Did you know that your car’s disc brakes are designed to squeak? They contain wear indicators that will rub against the brake rotor and squeak when the brake pads are nearly warn out. This is your warning signal to fix your brakes. Of course, you can probably get rid of the squeak without actually fixing the problem. Just apply some heavy grease to the brake rotors. You may not be able to stop your car after doing that but at least the brakes won’t squeak.
Some people get rid of noise problems in their system by using 3-to-2 prong adapters to lift the safety grounds. This is just as smart as greasing your brakes. You are eliminating a noise problem by defeating an important safety feature. Consequences be damned!
Just what are those consequences of lifting a safety ground? Well, death by electrocution is one consequence. Is it worth listing any others? If we just electrocute ourselves, we only have to worry about a few seconds of pain before we lose consciousness. However, if we electrocute a guest, then we have to suffer with the guilt, the lawsuits, the inevitable loss of our homes and let’s not forget the loss of future referrals.
A friend of mine was an expert witness on a wrongful death case involving a missing safety ground a few years ago. The victim was a young pastor in Waco TX. He entered the baptismal bath, grabbed a microphone and was immediately electrocuted in front of his wife and the entire congregation. There was nothing anyone could do. The sound system wasn’t at fault. The electrical water heater for the baptismal bath was missing the safety ground connection. It hadn’t been a problem until the heaters malfunctioned. Had it been properly grounded, a circuit breaker would have tripped during the malfunction. Guess who got sued? It was the electrical contractor that improperly installed the heater. The family collected.
Many DJs dismiss electrocution as a possibility because we don’t hear of these things happening very often. That’s true. We are much more likely to get into a car accident. However, that is no excuse for putting other people in danger. We work in the proximity of liquids. A guest can easily spill a drink on your system. If you are outdoors it can start raining or a sprinkler could turn on unexpectedly. All of these things have happened to me in the past and I’m sure they happened to many of you as well. I have been lucky. Nothing ever got wet enough to cause electrical problems. If they had, at least I knew my gear was properly grounded. Do you know that your gear is?
One frequent source of noise problems is the external AC power supply for your laptop computer. These can cause several problems including RF interference and ground loops. The problem you have will depend on the particular PC you use, the sound card you are using and your mixer. Therefore, finding the correct solution will require a little experimentation.
Several people have reported on the chat forums that purchasing an aftermarket power supply has solved the problem for them. Other remedies include placing transformer type of ground-loop isolators (such as Radio Shack part # 270-054 ~$17) in the audio path between the PC (or sound card) and the mixer. Placing a ferrite choke (Radio Shack # 273-105 ~$5) on the power cable can help with RF interference. These are relatively inexpensive remedies that leave the safety mechanisms of your gear in place.
A little explanation on ground loops is probably needed here. A ground loop sounds like a low hum or buzzing sound. They are caused by voltage differences between the grounds of two pieces of gear in a signal chain. If all your gear is plugged into the same outlet strip, you are not likely to get a ground loop. The problem is generally found when you plug powered speakers into the closest outlet instead of running the AC cords back to your mixer rack. In large sound systems, your power requirements demand that you use multiple AC circuits and you may find yourself with a ground loop.
The best way to eliminate ground loops is to use transformers in your signal path. Transformers will pass the audio but not the ground loop current. If you are using balanced interconnect lines (which I highly recommend) you will want to use transformers with XLR connectors. Jensen Transformer’s IsoMax DM2-2XX is among the best you will find. Another good choice is the ART-DTI. This is a two channel transformer unit that has XLR, RCA and ¼” connectors for the inputs and outputs. Better transformers support higher signal levels without distortion and will operate lower in frequency. Ideally you want to place a transformer near the input of your powered speaker. However, practically speaking you will probably place them near your mixer’s output.
Some pro audio gear offer a ground lift switch on their XLR connectors. If your mixer has unbalanced outputs (e.g. RCA connectors), a lift switch on your speakers or amp will be of no use. You will still need a transformer. I should point out that this ground lift switch does not change the safety grounding of your gear. It just lifts Pin 1 of your XLR cable. Pin 1 does not contain your audio signal.
Noise problems are tricky. At one venue your system may sound fine and at another venue the same configuration will produce noise. Ground loops, magnetic interference and power supply problems sound alike but the solution to each is different. It will take more space than this article to go over the differences. In fact, there are books and courses that you can take on just these subjects. There is a lot to understand and you shouldn’t feel bad if this is a bit confusing. Just stay safe, and keep a few transformers in your tool kit.