Let's take a short look at the history of the bass. Then it might be easier to choose some groundbreaking instruments.   Gamba family: fretless or frets, multi-string instruments double bass: fretless or frets, multi-string instruments   1910 Gibson: Mandobass   1931 George Beauchamp & Adolph Rickenbacker: frying pan and the horseshoe pickup 1936 Audiovox: fretted electric bass   1940's Ampeg (amplified peg) 1951 Clarence Leo Fender: