• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Fosi Audio V3 Mono Amplifier Review

Rate this amplifier:

  • 1. Poor (headless panther)

    Votes: 8 1.6%
  • 2. Not terrible (postman panther)

    Votes: 12 2.4%
  • 3. Fine (happy panther)

    Votes: 100 19.8%
  • 4. Great (golfing panther)

    Votes: 384 76.2%

  • Total voters
    504

rgruber

Member
Joined
Apr 6, 2022
Messages
19
Likes
14
No. Nor will I.

I listened to the Crown and the Rotel back to back and it wasn't even close. The Rotel is sitting in my storage unit. I replaced the Crown with the XTZ more for aesthetics than sound. Sound was similar with the XTZ having a darker background and less audible distortion (the more pricey Crown's have less distortion than the 1002).

I've done more intense listening between the Denon and the XTZ. The differences are more subtle but still apparent. I had the Denon in my system for several months (bought as my wife really wanted an integrated to simplify listening to music rather than the frankenstein tube pre-amp with linear power supply into the XTZ power amp I had before) and I just felt like something was missing. I hooked up the XTZ again but removed the tube pre, just went straight from my DAC and whatever was missing was back in spades. Mostly clarity, nuance and bass punch for which I sacrificed a bit of smoothness and warmth in female vocals in particular.

So admittedly non-scientific. I could live with either but definitely prefer class D.

The argument could be made that perhaps it's just having gobs of power on tap makes a bigger difference than people generally acknowledge.

That sounds about right when using a very high power amp on difficult loads/speakers.

I'm not so sure about this claim though. But you did go from a 60W/ch amp to hundreds of watts. Have you been able to do a A/B blind listening test with a switchbox to compare the amps?
 

Jim Taylor

Senior Member
Forum Donor
Joined
Apr 7, 2024
Messages
314
Likes
882
I listened to the Crown and the Rotel back to back and it wasn't even close

So admittedly non-scientific.


Very true. More importantly, it's not controlled. Because of the nature and strength of our biases, comparisons (in audio or any other sensory group) must be conducted under rigorous controls. This keeps the Evil Bias Monster :)) at bay, and allows us to draw conclusions more in line with reality.

There are many biases. They are used by our mind for fast and useful (but not necessarily accurate) reactions to stimuli, in order to survive.

Here is a list.

Jim

p.s. - I have seen some people scan through that list, pointing out certain biases and saying, "Yup, that one applies to me. And here's another one that applies to me, too." That's not the way bias works. They ALL apply to each and every one of us, although not mixed in the same degree of strength. :)
 
Last edited:

Doodski

Grand Contributor
Forum Donor
Joined
Dec 9, 2019
Messages
22,112
Likes
22,384
Location
Canada
The argument could be made that perhaps it's just having gobs of power on tap makes a bigger difference than people generally acknowledge.
Well... The argument can be made for any amp really... Plus you went to a powerhouse amp and that is going to change stuff.
 

Lednek

Member
Joined
Jan 17, 2023
Messages
52
Likes
45
With RCA red carries the signal and black is ground.

With a bridged amplifier the red and black can carry + and - signals with neither being tied to ground.
This would explain the problem with simultaneous low and high level hookups. But when running only speaker level connections to a subwoofer, how can the subwoofer or speaker for that matter differentiate a bridged amplifier from a non bridged?
 

Sokel

Master Contributor
Joined
Sep 8, 2021
Messages
6,522
Likes
6,714
This would explain the problem with simultaneous low and high level hookups. But when running only speaker level connections to a subwoofer, how can the subwoofer or speaker for that matter differentiate a bridged amplifier from a non bridged?
The speaker or the sub won't know.
If you're lucky and the amp is protected from such event it will go into protection.
If not,well...
 

antcollinet

Master Contributor
Forum Donor
Joined
Sep 4, 2021
Messages
8,142
Likes
13,834
Location
UK/Cheshire
This would explain the problem with simultaneous low and high level hookups. But when running only speaker level connections to a subwoofer, how can the subwoofer or speaker for that matter differentiate a bridged amplifier from a non bridged?
Lets say the sub connects one of the speaker terminals to ground.

Lets say the amp connects the same speaker terminal to +50V (or even -50V)

Now you have a short circuit. If you are lucky the short circuit protection kicks in, and the amp shuts down (if it has short circuit protection). If you are unlucky the magic smoke is ejected.
 

Lednek

Member
Joined
Jan 17, 2023
Messages
52
Likes
45
Lets say the sub connects one of the speaker terminals to ground.

Lets say the amp connects the same speaker terminal to +50V (or even -50V)

Now you have a short circuit. If you are lucky the short circuit protection kicks in, and the amp shuts down (if it has short circuit protection). If you are unlucky the magic smoke is ejected.
Thank you. I was looking at it completely backwards. Like what could it possibly do to the subwoofer. Thanks for expanding my understanding and saving someone from my hasty response.
 

SMen

Active Member
Joined
Jan 2, 2022
Messages
225
Likes
111
Lets say the sub connects one of the speaker terminals to ground.

Lets say the amp connects the same speaker terminal to +50V (or even -50V)

Now you have a short circuit. If you are lucky the short circuit protection kicks in, and the amp shuts down (if it has short circuit protection). If you are unlucky the magic smoke is ejected.
So this begs the question does the fosi v3 mono have such protection (or possibly you mean the one in the powered subwoofer it occurs to me)
 

Sokel

Master Contributor
Joined
Sep 8, 2021
Messages
6,522
Likes
6,714
So this begs the question does the fosi v3 mono have such protection (or possibly you mean the one in the powered subwoofer it occurs to me)
Don't know about the amp but it's chip does:

DS.PNG

That's always under sensible conditions of course.
 

somebodyelse

Major Contributor
Joined
Dec 5, 2018
Messages
3,883
Likes
3,188
More detail from the tpa3255 datasheet which seems to address similar situations:
9.4.1.3 DC Speaker Protection
The output DC protection scheme protects a speaker from excess DC current in case one terminal of the
speaker is connected to the amplifier while the other is accidentally shorted to the chassis ground. Such a short
circuit results in a DC voltage of PVDD/2 across the speaker, which potentially can result in destructive current
levels. The output DC protection detects any unbalance of the output and input current of a BTL output, and in
the event of the unbalance exceeding a programmed threshold, the overload counter increments until its
maximum value and the affected output channel is shut down. DC Speaker Protection is disabled in SE mode
operation.
 

ovi

Member
Joined
Mar 6, 2023
Messages
18
Likes
9
Check this out, may be useful:
May I ask a follow-up question? I'm still trying to wrap my head around it.

According to Fosi, the v3 mono can output 160W @ 6Ω with a 48V/5A PSU. So the formula would be one of these two using RCA and the 25/31 dB gain settings:

sqrt(160*6)*10^(-25/20)=1.74Vrms or sqrt(160*6)*10^(-31/20)=0.87Vrms

I have connected a RPI streamer via USB to a SMSL SU-1 DAC via RCA at 31dB gain settings. SMSL SU-1 has an output level of 2Vrms
Since neither the Fosi v3 mono nor the SMSL SU-1 DAC has volume controls, I control the volume via the RPI.

Q1: Is this a viable setup, I mean can the SMSL SU-1 fully satisfy the Fosi v3 mono's requirements?
Q2: Is my volume handling “alright”? I quite like only having one point of control for volume.
Q3: Can I get the full 160W power of the two Fosi v3 Monos with this setup provided the speakers support it?
 

gwing

Active Member
Forum Donor
Joined
Mar 19, 2022
Messages
193
Likes
181
So this begs the question does the fosi v3 mono have such protection (or possibly you mean the one in the powered subwoofer it occurs to me)
I think it begs the thought "just use a line level output" not the Fosi (or any other Tp3255 chip) amp's speaker level outputs. You really don't want to be driving the chip into protection, not if you don't want smoke - potentially shorting out that 48v output to earth isn't a good idea for any amplifier.
 

gwing

Active Member
Forum Donor
Joined
Mar 19, 2022
Messages
193
Likes
181
May I ask a follow-up question? I'm still trying to wrap my head around it.

According to Fosi, the v3 mono can output 160W @ 6Ω with a 48V/5A PSU. So the formula would be one of these two using RCA and the 25/31 dB gain settings:

sqrt(160*6)*10^(-25/20)=1.74Vrms or sqrt(160*6)*10^(-31/20)=0.87Vrms

I have connected a RPI streamer via USB to a SMSL SU-1 DAC via RCA at 31dB gain settings. SMSL SU-1 has an output level of 2Vrms
Since neither the Fosi v3 mono nor the SMSL SU-1 DAC has volume controls, I control the volume via the RPI.

Q1: Is this a viable setup, I mean can the SMSL SU-1 fully satisfy the Fosi v3 mono's requirements?
Q2: Is my volume handling “alright”? I quite like only having one point of control for volume.
Q3: Can I get the full 160W power of the two Fosi v3 Monos with this setup provided the speakers support it?
You'll be fine. If the SU1 is sending a 2V signal to the v3 on RCA it will be capable of driving it to full volume.

Personally though, I like to have a volume knob somewhere in the chain and wouldn't be comfortable just having the Pi for control, I do suggest setting the v3 to minimum gain, at least to start with.
 
  • Like
Reactions: ovi

SMen

Active Member
Joined
Jan 2, 2022
Messages
225
Likes
111
I think it begs the thought "just use a line level output" not the Fosi (or any other Tp3255 chip) amp's speaker level outputs. You really don't want to be driving the chip into protection, not if you don't want smoke - potentially shorting out that 48v output to earth isn't a good idea for any amplifier.
I've had no problems with either the A07 or the A08 which are BTL - no additional heat or such either, so I think that I should expect the same with the Fosi Monos (with my particular subwoofers).
 

gwing

Active Member
Forum Donor
Joined
Mar 19, 2022
Messages
193
Likes
181
I've had no problems with either the A07 or the A08 which are BTL - no additional heat or such either, so I think that I should expect the same with the Fosi Monos (with my particular subwoofers).
Good luck :)

Although, to be fair, I'm also good running speaker level connections from a little DDA amp (sta326) to an equally tiny REL sub - but I would use line level if I could. I'm certainly not planning to do the same with my monos.
 

ovi

Member
Joined
Mar 6, 2023
Messages
18
Likes
9
You'll be fine. If the SU1 is sending a 2V signal to the v3 on RCA it will be capable of driving it to full volume.

Personally though, I like to have a volume knob somewhere in the chain and wouldn't be comfortable just having the Pi for control, I do suggest setting the v3 to minimum gain, at least to start with.
Thanks. I mostly listen via Spotify Connect, so I control the volume from my Spotify Android app. The RPI runs moode audio and is set to allow max 60/100 volume. This all works out fine in practice, I was just double-checking with you guys. Also, sometimes when running late, I play music for my dog at home, so I need to be able to fully control the volume from my phone and be 100% sure what the output level will be.
 
Last edited:

SMen

Active Member
Joined
Jan 2, 2022
Messages
225
Likes
111
Good luck :)

Although, to be fair, I'm also good running speaker level connections from a little DDA amp (sta326) to an equally tiny REL sub - but I would use line level if I could. I'm certainly not planning to do the same with my monos.
Back in the day with REL and MJ Acoustics the speaker connection was the favoured one (often).

It's a moot point though for the V3 mono set up, that if you are in fact going to use the line level to run a subwoofer, you need a pre-amp with a line level subwoofer out.
 

HoweSound

Active Member
Joined
Apr 22, 2021
Messages
165
Likes
211
Location
BC, Canada
Dumb question: I have two of these coming. The XLR connector port on the V3 looks different than the standard XLR connectors on my other equipment. Is this some kind of mini XLR? will I need a hybrid cable to plug these into my Freya S pre-amp?
 

EddNog

Active Member
Joined
Mar 1, 2024
Messages
143
Likes
142
Dumb question: I have two of these coming. The XLR connector port on the V3 looks different than the standard XLR connectors on my other equipment. Is this some kind of mini XLR? will I need a hybrid cable to plug these into my Freya S pre-amp?
Fosi uses a type of port that accepts BOTH, standard XLR as well as TRS balanced connectors. You’ll be fine with your standard XLR cables.

-Ed
 

GoDawgs

Member
Forum Donor
Joined
Apr 30, 2024
Messages
45
Likes
42
Location
Tidewater, VA, USA
I'm curious about these Muse02 op amps that Fosi is throwing in with the V3 mono Kickstarter orders. I do believe the Kickstarter hit $500,000, so I believe we get 2 op amps per order (not per amp). Why should getting 2 op amps per order be a reward if, (as some folks have written in other threads), swapping op amps is normally ill advised and even risky in some instances? Are these Muse02 op amps properly matched with the existing V3 Mono amp components? Are these any real noticeable improvement to the amp output or will they be just a hobby test listen where I may get to say things like "detail", "fast", "wider stage", and other neat-o audio descriptive phrases?

By following this thread I think I understand that each V3 mono (I ordered 2), has 2 op amps that may positively affect sound if swapped. Even if I want to try swapping op amps I wouldn't get the full effect without buying another $120 worth of op amps (2 more Muse02s)? I was all ready to give it a try until I figured out I could only do one V3 mono amp without sinking more money. Would swapping one of the op amps in each V3 mono even be worth the labor of opening the case? (Would swapping both be worth it?)

I'll think I'll wait and hopefully some other folks will attempt to determine if their Muse02 op amp offers a real reward vs. just a possible slight change in sound.

But I will say thanks for the XLR cables Fosi, and I would wear an size XL t-shirt if it came with my order.
 
Top Bottom