Guitar Amplifier Guide   

Choice of amplifer is very important - not only is it an obvious and necassry accompaniment for the electric guitar, but it will also form an inseperable part of the instruments delivery of sonic tone. Preferred tone is a matter of subjective choice of course and to find it, people will often turn to the their favourite players to see the type of equipment they are using, and endorsing. You may not be able to afford those same luxuries, however, and with a little knowledge, you can understand what other options will meet your requirements equally well.

Output - Wattage:

If you are beginning to play the guitar, then you'll probably want to practice in your home. This would suggest an amplifier that is not going to be too loud, and quite probably not too big. Most players like to have an amplifier suitable to practice with, and often have another suitable for gigs if they happen to be a performer. An amplifier with an output of around 15 watts is often about the starting point when looking for a first practice amp, partly because quality amplifiers lower in output are seldom made. Be aware that even a 15 watt amplifier can be pretty loud when it is turned up. If you are going to need an amplifier to play in a small to medium venues, such as pubs and clubs, then 30 - 50 watts is more likely to be what you will be looking for. A 100 watt amp is intended more for larger stage use, but even then it is reasonable to use a lower wattage amp from which the output is sent to the public address system, combined with stage monitors, so that you are not close to something that can deafen you!

Transistors and valves:

Here is where you really begin to navigate the choices available in terms of tone and its character. The use of either transistors or valve components in a guitar amplifier leads to an appreciable difference in sonic performance. Most experienced guitarsts agree that amps using valves sound better. That is not to say that they are in fact better amplifiers because actually the transistr amps are very efficient and can reporduce the signal input very accurately. Nor does it mean that you would not want to own a transistorised amplifier because they can be very useful, they are very lightweight, therefore more portable, they are more affordable and some manufactrers have done a lot of work to evolve modern designs incorporating tranistors. Some very good amplifiers combine both transisors and valves in a sensible way.

What we tend to look for in an amplifier is something that can provide character in the tones that we seek, and valves, it turns out, are able to do that.

Clean Tones, Dirty Tones.

A clean tone is one in which the vibration of the strings, and the signal wave that is created via the guitars pickup, is faithfully ampified, albeit it coloured by the filtration of tone controls whose pupose is to heighten or diminish the bass, middle and higher frequencies. A dirty tone is one in which the waveform of the strings has been clipped. So instead of an uninterupted sine wave, as with a clean tone, the top and bottom tips of the wave have been chopped flat. Because this effect is clearly different from how the strings are vibrating, the sound is compartively distorted. The degree of distortion becomes a feature of tonal character and selection, though it is actually an unfaithul reproduction. If it sounds good though, it is good.

The feature is known as 'drive' because of the way in which the signal in the first stage of the amplifier is set to be offered up to a second stage of amplication but at a level that is is already overly amplified for the second stage to be able receive it without chopping the signal. The amp is said to be overloaded. This is what a 'Gain' control built into an amplifier will seek to do. Recently some amplifiers have been designed using light emitting diodes in their circuitry to determine and produce the level of gain. The brighter the intensity of the bulb, the greater the curent entering the following circuit. Some new versions of 'reissued' amplifiers, in moving onwards from the original vintage version, incorprorate this.

Not all, but many amplifiers will offer both a clean channel and another called a drive channel that can be selected via a footswitch and/or a switch on the amp itslef.

Reverb

Soundwaves reflect off walls and surfaces. So the ambient circumstances in which you are playing will colour the sound you hear, each room - a different sound. If your amplifier has a built in reverb effects unit of one form or another, then you will be able adjust this quality to suit your guitar sound. An amp without reverb will generally need something in the signal path to replicate this effect. An external effect box will do this, but these units, in the case of reverb, are not the cheapest of effects boxes and so can add expense to your amplifer. It is worth considering using, thereoire, an amplifier with a reverb unit built in.

The reverb unit may be fully electronic, or the signal may be used to cause a spring to vibrate that is inside the amplifier cabinet. This is called spring reverb ( not surprisingly), and tends to be fitted to the dearer and traditional models of amplifier. It is a nice sound and detectable from the electronic emulations.

Wet and Dry Tones

These terms are used to describe how the signal can be amplified in such as way that it is either be sent though the amp in the way it was intended once the internal and built-in controls have been set, or, the signal can have a further effect added and blended with it, known as a 'Wet' tone, or effect. A modern ampifier with built in effects may have a control featured that provides for this adjustment, called 'blend' or 'mix'. Among the more traditional and earlier designs of amplifier are some that feature a send and return control. The effect unit is connected between the output of the first amplifier stage, the preamp stage, and returns to the input of the second amplifier stage, the power amp. This method would be refered to as a series effects loop wheras blending the signal's path with an existing signal travelling though the amp is a parallel effects loop.

Open Back, Closed Back

Combo amplifiers are those that combine the amplifer circuity in the same cabinet as the speaker. Alternatively the amp can comprise two seperate units, an amplifier on top of a speaker cabinet below. Combo amps tend to have open backs, though partially closed by a 'baffle' board at the rear which shapes the sound also. The open back design allows sound from the rear of the cabinet to combine with that from the front. So it gives a good all round sound, but the lower bass tones are less pronounced in consequence. A closed back speaker cabinet gives better bass response.