AUDIOCLINIC (Q and A) (Oct. 1976)

Cartridge Aging

Q. My cartridge is almost two years old; the stylus is now ready to be replaced. Under these circumstances, I am wondering if it is best to replace the whole cartridge rather than just replacing the stylus.

Do cartridges which are two or more years old lose enough sonic quality to warrant replacement?

-Mark Pearl, Lancaster, Pa.

A.There is no reason to think that a cartridge should lose any sonic quality because of age; it should operate perfectly for years. Styli will wear out, bend from being dropped, and otherwise be detective from a number of causes, but the basic cartridge will keep right on going.

Sometimes a coil in the cartridge will open up, with the result that one channel will become completely inoperative. Barring such a failure, however, cartridge performance should remain substantially unchanged over the years.

Power Line Leakage to Chassis

Q. When touching the metal knobs or metal front panel of my receiver, a "buzz" or slight current can be felt by my fingertips. This can be felt even when the power is turned off. What gives?

-Willis C. Lewis, Sacramento, Ca.

A.There is often a bit of leakage between the power line and the chassis of a receiver, tape machine, etc. There is also something less than an infinite Ohmic resistance between you and earth ground. Thus, when you touch a chassis which possesses some leakage potential, this current passes through you to ground. You feel this slight "buzz" or vibration as the fingertips slide over the metal parts of a piece of equipment.

Sometimes this leakage is deliberately introduced in the form of a line bypass capacitor. (The purpose of this capacitor is to minimize transients or radio frequency energy present on the power line from adversely affecting the performance of the equipment, and also to reduce hum possibilities.)

This "feelable" leakage is generally not a problem. The condition can often be completely eliminated by interchanging the two prongs of the wall plug, i.e. reversing the polarity of the plug.

When a receiver or other piece of electrical equipment is grounded as instructed by its maker, the sensation of current leakage will disappear, regardless of the polarity in which the plug is inserted into the wall outlets.

If the leakage is still apparent after grounding, then the ground being used is not a good one or perhaps the interconnecting cable between chassis and ground is defective.

There can be rare instances where a direct short exists between the power line and the chassis, which can be quite dangerous. The sensation you have described will probably be no greater under these conditions than it would be with just a slight leak present. With a direct short between power line and chassis, a dangerous shock hazard exists if you were to simultaneously come into contact with the metal parts of the equipment and a good ground, such as a kitchen sink, radiator or a host of other items around the home. This is now much less likely with more and more devices equipped with grounded outlet line cords. In the case of the tiny, random leakages often found, coming into contact with a ground and the chassis of the equipment won't cause problems.

While power line leakage is not generally a problem, its presence may indicate a more serious condition.

Test for serious leakage conditions with an ohmmeter. Check between each prong of the wall plug of the suspect equipment and the equipment chassis. Have the power switch turned on. The resistance between chassis and the wall plug terminals should high, probably better than one meg.

These direct shorts between chassis and power line can be the result of a shorted line bypass capacitor or a short between the primary winding of the power transformer and its core.

Of course, it can also result from careless production.

Unity Gain From Sound Modifiers

Q. I plan to modify the sound of my acoustical guitar by running the output of an audio pickup through such devices as synthesizers, octave dividers, echo, attack delay, etc. I want such devices to have unity gain so that the volume will remain constant. Is there a device that will monitor/compare the input and output voltages in this system and make them equal?

-Howard R. Peters, Rockford, III.

A.To achieve "unity gain" all that is required is to adjust each sound modifier in turn, as follows:

1. Feed a test oscillator into the input of the device.

2. Keep the signal level low enough to prevent overload.

3. Measure the output of the audio oscillator.

4. Adjust the volume control on the sound modifier so that its output voltage equals the voltage from the generator.

5. Make certain that such frequency-sensitive items, as wah-wahs, are disabled during this adjustment.

Although the system is now set up to have unity gain, there may be times when the sound produced by the system appears to be louder than when no modifiers are involved. This has to do with the tonal and coloration characteristics of such things as "fuzz" boxes, ring modulators, wah-wahs, etc. These devices may cause frequencies in the so-called "presence" range to be louder, and make it appear that the overall volume is higher than when the devices are not in use.

A master gain control just ahead or after the sound modifiers should be the only volume control used to adjust the amount of sound heard from your loudspeakers.

In order to obtain the most efficiency, do not use high fidelity loudspeakers; use musical instrument speakers.

These are more efficient and produce the highly colored sound favored by many performers. Such speakers will not sound good in high-fidelity applications. When uncolored sound reproduction is required, switch to a conventional, high-fidelity unit.

Lubricating a Turntable

Q. What is the best method for lubricating a turntable?

-Richard Roland, Orchard Lake, Mi.

A.Before lubricating a turntable, check the maker's instructions. It is important to use the correct lubricants. I have run across instances where the use of an improper lubricant did physical damage to the turntable.

In general, the well should be oiled with a few drops of a light oil, no heavier than 10-weight, non-detergent oil.

Many turntables employ an intermediate idler to transfer motion from the motor to the turntable. A drop of light oil should be applied to the bearing. Make sure that no oil is deposited onto the idler's drive surface.

Record changers often require grease on sliding parts. The old grease should be removed with an appropriate solvent before new grease is applied.

It is often difficult to lubricate the motor shaft without completely dismantling the motor and soaking its bearings in the proper lubricant.

Some of the soft, porous bearings are designed to hold a certain amount of lubricant. The manufacturer may say these bearings are "life-time" lubricated but may not be literally true. I do this sort of "soaking business" with a light-weight oil for this purpose.

Sometimes the pivots of the tonearm become oxidized, with an audible crackling as the arm moves across a record. A little "spritz" of WD-40 in each pivot does a good job because it both lubricates and cleans them. The arm then becomes a better ground and shields the system against hum.

Checking Capacitance of Phono Cables

Q. I have several sets of phono cables of unknown capacitance. Because CD-4 reproduction requires cables rated at approximately 100 pF, I need to determine the specific capacitance of these cables. I have access to a Heathkit IT-28 direct-reading capacitor checker, but I am not familiar with the correct procedure by which to test the cables. Please advise me.

-Robert L. Gable, Jr., APO San Francisco, CA.

A. The capacitance of a shielded cable is measured between the center conductor and the shield. Therefore, in order for your capacitance checker to be used properly, one of its terminals is connected to the center terminal of the connector of the phono cable to be checked. The other terminal of the capacitor checker is connected to the outer portion, or skirt, of the same connector. If one of the terminals of the capacitance checker is at ground potential, this terminal is the one to be connected to the outer shell of the connector-the shield of the cable.

This will allow you to determine the amount of capacitance within the various interconnecting cables you have. You must, however, add the capacitance within the tonearm. To do this, remove the cartridge from the headshell and connect the terminals of the capacitor checker to the slide lugs. Try to keep the ground terminal of the checker connected to the ground terminals of the tonearm leads.

To determine the total effective capacitance of your phonograph system with any one of the cables you are about to test, you add the capacitance of that cable to that possessed by the tonearm.

Cartridge Output Versus Cost

Q. I just purchased the Empire 999 TE/X cartridge. When I installed it I found that I had to turn the volume control up higher to obtain the same output from my system that I had with a much cheaper magnetic cartridge.

Why is this?

-McDonald A.Layne, Jr., Bronx, N. Y.

A.The less expensive cartridges are designed for use with less expensive equipment which do not always have the sensitivity necessary for use with low output cartridges.

Manufacturing a cartridge which has a lot of output, however, involves moving quite a bit of mass. This, in turn, means more record wear and a degradation at high frequencies and transient response. The better cartridges, such as yours, are made with as small a mass as possible, thus making them more difficult to construct, and their output falls off. Therefore, a better amplifier is needed, one having a good noise figure in order to use one of these better cartridges.

The output from one of these cartridges would be even less if the tolerances in their manufacture were as loose as those in the less expensive models. This factor also adds to the overall cost of the more expensive cartridges.

The value of the parts used to make a magnetic cartridges is not high. The cost is really a matter of the labor involved in working with the small parts so that they will operate correctly over long periods of time. This means that, in addition to the actual process of manufacturing the cartridge, more inspections and testing must be performed to make certain that the unit you buy will perform as the maker intended.

(Audio magazine, Oct. 1976, JOSEPH GIOVANELLI)

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