Fosi V3 monophonic power amp

Our video review of the Fosi Audio V3 mono: don’t miss it!

Fosi Audio V3 monophonic amplifiers

Fosi is a relatively young company, born in 2017 from an idea of Ryan Huang with a clear mission: to make a quality audio experience accessible even to those without large budgets. The project started in China, like many emerging companies in the audio industry, and is based on a very concrete principle: to offer well-designed, efficient, and affordable devices, focusing everything on value for money. Within a few years, Fosi has greatly expanded its product range to cover a broad spectrum of home audio solutions. Today the catalog includes power and headphone amplifiers, DACs, preamplifiers and a range of dedicated accessories, such as power supplies and upgrade modules. Despite being a 100 percent Chinese brand-just like its main direct competitors, SMSL and Topping-Fosi has been able to build a solid reputation in the entry-level hi-fi scene, mainly through distribution via global channels such as Amazon and eBay. This direct-to-customer sales model allows the company to avoid the traditional steps in the commercial supply chain: the national distributor and the physical store. The result? More aggressive and affordable pricing, in line with the company’s initial goal. However, this approach also comes with limitations. The lack of a physical dealer network means that there is no local point of contact for advice, personalized service, or advanced technical support. And while it is true that Fosi offers support via email (at support@fosiaudio.com), our direct experience was rather disappointing: we tried to contact them with a simple question, in English both in the case of the ZD3 DAC/PRE trial and here, but received no response. In summary, Fosi is an attractive brand for those who are willing to sacrifice some after-sales support in exchange for a competitive, inexpensive, and, in many cases, very high-performance product for the price at which it is offered.

V3 Mono, a known architecture

The power amplifier is based on the TPA3255 chip, the “usual” one used by many companies, and which provides for both a stereo and a bridged configuration, thus in mono, with supply voltages ranging from 18V to 53.5V, with a power output (relying on the Texas Instruments datasheet) of 315W in stereo and 600W in mono, referred to an impedance of 4Ω and a THD distortion of 10%, obviously at maximum supply voltage, to arrive at more down-to-earth figures of 150W per channel on 8 Ω with 0.1% THD. A burly 48V 5A power supply comes with the V3, not very easy to accommodate, bearing in mind that for the stereo pair there are two, and they are much larger than the amplifiers themselves.

The Fosi Audio V3 mono power amplifiers have a simple front panel with two switches, one for ON/OFF/AUTO, the other for input selection between XLR and RCA. On the rear panel correspond XLR with center 6.3 mm jack input option, RCA with switch for gain control between 31dB and 25dB, and the small output binding posts (couldn’t be otherwise given the size) in addition to the power input jack. The only concession to Fosi orange are the two sides with a dense perforation where a colored grid is applied.

The PFFB technique of the Fosi Audio V3 mono

The PFFB technology of the Fosi Audio V3 mono has actually already been seen in other realizations, just remember that besides Texas Instruments, Hypex uses it (although it does not call it PFFB), the Purifi (with the 1ET400A module) or Orchard audio, in GaN technology. What PFFB is is quickly stated. Class-D amplifiers convert the signal to digital, reconstructing it to analog via a low-pass filter, which is one of the trickiest things to accomplish. This is where the PFFB technique comes in. Traditionally, the feedback system, feedback (that is, that mechanism that “checks” the output to correct any errors) is applied before the filter just described. But this can introduce distortion, because the system does not “see” what actually happens after the filter, that is, at the point where the signal is actually picked up, and thus with the interaction of the load, that is, the acoustic speaker. PFFB picks up the feedback signal after the output filter, allowing the amplifier to correct errors based on the actual signal arriving at the speakers.

Excellent components

Lots of and really nice components used, Nichicon filter capacitors, then ELNA, red WIMA, the Japanese Sumida inductors, and a very well done four-layer printed circuit board. The dissipation system is interesting, with the TPA3255 chip placed at the bottom and attached to the chassis, allowing effective heat dissipation through the case. Side ventilation holes improve internal airflow, ensuring stable operation even after long periods.

The op-swap

For the Fosi Audio V3 mono, as indeed for many of the Chinese manufacturer’s electronics, it is possible and indeed recommended by them to change the op-amps. There are 3 of them, number 1, the one immediately next to the input RCA pin, is the one that unbalances the XLR input and therefore if you don’t use it-something desirable since V3 is not balanced-you don’t need to replace it, then there are 2 others, those instead actively contribute to the sound, the most important being No. 2, and following No. 3. But which op-amp to buy ? The market is very varied, and it is necessary to make precise choices, since copies and clones are around the corner, and in the case of op-amps it is not at all easy to tell whether you are looking at a real or counterfeit specimen. It matters a lot where you buy, but in this regard we recommend that you read the article we published that explains quite clearly how to navigate the market

The listening test: fair, but with limitations

We put the Fosi Audio V3 mono speakers to the test in conjunction with the ZD3 DAC/PRE, already tested both on the YT channel and as an article a pairing we know well. The result, in the standard configuration, was all in all positive but not without criticism. At moderate volumes, the sound is decent, with a good overall performance, but already raising the listening level a bit some rigidities emerge: the soundstage compresses, details become blurred, and the bass loses presence and control, while the mid-high frequencies become more confused and less intelligible. A perceptible improvement is achieved by replacing the number 2 op-amp with a Sparkos: harshness fades, the soundstage warms up, and microcontrasts emerge more vividly. However, even with this upgrade, the problem of compression at high sound pressures remains evident. It is plausible to speculate that part of the limitation lies in the supplied switching power supplies, which may be the bottleneck of the system. An upgrade to quality linear power supplies could be a solution, but would incur additional costs.

Upgrade yes, but in moderation

And it is precisely on the issue of upgrades that a broader reflection opens up. Operations such as replacing op-amps or power supplies-while effective-risk significantly raising the overall cost of the system, bringing it into a price range where more traditional, integrated alternatives might offer superior sound performance already out of the box.

Good yes, but without illusions

The Fosi Audio V3 Mono are undoubtedly an attractive proposition for those looking for an inexpensive, compact desktop amplifier that performs within certain limits. As it is, they represent an honest purchase, capable of satisfying a user who is not too demanding or looking for a second system for the office or secondary rooms. However, one should not expect miracles: these small power amps are not “giant killers” and cannot be compared to higher-end products. They are honest and do their job well, as long as you don’t ask too much of them. If you then want to have fun with progressive modifications, the experience will certainly be educational and fulfilling from a hobby standpoint, but the real risk is that you will end up with an expensive and underbalanced performance system. Bottom line: the V3 Mono are worth every euro of their list price, but not one more.

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