FatMan Mini Calibration Procedure

This is a short synopsis of the FatMan calibration procedure.

This procedure does not include trouble shooting hints and assumes a known working FatMan. These notes would be appropriate for recalibration only and assumes that you've done it before with the manual.
Connect and configure MIDI on the FatMan and another synth so that when you play notes on the FatMan the other synth plays too.
  1. VCO 1/2 MIX full CW.
  2. Play C0, adj panel PITCH for unison.
  3. Play C1, adj DAC tuning (R13) for unison (should be an octave higher than previous step).
  4. Play C4, adj panel PITCH for unison.
  5. Play C3, adj OCT 3 trim (R18) for unison (should be an octave lower than previous step).
  6. Play C2, adj OCT 2 trim (R21) for unison (should be an octave lower than previous step).
  7. Play C1, adj OCT 1 trim (R24) for unison (should be an octave lower than previous step).
  8. Set VCO 1/2 MIX to MIDPOINT. (Both VCOs now audible). The remainder of the procedure adjusts VCO1 to track VCO2. Since you will need to hear the "beat" between these two sounds, turn off the sound from other the synth.
  9. Play C4, adj panel OFFSET for unison.
  10. Play C0, adj zero trim (R42) for unison.
Repeat steps 9 and 10 until both C0 and C4 are in unison. A slight imperfection here is not a bad thing. Having a slight error here will cause the VCOs to phase slowly as you play toward one end of the keyboard. I stress a slight imperfection here. A gross imperfection may sound unmusical.

Note: It is important that steps 1 through 7 be done as accurately as possible. These steps adjust the DAC for optimum linearity. If this is off, the FatMan will not track well with other instruments. The word "unison" means that there is no beat between the FatMan and the instrument you are tuning it to. I strongly recommend using a digital synth since they are extremely octave accurate.
I advise that either the "Lee Diode" modification be done OR replace the 555 timer ICs with ICM7555 CMOS 555 timers. Doing so before performing the above procedure will allow making the VCO1/VCO2 tracking adjustment (steps 9 and 10) more accurate. Either of these mods allow the two VCOs to run much closer together in frequency before they will soft sync (lock together). I have two FatMan synths, one with the Lee Diode mod, the other has ICM7555 ICs. I can calibrate the VCOs closer than 0.1 Hz on both. My preference is using the ICM7555.