Fosi v3 Mono - User Impressions | Owner's Thread

[Freshman1966]

Oh thank heavens, a user impression on a user impressions thread! I think you should install all, and make sure you are not mixing and matching any op amps and then compare with your Atoll.


I genuinely don't think that swapping one is going to be viable (make much of a difference ... I do not understand any benefit to mixing op amp types in a parallel circuit but anyone please correct me if I am wrong) But it is very good that you have the Atolls as a yardstick.

On a serious note, if you have a 3db variation between your monos, then this is serious and Fosi need to replace that.

Please would you verify this? 3db is clearly audible as a balance shift and would shift where instruments and voices might appear in the soundstage.

Many people will be using these without Dsp

Post edit: balance variation db with all same op amps

About the "gain problem" I mentioned - I cannot really explain it but it seems not to be a problem of the amps. I do have an imbalance in my room and especially when all DSP is off, I need to apply some kind of balance (through DSP, since I don't have any other means). With the monos I need to apply a 3 db higher correction as with the Atoll - you're welcome to explain where that comes from.

OK, I had actually already decided to pass the Monos on, but in the end courisosity got the better of me. So I put in the second pair of Sparkos op amps....

And now, you can beat me, but I really cannot tell which one is which, anymore. I chose three tracks which do not cover everyone's tastes but include many of the elements I appreciate:

• Boz Scaggs, Thanks To You
• Anette Askvik, Liberty
• Gregory Porter, It's Probably Me

I concentrated on voices, interpretation of instruments, deep bass performance and stage... I don't know if I could tell which amp I am listening to in a blind test. I actually switched the cables so often that sometimes I forgot which one was currently playing and I had look

Now, what do I do? Keep them or stay with the Atoll... For once, my wife has an opinion about Hifi - "the big silver thing looks much prettier". I guess, I keep both for a while.

Cheers
Stefan

@SMen Absolutely...1966 was a very good year, indeed

 

[SMen]

About the "gain problem" I mentioned - I cannot really explain it but it seems not to be a problem of the amps. I do have an imbalance in my room and especially when all DSP is off, I need to apply some kind of balance (through DSP, since I don't have any other means). With the monos I need to apply a 3 db higher correction as with the Atoll - you're welcome to explain where that comes from.

OK, I had actually already decided to pass the Monos on, but in the end courisosity got the better of me. So I put in the second pair of Sparkos op amps....

And now, you can beat me, but I really cannot tell which one is which, anymore. I chose three tracks which do not cover everyone's tastes but include many of the elements I appreciate:

• Boz Scaggs, Thanks To You
• Anette Askvik, Liberty
• Gregory Porter, It's Probably Me

I concentrated on voices, interpretation of instruments, deep bass performance and stage... I don't know if I could tell which amp I am listening to in a blind test. I actually switched the cables so often that sometimes I forgot which one was currently playing and I had look

Now, what do I do? Keep them or stay with the Atoll... For once, my wife has an opinion about Hifi - "the big silver thing looks much prettier". I guess, I keep both for a while.

Cheers
Stefan

@SMen Absolutely...1966 was a very good year, indeed

At first I did not follow but then I understood that after swapping you could not tell the difference vs the Atoll with level matching and an excellent "confusion technique" with cables...

No virtual corporal punishment from me!

Always useful to have a spare (pair) ;-) Or for taking on a camping trip!!

 

[antcollinet]

Ok,let's get serious about thermals now.

First we take the power losses figures from TI's datasheet:

View attachment 380861

I think it's fair to consider a middle 40W value for an output of 200W at 4 Ohm at ideal conditions.

Now let's take the above value along with the provided heatshink to see where it stands.
We will use this calc:

Dimensions is the (unfolded) case,not sure about it's thickness though cause it matters,I gave it a generous 1 cm thickness,so if anyone has an accurate measure please provide it and I will correct the value.


As is:

View attachment 380862

It seems that it falls short.
For more W and lower impedance things are more dire of course.
Until we have a better measure of case thickness.that's how it looks like though and that's for near ideal conditions.

You can also use the calc to calculate more normal than 200W output conditions where power losses are closer to 10-20W which seems adequate to provide.

(disclaimer,that's for my given thickness,if less than 1 cm demands in size will be ever bigger,proportionately,same stands for all dimensions obviously )

Why does that calculation focus on volume. From my experience, surface area is the primary performance variable for heatsinks (it is why they typically have fins). Volume is only needed to provide sufficient thermal conduction to the metal/air interface.

Plus the calculation is not taking into account air movement through the case openings. That heat does not go into the case/heatsink.

 

[antcollinet]

About the "gain problem" I mentioned - I cannot really explain it but it seems not to be a problem of the amps. I do have an imbalance in my room and especially when all DSP is off, I need to apply some kind of balance (through DSP, since I don't have any other means). With the monos I need to apply a 3 db higher correction as with the Atoll - you're welcome to explain where that comes from.

You may have a similar problem to mine. I spent ages trying to understand why my soundstage was pulled dlown and to the left. I needed sigificant balance shift to the right and it was sill sloping. I eventually worked it out.

Due to space constraints I have my sub placed just in front of the left speaker., and the top surface is just below the drivers. Reflections from the top surface were unbalancing the sound stage. I can manly solve this by putting sound absorbing material (a cusion ) on top of the sub

Not saying yours is exactly the same, but look out for any asymmetry in the surfaces/materials which reflections may come from. Eg glass on one side, and wood or plaster on the other. Wall on one side, open on the other etc etc.

 

[EddNog]

You may have a similar problem to mine. I spent ages trying to understand why my soundstage was pulled dlown and to the left. I needed sigificant balance shift to the right and it was sill sloping. I eventually worked it out.

Due to space constraints I have my sub placed just in front of the left speaker., and the top surface is just below the drivers. Reflections from the top surface were unbalancing the sound stage. I can manly solve this by putting sound absorbing material (a cusion ) on top of the sub

Not saying yours is exactly the same, but look out for any asymmetry in the surfaces/materials which reflections may come from. Eg glass on one side, and wood or plaster on the other. Wall on one side, open on the other etc etc.

I had a similar problem as well, and ended up pushing my system stand/rack back towards the wall, and moving the subwoofer in the center, in front of the system. This mostly solved my balance issues. It may look somewhat odd, but the rest of my room is cluttered anyway due to kids’ things, so I don’t care as much about the appearance as I do for the sound. Since the subwoofer moved forward, I ended up having to adjust the phase in the subwoofer DSP, but after that, all good.

-Ed

 

[antcollinet]

I had a similar problem as well, and ended up pushing my system stand/rack back towards the wall, and moving the subwoofer in the center, in front of the system. This mostly solved my balance issues. It may look somewhat odd, but the rest of my room is cluttered anyway due to kids’ things, so I don’t care as much about the appearance as I do for the sound. Since the subwoofer moved forward, I ended up having to adjust the phase in the subwoofer DSP, but after that, all good.

View attachment 380904

-Ed

Your cat looks like the perfect solution to reflections from the top of the sub. I might have to get one

 

[EddNog]

Your cat looks like the perfect solution to reflections from the top of the sub. I might have to get one

Sure if you are okay with the occasional vomit/hairball. Oh and this one (I have two) does not like to bury his poo when he uses the litter box. (╯°□°)╯︵ ┻━┻

Ironically after taking this photo, I noticed my right speaker placement is off; turns out my mother in law moved it while cleaning. 1.5” too far forward. Fixed it, so another benefit of participating in this forum.

-Ed

 

[Freshman1966]

You may have a similar problem to mine. I spent ages trying to understand why my soundstage was pulled dlown and to the left. I needed sigificant balance shift to the right and it was sill sloping. I eventually worked it out.

Due to space constraints I have my sub placed just in front of the left speaker., and the top surface is just below the drivers. Reflections from the top surface were unbalancing the sound stage. I can manly solve this by putting sound absorbing material (a cusion ) on top of the sub

Not saying yours is exactly the same, but look out for any asymmetry in the surfaces/materials which reflections may come from. Eg glass on one side, and wood or plaster on the other. Wall on one side, open on the other etc etc.

Thanks for your advice! But I am pretty sure it comes from the "corner problem" - on the right side there's just so much more open space. For my comparisons of the two/three amps I had not used any DSP and my sub was silent That's why I had to turn the balance to the right quite a bit.
About speaker placement: basically everywhere it is recommended to pull the Dynaudios away from the wall, which is what I did in the beginning. When I got my UMIK-1 and started to measure and play around with speaker positioning it turned out that they should be much closer to the wall (in my case). Placing the sub was also counter intuitive - but the corner is just the right spot and it dials in great with the Minidsp with help from REW. Anyway, the Minidsp with Dirac was the biggest game changer in my Hifi journey. Quite amazing.

I did try to get a furry cat to take advantage of their legendary absorbance factor - as you see I got stuck with a short haired dog which he spreads liberally around the house.

Btw, I like this discussion much better now. Still listening to the Fosi Monos...

 

[SMen]

Thanks for your advice! But I am pretty sure it comes from the "corner problem" - on the right side there's just so much more open space. For my comparisons of the two/three amps I had not used any DSP and my sub was silent That's why I had to turn the balance to the right quite a bit.
About speaker placement: basically everywhere it is recommended to pull the Dynaudios away from the wall, which is what I did in the beginning. When I got my UMIK-1 and started to measure and play around with speaker positioning it turned out that they should be much closer to the wall (in my case). Placing the sub was also counter intuitive - but the corner is just the right spot and it dials in great with the Minidsp with help from REW. Anyway, the Minidsp with Dirac was the biggest game changer in my Hifi journey. Quite amazing.

I did try to get a furry cat to take advantage of their legendary absorbance factor - as you see I got stuck with a short haired dog which he spreads liberally around the house.

Btw, I like this discussion much better now. Still listening to the Fosi Monos...
View attachment 380924

Oh to be a dog, and not 'give a monkies' about things like soundstage!

I'd suggest some sound absorption to counter feet reflections...


I have a dual mono volume control for when I am in funny spaces. I move around a bit and it has been indispensable.

 

[EddNog]

Thanks for your advice! But I am pretty sure it comes from the "corner problem" - on the right side there's just so much more open space. For my comparisons of the two/three amps I had not used any DSP and my sub was silent That's why I had to turn the balance to the right quite a bit.
About speaker placement: basically everywhere it is recommended to pull the Dynaudios away from the wall, which is what I did in the beginning. When I got my UMIK-1 and started to measure and play around with speaker positioning it turned out that they should be much closer to the wall (in my case). Placing the sub was also counter intuitive - but the corner is just the right spot and it dials in great with the Minidsp with help from REW. Anyway, the Minidsp with Dirac was the biggest game changer in my Hifi journey. Quite amazing.

I did try to get a furry cat to take advantage of their legendary absorbance factor - as you see I got stuck with a short haired dog which he spreads liberally around the house.

Btw, I like this discussion much better now. Still listening to the Fosi Monos...
View attachment 380924

I have a similar problem with my setup. If you see on the left behind the speaker in my photo, there is a white cabinet. That is a corner module cabinet, so I also have much more open space to the right side. However, my ceiling on the left does not slant down like yours. It also seems my speakers are farther forward from the back wall than yours. If you haven’t tried it, see if you can bring your speakers forward—it helps tame excess bass.

-Ed

 

[Freshman1966]

I have a similar problem with my setup. If you see on the left behind the speaker in my photo, there is a white cabinet. That is a corner module cabinet, so I also have much more open space to the right side. However, my ceiling on the left does not slant down like yours. It also seems my speakers are farther forward from the back wall than yours. If you haven’t tried it, see if you can bring your speakers forward—it helps tame excess bass.

-Ed

Well, I did write that I had them much further into the room. But measuring the frequency response in my listening position showed a much flatter graph when they were closer to the wall. It was an experiment with a surprising result - the bass became cleaner. From there I started with the setup of the sub and after that the Dirac configuration. That gave me a very nice curve - the best I can do without nailing hundreds of cats to the wall

 

[EddNog]

Well, I did write that I had them much further into the room. But measuring the frequency response in my listening position showed a much flatter graph when they were closer to the wall. It was an experiment with a surprising result - the bass became cleaner. From there I started with the setup of the sub and after that the Dirac configuration. That gave me a very nice curve - the best I can do without nailing hundreds of cats to the wall

Ah, I had the opposite. There is a MASSIVE room gain at 43hz if my speakers are too close to the back wall, even if I start using the included foam plugs for the ports. Even worse when the subwoofer is too close to the corner. Moving it out helped tremendously for that, with DSP/EQ managing the rest.

-Ed

 

[GoDawgs]

Received a pair of amps yesterday with two 5A power blocks. I haven't had much time to evaluate them yet but I did have to dial back my subwoofer volume when I put my new amps in my setup. I set both of mine on one of the little AC Infinity fans for breathing room, but I'm not running the fans. Last night my amps (inputted from SMSL DO100 DAC using XLR cables), were 88.2 and 88.4 degrees F in a 72ish degree F room with 2 ceiling fans running, at 40% volume. (I know, not very helpful with the room temp, but I'm old, lazy, tired and I don't care as much as you might ).

I haven't gotten everyone out of the house so I could just push the volume loud enough to run the dogs back to the bedrooms so I can monitor temperatures. My wife and daughter aren't huge fans when I test new amps or speakers!?? (My ladies are baffling sometimes but I love them just the same). I may follow up with pictures (with my dogs but no feet. NO! my dogs have feet, you just won't see my feet hopefully), and more details when I get a little free test time. So far, so great. I'm really liking what I hear (that is an official ASR calibrated "really liking").

 

[Doodski]

@GoDawgs. Can you use a DC ammeter part of your digital multimeter and meter out the value for the current draw from both power supplies separately? That would be awesome. I can instruct you how to do it you feel like being the one that finally makes the measurement for all of us. Has this measurement been done? Did I miss it or is this a cool idea?

 

[GoDawgs]

I'll try tomorrow during the day, I'm planning to go out with 'she who must be obeyed' for tonight. If I need instructions I'll let the forum know.

 

[GoDawgs]

He's gone to distant places! My new reward Muse op-amp is such a punk. It’s only been here for one day and already it’s moaning that “there’s nothing to do” at my house. I’d be willing to send the entitled little politician (oh sorry, please excuse my vulgarity), on a one way vacation if I could think of someplace for it to go. If anyone has any ideas, send me a message and I'll do my best to get it there. Just don’t ask me to help it come back here, I hope I never see the entitled little whiner again.

 

[keith_h]

Thermal overload and thermal protection applies only to the TPA3255 chip,not to the rest of the components of the amp like caps,resistors,even cables and connectors (yes,these can fail too under temp).
When talking heat in such a constrained space that applies to every single component and affects them all.

Fair point.

 

[keith_h]

Received a pair of amps yesterday with two 5A power blocks. I haven't had much time to evaluate them yet but I did have to dial back my subwoofer volume when I put my new amps in my setup. I set both of mine on one of the little AC Infinity fans for breathing room, but I'm not running the fans. Last night my amps (inputted from SMSL DO100 DAC using XLR cables), were 88.2 and 88.4 degrees F in a 72ish degree F room with 2 ceiling fans running, at 40% volume. (I know, not very helpful with the room temp, but I'm old, lazy, tired and I don't care as much as you might ).

I haven't gotten everyone out of the house so I could just push the volume loud enough to run the dogs back to the bedrooms so I can monitor temperatures. My wife and daughter aren't huge fans when I test new amps or speakers!?? (My ladies are baffling sometimes but I love them just the same). I may follow up with pictures (with my dogs but no feet. NO! my dogs have feet, you just won't see my feet hopefully), and more details when I get a little free test time. So far, so great. I'm really liking what I hear (that is an official ASR calibrated "really liking").

Sensitivity of XLR is 20db hence why the need to dial the sub back most likely. I had to turn the sub up using RCA in @ 31db.

 

[Sokel]

Why does that calculation focus on volume. From my experience, surface area is the primary performance variable for heatsinks (it is why they typically have fins). Volume is only needed to provide sufficient thermal conduction to the metal/air interface.

Plus the calculation is not taking into account air movement through the case openings. That heat does not go into the case/heatsink.

There are volumetric data to the right of the calc taking air circulation into account (passive,active,etc)
By volume they probably take real case heatshinks into account which they can't be 2-dimensional and the base thickens counts.

They usually have fins of course but it's easy to take this data and make the calcs on the other site I posted earlier in the other thread.

Edit: there's also the more precise calc at the same site which pretty much addresses all issues but assumes a minimum finned area.

 

[jvdburgt]

Hi all,

My V3 mono's have finally arrived (well, at least 2 out of the 5 I ordered, but the other 3 should arrive later this week). Only thing: my 4mm2 speaker cables don't fit in the small speaker post bindings on the V3's.

I'll order banana plugs from Amazon, but now I'm reading stuff that not all banana plugs fit all speaker binding posts (size difference?). What are your experiences with fitting banana plugs in the mono's? Any issues/tips/tricks I should be aware about?