Super VCO: prototype finished

My new “Super VCO” for Eurorack is now finished as a prototype, and it has become “a little more” complicated than planned 🙂 (48 op-amps, 9 other IC’s, ProMini w. I2C display, + lots of ‘discretes’). The main purpose has been to develop and test various design ideas, and then afterwards slice it down to four less complex units. Four internal boards on a small motherboard packs a lot of features, almost a complete synth. I even had to make an ad-on module for linear to exponential converters. Main module and add-on module looks like this from the front:

The features are many:

Main VCO
- Triangle generator with high linearity and stability.
- Front panel switch selection of normal/low frequency range.
- Four inputs for frequency control: Potentiometer, CV from panel or bus, envelope and FM.
- Five derived waveforms: Ramp, ramp with double frequency, square wave, pulse and sine.
- All waveforms are “true symmetrical” around zero volt.
- Four summed inputs for pulse-width control: Potentiometer, PW, envelope and PWM.
Modulating VCO’s
- Two extra generators
  - one VCO for frequency modulation (FM) of the main VCO
  - one VCO for pulse-width modulation (PWM) of the pulse output from the main VCO
- Both VCO’s are designed for a lower frequency span than the main VCO, but also have selectable ranges.
- Both VCO’s are designed with sine wave output, and FM-VCO also with square-wave output.
- Both modulators have built-in VCA’s for amplitude and AM.
White noise generator.
Sub-harmonic divider from main VCO frequency
- One-of-twelve dividing steps via rotary switch.
- Selected sub square wave is open collector.
- Selected square wave also produce a random level signal.
Envelope generators*
- Six generators, internally wired for
  - Main-VCO bipolar frequency envelope.
  - Main-VCO bipolar pulse width envelope.
  - Frequency-modulator-VCO bipolar frequency envelope.
  - Frequency-modulator-VCO unipolar amplitude envelope.
  - Pulse-width-modulator-VCO bipolar frequency envelope.
  - Frequency modulator VCO unipolar amplitude envelope.
- Amplitude envelopes produce start-stop signals for VCOs, to ensure start from zero.
- Each generator has six envelope steps.
- Each envelope step is defined by target voltage and time to reach target.
- Common Gate trigger signal can be analog, and trig level can be programmed.
- Gate delay can be individual for each envelope.
- Gate-release mode can be selected.
- A “next gate” 5V signal can be produced with a delay from the Gate signal.
- The “next-gate” can be programmed to repeat up to 16 times when triggered by Gate.
- All programming is done with 4 rotary pulse encoders and one mode switch.
- All parameters for a selected envelope and its envelope-steps are displayed.
Internal module temperature 0.1V/dgrC output (intended for any future compensation).
DC voltage reference, -10 to +10 volt via 3-turn potentiometer.
Jack-socket attenuation: Internally wired envelope- and modulating signals utilizes the jack-sockets builtin breaker-contacts, in a way where jack-connectors will disable, connect or activate attenuation when pushed in.
- Dummy-plugs (no internal/external connections) to utilize these functions without using cables.
Linear to exponential converters
- Two converters placed in extra-module.
- …one for Main VCO frequency control input.
- …the other for FM-modulator-VCO frequency control input, to make it track main VCO.
- Common bypass switch to enable linear mode.
- Converters based on the THAT2180.
- 1V/oct.- and offset-potentiometers are installed on front-panel.
- Linear and exponential FM possible at the same time.