AUDIOCLINIC (Aug. 1989)

Surge Protection and r.f. Filtering

Q. A friend of mine and I were discussing surge protectors for use with my stereo system. He suggested that I buy a surge protector that does not include r.f. protection. From what I can see, the better devices do include r.f. protection. Why wouldn't I want to filter my system against stray radio frequencies? I note with interest that my security alarm company is opposed to the use of r.f. protection. What is going on?

-Michael Coverman, Austin, Tex.

A. Most of the time, I agree that it is good to eliminate stray radio frequencies from your power supplies. They can ultimately find their way into the audio portions of your equipment, where they may be rectified and amplified. However, some devices which are supposed to filter r.f. from the input of your equipment don't do a good job; they are nothing more than r.f. line-bypass capacitors. Good filters must also contain series inductors.

As for your security alarm company not liking r.f. filters, this is understandable. Many alarm systems operate by sending their signals on the power lines because this is a very convenient way to pass information among the various sensors and receivers in their systems. If filters are in the way, the alarm will never sense the signals it is designed to "hear."

Preamplifiers with Different Features

Q. I plan to replace my integrated amplifier with a separate preamp and power amp. What I want to know is, how can two preamplifiers vary so widely in terms of what I thought were basic features? Examples are the Bryston 12B and the Carver 4000t. The Bryston offers just a volume control.

The Carver offers treble and bass controls, along with Sonic Hologram circuitry. My less than great integrated unit has tone controls, so how can the Bryston get away without them and still be considered a good preamp?

-Tim Swarek; Ont., Canada

A. Some equipment manufacturers believe that tone controls and other additions alter the sound in undesired ways. They feel that phase problems in tone controls affect clarity. Hence, they don't build such controls into their equipment. I have received letters from readers who don't even use a preamp, preferring to connect their CD player directly to the inputs of their power amp. Other equipment makers offer tone controls and similar features because they believe that flexibility is important and that these added circuits don't distort the sound in any significant way. The use of tone controls or other processing circuits, therefore, does not serve as criteria to help determine the quality of a given unit.

Amplifiers by the Pound

Q. I have noticed that most power amplifiers in the price class of my equipment are large-at least 7 inches high--and weigh about 75 pounds. My new power amp measures 17 1/8 inches wide and 3 1/4 inches high, and weighs only 25 pounds! Can a power amplifier as small as mine provide the same performance as the "heavyweights" in this same price and power class? What about durability? Will it sound as good? I drive this amp with a receiver, via its "Preamp Out" terminals. The sound is good, but I wonder if I can obtain better sound with a different preamp and tuner.

--John De Rosa, Mattapan, Mass.

A. I see no reason why a power amplifier weighing only 25 pounds can't sound as good as a much heavier unit--if it is designed correctly. I own a "little fellow" that weighs less than 10 pounds. It produces 50 watts per channel and employs a switching-type power supply. It has run well for the few years I have owned it; it measures well and sounds fine, and I have had no problems with component failure.

These days, it is possible to design a very light power supply. One way is to replace the bulky and heavy power transformer with a toroidal transformer. Thus, I have to believe that you will not have problems caused by owning a sophisticated piece of equipment.

I really can't say whether a new preamplifier/tuner will sound better than your present equipment. Much depends on how well your present equipment performs and on your tastes.

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(Source: Audio magazine, Aug. 1989, JOSEPH GIOVANELLI)

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