• 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: 7 1.5%
  • 2. Not terrible (postman panther)

    Votes: 11 2.3%
  • 3. Fine (happy panther)

    Votes: 95 19.9%
  • 4. Great (golfing panther)

    Votes: 364 76.3%

  • Total voters
    477

Sputnik

Member
Joined
Nov 14, 2021
Messages
70
Likes
150
Why not use RCA to XLR adaptors instead of RCA input for better performance?
RCA inputs have additional and innecessary gain as well as op-amp 'converter'.
XLR has enough input impedance to drive single-ended voltage.
Why do you think they put that op-amp there, to waste money?

You will lose quite a bit of output if you just feed se into the xlr. It will work, but it won't be better. You would need an active rca-xlr converter instead of an adapter. The 'innessary' gain and op-amp ARE your active converter, before they feed it into the balanced circuit of the amp.

So no, don't do that. It's a workaround for an amp that only had xlr in, it's not an improvement over Fosi's design.
 

PlasticDoc

Member
Joined
Nov 23, 2023
Messages
73
Likes
101
Location
Europe
This is indeed a well done FAQ.

The answer to: "How are you synchronizing the TPA3255 oscillator between the monoblocks in order to avoid Class D "Beat Tones" ? " ,
should have been a simple and honest: "We don't.".

This is another reason why the Fosi V3 Stereo PFFB will be a superior value proposition for the average consumer in comparison to the Fosi V3 Mono.
 
Last edited:

mike70

Addicted to Fun and Learning
Joined
May 9, 2021
Messages
933
Likes
665
Anyone willing to bet we're NOT going to hit the $300K mark by the deadline?

With 36 days left? :)
Wow! ... Take a free day, go to a park and enjoy some beautiful outland.
 

wyup

Active Member
Joined
Mar 29, 2018
Messages
199
Likes
76
Location
Bilbao, Spain
Why do you think they put that op-amp there, to waste money?
You will lose quite a bit of output if you just feed se into the xlr. It will work, but it won't be better. You would need an active rca-xlr converter instead of an adapter. The 'innessary' gain and op-amp ARE your active converter, before they feed it into the balanced circuit of the amp.
They've put the additional opamp mostly to provide more gain, if you need it, but you can bypass it. The fact is the XLR input has 9db more SINAD performance.
You don't need active converters. Hypex amps work balanced internally, and they advise users to use XLR adapters for unbalanced signal, which works well and has no penalty.

V3 amp has 20db gain for XLR, which is more than adequate for most 2V sources and volume requirements at home. RCA input has 25db and 31db with the gain switch. If you need that gain, ok, but my point is you may get better sound quality with XLR 20db gain, with less noise, and you don't need to attenuate that much for the same volume. Both opamp gain and source attenuation intruduce noise, which we can bypass by using XLR input.
 

Talisman

Major Contributor
Forum Donor
Joined
Mar 27, 2022
Messages
1,000
Likes
2,946
Location
Milano Italy
They've put the additional opamp mostly to provide more gain, if you need it, but you can bypass it. The fact is the XLR input has 9db more SINAD performance.
You don't need active converters. Hypex amps work balanced internally, and they advise users to use XLR adapters for unbalanced signal, which works well and has no penalty.

V3 amp has 20db gain for XLR, which is more than adequate for most 2V sources and volume requirements at home. RCA input has 25db and 31db with the gain switch. If you need that gain, ok, but my point is you may get better sound quality with XLR 20db gain, with less noise, and you don't need to attenuate that much for the same volume. Both opamp gain and source attenuation intruduce noise, which we can bypass by using XLR input.
But the point is that at those synad levels it is already practically impossible to hear anything.... Sinad is not an infinite parameter of sound quality, a Sinad of 140 does not indicate a "sound quality" better than 100.
Once distortion is so low and noise cannot be heard from the listening position in quieter musical passages, further increasing Sinad provides no benefit to sound quality.
 

SMen

Active Member
Joined
Jan 2, 2022
Messages
177
Likes
91
They've put the additional opamp mostly to provide more gain, if you need it, but you can bypass it. The fact is the XLR input has 9db more SINAD performance.
You don't need active converters. Hypex amps work balanced internally, and they advise users to use XLR adapters for unbalanced signal, which works well and has no penalty.

V3 amp has 20db gain for XLR, which is more than adequate for most 2V sources and volume requirements at home. RCA input has 25db and 31db with the gain switch. If you need that gain, ok, but my point is you may get better sound quality with XLR 20db gain, with less noise, and you don't need to attenuate that much for the same volume. Both opamp gain and source attenuation intruduce noise, which we can bypass by using XLR input.
I think this is a good point, but for me it just ticks an additional feature box. 20db and then options of 25db and 31db should anyone need it.
I think Fosi were criticized by a commentator for not having high enough gain with another model so they have simply covered all bases.

The Sylph Audio models have sometimes 14db gain into balanced and my understanding that this with the goal of better Sinad / measurements.

I'm interested that Fosi have hit 100 or 101 Sinad with higher gain.

I'll be using balanced ... and thankful the volume is not deafening with the volume control at the 9.00 o'clock position.
 

Sputnik

Member
Joined
Nov 14, 2021
Messages
70
Likes
150
They've put the additional opamp mostly to provide more gain, if you need it, but you can bypass it. The fact is the XLR input has 9db more SINAD performance.
You don't need active converters. Hypex amps work balanced internally, and they advise users to use XLR adapters for unbalanced signal, which works well and has no penalty.

V3 amp has 20db gain for XLR, which is more than adequate for most 2V sources and volume requirements at home. RCA input has 25db and 31db with the gain switch. If you need that gain, ok, but my point is you may get better sound quality with XLR 20db gain, with less noise, and you don't need to attenuate that much for the same volume. Both opamp gain and source attenuation intruduce noise, which we can bypass by using XLR input.
But you agree that you will lose output, correct?

Hypex advises adapters for amps that have only xlr input. As I said, it's a good workaround.

These amp designers would all love to get the same sinad on rca as they get on xlr. But let's pretend they're all incompetent, because they should just hotglue a $2 adapter into the back and their amps would sound and measure better.

How come Amir doesn't recommend this, he's all about sinad? Yet I don't see him suggesting you forego the rca input and get free extra performance with a $2 adapter. It would be one hell of a hack.
 

staticV3

Master Contributor
Joined
Aug 29, 2019
Messages
8,326
Likes
13,404
How come Amir doesn't recommend this, he's all about sinad? Yet I don't see him suggesting you forego the rca input and get free extra performance with a $2 adapter. It would be one hell of a hack.
Getting the most out of a given device isn't really Amir's forte.

If there's an RCA out on the DAC and a matching RCA in on the Amp, then that's what he's gonna use, even though connecting RCA to the XLR in has the potential of drastically higher CMRR resulting in less interference.
 

DavidM1

Member
Joined
Feb 7, 2023
Messages
66
Likes
53
This is indeed a well done FAQ.

The answer to: "How are you synchronizing the TPA3255 oscillator between the monoblocks in order to avoid Class D "Beat Tones" ? " ,
should have been a simple and honest: "We don't.".

This is another reason why the Fosi V3 Stereo PFFB will be a superior value proposition for the average consumer in comparison to the Fosi V3 Mono.
Yes, what does this mean for the average listener? It was a question I hadn’t heard asked before. Does using either one or two power supplies have any bearing on the answer?
 

Guddu

Addicted to Fun and Learning
Joined
Feb 10, 2020
Messages
929
Likes
837
But you agree that you will lose output, correct?

Hypex advises adapters for amps that have only xlr input. As I said, it's a good workaround.

These amp designers would all love to get the same sinad on rca as they get on xlr. But let's pretend they're all incompetent, because they should just hotglue a $2 adapter into the back and their amps would sound and measure better.

How come Amir doesn't recommend this, he's all about sinad? Yet I don't see him suggesting you forego the rca input and get free extra performance with a $2 adapter. It would be one hell of a hack.

Is there even a benefit of using RCA to XLR connection?
Will RCA to XLR cable carry or convert unbalanced to balanced signal!!!

It's more of a convenience, only.
 

SMen

Active Member
Joined
Jan 2, 2022
Messages
177
Likes
91
I remembered seeing this a while back...
But you agree that you will lose output, correct?

Hypex advises adapters for amps that have only xlr input. As I said, it's a good workaround.

These amp designers would all love to get the same sinad on rca as they get on xlr. But let's pretend they're all incompetent, because they should just hotglue a $2 adapter into the back and their amps would sound and measure better.

How come Amir doesn't recommend this, he's all about sinad? Yet I don't see him suggesting you forego the rca input and get free extra performance with a $2 adapter. It would be one hell of a hack.

I think these refer to the issue relating to gain. So Fosi are covering all bases here. So yes you will lose output, or need higher voltage input, either from the source or that additional op amp.
 

Talisman

Major Contributor
Forum Donor
Joined
Mar 27, 2022
Messages
1,000
Likes
2,946
Location
Milano Italy
I had never used kickstart, today I created an account to support this project.
Normally I don't like to put money forward but I want to help Fosi as a company and its policy of listening to users and collaborating.

Just a question. When creating the account I was not asked anything about the delivery address, how does it work?
 

EddNog

Active Member
Joined
Mar 1, 2024
Messages
109
Likes
114
I had never used kickstart, today I created an account to support this project.
Normally I don't like to put money forward but I want to help Fosi as a company and its policy of listening to users and collaborating.

Just a question. When creating the account I was not asked anything about the delivery address, how does it work?
If a crowdfund is successfully funded, then they will reach out to backers to confirm final delivery address as well as any additional add-ons desired (typically with something like BackerKit).

-Ed
 

Kayshot

Member
Joined
Apr 19, 2024
Messages
20
Likes
22
The pledge amount jumped 7k in the last 7 hours. With more than 30 days to go, I'd say we'll hit the 300k milestone with ease.

Not that I care much about receiving the reward, but for those who do.
 

Abstracted

Member
Joined
Feb 14, 2024
Messages
49
Likes
22
The pledge amount jumped 7k in the last 7 hours. With more than 30 days to go, I'd say we'll hit the 300k milestone with ease.

Agreed!
 

Lednek

Member
Joined
Jan 17, 2023
Messages
41
Likes
41
Just the fronts and the center speaker

Surrounds are fine with the internal amp
I am planning the same setup with my Dennom AVR3400. I anticipate significant improvement in all 7 Channels with the heavy lifting being done by the monoblocks. I agree the recievers internal amp section won't even come close to breaking a sweat powering the surrounds.
 

Fosi Audio

Senior Member
Audio Company
Forum Donor
Joined
Sep 10, 2021
Messages
325
Likes
1,608
I'm not sure what the benefit is of just one op amp.
Except on the single to balanced conversion.
This is presuming one per amp, and not one per order.
Anyone wanting to try these on the balanced inputs would need therefore to buy another 2 or 3!
Some confusion here @Fosi Audio
Thank you all for your support; we are indeed close to reaching our 300K goal. We have heard your voices and will explore new options for the stretch goal.:)
 

Kimbrough Xu

Active Member
Joined
May 18, 2022
Messages
234
Likes
103
I am planning the same setup with my Dennom AVR3400. I anticipate significant improvement in all 7 Channels with the heavy lifting being done by the monoblocks. I agree the recievers internal amp section won't even come close to breaking a sweat powering the surrounds.
What is the power of your surrounds?
 

gasolin75

Addicted to Fun and Learning
Joined
Sep 19, 2019
Messages
653
Likes
147
Location
Denmark
Could be fun to try the amps with a preamp with a streamer

Does fosi audio plna on making a preamp that matches the power amps ? (regardless if it has a built in streamer or not)

 
Top Bottom