Fosi Audio V3 Mono Amplifier Review

[somebodyelse]

No, that's actually not normal.

That doesn't mean it's a problem with the amps though - see a couple of posts above yours. If the speakers are high sensitivity then it could be normal for those speakers.

So would topping LA90's also have this slight hiss when putting my ear at the tweeter? Because its supposedly the cleanest signal amp on asr right? Or do all power amps have some sort of audible hiss to some extent

The LA90 and B100 both have significantly lower noise as you'll see if you compare the signal to noise ratio. They also have low gain settings which makes them especially good for very sensitive speakers. On the other hand they have lower power output than the V3, so if you need the higher power they may not be an option. Whether their lower self-noise will translate to lower noise at your tweeters depends on how quiet the source is. Make sure you read the review threads carefully, especially for the B100, as there are quite a lot of failure reports and reports of amps shutting down when driving fairly ordinary speakers. Also note that the B100 balanced input needs both hot and cold driven - if used with an 'impedance balanced' source or RCA-XLR cable only one half of the bridge will be driven (see pma's test). I don't know whether the same is true with the LA90.

 

[girtab]

they have lower power output than the V3

thats why I went with the fosis instead of topping la90s. I need at least 200WPC for my 87db floorstanders. Even 200WPC is pretty low for me atm. I probably need to look at hypex stuff but those are outrageously expensive

 

[Audionaut]

That doesn't mean it's a problem with the amps though - see a couple of posts above yours. If the speakers are high sensitivity then it could be normal for those speakers.

No, based on the FOSI measurements from Amir, the amplifiers should remain quiet even when connected to speakers with very high efficiency.

Distortion is still at provably inaudible -115 dB. I like that the gain is nominal 25 which is my new recommendation for amplifiers.
Noise performance is excellent and at full power, darn near approaches state of the art

What you can try @girtab is seeing how it behaves when the preamplifier is connected but not turned on.

 

[girtab]

What you can try @girtab is seeing how it behaves when the preamplifier is connected but not turned on

Will try when I get home

PS the preamp doesn’t have an on/off switch it just turns on when connected to usb, should I just leave the laptop off or preamp unplugged?

 

[burkm]

You positioned your ear at tweeter ? What does that tell you: very low hiss (if audible at all at the listening position...) and a gain structure, which might be sub-optimal...

 

[burkm]

This sounds to me more like hiss from a source or along the way...

 

[antcollinet]

but when putting my ear at the tweeter I hear hiss. Is that normal

Absolutely normal (depending - as @staticV3 points out on the specifics of your system). But unless you listen to the music with your ear at the tweeter it is not much of a problem. Even noise audible from the listening position isn't generally an issue - since as soon as the music is playing, it masks the noise.

 

[Audionaut]

I need at least 200WPC for my 87db floorstanders.

PS the preamp doesn’t have an on/off switch it just turns on when connected to usb, should I just leave the laptop off or preamp unplugged?

With 87 dB speakers the Fosi Audio V3 Mono should be essentially silent. What you are hearing is much more likely caused by floating/open inputs, USB or interface noise, or grounding noise coming from the Behringer UMC22 and laptop setup. Try testing the amps with a proper line source that can actually be switched off completely, or with the inputs properly terminated instead of left open.

 

[Audionaut]

PS
I have just for fun two TPA3255 amplifiers, the O-Noorus D1 and the Douk A5. Both are probably slightly inferior to the Fosi V3 (though we don’t know for sure about the O-Noorus).
Both are powered by a 48V 10A power supply, and when driven to full power through high-efficiency speakers with PA horns, I can’t hear a thing from either of them.

Slightly upgraded cooling solution

 

[somebodyelse]

Even noise audible from the listening position isn't generally an issue - since as soon as the music is playing, it masks the noise.

This may be one of the things that makes it a problem for some people but not others - I find it irritating when I become aware of the noise in a quiet passage, a track transition, or when the music stops entirely. Or when auto-muting cuts in, drawing attention to a noise level I might not have been conscious of because of a step change. Other people may be aware of it but not find it irritating, or just not be aware of it at all, based on the times I've had to point it out. It's similar to gap-free transitions in that respect.

 

[JohnnyNG]

My v3 Monos came in (after returning a broken one). They sound ok but when putting my ear at the tweeter I hear hiss. Is that normal

I can hear a slight hiss from mine (with only amps powered on) with my ear about 6" from the tweeter (SICA 5.5C1.5CP-8, ~93.5 dB sens.) . It's not ground or source noise. It's not an issue at all for a normal person not listening from that distance. In comparison, my Purifi 1ET400A-based amps are completely silent from 6" but again this is of academic interest only.

 

[antcollinet]

This may be one of the things that makes it a problem for some people but not others - I find it irritating when I become aware of the noise in a quiet passage, a track transition, or when the music stops entirely. Or when auto-muting cuts in, drawing attention to a noise level I might not have been conscious of because of a step change. Other people may be aware of it but not find it irritating, or just not be aware of it at all, based on the times I've had to point it out. It's similar to gap-free transitions in that respect.

Agreed - while audible hiss between tracks doesn't bother me at all, I've found mains hum very irritating.

 

[CedarX]

Both are powered by a 48V 10A power supply, and when driven to full power through high-efficiency speakers with PA horns, I can’t hear a thing from either of them.

Literally? This is definitely a problem…

 

[staticV3]

So would topping LA90's also have this slight hiss when putting my ear at the tweeter? Because its supposedly the cleanest signal amp on asr right? Or do all power amps have some sort of audible hiss to some extent

LA90 would have drastically lower hiss, but it might still be there depending on the factors listed above.

 

[gwing]

LA90 would have drastically lower hiss, but it might still be there depending on the factors listed above.

With 87 dB speakers the Fosi Audio V3 Mono should be essentially silent. What you are hearing is much more likely caused by floating/open inputs, USB or interface noise, or grounding noise coming from the Behringer UMC22 and laptop setup. Try testing the amps with a proper line source that can actually be switched off completely, or with the inputs properly terminated instead of left open.

As it happens I also have 87dB speakers and have just shoved my ears within an inch of the tweeters finding that there is zero audible hiss in my system no matter how close I am. The monos are powered by a shared 10A supply and fed through XLR inputs.

If you can hear hiss on just one channel I'd suspect a fault somewhere, if it is identical on both the problem is likely hiss from something else in your system or, as I think has been said previously, a problem with your gain structure.

 

[himey]

Where would one look for silent test files? I get zero noise from both my setups but that is without anything playing and the volume maxed out. I had a ground loop hum with a desktop pc connected but since moving to a mini pc, all is silent.

 

[girtab]

Where would one look for silent test files? I get zero noise from both my setups but that is without anything playing and the volume maxed out. I had a ground loop hum with a desktop pc connected but since moving to a mini pc, all is silent.

You can generate silence with audacity afaik

 

[girtab]

If you can hear hiss on just one channel I'd suspect a fault somewhere, if it is identical on both the problem is likely hiss from something else in your system or, as I think has been said previously, a problem with your gain structure.

I did some more listening and hiss issues aside (which are most likely from the dac) it seems like the other v3 mono that I thought wasn’t broken is broken too. I found out after one bass heavy track which kind of sounded like it clipped. After that I applied a low pass filter and switched the left and right amps to see if my left speakers crossover was broken because of how the tweeter was crackling when low passing. Turns out it wasn’t the speaker but the OTHER v3 mono. So BOTH fosi v3 monos that I ordered back then came broken. One was just much harder to notice especially when the other has unbearably loud static noise. But now I can’t even use Amazon Return anymore and have to contact fosi. Great.

 

[girtab]

@Fosi Audio what can I do in this situation, my last Amazon return date was last week so now I can’t return it through them anymore. If I send the amp to you directly is the return/repair process free in terms of shipping etc?

 

[gwing]

I did some more listening and hiss issues aside (which are most likely from the dac) it seems like the other v3 mono that I thought wasn’t broken is broken too. I found out after one bass heavy track which kind of sounded like it clipped. After that I applied a low pass filter and switched the left and right amps to see if my left speakers crossover was broken because of how the tweeter was crackling when low passing. Turns out it wasn’t the speaker but the OTHER v3 mono. So BOTH fosi v3 monos that I ordered back then came broken. One was just much harder to notice especially when the other has unbearably loud static noise. But now I can’t even use Amazon Return anymore and have to contact fosi. Great.

Just a thought, but you both mentioned earlier that you needed 200W amps which would normally drive 87dB speakers to ear damaging levels in any normal domestic listening situation and also mention possible clipping here, which shouldn't e anywhere near happening. Are you by any chance applying heavy EQ at loud volumes to extend bass response? Doing that could require extreme power levels and be responsible for driving the amps into protection/clipping.