balanced pre amp

Balanced refers to a different circuit design. Others will fill in the details on that. All pre-amps are NOT balanced. Balanced circuits require cables with XLR connectors. One known advantage is that balanced i/cs are less susceptible to noise on long runs. Some amps require and/or sound much better when run balanced. Some items wiht XLR inputs or outputs are not "Truly balanced" but actually function as a built-in adaptor. Stand alone adapters are available.

A true balanced design is a differential design, with both positive and negative legs going through mirror image gain stages, output stages, etc. To do balanced right is expensive, because you require duplicate circuits. A regular preamplifier has an input, buffer, gain and output stages, but only for the positive leg of the input. The balanced preamp will have identical circuits for both the positive and negative legs.
As stated previously, it is more expensive because of the additional circuitry. The benefits are basically a blacker background, but are really only noticeable when running fully balanced, from source through amplifier. If either the source, preamp or amp are not fully differential designs, then you will not be listening to 'balanced' output.

John

John not in all instances.I have a McIntosh C200 preamp that will convert an unbalanced signal to a balanced signal according to the owners manual.