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Thread: Draw Bar Organ MIDI Module

  1. #1
    Junior Member lsrichard's Avatar
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    Draw Bar Organ MIDI Module

    Introducing the Draw Bar Organ ver.12 by Richard Lingenberg. It is a modern open source 9 draw bar MIDI/ USB Host keyboard organ module. It makes extensive use of Teensy PJRC technology with a Teensy 4.0 attached to a Rev. D audio board and a Teensy 3.6 driving the ILI9341 type touch display. It uses a SD card that can be attached to the built in reader on the Teensy 3.6 to store 105 patches with 22 patches built into the program. The patches contain the 9 draw bar settings, the AHDSR settings and the patch display name. It uses the EEPROM to save the selectable default setting loaded at power up. It uses a dependable MIDI to USB adapter made by Fore attached to the USB host of the Teensy 4.0. It also makes extensive use of PJRC libraries.

    Features:
    * 61 voice/ note capacity. One voice for each note on a 5 octave keyboard.
    * 9 touch screen draw bars.
    * Attack/ Hold/ Decay/ Sustain and Release settings.
    * 105 savable to SD card patches. 22 built in patches.
    * MIDI channel and Program change options.
    * Default settings that load at power up: patch, MIDI channel, MIDI patch change, S10 mode, Sustain polarity, Transpose, Tuning and Bender range
    ( all saved in EEPROM memory ).
    * Volume control knob and isolated output.

    If interested I can share my schematics and source code. While I am experienced at building electronics and have done engineering work I am a bit of a newbe to coding. Some of the coding may look strange or disorganized but everything works as intended.

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    The Draw Bar Organ sounds best with some external effects added such as a chorus or rotary speaker simulator and a bit of reverb. I am using a MXR Micro Chorus and a mini reverb pedal. The MXR Micro Chorus I use has been modified to be able to change the rate speed controlled by the Teensy 3.6. This provides a pleasing fast and slow rotary speaker effect.

    A look inside the module:

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    Screen shot of the extensive Draw Bar Organ Audio System Design Tool setup:

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    I know the objects are too small to see. I was not sure the Audio System Design Tool or the Teensy 4.0 could handle this many connections or objects but luckily it did. The objects on the left are 101 sine wave generators. The next three columns are 61 nine input mixers made from 183 four input mixers. In the fifth column are the 61 Envelope objects. In the sixth column and the rest on the right are the 61 input mixer and output section. This is similar to how an analog draw bar organ is wired.

    As for a sound demo I will try to post a Sound Cloud link soon but I have not recorded it yet.

    Thanks

  2. #2
    Senior Member oddson's Avatar
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    Looks awesome, can't wait to see the details and hear the result.

  3. #3
    Junior Member lsrichard's Avatar
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    Here is a link to a sound cloud demo of the Draw Bar Organ module.

    https://soundcloud.com/lsrichard/draw-bar-organ-demo-1

    Here is the master wiring schematic.

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    IT uses a Teensy 4.0 attached to a Rev.D audio board and a Teensy 3.6 to handle the touch screen display and patch loading from the SD card.
    They communicate with each other with a standard serial connections sending different parameters to each other.

    Here is the power supply and audio output section ect.

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    I am not sure how to rotate images when I post them.

    I am using the stereo output of the audio board in a differential format with normal and inverted output.

    This is to help cancel out any digital noise and helps make the noise floor lower.

    The audio section also has a 7KHz low pass filter and is isolated with an output transformer.

    The isolation is mostly only needed when it is connected to a computer thru the programming ports.

    Thanks

  4. #4
    Junior Member lsrichard's Avatar
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    The sound cloud demo link will continue to play the other unrelated files on my sound cloud account after the organ demo has completed.
    Not sure how to stop this and I can not delete the other files from a project 6 years ago.

    Just push the pause button on sound cloud after the organ demo is done.

    Thanks

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