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  • Category Archives _diy Synthesizer
  • Update Midi to Voltage Interface

    Here is the first part of my project documentation.

    This document try to explain the control of an SPI DAC with an Arduino Board.

    MIDI to VoltageSPI Part1_en pdf

    To the original Post:

    http://itist.de/2013/10/midi-to-voltage-interface/ ‎

     

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  • MIDI to Voltage with Discrete DAC

    After my implementation of an SPI controlled DAC i was searching for an 14+ Bit Multiplying DAC. There were some from Linear but not available for an good price.
    So here is my try to build an DAC in CS Style. (YM26600). This DAC creates an voltage output for each semitone. For the octaves there is an similar circuit with 6 switches (nit built yet).

    For the first tests I started with 12 selected standard 100 Ohms Resistors. The 28.94k resistors are a combination of an 27k  and a 25 turn 5k trimpot. I trimmed the pots as calculated in the simulation and it and the voltages where spot on. The switches are cheap CD4066s. To control them from my Arduino board i build the TTL to CMOS converters.

    Here is a picture of the Digital Board with output Buffers an TTL to CMOS converter.

    Digi Board Web

     

    This is the Resistor Network.

    Resistor Network

    This is the output Voltega  for the Note B with a 4V Octave input voltage.

    Voltage Output B web

    Here is the Schematic:

    Discret DAC Schematic

    UPDATE 24.11.2013

    I finished the Wiring to the DAC Board and the Arduino

    .ARDUINO DAC Interface _web

    Interface ResistorNet _web

    Here a picture of the whole Setup

    Discreete DAC _web

     

    I wrote a little programm to test the whole circuit. It creates voltage steps in halftones.

    Stepped Out Voltage _web

     

    UPDATE 01.12.2013

    Now i have built the Octave DAC. Schematic and coding will follow soon.

    Here a short Video.

    UPDATE 02.12.2013

    Source Code here

    MidiToVoltage as .txt File

    or  on sourceforge.net

    https://sourceforge.net/projects/miditovoltage/

    UPDATE 15.12.2013

    Added first polyphonic code

    Midi to Voltage poly 1.05 as .txt File

    This picture shows the multiplexed analog Voltage output. I am not sure with the timing for the following S/H stages. I think is code is not the best but it works.

    octave steps2_web

     

    UPDATE 27.04.2014

    Made PCB Layout in KiCad and thanks to the members of the mikrocontroller.net Forum for their help.http://www.mikrocontroller.net/topic/331468#new

    Here is my last version:

    Discrete DAC Board v6

    will do some changes and will make one next weekend.

    It is a single sided PCB. I will upload the final Version incl. KiCAD files if it all works fine.

    Here the Schematic:Discrete DAC Schematic

     

    Next Steps:

    • Connection to the Arduino Board
    • Building a Gate Out Circuit
    • Writing the Basic Midi to Voltage code
    • Building an S/H circuit

     

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  • CS-style VCO core

    For a  long time im interested in the sound of the old CS Synths. So I started in spring 2013 making a clone of the VCO.
    After studying the Service Manuals, Interrnet Research (google Patent search) I breadboarded several circuits with more or less sucess.
    Some don’t oscillate reliable, some wheren’t linear etc.

    In a German Synthesizer Forum, Sequencer.de  I got help from Uwe Schüler and he designed a simple CS-Style VCO. Thank you Uwe.
    I read that one of the secrets where the 30µs rectangle step.
    You can see the waveform in the following pictures

    CS Style Oszi1_web
    CS-Style Saw

     

    CS Style Oszi2_web
    CS-Style Saw enlarged.

    The VCO is a linear sawtooth oszillator with a V/Hz characteristic.
    You can here the VCO in combination with my homebuild MIDI to Voltage Converter.

    As you can hear, it’s detuned in the low octave. The Reason for this is the 12Bit resolution of the DAC.
    In the following table you can see the small differences in the control Voltages, I think a 14Bit DAC will be fine.

     

    CS Style VCO thru a 24dB Ladder Filter:

     

    Note    CV
    C           0V
    C#        0,5297V
    D          0,5612V
    D#        0,5946V
    E          0,63V
    F          0,6674V
    F#        0,7071V
    G          0,7492V
    G#       0,7937V
    A          0,8409V
    A#       0,8909V
    B          0,9439V
    C’         1,0000V

    Here a picture  from the bench.

    Aufbau 1_web

     

    UPDATE 08.01.2014

    After Uwe, the developer of the VCO, wrote me an e-mail where he asked me about the used OpAmp, i wrote him that i used an OP07 (bipolar), he told me to use jfet type.

    So I changed it  to a LF356.

    Here the results:

    CV                   F
    0.125V              49.8Hz
    0.250V             99.01Hz
    0.5V                 197.4Hz
    1V                    393.8Hz
    2V                    784.9Hz
    4V                   1520Hz
    8V                   3140Hz

    I think this is very linear.

    I did a simple temperature check (hair dryer)

    15C°    1000Hz
    20C°      999Hz
    30C°      993Hz
    40C°      984Hz
    46C°      977Hz

    The circuit was build with standard metalfilm resitors with +- 50 ppm

    Thank you Uwe.

    Schematics:
    CS Style Schematic.pdf

    Patent No. for google search:
    Patent No: 3959743
    Patent No: 4191932
    Patent No: 4061987

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