Dual VCA


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This module provides two voltage controlled amplifiers, two bypass-able voltage controlled filters, a CV inverter, a simple mixer and a pair of meters all configured with normalized connections to provide maximum functionality and convenience in a fairly compact space.

When either LPF button is engaged then a voltage controlled low pass filter is inserted in the signal path. The cut-off frequency of the filter is proportional to the signal controlling the VCA gain.

This effectively turns the VCAs into West Coast style Low Pass Gates where loud signals are bright and quieter signals are duller. When fed with an envelope with a fast attack this produces something similar to a string pluck. When a slow attack is used the result is more like a brass sound.

The design isn’t an emulation of classic Buchla LPG circuitry, instead the characteristics where arrived at by experimenting with various parameters until things sounded nice with a wide range of input types.

Depending on how you connect the Dual VCA module and the setting of the LPF (low pass filter) and INV (invert) toggle buttons it can serve as any of the following…

  • Two independent VCAs / LPGs
  • A stereo VCA / LPG
  • A voltage controlled cross-fader
  • A voltage controlled panner
  • A voltage controlled two-channel mixer

The four sockets at the top are inputs, the three at the bottom are outputs.

Hopefully, it is fairly obvious from the schematic legend how things work.

If only one of the input sockets at the very top are connected then the horizontal line between them indicates that the other VCA will receive a copy of the signal.

The two sockets in the middle of the upper half of the module are the CV inputs. The top one will control the gain/cut-off of both VCAs/VCFs if the lower CV input socket is not connected to anything.

If the INV button is engaged then the CV for the right-hand VCA/VCF is inverted. In other words a CV of 5 volts will result in zero gain / minimum cut-off and a CV of 0 volts will result in maximum gain / maximum cut-off.

More information is available on the Adroit Synthesis website.

This module is also available as part of the Adroit Toolkit and the LSSP XL bundles.