Analog VCO calibration

All Erica Synths analog VCO modules can be calibrated in case they go out of tune. You will find a small brass flat-head screw on the front panel of each VCO - turning this right or left widens/narrows the octaves, respectively.

For calibration, you need to have a precise 1V/oct voltage sources and a tuner. Make sure to turn down any PWM, FM or overdrive parameters to get an accurate tuner reading. The calibration procedure for most VCO's is as follows:

1. Connect the VCO to the PSU. Let it "heat up" for ~25 mins.

2. Connect one of the wave outs to a tuner and the main out to a pair of headphones.

3.Connect a keyboard/midi-CV interface that generates 1V/oct CV to the 1V/oct input.

4. Play C4 on the keyboard and use TUNE potentiometer on the front panel to adjust tuning so that tuner shows C4.

5. Play C5 on the keyboard and see the tuner reading. If the tuner shows anything higher than C5, use the trim pot to INCREASE the frequency of the VCO slightly. If the tuner shows anything lower than C5, use the trim pot to DECREASE the frequency slightly.

6. Play C4 again and use the TUNE potentiometer to adjust the tuning so the tuner shows C4 again. Play C5 and see what you get. The tuning should be more precise. If it’s not exactly C5, go back to step 4.

7. Once you are happy with C5, check what you get on C6, C7 and C3. You may need to adjust it a little bit more as described on step 4. Since this is a single trim pot that adjusts the entire octave range, your goal is to make the tuning as approximately precise as possible across all octaves.