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Author Topic: Semantics  (Read 4980 times)

Jonathan Johnson

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Semantics
« on: October 15, 2013, 05:37:53 pm »

One term that is common in the audio industry, and an issue featured prominently in the "AC Power and Grounding" section of the forums, is ground loop hum.

It's really an unfortunate misnomer. The presence of a ground loop doesn't necessarily imply that there will be hum, and hum can be caused by currents on the ground even in systems with properly designed hub-and-spoke grounding systems. Of course, hum is more likely where there are loops than in hub-and-spoke systems.

It would be more precise to use the term ground current interference. Our goal is not necessarily to eliminate ground loops (in the physical topology), but to reduce ground currents and the problems they cause, typically by ensuring that ground voltage potentials between equipment is minimized. Often this means removing ground loops, but also important is ensuring that grounding conductors are of sufficient size that the conductor resistance is low enough to reduce those voltage differentials.

Probably a pointless rant, but using precise terminology helps people understand problems better, and better understanding leads to better solutions.
« Last Edit: October 15, 2013, 06:10:44 pm by Jonathan Johnson »
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John Roberts {JR}

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Re: Semantics
« Reply #1 on: October 15, 2013, 06:44:11 pm »

+1... thank you

Ground loops are real things (one turn windings) that designers actually encounter inside products like old school heavy iron power amps, or consoles with power transformers inside, etc. I do not doubt that there may be loops caused by shields in external interface wiring, but generally these do not have to be worried about, while lead dress can reduce loop area and may improve problematic unbalanced (consumer) interfaces. 

Ground contamination is a completely different issue, and not much of an issue with prudent design and professional interfaces.

JR 
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Frank Koenig

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Re: Semantics
« Reply #2 on: October 15, 2013, 08:09:52 pm »

It would be more precise to use the term ground current interference.

I am with you, but will add that Ground Current Interference is not the only source of hum. Capacitive coupling also can cause hum.

While we're at it, here's the classic reference, so far as I know:
http://www.amazon.com/Noise-Reduction-Techniques-Electronic-Systems-ebook/dp/B000VIIYAO
Happy I got mine when it was less that $126  :o

--Frank
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Mac Kerr

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Re: Semantics
« Reply #3 on: October 15, 2013, 08:12:51 pm »

I am with you, but will add that Ground Current Interference is not the only source of hum. Capacitive coupling also can cause hum.

While we're at it, here's the classic reference, so far as I know:
http://www.amazon.com/Noise-Reduction-Techniques-Electronic-Systems-ebook/dp/B000VIIYAO
Happy I got mine when it was less that $126  :o

--Frank

Hmm.. $126 for a Kindle edition, $90 for hardcover, and $16-$30 for used.

Mac
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John Roberts {JR}

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Re: Semantics
« Reply #4 on: October 15, 2013, 08:26:10 pm »

Maybe I should sell my old hardcover edition...

The bidding begins at one million dollars... .. :-)

JR
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Doug Fowler

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Re: Semantics
« Reply #5 on: October 16, 2013, 12:08:38 am »

One term that is common in the audio industry, and an issue featured prominently in the "AC Power and Grounding" section of the forums, is ground loop hum.

It's really an unfortunate misnomer. The presence of a ground loop doesn't necessarily imply that there will be hum, and hum can be caused by currents on the ground even in systems with properly designed hub-and-spoke grounding systems. Of course, hum is more likely where there are loops than in hub-and-spoke systems.

It would be more precise to use the term ground current interference. Our goal is not necessarily to eliminate ground loops (in the physical topology), but to reduce ground currents and the problems they cause, typically by ensuring that ground voltage potentials between equipment is minimized. Often this means removing ground loops, but also important is ensuring that grounding conductors are of sufficient size that the conductor resistance is low enough to reduce those voltage differentials.

Probably a pointless rant, but using precise terminology helps people understand problems better, and better understanding leads to better solutions.

"Out of phase" vs. "Reverse Polarity".
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John Roberts {JR}

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Re: Semantics
« Reply #6 on: October 16, 2013, 10:19:41 am »

"Out of phase" vs. "Reverse Polarity".
Audio phase vs mains power phase.

JR
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David J. Thomas

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Re: Semantics
« Reply #7 on: October 16, 2013, 10:57:08 am »

Henry Ott provides an excellent reference in "Noise Reduction Techniques in Electronic Systems". It is a comprehensive look at the sources of EMI in electronic circuits and also provides valuable insights into the reduction/elimination of the noise interference to meet the applicable test standards. It is must-read for novice engineers and a great refresher for the more experienced designer. No EMC engineer or system design engineer worth his/her salt should be missing this volume on their bookshelf!
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Kevin Graf

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Re: Semantics
« Reply #8 on: October 16, 2013, 11:38:01 am »

Henry Ott provides an excellent reference in "Noise Reduction Techniques in Electronic Systems". It is a comprehensive look at the sources of EMI in electronic circuits and also provides valuable insights into the reduction/elimination of the noise interference to meet the applicable test standards. It is must-read for novice engineers and a great refresher for the more experienced designer. No EMC engineer or system design engineer worth his/her salt should be missing this volume on their bookshelf!

This Henry W. Ott 300 page book is from 1988:
"Noise Reduction Techniques in Electronic Systems,"2nd Edition, by Henry W. Ott, publisher: John Wiley & Sons, 1988, ISBN#: 0-471-85068-3.

His new 850 page book is:
"Electromagnetic Compatibility Engineering"
 by Henry W. Ott,
publisher: John Wiley & Sons, hardcover 872 pages, 566 figures, 65 tables.
Publication date: August 2009, ISBN#: 978-0-470-18930-6.

http://www.hottconsultants.com/EMCE_book_files/emce_book.html


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John Roberts {JR}

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Re: Semantics
« Reply #9 on: October 16, 2013, 12:02:33 pm »

This Henry W. Ott 300 page book is from 1988:
"Noise Reduction Techniques in Electronic Systems,"2nd Edition, by Henry W. Ott, publisher: John Wiley & Sons, 1988, ISBN#: 0-471-85068-3.



My copy is C. 1976...

Bidding now starts at $2 million dollars..  ;D
=====
I recall seeing a few things in the '76 edition that seemed a little dated in light of the vast expansion of RF energy all around us today. The physics has not changed but the environment has a little. I suspect subsequent editions evolved over time to accommodate changing conditions. I doubt they seriously anticipated sending digital data over power lines, routine PFC for consumer products, etc. back then.   

The 2009 publication is surely up to date.
-------
I recall seeing an almost humorous reference in a very old acoustics text to a unit of absorption as being a "unit area open window".  These days an open window is a noise source.  ;D

JR
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