Fosi Audio V3 Amplifier Review

[Kimbrough Xu]

Oh, you can't do this blindly as what you get depends on the actual impedance of your speaker and not just my 8 ohm graph. In reality the high frequency impedance of your speaker is variable so the response variation in high frequencies would likewise modulate. Here is a sample speaker impedance graph:

Notice how the response varies around 6 to 6.5 ohm above 5 kHz. Every speaker will have a different range of values there, impacting the amplifier differently.

So the impedance of the speakers are not constant, they varies follows frequency?

 

[ROOSKIE]

So the impedance of the speakers are not constant, they varies follows frequency?

Yes, every speaker review here shows an impedance trace, have a look at one for reference.
Red is impedance vs frequency

 

[Brian Steele]

FWIW, if you're worried about the FR not being load invariant, then for a few $ in parts you can easily "linearize" the impedance of your speakers at high frequencies to match a target impedance with a simple cap and resistor connected between the speaker's terminals (or just add them to the internal x-over). The values of those components will depend of course on the speaker's impedance and the target that you're aiming for, but a bit of experimenting would get you there quickly enough. I was able to linearize the impedance at high frequencies of a DIY speaker design I'm working on at the moment to a target of 4 ohms with a 2.7uF cap and 4 ohm resistor. Impedance is now a flat 4 ohms from 5kHz up. This adjustment I guess makes it REALLY "Digital Ready", LOL...

 

[-Jim-]

Yes, we also provide the 48V/5A power supply here https://bit.ly/azus48v5a

@Fosi Audio I went looking at Amazon.ca for the V3 with the 48V PSU but can't find it. Can you provide a direct link for the V3 with that PSU? Thanks.

 

[Kimbrough Xu]

Wonderful! Thank you, Amir.

I have often though about asking for an efficiency test, because efficiency matters a lot to me, but never did.

Hi, what does the efficiency test do? What will it affect?

 

[keiron99]

If only it had a remote for the volume...

 

[Fosi Audio]

I would like to highly appreciate that Fosi Audio V3 has seriously tackled and improved some of the problems that have been pointed out in Chinese amplifiers.

Adoption of taper A volume pot
Adoption of 63V withstand voltage capacitor
Improvement of heat dissipation structure of amplifier IC
Improved part quality

There are still points to be improved, such as the adoption of PFFB, but I expect further improvements in the future.

We will take the PFFB into account. Would you please share your opinion on why PFFB is quite necessary with us?

 

[Jos]

Anybody checked the standby power consumption?

 

[Kimbrough Xu]

Hello everyone, I would like to thank Armin for this review of V3 and you for your instructive and enlightening comments.
Let me tell you that I am in a position to acquire a Fosi amplifier and I would love if you can help me decide between the BT20A Pro and the recently reviewed V3. regarding the latter I'm still not sure what "load dependency problems" means and how I could minimize that (I have to translate all ASR content to my native language) sorry.
Its use would not be for such an audiophile environment, if an advanced and growing listener.
The premises would be a balance between power, distortion, quality and theoretical duration of components.
I plan to connect them to two 3-way boxes with speakers, if possible of medium or high sensitivity, perhaps the bass design is with reflex. in the future some second amplifier only for sub woofer.
to the input I would connect a DAC Fiio KA5 dongle, or Tempotec HDII (humbly it is what I have) playing only music in high resolution MQA and Flac. I am subscribed to Tidal.
Thank you for your time, I hope you can help me with the choice, any comments are welcome.

If you don't need bluetooth and tone controls, of course V3 is better for you.

 

[Hiten]

And is some second hand class AB amplifier (like Yamaha A-S301) generally a better amplifier than these cheaper class D ones?

Better would be relative term. Cannnot find Yamaha A-S301 but Yamaha A-S300 has no problem uptill 100k.

copied from audio.com website.

regds.

 

[Hiten]

We will take the PFFB into account. Would you please share your opinion on why PFFB is quite necessary with us?

Few posts back there is distortion measurements posted by member 'badspeakerdesigner' Though others say some problems might not be solved completely.
I am newbie so pardon if posted anything not correct.
regards

 

[maudio]

Few posts back there is distortion measurements posted by member 'badspeakerdesigner' Though others say some problems might not be solved completely.
I am newbie so pardon if posted anything not correct.
regards

You are wrong. Badspeakerdesigner is a bit spamming this topic with measurements that are NOT done with Fosi V3 but taken out of the blue.

Then people just pick it up and refer to it like you do.

There are absolutely no reports from the field about Fosi V3 and speakers behaving the way as posted by badspeakerdesign.

Load dependency as measured by Amir is not removed by PFFB. PFFB would add another few dB of resolution to the amp and is nice to have.

 

[Jeromeof]

So, would this amp (or the Bt20a pro), with the 48v power supply, drive a pair of Aria 906 "correctly" ?
I wonder what the frequency response chart would look like in the particular case of the Aria 906.
What happens with a 15 ohms and 10 ohms load on the Fosi V3 or the Bt20a pro between 5khz and 20khz ? Would the frequency response be the same than at 8 ohms (not too bad), would it be more exaggerated starting at 5khz, would it start earlier?
If using the Bt20a pro which has tonal controls, would the tonal controls effectively act on that (btw, does anyone knows the frequencies covered by the treble tonal control...) ?

Wonder if the Fosi V3 or Bt20a pro, and Aria 906 would be a good match... ( depends on taste of course)

Thanks

I am absolutely no expert - but my reading would be that the Aria has a 10Ohm impedance in the 10K - 20K region which would probably cause the Fosi Audio (or any of these class D amps) to add 0.5 / 1 db to that region - so would sound brighter and might need some EQ. Maybe the tone controls on the BT20A Pro might be a simple solution - lower the treble slightly though that might affect more than just that region.

 

[amirm]

Hi, what does the efficiency test do? What will it affect?

It doesn't impact performance of the amplifier at all. It just gives you an idea of how much power is being used as you use the amplifier. Some people worry about their power consumption and cost of electricity. As well as amount of heat generated. It is not as important in such a small amplifier but I developed this new test so I thought I start using it.

 

[TonyJZX]

i think more than a few people expressed disdain for the 48v 5a power unit... i think this is a fair enough concern given many of us will be going for the upgraded psu to get some of that 89w at 8 ohms... and the fact that a good psu can be $75 or more... or even more than the $120 odd this unit costs w/ the psu...

and so here is the psu:

Fosi Audio 48V Power Supply Adapter for TB10D, BT20A PRO,V3

Power your audio devices with the Fosi Audio 48V 5A Power Supply Adapter. Perfect for TB10D, BT20A PRO, V3 models. Get powerful sound instantly.

fosiaudioshop.com

Amazon.com

this psu is used across multiple units inc. the BT20

here is our friend at Williston

they are able to sell such a psu at a lower price because they are amortising the cost across multiple devices and I bet this unit is already in use with printers or whaetver the hell else it can used for

it would have as good as reliability as any mass produced consumer psu

i would call this a safe bet and i think i trust fosi to have tested the 48v unit thoroughly... i mean they already have with the BT20 and all the other units it ships with

this is a safe buy

 

[Toku]

Better would be relative term. Cannnot find Yamaha A-S301 but Yamaha A-S300 has no problem uptill 100k.

copied from audio.com website.

regds.

The frequency response you point out is for the preamp section of the SA-CD input, not the power amp.
About the power amplifier part, the characteristic of 20Hz - 20kHz is declared.
It's a cunning way of describing a product.

 

[TonyJZX]

i think people are posting graphs of other TPA 3225 products and implying this one does the same thing

is this amp not "load invariant"? (no apologies to bob carver)

i dont doubt this amp will have issues with difficult to drive speakers but surely most of the common mass market speakers you expect to use on a $120 unit should pose no problem to this?

i'm not saying this amp will not have problems with a variety of speakers but i'm guessing the target audience is never going to encounter that?

show me a common speaker than the average V3 owner will come across that will show these bad results?

someone said the DBR62 may pose problems?

 

[restorer-john]

The frequency response you point out is for the preamp section of the SA-CD input, not the power amp.
About the power amplifier part, the characteristic of 20Hz - 20kHz is declared.
It's a cunning way of describing a product.

The Yamaha A-S300 has a response well in excess of 100kHz at 1W/8R. And it was no separable preamplifier in any case- it's integrated.

I have one here- happy to put a 100kHz sine into it if you want to see.

 

[maty]

show me a common speaker than the average V3 owner will come across that will show these bad results?

someone said the DBR62 may pose problems?

10-20 kHz: flat impedance, about 10 Ohms. With PEQ you can try to solve the problem. After, better idea with rePhase -> convolution filter -> software player as JRiver MC 64 bits

 

[Kimbrough Xu]

I don't know very much about amps. Under my probably incorrect mental model of how all this works, the biggest "problem" with this amp is the load dependency issue. Per the linked reference, the other benefits of PFFB relate to noise and THD, both of which are likely "good enough" without the PFFB?

Is the load dependency just a consequence of this TI chip, or can it be rectified with a different PFFB implementation or some other circuit?

Back to my faulty mental model. I have trouble understanding how big of a problem load dependency is. My speakers are 4ohm nominal, but is that the value I use to interpret the effect of the load dependency? I see that some (but far from all) of Amir's reviews have a frequency sweep, which usually shows much higher impedance at various frequencies. Are these the relevant values? If so, is it useful to only show 4 and 8ohm loads when speakers can have much higher impedances, including at much lower (i.e., audible to 40-year olds) frequencies?

To understand how big the problem is depends on your own hearing, if you can hear the difference, then it is a big problem, and if you cannot hear the difference, then it isnot a problem.

In my case, it is not a problem becasue I can not hear any difference, I cannot even hear the 20kHz.