Audio (balance and unbalance line)

[roomy]

HI,EVERYONE

how can balance line be geneated from unbalanced audio signal?

also another question how is the noise induced inaudio cable reduced by use of balance line,
i need more information about the above questions,

thank

 

[thannara123]

by using filter circut. noise can be reduce by using co-axial cable

 

[betwixt]

You can turn unbalanced into balanced in two ways, using a center tapped transformer or by using active circuits to invert the signal to one of the lines.

Electrical noise is not reduced in a balanced line but interference from outside the cable may be reduced or removed completely. The idea is that instead of using ground and one signal wire, you use ground and two signal wires. The signal wires carry identical but opposite polarity signals, as the waveform on one moves more positive, the other moves more negative and vice versa. As long as the wires are kept very close together, they are often twisted around each other, they should pick up an identical amount of interference from outside, The interference may be magnetic or electrical, what matters is that both signal wires pick up the same amount. At the receiving end of the cable, again either a transformer or differential amplifer is used to return the signal to unbalanced state. Lets call the signal 'A', so one wire carries 'A' and the other carries '-A', if the '-A' is inverted and added to 'A' the result is 2A, twice the wanted signal. Now look at the interference, call it 'B', it is the same on both wires because of their close proximity. When the invert and add circuit sees this it gives out 'B' + '-B' which is zero. So the wanted signal is doubled and the unwanted one is cancelled out.

Although balanced lines are often screened to give additional protection, it isn't always necessary to do so. It is quite common to see television signals sent hundreds of metres along CAT-5 network cable which is unscreened and there is almost no interference pick up.

Brian.

 

[roomy]

Thankyou.

if i said any noise that gets induced into the line will be common to both positive and negative sides in order to cancelled when it arrives it is destination .is this can be correct .

which is the method by using differential amplifier to balance line be generated from unbalance audio signal


thanks

 

[betwixt]

Yes, you are correct.

To drive the balanced line you need an amplifier with two outputs, one upside down and the other the 'right' way up. You can do this by splitting the signal and passing it through two amplifiers, one configured as non-inverting and the other configured as inverting.

The differential amplifier is used at the receiving end of the cable, basically it is a normal amplifier with + and - inputs. You feed one cable into the + and the other into the -. The output will be the difference between the two which is the signal you want.

Brian.

 

[FvM]

Traditionally, transformers have also been used for balanced audio receivers. But good audio transformers are bulky, expensive, and it's still difficult to achieve complete immunity against magnetic interferences. But it's not easy to get the same suppression of interfering signals with electronical balanced inputs (differential amplifiers). As far as I'm aware of, balanced lines are mainly used in professional audio systems, for line level as well as microphone signals.