(stjålet fra aqvox)
Why actually ballanced / symmetrical phono preamplification?
There are two clean- symmetrical (mass-free) signal sources. On the one hand microphones, which explains also the historical origination of the symmetrical signal transmission within the professional audio range, on the other hand the MovingCoil pick-ups. There it is actually amazing that symmetrical / balanced circuits are so rarely used in phonostages. Because here one has to do as also with microphones, with very small voltages/currents with those the advantages of symmetrical signal processing would fully take effekt: During the symmetrical processing two contrary-phased signals are transferred. The amplifier forms the difference between both signals. Thus with symmetrical processing not the difference of an electrical signal is used to the mass, but the difference of two electrical signals. Disturbances, which usually arise on both signal-lines, are so effectively erased. In addition the XLR input has 6db higher amplification, this is more effective and results in better signal/noise ratio.
During asymmetrical connection a half wave of the MC signal is connected with the often contaminated common-ground!
TRUE balanced with just two conductors?
Normally balanced connections have 3 conductors: positive, negative and ground.
But in the case of eg. cartriges or microphones, which are balanced sources with just 2 conductors - positive and negative. The technical term is floating balanced or balanced without ground. Yes this is TRUE balanced! The positive signal is connected to one dedicated amplifier stage and the negative signal is inverted and also connected to one dedicated amplifier stage = differential amplifier!
