Hi Martin

> the thing i'm looking for is a static wide band 90° phase shifter (90° shift from 40Hz-1kHz)

ok, then all classic audio phasers are not usable for you. Because the
OTAs have a too wide variance. If you do not need voltage control
anyway, then build the circuit as described in your link.

May be there are other circuits to achive a static phase shift over a
wide frequency range. But I do not know them.

Florian