https://www.cnet.com/reviews/headroom-airhead-review/

The AirHead portable headphone amp boosts the output and sound quality of the puny amplifiers in iPods and MP3 and portable CD players--and it works like a charm, although some users may find it too bulky. HeadRoom sells the AirHead online for $149.

This little amp is nonetheless slightly larger than an iPod--it measures 2.875 inches wide, 1 inch high, and 4.125 inches deep, and it weighs less than a pound fully loaded with 4 AAA batteries. That extra heft helps explain why the AirHead so easily betters the flyweight amps built into portable players.

4 AAA batteries babyyy