The NFB loop takes its ground reference from wherever your presence pot is grounded at the PI end and from the speaker terminals at the OT end, so there is the possibility of a ground loop if there is a difference in potential between the two. The fact that you are using a stand-off for your speaker jacks which is riveted to the chassis could make this more likely.soma_hero wrote:Excellent. Thanks for that, I didn't even think about it. Also, what do you mean by NFB ground? Do you mean the speaker out jacks grounding, because the NFB loop isn't grounded anywhere....paulster wrote:Once you fix that you might also want to check your NFB ground as that's relying on the riveted connection between the speaker jack panel and the chassis. That's a lesser problem than what you've already got though.
If it turns out to be an issue for you, use insulated speaker jacks and, as well as the NFB wire, run a ground connection from the speaker jacks back inside the main chassis to the presence pot ground or your PI ground stage.