Parasound Halo T 3 - Manual (Page 24)

Balanced and Unbalanced Input Lines
Recording and broadcast studios use balanced
connections exclusively because of their inherent
ability to reject noise and hum, thus assuring the best
sound. Certain high quality preamplifiers and
surround controllers built for residential use utilize
balanced connections with XLR jacks for the same
reasons. The Parasound P 3 Preamplifier and all
Parasound Halo power amplifiers have balanced
inputs with XLR jacks so you can take full advantage
of their inherent noise rejection capability and
superior sound quality.
Unbalanced connections with RCA jacks are found on
all home audio equipment. RCA jacks and two-
conductor wires are less costly than the additional
circuitry, higher priced XLR connectors and three-
conductor wiring required for balanced connections.
In an unbalanced line, the positive audio signal
appears at the center pin of the RCA jack and the
negative signal on the outer shield wire, which also
functions as the ground connection. Unbalanced
interconnect cables are vulnerable to hum from an AC
line, or other noise, such as RFI (Radio Frequency
Interference), which can be reproduced through your
loudspeakers. Since the unbalanced line’s ground
also carries the audio signal, there is no way for the
connected amplifier or preamplifier to distinguish
between the audio signals you want and unwanted
noise emanating from external sources.
Balanced lines are superior because they utilize
separate conductors for audio and ground: two inner
conductors carry the positive and negative audio
signal, and a third outer wire connects the grounds
and also shields the two signal conductors. When the
positive and negative signals appear at the
component receiving the signal they are equal, but
180 degrees out of phase with each other with respect
to ground. To send and receive balanced signals
requires special differential circuitry.
A differential input circuit amplifies only the
difference between the positive and negative signals.
For example, when a 1 Volt signal arrives at a
balanced input stage, the differential input “sees” a
positive 1 Volt
minus a negative 1 Volt, or 2 Volts total.
External hum and noise that somehow gets into a
balanced line is common to both its positive and
negative conductors with respect to ground.
Therefore, it is canceled or rejected by the differential
input circuit.
This phenomenon of rejecting noise signals common to
both positive and negative conductors is called
TECHNICALLY SPEAKING
common-mode rejection. Differential inputs are
specified according to how well they reject signals
common to both conductors. This is measured in dB and
is called the
common mode rejection rati o or CMRR.
Other Antenna Options
Outdoor Antenna
For best reception and maximum noise rejection, we
recommend the use of a high-quality outdoor FM
antenna. Although this requires a little extra effort, the
additional stations you can receive and the superior
sound quality will be worth the investment. For best
noise rejection, use a 75
Ω cable with an “F” connector
and connect it directly to the 75 Ω coaxial antenna
connector on your T 3. If you use 300 Ω “twin lead”
cable, use the balun adapter as described previously.
Cable TV Connection
Many cable TV companies include FM radio stations
and TV audio along with their cable TV channels.
Check with your local cable company about the
availability of FM stations and possible additional
charges for this service. FM quality depends on the
quality of the cable operator’s equipment. Your T 3
connects to the cable with a signal splitter in the same
fashion as you would connect a second television:
The signal splitter’s input connects to the incoming
cable and its outputs are a 75
Ω F connector for your
television and either a second 75 Ω F connector or 300
ohm terminals for your T 3.
Powered Antennas
A small powered indoor antenna is sometimes useful
when it's impractical to install an outdoor antenna or
where FM transmission is not available via cable or a
community TV/FM antenna. However, powered
antennas sometimes add noise and distortion to the
RF signal. In most cases, you can receive signals
better with the supplied dipole antenna.
Using the T 3 with Infrared Repeater Systems
External Remote Input and Loop Out
The External Remote input allows for infrared remote
control operation via a wired infrared repeater system
or system controller when infrared commands cannot
directly reach the front panel infrared receiver. This
input connector accepts a standard 1/8" (3.5 mm) two-
conductor mini-plug. The tip is positive and the
sleeve is negative. Your Authorized Parasound Dealer
or Custom Installer can recommend a compatible
infrared repeater system for the T 3. The External
remote circuit has a loop output so you can connect
additional IR controlled devices.
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