PMFoundations 3080 VCO v1.2 User manual

3080 VCO v1.2 –User Guide
This is the setup and user guide. The unit is designed for a monophonic Analog synthesizer.
The module is designed and sized for Eurorack systems. You will need a 16 pin Eurorack power
ribbon connector with –12/0/+12 which is connected to a synth power supply. You will also need a
trimmer adjustment tool, a digital volt meter, a frequency counter and, if possible, an oscilloscope.
Calibrating the 3080-VCO
If you bought PCBs or a kit, you should only need to calibrate the unit once. If you bought a pre-built
and tested unit, you can skip this section. Power up the device and allow it to warm up for 15 minutes.
1. Set R30 HF Trim to 0. This is done by turning the screw counter clockwise until it hits the end
stop. A quiet click can be heard.
2. Disconnect all CV sources from the inputs.
3. Set the coarse and fine tuning controls to their center position.
4. Put a frequency counter on the SIN output.
5. Offset adjustment: Adjust R1 Offset until the frequency is 16.35Hz.
6. Connect a CV source such (as a keyboard controller CV) into the 1V/octave jack.

7. VOLTS/OCTAVE adjustment: Repeatedly pay two notes one octave apart at the low end (say C2
65.4 Hz and C3 130.8 Hz) and adjust R20 V/Oct until the frequency of the high note is exactly
double that of the low note. Check the frequency of other notes separated by one octave. Fine
tune R20 until the best tracking is obtained.
TIP: If the high note is flat, turn R20 to make it flatter still. This reduces the gap between the
two notes. Then, while playing the lower note, turn the FINE tune panel control to the required
lower frequency (e.g. 64Hz) and check both notes again.
8. High Frequency trim: Repeatedly pay two notes one octave apart at the high end (say 1200 Hz
and 2400 Hz) and adjust R30 HF trim until the frequency of the high note is exactly double that
of the low note. Check the frequency of other notes separated by one octave. Fine tune R30
until the best tracking is obtained.
9. Tune the VCO using the coarse and fine pots until the output frequency corresponds to a known
keyboard note. e.g. C4 = 261.63 Hz.
10. Repeat the adjustments until you have the tracking as close as possible to 1V per octave.
11. SINE SHAPE: Using an oscilloscope or audio output adjust R19 Sine Symmetry and R2 Sine Round
until the best, balanced, least distorted sine wave is obtained.