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Fosi Audio V3 Mono Amplifier Review

Rate this amplifier:

  • 1. Poor (headless panther)

    Votes: 13 1.9%
  • 2. Not terrible (postman panther)

    Votes: 21 3.1%
  • 3. Fine (happy panther)

    Votes: 129 19.3%
  • 4. Great (golfing panther)

    Votes: 506 75.6%

  • Total voters
    669
I agree it would be a good thing to see in specs, but I don't remember ever seeing it from any manufacturer. From time to time a manufacturer will make a point of preserving absolute phase in marketing material, but that's the exception rather than the rule.
Just speculating, but most amps are stereo, and you expect the two channels to match. I remember years ago, talk about absolute phase and thinking it was BS.

It never occurred to me until recently that absolute phase would be an issue.
 
Just speculating, but most amps are stereo, and you expect the two channels to match. I remember years ago, talk about absolute phase and thinking it was BS.

It never occurred to me until recently that absolute phase would be an issue.
most likely because they are monoblocks and part of the usecase is to extend power in home theatre setup or just stereo with sub.
 
most likely because they are monoblocks and part of the usecase is to extend power in home theatre setup or just stereo with sub.
Lets put it simple.
If we,for example,have 3 fosi monos of which the 2 of them use the XLR input and one of them uses the RCA input,the later will be in inverted phase relatively to the other two.

See,they don't even mix even if no other amp is involved.
 
If they are non inverting it should be easy to integrate.

Let say you have an existing 5.1 receiver from reputable manufacturer. It will be safe to assume all output are in phase otherwise the room correction software would have complained.

if you want to use the same setup for music but looking for more power and cleaner amp then you can use another amp
 
Lets put it simple.
If we,for example,have 3 fosi monos of which the 2 of them use the XLR input and one of them uses the RCA input,the later will be in inverted phase relatively to the other two.

See,they don't even mix even if no other amp is involved.
Unless of course your XLR source and RCA sources are themselves in different phase. Then the Fosis would sort it all out for you rather than being a problem, the world isn't in a completely nice and tidy state so you have to look at the whole audio chain :)

It would be helpful to have a phase inversion switch for the RCA inputs though, or even an internal mod to match phase between RCA and XLR, especially for folks who might often switch between RCA and XLR inputs if they have multiple sources. Most folks need to either do nothing or just swap speaker connections though.
 
This should be stated in the technical specification online and in the paper included in the box.
Exactly, people need to know how their amps work.
 
Unless of course your XLR source and RCA sources are themselves in different phase. Then the Fosis would sort it all out for you rather than being a problem, the world isn't in a completely nice and tidy state so you have to look at the whole audio chain :)

It would be helpful to have a phase inversion switch for the RCA inputs though, or even an internal mod to match phase between RCA and XLR, especially for folks who might often switch between RCA and XLR inputs if they have multiple sources. Most folks need to either do nothing or just swap speaker connections though.
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.
 
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.
 
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?
 
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.
 
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.
 
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.
 
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.
 
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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
 
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.
 
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!
 
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? :)
 
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