After some years, the professional power amplifier portion of the business overtook the production of guitar amplifiers. Meanwhile, QSC developed more conventional sales channels in retail music and pro audio stores and also started working with export distributors. Beginning in the early 1980s, Pat Quilter pursued his interest in more electrically efficient methods of power amplification by refining class G (and later, class H) technology as an extension of class AB, primarily for higher-power models.