I'd like to know what metal the case of the Electrocompaniet AW75 (pictured) is made of. I think it's steel, but it might be aluminium instead. I am interested because I have two amps. One is an AW100 (using a 1mm case which seems to be aluminium) and the other's an AW75 which has the thick 4mm case (as pictured). I've seen a lot of AW100s which had the thick case, like the one in the picture (although I know the amp in the picture has AW75 on the back).