Fosi ZA3 Amplifier Deep Dive Review (with Data)

[@ErinsAudioCorner]

Re: Audible differences in amps, opamps, etc My personal take is this: Can differences be heard? Absolutely. Do measurements-only matter? Nope. Am I skeptical of claims of audibility? Yep. Now, let me explain... As someone who does have a bit of a following (albeit, quite small) I will always default to not talking about hearing things that I can't at least point to evidence with. It's not "just about measurements". It isn't. It's about being able to back up a claim. Whether that be providing measurements or results of a proper blind test. Either is acceptable to me as proof. The last thing I want to do here is to fool my audience into believing things that may not be true. None of this means that differences can't be a) heard and b) measured. In fact, I think there very well can be differences heard. But are those differences real or are they some form of sighted listening bias? In the case of Fosi ZA3 amp I have shown that its load dependency can effect the response of the speaker and that may very well be audible. The key is this: If someone can so easily hear differences in amplifiers, opamps, etc then it really should be easy to prove via a simple blind listening comparison. You don't have to have hardware or measurement experience. You just have to do a proper blind listening test with the help of a friend or friends. No one is doing that, though. At least not in the review space that I'm aware of. None of the above makes me a "non-believer". It just means that I take a reserved stance and am cynical of claims of audibility without some sort of evidence. I think that's a pretty reasonable approach to take. Especially when it comes to spending money based on claims. And, in my specific case, especially when I'm helping people decide if they want to part with their money on a product. I wouldn't feel good telling a friend to drop $300 on something I wouldn't buy. I am not going to tell my audience to do that, either. 👍 I prefer to report on things that I can prove or at the very least have some sort of pointer to. Whether that be from a blind listening test or measurements, doesn't matter to me. I just need to feel confident in telling you all that what I am reporting is accurate and not just words I used to fill space. I'm not saying any of this to get anyone to agree with me. I'm saying it so you understand where I'm coming from. Hopefully you can respect that. - Erin

[@joentell]

I reviewed a Burson amp a long time ago where they sent opamps that I could change. I could "sense" some kind of difference, but didn't have the tools to measure the change. See if you can get some of those or if they even still sell them. I'm curious as to what they did.

[@Douglas_Blake_579]

On the op-amp thing... (edit: In relation to these mini-amps) Get a copy of the NE5532 spec sheets and look at the various curves and ratings. Two things become readily apparent ... the chip has uneven gain below about 1 volt of input (which is where we use them!) and they don't even specify differential input specs because the two inputs are diode clamped together giving a maximum of 1.2 volts across the two inputs. (On the TI data sheet take a look at graphs 5, 6, and 7) Now you have your difference... a cheap as chips chip with uneven gain and very uneven input characteristics vs. any other chip that does not suffer these limitations. The real difference in op-amps with these small amps is NOT putting in an expensive chip ... it is getting rid of the stock chips. I commonly pull out all the NE5532 chips supplied and put in either RC4558 or TLO72 ... under $1.00 each in lots of 10. Yes that first step does make a noticeable difference ... beyond that, not so much.

[@editorjuno]

As long as both channels of the amp have the same "uneven gain" for any given input voltage, what's the advantage of swapping one type of cheap op-amp for another? Given that (e.g.) the NE5532 and TL072 are equally elderly designs, why is the NE5532 the overwhelming favorite for inclusion in mixing desks and other professional recording gear? I'm pretty certain the engineers of enormously pricey studio gear from the likes of Studer and Neve could have designed in any op-amp chip they wanted, so there must be something about the NE5532 that made it preferable, right? Then there's TI's decision to equip their own TPA3255 eval. board with NE5532s -- if the RC4558 is better for that application, then why that op-amp choice when TI makes both ICs?

[@davidfuller581]

@@Douglas_Blake_579The NE5532 and TL072 are pin compatible, but _not_ interchangeable. The 5532 is a bipolar input dual op amp, the TL072 is FET input. Wildly different input impedance.

[@Douglas_Blake_579]

@@editorjuno If I feed in 1 volt on a gain of 10 circuit... I expect 10 volts out. Not 7 or 13... 10. it's not rocket science. The advantage is that the 4558s and tl072s are linear gain, their input impedances are higher and their inputs are not diode clamped at 1.2 volts peak to peak.

[@slam854]

Subwoofer issue: I am very happy that the sub is not attenuated. With proper tuning on your sub the overall presentation is beautiful. I am glad Fosi did what they did.

[@richh650]

I have watched over a dozen of the ZA3 amp reviews and your review is the best review by far. You actually understand how to test and then associate that with how it really sounds and preforms. Your efforts are MUCH appreciated as you have become my go-to reviewer!!!

[@litzy7892]

After watching other reviews on this amp, my biggest question was how much power does it really have. And I knew if I were to ask in the comments they would just feed me the vague garbage that was provided by the manufacturer. But Erin came thru with the real measurements I wanted to see! I was impressed. Thanks you very much Erin.

[@mathumphreys]

I'm even later to the party, but I'm just glad to be here. I bought this amp after watching your review, so thanks for taking the time to put together a really useful practical review. In relation to the amp, I'm using it in a studio environment to power (secondary) monitors so I needed balanced inputs, flat response and silent. The performance is just brilliant for me - no fuss, does the job, run at around 75% all day and barely get warm and is transparent. Having the RCA inputs is a bonus because it has given me a couple of auxiliary inputs that I can flick when I want. I love this little thing.

[@HunterMikeWI]

Fosi is working on LPF and HPF filters for the next gen models. They are deciding on fixed or variable frequency.

[@ErinsAudioCorner]

That's great! I'd vote variable for sure.

[@markalot]

Thanks for an actual review, much appreciated. As an old guy getting back into amplifiers "hifi" I was surprised to see many golden ear reviews but few if any actual objective reviews. I probably shouldn't have been surprised. Soundstage, imaging, lol, different op amps, oh my! I've got the WiiM amp, very happy with it for what it is.

[@ErinsAudioCorner]

Thanks for watching! Glad to have you back (in the hobby!)!

[@JosephTongret]

This isn't really about the amp, but I'd LOVE to see you get in one of the Minidsp models (Flex/SHD/2x4) and do a few videos covering procedures to improve system performance. Time align, fir, crossovers, etc. There's a lot of guides already out there, but the way you explain what's happening and why ALWAYS leaves me with a better understanding than what I initially had. You have a way of making complicated topics so much easier to digest than most sources. Thanks for the content Erin, you're an invaluable source!

[@ErinsAudioCorner]

On it!!!! I am talking with MiniDSP about getting a FlexHT to do a video (or series) on how to use them to tune your system. I'm excited about it!

[@JosephTongret]

@@ErinsAudioCorner Wow, that's incredible news! I find their software a high value addition to a system. I'm looking forward to gaining a deeper understanding of any aspects you decide to cover. Thank you sincerely Erin!

[@peterdesmidt8742]

I"m really happy with my SHD. Dirac made a huge difference in my system. I have tso of the ZA3s. I biamp with them using my SHD. They work fine in my system.

[@kadajawi2]

​@@ErinsAudioCornerOh, awesome. I love my Flex HT, but I'm sure you can help me extract much more from it.

[@ItsElvis56]

An absolutely amazing video, Erin. I will be holding onto my Schiit Rekkr for my desktop setting. Almost 50k! Should be way over 100k at this quality.

[@user-xg6zz8qs3q]

I have a geology degree here. It's about as useful as a roll of toilet paper. But I can say that sand is classified under different diameters, usually under 30mm (max range). But salt crystals can grow larger.

[@ErinsAudioCorner]

Listen, this is the best reply I will get on this video. By far.

[@Audio_Simon]

We all appreciate toilet paper and your reply 😂

[@AdamMrozek84]

Hi, you do very good tests. I would love to see the Topping pa7 in the future. Regards​@@ErinsAudioCorner

[@michaelblumfield3933]

But as someone who has been a professional writer for his entire career, I would suggest looking closely at the meaning of the cliche. The grain of salt is to guard against the negative qualities of what is being consumed. So if you really want to distance yourself from an assertion, you use MORE salt, not less. Rather than a grain, you might suggest applying a spoonful of salt or even a salt mountain. Or just say "I'm highly skeptical about ... ."

[@dinoalden568]

I don’t know about anyone else, but I have found the aforementioned roll of toilet paper to being quite useful!😁🧻

[@ancientalien815]

I would have loved to see some mono testing.

[@tugbars4690]

Checking the frequency response of the amp with a reactive load is a genius idea.

[@gurratell7326]

And the conclusion is that load dependency is a thing, but it might just be barely audible. And anyone that's interested in audio should have a DSP anyways so those small frequency response deviation can easily be fixed together with the rest.

[@michaelsparrow4798]

I agree 100% on everything you describe. Suggestion: You mention multiple times that a high-pass would unload the speaker. I'm sure you know that it also would/should unload the amplifier, but unless stated explicitly, some newbies may not perceive this. Cheers!

[@ErinsAudioCorner]

Good point! Thanks!

[@Clobercow1]

Late or not, I'd rather hear it from you than most of those jokers out there.

[@GoggleAX]

100%

[@TheLevitatingChin]

Pull them bum cheeks apart.

[@2kdesignstudios72]

Facts

[@tacofortgens3471]

So for the most in depth reviews on youtube. Love this channel

[@MrBonger88]

I really like that you show us your testing methodology in detail. Thank you

[@ErinsAudioCorner]

Thank you!

[@ck17350]

I own one of Fosi's 2.1 board amplifiers and I agree that some of their design choices are baffling. Mine suffers from exactly the same problem and with the small Paradigm Titans I paired it with, I ended up with noticeable low-end distortion from the Titan's at higher volumes. Now here's what I found most interesting about that Fosi product. I checked Texas Instrument's page for the amplifier chip Fosi chose and found that Fosi copied Texas Instrument's very basic example design schematic and just called it a day. Granted, this is one way to save money since there's no need to hire someone to design an amplifier if you can just crib TI's example. At the end of the day, the amplifier board was cheap, far more powerful than I expected it would actually be and I'm happy enough with the performance for what I paid for it. I picked it up as a neat toy to play with and I absolutely enjoyed it as a toy. With just a little bit more work on Fosi's part, it could be more than just a toy but at the end of the day, that's really all their product's are; cheap toys. Nothing wrong with that as long as reviewers make that clear like you have done. Glad to see this review after doubting some other reviews I've seen recently on this product. Keep up the great work Erin! You are a breath of fresh air in this space.

[@BobbyBass-x6i]

Erin thanks for your measurements and explanation of what they mean. Very helpful. Keep up the great work!

[@Blewis-Diarrheo]

I found this channel because of the whole speaker controversy. I subbed because the content is really good, and the subject matter is very interesting and very informative.

[@JukeboxAlley]

I have to say, after many years in the hobby and after probably 300+ amps and receivers, i got 2 of these and a decent preamp and i love em (the right preamp is always the key component to separates, remember that). Keep in mind this is compared to old legends (but often a little noisy in the background due to age, power supply, blah blah blah) adcom gfa-555, nakamichi pa-5 class A, emotiva xpa2, and many more, and i liked these better and had just as much to give in any area as the others and are silent, zero noise. Also you dont need to see a chiropractor after moving them around, i think their the best for the money that one can ask for. Thats just me, you hobbyists gotta do whatever works for you but i will say this, when 2 of these are running together on a decent preamp, they are certainly no joke and tonally great. Also on a 4 ohm load driving the flagship polk sda srs 1.2 (6 ft tall and 180 pds each) and did a VERY good job with plenty of headroom and kept their composure even at 115-120 db levels and on 10, 15 and 20 hz sweeps, no problems for me. Sounded as good or better as nearly anything else ive tried, including "claimed" bigger and badder amps and of different classes, they work for me just fine and id buy a dozen more for backups if i could afford to have them around, anyway, to each their own its just my opinion.

[@JoseFerreira-zb7wh]

You should try the smsl a300. Seems like good competition for this. It can be used as monoblocks, has a remote, tone controls and eq presets and a high pass filter (100hz is the only option though) so at least from a feature/ functionality point of view, it kills this.

[@ErinsAudioCorner]

I'll look into it. Thanks for the suggestion.

[@stephenjarzombek2903]

I have one, purchased before any independent reviews came out and am not impressed. I find the interface clunky at best. In stereo mode, the power into 8 ohms is only 50 watts and has worse distortion than average these days. It has a lot of power as a monoblock into 4 ohms--over 400 watts---but at the expense of even more distortion.

[@JoseFerreira-zb7wh]

@@ErinsAudioCorner rsl also has a cheap one with hpf. Sabaj a30a is a digital amp with that option also.

[@JoseFerreira-zb7wh]

@@stephenjarzombek2903 yes, just checked asr's review. He wasn't impressed either. It's a shame because the featureset and price are great!. I don't understand why there aren't more amps with hpf. If one's into streaming only there's always something like bluesound node or the upcoming wiim ultra that have bass management, but other options are much pricier.

[@carlatdmf]

I just love the sound of measurements.

[@wesleyaardahl7278]

Thanks much for this review. Please review the Fosi V3, which is quite different and does not have a sub out. Many people (self incuded) are buying them and it will be helpful to have a similarly thorough, empirical review of it. Thanks much!

[@c0mbat15]

Totally agree on the subwoofer pre out. That's why I went for the Aiyima A07 Max amps at half the price of these. I'm using the line out from the WiiM Pro Plus in to the Kef KC62 and then use the high pass filter on that to feed anything above 85hz to two Aiyima A07 Max amps that then feed above 85hz to the Kef LS50 Meta.

[@mikeortiz2139]

I really like the approach of your reviews on these audio components. And more so for the amps than speakers. I guess it's bc speakers easily price themselves out, but budget amps like this, the deep objective dive is something to pay attention to. Thanks.

[@willbrink]

It's a great little desk top amp for my office set up, but not gonna replace my Anthem STR in the main system any time soon :)

[@MJ-ge6jz]

I purchased two Fosi ZA3 amps because of can bi-amp my speakers and get the full use of the amp, avoiding mono mode issue. Verdict, sound good! I seem to avoid that 4 ohm power problem talked about in this review. I was able to find these amps on that EEE bay site for $120 w/ 48 volt DC power supply.

[@forty5cal1911]

Priceless review as always Erin!

[@kraig7777]

I was wondering about an issue I have with the Fosi BT20a Pro (same chifi chip). Using the sub out to a Klipsch 10" sub it works but there's a rumble with the volume turned down. I have a 12" Dayton Audio sub with high level line inputs that I used with a vintage Yamaha receiver. I tried the Fosi with the Dayton sub and the sub only works from the RCA input. Using the high level speaker lead inputs the Dayton made no noise at all. It made me wonder what the Dayton sub high level inputs do to the ohm load of the amplifier and I was wondering if that contributed to my Yamaha's demise. Why did the sub work great hooked up to the Yamaha that way but not at all hooked up to the Fosi? The Dayton sub also doesn't have a filter so the high level speaker inputs and outputs are just pass through.

[@twebbas]

No doubt the best reviews out there. Thank you.

[@sk9592]

The subwoofer output issue you described is a feature, not a bug. At least as far as 2-channel audiophiles are concerned. For those of us from the home theater or car audio world, high-passing your speakers when you have a sub connected just seems like common sense. However, the "common wisdom" in the audiophile world is that subwoofers are a necessary (or unnecessary) evil. You want your speakers to cover as much of the full range as possible, and for the subwoofer to only come in at the very low-end as the speakers are already rolling off. You don't want to pick a crossover point. Your crossover point is determined by where your speakers bottom out. I personally don't agree with this logic, but if Fosi wants to sell to 2-channel folks, they likely need to cater to this approach.

[@ErinsAudioCorner]

I disagree. The use of a subwoofer alleviates the mains from playing lower frequencies so those speakers then improve in both a) distortion and b) dynamics. (These are objective things, btw.) "You want your speakers to cover as much of the full range as possible, and for the subwoofer to only come in at the very low-end as the speakers are already rolling off. You don't want to pick a crossover point. Your crossover point is determined by where your speakers bottom out.... personally don't agree with this logic" ^ I agree with your disagreement here but maybe for a different reason because this particular item doesn't offer control of where the filter is implemented. Maybe if they did I might be more apt to not be bothered by not having a HPF (i.e., mains roll off naturally at 60Hz so you apply the subwoofer to ~60Hz and below). But that's a moot point here, unfortunately.

[@sk9592]

​@@ErinsAudioCorner You mentioned the -3db point on the sub out as being 180Hz. I'm assuming Fosi picked this as a safe maximum for the highest people want their subwoofers to play. The idea being that you adjust the bandwidth of the signal yourself using the LPF built into your subwoofer. I've seen this same approach on $1000+ integrated amps that have a sub out: Speaker level outputs always play full range, and the sub out is not adjustable on the amp. You're expected to low-pass the signal on your sub. It's not ideal, since as you said, I can't pick a crossover point that minimizes distortion, improves dynamics, etc. It also assumes you're using a subwoofer that has a LPF built-in, and it leaves you SOL if your room is creating a null in the crossover region forced upon you. But for whatever reason, this has become the "common wisdom" that hi-fi amp and speaker manufacturers have settled on. To be clear, the lack of this functionality in this amp annoys me just as much as you. I feel like I'm taking crazy pills when I see integrated amps costing thousands of dollars that lack the most basic of bass management features,

[@michaelsparrow4798]

@@ErinsAudioCorner Not to mention, that although a driver/crossover combo has a point where it will no longer reproduce linearly, the speaker will still be forced to "overlay" frequencies above the crossover point on top of lower frequencies. Unloading the speaker by removing lower frequencies lets the upper-bass/mid frequencies drive the speaker's cone with less "interference".

[@bigbluetaurus]

@@ErinsAudioCorner not true! It all depends on how u wanna listen to your music! For example I have my AV always set to main and LFE for bass! But when I wanna listen to just music I have my SUBs turned off! So IMHO u should see it that way... ;)

[@buckaroobonsi555]

I agree I thought they should have have an automatic low pass on the sub output of 90hz and a switch to give you the option of high passing the mains!

[@991carreras3]

I have 3 sets of speakers and bought 2 of these za3 in December just for the mono function and there is absolutely no sound difference between stereo /mono on any of my speakers. I think all fosi is doing is just shutting off one channel this isn't true mono so theres no need to buy two. I did endup sending both back after a few weeks. I have tried many of these ti3255 amps and I'm done with all of them and I dislike those separate power supplies and they get annoying after a few hours.

[@ErinsAudioCorner]

Kinda... but there is a slight power increase in the mono channel. FWIW, I did measure the other channel in mono and nothing changed, so you have to make sure you are using the channel labeled as "mono" to get the extra power output.

[@991carreras3]

@@ErinsAudioCorner I do have everything set correctly. I was looking for a difference in sound quality and there's none that I noticed on my CSS, ELAC, or my PSB speakers.

[@ErinsAudioCorner]

@@991carreras3it may just be that the difference is so small that it might not sound louder. Otherwise, yeah, I dunno, man. Just weird stuff.

[@Douglas_Blake_579]

The problem here is one of expectations ... many people are stuck on the notion that bridging an AB amplifier does increase output power. Not so with Class D chip-amps. They are in fact, already bridged in the stereo mode. The TPA3255 chip as 4 independent power amplifiers in it. They can be combined in various ways to provide differing system topologies... 4 x SE (single ended) ... giving 4 independent outputs 2 x SE + 1 x BTL (bridge tied load)... your typical 2.1 stereo setup 2 x BTL ... two pairs of bridged SE outputs... the most common use. 1 x PBTL ... parallel connecting the 2 x BTL outputs for more current. They are *not* just turning off one channel. They are switching the chip into PBTL mode which allows it to drive loads as low as 1.5 ohms. The two stereo BTL channels are paralleled so there is no increase in speaker voltage (and thus power), it's all about the current needed to drive low impedance loads. If you're expecting some magical transformation in mono mode, you're clearly at the wrong alter. Above 4 ohm impedance it makes little or no difference at all. The only real advantage to running 2 monoblocks is that each amplifier has it's own power supply.

[@gameswong]

Thank you for the great review!!!!! ❤❤❤

[@ErinsAudioCorner]

No way! Thank YOU!

[@c0mbat15]

@ErinsAudioCorner What are your thoughts on the Sparkos SS3602 Op Amps? Is it snake oil or are they genuinely reasons why it could improve perceived audio quality?

[@AndiGomez-yu2dx]

That’s a really good question, I’d be interested to see him test this.

[@wric01]

Not snake oil, best upgrade you can do to your amp.

[@c0mbat15]

@@wric01 If it really is such a good upgrade then most manufacturers would be preinstalling more expensive op-amps. The fact that they don't tells your something. The reality is that Erin blind tests amps and can't tell the difference in sound between then (when the gains are matched between the two) so how is an op-amp going to change things so materially?

[@stu-po]

I really would like to see someone test these in Mono mode at 2-ohms. The PBTL should be more stable at 2 and 4 ohms than a single side of these amps.

[@maxrider2887]

Is it better than Aiyima A70?

[@rabscots910]

Just placed 4 LM 4562 chips into the ZA3. LM 4562 : "gift to the audio hobbyist from the industry". I left one subwoofer socket with the original chip...everything else replaced. Also placed one of the LM 4562's in the XLR chip socket..... One word: Wow ! Only £20 for four LM 4562's. The ZA3 copes very well with these high speed chips...no oscillation. Crystal clear instruments and vocals.

[@Static_Age]

You’re not late. You just took the time to do it right.

[@ErinsAudioCorner]

I appreciate the sentiment. I definitely put a lot of time into this to figure some things out that had me stumped for a bit. LOL

[@alexw890]

Hey Erin. Can you please review the RSL ia 2.55 mini amp? It has a switchable high pass for the mains.

[@tonyosicka]

You never mentioned the speaker's used...why? Second with my testing so far with surplus speaker's..... PMC OB 1. Quad 11s In a large room. It did a fantastic job. Wiim pro plus as the pre amp for streaming and cd playback and the parametric EQ.to fix your issues. Fantastic job from both units.

[@Douglas_Blake_579]

Because those are laboratory tests done with dummy loads.

[@Edward-Norton]

Doesn't this make quite a bit more power than the Wiim amp with it's 48 volt supply?

[@williewilson6832]

I own a pair of ZA3 monoblocks but I personally prefer the sound of FOSI TB10D stereo power amplifier. It can easily drive a pair of my 6ft tall Genesis APM-1 speakers. Sounds very detailed with crystal clear highs, excellent mids and very tight bass response.

[@maxrider2887]

Really ?

[@AbsoluteFidelity]

Honestly, not many amps have a high pass, especially chifi. I know of one or 2 that have a non adjustable high pass, but that just solves part of the problem. I really wish to see chifi amps with fully adjustable high pass and dual sub outs.

[@steveh545]

Agree. Even some of the bigger hifi companies don’t include high pass filters. It seems like that’s something if want, but you have to hunt around to find that. Or buy a WiiM amp 😂.

[@AbsoluteFidelity]

@@steveh545 I mean its not hard to make an amp with a fully adjustable high pass, dual sub outs, load indepedent and hdmi out. Lol! Infinite PEQ would be nice too. 😜

[@steveh545]

@@AbsoluteFidelity no idea how hard it is to make an amp… just many many more expensive amps don’t offer high pass filters, so I wouldn’t ding this amp for that. YMMV.

[@AbsoluteFidelity]

@@steveh545 its like amp manufacturers do not know what the consumer really wants, they keep churning out same ol products. It could be easily done by china, or any manufacturer for that matter.

[@DomSchiavoni]

What you all are talking about is easily and thoroughly solved with a minidsp. Pair a 2x4HD with Any amp (including this fosi) and you have the power to time align your individual subs and mains to maximize amplitude then dial in the frequency response as desired for multiple listening positions. It's a real game changer. Far superior to an amp with "dual sub outs".

[@TheTrueVoiceOfReason]

Most of the guys I follow that design/build/repair/improve amps, do tests at different frequencies in order to see, not only max output @ % thd, but also to compare thd @ many levels as well as how flat the amp really is. They also test @ the different impedancesfor everything including power supply sag. So yes, you are on the real comprehensive path. Keep it up and don't let anyone tell you any different.

[@NemoPropaganda]

Hi bro, is high pass common in these little chifi class D units? In my experience it's been pretty rare but I'm usually reiveweing more traditional full size stereo amps. Personally I like to run my speakers full range even when using a sub so its not a big deal to me but everyone has their preference and some speakers certainly may sound better when highpassed.

[@ubacow7109]

I'm excited to see the TPA3255 amps with PFFBs be implemented into Home theater amps. Super affordable and high performing and hi powered class D amps.

[@Panslapper]

PFFB is location bias. Depending on where you live in the world. Most electrical circuit feeding homes in Europe won't need PFFB and so the average consumer will not necessarily see any improvement anyway...apparently.

[@ubacow7109]

@@Panslapper measurements show significant improvement

[@Panslapper]

@@ubacow7109 So it appears...I can't sat either way myself as I have no way of testing but if offered with or without I would likely go with...

[@sudd3660]

Frequency Response with reactive load question from 7:46 . i also went to the website, it seems to be at max volume about 1% thd. does the Frequency Response still look wavy like that at lower volume?

[@ErinsAudioCorner]

I test at a lower input voltage around a couple watts too. So far I’ve not seen a difference.

[@versus023]

Woulds that work for a subwoofer dedicated amp @4ohm receving signal from AVR ?

[@rene_magritte]

I don’t get it. What’s the problem with running the speakers at full range and add the frequency they are missing by a sub. Why would you want to squeeze the speakers full potential? In stead of replacing a part of the speaker with a sub, you just add a sub for the missing low end.

[@ErinsAudioCorner]

Because they can actually work against each other depending on the rolloff profile of the mains. Aside from that, I answered the question in the video.

[@albe1796]

​@@ErinsAudioCornerSo my big 10 inch woofers would go dormant?

[@ErinsAudioCorner]

@@albe1796 not necessarily. But if you look at my reviews of many budget 10” subwoofers you’ll see they typically don’t have much extension past 40Hz. Most of them are just midbass modules. Obviously there are exceptions. And more expensive 10” subs typically use DSP to extend the bass response (but do run out of excursion at high volume).

[@acemacgruber6593]

Have you considered reviewing a vintage restored amp every so often and contrasting it with the new ones at a similar price point?

[@stackoverflow8260]

I had a similar experience with another class D, Purifi 1ET7040SA from Buckeye Amps rated at 950 watts@2ohms. I am using Thiel CS3.6 which are almost a resistive load from 80hz to 22khz at 3.3ohms. Whenever I played "When it's going wrong" by Marta and Tricky, the amp would experience bus pumping and go into protect mode. It happened even when crossed over at 50hz, it doesn't happen when crossed over to subwoofer at 70hz. Dylan from Buckeye will be sending extra capacitor boards to mitigate this issue.

[@ron5493]

Great Job! It is good to know about the lame sub out. Great information!

[@ErinsAudioCorner]

Glad it was helpful!

[@marinoint]

Excellent review as always. Hope Fosi will see this and fix the weird "subwoofer output" problem.

[@NickSim86]

It's not weird. It's the industry standard. Idk what Erin is on about

[@Douglas_Blake_579]

@@NickSim86 Exactly .... you gotta climb the price scale quite a bit before you find high pass filters on the mains.

[@hmurchison8123]

I've got Monitor Audio Radius 45 ( 3" Cubes ) so not only do a need High Pass but it has to be flexible enough to go to 120hz. I get that vendors want to "tick boxes" but just save the Sub out money , if you're not adding a HPF to the mains "you're doing it wrong" I don't care how cheap your product is if it's designed inflexible.

[@NickSim86]

@@hmurchison8123 you have very niche speakers and should use an AVR

[@anthony2010707]

I was using the subwoofer output in mono mode and it was quite weak, i did the same in the stereo mode and it was fine, now i have gone back to the mono mode using two ZA3'S with the P3 Preamplifier, running two subs from my P3 Preamplifier using a 3.5 mm to rca y splitter, lovely results, enjoying the music. 😊

[@sensibox]

Very thorough measurement! BTW Fosi is going to release a new monoblock amp with the PFFB implementation to devoid load dependency.

[@ErinsAudioCorner]

That’s good news.

[@lionelh152]

Does O-NOORUS D1 Amplificateur Class D TPA3255 PFFB already do that?

[@sasoesasoe]

This is exactly the answer I needed. In a home theater for more directional bass I had the idea to use 3xFosi as an amp for RCL with 3x sub. On the receiver I would define the RCL speakers as large. Ok, is not recommended. We knew that Fosi does not have a manual crossover setting when you connect a sub. Well now we know that it does not have an automatic one either. And also the output power is not a big step up. So, no go.

[@RanTausi]

I have the Fossi P3 tube preamp and after Three time of use in BT mode it starts to make some strange tik sounds like relay is clicking.

[@JukeboxAlley]

Same here mine acts glitchy sometimes, but I use external Bluetooth so I don't even use it for that, other than that it's great for the money. Especially with 12 db of bass gain and 6 db if treble gain and tube swap options. I like it well for the money, just waiting on a balanced preamp to be released next, gives you roughly another +6db of gain.

[@RanTausi]

@@JukeboxAlley I have ordered OP AMP OPA 828 to replaced the 5532 ones , I hope I will hear the difference hhh

[@Leo-tf7gu]

Thank you for bringing in the HPF issue to light. "Audiophiles" love running their speakers full range with a sub, not realizing that it causes the mains to do unnecessary work at the same time possible cancellation of low frequencies when all 3 speakers are playing them. Not to mention, the unnecessary load on the amp when playing low frequencies.

[@cbayardelle]

Love your channel, I’m using the Fosi v3 with elac ub5 which go down to 3.7 ohms, the amp never shuts down, even with music louder then I can stand, is the v3 different than the za3 ?

[@ErinsAudioCorner]

I’m honestly not sure about the differences. I haven’t looked into it yet.

[@jackdanyal4329]

there was a writing from REL Acoustic about a high pass filter where they stated, that it's fine not to have a high pass filter and just let the speakers sound with the whole range they can. Also integrated amps like Yamaha A-S301, 501, or Onkyo/Denon with the same price range don't have a High Pass filter. They just run main speakers with full range (I have a ZA3 for my desktop use and A-S301 for my living room).

[@EricRosenfield]

Lachlan at Passion for Sound said he thought the XLR input sounded better than the SE one. I’d be interested if there were any measurements comparing them.

[@ErinsAudioCorner]

He says a lot of things.

[@EricRosenfield]

@@ErinsAudioCorner LOL I know, I just mean did you measure the two inputs at all, so there might be evidence if the SE version is gimped somehow? (Yes, I know Lachlan did not measure anything.) Or did you only use one input?

[@ryanschipp8513]

Not sure where you are coming from on the subwoofer output. You can simply adjust the crossover on the subwoofer itself to control what frequencies it plays at. So how can you say it doesn't make sense to have the subwoofer output?

[@ErinsAudioCorner]

My point wasn't about the subwoofer. It's about how the mains don't have a high-pass filter applied to them to limit the bass frequencies and letting the subwoofer play that. Limiting the bass frequencies from the mains lowers distortion and improves dynamic range of your speakers.

[@ryanschipp8513]

@@ErinsAudioCorner I understand all of that. Still not sure how that's that big of a deal. I understand that's the ideal situation to be able to control what frequencies come out of your Mains and the subwoofer but I've got three rigs in my place add all three have full frequencies being played to the main speakers and then I'm controlling the frequencies for the subwoofer at the subwoofer. All three rigs sound very good.

[@ErinsAudioCorner]

@@ryanschipp8513 okay, then you don't see the need for mains to be high passed. I do. That's cool with me.

[@bbfoto7248]

@@ryanschipp8513 I have rarely, if ever, been able to PROPERLY integrate the main speakers to subwoofers in regards to ideal phase alignment/phase coherency if/when the main speakers are still playing full range w/o a HPF so that they are "overlapped" with the subwoofer(s). Ideal phase alignment between the main speakers and the subwoofer(s) is required in order to achieve a perfect "up front bass" experience where ALL of the low frequencies from the subwoofer(s) appear to be locked up front to the main speakers only and the bass will actually image properly within the soundstage (if that is part of the recording....play the intro to Malia & Boris Blank's "Celestial Echo" from the Convergence album). Sure, at particular frequencies, you will have some "constructive interference" where both the subwoofer & main speaker sum together in order to provide a boosted response. HOWEVER it is very unlikely for that constructive interference to be both Phase AND Time aligned. So while that scenario might provide MORE BASS at a certain frequency, it will not be "articulate/detailed/clean/fast" bass, and will not provide that perfect "up front bass" experience that is locked to the main speakers. This will be most noticeable with instruments such as an acoustic upright double bass which has lower fundamentals combined with lots of upper harmonics and transients, or fast "slap bass" on an electric bass. So the phase alignment through the crossover region and beyond will rarely be ideal between the subwoofer and main speakers when both are significantly "overlapped". In fact, you will usually want a Half Octave UNDERLAP between the subwoofer and mains center crossover frequency. As a starting point to achieve the easiest integration between the subwoofer and the main speakers, and as a most-likely scenario example, I would set the main speaker's HPF to 80Hz and the Subwoofer's LPF a half-octave lower to 60Hz, and use 4th Order Linkwitz-Riley (LR4) filters for both. While this is not a "set in stone" configuration that is guaranteed to always work perfectly every time, it is the most likely configuration to get the response and integration of both the subwoofer and the main speakers at least close or "in the ballpark" more so than others, especially if your subwoofer has a "Variable Phase" control knob rather than just a 0°/180° phase switch, i.e. "normal/reverse" polarity switch. What really matters is the actual Acoustic Crossover response of the system and the Phase Alignment between the mains and subwoofer(s) within and throughout the crossover region. And to achieve that, your crossover network filters (either passive or active) may need to be asymmetrical with completely different center frequencies and orders/slopes for the HPFs & LPFs that are applied to each driver. Achieving proper summation between a subwoofer and the main speakers is going to be difficult to achieve with the mains playing full range, at least if they also have response down into the subwoofer region below 50Hz-40Hz.

[@TD05SSLegacy]

@@ryanschipp8513 the normal way is a big deal. It can add mid range to speakers that don’t have that in the mix when they are trying to handle lows AND mids. Basically adding a sub and high passing can make mediocre speakers sound better. So huge deal.

[@Lokaminiac]

A excellent reviews and good catch on the subwoofer output issue. To compare, a low price (powered) Edifier speakers with sub output all have high-pass filters. Damn, I think I will wait for their next generation products. So close…

[@impuls60]

I wonder if the manufacturer have set the current limit lower than the TI guys have tested with. This chip has an adjustable current limit set by a voltage divider if I remember correctly. That 4 ohm result is so bad and I've never reached cutout on my Tps3255 DIY boards.

[@Douglas_Blake_579]

Given the crappy thermal solutions on these fully enclosed amplifiers, I would not be surprised. A quick check of pin 7 on the chip itself will tell the story. Table 4 on page 19 of the Spec Sheets will tell you what to look for.

[@bujin5455]

My concern with the sub output, is if they did implement low frequency filter for the mains, would they manage to turn that off when the sub wasn't present, or would they filter the lower frequencies all the time? Where they either filter the low frequency all the time, or they pass it all the time, I'm glad they screwed up on the side of the fence they did. The sub output is nice, but it's not even going to get used in most situations for me, and I wonder how many people truly plan to use the sub output.

[@METAL_SOLAR]

Excellent overview ! That sub pre-out conundrum *is* rather quizzical I was almost going to buy a couple of these, but that is a deal breaker ... :)

[@frequeencytv8130]

It takes 10 years to realize and appreciate 🙏 the CHIP use in these Amplifier, The arduous trial and error and Research and development sleeples nights, changes and alterations made to Improve the Chip, the team that made and designed the Chip is so delighted and very happy HiFi People are talking about the application of the Chip Projects finally making waves, making people enjoy a not too expensive Amplifier. Thanks to the Reviwers

[@chinmeysway]

class D has interesting history. maganovox employee discovered long time ago early 90s ? and was really unrecognized / misrepresented. but i don’t recall the deets very well and if chip was grown up yet n stuff

[@d.branch3604]

Erin - Is it normal for one channel to play before another? I noticed with the ZA3 that at very low volumes only one channel plays. I had to turn it up to a certain volume level to have both channels play simultaneously. Maybe it's user error, but I bought two of these and it's the same for both with the 32v and 48v power supply.

[@ErinsAudioCorner]

Definitely not normal.

[@speedking92]

If the volume control in these is a cheap potentiometer it's possible there's a lot of channel imbalance at lower volumes. I've ran across this with multiple products. In this case the channel imbalance decreases as you up the volume.

[@Douglas_Blake_579]

Yes that's pretty normal at extremely low volumes. It's in the way volume control 'pots' are made. They use mechanical wipers on a strip of carbon resist material to divide the input voltage onto their outputs. If those wipers are not tracking perfectly together you can have a noticeable low level balance problem. And no this is not Fosi or even a chifi thing... I've seen it on some pretty high end stuff, over the years.

[@shaolin95]

This must be why i tried to use this in stereo mode with two 4ohm shakers and it keeps cutting out. Only can get it to work fine in mono mode pushing one shaker per amp. So the tests at ASR clearly does not translate to all real world uses.

[@andreas_aus_d]

I actually own two of those things and I am happy with them so far. What is really necessary to provided with an equalizer, because in my opinion based delivery is kind of weak. It is a bit weird that your measurements look linear on the frequency graph Remember one thing however. Whenever you suggest something to fosi audio and it makes sense to them, then they will often listen. That's how the V3 Mono got started. Thank you for that review. I was already owning two of them when I watched it. I am however grateful for people who take the time to provide such a service.

[@RAW-CAt]

Erin, is this the first public amp review/measurements you have shared? I watch your channel, but never seen you doing amps.

[@ErinsAudioCorner]

Hey, thanks for asking. This is the 3rd electronics review I've done. I just started within the past few weeks. Here are my other two. NAD C 3050: kzbin.info/www/bejne/bpi0c2Vnidp5qKs WiiM Amp: kzbin.info/www/bejne/iJStcpaMl9ZorrM

[@c.s.herman860]

Is the Fosi ZA3 better than the internal Wiim Amp? Thinking about pairing it with the new Wiim Ultra (full bass management).

[@sandyjust]

I had this one. It's extremely loud and almost good. However I did notice dynamics were not enough and it was not responding well to details of music. I have returned

[@doncorleone7673]

Any budget friendly suggestion for a preamp with a sub out and highpass for mains?

[@ErinsAudioCorner]

Honestly, I’d just say get the WiiM Amp. All in one solution.

[@doncorleone7673]

@@ErinsAudioCorner good call in general mate, cheers. However, i do own a wiim mini, topping e30 and fosi v3 to drive my Elac DBR62. If i would not sit on that gear I would go for the wiim amp, even though it appears to be weak for hard to drive speakers in bigger rooms.

[@adame52]

@@doncorleone7673 In the same boat and still haven't figured out what I want to use to power my R3 Meta. The Wiim amp is great but I don't think it's the right solution for these speakers. Got a Pro Plus to use a streamer and good enough DAC (for now). I'm considering using the speaker level input on my RSL 10S since the Pro Plus doesn't have a subwoofer out and whatever amp I get might may/may not either.

[@doncorleone7673]

@@adame52 Ye, bass management is hard to get😅 For now Inam splitting the rca output from my dac to the amp and the sub. Realy hard to find a seperate solution.

[@theAbbeBusoni1]

Scientific Audiophile was right! ASR really needs to fix the way the measure these amps because a product that performs in this way seems to be as a result of poor measurement method at ASR (Fosi V3 was hailed there).

[@sk9592]

Any review methodology that chases a single number in its rankings will result in companies trying to game that one spec while ignoring everything else.

[@literalghost929]

@@sk9592 And then the 'measurement' type folks will scoff at people hearing differences which they didn't measure. I'm much more on the measurements side, but sadly, people take it to extremes, and ASR, although I hate to say it, might have gone ab it over the edge in that respect.

[@theAbbeBusoni1]

@@sk9592 I do agree, though most on ASR don't really do the SINAD chasing most people think they do. I would say the biggest problem is that the power numbers are greatly exaggerated on ASR in comparison to what actual music would take.

[@AzGael]

Not late at all, the sales start tomorrow so this is conveniently and precisely on time. Thanks for the review!

[@techsamurai11]

I’ve never heard these but they are a bit on the lush side with extreme dynamics especially in 4ohms at very high levels using the bias knob😂😂😂. Multi-tones really stand out on these.

[@paultravisano9403]

I think a great alternative would be the Arylic B50. I would love to see a reciew. It high passes the mains and has a nice app for a good price.

[@ErinsAudioCorner]

Thanks for sharing!

[@paultravisano9403]

@ErinsAudioCorner I've got the B50 SE which is a great value if you don't need the extra features. Awesome review as always 👏

[@euclidesortiz7766]

This model is good to music? And price?

[@riccitone]

Very comprehensive, and very much needed. Reactive load is important and widely overlooked. Also not terribly hard to understand, which is strange why it’s not more focused upon. But you do have the equipment so there. This may be too time consuming or even worth messing with, but wondering how swapping opamps could/would change anything? Many seem to like using Sparkos labs discreet amps for “better” sonics - would actually be fun to try 🙏🏼👍🏼

[@robsandler1818]

So get the subwoofer comment, but would the test results be different with SparkOS Op Amps? SInce many people who purchase these are upgrading the Op Amps, this may be a useful followup.

[@ErinsAudioCorner]

No, they wouldn't. I understand everyone likes to play with opamps (I used to as well) but we have to accept there is a lot of sighted bias into making these changes and expecting (therefore hearing) a change. I'm fine with that. I just wish others wouldn't push these things as absolutes because that's where we get into the realm of zany audiophilia. :D

[@badhusband1902]

most "entry level" amps will not apply a high pass filter to the sub/pre out, like cambridge audio axr100, audiolab 6000a, etc. which is a bummer.

[@dinoalden568]

I bought the Fosi DA2120C with the Nuemi Silk 4 for my mom a few months back for her TV viewing. Awesome little amp and speaker combo!! Fosi makes great stuff!

[@beprotishen]

what hi-fi speakers you can offer?

[@justincharnak1616]

I read that removing the unused op amps especially in mono mode can improve power and clarity. Any thoughts if that claim could hold any weight?

[@Douglas_Blake_579]

Best bet ... write to Fosi and ask them. If they are using true PBTL there might be ... but if they're using the outputs only hack I would strongly advise that you not do that.

[@34332]

Wondering about that too. VirtualHiFi guy did that and Fosi posted a guy (with a sub) claiming improvement.. One way to find out I guess 😅

[@kartikk127]

Would testing a real song/movie clip help understand dynamic power handling? Maybe one song with high compression, and one movie clip with a high crest factor.

[@Douglas_Blake_579]

Probably the most reasonable bench test would be to hit it with full range Pink Noise for a few seconds and see what it does.

[@firstprib7742]

Good review. A comment, 9:30 tell me another amp with subwoofer output which does a high pass at this price level. Sometimes less is more. Some high pass filters detunes the sound quality. I disagree in that having a pre-out definitely helps in being able to connect a sub with only rca inputs.

[@c.s.herman860]

RSL ia255 comes to mind, but there are several others. Even cheap $120 Edifier powered speakers do this when a sub is plugged in.

[@SixtyBee]

What is this vs fosi v3? I.e level the field without subwoofer output. I have Emotiva TA3 amp, but I am itchy to try Chi-Fi.

[@Douglas_Blake_579]

Bot this amp and the V3 are based on the TPA3255 Class D power amp chip (as are half of the mini-amps on the market right now.) Expect them to be far more alike than different.

[@darrylbrueckner2812]

I picked up a ZA3 to match with a pair of Micca RB42'S and Topping E30 I had kicking around. Pull the speakers out a couple of feet from the wall and sit nearfield and this combo delivers some audiophile fun on the cheap. So, a solid value compared to other budget Class D amps? Absolutely. GIANT KILLER like some of the more hyperbolic reviews? No. That being said, I'll probably upgrade to the Sparkos op amps because I can't stop myself 😂

[@Douglas_Blake_579]

I'd be careful with the ZA3/Micca combo ... the amp has enough kick to send those tiny speaker cones flying across the room...

[@kraig7777]

@@Douglas_Blake_579 Are you drunk? Only about a million people have that combo and no RB42s are blowing up. I have a Fosi BT20a Pro with 48v power supply and RB42s and they could use even more power. In fact my old Yamaha receiver finally croaked and I'm using the Fosi in the living room driving vintage Boston Acoustics A100s and the amp and the speakers are doing well.

[@OlaJustin]

You the best Erin! Super nice review!

[@Sam-t7c7j]

Erin, I’m looking to drive some Magnepan Mk 2 speakers in a relatively small 13x16 ft room. I of course could just throw money at it and be happy, but looking for suggestions on amps in different price tiers. Any suggestions?

[@Benjamin-nm4jd]

Look into Hypex Ncore/NCx/Nilai or Purifi, load of super clean power without breaking the bank. But if you just want something really cheap just to make some noise through your speaker, these Fosi/Aiyima little boogers would get the job done.

[@oliverosrecki7421]

Good evening. I have one question, if you can answer and explain it to me. My friend told me that these Fossi devices work better and have better sound than Quad 405, 44 and fm4? What do you think? Thanks in advance for your reply and greetings from Serbia! 

[@Roddy451]

If it is possible, may I suggest you test the (Nobsound) Douk Audio H7Pro TPA 3255 Digital Amplifier with VU Meters? (Out of breath after writing that name). It is another Ginger Man cookie digital amplifier... with VU meters (crickets)

[@johnwright8814]

The power supply current is 5A, according to it's rating, probably a bit more for peaks. How much current will any amplifier draw from the power supply at 100W, both channels driven, into a 4 Ohms load on each channel, ignoring quiescent current?

[@Douglas_Blake_579]

That's easy ... Three quick calculations... First we need the voltage on the speaker ... so V = sqrt( P x R) ... that is the square root of 100 x 4 or 400... so 20 volts rms. Next we need the peak voltage... so Vp = Vrms X 1.414 ... that's 28 volts peak. Finally the current ... I = V / R ... so 28 / 4 gives us 7 amps. If you're running stereo at those levels... that's 14 amps. So you would need at least a 15 amp supply to feed it properly. However ... Unlike bench testing, music is not a steady state. A musical waveform with minimal dynamic range will most often average 1/10th of what we put these amps through on our test benches. So in reality playing music at peak levels of 100 watts most likely averages about 10 watts (or less) with only occasional brief bursts that would hit the calculated maximums above... i,e 1.4 amps. This is why there are bulk reserve caps of 2200uf or more on most of these boards. When a short maximum impulse comes along they can fill in for the power supply and then renew their charge when things calm down. YES a fully engineered amplifier like the NAD that Erin tested will be up to the task but you can't expect that from these little amps that are 1/4 the price.

[@johnwright8814]

@@Douglas_Blake_579 I hoped Erin would calculate it. Did you see the switching power supply that was supplied? 48v, 5A. Switching supplies don't have the surge capacity that the usual 'transformer + bridge + capacitor' power supplies have. Maybe 50% more, but not 200% more. That was my point.

[@Douglas_Blake_579]

@@johnwright8814 This is a common misunderstanding. The linear supplies you find in older AB amps do indeed appear to have an elevated surge capacity... but the other side of that coin is to notice they are not regulated and tend to sag rather badly under heavy loads. SMP supplies are all regulated and can deliver constant voltage right up to their current limits. Thus the full "surge capacity" is always available to the amplifier all the time. What we are actually seeing is a power supply that doesn't sag under load.

[@34332]

​@@Douglas_Blake_579 Good info, thanks 👌

[@brydon10]

Don't most subwoofer outputs on integrated amps just let the speakers run full bandwidth though? My NAD does. I'm pretty sure this is the case for like 90% of integrateds or more. I think you get more into AVR territory when we're talking that kind of stuff. One of the only "audiophile" amps that do this that I know of is the PS Audio Sprout100.

[@tom6363]

I just bought this Fosi amp to drive only my rear SS (7.2.4). Will arrive this week and hopefully will suffice in this limited role.

[@ValerioCongeduti]

For me HPF is a must. However it seems to me that most amplifiers with sub out do lack HPF, even more costly and acclaimed ones: Hegel, Audiolab, Camdridge Audio, Naim, Rotel, Rega, etc.

[@alphacapo]

The dummy workaround is if u have good eq software you drop everything below 60hz a few db adjust your sub level at the sub. You get to your sweetspot volume for where u like to sit. And adjust levels from there. This is how you did it in the 90s anyway

[@lionelh152]

Is there many Microsoft audio player that support this? The software should be compatible with something like vst ? A vst name bundle?

[@AntonisAnastassiades]

What monoblocks would you suggest?

[@D1N02]

You can build a high pass pretty easily. Implementing it in such a basic amp seems hard. ideally it would need to be variable, but that would mean extra electronics and cost. Fosi sells GaNfet powersupplies. Those may be able to take the amp to higher levels.

[@Artcore103]

That power supply, even though it's 48v, is likely still holding back the amp in terms of max power, perhaps it simply can't provide enough current. But I'd use it in a bi-amp setup to only power a pair of compression drivers so the power capability it has is MORE than enough for me. Would love to have it!