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#1
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hum and grounding
This could be a little tricky to explain, so I'll try to be as clear as
possible. I'm getting problems with hum, when connecting my audio system to my computer system. I have a conventional stereo system and a PC system (pretty much the usual Wintel stuff, with PCI sound card). The PC has a three-prong cord, with ground. The stereo equipment has the typical polarized 2-prong plugs. (BTW This is North America, 110V.) The PC components all plug into a surge suppressor. I run the tape output from the stereo into the sound card of the PC, and I run the sound card output into the aux input of the stereo receiver. I find that, if I connect all three prongs of the PC equipment (through the surge suppressor) to the wall outlet, I get hum when I listen to the sound card. This seems to happen wherever I plug in the stereo: I can plug it into the surge suppressor, or the same wall receptacle, or a completely different receptacle. I still get hum. The thing that DOES get rid of the hum is to plug the PC system into the wall, separately from the audio stuff, through a 2-prong adapter, thus interrupting the ground connection. That's what I've done in the past. But I've been advised that this offers the PC less protection againsty surges and other line anomalies than using the ground, which is obviously there for a reason anyway. Should I ground the PC case to the stereo case? Will a UPS provide line isolation and thus eliminate the problem? (I've been planning to get one anyway for other reasons.) Or should I just cut out that pecky ground connection, the way I did in the past? --Ron Garrison |
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#2
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hum and grounding
RWG wrote:
This could be a little tricky to explain, so I'll try to be as clear as possible. I'm getting problems with hum, when connecting my audio system to my computer system. I have a conventional stereo system and a PC system (pretty much the usual Wintel stuff, with PCI sound card). The PC has a three-prong cord, with ground. The stereo equipment has the typical polarized 2-prong plugs. (BTW This is North America, 110V.) The PC components all plug into a surge suppressor. I run the tape output from the stereo into the sound card of the PC, and I run the sound card output into the aux input of the stereo receiver. I find that, if I connect all three prongs of the PC equipment (through the surge suppressor) to the wall outlet, I get hum when I listen to the sound card. This seems to happen wherever I plug in the stereo: I can plug it into the surge suppressor, or the same wall receptacle, or a completely different receptacle. I still get hum. The thing that DOES get rid of the hum is to plug the PC system into the wall, separately from the audio stuff, through a 2-prong adapter, thus interrupting the ground connection. That's what I've done in the past. But I've been advised that this offers the PC less protection againsty surges and other line anomalies than using the ground, which is obviously there for a reason anyway. Should I ground the PC case to the stereo case? Will a UPS provide line isolation and thus eliminate the problem? (I've been planning to get one anyway for other reasons.) Or should I just cut out that pecky ground connection, the way I did in the past? --Ron Garrison My 2 cents: Disconnect your cable TV connection from your stereo (assuming they're connected). If that solves it, get a cable isolator. Cable TV is a notorious introducer of hum via ground loops. Strapping the PC case to the stereo case would be a reasonable thing to try, and generally a good idea (since it introduces a safety ground to the stereo). A UPS is overkill, but might also help if you plan to get one anyway. |
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#3
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hum and grounding
CJT writes:
RWG wrote: This could be a little tricky to explain, so I'll try to be as clear as possible. I'm getting problems with hum, when connecting my audio system to my computer system. I have a conventional stereo system and a PC system (pretty much the usual Wintel stuff, with PCI sound card). The PC has a three-prong cord, with ground. The stereo equipment has the typical polarized 2-prong plugs. (BTW This is North America, 110V.) The PC components all plug into a surge suppressor. I run the tape output from the stereo into the sound card of the PC, and I run the sound card output into the aux input of the stereo receiver. I find that, if I connect all three prongs of the PC equipment (through the surge suppressor) to the wall outlet, I get hum when I listen to the sound card. This seems to happen wherever I plug in the stereo: I can plug it into the surge suppressor, or the same wall receptacle, or a completely different receptacle. I still get hum. The thing that DOES get rid of the hum is to plug the PC system into the wall, separately from the audio stuff, through a 2-prong adapter, thus interrupting the ground connection. That's what I've done in the past. But I've been advised that this offers the PC less protection againsty surges and other line anomalies than using the ground, which is obviously there for a reason anyway. Should I ground the PC case to the stereo case? Will a UPS provide line isolation and thus eliminate the problem? (I've been planning to get one anyway for other reasons.) Or should I just cut out that pecky ground connection, the way I did in the past? --Ron Garrison My 2 cents: Disconnect your cable TV connection from your stereo (assuming they're connected). If that solves it, get a cable isolator. Cable TV is a notorious introducer of hum via ground loops. This is the most common problem in this kind of systems. If you still need the cable TV connection, buy a suitable signal isolator for the cable TV signal, so you get the cable signal through without causing the humming. What applies to the cable TV connection applies to all common antenna systems, because they tend to be all grounded, and usually at some different place where your PC is (and this causes potential difference that is heard as humming). Strapping the PC case to the stereo case would be a reasonable thing to try, and generally a good idea (since it introduces a safety ground to the stereo). Usually this does not help in solving the hummign problem. A UPS is overkill, but might also help if you plan to get one anyway. UPS does not generally help in any this kind of ground loop problems. -- Tomi Engdahl (http://www.iki.fi/then/) Take a look at my electronics web links and documents at http://www.epanorama.net/ |
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#4
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hum and grounding
Ron,
Agree with Flint: you need an audio isolation transformer. Jenson makes good ones, but if the highest quality is not important - for example, if the connection is in the monitor path only - you could probably get away with a less expensive unit like the EbTech Hum Eliminator. --Ethan |
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#5
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hum and grounding
Thanks to everyone for the quick replies!
The cable TV might be a contributor, and I'll check it out. I really hadn't thought of that. I like the idea of the UPS if it will provide isolation, as it won't affect the stereo (unless I plug that into it too), so I don't have to worry about it softening the voltage regulation for the power amp. And I'm planning to get one anyway, so it's the old 2-birds-one-stone thing. For now, I think the first thing I'll do is strap the PC and receiver cases together. BTW don't a lot of receivers have 3-prong cords, at least the bigger ones? |
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#6
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hum and grounding
In , on 08/18/03
at 01:05 PM, "RWG" said: Thanks to everyone for the quick replies! The cable TV might be a contributor, and I'll check it out. I really hadn't thought of that. Cable systems are the most likely cause of this sort of problem, followed closely by PC's. The combination of PC and cable system is deadly. Actually, it takes two or more to play this game. You need a unit that is a bad neighbor by polluting the ground and you need a poorly designed partner that is offended by that ground pollution. (In the case of the cable system, that bad neighbor could be down the block.) While there are certainly good and bad designs, home audio equipment is more susceptible to this sort of problem than professional gear. Pro gear uses a much more expensive interconnection scheme that is less prone to this sort of mishap. (And studios are carefully designed to avoid grounding problems -- home audio systems are mostly haphazard interconnections.) I like the idea of the UPS if it will provide isolation, as it won't affect the stereo (unless I plug that into it too), so I don't have to worry about it softening the voltage regulation for the power amp. And I'm planning to get one anyway, so it's the old 2-birds-one-stone thing. You will compromise your protection somewhat if you plug signal cables from an unprotected device into a protected device. "Device" includes PC, stereo, phone line, cable system, TV, external TV antenna, Satellite dish, etc. For now, I think the first thing I'll do is strap the PC and receiver cases together. BTW don't a lot of receivers have 3-prong cords, at least the bigger ones? Some do, but as you've found out, that 3rd prong can cause heartburn. ----------------------------------------------------------- SPAM: wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15 13 (Barry Mann) [sorry about the puzzle, SPAMers are ruining my mailbox] ----------------------------------------------------------- |
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#7
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hum and grounding
Sounds like there are more aspects to this than I had guessed, particuarly
the cable TV element. And the cable TV part sounds like it has no easy cure, if I want to run its sound into my stereo. The idea of digital interconnections, using fiber optics, also looks better all the time. (-; |
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#9
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hum and grounding
In , on 08/18/03
at 06:35 PM, (Dave Platt) said: [ ... ] Well, today I had to do it again. I went to Rat Shack and bought two baluns -- an "inline" one with a female F-connector and pigtails for the 300-ohm lead, and a compact one with a push-on male F connector and screw terminals for the 300-ohm side. (This type is often supplied with TV sets.) Before hooking things up, I got out my trusty Fluke and measured the baluns. (Gasp, what a concept!) It turns out that the in-line one is a true transformer -- there's no common connection between the 300 ohm and 75 ohm sides. The compact one does have a common connection, but of course any single break in the "ground" chain is sufficient. [ ... ] Years ago, I had to make my own cable TV isolators. Rather than trying to explain to the electronics store counter person what I was attempting to accomplish, I asked for them to fetch a pile of baluns, which I then sorted through with my Ohmmeter. To them, all baluns were alike (a mystery) and they could not understand why I only wanted certain ones. ----------------------------------------------------------- SPAM: wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15 13 (Barry Mann) [sorry about the puzzle, SPAMers are ruining my mailbox] ----------------------------------------------------------- |
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#10
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hum and grounding
I use the Jensen CATV isolation product. Works perfectly.
Also, I have yet to see anyone hook up a PC to a stereo without getting a serious hum problem that can be easily fixed with an audio isolation transformer. I have several spares in my house for testing and in case a visiting friend wants to hook his notebook to my audio system. - Flint "RWG" wrote in message ... Sounds like there are more aspects to this than I had guessed, particuarly the cable TV element. And the cable TV part sounds like it has no easy cure, if I want to run its sound into my stereo. The idea of digital interconnections, using fiber optics, also looks better all the time. (-; |
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#11
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hum and grounding
I use the Jensen CATV isolation product. Works perfectly.
I tried hooking my laptop up to my receiver today to play RealOne Rhapsody over my audio system. Of course, I experienced hum. What specific Jensen CATV isolation product would you recommend? Does the isolator go between the laptop and the receiver? BTW, I do have audio from my cable box connected to my receiver. |
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#12
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hum and grounding
I have never found that a UPS can cure a hum problem.
The only AC power device I know if that cures hum issues is a "Balanced Power" conditioner. These are expensive, and everything in your rig needs to be plugged into the power conditioner. Not simple, but very effective. - FLINT "RWG" wrote in message ... Thanks to everyone for the quick replies! The cable TV might be a contributor, and I'll check it out. I really hadn't thought of that. I like the idea of the UPS if it will provide isolation, as it won't affect the stereo (unless I plug that into it too), so I don't have to worry about it softening the voltage regulation for the power amp. And I'm planning to get one anyway, so it's the old 2-birds-one-stone thing. For now, I think the first thing I'll do is strap the PC and receiver cases together. BTW don't a lot of receivers have 3-prong cords, at least the bigger ones? |
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#13
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hum and grounding
"RWG" writes:
Thanks to everyone for the quick replies! The cable TV might be a contributor, and I'll check it out. I really hadn't thought of that. I like the idea of the UPS if it will provide isolation, as it won't affect the stereo (unless I plug that into it too), so I don't have to worry about it softening the voltage regulation for the power amp. And I'm planning to get one anyway, so it's the old 2-birds-one-stone thing. UPS systems generally do not provide the ground isolation you need. For now, I think the first thing I'll do is strap the PC and receiver cases together. Did it help ? -- Tomi Engdahl (http://www.iki.fi/then/) Take a look at my electronics web links and documents at http://www.epanorama.net/ |
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#14
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hum and grounding
"RWG" writes:
This could be a little tricky to explain, so I'll try to be as clear as possible. I'm getting problems with hum, when connecting my audio system to my computer system. I have a conventional stereo system and a PC system (pretty much the usual Wintel stuff, with PCI sound card). The PC has a three-prong cord, with ground. The stereo equipment has the typical polarized 2-prong plugs. (BTW This is North America, 110V.) The PC components all plug into a surge suppressor. I run the tape output from the stereo into the sound card of the PC, and I run the sound card output into the aux input of the stereo receiver. I find that, if I connect all three prongs of the PC equipment (through the surge suppressor) to the wall outlet, I get hum when I listen to the sound card. This seems to happen wherever I plug in the stereo: I can plug it into the surge suppressor, or the same wall receptacle, or a completely different receptacle. I still get hum. The thing that DOES get rid of the hum is to plug the PC system into the wall, separately from the audio stuff, through a 2-prong adapter, thus interrupting the ground connection. That's what I've done in the past. But I've been advised that this offers the PC less protection againsty surges and other line anomalies than using the ground, which is obviously there for a reason anyway. The PC shoudl be grounded. Do not use those 2-prong adapters, beacause it cuts thr ground. Without the ground the surge suppressor does not work well and the whole ungrounded PC is potential electrical safety risk. Should I ground the PC case to the stereo case? Extra grounding wire from PC to stereo case can help sometimes soemwhat, but usually it does not remove the problem. The problem is elsewhere. http://www.epanorama.net/documents/g...oop/index.html Will a UPS provide line isolation and thus eliminate the problem? Generally UPS does not help in this. The ground connection is continuous through the UPS. It does not change the grounding of the system. (I've been planning to get one anyway for other reasons.) UPS might be OK for those other reasons and a good idea to get it. Or should I just cut out that pecky ground connection, the way I did in the past? No. Read the document http://www.epanorama.net/documents/g...oop/index.html instead. When you understand what is happening, pick a safe method from there to solve this problem. -- Tomi Engdahl (http://www.iki.fi/then/) Take a look at my electronics web links and documents at http://www.epanorama.net/ |
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#15
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hum and grounding
"Tomi Holger Engdahl" wrote in message
... .. .. .. The problem is elsewhere. http://www.epanorama.net/documents/g...oop/index.html Thanks for the URL. I have not read it just yet, but it looks very informative. GOOD NEWS: I disconnected the cable TV/cable Internet connection, and the problem went away completely. (Looking back, I guess the fact that the hum appeared only on the sound card and cable TV inputs to the stereo was a pretty good clue!) My sincere thanks to all those who promoted that theory. I guess I know what I need to do now... --Ron |
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