EMI Interference in Klein & Hummel O100 Monitors

[jeremynothman]

So, a few years back a bought a pair of these monitors second hand, and they aren't the youngest babes anymore. The recent thread about the Dynaudio BM6As had me think that I could possibly fix a problem that I've had with them, namely that the moment that my MacBook is plugged into mains power (which via a thunderbolt, or USB interface, is the source), there is a series of noises that the monitors make. Some of them are very clearly related to the computer (eg. at the same time as moving the mouse, writing to the drives), but some seems to be RF.
When I bought them, I also had the impression there was some hum/buzz, probably coming from the power transformer. At the current listening distance, that is completely inaudible, if it is there.

I have tried both a power supply with and without earthing, and it hasn't made a difference. I have just seen on the manual for the monitors (sorry no service manual/schematic), that there is an internal grounding switch which I'll also try out. Here's a link to the german manual https://www.manualslib.de/manual/451900/Klein-Plus-Hummel-O-100.html?page=4#manual

Any ideas? Has anyone had this with these speakers. Is it worth trying out building little faraday cages, or would that not possibly help? Obviously I can open one and take some photos.

 

[Khron]

Macbook? So the plug-pack is likely not earthed then, is it? And what about your interface(s)?

 

[jeremynothman]

Macbook? So the plug-pack is likely not earthed then, is it? And what about your interface(s)?

As said, I tried it with and without the earthed plug - it doesn’t seem to make a difference.

As for the interface, I’ve tried both an Audient ID4 MKII (bus powered USB-C) and a UA Twin (mains powered, non-earthed, thunderbolt interface)

 

[Khron]

Would be interesting to see if it's the same with an earth-referenced interface...

Either that, or disconnect the cable shield from the connector shell, and/or XLR pin 1, from one end of the cable or the other, between whichever interface you use, and the monitors.