Tape Guide (Q and A) (Mar. 1974)

Recording Current

Q. I have two tape recorders with a common problem. Although they are different brands, the circuit problem is common to both. I use the same kind of tape on both machines. I find that when I have the record bias adjusted properly (-1 db from the peak) I have more playback volume than I should have. I think the audio current to the record head is too high. Can this be lowered without any sacrifice of audio quality?

-John C. Frank, Santa Ana, California

A. Unless you are getting noticeable distortion, the recording current to the record head is not too high. If you reduce the amount of audio current to this head while the meter reads 0 VU, you will reduce the signal-to-noise ratio, which of course is undesirable.

In the event that distortion is noticeable at the 0 VU level, you can either reduce the signal to the record head, or else change the calibration of your VU meter, thereby getting a 0 VU indication at a lower and proper recording level. There may be an adjustment in your tape deck which will cause the VU meter to give a lower reading for a given playback signal.

If the VU meter reading in playback is a function of the setting of the playback gain control, you merely have to adjust this control to avoid over-driving the meter.

Indexing Tapes

Q. (1) I find it quite frustrating to attempt to locate selections, usually classical, on tapes indexed for one machine and played on another, since invariably the indexing for the two machines (of different makes) is not the same. I wonder if it might not be more practical to place some sort of indexing marks on the back of the tape which would aid in visual location of a selection while fast winding the tape. The question is what substance would be durable, non-damaging, etc. (2) Is it true that bulk erasing a new or reused tape prior to recording will result in a higher signal-to-noise ratio? My question is prompted by a desire to determine if it is worth investing in a bulk eraser.

-C. J. Hill, San Francisco, California

A. (1) I would strongly advise against pasting any substance onto the tape for the purpose of indexing, for this may cause the tape to stick in going through the system of guides, rollers, etc. More appropriate would be to inter-splice your tape with leader-tape, which is available in various colors if you wish.

(2) Bulk erasers can do a more effective job than the erase head of a tape machine. If a tape has been heavily over-recorded, the erase head may not be able to remove all the signal, and a bulk eraser is then recommended. It is claimed that a bulk eraser can lower the noise level of a virgin tape. However, this advantage is usually lost when the tape goes past the erase head, according to one correspondent, who claims that the erase head imposes some noise on the tape.

This correspondent states that he has therefore deactivated the erase head of his machine (check the bias going through the record head if you deactivate the erase head).

Speed Change With Age

Q. I have had the following experience with medium-priced Roberts tape recorders (770, 1630, 770X, etc.): increasing wow and flutter as the machine is used, starting noticeably after about 150 hours of use and getting awful after about 600 hours of use. Does anyone know the cure for this?

-Robert Colvin, Hayward, Calif.

A. Possibly the wow and flutter of which you complain may be due to accumulations of dirt, grease, etc. on the capstan. A thorough cleaning of the capstan and other parts contacted by the tape may help.

TreblePeak

Q. I have an Ampex 1455A. Everything about it is excellent except the 7 1/2 ips frequency response. Using Scotch 203 tape, setting the bias at one point gives a flat record-playback response at 33/4 ips to 10 kHz, down 2 db at 12 kHz. However, at 7 1/2 ips there is a peak from 3 kHz to 10 kHz of more than 5 dB. Setting the bias at 7 1/2 ips will not lower this peak below 3 dB at 8 kHz without totally wiping out anything above 12 kHz. In short, the 3 3/4 ips record-playback response is smoother than that at 7 1/2 ips.

The record equalization appears to be the same at both speeds, while one resistance is changed during playback. Is there any modification I can make to the equalization to correct the 7 1/2 ips response?

-W. Craig Chambers, Rantoul. Illinois

A. Use of low-noise tape requires both an increase in bias and a decrease in high-frequency record equalization. The additional bias is about 15%. The cut in treble is about 3 dB at 15,000 Hz. I would guess that you have been increasing bias too much in the attempt to remove the treble peak. As you recognize, a change is also needed in the record equalization. I cannot give you specifics as to what changes to make in your equalization circuit. This is a matter for the manufacturer, and I strongly advise you to consult him.

Demagnetizing Heads

Q. An article 1 read on tape recorder maintenance has raised some doubts in my mind as to whether I've been following the correct procedure in demagnetizing the heads of my recorder. According to the article, it is important to turn on the demagnetizer when it is about two feet or so from the heads, then slowly advance it toward the heads and proceed to demagnetize in the usual manner. Up to now, I've always started with the pole pieces next to the heads, and have heard no audible ill-effects. Assuming the recorder itself is turned off beforehand, is any harm likely to result to the heads or the recorder itself by switching the demagnetizer on when it is in close proximity to the recorder?

-Stephen Sarper, Pittsburgh, Pennsylvania

A. Instructions and procedures usually try to provide a healthy safety margin.

It is safer to turn on the head demagnetizer while it is a good distance away from the heads than when it is close to them. Whether the recorder is off or on does not matter. If you turn on the demagnetizer while it is next to the heads, this may magnetize them to an extent. That they cannot be demagnetized--at least not by a head demagnetizer with a relatively weak field.

Loop Connection Recording

Q. My question concerns a kind of "loop" connection of my two TEAC A4010S tape decks. I have occasionally made two tape copies of old discs at the same time, by connecting the tape output from the preamp to the first tape deck, the output of the first tape deck to the line-in on the second tape deck, and the output of the second tape deck back into the input jack on the pre amp. This setup seems to work quite well, but I have noticed on occasion a loss of high frequencies in the product of the second tape deck. I clean and demagnetize my tape heads once 'each week, so I am quite sure this is not the problem. Would there be a possible further loss of fidelity if a third tape deck is used in the same loop?

-Ronald Burnett, APO, San Francisco

A. Have you tried reversing the sequence of the two tape machines in your loop? If the output of formerly your "second" deck (and now your "first" deck) has adequate high frequency response, the fault would not appear to be in this deck. Rather, the fault would appear to be in the cumulative effect of a slight treble loss in each machine.

High quality tape machines, in order to obtain an optimum combination of low noise, low distortion, and good treble response, typically are down 2 to 4 db at 15,000 Hz at 7 1/2 ips. This is consistent with industry standards.

While such a drop tends to be inaudible if one goes through only one step of recording and playback, it becomes audible when one goes through two steps, as you do in your loop. Introducing a third machine into the loop would increase the problem.

Bias Requirements

Q. (1) I have many tapes recorded at 3 3/4 ips, and occasionally have to dub parts of one reel onto another, connecting the line out directly to the line in jacks of the tape recorders. This works OK, but of course it works twice as fast if the speed of both recorders is set at 7 1/2 ips. My question is, if I use the 7 1/2 ips speed, at which speed should I set the bias on the recorders? (2) When using a good brand of low-noise tape, what is about the average range of recording in dB from distortion on the top end to noise on the bottom end? Some program material ranges from sounds so low Mat the VU meters won't register to crescendos that peg the meters. (3) If one's machine is biased for low-noise tape, what is the result of using the so-called standard tape?

-L.N. Norman, Winthrop, Iowa

A. (1) Set the bias at 7 1/2 ips. Keep in mind that if you play and record at double the speed, all frequencies are doubled. This means that the electronics of your tape machines have to handle frequencies to about 30,000 Hz. Also, to avoid the possibility of beat frequencies between the oscillator frequency and the audio frequencies, the oscillator frequency of your recording machine should be about five times the highest audio frequency--about 150,000 Hz. (2) Good tape has a dynamic range of something like 65 dB. (3) Low-noise tape requires more bias than conventional tape. If conventional tape is used on a machine adjusted for low-noise tape, a falloff in treble response may be expected. This is made worse by the fact that a machine adjusted for low-noise tape employs less treble boost in recording than one set for regular tape.

Mono and Stereo Playback

Q. I am contemplating the purchase of two cassette recorders, specifically the Sony Model TC-100A and the Crown Model CSC 9350 M. The former is monaural, and the latter is a stereo recorder. The Sony recorder is to be used for voice type letter recordings made on the Crown recorder, and vice versa. I am told that because of the two different type heads (one stereo and the other mono), that playback may not be possible. It is this point that I am unfamiliar with and would appreciate your comments on.

-Jose F. Reyes, APO San Francisco

A. If the Sony (mono) machine has quarter-track heads (permitting four tracks to be recorded), then you should be able to interchange recordings made on the Sony and Crown machines.

That is, a recording on either can be successfully played back on the other.

If the Sony has half-track heads, then there is a problem of compatibility.

A recording made on the Sony can be played back on the Crown (although with some loss of signal-to-noise ratio; because the quarter-track head of the Crown does not cover all the track recorded by the Sony). However, a recording made on the Crown cannot be played back on the Sony, unless you avoid recording on tracks 2 and 3 (the middle tracks). The reason is that the half-track head of the Sony will span more than one of the quarter-tracks of the Crown.

(Audio magazine, Mar. 1974; Herman Burstein)

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