Fosi Audio V3 Mono Amplifier Review

[Sokel]

Apparently Fosi isn't the only company with opposite polarities for single-ended and differential inputs. For example:

Audio Research Reference 160S power amplifier Measurements

Sidebar 3: Measurements

www.stereophile.com

View attachment 382117

I listen to this one at least 2-3 times a week and it's a known fault (and a known trick for anyone who don't know) .
Another newbie mistake and at that price point is simply unforgivable.

 

[avdoc]

Do you people want me to do a test to see if running one V3 Mono balanced and the other channel single-ended and then level matched actually shows a phase mismatch? The level matching will be done with pink noise, a free app and *gasp* an iPhone mic, and the phase match/mismatch will be done *TRIGGER WARNING* by ear. However, I can do it very easily (since my preamp can output balanced and single-ended simultaneously, even in passive mode). And then report back?

Or you can just tell me that’s worthless to you and I’ll save my results for myself.

-Ed

Ed
I would be very interested as I just ordered 2 more V3s. Thanks!

 

[TonyJZX]

these things have hot local sales and they are hitting $200 usd for a PAIR.... SHIPPED

i mean that's pretty much cheaper than ONE Aiyima A70

 

[SMen]

When I say "by design" I don't necessarily mean they intended to invert phase. I mean the devices are "as specified" or "as drawn". The design - if I am correct - is faulty.

IE it is not (IMO) a manufacturing fault in that the people building them are making mistakes. So I suspect that all devices will be inverted.

It is looking like it.

Do you people want me to do a test to see if running one V3 Mono balanced and the other channel single-ended and then level matched actually shows a phase mismatch? The level matching will be done with pink noise, a free app and *gasp* an iPhone mic, and the phase match/mismatch will be done *TRIGGER WARNING* by ear. However, I can do it very easily (since my preamp can output balanced and single-ended simultaneously, even in passive mode). And then report back?

Or you can just tell me that’s worthless to you and I’ll save my results for myself.

-Ed

Yes definitely - go for it!!

If you face the speakers closely pointing at each other (an old fashioned way) they will go quiet when out of phase - but I'd expect out of phase to be clearly audible...

And anyone here with advanced measurement techniques ... great, but this appears to me to be a useful heads up by @EddNog.

I think I am right @Miser_Audioman does not have balanced to do his tests with his AV gear - unbalanced only.

 

[somebodyelse]

Apparently Fosi isn't the only company with opposite polarities for single-ended and differential inputs. For example:

This is no surprise. Many don't think that polarity / 'absolute phase' is audible, or at least important, so long as it's consistent on all channels in the system. We have at least one thread discussing that, so this thread is not the place for it. Most reviews don't check for inverting/noninverting in electronics, speakers or microphones, so presumably the reviewers don't consider it important enough to test.

Given the lack of consensus that it's even important, I don't think Fosi could reasonably be considered at fault if they have designed an inverting amp. I would only consider it a fault if there is inconsistency in production. I remember one example of this (but can't find it - probably buried in one of the very long Topping amp threads) where the wires from board to binding posts were crossed on one of the two channels. IIRC the supplier accepted this as a manufacturing fault and replaced the amp.

 

[Sokel]

This is no surprise. Many don't think that polarity / 'absolute phase' is audible, or at least important, so long as it's consistent on all channels in the system. We have at least one thread discussing that, so this thread is not the place for it. Most reviews don't check for inverting/noninverting in electronics, speakers or microphones, so presumably the reviewers don't consider it important enough to test.

Given the lack of consensus that it's even important, I don't think Fosi could reasonably be considered at fault if they have designed an inverting amp. I would only consider it a fault if there is inconsistency in production. I remember one example of this (but can't find it - probably buried in one of the very long Topping amp threads) where the wires from board to binding posts were crossed on one of the two channels. IIRC the supplier accepted this as a manufacturing fault and replaced the amp.

Old Quads were also inverted and people claimed they was sound different than the others.
Problem is we don't know if they already knew they were inverted before making these claims.

 

[Deleted member 72219]

Well then here we go…

Last night I went ahead and reran my experiment (there, does that word make you guys more comfortable?). I kept the right V3 Mono connected via balanced input and speaker cable connected, “in the normal manner,” so red to red and black to black at the amp and at the speaker. With the left channel, I initiated the experiment by changing out the balanced interconnect for a single-ended one by disconnecting my subwoofer (which is normally connected with a full stereo signal from my preamp’s single-ended output) and using the left channel RCA cable to connect the left V3 Mono and flipping that amplifier to RCA input. I turned on both amplifiers and played pink noise on loop, and level matched the left and right speakers as close as I possibly can from within 5mm in front of each driver (they’re coaxial, KEF LS50 Metas) using the balance plugin on my streamer (granularity level is only 0.5dB—apologies that I cannot get finer balance control than this, as my preamp does not have a separate balance control). Initially, I ran into a strange discovery in that if I use my preamp in any other setting than Passive preamp (no buffer) mode, I can max out the balance plugin to the left side and the right side would still be too loud, but that’s a separate topic all together. Anyhow, using passive pre mode did the trick. Then I sat back at my listening position and switched to music. Lo and behold, the left and right channels *TRIGGER WARNING* sounded clearly out of phase with each other. Finally, as the last step of the experiment, I shut off the left V3 Mono, flipped the cable connections at the amplifier end so that speaker had red to red and black to black, but connection was now red to black and black to red, and turned it back on, and now both amplifiers were back in phase and sounded as the system is supposed to sound (when I am not using a subwoofer).

There you go, end of experiment. After that I reverted my system to normal configuration and moved on. If this experiment is not good enough for you, feel free to ignore my post. I was asked to do this and post back by members other than you.

-Ed

 

[Sokel]

Well then here we go…

Last night I went ahead and reran my experiment (there, does that word make you guys more comfortable?). I kept the right V3 Mono connected via balanced input and speaker cable connected, “in the normal manner,” so red to red and black to black at the amp and at the speaker. With the left channel, I initiated the experiment by changing out the balanced interconnect for a single-ended one by disconnecting my subwoofer (which is normally connected with a full stereo signal from my preamp’s single-ended output) and using the left channel RCA cable to connect the left V3 Mono and flipping that amplifier to RCA input. I turned on both amplifiers and played pink noise on loop, and level matched the left and right speakers as close as I possibly can from within 5mm in front of each driver (they’re coaxial, KEF LS50 Metas) using the balance plugin on my streamer (granularity level is only 0.5dB—apologies that I cannot get finer balance control than this, as my preamp does not have a separate balance control). Initially, I ran into a strange discovery in that if I use my preamp in any other setting than Passive preamp (no buffer) mode, I can max out the balance plugin to the left side and the right side would still be too loud, but that’s a separate topic all together. Anyhow, using passive pre mode did the trick. Then I sat back at my listening position and switched to music. Lo and behold, the left and right channels *TRIGGER WARNING* sounded clearly out of phase with each other. Finally, as the last step of the experiment, I shut off the left V3 Mono, flipped the cable connections at the amplifier end so that speaker had red to red and black to black, but connection was now red to black and black to red, and turned it back on, and now both amplifiers were back in phase and sounded as the system is supposed to sound (when I am not using a subwoofer).

There you go, end of experiment. After that I reverted my system to normal configuration and moved on. If this experiment is not good enough for you, feel free to ignore my post. I was asked to do this and post back by members other than you.

-Ed

So XLR and RCA are not outputting the signal in phase?
Did I got it right?

-XLR - correct Phase
-RCA - wrong Phase.

 

[somebodyelse]

Old Quads were also inverted and people claimed they was sound different than the others.
Problem is we don't know if they already knew they were inverted before making these claims.

Given that recordings may or may not be inverted (or more likely have a mix of the two!), anyone who cares should have a switch on the preamp to change between inverting and non-inverting. It then doesn't matter whether any component inverts or not.

 

[Deleted member 72219]

So XLR and RCA are not outputting the signal in phase?
Did I got it right?

-XLR - correct Phase
-RCA - wrong Phase.

They are opposite phase. I will not venture a guess as to which one is correct and which one is wrong.

-Ed

 

[Deleted member 72219]

Given that recordings may or may not be inverted (or more likely have a mix of the two!), anyone who cares should have a switch on the preamp to change between inverting and non-inverting. It then doesn't matter whether any component inverts or not.

The PS Audio GCC-100 I used before getting into these modern chip amps had a phase inversion setting, in fact. Remote controllable for convenience!

-Ed

 

[Sokel]

They are opposite phase. I will not venture a guess as to which one is correct and which one is wrong.

-Ed

Given the fact that the reports for wrong phase came from those using the RCA inputs and running calibrations,I think we can safely assume that the wrong one is RCA.

 

[Miser_Audioman]

It is looking like it.

Yes definitely - go for it!!

If you face the speakers closely pointing at each other (an old fashioned way) they will go quiet when out of phase - but I'd expect out of phase to be clearly audible...

And anyone here with advanced measurement techniques ... great, but this appears to me to be a useful heads up by @EddNog.

I think I am right @Miser_Audioman does not have balanced to do his tests with his AV gear - unbalanced only.

That is correct, i do not. If someone would like to send me a Parasound preamp on 99 year loan…

 

[Basstölpel]

They are opposite phase. I will not venture a guess as to which one is correct and which one is wrong.

-Ed

Singe RCA is inverted when connected to a Denon AVR i think we can deduce that XLR is the correct polarity. Good work, @EddNog !

 

[DSJR]

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.

 

[Bleib]

Singe RCA is inverted when connected to a Denon AVR i think we can deduce that XLR is the correct polarity. Good work, @EddNog !

For me that means I'm done with some of these companies for quite a while. They need to get the basics right

 

[antcollinet]

Well then here we go…

Last night I went ahead and reran my experiment (there, does that word make you guys more comfortable?). I kept the right V3 Mono connected via balanced input and speaker cable connected, “in the normal manner,” so red to red and black to black at the amp and at the speaker. With the left channel, I initiated the experiment by changing out the balanced interconnect for a single-ended one by disconnecting my subwoofer (which is normally connected with a full stereo signal from my preamp’s single-ended output) and using the left channel RCA cable to connect the left V3 Mono and flipping that amplifier to RCA input. I turned on both amplifiers and played pink noise on loop, and level matched the left and right speakers as close as I possibly can from within 5mm in front of each driver (they’re coaxial, KEF LS50 Metas) using the balance plugin on my streamer (granularity level is only 0.5dB—apologies that I cannot get finer balance control than this, as my preamp does not have a separate balance control). Initially, I ran into a strange discovery in that if I use my preamp in any other setting than Passive preamp (no buffer) mode, I can max out the balance plugin to the left side and the right side would still be too loud, but that’s a separate topic all together. Anyhow, using passive pre mode did the trick. Then I sat back at my listening position and switched to music. Lo and behold, the left and right channels *TRIGGER WARNING* sounded clearly out of phase with each other. Finally, as the last step of the experiment, I shut off the left V3 Mono, flipped the cable connections at the amplifier end so that speaker had red to red and black to black, but connection was now red to black and black to red, and turned it back on, and now both amplifiers were back in phase and sounded as the system is supposed to sound (when I am not using a subwoofer).

There you go, end of experiment. After that I reverted my system to normal configuration and moved on. If this experiment is not good enough for you, feel free to ignore my post. I was asked to do this and post back by members other than you.

-Ed

So (TRIGGER WARNING - assuming you are genuinely hearing actual phase inversion ) the RCA is inverted and the balanced not.

Since the unbalanced RCA is using an additional circuit to create a balanced signal for driving the balanced input amp IC, together with gain options. They've clearly swapped the connections from this circuit from what they should be to achieve the same polarity as the balanced input.


EDIT : I'd still like @Fosi Audio to inform us clearly what is going on - and what (if anything) they are going to do about it.

 

[Sokel]

So (TRIGGER WARNING - assuming you are genuinely hearing actual phase inversion ) the RCA is inverted and the balanced not.

Since the unbalanced RCA is using an additional circuit to create a balanced signal for driving the balanced input amp IC, together with gain options. They've clearly swapped the connections from this circuit from what they should be to achieve the same polarity as the balanced input.

The most usual newbie mistake when doing opamps is routing the signal to the (+) of the opamp and then opamp's (-) to ground.
Nope,it's the other way around.

Edit:I'm talking about single end output obviously.

 

[antcollinet]

The most usual newbie mistake when doing opamps is routing the signal to the (+) of the opamp and then opamp's (-) to ground.
Nope,it's the other way around.

Edit:I'm talking about single end output obviously.

You can run input to + if you want a non inverting circuit, but feedback must always go to negative. So connecting negative to ground ain't gonna work.

In this case, they have a circuit that creates two gain options as well as balanced output. One possibility is a first op amp to create two gains with a switchable feedback resistor - likely an inverting configuration since this is simpler, and then a second op amp to provide an inverted version of the amplified signal. It would be an easy mistake to take the output of the first amplified (and inverted) stage and connect it into the + input of the amp IC.

 

[Freezak]

An affordable pre-amp/dac for these monoblocks? looking to drive them paired with DBR-62's both on PC and TV, thus USB and Optical ports are probably needed. I'm having a hard time finding a proper solution, any recommendations? remote control would be a nice addition, thanks