 In addition to this list, there are youth choir collections (sheet music for use by churches) which include studio recordings of professional singers and musicians performing those versions.There are several solo projects by members of Petra, namely those of Greg X. Volz (lead vocals, 1977–1985), John Lawry (keyboards & vocals, 1985–1995), and John Schlitt (lead vocals, 1986–2005, 2010–present).John Elefante, co-producer of Petra, also brought out a few albums.