Fosi v3 Mono - User Impressions | Owner's Thread

[Sokel]

You will not find it, not for the misterious KY series 63V 2200uF

I think that's the one:

https://chemi-con.com/wp-content/uploads/2021/05/KY-Series.pdf

 

[MCH]

I think that's the one:

https://chemi-con.com/wp-content/uploads/2021/05/KY-Series.pdf

Scroll down and try to find the 63V 2200uF reference. You can check at nippon semi-con website as well.

 

[Sokel]

Scroll down and try to find the 63V 2200uF reference. You can check at nippon semi-con website as well.

That's strange.
Mouser also has KYB,KYΩ and KMQ at that values but not KY.

On the other hand there's a gazillion knock offs at Ali and the usual,I don't know that the heck they copied.
However Fosi has showed in previous time that uses original stuff.

 

[MCH]

That's strange.
Mouser also has KYB,KYΩ and KMQ at that values but not KY.

On the other hand there's a gazillion knock offs at Ali and the usual,I don't know that the heck they copied.
However Fosi has showed in previous time that uses original stuff.

LCSC is the only reputable supplier that sells them, but even they fail to provide a valid datasheet. I have a bunch being shipped to me at the moment. Asked them for an explanation but they haven't answered yet. My current hypothesis is that it is (was) a custom reference, but as of today, it remains misterious to me.

 

[antcollinet]

Scroll down and try to find the 63V 2200uF reference. You can check at nippon semi-con website as well.

Regardless - they will be subject to the rule of thumb

which means that the lifetime is approximately halved for every 10°C rise in ambient temperature.

Lifetime of Aluminum Electrolytic Capacitors | Nippon Chemi-Con Corporation

www.chemi-con.co.jp

And that means ambient temperature next to the cap - ie after conduction/convection from the chip on the other side of the board.


This is a damn good reason not to let ANY kit containing aluminium electrolytic capacitors run 24/7, other than in a true standby mode.

 

[Guddu]

Regarding heat the product data sheet shows that its running well inside its limits.

This is just one factor only.

No need to fear the device exploding in flames.

Personally I would not ignore anything alarming but everyone has their own choices and preferences. It is already a lower cost product with decent performance and highlighting the experiences or anything alarming should be seen as something to be improved upon in next iterations.
A larger case work might have eliminated the heat dissipation concerns to great levels.

 

[PJ_Schmidt]

Very cool setup. Could you please do some measurements before and after adding thermal paste on the monos so we can see the difference in temperature it makes?

I have done this, but I only measured the outside case temperature. You can see my previous post to see the temperatures before adding paste.

The short version is that adding paste made no difference in the external temp of the case. This may not be intuitive to everyone, but there's a good chance the chip is running cooler even though the case temp is unchanged. Average external case temp, under steady state conditions, is directly related to energy the chip is dissipating and not the temperature of the chip itself. In a situation where the conduction is poor, the chip will run hotter to "force" the energy through the higher thermal resistance interface. When the conduction is good, the chip will run cooler since is "easy" for the heat to transfer to the case. In either situation, the amount of energy is transferred to the case is identical so its temperature remains the same (again all things being equal). If the room temp changes or you add a fan, then the case temperature will change since its thermal resistance has changed to transferring heat away from itself. In steady state, the chip will run a constant temperature above the case. Improving the thermal interface (adding paste) will reduce this delta.

Having said all of that, I'm not convinced adding paste is needed. I did it since I was opening them up for my own entertainment. For people who don't want to open their units, just use a 2mm hex to insure the two bottom heatsink screws are moderately tight and enjoy using the amp.

 

[keith_h]

I have done this, but I only measured the outside case temperature. You can see my previous post to see the temperatures before adding paste.

The short version is that adding paste made no difference in the external temp of the case.

Having said all of that, I'm not convinced adding paste is needed.

Thanks, I missed the earlier post. I felt that in this case adding paste likely makes no difference also. Appreciate your observations.

 

[keith_h]

Heat dissipation is not only about the chip itself.
Have a look at the pic below:


View attachment 379703

Caps are directly above the heatshink area.Now go to cap's datasheet and see how their life span varies with temperature.
One must also consider resistor's ppm (the better quality-the lower),etc.

We must look at the device as a whole and it's usually the weak links to pay attention first.Chip is not this link.

Good points. Nichicon caps are rated at 5000 hours @ 105C for the long life caps. I expect this variety sits in that category. Interesting there is no axial selector on their website to help find the part on the board.

 

[MCH]

LCSC is the only reputable supplier that sells them, but even they fail to provide a valid datasheet. I have a bunch being shipped to me at the moment. Asked them for an explanation but they haven't answered yet. My current hypothesis is that it is (was) a custom reference, but as of today, it remains misterious to me.

LCSC confirmed customized part. All specs are identical to the 1800uF version.

 

[thunderchicken]

I have done this, but I only measured the outside case temperature. You can see my previous post to see the temperatures before adding paste.

The short version is that adding paste made no difference in the external temp of the case. This may not be intuitive to everyone, but there's a good chance the chip is running cooler even though the case temp is unchanged. Average external case temp, under steady state conditions, is directly related to energy the chip is dissipating and not the temperature of the chip itself. In a situation where the conduction is poor, the chip will run hotter to "force" the energy through the higher thermal resistance interface. When the conduction is good, the chip will run cooler since is "easy" for the heat to transfer to the case. In either situation, the amount of energy is transferred to the case is identical so its temperature remains the same (again all things being equal). If the room temp changes or you add a fan, then the case temperature will change since its thermal resistance has changed to transferring heat away from itself. In steady state, the chip will run a constant temperature above the case. Improving the thermal interface (adding paste) will reduce this delta.

Having said all of that, I'm not convinced adding paste is needed. I did it since I was opening them up for my own entertainment. For people who don't want to open their units, just use a 2mm hex to insure the two bottom heatsink screws are moderately tight and enjoy using the amp.

I did not bother with the paste, but noted the heat sink to case interface was a relatively large chunk of metal and bolts more or less directly to the case. Good contact took negligible effort and I tightened the screws down until it felt like a single piece.

 

[Slowloris]

It seems pre orders for the main release are up. And there is 20% off

 

[BrooklynNick]

I just received my amps. They were fairly well packaged and arrived without any damage. Holding it my hand, I'm amazed at how small and light it is. I primarily got these for the electric/heat savings; my old monoblock amps used 60 watts each at idle. Also, for the power switch on the front. That might seem trivial until you have had to get on the floor and try to reach the back of your rack to turn on your amp a few times. Hopefully, I'll get them setup this weekend.

One oddity... they sent me a single long XLR cable. I'm not sure what use that is with a pair of monoblocks.

 

[Freshman1966]

Reporting I got my two V3s, as well. The sound great and I cannot hear any difference between them and my Atoll IN 300 (which I love) Probably, if I had some device to AB test properly, I might hear a different...
I am using the V3 behind a minidsp Flex to power Dynaudio Heritage Specials, not so easy to drive.
Now I am in a bit of a mess because I actually only got them to prove that AB is better than Class D... now what?
I also got 4 Sparkos Op Amps but I have never worked with Op Amps before and don't really know what to expect nor whether I will need them. If anyone is interested I can write if I can hear a difference when I replace 2 or 4.

Yes, they are hot, not warm. If they were bigger I could fry an egg on the surface. But since I don't intend to hold them in my lap any I do not listen to loud music, I guess I will be fine.

One thing is already very clear - it definitely was not a waste of money. Amazing what Fosi can do for this money.

 

[SMen]

Reporting I got my two V3s, as well. The sound great and I cannot hear any difference between them and my Atoll IN 300 (which I love) Probably, if I had some device to AB test properly, I might hear a different...
I am using the V3 behind a minidsp Flex to power Dynaudio Heritage Specials, not so easy to drive.
Now I am in a bit of a mess because I actually only got them to prove that AB is better than Class D... now what?
I also got 4 Sparkos Op Amps but I have never worked with Op Amps before and don't really know what to expect nor whether I will need them. If anyone is interested I can write if I can hear a difference when I replace 2 or 4.

Yes, they are hot, not warm. If they were bigger I could fry an egg on the surface. But since I don't intend to hold them in my lap any I do not listen to loud music, I guess I will be fine.

One thing is already very clear - it definitely was not a waste of money. Amazing what Fosi can do for this money.

I am hoping one could not actually fry an egg on these if they were bigger! ...

Still waiting for mine - finally departed from sort facility mainland China...

I think comparisons with other amps are interesting, including (especially) when you don't hear a difference. A lot of the comments here are regarding bias, where one perceives a difference (perhaps price or whatever subjective reason) ... rather than when one doesn't. I'd be interested in your comparison with op amps because at some point I intend to do likewise, but I think A/B'ing is essential or we will end up in the usual op amp debate merry go round. The Fosi monos could allow a/b comparisons without an addtional device.

What we need is a methodology that might generally be agreed upon. I'd be happy to not hear a difference.

 

[EddNog]

I am hoping one could not actually fry an egg on these if they were bigger! ...

Still waiting for mine - finally departed from sort facility mainland China...

I think comparisons with other amps are interesting, including (especially) when you don't hear a difference. A lot of the comments here are regarding bias, where one perceives a difference (perhaps price or whatever subjective reason) ... rather than when one doesn't. I'd be interested in your comparison with op amps because at some point I intend to do likewise, but I think A/B'ing is essential or we will end up in the usual op amp debate merry go round. The Fosi monos could allow a/b comparisons without an addtional device.

What we need is a methodology that might generally be agreed upon. I'd be happy to not hear a difference.

Well, as far as comparisons go, I did try one interesting thing, which was to swap one of my V3 Monos out for a ZA3, and I used the volume knob on the ZA3 for volume matching (gain on V3 Mono is lower than on ZA3) and no matter how I set it (stereo mode or mono mode), I could not get the system to sound right with a ZA3 driving one channel and the V3 Mono driving the other channel, so there is ABSOLUTELY a difference in how the two amps sound compared to each other. The difference is extremely clear and obvious.

-Ed

 

[antcollinet]

The difference is extremely clear and obvious.

As is the perception of difference due to bias.

I don't get how people who've been around here a while still say "it was an obvious difference so it must be real"

Bias or insufficiently accurate level matching are still likely explanations for what you are hearing. Especially if you were listening to them as a stereo pair, rather than AB comparing.

Although it is also possible that a FR variation due to the frequency/load dependency of the ZA3 without PFFB could also be responsible. Especially if your speakers have very peaky response.

 

[SMen]

Well, as far as comparisons go, I did try one interesting thing, which was to swap one of my V3 Monos out for a ZA3, and I used the volume knob on the ZA3 for volume matching (gain on V3 Mono is lower than on ZA3) and no matter how I set it (stereo mode or mono mode), I could not get the system to sound right with a ZA3 driving one channel and the V3 Mono driving the other channel, so there is ABSOLUTELY a difference in how the two amps sound compared to each other. The difference is extremely clear and obvious.

-Ed

Interesting. I would expect the volume control being active on the ZA3 side to influence too.

I find this with a volume control which I keep on maximum but sometimes switch into circuit. Subtle (in my case), but change all the same.

 

[EddNog]

As is the perception of difference due to bias.

I don't get how people who've been around here a while still say "it was an obvious difference so it must be real"

Bias or insufficiently accurate level matching are still likely explanations for what you are hearing. Especially if you were listening to them as a stereo pair, rather than AB comparing.

Although it is also possible that a FR variation due to the frequency/load dependency of the ZA3 without PFFB could also be responsible. Especially if your speakers have very peaky response.

This was not a bias issue. I think you’re misinterpreting what I am saying. My point is that when using one model amp on the left channel and a different model amp on the right channel, even after volume matching the two sides, there is a clear and obvious problem with how the system sounds. Try, for example, having the speaker cables attached (accidentally) in reverse terminal order on just one side with the same amps (so one speaker is out of phase), and you’ll notice a clear and obvious problem with how the system sounds. I experienced a similar effect when I tried using V3 Mono on one channel and ZA3 on the opposite channel and then volume matched. It was very clear and obvious that there is a mismatch between left and right channels.

How are you calling it bias if there is absolutely zero question that you could blindfold me, set up one room with two V3 Monos, and then a second room with one V3 Mono and one ZA3 (again, volume-matched), using identical speakers, and I am perfectly willing to bet my house that I will be able to tell you which room has matched amps and which room has mismatched amps? I never said I could tell which amp is on which channel, I said I could tell the amps are mismatched, that’s it. There are a number of perfectly logical and reasonable causes for this, such as slightly out of phase sound because of mismatched circuitry, design. Where is the bias in this? I find that insinuation insulting.

-Ed

 

[Sokel]

This was not a bias issue. I think you’re misinterpreting what I am saying. My point is that when using one model amp on the left channel and a different model amp on the right channel, even after volume matching the two sides, there is a clear and obvious problem with how the system sounds. Try, for example, having the speaker cables attached (accidentally) in reverse terminal order on just one side with the same amps (so one speaker is out of phase), and you’ll notice a clear and obvious problem with how the system sounds. I experienced a similar effect when I tried using V3 Mono on one channel and ZA3 on the opposite channel and then volume matched. It was very clear and obvious that there is a mismatch between left and right channels.

How are you calling it bias if there is absolutely zero question that you could blindfold me, set up one room with two V3 Monos, and then a second room with one V3 Mono and one ZA3 (again, volume-matched), using identical speakers, and I am perfectly willing to bet my house that I will be able to tell you which room has matched amps and which room has mismatched amps? I never said I could tell which amp is on which channel, I said I could tell the amps are mismatched, that’s it. There are a number of perfectly logical and reasonable causes for this, such as slightly out of phase sound because of mismatched circuitry, design. Where is the bias in this? I find that insinuation insulting.

-Ed

How did you level matched them?
What way?