I've finished the interface box for the Compact Phasing.
So it has two spst switches and a pair of jacks for the modulation DIN, and 3 jacks for the line in & outs DIN.
Everything works like a charm but I have not managed to find a good place to link the 4th pin of the 6 pin DIN connector (as you can see on my schematic I left it unconnected):
If pin 4 is connected to pin 6 or pin 3 it reduces a bit the depth of the LFO, but that's not better with or without this connection. Any idea?
On my original on/manual switch the pins 3&4 are linked together and pins 1&2 too; but this pedal only uses one switch and does not allow for fast/slow or expression pedal connection.
Note that you'll need a 7 wire cable because there is the ground on the seventh wire (the other cable to connect the line in/out DIN plug can be a standard 5 pin midi cable).
The expression pedal trick is ok with a simple volume pedal VPJunior from Ernie Ball (which has a 250K log pot, but I had to change the setting of the internal curve switch to make it usable with the CP1).
Thanks again for your help!