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#41
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10 metres audio cable going into PC = too long?
"David Nebenzahl" wrote in message
.com Floyd L. Davidson spake thus: David Nebenzahl wrote: Don Pearce spake thus: On Wed, 19 Apr 2006 07:26:25 -0700, "Richard Crowley" wrote: "Laurence Payne" wrote... There'll probably be 3 phases in the street. houses, or groups of houses will be allocated a single phase. Not in the parts of the USA where I have lived (up and down the west coast). They break up the 3 phases back at the main road and supply only one of the phases to each street (or 2-3 streets depending on the load) It is not economical to run all 3 phases along residential (or even small business) areas. So what do they do when somebody asks for three phase supply? Even a reasonably small business here in the UK might well do that if their power needs are significant. The power companies here actually prefer to supply businesses that way, particularly if they are also careful about their power factor correction. Reread my earlier post above. In it I described the situation where a business I once owned needed to have a power converter installed for 3-phase. This was in Berkeley, in a commercial district, not a residential one, and I think it's pretty typical of the Bay Area in general, probably the urban U.S for that matter. The power companies don't supply 3-phase power even to commercial areas; if someone needs it, they put in a converter. (We had a printing press that required it.) Most commercial businesses don't need 3-phase power. Large industrial customers do. I think the converters can be shared, so if a couple or a few neighboring businesses need 3-phase power, they can all use the one converter. What is a "converter"? I've never heard of anything described that way. It's a device--a big, honking piece of electromagnetic equipment--that generates 3-phase power from 2-phase power. In this case, it sits in an underground vault beneath the sidewalk, covered by one of them metal plates. Virtually all power is generated as 3-phase... Nope. What you actually get merely depends on what the transformer arrangement is. Single phase residential power is nothing other than one phase from a 3 phase distribution system. All that is required to have 3 phase power is *more wires*! http://www.kayind.com/basics/why.htm Apparently not. If you don't believe me, ask PG&E (Pacific Greed and Extortion, as they're known around here). They don't run all 3 wires as part of their normal power distribution. True for Detroit Edison, as well. I know this thing exists, because I saw the crews working on the damn thing in front of my shop when it malfunctioned and the press stopped working. http://www.homemetalshopclub.org/pro...nv/phconv.html |
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#42
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
In article , Don Pearce
writes On Wed, 19 Apr 2006 13:44:48 -0700, David Nebenzahl wrote: Virtually all power is generated as 3-phase... Nope. What you actually get merely depends on what the transformer arrangement is. Single phase residential power is nothing other than one phase from a 3 phase distribution system. All that is required to have 3 phase power is *more wires*! Apparently not. If you don't believe me, ask PG&E (Pacific Greed and Extortion, as they're known around here). They don't run all 3 wires as part of their normal power distribution. I know this thing exists, because I saw the crews working on the damn thing in front of my shop when it malfunctioned and the press stopped working. I'm stunned. This is the first time I've ever heard of power being generated as anything other than three phase. Apart from anything else, single phase is mega wasteful of copper. d Me too!, virtually every bit of wire string the electricity grid together in the UK is Three phase. Only in some remote places will you see overhead High voltage in Single phase, and that only is likely to serve a signal customer!.. Can't believe the USA is that different?. I know or hear that they have split centre tapped supplies for 115 and 240 volt domestic supplies... -- Tony Sayer |
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#43
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
On Wed, 19 Apr 2006 10:33:13 -0400, "mc"
wrote: So how does house wiring work in the UK? Is there more than one grounding ("earthing") point? And how is this better? As I understand it, the British ring system is to wire the outlets in a room in a ring so that each of them has two parallel paths to the point where power enters the room. As a result, a single high-resistance connection anywhere in the ring will have almost no effect. That should do a more reliable job of tying together all the ground connections for the different pieces of equipment. The electrician re-wiring my house 25 years ago told me ring-mains were originally developed on battleships. Less chance of localised damage taking out a load of equipment. The main advantage in domestic installations was that smaller cable could be installed for a given power load. With the demise of electric fires and 15 amp outlets, spur wiring was permissible and becoming more common. Earthing seems to be almost as much a black art as is car electrics :-) I don't pretend to understand it, but apparently changes in the UK system have introduced stringent new requirements for cross-bonding all kinds of things that weren't necessary before. Anyone know more about this? |
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#44
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
On Wed, 19 Apr 2006 10:33:59 -0400, "mc"
wrote: Mc doesn't understand ground loops. You can get them between two boxes plugged into the same double socket. Two boxes with 3-wire plugs? Could you elaborate? I thought a ground loop was due to difference in potential of the ground connections of 2 different pieces of equipment. Different resistance/impendence between different parts of the equipment and "ground". Whatever that is. |
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#45
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
On Tue, 18 Apr 2006 23:07:30 +0100, Palindr?me Gave
us: Andy wrote: I am in the UK. I would like to take a stereo signal from the line-out of my stereo (or TV) to the line-in of my PC. The equipment is in different rooms and the audio cable would be 10 metres. It will be this type: http://www.maplin.co.uk/images/full/130i0.jpg I don't understand the technical side but is 10 metres so long that it might cause audio problems with things like frequency response or voltage/current levels and so on? Will I need to get some higher specification audio cable to cover that distance? I want to keep cost down. I have used similar cable for a similar purpose over longer distances with no problems, for general purpose "listening" quality. Buying a higher spec cable is only going to give a very marginal improvement - if you really are interested in quality, you would link digital ports using an optical cable and not use analogue, anyway. Excellent response! The optical also reduces the number of elements in the run to one (TOS), or two in the case of speaker feeds. Heck, there are even speakers that have their amps integrated into them that take optical feeds. In fact, that is the best manner to reproduce sound is an amp right next to the acoustical transducer. One doesn't need crossover networks in one's speaker if each driver has its own amplifier. Just massage the corners a bit. |
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#46
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
On Wed, 19 Apr 2006 10:34:58 +0100, tony sayer
Gave us: I I seriously doubt that, because then the potential would have been more like 120 volts, right? I think that's grasping at straws: so far as I know, PG&E (local electricity dealer) doesn't even supply 3-phase to residential customers. In fact, not even in come commercial districts. I owned a small business in Berkeley (print shop) until last year, and I remember the previous owner telling me about all the headaches he had in having PG&E put in a 3-phase converter (in an underground vault below the sidewalk outside). So I know that utility lines don't usually carry 3-phase power, except to large industrial customers. What they tend to do is supply the area with a three phase line at around 11Kv and transform that down and then supply house number one with phase one, house two with phase two, three with phase three, four with phase one, five with phase two, house six with phase three and so on. Its called load balancing between the phases... Here, the pole transformer secondary (service side) is a center tapped 240 volt output (there are buck and boost taps on some). Homes here get the full 240 with the centertap (neutral), and within the home, it is routed about as a single side hot-to-centertap, 120 volt run. The oven, furnace, dryer, inline hot water, etc (high power devices) typically gets the full center tapped 240 feed. The center tap is ground at the service panel with a ground rod, and all fault returns (third wire) also come back to this grounded terminal bus. All the 240 volt branches get dual breakers and all the 120 volt runs get a breaker installed on that side of the service panel it will be drawing from. That makes any single run in the house 120 volts from ground (or neutral). Anyway, the pole transformer feeds several (4?) houses, then another transformer is used for the next quad of houses The HV feed at the top of the power distribution poles in Ohio was like 11kV IIRC (not sure), and I don't know if it was 3 phase or not. I do know that our 3 phase is not like California's. They are Delta. I think Ohio is Wye. They may balance their consumption by sending a different phase to an entire neighborhood, and another to the next neighborhood down the way. Seems costly to do it house by house by house as you say is the case where you are. |
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#47
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
On Wed, 19 Apr 2006 10:33:59 -0400, "mc"
Gave us: "Eiron" wrote in message ... Mc doesn't understand ground loops. You can get them between two boxes plugged into the same double socket. Two boxes with 3-wire plugs? Could you elaborate? I thought a ground loop was due to difference in potential of the ground connections of 2 different pieces of equipment. If it were two separate circuits, would it not make sense to think that there would be a small chaotic potential to be read across them? |
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#48
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
On Wed, 19 Apr 2006 17:02:04 +0100, Andy Gave us:
On 19 Apr 2006, wrote: "Andy" wrote in message ... I am in the UK. I would like to take a stereo signal from the line-out of my stereo (or TV) to the line-in of my PC. The equipment is in different rooms and the audio cable would be 10 metres. It will be this type: http://www.maplin.co.uk/images/full/130i0.jpg I don't understand the technical side but is 10 metres so long that it might cause audio problems with things like frequency response or voltage/current levels and so on? Will I need to get some higher specification audio cable to cover that distance? I want to keep cost down. I am using the exact same cable from Maplin, this is to go from my computer to my stereo amp. I would estimate it to be 10m-15m in length and I've had no problems with noise. sQuick.. Thanks to you and everyone else for the feedback. Seems it is less of a problem than i was anticipating. Actually my cable is not exactly the Maplin one I illustarted but a very similar one. Uh oh... all bets are off... ;-] Till we see that new photo posted. |
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#49
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
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#50
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
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#51
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
On Wed, 19 Apr 2006 23:48:39 +0100, Laurence Payne
lpayneNOSPAM@dslDOTpipexDOTcom wrote: On Wed, 19 Apr 2006 10:33:13 -0400, "mc" wrote: So how does house wiring work in the UK? Is there more than one grounding ("earthing") point? And how is this better? As I understand it, the British ring system is to wire the outlets in a room in a ring so that each of them has two parallel paths to the point where power enters the room. As a result, a single high-resistance connection anywhere in the ring will have almost no effect. That should do a more reliable job of tying together all the ground connections for the different pieces of equipment. The electrician re-wiring my house 25 years ago told me ring-mains were originally developed on battleships. Less chance of localised damage taking out a load of equipment. The main advantage in domestic installations was that smaller cable could be installed for a given power load. With the demise of electric fires and 15 amp outlets, spur wiring was permissible and becoming more common. Earthing seems to be almost as much a black art as is car electrics :-) I don't pretend to understand it, but apparently changes in the UK system have introduced stringent new requirements for cross-bonding all kinds of things that weren't necessary before. Anyone know more about this? Essentially everything metallic that is a fixture within a house must be bonded to mains ground. This includes everything in the plumbing system - sinks, bathtub etc. The ground wires for the ring mains just follow along with the power wires and ground all the metal outlet and switch boxes, d -- Pearce Consulting http://www.pearce.uk.com |
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#52
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
tony sayer spake thus:
In article , Don Pearce writes On Wed, 19 Apr 2006 13:44:48 -0700, David Nebenzahl wrote: Virtually all power is generated as 3-phase... Nope. What you actually get merely depends on what the transformer arrangement is. Single phase residential power is nothing other than one phase from a 3 phase distribution system. All that is required to have 3 phase power is *more wires*! Apparently not. If you don't believe me, ask PG&E (Pacific Greed and Extortion, as they're known around here). They don't run all 3 wires as part of their normal power distribution. I know this thing exists, because I saw the crews working on the damn thing in front of my shop when it malfunctioned and the press stopped working. I'm stunned. This is the first time I've ever heard of power being generated as anything other than three phase. Apart from anything else, single phase is mega wasteful of copper. Me too!, virtually every bit of wire string the electricity grid together in the UK is Three phase. Only in some remote places will you see overhead High voltage in Single phase, and that only is likely to serve a signal customer!.. Can't believe the USA is that different?. I know or hear that they have split centre tapped supplies for 115 and 240 volt domestic supplies... Yes, what's so strange about that? We get three wires coming into our houses: one neutral and two hots. The hots are each 120 (nominally) with respect to the neutral, with 240 between the hots. -- Pierre, mon ami. Jetez encore un Scientologiste dans le baquet d'acide. - from a posting in alt.religion.scientology titled "France recommends dissolving Scientologists" |
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#54
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
In article , Roy L. Fuchs
writes On Wed, 19 Apr 2006 10:34:58 +0100, tony sayer Gave us: I I seriously doubt that, because then the potential would have been more like 120 volts, right? I think that's grasping at straws: so far as I know, PG&E (local electricity dealer) doesn't even supply 3-phase to residential customers. In fact, not even in come commercial districts. I owned a small business in Berkeley (print shop) until last year, and I remember the previous owner telling me about all the headaches he had in having PG&E put in a 3-phase converter (in an underground vault below the sidewalk outside). So I know that utility lines don't usually carry 3-phase power, except to large industrial customers. What they tend to do is supply the area with a three phase line at around 11Kv and transform that down and then supply house number one with phase one, house two with phase two, three with phase three, four with phase one, five with phase two, house six with phase three and so on. Its called load balancing between the phases... Here, the pole transformer secondary (service side) is a center tapped 240 volt output (there are buck and boost taps on some). Homes here get the full 240 with the centertap (neutral), and within the home, it is routed about as a single side hot-to-centertap, 120 volt run. The oven, furnace, dryer, inline hot water, etc (high power devices) typically gets the full center tapped 240 feed. The center tap is ground at the service panel with a ground rod, and all fault returns (third wire) also come back to this grounded terminal bus. All the 240 volt branches get dual breakers and all the 120 volt runs get a breaker installed on that side of the service panel it will be drawing from. That makes any single run in the house 120 volts from ground (or neutral). Anyway, the pole transformer feeds several (4?) houses, then another transformer is used for the next quad of houses The HV feed at the top of the power distribution poles in Ohio was like 11kV IIRC (not sure), and I don't know if it was 3 phase or not. I do know that our 3 phase is not like California's. They are Delta. I think Ohio is Wye. They may balance their consumption by sending a different phase to an entire neighborhood, and another to the next neighborhood down the way. Seems costly to do it house by house by house as you say is the case where you are. Thanks for that enlightening post. It may well be that we don't have the centre tapped supply arrangement. In the local substation Y arranged, the centre is earth connected and referred to as the Neutral return and each phase is then carried on a three conductor cable with the wire armouring used as the neutral return and its also connected as the safety earth. as strange as that may seem  .....-- Tony Sayer |
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#55
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10 metres audio cable going into PC = too long?
On Wed, 19 Apr 2006 23:30:25 -0800, (Floyd L.
Davidson) wrote: (Don Pearce) wrote: On Wed, 19 Apr 2006 11:46:44 -0800, (Floyd L. Davidson) wrote: Try drawing a diagram of what you are describing. Done. You can find it here http://81.174.169.10/ I meant a diagram that *explained* what a ground loop is. Your diagram does nothing, and isn't even a electrical diagram, much less one of a ground loop circuit. Here is the electrical equivalent diagram for your "ground loop", Desired Signal Source o o | | | +-------+ | | Rload | | +-------+ | | | +------- connection =======//======= ------+ | | to cable (Induced Signal) | | +-------+ shield | | | Rgrnd | | | +-------+ | | | | +------+ --------- Ground Differential ---------- | | (Signal Source) | ----- Earth Earth ----- --- Ground Ground --- - - Mine isn't even an electrical diagram? At least it had the load at the right end of the cable. You have put it at the same end as the source. This is just nonsense. There are two resistors (Rload and Rgrnd) with one desired signal source and two others that affect the voltage drop across the resistors. It is easier to see what happens if we assume the "desired signal" is a current limited (i.e., high impedance) source. In addition to the "desired signal" sources, there would also be currents induced into the cable shield by external fields, and currents induced by ground differential voltages. All currents contribute to the voltage across Rgrnd. The voltage across Rload is affected by the voltage across Rgrnd, and thus the voltage drop across Rload. Current through the shield affecting the voltage across Rload is noise. If that is significant, it is commonly said to be a "ground loop". Lifting the ground from one side of the cable shield will stop the current flow, and thus "cure" the problem. However, reducing the resistance of Rgrnd, the common ground wire would have the same effect. Hence you have two choices. One is very easy and has no detrimental effects for short cables inside a building that has both ends on the same AC power distribution and a common ground or very low potential difference between two earth grounds. Note that long runs of comm cable do not fit that description, and therefore use the technique allowing only *very* *low* *impedance* common ground connections. (The only common part has to be a large, low impedance, cable that is preferably short.) Why are you telling me this? What does that mean in practice? Here is another version of your "diagram", except of course this one actually *is* an electrical diagram. +-------+ +-------+ | | | | | EQUIP | ------- signal wire/pair ------- | EQUIP | | | ========= cable shield ========= | | +-------+ | | +-------+ | | | | | | | +---+ +---+ | | | | | ----- Earth ----- Earth --- Ground --- Ground - - No more so than mine. This typically results in a ground loop *if* the size of the two wires from the EQUIP to Earth Ground is not large enough to provide a very low impedance (which is difficult to do if the wires are any length at all, such as if the path to Earth Ground is provided by AC power wiring for the building). As noted, there are two solutions, the most well known is to simply remove the ground connection to one side of the shielded cable. But the expedient of removing the ground at one end accomplishes several things in addition to eliminating the ground loop. It also removes common mode DC equalization, and it eliminates induced current flow in the cable shield thus preventing that current from reducing common mode noise induction in the signal wires for balanced circuits. Common mode DC equalization? What has DC to do with any of this, and what do you mean by equalization. Are you still insisting that in a ground loop there are two signal connections and one ground connection? Note that this is appropriate for use with cable existing within a single building. The benefit is the same, but the negatives are of negligible effect. +-------+ +-------+ | | | | | EQUIP | ------- signal wire/pair ------- | EQUIP | | | ========= cable shield ========= | | +-------+ | +-------+ | | | | | +---+ -- Single ground for shield | | | | | ----- Earth ----- Earth --- Ground --- Ground - - However, if the cable is a long run, and particularly if there is exposure to power lines, if the ground potential is different at the two ends, or if there are any other sources of induced noise in the cable, this arrangement has the best effect: +-------+ +-------+ | | | | | EQUIP | ------- signal wire/pair ------- | EQUIP | | | ========= cable shield ========= | | +-------+ | | +-------+ | | | | | | -- separate grounds -- | | o------+ +------o * * * -- low impedance ground connections -- * * * ----- Earth ----- Earth --- Ground --- Ground - - What do you mean by separate grounds? Separate from what? You have grounded the equipment at each end, and also connected them by the cable shield. This forms a ground loop and cures nothing. Note the minimum common path to ground. If correctly sized there will be no significant voltage drop across that small section. (Which is to say, that conductor should probably be copper strap between a copper terminal plate and the actual ground system connection.) Hence, there is no "ground loop" effect. However, the two grounds are connected electrically and the voltage is equalized between then. The second benefit is that voltages induced into the cable by exposure to external fields will have a low impedance circuit path, and therefore will conduct current. No, I think I have described what is going on perfectly - I suspect the confusion is at your end. It may be simply a semantic confusion over what constitutes the signal. I highly suspect that you will have a number of questions about the above. Note that it is not semantic confusion, and that this is a topic I've taught before. Please feel free to ask "What the Hellll does that mean?" about any part of it you like. Just keep in mind that it is *precisely* *correct*. I may not have gone into enough detail, or used words that clearly paint the right picture in the mind of any given reader though, so questions that cause the description to be restated in different ways are guaranteed to be helpful. No, the thread has effectively been killed by your diagrams that won't survive the threading process, and are hence not discussable in any meaningful way. If you want to carry on believing that a ground loop needs two signal paths and one ground path, I am happy to leave you to it. d -- Pearce Consulting http://www.pearce.uk.com |
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#56
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
"tony sayer" wrote in message
In article , Don Pearce writes On Wed, 19 Apr 2006 13:44:48 -0700, David Nebenzahl wrote: Virtually all power is generated as 3-phase... Nope. What you actually get merely depends on what the transformer arrangement is. Single phase residential power is nothing other than one phase from a 3 phase distribution system. All that is required to have 3 phase power is *more wires*! Apparently not. If you don't believe me, ask PG&E (Pacific Greed and Extortion, as they're known around here). They don't run all 3 wires as part of their normal power distribution. I know this thing exists, because I saw the crews working on the damn thing in front of my shop when it malfunctioned and the press stopped working. I'm stunned. This is the first time I've ever heard of power being generated as anything other than three phase. Apart from anything else, single phase is mega wasteful of copper. d Me too!, virtually every bit of wire string the electricity grid together in the UK is Three phase. Only in some remote places will you see overhead High voltage in Single phase, and that only is likely to serve a signal customer!.. Can't believe the USA is that different?. I know or hear that they have split centre tapped supplies for 115 and 240 volt domestic supplies... All true. It's called "legacy technology". Unlike Europe, the US missed out on the cleansing benefits of being the site of a world war. |
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#57
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
"tony sayer" wrote in message
Why do you still use 115-120 supplies what with the extra current demands, or is there still a perceived electric shock issue?..... Most US factories that use substantial amounts of power use 3 phase. It's mostly just the residential areas and isolated light industrial areas that lack it. Electric power use per capita in the US is closer to being uniform or decreasing, as opposed to there being extra current demands. http://www.eia.doe.gov/emeu/25opec/sld020.htm http://www.aceee.org/energy/effact.htm "Total primary energy use per capita in the United States in 2000 was almost identical to that in 1973. Over the same 27-year period economic output (GDP) per capita increased 74 percent" Since 2001 or so, there has been a major conversion of existing residential lighting to compact fluorescent bulbs which produce about 3 times as much light per watt. |
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#58
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
Jim Lesurf wrote:
In article , Andy wrote: I am in the UK. I would like to take a stereo signal from the line-out of my stereo (or TV) to the line-in of my PC. The equipment is in different rooms and the audio cable would be 10 metres. It will be this type: http://www.maplin.co.uk/images/full/130i0.jpg I don't understand the technical side but is 10 metres so long that it might cause audio problems with things like frequency response or voltage/current levels and so on? Will I need to get some higher specification audio cable to cover that distance? I want to keep cost down. To be able to give a complete answer we would need to know the output impedance values for your stereo and TV. The output impedance (resistance) will tend to combine with the cable capacitance to make an RC low-pass filter. This may or may not matter, but to estimate the effect we'd need to relevant values. A quick bit of mental arithmetic, with the sort of distances and cables mentioned by the OP, gives me an estimate of around 5k output impedance, or greater, before it should give a noticeable effect (OK, a bit lower if you can hear and are concerned about getting 10kHz stuff). I haven't come across a line out with a higher impedance than 5k, so I don't think it is going to be a problem. Even so, this can be compensated for by a tweak of the tone controls on the PC. -- Sue |
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#59
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
Why do you still use 115-120 supplies what with the extra current
demands, or is there still a perceived electric shock issue?..... At this point, changing voltages would be prohibitively expensive. We do have 240-volt outlets for major appliances. It's a trade-off. 120 V is safer from the electric shock standpoint, but 240 V greatly reduces the risk of starting a fire when a connection develops high resistance, since there will be only half as much current and thus 1/4 as much heat output. British ring wiring further reduces that risk. I wonder if ring wiring is legal in the US... if so, I might request it the next time I have something wired. |
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#60
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
To be able to give a complete answer we would need to know the output
impedance values for your stereo and TV. The output impedance (resistance) will tend to combine with the cable capacitance to make an RC low-pass filter. This may or may not matter, but to estimate the effect we'd need to relevant values. A quick bit of mental arithmetic, with the sort of distances and cables mentioned by the OP, gives me an estimate of around 5k output impedance, or greater, before it should give a noticeable effect (OK, a bit lower if you can hear and are concerned about getting 10kHz stuff). I haven't come across a line out with a higher impedance than 5k, so I don't think it is going to be a problem. The output impedance of any modern IC-based audio equipment is probably going to be quite low (under 100 ohms) because the output impedance of an op-amp is inherently low. This includes line-level outputs that are intended to drive high-impedance inputs. |
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#61
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
Laurence Payne lpayneNOSPAM@dslDOTpipexDOTcom wrote:
On Wed, 19 Apr 2006 10:33:59 -0400, "mc" wrote: Mc doesn't understand ground loops. You can get them between two boxes plugged into the same double socket. Two boxes with 3-wire plugs? Could you elaborate? I thought a ground loop was due to difference in potential of the ground connections of 2 different pieces of equipment. Different resistance/impendence between different parts of the equipment and "ground". Whatever that is. Differing impedances is harmless. The problem is *common* impedances. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#62
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10 metres audio cable going into PC = too long?
(Don Pearce) wrote:
On Wed, 19 Apr 2006 23:30:25 -0800, (Floyd L. Davidson) wrote: Done. You can find it here http://81.174.169.10/ I meant a diagram that *explained* what a ground loop is. Your diagram does nothing, and isn't even a electrical diagram, much less one of a ground loop circuit. Here is the electrical equivalent diagram for your "ground loop", Desired Signal Source o o | | | +-------+ | | Rload | | +-------+ | | | +------- connection =======//======= ------+ | | to cable (Induced Signal) | | +-------+ shield | | | Rgrnd | | | +-------+ | | | | +------+ --------- Ground Differential ---------- | | (Signal Source) | ----- Earth Earth ----- --- Ground Ground --- - - Mine isn't even an electrical diagram? At least it had the load at the right end of the cable. You have put it at the same end as the source. This is just nonsense. My appologies, I didn't mean to go that far over your head. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#63
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10 metres audio cable going into PC = too long?
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#64
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10 metres audio cable going into PC = too long?
On Fri, 21 Apr 2006 03:46:32 GMT, Roy L. Fuchs
wrote: On Thu, 20 Apr 2006 07:54:57 GMT, (Don Pearce) Gave us: No, the thread has effectively been killed by your diagrams that won't survive the threading process, and are hence not discussable in any meaningful way. You just proved that you are even more of an idiot than he proved you are. His diagrams didn't kill the thread, and no, you do NOT quote everything over and over again, dolt boy. I quote what I want to quote. I produced a simple diagram that showed the essentials of a ground loop - two ground connections and a single signal connection. This was the opposite of what he claimed. He then went on to produce a slew of poor ascii diagrams, none of which demonstrated his contention. It was clear at that point that the thread was going nowhere. So, are you saying he is right, and I am wrong? Do you believe that for a ground loop you need two signal connections and one ground connection? Go ahead - make my day. d -- Pearce Consulting http://www.pearce.uk.com |
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#65
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10 metres audio cable going into PC = too long?
(Don Pearce) wrote:
On Fri, 21 Apr 2006 03:46:32 GMT, Roy L. Fuchs wrote: On Thu, 20 Apr 2006 07:54:57 GMT, (Don Pearce) Gave us: No, the thread has effectively been killed by your diagrams that won't survive the threading process, and are hence not discussable in any meaningful way. You just proved that you are even more of an idiot than he proved you are. His diagrams didn't kill the thread, and no, you do NOT quote everything over and over again, dolt boy. I quote what I want to quote. I produced a simple diagram that showed the essentials of a ground loop - two ground connections and a single signal connection. This was the opposite of what he claimed. He then went on to produce a slew of poor ascii diagrams, none of which demonstrated his contention. It was clear at that point that the thread was going nowhere. You produced a _block_ diagram, not a circuit diagram. You did not demonstrate that it even produced a ground loop, and in fact what you showed does *not* necessarily constitute a ground loop. So, are you saying he is right, and I am wrong? Do you believe that for a ground loop you need two signal connections and one ground connection? Go ahead - make my day. You still can't get the right quote. Two signals, one common path. There need not be a ground, and there need not be a loop. And you can trust that everyone who actually does understand what happens is indeed saying you are wrong. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#66
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10 metres audio cable going into PC = too long?
On Fri, 21 Apr 2006 00:33:35 -0800, (Floyd L.
Davidson) wrote: (Don Pearce) wrote: On Fri, 21 Apr 2006 03:46:32 GMT, Roy L. Fuchs wrote: On Thu, 20 Apr 2006 07:54:57 GMT, (Don Pearce) Gave us: No, the thread has effectively been killed by your diagrams that won't survive the threading process, and are hence not discussable in any meaningful way. You just proved that you are even more of an idiot than he proved you are. His diagrams didn't kill the thread, and no, you do NOT quote everything over and over again, dolt boy. I quote what I want to quote. I produced a simple diagram that showed the essentials of a ground loop - two ground connections and a single signal connection. This was the opposite of what he claimed. He then went on to produce a slew of poor ascii diagrams, none of which demonstrated his contention. It was clear at that point that the thread was going nowhere. You produced a _block_ diagram, not a circuit diagram. You did not demonstrate that it even produced a ground loop, and in fact what you showed does *not* necessarily constitute a ground loop. The diagram demonstrated exactly what it needed to demonstrate - no more and no less. To get a ground loop, you need to make a loop from the ground. To make a loop, you need the ground from one piece of kit to another by two separate paths. This can be a problem in two ways. Either, if the loop is physically large it can intercept magnetic hum fields and generate a casement flowing around the loop, or if other equipment is using the circuit, those currents flowing through the main ground path will do the job for you. The mechanism that turns these currents into emfs that actually couple into the input was irrelevant to the point I was making. I was showing that for a ground loop, you actually need to make a loop from the ground. You diagrams, on the other hand were actually wrong. You were putting Earth symbols at locations where there is no Earth connection. In a house there is only one Earth connection, and that is on the company side of the consumer unit. All ground connections within the house are as I showed - simple wire connections between pieces of kit. In fact, the Earth connection is irrelevant to the phenomenon - ground loops would still happen if the whole lot were floating. Maybe I'm wrong of course - in your house does each mains socket have an individual ground which is actually a stake driven into the Earth? No? Didn't think so. So, are you saying he is right, and I am wrong? Do you believe that for a ground loop you need two signal connections and one ground connection? Go ahead - make my day. You still can't get the right quote. Two signals, one common path. There need not be a ground, and there need not be a loop. Wrong - as wrong as you can get. Let me tell you this again. You can have ground loops producing hum in a mono system. That is just one signal in case counting is a problem. What you need is the two ground connections. (Two is one more than one). And you can trust that everyone who actually does understand what happens is indeed saying you are wrong. I leave them to judge. d -- Pearce Consulting http://www.pearce.uk.com |
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#67
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10 metres audio cable going into PC = too long?
In article , Palindr-»me
wrote: Jim Lesurf wrote: To be able to give a complete answer we would need to know the output impedance values for your stereo and TV. The output impedance (resistance) will tend to combine with the cable capacitance to make an RC low-pass filter. This may or may not matter, but to estimate the effect we'd need to relevant values. A quick bit of mental arithmetic, with the sort of distances and cables mentioned by the OP, gives me an estimate of around 5k output impedance, or greater, before it should give a noticeable effect (OK, a bit lower if you can hear and are concerned about getting 10kHz stuff). Since I am reading (and replying) on an 'audio' newsgroup, my assumption is that people may be concerned up to around 20kHz, and want to be aware of any changes that might be considered worthy of note in the context of using good audio equipment in a domestic situation. If I assume a cable capacitance of around 100pF/m, then a 5kOhm source would, I think, give a roll-off of the order of 1dB in the 15-20kHz region. (Assuming I managed to push the right buttons on my guess-box. :-) ) On this newsgroup I'd normally expect people to regard that as being large enough to be worth at least being aware of it. I haven't come across a line out with a higher impedance than 5k, so I don't think it is going to be a problem. You are probably correct. Alas, consumer equipment sometimes dissapoints out expectations - particularly when the makers have failed to provide the relevant data for the users. ;- Even so, this can be compensated for by a tweak of the tone controls on the PC. Once one becomes aware of the problem, and knows what adjustment to make to correct for it appropriately. Hence my initial comment. :-) Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html |
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#68
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10 metres audio cable going into PC = too long?
In article , mc
wrote: The output impedance of any modern IC-based audio equipment is probably going to be quite low (under 100 ohms) because the output impedance of an op-amp is inherently low. This includes line-level outputs that are intended to drive high-impedance inputs. I would agree that modern circuits that use IC amps with feedback should be able to provide nominally low o/p impedances. However, although in general you are probably correct, the snag is that life may not always be that simple. :-) For example, some outputs may have a low nominal output impedance, but have a relatively low current limit. Hence they may act like a low impedance source for low currents, but show slew-rate limiting when asked to drive a high capacitance load (long cable). For this reason the designer may even have included o/p series resistors to protect against this and avoid the IC being overloaded. As I indicated, all we have so far is that the source is a 'stereo or TV' with no details of their actual outputs. Hence it will probably be OK, but as I pointed out, we can't really be sure in the absence of the relevant data. IIRC the old IHFA-707 specs required audio signal sources to be tested with loads of 1000pF//10kOhms as the 'worst case'. I don't know what standards (if any!) makers of domestic TVs routinely adopt these days, but 10 meters of cable does seem to me to bring us into the area where the 1000pF limit might be an issue. Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html |
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#69
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10 metres audio cable going into PC = too long?
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#70
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10 metres audio cable going into PC = too long?
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#71
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10 metres audio cable going into PC = too long?
(Don Pearce) wrote:
The diagram demonstrated exactly what it needed to demonstrate - no more and no less. To get a ground loop, you need to make a loop from the ground. To make a loop, you need the ground from one piece of kit to another by two separate paths. This can be a problem in two ways. Either, if the loop is physically large it can intercept magnetic hum fields and generate a casement flowing around the loop, or if other equipment is using the circuit, those currents flowing through the main ground path will do the job for you. Virtually *every* outside plant telephone cable is wired up exactly like that. There is a ground at both ends of each and every section (3000 or 6000 feet), and the shields from each coupled section are bonded to the other and to ground. A three mile long section of cable might look just like this: 6000' 6000' 6000' -----------o----------o----------- signal pair -----------o----------o----------- +==//==+ +==//==+ +==//==+ shield | | | | | | | +-+-+ +-+-+ | | | | | ----- ----- ----- ----- --- --- --- --- - - - - Yet there is no ground loop, ever. Your description says that would virtually *always* cause a ground loop. The problem is that you description does *NOT* describe the essence of a "ground loop". You have not shown where the coupling takes place, nor have you describe why it happens. You apparently were unable to read the equivalent electrical diagram that I posted showing exactly what the mechanism is. Here is is again, though this time I've rearranged it slightly to meet your requirement that the load resister be to the right of the input. I hope the irony of the difference is not lost on you... o---------+ | +-------+ | Rload | +-------+ Signal | Source +------- connection =======//======= ------+ | to cable (Induced Signal) | +-------+ shield | | Rgrnd | | +-------+ | | | o---------+ --------- Ground Differential ---------- | | (Signal Source) | ----- Earth Earth ----- --- Ground Ground --- - - The mechanism that turns these currents into emfs that actually couple into the input was irrelevant to the point I was making. I was showing that for a ground loop, you actually need to make a loop from the ground. You do *not* need a loop, and the "mechanism ... that actually couple" them *is* the only point that actually matters. If there is no interference, then there is no "ground loop". When there is interference, that mechanism is what causes it. The mechanism is having a single common path for two different signals. (It often involves a ground system and that might well have a loop, but in fact is there is no requirement for it to be a ground system and no loop is required other than the normal closed circuit required by *every* signal path.) You diagrams, on the other hand were actually wrong. You were putting Earth symbols at locations where there is no Earth connection. There of course *is* an "Earth connection" at the points where I showed them, *by definition*. In a house there is only one Earth connection, and that is on the company side of the consumer unit. All ground connections within the house are as I showed - simple wire connections between pieces of kit. In fact, the Earth connection is irrelevant to the phenomenon - ground loops would still happen if the whole lot were floating. There is not necessarily only a single earth connection point in any given house, but the circuit was not necessarily showing a circuit within a single house anyway. It could just as easily be between two houses a mile apart. Nothing in either scenario would change how it works as opposed to a single connection within one building. Maybe I'm wrong of course - in your house does each mains socket have an individual ground which is actually a stake driven into the Earth? No? Didn't think so. You've never lived in a house with 1) natural gas lines, 2) water pipes connected to a well, 3) any kind of a ground system for a transmitting antenna, or probably some other odd circumstance that I haven't thought of? (I've lived and worked in buildings with all of that, and I've worked in buildings with more than one electrical distribution system too. Your statement is absurd.) So, are you saying he is right, and I am wrong? Do you believe that for a ground loop you need two signal connections and one ground connection? Go ahead - make my day. You still can't get the right quote. Two signals, one common path. There need not be a ground, and there need not be a loop. Wrong - as wrong as you can get. Let me tell you this again. You can have ground loops producing hum in a mono system. That is just one signal in case counting is a problem. What you need is the two ground connections. (Two is one more than one). You cannot have "hum" and your desired "signal" without having two, count them, signals. Whether it is a "mono system", or something like RS-485 data, a telephone dial loop, a T1, video, or any of a number of other types of circuits and signals, the basics are exactly the same. Two signals does *not* define a stereo audio system! (Though your comment pretty much does indicate the extremely limited concept of a "signal" that you have... and that probably explains your limited understanding of ground loops too.) And you can trust that everyone who actually does understand what happens is indeed saying you are wrong. I leave them to judge. Has anyone suggested yet that you are even close to correct in any aspect of what you've said? Do you wonder why? -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#72
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10 metres audio cable going into PC = too long?
In article , Floyd L. Davidson
writes (Don Pearce) wrote: The diagram demonstrated exactly what it needed to demonstrate - no more and no less. To get a ground loop, you need to make a loop from the ground. To make a loop, you need the ground from one piece of kit to another by two separate paths. This can be a problem in two ways. Either, if the loop is physically large it can intercept magnetic hum fields and generate a casement flowing around the loop, or if other equipment is using the circuit, those currents flowing through the main ground path will do the job for you. Virtually *every* outside plant telephone cable is wired up exactly like that. There is a ground at both ends of each and every section (3000 or 6000 feet), and the shields from each coupled section are bonded to the other and to ground. A three mile long section of cable might look just like this: 6000' 6000' 6000' -----------o----------o----------- signal pair -----------o----------o----------- +==//==+ +==//==+ +==//==+ shield | | | | | | | +-+-+ +-+-+ | | | | | ----- ----- ----- ----- --- --- --- --- - - - - Yep, well thats balanced operation which as you say will go for miles over telephone copper lines without humm.. Oddly enough in the UK they don't as a rule use screened cable, the twisted balanced pair has very good rejection. I seemed to think we were talking about domestic unbalanced lines here?..... -- Tony Sayer |
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#73
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10 metres audio cable going into PC = too long?
On Fri, 21 Apr 2006 02:01:10 -0800, (Floyd L.
Davidson) wrote: (Don Pearce) wrote: The diagram demonstrated exactly what it needed to demonstrate - no more and no less. To get a ground loop, you need to make a loop from the ground. To make a loop, you need the ground from one piece of kit to another by two separate paths. This can be a problem in two ways. Either, if the loop is physically large it can intercept magnetic hum fields and generate a casement flowing around the loop, or if other equipment is using the circuit, those currents flowing through the main ground path will do the job for you. Virtually *every* outside plant telephone cable is wired up exactly like that. There is a ground at both ends of each and every section (3000 or 6000 feet), and the shields from each coupled section are bonded to the other and to ground. A three mile long section of cable might look just like this: 6000' 6000' 6000' -----------o----------o----------- signal pair -----------o----------o----------- +==//==+ +==//==+ +==//==+ shield | | | | | | | +-+-+ +-+-+ | | | | | ----- ----- ----- ----- --- --- --- --- - - - - Yet there is no ground loop, ever. Your description says that would virtually *always* cause a ground loop. The problem is that you description does *NOT* describe the essence of a "ground loop". You have not shown where the coupling takes place, nor have you describe why it happens. My circuit showed what kind of poor installation causes ground-loop induced hum. You get a ground loop in a domestic Hi Fi (and yes, that is what we are talking about here -forget your telephone cables).when you join to bits of kit together with coax cables, and also have them both connected to mains ground. You apparently were unable to read the equivalent electrical diagram that I posted showing exactly what the mechanism is. Here is is again, though this time I've rearranged it slightly to meet your requirement that the load resister be to the right of the input. I hope the irony of the difference is not lost on you... o---------+ | +-------+ | Rload | +-------+ Signal | Source +------- connection =======//======= ------+ | to cable (Induced Signal) | +-------+ shield | | Rgrnd | | +-------+ | | | o---------+ --------- Ground Differential ---------- | | (Signal Source) | ----- Earth Earth ----- --- Ground Ground --- - - No better. You need to understand that the load is on the far end of the cable, not the same end as the source. The mechanism that turns these currents into emfs that actually couple into the input was irrelevant to the point I was making. I was showing that for a ground loop, you actually need to make a loop from the ground. You do *not* need a loop, and the "mechanism ... that actually couple" them *is* the only point that actually matters. If there is no interference, then there is no "ground loop". When there is interference, that mechanism is what causes it. We are trying to work out how to prevent a domestic system suffering hum from a ground loop. So no, the exact mechanism by which the coupling takes place doesn't matter. What matters is how you connect your kit up. The mechanism is having a single common path for two different signals. (It often involves a ground system and that might well have a loop, but in fact is there is no requirement for it to be a ground system and no loop is required other than the normal closed circuit required by *every* signal path.) Wrong. If you connect two bits of kit with a single coax cable, and there are no other connections, you will not have a loop that causes hum. You diagrams, on the other hand were actually wrong. You were putting Earth symbols at locations where there is no Earth connection. There of course *is* an "Earth connection" at the points where I showed them, *by definition*. No there isn't, there is a connection to a bit of wire. Here in the UK that is a piece of thinnish bare copper contained within the twin-and-earth 2.5 squ mm cable that connects all domestic sockets to each other. At some distant point where the power enters the house there is an earth connection. In a house there is only one Earth connection, and that is on the company side of the consumer unit. All ground connections within the house are as I showed - simple wire connections between pieces of kit. In fact, the Earth connection is irrelevant to the phenomenon - ground loops would still happen if the whole lot were floating. There is not necessarily only a single earth connection point in any given house, but the circuit was not necessarily showing a circuit within a single house anyway. It could just as easily be between two houses a mile apart. Nothing in either scenario would change how it works as opposed to a single connection within one building. We are talking about a 10 metre cable connecting a PC to a Hi Fi. Maybe I'm wrong of course - in your house does each mains socket have an individual ground which is actually a stake driven into the Earth? No? Didn't think so. You've never lived in a house with 1) natural gas lines, 2) water pipes connected to a well, 3) any kind of a ground system for a transmitting antenna, or probably some other odd circumstance that I haven't thought of? (I've lived and worked in buildings with all of that, and I've worked in buildings with more than one electrical distribution system too. Your statement is absurd.) Good for you! And the connection with the current question is? So, are you saying he is right, and I am wrong? Do you believe that for a ground loop you need two signal connections and one ground connection? Go ahead - make my day. You still can't get the right quote. Two signals, one common path. There need not be a ground, and there need not be a loop. Wrong - as wrong as you can get. Let me tell you this again. You can have ground loops producing hum in a mono system. That is just one signal in case counting is a problem. What you need is the two ground connections. (Two is one more than one). You cannot have "hum" and your desired "signal" without having two, count them, signals. Whether it is a "mono system", or something like RS-485 data, a telephone dial loop, a T1, video, or any of a number of other types of circuits and signals, the basics are exactly the same. Learn some terminology. In electronic engineering generally as well as audio, "signal" refers only to the wanted stuff. Hum, noise and distortion are *not* signal. Two signals does *not* define a stereo audio system! (Though your comment pretty much does indicate the extremely limited concept of a "signal" that you have... and that probably explains your limited understanding of ground loops too.) Yes they do. You will find that there is a left signal and a right signal. That, I'm afraid, is your lot. I'm always open to learn something new of course. If you have other signals in your stereo do tell me all about them. Tell us all, in fact - I'm sure we would all be glad of the new knowledge. And you can trust that everyone who actually does understand what happens is indeed saying you are wrong. I leave them to judge. Has anyone suggested yet that you are even close to correct in any aspect of what you've said? Do you wonder why? I'm still perfectly happy to let my words stand for judgment. d -- Pearce Consulting http://www.pearce.uk.com |
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#74
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10 metres audio cable going into PC = too long?
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#75
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10 metres audio cable going into PC = too long?
tony sayer wrote:
In article , Floyd L. Davidson writes (Don Pearce) wrote: The diagram demonstrated exactly what it needed to demonstrate - no more and no less. To get a ground loop, you need to make a loop from the ground. To make a loop, you need the ground from one piece of kit to another by two separate paths. This can be a problem in two ways. Either, if the loop is physically large it can intercept magnetic hum fields and generate a casement flowing around the loop, or if other equipment is using the circuit, those currents flowing through the main ground path will do the job for you. Virtually *every* outside plant telephone cable is wired up exactly like that. There is a ground at both ends of each and every section (3000 or 6000 feet), and the shields from each coupled section are bonded to the other and to ground. A three mile long section of cable might look just like this: 6000' 6000' 6000' -----------o----------o----------- signal pair -----------o----------o----------- +==//==+ +==//==+ +==//==+ shield | | | | | | | +-+-+ +-+-+ | | | | | ----- ----- ----- ----- --- --- --- --- - - - - Yep, well thats balanced operation which as you say will go for miles over telephone copper lines without humm.. Oddly enough in the UK they don't as a rule use screened cable, the twisted balanced pair has very good rejection. Regular telephone cable does not have a shield on each pair, but does have a shield around the entire bundle of pairs. The above diagram shows the reason! The effects of shielding is almost useless at 50-60 Hz AC power frequencies, which means that noise immunity would be only the common mode rejection ratio if there was no shield or if a shield is grounded at only one end. Instead the shield is grounded at both ends, which allows any induction to not only induce current into the cable pairs, but also into the shield. The shield has is a larger conductor than the pairs, hence has less resistance and therefore significantly more current flows. That current flow in the shield causes an opposing current to be induced into the signal pairs! And that reduces the amount of noise in the signal pair significantly below what it would be if common mode rejection was the only noise reduction mechanism. I seemed to think we were talking about domestic unbalanced lines here?..... The ground loop part is exactly the same in either case. The example above is just a very convenient way to demonstrate positively that cables *are* grounded at both ends, and that it not only does not necessarily cause ground loop noise, but actually is a way to reduce noise in the signal wires. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#76
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10 metres audio cable going into PC = too long?
(Don Pearce) wrote:
On Fri, 21 Apr 2006 02:01:10 -0800, (Floyd L. Davidson) wrote: A three mile long section of cable might look just like this: 6000' 6000' 6000' -----------o----------o----------- signal pair -----------o----------o----------- +==//==+ +==//==+ +==//==+ shield | | | | | | | +-+-+ +-+-+ | | | | | ----- ----- ----- ----- --- --- --- --- - - - - Yet there is no ground loop, ever. Your description says that would virtually *always* cause a ground loop. So please do comment on the above. If what you say is true, nobody would install telephone cables like that, because it would cause *huge* ground loop currents every time! It fits *all* of your criteria perfectly. But it not only doesn't cause a ground loop, it is done specifically to *reduce* noise in the signal wires. Incidentally, the exact same technique would work if the above were applied to a coax cable with one single ended audio channel on it. For example, a 10 meter connection between stereo components! The problem is that you description does *NOT* describe the essence of a "ground loop". You have not shown where the coupling takes place, nor have you describe why it happens. My circuit showed what kind of poor installation causes ground-loop induced hum. You "circuit" was identical to the above. It clearly does *not* necessarily cause ground loop induced hum. You get a ground loop in a domestic Hi Fi (and yes, that is what we are talking about here -forget your telephone cables).when you join to bits of kit together with coax cables, and also have them both connected to mains ground. You get hum in domestic HiFi for *exactly* the reasons I've stated. If you ran separate ground cables all the way to the earth ground (or to some point which represents a low impedance connection to an earth ground), you would *not* have the common path that I've repeated demonstrated is the culprit. But instead people connect all of the equipment grounds to the ground wire in a power outlet, and because that is a very long *common* path, *all* signals on it are induced into each circuit that is connect to it. That includes 60 Hz power and any number of audio (e.g., mono or stereo), video, RF, or whatever signals. In your case, it is a stereo hifi, but the same applies to any other signal too. You apparently were unable to read the equivalent electrical diagram that I posted showing exactly what the mechanism is. Here is is again, though this time I've rearranged it slightly to meet your requirement that the load resister be to the right of the input. I hope the irony of the difference is not lost on you... o---------+ | +-------+ | Rload | +-------+ Signal | Source +------- connection =======//======= ------+ | to cable (Induced Signal) | +-------+ shield | | Rgrnd | | +-------+ | | | o---------+ --------- Ground Differential ---------- | | (Signal Source) | ----- Earth Earth ----- --- Ground Ground --- - - No better. You need to understand that the load is on the far end of the cable, not the same end as the source. You apparently have never worked with equivalent circuits, eh? The load is *not* at the far end of the cable. All that cable is doing is providing a connection to *two*, count them, signal sources. The point in the above diagram is to emphasize the voltage divider made up of the two impedances, Rload and Rgrnd. The cable is shown *only* because it was convenient to draw it that way and label it so that readers would understand what it was. If I weren't dealing with someone like you, it would have looked more like this: Signal Sources Desired Cable Induction Ground Differential o o o | | | +--------+ +--------+ +--------+ | Rload1 | | Rload2 | | Rload3 | +--------+ +--------+ +--------+ | | | o---------------------o---------------------o | +-------+ | Rgrnd | === common path the causes "ground loop hum" +-------+ | | ----- Earth --- Ground - But obviously that is a more difficult to relate to the problem described, and hence while it might be technically correct, it doesn't suit the pedagogical requirements. We are trying to work out how to prevent a domestic system suffering hum from a ground loop. So no, the exact mechanism by which the coupling takes place doesn't matter. What matters is how you connect your kit up. You have adequately demonstrated that understanding the mechanism is a requirement to *fixing* the problem! You've incorrectly described what happens, why it happens, and what can be done to correct it. Knowing how to avoid ground loops is what matters in how you "connect your kit up". The mechanism is having a single common path for two different signals. (It often involves a ground system and that might well have a loop, but in fact is there is no requirement for it to be a ground system and no loop is required other than the normal closed circuit required by *every* signal path.) Wrong. If you connect two bits of kit with a single coax cable, and there are no other connections, you will not have a loop that causes hum. You also can't turn it on, as there is no AC connection. The point is that people *do* want to turn it on, the do want various other components connected, and they *do* want to have various components grounded... both to avoid AC hum and to avoid electrical shock. Hence there *are* going to be other connections to active components. And regardless of that... an easy proof that what you say is not correct is known to almost anyone who has ever tried cabling microphone systems. Just hook up a microphone through several feet (10m would do!) of shielded cable and connect the shield at both ends... No other connections. No ground. No AC either. No loop. But just see what a nice ground loop that makes as soon as someone picks up the microphone! Bzzzzzzzzzzzzzz. You diagrams, on the other hand were actually wrong. You were putting Earth symbols at locations where there is no Earth connection. There of course *is* an "Earth connection" at the points where I showed them, *by definition*. No there isn't, there is a connection to a bit of wire. Here in the UK that is a piece of thinnish bare copper contained within the twin-and-earth 2.5 squ mm cable that connects all domestic sockets to each other. At some distant point where the power enters the house there is an earth connection. And of course *that* is what is shown in both the diagram I drew, and equally well in the one you drew! The points at which I place the ground symbol are the points where the system is connected, via whatever means, to a ground. The impedance of that connection is represented in the equivalent circuit by Rgrnd. You seem to have the mistaken idea that there has to be some sort of "kit", or equipment, connected on both sides of that cable to cause ground loop hum! Wrong! You do realize that in your diagram there were *two* ground loops, right? Not one, two. See if you can find them both. In a house there is only one Earth connection, and that is on the company side of the consumer unit. All ground connections within the house are as I showed - simple wire connections between pieces of kit. In fact, the Earth connection is irrelevant to the phenomenon - ground loops would still happen if the whole lot were floating. There is not necessarily only a single earth connection point in any given house, but the circuit was not necessarily showing a circuit within a single house anyway. It could just as easily be between two houses a mile apart. Nothing in either scenario would change how it works as opposed to a single connection within one building. We are talking about a 10 metre cable connecting a PC to a Hi Fi. It works exactly the same, whether 10 meters or 10 miles. Maybe I'm wrong of course - in your house does each mains socket have an individual ground which is actually a stake driven into the Earth? No? Didn't think so. You've never lived in a house with 1) natural gas lines, 2) water pipes connected to a well, 3) any kind of a ground system for a transmitting antenna, or probably some other odd circumstance that I haven't thought of? (I've lived and worked in buildings with all of that, and I've worked in buildings with more than one electrical distribution system too. Your statement is absurd.) Good for you! And the connection with the current question is? You brought it up, what *was* the point? (None. You didn't make a valid point.) You cannot have "hum" and your desired "signal" without having two, count them, signals. Whether it is a "mono system", or something like RS-485 data, a telephone dial loop, a T1, video, or any of a number of other types of circuits and signals, the basics are exactly the same. Learn some terminology. In electronic engineering generally as well as audio, "signal" refers only to the wanted stuff. Hum, noise and distortion are *not* signal. Signal in one circuit is noise in the other. Your audio of course does not bother the AC power lines, but regardless it is nothing but noise when coupled into the power line. The AC power is the desired signal when on the power line, but noise when on the audio line. The problem, once again, is having those two signals on a *common* *path* (where *both* are the desired signal). In that way each of them becomes a noise for the other's circuit, even though they are in fact both the *desired* signal on the common path. Two signals does *not* define a stereo audio system! (Though your comment pretty much does indicate the extremely limited concept of a "signal" that you have... and that probably explains your limited understanding of ground loops too.) Yes they do. You will find that there is a left signal and a right signal. That, I'm afraid, is your lot. Thanks for the laughs. That is hilarious. I'm always open to learn something new of course. If you have other signals in your stereo do tell me all about them. Tell us all, in fact - I'm sure we would all be glad of the new knowledge. You are confusing cause and effect. A stereo has two signals, but two signals does not make a stereo. There are *many* things that have two signals that are never described as "stereo". The most obvious at this point is a single channel of audio and a single channel of AC power. Two signals... no stereo. And you can trust that everyone who actually does understand what happens is indeed saying you are wrong. I leave them to judge. Has anyone suggested yet that you are even close to correct in any aspect of what you've said? Do you wonder why? I'm still perfectly happy to let my words stand for judgment. They are! -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#77
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
On Fri, 21 Apr 2006 05:52:27 -0800, (Floyd L.
Davidson) wrote: (Don Pearce) wrote: On Fri, 21 Apr 2006 02:01:10 -0800, (Floyd L. Davidson) wrote: A three mile long section of cable might look just like this: 6000' 6000' 6000' -----------o----------o----------- signal pair -----------o----------o----------- +==//==+ +==//==+ +==//==+ shield | | | | | | | +-+-+ +-+-+ | | | | | ----- ----- ----- ----- --- --- --- --- - - - - Yet there is no ground loop, ever. Your description says that would virtually *always* cause a ground loop. So please do comment on the above. If what you say is true, nobody would install telephone cables like that, because it would cause *huge* ground loop currents every time! It fits *all* of your criteria perfectly. But it not only doesn't cause a ground loop, it is done specifically to *reduce* noise in the signal wires. OK I will comment on the above. There are ground loops, and they induce hum. The hum doesn't reach the signal because it is common mode, while the signal is differential - the hum is thus cancelled. Incidentally, the exact same technique would work if the above were applied to a coax cable with one single ended audio channel on it. For example, a 10 meter connection between stereo components! The problem is that you description does *NOT* describe the essence of a "ground loop". You have not shown where the coupling takes place, nor have you describe why it happens. My circuit showed what kind of poor installation causes ground-loop induced hum. You "circuit" was identical to the above. It clearly does *not* necessarily cause ground loop induced hum. Yes it does. You get a ground loop in a domestic Hi Fi (and yes, that is what we are talking about here -forget your telephone cables).when you join to bits of kit together with coax cables, and also have them both connected to mains ground. You get hum in domestic HiFi for *exactly* the reasons I've stated. If you ran separate ground cables all the way to the earth ground (or to some point which represents a low impedance connection to an earth ground), you would *not* have the common path that I've repeated demonstrated is the culprit. But instead people connect all of the equipment grounds to the ground wire in a power outlet, and because that is a very long *common* path, *all* signals on it are induced into each circuit that is connect to it. That includes 60 Hz power and any number of audio (e.g., mono or stereo), video, RF, or whatever signals. In your case, it is a stereo hifi, but the same applies to any other signal too. Try and understand. There is only one signal - that is the wanted signal. The rest is interference. You apparently were unable to read the equivalent electrical diagram that I posted showing exactly what the mechanism is. Here is is again, though this time I've rearranged it slightly to meet your requirement that the load resister be to the right of the input. I hope the irony of the difference is not lost on you... o---------+ | +-------+ | Rload | +-------+ Signal | Source +------- connection =======//======= ------+ | to cable (Induced Signal) | +-------+ shield | | Rgrnd | | +-------+ | | | o---------+ --------- Ground Differential ---------- | | (Signal Source) | ----- Earth Earth ----- --- Ground Ground --- - - No better. You need to understand that the load is on the far end of the cable, not the same end as the source. You apparently have never worked with equivalent circuits, eh? The load is *not* at the far end of the cable. All that cable is doing is providing a connection to *two*, count them, signal sources. The point in the above diagram is to emphasize the voltage divider made up of the two impedances, Rload and Rgrnd. The cable is shown *only* because it was convenient to draw it that way and label it so that readers would understand what it was. If I weren't dealing with someone like you, it would have looked more like this: Signal Sources Desired Cable Induction Ground Differential o o o | | | +--------+ +--------+ +--------+ | Rload1 | | Rload2 | | Rload3 | +--------+ +--------+ +--------+ | | | o---------------------o---------------------o | +-------+ | Rgrnd | === common path the causes "ground loop hum" +-------+ | | ----- Earth --- Ground - You now appear to have three separate load resistors. This just gets more and more bizarre. But obviously that is a more difficult to relate to the problem described, and hence while it might be technically correct, it doesn't suit the pedagogical requirements. We are trying to work out how to prevent a domestic system suffering hum from a ground loop. So no, the exact mechanism by which the coupling takes place doesn't matter. What matters is how you connect your kit up. You have adequately demonstrated that understanding the mechanism is a requirement to *fixing* the problem! You've incorrectly described what happens, why it happens, and what can be done to correct it. I have not at any point addressed what should be done to correct it, but I will now. One must ensure that there is but a single ground connection between two pieces of equipment. In the UK these days that is simple. Amplifiers have mains plugs in which the ground is connected. All ancillary kit - tuners, CD players etc are safety-protected by double insulation, and have a mains plug with no ground connection. The only ground connection they have is via the coax cable, thus making sure that ground loops don't happen, and there is no hum. Knowing how to avoid ground loops is what matters in how you "connect your kit up". The mechanism is having a single common path for two different signals. (It often involves a ground system and that might well have a loop, but in fact is there is no requirement for it to be a ground system and no loop is required other than the normal closed circuit required by *every* signal path.) Wrong. If you connect two bits of kit with a single coax cable, and there are no other connections, you will not have a loop that causes hum. You also can't turn it on, as there is no AC connection. There are these things called batteries, you see.... The point is that people *do* want to turn it on, the do want various other components connected, and they *do* want to have various components grounded... both to avoid AC hum and to avoid electrical shock. Hence there *are* going to be other connections to active components. See my paragraph above. And regardless of that... an easy proof that what you say is not correct is known to almost anyone who has ever tried cabling microphone systems. Just hook up a microphone through several feet (10m would do!) of shielded cable and connect the shield at both ends... No other connections. No ground. No AC either. No loop. But just see what a nice ground loop that makes as soon as someone picks up the microphone! Bzzzzzzzzzzzzzz. Connect the shield to what at both ends? Try and write a little more clearly, please. And yes, I work regularly with microphones, and guess what? The shield is connected to things at both ends. And now you can explain how somebody picking a microphone up could create a ground loop. Or is that simply your name for anything that goes buzz? You diagrams, on the other hand were actually wrong. You were putting Earth symbols at locations where there is no Earth connection. There of course *is* an "Earth connection" at the points where I showed them, *by definition*. No there isn't, there is a connection to a bit of wire. Here in the UK that is a piece of thinnish bare copper contained within the twin-and-earth 2.5 squ mm cable that connects all domestic sockets to each other. At some distant point where the power enters the house there is an earth connection. And of course *that* is what is shown in both the diagram I drew, and equally well in the one you drew! I suggest you look at your diagrams again. They show no such thing. The points at which I place the ground symbol are the points where the system is connected, via whatever means, to a ground. The impedance of that connection is represented in the equivalent circuit by Rgrnd. No - you have placed final earth connections there - not the same thing at all. You seem to have the mistaken idea that there has to be some sort of "kit", or equipment, connected on both sides of that cable to cause ground loop hum! Wrong! No, the kit is there to reveal it. The hum will be generated whatever. You do realize that in your diagram there were *two* ground loops, right? Not one, two. See if you can find them both. There is one ground loop in my diagram. It comprises the coax screen in one direction, and the return via the mains ground cable. I challenge you to find a second. In a house there is only one Earth connection, and that is on the company side of the consumer unit. All ground connections within the house are as I showed - simple wire connections between pieces of kit. In fact, the Earth connection is irrelevant to the phenomenon - ground loops would still happen if the whole lot were floating. There is not necessarily only a single earth connection point in any given house, but the circuit was not necessarily showing a circuit within a single house anyway. It could just as easily be between two houses a mile apart. Nothing in either scenario would change how it works as opposed to a single connection within one building. We are talking about a 10 metre cable connecting a PC to a Hi Fi. It works exactly the same, whether 10 meters or 10 miles. Maybe I'm wrong of course - in your house does each mains socket have an individual ground which is actually a stake driven into the Earth? No? Didn't think so. You've never lived in a house with 1) natural gas lines, 2) water pipes connected to a well, 3) any kind of a ground system for a transmitting antenna, or probably some other odd circumstance that I haven't thought of? (I've lived and worked in buildings with all of that, and I've worked in buildings with more than one electrical distribution system too. Your statement is absurd.) Good for you! And the connection with the current question is? You brought it up, what *was* the point? (None. You didn't make a valid point.) No, I pointed out the errors in your diagrams. You turned it into this nonsense in a desperate attempt to deflect the criticism. You cannot have "hum" and your desired "signal" without having two, count them, signals. Whether it is a "mono system", or something like RS-485 data, a telephone dial loop, a T1, video, or any of a number of other types of circuits and signals, the basics are exactly the same. Learn some terminology. In electronic engineering generally as well as audio, "signal" refers only to the wanted stuff. Hum, noise and distortion are *not* signal. Signal in one circuit is noise in the other. Your audio of course does not bother the AC power lines, but regardless it is nothing but noise when coupled into the power line. The AC power is the desired signal when on the power line, but noise when on the audio line. In audio the signal is the music. All else is interference. AC power is not a signal - signal is information, not power. The problem, once again, is having those two signals on a *common* *path* (where *both* are the desired signal). In that way each of them becomes a noise for the other's circuit, even though they are in fact both the *desired* signal on the common path. What two signals are you talking about now? Two signals does *not* define a stereo audio system! (Though your comment pretty much does indicate the extremely limited concept of a "signal" that you have... and that probably explains your limited understanding of ground loops too.) Yes they do. You will find that there is a left signal and a right signal. That, I'm afraid, is your lot. Thanks for the laughs. That is hilarious. I'm glad you are amused. I'm always open to learn something new of course. If you have other signals in your stereo do tell me all about them. Tell us all, in fact - I'm sure we would all be glad of the new knowledge. You are confusing cause and effect. A stereo has two signals, but two signals does not make a stereo. There are *many* things that have two signals that are never described as "stereo". The most obvious at this point is a single channel of audio and a single channel of AC power. Two signals... no stereo. I know a little girl with an iPod. I suspect even should would call you an idiot. And you can trust that everyone who actually does understand what happens is indeed saying you are wrong. I leave them to judge. Has anyone suggested yet that you are even close to correct in any aspect of what you've said? Do you wonder why? I'm still perfectly happy to let my words stand for judgment. They are! They are? What is that supposed to mean? What are what? Get a grip, please. d -- Pearce Consulting http://www.pearce.uk.com |
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#78
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
(Don Pearce) wrote:
On Fri, 21 Apr 2006 05:52:27 -0800, (Floyd L. Davidson) wrote: (Don Pearce) wrote: On Fri, 21 Apr 2006 02:01:10 -0800, (Floyd L. Davidson) wrote: A three mile long section of cable might look just like this: 6000' 6000' 6000' -----------o----------o----------- signal pair -----------o----------o----------- +==//==+ +==//==+ +==//==+ shield | | | | | | | +-+-+ +-+-+ | | | | | ----- ----- ----- ----- --- --- --- --- - - - - Yet there is no ground loop, ever. Your description says that would virtually *always* cause a ground loop. So please do comment on the above. If what you say is true, nobody would install telephone cables like that, because it would cause *huge* ground loop currents every time! It fits *all* of your criteria perfectly. But it not only doesn't cause a ground loop, it is done specifically to *reduce* noise in the signal wires. OK I will comment on the above. There are ground loops, and they induce hum. The hum doesn't reach the signal because it is common mode, while the signal is differential - the hum is thus cancelled. If that were true, why would anyone in their right mind ever install a telephone cable that way? Common mode never cancels all noise, because the balance is never that perfect, so if what you say is true every telco cable in the country is installed *wrong* and the noise in the cable could be reduced simply by going around and cutting that ground connect. Has it yet occurred to you that you *can't* be right? You "circuit" was identical to the above. It clearly does *not* necessarily cause ground loop induced hum. Yes it does. And nobody in the entire telecom industry knows as much as you do about it, so they *all* do it wrong??? Or, just perhaps... you don't understand it? If I weren't dealing with someone like you, it would have looked more like this: Signal Sources Desired Cable Induction Ground Differential o o o | | | +--------+ +--------+ +--------+ | Rload1 | | Rload2 | | Rload3 | +--------+ +--------+ +--------+ | | | o---------------------o---------------------o | +-------+ | Rgrnd | === common path the causes "ground loop hum" +-------+ | | ----- Earth --- Ground - You now appear to have three separate load resistors. This just gets more and more bizarre. Actually 4 load resistors. The Rgrnd is also part of the load on each signal source. We could label them as Rl1, Rl2, Rl3 and Rlg just as well. You have adequately demonstrated that understanding the mechanism is a requirement to *fixing* the problem! You've incorrectly described what happens, why it happens, and what can be done to correct it. I have not at any point addressed what should be done to correct it, but I will now. One must ensure that there is but a single ground connection between two pieces of equipment. Wrong. A single low impedance connection to ground for each equipment is the key. In the UK these days that is simple. Amplifiers have mains plugs in which the ground is connected. And that is *exactly* where you get a common path for ground returns, which is what causes a ground loop. All ancillary kit - tuners, CD players etc are safety-protected by double insulation, and have a mains plug with no ground connection. The only ground connection they have is via the coax cable, thus making sure that ground loops don't happen, and there is no hum. Which works fine... as long as all of these cables are very short. And by the same token, it does not work so well when there are 10 meter cables or when there is more than one amplifier or other grounded device. Wrong. If you connect two bits of kit with a single coax cable, and there are no other connections, you will not have a loop that causes hum. You also can't turn it on, as there is no AC connection. There are these things called batteries, you see.... So now everything is going to have to be battery powered. You're grasping... And regardless of that... an easy proof that what you say is not correct is known to almost anyone who has ever tried cabling microphone systems. Just hook up a microphone through several feet (10m would do!) of shielded cable and connect the shield at both ends... No other connections. No ground. No AC either. No loop. But just see what a nice ground loop that makes as soon as someone picks up the microphone! Bzzzzzzzzzzzzzz. Connect the shield to what at both ends? Try and write a little more clearly, please. And yes, I work regularly with microphones, and guess what? The shield is connected to things at both ends. Connect it to the equipment! One end to the base of the microphone, and the other end to whatever it is plugged into. And now you can explain how somebody picking a microphone up could create a ground loop. Or is that simply your name for anything that goes buzz? Remember... two signals and a common path... Those of use who actually have worked with mic cables have a different experience than you. You do realize that in your diagram there were *two* ground loops, right? Not one, two. See if you can find them both. There is one ground loop in my diagram. It comprises the coax screen in one direction, and the return via the mains ground cable. I challenge you to find a second. There is a ground loop at each end. The ground lead from the box carries signals both from the box and from the cable shield. That is true at both ends, therefore there are two ground loops. Signal in one circuit is noise in the other. Your audio of course does not bother the AC power lines, but regardless it is nothing but noise when coupled into the power line. The AC power is the desired signal when on the power line, but noise when on the audio line. In audio the signal is the music. All else is interference. AC power is not a signal - signal is information, not power. The problem, once again, is having those two signals on a *common* *path* (where *both* are the desired signal). In that way each of them becomes a noise for the other's circuit, even though they are in fact both the *desired* signal on the common path. What two signals are you talking about now? AC power and audio. I know a little girl with an iPod. I suspect even should would call you an idiot. Just as you do? Of course that is simply because you understand just about as much of this as a little girl with an iPod would be expected to understand, so the comparison does seem apt. Thank you for point it out. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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#79
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
On Fri, 21 Apr 2006 08:02:00 -0800, (Floyd L.
Davidson) wrote: (Don Pearce) wrote: On Fri, 21 Apr 2006 05:52:27 -0800, (Floyd L. Davidson) wrote: (Don Pearce) wrote: On Fri, 21 Apr 2006 02:01:10 -0800, (Floyd L. Davidson) wrote: A three mile long section of cable might look just like this: 6000' 6000' 6000' -----------o----------o----------- signal pair -----------o----------o----------- +==//==+ +==//==+ +==//==+ shield | | | | | | | +-+-+ +-+-+ | | | | | ----- ----- ----- ----- --- --- --- --- - - - - Yet there is no ground loop, ever. Your description says that would virtually *always* cause a ground loop. So please do comment on the above. If what you say is true, nobody would install telephone cables like that, because it would cause *huge* ground loop currents every time! It fits *all* of your criteria perfectly. But it not only doesn't cause a ground loop, it is done specifically to *reduce* noise in the signal wires. OK I will comment on the above. There are ground loops, and they induce hum. The hum doesn't reach the signal because it is common mode, while the signal is differential - the hum is thus cancelled. If that were true, why would anyone in their right mind ever install a telephone cable that way? Common mode never cancels all noise, because the balance is never that perfect, so if what you say is true every telco cable in the country is installed *wrong* and the noise in the cable could be reduced simply by going around and cutting that ground connect. Has it yet occurred to you that you *can't* be right? No. The way telephones are connected cancels sufficient common mode noise to work. All of telephony is the business of doing just enough - expensive is the last thing you want. To quote a saying - "Don't let the best be an enemy to the good". You "circuit" was identical to the above. It clearly does *not* necessarily cause ground loop induced hum. Yes it does. And nobody in the entire telecom industry knows as much as you do about it, so they *all* do it wrong??? Er - no. It would just be you that has this wrong. Or, just perhaps... you don't understand it? If I weren't dealing with someone like you, it would have looked more like this: Signal Sources Desired Cable Induction Ground Differential o o o | | | +--------+ +--------+ +--------+ | Rload1 | | Rload2 | | Rload3 | +--------+ +--------+ +--------+ | | | o---------------------o---------------------o | +-------+ | Rgrnd | === common path the causes "ground loop hum" +-------+ | | ----- Earth --- Ground - You now appear to have three separate load resistors. This just gets more and more bizarre. Actually 4 load resistors. The Rgrnd is also part of the load on each signal source. We could label them as Rl1, Rl2, Rl3 and Rlg just as well. This is one load resistor. It is the input impedance of the amplifier. You have adequately demonstrated that understanding the mechanism is a requirement to *fixing* the problem! You've incorrectly described what happens, why it happens, and what can be done to correct it. I have not at any point addressed what should be done to correct it, but I will now. One must ensure that there is but a single ground connection between two pieces of equipment. Wrong. A single low impedance connection to ground for each equipment is the key. That's right. And the way it is done here in the UK is exactly as I described. But at last you have admitted that to avoid hum you do need a single ground connection - I call that progress, of a sort. In the UK these days that is simple. Amplifiers have mains plugs in which the ground is connected. And that is *exactly* where you get a common path for ground returns, which is what causes a ground loop. No. That is a single point of connection to ground for the entire system. You can't have a loop with just one connection - think about it. All ancillary kit - tuners, CD players etc are safety-protected by double insulation, and have a mains plug with no ground connection. The only ground connection they have is via the coax cable, thus making sure that ground loops don't happen, and there is no hum. Which works fine... as long as all of these cables are very short. And by the same token, it does not work so well when there are 10 meter cables or when there is more than one amplifier or other grounded device. It works perfectly with any domestic length of cable you like. The worst problem you would find with longer cables is capacitive losses. Wrong. If you connect two bits of kit with a single coax cable, and there are no other connections, you will not have a loop that causes hum. You also can't turn it on, as there is no AC connection. There are these things called batteries, you see.... So now everything is going to have to be battery powered. You're grasping... Follow the logic! I wasn't saying everything had to be battery powered, I was countering your claim that everything had to have an AC power connection. And regardless of that... an easy proof that what you say is not correct is known to almost anyone who has ever tried cabling microphone systems. Just hook up a microphone through several feet (10m would do!) of shielded cable and connect the shield at both ends... No other connections. No ground. No AC either. No loop. But just see what a nice ground loop that makes as soon as someone picks up the microphone! Bzzzzzzzzzzzzzz. Connect the shield to what at both ends? Try and write a little more clearly, please. And yes, I work regularly with microphones, and guess what? The shield is connected to things at both ends. Connect it to the equipment! One end to the base of the microphone, and the other end to whatever it is plugged into. OK. My microphones have a screen in the cable. At the equipment end it connects to the ground terminal. At the microphone end it connects to the casing. With my condenser microphones it also connects to the lower end of the amplifier circuit. And now you can explain how somebody picking a microphone up could create a ground loop. Or is that simply your name for anything that goes buzz? Remember... two signals and a common path... First - no buzz. None of my microphones buzzes when I pick it up. If yours do, you have a problem. And of course it isn't a ground loop, unless you are also grabbing something grounded. Those of use who actually have worked with mic cables have a different experience than you. No. Those who have worked with broken mic cables have a different experience. Fix them! You do realize that in your diagram there were *two* ground loops, right? Not one, two. See if you can find them both. There is one ground loop in my diagram. It comprises the coax screen in one direction, and the return via the mains ground cable. I challenge you to find a second. There is a ground loop at each end. The ground lead from the box carries signals both from the box and from the cable shield. That is true at both ends, therefore there are two ground loops. What on earth (pun) are you talking about? A single connection is not a loop - it is a connection. Do you even know what a loop is? I'm serious - you appear to have no concept. Signal in one circuit is noise in the other. Your audio of course does not bother the AC power lines, but regardless it is nothing but noise when coupled into the power line. The AC power is the desired signal when on the power line, but noise when on the audio line. In audio the signal is the music. All else is interference. AC power is not a signal - signal is information, not power. The problem, once again, is having those two signals on a *common* *path* (where *both* are the desired signal). In that way each of them becomes a noise for the other's circuit, even though they are in fact both the *desired* signal on the common path. What two signals are you talking about now? AC power and audio. You need to learn how to keep AC power signals out of your audio leads. Your system must be a disaster area. I know a little girl with an iPod. I suspect even should would call you an idiot. Just as you do? Of course that is simply because you understand just about as much of this as a little girl with an iPod would be expected to understand, so the comparison does seem apt. Thank you for point it out. Your grammar is sinking as fast as your logic at this point. Take a break. d -- Pearce Consulting http://www.pearce.uk.com |
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#80
Posted to alt.engineering.electrical,uk.rec.audio,rec.audio.tech
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10 metres audio cable going into PC = too long?
On Fri, 21 Apr 2006 07:10:08 GMT, (Don Pearce)
Gave us: On Fri, 21 Apr 2006 03:46:32 GMT, Roy L. Fuchs wrote: On Thu, 20 Apr 2006 07:54:57 GMT, (Don Pearce) Gave us: No, the thread has effectively been killed by your diagrams that won't survive the threading process, and are hence not discussable in any meaningful way. You just proved that you are even more of an idiot than he proved you are. His diagrams didn't kill the thread, and no, you do NOT quote everything over and over again, dolt boy. I quote what I want to quote. I produced a simple diagram that showed the essentials of a ground loop - two ground connections and a single signal connection. This was the opposite of what he claimed. He then went on to produce a slew of poor ascii diagrams, none of which demonstrated his contention. It was clear at that point that the thread was going nowhere. So, are you saying he is right, and I am wrong? Do you believe that for a ground loop you need two signal connections and one ground connection? Go ahead - make my day. You are so far off, you don't know how many PATHS are involved, so there is no way that you are going to discern anything about any LOOPS that may be present in one or more of those PATHS that you are so underinformed about. Therefore, I deduce that you will not garner ANY facts about ground loops until you reset your bent perception mindset. Try again. |
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