Joyo I-Plug Guitar Headphone Pocket Amplifier Amp with Built-in Overdrive Sound Effects for Iphone Ipad Ipod IOS / Android Windows Phone with headphone output built-in overdrive sound effects serve as a mini audio card when connected to smart devices such as Iphone, Ipad, Ipod,Android/Windows phones use this system to record your practice or performance has one mono Jack(6.35mm), one 4-pin 3.5 jack, 3.5mm stereo headphone output, a 3v battery, The control panel has a drive knob, a tone knob and a volume knob!