You'll probably find some specific info about micing Contra bass's by sifting through this search link:
http://www.google.com/search?hl=en&r...ss&btnG=Search
You'll probably want to run your mic through some sort of mic preamp first and then that could be connected to one of the Ampegs normal front inputs. (possibly the -10DB/try setting your mic preamp's output level very low to start out)
If your Ampeg has a Effects-return or a Poweramp-in jack, a better alternative might be conecting you mic pre through that instead to bypass the combos preamp and go directly to its poweramp stage/speakers (possibly with an external eq if you find the Ampeg's is also bypassed this way)
