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Fosi Audio V3 Mono Amplifier Review

Rate this amplifier:

  • 1. Poor (headless panther)

    Votes: 8 1.6%
  • 2. Not terrible (postman panther)

    Votes: 12 2.4%
  • 3. Fine (happy panther)

    Votes: 100 19.7%
  • 4. Great (golfing panther)

    Votes: 387 76.3%

  • Total voters
    507

amirm

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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.
Fosi Audio Mono V2 amplifier class d monoblock review.jpg

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:
Fosi Audio Mono V2 amplifier class d monoblock balanced review.jpg


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:
Fosi Audio Mono V2 amplifier measurement.png

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:
best class d desktop monoblock review.png

best class d desktop monoblock zoom review.png


RCA input costs you some performance but I was relieved to not see any mains interference:
Fosi Audio Mono V3 amplifier RCA Measurements.png


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:
Fosi Audio Mono V3 amplifier power SNR measurement.png


Now the all important frequency response and load dependency test:
Fosi Audio Mono V2 amplifier frequency response measurement.png


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:

index.php

Above we have 2 dB differential at 20 kHz.

Distortion is very low and only increases with frequency:
Fosi Audio Mono V2 amplifier Multitone measurement.png


Fosi Audio Mono V3 19 20 khz intermoduation distortion amplifier measurement.png


Let's see how much power we can get out of this little box:

Fosi Audio Mono V3 amplifier power 4 ohm measurement.png


Fosi Audio Mono V3 amplifier max and peak power 4 ohm measurement.png

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:
Fosi Audio Mono V3 amplifier power 8 ohm measurement.png


As note though, distortion does rise at higher frequencies:
Fosi Audio Mono V3 amplifier power 4 ohm vs frequency vs distortion measurement.png


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:
Fosi Audio Mono V3 amplifier power Reactive Voltage measurement.png


Translating into watts:

Fosi Audio Mono V3 amplifier power Reactive Power measurement.png


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:
Fosi Audio Mono V3 amplifier power on noise measurement.png


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.

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amirm

amirm

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Just read this from the company in their message to me when the amp was sent:

"We'll provide a bundle including two V3 mono amps and a 48V/10A psu for no more than 260USD. That single 48V/10A psu can power the two sets of v3 mono simultaneously."
 

natna

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Wow! Am I the first to post?

Thanks so much @amirm
Great job as always.

Power figures are impressive. Especially at 2 Ohms. That PSU is a monster.
XLR SINAD performance is very nice
RCA SINAD is fair enough but nothing really special. It still is almost 6 db better than the V3 stereo.
Load independency could be better. The outcome from the use of PFFB is only 0.5db better than without, if it's fair enough to compare with the old stereo V3.
Pricing is nice.
 
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amirm

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Am I missing something. I see a ~1.5 dB differential at 20 kHz <?>
That is the other amp I showed for comparison which does NOT have PFFP. This amp had the measurement just above it.
 

olieb

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Thanks for the review. Nice results. And a good price indeed.
Now I am waiting for the stereo version.
 

Eytsch

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Just read this from the company in their message to me when the amp was sent:

"We'll provide a bundle including two V3 mono amps and a 48V/10A psu for no more than 260USD. That single 48V/10A psu can power the two sets of v3 mono simultaneously."
I wish they first considered an Amp+PSU combo in a single chassis. That would be more welcome.

Topping, I'm also talkin' to you!
 

Doodski

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Thanks for the review. Nice results. And a good price indeed.
Now I am waiting for the stereo version.
I wish they first considered an Amp+PSU combo in a single chassis. That would be more welcome.

Topping, I'm also talkin' to you!
gg* You guys are so fussy! LoL. :D This Fosi V3 Mono is amazing.
 

Eytsch

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gg* You guys are so fussy! LoL. :D This Fosi V3 Mono is amazing.
Lol. Sorry. Let me retry:


This looks awesome. A $139 amp landing close to the middle of the blue zone is incredible. What more could one ask for?....

Well, just one simple thing - an Amp + PSU combo in the same chassis. I'd happily pay the extra cost for the slightly bigger enclosure.
 

Fosi Audio

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Thank Amir so much for the measurement! The V3 Mono is another amplifier co-created with members, following the V3 stereo amp. We would particularly like to thank @Toku, @ModDIY , @mike70 , @cyclo, and all the other members who have provided us with invaluable suggestions.

The V3 Mono is our first amp with PFFB implementation. During the period we sent the set to Amir for testing, our R&D team did not stop optimizing the V3 Mono, and we have now further improved its frequency response curve. Below is the chart for your reference.
IMG_5594.PNG



The V3 Mono is currently in production, and it will be launched on Kickstarter on the 20th of this month. There will be very attractive discounts available then, and we hope you'll stay tuned!:)
 

AdamG

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This amp is pure Science Fiction. This level of power and performance for less than $140 per channel? Wow. :eek:

Thanks for this delightful review Boss. The budget guys are cheering in the background. Look at that 4 and 2 ohm numbers. Real doubling for a Buck Fifty?

If I didn’t know better I would think this is a well done April Fools joke. But Amir doesn’t joke! :cool:
 

Bruce Morgen

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Thank Amir so much for the measurement! The V3 Mono is another amplifier co-created with members, following the V3 stereo amp. We would particularly like to thank @Toku, @ModDIY , @mike70 , @cyclo, and all the other members who have provided us with invaluable suggestions.

The V3 Mono is our first amp with PFFB implementation. During the period we sent the set to Amir for testing, our R&D team did not stop optimizing the V3 Mono, and we have now further improved its frequency response curve. Below is the chart for your reference.
View attachment 360736


The V3 Mono is currently in production, and it will be launched on Kickstarter on the 20th of this month. There will be very attractive discounts available then, and we hope you'll stay tuned!:)
Yes, I figured that was a matter of "fine-tuning" the PFFB implementation. Good on Fosi for (a) getting a pre-production sample to Amir so we can see the product's potential and (b) for continuing to improve the design until it's time to officially release it.
 

Mikig

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finally the mono without a potentiometer.
Similar performance in such a small space and at that price was unthinkable until a few years ago. The fact that it can go down to 2 ohms makes it almost universal, therefore suitable for most speakers on the market.
Now we no longer talk about devices "to start" the Hi-fi journey. Amplifications like this can easily replace, with all due respect, devices of decades-old users, or find space in an HT configuration, where we know, the multiplication of boxes is always a problem to consider and manage, in terms of weight, dimensions and logistics.
Thank you Amirm for the review and your time.
 
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amirm

amirm

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@amirm May I ask why this is your new recommendation? I'm glad you post the gain figure. I'm just curious on that number and why.

Thanks!
There are no standards for gain in amplification. When I first started to test them, I used 29 dB which was some recommendation by THX. That gain factor though assumed very anemic sources. Just about every DAC I test has far higher output voltage. A high gain amplifier adds noise then for no reason. I picked 25 dB as to not deviate too much from the old gain factor so tests would still be comparable for the most part. This amp gets full power with 2.8 volt input vs 4 volts that is available.
 

phoenixdogfan

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Thank again, Amir. This is an excellent review. I used to think of these Fosi and Aiyima chip amps as a useful and economical way to power your surrounds on a budget or a great way for someone getting into the hobby to max out on speakers and still have amps that play well though perhaps with one or two minor compromises like load dependency or lower power. But now we're seeing something at $260 for a pair that has none of those compromises. To me it looks every bit like a lot of very good Hypex and Purifi Class D offering with its 100 watts at 8 ohms, low output impedance, and 100 db Sinad.

While they won't be replacing my beloved Eval 1, if I ever build another system from scratch or expand my existing system to include Atmos height speakers, I know these will be on my short list.
 
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