8/15/2014

Introduction To Jazz Guitar Amplifiers

By Tanisha Berg


Guitar amplifiers usually have several signaling pathways (channels) with different sound characteristics. Clean channels only have a volume adjuster; sometimes it is even combined with a tone setting. Jazz guitar amplifiers channels with more distortion usually has a gain adjuster that affects the strength of distortion degree, coupled with a volume adjuster for the output volume. The channels can be selected by pressing a button on the amplifier. Combos incorporate one or more loudspeakers mounted in a common housing.

Guitar speakers typically have pronounced resonances; the speakers are hung tough and are less attenuated by the high source resistance of tube amplifiers. In contrast, hi-fi speakers convey music signals but do not have their own sound. The resonance behavior of the often open-back wooden housing is another reason for the lower attenuation and the warm sound with pronounced mid-shift. The output stages of tube guitar amplifiers operate mainly in AB mode, that is, it uses one tube to amplify the positive or negative half-wave (push-pull).

It is possible to experience some crossover distortion, which does not occur when the amplifier operates in class A operation. In some variants, the full signal from a single power tube is reinforced. The AB mode is usually employed for larger capacities, while the A-operation requires fewer components.

Nowadays electronics tubes are rarely used due to size, weight, heat generation, long-term stability and complex power supply. The quasi-modular design of modern tube amps (one or two series-connected precursors and a final stage) can create different distortions. The precursors are usually with double triodes, such as ECC81, ECC82 and ECC83.

Overdriving the precursor results in a distorted signal at the input or output stage. Regulating at the output stage leads to a distorted signal with relatively low voltage to the speakers. This is advantageous to the low overall volume, but the sound is not the same compared with that of a distorting amplifier.

The first tube amps from the 1950s could hardly control the precursors, but the distortion was achieved by setting the amp as loud as possible. This means the power tubes were overridden and the transformer went into saturation. This is what influences the sound of guitarists such as Jimi Hendrix and Alvin Lee (Ten Years After). Technically spoken messages are added to the signal in single-ended tube, which increases even-numbered harmonics (overtones) and the signal is increasingly soft (soft clipping).

The auditory impression of distorting tube amp is described as dense, loud, rough and groovy. This sound is important in all areas of rock music and a typical guitar sound is a vital part of music styles of hard rock and heavy metal. This is probably due to the well-configured override behavior and the higher internal resistance.

In some cases, digital signal processors (DSPs) are used to simulate the behavior of tube amplifiers on mathematical models. They are also known as modeling amps. Nowadays, there are numerous guitar amplifiers that use this method of sound production. Because of greater flexibility and range of sounds, this amp is replacing the classic guitar amps. Since 2006, a new generation of guitar amp simulators provides many musicians with advanced acoustic capabilities. Some equipment employ high quality analog-to-digital converters, and processors of high computing power. The dynamics of classic guitar amp is simulated with the help of fractal algorithms.




About the Author:



No comments:

Post a Comment