What is the fine-grained topic of the following text: Campbell then embarked on a solo career (also contributing vocals to two Heptones albums), and was a popular roots reggae singer during the 1970s, recording for producers such as Phil Pratt, Bunny Lee, and Joe Gibbs, and recorded at Lee Perry's Black Ark studio. Only return the topic.
Campbell's solo career in roots reggae during the 1970s