Gig Savers: Harmonica: Amplifiers The Gig Savers series has been designed to give studying harmonica players answers to common questions in a brief, affordable, yet informative fashion. Harmonica Amplifiers is the first published book to specifically cover harmonica amplifiers and their usage. Areas covered are: the head, EQ and effects section, speakers, extension cabinets, tube substitutions, amp size for venue and controlling feedback, and matching an amplifier with a microphone.