Fosi Audio V3 Mono Amplifier Review

[antcollinet]

Cherry picking a little there, I'll refrain from doing that myself.
The OP tempers their statements really well on the last page, as do many of the commenters.
Don't forget to enjoy the hobby .

I'm loving it.

I love it even more because I know I don't have to jump through a million and one hoops to generate top notch sound quality. This place is great for that.

 

[Rafaille]

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

Or you go with a proper analog cross over in the speaker and feed channels with separate amps, hence my question about amount of existing crosstalk when only using one amp.
I actually read too fast I thought that is what @quocheiser had in mind.
Although I agree doing this upstream and in the digital realm (+ some DSP) is preferable and offer more control.

 

[antcollinet]

Or you go with a proper analog cross over in the speaker and feed channels with separate amps, hence my question about amount of existing crosstalk when only using one amp.

I answered that above. Passive bi-amping doesn't change the frequencies in the amp. Both amps still amplify the full frequency band ( eg 20Hz to 20KHz), and deliver the complete frequency band to the speaker terminals. Separation is done in the crossover in the speaker, and that doesn't change whether you are bi-amping or not.

 

[Rafaille]

I answered that above. Passive bi-amping doesn't change the frequencies in the amp. Both amps still amplify the full frequency band ( eg 20Hz to 20KHz), and deliver the complete frequency band to the speaker terminals. Separation is done in the crossover in the speaker, and that doesn't change whether you are bi-amping or not.

True, fair enough I got confused re bi-amping (past midnight in the UK). Anyway let him have his quest, I am going the DSP and separate amps way for my part anyway.
Let us call it a day and get back to Fosi V3 mono.

 

[jdg78]

For the umpteenth time, I hereby testify that my two four year old A07s are still performing flawlessly after spending most of those years powered up 24/7 on 48VDC, despite their obviously deficient thermal design and 50V-rated Nichicon filter caps. Real world music listening is a far cry from rigorous bench testing with steady input from a signal generator, and in my particular use case (or others like it) even less-than-optimal little "chip amps" like my now-elderly A07s are likely to thrive long-term.

Same here. I've had a pair of these little A07's powering the front and rear channels of my HT setup going on close to 3 years now. I keep them powered on 24/7 and have had absolutely no issues at all during this time. They power my speakers as loud as I could possibly want in my medium size living room, delivering clean, punchy and transparent sound with absolutely no background noise or audible distortion. Dollar for dollar (I think I got them on sale for like $65 each?), I can't think of any better value in all my years of hi-fi.

If I were going to do it again today, I would probably get a bunch of these V3 monos if only because of the power standby mode, and because I don't really need a volume knob as I'm using these as pure power amps. But even then, I doubt they would sound noticeably better than what I currently have.

 

[Overseas]

'Transparent sound' - what would that be in the absence of measurements? Can you tell by ear which one of 10 amps is 'transparent' or how does this work?

 

[Fosi Audio]

What do you guys think about setting these amp upside down with some taller adhesive feet and applying these heatsink over the chip? Also considering applying new thermal compound to the chip itself. @Fosi Audio, any thoughts?

Yes, we have consistently been exploring ways to incorporate more effective cooling designs and technologies into our amplifiers, such as AirJet and micro fans.

 

[Bruce Morgen]

'Transparent sound' - what would that be in the absence of measurements? Can you tell by ear which one of 10 amps is 'transparent' or how does this work?

Most likely confirmation bias is involved in such opinions. I just "upgraded" my old A07s by giving them each their own 48V 10A SMPS, and my impression has been that the system sounds a little better -- but, knowing that such offhand observations have a huge psychological component, I'd never make a public assertion of any actual improvement.

 

[jdg78]

'Transparent sound' - what would that be in the absence of measurements? Can you tell by ear which one of 10 amps is 'transparent' or how does this work?

I mean it sounds clear and free from any obvious distortion or coloration to my ears. It’s a descriptive term, not a scientific claim.

 

[Overseas]

I mean it sounds clear and free from any obvious distortion or coloration to my ears. It’s a descriptive term, not a scientific claim.

From transparence to distorsion and coloration... Not contesting your statement, just want to understand how you can experience that by ears only. I guess even bad amplifiers do not distort in the first 1,2,3 watts.

 

[nitpicker1]

most amps struggle with lower Ohm because you need to push more current to achieve the same power which means more heat

Not even remotely correct.

Volts staying the same (volume level) divided on lower resistance = more current flowing freely. This inherently increases watts (I*V) per volume level. Which is why you'll see on any amp, that driving lower impedance speakers will offer more watts, as long as the amp can deal with the increased current flow. Better the components and conductors = the less heat.

It becomes more correct the other way around, needing more volts to reach same watts with higher impedance. Higher volt than current in a watts relationship will always run cooler because there's less current flow/ampere draw.

 

[ninetylol]

Not even remotely correct.

Volts staying the same (volume level) divided on lower resistance = more current flowing freely. This inherently increases watts (I*V) per volume level. Which is why you'll see on any amp, that driving lower impedance speakers will offer more watts, as long as the amp can deal with the increased current flow. Better the components and conductors = the less heat.

It becomes more correct the other way around, needing more volts to reach same watts with higher impedance. Higher volt than current in a watts relationship will always run cooler because there's less current flow/ampere draw.

Thats more correct true, @antcollinet described it pretty good in another Post too

What I wanted to say is that on a higher ohm speaker you need a bigger voltage supply to gain more max power, while on a lower ohm speaker you are most likely current limited first and wont gain much from going Let's say 40v5a to 48v5a

 

[Bruce Morgen]

Not even remotely correct.

Volts staying the same (volume level) divided on lower resistance = more current flowing freely. This inherently increases watts (I*V) per volume level. Which is why you'll see on any amp, that driving lower impedance speakers will offer more watts, as long as the amp can deal with the increased current flow. Better the components and conductors = the less heat.

It becomes more correct the other way around, needing more volts to reach same watts with higher impedance. Higher volt than current in a watts relationship will always run cooler because there's less current flow/ampere draw.

I've never felt more vindicated in my decision to run my old A07s on 48VDC -- that makes total sense and lines up nicely with actual measurements. I'm smiling because those little things are driving 8 ohm speakers, making the higher voltage an advantage.

 

[antcollinet]

I guess even bad amplifiers do not distort in the first 1,2,3 watts.

You'd guess incorrectly. Distortion will happen at all levels.

 

[jvdburgt]

RE bi-amping (thanks for all the feedback) I belive that the receiver does not have an active cross-over option for bi-amping, so I think I'll go with the skeptics on this one.

This does open up another question, given that surround channels often are less used than fronts and center (in terms of both sound volume and frequentness of sounds being played over these channels) will the auto on/off (triggered by 55db sounds if I remember correctly) work properly for the V3Ms driving the surrounds?

If this is not the case, I could still go with a smart plug setup for the surround-amps, but I'm not sure if that will result in the infamous "pops" of class D-amplifiers when turned on/off at the socket. Any insights on these two points?

 

[Rafaille]

RE bi-amping (thanks for all the feedback) I belive that the receiver does not have an active cross-over option for bi-amping, so I think I'll go with the skeptics on this one.

This does open up another question, given that surround channels often are less used than fronts and center (in terms of both sound volume and frequentness of sounds being played over these channels) will the auto on/off (triggered by 55db sounds if I remember correctly) work properly for the V3Ms driving the surrounds?

If this is not the case, I could still go with a smart plug setup for the surround-amps, but I'm not sure if that will result in the infamous "pops" of class D-amplifiers when turned on/off at the socket. Any insights on these two points?

According to @amirm measurements, there may be some pop when turning them on. Look at page 1.

 

[mike70]

but I'm not sure if that will result in the infamous "pops" of class D-amplifiers when turned on/off at the socket.

i have a well regarded british class AB amplifier (class "A" in Stereophile if that matters ) and have that noise at power on / off ... and i can say, very loud at power on.
we need to forget urban myths about "classes" and begin to think in the amplifier project / design

 

[quocheiser]

Or you go with a proper analog cross over in the speaker and feed channels with separate amps, hence my question about amount of existing crosstalk when only using one amp.
I actually read too fast I thought that is what @quocheiser had in mind.
Although I agree doing this upstream and in the digital realm (+ some DSP) is preferable and offer more control.

What I already have is a 31-band analog EQ between the source and amp, aka "upstream", which when used with a careful touch hopefully is reducing induced phase issues.
In the future if I bi-amp with these V3Ms I'd have to consider if getting an active crossover or even another EQ unit would be practical and cost-effective. If I can't hear the difference with any reduction in IMD distortion then it will be a costly part of the quest, but enjoyable nonetheless .
Luckily these V3Ms make it so cheap and easy to build/stack upstream components in a system as we go along.

 

[quocheiser]

But there isn't more power reaching each driver, unless the amp is being driven into clipping (the edge case I mentioned above). In which case the correct solution is to use an amp with enough power, rather than bi-amping.

In your case you already (will) have an amp with enough power. Don't waste them by using two per speaker.

Ah somehow forgot to reply to that.
Yeah you make a great point!
What I wrote was terribly worded, replace "more power reaching" with "more power available for" aka "headroom".
From what I understand, the closer you get to an amplifier clipping, the more likely distortion (from the amplifier) will increase.
I'd still prefer to stack amp power via these V3Ms than getting one bigger amp which offers way less flexibility AND costs more.

 

[Lednek]

RE bi-amping (thanks for all the feedback) I belive that the receiver does not have an active cross-over option for bi-amping, so I think I'll go with the skeptics on this one.

This does open up another question, given that surround channels often are less used than fronts and center (in terms of both sound volume and frequentness of sounds being played over these channels) will the auto on/off (triggered by 55db sounds if I remember correctly) work properly for the V3Ms driving the surrounds?

If this is not the case, I could still go with a smart plug setup for the surround-amps, but I'm not sure if that will result in the infamous "pops" of class D-amplifiers when turned on/off at the socket. Any insights on these two points?

Driving the front LCR stage of a home theater is an ideal use for the V3 mono. I've got three coming for just that purpose. My older Denon AVR-3400 will be more than adequate for driving the four surrounds. It shouldn't even break a sweat at very loud levels.