[Review] Fosi S3 - An all-in-one balanced streamer?

Product: Fosi S3 - streamer & DAC
Manufacturer: Fosi Audio - China
Price: ±€270
Reviewer: Matteo Bruni - TNT-Audio Italy
Reviewed: May, 2026

Introduction

In the history of the Hi-Fi market - and not only, of course - it has always been manufacturers who shaped consumers' desires: “our amplifier has only 0.00000000000001% THD”, “these huge tubes are not only visually impressive but also sound great”, “our transformers use 5% silver”, and so on.

Fosi Audio, on the other hand, takes a surprising and radically different approach: through its blog, it asks followers and customers what they want - or what they have been led to want by others - and then tries to build it. The streamer I'm about to discuss was born exactly this way. Fosi becomes a kind of Santa Claus who, collecting the “letters” from future buyers, tries to turn them into real products, without elves or reindeer - at least, I think so.

The Fosi Audio S3 is a compact streamer/DAC built around a modern platform and a carefully designed conversion stage for its price range. Looking at it both from a technical perspective and in real-world use, several interesting strengths emerge, along with some questionable choices and a few issues.

The well-known AKM “phoenix”: a chip born from the ashes of the fire that hit the Nobeoka factory about five years ago. It is a 32-bit stereo delta-sigma DAC from the Velvet Sound series by Asahi Kasei Microdevices. It supports PCM sampling rates up to 768 kHz, DSD512, with a typical SNR of 120 - 123 dB and THD+N around −113/−115 dB. These are datasheet values; real-world performance depends on implementation.

The balanced output stage is handled by two OPA1612 op-amps, ultra-low noise and ultra-low distortion dual amplifiers from Texas Instruments, essentially a standard choice in many modern DACs. The unbalanced output stage, on the other hand, is based on the classic NE5532 from Japan Radio Company. There is absolutely nothing wrong with using this historic and inexpensive op-amp; however, if the use of the excellent OPA1612 is highlighted for the balanced output, it would be appropriate to clearly state that the unbalanced section relies on the NE5532, to avoid misleading readers into thinking that both sections use more “prestigious” components.

The S3 also supports DLNA, Spotify Connect, and Tidal Connect. To use this streamer, you will need an Android or Apple device.

Listening impressions

The first surprise is the DAC: it delivers a clean, detailed, and neutral presentation. The mid and high frequencies are well resolved, without any obvious harshness. The low end is absolutely correct. I was genuinely impressed by its pleasant, natural, and engaging sound when listening to music: playback is fluid and non-fatiguing, the presentation is coherent and natural, and the music flows effortlessly.

The volume can be adjusted via the device knob, the remote control, or directly from a smartphone. A message to all DIY enthusiasts: before you jump on that poor knob like pirates boarding a cargo ship, be aware that it is NOT an analogue potentiometer. As with the vast majority of DACs (e.g., the Fosi ZD3 reviewed here), gain control does not pass through any physical resistive track but is handled in the digital domain - which is a good thing, as noise levels and channel imbalance are virtually eliminated, and volume can be conveniently controlled via app or remote. Therefore, replacing or removing it is completely pointless.

The component quality is not on the same level as its in-house rival, the ZD3, as can be seen from the images.

So, if you are a devoted follower of the SINAD “deity” and like to make offerings at its altar, be aware that this streamer may not reach the same scores as the ZD3. SINAD (Signal-to-Noise And Distortion) is not a Babylonian idol, but a parameter that measures how well an audio signal preserves its “purity” against noise and distortion introduced by electronics. The reality is that beyond about 95 - 100 dB, it becomes largely irrelevant, as it falls below the threshold of audibility. Keep this in mind when browsing SINAD rankings of DACs and choosing based on them. If you are interested in the (often weak) correlation between measurements and real-world listening, you might want to read this recent article, also involving Sean Olive.

Bluetooth works correctly but is about 5 dB lower than Chromecast at the same volume setting. This does not imply worse quality, but simply a different output level. In a comparative test, switching from Bluetooth to Google Cast reveals a noticeable level difference, which can easily be mistaken for greater detail, dynamics, sound-stage openness, or “air” between instruments-often wrongly attributed to the audio format. These impressions disappear once levels are precisely matched. So, if you want to compare Cast vs Bluetooth quality, you would need to boost the lossy transmission by about 5 dB using a multimeter or microphone-in other words: don't bother.

The same gain considerations apply to the analogue input, which allows the streamer to be used as a bridge with a phono preamp or other analogue sources. The analogue signal is digitally converted and reprocessed via a Texas Instruments PCM1804 - a 24-bit/192 kHz professional-grade ADC-and the digital equalizer can be applied. For purists of analogue signal integrity this is heresy; personally I'm more pragmatic, but the impression is that the A/D stage has not been refined to the same level as the D/A stage, and this is audible, particularly in the mid and upper-mid frequencies.

Streaming via Chromecast is the most problematic aspect. Quite often, when changing tracks within an album or a queue, there is about 20 seconds of silence after the track starts, after which playback restarts from the beginning. This does not occur in random playback mode or when playing an album continuously. It's unclear whether this can be resolved via firmware updates; at the time of this review, the issue is present. It's not constant, but it does impact the user experience. AirPlay 2, on the other hand, works flawlessly: no interruptions, stable synchronization.

The built-in digital equalizer is limited to 5 bands, with the highest at 16 kHz - a questionable choice.

For technical use or fine correction it is not ideal, but when using the streamer via HDMI with a TV, it proved extremely useful in some movies or TV series where the bass needed taming without constantly adjusting the volume. Speaking of HDMI, I noticed that when the TV is connected to the Fosi S3 via HDMI, turning the streamer back on after a full shut-down also automatically turns on the TV. This does not happen when the streamer is simply in standby.

In addition to the analogue outputs, the Fosi Audio S3 also features an optical output, which allows it to be used as a digital bridge for another DAC or a more advanced digital equalizer. The SUB output is a simple mono analogue output dedicated to low frequencies, with a non-adjustable filter.

The app is minimal but well designed; setup on the home network is quick and intuitive. With a simple tap, it is possible to quickly select inputs, outputs, gain, EQ, power, and mute. It has not crashed once in over a month of use.

A closer look

The central processor is based on an Amlogic A113X integrated into the Linkplay Stream1832AE module, a chip optimized for handling wireless protocols such as AirPlay 2, Spotify Connect, and more. A separate daughterboard hosts the Explore Microelectronics EP9512E controller. This modular design helps isolate electrical “noise” from the HDMI interface from the underlying analogue audio circuitry.

Output stage: the first OPA1612 performs the I/V (current-to-voltage) conversion for both channels immediately after the DAC. The other two OPA1612 op-amps are entirely dedicated to the balanced output stage. A separate op-amp, the NE5532, is placed near the unbalanced outputs, acting as a dedicated buffer for the RCA outputs and isolating their load from the main XLR signal path.

Power supply management: the internal circuitry is carefully protected from disturbances that the external 12V switching power supply might introduce. Right after the power input connector, a ferrite bead is used to filter out very high-frequency noise. Such noise could generate jitter-timing instability-in lower-cost clock circuits controlling the AKM 4493SEQ DAC.

A note on jitter: 10 - 15 years ago, it was considered the number one enemy of DACs, requiring complex and expensive external circuits to mitigate. Today, modern chips from AKM, ESS, and others integrate advanced jitter suppression technologies. Even if the incoming signal is not perfect, the AKM internally “re-clocks” it. Reflect on that...

Returning to the power supply: after the ferrite, there is a CL low-pass filter composed of a capacitor and an inductor. Upstream of the op-amps, there is another CL filter connected to the IVER HCES1-12D12 module (also found in the Fosi ZD3), which electrically isolates the analogue section from the digital one, effectively “regenerating” a clean dual supply voltage for the op-amps. The presence of relatively large capacitors (up to 1000 uF) near the output stage provides energy reserves for dynamic peaks and helps reduce residual ripple.

Conclusion

The Fosi S3 is a streamer/DAC with a surprisingly capable conversion stage, but with connectivity and A/D performance that do not fully match its other features. This is a real shame, in my opinion, because with the addition of a USB input - now a standard feature in DACs at this price range and beyond - a better A/D stage, and without the current Chromecast issues, it could have opened up very interesting possibilities for audiophiles. It could have been used as a unity-gain preamplifier for both digital and analogue sources.

It is well suited for those who primarily use AirPlay 2 and are looking for a compact, simple, musical, and good-quality streamer/DAC. It is less suitable for users who need USB or coaxial inputs for digital file playback, demand full stability with Chromecast, require more digital inputs beyond HDMI and optical, or are looking for a parametric equalizer. These limitations make it less flexible compared to direct competitors such as the Wiim Plus and Wiim Ultra, which generally offer more complete connectivity.

Is the lack of a display a drawback? That's entirely subjective. My current streamer has no display, and I honestly don't feel the need to stare at another screen just to know what I'm listening to - my phone is enough. Moreover, my electronics are completely hidden behind fairly heavy panel curtains, which I only move when using Class A power amplifiers. However, if you enjoy having a display on your equipment, be aware that the Fosi S3 does not include one.

I'll conclude with a personal note: for us DIY enthusiasts, modern DACs are frankly quite boring. The older, mediocre low-cost DACs were far more fun - we could experiment with expensive regulated linear power supplies, capacitor swaps, and so on. With modern DACs, unfortunately, we have to admit that they already work too well as they are.

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Fosi Audio S3

An all-in-one streamer?

Introduction

Listening impressions

A closer look

Conclusion