Noise with some microphones

Question

I have a high frequency noise when using some of my microphones?
The noise follows the operations on the front panel, i.e. follows the LEDs when these are flashing.

Answer

Please check the XLR cable(s) you are using.

We have seen that some cables (i.e. the cable attached to headset microphones*) where the XLR-housing is connected to pin 1.
The solder tag for the XLR-housing is typically labeled "G" and connects to "Chassis-Ground"

Pin 1 on the XLR plug is "Audio-Ground"
These two different grounds should not be connected.

Please refer to the picture below. The cable shield must be connected to pin 1 only.

* Note: i.e. the APEX-270 headset mic.


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