[Elecraft] Getting a buzz, the wrong way

[Jim Brown]

On 1/12/2011 12:10 PM, George & Jan wrote:
> For those of us who have a living in professional audio, video and RF,
> the proper term for what you call the "Pin #1" problem is a Ground Loop - or
> at least that is the term we have used for the 50 years I was in radio&  TV
> broadcasting&  video production.

Sorry to disagree George. Yes, we have used the words "ground loop" to 
somehow describe the coupling of hum and buzz into audio systems, but 
the words don't make sense if you try to draw an electrical circuit that 
demonstrates what you are talking about. As a teenager, and subsequently 
as an EE, I struggled to find any logic in anything I had seen on the 
topic. Indeed, the problem with the term "ground loop" is that it causes 
VERY muddy thinking and outright stupid conclusions about what are good 
and bad methods of bonding equipment together, to the power system, and 
to a ground system.

The first rational drawing I've ever seen was prepared by Bill Whitlock, 
the excellent engineer who owns Jensen Transformers.  Before joining 
Jensen more than 25 years ago, Bill designed consoles for Quad Eight and 
studios for Capitol Records. Bill uses that drawing to clearly show how 
hum, buzz, and noise is coupled into both balanced and unbalanced audio 
systems.  There are excellent tutorials on his website. google to find 
it. Bill is also the guy who showed conclusively that when interrupting 
the shield of balanced cable between line ins and outs to prevent shield 
current, that the interruption must be on the receiving end, not the 
sending end.  He did this by showing that a noise rejection in a 
balanced interconnect is the result of a balanced Wheatstone bridge, 
where the impedances of source and receiver are elements of the bridge. 
He was recently made a Fellow of the AES for his many contributions to 
our understanding of these issues.

I have adapted and expanded upon Bill's drawings for my own tutorials 
and lectures. You can see them in 
http://audiosystemsgroup.com/HamInterfacing.pdf   which addresses how 
these issues should be handled for the UN-balanced connections in a ham 
station. There's a lot more about these issues on my website.

http://audiosystemsgroup.com/publish.htm

73, Jim Brown K9YC