Fosi Audio V3 Mono Amplifier Review

[Petrushka]

Not only I check every component and the chain,I measure them also.
And I have yet to meet a source or a pre with a reversed phase (but some gave the choice )

The problem is not what it does with the rest of the chain,the problem is that the same device has reversed phases between it's own inputs and no warning about it.
Going further,when fosi was asked about it they seem to not even know what this is,same as with the el. crossover at the other thread where I had to explain what that is.

Is not exactly giving you confidence.

The people you talk to are in marketing.

 

[Miser_Audioman]

This should be stated in the technical specification online and in the paper included in the box.

I got the same response, and gently suggest some sort of warning is needed. Indeed the marketing aspect a bit off-putting

 

[Endibol]

My Bryston BP25P preamp had a phase-inversion switch. Made absolutely no sonic difference on the music I played and the three or so assorted speakers I used at the time. Inverting the phase at the speaker terminals *may apparently* appear to alter the sound slightly due to non-symmetrical crossovers in the speakers (bass impact I recall when I used to bother about such things). Amp output stages do seem to be symmetrical pretty much, so maybe a subjective falsehood in my case.

I think I read somewhere that some music instruments, like the saxophone, produce an asymmetric tone.
If that’s true then it would matter, assuming it’s audible. Does anyone know more about this?

 

[NTK]

I think I read somewhere that some music instruments, like the saxophone, produce an asymmetric tone.
If that’s true then it would matter, assuming it’s audible. Does anyone know more about this?

See this paper

E-library page - AES

AES E-Library ← Back to search

aes2.org

and this article in Audio (Dec 1993 issue) by the same authors.

https://acmebass.com/archive_files/mag_articles/audio_magazine/polarity_quest_for_audibility_12-1993.pdf

 

[Fosi Audio]

Well that is a bunch of nonsense, other than confirming the phase inversion, but without the specific information confirming RCA, XLR, or both.

Specifically, phase inversion has nothing to do with:


Which I'm assuming to be about the PFFB.

@Fosi Audio please can you get some valid and accurate technical information into this topic, and leave out the marketing spin. It doesn't wash here.

Thanks.

Hello friend, sorry to reply late. I just checked with our engineer.

Due to the implementation of the PFFB architecture, the phase is inverted when the input signal is processed, which can help enhance the audio quality. The polarity markings on the V3 mono align with the chip’s output and not the inverted phase. Using two V3 Monos together won't cause any phase issues. If you integrate the V3 Mono with other equipment, note that the phase might be inverted.

Sorry for any inconvenience caused by this. This is indeed a shortcoming in our work, as we failed to clearly inform everyone about this design in advance.

 

[SMen]

Hello friend, sorry to reply late. I just checked with our engineer.

Due to the implementation of the PFFB architecture, the phase is inverted when the input signal is processed, which can help enhance the audio quality. The polarity markings on the V3 mono align with the chip’s output and not the inverted phase. Using two V3 Monos together won't cause any phase issues. If you integrate the V3 Mono with other equipment, note that the phase might be inverted.

Sorry for any inconvenience caused by this. This is indeed a shortcoming in our work, as we failed to clearly inform everyone about this design in advance.

I'm not sure that this explains the balanced being different to the RCA because surely it would just require reversing the current RCA input +- for them to match?

I would be very interested to understand from the engineer about the balanced inputs / opamps. These I understand 'should' be in parallel but they look to be in series? Could we have feedback on this also from your engineer @Fosi Audio ? I am just curious. It has confused me your Muses02 offer prioritizing, the 'first' of the balanced inputs, and not requiring identical op amps (The NE5532 provided as standard are identical).

Even if one were to try this or not, it's the design principle behind Fosi's suggestions on these op amps that I am asking about.

 

[somebodyelse]

I'm not sure that this explains the balanced being different to the RCA because surely it would just require reversing the current RCA input +- for them to match?

RCA is single ended - you can't just reverse it. The XLR and outputs are both differential so could be reversed. Reversing hot and cold on the XLR would make it consistent between inputs, but would require a board revision. Reversing the outputs would make it non-inverting. That would be an assembly process change, but ideally with updated silkscreen on the board to match. Changing the black binding posts to blue to indicate they're driven not ground would be good too.

 

[antcollinet]

Hello friend, sorry to reply late. I just checked with our engineer.

Due to the implementation of the PFFB architecture, the phase is inverted when the input signal is processed, which can help enhance the audio quality. The polarity markings on the V3 mono align with the chip’s output and not the inverted phase. Using two V3 Monos together won't cause any phase issues. If you integrate the V3 Mono with other equipment, note that the phase might be inverted.

Sorry for any inconvenience caused by this. This is indeed a shortcoming in our work, as we failed to clearly inform everyone about this design in advance.

Thanks for your reply, but. You don’t fully answer the question. What about the rca/xlr difference. Some clear documentation is needed here. I need to know from Fosi rather than random peoples tests, how i should integrate these amps into my system if i were to buy them. My use case would be for the LR channels of a 7.1.4 AVR - clearly I need phase alignment with the other channels here.

 

[JeremyFife]

Hello friend, sorry to reply late. I just checked with our engineer.

Due to the implementation of the PFFB architecture, the phase is inverted when the input signal is processed, which can help enhance the audio quality. The polarity markings on the V3 mono align with the chip’s output and not the inverted phase. Using two V3 Monos together won't cause any phase issues. If you integrate the V3 Mono with other equipment, note that the phase might be inverted.

Sorry for any inconvenience caused by this. This is indeed a shortcoming in our work, as we failed to clearly inform everyone about this design in advance.

Hi, thanks for the reply @Fosi Audio . You said "... can help enhance the audio quality ... " Please can you, or members, explain that.

Cheers

 

[antcollinet]

RCA is single ended - you can't just reverse it

Fosi could have implemented a phase inversion in the input circuit to make it match xlr if they had thought about the design properly. Or just swapped the polarity on the xlr input. What they have now is a mess.

 

[DavidMcRoy]

What about the rca/xlr difference. Some clear documentation is needed here. I need to know from Fosi rather than random peoples tests, how i should integrate these amps into my system if i were to buy them.

Thanks for the clarification. I've come across audio equipment that inverts polarity for decades. In the case of the V3 Mono, it is an issue in my intended application in that I will be using them to drive woofers in a large, multi-way DIY speaker in conjunction with different amplifiers driving other drivers in the speaker, and crossing over to a subwoofer below the frequencies those woofers will be handling. In such an instance, I would have observed the polarity reversal in tests and simply swapped wires accordingly, no big deal. Still, it's nice to know what to expect ahead of time. I've actually seen a few manufacturers' product information/specifications sheets indicate whether or not a device inverts polarity. Usually you're left to discover it on your own. Looking forward to my four V3 Monos arriving in a few days time!

 

[antcollinet]

Thanks for the clarification. I've come across audio equipment that inverts polarity for decades. In the case of the V3 Mono, it is an issue in my intended application in that I will be using them to drive woofers in a large, multi-way DIY speaker in conjunction with different amplifiers driving other drivers in the speaker, and crossing over to a subwoofer below the frequencies those woofers will be handling. In such an instance, I would have observed the polarity reversal in tests and simply swapped wires accordingly, no big deal. Still, it's nice to know what to expect ahead of time. I've actually seen a few manufacturers' product information/specifications sheets indicate whether or not a device inverts polarity. Usually you're left to discover it on your own. Looking forward to my four V3 Monos arriving in a few days time!

Did you mean to reply to me?

 

[DavidMcRoy]

Did you mean to reply to me?

Sorry, I convoluted Fosi Audio's quote which was within your post!

 

[Borland]

I really wouldn't worry. Amps give off heat, it's one of their charms. Fosi has posted a video on the V3 monos and they point out that the entire case is a heat sink and it's going to be warm to touch. Not a problem and a good sized heat sink is a wonderful thing.

At room temperature 24 degrees (C):

After 3 hours (background music, German = Zimmerlautstärke) 45 degrees on the surface with the door of the lowboard closed. The lowboard has active ventilation.

After a further 2 hours 42 degrees with the lowboard door open.

This looks different in the video.

I will now try passive cooling of the V3 monos.

 

[EJK]

Looks like I had some movement since getting tracking info on July 11th. It is at the airport in China. Doesn't look like 1 to 2 weeks to receive the amps.

 

[Endibol]

See this paper

E-library page - AES

AES E-Library ← Back to search

aes2.org

and this article in Audio (Dec 1993 issue) by the same authors.

https://acmebass.com/archive_files/mag_articles/audio_magazine/polarity_quest_for_audibility_12-1993.pdf

Thanks a lot for these links, very interesting. It shows that it’s worthwhile to keep absolute polarity intact in the entire recording- processing-playback chain.

 

[Nopiano]

Thanks a lot for these links, very interesting. It shows that it’s worthwhile to keep absolute polarity intact in the entire recording- processing-playback chain.

I think in practice that’s well nigh impossible if you use LPs, radio or streaming as there’s no easy way to know how the source was recorded.

Some years ago I had a Meridian CD player-preamp with a polarity switch, and best of all it worked from the remote. But after a few trials, although I could hear a minute change, it was nigh on impossible to express a preference, so in the end I rarely touched it.

There used to be tables of absolute phase used by popular record labels, and these are probably just a Google away.

 

[gwing]

Thanks a lot for these links, very interesting. It shows that it’s worthwhile to keep absolute polarity intact in the entire recording- processing-playback chain.

Thanks for the links, very interesting. In practice though polarity is likely to be completely inaudible for actual music as opposed to isolated specially designed wave forms, and even if it were there will likely be a 50:50 chance of polarity in the recorded music being inverted or not so we wouldn't know which way to set up our system. Actually that's probably a best case, in practice the recording is likely to be a mismatched mess of phase/polarity inconsistencies for different instruments and mikes so there is no polarity that we could select to improve the mess. Good job it's likely to be inaudible in the first place

 

[audioguy272727]

I have seen some people just remove that orange-colored strip from the sides of the chassis for better ventilation, which sounds like a good idea, especially during these super hot summer months.
View attachment 382593

In my “testing” I found the V3M devices to be 10 to 11 degrees hotter than the PA7 (112 deg F for the V3M vs 102 degrees F for the PA7) with the devices being situated standalone - no other devices contributing ambient to heat. When I stacked the PA7 and the V3Ms on a Teac Dac I have that throws off quite a bit more heat, the V3Ms got to 118 degrees F while the PA7 only got to 105 degrees F. So the V3Ms seem to really like being solitary and I would expect cooled. And the PA7 just lived its life without reacting too much to the world around it. So I returned the V3Ms since there was little to no “audio pleasure benefit” vs the PA7 and it of course uses two supplies and two chassis so not really a tidy minimalist solution that I was hoping for as well. And for reference, I bought the PA7 used for about the same price as the V3Ms with the 20% discount from Amazon.

 

[Supernono]

Hello everyone,
I need advice on the fosi audio v3 mono amp
I want to connect it to the pre-out output of my home cinema amp.
Is this possible?
Thanks in advance