The 504 VC Low Pass Filter is a classic, ladder-style circuit with some clever additions. The module’s cutoff and resonance parameters can be adjusted using potentiometers. In addition, there are two frequency CV inputs. One of them features a bipolar attenuator. A third CV input can be used to modulate the resonance. The 504’s edge steepness is determined by a three-way switch. However, in total there are four options. Two jumpers decide whether the module operates at -6 dB or -18 dB per octave in the middle position of the switch. The options always available are -12 dB and -24 dB per octave. Another jumper makes it possible to (de)activate the bass compensation of the filter. Thus, you can choose between classic Moog behavior, meaning the low frequency range drops more and more in amplitude while the resonance is increased, or a modern character without any loss in bass.
Audio input and output
Two cutoff CV inputs
Resonance CV input
5U module in Moog form factor, one unit wide