TAPE GUIDE (Jan. 1988)

Advice on Tape Spillage

Some of the items in this column have dealt with the problem of tape spillage. A reader offers the following explanation and advice:

Most decks, when not in an auto-reverse mode, use a timer circuit that receives pulses from the take-up hub, keeping the drive engaged as long as it gets a pulse once in a while. At the end of the tape, the take-up hub stops, and eventually the drive disengages.

The pulses come either from a rotating magnet operating a reed switch or from a paddle wheel operating a photoelectric sensor. If the take-up hub does not have its own motor, and sometimes even when it does, the hub spindle is driven through a metal-to-rubber contact. Over time, the rubber ages and the metal gets polished, so the metal may randomly skid on the rubber every now and then. (Interestingly, a torque check will still show adequate torque.) Meanwhile, the drive capstan has been pulling tape out of the cassette, though the take-up hub has stopped; thus, tape is spilled.

If the hub drive recovers before the timing circuit notices it hasn't received a pulse recently, the loose tape may get pulled back into the cassette.

Sometimes, the drive doesn't recover soon enough, and tape spill occurs.

For a mechanically handy person, there are some temporary cures.

Cleaning the internal rubber pulley involved, using a rubber cleaner/conditioner (such as Teac RC-2), will help. In some two-motor decks, there are two side-by-side rubber pulleys which can be swapped without disassembly, and this may help as well.

-James P. De Clercq, Toledo, Ohio

To this I would like to add a warning:

If a deck is relatively new and still un der warranty, this warranty may be in validated if you open the deck. Also, particularly for the novice, there is al ways the possibility of doing more harm than good by tampering with the deck mechanism.

Mono-to-Stereo Miking

Q. Recently I bought a dual-well cassette deck which has one serious disadvantage: Instead of stereo inputs, it has only a mono mike input which feeds both channels. I plan to do some live stereo recordings. How can I do this with my deck? Neither receivers nor integrated amplifiers provide microphone inputs, and I believe that professional mike mixers are far too expensive for me. Is there a way to incorporate a stereo mike jack in place of the mono jack in my deck, with mi nor modification of the circuitry?

-Amitabha Sarkar, Pullman, Wash.

A. It is not feasible to modify a mono mike jack for stereo use unless you have exceptional knowledge and technical ability. Changing the jack from mono to stereo is simple, but adding a second mike channel, involving additional electronic circuitry, is not.

The way to go is to buy a mixer.

True, some of their prices go up into the many hundreds of dollars, and even into the thousands, but others are available for much less. For example, you might try Radio Shack or Fostex.

Using Alignment Tapes

Q. I have eight cassette decks, including one in my car, but they are out of azimuth alignment with each other.

Hence, if I record a tape on one deck, it may not play well on another. I plan to purchase an azimuth alignment tape and fix all of my decks once and for all.

If I purchase an alignment tape from one deck manufacturer, will I be able to use it to align the decks of other manufacturers? Also, is it difficult to align the heads for azimuth on a three-head deck?

-Joe Roberts, Wilbraham, Mass.

A. In theory, all azimuth alignment tapes, no matter who the manufacturer is, should be identical and therefore usable on all decks, resulting in compatibility among them. In practice, only those alignment tapes made by reputable companies are sufficiently similar to serve the purpose.

To use an azimuth alignment tape on a three-head deck, first align the play back head for maximum output of the tape's test tone. Next, using a signal generator and the same frequency as on the test tape, simultaneously record and play this generator tone, and ad just the record head for maximum out put in playback.

Bias Adjustment by Ear

Q. I own a three-head cassette deck that has a user-adjustable bias control. I am a bit confused as to its proper use. Inasmuch as my cassette deck lacks a tone generator, I use FM interstation noise, recorded at about-20 dB, to get as close a match as possible between the deck and the tape. Should I use this procedure with Dolby noise reduction on or off? Usually I use Dolby C.

-Nathan Losman, Belleville, N.J.

A. Since you are adjusting bias on the basis of frequency response, you must include in the bias-adjustment procedure all elements of the tape re cording and playback system that affect frequency response. Therefore, you should proceed with Dolby NR on-Dolby C, if that is the mode you are going to use in recording and play back.

Let me add that adjusting bias on the basis of FM noise, using your ear to judge when response is flattest, is a recommended procedure. After all, your ear will eventually do the listening to program material. Should you find that there is a range of bias-control settings which seem to produce equally flat response, go to the maximum bias in this range, thereby minimizing distortion.

Let me further add that Dolby C NR is generally preferable to Dolby B, not only because Dolby C results in approximately 8 dB greater signal-to noise ratio but also because, at high recording levels, it results in less tape saturation--and, consequently, less treble loss and distortion.

Dolby B and C Compatibility

Q. I have read in several periodicals about the incompatibility of Dolby B and C noise reduction. These articles indicate that I should expect audibly undesirable results when using Dolby B NR to play Dolby C-encoded tapes, and vice versa.

I do not hear weird effects when playing a Dolby C tape with Dolby B decoding, but I do hear strange modulation effects when I apply Dolby C decoding to a Dolby B tape. Does your subjective listening experience agree with my appraisal?

I believe that Dolby C NR should be recommended for almost all taping where the choice is between B and C.

The benefits of appreciably greater noise reduction and of headroom ex tension provided by Dolby C outweigh the disadvantage of exaggerated treble when only Dolby B is available to decode a Dolby C tape.

-Sterling Lawrence, Weaverville, N.C.

A. Essentially I agree with you, except that I do not hear a "strange modulation effect" when using Dolby C de coding with a Dolby B recording. This effect may depend upon the particular tape deck one is using.

The consequences of encoding/de coding mismatches are chiefly in terms of treble response. Decoding with Dolby C NR when Dolby B is called for results in some treble loss; the reverse produces treble boost. These consequences are not necessarily undesirable. If they are undesirable, judicious use of the treble control in one's audio system can often compensate adequately.

Pad Lifters and Demagnetization

Q. I own a Nakamichi cassette deck. Will the pressure-pad lifter on this or other Nakamichi models prevent proper demagnetization of heads when using cassette-type demagnetizers?

-B. Horne, West Lafayette, Ind.

A. To my knowledge, pressure-pad lifters will not have such an effect. If they did, it would be likely that cassette-type demagnetizers would come with warnings about this.

Type I vs. Type II Distortion

Q. When I look at distortion curves for cassette decks, I see that they stay below 1% only to 5 kHz and rise fast after that. Won't this hurt the quality of a recording? Also, 1 find that Type 11 tapes sometimes are measured as having more distortion than Type I. Therefore, wouldn't Type I be better for music?

-Ken Thorberg, Duluth, Minn.

A. The rise in harmonic distortion beyond 5 kHz or so is not important for two reasons. First, most program material has a substantial drop in energy in the treble range; this tends to reduce distortion, inasmuch as distortion varies with signal amplitude. Second, harmonic distortion on tape is primarily odd-harmonic; therefore, the first major distortion component for, say, 5 kHz would be 15 kHz, which is close to or above the hearing limit of most adults.

Yes, Type II tapes are often measured as having somewhat higher distortion than Type I, partly because of the greater treble boost applied in re cording for Type II. However, in tape systems, it appears that harmonic distortion doesn't become bothersome on program material until it exceeds about 3%. The measurements you are talking about usually involve distortion figures of roughly 0.5% to 1.5%. I think you should try a listening test, comparing a Type I tape with a Type II, to ascertain whether you hear a perceptible difference. If you do, then continue to purchase the type which is most satisfactory to your ears. If you don't, let your pocketbook be your guide.

Recording Warped Records

Q. I have an unusual problem in re cording songs from a warped phono record. My tape deck picks up distortion when the stylus hits the "bump" on the record. When playing the tape, this distortion is audible through the speakers, even though there is no noticeable distortion when listening to the record.

Can you explain?

- Stanley Terence Cina, Edina, Minn.

A. Record warp produces a frequency that is too low to be audible but is of substantial magnitude. Most preamps, power amps, receivers, and open-reel tape decks can handle the warp frequency without going into noticeable distortion. However, the re cord electronics of many or most cassette decks will be overloaded by such a frequency. The cure is to introduce a high-pass filter between your tape out put and the cassette deck; such filters are commercially available.

Automatic Misadjustment

Q. I recently bought a new cassette deck with automatic adjustment of bias, record level, and record equalization and began to re-tape my LPs and CDs. Later, I listened to a tape made on my old deck, and it sounded brighter than the tapes made with the new deck. I then recorded pink noise from an analyzer/equalizer using the auto-adjustment system, with and with out Dolby C NR and at four different levels. To my dismay, in playback I found a 10-dB roll-off from about 10 to 16 kHz. I repeated the test without the calibration system and found the play back response nearly flat to 16 kHz (the upper limit of my analyzer). I ex changed the new deck for another of the same model and ran the tests again; the results were identical. I got my first unit back and have been re cording without the automatic adjustment system. The manufacturer has suggested trying various tape formulations, but this has had no effect. Is there some defect in the deck?

-Tim Stevens, San Antonio, Tex.

A. If your automatic calibration sys tem is working properly, you should get results at least as good with it as without it. Considering that you get good results without the system but not with it, it seems there must be a fault in the deck, either in its design or in some internal adjustment for the calibration system. You may have been the victim of coincidence in being dealt two decks that work improperly. Perhaps your second deck came from the same production run as the first, and this run suffered from a design or manufacturing flaw absent from other runs.

I suggest that you take your deck to an authorized service shop and be prepared to show, convincingly and briefly, that it doesn't work properly when the system is on. If you bought your deck recently, it should still be under warranty. If the shop doesn't provide satisfaction, return to the dealer from whom you bought the deck, and have him replace it with another model or give you a refund.

Modernizing an Open-Reel Deck

Q. I have had an open-reel deck for almost 20 years. It is still in good working condition but has an S/N of only 45 dB. I would like to know how to improve it. I think dbx NR is an obvious answer, but I would like to keep my deck compatible with other open-reel decks not equipped with dbx decoding. Would installing modern tape heads be the answer?

-Steven Dunn, Hoover, Ala.

A. Modern open-reel decks operating at 7 1/2 ips with quarter-track heads can achieve a signal-to-noise ratio of about 65 dB without the benefit of noise-reduction devices. Inasmuch as your deck can achieve about 45 dB S/N, you are aiming at an improvement of something like 20 dB. I doubt that new heads would do much for you.

Modern tapes will help somewhat, but you need a good deal more: Improved electronic circuitry, low-noise resistors in place of the garden-variety sort, and improved low-noise transistors (or, if your deck uses tubes, low-noise tubes). Unless you are talented in this sort of work, I doubt that your project is feasible. The best course is to employ dbx NR. This will add about 30 dB to S/N, resulting in a very respectable ratio of about 75 dB. However, these tapes will not sound their best when played without dbx NR.

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

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