A TIP from the Designer: If you want to control the amplifier via a MIDI system, use jacks 20 and 21 and a Looper or MIDI Switcher (e.g. ENGL Z-11). Use two stereo 1⁄4" cords to connect the ENGL MIDI Switcher Z-11 (optional). You can then preset the four switching functions Clean/Lead, Gain Lo/Hi, V.L.S. and Reverb via the Switcher, store your custom switching setups as different MIDI programs and activate the presets via a MIDI board (e.g. ENGL Z-12).