This and That:
Small. Beautiful design, high build quality.
Four adhesive foam feet are included (they’re a bit smoother and less sticky than I’d like though).
The USB audio selector switch on the back is very nice as it makes the K3 compatible with about anything and doesn’t require any special drivers to be installed in 1.0 mode.
The line out on the device’s back is fortunately adjustable, which is awesome as it lets the K3 act as DAC that can be used as a monitor controller for loudspeakers, and since its volume is controlled digitally, there won’t be any channel imbalance even at low potentiometer positions; this makes the K3 a monitor controller DAC with perfectly volume-matched channels over the entire attenuation range.
The only thing that would make the K3 even better is an output selector switch to switch between headphone and line output.
It’s quite comparable to FiiO’s Q1 MkII, but intended as a desktop device (hence no internal battery) and with a somewhat more powerful headphone output as such, albeit no analogue inputs.
Seems like a logical replacement for/alternative to the E10k.
Volume Control:
The potentiometer-based volume control is implemented digitally, wherefore channel imbalance is completely avoided over the entire adjustment range.
Using the 3.5 mm headphone output, the lowest possible volume level is still reasonably low using very sensitive IEMs (Ostry KC06A, Shure SE846) and I rarely wish that it were lower. Even with extremely sensitive IEMs such as my Campfire Audio Andromeda, the lowest possible volume level is still reasonable most of the time.
Using my current power amp + speaker setup through the line out, the volume range is good as well and listening quietly is possible.
Sound:
As I don’t really care about the balanced 2.5 mm output, I’m not using it.
The only thing about the FiiO that isn’t as nice as the rest (I’m referring to the measurements and the rest below) is that it has a built-in automatic muting feature that mutes the audio output after a few seconds when there’s no signal. The issue with it is that there’s an audible popping/thumping noise transported through the headphone output using sensitive in-ears, that’s even more present through the line out (muting and un-muting are accompanied by those pops/thumps). To me, for a device that is clearly designed primarily for desktop application, this doesn’t make much sense at all and is definitely an annoyance.
Frequency Response, unloaded:
3.5 mm Headphone Output:
Line Out:
Bass Boost (3.5 mm Headphone Output):
That's still fairly good and won't skew most multi-driver in-ears' frequency response (well, or only a bit in case of divas such as my Triple.Fi 10, Campfire Audio Andromeda or Shure SE846, so the perfectionist in me would have preferred below 1 Ohm, but the K3’s output impedance is still fine and still reasonably low).
Hiss Performance (3.5 mm Headphone Output):
Using very sensitive in-ears (such as my Shure SE846 or Ostry KC06A), there is some mild to moderate hiss. It’s still on the quieter side though.
Using my extremely sensitive Campfire Audio Andromeda, there is a moderate amount of hiss.
With in-ears that are sensitive but not very or extremely sensitive, such as my Ultimate Ears Triple.Fi 10, there’s no perceptible hiss.
All in all, the K3 performs quite well in terms of hiss performance (think Cowon Plenue D-/Plenue J-tier) and is among the quieter devices (for example, its hiss performance is much better than that of comparable devices such as the HiFime 9018d that hisses strongly, and also better than that of my first-generation FiiO X3, a device that already performs really well in terms of hiss performance).
Subjectively perceived Sound Quality:
I’m on the objective side of things and not into flowery blah-blah impressions.
Using the headphone output in combination with sensitive and well-resolving in-ears, it sounds subjectively clean and neutral to me, without any flaws, just as it should, which is frankly no surprise at all. Compared to devices such as my REM ADI-2 DAC or the FiiO Q5 (with the AM1 module), it may appear just a little softer/”smoother” or ever so slightly less “transparent” in comparison, but it’s just a nuance and nothing I would care about in an everyday scenario (if I don’t imagine it, it would be small enough that I wouldn’t care).
Using the line out (or less sensitive in-ears/headphones), it cannot be distinguished from other devices anymore.
Conclusion:
The FiiO K3 is small, looks good, has got the great advantage of perfect channel matching thanks to its digitally implemented volume control and shows reasonably good to very good performance in all of the audio-related departments (still reasonably low output impedance, still reasonably good hiss performance with very sensitive in-ears, flat and neutral sound output, precise volume control). The only thing that doesn’t fit into the picture of a nice audio device that it is otherwise, is that it outputs one or two popping/thumping noises right when the playback starts/a few seconds after it stops (especially audible through the line out), which is due to its automatic muting/un-muting of the output.