Audioclinic (Jul. 1983)

Static Charges

Q. I am plagued by problems with static electricity when playing records. The problems are most frustrating when they occur with high-quality audiophile records. Even when there is no charge on the records, the charge--and problem--is often created in the process of cleaning the discs. My usual procedure involves slowly moving the record from its anti-static sleeve, hand-holding it, and "zapping" it four or five times with a Zerostat gun. I place the record on the turntable, put three drops of D4 fluid on the leading edge of a D4 Discwasher brush, push the turntable platter turn button, clean the record for five or six revolutions, and then dry it for five or six revolutions. This is followed by again "zapping" the record four or five times with the Zerostat while the disc is still on the turntable. When the record is played, I hear several rapid, consecutive "pops" which reoccur throughout the recording. If the record is played again without removing it from the platter or cleaning it, most of the pops disappear. Sometimes new, unplayed records have such a charge built up that they are difficult to remove from the sleeve.

My attempts to neutralize this charge are no better after I try cleaning them. Is there a safe, effective way to neutralize a charge that is present from the beginning or created in the cleaning process? The lack of humidity in the environment is not responsible; it has been rainy and humid in the Washing ton area.

-John M. Francis, Landover Hills, Md.

A. I must say that I have not run into a problem quite like yours. Your area would certainly appear to be sufficiently humid to ease virtually any static problems.

My thoughts run to the phono cartridge itself. Some cartridge installations call for a jumper to be placed between one of the ground terminals on the cartridge and a mounting screw which holds the cartridge in its shell.

Such jumper lugs are often supplied as part of the installation kit for either the shell or for the cartridge. Perhaps you can find one among the leftover hard ware; use it and see if the problem is at least reduced.

Try using only paper sleeves. I have had problems with some sleeves designed for "better record care"; I stopped giving them away with my lacquers years ago.

The Zerostat is a good aid. You know, of course, that neutralizing a charge requires both a squeeze and a release of the trigger while the gun is in proximity of the disc. It is, however, sometimes advantageous to actually place a charge on the disc. At least in the case of lacquer discs, I have found it best to use a positive charge. In other words, gently squeeze the trigger in the proximity of the disc and then release the trigger.

[Tracking the record with a grounded, carbon-fiber brush, such as those on some Shure cartridges or those sold for record cleaning by Hunt E.D.A. and others, might also help. –Ivan Berger.]

Adding Speakers

Q. I would like to add a second set of loudspeakers to my stereo system. I have 6-ohm speakers (90.5 dB SPL, 1 watt/meter efficiency), but I would like to add two 8-ohm speakers.

Is this advisable? If so, what efficiency should the 8-ohm speakers have if I want the same loudness from each set of speakers (when playing both sets at the same time in the same room)? Because of space restrictions, the 8-ohm speakers will have to be mini-monitor types with good highs and good midrange, but not necessarily with good bass response. The listening room is small enough so that the 6-ohm speakers will provide satisfactory bass.

-John C. Deuser, Appleton, Wisc.

A. If the instruction manual which was supplied with your power amplifier indicates that you should not operate your equipment at impedances below 4 ohms, I do not advise you to add another pair of speakers unless they are 16-ohm systems.

The combined impedance of the two pairs of speakers will be less than 4 ohms when using a pair of 8-ohm speakers. Why take chances, even though you might get away with it? What you could do, if you can find the space, is to obtain another, identical pair of speakers and connect a pair of speakers in series for each channel, for a combined impedance of 12 ohms. Because the speakers are of the same make and model, damping will not be compromised. Of course, use heavy-gauge speaker line for all connections. Much depends on the overall cable length, but No. 16 gauge line is generally a good choice.

I think that you will gain little by using four speakers instead of two. The main result gained from using four speakers is somewhat more bass. But you will not get the added bass where the additional speakers are deficient in it.

Noisy, Digitally Recorded Discs

Q. On my new, digitally recorded LP discs, I hear surface noise. I thought that such records were supposed to be noise free! Why aren't they?

-Ralph Wilson, Waynesburg, Pa.

A. The fact that an original master recording was made using digital techniques does not alter the fact that this digitally recorded tape was then transferred to an analog disc, with all of the stages of plating and pressing such discs. No matter how the master was created, the LP disc is the limiting factor unless it is recorded using dbx, CX or some other noise-reduction system, for which the listener would need an appropriate decoder.

Electret Microphones

Q. What is the working principle of the electret microphone?

-Ghislain Gauthier, Chicoutimi, Quebec, Canada

A. In a capacitor (condenser) microphone, the diaphragm forms one plate of a capacitor whose other plate is fixed. The fixed plate is charged by a high-voltage power supply in series with a high resistance (20 megohms or more), while the diaphragm is at ground potential. When the diaphragm is moved by the sound waves impinging on it, the charge which can be stored by the capacitor varies, increasing as the diaphragm moves closer to the charged plate and decreasing as it moves away. This changing charge produces a voltage across the resistor in series with the fixed plate--an audio signal. This signal then feeds an amplifier with a high-impedance input and a lower impedance output.

The electret version is similar in all respects but one: Its capacitor is not charged by a high-voltage power sup ply but carries its own, permanent charge. There are some waxes which, when heated in the presence of an electrostatic field, will assume the charge of that field and will retain it.

As I understand it, such a charged element is part of the diaphragm. As before, diaphragm motions change the charge on the capacitor, and the varying charge can be transformed into a usable audio voltage.

I have read that electret elements have limited lifetimes of perhaps 15 to 20 years because, during that time, their useful charges will diminish to a point where output falls too low to be of use. I can only say, however, that I have had some of these mikes for a long time (in some cases more than 15 years) and have noticed no significant lowering of output voltage.

Mono Mode Switch

Q. What are the purposes of the mono mode switch on an amp?

-Stephen I. Leibowitz, New York, N.Y.

A. The mono mode switch cleans up the sound on some monophonically recorded discs. Distortion caused by pinch effect is reduced, as well as vertical rumble. The switch allows you to listen to weak FM-stereo broadcasts with less background noise, and it can be used for combining program material not really intended as a stereo phonic source (such as sound-with sound recordings, which might, for ex ample, contain a voice on one channel and a guitar on another).

Spike Protection

Q. I am under the impression that voltage spikes can damage electronic equipment (TV, stereo equipment, computers, etc.). Every time I hear the rumble of thunder or the prediction of an electrical storm, I unplug all of my audio and TV equipment (sometimes at 3 or 4 AM!). What's the scoop, Joe? Do voltage spike protectors really work, or am I ready for the booby hatch?

-Don May, East Aurora, N. Y.

A. Some equipment is sensitive to voltage spikes, especially computers and computer-like equipment (including digitally controlled tuners, etc.). For this reason, spike protectors are generally used with such gear as a pre caution. These protectors are plugged between the power line and the equipment to be protected.

Where there are overhead power lines, a lightning stroke can introduce spikes which can cause problems. If the equipment is turned off, however, spikes will not find their way into the equipment unless the lightning scores a direct hit. Because such a hit is not common, I do not believe that you need to get up at some terrible hour just to unplug all of your equipment.

(adapted from Audio magazine, Jul. 1983; JOSEPH GIOVANELLI)

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