Fosi Audio ZA3 Amplifier Review

[Power Pop 23]

Hello there,
can someone tell me if the Fosi ZA3 is an improvement against my current setup?

Current setup is Project-Audio DS2 Amp Box -> Polk ES60

I use the Power Amp for Music (Wiim Ultra) and on the Front PreOuts from the Marantz Cinema 70s for Movies. I think the Project-Audio Speaker Noiselevel is kinda extreme. So compared with each other, would be the Fosi ZA3 better as the Project-Audio DS2 Amp Box Noiselevel- and Powerwise?

Sorry for my bad english

Hi,

I am uncertain you will hear a difference with the ZA3. Perhaps you can sample a ZA3 with return privileges.

 

[asa_g]

Works fine for two weeks but after I've noticed that right channel is louder then left one. Have changed everything and localize that the problem is in the Amp. Here is link to reddit with the same problem

https://www.reddit.com/r/BudgetAudiophile/comments/1cwj6ul/fosi_audio_za3_issue_right_input_louder

It will be nice if information with such common issue will be added to first post.

 

[obsessive9119]

Works fine for two weeks but after I've noticed that right channel is louder then left one. Have changed everything and localize that the problem is in the Amp. Here is link to reddit with the same problem

https://www.reddit.com/r/BudgetAudiophile/comments/1cwj6ul/fosi_audio_za3_issue_right_input_louder

It will be nice if information with such common issue will be added to first post.

I’m not sure it is common, unless you’re in the very low end of the volume control?

 

[asa_g]

As for me it almost independent from the gain of Amp but more depends on volume level. I clearly heard this issue till the 40% of the volume knob.(Didn't tried more high levels of amplification)

 

[TheRealLGC]

This might be the right time (for U.S. customers) to try out the ZA3 w/48v 5a adapter, from Amazon. Currently on sale & there's an additional 10% coupon listed on the landing page. Brings the total to $114.74 pre tax.

 

[Good Vibes]

Hi,

How detrimental to the sound is the load dependency overshoot of this amplifier? I have been thinking of building a 2nd system on a tight budget and have been considering the ZA3 but the frequency response looks problematic.

 

[Talisman]

Hi,

How detrimental to the sound is the load dependency overshoot of this amplifier? I have been thinking of building a 2nd system on a tight budget and have been considering the ZA3 but the frequency response looks problematic.

What speakers would you like to use them with?

 

[Good Vibes]

What speakers would you like to use them with?

I don’t have any as of yet, I am keeping an eye on the used market with a maximum budget of £200.

 

[TheRealLGC]

Hi,

How detrimental to the sound is the load dependency overshoot of this amplifier? I have been thinking of building a 2nd system on a tight budget and have been considering the ZA3 but the frequency response looks problematic.

I see the Fosi amps (either the ZA3/V3 Mono) as a gateway between low budget (minimum requirement) and mid level audio equipment. By giving you a decent taste of monoblocking, with separate AC adapters. I have two ZA3 setups, both setups use a WiiM streamer and or T.V.'s, as a source.

1. 2x ZA3 running in mono, feeding a pair of Polk R200, bookshelfs & a couple Definitive Technology SuperCube subs.
2. 1x ZA3 stereo, feeding a pair of Polk LSiM 703, bookshelfs

No issues with clipping, during playback, on either setup. Unless you're running some 2 ohm speakers or your goal is for critical listening, you won't have a an issue.

 

[Good Vibes]

I see the Fosi amps (either the ZA3/V3 Mono) as a gateway between low budget (minimum requirement) and mid level audio equipment. By giving you a decent taste of monoblocking, with separate AC adapters. I have two ZA3 setups, both setups use a WiiM streamer and or T.V.'s, as a source.

1. 2x ZA3 running in mono, feeding a pair of Polk R200, bookshelfs & a couple Definitive Technology SuperCube subs.
2. 1x ZA3 stereo, feeding a pair of Polk LSiM 703, bookshelfs

No issues with clipping, during playback, on either setup. Unless you're running some 2 ohm speakers or your goal is for critical listening, you won't have a an issue.

Hi

Thanks for sharing. I am 5 years into this hobby and still very much learning. The HF rise on the measurement of the ZA3 seems counterintuitive to me, isn’t it a bad thing? How would that affect the sound? From what I know those polks have a bit of a rise in the HF department. Is it essential to attenuate the effect of the ZA3 with EQ?

 

[somebodyelse]

Hi,

How detrimental to the sound is the load dependency overshoot of this amplifier? I have been thinking of building a 2nd system on a tight budget and have been considering the ZA3 but the frequency response looks problematic.

It depends on how the impedance and output of the speakers varies with frequency. A speaker with an impedance peak around 20R at 2kHz might see increased output around 0.5dB from what I remember of measurements on similar amps. A bigger impedance peak, or a peak at a higher frequency, would have more of an output increase. 0.5dB is probably audible, but also probably no worse than the variation between left and right speaker from manufacturing tolerances. If the speaker has a dip in response there then the increase would actually help. Conversely if there's already a peak in response at that frequency a further increase is worse.

 

[Good Vibes]

It depends on how the impedance and output of the speakers varies with frequency. A speaker with an impedance peak around 20R at 2kHz might see increased output around 0.5dB from what I remember of measurements on similar amps. A bigger impedance peak, or a peak at a higher frequency, would have more of an output increase. 0.5dB is probably audible, but also probably no worse than the variation between left and right speaker from manufacturing tolerances. If the speaker has a dip in response there then the increase would actually help. Conversely if there's already a peak in response at that frequency a further increase is worse.

That has helped me to get my head around it and understand it better. Thank you.

Not ideal but not overly detrimental.

 

[obsessive9119]

Has anyone measured this in stereo mode with 1ch driven? I’d be interested to see if it ends up with more power available but without the increases distortion of mono mode.

 

[solderdude]

That would depend on the drawn power (speaker impedance) and most of all the used power supply.

If there are any differences in output power between 1 and 2 channels driven then it is caused by the power supply sagging a little under maximum load.
That difference will be small as the power supplies are regulated and probably would remain under 1dB (so hardly audible).
'Normal' amps with mains transformers and rectifiers have power rails that drop a little under heavy loads.

A give away is this measurement which shows 0.8dB difference between continuous load and peak load in 4ohm:

 

[obsessive9119]

That would depend on the drawn power (speaker impedance) and most of all the used power supply.

If there are any differences in output power between 1 and 2 channels driven then it is caused by the power supply sagging a little under maximum load.
That difference will be small as the power supplies are regulated and probably would remain under 1dB (so hardly audible).
'Normal' amps with mains transformers and rectifiers have power rails that drop a little under heavy loads.

Well, we know the 48v power supply will get to 200W when the amp is in mono mode, and 140W in stereo with 2 ch (both into 4ohms).

I’m not really sure what the mono/stereo switch does - from what I’ve picked up in this thread it sounds like it’s just disabling one channel. So that makes me wonder a couple of things:

- why is the SINAD is worse in mono?
- can you extract more than 140W in stereo if you only drive one channel?

 

[solderdude]

Well, we know the 48v power supply will get to 200W when the amp is in mono mode, and 140W in stereo with 2 ch (both into 4ohms).

1: Most power supplies can squeeze out more peak power than the rated power.
2: Music is dynamic and not continuous.

- why is the SINAD is worse in mono?

Because in mono mode it becomes a bridged amp (BTL mode).
That would be interesting a little for 4ohm and 8ohm speakers as you gain 1dB in output power.
The amp is switched to P(arallel)BTL mode.
Hardly worth the trouble. Interesting if you plan to use power amps very close to the speaker and have a pre-amp that runs shielded interlinks all the way up to the amp.
Personally I would use substantially better performing amps in this case. This is a small sized budget amp that packs a punch of power. Nothing more, nothing less.

- can you extract more than 140W in stereo if you only drive one channel?

You can squeeze a bit more out of it when you allow more than 1% distortion but not when driving 1 versus 2 channels at the same time in stereo mode.
Note that the difference will be well under 1dB so inconsequential.

 

[obsessive9119]

Because in mono mode it becomes a bridged amp (BTL mode).

Oh, I must have misunderstood the earlier discussion- I thought I’d read that in mono it was not bridged.

 

[solderdude]

Well the manufacturer says this
PBTL Mono Mode Support


Amir says this:
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
O.K.
I was wrong.
Below is for a different chip but will apply to 3255 as well.

In PBTL mode the left and right amp (that are already bridged) are used in parallel.
It would explain the small difference in output power (just 1dB for all impedances) and explain the increased distortion.
The amps are both working 'against each other' a very tiny bit when in PBTL mode (as they are in parallel) because of tolerance differences between components in both channels.

When used in mono mode the chip itself will shut down one side completely lowering idle power and thus heating of the chip.
Maybe that's what is being done and this also affects the used channel increasing distortion.

The 1dB difference is inconsequential so would not recommend to use it in (whatever) mono mode.

 

[obsessive9119]

Well the manufacturer says this
PBTL Mono Mode Support


Amir says this:
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 thing is that usually the power difference between bridged and not bridged is much higher than 1dB (which it isn't) which would suggest Amir is right.
In such a case speakers have to be connected to L+ and R+ unless one has a relay that switches one of the output terminals.

The higher distortion in mono mode is weird (as it is higher in 5W too) so suggests something more is happening than just 1 channel not being used.
Maybe it is and there is a circuit engaged switching off one channel but at the same time 'distorts' the other channel.

Clearly though .. I would only use it in stereo mode and if it were used in mono mode I would simply put a shorting pin on the not used input and would set it in stereo mode.
The 1dB difference is negligible in practice anyway.

It’s higher gain in mono mode (28.5 vs 26.5db) - maybe that accounts for the extra distortion?

 

[solderdude]

I see about 2,7dB difference in gain. (0.23V vs 0.168V for 5W)
The question is indeed where this comes from.
Most likely it also has to do with the paralleling of the output stages (the PBTL mode).
I can see that mode being interesting at higher PS voltages (between 50V and 68V which the chip can handle but the amp might not) or when one wants to drive very low impedance loads, as PBTL allows double the output current (at the same voltage) in lower impedance loads, assuming the power supply and post filtering allows that.
It appears that the cost is a bit higher distortion.

In any case... the 1dB 'gain' in power isn't worth anything.
Maybe one would get a somewhat similar gain in 'available' output power in 4 or 8 ohm when just shorting the unused input and leave it in 'stereo mode' but would probably also be below 1dB anyway (regulated power supply)

1dB gain in power and you get a bit more gain (2.7dB) means you just need a little less voltage to drive it to max. power.
At least when switching to 'mono mode' while having only one speaker connected you will notice it goes louder (because of the gain).