Actually, most recorders and mixing boards have microphone preamps, you
plug your mike in directly, an outboard preamp is not necessary. The trick
is to find a quiet preamp and mike. The digital recorder I use has a very,
very quiet preamp, so the use of an external one is unimportant. Maki
mixers have quiet preamps, too. Perhaps the single largest issue that the
little digital recorders like the Olympus and Edirol have is that they have
noisy microphone preamps, though the Edirol is significantly quieter than
those found in the various Olympus models.
Noise in these preamps and microphones is measured in decibels, or db. The lowest number is all you get. By this, I mean that if your microphone has a signal to noise ratio of 75 db, but your preamp only has one of 65 db, the 65 is all you get. The same is true in reverse. Even if you are on a budget, getting the lowest noise gear that is within your cost parameters will give you the best sounding podcasts.