UR44 Mains Hum / Screening

Hello. First time post on this forum.

I’ve just got hold of a used UR44 (originally from Thomann in Germany). My setup is totally minimal. UR44 to iPad Mini Retina via CCK, so the only mains device connected is the UR44.

There is significant hum when using a condenser mic. This reduces significantly when any screen is touched such as the metal case or XLR. When using electric guitar humbucker really hums and single coil is just unbelievably bad. Hum is louder than signal. Again this almost entirely disappears when the UR44 case or jack screen is touched.

This can’t be a ground loop. There is no loop as the UR44 is the only item that’s powered.

I’m using a USB cable from a Focusrite 2i2 as the seller forgot to include the supplied cable. It does have a ferrite bead on it though.

Any clues? Could it be the PSU (original) which is continental via a UK adapter? I’ve tried turning the PSU around in the UK adapter and it makes no difference.

Surely this can’t be right?

Cured by grounding the chassis to mains earth.

Pity the PSU doesn’t have this facility with, maybe, a ground lift switch. Horrible little switched mode thing!

Maybe all the testing was done with the main outs connected to an amp or other grounded device. The UR44 certainly does not like floating.