Line in with a mic will always result in a low level recording, unless the mic is very sensitive or the source was very loud. Even with a loud show you can still run into level issues. A good preamp can handle the high signal level coming from the mic, and make it even hotter for the line input.
What this does is maximize your signal to noise ratio ( if the preamp in question has very little self noise) And in cases where the mic output is too hot even for the line input, a good preamp again can be used to attenuate the signal before it reaches the recorder.
The best preseason to use an external preamp is simple, All recorders that use a gain control that is digital * accessed via a single button or via on screen display, uses a digital attenuator. The main problem is that this digital potentiometer is not the first stage of the device's built in preamp. So it can be overloaded even before you ever get a chance to *turn down the signal via on board recorders attenuation.
But the advantage of an external preamp is lost, if it is not as good or better then the signal path in the recording device itself.
Chris Church
I was using line-in--
I think I may be switching over and making my primary unit the H120 though. How does this unit generally perform? Do people find themselves requiring a preamp or does it record at attiquit levels right off the bat?