Tape Guide (Feb. 1982)

EQ Quandary

Q. I have several classic performances recorded during the 1940s and 1950s by Horowitz, Toscanini, et al. and would like to do my own remastering before putting them on tape. I hope to improve the frequency range, remove coloration, etc. For my purposes, which type of equalizer would you recommend: Graphic, graphic with adjustable center frequencies, or full parametric?

John Oster; Sacramento, Cal.

A. Inasmuch as the full parametric equalizer offers the greatest flexibility permitting adjustment of amplitude, center frequency, and bandwidth of selected portions of the audio spectrum I tend to favor this choice.

What's Your Bias?

Q. I want to adjust the bias of my open-reel tape deck for optimum performance. According to the service manual, this requires that a 10-kHz signal be injected at a -20 dB level, with the bias then being adjusted according to a table in the manual. How critical is this frequency?

-Howard Sanner, Jr., Hyattsville, Md.

A. Accuracy of the signal frequency is fairly critical, so that you should have an accurate signal generator. You should probably be within 100 Hz of 10 kHz, because slight bias changes have a fairly pronounced effect on high-end response.

Steeling Signal?

Q. I have a Scandinavian-style audio and record storage system. It is designed so that I can place cassettes directly below or beside my receiver and tape deck. Although I'd like to do this, I never have because of concern that the magnetic fields of the power transformers of my equipment would slowly destroy the signals on the tape. A friend suggested that I obtain some steel sheet, cut it to fit, and place it below or beside my equipment to shield the tapes. Is this likely to do the job? Is it necessary?

-Robert Ericson; Cicero, Ill.

A. I believe that your fears are groundless and that you may do more harm than good if you introduce steel sheeting that cuts off air flow around your equipment. It could cause overheating of the equipment.

For a powerful magnetic field, such as that of a bulk eraser, to have perceptible effect on audio tape, it would have to be brought within three inches or less from the tape. The magnetic fields emanating from your equipment are much less powerful than that. You probably have more than three inches of spacing between your cassettes and your audio equipment or at least you should in order to permit adequate air flow. Chances are very great that your cassettes would be safe even if there were only an inch of spacing.

Limiter Limits

Q. My cassette deck incorporates a limiter to prevent signals from going above the 0-dB level and thereby causing distortion. Is the limiter that beneficial? Or could it be that the record level meters are inaccurate, so that I am unnecessarily limiting a signal not so large as to cause distortion or of too brief a duration to cause noticeable distortion?

-Charles Hopson; Madison, Ala.

A. The quality of limiters found in cassette decks varies from one design to another. For high fidelity, few serious recordists employ such a limiter. Therefore, it is advisable that you switch out the limiter when making music recordings from which you expect maximum fidelity. If your deck does not permit you to shut off the limiter, then be careful in recording not to let the record level meter go above 0 VU.

To tell how good a job your deck is doing, make a tape of a phono disc and play back the two in synchronization, alternating between them. If you hear little or no difference, things are working well.

Mike-to-Deck Matching

Q. I would like to use a microphone with an output impedance of 250 ohms for recording on a tape deck that has a mike input impedance of 30,000 ohms.

Is this a problem?

-Robert Shepard; Elk Grove, Cal.

A. Ordinarily there is no problem when you feed a low-impedance source into a high-impedance load, provided that the source delivers enough signal voltage to drive the load adequately. In your specific case, there is no problem if your mike furnishes enough signal to drive the deck to full recording level. If it does not, you will need a line transformer to step up the signal voltage. The transformer should be at the end of the cable nearest to the deck to prevent a possible loss of high frequencies.

Garage-Sale Find

Q. t recently purchased an old-model open-reel deck at a garage sale for a surprisingly low price of $45. When the monitor switch is in the "tape" mode, I hear a strange noise from the right channel; it sounds like someone blowing continuously into a microphone. This sound gets recorded onto the tape, and I would like to get rid of it. What might the problem be?

-Ron Salmon; Moorestown, N.J.

A. The strange noise from the right channel is probably why the former owner parted with the deck. This could be due to a noisy resistor, capacitor, or transistor. The cost of repair at an authorized service shop might run under $50; more likely it would approach $100 or more, as these things go these days.

Input Inclination

Q. More and more I see ads for receivers which feature mike inputs and mike/line mixing. If a recordist has a tape deck as part of his system, what considerations might make him decide to use the mike inputs of the receiver rather than those of the tape deck?

-Melvin Spencer; San Juan Capistrano, Cal.

A. One reason for preferring the receiver's mike facilities might be that it has a higher signal-to-noise ratio for mike input. Another reason might be higher gain when dealing with a weak mike signal, and a third might be convenience of access.

Trigger Unhappy

Q. My cassette deck has an automatic shut-off device that is very "quick triggered." When the line voltage drops (for example when my air conditioner goes on), it clicks off. Sometimes it operates fine for 10 or 12 hours but then shuts off several times in a row, which is very inconvenient if it happens during recording. I took my deck to the factory twice, but to no avail. Several other cassette decks are used in our house, and none of them have this problem. I am planning to get rid of my deck and buy a different one. But how can I know in advance that the new one will not end up doing the same thing?

-N.A. Bruscolini; Philadelphia, Pa.

A. Yours appears to be an unusual problem; no other reader has reported a similar one (yet). If you buy another deck, the odds are that the problem will not recur, although of course I can't promise.

It seems a shame to replace an otherwise satisfactory deck for the reason given. Have you tried taking your complaint to the manager of the factory, or to someone else at or near the top? Have you called your electric company to check whether your line voltage is unusually low even at "normal" times? Have you consulted an authorized service shop instead of the factory? If you are intent on a new deck, discuss your problem with the dealer. If he maintains a service shop, he will probably have a Variac which can vary the voltage supply and thus check for performance under low-voltage conditions.

Shopping Around

Q. I am in the process of shopping for a cassette deck. Is there a good way to compare decks? One store owner asked me what my taste in music is, but does this really matter?

-David Hellman; Suffern, N.Y.

A. It seems to me that your taste in music is irrelevant to your choice of tape deck.

Your first step in selecting a deck may be on the basis of equipment reviews, price, and specifications, which should give you a group of, say, half a dozen from which to choose. Next, you should listen to the decks you have listed as possibilities, and limit yourself to those which seem most accurate when comparing the playback signal with the source (for example, using FM noise as the source), and which seem to be the least noisy in playback. Operating features and conveniences would be secondary considerations, although not necessarily unimportant. Stay with well-known and reputable brand names, and inquire as to where you will have to go for service if the need arises. If all other factors are about equal, it is great to have an authorized service station nearby instead of having to settle for an unauthorized shop or having to ship one's deck to the manufacturer for service.

(adapted from Audio magazine, Feb. 1982; HERMAN BURSTEIN)

= = = =