SO ~ what gives an AMP it's character or tone ???

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ChrisMusicChrisMusic Frets: 1133
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 ?)

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Comments

  • GagarynGagaryn Frets: 1553
    Tone 'stack' is referred to that way due to the way it is depicted in schematics - stacked!
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  • ChrisMusicChrisMusic Frets: 1133
    Cheers Gagaryn, I had a feeling thats why it was termed that way.  Thanks for clarifying that for me.

    One issue down, so many more to go...

    I have to say I am really enjoying learning about all this stuff, this time round.  Before I thought that valves were just old technology and soon to be superseded.  Nothing changes, it seems.

    Breaking them open and making satellites and space craft out of the innards made a schoolboy very happy back then though.
    After that it was just a case of buying valve because they sounded so much better, and "fuck me, that's loud" !
    I do hope that I have grown up a bit since then though.  Wisdom comes with age, so they say, so bring it on...

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  • Speaker/Cab choice is a massive part of tone IMO, and massively overlooked too, by some. It seems very important for high gain sounds in particular.
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  • ICBMICBM Frets: 71956
    Circuit design
     - 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.

    Speaker/Cab choice is a massive part of tone IMO, and massively overlooked too, by some. It seems very important for high gain sounds in particular.
    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

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • Danny1969Danny1969 Frets: 10356

    In ssd design class A generally meant a single device was biased half way through it's effective transfer curve and handled both the pos and neg swings ..... pretty inefficient but simple design. Is this not the case for any valve design ?
    www.2020studios.co.uk 
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  • GrunfeldGrunfeld Frets: 4027
    So what... give[s] an amp its sonic character ?

    Probably the Big Muff on full pelt... image
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  • ICBMICBM Frets: 71956
    Danny1969 said:

    In ssd design class A generally meant a single device was biased half way through it's effective transfer curve and handled both the pos and neg swings ..... pretty inefficient but simple design. Is this not the case for any valve design ?
    No. Often the bias point - sometimes for preamp, and more often for power amp valves - is so far off half way that they probably can't really be considered Class A even if they're single-ended. And that's even before they distort, which automatically renders the Class definition invalid. So really, the whole concept is an oxymoron when applied to guitar amps.

    And that's even before you get into Class AB cathode-biased being confused with Class A, or lack of negative feedback being confused with Class A, or EL84s being confused with Class A - which seems to be about the only justification for calling some of them that! Even more ridiculous, some of the most desirable characteristics of so-called "Class A" guitar amps - the compression and "bloom" when driven hard - are specifically those of Class AB cathode-biased - true Class A won't do it.

    "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

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • ChrisMusicChrisMusic Frets: 1133
    So just to clarify the class A bit, a bit. 

    Is the more HiFi aim of class A design, the removal of the phase inverter and the distortion components associated with that ? 

    Does the PI contribute more sonically in the guitar amp sense ?

    I assume that the guitar amp class A biased heavily offset is to drive single ended clipping before both sides of the input wave clip.  That is assuming that it is an intentional design feature.  ???

    Am I getting a handle on this stuff, or am I losing the plot here ?

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  • ChrisMusicChrisMusic Frets: 1133
    What does that word "bloom" mean ?

    I have seen it written fairly often, but I can't really visualise what it is, (or should that be auralise).

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  • ChrisMusicChrisMusic Frets: 1133
    Thanks for the points about cab and speaker @guitarfishbay.

    As an aside, what was the quality of the clean channel on the Mesa Roadster you recently sold.
    Does it do Black/Silverface Fender well, and if so any particular comparison come to mind ?
    Is it right to assume that the clean channel voicing is either derived or copied directly from the LoneStar ?

    I am working on a strategy to test speakers and cabinets out in the hopefully not too distant future.

    Any advice on a strategy to ease the financial and time burden of narrowing things down would be appreciated.
    The initial "benchmark" starting point if the result of collective wisdom on here, so collective strategising seems an appropriate path to take too.

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  • ChrisMusicChrisMusic Frets: 1133
    edited August 2014
    Edit:  I have moved this post a little further down - read on, good reader, read on...

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  • ICBMICBM Frets: 71956
    So just to clarify the class A bit, a bit. 

    Is the more HiFi aim of class A design, the removal of the phase inverter and the distortion components associated with that ? 

    Does the PI contribute more sonically in the guitar amp sense ?

    I assume that the guitar amp class A biased heavily offset is to drive single ended clipping before both sides of the input wave clip.  That is assuming that it is an intentional design feature.  ???

    Am I getting a handle on this stuff, or am I losing the plot here ?
    The purpose of Class A is to minimise distortion!

    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

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • @chrismusic the Laney lionheart 50 is somewhat closer to class a apparently - it uses 5 el34s for 50 watts, rather than 2, which is (according to the blurb) closer to true class a than the usual way of doing things. How true that is, I've no idea but it's a fab sounding amp that's genuinely a bit different.
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  • ICBMICBM Frets: 71956
    It's a parallel single-ended. Depending on the bias point it could certainly be true Class A, although it doesn't necessarily have to be. But at that power, you're more likely to be running it in the part of the curve where it really makes no odds, so it effectively is anyway.

    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

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • ChrisMusicChrisMusic Frets: 1133
    Thanks for a great explanation ICBM, that does actually make sense to me.

    That either defines me not knowing what is beyond the boundaries of my own understanding, or that I am getting adept in the language from the land of the Gibber.  The alternative is that through the various discussions on here I have learned a fair bit, and with well explained posts like your one on class A, I am slowly stepping forward into the light of knowledge.  I think it may be the latter.  Thanks   :)

    It does lead me to ask about cathode biasing.  If you could encapsulate the basics into a paragraph or two that would be very helpful.  I think I sort of get it, but I could really do with some clarification.  I guess that shows I still have some fundamentals to iron out.  A bit more time on here should soon have that sorted though.

    As to the word "bloom", thanks for am excellent visualisation/auralisation of that.  I think that rather than a silly term, it is actually quite a good descriptive word.  It insinuates a factor and a time domain component, the spreading of any bloom over time is not dissimilar to the effect which you described.  It is also used in describing similar behaviours in imaging chip design which degrade their performance.

    It also adds weight to your previous assertions that "take what is true for HiFi or PA design, then do the opposite for guitar amps".  Sorry if I have used a little licence and mis-quoted that a bit, but that seems to be the spirit of it.

    Maybe we need to start "the Musos Lexicon" thread on here.

    That is one thing I have noticed, that since my past life experiences, everything seems to have a proper term or word associated with it.  Whatever happened to the anarchic rebellious frontier that I remember.  With maturity something is gained, but something is definitely lost.

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  • ChrisMusicChrisMusic Frets: 1133
    This keeps moving on while I am typing, that pleases me.

    If I answer a post I often miss anything that happened while I am typing, as the forum software takes me to the latest after mine, if that makes sense.
    So I have just moved this post down a bit in case it got missed.



    What a very excellent post ICBM, that one on the hierarchy, and also the division of factors and components.
    The dome of wiz has truly been earned and granted with that, thanks.

    Does valve manufacture and brand really come so far down the list.  I only have anecdotal evidence to ask that question on.  But the complete change in production technique, equipment and R&D experience between the defunct western manufacturers of old who actually developed and refined the technology, and then a hiatus before manufacture in the developing world would make me think that the products were re-engineered to be similar at best, and the refinement cycles probably all but absent.

    I had a bit of a smirk at the last few variables on the list, grille cloth, cabinet covering etc.

    I believe there may be some forums where we could start a "does snakeskin Tolex sound better than either lacquered tweed or purple Tolex" type thread, then step back and watch the fireworks, just don't mention bonding agents or techniques.

    I guess it does have a damping factor on the cabinet though.  And with microphonic valves the design and materials of the chassis (etc) would affect the resonance picked up.
    ;)

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  • ChrisMusicChrisMusic Frets: 1133
    Interesting stuff there @ThePrettyDamned, I'll have to check out the Lionheart sometime, and the schematics / circuit diagrams, once I have a bit more knowledge on how to interpret them.  5 EL34s sounds quite unusual, even to me.

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  • All amps are basically the same, what sets them apart sound wise is what you stand them on.  We ran a studio for ages with just a Carlsbro Panther and a selection of stands, chairs, chests and beer crates.  You could get any sound needed, from Fendery cleans to crushing Mesa metal tones just but changing what it was stood on.  Even differing brands of beer crates make drastic tonal differences.  Holsten crates are very mid heavy whereas Beck's crates tending you give you a very scooped sound.  Anybody who tells you that any other factor has any effect on amp sound is either talking complete crap or just buying all the marketing spiel.
    My muse is not a horse and art is not a race.
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  • ChrisMusicChrisMusic Frets: 1133

    All amps are basically the same, what sets them apart sound wise is what you stand them on.  We ran a studio for ages with just a Carlsbro Panther and a selection of stands, chairs, chests and beer crates.  You could get any sound needed, from Fendery cleans to crushing Mesa metal tones just but changing what it was stood on.  Even differing brands of beer crates make drastic tonal differences.  Holsten crates are very mid heavy whereas Beck's crates tending you give you a very scooped sound.  Anybody who tells you that any other factor has any effect on amp sound is either talking complete crap or just buying all the marketing spiel.
    But now I am tonally totally confused like.

    How do I deal with the double variability of my amp on a Holsten crate (other brands are available), and me standing on another surface.

    Even worse, what if I stand my amp head on the cat, the cab in the sink and play the guitar standing on that Becks crate on top of the sofa with me wearing a green T shirt ?

    No, this is all too complicated, give me class A, and a room with rubber wallpaper...

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  • Even worse, what if I stand my amp head on the cat, the cab in the sink and play the guitar standing on that Becks crate on top of the sofa with me wearing a green T shirt ?
    Well bizarrely that is exactly how Dave Mustaine gets his sound (except it's a black t-shirt naturally), so that should give you a ballpark sound.
    My muse is not a horse and art is not a race.
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