Fosi Audio MD3

Power, Resolution and an outstanding design. Fosi Audio gets it right yet again.

The high-performance portable audio ecosystem has undoubtedly experienced a dizzying evolution in a very short time. The race to capture the most attractive device on the market has forced manufacturers to pack digital conversion technologies that previously required stationary chassis into devices that fit in the palm of your hand.

Along the way, multiple obstacles have been resolved. Connectivity, power, digital filters, high-quality wireless formats, in short. We could dedicate several paragraphs to the subject. Better to move forward.

One issue remained pending: ergonomics and integration with what, without a doubt, are the portable transports par excellence: mobile phones. Enter Fosi Audio, one of the most enthusiastic companies in accessible audio which, with its tireless innovation, has very recently presented its latest portable DAC, the MD3.

With the MD3, Fosi Audio delivers a strike on the table in the competitive segment of ultra-portable dongle-format DACs and headphone amplifiers. The firm, widely known for its high-efficiency domestic amplification solutions, transfers its philosophy of squeezing the relationship between cost and performance here, delivering a pocket-sized device designed to transform any smartphone or computer into a full-fledged audiophile source.

Far from being a generic adapter just to get by, the MD3 postulates itself as a dedicated D/A processing source, in addition to having a very attractive and fun design and functions. It is designed for the sound enthusiast who refuses to compromise temporal resolution, transient control, or background silence when away from their main listening room and who, furthermore, likes to listen to their music with style. And the fact is that the MD3 presents a very attractive design. Let us analyze it in detail:

Construction

Physically, the Fosi Audio MD3 bets on a functional, compact, and highly robust design. Its chassis, machined entirely in aluminum via computer numerical control, acts not only as a resistant armor against the rigors of daily mobile use, but also as a passive thermal dissipator and an effective shield against electromagnetic interference generated by mobile phone antennas.

This is of great interest because, behind an imitation leather cover in the brand's usual orange tone, the rounded aluminum body hides a set of N52 magnets configured to couple to the MagSafe of the latest iPhones. It is enough to bring the MD3 close to the back of my iPhone 17 so that both stick together magnetically, thus solving one of the main problems that, to date, I had had with so-called "dongle DACs": what on earth to do with them once connected?

On its minimalist surface, the physical buttons for independent volume control stand out, an indispensable solution that allows regulating sound pressure with a precision far superior to that offered by the native controls of mobile operating systems.

Another button, called the Vista Button, allows interacting with the device's small circular screen. With it, we switch between the different collections of emojis and animations, which gives a touch of personalization to the device and, furthermore, allows us to quickly access the configuration menu as well as know, with a simple glance, the quality of the file in playback and the volume.

At the digital heart of this tiny device beats a conversion architecture signed by ESS Sabre, an industry standard valued for its overwhelming resolution capacity and its excellent dynamic range. However, the true added value of the MD3 lies in the deep level of customization that Fosi Audio has left in the hands of the user through its firmware. Unlike other closed-philosophy dongles, the MD3 allows alternating between various internal digital filters directly from the device.

Among them, the Slow Linear filter consolidates itself as the preferred option for critical listening sessions, by offering a more progressive and natural decay of the notes that drastically reduces digital pre-echo, bringing the temporal response closer to a purely analog sensation.

The versatility of the device is complemented by total support for high-sample-rate PCM data streams and native decoding of DSD files. In addition, power management has been optimized to ensure that, despite its generous output voltage, the battery consumption of the source device remains within strictly reasonable margins. In the connectivity section, the MD3 features the mandatory USB-C input and an analog output section with two different connections (3.5 mm and 4.4 mm) in SE and balanced format.

Finally, the amplification. Four ESS ES9603Q chips provide up to 180mW @32Ω on the balanced output. A by no means negligible number that doubles the output of the 3.5 mm jack.

How It Sounds

To evaluate the true technical and musical potential of the MD3, we configured it as the core of a portable stack composed of an iPhone 17 streaming through Qobuz and Roon ARC. The reference headphones were the IM4, from the same house. The original cable was replaced by a Tripowin cable. The connection cable between the mobile and the MD3 is the USB-C provided by the manufacturer.

The acoustic behavior of the Fosi Audio MD3 surprises immediately by the absolute cleanliness of its proposal. Thanks to a circuit design that isolates the noise of the power supply from the USB, the noise floor is completely inaudible, a critical factor so that the micro-details of the recordings emerge without effort through the sensitive IM4 IEMs. The sound signature, especially with the Slow Linear filter, stands out for a well-executed tonal balance, where the resolution of the ESS Sabre chips is presented in a good way.

1. Bobo Stenson Trio – "Contra la Indecisión" (Contra la Indecisión / ECM Records): We begin the session with a masterpiece of contemporary jazz where space, silence, and piano harmonics are the true protagonists. The MD3 manages the initial attack of Stenson's piano keys with a staggering clarity. The decay of the notes in the virtual room extends linearly and progressively into the dimness, demonstrating the extraordinary chronometric precision of the DAC's internal clock. The subtle work of the drum cymbals and the double bass is perceived perfectly stratified on the stage, with an air and instrumental separation uncommon for a device of this size.

   
   

2. Iron & Wine – "Flightless Bird, American Mouth" (The Shepherd's Dog / Sub Pop / Folk Rock): We move on to a folk rock production rich in acoustic textures and overlapping vocal layers. The IM4 monitors, fed by the clean current of the MD3, project Sam Beam's voice onto a forward plane, with a carnal, warm texture and an outstanding timbral realism. The acoustic guitars that intertwine through the track exhibit the real body of the wooden boxes and the subtle snap of fingers on the nylon strings. The Fosi Audio dongle handles the density of the arrangements with magnificent ease, preventing the mid-high frequencies from becoming aggressive or fatiguing.

   
   

3. Jan Vogler / The Knights – "Dvořák: Cello Concerto in B Minor, Op. 104" (Sony Classical): We close the test with a large-scale classical work to evaluate macro-dynamics and structural stability in the face of complex orchestral passages. The MD3 demonstrates an incontestable authority when it comes to guiding the transducers through the orchestra's crescendos. Vogler's solo cello is positioned precisely in the center of the scene, exhibiting rich textures in the lower registers and a clean, silky extension in the highest notes. Thanks to the implemented crossfeed configuration, the soundstage expands its natural limits, recreating the three-dimensional distribution of the orchestra with exemplary spatial coherence and technical stability.

Technical Data

• Digital Architecture: High-performance ESS Sabre ES9039Q2M conversion chip with advanced support for selectable digital filters.

• Compatible Formats: Native support for high-resolution PCM data streams (up to 32-bit / 384kHz) and direct decoding of DSD files.

• Digital Filters: Selection of internal filtering profiles, including the Slow Linear mode optimized for an analog temporal response.

• Input Connectivity: High-speed USB-C port with electrical noise isolation.

• Physical Controls: Dedicated buttons for volume management independent of the audio source.

• Secondary USB-C port for simultaneous charging and listening.

• Analog outputs: 3.5 SE and 4.4 Balanced.

• Circular screen for menu handling, volume control, data of files in playback, and custom screensavers.

Conclusions

The Fosi Audio MD3 consolidates itself as one of the best-executed portable DACs in its category. Its great success lies in combining design, technical solvency, functionality, and customization. It is, as colloquially said, "The complete package." With a somewhat larger size than its siblings but with excellent performance and the ability to customize the display, it positions itself as a clear choice for many lovers of portable audio.

Paired with demanding and transparent in-ear monitors like the Fosi Audio IM4, this small DAC demonstrates that portable high fidelity has reached an undeniable state of maturity. It is capable of delivering a detailed sound, with a nonexistent noise floor and an unquestionable musicality.

In my experience with the MD3, it turns out to be an easy-to-use piece of equipment. Its functions are intuitive, the control precise, and the aesthetics, combined with the dynamic animations of its small screen, make it very pleasant to the eye. Its elegant and well-resolved design makes it pleasant to the touch and, of course, the good sound, to the ear. I only lacked trying it by taste and, by the way, I did not detect any particular smells. Now that would indeed be a complete package!

I recommend, however, using the balanced output (4.4 mm), as its power has allowed for better results in terms of sound and dynamics.

For the Et Sona reader looking to squeeze the most out of their digital music library anywhere without the need to carry heavy dedicated players, the MD3 represents an intelligent, robust, and fully recommended investment. Furthermore, it is compact and easy to move.

Gallery.