AUDIOCLINIC (Dec. 1985)

SCA Interference

Q. Have you ever heard of multiplex signals from an FM tuner causing "beats" in recordings made off the air? What does this noise sound like? And can I adjust my tuner's SCA filter just by listening?

-O. O. Callaway, Carlsbad, Cal.

A. Yes, I have heard problems related to bias beating with SCA signals. The sound, however, is not a steady tone, because the frequency of the SCA subcarrier is constantly shifted by the signal modulating it. Thus, the sound heard is a kind of "swishing." It is possible to adjust the SCA filter by listening, but only if your cassette recorder has simultaneous record/ playback capability. Adjust the tuner's filter for minimum background noise.

Note that there are times when the subcarrier will not be present. Do not be misled by this into thinking that the adjustment is correct.

The more conventional alignment process involves the use of a signal generator and other equipment to modulate an FM carrier with a 67-kHz subcarrier. Once this is set up, follow the tuner manufacturer's alignment instructions.

If you never hear such interference, no matter which station you are tuned to, then follow the advice of the well worn proverb: "If it ain't broke, then don't fix it."

Pre-Echo on CDs

Q. On a few tracks of one of my CDs, I hear "pre-echo"--a faint hint of the music before the music actually begins. Until now, I had heard this phenomenon only on phonograph records, and associated it with the stylus playing the groove next to the one containing the music. How is this possible on a Compact Disc? Could it be from print-through caused by the master tape being wound too tight in storage? Is the CD defective?

-Edward Bauman, San Diego, Cal.

A. The "pre-echo" you mention is the result of print-through, just as you suggested. The master analog tape must have been wound tightly; this is always done to avoid edge damage during storage. Added to this is the fact that the tape was probably recorded at a high signal level. Chances are, too, that this tape had not been played since it was used to cut the disc master. Because the turns of tape are in intimate contact with one another, some of the magnetic data contained on one turn was transferred to the next one. This effect can be hastened if the tape is stored in a warm room. Be cause of this transfer of magnetic information, there is a faint echo or maybe a faint pre-echo, or "ghost."

Linear-Tracking Tonearm Noise

Q. I own a linear-tracking tonearm which makes an audible "kloonk" on soft passages and between songs.

Could this noise be related to the mo tor that drives the tonearm? Can it be stopped, or will I just have to accept it?

-Steve Wallace, Dillon, Colo.

A. I have limited experience with linear tonearms. With my own rather inexpensive one, I do not hear any noise resulting from the stepping motion of the arm servo motor. This does not rule out the possibility of such a sound occurring if the motor makes its moves too quickly or in too-large jumps.

Before deciding the motor is causing the problem, check your cartridge. If the tracking force is too great, the cartridge body may drag on a record, especially if the disc is slightly warped.

This warp could cause the cartridge to strike the disc; such contact could be translated by the cartridge as output.

Assuming that the noise you hear is the result of servo motor problems, I can't believe you should just have to live with it. I suggest you have it factory-serviced.

Intermittent Turntable Operation

Q. My three-year-old turntable recently stopped operating properly.

Now, after a few minutes of operation, the platter stops turning. After 30 S or so, the platter will accelerate to the right speed, run for a few seconds, and stop. The power light remains lit, which rules out any difficulties with the a.c. wall outlet. The tonearm remains on the disc's surface rather than rising as it would at the end of an album, which rules out a lead-out adjustment problem. I have looked into the unit for burned components and found none. I would appreciate any information you may have.

-Douglas Comstock, Bangor, Maine

A. A number of factors could result in the intermittent operation you have described. Most likely, a component (possibly the motor) becomes erratic after it heats up. To locate this component, wait for the turntable to stop turning. Then look underneath or inside and spray each component on the p.c. board with a coolant made for this purpose. You will likely find one component which, when the spray is applied, will permit the proper operation of your turntable.

It is also possible that the speed buttons need a contact cleaner. If oxide has formed, heat buildup might result in intermittent contacts. (Naturally, if these are momentary-contact switches, contact problems are unlikely.) Or it may be that there are hairline cracks on the circuit board or poorly soldered connections which act up when they become heated.

Tape Loops and AUX Inputs

Q. My cassette deck is plugged into one of my equalizer's two tape-monitor loops, and the equalizer is plugged into one of the two tape-monitor loops on my receiver. There are, therefore, two unused tape-monitor loops in my system, one on the receiver and one on the equalizer. My receiver also has an unused AUX input which, according to the instruction manual, can be used for any high-level source, such as a tape deck.

I plan to add another cassette deck and a CD player, connecting the cassette deck to the equalizer's second tape-monitor loop. But where should I connect the CD player if I want to be able to equalize the music-to the AUX input or the receiver's second tape-monitor loop?

-Victor Orellana, Culver City, Cal.

A. By all means connect the CD player to the AUX input. This will en able you to route its output to any of the components you have mentioned-the equalizer or either cassette deck. Engaging the appropriate tape-monitor switch on your receiver will pass signals from your CD player through the equalizer, just as it now passes signals from your other signal sources.

With any equalizer, this setup will also allow you to equalize the signals from either cassette deck in playback; with some equalizers, it will also give you the option of equalizing the signals going to the two decks in recording.

CDs and Static Discharge

Q. I am about to purchase a Compact Disc player but am concerned about how static electricity might affect its performance. My home is plagued with lots of static; when I walk across my living-room rug and touch my stereo equipment, I invariably get a shock from the static charge, and I hear it in the loudspeakers. What suggestions do you have for alleviating this? We already humidify our house.

-Andrew Hinds, Fort Collins, Colo.

A. I do not believe that the static discharges you have described will damage your CD player or the discs used with it.

Without actually curing anything, you can eliminate most of the "clicks" you have described by touching some metallic object other than part of your stereo system before operating the equipment. Of course, what you really need is a substance to spray on your carpeting which can eliminate the static buildup in the first place.

Humidifying your home is a good idea. I do it in my home, but I live in a climate where it's only necessary during winter months. It is likely that in drier climates this is necessary even in the summer. I am not a heating/humidity expert, but it seems to me that unless you have a hot-air system, humidifying a home is a difficult task. Even with hot air, I have found that some systems just cannot put out enough moisture to make a difference.

Heat Buildup in Amplifiers

Q. I recently purchased a new power amplifier which becomes quite warm to the touch soon after it has been turned on. The owner's manual advises against placing the unit in a bookcase or cabinet, or in any location with restricted ventilation. What will result from too much heat if I leave the amp in a cabinet, where it is presently situated? Will the heat harm nearby equipment? Can a small a.c. fan, installed in the rear of the cabinet to pull air through, solve the problem? And if not in a bookcase or cabinet, where can I place the amp safely without subjecting it to too much dust, etc.?

-John S. Cates, Atlanta, Ga.

A. If you use your amplifier for extended periods and allow the heat to build up, there is a risk of damage to its output stages. Excessive heat can also shorten the lives of other components, notably electrolytic capacitors. This is why the manufacturer of your amplifier recommends that it be used where air flow is not restricted.

If you are forced to keep the amplifier in an enclosure, the use of a fan, as you have suggested, can help greatly.

You may have to cut a hole in the rear panel of the cabinet so that cool air can be sucked into its interior and made to flow over the amplifier. Most of the heat is generated at the heat-sinks, usually at the rear of the amplifier but sometimes at the sides. So be sure that the fan directs cooler air onto the heat-sinks.

Additional heat will develop in the power transformer and other components. You may, therefore, need to take added steps to ensure that any vent openings in the amplifier's case receive a cooling air flow, too. This might require the use of a "muffin" fan if the one used to cool the heat-sinks does not force enough air over the rest of the amplifier.

Although heat dissipates with distance, it's still possible for an amplifier's radiated heat to affect other audio components, which will, theoretically, shorten their life. This applies not only to electronic devices but to the drying out of lubricants in turntables and cassette decks.

Putting the amplifier on an open shelf often reduces the amp's proximity to other components and ensures a clear air flow to all parts of the amp itself. I believe that dust is far less of a problem than heat. It would be a good idea, moreover, to vacuum the equipment occasionally, and to routinely dust its outer surfaces.

VCRs and Conventional Audio Recording

Q. I have heard that VCRs can deliver higher fidelity than cassette recorders can. How can this be, when a VCR has no level meters, noise reduction, etc.? What do you recommend as the best recording speed for audio on a VCR? Is fidelity increased significantly by using a PCM converter when recording?

-Steve Wallace, Dillon, Colo.

A. The "Hi-Fi" stereo soundtracks of Beta Hi-Fi and VHS Hi-Fi VCRs, which work by Audio Frequency Modulation (AFM) rather than straight, linear audio recording, have flat frequency response throughout the audio spectrum, with S/N ratios of perhaps 80 dB. Wow and flutter are virtually unmeasurable, and distortion is extremely low.

For more details, see "Beta Hi-Fi: Better Audio for Video" (Audio, May 1983) and "VHS Hi-Fi: Five Units Tested" (November 1984). The PCM stereo digital tracks on some of the newest 8-mm VCRs have similar performance, except for frequency response limited to 15 kHz. All these machines can re cord in stereo, and some can also re cord stereo television broadcasts off the air. There are meters and manual (as well as automatic) level controls to help you in setting proper recording levels.

These decks all have conventional audio tracks as well, for compatibility with existing tapes and players (though "conventional," in 8-mm's case, means monophonic AFM). In some VHS and Beta machines, even the conventional audio track has been improved, with wider, flatter frequency response, stereo recording and play back, and noise reduction.

There are both advantages and problems in using these decks to re cord audio alone. The Hi-Fi decks, at least, do a superb job of recording, and all VCRs can record for hours at a stretch, with no breaks for tape-changing. But editing and cueing are more cumbersome than with open-reel or even audio cassette machines. Most modern VCRs move the tape back wards a bit when the pause button is pressed, to avoid loss of sync and picture breakup when recording is resumed. Thus, pressing the pause but ton too soon after the end of a piece of music will cut the last note off.

Audio recording quality is independent of tape speed with AFM and PCM recording. With conventional (linear) audio tracks, the best recording speed for audio is the fastest one available on the VCR.

If you are purchasing a VCR with the idea of using it for stand-alone audio recording, be sure the machine has the built-in sync necessary for this application. Although most models are so equipped, I have seen one or two which required video input to provide this sync.

A PCM converter records digital sound in place of the audio sound tracks. This system has better fidelity than any of the systems described above--dramatically better than the standard linear tracks--and can be used with any VCR. When a Hi-Fi machine is fitted with a PCM converter, it can record four high-fidelity (and two low-fi ) channels simultaneously.

(Source: Audio magazine, Dec. 1985, JOSEPH GIOVANELLI)

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