Yankoulov showed interest in percussion instruments at a very young age. At the age of 10 he was the youngest drummer in his town's brass band (Elin Pelin). Meanwhile, Stoyan formed an amateur pop-rock band called Astronax (Bulgarian: Астронакс) in which he played drums. Their repertoire included songs by Supermax, Kiss, Deep Purple, Uriah Heep, Shturtzite, FSB, etc., but no original songs. His time with the band helped develop his sense of rhythm and gave him the confidence to be the spine of his group performances. Already engulfed in the world of percussion, Stoyan also continued piano lessons, which he had begun at age 8.