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Thread: New Teensy 4.1 DIY Synthesizer

  1. #101
    Senior Member Rolfdegen's Avatar
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    Hallo friends

    This is the control unit from Jeannie. For the button query, I use an ADC input to save output lines on the Teensy Board.

    The LED Driver IC8 is controlled via the same SPI bus as the ADC chip but with a different CS line. This saves additional lines from Teensy Board.

    The SPIN_1 - SPIN_4 lines on IC8 and 3 PWM lines from Teensy board are for the control of the SPIN FV-1 Effect chip.





    This is a my prototype and the arrangement of buttons, potentiometers, etc. will change a bit.



    Greetings. Rolf
    Last edited by Rolfdegen; 02-04-2021 at 11:40 AM.

  2. #102
    Senior Member Rolfdegen's Avatar
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    The Spin FV-1 effect module is mounted on the back of the Jeannie board.



    This is an old PCB version. I built it into my other DIY synthesizer "DEGENERATOR".

    Here are sound examples from Degenerator Synth with FV-1 chip: https://drive.google.com/file/d/1jG6...lCWHZS45M/view

    and Youtube: https://youtu.be/unN71yPqREU

    Greetings Rolf

  3. #103
    Member fdaniels's Avatar
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    What happens if you push 2 buttons simultaneously?

  4. #104
    Senior Member Rolfdegen's Avatar
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    Hallo..

    This function is not intended. But the key that was pressed first becomes active.

    Today I got the FV-1 chips. These are 28 pin SMD chips but it's not difficult to solder. For comparison, an 8-pin IC.



    Greetings. Rolf

  5. #105
    Senior Member Rolfdegen's Avatar
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    Hallo friends..

    Here are complete Jeannie circuit diagram with FV-1 card. PWM1-4 and SPIN1-4 are Spin FV-1 control lines.

    MCU unit


    Control unit


    Fx unit


    (subject to change):verwirrt:

    Greetings Rolf

  6. #106
    Member fdaniels's Avatar
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    What about an Audio IN so you can route a signal thru the Filter + FX, just like the Shruthi. Maybe you could even Sample?

  7. #107
    Senior Member Rolfdegen's Avatar
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    Hallo Daniel

    That is not provided in Jeannie. We want to build this synthesizer very small and inexpensive with good sound.

    But maybe in an XT version with many pots ans knops :mit den Augen rollen:

    Gruß Rolf

  8. #108
    Member fdaniels's Avatar
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    Quote Originally Posted by Rolfdegen View Post
    Hallo Daniel

    That is not provided in Jeannie. We want to build this synthesizer very small and inexpensive.

    But maybe in an XT version with many pots ans knops :mit den Augen rollen:

    Gruß Rolf
    Why dont you then use the internal Audio Systems Effects for "small and inexpensive"? Adding a simple circuitry for mixing audio input would allow to use it as an FV-1 FX/Filterbox additionally, which is a huge advantage. Then, sampling is just a ADC away.... You already add 10€+ of parts just for the effects, thus leaving the "small and inexpensive" world (btw, the Display also isnt "small" or "inexpensive"), so aditionally 1€ for an TL074 and associate Parts wont make it unsellable....

  9. #109
    Senior Member Rolfdegen's Avatar
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    Thanks for your good ideas. There is hardly any space left on the circuit board.

    It's open source and you can change it if you want

  10. #110
    Senior Member Rolfdegen's Avatar
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    Hello friends


    It is progressing. Corona also has something positive. You spend more time at home and on your computer.
    Before I start laying out the boards, I want to know if everything works. I may be there
    a bit old fashioned. But setting up an experiment on the breadboard always involves contact problems
    and disturbances connected. I prefer to solder and am sure that there is at least no contact
    problems are.



    The right board becomes the optional Fx board. The board will turn out a bit smaller and over later
    a contact strip on the back is connected to the motherboard.


    Greetings Rolf

  11. #111
    For better reliability of your MIDI IN consider 10k resistor between pin 7 and ground of optocoupler as explained here:
    https://electronics.stackexchange.co...edirect=1&lq=1

  12. #112
    Senior Member Rolfdegen's Avatar
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    Hello Tomas


    I am using a 6N137. Pin 7 is Monitoring node and does not have to be connected.



    Greetings from germany. Rolf

  13. #113
    Sorry. Apparently I need to get my eyes checked.

  14. #114
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    Very nice sounding Rolf. I will be getting a PJRC audio shield in a project in the coming weeks and look forward to following your path.

  15. #115
    Senior Member Rolfdegen's Avatar
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    Sorry.. double post
    Last edited by Rolfdegen; 02-17-2021 at 11:09 AM.

  16. #116
    Senior Member Rolfdegen's Avatar
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    Hello again..


    The prototype of the Fv-1 circuit is now completely soldered and works flawlessly. Will be a little smaller later because of SMD
    and relocation of the power circuit (+/- 5V) to the main board.







    https://youtu.be/Tq4jn6Mz5Ko

    The Fx menu in the synth is almost ready. The parameter values are still missing after a program change. I still have to change that.

    Greetings Rolf
    Last edited by Rolfdegen; 02-17-2021 at 11:10 AM.

  17. #117
    Senior Member Rolfdegen's Avatar
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    Hello and have a nice Sunday


    There are a few changes in the circuit diagram. The DAC output (PT8211) on the Teensy Board has an active 32KHz LowPass filter. This reduces high-frequency interference signals at the input of the effect chip.






    The OTA (IC5a / b) for the volume control of the effect signal (MIX) has now been moved to the output of the effect chip. This means that the noise floor at the synthesizer output is a little lower at low effect levels.



    Greetings Rolf

  18. #118
    Senior Member Rolfdegen's Avatar
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    Hello friends..


    We have started to route the boards. I'm curious how big they will be.


    Fx board


    Greetings from germany. Rolf

  19. #119
    Hello Rolf, fantastic work. I’m really enjoying see the progress on this.

    I love how informative your display is, and how it gives the user lots of real time feedback. Do you have any advice or resources on how to achieve that? I would like to do something similar for my synth (real time visualization of synth parameters, oscilloscope, etc).

    Thank you!

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