The Low Pass Gate (LPG) is a classic Buchla circuit which imparts great effects on audio signals as a combined VC Filter / Amplifier. In the BugBrand version it is coupled with a convenient Decay Envelope generator.
The key to the LPG is the Vactrol – a variable resistive element, driven by an LED, which changes the intensity of the audio processing. It is the slightly slow response of the Vactrol that gives the audio effects such a natural feel and is the wonderful strength of the module. The LPG can be run in three different modes – Low Pass (VCF), Gate (VCA) or a middle mode that combines the two.
The LPG is controlled by a sum of the main Initial control, external CV modulation via the attenuverting Mod control, along with a variable-decay envelope generator via the Hit input – this passes through a comparator so that any signal rising above c.+1V will trigger an envelope.
A basic Decay/Sustain/Release response is possible by patching a gate signal into both the Hit input and CV modulation. Use the gate via Mod control as the final sustain level after the transient hit from the decay envelope.
The module is AC-coupled.
Current: +ve 25mA, -ve 15mA