As Ed recommends, if you're just amplifying the melody end, get yourself a TBone CC75 from Thomann. If you want to amplify the bass end too, get another CC75. Use heavy duty stick-on Velcro to attach the mics (cuts out a load of mechanical noise on a moving instrument, and is easy to use). You can spend hundreds on mics, but bang for buck the CC75 is your best friend (my original has done five years heavy work so far and is still going strong). Beware though: ensure your desk has 48v phantom power available.