Headshell cabinets are for the most part built to house and protect tube amp "heads". An amp "head" is simply the amplifier without any included speakers. There are three main reasons for separating the amplifier "head" from the rest of the "stack".
In the case of a tube amplifier, there is a very physical reason why the amplifier would be separated from the speakers. That reason is has to do with the physical construction of a tube. Simply put, despite the fact that tubes amplify sound signals, they are vulnerable to the associated physical vibration. Any kind of vibration can, and usually does, shorten the life of a tube as the pieces that make up a tube (the heater, the cathode, the grid(s), and the anode) tend to be fragile and may be shaken to a point of premature failure. Housing the amplifier in its own cabinet prevents the tube from having direct proximity to the sound waves created by the loudspeakers. This physical separation of the tubes from the loudspeakers helps prevent them from being shaken unnecessarily and therefore failing prematurely.
All tube amps require at least two electric transformers:
- The power transformer's job is to change the (anywhere from) 117 to 123 volts (U.S.) alternating current (also known as "AC") to a voltage that is comparable to the operating parameters of the preamp and power tubes being used in the amplifier. This might be anywhere from 375 to 600 volts. It must also provide a 6.3 volt current to the vacuum tube heaters for all preamp tubes, and all power tubes. In the case of a 100-watt Fender Dual Showman, this can be 10-tubes (6 preamp, 4 power tubes). The typical 100-watt Marshall Plexi or JCM-800 is 7 tubes (3 preamp, 4 power tubes). In certain cases, like a 1965 Marshall JTM 45/100, the power transformer may also be called upon to power a tube rectifier. It should be no surprise that a typical 100-watt power transformer can easily weigh nine pounds.
- The output transformer's job is to take the 375 to 600 volts alternating current and "transform" it from a high-voltage, low-current signal into a low-voltage, high-current signal that is suitable for powering and pushing the speakers. A corresponding 100-watt output transformer can weigh seven-and-a-half pounds.
As the power ratings of the amplifiers increase, so too does the necessary weight of the transformers. So even 50 watt, but especially 100, and 200 watt tube amps require very heavy iron electric transformers for the tubes to be adequately electrified and the speakers to be adequately powered. Given that speaker cabinets can also have four high-wattage speakers, the magnets associated with those speakers tend also to be large and heavy. Speakers today tend to have speaker magnets that weight 30, 40, or 50 ounces. Presuming 40 ounce magnets on the speakers, a 4x12 speaker cabinet will have 160 ounces, or 10 pounds in magnets alone. For high-wattage tube amps, not only are the transformers heavy, the speaker motor magnets are heavy. It simply becomes unfeasible, in terms of human beings handling the equipment, for tube amps NOT to be split into headshell and speaker cabs.
In the 1960's, when the first 100-watt amps were being developed and sold to electric musicians, the aesthetic of "The Stack" was never a foregone conclusion. Jimi Hendrix and Dick Dale often used 100-watt Fender Showman and Dual Showman amps. These amps had the characteristic Fender clean tone, and were a typically a head amp into one or more 6x12 speaker cabinets. But this arrangement was never as tall or taller than the typical person, and so therefore isn't as visually imposing as "The Stack".
Briefly, "The Stack" consists of a headshell tube amplifier on top of two (also stacked) speaker cabinets. These speaker cabinets typically consist of four 12-inch speakers with those speakers patterned in a two-by-two arrangement. In the decades that have followed, this "stack" has become a defacto stage presentation format for bands who wish to communicate themselves as "heavy" to their audiences.
And here's why it wasn't ever a foregone conclusion: Before his passing, Jim Marshall told the story of how Pete Townshend of The Who first requested that he, Marshall, create a 100 watt amplifier. According to Marshall, Townshend believed that his guitar couldn't be heard by the audience, because it was being drowned out by Keith Moon's drum technique. So Pete placed an order to Jim Marshall for the first 100-watt Marshall amplifiers. Ironically, when Jim Marshall first delivered the 100-watt Marshall amplifiers to The Who, he had also built the first 4x12 speaker cabinets. Marshall relates that Pete Townshend actually refused delivery of the cabinets, demanding not 4x12s, but 8x12s! Marshall pleaded with Townshend to accept, arguing that the roadies would rebel due to the weight considerations. Townshend held firm and so Marshall had the 8x12s built. It was a month or so later after The Who had taken delivery of the 8x12s that Townshend came back to Marshall (presumably with his tail between his legs) and told him that Marshall was right, that the roadies had rebelled, and could Marshall please recreate the 4x12s?
With this aesthetic established and firmly rooted in the culture of heavy music, it follows that even when bands and players use solid state amplifiers, they often want to pay homage to "The Stack". So despite using solid-state amplification, which does not create the same vibration concerns as tubes, the cultural use of "The Stack" is one of the easiest ways for a band to visually present itself to an audience as "heavy".
Combo Cabinets are generally an open-backed combination of amplifier and speaker(s). The first guitar amplifiers built (by Leo Fender, Gibson, Supro, etc.) were combo amplifiers. Today, combo amps, despite a revolution in available features, still represent the most economical choice for any kind of electric-amplified instrument.
The earliest electric amplifier and combo cabinets were typically characterized by simple low-fidelity circuits, minimal controls, and poor reliability. Like every new industry created there were winners and losers. Beginning with the vacuum tube era, there were a number of companies that have come and gone. You probably haven't heard of Ampro, Silvertone, Supro, Garnet, or Watkins. From this era, Fender managed to live. Marshall managed to live. Others did as well; their names are a bit more obscure but can likely be found in this wiki. (Note: "likely" does not mean "assuredly".)
The trend reestablished itself with the transistor era when solid state amplification was made possible, and a whole new group of companies came and went. Reliability improved, but according to most, tone suffered as a result of going to solid state. Just like with tube amplifier companies that have come and gone, you've probably not heard of Acoustic, Audiovox, Plush, Earth, Woodson, or Univox. On the other hand, you probably have heard of Peavey. Peavey started out making solid state amplifiers.
So that leads us to the combo amplifiers of today. Most are reasonably good amplifiers. If you're looking for a low-wattage practice type of amplifier, there's absolutely nothing wrong with a more inexpensive solid state amplifier. Most combo amplifiers today also include some type of digital modeler that will allow you to layer many different kinds of effects.
Higher-value, high-volume combo amplifiers, especially tube combo amplifiers are of course available, but due to the vibration hazards described in the head amplifiers section above, we do not believe that most tube combo amplifiers, from a use and performance standpoint are a good long-term investment. As a financial investment, that mint 1951 Fender Tweed Super V-Front might have great collectability (and tone!), but we would not expect it to provide maximum tube life at high volumes.
Most venues that do not allow skull crushing volumes (clearly not our preference) are suitable for performances with combo amplifiers. Most bands that play in quieter, more intimate settings tend to use combo amps both for their convenience, but also for the somewhat more casual aesthetic that such amplifiers can provide.
Speaker cabinets are quite a bit different in that they do not have any kind of amplifier inside. They are purely for housing loudspeakers. There are many different configurations of speaker cabinets, as well as many different brands. In our case we're concerned with speaker cabinets for guitar, bass, and maybe for amplified synthesizer, organ, or electric piano.
Typically speaker cabinets consist only of an enclosure, some handles, the speakers, a baffle onto which speakers are mounted, wiring for the speakers, and a jack or two to plug a speaker cable into from the amplifier, or from another speaker cabinet.
There are other features that can be applied to a speaker cabinet including:
- closed back
- front face grill (protective, usually metal)
- grill cloth
- carpet or tolex covering
- corner guards
- additional handles
- rubber feet
- rolling casters
- top-side foot or caster cups
The most common types of amplified-instrument speaker cabinets (as described by an "A x B" configuration) include:
The first number, "A", in a "AxB" described speaker cabinet is the number of speakers. The second number, "B", is the size, in inches, of the speakers in the cabinet.
Clearly, there are other models available (Electric Amp Company offers a 6x12), and the speaker cabinet market is entrepreneurial and competitive enough to give just about any musician any kind of cabinet they could desire.
Currently, we are also very interested in some newer (and older!) innovations that have been suggested and implemented elsewhere. We would love to see and experience examples of the implementations listed below as we would love to gather and share that information:
- Fender's 1960's era Tone Ring (reported bass enhancement should be boon for stoner rock)
- Multi Impedance Selector (create different output impedances for a single speaker cabinet)
- Multiple Jacks for mixed/chorused/individual speakers (wet/dry signals within single cabinet)