Audioclinic (Mar. 1982)

Paint It Black

Q. I found while studying organic chemistry that polyvinyl chloride ranges from colorless to amber. All of the records I have ever seen are black. Why do record manufacturers add pigments to make the records black? Doesn't this degrade the quality of the record? If so, why do present audiophile records, which are supposed to be of superior quality, continue to use pigments which may have the potential to degrade the quality of the record?

-Filemon K. Tan, Jr., Arlington, Tex.

A. The pigment which was used for many, many years to produce the black coloring in phonograph records is called lamp black or carbon black. Today, however, a black liquid dye is used, so that you really don't have to worry about noise from non-pure PVC since the dye is not finely divided grains as was the carbon black. The reason the record makers issue black records is that the general public seems unable to accept records in any other color, save as a novelty item.

The Hole Story

Q. Please tell me why a standard 12 inch LP record has a small center hole while a 7-inch, 45-rpm record has a large one.

-Richard Savoy, Methuen, Mass.

A. The small center hole in phonograph records has been used from the inception of flat discs. When Columbia produced the first successful micro groove, 33 1/3 rpm disc, this center hole was retained. The difference consisted of a lower turntable speed along with a greater number of grooves per inch--with consequently smaller styli tip radii.

Naturally, the competition immediately went into action. To promote its development, Columbia Records introduced a very inexpensive record changer; it was practically given away. This changer was capable of playing microgroove discs, and micro groove discs only. No attempt was made to incorporate the then-existing 78 rpm record speed.

Not to be outdone, RCA introduced its own inexpensive record changer, again designed as a virtual giveaway to promote its new product: The 45 rpm record.

Thus there existed two completely different standards, not including the 78 rpm disc. One used a small center hole with a turntable rotational speed of 33 1/3-rpm; the other used a large center hole with a turntable rotational speed of 45 rpm. Rather than one of these giants be coming successful to the detriment of the other, both systems coexisted and caused the ultimate demise of the 78 rpm record. Inventive phonograph manufacturers were able to provide machines capable of playing all three varieties of phonograph record. This is essentially where we stand today.

Just You Weight

Q. I get a lot of distortion when playing warped records. This distortion consists of a wavering sound and some times includes a muffled "pop, " almost as if there was a scratch on the record.

Included with my turntable is a 7.5-gram weight to be used on the headshell if the phono cartridge weighs less than 6.0 grams. Because my cartridge weighs 5.5 grams, I added the weight.

When I set the balance weight at 0.5 to 0.8 gram, the tonearm bounces off the warp. Increasing tracking force beyond this point produces the muffled pop and wavering sound.

How can I eliminate this distortion? What does the headshell weight do?

- J.C. Fat, Sacramento, Cal.

A. The headshell weight is intended to balance light phono cartridges. With out it, you might not obtain proper tracking force or the tonearm might not even rest on the record. The problem is that such a weight also adds mass to the sys tem, and this added mass is sufficient to change tracking characteristics of the cartridge and tonearm such that they cannot follow a warped disc. The stylus is bouncing rather than tracking the grooves.

I suggest you remove the weight and try to adjust tracking force and anti-skating. If you are successful in obtaining ad equate tracking force, then try playing some of your warped discs. I think you will probably need to use an independent force gauge to verify the tracking force.

If the problem clears up, fine. If it does not or if you find that you do need to add the weight, I suggest that you add a subsonic filter to your system. This filter will reduce low-frequency response and reduce intermodulation distortion in both the speaker and the amplifier. It should also remove that pop, which may have resulted from the speaker's voice-coil moving beyond its design maximum (which could wreck the speakers in time) or from the action of your amplifier's protection circuits.

In any case, there appears to be a fairly serious mismatch between the characteristics of your tonearm and those of your cartridge. As you've noted, the cartridge alone, at 5.5 grams, is just under the minimum specified by your turntable's maker. But the cartridge and the weight together, at 13 grams, is too much for the cartridge to operate properly. Check with the maker of your turn table to see whether a 3- or a 5-gram weight is available. The combined weight of 8 to 10.5 grams seems to be the area where your cartridge operates best so as to track warped discs.

Separate Tables

Q. I have accumulated three turn tables and have use for each of them.

Can I hook up tables two and three to "Station 2" on my preamplifier by way of a "Y" connector? I would not be using them at the same time because they would be serving separate purposes.

-C.M. Flores, Saginaw, Mich.

A. You would not want to connect both turntables to a single preamplifier input. This arrangement could lead to added hum and loss of flat frequency response. The cable capacitance of one turntable would be added to that of the other; one phono cartridge would feed into the other one while driving the de sired preamplifier input. No harm can result from doing this, however. If the sound is at least satisfactory, all well and good.

A more sophisticated approach re quires connecting turntable 2 to "Station 2" of your preamplifier. Turntable 3 would be connected to a phono-stage preamp, sold by various mail-order houses and also manufactured by some phonograph cartridge makers. The out put of this unit would feed into one of the high-level inputs of your preamplifier.

Switch Before You Feed

Q. Can one set of speakers be hooked up to two power amplifiers by running wires from the speakers to one amplifier and another set of wires directly to another amplifier? By utilizing one amplifier at a time, would any damage be done to either the amplifiers or the speakers?

-Robert G. Delorme, West Warwick, R.I.

A. You cannot use one set of speakers connected to two separate amplifiers as you have proposed. Even if one amplifier is turned off, the amplifier being used will, in addition to feeding the speakers, feed into the other amplifier.

This second amplifier will present impedance to the amplifier being used and damage it. The fact that the speakers will likely not be damaged is academic.

Switching must be provided so that the speakers are connected only to the amplifier actually in use. This switching will eliminate the need to physically connect or disconnect the speakers to or from either of the two amplifiers.

On Cable

Q. I have considered locating my amplifier midway between the speakers, which would result in equal, 9-foot cable runs. I now have a 25-foot cable run on one speaker and 15 feet on the other.

Are there advantages in using equal cable runs?

-C.T. Lewis, Morrisonville, N.Y.

A. No problems will be encountered because of differing lengths of cable from amplifier to speakers.

No Morning Glory

Q. Before I bought my tuner and timer I had a problem with the volume control on my amplifier. Occasionally, when I tried to lower the volume, the sound level remained constant until I turned this control up and down several times.

Since I bought the tuner and timer, I have had a different problem. We use the timer, tuner and amplifier to wake us up at 6:30 a.m. and turn off at 7:30 a.m. After coming on and playing for perhaps 20 minutes, the volume gradually rises to a loud level all by itself, when no one is near the equipment! I wonder if this second problem is caused by the same source as the first one.

-Jeff Culbertson, Overland Park, Kans.

A. Both of these problems are the result of a volume control which, at the very least, is in need of cleaning with appropriate contact cleaner; at most, it will have to be replaced.

A volume control which is either defective or has oxidized contact surfaces will tend to change resistance at the point of contact between the wiper and the resistance element, leading to erratic changes in volume even if you have not touched the control.

If the volume control is not sealed, squirt some contact cleaner into it at the point where the connecting terminals emerge. If the problem still persists or if you cannot force cleaner into the control, replace it.

(Source: Audio magazine, Mar. 1982; Joseph Giovanelli )

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