System Problems & Equipment Manufacturers

R readers of this column know that I don’t hesitate to criticize equipment manufacturers for their technically parochial and/or deficient engineering which ultimately drives system installers, maintenance technicians and users crazy. Although I'm an instructor at a number of seminars and workshops each year, the by Bill Whitlock recent Syn-Aud-Con JENSEN TRANSFORMERS Grounding and Shielding Workshop provided me with three full days of valuable feedback from engineers, contractors and installers who work “on the front lines.” Even though the students begged us to identify makers of this frustrating equipment by name and model, we had to decline; I refuse to help any lawyer get rich. Perhaps we can work out a non-legally dangerous way to identify makers of good equipment (ideas anyone??). Nevertheless, such extended interaction with students and other instructors helps keep my presentations on track and reconfirms that dealing with interface problems still consumes an awful lot of time and produces an abundance of frustration because: l Contradictory “rules” about interfacing and grounding abound from many sources, l Customers expect a steadily increasing dynamic range from systems, l Input/output impedance specs and “matching” are still widely misunderstood, l Unbalanced “consumer” equipment is increasingly common in all kinds of “pro” systems, l Computers and CRT displays are now a major noise producer in many systems, l Must still believe that hum and buzz result from “bad grounding,” and l “Cut and try” is still the most popular method of fighting ground noise problems. “‘System friendly” equipment still not the rule. Regrettably, a large number of equipment manufacturers continue to “bury their heads in the sand” when it comes to system problems. The two biggest problems we common (shared) impedance coupling inside the equipment, a.k.a. the “pin 1 problem,” and poor performing “electronically balanced” inputs. These problems are not just academic curiosities, they are the real cause of most system hum, buzz and noise problems. Both continue to exist because standard lab tests used during product development and sub sequent production tests don’t correlate with real world “in-system” use of the equipment.