The problems with microphones
There are quite a few problems with the microphone:- Bleeding
- The microphone doesn't just pick up the sound of your banjo, it picks up all the sound around it to some degree. This "bleeding" can be a serious problem sometimes.
- Feedback
- Every soundengineer's worst enemy is just an extreme case of bleeding: The microphone picks up the sound from the speaker. The sound is then amplified and sent back out from the speakers, picked up by the microphone and so on in an endless howling noise. You can reduce feedback by careful positioning and equalisation, but the only real solution is to turn the volume down.
- Positioning
- Virtually all stage microphones are directional, that is they pick up more sound from one direction than others. This is a deliberate design feature to reduce bleeding and feedback. So what happens when the microphone is on a fixed stand and you move the banjo? You guessed it. If you use a microphone on a stand you can just forget most of your stage antics.
One common solution is to mount a small, high-quality (and expensive) microphone on the banjo itself, either in front of the head or even inside the instrument. This solves the positioning problem, but tends to reduce the sound quality since the microphone ends up too close to the instrument. I don't mean you should rule out this solution altogether. In many ways it's a kind of a middle-way between a fixed microphone and a transducer, with some of the advantages and disadavtages of both. - Price
- Using a cheap microphone is just silly. It often costs more than a modern transducer and still can't match the sound quality.
The 
Shure Beta 57 A is of the quality level you need. But the list price is twice that of a good banjo transducer, and quality microphones of other brands tend to cost even more. (That's the list price of course. Last time I checked Musician's Friend had them on sale at half price, and then it's a much different matter.)
Condenser vs dynamic
I won't go into technical details here, but there are two different kinds of microphones. Most (but not nearly all) singers seem to prefer dynamic microphones, while condenser microphones with their extra clarity and "openness" are generally regarded to be the best ones for most instruments.The banjo is an exception to this rule though. For some reason it seems dynamic microhones are better at picking up the banjo's characteristic sound than condensers are.
I've already meantioned the Shure Beta 57 A. Shure 57 has been the industry standard for instrument microphones for ages and this improved version of the old workhorse is a very good choice indeed.
But this is if you want to put the microphone on a stand. If you want to mount a microphone on the banjo itself, a condenser microphone will provide a lot of extra "openness" to compensate for the close misc positioning. The AKG C 416 seems to be an excellent choice here. It's got a warmer sound than other condenser "bugs" making it idel for the banjo. Unfortunately it seems AKG has stoipped making it, so I guess you'l have to go hunting for a used one if you want it.
