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Let’s take an initial look at the problem shown in Figure 1. There is a 120V isolation transformer with a common RF filter typical of many types of equipment. Look at the red current flowing through the capacitors. As more and more equipment is energized in the system, "the voltages present throughout the grounding system (signal reference grid) are raised relative to the impedance of the grounding system. This may be only a matter of millivolts but in high gain and high impedance audio equipment it can be very audible."

Our basic three-wire power delivery is unbalanced in "differential mode" with current flow equal but opposite in the two wires. However only one wire is "hot" at 120 Volts. Both neutral and ground are at zero. By its very nature "unbalanced power provides the means by which common harmonic and reactive currents build up on neutral wires and grounding circuits. Balanced RF filter capacitors and switching power supplies routinely shunt a small but constant trickle of current directly into grounded audio chassis from the "hot" side of the circuit which further degrades a system's grounding reference." Unfortunately the inherent design of our electric system tends to produce noise, attract RFI and act as a conduit for noisy reactive currents flowing throughout the power grid. What are these issues and what does all of this have to do with balanced power?

What is it?
Actually it’s quite simple. Figure 2 shows the standard residential electric system in the United States. Anyone who has installed an outlet knows that the black wire is "hot" at 120V, the white is neutral at 0V to ground and the green (or bare) wire is the ground also at 0V.

Balanced power is different. In order to fully understand it you must forget about the concept of hot and neutral wires. In the balanced world there is no such distinction. With balanced power both wires are at 60V to ground. Hook up a volt meter to either wire and ground and both will read 60V.

AC as you know alternates 60 times per second from positive to negative. The key with balanced power is that the 60V legs are 180° out of phase with each other with respect to ground. This "inverse phasing" between the two 60-volt mains means that the potential difference between them is always 120 Volts. Your equipment could not care less how the 120V potential is presented - 60/60 or 70/50 or the traditional 120/0. The absolute numbers are irrelevant. It’s only the voltage differential between the two mains that matters.

As you can see in Figure 3 the "system reference (ground) originates at the output center tap of an AC isolation transformer. In other words, the system's grounding reference (zero position) is located at the system's mean voltage differential or zero crossing point of the AC sine wave. This is a far more effective way to establish a reference potential for an AC system. The center tap is then grounded to Earth for electrical safety and for referencing shields."

In a properly designed balanced power system there is no voltage or current on the system ground. This is a major advantage for audio equipment and we will see the implications of that shortly.

AC Noise
My home outlet delivers 120V, I don’t live near industrial factories and I have relatively clean power. Well at least I think I do. Why would I send my hard-earned money to Equi=Tech to deliver 120V in a different manner? Since their system is essentially devoid of circuitry, how is it going to filter my power and make my system sound better? To get to the answers we have to take a little trip down an electric line and get an understanding about the type of noise that's present in every AC system.

When power is consumed by an appliance other than one of pure resistance like a light bulb, only part of the total power runs the equipment. Some of its energy is wasted and rolled back into the electrical system of your house and also your neighborhood. This wasted power is called reactive power (kVAR). The terms reactive power, reactive current, harmonic current and harmonic distortion are synonymously used in many discussions. As a non-engineer I’ll treat them as interchangeable in this discussion. 

Figure 4 represents a typical 120V residential power supply applied to any impedance load. In addition to the currents flowing to the load you notice in red reactive currents flowing from the load into the ground. These reactive currents are "basically capacitively discharged energy that is key to a modulating AC source – a "backwash" of non-active power. This is wasted energy not being actively processed by the load"

Note the circuit in Figure 5 and how the reactive currents are invading the circuit through the grounds (in red). This is exactly why lifting the ground to equipment chassis eliminates noise whilst providing its own share of issues, most importantly lack of safety. Additionally as a reactive current is applied to the source transformer, reactive voltages are generated and the combination of voltage and current produces kVAR (kilovolt-amperes reactive).

Do we care if reactive currents flow back into the power system? Yes we do or at least should. When we feed power to the amplifier, preamplifier and CD player, the equipment uses most of the energy to function as designed. The remainder ‘rattles around’ in your power system as reactive currents (noise and grunge) on your ground including cable shields and component chassis. Significant noise pollution has been introduced through a backdoor directly into your most sensitive electronic circuits. "These reactive currents complete the circuit back through sensitive signal-circuit electronics, looping in a matter of speaking through whatever grounding or signal path is available. This is noise commonly called hum. But as one might imagine, the harmonic structure can be infinite so all sorts of ‘sonic qualities’ in the noise are possible."

This is not a theoretical concern. It’s a real world problem with garbage flowing around causing noise, distortion masking fine detail in your audio system. The noise is intermingled with the subtle detailing cues that would add more realism to our systems. Once the noise is entwined and joined with low-level musical detail, unique detail is lost permanently. Focusing on the recording studio, Equi=Tech argues that "the dynamic range of the entire electronic signal chain determines the quality of the final product in all recording environments. The presence of any electrical interference at all lowers the S/N ratio of the recording. This limits the subtle detail and realism of the sound or image. Low level signals are lost in the noise floor of the system."