Except between the amplifier and speakers, audio signals usually travel from component to component at line or preamp level, meaning before they are amplified. Although some amplifiers can accept a high-level or amplified output, it’s always preferable to send signals between components at preamp level because it’s easier to match the input impedances between components, which makes for better sound quality.
Signal cable
Preamp cable is also called signal cable. Another name is RCA cable because the cable is typically terminated with RCA connectors (shown in Figure 18-7). Still another name for signal cables is interconnects, but they all do the same thing.
cables are the most common type of RCA cable and consist of a single, small- gauge center conductor, the wire that carries the audio signal. The center conductor is covered by a braided cable, which is the negative return lead and shields the center conductor from noise. The braided cable is in turn encased in a plastic jacket.
Twisted-pair signal cables cost more and offer better noise rejection than coaxial cables. They feature two small-gauge center conductors that are twisted together. Because the wires carry the same signal but are 180 degrees out of phase (or the mirror opposite of each other), noise is effectively canceled out.
Signal cables are usually sold in pairs (because you need one to carry each channel of a stereo signal) and range in price from cheap to expensive. They are also sold in lengths ranging from 6 inches to 20 feet. Although some hardcore home audiophiles spend thousands of dollars on signal cables, you shouldn’t have to pay more than $20 to $30 for, say, a 20-foot pair.
Other signal transfer options
RCA cables still rule in car audio applications, but there is another option to get a signal from point A to point B: balanced-line transmission. This technology is better at reducing noise that can enter a system through the low-level signal cables, but it’s also more expensive.
Borrowed from recording studio technology, balanced-line transmission can be thought of as an active signal transmission scheme. In essence, a transmitter at one end sends the signal via a special cable to a receiver at the other end. The two signals are compared, and any noise that was picked up in between is rejected.
Various balanced-line drive schemes have been offered over the years for the car audio market, but none have ever caught on. The only true balanced-line technology currently available in car audio is from Zapco. The company’s SymbiLink balanced-line transmission system (see Figure 18-8) uses one of several receivers and transmitters that can be used with Zapco and other amplifier brands.
Figure 18-8:
AZapco SymbiLink balanced- line
transmitter andreceiver.
Courtesy of Zapco
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