FiiO K3 Review – Hello, My Little Friend

FiiO K3 feat
Tested at $119

Hi there fam. For today’s review, we’re looking at a desktop USB DAC and headphone amp: the FiiO K3. This is the company’s Scion to the legendary E10K which played a big part in putting FiiO’s name on the audiophile map.

This tiny USB-powered DAC supports up to DSD256, has bass boost and my favourite part – an additional balanced 2.5 mm headphone output. And it’s from FiiO so you know it sounds good too.

  • Tiny footprint
  • DSD 256 support
  • Bass boost and gain settings
  • Versatility
  • Value for money
  • Nothing noteworthy

Buy on:

FiiO K3 Specifications
  • USB: Type-C
  • USB Audio Class: UAC1.0 + UAC2.0
  • Volume Knob: ADC
  • Gain: L/H
  • Bass Boost: 0/+6dB
  • Line Out: 3.5mm
  • Headphone Out 1: 3.5mm single-ended output
  • Headphone Out 2: 2.5mm TRRS balanced output
  • Coaxial Out: RCA for 192kHz, support DSD64 DOP
  • Optical Out: Up to 96kHz
  • USB Chip: XMOS XUF208
  • Audio DAC: AKM AK4452
  • LPF OP AMP: TI OPA1612
  • Driver OP AMP: OPA926×2
  • Output Power 1: (3.5mm headphone output) 220mW(16Ω) 120mW(32Ω)
  • Output Power 2: (2.5mm TRRS balanced headphone output) 320mW(16Ω) 200mW(32Ω)
  • Line Level: 1.9Vrms
  • DAC: 384kHz/32bit
  • DSD: DSD256
  • SNR: ≥113dB
  • THD+N: ≤0.004%
  • Frequency Response : 20Hz-80kHz
  • RGB indicator: Sample rate ≤ 48kHz – Bluem, Sample rate >48kHz – Yellow, DSD format – Green
  • Dimensions: 70×58×22mm
  • Weight: 82g

This sample was provided for the purpose of an honest review. All observations and opinions here are my own based on my experience with the product.

Package and Accessories

When you see the size of the box, you’ll start to get an idea of just how small the K3 is. On the front is a clear image of the DAC, as well as a little Hi-Res Audio certification label.

Inside the box is the K3 is a plastic bag and there’s another smaller box here that holds the accessories. Here’s a breakdown of all that’s inside:

  • FiiO K3
  • USB Type-C cable
  • 4 strips of non-slip foam feet
  • Quick Start Guide
  • Warranty card
FiiO K3 accessories

Build Quality and Design

FiiO K3 top shot

The FiiO K3 is literally palm-sized and easily fits in your hand. Its chassis is CNC crafted from a single block of aluminium and then has the faceplate and rear plate attached. Weighing in at just 82 g it’s also extremely lightweight.

Despite being so small and light, the K3 feels really well built, especially the knurled metal volume knob which is nicely weighted. There’s also an LED indicator behind the knob that changes colour depending on the bitrate of the file you’re playing.

On the top of the chassis are a FiiO logo and Hi-Res Audio certification. Rounded sides and low-key design give the device a modern aesthetic and it looks really sleek. On the front panel are (from left to right):

  • 2.5 mm balanced headphone output
  • 3.5 mm single-ended headphone output
  • Bass boost switch (top)
  • Gain switch (bottom)
  • Volume knob
FiiO K3 front panel

There’s just as much going on at the back panel, including (from left to right):

  • 3.5 mm line out
  • USB audio class switch (top)
  • USB Type-C port
  • Coaxial digital out
  • Optical digital out
FiiO K3 rear panel

If you’re reading all this, you’re probably starting to realize that the K3 is a very versatile and multi-functional unit. So, not only can you use it with your computer or phone and plug in your IEMs and headphones, but you can also use the K3 to output to an external amplifier or speakers. All this and it weighs 82 g and fits in your pocket!

The ability to switch USB audio class is very interesting. In 1.0 mode the K3 has wider compatibility with older/legacy computers and phones and also requires no drivers to function, so it works as a plug and play device.


On the receiving end, the K3 utilizes an XMOS XUF208 chip enabling it to decode up to 384kHz 32 bit PCM and native DSD256. Performing DAC duties is the AKM AK4452 which is some impressive hardware for such an affordable DAC.

Amplification is taken care of by dual OPA926 and a TI OPA1612 for the low-pass filter, providing high output with low-noise and low-distortion. That same OPA1612 can be found in my Topping DX7 (review here) and the XDuoo X20 DAP.

The FiiO K3 has an output power of 220mW at 16Ω or 120mW at 32Ω from the 3.5 mm output and 320mW at 16Ω or 200mW at32Ω. That’s not huge but keep in mind the K3 is not designed for use with hard to drive headphones. I’ll cover pairings and matchability later on.


For testing, I had the FiiO K3 hooked up to my Windows 10 PC via USB. Media players used were JRiver Media Center and MusicBee. Music files were exclusively flac except for some DSD tracks used for test purposes.

Full-sized headphones tested included the Brainwavz HM100, Acoustic Research AR-H1, Meze 99 Classics and Beyerdynamic DT990 Pro. For IEMs I went with the Custom Art FIBAE 3, TenHz P4 Pro and Sennheiser IE 800 S.


Overall the K3 is neutral and transparent with good imaging and soundstage. Frequency response is very even and I could barely discern any difference between it and the ARCAM irDAC-II when using easy to drive headphones.

The ADC volume control works perfectly meaning there is no channel imbalance whatsoever. You can easily do very fine volume adjustments at low volume without any electrical crackling or breaking up of the signal.

The bass boost works really well, adding about 6dB from the lowest registers until around 100Hz where it starts to fall off and leaves everything above 2kHz untouched to retain clarity and tone.

On high gain, the K3 boosts everything around 6dB across the board, maintaining the same flat response. Even using sensitive IEMs the K3 has a very dark background making it compatible with a wide range of transducers.



The FiiO K3 had no problems driving any of my selected headphones. I will say that there was not much headroom left With the AR-H1 and DT990 Pro on quieter recordings with high gain but they both sounded great without any compromise in sound quality.

Speaking of the AR-H1, the K3 can really make this planar sing and this is the 1 headphone where I would occasionally switch on the bass boost, though for the most part, I didn’t feel it was necessary.

The Brainwavz HM100 pairs wonderfully too and its neutral tuning highlights the flat response of the K3. For the most part, I can use this headphone on low gain but on some quieter recordings, it was necessary to switch to high gain.

With the Meze 99 Classics headphone, I was able to test the balanced output and I have to say this was probably my favourite pairing of all. On low gain, the bass is wonderfully deep but very tight and controlled, the midrange and vocals are heavenly. Stereo separation and imaging are eargasmically good with this setup. This here is the essence of synergy!


I tested the Sennheiser IE 800 S with the 2.5 mm balanced output and this was another excellent match, although, to be honest, this earphone always sounds amazing to my ears. Comfortable listening level for me was around 50% on low gain.

Custom Art’s FIBAE 3 was next up, again using the balanced output. This is a great pairing; vocals are forward, the resolution is outstanding and there’s an inviting warmth that stands in stark contrast to the clarity this monitor reproduces. Superb. In low gain, I had the volume at about 40% and by 50% things were getting uncomfortably loud.

For the TenHz P4 Pro, I chose to use single-ended from the 3.5 mm jack. This is a sensitive IEM and I couldn’t detect any background noise whatsoever. The volume pot was at about 40% on low gain. The K3 really brings out the best in this all-BA earphone. The bass really comes alive with this combo (bass boost was off) and the earphone’s warmth and detail shine.

FiiO K3 with phone, FIBAE 3, HM100, AR-H1, 99 Classics
The FiiO K3 connected to my smartphone with FIBAE 3 (front). Headphones (from left to right): Brainwavz HM100, Acoustic Research AR-H1, Meze 99 Classics.
Optical Output

Just for kicks, I tested the optical out by plugging it into my ARCAM irDAC-II. At first, I got nothing and was left sitting for a minute trying to figure out what was wrong. Then it hit me – I had the K3 set to the maximum bitrate (32 bit 384000 Hz) in the Windows settings but TOSLINK only supports 24 bit data rates. After I changed the settings to 24 bit 96000 Hz everything worked perfectly.


It’s a wonderful thing that even after testing so many audio products, something as small and inexpensive as the FiiO K3 can come along and genuinely put a smile on my face.

The K3 is tiny, well-built, inexpensive, extremely versatile and it sounds fantastic. I like it so much I want to make it my work office DAC but the 2.5 mm output is just so handy I feel it needs to stay on my desktop at home.

If you’re new to this hobby and are looking for an inexpensive upgrade to your computer’s or phone’s sound then this is a great place to start. Alternatively, if you’re someone like me who wants a desktop DAC with 2.5 mm balanced headphone out then this is just brilliant.

The FiiO K3 is a real gem and with its low asking price and high performance gets a solid recommendation from me. What a great way to start the new year – thank you FiiO.

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Founder of Prime Audio
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2 years ago

What a great review! I just ordered the new K3 to be my first dac/amp and this review gives me peace of mind on my choice. I’m excited for it to arrive.

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