Disclosure: I’d like to thank Fosi Audio for providing me with the MD3 for this review. All thoughts and opinions are my own, and Fosi Audio had no say or input on the contents of this review.

There’s been a surprising increase in the number of portable dongle DACs released over the last couple of years, with most of them consisting of uniform aluminum “bricks” that hang awkwardly from your phone’s USB-C port. This design can strain cables, clutter pockets, and generally just look unpleasant. Fosi Audio wants to break away from this design with the MD3 “MagDac”, a portable DAC and headphone amp designed to act as a part of your smartphone rather than as a cumbersome extension.

It does this by utilizing a strong magnetic backplate. The MD3 snaps cleanly to the back of your smartphone or case (assuming it’s MagSafe compatible or has a magnetic ring), completely changing the ergonomics for mobile listening. Fosi has also leaned into a more interactive and fun user experience by adopting a circular display that doesn’t just show basic file bitrates but acts as a customizable visual interface, complete with custom wallpapers and mini-games.

Released on May 25, 2026, the MD3 faces a lot of competition in the ultra-portable DAC category. To succeed, a modern portable DAC needs to solve the real-world frustrations that users experience, namely battery management and pocket ergonomics. Let’s get into the review to see if the Fosi Audio MD3 can solve these challenges.

• Fosi Audio MD3
• Angled USB-C to USB-C cable (charging supported)
• USB-C to USB-C cable
• USB-C to USB-A adapter
• Magnetic ring
• Manual

The Fosi Audio MD3 comes with a good amount of accessories. What I found interesting, and actually quite admire, is how the cables are packaged in anti-static bags. It may not be necessary, but it adds a special property to the whole unboxing presentation. I also appreciate that two USB-C cables are included, as well as a magnetic ring that you can use to stick to the back of your phone or case if yours doesn’t have one.

The MD3 is available in two finishes: anodized silver (Galaxy) and anodized black (Obsidian, which is what I have), both paired with an orange leather back. Visually, it is a very Fosi product, but with a bit more personality than some of their more utilitarian desktop gear.

The aluminum chassis feels solid, compact, and premium for something this small. Fosi says the body uses a refined aluminum unibody with sandblasted finishing, and in hand, that does come through. It feels more like a tiny audio gadget than a basic USB-C dongle, and that is clearly intentional.

The magnetic backplate is the main design feature here. Instead of dangling from your phone like a normal dongle DAC, the MD3 can snap to the back of a MagSafe-compatible iPhone or a compatible magnetic case. The magnets are hidden behind a Fosi-orange leather backing, which has a soft and pleasant texture. The orange also gives the MD3 a very unique look.

The magnetic attachment worked well with my iPhone 16 and Galaxy Fold 7’s case, but it doesn’t have that super-strong attachment that you get with, say, official Apple accessories. The MD3 stays on well enough, but it can be slid off the back of your phone if you’re not careful. The included magnetic ring also isn’t the strongest, so this is an area that I feel Fosi did not go far enough in perfecting. Overall, though, they did a pretty good job.

There are only 4 buttons on the MD3. On the right side are the volume up, volume down, and multifunction buttons, and on the front left side is the “Vista” button. The multifunction button is used for entering the onboard menu system, locking/unlocking the Vista button, and as the confirmation button within the menu system.

The 12mm thickness also feels well judged. Fosi specifically notes that this thickness was chosen to prevent bulky headphone plugs from lifting the MD3 off the phone when magnetically attached. That may sound like a tiny detail, but this is exactly the kind of practical consideration that matters with portable gear.

Display and Controls

The MD3’s 1.28-inch circular LCD display is one of the features that make it stand out. It is not just there for basic volume and sampling rate indications, either. Fosi includes screen rotation, brightness adjustment, auto screen-off, static and animated images, custom wallpapers, and even small built-in image-based games like rolling dice, wine bottle, and rock paper scissors. All of this can be selected through the Vista button.

Is all of that necessary? Absolutely not. Is it fun? Yes.

This is the kind of feature that will divide people. Some will see the display, photo album functionality, and Vista Button as unnecessary gimmicks. Others will appreciate that Fosi is trying to make a portable DAC/amp feel more personal and interactive. I fall somewhere in the middle. I do not need my DAC to show custom images, but I do like that the MD3 feels more alive than a basic dongle.

Pressing the multifunction button once will bring up the menu, with the volume up and down buttons allowing you to navigate through. Press and hold the multifunction button for a couple of seconds, and it will lock the Vista button so nothing gets accidentally activated. Long-press it again to unlock the Vista button.

The buttons themselves are very nicely done. They have a distinct tactile click to them that isn’t too loud or too sensitive (meaning you won’t accidentally change the volume when handling the MD3). The Vista button is a little bit more audible and clicky, but it’s not a huge issue, as it’s mainly for adjusting what’s on the screen.

The more important functional feature is the 100-step volume control. This is genuinely useful, especially with sensitive IEMs where small changes in volume can make a big difference in loudness. The volume steps are fine enough that I never felt stuck between “too quiet” and “too loud,” which is a common issue with simpler dongles.

The MD3 also supports volume memory, so it remembers your previous volume setting. That sounds simple, but it helps the device feel more polished.

Connectivity

The Fosi Audio MD3 features 3.5mm SE and 4.4mm balanced outputs on the bottom of the device. There isn’t much room on a portable DAC/Amp this size, but Fosi has spaced them practically so that they, for the most part, don’t interfere with the USB-C port on the very left. You’ll only encounter issues if you have an abnormally wide 3.5mm cable plugged in at the same time as the USB-C cable. I tested 8 separate cables from various IEMs, and all of them fit perfectly, so odds are most users will be fine.

The MD3 uses USB-C and supports both UAC 2.0 and UAC 1.0 modes. The UAC 2.0 mode gives you access to higher-resolution playback, including PCM up to 32-bit/384kHz and native DSD256, while UAC 1.0 is limited to PCM 16-bit/48kHz.

The inclusion of UAC 1.0 is useful because it improves compatibility with devices that do not support standard UAC 2.0 output, usually game consoles and older devices or computers.

The MD3 uniquely features a dual USB-C port design, with one on the top and one on the bottom. The top USB-C port can be used for audio decoding, image transfer, and charging, while the bottom USB-C port supports audio decoding, image transfer, and firmware upgrades. What this allows you to do is to connect external power to the top USB-C port while the bottom USB-C port connects to and charges your phone.

That charge-while-listening functionality is a big advantage over many compact dongles. One of the main downsides of using wired DACs with phones is that they occupy the USB-C port, which can make longer listening sessions annoying, especially since the dongles do rely on the connected device for power. The MD3 does not completely solve every cable-management routing issue, but it does give you more flexibility.

The 1.28-inch circular display is crisp, bright, and highly legible. It doesn’t feature auto-rotation, but you can quickly rotate 90 degrees by double-pressing the Vista button. Pressing the multifunction button on the right side brings you into the menu, where you will find all of the various options and settings.

As previously mentioned, Fosi built a “Photo Album” system directly into the device’s firmware. By clicking the physical Vista button, you can cycle through images, as well as mini-games like rolling dice, spin the bottle, and rock-paper-scissors. While purists might dismiss these additions as gimmicks, they inject a refreshing sense of playfulness and physical interaction that is entirely missing from rival dongle DACs.

Before copying your own images to the MD3, you need to first upload them to Fosi’s “MD3 Image Creation Tool” to have them properly cropped and formatted: https://cc.fosiaudio.com/#/md3

Then, you can plug in the MD3 to a computer, select the “Photo Sync” option under the USB Mode setting, and the device will appear as a USB drive on your computer. You can then copy your images to one of the three photo folders, and you’re good to go. I did notice that you need to power off and then power on the MD3 in order for it to recognize new photos.

PCM Filter Options

The ES9039Q2M DAC in the MD3 includes eight selectable PCM filters. In trying to find out more information about the filters, I researched several other products using the ES9039Q2M DAC chip. The names as shown on the MD3 are below in bold, with the proper filter name in brackets, as well as a description of the filter’s intended purpose:

• Minimum Phase (default filter)
  • Delivers natural timing with clear detail and overall balanced sound. Apodizing
  • For listeners seeking a natural and well-balanced everyday listening experience.
• Apodizing (Linear phase Apodizing fast roll-off)
  • Smooths harsh recordings and older CDs by reducing digital artifacts.
  • For users listening to early digital recordings or sensitive to harsh treble.
• Fast Linear (Linear phase fast roll-off)
  • Provides maximum accuracy and neutral frequency response.
  • For reference listeners and users prioritizing technical precision.
• Fast Linear LR (Linear phase fast roll-off low ripple)
  • Ensures pure tonal accuracy with minimal coloration.
  • For studio monitor users and listeners seeking tonal neutrality.
• Slow Linear (Linear phase slow roll-off)
  • Produces relaxed, smooth treble suitable for long listening sessions.
  • For users who prefer softer highs and fatigue-free listening.
• Fast Min (Minimum phase fast roll-off)
  • Delivers punchy, dynamic sound with clear transients.
  • For listeners who enjoy bass impact and energetic live music.
• Slow Min (Minimum phase slow roll-off)
  • Creates a warm, natural, and analog-like presentation.
  • Users who prefer smooth, musical, and less processed sound.
• Low Dispersion (minimum phase slow roll-off low dispersion)
  • Provides a nice balance of the low latency of minimum phase filters and the low dispersion of linear phase filters. Minimal pre-ringing is added to achieve the low dispersion in the audio band.
  • The rolled-off highs make it more forgiving on older or bright-sounding recordings.

To be honest, these filters make extremely subtle changes. They are nothing like EQ adjustments, so it is likely most people won’t notice significant differences between them. Personally, I can detect minor variations in presentation with tracks I’m very familiar with between some filters. It’s a nice touch for those who enjoy tweaking or have a favorite filter type. I usually use either the Minimum Phase or Linear Phase Fast Roll-Off filter when possible, as they sound the best to my ears and with the music I listen to.

The Fosi Audio MD3 offers 80mW per channel at 32 ohms from the 3.5mm output and 180mW per channel at 32 ohms for the 4.4mm balanced output.

For IEMs and easier-to-drive headphones, this is more than enough. The 3.5mm output has enough power for everyday listening, while the 4.4mm balanced output gives the MD3 some extra headroom for more demanding gear.

The MD3 is clearly designed with IEMs in mind, though, as it easily handled anything I threw at it, from more budget and easier to drive IEMs like the Kefine Klean, to sensitive IEMs like the Simgot EA1000, Campfire Audio Andromeda 10, and 64 Audio Solo. Tribrid IEMs like the ZiiGaat Horizon and Juzear Harrier were driven just fine, as were planar IEMs like my 7Hz Timeless II and Sivga Nightingale Pro. I also noticed absolutely zero background hiss with any of these IEMs, meaning the noise floor is low and the DAC itself has a fairly low minimum output impedance, which is exactly what you want in a portable DAC/Amp like the MD3.

Over-ear headphones can also be used as long as they are on the more efficient side. My Focal Azurys and Meze 105 AER sounded excellent, even the HIFIMAN Edition XV was able to get enough power from the 4.4mm balanced output with high gain. Sennheiser’s HD550 and HD620s are also two excellent pairings here. Where things started to really struggle was when I used headphones like the Sennheiser HD660S2 and the Audeze LCD-2. There just isn’t enough output power here to get the full sound of either headphone. For most, this will be a non-issue, though, as the MD3 is not intended to replace a desktop setup, but it’s good to know for those who have headphones like these.

Most importantly, the MD3 never gets warm, even when using high gain and with a higher volume set.

Given that there is no internal battery in the MD3, it relies solely on the device it’s connected to for power. What this means is that if you are using your smartphone, expect your battery life to take a bit of a hit. How much of a hit? That will depend on the amount of volume/output power you need.

I tested using an iPhone 16 and the Crinear Reference connected to the 3.5mm output. The screen was set to 100% brightness and stayed on all the time. Volume set to 35/100 on high gain. My iPhone 16 lost 14% over two hours consistently, and this basically amounts to 7-8% in an hour, assuming you are doing nothing else on your phone, and you are playing locally downloaded files (in this case, lossless files from Apple Music).

Setting the MD3’s screen brightness to 60%, as well as having the screen turn off after 10 seconds, the results were much better. My iPhone 16 only lost about 4-6% per hour, and about 10% through two hours. That is a decent improvement compared to leaving the screen on.

This type of power usage is not terribly great, but it’s not too bad either. You have to expect some battery drain when powering a dongle DAC, and the MD3 has reasonable usage, in my opinion. As I showed, lowering the screen brightness and having the display turn off after a set amount of time goes a long way to minimizing battery drain, so this is what I would recommend to those who are conscious of their battery usage.

If you do need to top up your smartphone’s battery during use, the dual USB-C design comes in handy here, as you can see from the above picture.

The Fosi MD3 has a clean, slightly smooth, and easygoing sound that fits well with its portable design philosophy. The audio output is clean, and the overall tuning is accurate but has a slightly warm tilt that gives a more natural presentation that is great for all-day listening. It does not sound overly sharp, thin, or clinical. Instead, it presents music with good clarity while keeping the overall tone comfortable and uncolored.

Below are my subjective audio impressions. This does not mean that this is exactly what you will hear, but it is simply my subjective experience with the MD3 while using the Crinear Reference as a baseline (meaning, all other DAC/Amps going forward will be tested using the Crinear Reference, to help keep comparisons equal).

The bass performance sounds controlled and is reasonably punchy. The MD3 gives bass notes enough body to avoid sounding sterile, and bass guitars and drum kicks have good texture and weight without sounding bloated or unnatural.

The midrange has a clean and natural sound. Vocals sit fairly evenly, neither forward nor recessed. Male vocals have enough warmth to sound full, while female vocals retain clarity without becoming piercing or edgy. Tracks with multiple guitars paired with pianos, strings, etc., all come through with good separation and a natural timbre.

The treble is detailed but not aggressive. The MD3 has enough upper-end presence to keep music from sounding dull, but it doesn’t have the overly etched Sabre-style sharpness that some people associate with ESS DAC implementations. Cymbals and higher-frequency details are easy to hear, but they do not dominate the presentation, and they are not fatiguing in the slightest.

The technical performance is really solid. Detail retrieval is good (or even great, really), imaging is stable and accurate, and the background is clean. The MD3 does not create an enormous soundstage, but it does a good job of keeping instruments separated and organized. Compared to cheaper dongles, it sounds more balanced and refined.

The Fosi Audio MD3 is not just another USB-C dongle DAC with slightly better specs. Its value comes from the way it balances all of the key features with some new and interesting innovations.

The magnetic backplate (hence the nickname “MagDAC”) is the feature that makes it stand out. If you use a MagSafe-compatible phone or case, the MD3 feels much more convenient than a traditional dongle DAC. It turns a messy portable wired setup into something more compact, more stable, and more enjoyable to use.

The sound quality is also strong. The ES9039Q2M DAC, four ES9603Q amp chips, low noise floor, and inclusion of a balanced output give the MD3 enough performance to be taken seriously as a proper portable DAC/amp. It is not the most powerful device in its class, and it will not replace a desktop setup, but that is not really the point. Others will be quick to knock the lack of output power, but to me, it provides just enough to satisfy the MD3’s intended use.

What Fosi has built here is a lifestyle-friendly audiophile accessory that still respects the audio side of the equation. The display, wallpapers, Vista Button, and playful extras will not appeal to everyone, but they give the MD3 personality.

At $149.99 USD, the MD3 is not the cheapest way to improve your phone’s sound, but it is one of the more interesting and thoughtfully designed portable DAC/Amps in this price range. If you only care about raw output power, there are stronger options. If you only want the smallest possible dongle, there are more compact options. If you want a portable DAC/amp that sounds good, feels premium, attaches neatly to your phone, adds some personality to wired listening, and feels like a well-balanced product, then I can highly recommend the Fosi Audio MD3.

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