On all Magica amps built since the third quarter of 2016, a mini two position switch has been placed near the back of the amp between the two tubes furthermost to the right. The switch points down towards the bottom of the cabinet. This may not be the most convenient location for the switch, but it is the shortest distance for the signal and does not create any unneeded noise.
When the switch is pushed toward the front panel, it is in "M" mode and when it is pushed toward the back of the amp, it is in "D" mode. The difference is "D" favors lower mids and "M" favors upper mids. This only effects the overdrive channel(s).
There might be a little pop when the amp is on and the toggle is switched, but is is safe to use when the amp is on so you can experience the difference for yourself.