Coffee Maker Built In Grinder

i have bought three different brands of coffee, new coffee maker and even store bought water, my coffee always tastes bitter, thought it was me but when i go out the coffee at the restaurant tastes great. my new coffee maker even has a filter built in for the water so it tastes better, but i'd never know it. i even tried a little salt in the grounds and bought a coffee grinder to grind fresh coffee. help me, i love coffee and don't know what i'm doing wrong. thanks.