DeadEars
100+ Head-Fier
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- Aug 13, 2009
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Quote:
Let me describe one of my hi-fi systems that is totally balanced to perhaps help you with this. I'm an analog/tube guy, so I'm going to stick with an analog description, but in theory the same thing holds true for digital.
My system starts with a phono cartrige. The phono cartridge converts physical motion into electrical current. It has a magnet in it and a coil attached to a stylus. When the stylus is placed on shiny black LP record, it wiggles sideways and up-and-down based on signals that are engraved on the surface of the record. The sideways movement generates one channel signal, and the up-and-down generates the other channel signal (a sligtht oversimplification). As the coil moves relative to the magnet, it generates a very very small voltage (0.25 millivolts). When the stylus moves one way, the current is induced in one direction, and when it moves the other way, it induces current in the other direction.
For each channel, the stereo cartridge has two wires, which connect to the amplifier. In a BALANCED configuration, there is no connection to ground (although there may be a separate grounding wire, which is not connected to the signal anywhere). So the signal actual "floats" across the two wires, with no reference to ground. This float is maintaned throughout the amplfication chain. In my system there is a phono amp, a preamp, and an amplifier which always keep the signal floating, and a separate ground wire. So balanced connectors have three wires for each channel, with the two wires for the signal (as it swings positive to negative and back) and one wire for the ground, as seen in your typical XLR connector. Each amplfiication stage simply boosts the voltage of the signal, hopefully in exact proportion to the original signal. The signal has to be made big enough so that it can drive the transducer at the end of the chain that moves air to make sound. It is exactly like the phono cartridge in reverse, converting electrical currents into physical motion. As the needle swings one way, it generates a signal which is amplified to move the speaker/headphone element an exactly proportionate amount in the same direction.
In an UNBALANCED configuration, at the junction with the amplifier, one wire is connected to a + terminal, and the other to a - terminal, which is grounded. Actually, the ground connection may be elevated by a resistor to a value above or below ground potential for the rest of the amplifier circuitry. The ground might be separate for each channel, or the two grounds might be connected together and referenced to the same point throughout the circuit. Each signal wire can then be thought of as having two components, the Plus which represents the whole signal relative to ground, and the Minus, which provides the ground reference point. The whole signal is super-imposed as positive-to-negative swings of the phono needle relative to ground. The Minus provides a return path for current to and from ground. When the voltage on the signal wire goes negative relative to ground, current flows from ground, whereas when it goes positive current flows to ground (physically the electrons move the other direction, but don't worry about that). So you only need two wires for each channel, usually connected via an RCA connector. The center pin carries the signal relative to ground, and the outer shield carries the return path for signal current to flow.
Under ideal conditions, these two connection approaches produce exactly the same results, regardless of whether they have two wires or three wires. Some people argue that the balanced approach is actually INFERIOR b/c it requires more active amplification components to keep the signal elevated and floating above the ground. The unbalanced amp requires fewer active components to achieve the same result, and every component has at least some chance of affecting the signal.
Of course, we all know that there is no such thing as ideal conditions. And the further we depart from ideal, the more valuable a balanced connection becomes. For instance, throughout the amplification process, there is usually a chance for power supply noise (in the form of ripple currents, or HF interference, or induced currents) to be picked up by the wiring and to be amplified along with the signal. In a balanced configuration a "blip" of power supply noise might be induced on both signal wires. But since one half of the signal is going positive, and the other half is going negative, the noise is cancelled out. It exists on both wires simultaneously, but in different polarity, so the transducer will not move and you will not hear the noise.
In an unbalanced system, when noise is induced, it will always be relative to ground. Since the signal is also referenced to ground, when noise is amplified along with the signal, it will also appear at the transducer, so you will hear it. Well-designed unbalanced systems are carefully constructed to minimize any chance for noise to enter the signal path. And most succeed, with noise anywhere from 70-110 db below signal. However, it is still easier to disrupt an unbalanced system, and noise can become apparent in many ways, such as through power contamination (HF modulation from the power company, or other stuff connected to power lines in the home) or through interference along signal transitions, such as at connectors, or along cables.
Equally excellent results can be achieved with either balanced or unbalanced connections. Given the exact same circuit, under ideal conditions, unbalanced can actually sound better. In real world terms, it mostly does not matter. You do NOT get more power from a balanced system. Nor does it sound any different (e.g. clearer/better) unless there are important noise components in your home or along your amplification chain. Most of the effects attributed to unbalanced connections are due to other factors, not the connection or the wires. So the whole balanced=better argument is frankly specious (and my name is Frank).
Hope this helps!
Frank
