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Fosi Audio V3 Mono Amplifier Review

Rate this amplifier:

  • 1. Poor (headless panther)

    Votes: 13 2.0%
  • 2. Not terrible (postman panther)

    Votes: 21 3.2%
  • 3. Fine (happy panther)

    Votes: 129 19.4%
  • 4. Great (golfing panther)

    Votes: 502 75.5%

  • Total voters
    665
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… ;)
 
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.
 
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
 
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 :p) 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.
 
So (TRIGGER WARNING - assuming you are genuinely hearing actual phase inversion :p) 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.

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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.
 
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 :)
 
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 :)
If you describe the problem finding a solution you are having it would help. From my point of view there are many affordable DACs with remote that have optical and USB ports.

EG : https://www.audiosciencereview.com/forum/index.php?threads/smsl-su-6-review-desktop-dac.28402/
 
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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 :)
Another possibility. Costs a bit more but has balanced outputs and a headphone amp and remote. This, along with a WiiM mini, a $20 Sony blu ray transport and a pair of B&W 601 v3 speakers makes up my entire system… including the v3 monos of course.

 
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.
This is something I wondered about just looking at the layout in the V3 monos - I've understood the RCA opamp converting single ended to balanced, but the two opamps that follow are set one behind the other, as if something sequential is going on ... and not parallel - which looks rather different than say the 3eaudio 3255 mono layout pictured down the page a bit in Amir's review here. Not sure I understand where the second op amp comes in.

Above my pay grade but just curious.

At least Fosi could say something along the lines of "in some scenarios where the v3 monos are being used in a multi-amp set up it may be necessary to invert speaker outputs when used in single ended mode because ____ ____ ___ ... ... " fill in the blanks here.
 
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It is difficult to get my head around this type of performance is such a small and inexpensive package. I have been looking to add an amplifier to my Onkyo RZ50 to drive my front speakers-ML Vistas (4 Ohm). I have no complaints with the RZ50, but the V3 Mono Blocks appear to perform better on the bench. I would be interested if people think that there would be a noticeable difference (Better or Worse) in sound quality.
 
Another possibility. Costs a bit more but has balanced outputs and a headphone amp and remote. This, along with a WiiM mini, a $20 Sony blu ray transport and a pair of B&W 601 v3 speakers makes up my entire system… including the v3 monos of course.

Damn thank you, this is golden, not sure how i've missed the SMSL on the forums here.
 
I've understood the RCA opamp converting single ended to balanced, but the two opamps that follow are set one behind the other, as if something sequential is going on ... and not parallel - which looks rather different than say the 3eaudio 3255 mono layout pictured down the page a bit in Amir's review here. Not sure I understand where the second op amp comes in.
Not possible to say without either a circuit diagram, or some time spent tracing out the PCB. Even if I had one, I'm not interested enough to spend the time doing the latter.

But position of the components on the board has nothing to do with the circuit. You don't need to place parallel circuits side by side.
 
Not possible to say without either a circuit diagram, or some time spent tracing out the PCB. Even if I had one, I'm not interested enough to spend the time doing the latter.

But position of the components on the board has nothing to do with the circuit. You don't need to place parallel circuits side by side.
Thank you, yes, that last point about the parallel circuit was the one nagging at me, and (and I don't want in any way to bring up op amp swapping) the confusion I was being caused by the proposal that one half of a parallel circuit should favor an op amp swap over another! Or be prioritized (so I am talking about confusion being caused relating to the circuit by this proposal).
 
Damn thank you, this is golden, not sure how i've missed the SMSL on the forums here.
Thanks. Another thought… I don’t actually use the usb input for computer but I leave a short gtg cable plugged in for hi res listening from iPhone or iPad.

I use Apple but if you’re using a PC you might need a driver from the SMSL web site.
 
Damn thank you, this is golden, not sure how i've missed the SMSL on the forums here.
It's my favorite DAC, tested up to 20 or so. Never seen reports of SMSL suddenly playing high volume out of nowhere like some Topping products
I'd still recommend turning down the volume of the DAC to lowest before turning on any power amps
 
It's my favorite DAC, tested up to 20 or so. Never seen reports of SMSL suddenly playing high volume out of nowhere like some Topping products
I'd still recommend turning down the volume of the DAC to lowest before turning on any power amps
Gotcha it's my favourite one right now - I'm guessing you've tested the Topping D50 III one or perhaps you, @DavidM1 ? it appears to have similar functionality with a slightly lower price tag, though i'm guessing only one of those will act better as a preamp combined with two Fosi V3 monos.
 
Gotcha it's my favourite one right now - I'm guessing you've tested the Topping D50 III one or perhaps you, @DavidM1 ? it appears to have similar functionality with a slightly lower price tag, though i'm guessing only one of those will act better as a preamp combined with two Fosi V3 monos.
C200 was an a deal quite recently, and yes I prefer it over D50 III as well, as I don't like its BT remote which goes to sleep too quickly and takes some time to wake up.
To me this is poor functionality, the C200 remote is far more responsive.
Obviously D50 III PEQ and 5v out can come to use for some, but I'd rather get a HQ headphone amp included for the price.
 
C200 was an a deal quite recently, and yes I prefer it over D50 III as well, as I don't like its BT remote which goes to sleep too quickly and takes some time to wake up.
To me this is poor functionality, the C200 remote is far more responsive.
Obviously D50 III PEQ and 5v out can come to use for some, but I'd rather get a HQ headphone amp included for the price.
Unfortunately from what i see i can only find the C200 on aliexpress (i'm located in Europe), where i'd probably have to pay for some custom duties. I happen to own the DX1 headphone amp and it does the job pretty well driving my HD560s with peace apo applied. Headphone amp is a bonus obviously, but in case i want to use it, it would be pretty problematic though, having my HD560s connected to C200 and DBR62 and using both on the PC where i'd have to disable the peace apo eq whenever i use my DBR62s on my PC, thus, i guess i'd rather use headphone amp and preamp/dac separately. In this case, if C200 does not get discounted any soon, would SMSL D6s be a good enough alternative? i'm reading conflicting descriptions on whether it supports remote control or not.
 
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