Fosi Audio V3 Mono Power Amp Review

If Google is showing you this page directly, click here to go to the start of the article.

Sound performances

For this review, I picked my faithful SMSL DO400, the tiny DO100, and the mighty Mamoritai Euphony for the pre-amp section, a good setup that should fit all genre and needs. For the speakers, I first used the the KEF LS50, but ended up with the Waterfall Iguescu, that will stay in the dining room for now.

As for the source, music was streamed directly from my computer with Apple Music (Hi-Res), my own Plex library (Hi-Res), and Spotify (Lo-Res) to a Sonos Port, or a FiiO SR11, linked to the pre-cited DAC.

Overall signature

So, how’s that tiny amp performing? Honestly, much, much better than I ever anticipated, even with my floor-standing speakers. I don’t know how they work with the 32V power supply, but paired with the 48V, the results were more than impressive for an amp of this size and price.

Straight out of the box, and paired with the SMSL, the V3 Mono Amp delivers straight, colorless, end-to-end amplification. Neutral, clean, and transparent, the amp manages to enhance a sound signature already resolving, revealing, reflecting the source and the track, without any coloration. The dynamic range was excellent, and even in complex tracks, the amp never felt like it was running out of breath, delivering a wide, open soundstage that added depth to every instrument. Voices remained clear and articulate, and even with bass-heavy tracks, mids weren’t overpowered—something that can be an issue with cheaper amps in this range.

Paired with my old LS50 the result was more than compelling and I still couldn’t phantom how an amp this small/affordable was able to extract this much information compared to some of the big amp that I carried over the years. And if I was already blown away by the value proposition offered by the V3 Mono amp, I was even more flagger blasted once linked to the Waterfall. I couldn’t hear any hiss or distortion, even on high gain, absolutely no background noise.

Even with plugged in quad-channel (Iguescu + LS50), I couldn’t hear a single trace of hiss or hum, whether the amp was idle or pushing higher volumes. The signal remained clean and controlled, with no noticeable distortion, even when pushed close to its limits. Honestly, I kept waiting for some kind of flaw to pop up—some harshness in the highs, a bit of muddiness in the lower mids—but no, nothing. It just worked, and worked well.

The midrange was articulate, clean, and airy, upper mids have great control and the extension was just brilliant – even more once paired with the Euphony, even if I preferred the DO400 on the long run. No peaks, no dips, no sibilance and, for the price, this is clearly one of the best power amp that I encountered those past years, the little box handling nuances and distortion like a champ, never sacrificing the wide sound stage. PRaT is excellent and technical-wise, this amp acts as if it is priced in a much higher price bracket. You can’t go wrong with it.

As advertised, power-wise, the Fosi V3 Mono punches way above its weight class. While small in size, it’s clear that the TPA3255 chip inside does wonders in terms of energy efficiency and raw output. With the 48V power supply, it had no trouble driving my Waterfall Iguascu, providing tight, controlled bass with excellent layering, something that’s usually reserved for much pricier amps. Even at low volume levels, the bass remained present and detailed, without the usual loss of impact found on many budget Class D designs.

On electronic tracks like Midra from Gridge, I was pleasantly surprised by how well-extended and punchy the sub-bass was, something I hadn’t expected at this price point. Paired with the KEF LS50, mid-bass was slightly more forward, but never overwhelming, creating a good balance with the rest of the spectrum.

Moving up the frequency range, the midrange remained precise and well-textured, giving a natural tonality to voices and acoustic instruments. On Wanderer – Mogli, vocals sounded airy and realistic, without the usual sharpness sometimes found on cheaper Class D amps. Guitars had good weight and texture, and despite its powerful bass response, the V3 Mono never felt congested or bloated in the mids. Highs were crisp and detailed, but never harsh. There was a good sense of extension and airiness, though I wouldn’t call it sparkling – it remains a smooth and controlled treble rather than an ultra-revealing one. Compared to something like the Nuprime STA-100, the Fosi Audio V3 Mono leans slightly colder, making it a better match for warm speakers.

If I had to nitpick, I’d say heat management could be a little better. After a few hours of use, the case gets noticeably warm, especially with the 48V power supply. It’s nothing alarming, but leaving some space around the amp for airflow is definitely a good idea. Aside from that, I couldn’t really find anything to complain about. The balance between power, clarity, and dynamics makes it one of the most enjoyable budget amps I’ve tested in recent years, and for under $200, I can’t think of a better option for anyone looking for an affordable, high-performance Class D amplifier.

Finally, I put the Atom Phono to the test, as a pure tone control in my setup – very like the Subjective3 before. Put between the SMSL DO400 and the Fosi V3, this was, once more, one of the best addition I did to that setup. The SMSL being as flat as it can be, the pairing with the Fosi always delivered a clean, analytical render – that I like – but the Atom Phono added a granularity that I’d have never expected. Playing with the lows makes a lot more sense with the JDS, than it ever did with the DO400 embedded filters, and that even at low volume listening. Add to that lower humming, cleaner outputs, the same power output, and you get one of the best, cheapest, tiniest, desktop setup you could imagine – in my opinion

Awesome!

Tonality

The sound signature is linear, but each frequency range has flaws and qualities—a quick overview.

Bass: deep, fast, accurate. The Fosi V3 Mono managed to reach deep notes with ease on my Iguescu, especially at high volume. It’s great with relatively sensitive speakers like those and amazing with speakers like Klipsch. Still, with the KEF LS50 the combo was more than impressive and, in this price range, the Fosi manages an terrific job.

Test track : Ylang Ylang – FKJ

Mids: flat and clean. Exceptionnal dynamic range combined with good accuracy and absolutely grain-less/flawless background make the V3 Mono Amp unsurprisingly good in this regard. In dual mono, it’s simply formidable.

Test track : Customer is King – Meute

Highs: straight and technical. If everything seems flat to my ears, some might find the Fosi V3 Amp a bit too linear, but not for me. The amp showed excellent control and definitely exceeded any other amp in this price bracket in my opinion, which is already a feat on its own.

Good test track : Omnia – Anyma

Conclusion

Long story short, the Fosi V3 Mono Amp is one of the best power amplifier I ever reviewed to this day.

A nifty device with the level of control and refinement you’d expect from brands like SMSL or FiiO, offering a quality/price ratio I never hoped for. Build quality is excellent, I/O is great, form-factor is perfect and, all-in-all the device is just flawless.

So yeah, if you’re in need of a compact/affordable amplifier for your speakers, and also want to beef up your setup, this is the one to get!

A steal!

Summary

Pros

• neutral sound signature and impressive raw-power
• excellent dynamic range and low-to-zero noise
• good I/O with unbalanced and balanced inputs
• great build quality
• amazing performance/price ratio

Cons

• can get hot
• nothing at this price range