Fosi Audio V3 Mono Amplifier Review

[Jukka]

WoW! Can you give examples so I can see the stuff they are offering with 10% distortion?

Fosi Audio V3

Using a minimalist design language, focusing more on enhancing the sound quality and performance of the product, making it the best-sounding power amplifier of Fosi Audio to date.

fosiaudio.com

 

[antcollinet]

If it is the chassis temperature that goes down, and assuming that the amp chip is generating the same amount of heat, a cooler chassis means that the heat conduction from the amp chip to the chassis is reduced.

This is my expectation also - and must consequently mean the power not going to the chassis is now causing other components in the design to get hotter - starting with the chip, then conducting to the PCB and then to the internal air.

which goes alongside my view that people messing about with thermal paste are just as likely to make things worse, as better. It is not simply a case of slapping it on and hoping for the best. The paste needs to be as thin as the design allows, with the pressure as high as the design allows.

High pressure doesn't just mean tightening the screws until the veins pop in the hapless modders forehead - this is likely to cause mechanical damage. It is about tightening the screws to the designed torque - which none of us know.

In a former life one of our most expensive design/manufacturing failures was incorrect application of thermal paste. And we got it wrong more than once.

True or it might be spread over a larger surface area of the sheet metal?

But that would only be the case where contact is made with the case - which might reduce a local hotspot there (I think on the underside where the chip makes contact - but this is not what people are touching). After that, a larger surface area of contact will result in better heat transfer to the case which will make it warmer.

 

[antcollinet]

Others might be able to clarify but I always thought that having an amp on without speakers connected risks damage.

That's another myth harking back to the days of tube amps - which could be damaged by running without load.

 

[MCH]

Others might be able to clarify but I always thought that having an amp on without speakers connected risks damage.

Actually, this has been discussed in TI audio forum.

IIRC (I can’t find the exact link), TI claimed it was safe to run their TPA3255 eval board without load, but also recommended to use, if in doubt, catch diodes to VDD and ground to avoid any potential issues. I noticed the Fosi V3 mono and the latest 3E boards have said diodes, so I would said it should be safe.

This other link to TI audio forum explains what the diodes do:
“In order to run a class-D amp open load, you will need to place some diodes from the outputs to power and ground to keep the voltage generated by the LC filter resonance from causing an over-voltage event on the output pins. These diodes are only needed if you plan to run the filter un-loaded.”

https://e2e.ti.com/support/audio-group/audio/f/audio-forum/368873/tas5630b-working-without-heatsink-and-load/1297169?tisearch=e2e-sitesearch&keymatch=unloaded%25252525252520catch%25252525252520diodes#1297169

 

[DavidM1]

That's another myth harking back to the days of tube amps - which could be damaged by running without load.

Thanks. I’m a guitarist who owns a tube amp so that would probably be why I’ve heard it.

 

[burkm]

Good - but the point I was making is that a high case temperature is not an indication that themal paste is not applied or insufficiently applied. That seems to be a mistake a lot of people are making.

"Wow - this amp feels hot - I'd better take it apart and apply more paste"

I am not inclined to judge, if high temperatures are common for this amp or not. I'm just looking, if any thermal paste has been applied to the chip's heatsink as is quite normal. That's it... => quite simple.
The other thing is, that due to that "split time" delivery a few days ago (difference now about > one week) and the situation, that I have to open the case anyway because of this, I would like to know, if any of those amps have been worked on, considering the stated "polarity" issue and the news released by Fosi Audio...
Depending on the outcome I might have to take some actions myself.

I'm just wondering, why this is named a "modification"...
For me it's just a "clarification" of what has actually been delivered...

 

[Doodski]

I'm just wondering, why this is named "modification"...

Anytime a stock piece of gear is modified by adding thermal paste, rolling OP amps etc it is referred to as a MOD and the action of it is called MODing.

 

[burkm]

I think of this rather as "omission during assembly", not a modification

 

[Lux_ury]

Weird if the monos were to be realised in winter would the threads of heat be less?
Weird it was around July they released the first batch correct? (Rub chin emoji)

 

[Doodski]

I think of this rather as an "omission", not a modification

I see that and don't doubt it would help if done properly. As @antcollinet stated in post #3222 the application of thermal paste and the integrity of the clamping of the chip heatsink to the chassis needs to be done properly or the situation will worsen and might cause the chip to go into thermal runaway. I don't have the amp in hand and so I can't see what is required and how the reassembly procedure is done but I can say be very careful with the heatsink mounting screws as the materials are soft.

 

[Sokel]

I see that and don't doubt it would help if done properly. As @antcollinet stated in post #3222 the application of thermal paste and the integrity of the clamping of the chip heatsink to the chassis needs to be done properly or the situation will worsen and might cause the chip to go into thermal runaway. I don't have the amp in hand and so I can't see what is required and how the reassembly procedure is done but I can say be very careful with the heatsink mounting screws as the materials are soft.

High end GPUs which is comparable to application advise about 0.4-0.5 Nm of torque.
But it should be specific to the application normally.
Since the device is meant to be opened for various reasons,I think a torque driver would be far more useful instead of the hex one or the silly op-amps.

 

[antcollinet]

I think of this rather as "omission during assembly", not a modification

You can call it what you like, but if the design doesn't call for paste then it is not an omission during assembly.

Now I've no idea whether this amp has been designed to work without paste or not. But if it has, then adding paste is, at best, pointless - assuming the design is competent.

But if you believe the design is incompetent, why would you ever want to pay good money for it.

 

[antcollinet]

High end GPUs which is comparable to application advise about 0.4-0.5 Nm of torque.
But it should be specific to the application normally.
Since the device is meant to be opened for various reasons,I think a torque driver would be far more useful instead of the hex one or the silly op-amps.

I don't think opening the case to fit Op Amps requires separating the heatsink from the base.

 

[EddNog]

I don't think opening the case to fit Op Amps requires separating the heatsink from the base.

It does.

-Ed

 

[Sokel]

I don't think opening the case to fit Op Amps requires separating the heatsink from the base.

As far as I have seen the pics they slide out the case by unscrewing the bottom heatshink screws.
Owners please correct me if I'm wrong.

 

[EddNog]

As far as I have seen the pics they slide out the case by unscrewing the bottom heatshink screws.
Owners please correct me if I'm wrong.

The screws on the back panel farthest to the sides and also the two screws on the bottom must be undone. Then the front panel can slide off and the back panel, which is permanently affixed to the PCB, can slide out from the enclosure, which is a full hoop (top, bottom, and both sides), not just a top cover.

-Ed

 

[antcollinet]

It does.

-Ed

As far as I have seen the pics they slide out the case by unscrewing the bottom heatshink screws.
Owners please correct me if I'm wrong.

Damn - I'm sure I'd seen pics with just the top half lifted off. But... even more reason for designing to not need paste.

 

[EddNog]

Damn - I'm sure I'd seen pics with just the top half lifted off. But... even more reason for designing to not need paste.

I’ve opened up the ZA3s too many times to count. I’ve also opened up original V3 twice and V3 Monos once, and they’re all basically the same (but no volume knob on V3 Mono so those are even easier).

-Ed

 

[antcollinet]

I’ve opened up the ZA3s too many times to count. I’ve also opened up original V3 twice and V3 Monos once, and they’re all basically the same (but no volume knob on V3 Mono so those are even easier).

-Ed

Do the ones you've opened have stock paste applied?

 

[EddNog]

Do the ones you've opened have stock paste applied?

ZA3s came from factory with thermal interface material applied. V3 and V3 Monos did not have any TIM from the factory.

-Ed