power-hungry planar magnetic headphones, like certain Meze models. For sensitive in-ear monitors, both units offer a gain adjustment.
All products mentioned in this article are available online and in-store in Montreal. Our team can help you choose the model suited to your needs, your system and your listening habits.
Explore FiiO R2R products at Fillion
