LM386 will not drive (no sound at all) 12ohm headphones. Input is output of a guitar preamp and coupled with .22uF. Power is 9V battery. I tried all circuit gains per datasheet and varied the 10k input pot. Included 10ohm and .05uF from pin 5 to ground and 250uF at output. Circuit will drive a guitar amp just fine. My goal is to use LM386 as headphone amp. Why can't it drive the headphones?? HELP!!