Kojak is right about the a5 in the gibson 57...but if its for another guitar then an SD59 will give extended and firmer bass as well as much more treble detail. its a great pickup - not really what you'd call similar tho, but similar in output. However, if you want the a2 smoothness, you can steal the a2 pups from the gibson set and make a 59 a2 set for really warm and fat (much nicer than stick gibson 57s) and you can put the a5s from the 59 set into the gibson pups thereby tightening the bass and opening the tops a little too. That way you get two killer sets of pups!