Fosi v3 Mono - User Impressions | Owner's Thread

[SMen]

Welcome to ASR!

The figures shown are from the TI's TPA3255 datasheet. The first figure is the max output (at 1% THD+N) when used in the stereo (2 output channels) mode. The blue dotted line indicates the supply voltage of 48 VDC. With 4 Ω load (black curve), the output is ~230 W. Assuming that the amp has reached is maximum output current with 4 Ω load, the maximum output with 3 Ω load is 230 * (3/4) = 173 W. (Since power = current^2 × load impedance, and when current limit is reached, max output power is drops with the load impedance.) The 173 W estimate is conservative as the current limit is likely not an abrupt hard limit, and the stereo amp can probably output a bit more than 173 W (1 % THD+N).
View attachment 381599

The second figure is for the mono (1 output channel) mode. With 4 Ω load (gray curve), the max output is marginally increased to ~255 W (~0.5 dB increase, a likely-not-noticeable difference). But since the current output capacity is doubled for the mono mode, the 3 Ω (red curve) max output is increased to 325 W, which is about 2.7 dB (at most) more than the stereo mode.

The summary is that there is little benefit if load impedance is over 4 Ω, with the mono setup the heat dissipation will be distributed to 2 amps instead of 1 and therefore less stress for the monos when power output demands are high. You'll need to decide for yourself whether the optimistic estimate of 2.7 dB power increase at 3 Ω is worth going with 2 monos vs 1 stereo.
View attachment 381594

I think that ultimately the PFFB applied to stereo is going to provide consumers (us) with very high quality for low price.
I am still listening to my new monos just received.

Hi, does anyone here have experience with a Schiit Magni (any generation) as a preamp/volume control for the V3 Mono’s? From what I can find, this should work good together.

I also received one of these balanced volume controls separately
and in combination with the v3 monos this relay volume control is very very (very) good indeed (obviously my subjective opinion).
This is a relay balanced volume control and I suspect very close to the Schitt Freya in passive mode and the Schitt Kara also.

IF you are using a balanced output dac with output >= 4v approx, or a phono preamp likewise (iFi phono for example) to drive your v3 monos then one of these is well worth considering. I am frankly amazed.

I am not sure what the difference is between one of these adjusting volume with a balanced driver upstream vs a Freya 2 with it's no gain but actively driven option.

If you are going unbalanced then a Schiit Magni (I have not experience but in theory) should be very good also.

 

[EddNog]

...I also received one of these balanced volume controls separately
and in combination with the v3 monos this relay volume control is very very (very) good indeed (obviously my subjective opinion).
This is a relay balanced volume control and I suspect very close to the Schitt Freya in passive mode and the Schitt Kara also...

If only that unit had a remote control, it would basically be perfect!

-Ed

 

[Jon L]

My biased and subjective impression: the pair plays just as loud as the TacT without distortion and just as clear.

Wait a minute. Unless the Fosi Mono's sound better than your very old TacT, wasn't it money wasted? I suppose you could now sell your TacT..

 

[SMen]

If only that unit had a remote control, it would basically be perfect!

-Ed

It really is good! from the off! ... or should that be 'on' ... A remote control would be nice. For me with my vinyl records I'd like some balance control - I'm a bit eccentric maybe, but dual mono volume controls for channel matching would be wonderful.

I don't own your Freya 2 but I sure do like the concept. And I suspect yes, the relay volume control gives you what I am hearing here too big time.

 

[T&T]

Almost two weeks on from my 1st post.....every day with the monos are audio heaven for me.

https://audiosciencereview.com/foru...o-v3-mono-amplifier-review.53474/post-2019325

Swapped from RCA to TRS / XLR cables, I do not have any issues with hiss / loops, I was interested in seeing if there was any other difference, other than a difference in gain. My ears have not noticed any audible difference.

I am looking at two MUSES02 chips on the shelf and would like to try them, if nothing else, to see if I prefer the sound....I thought I saw a picture of where to install them. I know the one near the RCA input does not need changing. Of the remaining two, which should be changed to effect the 'best' result......somewhere I think I read that position 2 was the first one to change....which one is that?

https://support.fosiaudio.com/hc/en-us/articles/33329687302297-The-V3-Mono-has-three-op-amps-What-does-each-one-do-And-if-l-want-to-get-abetter-sound-which-one-should-l-change

I notice in the video that for the v3 the notches in the chip face the capacitors - is this the same for the v3 mono?

https://support.fosiaudio.com/hc/en-us/articles/32538018953881-How-to-replace-the-Op-Amps-in-the-V3

Thank you.

I have several opamp the position 1 also change the sound, I have to pull out the Muses02 the bass was too much, also you can pull out the orange metal out, leaving big holes on the side.

 

[rhing]

I received the pair of V3 Monos, two 48V/10A power supplies, and two pairs of the MUSES02 op amps. First thing I did was open up the amps to insure it had some thermal compound on the heat sink plate. It was just a dab on both amps, so I added some Arctic MX-6 thermal compound. I used some strips of Saran wrap on top of the paste on the heat sink plates and carefully slid the amp boards back in place. Then I carefully pulled the Saran wrap off. This kept the thermal compound from getting smeared inside the case.

I’ve been playing music all day and the amps are sounding great. The dual mono amps with the excellent channel separation really do bring out the three dimensionality of a large, deep soundstage. The KEF LS50’s powered by some great Pass DIY Class A amps don’t create that large and deep of a soundstage as they do with the V3 Monos. The frequency extension at both ends of the spectrum is really nice with a greater sense of air and detail along with additional weight at the bottom. Bass notes are clear and articulate.

Playing music all day, the amps get warm, but I would not describe them as getting hot like the heatsinks on my Aleph J Class A amp can get. I can put the back of my fingers on the amps and leave them there. I’ve dabbled with the Texas Instruments TPA-3255EVM evaluation module amplifier in a DIY build that has a large, finned heat sink mounted on top of of the TI TPA-3255 IC, and I would describe the level of heat to touch as similar. Unfortunately, I haven’t had a chance yet to get a friend’s Fluke digital IR and k-type thermocouple thermometer to measure the temperature of the case in various spots. The area on the bottom of each case where the heat sink plate is coupled is noticeably warmer, but I wouldn’t describe it as hot like my Class A amp heatsinks. In my mind, I am not alarmed by the warmth of the cases after hours of playing music.

For the $320 I spent, I would consider this pair of monoblock amps a true bargain. It really is impressive in how effortlessly these little black boxes can drive the KEF LS50s and make them sing. Each of these little guys is about the same size as my Schiit Mani 2 phono stage amp.



All connections from my Denafrips Pontus II DAC to the Schiit Freya+ line stage to the Fosi V3 Mono amps are balanced XLR cables. I only used the balanced unity gain SS buffer mode today. Tomorrow, I will try the Freya+ in balanced tube mode using two matched pairs of 6SN7 tubes.

 

[EddNog]

I received the pair of V3 Monos, two 48V/10A power supplies, and two pairs of the MUSES02 op amps. First thing I did was open up the amps to insure it had some thermal compound on the heat sink plate. It was just a dab on both amps, so I added some Arctic MX-6 thermal compound. I used some strips of Saran wrap on top of the paste on the heat sink plates and carefully slid the amp boards back in place. Then I carefully pulled the Saran wrap off. This kept the thermal compound from getting smeared inside the case.

I’ve been playing music all day and the amps are sounding great. The dual mono amps with the excellent channel separation really do bring out the three dimensionality of a large, deep soundstage. The KEF LS50’s powered by some great Pass DIY Class A amps don’t create that large and deep of a soundstage as they do with the V3 Monos. The frequency extension at both ends of the spectrum is really nice with a greater sense of air and detail along with additional weight at the bottom. Bass notes are clear and articulate.

Playing music all day, the amps get warm, but I would not describe them as getting hot like the heatsinks on my Aleph J Class A amp can get. I can put the back of my fingers on the amps and leave them there. I’ve dabbled with the Texas Instruments TPA-3255EVM evaluation module amplifier in a DIY build that has a large, finned heat sink mounted on top of of the TI TPA-3255 IC, and I would describe the level of heat to touch as similar. Unfortunately, I haven’t had a chance yet to get a friend’s Fluke digital IR and k-type thermocouple thermometer to measure the temperature of the case in various spots. The area on the bottom of each case where the heat sink plate is coupled is noticeably warmer, but I wouldn’t describe it as hot like my Class A amp heatsinks. In my mind, I am not alarmed by the warmth of the cases after hours of playing music.

For the $320 I spent, I would consider this pair of monoblock amps a true bargain. It really is impressive in how effortlessly these little black boxes can drive the KEF LS50s and make them sing. Each of these little guys is about the same size as my Schiit Mani 2 phono stage amp.

View attachment 381687 View attachment 381686 View attachment 381688 View attachment 381689

All connections from my Denafrips Pontus II DAC to the Schiit Freya+ line stage to the Fosi V3 Mono amps are balanced XLR cables. I only used the balanced unity gain SS buffer mode today. Tomorrow, I will try the Freya+ in balanced tube mode using two matched pairs of 6SN7 tubes.

We’re running EXTREMELY similar chains! That’s bound to be a great sounding system you’ve put together, congratulations!

-Ed

 

[rhing]

The system where I use the Fosi V3 Monos is my apartment system. I spilt my time between two homes for my job. At my home in the Southeast, I have a larger system consisting of the following:

• Technics SL-1200GR turntable
• Audio Technica AT33PTG/III MC cartridge
• Raspberry Pi 3 running Volumio 3
• Denafrips Ares 12th-1 DAC
• Audio Research PH7 tube phono stage
• Audio Research LS7 tube line stage
• McIntosh MC240 tube power amp
• Pass DIY Sony VFET Class A power amp
• Fosi ZA3 used as a power amp
• Klipsch Forte II speakers with upgraded crossovers

Listening to music is therapeutic for me, and I enjoy listening to a wide range of music through great sounding gear.

 

[SMen]

The system where I use the Fosi V3 Monos is my apartment system. I spilt my time between two homes for my job. At my home in the Southeast, I have a larger system consisting of the following:

Technics SL-1200GR turntable
Audio Technica AT33PTG/III MC cartridge
Raspberry Pi 3 running Volumio 3
Denafrips Ares 12th-1 DAC
Audio Research PH7 tube phono stage
Audio Research LS7 tube line stage
McIntosh MC240 tube power amp
Pass DIY Sony VFET Class A power amp
Fosi ZA3 used as a power amp
Klipsch Forte II speakers with upgraded crossovers

View attachment 381706 View attachment 381708

Listening to music is therapeutic for me, and I enjoy listening to a wide range of music through great sounding gear.

I'm curious as to what you ZA3 is powering next to the others, a subwoofer? Unless you are switching between power amps through those Klipsch's to have different presentations.

 

[rhing]

I'm curious as to what you ZA3 is powering next to the others, a subwoofer? Unless you are switching between power amps through those Klipsch's to have different presentations.

I am switching between the amplifiers to power a pair of Klipsch Forte II speakers, and the Fosi ZA3 is sitting on top of the Pass DIY Class A amp using complementary pairs of Sony VFETs. This was the first Pass DIY amp I ever built and. It is a keeper. The Sony VFETs are near-unobtainium and the amp has that beautiful, warm sound that First Watt amplifiers are known by. However, this amp gets hot and can be a space heater.

 

[Miser_Audioman]

Ok some real world measurements. Basic set up is hk230 avr, fosi v3 fed by preout, 80hz low pass to rythmic pv12 sub, high pass to paradigm monitor 7 v3. Rew with umik. Hypothesis is no difference between avr and v3 at listening position. Data, hk in purple, v3 in green, 1/12 smoothing-

 

[Miser_Audioman]

Well that is interesting, there are differences in bass room mode. Crossover working through preouts and avr amps, so all good there. Room mode changed, presumably due to phase shift-

 

[Miser_Audioman]

Not sure i trust these phase measurements, but here they are. Yes i could benefit from some correction either way, the hk bass mode was easy to take out, whatever the fosi version is doing could be tougher with some boost maybe needed.

 

[Sokel]

Well that is interesting, there are differences in bass room mode. Crossover working through preouts and avr amps, so all good there. Room mode changed, presumably due to phase shift- View attachment 381804

Maybe one of them is connected with inverted polarity?
Can you do the same at nearfield?

 

[Miser_Audioman]

Thoughts? Why phase shift? I think I’ve checked for the obvious mistakes, seems to be a fair ab comparison

 

[Miser_Audioman]

Maybe one of them is connected with inverted polarity?
Can you do the same at nearfield?

Ha! I was thinking that but i checked. I think I need to triple check on this, will rerun just to be sure, as i agree this makes sense. Hk mapping and colors are a bit odd, and it is very crowded back there, i cant rule it out

 

[EddNog]

I mentioned noticing what sounded like a phase mismatch in the past when running one channel with a ZA3 and the other with a V3 Mono! Wondering now if the PFFB architecture inverts phase…

-Ed

 

[Sokel]

Ha! I was thinking that but i checked. Still will rerun just to be sure, as i agree this makes sense

Just try it with the sub control,reverse it and see.

 

[Sokel]

I mentioned noticing what sounded like a phase mismatch in the past when running one channel with a ZA3 and the other with a V3 Mono! Wondering now if the PFFB architecture inverts phase…

-Ed

if it inverts phase that's a major fail.
It may be minor when two identical amps are used but not in an active/multichannel/etc system that amps can mix and match.
At least there should be a warning about it.

 

[Miser_Audioman]

when i rerun this weekend, i will photo connections so we can be sure