To make an extremely long story short, I just received a replacement sub for one I've had tons of problems with over the past year and a half. While said problems did center around the power supply, I never had the ground loop hum with it. I also never hooked it up in this method.
I'm running this sub off the speaker level input (can't use my sub preout, another long story). When I first hooked it up it had a ridiculous amount of hum, but after two days of toying with it (removing components from the chain) I've gotten it down. There is one component I can't remove however, and that's the speakers themselves which seem to be the source of this.
When just the sub is hooked to the speaker jacks on my receiver, the auto switching stays off when the power is turned on as it should. when I add my speakers in parallel, I get hum. I moved my system into a different room earlier today, and found that putting the sub on the B outputs pretty much eliminated this, but now that I've got everything back in my room there is still hum even on the B outputs (doesn't matter if the receiver is on or off). I'm not sure what to do at this point.
Is there anything simple I can try to eliminate this? Google hasn't been much help as no one seems to really use speaker level inputs. Thanks...
-Freddie
Edit: Should add that the sub is a Cambridge Soundworks P205. The plug has no ground on it (cable does though....should I cut that off?). I also have a paid-shipping RMA ready to go should that be what gets recommended...But I'd rather make sure it's not my house's wiring first.
Nevermind, think I got it. Started unplugging other things elsewhere in the room (same circuit I guess) and it's silent now. Still confused as to why adding the speakers into the mix was causing hum though.
This seems to be temperamental. Sometimes with the volume all the way up I can turn it on and it will stay off as it should.....but then turn it off and back on again and it will switch on and hum. Maybe what lead me to believe adding speakers in was the cause and that I had fixed it. The hum definitely comes through the sub though....the driver is moving.
I've tried unplugging everything on this circuit and sometimes it won't happen (which makes me think it's fixed) but other times it does. The wiring in my house is awful, especially this part of the house, so I'm thinking that may be the culprit (what do I do in that case? Power conditioner?). No chance of getting a dedicated line at this time unfortunately.
I see lots of things like use/don't use cheater plugs, but the sub itself doesn't have a ground prong on the IEC jack. There's no ground screw on the back (there is a screw on the amp panel....but it's painted so I'm not sure that it would do any good as a ground). I think I am going to send the sub back just in the hope that the one I get back won't do this....but I'm not counting on it. This really is an annoying problem.
freddie, do not assume that the culprit is in the room with you. It could be that the sub is on a different breaker than the rest of your kit is an that something else running on that breaker, could be in another room altogether, might be the culprit. Also, any construction going on in your house recently? A contractor may have drilled a screw or hammered a nail into conduit somewhere causing an unwanted ground.
Try running the sub with an extension cord to another outlet before you ship it back.
I tried the sub on the other side of the house which is on a different circuit and the hum was still there (though it was quieter). This is where adding in the speakers seemed to make it worse.
There has been a bit of construction in the living room where my dad just redid the floors and in the process replaced the recessed outlets there (one of these outlets is what I tried the system on when I moved it). I believe that the back of the house is all on it's own circuit so basically the two outlets in my room, one in the hall, and one-two in my sister's room. There are a few things I didn't unplug which I'll probably try today but I'm not sure those are going to be what solves it.
My outlets are the old style metal box rather than the new plastic ones......Could this be causing it?