Audioclinic (Aug. 1978)

Tracking Force Measurements

Q. When setting up a turntable, does one measure the tracking force with or without the anti -skating force system connected?

-D. Henderson, Palmetto, Fla.

A. In some instances, it makes no difference at all whether the anti -skating force is activated or not. There are some approaches to anti -skating compensation which involve a weight attached by a thread to a portion of the tonearm, and these will have some affect upon the tracking force. So, to be on the safe side, attach the anti -skating system-or activate it if it is permanently attached.

Maximum vs. Rated Power

Q. The instruction manual for my receiver states "Maximum consumption, 650 watts; rated consumption, 435 watts." What is the meaning of these two ratings?

-Sam Notaro, Verona, N.J.

A. The power consumed by your receiver will vary because of the nature of the output stages. When no signal is applied, these stages draw less current than when they are driven, therefore the amount of power consumed varies depending upon whether the equipment is idling or being driven.

Also, the amount of power drawn varies with the instantaneous power required.

Car Radio Noises

Q. I have a problem with my car FM radio. I get static through my speakers, and no matter how 1 try to eliminate it, I have no success. 1 just bought a noise suppressor kit but have not installed it since I still hear the noise when the engine is turned off. I would like to know what you think the problem may be, and how can I correct it?

-Dennis Hennessy, Bradley Beach, N.J.

A. There can be a number of causes for noises in your automobile radio. It may be simply a matter that you are located quite far from most FM stations. This would mean that they are received at too low a signal strength, and this would prevent the limiters in your radio from working to suppress the noise. This is most likely if your receiver is stereophonic. Assuming that your equipment is functioning normally, there is nothing you can do about this kind of noise.

Another cause may be that your car antenna is shorted so that some of the signal is grounding out on the car frame. Perhaps the front end of your radio is misaligned or otherwise defective, leading to reduced signal strength.

It is possible that the noise is actually the result of some defect in the audio portion of your receiver and has nothing to do with the signals being received. A constant background noise, especially when receiving a strong local signal, means that something is definitely wrong with some portion of the equipment, and it should be serviced.

Album/Cartridge Replacement

Q. I would like to know if it is necessary to buy new albums when purchasing a new phonograph cartridge. Does the needle cut its own groove in the album? I've heard so many opinions on the subject that I'm really confused.

-Anthony Lingelbach, Fresno, Calif.

A. There is no need to buy new albums just because you've changed cartridges. A playback stylus in good condition doesn't cut any added grooves or change the existing ones in any way that would cause the old album to play better with a new cartridge than the existing one.

However, there are some extreme cases where a given disc has been played so many times that it will now sound either "broken up" or noisy, and here using a stylus of a different shape will sometimes improve the playback of such discs dramatically.

Slew Rate

Q. What is meant by "slew rate" in a power. amplifier?

-Gil Hampton, Dallas, Tex.

A. After a signal has been applied to the input of a transistor, some time must pass before the output voltage rises to its proper value. The time required for a transistor to arrive at some arbitrary output is generally measured in microseconds and the quicker the response at the output of the amplifier as compared to its input voltage, the more faithful the reproduction will be, or so the argument goes.

If you have a problem or question on audio, write to Mr. Joseph Glovanelli, at AUDIO, 401 North Broad Street, Philadelphia, Pa. 19100. All letters are answered. Please enclose a stamped, self-addressed envelope.

(Source: Audio magazine, Aug. 1978; Joseph Giovanelli)

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