Audioclinic (Dec. 1979)

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Anti-Skating

Q. As a collector of fine records, who wishes to keep them in excellent condition, I am concerned about reducing wear caused by the cartridge/stylus. Although my tracking force is set for one gram, and I have the anti-skating compensation set per the manufacturer's recommendations, I have read and heard many conflicting articles and stories about anti-skating, Please advise me how anti-skating can be set correctly with no uncertain ties.

-Name withheld.

A. Anti-skating compensation can never be set with certainty. The exact amount of compensation required changes from instant to instant, depending on the modulation level on the disc at that given instant. Turntable speed has some influence, plus friction of the stylus as it travels in the grooves. Groove depth plays some part in the amount of friction. I use a system which is at least reasonable. I set the tracking force as prescribed and then take a recording blank, which has no grooves, and place it on the turntable. I place the tonearm on this disc, with the table turning, and next adjust the anti-skating force so that the arm does not move inward or outward. This will achieve the minimum setting. You may need to strike a compromise with some tonearms by making adjustments so that, at one point, the arm drifts in an outward direction. At other parts of the disc, such an arm may drift in an inward direction.

If you cannot obtain a recording blank, use the blank side of one of those plastic sheet Eva-Tone recordings which are often used as promotional materials. Place a standard blank under the thin, plastic sheet so that the tonearm will be at its proper height.

If you have a good test record and an oscilloscope, you can sometimes fine-tune your adjustment just a bit by adjusting the anti-skating compensation for symmetrical distortion on each channel.

FM Reception Problems

Q. I recently tried to replace my FM antenna with a TV/FM antenna, given to me by a friend. The idea was to gain outdoor reception for my television set. The result was both terrible FM reception and a poor TV picture.

The FM antenna system includes a rotator. My tuner includes a switch which enables the user to hear multi-path distortion. Turning the TV antenna did little for signal strength and nothing at all for the distortion.

I replaced the coaxial cable and 300-ohm matching transformers and double-checked my work. No change. I spent a lot for parts, including a signal splitter and coupler.

Could I have damaged the tuner? I fed the lead-in into a coupler; one output from the coupler fed a band splitter for the TV set, and the other coupler output fed the tuner.

The FM signal is now affected by foot traffic in the room where the tuner is housed, and sometimes I lose the station completely. I had none of these problems before this installation.

Whom should I call, the repairman or an exorcist?

-Bob Breeden; Forestville, Md.

A. The fact that people moving about your listening room makes a difference to FM reception has to mean that the antenna is not feeding into the set.

The only antenna that you have right now is the piece of twin lead be tween the coupler and the tuner. The reason that signals come and go as people move around the room is that they absorb or add to the amount of signal reaching this small piece of cable.

Directly connect the lead-in 300-ohm cable (after the matching transformer) to your tuner-without using the coupler. If reception is still poor, I must suspect that one or both of your matching transformers is no good. If reception does become what you expect it should be, the coupler is probably defective. I say this because both the TV set and the tuner are affected, and the coupler is common to both.

These couplers usually work by virtue of the twin lead's being cut by the holding screws. If you fail to tighten these screws firmly, the cutting arrangement will not penetrate the insulation of the twin lead, and no contact will be made. This, in turn, will result in loss of signal.

There is always the possibility of strands of the coaxial cable shorting out the signal. If the cable was soldered to the transformer terminals, it is possible that excessive heat melted the jacket of the center conductor, causing a short to the shield.

Sound Quality Of "Pictures Discs"

Q. I have noticed that the sound quality of "picture discs" is not as good as the same music released on conventional discs. Why would the sound quality be poor just because it is a picture disc?

-Bob Hoffman; Worth, Ill.

A. The sound quality on a "picture disc" will not change just because there is a picture printed on it. What tends to change, however, is the amount of background noise which the disc will possess. The use of truly virgin vinyl material will yield a transparent record--not black. The black disc is made by adding lamp black to the vinyl mix before the disc is pressed. By being careful not to add too much lamp maintain a reasonably good noise figure during pressing.

The process by which a picture is printed onto a disc, however, adds more impurities. These impurities will produce increased background noise.

The sound quality, per se, will not change. Of course, if the background noise is high enough, some of the subtleties of high-frequency sound will be masked by this noise.

Phono Cartridge Channel Balance

Q. What is meant by "channel balance" in phono cartridges?

-T.P.S. Filho, Rio De Janeiro, Brazil.

A. By "channel balance" in a phono cartridge, we mean that we are discussing the difference in output from one channel of the cartridge to the other. The output voltage with an equal signal should be the same for each channel. Where there is a difference in output from one channel to the other, this difference is expressed in dB.

(adapted from Audio magazine, Dec. 1979; Joseph Giovanelli )

Also see: Picking at the Congress (Dec. 1979)

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