The Beepboop Passive LPG is a simple analog LOW-PASS GATE circuit based around a VTL5C vactrol. The module features an attenuator for adjusting the CV applied to the Vactrol, a switch to select the depth of the cutoff and another switch to change the decay time.
Feed a signal into the IN jack and then control the amplitude of this signal applied to the OUT jack with the CV jack and attenuator.
The CV input is designed for 0-5V signals. Using short triggers (10ms) result in that classic LPG ping and ring sound but the module as works well with gates envelope control signals.
The toggle switch has three positions which set the depth of the low pass gate resulting in different tones.
Top position = Dark
Middle position = Bright
Bottom position = DEEP Dark
A very small switch for enabling the LED behind the panel is hidden in the Vactrol symbol on the panel. When the LED is enabled the decay time becomes shorter giving you even more control of the vactrol response curve.
This new V2 version also has improved resolution of the CV attenuator which removes the “dead zone” before the LED inside the Vactrol starts to turn on.
Note the module has been designed for use with +5V signals such as standard triggers, gates and envelopes. When CV Voltages exceeding +7V are used on the CV input some audio bleed will occur.
Lovingly designed and hand soldered here at Beepboop Electronics Workshop in Bristol.
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