I can vaguely remember a time when nobody wanted to amplify an acoustic guitar, and I don’t want to remember some of the results when they began to try. There is one basic problem ~ the human ear does not want to recognise an acoustic instrument when it is played at electric volumes. There is too much going on in an acoustic guitar, and all the detail gets lost. Any attempt to wind up the volume turns the guitar into a microphone, and the result is feedback.

Today, professional musicians must have absolutely reliable amplification. They take several approaches, each of which involves a compromise for the reasons given above. 

The most common pickup on acoustic guitars has for a long time now been a piezo-electric wire or strip, under the saddle in the slot in the wooden bridge. It senses the string vibrations through the saddle and converts them into electricity, the same principle as the spark in a gas lighter. That output can be taken directly to an amplifier, but the impedance of these pickups is very high, so they do not handle all frequencies equally, and a small pre-amplifier with a battery inside the guitar makes a big difference. They are available with or without onboard control systems and external power sources.. They are not easy to fit properly, and there is a little "edgy" character to the sound, the opposite problem to magnetic pickups.

To avoid feedback (or almost avoid feedback) magnetic pickups attached to the soundhole take their signal source from the string rather than the vibrating soundboard. This is a very neat and successful solution, but it does lose a little of the acoustic property of the guitar, replacing it with a slightly softened, muted character, which a good sound engineer can trim to very good effect. It is a good solution, and new, even better systems based on this principle are becoming available. The pickups are detachable and easy to fit.