A 7day, 1 zone pass is €10.60 . Just go to the GVB office across from Centraal Station and ask for a 7 day season ticket. You'll need to bring with a passport size photo and they'll make up a transit i.d. card for you and sell you the ticket. The id card is good for 5 years. There's more info at
http://tinyurl.com/bcjzf . By the way, the passes are good on the tram, buses and metro but not the night buses.