Thorn.audio VC LFO Eurorack Module

Fully voltage controllable Eurorack format, externally syncable, 16 waveform low frequency oscillator with built-in VCA and sample & hold.

Suitable for precision modulation, live performance as well as educational purposes.

• Fully voltage controllable
• Externally syncable in three different modes
• Four frequency ranges by octaves, from 0.05Hz to 102.4Hz
• 16 distinct waveforms in two sets of eight
• Waveform distortion
• Sample and Hold
• VCA
• Gate output
• Inverted output
• Visual feedback on all incoming CV
• Easily reprogrammable

Photos Courtesy Of Paul D. Pape 

The core idea behind this module is all about control voltage. Hence all features are individually broken out to CV inputs, making the most use possible of the benefits of the digital wavetable oscillator. This means that the design is geared towards allowing hands-off control of all aspects and some concessions have been made to that effect.

Initial setup basically consists of connecting the power cable to the module and your bus. The cable has a slotted socket for correct orientation, but mind that the red stripe faces the white line on the edge of the pcb. The included screws are nylon in order to minimise rack-rash.

Tuning the module is possible by adjusting the small smd trim potentiometer on the back. It adjusts the offset voltage that affects the center point of the lfo oscillations. It should be close to its three o'clock position, but you can adjust it by turning the module on, reducing the output level to almost zero and turning the trim potentiometer until you find the point where the gate output led just barely turns off.

The LFO sync type is hard sync, meaning that it resets the current cycle to the beginning of the waveform. It does not control the duration of the cycles. This allows you to further shape the output to, say, three quarters of a sinewave by using external sync and adjusting the HZ knob so the duration of a cycle is just a little longer than the time between incoming sync pulses.

Color coded nuts indicate the type of jack, with gold representing Gate/Trigger input, black is +-5v CV inputs and red jacks are outputs.

The CV inputs are scaled down to +-2.5v and added/subtracted with the knob setting, meaning that to sweep the full range of the parameter with CV, the knob should be in center position. The inputs are clipped to the allowed range after mixing, so you can apply any eurorack voltage here.

The module's core processor is socketed, so using a simple PIC programmer and some basic Assembly knowledge you can modify its functionality to suit your needs.

The code is written by Electric Druid who supplies me the chips preprogrammed.