The Best Sound For Less
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Ground Loops
Warning Static
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The Church Speaker
Underpowered Speakers
How Much Should It Cost?
The History of Movie Sound
Leo Fender Interview

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Wright Sound Systems
1311 Cedar River Drive
Waverly, IA 50677

What is a Ground Loop ?

A "Ground Loop" is an electronic condition caused when an audio path has two or more possible routes.

The result is often a 60 cycle hum, and occasionally an oscillation above hearing in the ultrasonic or radio frequency range. This can draw a lot of power without an audible sound, and can result in equipment damage if prolonged. - It may be accompanied by a 120 cycle hum because of draining the power supply.

Example 1:

A sound mixer is connected to a grounded AC outlet at one end of the room and a power amp or powered speaker is connected at the other. The two are connected with a signal cord. This is a very common setup. The signal ground can travel on both the audio cable and through the ground wire in the AC outlet. This is what creates the loop.

It is not logical to cut the ground conductor in the signal cord so the best solution is simply unground either the mixer or the power amps. I usually ground the mixer and unground everything else.

***This is perfectly safe. All of the amplifiers I grew up with had 2 blade power plugs and worked, and still work perfectly fine. They have ground switches that connect a capacitor to one side or the other of the AC line. This is to minimize hum since one side is actually neutral, which is the same as ground. In fact, there is really no good reason to have that 3rd ground wire at all. (Other than it holds the plug in better.)

Example 2:

You have built a rack for all your equipment; power amps, equalizers, crossovers, limiters, etc., and you have run all the input and output wires to a patch panel. The units are all plugged into AC power, and they all are screwed to metal rack rails. Now you have a triple ground loop: the AC power cords, the signal cords, and the metal rack rails. I have seen this done many times and it nearly always leads to bizarre problems. High frequency oscillation, 60 cycle hum, and even damaged equipment. Do not use a patch bay in an amp rack. Just connect from one thing to another with patch cords. And be prepared to lift the ground on some or all of the components. A simple way is just pull out the ground pin on the power cords. I also prefer wood mounting rails because they do not ground one chassis to another. I also put carpet or vinyl between pieces so that they do not touch, plus it prevents scratching too.

Example 3:

You are connecting a portable sound system to an installed system. This will almost always cause a ground loop since the installed system is no doubt grounded, and your portable system will be grounded through a 3 pin power cord. The first thing to try is inserting a "cheater" on the power cord to your portable system. This will usually solve the problem. However, you may need an isolation transformer.

Example 4:

I once encountered a ground loop hum when connecting a wireless microphone receiver to a small sound system. It had a 3 prong grounded power plug, which most wireless nowadays do not, and this was the problem. Simply getting rid of this by using a cheater solved the problem completely.

Always carry around several AC adapters, commonly called "cheaters"

They will be very useful when encountering ground loops

 

Using an isolation transformer.

The Behringer HD400 "Hum Destroyer" is a dual isolation transformer. It has inputs and outputs which are 1/4" TRS (Tip, Ring, Sleeve) Be sure to use TRS cords when connecting or it will do nothing.

If you are connecting to or from XLR jaks, just use TRS to XLR adapter cords, but they MUST be TRS, not 2 conductor Tip Sleeve 1/4".

Sometimes you will have a mixer with 1/4" TRS outputs, and amps with XLR inputs - this will still work fine.

*NEVER NEVER use a microphone transformer adapter to connect a mixer output to anything, these are only for microphones and instrument level signals and will saturate and distort at mixer output levels.

TRS 1/4" plug

When connecting an instrument like bass or keyboard to a large sound system, often a direct box is used. Most of these have ground lift switches for exactly this problem. When using you will want to try the switch both ways to see which is better. However, occasionally even this does not solve the problem. You may need a combination of direct box and cheaters.

By the way - I don't like so called "active" direct boxes. They add noise, are easily overdriven, and perform no better than simple passive models.


SAFETY:

At some point someone will try to tell you that you need the grounded power cord for some safety reason. NONSENSE! All pieces of electronic equipment have power transformers, which isolate them from the AC power line. There is NO connection to the wall socket. The only way you would have a problem is if the AC cord frayed and the hot conductor were to touch the chassis. In over 40 years in this business I have never seen that happen. I have never even heard of it happening. The chance of it is so infinitesimally small as to be nonexistent.


URBAN LEGEND:

You have probably heard the story of a guitar player getting electrocuted by a guitar amplifier. NONSENSE! That could never happen. The ground capacitor in a typical amp can NOT pass current. It only passes static hum.

DO NOT be tempted to rewire your classic Fender or VOX or Kustom or whatever amp you have with a 'grounded' power cord. It is totally unnecessary. There is absolutely nothing wrong with the ground switch and grounding capacitor.