Conventional　half　bridge　class-D　audio　amplifier　(HB-CDAA)　systems　typically　suffer　from　serious　bus-voltage　pumping.　Such　a　bus-voltage　pumping　increases　the　device　stress　and　deteriorates　the　total　harmonic　distortion　and　noise　(THD+N)　of　HB-CDAA.　To　reduce　the　bus-voltage　pumping　of　HB-CDAA　system,　large　electrolytic　capacitors　are　usually　required　at　the　input　of　downstream　HB-CDAA,　which　seriously　affects　the　power　density　of　HB-CDAA　system.　In　this　article,　an　electrolytic　capacitor-free　HB-CDAA　system　without　bus-voltage　pumping　is　proposed,　which　consists　of　a　front-end　bipolar-symmetric-outputs　(BSO)　bidirectional　dc-dc　converter　and　a　downstream　HB-CDAA.　By　providing　a　bidirectional　current　flowing　path　in　the　front-end　dc-dc　converter,　the　bus-voltage　pumping　of　the　HB-CDAA　system　is　eliminated　without　using　large　electrolytic　capacitors.　Zero　voltage　switching　(ZVS)　of　all　switches　in　the　front-end　BSO　dc-dc　converter　can　be　achieved　over　the　full　audio　load　range.　Compared　with　the　HB-CDAA　system　with　a　unidirectional　front-end　dc-dc　converter,　the　proposed　audio　amplifier　system　benefits　from　high　power　density,　low-output　voltage　THD+N,　and　voltage　stress　of　switches.　The　bus-voltage　pumping　problem　is　identified,　the　operation　of　the　proposed　HB-CDAA　system　is　analyzed,　and　the　design　parameters　of　the　converter　are　derived　to　ensure　ZVS　of　all　switches.　Experimental　results　with　a　40-W　prototype　of　the　proposed　audio　amplifier　system　are　presented　to　verify　the　design.