Adding AO shader to other shaders properly?

I’ve been trying to add the Ambient Occlusion shader to a simple diffuse, but I haven’t been able to get the result I want.
Is there a way to multiply or add the black shadows to the diffuse shader while masking out the white?

My node setup has an AO shader plugged into a Mix node followed by a diffuse with a checker pattern on it.

-and I want to stay away from Vertex Painting! :no: