The Lopass Gate (LPG) from Pittsburgh Modular is a triple-mode module that combines three functions into a single module, including a VCA, low-pass filter, and low-pass gate. The voltage-controlled amplifier (VCA) controls the volume of a sound, while the low-pass filter utilizes a Sallen-Key design, which is a classic 2-pole, 12 dB per octave filter that is used in the Korg MS-20 and MS-10 synthesizers to produce a warm and buttery sound. Resonance has been added to further push the filter into sonic mayhem and snarls when approaching self oscillation.
The low-pass gate circuit combines the low-pass filter with the VCA to simulate the characteristics of natural instruments. Louder sounds have more harmonic content, while quieter sounds contain less harmonic content. The LPG utilizes a vactrol circuit offering a fast and tight attack with a slower decay, which lends itself to organic percussive sounds with a natural decay. The vactrol can be controlled by the "Ping" input, which reacts to any gate of square-wave signal. The Lopass Gate module is 8hp wide, 1.4" / 36.5mm deep, and requires 30mA of power. The module ships with a ribbon cable.
- Frequency Control Knob: In filter mode, the frequency knob controls the center frequency of the filter. In VCA mode, the frequency knob controls the pass-through signal level. In low-pass gate mode, the frequency knob controls both the center frequency of the filter and the pass-through signal level
- Resonance Control knob: In filter mode, the resonance knob controls the amount of resonance. In VCA mode and low-pass gate mode, the resonance knob is not active
- Mode Switch: Switch between the 3 module modes. VCA position (up) enables VCA mode, LPG position (center) enables low-pass gate mode, and FILTER position (down) enables low-pass filter mode
- Frequency CV Input Control Knob, CV Input, and Invert Switch: CV input controls. The CV input knob attenuates the incoming CV signal. Invert switch inverts the incoming CV signal
- Input Jack: Signal Input
- Ping Jack: Gate or trigger input used to ping the vactrol and quickly modulate the frequency of the module
- Output Jack: Signal Output