Tape Guide (Q and A) (Jun 1974)

Noise Reduction

Q. Is the Dolby Noise Reduction System (or any other) primarily for the improvement of cassettes? Could one expect "meaningful" improvement when the noise reduction system is applied to a top quality open-reel deck? I have the same question regarding Crolyn tape.

Is this being introduced only for the benefit of cassettes, or will the open reel decks be able to use and profit from this tape? How critical are the connecting cable lengths between a cassette deck and the preamplifier? I am toying with an arrangement which would place the deck in a room some 50 or 60 feet from the other components. Is this possible without deteriorating a fine system?

-Samuel Neiditch; Highland, California

A. When using high quality tape decks, the Dolby system will achieve the most "meaningful" improvement in S/N at tape speeds of 3 3/4 ips and lower. Thus cassettes, which operate at 1N ips, have much to gain from the Dolby. If you plan to copy tapes, and possibly re-copy and re-re-copy them, as recording studios do, it may be advantageous to use the Dolby system.

Small increments in noise with each copy eventually build up to a large addition of noise, and then the Dolby can be quite effective even at speeds of 7 1/2 ips or higher. So far as I know, the CrO2 tape is not available in open-reel format.

If the tape deck has a low output impedance, say on the order of less than 1,000 or 2,000 ohms, chances are that you can use 50 or 60 feet of cable with out significant treble loss. Use microphone cable of low capacitance per foot.

Insufficient Gain

Q. Recently I put a Nortronics head into a player to use as a reproducer for duplicating tapes. When I connected this head via shielded cable to the tape head input of a Dyna PAS-3, the gain did not seem sufficient at the normal volume level used for other sources. I then tried a tape preamp and plugged its output into an auxiliary input of the Dyna. Still there was not enough gain. Next I tried matching transformers (3,000 ohms to 50,000 ohms) between the head and tape head input. There was some improvement in gain, but still not enough to be useful. I've run out of ideas. Can you be of any help?

-Richard A. Shroyer, Charlotte, North Carolina

A. One possibility is that you have acquired a defective head. Another possibility is that the head is imperfectly aligned-with respect to azimuth and/or with respect to vertical position. Azimuth misalignment would mostly reduce treble. response. Vertical mis alignment would reduce gain in general.

Still another possibility is that you have mistakenly acquired a head in tended for recording rather than play back; if this were the case, treble response would be poor.

Improving Response

Q. I own a stereo tape recorder, which according to the manufacturer's specifications has a frequency response of 100 to 10,000 Hz. I would like to know if there is any way short of complete overhaul to extend the response, preferably approaching 20 to 20,000 Hz.

-David E. Campbell, Tallahassee, Fla.

A. It would be a substantial task to extend the response to 20-20,000 Hz. And this could be done only at 7 1/2 ips, not at 3 3/4 ips. Making the change would probably involve a new playback head (with a narrower gap than the original head for a good treble response) and modification of the record and playback equalization circuits. The new head would probably entail changes in bias and signal drive circuits for recording, plus a change in calibration of the record-level indicator; and the new head would have to be aligned for azimuth and correct vertical position.

Extending response down to 20 Hz may bring out hum to an unpleasant degree. Substantial hum is often found in less expensive machines, and manufacturers often get around this by limiting bass response.

My guess is that response from 100 to 10,000 is close to optimum for your machine, and that extending response beyond this range may bring up more problems than it will solve.

Low Frequency Crosstalk

Q. I have a used Sony 355 tape deck, and the only problem with it is excessive low frequency crosstalk with the adjacent track. I bought new heads, but the problem is still present, though not as bad as before. I own an Eico PR-100 tape deck, and the Nortronics heads on that unit exhibit no such problem. Would replacing the Sony heads with Nortronics heads cure the problem? Another question. Would checking the play response of a 4-track stereo deck with a full-track alignment tape yield different results from a 4-track stereo alignment tape, assuming both tapes are otherwise the same?

-John J. Cormack, Manlius, New York

A. Your crosstalk problem may be due to vertical mis-positioning of the heads, to excessively long gaps in the Sony heads, or to some characteristic of the head that causes the entire head and not merely the gap to respond to low frequencies. Normally there is a tendency of the entire head to respond to low frequencies, but not to such an extent as to cause a serious crosstalk problem. I can't say for sure that use of Nortronics replacement heads would cure the problem. Your experience suggests they would.

Using a full-track alignment tape instead of a quarter-track one will produce somewhat different results in testing playback response; that is, the full-track tape tends to result in some what more bass.

(Audio magazine, Jun. 1974; Herman Burstein)

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