Product Review

ExactPower EP15A AC Power Conditioner

November, 2004

Jason Victor Serinus



● Input Voltage Range: 90 to 135 Vrms
● Nominal Output Voltage: 1 Amp to 15 Amps
    120VRMS with 1% Tolerance
● Low-pass Filter: Dynamic, not Passive
● Protection: Over Voltage, Over Temperature,
    Over Current, Under Voltage
● Peak Repetitive Output Current: 46A Peak-to-
● Dimensions: 3.5" H x 17" W x 14.2" D

● Weight: 30 Pounds
● Surge Protection: 300 Joules 6,500 Amps
● Other Options: 19" Rack-mount
● MSRP: $2499




I have long known of the ExactPower unit. Though it works differently than the PS Audio Power Plant, regulating and correcting power rather than completely regenerating it, the ExactPower is claimed to have equally major and positive effects on the sound of one's system.

A number of years back, when the first ExactPower units were released, Mark Schifter of sent me one for evaluation. Alas, it emitted an unacceptable hum that interfered with my listening. Unable to evaluate music over the noise, I returned it.

Two years ago, JEJ reviewed the EP15, so we felt it was time for a follow-up, testing the changes that have been made with the EP15A.

I am happy to report that such noise problems have been corrected. The ExactPower EP15A operates flawlessly, emitting very little noise even when channeling tons of current to current-hungry Parasound Halo JC 1 monoblocks.

My revisit to the ExactPower (which still resides in my system) was triggered by the need to review those self-same Parasound Halo JC 1 monoblocks (see review in the Secrets archives). These amps require more power than my P600 Power Plant can deliver. The ExactPower unit can supply up to 1650 watts of clean power when fed 120 volts from an AC wall socket. It easily provides enough clean power for the monoblocks and my entire front end.

When I told Joe Reynolds of Nordost that I was having difficulty reviewing the Parasounds because of the limitations of my otherwise highly prized P600 Power Plant, he strongly recommended that I contact Quan of Sonic Integrity, U.S. distributor of ExactPower. Nordost has spent quite awhile evaluating various power conditioners, regenerators, and the like, and is firmly convinced of the ExactPower's efficacy.

For those wondering why I didn't simply plug the mighty Parasounds directly into the wall or something simple like the PS Audio Ultimate Outlet, the answer is that the sound was unacceptable. Even with a dedicated 30-amp power line, Oakland's power is too �dirty� to permit optimal listening. The difference between the sound of these amps and the rest of my components when switched from wall power to clean power is huge. We're not talking gray to white; we're talking congested, cacophonous, monochromatic, brittle, and uncontrolled, to musical. The noise floor drops tremendously, instruments ring out from an otherwise flat and gray soundstage, the soundstage size increases, bass gets much fuller and in far more control, highs become listenable, and the enhanced level of detail throughout the spectrum makes all the difference. Most of all, instruments and voices begin to take on their proper color and size perspective. Major, dude, major.


The ExactPower website supplies a fairly complete description of what the unit can accomplish. In addition to quoting and paraphrasing some of that information below, I include a conversation with Bill Whitlock, the designer of the original technology. I also relay information shared by Quan of Sonic Integrity, the organization that handles the business affairs of ExactPower worldwide.

The ExactPower unit is capable of supplying 15 amps of clean current through its eight high quality AC outlets. These are claimed to work substantially better than �hospital grade� devices. ExactPower claims that the EP15A will not vary beyond 120 Vrms
1% when loaded from 1 amp to 15 amps.

If a fault occurs, the unit shuts down and turns back on once the fault is eliminated. If, for example, an over-current occurs when an amplifier is being powered up, the EP15A does not shut off; instead, it automatically switches to wall power. After the over-current event has passed, the unit switches the outputs back to regulated mode. Having just observed this phenomenon in action when I powered up the two Parasound monoblocks, I can attest that the process proceeds smoothly and without the need for user intervention.

The ExactPower 15A actively removes high frequency irregularities from the waveform; it does not filter them. The work is accomplished by a high efficiency, pulse width modulated power amplifier. Instantaneous correction and wide bandwidth automatically improve the THD of the waveform. Current is stored, supplying bursts when needed. Output impedance is significantly lower than the impedance of the power delivered by the wall receptacle, allowing equipment to function more efficiently. Custom EMI and RFI filtering are included. A detachable AC power cord is provided, with the option of ordering a unit with a Nordost Vishnu. (I powered the unit with Nordost Valhalla.) Optional brackets are available for mounting in a standard 19� rack. (I floated the unit on Ganymedes.)

Quoting from the website:

�ExactPower's engineers designed a patent-pending [the U.S. Patent, No. 6,653,824, was granted Nov. 25, 2003], error-free, 'feed forward' technique.

A sophisticated differential comparator circuit monitors incoming AC power from the wall socket, instantaneously compares it to an internal amplitude-stabilized AC reference source. It then corrects any imperfections in the incoming AC signal. That corrected signal, in turn, serves as the source for a high efficiency power amplifier. Since this technique's speed is theoretically unlimited, it corrects even high frequency sub-cycle disturbances without the instabilities that can cause oscillation problems in functionally comparable but far less sophisticated products.

ExactPower products provide rock-stable 120 volt output with up to 46 amps of peak-to-peak current capability even when wall socket AC voltage varies from 90 through 135 volts. In fact, the ExactPower EP15A high current output means that even large power amplifiers will rarely tax its capabilities.�

A Talk with Bill Whitlock

When I contacted Bill Whitlock, originator of the ExactPower Technology, he supplied the following bio:

Bill Whitlock has designed pro audio and video electronics and systems for 30 years. In 1989, after seven years with Capitol Records, he became president of Jensen Transformers. He has become a recognized expert on system interfacing issues through his writing and teaching. His paper on balanced interfaces appears in the June 1995 AES Journal, which has become the most popular ever printed. Other writing includes the popular "Clean Signals" column for S&VC magazine, three chapters for Glen Ballou's 1500-page "Handbook for Sound Engineers," and numerous magazine articles and Jensen application notes. Since 1994, he has helped thousands unravel the mysteries of grounding and signal interfacing by teaching at trade shows, technical colleges, and professional organizations. Bill holds several patents including the InGenius(R) balanced input circuit and the ExactPower(R) waveform-correcting AC power voltage regulator. He is an active member of the Audio Engineering Society and the Institute of Electrical and Electronic Engineers.

BW: I'm a well-known lecturer on the subjects of ground loops and system noises such as hum and buzz, an area that the industry as a whole seems to treat as some sort of a black art. I have an upcoming tutorial seminar scheduled for the San Francisco AES the first week of November, and another for Lighting Dimension International. I deliver about a dozen lectures or tutorials a year at trade shows, universities, and technical societies. I also write magazine columns for Sound and Video Contractor and Live Sound, and have written chapters in textbooks about grounding and interface issues. It's my specialty niche.

JVS: One difference between the ExactPower unit and the PS Audio Power Plants is that the latter produce balanced power. The EP15 by itself does not. Please discuss the issue of balanced power.

BW: Balanced power is largely overrated in terms of its noise-killing ability. With that being said, the ExactPower people have chosen to make their own balanced power transformers available as an accessory to the regulator. (See below.)

If you look at what balanced power does, you can typically expect about 10 dB of noise reduction. It's not a breathtaking reduction in noise. Given what it costs, that's not a very cost-effective way to fight noise. I recommend the silver bullet solutions made by the company I own, Jensen Transformers (

JVS: You work with hum issues. I have a long-standing ground loop in my system that I usually solve by putting a cheater plug on my Jadis amplifier or other unbalanced amps I review.

BW: The academically correct way to solve hum problems is to find out where the problem interface is and then install a ground isolator transformer. Our Jensen ground isolator transformers don't compromise sound in any way. We have hundreds of thousands of our transformers in recording facilities � even on the space shuttle. We are the world's premiere quality audio transformer manufacturer.

JVS: Why would we not want that 10 dB of noise-quieting capacity?

BW: If you don't care about parting with your money, you can buy any transformer you want. ExactPower, Equitech, Furman and others make them. They usually list for well over $1000.

Our transformers are passive, go in the signal path, and fully deal with the problem.

JVS: Talk about the differences between your technology and PS Audio's.

BW: The PS Audio Power Plant is a total regenerator � it regenerates 100% of the power. The problem with doing that is that the unit is inefficient � it's hot, big, heavy, and costly. We instead convert only what is required to correct the impurity of the incoming power.

The basis of our patent is that the process is extremely high-speed � it can actually fix the sine wave on the fly. There's nothing else on the market that is as fast. Therefore, the ExactPower runs at 90% plus efficiency. (It's definitely lighter, cooler, and more efficient than the Power Plant. And it can deliver a lot more power than the mighty and far more costly P1200.)

ExactPower units do have a peak current limitation, but you have that limitation from a power cable as well. Every time you add resistance to a circuit via a wire, you lower the amount of current available.

JVS: The EP15A has four outlets for digital equipment, and four for analog. What's the difference between them?

BW: The ExactPower unit offers different filtering on analog and digital outputs. We do this largely to keep the two from talking to each other. The analog outputs use a combination of common mode and low-pass filtering, a technology pretty well known in the industry.

JVS: How would I go about correcting the ground loop problem that makes my Jadis hum?

BW: We have a troubleshooting guide posted at our website that will help pinpoint where the problem is. The process involves using shorting plugs with resistors in them and moving them around. You can make the shorting plugs on your own by soldering in resistors available at Radio Shack. Or you can buy them readymade from us.

JVS: Why do you oppose lifting the ground or using cheater plugs?

BW: It's a legal liability and safety issue. There are a number of people killed each year from ground lifting. If you lift the pin, there's the possibility that the entire frame of the equipment can become alive at 120 volts. To make matters worse, the 120 volts then travels through all of your signal interconnects and makes all the other equipment a live 120 volts, thereby creating an intense electrocution hazard.

Lifting the ground has also been known to cause fires. Let's say there's a ground on the cable TV connection. The defective piece of equipment will try to send its current flowing through all the intervening audio cables to try to get to the grounded cable TV connection. In the process, these high currents will often set the cables on fire.

While researching my seminars, I've spoken with some product liability attorneys. They tell me that there have been a number of lawsuits brought by customers of installers who have used ground lifters to fix ground loop and hum problems.

JVS: PS Audio touts the Power Plant's ability to lower impedance and help equipment run more effectively. They also offer a variety of sine wave manipulations via MultiWave.

BW: We make no attempt to manipulate the sine wave other than to make it pure and correct the flattop distortion commonly experienced on the top of the waveform. Because high current devices on power lines especially need the current at the top of the waveform, voltage tends to be reduced at the top of sine wave and the wave gets flattened out. This results in voltage drops in the distribution grid. It's a very common phenomenon, and limits the amount of power that comes into your home and is available to your equipment.

This means your amp, when plugged directly into the wall, will be starved for power exactly where it wants it most. We restore the sine wave to its optimal form, enabling your amplifiers and other equipment to get all the power they need.

I have no bones to pick with PS Audio's product. It is just larger, less efficient, and more costly than ours.�

More on the ExactPower

After speaking with Bill, I received further clarification from Quan of Sonic Integrity as to what the ExactPower EP15A offers in the way of power regulation, conditioning, and protection.

Long-time readers of audiophile reviews will discover that the price of the EP15A has risen from $1799 to $2499 since the spring of 2002. Besides the rising costs of material and commerce, the price increase reflects major changes in EP15A's construction and design. The unit has cleaner lines and improved metalwork. There have also been many costly changes in the circuitry to improve performance. The EP15A now offers active surge protection; it will recognize anything that could potentially damage your equipment that it can't correct and shut itself down. It can even protect your equipment against huge voltage swings (brown outs).

The company makes a number of different units in addition to the EP15A. Even though the EP15A does not supply balanced power, they consider it the best single solution, especially for those using it with power amplifiers. When you plug an amplifier into balanced transformer-based units and place large power demands on the amplifier, you will create a voltage drop in the amplifier that causes current limiting. This is due to the extra resistance created by an additional transformer. What this can translate into is sound that seems slow or sluggish with less pace, rhythm and dynamics.

(It is important to note that the PS Audio Power Plant does not create such a problem. The Power Plant produces balanced power while regenerating power totally; it does not create extra resistance. It does, however, have limits as to how much current it can produce, especially on peaks when current requirements momentarily balloon.)

For those wanting balanced power, the ExactPower SP15A is a separate balanced transformer-based unit designed for low-powered front-end gear (CD player, processor, preamp, DAC, etc.). The SP15 balances power by producing two 60-volt legs to make 120 volts and running residual noise down the ground. While the SP15A does provide extra noise-reducing benefits, the majority of clean power benefits come from the EP. The SP retails for $1099.

ExactPower also manufactures the SPX4. This unit takes balanced power one-step further. Most balanced units employ only one transformer for all equipment plugged into them, placing filters between the outlets to reduce noise. This results in less than perfect noise isolation. The SPX4 provides a separate 500W transformer for each of its four outlets, resulting in total and complete isolation. It retails for $1599.

Comparison Methodology

I spent considerable time comparing the ExactPower EP15A to the PS Audio P600 Power Plant. I listened extensively on many occasions, inviting a visiting dealer to listen with me at one point, playing many different kinds of music. The EP15A in fact remains with me, for use during the blind power cable comparison test Secrets is running in conjunction with the Bay Area Audiophile Society.

Nordost Valhalla Power Cables powered all components in the chain including the PS Audio and ExactPower units. Since I don't have a zillion of these power cables on hand, I had to plug and unplug when moving between units. Readers who adhere to the belief that power cables do not make a difference may wonder why I went to the trouble of switching cables on four pieces of equipment each time.

The long and short of it is that I do hear differences between power cables. PS Audio's Paul McGowan hears differences, recommends upgrading power cables on the Power Plant, and manufacturers a variety of power cable models. EP15A distributor Sonic Integrity also hears differences and makes the Nordost Vishnu Power Cable available as a purchase option for improved sound. I stick with the Nordost Valhallas because I think they deliver more extended and open sound throughout the spectrum with astounding vibrancy and transparency. Though I acknowledge that I've tried only a fraction of the after market power cables currently available, the Nordost Valhallas are the most neutral, revealing, and sonically satisfying power cables I've ever worked with.

Because I had to constantly move power cables between two different units in the cramped space behind my rack, comparing the P600 to the EP15A was no easy task. The process also necessitated repositioning Styrofoam squares between power cables and interconnects to minimize interaction. Doing so does not a relaxed listener make; it most certainly tests one's sonic memory. While I have done my best to figure out which way was up, if I were called to testify before Judge and Jury, I'd be tempted to take the Fifth.

What I Heard

Despite their differences in technology and approach, both units do a fine job. The Power Plant's advantages, in addition to fully balanced, completely regenerated, voltage-adjustable clean power, include its MultiWave options, which alter the sine wave and definitely affect the quality of the listening experience. While the EP15A offers neither balanced power, voltage adjustment, nor MultiWave, it cleans up the sine wave, uses much less electricity, runs cooler and more efficiently, and can easily power amplifiers that tax even the largest, heaviest, and most costly Power Plant beyond capacity.

How does that translate sonically? Auditioning the P600 in SIN mode, without utilizing MultiWave, I found that the EP15A gave Ariana Savall's exquisite soprano and harp on Bella Terra a bit more life. There were beautiful overtones to the harp, a glow to the sound, with very natural edges on everything. The sound was also remarkable quiet.

On Rachmaninoff's Symphonic Dances (a Reference Recording disc that never fails to stun listeners), I initially found the EP15A's bass leaner and less impactful, yet paradoxically more in control. Was this because less bass meant less room interaction? Did it mean that what I considered the P600's extra slam was actually extra smudge? Going back and forth between the units, I felt the P600 had more snap, but the ExactPower sounded less bloated and more in control in the bass. If it had leaner bass, it was nonetheless cleaner.

The dealer who dropped by days later (who does not sell either of these products) favored the P600. He thought the sound more three-dimensional, the soundstage larger, and the percussion more correctly positioned and stronger. I continued to sense more clarity from the EP15A.

In a subsequent listening session, I pulled out my favorite Terry Evans �Puttin' it Down� track from Blues No More and the first movement on Michael Tilson Thomas' hybrid SACD of Mahler's dynamic Symphony No. 3. I also revisited the Rachmaninoff. Perhaps the Nordost power cables, not fully broken in before, needed the extra time, because my feelings were now different.

Listening to the last few minutes of Mahler's massive first movement, I actually heard more bass impact from the ExactPower. While I personally continue to favor the P600's P-1 MultiWave setting for the outstanding clarity, three-dimensionality, and bass slam it lends to recordings (and others complain that the results sound artificial with highs overly etched and midrange slightly constricted), I thought the P600 in normal SIN setting sounded a little less crisp and clear than the EP15A. Instead of delivering leaner sound, might the ExactPower render sound just a bit more exact?

The bottom line is that you cannot go wrong with either unit. If you prefer the sound of the Power Plant and have or may eventually upgrade to multiple power hungry amps, you will need multiple Power Plants and power cables, silent air conditioning, and/or a very large room, and enough money to pay a substantial electric bill. The ExactPower EP15A, with its 1650-watt maximum capacity and 90% efficiency, presents a more flexible and cost-effective solution.

In the end, it's the difference between oranges and grapefruits dyed the same color. Both units have their strengths. Beyond the differences I hear between them when using premium components, cabling and supports � differences that will be less noticeable (albeit nonetheless present) on more modest systems � lies the reality that both units perform wonders by transforming sonic hash into music.


The most significant choice you can make is whether you compromise your listening and viewing pleasure with dirty power, or whether you will allow yourself more of the joy your gear can deliver. If you opt for clean power, the unique attributes of the Exact Power EP15A make audition indispensable.

- Jason Victor Serinus -


Digital Front End
Sony 707ES transport modified by Alexander Peychev of APL Hi-Fi
Theta Gen VIII DAC/Preamp
Theta Carmen II transport

Jadis Defy 7 Mk III or IV modified with a Siltech silver harness
Parasound Halo JC 1 monoblocks

Talon Khorus X speakers MK. II (with latest modifications and Bybee filters on woofers and tweeters)

Nordost Valhalla single-ended and balanced interconnects and balanced digital interconnects
Nordost Valhalla bi-wired speaker cable
Nordost Silver Shadow digital interconnect for DVD-V
Nordost Valhalla Power Cables

Also on hand and sometimes used:
Interconnects: WireWorld Gold Eclipse 5 and Gold Starlight 5 digital, Harmonic Tech Magic One, Acoustic Zen Silver Reference II balanced, and Nirvana BNC-terminated digital.
Power cables: Elrod EPS Signature 2 and 3 plus EPS 1, 2, and 3; WireWorld Silver Electra 5, PS Audio X-treme Statement, Harmonic Tech, and AudioPrism SuperNatural S2.

PS Audio P600 Power Plant power synthesizer with MultiWave II
ExactPower EP15A
PS Audio Ultimate Outlet; PS Audio Power Ports
Michael Green Deluxe Ultrarack, Basic Racks and Corner Tunes
Ganymede supports in main digital chain and under speakers
Michael Green Audiopoints, and Black Diamond Racing Cones elsewhere
Shakti stones on amp, Theta, and transport
Stillpoints ERS EMI/RFI sheets on most components
Bedini Dual Beam Ultraclarifier
Audioprism CD Stoplight
Marigo Signature Mat for use atop CDs
Ayre demagnetizing CD and the original Sheffield/XLO demagnetizing and break-in CD.



� Copyright 2004 Secrets of Home Theater & High Fidelity

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