Fosi v3 Mono - User Impressions | Owner's Thread

[jEDGEc0m]

I bought a pair of V3 Monos/48V PS from Amazon, received them a few days ago. On examination out of the box they have different labels. One is a QR Code, the other is a standard barcode with what I assume is the S/N. The QR Code doesn't show a S/N when read with my phone QR scanner. I find it odd that a single purchase has two different versions like this. I bought a V3 Mono last year for a dedicated measurement rig. It has the same kind of QR code. I never confirmed if that one has the inverted output voltage wiring internally because it's immaterial in my measurement rig. But a stereo pair may be affected by that. In addition the QR code on the new one is on the opposite side of the base from my original one. Tag location isn't important for function, but I find it all a bit odd. I have yet to even connect the new pair to check them out. Anyone out there have a similar experience? The different codes actually give me a bit of concern. These both also have the new 25/19 gain labelling, so evidently the newer variety. I had not been keeping up with this thread, had no clue that there was a gain change in the newer ones, but I'm fine with it.
View attachment 485575

Hopefully they're consistent and serve you well.

I just checked mine - they both have a barcode, and a QC sticker, placed the same on both. They don't have a QR code. The barcode is similar place to yours, . and the QC sticker on the opposite end.

I've had no issue with mine. probably use them a few hours a day at least, and likely never pushed hard at all.

 

[Jorj]

I've had my v3 monos for about 10 months and one of them died over a month ago. The lights come on, the relays click but no sound comes out. The other is fine. I worked with Fosi (bought direct) and they refused to send me a matched pair, telling me to just use the 25dB gain. That sucks, but I can live with it. They sent a replacement board but used some fly-by-night Chinese last-mile service who delivered to the wrong address and never let me know they had dropped it off. Still working with Fosi to get a replacement. Grrr.

My system is still down, so I need to know if there is any commonly burned-out part on these when this happens. It sounds like the one that died did so in a very common way, so was hoping maybe one of my intrepid electronics-savvy audiophiles would help a brother out by pointing out some testing/parts replacement ideas. I suppose it is too easy for it to be an easy-to-swap op-amp?

 

[Guddu]

Sorry to hear but mine got a few unavoidable issues sooner and made me stop using them then.
Part of me isn’t surprised seeing such issues looking at too compact no-ventilation case for 48v operation (not just limited to v3 mono).

they refused to send me a matched pair,

What do you mean by “matched pair”? I don’t think they do match a pair of amps to sell, and don’t think it’s necessary as well.
Setting the same gain on both units is all that matters.

 

[antcollinet]

Sorry to hear but mine got a few unavoidable issues sooner and made me stop using them then.
Part of me isn’t surprised seeing such issues looking at too compact no-ventilation case for 48v operation (not just limited to v3 mono).

What do you mean by “matched pair”? I don’t think they do match a pair of amps to sell, and don’t think it’s necessary as well.
Setting the same gain on both units is all that matters.

There has been a design change resulting in different gain settings. @Jorj naturally wants a replacement that has the same gain settings as his still working unit.

It is disappointing that @Fosi Audio cant acccomotdate this - or replace both with the new design. Poor service when something has failed.

 

[Guddu]

There has been a design change resulting in different gain settings. @Jorj naturally wants a replacement that has the same gain settings as his still working unit.

It is disappointing that @Fosi Audio cant acccomotdate this - or replace both with the new design. Poor service when something has failed.

I see, I wasn’t aware of any such change.
The units I had 1.5 yrs back also had 25/31 dB selectable gain and I see same on Fosi’s page now for RCA.
Am I seeing different than what we are talking here?

 

[early rejecter]

Am I seeing different than what we are talking here?

Yes, the current models are 19/25 dB selectable. Fosi is suggesting he just set both to 25 dB.

 

[Guddu]

Yes, the current models are 19/25 dB selectable. Fosi is suggesting he just set both to 25 dB.

All right, looks like their website page isn’t updated yet then.
Well this situation surely brings doubts in mind though technically 25 db set on both should be okay.

 

[DavidR]

Rather than put my V3 Mono pair into a system I ran distortion measurements. I first ran the RTA on my original V3 as a baseline (had it since July 2024), 5W into 4 ohms. It has performed flawlessly. However, long story short, I'm returning these two new ones based on distortion results. All I did was swap amps and allow a fair amount of time for the next one to warm up sufficiently. This is one reason I prefer to buy through Amazon, ease of return. The option to get "help" from the manufacturer in this case can't help. I also rejected replacement.

The difference initially doesn't look bad, but when you look at the numbers, especially HD2, it's clear how much worse these two are in comparison to my first one.

Edit: Correction on the graph comments. The gain was 18dB, but the feedback was through my hand-built passive attenuator.

RTA Overlays

Individual RTAs

Edit: REW was indispensable for this. I would have used these not knowing about the questionable results here. It may be that I would not have heard a difference, but given the levels it's very possible. There was no indication that these had been returns to Amazon by someone else, the packaging all appeared new.

 

[jEDGEc0m]

Rather than put my V3 Mono pair into a system I ran distortion measurements. I first ran the RTA on my original V3 as a baseline (had it since July 2024), 5W into 4 ohms. It has performed flawlessly. However, long story short, I'm returning these two new ones based on distortion results. All I did was swap amps and allow a fair amount of time for the next one to warm up sufficiently. This is one reason I prefer to buy through Amazon, ease of return. The option to get "help" from the manufacturer in this case can't help. I also rejected replacement.

The difference initially doesn't look bad, but when you look at the numbers, especially HD2, it's clear how much worse these two are in comparison to my first one.

Edit: Correction on the graph comments. The gain was 18dB, but the feedback was through my hand-built passive attenuator.

RTA Overlays
View attachment 487183

Individual RTAs
View attachment 487184

Edit: REW was indispensable for this. I would have used these not knowing about the questionable results here. It may be that I would not have heard a difference, but given the levels it's very possible. There was no indication that these had been returns to Amazon by someone else, the packaging all appeared new.

It's a concern with changes in products, and tests on early versions, or maybe even pre-production versions.

I'd be disappointed if they don't perform as well as the originally measured ones that no doubt lots of us have based our purchase on. I'm going to hopefully keep being in blissful ignorance with mine - I'm not hearing anything wrong, and the basic distortion measurements of the speakers they power with UMIC and REW seemed to show low levels of distortion.

Thanks for your post.

 

[antcollinet]

Rather than put my V3 Mono pair into a system I ran distortion measurements. I first ran the RTA on my original V3 as a baseline (had it since July 2024), 5W into 4 ohms. It has performed flawlessly. However, long story short, I'm returning these two new ones based on distortion results. All I did was swap amps and allow a fair amount of time for the next one to warm up sufficiently. This is one reason I prefer to buy through Amazon, ease of return. The option to get "help" from the manufacturer in this case can't help. I also rejected replacement.

The difference initially doesn't look bad, but when you look at the numbers, especially HD2, it's clear how much worse these two are in comparison to my first one.

Edit: Correction on the graph comments. The gain was 18dB, but the feedback was through my hand-built passive attenuator.

RTA Overlays
View attachment 487183

Individual RTAs
View attachment 487184

Edit: REW was indispensable for this. I would have used these not knowing about the questionable results here. It may be that I would not have heard a difference, but given the levels it's very possible. There was no indication that these had been returns to Amazon by someone else, the packaging all appeared new.

10dB worse on THD+N for one of them - 5dB worse on the other. That is not good at all.

How many times did you repeat the test (including interconnect set up) to discount run to run variations.

 

[DavidR]

10dB worse on THD+N for one of them - 5dB worse on the other. That is not good at all.

How many times did you repeat the test (including interconnect set up) to discount run to run variations.

I substituted them twice each in my rig, but there's no interconnect setup or movement other than what it takes to disconnect one and connect the other one at the amp, I wanted to ensure that I didn't have the problem like what you suggest. The only cabling changes are power, banana plugs and XLR cable at the amp. I made sure to not move or change anything else, REW as well. Amp substitution was the only change and I only turned on the REW generator and the RTA each time, no other actions. I did run the RTA several times each and checked to be sure all connections and REW settings were good. As a sanity check I put the original one back in. The measurement results were nearly identical to those just before I substituted the new ones.

One of the new ones has HD2 that is ~15dB worse than the original while the other one is ~20dB worse. HD2 and HD3 are the what I focus on, but interesting that the noise measurements are within 0.1dB for all three and the odd-order harmonics are within a typical range of run-to-run, so that gives me some confidence that the measurements are accurate (for the hardware and settings I was using).

 

[antcollinet]

I substituted them twice each in my rig, but there's no interconnect setup or movement other than what it takes to disconnect one and connect the other one at the amp, I wanted to ensure that I didn't have the problem like what you suggest. The only cabling changes are power, banana plugs and XLR cable at the amp. I made sure to not move or change anything else, REW as well. Amp substitution was the only change and I only turned on the REW generator and the RTA each time, no other actions. I did run the RTA several times each and checked to be sure all connections and REW settings were good. As a sanity check I put the original one back in. The measurement results were nearly identical to those just before I substituted the new ones.

One of the new ones has HD2 that is ~15dB worse than the original while the other one is ~20dB worse. HD2 and HD3 are the what I focus on, but interesting that the noise measurements are within 0.1dB for all three and the odd-order harmonics are within a typical range of run-to-run, so that gives me some confidence that the measurements are accurate (for the hardware and settings I was using).

Perfect answer - thanks. I wonder what they have changed in the design or BOM to create this stark difference.

@Fosi Audio - are you able to comment?

 

[DavidR]

Perfect answer - thanks. I wonder what they have changed in the design or BOM to create this stark difference.

The one difference (other than the label differences between the two that I noted earlier) is that these two have the change to the unbalanced input gains, 25/19 vs 31/25 on my original. That shouldn't affect the XLR input, I would think.

 

[antcollinet]

The one difference (other than the label differences between the two that I noted earlier) is that these two have the change to the unbalanced input gains, 25/19 vs 31/25 on my original. That shouldn't affect the XLR input, I would think.

Nor would it hit distortion - and if anything it should lower noise on the unbalanced inputs.

 

[Jorj]

Sorry to hear but mine got a few unavoidable issues sooner and made me stop using them then.
Part of me isn’t surprised seeing such issues looking at too compact no-ventilation case for 48v operation (not just limited to v3 mono).

What do you mean by “matched pair”? I don’t think they do match a pair of amps to sell, and don’t think it’s necessary as well.
Setting the same gain on both units is all that matters.

As others stated, they changed the design of the V3 and told me that they are sending me a new version with different gain settings. I also know that others objected to this change and Fosi did send them a new pair.

As I stated in the review thread, be sure you don't do what I did; don't order direct. They ship cut-rate and have no control with their delivery services. Amazon is the way, at least for US customers.

 

[djlotfi]

Hello everyone

Do these differences affect both RCA and XLR inputs or RCA only ?

 

[Stoutblock]

Hello everyone

Do these differences affect both RCA and XLR inputs or RCA only ?

I asked that same question back in March and not sure I ever got an answer?