The Sound Application Model CF-X Power Line Conditioner

Dick Olsher

Several years ago, in an article titled “Power To The People,” I explored the various aspects of power line conditioning. I pointed out then that the average audio Joe takes it for granted that at the flick of a switch his audio system would be energized with pure electric power. Even with the proliferation of various filters and conditioners in the intervening years, audiophile naivet√© about the subject has only been replaced with a moderate awareness about the importance of power conditioning for audio (and video) systems. Guys, it’s time to wake up and smell the coffee! AC line conditioning is far more critical to audio quality than speaker cables and interconnects. How many friends do you know who’ve spent thousands of dollars on cable, but don’t own a line conditioner? There’s a classic case of misspent resources. Given a limited accessory budget, I would spend it in a heartbeat on the Sound Application CF-X conditioner and simply make do with my old cable.

The three basic problems that afflict AC power are chronic over or under voltage, transient sags or surges in line voltage, and radio frequency (RF) and electro-magnetic (EM) noise pollution from a variety of sources. In all fairness, only the first two problems can be laid at the feet of your local power utility company. To accommodate peak hour demand within an inadequate distribution grid, voltages are cranked up above nominal. This, I’m told is a national problem. In my neighborhood, the long-term voltage average is 127 volts with short-term sags as low as 80 volts and surges up to 141 volts. Not so cool for most audio gear. For example, the plate supply voltage (B+) in tube amps is rarely regulated. Its exact value is dependent on the voltage impressed upon the primary of the power transformer. Change the AC mains voltage and you’re in effect shifting the operating point of the amp. Tube heater voltages are also typically unregulated, being simply tapped off the power transformer, and so are subject to drift in concert with AC mains fluctuations. That’s bad too, because such heater voltage variations do shorten tube life. The most efficacious, low-cost, solution to these sorts of issues is the Autotransformer – also known as a Variac. A Variac features a single winding which may be tapped continuously in order to vary line voltage, typically from 0 to 140 volts. A desired voltage is selected by rotating a large dial that actually moves a contact along the winding. Some units have a built-in voltmeter; otherwise use your own meter to precisely calibrate the dial. It offers no noise rejection or any line isolation because of the DC path from input to output, and while a Variac is only useful in controlling long-term trends in line voltage, it is still very helpful in controlling the operating point of tube amplifiers. Certainly, my AirTight ATM-2 power amp benefited sonically from a reduction in the line voltage from its initial 127 volts to 117 volts. As a result, imaging focus and the purity of the treble range were improved. Don’t fool around with anything sporting less than a 1.4 KVA rating, which buys you a nominal 10-amp capability. Such a package is also a pretty economic deal. I’ve used both Staco and Superior Electric units with good results. Both of these brands are readily available; try your nearest electronics distributor or Newark Electronics. Another piece of good news: these puppies are silent, so sitting is not critical.

Another form of sonic trespass that simply creeps in through the wall is EM noise interference. Electric motors and compressors are ubiquitous. Kitchen and workbench appliances generate lots of EMI within a typical household. But the problem is even more global than that as pole-top transformers are poor at filtering noise, so the noise from down the block can also trickle into your home. Then there is the ubiquitous sea of RF energy we live in, from TV and radio to cellular phones. Environmental levels of RF energy have climbed a factor of a million since the turn of the century. Power lines and even the wiring in your house act as an RF antenna, coupling RF noise to your audio gear’s power supply where it can demodulate and pollute the audio signal.

One possible line of defense is the isolation transformer (IT), which is quite common in scientific labs for isolation of test and measurement gear from mains noise. I own several vintage Berkleonics Model CEA-25 ITs rated at 2000 VA. These are heavy-duty lab-grade transformers that have proven effective in filtering RF and EM noise artifacts. Unfortunately, there are several practical limitations in using such units. A high-grade IT is difficult to find these days; in other words, they don’t build them like they used to. Most of the ITs sold to audiophiles today are rated at only 500 VA, which makes them current limited and unsuitable for filtering power amplifiers. Second, an IT is most effective in cleaning up common mode noise and far less so in reducing transverse mode (between hot and neutral lines) noise. As long as a proper ground is established for the neutral conductor at the circuit breaker box, transverse mode rather – than common mode noise – is the big concern in single-family homes. This means that additional filtering is usually required, above and beyond that afforded by an IT, for transverse mode noise reduction. Finally, large transformers typically generate low levels of mechanical hum, which may necessitate positioning the unit far away form the listening seat so as not to create an active nuisance.

All of this leads me to present the Sound Application CF-X as the perfect solution for the filtration of EM and RF noise (EMI and RFI). This filter uses no transformers or other current limiting devices. It is designed to provide an extremely low impedance capacitive shunt to ground for EM and RF energy over a bandwidth from 10 kHz to 2.5 GHz. That’s an upper limit of 2.5 Gigahertz – clear out to the microwave range! I’m not aware of any competing models that can claim a bandwidth beyond the megahertz range. Noise reduction of up to -60 dB is claimed across this bandwidth. Designer Jim Weil, to put it bluntly, is fanatical about construction detail and parts quality. He’s the kind of guy that has apparently never read the book “Don’t Sweat the Small Stuff,” because he constantly worries over small details. The CF-X represents the culmination of 12 years worth of development effort and tweaking. It’s interesting to note that Jim uses the video quality of his Sony XBR TV to gauge the effect of various part substitutions. He maintains that visual sensory input in this case is more refined and reliable in making fine judgments. In what follows, I can only give you a glimpse of his attention to detail that is essential in making a parallel filter work effectively over a bandwidth extended beyond 2 GHz.

All of the circuitry is housed in a machined aluminum case. The internal power distribution is via 4N (99.99% pure) 1/8-inch copper bus bars and 6N (99.9999% pure) copper wire. All internal wiring is point-to-point, and is rated at 100 amps. The unit can safely handle 6 kilowatts of power, well beyond the rating of a standard 15-amp circuit breaker. The filter stages are preceded by spike and surge protection circuitry. A custom high-speed magnetic circuit breaker provides an interrupt time of less than one millisecond for high-current transients – much faster than the thermal breakers commonly used in competing products. A bank of eight varistors follows for voltage spike suppression and protection. A 23-step stage filter bank of high-quality capacitors, mainly film and foil types, is used to provide a near-zero impedance pathway for both transverse and common mode noise. The primary emphasis, however, is on transverse mode EMI and RFI rejection. For effective filtering, it is necessary to cover the desired bandwidth with multiple capacitor sizes, as each capacitor’s high-frequency self-resonance limits its upper range of applicability. Did I mention the several pounds of Cascade Audio dampening compound used internally, or that all soldering is performed in an inert argon gas environment to eliminate the formation of surface oxides?

The CF-X features a total of six Hubbell duplex outlets, and is shipped with the MAC Delta power cord, or optionally without a cord. A long and hard break-in protocol is specified in the installation instructions. The initial break in period is about 300 hours and can be expedited by plugging high-current devices such as vacuum cleaners into the unit. The break-in of the high-voltage caps will take much longer. Expect slight sonic improvement for many months to come.

Sonic Impressions

The following is a composite synopsis of my impressions collected over many months of evaluation in the context of many systems. It’s important to realize that your own experience may vary somewhat depending on specific system components or even on the time of day you happen to listen. There is considerable variation in the response of audio equipment to EMI and RFI. The high-frequency noise has to be rectified by the component’s power supply into audio bandwidth contaminants, and some power supply circuits are more susceptible than others. Also, the amount of line noise is not constant during the day, but varies over time. The peak probably occurs during the early evening when everyone is home using a variety of appliances and the airwaves are jammed with RF transmission. The opposite extreme is around midnight. Many audiophiles have described magical listening sessions late at night when apparently the AC line is relatively free of gremlins.

In general, with the CF-X in the system, harmonic textures are given a major Windex treatment. Grain and grit are wiped clean. As a result, the music’s tapestry sounds purer, closer to velvet in texture. Digital program sources sound more like analog, that is, less bright and edgy. On high-resolution speakers, the transformation is quite dramatic. These are no subtle changes that require the intervention of golden-eared audiophile gurus to resolve. They should be apparent to anyone with a foundation in live music. Dissonance and distortion products dissolve away, so that reproduced music sounds more like the real thing.

Dynamic contrasts are also improved. Without the CF-X, a system may sound like it only has a couple of gears in going from soft to loud. Connect the CF-X and the system gains at least a couple more gears. Fasten your seat belt! An ordinary, plain vanilla, listening experience is about to turn into something extraordinary. The CF-X infuses dramatic life into the soundstage as the music unfolds with greater conviction. Finally, image outlines are better defined as spatial detail snaps into greater focus. It’s as though a veil lifts from in front of the soundstage. The perceived effect is increased transparency; it becomes easier to localize the inner recesses of the soundstage.


Make no mistake about it: the Sound Application CF-X is the most effective line filter money can buy. It provides an interface between your audio/video gear and the AC line that protects against spikes and surges and filters RFI and EMI over a bandwidth extended into the gigahertz range. Together with the MAC Delta power cord, this unit is currently my absolute reference. To my mind, the CF-X should be an essential component of every high-end audio system: it simply wipes the X-factor from the AC line and makes the listening experience much more predictable and enjoyable.