Minimizing Noise in the System
Hum is caused by amplification of the 50 or 60 Hz AC power line signal that is transmitted via the
magnetic fields around power transformers and power cables. RF interference usually comes from
inadequate shielding of cables or components. If any of these types of noises are encountered, one or
more of the following pointers concerning proper component positioning and grounding may be of use:
➣
Ensure that each system component, especially the preamplifier, is located far enough away from the
other components so that they will not pick up hum from them, and that the AC power cables are not
in close proximity to audio cables.
➣
Ensure that all audio cables are securely pushed into their respective jacks. A faulty audio cable,
although rare, can be a source of hum if its outer shield is broken or disconnected from an RCA plug
at one end of the cable.
➣
The best system grounding scheme is to have your preamplifier well grounded to an earth ground
point and function as the system's main ground reference. Other system components are then quite
adequately grounded via their audio cables to the preamplifier’s ground. Using this grounding
scheme can be as simple as just plugging the preamplifier’s power cable into a three prong AC outlet.
However, if the AC outlet itself does not provide a really "good" ground, the preamplifier power
cable can be plugged into a three-to-two prong adapter and a wire can be run from the tab on the
adapter to the nearest cold water pipe.
➣
Another solution to AC power cable "ground loop" hum problems is to plug the AC power cables
from all of the system components into a common "socket strip" (available from most hardware
stores).
➣
If RF noise (usually an AM radio station or CB transmission) is a problem in your area, an AC power
filter can be purchased into which some or all of your system power cords can be plugged. This is
done if the RF is coming in through the building's AC wiring. However, if RF gets into the system
via your turntable, you may have to use tonearm cables with better shielding. (This is tested by
unplugging the turntable from the system and putting "shorting plugs" in the preamplifier’s phono
inputs before listening again.) RF noise is sometimes eliminated by simply moving the turntable or
other components to another location in the room.
➣
Hum from a turntable is usually traced to an adjacent power transformer or a missing or improper
ground. Check to see that the turntable motor is grounded via a wire to the preamplifier’s grounding post
- (or try removing this wire from the ground post if it is already connected there).
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