I just built a sonosub (one tempest, wired to 4 ohms), and I finally got the amp for it today. The amp is a mackie 1400i pro amp, so it has the standard fare .25" balanced/unbalanced, and balanced XLR inputs. I consulted a previous post, and I'm hooking it to my receiver with an acoustic research RCA cable to the sub-out, with the other end going into an RCA to .25" phono adapter (into the bridged ch). All settings are correct (set to bridged, low cut filter off, etc.), and the amp seems fine (powers up, shows sig present when there is one). However, when I give it a signal, and slowly turn the amp's gain up from 0, it only makes a humming noise! I also called a Mackie tech, and he mentioned that if I pull out the RCA from the back, and the humming stops, then it's probably not a problem with the amp (which is the case). And I know my receiver is working fine because I had it hooked up to a velodyne va1215 just before trying this. For informational purposes, i use an Integra DTR-7 (basically an onkyo 777), and the adapter i'm using is an RCA (brand) bought at home depot that has only one black band on the phono tip (this is mono right?). Please help guys, this is killing me!