The manufacturer is actually mainly a child's electronic toy kit supplier.
I like the package design.
Comes with a 3.5 mm male to 3.5 mm male cable.
No rubber feet attached or included.
Good build quality.
Rather boring/uninspired design.
Two-piece shell design with one knurled screw on the back to open the case.
Runs on four normal AA batteries, which I think is very nice. Quite impressive battery life of more than 50 hours (Eneloop Panasonic 3MCCE 1.2 V, 1900 mAh rechargeable batteries, Superlux HD681 headphone as load, low gain, volume set to 1 o'clock).
Battery indicator ("Virtual Triode" illumination turns from green to red when the batteries are running out of capacity).
Two-stage gain switch.
Volume control:
Analogue volume control with the typical disadvantages that come with it compared to digitally implemented volume control solutions (some varying channel imbalance at low volume settings that).
Potentiometer also acts as on/off switch.
Used with sensitive in-ears, I don't find the volume control to be precise enough at low potentiometer settings. Nah, it's better suited for full-sized headphones.
Sound:
-1 dB gain in Low Gain mode and +9.5 dB in High Gain mode.
Discrete amplification circuit with additional circuit that adds some 2nd-order distortion to the sound in order to mimic the tube amplifier experience. Elekit refers to it as being "trioderized".
Frequency Response (no Load):
Just as flat as it should be.
Output Impedance:
Based on the frequency response deviation of my usual critical load (my Ultimate Ears Triple.Fi 10), the calculated output impedance is just a tad below 2 Ohms.
Hiss Performance:
Quite hissy with near-extremely sensitive in-ears such as my Shure SE846 or Ostry KC06A; only moderately less hiss than the iBasso DX80's hissy headphone output.
Pretty much hiss-free with my less sensitive Sennheiser IE 800 or full-sized headphones.
Moderate hiss with in-ears such as my Ultimate Ears Reference Monitors or Triple.Fi 10.
Subjective Listening Impressions:
The effect of the "trioderized" circuit that adds some 2nd-order distortion to the signal is much more gentle than expected. Definitely much more subtle that what I had initially expected - I'd even go as far to say that it is rather close to the point of being indistinguishable unless directly compared to its connected source device without any added distortion.
What is noticeable to me is that compared to the originally connected source device, the soundstage output of the TU-HP02 appear somewhat narrower, however with a bit of added depth so that it even adds a bit of spatial depth to my Ultimate Ears Triple.Fi 10's rather flat but wide stage.
In addition, when directly compared to the source device, high notes appear subjectively just a tad softer - the amplitude remains the same, however "splashy" sounding treble and cymbal attacks are just a bit more "spread".
So yeah, just a mild difference and something that's only really distinguishable in a direct comparison with the source device that the amplifier is connected to.
Conclusion:
Interesting concept. Would be even cooler if there were a way to disable or change the amount of the added distortion.
Overall it is a solid headphone amplifier, but there are better alternatives as pure portable headphone amplifiers available at around the same price.