In this review, we take a close look at the Fosi Audio V3 Mono Power Amp, the third generation of the brand’s ultra compact power amplifier, selling for just $249,99 USD.
Disclaimer: the Fosi Audio V3 Mono Power Amp was provided to us, free of charge, by the brand in exchange for our honest opinion. You can check their website through this link directly.
Fosi Audio
Since its inception in 2017, Fosi Audio has steadily carved its niche in the audiophile world, delivering a compelling range of affordable, high-quality audio solutions. While relatively young compared to industry giants, the brnd rapidly gained recognition for offering no-nonsense, budget-friendly gear that doesn’t compromise on performance – chi-fi at core.
Covering every genre, from DAC, to power amplifiers and headphone amplifiers, the brand gained a lot of fame in the audiophile community, thanks to their excellent quality/price ratio. And if models like the Fosi BT20A has become a staple for budget-conscious enthusiasts, what really intrigued me were their super compact stereo and mono amplifier : the V3 Mono Power amp (or stereo).
A device that became the benchmark for many users in the sub-$500 configuration, even when compared to the like of WiiM and their (awesome) Amp, or SMSL and their extensive range of power amp. And so, when Fosi offered me to test their new V3 Mono, in dual mono configuration (hurray), I immediately jumped on the occasion.
A new reference? Time to find out!
Fosi audio V3 Power Amp
Design and Build Quality
Casing
Small and sturdy, the Fosi Audio V3 Mono is one of the tiniest power amps I ever had the chance to hold in my hand, by a long shot.
A pocket box, rectangular-shaped, made of CNC-milled aluminium that would feel like a toy, if not for the thick aluminum panels and extended I/O at the back of the device. An impression further reinforced by its dimensions: 142mm long, 105mm wide, 35mm tall and just 480g on the scale – a far cry from your traditional power amp, that usually takes a full stack on your audiophile ladder. And, when compared to the Mamoritai Euphony, another high-end pre-amplifier produced by Fosi under a subsidiary company, the difference is even starchier, the latter being the complete opposite : bold, glossy, heavy.
In fact, even compared to brands like SMSL, which prioritize compact and lightweight designs, the V3 Mono form factor feels unapologetically tiny. And, for anyone seeking a stealthy amp to pair with their desktop speakers, this one will be hard to beat… That if you manage to fit the corresponding power supply unit!
Because yes, when most of SMSL recent products embedded the supply stage, inside, the Fosi relay on a separate power-supply that appears to be bigger than the amp itself. Not a real issue on a daily basis, but cable management might not be as easy to manage as it could be with something like the AO300 – even more if you take two units, as I did.
But, all in all, for the price, the V3 Mono Amp remains an impressive device as it is, even more taking account of the price, and the rated power.
Build Quality
Again, if visually the Fosi V3 Mono isn’t the most impressive device you can think of, it’d be unfair not to praise how sleek looking that amp looks and feel. Weighing 0,48kg, this is one of the lightest mono amplifiers on the market, and the only other amp – pushing equal numbers -that I could think of was the Nuprime STA-100 (another amazing device, that I’d love to put on the bench). But, overall the amp inspires confidence, and once installed, the presence it exudes truly lends a premium feel : no gaps, impeccable junction, premium materials everywhere you see/touch, and red-tinted grill on each sides for thermal dissipation.
And, once paired with a JDS Labs Atom, or a the SMSL HO100, or even the FiiO KA11, you get an amazingly potent setup for less than $500, delivering the same minimalist impression as its siblings. In fact, you could easily add the full JDS Labs Atom stack and still maintain a smaller footprint than my SMSL DO400 on its own. A feeling enhanced by the various toggles, as well as the sturdy connectors and, if this was my first interaction I found the overall build quite impressive, even more so when I hooked it up to my dining room speakers.
Speaking of layout, let’s check on that.
Layout
As expected, the Fosi Audio V3 Power Amp comes with a minimalistic I/O, as it sits at the end of the audiophile chain. But, that doesn’t mean the brand didn’t put some interesting features here and there.
Upfront, you get:
- 1x power toggle with three settings available: on, auto, off
- 1x input toggle : XLR, RCA
And at the back you have:
- 1x RCA input, for your unbalanced sources
- 1x XLR input, for your balanced sources
- 1x speaker output (+ and -)
- a gain toggle with a 31dB level, or 25dB level
- a DC port, compatible with 32-48V power input
Please note that the gain switch only work when plugged in RCA though, via the XLR input the Fosi always work at 20dB though.
So, let’s set up the Fosi Audio V3 and see how it goes.
The review continues on Page Two, after the click HERE or by using the jump below.





Dana Shay
So, mono amp, I need two of them.
Is your listed price for two amps?
Just the one would be pretty worthless in a stereo rig…