thanks for your answer!
Unfortunately neither changing the pedal type nor changing the input did anything.
I couldn´t find another trs cable in my pile of unused cables, so I couldn´t check that.
So, could still be the cable...
That reminds me a couple of months ago I bought a 6 pack of trs cables from a well known auction site - cheap, I might add - and found only 3 of them worked 'properly' ...... They all had molded ends and were from the Far East so may well be worth checking .....