Outlaw Audio 200 M-Block A Few Words About Hum and Noise, Suggestion #1, Suggestion #2, 60Hz AC

Owner’s Manual

A Few Words About Hum and Noise

Ground Loop Diagram

Coax Cable

Set-top Box

Cable Feed

60Hz AC

A/V

Cables

60Hz AC

Ground Loop

Main House

Grounding

	Ground Loop
AC Line	AC Line
AC Ground

A Few Words About Hum and Noise

Audible hum, or a discernable low frequency noise, is one of the most com- mon problems in audio/video systems. This hum, which may be present even when the volume is at a low level or when the power is off, is usually caused by a problem known as a “ground loop”. A ground loop occurs when there is a difference in ground voltages between two or more components that are connected electrically. This, in turn, creates multiple current paths and causes the low-level noise, or hum.

The growing sophistication of home theater systems, and the increased number of components used to create these systems has dramatically increased the potential for the possibility of ground loops. While it is natural to suspect that the components in your system are the cause of the hum, in many cases the cause may be due to other conditions. In particular, cable TV connections from outside the house have become a major source of hum.

In most cases, one of the following suggestions should help you to solve a hum problem in your system. Please try these steps in the sequence shown, proceeding from one step to the next if the prior suggestion does not eliminate the problem.

Potential Ground Loops in a Complex A/V System

Suggestion #1:

To determine if a cable TV connection is responsible for the hum, first turn all components off. Disconnect the cable TV feed to your system at the first place where it connects to your components. Alternatively, disconnect the cable TV

wire where it is connected at the wall outlet. Turn your system back on, and listen if the hum has disappeared. If removing the cable TV feed has eliminated the hum, you will need to insert a Ground Loop Isolator before reconnecting the cable TV feed, or contact your cable TV operator to see if they can better isolate your cable feed.

Suggestion #2:

Turn off all components in your system, and then disconnect the input cables at the amplifier. Turn the amplifier back on, and see if the hum is still present. If the hum disappears, the fault may be in the input cables used. Try replacing them with cables that have better shielding, and make certain that the input cables are not running on top of any AC power cords. Change the cables one at a time to determine if one, or all cables is responsive. If the hum disappears when the input cables are disconnected, but returns after the cables are changed and the system re-connected, the problem may be caused by your processor, receiver or preamplifier.

Suggestion #3:

Poor grounding of the electrical system in your home may also cause ground loop problems, particularly when there are multiple components with three prong, grounded, power cords. Try unplugging these components one at a time, and see if one or all of them is causing the problem. The ultimate solu- tion to this type of problem is to re-wire your house with an isolated, star-type grounding configuration. We recognize, however, that this may be impracti- cal and expensive. In some cases, the use of an approved AC Power Isolation Transformer of sufficient capacity may solve this problem.

Model 200 M-Block Power Amplifier

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