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A good microphone is always nice, through a dedicated PA system. However, for the budget-minded, the Kremona pickup combined with a good "acoustic" style amplifier with decent EQ control is very effective, and needs no altering of the instrument. I like to run through a Bose Compact, but that is somewhat pricy, although a great value, and needs an outboard processor for EQ, reverb etc.
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I have had very good experiences with the Hughes & Kettner ERA 1 (which was developed under supervision of Michael Eisenmann, Co-Founder of AER...) equipped with DPA 4099 for smaller venues, especially as the DPAs free you of carrying extra mic stands with you. I do agree with Ronjazz that a good microphone with a dedicated PA system is always nice, but as a run and gun situation I really dig my setup.
It does reach its limits if you want to amplify for a bigger venue, but since you could run the the output to another active monitor (or a mixer and hook up multiple monitors) you have a certain level of modularity.