Table of Contents

Testing and Calibrating the VCF


  1. Re-attach the power supply (with J4)
  2. Apply 3volts to R90 (either with 2 AA batteries or a benchtop supply)
  3. Probe the resonance pot with either a cheap pair of headphones or your oscilloscope. With the cutoff all the way anti-clockwise, you should see mostly a sinewave. If you're probing with headphones, you should hear a low, soft tone. When you turn the cutoff up, you should see a waveform similar to the one you have selected on the VCO. Using headphones you should hear a lot of higher overtones to the sound, and it might be buzzier and more 'acidic'.


According to the TB-303 service manual, the resonance frequency should be at 500Hz.

  1. Set the waveform to saw
  2. Set Cutoff to 50%
  3. Set Resonance to 100%
  4. Apply 3V DC to the VCO (or press the lower C key if your sequencer is done)
  5. Ajust TM3 so that the resonance frequency is 500Hz