BN,
A stereo preamplifier provides increased signal stength to the line in of the PA system, which in some instances, will improve the quality of the signal to the point where there is significantly more clarity between the highs, mids and lows. Consequently, you get very crisp, distinct sounds instead of sounds that seem to be layered over each other or all mixed together. Naturally, you must also have a quality PA system as well or the preamp will not do a thing for you.
Cheers,
Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)