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Two problems with my A 100--I could use some help

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  • Two problems with my A 100--I could use some help

    I have been working with my son (who is an electrical and production engineer) on my Hammond. He rebuilt the console amp and rewired speakers, devised a Leslie switch kit, replaced some tubes and some capacitors, cleaned up the AC line and grounded the organ, created a line out to effects processor and amp, rebuilt the crossovers in my Leslies and we also did a lot of cosmetic work. The organ sounds better than I ever remember it sounding except for two things:

    On E and D sharp (almost entirely only on the middle C octave) there is a strange whistle sound kind of "motor boating" sound above the note. It is not wildly pronounced--impossible to hear in the playing of individual note, present but subtle in held chords but pretty apparent if the single note is held. Much less apparent when only the lower drawbars are in use-- much more obvious with higher ones, especially the last two white ones. Unaffected by chorus/vibrato or percussion being on or off. Although the sound is slightly more obvious when those are off.

    Then there is a sound similar to when you adjust volume on the pre-amp and the pot is a little dirty--kind of a typical electronic "scratchy" sound --or maybe even a bad speaker sound like a small tear. I am not too worried about this one as it is intermittent and i am sure my son can track it down. The sound might be in one of the speakers we installed--we used 12's from a PR-40; they looked OK but could fail quickly. Those even I can test.

    The whistle is more bothersome and harder for my son to maybe diagnose in that he is no Hammond tech, but does understand schematics and would certainly understand fairly technical explanations that I would not be able to interpret.

    And the last question is why the Leslies cross over at 800 rather than, say 1200, to take some strain of the fairly delicate horns. Should the Leslie as a unit be 8 pr 16 ohms? I have 2 45's and 1 22H

    Thanks for any help in advance!


  • #2
    First of all, if your son really has done as much as you say he's done, then he would greatly benefit from a thorough reading of the Hammond Service Manual. It's laid out in a way that a non-musician can understand, and even provides explicit advice for how technicians should troubleshoot common issues.

    That being said, it sounds like a lot of things may have changed in this organ, and there are too many variables to fully understand whether the issue you've described is directly related to the work he's done or not.

    My off-the-cuff diagnosis of that issue is tonewheel flutter. Play the affected tone, and pull only one drawbar out at a time and listen. Which notes, of which drawbars sound this way? If you can provide an audio recording, this may also help us.

    The "dirty pot" sound could be a lot of things, but most common issues are dirty or loose tube sockets, or a dirty tone control pot. He should follow the advice in "SECTIONALIZING TROUBLE" in the Hammond Service Manual. Divide and conquer.

    My name is not Don Leslie. I did not design the thing. However, I can tell you the spec crossover point is 800 Hz, and the Leslie speaker drivers are 16 ohms for all of the common tube models. (including the 45 and 22H). 16 ohm speakers, and a crossover designed around 16 ohms. If you're worried about the horn diaphragm being blown, then don't dime your amp and don't play 888888888 and full volume so much. Or... replace the stock V21 driver with something that can handle more power.


    • #3
      Thank You. I did find the Hammond Service manual link. My son did a lot of stuff he is familiar with, like amps, speakers and crossovers but nothing with the tone wheel generator. More importantly I found a lot of stuff on the tone wheel generator flutter in another thread, some of it looked really useful. The flutter is an old thing; and the static sound is actually less than it used to be. I think you are very likely right about the tone control pot. So again, thanks. Just have to figure where those notes are on the TWG, because the problem is entirely limited to them.



      • #4
        After you have identified the tones involved, if they are between 37 and 48, check out TSB16 which adds RC filtering to those tones. You may or may not have these installed.



        • #5
          Thank you. I think I understand.