Fosi Audio's First Dual-Mode Balanced Amplifier ZA3

[TikBLang]

I have tried to find out more on this earlier, but couldn’t find anything that suggests bridged mono. Fosi documentation also doesn’t have this information.
Most amplifiers use different speaker connections when switched to mono, but ZA3 uses terminals of one of the speaker as it is (right speaker in this case).

Is there a test speaker on YouTube that will tell if you are playing 'left' left, then 'right, right, right, and left combo to test if the output is the sum of L and R channels?

 

[space_duck]

Is there a test speaker on YouTube that will tell if you are playing 'left' left, then 'right, right, right, and left combo to test if the output is the sum of L and R channels?

My favourite track for this is Armin van Buuren - This Is A Test (Shinovi Remix), though it will only test whether the amp sums the stereo inputs in mono mode. It would not test whether you get any power benefit from it.

 

[Fosi Audio]

My favourite track for this is Armin van Buuren - This Is A Test (Shinovi Remix), though it will only test whether the amp sums the stereo inputs in mono mode. It would not test whether you get any power benefit from it.

We'll try to record a demo for you.

 

[Guddu]

My favourite track for this is Armin van Buuren - This Is A Test (Shinovi Remix), though it will only test whether the amp sums the stereo inputs in mono mode. It would not test whether you get any power benefit from it.

Although I think I am not getting what and how this song will help with testing, but let’s try to break it down:
In mono, we only input on right channel rca/xlr and speaker output is on right channel out. In this case, there is no left channel input fed in and there is no R+L sum up happening based on R and L inputs.
I think only Fosi can explain here how mono mode operates in ZA3 configuration.
I could think of the following options:
a) Left channel is shutdown and Right channel input gets amplified based on max available power for Right channel.
b) Left channel is shutdown on input, but Right channel input routes in on both channels internally and bridges the available power to Right channel out.

 

[Joe0429]

Unlike the A07 Max, which explicitly states that it uses PBTL mono mode, Fosi ZA3's introduction does not mention PBTL at all.
Based on the TPA3255 datasheet, I speculate that Fosi ZA3 uses mono BTL configuration, not PBTL.
This also explains why ZA3's mono mode uses the right channel instead of L+ and R+.

@Fosi Audio, please clarify whether ZA3's mono mode is in PBTL mode.
If my speculation is wrong, I am willing to apologize to @Fosi Audio.
However, if my speculation is correct, I believe that this is the biggest design decision mistake of ZA3.
This makes ZA3's mono mode seem like a rushed design that was made to compete with the A07 Max.
Before @Fosi Audio provides an explanation, I should not make such a judgment.

 

[K.Kevin]

View attachment 329705

Unlike the A07 Max, which explicitly states that it uses PBTL mono mode, Fosi ZA3's introduction does not mention PBTL at all.
Based on the TPA3255 datasheet, I speculate that Fosi ZA3 uses mono BTL configuration, not PBTL.
This also explains why ZA3's mono mode uses the right channel instead of L+ and R+.

@Fosi Audio, please clarify whether ZA3's mono mode is in PBTL mode.
If my speculation is wrong, I am willing to apologize to @Fosi Audio.
However, if my speculation is correct, I believe that this is the biggest design decision mistake of ZA3.
This makes ZA3's mono mode seem like a rushed design that was made to compete with the A07 Max.

Can you explain the practical difference for people like us who don’t know what that means?

 

[Joe0429]

Can you explain the practical difference for people like us who don’t know what that means?

I would like to apologize for my previous emotional statement.

If it is not used to drive a 2-ohm beast, I think that for most applications, the difference between the two is not that obvious.
However, it may be disappointing for Mono mode users who hope to get more power through PBTL mode.

Stereo BTL mode:
Most TPA3255 amplifiers use this mode to provide stereo sound. It is composed of 2 BTL channels.

Mono BTL mode:
One of the BTL channels is disabled. I am not sure if the BTL channel in operation can provide more power as a result.

Paralleled BTL mode:
2 BTL channels are connected in parallel to form 1 PBTL channel to drive 1 speaker. In theory, it provides 2 times the BTL power (This is also why A07 Max claims to provide 600W/2Ω (48V/12A)). In practice, it is limited by the power supply and many factors.

 

[Toku]

View attachment 329705

Unlike the A07 Max, which explicitly states that it uses PBTL mono mode, Fosi ZA3's introduction does not mention PBTL at all.
Based on the TPA3255 datasheet, I speculate that Fosi ZA3 uses mono BTL configuration, not PBTL.
This also explains why ZA3's mono mode uses the right channel instead of L+ and R+.

@Fosi Audio, please clarify whether ZA3's mono mode is in PBTL mode.
If my speculation is wrong, I am willing to apologize to @Fosi Audio.
However, if my speculation is correct, I believe that this is the biggest design decision mistake of ZA3.
This makes ZA3's mono mode seem like a rushed design that was made to compete with the A07 Max.
Before @Fosi Audio provides an explanation, I should not make such a judgment.

I, like you, have big doubts about the PBTL behavior of the ZA3 and A07 Max.

However, contrary to you, I understand that with ZA3, the speaker is connected to one channel, so it is a correct PBTL connection.
The PBTL operation of TPA3255 simply connects the 2cH output of BTL operation in parallel, so the connection of ZA3 matches this. You can easily configure the circuit with the two built-in relay circuits.

On the other hand, the A07 Max uses an unprecedented connection method in which the speaker is connected between the + terminal of the R/L SP output. Achieving this kind of connection is not possible with just the two circuit relays installed in the A07 Max. I suspect that the A07 Max's mono operation is the 1xBTL method you point out in the datasheet.

 

[K.Kevin]

I would like to apologize for my previous emotional statement.

If it is not used to drive a 2-ohm beast, I think that for most applications, the difference between the two is not that obvious.
However, it may be disappointing for Mono mode users who hope to get more power through PBTL mode.

Stereo BTL mode:
Most TPA3255 amplifiers use this mode to provide stereo sound. It is composed of 2 BTL channels.

Mono BTL mode:
One of the BTL channels is disabled. I am not sure if the BTL channel in operation can provide more power as a result.

Paralleled BTL mode:
2 BTL channels are connected in parallel to form 1 PBTL channel to drive 1 speaker. In theory, it provides 2 times the BTL power (This is also why A07 Max claims to provide 600W/2Ω (48V/12A)). In practice, it is limited by the power supply and many factors.

Thanks, but why does the power ratings Fosi provided on their kickstarter not already answer your question?

It seems like the mono power ratings is not necessarily doubled in mono, so it’s not really clear how it could be PBTL

 

[IPunchCholla]

Thanks, but why does the power ratings Fosi provided on their kickstarter not already answer your question?

It seems like the mono power ratings is not necessarily doubled in mono, so it’s not really clear how it could be PBTL
View attachment 329794

Those look like current limited PBTL numbers to me. If it was a 48v/10A PSU they would likely double.

 

[Joe0429]

I, like you, have big doubts about the PBTL behavior of the ZA3 and A07 Max.

However, contrary to you, I understand that with ZA3, the speaker is connected to one channel, so it is a correct PBTL connection.
The PBTL operation of TPA3255 simply connects the 2cH output of BTL operation in parallel, so the connection of ZA3 matches this. You can easily configure the circuit with the two built-in relay circuits.

On the other hand, the A07 Max uses an unprecedented connection method in which the speaker is connected between the + terminal of the R/L SP output. Achieving this kind of connection is not possible with just the two circuit relays installed in the A07 Max. I suspect that the A07 Max's mono operation is the 1xBTL method you point out in the datasheet.

At first, I thought that the PBTL circuit was as shown in the figure below, so the speaker terminals were connected to L+ and R+.

Toku reminded me that the ZA3's PBTL might be the following way, with the speaker terminals connected to R+ and R-.

 

[Fosi Audio]

Thanks, but why does the power ratings Fosi provided on their kickstarter not already answer your question?

It seems like the mono power ratings is not necessarily doubled in mono, so it’s not really clear how it could be PBTL
View attachment 329794

Hi friend, these power ratings are measured with our available 48V/5A and 32V/5A power supplies. It's true the output power is literally limited by the power supply so we cannot simply get double power ratings in mono mode.

Anyway, we're making an effort to develop our own 48V/10A power supply which will possibly exceed the limitation.

 

[TikBLang]

Since Fosi is very much

Anyway, we're making an effort to develop our own 48V/10A power supply which will possibly exceed the limitation

Thank you. Looking forward for this. A decent 48v/10A DC power supply that has negligible AC hum is a must.

 

[Joe0429]

Thanks, but why does the power ratings Fosi provided on their kickstarter not already answer your question?

It seems like the mono power ratings is not necessarily doubled in mono, so it’s not really clear how it could be PBTL
View attachment 329794

Yes, I also noticed the power of Mono Mode before buying.

Many manufacturers label the theoretical value of PBTL. At that time, I thought that Fosi's Mono Mode power was the real PBTL power limited by power supply and other factors. Just like IPunchCholla said.

It is also possible that Fosi's power is in Mono BTL mode, with 48V/5A supply to a single BTL channel, so it can provide higher power. Just like guddu said.

And, Fosi still has not answered whether Mono Mode is PBTL.

 

[Fosi Audio]

Many manufacturers label the theoretical value of PBTL. At that time, I thought that Fosi's Mono Mode power was the real PBTL power limited by power supply and other factors. Just like IPunchCholla said.

Sorry for not replying timely. It's PBTL on our ZA3.

And we just uploaded a video to demonstrate using two ZA3s in mono mode to build up a stereo system. Pls check @TikBLang

 

[vicenzo_del_paris]

@Fosi Audio when will the ZA3 be available ?

 

[amirm]

On the other hand, the A07 Max uses an unprecedented connection method in which the speaker is connected between the + terminal of the R/L SP output. Achieving this kind of connection is not possible with just the two circuit relays installed in the A07 Max. I suspect that the A07 Max's mono operation is the 1xBTL method you point out in the datasheet.

I just measured that it doesn't produce much more power in 4 bridged mode:

 

[dweeeeb2]

Sorry for not replying timely. It's PBTL on our ZA3.

And we just uploaded a video to demonstrate using two ZA3s in mono mode to build up a stereo system. Pls check @TikBLang

I know I’m nitpicking but of all the content that could have been used why was a headphone demonstration of ATMOS used? I hope this doesn’t confuse the shoppers.

 

[Joe0429]

Sorry for not replying timely. It's PBTL on our ZA3.

And we just uploaded a video to demonstrate using two ZA3s in mono mode to build up a stereo system. Pls check @TikBLang

@Fosi Audio, thank you for the confirmation.
I sincerely apologize for my previous doubts.
This is great news for users who want to use ZA3 in mono mode.

 

[Azertix]

I wish this new ZA3 had a high-pass filter

We're going to add the adjustable high pass filter in another model. It won't introduce distortion.

@Fosi Audio : Could you tell us a bit more about this amp ? Launched ? Not yet ? Price ?

Thanks for your answer