OTHER TECH

Matchmaker Madness

Q. I have been using the surround processor in my receiver, fed to a multichannel amplifier, and am considering doing so again. Can you clear the air regarding voltage output from a receiver or preamplifier, amplifier input sensitivity, and amplifier input impedance. What's relevant, and what's not when matching a processor to an amp? Matt Anderson Omaha, NE

A. Ian G. Masters says: It's no big deal. The industry has built enough flexibility into their products so that compatibility isn't much of an issue. Except at an amplifier's output, almost everything in an audio system operates at what is known as "line level" - an informal standard that lets the input of each component in the chain "see" roughly the level it needs to work properly; small mismatches can be corrected by adjusting the volume or trim controls on the components. The trick is to make sure the output of one component is high enough so that the signal is not lost in a mire of noise, and low enough not to overload the input it's feeding into. This can usually be set by ear.

As for impedance, there are critical applications where the internal output impedance of one device must match the internal input of the device it's attached to for maximum transfer of power, but your audio system isn't one of them. As long as the output impedance see's a higher input impedance - virtually always the case - there should be no problems (such as increased distortion, which might happen with a high impedance feeding a lower one). Any slight loss of power can be compensated for by turning up the level a tad.

Uptight on Upconversion

Q. I'm looking for a new HDTV to replace my old, tube-based rear-projector, but I've been reluctant to buy. I will probably continue to watch a lot of non-HD programs and my experience indicates that the most current HDTV's don't provide as good a picture with non-HDTV programs as my CRT-based set does.Your reports generally don't comment on picture quality with non-HD programs, but I sure wish they did - it would help me a lot. Do you have any advice to help me make this decision? Jim Evans Bridgewater, CT

A. Al Griffin says: We actually do remark on a TV's handling of standard-def, non-HD material in our reviews, although space limits this to a few lines. Look for comments on the set's "upconversion," or its performance with DVDs and standard-def cable shows. Any comments concerning the set's video noise reduction processing should also apply to its handling of non-HD programs.

Long Sub Runs

Q. I want to move one of my two subwoofers to the back of the room, but I would need to run about 31 feet of RCA cable. Are there any drawbacks to using cable that long? Steve Prescott Milford, NH

A. Ian G. Masters says: Long cables run the risk of degraded high frequencies caused by the capacitance of the cable, but that's no concern with a sub. What you might encounter, though, is 60-Hz hum. Usually, careful routing can avoid such problems. Don't run the wire in parallel with an AC line (including those behind walls), and if it must cross a power cable, it should do so at a right angle. Intractable hum may be caused by a ground loop, in which case an isolating transformer or a special cable in which the shield is only grounded at one end might be the solution.

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