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5/04/2010

Guitar amps explained

A guitar amplifier (also called amp) receives the signal from your guitar pickups and turns it into a pleasant, audible sound.

Basically, there are two components in a guitar amplifier: the pre-amp and the power-amp.

The pre-amp is the first place the signal goes through. This is where it is processed by the knob settings. There is always at least one knob: the volume. But the knobs on the pre-amp can be several; the other most common are three: bass, middle and treble. These three knobs put together are also known as the tone stack, and are responsible for shaping 3 frequency bands of the sound to your taste. By other words, they give you control over the volume of the different components that make up your tone, so you can increase/decrease the volume of the notes you play on the lower octaves, the higher octaves and the ones in between. There are also other knobs on some pre-amps, such as distortion.

After the pre-amp, the signal is passed to the power-amp. This is where the speakers are; this is where the sound is ultimately reproduced.

Now, amplifiers are classified in two groups, depending on whether the pre-amp and the power-amp come physically stuck together or apart. If they are all in "one box", they are called combo. If they are two separated boxes, they are called head (pre-amp) and cabinet (power-amp). When the head and the respective cabinet are on top of each other, they are also called stack.

Combos are more portable and usually smaller than their head and cabinet cousins. They also usually attain lower maximum volumes. So, head and cabinet are more prepared for larger venues, such as outdoor concerts in stadiums. Nowadays, with the possibilities of PA systems (Public Address systems), combos can also be used for larger venues, with amplification of their sound using microphones and more powerful standalone cabinets than the one on the combo.

A PA has mainly a mixer (used as a control panel to manage the volume of each sound input, in cases where the PA is shared with other musicians), an amplifier (used to amplify the signal received from the mixer) and loudspeakers (responsible for reproducing the sound at the desired volume).

The power (expressed in watts) an amplifier needs to have depends on two factors: the circumstances it will be used in and wether it is a tube or a solid state amp. Tubes sound louder than solid states with the same wattage; one could say approximately (only a rule of thumb!) that 15 tube watts correspond to 50/60 solid state watts, and 30 tube watts correspond to 100 solid state watts. Now, for bedroom practice/studio recording, 15 tube watts are more than enough. For small/medium venues (on bars, pubs, etc...), 30 tube watts will do the trick. In case you need more power, keep in mind that the maximum sound volume doubles for each tenfold power increase - this means that, for example, an amp with 50 watts will sound "double-louder" than another one with 5 watts. Not ten times louder!!

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