Parasound A 21 manual Choosing Interconnect Cables and Speaker Wire, Loop Out Jacks, Gain Controls

TECHNICALLY SPEAKING continued 16

Choosing 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.

Ground Loops - Eliminating 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 A 21. (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 A 21 to eliminate most ground loops. This separates the A 21’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.

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 21 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 21 then connect its Loop Out jacks to the Unbalanced Input jacks a second A 21 (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 21 drives only the woofers and another A 21 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 21 to power the woofers, and then connect its Loop Out jacks to the second A 21 to power the tweeters.

Gain Controls

When the gain knobs are turned fully clockwise, the actual gain controls are essentially out of the circuit. The left and right channels are perfectly matched, and your A 21 can reach its fullest sonic potential.

In some cases, you’ll need to reduce the gain 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 21’s gain. 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 gain settings on the A 21. The A 21 gain adjustment that optimizes the range of motion on the preamplifier’s volume control is sometimes called “gain staging”.