Colourupter Troubleshooting

Last modified: 2026-08-24

Table of Contents
  1. General resources
  2. 1. Output jumps up (or down) as soon as the Colourupter engages, even with Colour at zero
  3. 2. Distortion, sudden volume drops, or LED behavior that changes after the unit worked fine initially
  4. 3. No distortion/compression
  5. 4. Can't hit the calibration spec at step 6.3 (target -15dBFS)
  6. Request Troubleshooting Support

The sudden jump in level when you engage the Colourupter is normal, not a fault, and most of what's left comes down to a resistor value that doesn't match the parts sheet or a cold solder joint. The sections below are ordered by likelihood, so work down from the top.

General resources

Output jumps up (or down) as soon as the Colourupter engages, even with Colour at zero

This is expected behavior. The Colourupter has substantial built-in makeup gain, because it's capable of much more compression than a gentler Colour module. The exact amount varies with the natural tolerance of the opto/vactrol cell.

Distortion, sudden volume drops, or LED behavior that changes after the unit worked fine initially

When something stops working after working for a while, this almost always indicates a cold solder joint. Reflow any joints that look dull or "blobby." See Cleaning Up Solder Joints.

No distortion/compression

  1. Double check the orientation of the vactrol against the assembly guide.
  2. Check all resistor values.
  3. Check solder joints.

Can't hit the calibration spec at step 6.3 (target -15dBFS)

  1. Double check the orientation of the vactrol.
  2. Check all resistor values.
  3. Check solder joints.

Request Troubleshooting Support

If you weren't able to solve your issue from this guide, you can request email support from one of our troubleshooting experts here: Request Troubleshooting Support.