Tape Guide (Sept. 1977)

Taping Choice

Q. I am using a Marantz tuner, pre amp, and amplifier, Bose 901 speakers, a Thorens TD -125 turntable with an SME tonearm, and a Shure V15 cartridge. Will I get better quality by taping records played on FM or by taping my records directly from my turntable?

-H.S. Liu, Los Angeles, Cal.

A. With your equipment, you will do better to record your phono discs directly. Too many FM stations fail to live up to the performance potential of FM and put out a miserable signal-over-compressed, distorted, and with a narrow frequency response.

Deck Thumping

Q. My Sony 630-D makes a thumping sound either when idling or in the forward position. This noise goes away at times but always returns.

-Thomas Dixon, Junction City, Kans.

A. It seems that something is out -of round, most likely the rubber idler. It is typical for the thumping to disappear after the machine has been in operation for awhile. But the idler "remembers" its original out -of roundness and the thumping resumes when the machine is cold. Try replacing the idler. If this doesn't help, you will need the help of either the manufacturer or an authorized service agency.

Cassette Treble Response

Q. Tape cassettes today at speeds of 1-7/8 ips are capable of reproducing frequencies of 12,000 Hz or more.

Yet, how can that be? Doesn't tape speed affect treble performance, the faster the better?

-Howard Wong, Jackson Hgts., N.Y.

A. Cassette tapes are able to go up to 12 kHz and higher at the speed of 1 7/8 ips owing to the development of tapes with improved treble response; to playback heads with very narrow gaps to minimize playback treble losses; to reduced amounts of bias, which causes partial erasure of the higher frequencies; to improved electronics, including the Dolby noise reduction system, which reduces noise and therefore overcomes the disadvantage of bias reduction, and the improvements in the tape formulations that provide for lower noise and increased signal level recorded on the tape.

Cassette Pressure Pads

Q. Most cassettes have pressure pads built into them. I've read that pressure pads increase the wear characteristic at one point in the tape head. How do tape manufacturers know how much pressure to apply to the tape. By buying brand name tapes would there be less head wear caused by these pressure pads?

Howard Wong, Jackson Heights, N.Y.

A. Pressure pads are adjusted for the minimum pressure that will maintain good tape -to -head contact so that the high frequency response meets its potential .... taking into account tape speed, gap width of the playback head, bias, kind of tape, etc.

By buying good tapes, you reduce the amount of head wear due to the abrasive effect of the tape.

Add-On Distortion

Q. To what degree do devices such as the Dolby unit, a four -channel decoder, or a reveberation unit introduce distortion into a music system?

-Frederick Kistler, APO, San Francisco.

A. The Dolby unit introduces very little distortion. However, a reverberation unit of the home type introduces somewhat more distortion, but exactly how much depends on the unit. The four -channel decoders generally introduce little distortion, and if they are passive devices (no transistors or tubes), they introduce no distortion.

Separation Explanation

Q. Figures are often given for "channel separation" for recorders, tuners, and amplifiers. Why wouldn't separation be complete? It would seem that if two separate microphones are used to produce two channels on the tape, there should be no reason for overlapping channels on playback.

-Frederick Kistler, APO, San Francisco.

A. Let's take tape as an example. Because the tape tracks are so close together, there tends to be signal leakage from one track to another.

Similarly, because the electronics for the two channels are in close proximity, or because the two sections of tape head are close together, there tends to be leakage.

Shut-off Timer

Q. Would it be harmful to my tape deck if I use a timer between the amplifier and wall socket so I might shut off the entire system at a desired time? Is turning off the power switch any different than pulling the plug?

-Robert McCue, Shreveport, La.

A. Having a timer shut off the entire audio system is not harmful except for the possibility that if your tape deck is in operation when the power goes off, the tape may become snarled.

However, this depends on the design of the deck, as some tape decks designs protect against tape snarl in case of power failure. If the pressure roller continues to make contact with the capstan when the power goes off, this tends to make the roller go out of round. Similarly, an idler in the transport may remain in contact with the motor shaft, causing the idler to go out of round. Again, all of this depends on the design of your particular tape deck.

Distortion Differences

Q. Three percent harmonic distortion in an amplifier would be considered horrendous, yet the spec sheets for many tape recorders give distortion as 3 percent at 0 VU. What is the difference between 3 percent harmonic distortion in an amplifier and in a tape machine?

-Frederick Kistler, APO, San Francisco.

A. Harmonic distortion should not exceed about 1 percent at 0 VU in a properly calibrated tape recorder. It seems that such a level of distortion, (3 percent) which occurs only on signal peaks and probably over a limited frequency range, is quite acceptable to the ear when coming from a tape recorder. Another reason might be that some of the higher distortion frequencies are outside the reproduction capability of the machine and/or the hearing range of the human ear.

(Source: Audio magazine, Sept. 1977; Herman Burstein)

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