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Digital VCA MKIII

Digital VCA MKIII front panel: a black 8HP Eurorack panel with two BIAS knobs and two CV knobs at the top, a row of toggle switches (ZCD/TR/INST, BIPOLAR VCA/VCA), a NOISE and +5V horizontal toggle, and two columns of jacks labeled UPD A, CV A, IN A, OUT A, OUT ZCD B, OUT ZCD A, OUT A+B, UPD B, CV B, IN B, OUT B.

Non Traditional Fully Featured VCA

1Introduction

Thank you for purchasing the MKIII version of my classic Digital VCA. This is a design I'm super fond of for how it works behind the panel, and for its creative potential in many patches. This module combines several tools into a small package and will become a staple in your system. Thank you for supporting WMD! - William Mathewson

2Controls

  1. BIAS: Sets the baseline level of the VCA. In unipolar mode, fully counter-clockwise (CCW) is fully closed. In Bipolar Mode, noon is fully closed.
  2. CV: Jack and attenuator for CV. CCW is off, fully clockwise (CW) is full open. 5V with fully CW will open the VCA completely.
  3. LED: Shows the current state of the VCA. If it's off, the VCA is closed. Brighter is more open. If it's not changing, it's probably because you're in ZCD or TR mode.

3Update Modes

The ZCD/TR/INST switch controls when the VCA level is updated.

  1. INST: Continuous, like a normal VCA.
  2. TR — Trigger Mode: Updates the VCA on a rising edge (trigger or gate) into the UPD jack. The threshold for updating is +3.3V.
  3. ZCD — Zero Crossing Detector Mode: The signal on IN is analyzed, and every time it crosses 0V a trigger is sent to the VCA allowing it to update. This allows for fast changes in amplitude that don't click. This mode applies an amount of latency to the VCA that is at maximum 1/2 of a period of the fundamental frequency.

4Bipolar VCA / VCA Switch

VCA — normal unipolar VCA mode, like other VCAs.

BIPOLAR VCA — negative CV inverts the output signal, aka ring modulator mode. This mode moves the off point of BIAS to noon.

5Normaling

  • CV A has a noise source normaled to the jack. This makes the Digital VCA a Sample & Hold module in TR mode.

  • IN A has 5V normaled to it for use as S&H with just the TR in.

  • CV B can have Noise or the A CV input normaled to the jack by flipping the horizontal toggle.

  • IN B can have OUT A or +5V normaled to it by flipping the horizontal toggle.

  • CV B's Noise source is different than CV A's, so you can have two independent S&H circuits.

6Patch Examples

Two Digital VCA MKIII panels side by side with labeled callouts. Left panel (Sample & Hold patch): BIAS sets the baseline voltage, CV sets the S&H output amplitude, the left mode switch is set to TR, the +-5V toggle is down for 0-5V output or up for +-5V output, UPD takes the clock, IN A takes the signal to be sampled or is left empty for internal noise, and OUT A is the output. Right panel (Ring Mod patch): the left mode switch is set to INST or ZCD, the BIPOLAR VCA toggle is up for ring mod and down for amplitude mod, CV takes the modulator, IN takes the carrier, and OUT A is the output.
Left: Sample & Hold patch settings. Right: Ring Mod patch settings.

6.1Sample & Hold Patch

  • Connect your clock source to UPD.

  • CV input is the signal to be sampled. Leave unpatched for internal noise.

  • Turn Bias to select the baseline voltage of the output.

  • Turn CV to control the range of the output.

6.2Ring Mod Patch

  • Connect your modulator to CV.

  • Connect your carrier to IN.

  • Turn Bias to 12 o'clock.

  • Turn CV fully Clockwise.

  • Experiment with ZCD or INST modes.

  • Set 2nd switch to Bipolar VCA.

7Specifications

Dimensions:

  • Size: 8HP
  • Depth: 35mm (with cables)
  • Board Height: 112mm

Power:

  • +12V: 65mA
  • -12V: 45mA

Inputs:

  • 100k ohm impedance
  • 3.3V Threshold for UPD
  • CV Range: 0-5V for full opening

Outputs:

  • All Outputs: 1k ohm impedance / 20Vpp range

8Videos & Patch Examples

Check out our YouTube channel for in depth videos and patch examples.

Watch on YouTube (opens in a new window)