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Subsonic Filters Q. I always leave my amplifier's subsonic filter switched in. I use a Nakamichi noise-reduction unit with its subsonic filter switched in, too. I also use my equalizer's 16-Hz band as a subsonic control. I know that such filters are helpful, but how much is enough? And does all this subsonic filtering degrade my system's bass response? -Terry O'Shea, Canadian Forces, Europe A. Chances are you're using more subsonic filtration than is necessary. And it is certainly possible that you're losing some deep bass (30 Hz and lower), especially because of the 16-Hz equalization control, whose effect extends to 32 Hz or higher. Depending on your cartridge, the flatness of your records, your turntable's rumble level, the internal circuitry of your amplifier and the design of your loudspeakers, you may not need any subsonic filters. For sources other than phono, you probably need none at all. One way to check, for each source, is to remove your speaker grilles and ob serve your woofer cones during silent or very quiet passages in the program material. If you can see your woofers moving slowly in and out, you need some subsonic filtration. Back-Cueing Phonograph Records Q. How bad is it to back-cue records? I have heard everything from "disastrous" to "harmless." -Joseph M. Roberts, Wilbraham, Mass. A. For those unfamiliar with the practice, "back-cueing" is a two-step process used by disc jockeys and the like to start a recording precisely on cue. First, the stylus is placed in the groove and the disc turned forward until the beginning of the first recorded note is heard. Then the disc is turned backward, just far enough so that, when the turntable is started, the first note will reach the stylus just as the turntable has attained full speed. (This distance must be measured individually for each turntable.) If we were still using phonograph cartridges which required high tracking force, back-cueing would degrade records. Even so, radio broadcasters have used this technique over the years. When a record was popular (and therefore played a lot), one could hear a bit of noise at the beginning of the disc. Otherwise, one would never realize that the discs were back-cued. Today, back-cueing is more likely to cause damage to delicate styli. Most major cartridge manufacturers offer special styli, designed to withstand back-cueing, for at least some of their cartridges. However, I back-cue frequently without such styli, even with moving-coil and other delicate cartridges, and have never had a problem. Perhaps your luck won't be this good, but if you don't do it very often, I don't think you need to worry. Gauging Tracking Force Q. When I set my turntable's anti-skating force to zero and its counter weight to have zero tracking force, and when I next set the arm's tracking-force and anti-skating adjustments for 1.25 grams each, my independent, external tracking-force gauge reads only 1.0 gram rather than the 1.25 grams I expect. Should there really be such a wide discrepancy between readings obtained by the calibration controls on my tonearm and those indicated by an independent tracking-force gauge? When the arm "floats" (at zero tracking and anti-skating force), should it float all the way to the spindle? Mine floats about one-third of the way and stops. Does this suggest, perhaps, friction in the pivots? -Name withheld A. I would trust a good, independent tracking-force gauge more than I would a tonearm's calibration adjustments. Even if the arm's calibration scale is correct, you can throw the results off by not correctly balancing the arm to zero before you set the tracking force. Suppose, for instance, that the arm is neutrally balanced when it floats just slightly above a disc placed on the turntable; if you float it too high above that, or just above the turntable mat, subsequent calibrations will be off. As for the tonearm's drift toward the spindle, check the arm's instructions. If the arm is floating freely, the anti-skating force is really zero, and the turntable and arm are level, I believe it should not drift at all. Once you have set all adjustments in accordance with the manufacturer's instructions, I believe the best way to get maximum performance from your cartridge is to use a test record designed to aid in setting tracking force. This takes into account the performance of your particular arm and cartridge. Shielded Cable for Speakers Q. I have heard that shielded cable should not be used as speaker wire. Why is this so? -Thomas W. Ward, Manchester, Conn. A. Shielded cable is too light-gauge to handle the power from an amplifier, and some amplifiers may not tolerate the capacitance of shielded cable. Shielded cables are used between other audio components, where the signal levels are much more nearly the same as ambient electrical noise fields. Without shielding, the cables might pick up hum and other noises. Even with shielding, cables may pick up fields radiated by the sizable cur rents flowing in speaker cables, which could lead to oscillation. If the speaker lines are kept well clear of the other cables, such interference is unlikely. Stereo/Mono Switch Q. I have heard that the "stereo/mono." switch on a preamplifier affects the way a phonograph cartridge works. Would you explain the function of such a switch? -Eugene Gash; Washington, D.C. A. Unfortunately, these switches are not found too often, but most audiophiles may not really need one. When the switch is set to "mono," the differences between the two channels-including any noise that is part of this difference signal disappear. This is especially useful when playing monophonic material, whose difference signal would consist only of noise. When playing mono phono graph records, the "mono" setting may also eliminate rumble, which is often more pronounced in the vertical plane. On stereo records, the difference signal is cut vertically. This rumble may be recorded on the disc, or it may come from your own turntable. Thus, the switch does not affect the cartridge's operation, but it does affect the signal' that the cartridge produces. The "mono" setting is also useful in listening to weak, noisy FM-stereo signals. Most noise rides on the L-R difference signal, and when this signal is cancelled, the noise disappears. Of course, the signal then becomes monophonic, with the same sound coming from both speakers. The "mono" switch on a tuner does the same thing; many tuners also have automatic or manual "high-blend" switches which eliminate most of the difference-signal noise (most audible at high frequencies) while leaving some stereo information in the signal. My most common use for a high-blend switch is when playing or dubbing a monophonic signal source such as an old tape. When the switch is set to "mono," a signal feeding into just one input channel will automatically be fed into both output channels. Such a switch is not indispensable. Lacking one, you can use a Y-connector to patch a monophonic signal source into two channels, or two Y-connectors, back-to-back, to eliminate the difference signal from a stereo channel. Recording Discs at Home Q. If a CD player cannot be used to record, why waste money on it? -Greg J. Weimer, Quincy, Ill. A. Do you own a phonograph? Can that phonograph be used as a recording device? Consider these questions, and you might see the matter in a new way. However, as a matter of fact, at one time the home enthusiast did enjoy making phonograph recordings as a hobby. The discs used were quite ex pensive. Once recorded on, they could not be reused. Stereophonic recording on phono disc was quite a challenge in the home, and required bulky equipment. There will probably come a time when it is possible for the consumer to record on CDs, but this is definitely impractical at this time. Hiss on CDs Q. I have several CDs which are digitally recorded, mixed and mastered. Nevertheless, I hear a faint hiss in the background when I play them. What is causing this? When I listen to my integrated amplifier at full volume, with no input or with the CD player on pause, I hear no hiss at all. -Bill Law, Bolingbrook, Ill. A. Sometimes there is audible hiss present even where a recording is digital "all the way." This hiss is, in most instances, caused by inherent noise in such analog equipment as the recording/mixing console and the micro phones used in the recording studio. (Few studios have digital consoles yet, and I know of no digital microphones.) This hiss is usually not in the least annoying. But when listening levels are very loud, and when the treble is pushed up or the tweeters are very bright, the hiss will be apparent. (Audio magazine, Mar. 1986, JOSEPH GIOVANELLI) = = = = |
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