Fosi Audio V3 Mono Amplifier Review

[burkm]

Is there a reason I need to turn the preamp volume up higher for the v3 monos to get the same loudness as a single ZA3?

For Heresy IV speakers, the V3 monos require about 10% to 15% more preamp volume vs the single ZA3. I expected the opposite to be true.

Using an Eversolo DMP-A6 as the preamp. It is the same streaming or playing CDs through the optical port.

I don't hear a sound quality difference between the V3 monos vs the ZA3. Haven't done any measurements other than temperature. The ZA3 stays a lot cooler without a fan blowing across them.

I don't really know what the PFFB is supposed to do in the V3s. Would that account for the different required preamp volume levels?

The volume position of the preamp is not really relevant, because it depends on the individual sensitivity of the amp (and preamp), the established over-all gain structure (preamp => amp) and the layout (type) of the specific volume control, which is been used.
As long as You reach the required loudness from Your speakers everything is supposed to be "fine"...

 

[Brian Hall]

As long as You reach the required loudness from Your speakers everything is supposed to be "fine"...

No issues there.

 

[burkm]

You are measuring the wrong thing. I wouldn't really expect that doing anything with thermal paste, even removing it, would change the case temperatures.

Think of it like this, the chips are producing heat inside the case, the case temperature is going to rise until it dissipates the amount of heat produced by the chips at which point the temperature stabilises. The same amount of heat is being produced whether there is paste there or not so the case temperature is unaffected.

Inside the case it is a different matter of course. The poorer the thermal mating between chip and case the more the board and air inside will have to carry heat transfer to the case and so the internal components will be warmer. If you are concerned this is what you should be measuring.

Should be quite "hard" to get hold of the individual components temperature within the closed cabinet for a "private" user

My intention: I just gather the temperature on the surface of the cabinet and try to get it => hotter (!), so the temperature transfer between the case (and its components, especially the heat "generator" TPA3255) is improved. That'all, but some are misinterpreting what I'm doing Applying new thermal past is needed anyways, as soon as I remove the PCB from the cabinet, which i have to do to get a climps of the speaker connections soldering.

If it helps in doing what I did is at least "doubtful" because I don't know, if the heat transfer as a whole has been really improved by my actions. Both cases (I just changed two of those amps I got) showed signs of slipping in the PCB whilst thermal paste had already been applied, so i think, the one, who inserted the PCB into the casing originally, was facing the same problems I had. They just applied the thermal paste in between the 2 screws, while this might have been the place with max. even pressure. At least both amps appeard to be the same in this respect, so it's probably done by purpose and cost considerations (labor, time and amount of themal paste used).

 

[MCH]

I think it's probably good enough to measure just at a single point in time when the amp has been on long enough for its temperature to stabilise. Personally I'm not at all interested in details of how quickly it reaches that temperature.

How quickly it reaches that temperature is telling you how good is the thermal coupling between chip and heatsink, and indirectly, how "cold" the chip will be. Faster case warmup <- better thermal coupling -> cooler chip

All we can know from a case measurement is that the chips are going to be at some temperature hotter than the case.

And that's why the single point measurement at the case is useless.

What I was addressing is the people aiming to have an idea of how good the thermal coupling is, like the discussions about thermal paste Vs no thermal paste etc. I agree that at the end the important thing is the temperature of the chip and other components, but that is going to be a result of how efficient the heat sink is.

 

[SMen]

Thanks...that I can clearly understand, but I wonder about others.

I differ ...

Why would you want to digitize ... well possibly for convenience (for adding to a play list or for use with portable player). ...

Many recordings were not so well transferred to the digital format. Analogue to digital converters have improved ... so compare an 80s CD of 60s Jazz by Stan Getz or Paul Desmond / Dave Brubeck to a good modern transfer made with better ADC's , and hopefully it will sound as good or better than the original recording on vinyl.

A lot of digital remasters were simply not a patch on the originals. The vinyl revival did not just happen because of artwork, or 'tactile' play back. For many people, myself included, I just said ... hold on a minute ... if I just listen to some of these recordings on vinyl the digital version does not compare.

In 2024 however, digital playback is greatly improved.

There are also issues about 'loudness' ... recordings are 'jacked up' or 'peek limited' to such a degree that the vinyl can sound more natural ... ironically because mechanically the loudness can't work on the inner grooves of the record! Look up the saga regarding Michael Jackson's "Bad" ... the producer Quincy Jones successfully sued because the record company added so much peak limiting to his production in later production runs of the record ... 'the loudness wars' ...

For whatever reason though ... I still just prefer listening to the records rather than a digital transfer, even if A/B ing them shows little perceptable (if any) difference with a pretty good ADC I have. It's a whole different way of listening - you listen to the album.

 

[SMen]

Most people round here are perfectly aware that a ADC/DAC pair with competent electronics is 100% transparent** to the usual analogue sources - including vinyl.

**the analogue output from the DAC is 100% audibly identical to the "beloved vinyl sound" going into the ADC.

Just come across this after replying to @courtesy ... at what date in the development of ADC's do you think that they became 100% audibly identical?

80s, 90s, 2000's, 2010's, 2020's

or have they been perfect since the 1980's in your view / measured performance?

 

[Bernard23]

I differ ...

Why would you want to digitize ... well possibly for convenience (for adding to a play list or for use with portable player). ...

Many recordings were not so well transferred to the digital format. Analogue to digital converters have improved ... so compare an 80s CD of 60s Jazz by Stan Getz or Paul Desmond / Dave Brubeck to a good modern transfer made with better ADC's , and hopefully it will sound as good or better than the original recording on vinyl.

A lot of digital remasters were simply not a patch on the originals. The vinyl revival did not just happen because of artwork, or 'tactile' play back. For many people, myself included, I just said ... hold on a minute ... if I just listen to some of these recordings on vinyl the digital version does not compare.

In 2024 however, digital playback is greatly improved.

There are also issues about 'loudness' ... recordings are 'jacked up' or 'peek limited' to such a degree that the vinyl can sound more natural ... ironically because mechanically the loudness can't work on the inner grooves of the record! Look up the saga regarding Michael Jackson's "Bad" ... the producer Quincy Jones successfully sued because the record company added so much peak limiting to his production in later production runs of the record ... 'the loudness wars' ...

For whatever reason though ... I still just prefer listening to the records rather than a digital transfer, even if A/B ing them shows little perceptable (if any) difference with a pretty good ADC I have. It's a whole different way of listening - you listen to the album.

I use a £30 mic from Dayton that has an ADC built into it that's perfectly capable digitalising analogue sound waves as a reference instrument. I think the device in the Ultra is inherently better than the majority of analogue phono preamps. Preserving the sound of an LP is a non issue, anything else is likely placebo.

 

[burkm]

Notwithstanding the ongoing arguments

It's about 14:00 hours now over here (mids of Germany) and both units have reached average surface temperatures of 42°C - 43°C on top (room temperature - nearest wall - reached about 24.3°C).
I measured about 10 places each on top of the V3 mono cabinets (still idle) and it seems, depending on the rising room temperature, that they have stabilized right now at that appr. surface temperatures. The temperatures show a deviation of around 1°C, depending on where I measured. Fans have not been used and both amps have been placed side-by -side horizontally within a distance of appr. 1 inch (2,54 cm). Lateron I will do a "stress" test and measure again with source material playing - endlessly (loop) - at an average loudness of ???. In combination with other user measurements it should give an appr. impression, how the amps behave temperaturewise during "normal" use.

 

[tkst3llar]

I have the opportunity to get some 48V PSUs from work that are plenty big, Meanwell lighting switching power supplies, dimmable power supplies, industrial power supplies etc. Is there something special about the PSUs that Fosi provides or will any reasonable one suffice, even laptop PSUs?

 

[burkm]

There is no Info available, if anything "special" is provided for the V3 mono power supply, except the size of its connector.

 

[EddNog]

There is no Info available, if anything "special" is provided for the V3 mono power supply, except the size of its connector.

5.5mm external, 2.5mm internal DC.

-Ed

 

[antcollinet]

Is there a reason I need to turn the preamp volume up higher for the v3 monos to get the same loudness as a single ZA3?

Probably - most likely the gain of the two amps is different. Try the V3 mono on the higher gain setting.

If you are on the balanced input this is limited to 20dB which is on the low side - so not surprising you need more volts from the source. (ZA3 is about 26dB on XLR)

 

[antcollinet]

My intention: I just gather the temperature on the surface of the cabinet and try to get it => hotter (!),

That won't work. As has been pointed out, power into the case is the same. Case is "downstream" of the paste (In fact is the last component dissipating heat to the environment.

If power into the case is not changed, then case temperature will not change regardless of the paste. Only components upstream of the case will get hotter if it is not doing its job well.

 

[SMen]

I use a £30 mic from Dayton that has an ADC built into it that's perfectly capable digitalising analogue sound waves as a reference instrument. I think the device in the Ultra is inherently better than the majority of analogue phono preamps. Preserving the sound of an LP is a non issue, anything else is likely placebo.

Thank you for your reply. ADC's have improved over the last 40 years I believe, but we were told that digital measured perfectly and so was perfect back in the day.

My ADC is not expensive but very good. The 'anything else' you refer to is probably more measurable with phono stages than any (most) other piece(s) of gear these days.

To quote the wisest of members here (approximately) - why not do a blind test to be sure, with all these phono preamps!

No, what interests me most about these V3 monos, and a couple of other devices I am trying, is in fact related to your statement ... what is the point at which the measurements don't count because even the cheapest devices measure and perform so well? x distortion vs slightly worse distortion? The point of zero returns.

Historically measurements (it seems to me) have often been abused, and amazingly the equipment has got better (when it was of all perfect before). But these days, it does seem to be a very good time to be buying 'value' gear because it performs so well.

 

[antcollinet]

How quickly it reaches that temperature is telling you how good is the thermal coupling between chip and heatsink,

Not really - how quickly the case heats up will depend on how quckly heat is pumped into it. This is a result of the temperature differential between the chip/heatsink and case. The problem is the chip has very low thermal capacity - it will heat up very quickly - as will the transfer plate. So the rate of heat flow from chip to case will ramp up to full much quicker than the case will heat up. So the rate of temperature rise will not vary significantly with or without well performing paste.

 

[LSPhil]

I have the opportunity to get some 48V PSUs from work that are plenty big, Meanwell lighting switching power supplies, dimmable power supplies, industrial power supplies etc. Is there something special about the PSUs that Fosi provides or will any reasonable one suffice, even laptop PSUs?

there are no restrictions, you can use anything from 24V to 51V DC. Of course, the MW 600W 48V power supply will be very good. It will allow you to extract 2x250W at 4 Ohms or mono 500W from the system

 

[MCH]

Not really - how quickly the case heats up will depend on how quckly heat is pumped into it.

exactly

This is a result of the temperature differential between the chip/heatsink and case.

and the heat transfer coefficient, that is what we are trying to (roughly) evaluate here. h=q/ΔT

The problem is the chip has very low thermal capacity - it will heat up very quickly - as will the transfer plate. So the rate of heat flow from chip to case will ramp up to full much quicker than the case will heat up

most probably, but again, you are missing the different heat transfer coefficients. that "full heat flow" during warm up will be different in one case vs the other.

. So the rate of temperature rise will not vary significantly with or without well performing paste.

the rate of temperature rise, besides the heat transfer rate, will depend on many things, like for instance the mass and surface area of the case, but in any case, being alll other things equal, there will be a difference. How significant the difference is will only depend on how precise your measurement is.

 

[Killingbeans]

No, what interests me most about these V3 monos, and a couple of other devices I am trying, is in fact related to your statement ... what is the point at which the measurements don't count because even the cheapest devices measure and perform so well? x distortion vs slightly worse distortion? The point of zero returns.

Here's some qualified guessing:

Audibility thresholds of amp and DAC measurements

Introduction A recurring theme on ASR is whether or not the various measured qualities of the devices are audible. In this post, I'll present some clear and visual thresholds for when those imperfections can be considered a potentially audible concern. I will not explain the basics of amp/DAC...

www.audiosciencereview.com

 

[antcollinet]

Just come across this after replying to @courtesy ... at what date in the development of ADC's do you think that they became 100% audibly identical?

80s, 90s, 2000's, 2010's, 2020's

or have they been perfect since the 1980's in your view / measured performance?

I don't know - I don't have data on ADC performance over time.

If I were to guess I would say digital could audibly perfectly record vinyl probably from the early 80s. Some early CD players had 14 bit converters. 14 bits still has 84db of dynamic range - which matches or exceeds that of vinyl. Even if ADC's of the day only had 14 bit, they'd probably still be transparent to vinyl. But even by the Mid 70s, 16 bit 50kHz recording was in use in studios. By 1980 the redbook standard had been released in 1981 Sony released gear that could be used at home for recording redbook standard digital to VCR tape.

 

[antcollinet]

different heat transfer coefficients. that "full heat flow" during warm up will be different in one case vs the other.

Only until the chip heats up to the point where the heat is transferring through the thermal interface/resistance as fast as it is created. My expectation (though tests or calculations would be needed to verify) is that would be a very small time (a few seconds) compared to the temperature ramp up of the case. It would be difficult (or impractical if all you are using is a thermal probe and a stopwatch) to measure the difference.