AUDIOCLINIC (Dec. 1998)

Sequential Turn-On

Q. B there a correct sequence for turning the components in an audio system on and off? What possible harm can occur if this is not performed correctly?

A. Your amp should usually be the last component you turn on and the first you turn off. That way, any noises your other components make when they’re turned on or off will not be amplified and fed to your loudspeakers. These noises are frequently annoying and, in rare instances, can damage speakers. Many power amplifiers also pro duce transient pulses, which come through the speakers as thumps. Although annoying to some, they will not damage the speakers.

In any case, I encounter less and less gear that generates turn-on or turn-off pulses.

Audio Adjectives

Q. What is meant when reviewers use words like “dark,” “light,” “bright,” sweet,” or “sour” to describe a component’s sound?

A. Describing the way a component or speaker sounds is not a science, and thus we find ourselves using a specialized vocabulary to convey our thoughts to a per son who has not heard the product for him self. Hence, to understand terms such as “light” and “dark,” try imagining what the reviewer might be visualizing when he uses those words. (It’s why such reviewing is called subjective.)

Nevertheless, if you polled audio reviewers, I think there would probably be a consensus that terms like light, dark, and bright suggest a deviation from flat, smooth frequency response. For example, if the sound is “light” (as in “lightweight,” perhaps), chances are that it is not rich in bass but has rather smooth highs. By contrast, “dark” sound is likely to be somewhat bassy, with dull or rolled-off treble. “Bright,” on the other hand, usually implies somewhat emphasized upper midrange and high frequencies, almost, but not quite, to the point of harshness. Really exaggerated highs are sometimes labeled “tizzy” or “zippy.”

As for “sweet” or “sour,” well, it’s difficult to tell you for sure what these terms connote. “Sweet” perhaps suggests a very open and smooth overall sound. And “sour”? If I read that, I’d conclude that the sound had a harsh quality.

Each of us hears or interprets sounds in a unique way, despite the fact that we’re all equipped with the same hearing mechanism. Were this not so, we would likely have fewer makes and models of speakers. Even reviewers differ in their opinions of what sounds good or bad.

Adding Anti-Skating Compensation to a Tonearm

Q. I recently bought an old turntable whose arm has no anti-skating compensation. How can I add this feature?

A. If the tonearm’s tendency to skate in ward, toward the record label, is not too great and if your cartridge does not have high compliance, you may not need to add anti-skating compensation. You can determine the amount of drift by placing the tonearm on a blank vinyl disc while the platter is turning. If the tonearm remains at the center of the disc or drifts very slowly inward, it doesn’t require anti-skating force. Making and adding anti-skating compensation isn’t too difficult, but a blank disc is indispensable for testing and setting the correct counterforce. You might find one at a local disc-cutting studio (though there aren’t many of those), or you could use one of those old, flexible, plastic pro motional discs that were bound into magazines years ago. One side is usually unrecorded and will work fine when placed atop a regular disc. Alternatively, careful inspection of record bins at garage sales might turn up an old test record (Shure’s Audio Obstacle Course, for example) with a blank band or tests for calibrating anti-skating force.

To add anti-skating to your tonearm, make a small bracket just high enough to parallel the arm. Attach a piece of piano wire to this bracket, and align it parallel to the arm’s direction of motion. Next, tie a piece of thin monofilament fishing line to the tonearm, just forward of its pivot point. Make certain that the arm’s position cannot change. Tie a small weight—a smallish lead shot or sinker from a tackle shop will do nicely—to the other end of the line. The line passes over the piano wire and the weight will tend to pull the tonearm out ward, thereby compensating for its tendency to drift inward. Adjust the line’s length so that when the arm reaches the innermost grooves at the center of the record, the weight doesn’t touch the piano wire. Similarly, when the arm is at the disc’s outer edge, the weight shouldn’t rest on the turntable base.

If the weight overcompensates, use a lighter weight; if it doesn’t compensate enough, use a heavier one. You also can slide the string toward the arm pivot if the compensation is too great or slide the string away from it if the force is insufficient. I wrapped the line around my tonearm a couple of times and then put a layer of sealing tape around the arm where the line is attached.

Adjust the anti-skating force by moving the tonearm across the surface of the blank disc while the turntable is running. Stop at various diameters and note which way the arm drifts. It is unlikely you will entirely compensate for skating at every point on the disc, but you will find a setting where there is minimal drift over much of the record’s surface.

Running an Audio System Without a Power Line

Q. My cabin is far from power lines. It does, however, have a solar panel that charges a bank of 12-volt batteries that can power a 3-kilowatt inverter that gives me standard 117-volt AC. I also have a 4-kilowatt AC generator.

Should I install a DC sound system run from the 12-volt battery bank? Or an AC sound system powered either b’ the inverter or by the generator? I already own an AC system, but inverters are inefficient and produce spiky, noisy output rather than clean AC sine waves. Although a DC system would be more efficient and not suffer from the inverter’s “hash” I would have to buy one from scratch, and I’m not aware of any 12-volt turn tables.

A. There’s plenty of excellent 12-volt audio equipment made for cars these days, including CD players and powerful amplifiers. And you can use those amps to drive any home speakers you like except self-powered models or electrostatics. You might also be able to find a phono preamplifier with an external power supply (or one constructed as a module for installation in a line-stage preamp) that can run from 12-volt DC.

The problem is the turntable. I don’t know of any 12-volt models, either, so you’ll probably need an AC model with servomotor speed control. That’s necessary because generator speeds tend to vary with the load they’re feeding, and inverters, though more stable, don’t necessarily run at precisely 60Hz.

You may also want a small inverter, such as those used to power laptop computers in cars, to drive the turntable when you’re not running other AC devices. A 3-kilowatt inverter draws a lot of current, even when it’s only driving a low-power device, and generators gobble fuel and make noise.

If you use AC-powered gear, get a surge suppressor to protect your equipment against power spikes that will occur when your inverter and generator start up or wind down or when any other appliances on the same line kick in.

I live in an area that is subject to power outages that can last for days if a good storm hits. I solved the problem by in stalling a 7.5-kilowatt generator that runs on the same propane supply that heats my house. Generators of this size can be made with really good governors that keep speed fluctuations to a minimum despite changing loads. These generators art designed to produce very dean waveforms and make little noise. I prefer generators made by Onan or Generac, although they’re more expensive than the brands you will find in builders’ supply store. I have no fear of using any (tiny music, and audio gear on line).

(Audio magazine, JOSEPH GIOVANELLI, Dec. 1998)

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