Fosi Audio V3 Mono Amplifier Review

[antcollinet]

Hight current has to be handled by the power transistors (for output) no matter, what class the amps have. It is this matter and its corresponding cooling, which i.e. limits the output of the amp.

Correct - but my comment regarding the difference for class D, was referring to phase shift - not current.

As pointed out in the quote above - a 45 to 90 degree phase shift will significantly increase the dissipation in the output transistors of a class A or Class AB amp even if the current remains the same. This does not happen in class D amps.

 

[burkm]

Correct - but my comment regarding the difference for class D, was referring to phase shift - not current.

As pointed out in the quote above - a 45 to 90 degree phase shift will significantly increase the dissipation in the output transistors of a class A or Class AB amp even if the current remains the same. This does not happen in class D amps.

...But the power transistors, no matter what they are, still have to handle the resulting current even in class D amps. This (plus the power supply and transistor cooling, even when only switched) limit their power output, because current handling, no matter what is responsible for it, must still be handled by the amps power transistors.

 

[antcollinet]

...But the power transistors, no matter what they are, still have to handle the resulting current even in class D amps. This (plus the power supply and transistor cooling, even when only switched) limit their power output, because current handling, no matter what is responsible for it, must still be handled by the amps power transistors.

Yes, As I said:

Correct

But, amps (like class A and AB) which operate their output transistors in the linear region also have to cope with the the significant increase in power losses resulting from phase shift - regardless of what the current is.

 

[mike70]

class A / AB are the valves of 21th century

 

[jmc06]

Does this reflect the dynamic music index of the power amplifier? Is this good or bad? What I mean is in comparison with ordinary power amplifiers

 

[q2klepto]

Here are my comparisons between the Fosi V3 Monoblocks (with 10a splitter) going into my KEF Reference One Metas, in my room (13.5x20x8.5 Treated)

Mic position unchanged, Denon X8500HA AVR (-10db) and RCA pre-outs, EQ disabled, Fosi (voltage gain +31db) vs Monolith 3x200wpc (voltage gain +28db). Sweeps was 55hz to 20khz

Frequency Response

Difference

Monolith Distortion

Fosi V3 Distortion

For about 1/5th of the price when i factor in Shipping/Duties/Taxes - the Fosi V3 come out *WAY* ahead. I may grab 2 more 10a power supplies not sure if its worth it.

 

[staticV3]

Does this reflect the dynamic music index of the power amplifier? Is this good or bad? What I mean is in comparison with ordinary power amplifiers

See here: https://www.audiosciencereview.com/forum/index.php?threads/is-sinad-around-5-15-khz-relevant.55839

 

[antcollinet]

Does this reflect the dynamic music index

what is that?

 

[jEDGEc0m]

The 600W industrial power supply has arrived. The power from the socket is 250W European, and at 3.9 Ohm Vrms0 30V, which corresponds to a power of around 230W.
The conclusion is that this TPA3255 delivers what its manufacturer promises.
I personally doubt the desktop power supplies. From around 160W input power, the fan on the industrial power supply starts to turn on and makes a lot of noise. It is a Mean Well.View attachment 389438

Thanks for your info @LSPhil regarding power supplies.

Hey, just a little update.

No issues with my Fosi V3 Mono.

Anecdotally, seems running them vertical might help heat dissipation, but in the interests of longevity, and upcoming summer, I got a fan that blows at the vertical pair from a distance - the case then seems to stay about room temp feeling.

I am now just turning them on/off with switch on the amps (Rather than pulling plug from mains).

I (needlessly) decided I wanted more 48V power, to run the 2 x Fosi V3 (the normal stereo version) that are each powering one sub each (up from the 32V bricks they came with)
So wanted 2x more power supplies, to supplement the ones that came with the V3 mono, which look like this, and might actually be a GaN model

I got Mean Well LRS-200N2-48

rated 211W and 4.4A. no fan - passively cooled. Source is 240V mains.
But is capable of short term 200% current. I'm pretty sure I'm not pushing the amps anywhere near limits, so this should be ideal, and able to handle peaks to the limits of the amp.

also - specs of LRS-200N2-48 derating for ambient temp. i.e. I don't expect to ever be derating.

Thanks to posts from others, from memory, notably @Roland68 who I've seen a lot of power related commentary about.

I was going to set their voltage a bit below 48v. Set them to 46V. Then with same voltmeter (basic old cheap digital thing), checked the bricks that came with V3 mono - they were reading about 45-46V anyway.

The Mean well were very well priced and seem quality. Quick delivery (from mouser - came from Texas).

 

[nn_in]

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!

In future a if a "one box" with two V3 mono blocks and power supply would be a compact solution.

 

[Roland68]

In future a if a "one box" with two V3 mono blocks and power supply would be a compact solution.

That's exactly what 3E Audio has released with the A7, only with an external power supply.
A case with an integrated power supply is significantly larger and more expensive. There's also the problem of interference from the power supply into the amplifier. Cooling is also more difficult.
Another factor contributing to higher costs are the additional tests required for the EU and US, which are additionally required with a built-in power supply and are both complex and expensive.
These are already included with purchased external power supplies.

Addendum:
3E Audio just announced elsewhere in the forum that they plan to produce 2/4/6/8-channel amplifiers based on the TPA3255.

 

[ChrLen]

I just ordered a pair from Amazon and one of the amplifiers arrived dead on arrival. Is this a common issue? The replacement is coming tomorrow.

 

[Roland68]

I just ordered a pair from Amazon and one of the amplifiers arrived dead on arrival. Is this a common issue? The replacement is coming tomorrow.

A DOA can happen even with the best device and the best manufacturer.
Just think of the transport route as quality control.

 

[MajorTom]

Hey, I have niw the v3 stereo with speakers focal profile 918 :
Réponse en fréquence (+/- 3dB) : 40 Hz à 30,5 kHz
Réponse à -6 dB : 36 kHz
Sensibilité (2,83 V/1 m) : 90 dB
Impédance nominale (EN 60065) 8 ohms
Impédance minimale 3,2 ohms à 110 Hz
Fréquences coupure filtre : 180 Hz / 2600 Hz

It is obvious that the v3 stereo shows his limit while i push the volume up. Less details.
Should these mono blocks would be ok? I read about the hypex ncore nc252mp which gives a lot more of power.

Thx

 

[Roland68]

Hey, I have niw the v3 stereo with speakers focal profile 918 :
Réponse en fréquence (+/- 3dB) : 40 Hz à 30,5 kHz
Réponse à -6 dB : 36 kHz
Sensibilité (2,83 V/1 m) : 90 dB
Impédance nominale (EN 60065) 8 ohms
Impédance minimale 3,2 ohms à 110 Hz
Fréquences coupure filtre : 180 Hz / 2600 Hz

It is obvious that the v3 stereo shows his limit while i push the volume up. Less details.
Should these mono blocks would be ok? I read about the hypex ncore nc252mp which gives a lot more of power.

Thx

Which power supply do you use?

 

[Roland68]

Hey, I have niw the v3 stereo with speakers focal profile 918 :
Réponse en fréquence (+/- 3dB) : 40 Hz à 30,5 kHz
Réponse à -6 dB : 36 kHz
Sensibilité (2,83 V/1 m) : 90 dB
Impédance nominale (EN 60065) 8 ohms
Impédance minimale 3,2 ohms à 110 Hz
Fréquences coupure filtre : 180 Hz / 2600 Hz

It is obvious that the v3 stereo shows his limit while i push the volume up. Less details.
Should these mono blocks would be ok? I read about the hypex ncore nc252mp which gives a lot more of power.

Thx

I just saw that you're running the V3 at 48 volts.
Then you don't need to look at other TPA3255 amplifiers, whether WiiM, 3E Audio, etc.
Double the wattage is just a doubling of the volume, so I'd look for at least 180-200 watts, or more.
The NC252MP are also only a few watts more powerful than, for example, 3E Audio A7 or TPA3255 monoblocks.

The Buckeye Hypex NC502MP 2-channel 500W costs €750.00 and should deliver over 200 watts into 8 ohms. That should be plenty of headroom.

As a cheap alternative, you could use two bridged SMSL A300s, which are available for €160-200 each.
These amplifiers can deliver 220 watts into 8 ohms and 400 watts into 4 ohms in bridged BTL mode; both values were measured by Amir in his test.

A completely different approach would be to purchase a larger subwoofer (or two smaller ones) and a DSP to set up the appropriate high-pass and low-pass filters. The ability to equalize and correct the room would be an added bonus.
The V3 should be perfectly adequate for this and would also gain some headroom.
However, you could also use a larger WiiM or WiiM Amp Pro/Ultra for this.

 

[ChrLen]

I received a replacement from Amazon and the amp works fine. I am using this with an WiiM Ultra and a set of Tannoy bookshelf speakers on my desk. I judge amps by their ability to stretch the soundstage vertically, horizontal imaging is easy. These amps are a noticeable improvement over my Adcom 525 I was using previously. They sound much better than they should for $300 shipped. I am very impressed.

They do have an annoying pop when coming off of power save mode. I also wish the power supplies were integrated into the chassis.

 

[Jost Buergi]

I got my amp yesterday and am a bit disappointed because the RCA gain switch on the back still states 31/25 dB. I liked that Fosi went for 25/19 dB instead and when they wrote "We changed the output a little down to avoid Problems, the RCA input has been lowered by 6dB" almost 4 months ago.

Purchase was made from Fosi's german ebay shop. Any ideas when their local warehouse will sell current production units, or which shops do?

 

[staticV3]

I got my amp yesterday and am a bit disappointed because the RCA gain switch on the back still states 31/25 dB. I liked that Fosi went for 25/19 dB instead and when they wrote "We changed the output a little down to avoid Problems, the RCA input has been lowered by 6dB" almost 4 months ago.

Purchase was made from Fosi's german ebay shop. Any ideas when their local warehouse will sell current production units, or which shops do?

It's possible that your V3 Mono PCBA is revised with reduced gain, but installed in an old housing with the wrong prints.

You can use a basic multimeter to measure gain yourself, irrespective of what the numbers on the back say.

 

[Roland68]

I got my amp yesterday and am a bit disappointed because the RCA gain switch on the back still states 31/25 dB. I liked that Fosi went for 25/19 dB instead and when they wrote "We changed the output a little down to avoid Problems, the RCA input has been lowered by 6dB" almost 4 months ago.

Purchase was made from Fosi's german ebay shop. Any ideas when their local warehouse will sell current production units, or which shops do?

At the 25 dB setting, there's no difference anyway; both versions behave the same.
I'd contact Fosi about this; you might get a discount if you keep them.