The raison d'etre of balanced line is to be able to use any balanced cable cable of any length (or cost) and have that cable have zero sonic artifact. So it does not matter the length (nor price); there is always an advantage to balanced lines.
In order to achieve that, the balanced line standard requires a low output impedance of its sources. This is poorly understood by the (IMO) majority of high end audio manufacturers, who often seem to regard balanced lines as trendy rather than the serious sonic boon that it is. As a result many high end audio products do not handle balanced signals nearly as well as they should, leading to varible results. This is why you see this question come up time and again on these forums!
A common myth is that balanced circuits require twice as much circuitry. This is untrue- quite often they require **less** circuitry as you have less noise, and thus less need for as many gain stages. Also, to build a differential balanced circuit does not require double the parts of its single-ended counterpart!
Yet another myth is that there is no advantage to using a balanced circuit with a single-ended input. As pointed out by Al, you retain the advantages of the circuit, you only loose the advantage of the cable. The gain **does not** change- that is to say you do not loose 6 db, as, at least with differential circuits, the input is looking for the *difference* between the inputs, which might be 2 opposite phases, or it might be the non-inverting input and ground. The differential input does not care.
In order to achieve that, the balanced line standard requires a low output impedance of its sources. This is poorly understood by the (IMO) majority of high end audio manufacturers, who often seem to regard balanced lines as trendy rather than the serious sonic boon that it is. As a result many high end audio products do not handle balanced signals nearly as well as they should, leading to varible results. This is why you see this question come up time and again on these forums!
A common myth is that balanced circuits require twice as much circuitry. This is untrue- quite often they require **less** circuitry as you have less noise, and thus less need for as many gain stages. Also, to build a differential balanced circuit does not require double the parts of its single-ended counterpart!
Yet another myth is that there is no advantage to using a balanced circuit with a single-ended input. As pointed out by Al, you retain the advantages of the circuit, you only loose the advantage of the cable. The gain **does not** change- that is to say you do not loose 6 db, as, at least with differential circuits, the input is looking for the *difference* between the inputs, which might be 2 opposite phases, or it might be the non-inverting input and ground. The differential input does not care.