[alanross]

xxyzz,
There are several reasons for humming or buzzing noises. Some of the more common ones are:
1) Hum from a system that shares a video signal with a video signal coming from the cable into the building. In other words, if you have your system running to a TV in the bar that also has cable coming in from the cable company, you will get a buzzing or humming noise. You can purchase an in-line filter that gets inserted anywhere along the path of the coax to eliminate this.

2) Hum from a ground loop. An Ebtech Hum Eliminator will cure this completely. It's a passive unit which means it doesn't require power from a battery or wall outlet. Insert it just before whatever line runs to your amp (either from your mixing board or EQ). In other words, if you run a line directly from your mixer into the amp, run that line from your mixer into the Hum Eliminator first, then run a line out of the H.E. and into your amp. This solves your ground loop hum.

3) The same remedy works when you are combining balanced and unbalance signals by using equipment pieced together from multpile manufacturers. The Hum Eliminator will convert the singals so everything is balanced.

4) Bad mic or line cords. If you have cords that you connect and disconnect every show, there is a high probability that your cords can go bad - especially if you don't wrap them with care. Also, if you are using mic extension cords, you can have a bad connection at the female plug end. Although usually the sound a bad cord can make would be described more as a buzzing than a humming. As previously suggested, remove one mic cord at a time to see if the buzzing persists. If, so, then you know your mic cords are not the problem.

5) Mixer noise. After powering up your system, set you mixing board's main volume to about 3/4 full. Then, set your amp volumes to full. Now, don't think in terms of volume. Think in terms of signal. When you push a slide up, you're not sending more sound to your amp; you're sending more signal.

If the signal you send to the amp has noise, then the amp will siimply send that signal to the speakers. Therefore, you want to send a clean signal to your amp so it can send clean sound to the speakers. All mixers have some noise. The more signal you send out of the mixer, the more noise you will send also. This is why you should have the amp volume at full - so you can reduce the amount of signal your mixer pours into the amp, therefore reducing the corresponding noise.

Fortunately, with experience, you will learn how to read the humming. Each buzz or hum has its own unique sound. Once you've been performing long enough, you can usually identify the problem by the way the humming sounds.

Hope this was helpful in deciding which fix is best for you.

- Alan