I bought Topping NX2 through Ebay for 42USD. It arrived from China to Malaysia in 3 week which is quite fast considering most of my other shipment from China usually took 4-6 weeks.
As usual they provide accessories like mini USB charger, short 3.5mm male to male jack, 5 pairs of round Velcro and 2 stacking band. First impression; it's housing is smaller than I ever imagined. Pictured above with one of my smartphone Samsung Galaxy S advance (2012) which has 4 inch screen.The housing itself was made with metal. There is some small gap at the top plate. Not more than 0.5mm but still noticeable. The top and bottom plate are secured with 4 screws (with Allen key hole) at both side of housing.
Stacking with Samsung Galaxy S advance using provided rubber band. Top and bottom screws used to secure bottom, top plate. Most likely removable with correct Allen key.
The top side of Topping NX2 matched with bottom side of Samsung Galaxy S advance. This was one of the rarest phone with earphone hole at the bottom together with micro USB charging port. This is my favorite combination for ease of charging and listening to music at the same time. Even better if both earphone hole and micro USB port are located at the top but unfortunately not many phone has this kind of combination.On Topping NX2 top plate there is volume control (0-10). Beside that there are aux in hole and earphone out hole. And at the other corner the is short stick for on and off switch. I call it stick because it is not a button and it protruding about 3mm from top plate. There is blue LED button in between the earphone hole to indicate that Topping NX2 is functioning.
Sound;
This is my first ever portable amplifier, so I have no idea how it affecting the sound from headphone/earphone. Generally the end effects are; slightly lowered bass quantity with dampened bass response. So the bass somehow sound less impact-ful and some user commented that it sound muddy (what ever it is). Otherwise the other effects are it widen the soundstage making the sound fuller and heavier. Treble and detail are become slightly more prominent . The end effect/summation making overall sound more engaging and even fun. I tried it on my biggest impedence earphone Audio Technica CKB50 (65 ohm) and Topping NX2 can easily drive it to insanely loud volume.
Power;
The battery last almost forever (or 100hours as claimed by manufacturer). Even when on charging it can still fully functional. Full charging take about 1 hour.
USB DAC;
I tried it on my Acer AIO desktop and old Acer laptop (2007). Both detect Topping NX2 automatically and install the intended driver. All my smartphone has no OTG function so I never tried USB DAC from smartphone.
Conclusion:
I have second thought about this whole amplifier thing. While it generally give a whole new sound to my earphones I think it is better to get a player with built in powerful amplifier. This is why I am missing my late Lenovo S930. Most of the time I only use about 10% of the volume and some loud earphone like Soundmagic E10 already sound too loud with lowest volume. Subsequently I bought HTC Desire 820s. Bad mistake, now I use 40-50% of volume to drive most earphone. With AT CKB50 I even have to use up to 60% volume. Topping NX2 did help with this problem but if I have both player and powerful amplifier it will be great. Maybe there is LG V10 which will cost me an arm and leg.
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