Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Inc.

Fuses

Here’s a subject that simply drives some people nuts. Fuses.
Change the power fuse in a DAC or preamp and the sound changes, depending on the type of fuse you change to.

I first became aware of fuses and their sonic differences in the 1980s. We were working on releasing the 200C power amplifier, designed by Bob Odell. This 200 watt per channel amplifier was the best sounding power amplifier we had ever produced and we labored long and hard polishing every part and decision to perfection. In those days we relied upon an output fuse to protect the loudspeaker and the amp from each other. Too much current passes through the amp and the fuse blows, disconnecting the power amp’s output.

The prototype amplifiers didn’t have output fuses. It wasn’t until we got to the production versions that we added them, and that’s where the trouble started. The production amplifier didn’t sound as good as the prototype. Thinner, weaker, with less bloom and midbass strength characterized the sound of the production version, relative to the prototype. Why the two sounded so different was a real head scratcher. When faced with such differences, you start removing any differences between the two until they sound the same. It didn’t take long before we discovered the biggest difference was the damn output fuse. Short the output fuse with a clip lead and the fullness of the music returned.

This vexed us greatly because we wanted the sound of no fuse while enjoying the benefits of its protection. Different types of fuses sounded differently too. We gold plated the fuse and its holder to see if that would help. It did. But not a lot. We even tried bypassing it with a small capacitor. That helped to, but wasn’t a good idea. And neither solved the problem.

In the end we came up with a clever scheme. We took the feedback for the amplifier not from the amplifier’s output, but from the output of the fuse. Thus, the fuse was included in the amplifier’s corrective feedback loop, and the fullness returned to the music. (For those of you giving this some thought, we also added a 100Ω resistor in parallel with the fuse so if the fuse blew the amp would remain stable).

With the clarity of hindsight there are many explanations of why this mattered, damping factor changes not the least of them.
The point of the story is simple. Fuses matter. But why should they matter in the AC circuit? I don’t have a great answer handy. But we’ll look some more tomorrow.

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Inc.

Measuring the wrong thing

There’s nothing wrong with using measurements to prove something – as long as you’re measuring the right thing – which is where the subjectivists and the measurementists often get off on the wrong foot.

Take for example, heart attacks. If you suffer cardiac arrest, you’re dead within moments. Right? Stopped heart = stopped life. Turns out that’s not actually true. Scandinavian scientists have discovered packing a person’s head in ice after cardiac arrest buys them time, and lots of it. In fact, they may not even perform CPR on them. We die not directly from the stopped heart, but from brain failure. In other words, when the heart stops the brain fails: one is the cause, the other the result.

When your heart stops pumping, blood to the brain stops flowing, calcium floods in, and your brain cells die. Pack it in ice, calcium does not flow, and you can survive without a heartbeat for quite a long time without damage. It’s why people falling into frozen lakes can sometimes be revived after even a few days. We don’t die from cardiac arrest, we die from the brain not getting blood (because of the heart failure). So measuring a person’s pulse tells us not the whole story, but a clue as to the outcome -which can be changed.

The point of all this is not to carry a bucket of ice if you’re prone to heart attacks. But rather to point out the fallacy of believing a limited set of measurements. Before our recent understanding of brain cell death, we could say with certainty that heart failure = death. Today that same measurement is not accurate. Wrong conclusion based on accurate measurement.

We have many means of measurement: our senses and our machines. Let’s be cautious in our proclamations based on our measurements.