This doesn't appear to be a ground loop issue but please correct me if i'm wrong.
When I power on my 65" Panasonic VIERA TC-P65VT50 plasma TV, it causes both my subs to have an very noticeable oscillating hum. It seems worse with a bright / white screen. With a black screen, the hum is not noticeable. No other part of system needs to be powered on or connected. The amps, pre-pro, BD player are all unplugged from the wall. I don't have a cable box. The subs do not have their XLR cables connected to the pre-pro. All i am talking about here are the power cords for TV and subs. All I have to do is power on the TV and pick a white screen and the sub hum starts. One complete cycle of the audible hum takes around 8 seconds. There are about 2 seconds out of the 8 seconds where the subs are silent. Eight seconds is a bit weird for cycle time but i'm not a plasma expert.
The TV has a three prong power cord and so do the subs. If I plug both the TV and the subs into a power strip so that they all use same wall outlet, hum is still there. If I plug TV into an outlet across the room, far away from wall/outlet with sub but still same circuit, hum is still there. It seems that if I plug TV and subs into same outlet or different outlets in the room, the hum is always there. All I need to do to get rid of hum is turn TV off or make the screen black.
If I put 65" plasma TV on a different circuit in the house than the subs in HT room (i had to go out of HT room to an adjacent room with a really long extension cord), the very loud oscillating subwoofer hum that is audible with a white screen completely disappears and is replaced with a constant hum that is only barely noticeable with my ear right up against the subwoofer. The subwoofers appear completely silent when i'm at the MLP. It is a huge improvement.
So apparently, the plasma on white screen draws enough power for the subs to generate a hum.
The HT room is on a normal 20 amp circuit.
The breaker has never tripped while playing loud bass heavy movies but i am curious how close to 20 amps i am getting.
Possibly dumb question:
Can the 65" plasma TV on a white screen cause a big enough voltage drop in the room circuit that the subs "see" it and produce a hum? Why is the hum cycle time 8 seconds?
thanks in advance
When I power on my 65" Panasonic VIERA TC-P65VT50 plasma TV, it causes both my subs to have an very noticeable oscillating hum. It seems worse with a bright / white screen. With a black screen, the hum is not noticeable. No other part of system needs to be powered on or connected. The amps, pre-pro, BD player are all unplugged from the wall. I don't have a cable box. The subs do not have their XLR cables connected to the pre-pro. All i am talking about here are the power cords for TV and subs. All I have to do is power on the TV and pick a white screen and the sub hum starts. One complete cycle of the audible hum takes around 8 seconds. There are about 2 seconds out of the 8 seconds where the subs are silent. Eight seconds is a bit weird for cycle time but i'm not a plasma expert.
The TV has a three prong power cord and so do the subs. If I plug both the TV and the subs into a power strip so that they all use same wall outlet, hum is still there. If I plug TV into an outlet across the room, far away from wall/outlet with sub but still same circuit, hum is still there. It seems that if I plug TV and subs into same outlet or different outlets in the room, the hum is always there. All I need to do to get rid of hum is turn TV off or make the screen black.
If I put 65" plasma TV on a different circuit in the house than the subs in HT room (i had to go out of HT room to an adjacent room with a really long extension cord), the very loud oscillating subwoofer hum that is audible with a white screen completely disappears and is replaced with a constant hum that is only barely noticeable with my ear right up against the subwoofer. The subwoofers appear completely silent when i'm at the MLP. It is a huge improvement.
So apparently, the plasma on white screen draws enough power for the subs to generate a hum.
The HT room is on a normal 20 amp circuit.
The breaker has never tripped while playing loud bass heavy movies but i am curious how close to 20 amps i am getting.
Possibly dumb question:
Can the 65" plasma TV on a white screen cause a big enough voltage drop in the room circuit that the subs "see" it and produce a hum? Why is the hum cycle time 8 seconds?
thanks in advance
