Unbalanced and Balanced output voltage

I have always seen that most sources with unbalanced (RCA) and balanced (XLR) have an ouput voltage that is double for the XLR, e.g. RCA=2Vrms, XLR=4Vrms. However, I have noticed that quite a few sources (Esoteric players are a good example) have the same output voltage for balanced and unbalanced. How does it affect the preamplifier? Thanks