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TECHNICALLY SPEAKING continued
14
hum (or 50 Hz hum in regions with 50 Hz AC). The
harmonics of these frequencies (120 Hz, 240 Hz, 480
Hz or 100 Hz, 200 Hz, 400 Hz) may add buzz in addi-
tion to the hum.
The ideal of zero voltage ground for all the compo-
nents in a system is practically impossible, because
some resistance between the ground points of differ-
ent components is inevitable. By keeping components
close together with their power cords plugged into a
common AC outlet or power strip, you’ll avoid the
problems created by resistance in the house’s wiring.
Hum and buzz is also caused when unwanted voltage
flows through multiple component ground points
called ground loops. Here are three tips to avoid
ground loops:
1. Use balanced input lines with your Parasound A 51.
(See Balanced and Unbalanced Lines in this section).
2. When rack mounting, always use the insulated
“shoulder” washers. These break the ground loops
caused by metal-to-metal contact between the rack,
the components, and their rack-mount bolts. Extra
washers are available from rack manufacturer Middle
Atlantic Products, www.middleatlantic.com.
3. Use the Ground switch on the A 51 to eliminate
most ground loops. This separates the A 51’s signal
input ground from its chassis ground to isolate
unwanted voltage in the ground shield of the
unbalanced (RCA) input cable. Be sure your system
installation is finished before you try moving the
Ground switch from its Normal to its Lift position.
Ground Switch, set to up position
Parasound Products, Inc.
San Francisco, CA USA
Manufactured under
license from Lucasfilm
Ltd. Lucasfilm and THX
are registered Trademarks
of Lucasfilm Ltd.
CAUTION
To Prevent Electric Shock,
Do Not Remove Cover. No
User-Serviceable Parts Inside,
Refer Servicing To Qualified
Service Personnel.
L U CA SF I LMLM
A51 Amplifier
WARNING
To Prevent Fire Or Shock
Hazard, Do Not Expose This
Unit To Rain Or Moisture.
AC 115V 60Hz
AC 230V 50Hz
Power Consumption: 1800W
Input
12 V
Man
Audio
50 mV 250
Ground
Normal
Lift
Auto Turn On
Sensitivity
Fuse
T15A/250V1-115V Area
T8A/250V-230V Area
Ch 1
Ch 2
Ch 3
Ch 4
Ch 5
Balanced Unbalanced
Input Select