David Fiori, Jr. is the managing director and chief scientist of Anamir Electronics, Inc., manufacturer of Crystal-Line™ preamplifiers and cable enhancement products among other innovative noise control devices. He may be reached at Anamir Electronics, Inc. at (215) 638-1600.

Summary of Part 1

Ground loop isolators are useful in eliminating interference related to signal cables or the ground circuits they create. Although they are often called "RCA noise filters" their effectiveness has nothing to do with filtering, even though they do unfortunately suppress bass. Instead, they are effective because they convert all RCA cables connected to them into current balanced lines that offer many of the same noise cancelling advantages that professional balanced lines provide, but with the additional advantage of breaking all possible ground loops. Their deficiencies in fidelity and noise cancellation entirely stem from the limitations of the magnetic field physics of the transformers they incorporate. Their location and orientation in the vehicle — as far as possible from the alternator and battery cables — can help minimize some of these deficiencies.

Ground Management

Proper handling of the RCA grounds is important to obtaining the best possible results with any current balancing device- including a ground loop isolator. For example, when the ground loop isolator breaks all possible ground loops, it may also break the conductivity of the RCA shield conductor to a ground. Since cable shields need conductivity to ground to properly drain any noisy electric field currents away from the center signal carrying conductor of the RCA cable, installation of the ground loop isolator can sometimes defeat the action of the RCA cable shield.

The best strategy for managing grounds with any current balanced device involves three basic principles:

First, every current balanced RCA cable should be terminated by a connection between its shield and battery ground to maintain the effectiveness of the cable's shield.

Second, current balancing can work through other pieces of signal processing equipment, to some extent, if that equipment is able to isolate their own signal grounds from battery ground. Most equipment that features switch mode power supplies and/or opto-coupling can relay the current balance if the grounding is properly handled.

Third, the advantages of current balancing can be made to extend from the inputs of the ground loop isolator, through any intermediate isolated signal processors, up to the point where the signal ground connects to the battery ground.

Installation Strategy

These principles suggest a very effective 3 step ground managment strategy for including as many of the system's cables as possible in the scope of the ground loop isolators' current balancing:

#1. Be sure every processor between the ground loop isolator's input cables, and including the furthest upstream non-isolated signal processor all connect their input RCA grounds to their output RCA ground connections. If they don't, make the connection yourself by soldering small wires to make that connection.

#2. Be sure every processor between the ground loop isolator and the furthest downstream non-isolated signal processor all connect their input RCA grounds to their output RCA ground. If they don't, make the connection yourself by soldering small wires to make that connection.

#3. As long as all the intermediate processor in the signal chain after the ground loop isolator are isolated, Connect the RCA input shield of the system's most critical amplifier - which is usually the front stage tweeter amplifier channels — to that amplifiers battery ground terminal where it connects to its power ground cable.