I recently purchased a Quad Cortex and tested it using the included non-grounded power adapter, as well as the 12V 2A output from a Voodoo Lab Pedal Power 3.
After connecting an XLR cable and completing my tests, I pressed the shutdown button—and at that moment, a very serious low-frequency hum occurred.
When using outputs 3 and 4 (TRS), everything works fine with no hum at all.
What could be causing this issue?
Yeah, that’s normal. You should turn off the speakers it’s connected to before turning off the QC.
The way it grounds itself occurs when the unit is on. The hum that you’re getting after it’s off it’s part of the design. It’s not grounded the same way when it’s off, so you’ll get a hum sometimes.
Always turn off your speakers first before turning off any piece of audio equipment plugged into them. Not exclusive to QC.
I have turned the quad off numerous times running stereo XLR’s to dual PA speakers in FRFR mode with them set to decimate and the unit powers down silently and no hum from the speakers. Using the wall wart in a surge protector with both Pa systems plugged into the same strip.
What doesnt make sense is that it does it on your XLR but not your TRS. The quad uses whatever you are plugging into as its ground source and the XLR outputs are supposed to provide better grounding than TRS. If it did it on both types of outputs I would say its normal. But if it only does it on the XLR that doesnt sound proper.
There have been multiple threads and posts about this same scenario on here
Guess I will just consider myself lucky.