Since the beginning of AC power, audio equipment has often had hum problems. Hi Fi gear needs to amplify signal in the tenth of a volt range, always working in the close proximity of large audio signals in the 110 to 230 volt range. These large audio signals are the AC power lines operating at 50 or 60 Hz, an audio tone corresponding to a low hum.
Minimize Ground Loops If More than One Piece of Audio Equipment Has a Grounded Plug
If just one component of the audio system has a ground connection and there is no antenna connection, ground loops cannot occur. If there are hum problems then follow the guidelines in this article on how to fix audio hum problems to trace the cause. However, if more than one component is grounded, then there is the possibility of a ground loop. This article describes how to identify if audio equipment is grounded.
The simplest solution to multiple ground connections is to use a single mains distribution panel and to plug the grounded components into the distribution panel next to each other. Hum and buzz problems due to ground loops start to make their presence known when audio components are plugged into separate ground connections which carry leakage currents and noise from other mains-powered gear.
This is usually good enough for line level connections such as most modern sources. However, if the system includes a turntable or microphone input then it may be necessary to ensure than not more than one audio component has a grounded plug.
Plugging grounded audio components into their own wall sockets, particularly widely separated ones can result in a long loop between the earth connections. This is particularly likely in Continental Europe and North America where star-wired mains wiring is common. The ground loop may extend all the way to the fuse board in these cases.
One common situation is where a separate pre-amplifier/power amplifier combination is used with long pre-power signal cables to keep the power amplifier closer to the loudspeakers. If a grounded power amplifier is plugged in at one end of the room, and one of the audio signal sources is grounded at the other end of the room, hum due to a ground loop often results.
Use Optical Digital Connections to Break Ground Loops and Solve Computer Audio Hum Loops
Optical digital connections can break earth loops. This can either be from a grounded CD player to a grounded amplifier or from DVD players or multimedia audio components. A TOSlink optical digital connection is a great way to isolate a grounded computer from a grounded audio system.
If connecting to a computer sound card causes hum in a Hi Fi system then upgrading to a USB sound card with optical output can be a solution. However, this does mean that the Hi Fi system has to be able to accept a optical digital input. Sometimes separates like CD recorde5rs, DAT recorders or Minidisk recorders can accept optical inputs even if the main system cannot.
Antennas and Cable TV Connections May Cause Ground Loops Too
If hum only occurs in the system when an aerial or a CATV connection is made to the Hi Fi tuner, then what is needed is an aerial isolator. These are often supplied by the CATV operator. However, the problem can arise in a domestic distribution system where TV and radio signals are distributed around the home where a grounded component is plugged into the system in a room separate from the Hi Fi system.
Keep Hum Problems Out of Hi Fi Systems by Minimizing Ground Loops
Not all audio hum problems are caused by ground loops, but ground loops are among the most common cause of hum problems in Hi Fi systems. The best way to tackle audio hum is to take a methodical approach to diagnosing the cause.
Richard Mudhar - Originally from London, now enjoying a less hectic pace of life in Suffolk, Richard Mudhar is a keen wildlife sound recordist and ...
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