AUDIOCLINIC (Q and A) (Jan. 1977)

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Because of the ever-increasing volume of mail this writer must handle, it is more important than ever for those who send in questions to enclose a stamped, self-addressed envelope with each letter. This speeds up the replies, as the time taken to fill out envelopes could be spent in answering the questions.

Your cooperation in this matter will insure a quicker response to your letter and will also help others receive quicker answers to theirs. Thank you for your cooperation.

While I'm at it, I wish each and every one of you a happy, healthy and prosperous 1977.

-J.G.

Stylus Wear from Albums and Singles

Q. My record collection consists of both Lp albums and 45-rpm "singles." I am concerned that, by playing the singles frequently, I might be significantly increasing the wear on my stylus. Do 45-rpm records cause more wear than albums? I wonder if you would recommend purchasing another cartridge for use specifically with the singles?

-William H. Malashock, La Mesa, Ca.

A. I have never made any attempt to check the relative life expectancy of a stylus when playing 45s as opposed to playing Lp albums. I suspect that some additional wear might be expected when playing 45s. This wear might be caused by a poorer grade of material used to press the 45s and possibly because of the higher recording signal levels used when making such records. I really cannot see, however, that these would be significant, especially with today's cartridges. A stylus lasts so long 'these days that you can ignore any possible added wear from 45s.

Interference to AM Reception

Often, when listening to AM, an annoying "buzz" is present, especially at the low end of the dial. This is caused by the high current power supplies of associated equipment, and the fast switching of the power supply's silicon diodes. This is not present with all-tube equipment as vacuum tube rectifiers do not "turn on" quickly.

What takes place is that large current loads are demanded from the power line at a rate of 120 times per second.

This causes radiation or reradiation on harmonics of 60 Hz.

The cure is to place a 0.01 to 0.001 µF disc capacitor across each silicon diode. The voltage breakdown rating of such capacitors must be 2.4 times the power supply voltage.

-Michael Stosich, Bolling Brook, Ill.

Phono Preamp Input Capacitance

In your September [1976] Audioclinic column you were wrong in stating that phono preamplifier input capacitance always amounts to only a few pF at most. While many preamplifiers do have a stray input capacitance of under 50 pF, some designers deliberately put a 300 pF cap across the phonograph input terminals to minimize r.f.i. problems. This was especially prevalent in amplifiers and receivers manufactured during the late '60s and early '70s, and may now become even more widespread in view of the proposed law requiring consumer audio gear to be made more immune to r.f. interference. So, depending upon one's choice of amplifier, it may not be necessary to add capacitance in order to provide an optimum load for a Shure cartridge, for example. The only way to know is to ask the manufacturer of your particular amplifier.

Peter W. Mitchell, Technical and Marketing Advisor, Audio-Pulse, Inc.

Bedford, Mass.

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Dept. of Aux Inputs

It seems our Maxwell's Demons got loose again at the typesetters; this time they managed to delete one byline on the profile of the Crown M-600 power amp which appeared in the November issue. Geoffrey Cook, a West Coast engineer, should also have gotten credit for the review.

Our sincere apologies, Geoff.

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If you have a problem or question on audio, write to Mr.

Joseph Giovanelli, at AUDIO, 401 North Broad Street, Philadelphia, Pa. 19108. All letters are answered. Please enclose a stamped, self-addressed envelope.

(Source: Audio magazine, Jan. 1977, JOSEPH GIOVANELLI)

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