Hello Joe,thanks for your responce.

The H90 is in Global Kill dry mode, the amps loop has a dry/wet balance but 100% is

still parallel! It’s not possible to make it serial.

There is a 50Hz noise when the H90 (in dual mode) is connected like this:

Guitar->H90 input1

H 90 output1->Duotone  H&K input

DuotoneH&K send->H90 input3

H90 output3->DuotoneH&K return

In the amps clean mode it’s not a problem.

In overdrive mode it’s a lot worse,

and in boost mode it’s almost unusable.

When I connect usb then it’s only usable in clean mode! I’ve made recordings off the noise.

But when I put the H90 only in the parallel loop there’s no 50Hz noise, and almost no usb noise, but then I can’t use Whammy, Octaver, Wah, Weedwacker…….