Audioclinic (Mar. 1978)

Ohms per Volt

Q. I need a way to find out the ohms per volt rating of my voltmeter. The manufacturer is now out of business, so I cannot check there.

-Michael D. Snyder, Pittsburgh, Pa.

A. A simple way to determine the "ohms per volt' of your voltmeter is to set this meter to its lowest d.c. range and with another meter measure its resistance. Should it happen that this lowest range is one volt, you will have your answer directly. However, if the full scale indication is something other than one volt, such as 1.5 volts, then divide the resistance by the 1.5 volts.

This will be the answer in "ohms per volts."

Large Midrange Speakers

Q. Do you approve of a wide-range, 15-in. speaker for use as a midrange (700 to 5,000 Hz) speaker?

-Robert Watson, Dover, Del.

A. In general, I would say that a 15 in. speaker used as a midrange unit would not be acceptable. While it is true that some 15 -in. speakers will produce an output up to 5 kHz, this range beyond a few hundred Hertz tends to be colored. Smaller cones vibrate more easily at higher frequencies, so will work better; also smaller speakers produce less "beaming" of the higher frequencies than a larger one.

Record Changer Repairs

Q. I have a problem with an old record changer. . . the platter spins normally until the record is over, but the unit does not complete the change.

The platter slows down and stops, then, given a little push, it begins to turn again and complete the cycle. In an effort to solve the problem, I took off the platter and cleaned it -- I also cleaned the idler and drive wheel.

When I put it all back together again and turned it on, there was no difference, it acted the same way. What can I do?

-Doug Stadler, Allison Park, Pa.

A. What kind of solvent did you use to clean the parts? Alcohol is probably the best solvent for this purpose as it won't damage the rubber parts as some other solvents will. Clean the motor shaft "steps" as well as the inside rim of the turntable and the rubber drive idler. If this cleaning doesn't improve the operation of the changer, very lightly sandpaper the idler to roughen it up a bit. It is possible that it has become glazed so there is insufficient friction to maintain good drive during the loading that occurs during the change cycle.

There is also a compound called "No Slip" which may be used on rubber wheels to increase friction.

There should be a spring associated with the idler which pulls the idler into the space between the turntable rim and the motor shaft. If this spring is loose or missing, pressure may not be sufficient to bring about adequate drive at the time of increased loading during the change cycle.

Finally, remove all the old grease and oil from the changer portion of the mechanism. Here a more powerful degreasing solvent, rather than alcohol, should be used. Clean the turntable bearing in the same way.

Then, re-lubricate the entire mechanism, making sure not to get any lubricant on either the inner rim of the platter or the rubber drive pucks.

Component Ventilation

Q. Because the room in which my component cabinets are located has relatively poor air circulation, I am concerned with heat buildup, so I have hooked up a.c. cooling fans with adjustable bi-metalic switches. These are connected in parallel with an a.c. relay, which in turn operates the fans. The circuit works fine, however, when the relay closes unacceptable interference in the form of "pops" is produced. To remedy this I have tried to locate a switch that operates on a.c. which will close at a preset temperature in order to eliminate the relay, but with no luck. Is there a circuit that could be designed to eliminate the noise? Can you recommend something neither too complex nor expensive?

-Gary L. Mull, Morton, O.

A. Generally speaking, most rooms don't have much moving air in them and most equipment is designed with that in mind. Given good ventilation at the rear of the cabinet (and sometimes at the bottom), convection will usually take care of air flow problems. Furthermore, where heat can be a real problem, there are slow-speed fans which can be left constantly on during the time when the equipment is operational so there is never any heat build up. These fans operate quietly and will not disturb the listener, and with such fans there is no need for complex switching arrangements.

Any fan can be made to turn more slowly if a light bulb is placed in series with it. The wattage, of the bulb will determine the speed of the fan, the lower the wattage, the slower the fan will turn. Because it only requires a small amount of air to remove the heat from most equipment, a fan slowed down in this manner should prove satisfactory.

Circuitry of the kind you are now using can be made to perform with a minimum of interference to your audio system if a network consisting of a 100-ohm resistor and a 0.2-µF capacitor in series can be placed across the contacts of the bimetal element and across the contacts of the relay.

Record Care

Q. It is important to me that my large LP album collection is kept in the best possible condition. Someone suggested that the frequent removal from and insertion of the disc into the record sleeve is harmful to the disc's surface.

Certainly it would be easier to discard the paper sleeve and simply slip the record into the album jacket only. Ease of handling, however, is not as important to me as proper record care and handling.

-Kent Wingerson, Topeka, Kan.

A. Don't discard the paper sleeves which are included with the disc and album cover. True, there is friction when the discs are either inserted or withdrawn, but more friction would result from the same process with the album covers. Furthermore, the sleeves provide added dust protection when properly inserted at right angles to the opening of the jacket.

Never touch the surface of the record with your fingers as oil from your fingers will be deposited upon the record surface, which, in turn, will attract dust to the surface of the record.

If you have a problem or question on audio, write to Mr. Joseph Giovanelli, at AUDIO, 401 North Broad Street, Philadelphia, Pa, 19108. All letters are answered. Please enclose stamped, envelope.

(Source: Audio magazine, Mar. 1978, Joseph Giovanelli)

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