This article applies to analog oscillators such as the Dixie, Dixie II, Dixie II+, Atlantis and Rubicon.
Regarding Rubicon 2: The VCO OFFSET trimmer is located on the front of the module just above the PITCH knob between the two yellow LEDs. For adjusting CVGAIN use the VR-EXPO-VC trimmer.
Note: Our oscillators have additional trimmers to shape the sine and saw waveforms that are not covered in this guide. The Rubicon has further trimmers for its thru-zero FM, Symmetry Lock, and wave shaping circuits. If tuning the Rubicon, turn the SYMMETRY knob fully clockwise with LOCK off.
Warning: Calibration is not easy and takes practice. If you are not sure of what you are doing do not attempt to change the calibration on your module. Please contact firstname.lastname@example.org if you need assistance.
You will need:
- An accurate voltage source capable of exact 1 V intervals from 0 to 10 V.
- A multimeter / frequency counter. The higher the resolution the better.
Calibration is an iterative process, so parts of this procedure will need to be repeated several times to complete.
In the steps below VS (Voltage Source) refers to the octave voltage generator which should be connected to the module's 1V/OCT input. The module should be set in VCO mode. Connect the Pulse waveform output to your multimeter in frequency mode and set the pulse width slightly off center.
1. Allow the oscillator to warm up for around 10-20 minutes
2. Set VS to 0 V
Adjust the frequency via the COARSE and FINE knobs until the meter reads exactly 8.00 Hz. If the frequency does not go low enough you will need to adjust the VCOOFFSET trimmer to lower the frequency range. Some older modules may have the lowest frequency set to 32 Hz with the tuning knobs centered, the current factory default is 16 Hz.
3. Set VS to 3 V
The frequency should be close to 64.00 Hz, make a note of the difference between 64 and the value displayed on your voltmeter. If the value is higher than 64Hz, use the CVGAIN trimmer to further increase the value by the difference from 64 Hz (Eg. if the Voltmeter reads 68 Hz, adjust CVGAIN to 72 Hz). If the value is lower, decrease it by the difference (Eg. Voltmeter reads 62 Hz, adjust to 60 Hz).
NOTE: CVGAIN is the only trimmer where you tune down to increase frequency.
4. Repeat steps 2 and 3 until 0 V = 8 Hz. 3 V = 64 Hz within a margin of error of 0.2 Hz.
5. Set VS to 9V
The frequency should ideally be 4096.0 Hz. Adjust HFBIAS until you are close to this (4090 to 4100 Hz is fine).
6. Set VS to 0 V
Adjust the frequency to 8 Hz.
7. Set VS to 6 V
The frequency should be close to 512.00 Hz. Adjust HFGAIN until it is as close as possible to 512.00. You will never be perfect. The goal is to be in the range of about 511.40 Hz to 512.7 Hz
8. Step through the voltage range and ensure that each addition of 1 V causes a doubling in frequency.
9. Adjust VCOOFFSET until 0 V = 16 Hz.
For the Atlantis, Dixie II+ and Rubicon 2
There's an additional trimmer labelled OCT-ADJ which adjusts the octave offset of the octave switch. If you find your octave switch is not stepping in 1V increments you can tune it with this trimmer.