But was it really our inputs? Or was it something else? Sometimes it’s so hard to tell. You turn the channel fader down and it doesn’t stop, then you pull out the input cable and abracadabra, no more buzz. What the shit? That probably means there’s a ground loop occuring in the sheilding of the input cable, so even if you turn down the channel fader it doesn’t stop. You have to lift the ground.
But before we discuss ground loops, we should acknowledge that there are many reasons why a system might buzzzzzz. A few days ago someone mentioned that all the inputs on our mixer were buzzing. But then I took it to the shop and actually only Channel 1 was buzzing. In other words, it probably wasn’t the mixer itself that was buzzing.
The first thing to check is your “gain structure.” For the record: all audio electronics buzzes and makes noise. The trick is to make it buzz as little as possible. Crappy quality machines tend to buzz more than the big money stuff (but not always: the AKG The Tube is a $2000 microphone that’s noisy as hell and still manages to sound like gold, and a lot of inexpensive stuff can sound very good).
But there are ways to make things buzz less depending on how you set the levels and how you hook things up. It’s possible in the above situation that the ‘trim’ knobs on the channels were not set high enough, meaning you would have had to crank either the channel faders (on our mixer for some reason labeled ‘gain’) or the master volume, or both, amplifying all the noise in the entire circuit. But if you set your ‘gain structure right,’ on the other hand, you get a better signal to noise ratio. To do this, set your channel fader to zero dB, then talk into a mic until it’s as loud as it can be without distorting or feeding back.
Another possibility is that something else in the signal chain was buzzing, most likely one of our powered speakers or two, or maybe even a faulty cable picking up interference.
Another possible cause is the elusive phenomenon we call ground loops, induction etc. This means that it wasn’t necessarily a piece of equipment itself that was buzzing, but rather, there’s noise on the ground path (i.e., the third pin on the AC power cable.
When you have more than one path to ground (or no real path to ground as is kinda the case when we use the inverter), then stuff, especially chassis and ‘ground planes’ (but also signal conductors – hence the reason we ‘balance’ circuits) tend to pick up electromagnetic ‘noise’ from the air or from the ground itself. This changes the voltage level of our ‘ground’ or reference point and makes everything sound all garbagey.
The best way to avoid this is to make sure everything`s plugged into the same source, and that this source is well-grounded. If something still buzzes, try ground-lifting it or other units in various combinations (if there`s no ground-lift switch you can buy special adaptors that bypass the earth-ground pin… or you can rip it off, but that`s sketchy). Sometimes people even disconnect the grounded sheilding on a signal cable (xlr, etc), if the noise is being induced there.
Ground lift as little as possible because it’s slightly unsafe. Never lift the ground on a mixer cause then people using the mic could get a little shock.
If none of this works, one of your machines might just be naturally buzzy. Use process of elimination!
Also for some reason all the nuts on the 1/4in jacks on our mixer were loose. if they`re not tight the chassis and sleeve of the jack itself may not be properly grounded, allowing it to pick up interference, induction, 60hz hum. like an antenna.