Acoustic Guitar Amplifiers
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Unlike electric guitar amplifiers, acoustic amps are designed to reproduce exactly the sound of the instrument without coloring the tone. Anps which don't change the tone of the instrument are refered to as transparent. It is impossible to produce a comletely transparent amplifier. Different frequencies (notes and overtones) travel through air at different speeds. The process of amplification changes the rate at which these frequencies travel resulting in a sound which differs from the original sound. There are many other problems associated with amplifying acoustic instruments. The bottom line is that acoustic instruments are difficult to amplify well. Typically, the closer an amp comes to reproducung the original sound, the higher the price tag.

Many acoustic amps have different types of equalization and feedback control as well as analog and digital effects. Some even have microphone inputs. There are many good amplifiers. When selecting one, listen to it with your own instrument and, if possible, in different sized room. Listen with the same objectivity as you would when buying a new guitar. Below, is an overview of the controls and features which are common to many acoustic amps.

  
 

 

    

 

Input Level Controls the level of the signal from the guitar to be optimized for the the rest of the amplifier. Generally, it is best to run the input up as much as possible before causing distortion. Amps operate best when given a strong signal. For guitars with extremely high output electronics, this control can be used to reduce the input as well.  
 
Equalization Equalization refers to boosting or cutting frequencies to give the balance from bass to treble desired by the player. There are different methods of equalization (EQ). Some amps employ more than one.  
 
Graphic Graphic EQs are made up of sliders that control various frequencies (bands). In the center position, the slider neither boosts or cuts that frequency (flat).  
 
Parametric Parametric EQ allows the user to select a frequency (note) and boost or cut just that frequency. Additionally, there is a often a control for bandwidth which determines how far into surounding frequencies the boost/cut control effects. Parametric EQs are usefull for pinpointing problem frequencies and making surgical adjustments without effects others. They are often used for feedback control.  
 
Shelving Shelving type EQ is typically incorporated in standard bass, mid and treble contols. The term shelving refers to the predetermined frequencies each control acts on. Everything below the bass shelf is controlled by the bass control. Above that but below the treble shelf is controlled by the midrange knob. Above the treble frequency shelf, the treble control takes over.  
 
Feedback Control Feedback control is essentially a parametric EQ that is only capable of cutting the selected frequency but not boosting it. Pinpointing a feedback frequency and cutting just that frequency often eliminates the problem with minimal impact on the overall tone.  
 
Volume Volume controls the overall loudness (dB) of the amp. It is important that the input level be set so as not to overdrive this section of the amp. When in doubt, err on the high side and reduce the input level. This way, the sound will not be distorted.  
 
Input Plug the guitar in here.  
 
Phone This is a standard 1/4 inch connection. There is some signal loss when using long cables. This type of connection is the most common..  
 
Balanced XLR XLR connectors use three conductors instead of the usual two. This type of connection is often used in big stage situations where extremely long cable lengths are necessary. There is little signal loss with balanced connections.  
 
Reverb Reverb simulates the echo effect produced in large empty rooms or when singing in the shower. Reverb adds richness to an instrument without it sounding overly processed. It's a very usefull effect.  
 
Effects Effects either controls outside effects plugged into a special circuit (called an effects loop) or it controls effects built into the amplifier.The effects control is a level control effecting the level of all the effects in the chain.