Fosi Audio V3 Amplifier Review

[early rejecter]

Current testing suggests that when volume is raised on the V3, it does not increase volume on the subwoofer. I have to manually calibrate both, correct? I also powered off the V3; the pre-out still sends the signal to the subwoofer.

Is your V3 new, or did you purchase secondhand? On the original run the “pre-out” actually acted as a fixed line out, bypassing the volume control. In response to the outcry this was supposedly corrected in later production units with what Fosi somewhat amusingly called an “enhanced pre-out.” If yours has the older setup you’ll want to control volume before the signal hits the V3 so you don’t have to adjust your subwoofer manually.

And yes on those early units the “pre-out” would pass a signal whether or not the amp was powered on.

 

[Zek]

And yes on those early units the “pre-out” would pass a signal whether or not the amp was powered on.

Because that "pre out" is actually directly connected in parallel to the input connectors and can also be used as an additional input signal.

 

[HighFutility]

Is your V3 new, or did you purchase secondhand? On the original run the “pre-out” actually acted as a fixed line out, bypassing the volume control. In response to the outcry this was supposedly corrected in later production units with what Fosi somewhat amusingly called an “enhanced pre-out.” If yours has the older setup you’ll want to control volume before the signal hits the V3 so you don’t have to adjust your subwoofer manually.

And yes on those early units the “pre-out” would pass a signal whether or not the amp was powered on.

I bought it from Amazon on April 8th. The seller was Fosi Audio. I should reach out to them.

 

[early rejecter]

I bought it from Amazon on April 8th. The seller was Fosi Audio. I should reach out to them.

Yeah if it’s a new one it shouldn’t have those issues. See here.

 

[HighFutility]

Yeah if it’s a new one it shouldn’t have those issues. See here.

all the fosi v3 on amazon have this disclaimer which I have just now fully read.

Even the Fosi website says the pre-out is not scalable with volume in the manual. It looks like they only sold a limited batch of these 2024 models.

 

[PlasticDoc]

On the 2025-05-30, I received this from Fosi Audio:

"Thank you for your interest in our PFFB-implemented V3 stereo amplifier and your continued support. Our R&D team is indeed working on a new version. In this upcoming upgrade, we’re not only refining the implementation of PFFB technology but also considering improvements in other key areas.

While we don’t have a confirmed release timeline just yet, we typically share early details about our new products on the ASR forum. Please stay tuned there for future updates, and thank you again for your support!"

 

[fedealvarezar]

Is your V3 new, or did you purchase secondhand? On the original run the “pre-out” actually acted as a fixed line out, bypassing the volume control. In response to the outcry this was supposedly corrected in later production units with what Fosi somewhat amusingly called an “enhanced pre-out.” If yours has the older setup you’ll want to control volume before the signal hits the V3 so you don’t have to adjust your subwoofer manually.

And yes on those early units the “pre-out” would pass a signal whether or not the amp was powered on.

I just read this and you made me happy, I bought the fosi v3 48v to feed some feather SS-II 6ohm columns. And I was thinking how I was going to do with my subwoofer.

I bought it on ebay, it hasn't arrived yet, I think I'll have it in a week or two. But if it is as you say, you gave me a joy.

 

[john11]

What do you think of the fosi audio v3 versus its competition the topping B100

 

[mike70]

What do you think of the fosi audio v3 versus its competition the topping B100

if they have enough power for your requirements (considering speakers, room size, sound pressure at listening position) they will be indistinguishable from each other.

buy the one is cheaper / you like / warranty you expect / etc etc ... but the only technical / performance aspect to check in your home is the power needed.
my opinion, based on the measurements we have thanks to Amir

 

[HighFutility]

What do you think of the fosi audio v3 versus its competition the topping B100

the b100 is a mono block not the same thing.

 

[john11]

the b100 is a mono block not the same thing.

Fosi V3 is available as mono version as well, and has the same model number as the stereo version for some strange reason

Fosi Audio V3 Mono Amplifier Review

This is a review and detailed measurements of the Fosi Audio V3 Mono class D amplifier. It was sent to me by the company. The price with the power supply I tested is US $139.99. I must say the concept of a "monoblock" amplifier in such a small size runs foul of any expectation a longtime...

www.audiosciencereview.com

 

[HighFutility]

Fosi V3 is available as mono version as well, and has the same model number as the stereo version for some strange reason

Fosi Audio V3 Mono Amplifier Review

This is a review and detailed measurements of the Fosi Audio V3 Mono class D amplifier. It was sent to me by the company. The price with the power supply I tested is US $139.99. I must say the concept of a "monoblock" amplifier in such a small size runs foul of any expectation a longtime...

www.audiosciencereview.com

Not even semantics, it has mono in the name, stereo vs mono. It 's a different product.

 

[Abdo]

Good morning everyone, I had an old Marantz SR5004, which I always hated, in a separate place at home from my main sound system. This Marantz is very complicated to set up and depends on the TV screen, etc. Anyway, I exchanged it for a Fosi V3, which is now connected to a Cambridge CXN and two Tannoy speakers. I was impressed with the capacity of this little Fosi, in addition to the price, which is really very good. I have some questions, my Fosi came with a 32v power supply, I see that there are two options for a 48v power supply with 5a and 10a. My question is, is it better to change the power supply? Would there be much difference in this change? What do you think? Thanks.

 

[NTK]

Good morning everyone, I had an old Marantz SR5004, which I always hated, in a separate place at home from my main sound system. This Marantz is very complicated to set up and depends on the TV screen, etc. Anyway, I exchanged it for a Fosi V3, which is now connected to a Cambridge CXN and two Tannoy speakers. I was impressed with the capacity of this little Fosi, in addition to the price, which is really very good. I have some questions, my Fosi came with a 32v power supply, I see that there are two options for a 48v power supply with 5a and 10a. My question is, is it better to change the power supply? Would there be much difference in this change? What do you think? Thanks.

The main difference is that you'll increase the max output of the amplifier by more than 2X when going to the 48 V power supply. Compare the solid red curves (32 V PS) to the solid blue curves (48 V PS). The amp may, however, dissipate a little more heat with the 48 V PS.

 

[Abdo]

The main difference is that you'll increase the max output of the amplifier by more than 2X when going to the 48 V power supply. Compare the solid red curves (32 V PS) to the solid blue curves (48 V PS). The amp may, however, dissipate a little more heat with the 48 V PS.

Practically double the power... that's incredible. Now, would the fact that it's 5a or 10a also change? Because Fosi offers a 10th for twice the price...

 

[NTK]

Practically double the power... that's incredible. Now, would the fact that it's 5a or 10a also change? Because Fosi offers a 10th for twice the price...

The output power of class D amplifiers is limited by the power supply voltage (which limits the amplifier output voltage swing), and then the power supply power.

The 48 V 5 A PS, when go by the spec, can output 240 W. Therefore, the amp may not be able to output the 141 W per channel Amir rated continuously. But this situation is not going to happen outside of a lab bench. The amp's thermal design is also not sufficient for very high continuous output, and its thermal protection will (or should) kick in after some time. However, it should not be a problem in actual use, when the amp is well ventilated.

 

[Abdo]

Now another question in the case of the Fosi mono, would it be better to choose to buy two separate ones and have separate sources, or buy the Kit that comes with a single 10A source? What would be more recommended?

 

[NTK]

Now another question in the case of the Fosi mono, would it be better to choose to buy two separate ones and have separate sources, or buy the Kit that comes with a single 10A source? What would be more recommended?

Definitely two separate power supplies. See post:

Fosi Audio V3 Mono Amplifier Review

I am wondering if this amp (or looking for other suggestions) would be a good addition to my setup. I currently use a Denon AVR but it can only power 9 channels and so it is running 7.2.2 but I am looking for a separate amp to get to the 7.2.4 setup that I want. I initially was thinking of...

www.audiosciencereview.com

 

[john11]

Now another question in the case of the Fosi mono, would it be better to choose to buy two separate ones and have separate sources, or buy the Kit that comes with a single 10A source? What would be more recommended?

Fosi say : "We'll provide a bundle including two V3 mono amps and a 48V/10A psu for no more than 260USD. That single 48V/10A psu can power the two sets of v3 mono simultaneously."

 

[motorstereo]

Would the dual power supplies be an improvement at sane-normal listening levels? If so would it be enough to swap out the very convenient single ps with the filter or is it just a barely noticeable change?