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Attenuator bypass?!?

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  • Attenuator bypass?!?

    A strange thing happened to me today with my amp and my attenuator. Usually I use an attenuator at home, and sometimes I like to push up the volume for overdrive. And suddenly, it's like the attenuator bypass him... and don't actuate over the amp... I can't regulate the atteunator volume knob, he goes from no sound to a full sound.

    Anybody can explain what happen?

  • #2
    The attenuator might have lost a ground connection. But how could we really know without seeing what's inside the attenuator or having a schematic?
    - Own Opinions Only -

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    • #3
      It's a Harley Benton power attenuator. This is the schematic:

      https://blog.brixit.nl/static/image/hbpa/schematic.jpg

      https://blog.brixit.nl/blog/2016/2/h...-and-teardown/

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      • #4
        I would start with checking all ground connections with an Ohmmeter. Should measure below 0.5 Ohm with a calibrated meter.
        - Own Opinions Only -

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        • #5
          The grounds seems okey.

          I measure the resistance of every input:

          4Ohm:
          lpad min: 8.3R
          lpad max: 16.6R

          8Ohm:
          lpad min: 12.3R
          lpad max: 20.6R

          16Ohm:
          lpad min: 16.3R
          lpad max: 24.8R

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          • #6
            I think that I solved. The switched jack from 16Ohm are always open. The attenuator was always at 16R!!!!

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            • #7
              Seems the "L-pad" (actually a simple power pot) is not properly grounded.
              - Own Opinions Only -

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              • #8
                I replaced the switched jack from 16Ohm, and now I have this readings:

                4Ohm:
                lpad min: 4.2R
                lpad max: 5.7R

                8Ohm:
                lpad min: 8.5R
                lpad max: 9.8R

                16Ohm:
                lpad min:16.3R
                lpad max: 24.4R

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                • #9
                  I disassembled the lpad and it's burned...

                  https://ibb.co/rf9GbrP

                  My amp is a Bassman aa864 50W I can use this Attenuator no?

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