i have a crappy silvertone 26 watt GUITAR amp. control from left to right: input jack, "overdrive" knob, "drive" button, "level" volume knob, "treble" knob, "bass" knob, "tape/CD" jack, "phones" jack, power switch. sounds really bad, and gives a lot of feedback when playing. even more crappy feedback and buzz if i use the drive and overdrive. how can i mod my amp to be useable?