Thanks for the input. Might be bad design also since there are units out there which act this way.
I could ask the previous owner of course, if it ever worked on this one, but he hasn't replied to my mail when I asked about the adapter.
I've also read that the different units may sound different when compared side by side, but that's no problem for me.
But I guess I can do without distortion or use a pedal if needed, unless of course somebody figures this out, I'm not much of an electrician myself and don't really know where to start poking.