E02i is one kind of multifunctional portable headphone amplifier which is specially designed for products from APPLE Company. Connecting with headphone output jack of iPhone can not only improve sound quality and but also realize all functions of original line-control headphone.
It is a update to the aging E1 and E3 designs. It features a small size but packed with features. It has a built in headphone amplifier, "High SNR" Microphone, bass boost, bypass option, 10 hour battery, inline control compatible with iPhone, metal shielding to better "shield the disturbance"(EMI presumably), and "excellent circuit design".