When it comes to electric guitars, a half stack is an amplifier stack that consists of a head on top of one cabinet. A full stack on the other hand, refers to a head on top of two cabinets. The cabinet which supports the head tends to have an angled top in front, while a full stack has a straight fronted lower cabinet.
The Marshal Stack
The earliest adaptation of the Marshal stack included an amplifier head sitting on an 8 X 12 cabinet. In other words, this was a single speaker cabinet consisting of 8 guitar speakers of 12” each. After 6 such cabinets had been produced, the configuration was changed to feature an amplifier head sitting on two 4 X 12 cabinets, i.e., 4 speakers of 12” each.
Double or Full Stack
Heavy metal band guitarists use the term “full stack” or “double stack” to allude to two stacks. Here, a second amplifier head served as a slave to the first amplifier head with a total of 4 speaker cabinets. In the 1960s and 1970s, the “head and cab” gained popularity, and this was also known as “piggyback.” Vox amplifier stacks could be placed on a frame with casters. Fender heads could then be affixed to the cab.
Usually a guitar amplifier’s preamplifier section allows for sufficient gain, enabling you to connect the instrument directly to its input, as well as sufficient power for loud speakers to be connected directly to its output. Both of these can be accomplished without the need of additional amplification. Another configuration is to allow 2 amplifying stages in separate units. Here, a mixer or preamplifier is made use of to improve the instrument output to line level, and even to blend signals from several separate instruments. The output that is generated from this preamplifier is then fixed to a power amplifier input, which in turn, powers the loud speakers. This system is often used in public address systems.
Musicians who prefer to use this two stage approach to amplification also often choose to design a special permutation of equipment that suits their needs best. For instance, some guitarists need pre amplifiers that incorporate certain specific features, like acoustic guitarists who may need preamplifiers equipped with notch filters that discourage feed back, an XLR DI output, reverb or parametric equalization. In the case of hard rock, punk or metal bands, guitarists may want preamps that include a wide range of distortion effects. Some guitarists also have very particular needs with their power amplifier, like one that includes high wattage, a design that’s low noise, as well as features that discourage speaker damage or distortion.
In the case of the two stage amplification method, both the power amplifier as well as the pre amplifier are generally based together in a rack case which may either be placed atop a loudspeaker cabinet, or left free standing. If several such rack mounted designs are used, the result is often a large sized unit on wheels. Several such rack mounted effects are made use of by guitarists who need to replicate the sounds that they have created in the studio, on stage. However if a smaller rack case that includes both the power amplifier and preamplifier is put atop the speaker cabinet, then there is very little difference between a traditional amplifier head and a rack. Yet another method is to incorporate the power amp into the speaker cabinet in a configuration that is termed a powered speaker. This can then be used along with a separate pre amplifier, and can be integrated into a floor preamplifier or an effects pedal board.
How to Correctly Configure Your Guitar Amplifier:
Preamplifiers can also be made use of to connect low output instruments to amplifiers. In the case of acoustic instruments, battery powered preamplifiers are used to correct problems with weak signals and incorrect impedance.