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MXR Carbon Copy Dry Kill Mod

A customer requested a mod to their Carbon Copy to add a switch to remove the dry signal. The Carbon Copy has an unusual mix knob, in that it doesn't sweep from fully dry to fully wet, but rather it just increases the volume of the wet signal. A switch could be handy to kill the dry completely if you only want the trails, or you just want to have some fun with this lil' guy.

Going through the PCB (I couldn't find a reliable schematic) I found the following configuration:

The Mix knob adjusts the volume of the wet signal, and then goes through a 1:1 summing amplifier. Our goal here is to yeet R48 and wire up a switch to switch it back in and out.

I used a DPDT switch because that's what I had, but a SPDT would work just the same.

One yellow wire going through a 43K resistor and to the middle lug of the switch, one yellow wire completing the circuit in 'stock' mode. The black wire goes to a ground point to keep that input from floating. Without the black wire I had lots of clock noise being picked up by the yellow wires.

Heatshrink these wires, since it's a tight squeeze and the parts might start getting to know each other.

If you find that the volume is substantially lower, you might have the two yellow wires reversed, swap them around.

Bing bang boom, you got yourself a dry kill switch.