Fosi v3 Mono - User Impressions | Owner's Thread

[MCH]

I use one of these for my projects, I am quite happy with it, they can be get at ca. 50 euros. I am surprised that nobody has yet shown oscilloscope measurements in this thread, I thought every electronics nerd has one.

 

[Sokel]

REW also has a scope,just plug your mic,get it near the speaker pointed at it,some low level signal like a 1kHz tone at -20dB,and watch while plugged one way or the other:

 

[early rejecter]

If you run the Ultra as a fixed output device, then it has no advantage over a pro plus, and you can't run the ultra as the master pre-amp into the Yamaha as it doesn't have a pre-out / main in capability.

A main-in connection isn’t required for a setup like that; the Ultra can be connected to any of the standard inputs on the Yamaha while in variable output mode. The Yamaha volume knob would be left at a high level and volume adjustments made via the Ultra (similar to the way many people are using the Fosi V3 Stereo or ZA3 as power amps).

Your setup now is more compact and you’ve eliminated redundant components, but the 501 could’ve been repurposed for that role.

 

[burkm]

I have done this, but I only measured the outside case temperature. You can see my previous post to see the temperatures before adding paste.

The short version is that adding paste made no difference in the external temp of the case. This may not be intuitive to everyone, but there's a good chance the chip is running cooler even though the case temp is unchanged. Average external case temp, under steady state conditions, is directly related to energy the chip is dissipating and not the temperature of the chip itself. In a situation where the conduction is poor, the chip will run hotter to "force" the energy through the higher thermal resistance interface. When the conduction is good, the chip will run cooler since is "easy" for the heat to transfer to the case. In either situation, the amount of energy is transferred to the case is identical so its temperature remains the same (again all things being equal). If the room temp changes or you add a fan, then the case temperature will change since its thermal resistance has changed to transferring heat away from itself. In steady state, the chip will run a constant temperature above the case. Improving the thermal interface (adding paste) will reduce this delta.

Having said all of that, I'm not convinced adding paste is needed. I did it since I was opening them up for my own entertainment. For people who don't want to open their units, just use a 2mm hex to insure the two bottom heatsink screws are moderately tight and enjoy using the amp.

The thermal paste used by Fosi Audio for the V3 mono's cooling seems to be a very cheap variant because several of my (new) amps were already "poluted" what seems to be probably silicon oil (?). The remains of that paste looked quite "wet" to me, which would support my observations. Therefore I removed the original paste and substituted it using my own variant, which I use for my PCs CPU cooler. The temperature measured (contactfree) before and afterwards did not deviate much and the amps seem to be functioning OK.

 

[Deleted member 72219]

The thermal paste used by Fosi Audio for the V3 mono's cooling seems to be a very cheap variant because several of my (new) amps were already "poluted" what seems to be probably silicon oil (?). The remains of that paste looked quite "wet" to me, which would support my observations. Therefore I removed the original paste and substituted it using my own variant, which I use for my PCs CPU cooler. The temperature measured (contactfree) before and afterwards did not deviate much and the amps seem to be functioning OK.

It’s cheap crap. I never would’ve applied such junk on my CPU in my overclocking youth days.

-Ed

 

[Bernard23]

A main-in connection isn’t required for a setup like that; the Ultra can be connected to any of the standard inputs on the Yamaha while in variable output mode. The Yamaha volume knob would be left at a high level and volume adjustments made via the Ultra (similar to the way many people are using the Fosi V3 Stereo or ZA3 as power amps).

Your setup now is more compact and you’ve eliminated redundant components, but the 501 could’ve been repurposed for that role.

Hmm I hadn't thought of doing it that way. I could still run the sub out of the Ultra and do full RC. Plus the Yamaha has a million inputs as a fall back.
Maybe the Fosi isn't needed as it won't sound any better. I'll try it out, assuming it works practically then the V3s are going back.

 

[gwing]

I don't think that is going to work. Whatever the polarity of the amp (normal or inverted), you are putting the speakers out of phase with respect to each other. It will only cause a destruction of the sound - especially bass.

Both out of phase sounds fine if not playing with another speaker that is not out of phase.

The only reliable way to measure for this is to look at the waveform of the input compared with the output using an oscilloscope or similar

Yes indeed, that was just a solution for a single pair of speakers.
If we add another speaker then we need to do the same test and if necessary change for that extra speaker against the originally tested pair.

I wasn't trying to 'fix' any inverted/non-inverted phase 'issues' as that wasn't explicitly requested in the original question and I don't think it matters at all, as long as all speakers are playing in phase with one another all is good. To be fair the original question was possibly intended as something like "how do I easily measure/check if my speaker is in inverted or non-inverted phase" but that wasn't what was asked and I sort of chose to selectively answer

 

[burkm]

The simplest way would be to check how the speaker outputs are been soldered to by its corresponding cables, because Fosi Audio won't do a PCB or a back plate redesign, which would solve that "problem" once and for all, without telling everyone by an official note. The solution then is quite simple: either exchange those cables internally (by soldering) or externally by exchanging the speaker cables (+) and (-).

 

[burkm]

It’s cheap crap. I never would’ve applied such junk on my CPU in my overclocking youth days.

-Ed

If you removed the V3 mono PCB from its case, one has to reapply thermal paste afterwards. What did You use ???

 

[Deleted member 72219]

If you removed the V3 mono PCB from its case, one has to reapply thermal paste afterwards. What did You use ???

ARCTIC MX-4

Amazon.com

-Ed

 

[NTK]

Deleted. See post #853

 

[Deleted member 72219]

Here is the problem with the Fosi thermal design. There is no mechanical control of the contact surfaces between the heat spreader and the amplifier case. Good contact is essential for good heat transfer. If you look at CPU coolers, they are pressed firmly against the CPU (contact pressure control). Good implementations also require machined (or if you are really fussy, precision ground and polished) surfaces to specific flatness and surface roughness specs.

Below picture is from Archimago's review showing how the PCB is mounted to the case. No attention is paid to the mechanical contact between amp chip heat spreader and the case. With this Fosi design, the effectiveness of heat transfer from the chip to the case is all over the place.

Part I: Fosi Audio V3 Mono Amp; Class D + PFFB, TI TPA3255 - Retail box with single 48V/10A power supply and filter. [With initial measurements.]

A blog for audiophiles about more objective topics. Measurements of audio gear. Reasonable, realistic, no snakeoil assessment of sound, and equipment.

archimago.blogspot.com

View attachment 388972

Have you ever opened one of these things? There are two threaded fasteners (a.k.a. screws) that ensure tight adherence of the heat spreader and the case.

 

[NTK]

Have you ever opened one of these things? There are two threaded fasteners (a.k.a. screws) that ensure tight adherence of the heat spreader and the case.

Doh

 

[nitpicker1]

I played around a little today with a cheap scope, and from what I can gather, polarity is OK on both. Also tried the visual movement inspection on drivers on a test speaker, looked fine as well. What surprised me most was the response from an AVR I have standing, which gave a very... anemic... response, but with correct polarity. Doesn't look like wires are crossed on terminals. Cleaned up paste surfaces which looked like it was mixed with oil, gonna get some free noctua nt-h2 from work tomorrow.

Source audio:


V3 first:


V3 second:


Random miniamp while I was at it:


A Panasonic AVR... weird anemic result:


Both V3 disassembled:

 

[early rejecter]

Hmm I hadn't thought of doing it that way. I could still run the sub out of the Ultra and do full RC.

Coincidentally someone in the Ultra thread posted about using their integrated amp as if it were a power amp with the Ultra in variable output mode just this morning: post

 

[Bernard23]

Coincidentally someone in the Ultra thread posted about using their integrated amp as if it were a power amp with the Ultra in variable output mode just this morning: post

Oh well, every day is a school day. It's obvious when you think about it, all my yamaha is doing is operating as an most infinitely variable gain power amp, so I can mess about with the volume ranges on both devices (the Ultra jumps in steps of 3 using the remote which is too crude for my taste).
I tried the Fosi pair out, sounds fine, they get hot, and whilst there is a DC filter on the psu input it still hums if one channel is off and the other on, if that matters of course.

Anyway I've decided to keep the Yamaha, I think it sounds slightly better though that's probably placebo but that's OK with me. I get to save £265 too.
If I didn't already own an amp it does make for a great combo, as a small form high performance and power system it's brilliant value for money.

 

[antcollinet]

I had an idea earlier today about trying something like Audacity to visually inspect a phase wave during play while comparing it live with an oscilloscope directly on the terminals, something slow and low Hz going so I can see clearly if it's reversed vs its input. I considered it interesting enough to try out at least.

Unlikely to work due to the inevitable delays between audacity - and the output in analogue form. Probably longer than a full cycle at 20Hz.

But if you have an oscilloscope, put one channel on the analogue input to the amp, and the other on the speaker output. Job done.

 

[burkm]

@nitpicker1
Would surpise me, because Fosi Audio didn't announce any significant changes, just the official message, that inverting amps have 1 QC whilst non-inverting amps have 2 of those (see foto of the Fosi Audio Service department).
All V3 mono, which have been bought from Fosi Audio partners (Amazon, Ebay etc.), haven't been converted yet to my knowledge, because of existing inventory as far as I know. New shipments might be available soon...

If Your V3 mono amps carry 1 QC sticker they should still be of the inverting type, as long as they weren't shipped from Fosi Audio directly beginning with August 2nd 2024.
All partners to my knowledge are delivering still the "old" inverting version.
PCB version: The PCB should carry the imprint 03/28/2024 (?) if the PCB had not been modified yet...
Your amps should thus (probably) be of the inverting type...
Are You sure that isn't the case here... ???

Note: Looking at Your photos I am identifying a PCB version dated December 28th 2023. At that time there wasn't even known to Fosi Audio, that the V3 mono was inverting the signal... so Your conclusion might be erroneous ...

 

[Nopiano]

it’s captured in the first post of this thread.

Thanks so much, I’d completely overlooked that! It also coincides with my estimate. In the EU I thought all standby settings had to be 0.5 watts or lower

 

[Unbalanced]

UPDATE: It seems that setting the gain of my Fosi V3 Monos to 25db instead of 31 makes them not turn on at random as they did before. At least they no longer do after having switched the gain settings on them. Still hooked up to my WiiM ULTRA.

I have a similar setup. Two V3 Monos fed from a WiiM Pro Plus using the RCA cable that came with the WiiM. Two separate 48V 5A power supplies. Gain on the Monos is set to 25db. All items received this past Sunday from Amazon Canada. Both units packaged in fancy printed box.

Everything works great and sounds great with the exception that one of the Monos does not enter standby. I tried reversing the RCA inputs. Same unit does not enter standby. I tried side by side placement and reverse stack order. Same unit does not enter standby.

I contacted Fosi. They asked me to disconnect the inputs and then power up the Monos to auto. They should enter standby after 20 seconds which they both do. Fosi told me to get better RCA cables.

Final test that I did was to play music and then disconnect the RCA input from the offending unit. The unit does not enter standby after 10 minutes, 20 minutes ...

I have ordered a replacement from Amazon and will be returning the offending unit.