Parasound A 23 - Manual (Page 19)

TECHNICALLY SPEAKING continued 16
Choosing Brands of Interconnect Cables and
Speaker Wire
We are often asked to recommend specific
interconnect cables and speaker wire. It’s true that
with some amplifiers, sound quality will vary greatly
according to interconnect cables and speaker wires.
However, Parasound amplifiers use robust circuitry
that sounds superb regardless of interconnects and
speaker wires. Therefore, we feel that choosing a
brand of cable for Parasound amplifiers is purely a
matter of personal taste.
Eliminating Hum and Buzz - Ground Loops and the
A 23 Ground Lift Switch
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 balanced input lines with your Parasound A 23.
(See Balanced and Unbalanced Lines in this section).
2. When rack mounting, always use insulated
“shoulder” washers. These break the ground loops
caused by metal-to-metal contact between the rack,
the units, and their rack-mount bolts. Washers are
included in Parasound rack mount kits. Extras are
available from rack manufacturer Middle Atlantic
Products, www.middleatlantic.com.
3. Use the Ground Lift switch on the A 23 to eliminate
most ground loops. This separates the A 23’s signal
input ground from its chassis ground to isolate
unwanted voltage in the ground shields of the
unbalanced (RCA) interconnect cables. Be sure your
system installation is finished before you try moving the
Ground Lift switch from its "Normal" to its "Lift" position.
Loop Out Jacks
The Right and Left Loop Out jacks are convenient
connections to route the same input signals from
your preamplifier or surround controller to an
additional power amplifier. These jacks eliminate the
need for “Y” connectors to split the source signal
between your A 23 and another amplifier. The Loop
Out jacks work with either the Balanced or the
Unbalanced Input jacks. Here are some examples of
where you could use the Loop Out jacks:
1. When multiple speakers and amplifiers are to be
played simultaneously, you can route the output of your
preamplifier or controller to the first A 23 then connect
its Loop Out jacks to a second A 23 (or other amplifier)
to power additional speakers for the same channel.
2. Some high-end speaker manufacturers recommend
bi-amplifying or “bi-amping” without using an
electronic crossover. When bi-amping this way, one A 23
drives only the woofers and another A 23 drives only
the tweeters. For example, you could connect the left
and right channel outputs of the preamplifier to the
inputs of the first A 23 to power the woofers, and then
connect its Loop Out jacks to the second A 23 to
power the tweeters.
Level Controls
When the Level knobs are turned fully clockwise, the
actual level controls are essentially out of the circuit.
The left and right channels are perfectly matched, and
your A 23 can reach its fullest sonic potential.
In some cases, you’ll need to reduce the level
settings. For example, if you find it difficult to make
precise volume adjustments at low listening levels,
your preamplifier or surround controller probably has
a very high output (or gain) that you can match by
reducing the A 23’s level. Conversely, if you need to
advance your preamplifier or surround controller’s
volume to nearly the top of its range for average
listening levels, you should increase the level settings
on the A 23. The A 23 Level adjustment that optimizes
the range of motion on the preamplifier’s volume
control is sometimes called “gain staging”.