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Ampeg Ba 210 SP High EQ mod?

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  • Ampeg Ba 210 SP High EQ mod?

    I have an Ampeg in here that a friend dropped out. He says two different bass players have complained that the high eq doesnt do anything. I plugged it in, and I can tell that it works, however it does seem a little bit high in the frequency spectrum to be effective. Looking at the schematic, can I change C47 to another value to reach down lower into the mid range? Can I also change the pot value to 100k at P8 for more range on the sweep?Preamp.pdf

  • #2
    Changing the pot value also changes the gain. That is an active EQ stage, the pot is part of the feedback around that op amp. Nothing says you can't try a different value pot in there for science. You can always change a cap value in a tone stack. Up to you if you like the results.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      Originally posted by achase4u View Post
      I have an Ampeg in here that a friend dropped out. He says two different bass players have complained that the high eq doesnt do anything.
      I suspect you have a broken pot , cracked track or solder, broken C47, because normally that treble control does work.
      FIRST repair it, THEN if necessary mod it.
      As is, it works at correct 1500Hz and higher, doubling C47 will make it work from 800Hz up, but again, I suspect now itīs working with some parasitic capacitance (very low value) so the perceived effect is very weak.
      I plugged it in, and I can tell that it works, however it does seem a little bit high in the frequency spectrum to be effective. Looking
      Keep the pot as is, unless itīs broken, in that case you might use 100k, but any change will be small.
      Juan Manuel Fahey

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      • #4
        Originally posted by Enzo View Post
        Changing the pot value also changes the gain. That is an active EQ stage, the pot is part of the feedback around that op amp. Nothing says you can't try a different value pot in there for science. You can always change a cap value in a tone stack. Up to you if you like the results.
        Cool. Thanks!

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        • #5
          Originally posted by J M Fahey View Post
          I suspect you have a broken pot , cracked track or solder, broken C47, because normally that treble control does work.
          FIRST repair it, THEN if necessary mod it.
          As is, it works at correct 1500Hz and higher, doubling C47 will make it work from 800Hz up, but again, I suspect now itīs working with some parasitic capacitance (very low value) so the perceived effect is very weak.
          I plugged it in, and I can tell that it works, however it does seem a little bit high in the frequency spectrum to be effective. Looking
          Keep the pot as is, unless itīs broken, in that case you might use 100k, but any change will be small.
          Interesting. I will take a stab at fixing it then. Replacing c47 and the pot. That's how I have to go about it, because I have no oscilloscope yet. Relatively cheap to find out. Thanks!

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