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Allen MOS 1105 8' Gedackt

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  • Allen MOS 1105 8' Gedackt

    I'm well aware that the Gedackt typically is very "chiffy." However (maybe this is the first time I've noticed, or a new issue), yesterday I noticed an almost "click" more than "chiff" with the Gedackt. Knowing roughly how the MOS system is designed, I'm fairly certain is near to impossible for something to happen to one voice and not effect all others on the same computer.

    There was an audible "hiss" with the Gedackt for about the first 10 or so notes before the more "click" type sound with each key depressed.

    Thoughts?
    Allen MOS 1105 (1982)
    Allen ADC 5000 (1985) w/ MDS Expander II (drawer unit)
    Henry Reinich Pipe 2m/29ranks (1908)

  • #2
    Originally posted by organman95 View Post
    There was an audible "hiss" with the Gedackt for about the first 10 or so notes before the more "click" type sound with each key depressed.
    Not having the slightest clue, but having a few Allens, it feels to me like something in the electrical chain that produces the articulation has gone bad--perhaps a capacitor? The hiss almost sounds like what was happening with one of my ADC amplifiers before it finally stopped working.

    Is it intermittent, or is this a one-time event? One-time event: Something's gone bad and needs to be replaced. Intermittent: A loose disconnection, humidity, or something like that.

    Again, these are only my non-professional, first-time, gut-reaction impressions. Now, we wait until the real professionals weigh in.

    Michael
    Way too many organs to list, but I do have 5 Allens:
    • MOS-2 Model 505-B / ADC-4300-DK / ADC-5400 / ADC-6000 (Symphony) / ADC-8000DKC
    • Lowrey Heritage (DSO-1)
    • 11 Pump Organs, 1 Pipe Organ & 7 Pianos

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    • #3
      One time, hopefully. Didn't notice it today during a funeral.
      Allen MOS 1105 (1982)
      Allen ADC 5000 (1985) w/ MDS Expander II (drawer unit)
      Henry Reinich Pipe 2m/29ranks (1908)

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      • #4
        The chiff on the Gedeckt of the 1105 is almost certainly a "custom" effect rather than a standard MOS sound. One of the EPROMs on one of the primary MOS boards (A or B) produces the chiff, so it's possible that the EPROM is not well seated in the socket. This could produce a problem similar to an issue that appeared on our MDS organ at church, a hiss or distortion-type sound related to the articulation effects produced by a specific EPROM on a specific board.

        One thing we often do when servicing a MOS-2 Allen (or even ADC or MDS) is the pull EPROMs from sockets, wipe the legs of the EPROMs with a Q-tip, applying a super-thin coat of Vaseline with the Q-tip, then re-insert them carefully, making sure not to bend or roll any pins, and observing the correct orientation by the notches on one end of the chip and the socket.

        Of course, it's always possible for the problem to be in an amp or any other part of the system, but if it is definitely related to the chiff on that one stop only, it is probably the EPROM or perhaps even a malfunction of the MOS board itself.
        John
        ----------
        *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

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