The microphone preamp is possibly one of the most important component in the whole recording chain apart from the microphone itself. Between them, these two units bring the minuscule voltage coming from the diaphragm up to the 1+volts that we work with. From that point on everything is operating at normal levels and the signal can be recorded, EQ’d etc. without problems with noise and distortion. The typical mike preamp can have the following controls.
I said “can have” because not all do. First there is the mike input level knob. This is the gain control for the preamp.
A special note here – Before you start to set the mike input level you must set the console up for unity gain. This involves first setting the console output faders to Zero, then the channel fader to zero. If you are going out a group put that fader to zero. This first step is vitally important because a console is capable of increased noise and distortion if not setup with correct gain structures. If you have a little Mackie or something which doesn’t have a separate control over monitoring turn your amp and speakers down. Basically if you run the output faders low you have to get the gain from somewhere so you turn up the mike preamp which is capable of adding noise and distortion.
If you find that you are fully counterclockwise and still have too much signal you must insert the Pad. The pad drops the level by 10 – 20db (depending in the console) and stops the preamp from overloading. Some consoles will include a phase reversal button which is a very handy option to have. There is also a button for Phantom Power which will supply power to your mikes if required. (See microphones) It often comes as a single on/off switch on the rear of the console. There is often an optional line input knob with an associated mike/line switch. This allows you to trim the level of the line inputs. Finally you will probably find a mike/line button that allows you to adjust the level of the line input individually. The flip button is only on certain consoles. It swaps the two main faders over (line and monitor), More about this option later when we look at monitoring..