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Praeludium 111

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  • Praeludium 111

    Hi, I am new here. I have a spendid Praeludium 111 and for some 10 years it has been great. It still works extremely well, in all aspects, with two speaker cabinets to the main outputs. However now, every time I turn it on, play any manual for a minute or so the volume decreases dramatically for another minute or so and then recovers to full and normal volume for as long as it is used. Each time it is switched on the same thing happens.
    I wondered if anyone has any ideas please ?
    Rodney
    Last edited by myorgan; 09-15-2022, 05:01 PM. Reason: Moved to more relevant thread for more views.

  • #2
    Not directly familiar with the Praeludium, but have had quite a bit of experience working on an Ahlborn SL-250 and, in doing so, I experienced a variety of weird symptoms, so I'll start with a few diagnostic type questions:

    Is the symptom also evident through headphones?
    Does the master volume setting have any effect on the symptom?
    Do the Great and Pedal volume slider settings have any effect on the symptom?
    Do you use the swell pedal in that first minute? If not, does using/moving that pedal have any effect of the symptom?
    Does the symptom occur regardless of stop settings?
    -------

    Hammond M-102 #21000.
    Leslie 147 #F7453.
    Hammond S-6 #72421

    Comment


    • Silver Spirit
      Silver Spirit commented
      Editing a comment
      Hi, thank you for your interest.
      Master volume, Great & pedal sliders, and swell pedals all work during the "quiet period", increasing volume as expected. However upon returning them the "quiet period" continues until the same time passes and sound levels are restored. Likewise whichever stops or manuals are selected the same thing happens.
      Interestingly this does not happen with headphones ! I have assumed therefore that the output board is faulty somewhere, but I have no idea where in the system the headphone connections are made.

  • #3
    Originally posted by Silver Spirit View Post
    Interestingly this does not happen with headphones !
    This may indicate that there's a fault with the "de-thumping" relays which delay connection of the amplifier output stage to the speakers to eliminate the thump that can occur when a solid state amplifier is switched on. These can also operate if there's a problem with the stability of the DC voltage rail.
    -------

    Hammond M-102 #21000.
    Leslie 147 #F7453.
    Hammond S-6 #72421

    Comment


    • Silver Spirit
      Silver Spirit commented
      Editing a comment
      Good morning, I will look into that possibility, and assume the relays are in the amp/speaker cabinets, which of course are remote on the P111.
      I only run two amp/speakers but could connect only to one at a time to check it out.
      Thanks for that, I'll let you know in due course.

    • gtc
      gtc commented
      Editing a comment
      I would expect those relays to be inside the organ and maybe on the power supply board, if not the audio output board.

      In the case of the SL-250, they can be heard releasing (clicking off) about 15 seconds after power is switched on.

  • #4
    Hello again. Well, success I hope. I never hear a speaker thump when turning on or off, however on your advise I examined the power supply board. Six major transistors, i.e., ones with heat sinks attached, one of which runs in excess of 70C. Whilst I didn't consider that a problem for a transistor I thought it odd that the others were constantly no more than 30+c. So I have replaced them all, cleaned all accessible contacts and fitted a small ( computer style ) cooling fan to run across the board, with grill covered air holes in the back panel at each side. All the resistors now test below 35c, and the organ performs well every time I use it. So I am thinking 30 plus year old electronic components were worth an update.
    I also removed the CPU board, checked the contacts and replaced the battery which was just beginning to show signs of leakage, although not in a position to harm anything.
    I am therefore very pleased with the outcome and very grateful for time and support. Thank you very much. Rodney

    Comment


    • #5
      Glad to hear that you have solved the problem. Happy to have been of assistance.

      Just to be clear, you should never hear a thump when powering up. It's the job of the de-thump relays to suppress that noise by holding the speakers disconnected for 15 seconds or so to allow the large capacitors to fully charge before the speakers are connected into circuit. In the SL-250 you can hear the small click (not thump) of those relays operating after the 15 second time period has elapsed.

      Originally posted by Silver Spirit View Post
      and replaced the battery which was just beginning to show signs of leakage, although not in a position to harm anything.
      Good that you attended to the battery. In order to avert future disaster and to make battery replacement much easier, it is usually recommended to relocate the battery off the CPU board. I note that Ahlborn themselves did that with the AG2200.


      -------

      Hammond M-102 #21000.
      Leslie 147 #F7453.
      Hammond S-6 #72421

      Comment

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