Fosi Audio ZA3 Amplifier Review

[EddNog]

Got the amps back from my dad, swapped all of the stock op-amps back in, and swapped them into my chain in place of my V3 Monos to test them and they’re both working fine now. Guessing either their internal safeties got kicked and disconnecting them from power reset their safeties so they work again, and/or the aftermarket op-amps were fried (did not get to test them yet, but I really hope they are okay too!). Now I have…way too many amps. Hah!

(Please disregard the doorstops—they are just to weigh the amps down in case one of my cats trips the speaker cable with their luscious little bodies)

-Ed

 

[EddNog]

No issues with the op-amps, either. All is well. Looks like it was purely a safety lockout.

-Ed

 

[dayronch]

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
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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/

Excellent data I believe it will help a lot of us looking for specific measurements to make a choice, thank you a lot.

 

[nongnet]

Please excuse me if my question does not make sense.
I have spare 2m long RCA coaxial 75ohm cable.
Can I use it for ZA3's subwoofer out to connect subwoofer ?

 

[Guddu]

Please excuse me if my question does not make sense.
I have spare 2m long RCA coaxial 75ohm cable.
Can I use it for ZA3's subwoofer out to connect subwoofer ?

Surely you can.
I guess you have monoprice cable!

 

[Dennis_FL]

I never saw a SUB OUT on an amp before. So what happens if you have your sub hooked up to the preamp and don't use the sub out on the Fosi?

 

[EddNog]

I never saw a SUB OUT on an amp before. So what happens if you have your sub hooked up to the preamp and don't use the sub out on the Fosi?

It is mostly there for people not using a source with a second output or a preamp with multiple outputs. Nothing wrong with ignoring that sub output all together; I have my sub hooked up to my preamp.

-Ed

 

[Dennis_FL]

It is mostly there for people not using a source with a second output or a preamp with multiple outputs. Nothing wrong with ignoring that sub output all together; I have my sub hooked up to my preamp.

-Ed

Thanks. Just ordered it (my 30 yr old 125 W/ch AB amp died this morning). But I still am wondering what happens to the lower frequencies. Do they cut off the main speakers at 80 Hz and send those to the sub? So the MAIN speakers aren't full range output?

 

[EddNog]

Thanks. Just ordered it (my 30 yr old 125 W/ch AB amp died this morning). But I still am wondering what happens to the lower frequencies. Do they cut off the main speakers at 80 Hz and send those to the sub? So the MAIN speakers aren't full range output?

It is low-pass filtered, but at some completely ridiculous and useless frequency, around 300hz.

There is no high-pass filtering to the main speakers.

-Ed

 

[Dennis_FL]

OK John, I’m getting the sense that you don’t like this little Amp. But tell us what you really think?

For someone on a budget and looking for an affordable amp for a small two channel setup it does have some value here. No Remote is a big miss. But every little feature adds cost. To achieve your list above can you offer any alternative amp(s) with similar performance but all these features for a Buck Fifty? I know you know what you’re talking about and it would be interesting to see what you have in mind that compares but has more of these features you list.

Power amps with a remote? That’s new to me.

 

[EddNog]

Power amps with a remote? That’s new to me.

@AdamG are you looking for an Integrated amplifier?

-Ed

 

[AdamG]

@AdamG are you looking for an Integrated amplifier?

-Ed

No. All set.

 

[AdamG]

Power amps with a remote? That’s new to me.

Was thinking volume/gain control if used independently.

 

[Dennis_FL]

Got the amps back from my dad, swapped all of the stock op-amps back in, and swapped them into my chain in place of my V3 Monos to test them and they’re both working fine now. Guessing either their internal safeties got kicked and disconnecting them from power reset their safeties so they work again, and/or the aftermarket op-amps were fried (did not get to test them yet, but I really hope they are okay too!). Now I have…way too many amps. Hah!

View attachment 383680
(Please disregard the doorstops—they are just to weigh the amps down in case one of my cats trips the speaker cable with their luscious little bodies)

-Ed

I’m also using the ZA3 with KEF LS50 metas. I was going to ask if you tried stereo or did you always use them in mono…..but Amazon has one day delivery so I’ll soon find out.

 

[EddNog]

I’m also using the ZA3 with KEF LS50 metas. I was going to ask if you tried stereo or did you always use them in mono…..but Amazon has one day delivery so I’ll soon find out.

I’ve tried both. Since this is ASR, I won’t speak to any difference I may or may not have heard between stereo and mono modes. I will state that I keep them in stereo mode even though I am running two as monoblocs.

-Ed

 

[Witterings]

Power amps with a remote? That’s new to me.

Maybe .... but wouldn't it be great .... absolutely no idea why they don't, just seems a bit dumb.

I'd be interested to hear what the negatives are and reasons not to offer it as an option.

 

[EddNog]

Maybe .... but wouldn't it be great .... absolutely no idea why they don't, just seems a bit dumb.

I'd be interested to hear what the negatives are and reasons not to offer it as an option.

Well, because there are integrated amps for this, for one.

And for two, when you’re talking about amps that are at or below $150 (not including power supply), a remote control adds a lot to the cost, proportionally. Different story on a $300 amp.

-Ed

 

[Witterings]

Well, because there are integrated amps for this, for one.

That's all well and good but but if you're using a software controlled Pre Amp you run the risk of blowing your speakers which really isn't very clever

Power amps with a remote? That’s new to me.

I also don't think this reply was budget specific.

Overall though, my point was, whilst they don't .... maybe they should and as I say I can't see a reason not to, if it pushes the price up by £10/20 but makes it a lot more usable, I think a lot of people would happily pay the extra.

Just my 2p's worth.

 

[Dennis_FL]

I’ve tried both. Since this is ASR, I won’t speak to any difference I may or may not have heard between stereo and mono modes. I will state that I keep them in stereo mode even though I am running two as monoblocs.

-Ed

I was curious if the 90 WPC in stereo was enough oomph for the KEFs.


But the new amp arrived and I fired it up today and played "Tubular Bells." There was mid frequency distortion with the lead up to the tubular bells intro but the bells themselves were fine. I think I need to do another room correction again and repeat this.

 

[Dennis_FL]

I just hooked mine up. Been waiting for over a month. Replacing a PA5. First impression is it sounds a tad dark? I like it. The gain is higher than the PA5 because I barely have to turn up my preamp. Really nice case. I'll run it a couple weeks and if it's ok I'll buy another for monoblocks.

I also just hooked mine up. Mine seems to produce more detail than the 30 year old A/B it replaces. But that's probably an artifact of new gear wishing or something. I'm only a few hours of listening with it so maybe more later.

But I was curious if anyone in ASR land has tried a different op amp in the Fosi. Certainly an unusual option as they have a budget amp with instructions for users to open it up and replace integrated circuits.