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Rodgers 840 involuntary Unda Maris problem

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  • Rodgers 840 involuntary Unda Maris problem

    Kind of a cutesy name for the problem, but it's been driving me crazy.

    We tried tuning the beast. It has 3 oscillator sections: notes 1-85, then something called "ensemble", and then a set of celeste generators.

    We figured the first to tune is the set of 85 notes: we used the 8' Bourdon on the Great. That is where the problem appeared; not only on that setting but just about everything has a "celeste" to it , more like an Unda Maris. Yet on some stops it sounds like Gedackt 8" on the Swell it is perfectly solid. I have 2 short videos to demonstrate both cases, but too large a file to attach here.

    Any idea where to start looking?
    Thanks in advance!

    John
    Can't play an note but love all things "organ" Responsible for 2/10 Wurli pipe organ, Allen 3160(wife's), Allen LL324, Allen GW319EX, ADC4600, many others. E-organ shop to fund free organ lessons for kids.

  • #2
    A couple of things come to mind, offhand:

    (1) You MIGHT be hearing the "Main Chorus" effect on all the stops as you are trying to tune. It is adjustable, and the adjusting pots are shown on the voicing chart, but if it happens to be way over-boosted, you may be hearing a big annoying wobble on all the stops, which could well be described as an unwanted "celeste"! So find the piston or tab that turns OFF the Main Chorus and see if the trouble goes away.

    (2) The problem may go away when you finish tuning all the oscillators. The "main" set provides the pitches for many of the stops throughout their entire range, as it goes all the way from the bottom of a 32' stop to the to of a 2' stop.

    The "ensemble" rank is shorter and provides a set of alternative pitch sources for just a few octaves, maybe about five in the center of the organ's pitch range.

    Since some stops use only the main rank, some use only the ensemble rank, and some use part of each rank, you need to have them all tuned accurately or else you may well get some beats going on when you don't expect them. The ensemble rank can function almost like a secondary celeste rank if it is not tuned to match the main rank.

    So be sure to get them all tuned before you look for any other malfunction.

    Best I recall, if the 840 is like the 890 I used to own, the great principal keyer draws all its pitches from the main rank, so you can use its various stops to tune that rank, and use the 16' and 32' pedal stops to tune the bottom two octaves of that rank.

    The ensemble rank can probably be tuned using the Swell Viola Pomposa. And of course the celeste rank will be tuned using the Swell Viola Celeste.

    If I am remembering right, the Erzhaler Celeste on the choir does not actually use the celeste rank though. It gets its wobbling from a "fake celeste" bucket brigade device on the preamp board.
    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!

    https://www.facebook.com/pages/Birds...97551893588434

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    • #3
      Very interesting, gives me some things to try. I was warned earlier about oscillators 24 and 36, and not to touch them after setting them initially. (here, and on the schematic) Apparently there is some phase lock loop thing going on. I 'm trying to understand it. Does that help to keep the tuning locked in?
      Can't play an note but love all things "organ" Responsible for 2/10 Wurli pipe organ, Allen 3160(wife's), Allen LL324, Allen GW319EX, ADC4600, many others. E-organ shop to fund free organ lessons for kids.

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      • #4
        Definitely need to use the "Main Chorus Off" piston to disable the chorus effect, especially when tuning.

        There may also be a "jitter" circuit to add a random noise to the tuning--different from "air puff"; not included in the original 840 design, but optionally added by dealers. If it has this circuit, it needs to be disabled for tuning. If added it would likely be a small circuit board installed near the oscillators.

        Make sure the tuning switch is "off" especially when tuning--this is used for tuning the oscillators to match pipes. Push in the tuning knob to turn it off, pull out to make the tuning variable.

        The celeste oscillators are used for the Swell Viola Celeste, Swell Flute Celeste, and Choir/Positiv Erzahler Celeste. All the celestes voices on the 840 are true celestes, not the phase shift approach that JBird mentions--that was used on some of the lower end models of this series, but not the 840.

        So multiple possibilities for erroneous tuning, but none are indications of any malfunction, just selections/options that need to be attended to when tuning.

        The "Phase Lock Loop" is to keep the LC oscillators and RC oscillator tracking to each other when the tuning knob is pulled out to tune the pipes--the PLL creates two different correction voltages to shift the overall tuning per the knob adjustment. When the knob is pushed in, variable tuning is off, and the PLL doesn't do anything.

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        • #5
          It's like having a library at your finger tips! THANKS Toodles and JBird for the priceless info. I can't wait until I can get back to this tomorrow. The thing is in such perfect shape, I find it hard to believe it has an actual defect. Now I am beginning to think it is the "operator!" ;-)
          Can't play an note but love all things "organ" Responsible for 2/10 Wurli pipe organ, Allen 3160(wife's), Allen LL324, Allen GW319EX, ADC4600, many others. E-organ shop to fund free organ lessons for kids.

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          • #6
            The Main Chorus on the 840 is labelled "Main Chorus", not "Main Chorus Off", but it comes on by default. So make sure the piston is un-lit.

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            • #7
              Also, note that the Swell Vox Humana always has tremulant on.

              I checked the schematic diagrams and division of the Main vs. Ensemble Oscillators is as follows:

              Notes 001 through 012 (i.e., 32 ft. pitches and 16 ft pitches) as well as notes 62 trough 85 of all voices come from the main. The following is for notes 1 through 61 only:

              Main Oscillators: Choir Principal/Erzahler, Krummhorn, Swell Pulse Voices (Gamba, Oboe, and Festival Trumpet), Great Flute, Swell Principal.

              Ensemble Oscillators: Swell Trompette, Swell Flute, Great Principal and Choir Flute.

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              • #8
                Glad you posted that list, toodles. I had told him just the opposite. On the 890 I used to have, it was the other way around, but of course that was an entirely different model.

                I've gone out to service one of those now and then and found that "Main Chorus" was set to such a depth that it really did sound like Unda Maris -- made the organ swim so that it nearly made me seasick! You sure can't tune the oscillators with that turned on, but of course the effect can be adjusted for both speed and depth, independently on each rank, I think.
                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!

                https://www.facebook.com/pages/Birds...97551893588434

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                • #9
                  Generally the trick to setting these phase shift effects is to set them at moderate levels. I guess some organists want to "swim" in the chorus, but since the 840 & 890 both have 3 separate celeste, with sub & super couplers I don't see the need.

                  I, too, was surprised that the 840 has the Gt Principal running off the ensemble oscillators when I looked at the chart. But it is mounted on the same rack with the ensemble oscillators, so I suppose it makes some sense to keep wires shorter.

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                  • #10
                    That "swimming" effect can actually be nice for certain sounds and certain situations. I can imagine that a fairly decent fake celeste could be created with it adjusted just right, and of course that's more or less what Rodgers did on the 740, with it's "Celeste" tab.

                    The old Baldwin model 630 had its "Tone Expander" circuit which was basically the same effect but more complicated. As I recall, a set of filters divided the audio stream into three frequency ranges, low, mid, and high, and sent each portion of the stream into a separate phase-shifter circuit. The low frequencies got a very slow chorus, the mid frequencies a little faster, and the highs even faster. The result was either a nice rich ensemble effect (in the "chorus" position) or a quite convincing celeste in the "celeste" switch position. I don't know why other organ builders never picked up that idea, it worked so beautifully. Made those very plain vanilla analogs sound much richer. Even Allen's MOS organs could've benefited from adding on something like that. I guess they were too proud to copy Baldwin!
                    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!

                    https://www.facebook.com/pages/Birds...97551893588434

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                    • #11
                      On Wednesday I got back to it, and looked hard for a piston related the "Chorus". - Nada!
                      BUT, with the General tabs, there was indeed one "Chorus Off". That did the trick, the 'swimming' was gone. We were now able to tune everything in short order, thanks to the info give here regarding which ranks were on which oscillator board.
                      So, why would that tab be Chorus OFF instead of Chorus ON? Seems backwards to me. Wouldn't the organist rather have it the other way? Now it always comes on by default.
                      John
                      Can't play an note but love all things "organ" Responsible for 2/10 Wurli pipe organ, Allen 3160(wife's), Allen LL324, Allen GW319EX, ADC4600, many others. E-organ shop to fund free organ lessons for kids.

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                      • #12
                        When Rodgers first introduced this series of organs, the "Main Chorus" was off by default; later models had it on by default. I can only suspect that they made the change at the request of dealers--both Allen and Rodgers were very influenced by dealers' input. The advantage of having it come on automatically is that it gives a bigger organ sound.

                        Allen did a similar thing when they introduced "Romantic Tuning"--initially it was off--i.e., the tab said "Romantic Tuning"--later models hand "Romantic Tuning Off". Maybe it was a sign of the times??

                        By the way, I don't think this is a model 840--the 840 is 3 manuals and has LED tabs. To my knowledge--the general tabs are suppose to be Main Off, Antiphonal On, Pipes Off, Ancillary On. All the other "general" controls are on lighted pistons. Maybe it is an 830? 2-manual with lighted drawknobs. It is worth verifying the model number, as there are some electronic differences, such as the Main Chorus control.
                        Last edited by toodles; 12-02-2018, 02:45 PM.

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                        • #13
                          Using the layout diagram showing the control pots on the output preamp, one can find and turn down the depth of the chorus effect (which is separately adjusted for each of the primary choruses in each division). When the depth is turned down all the way, the chorus of course disappears, regardless of the tab setting. But a useful strategy would be to set the depth so that it is audible but not bothersome. It might also help to increase the speed very slightly so it doesn't sound so much like a pitch bend going on.

                          Getting these adjusted just right is very much a matter of taste and opinion. Personally, I'd want only a tiny bit of it. But I understand why Rodgers put this on their organs. It does help to compensate for the lack of pitch variation among the ranks, since so many are drawn from the same oscillators.

                          If you turn it completely off you of course won't have to bother with it at all in the future. But any small benefit from it will then be lost. I'd at least play around with the controls first to see if it can be set to a pleasing depth and speed that doesn't sound like an unwanted celeste. Then when you really need a dead-on unwavering pitch instead of a rich and slightly wobbly ensemble, you can turn it off with the tab.
                          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!

                          https://www.facebook.com/pages/Birds...97551893588434

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