TAPE GUIDE (Feb. 1988)

A Colleague's Amplifications

My colleague Howard A. Roberson, an Audio Senior Editor, writes the following:

"I'd like to comment on and amplify some topics covered in two recent 'Tape Guide' columns.

"In the October 1987 issue, Tom Whang of Glendora, Cal. complained that his tape deck's playback head had apparently been ruined by his cleaning it with 70% isopropyl alcohol.

Usually, isopropyl alcohols do a fairly good job of cleaning oxides and other residues from heads and other metal parts of the tape path. It is essential, however, that only 91% alcohol be used. Versions with lower percentages may be rubbing alcohol with various skin-conditioning additives, such as lanolin, which may leave a deposit on the head surface. The alcohol itself can attack materials that would be dam aged by loss of moisture, and it is damaging, over time, to rubber pinch rollers. Trichlorotrifluoroethane (TCF) solvents, sold by Geneva and others, are superior to alcohol in cleaning the metal parts of the tape path and will not damage rubber rollers or plastic parts. Intraclean S-711, a halogenated hydrocarbon, does an even better job of cleaning metal parts, and it also cleans rubber pinch rollers very well.

However, it will damage some plastics, including some non-rubber rollers.

"In the November 1987 issue, Anthony Hudaverdi of Santa Monica, Cal. voiced concern that the tapes he makes on his Nakamichi deck sound muddy when played on other machines. Deck-to-deck misalignment and Dolby mistracking problems were discussed, and these are certainly possibilities. There could, however, be dulling effects from playback equalization differences, as Mr. Hudaverdi had suggested. This does not mean that Nakamichi decks don't follow the IEC tape recording and playback Standard, only that their approach to realization of the Standard is different from the ones some other makers follow.

The official Standard, IEC Publication 94, gives specific formulas for ideal playback characteristics. Nakamichi playback heads were and are very close to the ideal expressed in the formula for the cassette format; some other makers' heads, including the first calibration heads used in generating standard alignment tapes, were much farther from the ideal. As a result, Nakamichi decks have required less high frequency boost in record equalization than was used to make the IEC alignment tapes. In practice, however, the IEC Standard is considered to be rep resented by these standard alignment tapes. Tape decks designed around the tapes will therefore use more re cord boost than Nakamichi decks do, and the less-boosted tapes made on a Nakamichi will sound dull when played on such decks. However, recent changes have brought the IEC tapes closer to the ideal and to the Nakamichi equalization, which is now well within the tolerances of the in-practice standard. Dulling of sound will there fore be most noticeable when tapes made on a current machine are played on older decks of other brands.

"Also in the November 1987 issue, Ivo Rokovich of Hialeah, Fla. wondered about the effects of using high-bias cassettes on decks with only normal-bias settings. As was discussed, recording Type II cassettes with Type I (normal) bias will yield a large boost on high-frequency levels, with relatively little change in the level of the low and middle frequencies. In the case of Type IV tapes, on the other hand, there will be a drop in level across the entire band, including the low and middle frequencies. Depending on the tape, this drop will be perhaps 15 to 20 dB, though it will be relatively less at the highest frequencies."

Popping Caused by Static

Q. I have a problem with popping noises during tape playback, which I believe are caused by static electricity.

The problem first appeared in my personal-portable tape player. Recently I bought a cassette deck that has dual transports. When I used this deck to play back a tape I'd made on it, I started to hear popping sounds about halfway through the tape. I moved the tape to the second well, but the pop ping continued. Thus far, commercially prerecorded tapes have not done this in my dual deck, but they have in my personal player.

-Lisa Gray; Placerville, Cal.

A. Static electricity seems to be a logical explanation, perhaps due to excessively low humidity. If you have been putting a tape through fast wind or rewind after use this might cause static buildup. See what happens if you play a tape only after it has been transported through its length at operating speed. Also try rapping the cassette sharply against your hand or a solid object, such as a book.

Parameters of High Quality

Q. I have purchased a cassette deck which I understand is a high-quality product, at a corresponding price. I would like to know the advantages of this machine over similar but lower priced decks.

-Victor M. Leon, Bay Shore, N.Y.

A. A high-quality deck tends to be superior with respect to flat and ex-tended frequency response, low distortion, accurate and steady motion, minimal electronic noise, minimal noise due to distortion in the bias waveform, and high quality of parts and construction with attendant reliability.

The Death of Type III

Q. I am curious as to whether or not there is such a thing as a Type III cassette tape. I have asked several people, including audio dealers, about this question, but no one seems to know the answer.

- Justin DeCrescente; Hewlett, N.Y.

A. Until a few years ago, several tape manufacturers made Type III cassettes. This type, called ferrichrome, consisted of a layer of chromium dioxide atop a layer of ferric oxide. Whereas the bias requirement for each of the other cassette types became pretty well standardized, bias for ferrichrome tended to vary appreciably from one tape manufacturer to another. Also, ferrichrome did not appear to offer any marked advantage over the other types. For these and possibly addition al reasons, Type III never acquired the popularity of the other types, and it gradually disappeared. That's just as well, because it reduces the perplexing number of choices confronting the audiophile.

(Source: Audio magazine, Feb. 1988, HERMAN BURSTEIN)

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