Burillo wrote:doesn't gain knob essentially act like an input volume knob? i remember someone explaining to me that amp's "gain" is basically a pot that's leaking more or less signal to the ground, so "more gain" is equivalent to hotter input signal.
They are not exactly the same, but if you want to (over)simplify things, then yes, you could say something like that.
Pushing the input level will create more gain, but that doesn't mean that exactly the same is happening.
Most simple example: An amp could be changing it's EQ slightly depending on where the gain is set. For example, if you raise the gain knob, the amp 'automatically' cuts of some bass on the input.
If you raise the input level that EQ change will not happen, because the gain knob is not touched.
It all depends what the amp is exactly doing when you turn the gain knob, how the gain stages are done, etc.. Slamming the input hotter or not can have a _similar_ effect, but that doesn't mean the same is happening.
The input level can be thought of as a perfectly clear pure boost pedal in front of an amp, making the signal you're feeding into the amp louder or not.
So you get the always-not-wanted-but-true answer: 'it depends'. But generally: Similar yes, the same? Probably not.