Fosi Audio ZA3 - Initial Review

In this review, we will get into the details of the new Fosi Audio ZA3 Amplifier - the latest TPA3255 amplifier Fosi Audio. I received my via their Kickstarter program at roughly $125 with the 48V power supply but it now appearing in other retail stores like audiophonics.fr



What is in the Box, internals and overall Build Quality
The ZA3 arrives in a larger package compared to other Fosi amplifiers. Contents include the ZA3 amplifier itself, a robust 48V 5A power supply unit (PSU) similar to the one that comes with the V3, and a comprehensive manual detailing connectivity options.

Note: depending on your order you will also either get an orange or a black volume control, I picked the orange one.

Here is the excellent power supply:


Internally the ZA3 is as nicely built as it is externally with the opportunity to swap out the NE5532 op-amp’s for tweaking the sound.


The build quality is outstanding, basically using the lesson learned with the V3, Fosi Audio have gone up to the next level with this Amplifier. I love the little design touches for example the quality of the vent holes on the side have a certain class about them:



The ZA3 is a little bit bigger than the V3 and the new Aiyima A07MAX:

This photo from above really shows how much larger the ZA3 is:

The extra size does allow more space for more connections (which I will get to in the Features section below) but also more space between the binding posts.

Though what really sets the ZA3 apart from these 2 other class D amplifiers is its feature, lets look at the features now in detail:

Features
Compared to the Class D amplifiers that Fosi Audio have previously released, the ZA3 has many new features specially designed to get the best sound quality out of your system. The features alone make it a significant device in the history of class D amplifier, this is the moment when Fosi Audio have upped their audiophile game and we the users who appreciate great sounding music benefit from the extra quality audio experience the ZA3 helps to provide.

Volume Control / Power toggle
Some recent Class D amplifier can only be turned off my moving the volume back to 0 but for a Mono block especially this can be problematic, not so much with the ZA3. You can fix the volume and press and hold the Volume button to switch on the ZA3. Therefore, when you have matched the volume on 2 setup as monoblock it is key not to have to touch the volume again (typically you would control the volume to both ZA3’s via a pre-amp or in my case via the WiiM Pro Plus).

Mono Switch
The Mono Mode switch on the front of Fosi Audio ZA3 is a probably its key new feature, enabling users to get the benefits of more power from 2 ZA3 acting in parallel, one ZA3 feeding the left speaker and the other feeding the right Speaker.

Here are the back of 2 ZA3 setup in Mono block mode, in this case one ZA3 is handling the Left and the other is handling the right:


I also subjectively thought this not only provided more power but a cleaner signal, where there is no chance of channel leakage within a ZA3.

Balanced Inputs (as well as the usual RCA)
Another of ZA3’s standout features is including balanced RCA and XLR/TRS inputs, offering versatility and improved audio quality. Here is an example where I have feed a TRS input into 2 ZA3 to provide extra clean audio using the Mono block setup:

Here is the back of a ‘fully loaded ZA3’ where both the balanced and RCA inputs are connected:

Simply using the RCA/BAL switch on the front will select the appropriate input. It should go without saying that a Balanced (XLR or TRS) input will potentially have less noise than an RCA but in practice the RCA will also be incredible clean sounding.

Subwoofer Output
It also features a proper subwoofer output, so unlike previous Class D Amplifier that had a ‘aux out / subwoofer out’ this is a dedicated subwoofer that is controlled by the volume so can be blended with your speakers to provide that extra sub-bass when required. For example, here is an example of a measurement I made with a subwoofer added to the ZA3 providing subbass down to 30Hz where my speakers were rolling off at 50hz:I believe the sub-woofer output also has a fixed Low pass filter of 300Hz but there is no high pass filter on the speaker output when the sub-woofer is connected - something to work on in a future version in my opinion.

12V Trigger input
The 12V trigger input for integrated system control, currently I am using a Wiim Pro Plus as a Streamer and DAC feeding the ZA3 and using the trigger to wake up the ZA3 whenever the music is about to start playing.



So one nice side effect of this feature is the Amp is only drawing power when its music. A quick comparison of the energy used when in Standby waiting for a trigger and being triggered and playing music is:

Mode Power used watts
Standby 0.9w
Triggered 7.0w
Here is a typical 3.5mm trigger needed for the ZA3 (to work with a WiiM Pro Plus I had to buy a 3.5mm to 2.5mm cable such is the inconsistencies with trigger cables):



Because the Amp is switching itself on there is no danger of a power on signal damaging your speakers.

Sound quality, Measurements and Specifications
The ZA3 exhibits clean, powerful sound with excellent stereo separation (especially when used as Mono blocks). The sound will be punchier compared to similar amplifiers due to its neutral frequency response (some similar priced Amplifiers will roll off before the sub bass and roll off the upper treble regions and therefore will not sound as rich and dynamic as the ZA3), When you then add a subwoofer to the ZA3 it is no competition at all with similar priced Class D amplifiers, the ZA3 has a unique set of features at this price point. The unit runs cool even at higher volumes, maintaining energy efficiency.


Listening Spaces - comparisons

I setup the ZA3 in 2 different listening spaces where I had to different requirements:

1. In medium sized space a converted garage ( my work from home space - this was when I had the Mono block setup) with a pair of Polk ES20, so each ZA3 connected to a single Polk.

Subjectively this was excellent, this space allows me to play very loud (as it a detached garage from the house), I was able to drive the ES20 - these can do down to about 40hz and the ZA3 never blinked, Bass was tight and clean, vocals were all nicely forward in the midrange and the treble as good as I have heard from these Polk's, lots of details. The soundstage in this setup is great and it's my preferred space during the day and this was as good as it has sounded in the past year (comparing against many other amplifiers). During this setup I also compared the ZA3 with the Aiyima A07MAX (both in mono block configuration) and the ZA3 was able to drive the speakers louder and clearer.

2. In a smaller 'den' room in my house, this was a single ZA3 with a Kef kube 8c subwoofer and 2 Q-Accoustic 3020i speakers.

In this configuration I was able to get down to 25/30hz and get a proper sub bass rumble from the subwoofer while the Q-Accoustics are more musical than the Polk so it was a very nice match where this configuration of the ZA3 was able to bring out the best in this space also. In this space I was mostly comparing the setup with a Denon class A/B Receiver and it compared very favourable, though the Denon has more options for tweaking the sound including room correction with Audyssey, the ZA3 with the subwoofer held its own in terms of the sound quality.

I will update this review with independent measurements when they become available but currently the official measurements provided by the Fosi Audio for the ZA3 have a SINAD value of 88db which is exactly the same as the Fosi Audio V3 and I would imagine independent measurements will back up this value. The SNR of 106db is actually better than the V3 (but again would need to be verified independently).

Specifications - I have highlight the key measurements below:

• Amp Chip: Texas Instrument TPA3255
• SINAD: 88dB
• SNR: 106dB
• Dynamic Range: ≥106dB
• THD: <0.005%
• Terminating Impedance: 2-8 Ohm
• Rated Output Power:
  • Stereo Mode: 180W*2 @ 4 Ohm
  • Mono Mode: 240W @ 4 Ohm
• Frequency Response: 20Hz-20kHz (‡0.1dB)
• Power Input: DC 24V-48V

Overall these are exception, but its probably worth nothing that when in Mono Mode you do not get double the power as each ZA3 would get a max 240W into 4 Ohms.



What could be improved
Very little at the price but possible the following could be implemented in a future ZA3 (maybe the ZA4):

1. Move mono switch to the back (or underneath as with the Aiyima A07MAX)
   
   
2. Add a switch and implement a High pass filter on the outputs to further take advantage of the subwoofer output.
   
   
3. An implementation with Post Filter Feedback (PFFB) - this is an extension of the TPA-3255 design to better handle distortion and provide a more linear frequency especially in the upper treble when connected to specific speakers with high variations in speaker impedance.
   
   This will also improve the already impressive THD+N / SINAD of 88db
   
   
4. A trigger out to pass the trigger onto a second ZA3 - this would be useful when the ZA3 is set up as a Monoblock, but you still want triggered input to wake both ZA3’s.
   
   
5. A remote to switch the inputs and control the volume

Summary
The Fosi Audio ZA3 is an impressive amplifier, offering high-quality sound, versatile features, and efficient operation. Its ability to run cool, coupled with its mono block support and balanced input options, positions it as a competitive option in the audiophile market.

 

On top of SINAD being meaningless, could you compare the amp to others from different manufacturers? Also, I'm ignorant but I've never heard of Wiim, let alone tried out any of their streamers/DACs. Would be useful to have impressions of that as well for context.

 

When there are more independent measurements I will update this review (as I said) - I just included the SINAD as those are number Fosi has published and I believe they have their own Audio Precision analyser.

As for similar amps, I have a few Aiyima amplifiers, e.g. the new A07MAX which also supports Mono block support, while the Aiyima is small and cheaper it does not have the features of this amplifier. But they both use the TPA3255 chipset (like lots of other amplifiers from Fosi Audio and Aiyima and others like the 3E Audio 480-1-29A) and when I volume matched and measured the frequency response in my room I found these amplifier to have very similar FR graphs, unlike the amplifiers based on the TPA-3116 which I mostly found to be both more noisy ( so less detailed ) and have bass rolloff and odd treble which cause them to sound thin and hollow. Where the ZA3 shines is in the extra features (and build quality) having balanced inputs means less potential for interference (and therefore less potential for noise) and especially the Sub-woofer output which can really allow you to fill out the sound in your room (as I hopefully showed in the FR graph I included in the review).

As for WiiM I presumed everyone would know or have tried a WiiM streamer at this stage, WiiM have excellent streamers starting at < $99 (WiiM Mini) as long as you use their optical output, but starting with the WiiM Pro Plus (about $250) they included an excellent DAC as well as a trigger output so the perfect cheap companion for an amplifier like this one, adde to that WiiM include some basic PEQ filters you can really tune you room for very little money. These are good times for 'cheaper' audiophile solutions.

Note: WiiM also have just released their own TPA-3255 Amplifier the WiiM Amp which I also have bought and I will write up a review soon. Here are details of these WiiM Streamers https://www.wiimhome.com/

 

Are the opamps swappable on these? I swapped out the opamps in my Fosi v3 and it took the sound up a notch or three.

Nevermind, I found the listing on Fosi’s site, it does have swappable opamps.

 

I'm keen to read some more subjective impressions and comparisons. What speakers are you using? Nearfield or midfield or farfield setup?

 

I will update the review later - but I was using these in 2 different spaces in my house:

1. In medium sized space a converted garage ( my work from home space - this was when I had the Mono block setup) with a pair of Polk ES20, so each ZA3 connected to a single Polk.
Subjectively this was excellent, this space allows me to play very loud (as it a detached garage from the house), I was able to drive the ES20 - these can do down to about 40hz and the ZA3 never blinked, Bass was tight and clean, vocals were all nicely forward in the midrange and the treble as good as I have heard from these Polk's, lots of details. The soundstage in this setup is great and it's my preferred space during the day and this was as good as it has sounded in the past year (comparing against many other amplifiers).

2. In a smaller 'den' room in my house, this was a single ZA3 with a Kef kube 8c subwoofer and 2 Q-Accoustic 3020i speakers. In this configuration I was able to get down to 25/30hz and get a proper sub bass rumble from the subwoofer while the Q-Accoustics are more musical than the Polk so it was a very nice match where this configuration of the ZA3 was able to bring out the best in this space also.

I was mostly comparing these with a Denon class A/B Receiver but also some other Class D amplifiers (in my garage space I usually have different class D amplifiers going).

Anyway I hope this helps

 

No I will ask Fosi Audio over the next few days, but ultimately as I mentioned, I will replace this section of the review with proper independently derived measurements when I get them.

That said these are mostly very similar to the ones measured on ASR for the Fosi Audio V3 and the ZA3 is effectively the next generation of that device with the same chipset and power supply. I believe Amir measured SINAD of 88db for the 48V power into 4 Ohm load with both channel driven for the V3 and SNR of 102db on max power of 160 watts, so Fosi might be exaggerating that value on the ZA3. I will update the details when I get more accurate measurements.

 

I’m interested in this amp, but copy/pasting manufacture spec without verifying yourself is a bit disingenuous. Could you please give a subjective review where you use songs to highlight strengths and weaknesses? A complete chain would be useful too. In this way we would have common reference points.

IMO using specs and measurements from a different amp as a trust me bro is pretty bad. Please don’t do that.

 

@RenEH if you're looking for a bit of corroboration, I've had the za3 in and out of my main speaker system for about a month now. I've probably put about 50 hours of music listening on it. I would definitely say it's a step up from the V3 in mid and treble coherence and composure. There is very little grain/disjointed treble that just about every other class-d amp I've had in my system have all shared to some extent. The za3 stages a little closer into the room compared to my daily driver Elekit 8600. Overall tonality is a bit more "HiFi" than the V3 (and Elekit) in that the lower midbass/upper bass is a bit recessed. That being said, I'm pleased to call my little class-d amp search done for now, i.e., good enough for hot summer listening with no tube amps, if I dial in a touch (1-2db) of extra bass via Loki while listening via za3.

Edit forgot to add, I'm running the Sparkos discrete opamps in the front two positions, i.e., L & R SE channels; I wouldn't bother running balanced in.

 

That sounds perfect, thank you! I’m looking for a class d amp for the master bedroom that gets too hot in the summer even with AC. Seems like this will fit the bill for a cheap and cheery 2 channel set up. Do you think it would pair well with the Elac house sound?

May I ask how much the upgraded op amps bring up this things level?

 

I don't have any experience with ELAC speakers, so I can't comment there, other than my current speakers are AN-E HE kits, so probably 92-ish dB/w actual in room, and smooth but slightly falling response at the listening position. To be honest, i didn't even bother listening with the stock opamps in the za3 - in every other cheap chip amp the Sparkos smoothed out the treble (but didn't fix everything). I'm not getting any hint of edge or rasp with the za3. But like i said, I'd prefer a little more 100Hz energy though that's easier to fix IME than any kind of grating or glassy treble response typical with class-d.

 

Looks like there is only one other TPA3255 amp with balanced inputs.
I wanted something small with decent power and low idle power usage that also has a flat FR to 100kHz, so I got a Topping PA3s as a portable measurement amplifier. I haven't yet done so, but I could use it from a small power station and use it in remote locations for more accurate measurements than I can get in the garden.

I've heard good things about OP amp swapped Aiyima A07s and Fosi V3s, so I really wonder how a balanced version would compare to my lower power Topping. Probably still has load dependent FR, so not usable for measurements, but I imagine it might sound better.

 

That seems pretty fair. Glassy treble/upper mid range is the biggest issue with class d, you're right. I guess with a sub out you can always add in some bass. Sounds pretty good for near field either way. Not sure if I want to cough up for those pricy op amps though. I know everyone says it makes a big difference, but there are 5 of them in there at $75 USD each, yikes. Did you replace only the one's for the left and right channel? If I end up going nuts and staring replacing things in mine, I'll post impressions before/after.

 

Correct, no sense in replacing the subwoofer or balanced section opamps IMO; just replace the L&R channel chips.

 

I ended up pick up the V3 with 48V supply so I thought I’d post my impressions here.

I’m using them near field for a budget desktop/gaming speaker set up.

Chains is Windows Strawberry player->motherboard toslink->Celibdache DAC->Fosi V3->Elac Debut B6

Note that the Celibdache is a true NOS r2r dac. It’s the big brother of the decadac.

This little amp is freaking surprising. It’s layered, micro dynamic, and has a room filling 2D stage. It doesn’t sound like the cheap class D I’ve heard before. Upper mid range is smooth and not shouty. Bass feels like it’s has more than enough power on tap as well.

It’s shockingly good for the price and in one metric it even outclasses my Akitika amp; you can feel that it has more power on tap and the bass is more control’d than what my Akitika can provide.

It’s not perfect though. It has no depth to its staging, it’s a little on the boring and polite side. It’s a bit unengaging. This usually means to me that the bass and lower mid range aren’t up to snuff.

I have sparkos op amps waiting to be installed, so I’ll post again after I’ve listened to them for a while.