Fosi Audio ZA3 Amplifier Review

[312elements]

I’ve read through this whole thread and didn’t see a definitive answer to this: the way that the ZA3 is designed, would the sound be cleaner with the volume attenuator maxed out than set somewhere in the middle, the other way around, or no difference either way? Sorry if I somehow missed it. Wasn’t clear than any of the discussion on this topic was definitive to me.

Would most people agree that, based on measurements, even when running a pair of these as monoblocs, it is best to leave the switch set to stereo instead of mono (assuming speakers that don’t consistently drop to 2ohms)? I’m driving a pair of KEF LS50 Metas with these.

-Ed

That seems fair. Ive not had issues driving my ls50 metas as loud as I want with the a single V3 for each channel. Switching to mono would get you more power (that you presumably don’t need) and increase SINAD by 13db which you presumably don’t want.

 

[EddNog]

That seems fair. Ive not had issues driving my ls50 metas as loud as I want with the a single V3 for each channel. Switching to mono would get you more power (that you presumably don’t need) and increase SINAD by 13db which you presumably don’t want.

Thanks! Agreed, it gets plenty loud even when not set to Mono on the front. I was actually wondering how the frequency response might change with the LS50 Metas between Stereo vs Mono mode, although most people believe that whatever difference there may be will be inaudible in practical terms.

-Ed

 

[twistedin]

I have a spare 36V6A power supply from an AIYIMA D03.
Would it work with this amp?

 

[312elements]

Thanks! Agreed, it gets plenty loud even when not set to Mono on the front. I was actually wondering how the frequency response might change with the LS50 Metas between Stereo vs Mono mode, although most people believe that whatever difference there may be will be inaudible in practical terms.

-Ed

I haven’t noticed any data that suggested the load dependent frequency anomalies differed between stereo and mono operation. There’s no PFFB so my understanding is that they’d share similar characteristics regarding load dependency.

 

[EddNog]

I haven’t noticed any data that suggested the load dependent frequency anomalies differed between stereo and mono operation. There’s no PFFB so my understanding is that they’d share similar characteristics regarding load dependency.

Thanks again; for some reason I thought I had read somewhere earlier in this thread that the PBTL mode changes how the amp reacts to the given load, and as a result would potentially exacerbate the high frequency roll-off effect because the amp would experience half the impedance for the same speaker load. Maybe I just read it wrong because I was skimming so quickly.

Still curious if/what effect using less than full volume on the dial might have on the overall sound, too.

-Ed

 

[Talisman]

Thanks again; for some reason I thought I had read somewhere earlier in this thread that the PBTL mode changes how the amp reacts to the given load.

In fact this is the case, see the smsl A300 review, where in PBTL the load dependence performance deteriorates drastically.
https://www.audiosciencereview.com/forum/index.php?threads/smsl-a300-stereo-amplifier-review.46742/

However this amplifier does not seem to use true PBTL but rather excludes one channel to provide all the power to just one, so it may not be a problem in this case

 

[312elements]

Thanks again; for some reason I thought I had read somewhere earlier in this thread that the PBTL mode changes how the amp reacts to the given load, and as a result would potentially exacerbate the high frequency roll-off effect because the amp would experience half the impedance for the same speaker load. Maybe I just read it wrong because I was skimming so quickly.

Still curious if/what effect using less than full volume on the dial might have on the overall sound, too.

-Ed

If I recall the ls50 metas impedance is relatively flat above 4khz (6ish ohms) so my understanding is that this speaker is more immune to these amps than other speakers. It’s probably in the ls50 meta review here if you search around.

 

[EddNog]

If I recall the , ls50 metas impedance is relatively flat above 4khz (6ish ohms) so my understanding is that this speaker is more immune to these amps than other speakers. It’s probably in the ls50 meta review here if you search around.

Ah, that would partially explain why (at least to my ears!) these speakers sound so wonderful driven by these amps (I A/B’d the Douk H7 against my dad’s hand-down PS Audio GCC-100 driving my LS50 Metas and ended up preferring the Douk, which is bonkers, but true, and then when I saw the ZA3s come out, I immediately decided to upgrade for the improved build quality and to play around with the mono and swappable op-amp functions).

-Ed

 

[312elements]

Ah, that would partially explain why (at least to my ears!) these speakers sound so wonderful driven by these amps (I A/B’d the Douk H7 against my dad’s hand-down PS Audio GCC-100 driving my LS50 Metas and ended up preferring the Douk, which is bonkers, but true, and then when I saw the ZA3s come out, I immediately decided to upgrade for the improved build quality and to play around with the mono and swappable op-amp functions).

-Ed

That doesn’t surprise me much. The class D modules in those GC amps are quite dated now in comparison to what’s available today.

 

[nvidia_7]

That seems fair. Ive not had issues driving my ls50 metas as loud as I want with the a single V3 for each channel. Switching to mono would get you more power (that you presumably don’t need) and increase SINAD by 13db which you presumably don’t want.

Nvm, I read the graph upside down. The straight red line shown below is the amp reversing power as it goes into clipping/protection. The bottom curved line is the output.

 

[EddNog]

This is actually incorrect. Looking at the data presented by amir, you get worse SINAD only when you are at the increased power of 200w. For example, at 100w of output, stereo mode has -74dB SINAD. In mono mode at 100w, you get -78dB SINAD. In fact through the entire power range, right up until 200w, mono mode has a much more stable and better SINAD.

The gain is also higher in mono mode by 1.5dB allowing him to keep the volume control lower on his preamp.

Wow, I didn’t even realize this!

Is there a benefit to keeping preamp gain lower? I’m using a Gustard H16 as preamp.

-Ed

 

[312elements]

This is actually incorrect. Looking at the data presented by amir, you get worse SINAD only when you are at the increased power of 200w. For example, at 100w of output, stereo mode has -74dB SINAD. In mono mode at 100w, you get -78dB SINAD. In fact through the entire power range, right up until 200w, mono mode has a much more stable and better SINAD.

The gain is also higher in mono mode by 1.5dB allowing him to keep the volume control lower on his preamp.

Added the data to show what I mean. The blue line is in mono, as you see even at very low volume it stayed at -70dB or better. In stereo you dont read -70dB until 30 watts.

Thanks for clearing that up.

 

[nvidia_7]

Sorry for the confusion, I was reading the amps clipping/protection back tracking as the measurement.

 

[EddNog]

Nvm, I read the graph upside down. The straight red line shown below is the amp reversing power as it goes into clipping/protection. The bottom curved line is the output.

Wait, so…I’m confused now haha…

I tend to listen at low to medium volumes. Am I better off using Mono mode, or should I keep it set to Stereo and just enjoy the benefit of better separation and more power headroom (since it’s two 48V/5A power supplies feeding the complete setup as opposed to just one)?

-Ed

 

[nvidia_7]

Wait, so…I’m confused now haha…

I tend to listen at low to medium volumes. Am I better off using Mono mode, or should I keep it set to Stereo and just enjoy the benefit of better separation and more power headroom (since it’s two 48V/5A power supplies feeding the complete setup as opposed to just one)?

-Ed

Regardless of whether you use them as monoblocks or not, keeping them in the "stereo" setting will give you better SINAD. Depending on what you consider low volume though, the ls50's require a lot of power. I would not power them with anything less than 200w a channel. Also remember class D amps have virtually no dynamic power headroom.

 

[Talisman]

I would not power them with anything less than 200w a channel.

As insensitive as they may be, AT LEAST 200 watts per channel really seems like an exaggerated value to me....

 

[312elements]

Regardless of whether you use them as monoblocks or not, keeping them in the "stereo" setting will give you better SINAD. Depending on what you consider low volume though, the ls50's require a lot of power. I would not power them with anything less than 200w a channel. Also remember class D amps have virtually no dynamic power headroom.

I’ll agree to disagree with that (not trying to start an argument just for the sake of others who read it) , especially if you’re running a subwoofer, you can get away with significantly less power than 200w. I’ve run my ls50 metas with Schiit agier amps as mono blocks just fine to 90db peaks with 40w into 4ohms. From there I upgraded to a NAD c298, but the difference was nowhere near what I expected and the V3’s perform similarly (subjectively speaking).

 

[nvidia_7]

As insensitive as they may be, AT LEAST 200 watts per channel really seems like an exaggerated value to me....

Im not speaking in RMS values. With an amp like the ZA3 and many other class D amps you have to factor in that the rated RMS power is going to be near the dynamic or peak power.

 

[EddNog]

I’ll agree to disagree with that (not trying to start an argument just for the sake of others who read it) , especially if you’re running a subwoofer, you can get away with significantly less power than 200w. I’ve run my ls50 metas with Schiit agier amps as mono blocks just fine to 90db peaks with 40w into 4ohms. From there I upgraded to a NAD c298, but the difference was nowhere near what I expected and the V3’s perform similarly (subjectively speaking).

I’m running a subwoofer as well, SVS SB-3000. Part of why I am using the Gustard H16 as a preamp, since I have the sub hooked up to the single ended outputs on that, and the ZA3s to the balanced outs. I find the bass is tighter this way than running it out from the sub outs on the ZA3s.

-Ed

 

[nvidia_7]

I’ll agree to disagree with that (not trying to start an argument just for the sake of others who read it) , especially if you’re running a subwoofer, you can get away with significantly less power than 200w. I’ve run my ls50 metas with Schiit agier amps as mono blocks just fine to 90db peaks with 40w into 4ohms. From there I upgraded to a NAD c298, but the difference was nowhere near what I expected and the V3’s perform similarly (subjectively speaking).

Amir measured the Aegir as having 280% headroom at 4ohm. The Aegir also has a gain of 22dB, so you likely never ran into clipping, and on top of that you had plenty of power for transients.