S&V Q&A — June 2006

A Classic Hummer

Q. When I connect my subwoofer to my receiver, a humming noise is generated through my center-channel speaker that almost drowns the output. When I switch off the center channel on my receiver, the noise transfers to my main speakers. If the subwoofer is disconnected from the receiver, the noise stops. Each component works fine on its own. How can I stop this humming? Bradford M. Boyce Brooklyn, NY

A. Ian G. Masters says: It's a classic case of a ground loop - one of the trickier things to cure in an audio system. The problem is that your subwoofer and your receiver are both connected to ground separately, and a small voltage (at 60 Hz) is passing between the grounds and being picked up by the main audio circuits. The best solution is to interrupt the path this spurious signal is following: the shield on the audio connection between the receiver and the subwoofer. If you carefully cut away a short section of the shield at one end, you'll still get the shielding effect, but not the ground loop. If you aren't keen on chopping up the wire yourself, electronics stores sell cables with the shield connected at only one end for this very purpose.

Cable Disconnect

Q. I have a reasonably up-to-date home theater system and am about to add Sony's 60-inch SXRD HDTV. I always connect my components with the best cables I can afford, and I currently run component video between my Denon DVD player and receiver, and then again to the TV. I bought component-video cables to connect a new HDTV cable box to the receiver, thereby completing the chain. But then a thought occurred to me: How much am I really accomplishing by using expensive video cables when the signal enters my house via an old-fashioned coaxial cable? I can see using them for sources that originate within my system (DVD, for example), but is the picture going to look any different with cable? Matt Philbin Tinley Park, IL

A. Al Griffin says: Possibly (although good cables aren't necessarily expensive). Video cables don't make that big a difference for analog cable TV, but you've upgraded your cable box to a digital model. That means the signal coming into your home through the coax line (which was presumably upgraded along with the box) is digital as well. Your new cable box takes this digital signal and translates it into a high-definition format that requires either a high-quality analog component-video or digital HDMI connection to the TV. You could use either one with your new Sony. However, if you go with HDMI, you won't be able to use your current receiver for video switching.