KLING & FREITAG K&F SWi 118E - Manual (Page 22)

User's Manual K&F ‘SW’ Series Subwoofer Systems
KLING & FREITAG GMBH ©1998 - 2015 Version 5.1, 29.05.2015 Page 22 of 22
8.2 Avoiding Ground Loops
8.2.1 What is a Ground Loop?
Every component of a P.A. or Hi-Fi System has its own internal 0V reference (ground). This
point is often connected to the protective earth connector (PE / Ground). If two or more
units are connected to one another with a line level audio cable, there may be a ground
connection through the ground of the power supply cable (yellow-green) as well as
through the shielding of the audio cable. The voltage difference between these two
ground points causes audible interference to come from the speaker.
8.2.2 Avoiding Ground Loops
If there is a loud humming or buzzing after the speaker has been connected, then check
that a ‘ground loop’ has not been built into the system. Some power amplifiers and
system controllers facilitate a ground lift switch. Set these ground lift switches to the
‘Lift’ position one after the other. If the noise is still audible, check if,
1. the noise is caused by a ground loop before the power amplifiers or controllers
(e.g. mixing console, effects or equalizers).
2. the system or parts of the system are connected to an ‘unclean’ power supply -
meaning one which is also running large motors or lighting systems. An ‘un-
clean’ supply voltage, electrostatic and electromagnetic fields can cause inter-
ference.
Please observe the following basic rules:
− Never!!! try to avoid a ground loop by disconnecting or taping the protec-
tive earth contact at the mains connector! Extremely dangerous! Extremely
dangerous!
− If possible, only use high-quality audio appliances with balanced signal outputs and
with power cables with PE connectors.
− Use high-quality cables with good shielding.
− The point of ground for all connected components should merge at one central
point. The power connections should lead out in a radial manner from one point
and not be linked from one unit to the next.
− When installing appliances that create strong electrostatic or electromagnetic fields
(large transformers, switch-mode power supplies), maintain some distance from
other audio appliances. In extreme cases, the only solution is to create a completely
independent ‘audio ground’; in other cases, it is sufficient to connect a filter in front
of the audio equipment.
Warning