TAPE GUIDE (Oct. 1985)

Head Demagnetizers

Q. I recently purchased a battery powered head demagnetizer which operates in the same manner as the cassette-type units that produce an electronically generated, decaying magnetic field. The field is activated by a momentary pressure on a pushbutton switch. One simply holds the tip against the head, capstan, or guidepost for a 2 to 3-S interval; the decaying field makes it unnecessary to physically move the tip slowly and smoothly away from the head, etc. My question is, are these electronic demagnetizers as effective as the regular, line-operated (120-V a.c.) models?

-Roy S. Kikuta, Mililani Town, Hawaii

A. To my knowledge, electromagnetic demagnetizers that operate off the power line can develop a more intense magnetic field and therefore operate more effectively than other types. But this does not necessarily signify that the other types, such as yours, are ineffective. The material of which the head (or other component) is made, degree of magnetization, design and quality of the other types of demagnetizers, and so on, are factors in how well these other types perform.

Azimuth Alignment Tapes

Q. About two years ago I purchased a TDK AC-337 cassette alignment tape, and recently I purchased a TEAC MTT-256 alignment tape. On each of my two cassette decks, which are of good quality, both of these tapes play back about 4 dB lower at 10 kHz than at 1 kHz.

There was a slip of paper with the TEAC tape stating that it conforms to the characteristic specified in IEC Publication 94-1, Fourth Edition. Is it possible that a new playback standard is in use? My old Nortronics AT-200 alignment tape plays back at the same level at 10 kHz and 1 kHz. If this is the case, one would have to increase the high frequency equalization when using ordinary tape and when playing old libraries of music. Where could I get a copy of the aforementioned IEC Publication 94-1, Fourth Edition?

-John M. Kaar, Menlo Park, Cal.

A. Azimuth-alignment tapes made by reputable companies do not necessarily agree with each other. For example, differences have been noted between the TDK and BASF tapes.

Hence, differences could also exist between the TDK and Nortronics tapes.

Fortunately, according to Howard Roberson, who does Audio's tape and tape-deck reviews, these differences are smaller among the newer alignment tapes than among the older ones, and are beginning to approach the vanishing point.

Perhaps the best answer to the problem of varying azimuth of different decks (or of the same deck over time), and therefore of different recorded tapes, is to have easily adjustable playback azimuth. An example is the Nakamichi TD-800 car-stereo unit (see the review in September 1984). Both Nakamichi's TD-1200 car stereo and Dragon home deck adjust themselves automatically for correct playback azimuth by eliminating phase differences between split sections of the playback gap for one of the tracks. Hopefully, an increasing number of decks will facilitate adjustment of playback azimuth, with an easy return to "normal." When treble loss due to azimuth alignment is moderate, the treble control in one's audio system may be somewhat helpful. A graphic equalizer, which permits sharper correction over a narrower band, can be more helpful in this respect.

The address of the IEC is 1 Rue de Varembe, Geneva, Switzerland.

Generic Tape

Q. Have you come across the new "generic tape"? Does it offer quality for the money or is it a repackaging of the three-for-$3 schlock?

-Oliver Bassett, Omaha, Nebr.

A. What used to be called "white box tape" in open-reel appears to be called "generic tape" in cassette.

Those seeking high-quality results have usually been warned away from white-box tape. Such tape could be unsuitable for quality recording for a variety of reasons, such as poor slitting, inadequate lubrication, nonstandard bias requirements, or improper treble response. White-box tape sometimes consisted of rejected audio tape sometimes of computer tape slitted to audio size. On the other hand, sometimes it consisted of perfectly good audio tape that, for one reason or another, was available at a bargain price.

The same or similar comments probably apply to generic cassette tape.

Perhaps the wise course is to buy just one cassette-if that is possible-and see how well it works.

One reader, Robert Yeager of Avon, Maine, did just that with white-box tape, and has written of his favorable experience. He responded to an ad for 1,800-foot, open-reel tape at only $1 per reel, and says that he found it to be "government surplus, mostly made by Ampex, used once, and bulk erased. It is of excellent quality. I have used countless reels with never a problem of any kind."

Anyone care to comment?

Repair or Buy?

Q. I have a four-year-old cassette deck which I purchased for $250. It has three heads, Dolby B NR, signal-to-noise ratio of 61 dB with Dolby B, and rated frequency response of 25 Hz to 17.5 kHz with Type I and II tapes.

Two years ago I had it repaired at a cost of $78, and now it is in need of repair again. Recently I saw a deck for $300 with two heads, Dolby B and C NR, signal-to-noise ratio of 71 dB with Dolby C, and rated response of 20 Hz to 18 kHz. However, I have been told that decks in this price class just do not put enough signal on the tape. Is this true? I would like your advice on whether to fix the old deck or purchase the new one.

-John de Rosa; Matta pan, Mass.

A. I vote for a new deck. Even if another $78 restores your present deck to satisfactory operation, the need for repair is likely to crop up ever more frequently as the deck gets older.

And at best its performance won't match that of today's decks in your price range. As far as noise reduction is concerned, Dolby C will give you a worthwhile improvement over Dolby B, particularly if you play at high levels.

I have never come across the claim that inexpensive decks do not put enough signal on the tape. Of course there might be an odd deck somewhere that, through poor design or alignment, doesn't record at sufficiently high level. But basically, your fear is unfounded. On the other hand, there may be a misunderstanding. Perhaps what was meant is that the signal-to-noise ratios of the less expensive decks are not as great as those of the more expensive ones. This does tend to be true. One reason is that a deck with separate record and playback heads tends to have a somewhat higher S/N ratio, because its playback head can be designed for maximum output (as well as extended treble response). However, the S/N superiority of the expensive decks tends to be only about 3 or 4 dB. An S/N of 71 dB (with Dolby C), such as that of the deck you are contemplating, is very good.

NR Compatibility

Q. How do Dolby B NR and JVC's ANRS differ? To what degree are they compatible?

-Russell Stepanchak; Columbia, Pa.

A. Dolby B NR and ANRS are more similar than different-similar enough to be generally considered compatible by many listeners. Results are usually satisfactory if one records with Dolby B noise reduction and plays back with ANRS, or vice versa. Both work on the principle of variable treble boost in recording and variable treble cut in playback; the treble cut restores response to flat (or nearly so) and at the same time reduces noise in the tape system.

The two processes differ slightly in the time constants employed and the amount of boost and cut applied. In both cases, the amount of boost and cut decrease as signal level increases; thus, tape saturation is avoided or minimized.

Head Replacement

Q. I have read that cassette-deck heads need to be replaced periodically. How can one tell when this is needed?

-Tim Colvin, Dixon, Ill.

A. Head life depends on the material from which the heads are made, the pressure of the tape against the heads, the angles at which the tape approaches and leaves the heads, and the tension exerted by the supply and take-up reels. A head's life can thus vary substantially. For most heads, according to various claims, it can range from 10,000 to as much as 200,000 hours of use; some manufacturers claim only 2,000 hours.

The best procedure for checking the condition of the tape heads is by measuring their performance with the proper test instruments, and by visual inspection under magnification.

The principal aural clue to a deteriorated playback or record-playback head is an audible decline in high frequency response, assuming that the head has been cleaned and demagnetized. (Thus, a person with excellent hearing in the very high-frequency range may desire earlier tape-head replacement than a person with limited hearing in the range above 10 kHz or so.) On the other hand, the decline in high-frequency response of a separate playback head may be due not to head wear but to a change in azimuth, either of this head or of the separate record head. Poor erasure would be a clue to a deteriorated erase head, and the presence of distortion might be a clue to a worn record head.

All in all, the time for head replacement (and/or alignment) is best determined by instrument, and not by ear.

Mystery Hum

I'm forced to summarize a problem, because several letters went back and forth before it was solved. The original complaint, from Thomas P. Madero of Ozone Park, N.Y., was that his two tape decks, both of the same make, hummed severely in both playback and recording. Mr. Madero tried all the usual solutions: He inverted the power plugs of his decks in the a.c. outlets, disconnected the ground pigtails of his audio cables, took one deck out of the system, and disconnected his receiver from its earth ground (an I-beam in his basement). Nothing worked.

I suggested that, since the hum occurred with two decks of the same make, the problem might be a design fault, such as a defective filter capacitor, or that it might be in his receiver. I advised that he have these components checked.

Meanwhile, Mr. Madero took his components to a friend's house, where the hum disappeared. When the system was assembled back home, the problem reappeared.

I suggested that Mr. Madero borrow a friend's deck and receiver to substitute for his own, thinking that this would uncover the guilty component. I also suggested using different cables between the decks and the receivers, and that the plugs be twisted back and forth a few times after insertion into the jacks, to ensure that they made good connection. As an afterthought, I asked if Mr. Madero had changed the locations of any of his components.

At that point, he wrote the following to me: "I am happy to inform you that my problem has been solved: Stacking. I failed to tell you that I had my components stacked one atop the other.

When my tape decks checked out okay at the factory repair place, the technician and I both thought my receiver must be at fault. The technician graciously checked my receiver for me, but found nothing wrong. I was ready to send it to its manufacturer when the technician said, 'By the way, where do you keep your equipment?' When I told him, he smiled and said,

'Let me show you something.' He set my deck atop a receiver, and-lo and behold-the hum appeared. My components are now properly located, and I am enjoying music again."

Speed Control

Q. My cassette deck runs about a quarter-tone fast. Can this be corrected? Better yet, can I make or buy a variable-speed unit for it?

-Ward G. Erwin; Kissimmee, Fla.

A. While it is possible to build a speed control, this would require a fair amount of effort, technical knowledge, and expense. Articles have been written on the subject, such as the one by Gary McClellan, "Programmable Control," in the April 1981 issue of Popular Electronics. I do not know of any speed control unit on the market.

Have you consulted the manufacturer of your deck about your problem? Or an authorized service shop? Sometimes a fairly simple change is all that's needed, such as installing a pulley of slightly different diameter in the transport mechanism. If your deck truly runs about a quarter-tone fast, this corresponds to an error of about 3%, which is far outside the usual tolerance. Most cassette decks stay within 0.5% of correct speed. So you do indeed have a legitimate gripe.

(Source: Audio magazine, Oct. 1985, HERMAN BURSTEIN)

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