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STurtle · 24-10-2009, 17:24

Whenever my VirginMedia ScientificAtlanta 4200DVB is connected to my brand new A/V surround receiver, the subwoofer starts to hum loudly.

How do I fix this?

So I eagerly unwrapped my surround receiver today - and was immediatly greeted by this bad ground humming. So I disconnected my equipment piecewise to determine the culprit. Expecting some kind of bad ground, I started pulling power plugs, especially unrelated light equipment connected to the same socket, and to my surprise the humming only immediately stopped once I unplugged the set-top box. This is surprising, the SA 4200DVB only has a two wire connection, without any ground! The STB, receiver and powered subwoofer were the only devices connected to that mains outlet.

Of course, it has grounding through the cable, so I unplugged this, too, but this did not affect the humming noise.

So all I need to re-produce the annoying humming in the powered subwoofer is to connect the STB to the mains and run one cable from the STB to the AV-Receiver. Everything else unplugged, including the outside cable from VirginMedia. The cable from the STB is a SCART to Composite+Stereo adapter. I tried three different adapters. It is enough to connect any single RCA-plug (video, left or right) to produce the humming, so it is the shielding somehow, but I wonder how, since there is no other ground going to the STB.

Of course, TOSLINK cable for digitial audio does not affect the humming at all, but how do I get the picture across? Are there any galvanic isolators for RCA or SCART plugs?

Or is my STB simply

Any help greatly appreciated!

24-10-2009, 17:24	#1
STurtle Inactive Join Date: Dec 2007 Posts: 21	STB + AV Receiver = Subwoofer Humming? Whenever my VirginMedia ScientificAtlanta 4200DVB is connected to my brand new A/V surround receiver, the subwoofer starts to hum loudly. How do I fix this? So I eagerly unwrapped my surround receiver today - and was immediatly greeted by this bad ground humming. So I disconnected my equipment piecewise to determine the culprit. Expecting some kind of bad ground, I started pulling power plugs, especially unrelated light equipment connected to the same socket, and to my surprise the humming only immediately stopped once I unplugged the set-top box. This is surprising, the SA 4200DVB only has a two wire connection, without any ground! The STB, receiver and powered subwoofer were the only devices connected to that mains outlet. Of course, it has grounding through the cable, so I unplugged this, too, but this did not affect the humming noise. So all I need to re-produce the annoying humming in the powered subwoofer is to connect the STB to the mains and run one cable from the STB to the AV-Receiver. Everything else unplugged, including the outside cable from VirginMedia. The cable from the STB is a SCART to Composite+Stereo adapter. I tried three different adapters. It is enough to connect any single RCA-plug (video, left or right) to produce the humming, so it is the shielding somehow, but I wonder how, since there is no other ground going to the STB. Of course, TOSLINK cable for digitial audio does not affect the humming at all, but how do I get the picture across? Are there any galvanic isolators for RCA or SCART plugs? Or is my STB simply Any help greatly appreciated!