The owner's manual for my Dual 1229Q turntable suggests that the vertical tracking force (VTF) applied to the phono cartridge be slightly less than the maximum specified by the cartridge manufacturer. I have noticed recently that many audio specialists suggest the opposite: that optimum VTF can best be achieved by setting the force closer to the minimum requirements of a cartridge. Which of these opinions is correct?
-Joseph R. Sutton, New York, N.Y.
As far as we are concerned, neither is correct.
We would suggest setting the VTF at the center point of the range recommended by the pickup manufacturer and increasing it slightly if optimum tracking is not achieved.
If you have to exceed the maximum VTF, the cartridge is probably in the wrong arm. Generally, any VTF setting is a compromise be tween a reserve of tracking capability (for coping with warps, unusually heavy modulation, and the like) and pressure against the vinyl of the disc that might cause excessive wear. We note that some manufacturers have taken account of this by indicating a preferred VTF with limits, as for example, 1.5 grams, -0.5. + 1 gram.
Recently I came across an old issue of Popular Electronics (March 1973, page 16) stating that researchers at Memorex and other companies had found that the high frequency response of cassettes fell off progressively with each play. Cobalt-doped iron oxide tapes lost 8 dB at 15 kHz and 4 1/2 dB at 10 kHz after 25 plays! Ordinary iron oxide and chromium dioxide tapes lost 1 1/2-2 1/2 dB at 15 kHz after 25 plays. They also indicated that, although the loss with iron oxide and chrome tapes tended to stabilize, the loss with the cobalt-doped tapes continued with each play.
Is this true of today's cassette tapes? Which popular premium cassette tapes are cobalt-doped? Does the same problem affect open-reel tapes?
-Richard Zultner; Williamsburg, Va.
It is still true. The mechanical stresses involved in play (and fast winding) cause progressive erasure of cobalt-doped ferric tapes, open-reel or cassette. These findings do not, however, apply to ferri-cobalt tapes like TDK SA and Maxell UDXL II, in which the cobalt ions are incorporated into the basic magnetic particle. causing the tapes to behave more or less the way standard ferrics and chromes do in this regard. We know of no current premium tapes that use the kind of doping to which you refer.
Recently I purchased a Technics SL-1500 turntable and a Shure V-15 Type III cartridge.
A report on this combination appeared in your March 1976 issue. If the CBS Technology Center aimed to obtain optimum test results, I would like to know the VTF and antiskate knob settings chosen (which didn't appear in the report) and for what reasons.
Since it would be difficult for me to borrow a distortion analyzer, are there any test records that you would recommend to set the VTF and antiskate?
-Joseph P. Campbell; Binghamton, N.Y.
According to the Technics engineers, the variation in antiskating bias for various types of styli is on the order of ± 5%. Accordingly, they have designed their bias mechanism with a single scale that provides a value acceptable for all cartridges. The skating force developed by a cartridge depends, among other things, on the exact composition of the vinyl and the level of modulation; thus it is not constant even for successive sections of the same selection. Using a test record with or without a distortion analyzer will optimize your equipment for the test record and accomplish little else. Since anti-skating bias is a ballpark matter at best, it would seem preferable to accept the settings arrived at by Technics rather than quibbling about the exact geographical center of the ballpark. The March '76 report, incidentally, was on the turntable alone. The Shure pickup was used in testing it, but only with the standard tracking force recommended by Shure and the corresponding antiskating as recommended by Technics.
Because of some misinformation given in a mail-order catalog, I bought four Bose 501 speakers to go with my Sansui QXR-7500A receiver, thinking that their impedance was 8 ohms. I have recently learned that the impedance is 4 ohms. How will this affect my receiver and speakers? Could I hook up two sets of four speakers to the receiver and run both sets at once? Can I run an 8-ohm set and a 4-ohm set from the A and B selectors without causing damage?
-James H. Villazon, FPO, New York, N.Y.
Since the Sansui is rated at 4 ohms minimum impedance, the only parallel connections that are permissible are those in which both of the speakers connected to a single output are 8 ohms or more in impedance. Thus two sets of Bose 501s or a set of Bose 501s and a set of anything else can only be used singly.
Again, the stereo mode is perfectly safe as long as these restrictions are met.
I own a BSR 520 that came with an ADC K7E.
With antiskate properly adjusted, at nearly the end of every record I hear a very distorted high frequency spectrum on the left channel; the right isn't as bad. Should I buy a new stylus (about $10) or a whole new cartridge? Would a Shure M-91ED solve my problem?
Javier Camba, Houston, Tex.
Your antiskating mechanism is not necessarily properly adjusted. Assuming comparable levels of modulation in the two channels. the distortion should be about equal. It is possible that you have set the antiskate too high and are reducing the effective tracking force on the left channel to too low a value. It is possible that your tracking force is too small altogether. There is nothing wrong with tracking a cartridge in the upper part of its force range. As you suggest, your stylus should be checked for wear. We have no way of knowing whether a new cartridge will help.
Does radiation from a color television affect records or prerecorded tapes? If so, how far away should they be stored? Also, since I understand that radiation from a color television is usually emitted backward or down ward and perhaps in front of it, does it help to place the recordings to the sides of the set? I also store records and tapes on a wall in an adjacent room directly behind a color tele vision set.
-Morris Y. Mintz, Paramus, N.J.
While the soft X rays emitted by some color television sets may be a health hazard, they have very little potential for affecting records or tapes. The more serious problem is magnetic fields emanating from the power trans former and other components of the TV chassis. To adequately protect recorded tapes, we suggest that you keep them at least 3 to 4 feet away from the television. Intervening walls are of no help unless they are made of materials like iron or steel.
A salesman recently told me that moving-coil cartridges are much superior to even the best moving-magnet types but that people don't buy them very much because they require a separate pre-preamp. Would you call this a fair statement? If so, are there any receivers or integrated amps with this pre-preamp built in? Will a good integrated amp, say McIntosh or Lux, offer any advantages over a good receiver, say Tandberg or Yamaha? I do not listen to FM very much and would gladly buy an integrated amplifier if such advantages do ex ist; otherwise I would like to have the tuner section of the receiver around for occasional use. Also, a recent brochure from Yamaha mentions the possibility of using its integrated amp in Class A mode in which power output seems to drop to about one-sixth. Is this a desirable feature?
-Anil Trivedi; New York, N.Y.
The statement about moving-coil cartridges is not altogether correct. They have their ad vantages. but they tend to be considerably more expensive than cartridges of other types. Typically, their styli are not replace able except by the factory, and they require pre-preamps in most, but not all, cases. We have found that they are generally low in IM distortion and output impedance, the latter characteristic making them less prone to undesirable preamp interactions than other types. Several companies offer moving-coil phono inputs in various forms.
Assuming comparable prices, the integrated amp is likely to perform better than the receiver, if only because the receiver manufacturer has to provide more at the same cost. We have heard (and seen) the Yamaha amp demonstrated in both Class A and B, and while Class A is excellent in this case, Class B is very nearly as good. Most of the improvement in distortion is at ultra sonic frequencies. This may reduce long term listening fatigue, but we'd probably go for Class B and the extra power.
(High Fidelity, May. 1977)
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