Keep in mind that the amp may have been damaged by trying to run it on double voltage. I don't think it will suddenly start working when you do give it the correct voltage. If nothing else, a fuse will have blown. You may need a technician to take a look at it.
It's surprising to me how many consumer electronics products--stuff that uses a transformer already, like laptops, tablets, phone--are able to charge at either 110 or 220. But not your hairdryer (or your amp).
There's a label on the back that states which mains voltage it is designed for, and the amp doesn't seem to have a voltage selector (at least not one that the user can change). You'd need to take it to a tech and have it checked out - if you're really lucky, the mains transformer has a 230v input as well, and it's merely a rewire job + replace the mains fuse with the correct (for 230v) value. If not, you'll need to use a step-down transformer (like this one: http://www.maplin.co.uk/p/maplin-230v-to-110v-300w-voltage-converter-vr05f). And the tech still needs to check it out, in case you damaged something when feeding it twice the mains voltage it was expecting.