AUDIOCLINIC (Jul. 1987)

Direct-to-Disc Signal Level

Q. I have a Boston Pops direct-to disc recording. How does its signal level compare with that found on a standard LP that has been mastered from tape?

-June E. Thomas, Wantagh, N.Y.

A. Just as is true of other LPs, direct-to-disc recordings vary in level, depending on the philosophies of the record producers. The two approaches-tape-to-disc and direct-to-disc have no meaningful effect on groove modulation levels.

Ozone and Electrostatics

Q. Do electrostatic loudspeakers present a possible health hazard? This question occurred to me after reading about a nonaudio product based on the electrostatic principle, namely an air filter/ionizer. These ionizers work by generating millions of negatively charged ions and sending them into the air. Unfortunately, certain brands have been said to release ozone as a byproduct, and ozone can be harmful.

I would like to know, therefore, if electrostatic loudspeakers also release ions (positive or negative) and, more importantly, if contamination of the air is even a remote possibility.

-Nario Brenes, Brooklyn, N.Y.

A. I do not believe that electrostatic loudspeakers release ions, produce ozone, or generate any other dangerous or harmful elements. There are no sharp points on the surface related to the electrostatic fields. Thus, arcing (which would produce ozone) is pre vented. Such arcing would also dam age the loudspeaker diaphragms.

Backup Power Supplies

In the November 1986 "Audioclinic," your answer to Steve Dusik, who had experienced power failures while re cording, was basically correct, but the terminology was not quite right.

You suggested the use of an "uninterruptible power supply (UPS)," but what you described is a standby power supply (SPS). An SPS is designed to come on line a few microseconds after a power failure. With a UPS, the power is, in fact, truly uninterruptible because the components attached to it are al ways powered through the batteries and inverter circuitry. When there is a power failure, no switching takes place because the batteries are already on line. The only condition which has changed is that the batteries are no longer being charged.

As you indicated, the most common use for either the UPS or the SPS is with computers. While an SPS is appropriate for most computers, some cannot tolerate even a few microseconds of interrupted power without losing data in memory and rebooting. In such an instance, a UPS is definitely required. Whether or not a computer or other equipment can tolerate an infinitesimal interruption depends on whether its power supply can continue to supply steady d.c. power to its internal components during the interruption.

For more information on backup power systems, I suggest that your readers look at the September 16, 1986 issue of PC Magazine (Vol. 5, No. 15). It contains an article on backup power systems and test reports on several units of both types.

-John T. Wehlitz, Portland, Ore.

Loudness-Control Action

Q. What is the effect of switching in the loudness control when the volume control is well advanced?

-Name withheld

A. The purpose of a loudness control is to add bass and treble to compensate for deficiencies of the human ear, which make us perceive a lack of bass and of extreme highs when we listen at low volume. A properly de signed loudness control should pro duce no audible effect when switched in and out while volume is set for loud listening levels. If switching it in does have an effect at loud levels, it was not designed properly. To check this circuit's operation, attenuate the level from the program source. Then advance the volume control to the point where the loudness action ceases during high-volume listening. Turning the volume control down from that setting should reveal increasing compensation by the loudness circuit while it is switched in.

Miswired Antenna Input

Q. My receiver is fed by a 300-ohm twin lead transmission line. The antenna is an omnidirectional model, located in the attic of a two-story frame building. I find that I get better reception from some FM stations when I have one of the two 300-ohm leads connected as it is supposed to be and the other lead connected to the AM antenna terminal. Is it possible that the internal leads are not wired to the right parts of the circuit?

-Stan Nesbitt, Annapolis, Md.

A. Of course, a wiring error is al ways possible, and if you received all stations best with the wrong connection, one might have to conclude that such an error were indeed the problem. However, I think you will find, if you move the FM antenna to a different location in the attic, that some of the stations which you now receive with incorrect connections will be received best with normal connections. Maybe other signals will then be received less well. But you may be able to find a location which provides best reception on all stations with correct wiring.

As is always true, if you can use an outdoor antenna mounted well clear of surrounding objects, your overall reception will improve. A directional array, if aimed properly, will bring about a greater improvement, especially regarding weak signals.

Phono Cartridge Life

Q. I purchased a moving-magnet phonograph cartridge in 1980 and have replaced its stylus a number of times. I would like to know if a cartridge has a finite life expectancy. What are some of the symptoms of a cartridge that is "going bad"?

-Cornell Coco, Clifton, N.J.

A. A phonograph cartridge should last indefinitely. When a cartridge does go bad, the problem is usually of a catastrophic nature. In other words, it simply stops functioning.

The most likely causes of failure are either internal wires which come loose from their terminals or coils which open. In this regard, I recall an in stance when the varnish which insulated the wire reacted with the copper, finally eating through it. The coil then opened. In any event, there is no remedy for such failures.

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(Source: Audio magazine, Jul 1987, JOSEPH GIOVANELLI)

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