TAPE GUIDE (Sept. 1983)

Unbalancing Act

Q. I have been using AKG microphones in a balanced-line configuration, terminating in line transformers to plug into the high-impedance input of my tape deck. I recently acquired a mixer whose instructions indicate that the inputs are low impedance. My problem is how and whether to convert to unbalanced line for the input to this mixer. I assume that one of the two balanced-line terminals from the microphone should be grounded to the cable shield, leaving only one hot connection. Which one should be grounded? Where should this ground connection be made? May I continue to use my existing three-wire (two inner conductors plus shield) microphone cable in an unbalanced line configuration? Should I leave the unused conductor unconnected at both ends?

-Wayne Welty, Decatur, Ga.

A. I don't think it makes any difference which hot lead is grounded. Ordinarily, the ground connection should be made at both ends of the cable.

Sometimes, however, it may turn out that grounding just at one end or the other minimizes hum. I think you can continue using your present cable without problems. You will have higher capacitance than with two-wire cable, but this should not raise a problem with a low-impedance mike and a cable that is not excessively long.

[Editor's Note: Make sure, though, that you ground the same pin on each mike, to maintain polarity. -I.B.]

Can A New Head Cause Static?

Q. My portable cassette deck recently had a new head installed. At first it sounded great, but now I occasionally hear a static noise that I never heard before. This happens only when playing back tapes recorded from TV pro grams; I place the mike in front of the TV speaker and keep the TV at normal volume. When I record my voice, there is no such noise. Do you know what could cause this?

-Wade Marshall, Chicago, Ill.

A. Inasmuch as your problem occurs only with tapes recorded from TV and not from other sources, it seems most unlikely that the fault could be in your deck. Perhaps your new tape head is reproducing high frequencies better than the old one, and therefore allows you to hear things you didn't before.

Perhaps when your deck was in for repair, its bias was adjusted for better treble response. And there is the possibility that your TV isn't working as well as before. For example, if there is high-voltage arcing in your set (more likely to occur when the weather is humid), a mike placed close to the set could pick up the snapping sound although your ears don't pick it up where you sit.

Tape Squeak

Q. I have a problem with a well known tape brand that I have been using lately. These tapes usually develop an annoying squeak or chirping near the end. Sometimes the problem occurs nearer the beginning, and the squeak is accompanied by a slowing of the tape. Tapes of other manufacturers do not seem to have this problem. Could you tell me what the problem might be?

-Mary Mulry, Gainesville, Fla.

A. It has been found on a number of occasions that some very good tapes are not compatible with some very good decks from the aspect of squeal or squeak. This might be true of al tapes of a particular type made by a manufacturer, or it might be true only of a particular batch of these tapes. If you can exchange your troublesome tapes for new ones of the same brand, the latter might work satisfactorily.

The squeak may be due to the environment in which the tapes are used (temperature and humidity conditions), to an incompatible lubricant contained in the tape, or to a set of cassette shells which are difficult for your deck to handle. It is hard to be more precise without getting involved with a great deal of highly detailed measurement and analysis.

Fielding a Question

Q. I scanned the tape path of my deck with a magnetometer and was surprised to find some fields of about 12 Gauss right in the region of the tape path. These fields are present only while the reel motors are running, and the meter returns to zero when I push stop. I've had the deck a couple of months and so far have not noticed any sign of erasure or high-frequency loss, but with this high a measured value of magnetic field, it may be that over a period of time the tapes will experience such effects. If the magnetometer readings seem excessive to you, please tell me if you think I should have the matter checked by the manufacturer.

-J. M. Reilly, New Castle, Del.

A. It doesn't seem that the field strength you measured presents a problem. I go partly on the basis that you have noticed no signs of high-frequency loss. Further, the spacing of the tape from the fields and its orientation with respect to the fields may be such as to minimize the loss. (The greatest danger is when the heads show an appreciable magnetic field.) On the other hand, I see no reason why you should not bring the matter to the attention of the deck manufacturer.

If you get an interesting reply, I would appreciate hearing further from you.

(Mr. Reilly did query the manufacturer and received the following reply:

"The magnetic field you are encountering is caused by a solenoid and should not affect the deck's performance.")

Brand X Tape

Q. I see advertisements for 1800-foot tape reels, used once, for about $1 per reel. Do you know the source of this tape? Would it be dependable? It seems odd that such tape be used only once and then discarded and re-sold.

-James E. Allan, Fairborn, Oh.

A. I have no way of knowing the source of this tape and what kind it is. I do not even know whether it is truly audio tape; it might be slitted video or computer tape. And I usually have suspicions about such "bargains;" for ex ample about its lubrication, its shed ding characteristics, its magnetic properties (whether it will work suitably with the bias and equalization typically found in home decks), with the accuracy of its slitting (whether it will tend to skew or jam as it travels between the guides and other elements of the tape path), with the number of splices in the tape, and so forth.

You might buy one of these tapes and determine for yourself whether it is satisfactory.

(Source: Audio magazine, Sept. 1983, HERMAN BURSTEIN)

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