Citation:
55 MIDI IN
This 5-pin DIN port accepts data sent by a MIDI sender (for example, the ENGL MIDI
Z-12, Z-15, or Z-9 foot controllers) or from or routed through another MIDI device.
Switch no. 56 lets you activate the preamp's power supply if you have an ENGL MIDI
foot controller connected to this port.
CAUTION: Before you connect any other MIDI footswitch or effects device, always
make sure that switch no. 56 is set to the right to avoid damaging the device
Voilà, je sais pas à quoi correspond ce switch n°56 mais regarde un peu.