After integrating its in-house R2R technology into desktop DACs (K11 R2R, K13 R2R) and a portable CD player (DM15 R2R), FiiO takes things a step further by bringing it to a full Android portable player. The M33 R2R is the brand’s first DAP to feature a resistor ladder converter, a radically different approach from the delta-sigma chips found in the vast majority of today’s portable players, including the M23 it replaces and the M27, the flagship model in the range.
The M33 R2R’s converter is based on a network of 192 thin-film resistors, matched to 0.1% tolerance with low thermal drift. The whole system operates in a fully differential four-channel topology (left +/-, right +/-), with 24-bit resolution. Where a delta-sigma DAC reconstructs the analog signal through massive oversampling and noise shaping, an R2R DAC converts each bit of the digital signal into a proportional voltage via its resistor ladder. The processing is more direct, shorter, and the sonic result reflects that: playback often described as more organic, rounder, with a sense of timbre and temporal fluidity that delta-sigma chips struggle to reproduce.
This technical choice comes with a significantly higher manufacturing cost than an integrated DAC, which partly explains why R2R portable players remain rare on the market.
Digital signal processing relies on the DAPS (Digital Audio Purification System) developed by FiiO, already featured in the M27. It is based on a new-generation FPGA with 4480 logic units (versus 1152 on the previous M23 generation), coupled with two dedicated femtosecond oscillators, calibrated respectively at 49.152 MHz and 45.1584 MHz to cover the two sampling-rate families. This clocking foundation manages synchronization between the Qualcomm SoC, the XMOS XU316 USB interface, and the four R2R channels in I2S and native DSD, with the goal of minimizing jitter across the entire chain.
The XMOS XU316 interface is a common component in high-end DACs. It supports PCM up to 768 kHz / 32-bit and DSD512, and ensures very low latency in USB DAC mode, a welcome point for video playback or gaming.
The amplification stage borrows from FiiO’s higher-end models. The preamplification stage uses TI Burr-Brown OPA1637 operational amplifiers for I/V conversion and an OPA1662 low-pass filtering stage, while four INA1620 amplification chips in parallel configuration drive the headphone outputs. Volume control is handled by an NJW1195A, a precision electronic potentiometer that offers fine adjustment and good channel consistency.
Output power reaches 1100 mW per channel on the balanced 4.4 mm jack and 470 mW on the 3.5 mm jack. Four gain levels allow the M33 R2R to adapt equally well to sensitive IEMs and to planar or high-impedance headphones. The analog and digital circuits are physically separated and independently shielded, and the analog power supply itself is divided into three distinct circuits for the R2R network, the preamp, and the amplifier.
The M33 R2R offers two digital processing modes, OS (oversampling) and NOS (non-oversampling), which can be combined with two sound profiles, Flat and Warm. NOS mode preserves the original sampling rate for a rawer, more direct signal, while OS mode applies conventional filtering. The Flat profile stays neutral, while the Warm profile slightly thickens playback and softens the upper range. This gives four distinct combinations that noticeably alter the character of the portable player, from the most analytical (OS + Flat) to the most musical (NOS + Warm).
In addition, a 10-band parametric equalizer is available, with an Auto EQ mode that automatically adapts the correction curve to FiiO IEMs and headphones. An All-to-DSD mode allows all streams to be converted to DSD. These settings also work with third-party apps, not only with the FiiO player.
At 138.2 × 71.5 × 17 mm and 258 g, the M33 R2R is smaller and lighter than the M21, its predecessor in size, despite offering greater capabilities. Its 18:9 format gives it handling close to that of a smartphone, and the beveled edges prevent unpleasant sharpness during extended listening sessions. The chassis is aluminum, and the back is matte AG glass (anti-glare and fingerprint-resistant). Three color options are available: black, dark blue, and retro gold, each supplied with a matching leather case and a tempered glass screen protector.
The 5.5-inch IPS touchscreen has a resolution of 1080 × 2160 pixels with a laminated panel. The 3.5 mm and 4.4 mm headphone outputs are placed on the top edge, allowing the portable player to be laid flat or slipped into a pocket with the cable facing upward. The side edge houses the volume wheel, power button, a dedicated desktop mode button, and a programmable multifunction button.
The M33 R2R runs Android 13 with a Qualcomm Snapdragon 680 SoC, 8 GB of LPDDR5 RAM, and 128 GB of internal storage (around 112 GB usable), expandable via microSD up to 2 TB. The Google Play Store provides access to Spotify, Deezer, Qobuz, Tidal, Apple Music, Amazon Music, and any other Android app. Navigation is smooth, startup is fast, and switching from one app to another suffers from no noticeable latency.
In addition to standard Android mode, the M33 R2R offers a Pure Music mode (lightweight system for local playback), a Roon Ready mode, Bluetooth mode (reception), AirPlay, and DLNA for network playback. Dual-band WiFi (2.4 and 5 GHz) ensures a stable connection for high-resolution streaming.
Bluetooth 5.0 is bidirectional: in transmission mode, it supports the SBC, aptX, aptX HD, LHDC, and LDAC codecs; in reception mode, SBC and LDAC. The portable player can therefore serve as a Bluetooth receiver from a phone, a practical option for those who want to centralize playback on the M33 R2R without a cable.
Two USB-C ports share the tasks. One handles USB audio, data transfer, and the external DAC function; the other is dedicated to charging and desktop mode. This desktop mode, activated by a physical button, bypasses the battery to power the portable player directly from mains power. The benefit is twofold: extend battery life (fewer charge/discharge cycles) and unlock higher output power for the most demanding headphones.
The 3.5 mm jack output is versatile: it serves as a headphone output, line output, and optical or coaxial digital output (with a suitable cable sold separately). The balanced 4.4 mm output works in headphone or line mode. The line outputs have their own amplification circuit, separate from that of the headphone outputs.
The 4400 mAh battery provides up to 14 hours of listening via the 3.5 mm output and around 12 h 30 via the balanced 4.4 mm output (FiiO even claims 15.5 h and 13.5 h in certain configurations). Low-temperature fast charging (12 V / 1.5 A) allows a full cycle in around 1 h 30, without excessive overheating. Battery life is an improvement over the M23, thanks to Android 13 software optimization and the efficiency of the Snapdragon 680.
The M23 used delta-sigma DAC chips (ESS). The M33 R2R adopts a discrete resistor R2R converter developed by FiiO, a totally different technology that produces a more organic sound rendering. It inherits the M27’s DAPS clocking system, has 8 GB of RAM (versus less on the M23), moves to Android 13, and gains battery life.
No. NOS mode (non-oversampling) preserves the signal at its original sampling rate, without additional digital filtering. The rendering is more direct, with a warmer and more fluid character. OS mode (with oversampling) delivers a cleaner, more analytical sound. Both are aesthetic choices, not quality compromises.
With 1100 mW per channel from the balanced 4.4 mm output and four gain levels, the M33 R2R can drive most planar and high-impedance headphones. Desktop mode, powered from mains, unlocks even more power for the most demanding loads.
The integrated Auto EQ is calibrated to the target curves of FiiO IEMs and headphones. It does not offer automatic profiles for models from other brands, but the 10-band parametric equalizer allows precise manual adjustments compatible with any transducer.
Yes. Connected via USB-C to a computer, the M33 R2R works as an external DAC/amp and supports PCM up to 768 kHz / 32-bit and native DSD512, thanks to its XMOS XU316 interface.
Eduardo
excellent product with one limitation: the manual is too brief!!!
Comment from August 19, 2026 — Experience from August 08, 2026
