This is an old revision of the document!
had a nice page in oldwiki, here's a reboot. im placing it for now.
a lot of the info starts from collinshandmade_electronic_music.pdf, if there is a mention to chapter number bellow, its from this ebook
see: how to make a contact mike: using piezo disks to pick up tiny sounds
homemade-circuits.com/diy-contact-mic-circuit and https://www.youtube.com/watch?v=CKZPcnwD57U
amplification and distortion: a simple circuit that goes from clean preamp to total distortion