Fosi Audio V3 Mono Amplifier Review

[tmtomh]

They are required to donate if they want to list items for sale, like any normal member. Otherwise they are free to donate or not.

Thanks to you and @antcollinet for this clarification.

 

[Urib]

This is a review and detailed measurements of the Fosi Audio V3 Mono class D amplifier. It was sent to me by the company. The price with the power supply I tested is US $139.99.
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I must say the concept of a "monoblock" amplifier in such a small size runs foul of any expectation a longtime audiophile would have! But monblock it is even though it is a very small block. Controls are on/off/trigger audio and selection of XLR vs RCA inputs -- just like the big boys! I am not showing the sides of the amp but there are very large holes with attractive orange color grid showing through. Nice. Back panel is again a bit of a shock to the system seeing XLR input:
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The power supply as noted, is quite beefy with 48 volts at 5 amps on tap (240 watts). The amplifier is stated to have PFFB implementation which for a class D amplifier means it should have no load dependency together with lower distortion. Let's see if we get these with our measurements.

Fosi Audio V3 Mono Amplifier Measurements
Let's start with XLR input:
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Wow, I did not expect this class of amplifier to break through the 100 dB SINAD barrier but the V3 Mono does exactly that, placing it in our prestigious category of "excellent:
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RCA input costs you some performance but I was relieved to not see any mains interference:
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Distortion is still at provably inaudible -115 dB. I like that the gain is nominal 25 which is my new recommendation for amplifiers.

Noise performance is excellent and at full power, darn near approaches sate of the art:
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Now the all important frequency response and load dependency test:
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There is essentially no impact up to 20 kHz between the 4 and 8 ohm indicating very low output impedance, albeit with a bit of peaking. Compare that to non-PFFB amps such as Fosi Audio V3 stereo Amp:

Above we have 2 dB differential at 20 kHz.

Distortion is very low and only increases with frequency:
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Let's see how much power we can get out of this little box:

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Efficiency must be quite high as we get essentially the power we put in (the power supply likely has some headroom).

There is decent amount of power even with 8 ohm and with very low noise:
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As note though, distortion does rise at higher frequencies:
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Fortunately it is good where our hearing is very sensitive (below 5 kHz).

I also threw my suite of my punishing reactive loads at it:
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Translating into watts:

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Amazing that this little amplifier can handle even 2 ohm load! Note that these are short term power ratings.

There may be a bit of power on noise:
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Conclusions
All I can say is wow! It is incredible how far these small amplifiers have come. It is the result of a manufacturer listening to our needs, implementing features such as balanced and trigger inputs, and proper feedback mechanism to essentially eliminate load dependency. I can't imagine asking for more from Fosi when it comes to such an amplifier. Everything is as good as you could possibly want.

It is my pleasure to recommend Fosi Audio V3 Mono amplifier.

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As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

Hi, you write that it is possible to connect 2 amps to 1 48v power block. Is this degrades the power of the amps? To get full power should I use 2?

 

[staticV3]

Hi, you write that it is possible to connect 2 amps to 1 48v power block. Is this degrades the power of the amps? To get full power should I use 2?

Splitting one power supply to two Amps will naturally cut the available power for each Amp in half.

However, Fosi sell a 48V 10A supply, which when split to two V3 Monos, should give each Amp roughly as much power as what Amir measured with the 48V 5A supply.

 

[MCH]

The power supply sharing is something interesting to me. Actually, various TPA3255 can be operated in master/slave mode so that they delay the switching between each other, apparently to "minimize noise coupling between audio channels through the power supply." and "Inter-channel delay is needed to optimize audio performance and to get better operating conditions for the power supply" according to the datasheet (below).
Given the fact that most probably two fosi sharing PSU with one of these Y cables are in fact directly connected in between, but not in master/slave mode, i would be curious to understand what this means for the performance of the amps and the power supply.

 

[mike70]

Maybe future measurements with the shared 10A power supply will be available

 

[billymac]

Please forgive the potentially elementary question. I've searched the thread (I'm on page 9 so far), but haven't come across what I'm after.

Could I use one of these to power a passive sub, using the SE sub out of a Sonos Amp and rely on the crossover settings and level control within the Sonos App, or do I still need something else to make this work properly? I'm looking to power an outdoor sub on our patio at lower, respectful volumes. I tried using one channel of my Buckeye NC502MP, but I believe the 25dB gain setting is causing fairly anemic output at lower volumes. The 32dB setting and auto-off on this caught my eye and is the reason for asking. I just plugged in a Fosi M03 and while it's working better than the Buckeye, there's no auto-off and it's not as aesthetically pleasing as this upcoming model. Thanks in advance.

 

[Guddu]

Please forgive the potentially elementary question. I've searched the thread (I'm on page 9 so far), but haven't come across what I'm after.

Could I use one of these to power a passive sub, using the SE sub out of a Sonos Amp and rely on the crossover settings and level control within the Sonos App, or do I still need something else to make this work properly? I'm looking to power an outdoor sub on our patio at lower, respectful volumes. I tried using one channel of my Buckeye NC502MP, but I believe the 25dB gain setting is causing fairly anemic output at lower volumes. The 32dB setting and auto-off on this caught my eye and is the reason for asking. I just plugged in a Fosi M03 and while it's working better than the Buckeye, there's no auto-off and it's not as aesthetically pleasing as this upcoming model. Thanks in advance.

If you can control crossover and volume on preamp (sonos in case here) then there shouldn’t be any issues.
Although it seems to be okay for 2 ohm load in theory, still knowing your subwoofer driver’s lowest impedance will help. Do you know it?

 

[billymac]

If you can control crossover and volume on preamp (sonos in case here) then there shouldn’t be any issues.
Although it seems to be okay for 2 ohm load in theory, still knowing your subwoofer driver’s lowest impedance will help. Do you know it?

Yeah, it's 8 ohm dual voice coil (Polk Atrium Sub100). I'm running it parallel at 4 ohm, so should be no issue. I think I'm going to switch back to the Buckeye, box up this M03 and wait for the release of this product. Thank you very much for the reply!

 

[Jomito83]

My request with these monoblocks, and monoblocks in general, is a 2.1 preamp. This would include:

1 quantity 2 balanced inputs and 2 unbalanced inputs (channels combined)
2 quantity 1 balanced output and 1 unbalanced output
3 quantity 1 sub output
4 volume knob
5 changeable op amps (shout out to Sparkos)
6 a frequency dial for speakers (high pass) and sub (low pass) crossover
7 input selection capability

i love my sub-bass, I love how monoblocks give channel separation, and I love phono and digital (2 channels).

Something like this should not cost more than $120 (without the expensive op amps of course).

 

[Xcaliber]

Since a lot of people will be buying two of these monoblocks to run in stereo mode, why Fosi didn't just put two modules in a single bigger chassis and offer them in a stereo configuration at similar price range of $250~280 instead?

 

[Doodski]

Since a lot of people will be buying two of these monoblocks to run in stereo mode, why Fosi didn't just put two modules in a single bigger chassis and offer them in a stereo configuration at similar price range of $250~280 instead?

Perhaps the company is small and wants to field test the sales of this model while they go about other matters.<?>

 

[tmtomh]

Since a lot of people will be buying two of these monoblocks to run in stereo mode, why Fosi didn't just put two modules in a single bigger chassis and offer them in a stereo configuration at similar price range of $250~280 instead?

Because some people like to have monoblocks rather than a single stereo amp.

 

[mike70]

Because some people like to have monoblocks rather than a single stereo amp.

I'm in ... If I can have a pair of decent monoblocks at THAT price AND size ... why not?

Totally 0 crosstalk, better thermal management, more current to hard speakers, you can put that amp close to the speaker with very short speaker cable (long signal cable ... but is balanced), ...

why not? Why is madness?

People who like the stereo version, only wait a little more

 

[billymac]

Any ideas on when this will be available? I see 4/20, but is that actual release, or just more details. I’m not familiar with the kickstarter process. Also, I see others were able to at least indicate preorder interest, but I was only given the option to be notified of release from within kickstarter and from within the Fosi webpage for the product. Is there a difference and did I already miss the boat on the first run?

 

[Watire]

The PFFB treatment brings -10dB better specs here and -6dB better specs there. It is a true validation of the effort and continuing improvement of this TI chip platform at this price range. V3 Mono is clearly a gift for XLR users, and a promise of greater things to come for the platform.
It seems to me that the V3 Mono measurements validate the value of the original V3 and its cute 32 bands input tone graph, more so if you intend to stay on a RCA signal feed.

FOSI is on a glorious path.
Bravo !

Good to know that working on the PFFB helps the overall performance because from my music listening perspective the load dependency does not seem to be a big out of the lab issue. Particularly when I inspect the spectrum of my heaviest sources. Can Load Dependency fry tweeters ?

A Pop/Rock song @1985 from a vinyl.

J-POP track @ 2012 from Spotify @ 320kbps

 

[Zuiko]

Since a lot of people will be buying two of these monoblocks to run in stereo mode, why Fosi didn't just put two modules in a single bigger chassis and offer them in a stereo configuration at similar price range of $250~280 instead?

In addition to the other responses, flexibility:
- Can use two in stereo, add another for a passive subwoofer or center channel, add 2 more for a 5.1 surround, etc.
- Can place them side by side, or in case of desktop use stack them one on top of the other (pending heat). Heck maybe on their sides

 

[TonyJZX]

a question i would love to be answered would be...

is there a difference with...

1. 2 x V3 monos + 1 x 48v 10amp with double header

2. 2 x V3 monos + 2 x 48v 5amp ie. true mono all the way down... also maybe have two extension cords to two different sockets... NAY two different phase household circuits (i'm kidding about that! or maybe i"m not.... )

would there be measureable crosstalk / better or different LR seperation?

also if you want to be completely psychotic I wonder if you would be able to get two AGM camping batteries and get them to feed a pair of V3 monos, would that result in some good measurements?

is getting 12v car batteries to 48v 5a a hard thing? probably not?

some folks dig batteries

 

[Doodski]

also if you want to be completely psychotic I wonder if you would be able to get two AGM camping batteries and get them to feed a pair of V3 monos, would that result in some good measurements?

is getting 12v car batteries to 48v 5a a hard thing? probably not?

some folks dig batteries

Car batteries have acid inside that eats most things. Even worse is the off-gassing they do. It is veryyy explosive. Trust me you do not want car batteries in your home it is very dangerous. I have seen car batteries explode (Twice.) into pieces and dump acid all over in the process.

 

[Doodski]

is there a difference with...

1. 2 x V3 monos + 1 x 48v 10amp with double header

2. 2 x V3 monos + 2 x 48v 5amp ie. true mono all the way down... also maybe have two extension cords to two different sockets... NAY two different phase household circuits (i'm kidding about that! or maybe i"m not.... )

-Two different AC mains circuits is absolute overdoing it! No gains there at all.
-Two power supplies will give you less power supply induced issues although the difference with musical source operation will be tiny tiny. If the price for 2 power supplies is reasonable and allows you to place the amps near the speakers then go for 2 power supplies but don't expect to hear a audible difference unless you are really driving them very very hard and I mean crazy hard.

 

[kibs]

In addition to the other responses, flexibility:
- Can use two in stereo, add another for a passive subwoofer or center channel, add 2 more for a 5.1 surround, etc.
- Can place them side by side, or in case of desktop use stack them one on top of the other (pending heat). Heck maybe on their sides

How will you split the source signal though? Multiple Y splitters?