Wherever possible, it is recommended that balanced power be used to cover the entire production facility including remote equipment that is interconnected through a/v cables. There are, however, acceptable wiring methods that have proven to work well when the supply of balanced power is limited in an area or where remote equipment running on unbalanced AC is patched into the balanced system. The approach to such situations is similar in every case.
A good example of this approach is in live sound reinforcement applications where amplifier load can be extremely large. Power amps usually add very little noise to a sound system. Most of the noise in a typical P.A. system is created in the front of house gear, the back line amps and instrument racks. These are the primary areas to be covered with balanced power — areas where low level signals are being processed. Mic preamps, guitar amps, instrument preamps and effects fall under this low-level signal category. These components must run on balanced AC to demonstrate a significant effect on noise levels and to eliminate the source of possible problems before they occur.
When connecting a system running on balanced power and a system running on unbalanced power, the signal grounds of the systems need to be isolated. With balanced audio signals, lift the shields at the inputs. With unbalanced audio or video signals, use an isolation transformer.
These rules apply for remote hook-ups to permanent facilities, especially where one of the systems has not yet been set up for balanced power but the other has. Simply lift the shields at the inputs on the remote system in similar fashion as is common practice in most splitter snakes used in remote facilities.
When mixing balanced AC and unbalanced AC, keep in mind that a/v cabling is the primary path of grounding noise. Lifting audio shields at the inputs or using isolation transformers where systems are interconnected works well to eliminate interference anywhere unbalanced power must be used with balanced power. If fiber optics are used for all signal links, disregard all of the above and don’t worry about it.