I recently got a 15 watts spider III and am because It's new and very different from my past amp (a small starter amp) I don't really know how to work certain parts of it.

My first Problem is the feedback. I plug in my guitar (Semi-acoustic Fender 60 - CE) and if I try the crunch setting (easily my favourite) I can play totally normally with the volume up to about 5. If I go past 5 on the volume knobs, i get HEAVY feedback which is just really loud noise. I have tried loads of different methods and none seen to work so help or suggestions would be hugely appreciated. It is not just the guitar as I've tried my electric and that has the same problems.

The second problem is probably just my lack of knowledge. Can you create a custom tone on the 15 watt amp / do you have to use a computer?