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Hammond B200 Annoying Loud Buzz!

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  • Hammond B200 Annoying Loud Buzz!

    Hi all!

    Earlier this year I managed to fix up a Hammond B200 (which I'm extremely proud of; my first organ!) All was well until one morning I plugged it into my guitar amp (still fixing up my Leslie HL822) when it developed a loud buzz.

    The buzz stays the same volume regardless of the volume of the organ, and the actual organ sound and functions aren't affected at all... There is also a change in the buzzing if I play with the 1/4" jack lead going into the back of it.

    I've attached an MP3 of the sound if it helps!

    This makes me think it might be a grounding issue, somewhere on the output board. I pulled out the output PCB but couldn't see anything obviously wrong.. does anyone have ideas? I must admit grounding/hums/buzzes etc. always stump me. It's a shame because I absolutely love this thing and was looking forward to recording it on some of my own music. Cheers!
    Attached Files

  • #2
    Apologies for the bump, but does no one have even the slightest inkling where I can start with this?

    I've already recapped both the power and output boards so I can't see how they're the problem. All I hear is buzz!

    Comment


    • #3
      I'm not an analog electronics expert, so JMO/YMMV with no warranty. If you have an oscilloscope and schematics, I'd try tracing the problem back. A loud buzz should show up nicely on the 'scope. If it's from 60 Hz you can trigger the 'scope with the line frequency and get a stable display. Start at the output and walk back through the schematic until the buzz is no longer visible. That should narrow down what area has the problem.

      As always, observe the electrical safety precautions in the sticky and it's a good idea to have a grounding wrist strap to prevent zapping circuit inputs.

      Comment


      • #4
        Sounds to me like you have a bad ground connection between the organ and the guitar amp. So that could be 1) at the output of the organ, 2) at the input of the amp, or 3) in the cable itself. To troubleshoot, try a different cable and/or amp. Odds of success if you change both is 67%. But if you change both and the hum is still there, then the problem is at the output of the organ, so now you're at 100% and you know where to troubleshoot. The audio clip that you sent sounds much more like an input problem (including the output connection at the organ) than an output problem (power amp or power supply). Translated: cheap and easy to find and fix. Does the organ have a headphone jack? Can you hear the buzz there when the amp is not connected?

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        • #5
          Before you do anything, try inverting one of the mains plugs. I'm assuming that your organ has a two prong plug. I'm also going to assume that your guitar amp has a three prong plug. So turn the organ plug upside down.

          Comment


          • #6
            I know I already posted this, maybe I didn't hit the post button ..

            Please don't ever wear a grounding wrist strap when working on these kinds of things. You should be insulated from ground when working on anything live. If there are MOSFETs subject to zapping, only worry about them when the power is off. And then, momentarily ground yourself by touching something grounded. And still don't wear a wrist strap: or finding a charged capacitor could ruin your day.

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            • #7
              Thanks Hurdy Gurdy. I'll try a different amp and cable as a first check.

              I've listened through headphones at the headphone jack and whilst there is still a buzz it is drastically quieter than through the main 'mix' output jack!

              If there is a difference like that it should suggest the problem is not in the power supply at all, correct?

              Comment


              • #8
                Correct. If headphone sound is OK, power supply is innocent.

                Comment


                • #9
                  Hallelujah! It works! Thanks Hurdy Gurdy and others for the help.

                  I replaced a load of tantalum drop caps (heard they go bad) and a couple of the IC’s, as well as reflowing a load of solder joints. The buzz has almost completely gone.

                  I’m now having distortion problems when the volume pot is turned up. I don’t remember having this before. Perhaps I should change more caps and a transistor or too. Organ repairs are never ending it seems!!!!! The end seems to be in sight though.

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