Sunday, March 04, 2007

How Do Guitar Amplifiers Work?

By: Max Cane

Guitar amplifiers amplify the sound fed into it from the guitar
and drive the guitar loudspeaker. The sound waves generated by
the guitar strings are converted into minute electrical signal
with the help of the guitar pick up and then fed into the guitar
amplifier (or simply guitar amp). Depending on whether or not
the input of the guitar amp can work with the minute signal
coming from the guitar, the guitarist may need to feed the
guitar signal first into a pre-amplifier and then take the
output from the pre-amplifier to feed the guitar amp.

The working of a guitar amp typically has four stages - input,
signal modulation, signal amplification and then finally the
output stage.

Input Stage

The input stage of the guitar amp accepts the input signal
either from the guitar pre-amp or directly from the guitar
itself. Normally, there are input female jacks installed onto
the amplifier where you attach the input signal cable. If the
guitar signal is too weak to be fed into the guitar amp, the
signal should first pass through a guitar pre-amp. It is very
important that there is proper impedance matching between the
available input signal impedance and specified guitar
amplifier's input signal impedance. More often than not, signal
impedance mismatch is the cause of deterioration of the final
guitar sound on the loudspeaker.

Nowadays, there are many guitar amps, which have a
pre-amplification stage incorporated into them. For such amps,
you do not need to pass the guitar signal into a separate
pre-amp. You can directly feed the signal into the amp itself.

Signal Modulation Stage

Plain in and plain out is not exactly the way normal electric
guitarist likes it. He wants the guitar sound to be jazzed up,
twangy, funky, heavily distorted etc. etc. For such sounds, the
input signal has to under go modulation before they can be
amplified. Say suppose the guitarist wants a heavy distortion
akin to heavy metal rock sound. To get this type of sound, the
input signal is fed into the signal modulation stage where the
signal undergoes the required (but controlled) distortion. The
same applies to other sound effects like wah-wah sound, reverb
etc. Many guitar amps have equalizers and other tone control
knobs, which also come under the signal modulation stage.

Signal Amplification Stage

The signal amplification stage is the 'business' stage of any
guitar amp. It is here where the guitar sound is actually
amplified. Good guitar amps will faithfully magnify the signal
coming from the Signal Modulation Stage, i.e. the incoming
signal will be the exact replica of this stage's outgoing
signal, only that it will be of much greater amplitude. It is
the 'business' of any amplifier (be it voice or guitar amp) to
faithfully amplify the incoming signal.

Output Stage

This is the final stage of all guitar amps. Some guitar amps
have the output driver stage as a part of the output stage,
while some of them do not. In some cheap guitar amps, the
outgoing signal from the signal amplification stage is directly
fed into the loudspeaker. However, good guitar amps have proper
signal conditioning output stage where it is ensured that output
signal is properly matched to the input specifications of the

Every good guitarist should have good knowledge about guitar
amps. Getting a good guitar amp is very important if you wish to
have a reliable and predictable output musical sound whilst
playing your guitar.

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