John Mayer has used two overdrives for decades. The first is almost always a Tubescreamer, but the second? Well, it's changed a lot. On the Trio tour it was the Keeley modded Boss BD-2, then for WTLI he used the Marshall Bluesbreaker MkI, then from 2010 onwards he's used the Klon, with periods in 2019/2021 where he used the SoloDallas Storm.

Here I've done a little comparison of these pedals. It's not perfect, but it may help to show people what the variances are. Everything here was a first take, and not to a clicktrack (I struggle to play well without one) so playing isn't great, apologies!