AUDIOCLINIC (Sept. 1987)

Removing Transient Clicks

You occasionally write about the causes of transient clicks in audio equipment. I'd like to relate my own experience with the problem.

I lived with annoying clicks for sever al months after purchasing new equipment. Every time the refrigerator cycled or a light switch was thrown, a loud click was heard in my loudspeakers. Elaborate grounding schemes and even the use of an expensive a.c. line-interference filter were to no avail.

Finally I borrowed an oscilloscope and examined various points in the signal path. A very large high-frequency signal corresponding to the clicks was apparent at the outputs of the preamplifier. Further investigation revealed that the preamplifier had nearly a 1-MHz bandwidth! Installation of capacitors across the circuit's feedback resistors to reduce the bandwidth to a more reasonable 40 kHz completely eliminated the clicks...

-G. Ramian; Santa Barbara, Cal.

Weak FM Reception

Q. I live between New York and Philadelphia. Though I have a rooftop FM antenna on a 12-foot mast, my FM reception is poor. Yet my TV antenna, on a shorter mast, brings in excellent video and stereo sound, with virtually no noise!

Is the distance between my home and the desired stations too great for my antenna and tuner? Could my poor FM reception be the result of using 300-ohm lead-in instead of the 75-ohm coaxial cable used with my TV's antenna? The antenna installer elected to use 300-ohm twin-lead ribbon for the FM, explaining that less signal loss would occur because there would be no need for the usual transformers.

Can anything be done to improve my reception?

-Joseph W. McGuire, address withheld

A. As an experiment, connect your TV antenna to your FM tuner (using a matching transformer if the tuner has no provisions for coaxial cable). If your FM antenna system is working properly, there should be little change in reception; if there's a noticeable improvement, your FM system needs attention.

First, make sure the FM antenna's leads are connected to the proper antenna terminals and that there are no strands of wire bridging the terminals together. If you have an ohmmeter, disconnect the leads from the tuner and measure the resistance across them. A low resistance reading or a dead short indication are usually okay, an infinite resistance probably signifies a break in the lead-in, and a high resistance probably indicates a poor connection somewhere.

Next, inspect the FM antenna installation. Check that there are no shorts caused by strands of wire bridging the antenna terminals or by improper antenna assembly. Check all connections for corrosion too.

Examine the twin-lead to be sure it does not run along ducts, gutters, or other metal structures. Remove any staples holding the twin-lead in place, and use the appropriate stand-offs and tacks. Staples can short the conductors together, either by direct contact or capacitively.

If the FM antenna system checks out, and the TV antenna gives no significant improvement, try another tuner. If the second tuner performs properly with your FM antenna, you will know that something is wrong with your present tuner.

The main advantage of 75-ohm over 300-ohm systems is greater immunity to noise pickup from local sources, largely because the 75-ohm cable's coaxial construction shields the center conductor.

Stereo Imaging

Q. What is "imaging"?

-Jerome Swabb, Erie, Pa.

A. Imaging refers to the ability of a stereo sound system (especially its loudspeakers) to convey the sense that music is being performed in a perceptible space (the "sound stage"), and to accurately convey the locations of instruments and other sound sources within that space.

Excess Sibilance

Q. My problem is that of vocal sibilance, sometimes appearing on an en tire record and sometimes in just one or two cuts. I checked my tonearm balance and stylus pressure, made sure that the anti-skating force was set correctly, and finally brought the turn table to my dealer to have all of this re examined. After checking the turntable's performance with a test record, he increased the stylus tracking force from 1 to 1.2 grams and said that all was well. He also told me that the vocals on most discs are typically recorded "hot" to compensate for the inadequacies of less elaborate playback systems. Therefore, the sibilance I am hearing is the result of this recording procedure. My dealer also said that sibilance can result from a bad record pressing. Admittedly, sibilance is not present on every record that I buy, but when it is, this knowledge doesn't make listening a pleasure.

-James O'Malley, Gillette, N.J.

A. I have been in the sound-recording field for many years. In a few in stances I have noticed sibilance as a result of electroplating difficulties, but I believe this is rare.

I do agree that many LPs are recorded with either too much treble or too much signal level, or both. Therefore, the stylus has difficulty tracing the fine undulations of the grooves. This leads to the distortion heard on "s" sounds, usually referred to as sibilance.

Some styli and cartridges have more trouble in this regard than others. It all has to do with tip geometry, tip mass, and stylus assembly compliance.

If you can borrow a friend's cartridge, install it into your tonearm and see if some of your "problem" discs play with less sibilance. If you find an improvement, it may be time for you to switch to a different cartridge. Alternatively, you might add a bit more tracking pressure (still using your present cartridge), to see if some of the problem disappears.

Amp-to-Amp Connection

In the September 1986 "Audioclinic," you neglected to mention to Keith Ling that one possible way of connecting an integrated amplifier to a second power amplifier is via the headphone jack on the integrated amp (with the addition of attenuating resistors, if needed).

-Ralph Gonzalez; Philadelphia, Pa.

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(Source: Audio magazine, Sept. 1987, JOSEPH GIOVANELLI)

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