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Gain, what it is, what it isn’t?

Discussion in 'Amp Tech Center' started by peteb, Jan 5, 2019.

  1. peteb

    peteb Friend of Leo's

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    now that Elpico's SPICE test has generally been accepted as a legitimate comparison of gain between two amps


    are we ready to agree that measuring the gain in the pre amp, Vout / Vin is the standard way to measure gain?
     
  2. clintj

    clintj Friend of Leo's

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    No, that still doesn't account for preamp compression limiting how much output voltage signal you can develop, plus that there's a practical upper limit to the PI input signal determined by the ability of the power tube bias circuit or grid stoppers to limit bias drift in Class AB2.

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  3. Lynxtrap

    Lynxtrap Tele-Holic

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    No. You have compared two different amps, and that could be of some theorethical use when designing an amp, had you at least kept all variables as similar as possible.
    The standad way to measuere gain won't be changed by your test, not in this thread and not on any internet forum for that matter.
     
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  4. elpico

    elpico Tele-Afflicted

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    A "standard way" to measure voltage gain that isn't Vout/Vin expressed in dB? Well hot diggity, should I be looking on the ANSI or IEC website for this wild new standard?

    :lol: I'm sorry, I know I'm not helping. I shouldn't do that. You guys got your own thing going on here. Ping me if something specific needs counting again.
     
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  5. clintj

    clintj Friend of Leo's

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    Pete's talking about measuring preamp gain. Up to a point, out/in works great. Until you hit the limit of the last stage to develop voltage swing, anyway. I'm just saying there's cases that that won't work, and if there's an exception to a rule then the rule ceases to be valid for all cases.

    Edit to clarify: think of those guys who dial in Moar Gain to be louder, or stick a boost in front a 5150 on the lead channel. The amp doesn't get louder, it just distorts a little more.

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  6. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    I'm a submissive sycophant who for now bows down to this old-school and potentially heretical (((("theory")))).

    Amplification: voltage ratio V2 / V1 = Vout / Vin, and voltage gain in dB = 20 × log (V2 / V1).
     
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  7. elpico

    elpico Tele-Afflicted

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    How large of a signal the circuit can pass before it clips is a completely different spec than gain. I'm sure everyone here understands that headroom is not infinite. It's not necessary to abandon all hope of quantifying a circuit's gain simply because headroom isn't infinite. You can still make a meaningful measurement of how much gain a circuit is capable of producing simply by using an appropriately sized input signal to avoid running out of headroom. Quantifying how large of a signal a circuit can pass would be separate test on your spec sheet. No need to mix them up.

    Of course you can use the circuit in a way that gives less gain than the maximum the circuit is capable of, we almost always choose to do exactly that, but a user choice or combination of knob settings is not an intrinsic property of the circuit.
     
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  8. Old Tele man

    Old Tele man Friend of Leo's

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    AMPLIFICATION is when output is a faithful reproduction of the input, usually (but not always) larger in magnitude.

    CLIPPING is when sinusoidal input is driven into becoming a squarewave output (bounded by saturation and cutoff) due to creation of odd harmonics.
     
    Last edited: Jan 17, 2019
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  9. Lynxtrap

    Lynxtrap Tele-Holic

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    I was answering this question (my bolding): "are we ready to agree that measuring the gain in the pre amp, Vout / Vin is the standard way to measure gain?"
    Go see if you can find that standard.

    EDIT: I see now that I might have misinterpreted the question. Perhaps it was ment as "is Vout/Vin the standard way to measure gain in a preamp".
    In that case the answer would of course be "yes" or mostly.

    And still, you can't compare gain in two preamps with different settings of the EQ.
     
    Last edited: Jan 17, 2019
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  10. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    NO.

    Let me explain it another way: ****NO****!

    It is only a way to measure gain in the PREAMP. It does not measure gain in the ENTIRE amp. You're using the word "gain" like it's one thing - and that's NOT correct, which has been repeated2 by several people about a dozen times in this endless thread.

    If you want "agreement" you HAVE to define your terms.

    Not necessarily. It would depend on the individual circuits and...in the case of tube amplifiers...which tubes AND which sections (in some cases) supply part of the gain.

    Compared the HRD clean channel preamp? Or the total amplifier gain using only the clean channel? "...to the Bassman *what*? BAssman TOTAL gain, or preamp gain, or the gain of ONE stage?

    DEFINE YOUR TERMS.

    :lol::lol::lol::lol::lol:..."vintage features?:lol::lol::lol::lol::lol:

    Now what in the world are you talking about? PLEASE - find us ANY accepted, standardized, in current use definition of "vintage features".

    AND in the proper context.

    Pete, besides all these "standards" you have decided are accepted - and they are NOT - and the lack of precisely defining what the heck you are talking about -

    Why do you do "this":


    Type all your posts in single sentences.


    And have HUGE line breaks between them?



    Sometimes even using 4-5 line breaks between them - like this?



    Is it in hopes of starting a thread that will take up more pages than any other thread on the forum?




    Or do you write notes on your screen with a Sharpie? You know - the big pen they give you.






    To avoid you handling sharp objects.







    :D
     
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