Fosi Audio V3 Mono Amplifier Review

[Ze Frog]

Maybe future measurements with the shared 10A power supply will be available

I would doubt any difference really. I am going to buy a pair, and run 2 of Fosi's 48v 5amp supplies, mainly because a monoblock in my eyes should have it's own power source. Seeing the power it makes with 48v 5amp I would say there really is no need to worry at all, the 5amp was enough for Amir to get beyond power specified as is.

 

[antcollinet]

Please forgive the potentially elementary question. I've searched the thread (I'm on page 9 so far), but haven't come across what I'm after.

Could I use one of these to power a passive sub, using the SE sub out of a Sonos Amp and rely on the crossover settings and level control within the Sonos App, or do I still need something else to make this work properly? I'm looking to power an outdoor sub on our patio at lower, respectful volumes. I tried using one channel of my Buckeye NC502MP, but I believe the 25dB gain setting is causing fairly anemic output at lower volumes. The 32dB setting and auto-off on this caught my eye and is the reason for asking. I just plugged in a Fosi M03 and while it's working better than the Buckeye, there's no auto-off and it's not as aesthetically pleasing as this upcoming model. Thanks in advance.

Yes you can - but it is not the lower gain of the 502 causing any anemia. Lowering the gain is exactly the same as lowering the volume. in other words you can compensate the lower gain by turning up the volume.

So if the sub is sounding anaemic at the lower volume, it is probably the volume you have selected that is causing the issue. Bear in mind also that a sub is going to struggle to generate impact much more outdoors than it is in a room.

 

[Rottmannash]

I bought a 3e stereo amp board for 134 dollars shipped. Its 6 amp 48 volt power supply was another $40.00. For $174.00 I got 99% of what two of these give me (Not to mention that the 3e has 2 db better SINAD) . If you want to spend $106.00 more to get a bit less than be my guest.

I suppose you're going to lay the board and power supply on your desk for all to see? Factor in the cost of casework, binding posts, etc and your labor and then give us a total.

 

[Rottmannash]

Well, there may be people how who know better about that device than reading this thread only.

You really seem to have it in for this little monobloc amp.

 

[Rottmannash]

I have so much kickbacks I don't know what I'm going to do with it all! /s

...that's where you're getting the $ to donate to Erin's legal fund!

 

[Rottmannash]

I see, a poster that is now defined as a dick that needs to be stopped... so it does indeed seem to be Cancel culture.

• Cancel culture: "a cultural phenomenon in which some who are deemed to have acted or spoken in an unacceptable manner are ostracized, boycotted, or shunned."
• Shun: "often implies an avoiding as a matter of habitual practice or policy and may imply repugnance or abhorrence."

So, once again: "Be conservative in what you do, be liberal in what you accept from others."

Perhaps you haven't read the entire thread-this member has consistently and persistently disparaged the amp, its manufacturer and anyone who may purchase it. It's getting a bit tired so forgive us for being "over him".

 

[wyup]

You can calculate input sensitivity with
sqrt(Rated power [W] * load impedance [Ω]) * 10 ^ (gain [dB] * -1 / 20)

So for 240W at 4Ω, XLR input you need sqrt(240*4)*10^(-20.5/20)=2.93Vrms

With RCA in, it's sqrt(240*4)*10^(-25.5/20)=1.64Vrms

Why is gain 5db higher for RCA than XLR?
Isn't gain constant?

I wish gain was selectable like in Purifi buffers or headphone amplifiers in order to use digital volume from dacs with minimal attenuation and highest SNR. This would be a way to avoid preamplifiers.

 

[antcollinet]

Why is gain 5db higher for RCA than XLR?
Isn't gain constant?

RCA signals typically have half the voltage of XLR (single ended rather than two differential signals)
So that is actually 6dB less.

 

[wyup]

RCA signals typically have half the voltage of XLR (single ended rather than two differential signals)
So that is actually 6dB less.

But amplifier gain is independent from source voltage, or isn't It?

 

[Hunter Mike]

I would doubt any difference really. I am going to buy a pair, and run 2 of Fosi's 48v 5amp supplies, mainly because a monoblock in my eyes should have it's own power source. Seeing the power it makes with 48v 5amp I would say there really is no need to worry at all, the 5amp was enough for Amir to get beyond power specified as is.

Fosi claims the 10a power supply performs the same as two 5a supplies.

 

[antcollinet]

But amplifier gain is independent from source voltage, or isn't It?

Amp gain multiplies whatever the input voltage is. Input 2V with 20dB (x10) gain, and you get 20V out.

Input 4V with 20dB gain and you get 40V out.

So with the RCA input you have the option of switching the gain to a higher level so you can achieve the same output power with the lower input voltage.

 

[staticV3]

Why is gain 5db higher for RCA than XLR?

Because Fosi made it so:

 

[Guddu]

Fosi claims the 10a power supply performs the same as two 5a supplies.

Yes, under idle conditions.
Just one simple consideration that if same psu is powering up 2 amplifiers then one can consume more power in certain conditions, presenting some limitations for other amplifier. It may not be an issue if total output from both amplifiers is under the limit of psu.
It’s hypothetical, and most people won’t run into such situations.
I personally would do just do 1 psu for 2 amplifiers considering my playing conditions won’t need that much power per amplifier.

 

[wyup]

Because Fosi made it so:
View attachment 362083 View attachment 362084

Ah, that's why it performs 6db poorer in SINAD on RCA: They are different circuits with different gain. ¿Topology is balanced/differential or single-ended? I ask so because Purifi and Hypex amps are differential, RCA and XLR inputs are the same with the same gain, it only changes the input impedance that it sees.

 

[AudioTodd]

The great engineers behind these products have completely changed the meaning of “ChiFi” and this wonderful site has spread the word and, I believe, really made it possible for these talented people to thrive!

Both have been a great boon to our beloved hobby!

 

[gwing]

Fosi claims the 10a power supply performs the same as two 5a supplies.

And don't forget that the single 10A supply also leaves you the opportunity to waste more money further improve your system later on with a second 10A supply added whereas two 5A supplies don't have that flexibility.

 

[billymac]

Yes you can - but it is not the lower gain of the 502 causing any anemia. Lowering the gain is exactly the same as lowering the volume. in other words you can compensate the lower gain by turning up the volume.

So if the sub is sounding anaemic at the lower volume, it is probably the volume you have selected that is causing the issue. Bear in mind also that a sub is going to struggle to generate impact much more outdoors than it is in a room.

Thank you. Totally get it. I was trying to be concise, but obviously at the risk of being unclear. It was more of a level-matching issue with the 502. The sub performed great when I turned it up, but I had to turn it up to a point where the L&R were too loud given the environment.

 

[Zuiko]

How will you split the source signal though? Multiple Y splitters?

Each mono amp gets one cable, either the left or the right.
No need for splitters.

 

[antcollinet]

Thank you. Totally get it. I was trying to be concise, but obviously at the risk of being unclear. It was more of a level-matching issue with the 502. The sub performed great when I turned it up, but I had to turn it up to a point where the L&R were too loud given the environment.

Ah - understood - so then I assume you have set the SONOS sub settings to maximum output level?

If so then an alternative to a new amp with higher gain would be to put a simple preamp in front of the 502. Something like:

preamp

 

[PlasticDoc]

Perhaps you haven't read the entire thread-this member has consistently and persistently disparaged the amp, its manufacturer and anyone who may purchase it. It's getting a bit tired so forgive us for being "over him".

The other characteristic of the Cancel culture is that its brave members need to act in packs. You just can't resist, can you?

In your eagerness to bite you just missed this post: https://www.audiosciencereview.com/...o-v3-mono-amplifier-review.53474/post-1933746

Go and see that post. You don't even need to apologize.

So, once again: "Be conservative in what you do, be liberal in what you accept from others."