Audioclinic (May 1980)

Use of Record Changers

Q. My friend thinks that using her changer in its automatic mode will result in damage to her records, but I think that the label and outer edge of records are built up to prevent contact with the grooves of other records in the stack.

-Name withheld

A. Because so many consumers were using record changers, the recording industry recognized the need to protect records from surface scratches when one disc fell on the one below.

Therefore, the thickness between the recorded groove surfaces was reduced, leaving the center label area, as well as the outer edge, built up to prevent accidental contact between the upper groove surface of the lower disc and the lower groove surface of the upper disc. These thicker areas helped pro duce strong, rigid discs, but overall this meant that the records were made thinner than formerly. In addition, the air cushioning which takes place when the new records descend helps to eliminate damage. Some of the audiophile disc makers feel, however, that the thinner records are too prone to warp, though this problem has a variety of sources, e.g. too short a cooling cycle during pressing.

Older changers tracked so heavily that stylus and record wear were a problem, but tripping mechanisms have been so much improved that tracking forces of a gram or so are common, rivaling those forces obtain able on manual turntables. This means that record wear from this source will be kept low.

Multiple Speakers With Low-Power Amplifiers

Q. I have a 10-watt amplifier with 4, 8, 16, and 600 ohm output taps. I wish to feed not more than one watt (back ground music) to five to ten speakers in as economical a manner as possible.

How do I connect 10 speakers, each equipped with a line-to-voice-coil matching transformer? How should I connect 10 speakers with 8-ohm impedance not equipped with line transformers?

-Name withheld.

A. The problem of how to connect ten speakers to a single amplifier is not difficult to solve, provided that the leads used to supply power to the speakers are short or are of heavy gauge. In your case, where 10 speakers are to be used, they can be connected in groups of five each. The impedance will be a bit low but not low enough to cause trouble.

Assuming you have 8-ohm speakers, connect four of them in parallel and then connect the next four in parallel. Each group of four speakers has an impedance of two ohms. Connect the two groups in series. You then have a total impedance of four ohms, and this is just about what is needed. The combination of speakers is connected be tween the four-ohm tap of your amplifier and ground.

In the case of loudspeakers equipped with line-to-voice-coil matching transformers, these transformers should take the form of those used for 70-volt line operation. It just so happens that with a 10-watt amplifier, running "flat out," the 600-ohm winding will produce 70 volts.

Each speaker can be adjusted so that one watt will be fed to it merely by connecting it to the appropriate tap on the transformer. For best results, follow instructions which may be sup plied with the transformer so that you will know to use the best combination of primary and/or secondary taps.

Gold-Plated Switch Contacts

Q. Are gold-plated switch contacts more effective than the conventional kind?

-Mike O'Leary; Waiwaialua, Hawaii

A. Gold-plated switch contacts do not oxidize as do contacts made from some other materials and therefore switches which employ gold-plated contacts are very reliable. This reliability is especially important in low-level signal applications in which a minute amount of oxidation can mean high electrical resistance and hence improper operation of their associated circuits. (High-quality electronic key board musical instruments use such contacts.) It is not necessary to use switches of this kind in such applications as 117-V power circuits; oxidation is seldom a problem here.

(Audio magazine, May 1980; Joseph Giovanelli )

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