Audioclinic (May 1984)

Loudness Control

Q. What, specifically, is a loudness Control?

-William Kay, Yonkers, N.Y.

A. The loudness control is designed to compensate for human hearing deficiencies. As the sound level decreases, the ear loses sensitivity to low frequencies. (This is why listening at low volume produces a subjectively "thin" sound, and is probably part of the reason that we like to listen to our music at high sound levels.) There are occasions when it is impossible to listen at high volume levels.

The loudness control is intended for use at such times. It acts mainly by boosting the low frequencies as the volume control setting is reduced.

Conversely, the bass is restored to normal balance when the volume control is advanced.

The ear also tends to lose some treble sensitivity. The better loudness control circuits take this into account by boosting treble as volume is lowered, and restoring to normal as volume is raised-just as was done for low-frequency loudness compensation.

Thumps and Record Rotation

Q. My turntable has developed a noise that sounds like a heart murmur, with rhythmical, low-frequency bursts which are in step with the rotation of the platter at 33 1/3 rpm. It is not audible at 45 rpm. These bursts are heard through the speakers, especially when listening to quiet passages of music.

Also, the sound becomes more audible as the tonearm moves further and further towards the center of the record. When the arm is placed in its rest, there is no audible sound. The turntable is a direct-drive unit.

-Patrick Carrington, Shreveport, La.

A. What immediately comes to mind is that you may be tracking at too great a force. Under the right conditions--including even slightly warped discs--the warp will push the arm upward.

The underside of the cartridge bogy may strike the disc, thereby causing the sound you hear; it would certainly account for the once-around nature of the sound you have described.

Similar results may be noticed if you play seriously warped discs, even where tracking force has been correctly set.

This does not, in itself, explain the lack of sound when playing 45-rpm discs. The geometry of the arm may be such that it will not come into contact with the disc when only 7-inch discs are played, regardless of rotation speed. If you use 12-inch, 45-rpm discs, however, and if the sound is not heard with their use, I can only think of one possibility. Perhaps the bearings on which your table rotates are "sloppy." At slow rotating speed, the table may move to and fro, causing the table to rise and fall. At higher speeds, the platter may exhibit better flywheel action. It might then run truer, being less dependent on its bearings for guidance.

Vocal Clarity

Q. When I listen to my FM receiver, I notice a vocal clarity that I do not experience when playing records on my turntable. Do I need some kind of signal processor?

-Rod Stankey, Canoga Park, Cal.

A. FM stations often employ a number of signal processors. Chances are that this accounts for the difference in sound quality when listening to discs from your turntable as opposed to listening to discs broadcast on an FM station.

Are you listening to the same discs in each instance? If not, it well could be that the disc played over FM was intrinsically better than that which was playing on your turntable.

Much of the vocal "clarity" or "presence" is achieved by boosting frequencies in the region of 2.5 to 5 kHz by just a few dB. If this is the effect you desire, it can be produced by an equalizer.

Static Build-Up on Records

Q. Is there a way I can eliminate the static charge which builds up during record play? By the time a 12-inch disc has played through, a significant charge has been transferred to it.

When I lift the disc from the turntable, I can feel the charge 1/2 inch away. The cartridge/arm combination is also charged, which I determine by lifting the arm. As I do this, I hear crackling static in the loudspeakers. Both the arm and turntable are grounded.

-Bob Bianconi, Baltimore, Md.

A. The crackling you hear may not have anything to do with your static problem. I have encountered a number of tonearms which depend on their pivots to carry the ground from the arm proper to its mounting base. Lifting and moving the arm will produce intermittent grounding and un-grounding.

This results in sounds similar to what you have described.

To cure this condition, you must either clean the bearings with an appropriate contact cleaner or perhaps run a flexible wire from the arm proper to its base, where it will pick up a solid ground.

This solution may result in the body of the cartridge being better grounded and may help to discharge static before it attains the proportions you have described.

I recall one instance in which the headshell was plastic, as was the cartridge body. Static build-up was a very serious problem indeed. I cured it by wrapping the cartridge in aluminum foil (except, of course, for the front) and grounded the foil to one of the ground terminals.

Broadcast Tape Cartridges

Q. What type of recorders do broadcasters use? I have heard they use machines which record onto a cartridge similar to the 8-track system. I gather that the broadcast version has just three tracks (left, right and one which automatically stops the tape when it has finished playing). What makes this system so spectacular? Also, if it is so great, why isn't it available to the public?

-Jay Sanders, Whittier, Cal.

A. You are correct as to the operation of the recording systems often used by broadcast stations. Cartridges are used, not because they are so spectacular in their sonic qualities, but because of the convenience of using them. They are easily loaded into a player; the stop-cue tone from one player can be arranged to start the next one. This rapidity of control is what is required by many stations; the rule appears to be that silence is never golden.

The equipment needed to produce and to play these cartridges is available to anyone who wishes to purchase it. In order to take advantage of this system, care must be taken when introducing the stop tone. It must not be at the end of the selection or program, but recorded just prior to the start of the selection. This is because the cartridge is an endless loop. If the selection is to start immediately after the start button has been pressed, means must be provided so that the tape stops at the correct place-which is not at the end of the selection, unless the cartridge has been loaded with just enough tape for it. Unless you are prepared to spend a considerable amount of time producing cartridges, you will be better served by other recording systems.

Volume vs. Channel Balance

Q. I have a receiver which is four years old. It has a problem, however.

When the volume control is adjusted between 0 and 2, there is a slight channel imbalance, favoring the left channel. With settings between 2 and 4, channel balance is even--as it should be. With any setting above 4, the unbalanced condition returns.

What could be causing the problem? What is its solution?

-Carl A. McGhee, Bethesda, Md.

A. If the problem you have described was not present when you obtained your receiver, I suspect that the volume control needs to be cleaned or replaced.

If this condition was present when you purchased the receiver, the volume control was defective. The part should be replaced. Hopefully, the new control will track better than the original potentiometer does. By "tracking" I refer to the two sections of the control (one for each channel) exhibiting similar changes in resistance versus shaft rotation.

(adapted from Audio magazine, May 1984; JOSEPH GIOVANELLI)

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