10 metres audio cable going into PC = too long?

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?
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?
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.
Wrong. A single low impedance connection to ground for each equipment is the key.
And that is *exactly* where you get a common path for ground returns, which is what causes a ground loop.
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.
So now everything is going to have to be battery powered.
You're grasping...
Connect it to the equipment! One end to the base of the microphone, and the other end to whatever it is plugged into.
Remember... two signals and a common path...
Those of use who actually have worked with mic cables have a different experience than you.
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.
AC power and audio.
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.
Reply to
Floyd L. Davidson
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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".
Er - no. It would just be you that has this wrong.
This is one load resistor. It is the input impedance of the amplifier.
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.
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.
It works perfectly with any domestic length of cable you like. The worst problem you would find with longer cables is capacitive losses.
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.
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.
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.
No. Those who have worked with broken mic cables have a different experience. Fix them!
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.
You need to learn how to keep AC power signals out of your audio leads. Your system must be a disaster area.
Your grammar is sinking as fast as your logic at this point. Take a break.
d
Reply to
Don Pearce
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.
Reply to
Roy L. Fuchs
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.
Reply to
Roy L. Fuchs
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.
Reply to
Roy L. Fuchs
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.
Reply to
Roy L. Fuchs
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.
Reply to
Roy L. Fuchs
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.
Reply to
Roy L. Fuchs
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...).
64.70.157.146/pdf/Bondingcableshields.pdf
"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:
12 Conclusions
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.
Reply to
Floyd L. Davidson
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.
d
Reply to
Don Pearce
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..
Reply to
Palindr☻me
In article , Floyd L. Davidson writes
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;-?....
Reply to
tony sayer
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.
d
Reply to
Don Pearce
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.
64.70.157.146/pdf/Bondingcableshields.pdf
Reply to
Floyd L. Davidson
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...
Reply to
Floyd L. Davidson
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.
d
Reply to
Don Pearce
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.
d
Reply to
Don Pearce

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