The gain issue that I noted in my post about the ADDAC805.VS2 has been fixed by a modification I received from support at ADDAC.

Test Setup

Photo above shows the test patch. The module is DC-coupled. A fixed +5V source is patched to the clockwise inputs to both left and right X-Faders (yellow patch cable, input 4 normals from input 2). A positive triangle wave is patched to the left CV input, which normals to the right CV input (green cable). The left and right outputs are monitored on the Mordax DATA scope (orange cables).

The top (green) trace displays a 0 to about 3 volt triangle wave sent to the inputs of both left and right cross faders (scale is 2V/division). The middle trace (blue) is the left output and the bottom trace (red) is the right output (scale is 5V/division). Why are the left and right outputs different? The right output has more gain.

The Fix

Andre at ADDAC was very helpful and responded to my email with the following.

“I just plugged in a few of our modules and tried to reproduce the issue you described and noticed that most were OK but one had the same issue! Thanks for bringing this to our attention. You’ll need a couple 56pf 0603 capacitors and place them on top of 2 resistors, do not remove the resistors just place the capacitors on top and solder them to the resistor bellow so that the capacitor and resistor are in parallel, attaching picture!”

I added the two 56pf capacitors, but used small axial lead caps instead of surface mount.

Testing after mod

Photo above shows triangle wave CV, a little over 2 volts, and the outputs of left and right X-Faders. The scope ranges for the outputs are 2V here, showing the maximum voltage out at +5V, i.e. unity gain. Note that the two outputs are identical (with different offsets on the display).

Photo above shows a smaller amplitude triangle wave CV and the corresponding lower outputs (about 3V max). Again, the shapes are identical. The exponential response curve is clear.

Photo above now shows the triangle CV with a larger amplitude. Again the outputs are identical. The outputs are limited to the input value of +5V.

Conclusion

The recommended fix worked! I’m completely satisfied with the module now.