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.

There is another group of pickups, which are perhaps better described as “sensors”,  piezo ceramic strips or discs which are glued onto the soundboard. These are very simple and can be very successful, but perhaps a challenge to fit properly.

Many serious players now choose a “system” which mixes two pickup sources together. One source is  usually an under saddle piezo, the other source can be any of the  other pickup types, but is often a tiny microphone attached to the soundboard, or the back of the guitar.

Using the piezo to get the message across, and the microphone, or other second source , to add a little "air" to the sound has been the best approach for many. There is always the potential for feedback with a microphone, but with a separate mixer for the two signals, the sound can be tailored for the venue, and there are many systems and refinements that use that combination. It is also very popular for players with a percussive playing style.

Some systems have simple controls mounted on the guitar, and there can be a choice of stereo or mono output, plus a range of control options.   

The better-quality systems are very good, and feedback problems are low.  I do dislike cutting holes in the sides of an expensive handmade instrument, so I prefer to use the simplest of systems, but I am always happy to discuss all these options with a customer.

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