10 metres audio cable going into PC = too long?

On Fri, 21 Apr 2006 07:10:08 GMT, snipped-for-privacy@pearce.uk.com (Don Pearce) Gave us:

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.

On Fri, 21 Apr 2006 08:47:55 GMT, snipped-for-privacy@pearce.uk.com (Don Pearce) Gave us:

Bullshit. A few milliohms down a wire is as close to "earth" as it needs to be to be called "earth ground". Every outlet in an American home has a copper strand connected to earth available (and used) in it.

When the ground wire is several hundred feet of wire like in a building, it can be argued as not being "earth", and I have installed driven ground rods INSIDE large buildings for ESD grounding, so I know that chaotic potentials can exist on the "ground" wire included in electrical systems at those lengths. In the home it is far less, yet still can be present under certain conditions.

On Fri, 21 Apr 2006 08:47:55 GMT, snipped-for-privacy@pearce.uk.com (Don Pearce) Gave us:

You're an idiot.

On Fri, 21 Apr 2006 10:53:54 GMT, snipped-for-privacy@pearce.uk.com (Don Pearce) Gave us:

"Bits of kit"? That's some fine, technical talk you have there... Not!

Line level inputs are low voltage, high impedance inputs, so the baseline noise is higher with respect to the actual desired signal. That is ONE source of noise. The ground loop noise is another SIGNAL, that can end up getting INJECTED into the amplifier as part of the desired signal content. From that point on, it is included, and can even be recorded. When you find a ground loop, then analyse how you take steps to curtail the UNdesired SIGNAL, you will find that your analysis of the fix proves that Floyd is correct.

Just out of your head, what is the fix for this situation, and tell us about the electrical observation of the CIRCUIT(S) while the undesired noise SIGNAL is present, and when you have either disconnected or CLAMPED it.

Once you have made that report, and you face what it means, Floyd will accept your apology.

On Fri, 21 Apr 2006 14:26:10 GMT, snipped-for-privacy@pearce.uk.com (Don Pearce) Gave us:

The elements of his circuit diagram are 100% accurate.

On Fri, 21 Apr 2006 14:26:10 GMT, snipped-for-privacy@pearce.uk.com (Don Pearce) Gave us:

The person's body creates an additional SIGNAL PATH.

Maybe one day, you will get it.

On Fri, 21 Apr 2006 17:18:33 GMT, snipped-for-privacy@pearce.uk.com (Don Pearce) Gave us:

Tell us again how a person that is NOT connected to anything else at can touch a microphone and cause "hum" then. Then tell us how many SIGNAL PATHS there are while said person is causing said noise.

Don't duck this one, Chucko. You cannot avoid the righteousness of the Floyd.

Hilarious. Regardless, virtually *any* engineering text on cable systems will explain that what you say is not true, and in fact the very reason cable sheaths are grounded is to reduce noise and *improve* on common mode rejection, simply because otherwise there would often be too much power line influence on the cable pairs.

Regardless... I ran across something that explains it in terms closer to what you claim to understand: audio sound systems (granted, not at the home user level you deal with, but...).

"Bonding Cable Shields at Both Ends to Reduce Noise", by Tony Waldron and Keith Armstrong. To be quite honest, I was surprised at how much the effect was when applied to short cable runs. I had thought it was only that significant when the cable lengths were in thousands of feet, but they demonstrate very effectively that even when used with cables only a few meters in length the effect is significant.

Here is the part you need to know:

We have shown that concerns about 50/60Hz noise generated by ground loops when bonding both ends of the shields of balanced audio cables are without basis. Ground loop currents are not a real problem for correctly-designed pro-audio equipment, in fact they are a real benefit. Ground loop currents flowing in the shield of a balanced cable cannot give rise to significant DM noise due to inductive coupling between the shield and the signal conductors within a cable, because this mode of coupling only has a small effect and is intrinsically very well balanced. (With attention to the practical details of the shield-chassis connection at each end of the cable, no significant inductive coupling need occur there either.)

As one addition, since it is not mentioned in that article, I'll comment on the use of a PEC (Parallel Earth Conductor). There is one included within the sheathing of virtually all shielded cables intended for long (more than 10-20 feet) cable runs. Generally the "shield" is a metal foil. The PEC is a single copper conductor.

The above cited document demonstrates, *in* *detail*, with measurements and the required theory, exactly why that is not true.

If you would spend less time on petty personal attacks and more on technical accuracy, you might actually be able to learn enough to understand what I've shown you.

OK, I've had it with you pair of incompetents, and this is going to be my last word on the subject.

I have made a recording and put it on my web site

http://81.174.169.10/ It is of me speaking into the most insensitive microphone I have - a high impedance ribbon.

Halfway through I take hold of the microphone body. I am sure you will be amazed to hear that the result is absolutely no hum whatever. Do you have any idea why this surprise result should come about? No? Well, I'll tell you. It is because I know what I am doing, I understand ground loops and I don't allow them in my system.

That, as far as I am concerned, is it.

Have a nice day, the pair of you, and remember - if you don't know the words, you can always hum.

My hearing isn't what it was - so I compensate for that by setting the controls to give me what I imagine I would be hearing if I was 18 years young again.

Pure heresy, I am sure, but I can no longer make out the fine detail and nuances whilst listening in a concert hall - so, at home, I tweak the settings so that I can. Heaven knows what it sounds like to anyone else, but, living alone, that isn't a problem. Compensating for the odd few dB loss over 10kHz due to cable characteristics gets rather swamped by the compensation needed due to not always having worn earplugs when I should have...

But then, I am writing on the "electrical" group - where I suspect many, like me, are rather grateful our hearing has deteriorated to the point we don't notice the noise from lopts, static inverters, brushgear, etc, as much as we once did. The workplace sure has got quieter over the years..

Over here it seems to, well the half a dozen or so I've looked at!. We 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....

Balanced working.. ever read up about it or used it in practice?...

Really;-?....

Whatever is going on, on your planet?.. This doesn't happen here!....

They have both passed Magna Cum Laude in advanced incompetence. I hope they aren't allowed sharp objects - you may have heard that a knife will cut a few millimetres off your fingers every time you pick it up.

I'm not sure what you are agreeing with there... that cables do or don't! :-)

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.

When done right, it works *extremely* well.

About 40 years of working with it every day in a huge variety of situations.

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.

It *does* happen, under the circumstances described. If all you do is extend the shield to surround the microphone element, and do *not* connect to it, then you get no noise. Try hooking that shield to the microphone element and see what you get!

For a fellow who has posted exactly *zero* evidence that he understands anything at all about electricity, that is a very telling bit of ad hominem. It says you are so insecure that gratuitous insults are the closest thing you have to an argument...

OK, now I'm actually laughing.

So you haven't listened to that piece of evidence I posted on my web site? Thought you might want to avoid that.

Just as your supposed "diagram" didn't show what a ground loop is, your "evidence" isn't evidence.

Your posting was essentially an assertion that if you connect up a microphone wrongly, it doesn't work properly. Now maybe you don't understand why you shouldn't connect a microphone the way you suggest, but it is a fact.

My web site evidence showed - and yes it did show - that when you know what you are doing and connect everything up properly, there is no hum when you touch a microphone body.

Really? I'm not aware of any large scale generating facilities that generate single phase, since you can always extract single phase from 3-phase.

No doubt 3-phase delivery is a problem in areas where they run just a single phase. But using the original 3-phase rather than reconstructing 3-phase from single phase has got to be more efficient. It also seems more reliable, since the converter is a piece of rotating equipment (basically a motor/generator set, IINM). Yuck. I bet the energy conversion efficiency is less than 70%.

It would be extremely expensive to retrofit large areas of legacy 1-phase distribution with 3-phase today. However, I'll bet that the main substation gets 3-phase feeds, which it parcels out as single phase in some load-balanced arrangement from each of the 3 phases.