VCO with Suboctave based on SSM 2033

Features

  • Saw 0-10v, Triangle +/-5v, Pulse 0-5v, Sine +/-5v outputs
  • Suboctave output is a 0-10v pulse with fixed pulse width modulation, at half the standard pulse output frequency
  • Two Exponential 1 v/octave control voltage, and one Linear FM inputs
  • Course and fine frequency controls
  • LFO switch drops low frequency limit into subaudio
  • Hard and soft sync inputs
  • Pulse width control and PWM control voltage input

    • Notes

    Use high slew rate opamps, such as JFET types or LM318 for opamps in the signal path. I used OP-16's, which are LF356 types, because they were readily available to me. The U4 dual opamp in the suboctave circuit are not critical. I used a 4558, but a TL072 or 747 could be used.

    V/octave scale adjustment: Set coarse and fine frequency pots to give 100hz output with 0v C.V. Make sure LFO switch is off. Apply 2 volts to a control voltage input. Adjust R10 until the frequency is 400hz (two octaves).

    Hi frequency tracking adjustment: Set coarse and fine frequency pots to give 1000hz output with 0v C.V. Make sure LFO switch is off. Apply 4 volts to a control voltage input. Adjust R13 until the frequency is 16000hz (four octaves).

    Sine shaper adjustment: This is easiest to do if you have access to an oscilloscope. Adjust R33 until the waveform at the output of U3 is symmetrical about zero, then adjust R35 for a nice rounded sine. There may be some interaction between the two adjustment trims.
    Without a scope, you'll just need to listen to the sine output and adjust for the "smoothest" tone. Use a frequency of a couple hundred hz.