Q: Can you recommend a good and reasonably-priced service shop for my stereo equipment?

A: Offhand, no. However, I can advise you on what to look for when canvassing a place for service. Ask to see the service area. Look for an array of dust-free test equipment; see how many other customers' units are stacked up for repair. Observe the (technicians) at work: Are they actually probing the innards of a chassis? Do they have service manuals at hand? Finally, talk price and try to get some information on the cost of parts and of labor, not to mention a guarantee on both.

Q: What is your opinion of rack-mounting a stereo system?

A: It depends on the rack-mount used. A true (studio) rack-mount has open sides and back, and is designed to hold equipment that is 19 inches wide by means of bolts through holes near the ends of the overlapping front panels. There are "home" variations on this basic type, but some are suited for only one brand of equipment, so bear that in mind when shopping. Some "racks" are actually modified bookcases. They may look nice and they may hold all your equipment, but I'd be cautious about stuffing a lot of high-powered gear into one unless you can be sure the equipment will get adequate ventilation.

Q: I have heard that Tandberg is folding. Is it wise to buy any of their rather expensive equipment now?

A: Tandberg's demise, which was rumored around the first of the year, has been halted by an infusion into the company of several millions of dollars from the Norwegian government. Latest reports have it that Tandberg's product line -- recorders and receivers -- will continue in good shape in the United States.

Q: I read recently that the difference between low-priced and high-priced speakers is the stronger bass response of the latter. Isn't there more to it than that?

A: In a word, yes. In several words -- assuming the speaker system designer is not an idiot, when he beefs up the bass response of a system, he also modifies the midrange and highs for overall tonal balance. A costlier system produces not only stronger bass, but truer bass. It also presumably offers better dispersion of the treble along with a smooth and extended high-end response. It also should be expected to handle higher power from the amplifier for better sound coverage in a larger room, or improved dynamic range in any room.

Q: Why are some amplifier manufacturers touting "DC amplifiers?" Who needs to amplify direct current?

A: Nobody does outside a laboratory. But the term really means "direct-coupled" and this in turn refers to the absence of capacitors in both the feed-back loop from output to input, and in the signal path from one stage to the next. The lack of capacitors is intended to reduce transient intermodulation distortion (TIM), and to improve phase response. The amplifier's ability to amplify "direct current" or "zero Hertz" frequency is a by-product of direct-coupling. It is not the reason for designing an amplifier this way. Indeed, an amplifier for use in a music system had better not amplify and pass direct current lest it damage the speakers. Strongly amplified frequencies near the "zero Hertz" region also can waste power, and emphasize unwanted, spurious signal elements such as turntable rumble. For this reason, a well-made DC ("direct-coupled") amplifier will have provision for blocking any DC ("direct current") from the preamp, and usually some special safety circuits, all of which add to its cost. It also should be used with the best and cleanest available program material and input equipment.