Repair Log #1
I recently repaired a XLR contact ground noise issue resulting from a loose chassis anchoring screw on a Sennheiser MKH 416 P48 shotgun microphone.
I discovered this issue while positioning the microphone to capture location sound as I was shooting assets for my senior portfolio. I originally suspected a cable with a compromised shield, which has reached epidemic levels among the 25 foot XLR’s available for checkout at the Media Lab.
Here is the sound of the ground interference transmitting through the hot contact when the female cable XLR was wiggled inside the male XLR connector on the microphone.
Loose Ground Screw Feedback Waveform
However, when the feedback remained solidly present after going through 3 more XLR cables, 2 of which were straight out of their original packaging, I realized the microphone was the source of the problem. A ground issue on a $1000 microphone was a perplexing predicament, something I would expect on the Rode NTG2’s ($300). The stock of older NTG2’s currently present in the media lab currently have a problem where the XLR pin retainer plate (plastic) wants to come out of the rear of the mic body
As it turns out, the casing screw not only keeps the electronics sled secured inside the brass body of the microphone, but also provides the continuity between the ground pin and the body of the microphone that allows the recording interface to absorb the ground feedback. This was discovered when I heard a ground pop after unscrewing the anchor while monitoring the microphone
Here is the sound of the ground isolation breaking as the screw is removed from its thread seat.
Ground Screw Disconnection Waveform
Reseating the screw to the proper depth in the threads resolved the issue immediately by providing continuity to the ground isolation once again. I will take this into consideration from now on when I am testing cables to make sure I do not jump to conclusions.
I just recently checked two Auray integrated wire boompoles that had been taken out of circulation due to reports of ground feedback, and found nothing wrong. Neither generated one ounce of feedback.
Diagnostic testing was conducting using a Digidesign MBox Mini USB Interface.
XLR Cable construction consisting of Kopul 3000 Series Noiseless Microphone Cable with Neutrik nc-mxx and nc-frx connectors.
