The Topping NX1 headphone amp doesn’t amplify as much as I had hoped (the Samsung S5 doesn’t output much and the Beyerdynamic T-90 is hungry), but for less than 30 Euro, it’s a keeper. Good sound, plus enough knobs to twiddle.
Having the headphone plug on the left bugs me (should have been on the right), but that’s about it. It’s supposed to keep chugging away for a minimum of 50 hours, and that’s after about 2 hours of charging. Not bad at all.
P.S.: To have the headphone plug on the right, I flipped the amp over.