Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums > AC Power and Grounding

Semantics

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Jonathan Johnson:
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.

John Roberts {JR}:
+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 

Frank Koenig:

--- Quote from: Jonathan Johnson on October 15, 2013, 05:37:53 PM ---It would be more precise to use the term ground current interference.
--- End quote ---

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

Mac Kerr:

--- Quote from: Frank Koenig on October 15, 2013, 08:09:52 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

--- End quote ---

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

Mac

John Roberts {JR}:
Maybe I should sell my old hardcover edition...

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

JR

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