Fosi Audio V3 Mono Amplifier Review

[Endibol]

Isn’t this fairly easy to sort out? Simply listen to them. If your sub woofer is out of phase with your monos it will be audible. Reverse the polarity of either and when it is in phase it will sound fuller, richer, less nasal.

Inverted polarity is not only an issue if you use both outputs (XLR and RCA) assuming inverted polarity between them.
The absolute polarity of the musical signal is important anyway since many musical instruments produce asymmetric wave patterns.

 

[Petrushka]

Inverted polarity is not only an issue if you use both outputs (XLR and RCA) assuming inverted polarity between them.
The absolute polarity of the musical signal is important anyway since many musical instruments produce asymmetric wave patterns.

That makes no sense at all. Maybe I’m just stupid.

 

[somebodyelse]

The absolute polarity of the musical signal is important anyway since many musical instruments produce asymmetric wave patterns.

That might be true if there were any consistency in absolute phase of recorded music, but there isn't. If it's something you care about then you need a phase switch somewhere in your system to let you change it on a per-recording or even per-track basis.

 

[Endibol]

That makes no sense at all. Maybe I’m just stupid.

See the contribution of @NTK earlier in this thread.

 

[Petrushka]

That might be true if there were any consistency in absolute phase of recorded music, but there isn't. If it's something you care about then you need a phase switch somewhere in your system to let you change it on a per-recording or even per-track basis.

Still makes no sense. Someone needs to draw me a picture illustrating this asymmetry.

 

[Endibol]

Still makes no sense. Someone needs to draw me a picture illustrating this asymmetry.

See #2853 in this thread by NTK. He responded to my question on this topic with some interesting articles.

 

[somebodyelse]

Still makes no sense. Someone needs to draw me a picture illustrating this asymmetry.

There's a whole thread about it. Any discussion of phase/polarity in general really belongs there not here.
https://www.audiosciencereview.com/...ds/absolute-polarity-myth-or-important.29391/

 

[Rgv250]

Hi, I have a 2.1 system with two v3 monos and an SVS sub. Will inverting the output of my miniDsp Flex to sub LFE do the same thing as swapping + and - on left right speaker terminals and correct polarity issues?

 

[somebodyelse]

That might be true if there were any consistency in absolute phase of recorded music, but there isn't. If it's something you care about then you need a phase switch somewhere in your system to let you change it on a per-recording or even per-track basis.

Some evidence of the lack of consistency in recording phase/polarity by record label, showing a fairly even split. Note the use of 'predominant' in there - it's not even consistent for all releases on a given label.
https://web.archive.org/web/20030621191023/http://home.attbi.com/~analyst18/Absolute_Polarity.htm

 

[somebodyelse]

Hi, I have a 2.1 system with two v3 monos and an SVS sub. Will inverting the output of my miniDsp Flex to sub LFE do the same thing as swapping + and - on left right speaker terminals and correct polarity issues?

Yes - inverting the output in the Flex will do the same as swapping the speaker connections. Also your SVS sub will almost certainly have a phase switch or knob because it's a normal thing to check when setting up a sub, probably described in the SVS manual. If you've got the frequency and slope of the sub crossover correct then incorrect phase will show as a big dip at the crossover frequency, while correct phase would have a flat response, or at least flatter. You might be unlucky and have a room response null at crossover frequency, in which case it may be hard to spot the difference.

 

[iLoveCats]

How do You know wihout looking at them opened? Some have received units without or had it only partially applied...

There's been at least one report of one unit being hotter than the other but I didn't see any follow up. The cooler one likely did not have paste. Open it. But you better have paste on hand to replace it from opening it. Mine are very warm and I don't suspect missing paste.

 

[burkm]

There's been at least one report of one unit being hotter than the other but I didn't see any follow up. The cooler one likely did not have paste. Open it. But you better have paste on hand to replace it from opening it. Mine are very warm and I don't suspect missing paste.

But how do You change or add thermal paste ? There has only been one person, who answered this, but I like to get more alternative answers to the "How to..." procedure.

 

[Rgv250]

Yes - inverting the output in the Flex will do the same as swapping the speaker connections. Also your SVS sub will almost certainly have a phase switch or knob because it's a normal thing to check when setting up a sub, probably described in the SVS manual. If you've got the frequency and slope of the sub crossover correct then incorrect phase will show as a big dip at the crossover frequency, while correct phase would have a flat response, or at least flatter. You might be unlucky and have a room response null at crossover frequency, in which case it may be hard to spot the difference.

Oh, so I get a big dip when inverting phase, but not at the frequency I chose for crossover. I am new to using a sub and miniDsp etc so followed miniDsp instructions on setting up my Flex. I was a bit confused as to where they got their crossover frequency from in the online guide. I choose 85hz and to be honest it does drop on inversion but only by a few dB. But, at 103hz there’s a massive sharp drop on inversion. So, does that mean I should use 103hz as crossover and that the SVS sub is actually in phase with the V3 monos? All interesting stuff even if I don’t fully understand

 

[vuittion]

Mines all packed up ready to ship back to Amazon UK.

Things I dont like.

1) I dont like the nasally glass like tone/sound of the amps.

2) ) Poor musicality/fatiguing

3) They run far to hot considering they are class d, I thought they where suppossed to run cooler.

4) The wiring inside looks a complete mess.

5) The inverted polarity fu#k up.

6) This is about the 6th class d amp i've purchased and they all sound shite.

7) Even the excellent measurements couldn't save it.

8) Back out of storage comes my lovely Arcam FMJ A39.
Lets make sweet music, Oh, how I've missed you.

9) Bye bye class d.

 

[Doodski]

This signals to me, that the thermal paste should be applied to the chip or to be exact, to its alu heatsink, and not to the bottom of the alu casing marked by the two screw positions.
Should the thermal paste be - thinly - covering the chips complete heat sink ?

That depends on the clearances when removing and reinstalling the PCB. You only need to coat one side as in either the chip or the heatsink.

The needed slide-in of the 4-layer PCB with its attached components does not (at least partially) remove or damage the layer of the rather thin thermal paste covering the alu heatsink during its movement ?

You will need decide if the clearance is enough. I do not have the unit in hand.

 

[burkm]

Mines all packed up ready to ship back to Amazon UK. Things I dont like.

1) I dont like the nasally glass like tone/sound of the amps.

2) They run far to hot considering they are class d, I thought they where suppossed to run cooler.

3) The wiring inside looks a complete mess.

4) The inverted polarity fu#k up.

5) This is about the 6th class d amp i've purchased and they all sound shite.

6) Back out of storage comes my lovely Arcam FMJ A39.
Lets make sweet music. Bye bye class d.

My NCore 400 stereo amps run quite hot too (can't touch the casing), thus I installed fans above it and increased some of the top case holes to get more (hot) air circulating...
Individual preferences for specific audio styles are widly (and subjectivly) devergent and determined by ones taste, thus some will like class D amps other won't for whatever reasons and most don't care about the class type of theyr amps. At least for me it's thus a "non event..."

 

[Doodski]

My NCore 400 stereo amps run quite hot (casing), thus I installed fans to it and increased some of the case holes to get more air exchange...

Heatsinking to a thin metal case is not the best method of dissipating the heat. So some heat is expected when touching the case.

 

[burkm]

Heatsinking to a thin metal case is not the best method of dissipating the heat. So some heat is expected when touching the case.

But it reduced the heat to the touch by quite a margin ...

 

[Doodski]

But it reduced the heat to the touch by quite a margin ...

You applied the thermal paste now?

 

[burkm]

No, not yet. I will tackle that tomorrow and will see during that action, if the polarity of the amps I got in diverse deliveries, have been changed already or I will - probably - attach a sticker to the rear plate if I don't switch the polarity of the speaker cables myself.