Brilliant thread, just in time because I installed my Stealthbox and Zapco i-250 amp this week and am getting very low frequency high excursion noise that looks like it will kill my woofer if I don't get rid of the noise. In my case, I'm using speaker level balanced differential inputs on the Zapco amp so no need for a line output converter. I also thought that balanced inputs would be better for noise rejection but I was wrong. Anybody else use speaker level balanced inputs on their Zapco or JL amps?

I wasn't sure at first where to ground the balanced input signal so I called Zapco and the guy said to ground to the amp chassis. He said that was the signal ground and was not the same as grounding to the car chassis. Our stock amps are not easily accessible, so I figured the top amp mounting bolt would be good enough as a amp chassis ground. The noise did get quieter, but is definitely still there. I can hear the cabin lights dim!

Does anyone know if the amp mounting bolts and tabs are conductive enough to be used as grounds? I'm not sure what the amp really looks like because I've never taken it completely out, so maybe there's a better spot to connect to the amp chassis? Better yet, is there a wire from the amp that is acting as a grounding wire that I can tap into? Some previous posts listing the amp (non DSP) pinouts are a little confusing.

I was going to try using a line output converter to see if that would get rid of the noise, but I can see here that people still have noise problems with LOCs.