Onkyo RDA-7.1 - Manual (Page 14)

14
Cautions regarding humming noise
If humming is heard even when the volume is turned
down or the RDA-7.1 is turned off, then a “ground
loop” may be occurring. A ground loop is a potential
difference in the grounding of two or more
electrically connected components. This potential
difference creates multiple current routes when there
should only be one. This potential difference results
in a hum noise and at times it can be just a low level
noise. With the increased sophistication of home
theaters, the chance of grounding loops occurring has
greatly increased. If humming occurs, before
considering it due to faulty equipment, read the
following information listed to the right. 1. Your cable television system wiring
may be causing the hum.
To determine whether the cable television is the cause of
the hum, disconnect the cable television cable (round 75-
ohm cable) or the first component that the cable is
connected to (the set-top box or VCR). If the humming
stops, connect a commercially-available 75-ohm ground
loop isolator before reconnecting the system. If the
humming still continues, read 2, 3, and 4 below.
2. An input cable is causing the hum
Turn off the entire system and disconnect all input cables.
If the humming stops, reconnect the cables one at a time
to determine the faulty cable. If the hum continues after
all input cables are reconnected, contact an Onkyo service
station or representative.
3. AC ground terminal loop
An AC ground terminal loop will cause the loudest hum.
When grounding a system that uses a power cord with a
three-pronged plug, be aware of components with a
grounding terminal. If you cannot alter your home wiring
to an insulated star-shaped grounding configuration, try
an insulation transformer.
Caution
Never remove the ground terminal (the third round
terminal) from the plug of the power cord that comes with
the RDA-7.1. Doing so is very dangerous for it may cause
an electrical shock or even electrocution.
4. Improper grounding in your home is
causing the hum
In most cases, a water pipe is used as the ground in your
home. Make sure that the connection is strong by
checking for loose pipes or excessive corrosion. The most
certain remedy is to ground the system independently.
Drive a 5-foot (1.5-m) or longer copper-plated steel
grounding pole into the ground and use this as the system
ground. If you have questions regarding this procedure
consult an electrician or your local electrical company.
If after exhausting all the possibilities given above the
humming continues, contact an Onkyo service station or
representative.
5. Both the balanced-line inputs and RCA
inputs are connected
Unconnect either set and make sure the input selector
switch is set to the correct position.