Sometimes noise comes out of a guitar rig without any contribution from the player. Hums, buzzes, clicks, pops, whistles - all having nothing to do with the vibrations of the guitar guitar strings or the machinations of the effects pedals - these are the noises about which I'll discuss causes and resolutions.
Some noises are largely unavoidable. If you play a guitar with single-coil pickups, you know to expect a certain amount of hum and buzz depending upon how much gain you apply and your proximity to sources of electromagnetic fields (motors, transformers, neon signs, flourescent lights, electrical wiring, etc.)
It's always easy to test whether the noise you hear originates at the pickups: turn down the volume at the guitar; if the noise stops, it's coming in through the pickups. Likewise, the fixes are few and relatively obvious: use humbucking pickups, use less gain, or move the guitar away from the noise source.
There's another class of noise problems that's less easy to diagnose. Many guitarists refer to these as "power problems". The noise appears with a change of venue. What changed? Obviously, the power. This is occasionally, but not always, an accurate diagnosis. Many guitarists attempt to solve "power problems" by buying a power conditioner and are surprised when the solution isn't reliable.
The remainder of this article will explore more detailed and accurate diagnoses, in the hope that you'll be able to properly diagnose and solve noise problems in your guitar rig.
"Power problems" come in various forms:
- Missing ground.
- Even if you're plugging into a grounded outlet, it may not be grounded. The only way to know for sure is to buy one of those grounded outlet testers (under $10 at places that sell electrical hardware, including most big-box retailers). When you don't have a proper ground, leakage current from your gear gets onto the sheild of your guitar cable and from there into the signal chain.
- Ground loop.
- This tends to be a thing for more complex systems - dual amps, racks, and the like - but can also manifest in simpler rigs. Things to watch out for include running connected gear from different outlets and ungrounded wall warts. For the latter, sometimes flipping the wall-wart around the other way in the outlet helps.
- Radiated noise pickup.
- Pickup is the operative word here. Most commonly, electromagnetic noise in the room is received by your guitar's pickups. This is exactly the same problem discussed at the beginning of the article. If the noise changes at all with the orientation of your guitar, then radiated noise is likely your problem. I mention it again here because some venues are more likely to have radiated noise issues than others. Unfortunately there's not much you can do about this short of changing venues (or rewiring, but sometimes the source of interference is from outdoor power lines rather than those in the house) or swapping out your pickups for some that are less susceptible to noise. Any humbucker will have less noise susceptibility than and single-coil pickup, but may not entirely eliminate susceptibility to radiated noise. A friend had very good results in a difficult venue by swapping out his Tele's pickups for active EMGs.
- Conducted noise pickup.
- This is, IME, the least common cause of noise in a guitar rig, and the only cause that may be helped by using a line filter. "Dirty power" is caused by other loads turning on and off. The usual symptoms are clicks and pops rather than buzzes, although light dimmers and neon signs can cause buzzing. (But light dimmers and neon signs can also contribute to radiated noise, particularly if they're in the same room as your guitar.) This kind of noise decreases rapidly with distance from the source. The most common causes are large motors starting and stopping (refrigerator, washing machine, clothes dyer, sump pump), ignitors on old furnaces (if you hear a buzz for a few seconds when the furnace starts up, that's the ignitor) and electrical heaters (ovens, space heaters, electric clothes dryer, electric water heater).
A "power conditioner" will only help with the case of conducted noise. If the noise comes into your rig through any of the other paths, buying a power conditioner is a waste of money.
Also, there's a difference between a surge suppressor and a power conditioner. A surge suppressor simply clamps transients. Although these are sometimes sold as "lightning protection", they aren't. Virtually all modern gear has its own surge supression built in, so buying an external surge strip is, again, wasted money. A good power conditioner costs more to manufacture than a surge suppressor. A power conditioner has filters to reduce (never eliminate) certain high-frequency noise on the power line; in difficult cases involving conducted noise, this can make the difference between your rig being usable or not.
Ground Loops, in detail
You need to be thorough about diagnosing noise problems. It's easy (and far too common) to make the mistake of assuming that some new situation is the cause of a new noise problem. For example, you may find yourself in a venue where you can't run the band from a single power line, encounter noise, and suspect a ground loop issue. That's not necessarily the case.
Remember that ground loops affect only interconnected gear. If you're powering your guitar rig from one outlet and your bass player powers his grear from another outlet and one of your encounters a hum that wasn't present before, that hum is probably not due to a ground loop.
You should suspect a ground loop when the noise is a hum rather than a buzz and when rolling off your guitar's volume doesn't eliminate the hum. Confirmation of a ground loop is achieved by selectively unplugging interconnected gear (either power or signal); this will kill the hum when you disconnect the gear (while otherwise maintaining singal flow) of the gear that's injecting current to cause the ground loop.
Remember: running on different outlets doesn't always cause noise. You need to do some isolation to discover the actual source. Also, you can have ground loops even in cases where you're running all of your gear from one power outlet. How's that for confusing...?
If you're actually dealing with a ground loop, the only way to fix it is to eliminate one of the redundant ground paths. Every piece of interconnected gear has at least two ground paths: the connection to the safety ground on the third pin of the power plug and at least one connection via the signal ground on a cable that goes to another piece of gear.
In case you're wondering: yes, you can have a ground loop even if your gear is powered from an ungrounded wall-wart. There's always a small leakage current from the AC line to the low-voltage side of the power supply; that leakage can sometimes superimpose itself onto the gear's signal ground.
You can get rid of a redundant ground path by "lifting" the ground. (Yes, this is exactly what the "lift" switch is for on a DI box.)
You can lift the safety ground by using a ground cheater (3-wire to 2-wire plug adapter) on a power cord. This is the least expensive approach. It will certain do the job for the rest of your life. Thing is, there's a small chance that your lifespan may be suddenly terminated by this practice. On the one hand, the chances of terminal harm are actually very small. On the other hand, that one chance will be your last chance. The safety ground is named for a reason. It's for your safety and the safety of anyone else who will come into contact with your gear. My advice (which I follow religiously) is to only use a ground cheater for diagnostic purposes; never for a performance.
So let's say you diagnose a ground loop. What can you do to eliminate the noise without tempting fate (because, as we all know, fate can have a vicious sense of humor...)?
If your signal connections are balanced (TRS or XLR line-level connections as found in pro audio gear, but hardly ever in guitar gear), you can simply cut the ground wire at one end of the interconnect cable that ties together two pieces of gear that cause a ground loop. This always works with a balanced signal because the input circuitry is designed to cancel common-mode (ground) noise. Keeping the ground connection at one end of the cable provides a "telescoping sheild" to protect the wiring from radiated noise pickup.
The same approach (cutting the shield at one end) works with unbalanced lines once in a while, but is not an effective solution in the general case. It doesn't hurt to try it if you're willing to sacrifice a cable or have the skills to resolder the connector if the lifted ground doesn't help.
There are two general - but more expensive - solutions that can be applied regardless of whether your interconnects are balanced or unbalanced.
The first solution is to use a signal isolation transformer. Ebtech sells these as "hum eliminators". It'll cost you about $60 for a box that'll isolate two distinct interconnects. Other manufacturers offer similar boxes. IIRC, Behringer offers one for about a third of the cost of the Ebtech box.
The second solution is to use a "safe" ground cheater. To the best of my knowledge, Ebtech is the only company that makes these. The product is called the Hum-X, and will also cost you about $60. The Hum-X is an adapter that - like a ground cheater - you plug in between your gear and the power outlet. Unlike a ground cheater, the Hum-X is a 3-wire to 3-wire adapter. The Hum-X works by providing enough ground voltage compliance to eliminate the loop, but still provides a safety ground that'll trip a circuit breaker in the unlikely event that something goes horribly wrong.
I've used both the Hum Eliminator and the Hum-X. I prefer the Hum-X because it's easier to apply and because it doesn't affect any signal paths. I keep one in my toolbox. I rarely need it, but it's invaluable when I cobble together something that causes a ground loop.
At any rate, I'll remind you once more to diagnose the source of your noise before you try to apply a particular solution. Different noise sources are dealt with using different techniques.
What does it mean when touching metal parts on my guitar reduces the noise?
When this happens, the most likely causes are either a floating ground (cause by an improperly-grounded outlet) or radiated noise (which is still a potential source even when you have a proper ground connection). Touching metal on the guitar (assuming it's grounded, as is usually the case with metal knobs and is often the case with the bridge and strings) shunts some of the conducted or radiated noise through your body.
The fix for this problem varies with the specifics of the instrument involved. Sometimes shielding the guitar's cavities helps. Shielding is more likely to solve your noise problem when the guitar's wiring lacks shielding to start, which is much more common in single-coil guitars than in humbucker-equipped guitars.
Sometimes grounding the bridge and (though the bridge) the strings - by connecting them to the guitar's internal ground connection - will help to reduce pickup of radiated noise. The practice of wiring this ground used to be common, but seems less so nowadays as it puts your body in constant contact - through the signal ground of your instrument cable - with the chassis of your amp and pedals. This is viewed as a potential safety (and liability) hazard in the even that your rig is plugged into an improperly-wired power outlet. That shouldn't happen, but it can when a venue cuts corners by using amateur electricians. (For that matter, even a licensed electrician can make a mistake...)
Noise problems have various causes. The proper solution varies with the actual cause. Before you spend money on a "fix", do some diagnostics to determine how the noise gets into your rig; that diagnosis will guide you to the proper solution.
In particular, power conditioners solve the problem that's statistically least likely to affect your rig. A lot of players run out and buy a power conditioner when they encounter noise, and are subsequently disappointed when the conditioner turns out not to be a reliable fix.