The Fosi Audio ZA3 is exactly the kind of amplifier I like seeing from Fosi.

I've reviewed enough compact Class-D amplifiers at this point that simply being small and powerful isn't particularly exciting anymore. That's almost expected. What gets my attention is when manufacturers start bringing features normally associated with larger and considerably more expensive equipment into these tiny boxes.

And that's exactly what Fosi has done with the ZA3.

Balanced XLR inputs, RCA inputs, a 12V trigger, and stereo or mono operation are all here. These are the kinds of features that make the ZA3 feel less like a basic mini amp and more like a serious piece of two-channel audio gear.

Then Fosi wraps everything in its familiar black-and-orange industrial design, gives the chassis some surprising weight and solidity, and builds the entire thing around the Texas Instruments TPA3255 Class-D amplifier platform.

This is much more my speed.

Build Quality: Small, Heavy and Very Fosi

The first thing that surprised me about the ZA3 wasn't the specification sheet. It was picking the thing up. There's some real heft here.

For such a compact amplifier, the ZA3 feels incredibly solid in the hand. Nothing about it feels hollow or cheap, and the metal chassis gives it the kind of density I want from a piece of audio equipment.

I also continue to love Fosi's current design language. The predominantly black chassis with that bright orange volume knob has become immediately recognizable as Fosi without becoming obnoxious. It's clean, industrial and simple. Put the ZA3 on a desk next to a DAC or streamer and it looks like a legitimate piece of enthusiast audio equipment rather than a generic mini amp from Amazon. That's an important distinction as Fosi continues moving further into enthusiast hi-fi. Small doesn't have to mean cheap.

Finally, Balanced XLR Inputs

This is what I really wanted to see. Around back you'll find RCA alongside balanced combo inputs supporting XLR and 1/4-inch TRS connections.

That immediately makes the ZA3 more interesting for a serious desktop or two-channel system. Balanced connectivity can provide better resistance to interference and noise, particularly with longer cable runs or when you're combining multiple pieces of equipment. More importantly, it makes sense with the direction Fosi's ecosystem has been heading.

Pair the ZA3 with a quality balanced DAC or preamp and you can put together an impressively capable little separates system without needing a giant rack full of traditional hi-fi components. There's also a 12V trigger input, which I love seeing on equipment like this. Connect it to compatible upstream equipment and the ZA3 can power up and down along with the rest of your system. It's a little feature that makes a separates system feel much more polished in everyday use.

Stereo Today, Monoblocks Tomorrow

One of the ZA3's coolest tricks is its ability to operate in either stereo or mono. In stereo, a single ZA3 can power a conventional pair of passive speakers. According to Fosi, using its 48V/5A power supply produces a rated 155 watts per channel into 4 ohms. Flip the amplifier into mono operation and Fosi rates output at 235 watts into 4 ohms.

That creates a really nice upgrade path. Start with one ZA3, and if you eventually want more power or simply want to experiment with dedicated monoblocks, buy another ZA3 and run one amplifier for each speaker. That's the kind of flexibility I love in affordable audio equipment because you're not buying yourself into a dead end.

Fosi Audio ZA3 Specifications

There's Even a Subwoofer Output

Another feature that makes the ZA3 considerably easier to build a complete system around is its powered subwoofer output. That's particularly useful for desktop and bookshelf-speaker systems. You can run your passive speakers from the ZA3, connect an active subwoofer and suddenly this tiny amplifier becomes the center of a proper 2.1-channel system.

There isn't a DAC or Bluetooth built into the ZA3, and I actually don't mind that. This is fundamentally a power amplifier. Feed it from the source, DAC, streamer or preamp of your choice and let it do the amplification. That simplicity is part of the appeal.

Replaceable Op-Amps Make It Even Nerdier

Fosi hasn't forgotten about the enthusiasts who can't leave anything alone. The ZA3 uses replaceable op-amps, allowing owners to experiment with compatible alternatives and potentially alter aspects of the amplifier's sound. Do you need to do this? Absolutely not. But that's exactly why I like that Fosi gives you the option.

For someone who simply wants an amplifier, leave it alone and enjoy it. For the person who enjoys opening equipment and experimenting with different components, the ZA3 gives you another rabbit hole to disappear into.

Sound Quality

This is ultimately where the ZA3 has to prove itself, and the first thing that stands out is just how much amplifier you're getting from such a small chassis.

The ZA3 has the clean, controlled character I've come to expect from modern Fosi Class-D designs. There's plenty of detail, a low noise floor, and enough power available that this doesn't feel limited to tiny desktop speakers.

Bass comes through with good control and authority rather than becoming loose or bloated. The midrange stays clean and relatively neutral, while the top end has enough detail to keep recordings sounding open without the amplifier imposing an enormous sonic personality of its own.

That's exactly what I want from a power amp. I don't want an amplifier dramatically changing the character of my speakers. I want clean amplification, enough headroom to handle dynamic material and as little unwanted noise as possible.

The ZA3 delivers that remarkably well for something this small, and using the balanced inputs makes the whole package even more compelling when paired with a proper DAC or preamp.

The 48V Power Supply Is the One I'd Want

There is one important specification buyers should pay attention to: the power supply matters. Fosi supports both 32V/5A and 48V/5A supplies with the ZA3.

With the 32V supply, Fosi rates the amplifier at 95 watts per channel into 4 ohms in stereo and 110 watts in mono.

Move to the 48V/5A supply and those figures increase to 155 watts per channel in stereo and 235 watts in mono.

That's a substantial difference.

For an easy-to-drive desktop speaker, the smaller supply may be perfectly adequate. But if I'm buying the ZA3 because I want a surprisingly serious amplifier hiding inside a tiny chassis, I'm going with the 48V supply. Give the little thing some room to breathe.

Who Is the Fosi Audio ZA3 For?

I think the ZA3 makes the most sense for someone building a compact separates system.

If you've already got—or plan to buy—a DAC, streamer or preamp with balanced outputs, the ZA3 slots into that system beautifully.

It's also a great option for someone who wants to start simple. Run one ZA3 in stereo today, add a powered subwoofer if you want more low-end extension, and potentially add a second ZA3 later to experiment with monoblocks.

That's a lot of flexibility from one little amplifier.

Final Thoughts

The Fosi Audio ZA3 represents exactly what has made compact Class-D amplification so interesting. It's not just small; it's usefully small.

You get balanced XLR/TRS inputs, RCA, a powered subwoofer output, 12V trigger support, stereo and mono operation, replaceable op-amps and substantial output capability from a chassis that takes up very little space.

And I love the physical execution. The ZA3 feels solid, has some surprising heft to it, and Fosi's black-and-orange design looks fantastic. It manages to feel like a proper piece of audio equipment despite its tiny footprint.

Most importantly, there's room to grow with it. One ZA3 can anchor a compact stereo system. Add a subwoofer and you've got 2.1. Add a second ZA3 and suddenly you're running dedicated monoblocks. That's a lot of enthusiast-level flexibility packed into one very small black box.

The Fosi Audio ZA3 is exactly what affordable Class-D audio should be: compact, powerful, flexible and just nerdy enough to make you want to start experimenting.