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#1
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60Hz (ground loop?)
I'm having some nasty 60Hz hum which I don't know how to avoid. I'm hoping someone here can help. I've reduced the problem to this: RCN Coax +-------------------+ RCA Audio +----------+ /| ========| Digital Cable Box +=+=========+|Audio Amp +=[] | RF in | ("off") | | : +----------+ \| +-------------------+ | : +-+ : Ground A | .......: | : Ground B | : +---------+-+---+ |TV ("off" but | | plugged in)| +---------------+ Ground A and B are just a single conductor connecting the outer conductor of any video input on the TV to the shield at either end of the RCA cable feeding audio from the cable box to the audio amp. When Ground B is connected we get a nasty 60Hz hum. * It doesn't matter whether Ground A is connected or not -- I just put it in the diagram to show that connecting that ground doesn't, by itself, cause the problem -- you need to have a ground connection between the TV and the audio out cable but not right at the cable box. Halfway down the audio cable the ground still causes the hum. * Disconnecting the TV's power plug makes the problem go away * Disconnecting the RF input fromt the cable box makes the problem go away. * We've heard some hum even when the cable box's power plug is unplugged, though it gets worse when it's plugged in. * The problem happens with any audio amp or speaker. * I wrote "off" above because as you know most devices these days are never entirely off. On the TV, for example, there's an LED glowing on the front even when it's off. * We're using only high-quality monster cable to connect everything. In case you're wondering, we need to connect ground B if we want to switch video from the cable box and a VCR through our receiver, which does video routing. Thanks in advance, -- Dave Abrahams Boost Consulting www.boost-consulting.com |
#2
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60Hz (ground loop?)
I suspect that the biggest problem is the ground loop leg going up the RCN coax since it is grounded so far away. The fact that removing it corrects the situation is evidence of this. Nearly all of the problems that occur similar to yours can usually be fixed by isolating the coax ground using a quality wide-band isolation transformer such as Jensen's VRD-1FF. There is a picture of one and you can order them from:
http://www.jensen-transformers.com/ Hope this helps - Jeff David Abrahams wrote: I'm having some nasty 60Hz hum which I don't know how to avoid. I'm hoping someone here can help. I've reduced the problem to this: RCN Coax +-------------------+ RCA Audio +----------+ /| ========| Digital Cable Box +=+=========+|Audio Amp +=[] | RF in | ("off") | | : +----------+ \| +-------------------+ | : +-+ : Ground A | .......: | : Ground B | : +---------+-+---+ |TV ("off" but | | plugged in)| +---------------+ Ground A and B are just a single conductor connecting the outer conductor of any video input on the TV to the shield at either end of the RCA cable feeding audio from the cable box to the audio amp. When Ground B is connected we get a nasty 60Hz hum. * It doesn't matter whether Ground A is connected or not -- I just put it in the diagram to show that connecting that ground doesn't, by itself, cause the problem -- you need to have a ground connection between the TV and the audio out cable but not right at the cable box. Halfway down the audio cable the ground still causes the hum. * Disconnecting the TV's power plug makes the problem go away * Disconnecting the RF input fromt the cable box makes the problem go away. * We've heard some hum even when the cable box's power plug is unplugged, though it gets worse when it's plugged in. * The problem happens with any audio amp or speaker. * I wrote "off" above because as you know most devices these days are never entirely off. On the TV, for example, there's an LED glowing on the front even when it's off. * We're using only high-quality monster cable to connect everything. In case you're wondering, we need to connect ground B if we want to switch video from the cable box and a VCR through our receiver, which does video routing. Thanks in advance, -- Dave Abrahams Boost Consulting www.boost-consulting.com |
#3
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60Hz (ground loop?)
David Abrahams wrote:
I'm having some nasty 60Hz hum which I don't know how to avoid. I'm hoping someone here can help. I've reduced the problem to this: RCN Coax +-------------------+ RCA Audio +----------+ /| ========| Digital Cable Box +=+=========+|Audio Amp +=[] | RF in | ("off") | | : +----------+ \| +-------------------+ | : +-+ : Ground A | .......: | : Ground B | : +---------+-+---+ |TV ("off" but | | plugged in)| +---------------+ Ground A and B are just a single conductor connecting the outer conductor of any video input on the TV to the shield at either end of the RCA cable feeding audio from the cable box to the audio amp. When Ground B is connected we get a nasty 60Hz hum. * It doesn't matter whether Ground A is connected or not -- I just put it in the diagram to show that connecting that ground doesn't, by itself, cause the problem -- you need to have a ground connection between the TV and the audio out cable but not right at the cable box. Halfway down the audio cable the ground still causes the hum. * Disconnecting the TV's power plug makes the problem go away * Disconnecting the RF input fromt the cable box makes the problem go away. If you would have read ANY of the threads here within the past month that address ground loops, you wouldn't have had to take the time to post all of this. * We've heard some hum even when the cable box's power plug is unplugged, though it gets worse when it's plugged in. * The problem happens with any audio amp or speaker. * I wrote "off" above because as you know most devices these days are never entirely off. On the TV, for example, there's an LED glowing on the front even when it's off. * We're using only high-quality monster cable to connect everything. In case you're wondering, we need to connect ground B if we want to switch video from the cable box and a VCR through our receiver, which does video routing. Thanks in advance, |
#4
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60Hz (ground loop?)
Jeff Wiseman writes:
I suspect that the biggest problem is the ground loop leg going up the RCN coax since it is grounded so far away. The fact that removing it corrects the situation is evidence of this. Nearly all of the problems that occur similar to yours can usually be fixed by isolating the coax ground using a quality wide-band isolation transformer such as Jensen's VRD-1FF. There is a picture of one and you can order them from: http://www.jensen-transformers.com/ Hope this helps Thanks; I was beginning to think that this would be the solution, but it really helps to have someone else say so with a reasonable degree of confidence. I really appreciate your guidance. -- Dave Abrahams Boost Consulting www.boost-consulting.com |
#5
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60Hz (ground loop?)
CJT writes:
If you would have read ANY of the threads here within the past month that address ground loops, you wouldn't have had to take the time to post all of this. [insert cat noise here] -- /"\ ASCII Ribbon Campaign | Todd H \ / | http://www.toddh.net/ X Promoting good netiquette | http://triplethreatband.com/ / \ http://www.toddh.net/netiquette/ | "4 lines suffice." |
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