It seems to me that the genre of power-line conditioners has seen little progress over the past decade, with no compelling new product introductions. Over the years, many devices have been marketed in an effort to clean up power-line noise due to conducted radio frequency interference (RFI) and electromagnetic interference (EMI). I have experimented with a host of such devices, including isolation transformers, line filters, and AC regenerators, but in hindsight it is clear that they didn’t achieve more than limited success. That is until Sound Application designer Jim Weil’s latest TT-7 power-grid interface, designated as the San Francisco Standard (SFS). Sound Application (SA) was founded by Jim and Connie Weil over two decades ago and has been laser focused since then on power-line filtration. That sort of dedication to the cause has clearly paid off. Spoiler alert: The SFS is an absolutely incredible power-line filter that advances the state-of-the-art.
I’m currently at the mercy of Xcel Energy’s Denver Metro power grid, which is likely no better or worse than your typical grid as far as power outages and chronic power-line noise. That means that pure AC mains power is all but a dream without effective line conditioning. We often take the power grid for granted. It’s indispensable to our way of life. But when something goes wrong, we’re plunged into darkness; a stark reminder of how much we’re dependent on it. Even if a grid works as intended, it is never free from power-line noise.
As a prelude to the following discussion on AC mains filters, it would be useful to review some basics. Every house outlet is connected to the grid via the main circuit breaker box, which itself is connected to a step-down distribution transformer via a 3-wire system. One wire, denoted as “neutral,” is grounded at both the transformer and breaker box. The other two are “hot” 120V, but 180-degrees out of phase to provide for 240V circuits. The common 120V house circuit uses a ground wire connected to earth ground, one hot 120V wire, and the neutral wire.
In an ideal world only 50/60Hz current would flow into the breaker box. Unfortunately, high-frequency noise currents are also conducted into the box. A common source of power-line noise originating from the utility company is caused by micro-arcing of high-tension power-line hardware. According to the ARRL, the National Association for Amateur Radio, “arcs can occur for several reasons, including loose hardware, a cracked insulator, [surface] tracking, corrosion between two pieces of metal, or a loose tie wire.” Arcing produces broad-band radio frequency interference, which is an issue for amateur radio reception. Some of this RFI is also conducted into the circuit-breaker box, which is the problem we’re concerned with.
According to SA’s measurements, the preferential pathway for power-line noise on the U.S. grid past the circuit-breaker box is in transverse mode (also referred to as normal mode), measured between neutral and hot wires. However, common-mode noise is also present, as measured between ground and neutral, and ground and hot wires. To add insult to injury, there are also sources of electromagnetic interference inside the home, most notably from electric motors turning on and off. Think of refrigerators and HVAC systems. In fact, there are many potential sources of unintentionally conducted and radiated EMI in the home. Devices such as Wi-Fi routers, fluorescent and LED lighting, and wall-wart switching power supplies, may all be culprits if they fail to comply with FCC emission limits.
The purpose of the SFS power-grid interface is to filter out high-frequency noise currents present on the AC power lines. It operates as a low-pass filter shunting both transverse and common-mode high-frequency noise to ground, while allowing clean 60Hz current (or 50Hz as used in much of the world) to reach the load, in this case costly audio gear. In my experience, spanning decades of critical listening, clean AC power has proved to be a critical determinant in achieving definitive sound quality.
For the past 20 years or so, SA power-grid interfaces have held court in my audio system. The fact that these devices feature zero current limiting made them ideal for power amplifier use. And being designed specifically to address micro-arcing-generated power-line noise, they worked very well to purify the AC mains. Since 2021, I have been living quite happily with Jim Weil’s older version of the TT-7 grid interface. That is until he contacted me during 2024 with a major announcement, the release of the new 120/240-volt SFS TT-7 power-grid interface. According to Jim, all recent variations are referred to as “TT-7: Teflon—titanium—7N wire, since we began using heat-treated medical-grade Teflon caps, G5 titanium hardware, and 7N 10AWG power wire.”
But the SFS design is crucially different. “We are addressing the one fundamental problem with power-line conditioner design, excessive reactance, whether capacitive or inductive, leads to poor sound quality. For many decades our designs have been created with the premise that any capacitance over 0.5µF is detrimental to sound. Even 0.5µF is way too much.” He changed his entire approach to now use a “complex derivative of an LC network” to further reduce reactance at 60Hz. The new universal SFS design has a 3GHz-bandwidth transverse-mode filter and a 1.1GHz common-mode filter. Because the power grid is engaged at such high frequencies, reactive impedance is essentially non-existent at 60Hz. For example, inductance is barely out of the nano-Henry range. The interface is therefore invisible at 60Hz: Audio gear sees nothing but pure AC mains.
Externally, an obvious improvement is the 5-kilogram CNC-machined solid-brass base, referred to as the PowerBase. It mass-loads the chassis to control low-frequency vibrational issues and is threaded for ¼” x 20 spikes. The filter networks are located inside a single-shell aluminum chassis, which is tunable to control the vibrational spectrum of the enclosure. The final tuning is performed after the PowerBase has been attached. The ability to tune the enclosure is said to be critical to obtaining truly superior performance. At the heart of the filter networks are custom REL Cap TFT Teflon™ tin-foil capacitors, designed for SA by none other than Bas Lim, the founder of REL Cap (REL Cap is now owned by Wilson Audio). In addition, the networks also use RF inductors with GHz bandwidth. Connections in the AC-current pathway are cold-welded and wired point-to-point.
The physical layout consists of a 20-amp IEC input receptacle, matched with a 20-amp Carling high-speed magnetic circuit breaker. An input power cable is not provided, as choice of length and make is best left to the individual user. The circuit breaker is followed by three 20-amp duplex U.S.-style outlets that accommodate up to six power cords. SA states that the performance of the TT-7 is optimized when audio gear is inserted as follows. Outlet #1, nearest the circuit breaker, is for digital gear. The center outlet is for sensitive equipment such as preamps and phonostages. Outlet #3 is for all high-current devices such as a power amp. A vital feature of the TT-7 design is that a greater current draw actually improves overall performance. That means that it absolutely does not interfere with the music’s macro-dynamics.
While an audio amplifier (or preamplifier) isn’t supposed to respond to RF signals, broadband power-line noise is rectified by the power supply into the audio bandwidth. This noise makes it past the power supply’s filter network and contaminates the audio signal. To be sure, there are skeptics out there who question the sonic impact of “dirty” AC mains. These individuals might argue that AC line-noise effects pale in comparison with the audio gear’s inherent and possibly dominant distortion products. That, however, wasn’t the case in my experience, at least in the context of high-end audio. Having auditioned many audio systems with and without decent power-line filtration, it had become apparent that the effects of power-line noise are not only audible but are superimposed over an amplifier’s inherent sonic character. Granted, the effects may be subtle at times, but they are generally disruptive to the enjoyment of music as they exacerbate intrinsic distortion products.
It has been said that “AC related distortion hides in background, resulting in haze, grain, or glare”—a sonic trifecta from hell. These distortions are not pretty or euphonic. They are, metaphorically speaking, snakes in the grass capable of biting you in the proverbial derrière when you least expect it. You may end up pointing a finger at and blaming a particular component for what is actually AC mains distortion products. And that can become a frustrating and expensive exercise as you replace or upgrade system components in an attempt to eliminate the problem.
For me, the most annoying AC-related distortion aspects have been upper midrange glare and grainy harmonic textures, especially noticeable on violin overtones. The degree of annoyance has been recording dependent and would become nearly fatal on poor recordings. I was surprised at how much better the TT-7 SFS performed in these regards versus the older version. It was hard to quantify other than to say that the SFS offered stunning improvement in these areas. In fact, on album after album it became clear that it was a case of problem solved. Issues to do with textural granularity and glare simply evaporated. The level of textural purity was now an absolute joy to behold.
There were other benefits, as well. First, let me rave about the fabulous background silence. The noise floor dropped to the point of being able to resolve substantially more low-level detail. For example, while listening to a recording of Bach’s Toccata and Fugue in D minor, Pierre Bardon performing on the historic French organ at Saint Maximin-en-Provence (Pierre Verany PV 10811), I marveled at the clarity of the cathedral’s wet acoustic, boasting a lovely reverberation of about six seconds. In general, transient decay became easier to discern, which served to close the gap between live and reproduced music.
Spatial resolution also gained solidity. In particular, soundstage depth perspective and width dimension improved yielding a more convincing and stable 3D impression. Massed voices exhibited exquisite separation of individual voices. My old faithful standard in this regard is the choir on Laudate! (Proprius 7800). The album was recorded using a purist miking technique that allowed the voices to mix naturally. With the SFS in the system, it was gloriously easy to pinpoint individual singers.
In total, the new Sound Application TT-7 SFS power-grid interface resolved power-line noise issues in massively superior fashion to all other line filters and power conditioners I’ve auditioned. Projected lifespan for the unit is 50 years: “Your equipment can be plugged into an SA, and you can forget about it for the next half-century.” The SFS represents Jim Weil’s crowning achievement and is without a doubt an amplifier’s best friend. Once heard, it is nearly impossible to do without. Its impact has become addictive. To be honest, I can’t live without it. I’m well aware of the cost, and I wish it were lower. But if you’re looking for the best there is, it’s the only path to follow.
Specs & Pricing
Power input receptacle: 20 amp IEC
Outlets: Three 20-amp high-conductivity duplex U.S. outlets
Circuit breaker: 20-amp Carling high-speed magnetic breaker
Transverse mode filter: 3GHz bandwidth
Common mode filter: 1.1GHz bandwidth
Dimensions: 6.3″ x 3.3″ x 16″
Weight: 17 lbs.
Price: $25,000
SOUND APPLICATION, LLC
2036 Nevada City Hwy. #163
Grass Valley, CA 95945
soundapplication.com
Associated Equipment
Phono front end: Kuzma Reference turntable; Kuzma Stogi Reference 313 VTA tonearm; Clearaudio da Vinci V2 MC phono cartridge
Phonostage: PrimaLuna EVO 400
Line preamplifier: PrimaLuna EVO 400, Joule Electra LA-150 MKII
Digital front end: Denafrips Terminator DAC
Digital source: Qobuz streaming via Audirvana Studio software, Ideon Audio 3R Renaissance mk2 Black Star USB regenerator/reclocker
Loudspeaker: Fyne Audio F703SP, Analysis Audio Omega planar-magnetic
Power amplifier: PrimaLuna EVO 400 monoblocks, Audio Research VS115, SMc Audio DNA-1/GT-21 Ultra upgrade
Cables: Kimber Select KS1016 and KCAG interconnects; 8N OCC speaker cable
Tags: AC POWER DISTRIBUTION
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By Dick Olsher
Although educated as a nuclear engineer at the University of Florida, I spent most of my career, 30 years to be exact, employed as a radiation physicist at the Los Alamos National Laboratory, from which I retired in 2008.
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