What mostly amazed me about this guy was not the quality of the sound itself. More the peacefulness and grace that surrounded him when he quietly entered the tube, set up the portable amplifier, connected his electrical violine and then started playing without any announcement.
I could really feel that he was proud about what he was doing. Probably not many people in the carriage with "proper" jobs could say the same about their line of work.
And I will also never forget his passionate happy expression while fiddling away.
Needless to say the hew got a few quid of my hardearned money. I love buskers like that.