Language is a funny thing. It helps us get close to truth—but it rarely brings us all the way.
We say a preamp is “direct coupled from input to output,” and it sounds like a promise—as if we're actually hearing that same input signal only amplified. A straight shot. Nothing in the way.
Except that’s not what’s really happening, as I have been trying to point out these last few days (sorry for the repetition, as I am still getting notes from folks who don't quite get it).
What flows through the preamp isn’t the music. It’s a version that starts out as power in the supply. The signal coming in—say, the brush of a snare or the tail of a piano note—isn’t passed along like a baton. It’s more like a command. A suggestion. The active circuitry—FETs, BJTs, whatever we’re using—responds to that signal by shaping voltage from the power supply into a brand new version of the music.
The truth is, what you’re hearing isn’t the input signal. It’s what the circuit does with power. Every breath of sound is drawn from the reservoir of the supply.
We are listening to a modulated power supply, not the amplified input signal.
