AUDIOCLINIC (Mar. 1990)

Comments on Voltage-Spike Protectors

When discussing surge protectors in the May 1989 issue, you said that the house fuse will blow or the circuit breaker trip if a surge protector goes bad. However, some devices, such as GE's Voltage Spike Protector and their Electronic Protection Center, do not depend on a circuit-interruption device within the house's wiring system.

I had a question about testing the voltage-spike protector to determine whether or not the metal-oxide varistor (MOV) was still good. It was answered by a GE engineer, who said that larger and later devices, such as the Electronic Protection Center, may eventually incorporate an indicator light which would show the condition of the MOV. I decided that one could determine whether an MOV was still functioning by measuring its leakage current and comparing it to the leakage current measured when the unit was still new.

If, in the later measurement, the current decreases, one can assume that the thermal fuse in series with the MOV has blown. In normal service, one would expect a slight increase, or no increase, whenever measurements are made.

-Name withheld

Absolute Phase . . . er, Polarity

Q. I can't tell if I have my system hooked up properly. I have heard a lot about absolute phase. Because of the way my system appears to work, I don't see how I can ever hook it up right. My preamp's manual shows: Phono In through Main Out-inverted Tuner In through Main Out-inverted AUX In through Main Out-inverted Tape In through Main Out-inverted Phono In through Tape Out-noninverting Tuner In through Tape Out-noninverting AUX In through Tape Out-noninverting Maybe I just don't know what absolute phase means.

-Robert Forman; Westbury, N.Y.

A. By reading your letter, I believe you have a pretty good idea of what is meant by absolute phase. If one looks at the signal path through a device-or perhaps a whole audio system-from input to output, that device or system will have correct absolute phase (or, more properly, polarity) if the signal at its output is non-inverted as compared Audio signals are alternating current (a.c.), which means that the signal voltage is alternately positive and negative with respect to ground. If your system reproduces the positive half-waves as negative, and vice versa, it's inverting.

There are those who believe that absolute phase must be maintained between the input and output of a system for best sonic results. While I myself am not convinced of this concept's validity, I can see that your preamp poses no obstacle to this. Note that all signals coming from the main outputs are inverted. If your amplifier also inverts polarity, then the two inversions cancel out. If your amp is noninverting, you need only reverse the connections of both speakers, connecting each speaker's positive terminal to the negative terminal of the amp. (Make sure you only reverse the connections at one end of the speaker cable, or you'll be right back where you started.) Signals fed to your tape outputs are not inverted. As long as your tape deck does not invert polarity, you have no problem, since the tape's output will have the same inverted polarity as all other signals when fed to your amp and speaker system. And the amp and speaker, as we've just seen, can re invert the signal for you.

There are still two problems left. Do the other components in your system invert polarity or not? And how accurate is the polarity in the recordings and broadcasts you listen to? If all your signal sources have the same polarity, inverting or not, you can maintain absolute phase in your system as described above; if not, you'll have to set your system's polarity to be correct for whatever signal source is most important to you.

The polarity of recordings and broadcasts is beyond your control. Many recordings are made with no attention to polarity whatsoever, which means that some are correct, some are inverted, and some have inverted polarity for some instruments and voices but not others. Moreover, you have no way of knowing which FM stations invert polarity and which do not; conceivably, a station might invert some programs and not others, depending on the studio or control room in use.

If you're willing to go to the trouble, speakers (or at your amplifier output, if that's accessible) to see how much difference you hear from this and which signal sources sound best each way. Remember, you'll have to check polarity for each recording you play.

Editor's Note: A further discussion of the audible effects of polarity can be found in The Wood Effect by R. C. Johnsen, which was reviewed here in August of last year. Richard C. Heyser's "Acoustic Rosetta Stone," which was published in Audio in January 1979, details a method by which recordings, and indeed the entire signal chain, can be placed in a non-inverted state.

-E.P.

Damage to CD Players

Q. Is it harmful to leave a Compact Disc player in the pause mode for an extended length of time? Would any mechanical components be damaged? I understand that it is not advisable to leave a tape deck in pause for long periods and would think the same holds true for a CD player. Also, is it harmful to leave a CD in the player when the unit is not in use?

-S. F. Brogden; Placentia, Cal.

A. The CD players I have used shut down both their mechanical and electronic circuits if left in pause mode.

Thus, no damage to the turntable motor or laser should occur. No owner's manual I have seen refers to such problems. Not all players do shut down, however.

A tape deck is something else again.

If the pause is to be effective, the deck's motor must be running continuously when the unit is in pause mode.

Because of this, the pause feature should not be used if the deck is to be left idling for any length of time.

I cannot see any reason to expect a CD to be damaged if it is left in the player-even when the unit is not in use. I have seen players which don't have anything approaching an airtight seal around their disc trays. Thus, dust could settle on the disc, so CDs should be returned to the box immediately after they have been played.

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(Source: Audio magazine, Mar. 1990, JOSEPH GIOVANELLI)

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