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Poor design results to raspy radios

18 Apr 2016  | John Dunn

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We were in the market for a new radio one day when I discovered that trying to evaluate this one or that one by listening in the store took a lot of effort. Why? There was a noticeable (to me) effect in some sets that I had not expected to encounter. Some radios had high distortion at high volume which was not really such a surprise, but some radios had high distortion at low volume as well. The result was (to me again) to make speech and music always take on a "raspy" effect. I don't have a better word for it, but I found it to be very objectionable.

I suspect that the raspiness was caused by poorly designed class-B output amplifiers with severe crossover distortion as in the following sketch.

Audio performance as seen on the left would be great, but with a radio at high volume where distortion due to clipping can make the music sound bad, I often found distortion at low volume to be every bit as objectionable as the clipping distortion had been. I attribute this to crossover.

Listening for crossover distortion in the store could be difficult because there almost always seemed to be somebody joyfully blasting out high volume sound from something else somewhere near by but by waiting and biding my time, I was able to pick out the one and only radio amidst the many on display that didn't seem to exhibit the crossover problem.

Several years later, that radio is in my kitchen and I'm glad that I persevered.

About the author
John Dunn contributed this article.

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