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Fosi Audio V3 Mono Amplifier Review

Rate this amplifier:

  • 1. Poor (headless panther)

    Votes: 8 1.5%
  • 2. Not terrible (postman panther)

    Votes: 15 2.8%
  • 3. Fine (happy panther)

    Votes: 108 19.8%
  • 4. Great (golfing panther)

    Votes: 414 76.0%

  • Total voters
Great review Amir! Thank you!
Looks like I need to return my Topping PA7 :facepalm:

@Fosi Audio How do we use the Fosi Audio V3 Mono Early Bird Discount? And how do we pre-order?
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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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.

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/
Thanks @amirm
Great timing :)
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:
This is one of the most exciting gear releases in a long time for me. It's a game changer for sure. I'm really desiring a schematic to see what they did here. :D
Great review, thank you Amir!

Impressive specs, the Frequency Response is terrific compared to most others [in any price range].


These Fosi mono blocks with their expanded XLR SINAD [compared to RCA] seemingly make a good use case for using my Oppo 105D XLR outs (wonder if a pre-amp would be needed?):
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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.

Thanks for the detailed reply. Do you think 25db is enough for low sensitivity speakers? Let's assume 84db/2.83v bookshelf speakers at 2 meters and I want reference level audio while watching a movie. That's about 104db per speaker if I got this right. That's pretty close to THX recommended reference level cited at 85/db with 20db of headroom.

Do you think 25db is enough for low sensitivity speakers?
It doesn't matter what the sensitivity of the speaker is. The only thing important is whether the max power of the amplifier can be reached given the input voltage you have. As I noted, this amplifier needs 2.8 volts input to do that. Since most DACs have 4 volts output, you are good to go regardless of speaker you use.
Holy crap! This is not April Fool's Joke. 140 clams for that performance, or $280 for two channels. Yeeesh.
Less than that if you're a veteran chip-amp user like me and already own a suitable PSU or two -- but it's not a sensible upgrade in my particular use case, just a very impressive product to read about. :cool:
I know I'm gonna get a lot of hate for this. But here goes, these amps are great, no doubt and an excellent value. But what is the deal with external power supply? And what is the deal with that cute little miniature size form factor, is it meant to be a desktop amp?

Can't we just put two of these mono and their power supply into one case? Who started this silly trend? It screams dorm room HiFi component. :p
what is the deal with external power supply?
This package solves multiple issues.

- International safety certification for the power supply may be done to one power supply and then that power supply may be sold to manufacturers to be included with the device requiring the power supply. This saves lots of money and time as compared to being required to have each amplifier with power supply included be safety tested and certified.

- By having the power supply external from the amplifier circuitry the SNR can be reduced.

- BY having the power supply external if the power supply fails it is easily replaced as compared to repaired if repairs can be done.
I wouldn't want to be a seller of Hypex or Purifi at this point. Fosi and Aiyima are iterating so quickly that they're already highly competitive with Hypex and Purifi at, what, close to one fifth the price for comparable units at retail?
Thanks for the review. I have a Fosi Audio ZA3 that has provided really impressive results. I had a chance to try two ZA3 amps in monoblock form connected via balanced XLR cables to my Schiit Freya+ line stage, and as monoblocks, the sound quality was great.

I was going to pull the trigger on another Fosi Audio ZA3, but saw on this forum posts about the V3 Mono. After reading the review, I will sell my ZA3 and purchase two V3 Mono amps and separate power supplies. Can’t wait for the Kickstarter campaign to begin.
I wouldn't want to be a seller of Hypex or Purifi at this point. Fosi and Aiyima are iterating so quickly that they're already highly competitive with Hypex and Purifi at, what, close to one fifth the price for comparable units at retail?
if only those... I am also thinking of all the other manufacturers, the so-called "noble" brands that have prices x10 x20 and which very often do not come close to these performances….
I wouldn't want to be a seller of Hypex or Purifi at this point. Fosi and Aiyima are iterating so quickly that they're already highly competitive with Hypex and Purifi at, what, close to one fifth the price for comparable units at retail?
The amp torture testing has yet to begin/be done and so don't get too far ahead of yourself here. There is a reason Hypex and Purifi are more money and bigger.
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