The Mule is mellower than the Riff Raff but not dull! I have a Mule with my Emerald and love the sound. I put the Stormy Monday with the Riff Raff (actually Tim chose the combination - not me!). I wonder if it is the soldering? If you have a bad joint you could still get signal, but loose the top end because I think air in the joint acts like a capacitor (HJM will probably come in here and say I'm talking a load of b*ll*cks - but I am sure I heard this).