9 a few words about hum and noi, 9 potential ground loops in a complex a/v syst, A few words about hum and noise 9 – Outlaw Audio 200 M-Block User Manual

Page 9: Potential ground loops in a complex a/v system, A few words about hum and noise, Suggestion #2, Suggestion #3

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Outlaw Audio

Owner’s Manual


Model 200 M-Block Power Amplifier

Owner’s Manual

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.

60Hz AC

Ground Loop

60Hz AC

Ground Loop

AC Ground

AC Line



Main House


Cable Feed

Coax Cable

Ground Loop Diagram

AC Line

A Few Words About Hum and Noise

Set-top Box