It has been brought to my attention that a few folks are having nasty ground loop hum when plugging Hapa cables into certain equipment. This issue universally has been because of a slight compatibility problem that the KLE-I connectors have with WBT Nexgen female connectors.
As you can see, the Nexgen connectors utilize this spiral profile on their barrels in order to reduce mass. It's a very clever design, however, it can cause issues with the KLE connector.
If you look closely at the photo I took you can see the tiny singular connection point that the KLE-I common/ground pin has. It's single point of contact combined with the Nexgens spiral design can fail to contact each other and cause a nasty ground loop issue.
Here's some dos and don'ts on how you resolve the issue:
What to do: try your best to eyeball the point where the spiral overlaps slightly. This location is the best bet for you to make contact on the ground pin of the KLE connector. TURN YOUR PRE-AMP/SOURCE OFF PRIOR TO PLUGGING/UNPLUGGING AS WELL AS YOUR AMP this is just best practice. Next turn your preamp volume low, but not completely off. turn on your preamp/source and then your amp. if you made proper contact your system should be relatively quiet. Proceed to turn things up and test with music.
If you are getting ground hum, repeat the previously outlined process. Unplug the connector and rotate it 15 degrees prior to plugging it back in (again make sure to practice good power cycle hygiene!)
What to avoid: don't rotate the connector while plugged in. The KLE ground pin is somewhat pointy and you risk gouging your female connector if you do this. You may also accidentally loosen the KLE connector barrel, easy to tighten back down, but again, something you want to avoid. Once again, don't do any of this with your equipment on, this goes for any time you're making a connector change regardless.