Fosi Audio V3 Mono Amplifier Review

[jmdesignz2]

Is it correct that the ASR review was done with the 48v/5a supply?

Has it been measured with the 48v/10a supply?

 

[Power Pop 23]

Is it correct that the ASR review was done with the 48v/5a supply?\

Yes

Has it been measured with the 48v/10a supply?

I am not aware of any measurement by ASR.

 

[jEDGEc0m]

It seemed like there may have been a revision to the Fosi V3 Mono at some point since the model measured by Amir - fixing the polarity issue of early models, reducing the RCA gain settings, and maybe some PFFB improvements?

I'd be fairly interested in a remeasure of an independently obtained one or pair, with a variety of power supplies. That said, I've just ordered some anyway with the 2 separate 48v 5A power supplies. Incidentally, I plan to use it with 32v 5A power supplies as I suspect I won't need the limits of power - mostly getting them for balanced and PFFB. the Fosi V3 stereo heat of 32v vs 48v seemed substantial to me, and at the levels I was using it, I heard no sound difference.

As an aside, it seems frequently "XLR" is the term used, when really the point is "balanced". I am pleased these have combo XLR/TRS jacks. TRS jacks are effectively equal to XLR.

 

[totti1965]

I appreciate that, but everything I'm reading about the speakers suggests they like Class A/B amps, and sound better with them.

Keep dreaming!

 

[Ordin Aryguy]

I appreciate that, but everything I'm reading about the speakers suggests they like Class A/B amps, and sound better with them.

There are myths and untruths that have existed around Magnepans forever. "Lots of Power", "Lots of Current", etc.

Look at the impedance curve for any Magnepan, and they are all just about the same, from the LRS through the 3.7's, and you'll see it's nearly flat and something in the range of 4-ish Ohms. They are not that difficult to drive from a modern amplifier's perspective. Fifty years ago, with far lesser performing electronics than are available today, amplifiers did have a little more difficulty with that 4 Ohm impedance versus most speaker's 8 Ohm impedance. Amplifiers with tubes as their final stage faired even worse, as the tubes capable of high current were (and still are) not cheap and not plentiful.

No one will talk you out of the Class A/B amp if you've made up your mind that's what you want. Just don't fall into the old, persistent myths trap.

 

[antcollinet]

I appreciate that, but everything I'm reading about the speakers suggests they like Class A/B amps, and sound better with them.

In all those things you are reading - what objective evidence is presented for the claims made.

Measurements? Fully controlled blind testing?

Or is it just the normal talking heads spouting "opinions" based only on sighted listening?


This is what tells you that it will drive your speakers (and pretty much any other) without issue:

 

[JohnnyNG]

Is it correct that the ASR review was done with the 48v/5a supply?

Has it been measured with the 48v/10a supply?

Looks like this one is with the 10a:

archimago.blogspot.com/2024/08/part-ii-fosi-audio-v3-mono-amp-class-d.html

 

[jmdesignz2]

In all those things you are reading - what objective evidence is presented for the claims made.

Measurements? Fully controlled blind testing?

Or is it just the normal talking heads spouting "opinions" based only on sighted listening?


This is what tells you that it will drive your speakers (and pretty much any other) without issue:

View attachment 474885

Since that picture is from the test with a 48v/5a SMPS, what would it look like if it was under a 48v/10a?

 

[antcollinet]

Since that picture is from the test with a 48v/5a SMPS, what would it look like if it was under a 48v/10a?

Not much different. Even Fosi has said as much in this thread.

 

[CraigVMN]

There are myths and untruths that have existed around Magnepans forever. "Lots of Power", "Lots of Current", etc.

Look at the impedance curve for any Magnepan, and they are all just about the same, from the LRS through the 3.7's, and you'll see it's nearly flat and something in the range of 4-ish Ohms. They are not that difficult to drive from a modern amplifier's perspective. Fifty years ago, with far lesser performing electronics than are available today, amplifiers did have a little more difficulty with that 4 Ohm impedance versus most speaker's 8 Ohm impedance. Amplifiers with tubes as their final stage faired even worse, as the tubes capable of high current were (and still are) not cheap and not plentiful.

No one will talk you out of the Class A/B amp if you've made up your mind that's what you want. Just don't fall into the old, persistent myths trap.

That's just it, I haven't made up my mind, indeed I came here looking for exactly the answers I got to let me know I don't need to buy anything else.

 

[CraigVMN]

In all those things you are reading - what objective evidence is presented for the claims made.

Measurements? Fully controlled blind testing?

Or is it just the normal talking heads spouting "opinions" based only on sighted listening?


This is what tells you that it will drive your speakers (and pretty much any other) without issue:

View attachment 474885

I absolutely believe, like in other cases of "lore", somethings are retold so often they become truth. But as you point out, measurements don't lie.

 

[totti1965]

Since that picture is from the test with a 48v/5a SMPS, what would it look like if it was under a 48v/10a?

Power supplies: I remember that I read something like 2 x 48 V / 10 A = 196 Watt @ 1 % Distotion and
2 x 48 V / 5 A = 192 Watt @ 1 % Distortion
So, no difference and 2 x 48 V / 5 A are absolutely perfect!

And: Absolutely no difference in power between 1 x 48 V / 10 A with two outputs and 2 x 48 V / 5 A
I would prefer the last, because: why Monoblocks if you have just one power supply?

32 V / 5 A is a different thing: Roughly 50 % (or 3 dB) less power output (@amirm‘s measurement of the Fosi V3 stereo Version) than with 48 V / 5 A.
That’s maybe because it is possible that the 48 V / 5 A Fosi power supply is a bit more capable than rated in the specs.

 

[telemike]

You can run each amp with its own 5A supply or use a splitter cable with a single 10A supply for both

 

[antcollinet]

You can run each amp with its own 5A supply or use a splitter cable with a single 10A supply for both

You can - but unless things have changed with a single supply you also need a filter to stop interference between the two amps. So you still have two boxes, and therefore no advantage (IMO)

 

[norman bates]

Do they run cooler on the 32v supply ?

 

[rsqt]

Yes.

 

[telemike]

You can - but unless things have changed with a single supply you also need a filter to stop interference between the two amps. So you still have two boxes, and therefore no advantage (IMO)

Yes, I forgot to mention the filter

 

[CraigVMN]

What's true of the Magnepan is true of any speaker/amp combination - The amplifier has to be up to the task of giving what the transducer/speaker/load demands in terms of current/voltage/wattage. Either the amp can, or it can not. Everything I've read about the speaker & Fosi amp suggests the amp is perfectly capable.

 

[CraigVMN]

The pair of amps I have each have their own 48v 5amp power supply. Although each having their own 48v 10amp PS would not appreciably increase the wattage, would it allow for the amp to draw more energy when needed?

 

[Nopiano]

The pair of amps I have each have their own 48v 5amp power supply. Although each having their own 48v 10amp PS would not appreciably increase the wattage, would it allow for the amp to draw more energy when needed?

It would indeed enable more current to be demanded by the amp, though my recollection is that it’s very unlikely in practice that would arise with this combination. Possibly on the test bench, however.

Someone might be able to do the maths with the specs to hand, but that’s beyond me I’m afraid!