Fosi v3 Review - The Good, The Bad & The Ugly

We review the FOSI v3 amplifier and compare it to a top flight Yamaha A-S2100 Integrated amp.

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Chapters:
0:00 Introduction FOSI v3
0:25 Unboxing FOSI v3
2:32 Background
3:59 The Good
5:29 The Bad
7:50 The Ugly
12:51 Yamaha R-S300
14:00 Equipment Used for Testing
14:40 Setting Levels
16:00 Music Test - Jack In The Green
18:33 16 kHZ Test
19:18 Music Test - Good Times Bad Times
20:00 REW Test Sweeps
23:40 Conclusion
24:40 Wine Rating

[franklekwan]

One thing to remine you, Fosi V3 (and many other small amps using the TI TPA3255 chip) is that this chip has a very low gain of 21.5dB (or about 11.9x). So if you use a standard line input level (1Vrms) to feed into this amp, the maximum output of this amp will be 17.7W at 8Ω and 35.4W at 4Ω, no matter which power supply you use. And probably the integrated amp you used to test has will have a gain matched to the line input level. Anyway, wish you happy listening to white noise!

[MiguelAngelVelazquez]

The V3 is capable of producing the amount of power that was previously measured by other reviewers. The problem is that music is 12dB lower than test tones. That means 4 times less input voltage signal to the amplifier. So, with the potentiometer at maximum your amplifier gets 0.5V(with a good DAC). The amplifier gain was measured at 26dB, this means 20 times the input voltage at the output. 0.5V x 20 = 10V. Now, Power= V^2/R, then 10x10/8 =12.5W. Far from the 50 to 60w measured with test tones. What's the solution? Get a preamp and increase the input signal to the amplifier. Buying a bigger power supply does not magically give you more power. You need an input signal high enough for the amplifier to require more voltage and current from the power supply.
People think that DACs produce 2V music input signal. But that's only for test tones at OdbFs, music is way lower than that.
Additionally the V3 has a Logarithmic potentiometer which at half only allows 10% and at 3/4 it allows 30% of the input signal to pass. Only at the last 1/4 it's where you get most of the power. At 90% of the pot you only get 50% of the signal. Just give you an idea. Basically people are not giving the amp the right input signal.

[MiguelAngelVelazquez]

I have some spare time while waiting at the tire shop. So I'll explain a little bit about power, gain, input signal, etc... let's do a math exercise. For example to get 100W per channel with a 4 ohm load we have P=V^2/R. 100W=V^2/4. Then V=20V. We need 20Vrms at the amplifier output. How do we get those 20V depends on the input signal and the amplifier gain. For simplicity let's max out the volume pot. That means that whatever input signal we apply to the amplifier via the RCA connectors go into the TPA3255 chip. According to other testing the amplifier has 26dB gain(just as a reference the Aiyima A07 has 29db gain, this means the output Power will be double or 3dB more than the V3 at any input signal voltage) 26dB means a 20x voltage gain compared to the input signal. So if we need 20V at the output with a 26db gain we need a 1Vrms input signal. You may think this is not much but the truth is that it is very hard to get 1Vrms with music or white/pink noise. Just try measuring the voltage at the RCA connector to realize you hardly get 0.5V even with a good DAC, why?. Because music signals are not at 0dBFS (like with test tones 1kHZ or whatever frequency). Music has in average -12dBFS, this means 4 times less voltage than what the DAC is capable of producing. So a good 2Vrms DAC will produce 0.5Vrms music signal. And a 0.5V input signal produces 4 times less output Power or 2 times less output voltage compared to 1Vrms. In the end 0.5V will only produce 25W on the V3. To get more power to need a bigger input signal.
Now, let's do the same exercise with the A07 which has 29dB gain, 3dB more than the V3. Just to simplify the output power will be 2 times the V3 power at the same input signal. This means 50W with a musical signal of 0.5Vrms, which again its not that easy to produce.
So, all in all. Without knowing what input signal voltage was used on this video, and based on the poor output power, I can assume it was not very high, probable 0.1Vrms or something like that.

[MiguelAngelVelazquez]

Something that "bothers" me from the ASR site is it does not say what input voltage was required to produce those power figure. I mean, I know hoy to calculate them but many people don't, so an expectation is created and people think they will get those high numbers by just connecting their phones and buying a 48V power supply. My friends you need a high input signal which sometimes can only he achieved with a preamp.
And the lower the amplifier gain the higher input signal is required.
I really don't care about power figures. I don't need more than 5W. I just use a good input signal from my DAC and preamp and leave the potentiometer around 20%, and then use the remote control from the DAC. That gives me plenty of power for my needs.

[DCZG-gziu]

What's the point having even best amp in the world if that can not drive your speakers loud enough?
Good test for V3 would be comparison with TI 3255 evaluation board..

[scottbennett]

Fun review! Thanks. I have the Fosi TB-10D, I use it for casual listening because it doesn't heat my room much and cause the AC to come on. It sounds pretty good too. I use my Yamaha A-1020 integrated amplifier for serious hi fi listening though.

[middleearthltd]

I am shocked that there are less than 5k subscribers. You need to run a test on that.

[marckroll]

“Songs From the Wood”, is an absolutely brilliant album, and excellent for auditioning gear.

[pascalmartin]

I wonder why audiophiles are so obsessed with 90 DB at 2m. I tried, and my whole family screamed at me. It was too loud for me too. I guess a real audiophile has a sound proof room (to avoid conflicts) and has lost hearing after going to too many rock concert.
Disclosure: I am more of a classical, jazz and folk music fan, and I listen to much lower DB levels.

[billsmith]

Great review. Just purchased the new fosi ZA3 and had the exact same problem. Even cranking the fosi to max volume couldn’t compare to my HK amp rated at 80W in 8 ohms. Further more, it didn’t matter if I was using a turntable with a preamp, CD player or Tuner. The results were the same with very low volume on every device unless I turned volume to max. Also, both rca back terminal came off switching cables. Fosi customer service was fantastic and has offered to replace the amp but not sure if a new amp will be any better.

[MrRonnmaui]

Honest review and all the receipts! I have a XTZ A2 300 I use for outdoor speakers and it is outstanding with any loud music levels. I recently bought the RSL iA255.1 to try and it sounds pretty nice, but a bit harsh at comparable loud levels. Sounds like the Fosi V3 might have issues too.

[nishamnazar]

I think you are mixing up "gain" and wattage @scientific audiophile

[guystewart]

hi. what do you mean, not really a pre out? can you connect stereo jack to twin rca to a power amp?

[howardperry]

Fosi v3 must be really good to garner this kind of attention.

[nekomancer]

At what distance was the testing done?

[galactusgalan]

Strange. I have 2 Fosi V3 with 48v power supply. With my PSB Stratus Gold 4 ohm 88 db, I can get peaks just a bit over 100 db with music. Preamp is using Topping E50. The sound is very clean at max volume. Zero issues with bass. Clean and tight. FYI the 48v version is currently $95 on their website. We do get it though. You like Yamaha. You don’t like Fosi.

[ujase]

I would argue most people are not hung up about the measurements but more tuned into it's sonic merits and as a bona fide owner of Fosi V3 it more than punches above its weight in terms of sound quality (which is subjective I know, one man's meat is another man's poison etc.). Kudos to you, nevertheless, for not going with the main stream and putting your own unique spin on it. It's always good, someone can step back, and look at it with a fresh perspective :)

[Jayboulders]

I've had the v3 for a few months now on my desk, use it 5 days a week. I have to say that I absolutely hate it. It sounds fine on low volumes, but start cranking it beyond 10 on the dial and it falls apart. The music sounds compressed, the bass is flabby, and the sound is harsh and grating. I'm glad I stumbled on this video because you're the first reviewer to mention the shortcomings of this amp. Cheers and thanks

[bujin]

23:55. Now that's an interesting statement. Would have been a better video if you had spent the time proving that assertion. I'd like you to find a bunch of other ~$80 amps, with more features, that you then definitively demonstrate have the same or better audio quality to the Fosi v3. Otherwise, the v3 probably is providing you the best audio quality you can get for ~$80. Though form factor is an important consideration in many cases, but you mentioned that, so I'll table that objection.

[eteddy]

believe it or not some people buy it connect it and listen to music