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Thread: How to determine class of Amp

  1. #1
    Tone Member
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    Default How to determine class of Amp

    Good day,

    Is there some formula or just a bit of knowledge to determining the class of an amp without the manufacturer just stating the class directly (eg, it is in the owner's manual or something)?

    For example, as far as I know, nearly all Solid State amps are class D.

    I am more curious than anything.

    Thanks
    Last edited by GreatOz; 10-05-2019 at 05:42 PM.

  2. #2
    Super Toneologist DavidRavenMoon's Avatar
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    Default Re: How to determine class of Amp

    First off, most solid state amps are not class D. That’s a switching amp. They output a series of pulses, not a linear signal. They didn’t get popular with audio until around 1996 with the Tripath amps.

    Class D amps were used as servo controllers for electric motors.

    I have a solid state Hartke bass amp. It’s probably a Class A/B push pull power amp like a Fender Twin, but without tubes or an output transformer.

    A Class A amp is conducting through all the period of the signal; Class B only for one-half the input period, class C for much less than half the input period. A Class D amplifier operates its output device in a switching manner; the fraction of the time that the device is conducting is adjusted so a pulse width modulation output is obtained from the stage.


    https://www.sweetwater.com/insync/cl...b-guitar-amps/


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  3. #3
    BadHairDayologist Empty Pockets's Avatar
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    Default Re: How to determine class of Amp

    Save yourself the stress and just play amps that sound good.
    green globe burned black by sunn

  4. #4
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    Default Re: How to determine class of Amp

    It is mostly trivial in the long run. Solid-state and tube amps can run pretty much the same for many different topologies. Class D is probably the only exception where a tube amp cannot run in such a way ( or at least hasn't yet ). Class A/B is probably the most popular still, while class D is prominent in newer designs that have come out in the last 10 years. For solid-state amps, the difference is moot I feel, once it clips, it doesn't sound the same anymore; no matter what class it was. Tube amps tend to carry more of a character from the different topologies. Tube amps mostly being either class A or class A/B, tend to sound a particular way and can have another character if cathode or fixed bias. In the long run it comes down to how you play and how the amp responds. If you depend on power amp section breakup, then tube amps are probably the only thing that will work for you. If you like a 100% clean power section, then a solid-state amp can honestly be the best thing going.

  5. #5
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    Default Re: How to determine class of Amp

    Thank you for the responses; looks like I was misinformed on most Solid State amps being class D.

    Definitely agree with the whole "it does not matter if it sounds good" point though; I more curious than using the outcome to determine what I get.
    Last edited by GreatOz; 10-06-2019 at 04:22 PM.

  6. #6
    LoveMachineologist jeremy's Avatar
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    Default Re: How to determine class of Amp

    many modern ss amps are class d but thats a fairly recent occurrence. if your amp is very light, its probably class d.

  7. #7
    Ultimate Tone Slacker NecroPolo's Avatar
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    Default Re: How to determine class of Amp

    I have a snobbish friend. Whenever he says "That's classy" then the class is determined.

    Wihtout opening the case, you can tell it easliy:

    - If it is a ton and it burns tubes frequently, it's class A
    - If it is a ton and burns tubes less frequently, it's class A/B
    - if it is a ton and sounds crap and doesn't burn tubes, it is class B as it became off-biased
    - if it is a ton and snobbish guys tell you it has no class without even being turned on, it is solid state (they don't know it is class A/B really)
    - if it is not a ton it's class D (that is the bastard child of a solid state amp, a switching power supply and a porn star from the late '90s)
    Last edited by NecroPolo; 10-07-2019 at 03:38 PM.

  8. #8
    Glossless SlyFoxx's Avatar
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    Default Re: How to determine class of Amp

    If there's only one power tube, it's class A.

  9. #9
    LoveMachineologist jeremy's Avatar
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    Default Re: How to determine class of Amp

    singled ended class a even!

  10. #10
    Mojo's Minions
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    Default Re: How to determine class of Amp

    Almost any decent guitar amp is either Class A or A/B (push/pull)
    “For me, when everything goes wrong – that’s when adventure starts.” Yvonne Chouinard

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