Electrical noise from all types of sources can cause severe problems in electronic circuits, so designers spend much time wrestling with ways to reduce or eliminate it. In audio equipment, low-frequency noise can easily couple with sensitive circuits to distort signals. In many measurement systems, ground-loop noise causes problems that sometimes prove almost impossible to overcome.

I recently found two documents and a book that engineers will find useful when they face noise problems.

1. The Audio Engineering Society (AES) publishes "AES Standard on Interconnections--Grounding and EMV Practices--Shields of Connectors in Audio Equipment Containing Active Circuitry," AES48-2005. Although the document title is a mouthful, the document itself takes only 11 pages. It provides much useful information about shielding, connectors, and grounding techniques that benefit almost any design. You can read the document at: http://campuspa.com/downloads/aes48-2005-f.pdf. On the same Web site, you'll find a tutorial about grounding created by Bill Whitlock of Jensen Transformers: http://campuspa.com/downloads/grounding_tutorial.pdf.
2. Texas Instruments published an Application Report, "Ground Loop Break Circuits and Their Operation," as SLOA143 in October 2009. You will find that 14-page document at http://tinyurl.com/yjsmxx6. Of course, TI notes how to use its ground-loop-break (GLB) components, but it also provides guidance about ground loops and how to defeat them.

While doing some research, I found Henry W. Ott, an electromagnetic-compatibility consultant. Taking a chance, I sent him an email with several questions and hoped he might clarify a few points about shielding low-level signals. Mr. Ott responded quickly and gave his advice freely. He also pointed me to his book, Electromagnetic Compatibility Engineering," John Wiley & Sons, 2009. ISBN: 978-0-470-18930-6. The book provides a lot of practical information and it doesn't swamp readers with theory and math. The book has a retail price of $US 120, but Amazon sells it for $US 96, and you can review the book's table of contents on the Amazon Web site. I bought this book and found it very helpful and a valuable resource. I think you will, too.

--Jon Titus