Tape Guide (Q and A) (Oct. 1970)

Tape Dust

Q. I have been using a very high quality tape on my recorder. After a few reels of use there is a residue of tape dust on the guides. This causes me to wonder if the tape is as good as I think it is.

(William Mock, Baltimore, Md.)

A. I suggest that you compare the performance of your tape with that of other quality brands in order to ascertain whether it is the tape or your tape machine that is primarily at fault. All tapes produce some residue, so the real question is whether your present tape produces excessive residue.

Bias Traps

Q. I have three tape recorders, all of which use 100-kHz bias. For overall response measurement and equalization adjustment, I use a bias trap, which gives about 40 dB attenuation at 100 kHz but does not affect the audio range. Is there any reason I shouldn't wire such a trap permanently in the output of each channel of each recorder? This would save the bother of hooking it up for tests. (Richard S. Field, Jr., Pacific Palisades, California)

A. The best way to know is to try. You might try building a bias trap into your tape machine to see if there are adverse effects. However, unless the inductances in the trap are adequately shielded, they may pick up hum or stray signals, such as radio signals.

Head Demagnetization

Q. How often does one really need to demagnetize heads? I suspect very seldom. My manual says "every 8 hours of operation." This is a bother. I put it in the class of maintenance instructions that one gets on all the hundreds of household gadgets and appliances that people use. If you follow them all, you will not have time for anything else. (Richard S. Field, Jr., Pacific Palisades, California )

A. Demagnetizing the heads after every 8 hours of use is a fairly standard recommendation, although a few manufacturers indicate otherwise. Depending on the machine you are using and the material you are recording, less frequent demagnetization may be satisfactory. The recommendation is a precautionary one, and you might find that demagnetizing after, say, every 20 hours is adequate in your case. One just doesn't know. Getting topflight performance out of a tape recorder involves paying attention to details, the same as for an automobile or a camera.

Tape Choice

Q. What type of recording tape would you recommend, bearing in mind the following requirements? It must be capable of reproducing wide, uniform response with minimum noise and print-through.

It must be capable of being stored for long periods of time under normal household conditions. I will need as much tape per reel as feasible.

(Charlie Perry, Jr., Ansonia, Connecticut)

A. I suggest that you try the low-noise tapes made by manufacturers of established reputation. Use tape with a polyester (Mylar) backing. To avoid the possibility of noticeable print-through, particularly after long storage, use 1 1/2 or 1-mil tape. Do not use 1/2-mil tape, although this would more nearly serve your wish to get as much material as possible on one reel.

Cross-Field Heads

Q. What are the advantages and disadvantages of the cross-field head?

(E. C. Smiley, APO San Francisco, California)

A. Some machines using the cross-field head claim response to as high as about 18,000 Hz at 3.75 ips. However, high quality tape machines in general-with or without the cross-field head-can achieve such response if they are willing to make sufficient sacrifice in terms of noise and/ or distortion. Manufacturers now using the cross-field head claim that for a given amount of noise and distortion, they can achieve a more-extended treble response by using the cross-field head. Inasmuch as a number of manufacturers of high quality machines have not yet gone over to the cross-field principle, there is not yet any clear-cut evidence of its superiority. I don't know of disadvantages of the cross-field head, other than its added complexity ( involving an extra head for recording, this head being located at the backing side of the tape), and therefore added cost.

Microphone Overload

Q. I would like to use the AKG condenser microphone with both my tape deck and my P.A. amplifier. These mikes have relatively high output. What can I do to prevent overloading the inputs of my tape deck and amplifier?

( John D. Moss, Hartselle, Alabama )

A. Offhand, I am inclined to doubt that the output of the microphone would overload your tape deck or amplifier. To find out whether there is a real possibility of this, and what steps to take in case the possibility exists. I suggest you consult the manufacturers of the microphone, the tape deck, and the amplifier. I would rather not venture a suggestion that might impair the frequency or other performance aspects of a fine microphone. Possibly the microphone incorporates a facility for decreasing its output; or perhaps a simple voltage divider across the microphone output, using values recommended by the manufacturer, may be the answer.

Dubbing Speeds

Q. Can a tape recorded at 15 ips be played at 7 1/2 ips on one machine while recording from that machine onto another machine at 3 3/4 ips, so that the second tape can then be played back at 7% ips? Will it sound as good as the original 15-ips tape except for the extra machine involved?

(John D. Moss )

A. Yes, you could follow the procedure you describe in order to duplicate a 15-ips tape for replay at 7 1/2 ips. But I would not vouch for the frequency response characteristics of the duplicate tape in view of the varying speeds employed. To maintain good frequency response you should play and record at the same speed.

This would mean playing the original at 15 ips and rerecording it at 7 1/2 ips.

Recording Quality

Q. My tape recorder has a cross-field head. Would I obtain quality equal to the original by recording at 1 7/8 ips? If I record at 7 1/2 ips, would I obtain better quality than the original?

( Vernon T. Rose, APO San Francisco)

A. If you wish to preserve the original quality of the source, record at the maximum speed available. You cannot improve on the original quality. If your source is of low quality, you may lose very little if anything by recording at a reduced speed.

(Audio magazine, Oct. 1970; Herman Burstein)

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