New to forum so if this is in the wrong place let me know. I built a sonosub with a Mach 5 audio mj18. My receiver is an onkyo tx-nr609. I bought a behringer km1700 to use to power the sub. I bought rca to 1/4" adapter cable. But when I have the rca plugged to the sub out (on receiver) and into channel A of the amp and when I power it all on I get a low hum from the sub but it doesn't respond to any music I play. Help me?