Hi Frontier1,
To be safe, unit should be off/unplugged for at least 5 minutes before removing top and reaching inside. There are two jumpers (L & R). They are at the left and right sides at the front of the circuit board on the left of the unit. Mine are yellow but I don't know about others. The block on the board has three pins and the jumper is positioned to connect two of those. Connected to the front two pins (closest to faceplate) is the higher position. Connecting the two toward the rear is the lower gain.
Good luck and be careful what you touch.
To be safe, unit should be off/unplugged for at least 5 minutes before removing top and reaching inside. There are two jumpers (L & R). They are at the left and right sides at the front of the circuit board on the left of the unit. Mine are yellow but I don't know about others. The block on the board has three pins and the jumper is positioned to connect two of those. Connected to the front two pins (closest to faceplate) is the higher position. Connecting the two toward the rear is the lower gain.
Good luck and be careful what you touch.