Mic Buzz Be Gone!

 

Is there a constant noise, like a ground hum, a mid-frequency static, a high frequency hash, or an annoying radio station signal hitchhiking on your recording chain? In almost all cases the cause is incorrect termination of the microphone cable.

Due to misinformation, negligence or a deliberate decision by the manufacturer, ground and/or shield of microphone cables are often terminated incorrectly.

 

A bit of background. 

3-pin XLR cables are sold as mic cables (between mic and preamp) AND interconnects (between AC-powered components like preamps, compressors, recorders). Though there is only one correct way to terminate mic cables (detailed below), there are cases where a cable’s shield when terminated at both ends of powered units may introduce ground hum.*

Mics, being at the beginning of the recording chain will act as antennas picking up stray radio waves or electro-magnetic noise, unless all housing parts that envelope the audio signal - from the mic’s head grill to the shell of the XLR connector that’s plugged into the mic pre - are 100% covered by a shield that is also grounded. 

Here is the rule for terminating mic cables. It has no exception: 

1. Terminate Ground AND shield of the cable at BOTH connectors to pin #1 (XLR 3-pin connectors) or to the corresponding ground pins of a multi-pin microphone cable. 

2. Make a wire connection from the connector’s ground pin to the connector shell, on BOTH connectors. You can solder a piece of wire (any type will do) between the ground pin and the little solder tab or loop that connects to the housing of the connector. Or you can twist the cable shield into two strands, soldering one to the connector’s ground pin, the other to the housing tab (see photo).

Tube mic cable connectors rarely have a grounding tab, so use the connector’s strain relief clamp to attach a section of the shield, or the bare end of a piece of wire (the other end is soldered to the ground pin).

 

* Powered components connected by an interconnect cable have their own ground supplied from the AC outlet. A slight ground voltage differential between these components and the cable’s ground can introduce a 60 Hz hum.

Yet, even with interconnects, I always start with the mic grounding/shielding scheme: if there is no ground hum, RF protection will be optimal. Only if there is audible ground hum, I cut the shield on the receiving end of the cable.