Knowledge and power
DIY tips for reducing power-related noise
in your studio.
By Eddie Ciletti
No matter what size of a studio you have,
power-related noise can cause serious problems. The typical scenario in
the personal studio goes something like this: the console is on one side
of the room, and the keyboard and rack modules are on the other side. However,
the system always has some sort of power-related noise, sometimes even
with the faders down.
Power-related noises with analog gear are
obvious and fairly easy to troubleshoot, because changes are instantly
audible as you experiment. Hums and buzzes in the analog domain may be
the only clue to mysterious problems in your digital devices; power-related
noises may not be audible, but they can affect equipment performance.
When I used to make house calls for a living,
more often than not, I was able to pinpoint and resolve such issues. Sometimes
I offered advice over the phone, although it was never quite enough and
my presence was requested anyway. Perhaps my explanation was too matter-of-fact,
or the client never believed they had the power to fix many of the problems.
However, you do have that power. In this article, I will address a number
of power-related topics, from chasing down and minimizing a variety of
noise problems to determining your power capacity and optimizing distribution.
If you choose to take the DIY approach,
have respect for electricity: wear socks and shoes, don't stand in a puddle
of water while working and always keep one hand in a pocket while probing
(with a meter, for example). Basically, you don't want the jolt to hit
you across the chest, from hand to hand or hand to foot. Once the electrical
investigation requires going beyond your comfort level, find a knowledgeable
electrician who is sensitive to the needs of a multimedia system.
Tree, Trunk, and Limbs
Randomly plugging your gear into the most
convenient outlets around a room can be the beginning of trouble. Power
distribution in a home or office is not to audio standards and as such,
there is an increased potential for noise when using more than one outlet.
The first thing I ask a customer is how
many outlets are in the room and how many are being used. Then I suggest
that everything be plugged into one outlet using the Tree, Trunk, and Limbs
approach to power distribution (see Fig. 1). Think of the outlet as the
bottom of a tree trunk into which is plugged an outlet strip. From that
run the branches (more outlet strips). Plug your gear into the branches.
If you had noise problems, this approach will most likely reduce or eliminate
most of them.
Typically, when I pay a visit, at least
two different outlets are being used. When asked why, the customer usually
explains that he or she didn't think one extra outlet would make
a difference and, besides, it was inconvenient to use only one outlet.
I really don't want to charge my $300 minimum fee to grab an extension
cord and reconnect the remote outlet strip. However, there are usually
plenty of other things to sort out.
Although it may not be an ideal solution—and
it does have limits—the Tree, Trunk, and Limbs method distributes the same
power and ground to all your outlet strips and gear, which is the ultimate
goal no matter what size your system is.
Here Comes the Noise
Every electronic product you own dumps
noise back into the power line. Power-related noises can be distributed
by the power wiring or through the air by induction. The best receiver
is the electric guitar, which acts as a divining rod for radiated electrical
noises. That's because a single-coil guitar pickup and a power transformer—such
as those found in amps, power supplies, and wall-warts—have something in
common: both are coils of wire wrapped around a hunk of iron. A transformer
radiates an electrical field, and a single-coil guitar pickup does as its
A humbucking pickup has two coils, one
of which is wired out of phase with the other. Any noise that is common
to the coils and in phase is rejected. This type of phase cancellation
technique is a common strategy for dealing with noisy lines.
Computer and video monitors also have coils,
which coerce electrons into creating recognizable images on screen. Flat-panel
displays have coils to generate voltage for the light source behind the
panel. Both technologies radiate noise, so gather your audio harnesses
with cable ties and dress them as far away from power sources as possible.
Light dimmers and fluorescent lights also
generate Electromagnetic Interference (EMI), a very big term for a very
annoying family of noises. Bill Whitlock, president of Jensen Transformers,
recommends using an AM radio to track down noise sources, such as defective
transformers in fluorescent light fixtures. Tune the radio to an unused
frequency and walk close to any potential sources: the radio will pick
up and amplify the interference.
While on the subject of noisy lights, the
small, affordable dimmers you find everywhere do not belong in a recording
environment. These super-efficient dimmers don't vary voltage to change
bulb brightness, but chop up the 60 Hz wave instead: small pieces for dim,
full wave for bright. If your light need "atmospheric control," chose a
Variac-based dimmer. Although these are transformers and should be located
away from sensitive gear, they don't generate high-frequency noise which
tend to travel better through the air, just like Radio Frequency Interference
Power transformers not only radiate energy
into the air, but also into nearby metal objects, such as the chassis that
houses your gear. Connect any two devices and noise current from one chassis
will flow through the signal cabling to the other (and vice versa), specifically
via the shield that is supposed to protect the signal wire(s) from radiated
noise. All mic- and line-level audio cables have a shield, no matter what
type of connector is at the end.
How the mating connector is mounted to
the chassis determines a device's noise immunity. What you want is an electrical
firewall, a safe place for the shield to dump its noise so it doesn't get
into the box. (Once it is inside, it's harder to remove.) Renowned Toronto-based
engineer Neil Muncy named this the Pin-1 issue, but it's not exclusive
to XLR connectors. Quarter-inch, RCA and even Firewire and USB are all
vulnerable IF the Shield / PIN-1 connection does not go directly to the
metal chassis. This is the case for some connectors that are isolated from
the chassis for ease of manufacturing. IF the path from "pin-1" to the
chassis is through a printed circuit board trace, THEN all the noise infiltrates
the ground scheme, where it can be amplified.
An unbalanced audio cable has two conductors:
one wire for signal plus a protective shield (as a multi-stranded wire-wrap,
a braided "screen" or as an aluminum foil wrap). A balanced audio cable
has three conductors: the shield plus a twisted pair of wires for the signal.
In either case, the shield alone is not enough to stop a transformer's
strong electrical field both for the aforementioned "pin-1" issue as well
as the system's inherent ability to reject noise.
For example, If an unbalanced cable is
too close to a wall-wart, the electrical field radiating from the transformer
will pass through the shield and into the signal wire, producing a pronounced
hum. Even if "pin-1" is correctly implemented, you can't change the laws
of physics, in this case, breaking the law, a.k.a. death by Induction!
But if the source and destination are balanced, the noise will be minimized
as well as the circuit topology allows.
Balanced input and output circuits come
in two primary forms: as active electronics or as a passive device known
as a signal transformer. Transformers are more tolerant than poorly implemented
transformerless designs. Both amplify a differential signal pair (that
is, two signals of opposite polarity), but reject noise that is common
to both signal wires. This relationship is known as the common mode rejection
ratio, or CMRR. Look for it when checking out mic preamp specs; it also
applies to line inputs, where it’s usually taken for granted.
In Figure-2, the audio signal is on the
red and black wires, connected to pin-2 and pin-3 respectively. Notice
that the two sine waves are out of phase with each other, but the red noise
spikes (common-mode noise) are in phase. (Another common mode signal, 48V
phantom power, travels over the yellow wire feeding the two resistors.
It's called "phantom" because no additional wires are required to power
There are two types of active balanced
configuration: full balanced and impedance-balanced. We're all familiar
with the former, which has two identical signals traveling down a shielded
twisted-pair cable, one 180 degrees out-of-phase with the other. The amplifier
driving each wire has a "defined" output or "source" impedance just as
some vacuum tube guitar amps have a back panel selector switch to match
the impedance of the amp with that of the speaker cabinet.
The math of amplification and rejection
in an ideal balanced system is as simple as 1+1. Let's call the positive
(pin-2) signal +1 and the negative (pin-3) signal -1. If each of these
signals were on a mixer fader, the result of the addition would be zero,
or cancellation. But a balanced input amplifier, also known as a differential
amplifier, looks for differences in a signal. A differential amplifier
subtracts what is common to both wires—in this case, the noise. But when
it attempts to subtract two mirrored signals ([+1] - [-1]), the double
negative becomes addition, yielding a two instead of zero.
Since an impedance-balanced configuration
has only one modulated signal wire, it is crucial that the un-modulated
signal wire be "sourced" by the same impedance. Don't get your panties
in a bundle; it's just a resistor to ground. Matching these two impedances
allows the differential amplifier at the other end of the cable to do its
job. Maximum noise rejection "happens" when both wires are equally susceptible
to noise. For really troublesome noises, a transformer at the input (destination)
is more tolerant of circuit idiosyncrasies and can deliver 90 dB of CMRR.
In the Unbalanced World
If you are using unbalanced gear, the devices—including
the mixer—should be physically close together (preferably in the same rack),
so that the interconnecting cables can be as short as possible. Long cables
act as antennas for noise, so if the mixer can't be in the same rack, use
high-quality cables with robust shields.
While most sound modules and keyboards
are unbalanced, it doesn't hurt to route them to a balanced mixer using
balanced audio cable. While it's far from an optimum solution, there will
be some noise canceling benefit from doing so. In hostile environments,
installing unbalanced-to-balanced converters at these sources will give
you a fighting chance against noise. Use digital outputs wherever possible
(it's worth the extra money to buy gear that has this option). And finally,
make sure you have separate physical paths for power and audio. It's always
a good idea to keep wall warts and power cables as far apart from audio
cables as possible.
There has always been considerable fuss
about the dreaded and misnamed ground loop, which is in reality
the unavoidable ground current. As soon as a piece of gear is rack
mounted, plugged in, and connected to another piece of gear, there will
be ground currents in all cables. It would seem as if we are doomed at
the start and that meeting any electrical code and achieving a quiet system
are disparate goals, but that is not the case.
The most common bad-practice electrical
activity is the misuse of the ground adapter as a ground lifter (see Figure-3).
Use it only as a testing tool, never as a fix. Nothing is more permanent
than a temporary solution.
There are many so-called fixes applied
to how the ends of interconnecting cable wiring are terminated. Tricks
such as flying shields, where the shield at one end of the cable is not
connected, complicate the wiring scheme. I prefer to keep things simple
by connecting the shield at both ends to let the noise-prone gear reveal
itself. Rather than compromise or complicate the system, the funky gear
should be fixed, modified, or thrown away. There are several products that
can interface unbalanced gear with balanced gear. Transformers may cost
a bit more, but they are more effective.
Gear modifications, wiring and soldering
techniques are outside the scope of this article but you are welcome to
e-mail and send pix. If we get a good sampling of your problems (that can
be fixed by remote control), perhaps they can be compiled into a future
Using the Tree, Trunk and Limbs method
to solve power-related noises might also push the limits of the single
circuit breaker now powering the entire system. For example, you might
not want to turn everything on at once because the power-up current draw
is much more than current draw once everything is on. The total power-draw
for any breaker should be 75 percent of its rated value, such as 15 amps
for a 20-amp breaker.
If you are concerned about overloading
the electrical system or are popping breakers or fuses, there are two ways
to determine your total power consumption. The easy way is with a clip-on
ammeter (see Figure- 4). It eliminates all of the guesswork, but requires
a professional electrician's respect for electricity.
Start by determining which circuit breaker
feeds each outlet. Current is measured with a clip-on ammeter, while your
gear is on and doing work. The red-orange jaws of a clip-on ammeter open
so that a SINGLE wire from a breaker can be inserted. The jaws are then
closed. Current is measured without making a physical or electrical connection,
proving that wires radiate an electromagnetic field.
After measuring all of the circuit breakers
to which all of the audio equipment is connected, add up each reading.
If the total is within 75 percent of 20 amps (15 amps or less), you are
safe to plug all gear into one outlet using the TTL method.
Another way to determine your power consumption
is to calculate using the specs from each device you use. Circuit breakers
are rated in Amps (A), but appliance power consumption may be rated in
amperes, watts, or volt-amperes (VA). Remember that power (in watts) equals
volts times amps. The difference between watts and VA is the power factor.
Unless the power factor is known, use the following formulas.
(watts to VA) watts/0.85 = VA
(VA to watts) VA x 0.85 = watts
Depending on your enthusiasm for calculating
the total power consumption of your system, this might be the time to look
in the yellow pages for a local electrician.
If the total draw of your system exceeds
15 amps, power down any items that do not seem relevant to the problem
but leave everything plugged in to maintain the conditions that may be
causing the hum or buzz. We don't want to pop the breaker from excess current
and, as mentioned, the goal is to localize / weed out the noise prone gear.
If your system requires more than 15 amps and you have the luxury of rewiring,
put each outlet on its own breaker with its own ground wire back to the
box using the isolated ground outlet detailed in the "Faulty Outlet" section.
Another warning sign that you are pushing
the power strips and extension cables to their limit is when power plugs
are warm to the touch. However, plugs can become warm if the wires in the
plug or socket are not secure. Molded power plugs should have spot-welded
connections. Unfortunately, cheaper products only crimp the wires to the
prongs. Over time, and through repeated cycles of heating and cooling,
oxidation builds up resistance at the junction of wire and prong causing
the plug to warm. The same is true for outlets that have lost their grip.
Replacing power strips is easy, but you
should also have your electrician inspect all power outlets, tightening
or replacing them as necessary. Use either heavy-duty outlets or the orange
hospital-grade power outlets as shown in Figure-5.
If plugging everything into one outlet
lowered the noise, then your problem may be related to the wiring in one
of the outlets. Use an outlet tester, available at most hardware stores,
to confirm that your outlets are correctly wired (see Figure-6). An outlet
tester can detect gross wiring errors, although problems are typically
more subtle than that.
Figure-7 shows how an outlet should
be wired: black for hot, white for neutral, and green for ground. Neutral
is also referred to as the return wire that completes the circuit.
In the wiring of a standard household
electrical socket, ground travels through the round prong of a power plug.
It's important to note that ground is there for safety purposes, not for
providing low-noise audio. Standard outlets receive ground when the mounting
screw touches the outlet box. Hospital-grade orange power outlets have
a ground screw that is isolated from the mounting flanges (see Figure-5,
above). This provides an isolated ground wire all the way back to the breaker
box, rather than relying on potential interruptions such as loose screws
at each conduit extension or the spiral metal jacket of BX cable.
The route from orange outlet to a dedicated
ground wire terminating into a 6-foot spike set into damp earth requires
extra time and money, but it's not cost prohibitive. That said, it still
doesn't ensure a quiet ground connection. The isolated ground wire is easily
contaminated by noise currents in the black and white power wires because
of their close proximity within the conduit. To prove this, I have experimented
with running ground wires outside the conduit with greatly improved results,
but, I have never investigated the electric code to know how this might
be legally and safely implemented. Consult your local electrician.
In a typical home or office building, outlets
are daisy-chained, and every loose connection between them—whether it is
on the hot, neutral, or ground line—is a potential noise source. With the
breaker off, each outlet should be pulled, inspected, and tightened if
necessary by a licensed electrician.
In the breaker box, there should be two
buss bars, which are hunks of aluminum, copper, or copper-alloy, tapped
with screws for multiple wires (one bar for neutral and one for ground).
Because every connection is a potential noise source, all of the buss bar
screws should be checked and tightened if necessary (see Fig. QQQ).
As mentioned earlier, all of your gear
reflects noise back into the power wiring, but if a more serious variety
of noise is coming from outside your facility, the best way to tame it
is with an uninterruptible power supply (UPS). A UPS converts AC power
to DC by charging up batteries instead of capacitors, then converts the
power back to AC. Not only is it effective at cleaning up noise, it also
provides a safeguard against spikes and power failures. Remember that isolation
and balanced power transformers do not filter noise, and to be truly effective,
they must be properly installed where power enters the building.
I'm not a big fan of rack-mount voltage
regulators and surge protectors. I prefer a UPS to do all that, as well
as provide back-up in case of power failure. Not every model of UPS offers
voltage regulation—such as the American Power Conversion (APC) Back-UPS
Pro line at www.apcc.com. But unless you live in an area with wide voltage
swings, from brownout to danger, most of your gear has sufficient internal
regulation. Most computers, for example, will run on 90V to 200V by design.
Heavy Metal Noise
Balanced power enters the home as 220V
to 240V. Neutral comes from a center tap on the utility pole transformer,
hence our 110V to 120V standard outlet power (see Figure-9). Neutral is
tied to ground as it enters the home, but it tends to get dirty from all
the appliances that are constantly switching on and off (microwave oven,
fridge, washer, and dryer). It's even worse in a commercial building, which
may have elevators and HVAC.
A 1:1 isolation transformer can help avoid
the neutral noise by taking the 220V on its primary side. A new, clean
neutral is then established on the secondary side for your audio power
network. It's not a big deal to add one, but it's not a DIY project. As
for balanced power, I have mixed feelings. It is somewhat effective, but
not a panacea. Understand that I am not looking to modify your gear, but
I can say than when noise-prone gear is "fixed" it sounds better too.
Like the aforementioned impedance-balanced
method of interconnecting audio gear, to be effective, Balanced Power requires
a similar form of "impedance equity" in the power distribution system.
Not all gear treats incoming power in the same way. A customer once bought
a balanced power transformer because he had read in a magazine that it
was a miracle box. When it showed up, it was too heavy to move and there
was nowhere to put it. However, the real problem was summer brownouts,
something a balanced-power transformer doesn’t fix.
All transformers that are big enough to
run an entire recording area—including lights—are big, heavy, and potentially
noisy. They make physical noise as well as radiated noise so location is
key, preferably where the power lines enter the facility, as far away from
guitars and analog tape machines as possible. Although there are project-studio-sized
transformers available, do yourself a favor by consulting an electrician
about the best solution for your needs, as well as the optimum place to
install a transformer if you really need one.
RFI and Television Interference—also known
as RFI/TVI—is a lot more squirrelly than your garden variety hums and buzzes,
but the root of their evil is the same. RFI has an obvious sound. TVI,
on the other hand, sounds very similar to a power-buzz, except it tends
to vary in character, with a phase-sweeping quality. That is because TVI
is video picture noise with a 59.95 Hz fundamental—0.05 cycles per second
less than 60 Hz AC power. Hearing them together causes the slow phasing
One of the DIY solutions for eliminating
RFI/TVI is the ferrite clam, which is easy to apply to cable ends (see
Fig. 10a and 10b). You have probably seen these before on computer video-monitor
cables, hidden under shrink tubing. In essence, the ferrite acts as a near-short
circuit at frequencies from 1 MHz to 100 MHz—exactly where you need them
to work. The clam shell filter comes in various sizes to accommodate wire
thickness. Guitar cables are also good candidates for ferrite clam filters.
Another RFI/TVI fix requires the most basic
soldering and mechanical skills and it applies to the male end of an XLR
cable. A standard 3-conductor XLR configuration has shield/ground on pin-1,
signal high/hot on pin-2, and signal low/cold on pin-3. There is also a
fourth pin that connects directly to the chassis by means of the connector
shell. XLR pin-1 is supposed to go directly to chassis, but when it takes
a more circuitous route, high-gain mic preamplifiers see not only hum and
buzz but also RFI/TVI. If adding a jumper wire from pin-1 to the chassis-lug
fixes your problem, you may want a technician to go inside the box to make
Video and Computer monitors have their
own way of displaying hum, as a rolling horizontal bar. You will typically
see and hear hum when integrating a cable TV box into an audio system because
the cable is grounded when it enters the building and this will not be
at the same potential as the audio system ground. As a result, current
will flow. The fix for that noise is to insert an isolation transformer
between the cable wire and the cable box or video recorder (see Figure-11).
Cable quality can also affect noise reception
in hostile environments. Typically, multi-channel snakes have a foil shield
with a drain wire. These may be acceptable for line-level applications,
but for mic and unbalanced lines, a heavy copper braid or wrap is better
because it reduces noise by 15dB. Canare Star Quad cable, which has a braided
shield and two pairs of signal conductors, is best, offering a 40 dB reduction.
Now it's time to address the wiring in
the rack. Here it would be helpful if all manufacturers adhered to a standard
location for the power connector. When applicable, I place a vertical power
strip on the cabinet side that has most of the power inlets, using short,
18-inch IEC power cords. You should avoid coiling any cables—power as well
as audio—to minimize noise generation and pick-up. Don't forget to use
cable ties to bundle audio cables on one side of your rack, and power cables
on the other side.
The Knowledge of Power
Understanding potential noise sources and
using the Tree, Trunk and Limbs method of power distribution should allow
you to identify, and in most cases reduce, the major problems in your system.
However, there are situations that require the combined support of an experienced
technician along with an understanding and sympathetic electrician, one
that may also be a musician, for example. Although it may be more expensive
than the DIY approach a system that is consistently safe and quiet will
be worth the investment.
Eddie Ciletti provides childcare by day, winds up by repairing and
modifying gear (www.tangible-technology.com), and unwinds by editing a
new instructional music video. He also teaches recording and maintenance
one day a week at www.iprschool.com.
One of the most deceptive noise challenges is an audio system that
began life "quiet enough," but over time gradually becomes noisier until
things eventually get out of control. There are numerous possibilities,
but it doesn't hurt to disconnect everything and clean the connectors with
99 percent isopropyl alcohol. Then, apply a contact cleaner using a cloth
or cotton swab. Avoid spraying the cleaner on anything because it will
attract more funk than is washes away.
And while beyond the scope of this article, the propellant that forces
the cleaner/lubricant out of the can is so cold that water vapor will condense
on cold connectors causing additional corrosion. Circuit board edge connectors
are particularly vulnerable because even when gold plated, the underlying
metal is copper and we all know what happens when this metal attempts self-preservation.
Buzz by Design
Noise-prone equipment is not necessarily due to poor design. More
likely, it is due to shortcuts taken to aid mass production. Eighties-era
gear often used plastic-insulated jacks mounted directly to a printed circuit
board (PCB). As a result, the noise was dumped directly to the PCB ground,
to which many high-gain amplifiers are referenced, instead of being stopped
at the "firewall," the metal chassis that houses your magic circuitry.
For an example of good design, check out any Mackie mixer and notice
that all of the 1/4-inch jacks have metal threads and a metal nut securing
them directly to a metal chassis. Minimizing noise susceptibility is almost
that simple and it certainly starts there.