which direct object does not require the personal a

In Spanish, the direct object pronouns "lo" and "la" do not require the use of the personal "a" before them.

For example:
- Voy a visitar a mi amigo (I am going to visit my friend)
- Lo voy a visitar (I am going to visit him)

In this case, "mi amigo" requires the personal "a" while "lo" does not.