Getting The Right John Mayer Tone in M5 / M9 / M13 Posted January 30, 2014 Apart from what is in the fingers of the player which is at the top of the list. From what I have gleened over the years with big acts with a tech staff, you'll find the Amps are highly modified. Many use rare and very expensive rack FX it not uncommon for their techs to own what gets used. Some of those harmonizer FX spacial FX are expensive boxes. Make no mistake about it. Hopefully you can make some sort of semblance with what you got.