I just received my new 20-39CS this morning. I wired it up to my Samson S700 via speaker cable and used the 1/4 to rca connector to connect the amp to my Sony DE945 Receiver's sub-out. When I turn on the amp, however, I get a humming but no bass from the sub. If I increase the gain on the amp, the humming increases and if I dial it down, it decreases. Did I do something amiss? I used the channel 1 input and output and used Stereo mode on the S700. Thanks.