Hum and buzz in audio systems and home theaters

by Nyal Mellor April 08, 2013

What effect does 'hum' and 'buzz' have?

'Hum' and 'buzz' can cause major noise issues with our high performance audiovisual systems.

• Hum is a superposition of the 60Hz mains AC frequency on the audio or video signal.
• Buzz is a superposition of the harmonics of the 60Hz (120Hz, 180Hz, etc) mains AC frequency on the audio or video signal.
  
  

How is hum and buzz caused?

There are three main mechanisms that cause hum and buzz:

• Interchassis currents between pieces of equipment with OR without a saftey ground as a result of 'stray' capacitance in the power supply
• Ground loops - more specifically differences in the voltage of the safety ground wire between interconnected equipment
• Electromagnetic coupling of AC and signal cables

For a more detailed discussion we suggest reading the Jensen Transformers guides below.

How do I solve hum and buzz?

A common root cause of hum issues are ground loops caused by equipment being on different electrical circuits or being plugged into different outlets on the same electrical circuit. The solution to this is to use good grounding practices - i.e. having a single grounding point for equipment and connecting all equipment to this with short, high gauge (low impedance) power leads. Powerbridges (in wall electrical circuits that are not always connected to the home electrical system; they are essentially normally de-energized electrical circuits that are energized when one end is plugged into the outlet of a power conditioner or UPS) can be used for subwoofer and projector in wall runs. In most other cases the root cause of hum and buzz can be tracked down to a single interface between two pieces of equipment. We suggest using the Isomax Troubleshooting Guide to identify the root cause of the hum and buzz issue. The solution is generally to isolate the two components as follows:

• HDMI - use fiber optic HDMI cable
• Cable TV - use a Jensen VRD-1FF CATV isolation transformer
• Audio - use an appropriate Jensen transformer. Both single ended and balanced models are available
• RS232 - use an optical isolator
• Ethernet - use an optical isolator

Whatever you do, do not float the ground using a cheater plug! The ground is there to protect you from electrocution.

References and further reading:

Understanding, finding and eliminating AV ground loops, Bill Whitlock, Jensen Transformers. Balanced lines in audio systems: fact, fiction and transformers, Bill Whitlock, Journal of the Audio Engineering Society, Vol 43, June 1995 Hum and buzz in unbalanced interconnect systems, Bill Whitlock, Jensen Transformers application note AN-004. Isomax troubleshooting guide, Bill Whitlock, Jensen Transformers

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