practices established over a century ago, when electric power use was limited to lighting and motors, long before any AC noise sensitive applications existed. The emphasis then was on convenience (from the power utilities’ standpoint) and safety, but not noise cancellation. The result was a three-wire distribution scheme in which 120V branch circuits have a hot wire and a neutral wire, with the neutral tied to a third wire connected for safety to an earth ground. The third wire does not carry any current unless there is a fault. This unbalanced scheme can create hum in audio circuits for two main reasons. First, the current flowing in the hot wire induces hum in any other nearby wires, which may carry vulnerable low-level audio or video signals. Second, because the impedance of chassis and cable shielding to ground is always greater than zero ohms, ground current flowing from power supply capacitors and from EMI pickup causes a voltage drop at 60Hz and its harmonics. This low level noise becomes part of the audio signals.
With a center-tapped isolation transformer, the AC power feeding a studio can be balanced at its source. The current-carrying wires then are no longer “hot” (120V) and “neutral” (0V), but two 60V lines of opposite polarity (referenced to ground connected to the center tap), whose difference is 120V. This type of power, when run around a room, does not induce hum into nearby audio wiring because the two conductors induce equal and opposite voltages that cancel each other. Similarly, ground currents are all but eliminated by the same common-mode cancellation effect. No longer is it necessary to adopt cumbersome and expensive star-ground systems or use massive bus bars or heavy ground rods. Further, with features such as our center tap ground lift, ground induced noise may be reduced even further.
Of course Balanced AC Power is only the beginning of a system free of AC noise.
Asymmetrical noise, or what is called “differential mode,” is responsible for well over half the noise present in today’s AC lines. For this reason we employ our exclusive Linear Filtering Technology (LiFT). This assures that your audio, video, or computer signals are as pure and uncorrupted as possible.
Linear Filtering Technology (LiFT)
Unfortunately, traditional AC filter conditioners have been designed for unrealistic laboratory conditions. Prior technologies could actually harm audio and video performance more than they help, due to the resonant peaking of their antiquated, non-linear designs. Under certain conditions, these designs can actually add more than 10 dB of noise to the incoming AC line! Worse still, lost digital data, the need to re-boot digital pre-sets, or destroyed digital converters are frequently caused by excessive voltage spikes and AC noise contaminating the equipment ground. Furman’s LiFT takes another approach, ensuring optimal performance through linear filtering and no leakage to ground.
Series Multi-Stage Protection Plus
(SMP+)
Traditional surge suppression relies on circuits that “sacrifice” themselves when exposed to multiple transient voltage spikes, requiring the dismantling of your system and repair of your surge suppressor. With Furman’s SMP+, however, damaging transient voltages are safely absorbed, clamped and dissipated. No sacrificed parts, no service calls, no downtime. Also unique to Furman’s SMP+ is its unparalleled clamping voltage. While other designs offer clamping voltages that are well above 300Vpk, Furman’s SMP+ clamps at 188Vpk, 133 VAC RMS, even when tested with multiple 6000Vpk, 3000 amp surges! This unprecedented level of
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