CGS organ interface

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The CGS organ interface was created to give Ken Stone a convenient way to interface an early 1970s Lowrey Citation Theatre Spinet to the synth. From top to bottom there are connections for:

  • Lower Manual output
  • Rhythm Unit
    • Clock Out
    • Divider Out
    • Down Beat
  • Amplifier inputs
    • Leslie
    • Main

The lower manual output is a mixture of 8' and 4' unfiltered square waves from the lower keyboard of the Citation. The 4' range is switched by the organ's 4' coupler. This signal is amplified by an ETI 3600 synthesizer external input amplifier module, and can then be processed with various synth filters or modulators.

The fast clock signal from the organ's rhythm unit is routed straight to the front panel, as well as being fed through a 4017 decade counter, so it can be adjusted as needed. The thumbwheel switch selects the division. The resultant signal is available from the "Divider Out" jack. The third rhythm related output is the downbeat signal, which has been AND gated from a couple of the internal rhythm unit signals. This signal is used to reset sequencers every two bars, so they stay in sync.

The signals from the amplifier inputs are mixed into the organ before the expression pedal, allowing control of all volumes with the expression pedal.


Readers are permitted to construct these circuits for their own personal use only. Ken Stone retains all rights to his work.

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