Fosi Audio V3 Mono Amplifier Review

[DavidR]

Even at 90 out of 100 you are still putting 2K in series with your input, assuming the pot is linear - and the rated input impedance of the Fosi may only apply with power on - depending on what the input circuit is.

I think you just have to take the "it is what it is" approach - unless you are prepared to work out what the input circuit looks like - or ask Fosi to provide it for you.

Agreed about the 90 setting. My start was at 10 when the problem was observed. I tried the 90 setting to compare.

The pots are standard 10k Bourns pots. The 2i2 output sees 20k with the tap to the V3. Granted the somewhat low V3 input impedance is a factor such that the effective impedance seen by the 2i2 varies more than would be desired, but at the 10 setting, even if the V3 impedance was zero, the 2i2 would still see 18k. So we have 5k parallel to what point the attenuator tap happens to be. At attenuator 10 the 2i2 sees 18k with a (remaining) 2k/5k parallel in series with the 18k. If I've figured this correctly.

Edit: I never measured the 2i2/V3 input when I had the 2i2 directly connected and got good results. I added the attenuator to the output to be able to set the 2i2 output near maximum and then attenuated to the desired V3 input voltage in order to run the 2i2 output with lowest possible relative noise level together with the REW added distortion option. That worked exactly as desired for the 2i2 loopback, but the V3 issue is a no-go unless I can solve this problem. It may not be solvable, I'll grant that.

 

[Power Pop 23]

FYI,

The 'Fosi Audio Official Store' on Ebay is currently selling a package of gear that includes two V3 Mono amplifiers, a 48 volt, 10 ampere power supply with power filter and power splitter cable for $237.99 with a 15 percent off digital coupon available at checkout for price of $202.99. The listing says the coupon is good through 9/21/25.

 

[burkm]

The price seems to be of general interest, because the 48V/10A option at 1 power supply for both amps might not be so common.

 

[antcollinet]

FYI,

The 'Fosi Audio Official Store' on Ebay is currently selling a package of gear that includes two V3 Mono amplifiers, a 48 volt, 10 ampere power supply with power filter and power splitter cable for $237.99 with a 15 percent off digital coupon available at checkout for price of $202.99. The listing says the coupon is good through 9/21/25.

I would rather have 2x 5A PSU than 1x10A plus filter. Still two boxes to do something with. But the separate PSU is more flexible with positioning of the amps -especially if you want the amp close to the speaker, plus I can't help thinking the filter must be a compromise on the performance (no filter is perfect)

 

[mike70]

Thinking on recent discussions about power supply, current, etc.

I have a Purifi amp with better specs than Fosi (sinad, treble distortion, etc)... and it should be... price tag is 8x more.
Power isn't really higher, close to 200 watts in 8 ohms vs close to 150 with Fosi.

But... but... the power supply is something over 20A vs 5A in the Fosi.
That's part of the difference in performance or that numbers are only isolated numbers?

 

[Yersinia Bestmate]

^ Ability to give enough amperage is a major factor in amplifier performance.

 

[TurtlePaul]

Thinking on recent discussions about power supply, current, etc.

I have a Purifi amp with better specs than Fosi (sinad, treble distortion, etc)... and it should be... price tag is 8x more.
Power isn't really higher, close to 200 watts in 8 ohms vs close to 150 with Fosi.

But... but... the power supply is something over 20A vs 5A in the Fosi.
That's part of the difference in performance or that numbers are only isolated numbers?

The amp tested here does 98 watts into 8 ohms. The PSU needs to be more than 48V to get higher than 100 watts into 8 ohms.

Multiply the power supply voltage by the max current to get the max power. You should only directly compare the current capacity of power supplies if they are also the same voltage. For example, a 70 volt 4 amp (280 watt) power supply is more powerful than a 48 volt 5 amp supply (240 watt). Another funny thing to keep in mind is that the actual power limits of a lot of these power supplies can be up to 40% higher than the actual rating - for example, the Fosi 48V5A power supply seems to cut out around 7 amps instead of the 5 specified.

The maximum power limit of the power supply will limit how low of an impedance the amp can drive while continuing to double down in power each halving of impedance. As you can see in this review, the power doubles going from 8 ohm to 4 ohm. It increases substantially, but doesn't double, when going from 4 ohms to 2 ohms. With a 48V 20A power supply, it would be possible to make an amp that can double power into 2 ohms and maybe even come close to doubling again into 1 ohm.

One way to think of this is that the amp is tasked with holding the output at a certain voltage, which is based on multiplying the source voltage by the gain. To output a 25 volt sine wave into a 4 ohm speaker requires twice as much current in the output (and hence twice as much power from the power supply) as holding the 25 volt output voltage of that sine wave into an 8 ohm speaker.

 

[rsqt]

The 3E 480 does better, it nearly doubles the power from 4 to 2Ohms with the same 3255 chip.

 

[Bruce Morgen]

Thinking on recent discussions about power supply, current, etc.

I have a Purifi amp with better specs than Fosi (sinad, treble distortion, etc)... and it should be... price tag is 8x more.
Power isn't really higher, close to 200 watts in 8 ohms vs close to 150 with Fosi.

But... but... the power supply is something over 20A vs 5A in the Fosi.
That's part of the difference in performance or that numbers are only isolated numbers?

First question: At what output voltage is that 20A PSU operating?

The following assumes the same 48V used to power the Fosi: 20A at 48V -- 20A*48V=960(!) watts -- which seems very conservative (AKA "overkill") for a 200 watt amp given Class D's typically very high efficiency.

5A at 48V -- 5A*48V=240 watts -- is entirely adequate for a 150 watt amp of similar efficiency. 7 or 8A at 48V might theoretically be better for a TPA3255-based amp (based on what at least one Shenzhen manufacturer has recommended), especially when driving the relatively low output load impedances at which power is current limited, but such a difference is unlikely to be audible in the context of actual music listening.

 

[burkm]

The final question is: are those better specs really audible or are they beyond this and only "better specs" ?
I have two amps using the Hypex NCore 400 modules and I am questioning, if they are really better at this audibly ?

 

[mike70]

The final question is: are those better specs really audible or are they beyond this and only "better specs" ?
I have two amps using the Hypex NCore 400 modules and I am questioning, if they are really better at this audibly ?

Well, audible in standard contexts... I think it's not. But, with hardcore speakers and high spl... yes.

And that's why I opted for purifi... I want to have Maggie's in the future. Unless some measurements shows that the Fosi are enough for them, but surely you'll need the 48V power supply and the heat problem.

 

[Jeff29]

Well, audible in standard contexts... I think it's not. But, with hardcore speakers and high spl... yes.

And that's why I opted for purifi... I want to have Maggie's in the future. Unless some measurements shows that the Fosi are enough for them, but surely you'll need the 48V power supply and the heat problem.

There is no heat problem by adding fans for 20 € ...

 

[TurtlePaul]

Well, audible in standard contexts... I think it's not. But, with hardcore speakers and high spl... yes.

I disagree. 40 years ago there was the Carver Challenge where stereo reviewers could not identify high-end amps vs. cheaper amps Bob Carver tuned to sound like them. Now all of the amps we are comparing are 15-30 dB better than anything from the Carver Challenge, and you think you could win the million?

 

[burkm]

Well, audible in standard contexts... I think it's not. But, with hardcore speakers and high spl... yes.

And that's why I opted for purifi... I want to have Maggie's in the future. Unless some measurements shows that the Fosi are enough for them, but surely you'll need the 48V power supply and the heat problem.

I do have both, the 48V/5A per channel power supply and the increased heat output, for which I use a temperature controlled fan.
It turns the fan on as soon as the case temperature reaches 30°C or more.
I am not sure, if I hear (really) any differences comparing it closely with my Hypex NCore 400 amps (3 channels), no matter, what output is been used by my speakers.
The problem lies in the subjectiveness of what I am "really" hearing or just imagine by my "brain". It's hard to tell, because no one can be sure, that the difference he hears are really imaginations of our brain, which is strongly involved in that hearing process. Ears and the hearing process itself are no known (calibrated) measurement microphones involved in that very process.
Hard to tell...

 

[SMen]

The final question is: are those better specs really audible or are they beyond this and only "better specs" ?
I have two amps using the Hypex NCore 400 modules and I am questioning, if they are really better at this audibly ?

I do have both, the 48V/5A per channel power supply and the increased heat output, for which I use a temperature controlled fan.
It turns the fan on as soon as the case temperature reaches 30°C or more.
I am not sure, if I hear (really) any differences comparing it closely with my Hypex NCore 400 amps (3 channels), no matter, what output is been used by my speakers.
The problem lies in the subjectiveness of what I am "really" hearing or just imagine by my "brain". It's hard to tell, because no one can be sure, that the difference he hears are really imaginations of our brain, which is strongly involved in that hearing process. Ears and the hearing process itself are no known (calibrated) measurement microphones involved in that very process.
Hard to tell...

I don't have the Hypex NCore 400s but I do have the v3 Monos and 3eAudio A7s and A5s, and in my experience the last three do have differences but not really in perceived power. I do have a clear order in which, should I be put on the spot, I might keep or relinquish each one. In fact I am only listening to the first one on the list now. I am selling the others.

In order of keeping preference:
1. A7s with 10A supply
2. A5s
3. V3 Monos

I think that you are right that it is difficult, and the brain can trick us etc. But which would you rather give away in your case, without actually thinking about it too much? Just after a bit of time with each at different times of the day and volumes?

Without trying hard at all for me it is the A7 that stays after the above unscientific test!

 

[burkm]

For me the question is: what is real (straight wire with gain) ?
Personal preferences are commonly to be used, but are we then still listening to "HiFi" in its intentional basis ?
We do love things, which follow our own preferences, but then everything has to be following its individual "preference" and we don't know, if that has been really recorded as it is or as we personally "love" it ? I rather think, we should follow the "real thing" as it is even if it doesn't follow our own preferences.

In history power was an ultimate goal to archive with some common measures. Nowadays power is quite common and easily to be archived but the quality of that power is still in question.

 

[mike70]

The core goal of the amplifier is to amplify the signal. Done.
With the right context (enough power for the spl needed in the room / speakers combo) any "decent" amplifier (low noise, 80dB sinad or more, flat frequency response, etc) will sound "the same".

Fosi IS a decent amplifier, you only need to check if it's enough for your use case.

 

[JohnnyNG]

I ran a couple Purifi 1ET400A mono amps for a few years on my Revel M106 until I went to a 4-way active setup. Now I run the Purifi for midbass and a couple V3 mono for the midrange and tweeter. The Fosi don't sound intimidated at all.

 

[SoySalsaPicante]

I ran a couple Purifi 1ET400A mono amps for a few years on my Revel M106 until I went to a 4-way active setup. Now I run the Purifi for midbass and a couple V3 mono for the midrange and tweeter. The Fosi don't sound intimidated at all.

V3 Monos present perfectly fine performance for the price, especially for anyone who doesn't mind the separate power supply clutter, the slightly low gain in XLR input mode (really only an issue with low-sensitivity speakers combined with large headroom cuts for heavy room correction), and the (potential) thermal issues.

 

[Carlton80@0]

I would be delighted to run the cute little monos in a test of low impedance performance with the amp killing Apogee Scintilla. Although many amps baulk at the driving requirements of the 1 ohm load. I would not be surprised if it was able to play at a reasonable level before protection kicks in.

Currently testing the V3 Mono with a torturous 1 ohm Apogee Scintilla.