Compact Quad VCA

Advanced 9HP Quad VCA with dual Ring Modulator and dual Voltage Controlled Crossfader

Advanced Quad analog VCA module carefully designed by L-Fusion Modular. Offers 4 quality SSI2164 based VCAs with linear/exponential control and over 85dB of dynamic range, ultra-low noise and virtually no crosstalk. Module provides inputs to control the VCAs from 0 to 5 Volt CV or bipolar -5V to 5V CV or audio signal. Can be used to attenuate both audio signal and DC coupled CV.

Apart of basic VCA functions module provides very accurate dual ring modulator (four quadrant multiplier) and dual voltage controlled crossfader functions.

Ring modulators: To use ring modulator one signal is patched to ring modulator input and another one in bipolar control voltage designed for modulating with audio signal. Function provides accurate multiplication of both signals which can be used to obtain a large variety of interesting tones. Different wave forms from the same oscillator can be patched to these inputs as well to obtain more exotic wave shapes.

Power saw wave shape: When ring modulator module is paired with our Dual Triangle VCO module and patched saw and pulse waves from the same oscillator it can generate a very interesting wave shape that consists of ramp wave inside of saw wave. Pulse wave can then be modulated with CV which affects the proportion of saw and ramp inside the pattern.

Crossfaders: This function allows connecting input 1 and input 2 and crossfade between them using 0 to 5 Volt CV or bipolar -5V to 5V CV. If more crossfaders are needed module provides jumper to convert second ring modulator to crossfader. Same as ring modulators crossfaders can be modulated with audio signal to generate interesting wave shapes as well.

Analog compression: L-Fusion VCA module can also be paired with our (or third party) envelope follower to be used as a compressor. Compressor function attenuates high gain signal more compared to lower gain evening out overall signal strength. When nothing is patched to positive voltage control VCAs are designed to stay open so their voltage could be attenuated via envelope follower patched to subtractive/negative socket. Envelope follower should have to be fed through an attenuator which sets compression ratio. VCA output potentiometers provide high gain of +12Db to compensate for gain loss without the need of external amplifiers.

Sidechain compression lowers one signal strength when another signal is present. This is typically used with signals of similar frequencies such as kick drum lowering the gain of a low frequency base line. Kick signal is sent to envelope follower and then its envelope is used to lower synth gain.

To save VCAs it is possible to use the same VCA for synth gain control via CV+ input and sidechain signal strength reduction fed from envelope that would reduce the gain. This method is called ducking however it is not a real sidechain compression as this way the signal fed to CV- simply gets subtracted from the positive envelope and zeroed if it becomes negative. Real sidechain lowers the actual signal according to CV- gain, gain gets divided instead of subtracted resulting in much higher dynamic range and accuracy.

All potentiometers are precision closed shaft Alpha variety, module is made with high quality electronic components, features rubber knobs with soft touch for easy grip and tactile feedback.

Geeky stuff: Module consists of 8 analog SSI2164 VCA blocks + 38 OpAmps – 317 components in total. Al OpAmps are audio grade from Texas Instruments, with very low drift and offset rated at 0.5milivolt. All OpAmps in audio path are ultra-high dynamic range Soundplus/Burr-Brown type making sure of excellent audio quality and supply voltage noise rejection. Analog calculations are performed with 0.1% precision sourced from high end voltage reference from Analog Devices. Module is carefully designed using 4 layer PCBs to filter out noise and minimize crosstalk between different VCA channels, it provides plenty of decoupling for all ICs based on high end US Kemet and Japanese Nichicon capacitors.

https://reverb.com/item/85347261-compact-eurorack-quad-analog-vca-with-dual-ring-modulator-and-voltage-controlled-crossfaders