How to Eliminate Guitar Buzz
Noise seems to be every guitar player's nightmare. It can be buzz, hum, hiss, air-traffic control ... (This Is Spinal Tap, anyone?)
I'll start off by saying that guitar rigs are a noisy environment to begin with. Gain has a lot to do with noise, but if things are clean before it hits the gain stage, your rig can be quiet (er).
There are so many ways noise can get into your rig. It can be a tangled web. Sometimes noise is just a side effect of what we are trying to achieve, but eliminating noise before it gets amplified will lead to better results in the end.
Make sure your amp has a ground pin on the AC cable and your power source is properly wired and grounded. You can find an AC wiring tester at your local hardware shop for around $10. I carry one at all time. This will tell you if your power source is wired properly and that it is grounded. You really want everything grounded; you don't want to become the ground; that would be bad.
NOISE IN THE LIVE SETTING:
Most times when I'm on tour and having noise issues, it's because the house lighting rig is tied into the same power source as the back-line power. You can hear the lighting dimmers as noise in your amp. When the lights are on 100 percent, the noise goes away. This is poor planning on the venue's part.
I can't tell you how many times I've had to make the local crew fix the issue while on tour with Lou Reed. He doesn't like any extra noise, and who can blame him? In a perfect world, you would have a power source dedicated to back-line with no lighting dimmers plugged in anywhere on the power circuit. Some motorized devices (like fans) also can add noise.
I also find that there can be a grounding issue between the back-line power and audio power. A perfect example is when an acoustic guitar is plugged into a multi-FX box that is plugged into an amp on stage, as well as a D.I. connected to the house console (monitors and front-of-house PA).
When the D.I. is not connected, things sound fine. When the D.I. is connected, you get buzz. When you flip the ground on the D.I., your rig sounds fine but the monitors and house PA has buzz.
The stagehand, tech or sound guy/gal puts a ground-lift adapter on your amp, and everything seems OK. But you might be in danger. (Ugh!) This same scenario can happen for just about any D.I. device that also gets connected to an amplifier.
My favorite solution is a passive isolation transformer such as the Lehle P-Split II.
"The new Lehle P-Split II stands for 'passive splitting' with maximum signal fidelity, making it possible to route an instrument to two amps simultaneously. The outputs are electrically isolated from one another by the Lehle LTHZ high end transformer, so hum loops are excluded from the start. The Lehle LTHZ transformer is specially designed for use with high-impedance signals, but also splits low-impedance signals with line levels cleanly and reliably. It provides the signal either balanced or unbalanced at the ISO output. In addition, the Lehle P-Split II also features phase-reversal and ground switches with gold-plated contacts, making it a passive high end DI Box for all signal types. Last but not least, the Lehle P-Split II features an ultra-compact design, assuring totally reliable functioning in the smallest possible housing."