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Gain, what it is, what it isn’t?

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

  1. Lynxtrap

    Lynxtrap Tele-Holic

    558
    Feb 29, 2016
    EU
    Not exactly. The pentodes are a reason this amp has "high over-all gain" and gives "quite a few watts of power from a standard magnetic pickup unit". It's all there in the text.
     
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  2. LeicaBoss

    LeicaBoss Tele-Meister Gold Supporter

    420
    Oct 16, 2015
    New Jersey
    1. Are you using the book definition of the colloquial definition of gain? Big difference

    2. How are you mesuring Watts? When you're testing wattage with a sine wave at one frequen, RMS - that's a pretty wide range of received outage and peak "gain" that can result from a nominally 15 watt amp

    3. The other thing is how you actually measure gain, in the context of compression. A given stage might amplify a signal say 5x but that is compressed to a max of 3x by the input of the next stage or whatever, whacking off part of the signal. That may result in two amps with the same net gain but one having much higher total gain in all the stages.

    4. I realize I just typed "whacking off the signal"
     
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  3. Lynxtrap

    Lynxtrap Tele-Holic

    558
    Feb 29, 2016
    EU
    3. It seems to have been established in the thread that we should be talking about net gain input to output, with a set limit for THD.
     
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  4. LeicaBoss

    LeicaBoss Tele-Meister Gold Supporter

    420
    Oct 16, 2015
    New Jersey
    Maybe that definition doesn't really address what most people think of as "high gain" - which really should be called "highly compressed"
     
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  5. mrmousey

    mrmousey Tele-Meister

    Age:
    68
    326
    Aug 6, 2016
    Largo, Fl
    What was the question ???

    ( This whole thing is so confusing )
     
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  6. Lynxtrap

    Lynxtrap Tele-Holic

    558
    Feb 29, 2016
    EU
    I get a feeling you haven't read the whole thread...? I think we have come to the end of the road with the "what most people think" angle.
     
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  7. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia


    I am sorry, did not mean to offend.
     
  8. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia


    Thank you for your clear answer.



    Did you read my post(s) that similar amps with different output impedances are going to measure as having much different gains when they are essentially the same amp.


    Example, blackface pro amp into an 8 ohm load versus a blackface concert amp into a 2 ohm load.






    You have to admit that I have thought the problem all of the way through to the end. I know what I’m talking about.
     
  9. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia


    I’m sorry you feel that way.
     
    Last edited: Jan 12, 2019
  10. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia



    I don’t disagree with anything written here. I do read that if the power out and the load are fixed the gain will be the same.



    Is that your conclusion? Your answer to the original question. I accept that, and I accept that as a good answer.
     
  11. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia


    I am specifically talking about a single speaker 8 ohm load versus a 2 ohm load for a similar amp. Fender often connected four 8 ohm speakers parallel parellel for a 2 ohm load as in the tweed bassman and the super reverb and I assume the black face concert.




    And I’m not talking about the sound of the speakers or the cabs I’m strictly taking about the effect the output load has on the speaker voltage.



    It’s because


    50 Watts has to equal v*v/8 = v*v/2








    The one v and the other v obviously cannot be the same, or even close.
     
  12. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia
  13. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia




    Thank you Silverface, I like your answer.
     
  14. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia

    I totally agree with this.




    I’m surprised that there is no documented method to compare gain between two amps, beyond Vout/Vin.






    When I started this thread I did it without the benefit of researching how gain is compared between two amps. I was under the impression that if I did look it up, I was very certain that the gain in the pre amp would be the number one way to do it.


    So then I did look it up. There is no standard that I could find other than Vout/Vin.
     
  15. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia


    That’s interesting Bendyha. The first thing I think when they say high gain is by what standards are taking about. It certainly can’t be high gain by our current standards.


    It has one pre amp tube? That’s not going to be very gainy.


    I like the simplicity that the volume control serves as the the first grid leak.


    Is the tone control between the power tube and the OT? Why not?
     
  16. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia

    Do you know what those high values are?


    Thanks
     
  17. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia


    I’m using both definitions of gain and I’d like for them to align.


    An amp that sounds high gain should measure high gain


    And an amp that sounds low gain should measure low gain.



    Why wouldn’t they?



    I’m not sure that I understand question 2. I’m famiar with measuring signal voltages at different points of different amps, both fixed frequency and full frequency. I’ve done it enough that I know what to expect on any of the old fender amps. Fortunately for this excercise I don’t have to measure anything. It’s already been done by the standard ways.




    15 W = v*v/8


    The voltage on the speaker needs to be 10.95 RMS, 1K frequency at or below 5% THD.
     
    Last edited: Jan 12, 2019
  18. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia


    Agreed, that’s all part of it
     
  19. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia


    It’s the whole idea that high gain is low gain




    I’m trying to fix all that. Having high gain be high gain.




    An amp that sounds high gain should measure high gain.
     
  20. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia
    +1
     
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