Question:
I'm in the middle of researching the difference among several major amp manufacturers so your input is greatly appreciated.
The question is simple, what characterizes: a Marshall, Mesa, Vox, and Fender amps--what's it that when people hear a specific amp, they can immediately refer to a respective manufacturer?
Answer:
For fender, vox and marshall, the actual speakers have a lot to say with the characteristic tone, which is probably the only real characteristic that is worth anything in amp stakes.
As marshall and vox are English, their speakers are different to the fender, and vox is renown for the blue speakers, along with having a tube rectifier. The AC30 isn't really hot and is prized for a clean to breaking up quality.
The marshall is characterised by two or four (or even eight) 12" celestion speakers, and greenbacks are again prized. The story for marshall is that Jim Marshall repaired amps, and ripped the amp section from a fender bassman and linked it up to a 4x12 or and 8x12 (not 100% on the story) and started to refine the marshall tone. Apparently, it works as well. Bear in mind, if you listen to early marshall tone like Clappers on John Mayall and the bluesbreakers with Eric Clapton album, its not a really hot tone either like the later marshall sound, so some people say that the 'marshall sound' is the later JCM800 and 900's. Look at the thread about it called marshall amplifier question.
Fenders, being American, are characterised by their high headroom and clear, *sparkly* tone. That being said, fenders differ so greatly, between the tiny little single ended champs that are 5w and make a thick squashy tone that is compressed to the twin amps which are around 100w depending on the model which are the more characteristic tone. This is a result of a powerful poweramp which is impractical to drive to overdrive (ears bleeding territory) and the speakers, which are jensen 2x12s. These generally are clearer and handle more volume before breaking up.
Of what I know about mesa boogies, the big thing with them is a cascading gain section, whereby I believe that tube outputs feed further tubes, which creates a high gain situation. They are clear, punchy and overdrive really clearly.
To get a good idea of the difference between marshall and mesa boogie dirty, try to dig up a video of the darkness playing live, and listen to the different tones of the two guitarists. Dan Hawkins, the more sensibly dressed fella, uses Marshalls, while Justin, the silly looking fella, uses a Mesa dual rectifier (i think). They both use les pauls, but their solo and rhythm tones are really different.
That is by no means comprehensive by the way.
Answer:
The above is well put. Just wanted to add.
Mesa's are hard to nail. They have models that are truly all over the board as far as tone is concerned. The dual/trip recs. are known for cascading gain, but I'm not sure that's applicable across the board. Santana used/uses Boogies(among other things.) and he's definitely not in the high gain area.
Speakers are great for swapping around, tonal changes etc. It's difficult though to pin a certain amp's tone on a speaker. There are no doubt speakers that are voiced for British or American amps, but it's hard to define a tone by a speaker. Like Greenbacks work very well in AC30's, Celestion Blues in Marshalls. Etc. You will find that certain examples will be more commonly found in certain amps, but there are alot of options involving certain amps. Speakers make a huge difference in general, so alot of it is just swapping around and see what works best.
Answer:
Tonally:
Marshall's have a distinctive mid range bump that gives them a lot of their characteristic sound, you find this same thing with most british amps, almost no low end, and lots of midrange.
Vox has a very distinctive "boxy" sort of mid range, and is more or less Class A giving it a lot of tube sag in the power amp section, and a nice compressed overdrive sound.
Fenders fall into two basic categories: Blackface and tweed (if you want to get really technical there's also brownface and silverface)
Blackface is the sound most commonly asociated with Fender amps, its a tone with a lot of high end brilliance, good presence, and a tight fat low end. The mid range is almost "scooped" there is little of it in the tone. Tweed is a little dirtier, and has more of a mid range bump to it that gives it more grind than the blackface sound
Mesa is based after american designs (Fender), and has the tonal characteristics of an american amp; big low end, lots of presence, and nonexistent mid range. They also are very clean sounding amps, designed to get their tone from driving cascading sections of preamp rather than pushing the power amp.