OCT-BASS/4 Esteve Special Model contrabass guitar RB-60-E Richwood acoustic bass guitar RB-60-EBK Richwood acoustic bass guitar RTB-80 Richwood acoustic travel bass 620mm scale RTB-80-BK Richwood acoustic travel bass 620mm scale RB-102-CE Richwood acoustic bass guitar RB-102-CEBK Richwood acoustic bass guitar