What are the advantages of using balanced interconnects?
Balanced interconnects use a three-wire system as opposed to unbalanced (RCA) which is a two-wire system (signal and return/ground wire). One of the three wires in a balanced cable connects the grounds of two components together, but there is no signal current flow through this wire. This is similar to the ground wire in house wiring. No current flow there either. Current flow only occurs in hot and neutral. The other two wires in a balanced cable both carry signal. One carries the uninverted signal and the other carries the inverted version of the same signal. Because the two signal wires carry inverted versions of each others signal, the receiving component only needs to sense the difference in the two signals. It will ignore any signal that is identical and common to both wires. This is a great advantage, because most noise sources will generally cause the same noise to appear on both wires (common-mode), such as 60 Hz noise from ground-loops or strong RF. The receiving component will automatically remove this noise because it responds only to the difference signal. The receivers ability to remove this common noise is referred to as Common-Mode-Rejection-Ratio or CMRR. The higher the CMRR, the better. Balanced signaling also is generally terminated into a 600 to 1K resistor that is connected as a shunt between the inverted and uninverted signal at the receiving end. This is a carry-over from the professional sound use of balanced signaling, where standards defined the impedances and levels etc.
The advantages of balanced signaling are significant. So why are systems with balanced capability often used unbalanced? The problem is in the design of the differential or balanced drivers and receivers. These are more difficult to design with very linear low-distortion circuits. Often, the unbalanced circuits sound better because of simpler design. If the component is not designed balanced from the ground-up, the balanced circuitry often adds an additional stage to the preamp or amp. Additional stages are undesirable in principle, because each stage adds its own distortion, noise and frequency roll-off. In general, it is best not assume that the balanced and unbalanced connections on a component will sound alike , so the best advice is to try both.
Does balanced cabling need to be as high-performance as unbalanced?Our experience with many high-end components, some designed balanced end-to-end and some not, is that optimized balanced cables make as much difference as optimized unbalanced cables. There is a perception that because balanced systems are terminated in a low impedance, and they have good common-mode noise rejection, that one can utilize less expensive interconnects with good results. Our experience is just the opposite. Most balanced drivers seem to roll-off the high-frequencies more readily and therefore require very low capacitance cables for good results. We recommend that our customers do not scrimp on cables just because they are balanced.