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Fosi v3 Mono - User Impressions | Owner's Thread
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Down South
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Why do you expect amps to get toasty/
Amps get toasty because designers (1) create enclosures that fail to enable heat to dissipate by simple convection aka heat rises. (2) fail to use simple quiet computer fans in enclosures that allow said fans to operate optimally.
In the 1950s tests were done that showed that components, especially caps and resistors remained operating optimally if heat was dissipated quickly lowering operating temps for 3 -4 times longer where heat was ignored. This of course meant that joe punter was forced to replace equipment sooner rather than later.
I had a hybrid h/amp that used mosfets by lifting the mosfets off their base and using a virtually silent computer fan underneath, the whole amp operated at normal room temperature. Maybe a placebo effect but I found the sound was a little sweeter. I still have that h/amp. Why don't I use it because the excellent Marantz 6007 has an equally good sounding h/amp built in.
DavidM1
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Experience I suppose. My first guitar amp more than 50 years ago was a brown faceplate Fender Pro. I’m not sure how many amps I’ve had but I currently have three that I use professionally: a Boogie, an AER and a Katana. Stereo amps include Quad 33/303 (twice) a 70w Denon and the V3 monos. None have had fans and all get warm to touch, some more than others. The Denon has been on 24/7 for almost twenty years. Toasty.
I think you’ve mentioned the 1950s research in the past when discussing the Fosi amps. Three quarters of a century seems kinda old for component research and even predates my earliest amps but maybe it still has some relevance. I wouldn’t know.
I thoroughly enjoy my V3 monos and use them daily. They’re great.
Blew
Active Member
How hot is "toasty" when measured in degrees Celcius? My V3 Monos get a little warm to the touch, but I wouldn't describe them as "hot" or "toasty". They drive a pair of Audio Physic Classic Compact speakers which are 8 Ohms impedance and 86dB sensitivity. I use 2x 48v/5A power supplies. They're the original version with 25/31dB RCA gain, but I use XLR balanced input so presumably that doesn't matter. I crossover at 90hz to a pair of subwoofers though, so I'd expect the V3 Monos would be warmer if I didn't do that. I should also note that they're set to auto on mode but I switch everything at the power board when not in use, so they don't consume any power when not in use and therefore are at room temperature for the vast majority of their life.
I'll try to remember to measure the temperature after playing music for a while and report back.
I'll try to remember to measure the temperature after playing music for a while and report back.
Down South
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The time when the research was conducted is totally irrelevant. Caps and resistors have changed a lot over the years but the effect of heat is the same. Have you actually measured the caps and resistors in your Denon amp? You may get a nasty surprise when you do. Also changes in sound will have been gradual. When I've changed out resistors for Z foils in the signal path the clarity/tone has improved an awful lot. The construction of these resistors is very different from the usual construction of resistors. Check out the operating temps of these and you will see that they remain within their very tight parameters up to 70C, this is not true for trditional resistors.
DavidM1
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Not very. It’s just a word. All amps generate a little heat and I don’t think it signifies anything at all to be worried about.
Yes, I have had the Quad amps overhauled but they date from late 1960s or early 1970s. It’s an issue for all old amps. The Quads run relatively cool and the 303 is well known for its huge heat sink but age eventually catches up with old electronics.
The Denon sounds great but will eventually get to that point too, perhaps in another decade or so. We’ll see.
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TLDR: I received 2x Fosi V3 mono with 2x 48V 5A.
Their phase is correct. they have 19-25dB gain switch on RCA. They have only 1 QC sticker.
They don't make any concerning amount of noise when turned on and off, even yanking or plugging in at mains with switch on amps set to "On".
They are not disturbingly warm after a few hours use at moderate volume, though the room is pretty cold at present.
They work. Music is being amplified and sounds as such. success! but it's only been mere hours.
I just received a pair of Fosi V3 Mono today, with 2x 48v 5A power supplies. (Previously had and was using Fosi v3 stereo. 32v 5A power supplies)
I personally think external power supplies are often favourable, and do not wish for internal.
The models delivered are both 19-25 dB gain switch on the RCA in. Purchased from amazon, Australia. Delivery was quick from opposite side of the large island. The amazon box was a great efficient fit for the 2x amp packages.
The 48v 5A supplies are the same in each box, seem quality enough, but aren't Fosi branded like the 32V ones i have with V3 Stereo amps purchased early 2024. Here's a blurry low light photo:
I first installed a V3 mono on just one channel, and played music (stereo downmixed to mono signal), with a V3 stereo on one side, and a new V3 mono on the other. with V3 mono gain on 25dB, RCA input, there was still a little gain/volume difference comapred to the V3 Stereo. not unexpected. but it otherwise sounds fine - Most notably, this confirms these have the correct phase. Only one QC sticker exists on the bottom of the amps.
Swapping 32v power supply and the 48v, sounds the same at the volume I had - ~80dB A-weighted, 2m distance from 6" bookshelf speakers, in a smallish 3.5x3.5x2.4m room, Gain/volume is unchanged with different voltage power supply, as expected.
Now I have both of the V3 monos connected with balanced source/input (source is MOTU Ultralite mk5).
With output level from MOTU adjusted, feeding the V3 mono signal strength to match subs, all is well. Which is to say it's the same as it was. I ordered the V3 mono somewhat on an impulse, and for peace of mind of PFFB freq response, and balanced is nice to have.
How can i resist to comment on heat??
early days, and it's not warm in here at present.
Firstly - my existing V3 Stereo, 2 of them, are powering a pair of passive subs, which are probably about 3ohm load each. I'm using just one channel from each of the V3 Stereo. In the past, I had tried 48V on those, and they got a whole lot hotter than with the 32V power supply. Since I am unlikely needing the extra power, I kept using 32v. That was ~18 months ago.
Just now, i put a 48v on one of those 2 V3 Stereos. it got noticeably warmer. it sounded the same (it's one sub of two, not played all that loud - gonna be hard to tell). the other one seemed basically cold to the touch.
The V3 mono, with 32V 5A power supplies had some slight warmth. for a while, have had one of those two mono powered with 48V 5A, the other with 32V 5A. the 48V is perceived as noticeably warmer to the touch, but not by all that much. i don't have any measuring equip. not listening very loud.
With 48v, absolutely not a temperature i would have any concerns about. but with passive cooling, when this room gets warm, it may make a big difference and change that thinking. I am not against perhaps cooling them in the interests of potential enhanced longevity.
I will probably run both mono at 48v for now at least. while under warranty, and through a summer. I'll be turning them off when not in use. don't care about auto standby option for now at least.
I cut the power from from the mains, and heard no concerning sounds, mechanically nor amplified through speakers. same when turning them back on by plugging into mains. i probably won't power on or power off my Motu source with amps powered. Though the thump that makes hasn't been disturbingly loud.
Oh, it does seem like the DC barrel power jack into the amp on one of them at least can fail to deliver power with only a minor disturbance. not a great connection perhaps, but cramming it in fairly firmly and it seems ok.
Amps seem very fine. they do amping. music plays. and i can have placebo of so much magical SINAD, perfect absence of crosstalk and superior balanced connection, and PFFB. veils! nights! days! (not.) It subjectively sounds the same. it sounds fine. it sounds great. it sounds just like it did before with different, adequate amplification.
I did that Kippel Distortion listening test.
https://www.klippel.de/listeningtest/ i did the two-tone 70hz 800hz stimulus.
I'm probably pretty mediocre at "listening". good. I hear plenty enough that I don't like in some recordings/productions. I don't need to be hearing more of my equipment.
Your personal audibility threshold for the particular test combination (stimulus and DUT) is -33 dB!
With volume up a bit towards louder end of what I might sometimes enjoy for a while, playing music, JBL Studio S26 standmount speakers, high-passed at 76hz LR8/48dB octave, I just shoved the mutlimeter on a speaker output of the V3 mono, and saw about 8Volts. presumably i'm not needing that many watts? but quick peaks could well be much higher I guess. But the 32V power supplies would probably be adequate.
Was listening to Pineapple Thief's "Versions of the Truth" earlier - nice sounding recording, with great drummer and great sounding drums.
I also did this, as a crude, perhaps practical test to see whether PFFB was making any freq response difference with those JBL S26:
Right after unboxing one of the V3 mono, I put UMIK-1 in a mic stand nearfield to one speaker. position fixed. A sweep measured with V3 stereo amp.
changed amp to V3 mono, adjusted output of test sweep to make it close to SPL match. Comparison below. (ignore the 23hz difference, as that would surely be real-world noise floor variation - speaker was high passed at 24hz)
i would say that'd be inaudible to me with real music content. maybe even some mic/measurement variation accuracy? though i did do several sweeps and for a fixed amp, the lines generally overlayed better than this, so some confidence that the difference might be "real". I conclude with these speakers, PFFB or change of amp makes very little difference.
Their phase is correct. they have 19-25dB gain switch on RCA. They have only 1 QC sticker.
They don't make any concerning amount of noise when turned on and off, even yanking or plugging in at mains with switch on amps set to "On".
They are not disturbingly warm after a few hours use at moderate volume, though the room is pretty cold at present.
They work. Music is being amplified and sounds as such. success! but it's only been mere hours.
I just received a pair of Fosi V3 Mono today, with 2x 48v 5A power supplies. (Previously had and was using Fosi v3 stereo. 32v 5A power supplies)
I personally think external power supplies are often favourable, and do not wish for internal.
The models delivered are both 19-25 dB gain switch on the RCA in. Purchased from amazon, Australia. Delivery was quick from opposite side of the large island. The amazon box was a great efficient fit for the 2x amp packages.
The 48v 5A supplies are the same in each box, seem quality enough, but aren't Fosi branded like the 32V ones i have with V3 Stereo amps purchased early 2024. Here's a blurry low light photo:
I first installed a V3 mono on just one channel, and played music (stereo downmixed to mono signal), with a V3 stereo on one side, and a new V3 mono on the other. with V3 mono gain on 25dB, RCA input, there was still a little gain/volume difference comapred to the V3 Stereo. not unexpected. but it otherwise sounds fine - Most notably, this confirms these have the correct phase. Only one QC sticker exists on the bottom of the amps.
Swapping 32v power supply and the 48v, sounds the same at the volume I had - ~80dB A-weighted, 2m distance from 6" bookshelf speakers, in a smallish 3.5x3.5x2.4m room, Gain/volume is unchanged with different voltage power supply, as expected.
Now I have both of the V3 monos connected with balanced source/input (source is MOTU Ultralite mk5).
With output level from MOTU adjusted, feeding the V3 mono signal strength to match subs, all is well. Which is to say it's the same as it was. I ordered the V3 mono somewhat on an impulse, and for peace of mind of PFFB freq response, and balanced is nice to have.
How can i resist to comment on heat??
early days, and it's not warm in here at present.
Firstly - my existing V3 Stereo, 2 of them, are powering a pair of passive subs, which are probably about 3ohm load each. I'm using just one channel from each of the V3 Stereo. In the past, I had tried 48V on those, and they got a whole lot hotter than with the 32V power supply. Since I am unlikely needing the extra power, I kept using 32v. That was ~18 months ago.
Just now, i put a 48v on one of those 2 V3 Stereos. it got noticeably warmer. it sounded the same (it's one sub of two, not played all that loud - gonna be hard to tell). the other one seemed basically cold to the touch.
The V3 mono, with 32V 5A power supplies had some slight warmth. for a while, have had one of those two mono powered with 48V 5A, the other with 32V 5A. the 48V is perceived as noticeably warmer to the touch, but not by all that much. i don't have any measuring equip. not listening very loud.
With 48v, absolutely not a temperature i would have any concerns about. but with passive cooling, when this room gets warm, it may make a big difference and change that thinking. I am not against perhaps cooling them in the interests of potential enhanced longevity.
I will probably run both mono at 48v for now at least. while under warranty, and through a summer. I'll be turning them off when not in use. don't care about auto standby option for now at least.
I cut the power from from the mains, and heard no concerning sounds, mechanically nor amplified through speakers. same when turning them back on by plugging into mains. i probably won't power on or power off my Motu source with amps powered. Though the thump that makes hasn't been disturbingly loud.
Oh, it does seem like the DC barrel power jack into the amp on one of them at least can fail to deliver power with only a minor disturbance. not a great connection perhaps, but cramming it in fairly firmly and it seems ok.
Amps seem very fine. they do amping. music plays. and i can have placebo of so much magical SINAD, perfect absence of crosstalk and superior balanced connection, and PFFB. veils! nights! days! (not.) It subjectively sounds the same. it sounds fine. it sounds great. it sounds just like it did before with different, adequate amplification.
I did that Kippel Distortion listening test.
https://www.klippel.de/listeningtest/ i did the two-tone 70hz 800hz stimulus.
I'm probably pretty mediocre at "listening". good. I hear plenty enough that I don't like in some recordings/productions. I don't need to be hearing more of my equipment.
Your personal audibility threshold for the particular test combination (stimulus and DUT) is -33 dB!
With volume up a bit towards louder end of what I might sometimes enjoy for a while, playing music, JBL Studio S26 standmount speakers, high-passed at 76hz LR8/48dB octave, I just shoved the mutlimeter on a speaker output of the V3 mono, and saw about 8Volts. presumably i'm not needing that many watts? but quick peaks could well be much higher I guess. But the 32V power supplies would probably be adequate.
Was listening to Pineapple Thief's "Versions of the Truth" earlier - nice sounding recording, with great drummer and great sounding drums.
I also did this, as a crude, perhaps practical test to see whether PFFB was making any freq response difference with those JBL S26:
Right after unboxing one of the V3 mono, I put UMIK-1 in a mic stand nearfield to one speaker. position fixed. A sweep measured with V3 stereo amp.
changed amp to V3 mono, adjusted output of test sweep to make it close to SPL match. Comparison below. (ignore the 23hz difference, as that would surely be real-world noise floor variation - speaker was high passed at 24hz)
i would say that'd be inaudible to me with real music content. maybe even some mic/measurement variation accuracy? though i did do several sweeps and for a fixed amp, the lines generally overlayed better than this, so some confidence that the difference might be "real". I conclude with these speakers, PFFB or change of amp makes very little difference.
I've had the pair a few days now.
I'd previously reported that cutting or supplying power to them from the mains, with the Fosi's power switch left in "On" position didn't make any relevant audible sound through the speaker... I think that might have been when I was trying with the 32V 5A power supply. I purchased them with 2x separate 48V 5A power supplies.
Using the 48V 5A power supply, when cutting power to them by pulling the plug at the source/powerboard, I have noticed the speakers make a brief static sound - not much bass in it by the sounds. Maybe a quarter of a second in duration. Audible, but not loud. Certainly doesn't seem hazardous in level.
Is this unique?
Will test again when I have the chance whether it occurs only with 48V, and not with 32V.
I'd previously reported that cutting or supplying power to them from the mains, with the Fosi's power switch left in "On" position didn't make any relevant audible sound through the speaker... I think that might have been when I was trying with the 32V 5A power supply. I purchased them with 2x separate 48V 5A power supplies.
Using the 48V 5A power supply, when cutting power to them by pulling the plug at the source/powerboard, I have noticed the speakers make a brief static sound - not much bass in it by the sounds. Maybe a quarter of a second in duration. Audible, but not loud. Certainly doesn't seem hazardous in level.
Is this unique?
Will test again when I have the chance whether it occurs only with 48V, and not with 32V.
With 32V 5A power supply, pulling the power while the Fosi amp's switch is "On" does not make the static noise. Just a tiny click. 48V does make the static noise.
Standby power consumption:
48V 5A power supply:
19W on, with no signal/sound.
it very quickly went to standby - just a few minutes it seems.
about 9W in standby. This is kinda stupid, and way too much. But hey, it's still half the power. That's something.
I'll be turning them off when not in use.
With 32V 5A power supply:
12W on, no signal.
7W standby. (still too much.)
Edit: unofficial values. Just measured with hardware store thing of this type:
and also values were lower later... maybe after amps warmed up a bit??
edit2: next day, tried again, with them from cold, and got the lower values as below.
with 32V 5A powersupply, no signal, after amps been on a while - 5.8W
3.3W when it went to standby
With nothing connected, that 32V 5A fosi powersupply from a V3 stereo model is reading 0.1W
With nothing connected, 48V 5A powersupply is fluctuating between 0.3W and 0.6W
with no signal, amp on, 9.4W
went to standby quick - heard relay tick - 4.2W
19W on, with no signal/sound.
it very quickly went to standby - just a few minutes it seems.
about 9W in standby. This is kinda stupid, and way too much. But hey, it's still half the power. That's something.
I'll be turning them off when not in use.
With 32V 5A power supply:
12W on, no signal.
7W standby. (still too much.)
Edit: unofficial values. Just measured with hardware store thing of this type:
and also values were lower later... maybe after amps warmed up a bit??
edit2: next day, tried again, with them from cold, and got the lower values as below.
with 32V 5A powersupply, no signal, after amps been on a while - 5.8W
3.3W when it went to standby
With nothing connected, that 32V 5A fosi powersupply from a V3 stereo model is reading 0.1W
With nothing connected, 48V 5A powersupply is fluctuating between 0.3W and 0.6W
with no signal, amp on, 9.4W
went to standby quick - heard relay tick - 4.2W
Last edited:
Sokel
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How did you measure that?
We better be sure about such measurements, gear should consume less than 0.5W under European law when in stand by.
Maybe not a true standby?
How much PSU's consume without connecting the amps?
Their efficiency marking (VI) indicates about 0.2W under no load.
measured with some supermarket thingy like this.
Mains is reading 233V 50hz.
Hmm, do they maybe get more efficient after a little warm up??
With 32V powersupply, Just now playing music quietly, it was about 10W (powering one bookshelf speaker from >76hz
with no signal, it's now 5.8W
3.3W when it went to standby
With nothing connected, that 32V 5A fosi powersupply from a V3 stereo model is reading 0.1W
With nothing connected, 48V 5A powersupply is fluctuating between 0.3W and 0.6W
with no signal, amp on, 9.4W
went to standby quick - heard relay tick - 4.2W
Fair to say, this meter could be a piece of junk.
But it probably is doing its job near enough.
Sokel
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That explains it, you need a very accurate one before we put some judgment.
I mean, that's not about opinions, there's laws involved to it.
That is fair to say. Will edit my earlier comments to say they're just measured with consumer trash gear.
I'll try again another day from cold to warm. but it certainly isn't official.
though if there's any warmth felt from them when they've been in standby for a long period, that would probably indicate it is more than 0.5W
Karlaka
Member
Hi, jEDGEc0m.
I have two Fosi V3 mono amplifiers with independent 48V 10 amp power supplies, connected to a power strip.
When I disconnect the power supply from the power strip or turn the amplifiers to OFF, I also hear a considerable amount of static noise (although I don't consider it dangerous).
After several attempts, I've noticed that if I put the V3s in AUTO and wait for them to enter STANDBY mode, I can turn off the power strip without hearing anything at all. I've tested this several times with the same result.
Best regards!
Thanks for the reply and info - That's interesting that even using the switch on the amp to "Off", yours make the short static noise - mine don't make the noise if i use the switch on the amp from on to off.
How long have you had yours/when were they purchased? Wonder it we have potentially different revisions....
(Either way, it doesn't really matter - the static noise doesn't seem to bother either one of us - if it's like mine, it's low level - would be very minimal power to the speakers)
Karlaka
Member
That's right, that's how they behave. Only when I let them go into sleep mode can I cut off the power supply, without hearing the damn noise, which actually doesn't bother me that much, but enough to make me wait those 10 minutes it takes the V3 to "go to sleep."
I have a Kickstarter version, I guess. I bought them as soon as they came out.
Hey, just a little update.
No issues with my Fosi V3 Mono.
Anecdotally, seems running them vertical might help heat dissipation, but in the interests of longevity, and upcoming summer, I got a ran that blows at the vertical pair from a distance - the case then seems to stay about room temp feeling.
I am now just turning them on/off with switch on the amps.
I (needlessly) decided I wanted more 48V power, to run the 2 x Fosi V3 (the normal stereo version) that are each powering one sub each (up from the 32V bricks they came with)
So wanted 2x more power supplies, to supplement the ones that came with the V3 mono, which look like this, and might actually be a GaN model
I got Mean Well LRS-200N2-48
rated 211W and 4.4A. no fan - passively cooled. Source is 240V mains.
But is capable of short term 200% current. I'm pretty sure I'm not pushing the amps anywhere near limits, so this should be ideal, and able to handle peaks to the limits of the amp.
also - specs of LRS-200N2-48 derating for ambient temp. i.e. I don't expect to ever be derating.
Thanks to posts from others, from memory, notably @Roland68 who I've seen a lot of power related commentary about.
I was going to set their voltage a bit below 48v. Set them to 46V. Then with same voltmeter (basic old cheap digital thing), checked the bricks that came with V3 mono - they were reading about 45-46V anyway.
The Mean well were very well priced and seem quality. Quick delivery (from mouser - came from Texas).
No issues with my Fosi V3 Mono.
Anecdotally, seems running them vertical might help heat dissipation, but in the interests of longevity, and upcoming summer, I got a ran that blows at the vertical pair from a distance - the case then seems to stay about room temp feeling.
I am now just turning them on/off with switch on the amps.
I (needlessly) decided I wanted more 48V power, to run the 2 x Fosi V3 (the normal stereo version) that are each powering one sub each (up from the 32V bricks they came with)
So wanted 2x more power supplies, to supplement the ones that came with the V3 mono, which look like this, and might actually be a GaN model
I got Mean Well LRS-200N2-48
rated 211W and 4.4A. no fan - passively cooled. Source is 240V mains.
But is capable of short term 200% current. I'm pretty sure I'm not pushing the amps anywhere near limits, so this should be ideal, and able to handle peaks to the limits of the amp.
also - specs of LRS-200N2-48 derating for ambient temp. i.e. I don't expect to ever be derating.
Thanks to posts from others, from memory, notably @Roland68 who I've seen a lot of power related commentary about.
I was going to set their voltage a bit below 48v. Set them to 46V. Then with same voltmeter (basic old cheap digital thing), checked the bricks that came with V3 mono - they were reading about 45-46V anyway.
The Mean well were very well priced and seem quality. Quick delivery (from mouser - came from Texas).
I bought a pair of V3 Monos/48V PS from Amazon, received them a few days ago. On examination out of the box they have different labels. One is a QR Code, the other is a standard barcode with what I assume is the S/N. The QR Code doesn't show a S/N when read with my phone QR scanner. I find it odd that a single purchase has two different versions like this. I bought a V3 Mono last year for a dedicated measurement rig. It has the same kind of QR code. I never confirmed if that one has the inverted output voltage wiring internally because it's immaterial in my measurement rig. But a stereo pair may be affected by that. In addition the QR code on the new one is on the opposite side of the base from my original one. Tag location isn't important for function, but I find it all a bit odd. I have yet to even connect the new pair to check them out. Anyone out there have a similar experience? The different codes actually give me a bit of concern. These both also have the new 25/19 gain labelling, so evidently the newer variety. I had not been keeping up with this thread, had no clue that there was a gain change in the newer ones, but I'm fine with it.
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