Imported from GitHub: JordanAceto/micro-pico · commit db0dd1e · license CC-BY-4.0

Description

Tiny analog monosynth with 2 SSI2130 VCOs and swappable filter

README

Micro-Pico tiny monosynth

A lil' analog synth with:

• Two SSI2130 VCOs
  • sine, triangle, sawtooth, and pulse waves available
  • VCO B can by syncronized to VCO A (hard and soft sync available)
  • the VCOs share a single manual pulse width control
• Two minimoog style ADS envelope generators
  • These envelopes cycle through all four A, D, S, and R stages, but the Decay and Release stages share a single potentiometer
• Modulation LFO
  • triangle, square, and sample & hold waveforms
  • can be routed to VCO FM, PWM, or VCF modulation
  • MOD CV input controlls the LFO depth along with the LFO LEVEL knob, for mod-wheel antics
• Swappable VCF port
  • the VCF can be changed by plugging in a variety of VCF plug-in boards
  • you need at least one of the above VCF boards to finish the synth
• Final linear VCA
  • simple linearized SSI2162 VCA
• Extra patch points on the pcb for mods and experimentation
  • independent aux FM inputs for the VCOs [-5v, +5v]
  • aux PWM CV [-5v, +5v]
  • aux VCF cutoff CV [-5v, +5v]
  • aux VCA amplitude CV [0v, +5v]
  • white noise out [-5v, +5v]
  • patch points for most of the important signals
• Powered with a standard guitar pedal style 9VDC center negative adapter
  • current draw is approximately 220mA without a VCF plug-in board installed
  • expect another 100mA or so depending on the VCF board used
  • so use a 9v adapter with at least 500mA capacity or greater

The feature set is quite limited. The emphasis is on small, simple, and all-analog signal path. A fun little jammer to hook up to a sequencer or CV keyboard.

Construction notes:

• It is easier to install the trimpots, VCF port headers, and various through-hole parts before installing the pots and switches
  • you can still get to everything if you forget, or need to change something later
• When installing the front panel components
  • dry fit all of the pots, switches, and jacks before soldering
  • the rotary switches need a nut or spacer under the panel to match the height of the pots
  • the 9VDC connector needs a nut or spacer under the panel, and needs to be lifted off the board a little, so that it protrudes far enough to tighten the outer nut
  • tighten down all of the components, check for alighment and height issues, and only then start soldering
• The rotary switches need a sleeve adapter for the knobs to fit nicely
  • something like this
  • or use a bit of tubing if you're DIY happy
• It's designed to fit in a Hammond 1590XX aluminum box
  • these are available pre-painted in a few colors
  • with a VCF plug-in board installed, the 1590XX is the teensiest bit too short, the trimpots hit the lid when tightened
    • you can put some 2mm-ish washers between the lid and the box
    • eventually I hope to make a gasket that adds a few mm height and looks cleaner
    • or it could even have an acrylic light plate like some people do with pedals
  • other chassis at least as big as the 1590XX (plus a few mm taller) could work

Calibration:

• follow the SSI2130 datasheet Tuning Process for the VCOs, or tune by ear
• calibrate the VCF according to the instructions on the main VCF plug-in board repo
• check that the white noise is about +/-5V in amplitude. You can try different BJTs or mess with the gain setting resistors, but as long as it's reasonably close the S&H setting will sound fine, it's not critical

Status:

Safe to build!