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Sonic Differences Between Even and Odd Order Harmonics?

Discussion in 'Amps and Cabs' started by forgivenman, Feb 5, 2009.

  1. pgissi

    pgissi Member

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    Yes the aiken amps article is excellent and the opening statement above is related to my point and can be applied beyond the ac30 to any clas ab as it states. This is a little understood aspect of this topic and I am simply saying the ac30 stays in class a longer due to its hotter bias, for a given output in a comparison.

    And once again, if run before the onset of clipping, which occurs later in an ac30 in comparison to a marshall push pull class ab design with a colder bias, this makes comparing the 2 a reasonable example within reason once again, below an established output.

    Not taking offense but your misunderstanding because of my inaccurate statement and I believe that class a is a factor in a watt for watt comparison, the vox stays there longer.

    Many dont realize that that just above bedroom tone their amp is in class a, its the beauty of the tube amp. Translated another way in a practical sense is any amp turned up for stage level to where the output stages clips with the guitar pot up is in class ab and rolling it back is not driving the output stage into class ab.

    When you think about how to use this it becomes obvious that the guitar pot is bascially controlling more than just overall volume and it becomes a useful tool in getting tones, tones that are sweeted some, absent of crossover distortion and clipping the output, allowing the even order emphasis in the triode staged pre-amp be more apparent. Of course there is cancellation in the output stage and to what degree could be the subject of a nasa study.

    In my example, if comparing a ac30 to a comporable traditional fixed bias pp ab design in a watt for watt comparison given other factors, the vox will deliver more useable travel on the guitar pot to the onset of clipping.

    That is why I suggested it would make a good comparison and is where my opinion is rooted.

    I have compared my 30 watt rivera with a buddys ac30 and can hear this when the amps are set roughly for the same level, in the rivera some clip creeps in with a slight crunch and imo is in class ab sooner where the vox is fat and round with that sweeted chime, still in class a. I think its a valid comparison.

    Now I can appoximate the vox tone with the rivera using a compressor set to squash and limit slightly and bring on some mid and high end chime at the same time to where its as loud but yet cleaner if you will. With the compressor off the output on the rivera has that characteristic crunch as the limiting is bypassed and drives the output harder, imo the output stage gets pushed into ab and with it on its in class a, I am hearing the transition and thats what I believe. In combination with the guitar pot, preventing the rivera from being driven into class ab, I can get it at a stage volume.

    At this point its departing from the natural character of fixed bias class ab amp to a point where it has to be driven harder/louder to get into ab and when you think about class of operation in a tube amp, you soon realize its the magic of the tube amp, the ability to control the transition of class of operation.

    To some degree simplisitcally, its a matter of dialing it in or out, class that is.
     
  2. Jay Mitchell

    Jay Mitchell Member

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    And you are wrong. An output stage doesn't "stay in class A" and transition to AB, it is either one or the other. Period. The AC30 has a Class AB output stage. It is always Class AB, because it fits the definition of Class AB: the output devices do not conduct through the entire range of signal swings.

    No. As with so many other things, you've got this exactly backwards. Hotter bias reduces the available voltage swing before saturation. Hotter bias makes a push-pull stage hit clipping earlier, not later. You should go back and actually read the article I linked. It makes this fact perfectly clear, if you pay attention.

    Because it is not.
     
  3. Jay Mitchell

    Jay Mitchell Member

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    Interesting. Because I'd never seen a Rivera schematic, I had to do a bit of research to respond to this - unlike some, I don't believe it's productive to speculate or fabricate in discussions of matters technical - but here's what I found: the only 30 watt Rivera is the 30-12, which is now discontinued. If that's the amp you have, its output stage has many differences with an AC30: different tube type (EL34 vs. EL84, a world apart), different quantity of output tubes (two vs. four), fixed bias, and negative feedback. Any single one of these can cause major sonic differences, so a comparison of the two reveals nothing about differences due to bias current (what you mistakenly refer to as "class").


    First, it is in "class ab." All the time. Until you learn the definitions of Class A and Class AB, you should stop pretending to understand this. Second, you have no idea at which point in the signal swing the low-side output tube turns off - for that matter, a low-power amp using EL34s could be biased Class A and still easily produce 30 watts. Third, without specific knowledge of the gain structure, you have no idea where in the signal chain the distortion you're hearing is being introduced. If it is occurring in the output stage, it contains odd harmonics, independent of quiescent bias.

    I note that you've abandoned your assertions about even vs. odd harmonics. Good decision. Now all you need to do is learn a bit more about output stage design, and you might begin getting a grasp on this. Right now, you're basing what you say on superstition.
     
    Last edited: May 26, 2017
  4. pgissi

    pgissi Member

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    I agree, the Rivera is a different beast and yes it is an R30-12

    But what I am really saying is that its simplistic a comparison and I am comparing the Rivera only in the sense that by using a compressor to bring up some freq and bring down some hence compression in combination to using the comp as a limiter carefully setting the attack and output gain to acheve that, the Rivera emulates an ac30 pushed to just prior to clip, still clean. Sure thats not an exact method since I am using my ears but they do tell me that the tone I end up with is still cleanish and is sweetened, not as aggressive as the sound of an amp in class ab with some crossover dist and clip hence with odd order more prevalent as the rivera would normally sound, a little harsher.

    It is my understanding that a pp class ab output fixed bias amp with a colder bias is producing odd order harmonics. Delaying the Rivera's transition to ab while altering the response does not mean odd order harmonics cease to be produced nor does it mean even order is not cancelled in the output but it is tonally different and the Rivera starts to chime like a Tom Petty, Byrds record. Its only possible with a compressor since the Riveras natural tone is marshall in chan 1 and fender chan 2 with selectable mid for tweed at 550 and blackface at 250. I use the Fender chan, pull the mids, reduce the preamp gain, increase the master with no boost selected and it becomes voxy run clean.

    Its a nice trick

    So you then disagree with the opening statement of the Aiken article along with others who state in one way or another "A push-pull amplifier is defined as operating in class A if, at the full undistorted output (just prior to clipping), the plate current flows in each tube for a full 360 degrees of the input conduction cycle..".

    To take it further, from Randall Smith-


    This is what I am talking about, small signals meaning reducing gain in one or more ways, keeping things just prior to cutoff and imo a class ab amp can be used to identify this tonally.


    Technically on a scope no, but having played for 30 years, I can identify when the power stage is clipping to where its audible at least, and when Randall Smith talks about "class a zone of overlap" it represents the output stage transition where crossover distortion and odd order dominate.

    I dont think its a stretch to say it is audible to some point after the onset of those characteristics and no, the ear will not hear what the scope sees. But the ear can hear the tonal character change over a wider range meaning less accurately.

    The botton line for me, its the class a zone of overlap that for me is what I am listening for, more accurately the region before it, through it and after it is imo more identifiable than the exact point of cutoff. Isnt that what all players do with their amp, listen. Its not a stretch to think so.

    I believe your less than accurate when you state "First, it is in "class ab." All the time." Technically from a configuration perspective your correct, its biased class ab but your glossing over the "class a zone of overlap" aspect, cutoff. And because their is this zone of overlap, then there is the previous condition, class a like and once again per Randall-

    Small signals, low gain, clean signals, prior to clip. I believe this clean signal is sweetened with even order despite the cancellation in the pp output, its probably the reduction of odd order post cutoff that past the "class a zone of overlap"

    So maybe a more accurate perspective is what I am able to achieve with my Rivera is a characteristic of class a operation using "merely modulating the idle current flowing through them, neither turning off nor requiring an increase in input power." to represent my argument.

    I believe this is audible and the key is signal level. You can continue to critizise me with your smugness but your view is a static one and not allowing for some interpretation when Randall says-

    "Work just like a class a" and for me, produce some character of class a tonally, Randall described it better than I could when he said "class a like" I did not accurately describe what I believe and if its "class a like", meaning not driven into cutoff at that point, its tonally different than when in cutoff.

    Sure a Vox, cathode biased and no neg feed, all part of the equation in addition to other design aspects but the difference between an output stage in cutoff and before cutoff, class a like , is a valid perspective.

    Albeit simplistic but is audible for sure.
     
  5. dtube

    dtube Member

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    Pardon the interruption, but a quick note of thanks to Jay for a really good thread. This has been excellent reading. No offense to the other party, but I've really enjoyed reading this.
    -Darren
     
  6. Julia343

    Julia343 Member

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    My eyes are glazing over and I'm getting the "deer in the headlights" stare going. That said I'm quite familiar with harmonics. I've voiced my own piano. I know which AH's have a warm sound and which ones have that ice pick you want once in a while on the guitar. But this is getting into amps, preamp distortion, tube distortion, class A vs class AB and all this other stuff....

    Would someone please explain why I prefer having the power section cranked hard and dial back on the gain (moderate levels) in from the preamp to get the distortion I like for rock? I've tried it both ways. High preamp gain with lower power level (similar volume) sounds fizzy to me.
     
  7. Jay Mitchell

    Jay Mitchell Member

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    As I have already pointed out, there is no difference between bias classes in this regard. All push-pull tube output stages are symmetrical, and they therefore all produce odd harmonics when driven nonlinear. This is just as true of Class A as it is of Class AB, although the distinction is completely irrelevant here, since the AC30 is Class AB.

    No, that is a correct statement of the definition of Class A. You apparently do not comprehend that statement. It makes it perfectly clear that the Vox AC30's output stage is Class AB.

    No. It is what your superstition tells you you are listening for, but it is not what you hear.

    Thank you for acknowledging that you have been mistaken on this point. In a discussion of "technical configuration" issues such as bias class, "technically from a configuration perspective" is all there is.

    If you have really convinced yourself that you can hear the point at which the low-side tube cuts off, then you are making a compelling argument against the AC30 and in favor of the Rivera. Since the AC30 has no negative feedback, it will produce more distortion during this transition period than the Rivera. Negative feedback corrects any output error that occurs during the transition. The error is actually quite small, which is why zero-negative-feedback designs can be made acceptable. Crossover distortion is a particularly onerous-sounding animal, and I've never met a guitarist who likes the sound of it. The biasing technique I use with tube amp output stages involves watching the output of the amp with a sine wave input on a scope and increasing the bias just past the point at which the crossoover distortion cleans up. This gives you the lowest bias current - and therefore the greatest linear voltage swing and lowest idle power - consistent with no crossover distortion.
     
  8. Jay Mitchell

    Jay Mitchell Member

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    I can't explain your preferences, but I can explain some of the differences.

    A preamp stage driven nonlinear produces clipping behavior with substantial asymmetry, meaning higher levels of even-order harmonics. Depending on the gain structure of the amp, it is possible that multiple preamp stages will clip. Because the common-cathode gain stages used in tube amps are inverting, a signal that is clipped in two successive stages may appear more symmetrical as a result of the clipping in the second stage. In that case, odd harmonics will be added to the signal.

    Power amp stages have much more complex reactions when driven into nonlinearity. Because the signal is coupled through a transformer, there is the possibility of core saturation. Additionally the power supply ("B+") DC voltage may begin to sag, causing a type of compression. The onset of nonlinearity is affected by the amount of negative feedback in the design. Zero-feedback designs enter nonlinearity earlier and more gradually, whereas designs with negative feedback tend to stay clean longer but clip more abruptly. A power stage driven into nonlinearity will often lose high frequency bandwidth as it is driven further into clipping, then recover the bandwidth as it comes out of clipping. This has a profound effect on the tonality and dynamics of single notes vs. chords.
     
  9. pgissi

    pgissi Member

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    I take no offense, I am learning as others are as they read and I think my last post clears up the confusion over what I am talking about. In that I think I brought something to the table and Randall Smiths and the Aiken article are providing some additional information, with Smiths article really pointing out what I wanted to say but could not.

    If an AB amp at some point is Class A like then guess what, its producing some characteristic tone of the same.

    If you have been paying attention, its not me saying that and I linked that information.

    The reason its not Class A in the technical sense is due to the lack of several other operating conditions and if you read the Aiken article, he coaxes Class A from the AC30 by reducing the stock plate volts and rebiasing, allowing the amp to run within the max dissipation prior to clipping of 4 el84s but at the same time reducing the input signal level to compensate in order to accomplish this. Lower plate volts, the onset of clipping occurs earlier.

    My conclusion, reducing signal level should render some Class A like tone from any class ab amp, thats what I have been saying.

    Hence the classification as Class AB

    The way Jay approaches it, it does not adress the zone of overlap and more importantly whats happening before that zone, Class A like operation.

    You can cuddle up to who you want but sorry, no point for Jay there in his static model and if you noticed he did not point that out, I did. In fact he alludes to this with "Second, you have no idea at which point in the signal swing the low-side output tube turns off - for that matter,", meaning before that, there is no turn off like in Class A operation and the real debate is-

    -at what signal level this occurs for a given circuit and operating volts
    -is it audible

    I imagine jazz players with their clean tone, probably set their class ab amps to live before the zone of overlap occurs with some room left for interpretation for where that audibly occurs at least to which one can say in this setting, there is more or less of it.

    With Randall Smith saying it, the Aiken article alluding to it, beyond that I have read along the same lines from Gerald Weber and others, its not my observation. I have read it and set out to listen for some characteristic to tell me I am close to it.

    If you only read Jays posts, you get- "First, it is in "class ab. All the time", that doesn't tell the whole story and the AC30 which according to Aiken is really Class AB fits with Randalls Smiths perpective in that "small signals driving a class ab amp works like class a."

    In regard to your latest post, I think I can hear it, its not my superstition, and can my ear match a scope, no but I think a good ear can hear some amount of this. Whether I am just into cutoff or just before is what I cant say but once again, a tube amp, driven my a complex wave i.e. guitar signal versus a signal generator is where your argument is rooted in, are 2 different things.

    Your just trying so hard now to prove me 100% wrong which I dont believe I am. I am here to learn and not to be insulted. Additionally if you can get past yourself what I am really saying is using your guitar pot or any other means of controlling gain i.e. signal level, your not only selecting the operating level of your amp but actually controlling its tonal character from class a like to strict class ab in cutoff.

    No wonder a guitar into a tube amp with just using a volume knob is so much fun.

    Against the AC in favor of the Rivera, I dont think so and in spite of your technical expertise, you lack reading comprehension and what did I say about the Rivera, I am emulating the AC 30 in a Class A like state, before the zone of overlap to the best my ears can say it is, by using compression and limiting to prevent the output stage from clipping or better yet, clipping more or too much.

    You say superstition, I say ears and your stuck on the theoretical and what you see on a bench with a signal generator and not a guitar pup with a player using attack and gain controls available.

    If you dont see that, you may want to put the probe down and pick up the guitar.


    Lastly, do you really think you are dialing out all crossover distortion, I dont think so-


    But this bolsters my argument for the AC 30 (as a good comparison with a a marshall, a feedback design) in my original post when I compared my Rivera with my buddys AC30 and its your words and your poiting out that the 0 feedback design is the key to enter nonlinearity more gradually versus feedback designs more abruplty, its what I was hearing in the comparison.

    If one understands this distinction, one can use the amp more effectively and my conclusion is the AC30 will stay class a like, longer in an a to b comparison, hence my use of compression with the rivera, limiting to prevent nonlinearity later than its design permits it.

    I dont think thats crazy or supersition, its audible and to what degree the ear can match your signal generator and scope, is where we disagree

     
  10. Jay Mitchell

    Jay Mitchell Member

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    There are strong similarities between the sound of the two, the primary difference being that Class AB allows for substantially higher voltage swing - and therefore power - from a given tube type. That does not alter the fact that they are separate and distinct bias classes, nor the fact that the AC30 is Class AB.

    If you had understood the Aiken article, you would know that he was establishing definitively that the AC30 is a Class AB design.

    I say you don't know the difference. Unless you actually perform Aiken's changes to an amp - not a particularly trivial task - and compare its sound directly to that of an identical, unmodified amp, you cannot possibly attribute the cause of the differences you hear to the difference between Classes A and AB.

    You compare two amps with half a dozen major differences and claim that what you hear is due to the amount of bias current in the output stage. That's nothing but audio masturbation. There's a difference, sure, but it isn't caused by what you claim it is.

    BZZZT. Fail. The AC30, with no negative feedback, does nothing to address correcting the transition issues, whereas amps with negative feedback do. Read my prior message, and you'll see this information there.

    Uhh, no. It really takes very little effort when you are 100% wrong.

    OK, so it was "Class A," and now it's "zero negative feedback." There you go backing off your prior incorrect statements again. Keep it up, and you'll eventually reverse all of your mistaken assertions.
     
    Last edited: Jun 18, 2016
  11. pgissi

    pgissi Member

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    Hey Jay BZZT, maybe its time to put the probe down and once again your a rude thug.

    1) I have come to understand
    2) your glossing over my point, once again, class ab amps spend some
    time in class a
    3) and the Aiken modded vox rendered class a although an ab design

    I guess this guy below is wrong also

    [SIZE=+1]No, I guess I cant hear whats described above, its just my imagination.

    [FONT=Arial, Helvetica, sans-serif]I guess your your ego is too big and I dont think, in fact I know I am not the only one thats says it, within some reasonable range of more or less of it, it is audibly discernable[/FONT]

    [FONT=Arial, Helvetica, sans-serif]


    Then I guess all those single ended players dont hear the difference either. I mean how many players have a variety of amps single ended and class ab, you dont think they hear a difference. Thats funny, this forum is full of their posts. The sole reason for this place, we hear differences in everything.

    Quantifying, sure short of scientific inquiry it remains subjective but nevertheless, there and when there is some opinion that below 20 or 22 watts is where this tone lives, well that is almost audibly quantifiable within the limits of the ear but could be tested and some point of reference established, to relate it to a perceived loudness i.e. level setting on the amp.




    I have no problem and never pretended to be 100% confident in all my assertions, as I stated, I am here to learn and you have to admit, my central assertion, although incorrectly attributed, was correct in regard to the AC30, the focus of my first post is operating in class a up to some point and maybe thats framing it simplistically but yet its also there.

    you know jay, there is a better way to communicate

    [/FONT]
    [/SIZE]
     
  12. reaiken

    reaiken Member

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    Okay, if you guys don't mind, I'd like to step in and try to keep this discussion civil! This is a *very* confusing topic, so I can see how it can be easily misunderstood. We're all in it for the same thing, to learn something and spread the knowledge, so I'll try to clear up my position on the subject.

    Technically, amplifier class does not change based on operating point, because the definition of the classes has to be made at a specific operating point (typically prior to clipping for class A and class AB stages), otherwise the amplifier classes wouldn't make sense, because you could spec your amp at, say, 10% duty cycle and claim it was a "class A" amp, when in reality, it might go into cutoff at 11% conduction. Clearly, there has to be some sort of guiding constraint in the class specification, so it is made at full unclipped output.

    Having said that, here's where the confusion comes in: Does a class AB amp become class A at points where the conduction angle is 100%? Some say yes, and some say no. It is my contention that it does not become a class A amp at that point, it merely operates in conditions *similar* to class A (because of the 100% conduction) and here is why, from my "Tech Info - Q&A" page:



    Q: Are class AB amplifiers actually running in class A at lower volumes, as is commonly claimed?
    A: No. They are operating in conditions similar to class A, but they are not actually "class A at lower volumes". Now, what are the differences, you might ask? Well, for one, the Class AB amplifier is biased in a more non-linear portion of the characteristic curves, which means it has more harmonic distortion than a true class A amplifier, even when running "clean". Also, the efficiency will be greater than is theoretically possible with a class A amplifier at these levels. There is a very real difference in tone and operating conditions between a true class A 10W amplifier running at say, 1W, and a 10W class AB amplifier running at 1W. Same output level, same overall power level,but a different class of operation, different amount of distortion, different efficiency, and a different tone, even though neither one of them is in cutoff for any portion of the output cycle at that low level. This is due to the bias point differences and load line differences. The differences become even more apparent when the amplifiers are run at their full undistorted output power. The true class A amplifier will have no crossover distortion, while the class AB amplifier will. The average plate current for the true class A amplifier will not change, or will change very little, from idle to full output power, while the average plate current in a class AB amplifier will increase dramatically. This will lead to "sag" in the power supply that doesn't exist in the true class A amplifier, which again results in a tonal change.



    Now, am I right or wrong? Obviously, I think I am correct, or I wouldn't have written it that way! :) However, bear in mind that I am far from an expert on the subject, and am not infallible! You should read all you can on the subject and make up your own mind based on verifiable, provable information and your own tests.

    Some people contend that the only required condition for "class A" is a 100% conduction angle. If you subscribe to this definition, then you would indeed be correct in saying the amp is operating in class A at lower levels. To be honest, it really is splitting hairs to differentiate between "operating in class A" and operating in conditions similar to class A". However, I think it is an important distinction, based on the reasons stated above.

    Now, go play your guitars and enjoy yourselves and stop worrying about amplifier classes!!

    Randall Aiken
     
  13. Jay Mitchell

    Jay Mitchell Member

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    Thank you for that. The definition in one of my engineering textbooks, ca. 1969 - one of the last texts of which I'm aware that still bothered with vacuum tubes - is for single-ended circuits and includes A, B, and C. In that case, the distinction is more obvious, and there is no Class AB. Class AB is only defined for push-pull (or complementary) circuit topology.

    Sorta like Vox did with the AC30, huh?:banana

    That description would apply to the AC30 output stage.

    However, what about a Class AB output stage with negative feedback vs. Class A (or "hot" Class AB a la AC30) with zero feedback? How do small-signal distortion values compare between those two? There's a reason for using negative feedback, and a large part of it is related to reducing small-signal distortion.

    A valid point. However, can you identify a guitar amp with push-pull output stage (the only output topology for which the choice between A and AB is viable) that is biased Class A? I don't know of any, but that is not to say they don't exist.

    What he said.

    By itself, that is not the definition of "Class A." Class A operation requires that devices remain in "linear" operation at all possible unclipped signal levels. I can't go along with altering the definition based on a misconception, no matter how widespread. That tendency exists throughout audio (try having a discussion of phase response), and it only compromises the quality of communication when it is allowed to spread unchecked.

    FWIW, I play my guitar every day and still gig at least once a week, although I haven't done so for a living since 1983.
     
    Last edited: Mar 1, 2018
  14. Jay Mitchell

    Jay Mitchell Member

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    One last response, and I'm done with you. Here is a quote from your first post in this thread:

    "Guys, loving the enlightening engineering talk but its reminiscient of when CBS bought fender and the new marketing dept had their sectretaries carry the specifications down to the engineers instead of doing it themselves and the result was the sterile ultralinear silverface series that only got worse as it was ahem...developed."

    The attitude you express in this sentence is not only offensive, it implies that you think you know something about the subject. As the interchange progressed, it became increasingly apparent that you do not. If you don't want a confrontational response, the best way to avoid that is to refrain from a making a confrontational approach. If you don't want to be called on your ignorance, then you might consider not pretending to be knowledgeable when you really aren't. Just a thought.....
     
  15. Mike Fleming

    Mike Fleming Member

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    There aren't many, but Alessandro makes a few:

    Beagle
    A 10 Watt, 2xEL84 based amp
    Plott Hound
    A 10 Watt, 2x6V6 based amp
    English Coonhound
    A 20 Watt, 4xEL84 based amp
     
  16. Robert Rowe

    Robert Rowe Member

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    To be quite honest ... I no longer understand all that I know about this. :messedup
     
  17. pgissi

    pgissi Member

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    Here is the continuing love flowing from Jay-



    Hey Jay, I was done with your from jump street and if your interpretting my opening sentence as the legit kickoff for this ridiculous volley of smug contempt for me from you, then you sir are lacking a sense of humor. Did you interpret my cut on the CBS Fender engineers personally? FYI the line about the engineers getting their secretaries to carry the specs to the marketing dept is from the movie "office space" and was really just my attempt to break in an say, the reponses to the OP were too technical and this whole scenario resembled my imagined over-think at CBS era Fender engineering.

    Additionaly Jay, you once again insult me with your last post, I do know something about the subject and regardless of how much you have memorized the data and can recite the technical vernacular, doesn't mean you are 100% accurate and in fact, Randall Aikens response does to some extent qualify some of what I have presented while highlighting your less than expert handle on the topic (despite knowing all the classical theory, at least in text) while showing that having a conversation with you is tedious, and all at the same time Jay.

    So when being called on your ignorance, then you might consider to stop pretending to being so knowledgable when your not, just a thought Jay!

    Jay, are you still peeved when we went at it over my opinion on digital modelling and how I pointed out the absence of a 100% unbroken RCL signal chain was a key factor in me forming opinion in favor of tubes and why modelling will always fall short, once again Jay my opinion! Of course at the time I mistated RCL as RCI (resistive capacitive inductive) and thats when I got the first taste of real Jay Mitchell love.

    Jay you know where I am telling you to put that stupid little banana


    Dear Mr Aiken, you sir are a gentleman and a scholar and its because of people like you who share their passion and expertise on this topic (while avoiding the need to hurl insult or smugness) that the elevation and continued progression of the art and science that this topic is will continue.


    This is where Jay will berate you if you stray from the vernacular while considering that communicating whats in the mind effectively in regards to this topic is difficult (class a like instead of true class a) especially for a knowledgeable laymen but this was essentially my point and for better or worse, I used the AC30 versus a typically pp Marshall.

    Maybe I am wrong about being able to distinguish that by ear, I have only stated my opinion but of course to Jay, that was lost.

    Below is how the conversation could have gone....

    Thanks Again Randall!


     
  18. rockon1

    rockon1 Member

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    Excellent wrap up! Thanks Randall -(and Jay) Bob
     
  19. pgissi

    pgissi Member

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    Yes thanks to Jay for his wonderful demeanor and 100% accurate recollection of what he has read and regurged (like the vast majority of us including jay) in addition to his honesty and tact when replying to my posts, he did not misconstrue my position in any way, made every attemtp to assist me in defining my point and was 100% intellectually honest in regard to his level of expertise:NUTS

    thanks boB:eek:

    Correction, thanks only belongs to Randall for being respectful and honest and of course sharing.


    Interesting how this below is what Jay has criticized me for stating in so many words in regard to Even versus Odd Order where he insists, its not audible and in the example below, its just addressing Triode versus Pentode Operation, one facet (out of many) of amp design and it does not even address class of operation and the tonal differences that imparts, regardless of whether I can hear it or not in someone elses opinion.

    Oh wait, Jay says its not audible, carry on and take Randalls advice, go listen for yourself, form your own opinions because those who form opinions beyond todays construct, invent the impossible tomorrow!

    Or you can just memorize what you have been told and never ever deviate and live in the static universe where "experts" with "facts" steer your belief system 100%. Just dont venture too far to the edge, you'll fall off.

    You see a real expert knows he is not an expert and doesn't know everything-

    Guess who?

    Originally Posted by radioboy950 [​IMG]
    This doesn't explain anything at all from a technical standpoint, but if you listen to these amp demos below you will hear the sonic differences when the amp is switched between triode/pentode mode. Rivera calls it a "Modern/Vintage" switch, which toggles between 55W/25W and emphasizes different harmonics.

    From the Users Manual:
    Vintage-Modern switch Switching amongst the two settings will produce a change of output power as well as harmonic balance. In Modern mode, the output power amplifier operates in "Pentode" and will sound the cleanest, have the most headroom, and sound bright, with odd harmonics (i.e.1,3,5,7, etc.) more noticeable. Vintage mode brings the output tubes to work in "Triode" mode, halving the power selected by the High-Low power switch, and lowering the odd harmonics while raising the even (2,4,6,8, etc.) resulting in a sweeter, darker tone.

    The vintage mode and the even harmonics are more pleasing to my ears. That's where I leave it set most of the time.

    I found these clips when I was doing some research before I bought my Quiana.
     

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