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Rodgers 925 Oscillator Noise on Reverb Channel

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  • Rodgers 925 Oscillator Noise on Reverb Channel

    My Rodgers 925 (from about 1982) has an issue with excessive oscillator noise, especially on the Choir/Positiv, whenever the reverb pot is turned up. Hard to describe what it sounds like it, but it's driving me nuts!

    Any ideas?
    Last edited by TubaMirabilis123; 12-09-2013, 08:04 PM.
    Rodgers Oxford 925 built in 1983
    Kimball K-800 Fascination - Sold

  • #2
    Sounds to me like your reverb preamp is causing the noise. Time to switch to a digital reverb!
    -----------------------------------------------------------------------------------------------------------
    Keeping (too many) old organs alive.
    Allen ADC 2110-T, Rodgers Trio 321B
    Conn 651, 713
    Hammond M-3 w/Leslie 120
    Hammond Solovox
    Mass-Rowe model 96 Carillon

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    • #3
      Where is this reverb preamp of which you speak and how can it be fixed, if at all? Can it be bypassed?

      I should mention that I am running a Lexicon MX-200 sound processor through the reverb loop on the output board, with resistors in both the input and output lines to bring them down to levels that the MX-200 and the return line on the Rodgers can handle without distorting.

      Any ideas?
      Rodgers Oxford 925 built in 1983
      Kimball K-800 Fascination - Sold

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      • #4
        Digital synthesisers producing sounds for hearing, whine at the divider frequency, and also the oscillator frequency. I designed one for the JSC 36 years ago, I know. Engineers filter this stuff out with filtars, which usually involve capacitors, resistors and inductors. Two types of capacitor, the electrolytic and the tantalum electrolytic, are notorious for drying up and changing capacitance after a few years. They also becomre temperature sensitive and the capacitance varies over a few minutes. When this happens, the frequency at which the filtering occurs, changes. Thus an old appliance needing filters sounds funny or makes weird noises, or if the power supplies are not stable in the divider areas, the digital parts hiccup.
        I've seen eidence that Rodgers and allen are not using 3 years capacitors (500 hours life) but no evidence they are using 50 year electrolytic capacitors (epoxy seal instead of rubber).
        So, sounds funny, calender says electrolytic capacitors are over 15 years old, change them is my policy. here is a thread with some basic info: http://www.organforum.com/forums/sho...gan-Model-3051
        Read the safety sticky thread at the top of the forum, follow some simple rules and you won't get hurt.
        Your aftermarket device may have even shorter life capacitors than 15-20 years. My TV remotes are running down the battery and getting weak at 4 years, and the **** DTV converter had lines in the output signal that went away after 5 minutes turned on, the day after I bought it. Another W***-M*** price buster product.
        See this about a guy that fixed a whine in a Jazz Chorus Roland with new PowerSupply capacitors. http://www.diyaudio.com/forums/instr...orus-77-a.html You have a church Roland.
        city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112

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        • #5
          How hard and how long to replace those capacitors? Is it a major undertaking?
          Rodgers Oxford 925 built in 1983
          Kimball K-800 Fascination - Sold

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          • #6
            Did it always do this or just after you added the reverb? Do the wires to the reverb run over the oscillator boards? The shields on the cables to/from the reverb may be faulty or not grounded properly and you're hearing the oscillators injecting into the cables. Try moving the cables around.

            Greg

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            • #7
              It does this whenever you turn the reverb pot up on the organ's output board, whether the Lexicon box is connected or not. It's done this since I got it about 6 months ago, and who knows how long before that.
              Rodgers Oxford 925 built in 1983
              Kimball K-800 Fascination - Sold

              Comment


              • #8
                Originally posted by TubaMirabilis123 View Post
                How hard and how long to replace those capacitors? Is it a major undertaking?
                Tales about $70 in tools and the patience to try try again until you get it right. Most successful musicians have the patience and focus it takes. Most musicians have the fine motor control of the hands it takes to manipulate small objedts. I'm starting to need reading glasses to do it, but that is a $3 tool. I've been doing it since I was 20 and the MacIntosh amp salesman told me my 70 watt amp was putting out 14 watts due to bad e-caps and a rectifier tube. He sneared at my bad looking job when I took it back next year, but it was putting out 70 watts. My efforts have gotten better.
                If you have PC boards, my advice to the newbie is cut the leads at the ends of the old cap, don't try to remove them from the board. Hook the old ends over, hook the new ends over, new cap is supported mechanically by the hooks, then solder. After every two, reassemble and test, newbies make a lot of bad joints. When you have just done two joints, and it works worse afterwards instead of better, you know right where the problem is, no fooling around with meters and probes. There is a solder tutorial at Jameco.com, but I learned from little black and white pictures that came with my first soldering iron. The skill moved on to welding, you just have to use dark glasses in welding, but most of the same skill in looking at what you are doing and have done.
                This organ is over 15 years old, isn't it? 20?
                Yes corroded wires under ground screws, or oxidized pins on cables between sections can cause noise pickup. Brass and tin oxydize working or sitting still. I thought I understood Rodgers used less brass and tin connectors than other brands, but if the reverb box is separate that is one pair of obvious connectors to reseat or even spray off. Warning, proper contact cleaner is flammable, no smoking open flame or pilot lights, electricity turned on or off within 10 m. Set up a fan before hand to dissipate the fumes. I use spray heptane, hexane, aliphatic hydrocarbons, etc. Do not use brominated hydrocarbon non-flammable contact cleaner, it will dissolve PVC and styrene plastics used in organs.
                Have fun.
                city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112

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                • #9
                  Actually, I just remembered something. I was working on the organ the other day doing a bit of voicing. It just so happens that I had the first "rack" of boards swung out away from the second. With the organ on, there was no oscillator noise. When I put the "rack" back in its place, the noise started again. There is A LOT of bare copper wire in this organ, so I'm wondering if the cause is proximity to the oscillators. And yes, the organ is from 1982, so more like 30 years old!
                  Rodgers Oxford 925 built in 1983
                  Kimball K-800 Fascination - Sold

                  Comment


                  • #10
                    Well yes, long wires parallel to a noise source will pick up noise more, particularly high frequency noise. the antenna on an FM radio is a wire stick, that is the "rabbit ears". Again, Rodgers installed enough capacitance to short these high frequencies out preferentially. The impedance of a capacitor goes down as the frequency goes up, so a capacitor between a high gain amp input and ground tends to reduce the high frequency noise getting through. Unfortunately, electrolytic caps in old age have lower capacitance than stated on the label, and higher parasitic resistance (ESR) than when new, so the noise level creeps up, particularly high frequencies.
                    city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112

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                    • #11
                      Originally posted by TubaMirabilis123 View Post
                      Actually, I just remembered something. I was working on the organ the other day doing a bit of voicing. It just so happens that I had the first "rack" of boards swung out away from the second. With the organ on, there was no oscillator noise. When I put the "rack" back in its place, the noise started again. There is A LOT of bare copper wire in this organ, so I'm wondering if the cause is proximity to the oscillators. And yes, the organ is from 1982, so more like 30 years old!
                      Yes, that's what I suspected. That noise you're hearing is the sound of some, or all, of the oscillators simultaneously coupling to the output, though I would expect it to be the same volume in all the channels.

                      Some dumb questions: when you connected the Lex, did you disconnect the Rodgers reverb and then use the same jacks? Or did you solder something in? You don't have both connected at the same time, do you? (I'll bet you disconnected the Rodgers and used the jacks already there but I have to ask.) In any case, once again, I would try disconnecting all the reverb stuff, at the board, including yours and Rodgers, if still connected. Based on what you already said, probably won't make any difference but worth a try.

                      I'm wondering if somebody removed a shield that may have been over the back of the Output/Preamp Board. Don't know if there should be one but if there isn't one present, look carefully at the frame around the board for any empty screw holes, indicating something was removed.

                      Greg

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