GROUNDING CONSIDERATIONS

Proper grounding is essential to maintaining equipment safety; however, within an audio facility, small AC voltage potentials between various devices in an audio system can leak into a system’s grounding circuit. Although these potentials are small, they are sometimes large enough to induce noise in the form of hums, buzzes or radio-frequency (RF) reception that can be injected (and amplified) directly into the audio signal path. These unwanted signals generally occur whenever improper grounding allows a piece of audio equipment to detect two or more different paths to ground.

Because grounding problems arise as a result of electrical interactions between any number of equipment combinations, the use of proper grounding techniques and troubleshooting within an audio production facility are by their very nature situational and often frustrating. As such, the following procedures are simply a set of introductory guidelines for dealing with this age-old problem. There are a great number of technical papers, books, methods and philosophies on grounding, and it’s recommended that you carefully research the subject further before tackling any major ground-related problems. When in doubt, an experienced professional should be contacted, and care should always be taken not to sacrifice safety.

■ Keep all studio electronics on the same AC electrical circuit—most stray hums and buzzes occur whenever parts of the sound system are plugged into outlets from different AC circuits. Plugging into a circuit that’s connected to such noise-generating devices as air conditioners, refrigerators, light dimmers, neon lights, etc., will often invite stray noise problems. Because most project studio devices don’t require a great deal of current (with the possible exception of power amplifiers), it’s often safe to run all of these devices from a single, properly grounded line from the electrical circuit panel.

■ Try to keep audio wiring away from AC wiring—whenever AC and audio cables are laid side-by-side, portions of the 60-Hz signal might be induced into a high-gain, unbalanced circuit as hum. If this occurs, check to see if separating or shielding the lines helps reduce the noise.

■ When all else fails: If you only hear hum coming from one particular input channel, check that source device for ground-related problems. If the noise still exists when the console or mixer inputs are turned down, check the amp circuit or any device that follows the mixer. If the problem continues to elude you, then …

■ Disconnect all of the devices (both power and audio) from the console, mixer or audio interface, then methodically plug them back in one at a time (it’s often helpful to monitor through a pair of headphones).

■ Check the cables for bad connections or improper polarity. It’s also wise to keep the cables as short as possible (especially in an unbalanced circuit).

■ Another common path for ground loops is through a chassis into a 19-inch rack that not only provides a mount for multiple devices, but often a common ground path. Test this by removing devices from the rack one at a time. If needed, a device can be electrically isolated from the rack by using special nylon mounting washers.

■ Investigate the use of a balanced power source, if traditional grounding methods don’t work.

■ Lastly, it’s definitely not a good (and potentially dangerous) idea to get rid of your ground noise by removing the ground pin leads from your power connectors. These connections are there to make sure that a problematic power voltage is routed to earth (ground) and not through you. Any grounding problems in the system should be able to be corrected for without resorting to improper wiring techniques.

Troubleshooting a ground-related problem can be tricky and finding the problem’s source might be a needle-in-a-haystack situation. When putting on your troubleshooting hat, it’s usually best to remain calm, be methodical and consult with others who might know more than you do (or might simply have a fresh perspective).

POWER CONDITIONING

As was said earlier, one of the best ways to ensure that the power that’s being delivered to your production system is as “clean” as possible is get power from a single circuit source. If you have the luxury of building your facility from the ground-up, one of the best ways to ensure that you have clean and reliable power is to take care to deliver power directly from the circuit box (over one or two lines) directly to the studio. If this isn’t possible, then pulling your power from a single circuit or power socket might be your best bet. The latter scenario is possible for many home project studios, as the combined power requirements are well below the maximum load of a wall socket before the breaker trips (15A × 120V = 1800 watts or (20A × 120V = 2400 watts).

One of the best and simplest ways to connect all of your studio electronics to the same AC electrical circuit is by using a power conditioner (Figure 14.1). In addition to obtaining power from a single source, such a device can regulate, isolate and protect the voltage supply that’s feeding one of your studio’s most precious investments (besides you and your staff)—the equipment! Other added benefits to using power conditioning can be broken down into two important topics:

■ Voltage regulation (fluctuations and surges)

■ Keeping the lines quiet (reducing noise and interference)

FIGURE 14.1
Furman M-8Lx power conditioner. (Courtesy of Furman Sound, Inc., www.furmansound.com)

In an ideal world, the power that’s being fed to your studio outlets should be very close to the standard reference voltage of the country you are working in (e.g., 120V, 220V, 240V). The real fact of the matter is that these line voltages regularly fluctuate from this standard level, resulting in voltage sags (a condition that can seriously under-power your equipment), surges (rises in voltage that can harm or reduce the working life of your equipment), transient spikes (sharp, high-level energy surges from lightning and other sources that can do serious damage) and brown-outs (long-term sags in the voltage lines). Through the use of a voltage regulator, high-level, short-term spikes and surge conditions can be clamped (stopped or reduced), thereby reducing or eliminating the chance that the main voltage will rise above a standard, predetermined level.

While most power conditioners are meant to work best in a rack-mounted scenario, a number of power strips on the market offer protection against surges, as well as RF and electro-magnetic interference (Figure 14.2). These corded power strips can offer better protection over cheaper power strips and can be used in portable settings and go into tight spots where many larger conditioners simply can’t go.

FIGURE 14.2
Furman SS-6B power conditioner/strip. (Courtesy of Furman Sound, Inc., www.furmansound.com)

Certain devices that are equipped with voltage regulation circuitry are able to deal with power sags, long-term surges and brown-outs by electronically switching between the multiple voltage level taps of a transformer so as to match the output voltage to the ideal mains level (or as close to it as possible). One of the best approaches for regulating voltage fluctuations both above and below nominal power levels is to use an adequately powered uninterruptible power supply (UPS). In short, a quality UPS works by using a regulated power supply to constantly charge a rechargeable battery or bank of batteries. This battery supply is again regulated and used to feed sensitive studio equipment (such as a computer, bank of effects devices, etc.) with a clean and constant voltage supply.

Multiple-Phase Power

Another good defense against noise, power drops and other equipment-related power problems is to make use of multiple circuits in your overall studio power design. This approach reduces the amount of potential interference between power systems by physically placing the major system groups on their own power circuit. For example, an ideal scenario would place each of the following groups on their own power phase (separate circuit):

Phase 1: Equipment, computer (UPS isolated) and studio power

Phase 2: Lighting

Phase 3: Air conditioning and heating

The use of such a separate circuit design can greatly help to guard against the everyday surges, noise and any other number of gremlins that might creep into your beloved production system.

BALANCED POWER

For those facilities that are located in areas where power lines are overtasked by heavy machinery, air conditioners and the like, a balanced power source might be considered. Such a device makes use of a power transformer (Figure 14.3) that has two secondary windings, with a potential to ground on each side of 60V. Because each side of the circuit is 180º out of phase with the other, a 120V supply is maintained. Also, since the two 60V legs are out of phase, any hum, noise or RF that’s present at the device’s input will be canceled at the transformer’s center tap (a null point that’s tied to ground).

FIGURE 14.3
Furman IT-1220 balanced-output power conditioner and basic equivalent circuit. (Courtesy of Furman Sound, Inc., www.furmansound.com)

A few important points relating to a balanced power circuit include:

■ A balanced power circuit is able to reduce line noise if all of the system’s gear is plugged into it. As a result, the device must be able to deliver adequate power.

■ Balanced power will not eliminate noise from gear that’s already sensitive to outside induced hums and buzzes.

■ Choosing when to use balanced power is often open to interpretation, depending on who you talk to. For example, some feel that a balanced power conditioner should be used only after all other options to eliminate noise have been explored, while others believe it is a starting point from which to build a noise-free environment.

HUM, RADIO FREQUENCY (RF) AND ELECTROMAGNETIC INDUCTION (EMI)

In our modern world, where electrical and electronic gear are everywhere and where radio frequencies literally surround us as urban densities increase, the need for keeping noise out of our production system becomes more and more problematic.

The equipment in our system usually has lots of analog amplifiers, and most of them have one task—provide gain to make lower-level signals LOUDER. Unfortunately, whenever noises, buzzes, pops and ticks make their way into the signal before this gain stage, they too, are amplified and quickly become a nuisance in the audio chain. These pests can be introduced into a system as hums (noise that occurs as a result of improper grounding or shielding) and electromagnetic interference (noise from radio and cell phone transmissions, lights or other electrically induced signals).

Several options for keeping electrically-induced signal out of the audio path include:

■ Use a clean power source (see the above section on power conditioning).

■ Make sure that the devices and audio cables are properly shielded to ground. This can be best done by using quality cables that have metal shielding.

■ Whenever possible, use balanced cable connections (cables that have 2 audio conductors “plus” a ground connection—see the wiring explanations in Chapter 4 for more info).

■ Whenever it’s practical and possible, keep your audio and power signals separate.

■ There is talk that the use of ferrite beads (you know those heavy lumps that you’ll find at the end of USB cables, etc.) can be useful for reducing high-frequency (MHz) transmission through cable lines. Since there are definitely debates on this subject, I’ll let you research, as to whether this might be helpful in your situation or not.

When talking about power, grounding and interference, one thing’s for certain—there’s usually no one-size-fits-all answer to problems that might creep up in an audio signal’s path. You will probably be called upon to be patient, methodical, insightful and even a bit psychic, so as to best understand and correct any of the innumerable problems that you might encounter. Oh, I almost forgot the last (but not least) element in helping to get this elusive job done—luck!