https://www.youtube.com/watch?v=XI_lik00SMI&list=RDXI_lik00SMI&start_radio=1 John Mayer occasionally sits in with the remnants of The Grateful Dead. Killer version of "Bertha". Great Mayer solo from 2:50 clear through to 6:00. At the 5:00 mark he stomps down on a boost or OD pedal and gets a nice kick to the solo. One can almost imagine Jerry Garcia playing this solo. Mayer is one bad-a*s git player. Check out Mayer's heavily-modded guitar with a bunch of switches between the Tone and Volume controls.