One of many PFFB (Put up-Filter Suggestions Know-how)-based Class D audio amplifiers showcased in a current writeup of mine was Fosi Audio’s V3 Mono, which can get sole billing at the moment:

It apparently (at the least to me) initially launched as a Kickstarter undertaking in April 2024:

Because the title implies, it’s a monoblock unit, supposed to drive solely a single speaker, with each single-channel XLR balanced and RCA unbalanced enter choices.

I personal 4 practical (for now, at the least) units, plus the nonfunctional one whose insides we’ll be seeing at the moment. Why 4? It’s not as a result of I plan on driving each entrance left and proper important audio system and a middle speaker and subwoofer, or for that matter, the 2 important transducers plus two surrounds. As a substitute, it’s for spares, notably ones obtained pre-higher tariffs, and particularly to do with that useless fifth amp.

Design evolution, manufacturing, and reliability points

Earlier than I am going all Debbie Downer on you, I’ll start with the excellent news. The V3 Mono is very reviewer-rated (see, for instance, the write-up from my long-time tech compatriot Amir Majidimehr) and has additionally garnered no scarcity of enthusiastic suggestions from homeowners like Tim Bray, who had heard about it from Archimago (right here’s half 2). Alas, amidst all that constructive press are additionally a notable variety of complaints from people whose items let the magic smoke escape, generally on simply the primary use, or whose amplifiers had extra modest however nonetheless annoying points.

Mis-wired connections

I’ll begin with probably the most innocuous quirk and finish with the worst. Preliminary items had been mis-wired from the PCB to the speaker banana plugs (due, I truly suspect, to a basic PCB hint format concern) in such a means that they ended up with inverted-polarity outputs, i.e., alerts being 180° out of part from how they need to be.

This wasn’t significantly an issue if all the items in your setup exhibited the difficulty, as a result of at the least then the part was constantly inverted. Nonetheless, if one (or some, relying in your setup complexity) of them had been in part and different(s) had been out of part, the inconsistency resulted in a collapsed stereo picture and general decreased quantity as a result of harmful interference between the in- and out-of-phase audio system.

The identical goes should you mixed-and-combined out-of-phase V3 Monos with in-phase different units, whether or not from different producers and even from Fosi Audio itself. The repair is fairly straightforward; join the purple speaker wire to the black speaker terminal of the affected V3 Mono as a substitute, and vice versa, to externally reinvert the part again to the way it needs to be. However from my expertise with these items, it’s not doable to discern if a specific machine is wired appropriately with out disassembling it; this man’s sticker-based methodology, for instance, didn’t pan out for me:

As commenter @TheirryG01210 wrote in response to the above video, “A greater means to determine if part is right is to examine that cables are cross-connected (left solder pads cable goes to the proper banana socket and vice versa).”

That’s spot-on recommendation. Right here, for instance, is one in every of my practical items, which has the wires un-crossed, subsequently working in an inverted-output vogue. That mentioned, this method appears like the way it ought to be wired, proper? Subsequently, my conjecture that this truly is inherently a PCB format concern, with wire-swapping the cheaper, simpler workaround to the choice costlier and in any other case extra sophisticated board “flip”.

My picture additionally matches one of many two in this Audio Science Assessment dialogue thread put up:

The different image in that put up reveals the wires crossed; it’s not clear to me whether or not that is one thing that the proprietor did post-purchase with a soldering iron or if Fosi Audio revamped items nonetheless in its stock, after discovering the issue and previous to transport them out:

Conceptually, it matches the from-factory crossed wiring of my different three practical units, together with at the moment’s teardown sufferer, though the wire colours are additionally swapped with my items:

However shade doesn’t matter. A crossed-wires configuration is what’s key to a correct-phase output.

The subsequent, extra just lately launched concern includes gain-setting inconsistency. Take a look at the latest model of the “inventory” picture for the product on Amazon’s web site, for instance:

And also you’ll see that the 2 gain-switch choices supported for the RCA enter (the swap doesn’t have an effect on the XLR enter) are 19 dB and 25 dB. That mentioned, the achieve choices proven within the on-line person guide are as a substitute 25 dB and 31 dB, which match the unique items, together with all of mine:

Right here’s the important thing excerpt from an e-mail by Fosi Audio quoted in a related Audio Science Assessment put up (bolded emphasis is mine):

We want to affirm whether or not your V3 mono achieve is the outdated model or the brand new model. Since V3mono doesn’t have a quantity adjustment knob. It has already obtained a big energy output when it’s turned on, so we’ve lowered the achieve of 31db to 25db, and 25db to 19db within the new model, which might successfully make sure the secure output of V3mono, secure use and lengthen the service life.

Loud “pop” sound

Which results in my final, and probably the most regarding, concern. After a seemingly random length of operation, however generally simply the primary use, judging from feedback I’ve seen on Audio Science Assessment, Amazon, Fosi’s on-line retailer, and elsewhere, the amplifier emits a loud “pop” and the sound disappears, by no means to return.

The entrance panel gentle nonetheless glows, and you’ll nonetheless hear the “click on” when the amp initially activates or transitions out of standby in response to sensing an lively enter supply (or if you transition from one enter to a different, for that matter), however as for the output…nothing however the sound(s) of silence. This very concern occurred with one of many units I bought model new, thankfully, throughout the return-for-full-refund interval.

A number of of the opposite V3 Monos I acquired “open field” off eBay additionally arrived already DOA. In a single significantly thoughts (and amp)-blowing case, I purchased a single-box two-device set. After I opened it up, one of many amps had a bit of blue tape caught to the highest with the phrase “good” scribbled on it. Yep, the opposite one was not “good”. 

What the eBay vendor defined to me within the strategy of issuing a ship-back-for-full-refund is that when massive retailers get a return, they generally simply flip round and resell it discounted to eBay sellers like her, apparently with out remembering to check it first (or, extra cynically, perhaps simply not caring about its present situation).

A blown-output case examine

At present’s sufferer (1,000+ phrases in) was one other eBay-DOA instance. On this case, the vendor didn’t ask me to return it previous to issuing a refund, and it subsequently turned a teardown candidate, hopefully enabling me to discern simply the place the Achilles’ Heel on this design is.

To Fosi Audio’s credit score, by the best way, the tempo of complaints for this specific concern appears to have slowed down dramatically of late. After I first seemed on the buyer suggestions on Amazon, and many others., earlier this 12 months, feedback had been overwhelmingly destructive. Now, revisiting numerous suggestions boards, I see the combination has notably shifted within the positive-percentage path. That mentioned, my cynical facet wonders if Fosi and Amazon may simply now be nuking destructive posts, however hope springs everlasting…

I’ll begin with some overview photographs of our affected person, one in every of which you’ve already seen, as standard, accompanied by a 0.75″ (19.1 mm) diameter U.S. penny for measurement comparability functions (the V3 Mono, not together with its bulbous suite of exterior energy provide choices, has dimensions of 105 x 35 x 142 mm and weighs 480 grams).

Take away the 2 facet screws from the again panel:

And the entrance panel slides proper out:

The “Aesthetic and Sensible Mud-Proof Filter Screens” (I’m quoting from Fosi Audio’s web site, although I concur that they each look cool and act cooling) additionally then slide proper out if you want:

Eradicating two extra screws on the underside:

Now permits for the extraction of the inner meeting (right here once more, you noticed one picture already):

PCB extraction and examination

The back and front halves of the “Sturdy and Sturdy All-Aluminum Alloy Chassis” are equivalent (and an apart: fairly snazzy photographs, eh?):

Returning to the PCB topside (with still-attached again panel), let’s take a better look:

One factor I didn’t discover at first is that not one of the ICs are PCB-silkscreened as to their kind (R for resistor, for instance, C for capacitor, L for inductor, U for IC, and many others…), removed from their specific-device figuring out quantity (R1, C3, L5, U2…). Alongside the left facet, high to backside, are:

• The three-position swap for on, auto, and off working modes
• The ability standing LED
• The 2-position XLR-vs-RCA enter selector swap, and
• A nifty two-contact spring-loaded swap that’s depressed when the entrance panel is in place. I think, however didn’t take a look at for myself, that it prevents amplifier operation each time the entrance panel is eliminated.

Notice, too, the 4 screw heads in between the 2 multi-position switches, together with the ribbon cable. Look intently and also you’ll notice that the primary three objects talked about are literally positioned on a separate mini-PCB, related to the principle one mechanically by way of the screws (which, as you’ll see shortly, are literally bolts) and electrically by way of the ribbon cable.

And actually, the silkscreen marking on the mini-PCB says (amongst different issues) “SW PCB” (SW which means swap, I assume) whereas the principle PCB silkscreen within the decrease left nook says…drumroll…”MAIN PCB”.

Why Fosi Audio went this multi-PCB route is frankly a thriller to me. Till I observed the labeled silkscreen markings (admittedly simply now, as I used to be scripting this part) I’d thought that maybe the principle board was widespread to a number of amplifier product proliferations, with the entrance panel switches, and many others. differentiating between them. However on condition that each boards’ silkscreens additionally say “Fosi Audio V3 MONO” on them, I can now toss that concept out the window. Readers’ concepts are welcome within the feedback!

In the course of the picture are two 8-pin DIP socketed chips, op-amps the truth is, Texas Devices NE5532P twin low-noise operational amplifiers to be exact.

They’re socketed as a result of, as Fosi Audio promotes on the product web page and akin to the 2 Douk Audio amplifiers I showcased in my prior protection, too, they’re supposed to be user-swappable, analogous to the “tube rolling” carried out by vacuum tube-based audio gear lovers.

Quite a few (Elna) electrolytic and surface-mount capacitors (together with different SMD passives) dot the panorama, which is dominated by two huge Nichicon 63V/2200μF electrolytic filtering capacitors (explicitly recognized as such, together with the Elna ones, by visible and textual content shout-outs on the V3 Mono product web page, consider it or not). And one different, smaller Texas Devices 8-lead IC (soldered SOP this time) on the underside towards the proper bears mentioning. It’s marked as follows:

N5532
TI41M
A9GG

Its first-line mark similarity to the beforehand talked about NE5532P is notable, albeit doubtlessly additionally coincidental. That mentioned, Google Picture search outcomes additionally suggest that it’s certainly one other twin low-noise op amp. And it’s not the final of them we’ll see. Talking of which, let’s subsequent take a look at the opposite half of the PCB topside:

There it was on the backside; one other socketed TI NE5532P! Straddling it on both facet are Omron G6K-2P-Y relays. On the high are much more relays, this time with practical image marks on high to eradicate any identification confusion: one other white-color one, this time a Zhejiang HKE HRS3FTH-S-DC24V-A, and under it a darkish gray HCP2-S-DC24V-A from the identical provider.

Keep in mind after I talked about earlier that after one V3 Mono stopped outputting amplified audio, I may nonetheless hear relay clicks after I toggled its energy and input-select switches? Voila, the click-sound sources.

These coupling capacitors are one other curious part call-out on the V3 Mono product web page; they’re apparently sourced from German provider WIMA. The latter two, on both facet of the aforementioned PCB solder pads that find yourself on the speaker’s banana plug connectors, are gray right here however yellow coloured at Fosi Audio’s web site, so…

To the left of the purple coupling caps is a gray metallic field with two slits on high and copper-color contents seen by them; maintain that thought. And final however not least, alongside the proper fringe of the PCB are (high to backside) the power-input connector, two hefty resistors, the XLR enter, and the RC enter. The 2-wire harness within the decrease nook goes to the aforementioned achieve swap.

Inadequate thermal safety?

Now for the opposite facet:

That IC at far left was fairly a problem to determine. To the proper of an “AB” firm brand is the next three-line mark:

TNJB0089A
UMG992
2349

Google searches on the textual content, both line-by-line or its entirety, had been fruitless (at the least to me). Nonetheless, I discovered a photograph of a chip with an identical first-line mark right here. About the one factor on that web page that I may learn was the phrases “AB137A SOP16”, however that was the clue I wanted.

The AB137A, is (extra precisely was) from the corporate Shenzhen Bluetrum Know-how, which Web Archive snapshots recommend modified its title to Shenzhen Zhongke Lanxun Know-how initially of this 12 months. The bluetrum.com/product/ab137a.html product web page not appears to exist, nor does the hyperlink from there to the datasheet at bluetrum.com/add/file/202411/1732257601186423.pdf. However once more, due to the Web Archive (the final legitimate snapshot of the product web page that appears to exist there may be from final November) I’ve been in a position to discern the next:

• CPU and Versatile IO
  Excessive-performance 32-bit RISC-V processor Core with DSP directions
  RISC-V typical pace: 125 MHz
  Program reminiscence: inner 2 Mbit flash
  Inner 60 KB RAM for knowledge and program
  Versatile GPIO pins with programmable pull-up and pull-down resistors
  Assist GPIO wakeup or interrupt
• Audio Interface
  Excessive-performance stereo DAC with 95 dB SNR
  Excessive-performance mono ADC with 90 dB SNR
  Assist versatile audio EQ regulate
  MIC amplifier enter
  Assist Pattern fee 8, 11.025, 12, 16, 22.05, 32, 44.1, and 48 kHz
  4-channel Stereo Analog MUX
• Bundle
  SOP16
• Temperature
  Working temperature: -40℃ to +85℃
  Storage temperature: -65℃ to +150℃

So, there you could have it (at the least I feel)!

The opposite half of this facet of the PCB is much less thrilling, except you’re into blobs of solder (together with, let’s not overlook, one other glimpse of these hefty resistors), that’s:

However it’s what’s within the center of this facet of the PCB, subsequently widespread to each of these PCB footage, that had me significantly intrigued; you too, I think. Take away the 2 screws whose heads are on the PCB’s different facet:

Carry off the plate:

Clear the thermal paste off the highest of the IC, and what comes into view is what you’ve most likely already suspected: Texas Devices’ TPA3255, the design’s Class D amplification nexus:

At this level within the write-up, I’m going to supply my conjecture on what occurred with this machine. The within of the metallic plate, performing as a heatsink, paste-mates with the TPA3255:

whereas the surface, additionally thermal paste-augmented, is meant to additional switch the warmth to the underside of the aluminum case by way of the 2 screws I eliminated previous to pulling the PCB out of it:

Key to my concept are the phrases and phrases “backside” and “thermal paste”. First off, it’s a bit odd to me that the TPA3255, the design’s apparent major heat-generation supply, is on the underside of the PCB, on condition that (duh) warmth rises. The tendency would then be for it to “prepare dinner” not solely itself but additionally circuitry above it, on the opposite facet of the PCB, though the metallic plate-as-heatsink ought to at the least considerably mitigate this concern or at the least unfold it out.

This results in my different remark: there’s scant thermal paste on both facet of the plate for heat-transfer functions, off the IC and finally to the surface world, and what exists is pockmarked. I’m subsequently guessing that the TPA3255 thermally destroyed itself, and with that, the music died.

Wrapping up

Earlier than I overlook, let’s detach that mini-PCB I discussed earlier. Listed below are the bottom nuts:

And the front-side bolt heads:

Disconnect the ribbon cable:

And also you already know what comes subsequent:

Not too thrilling, however I’ve gotta be thorough, proper?

At this level, it occurred to me that I hadn’t but taken any main-PCB facet photographs. Entrance:

Left facet:

The again:

The correct facet:

And after eradicating the 2 screws surrounding the XLR enter:

I used to be in a position to raise the again panel away, exposing to view much more PCB circuitry:

In closing, do not forget that “gray field with two slits on high and copper-color contents seen by them” that I discussed earlier? Had I seemed intently sufficient on the V3 Mono product web page earlier than continuing, I might have already realized what it was (though, in my slight protection, the picture is mis-captioned there):

Then once more, I additionally may have recognized it by way of the picture I included in my earlier write-up:

As a substitute, I proceeded to make use of my flat-head screwdriver to tear it off the PCB within the strategy of trying to extra conservatively detach simply its “lid”:

As I already suspected from the “copper-color contents seen by the 2 slits on high”, it’s a twin wirewound inductor:

from Sumida, providing “superior sign purity and noise discount, elevating the amplifier’s sound efficiency,” per Fosi Audio’s web site.

Crossing by 3,000 phrases, I’ll wrap up at this level and switch the keyboard over to you to your ideas within the feedback!

—Brian Dipert is the Principal at Sierra Media and a former technical editor at EDN Journal, the place he nonetheless recurrently contributes as a freelancer.

 Associated Content material

• Class D: Audio amplifier ascendancy
• Audio amplifiers: How a lot energy (and at what tradeoffs) is basically required?
• Class D audio energy amplifiers: Including punch to your sound design
• How Class D audio amplifiers work

The put up The Fosi Audio V3 Mono: A compelling energy amp with an inclination to blow appeared first on EDN.