10 metres audio cable going into PC = too long?



I would almost bet that at least one of them wasn't really grounded (to the earth).
Second choice is that high voltage is being conducted directly into the earth from some kind of unintended connection. A bad thing.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Then there would have been no differential, and hence no voltage and no tingling... ;-)

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) snipped-for-privacy@apaflo.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 19 Apr 2006 07:22:42 -0700, "Richard Crowley"

"Ground" is not all created equal. Dirt sucks as a conductor and you can see significant voltage differences between two grounding electrode systems. If you are connecting signal lines between two buildings be sure you also bond the grounding systems together.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 19 Apr 2006 12:12:25 -0400, snipped-for-privacy@aol.com Gave us:

Reminds me of an ESD fiasco I had at one place I fixed up while I worked there.
We drove a ground rod in the shop, into the earth at a little breakout point in the slab of our floor.
The potential between the grounded benches and the AC system grounded SMD reflow bench was 90 volts. Enough that I could feel the tinge in my arms if I rested them on the mat for that bench. That shop was in sad shape.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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) snipped-for-privacy@apaflo.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

A "ground loop" is caused by having a common ground path for two different signals. Current from each signal causes a voltage drop, due to Ohmic losses, across the ground path for both circuits. The effect is that each circuit affects the signal of the other. Typically if one of those signals is 60 Hz power and the other is something in the audio range, the audio signal will then have a 60 Hz "buzz" on it.
Obviously, if the only ground path is through a common 3-wire socket, yes it is possible for two boxes to have a ground loop.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) snipped-for-privacy@apaflo.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 19 Apr 2006 09:03:21 -0800, snipped-for-privacy@apaflo.com (Floyd L. Davidson) wrote:

You got this backwards. A ground loop is caused by having two ground paths for a single signal wire. A hum signal is induced into the signal wire by means of a hum current flowing round that ground loop. That current can be generated in either of two ways - a simple potential difference between the two grounds, or alternatively magnetic induction into the loop; generally the first will generate the bigger signal.
d
--
Pearce Consulting
http://www.pearce.uk.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@pearce.uk.com (Don Pearce) wrote:

Actually, what I said was *precisely* correct.

Your language is a mess, but what you just said is *exactly* the same thing. One wire is a common path...

Wrong. There is no loop involved. It is current flowing on the *common* portion that causes interaction.

Get a book or two... and study what happens. Try drawing a diagram of what you think is happening!
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) snipped-for-privacy@apaflo.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 19 Apr 2006 11:23:24 -0800, snipped-for-privacy@apaflo.com (Floyd L. Davidson) wrote:

Nonsense - you claim one ground path and two signals. It is one signal and two ground paths - it is those two ground paths that form the ground loop.

No, my language is just fine, and it is the exact opposite of what you said.

There is a loop involved. That is why it is called a ground loop. The loop is necessary for the current to flow round and generate the emf that appears on the signal wire.

Thank you, I have designed a great deal of high precision measuring equipment and I know exactly what signal paths are present in a ground loop. And they aren't what you claim.
d
--
Pearce Consulting
http://www.pearce.uk.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@pearce.uk.com (Don Pearce) wrote:

And I have it *precisely* correct. (Hint: I'm not guessing.)
If there were only one signal... what problem would there be???? The trouble is that one signal causes interference with another. It does that because they share a common path. Ohmic losses across that conductor affect *both* signals, even when caused by only one of them. Bingo, that *is* the problem.

Two ground paths and one wire... does *not* make sense. Signals have paths. Those paths can be wires. You can't have two paths in one wire...
But the common "ground loop" is indeed caused by grounding a single conductor at two points. That provides a common path through the single wire... for *two* signals. One is the "desired" signal, and the other is a current between the two ground points.

Try drawing a diagram of what you are describing.

If you do know what it is, you certainly have a problem describing it in terms that make sense. I'll vote for you don't know...
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) snipped-for-privacy@apaflo.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 19 Apr 2006 11:46:44 -0800, snipped-for-privacy@apaflo.com (Floyd L. Davidson) wrote:

So what are you saying here - that a mono signal can't suffer a ground loop? Stereo is the minimum that can show the problem?
You only need one signal. Here's a hint as to where you may be going wrong. Signal is the term used to describe the wanted stuff. The rest isn't signal - it is hum.

Of course it makes sense. The commonest scenario for two ground paths is that one is the outer of the coax, and the other is a pair of ground wires in the mains leads, meeting at the mains ground. The single signal wire is the inner of the coax. This just isn't that hard to understand.

No it doesn't. It means that the ground is connected via two separate paths - you need those two separate paths to form the loop.

Done. You can find it here http://81.174.169.10 /

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.
d
--
Pearce Consulting
http://www.pearce.uk.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@pearce.uk.com (Don Pearce) wrote:

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 --- - -
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.)
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 - -
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.
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 - -
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.

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.
-- Floyd L. Davidson <http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) snipped-for-privacy@apaflo.com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 19 Apr 2006 23:30:25 -0800, snipped-for-privacy@apaflo.com (Floyd L. Davidson) wrote:

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.

Why are you telling me this?

No more so than mine.

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?

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.

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
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@pearce.uk.com (Don Pearce) wrote:

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) snipped-for-privacy@apaflo.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 20 Apr 2006 07:54:57 GMT, snipped-for-privacy@pearce.uk.com (Don Pearce) Gave us:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 21 Apr 2006 03:46:32 GMT, Roy L. Fuchs

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
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@pearce.uk.com (Don Pearce) wrote:

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.

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) snipped-for-privacy@apaflo.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 21 Apr 2006 00:33:35 -0800, snipped-for-privacy@apaflo.com (Floyd L. Davidson) 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. 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.

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).

I leave them to judge.
d
--
Pearce Consulting
http://www.pearce.uk.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@pearce.uk.com (Don Pearce) wrote:

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 --- - -

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.)

There of course *is* an "Earth connection" at the points where I showed them, *by definition*.

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.

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.)

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.)

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) snipped-for-privacy@apaflo.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.