What would the effect be if...

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by BluePat, Feb 24, 2009.

  1. BluePat

    BluePat Member

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    I trace the purple wire that runs from the presence control, through the circuit board to the 8 ohm output lug, and soldered it to the 16 ohm one? Would there be an increase/decrease in gain, or an adjustment in tonal range?

    I understand there is a relationship between NFB and the various OT taps with respect to overall gain, but how does the presence control fit in to this relationship?

    Pat
     
  2. elkym

    elkym Member

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    Ooo, technical stuff... I'd like an answer to this one, too.
     
  3. tybone

    tybone Member

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    The Presence control sounds like it is just a variable resistor in series with the NFB loop. The VR just lets you adjust how much of the output signal is fed back. So if you changed the tap from 8 ohms to 16 you will Increase NFB and as a result Reduce the overall gain of the amp.

    My story and sticking to it.
     
  4. hamfist

    hamfist Member

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    Yup, changing the NFB to a higher ohm lug will increase the NFB, which will slightly reduce gain, and tighten up the whole amp a bit.
     
  5. RussB

    RussB low rent hobbyist Silver Supporting Member

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  6. hasserl

    hasserl Member

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  7. CopperTop

    CopperTop Member

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    Yeah same thing here
     
  8. RussB

    RussB low rent hobbyist Silver Supporting Member

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    Sorry about that webpage. It seems to dissappear some cyberspace every now and again. Too bad, because it describes the individual sections of a Marshall circuit, and their tonal variations and suggested mods
     

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