Cautions Regarding Humming Noise - Integra RDA-7 Instruction Manual

Cautions regarding humming noise

If humming is heard even when the volume is turned
down or the RDA-7 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.
14
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. 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 1.5-m (5-foot) 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.