inputs.text: great amp - great nice amp small powerful device thats simple install worth money give 5 stars no background hiss powerful add small size winnerthe hiss referring actually every amp tried price point subtle many people not big deal not referring large loud hiss wiring etc general background noise amp quality generally pdx f4 not hiss background noise hear amazingi returned mrxf65 fior pdx f4 though pdx f4 sightly lower rated power sounds noticeably better even louder mrxf65if deciding whether 3500 5500 worth pdx f4 teh mrx f65 definitely slight background noise heard mrxf65 amp inaudible using pdx f4 anyone says snr difference meaningless wrong least case higher snr pdx f4 mrxf65 paper actually translates huge difference type music quiet silent background cari tested several amp anoung alpine mrxf65 cost 3500 less today getting pdx f4 amounted large gain sound qualitybackground sound dead silent small amount money scheme 200000 car stereo systemmrxf65 good 26900 today solid amp great long gain set correctly clipdid extended usage higher volumes pdxf4 great 30400 today silent background useable power gain set bit higher mrx f65 no clipping extended loud volume sessionsi verified buyer mrxf65 pdxf4 hooked car listened cd songs virtually side side used iasca official sound quality reference cd suggest anyone really wants test tune system get cd although cd testing setting car audio system also demonstrates differences amps speakers etc luxury different things test side sideor buy items return not sound best playing first track instantly showed alpine pdx f4 better alpine mrxf65 fair margin iasca test cd nice complement competition bass test cds easily found amazoni wholeheartedly recommend alpine pdx f4ally side side used iasca official sound quality reference cd suggest anyone really wants test tune system get cd although cd testing setting car audio system also demonstrates differences amps speakers etc luxury different things test side sideor buy items return not sound best playing first track instantly showed alpine pdx f4 better alpine mrxf65 fair margin iasca test cd nice complement competition bass test cds easily found amazoni wholeheartedly recommend alpine pdx f4