Fosi v3 Mono - User Impressions | Owner's Thread

[Petrushka]

A state of madness currently exists wherein several international markets are discriminating against some excellent audio equipment simply because it doesn't have balanced signal connections. This is madness; there's no reliable proof that an audio system with balanced connections sounds any better than a well-designed normal system. In fact, time and again, top-line components that come my way for evaluation suggest no advantage—and, in some cases, even demonstrate performance loss—for balanced operation.

Balance: Benefit or Bluff?

If you read much promotional literature for recently introduced high-quality equipment, you'll notice a common theme emerging: balanced connection. Balanced inputs and outputs are becoming a must for any audio equipment that has any claim to quality. The word itself has promotional value...

www.stereophile.com

 

[Sokel]

Balance: Benefit or Bluff?

If you read much promotional literature for recently introduced high-quality equipment, you'll notice a common theme emerging: balanced connection. Balanced inputs and outputs are becoming a must for any audio equipment that has any claim to quality. The word itself has promotional value...

www.stereophile.com

That trend began with PC audio and goes hand by hand with it.
For some reason people think that a balanced device will prevent all the garbage that come from a PC (PCU/GPU/fan/name it noises,etc) .

And that MAY happen in some cases.
But if you get on forums long enough (specially pro ones) there's no passing week without someone complain about it WITH balanced gear (and in most cases active speakers) .

I would suggest it would be FAR more useful all PC connected audio stuff to include galvanic isolation schemes.
Yes,that chips are expensive (comparing only with high-end DAC chips if go full-speed),implementation adds teal estate so cost can go way up and a cheap DAC will no more be competitive in price.

But...

 

[gwing]

Balance: Benefit or Bluff?

If you read much promotional literature for recently introduced high-quality equipment, you'll notice a common theme emerging: balanced connection. Balanced inputs and outputs are becoming a must for any audio equipment that has any claim to quality. The word itself has promotional value...

www.stereophile.com

Everyone's entitled to their opinion - even Stereophile

 

[SMen]

Balance: Benefit or Bluff?

If you read much promotional literature for recently introduced high-quality equipment, you'll notice a common theme emerging: balanced connection. Balanced inputs and outputs are becoming a must for any audio equipment that has any claim to quality. The word itself has promotional value...

www.stereophile.com

I slightly agree and have been thinking about this.

Michael Fiedler with his balanced phono pre-amps makes a strong case for not having additional op amps in the path. The balanced output is useful for long cable runs and connecting to active speakers. So to wire the tonearm for balanced requires additional op amps on the input.

I have a DAC which has balanced output that then use an additional op amp to drive the additional RCA.

With the Fosi Mono v3 there is an additional op amp for the RCA ... so the first set up has additional op amps for the balanced, and the second set ups have additional op amps for the RCA ...

For me this would be a good reason to delve a little deeper into when balanced or RCA might be best. Just a thought.

 

[avdoc]

I was able to drop the temperature of my V3s by 20 degrees Fahrenheit (from 117 to 97) by placing one of these fans under each:

Amazon.com

On low speed, the fans are almost totally silent and I can't hear them from my listening position 10 feet away. Both fans run off the same USB plug which I'm using with a 5V USB plug I had left over from an old phone (if you don't have one, you'll need to purchase it separately). Each fan has 4 rubber feet on the top and bottom and they are perfectly sized to allow the V3 to sit on top. The rubber feet allow for vibration mitigation from the fan and also isolate the amps from the shelf. I'm really happy with them and think the $15 I spent is worth it if the amps last longer. The fans may not be necessary, but it makes me feel better that the amps are running cooler.

 

[EddNog]

I slightly agree and have been thinking about this.

Michael Fiedler with his balanced phono pre-amps makes a strong case for not having additional op amps in the path. The balanced output is useful for long cable runs and connecting to active speakers. So to wire the tonearm for balanced requires additional op amps on the input.

I have a DAC which has balanced output that then use an additional op amp to drive the additional RCA.

With the Fosi Mono v3 there is an additional op amp for the RCA ... so the first set up has additional op amps for the balanced, and the second set ups have additional op amps for the RCA ...

For me this would be a good reason to delve a little deeper into when balanced or RCA might be best. Just a thought.

ZA3 is the better option if you want to run single-ended and avoid the extra op-amp in your signal path since the balanced input is the one with the extra op-amp in the signal path on the ZA3. Of course then you have an added volume attenuator in the signal path and you don’t get the benefit of PFFB, so pick your poison.

-Ed

 

[EddNog]

I was able to drop the temperature of my V3s by 20 degrees Fahrenheit (from 117 to 97) by placing one of these fans under each:

Amazon.com

On low speed, the fans are almost totally silent and I can't hear them from my listening position 10 feet away. Both fans run off the same USB plug which I'm using with a 5V USB plug I had left over from an old phone (if you don't have one, you'll need to purchase it separately). Each fan has 4 rubber feet on the top and bottom and they are perfectly sized to allow the V3 to sit on top. The rubber feet allow for vibration mitigation from the fan and also isolate the amps from the shelf. I'm really happy with them and think the $15 I spent is worth it if the amps last longer. The fans may not be necessary, but it makes me feel better that the amps are running cooler.

I am using the same exact product sold under AC Infinity brand name for my V3 Monos as well. From my listening position 10 feet away, even the medium speed setting is not particularly audible. I am also using a larger version for my preamp, which gets pretty hot (Schiit Freya+), and being able to daisy-chain them all and control them from a single switch is very handy!

-Ed

 

[rhing]

I am using the same exact product sold under AC Infinity brand name for my V3 Monos as well. From my listening position 10 feet away, even the medium speed setting is not particularly audible. I am also using a larger version for my preamp, which gets pretty hot (Schiit Freya+), and being able to daisy-chain them all and control them from a single switch is very handy!

-Ed

Hi Ed,

I noticed that you have a similar setup as mine. I just received notification that my order for:
2x V3 Mono amps
2x 48VDC/10A power supplies
2x MUSES02 op amps are on their way.

My digital audio chain is:
Raspberry Pi 3 running Volumio 3 > USB cable >
Denafrips Pontus II > balanced XLR >
Schiit Freya+ > balanced XLR >
Fosi Audio ZA3 > speaker cable >
KEF LS50 speakers



This setup sounds great and I am looking forward to running the Fosi V3 Monos in PBTL mode with the PFFB in place of the ZA3 in stereo mode. The attached photo shows two Fosi Audio ZA3 amps running in mono mode with balanced connections. I had this setup temporarily as a fellow audiophile asked me to install a pair of the MUSES02 op amps and ensure there was thermal paste in his new Fosi ZA3 that he had drop shipped to me since he wasn’t confident in installing the op amps himself.

The big power amp in bottom shelf is a Pass DIY Aleph J that I had built in 2020 in the middle of the pandemic. This Class A amp designed by Nelson Pass of Pass Labs and First Watt sounds awesome and the dual ZA3 mono setup I temporarily had could give the Aleph J some healthy competition in terms of a wide and deep soundstage and excellent tonality, especially when running the Schiit Freya+ in differential (balanced) tube mode.

The Fosi ZA3 has the MUSES02 op amps in it, and I plan to use the two op amps in the ZA3 along with the additional two op amps that are shipping with my V3 Mono amps. While I have the amps open to install the MUSES02 op amps, I’ll add some Arctic MX-6 thermal compound to the thermal coupling plates. This is what I use with the ZA3 amp and I leave it on all the time since it gets warm at most. I don’t think I’ll be able to do this with each of the V3 Monos powered by an individual 48VDC/10A power supply per amp.

 

[EddNog]

Hi Ed,

I noticed that you have a similar setup as mine. I just received notification that my order for:
2x V3 Mono amps
2x 48VDC/10A power supplies
2x MUSES02 op amps are on their way.

My digital audio chain is:
Raspberry Pi 3 running Volumio 3 > USB cable >
Denafrips Pontus II > balanced XLR >
Schiit Freya+ > balanced XLR >
Fosi Audio ZA3 > speaker cable >
KEF LS50 speakers

View attachment 379624

This setup sounds great and I am looking forward to running the Fosi V3 Monos in PBTL mode with the PFFB in place of the ZA3 in stereo mode. The attached photo shows two Fosi Audio ZA3 amps running in mono mode with balanced connections. I had this setup temporarily as a fellow audiophile asked me to install a pair of the MUSES02 op amps and ensure there was thermal paste in his new Fosi ZA3 that he had drop shipped to me since he wasn’t confident in installing the op amps himself.

The big power amp in bottom shelf is a Pass DIY Aleph J that I had built in 2020 in the middle of the pandemic. This Class A amp designed by Nelson Pass of Pass Labs and First Watt sounds awesome and the dual ZA3 mono setup I temporarily had could give the Aleph J some healthy competition in terms of a wide and deep soundstage and excellent tonality, especially when running the Schiit Freya+ in differential (balanced) tube mode.

The Fosi ZA3 has the MUSES02 op amps in it, and I plan to use the two op amps in the ZA3 along with the additional two op amps that are shipping with my V3 Mono amps. While I have the amps open to install the MUSES02 op amps, I’ll add some Arctic MX-6 thermal compound to the thermal coupling plates. This is what I use with the ZA3 amp and I leave it on all the time since it gets warm at most. I don’t think I’ll be able to do this with each of the V3 Monos powered by an individual 48VDC/10A power supply per amp.

That’s a really nice setup! The Pontus II must be awesome. I gave my dad my Ares II and got a Musician Draco so that I could use I2S input from a Gustard U18 DDC. I feel like the Ares II might be a little bit better sounding than the Draco when compared with USB or Coax input, but the Draco pulls ahead with I2S, which the Ares II doesn’t have (need Enyo 15th, Ares 12th, or Pontus II to get I2S input with Denafrips).

-Ed

 

[keith_h]

I've added a pair to an NAD M10 V1 and I've documented my experience in the M10 thread. In short, its delivering a better listening experience than the onboard nCore amplification it replaced vindicating the measurements in the review. There's DSP involved as well, that's an M10 thing and icing on the cake.

I see a fair amount of conjecture about heat so I thought I would RTFM and thoughtfully share the good news that its operating well within its design parameters and those wringing their hands in despair over the thought its getting "hot" and burning up should now be able to relax. Turns out 75C heatsink temp is considered normal, testing is done at 75C and reports are case temps are showing far less than that in operation. Mine are at 30C at idle and maybe 40C in operation. I've used the very non scientific method of laying a regular non-calibrated thermometer over my vertically aligned units so a few degrees of error is almost certainly assured, but hardly enough to cause real concern.

Thermal warning is activated from 120C and the device completely shuts down at 155C. The NAD M10 reports up to 60 in operation using its onboard amps. I'd say its a non issue and the thermal management design is just fine for this application.

If anyone has some before/after temperature data after adding thermal paste, that may provide another layer of confidence. While TIM may add a little more effective heat transfer I doubt its essential in this application.

OTW = over temperature warning
OTE = over temperature error

9.4.1.5 Overtemperature Protection OTW and OTE
TPA3255 has a two-level temperature-protection system that asserts an active-low warning signal (CLIP_OTW) when the device junction temperature exceeds 120°C (typical) and, if the device junction temperature exceeds 155°C (typical), the device is put into thermal shutdown, resulting in all half-bridge outputs being set in the high-impedance (Hi-Z) state and FAULT being asserted low. OTE is latched in this case. To clear the OTE latch, RESET must be asserted. Thereafter, the device resumes normal operation.

Also discussed is the mechanism that controls startup pop for anyone interested.

https://www.ti.com/lit/ds/symlink/tpa3255.pdf

@Guddu many thanks for taking the time to detail your experience.

 

[SMen]

ZA3 is the better option if you want to run single-ended and avoid the extra op-amp in your signal path since the balanced input is the one with the extra op-amp in the signal path on the ZA3. Of course then you have an added volume attenuator in the signal path and you don’t get the benefit of PFFB, so pick your poison.

-Ed

This for me is something that could be investigated, namely the volume control.
This is required for the Fosi V3 monoblocks with PFFB. Volume could be provided by a balanced output DAC with (I presume) lossless volume control, or a balanced pre amplifier like the Freya + or .. I'm trying out a couple of external passive volume control options including a stepped relay device which are also balanced, but can also connect to the monos with RCA (unbalanced).

@antcollinet replied to an earlier post about this by me.
Impedance does not seem to matter?
But in this Lundahl review says here, it does.

I would like to understand this better.

 

[EddNog]

This for me is something that could be investigated, namely the volume control.
This is required for the Fosi V3 monoblocks with PFFB. Volume could be provided by a balanced output DAC with (I presume) lossless volume control, or a balanced pre amplifier like the Freya + or .. I'm trying out a couple of external passive volume control options including a stepped relay device which are also balanced, but can also connect to the monos with RCA (unbalanced).

@antcollinet replied to an earlier post about this by me.
Impedance does not seem to matter?
But in this Lundahl review says here, it does.

I would like to understand this better.

I require a remote control for volume, which the ZA3 does not provide, hence why I have a Schiit Freya+ in my chain; the passive pre mode is truly transparent and I can control volume from my listening position.

-Ed

 

[keith_h]

@SMen have a read of the product data sheet at the link I provided previously where this is explained.

 

[keith_h]

The Fosi ZA3 has the MUSES02 op amps in it, and I plan to use the two op amps in the ZA3 along with the additional two op amps that are shipping with my V3 Mono amps. While I have the amps open to install the MUSES02 op amps, I’ll add some Arctic MX-6 thermal compound to the thermal coupling plates. This is what I use with the ZA3 amp and I leave it on all the time since it gets warm at most. I don’t think I’ll be able to do this with each of the V3 Monos powered by an individual 48VDC/10A power supply per amp.

Very cool setup. Could you please do some measurements before and after adding thermal paste on the monos so we can see the difference in temperature it makes?

 

[rhing]

Very cool setup. Could you please do some measurements before and after adding thermal paste on the monos so we can see the difference in temperature it makes?

Thanks. I’ll have to borrow a friend’s Fluke temperature meter. It has both infrared and K-type thermocouple sensors. My job has me traveling a lot, but I’ll try to squeeze in some experimentation. I much prefer listening to music over testing equipment during my free time.

 

[EddNog]

Thanks. I’ll have to borrow a friend’s Fluke temperature meter. It has both infrared and K-type thermocouple sensors. My job has me traveling a lot, but I’ll try to squeeze in some experimentation. I much prefer listening to music over testing equipment during my free time.

Agreed. The system sounds so good with the V3 Monos that it just doesn’t seem appealing to deal with testing! For me, I’ve achieved end game with this chain. Since I’ve gotten the V3 Monos in, all I’ve done is listened to and enjoyed me music. Haven’t been putting a single further thought into component. I did make a speaker and subwoofer placement change that further improved my system but at this point I’m done messing with it. Just enjoying reading forums however to see other people’s experiences and results.

-Ed

 

[Hot Mason]

There has only been 2 issues reported:

1) Excessive Noise when using single psu but only 1 amplifier, Fosi said they have resolved the issue and issue is limited to pre-production units
2) Heat or thermal performance- many users here, including me, have reported that the units are running on hotter side. Even you reviewers have said the same thing.

By the way, I am running v3 mono pair with 36v psu from last 2 days and I am not seeing any thermal performance improvements.

Sounds good.

 

[keith_h]

Sounds good.

Regarding heat the product data sheet shows that its running well inside its limits. No need to fear the device exploding in flames.

 

[Sokel]

I've added a pair to an NAD M10 V1 and I've documented my experience in the M10 thread. In short, its delivering a better listening experience than the onboard nCore amplification it replaced vindicating the measurements in the review. There's DSP involved as well, that's an M10 thing and icing on the cake.

I see a fair amount of conjecture about heat so I thought I would RTFM and thoughtfully share the good news that its operating well within its design parameters and those wringing their hands in despair over the thought its getting "hot" and burning up should now be able to relax. Turns out 75C heatsink temp is considered normal, testing is done at 75C and reports are case temps are showing far less than that in operation. Mine are at 30C at idle and maybe 40C in operation. I've used the very non scientific method of laying a regular non-calibrated thermometer over my vertically aligned units so a few degrees of error is almost certainly assured, but hardly enough to cause real concern.

Thermal warning is activated from 120C and the device completely shuts down at 155C. The NAD M10 reports up to 60 in operation using its onboard amps. I'd say its a non issue and the thermal management design is just fine for this application.

If anyone has some before/after temperature data after adding thermal paste, that may provide another layer of confidence. While TIM may add a little more effective heat transfer I doubt its essential in this application.

OTW = over temperature warning
OTE = over temperature error

9.4.1.5 Overtemperature Protection OTW and OTE
TPA3255 has a two-level temperature-protection system that asserts an active-low warning signal (CLIP_OTW) when the device junction temperature exceeds 120°C (typical) and, if the device junction temperature exceeds 155°C (typical), the device is put into thermal shutdown, resulting in all half-bridge outputs being set in the high-impedance (Hi-Z) state and FAULT being asserted low. OTE is latched in this case. To clear the OTE latch, RESET must be asserted. Thereafter, the device resumes normal operation.

Also discussed is the mechanism that controls startup pop for anyone interested.

https://www.ti.com/lit/ds/symlink/tpa3255.pdf

@Guddu many thanks for taking the time to detail your experience.

Heat dissipation is not only about the chip itself.
Have a look at the pic below:




Caps are directly above the heatshink area.Now go to cap's datasheet and see how their life span varies with temperature.
One must also consider resistor's ppm (the better quality-the lower),etc.

We must look at the device as a whole and it's usually the weak links to pay attention first.Chip is not this link.

 

[MCH]

.Now go to cap's datasheet

You will not find it, not for the misterious KY series 63V 2200uF