by
LARRY KLEIN, Technical Editor
Proliferation of Power
Q. Recently, I find, my audiophile friends are sneering at my "underpowered" 60-watt-per-channel system. This has given rise to two questions: are they simply playing a one-upmanship game, and why are there suddenly so many high-power amplifiers available anyway?
MARTIN GREENE; New York, N.Y.
A. First question: I'm sure that there are lots of audiophiles out there who aren't happy unless they own the biggest amplifier on the block. But aside from the psychology of the matter, there are valid sonic reasons for high-power amplifiers. We have investigated the question in depth several times over the past few years (What the Music Demands of the Amplifier, December 1966; Super-Power Amplifiers, April 1972; and Loudspeaker Power Needs, September 1973), and all the tests showed that often far more amplifier power is required than is generally appreciated.
As for the second question, there seem to be several interdependent reasons why so many high-power amplifiers are suddenly available from so many different manufacturers. For one, the special high-power output transistors required are now available at reasonable prices. For another, the designers have lately been developing new circuits to use them in. Last, audiophiles have encouraged manufacturers to turn out higher-power units by snapping up each new one as it appears.
Interestingly, although power-output circuits themselves do not trouble the designers, the power-output stage's protective circuits are still a problem-for full protection under all possible circumstances, the amplifier engineer has to design something close to a mini-computer that can tell the difference between normal surges of current and voltage produced by the signal and the abnormal surges produced by some peculiar, potentially damaging circumstance. One manufacturer has estimated that if he were to provide full protection for every conceivable type of improper-load situation, he would have to raise the cost of his amplifier by perhaps 30 percent.
Another manufacturer, when asked why he had not patented his very efficient high-power output circuit, replied that the circuit wasn't really worth patenting since it was unreliable without the ac companying protective circuit--which he had patented.
Cassette Drag
Q. A few of my many cassette tapes get draggy in spots--I guess you could call it wow, except that it doesn't happen regularly and is far worse than anything I have heard on records or open-reel tapes. What is causing the problem? Is there any cure that you know of?
RICHARD BREWSTER; Port Tucker, R.I.
A. Once again we are faced with the question of whether the fault lies with the cassette itself, the machine on (or is it "in"?) which it is being played or both. Since you say that only a few of your many cassettes suffer from speed irregularity, let us assume that the major part of the blame lies with them.
It is unfortunate that you don't say whether the machine you are using is a battery-operated portable or an a.c.-operated deck. Most of the better late model cassette portables have electronic regulators built into their motor circuits that will maintain correct speed even when the battery voltage falls somewhat.
However, when the batteries grow too weak, then the motor torque becomes inadequate, and any greater-than-normal frictional drag inside the cassette will tend to cause wow. In every case, the longer-length cassettes (C90's or 120's) will be more of a problem for a marginal drive mechanism to handle than the shorter lengths will. But, assuming that your battery voltage and the speed-regulation circuit in your machine are okay (and that there are no other mechanical problems in the transport, such as a glazed or oxide-coated rubber idler wheel), the cassette is suspect.
I am assuming, to start, that you are using standard-brand, good-quality cassettes. Aside from the superior quality of the tape they contain, one of the big differences between the cheapies and the established and recognized standard brands is in their mechanical assemblies.
It is obvious that irregularities in the tape path, in the operation of the internal guides, or in the hub area will offer enough resistance to tape flow to cause the wow you mention. Sometimes these problems occur even with good-quality cassettes because the tape has been shuttled back and forth with numerous stops and starts. This tends to cause pile ups and tensions in the tape pack. If you look at the tape pack through the little window during play and it seems to be wobbling back and forth, bumping, or jerking, this may be the problem. It is sometimes helpful to hit the large flat side of the tape cassette several times against a flat surface (but not hard enough to crack the case!) to loosen up the tape layers that may be binding.
Then a run-through at normal playing speed may put things right. Another procedure that has also proved helpful is to add a spot of lubrication to the tape hubs.
A silicone lubricant (available in either spray can or liquid dispenser) would be best. Be very careful to keep the silicone away from the tape itself, because if it gets on the tape and is subsequently transferred to the pressure roller, speed irregularities will almost surely develop because of slippage at the drive capstan.
If you have a spray can, spray a bit of the fluid into a small container, extract a couple of drops with a toothpick and apply them sparingly to both sides of both tape hubs in the area where they touch the shell. Wow-producing friction is frequently caused by an accumulation of several factors, and, to be effective, a trouble-shooting procedure must take them all into account.
Dust-Bug Sound
I recently bought a Dust Bug, and it works fine for cleaning my records--except for one thing. When I turn down the volume of my amplifier and take the tone arm off the record, the dust-collecting brush produces sound from the record groove. Is the company right in saying that it isn't harmful?
GARY WORRELL; Sayville, N.Y.
A. The bristles in the Dust Bug brush are neither hard enough nor applied with enough force to damage the groove walls. What you are hearing is the bristles themselves being set into vibration by the sound modulations in the record groove.
Also see:
TECHNICAL TALK--What Is Noise?
AUDIO NEWS--Views and comment on recent developments.