Tape Guide (Q and A) (Feb. 1971)

Condenser Microphones

Q. I plan to buy a Roberts 400X tape machine, operating at 15 ips. 1 would appreciate any comments on the quality of this machine, and on its advantages and disadvantages. If condenser microphones are the best, can you please tell me the ones that would operate the best with the above machine.

-John Mastronaidi, Cortland, N.Y.

A. The policy of AUDIO prohibits me from commenting on specific items of audio equipment. Therefore I cannot comment on the tape recorder you mention nor suggest specific condenser microphones.

However, I can offer the following general comments. Condenser microphones are considered by many to be the best type available. But also they cost the most. Most audio stores are willing to demonstrate their high-price microphones, enabling you to choose by ear.

If you plan to do live recording, it is a good idea to have a tape recorder that operates at 15 ips, because it will provide a wider dynamic range than one operating at 7 1/2 ips. The reason is that more treble boost is supplied at 7 1/2 ips than at 15 ips; with more treble boost there is more danger of running into tape saturation. When recording material with strong transients, for example guitar music, you are apt to run into the problem of insufficient "headroom." VU Meter Calibration Q. I have just purchased a tape deck.

How do I know if its VU meters are calibrated right? If they are not, what can I do to correct them?

-Leroy Mowatt, Bronx, N.Y.

A. To check calibration of your VU meters, you probably need the assistance of an authorized service agency.

The meter should read O VU when the machine is fed a 400 Hz signal that produces 1% harmonic distortion on the tape.

Life of Acetate Tape

Q. I have heard of acetate tape lasting through 15 years of storage, and I have read of a person who discards acetate tape after three years of use. How long does acetate tape last, and what factors affect its life?

-Leroy Mowatt, Bronx, N.Y.

A. Life span of an acetate tape depends upon the quality of the tape and conditions of storage. A good tape stored under conditions of moderate temperature and humidity can probably last 15 years or more. I have some acetate tapes purposely stored under extremes of heat and humidity (temperatures from about freezing to over 100 degrees and humidity from very damp to very dry), and they still play well after more than 10 years.

Speed of Head Wear

Q. I have an Akai M-8 which a friend is letting me use. He purchased the unit in Japan and used it for approximately 20 to 25 hours. No one else has used the recorder. The heads are worn badly enough to make 3 3/4 ips unacceptable; 7 1/2 ips is all right but could be better. The unit has been used about 50 hours total. What caused the heads to wear so quickly?

-George Harris, Chicago, Ill.

A. If the machine uses pressure pads, the cause might be excessive pad pressure. If the machine relies on tape tension, the cause could be excessive tension. Also, the heads themselves could be at fault. Good heads are made with deep gaps so that they can withstand considerable wear before serious deterioration in performance occurs, and they are made of materials resistant to wear. Cheap heads are not.

Still another possibility is the absence of tape lifters to space the tape away from the heads during rapid wind and rewind.

Sound-on–Sound

Q. In reading about the Sony 255 tape deck, I noticed that you must purchase a mixer so that the deck can make sound-on-sound recordings. This is a two-head deck, and I thought that in order to have sound-on-sound there must be three heads. Could you explain how the mixer can add sound-on-sound?

-Leroy Mowatt, Bronx, N.Y.

A. To make true sound-on sound recordings does require three heads in the case of a mono machine. However, in the case of a stereo machine, one channel of the record-playback head can serve for playback, while the other simultaneously serves for recording.

It would seem that the role of the mixer is to combine Signal I obtained in playback with the new Signal 2, and feed the combined signal into the tape machine for recording.

Recording-Only Problem

Q. Is it possible for a 4-track record playback head to be defective only during recording and perfectly all right in playback? My problem is exactly that. Playback of 4-track stereo prerecorded tapes as well as my mono tapes (4-track) previously recorded on my machine is all right. But for stereo recording, while the right channel is okay, the output from the left channel is very, very weak. I have tried checking the selector switch and the tubes; thoroughly cleaning both the erase and the record-playback heads, as well as demagnetizing them-and testing with used and virgin tapes of reliable brands.

-Rodolfo C. Penserga., Ormoc City. Philippines.

A. While few things are absolutely impossible. I am strongly disinclined to think that a tape head which operates satisfactorily in playback will not also do so in recording. Your difficulty seems to lie in a defective part in the left recording channel, such as a resistor or capacitor. Possibly this defect prevents bias current from reaching the left channel, or it cuts down the audio drive signal, or both. Low or missing bias current would result in very weak, and very distorted, sound. If the sound is only weak but not distorted, then the problem lies somewhere in the audio portion of the recording circuit. Signal tracing would be necessary to establish in what part of the circuit lies the fault.

Taping Discs

Q. I have had problems in taping records, and I do not know what the cause might be. I recently purchased an Angel stereo recording of Don Giovanni and have tried several times to make a tape of this. However, the level of my tape on playback is about half the level of the recording when played through my record player and amplifier. Also, the sound quality of the tape is not nearly equivalent to the records. The output of my phono pickup is stated to be 7.5 mV, and I have put the phono sensitivity switch of my audio amplifier in the maximum position. I have made the tape recording at the highest level according to my VU meters. Am I doing something wrong? Or is it normal to expect the taping of a record through a system such as mine to be inferior to the recording itself? My equipment consists of an Ampex model 2160 tape recorder, a Scott 260B amplifier, a Garrard record player, and Pickering V-15/3 cartridge.

-Charles B. Baker, Brussels, Belgium.

A. It is quite possible and not unusual for the recording level on tape playback to be less than on phono playback. The factors involved are the output of the particular tape machine used, the output of the phono cartridge employed, and the gain of the phono pre amp in the amplifier employed. You need not be over-concerned about the differences in level, provided you get as much level as you desire on tape playback.

The deterioration in sound quality when taping records may be due to the following. First, you are using a pickup with relatively high output. If your amplifier's sensitivity switch is in the position for maximum gain, you may be overloading the phono preamp, with consequent distortion. Second, you state that you have made the tape recordings at the highest level according to the VU meters. Recording at excessive level would have two deleterious results: It would result in distortion, and it would saturate the tape at high frequencies. causing treble loss.

Cross-Field Heads

Q. What is the function of the cross field head?

-E. Richmond Bauer, APO 96308

A. Its purpose is to reduce the erasing effect of bias current on high frequencies when recording, thus leading to better treble response. Bias current is necessary in recording in order to reduce distortion and increase the amount of signal recorded on the tape (i.e. to improve the signal to noise ratio).

Equalization at Different Speeds

Q. I would like to ask you a question in reference to extra preamp gain. I happen to own a Fisher X 101-C amplifier. This is a tube amplifier. I also own a Viking 88 stereo tape recorder, and a Viking 807 stereo playback transport without preamps. I do a lot of recording with the Viking 88, off the air and from records. The reason I bought a separate playback deck was to save my other recorder a lot of wear and tear on the heads. The way I see it, wearing out one head is a lot better than wearing out three, and less costly. My Fisher amplifier has a provision for TAPE HEAD and for TAPE PLAY. After I finish making a recording on the Viking 88 and play it back through the stereo system using the TAPE PLAY switch on my amplifier, the results sound great. But if I take that same recording and play it back using the Viking 807, and with the equalization switch of my amplifier in the tape position, I automatically get a bass boost and treble cut. What I'd like to know is what can I do to overcome this problem? The technical specifications of my Fisher state that the TAPE HEAD input requirement is 2 mV at 1 kHz, and the Viking 807 output is 2 mV at 1 kHz. Since these two units are matched up sensitivity-wise, why am I getting bass boost and treble cut? Is there anything I can do to correct this problem?

-Artis W. Evans, Jr., Brooklyn, N.Y.

A. So far as I can see, the input and output sensitivities of your amplifier and Viking 807 have nothing to do with your problem of frequency balance.

Inasmuch as your playback deck has no preamp, you are feeding the tape playback head signal directly into your Fisher TAPE HEAD input. Therefore the only equalization supplied is by the Fisher. And this equalization should properly consist of a very substantial amount of bass boost-36 dB in all at 7 1/2 ips. Inasmuch as ' the bass boost begins at 3,180 Hz (3 dB up at this point), it sounds like a combination of bass boost and treble cut. However, you complain that the net result is too much bass boost and treble cut. One reason for this excess could be that you are operating at 3 3/4 ips, but using equalization intended for 7 1/2 ips. The required playback equalization for 3 3/4 ips involves less bass boost and treble cut than at 7 1/2 ips. Another possibility is that either the record head of your Viking 88 or the playback head of your Viking 807 (or both) is out of azimuth alignment, resulting in treble loss. Checking and correcting azimuth alignment requires an azimuth test tape, a VTVM, and the necessary knowhow: this is usually best left to a competent technician.

(Audio magazine, Feb. 1971; Herman Burstein)

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