Fosi Audio V3 Amplifier Review

[Zek]

Why? What is wrong with this cheap solution?

I didn't mean rubber mats, but the position of the speakers directly on the floor.
First, that's not the optimal height for that speaker.
Second, dust from the floor will quickly accumulate on the speakers.
It has already been said that the most optimal speaker height is for the tweeter to be at ear level at the listening position (only if you don't lie on the floor and listen to music that way).

 

[KLi]

I didn't mean rubber mats, but the position of the speakers directly on the floor.
First, that's not the optimal height for that speaker.
Second, dust from the floor will quickly accumulate on the speakers.
It has already been said that the most optimal speaker height is for the tweeter to be at ear level at the listening position (only if you don't lie on the floor and listen to music that way).

Mhmm, maybe I give it a try. (But the Linton stands are really not that nice and they are expensive. I could, of course, use some chairs and make a test if it sounds better this way. Would be no blind test, of course... see: https://audiosciencereview.com/foru...ents-everything-or-nothing.29062/post-1015158 .) Thanks guys. I'm here exactly for this: to learn. ASR is exactly the place you can go and get good - and friendly - answers and not that crap you get on subjective sites. I have bought most of the gear you see in my pic, the Fosis for instance, based on measurements and commentaries in this very forum and got absolutely not disappointed. Quite the contrary. Kind regards and have a nice evening!

 

[wineaholic]

Is the built-in potentiometer of high quality? It has no labelling. I have two units, one of which runs very unevenly in the lower volume range. Would you send it back or should I just accept it?

The second point is that I would be pleased if blue LEDs were not used in future. The power supply unit in particular is completely annoying. Why not orange, red or green?

 

[JustAnAudioLover]

I'm going to ask what may be a pretty stupid question but: would one be able to tell the difference, using high-end speakers, with an amp like Topping's A90, as long as you're playing on relatively low volume? The Topping is 7x the price, but I'm wondering how much of a difference it would make if you only need a few watts of power to listen in a calm environment.

 

[NTK]

I'm going to ask what may be a pretty stupid question but: would one be able to tell the difference, using high-end speakers, with an amp like Topping's A90, as long as you're playing on relatively low volume? The Topping is 7x the price, but I'm wondering how much of a difference it would make if you only need a few watts of power to listen in a calm environment.

Here is an old Dr Toole post at AVS Forum on his experience with blind testing various amplifiers. TL/DR: Extremely likely no difference (when compared with proper controls).

https://www.avsforum.com/threads/official-jbl-synthesis-pro-revel-home-theater-thread.2515137/page-86?post_id=53745009#post-53745009

 

[KLi]

I'm going to ask what may be a pretty stupid question but: would one be able to tell the difference, using high-end speakers, with an amp like Topping's A90, as long as you're playing on relatively low volume? The Topping is 7x the price, but I'm wondering how much of a difference it would make if you only need a few watts of power to listen in a calm environment.

Hi Clement, I can only answer with my subjective observations, as I am listening mostly at low volumes and would consider the Linton 85th better speakers, albeit, I guess, not high end (for me they are, though). I've switched my Topping D10s for a Topping D 50 III with a Linear Power Supply (Topping P 50). But, frankly, I cannot hear a difference. Have not yet tested it on loud volumes and haven't done a blind listening test, since I don't have the D10s any longer. Since, as is the prevailing view here, all of those DACs sound alike, I would assume, you would not hear any difference.

 

[JustAnAudioLover]

@NTK @KLi thanks for your answers

This confirms a suspicion I had, but unfortunately it's very hard to find relevant informations on this kind of thing.

 

[Kolner]

Do these Fosi amps have speaker protection?

 

[somebodyelse]

Do these Fosi amps have speaker protection?

A bit, but probably not as much as you mean.

There is protection built into the TPA325x chip. This is more about protecting the amp than the speakers, but does shut it down in at least one scenario that could put DC across the speaker. See datasheet section 9.4.1 for the protection modes, 9.4.1.3 for the DC protection mode. It's not entirely clear whether this would also cut in if one of the output devices failed, but my guess is not, because the current would still be going through that amp channel. Plus if the output device has failed short it can't be turned off. Fosi don't appear to have added anything to monitor for DC on the output and disconnect the amp power, and there aren't any switching devices in the speaker output path.

 

[Kolner]

A bit, but probably not as much as you mean.

There is protection built into the TPA325x chip. This is more about protecting the amp than the speakers, but does shut it down in at least one scenario that could put DC across the speaker. See datasheet section 9.4.1 for the protection modes, 9.4.1.3 for the DC protection mode. It's not entirely clear whether this would also cut in if one of the output devices failed, but my guess is not, because the current would still be going through that amp channel. Plus if the output device has failed short it can't be turned off. Fosi don't appear to have added anything to monitor for DC on the output and disconnect the amp power, and there aren't any switching devices in the speaker output path.

So why is Amir recommending these (and other amps) that don’t have speaker protection?

I hope that doesn’t sound snarky but it would seem most of these really inexpensive amps don’t address as would add $$ to the cost.

All of my older amps have dc protections either via speaker coupling capacitors or protection circuits. The former is easily understood. On the latter, perhaps the protection circuits in these older amps that I own are similar to that of the Fosi…exist more to protect the amplifier. I’m not technical enough to understand nor remember from my research.

 

[trevor_bartram]

So why is Amir recommending these (and other amps) that don’t have speaker protection?

I hope that doesn’t sound snarky but it would seem most of these really inexpensive amps don’t address as would add $$ to the cost.

All of my older amps have dc protections either via speaker coupling capacitors or protection circuits. The former is easily understood. On the latter, perhaps the protection circuits in these older amps that I own are similar to that of the Fosi…exist more to protect the amplifier. I’m not technical enough to understand nor remember from my research.

Amir recommends these on a performance basis. ASR's readership is educated & therefore unlikely to short an output. More importantly we've heard stories of these Class-D amps blowing up for no obvious reason, possibly resulting in speaker damage, that concerns me enough to purchase a 32V version of a 48V capable amp & hope for the best.

 

[Kolner]

Amir recommends these on a performance basis. ASR's readership is educated & therefore unlikely to short an output. More importantly we've heard stories of these Class-D amps blowing up for no obvious reason, possibly resulting in speaker damage, that concerns me enough to purchase a 32V version of a 48V capable amp & hope for the best.

I haven’t yet read of a tale of someone experiencing speaker damage. I wonder if anyone else has.

 

[Elgered]

What I am looking forward to is an improved "stereo version" of the V3 Mono:
- auto on/off,
- input gain instead of volume pot
- no effective load impedancy impact

I don't need volume control with an active pre-amp, but love the auto on/of detection.
I am totally happy with my V3 Monos, but never need the power they offer. So a stereo version with the features and benefits of the "Mono" would really make me happy...

 

[LtMandella]

So why is Amir recommending these (and other amps) that don’t have speaker protection?

I hope that doesn’t sound snarky but it would seem most of these really inexpensive amps don’t address as would add $$ to the cost.

All of my older amps have dc protections either via speaker coupling capacitors or protection circuits. The former is easily understood. On the latter, perhaps the protection circuits in these older amps that I own are similar to that of the Fosi…exist more to protect the amplifier. I’m not technical enough to understand nor remember from my research.

I bought an external speaker protection unit. takes speaker level banana plug inputs from an amp and outputs through protection circuitry to second set of banana jacks (power on delay and DC blocker).
But I agree it would be better to have it built into the amps.

 

[buyman]

Hi.

My final scheme for the 'MOD' was as follows ->

Are you sure C21 is the first 10µF capacitor in the right channel? When tried to debug my unit (bought end of 2023) the potentiometer was connected to C23 according to my measurements. Anyway, I wanted to thank you for the schematic - it made debugging/measuring a lot easier.

As it's the review thread: anyone observed / measured the unit after some usage time? As I said, I have my unit since end of 2023 paired with a 48V power supply. I noticed that I hear a scratching noise when turning the volume knob. After a while, the right channel output was less than the left one. It happened not always, so I rewired and checked everything multiple times, including changing R/L channel to single out the issue to DAC, AMP, speakers or wiring.

Yesterday I opened my unit und measured the potentiometers (but didn't desolder them). I noticed a different resistance on right and left channel which would fit to the error. After turning it again for some times both values are now again the same, so issues solved for now - but I still think the potentiometer is slowly failing. So I probably will exchange the unit or the potentiometer itself if I can find a suitable spare part.

I'll also try to measure it the next time it fails - but have to figure out first a suitable way for doing so. I don't have differential probes at home, so I'll probably just do a voltage measurements on the outputs with my DMM at a 50Hz Input signal and 4 Ohm resistors. Or take the longer route and take unit with my and use company equipment with insulated inputs or differentiol probes.

 

[mackat]

I’m having a very strange issue indeed. I just got a Fosi V3 and an Aiyima 48v GaN power adapter off Aliexpress delivered about 30 mins ago.

When I connect it to my iPhone or iPad via a RCA to 3.5mm cable to Apple or third party USB-C adapter, it causes the touchscreen of the device to not behave properly!

Things will randomly open or won't close, or the app next to the icon you touched will open, etc. It becomes completely unusable.

It only happens when the RCA cable (either or both channels) is connected to the Fosi V3 and it is powered on.

What on earth could be causing this?

(Edit: Uh oh! I’m measuring 4 to 5 volts AC between the left/right signal and ground on the 3.5mm cable. What the …?)

(Second edit: I just measured 120V AC with one probe on either left or right channel and the other not touching anything WTF?)

 

[trevor_bartram]

I’m having a very strange issue indeed. I just got a Fosi V3 and an Aiyima 48v GaN power adapter off Aliexpress delivered about 30 mins ago.

When I connect it to my iPhone or iPad via a RCA to 3.5mm cable to Apple or third party USB-C adapter, it causes the touchscreen of the device to not behave properly!

Things will randomly open or won't close, or the app next to the icon you touched will open, etc. It becomes completely unusable.

It only happens when the RCA cable (either or both channels) is connected to the Fosi V3 and it is powered on.

What on earth could be causing this?

(Edit: Uh oh! I’m measuring 4 to 5 volts AC between the left/right signal and ground on the 3.5mm cable. What the …?)

(Second edit: I just measured 120V AC with one probe on either left or right channel and the other not touching anything WTF?)

It could be a couple of things:
1. Either or both of the power adapters is faulty. The only way to test this is by substitution using known good (brand name?) adapters.
2. Common-mode AC noise entering via adapter internal transformer inter-winding capacitance. Wrap a ferrite common mode choke on either or both adapter DC power leads (the more turns the better!). Why the DC leads & not the AC lead? Some power adapters do not have AC leads. Common-mode chokes utilize mutual inductance that is more effective on the lower impedance (higher current) DC side of a power adapter. Good luck. Let us know if you solve the problem.
P.S. as a precaution I use common-mode chokes (the're cheap!) on ALL DC power leads in my HiFi system to prevent AC common mode noise entering.

 

[mackat]

It could be a couple of things:
1. Either or both of the power adapters is faulty. The only way to test this is by substitution using known good (brand name?) adapters.
2. Common-mode AC noise entering via adapter internal transformer inter-winding capacitance. Wrap a ferrite common mode choke on either or both adapter DC power leads (the more turns the better!). Why the DC leads & not the AC lead? Some power adapters do not have AC leads. Common-mode chokes utilize mutual inductance that is more effective on the lower impedance (higher current) DC side of a power adapter. Good luck. Let us know if you solve the problem.
P.S. as a precaution I use common-mode chokes (the're cheap!) on ALL DC power leads in my HiFi system to prevent AC common mode noise entering.

Thank you for the advice, I will look into that. Just to clarify, I only have one power adapter - the Aiyima.

 

[antcollinet]

It could be a couple of things:
1. Either or both of the power adapters is faulty. The only way to test this is by substitution using known good (brand name?) adapters.
2. Common-mode AC noise entering via adapter internal transformer inter-winding capacitance. Wrap a ferrite common mode choke on either or both adapter DC power leads (the more turns the better!). Why the DC leads & not the AC lead? Some power adapters do not have AC leads. Common-mode chokes utilize mutual inductance that is more effective on the lower impedance (higher current) DC side of a power adapter. Good luck. Let us know if you solve the problem.
P.S. as a precaution I use common-mode chokes (the're cheap!) on ALL DC power leads in my HiFi system to prevent AC common mode noise entering.

Could also be the very fast switching edges of the GAN devices in the PSU coupling directly onto the DC output - or even directly onto the phone cables.

I would suggest getting a bluetooth receiver and connecting that to the amp input, then using bluetooth from the phone.

Or returning the GAN PSU and replcing with the sock FOSI PSU. There is no audible benefit for GAN.

 

[Sokel]

I won't get tired saying that any device should measured out of the box before connecting anything to it.
@mackat maybe got lucky that didn't end up with a burned phone, and probably the measured AC is very, very low in current (we hope) but it literally takes seconds to test.