TAPE TALK--Theoretical and practical tape problems solved ( Nov. 1977)

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I Was Wondering If ...

Q. You could recommend a reliable reel-to reel service station?

Q. Our parish needs a good cassette deck to record services for the shut-in, and we were wondering if you could help us...

Q. My husband is legally blind, and music is all he enjoys, but I don't know what to get for him and I don't understand any of your test reports. I promise I won't tell anyone else if you'll only suggest...

A HUNDRED READERS; Everywhere, USA (and abroad)

A. Deeply as it hurts me (for many of the extenuating circumstances pleaded are genuine and heartrending), inquiries like this simply have to go into my "Don't Answer" file. I'm flattered by the confidence so many readers have in my judgment of equipment, and I would be less than candid if I were to re ply that because I haven't personally tested everything in the field, I have no opinions on anything. My consulting business-which is wholly unconnected with STEREO REVIEW could hardly operate if that were true. How ever, inasmuch as reader inquiries reach me in my capacity as Contributing Editor to this magazine, I must consistently follow the magazine's policy against making any recommendation of one product over another beyond what is contained in published test re ports-actual testing is the only fair test.

Backcoating

Q. Why are some tapes back-coated? Is there any real advantage, or is it just an advertising gimmick?

MONTY FELS; Oklahoma City, Okla.

A. Providing a tape with a back-coated layer (made up largely of carbon particles) offers at least three advantages. First, as the tape is squeezed between the puck roller and the rotating capstan shaft during normal playing, the slightly roughened back-coating gives the rubber roller a better grip. Second, during high-speed winding, the textured back surface allows air trapped between the layers to bleed out. This results in a smoother tape pack with less danger to exposed tape edges. Finally, by putting a conductive coating on the back of the tape, it becomes unnecessary to put so much-carbon into the oxide-plus-binder material that gets coated onto the front side. Static electric charges are drained off just as effectively with the carbon on the back, but there is now proportionately more room for oxide needles, making for potentially improved magnetic performance.

Eight-track Feedback

Q. In one of your columns, you made some negative remarks about eight-track cartridges. Okay, I'm ready to switch to the cassette format as soon as you tell me where I can get four-channel (discrete) cassettes.

CHRISTOPHER JAMES BAUMBACH; Oak Park, Ill.

A. Fair enough. The reason there are no four-channel cassettes is not technological: there are plenty of four-channel cassette heads available (with 60-dB or better crosstalk rejection) which are used currently by duplicators who record both "sides" of a stereo cassette at a single pass.

Unhappily, Philips-which controls the licensing structure for all "compact cassettes"-will not permit their licensees to produce a four-channel home deck using these heads. Their reason is that such one-direction, four-channel cassettes could not be played compatibly on existing stereo and mono cassette decks, and it has been an abiding principle with Philips that full compatibility must be maintained within their proprietary format from pole (North) to pole (South).

(They had to bend their rule a bit to permit chromium-dioxide and Dolbyized cassettes.) It is theoretically possible to make a four-channel cassette that is compatible with the Philips standards, and one or two laboratory machines have been constructed that do so.

This involves using eight recorded tracks (four in each direction) that are only approximately 0.008 inch wide, however. Mass-produced heads capable of handling four such tracks with the exacting alignment required are currently not in the cards. And even if they were, signal-to-noise ratio would suffer by about 10 dB--a degradation that today's cassettes just can't afford.

As far as matrixed four-channel cassettes are concerned (Ralph Hodges discussed them in his October 1976 report on the new Angel cassette releases), manufacturers have apparently decided not to pursue this development for the time being.


Take-up Trouble

Q. I have a three-motor cassette deck that is plagued with a problem often experienced with less expensive recorders. If I am near the end of the tape, the deck often will not fast-forward the tape to the end. And if I take the cassette out and turn it over, it won't rewind the remaining distance either. Is this because the deck is a front-loader, or does the solenoid control or the automatic shut-off have anything to do with it? Can it be fixed?

DAVID BAUGHMAN; Hanover, N.H.

A. Your problem has nothing to do with front-loading, a solenoid control sys tem, or the automatic shut-off. Without a service manual and the ailing deck itself it's hard to make more than a guess at a diagnosis, but if your particular three-motor cassette transport operates on the principle used by many three-motor open-reel decks, the problem may arise from the following cause: In fast-wind modes, full power is applied to whichever reel motor is winding, but some power is fed--via a resistor--to the other reel motor as well. The reason for this is to create a certain amount of "holdback" tension to ensure a smooth wind. The two reel motors tend to rotate in opposite directions when powered, and the reduced power fed to the trailing reel the tension by causing that motor to oppose the motion of the tape. The same resistor is often switched be tween motors (depending on which is pulling and which is holding back), so if slightly too much holdback tension is being supplied-by an out-of-tolerance resistor-it would show up in both directions and under precisely the conditions in which you are experiencing difficulty: a nearly full reel (whose large tape pack reduces the take-up torque) trying to pull a nearly empty reel (whose small diameter ensures maximum holdback torque).

Many cassette mechanisms do not employ such a voltage-controlled holdback tension, however, relying solely on the frictional forces built into cassettes and on a none-too-hefty take-up motor. In this latter case, I fear there's little you can do yourself, although the machine's manufacturer may be able to help.

Adding a Volume Control

Q. I have a stereo tape recorder that has no output-level controls. Is there anyone who makes an add-on playback control for decks like mine?

THOMAS A. CALI; Freeport, Ill.

A. The Switchcraft #669P1 Stereo Volume Control, which currently lists for $8.45, is designed for precisely this kind of application. Since it consists simply of a two-gang ("stereo") audio volume control, with input and output connectors, there may be other companies that make a similar product.

Note, however, that with this or any similar "passive" control you can turn the playback level down but not up.

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Also see:

AUDIO QUESTIONS and ANSWERS: Advice on readers' technical problems

 

JVC KD-35 cassette deck

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