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10 metres audio cable going into PC = too long?
"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.. |
10 metres audio cable going into PC = too long?
On 19 Apr 2006, wrote:
mc spake thus: I gather that you are in the UK (hence "ring" wiring structure, which I like, instead of the American daisychain) and that everything is in the same room. It should work fine. So how does house wiring work in the UK? Is there more than one grounding ("earthing") point? And how is this better? (Here, the Merkin practice is to ground the "service panel"--the box where the big wires come into the house--to a single ground rod, with everything running downstream from that.) By the way, this brings up a strange experience I had recently doing some wiring. I was working for a guy who owns two houses right next to each other, and he wanted to run a cable TV connection from one house to the other. I was about to connect the cable in the attic of the house that was the source of the signal when I got a little tingle. After grabbing a VOM, it turned out that there was about a 20 volt difference between the two cable grounds. Mc doesn't understand ground loops. You can get them between two boxes plugged into the same double socket. Your tingle was because your equipment is not grounded, and is perfectly normal. Does your "perfectly normal" mean: "there is no fault and no danger (until the ground is actually needed and then will be a danger)" |
10 metres audio cable going into PC = too long?
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. |
10 metres audio cable going into PC = too long?
"Richard Crowley" wrote:
"David Nebenzahl" wrote ... No, my tingle was because I was holding two cables strung between two different houses, each grounded at its end. Doesn't seem normal at all to me. If they were each properly "grounded", you would NOT have seen any voltage differential. BY DEFINITION. (Or else the two houses were on differen planets. :-) That is not true. Granted that the 20 Volt differential he mentions in another article is high (for a residential area), it is not at all uncommon. What is uncommon though, is a person who can actually feel 20 Volts! -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
10 metres audio cable going into PC = too long?
"mc" wrote:
"Richard Crowley" wrote in message ... "David Nebenzahl" wrote ... No, my tingle was because I was holding two cables strung between two different houses, each grounded at its end. Doesn't seem normal at all to me. If they were each properly "grounded", you would NOT have seen any voltage differential. BY DEFINITION. I would almost bet that at least one of them wasn't really grounded (to the earth). Then there would have been no differential, and hence no voltage and no tingling... ;-) Second choice is that high voltage is being conducted directly into the earth from some kind of unintended connection. A bad thing. Not a bad thing, just a rather common thing in many industrial areas. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
10 metres audio cable going into PC = too long?
(Don Pearce) wrote:
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 The above does describe typical residential power distributionn. However, anywhere that industrial power (i.e., 3 phase) is available, there will in fact be all three phases available... 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. Same in the US. Or are zoning laws in the States such that it is not possible to set up a business in an otherwise residential area? That might be, might not be... it would depend on local laws. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
10 metres audio cable going into PC = too long?
In article , Floyd L. Davidson
writes tony sayer wrote: In article , Floyd L. Davidson writes tony sayer wrote: In article , Floyd L. Davidson writes 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! Over here it seems to, well the half a dozen or so I've looked at!. We I'm not sure what you are agreeing with there... that cables do or don't! :-) Doesn't matter either way as long as its balanced working and in any case telephone bandwidth isn't that responsive to 'ummmm... Anyways these days in the UK the copper part isn't that long in new cable co installations, the fibre to copper conversion is done very locally to a subs premises and in the BT system the copper is longer but doesn't humm.. Typically of course a customer never sees any part of such a telephone cable. What you see is a "drop wire" run from that cable to your location. That cable will not be shielded. Yep but they don't use shielding on a lot of phone multicore in the UK and it wouldn't matter anyway.. we're involved in a short term radio broadcast some years ago and the cable co supplied free of charge a few circuits about 3 odd miles to link Two studios together, and apart from a small amount of HF loss..no hum at all or other noise for that matter and all that cable was unshielded.... When done right, it works *extremely* well. 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. Balanced working.. ever read up about it or used it in practice?... About 40 years of working with it every day in a huge variety of situations. 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. Really;-?.... Yup. I posted this URL in another message, but just in case... here is a very interesting, if somewhat technical, article about measured effects of grounded shielding. It is very interesting in the context of this particular thread. 64.70.157.146/pdf/Bondingcableshields.pdf Yes.. Thats got some good points but they don't seem to be very savvy on some matters about EMC and RF and you can pick a few holes in that but yes their correct in screening or shielding earthing at both ends provided that the balance in the sending and receiving ends is what it should be, injecting current into the shield won't affect what's carried in the encased conductors. However in practice the final result is and can be affected by transformer and electronic balanced inputs and how "floating" they are. I think we could all agree that balanced working isn't really a problem. Now they mention unbalanced working, but haven't given it much attention. Now ASCII art permitting are we agreed that the following isn't going to cause too much upset?.. -------------------------------------------------------------- A __________________________________________________ ______________ M ------------------------------------------------------------- Poxy ASCII!. Now consider A is an amp input and M is a source microphone The dotted lines are the shield on a lump of single cored microphone cable. Now the amp is connected A to the centre conductor at the amp end the screen to the earthed side of the amp input, at the other end the microphone has say a phono type connector, and the mic is a dynamic moving coil type with one end connected to the inner shielded conductor of the cable, the other end is connected to the outer shielded conductor, the mic is in a metal case and is connected to the shield of the cable too. The mic case is not connected to any earth, other than the outer shield of the connecting cable, and lets say thats 10 meters long or 12 yards;) The mic is suspended in free space by a lump of nylon cord and isn't connected to anything else at all... Now are we agreed that that arrangement will or won't hum?...... -- Tony Sayer |
10 metres audio cable going into PC = too long?
tony sayer wrote:
In article , Floyd L. Davidson writes 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! Over here it seems to, well the half a dozen or so I've looked at!. We I'm not sure what you are agreeing with there... that cables do or don't! :-) Doesn't matter either way as long as its balanced working and in any case telephone bandwidth isn't that responsive to 'ummmm... Ahem. That is absolutely false. Telecom engineering necessarily goes to an extreme effort to reduce what is called "power line influence". The reasons should be obvious: telephone and power cables are often run side by side, on the same poles, and in the same crawl spaces, sometimes for miles at a stretch. It is not uncommon to see as much as 40 to 50 volts of power line AC on a telecom cable. That requires an astounding amount of noise immunity to allow a circuit to work. Consider that the test tone level at a customer premise telephone set is nominally targeted at -9 dBm, and the worst case acceptable Signal-to-Noise ratio is 24 dB, which means that all noise should be at least at -33 dBm, which is about 0.0000005 watts. But a 40 volts hum across a 600 ohm impedance is 2.7 watts, and there is roughly 67 dB difference! Do you have any idea how many telephone lines actually have a 67 dB SNR? Anyways these days in the UK the copper part isn't that long in new cable co installations, the fibre to copper conversion is done very locally to a subs premises and in the BT system the copper is longer but doesn't humm.. So? "Very locally" can mean more than a *mile*... What do you mean by "BT system the copper is longer but doesn't humm.."? They have hum resistance copper??? ;-) Typically of course a customer never sees any part of such a telephone cable. What you see is a "drop wire" run from that cable to your location. That cable will not be shielded. Yep but they don't use shielding on a lot of phone multicore in the UK and it wouldn't matter anyway.. Virtually *all* "multicore" telecom cable is shielded. (Some customer premise cable is not. But you won't find anything within a telephone central office that isn't, and you won't find any outside plant distribution cable that isn't.) Where are you coming up with these ideas? Have you ever even seen the specs for any of this? Yup. I posted this URL in another message, but just in case... here is a very interesting, if somewhat technical, article about measured effects of grounded shielding. It is very interesting in the context of this particular thread. 64.70.157.146/pdf/Bondingcableshields.pdf Yes.. Thats got some good points but they don't seem to be very savvy on some matters about EMC and RF and you can pick a few holes in that but Heh heh, lets see you try picking any holes in it! yes their correct in screening or shielding earthing at both ends provided that the balance in the sending and receiving ends is what it should be, injecting current into the shield won't affect what's carried in the encased conductors. You didn't read it, did you? It *does* affect the signal pairs. It reduces the noise on them, significantly. However in practice the final result is and can be affected by transformer and electronic balanced inputs and how "floating" they are. In practice, what they showed was that it improves noise immunity. "Floating" makes no difference at all. Longitudinal balance is the most significant factor. Magnetic shielding is ineffective below about 10 kHz, and reverse induction via the shield (by grounding it at both ends) is much more significant for power line frequencies and their harmonics (which commonly exist up to 2 or 3 kHz). I think we could all agree that balanced working isn't really a problem. We could all agree that common mode rejection is not always sufficient, and that reverse induction is virtually *always* applied to outside plant communications cables because of that. Exactly what you mean by "balanced working", I'm not sure. Now they mention unbalanced working, but haven't given it much attention. It is rarely used for critical circuits where induction interference from power lines would be important. (For obvious reasons...) Now ASCII art permitting are we agreed that the following isn't going to cause too much upset?.. -------------------------------------------------------------- A __________________________________________________ ______________ M ------------------------------------------------------------- Poxy ASCII!. Now consider A is an amp input and M is a source microphone The dotted lines are the shield on a lump of single cored microphone cable. Now the amp is connected A to the centre conductor at the amp end the screen to the earthed side of the amp input, at the other end the microphone has say a phono type connector, and the mic is a dynamic moving coil type with one end connected to the inner shielded conductor of the cable, the other end is connected to the outer shielded conductor, the mic is in a metal case and is connected to the shield of the cable too. The mic case is not connected to any earth, other than the outer shield of the connecting cable, and lets say thats 10 meters long or 12 yards;) The mic is suspended in free space by a lump of nylon cord and isn't connected to anything else at all... Now are we agreed that that arrangement will or won't hum?...... Nothing you have said suggests it could possibly hum, given that you have not mentioned the presence of any power line related equipment at all. If this thing is located out in the ocean, on a floating barge that has no AC electric power, it won't hum. On the other hand, if you place a fluorescent light fixture close to it, it might well hum! Regardless, that is one of the worst possible ways to wire 10 meters of cable to a microphone. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
10 metres audio cable going into PC = too long?
In article , Floyd L. Davidson
writes tony sayer wrote: In article , Floyd L. Davidson writes 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! Over here it seems to, well the half a dozen or so I've looked at!. We I'm not sure what you are agreeing with there... that cables do or don't! :-) Doesn't matter either way as long as its balanced working and in any case telephone bandwidth isn't that responsive to 'ummmm... Ahem. That is absolutely false. Telecom engineering necessarily goes to an extreme effort to reduce what is called "power line influence". The reasons should be obvious: telephone and power cables are often run side by side, on the same poles, and in the same crawl spaces, sometimes for miles at a stretch. It is not uncommon to see as much as 40 to 50 volts of power line AC on a telecom cable. That requires an astounding amount of noise immunity to allow a circuit to work. Yes they do, in fact we've got a broadcast transmitter site which is fed by a bit of BT, (British Telecom, the national Telco), overhead wire for some miles and no hum at all!. And that is on the same pole set as 240 volt mains wiring and I've actually seen 11 kV lines with phone lines near them. Not that advisable owing to the safety factor!. Yes of course you can get leakage via induction and capacitance into the telecom lines but this does not matter as it will inevitably be induced in both conductors and cancelled out by common mode rejection. Doesn't matter providing the insulation in the line and transformers will stand it to have some kilovolts actually on the line as such... Consider that the test tone level at a customer premise telephone set is nominally targeted at -9 dBm, and the worst case acceptable Signal-to-Noise ratio is 24 dB, which means that all noise should be at least at -33 dBm, which is about 0.0000005 watts. But a 40 volts hum across a 600 ohm impedance is 2.7 watts, and there is roughly 67 dB difference! Can you explain how your measuring or have that configured please?.. Do you have any idea how many telephone lines actually have a 67 dB SNR? Anyways these days in the UK the copper part isn't that long in new cable co installations, the fibre to copper conversion is done very locally to a subs premises and in the BT system the copper is longer but doesn't humm.. So? "Very locally" can mean more than a *mile*... Often less than in ntl or telewest installations but longer in BT ones. Ntl care the cableco in the UK but that name is to disappear and their to be called Virgin!... What do you mean by "BT system the copper is longer but doesn't humm.."? They have hum resistance copper??? ;-) Nope;!, just a way of putting that, see above,... Typically of course a customer never sees any part of such a telephone cable. What you see is a "drop wire" run from that cable to your location. That cable will not be shielded. Yep but they don't use shielding on a lot of phone multicore in the UK and it wouldn't matter anyway.. Virtually *all* "multicore" telecom cable is shielded. (Some customer premise cable is not. But you won't find anything within a telephone central office that isn't, and you won't find any outside plant distribution cable that isn't.) In a central office most all of it here is twisted pair. I think some terminology things betwixt the UK and USA are showing up here. All the cable co Telco multicores I've seen, though not all, are unshielded. What do you define shielding as, just a wrap of aluminium foil with a drain wire or a fully woven copper mesh?.. Where are you coming up with these ideas? Have you ever even seen the specs for any of this? Yup. I posted this URL in another message, but just in case... here is a very interesting, if somewhat technical, article about measured effects of grounded shielding. It is very interesting in the context of this particular thread. 64.70.157.146/pdf/Bondingcableshields.pdf Yes.. Thats got some good points but they don't seem to be very savvy on some matters about EMC and RF and you can pick a few holes in that but Heh heh, lets see you try picking any holes in it! OK then, part 2 "On the other hand cable shields which are bonded at one end etc". Read that thorough carefully, doesn't make sense. Then take a lump of Andrews 4-50 Heliax and see what a good radiator that is even greater number of wavelengths . They didn't even state if it were open circuit or terminated on a load... Actually we've had a lot of EMC experience over the years in radio, audio and automotive environments and what's made by far and away the biggest effect is bypassing of transistor junctions at RF frequencies.... yes their correct in screening or shielding earthing at both ends provided that the balance in the sending and receiving ends is what it should be, injecting current into the shield won't affect what's carried in the encased conductors. You didn't read it, did you? It *does* affect the signal pairs. It reduces the noise on them, significantly. Were is this noise coming from then?... However in practice the final result is and can be affected by transformer and electronic balanced inputs and how "floating" they are. In practice, what they showed was that it improves noise immunity. "Floating" makes no difference at all. Well think about that, Say we have a cable the inner pairs are wrapped around one of the power lines that you describe, and there are a LOT of volts induced on that wiring. OK now into a transformer there will be galvanic isolation i.e. the ends or centre tap of that transformer isn't connected to anything. Now take a electronically balanced input. At some point that will be connected to say an input IC which will have supply rails etc, and that IC will be coupled through to the output of that line receiving amplifier now don't you think that if there were some matter of kilovolts on said line, then that will break down the transistor junctions ?.. Longitudinal balance is the most significant factor. Magnetic shielding is ineffective below about 10 kHz, and reverse induction via the shield (by grounding it at both ends) is much more significant for power line frequencies and their harmonics (which commonly exist up to 2 or 3 kHz). I think you have that wrong. Provided that the rejection is what it should be then whatever is induced on the pairs will cancel out. I think we could all agree that balanced working isn't really a problem. We could all agree that common mode rejection is not always sufficient, and that reverse induction is virtually *always* applied to outside plant communications cables because of that. Exactly what you mean by "balanced working", I'm not sure. What we've been discussing. Take a signal source and connect a transformer thereto and connect that to a pair of wires twisted together and then connect that to another transformer and the out put winding of that to a load. That do?.. Now they mention unbalanced working, but haven't given it much attention. It is rarely used for critical circuits where induction interference from power lines would be important. (For obvious reasons...) Yes.. Now ASCII art permitting are we agreed that the following isn't going to cause too much upset?.. -------------------------------------------------------------- A __________________________________________________ ______________ M ------------------------------------------------------------- Poxy ASCII!. Now consider A is an amp input and M is a source microphone The dotted lines are the shield on a lump of single cored microphone cable. Now the amp is connected A to the centre conductor at the amp end the screen to the earthed side of the amp input, at the other end the microphone has say a phono type connector, and the mic is a dynamic moving coil type with one end connected to the inner shielded conductor of the cable, the other end is connected to the outer shielded conductor, the mic is in a metal case and is connected to the shield of the cable too. The mic case is not connected to any earth, other than the outer shield of the connecting cable, and lets say thats 10 meters long or 12 yards;) The mic is suspended in free space by a lump of nylon cord and isn't connected to anything else at all... Now are we agreed that that arrangement will or won't hum?...... Nothing you have said suggests it could possibly hum, given that you have not mentioned the presence of any power line related equipment at all. If this thing is located out in the ocean, on a floating barge that has no AC electric power, it won't hum. On the other hand, if you place a fluorescent light fixture close to it, it might well hum! Why?. Regardless, that is one of the worst possible ways to wire 10 meters of cable to a microphone. Yes agreed and you wouldn't do that, well not in a pro environment anyway. Now if say you ground that to the local mains earth at one end, and say 10 meters away at the microphone case end earth that to a driven rod earth, will it or wont it hummmmmmmmmmm?..... -- Tony Sayer |
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