Well Im tell all of you mt troubles,I received a Adcom gfa-7807 used balanced inputs with bettercables,the amp buzzed & clicked with no audio at all.Returned it got Adcom 7505 done the same thing! Got another Adcom did it again,this time I returned the Adcom gfa-870hd pre-pro.Could all of this be the xlr cables? Onecall told me they couldnt find anything wrong with the amps or pre-pro!ps when it didnt work with balanced I used rca & it still had the problem! thanks