Fosi Audio V3 Mono Amplifier Review

[rhing]

I am using the balanced XLR inputs and verified with in-phase and out-of-phase test tracks that the amps are in-phase. I am not using a subwoofer or another amp with the V3 Mono amps. I feed balanced connections from a Denafrips Pontus II to a Schiit Freya+ line stage preamp to a pair of Fosi V3 Mono amps driving a pair of KEF LS50 speakers. The system sounds wonderful with a wide range of music genres. The bass is nicely defined and the sound is clear, detailed and smooth.

Today, I take delivery of a Schiit Skoll phono stage preamp where I will make unbalanced RCA connections between a restored Dual 1229 turntable with Shure V15 Type III MM cartridge, and the Schiit Skoll, and balanced XLR connections from the Skoll to the Freya+. Can’t wait to try it out.

As a reference power amplifier, I have a Pass DIY Aleph J Class A with unbalanced and balanced inputs which I use with the Freya+. I built this in 2020 during the height of the COVID pandemic. I enjoy the Fosi V3 Mono amps as much as I enjoy the Aleph J with the additional benefit that the Fosi amps do not generate as much heat as the Aleph J Class A amp.

I did add Arctic MX-6 thermal conductive compound to each amp as the amps came with sparse coverage of the TPA3255 amp IC heat sink plates. I also installed MUSES02 op amps in both amps. The KEF LS50’s can fill the listening room nicely. In my opinion, these amps are a bargain.

 

[gwing]

Does the inline DC Filter degrade the audio in anyway.

It is a power supply filter, how could it possibly degrade the audio?

 

[Deleted member 72219]

Sorry to have made many friends confused. We can confirm the phase is the same for both RCA and XLR input based on the measurement using an AP analyzer.

Our engineer connected two V3 Monos, one with RCA input and the other with XLR input. We can find that the phases are the same based on the AP test result.
View attachment 386999

Thank you very much!!!

-Ed

 

[Stoutblock]

Sorry to have made many friends confused. We can confirm the phase is the same for both RCA and XLR input based on the measurement using an AP analyzer.

Our engineer connected two V3 Monos, one with RCA input and the other with XLR input. We can find that the phases are the same based on the AP test result.
View attachment 386999

The question of the hour is why are the speaker outputs on the RCA example obviously modified and tape covering the wire routing? Can we see the same test run with both RCA and XLR examples tested with the exact same production units? Not trying to question integrity but it does beg the question??? Why the mod on the RCA example?

I care less about correct phase and more that RCA and XLR are the same.

 

[Killingbeans]

The question of the hour is why are the speaker outputs on the RCA example obviously modified and tape covering the wire routing?

Looks like it's just a PCB that hasn't had the back plate mounted yet, and they simply put some loose shrink tubing over the speaker terminals to avoid a short circuit.

I don't see any modification of the RCA port? The gain switch just isn't connected to the PCB, that's all?

 

[SMen]

I am using the balanced XLR inputs and verified with in-phase and out-of-phase test tracks that the amps are in-phase. I am not using a subwoofer or another amp with the V3 Mono amps. I feed balanced connections from a Denafrips Pontus II to a Schiit Freya+ line stage preamp to a pair of Fosi V3 Mono amps driving a pair of KEF LS50 speakers. The system sounds wonderful with a wide range of music genres. The bass is nicely defined and the sound is clear, detailed and smooth.

Today, I take delivery of a Schiit Skoll phono stage preamp where I will make unbalanced RCA connections between a restored Dual 1229 turntable with Shure V15 Type III MM cartridge, and the Schiit Skoll, and balanced XLR connections from the Skoll to the Freya+. Can’t wait to try it out.

As a reference power amplifier, I have a Pass DIY Aleph J Class A with unbalanced and balanced inputs which I use with the Freya+. I built this in 2020 during the height of the COVID pandemic. I enjoy the Fosi V3 Mono amps as much as I enjoy the Aleph J with the additional benefit that the Fosi amps do not generate as much heat as the Aleph J Class A amp.

I did add Arctic MX-6 thermal conductive compound to each amp as the amps came with sparse coverage of the TPA3255 amp IC heat sink plates. I also installed MUSES02 op amps in both amps. The KEF LS50’s can fill the listening room nicely. In my opinion, these amps are a bargain.

Oh very nice (turntable and cartridge)...!

I went for a Michael Fidler MMPro. Just got it, along with a balanced switch relay volume control. What stylus are you using with that V15 Type III? Just curious. Using an old Technics p205 myself (and a couple of others)... always hankered after an old V15 ... but not an option with that 'P' in front of the 205 (SL15).

Regardless, the V3 monos are a great match! No sense of anything lacking ... just a sense of everything being reproduced with power and transparency. Bargain indeed. Haven't tried the Muses02's. I'm sure I will at some point.

 

[Stoutblock]

Looks like it's just a PCB that hasn't had the back plate mounted yet, and they simply put some loose shrink tubing over the speaker terminals to avoid a short circuit.

I don't see any modification of the RCA port? The gain switch just isn't connected to the PCB, that's all?

Understood, but why confuse the question? If Fosi wants to prove that the new amps have the same and correct phase for both XLR and RCA, why not show two identical production units with the only variable being RCA vs XLR input? There is no evidence they revised the RCA input to fix the phase problem? All they did to correct phase on the newer amps was to reverse the speaker output wires to the speaker lugs which is an acceptable solution if both RCA and XLR have the same phase. Fosi says they are, some others say they are not. This demonstration was made by Fosi to prove they are. This photo does not convince me.

But this video does convince me they are the same so I am good.

It's not been a terribly productive evening so far.
I've already posted a screenshot of measurements which is a clearer indication than this video IMO but learning how to make this video was a very effective way of avoiding paperwork duties.
As I've previously said, I backed the kickstarter and received my two units a few weeks ago before Fosi would have made any modifications. RCA and XLR are matched and inverted in my units.

 

[Sokel]

The question of the hour is why are the speaker outputs on the RCA example obviously modified and tape covering the wire routing? Can we see the same test run with both RCA and XLR examples tested with the exact same production units? Not trying to question integrity but it does beg the question??? Why the mod on the RCA example?

I care less about correct phase and more that RCA and XLR are the same.

Can't see all the cable routing but it seems legit.
And it seems like it's the first version that they test there (it doesn't matter thought)

The pic as a proof could be more tidier with two of-the-self units but even as is is ok,specially if we combine it with the user test who posted the video.
I wouldn't worry for that.

 

[A.wayne]

After seeing the soldering my two Fosi Audio V3 Mono's are going back to Amazon UK for a refund.

Im not sold on the sound quality and now seeing this it's the excuse I needed. I've had a few Class d amps and each and everyone makes my ears bleed.

Tried quite a few myself same thoughts...

 

[A.wayne]

I'm guessing all of them was the kind with no post filter feedback, and you used them to drive speakers with high impedance in the treble region. Or maybe they were underpowered for your use case and were clipping like crazy.

Either that or the countless scary bedtime stories being told about Class D have taken root in your brain and won't let go

Maybe he has working ears ....

 

[Killingbeans]

Understood, but why confuse the question?

Because engineers aren't good at predicting how easy it is to make non-engineers confused

 

[Killingbeans]

Maybe he has working ears ....

Or just a normal human brain, that naturally loves to superimpose experiences with the things it expects

 

[totti1965]

Here is a photo from the Fosi FB group that shows new vs old.

They just reversed the output wires to the speaker terminals.

Isn’t it more old vs new??? So old is the picture on top?

 

[antcollinet]

I just received my six V3M amps today and I can confirm they have all been updated (output wires switched). I had the cycle time for checking down to four minutes after doing it six times! I'm using the RCA inputs on my HT system, and I don't have a clue if they are in phase or out of phase but at least they are all the same. They sound just fine! Have to do some wire routing...

View attachment 386893View attachment 386894

Shockingly bad soldering quality though. Clearly modified by a person who has. no idea how to do it.

 

[Brian Hall]

Got two of these delivered today and hooked them up in my office setup replacing a single Fosi ZA3.

I haven't done any proper testing, but it seems like everything sounds a bit better. It may just be expectation bias, but they sound great.

It is probably just be the power difference. I'm using a Wiim Ultra as a preamp (and streamer/DAC/headphone amp). With the single ZA3 in stereo mode (gain maxed out), I had to take the volume control on the Ultra to over 50 to get the same sound level as I get with 27 on the V3 monos.

I just ordered another pair for the stereo setup on my main system.

I've been measuring the temperature to see how hot they get. The temperature in this room is 72F. After running for about 3 hours, one is showing 104.0F and the other is 103.9F. I have them side by side with a gap of two inches between them.

 

[Stoutblock]

Because engineers aren't good at predicting how easy it is to make non-engineers confused

But I am actually an Engineer and quite knowledgeable on how to set up a valid test…

 

[rvsixer]

Hang on. Fosi has said rca and xlr are the same and there was a post earlier where someone tested it and agreed. I don’t understand all the negativity. It was the same when there was a thread panic about heat.

Phase issues with speakers are typically easy to hear by a/b comparison. If it isn’t audible at all to the listener because one speaker is a sub then perhaps the polarity difference isn’t all that important.

@Stoutblock tested his old units (and that he would check his six new units as well). And AFAIK up till Fosi's latest testing post, we had no one else that had tested the new units (and no "I got my reworked units and they sound okay" does not count). Until I saw Fosi's confirmation of new unit actual measurements, I was simply seeking the truth, sorry you took this as negativity.

Also sorry a few posters here trying to explain proper sub integration to you is explained away by its an easy a/b comparison and perhaps it isn't that important, if one has dabbled in LF phase audibility and LF in rooms and shaping it via sub(s) one can see it is important indeed. Grimani has some excellent material on this if interested.

 

[rvsixer]

There's literally a video demonstration by a member in this thread showing the phase is exactly the same on XLR and RCA inputs.

That was on old units, and he was going to test (6) new reworked units when he (@Stoutblock) got them. He has rec'd those, awaiting a non-Fosi confirmation on new units, that speaker polarity does not change with input selection.

 

[rvsixer]

I care less about correct phase and more that RCA and XLR are the same.

THIS

 

[Killingbeans]

But I am actually an Engineer and quite knowledgeable on how to set up a valid test…

Then I honestly don't understand why this is such a big deal to you.

Sure, it would look more professional if they hadn't just grabbed two units from different stages of the assembly line, but we can only assume that the PCBs themselves have both passed testing. The result will be the same from the setup you're suggesting, so I don't see what makes it more valid.

Fosi Audio would have zero reason to mess with their test setup in order to get a fake result.