Parasound JC 1 Amplifier - Manual (Page 17)

TECHNICALLY SPEAKING continued 14
Eliminating Ground Loops - Hum and Buzz
Audible hum and buzzing noises in a system are usually
related to issues with the component grounds. Ground
(sometimes called common) is a point of reference for
voltages in virtually all audio and video components.
Ground is supposed to remain at zero volts while the
audio signal swings positive (voltage above ground)
and negative (voltage below ground). If ground isn’t
at zero, there can be an audible 60 Hz 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 addition to the hum.
The ideal of zero voltage ground for all the components
in a system is practically impossible, because some
resistance between the ground points of different
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 a balanced input line with your Parasound JC 1.
(See Balanced and Unbalanced Lines in this section).
2. When rack mounting, always use the included
insulated “shoulder” washers. These break the ground
loops caused by metal-to-metal contact between the
rack, the units, and their rack-mount bolts. Extras
are available from rack manufacturer Middle Atlantic
Products, www.middleatlantic.com.
3. Use the Ground switch on the JC 1 to eliminate most
ground loops. This separates the JC 1’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 Lift switch from its
“Normal” to its “Lift” position.
Level Control - Omitted by Design
There is no level (gain) control on the JC 1 to avoid
compromising the audio signal. We expect you’ll be
using a preamplifier or surround controller with a high
quality volume control and S/N ratio.
Two Sets of Binding Posts
The JC 1 is equipped with a second set of binding
posts to facilitate bi-wiring. This feature enables you to
“bi wire,” or connect two lengths of speaker cables to
the same speaker for improved performance. Refer to
the owner’s manual of your loudspeaker to determine
if the manufacturer recommends bi-wiring.