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Analog Organ Circuitry Question

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  • Analog Organ Circuitry Question

    Hello all,
    I've had an idea for a while, and want to bounce it off of people who know more about these older organs and I.

    I'm trying to learn about the circuitry of the analog individual oscillator organs. What I would like to do is make kind of an organ synthesizer if you will. I'm trying to find some of the external oscillator racks that were part of the larger organs.

    Basically use the oscillator banks, trigger them with some kind of a keyboard (perhaps using CV?), tap the output before it goes into the fixed filters, and run it into analog Moog style adjustable filters. My thought was this could be an unlimited polyphony organ/synth, sort of it's own thing going on.

    Here's the circuitry questions. How are the oscillators triggered? Is it similar to an electro-mechanical pipe organ console where there's a contact for each key and stop? What kind of voltage do they run on? Do the banks run on AC, or use some kind of step down power supply? I'm assuming there's a static voltage to power them, and another voltage to trigger them?

    Anyone know of a way to find the outboard oscillator banks? I haven't had any luck, only found the organs themselves. Unfortunately my doors are too small to fit an AGO console through, so I have to find just the oscillator racks and build everything together myself.

    I know this sounds kinda crazy, but I would really appreciate any input you guys may have on this. This is something I've wanted to do for a long time, and am really enthusiastic about pursuing. I think it could give me some really creative sound possibilities.


  • #2
    Organs using multiple individual oscillators fell into two broad categories: those with keyed oscillators and those with continuously running oscillators. The keyed oscillators did not oscillate until they were keyed with a DC voltage. All Allen analog organs were of this type, as were early Conn organs and Artisan kit organs. Later Conn organs used continuously running oscillators, with some electronic keying of the audio signal and some contact switch keying.

    Rodgers organs originally used a mix of keyed and continuously running oscillators; their continuously running oscillators always used electronic keying of the audio signal. Rodgers mostly abandoned the keyed oscillators, and adopted the continuous approach as it provided greater use of limited resources.

    Keying of the oscillators was done either using multiple contact key switches or diode equivalent electronic switches. The use of multiple contacts (or diode equivalent) was to permit multiple pitch registers.

    On most transistor organs, the keying voltage was in the range of 12 to 15 VDC; tube organs typically used higher voltages, but I can't recommend going with tube designs. The DC voltage was provided by a power supply running off line voltage, 120 VAC in the USA and Canada.

    For keyed oscillators--which would be the easiest to adapt to your concept--the keying voltage is the voltage that powers the oscillators.

    I recommend you find a copy of Electronic Musical Instruments by Richard H. Dorf, 3rd edition (1968). It's a very good teach text on the technology of analog organs and is quite common to find on used book sources. is currently showing used copies available. Note: be sure to get the 1968 edition; the other 2 editions cover tube designs, while the 3rd edition is covers almost 100% transistorized designs.


    • #3
      Thanks so much for the informative reply. That really helped a lot. I'll have to keep my eyes out for some Allen oscillators, as it sounds like that would work the best for my concept. Sounds like I should definitely check out that book, as it could teach me a lot.



      • #4
        You might check with Britson Organ in Washington State. They might have parts from old Saville instruments that would work for your purpose.


        • #5
          I've got two T-12 Allen organs here, and I am intending to part them out ( taking up space, and no one wants them ). I actually never considered that anyone might want the oscillator racks out of them. The T12s have a single bank each, and they are basically flute sounding. They synthesize the other sounds by combining the flute pitches in various combinations and levels.

          It is likely that I will not get to doing the part - out till January though ( so says the plan right now anyhow ), but if you are willing to wait till then, you can have them. Let me know if you might be, and I will keep you in mind.
          Regards, Larry

          At Home : Yamaha Electones : EX-42 ( X 3 !!! ), E-5AR, FX-1 ( X 2 !! ), US-1, EL-25 ( Chopped ). Allen 601D, ADC 6000D. Lowrey CH32-1. At Churches I play for : Allen Q325 ( with Vista ), Allen L123 ( with Navigator ). Rodgers 755. 1919 Wangerin 2/7 pipe organ.


          • #6
            Hi Larry,
            Yes that is fine. I'm certainly in no rush. I've waited this long, a few more months certainly won't hurt. Thanks for keeping me in mind.