A preamp ahead of the microphones can help out your recordings considerably, especially on inexpensive equipment (4-tracks, audio cards, mixers) that may have so-so internal preamps. For instance, on my Tascam Porta 02MKII Portastudio 4-track cassette an inexpensive Midiman Audio Buddy preamp allowed me to turn the level setting down to 'line' (reducing noise), and brought out the capability of the Shure SM-57 and Shure SM-58 microphones, improving overall quality of the recording of the nylon string acoustic (the playing is another matter). Try the comparison below.