Amplifiers

Knobs

Nearly all knobs cut, they don’t add. When you turn a volume knob all the way up, that’s the whole signal. When you turn it down, you are sending a portion of the signal to the ground. Turn down the treble and you are cutting a portion of the eq above a certain threshold.

Gain

Gain can be thought of as the input volume to the preamp stage, although it's more of a tone control than a volume control. Your gain setting determines how hard you're driving the preamp section of your amp. Setting the gain control sets the level of distortion in your tone, regardless of how loud the final volume is set.

gain adjustments can produce changes in overall volume, which might account for some of the confusion between the terms

Think of gain as sensitivity. Guitar pickups, microphones, all things in audio. Gain has the connotation of both tone and volume.

Gain adjusts the sensitivity of an audio transducer. As you go up in gain you go up in the amount of electricity flowing through the transducers and subsequent transformers.

Volume

volume on a tube amp is more than just making it louder, it actually increases how much drive the sound has as well.

Volume and gain are similar, with the difference being at what stage the overall gain of the amp is being set. Volume is intended to set a secondary preamp gain stage.

MasterVolume

Master volume lives in the second stage of your amp, the power amp section. It provides the muscle. Think of it this way: the preamp (and gain control) provides the shape of the sound; the power amp provides the overall strength of the sound.