Double edged swords

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Fuses are a double edged sword. They protect most of the equipment in our stereo systems, yet impact the way those systems sound. And the question lingering in the room is, why? I wish I had a ready answer the measurementists would be happy with, but none satisfy the engineer in me either. My ears tell me one thing, my engineering brain another. I can only speculate on the possible causes for changes to sound quality. Let's first understand some particulars about fuses. There are several types of fuse, the two most common are fast and slow. As their names imply, fast and slow fuses take differing amounts of time to blow and serve different purposes. Fast blow fuses are common in speaker and amplifier power supply protection, slow acting fuses are more often found in the incoming AC power line. Fast fuses are made from a tiny whisker of wire, slow acting fuses are made from stouter materials, often resembling a spring. Here's a photo of the two types. slowblow Fast blo These are simple devices. The fastblo on the right is the single whisker of wire, the sloblo on the left a heavier, coiled conductor. The reason one is used over the other may be interesting to you. The sloblo fuse, found in the AC input of most audio equipment, takes its time because we don't want to lose the fuse the moment the product is powered up. When a piece of equipment first receives power from the wall, there is an incoming surge as the power supply capacitors fill up. Once full, the power requirements drop. The fuse has to be stout enough to withstand the inrush current, but weak enough to melt if the long term power runs too high. Fastblo fuses serve a different purpose. Placed in a speaker, their value is their quickness. A tweeter cannot handle too much power for any length of time and there is no initial inrush current. Fastblo fuses protect without compromise. Exceed power limits and the tiny wire melts and breaks the connection, saving the tweeter from damage. Each type of fuse has its own sonic signature and you can begin to guess part of the reason why, simply by looking at their two construction techniques. Pay particular attention to the wire thickness. We'll cover more tomorrow.
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Paul McGowan

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