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Fosi Audio's First Dual-Mode Balanced Amplifier ZA3

Fosi Audio

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Audio Company
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Greetings! We're happy to share with ASR members that our first dual-mode balanced amplifier ZA3 is about to be released! Here are some details about this amp.

•Mode: Stereo, Mono
•Input: RCA, XLR
•Output: Speaker Out, Sub Out
•Amp Chip: Texas Instrument TPA3255
•SINAD: 88dB
•SNR: ≥106dB
•Dynamic Range: ≥106dB
•THD: <0.005%
•Terminating Impedance: 2-8Ω
•Rated Output Power(1kHz, 1% THD):
•Stereo Mode: 180W*2 @4Ω
•Mono Mode: 240W @4Ω
•Frequency Response: 20Hz-20kHz (±0.1dB)
•Power Input: DC 24V-48V

This amazing amp will be officially released and available for sale in December. Before that, we will keep optimizing its performance. If you're interested in this amp you can back us on Kickstarter:)
https://www.kickstarter.com/project...za3-hifi-stereo-mono-balanced-power-amplifier


Of course, we're looking for any advice you have on this amp too!;)

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to me this is ok

it has a few things a bit weird

like what is the sub cutoff?

also you prob. get 90w real and 110w mono real so is it worth monoblock????


i would treat this is a good tpa xlr stereo and amp leave it at that
 
Looks really good.
Following info would be useful:

XLR inputs - Is it a fully balanced design, or just xlr input, single ended?
Xlr connector- looks like it can accept TRS too?
For sub out - whats the cut off frequency?
Does it show typical load dependency as other 3255 amplifiers?
 
Of course, we're looking for any advice you have on this amp too!;)
I like it a lot, ordered! (#3).

Some suggested changes before release:

- Mono/Stereo should be moved to bottom or back to avoid expected volume changes or electrical failures. What happens if you switch it by mistake?

- The Mono Balanced/Unbalanced input on the back should be labeled. What happens if you have both L/R inputs connected in mono mode?

- The Power switch should be moved from the volume knob to where the Input switch is now, and the Input moved to the Mono/Stereo spot. This is no big deal on the V3, but on dual mono amps keeping the volume precisely the same, and controlling things through a pre-amp is important. With the power switch in the volume you have to re-adjust each time. What happens when you have 2 amps connected in mono? Could there be a way to have one amp control both? A volume controlled Pre-out could perhaps work that way.

Trey To asks a good question in the Kickstarter comments: "When the amplifier is off, is the signal still getting passed through the sub out?" If you move the power switch that would become more important.
 
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How about adding an adjustatble high pass filter? Would that introduce too much distortion?
We're going to add the adjustable high pass filter in another model. It won't introduce distortion.
 
to me this is ok

it has a few things a bit weird

like what is the sub cutoff?

also you prob. get 90w real and 110w mono real so is it worth monoblock????


i would treat this is a good tpa xlr stereo and amp leave it at that
The cut-off frequency range for the sub out is 20-300Hz.

Due to the restriction of the 32V/5A PSU, the power difference is not much. Anyway, we'll put a 48V/5A PSU as standard so you can get enough power.:)
 
Glad to see balanced inputs.

PFFB is the next step in performance.

Stereo/Mono switch should not be so easily accessible, better on the back, but in front On/Off switch.

Usually people use active subs which already have variable low pass filter. What sets apart is having variable high pass filter for the speakers, as this is undoable for the regular user.

Looks like the orange knob is here to stay. Became somewhat like your brand distinction, which is nice to have. But still regular all black option is important, as not everyone wants something shiny.
 
Usually people use active subs which already have variable low pass filter. What sets apart is having variable high pass filter for the speakers, as this is undoable for the regular user.
I agree - can @Fosi Audio confirm a high pass filter frequency for the speakers e.g. when the sub-out is connected the high pass filter is then enabled on the speaker outputs, allowing more available power for the speakers (and less distortion)
 
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Looks nice and will provide more power to those looking for same. I'll be interested to see details on the subwoofer output. Does the volume scale? Also, if creating mono blocks, how to sum the subwoofer outputs into one input for subwoofers that only have one input?

The thing that will bring Fosi to the next level will be filtering, allowing flat and load-independent frequency response. That's where the value prospect meets the objective performance sweet spot. Many of the posts I see in forums about Aiyima and Fosi chip amps include negative comments about the load dependence. Now, for many/most of us, that issue exists on testing but isn't an audible concern, BUT it holds these amps back in the collective 'hive mind'.

I own two V3s and have been very happy with them, but there is the nagging issue (in my mind) of the load dependence that places these amps in a performance tier below the best ones available. Topping has figured out the filtering aspect, albeit with unreliable and kludgy potted 'modules' in their models that has severely damaged their reputation IMO.

Fosi, there is a great opportunity here for you. Your latest offerings stand out IMO. They look like substantial devices, they sound great to boot and you're offering power bricks that are large enough to get serious power from these devices. Once you get the filtering figured out you can jump to the figurative head of the space where (arguably) Topping has been a leader.
 
If a main output high pass filtering option is implemented, please use at least second-order filters (12 dB/octave slope), and my personal preference is 4th order (24 dB/octave slope).
 
My comment from another thread...

Mono/stereo switch on the front panel (and a toggle switch at that) looks like a disaster waiting to happen.

It needs to be on the back, and not possible to hit by mistake. A toggle switch is not appropriate, especially if you can suddenly output double or more power to a speaker. Or invert one of the terminals causing a big transient.

I'll second the comment that in a mono design you can't have the on/off tied to the volume knob.
 
My comment from another thread...



It needs to be on the back, and not possible to hit by mistake. A toggle switch is not appropriate, especially if you can suddenly output double or more power to a speaker. Or invert one of the terminals causing a big transient.

I'll second the comment that in a mono design you can't have the on/off tied to the volume knob.
I thought it was some kind of mono stereo source button. Really strange to have a bridge button on the front.
 
Similar to my comments elsewhere:

The Mono/Stereo could be a small slider just above the Subwoofer out RCA on the rear panel, making that toggle available for on /off. The volume control should just be a volume control. The High Pass filter option should have been included in his generation.

As long as the load dependency issue, and the Sub Out is tweaked to be a variable output (as Fosi told me it would on their YouTube Video) along with the new changes this should be a winner.
 
Looks really good.
Following info would be useful:

XLR inputs - Is it a fully balanced design, or just xlr input, single ended?
Xlr connector- looks like it can accept TRS too?
For sub out - whats the cut off frequency?
Does it show typical load dependency as other 3255 amplifiers?

@Fosi Audio
Any details on design query - is it balanced amplifier design when using xlr, or is it single ended design but with convenience of xlr connection?

If it is fully balanced design then probably the best bang for buck.
 
to me this is ok

it has a few things a bit weird

like what is the sub cutoff?

also you prob. get 90w real and 110w mono real so is it worth monoblock????


i would treat this is a good tpa xlr stereo and amp leave it at that
On the output power specs, Good thing is that these Fosi amps are using 63v caps etc. to keep 48v psu option in check, so 48v psu is always an option to get a bit more power.
Don't know when we get this one measured, but that should tell us the limits.
 
on the a07 max the monoblock switch is a tiny slider tab you need a toothpick to operate

i agree placing the monoblock switch on the front is an odd choice given its somehting you would hardly ever use except on initial setup

also as far as fully balanced... if you look at the board pics it looks very similar to the older design so one might assume its not fully balanced but i dont think it matters
 
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