A pre-amp will produce some noise if nothing is plugged into it (i.e., not terminated) and you turn it up. Best practice is to mute or minimize any inputs that do not have an audio source plugged into them.
A pre-amp will produce some noise if nothing is plugged into it (i.e., not terminated) and you turn it up. Best practice is to mute or minimize any inputs that do not have an audio source plugged into them.