GUITAR AMPLIFIERS

A guitar amplifier is an electronic amplifier designed for use with an electric or electronic musical instrument, such as an electric guitar.
Guitar amplifiers are manufactured in two main forms. The "combination" (or combo) amplifier contains the amplifier head and guitar speakers in a single unit. The amplifier head or "amp head" contains the electronic circuitry constituting the preamp, built-in effects processing, and power amplifier. In the other form, the amplifier head is separate from the speakers, and joined to them by cables. The separate' amplifier is called an amplifier head, and is commonly placed on top of one or more loudspeaker enclosures. A separate amplifier head placed atop a guitar speaker enclosure or guitar speaker cabinet forms an amplifier stack or "amp stack".
Some amplifiers used with electric guitars are solid state, because they are easy to repair, lighter, and less expensive. Many guitarists, particularly in the genres of blues and rock, prefer the sound of vacuum tube amplifiers despite their drawbacks such as higher cost, heavier weight, the need to periodically replace tubes and need to re-bias the output tubes (every year or two with moderate use). Some companies design amplifiers that require no biasing as long as properly rated tubes are used. Some modern amplifiers use a mixture of tube and solid-state technologies. Since the advent of microprocessors and digital signal processing, "modeling amps" have been developed in the late 1990s, these can simulate the sounds of a variety of well-known tube amplifiers without always using vacuum tubes. Amplifiers with processors and software emulate the sound of a classic amp well, but from the player's point of view the response of these amplifiers is not quite the same due to the digital element of modeling. In blind auditory tests tube amplifier fans may not be able to tell the difference, but most will always choose to play a tube amp because of its analog sensitivity.
Most low-end guitar amplifiers currently produced are based on semiconductor (solid state) circuits, and some designs incorporate tubes in the preamp stage for their subjectively warmer overdrive sound. Tubes create warm overdrive sounds because instead of cutting the peaked signal off, they more or less pull the peaked audio information back (like natural compression) which creates a fuzzy overdrive sound. While this is a desirable attribute in many cases, the tube's characteristic will "color" all the sounds at any volume, unlike solid state. However, solid state in general have the quickest response time, perhaps even more so than modeling amps. High-end solid state amplifiers are less common, since many professional guitarists tend to favor vacuum tubes. Some jazz guitarists, however, tend to favor the "colder" sound of solid-state amplifiers, preferring not to color the sound of their guitar with the tube distortion and compression so popular with rock, blues, and metal musicians. Solid-state amplifiers vary in output power, functionality, size, price, and sound quality in a wide range, from practice amplifiers to professional models. Some purist or inexpensive amplifiers have only volume and tone controls.
Modeling amplifiers simulate the sound of well-known guitar amps, cabinets, and effects. This is usually achieved through digital processing, although there are analog modeling amps as well, such as the Tech 21 Sansamp (used by many known artists). Modeling technology offers several advantages over traditional amplification. A modeling amp typically is capable of a wide range of tones and effects, and offers cabinet simulation, so it can be recorded without a microphone. However, many guitarists consider modeling amps to be inferior to the amps they model, because the digital simulation fails to capture many nuances of a guitar amp's tone.[citation needed] This is partially due to the fact that speakers in Modeling amplifiers are often different from speakers in real amps and speakers are an important part of any amp's sound. Most modeling amps digitize the input signal and use a DSP, a dedicated microprocessor, to process the signal with digital computation. Some modeling amps incorporate vacuum tubes, digital processing, and some form of power attenuation.

Marshall MG15DFX Combo Review:

Features : 8 This is a great practice amp with 15 loud watts and effects. Only features I wish it had are a seperate reverb control and footswitchable channels.
Sound Quality : 9 Cleans are excellent! Sounds best around 5. At this level it's pretty loud and fatter than this thing should be for a little solid state. The effects sound good and the level control allows great control.Distortion is brutal and pretty versatile if you adjust the eq.With the delay or reverb set for long decay/delay time and level control set low you get a wide but almost transparent effect. The chorus and flange are decent, again better with the mix(fx level) low. I get a wide range of sounds, clean to metal. You cant really get a great overdrive type sound. Nothing is perfect. Sounds overall much more "real" than modeling amps in this range.
Reliability : No Opinion Since it is simple 2 channel s.s amp I expect it to last a long time. I bet these will still be rockin while the modeling amps are clogging the landfill. Not built as solid as my old peavey rage but I easy on my stuff so...
Overall Rating : 9 Been playing for 17 years and own lots of amps both tube and solid state. I bot this 6 months ago. Love it. I recommend it to anyone who wants great sounds and effects built in but doesn't want the hassles of programming. Just plug in and play kinda amp. I see no need to change the speaker as this one sounds fine and if you need to crank it so much that the speaker can't deal then you need a bigger amp.