SB2 Troubleshooting

Last modified: 2026-08-27

Table of Contents
  1. General resources
  2. 1. One or more channels quieter, louder, or attenuated by a fixed amount
  3. 2. Silence, dropped channels, or the whole unit not passing audio
  4. 3. Hum, buzz, or crackling noise
  5. 4. Output seems very quiet after summing
  6. 5. XLR jack screws won't seat
  7. Request Troubleshooting Support

Most SB2 problems trace back to one of the yellow resistor arrays soldered in backward, or a cold solder joint on the DB25 connector. A quiet output after summing is also often just how a passive summing mixer behaves, not a fault.

General resources

One or more channels quieter, louder, or attenuated by a fixed amount

  1. Check the orientation of the yellow resistor arrays against the manual. The pin 1 dot should line up with the PCB's square pad. A reversed array here is the single most common cause of a channel imbalance.
  2. Reflow or inspect the solder joints on the DB25 connector and the resistor arrays for a cold or bridged joint.
  3. If an array is confirmed reversed, desoldering and replacing it is more reliable than trying to reflow around it.

Silence, dropped channels, or the whole unit not passing audio

  1. Check for reversed resistor arrays first, the same as in Section 1.
  2. Look closely at the DB25 connector pads for a solder bridge or short between adjacent pins.
  3. Check for excess flux or rosin residue around the joints. This can interfere with a connection even when the joint looks intact, and cleans up with isopropyl alcohol.
  4. If you have a multi-meter you can check your build by confirming the resistance between the points in this chart: SB2 Resistance Testing Values (Google Sheets).

Hum, buzz, or crackling noise

  1. Reflow the solder joints on the affected channel.
  2. Try a different cable. A bad cable produces the same symptom as a board issue and is worth ruling out first.

Output seems very quiet after summing

This is expected. The SB2's passive design has roughly 30 to 45dB of gain loss built in, so you'll need mic preamps after it to bring the signal back up to a usable level. If your channels are quiet by that much and evenly across the board rather than on just one channel, this is normal operation, not a fault. Go to Section 1 if only specific channels are affected.

XLR jack screws won't seat

The XLR jacks need plastic-cutting screws, not machine-thread screws. If yours won't catch, you likely have the wrong screw type rather than a stripped hole.

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.