Power "class" and its effect on tone

Discussion in 'Gear & Equipment' started by vilk, Oct 9, 2019.

  1. vilk

    vilk Very Regular

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    Recently the bassist in my band got an Aguilar Tone Hammer amp. It's the size and weight of an internet modem. It's my understanding that the way this is possible is because it's "class D", and it uses a special kind of cable from the amp to the cab rather than a normal 1/4". I'm a little jealous.

    If this kind of shit is possible, then why aren't there guitar amps like this? Or since it's so small and light, why not just build it right into the Kemper or Fractal unit?

    I once owned a Vox modeling amp that had a button to change the "tone" between "class A" and "class B", and it changed the tone in a marginal way. Though this difference is just a simulation on that Vox, its basis must be in the reality that the power class does has some kind of effect on tone. What is that effect? Is it specific, quantifiable?

    If I'm being totally honest, I don't really understand what these classes are. Premium tube amps are class A, I know that. I've seen a Laney amp that though it is all tube does allow you to switch between class A and class B (would that give it a volume boost?). These super high wattage amps like the Aguilar are class D. Where is class C? Is it like B batteries? B batteries and class C power weren't rescued from their bunker in Area 51?
     
    Last edited: Oct 9, 2019
  2. GunpointMetal

    GunpointMetal SS.org Regular

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    Kemper does have a powered rack, BluGuitar and H&K both have floor pedals with built-in amps. The thing with class D is that you need it to have a lot of headroom because if you get close to clipping its gonna sound like a bag of ass.
     
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  3. budda

    budda Guiterrorizer Contributor

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    There are small power amps that are class D. Quilter, seymour duncan come to mind.

    They arent built into high end modelers because those companies want the user to choose what they run the unit into.

    Also why does the TH have a weird cable and not just an IEC?
     
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  4. TedEH

    TedEH Cromulent

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    My understanding is that class D is just a very efficient solid state kind of thing. Great for when you just need a lot of transparent power, but not great if you want "the sound of a power amp", which is more important (IMO) in a guitar amp than a bass amp. A and B classes (again, based on my very limited understanding) are about how tubes or transistors etc are used / biased. Something like A biases your signal so that it swings around .5 of the capacity of the tube (between 0 and 1) meaning it's always using some power, but B would use pairs together to each handle a half of the signal so that the zero point is just everything off and not using any power (one side handles positive, the other negative, I think?).

    I'm probably describing this terribly and might be wrong. I generally think of it though as:
    a) Tubes that aren't super efficient
    b) Pairs of tubes that are efficiently used
    a/b) Similar to b, but with a bit of a bias away from 0 to solve for something, but I forget what
    c) Not really used in amps like this
    d) Solid state, very efficient, but sonically adds no character
     
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  5. vilk

    vilk Very Regular

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    I just looked at a picture of the amp, and I think I was mistaken. It must not be the cable to the wall that's different, it's the cable to the speaker.
     
  6. TedEH

    TedEH Cromulent

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    Lots of bass amps use those speakon connectors, maybe that's what you're seeing? They're a little bulkier and turn/click into place.
     
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  7. stevexc

    stevexc Contributor

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    Definitely Speakon.
     
  8. Thaeon

    Thaeon Cosmic Question Asker

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    My Powered by Omega 112 uses a speakon combo jack. I prefer the speakon connector. Cable between the jacks is the same. Class A amps always produce the most accurate reproduction of the original signal. They're just inefficient at using power because they are single ended and one valve/transistor produces 360 degrees of the wave form so you get less headroom. Class be splits the difference and works in Push/Pull. One transistor does half the wave and the other does the other half. B is more power efficient but has more distortion. AB combines these. At lower voltages the amp will work at class A and as more voltage is applied, it switches to B. Basically giving you better signal reproduction and better power handling.
     
  9. mnemonic

    mnemonic Custom User Title

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    https://www.electronics-tutorials.ws/amplifier/amplifier-classes.html



    Class A

    9E913D25-3644-4728-A98B-EB295EA118DE.png

    The most simple, and also least efficient. One output device (transistor, tube, etc) does both the positive and negative side of the sine signal.


    Class B

    5DC36864-E338-4902-BE23-E75DED1DCFF8.png

    More efficient than class A, two output devices, one does positive side of the signal, other does negative. When one is on, the other is off. This causes bad crossover distortion at the zero point so it is not very useful for guitar amps.


    Class AB

    52DB3C88-93AF-4259-8D49-99D2357CB259.jpeg

    Class AB, like class B but the tubes (or transistors) do a little bit of the other sides signal, to reduce crossover distortion.

    Most mosfet amps and tube amps are class AB. Even a lot of tube amps that claim to be class A are actually technically class AB.

    My Fryette 2/50/2 power amp has a switch to choose class A, but it actually just switches to cathode bias and I believe is still technically operating in class AB.

    7326E362-D2EA-4EE4-ACAF-C5844AACC69E.jpeg

    Here is a scale of efficiency and also has the only good graph of class D from the above link.

    Class D is the most efficient, which means it can be very light weight while also delivering a lot of power. No huge heat sinks or power supplies needed.

    It is switchmode, so from what I understand, the output device is at full power or it’s off, so it ‘digitises’ the signal it receives and outputs an approximation Like the graph above.

    You don’t get a smooth sine wave output from a smooth sine wave input, you get that square wave output shown.

    This I think can lead to weird phase distortion in the high end but some more expensive class D amps will use dsp correction (or maybe some other kind) to correct that.

    Kemper uses a high-end class D chip amp board in their powered Kemper. The SD powerstage is a similar unit with a high end class D chip amp in it (same brand if I remember correctly, B&O).
     
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  10. r33per

    r33per SS.org Regular

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    A little 15 minute guide from a Glaswegian.
     
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  11. DudeManBrother

    DudeManBrother Hey...how did everybody get in my room?

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    Without geeking too hard: when people say “class A” they’re probably talking about a single ended amp, which isn’t actually class A. The classes are measured with a minimum of 2 power tubes, and without distortion.

    You have a scale of efficiency, and on the opposite end is faithful signal reproduction. The more efficient an amp is, the less faithful the signal reproduction.

    Class A is basically the least efficient, but highly linear, most faithful reproduction, of a signal. The output stage is always conducting, and completes a 360* waveform. It also creates a ton of heat, which further decreases its efficiency.

    Class B splits the load in half. One tube does 180* and the other tube does the other 180* and are then combined to create the full waveform. There can be distortion at the 0 point, where one shuts off as the other engages. This is dealt with by a portion of the signal not being reproduced.

    Class AB combines both classes. It takes the on/off approach from class B, but allows the first tube to stay on beyond 180* so the crossover distortion doesn’t occur. The bias determines how close to class B or A the amp will operate.

    There are class C amps, but they aren’t used in audio reproduction, so I don’t know a ton about them off the top of my head, other than they use less than 180* of the waveform.

    Class D, and other Pulse Width Modulation based classes, are non-linear, extremely efficient amplifiers. I don’t know too much about these amps either. I’ve played some that sound great, and some that sound terrible, but that comes down to design. The same thing can happen with tube circuits.
     
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  12. TedEH

    TedEH Cromulent

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    I wonder if some of the "class" confusion comes from Mesa amps and their switching options - from what I understand, they tend to label some of their options inaccurately, or at least not intuitively. Like my Mark IV has a "Class A / Simulclass" switch, but I don't think it actually switches classes so much as just turns off one pair of tubes.
     
  13. DudeManBrother

    DudeManBrother Hey...how did everybody get in my room?

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    Yeah I’d assume the switching options on the Mark IV are shutting off a pair, pentode/triode switching, and the various combinations of those. Their “class A” might just bias the outer pair of tubes hotter than the inner pair; giving the inner pair a more typical AB output of 50-60 Watts, and the outer pair a more linear, less efficient 15-25 watts, closer to class A.
     
  14. TedEH

    TedEH Cromulent

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    I might have been wrong a bit - I think I read somewhere that one of the pairs is A, and another pair is A/B, so running them together teeeeechnically runs two classes at once or something? No idea.
     
  15. MASS DEFECT

    MASS DEFECT SS.ORG Infiltrator

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    All is know is that Class A tube amps don't really have "sag". Kinda like it.
     
  16. Shask

    Shask SS.org Regular

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    A lot of good technical explanations above. I will try to add "tone" answers. :)

    Historically, Class A amps dont have sag, and are typically used for smaller tube amps. They dont have feedback circuits, so they dont get the depth/presence controls to really dial in the thump and scream, so they tend to be best on mid gain amps.

    Class AB is your typical large tube amp. Marshall, Mesa, etc.... They have feedback circuits, so you can dial in the depth and presence. They also have Phase Inverter circuits. These are typically known for the "best" tone, at least in terms of high gain. They have the low end punch and all that by the design.

    Class D is your newer smaller solid state amps. In the past, these were known for having a lack of low end and punch. They are small and loud as hell, but no tone, lol. That is why even the best solid state designs are typically Class AB. Class AB is known to have the best feel and interaction with the speakers. However, it does seem like Class D is getting better every year, and they are getting much more transparent, more like the Class AB amps.
     
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  17. TedEH

    TedEH Cromulent

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    This is the bit that I'm not quite sure we have strait...
    We don't use tube power amps (regardless of class) because we want transparency - we use them specifically for the distortion and colour they add. I'm pretty sure we avoid D for guitar because they're too transparent, unless you're throwing amp sims / impulses / etc. into the mix.
     
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  18. LiveOVErdrive

    LiveOVErdrive CNC hack

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    The class of an amp technically only refers to how the tube or transistor is biased (for a, b, and ab). Single ended and push pull are a different matter. That said, you rarely/never see a single tube or fet biased in class b. Push pull class A amps are a little more common. They are just as inefficient as a single ended class A amp but they are supposed to be more linear or at least more consistent because the two tubes run opposite each other so any nonlinearities in the tube affect each side of the wave equally.

    But in layman's terms, class A is a really hot bias, class B is a really cold bias.

    I BELIEVE the simul-class amps have one pair of tubes biased in AB and the other pair biased in A. That way you get a blend of a colder bias sound and a hot bias sound.

    Class D amps run like a switching power supply. You have a really high frequency square wave that goes between 0v and your max voltage for your output. You vary the pulse width (the percentage of time the wave spends "on") to set the output voltage to the output value of the signal. This is really handy because the percentage of "on time" (aka "duty cycle) maps directly to the output voltage. So they're super linear. And as long as the switching frequency is well above human hearing (and there is filtering in place or whatever), that frequency doesn't harm the sound at all.
     
  19. Adieu

    Adieu SS.org Regular

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    ...if only it were in English
     
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  20. wakjob

    wakjob SS.org Regular

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    My powered Kemper had a class D power section...
    didn't like it so much.

    Wish I held onto it until I got my Matrix (class A/B)...
    that thing I LOVE. Everything sounds better through it.

    The key to getting the blank canvas of class D to work and sound good for electric guitar is tube poweramp modeling or poweramp sims ect...
     
    Last edited: Oct 9, 2019

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