A device for mounting a sensor on a musical instrument comprises at least a first sensor held by a first arm so that a user can place the first sensor at a desired first distance measured normal to the first string and can place the first sensor at a desired first position anywhere in a first range along the first string, the first range being at least seventy percent of a least distance between termination of a fingerboard and a bridge, where the user can change the first distance during normal playing and can also change the first position during normal playing, and where the first sensor stays at the first distance during normal playing unless changed by the user and the first sensor stays at the first position during normal playing unless changed by the user.