by David Fiori, Jr.

Summary of Part 1 & 2

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 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.
Part 2 explained a 3 step ground management strategy that obtains the best possible results from any current balancing device such as a ground loop isolator.

Frequency Response Problems

Just like crossover inductors, the coils used in the ground loop isolators are inherently frequency dependent devices whose performance deteriorates at higher current levels. In particular they do not work as well at low frequencies. They present a frequency dependent inductive loading at their inputs which makes driving them very difficult. Driving ground loop isolators with low output impedance sources, and adjusting them for low voltage levels is recommended to minimize distortion caused by their loading on the source and their saturation characteristics which cause distortion.

Because of the physics of the transformer used in the ground loop isolator, ground loop isolators have difficulty delivering bass frequency without losses and distortion. This loss can be compensated to some extent by a suitable electronic equalizer or by increasing the level of the bass. But any bass equalization is best applied after the ground loop isolator to keep the source signal levels applied to the ground loop isolator at bass frequencies as low as possible to minimize distortion.

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.

Also, because of the operation of the physics of their transformers, ground loop isolators deliver their signal with much greater inductance, and with greater output impedance than their source. For this reason, the capacitance characteristic of the output cable they connect to is more critical to high frequency fidelity. In addition, the quality of the cable shield is also more critical as any electric fields that may find their way into the cable are not as effectively suppressed because of the higher cable drive impedance. Placing the ground loop isolator at the destination end of the system to minimize the length of the output cable will help achieve better high frequency fidelity by minimizing the output cable capacitance. Shorter output cable length also reduces the possibility of picking up any stray electric field interferences.

Achieving Ultimate High Fidelity

When greater levels of performance are required than ground loop isolators can provide, current balanced devices, such as the Crystal-Line™ drivers, exclusively manufactured by Anamir Electronics, Inc., provide every noise cancelling feature ground loop isolators provide without any compromise in fidelity. This is possible because they use extremely high performance solid state electronics instead of transformers to achieve the balance of all signal currents. In addition, the Anamir device can actually enhance the fidelity of signal delivery with its unique combination of current balancing and extraordinary low cable drive impedance — which together remove every possible sonic effect of the cables on signal fidelity — including all possible interference noises.