Oldschool modular synthesizer

Moog-like modular analog synthesizer

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I've always dreamed of being the proud owner of a huge modular synth. In order to simplify the overwhelming task, I am going to use CEM and SSM chips which are full Voltage Controlled Oscillators and Filters on integrated circuits, and which have been recently relaunched. The same chips were aboard infamous vintage synths such as the Memorymoog and the Prophet V. Doing so, no worry about temperature compensation and exponential converters.
I may throw a few Arduinos here and there, but I will abstain to put them in the audio signal flow. I will only allow myself to use them to generate control voltages such as Envelope Generators and Low Frequency Oscillators, and of course, the MIDI to CV interface.

The goal is to build the following modules:

  • 3x VCO based on CEM3340 chips
  • 3x Low Pass VCF based on SSM chip
  • 1x noise generator
  • 4x VCA
  • 3x AHDSR EG with auto trig
  • 3x LFO
  • A few mixers and arbitrary voltage generators
  • MIDI-CV interface with multichannel arpeggiator/sequencer

Everything will be fully patchable with jack cords, and compatible with commercial modular synth modules standards regarding control (1v/oct), audio voltages, and format (eurorack modules).

  • Breadboarding the VCO

    Alexandre Allali07/15/2017 at 17:28 0 comments

    Top breadboard is the VCO with the CEM chip on the left. Bottom breadboard is the power supply.

    The small one on the left is a simple CV pot. I used it to test the pulse width.

    I know it is such a mess..

    The design is mostly inspired by the Memorymoog, but I'd like to include VCOs sync, which is lacking in it.

    Next step is calibrating the 3 variable resistors to tune it at 1v/oct. it won't be an easy task...

  • The CEM3340 have arrived !

    Alexandre Allali06/10/2017 at 10:47 0 comments

    These chips are the heart of the VCO

  • Power supply

    Alexandre Allali05/30/2017 at 21:25 0 comments

    For analog synths, a very stable power supply is of the utmost importance, because pitches are dependent of voltages. For a 1v increase, the VCOs frequency double. So a small instability in the voltage of the power source may result in an uncontrollable pitch variation, making the instrument unplayable.

    Having in mind the chips I am going to use, the different modules will need different voltages simultaneously :

    • +15v/-15v for the VCOs and VCFs, and all op amps
    • +5v for the control voltage modules, especially those built around Arduinos

    I don't want to mess with main voltages, so I'll start with a wall wart adapter providing 15v AC, rectify and filter it and use LM7xxx regulators. This design is inspired by Ray Wilson's one, from Music From Outer Space.

    There are two small issues with that design:

    1. I had troubles finding a euro plug 15v AC wall wart adapter. The only one I've found provides only 650 mA. I hope that will be sufficient
    2. As of today, I am unsure where is the best place to put the 5v regulator : just after the big filtering caps of the rectifier section and thus at the same level of the other regulators, or after the 15v regulator, placing both in series. I'll try and see which one is better.

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