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  • madison divinity "shape"

    madison divinity 2
    One of the complaints on this amp was that the shape control didn't do much, and I haven't found a scematic that shows it, it has a b25k attached to both sides R160 3.3k (schem I have shows 2.2k.
    the control did a little bit but only from 9 to 10 (10 being full cw)
    does anyone know what this all should be in this amp, or have any ideas on how to improve it?
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  • #2
    R160 (2k2) and C41 (.1uF) located in the NFB circuit (R102; C64) and form a fixed presence boost that is controlled by R160 (2k2).
    Carefully decrease R160 gives more presence boost. If you are not satisfied with the presence work, check (replace) C41; R102; C64.
    Who does not know and knows that he does not know - teach him Confucius)
    Who knows and does not know that he knows - wake him Confucius)

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    • #3
      I have sent the amp back to it's owner since posting this thread, it had a 25k pot across r160, it was dropping r160 to 0 but only between 9-10 on the pot, I added a 3.3k resistor across the pot since I didn't have any to try and he was in a hurry, adding that seemed to make it adjust from 2.2k to 0 across the whole range instead of just between 9-10 as before, I'm waiting to hear from the owner to see if he's satisfied with this, along with the fix to the effecs loop, the tube bias being set way too low, and bad cables for the foot switch that were all fixed.

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      • #4
        Originally posted by boog View Post
        I have sent the amp back to it's owner since posting this thread, it had a 25k pot across r160, it was dropping r160 to 0 but only between 9-10 on the pot, I added a 3.3k resistor across the pot since I didn't have any to try and he was in a hurry, adding that seemed to make it adjust from 2.2k to 0 across the whole range instead of just between 9-10 as before, I'm waiting to hear from the owner to see if he's satisfied with this, along with the fix to the effecs loop, the tube bias being set way too low, and bad cables for the foot switch that were all fixed.
        I had recently thought to do the same on one of my own amps, that is change from a 50k precense pot to a 5k pot, as the last 5k are where the noticable changes are in precense on my amp. You might also see if changing the filtering of the precense signal is what your customer is after, or boost the amount of negative feedback overall. If you add more feedback and tailor the frequencies by adding more bass (leaving the mids and treble frequencies uncancelled) it will sound more dramatic, even if it is not the classic style of what a presence control is thought sound like.

        Some others can chime in on what values could make that happen. I am a novice, and usually get the job done by trial and error ! not generally the best way to proceed.
        " Things change, not always for the better. " - Leo_Gnardo

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