We're all familiar with the terms amplifiers and valves. We use electronic valves like vacuum tubes and transistors to amplify audio signals. Yet, even writing those words makes me a bit nervous because I can see how they might be misunderstood. When we talk of amplifying the input signal it sounds like we are taking a small signal and somehow boosting it. Maybe a good analogy can be found in an airport and its moving sidewalk. You're walking along at your pace and then step onto the moving conveyor belt, boosting your speed. That's amplifying your walking. That's not what's happening in an amplifier. In fact, the input signal never reaches the output. It does its work and then is discarded, never to be seen or heard again. We don't amplify the input signal in the same way a moving sidewalk amplifies our forward motion. Instead, the input signal turns a virtual valve up or down to release more or less voltage and current from the power supply. What gets passed on to our speakers and headphones is not the input signal, but voltage and current straight from the power supply. It's more than semantics. Our input signals are but instigators. Once they do their work they are gone forever.
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