Fosi Audio V3 Mono Amplifier Review

[MCH]

Sharing power supplies is irrelevant to that though. The linkage is between the clocks in the amp chips. In principle clock drift between chips can create lower frequency “beating” signals that cause interference with low frequency radios. It’s got nothing to do with noise and even less to do with the power supplies!

For full disclosure:

From here:

https://www.ti.com/lit/pdf/slaa787

I don't see any mention to radio stations whatsoever, only to issues related to power supplies and noise. If you are referring to the choice of a different switching frequency to avoid radio interferences is a completely different thing.

 

[Ze Frog]

See their most recent post. As a direct result of this forum they are going to make the option of buying 2 amps and just the single 10A supply available. Problem solved!

I know, impressive stuff.
This is exactly why I'm buying a pair, and likely to use in my main system. Could spend £1000's elsewhere and not have such customer interaction and service. Love this kind of company where customer is the inspiration. Many other companies could learn a lot from Fosi and other vendors who have a similar approach.

 

[Deleted member 72219]

Out of curiosity, I noticed it has two swappable op-amps...is one for the XLR input and one for the signal stage, or are both for the signal stage (due to PFFB design)? The ZA3 has one signal stage op-amp per channel, so two since it's a stereo amp, and then a single separate op-amp for the XLR input, and then two more for the subwoofer output. It makes sense that the subwoofer ones are out of the equation, but I just wanted to confirm exactly what the two swappable op-amps are actually for. I want to bring over the op-amps from my current ZA3s to the new V3 Monos when I get them, but I'd hate to have to order an extra pair of op-amps in the event the V3 Mono needs two op-amps just for the signal stage. I am currently running just 1 Burson V7 Vivid op-amp per ZA3 on the right channel only (leaving the left channel one stock), and am really hoping that I would not need to order 2 more to use the ones I currently have in the new V3 Monos.

I also went ahead and ordered a pair of the 10amp, 48volt power supplies from Fosi. I am currently running a pair of 5amp power supplies with my two ZA3s, but when I ordered them, I ordered them without any power supplies, so I will just include these 5amp ones with them when I sell them (after putting the stock op-amps back in).

-Ed

@Fosi Audio would you be able to advise on this?

-Ed

 

[amix]

Sorry for the inconvenience. We'll provide the option of one 48V/10A PSU+Two V3 Monos on Kickstarter.

Hello @Fosi Audio , I hope to get two monos and two 10A PSUs on Kickstarter! Do you know the time in UTC when the campaign will start?

Thank you.

 

[Fosi Audio]

Hello @Fosi Audio , I hope to get two monos and two 10A PSUs on Kickstarter! Do you know the time in UTC when the campaign will start?

Thank you.

Yes, we'll provide that option too. The campaign will launch on April 20.

 

[early rejecter]

See their most recent post. As a direct result of this forum they are going to make the option of buying 2 amps and just the single 10A supply available. Problem solved!

Fosi is certainly responsive to user requests, but to be fair this particular case was just some confusion due to a typo in their initial response to your inquiry. The single power supply was already one of the planned Kickstarter options — see post #664 in this thread.

 

[wilbur1]

Fosi is certainly responsive to user requests, but to be fair this particular case was just some confusion due to a typo in their initial response to your inquiry. The single power supply was already one of the planned Kickstarter options — see post #664 in this thread.

Indeed, although I don't think it was a "typo" in their response to me (a couple of weeks ago, and well before #664). It was simply an error on that particular person's behalf, OR it could also have been that the question I asked prompted a change of potential proceedure on their part. I will give them the benefit of the doubt, either way. Fixed now!

 

[CMB]

Following this thread from the start, but am I bit confused about the early order discount. I understood that it will be limited to the first 200 and that this will start on April 20th.

- Do I need to register and order on Kickstarter ?
- Do they deliver to Europe, for instance to Luxembourg (for those who don’t know, it’s a tiny country close to France, Germany and Belgium).
- When would it then be delivered ?
- What about delivery costs?
- Or does this work only for the US?
Thanks for help.

 

[potfur]

Following this thread from the start, but am I bit confused about the early order discount. I understood that it will be limited to the first 200 and that this will start on April 20th.

- Do I need to register and order on Kickstarter ?
- Do they deliver to Europe, for instance to Luxembourg (for those who don’t know, it’s a tiny country close to France, Germany and Belgium).
- When would it then be delivered ?
- What about delivery costs?
- Or does this work only for the US?
Thanks for help.

Yes, you need to register and order on Kickstarter.

I bought the V3 via Fosi's Kickstarter campaign. It was delivered to Poland without any problems, at no additional cost. No customs charges/VAT were added although your mileage here may vary depending on local rules/customs or tax authority vigilance - this also depends from where exactly the package is shipped (China or the EU). Fosi may be able to advise whether any such charges can be expected.

I backed the project (made the pledge) on 25 April 2023, the pledged amount was debited to my card account on 25 May, the amp was shipped on 13 June and I received it a few days afterwards, so the whole process took around two months.

 

[StefanC]

Not too good for passive preamps, tube preamps or tube output dacs with digital domain volume then.

Cheers George

Apologies for my ignorance, but what would the XLR input impedance of two bridged V3 monos be? Fosi says the XLR input impedance of one V3 mono is 5kOhm.

 

[gwing]

Apologies for my ignorance, but what would the XLR input impedance of two bridged V3 monos be? Fosi says the XLR input impedance of one V3 mono is 5kOhm.

No apology needed, we all start somewhere and learn from there

Each V3 mono would have the same 5kOhm input impedance. Just as each input of a stereo version would have, i.e. the input impedance is a property of an individual input connection not some sort of summed value for the amplifier(s) as a whole.

 

[CMB]

Yes, you need to register and order on Kickstarter.

I bought the V3 via Fosi's Kickstarter campaign. It was delivered to Poland without any problems, at no additional cost. No customs charges/VAT were added although your mileage here may vary depending on local rules/customs or tax authority vigilance - this also depends from where exactly the package is shipped (China or the EU). Fosi may be able to advise whether any such charges can to be expected.

I backed the project (made the pledge) on 25 April 2023, the pledged amount was debited to my card account on 25 May, the amp was shipped on 13 June and I received it a few days afterwards, so the whole process took around two months.

Many thanks for these explanations

 

[StefanC]

No apology needed, we all start somewhere and learn from there

Each V3 mono would have the same 5kOhm input impedance. Just as each input of a stereo version would have, i.e. the input impedance is a property of an individual input connection not some sort of summed value for the amplifier(s) as a whole.

Thank you! So if my DAC has an output of 100 Ohm, the output/input impedance ratio is going to be 1:50, correct? I read it needs to be smaller than 1:10.

 

[Abstracted]

@Fosi Audio

1. Will the first batch be limited to 200 units?
2. And when will the first batch be shipped approximately?

 

[gwing]

Thank you! So if my DAC has an output of 100 Ohm, the output/input impedance ratio is going to be 1:50, correct? I read it needs to be smaller than 1:10.

I think the rule of thumb was that the input impedance should be at least 5x the output impedance and ideally 20x or higher - so I would expect 50x to be perfectly fine.

That said this is only a rule of thumb and the required ratio depends on the design of the DAC's output circuitry, a good one may work well even with less than 5x.

 

[Fosi Audio]

@Fosi Audio

1. Will the first batch be limited to 200 units?
2. And when will the first batch be shipped approximately?

Hi there,
1. You can enjoy the highest discount for the first 200 units, and you can still place order without limitation after the 200 units.
2. We'll ship the orders in June.

 

[mcdn]

For full disclosure:

View attachment 363206
From here:

https://www.ti.com/lit/pdf/slaa787

I don't see any mention to radio stations whatsoever, only to issues related to power supplies and noise. If you are referring to the choice of a different switching frequency to avoid radio interferences is a completely different thing.

I'm not going to argue with TI, it's their chip . However in practice this isn't an issue for complete amps or amps using typical modules. Take two Fosi V3 monoblocks, it doesn't matter if they share a DC power supply (shared 10A) or an AC power supply (2x5A). Each amp has its own internal power supply (PVDD) reservoir caps. The TI app note is more relevant for amps with common supply _after_ the PVDD caps. Which may be an issue for you in your compact DIY build but not for these Fosi amps or any others using modules with separate reservoir caps for each chip.

Power supply pumping is a concern but usually handled by wiring each module in alternate senses at input and output, so module A has inputs and outputs wired as normal, while module B has input signals inverted, and speaker outputs also inverted, for the same result but opposite power draw. Once that is dealt with the clock sync question is mostly moot I think, especially for music signals.

Back to the main point though, there is no downside to having a shared 10A supply instead of two 5A supplies for the Fosi amps.

 

[TonyJZX]

as people have said getting a single dual head 48v 10a or 2 x 48v 5a depends on how you got your system laid out

if its typical with the amps in the center and L/R speakers the 10a is good

but if you have the speakers wide apart and you have a power socket in each corner of the room then get 2 x 5a psus and treat them as quasi active speakers

run long speaker wire

48v 5a psus arent too expensive now?

 

[mike70]

I'm not going to argue with TI, it's their chip . However in practice this isn't an issue for complete amps or amps using typical modules. Take two Fosi V3 monoblocks, it doesn't matter if they share a DC power supply (shared 10A) or an AC power supply (2x5A). Each amp has its own internal power supply (PVDD) reservoir caps. The TI app note is more relevant for amps with common supply _after_ the PVDD caps. Which may be an issue for you in your compact DIY build but not for these Fosi amps or any others using modules with separate reservoir caps for each chip.

Power supply pumping is a concern but usually handled by wiring each module in alternate senses at input and output, so module A has inputs and outputs wired as normal, while module B has input signals inverted, and speaker outputs also inverted, for the same result but opposite power draw. Once that is dealt with the clock sync question is mostly moot I think, especially for music signals.

Back to the main point though, there is no downside to having a shared 10A supply instead of two 5A supplies for the Fosi amps.

And if your main speakers have a HPF (generally 80hz or something like that) ... the power current requirements are ridiculous, I mean, the PSUs will be laughing all the time.

 

[wyup]

Okay, but the question everybody wants to know is: Does a single V3 mono perform better with the 10A supply instead of the 5A?
Meaning more juice to the bone?
Or the caps feeding the chip can't release over 5A?