Introduction
Nowadays the space is cluttered with electromagnetic noise that is emitted by everyday appliances. From good old mains hum to interference caused by mobile phones, Wi-Fi... you name it! Cables are particularly prone to these types of noise. In a sense, all cables act like antennas. The longer the cable the more noisy the signal will become at the end. Be it a digital video cable in a stadium or an analogue microphone cable in a home recording studio, this makes it very important to have reliable means of rejecting noise.
Balanced
This is where balanced lines come in. In a twisted pair, one signal is carried by two wires – one caries the original signal, while the other carries the inverted version of the original (and ground signal is carried by the shield). At the receiver, a device, such as a transformer or an inverting op-amp, negates the inverted signal and adds it to the original. This way the noise that was picked up along the cable is cancelled out.
Starquad
While twisted pairs are very effective at rejecting noise, in some situations, especially where the interferer is very close, starquad cables can be a salvation. Where in a twisted pair, the two wires can never be in exactly the same position in space (and, therefore, will never pick up exactly the same amount of noise, although twisting helps), starquad cables have four wires – two for the positive and two for the negative signals – that are positioned inside the cable in such a way that both legs of the signal pick up virtually the same amount of interference which maximizes noise rejection.
Conversion
For the balancing to have an effect, both ends of the line must be balanced. However, not all devices have balanced outputs or inputs. For instance, media players commonly have RCA outputs that are unbalanced and electric guitars have unbalanced 2-pole jack outputs, while some active loudspeakers have unbalanced inputs. But fear not because Canford offers a range of unbalanced-to-balanced and balanced-to-unbalanced converters (as well as, balanced cables). The converters could be categorized into two main types – active and passive. DI boxes can be either passive or active and they not only convert from unbalanced to balanced signals but also help to prevent ground loops and match the impedance. While DI boxes are probably the most common examples of unbalanced to balanced converters, other types of converters exist, as well.
Passive
Some of the passive converters can look a lot like simple adaptors, however, they actually have 1:1 transformers inside. They are wired to present an unbalanced pin configuration at one end and a balanced pin configuration at the other. In most cases, they can be used either way round! Passive converters don’t require a power supply and, therefore, are very convenient means of conversion between balanced and unbalanced signals.
Active
Active converters are different from passive ones because they don’t suffer from the insertion loss and most of them provide adjustable gain. This can be particularly useful for amplifying signal before long cable runs which help to further increase the signal to noise ratio.