Isolation Transformer. Sometimes a misunderstood technology. A true isolation transformer will have two windings, one primary and one secondary. The primary winding is connected to the electrical system and couples power via an electromagnetic field to the secondary winding, which powers the electronic load. There are two main benefits to using a true isolation transformer.
First, no direct electrical connection exists between the electronic load and the electrical system. Isolation transformers often have at least one Faraday Shield between the windings, which acts to increase the inter-winding capacitance slightly and to function as a path to ground for noise currents. This allows the transformer to act as a buffer against low-voltage, high frequency disturbances.
A second benefit of the isolation transformer is that the National Electrical Code (NEC) allows the output neutral conductor to be re-bonded to the safety ground conductor. This simple action eliminates neutral-to-ground voltages that exist in the branch circuit wiring.
It also permits surge diverters and noise filters, when connected across the transformer secondary, to function without creating a neutral to ground disturbance. Isolation transformers create a very friendly electrical environment for microprocessor-based systems.
A second configuration for isolation transformers is gaining recognition. This configuration is referred to as balanced power, where the transformer secondary does not have its output neutral bonded to ground. Instead, the secondary winding is center-tapped with the center tap acting as the ground for the connected load.
The phase and neutral conductors of the secondary (while still maintaining a full voltage potential between them) each measure 50 percent of the source voltage to the center tapped ground. Balanced power technology assumes that electrical noise at any frequency will be imposed in equal amplitude but exactly opposite phase across each half of the center-tapped transformer secondary. Full cancellation of any noise currents is assumed to occur under such circumstances.
There is some debate over the effectiveness of balanced power configurations, but it is reasonable to assume that, when correctly designed and constructed, balanced power can reduce electrical noise at least as efficiently as other technologies.
Balanced power transformers do not offer a quiet neutral to ground reference required for computer systems to operate reliably since bonding of neutral to ground is not permitted with balanced power configurations.
Isolation transformers are viewed negatively by some in the audio industry because of a perception that they alter sound characteristics. This is true for isolation transformers with high impedance characteristics.
When a sudden change in load current occurs (as can happen with higher powered sound systems) a high impedance isolation transformer cannot rapidly transfer current from primary to secondary. This starves the load for current, distorts the secondary voltage waveform and sound reproduction suffers.
It’s important to note, however, that newer isolation transformer technology is available that is low impedance in nature. One common design of low impedance isolation transformer provides a steady state run current of 12 amps with the ability to supply up to 192 amps for 1 second without any accompanying voltage distortion appearing on the transformer secondary. Low impedance transformer designs are acoustically quiet and completely compatible with audio and video systems.