February Meeting Notice

February 2005 Meeting Notice

Think audio system grounding and interfacing is a black art? Do signal cables really "pick up" noise from the air like a radio receiver?  Equipment manufacturers, installers, and users rarely understand the real sources of system noise and ground loop problems, often overlooking or ignoring basic laws of physics. This tutorial intends to replace myth and misinformation with insight and knowledge.
Signals accumulate noise and interference as they flow through system equipment and cables. Both balanced and unbalanced interfaces transport signals but are also vulnerable to coupling of interference from the power line and other sources. The realities of ac power distribution and safety are such that some widely used noise reduction strategies are both illegal and dangerous. Properly wired, fully code-compliant systems always exhibit small but significant residual voltages between pieces of equipment as well as tiny leakage currents that flow in signal cables. The unbalanced interface is inherently vulnerable to noise caused by these currents.  The balanced interface, because of common-mode rejection, can theoretically nullify such noise problems. But balanced interfaces are widely misunderstood and most suffer severe degradation of noise rejection in real-world systems. Many pieces of equipment, because of an innocent design error, have a built-in noise coupling mechanism dubbed the "pin 1 problem" by Neil Muncy. Simple troubleshooting methods that use no test equipment will be described. They can pinpoint the exact location and cause of system noise. Most often, devices known as ground isolators are the best way to eliminate noise coupling. Signal quality and other practical issues are discussed as well as how to properly connect unbalanced and balanced interfaces to each other. Finally, RF interference and power line treatments such as technical power, balanced power, power isolation transformers, and surge suppression will be discussed.

Bill Whitlock has designed pro audio and video electronics and systems for 30 years. In 1989, after seven years with Capitol Records, he became president of Jensen Transformers. He has become a recognized expert on system interfacing issues through his writing and teaching. His paper on balanced interfaces appears in the June 1995 AES Journal, which has become the most popular ever printed. Other writing includes regular columns in Sound & Video Contractor and Live Sound magazines, three chapters for Glen Ballou's 1500-page "Handbook for Sound Engineers," and numerous magazine articles and Jensen application notes. Since 1994, he has helped thousands unravel the mysteries of grounding and signal interfacing by teaching at trade shows, technical colleges, and professional organizations. Bill holds several patents including the InGenius® balanced input circuit and the ExactPower® waveform-correcting ac power voltage regulator. He is an active member of the Audio Engineering Society and a senior member of the Institute of Electrical and Electronic Engineers.

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