Fosi Audio V3 Mono Amplifier Review

[ninetylol]

Just posted in thread 'Fosi v3 Mono - User Impressions | Owner's Thread' about the same issue. I feel with you.

Same here. I Was already wondering if demons are in my room.

 

[badie]

Well ... Fosi made a well-working thermal design on the V3 Stereo.

As stated on their website the thermal design of the V3 monos is "advanced" (i believed it, as i do own a V3 stereo).
But I was really surprised when I unpacked the V3 monos and found out that the ventilation holes on top and bottom got cancelled.

Measuring temp side by side the thermal design of the V3 monos is clearly way worse.

Why did they got rid of the holes on bottom and top??? (this is very basic thermal dynamics)???
Tried to use incencse sticks to see if there is any significant airflow through/in/out the orange side-ventilation and guess what?
Pretty much nothing.

Maybe I find the time to elaborate on this but for the moment this post must suffice.

 

[badie]

regarding ventilation:

They really sell the V3 monos with a ventilation setup now! (see fosis website)

Well. I put one average-quality 120mm PC vent (with an old 5V 350mA phone wall brick) that is throwing air over all my three units (V3 Stereo and 2xV3 mono) ... everything is down to ~30 °C.

So i think a very faint breeze of air make a huge difference. No need for individual fans under each unit.
(Hope to find the time to make some measurements)

 

[antcollinet]

Op-amp rolling is the new tube rolling. You’re looking for your preferred flavor of distortion coloring, not a perfect signal.

Take a Big Mac and then put something else in it—BBQ sauce, fried onions, ranch dressing, banana peppers, whatever…it’s no longer a, “perfect Big Mac,” it’s your own twist.

ASR crowd doesn’t understand anything other than the perfect Big Mac, but these people want it their way; they’re the Burger King types.

-Ed

ASR crowd understand that you are not putting a flavoursome BBQ sauce on your big mac, but an undetectable tiny micro drop of water.

It is not that “ASR Crowd” only want a perfect big mac - it is that they recognise op amps as bringing only micro drops of water rather than a good dollop of BBQ/onion/etc flavour.

It is of course possible (though unlikely) that an op amp swap might go badly wrong and bring a big squirt of sewerage to the burger - but it is unlikely that anyone would prefer that.

Hope that helps.

 

[antcollinet]

Typically 30-40x for the TPA3255 chip.
It's fine.

That would be without post filter feedback though, wouldn’t it?

 

[Sokel]

That would be without post filter feedback though, wouldn’t it?

Yes,in Fosi's case is close to 150x (300x at 8 Ohm),I wrote couple of posts after that.

 

[antcollinet]

Yes,in Fosi's case is close to 150x (300x at 8 Ohm),I wrote couple of posts after that.

So you did. I am travelling, and just catching up.

 

[Inertiaman]

Measuring temp side by side the thermal design of the V3 monos is clearly way worse.

Why did they got rid of the holes on bottom and top??? (this is very basic thermal dynamics)???
Tried to use incencse sticks to see if there is any significant airflow through/in/out the orange side-ventilation and guess what?
Pretty much nothing.

It does seem a rather dumb design choice. Even if one accepts a design requirement to not have holes on the top (avoiding dust ingress or god forbid fluid spills), there are thermally better ways to vent than their current mid-panel side vents. For example, holes on the bottom combined with holes on the very top edges of the sides would provide passive flow-through nearly as well as holes in the top.

 

[antcollinet]

It does seem a rather dumb design choice. Even if one accepts a design requirement to not have holes on the top (avoiding dust ingress or god forbid fluid spills), there are thermally better ways to vent than their current mid-panel side vents. For example, holes on the bottom combined with holes on the very top edges of the sides would provide passive flow-through nearly as well as holes in the top.

There is (and can be) almost no vertical air flow in this design. The entire area is blocked by the PCB - where are you expecting air entering the bottom of the case to go?. The thermal design relies almost entirely on conducting heat to the chassis. There will be some small trickle of air out of the side vents, fed though the small gap between the edges of the PCB and the housing.

 

[Inertiaman]

There is (and can be) almost no vertical air flow in this design. The entire area is blocked by the PCB - where are you expecting air entering the bottom of the case to go?. The thermal design relies almost entirely on conducting heat to the chassis. There will be some small trickle of air out of the side vents, fed though the small gap between the edges of the PCB and the housing.

Good point, I hadn't reviewed the photos of the enclosure. Having now done so, I still see simple opportunities for improvement. Maximizing airflow on all surfaces of the chassis (both interior and exterior) would benefit heat dissipation. So offsetting the holes on the side panels (left side high, right side low, for example) would improve the passive convective airflow through the unit. I can't quantify the scale of the benefit, but certainly it would improve, no?

Frankly I wonder if, given the orientation of the TPA3255/heatsink/chassis, would the unit run cooler if placed upside down??

 

[EddNog]

…Frankly I wonder if, given the orientation of the TPA3255/heatsink/chassis, would the unit run cooler if placed upside down??

You would not be the first person to guess this.

-Ed

 

[Inertiaman]

You would not be the first person to guess this.

-Ed

Yeah, I'm coming in about 180 pages late here!

Probably even better to place it on edge: you get top and bottom holes + the largest surfaces (chassis top & bottom) have constant convective airflow.

Waiting now for you to point me at some post 100 pages earlier where someone 3D printed some clips/feet to hold a pair of these side by side

 

[EddNog]

Yeah, I'm coming in about 180 pages late here!

Probably even better to place it on edge: you get top and bottom holes + the largest surfaces (chassis top & bottom) have constant convective airflow.

Waiting now for you to point me at some post 100 pages earlier where someone 3D printed some clips/feet to hold a pair of these side by side

Hah…yes, someone did actually do that. Unfortunately, it is so far back that I don’t have enough time to find it for you!

-Ed

 

[antcollinet]

I can't quantify the scale of the benefit, but certainly it would improve, no?

I very much doubt it - not nearly enough vertical difference in hight to create airflow.

 

[Endibol]

I have two splitter cables thanks to Fosi ... But if I understand you correctly, we could junk the DC filter and just have a better splitter cable.
So the problem was with the splitter cable? Thank heavens they sound good despite all this (the V3 monos)!

If I remember correctly Fosi sent a second splitter cable with the filter. This was necessary because a splitter cable with a different configuration male/female connectors was needed to insert the filter.

 

[Endibol]

I'm planning on using both the RCA and XLR inputs (for two different sources) - RCA being driven from the preouts on my Arcam AVR360 (quite curious to see how the v3 monos compare to a reasonably high end AVR which claims 90wpc...). This will cover Film, TV and streamed music use through the AVR. How do people find the manual switches on the front? Robust? Any audible pops or clicks when switching? Should I worry about the RCA noise issue with the single 10a supply? How do people find the auto power switching? Is it useful/works as intended?

The switches are robust. You can switch from XLR to RCA and back without any clicks or plops. Upon switching the amp there is silence for a few tenths of a second and than switches to the selected mode. The Fosi feels very robust and solid anyway. They sound great with the fairly insensitive Ascend Sierre -1 v2 speakers.

 

[badie]

There is (and can be) almost no vertical air flow in this design. The entire area is blocked by the PCB - where are you expecting air entering the bottom of the case to go?. The thermal design relies almost entirely on conducting heat to the chassis. There will be some small trickle of air out of the side vents, fed though the small gap between the edges of the PCB and the housing.

V3 Stereo seems to have an evenly big PCB (didn´t make any measeurements) and there is significant airflow through the unit (bottom to top).
You can feel it and make it visible with a little smoke.

But I do agree - V3 mono relies almost entirely on conducting heat to the chassis.


This is the marketing image for V3 stereo taken from FOSI website for the V3 stereo:

Result: maximizing conductive cooling by heatsinking the IC to the chassis (I believe this to be a good choice) and benefiting from airflow.

This is the marketing image taken from FOSI website for the V3 Mono:

Result: Nicer looking unit same conductive design BUT no more (significant) airflow.
I did believe in the advancement, thinking the hole on the sides were additional and not the only ones)

The measurements I made upuntil now (Post #3339 in this thread) show clearly that the V3 stereo thermal design is way more effective. I think FOSI made a visual design choice without testing the thermal performance and called it "Advanced Cooling Design".

I would really like to see how the V3 mono would perform thermally if you were to put holes in bottom and top. But I am too scared to drill holes in anodized aluminium. (maybe chipping of black color) - did anybody tried this?

@Fosi Audio Maybe it would be possible for FOSI to offer/send out a replacement for just the middle part of the case with holes in it. So that users could replace it on their V3 monos and hopefully get the same thermal performance as with V3 stereo. I wonder how much the middle part of the case does cost in production. Probably the mono one with the orange side-holes was more expensive, than the original (V3 Stereo) one.

And I myself really do like the design of these holes. If I were afraid of dust i would just glue a black net underneath - same as my computers do protect themselves against dust.

 

[antcollinet]

The measurements I made upuntil now (Post #3339 in this thread) show clearly that the V3 stereo thermal design is way more effective. I think FOSI made a visual design choice without testing the thermal performance and called it "Advanced Cooling Design".

But you don’t actually know, because you are only measuring case temperature, not how effectively the internal components are being cooled. (But kudos for doing the measurements - far more than I have ever done post retirement )

Obviously if you are optimising heat transfer by letting hot air out of the enclosure, then the case will not get as hot. However it is possible the build up of heat in the air inside the case (because all the power losses must first be transferred to the internal air) may be much worse.

If you are optimising heat transfer through direct coupling to the chassis, then obvously the chassis will get hotter. But the internal air may well be cooler since you are not putting all the power losses into it.

The only way you can know for sure is by measuring the temperature of internal components - and the only way of doing that effectively is by glueing thermocouples or other temperature sensors directly to the components.

In my former life we even had capacitors specially made by the manufacturer with thermocouples inside them, so we could measure the internal capacitor temperature.

 

[badie]

But you don’t actually know, because you are only measuring case temperature ...
The only way you can know for sure is by measuring the temperature of internal components - and the only way of doing that effectively is by glueing thermocouples or other temperature sensors directly to the components.

you are right. Best I can measure is case temp at heatsink position. Might not be right in absolute temp of the IC itself - maybe good enough for comparing V3 stereo vs V3 mono thermal design.

But good point we have no idea how hot all other components are ...
Maybe we can assume, that without airflow (convective heat transfer) other components might even be hotter ...
Because conductive heat transfer is mostly-only happening for the IC.

And we do seem to be more worried about the life expectancy of the capacitators?

 

[antcollinet]

you are right. Best I can measure is case temp at heatsink position. Might not be right in absolute temp of the IC itself - maybe good enough for comparing V3 stereo vs V3 mono thermal design.

But good point we have no idea how hot all other components are ...
Maybe we can assume, that without airflow (convective heat transfer) other components might even be hotter ...
Because conductive heat transfer is mostly-only happening for the IC.

And we do seem to be more worried about the life expectancy of the capacitators?

If measuring heatsink temperature then you’d need to measure both heatsinks a similar distance from the IC.


The internal air temp assumption won’t work because it depends on both airflow, AND losses into the internal air - and we don’t know either.

But as you say, capacitor temperature is probably most critical - measuring some of the capacitor temps would be best.

An approximation would be measuring the air temperature close to the capacitors which would give an idea regarding which design has the coolest internal air temperature. In that case you’d need to measure air temp sufficiently far from the cap that the cap is not directly heating it (perhaps about 1cm away, and to the side - so not in any rising air from the cap)