Steffcorp VCF-12 Eurorack Filter Module (ARP 2600)
The STEFFCORP VCF-12 is a voltage-controlled fully discrete filter, based on the 4012 filter used in the ARP 2600.
The VCF-12 features:
• Two Keyboard CV inputs. (calibrated to track 1V/Oct)
• Two FM inputs with attenuators. The first FM input allows inversion of the FM CV, as well as attenuation.
• Two Audio inputs with attenuators.
• Capable of self-oscillation. (watch your levels though!)
• Two Low-Pass outputs. (2-pole and the original 4-pole response)
• In addition, the VCF-12 has a “Slope” output, which can crossfade between 1-pole and 4-pole Low-Pass responses via a Band-Pass response in the centre of the crossfade.
• The Slope crossfade is controlled by a manual knob and a CV input with an attenuator that also allows inversion. A pair of LED’s give visual feedback on the position of the crossfade.
More about the Slope circuitry:
• The Slope CV input expects an input voltage in the range of either 10VPP or 5VPP (selectable via jumper on the PCB) to fully crossfade from 1-pole to 4-pole Low-Pass responses. Using the manual knob to offset the crossfade position, it is possible to use either bipolar or unipolar CVs to modulate the crossfade.
• A precision reference voltage and limiting circuit is used on the CV input to ensure the crossfade behaves predictably, even if the CV exceeds the selected range.
• The signal path of the crossfade circuit is based on an ARP 2500 circuit, and is fully discrete.
Parts are carefully selected after a lot of testing and comparison, and values are recalculated for eurorack levels to match the original behavior and sound.
• Power protection
• Buffered inputs & outputs
• Tracking well over at least 5 octaves during self-oscillation
• Frequency control 10Hz – 10KHz
• Power 64mA +12V / 49mA -12V
• Width 14HP
• Depth about 40mm