| Depends on how you design it, literally. Yes, a preamp typically provides gain boost, but "how much boost" depends on the design. Many, many commercially-built mic pre's have an instrument input on the front panel. Note that your instrument signal is unbalanced, and a mic signal is typically balanced. So in order to run your instrument into a typical mic pre, your signal has to be converted from unbalanced to balanced. Figure that into your design, and design for maybe 30dB boost (somebody check me on that amount), and it will probably work out great. | 
