Tone Amplified! With its deluxe appointments and Fishman® Nashville pickup, the Bobtail Square-Neck stands out in the mix in multiple ways. The vital feature of all Gretsch resonator guitars is the Grestch Ampli-Sonic™ diaphragm (resonator cone), which is hand-spun in Eastern Europe from nearly 99 percent pure aluminium, yielding an impressive quality and volume of tone.