Octave V 70 Class A, Owner'S Manual

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11. TROUBLESHOOTING
11.1 Faults caused by external issues
Buzzing and hum in the speakers
 Possible cause: multiple grounds
Hum in an audio system is often caused by several system components having their own separate
grounds. It is particularly common in systems containing tuners, VCRs or satellite receivers, as
these components are connected to an aerial. Because aerials and cables are always grounded,
ground loops can form between the aerial connection and other grounded equipment. Other
equipment that is normally grounded may include PCs with sound cards, and some CD/DVD
players and DACs.
Although the V 70 Class A is grounded, its signal ground is a "floating" ground, which means that
the V 70 Class A cannot itself create ground loops. Hum can only be caused when it is connected
to other items of equipment.
To fix the problem
Before trying to fix the problem, find out which of your system components is responsible for
generating the hum.
Procedure:
-
Unplug all source equipment, including any equalizer if used, from the V 70 Class A, leaving
only the loudspeakers connected.
- Reconnect the components back to the V 70 Class A one at a time. As soon as the hum
reappears, you have two grounded components connected to the V 70 Class A. You must now
unplug your components in reverse order to find out which of them is grounded.
Usually, the hum will still appear even when the problem components are switched off. The ground
causing the problem is always connected, since it is not broken when the power switch is operated.
Now that you know which components are grounded, you can discuss the problem with your
dealer.
One option might be to use a signal-isolating filter on the aerials or cable networks. These devices
do not normally have any adverse effect on the sound or picture quality of tuners or TVs. Other
possible solutions could include using an isolating transformer or an isolating device offering
complete galvanic isolation. Please seek the advice of a specialist.
Power strips with built-in filters, mains filters or replacement mains cables are not appropriate
solutions.
Note
Switching power supplies are quite common nowadays. These are often fitted with a protective
earth terminal (PE) and an RFI filter. When using such units, the protective earth terminal
must be
connected to the wall socket. You must never remove this protective terminal, as doing so
could cause high levels of radio frequency interference to enter your system, which could
affect the operation of other digital equipment, including remote controls.