FiiO M33 R2R blue

After integrating its in-house R2R technology into desktop DACs (K11 R2R, K13 R2R) and a portable CD player (DM15 R2R), FiiO is taking things up a notch by bringing it to a full Android music 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 lineup.

A passive R2R DAC with 192 resistors

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.

Clocking and digital processing inherited from the M27

Digital signal processing relies on the DAPS (Digital Audio Purification System) developed by FiiO, already found in the M27. It is based on a new-generation FPGA featuring 4480 logic units (versus 1152 on the previous generation in the M23), coupled with two dedicated femtosecond oscillators, calibrated respectively at 49.152 MHz and 45.1584 MHz to cover the two families of sampling frequencies. This clocking foundation handles synchronization between the Qualcomm SoC, the XMOS XU316 USB interface, and the four R2R channels in I2S and native DSD, with the aim of minimizing jitter throughout 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, an appreciated point for video playback or gaming.

Powerful, segmented amplification

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 filter 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 through the balanced 4.4 mm jack and 470 mW through the 3.5 mm jack. Four gain levels allow the M33 R2R to be used equally well with sensitive IEMs and with planar or high-impedance headphones. The analog and digital circuits are physically separated and independently shielded, and the analog power supply itself is split into three distinct circuits for the R2R network, the preamp, and the amplifier.

Four sound colors in a single device

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 remains neutral, while the Warm profile slightly thickens the presentation and softens the top end. This gives four distinct combinations that noticeably alter the character of the 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 makes it possible to convert all streams to DSD. These settings also work with third-party apps, not only with the FiiO player.

A compact format and refined chassis

Measuring 138.2 × 71.5 × 17 mm and weighing 258 g, the M33 R2R is smaller and lighter than the M21, its predecessor in size, despite offering higher capabilities. Its 18:9 format gives it a grip similar to that of a smartphone, and the beveled edges avoid unpleasant sharpness during extended listening sessions. The chassis is aluminum, with an AG matte glass back (anti-glare and resistant to fingerprints). Three colors 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 displays 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, making it possible to lay the player flat or slip it 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 key.

Android 13 and extensive connectivity

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 (streamlined 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 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 and a desktop mode

Two USB-C ports divide 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 player directly from mains power. The benefit is twofold: extend battery lifespan (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.

Battery life and fast charging

The 4400 mAh battery offers up to 14 hours of listening through the 3.5 mm output and around 12 h 30 through the balanced 4.4 mm output (FiiO even states 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 represents an improvement over the M23, thanks to Android 13 software optimization and the efficiency of the Snapdragon 680.

Technical specifications

Digital-to-analog conversion

• 24-bit passive R2R DAC
  • Network of 192 matched resistors
  • Non-oversampling conversion (native R2R approach)
• 4-channel architecture in fully differential topology
• Supported formats: up to 32-bit / 768 kHz and DSD512
• All-to-DSD mode: conversion of all streams to DSD

Amplification

• Configuration: 8 operational amplifiers in parallel
• End-to-end balanced topology
• Output power
  • 4.4 mm balanced jack: up to 1100 mW
  • 3.5 mm single-ended jack: up to 470 mW
• Separation of analog / digital circuits

System and interface

• Operating system: Android 13
• Processor: Qualcomm Snapdragon 680
• RAM: 8 GB
• Internal storage: 128 GB (expandable via microSD up to 2 TB)
• Operating modes
  • Android
  • Pure Music
  • Roon Ready
  • Bluetooth
  • AirPlay
  • DLNA

Streaming and applications

• Access to the Google Play Store
• Compatible streaming services: Spotify, Deezer, Qobuz, Tidal, Apple Music, Amazon Music
• Network protocols: DLNA / UPnP
• FiiO Link function (remote control)

Wireless connectivity

• Dual-band WiFi 2.4 / 5 GHz
• Bidirectional Bluetooth 5.0
• Supported codecs: SBC, AAC, aptX, aptX HD, LDAC, LHDC
• Hi-Res Audio Wireless certification
• Apple AirPlay compatible

Connectivity

• USB-C (x2)
  • USB Audio / USB DAC / data transfer
  • Charging and desktop mode
• Outputs
  • 3.5 mm jack: headphones / line / optical / coaxial
  • 4.4 mm balanced jack: headphones / line

Screen and ergonomics

• 14 cm (5.5-inch) IPS multi-touch screen
• Resolution: 1440 x 720 px (312 ppi)
• Display: 16 million colors
• Physical controls
  • Rotary volume knob
  • Playback / navigation buttons
• Dedicated desktop mode

Power supply and battery life

• Battery: 4400 mAh
• Battery life
  • Up to 14 h (3.5 mm output)
  • Up to 12 h 30 (4.4 mm output)
• Fast charging: approximately 1 h 30 (12 V / 1.5 A)
• Desktop mode: optimized mains power supply

Advanced functions

• 10-band parametric equalizer
• Selectable digital filters
• Configurable oversampling
• Use as an external USB DAC
• NAS compatible / network playback

General information

• Aluminum chassis
• Format: portable audiophile player
• Interface: touchscreen and physical controls