Fosi Audio V3 Mono Amplifier Review

[Dave TR3A]

Can anyone please help me understand why, even at max volume, my pair of V3 monos are not very loud?

I am using the 48v 5 amp power supply.

I am using with a Wiim Ultra streamer/DAC (I have checked they it's set to the 2 volt output) and a pair of Neat Petite Classic speakers (nominal impedance of 6 ohms, sensitivity of 87 dB.

On the 25dB gain setting, even with the volume at 100%, it's loud but far from ear splitting. It's better on the 31dB obviously, but I don't understand why it is I have to crank the volume up so far even for moderate listening levels.

When I had a similar concern I found that I had not matched the levels of the components in my audio chain (Bluesound Node -> MiniDSP Flex Eight -> Aiyima A07). I used a multimeter to verify the voltages being output by each component (and an oscilloscope to watch for clipping). What I measured was different from what the manufacturers published (and varied between channels).

I ended up matching the output of one device to the (measured) input sensitivity of the next device. I set all three of my amps (my speakers are tri-amped) at the same level (so that they can output the maximum signal before clipping) and leave the there. I used the MiniDSP to set the parameters (gain, delay, polarity, etc) and EQ for each driver. Having done that I leave it alone. I control the volume of my system via the Bluesound Node.

Properly gain matching my components addressed the problem.

 

[keiron99]

Thanks for the responses. Alas I'm a bit out of my depth here I don't have any test equipment.

Assuming there is no fault with the Wiim or Fosis, and lower volume is just the way it is with the equipment I have, would a more powerful amp/amp with more gain fix the issue? Mindful of what @staticV3 said, would something like AUDIOPHONICS AP300-S500NC Power Amplifier NCore NC502MP (400W at 4 ohms, apparently 25 dB gain) fix the issue?

 

[Dave TR3A]

Thanks for the responses. Alas I'm a bit out of my depth here I don't have any test equipment.

Assuming there is no fault with the Wiim or Fosis, and lower volume is just the way it is with the equipment I have, would a more powerful amp/amp with more gain fix the issue? Mindful of what @staticV3 said, would something like AUDIOPHONICS AP300-S500NC Power Amplifier NCore NC502MP (400W at 4 ohms, apparently 25 dB gain) fix the issue?

A more powerful amp would “kick the can down the road” so that you could get higher volume, but the underlying problem would still be there.

You could buy the necessary test equipment for the cost of that amp (and likely have money left over).

 

[staticV3]

Mindful of what @staticV3 said, would something like AUDIOPHONICS AP300-S500NC Power Amplifier NCore NC502MP (400W at 4 ohms, apparently 25 dB gain) fix the issue?

Same gain -> same volume.

As for the test equipment, all you need is a $10 multimeter from the nearest home improvement store. Nothing special.

 

[jEDGEc0m]

Thanks for the responses. Alas I'm a bit out of my depth here I don't have any test equipment.

Assuming there is no fault with the Wiim or Fosis, and lower volume is just the way it is with the equipment I have, would a more powerful amp/amp with more gain fix the issue? Mindful of what @staticV3 said, would something like AUDIOPHONICS AP300-S500NC Power Amplifier NCore NC502MP (400W at 4 ohms, apparently 25 dB gain) fix the issue?

Do you primarily stream your program material from say, Spotify?

If so, it probably defaults to having volume normalisation enabled - depending on what kind of music you listen to, spotify might be turning it down quite a lot - and you maybe can get some free volume back by changing that setting. Though looks like that might only increase it by 3dB on the "Loud" setting.

But bearing in mind that 3dB of volume increase requires double the amp wattage, it's not insignificant.

I don't know if it has the option to turn off normalisation entirely (I don't use Spotify) - with loud masters being the norm in many genres, that might get you a bunch more dB of gain.

Could be a way to get some more volume with the equipment you have.

Loudness normalization on Spotify - Spotify

support.spotify.com

But if you can get loud enough, even if you're near 100% volume on the source, maybe you don't have a problem that needs to be addressed?

I was at someone's place listening to their system with a recent WiiM Ultra and what I think is probably a pretty powerful older big Rotel power amp - and being older, it probably has higher gain too - we were listening loudish (Would guess ~80-85dB A-weighted), and was about 75 on the WiiM dial, from memory, in a room probably like a master bedroom size. But perhaps like you, I sort of thought there'd be more volume. Spotify normalisation was most likely on its normal -14LUFS setting.

 

[Blew]

Check the voltage output of the interface. If it is 4v or less I wouldn’t worry.

The MOTU M4 manual specifies the max output voltage as 3.6V and max level out as 16 dBu on the TRS output:

According to ChatGPT, that can still cause issues for the V3 Mono's input:

the manual’s “3.6 V” is almost certainly a peak voltage per leg, not Vrms.


Here’s how the numbers line up.

---

Reconcile​

1) Convert +16 dBu to Vrms (the standard definition)​

dBu is referenced to 0.775 Vrms:

Vrms=0.775×10(16/20)≈4.89 VrmsV_{\mathrm{rms}} = 0.775 \times 10^{(16/20)} \approx 4.89\ \mathrm{Vrms}Vrms=0.775×10(16/20)≈4.89 Vrms
So +16 dBu ≈ 4.89 Vrms (this is the balanced differential “max level out” figure).

---

2) Interpret “Maximum output voltage 3.6 V”​

If 3.6 V were Vrms, the level would not match +16 dBu.


But if 3.6 V is Vpeak per leg (very common in spec tables), then:

Vrms,per leg=Vpeak2=3.61.414≈2.55 VrmsV_{\mathrm{rms, per\ leg}} = \frac{V_{\mathrm{peak}}}{\sqrt{2}} = \frac{3.6}{1.414} \approx 2.55\ \mathrm{Vrms}Vrms,per leg=2Vpeak=1.4143.6≈2.55 Vrms
Balanced differential (tip-hot, opposite polarity on ring) is ~double in Vrms:

Vrms,diff≈2×2.55=5.10 VrmsV_{\mathrm{rms, diff}} \approx 2 \times 2.55 = 5.10\ \mathrm{Vrms}Vrms,diff≈2×2.55=5.10 Vrms
Convert that back to dBu:

20log⁡10(5.10/0.775)≈16.4 dBu20\log_{10}(5.10/0.775) \approx 16.4\ \mathrm{dBu}20log10(5.10/0.775)≈16.4 dBu
That matches the +16 dBu spec perfectly (within normal rounding).


So the consistent interpretation is:

• 3.6 V = peak voltage per leg
• +16 dBu = max differential level (Vrms)

---

What this means for your V3 Mono safety math​

It means your “0 dBFS = ~4.9 Vrms” estimate is basically correct; if anything it’s closer to ~5.1 Vrms differential at the absolute max.


So your previous safety ceilings don’t change materially — you’re in the right ballpark.

---

Practical takeaway​

• The M4 can deliver ~5 Vrms balanced at the top end.
• The V3 Mono XLR input clips lower than that.

So, I have reduced gain in my system by 6dB to account for this.
Any thoughts?
@igfarm

 

[staticV3]

The MOTU M4 manual specifies the max output voltage as 3.6V and max level out as 16 dBu on the TRS output:
View attachment 503265

According to ChatGPT, that can still cause issues for the V3 Mono's input:



So, I have reduced gain in my system by 6dB to account for this.
Any thoughts?
@igfarm

The V3 Mono's output clips, when fed with >3Vrms Balanced input.

Though as long as you have a volume control somewhere and know to stop pushing once you hear the Amp distorting, you don't have to worry about your DAC's output voltage or matching voltages.

 

[TurtlePaul]

So, I have reduced gain in my system by 6dB to account for this.
Any thoughts?
@igfarm

You are over thinking this. Just set the volume to be a comfortable listening level. As long as you have enough gain and power, don’t worry about it.

 

[Blew]

The V3 Mono's output clips, when fed with >3Vrms Balanced input.

Though as long as you have a volume control somewhere and know to stop pushing once you hear the Amp distorting, you don't have to worry about your DAC's output voltage or matching voltages.

In this system the volume control is in the digital domain (CamillaDSP) before outputting to the MOTU M4 DAC. The speakers are also small and inefficient 8-ohms, and the room is large. I started investigating this after I noticed the clipping at relatively high volume. I prefer a maximum volume limit in place to prevent the MOTU M4 output volume from overdriving the V3 Mono.

 

[mike70]

In this system the volume control is in the digital domain (CamillaDSP) before outputting to the MOTU M4 DAC. The speakers are also small and inefficient 8-ohms, and the room is large. I started investigating this after I noticed the clipping at relatively high volume. I prefer a maximum volume limit in place to prevent the MOTU M4 output volume from overdriving the V3 Mono.

You can buy pro attenuators... that limits the input.

 

[peng]

In this system the volume control is in the digital domain (CamillaDSP) before outputting to the MOTU M4 DAC. The speakers are also small and inefficient 8-ohms, and the room is large. I started investigating this after I noticed the clipping at relatively high volume. I prefer a maximum volume limit in place to prevent the MOTU M4 output volume from overdriving the V3 Mono.

Have you estimated, or calculated your amplifier output requirements for your use case yet? If not, then your concern may or may not be relevant at all. For example, the V3 Mono was measured about 190 W, 4 ohms at the knee point, the gain of the amp is 20 dB, so it needs about 2.75 V to reach that point.

If you turn the volume high enough, power amps, especially the mini types such as the V3 Mono will of course clip. You can set a limit somewhere, some way, but then how about the input further up stream, even the source content, can still push your MOTU or something else in the signal path to clip anyway.

 

[beaker152]

i received the pair bundle with the 48V/10A power supply and the DC filter yesterday and enjoyed listening to my system for several hours. when i turned off my preamp, i put my hand on top of one to see how warm it was and heard an odd sound from the connected speaker. this morning i found that the LEDs were still on (then read in the manual that the units go into standby mode after 10 minutes of no signal rather than powering down) and were pretty warm. i then flipped both amps to off—all fine. turned one amp on and heard the noise again. turned the other amp on and the noise stopped. turned the first amp off and then heard the noise from the other speaker.

sitting here quietly as i type, i heard the left amp click (to go into standby?) and heard the noise from the right channel, then the amp clicked again (out of standby?) and the noise stopped (happened 3 times now typing this)

as an experiment, i tried unplugging one of the amps from the filter instead of just turning it off and the noise was no longer present. plugging it back in and turning jt off with the switch then led to the noise again.

tried to attach a recording of the noise but was unsuccessful—but you know that low frequency sound you sometimes get when driving with one window down as the vortex wobbles in/out of the car? it sounds like that…
sort of like a low budget sound effect for a ufo…

a few questions:
is the DC filter that splits the power to both amps is the culprit?

is this design behavior?

should the amps be drawing enough current in standby mode to be warm to the touch after several hours?

are sound/video files disallowed as attachments?

thanks!

p.s.
@Fosi Audio
@MajorTom

 

[NTK]

i received the pair bundle with the 48V/10A power supply and the DC filter yesterday and enjoyed listening to my system for several hours. when i turned off my preamp, i put my hand on top of one to see how warm it was and heard an odd sound from the connected speaker. this morning i found that the LEDs were still on (then read in the manual that the units go into standby mode after 10 minutes of no signal rather than powering down) and were pretty warm. i then flipped both amps to off—all fine. turned one amp on and heard the noise again. turned the other amp on and the noise stopped. turned the first amp off and then heard the noise from the other speaker.

sitting here quietly as i type, i heard the left amp click (to go into standby?) and heard the noise from the right channel, then the amp clicked again (out of standby?) and the noise stopped (happened 3 times now typing this)

as an experiment, i tried unplugging one of the amps from the filter instead of just turning it off and the noise was no longer present. plugging it back in and turning jt off with the switch then led to the noise again.

tried to attach a recording of the noise but was unsuccessful—but you know that low frequency sound you sometimes get when driving with one window down as the vortex wobbles in/out of the car? it sounds like that…
sort of like a low budget sound effect for a ufo…

a few questions:
is the DC filter that splits the power to both amps is the culprit?

is this design behavior?

should the amps be drawing enough current in standby mode to be warm to the touch after several hours?

are sound/video files disallowed as attachments?

thanks!

p.s.
@Fosi Audio
@MajorTom

TI does not recommend sharing the same power supply between multiple TPA amplifier chips without synchronizing their oscillators, which obviously is not being done here.

 

[peng]

a few questions:
is the DC filter that splits the power to both amps is the culprit?

is this design behavior?

I think the filter might help reducing the noise but if you have one amp on and the other off, you will get noise from the one (the speaker) that is on, at least that's my understanding. Are you using RCA of XLR? If RCA, you may want to try XLR.

should the amps be drawing enough current in standby mode to be warm to the touch after several hours?

I found that if I left the switch in "on" it could get quite warm. In Auto, it is supposed to go into standby after 10 minutes (if I remember right), and it would stay cool.

Archimago recorded the noise, just take a listen and see if yours sounded similar:

Part I: Fosi Audio V3 Mono Amp; Class D + PFFB, TI TPA3255 - Retail box with single 48V/10A power supply and filter. [With initial measurements.]

A blog for audiophiles about more objective topics. Measurements of audio gear. Reasonable, realistic, no snakeoil assessment of sound, and equipment.

archimago.blogspot.com

 

[keiron99]

Do you primarily stream your program material from say, Spotify?

No I don't have spotify. I stream from files stored on a hard disk attached to my computer, using the wifi network.

I downloaded a decibel meter app on my iPhone. I have no idea how accurate these are. But as a test I just played Rush's Tom Sawyer and had the amp on 100%. It registered about 74dB on the meter. I would have liked to have listened at a louder volume.

I'm rather stuck as to know what the solution is. May look at getting a test meter but seems daft just to test the output of my Wiim.

 

[beaker152]

I think the filter might help reducing the noise but if you have one amp on and the other off, you will get noise from the one (the speaker) that is on, at least that's my understanding. Are you using RCA of XLR? If RCA, you may want to try XLR.

I found that if I left the switch in "on" it could get quite warm. In Auto, it is supposed to go into standby after 10 minutes (if I remember right), and it would stay cool.

Archimago recorded the noise, just take a listen and see if yours sounded similar:

Part I: Fosi Audio V3 Mono Amp; Class D + PFFB, TI TPA3255 - Retail box with single 48V/10A power supply and filter. [With initial measurements.]

A blog for audiophiles about more objective topics. Measurements of audio gear. Reasonable, realistic, no snakeoil assessment of sound, and equipment.

archimago.blogspot.com

i’m using a fosi p4 preamp, so XLR isn’t available, just RCA.

archimago’s recording of the noise sounds a bit different than what i heard, but the cause seems to be the same.

i purchased from the online river place, and will be returning the bundle i got and have ordered two of the single amp/45V 5A bundles instead.


i don’t believe hardware should require workarounds for proper performance, so i am somewhat disappointed at what seems to be a basic problem, but i get that it’s early in their product cycle and i’m happy enough with the rest of it to not give up yet.

 

[jEDGEc0m]

No I don't have spotify. I stream from files stored on a hard disk attached to my computer, using the wifi network.

I downloaded a decibel meter app on my iPhone. I have no idea how accurate these are. But as a test I just played Rush's Tom Sawyer and had the amp on 100%. It registered about 74dB on the meter. I would have liked to have listened at a louder volume.

I'm rather stuck as to know what the solution is. May look at getting a test meter but seems daft just to test the output of my Wiim.

Some Rush Moving Pictures masters are certainly not "Loud" digital audio, but if that dB app is even close, yeah, 74dB seems far too weak, and bottom line is that you are at max, and you want more volume - and really seems the Fosi V3 mono pair should be providing quite a lot, given a suitable signal - which the WiiM should be ok for.

My source is a recording type audio interface, which can have a strong line out - but I get loud enough well before the audio interface is nearing its full output.

Hmm. Curious. I don't know what might be going wrong. It certainly doesn't sound right.

 

[peng]

i’m using a fosi p4 preamp, so XLR isn’t available, just RCA.

archimago’s recording of the noise sounds a bit different than what i heard, but the cause seems to be the same.

i purchased from the online river place, and will be returning the bundle i got and have ordered two of the single amp/45V 5A bundles instead.


i don’t believe hardware should require workarounds for proper performance, so i am somewhat disappointed at what seems to be a basic problem, but i get that it’s early in their product cycle and i’m happy enough with the rest of it to not give up yet.

Mine came with two 48 V 5 A bricks, no issue at all.

 

[keiron99]

Hmm. Curious. I don't know what might be going wrong. It certainly doesn't sound right.

I have now ordered a Wiim Amp Ultra. Out of desperation really (and in any case, it gets good reviews here). It will be interesting to compare. I can always send it back anyway.

 

[jEDGEc0m]

I have now ordered a Wiim Amp Ultra. Out of desperation really (and in any case, it gets good reviews here). It will be interesting to compare. I can always send it back anyway.

Should be a really nice single box solution. Hopefully you find enough volume. Still seems weird such a lack of dB from wiim streamer + v3 mono. Good luck. Keep us posted.