For a USB solution, direct to your computer, you might try one of the Samson Mics. I have the Go Mic and it does a pretty good job with voices. Don't know how it would do with violin.

If one of these catches your eye, do a google search for that specific mic and try to find user reviews. They can be helpful.
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Jack

"People generally quarrel because they cannot argue." - G. K. Chesterton