Fosi Audio continues to make a name for itself, delivering audiophile-grade equipment at surprisingly wallet-friendly prices. The Fosi Audio V3 Mono amplifier aims to offer monoblock performance (usually reserved for high-end systems) in a compact, accessible package.
Having been suitably impressed with their Audio Box X5 phono preamp, can they impress me again with the V3 Mono?
Listening to Customer Feedback
If there’s one thing Fosi gets spot on, it’s listening to customer feedback.
Following the launch of their V3 stereo amplifier in 2023, Fosi received a great deal of customer feedback, all of which they’ve poured into the VS Mono. Requests for Post Filter Feedback (PFFB) to remove load dependency was one of the most recurring requests, along with calls for a monoblock version with a simplified signal path and balanced inputs.
More on the all-important PFFB shortly….
Firstly, what is a Monoblock Amplifier?
Before we delve deeper, let’s clarify what a monoblock amplifier is.
Unlike traditional stereo amplifiers that power two speakers, a monoblock drives just one speaker per amp.
Why choose this setup?
- Dedicated Power: Each speaker receives focused amplification, which may reduce distortion and enhance sound clarity.
- Better Channel Separation: No crosstalk between channels means a wider soundstage and improved imaging.
The downside is, you’ll need two of these units to power a set of speakers. That said, the V3 Mono is impossibly compact, sporting the same tiny dimensions as the Phono Box X5 phono preamp.
There’s also no preamp section or volume control to the V3 Mono, so you’ll need a preamp stage for your source inputs or an integrated amplifier with a variable output option.
For my review, I’m using the variable output on my Pro-Ject Stereo Box DS2 amplifier and my speakers are a set of Klipsch RP-500Ms.
Assuming you’re using the larger 48V power supply option, the V3 Mono amplifiers will deliver 120w Rated (RMS) Power at 8Ω (ohms) per channel, giving ample power to my speakers with plenty of headroom. There shouldn’t be any need to worry about distortion by powering the RP500s with the V3 Mono. The RP500s have a continuous power handling of 75w with a nominal impedance of 8 Ohms.
There’s a handy power rating chart on the Fosi Audio website, which I’ll provide below for your convenience:
RCA or XLR? Controls and Front Panel
The V3 Mono allows for RCA or XLR inputs. XLR inputs are superb for canceling out any unwanted potential interference and should produce an overall cleaner audio performance.
The RCA input on the Fosi Audio V3 Mono offers selectable gain settings of 25dB and 31dB, providing flexibility to match the amplifier’s sensitivity to various audio sources.
Lower gain (25dB) helps minimize noise and distortion when using sources with strong output signals, while higher gain (31dB) boosts weaker signals, allowing optimal volume and performance across different setups and components. This makes the V3 Mono very adaptable across multiple systems and is a very welcome feature in my books.
The front panel is beautifully minimalistic, giving you smart and robust switches for selecting the RCA or XLR inputs and for toggling between Off, On, and Auto. (Auto mode will switch the device into standby mode automatically when no signal is received for 10 minutes saving power in the process).
Key Feature: Solving Load Dependency with “Post Filter Feedback” (PFFB)
One of the key selling points of the V3 Mono is its solution to “load dependency”. A phenomenon in class D amplifiers where the amps performance varies with different speaker impedances.
The V3 Mono addresses this issue using Post Filter Feedback (PFFB)—a feedback method that stabilizes the frequency response regardless of speaker load.
While PFFB isn’t new, it usually appears only in significantly more expensive Class D amplifiers and attempts to give the V3 Mono a consistent, accurate sound typically reserved for higher-end Class A or AB amplifiers.
Sound Tests
Though I’ve never been dissatisfied with my Pro-Ject Stereo Box DS2, a move away from an integrated amp has always been on the cards — budget permitting.
I was immediately struck by the obviously wider stereo separation when moving to the V3 Mono. There was also an overall opening up of clarity in general.
The sound is balanced, crisp, and clean, with a low end that is noticeably deeper than my existing amp while still remaining controlled.
In general, it’s quite a neutral-sounding amplifier, and thanks to the lack of load dependency, it should pair well with a wide range of speakers.
Teething Problems
I was first sent these amps for review all the way back in November of last year. In the usual way, I excitedly set them up, ran a few of my favorite and familiar records through them and was very happy indeed.
And then, out of nowhere the following day, one channel stopped working.
I did the usual process of elimination channel cable swapping to see if one of my RCA cables or another device had failed, but sadly, it turned out to be the V3 Mono at fault.
Speaking to Fosi Audio directly, it turned out that a batch of the V3 Monos manufactured late last year had some issues, and they very promptly sent me a replacement.
For this reason, though, I’ve sat on the V3 Monos for longer than I usually would before releasing this review; I needed to be entirely sure the problem had been resolved before giving any potential product recommendation.
The replacements are still running strong months later, but I wouldn’t be doing my due diligence as a reviewer if I didn’t highlight my experience here.
Summary: Should You Buy The V3 Mono
I’m by no means the first person to review the V3 Mono. Audio Science Reviews gave a very favorable review in their usual fashion for those who like to dig into specifications and measurement charts. I’ll put a link in the description for those who’d like to see how the V3 Mono performs. On paper, it’s impressive.
Cheap Audioman gives a rave review, Scientific Audiophile also gives a hugely favorable review, while one other review by Passion for Sound gives a much more underwhelmed conclusion—that is, until performing the optional op-amp upgrade.
Sound quality, of course, is often highly subjective, and for those who wish to squeeze as much value from their gear as possible, the option to swap out op-amps gives you a potential upgrade path and a way to tailor the amp to your own personal taste.
My personal take? The V3 Mono is excellent – hugely impressive, in fact, considering the budget-friendly price.
It’s worth noting that my review was conducted with two separate 48V/5A power supplies rather than the optional 48V/10A power supply capable of powering two amps via a splitter.
Two separate power supplies will improve performance compared with using one power supply to power both amps, but it does add to the clutter as the power supplies are not exactly small.
Despite my initial issue (promptly resolved by Fosi Audio’s customer support), my long-term experience has been overwhelmingly positive.
The V3 Monos brought new life to my speakers, and as things stand, I prefer how they sound to my integrated amplifier meaning they’re not going anywhere—they’re staying in place.
In short: the Fosi Audio V3 Mono absolutely delivers on its promise of premium sound at an attainable price. It’s a firm recommendation from Sound Matters.
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