Review on 🎧 Portable Headphone Amplifier with Bass Boost - Mini Headphone Booster with Volume Control, Rechargeable Battery, Durable Metal Casing, USB/Stereo Cables - Compatible with iPod, MP3 Players, Laptops, and Mobile Phones - Pyle PHE5AB by Kenneth Rich

This headphone amp has amazing electronics, so unfortunately Pyle put a dead battery in it. I would give 6 stars if the battery wasn't bad. I bought a new one that was broken (bad battery) so I returned it. But I liked the sound. So I bought a half price returned unit that also had a bad battery and I installed a battery from a cheap MP3 player I already had. Now it runs for several days on battery power. I have gain, of course, but also an EQ mode that sweetens even the cheapest headphones and rocks the most expensive ones. Also, these little amps solve a BIG headphone problem, impedance mismatch. While it doesn't really fix anything, the output is designed to make headphones play well from 8 to 40 ohms, with the gain and EQ adding to the enjoyment. I also use this on an airplane with a dual volume headphone splitter. Now my wife and I have enough volume to hear the movie we are watching together. So for the electronic functionality I give 5 stars, for the battery defect I give zero stars.