Fosi Audio's First Dual-Mode Balanced Amplifier ZA3

[charlielaub]

I'm waiting for a fully bridgeable PFFB implementation from these guys, which I'd like to use as monoblocks into some Wharfedale Lintons.

From my understanding of the product, the mono mode of the ZA3 is about as "fully bridgeable" as you can get from that chip... The TPA32xx chip has four independent onboard amplifiers. The "stereo" mode already has two pairs in "bridge" (BTL) mode. The "mono" mode then puts those in parallel - this doesn't significantly improve the 4 Ohm power rating but allows more power into 2 Ohms. It is a little odd that Fosi doesn't provide a 2Ohm mono power rating. Maybe there is not enough current on tap for 2 Ohm operation?

Edit:
I found this in the text on the Fosi audio web site page for the ZA3:
Dual-Mode Innovation: This new generation mini amplifier offers both stereo and mono modes, and adapts flexibly to your diverse needs, allowing seamless mode switching. In stereo mode, it delivers a robust output of up to 155W, while in mono mode, the power soars to a maximum of 235W. Pair two ZA3 units in mono configuration to create a powerful audio system, significantly enhancing your listening experience.

 

[doug s.]

From my understanding of the product, the mono mode of the ZA3 is about as "fully bridgeable" as you can get from that chip... The TPA32xx chip has four independent onboard amplifiers. The "stereo" mode already has two pairs in "bridge" (BTL) mode. The "mono" mode then puts those in parallel - this doesn't significantly improve the 4 Ohm power rating but allows more power into 2 Ohms. It is a little odd that Fosi doesn't provide a 2Ohm mono power rating. Maybe there is not enough current on tap for 2 Ohm operation?

Edit:
I found this in the text on the Fosi audio web site page for the ZA3:
Dual-Mode Innovation: This new generation mini amplifier offers both stereo and mono modes, and adapts flexibly to your diverse needs, allowing seamless mode switching. In stereo mode, it delivers a robust output of up to 155W, while in mono mode, the power soars to a maximum of 235W. Pair two ZA3 units in mono configuration to create a powerful audio system, significantly enhancing your listening experience.

if it's anything like the v3, which does seem to get nice reviews, as does this amp, its power ratings are quite a bit optimistic.

doug s.

 

[gasolin75]

 

[OldTimer]

no it's not - the same frequencies travel through both cables when bi-wiring; and they're split at the speaker binding posts; just as the signals are split with single-wire.

doug s.

It’s the speakers which pull the signal from the amp, not the other way around.

 

[charlielaub]

if it's anything like the v3, which does seem to get nice reviews, as does this amp, its power ratings are quite a bit optimistic.

doug s.

The maximum power level is dependent on how you define "maximum". It's typically done via inspection of the distortion level. In the old days it was typical to state maximum power as the power level for which 1% distortion was reached. Over the past 10 years or so, class-D amps for some reason decided to use a 10% distortion level as the criteria. Here on ASR, the criteria is where the distortion curve "turns up" and this can be at much less than 1% distortion. All of these are valid but different ways to state the "maximum" power rating. I would not say that the MFG power ratings are "optimistic" but instead that they are defined more liberally than e.g. class AB amps. Also, the ASR definition is IMHO a bit too stringent but Amir does provide "peak power" ratings that give you more info in a single number. The problem is that the distortion profile is more complicated that a single number can capture and is therefore subject to interpretation.

 

[doug s.]

The maximum power level is dependent on how you define "maximum". It's typically done via inspection of the distortion level. In the old days it was typical to state maximum power as the power level for which 1% distortion was reached. Over the past 10 years or so, class-D amps for some reason decided to use a 10% distortion level as the criteria. Here on ASR, the criteria is where the distortion curve "turns up" and this can be at much less than 1% distortion. All of these are valid but different ways to state the "maximum" power rating. I would not say that the MFG power ratings are "optimistic" but instead that they are defined more liberally than e.g. class AB amps. Also, the ASR definition is IMHO a bit too stringent but Amir does provide "peak power" ratings that give you more info in a single number. The problem is that the distortion profile is more complicated that a single number can capture and is therefore subject to interpretation.

i get this. but i think, however you measure, the specs are a bit optimistic.

doug s.

It’s the speakers which pull the signal from the amp, not the other way around.

yes, but at the end of the day, the amp is seeing the same load, and that affects what gets to the speaker drivers. the bottom line is this - assuming you're using properly engineered speaker cables for the task at hand, the only advantage to biwiring, (not bi-amping, that is different), is to the speaker cable manufacturers and vendors, who sell more product..

doug s.

 

[charlielaub]

It’s the speakers which pull the signal from the amp, not the other way around.

No, the amplifier is the active device. The speaker is just a fancy load (a load with complex impedance).

The amplifier simply takes the input signal and increases the voltage swing. Within its normal operating range the amp delivers as much current as the load requires in order to maintain tracking of the input signal.

 

[doug s.]

No, the amplifier is the active device. The speaker is just a fancy load (a load with complex impedance).

The amplifier simply takes the input signal and increases the voltage swing. Within its normal operating range the amp delivers as much current as the load requires in order to maintain tracking of the input signal.

i think what oldtimer is saying it that the electrical current that passes thru the wire when biwired is a bit different for each set of cables, as the hi-pass section of the crossover sees different load than the low pass. i'm not certain this is true, but the bottom line is a correctly engineered speaker cable (which would cover most), will have the speaker sound the same as running two different sets of cables.

doug s.

 

[Petevid]

In biwiring the signal in both wires is the same. The speakers are a passive load on the amp. It is the high pass and low pass filters in the speaker’s crossover that filters the high frequency signal to the tweeter and lower frequency signal to the woofer.

 

[doug s.]

In biwiring the signal in both wires is the same. The speakers are a passive load on the amp. It is the high pass and low pass filters in the speaker’s crossover that filters the high frequency signal to the tweeter and lower frequency signal to the woofer.

thanks; that is as i thought.

doug s.

 

[Gratefuldad]

Hello and greetings from Germany.

I have a question about my fosi.

I have a little problem with that. When I turn up the volume control from zero to the first tone, I first get sound on the left channel and later also on the right.

Do you have that too?

Can you please try it out? That would be very nice.

Have a nice day

Perhaps this has been answered. I deduced that you have inequal volume between channels upto a certain point and later it becomes okay. If this is the case, most likely the volm potentiometer sliders are not making contact for the right channel initially or in rare case the are inqueal resistance value. Under this circumstances, the pot cane be replaced.

 

[charlielaub]

The first batch of ZA3 amplifiers has shipped. I received mine yesterday. I don't have the gear to do a proper test but I hope that someone else is able do it and post the results.

 

[jooc]

based on the impedance curve i've seen on the lintons, if you were to compare amps whose only difference was pffb implementation in one, it's highly unlikely you'd be able to hear any difference. and any measured difference of the frequency response of the speakers would be minimal, if any, as well.

doug s.

Agreed, but it's pretty much the standard audio need: I have a room audio application in mind that I'd like to build for $X, and doing so I might as well get state-of-art within that $X range.

If I time it right I can build that room with the best current (inexpensive) amplifier implementation, and that excellent amplifier can then be matched with other components later if I wish.

I want the Wharfedales for that room but also they seem versatile in that I could use them in an impromptu outdoor setting with powerful, clean, bridged amps that can be played very loudly with no distortion.

 

[doug s.]

Agreed, but it's pretty much the standard audio need: I have a room audio application in mind that I'd like to build for $X, and doing so I might as well get state-of-art within that $X range.

If I time it right I can build that room with the best current (inexpensive) amplifier implementation, and that excellent amplifier can then be matched with other components later if I wish.

I want the Wharfedales for that room but also they seem versatile in that I could use them in an impromptu outdoor setting with powerful, clean, bridged amps that can be played very loudly with no distortion.

totally understandable. and if it's within your budget, find something similar with pffb implemented, if you want. but the odds are, that even w/future upgrades, the differences due to pffb implemented or not, won't be audible. and if it is, there will then be some other future pffb amp(s) (new or used) that is/are either better or less expensive, or both.

my opinion, of course!

doug s.

 

[jooc]

From my understanding of the product, the mono mode of the ZA3 is about as "fully bridgeable" as you can get from that chip... The TPA32xx chip has four independent onboard amplifiers. The "stereo" mode already has two pairs in "bridge" (BTL) mode. The "mono" mode then puts those in parallel - this doesn't significantly improve the 4 Ohm power rating but allows more power into 2 Ohms. It is a little odd that Fosi doesn't provide a 2Ohm mono power rating. Maybe there is not enough current on tap for 2 Ohm operation?

Edit:
I found this in the text on the Fosi audio web site page for the ZA3:
Dual-Mode Innovation: This new generation mini amplifier offers both stereo and mono modes, and adapts flexibly to your diverse needs, allowing seamless mode switching. In stereo mode, it delivers a robust output of up to 155W, while in mono mode, the power soars to a maximum of 235W. Pair two ZA3 units in mono configuration to create a powerful audio system, significantly enhancing your listening experience.

Yes but ZA3 is not PFFB. I feel like we're on the verge of something like the ZA3 but PFFB, for about exactly the same cost, and possibly from the same manufacturers. These product iterations are reaching a dizzying pace but that's where I want to land for the time being.

That said this ZA3 really checks all my boxes for that application, it seems exceptional for the $. But I still want my pffb monoblocks from Fosi

 

[doug s.]

Yes but ZA3 is not PFFB. I feel like we're on the verge of something like the ZA3 but PFFB, for about exactly the same cost, and possibly from the same manufacturers. These product iterations are reaching a dizzying pace but that's where I want to land for the time being.

don't forget to keep an eye on aiyima, as well. as i'm not concerned about pffb the more i investigated it, and especially for my use/needs; i went and sprung for two of the aiyima a07 max's with 48v/5a(6.3a max) p/s's; plus four discrete opamps. total damage is $227, so i can't complain; at least not yet - heh!

doug s.

 

[amix]

?

Edit:
I found this in the text on the Fosi audio web site page for the ZA3:
In stereo mode, it delivers a robust output of up to 155W, while in mono mode, the power soars to a maximum of 235W.

Williston Audio Labs on YouTube dyno'd the amp and it went mostly as specced by the manufacturer (even better) except the 235W in mono, where it went to 193W@1%, 214W to clipping and 210W burst, all at 4 ohms.

 

[charlielaub]

Williston Audio Labs on YouTube dyno'd the amp and it went mostly as specced by the manufacturer (even better) except the 235W in mono, where it went to 193W@1%, 214W to clipping and 210W burst, all at 4 ohms.

You are missing the point that I was trying to make. Please see the results table around the 7:20 mark of the video for the operational modes that were tested.

Williston labs did NOT test it in mono mode into 2 Ohms. He only tested mono mode into 8 Ohms and 4 Ohms. These loads are what most normal amplifiers would be rated for in mono. It's hardly ever the case that an amplifier can do 2 Ohms in mono, but this amp and others that have the TPA3255 configured for mono operation can easily deliver lots of power into a 2 Ohm load, probably more than what Fosi claims based on the mono 4 Ohm results.

He did test the amp in STEREO at 2 Ohms, which is outside what the amp is specd' for. But again, not 2 Ohms MONO where the amp will delivery more power into a 2 Ohm load than into 4 Ohms. If the power supply was perfectly stiff, power would be twice as much into 2 as into 4 Ohms. The 235W that Fosi claims are for 2 Ohms, where the "maximum" power (their words) can be delivered by the amp.

I think he (Williston Labs) did not pay attention or made a mistake, is not familiar with this sort of amp, or maybe his test rig does not have a 2 Ohm mono test mode.

 

[amix]

You are missing the point that I was trying to make. Please see the results table around the 7:20 mark of the video for the operational modes that were tested.

Sorry, then there seems to be a misunderstanding: I did not want to disprove or discuss anything of what you said.

I just wanted to share the resource I mentioned, since it was the only reliable source, so far, to test the power, this amplifier delivers. I thought readers may be interested in some independent data. That's all!

 

[JC!]

Long time lurker here. First time poster. I ordered 2 ZA3’s and they were delivered today. For $250 the build quality of these is pretty nice. I don’t mind the small binding posts either. A couple hours ago I hooked those puppies up in mono with the volume all the way up, to my Polk R700s and a bluesound node 2i. Used the bluesound to control volume. No run in or anything. I fired them up with some Tool and at first the sound was kinda brash or crunchy but that went away quickly. Punchy is a good word for them and they never seemed to run out of gas. They aren’t perfect but the sound was way better than I expected and I could easily live with them and be happy.