Audioclinic (Oct. 1984)

Tuner Volume Control

Q. My FM tuner has an output-level control marked "0" to "10." To me, it is like an extra volume control. What is the correct setting for it?

-John Drouzek, Southbridge, Mass.

A. The correct setting depends on your needs. It can be used to match the listening level from your FM tuner to that provided by your turntable or, if you have a bare-bones system where the tuner directly feeds the input of your power amplifier, you can use it as an ordinary volume control.

Dust on Phonograph Stylus

Q. I have a dust problem. The tip of the stylus accumulates lots of dust. Although I clean it before and after each play, dust gathers between playing sessions. Can I cover the cartridge to prevent this?

-C. K. Chan, Long Island City, N.Y.

A. Your first precaution in terms of preventing dust from being deposited on the stylus tip or anywhere else, is to keep the dust cover in place whenever the turntable is not in use.

At the time of purchase, the cartridge probably was equipped with a stylus protector. If you still have this, use it. It should be a good dust shield for the stylus.

Cleaning Compact Discs

You may wish to pass on to your readers something which I have found to be invaluable for Compact Disc cleanliness, the "Static Master" brush.

Small particles of dust or lint are easily removed without the risk of scratching the surface.

-Gary Lewis, Wichita Falls, Tex.

Sampling Rate

Q. I would like the term "sampling rate" explained. I have heard that one of the negative aspects of digital discs involves the sampling rate.

-Bill Fox, Alexandria, Va.

A. Audio signals are converted to digital form by "sampling"-measuring the signal voltages at frequent intervals. The frequency with which this is done is called the "sampling rate." One widely quoted theory says that the sampling rate must be at least twice the highest frequency to be recorded, or 40 kHz for audio frequencies up to 20 kHz. In practice, a slightly higher rate (44.1 kHz for the Compact Disc, and higher still for studio master recordings) is used, mainly to make it easier to filter out the sampling frequency without filtering any of the audio band.

Some critics feel this sampling rate is too low to accurately reproduce the waveshape of high frequencies. Others feel that any irregularities in the shape of a 20-kHz wave represent frequencies too high to hear, so the loss of these frequencies will not affect the sound. At this point, the debate is still an active one, and neither side has completely proved its case.

Apparent Noisy Volume Control

Q. My question concerns a phenomenon I have observed with some, but not all, solid-state amplifiers. The effect is this: If, when power is first applied to the amplifier, the volume control is moved back and forth between zero and some low setting, a sound, not unlike that of a noisy control, will be heard. This effect disappears after a couple of seconds. One might think that the control was indeed noisy, and that moving it caused a temporary cleaning effect. If, however, the control is not moved till the amp has warmed up for a few seconds, no "noisy control" sound is heard. What is the real cause of this effect?

-Jack Rubeck, Portland, Ore.

A. This "noisy control" phenomenon is quite common and is the result of the coupling capacitor which feeds signal into that control charging up while the control is being adjusted. During the charge-up, d.c. is present across the control. The resistive element of the control is not absolutely smooth. Thus, the contact wiper, as it moves across the element, will encounter slightly erratic changes in resistance. These, in turn, will lead to slight changes in d.c. voltage at the wiper. The wiper will feed these changes into the rest of the circuitry, where they will appear as "static." Because the d.c. disappears once the capacitor has fully charged, no further static is heard.

Compact Disc Requirements

Q. What, specifically, does a Compact Disc player require of the rest of a stereo system in order to produce maximum fidelity? Is the amplifier the main component of concern? What about the cassette deck that will be used to tape these discs? And the loudspeakers?

-Samuel J. Neiditch, Redlands, Cal.

A. I am not thoroughly convinced that a CD player requires anything more by way of a sound system than what you now have. I have used my old, reliable 35-watt-per-channel power amplifier and made all the noise I wanted to when playing these discs.

Most people believe that louder sound levels are required in order to take advantage of the wide dynamic range found on many Compact Discs. I believe that if you are now listening to music at a suitable, comfortable level, it should not be increased. Rather, let the softer passages be heard at a lower volume than one generally is used to hearing. In analog systems, such passages are either artificially boosted during recording or are buried in the noise and hiss.

If you are driving your present amplifier close to its limits in order to obtain suitable listening levels, you may have to consider an amplifier of higher power. Rather than buying a more powerful amplifier, however, it is sometimes better to buy more efficient loudspeakers.

This is especially true if you are already considering new ones. Keep in mind that the loudspeaker system makes the single, largest contribution to the overall sound of your system. It may well be that by changing to more efficient loudspeaker systems, which also sound better to you, you will have made a far more significant contribution than would be the case if you obtained a new power amplifier.

The cassette recorder needed to tape CDs must be good and should be equipped with either Dolby C or dbx noise reduction. Compact Discs, however, will not deteriorate with time and with repeated plays, so you may not have many reasons for taping them.

We'll have portable equipment soon enough so that these discs can be taken anywhere without having to carry the entire sound system along.

Direct Metal Mastering

Q. Some albums on sale here in Germany are manufactured with Teldec's DMM (Direct Metal Mastering) technology. What is this process?

-Jerry Crayton, APO, N.Y.

A. A conventional master disc is made by cutting into a lacquer surface (on an aluminum substrate). This "lacquer master" is then electroplated, and the plated-on metal is removed to make a "metal master." The metal master is a negative mold of the lacquer which can be used, in turn, as a mold from which a small number of records can be pressed directly.

Usually, though, the metal master is replated and that plating stripped off to make a "mother," which is a negative of the metal master (and therefore like the original lacquer). The mother is then plated to make more negative molds, called "stampers," from which the actual records will be pressed.

With care, a master can make several mothers, each of which can make several stampers, from which a great many records can be pressed.

In Direct Metal Mastering, however, the cutter works directly on a metal master disc, which then becomes the mother. By cutting down the number of steps, the sonic accuracy can be improved, and noise kept to a minimum.

Unexpected Cone Excursions

Q. I noticed recently that my speakers' 5-inch cones exhibit strange excursions. Specifically, the cones will bottom out and then return to their rest positions. This cycle takes about 1 S to complete. There is usually just one oscillation cycle per occurrence. These excursions occur in the presence or absence of program material, even with the volume control at minimum.

Further, it occurs even when my 18 dB/octave filter is employed. What is the cause of this phenomenon? How can I trace and remedy it? Is there a danger to my speakers?

-Steve Williamson, Wayne, Mich.

A. Whatever the cause of your problem, it affects the later stages of your equipment, after all of its controls and filters. It may be that the voltage regulation of the equipment is not good and/or that your power-line voltage is unstable. You must monitor your power-line voltage to see if it changes drastically during these strange episodes.

Another possibility is that the power-supply capacitors may be lower in value than they should be. This, in turn, could give rise to amplifier instability.

The amplifier might break into a cycle of low-frequency oscillation when a transient of any kind enters the equipment. Even small changes in power-line voltage (which are to be expected) could cause the problem.

Perhaps you can move the equipment to another circuit in your home, one which is less prone to the problem.

You may have old house wiring. Rewiring to heavier cable, plus segregating the house into a greater number of individual circuits, may be required before the problem can be solved.

The repeated "bottoming" of your speaker cones can eventually produce voice-coil damage. You should take steps to solve the problem as quickly as possible.

Phono Capacitance Too High

Q. My integrated amplifier has phono input capacitance settings for 100, 200 and 300 pF. My turntable's cable capacitance of 200 pF plus my amplifier's lowest capacitance setting (100 pF) add up to 300 pF. This is far higher than the 225 pF required by my cartridge. I guess this makes my system's high-frequency response roll off too fast.

What can I do to solve this problem? Is there any way I can lower the capacitance of the turntable?

-Arquimedes Sayas, Miami, Fla.

A. It is true that your high frequencies may be somewhat affected because there is a bit too much capacitance across your phono cartridge. But the amount of capacitance is not terribly critical. A considerable error in this regard can occur without audible degradation. This is why the input capacitance is switchable in steps of 100 pF. I suggest that you disregard the extra capacitance.

If you wish to trim it, you can shorten the cable which connects the turntable to the phono input of your equipment.

The amount by which the cable can be shortened depends on the amount actually required to make the connections. To know just how much capacitance will result from cutting the cable depends on the capacitance per foot of the cable used. Check the manufacturer for this information or find someone to measure it.

In the event that the cable cannot be shortened, you should be able to locate cable having a lower capacitance per foot and replace the original cable with this alternate.

And, most important, when you say you "guess" this rolls off the high end, are you actually hearing this effect? Or are you just assuming, on theoretical grounds, that it must be so? It would be interesting to know whether trimming cables, as suggested above, had any audible effect or not.

Tonearm Problems

Q. I have a turntable with a straight, low-mass tonearm. I had no problems with this equipment until I took it for a simple adjustment to correct the cueing. The tonearm was not being lifted at the end of the side.

When the turntable was brought home, cueing worked fine. Ever since, however, some grooves will stick on almost any recording. Different technicians suggest that perhaps the tonearm pivot is sticking slightly, restricting horizontal motion. When this was checked, it was not so.

-Dom Gray, Wausau, Neb.

A. Your problem is a bit unusual. I do wonder, however, if this mistracking has to do with the repair of the cueing system. It could be that the lifting device is now so close to the tonearm that, when the stylus is supposed to rest on the disc, some of the weight of the arm is also taken by the cueing lifter. Thus, while tracking force might appear fine, insufficient force would be applied at the stylus tip. This would also manifest itself in higher distortion, especially on loud passages, as well as skipping.

I agree that pivots can also cause this problem. Pivot friction is not always easy to check. About all you can do is to lubricate them and hope for improvement. You should also check the pivots to see if perhaps there is an adjustment which is designed to remove "slop" in the bearings. If this is made too tight, the pivot will bind.

How about the anti-skating system? Can you examine it to see if it is introducing drag?

(adapted from Audio magazine, Oct. 1984; JOSEPH GIOVANELLI)

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