This will be hard for some to believe, but I just finished a workout for 4 weeks where all I did for back was pull ups. I did 4 sets each of wide grip, close grip palms in, close grip palm facing each other, and regular grip palms away. I did 1 set with no weight, then the following three with the dip belt and 25lbs-45lbs hanging. It was one of the best back workouts I ever did. The only time I was on machines was for warmup. It puts a lot of stress on your shoulders.