Synthesis Technology - E490 Ladder VCF Lowpass VCF based on the Moog 904A and MOTM-490 Paul T Schreiber · E490 PG PatSeg The E490 Ladder VCF is a 10HP, Moog 904A 4-pole lowpass filter using modern transistors, but exactly matching the characteristics of the original. Using these new, matched dual and quad transistors allows the E490 to have lower noise and better tracking than the 904A without changing all the ‘quirks' in the sound. The 904A has several distinct characteristics which the E490 duplicates: • Low frequency self-resonance begins at 72Hz• There is a mid-frequency ‘dip and bump' due to phase shifts• The output amplitude drops as resonance increases• The resonance drops as the amplitude increases• The filter will ‘track sharp' past 400Hz (it tracks OK 100 – 400Hz)• If you push the RANGE trimmer to max, it can oscillate to over 20KHz Specifications • Depth w/power cable: 31.6mm• CVinput range: 10vpp (-5v to +5v), dc to 8khz• Audio input: 50k nominal input impedance, 10v pk-pk• Audio output: 12vpp (-6v to +6v), 20hz to 22khz frequency range Panel controls • Frequency: sets the initial filter frequency• Input 1 & 2: level knobs for the two audio inputs• Resonance: sets the initial filter resonance• FM level: inverting attenuator for the FM CV inputs• Distortion: adds 2x input gain when engaged Inputs and outputs • 1v/oct: 1 volt per octave control for the filter frequency• 2/3 oct: partial frequency tracking• FM 1: filter frequency modulation• In 1 & 2: audio signal inputs• Out: final output of the filter
