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Electronic circuit to produce gyro speaker effect?

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  • Electronic circuit to produce gyro speaker effect?

    Does anyone know of an electronic circuit that would reproduce a gyro speaker effect that I could use on my Allen Series 620 Theatre Organ. I want to build some headphone amplifiers and would like to be able to generate a gyro effect for the tibia and vox humana stops that would play through the headphones. I am a retired electrical engineer, so I'm familiar with schematics, etc.

  • #2
    The Allen Tremulant/Vibrato generator does this using a bucket-brigade-device--a charge coupled analog delay line and it adds an amplitude modulation to it. The analog delay line requires a clock, and that clock is modulated with a tremulant frequency generator; earlier Allen Trem modules had a slow speed as well as a fast speed, but the latest versions only had fast speed. Supporting circuits provide bass frequency cut prior to the BBD and bass boost after so the bass doesn't saturate the signal. After the BBD signal is filtered to remove the clock frequency.

    Rodgers used this same approach for vibrato (which they called tremulant) in their 1980's models, but did not include the AM.

    Schober Organs, and others, used a phase shift circuit (which is what the BBD approach does) using LDRs and transistor buffer stages.

    The easiest way would be to acquire some Allen Trem-3 or Trem-4 units. You might also find some Devtronix Audio Trem units, which used the same approach as Allen, but a little simpler circuitry.

    If you are interested, send me a PM (private message) with your email address and I can scan and forward the Devtronix circuit diagram.


    • #3
      You could also start with a $25 Behringer tremolo pedal and modify it if need be.
      Keep in mind that a large part of the gyro (and Leslie) sound depends on room acoustics.

      Servicing electronic organs since 1969.


      • #4
        Thanks Toodles and Tucsondave for your kind information. These suggestions are a great help. I am just getting started so it will take me a while to work out how I want to do this and how to wire it in to my organ. Thanks again.


        • #5

          The Rotoshere Hughes and Kettner can interest you.
          This is a guitar effect pedal.
          Schematics can be found on the internet. Use MN3102 clock generator and MN3207 delay line.
          I had modified one to change the low speed.
          Not really simple.

          Last edited by Jyvoipabo; 07-21-2018, 11:26 AM.