Tape Guide I and II (April 1977)

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Tape Deck Choice

Q. I am writing the type of letter which you must dislike receiving.

What brand of tape deck should 1 buy? When I first began investigating the decks available, I was thinking in the $500.00 range, but I don't want to spend any more than necessary to meet my needs. I am looking for a deck to be used, primarily, for taping from a fairly extensive record library, and for playing these and prerecorded tapes, in addition to limited live recording. What would be your choice: Revox, TEAC (several models mentioned), or Tandberg (several models mentioned)? I hope this letter doesn't ruin your whole day.

-L.E. Ray, Adrian, Mich.

A. As I have stated repeatedly, the policy of Audio magazine forbids me to recommend particular brands, or models, of audio equipment, although I would be happy to recommend a good Chinese restaurant or a book on statistical sampling. Hence you are thrown to your own resources which means reading equipment reviews, talking to trusted friends, talking to trusted salesmen, and most important of all using the evidence of your own ears and eyes. If the machine appears to faithfully reproduce sound, comes at a price you can afford, and stands up well in equipment reviews, it may well be a good bet.

You can save a fair amount of money, without giving up quality, by sacrificing such features as reverse operation, sound on sound, and simultaneous record and playback. Don't be afraid of one -motor recorders, since with good engineering they can closely rival the performance of those with two or three motors. Also, one motor units are usually lighter and more portable. No, you haven't ruined my whole day, just half of it.

Erase Eliminator

Q. I would like to make multiple recordings on the same tape track and, therefore, would like to defeat the erase head. Would it hurt to disconnect the erase head and hook it to an external load via a switch? This would still leave a load on the oscillator circuit without erasing the tape.

-Carl Ford, APO, N.Y.

A. If the external load presents the same impedance as the erase head, there should be no problem. But if the impedance is different, then this will tend to change the amount of bias current that reaches the record head, with consequent effects on the distortion and treble characteristics of the tape recording.

Demagnetization Frequency

Q. I clean my heads after five hours of use, but how often should I demagnetize them? The operating manual for my tape deck says that after long periods of operation the magnetic heads will build up a certain degree of residual magnetism. Does it hurt to demagnetize the heads, even if they don't have to be? I was told that if I touch the heads with the demagnetizer off. I could permanently magnetize them. Is this true?

Thomas Sabol, Fullerton, Pa.

A. Ordinarily manufacturers recommend demagnetizing the heads after about eight hours of use, the same for cleaning. Sometimes the recommended period is longer, although seldom more than 15 hours. To the best of my knowledge, no harm will come from subjecting a non -magnetized head to the demagnetizing process. Of course, it is possible to scratch a head with the demagnetizer unless its tip is covered with a soft or plastic materials.

The negative effects of a magnetized head are an increase in noise and a reduction in the treble response, and both these effects are permanently impressed on the recorded tape.

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Tape Guide II

Computer Tape for Audio?

Regularly we receive reader inquiries as to the suitability of computer tape for audio purposes. The problem is two-fold: (1) accurately slitting 1/2 -in. computer tape to produce a tape with 1/4 -in. (nominal) width for home tape decks, and (2) magnetic compatibility of computer tape with home tape decks in terms of bias, equalization, frequency response, etc.

We have taken a dim view on the matter, feeling that the two aspects of the problem are too serious to warrant use of computer tape even if obtained at minimal cost, as some audiophiles apparently can do. However, we don't feel that ours is a definitive view and have therefore sought the opinions of two authorities in the field of magnetic tape. Following are very helpful responses from Mr. Delos A. Eilers, Magnetic Audio/Video Products Division, 3M Company, and Mr. William A. Manly, The Cobaloy Company, Division of Graham Magnetics, Incorporated.

Slitting

Mr. Eilers:

"The assumption that an individual can accurately re-slit computer tape is not a very good one. The precision and skill required to slit tape is considerable, and then to assume that you can slit a 1/2-in. wide tape down the center without under- or over-width problems is very naive." Mr. Manly: "One big problem concerns the accurate slitting to 1/4-in. The proper width for audio tape is 0.246 ± 0.002 in. Computer tape is 0.498 ± 0.002 in., and just cutting a 1/2-in. computer tape down the middle means it will be too wide for proper audio use. On a new set of heads, this makes little difference, but after the heads are worn a bit, the slit -down computer tape will not fit into the groove. A better way is to slit the 1/4 -in. tape out of the center of 1/2-in. computer tape, but of course this wastes half the tape." (We would like to add that if the tape is too wide after slitting, it may stick in the tape guides. -H.B.)

Magnetic Compatibility

Mr. Eilers:

"Magnetic performance of computer tape is not the same as today's audio tape. Most computer tape is made with a standard, non-low noise oxide, while most of today's audio tape is made with low noise oxide.

Computer tape's electro -magnetic characteristics are similar to our obsolete #111 tape, and thus today's recorders would generally be over biased for a computer tape (resulting in reduced treble response-H.B.). Computer tape is also quite likely to have poorer short wavelength sensitivity than today's hi-fi quality audio tape; thus most of today's recorders would be short of the proper amount of equalization (treble boost-H.B.) to give an extended, flat frequency response on computer tape. It is impossible to be more specific unless we choose a specific computer tape and a specific audio tape to compare." Mr. Manly: "As to whether or not the bias and equalization will work properly, sometimes they will, and sometimes they won't. Most audio tape is coated to a thickness of 0.00035 in. to 0.0004 in., while computer tapes have a wider range of 0.00025 to 0.00045 in. Both bias and equalization are affected by coating thickness changes. Computer tapes are also designed to be most effective for a limited range of wavelengths on the tape (i.e., limited range of frequencies--H.B.), while audio tapes are quite wide band in terms of wavelength. Nevertheless, some computer tapes might be satisfactory for some audio applications. To give a more definitive answer, I would have to know what tape the audio transport was set up for, and which computer tapes were to be used."

Other comments

Mr. Eilers:

"Computer tape is designed for exceptionally good durability, which should be advantageous. However, this can also mean that the tape is highly abrasive to the heads compared to audio tape. If the recorder's heads are not extremely hard and durable, premature head failure due to severe wear could result from using re-slit computer tape. Often the reason computer tape is made available for some bargain price is that it is being retired because it is worn out. It has become so scratched and battered from use that the tape is no longer reliable. To use a such a tape for audio purposes could give this user poor reliability.

"To summarize, re-slit computer tape can work for audio applications but only for non -critical usage. The likelihood of having performance problems on today's slow speed, four track, hi-fi quality recorders is great, and thus we do not recommend using a re-slit computer tape for audio applications. We believe that the salvaging of old computer tape is really false economy and brings on more problems than the savings are worth."

Cure for a Noise Problem

Steven L. Bender, Brooklyn, N.Y., has found the solution to a noise problem that may afflict owners of some reversing tape decks. He writes: "I own two AKAI GX-230D tape decks, excellent in most respects."

There was a problem that plagued both of them: an FM noise type of static on playback that occurred about 45 dB below 0 VU. Since the hiss level is some 56 dB below 0 VU, this 'static' was causing about 10 dB reduction in signal-to-noise ratio. Some six months of investigation eventually determined the cause of the disturbance.

"The deck is an auto-reversing type, and the disturbance occurred only in the forward mode of playback, and only with certain tapes. The problem was found to lie in the auto -reversing post/guide, which has a d.c. potential of about 13 volts on both my machines in the forward playback mode.

In the reverse playback mode, the post-guide has only about 1/2 volt on it, so there is no noise problem then.

"When the tape passed over the charged post/guide, a field was set up that caused the static sound once the tape came to the playback head. This occurred only on back-coated tapes; only tapes were not susceptible to this phenomenon. When the back-coated tape was prevented from contacting the post/guide, the noise disappeared. Therefore, it is suggested that the owner not use back-coated tapes with the AKAI GX-230D. Possibly other reversing tape decks that use the foil method of automatic reversal may have a similar problem with back coated tape."

(Source: Audio magazine; Herman Burstein)

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