Fosi Audio V3 Amplifier Review

[antcollinet]

When playing the tt it produces music with the accompanying hum (this is more then a standard low frequency ground hum that im used to, its more high pitched).

Ill give the unplugging a go when im home next thans.

The problem might be that there is no actual earth ground to the system at all. I have a similar situation with my turntable, and have eliminated nearly all the noise by running a ground wire from the phono preamp ground terminal to a ground connection in an electrical socket.

If you do this take great care to ensure you are connecting to ground and not live or neutral. I removed the ground/neutral pins on the plug to be sure - we can do that in the UK.


EDIT - I've just looked up a couple of CA phono preamps, and they both have 3 pin power connectors which should mean this solution is not needed. Which Preamp is is you have? Does it have a 3 pin power connection, and is the earth terminal on the back connected to the earth terminal in the power connector? And do you have proper earthing in your mains supply?

 

[firestart3r]

Hi all!

Does someone know how big is the 48V 5A power supply?

I can't find the dimensions on Fosi's website.

Thanks !

 

[ICIETDIYEUR]

Hello.

Just a question in pictures to Fosi Audio or to a "specialist" ->

 

[Old_School_Brad]

Hello.

Just a question in pictures to Fosi Audio or to a "specialist" ->

View attachment 409849

View attachment 409850
View attachment 409851

Built-in speed limiter.
Normally you'd see a fuse in the main supply.

 

[ICIETDIYEUR]

Hi.

Sorry but I really don't understand the meaning of your answer

 

[Old_School_Brad]

Hi.

Sorry but I really don't understand the meaning of your answer

It's a surge current limiter.

 

[ICIETDIYEUR]

Right, you're not telling me anything but did you look at the photos well?
My question here is about the use of the 48V/10A Gan power supply that "everyone" wants to own or owns and precisely this "NTC" component on the FOSI V3 stereo PCB.
Do you see nothing that can make you ask a question or inform users in the form of a warning?

 

[ICIETDIYEUR]

What's funny is that this doesn't cause any problems with the AIYIMA A07 MAX amplifier while they don't offer 48/10A Gan PSU like FOSI AUDIO ->

LOL

 

[Old_School_Brad]

Right, you're not telling me anything but did you look at the photos well?
My question here is about the use of the 48V/10A Gan power supply that "everyone" wants to own or owns and precisely this "NTC" component on the FOSI V3 stereo PCB.
Do you see nothing that can make you ask a question or inform users in the form of a warning?

Its rating is not matched well with the PSU current rating. If overloaded it'll probably develop higher nominal resistance over time (not opening correctly) and eventually crack.

 

[antcollinet]

Right, you're not telling me anything but did you look at the photos well?
My question here is about the use of the 48V/10A Gan power supply that "everyone" wants to own or owns and precisely this "NTC" component on the FOSI V3 stereo PCB.
Do you see nothing that can make you ask a question or inform users in the form of a warning?

You can use a 10A supply if you like. But this amp won't take 10A out of it. It will do a maximum of 190Wx2 into 4ohm, so 380W total.

That is about 7.9A - oh look, how about that.

Plus in real use (with music) the average power will be much less (of the order of 10x less or lower) - so an average of 0.8A.


Furthermore, FOSI doesn't - as far as I can tell - sell this amp in combination with a 10A PSU.

 

[Wolf11Man]

There are relays near the current limiter. They might bridge the limiter after a few seconds.

 

[antcollinet]

There are relays near the current limiter. They might bridge the limiter after a few seconds.

Good point. And quite likely..... (wanders off to check)

 

[antcollinet]

Good point. And quite likely..... (wanders off to check)

Yes there is a relay that switches after power is applied. It sounds instant when connecting the PSU (with volume switch on) but that is to be expected : 4400uF with 3ohm will be 90% charged in about 40ms.

When pulling the plug there is a delay of about 1/2 second before it switches off again.

So the current rating of the thermistor is irrelevant - the current goes through the relay after charging the caps.

 

[Finn]

First of all thanks for all the reviews. I am looking to pair my Aurora DSP with 4 * Fosi V3. At the moment the 48 V PSU would be 40 € extra than just the amplifier. I could get a Mean Well LRS-300-48 (48 V, 7,3 A) for 30€. Did anyone try that? I have read that people had some audible problems (Noise) with other PSU.

The DSP/AMP Build is for active 3-Way speakers plus two subs so I would think about using 3 PSU and having Highs/Mid share one PSU.

Looking forward to your opinions!

 

[antcollinet]

First of all thanks for all the reviews. I am looking to pair my Aurora DSP with 4 * Fosi V3. At the moment the 48 V PSU would be 40 € extra than just the amplifier. I could get a Mean Well LRS-300-48 (48 V, 7,3 A) for 30€. Did anyone try that? I have read that people had some audible problems (Noise) with other PSU.

The DSP/AMP Build is for active 3-Way speakers plus two subs so I would think about using 3 PSU and having Highs/Mid share one PSU.

Looking forward to your opinions!

Personally I wouldn't mess about with third party PSU's - too unpredictable.

Similarly I would be wary of sharing a PSU between two amps. Fosi ran into issues with that with the V3 mono powering two of them from one 10A psu, and had to introduce a special filter to fix. You could of course try it, and then buy the extra PSU's only if there are problems.

 

[Wolf11Man]

The data sheet tells you what kind of PSU to use. Any SMPS from a reputated brand should be OK.

There are two things that can happen, if something goes wrong:

1. the PSU is too small and enters hickup mode or goes into protection.
Many Chinese no name SMPS that can only give the rated output for a second or two. That may lead to short "cut out's", complete shut down until a power cycle or worst, an on/off bang from the speaker. For subwoofer use or very high SPL the PSU should have at least the same Watt rating as the maximum power output of the amp. In this case cooling often becomes a problem, so some fan assistance may be needed or thermal shut down may happen.

2. You are running two D-amps on the same supply. A small difference in working frequency of the amps can give a high pitched noise in the speaker. One amp will have a sound of lower frequency than the other if this is the cause. There are no options in any amp I know, giving the option to syncronize them the way as the chip manufacturer has planed. It is a procedure to make one amp the "master clock" and the following amp(s) the slave(s). It needs a switch and a two wire connection. The section of the data sheet is a bit hard to understand, so most Chinese D-amp "designer" don't bother about it and not even spent the 10 minutes to realize a jumper and two contact points on the PCB.

PS I have used Mean Well and MEISHILE without problems. MEISHILE is a low cost brand with useable products, but banned from the US market I have read.

 

[Finn]

Personally I wouldn't mess about with third party PSU's - too unpredictable.

Similarly I would be wary of sharing a PSU between two amps. Fosi ran into issues with that with the V3 mono powering two of them from one 10A psu, and had to introduce a special filter to fix. You could of course try it, and then buy the extra PSU's only if there are problems.

I actually thought that it would be possible because I saw that they were selling two V3 Mono with one PSU. Good to know that I will not be able to share them, reason is explained in the next post.

The data sheet tells you what kind of PSU to use. Any SMPS from a reputated brand should be OK.

There are two things that can happen, if something goes wrong:

1. the PSU is too small and enters hickup mode or goes into protection.
Many Chinese no name SMPS that can only give the rated output for a second or two. That may lead to short "cut out's", complete shut down until a power cycle or worst, an on/off bang from the speaker. For subwoofer use or very high SPL the PSU should have at least the same Watt rating as the maximum power output of the amp. In this case cooling often becomes a problem, so some fan assistance may be needed or thermal shut down may happen.

2. You are running two D-amps on the same supply. A small difference in working frequency of the amps can give a high pitched noise in the speaker. One amp will have a sound of lower frequency than the other if this is the cause. There are no options in any amp I know, giving the option to syncronize them the way as the chip manufacturer has planed. It is a procedure to make one amp the "master clock" and the following amp(s) the slave(s). It needs a switch and a two wire connection. The section of the data sheet is a bit hard to understand, so most Chinese D-amp "designer" don't bother about it and not even spent the 10 minutes to realize a jumper and two contact points on the PCB.

PS I have used Mean Well and MEISHILE without problems. MEISHILE is a low cost brand with useable products, but banned from the US market I have read.

Thanks for you reply. That sounds usefull. I was planning to use Mean Well PSUs because i have heard bad things about noname PSUs for Amps. The Meanwell PSUs are using 40 mm fans that I was planning to change to 120 mm fans with 3d printed adapters. I was also thinking about putting the PCBs in a new case to also add SpeakOn connectors and replace the RCA with XLR Connectors. Does anyone know if there are some 0 Ohm resisitors/jumpers that can be desoldered to use symmetric inputs? The traces from the rca connector do look like there is only two signal lines going to the op amps.

Also I would add heatsinks to the ICs to increase cooling capacity. Overall I would not drive them very hard and use limiters in the DSP.

 

[ICIETDIYEUR]

Hi Finn.

This PCB (XLR TO RCA) exists at ALIEXPRESS: search by photo ->

It requires a PSU as you see.

The other solution but without power supply is to use de-symmetrizing transformers but the cost of the PCB is 5 to 10 times higher ->

The advantage of the latter is that it ensures 'galvanic isolation' (total electrical isolation) between two audio equipment (source and amplifier), avoiding - among other things - ground loops that are often a source of 'hum'

Regards.

 

[Wolf11Man]

Thanks for you reply. That sounds usefull. I was planning to use Mean Well PSUs because i have heard bad things about noname PSUs for Amps. The Meanwell PSUs are using 40 mm fans that I was planning to change to 120 mm fans with 3d printed adapters. I was also thinking about putting the PCBs in a new case to also add SpeakOn connectors and replace the RCA with XLR Connectors. Does anyone know if there are some 0 Ohm resisitors/jumpers that can be desoldered to use symmetric inputs? The traces from the rca connector do look like there is only two signal lines going to the op amps.

Also I would add heatsinks to the ICs to increase cooling capacity. Overall I would not drive them very hard and use limiters in the DSP.

If you are going to take out the PCB and plan to put into another case, I see no need to buy the Fosi V3. There are lots of bare PCB out there.

If you spend just a few $ more, the 3e Audio PCB have symetric inputs. Maybe they even can tell you how to syncronize two or more amps in the correct, by Texas Instruments defined way. 3e sometimes answers technical questions, they only go silent when they don't know or you touched a sensitive spot of their "engineering" capability. Like known problems they can't fix...

Adding any filter is pure ignorance of the data sheet and shows a severe lack of technical skills. A filter doesn't cure the cause and will only reduce noise level, while the cross oscillation is still messing up the amps function.

Meanwell has a new line of low cost, 200% overcurrent cabable supplies. LRS with a "N2" in the product code. These have a fan that will only come on at 50°C. Which is not reached in normal use. A single MEAN WELL LRS-350N2-48 should be able to drive a single TPA3255 board under any load. Except maybe subwoofer use at constant full level. Which would need extra forced cooling for the TPA3255 and it's external components anyway.
These are no more expensive than the old LRS line.
From my experience they don't even get warm to the touch in normal audio and HT use.

If you are looking for a double TPA3255 PCB with symetric input, there is this one on AliEx:

It looks well build and has a reasonable price. The golden heat sink only makes it look cheap for an European technicians eye (-: May be the ticket for a three way active speaker. You don't need to use all channels, just ground the unused input.

 

[nerone]

Hi, I ordered a double V3 with 10A power supply from Amazon.It, from what I read it shouldn't work well, do you recommend canceling the purchase?