Fosi v3 Mono - User Impressions | Owner's Thread

[SMen]

New poster here, after reading a lot. I have received the package with two V3 Monos, the 10A power supply and the filter.

I am quite disappointed, I got a hum in the lower/middle frequencies, despite the filter. It vanishes if I pull out one power cable from one amp.

I am driving Wharfdale Diamond 12.2s, using a Wiim Pro Plus as input. The bass is very lean compared to the Alesis RA 150 poweramp I used before and am now using again. I will return them. The sound is very transparent, but it simply lacks bass. The Alesis is much more powerful in producing bass frequencies. Well, this is all subjective of course, but personally I do not think the amps live up to the hype.

What you are describing sounds like a fault or something with the set up. I have no hum with or without the filter when both are plugged in, and lots of drive (including the bass).

 

[whit]

I am driving Wharfdale Diamond 12.2s, using a Wiim Pro Plus as input. The bass is very lean compared to the Alesis RA 150 poweramp I used before and am now using again. I will return them. The sound is very transparent, but it simply lacks bass. The Alesis is much more powerful in producing bass frequencies.

That Alesis was marketed for recording studios, where the design standards differ from hi-fi. Someone using a low-priced studio amp is likely to pair it with low-priced studio monitors, small speakers where a bass boost from the amp is a good thing. In hi-fi, the design goal for power amps is to have them flat across the frequency spectrum.

 

[voidhawk]

I need to correct myself, I just saw I mistyped something yesterday, the speakers are Wharfedale 12.4s, floorstanders. Sorry for the confusion.

I also have an Aiyima A70 for my desktop setup with Magnat Quantum 603s and an active subwoofer. Tried the A70 (which sounds amazing in the desktop scenario btw) with the 12.4s and there was a lot more bass than with the Monos.

I'll check the Monos once again, maybe I set them up wrongly, though I can't imagine where I've gone wrong.

 

[Borland]

Mindset?

 

[voidhawk]

No, just wrong connections, phase problem... Now they sound as they should. BTW, the Alesis is quite linear. I would not dismiss it so easily, you can get these things for a small buck second hand. Paid 70 € for it (Germany).

The bass output of the Monos is roughly the same now, seems more controlled though. The slight humming if both amps are connected via the splitter is still there, but I'll tackle that later.

 

[voidhawk]

I just listened to the Berlin Concert by John Williams and the "Berliner Philharmonie"... Superb dynamics . I stand corrected. These amps are very good for the money.

 

[martinus]

My V3 mono with attached heat sink using a 2mm thermal pads and turn to vertical ventilation. Looks ridiculous but cool enough.

my solution..

 

[CReeDeR]

I finally got my two monos the day before yesterday. I had pre-ordered them directly from Fosi at the end of July, including a more powerful power supply and the filter. In the end, I still connected them with two individual 48V 5A GaN power supplies from Fosi (one of which I already had for my V3 Stereo).

They are connected via XLR for stereo to a Topping DX5, which receives the music from a WiiM Pro Plus via Tidal and my NAS. For home cinema, the monos are also connected via RCA to the pre out of a Marantz AVR.

I'm delighted with the sound. It feels like a further improvement on the V3 Stereo, which doesn't sound bad either.

Yes, they get warm. But not unpleasant. You can put your hand on them without any problems. They just feel just as warm as the Marantz (I haven't measured the temperature yet). And the Marantz has been doing this for years without any problems.

The phases also seem to be correct. Although the monos only have one sticker on the underside. I also contacted FosiAudio again beforehand because the dispatch had been delayed until the end of August. In response, I was told that the delay was due to the phase problem, but that I would receive a device without this problem.
I checked the phase when listening via the AVR in combination with my subwoofer and the other speakers. I also tested the phase via a test app on my iPad using test tones.

So far, I am completely satisfied. The only thing I don't know yet is that my monos don't switch on at exactly the same time in 'Auto' mode. The right amplifier already starts together with the Marantz. The left amplifier only switches on, as it should, when a signal is being played. They switch off at the same time. I'm already thinking about plugging the two monos into a smart plug to switch them on and off. Automation is helpful for me because I am a wheelchair user.

 

[nitpicker0]

Would be interesting to learn what ways other people choose to automate amps on last/off first, in general, not just with V3.

 

[vuittion]

I returned my Fosi v3 Mono's a while back (wasn't a fan). I purchased a Topping PA7 Plus in mint condition for £270 (Bargain).

I'm now a believer that not all Class D amps sound the same. It plays on a completely different level to the Mono's.

 

[Jon L]

I returned my Fosi v3 Mono's a while back (wasn't a fan). I purchased a Topping PA7 Plus in mint condition for £270 (Bargain).

I'm now a believer that not all Class D amps sound the same. It plays on a completely different level to the Mono's.

In what way does it sound better than Fosi?

 

[Rafaille]

I am confident it is in an objective, unbiased, and measurable way. Is it not?

 

[SamuV]

I'm typically running 3-way active (DIY = needs 6 amplifier channels - I build speaker prototypes as hobby so I switch almost every month, sometimes I have 4-way and sometimes 2-way, but mostly 3-way). And always 4 separate subs (4 channels) for getting good bass in my difficult room. I needed to replace my 4-channel subwoofer amplifier and decided to move two of my main amplifiers (Behringer A800) to subwoofer duty, and get new 4 channels of amplification for mids and tweeters.

I ordered pair of Fosi V3 Mono (both with their own 48V 5A) for testing at mid August from Soundimports.eu. They came 2 days later. I tested the Fosis and they seemed great. So I ordered two more (again with their own 48V 5A) beginning of this month, and they came few days later as well. All 4 amps have two quality stickers at bottom. Seeing here (and other places) how much misery some people have caused themselves pre-ordering etc. I'm happy that they are now available via "normal stores", so ordering and returns are easy.

Already with just two Fosi V3 Mono I found out that they create more heat than 3pcs of Behringer A800 (according to Amir's test 142w@8ohm or 241w@4ohm = similar power as pair of Fosi V3 Mono). So I duplicated amplifier cabinet "inflow" fans from one 120mm to two 120mm fans, which seemed to compensate.

Without active cooling outside amplifier cabinet with 15mm rise from the surface the Fosis did heat up about Δ16°C [Δ28.8°F] above the room temperature (I don't have AC, so my room temperature is around 24-25°C [75.2-77.0°F] => Fosi 40-41°C [104-105.8°F]).

In amplifier cabinet the Fosi surface temperature with active cooling is Δ10-11°C [Δ18-19.8°F] above room temperature. Playing music at sound pressure levels I use did not have ANY effect to Fosi temperature, they get same surface temperature just by having them turned on. I quess if I would use Fosi for subwoofers and have session of loud listening they get hotter, but I plan to use them for mids and tweeters => they rarely need to produce over 1w. I used 15mm risers (some random plastic cable holder, need to 3D print permanent solution for this) below bottom Fosi and between two Fosis in each "stack". Without the 15mm airspace below and between Fosis they did get significantly hotter (over Δ10°C [18°F] hotter), so I would never stack them without some spacers.

I would have appreciated internal power source, but I managed to fit the powerbricks into my "snake's nest". Powerbricks do not heat up, at least not in my use. I have temporarily subwoofer's DSP connected to subwoofer amps with RCAs, and the power cables pass the RCAs and there has been no extra noises from subwoofers.

With Behringers I never used their power buttons, I just switched them on and off using the switch in extension cord. They have good protection against power loss and immediately shut down the sound to speakers when power is lost. This does not seem to be the case with Fosi V3 Mono. When I was testing the first pair of Fosis I accidentally switched off the amplifier extension cord while music was playing - this resulted >100dB "pop and scratchy noise" from midrange drivers Fosis was connected. If Fosis would have been connected to tweeters, they would have been destroyed. So I started shutting down the amps manually from their power switches. But if there is power outage this could happen again - luckily we have them only ~once in every 5 years. This is not significant if I would be using passive speakers, but I use the amps to drive individual drivers in active speaker system without any filters. I guess I'll need to start considering to add some large ~30µF "protection" capacitor for my tweeters.


Subjectively:
I tested Fosi V3 mono in all duties except full range, I don't have any passive speakers to test with... As subwoofer amplifier I could not detect any difference compared to my old subwoofer amp (Behringer NX4-6000) or Behringer A800. As midbase amplifiers A800 and Fosi both sounded the same. As midrange amp there was small difference (upper mids "sound cleaner and brighter") compared to A800, but most likely I would not be able recognize the difference 100% in ABX test, unless I could find some perfect test track (if even then).

And as tweeter amp I noticed the biggest difference, which I don't understand as according to measurements by Amir both have similar frequency response. And A800 worse signal to noise ratio can't explain the difference (if I push my ear to tweeter there is no "hiss" with Fosi like there is with A800, but with medium sensitivity 89.5db/2.83V tweeters the "hiss" is not strong enough to be heard from listening position). Difference is hard to explain but I would mostly describe it as "sound is brighter and clearer" and I very much prefer Fosi sound for tweeter compared to A800. I mostly noticed this on 2500-5000Hz range e.g. higher notes of guitar. I did near field measurement of tweeter with A800 and Fosis and the frequency and impulse responses were exactly same, so from frequency response point of view there was no difference.

As this didn't make much sense I switched tweeter amplifier multiple times and it seemed to be very easy to hear, but comparing was difficult as switching the amps took 10min. So I changed DSPs crossover by removing midbasses (freeing up one A800 for comparisons) and changed midrange highpass from 300Hz to 80Hz (not ideal for 4" driver but it can do it). And sent tweeter signal to one pair of Fosis and A800, and naturally I did level matched based on output voltage so both amps were as loud. Now I could switch amplifier just by removing the tweeter Speakon connector and replacing with another, this takes only ~20 seconds, but requires moving from listening position. This made it possible to do blind test by having other person to do the Speakon change - I was able to recognize blind Fosi vs A800 5 out of 5 times when used as tweeter amplifier (tweeter: Scan-Speak D3004/602010 with 2.5kHz Bessel 12db/oct high pass).

Before getting Fosi I had assumed that all digital amplifiers sound more or less the same, but some have frequency response issues based on load of the speaker (e.g. Fosi stereo versions have this issue). I purchased the Behringers 2019 and I had never compared A800 to any other digital amplifier, just to old AB-class amps and to me A800 didn't sound worse (back then digital had bad reputation and I wanted to make sure I'm not getting worse amplifiers than my old AB-class). This leaves me little confused, but happy as I like the sound Fosi produces.

 

[NoMoFoNo]

As an owner of the V3 I find comments about rising load-dependent response and its audibility unconvincing. Go back and look at the charts and you'll see that the rise is very small and I would doubt that most, perhaps any, listeners would be able to ID that load-dependency in any kind of blind test. I'm happy that these companies (Fosi and AIyima at this point) are implementing PFFB at these very low price points and I'll likely wind up with a pair of the V3 monos at some point. However, when discussions veer into being able to hear the difference in these chip amps my audiophool alarm starts ringing.

 

[SamuV]

As an owner of the V3 I find comments about rising load-dependent response and its audibility unconvincing. Go back and look at the charts and you'll see that the rise is very small and I would doubt that most, perhaps any, listeners would be able to ID that load-dependency in any kind of blind test. I'm happy that these companies (Fosi and AIyima at this point) are implementing PFFB at these very low price points and I'll likely wind up with a pair of the V3 monos at some point. However, when discussions veer into being able to hear the difference in these chip amps my audiophool alarm starts ringing.

Sorry that your feelings got hurt... I did not see in last few pages any comments about load dependency, so I assume your feelings got hurt by me referring to load dependency in the last paragraph "...but some have frequency response issues based on load of the speaker (e.g. Fosi stereo versions have this issue)"

Seems you are inventing things inside your head, which I did not write. So in future before you hurt your own feelings with your false assumptions, you may want to read twice before you invent what somebody else wrote.
1) There was no claim of "audibility" of rising load-dependent response, that is 100% your imagination. I was just referring to known measured frequency response issues. You made the conclusion in your head that frequence response issue are "audible", for that I can't help. Some people on various forums has been "worried" about this "issue", most likely majority of those people complain about it who don't own the V3 stereo amp and have never heard similar behaviour (and if they would most likely they would not be able to recognize it like you say) - such is internet... must be hard if you interpret every discussion where your loved amp is mentioned negatively, but I kind of understand your negative bias because these forums are full of people whom negatively comment issues which they have no connection (=don't own equipment in question) and/or no experience/knowledge of discussed topic/product.
2) About "being able to hear the difference in these chip amps"; I don't know of what is your definition of "chip amp", I would assume Behringer A800 (rack mountable 2U size PA-amplifier from 2018) is most likely not what is called as "chip amp"? Compared to Fosi the A800 electronics looks totally different and the main board has ~10x area compared to Fosi and has ~10x more components - also A800 don't look like to have one central chip doing everything like in Fosi (but I'm not electrician). I have never compared or even listened properly any other digital amplifers than these two mentioned and therefore I would not be able to claim any differences of your V3 stereo or whatever your "chip amps" are.


PS. If I would make any audibility claim of 2.8 dB peak at 40kHz (what I eyeballed from Amir's V3 stereo review for 8ohm), I would assume I would say "not audible". But I don't have any such amp so I can't test is it "audible" and therefore I simply won't claim "audible" or "not audible". In general I would avoid making claims is something "audible" without personal experience (why would anyone do that?). If I would have the V3 stereo (or other amp with similar behaviour) I would test the "audibility" with real world tweeter, which impedance raises above 20ohm at 20kHz (e.g. most 8ohm tweeters with only serial resistor for attenuation or 16ohm compression driver with medium to high inductance), which still most likely would not make it "audible", but peak would be higher and spreads therefore more to lower frequencies making it little more possible hearing it. I hope it's understood by everyone that Amir's measurement were using few predefined impedances and in real world 8ohm is not some magical maximum value, and the frequency response peak is relevant to how high the impedance is at high frequencies. With this kind of amp using 4ohm tweeter and L-pad instead of just serial resistor are good ways to mitigate whole issue (if there even is any issue) OR if one uses commercial speakers select one where impedance doesn't raise towards 20kHz. For me the issue would be trivial; I always measure and EQ my speakers during the design and build process of speaker, and if there would be excessive peak at 20kHz in measure speaker response it would be corrected. So I'm personally neither worried or interested about this load-depent frequency response issue.

I'm happy that these companies (Fosi and AIyima at this point) are implementing PFFB at these very low price points

Me too, not only PFFB but them bringing in general the amplifier prices down. Last time (in 2018/9) when I was searching amplifiers the selection was non-existent for not-too-expensive amplifiers with symmetric XLR/TRS input and digital amplification (I had earlier 5pcs 2 channel AB-class PA amplifiers, the generated heat was just too much to bear even at winter). There basically was nothing else decent and not-too-expensive than Behringer A800 available and I more or less had to chose the A800 for my main amplifier model at 2019. Now because of competition we have plenty of selection on these "small enclosure + power brick" D-class amplifiers.

 

[antcollinet]

Sorry that your feelings got hurt...

Please leave that sort of mocking nonsense (and all the rest of it in your post) out of it. This is not the place. This is not how we discuss.

 

[centonom]

I'm typically running 3-way active (DIY = needs 6 amplifier channels - I build speaker prototypes as hobby so I switch almost every month, sometimes I have 4-way and sometimes 2-way, but mostly 3-way). And always 4 separate subs (4 channels) for getting good bass in my difficult room. I needed to replace my 4-channel subwoofer amplifier and decided to move two of my main amplifiers (Behringer A800) to subwoofer duty, and get new 4 channels of amplification for mids and tweeters.

I ordered pair of Fosi V3 Mono (both with their own 48V 5A) for testing at mid August from Soundimports.eu. They came 2 days later. I tested the Fosis and they seemed great. So I ordered two more (again with their own 48V 5A) beginning of this month, and they came few days later as well. All 4 amps have two quality stickers at bottom. Seeing here (and other places) how much misery some people have caused themselves pre-ordering etc. I'm happy that they are now available via "normal stores", so ordering and returns are easy.

Already with just two Fosi V3 Mono I found out that they create more heat than 3pcs of Behringer A800 (according to Amir's test 142w@8ohm or 241w@4ohm = similar power as pair of Fosi V3 Mono). So I duplicated amplifier cabinet "inflow" fans from one 120mm to two 120mm fans, which seemed to compensate.

Without active cooling outside amplifier cabinet with 15mm rise from the surface the Fosis did heat up about Δ16°C [Δ28.8°F] above the room temperature (I don't have AC, so my room temperature is around 24-25°C [75.2-77.0°F] => Fosi 40-41°C [104-105.8°F]).



View attachment 392174

In amplifier cabinet the Fosi surface temperature with active cooling is Δ10-11°C [Δ18-19.8°F] above room temperature. Playing music at sound pressure levels I use did not have ANY effect to Fosi temperature, they get same surface temperature just by having them turned on. I quess if I would use Fosi for subwoofers and have session of loud listening they get hotter, but I plan to use them for mids and tweeters => they rarely need to produce over 1w. I used 15mm risers (some random plastic cable holder, need to 3D print permanent solution for this) below bottom Fosi and between two Fosis in each "stack". Without the 15mm airspace below and between Fosis they did get significantly hotter (over Δ10°C [18°F] hotter), so I would never stack them without some spacers.



View attachment 392175

I would have appreciated internal power source, but I managed to fit the powerbricks into my "snake's nest". Powerbricks do not heat up, at least not in my use. I have temporarily subwoofer's DSP connected to subwoofer amps with RCAs, and the power cables pass the RCAs and there has been no extra noises from subwoofers.

With Behringers I never used their power buttons, I just switched them on and off using the switch in extension cord. They have good protection against power loss and immediately shut down the sound to speakers when power is lost. This does not seem to be the case with Fosi V3 Mono. When I was testing the first pair of Fosis I accidentally switched off the amplifier extension cord while music was playing - this resulted >100dB "pop and scratchy noise" from midrange drivers Fosis was connected. If Fosis would have been connected to tweeters, they would have been destroyed. So I started shutting down the amps manually from their power switches. But if there is power outage this could happen again - luckily we have them only ~once in every 5 years. This is not significant if I would be using passive speakers, but I use the amps to drive individual drivers in active speaker system without any filters. I guess I'll need to start considering to add some large ~30µF "protection" capacitor for my tweeters.


Subjectively:
I tested Fosi V3 mono in all duties except full range, I don't have any passive speakers to test with... As subwoofer amplifier I could not detect any difference compared to my old subwoofer amp (Behringer NX4-6000) or Behringer A800. As midbase amplifiers A800 and Fosi both sounded the same. As midrange amp there was small difference (upper mids "sound cleaner and brighter") compared to A800, but most likely I would not be able recognize the difference 100% in ABX test, unless I could find some perfect test track (if even then).

And as tweeter amp I noticed the biggest difference, which I don't understand as according to measurements by Amir both have similar frequency response. And A800 worse signal to noise ratio can't explain the difference (if I push my ear to tweeter there is no "hiss" with Fosi like there is with A800, but with medium sensitivity 89.5db/2.83V tweeters the "hiss" is not strong enough to be heard from listening position). Difference is hard to explain but I would mostly describe it as "sound is brighter and clearer" and I very much prefer Fosi sound for tweeter compared to A800. I mostly noticed this on 2500-5000Hz range e.g. higher notes of guitar. I did near field measurement of tweeter with A800 and Fosis and the frequency and impulse responses were exactly same, so from frequency response point of view there was no difference.

As this didn't make much sense I switched tweeter amplifier multiple times and it seemed to be very easy to hear, but comparing was difficult as switching the amps took 10min. So I changed DSPs crossover by removing midbasses (freeing up one A800 for comparisons) and changed midrange highpass from 300Hz to 80Hz (not ideal for 4" driver but it can do it). And sent tweeter signal to one pair of Fosis and A800, and naturally I did level matched based on output voltage so both amps were as loud. Now I could switch amplifier just by removing the tweeter Speakon connector and replacing with another, this takes only ~20 seconds, but requires moving from listening position. This made it possible to do blind test by having other person to do the Speakon change - I was able to recognize blind Fosi vs A800 5 out of 5 times when used as tweeter amplifier (tweeter: Scan-Speak D3004/602010 with 2.5kHz Bessel 12db/oct high pass).

Before getting Fosi I had assumed that all digital amplifiers sound more or less the same, but some have frequency response issues based on load of the speaker (e.g. Fosi stereo versions have this issue). I purchased the Behringers 2019 and I had never compared A800 to any other digital amplifier, just to old AB-class amps and to me A800 didn't sound worse (back then digital had bad reputation and I wanted to make sure I'm not getting worse amplifiers than my old AB-class). This leaves me little confused, but happy as I like the sound Fosi produces.

Thanks for sharing your experience with the A800 in comparison to the Fosi Monos in such detail. I’ve needed amps to expand my surround setup and have been debating whether to stick with what I know, the A800, or try the hot new thing. I was especially curious about hiss with the Fosi Mono as the A800 definitely hisses with the inefficient NHTs I have so I appreciate you taking the time to write such a detailed comparison post.

 

[DavidM1]

I'm surprised the chat about Mono V3 temperatures is still going. I'd quite forgotten about it. Currently listening to Emma Kirkby and Jakob Lindberg and enjoying it greatly. Out of curiosity I walked over and felt the amps with the back of my fingers. Slightly warm as expected. The right channel perhaps a tad warmer than the left, as usual. Perhaps it got a bit more thermal paste. The temperature is cooler than the 70w Denon amp we have upstairs in a cabinet that has been on for more than two decades. They are also much cooler than my Mesa guitar amp that has been doing professional duty off and on for more than thirty years.

I offer this entirely meaningless observation as a personal reflection on how weird it is to see people fussing and worrying about amps being warm. I have always assumed it was part of the deal.

 

[RCL162]

I'm hoping these amps are engineered to dissipate heat without needing the fans, but at $12 each it's worth trying. Hopefully the fans will be relegated to the "I might have something to fix that" box after a few weeks of testing. After this wait I'd hate to have to decide on a new product to replace them because of temperature issues.

Just get a Colling pad for laptop. Cheaper $3-$5.

 

[JLB321GO]

After a couple of months of using my v3 Mono's through the XLR inputs, I decided to try them on the RCA's.

Well, through RCA, the volume output of one of the monoblocks is noticeably lower than the other's. Through XLR, they are perfectly well balanced.

Did anybody notice such a situation with their's?