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AC Power
The Foundation of Every Home Theater System

Today's home theaters feature audio and video quality that was hardly imaginable 20 years ago.
Far from the 27" Sony Trinitron or the Kloss Novabeam, today's premium home theaters possess video quality that is on par with some of the world's finest broadcast facilities, and sound quality that would please even the most discriminating audiophile.

However, as the performance and sophistication of Home Theater systems have increased, so to have the AC noise level and bandwidth. Additionally, power regulation, power factor, brown-outs and transient surges have become increasingly problematic to the sensitive circuits we currently employ.

Why Do We Need AC Power Management?

Why do I need an AC power conditioner or regulator? Isn't the transient surge protector in my AC power strip enough?

Well, it's important to understand two things:

First, AC power is far noisier and more contaminated than at any time since its inception. This is due not only to an increased population taxing the utility line, but it's primarily due to the proliferation of computers and microprocessors. These are typically run from switching power supplies, and this has had a devastating effect on noise levels as well as the bandwidth and character of that noise. The last twenty years have brought more than a 100 fold increase in AC noise levels (see illustration 1), while the expectations from audio and video have risen dramatically. We'll cover this subject in depth as we go on, but what must be made clear is that AC power is the life blood and foundation of every critical component you own. As the AC power deteriorates, so too does audio and video performance.

Second, poor power can limit, obfuscate, and distort hi-resolution signals, seriously compromising performance. This AC distortion arrives from your wall outlet, and ultimately couples into every sensitive circuit. Experiencing the benefit of a video scalar, or a superior audio processor, improved loudspeakers, or a superior digital projector requires RESOLUTION. To achieve this, low level audio and video information must be rendered unfettered - pristine. As the noise level of AC power continues to rise, these
advanced technologies will yield less and less of an improvement over conventional components. Clearly, today's Home Theater market is more competitive than ever. People want and expect a superlative presentation that is emotionally engaging. A truly great Home Theater should disappear and transport the viewer into another reality, with sound and picture quality far beyond their expectations. When this is achieved, their friends are invited to experience what you've created, and these friends become your NEXT CLIENTS.

For purposes of this seminar, I will define "power conditioning" as AC noise reduction.

In real world installations, a group of components that has been trouble free in ten prior installations, may hum, buzz, and produce video hum bars on the eleventh. Why? Because the circumstances that produce ground loops can be quite complicated. In spite of attempts to create dedicated AC lines and "home run" cable grounds, in the end, a dimmer on the far side of the house or studio, or a large appliance down the block could create ground noise. Additionally, many times an installation cannot allow for "new construction", and existing wiring must be used. Any of these scenarios can create AC ground contamination, loops, and distortion.

Many times these problems occur when deadlines have reached their final hour, and without a solution, your reputation is at risk. One real world solution that's been used by broadcasters for decades is the isolation transformer. This effectively isolates incoming AC power (particularly the AC ground), eliminating the source of many AC noise problems. Additionally, it's important that today's high speed processor circuits are never subjected to "ground contamination." Many have experienced jammed or lost presets, or the outright failure of digital audio converters. Yet few realize that the inexpensive - basic surge protector you installed may have actually assisted in the components destruction. This is because many of today's circuits cannot stand even modest voltage transients on the ground lines. Since many conventional Surge protectors and AC conditioners leak and dissipate voltage to ground, they create a path for this damage and distortion. (see illustration 2)

Further, just as there are noises present in your AC wall tap, components can "back feed" distortion, generating noise into adjacent components tied to a common strip. With the use of multiple secondaries, or additional isolation transformers within a system, we not only have total isolation from the incoming source, we have isolation component to component. With multiple shielded secondary taps, your Power Amplifier will not modulate your DVD player, the DVD will not interfere with your processor, and neither of those will create hum bars in your projector. Discrete Isolated Conditioning vastly increases noise reduction, and virtually assures no ground loops - no hum bars, they simply can't exist.

AC Noise Types - Common Mode Noise Reduction:

When we speak of AC noise, it's important to define the type of noise that's present, how it couples to the power line, and the best means of reducing it.

There are essentially two types of AC noise; the first is "common mode" (see illustration 3). Common mode noise attaches itself to the AC lines in even proportion, (both the Line and Neutral wiring referenced to ground). This noise comes primarily from AC fields and all 60 cycle harmonics, as well as a sizable portion of RF (radio frequencies inducing noise on the AC line). Though some products are designed with extraordinary common mode rejection from input to output (such as most Power Amplifiers), the majority of products is very susceptible to performance corruption from this noise being induced into their circuitry.

There are three methods used to reduce common mode noise. One is with a simple common mode choke. These are found in numerous RFI filters in moderate priced AC conditioners. They have limited bandwidth in terms of the range of frequencies they can effectively attenuate. Further, they are typically small and create some non-linear distortions as current draw is increased. The second is full active regeneration of the AC line. This is typically done with an amplifier / oscillator that takes the 120 VAC 60 Hz signal, converts it into DC, then regenerates it into a synthesized 120 VAC 60 Hz output (ideally with low distortion and great regulation. The problem with this scheme (where common mode noise is concerned), is that it stops working when the amplifier exceeds its frequency response limit which is typically where most RF noise BEGINS. The best means of reducing this noise is with a Symmetrically Balanced transformer (see illustration 4). Symmetrically Balanced power is achieved by running the incoming AC into a 1:1 ratio isolation transformer, with a center tap on the secondary. What this does is to take the incoming voltage 120VAC on the Line terminal, and 0VAC on the Neutral and Ground, and splits it in perfect halves on the output secondary of the transformer. The output Line terminal now has 60VAC, and the Neutral terminal has 60VAC, when referenced to its center tap Ground, which remains at 0VAC. What's significant about this is that the two 60VAC terminals are now in opposite polarity. So, like opposing magnets, the fields cancel. Further, this "canceling of common mode noise" is extraordinarily efficient and linear across a huge bandwidth. Recording and Broadcast microphones have utilized this same noise reduction principle for 80 years.

As you can see, Symmetrically Balanced Power is a significant technology in the pursuit of AC noise reduction. However, not all "Balanced Power" products are equal. Low current isolation transformers with less than 6-7 Amp capacity will not be able to handle even one large Plasma screen. Some contend that a conventional isolation step-down transformer that is derived from a 240 VAC split load is inherently "balanced." This is simply not true. Maximizing linear common mode noise reduction requires that the center tap of the transformer secondary be transmitted to the load. With the exception of many Power Amplifier designs (which have inherently high common mode rejection due to their balanced circuit designs), virtually any high resolution audio or video product will benefit from linear common mode noise reduction.

Transverse (differential) Mode Noise Reduction:

The second type of noise that's found on AC power lines is Transverse Mode (see illustration 5). This is essentially the opposite of common mode, in that the noise does not attach itself to the lines in even proportion. This noise is even more devastating than common mode, and common mode filter schemes such as Symmetrically Balanced Power are useless in defeating this noise. Transverse mode noise is typically produced from motors, appliances, switching power supplies and digital processing circuits. To
significantly reduce this noise requires a low-pass filter of considerable range. Typical AC filter- conditioner designs fall short where Transverse mode noise is concerned. Here's why.

As mentioned previously, there has been over a hundred fold increase in AC line noise in the last 20 years. What's just as critical is that the character and bandwidth of the noise has changed (see illustration 6). In as late as 1980, most electronic circuits used large transformers and linear power supplies. With the massive rise in personal computers for both home and office, the character of the AC noise changed forever. Twenty-five years ago, AC noise was mostly limited to 60Hz harmonics up to almost 400Hz, followed by virtually un-measurable noise levels up to approximately 100kHz. Most of the noise appeared in the AM radio band and beyond from 200kHz to 1Ghz. This is significant, because it's the model or, architecture of nearly every AC conditioning filter produced today.

Some engineers have created AC conditioners utilizing multi-stage filtering, special ferrite materials, exotic wiring, and capacitor topologies. However, all these designs are merely refinements of filters that were designed by Bell Laboratories nearly 100 years ago. They were tremendous engineers, but their designs were created to meet the standards of the 1920's.. an AM radio was the pinnacle of technology, all electronic circuits were vacuum tube, and nobody had designed a switching power supply or a
microprocessor. In 2004 we're faced with a new world, new technologies, and a properly designed AC filter must meet today's and tomorrow's challenges. In 2004 it is possible to measure more noise at 3kHz, 8kHz, or 15kHz, than octaves above in the RF band.

Though it is as important as ever to filter the RF bandwidth, it is just as important to reduce noise in the audio band, particularly where all the low level harmonics will occur, 2kHz to 20kHz. This is significant for both high resolution audio and video. It affects video, because the bandwidth in video covers both audio and RF frequencies. The sheen, brilliance, black level and black to gray definition depends on extremely low noise AC power over a suitably wide bandwidth. For premium audio, any noise in the upper octaves is devastating. This is because of the way we hear music, and the way in which musical instruments work.

For example, if we are listening to music at an average level of 95 decibels, most of the frequency content will be lower midrange and bass frequencies, and this will be primarily sustained energy. However, the harmonics, upper partials of music, as well as all the acoustic and ambient information, percussive transient attacks and high pitched instruments will be riding along at a FAR LOWER decibel level. In fact a great deal of information in these upper frequencies will be 20dB, 40dB, even 60dB below the upper decibel level. Nevertheless, this is how we hear music.

In fact, the reason a musician will pay a quarter of a million dollars for a Stradivarius or Guenarri Violin, or the reason we can hear a significant difference between a Hamburg Steinway, and a Young Chang grand piano is essentially the quantity and quality of harmonics that are typically very low in level compared with the fundamental tone. Yet, this is the way we hear and see. We are capable of deciphering layers of information simultaneously, and often it's these low level sounds or signals that are most prized (see illustration 7). So, if we are attempting to faithfully reproduce audio and video material, any induced AC noise will clearly contaminate and distort the signal. For today's Home Theater, Recording and Broadcast Studios, contaminated low level signals are unacceptable.

Linear Noise Reduction:

Most traditional RFI / EMI filters are based solely on filtering or notching out specific radio frequencies at a fixed impedance. Far too often, this can create a noise attenuation curve that resembles a roller coaster (see illustration 8). Prior filtering schemes assumed impedances were constant, which is far from realistic. Further, these designs did not anticipate ultra high resolution audio and video at the root of their design.If noise reduction is non-linear and subject to strong ringing patterns that vary with load and dynamics, the AC filtering "cure" can be WORSE THAN THE DISEASE!

A filter that is non-linear will sound and look discordant because of the way we hear and see. You cannot lower noise in one octave (thereby unveiling far more information), only to increase the noise an octave away and, further, dramatically reduce noise _ octave from there. This is akin to a poor job of equalizing a recording, a bad loudspeaker cross-over design, or vivid reds and greens with horrible blacks and yellows in a video presentation. For years, discriminating Audio and Videophiles have complained that many AC conditioners somehow "re-equalized" their carefully calibrated systems. Indeed they did. In the strictest sense, a 400Hz tone at 90dB will be rendered unchanged regardless of AC noise, or the filtering system that's used. However, a 10kHz signal that is occurring simultaneously at 30dB will certainly be effected by AC noise that is induced at 40dB.

So, it should be clear. We need a great deal of noise reduction, the reduction must be in both Common and Transverse Mode, and the reduction must be as linear as possible under real world conditions.

High Current Capacity - AC Power Correction

Power Amplifiers are typically constructed to suppress Common Mode noise via push-pull type designs that cancel this noise very effectively. However, they are always subject to Transverse Mode noise, so proper linearized AC filtering is still critical to their ultimate performance. Yet, many conventional AC filters can create problems for Power Amplifiers, Powered Subwoofers, and Powered Loudspeakers. The problem is current compression. This occurs when the Power Amplifier attempts to draw power for fast transient signals that exceed the capabilities of the unit's power supply. Because of the relative inefficiency of today's loudspeaker designs, and an ever increasing quest for greater fidelity and frequency extension, many power amplifiers routinely drain the AC power tap from your service. The percentage of voltage drop is typically small and rarely sustained for more than fractions of a second. However, this distortion is quite audible, particularly in a premium system.

One of the reasons for the proliferation of after-market AC cords for Home Theater and Audiophiles is that any attempt to lower the resistance or impedance from Your AC service to the Power Amplifier will aid in reducing this unwanted compression. Unfortunately, many AC conditioners have filtering circuitry that can actually raise the incoming AC line impedance, and compromise system performance.

One strategy to aid in this is AC Power Correction. By creating a reactive shunt network of sufficient size and proper tuning, the capacitors and inductors utilized will not only provide the level of linear noise suppression required for transverse mode filtering, but the circuit can actually lower the line impedance.

There are some inductive shunt circuits that make similar claims. Their designs are said to posses a "current fly-wheel effect". Though this is claimed to provide some additional current reserve, these technologies are not capable of yielding much more than 4 amps of instantaneous reserve current and exhibit large inductive kick-back transients (>480V) that are only limited by the included MOV. They are, by definition, high-pass filters that will allow virtually all transverse and common mode noise to pass through (with the exception of some ultrasonic filtering due to the capacitance to case caused by multiple windings). (see illustration 9)

AC Voltage Regulators

Another valuable tool in the management of AC power is Regulation. An AC Regulator takes incoming voltages, which are either too low, or dangerously high, and converts them into a constant, stable120VAC (see illustration 10). This is important in installations where the incoming voltage is either continuously or intermittently above 123VAC, or below 117VAC. Low voltage can be particularly troublesome for Power Amplifiers, since their rated power specifications are based on a constant 120VAC. If the incoming voltage is as low as 110VAC, the Power amplifier will only produce a fraction of its rated power. Further, high voltage or poor power regulation can play havoc with video projectors. Image intensity and calibration depend on stable power supplying the bulbs. Realistically, only about 40% of North America experiences regular sustained voltage surges and brown outs in residential environments. However, the only means of determining if this is a problem for a given system is by measuring the line voltage at the installation, preferably under load at various times throughout the day and evening.

Many make assumptions about being in populated areas, out in the country, in a new construction area, or at the end of a power pole, but none of these necessarily means your voltage will be in or out of regulation. You must measure the AC voltage. There are various schemes for creating AC voltage regulation from ferro-resonant circuits, full regeneration differential amplifiers, feed-back and feed-forward amplifier designs, motorized variacs, and multi-tap autoformers with solid state switching. Each has its advantages and disadvantages. Let's go through them:

Ferro Resonant - A complex circuit of capacitance and inductance is tuned with a transformer to create constant voltage, and greatly reduce transverse mode noise. The circuit is moderately expensive, and can work well in laboratory environments. Unfortunately, it creates heat, has little tolerance for dynamic loads such as power amplifiers, makes a very audible buzzing sound, and throws a magnetic field for several feet. Not an acceptable technology for Home Theater.

Full Regeneration Amplifier / Oscillator - This is essentially the equivalent of a very large power amplifier with a 60Hz oscillator driving the input. It takes the incoming AC voltage, converts it into Direct Current, and then synthesizes it back into low distortion AC power. This has the advantage of having exceptionally tight regulation (typically +/- 0.1 VAC). Additionally it lowers the AC line distortion, and eliminates some common mode noise. Unfortunately it is extremely inefficient. A mere 10 Amp output capability can cost several thousand dollars, heat an entire room, and severely current compress when capacity is exceeded.

Boost - Buck Active Correction - This design compares the AC voltage to an amplitude and distortion controlled reference and adds or subtracts a correction to the incoming AC (maximum correction of +/- 20%). Regulation can be very good (typically +/- 0.5 VAC). It is far more efficient than 100% regeneration, but it can suffer form current limiting under transient conditions, as well as creating AC noise of its own, due to the switching circuits that are typically employed.

Motorized Variac - This design uses a multi tapped boost - buck autoformer. On the top surface of the autoformer are exposed shaved windings with which a carbon brush makes contact. When the brush makes contact with the proper winding, the appropriate AC voltage is created by either boosting (to raise), or bucking (to lower). A microprocessor constantly monitors the input voltage versus output, and a motor moves the brush accordingly. This technology has good regulation (+/- 1 VAC). The disadvantage is that the motor is audible if the regulator is placed in a listening area. This technology was created for laboratories making steady state voltage readings. Because the windings are covered with grease, and are contacted by a carbon brush, high current demands will spark and create AC line noise. The brush is meant to be replaced, and the windings cleaned every one to two years. This makes this technology impractical for long term use in a home theater.

Multi-Tapped Autoformer with Solid State Switching - This circuit works very much like the motorized variac, except when the microprocessor tells the circuit to boost or buck voltage; this is accomplished via solid state zero-crossing switches. Since multiple switches are utilized, there are no exposed windings, and contact is tight and secure for many years. The regulation can be quite good (+/- 1 VAC) with a reasonably restricted capture ratio (110 VAC - 128 VAC). This circuit also has very good transient power handling characteristics with very little current compression. Unfortunately the solid state switching can create some AC noise if it is not precisely calibrated, so a good design without this noise can easily cost over $1000. If the budget is available, this is an excellent candidate for a home theater.

Uninterruptible Power Supplies

Typically referred to as UPS's, these are essentially "battery backup" for any component that can't ever be down (such as the brain and touch screen for Crestron or AMX AC switching controllers). These typically come in either true sine or stepped sine wave. For audio or video products that must be run through a UPS that is always "on line"," it is important that the unit be true sine, otherwise the AC feed to the components power supply will be very distorted, and performance will suffer. If the UPS is only utilizing its battery under brown out and black out conditions, a stepped sine is more than adequate.

The important thing to understand with either technology is that UPS's will inherently add noise to sensitive audio and video components due to the nature of their internal circuitry. Ideally, a UPS should be limited to components that contain control memory that cannot go down. Battery back up of sensitive audio and video components will actually impair their performance, and typically not allow enough additional viewing time to justify their cost.

Power Conditioning at the Electrical Panel vs. Discrete Component AC Conditioners

As with any other controversy, the answer is not always simple. Information is necessary for an informed choice to be made. Full AC power management may require Transient Surge Protection, Power Conditioning (AC noise suppression), Voltage Regulation, Sequencing and Remote Component / Appliance Switching, and Uninterruptible Power.

For premium whole-house installations, all of these technologies can have an important role to play, depending on the technical requirements of the system, and demands of the client. Certainly, there is an attraction to a one-size-fits-all package. The box or panel would be connected between the 240 VAC split phase AC mains and breaker panel, installed by an electrician, and all AC worries disappear.

Not so fast...

The 240 VAC split phase line is distributed to multiple 15, 20, 30 amp branch circuits in a typical installation. Finding a quality Voltage Regulator, or True Sine UPS that can handle a 100 amp (or greater) circuit is problematic at best. The size, cost, and heat generation prevent anyone from manufacturing such a product. Yes, there are custom made units that are manufactured to spec for heavy industrial applications. However, unless you have a large air-conditioned room to place these in, and an unlimited
budget, this is terribly unnecessary.

Appliances such as your electrical stove, washer, oven, and pool heater simply do not require AC voltage regulation. Even for clients with zero tolerance for power outages, a gas powered AC generator makes more sense than relying on a room full of series-paralleled UPS batteries.

Surge suppression can be accomplished at the panel, but not without some drawbacks. If lightning is the concern, then a lightning arrestor (by the panel) is mandatory. Most quality power products feature extensive transient voltage surge suppression circuitry, making an additional unit at the panel redundant. Most transient voltage surges are not lightning related, and though they have a negative effect on performance and longevity of sensitive electronic components, your dishwasher is fairly immune to them.

Where power conditioning and remote sequencing is concerned, discrete AC components have an obvious advantage. The more that an AC branch circuit is split, the easier it is to control the components that are fed by the conditioner. Plus, AC noise is generated not only via the incoming AC line, but also component
to component. No matter how fine the AC conditioner's noise suppression, at the panel it will only guard against the incoming noise. In a premium system, it is just as important to isolate the video from the audio, the analog from the digital, and the linear power supplies from the switching. This is possible with several
discrete isolated power conditioners, or a component with several discrete isolated taps.

Finally, if a substantial lightning hit occurs, either scheme will protect the valued componentry, but the panel method requires an appointment with an electrician before the Home Theater and Security System can resume operation, while the other, (transient surge protected power components) allows either your staff or the client to sub out the power product that absorbed the hit, and restore safe operation immediately.

Figure 1: AC Power

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Figure 10: AC Power

Figure 11: AC Power