Norbert Brainin ( March 12 , 1923 â `` April 10 2005 ) was the first violinist of the Amadeus Quartet , one of the world 's most highly regarded string quartets . Norbert Brainin , ( March 12 , 1923 â `` April 10 , 2005 ) , was the first violinist of the Amadeus Quartet , one of the world 's most highly regarded string quartets .