Fosi Audio ZA3 Amplifier Review

[Jimi Floyd]

I can't understand the filtered sub out. An unfiltered pre out is more flexible, subwoofers have their own filter anyway.

 

[Bruce Morgen]

While I see your point, the volume control here gives you variable gain settings. In my testing I just set it to max and ran all the tests.

I don't understand these gripes about a power amp having a volume control. Many power amps over the years have had volume controls -- check out this 1960s McIntosh with its two "GAIN" knobs -- which can just be "dimed" if you want a DAC, preamp, or processor to control system volume.

 

[Bruce Morgen]

I can't understand the filtered sub out. An unfiltered pre out is more flexible, subwoofers have their own filter anyway.

It's harmless and allows use of a passive sub driven by a separate amp that doesn't have its own low-pass filter -- e.g. a second ZA3 in mono mode.

 

[ampguy]

I can't understand the filtered sub out. An unfiltered pre out is more flexible, subwoofers have their own filter anyway.

Yes, that's a limitation, but buyers of this unit will likely have a sub that works fine with the sub's filter all the way up, minimizing distortion of two sloped filters (one on amp, one on powered sw amp), fine tuning, some will wish it were adjustable and that costs more or requires using fiterling on both amp and sub.

 

[Power Pop 23]

@Fosi Audio,

Can you provide an update as to the features and expected release date for your proposed preamplifier with a differential output ?

What's a Balance Preamplifier Should Be Like?

This is another thread to make Fosi Audio closer to users. We always look forward to co-creating amazing audio gear with audiophiles. We have received a lot of advice that we should incorporate balance input/output to an amp or preamp. Our team is now developing a balance preamp and here is a...

www.audiosciencereview.com

 

[3eaudio]

@amirm
can you add frequency response at Mono mode?
also Sub out THDN curve if possible.

 

[Gwreck]

@amirm I was one of the 1st za3 owners as I did the kickstarter campaign for it. How would a person know if their unit has the gain issue you mentioned? Is Fosi doing any fixes for people with the gain issue?

 

[CedarX]

About the “mono/stereo” switch: I suspect it switches the internal TPA3255 from BTL to PBTL mode. So it’s not really switching to a “bridged” mode—it is always in bridged mode—but to this parallel bridged mode (the TPA3255 is a 4-channel chip).

Labeling the switch “BTL/PBTL” may have better (correct), but I’m not sure it would have been less confusing!

 

[staticV3]

@amirm I was one of the 1st za3 owners as I did the kickstarter campaign for it. How would a person know if their unit has the gain issue you mentioned? Is Fosi doing any fixes for people with the gain issue?

You can use a basic multimeter to measure input voltage vs output voltage, then calculate the gain using
20*log10(voltage ratio)=gain in dB

For example, if you put in 0.5Vrms and get out 10Vrms, then that equates to
20*log10(10/0.5)=26dB of gain.

Of course this needs to be measured with the Amp's volume turned up all the way.

 

[restorer-john]

I don't understand these gripes about a power amp having a volume control. Many power amps over the years have had volume controls -- check out this 1960s McIntosh with its two "GAIN" knobs -- which can just be "dimed" if you want a DAC, preamp, or processor to control system volume.

I wouldn't want a power amplifier without attenuators- it's just a totally dumb idea to not put them on. Come to think of it, I think I've maybe got one or two without attenuators, but they were matched to their corresponding preamplifiers.

But all the mainstream vintage power amplifiers from Sony, Denon, Yamaha, Pioneer, etc. I own all have twin adjustable attenuators, mostly on the front panels, but several on the rear.

And let's not call them gain controls, 99% of them are attenuators- the power amp stage gain is fixed.*

*except for the 'fingers of one hand' amplifiers with actual internally adjustable gain via the feedback loop.

 

[restorer-john]

So the major improvements over the V3 are the XLR inputs and the mono-bridging switch.

It’s not a bridging switch. It’s just a single channel driven- suck less power from the PSU mode…

 

[Blumlein 88]

I wouldn't want a power amplifier without attenuators- it's just a totally dumb idea to not put them on. Come to think of it, I think I've maybe got one or two without attenuators, but they were matched to their corresponding preamplifiers.

But all the mainstream vintage power amplifiers from Sony, Denon, Yamaha, Pioneer, etc. I own all have twin adjustable attenuators, mostly on the front panels, but several on the rear.

And let's not call them gain controls, 99% of them are attenuators- the power amp stage gain is fixed.*

*except for the 'fingers of one hand' amplifiers with actual internally adjustable gain via the feedback loop.

Guess I have only owned dumb idea power amps then. I think the only one I had with attenuators was a McIntosh 752 stereo SS power amp. These were little knobs with a slot in the rear. Never cared about it. Why is this a dumb idea?

 

[amirm]

@amirm I was one of the 1st za3 owners as I did the kickstarter campaign for it. How would a person know if their unit has the gain issue you mentioned? Is Fosi doing any fixes for people with the gain issue?

If you bought it before January, you likely have the higher gain version. I am unclear as to when the version I tested rolls into production.

 

[1st.Virtual.Me]

Fosi ZA3 document at: https://fosiaudio.com/pages/user-instruction-za3#gulHVCgYAm
States: "Setup Instruction
The ZA3 supports stereo and high-power mono modes. In mono mode, the minimum load is set to 2 ohms."
Has anyone measured with 2-ohms in PBTL mode?

 

[Kimbrough Xu]

In US, where do you buy it at that price?
I have only seen non-XLR version?

Non-XLR version?

Do you mean fosi audio V3?

 

[Mr_RGB]

I would love to see measured power output comparing only one channel driven with the mono/stereo switch in both positions. How much of a power boost is there in "mono" versus just connecting only one channel? I assume the switch does more than just disconnect on input channel. Also any comparison chart using a 48v 10A power supply?

 

[Kimbrough Xu]

I received my unit much quicker than expected and I couldnt wait to set it uo. I would say the sound is really clean and the bass shakes, and I can not hear any hiss from my speakers as near as I can. The subwoofer out is most appreciated for my 2.1 setup, It makes the thing much easier than pre out.

Audiophile quality at a crazy good price.

 

[amper42]

I would never buy an amp with an external power brick. It's as big as the amp and you have to put it somewhere. It would be interesting to know how hot that external brick gets after an hour of use. Made in China Fire Hazard? I would certainly unplug the power brick when not in use.

 

[pavuol]

Credit and glory to the reviewer and the brave company, may both live long and prosper.

May I ask, why do we constantly see chinese power supplies without the Roman numeral for efficiency level? (I asked in some Topping review as well)

Spoiler: efficiency standards markings for External Power Supplies - compulsory for which markets?

below a Bing AI reply, hopefully correct:

According to my web search, the EFFICIENCY STANDARDS markings for External Power Supplies are compulsory for the following markets:
• The United States, where the Department of Energy (DOE) Level VI regulations took effect in February 2016 https://www.cui.com/efficiency-standards.
• The European Union, where the Ecodesign 2019/1782 regulations took effect in April 2020 https://commission.europa.eu/energy...efficient-products/external-power-supplies_en.
• China, where the GB 4943.1-2011 and GB 20943-2014 standards apply to external power supplies https://www.energystar.gov/ia/partners/prod_development/downloads/efficiency_challenge.pdf.
• Australia and New Zealand, where the Greenhouse and Energy Minimum Standards (GEMS) Act 2012 and the GEMS (External Power Supplies) Determination 2012 set the minimum energy performance standards for external power supplies https://www.energystar.gov/sites/default/files/InternationalEfficiencyMarking.pdf.
• Canada, where the Natural Resources Canada (NRCan) Energy Efficiency Regulations 2016 require external power supplies to meet the Level VI standards.

These markets have adopted the International Efficiency Marking Protocol, which defines the minimum active and no-load efficiency levels for external power supplies, and assigns them a Roman numeral from I (least efficient) to VII (most efficient). The markings are intended to reduce confusion between different standards and help consumers and manufacturers identify the efficiency level of the product. I hope this helps you understand the EFFICIENCY STANDARDS markings for External Power Supplies.

 

[Power Pop 23]

I would never buy an amp with an external power brick. It's as big as the amp and you have to put it somewhere. It would be interesting to know how hot that external brick gets after an hour of use. Made in China Fire Hazard? I would certainly unplug the power brick when not in use.

Sample size of one......

The 48 volt power supply included with my ZA3 feels lukewarm in operation.