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#1
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Powered monitors ground loop
I installed a pair of bi-amp'd monitors. All seems well
except there is a very faint 60Hz hum present even with the sound card muted. The computer and monitors are plugged into the same outlet, though the computer is hooked to a UPS, not directly to the outlet (as the monitors are). Listening with headphones I don't hear the hum. I even listened through a small battery-powered amp I built for another purpose and there's no hum audible at pretty high gain. So I figure it's a ground loop. A better quality external audio interface is in the future, so I'm not losing much sleep over this yet, but I wonder how I'd go about addressing this since I don't really have the option of "turning the plug around" in this configuration. I'm guessing that the UPS is "turning the plug around" internally somehow. There are not unusued UPS outlets, else I'd attach the monitors to one. I can narrow it down to the UPS by removing it from the picture, but that's quite a hassle. I guess I'll give it a try. I could also fabricate a pair of 1:1 transformers to isolate the monitor inputs, but I wonder how badly that would compromise the sound. Jason |
#2
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Powered monitors ground loop
"jason" wrote in message .. . I installed a pair of bi-amp'd monitors. All seems well except there is a very faint 60Hz hum present even with the sound card muted. The computer and monitors are plugged into the same outlet, though the computer is hooked to a UPS, not directly to the outlet (as the monitors are). That's a major risk factor. You have two choices: 1. Plug the speakers into the UPS. 2. Use transformers for isolation. Listening with headphones I don't hear the hum. I even listened through a small battery-powered amp I built for another purpose and there's no hum audible at pretty high gain. So I figure it's a ground loop. A better quality external audio interface is in the future, so I'm not losing much sleep over this yet, but I wonder how I'd go about addressing this since I don't really have the option of "turning the plug around" in this configuration. I'm guessing that the UPS is "turning the plug around" internally somehow. It is not "turning the plug around." The inductors in the surge protector are one cause, though I have found a ground loop to become audible just from adding the fraction of an ohm of resistance of a relay contact. It certainly is a recipe for trouble. There are not unusued UPS outlets, else I'd attach the monitors to one. Stick an octopus plug on. $3.00. It may not compromise the UPS backup time, if the monitors have little no-signal current draw. I can narrow it down to the UPS by removing it from the picture, but that's quite a hassle. I guess I'll give it a try. I could also fabricate a pair of 1:1 transformers to isolate the monitor inputs, but I wonder how badly that would compromise the sound. Jason It inevitably does, but in my experience, it still sounds decent. Bob Morein (310) 237-6511 |
#3
Posted to rec.audio.pro
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Powered monitors ground loop
In article ,
jason wrote: I installed a pair of bi-amp'd monitors. All seems well except there is a very faint 60Hz hum present even with the sound card muted. The computer and monitors are plugged into the same outlet, though the computer is hooked to a UPS, not directly to the outlet (as the monitors are). Listening with headphones I don't hear the hum. I even listened through a small battery-powered amp I built for another purpose and there's no hum audible at pretty high gain. So I figure it's a ground loop. A better quality external audio interface is in the future, so I'm not losing much sleep over this yet, but I wonder how I'd go about addressing this since I don't really have the option of "turning the plug around" in this configuration. I'm guessing that the UPS is "turning the plug around" internally somehow. There are not unusued UPS outlets, else I'd attach the monitors to one. I can narrow it down to the UPS by removing it from the picture, but that's quite a hassle. I guess I'll give it a try. I could also fabricate a pair of 1:1 transformers to isolate the monitor inputs, but I wonder how badly that would compromise the sound. Well, you don't mention what kind of monitors they are, or what kind of connection you are using. But if you are using a balanced connection, you effectively have an electronic transformer at each end, and you can just break the ground connection on the audio cable at one end and be done with it. It gets more complicated if one end is balanced and the other is not, but you can run tip and ring of an unbalanced source to pins 2 and 3 of a balanced destination, leaving pin 1 floating. The UPS is throwing lots of trash on the grounds, because that is what UPSes do. Unless you spend the money for a serious technical power UPS, in general UPSes will degrade rather than improve the line waveform. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#4
Posted to rec.audio.pro
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Powered monitors ground loop
"jason" wrote in message
I installed a pair of bi-amp'd monitors. All seems well except there is a very faint 60Hz hum present even with the sound card muted. The computer and monitors are plugged into the same outlet, though the computer is hooked to a UPS, not directly to the outlet (as the monitors are). Listening with headphones I don't hear the hum. I even listened through a small battery-powered amp I built for another purpose and there's no hum audible at pretty high gain. So I figure it's a ground loop. A better quality external audio interface is in the future, so I'm not losing much sleep over this yet, but I wonder how I'd go about addressing this since I don't really have the option of "turning the plug around" in this configuration. I'm guessing that the UPS is "turning the plug around" internally somehow. There are not unusued UPS outlets, else I'd attach the monitors to one. I can narrow it down to the UPS by removing it from the picture, but that's quite a hassle. I guess I'll give it a try. I could also fabricate a pair of 1:1 transformers to isolate the monitor inputs, but I wonder how badly that would compromise the sound. What powered monitors? Pro or cheap computer speakers? If your monitors have balanced inputs, you need not provide a balanced source. Correct wiring can make a lot of hum go away. |
#6
Posted to rec.audio.pro
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Powered monitors ground loop
"jason" wrote in message .. . In article , says... What powered monitors? Pro or cheap computer speakers? If your monitors have balanced inputs, you need not provide a balanced source. Correct wiring can make a lot of hum go away. They are KRK monitors. They have both balanced & unbalanced inputs. I am using the unbalanced RCA inputs with my cheap sound card, but as you and Scott both note, I can use the balanced inputs and float pin 1. I think I'll give that a try first. Thanks! Hi, Jason, option "B" Radio Shack part # 270-054 Audio System Ground Loop Isolator $16.99 2 isolation transformers in a little pod, phono males on one end, females on the other comes with a mini phone plug Y to phono males. They are not fantastic, they are inexpensive and they work reasonably well, always an option "B" Best Regards, Dave__________ |
#7
Posted to rec.audio.pro
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Powered monitors ground loop
On Jan 11, 10:20 pm, jason wrote:
They are KRK monitors. They have both balanced & unbalanced inputs. I am using the unbalanced RCA inputs with my cheap sound card, but as you and Scott both note, I can use the balanced inputs and float pin 1. I'd bet that your hum isn't (only) a ground problem. When you "mute" the sound card, all you're doing is muting the audio going to its analog output stage. The hum is probably coming right in through the cable to the input of the monitor's amplifier, just like any other audio signal. I wrote an article a while back about grounding problems, with some insight about using transformers (or packaged "isolators") to solve those problems. I tested a few commercial products and included that inexpensive Radio Shack unit. It actually had lower distortion and better frequency response than the next higher priced "hum eliminator" that I tested, which cost about $100. If you're in the US, buy one at your neighborhood Radio Shack and try it. If it improves your situation, keep it. If it doesn't make any difference, return it and get a refund. They'll take anything back. http://www.radioshack.com/product/in...ductId=2062214 |
#9
Posted to rec.audio.pro
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Powered monitors ground loop
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#10
Posted to rec.audio.pro
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Powered monitors ground loop
On Jan 12, 3:50*pm, jason wrote:
I picked up the Radio Shack isolation gadget and I can now turn up the input gain on the monitors way beyond where it makes sense and *no* hum. Unfortunately, that RS part only confirms that your grounding problem still exists AND that the ground loop circuit included that connection. IOW number of reasons for the problem are significantly reduced. May not (or might) imply a human safety problem. But the problem does still exist. Keep that in mind to eventually find the actual defect. |
#11
Posted to rec.audio.pro
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Powered monitors ground loop
If both speakers have 3 prong plugs, use an ac ground lift adapter from Walmarts. |
#12
Posted to rec.audio.pro
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Powered monitors ground loop
On Jan 12, 3:50 pm, jason wrote:
I picked up the Radio Shack isolation gadget and I can now turn up the input gain on the monitors way beyond where it makes sense and *no* hum. Well, then maybe it was a ground problem. Glad you're happy. |
#13
Posted to rec.audio.pro
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Powered monitors ground loop
"Frank Vuotto" wrote in message ... If both speakers have 3 prong plugs, use an ac ground lift adapter from Walmarts. This made me think......if you don't have a ground ,can you have a ground loop?. My monitors are two pronged 'double insulated', my laptop picks up its 19v DC via the usual transformer......so...no ground and my sound is quiet but not 'pure'. Could the transformer be introducing a ripple DC current in my system and the OP's?. Keith. |
#14
Posted to rec.audio.pro
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Powered monitors ground loop
On Wed, 14 Jan 2009 15:02:12 +1100, "Keith."
wrote: If both speakers have 3 prong plugs, use an ac ground lift adapter from Walmarts. This made me think......if you don't have a ground ,can you have a ground loop?. My monitors are two pronged 'double insulated', my laptop picks up its 19v DC via the usual transformer......so...no ground and my sound is quiet but not 'pure'. Could the transformer be introducing a ripple DC current in my system and the OP's?. First of all, responding to an earlier post, *never* remove a safety ground. There's always another solution. Just Say No (in this case...) WRT your laptop question: it's such a complex issue that folks who troubleshoot these kinds of problems regularly *still* see head-scratchers often. A coupla notes: Everything has grounds, so everything has ground loops. Sometimes the fix for an issue is simply to make the loop small enough that the coupled noise drops down far enough to make you happy enough. Everything couples to ground(s), in bigger or smaller amounts, but always some. This seems to be the predominant problem with many folks' laptop power supplies. They may have no safety ground, and the whole system may float above safety ground, yet "ground loop"-like issues are observed. "Ground" contamination. There really is no such thing as capital-g Ground. (There's a big ball that we're too weak to jump off of, but ). Electrically, there's only ever an approximation that has *some* actual, measurable, probably important, impedance between itself and some other local (!) definition of Ground. A good way of looking at the issue of grounds is to remember that all "grounds" are local. And that these local grounds all have their turf wars. Between any pair of "grounds" is some geography, noisily fought over, perfect access impeded. Electronic equipment has *internal* grounds that are internally contaminated by internal ground loop issues. (Laptops are so difficult to build that they seem especially prey, and are the current hot topic, but it's true everywhere and always). But also, all "grounds" are contaminated both by noise and by signal. Way more than anybody cares to read, sorry, but maybe useful as a framework someday for a head-scratcher, Chris Hornbeck |
#15
Posted to rec.audio.pro
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Powered monitors ground loop
"Keith." wrote ...
"Frank Vuotto" wrote ... If both speakers have 3 prong plugs, use an ac ground lift adapter from Walmarts. This made me think......if you don't have a ground ,can you have a ground loop?. My monitors are two pronged 'double insulated', my laptop picks up its 19v DC via the usual transformer......so...no ground and my sound is quiet but not 'pure'. Could the transformer be introducing a ripple DC current in my system and the OP's?. Many (most?) of those laptop 19V "brick" power supplies are horribly noisy. It is rather common to require isolation transformers coming out of a laptop (or else run it isolated on battery.) If you have a quiet 19V brick, then you are in the fortunate minority. |
#16
Posted to rec.audio.pro
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Powered monitors ground loop
This made me think... if you don't have a ground,
can you have a ground loop? Perhaps. "Ground loops" occur when the "ground" sides (that is, the sides with the lowest potential) are at different AC voltages. This is theoretically impossible in a balanced circuit, but perhaps there's some quirky situation that can cause a shift in AC potential... |
#17
Posted to rec.audio.pro
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Powered monitors ground loop
In article , "Keith." wrote:
"Frank Vuotto" wrote in message .. . If both speakers have 3 prong plugs, use an ac ground lift adapter from Walmarts. This made me think......if you don't have a ground ,can you have a ground loop?. My monitors are two pronged 'double insulated', my laptop picks up its 19v DC via the usual transformer......so...no ground and my sound is quiet but not 'pure'. Could the transformer be introducing a ripple DC current in my system and the OP's?. Most laptops ARE grounded. greg |
#18
Posted to rec.audio.pro
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Powered monitors ground loop
Frank Vuotto wrote:
If both speakers have 3 prong plugs, use an ac ground lift adapter from Walmarts. No. This is not only stupid and hazardous, but also illegal. Safety grounds are there for a reason. Don't ever lift the safety ground, lift the audio ground. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#19
Posted to rec.audio.pro
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Powered monitors ground loop
Keith. wrote:
"Frank Vuotto" wrote in message .. . If both speakers have 3 prong plugs, use an ac ground lift adapter from Walmarts. This made me think......if you don't have a ground ,can you have a ground loop?. No. A ground loop is caused when there is more than one ground path between two pieces of equipment. My monitors are two pronged 'double insulated', my laptop picks up its 19v DC via the usual transformer......so...no ground and my sound is quiet but not 'pure'. Could the transformer be introducing a ripple DC current in my system and the OP's?. Your laptop power supply is spewing out huge amounts of RF trash and contaminating the ground on the laptop. Many of them are like this. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#20
Posted to rec.audio.pro
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Powered monitors ground loop
William Sommerwerck wrote:
"Ground loops" occur when the "ground" sides (that is, the sides with the lowest potential) are at different AC voltages. Yes. This is theoretically impossible in a balanced circuit, but perhaps there's some quirky situation that can cause a shift in AC potential... It is quite readily possible in a balanced circuit. Once you have currents circulating through your ground system, all bets are off. Balanced circuits just reduce the problems.... but if the ground is contaminated, everything else bundled with the ground wire will eventually be contaminated by induction or capacitive coupling, cables being what they are. Current should never circulate through signal grounds if you can help it. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#21
Posted to rec.audio.pro
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Powered monitors ground loop
x-no-archive:
On Jan 13, 11:02*pm, "Keith." wrote: "Frank Vuotto" wrote in message ... If both speakers have 3 prong plugs, use an ac ground lift adapter from Walmarts. This can be hazardous to your health! This made me think......if you don't have a ground ,can you have a ground loop?. A device with a two wire power plug and that is not electrically connected to anything else and not bolted into a rack and not internally miswired can be considered electrically floating and balanced (at audio frequencies) and normally cannot create an audio ground loop. Notice there are a lot of conditions there that have to be met. My monitors are two pronged 'double insulated', my laptop picks up its 19v DC via the usual transformer......so...no ground and my sound is quiet but not 'pure'. Could the transformer be introducing a ripple DC current in my system and the OP's?. Yes, there are many other ways to inject hum and noise besides ground loops. Mark |
#22
Posted to rec.audio.pro
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Powered monitors ground loop
A ground loop is caused when there is more than one ground path
between two pieces of equipment. Actually, you can have multiple ground paths without having a ground loop. Any system in which the devices are plugged into different outlets -- even on the same circuit -- have a ground loop. The issue is the difference in AC potential between the grounds. It would be more-correct to say... When the ground paths are not electrically "equivalent". |
#23
Posted to rec.audio.pro
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Powered monitors ground loop
In article , "William Sommerwerck" wrote:
A ground loop is caused when there is more than one ground path between two pieces of equipment. Actually, you can have multiple ground paths without having a ground loop. Any system in which the devices are plugged into different outlets -- even on the same circuit -- have a ground loop. The issue is the difference in AC potential between the grounds. It would be more-correct to say... When the ground paths are not electrically "equivalent". You can have loops caused by the capacitance between the power line and the equipment. Its almost always referenced to ground. That would be common mode noise, primarily 60 Hz. In sensitive circuits there can be a need for less than 30 pF leakage from AC to the circuit or use battery. If the switching power supplies are well above the used frequencies, they are often not noticed, but they still leak AC 60 Hz which must be tied to ground or isolated. greg |
#24
Posted to rec.audio.pro
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Powered monitors ground loop
William Sommerwerck wrote:
A ground loop is caused when there is more than one ground path between two pieces of equipment. Actually, you can have multiple ground paths without having a ground loop. No, you cannot. You can have small and quiet ground loops, rather than big and noisy ones. But if there are multiple ground paths between any two pieces of equipment, by definition there is a ground loop. Any system in which the devices are plugged into different outlets -- even on the same circuit -- have a ground loop. ONLY if the devices have safety grounds AND if the devices have additional signal grounds being shared between them. If all the devices have balanced connections with signal grounds telescoped at one end, there are no ground loops. The issue is the difference in AC potential between the grounds. Yes, this is true. But once you have a ground loop, sooner or later you will be in some situation in which noise is induced in it. The vast majority of ground loops are small and harmless, but that doesn't mean that they will always stay that way. It would be more-correct to say... When the ground paths are not electrically "equivalent". For them to be electrically equivalent they have to be located in the same point in space. Once two wires are located at different points in space and connected at the ends, a shorted turn is formed and circulating currents can be induced. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#25
Posted to rec.audio.pro
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Powered monitors ground loop
GregS wrote:
You can have loops caused by the capacitance between the power line and the equipment. Its almost always referenced to ground. No. The LOOP is caused by the physical configuration. The induced current in the loop is caused by capacitive coupling. That would be common mode noise, primarily 60 Hz. In sensitive circuits there can be a need for less than 30 pF leakage from AC to the circuit or use battery. If the switching power supplies are well above the used frequencies, they are often not noticed, but they still leak AC 60 Hz which must be tied to ground or isolated. Yes. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#26
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Powered monitors ground loop
"Scott Dorsey" wrote in message
Once two wires are located at different points in space and connected at the ends, a shorted turn is formed and circulating currents can be induced. It's good that someone finally outed the real cause of the problem. The modern world is full of all kinds of conductive loops carrying all sorts of currents. The power line is usually the 500 pound gorilla, but it may not be the only monkey flying around. ;-) Make a conductive loop, and magnetic induction will make sure that there is a noisy current circulating in that loop. The bigger the area of the loop, likely the larger the current that will flow. The smaller the area of the loop, usually the less current. Twisted pair is a common means for reducing the area of the loop. There are some interesting twists. For example if you have a loop going from A to B to C and then back to A: Then the voltage flowing between A and B will be due to the induced current flowing through the resistance between A and B. Reduce the resistance between A and B, and you will decrease the voltage A and B - common sense and intuitive. Trouble is, this is often hard to do. Increase the resistance between B and C, or C and A, and the voltage between A and B will usually also drop. Not so intuitive. |
#27
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Powered monitors ground loop
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#28
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Powered monitors ground loop
"Scott Dorsey" wrote in message
... William Sommerwerck wrote: A ground loop is caused when there is more than one ground path between two pieces of equipment. Actually, you can have multiple ground paths without having a ground loop. No, you cannot. You can have small and quiet ground loops, rather than big and noisy ones. But if there are multiple ground paths between any two pieces of equipment, by definition there is a ground loop. I meant to say (really!) an _audible_ ground loop. (Really.) |
#29
Posted to rec.audio.pro,rec.arts.movies.production.sound,rec.audio.opinion,aus.hi-fi
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Powered monitors ground loop
On Jan 13, 7:31*pm, Soundhaspriority wrote:
In article , "jason" wrote: In article , says... Excellent advice, Mike and David. I'll give it a try! I picked up the Radio Shack isolation gadget and I can now turn up the input gain on the monitors way beyond where it makes sense and *no* hum. I listened to some files I'd been working on intensively the past few days and I cannot hear any difference in the audio quality either. You shouldn't follow Arny's "simple" non-engineer solutions. *You're aware Arny is a liar, aren't you? I'm a degreed engineer, and I gave you much more expensive and reliable solutions to choose from. If you've ignored my advice, I can only wish a pox on your house. Oh, You're a "degreed engineer" huh? Let us know which window at McDonalds you're working at, and we'll all stop by for fries. Jerry www.boskolives.wordpress.com "I don't really have a replacement career," Morein said. "It's a very gnawing thing." http://robertmorein.blogspot.com/ Bob Morein (310) 237-6511 |
#30
Posted to rec.audio.pro
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Powered monitors ground loop
Arny Krueger wrote:
"Scott Dorsey" wrote in message Once two wires are located at different points in space and connected at the ends, a shorted turn is formed and circulating currents can be induced. It's good that someone finally outed the real cause of the problem. A Mr. Black at Bell Telephone did that nearly a century ago. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#31
Posted to rec.audio.pro
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Powered monitors ground loop
"Scott Dorsey" wrote in message
Arny Krueger wrote: "Scott Dorsey" wrote in message Once two wires are located at different points in space and connected at the ends, a shorted turn is formed and circulating currents can be induced. It's good that someone finally outed the real cause of the problem. A Mr. Black at Bell Telephone did that nearly a century ago. --scott How so? I know he invented negative feedback, but can find nothing about him in connection with grounding problems and/or techniques. |
#32
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Powered monitors ground loop
Arny Krueger wrote:
"Scott Dorsey" wrote in message A Mr. Black at Bell Telephone did that nearly a century ago. --scott How so? I know he invented negative feedback, but can find nothing about him in connection with grounding problems and/or techniques. I think it was a different Black, actually. Let me see if I can dig up a cite... it actually predates the BSTJ by by more than a decade and I think it was in the IEE Journal. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#33
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Powered monitors ground loop
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#34
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Powered monitors ground loop
Give it a break, his speakers have NO AC grounds. Are they illegal? On 14 Jan 2009 09:33:48 -0500, (Scott Dorsey) wrote: Frank Vuotto wrote: If both speakers have 3 prong plugs, use an ac ground lift adapter from Walmarts. No. This is not only stupid and hazardous, but also illegal. Safety grounds are there for a reason. Don't ever lift the safety ground, lift the audio ground. --scott |
#35
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Powered monitors ground loop
On Jan 15, 6:26 pm, jason wrote:
Agreed. A new (external Firewire or USB) box is in the near- I-hope future. I think Scott has it right, namely that the UPS does funky things to the power. First appreciate what you have. You have a low frequency AC current flowing down that signal cable from one box to the other. The Radio Shack isolation transformer blocked that current - broke the ground loop. Second, that current must have never existed. Safety ground on both units means there is no ground voltage difference - therefore no ground loop current. But as you have proven, you have a low frequency ground loop current. Why? Safety grounds mean there should be no such voltage difference; therefore no current. Third, UPSes must connect that safety ground to the third (safety ground) prong without anything (even a filter) in that connection. Then all grounds have shortest and single point connections - no reason for current to flow thought that signal wire. Implied is a missing safety ground inside that UPS or a safety ground with filter circuits. Either way, a violation or the failure you are looking for. Of course, UPSes output much 'dirtier' electricity. The UPS itself could be culpriut. Popular myths hype UPS as 'cleaner' electricity. Only true when a UPS connects a load directly to AC mains. But again, you have a tool - the Radio Shack filter - to identify part of that ground loop current path; to help identify the still existing failure. Of course, you don't know which wire in that cable is carry current. But when the failure is found and corrected, install nothing or less hardware to have no hum. |
#36
Posted to rec.audio.pro
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Powered monitors ground loop
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#37
Posted to rec.audio.pro
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Powered monitors ground loop
* Second, that current must have never existed. *Safety ground on both units means there is no ground voltage difference - therefore no ground loop current. *But as you have proven, you have a low frequency ground loop current. *Why? *Safety grounds mean there should be no such voltage difference; therefore no current. That is not true. If you take a piece of wire, form it into a loop connecting the two ends, there is NOMINALLY no voltage diff between the ends but if the loop is in a magenttic field there can be a small difference and when you connect the ends together, the small voltage can create a large current because the resistance is so low. There are other ways for rather large currents to flow in saftey grounds that are "nominally the same voltage". A voltage diff of only 1 volt would be considered the "same voltage" from the point of view of a saftey ground, you would never get a shock from 1 Volt, but from the point of view of the audio, that 1 Volt can be a hugh difference. Mark |
#38
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Powered monitors ground loop
wrote in message ... Second, that current must have never existed. Safety ground on both units means there is no ground voltage difference - therefore no ground loop current. But as you have proven, you have a low frequency ground loop current. Why? Safety grounds mean there should be no such voltage difference; therefore no current. That is not true. If you take a piece of wire, form it into a loop connecting the two ends, there is NOMINALLY no voltage diff between the ends... You're assuming the wire has literally zero resistance and thus can "force" both ends to the same potentional. This is not necessarily the case. |
#39
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Powered monitors ground loop
On Jan 17, 12:28*pm, wrote:
If you take a piece of wire, form it into a loop connecting the two ends, there is NOMINALLY no voltage *diff between the ends but if the loop is in a magenttic field there can be a small difference and when you connect the ends together, the small voltage can create a large current because the resistance is so low. * Now calculate how much current is created by that magnetic field. Once numbers are provided in that post (and that also comes from experience), then the few feet of wire must never create that kind of voltage. Nothing even approaching 1 volt should exist. Even more than two volts between electronics and the mains breaker box is completely unacceptable for human safety. Magnetic fields on short AC cords create 1 volt. Nonsense. Properly noted is that wire is an electronic component - which is why the safety ground must join at a common point nearby all components. Safety ground performs many functions beyond protecting human life. Safety ground between two adjacent components at 1 volt? Complete nonsense or an indication of a serious problem that is also a major human safety threat. If both components are properly safety grounded to a common point, then voltage differences created by massive magnetic fields are so low as to not cause measureable hum. First, safety ground serves many functions beyond human safety - if properly connected. Second, magnetic fields do create such currents. Current that must be so trivial as to be virtually zero. Furthermore, no such massive magnetic fields should exist there anyway. Two reasons why magnetic fields do not create as speculated without numbers. Remove the hypothetical massive magnetic field generator that is drawing maybe 100 watts if those hypothetical fields exist. Another example of curing the problem rather than its symptoms. Meanwhile, if the safety grounds are properly connected (and that includes how grounds connect inside each component), then no significant voltage difference should exist on that signal cable. The Radio Shack transformer is blocking currents due to a design deficiency that must never exist if all safety grounds are properly connected (ie not compromised by a UPS) and if a design or component defect does not exist inside one component. Fix the problem. Do not invent excuses or cure symptoms. Magnetic fields creating such currents on short wires is only speculation not supported by numbers or cured by removing a defective massive field generator that should never exist. Safety ground serves many functions beyond human safety - including no hum on signal wires. That is why safety grounds meet at an adjacent and common point - which is clearly not required for human safety - which is clearly done to make those currents blocked by the Radio Shack isolator not possible. Maybe safety ground is perverted by the UPS as the OP suggests. Therefore the RS isolator is curing a symptom. Instead, cure the problem. No such noise currents should exist if all components are properly safety grounded to a common and nearby point. |
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Powered monitors ground loop
On Jan 17, 12:30*pm, "William Sommerwerck"
wrote: You're assuming the wire has literally zero resistance and thus can "force" both ends to the same potentional. This is not necessarily the case. If I was assuming (ignoring 40 years of design experience), then safety grounding all components to a common point inside the mains breaker box would eliminate that hum. I said otherwise. Wire is an electronic component which is why safety grounds must meet a common point AT electronics. That common point is necessary so that ground loop current need not flow through that signal cable. Further implied was defective safety grounding in one UPS. If safety ground is properly wired, then nothing but wire - not even a noise filter - exists between all safety ground connectors. A Radio Shack isolator may mask a design deficiency or an internal part failure. But again, for some reason, safety ground did not put both components at a common potential. No ground loop currents should be flowing between components on that signal wire. Cure the problem; not its symptoms. |
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