So what are the hierarchy of design choices which give an amp its sonic character ?
Fender cleans, Tweedy breakups, Marshall roar, Mesa annihilation, etc...
It is a tough learning curve, especially as I knew nothing about valve amp design before this forum started a year ago.
I owned and played them, but that was as far as it went.
• Pre amp design ?
• Tone stack ? (& what is a stack anyway?)
• General circuit topology ?
• Pre-amp valves ?
• Power amp valves ?
• All that class A or class AB stuff that I don't really understand ?
• Speaker choice ? (another can of worms)
• Cabinet choice ? (likewise)
What else have I missed ?
I know it is all of the above, but what has the most significant impact, and what has the least influence ? (and what about the influence of the others ?)
Comments
- preamp topology
- power amp topology
Speakers
Cabinet design
Valve type
Cabinet material
Circuit layout
Wiring dress
Component types
Valve brand
Grille cloth
Cabinet covering
Chassis material
... in roughly that order probably. Although it gets a bit tenuous after the first three or four .
The most important single *factor* is the circuit design, and the most important single *component* is the speaker.
The tone stack is part of the preamp, so is pretty important - both its design and where it is in the circuit. It's called a 'stack' because the most common designs look like that on a circuit diagram, as Gagaryn said.
Class A/AB is part of the power amp design. While there is no real difference in guitar amp terms - Class A is usually either marketing BS or a misunderstanding of what it means and applies to - the type of designs which are most closely associated with "Class A" (which are usually hot-running Class AB) do sound different from the ones which are more typically Class AB. The type of bias and any negative feedback (NFB) is part of this, although actually nothing to do with the operating class.
Agreed - there seem to be only two schools of thought… "I don't know/whatever the amp company fitted/whichever one their accountants specified" and "a V30".
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
All push-pull amps have a phase inverter of some sort whatever class they are. Single-ended amps don't, and are theoretically all Class A - or they would be if they were biased correctly. In some ways the definition of Class A doesn't even apply to single-ended, since there is no other way of doing it, if you're avoiding distortion.
The phase inverter can contribute a lot, or not - it depends whether it reaches clipping before or after the stages before and after it, and whether the amp has power stage negative feedback, which is usually fed back in here.
It's unlikely the bias offset of most SE guitar amps is intentional, since so little of their design is. Mostly they were just thrown together by adapting old radio or primitive "hi-fi" (lo-fi, really) circuits and in most cases increasing the voltages to get more output power and damn the consequences.
"Bloom" means the way the notes tend to swell and change harmonic content as they decay, I think. (I assume it does, since that's how I think of it.) It's a bit of a silly term but you'll find it used a lot, particularly with amps where there's heavy compression in the power amp when they're driven hard, which then stops when the level drops below a certain point and the more natural clean sound seems to open out. This happens when a cathode-biased Class AB section is overdriven because the bias voltage sharply increases as the valves go into forward clipping and hence decreases again as the signal drops out of clipping. It doesn't happen in a true Class A amp because the current is constant, so the bias voltage is.
In some single-endeds it can even be more extreme because the bias point can be so far forward that the valve goes into a sort of almost Class C operation where it's cut off for more time than it's on.
If all this sounds like gibberish, just forget about the whole Class A thing and concentrate on what type of bias arrangement - cathode or fixed - the amp has, because it's more important. NB, fixed bias does not mean that it can't be adjusted, quite the opposite! It means it's fixed *by* the bias circuit rather than generated by the cathode current. Usually only fixed-bias amps are adjustable.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
I haven't played that one, although I have the smaller 20W one - I thought it sounded nice, but not really any more so than a more standard push-pull amp of similar spec... just a bit different.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
But now I am tonally totally confused like.