Avalon Harmonics iVCA (Built Module)

Stereo VCA with CV attenuverter and full range offset.

This article is for the fully built Eurorack module.

Includes:
1x Avalon Harmonics iVCA Module
1x 15cm Eurorack Power Cable
2x 3mm Knurlies

Built and tested by Thorinair.

iVCA is a simple stereo VCA, with a focus on manipulating the incoming CV by allowing for full range offsetting and attenuverting. The VCA circuits are a classic simple transistor type.

The L and R IN jacks accept an incoming audio signal, while the L and R OUT jacks are for the output. The inputs have around 14 Vpp capacity and are best suited for audio signals. VOL knob can be used to adjust the volume of the incoming signals and can be used to tame very loud signals if necessary. When set above around 3 o'clock, the signals will have some additional gain applied to them.

The main focus of the module is to allow for easy manipulation of the control signal. OFS knob can be used to offset the CV signal in a full range into both positive and negative values. It can also be used to fully open the VCA when turning it all the way clockwise. ATN knob is an attenuverter for the CV signal. The signal has no effect when set to the middle, has around 2x the effect when set all the way clockwise, and around 2x the inverted effect when set all the way counter-clockwise. This allows the module to be easily adjusted to behave like a normal VCA to control notes, or as a ducking effect to do some sidechain action.Thanks to the multiplied CV input, the VCA can fully open even with a 5V CV input. Both knobs have a centre detent for easier tactile use.

A bipolar LED is also included and shows the current state of the CV. Green represents positive values, while red represents negative values. This allows for easy monitoring how the CV is affecting the audio signals, even when there is nothing to be heard.

NOTE: The module's offset knob needs to be calibrated for the PSU in your rack before use:
1. Set the OFS and ATN knobs to middle position. Leave CV input disconnected.
2. Set the VOL knob all the way clockwise and input a loud signal to both L and R IN.
3. Listen to the L and R OUT signals and adjust T_OFFS so that it is silent, but right on the edge of being silent.

Website Page: https://avalon-harmonics.com/module/iVCA/
ModularGrid Page: https://modulargrid.net/e/avalon-harmonics-ivca
GitHub BOM & Source: https://github.com/Thorinair/Avalon-Harmonics/tree/master/Modules/iVCA

Features:
- Compact 4 HP design
- Input volume knob with some extra gain
- CV full range offset and attenuverter knobs
- VCAs fully open with 5V CV
- Status LED for CV
- Wrong polarity protection
- Size: 4HP
- Depth: 36mm
- Power: +12V: 22mA, -12V: 22mA