FiiO M33 R2R review: the most musical of FiiO’s DAPs?

Priced at €649, the FiiO M33 R2R DAP is the brand’s first portable player to feature a passive R2R DAC. This architecture, which is gradually being rolled out across the manufacturer’s entire product line, aims to deliver a more organic sound that’s closer to analog thanks to fully passive conversion via a resistor network. Compatible with 32-bit/768 kHz and DSD512, capable of delivering up to 1,100 mW into 32 ohms, and equipped with Android for streaming access and a Desktop mode, the FiiO M33 aims to combine the convenience of modern technologies with an analog listening experience unprecedented in a player at this price point.

Presentation

R2R DAC: FiiO’s shift to analog

R2R DACs are definitely on the rise and are playing an increasingly central role in the Asian manufacturer’s strategy, which has been widely implemented in its recent devices. From the FiiO K11 R2R and FiiO K13 R2R DACs to the FiiO DM15 R2R CD player, this architecture has established itself as a true signature sound. With the new FiiO M33, this approach takes a major leap forward by making its debut at the heart of a DAP.

The FiiO M33 R2R therefore moves away from the ESS Sabre or AKM delta-sigma DACs traditionally used in the brand’s portable audio players in favor of a fully passive 24-bit conversion system based on a network of 192 resistors arranged in a symmetrical configuration, with 96 resistors per channel. This approach—still very rare in DAPs and typically reserved for high-end models such as the iBasso DX270 R2R and Hiby RS8 II—involves directly converting the digital signal without resorting to the heavy oversampling and noise modulation processing typical of modern delta-sigma DACs. This architecture better preserves the signal’s temporal coherence and reduces the sense of digital harshness sometimes perceptible in certain highly analytical audio devices.

This approach fundamentally changes the device’s sound philosophy. Whereas previous FiiO DAPs focused primarily on absolute transparency, dynamics, and surgical precision, the M33 now prioritizes a smoother, denser, and more organic listening experience. This shift marks a real departure from the rest of the FiiO lineup. The M33 almost seems like the sonic antithesis of the FiiO M27, with its very neutral sound reproduction.

These various resistors are matched with a tolerance of just 0.1% and exhibit stable thermal behavior to ensure consistent conversion quality. The powerful FPGA (programmable chip) processor, coupled with two femtosecond oscillators, ensures perfect data synchronization to prevent any jitter that might affect the natural listening experience. Thanks to this architecture, the FiiO M33 R2R DAP delivers optimal playback of PCM streams (FLAC, WAV, WMA files, etc.) up to 32-bit/768 kHz, as well as DSD tracks up to DSD512. It is therefore fully compatible with a Hi-Res music library and HD streaming services.

Note from the expert
R2R (resistor-to-resistor) conversion is one of the very first digital-to-analog conversion architectures, widely used as early as the 1980s in professional equipment and the first digital audio players. Its principle is based on a network of weighted resistors, typically organized on a binary scale, with each bit of the digital signal corresponding to a specific combination of resistors. Unlike modern delta-sigma DACs, which rely on heavy oversampling and noise modulation followed by complex filtering, R2R performs a direct and instantaneous conversion of each piece of digital information. This approach minimizes intermediate digital processing and preserves the signal’s temporal structure.    

The FiiO M33’s R2R architecture can operate in either NOS (Non-Oversampling) or OS (Oversampling) mode. In OS mode, the signal is oversampled before conversion to deliver a sound reproduction that’s closer to that of modern delta-sigma DACs, with superior transparency and a more incisive soundstage. NOS mode, on the other hand, takes a much more direct approach by converting the signal without intermediate oversampling. It is in this configuration that the FiiO M33 R2R fully reveals its character. The listening experience then gains in fluidity, naturalness, and harmonic coherence, with denser tones, particularly lifelike vocals, and a sound that is more reminiscent of analog electronics.

Powerful amplification and desktop mode

To complement this R2R conversion, FiiO has equipped the M33 with an analog amplification section that is carefully isolated from the digital circuits to minimize interference and preserve signal integrity. Its fully balanced architecture relies on a preamplification stage powered by Texas Instruments OPA1637 modules, which deliver high gain with remarkable transparency and very low distortion.

This stage is paired with a power section based on eight INA1620 operational amplifiers in a parallel configuration. This design promotes an excellent signal-to-noise ratio, improved channel separation, and a particularly open soundstage. The power supply also features high-capacity Rubycon audiophile capacitors, capable of instantly delivering the necessary current during the most demanding dynamic shifts. Finally, volume control is handled by a high-precision NJW1195A circuit, ensuring smooth adjustments that are perfectly balanced between channels and completely free of noise.

This architecture allows the FiiO M33 R2R DAP to deliver up to 1,100 mW per channel into 32 ohms via the 4.4 mm balanced output and 470 mW via the 3.5 mm unbalanced output. These figures are more than sufficient to easily power the majority of earbuds and headphones, including some relatively demanding planar models. The portable player also features a “Desktop” mode, now a hallmark of FiiO. When powered via USB-C from a mains socket, the M33 bypasses its battery to preserve battery life while boosting the performance of the amplification stage. This is a particularly interesting approach for sedentary use as a desktop DAC/headphone amp. This mode is easily activated using a dedicated switch located on the right side of the player.

For home use, the FiiO M33 R2R can also be a source for a living room hi-fi system or a pair of active speakers. To do this, you can configure its two headphone outputs to line level. It can also be paired with an external DAC via the bidirectional USB-C port and the coaxial mini-jack output.

Optimized power supply

FiiO has also paid special attention to the quality of the power supply to each stage of the circuit. After an initial filtering of the current to eliminate high-frequency noise, the electrical signal is distributed to several independent converters and regulators. In particular, FiiO uses eight low-noise regulators dedicated to the various analog stages, with separate power supplies for the left and right channels of the R2R DAC, for the current-to-voltage conversion stages, and for the amplification sections. This approach, inherited from the flagship FiiO M27, proves essential here given that the R2R architecture is particularly sensitive to power supply fluctuations and electrical noise.

Power management also relies on high-capacity MOSFETs capable of handling up to 65 A. Their low internal resistance facilitates instantaneous energy transfer while minimizing losses. They are paired with high-capacity capacitors that provide a substantial current reserve, thereby preventing any dynamic flattening. The entire system is orchestrated by a power management platform capable of delivering up to 15 W of power, providing ample headroom to simultaneously power the circuit’s various stages without ever compromising stability.

The 4,400 mAh battery offers a claimed battery life of up to 15 hours and 30 minutes via the 3.5 mm headphone jack and approximately 13 hours and 30 minutes in balanced mode. These figures proved to be particularly accurate in our tests, although battery life varies slightly depending on usage conditions. Expect about 1 to 2 hours less battery life when streaming over Wi-Fi with demanding headphones, while listening to locally stored music with highly sensitive IEMs can add up to an extra 1 hour and 30 minutes. Charging is done via the USB-C port and is particularly fast. With a Power Delivery 3.0-compatible charger, it takes about 1 hour and 30 minutes to fully charge the battery. The DAP is, of course, compatible with any standard USB charger; only the charging speed may vary in that case.

Last but not least, the Desktop mode allows you to power the player from the mains (requires a USB Power Delivery 3.0 adapter, not included). This results in a higher voltage, unleashing the full power of its amplifier stage while bypassing the battery to preserve its lifespan during extended use at home.

Compact design and ergonomics

All of these technologies are integrated into a remarkably compact chassis that’s less than 2 cm thick and weighs just 258 g. This is light-years away from the almost sedentary design of the FiiO M27 and its 630 grams, whose bulkiness makes it less suitable for on-the-go use. In contrast, the FiiO M33 returns to the original spirit of the DAP, with a device light and compact enough to accompany the user in their daily life—whether in a pocket or a bag.

Remarkably, this compact design comes without compromising build quality. The chassis, made entirely of aluminum alloy, gives the audio player a solid, durable feel. On the back, a frosted glass panel adds an extra touch of elegance while improving grip. Its slightly textured finish minimizes fingerprints and reduces the risk of it slipping during use. The grooved sides complement this ergonomic design.

To effectively protect the DAP while on the go, FiiO provides a hard leather case specially designed to fit the contours of the M33. The case features a metal plate on the back to improve heat dissipation from the internal electronics, particularly during long listening sessions or when in Desktop mode. In practice, however, we mostly used the music player without this case. Not because it isn’t effective, but simply because the M33’s build quality deserves to be fully appreciated.

The FiiO M33 R2R’s physical controls are thoughtfully arranged on both sides of the device. The right side houses the playback controls for starting or pausing playback, as well as skipping to the next or previous track. It also features the dedicated Desktop Mode selector. The left side features the volume controls. These allow for particularly smooth adjustment across a scale of 0 to 100. While this solution proves effective for everyday use, it’s a shame there isn’t a true rotary knob, which is often more pleasant to use. Finally, a customizable button can be configured to shuffle tracks, change filters or EQ settings, or switch to USB DAC or Bluetooth mode.

On the front, the FiiO M33 R2R features a 5.5-inch IPS touchscreen, measuring nearly 14 cm diagonally. With a resolution of 1440 x 720 pixels, it doesn’t aim to compete with the high-resolution screens of today’s smartphones, which offer superior display clarity. That said, it perfectly fulfills its purpose of controlling music playback. Album covers are brought to life with natural colors and well-balanced contrast, while text and menus remain perfectly legible.

The experience remains enjoyable thanks to the interface’s excellent responsiveness. Navigating menus, scrolling through large music libraries, or switching between streaming apps is smooth and happens without any noticeable lag. The screen’s high brightness is also a significant advantage when on the go. Despite a glossy surface that’s naturally prone to glare, the display remains sufficiently readable in most environments, including outdoors. During playback, the music player offers several interfaces to suit user preferences, including a mode that mimics the style of the first iPods—which will appeal to nostalgic users.

Android and streaming

Like all of the brand’s DAPs, the FiiO M33 R2R runs on Android 13, offering a familiar interface for Android smartphone users. Thanks to the Google Play Store, you can install any mobile app, including online music services such as Deezer, Spotify, Tidal, and Qobuz. These apps are seamlessly integrated, providing an experience identical to that of their mobile versions. In addition to Android mode, the M33 offers a Pure Music mode. In this mode, the FiiO Music interface takes over, providing access only to stored music and tracks shared on the local network. Other apps are no longer accessible. Finally, you can configure the player to function as a USB DAC, AirPlay receiver, or Bluetooth receiver.

In Bluetooth mode, the FiiO M33 R2R DAP can receive music from a smartphone, tablet, or computer via a Bluetooth 5.0 controller. This controller supports most Bluetooth codecs, including the standard SBC and AAC, as well as high-resolution codecs such as LDAC. As a result, it is naturally Hi-Res Audio Wireless certified, making it a serious option for wireless listening. In addition, the M33’s Bluetooth controller is reversible, allowing you to pair it with wireless headphones or earbuds. In this mode, it supports the same codecs plus Bluetooth aptX HD and LHDC.

Advanced equalizer and headphone profiles

The FiiO M33 R2R DAP incorporates some of the advanced customization features first introduced on the flagship FiiO M27 in a deliberately simplified version. Notably, it features a 10-band parametric equalizer—compared to the M27’s 31 bands—allowing for precise adjustment of different areas of the audio spectrum. Each band can be adjusted independently for frequency, gain, and bandwidth (Q factor), providing fine-tuned control over the frequency response curve. Even the most discerning users will be able to correct certain acoustic characteristics of their headphones or in-ear monitors, attenuate a frequency range that is too prominent, boost a range deemed too subdued, or even compensate for certain hearing-related characteristics.

To make these tools easier to use, FiiO has also integrated an Auto EQ system based on a database of preset profiles for most headphones and earbuds on the market, including models from Focal, Sennheiser, FiiO, Audeze, AKM, Meze, and more. This approach—which is very rare on an HD DAP—allows users to select their headphones and automatically apply a correction curve based on reference measurements. If needed, the settings can be fine-tuned using either the equalizer or four digital knobs to adjust channel balance, bass and treble levels, or enhance the stereo image.

Configuration

Right from the first time you turn it on, the FiiO M33 R2R is remarkably easy to use. All you need to do is connect to the Wi-Fi, select your language, and access the Google Play Store to install streaming apps—and you’ll be listening to your music in just a few minutes. The experience is immediate, with no tedious setup required. You’ll quickly get the hang of the interface, especially if you’re already familiar with Android devices.

For this test, we paired the FiiO M33 DAP with the FiiO FT1 Pro and Meze 105 Silva open-back headphones, as well as the FiiO FT1 and Meze 99 Classics closed-back headphones. We listened to Hi-Res FLAC and DSD audio files stored on a micro SD card, as well as 24-bit/192 kHz tracks streamed from Qobuz.

Listening impressions

While FiiO digital audio players typically prioritize clinical transparency and analytical sound reproduction, the M33 offered a much more sensual and emotional approach. On Amy Winehouse’s Back to Black, the British singer’s voice was reproduced with great texture and remarkable presence. It was brought to life with rich harmonics and plenty of substance.

The midrange was exceptionally rich, with the R2R DAC lending a very flattering smoothness to this frequency range. On acoustic recordings, the instruments took on an almost palpable texture. Nils Lofgren’s Keith Don’t Go perfectly illustrated this quality. The strings of the acoustic guitar revealed exceptional harmonic richness, with each pluck reproduced with great depth and naturalness. The resonance of the drum lingered smoothly, while the harmonics bloomed freely in the soundstage. The brass instruments shone with precision without ever becoming harsh, while the piano captivated with the subtlety of its nuances and realistic resonance. The M33 succeeded in giving this instrument a great deal of body and space. The sense of openness was very impressive, with perfectly layered sound planes.

This organic approach extended all the way to the high frequencies, which prioritized smoothness and naturalness over analytical precision. The highs came across as slightly softened, but without ever sounding muffled or dull. This reflects a philosophy reminiscent of certain tube-based amplifiers, with a relaxed sound and slightly rounded attack. Admittedly, the level of resolution and the emphasis on micro-details were slightly less pronounced compared to models like the FiiO M23 or M27. But this slight restraint directly enhanced listening comfort. The M33 never tried to impress with an overabundance of detail or artificial brightness. On the contrary, it integrated them naturally into the musical presentation.

The bass was particularly dense and rich—sometimes even a bit too prominent when paired with headphones or earbuds that already have a warm sound signature. However, this was easily adjusted in a matter of seconds using the built-in parametric equalizer. On Chris Jones’s No Sanctuary Here, the bass was dense, robust, and remarkably textured. Each note had weight and substance while maintaining excellent articulation. The bass was tight and perfectly controlled, while the vocals retained their full presence at the center of the soundstage.

FiiO M33 R2R vs. FiiO M23

Compared to the FiiO M23, the new M33 R2R takes a radically different approach. Both music players share excellent build quality, an Android operating system with full access to streaming services, and ample amplification power. However, their sonic personalities make them suited for distinct audiences. Equipped with an AKM delta-sigma DAC, the FiiO M23 prioritizes a very transparent, dynamic, and analytical sound. Its level of detail is impressive, with excellent separation of instruments and a remarkable ability to bring out even the subtlest nuances of a recording. It will particularly appeal to listeners seeking neutrality and precision. The FiiO M33 R2R, on the other hand, takes a more emotional approach. Its R2R architecture lends more body to the timbres, delivers more lifelike vocals, and provides an overall smoother and more organic listening experience. The highs are smoother, the bass is more substantial, and the soundstage gains in coherence rather than analytical precision.

Who is the FiiO M33 R2R designed for?

The FiiO M33 R2R is designed primarily for music lovers who prioritize emotion and musicality over technical performance alone. While some high-end DAPs rely on extremely detailed signal analysis and a highly demonstrative sound, the M33 captivates with its more organic and natural approach. It will be particularly well-suited for fans of jazz, acoustic music, vocals, classical music, or even rock, who will appreciate the richness of the tones, the smoothness of the harmonics, and the absence of listening fatigue even after several hours.

With its ample power, Desktop mode, and full-featured Android environment, the FiiO M33 R2R is also ideal for those looking for a versatile device that can accompany them both on the go and at home. More compact and lighter than an M27, yet with a more distinctive sound signature than an M23, it is undoubtedly one of the best choices in the FiiO catalog.

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