Furman Lift


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As the capabilities of electronic equipment continue to increase, the quality of the electricity that powers them is following an opposite path. The two even work together to force power quality into a downward spiral — as more and more PCs are plugged in across the country, their switching power supplies add noise to the electrical grid, distorting low-level information and corrupting digital data. Many people know that a lightning strike can cause a devastating power surge, but few realize that hundreds of surges pass through ac lines every day, caused by power utilities as they switch from one transformer to another throughout the day to adjust for peak demands. While noise and small surges don't carry the dramatic finality of a major surge, they do have a destructive cumulative effect that shortens the life of components and impairs their performance.

As the quality of ac power continues to worsen, the only solution is to condition power before it reaches sensitive electronics — something that many people never take into consideration. Most people are familiar with the plastic $10 or $20 power strip surge protectors available at just about any department store. While they are effective at adding outlets, they provide little protection from surges and zero filtration of noise.

A better way

A better solution is a power conditioner that holistically improves the quality of the power running from the wall into expensive electronic equipment. Furman Sound is a manufacturer of power conditioners and related products. Some of the applications for its range of conditioners are sound reinforcement, audio and video recording, broadcasting, data processing, telecom and home theater. The power conditioning needs of many facilities are met with the PL-8 II, a base model that provides nine protected outlets for a rack full of equipment. The Power Factor Pro (floor/stage) and Power Factor Pro R (rack-mount) power conditioners are capable of lowering the ac line impedance supplied by wall outlets while reserving a current surplus for peak demands. The company's AR-15 and AR-20 are voltage regulators that not only control the level of incoming voltage, but also provide the protection and filtration of a power conditioner. A common factor between these devices that sets them apart from common surge protectors and even other power conditioners is Furman's proprietary Series Multi-Stage Protection Plus (SMP+) technology, which incorporates non-sacrificial surge suppression with an advanced filtration system and automatic shutdown capabilities.

Comparison of a non-linear filter with the Furman Lift noise reduction system.

Extreme Voltage Shutdown (EVS) is an SMP+ technology that protects equipment against sustained overvoltage situations such as accidental connections of 120V equipment to a higher-voltage outlet (usually 220V). These accidents are most likely to occur when setting up equipment in unfamiliar outside venues, or in new builds or during renovations where new power drops get mislabeled, or even go unlabeled. While surges are transitory, extreme voltage situations last as long as the equipment remains plugged in — or until an EVS-equipped power conditioner blocks the power supply to all connected components and critical circuits, which it does if the voltage rises to 15 percent above nominal or higher.

The surge of power

Surges are a different matter, both in their cause — a variety of events not directly related to human error — and in their transitory nature. Powerful surges can be as suddenly destructive as extreme voltage situations, and their dangers are well known, even if people inaccurately believe that lightning is their sole source. However, also dangerous are the small surges that occur dozens to hundreds of times daily, causing accumulative damage to sensitive circuitry. Look for a power conditioner that can protect equipment from surges of any size or frequency without sustaining any damage, and therefore don't require maintenance. Power conditioners equipped with Furman's Series Multi-Stage Protection (SMP) circuit can handle multiple 6,000V and 3,000A pulses without sustaining any damage.

Another important criterion for determining a surge suppressor's effectiveness is its clamping voltage — the specification that indicates how much voltage will pass through the device into the electronics it protects. Furman's SMP circuit clamps surges at 188V peak. Other conditioners on the market that claim to be non-sacrificial employ circuits with extremely high clamping voltages. Though this may save the power conditioner from sacrificing itself, it thwarts the unit's main purpose of preventing high voltages from passing through to connected equipment.

The third feature of SMP+ is Linear Filtering Technology (Lift), which is designed to counter electrical noise. Particularly through the 1980's, ac contamination has steadily grown worse; a trend that closely correlates with the proliferation of the personal computer and its accompanying switching power supplies. Noise distorts low-frequency information, which defines the harmonics, instrument timber, spatial cues and other signals that provide resolution and depth to high-end audio. Linear filtration significantly lowers the noise floor, thereby uncovering this important low-level information.

Traditional non-linear filters can lower noise in some octaves but not others, which results in resonant peaking that can actually add more than 10dB of noise to the incoming ac line. The error they make is in assuming that real-world electrical impedances are constant, such as the type manufacturers produce in the lab environment. The effect of non-linear filtration is perhaps most noticeable by discriminating technicians who have complained — rightly so — that many power conditioners re-equalized their carefully calibrated systems. 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 60dB below the fundamental 400Hz tone will be affected by ac noise that is induced 50dB below the 400Hz tone. Simply put, the ac noise that is coupled into electronics may be higher in level than much of the low-level signal it is attempting to record or reproduce, resulting in a masking effect. Furman's Lift ensures noise reduction along a smooth, linear curve with no resonant peaking to preserve low-level signals.

Producing audio is more than knowing how to play an instrument or handle a workstation mixer. Because electricity is a key component of producing sound, manage the power that is fed into sensitive electronic equipment carefully.


Powell is senior product designer at Furman Sound, Petaluma, CA.




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