Fosi Audio V3 Mono Amplifier Review

[peng]

Has anyone seen this post in the Fosi V3 Mono user-impressions thread?

Fosi v3 Mono - User Impressions | Owner's Thread

I bought a pair of V3 Monos/48V PS from Amazon, received them a few days ago. On examination out of the box they have different labels. One is a QR Code, the other is a standard barcode with what I assume is the S/N. The QR Code doesn't show a S/N when read with my phone QR scanner. I find it...

www.audiosciencereview.com

The newer gain versions (19–25 dB) seem to measure noticeably worse than the units Amir originally tested - roughly 10 dB worse in THD+N for one mono and about 5 dB for the other.

Can someone with a newer unit run their own measurements and confirm or contradict this?

If the newer batches don’t meet the published specs, that’s a problem.

The QA403 that I have been wanting to buy costs almost $900 before shipping, import duty/tax etc., so unfortunately I won't be getting one soon to do any measurements. 10 dB worse is okay for me though, as I am going to be using it to drive my ancient 8 inch subwoofer that has the amp board failed twice, and I am not going to buy another one even if it might still be available. I rewired it to use external amp, currently using a Nosound G2 Pro that uses the same TI Chip as Fosi's but it just doesn't seem to offer enough juice, hoping the Fosi amp would make a difference.

 

[peng]

The gain setting is only for RCA, balanced has a fixed gain.

What is it for the xlr then, fixed at 19 dB?

 

[Timegroove]

What is it for the xlr then, fixed at 19 dB?

Around 20 dB. You see it in the measurements in the first post.

 

[Russ_L]

Haha. This guy is engineering dad funny. Amir should implement more engineering dad jokes in ASR videos.

Also @Fosi Audio , Let's talk about the thermal design. It's better than an internal heatsink, but the linkage is still not good. That tube extrusion is not flat internally, so the distribution block makes poor contact with it. That increased distance is bad for heat transfer. We should instead move to a clam shell, that way you can have a perfectly milled surface to drop the chip against, doing away with the spreader block altogether. Reducing the distance is key to good heat conduction. It also saves on material.

It's a real pain to work with thermal paste in the current design, it slathers paste all across the bottom when you slide in and out. You waste paste, and it's kinda gross looking.

A thin thermal pad would work well. Who uses thermal paste anymore?

Russ

 

[Russ_L]

Those are describing the case I mentioned above - where you remove the speaker crossover, and implement an active crossover filter UPSTREAM of the amps (between source and amp)

You are not proposing to do that.

Here is what the article YOU linked to (I suggest you try reading it) says about the passive bi - amping you are proposing...

View attachment 368028

But my Emotiva XSP-1 preamp has low and high pass outputs for the L and R channels. Wouldn’t t=hat discount the above example?

Russ

 

[antcollinet]

But my Emotiva XSP-1 preamp has low and high pass outputs for the L and R channels. Wouldn’t t=hat discount the above example?

Russ

You are replying to a post more than 1 1/2 years old. Can you clarify in more detail what you are trying to do - and the facilities in the XSP-1 that allow yo to do it?

 

[Russ_L]

Sorry but I’ve only came onboard a few days ago (up to page 102). I’m planning on biamping my front L and R speakers using four V3 monoblocks. My Emotiva XSP-1 Gen II preamp has a built in “passive” crossover that provides two each low pass and high pass outputs. So the example shown in the old thread, while it refers to receivers, would not apply to my situation.

I know that a “passive” crossover is less than ideal but it’s a starting point. I’m going to research an “active” external crossover later at some point. An external crossover is preferred when the preamp is in HT pass through mode as all four preamp outputs just mirror the processors FULL range outputs.

Russ

 

[Russ_L]

Going to ask some more pertinent questions as further reading past page 102 seems non productive. Don’t cares care about opamp rolling and other issues constantly being re addressed.
Russ

 

[antcollinet]

Sorry but I’ve only came onboard a few days ago (up to page 102). I’m planning on biamping my front L and R speakers using four V3 monoblocks. My Emotiva XSP-1 Gen II preamp has a built in “passive” crossover that provides two each low pass and high pass outputs. So the example shown in the old thread, while it refers to receivers, would not apply to my situation.

I know that a “passive” crossover is less than ideal but it’s a starting point. I’m going to research an “active” external crossover later at some point. An external crossover is preferred when the preamp is in HT pass through mode as all four preamp outputs just mirror the processors FULL range outputs.

Russ

What speakers are you planning on using? That will only work, if your speakers have the internal crossover removed. Or if they are home built with no crossover to start with.

And then - if the crossover in the XSP is passive, at best, it won't be any better than the speaker internal crossover. Most likely it will not perform as well, and will mess up the frequency response, since the speaker manufacturer knows how to crossover their particular design to get the best out of it. Your XSP does not. If you are home building, then it might be an acceptable short term solution while you do your research on active filters.

The only benefit you can get from bi amping is from the use of much better performing, highly tuneable DSP filtering.

 

[JohnnyNG]

My Emotiva XSP-1 Gen II preamp has a built in “passive” crossover that provides two each low pass and high pass outputs. So the example shown in the old thread, while it refers to receivers, would not apply to my situation.

I know that a “passive” crossover is less than ideal but it’s a starting point. I’m going to research an “active” external crossover later at some point.

Not sure why you're calling it "passive". It's an active preamp with high-pass and low-pass outputs. IOW, a full active crossover.

It's intended for subwoofer use for which it is an excellent and somewhat rare inclusion in a stereo component. The "SUB WOOFER" labeling and 250Hz limit for HP/LP also imply this. To Ant's point, replacing a passive crossover in an existing speaker is a whole new ball game.

 

[antcollinet]

Not sure why you're calling it "passive".

I suspect he is referring to it filtering using passive components (RCL) rather than DSP.

 

[Russ_L]

What speakers are you planning on using? That will only work, if your speakers have the internal crossover removed. Or if they are home built with no crossover to start with.

And then - if the crossover in the XSP is passive, at best, it won't be any better than the speaker internal crossover. Most likely it will not perform as well, and will mess up the frequency response, since the speaker manufacturer knows how to crossover their particular design to get the best out of it. Your XSP does not. If you are home building, then it might be an acceptable short term solution while you do your research on active filters.

The only benefit you can get from bi amping is from the use of much better performing, highly tuneable DSP filtering.

The speakers are NHT 2.9s. They are four way towers. The lower set of the speaker terminals are connected to a 10-inch woofer in a sealed chamber. The upper set of terminals are connected to the lower midrange, upper midrange and tweeter drivers in their own sealed chamber. Quite amenable to Biwiring (current situation) or Biamping.

I’m in this hobby since my Freshman year in college 1960. I’ve done everything one can do in this hobby during the intervening years EXCEPT biamping. So I want to give it a try regardless of the outcome.

Two extra V3 monoblocks each with a 5A supply. $400. Pishka.

Russ

 

[Russ_L]

I suspect he is referring to it filtering using passive components (RCL) rather than DSP.

That is correct.

Russ

 

[Russ_L]

Not sure why you're calling it "passive". It's an active preamp with high-pass and low-pass outputs. IOW, a full active crossover.

It's intended for subwoofer use for which it is an excellent and somewhat rare inclusion in a stereo component. The "SUB WOOFER" labeling and 250Hz limit for HP/LP also imply this. To Ant's point, replacing a passive crossover in an existing speaker is a whole new ball game.

I do not have the schematic for the XSP-1. I’m assuming (usually not a good idea) that the implementation is passive as ant indicated RCL. If I could get the schematic (Emotiva provides schematics only for discontinued products) I could very easily determine the exact implementation as I’m MSEE.

Again, just interested in giving it a try regardless of the outcome.

Russ

 

[Russ_L]

I currently have a 3-channel ATI AT523nc amplifier which consists of three Hypex Ncore modules driven by a linear PS. An excellent amp. A second 523nc at $2,700 (10% discount) is an expensive solution when I’m unsure of the biamp outcome.

The Fosi solution is worthwhile trying.

Russ

 

[antcollinet]

So I want to give it a try regardless of the outcome.

your problem - if you leave the speaker crossovers in place - is you'll leave holes in the frequency response unless you precisely match the external crossovers (cut off frequency and rolloff) to the built in crossovers. This will be pretty much impossible, and you'll suffer the effects of cascaded filters, creating a steeper rolloff and unbalancing the crossover.

For example, lets say the crossover in the speakers between the woofer and the higher frequency set is set to 300Hz, and you set the external crossover to 350Hz. So you only send 350Hz an up to the HF drivers, and the Sub is only going to play 300Hz and lower - so 300 to 350Hz goes nowhere.

Worst though - if the max frequency cross over in the amp is 250Hz, then you can't even fix it, because you can only send 20 to 250 to the sub, and the HF drivers will only play 300 up. then 250 to 300Hz goes nowhere.
(Edit - I've just looked up the speaker - lowest crossover is 100Hz, so the 250Hz limit of the amp won't be an issue)


And this is ignoring any problems caused by the filters having different rolloff characteristics.

 

[Russ_L]

Ant $400 not an issue. But thanks for laying out the technical issues.

Russ

 

[antcollinet]

Ant $400 not an issue. But thanks for laying out the technical issues.

Russ

Fair enough - and if just playing for fun, you're not going to break anything you can't revert back.

 

[JohnnyNG]

Again, just interested in giving it a try regardless of the outcome.

Russ

I get that. Here's a cool related article.

BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1

ESP - The Audio Pages. How to biamp or triamp your hi-hi speaker system for greatly improved sound, and higher sound levels with less distortion.

sound-au.com

I went full 4-way active (total of 7 amps, 4 of them V3 Monos) but I was starting from scratch.

 

[Blainethemono]

1 year update.... I previously switched to the 10amp power bricks & USB fan kit. Recently added the LC30 Amp/Speaker switch with illuminated VU meters.

Amps are still going strong, still loud, clean & MUSICAL, pushing my Montana EPS2's just fine & dandy.