Squirrel comes back in spades in Helix 2.81 (Tweed Nrm)? LOL

Discussion in 'Digital & Modeling Gear' started by Mark Al, Sep 5, 2019.

  1. mbenigni

    mbenigni Member

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    This. Because there are two different phenomena being discussed, similar but not the same.
     
  2. cliffc8488

    cliffc8488 Member

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    I didn't listen to the clips or read most of the posts but a "Tweed" amp has a cathode biased power amp. Most Fenders are fixed bias but some of the earlier ones, like the 5E3, are cathode biased.

    Most cathode biased amps (often erroneously referred to as Class A) will go into Class-B operation when driven. Class-B operation creates crossover distortion. The reason a cathode biased amp goes into Class-B operation is because the capacitor in the cathode bias network charges up when the tubes conduct.

    For example with no input signal the voltage on the cap might be, say, 10V. When each tube conducts more current flows from the supply which charges the cap up and increases its voltage to, say, 20V. The bias voltage has effectively doubled which means the tubes are now biased very cold and the amp runs Class-B.

    When you stop playing the bias voltage settles back to 10V. Start playing again and the cathode cap charges up again. The time constant to charge the cap is on the order of milliseconds so it takes some time, it's not instantaneous.

    Some amps use separate cathode networks to reduce the amount of bias shift, i.e. Matchless, Bad Cat, etc. but this increases cost.

    The sound of Class-B operation is a raspy, fizzy, crackly sort of sound as crossover distortion creates a very different spectrum than clipping. Some people like the sound and there are actually pedals that intentionally create crossover distortion. Rumor has it that EVH liked his amps biased cold so he would get more crossover distortion.

    Crossover distortion is mostly in the high frequencies. When listening to the proverbial "amp in the room" the high frequency rolloff of the speaker will mask it to a great extent. Close micing an amp yields a lot more high frequencies which will make crossover distortion more noticeable.

    If you have an Axe-Fx you can experiment with the bias shift in these types of amps via the P.A. Cathode Resistance parameter. Turn it up and the bias will shift more resulting in more crossover distortion as the power amp is driven. Turn it down and the bias will not shift as much and the amp will remain in Class-AB operation longer. You can tell if an amp is cathode biased by the default value. If it is 0.0% then it's a fixed bias amp, otherwise it's cathode biased.

    Some amps exhibit this more than others. The Suhr Badger has a lot of bias shift but it's still a great sounding amp, probably because the conjunctive filter rolls off the high end which helps mask the crossover distortion.
     
  3. XTC Blue

    XTC Blue Silver Supporting Member

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    I wish people would stop telling me I'm not hearing a strange digital only artifact.
     
    Last edited: Sep 10, 2019
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  4. XTC Blue

    XTC Blue Silver Supporting Member

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    What I'm hearing with digital is not the same as what I hear with tubes. So I disagree.
     
  5. caledoneus

    caledoneus Member

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  6. mbenigni

    mbenigni Member

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    I don't "disagree" and I certainly wouldn't presume to challenge Cliff's knowledge here. But I maintain that there's something present in the Helix output that is similar but not the same vs. what he's describing - i.e. the intended and accurate modeling of any given amplifier's behavior. This "something" is not necessarily "digital" but definitely SS, part of the Helix signal path in general, as opposed to the algorithms describing a specific amp.

    But I'm on the wrong side (the outside) of the proverbial black box. So... :dunno
     
    Last edited: Sep 10, 2019
  7. JiveTurkey

    JiveTurkey Trumpets and Tants Silver Supporting Member

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  8. mbenigni

    mbenigni Member

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    :rotflmao

    I'm in.
     
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  9. JiveTurkey

    JiveTurkey Trumpets and Tants Silver Supporting Member

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    AS LONG AS WE DON'T USE REAPER. APPROPRIATE NAME FOR THE PROJECT GIVEN THE LYRICAL SUBJECT MATTER; BUT NO.
     
  10. XTC Blue

    XTC Blue Silver Supporting Member

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    I disagree with the whole tube amps do it too rationale. I'm in no way disagreeing with Cliff's description of crossover distortion or his knowledge of tube amplifier circuits. But I have some pretty darn good ears and have owned a large number of amps through the years. And it has nothing to do with the type of amp circuit being digitally copied. You hear it with Helix. I narrowed down 2,000 files to 5 on the Kemper - and NOT hearing that sound was part of the elimination process. And I couldn't get rid of it 100%
    ftr, when I say digital I'm not meaning a brand - just the type of pre-amp circuit.

    I hear a weird digital only attribute.
    You hear a weird digital only attribute.
    At least a half dozen others are in agreement.
    Sounds like all of us a) have extensive experience with analog amps, and b) know a thing or two about what we talk about.

    Why can't people stop trying to tell us we're hearing normal 'amp' things?
     
  11. cliffc8488

    cliffc8488 Member

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    Nothing I wrote has anything to do with tubes vs. digital. Some cathode biased tube amps exhibit more bias shift than others because of their design. The higher the cathode resistor value, the more bias shift. For example, the aforementioned Suhr Badger has a 160 ohm cathode resistor. An AC-15 has 130 ohms so the bias shift is less. Likewise a Morgan AC-20 has 125 ohms.
     
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  12. mbenigni

    mbenigni Member

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    I'm partly with you, but partly I'm not. Some amps do make noises that are somewhat similar under some conditions. It's worth noting that those noises vary from one "real" amp to the next. I appreciate that HX, Ares, etc. attempt to model those behaviors, but I'm pretty certain I'm hearing something in HX whose consistency implies a systemic problem. (This is not meant to give Ares - which I've never heard - a pass, by the way.)

    Here's where things get weird: I don't recall hearing these artifacts on Kemper; I even have a theory that Kemper would be incapable of reproducing them (for instance, if you were to profile a Helix amp model), because it's more limited in profiling behaviors as they change over elapsed time. So it's possible you and I are talking about two separate problems/ characteristics, both of which are outside the scope of "real amp" behavior, as Cliff describes.

    P.S. I'm 100% certain Cliff knows more about real amp behavior than I know about anything.
     
  13. XTC Blue

    XTC Blue Silver Supporting Member

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    I call lead guitar.

    [​IMG]
     
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  14. XTC Blue

    XTC Blue Silver Supporting Member

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    Will all due respect, what does any of that have to do with a weird artifact I only hear with digital?
     
  15. MojoRisin

    MojoRisin Member

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    May I suggest your first single be called “Squirrel Factory”
     
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  16. cliffc8488

    cliffc8488 Member

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    Absolutely nothing. You said you disagreed that some amps exhibit this more than others. I offered examples of amp designs that prove that, in fact, some do.

    I don't doubt you hear something only in some digital simulations. Most of the popular simulations don't use very much oversampling. Hence they alias. This could be what you are hearing.

    I wrote what I wrote to offer a possible explanation to what people are hearing. It's entirely possible it's a "digital artifact". I'm just stating that a lot of what people attribute to these "digital artifacts" are actually distortion products that real amps also generate.
     
  17. XTC Blue

    XTC Blue Silver Supporting Member

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    Understood. You mentioned you hadn't read the thread so I'll put this here so you can see where my comments come from:

     
  18. JiveTurkey

    JiveTurkey Trumpets and Tants Silver Supporting Member

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    My I propose something more in the Carcass vein? "Embryonic Squirrel Surgery sans Anethesia"? :Devil
     
  19. XTC Blue

    XTC Blue Silver Supporting Member

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    I say a multi-part full album side progressive metal suite.
    'Operation Sciuridae'
     
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  20. JiveTurkey

    JiveTurkey Trumpets and Tants Silver Supporting Member

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    I'M NOT GOOGLING THAT
     
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