What are the differences between guitar amplifiers used for blues, rock, or heavy metal genres? Are there any major distinctions between them or are they almost the same?
Amplifiers for Blues are still more or less equivalent to the amps from the early days of electrified music. Back then, people didn't really have distortion in mind at all when thinking about electric guitar. The amps were simply designed to produce a lot of volume and a sound that was suited for Jazz and Country – warm / clear, depending on the guitar.
In many cases, this meant the circuitry was roughly set up to counteract the typical mid-heavy uneven response of single-way cabinets. The classical Fender amps are typical for this: they boost the bass/low-mid and quite a wide treble range. This is most obviously exploited by Country guitarists playing Telecaster – very bright and clean thanks to the combination of solid ash body, bolt-on neck, quite low-impedance single coils and those amps.
Blues guitarists however rather preferred guitars with less bright, twangy signal, often Gibson semiacoustics or Les Paul, which are better suited for layed-back, painful “singing” solo play. This actually needs quite a bit more power from the amp to cut through a band mix, especially when the guitar needs to fulfill both a rhythm and lead role. As these were still not-too powerful (considering you usually didn't go into the PA!) tube amps, it was quite inevitable to make use of some overdrive, which happens automatically when plugging in a higher-impedance guitar and cranking the volume. The simple circuitry meant that the amps have a pretty wide crunch range, and that warm, dynamically responding sound with just a bit sustain-enhancing compressing overdrive is what I'd consider the typical blues amp character.
In Rock music, much the same sound was the starting point, but the guitarists wanted on one hand a bit of a faster response again, on the other hand were quite happy with the fatter midrange that was so useful for filling up the sound in a small band, and they simply needed ever more volume.
Marshall was on the forefront in adressing that need. Their concept was to forego the “scooped out” Fender guitar sound, and deliberately go for the fat, agressive frequencies in the midrange. In fact, the early Marshall amps are often compared to the Fender Bassman bass amp, rather than the guitar models! (However, the Marshalls actually don't spend as much energy as Fenders pumping the low end which the cabinet doesn't transmit that well anyway.)
Distortion was now not only accepted as an unevitable side-effect, but deliberately included in the plan how to achieve the required volume. Still, those classical Rock amps aren't in the modern sense high gain – for the strongest breakup – mostly, screaming soloes – guitar players mainly relied on fuzz pedals, later Tube Screamers et al. Now, the thing with Fuzz is that it extremely compresses the sound, reducing the waveform to almost a square wave which is then smoothed a bit again with tone controls. This is great for psychedelic stuff, and in connection with other effects (chorus, tape echo, Wah-Wah) it also allows enourmous expressivity, but there we're essentially again in very Bluesy territory.
Heavy metal bands wanted something more evil but also straighter, suited for tight rythmic playing, without however alluding to the kind of rawness found of Punk or back to a beat- or even country-like sound.
Hence the quest for more relentless, unmuffled distortion in the amp itself while retaining good transient response. The culmination of this are “modern metal amps” like Peavey 5150 or Mesa Boogie Dual Rectifier. Frequency-wise these amps actually go rather a bit back to the older clean amps (lots of bright treble for clarity but deep bass too), also in that they rely completely on tubes for overdrive (unlike the transistor pedals of the Rock era), but because they have just so much more gain and are designed upfront to handle heavy distortion throughout the circuitry, the result is very different.
For stereotypical Fender e.g. Super Reverb vs. Marshall e.g. Plexi vs. Mesa Dual Rectifier, with no effect pedals. Subjectively, I would rate them the following way:
- Gain/distortion: Blues < Rock < Metal
- Treble clarity: Rock < Blues < Metal
- Midrange blare: Metal < Blues < Rock
- Bass resonance: Rock < Metal < Blues
- Dynamic crunch: Metal < Rock < Blues
- Transient response: Blues < Metal < Rock
Amps are today quite versatile but there are still reference sounds. So Mesa Dual rectifier is one of the reference metal sounds. Fender Twin and Roland Jazz Chorus are one the basic way to go with cleans while Marshall Plexi is commonly identified as the rock sound.
Now most of the amps will have more than one channel and producers try to voice them differently so you can basically get few or more sounds from one amp. Digital amps and other simulating/modeling stuff will use even similar names. The same with overdrive pedals that promise to change your clean amp into something specific like Plexi-Drive.
Please notice that cabinet has big impact on overall sound and running different amp though same cab will make them less different than you may think in the beginning. Also not every pedal will sound the same with every channel of every amp.
The easiest (and the cheapest way) is to buy digital unit with many sounds inside instead of buying classic amp and realize you wanted something different. For example I love to run overdrive pedal into Twin like sim some people will get prefer metal sound from Marshall and so on.
This is a hugely complex subject and it very much comes down to personal taste and playing style and the particular instrument you are using.
Equally the speaker enclosure (whether separate or as a combo) will have significant effect on the sound.
This is further complicated that all the styles you mention will often use outboard effects to alter the overall sound.
Having said that there are certainly quite a few 'classic' or stereotypical amp sounds.
If you really want to explore a wide range of sounds there is something to be said for getting your hands on an amp simulator eg a Line6 POD whcih will give you a huge range of sounds to play with fairly cheaply.
IF you are interested in blues, rock and metal then something like a Marshall valve combo eg a DSL should cover you pretty well, especially with a few effects pedals to get specific sounds.
Going further a small combo amp is easier to overdrive, especially for practice and while it won't ever deliver the sort of muscular output that you want for really heavy metal is still a sensible option for practice and excellent for blues and heavy rock.
For a really heavy sound typical of modern metal (ie late 90s onward) something like a Mesa Boogie Triple Rectifier head with a 4x12 cabinet is standard but this may be way too loud for normal practising.
Some of the more low-fi heavy styles ( eg Thrash, Death Metal etc) actually favour solid state heads with big cabinets eg the H&K Warp 7
Often the most difficult thing to achieve is the middle ground typical of the heavier end of blues and proto-metal bands like Led Zep where you need a lot of warmth and tonal range from single note runs.
Not a lot, though each genre has its own preference for degree and type of distortion, both from intentional overload and from effects pedals, and may have traditional preference for a particular make and model. However, there is a BIG difference from amplifiers/speakers designed for 'clean' sound.
The amps you look at and listen to will have a lot to do with the type of music you intend to play. Most amps have a certain type of sound, a house sound if you will. Fender amps have more of a clean sound until they are turned up to a high volume. They are used for a variety of music types. Marshall amps begin to break up or distort sooner or at a lower volume than the Fender. Mesa and amps of it's ilk will turn out tons of distortion for a more modern type of sound almost in the metal category. Of course there are myriad boutique amps with all types of sound. You need to decide whether you want a combo amp (speaker and amp all in one box) or a separate amp head and cabinet. The open back type of cabinet of a combo amp has a completely different sound than does a closed back separate amp cabinet. Wattage is another question. Where will you be using the amp. For almost everyone the days of needing 100 watts are long gone. Even a 50 watt amp is too loud for most places. For home use a small combo amp of say 20 watts or under is more than enough. With 20 watts you will most likely never turn it past 4. I would recommend a 12 inch speaker as it will produce a wider range of tones than a 10 inch or smaller. One thing I think is most important is to get a tube amp. Almost all acknowledge that tube sound is much more pleasing to the ear than a solid state amp. Don't just order am amp either take your guitar and audition it your self then you can hear the vast differences between all your choices.