Iso-Float Ground Isolation

Since the earliest modern audio systems, there has been a problem with ground loops. Ground loops result from equipment being connected to different points of an AC distribution system, giving rise to a potential difference between the interconnected audio devices. Since audio circuitry is sensitive, any noisy ground signals will interfere with the audio signal, resulting in buzzes or hums in relationship to the fundamental frequency of the AC distribution system.

Historically, ground loops have been removed by using isolation transformers. Transformers provide an excellent isolation barrier, but they have other less-than-ideal attributes, including both level attenuation and high-frequency loss. Some highly optimized transformer designs can minimize these problems, but at a very high cost.

The Dolby^® Lake^® Processor, Lake Contour™, and Mesa Quad EQ™ utilize a unique approach that provides all the benefits of transformer isolation with none of the negatives. This is performed by electrically isolating input and output audio signals through the use of high-speed opto-isolators and high-speed digital signal transformers (not audio signal transformers) to create a barrier between the processor and possible grounding aberrations from the outside electrical environment (Figure 1).

Figure 1 Isolation Barrier Between Analog and Digital

By isolating all of the digital signals and locally deriving the power source for the highly sensitive analog audio circuitry (Figure 2), Iso-Float™ represents a truly unique and highly effective ground isolation system.

Figure 2 Local Power Derived via Custom Planar Transformers

Each converter card of the Dolby Lake Processor includes an Iso-Float switch (Figure 3) that allows the card to be grounded or lifted. In the lifted position, the converters are also placed into Software Control (SC) mode, allowing for the Dolby Lake Controller software to switch the ground state remotely. This feature allows for fast troubleshooting from a centralized control interface for a large distributed signal processing system.

Figure 3 Iso-Float Switch