As we have already seen in the initial page of this section, the electric guitar must be amplified so that the sound, the volume and the equalization are what we want. What we will see next is another type of amplification system, that divides the work of the amplifier in two parts: the preamplifier and the power amp. This way we can even use two different brands
(pre of one model, power amp of another), that can also have different constructive philosophies (for example, an English preamplifier with its typical British sound thats specializes in the highs and lows, and an American power amp that
generally offers a more complete sound). The two amps are generally rack, therefore they can belong to complex systems, are programmable and are also easily replaceable (but if you are unhappy with the preamp or the power amp in a compact amplifier, you must replace everything).
The most important part of the construction of the sound comes from the premplifier: it gives the body of the sound. We must therefore remember that if we use effects, equalizers, compressors, etc. and the body of the sound isn't right, then its surely the fault of the preamp.
When purchasing a preamp you first of all need to consider your personal taste, instead of what "someone said": try the power amp with the speakers without adding effects and see if the preamp satisfies your taste.
Of course you should listen to suggestions, but personal taste should always have the last word! Next perform a verification test on the preamplifer, which evaluates the constructive and sound quality of the preamp: adjust the gain control in order to obtain the maximum distorsion that the preamp can offer, then gradually lower the volume of the guitar to its minimum.
At this point the preamp should no longer have any distorsion but instead a sound that is quit clean (useful for arpeggios, for instance) if you play lightly with the right hand, otherwise if you play with more force the sound becomes slightly crunch with good dynamics.
If the preamp doesn't pass this test, it's best not to purchase it seeing that it doesn't have sensibility and dynamics, which are fundamental in obtaining the correct sound. You make the choice!
Rack preamplifers are divided into two categories: Channel preamplifiers and programable midi preamplifiers. Let's look at the differences.
Channel systems
Conceptually these are very similar to those included in the amplifiers. Their job is to enhance the sound, for every channel (usually two, three or at the most four). They can therefore produce clean sounds, crunch, and distortion.
The usable sounds in real time can vary from model to model. Usually they are equiped with output switchs or command pedals that control the distance of the preamp. With respect to the programmable midi preamp,
the main difference is that channel systems are very simple to operate (like using an amplifier), and much less expensive. Many manufacturers offer both normal and programmable models.
You should determine what your requirements for the preamp are: if you only need two or three sounds, obviously the simple non-programmable version is better.
Keep in mind however that a simple system can also be programmable. We will talk more about this later.
Programmable midi preamplifiers.
This kind of preamplifier allows you to program the sounds accoding to the requested use, so that they can be recalled in real time during a performance. The connection system, called Midi, is common to all programmable equipment
that we will analyze in the next section.
A Midi preamp's main use is when you required many different sounds. Some think that because it's programmable it is a lesser quality preamp with respect to a similar non-programmable midi. This may be true to an extent, because of the space that has to be dedicated to manage the loss of qualitative efficiency of the preamp, but in almost all of today's models the sound quality and mechanics are surely of high-level. Therefore, using a Midi preamp,
besides having many different sounds (clean, distorted, crunch in various numbers), you can also have the same repeated sound, but maybe at a higher volume with respect to the original. For example, program 5 has a clean sound that we would also like to use in a solo. Copy it to another program and slightly increase the volume. With the simple press of a button we can change from one sound to another in the middle of a song, therefore passing from a clean rhythmic sound to a clean sound for the solo (at a higher volume).
Both the Midi and programmable preamps perform the same job. They can be built with either transistor or valve
circuits. The controls are similar, but there can be some variations and options, as we will see now: we will speak in general terms because some preamps have these systems, others do not.
Pre-Distortion EQ.
Before reaching the gain stage, the signal can go through a "pre-distorsion" equalizer. Up to this point, the preamp has not begun its work, and therefore you can compare the pre-distorsion equalizer to a tone control on the guitar
or to a pedal equalizer between this and the preamp. The only difference is that the equalizer is found inside the rack box and can be programmed. Therefore with this control, we are dealing with the pure sound of the guitar. Attention:
an incorrect adjustment negatively influences the entire final sound and therefore must be done in small increments. Try to turn off the tone of the guitar: its impossible to get a clear and crystalline sound without the use of a pre-distortion EQ, which must therefore be used as a minimum sound adjuster.
Gain
Now we come to the gain stage, and here you will find the following controls:
In the last few years we have seen the evolution of preamplifer technology. For example, there has been a tendency to simulate the typical vintage sounds (1950-60), thanks also to the return of certain typical sounds from that period. Let's look at some.
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