Fosi Audio V3 Mono Amplifier Review

[Dave TR3A]

@Ande3200 Without any measurements to back up a claim all we have is your opinion. Can you provide any measurements (e.g., SPL at listening position, voltage at speakers, etc.)?

Doubtless, the Hegel is more powerful amp than the Fosi.

• The Hegel H390 amps are spec'd at 250W/channel into 8 ohms (at 1% THD using a 1 kHz input). Hegel does not provides power ratings into other loads (such as the 4 ohms that the Arendal speakers are rated at). It would not be unreasonable to think that the Hegel might deliver around 500W into 4 ohms at 1% THD.
• Amir measured the Fosi V3 Mono as delivering about 240W into 4 ohms at 1% THD.

The Hegel ought to have about twice the power of the Fosi V3 Mono. But twice the power is only +3 dB.

The Arendal 1528 monitor 8 speakers are just 85 dB @1W @1m sensitive so that it may take a fair amount of power to achieve the desired SPL in a largish room. Even so, both the Fosi and the Hegel can drive your speakers to >100dB SPL. That volume can cause hearing damage.

Is that extra power being used at your typical listening volume? I suspect not.

By all means enjoy your Hegel amp. But don't be surprised when others reject your claims about the Fosi being underpowered.

 

[Talisman]

Amir measured the Fosi V3 Mono as delivering about 240W into 4 ohms at 1% THD.

However, at deep bass levels, the power, as is logical to assume, drops significantly, and it is precisely in this range that the greatest amount of power is needed, certainly not at 1 kHz.
If we add that when listening at a medium-high volume, you're not hearing a continuous tone at 98 dB, but rather listening to music that, depending on the song and the dynamics, can require an enormous amount of instantaneous power. Precisely where the speaker can deliver the least, this could translate into a perception of reduced dynamics, and this is not at all an unlikely scenario.
Music is not a continuous tone.

 

[Dave TR3A]

However, at deep bass levels, the power, as is logical to assume, drops significantly, and it is precisely in this range that the greatest amount of power is needed, certainly not at 1 kHz.
If we add that when listening at a medium-high volume, you're not hearing a continuous tone at 98 dB, but rather listening to music that, depending on the song and the dynamics, can require an enormous amount of instantaneous power. Precisely where the speaker can deliver the least, this could translate into a perception of reduced dynamics, and this is not at all an unlikely scenario.
Music is not a continuous tone.

Have you any measurements to support up your assumption about the Fosi's power at deep bass frequencies? Or about the Hegel's performance there?

I don't disagree about brief dynamics requiring power. But how much? 10 dB above typical listening levels? 12 dB? 20 dB? If a typical listening level is around 85 dB (the threshold at which sound becomes harmful), the Fosi should be able to handle peaks of 15 dB or more.

I'm unwilling to accept that the extra 3dB (from say 105 dB SPL to 108 dB SPL) available from the Hegel will make much difference.

 

[mike70]

- room size
- listening position distance
- SPL at listening position

with that parameters, everything will be more clear

 

[Talisman]

Have you any measurements to support up your assumption about the Fosi's power at deep bass frequencies? Or about the Hegel's performance there?

I don't disagree about brief dynamics requiring power. But how much? 10 dB above typical listening levels? 12 dB? 20 dB? If a typical listening level is around 85 dB (the threshold at which sound becomes harmful), the Fosi should be able to handle peaks of 15 dB or more.

I'm unwilling to accept that the extra 3dB (from say 105 dB SPL to 108 dB SPL) available from the Hegel will make much difference.

This simply HAPPENS. There's nothing to "prove"; it's a power limitation of a less powerful amplifier compared to a more powerful one. I don't know if you realize the nonsense of questioning it.
It's not a question of IF, it's just a question of WHEN a less powerful amplifier will start clipping compared to a more powerful one. No additional measurements are needed beyond those already present; if an amplifier has half the power, it will clip sooner.
Now what's your question? Does the user reach this value or not? Ask him, he says yes, and I have no reason to doubt it. Despite the "hearing damage threshold," sometimes I really want to blast music with dynamic peaks above 100 dB, and I have no desire for my amplifier to work at its limit or cut those peaks, which is why I use a buffer that has much, much more power than I usually need.
I also own the Fosi V3 mono, I use it as the power amp for my home theater center channel and it does a fantastic job, but for the towers I have a Hypex 500watt power amp on 4ohm.

 

[Dave TR3A]

This simply HAPPENS. There's nothing to "prove"; it's a power limitation of a less powerful amplifier compared to a more powerful one. I don't know if you realize the nonsense of questioning it.
It's not a question of IF, it's just a question of WHEN a less powerful amplifier will start clipping compared to a more powerful one. No additional measurements are needed beyond those already present; if an amplifier has half the power, it will clip sooner.
Now what's your question? Does the user reach this value or not? Ask him, he says yes, and I have no reason to doubt it. Despite the "hearing damage threshold," sometimes I really want to blast music with dynamic peaks above 100 dB, and I have no desire for my amplifier to work at its limit or cut those peaks, which is why I use a buffer that has much, much more power than I usually need.
I also own the Fosi V3 mono, I use it as the power amp for my home theater center channel and it does a fantastic job, but for the towers I have a Hypex 500watt power amp on 4ohm.

I’d like to think you didn’t intend to be rude.

The question? What SPL is the typical listening level and how much “headroom” (in dB) is needed?

If you’re looking to be able to accommodate peaks of 100 dB (or slightly more) the Fosi would be just fine. A more powerful amplifier would be fine too, but the extra power would be unused.

 

[rgpit]

OMG! Folks are comparing a great little amp to a Hegel amp which is 25 times it's price! Okay, the Hegel is better. That doesn't take away the excellent value of the Fosi. ... Lord, please make it stop!

 

[kyuu]

View attachment 552631
However, at deep bass levels, the power, as is logical to assume, drops significantly

It's weird that you said this after posting a graph that demonstrates quite clearly that you're incorrect. The orange line shows power versus distortion at 20Hz, and it quite clearly gets over 200W before hitting 1% distortion (-40dB THD+N on the graph).

Music is not a continuous tone.

No it's not, and in general it is significantly less demanding than a continuous tone. A continuous tone is a significant stress test for an amp compared to actual content. If the amp can handle a continuous tone at 20Hz at 200+W, it should be to do that with a transient from actual content as well.

 

[mike70]

A continuous tone is a significant stress test for an amp

Exactly, and many people have a misunderstanding about this. They think music is harder than play a perfect sinusoid.

 

[Talisman]

No it's not, and in general it is significantly less demanding than a continuous tone. A continuous tone is a significant stress test for an amp compared to actual content. If the amp can handle a continuous tone at 20Hz at 200+W, it should be to do that with a transient from actual content as well.

Of course it's much easier, but that's not the point. The point is that it makes no sense to talk about "just 3dB more" as if music were being listened to with a single tone that increases by 3dB. Music has peaks of power, especially when recorded with high dynamics, and the point is that even when listening at medium levels, well-recorded music can reach instantaneous peaks of truly remarkable power that draw on the power reserve. And a Power amplifier that handles an average load of 20 watts very well can still cut them.

 

[Talisman]

I’d like to think you didn’t intend to be rude.

The question? What SPL is the typical listening level and how much “headroom” (in dB) is needed?

If you’re looking to be able to accommodate peaks of 100 dB (or slightly more) the Fosi would be just fine. A more powerful amplifier would be fine too, but the extra power would be unused.

Then do it, and let it melt in the process.
As I've already said, pushing an amplifier to the limit of its capabilities, especially if it doesn't have top-notch thermal management, is just a prelude to damage.
The audio source will be perfect and indistinguishable from a more powerful amplifier, within its power limits, WITHIN ITS POWER LIMITS. Denying this simple point makes no sense.

OMG! Folks are comparing a great little amp to a Hegel amp which is 25 times it's price! Okay, the Hegel is better. That doesn't take away the excellent value of the Fosi. ... Lord, please make it stop!

I totally agree with you, that's why I have a pair, and it can do 99% of what a hegel h390 does, at a ridiculous fraction of that price, it's exceptional, so why ask and demand only that 1% that objectively it can't do?

 

[mike70]

Denying this simple point makes no sense.

We aren't denying, we're saying we don't have a proof about it. It's only subjective talk, what you hear without control can or can't be true. Please, give the data about distances and SPL in the listening position and then we see.

This forum is all about scientific data to do that kind of claim. Opinion is opinion.

 

[Talisman]

We aren't denying, we're saying we don't have a proof about it. It's only subjective talk, what you hear without control can or can't be true. Please, give the data about distances and SPL in the listening position and then we see.

This forum is all about scientific data to do that kind of claim. Opinion is opinion.

I listen at 5m, in a large room, 85bd speakers, average listening 83 sol with peaks of 20db

 

[mike70]

If you need 83 dB at 5 meters with 4 ohms and 85 dB sensitivity speakers, the average power is... 4 watts at 4 ohms (Fosi have 200).

With 15 dB headroom (98 dB SPL, entering ear damage zone), you will need... 126 watts in 4 ohms. Fosi have 200 watts, that means 17 dB of headroom and 100 dB of SPL.

If you're talking about the vast majority of recordings , DR above 15 dB is extremely rare. I mean , the theory of low power isn't very strong.

 

[Karls_speaker_works]

Perhaps this is a good time to propose a practical application question about the Fosi V3 Mono amp.

I want to put one in the basement in place of a large homemade stereo amp that's currently (successfully) powering a Sonic Immersion VT200 tactile transducer.

Specs:

• Force / Watt: 2.2 lbs./Watt (9.7 Newtons/Watt)
• Continuous Power Handling: 100 Watts
• Max Program Power: 250 Watts
• Overload Protection: PPTC self reset fuse
• Impedance: 4 ohms
• Frequency Response: 20Hz – 800Hz

I feel like the Fosi is an ideal choice for powering the VT200, but after reading this extremely long thread, I am concerned about it's reliability/thermal performance. The basement is 65F +/- 10deg year-round.

For the record, I am using the Fosi V3 Stereo (48V) to power Monoprice 8" angled in-ceiling Atmos speakers (8 ohm.)

 

[Ande3200]

@Ande3200 Without any measurements to back up a claim all we have is your opinion. Can you provide any measurements (e.g., SPL at listening position, voltage at speakers, etc.)?

Doubtless, the Hegel is more powerful amp than the Fosi.

• The Hegel H390 amps are spec'd at 250W/channel into 8 ohms (at 1% THD using a 1 kHz input). Hegel does not provides power ratings into other loads (such as the 4 ohms that the Arendal speakers are rated at). It would not be unreasonable to think that the Hegel might deliver around 500W into 4 ohms at 1% THD.
• Amir measured the Fosi V3 Mono as delivering about 240W into 4 ohms at 1% THD.

The Hegel ought to have about twice the power of the Fosi V3 Mono. But twice the power is only +3 dB.

The Arendal 1528 monitor 8 speakers are just 85 dB @1W @1m sensitive so that it may take a fair amount of power to achieve the desired SPL in a largish room. Even so, both the Fosi and the Hegel can drive your speakers to >100dB SPL. That volume can cause hearing damage.

Is that extra power being used at your typical listening volume? I suspect not.

By all means enjoy your Hegel amp. But don't be surprised when others reject your claims about the Fosi being underpowered.

There is measurements on plenty of sites on Hegel h390. Hifinews ex, the Fosi measurements is peak power which is short term.

Those 240 watts into 4 ohms is peak power and they can’t put out that consistantly, its closer to 170-180 watt rms into 4 ohms.

Hegel h390 puts out 490 watts into 4 ohms rms at 1% thd. 544 watts peak.

And we have not seen Fosi measurements of what they can handle longterm.

It sure was not enough for me. So stop trying to tell me Fosi v3 monos is enough.

V3 monos is incrediable for the price, but its not even close in the same league as Hegel h390. And i would never be satisfied with v3 monos longterm.


Its not strange people avoid those forums because you only care for measurements, but in the end of day you dont listen to graphs you listen to music.

 

[Dave TR3A]

There is measurements on plenty of sites on Hegel h390. Hifinews ex, the Fosi measurements is peak power which is short term.

Those 240 watts into 4 ohms is peak power and they can’t put out that consistantly, its closer to 170-180 watt rms into 4 ohms.

Hegel h390 puts out 490 watts into 4 ohms rms at 1% thd. 544 watts peak.

And we have not seen Fosi measurements of what they can handle longterm.

It sure was not enough for me. So stop trying to tell me Fosi v3 monos is enough.

V3 monos is incrediable for the price, but its not even close in the same league as Hegel h390. And i would never be satisfied with v3 monos longterm.

You are, of course, free to prefer whatever you wish.

No one has argued that the Hegel isn’t a fine amplifier. It is. We have, however, pointed out that your claim about the Fosi being underpowered is not supported by the facts.

You haven’t proven any of your claims. But you have strongly objected to those who have shown that your claim about the Fosi is overblown.

Its not strange people avoid those forums because you only care for measurements, but in the end of day you dont listen to graphs you listen to music.

Your subjective and unsubstantiated impressions don’t override science. You shouldn’t expect others to blindly accept your claims.

Perhaps this forum isn’t a good match for you.

 

[Ande3200]

You’ve proven none of your claims.

You are, of course, free to ignore what math, science, and engineering tell us. But don’t expect others to blindly accept your claims.



Perhaps this forum isn’t a good match for you.

Read the measurements then Instead on hifinews instead of rambling.

Hegel h390 has superior power measurements specs to Fosi audio v3 mono.

You just choise to ignore it.

Or is you part of that sect that only reads asr measurements.

I dont mind measurements and in fact thats what i look up first when buying a product but you still have to try it at home and that will still be the deciding factor. Just because a product measure well dosent mean you will like the product.

You can’t just blindly just look at measurements and not listen to the products and thats the main proplem with this forum. We dont listen to graphs.

Fosi v3 monos is not enough for me what part of that dont you understand. More powerful amps excist for us that needs it and want it.

A pair of v3 monos is not going to cut it for everyone. Maybe its enough for you but sure is not for me. Its not a giant killer.

 

[Talisman]

You’ve proven none of your claims.

You are, of course, free to ignore what math, science, and engineering tell us. But don’t expect others to blindly accept your claims.



Perhaps this forum isn’t a good match for you.

Instead, I think it's suitable for me, having been on this forum for a while and having written extensively, and I agree with him.
Unfortunately, sometimes some users don't understand the difference between hearing differences in two transparent DACs (which is unlikely) and hearing a lack of power in an amplifier at its limits, but this isn't the site's fault, it's the fault of those who take a positive attitude and turn it into dogma.

 

[Talisman]

You can’t just blindly just look at measurements and not listen to the products and thats the main proplem with this forum. We dont listen to graphs.

Please don't digress beyond what each individual writes, we are not a collective mind and we all like music and listen to it at its best.

Its not a giant killer.

It is.
A product that at this price has these performances in terms of audio quality and power and can cover 90% of what an amplifier 10 times the price can do is exceptional and is by definition a giant killer. But that doesn't mean it doesn't have some limitations that might be too much for some, and that's what I wrote too.