Fosi Audio V3 Mono Amplifier Review

[staticV3]

I measured five minutes ago with the sound level meter, 8dB difference with gain on high...same speakers and same distance

Yup, that just means the Maranz's internal Amp has 8dB more gain than the A5 or about 34dB, which is plausible.

 

[peng]

I measured five minutes ago with the sound level meter, 8dB difference with gain on high...same speakers and same distance

Wish I were there to help troubleshoot, something is not right. Did you use the avr’s tone and a good spl meter, C weighting, and not just a phone app?

You are using preamp mode right, though that’s not related, just want to remind you that it is better to use preamp mode regardless.

 

[peng]

Just a thought, what if e 3 wired the hi/lo gain connections wrong, maybe try the lo gain and see what happens?

 

[peng]

Yup, that just means the Maranz's internal Amp has 8dB more gain than the A5 or about 34dB, which is plausible.

Possible, but highly unlikely. D+M avr amps typical have 28-29 dB.

 

[DenonMate]

My Fosi V3 mono has been dead since yesterday. I turned on the Denon as usual. It took me a while to realize that there was no sound coming from the right front speaker (my center speaker is quite dominant).

The orange LED isn’t lit anymore. I checked the cables. I also tested the power supply from the second Fosi. Still dead. So it’s not the 48/5.

What could be the most likely (already reported) cause? Are there any official or DIY repair experiences? I have the newer version with 19/25 gain.

 

[Sokel]

My Fosi V3 mono has been dead since yesterday. I turned on the Denon as usual. It took me a while to realize that there was no sound coming from the right front speaker (my center speaker is quite dominant).

The orange LED isn’t lit anymore. I checked the cables. I also tested the power supply from the second Fosi. Still dead. So it’s not the 48/5.

What could be the most likely (already reported) cause? Are there any official or DIY repair experiences? I have the newer version with 19/25 gain.

Can you open it and take some good pictures?

 

[DenonMate]

Can you open it and take some good pictures?

Thanks for your reply. For sure, will take some pictures this evening and look for some swollen capacitors, blown coils, or discolored resistors. Depending on the component and its location, soldering wouldn't be a problem—the main thing is to get the component individually or a compatible one of better quality.

 

[DenonMate]

Can you open it and take some good pictures?

Pics. Honestley don’t know where to start… Tested again with both 48V/5A. Dead incl. LED.

 

[Roland68]

Pics. Honestley don’t know where to start… Tested again with both 48V/5A. Dead incl. LED.

If you have a multimeter, I would check a few basic things.
First, check whether the 48 volts are present at the two main capacitors.
However, since the TPA3255 relies on a 12-volt supply for the entire control system, I would check the 12-volt supply next.

But if the device is still under warranty, you're better off sending it in.

 

[Roland68]

Pics. Honestley don’t know where to start… Tested again with both 48V/5A. Dead incl. LED.

I would also test the on/off switch. I’ve come across switches like that before that had fallen apart internally.

 

[DenonMate]

I would also test the on/off switch. I’ve come across switches like that before that had fallen apart internally.

Thanks, Very good tipp. Will test it next weekend.

 

[georgeT]

I might have been the person who "introduced" this concept that better heat transfer means a hotter amplifier case. It is not strictly true as there are some (important) nuances to it that need explanation.

If you have two devices of equal size and shape and generate the same amount of heat, at steady state, the average chassis temperature will have to be roughly the same. The reason is: At steady state, heat generated = heat dissipated.

Heat transfer to the surrounding is governed by the difference between the chassis surface temperature and the ambient air temperature. If the amounts of heat dissipated to the surrounding are the same, with amp chassis of similar similar dimensions, their surface temperatures must also be similar (when averaged over the chassis surfaces), regardless of how well or poor the heat conduction paths from the heat sources to the amp chassis are.

What a poor thermal conduction path will affect is the time response, i.e. how quickly the chassis temperature will rise. To demonstrate I'll show simulation results of both cases (good and poor thermal conduction paths to the chassis).

Only a quarter of the geometry needs to be modeled due to symmetry. The heat released by the amp chip is transferred to a heat spreader (or heat sink). The heat spreader is mounted to the chassis, with thermal interface materials (TIM) applied to fill the gaps between mating surfaces of the heat spreader and the chassis. The chassis is cooled by convection (convection heat transfer coefficent of 7.2 W/m²·°C and 25 °C ambient temperature). We'll look at the differences between effectively applied TIM and poorly applied or no TIM (50x higher thermal resistance).
View attachment 541948
In the first scenario, the amp chip released 22 W of heat for 300 seconds and then the heating stopped. Below is an animation of the 2 temperature charts. When thermal conduction was poor, we can see that the amp chip temperature rose quickly and to a level much higher than when conduction is good. However, the chassis temperature rose slower and the peak temperatures didn't reach as high as with the good heat conduction case. Therefore, in this scenario, the amp with the poorer heat conduction will have a cooler amp chassis.
View attachment 541949

In the second scenario, we kept the heat generation on continuously. We can see that for this scenario the eventual steady state chassis temperatures are the same for poor and good thermal conduction. It just took the poor conduction case longer to reach the same temperature. Notice that with poor conduction the amp chip temperature went off the chart. That means the amp would probably shut itself down or destroy itself.
View attachment 541950

Therefore, the more accurate statement is that for a system with high thermal conduction to the chassis (or heat sink), the chassis will heat up faster than one with poor heat conduction. If you have enough patience and keep the test running for a long time, the one with poor heat conduction will eventually catch up. But you may need to keep the test on for half an hour or longer.

Below are the temperature profiles with heating on for 300 seconds.
View attachment 541951
View attachment 541952

Also keep in mind my A10K Pioneer amp has a linear Power supply... inside the case, and it never felt warm even in the winter when I put my freezing hand on it. Last winter I used the Fosi V3 to warm my hands,

 

[Ande3200]

My first comment here, recently i have had my Hegel h390 sent on repair because something not right with it, did not have spare amplifier,

But went through this thread and read a lot of good things about Fosi audio v3 mono.

So ordered 2 of them with zp3 preamp think i paid like $450 for that combo, have had day with it so far i most say i very impressed with them,

I am currently trying them with a pair of b&w 702 s2 played up towards 75 db so far and it sounds great, but the question does they have enough power to drive them futher than that medium sized room listening distance 5-6 feet.

I also have pair of Arendal 1528 monitor 8 which i love more than the b&w but they are lower in sensitivity so not sure if i dare to use them until get my Hegel h390 back its expected to take 3 weeks. But i do belive the Arendal has better impdence load 3.8 minimum while b&w has 2.8. At least according to measurements,
I am less worried if something happens to the b&w because their local dealers that can fix them pretty easy. Arendal is nightmare if i have to send them back for repair.

And if i look at measurements on the web site the numbers are good for 8 and 4 ohms, and even solid for 2 ohms.

I know i might not have ideal speakers for those Fosi amps, i am more than happy if i can just use my speakers on moderate volume 75-85 db at 6 feet,

But already what i experinced Fosi v3 mono performs better than i expected given they price,

The case does get warm but if am not wrong, the case acts like heatsink or is that wrong,


I am not a big measurement guy in general but i do think seeing amplifiers power in different ohms and seeing speakers impdence loads is important for me, they is offen you can see brands having inaccurate specs and you might not find out the accurate impdence loads for speakers, or amplifiers power without measurements to the public.

 

[Pulkass]

Stop press !!!! After returning non working 3 of such amps, finally, 2 are on and l must say the sound is very good, authoritative, powerful, detailed, strong, no hiss when no signal, they are running hot.... With fans, after my new other one Hypex 500x, almost tackling. Hope they won t die ...

 

[Pulkass]

My first comment here, recently i have had my Hegel h390 sent on repair because something not right with it, did not have spare amplifier,

But went through this thread and read a lot of good things about Fosi audio v3 mono.

So ordered 2 of them with zp3 preamp think i paid like $450 for that combo, have had day with it so far i most say i very impressed with them,

I am currently trying them with a pair of b&w 702 s2 played up towards 75 db so far and it sounds great, but the question does they have enough power to drive them futher than that medium sized room listening distance 5-6 feet.

I also have pair of Arendal 1528 monitor 8 which i love more than the b&w but they are lower in sensitivity so not sure if i dare to use them until get my Hegel h390 back its expected to take 3 weeks. But i do belive the Arendal has better impdence load 3.8 minimum while b&w has 2.8. At least according to measurements,
I am less worried if something happens to the b&w because their local dealers that can fix them pretty easy. Arendal is nightmare if i have to send them back for repair.

And if i look at measurements on the web site the numbers are good for 8 and 4 ohms, and even solid for 2 ohms.

I know i might not have ideal speakers for those Fosi amps, i am more than happy if i can just use my speakers on moderate volume 75-85 db at 6 feet,

But already what i experinced Fosi v3 mono performs better than i expected given they price,

The case does get warm but if am not wrong, the case acts like heatsink or is that wrong,


I am not a big measurement guy in general but i do think seeing amplifiers power in different ohms and seeing speakers impdence loads is important for me, they is offen you can see brands having inaccurate specs and you might not find out the accurate impdence loads for speakers, or amplifiers power without measurements to the public.

They drive my Magnat floorstanders very very well.

 

[Wooferhead]

I am quite interested in a pair of Fosi V3 Mono but I am hesitated to buy them mainly because of its tendency to overheat.

Excessive heat could drastically reduce the life span of an amp. I understand that it is designed to use its metal shell as heatsink, hence the high heat.

But I don't like that approach at all, apparently, I am not the only one. Some guy on YouTube added a heatsink on top to help cool down the amp.

Has anyone here done anything similar? If so, what did you do? Did your Fosi V3 Mono die of overheating? I want to find out how this amp performs in the real world.

 

[Pulkass]

I have them! Just two 5 volt fans- usb- is enough, yes they run very hot, but they sound very very good. Fans are needed.

 

[Joe Smith]

I am quite interested in a pair of Fosi V3 Mono but I am hesitated to buy them mainly because of its tendency to overheat.

Excessive heat could drastically reduce the life span of an amp. I understand that it is designed to use its metal shell as heatsink, hence the high heat.

But I don't like that approach at all, apparently, I am not the only one. Some guy on YouTube added a heatsink on top to help cool down the amp.

Has anyone here done anything similar? If so, what did you do? Did you Fosi V3 Mono die of overheating? I want to find out more how this amp perform in the real world.

You know, I'm a big Fosi booster in general, but I would not buy a set of V3 Mono amps at this point. Enough people reporting problems with them, and over a fairly long span of time. Given the way Fosi works, I would not be surprised to see them develop a new version of this pretty soon on the budget side to mirror what they are doing with those higher end mono amps they have teased. Or, in you need monos right now, Aiyima just came out with a new attractive product, the A20. Their site says sold out for now, but I imagine they will ramp up production on this quickly if it is selling well.

 

[Pulkass]

You know, I'm a big Fosi booster in general, but I would not buy a set of V3 Mono amps at this point. Enough people reporting problems with them, and over a fairly long span of time. Given the way Fosi works, I would not be surprised to see them develop a new version of this pretty soon on the budget side to mirror what they are doing with those higher end mono amps they have teased. Or, in you need monos right now, Aiyima just came out with a new attractive product, the A20. Their site says sold out for now, but I imagine they will ramp up production on this quickly if it is selling well.

Yes l had to send 3 of Them back, non working, (!)

 

[Wooferhead]

I am quite impressed by Aiyima A20 Mono amps. I was wondering which one would be a better choice. I suppose I will go with Aiyima A20 Mono amps now.

It has slightly lower power output than I would like compared to Fosi V3 Mono, but at least it won't be having any issues with excessive heat.