Fosi Audio ZA3 Amplifier Review

[NeLey169]

I plugged the opamp buffer in the ZA3 in the wrong direction (because it has the opposite direction to the other opamps and I didn't pay attention to the symbols on the circuit board), so there was no sound. After discovering it and plugging it back in, there was normal sound. But I don't know if the opamps and capacitors in the opamp buffer are still working well or if there is something broken that I haven't discovered yet?
@Fosi Audio

 

[solderdude]

When it still works then the part (and ZA3) are still O.K.

Yet another, never mentioned, issue that can happen with this pointless 'op-amp swapping' business.

 

[mike70]

It was proven by scientific measurements that op-amps differences aren't audible.
Stop wasting money

 

[bboris77]

When it still works then the part (and ZA3) are still O.K.

Yet another, never mentioned, issue that can happen with this pointless 'op-amp swapping' business.

@solderdude , I really respect your opinion so I want to ask for an advice. I’ve always had class A/B speaker amps such as my current one, Yamaha A-S501, and I’m happy with it. On the other hand, I’ve always wanted to have a class D amp as a backup. Would you recommend the ZA3 for this purpose, or should I be looking at another one of these devices? I would be using RCA inputs exclusively.

 

[NeLey169]

https://www.reddit.com/r/BudgetAudiophile/comments/1juys54/fosi_audio_za3_opamp_swap_no_sound_after_upgrade

a guy plugged opamp in za3 upside down had the same problem as me

 

[solderdude]

@solderdude , I really respect your opinion so I want to ask for an advice. I’ve always had class A/B speaker amps such as my current one, Yamaha A-S501, and I’m happy with it. On the other hand, I’ve always wanted to have a class D amp as a backup. Would you recommend the ZA3 for this purpose, or should I be looking at another one of these devices? I would be using RCA inputs exclusively.

This behavior would be a reason for me not to buy this amp.
If I ever wanted to buy a class-D (but not as backup) I would buy something 'better'.
If I wanted some temporary device that may never see any usage or maybe used in the future perhaps something like this:

3e audio A7/A7 Mono Amplifier Review

This is a review and detailed measurements of the A7 / "A7 Mono" stereo power amplifier with balanced inputs. It was sent to me by the company. I have no idea what it costs in US. Audiophonics lists it for 379,00 €tax incl. While the A7 may look like its competitors, it has a heft to it that I...

www.audiosciencereview.com

a guy plugged opamp in za3 upside down had the same problem as me

Except.... yours still works even after you put in the op-amps in the correct orientation. (at least that's what I got from your post)

Lesson to be learned... stop playing around with the pointless and potentially harmful (when not educated enough) 'op-amp swapping'.
In this kind of amps it is totally pointless as all suitable 'audio'op-amps' have better performance than the output stage following those op-amps.
This output stage is what is called the bottle neck.
Technical performance won't improve (signal coming out of the amp is exactly the same).

 

[AndreaT]

I could not resist: Amazon offers it on a discount with final cost, taxes included, lower than the original price…it will sit next to the excellent DAC by Fosi…see what you do to me ASR!

 

[Mr_RGB]

I could not resist: Amazon offers it on a discount with final cost, taxes included, lower than the original price…it will sit next to the excellent DAC by Fosi…see what you do to me ASR!

I couldn't resist either, bought two ZA3s for $93 each (after discounts ) (no power supplies, I have MANY) on the Fosi Ebay store. For me these are like Audio LEGOs (Fosi, Aiyima, Douk, Nobsound,...). I love playing with them!

 

[Mr_RGB]

Looking at two different power supplies
Mean Well
HEP-320-36
320 watts - 36 volts - 8.9amps
HEP-320-48
320 watts - 48 volts - 6.7amps

Both 320 watts. Would they both produce the same audio power? Would the 36 volt run cooler?
This is really a more general question of lower voltage and more amps or higher voltage with less amps.

 

[Pulkass]

This is a review and detailed measurements of the Fosi Audio ZA3 stereo amplifier with balanced XLR inputs. It was sent to me by the company and costs US $149.99 with 48 volt power supply.
View attachment 348770
The amplifier has really dressed up from its earlier origins of common enclosures in budget class amplifiers. It looks a lot more "beefy" and substantial. It also looks a lot better with nice series of holes on the sides where copper color is seen through it. Maybe due to these reasons the amplifier kept its cool for the entire test.

On controls, you push the volume control in to turn it on and off. Turning on causes an orange LED to light. Turning it off causes a delay in the light going out even though the output shuts off. Not an issue if you are listening to it but in testing, I am not so it was a bit confusing at first.

There is a misnamed "mono" vs "stereo" switch. Mono doesn't make both channels the same but rather, shuts off one channel allowing for more power in the channel that is left running. The other button is key in book which is support for balanced XLR input to help in avoiding ground loops:

View attachment 348772

The connectors are combo so you can either use XLR or 1/4 inch. There is still RCA inputs of course and support is provided for a filtered, and volume controlled subwoofer output. Finally we have trigger input so you can turn the amplifier on automatically if you power on your upstream product and it has trigger out, and vice versa.

You may have noticed that it has taken a bit of time to get this review out. I received a sample a while back. Upon testing, I noticed that the gain was substantially increased due to user feedback for louder volume. This was a regression from V3 amplifier and as a result, caused the ZA3 measured performance to drop by a a few dBs. I provided the feedback to Fosi and they made the decision to back out the extra gain and shipped me a new sample a couple of weeks ago. I am assuming newer models being sold are what I have tested but they would have to confirm.

Fosi Audio ZA3 Measurements
Let's start with our dashboard using XLR input:
View attachment 348774
This is the level of performance I expect. Using RCA, you get similar performance but gain is a bit higher:
View attachment 348775

This nicely lands ZA3 above average of all amplifiers tested regardless of price and almost next to its V3 sibbling:
View attachment 348776

View attachment 348777

Continuing with XLR input testing, noise performance is excellent especially for the class:
View attachment 348778
It takes around 1.2 volts to cause clipping which is well within the output level of just about any source.

Frequency response shows load impedance dependency which is part and parcel of class D amplifiers at this price point and lower:
View attachment 348779
This means depending on your speaker impedance, high frequencies may be exaggerated a bit.

I measured subwoofer out and it seems good enough:
View attachment 348780
Note that I was driving it from XLR input and it still routed that to the RCA sub out.

Crosstalk is very good:
View attachment 348781

Using balanced input nicely eliminated low frequency spikes in low frequencies:
View attachment 348782

Distortion does increase at higher frequencies though so 19+20 kHz intermodulation doesn't impress:
View attachment 348783

Inclusion of beefy 48 volt power supply pays dividends in available power:
View attachment 348784
View attachment 348785
View attachment 348786

Running power sweeps at different frequencies shows again the issue with jump in distortion at higher frequencies:
View attachment 348787
Optimization at lower frequencies is impressive though with ultra smooth graphs at or below 1 kHz.

"Mono" Mode Amplifier Measurements
I switched to Mono and measured the dashboard again:
View attachment 348788
Distortion is increased causing SINAD to drop by some 13 dB. In exchange for that, you do get more power:

View attachment 348789

Other Amplifier Measurements
ZA3 was stable on power up:
View attachment 348790

Pop noise was slightly reduced compared to V3:
View attachment 348791
This could be sample to sample variation though.

Conclusions
It is nice to see this class of amplification with its bargain prices come in much more serious and substantial packaging while still remaining small and desktop oriented. Performance is as great as ever and inclusion of features such as balanced input is very much welcome. Load dependency remains and solving that would be the next logical feature request.

I am going to recommend the Fosi Audio ZA3 amplifier.

------------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

Can l power it with 48 v 10 amperes ?

 

[Power Pop 23]

Can l power it with 48 v 10 amperes ?

Yes, I believe so. The listing at Amazon USA for the 48 volt 10 ampere power supply unit sold by Fosi Audio mentions the ZA3 amplifier:

Amazon.com

 

[MGJ]

Looking at two different power supplies
Mean Well
HEP-320-36
320 watts - 36 volts - 8.9amps
HEP-320-48
320 watts - 48 volts - 6.7amps

Both 320 watts. Would they both produce the same audio power? Would the 36 volt run cooler?
This is really a more general question of lower voltage and more amps or higher voltage with less amps.

I did some testing of my own with my ZA3 and two Mean Well power supplies: LRS 350N2-36v and LRS 350-48v. Using a 4/8 ohm resistor load and oscilloscope, increasing gain until I see the output clipping (40hz sinewave). My results: (per channel)

The 36v PS was adjusted to output 38v: 4ohm x2 - 19.5vrms, 4.9A, 95W. 6.5A was being drawn from the PS (246W).
The 36v PS was adjusted to output 38v: 8ohm x2 - 20.8vrms, 2.6A, 54W. 3.4A was being drawn from the PS (131W).

The 48v PS was set to output 48v: 4ohm x2 - 23.5vrms, 5.9A, 138W. 7.7A was being drawn from the PS (374W).
The 48v PS was set to output 48v: 8ohm x2 - 26.0vrms, 3.3A, 84W. 4.4A was being drawn from the PS (211W).

Looking at the results the 36v(38v) PS was not being pushed hard at all. The 48v PS put out more watts than its rating. Neither got warm during testing.
The 36v PS has a voltage output range of approximately 30v-40v. The 48v PS has a voltage output range of approximately 42v-50v.
Hope this helps.

 

[Mr_RGB]

I did some testing of my own with my ZA3 and two Mean Well power supplies: LRS 350N2-36v and LRS 350-48v. Using a 4/8 ohm resistor load and oscilloscope, increasing gain until I see the output clipping (40hz sinewave). My results: (per channel)

The 36v PS was adjusted to output 38v: 4ohm x2 - 19.5vrms, 4.9A, 95W. 6.5A was being drawn from the PS (246W).
The 36v PS was adjusted to output 38v: 8ohm x2 - 20.8vrms, 2.6A, 54W. 3.4A was being drawn from the PS (131W).

The 48v PS was set to output 48v: 4ohm x2 - 23.5vrms, 5.9A, 138W. 7.7A was being drawn from the PS (374W).
The 48v PS was set to output 48v: 8ohm x2 - 26.0vrms, 3.3A, 84W. 4.4A was being drawn from the PS (211W).

Looking at the results the 36v(38v) PS was not being pushed hard at all. The 48v PS put out more watts than its rating. Neither got warm during testing.
The 36v PS has a voltage output range of approximately 30v-40v. The 48v PS has a voltage output range of approximately 42v-50v.
Hope this helps.

Thanks this is helpful. I'm using the 48V 6.7amp power supply. The za3 gets warm but not hot. Knowing the available power at different voltages helps when matching speakers.

 

[NeLey169]

My fosi za3 sometimes suddenly turns off while in use, cannot be turned back on for a period of time, have to wait a period of time (several hours) to be able to turn back on, so what is the error?
@Fosi Audio

 

[NeLey169]

It seems the problem is the power cord. I bought 2 za3s in 2 different countries, one in China and one in Vietnam. The version I bought in Vietnam has a smaller power cord. The EU Plus instead of US plug and 48v power supply are the same.

 

[xanalog]

It seems the problem is the power cord.

Has this been confirmed?
I ask because it had initially sounded like a heat-related problem... either with the power-brick or internal to your ZA-3.

 

[xanalog]

When used in mono mode the chip itself will shut down one side completely lowering idle power and thus heating of the chip.
Maybe that's what is being done and this also affects the used channel increasing distortion.

The question is indeed where this comes from.
Most likely it also has to do with the paralleling of the output stages (the PBTL mode).

Amir says this:
There is a misnamed "mono" vs "stereo" switch. Mono doesn't make both channels the same but rather, shuts off one channel allowing for more power in the channel that is left running

[2-types >>Pre-Filter and Post-Filter PBTL]
[Either filter is costly with large footprint inductors due to additional current/power needs]
[The TPA32xx family of devices however support pre-filter PBTL, which reduces the number of inductors needed by half.]

-----------------------
Per TexasInstruments' Application Report [SLAA822–September2018]:
"Pre-Filter Parallel Bridge-Tied Load (PBTL)"
One solution to provide greater output power and efficiency is to run the device in parallel bridge tied load (PBTL) configuration.
In this configuration two half-bridges are placed in parallel to supply twice the current and reduce the RDS(on) of the output MOSFETs.
The difference between a pre-filter PBTL configuration and a post-filter PBTL configurations is [the location of] the half-bridge [outputs] are connected in parallel.

Despite the fact that TI’s TPA32xx devices can be configured to support two bridge-tied loads (BTL) amplifiers, it is not uncommon to see only one BTL channel used to drive a speaker and the other left unused.
However, by using pre-filter PBTL the designer now has the option to connect both amplifiers before the filter, and improve the efficiency of the amplifier.
Using the exact same load, and inductors, pre-filter PBTL improves the efficiency of a single BTL channel by nearly 10%, and the power loss per channel is reduced by 40 W both at full output when compared to a single BTL channel.

Pad Down Devices
With the design of high powered audio speakers and amplifiers becoming more and more compact, the size of a design matters more than ever. Many manufacturers are turning to Pad down devices, eliminating bulky heatsinks in favor of a thick ground plane on a PCB.
In these scenarios, using a TI device in pre-filter PBTL mode reduces the effective RDS(on) of the output devices, increasing the efficiency and thus reducing the heat produced.
Additionally, because the entire die is being used the thermal transfer is more efficient. Thus, less heat is produced, and it is more efficiently dissipated
https://www.ti.com/lit/an/slaa822/slaa822.pdf?ts=1736469099112

 

[solderdude]

There are only 2 inductors in the amp, also measurements suggests pre-PBTL (so basically paralleling the output stages before the filter.
Basically to spread the load current over 2 output stages and thus halving the current through each 'amp' and lowering the output R.

 

[Pulkass]

Yes, I believe so. The listing at Amazon USA for the 48 volt 10 ampere power supply unit sold by Fosi Audio mentions the ZA3 amplifier:

Amazon.com

I bought one, it seems less upwards highs than the

It may be lacking some bright compared to the PA5 and Aiyima A07 in the exact same system. Purely subjective. It's my system and I listen to it every day and 'dark' was the first thing I thought when I played this amp, but like I said, it's probably just less bright.

Yes it seems a bit dark to me, just arrived, it s going to replace Behringer A 800-highs section- in my 3 way , 3 amped ,elec. x overed system, by chance I have the Ayima a 70 on test at home, it seems much better on highs. Testing goes on.....

 

[Pulkass]

It may be lacking some bright compared to the PA5 and Aiyima A07 in the exact same system. Purely subjective. It's my system and I listen to it every day and 'dark' was the first thing I thought when I played this amp, but like I said, it's probably just less bright.

same thought on comparison to Ayima 07