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Fosi v3 Mono - User Impressions | Owner's Thread

Lednek

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What do you guys think about setting these amp upside down with some taller adhesive feet and applying these heatsink over the chip? Also considering applying new thermal compound to the chip itself. @Fosi Audio ,any thoughts?
 

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antcollinet

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What do you guys think about setting these amp upside down with some taller adhesive feet and applying these heatsink over the chip? Also considering applying new thermal compound to the chip itself. @Fosi Audio ,any thoughts?
The amp has already been designed to work thermally. There really is no need for this.

In fact I'd guess you are far more likely to cause problems than solve them.
 

Sokel

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I think any frequency response change would be unexpected, especially one as variable as you've shown here. It looks like +/-3 dB in some places which you could definitely hear on an a/b.

My first guess is the mic could have moved in between measurements - possible?
The difference is huge,chart can't be right.
I would justify any minor deviation up high but this mid-bass difference is enormous and not justifiable by the measurements.

One of these amps,contrary to the common sense and their measurements have way to much of a character of it's own.
 

antcollinet

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Sometimes Yes.


mic was at the same random position, along with other settings.
What about you? Were you in the exact same position for each reading? :p
 
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Guddu

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The difference is huge,chart can't be right.
I would justify any minor deviation up high but this mid-bass difference is enormous and not justifiable by the measurements.

One of these amps,contrary to the common sense and their measurements have way to much of a character of it's own.
I wish if I could find out why and how, but both the measurements were taken with same settings like same mic at same position, same calibration file, same laptop running same REW software, same SPL matched and 4 repetitions to capture response.

What about you? Were you in the exact same position for each reading? :p
out of the room ;)
 

Sokel

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I wish if I could find out why and how, but both the measurements were taken with same settings like same mic at same position, same calibration file, same laptop running same REW software, same SPL matched and 4 repetitions to capture response.


out of the room ;)
That would need it's own thread if results are captured the way you describe and it would need a VERY careful set-up (mic steady at one meter maybe) plus an MMM measurement for sanity.

If then the results are the same,something is either broken,badly designed or deliberately "tuned" far from neutral.
 
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Guddu

Guddu

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That would need it's own thread if results are captured the way you describe and it would need a VERY careful set-up (mic steady at one meter maybe) plus an MMM measurement for sanity.

If then the results are the same,something is either broken,badly designed or deliberately "tuned" far from neutral.
This measurement wasn’t taken on listening position, mic was near back wall and room anomalies were in play. Purpose was basically to see difference quickly, rather than optimally performing this for corrections.

I have taken captures for other amplifiers with mic closer to speaker (less than a feet):
1715035193444.jpeg
 

Sokel

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This measurement wasn’t taken on listening position, mic was near back wall and room anomalies were in play. Purpose was basically to see difference quickly, rather than optimally performing this for corrections.

I have taken captures for other amplifiers with mic closer to speaker (less than a feet):
View attachment 368036
The room response is ok,understandable and of no interest here.
Of course it will have dips and anomalies before correction.we're not looking for a flat room response here.

What is odd is the amp's differences if measurements taken carefully.
All else been equal and untouched,there's no way two well measuring amps having a difference like that.
 

kemmler3D

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I wish if I could find out why and how, but both the measurements were taken with same settings like same mic at same position, same calibration file, same laptop running same REW software, same SPL matched and 4 repetitions to capture response.


out of the room ;)
I just did some in-room measurements to EQ my desktop setup, and even though I have done it before I was surprised by how much difference you can see in levels by moving the mic, especially at single frequencies. Moving the mic 1-2 inches can cause a single frequency to change by 3dB or more. So unless the mic position was EXACT (and I mean by +/- 1mm in 3 dimensions) then I wouldn't say we would discard mic position as the likely cause of differences here.
 
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Guddu

Guddu

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I just did some in-room measurements to EQ my desktop setup, and even though I have done it before I was surprised by how much difference you can see in levels by moving the mic. Moving the mic 1-2 inches can cause a single frequency to change by 3dB or more. So unless the mic position was EXACT (and I mean by +/- 1mm in 3 dimensions) then I wouldn't say we would discard mic position as the likely cause of differences here.
agreed, change in mic position may yield different measurements.
 

gwing

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What do you guys think about setting these amp upside down with some taller adhesive feet and applying these heatsink over the chip? Also considering applying new thermal compound to the chip itself. @Fosi Audio ,any thoughts?
Perhaps weld a small pipe to the underside of the chassis (underneath the chip) and run cold water through it?
 

Talisman

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Moving the mic 1-2 inches can cause a single frequency to change by 3dB or more.
In my humble and very limited experience I have not found such large variations in such small measurement distances, but I am not denying that they may exist, it simply hasn't happened to me.
Of course the immediate next consideration would be, what do I measure myself to do and equalize with absolute precision to have a flat response if then swaying my head to the rhythm of the music can make me make changes in frequency response worthy of the worst speaker design
 

kemmler3D

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Of course the immediate next consideration would be, what do I measure myself to do and equalize with absolute precision to have a flat response if then swaying my head to the rhythm of the music can make me make changes in frequency response worthy of the worst speaker design
Yeah, that's the thing, you basically can't do this above the Schroeder frequency except when the speaker has really good directivity at a given frequency.

Reflections and off-axis deviations in frequency response mean that if you EQ a single spot perfectly, another spot gets worse. Unfortunately "another spot" is closer to the first spot, the higher in frequency you go. This is the "head in a vise" phenomenon that gets talked about. If you EQ too high in frequency the "sweet spot" for listening becomes proportionally smaller.

For example, If you have any comb filtering in your room then you'll probably see more than 3dB swings with 1-2" movements depending on frequency. The wavelength of 3khz is 4.5", meaning you can have a peak and a null 2.25" from each other. So if you EQ up to 3khz then you can only move your head less than 2" from the mic position before (potentially) the EQ is totally off. It's worth mentioning here that your head is more than 2" wide. ;)

The exception to this rule is when A) the speaker has good directivity and B) changes to the EQ are relatively broad, like 1/2 - 1 octave. So, at frequencies above ~300hz you should treat EQ more like a variable tone control.
 

Sokel

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In my humble and very limited experience I have not found such large variations in such small measurement distances, but I am not denying that they may exist, it simply hasn't happened to me.
Of course the immediate next consideration would be, what do I measure myself to do and equalize with absolute precision to have a flat response if then swaying my head to the rhythm of the music can make me make changes in frequency response worthy of the worst speaker design
At a distance like my MLP at 3m,I can literally throw the mic (I won't,I treat it gently :) ) close to the sweet spot and will make very little difference at lows and up to 100-200Hz.
3-4 db as we saw in the chart is an enormous difference.In power terms is like one of the amps delivers half (or double) the power,that's crazy.

And then it's the pattern.The two amps follow it closely up to 200Hz but with a 2db difference and then rapidly changes as if it was in another room.
Something is amiss here.
 

capslock

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Where can you buy this amp already? The Fosi site links to the kickstarter page which says the campeign will be running until May 30th and units will ship in June.

Has anyone figured out whether units ordered through the kickstarter page and likely shipped by Fosi will have EU tax prepayed like Aliexpress, Hifigo, Linsoul?
 

jvdburgt

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Great review! What I am very interested in - given the 5W standby use - is the following: after the amp goes into auto off (so after 10 minutes), you disconnect the power plug (e.g. via the smart plug you use), and later turn in back on with the plug: does the amp turn on in standby mode (so without any 'plop'), or does it turn back on in 'on' mode?

Hopefully you can do this little test, as this might provide a smart home ready solution to the high standby power usage.
 
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